Anastasia V Arzhannikova
email: arzhannikovaanastasia@crust.irk.ru

Elena I Demonterova

Alexander V Sizov

Marc Jolivet

Ekaterina A Mikheeva

Alexei V Ivanov

Sergey G Arzhannikov

Valentin B Khubanov

Early cretaceous topographic evolution associated with the collapse of the Mongol-Okhotsk orogen in Western Transbaikalia: an integrated analysis

Keywords: U-Pb detrital zircons dating, sediment source-to-sink analysis, topographic evolution, 38 Western Transbaikalia

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 215-245, 250-270 and 280--300Ma. The youngest zircon has an age of 136.1 ± 43.9 Ma 313 (Fig. 6A; Supplementary Data, Tables S1). In the Lower Selenga Sfm. (sample Gus-14-6), 76 314 concordant U-Pb zircon ages were obtained. The main age population ranges 175--210 Ma, and 315 is complemented by a minor group with ages of 225--245 Ma and few, scattered older ages. The 316 youngest zircon present in the sample has an age of 1165.9 ± 21.7 Ma (Fig. 6B; Supplementary 317 Data, Tables S2). In the Kholboldzhin Fm. (sample Gus-14-1), 103 concordant U-Pb zircon ages 318 were obtained. Zircon ages are distributed into one major population at 160--230 Ma with a main 319 peak at 191 Ma. A few older outliers are also present as in the Lower Selenga sample. The youngest 320 zircon in the sample is 159.860 ± 21.75 Ma (Fig. 6C; Supplementary Data, Tables S3).

321

The 40 Ar/ 39 Ar plateau age of lamprophyre sample Mur-17-1 lamprophyres collected from 322 the Murtoi dike is 130.0 ± 10.7 Ma (Fig. 7A). The same plateau steps form an inverse isochron 323 with age of 130.2 ± 1.4 Ma and initial 40 Ar/ 36 Ar=285 ± 63. Because the initial argon isotope 324 composition is equal to the atmospheric value (~300), the calculation of the plateau age, which 325 assumes the atmospheric initial value, is justified. Further, we use the plateau age because it has 326 lower analytical uncertainty. Age and evolution of provenance of the Gusinoozersk Basin deposits 330

In sample Gus-17-1 from the Murtoi Fm. the age population of 150--160 165 Ma forms a 331 significant age peak (see Fig. 6A). This age range corresponds to that of the "Ichetui" bimodal 332 volcanics identified in the southern part of the Khambin Ridge (see Fig. 2). The main age 333 population of 215--270 Ma corresponds in age to the Sogotinsk igneous complex identified in the 334 southern northern part of the Khambin Ridge (see Fig. 2). The small age population of 280--300

335

Ma zircons in this sample can also be attributed to the Angara-Vitim batholithSogotinsk complex.

336

Finally, tracing the provenance of the 170--185 Ma zircons is a challenge. The youngest generations of zircons in the samples were found in the Murtoi Fm. and 391 Lower Selenga Sfm. These are composed of a very few single grains with ages ranging from ~116 392 to 145 Ma (Fig. 6 A,B). These ages correspond to the ages of single paleovolcanoes of Early Cretaceous (Komarov, 1962;Martinson, 1961;Kolesnikov, 1964;Otchirov, 1964 spectra from the Murtoi Fm., which correspond to those that were widespread across Siberia in the 420 Lower Cretaceous. For some species (Foraminisporis asymmetricus and Rouuseisporites 421 reticulatus), the lower stratigraphic limit corresponds to the middle of the lower Valanginian 422 (Averianov et al., 2022), which is in good agreement with the lower age limit of the formation at 423 ~136 Ma obtained in our work from the dating of the youngest zircon. This result suggests that the 424 Jurassic spore-pollen spectra found in the Selenga and Kholboldzhin Fms. (Jolivet et al., 2017) 425 were indeed recycled from the Jurassic sediments widespread in the region in the Lower

426

Cretaceous. This would explain the discrepancy between those Jurassic spore-pollen spectra and 427 the Lower Cretaceous age of the flora macro-remains found in the same formations. Indeed, while 428 spores and pollens are small and resistant enough to be recycled from older sediment deposits 429 (Stanley, 1966), macro-remains, and especially soft parts such as leafs are impossible to recycled.

430

Since the 40 Ar/ 39 Ar dating of the Khurai-Baiba dike complex, intruding the deposits of the Murtoi 431 Fm., showed an upper age limit of 130.0 ± 10.7 Ma for the basal formation, we suggest that the 432 formation of the Gusinoozersk Basin started at 130136-136 130 Ma. These data are consistent 433 with the biostratigraphic age of the Murtoi Fm.; Hhowever, our new geochronological data 434 narrows the age interval for the beginning of sedimentation in the Gusinoozersk Basin. randomly scattered in the sediments. There are no articulated skeletal elements here, and most of 448 the bones are highly fragmented. Some bones were carried by water currents and rounded.

449

The main partA major amount of the fossils belongs to the sauropods Tengrisaurus starkovi 450 (Averianov and Skutschas, 2017;Averianov et al., 2021) belonging to the titanosaurs group.

451

Remains of another sauropod (Sauropoda indet.) are also present but yet under study (Averianov 452 et al., 2022). Three theropod groups have been identified from the Mogoito locality based on the 453 isolated bones and teeth: Ornithomimosauria, Therizinosauroidea, and Dromaeosauridae 454 (Averianov et al., 2003;Averianov and Skutschas, 2009;Averianov et al., 2022) (Markwick, 1998;Mannion et al., 2015;Amiot, 2011). The sedimentation age of the Murtoi Fm.

482

(136--130 Ma, this study) coincides with the global cooling Weissert Event, which took place at 483 ~133 Ma (Cavalheiro et al., 2021) during the earliest Cretaceous (Berriasian to Barremian) and 484 can be characterized as something "in-between" a hothouse and an icehouse (Fig. 8).

503

In the upper part of the formation, the faunal complex changes. Forms characteristic of small 504 marshy lakes appear. The complex of bivalves given by (Kolesnikov, 1977) Ferganoconchidae correspond to the facies of shallow stagnant bodies (Skoblo et al. 2001).

514

According to (Vakhrameev, 1964(Vakhrameev, , 1982)) basin, which started with the beginning of the accumulation of the Selenga Fm. (Fig. 9).

559

The Khambin and Monostoy faults are trending obliquely to the direction of the Buteel 560 metamorphic core complex, and their activation is not directly related to its tectonic exposure.

561

However, the coincidence in time between the onset of active subsidence in the Gusinoozersk

562

Basin and the exhumation of the Buteel core complex suggest that they interacted structurally

628

From the middle of the Aptian, Western Transbaikalia developed in a relatively calm 629 tectonic regime, as evidenced by fine-grained deposits of the Selenga Sfm. and Kholboldzhin Fm.

630

Within the general pattern of a significant smoothing of the topography, the exposed metamorphic 631 cores complexes continued to be a source of sediments for the basins of Transbaikalia.

632

The subsidence of the Gusinoozersk Basin was controlled by two side faults: at an early Zonenshain et al., 1990;Sengör and Natal'in, 1996;Yin and Nie, 1996;Zorin, 1999) Permian to the Middle Jurassic (Zonenshain et al. 1990;Nie et al., 1990;Nie, 1991;Yin and Nie, 48 1993;1996;Zorin et al., 1998;Davis et al., 1998;Gordienko, Kuzmin, 1999;Zorin, 1999;Darby 49 et al., 2001;Parfenov et al., 2003;Donskaya et al., 2013;Demonterova et al., 2017;Sorokin et al., 50 2020;Wang et al., 2022 and others). Recent detrital zircon U-Pb data from marine and continental 51 deposits along the Mongol-Okhotsk suture showed that the last stage of oceanic closure was 52 segmental. Some terranes in the central part of the ocean accreted to the Siberian continent 5-10 53 Ma later than in the western and eastern parts (Guo et al., 2017;Arzhannikova et al., 2022). et al., 2001;Metelkin et al., 2004Metelkin et al., , 2010)) Yang et al., 2016;Arzhannikova et al., 2020;2022). The main stage of collapse of the Mongol-

69

Okhotsk orogen is associated with the exhumation of metamorphic core complexes and the 70 formation of rift basins, widely distributed over Transbaikalia, North Mongolia (Fig. 1B), and 71 within the North China Craton. This widespread, highly distributed extension phase occurred 72 between 138 Ma and 110 Ma, with a peak at 130-125 Ma (Zheng et al., 1991;Sklyarov et al., 73 1997;Zorin et al., 1997;Zorin, 1999;Donskaya et al., 2008;Daoudene et al., 2013Daoudene et al., , 2017;;Wang 74 et al., 2011Wang 74 et al., , 2012;;Ivanov et al., 2015;Zhang et al., 2019). Numerous paleontological, 75 paleobotanical, lithofacies and biostratigraphic studies have been carried out from the sedimentary 76 deposits of the Transbaikalia rift basins (e.g. Martinson, 1961;Kolesnikov, 1961;1964;Otchirov, 77 1964;Serdobolskaya and Kozubova, 1976;Skoblo et al., 2001;Jolivet et al., 2017;Arzhannikova 78 et al., 2018). However, the absence of absolute ages for the sedimentary series did not allow to 79 accurately characterize the regional topographic and environmental evolution. Gordienko et al., 1997;Ivanov et al., 1995;Vorontsov 129 et al., 1999;Andryushchenko et al., 2010;Arzhannikova et al., 2018). Specifically, for the The age of the sedimentary deposits is debated. The main studies were carried out in the (1961( ), Kolesnikov (1961;;1964) or Otchirov (1964)). In 175

The sorting and rounding of pebbles increase up section, which is interpreted as a decrease in 176 fluvial-environment deposits and a correlative increase in lacustrine deposits (Skoblo et al., 2001). , 2001;2009;Averianov et al, 2003;Skutschas, 2008). New data on fauna and 182 palynology from the Mogoito locality make it possible to estimate the age of the formation as Late Gusinoozersk Basin (Fig. 3). It has a thickness of up to 1200 m and conformably overlies the 210 Selenga Fm. The deposits are represented by polymictic arkose sandstones, siltstones and coal.

Skutschas

211

The coal occurrence in this formation is the highest in the Gusinoozersk Basin, displaying more collected from a medium-grained sandstone at 61 m from the base of the logged section (Fig. 5A).

273

The Kholboldzhin Fm. is represented by a 70-meter thick section within the Gusinoozersk

Analytical methods and results

284

Sample preparation for detrital zircons analysis was carried out at the Centre for S1-S3). Therefore, we 302 used only grains younger than 400 Ma to plot the diagrams (Fig. 6). zircon in the sample is 160 ± 2 Ma (Fig. 6C; Supplementary Data, Tables S3).

319

The Early Cretaceous (Komarov, 1962;Martinson, 1961;Kolesnikov, 1964;Otchirov, 1964 Ferganoconchidae correspond to the facies of shallow stagnant bodies (Skoblo et al. 2001).

511

According to (Vakhrameev, 1964(Vakhrameev, , 1982)) and Kholboldzhin times, there were again a series of small swampy lakes. of the Selenga Fm. (Fig. 9).

557

The Khambin and Monostoy faults are trending obliquely to the direction of the Buteel 558 metamorphic core complex, and their activation is not directly related to its tectonic exposure. , 1981;Donskaya et al., 2008;Mazukabzov et al., 2011).

576

The basal Murtoi Fm. is composed mainly of poorly sorted conglomerates, which we 577 interpret as representing rapid erosion linked to the active subsidence of the depression at the initial 578 stage and the formation of alluvial fans at the foot of the Khambin Ridge (see fig. 9A). The remote 579 provinces located to the south of the basin also took a small part in the sedimentation during that 580 time -the rivers started transporting clastic material from the Buteel metamorphic core complex.

581

A modern analogue of such rivers could be the Selenga River, whose catchment includes this 582 region. The Selenga River flows to the northeast, passing near the Gusinoozersk Basin through the 583 Monostoy Ridge, and flows into Lake Baikal (see fig. 1B). Among the detrital zircons extracted Basin also made a contribution to sedimentation indicating the rise of a positive topography 624 associated with the exhumation of the metamorphic core complexes.

625

From the middle of the Aptian, Western Transbaikalia developed in a relatively calm 626 tectonic regime, as evidenced by fine-grained deposits of the Selenga Sfm. and Kholboldzhin Fm.

627

Within the general pattern of a significant smoothing of the topography, the exposed metamorphic 628 cores complexes continued to be a source of sediments for the basins of Transbaikalia.

