Etienne Jaillard
email: etienne.jaillard@ujf-grenoble.fr

Peter Bengtson
email: bengtson@uni-hd.de

Martha Ordoñez

Wilmer Vaca
email: wilmerjrvaca@hotmail.com

Annie Dhondt

SEDIMENTARY RECORD OF TERMINAL CRETACEOUS ACCRETIONS IN ECUADOR: THE YUNGUILLA GROUP IN THE CUENCA AREA

A reappraisal of the "Late Cretaceous Yunguilla Formation" of the Cuenca area made it possible to define four distinct formations, correlatable with those of southwestern Ecuador. A mid to late Campanian marine transgression (Jadán Fm) is overlain by quartz-rich conglomerates of fan-delta to turbiditic fan environment (Quimas Fm) of latest Campanian-earliest Maastrichtian age, which are interpreted as evidence of the accretion of a first oceanic terrane (San Juan). Disconformable, arkosic turbidites and cherts (Tabacay Fm) of early Maastrichtian age are thought to represent the erosion of the newly accreted oceanic terrane. A major unconformity of late Maastrichtian age, caused by the accretion of a second oceanic terrane (Guaranda), is followed by the deposition of quartz-rich micaceous shelf sandstones (Saquisilí Fm) of Paleocene age. A third accretion event (late Paleocene) is recorded in coastal Ecuador. Each accretion event correlates with the uplift and erosion of the Eastern Cordillera, and with a sedimentary hiatus in the eastern areas. This suggests that in Ecuador, accretion of oceanic terranes contributed to the build-up of the Andes through tectonic underplating of low-density material, and that the eastern areas did not behave as a flexural foreland basins during late Cretaceous-Paleogene times.

Introduction

The Andes of Ecuador differ from the Central Andes by the presence of mafic magmatic terranes [START_REF] Goossens | Chemical composition and age determination of tholeitic rocks in the basic Cretaceous Complex, Ecuador[END_REF][START_REF] Gansser | Facts and Theories on the Andes[END_REF], interpreted as oceanic fragments accreted during Late Cretaceous and Eocene times [START_REF] Feininger | Cretaceous and Paleogene history of coastal Ecuador[END_REF][START_REF] Lebrat | Geochemistry and tectonic setting of pre-collision Cretaceous and Paleogene volcanic rocks of Ecuador[END_REF][START_REF] Daly | Correlations between Nazca/Farallón plate kinematics and Forearc basin evolution in Ecuador[END_REF][START_REF] Reynaud | Oceanic plateau and island arcs of southwestern Ecuador: their place in the geodynamic evolution of northwestern South America[END_REF][START_REF] Kerr | The nature and provenance of accreted terranes in Western Ecuador: Geochemical and tectonic constraints[END_REF]. More recently, some authors [START_REF] Arculus | A geochemical window into subduction-accretion processes: the Raspas Metamorphic Complex, Ecuador[END_REF][START_REF] Guillier | Seismological evidence on the geometry of the orogenic system in Central-Northern Ecuador (South America)[END_REF][START_REF] Jaillard | Andean geodynamics: main issues and contributions from the 4th ISAG, Göttingen[END_REF][START_REF] Toro | Provenance of the Upper Cretaceous to Upper Eocene clastic sediments of the Western Cordillera of Ecuador: Tectonic and geodynamic implications[END_REF] proposed that the accreted oceanic material has been tectonically underplated and constitutes the crustal root of the Andes of Ecuador.

In order to constrain the date, processes and consequences of the accretions on Andean tectonics, we studied the dominantly clastic sediments coeval with the accretions (Late Cretaceous-Eocene), located on the western edge of the continental margin, i.e. in the present-day Cordillera of Ecuador.