629

The subsidence of the Gusinoozersk Basin was controlled by two side faults: at an early

  and environmental evolution of Transbaikalia was largely driven by 42 the tectonic evolution of the Mongol-Okhotsk orogenic belt (see fig. 1A for location). The belt of Transbaikalia are nonetheless key objects to study the destruction 81 of the Mongol-Okhotsk orogen and the corresponding paleoenvironmental evolution. These basins 82 represent a unique record of the Cretaceous fauna, flora, climate and topography of this huge 83 region. One of the key depressions, where extensive sedimentary sections of Cretaceous deposits 84 have been preserved, is the Gusinoozersk Basin of Western Transbaikalia (see fig. 1B for location). 85 Sediments of this depression are well characterized by fossil fauna. Bonebeds containing the the Late Mesozoic sedimentary deposits of the basin, nor data on the evolution

  occasional supply of coarser alluvial material associated with erosion of the 365 sides of the basin. All formations contain a few zircons with ages of 290280--330 Ma that match 366 the age of the Angara-Vitim batholith (Litvinovsky et al., 2011) located to the north of the 367 Gusinoozersk Basin. Judging by the significant occurrence of Late Carboniferous-Early Permian 368 detrital U-Pb zircon ages in the Lower-Middle Jurassic deposits of the Verkhoyansk margin and 369 the Irkutsk Basin (see fig. 1B for location), the Angara-Vitim batholith region represented an 370 uplifted area up to the beginning of the Middle Jurassic (Prokopiev et al., 2008; Demonterova et 371 al. , 2017; Mikheeva, 2017). Until that time, the rivers draining the southern partregion of the 372 Angara-Vitim batholith transported the clastic material southward to the Mongol-Okhotsk 373 continental margin. The closure of the Mongol-Okhotsk Ocean in the region of Western 374 Transbaikalia at the Early and Middle Jurassic boundary led to a reorganization of the drainage 375 network and a change in the direction of transport of sedimentary material to the north 376 (Arzhannikova et al., 2020). The occurrence of zircon ages corresponding to sources both north 377 and south of Western Transbaikalia in one sample indicates recycling of sediments from previous 378 deposits (Yang et al., 2013), as it has been observed for the Middle Jurassic deposits of the 379 neighboring Tugnui Basin (Arzhannikova et al., 2020) (see fig. 1B for location). The pre-existing 380 cover sequence at the Mongol-Okhotsk continental margin, containing zircons derived from the 381 Angara-Vitim batholith, was probably still largely preserved by the Early Cretaceous and 382 participated to the clastic material source. Although the contribution of recycled zircons to the 383 deposits of the Gusinoozersk Basin is not significant: in the Murtoi Fm., zircons with the age of 384 the Angara-Vitim batholith do not exceed 7%, and only single grains of this age are found in the 385 overlying formations. 386 Single zircon grains with ages ranging from 330 to 400 Ma are found in samples from the 387 Lower Selenga Sfm. and Kholboldzhin Fm. There are no zirconss of this age in the sample from 388 the Murtoi Fm. In the adjacent areas, volcanic rocks with such ages are not known (Wang et al., 389 2022); therefore, the question of the provenance of these zircons remains open.

393

  trachybasaltic and trachyandesite composition in the Khambin Ridge (124127-127 124 Ma) 394 (Andryushchenko et al., 2010), large volcanoes of alkaline rhyolites (~140 Ma), including those 395 within the Monostoy Ridge (Yarmolyuk et al., 2000), as well as two stages of magmatic activity 396 that occurred in Western Transbaikalia at 135143-143 135 Ma and 111131-131 111 Ma 397 (Vorontsov et al., 2016). In their study, Vorontsov et al. (2016) pointed out that after 135 Ma, the 398 emitted volume of volcanic rocks sharply decreased and their composition changed from bimodal 399 associations to basaltoid ones. The predominance of mafic rocks among the Early Cretaceous 400 volcanics (up to 90%) (Donskaya et al., 2013; Sheldrick et al., 2020) possibly explains the small 401 amount of zircons of this age in the samples. 402 Thus, our geochronological studies made it possible to clarify the onset time of the 403 formation of the Gusinoozersk Basin. While it was previously considered as Middle Jurassic to 404

  fossils found at the Mogoito locality, we can model the paleoenvironment at 437 the time of the onset of sedimentation in the Gusinoozersk Basin during deposition of the Murtoi 438 Fm. It yielded the largest number of vertebrate remains from the Gusinoozersk Basin. The Mogoito 439 locality consists of a series of natural outcrops in shallow ravines and scours on the western bank 440 of Lake Gusinoe exposing sediments from the Murtoi Fm. The locality represents an important 441 source of information about the Early Cretaceous vertebrate fauna of Central Asia. The lower part of the Murtoi section in Mogoito locality is made of large and medium 443 pebble conglomerates of varying rounding, gravelstone and sandstone containing rare fragmentary 444 dinosaur fossils and remains of petrified wood. The upper alluvial part of the section is composed 445 of alluvial cross-bedded fine-to-coarse grain sandstone alternating with a thinner layer of shale and 446 siltstone with remains of bivalve mollusks and vertebrates. The remains of fossil bones are 447

563

  during a single process of crustal extension. The Khambin Fault participates to the Dzhida-Vitim 564 structural suture (see fig. 1B for location), which is the boundary between the regions of Late 565 Proterozoic Baikalian and Early Paleozoic Caledonian folding (Luchitsky, 1975). The Mesozoic 566 reactivation of the Dzhida-Vitim structure has been evidenced along its entire length. It controlled 567 the development of the Dzhida-Vitim depression zone, represented by a chain of Mesozoic 568 depressions, which include the Gusinoozersk Basin. Cretaceous reactivation has also been 569 recorded along the Primorsky structural suture in the neighbouring Baikal region (see fig. 1B for 570 location). The apatite fission track data from the Primorsky Ridge and the Olkhon block show Monostoy Fault still played the main role in the subsidence of the depression. This is 598 confirmed by the deposition of the "Monostoy" conglomerates at the foot of the Monostoy Ridge, 599 laterally replacing the fine-grained sediments of the Selenga and Kholboldzhin fms, and by the 600 occurrence of zircons derived from volcanic rocks located in the Monostoy Ridge. The 601 "Monostoy" facies corresponds to the proximal parts of the alluvial fans deposited by the rivers 602 that were draining the Monostoy Ridge. In the central part of the basin, distal alluvial plain 603 sediment facies accumulated in fluvial and lacustrine-swamp environments (see fig. 9B). The 604 decrease in the subsidence rate of the depression and smoothing of the topography led to the 605 overfilling of the depression with sediments, swamping and peat formation, which gave rise to the 606 formation of coal. 607 Thus, by the end of the Early Cretaceous, the topography finally flattened out and the 608 Gusinoozersk Basin ceases to be an area of sedimentation. However, it seems that the process of 609 collapse of the Mongol-Okhotsk orogen does not end there, and the extension is shifted closer to 610 the boundary of the Siberian Craton to the area of the Baikal rift system. For example, Van der 611 Beek et al. (1996) and Jolivet et al. (2009) based on apatite fission track data showed the 612 reactivation of the Primorsky and Barguzin faults of the Baikal rift system (see Fig. 1 for location) 613 in the Late Cretaceous and interpreted it as a continuation of postorogenic extension in sedimentary and igneous rocks of the Gusinoozersk Basin 618 made it possible to clarify the age of paleogeographic events associated with the collapse of the 619 Mongol-Okhotsk orogen in Western Transbaikalia. U/Pb (LA-ICP-MS) dating of detrital zircons 620 from sedimentary deposits and 40 Ar/ 39 Ar dating of intruding volcanic rocks showed that the 621 formation of the Cretaceous basins of Transbaikalia began around 130136--136 130 Ma. It is main episode of extension associated with the exhumation of metamorphic core 623 complexes. 624 The lowest coarse-clastic Murtoi Fm. characterizes the rapid subsidence of the basin and 625 the predominance of proximal sediment sources. The provinces located south of the Gusinoozersk 626 Basin also made a contribution to sedimentation indicating the rise of a positive topography 627 associated with the exhumation of the metamorphic core complexes.

  event has been widely studied, the topographic evolution of the 55 Mongol-Okhotsk belt is still poorly understood. Widespread magmatism and thrusting related to 56 subduction and collision suggested that the Mongol-Okhotsk belt formed as a plateau-like uplift 57(Zorin, 1999). Paleomagnetic data obtained from the Mesozoic deposits of Southeastern Siberia 58 and Northern Mongolia indicate left-lateral strike-slip motion along the Mongol-Okhotsk suture 59 zone during and after the collision, caused by the clockwise rotation of the Siberian continent 60 (Parfenov

  of Transbaikalia are nonetheless key objects to study the destruction 81 of the Mongol-Okhotsk orogen and the corresponding paleoenvironmental evolution. These basins 82 represent a unique record of the Cretaceous fauna, flora, climate and topography of this huge 83 region. One of the key depressions, where extensive sedimentary sections of Cretaceous deposits 84 have been preserved, is the Gusinoozersk Basin of Western Transbaikalia (see fig. 1B for location). 85 Sediments of this depression are well characterized by fossil fauna. Bonebeds containing the 86 remains of dinosaurs and other vertebrates were found in the sediments of the basal Murtoi 87 Formation. Based on the correlation of vertebrate faunas, the age of the sediments was estimated 88 ranging from Late Baremian to Middle Aptian (Dmitriev, 1960; Nessov and Starkov, 1992; 89 Averianov et al, 2003), thus from ~127 to 120 Ma (here and further the stratigraphic age is 90 established according to www.stratigraphy.org assessed on 30 th May 2022). However, later studies 91 of the fauna suggested that deposits in the Gusinoozersk Basin could begin to accumulate earlier, 92 starting from the Late Berriasian -Valanginian (Skoblo et al., 2001) (~140 Ma) or Late 93 Valanginian -Barremian (Averianov et al., 2022) (~133-125 Ma). Constraining the time span in 94 the geological record of well-preserved sediments is key to determine the paleoenvironment of the 95 region, as well as the age and correlation of non-marine vertebrates of the Early Cretaceous in 96 Transbaikalia, Mongolia, and China. 97 The objective of this study was to bracket the age of the sedimentary series of the 98 Gusinoozersk Basin based on U/Pb (LA-ICP-MS) dating of detrital zircons and 40 Ar/ 39 Ar dating 99 of an intruding dike. Carrying out absolute dating made it possible to clarify the age of the 100 paleogeographic events associated with the collapse of the Mongol-Okhotsk orogen, as well as to 101 correct the age of faunal complexes in Western Transbaikalia. This last point represents a leap 102 forwards to biostratigraphic correlations in various regions of Central Asia.103A recent revision of the dinosaur fauna(Averianov et al., 2022) has made it possible to 104 take a fresh look at the faunal list of the complex of fossil vertebrates in the Gusinoozersk Basin.

  with new data on age and paleogeography in this study, provides a more complete 106 picture of the Early Cretaceous paleoenvironments of Western Transbaikalia. is a Cretaceous NE-SW oriented depression bounded to the NW 110 and SE by the Khambin and Monostoy ridges, respectively (Fig.2). The Gusinoozersk Basin was 111 first described as a typical graben(Luchitsky, 1975). According toLeonov (1983), two 112 synsedimentary tectonic structures, the Khambin and Monostoy faults, were involved in the 113 formation of the basin, and the onset of sedimentation was associated with the activation of the 114 Khambin Fault (see fig. 2 for location). Later, Bulnaev (2006) established this depression as 115 monoclinal, formed due to unilateral synsedimentary subsidence along the Monostoy Fault, which 116 runs along the eastern flank of the basin (see fig. 2 for location). Indeed, the thickness of sediments 117 in the depression is not constant, increasing from the western edge to the East. This indicates that 118 the role of the Monostoy Fault in the development of the basin was predominant (Bulnaev, 2006). 119 Below we present a description of the igneous complexes within the Khambin and Monostoy 120 ridges, as potential sediment sources, as well as a description of the sedimentary deposits of the 121 , framing the Gusinoozersk Basin to the west, is composed of two 124 igneous complexes. The "Ichetui" bimodal volcanics are identified in the southern part of the ridge 125 (see fig. 2). They are also distributed within several grabens of Western Transbaikalia and 126 composed of trachybasalts, trachyandesites, trachydacites and trachyrhyodacites. The "Ichetui" 127 volcanic rocks have been dated by different geochronological methods from 168 to 145 Ma in 128 different places of Western Transbaikalia (

  148 1950-1960s. Various complexes of freshwater mollusks characteristic of the Middle, Upper 149 Jurassic -Lower Cretaceous were found in different parts of the sedimentary section of the basin 150 (e.g. Martinson, 1955). According to Otchirov (1964), sedimentation began in the Gusinoozersk 151 Basin from the Early Jurassic and continued up to the upper Lower Cretaceous. Kolesnikov (1961; 152 1964), based on lithological, paleontological and geological data, attributed the entire section of 153 the Mesozoic continental deposits to the Middle Jurassic -Lower Cretaceous. Based on geological 154 mapping, Komarov (1962) divided the stratigraphic section, from base to top, into the Sanga, 155Selenga, Bain-Zurkhen and Kholboldzhin Fms. All formations were described as conformable and 156 span from the Upper Jurassic to the Lower Cretaceous (Fig.3).

  rich collection of fossil mollusks, ostracods and plants, as well as 158 fragmentary remains of bones and teeth of dinosaurs was collected(Scoblo, 1967). This new 159 collection, as well as geological drilling data for coal exploration, raised disagreements on the 160 Mesozoic stratigraphy of the Gusinoozersk Basin, leading to different interpretations of the 161 complex geological structures of this region. The scheme proposed by Scoblo (1967) differs 162 significantly from those of Martinson

  163 particular, it suggests a complete absence of Middle and Upper Jurassic sediments in the 164 Gusinoozersk Basin. Later, numerous fossil findings made it possible to expand the lists of ancient 165 fauna and flora and significantly correct the stratigraphy and distribution of fossil organisms 166 (Scoblo et al., 2001). In our work, we adhere to the stratigraphic scheme published in (Scoblo et 167 al., 2001), which is best characterized by fossil fauna. The Gusinoozersk series are subdivided into 168 four formations (bottom-up) (Fig. 3): 169 1. The Murtoi Fm. (K 1 mr) (analogous to the lower sub-formation of the Sanga Fm.

170

  according toKomarov (1962), (Fig.3)), is 300-450 m thick and occurs along the western side of 171 the Gusinoozersk Basin, at the foot of the Khambin Ridge. The Murtoi Fm. rests on the underlying 172 Middle and Upper Jurassic volcanic rocks through an erosional unconformity. It is composed of 173 interbedded conglomerates, gravelstones, sandstones and silicic volcanic rocks. Up section, the 174 conglomerates become finer, and the number and thickness of the sandstone interlayers increase.

177

  In the Mogoito locality (see fig.2) the Murtoi Fm. contains various fossil bivalves, gastropods, 178 scattered fragmental remains of vertebrates such as palaeonisciform, acipenceriform and 179 teleostean actinopterygians, macrobaenid turtles, lizards, various ornithischian and saurischian 180 dinosaurs, pterosaurs, birds, and eutherian mammals(Skoblo et al., 2001; Averianov and 181

  , although some of the data are quite contradictory and 184 require further clarification(Averianov et al., 2022). 185 2. The Ubukun Fm. (K 1 ub) (analogous to the upper sub-formation of the Sanga Fm. 186 according to Komarov (1962), (Fig. 3)) is 300-450 m thick and characterized by deep-lake 187 sediment facies. Mudstones are widespread in the lower part of the formation, interbedded with 188 siltstones and fine-grained sandstones higher-up in the section. Sandstones with small coal lenses 189 dominate the upper part of the section. The fossil fauna (mostly ostracods) is exclusively 190 limnophilic, characteristic of a lake at least 50 m deep (Skoblo et al., 2001). Sandy facies with coal 191 lenses in the upper part of the formation indicate shallowing of the lake and development of 192 swamps. The biostratigraphic age of the Ubukun Fm. is determined as Hauterivian (132.6-129.4 193 Ma) (Skoblo et al., 2001).194 3. The Selenga Fm. (K 1 sl) forms the lower part of the coal-bearing strata of the 195 Gusinoozersk series, and shows the greatest regional distribution. It is characterized by 196 transgression-regression cycles and divided into two sub-formations. The Lower Selenga sub-197 formation (K 1 sl 1 ) corresponds to the Selenga Fm., and the Upper Selenga sub-formation (K 1 sl 2 ) 198 corresponds to the Bain-Zurkhen Fm. according to Komarov (1962), (Fig. 3)). The Lower Selenga 199 Sfm., with a total thickness of up to 600 m is represented by interbedded gravelstones, sandstones, 200 siltstones, mudstones, and coal. The grain size is decreasing up section. The sub-formation is 201 characterized by three ostracod horizons. The Upper Selenga Sfm., up to 500 m thick, lacks 202 gravelstones and is dominated by finer-grained sediments. The number and thickness of coal seams 203 in the Upper Selenga Sfm. is greater than in the Lower Selenga Sfm. Different parts of the section 204 display carbonaceous sandy shale layers ("paper" oil shale) with fish, pelecypod and ostracod 205 horizons. The sub-formation is also characterized by various bivalves and gastropods. The 206 biostratigraphic age of the entire Selenga Fm. is determined as Hauterivian-Barremian (~130 Ma) 207 (Skoblo et al., 2001).

  Kholboldzhin Fm. (K 1 hl) forms the upper part of the Mesozoic deposits in the 209

212

  than 16 coal seams with a thickness of 2-4 to 53 m. The deposits contain ostracods and small 213 bivalves. The biostratigraphic age of the Kholboldzhin Fm. is determined as Barremian-Aptian 214 (~129.4-113 Ma)(Skoblo et al., 2001). 215 The Monostoy foothill series form a separate stratigraphic unit along the foot of the 216 Monostoy Ridge and is represented by colluvions, conglomerates, breccias, gravelstones with 217 sandstone interbeds. Drilling data show that sediments of this series are laterally correlated to fine-218 grained sediments in the basin, starting from the Lower Selenga Sfm. (Bulnaev, 2006; Skoblo et 219 al., 2001) (Fig.3). This indicates that, starting from the time of the accumulation of the Lower 220 Selenga Sfm., the Monostoy Fault played the main role in the subsidence of the basin. 221 The correlation of sections in several areas of the Gusinoozersk Basin is based on the 222 complexes of fauna (especially ostracods and mollusks) and takes into account all the geological 223 and structural data. Though numerous intra-formation erosion surfaces are exposed, the overall 224 stratigraphy seems conformable, without major erosion lags. Biostratigraphically, this is 225 confirmed by the succession of faunal complexes and the stability of the plant association 226 throughout the Lower Cretaceous. The composition of the flora from individual formations and 227 sub-formations indicates that they evolved under similar paleoenvironmental conditions (Skoblo, 228 1967; Skoblo et al., 2001). At the same time, the variations in sediment facies assemblages and 229 depositional environments indicate different dynamics of basin subsidence. 230 The discussion above clearly shows that the age and stratigraphy of the deposits of the 231 Gusinoozersk Basin have been debated for many decades. So far, no geochronological data have 232 been published on the Late Mesozoic sedimentary deposits of the basin, nor data on the evolution 233 of sediment sources. Such data are nonetheless necessary to fully constrain the onset of formation basins in Transbaikalia and assess the morphostructural and paleoenvironmental 235 evolution associated with the collapse of the Mongol-Okhotsk orogen. , we selected samples from three key formations of the Gusinoozersk Basin 240 and performed U-Pb (LA-ICP-MS) analysis of detrital zircons to clarify the depositional age and 241 determine the evolution of the source-to-sink pattern. The samples were taken from the basal 242 Murtoi Fm., the Lower Selenga Sfm. and the Kholboldzhin Fm, covering the entire section of the 243 Cretaceous deposits (Figs. 2, 3). 244 The Murtoi Fm. was sampled from an outcrop located near the Murtoi Valley 245 (N51°09.745´; E106°13.630´) (Fig. 4, sample Gus-17-1, see Fig. 2 for location). The deposits are 246 poorly sorted conglomerates composed of largely self-supported, moderately to well-rounded 247 pebbles and cobbles up to 20 cm in size with a limited sandy matrix. Pebbles and cobbles consist 248 mainly of intermediate and felsic volcanic rocks with mafic inclusions. The deposits are interpreted 249 as proluvial-alluvial facies from braided rivers. Sample Gus-17-1, collected for U-Pb (LA-ICP-250 MS) detrital zircon dating was taken from the sandy matrix (Fig. 4C). 251 Within the studied outcrop, the conglomerates are intruded by the Murtoi dike belonging 252 to the Khurai-Baiba dike complex (Komarov, 1962) (Fig. 4A, B). The apparent width of the dike 253 is 9 m. The dike has a lamprophyric composition with inclusions of granitoid xenoliths (Khubanov 254 et al., 2017). There are at least three magmatic intrusion phases, similar in composition but 255 different in degree of crystallization (Andryushchenko et al., 2010). The dike was previously dated 256 by Rb-Sr and K-Ar methods, which yielded ages of 117 ± 6 Ma and 122 Ma (without stated 257 uncertainty), respectively(Litvinovsky et al., 1989). To clarify the age of the intrusion within the 258 studied outcrop and to establish the upper limit of the age of the sampled sedimentary unit, a 259 sample Mur-17-1 was taken from the dike for 40 Ar/ 39 Ar analysis.

  fig.2for location)(Jolivet et al., 2017). The deposits are tilted westward. The lower (eastern) part

  274coal deposit on the eastern shore of Lake Gusinoe (N51°09.284´; E106°25.795´) (see position of 275 sample Gus-14-1 on fig.2for location)(Jolivet et al., 2017). The section displays interbedded grey 276 siltstones with plant remains, rare interlayers of fine-to medium-grained sandstone, and coal 277 seams up to 3 m thick (Fig.5B, C). This facies assemblage is interpreted as lacustrine to marsh 278 depositional environments. The upper ~20 m of the section are represented mainly by fine-to 279 medium-grained sandstones with a calcareous and clay cement, interpreted as meandering river 280 facies(Jolivet et al., 2017). A sample for detrital zircon dating (Gus-14-1) was collected from one 281 of the fine-to-medium-grained sandstone interbeds in the lower part of the section (23 m from 282 bottom) (Fig.5B).

  283

  of detrital zircon ages in the sample of the Murtoi Fm. correspond to the 525 age of the volcanic rocks of the Khambin Ridge bordering the basin to the West. There are almost 526 no zircons with ages corresponding to the volcanic rocks of the Monostoy Ridge in the sample.527These two results suggest that most of the topographic relief was mainly localized to the West, 528 further suggesting that the subsidence of the Gusinoozersk Basin at the initial stage was mainly 529 controlled by the Khambin Fault. The basin thus initially developed as a west-tilted (actual 530 reference frame) semi-graben (Fig.9A). By this time, the predominant deposits were proximal 531 deposits from braided rivers draining the Khambin Ridge. In the overlying formations, represented 532 by fine-grained material, there is only minor amount of zircons with ages matching the Khambin 533 volcanic rocks (see Fig.6B, C). However, these samples contain a zircon age population consistent 534 with the age range of the Early Jurassic bimodal association, identified within the Monostoy Ridge 535 to the East (Yarmolyuk et al., 2000) (see Fig. 2). The absence of "monostoy" zircons in the basal 536 Murtoi Fm. and their presence in the Lower Selenga Sfm. and Kholboldzhin Fm. indicate the 537 formation of a positive relief to the East. This suggests an activation of the Monostoy normal fault 538 later than the accumulation time of the Murtoi Fm. (Fig. 9B). The beginning of the subsidence of 539 the eastern side of the basin was accompanied by simultaneous erosion of the Monostoy Ridge. 540 This is also supported by the deposition of the coarse-grained "Monostoy" facies sediments, 541 starting from the Lower Selenga Sfm. and higher along the section, which facially replaced coal-542 bearing deposits (Skoblo et al., 2001) (see fig. 3 and 9B

559

  However, the coincidence in time between the onset of active subsidence in the Gusinoozersk 560 Basin and the exhumation of the Buteel core complex suggest that they interacted structurally 561 during a single process of crustal extension. The Khambin Fault participates to the Dzhida-Vitim 562 structural suture (see fig. 1B for location), which is the boundary between the regions of Late 563 Proterozoic Baikalian and Early Paleozoic Caledonian folding (Luchitsky, 1975). The Mesozoic 564 reactivation of the Dzhida-Vitim structure has been evidenced along its entire length. It controlled 565 the development of the Dzhida-Vitim depression zone, represented by a chain of Mesozoic 566 depressions, which include the Gusinoozersk Basin. Cretaceous reactivation has also been 567 recorded along the Primorsky structural suture in the neighbouring Baikal region (see fig. 1B for 568 location). The apatite fission track data from the Primorsky Ridge and the Olkhon block show 569 rapid exhumation at 140-120 Ma along the Primorsky suture (Van der Beek et al., 1996; Jolivet 570 et al., 2009). Thus, during the Cretaceous extension, large inherited structures were activated. The 571 basins of Transbaikalia were formed both in conjunction with the exhumation of metamorphic mainly located along reactivated structural sutures. While middle to lower 573 crust was exhumed to the surface within the metamorphic core complexes, the probably 574 Cretaceous basins developed along listric faults rooting in the ductile decollement zone at depth 575 (Wernicke

584

  from modern deposits of the Selenga River Delta(Ivanov et al., 2016), some display U-Pb ages 585 corresponding to the age of syenites of the Burgutuy massif of the Buteel metamorphic core 586 complex. We thus assume that during the accumulation of the Gusinoozersk Basin such a river 587 flowed through the basin towards the Siberian Craton, unloading sediments transported from the 588 southern provinces within the basin. An increase in the contribution of the southern sources up the 589 section indicates either that they have become more eroded or that local sources have decreased. 590 Fine-grained sediments of the Selenga and Kholboldzhin Fms. (sandstones, siltstones, 591 mudstones with interlayers of coals) indicate that, starting from the middle Aptian (considering 592 that the ~116 Ma zircon age corresponds to the lower limit of sedimentation), Western 593 Transbaikalia evolved in a relatively calm tectonic regime, characterized by the slow subsidence 594 in the various basins and the continuing denudation of not yet completely eroded ridges. At that 595 time, the Monostoy Fault still played the main role in the subsidence of the depression. This is 596 confirmed by the deposition of the "Monostoy" conglomerates at the foot of the Monostoy Ridge, 597 laterally replacing the fine-grained sediments of the Selenga and Kholboldzhin fms, and by the derived from volcanic rocks located in the Monostoy Ridge. The 599 "Monostoy" facies corresponds to the proximal parts of the alluvial fans deposited by the rivers 600 that were draining the Monostoy Ridge. In the central part of the basin, distal alluvial plain 601 sediment facies accumulated in fluvial and lacustrine-swamp environments (see fig. 9B). The 602 decrease in the subsidence rate of the depression and smoothing of the topography led to the 603 overfilling of the depression with sediments, swamping and peat formation, which gave rise to the 604 formation of coal. 605 Thus, by the end of the Early Cretaceous, the topography finally flattened out and the 606 Gusinoozersk Basin ceases to be an area of sedimentation. However, it seems that the process of 607 collapse of the Mongol-Okhotsk orogen does not end there, and the extension is shifted closer to 608 the boundary of the Siberian Craton to the area of the Baikal rift system. For example, Van der 609 Beek et al. (1996) and Jolivet et al. (2009) based on apatite fission track data showed the 610 reactivation of the Primorsky and Barguzin faults of the Baikal rift system (see Fig. 1 for location) 611 in the Late Cretaceous and interpreted it as a continuation of postorogenic extension in sedimentary and igneous rocks of the Gusinoozersk Basin 616 made it possible to clarify the age of paleogeographic events associated with the collapse of the 617 Mongol-Okhotsk orogen in Western Transbaikalia. U/Pb (LA-ICP-MS) dating of detrital zircons 618 from sedimentary deposits and 40 Ar/ 39 Ar dating of intruding volcanic rocks showed that the 619 formation of the Cretaceous basins of Transbaikalia began around 136-130 Ma. It is related to the 620 main episode of extension associated with the exhumation of metamorphic core complexes. 621 The lowest coarse-clastic Murtoi Fm. characterizes the rapid subsidence of the basin and 622 the predominance of proximal sediment sources. The provinces located south of the Gusinoozersk

Fig. 1 .Fig. 2 .Fig. 3 Fig. 5 .Fig. 7 .Fig. 9 .