Geological setting

The coast and Western Cordillera of Ecuador are made up of terranes of oceanic origin, whereas the continental Andean margin comprises the deformed Eastern Cordillera [START_REF] Litherland | The metamorphic belts of Ecuador[END_REF] and the Subandean Zone and Oriente Basin [START_REF] Jaillard | Síntesis estratigráfica y sedimentológica del Cretáceo y Paleógeno de la cuenca oriental del Ecuador[END_REF]Fig. 1). In northern and central Ecuador (1°N-2°S), the Western and Eastern Cordilleras are separated by the Inter-Andean Valley, infilled by products of the Neogene to Quaternary volcanic arcs [START_REF] Lavenu | Stratigraphie des dépôts tertiaires et quaternaires de la dépression interandine d'Équateur (entre 0° et 2°15'S)[END_REF]Hungerbüler et al., 2002). Farther south (2°S-5°S), the tectonic boundary between the allochtonous, oceanic units and the autochtonous continental margin is located west of the Western Cordillera (Fig. 1), and the well-defined Inter-Andean Valley vanishes. The Cuenca area ( 3°S) is situated on the western edge of the Eastern Cordillera [START_REF] Litherland | The metamorphic belts of Ecuador[END_REF], and is bounded to the west by uplifted Tertiary arc volcanic piles, the basement of which is most probably continental, as evidenced by crystalline outcrops west of Cuenca [START_REF] Dunkley | Mapa geológico de la Cordillera Occidental del Ecuador entre 2° -3° S., escala 1/200.000[END_REF][START_REF] Pratt | Mapa geológico de la Cordillera Occidental del Ecuador entre 3° -4° S, escala 1/200.000[END_REF]. This relative depression received thick, marine to subaerial deposits during the Mid Miocene, and subsequent compressional deformations were controlled by major NE-trending faults [START_REF] Bristow | Mapa geológico al 1/100.000[END_REF][START_REF] Noblet | Étude géodynamique d'un bassin intramontagneux tertiaire sur décrochements dans les Andes du Sud de l'Équateur: l'exemple du bassin de Cuenca[END_REF][START_REF] Hungerbühler | Neogene stratigraphy and Andean geodynamics of southern Ecuador[END_REF]. As for the Celica area of southwestern Ecuador [START_REF] Kennerley | Geology of the Loja Province, Southern Ecuador[END_REF]Jaillard et al., 1996;1999), the basement of the Tertiary deposits of the Cuenca area is mainly represented by Jurassic-Paleozoic metamorphic rocks, as well as by Cretaceous-Paleogene sedmentary deposits [START_REF] Bristow | Mapa geológico al 1/100.000[END_REF][START_REF] Litherland | The metamorphic belts of Ecuador[END_REF][START_REF] Hungerbühler | Neogene stratigraphy and Andean geodynamics of southern Ecuador[END_REF]. The latter sediments are the goal of the present study (Fig. 2).

Previous work

The name "Yunguilla Formation" was introduced by [START_REF] Thalmann | Micropaleontology of Upper Cretaceous and Paleocene in western Ecuador[END_REF] for a succession of black shales and sandstones, dated with foraminifers as Maastrichtian, exposed northwest of Quito. Since then, comparable Maastrichtian sediments were identified and dated with microfossils in the Western Cordillera of Ecuador, between Quito and Cuenca [START_REF] Tschopp | Geologische Skizze von Ekuador[END_REF][START_REF] Sigal | Quelques acquisitions récentes concernant la chronostratigraphie des formations sédimentaires de l'Équateur[END_REF][START_REF] Kehrer | Die oberkretazische San Juan Formation der Westkordillere Ecuadors[END_REF][START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF][START_REF] Bristow | Guide to the geology of the Cuenca Basin, southern Ecuador[END_REF][START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF], in southwestern Ecuador (Loja area; [START_REF] Sigal | Quelques acquisitions récentes concernant la chronostratigraphie des formations sédimentaires de l'Équateur[END_REF] and locally in the subandean zone (Limón area; [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF]. Later, many rocks referred to as the Yunguilla Formation have been dated as Paleocene or Eocene, and new Paleogene units have been defined [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF][START_REF] Henderson | The volcanic Macuchi Formation, Andes of Northern Ecuador[END_REF][START_REF] Egüez | La formación Apagua: edad y posición estructural en la Cordillera occidental del Ecuador[END_REF][START_REF] Santos | La Formación Apagua, una nueva unidad eocénica en la cordillera occidental ecuatoriana[END_REF][START_REF] Hughes | Mapa geológico de la Cordillera Occidental del Ecuador entre 0°-1°S, escala 1[END_REF]Fig. 2: Geological Map of the Cuenca area, compiled from Bristow (1980), [START_REF] Noblet | Étude géodynamique d'un bassin intramontagneux tertiaire sur décrochements dans les Andes du Sud de l'Équateur: l'exemple du bassin de Cuenca[END_REF][START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF], [START_REF] Dunkley | Mapa geológico de la Cordillera Occidental del Ecuador entre 2° -3° S., escala 1/200.000[END_REF], [START_REF] Pratt | Mapa geológico de la Cordillera Occidental del Ecuador entre 3° -4° S, escala 1/200.000[END_REF], [START_REF] Hungerbühler | Neogene stratigraphy and Andean geodynamics of southern Ecuador[END_REF] and personnal observations. Figures 4,5 and 6 are located.