 123579 Fig. 1. A -Location of the Mongol-Okhotsk orogenic belt (M-O belt) on the map of Asia; B -Geological setting of Transbaikalia and adjacent areas (Qi and Wang, 2008; Jolivet et al., 2013; Yarmolyuk et al., 2016): 1 -Siberian craton, 2 -Lakes, 3 -Jurassic basins (TGB -Tugnui Basin), 4 -Cretaceous basins (GSB -Gusinoozersk Basin), 5 -Cenozoic basins of the Baikal rift system, 6 -Metamorphic core complexes (BUT -Buteel MCC), 7 -Granitoid batholiths, 8 -Suture zone: M-O S -Mongol-Okhotsk, D-V S -Dzhida-Vitim, P S -Primorsky, 9 -Main Cenozoic faults: BF -Barguzin Fault. 175x144mm (300 x 300 DPI)

  Ma) is situated in the Burgutuy massif of the Buteel metamorphic 339 core complex (Mazukabzov et al., 2006) (see Fig. 1B for location).

	338	of syenites in this range (178 ± 3
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Almost no igneous 337 rocks of this age have been found in Western Transbaikalia or Northern Mongolia. The only dating

  Jolivet et al. (2017) also reported the occurrence of few Cretaceous spores and pollens 417 from the Selenga SFfm., finally suggesting that the Selenga, Bainzorkhen and Kholboldshin Fms 418 beare of late Late Jurassic -Early Cretaceous age. Averianov et al. (2022) identified spore-pollen

	416 al., 2017). 419
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	411	estimated the age of the Murtoi Fm as Berriasian -Valanginian (~145--132.9 Ma). Based on the
	412	age of the ostracods, Scoblo et al. (2001) dated the Murtoi Fm. as Berriasian-Hauterivian (~145-
	413	-129.4 Ma). The spore-pollen assemblages associated with the overlying Selenga and

; Skoblo 405 et al., 2001 and others), our detrital zircon U-Pb age data from the basal Murtoi Fm. indicate that 406 the basin began to subside not earlier than ~136 million years ago (according to the age of the 407 youngest zircon in the sample). However, this age of ~136 Ma relies on a single grain and is 408 therefore statistically very weak. A more representative number of young zircons (3 grains) have 409 an age of 150--153 Ma (Supplementary Data, Tables S1). However, the age of ~136 Ma is in 410 better agreement with the biostratigraphic data. Based on freshwater mollusks, Kolesnikov (1980) 414 Kholboldzhin Fms. are characterized by Late Jurassic species, while the flora macro-remains in 415 the same deposits are Early Cretaceous (see for example the Old Zagustay samples in Jolivet et

  Irenichthys sp. (Averianov and Skutschas, 2009) are found in alluvial deposits. The The Mogoito locality is largely similar to the Khuren Dukh locality of Mongolia, sharing the 468 macrobaenid turtle Kirgizemys and the long-necked choristodere Khurendukhosaurus (Averianov 469 and Skutschas, 2000). However, abundant remains of Psittacosaurus at the Khuren Dukh locality 470 (Kalandadze and Kurzanov, 1974) are not known in the Mogoito locality. Apparently, this 471 indicates an older age of the sediments in Mogoito, because when present, Psittacosaurus is the 472 most abundant dinosaur taxon in an assemblage (Averianov et al., 2022).We cannot use dDinosaurs cannot be used as good indicators of climate because some of 474 them thrived and even bred in the cool temperate climate above the Arctic Circle, such as in

	467
	473
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. All available 455 remains previously identified as Ornithopoda indet. as well as a Psittacosaurus sp. (Averianov and 456 Skutschas, 2009) from Mogoito locality can be attributed to a representative of the basal 457 ornithischian clade Jeholosauridae indet. (Averianov et al., 2022). Remains of other diapsid 458 reptiles such as lizards, pterosaurs, turtles Kirgizemys dmitrievi and choristoderes 459 Khurendukhosaurus sp. (Skutschas and Vitenko, 2017) are also found. The fossil crocodyliforms, 460 another reptile group found in more southern Late Mesozoic vertebrate faunas in Mongolia, have 461 not been recorded so far from there. This is most likely due to the cool climate, which is not 462 suitable for crocodyliforms,. Although although it is impossible to exclude the possibility that they 463 simply did not get into the paleontological record. Fish remains Stichopterus sp., Paleonisciformes 464 indet., cf. 465 discovery of the eutherian mammal Murtoilestes abramovi (Averianov and Skutschas, 2001) in 466 one of the Mogoito gullies is noteworthy. 475 Kakanaut locality (Chukotka, Russia). A CLAMP analysis of the Maastrichtian Kakanaut coastal 476 paleoflora, using the Physg3brcAZ and the WorldClim2 calibration data sets, yielded a mean 477 annual temperature of ~12 °C, the warmest month having a mean temperature of ~21 °C, and the 478 coldest month a mean temperature of ~5 °C (Zolina et al., 2020). However, the absence of 479 crocodyliforms and the presence of turtles and choristoderes in the Mogoito locality suggest a 480 temperate climate, with an annual mean temperature well above freezing level but below 14°C

  The overlying Ubukun Fm. is represented by lacustrine sediments. All fossil fauna found 500 here is limnophilic. The morphological features of ostracods in the lower part of the formation

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The average 485 global temperature was about 17•C (Scotese et al., 2021). 486 All palynological samples from the Mogoito locality revealed only rare palynomorphs 487 including spores and pollen of terrestrial plants and freshwater microphytoplankton. The low 488 counts in palynomorphs could be probably attributed to a taphonomic bias related to the coarse-489 grained character of the deposits less favorable to the accumulation of light-weighted organic 490 material. Terrestrial palynomorphs are represented by spores of cyatheaceous/dipteridaceous, 491 osmundaceous and schizaeaceous ferns, liverworts and lycopods, ginkgoalean pollen grains and 492 saccate pollen of conifers. Stratigraphically important taxa include Cicatricosisporites sp., 493 Foraminisporis asymmetricus and Rouseisporites reticulatus, which were widespread across 494 Siberia in the Lower Cretaceous (Averianov et al., 2022). 495 Taking into account the data on ostracods and malacofauna, it can be assumed that in the 496 Murtoi time there were no large deep lakes in the Gusinoozersk Basin. Water bodies rather 497 consisted in a series of small open lakes and oxbow lakes. The climate was cooler than in 498 subsequent ages although absolute temperature ranges are difficult to estimate. 499 501 indicate a depth of the paleolake of 50-100 m. The main representatives of ostracods here are 502 Mongolianella subexsortis, M. rocodi, M. substriata, Limnocypridea grammi (Skoblo et al. 2001).

  , plant remains, such as Cyparissidium gracile,Skoblo et al., 2001) (see fig.3 and 9B). Since the age of the Lower Selenga Sfm., 546 according to the youngest zircon in the sample, is younger than ~116 Ma, it can be argued that the 547 Monostoy Fault began to control the subsidence of the basin not earlier than this time. As in the 548 case of the Murtoi Fm., the age is estimated from a single grain and should be taken with caution.

	522 523 545 bearing deposits (549 marshes of the Murtoi Fm., deep lakes (or a single, large lake) formed during the deposition time of the Ubukun Fm. This is supported both by the sediment facies and the rich ostracod fauna. Later, The next young zircon has an age of ~171 Ma (Supplementary Data, Tables S2), which is
	550	obviously older than the age of the underlying Murtoi Fm. The absence of a sufficient amount of
	551	young zircons, corresponding to the age of sedimentation of the Selenga Fm., is possibly related
	552	F F to the mafic composition of volcanism characteristic of this time (Vorontsov et al., 2016). Thus,
		o r o r
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	515	Pterophyllum sensovianum, Coniopteris (Birisia) onychioides, Sphenopteris (Ruffordia)

516

goeppertii, Onychiopsis elongate, Scleropteris dahurica, belong to typical Early Cretaceous forms.

517

A large number of fossil remains of flora and fauna thus make it possible to reconstruct the 518 paleoenvironmental evolution of the basin. The onset of formation of the Gusinoozersk basin Basin 519 coincided with the global cooling Weissert Event. During that period the temperate climate 520 prevailing in Transbaikalia was favorable to the existence and reproduction of dinosaur, turtles 521 and choristoderes, but not suitable for crocodiles. Following the small-scale open-water lakes and 553 we rely on the only obtained date of ~116 Ma to characterize the age of the Lower Selenga Sfm., 554 but at the same time we assume that the beginning of its deposition may be older, but not older 555 than ~130 Ma. Since the thickness of the sediments in the basin is not constant (there is a trend 556 towards an increase in thickness from the western to the eastern side (Bulnaev, 2006)), the 557 Monostoy Fault most probably played a major role in the second stage of the development of the 558

Early Cretaceous topographic evolution associated with the collapse of the Mongol- 2 Okhotsk orogen in Western Transbaikalia: an integrated analysis 3 Anastasia V. Arzhannikova a,* , Elena I. Demonterova a , Alexander V. Sizov a,b , Marc Jolivet c , 4 Ekaterina A. Mikheeva a , Alexei V. Ivanov a , Sergey G. Arzhannikov a , Valentin B. Khubanov d

  About stratigraphy of the Mesozoic continental deposits in Zabaikalye.

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	649 779 904 928 952 978 29	935. Doi: 10.1016/j.gr.2012.07.017 Russia. Neues Jahrb. fur Geol. Palaontol. -Abh. 247, 63-78. rifting magmatism in the Uda sector of Western Transbaikalia. Russ. Geol. Geophys. 57(5), Mongol-Okhotsk collisional orogeny in latest Jurassic-earliest Cretaceous. Gondwana Tomurtogoo, O., Khosbayar, P., Arvisbaatar, N., Byambaa, Ch, 1998. Terranes in east the rise of a positive topography characterizing the exhumation of the metamorphic core
	905 929 953 979 30	Skutschas, P.P., Vitenko, D.D., 2017. Early Cretaceous choristoderes (Diapsida, Choristodera) 723-744. Research 28(3), 1096-1116. Mongolia and central Transbaikalia and evolution of the Okhotsk-Mongolian fold belt. complexes. Overlying fine-grained formations indicate a significant smoothing of the topography,
	881 906 930 954 980 31	of alkaline and peralkaline syenite-granite suites in the Mongolian-Transbaikalian Belt, from Siberia, Russia. Cretac. Res. 77, 79-92. Wang, T., Guo, L., Zheng, Y., Donskaya, T., Gladkochub, D., Zeng, L., Li, J., Wang, Y., Yarmolyuk, V.V., Kozlovsky, A.M., Savatenkov, V.M., Kovach, V.P., Kozakov, I.K., Kotov, Russ. Geol. Geophys. 39(1), 11-25. suggesting that from middle Aptian, Western Transbaikalia developed in a relatively calm tectonic
	882 907 931 955 981 5 32	Russia: Evidence from U-Pb geochronology and whole rock geochemistry. Chem. Geol. Sláma, J., Košler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S.A., Mazukabzov, A., 2012. Timing and processes of late Mesozoic mid-lower-crustal A.B., Lebedev, V.I. and Eenjin, G., 2016. Composition, Sources, and Geodynamic Nature Zorin, Yu.A., Sklyarov, E.V., Mazukabzov, A.M., Belichenko, V.G., 1997. Metamorphic core a Institute of the Earth's Crust, Russian Academy of Sciences, Siberian Branch, Irkutsk, Russia regime. We also show that the basins of Transbaikalia were formed both in conjunction with the
	883 908 932 956 982 6 33	273(1-2), 120-135. http://dx.doi.org/10.1016/j.chemgeo.2010.02.017 Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., extension in continental NE Asia and implications for the tectonic setting of the destruction of Giant Batholiths in Central Asia: Evidence from the Geochemistry and Nd Isotopic complexes and Early Cretaceous rifting in the Trans-Baikal region. Russ. Geol. Geophys. Geological Institute, Russian Academy of Sciences, Moscow, Russia exhumation of metamorphic cores complexes and reactivated structural sutures. Revised data on b
	884 909 933 957 983 7 34	Scotese, C.R., Song, H., Mills, B.J.W., van der Meer, D.G., 2021. Phanerozoic paleotemperatures: Whitehouse, M.J., 2008. Plesovice zircon -A new natural reference material for U-Pb and of the North China Craton: mainly constrained by zircon U-Pb ages from metamorphic Characteristics of Granitoids in the Khangai Zonal Magmatic Area. Petrology 24(5), 433-38, 1574-1584. c Laboratoire Géosciences Rennes, CNRS-UMR6118, Université de Rennes, Rennes, France dinosaur fauna and palynology, together with the dating of host deposits, provide insights on the
	835 885 910 934 958 984 8 35	F F F F F F F F Dokl. Akad. Nauk SSSR 105 (2), 335-338 (in Russian). F F The Earth's changing climate during the last 540 million years. Earth-Sci. Rev 215, F Hf isotopic microanalysis. Chem. Geol. 249, 1-35. F core complexes. Lithos 154, 315-345. F 461. F al., 2020). F d Geological Institute, Russian Academy of Sciences, Siberian Branch, Ulan-Ude, Russia F Early Cretaceous paleoenvironmental evolution.
	886 911 935 959 9 10 36	o r o r o r o r o r o r o r o r o r o r 103503. https://doi.org/10.1016/j.earscirev.2021.103503. o r Sorokin, A.A., Zaika, V.A., Kovach, V.P., Kotov, A.B., Xu W.L., Yang, H., 2020. Timing of o r Wang, T., Tong, Y., Xiao, W.J., Guo, L., Windley, B.F., Donskaya, T., Li, S., Narantsetseg, T. o r Yarmolyuk, V.V., Vorontsov, A.A., Ivanov, V.G., Kovalenko, V.I., Baikin, D.N. and o r o r *Corresponding author: Arzhannikova Anastasia, arzhan@crust.irk.ru o r
	887 888 889 912 913 914 936 937 938 960 961 962 11 12 13	P e e r P e e r P e e r P e e r P e e r P e e r P e e r P e e r P e e r P e e r Sengör, A.M.C., Natal'in, B.A., 1996. Paleotectonics of Asia: fragments of a synthesis. In: Yin, A., Harrison, T.M. (Eds.), The Tectonics of Asia. Cambridge Univ. Press, New York, pp. 486-640. P e e r closure of the eastern Mongol-Okhotsk Ocean: Constraints from U-Pb and Hf isotopic data of detrital zircons from metasediments along the Dzhagdy Transect. GR. 81, 58-78. Stanley, E.A., 1966. The problem of reworked pollen and spores in marine sediments. Marine P e e r and Zhang, J.J., 2022. Rollback, scissor-like closure of the Mongol-Okhotsk Ocean and formation of an orocline: magmatic migration based on a large archive of age data. Natl. Sci. Rev. 9(5), nwab210. P e e r Sandimirova, G.P. 2000. Stages of Bimodal and Alkaline Granite Magmatism in the Western Transbaikal Region: Geochronological Data on Rocks from the Tugnui Depression. Dokl. Earth Sci. 373, 811-815. P e e r P e e r P Abstract The Early Cretaceous topographic evolution of Transbaikalia was largely governed by the tectonic evolution of the Mongol-Okhotsk orogen. The collapse of the Mongol-Okhotsk orogen e e r
	890 891 892 893 894 915 916 917 918 919 939 940 941 942 943 963 964 965 966 967 14 15 16 17 41 42 43 44	R e v i e w R e v i e w R e v i e w R e v i e w R e v i e w R e v i e w R e v i e w R e v i e w R e v i e w R e v i e w Serdobolskaya, I.N. and Kozubova, L.A., 1976. On the age of the Ichetui suite in West Transbaikaliya. Russ. Geol. Geophys. 7, 90-93 (in Russian). Sheldrick, T.C., Barry, T.L., Dash, B. et al., 2020. Simultaneous and extensive removal of the East Asian lithospheric root. Sci Rep 10, 4128. https://doi.org/10.1038/s41598-020-60925-3 Sklyarov, E.V., Mazukabzov, A.M., Mel'nikov, A.I., 1997. Metamorphic Core Complexes of the R e v i e w Geology, 4(6), 397-408. Vakhrameev, V.A., 1964. Jurassic and early Cretaceous floras of Eurasia and the paleofloristic provinces of this period. Moscow, 263 pp. (in Russian). Vakhrameev, V.A., 1982. Division and correlation of continental deposits according to paleobotanical data // Soviet Geology 1, 58-67 (in Russian). R e v i e w Wang, T., Zheng, Y.D., Zhang, J.J., Zeng, L.S., Donskaya, T.V., Guo, L., Li, J.B., 2011. Pattern and kinematic polarity of late Mesozoic extension in continental NE Asia: perspectives from metamorphic core complexes. Tectonics 30, TC6007. https://doi.org/10.1029/2011TC002896. Wernicke, B., 1981. Low-angle normal faults in the Basin and Range Province: nappe tectonics in R e v i e w Yin, A., Nie, S., 1993. An indention model for North and South China collision and the development of the Tan Lu and Honam fault systems, eastern Asia. Tectonics 12, 801-813. Yin, A., Nie, S., 1996. A Phanerozoic plinspatic reconstruction of China and its neighbouring regions. In: Yin, A., Harrison, T.M. (Eds.), The Tectonic Evolution of Asia. Cambridge University Press, Cambridge, pp. 442-485. R e v i e w R e v i e w triggered the formation of metamorphic core complexes and associated extensional basins, widespread throughout Transbaikalia, North Mongolia, and North China. Numerous lithofacies and biostratigraphic studies have been carried out from the sedimentary deposits of the Transbaikalia basins. However, the absence of absolute ages for the sedimentary series, as well as 1. Introduction R The Mesozoic topographic and environmental evolution of Transbaikalia was largely driven by e v the tectonic evolution of the Mongol-Okhotsk orogenic belt (see fig. 1A for location). The belt i e was formed as a result of the closure of the Mongol-Okhotsk Ocean which extended between the w Siberian and Mongolian-North China continents from the Late Paleozoic to the Mesozoic
	895 896 897 920 921 922 944 945 946 968 969 18 19 970 20	O n l y O n l y O n l y O n l y O n l y O n l y O n l y O n l y O n l y O n l y Cordilleran Type. SPC UIGGM Siberian Branch of the RAS, Novosibirsk, pp. 176 (in Russian). Skoblo, V.M., 1967. The biostratigraphic scheme of the Lower Cretaceous in the western O n l y Van der Beek, P., Delvaux, D., Andriessen, P.A.M., and Levi, K.G., 1996. Early Cretaceous denudation related to convergent tectonics in the Baikal Region, SE Siberia // J Geol Soc, London 153, 515-523. O n l y an extending orogen. Nature 291, 645-648 Wiedenbeck, M., Allé, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., Van Quadt, A., Roddick, J.C., Spiegel, W., 1995. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element O n l y Zhang, K.-J., Yan, L.-L., and Ji, C., 2019. Switch of NE Asia from extension to contraction at the O n O n sediment source-to-sink analysis do not allow to accurately characterize the regional topographic evolution. We focused our study on the Gusinoozersk Basin of Western Transbaikalia, where O n mid-Cretaceous: A tale of the Okhotsk oceanic plateau from initiation by the Perm Anomaly to extrusion in the Mongol-Okhotsk ocean? Earth-Science Reviews 198, 102941. l y l y l extensive sedimentary sections of Lower Cretaceous deposits have been preserved. We provide y
	21	new U/Pb (LA-ICP-MS) data on detrital zircons from sedimentary series and 40 Ar/ 39 Ar data on
	898 923 947 971	Zabaikalye. In: The problems of geology of Pribaikalye and Zabaikalye, issue 2(4). Chita Vorontsov, A.A., Ivanov, V.G., Yarmolyuk, V.V., Kuzmin, M.I., Sandimirova, G.P., Smirnov, and REE analyses. Geostandards Newslett. 19, 1-23. Zheng, Y., Wang, S., Wang, Y., 1991. An enormous thrust nappe and extensional metamorphic
	22	intruding rocks. We review the paleontological data to clarify the age of the paleogeographic
	643 899 924 948 972	prevailing in Transbaikalia was favorable to the existence and reproduction of dinosaur, turtles (in Russian). V.N., 1999. Late Mesozoic bimodal alkaline volcanic association of Western Transbaikalia Yang, W., Jolivet, M., Dupont-Nivet, G., Guo, Z., Zhang, Z., Zhang, Z., 2013. Source to sink core complex in Sino-Mongolian boundary area. Science in China, ser. B 34, 1145-1152.
	23	events associated with the collapse of the Mongol-Okhotsk orogen, as well as to correct the age of
	644 875 900 925 949 973	and choristoderes, but not suitable for crocodiles. The time of the onset of sedimentation in the Geol. 583, 120437 DOI: 10.1016/j.chemgeo.2021.120437 Skoblo, V.M., Lyamina, N.A., Rudnev, A.F., Luzina, I.V., 2001. Continental Upper Mesozoic of and the age of its formation: geological and geochronological (Rb-Sr and K-Ar) data. Dokl. relations between the Tian Shan and Junggar Basin (northwest China) from Late Palaeozoic Zonenshain, L.P., Kuzmin, M.I., Natapov, L.M., 1990. Geology of the USSR: A Plate tectonic
	24	faunal complexes in Western Transbaikalia. Our geochronological results show that the formation
	645 876 901 926 950 974	Gusinoozersk Basin probably coincides with the Weissert Event ~133 million years ago marking Prokopiev, A.V., Toro, J., Miller, E.L., Gehrels, G.E., 2008. The paleo-Lena River -200 m.y. of Pribaikalia and Transbaikalia (Stratigraphy, Sedimentation Conditions, Correlations). Izd-Earth Sci. 369(2), 220-224 (in Russian). to Quaternary: evidence from detrital U-Pb zircon geochronology. Basin Res. 25, 219-240. synthesis. American Geophysical Union. Geodyn. 21 https://doi.org/10.1029/GD021.
	25	of the Cretaceous basins of Transbaikalia began around 136-130 Ma, accompanying the main
	902 975	vo SB RAS, Novosibirsk, pp. 332 (in Russian). Zorin, Yu.A., 1999. Geodynamics of the western part of the Mongolia-Okhotsk collisional belt,
	26	episode of extension associated with the exhumation of the metamorphic core complexes. The
	976	Trans-Baikal region (Russia) and Mongolia. Tectonophysics 306, 33-56.
	27	lowest coarse-clastic formation characterizes the rapid subsidence and the predominance of
		URL: https://mc.manuscriptcentral.com/tigr E-mail: rjstern@utdallas.edu

633 stage, by the Khambin Fault, and at a later stage, by the Monostoy Fault. The Khambin Fault is an 634 inherited Paleozoic structure reactivated during Cretaceous extension. The basins of Transbaikalia 635 were formed both in conjunction with the exhumation of metamorphic cores complexes and 636 reactivated structural sutures. 637 New data on dinosaur fauna and palynology, together with the dating of host deposits, 638 made it possible to correct the age of faunal assemblages in Western Transbaikalia, which is very 639 important for biostratigraphic correlations in various regions of Central Asia. The currently known 640 data on the palaeoenvironment of the Mogoito locality suggest that the climate was moderately 641 warm but too cold for thermophilic crocodyliforms. The onset of formation of the Gusinoozersk

642 Basin coincided with the global cooling Weissert Event. During that period the temperate climate 646 a profound global cooling that punctuated the Early Cretaceous greenhouse (Cavalheiro et al., 647 2021; Scotese et al., 2021). 828 Mannion, P.D., Benson, R.B.J., Carrano, M.T., Tennant, J.P., Judd, J., Butler, R.J., 2015. Climate 829 constrains the evolutionary history and biodiversity of crocodilians. Nat. Commun. 6, 830 8438. https://doi.org/10.1038/ncomms9438 PMID: 26399170 831 Markwick, P.J., 1998. Fossil crocodilians as indicators of Late Cretaceous and Cenozoic climates:

832 implications for using palaeontological data in reconstructing palaeoclimate. Palaeogeogr. 833 Palaeoclimatol. Palaeoecol. 137, 205-71. 834 Martinson, G.G., 1955. 836 Martinson, G.G., 1961. Mesozoic and Cenozoic mollusks of the continental deposits in the 837 Siberian platform, Zabaikalye and Mongolia. In: Tr. Baikal limnological station, issue 19. 838 Izd-vo Akademii Nauk SSSR, Moscow-Leningrad, 332 pp. (in Russian). 839 Mazukabzov, A.M., Donskaya, T.V., Gladkochub, D.P., Sklyarov, E.V., Ponomarchuk, V.A. and 840 Salnikova, E.B., 2006. Structure and age of the metamorphic core complex of the Burgutui 841 ridge (southwestern Transbaikal region). Dokl. Earth Sci. 407, 179-183. 842 Mazukabzov, А.М., Sklyarov, Е.V., Donskaya, Т.V., Gladkochub, D.P., Fedorovsky, V.S., 2011. 843 Metamorphic core complexes of the Transbaikalia: review. Geodyn. Tectonophys. 2(2), 844 95-125. 845 Metelkin, D.V., Vernikovsky, V.A., Kazansky, A.Y., and Wingate, M.T.D., 2010. Late Mesozoic 846 tectonics of Central Asia based on paleomagnetic evidence. Gondwana Research 18, 400-847 419. 848 Metelkin, D. V., Gordienko, I. V. and Zhao, X., 2004. Paleomagnetism of Early Cretaceous 849 volcanic rocks from Transbaikalia: argument for Mesozoic strike-slip motions in Central 850 Asian structure. Russ. Geol. Geophys. 45(12), 1349-1363. 851 Mikheeva, E.A., 2017. Age Limits, Correlation and Source Areas of the Jurassic Sediments in the 852 Irkutsk Basin. Synopsis of the M.S. thesis, IEC SB RAS, Irkutsk, 16 pp. (in Russian).

853 Nesov, L.A., Starkov, A.I., 1992. Cretaceous vertebrates of Gusinoe Lake depression in 854 Transbaikalia and their contribution into dating and determination of sedimentation 855 conditions. Russ. Geol. Geophys. 6 (378), 10-19 (in Russian). 856 Nie, S., 1991. Paleoclimatic and paleomagnetic constraints on the Paleozoic Reconstructions of 857 south China, north China and Tarim. Tectonophysics 196, 279-308. 858 Nie, S., Rowley, D.B., Ziegler, A.M., 1990. Constraints on the location of Asian microcontinents 859 in Paleo-Tethys during late Palaeozoic. In: McKerrow, W.S., Scotese, C.R. (Eds.), 860 Palaeozoic Palaeogeography and Biogeography, vol. 12. Geol. Soc. Mem. Am., pp. 12397-861 12409. 862 Otchirov, Ts.O., 1964. Geology of the Gusino-Ivolginsk part of Buryatia. Buryat Publ. House, 863 Ulan-Ude, 155 pp. (in Russian). 864 Parfenov, L.M., Berzin, N.A., Khanchuk, A.I., Badarch, G., Belichenko, V.G., Bulgatov, A.N., 865 Dril, S.I., Kirillova, G.L., Kuzmin, M.I., Nockleberg, W., Prokopyev, A.V., Timofeev, 866 V.F., Tomurtogoo, O., Yan, X., 2003. A model for the formation of orogenic belts in 867 Central and NE Asia. Russ. J. Pac. Geol. 22 (6), 7-41. 868 Parfenov, L.M., Popeko, L.I., Tomurtogoo, O., 2001. Problems of tectonics of the Mongol-869 Okhotsk orogenic belt. Russian Journal of Pacific Geology 16, 797-830. 870 Platov V.S., Tereshchenkov V.G., Savchenko A.A., Busuek S.M., Anosova G.B., Polyansky S.A., 871 2013. State geological map of the Russian Federation, scale 1:200,000. Sheet M-48-V. 872 Selenga series. Explanatory note. MF VSEGEI, Moscow. 873 Powerman, V.I., Buyantuev, M.D., Ivanov, A.V., 2021. A review of detrital zircon data treatment, 874 and launch of a new tool 'Dezirteer' along with the suggested universal workflow. Chem. 877 transcontinental zircon transport in Siberia. Geology 36 (9), 699-702. 878 Qi, X., and Wang, Z. (Eds.), 2008. Geological map of Central Asia and adjacent areas 1:2500000. 879 Geological Publishing House, Beijing. 880 Reichow, M.K., Litvinovsky, B.A., Parrish, R.R., Saunders, A.D., 2010. Multi-stage emplacement 45 (

. Most 46 geodynamic models indicate a scissor-like closure of the ocean from West to East from the 47

Sedimentary deposits of the Gusinoozersk Basin 147

	F
	o r
	P
	e e r
	R e v
	i e w
	O n
	l
	y

130 Khambin Ridge, two dates were obtained with ages of ~159 and ~156 Ma (Andryushchenko et al., 131 2010). The northern part of the Khambin Ridge is characterized by the Sogotinsk igneous complex 132 (see fig. 2). Three phases of intrusion are distinguished within the complex: monzonites and quartz 133 monzonites; syenites, quartz syenites and granosyenites; and moderately alkaline granites and 134 leucogranites. Geochronological dating of the Sogotinsk complex by the K-Ar method provided 135 an age range of 271-220 Ma for the granitoids, while the Rb-Sr method gave an age range of 287-136 267 Ma (Platov et al., 2013). 137 The Monostoy Ridge is mainly composed of Paleozoic meta-sedimentary series, locally 138 intruded by the Triassic granitoids of the Malo-Kunaley complex and some Early Jurassic bimodal 139 association (Fig. 2). The Malo-Kunaley complex is represented by peralkaline granites, 140 granosyenites and alkaline syenites. A Late Triassic age of 220-212 Ma was determined for the 141 Malo-Kunaley granites from whole rock Rb-Sr and zircon U-Pb analysis (Yarmolyuk et al., 2000; 142 Litvinovsky et al., 2001; Reichow et al., 2010). The Early Jurassic bimodal association is 143 widespread in Western Transbaikalia. Within the Monostoy Ridge it is composed of a thick (over 144 2000 m) bimodal volcanic sequence (trachybasalts, trachyandesite-basalts, alkaline trachydacites) 145 with an age, determined by whole rock Rb-Sr analysis, of ~194 Ma (Yarmolyuk et al., 2000).

146 2.2.

  MS) analysis was made at the Analytical center of mineralogical, geochemical and isotope studies 287 at the Geological Institute, SB RAS. The sample preparation and analytical procedures are the 288 same as described inArzhannikova et al. (2020). The isotopic ratios measurement technique is

	286
	289	described in detail in Khubanov et al. (2016) and Buyantuev et al. (2017). For this study, more
	290	than 100 zircon grains were selected from each sample, with no differentiation of size (the size of
	291	the analyzed grains varied from 60 µm to 180 µm) or morphology. U-Pb analysis was performed
	292	using an ICP-MS Element XR (ThermoFisher Scientific) coupled to an UP-213 laser (New Wave).
	293	F Zircons 91500 (1065 Ma) (Wiedenbeck et al., 1995), Plešovice (337 Ma) (Slama et al., 2008), and
		o r
		P
	296	r e e 208 Pb/ 232 Th, 2.1%-2.6% for 207 Pb/ 206 Pb, 1.1%-2.6% for 206 Pb/ 238 U and 2%-2.5% for 207 Pb/ 235 U.
		R e v
		i e w
		O n
		l
		y

285

Geodynamics and Geochronology of the Institute of the Earth's Crust SB RAS. U-Pb (LA-ICP-

294

GJ-1 (608.5 Ma)

(Jackson et al., 2004)

were used as external standards. The relative errors in the 295 measurement for isotope ratios in the reference standards varied within ranges of 1%-2.3% for 297 Analytical results were processed using the GLITTER

(Griffin et al., 2008)

software. Only data 298 with a concordance >90% were taken into account in the interpretation. The abundance histograms 299 and probability density curves for each sample were plotted for 206 Pb/ 238 U ages with 2σ analytical 300 uncertainty using the Dezirteer software (Powerman et al., 2021). Most U-Pb ages cluster below 301 400 Ma with few outliers showing older ages (Supplementary Data, Tables

  Pb zircon ages were obtained. The main age population ranges 175-210 Ma, and is 313 complemented by a minor group with ages of 225-245 Ma and few, scattered older ages. The 314 youngest zircon present in the sample has an age of 116 ± 2 Ma (Fig. 6B; Supplementary Data,

	312 U-315 Tables S2). In the Kholboldzhin Fm. (sample Gus-14-1), 103 concordant U-Pb zircon ages were
	316	obtained. Zircon ages are distributed into one major population at 160-230 Ma with a main peak
	317	at 191 Ma. A few older outliers are also present as in the Lower Selenga sample. The youngest
	318
		F
		o r
		P
		e e r
		R e v
		i e w
		O n
		l
		y
	306	18.885 ± 0.097 Ma, which makes it possible to directly compare the 40 Ar/ 39 Ar and U-Pb ages
	307	(Ivanov et al., 2017).

303 40 Ar/ 39 Ar dating was carried out at the Centre for Geodynamics and Geochronology of the 304 Institute of the Earth's Crust SB RAS using an ARGUS VI mass spectrometer coupled to a double-305 vacuum resistance oven. The age was calculated relative to the BERN4M standard with an age of 308 Ninety-one concordant U-Pb zircon ages were obtained from the basal Murtoi Fm. 309 (sample Gus-17-1). They are statistically distributed into the following populations: 150-165, 170-310 185, 215-245, 250-270 and 280-300 Ma. The youngest zircon has an age of 136 ± 4 Ma (Fig. 6A; 311 Supplementary Data, Tables

S1

). In the Lower Selenga Sfm. (sample Gus-14-6), 76 concordant

Age and evolution of provenance of the Gusinoozersk Basin deposits

  40 Ar/ 39 Ar plateau age of lamprophyre sample Mur-17-1 lamprophyres collected from Ma and initial 40 Ar/ 36 Ar=285 ± 63. Because the initial argon isotope compositionIn sample Gus-14-6 from the Lower Selenga Sfm., most zircons ages range 175-210 Ma 339 (see fig.6B), which can be attributed to the syenites of the Burgutuy massif, as well as to the Early 340 Jurassic bimodal association, identified within the Monostoy Ridge. A small population with an 341 age of 225-245 Ma matches the age of the Sogotinsk igneous complex. Judging by the significant occurrence of Late Carboniferous-Early Permian 366 detrital U-Pb zircon ages in the Lower-Middle Jurassic deposits of the Verkhoyansk margin and Vitim batholith transported the clastic material southward to the Mongol-Okhotsk continental 371 margin. The closure of the Mongol-Okhotsk Ocean in the region of Western Transbaikalia at the

	338 390	trachybasaltic and trachyandesite composition in the Khambin Ridge (127-124 Ma)
	391	(Andryushchenko et al., 2010), large volcanoes of alkaline rhyolites (~140 Ma), including those
	392	within the Monostoy Ridge (Yarmolyuk et al., 2000), as well as two stages of magmatic activity
	367 393	the Irkutsk Basin (see fig. 1B for location), the Angara-Vitim batholith region represented an that occurred in Western Transbaikalia at 143-135 Ma and 131-111 Ma (Vorontsov et al., 2016).
	342 368 394	In sample Gus-14-1 from the Kholboldzin Fm., almost all zircons ages are 160-230 Ma, uplifted area up to the beginning of the Middle Jurassic (Prokopiev et al., 2008; Demonterova et In their study, Vorontsov et al. (2016) pointed out that after 135 Ma, the emitted volume of
	343 369 395	with the maximum number occurring between 160 and 200 Ma (see Fig. 6C), as in the Selenga al. , 2017; Mikheeva, 2017). Until that time, the rivers draining the southern part of the Angara-volcanic rocks sharply decreased and their composition changed from bimodal associations to
	344 370 396	Sfm. basaltoid ones. The predominance of mafic rocks among the Early Cretaceous volcanics (up to
	397	F F F 90%) (Donskaya et al., 2013; Sheldrick et al., 2020) possibly explains the small number of zircons
		o r o r o r
		P P P
		e e r e e r e e r
	325 326 327	4. Discussion 4.1.	R e v R e v R e v i e w i e w i e w
			O n O n O n
			l l l
			y y y
	333 385	in this sample can be attributed to the Angara-Vitim batholith. Finally, tracing the provenance of the Murtoi Fm. In the adjacent areas, volcanic rocks with such ages are not known (Wang et al.,
	334 386	the 170-185 Ma zircons is a challenge. Almost no igneous rocks of this age have been found in 2022); therefore, the question of the provenance of these zircons remains open.
	335	Western Transbaikalia or Northern Mongolia. The only dating of syenites in this range (178 ± 3

320

the Murtoi dike is 130 ± 1 Ma (Fig.

7A

). The same plateau steps form an inverse isochron with 321 age of 130 ± 1 322 is equal to the atmospheric value (~300), the calculation of the plateau age, which assumes the 323 atmospheric initial value, is justified. Further, we use the plateau age because it has lower 324 analytical uncertainty.

328

In sample Gus-17-1 from the Murtoi Fm. the age population of 150-165 Ma forms a 329 significant age peak (see Fig.

6A

). This age range corresponds to that of the "Ichetui" bimodal 330 volcanics identified in the southern part of the Khambin Ridge (see Fig.

2

). The main age 331 population of 215-270 Ma corresponds in age to the Sogotinsk igneous complex identified in the 332 northern part of the Khambin Ridge (see Fig.

2

). The small age population of 280-300 Ma zircons 336 Ma) is situated in the Burgutuy massif of the Buteel metamorphic core complex (Mazukabzov et 337 al., 2006) (see Fig. 1B for location).

345 As evidenced by the histogram of the age distribution of detrital zircons from the Murtoi 346 Fm. (Fig. 6A), the contribution of proximal sources located in the Khambin Ridge in the total 347 amount of zircons is major. The mostly coarse-grained deposits suggest that most of the clastic 348 material was transported by braided rivers draining the Khambin Rigde. The minor zircon 349 population of 170-185 Ma indicates a small contribution to the sedimentation from more distant 350 provinces located to the south in the area of the Burgutuy massif of the Buteel metamorphic core 351 complex (see fig. 1B for location). In the overlying Selenga and Kholboldzhin Fms., zircons 352 brought from the Khambin Ridge are practically absent, except for a small population with an age 353 of 225-245 Ma. The main source of sediments in these formations appears to be the Monostoy 354 Ridge and the Buteel metamorphic core complex. Syn-tectonic biotite 40 Ar/ 39 Ar age and U-Pb age 355 of metamorphic zircon from the footwall of the Buteel metamorphic core complex indicate that its 356 exhumation occurred between 138 Ma and 122 Ma (Mazukabzov et al., 2011), possibly exposing 357 the 178 ± 3 Ma Burgutuy massif to erosion and providing a new sediment source for the 358 Gusinoozersk Basin. A fine-grained lithology of the Selenga and Kholboldzhin Fms. sediments 359 reflects a smoothing of the topography in the region, suggesting a low-intensity tectonic regime. 360 The slow subsidence of the basin during the accumulation of the Selenga and Kholboldzhin Fms.

361 was largely compensated by sedimentation mainly occurring in lacustrine-swamp depositional 362 environments with an occasional supply of coarser alluvial material associated with erosion of the 363 sides of the basin. All formations contain a few zircons with ages of 280-330 Ma that match the 364 age of the Angara-Vitim batholith (Litvinovsky et al., 2011) located to the north of the 365 Gusinoozersk Basin. 372 Early and Middle Jurassic boundary led to a reorganization of the drainage network and a change 373 in the direction of transport of sedimentary material to the north (Arzhannikova et al., 2020). The 374 occurrence of zircon ages corresponding to sources both north and south of Western Transbaikalia 375 in one sample indicates recycling of sediments from previous deposits (Yang et al., 2013), as it 376 has been observed for the Middle Jurassic deposits of the neighboring Tugnui Basin 377 (Arzhannikova et al., 2020) (see fig. 1B for location). The pre-existing cover sequence at the 378 Mongol-Okhotsk continental margin, containing zircons derived from the Angara-Vitim batholith, 379 was probably still largely preserved by the Early Cretaceous and participated to the clastic material 380 source. Although the contribution of recycled zircons to the deposits of the Gusinoozersk Basin is 381 not significant: in the Murtoi Fm., zircons with the age of the Angara-Vitim batholith do not exceed 382 7%, and only single grains of this age are found in the overlying formations. 383 Single zircon grains with ages ranging from 330 to 400 Ma are found in samples from the 384 Lower Selenga Sfm. and Kholboldzhin Fm. There are no zircons of this age in the sample from 387 The youngest generations of zircons in the samples were found in the Murtoi Fm. and 388 Lower Selenga Sfm. These are composed of a very few single grains with ages ranging from ~116 389 to 145 Ma (Fig. 6 A, B). These ages correspond to the ages of single paleovolcanoes of 398 of this age in the samples. 399 Thus, our geochronological studies made it possible to clarify the onset time of the 400 formation of the Gusinoozersk Basin. While it was previously considered as Middle Jurassic to 401

2. Taphonomy of the Mogoito locality series and paleoenvironmental application

  Murtoi Fm., which correspond to those that were widespread across Siberia in the Lower 417 Cretaceous. For some species (Foraminisporis asymmetricus and Rouuseisporites reticulatus), the 418 lower stratigraphic limit corresponds to the middle of the lower Valanginian (Averianov et al., 419 2022), which is in good agreement with the lower age limit of the formation at ~136 Ma obtained 420 in our work from the dating of the youngest zircon. This result suggests that the Jurassic spore-421 pollen spectra found in the Selenga and Kholboldzhin Fms. (Jolivet et al., 2017) were indeed 422 recycled from the Jurassic sediments widespread in the region in the Lower Cretaceous. This 423 would explain the discrepancy between those Jurassic spore-pollen spectra and the Lower It yielded the largest number of vertebrates remains from the Gusinoozersk Basin. The 436 Mogoito locality consists of a series of natural outcrops in shallow ravines and scours on the 437 western bank of Lake Gusinoe exposing sediments from the Murtoi Fm. The locality represents 438 an important source of information about the Early Cretaceous vertebrate fauna of Central Asia. alluvial cross-bedded fine-to-coarse grain sandstone alternating with a thinner layer 443 of shale and siltstone with remains of bivalve mollusks and vertebrates. The remains of fossil bones 444 are randomly scattered in the sediments. There are no articulated skeletal elements here, and most 445 of the bones are highly fragmented. Some bones were carried by water currents and rounded. Sauropoda indet.) are also present but yet under study (Averianov et al., 2022). Three 449 theropod groups have been identified from the Mogoito locality based on the isolated bones and age of the sediments in Mogoito, because when present, Psittacosaurus is the 469 most abundant dinosaur taxon in an assemblage (Averianov et al., 2022). Dinosaurs cannot be used as good indicators of climate because some of them thrived and 471 even bred in the cool temperate climate above the Arctic Circle, such as in Kakanaut locality series of small open lakes and oxbow lakes. The climate was cooler than in 495 subsequent ages although absolute temperature ranges are difficult to estimate. The overlying Ubukun Fm. is represented by lacustrine sediments. All fossil fauna found 497 here is limnophilic. The morphological features of ostracods in the lower part of the formation 498 indicate a depth of the paleolake of 50-100 m. The main representatives of ostracods here areIn the upper part of the formation, the faunal complex changes. Forms characteristic of small 501 marshy lakes appear. The complex of bivalves given by(Kolesnikov, 1977) contains forms

	416 442 472 is composed of 446 A major amount of fossils belongs to the sauropods Tengrisaurus starkovi (Averianov and (Chukotka, Russia). A CLAMP analysis of the Maastrichtian Kakanaut coastal paleoflora, using 468 indicates an older 470 494 consisted in a
	447 473	Skutschas, 2017; Averianov et al., 2021) belonging to the titanosaurs group. Remains of another the Physg3brcAZ and the WorldClim2 calibration data sets, yielded a mean annual temperature of
	448 474 475	F F ~12 °C, the warmest month having a mean temperature of ~21 °C, and the coldest month a mean sauropod (F temperature of ~5 °C (Zolina et al., 2020). However, the absence of crocodyliforms and the F
		o r o r o r o r
		P P P P
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		l l l l
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	411	Fms. are characterized by Late Jurassic species, while the flora macro-remains in the same deposits
	412	are Early Cretaceous (see for example the Old Zagustay samples in Jolivet et al., 2017). Jolivet et
	413	al. (2017) also reported the occurrence of few Cretaceous spores and pollens from the Selenga

; Skoblo 402 et al., 2001 and others), our detrital zircon U-Pb age data from the basal Murtoi Fm. indicate that 403 the basin began to subside not earlier than ~136 million years ago (according to the age of the 404 youngest zircon in the sample). However, this age of ~136 Ma relies on a single grain and is 405 therefore statistically very weak. A more representative number of young zircons (3 grains) have 406 an age of 150-153 Ma (Supplementary Data, Tables S1). However, the age of ~136 Ma is in better 407 agreement with the biostratigraphic data. Based on freshwater mollusks, Kolesnikov (1980) 408 estimated the age of the Murtoi Fm as Berriasian -Valanginian (~145-132.9 Ma). Based on the 409 age of the ostracods, Scoblo et al. (2001) dated the Murtoi Fm. as Berriasian-Hauterivian (~145-410 129.4 Ma). The spore-pollen assemblages associated with the overlying Selenga and Kholboldzhin 414 Sfm., finally suggesting that the Selenga, Bainzorkhen and Kholboldshin Fms are of late Late 415 Jurassic -Early Cretaceous age. Averianov et al. (2022) identified spore-pollen spectra from the 424

Cretaceous age of the flora macro-remains found in the same formations. Indeed, while spores and 425 pollens are small and resistant enough to be recycled from older sediment deposits

(Stanley, 1966)

, 426 macro-remains, and especially soft parts such as leafs are impossible to recycled. Since the 427 40 Ar/ 39 Ar dating of the Khurai-Baiba dike complex, intruding the deposits of the Murtoi Fm., 428 showed an upper age limit of 130 ± 1 Ma for the basal formation, we suggest that the formation of 429 the Gusinoozersk Basin started at 136-130 Ma. These data are consistent with the biostratigraphic 430 age of the Murtoi Fm. However, our new geochronological data narrows the age interval for the 431 beginning of sedimentation in the Gusinoozersk Basin.

432 4.433 Based on the fossils found at the Mogoito locality, we can model the paleoenvironment at 434 the time of the onset of sedimentation in the Gusinoozersk Basin during deposition of the Murtoi 435 Fm. 439 The lower alluvial-proluvial part of the Murtoi section in Mogoito locality is made of large and 440 medium pebble conglomerates of varying rounding, gravelstone and sandstone containing rare 441 fragmentary dinosaur fossils and remains of petrified wood. The upper alluvial part of the section 450 teeth: Ornithomimosauria, Therizinosauroidea, and Dromaeosauridae (Averianov et al., 2003; 451 Averianov and Skutschas, 2009; Averianov et al., 2022). All available remains previously 452 identified as Ornithopoda indet. as well as a Psittacosaurus sp. (Averianov and Skutschas, 2009) 453 from Mogoito locality can be attributed to a representative of the basal ornithischian clade 454 Jeholosauridae indet. (Averianov et al., 2022). Remains of other diapsid reptiles such as lizards, 455 pterosaurs, turtles Kirgizemys dmitrievi and choristoderes Khurendukhosaurus sp. (Skutschas and 456 Vitenko, 2017) are also found. The fossil crocodyliforms, another reptile group found in more 457 southern Late Mesozoic vertebrate faunas in Mongolia, have not been recorded so far from there.

458

This is most likely due to the cool climate, which is not suitable for crocodyliforms, although it is 459 impossible to exclude the possibility that they simply did not get into the paleontological record. 460 Fish remains Stichopterus sp., Paleonisciformes indet., cf. Irenichthys sp. (Averianov and 461 Skutschas, 2009) are found in alluvial deposits. The discovery of the eutherian mammal 462 Murtoilestes abramovi (Averianov and Skutschas, 2001) in one of the Mogoito gullies is 463 noteworthy. 464 The Mogoito locality is largely similar to the Khuren Dukh locality of Mongolia, sharing the 465 macrobaenid turtle Kirgizemys and the long-necked choristodere Khurendukhosaurus (Averianov 466 and Skutschas, 2000). However, abundant remains of Psittacosaurus at the Khuren Dukh locality 467 (Kalandadze and Kurzanov, 1974) are not known in the Mogoito locality. Apparently, this 476 presence of turtles and choristoderes in the Mogoito locality suggest a temperate climate, with an 477 annual mean temperature well above freezing level but below 14°C (Markwick, 1998; Mannion et 478 al., 2015; Amiot, 2011). The sedimentation age of the Murtoi Fm. (136-130 Ma, this study) 479 coincides with the global cooling Weissert Event, which took place at ~133 Ma (Cavalheiro et al., 480 2021) during the earliest Cretaceous (Berriasian to Barremian) and can be characterized as 481 something "in-between" a hothouse and an icehouse (Fig. 8). The average global temperature was 482 about 17•C (Scotese et al., 2021). 483 All palynological samples from the Mogoito locality revealed only rare palynomorphs 484 including spores and pollen of terrestrial plants and freshwater microphytoplankton. The low 485 counts in palynomorphs could be probably attributed to a taphonomic bias related to the coarse-486 grained character of the deposits less favorable to the accumulation of light-weighted organic 487 material. Terrestrial palynomorphs are represented by spores of cyatheaceous/dipteridaceous, 488 osmundaceous and schizaeaceous ferns, liverworts and lycopods, ginkgoalean pollen grains and 489 saccate pollen of conifers. Stratigraphically important taxa include Cicatricosisporites sp., 490 Foraminisporis asymmetricus and Rouseisporites reticulatus, which were widespread across 491 Siberia in the Lower Cretaceous (Averianov et al., 2022). 492 Taking into account the data on ostracods and malacofauna, it can be assumed that in the 493 Murtoi time there were no large deep lakes in the Gusinoozersk Basin. Water bodies rather 496 499 Mongolianella subexsortis, M. rocodi, M. substriata, Limnocypridea grammi (Skoblo et al. 2001). 500 502 characteristic of the entire Gusinoozersk Series. Vertebrate remains have not been found here, with 503 the exception of one aquatic macrobaenid turtle Kirgizemys (similar to those found in the Murtoi 504 Fm.), which, most likely, comes from the Ubukun Fm. (Danilov et al., 2006). 505 The Selenga and Kholboldzhin Fms. are represented by alluvial and lacustrine-alluvial 506 deposits. The lakes were periodically swamped, and the lacustrine-swampy sediments were later 507 repeatedly eroded by the river. In the Selenga Fm. several marker horizons contain (from bottom 508 to top) Limnocypridea defense, Darwinula murtoensis, Cypridea selenginensis, which were living 509 in large open lakes (Skoblo et al., 2001). Marking horizons containing Cypridea zagustaica and 510

  520of the Ubukun Fm. This is supported both by the sediment facies and the rich ostracod fauna. Later, 521 in the early Selenga Sub-fm. time, the lakes periodically decreased in size, and in the late Selenga

	522
		F
		o r
		P
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		i e w
		O n
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		y
	515	paleoenvironmental evolution of the basin. The onset of formation of the Gusinoozersk Basin
	516	coincided with the global cooling Weissert Event. During that period the temperate climate
	517	prevailing in Transbaikalia was favorable to the existence and reproduction of dinosaur, turtles

, plant remains, such as Cyparissidium gracile, 512 Pterophyllum sensovianum, Coniopteris (Birisia) onychioides, Sphenopteris (Ruffordia) 513 goeppertii, Onychiopsis elongate, Scleropteris dahurica, belong to typical Early Cretaceous forms. 514 A large number of fossils remains of flora and fauna thus make it possible to reconstruct the 518 and choristoderes, but not suitable for crocodiles. Following the small-scale open-water lakes and 519 marshes of the Murtoi Fm., deep lakes (or a single, large lake) formed during the deposition time

  ). Since the age of the Lower Selenga Sfm.,The next young zircon has an age of ~171 Ma (Supplementary Data, TablesS2), which is 547 obviously older than the age of the underlying Murtoi Fm. The absence of a sufficient amount of 548 young zircons, corresponding to the age of sedimentation of the Selenga Fm., is possibly related 549 to the mafic composition of volcanism characteristic of this time(Donskaya et al., 2013; Vorontsov 550 et al., 2016; Sheldrick et al., 2020). Thus, we rely on the only obtained date of ~116 Ma to 551 characterize the age of the Lower Selenga Sfm., but at the same time we assume that the beginning 552 of its deposition may be older, but not older than ~130 Ma. Since the thickness of the sediments 553 in the basin is not constant (there is a trend towards an increase in thickness from the western to 554 the eastern side(Bulnaev, 2006)), the Monostoy Fault most probably played a major role in the 555 second stage of the development of the basin, which started with the beginning of the accumulation

	546
		F
		o r
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	556	r e e
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	543	according to the youngest zircon in the sample, is younger than ~116 Ma, it can be argued that the

544

Monostoy Fault began to control the subsidence of the basin not earlier than this time. As in the 545 case of the Murtoi Fm., the age is estimated from a single grain and should be taken with caution.

  630stage, by the Khambin Fault, and at a later stage, by the Monostoy Fault. The Khambin Fault is an Pb detrital zircon data(Powerman et al., 2021). The latter can be downloaded 650 for free at http://dezirteer.com/ or used online at https://dezirteer.crust.irk.ru/. We thank three Sklyarov, Е.V., Donskaya, Т.V., Gladkochub, D.P., Fedorovsky, V.S., 2011. Berzin, N.A., Khanchuk, A.I., Badarch, G., Belichenko, V.G., Bulgatov, A.N., Harrison, T.M. (Eds.), The Tectonics of Asia. Cambridge Univ. Press, New York, pp. Sorokin, A.A., Zaika, V.A., Kovach, V.P., Kotov, A.B., Xu W.L., Yang, H., 2020. Timing of 903 closure of the eastern Mongol-Okhotsk Ocean: Constraints from U-Pb and Hf isotopic data 904 of detrital zircons from metasediments along the Dzhagdy Transect. GR. 81, 58-78. Zheng, Y.D., Zhang, J.J., Zeng, L.S., Donskaya, T.V.,Guo, L., Li, J.B., 2011. Pattern Yin, A., Nie, S., 1993. An indention model for North and South China collision and the 955 development of the Tan Lu and Honam fault systems, eastern Asia. Tectonics 12, 801-813.

	649 674 675 725 802 803 902 928 929 954 the analysis of U-651 of the Irkutsk basin and Southwestern Transbaikalia from the paleobotanical and geochronological data. Russ. Geol. Geophys. 59 (6), 773-791. of the southern Siberian continent (Transbaikalia) recorded in sediments of the Siberian Komarov, I.V. (ed.), 1962. Geological map of the USSR, scale 1:200,000. West-Zabaikalskaya series, sheet M-48-XI. VSEGEI, Leningrad (in Russian). formation of an orocline: magmatic migration based on a large archive of age data. Natl. Sci. Rev. 9(5), nwab210. anonymous reviewers for their valuable comments, which greatly improved the original 804 Leonov, Yu.G., 1983. Mesozoic tectonics and magmatism of East Asia (Correlation between time 880 486-640. 956 Yin, A., Nie, S., 1996. A Phanerozoic plinspatic reconstruction of China and its neighbouring
	652 677 805 830 856 881 905 931 957	manuscript. P.P., 2022. New data on dinosaurs from the Lower Cretaceous Murtoi Formation of of manifestation of tectonic movements and magmatism). Nauka, Moscow, 232 pp. (in Mazukabzov, A.M., Donskaya, T.V., Gladkochub, D.P., Sklyarov, E.V., Ponomarchuk, V.A. and Dril, S.I., Kirillova, G.L., Kuzmin, M.I., Nockleberg, W., Prokopyev, A.V., Timofeev, Serdobolskaya, I.N. and Kozubova, L.A., 1976. On the age of the Ichetui suite in West Stanley, E.A., 1966. The problem of reworked pollen and spores in marine sediments. Marine and kinematic polarity of late Mesozoic extension in continental NE Asia: perspectives regions. In: Yin, A., Harrison, T.M. (Eds.), The Tectonic Evolution of Asia. Cambridge
	653 678 806 831 857 882 906 932 958	Transbaikalia, Russian). Salnikova, E.B., 2006. Structure and age of the metamorphic core complex of the Burgutui Russia. Cretaceous Res. 138, 105287. V.F., Tomurtogoo, O., Yan, X., 2003. A model for the formation of orogenic belts in Transbaikaliya. Russ. Geol. Geophys. 7, 90-93 (in Russian). Geology 4(6), 397-408. from metamorphic core complexes. Tectonics 30, TC6007. University Press, Cambridge, pp. 442-485.
	654 807 832 858 883 907 933 959	Litvinovsky B.A., Posokhov V.F., Shadaev M.G., Shalagin V.L., 1989. New data on the age of ridge (southwestern Transbaikal region). Dokl. Earth Sci. 407, 179-183. Central and NE Asia. Russ. J. Pac. Geol. 22 (6), 7-41. Sheldrick, T.C., Barry, T.L., Dash, B. et al., 2020. Simultaneous and extensive removal of the East Vakhrameev, V.A., 1964. Jurassic and early Cretaceous floras of Eurasia and the paleofloristic https://doi.org/10.1029/2011TC002896. Zhang, K.-J., Yan, L.-L., and Ji, C., 2019. Switch of NE Asia from extension to contraction at the
	655 656 662 808 809 834 835 859 860 884 885 908 909 910 934 935 960 961	F o r P e e r R e v i e w Amiot, R., Wang, X., Zhou, Zh., Wang, X., Buffetaut, E., Lécuyer, C., Ding, Zh., Fluteau, F., References: Transbaikalia). Russ. Geol. Geophys. 51 (7), 734-749. F o r P e e r R e v i e w F o r P e e r R e v i e w F o r P e e r R e v i e w F o r P e e r R e v i e w F o r P e e r R e v i e w F o r P e e r R e v i e w the Early Cretaceous volcanic rocks of the Western Transbaikalia (Rb-Sr and K-Ar datings). Dokl. Akad. Nauk SSSR 308 (4), 946-949 (in Russian). F o r P e e r R e v i e w Metamorphic core complexes of the Transbaikalia: review. Geodyn. Tectonophys. 2(2), 95-125. F o r P e e r R e v i e w Parfenov, L.M., Popeko, L.I., Tomurtogoo, O., 2001. Problems of tectonics of the Mongol-Okhotsk orogenic belt. Russian Journal of Pacific Geology 16, 797-830. F o r P e e r R e v i e w Asian lithospheric root. Sci Rep 10, 4128. https://doi.org/10.1038/s41598-020-60925-3 Sklyarov, E.V., Mazukabzov, A.M., Mel'nikov, A.I., 1997. Metamorphic Core Complexes of the F o r P e e r R e v i e w provinces of this period. Moscow, 263 pp. (in Russian). Vakhrameev, V.A., 1982. Division and correlation of continental deposits according to paleobotanical data // Soviet Geology 1, 58-67 (in Russian). F o r P e e r R e v i e w Wernicke, B., 1981. Low-angle normal faults in the Basin and Range Province: nappe tectonics in an extending orogen. Nature 291, 645-648 F mid-Cretaceous: A tale of the Okhotsk oceanic plateau from initiation by the Perm Anomaly to extrusion in the Mongol-Okhotsk ocean? Earth-Science Reviews 198, 102941. F o r o r P e P e e r e r R e R v e v i e i e w w O
	640 641	Acknowledgments	l l l l l l l l l l l l l O n O n O n O n O n O n O n O n O n O n O n O n O n l n y
	642 821	The study was conducted in the frame of the grant of the Ministry of Science and High y y y y y y y 8438. https://doi.org/10.1038/ncomms9438 PMID: 26399170 y y y y y y
	643 822 948 974	Education of the Russian Federation No. 075-15-2022-1100. Detrital zircons were extracted from Markwick, P.J., 1998. Fossil crocodilians as indicators of Late Cretaceous and Cenozoic climates: Characteristics of Granitoids in the Khangai Zonal Magmatic Area. Petrology 24(5), 433-38, 1574-1584.
	644 670 823 848 874 899 949 975	the bulk sample and prepared for U-Pb analysis at the Centre for Geodynamics and Ocean: insight from detrital geochronology in the East Transbaikalia Basin. Geosci. Front. implications for using palaeontological data in reconstructing palaeoclimate. Palaeogeogr. south China, north China and Tarim. Tectonophysics 196, 279-308. 273(1-2), 120-135. http://dx.doi.org/10.1016/j.chemgeo.2010.02.017 Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., 461. al., 2020).
	645 671 824 849 875 900 950	Geochronology of the Institute of the Earth's Crust SB RAS (Irkutsk, Russia). U-Pb isotope 13(1), 101254. https://doi.org/10.1016/j.gsf.2021.101254 Palaeoclimatol. Palaeoecol. 137, 205-71. Nie, S., Rowley, D.B., Ziegler, A.M., 1990. Constraints on the location of Asian microcontinents Scotese, C.R., Song, H., Mills, B.J.W., van der Meer, D.G., 2021. Phanerozoic paleotemperatures: Whitehouse, M.J., 2008. Plesovice zircon -A new natural reference material for U-Pb and Yarmolyuk, V.V., Vorontsov, A.A., Ivanov, V.G., Kovalenko, V.I., Baikin, D.N. and
	646 672 850 876 901 951	analysis of zircons was made at the "Analytical center of mineralogical, geochemical and isotope Arzhannikova, A.V., Frolov, A.O., Arzhannikov, S.G., Demonterova, E.I., Ivanov, A.V., Jolivet, in Paleo-Tethys during late Palaeozoic. In: McKerrow, W.S., Scotese, C.R. (Eds.), The Earth's changing climate during the last 540 million years. Earth-Sci. Rev 215, Hf isotopic microanalysis. Chem. Geol. 249, 1-35. Sandimirova, G.P. 2000. Stages of Bimodal and Alkaline Granite Magmatism in the
	852	12409.

631 inherited Paleozoic structure reactivated during Cretaceous extension. The basins of Transbaikalia 632 were formed both in conjunction with the exhumation of metamorphic cores complexes and 633 reactivated structural sutures. 634 New data on dinosaur fauna and palynology, together with the dating of host deposits, 635 made it possible to correct the age of faunal assemblages in Western Transbaikalia, which is very 636 important for biostratigraphic correlations in various regions of Central Asia. The onset of 637 formation of the Gusinoozersk Basin coincided with the global cooling Weissert Event. During 638 that period the temperate climate prevailing in Transbaikalia was favorable to the existence and 639 reproduction of dinosaur, turtles and choristoderes, but not suitable for crocodiles.

647 studies" at the Geological Institute, SB RAS (Ulan-Ude, Russia). After reduction of data in Glitter 648

(Griffin, 2008)

, all calculations were conducted using Dezirteer program, specially designed for 657 Hibino, T.,

Kusuhashi, N., Mo, J., Suteethorn, V., Wang, Y., Xu, X., Zhang, F., 2011. 658

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Acknowledgments

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