In the Cuenca-Azogues area (Fig. 2), [START_REF] Bristow | Mapa geológico al 1/100.000[END_REF] considered that the "Yunguilla Formation" rests on Cretaceous volcanic rocks. The latter, however, were subsequently dated by fission tracks analysis as Oligocene [START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF]. The Late Cretaceous-Paleogene succession seems to constitute the basement of the Miocene intermontane basin, and rests on metamorphic rocks of the continental basement of Ecuador [START_REF] Noblet | Étude géodynamique d'un bassin intramontagneux tertiaire sur décrochements dans les Andes du Sud de l'Équateur: l'exemple du bassin de Cuenca[END_REF][START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF][START_REF] Dunkley | Mapa geológico de la Cordillera Occidental del Ecuador entre 2° -3° S., escala 1/200.000[END_REF][START_REF] Pratt | Mapa geológico de la Cordillera Occidental del Ecuador entre 3° -4° S, escala 1/200.000[END_REF][START_REF] Hungerbühler | Neogene stratigraphy and Andean geodynamics of southern Ecuador[END_REF][START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF]. The "Yunguilla Formation" crops out East of Cumbe, Cuenca and Azogues, along a NNE-trending belt (Fig. 2). Further north, in the Pallatanga area, the "formation" is tectonically associated with accreted oceanic terranes, whith which it is assumed to have been in stratigraphic contact [START_REF] Mccourt | Mapa geológico de la Cordillera Occidental del Ecuador entre 1°-2° S., escala 1/200.000[END_REF][START_REF] Hughes | Mapa geológico de la Cordillera Occidental del Ecuador entre 0°-1°S, escala 1[END_REF][START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF]. To the southwest, the uppermost Cretaceous succession rests unconformably on Paleozoic to middle Cretaceous rocks of the forearc zones of southern Ecuador and northwestern Peru [START_REF] Olsson | Contributions to the Paleontology of Northern Peru. Part VII: The Cretaceous of the Paita region[END_REF][START_REF] Jaillard | Revisión estratigráfica del Cretáceo superior del Noroeste peruano y Suroeste ecuatoriano. Datos preliminares y consecuencias tectónicas[END_REF]1999).

In the Cuenca-Azogues area, [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF] and [START_REF] Bristow | Guide to the geology of the Cuenca Basin, southern Ecuador[END_REF] identified three distinct lithologic units.

1. Cherts and greywackes, commonly silicified, yielded scarce and poorly preserved fossils referred to the Maastrichtian. They considered this unit to be the lower part of the "Yunguilla Formation" (but see below under Tabacay Formation).

2. Poorly consolidated shales with limestone lenses and arkosic sandstones beds, were dated with microfossils as Maastrichtian. These rocks were interpreted as the upper part of the "Yunguilla Formation" [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF]. Ammonites were collected from these units and were assigned to the lower Maastrichtian [START_REF] Bristow | Ecuador. Lexique Stratigraphique International[END_REF].

3. According to [START_REF] Bristow | Ecuador. Lexique Stratigraphique International[END_REF], marine shales and limestone lenses of the Cumbe area, referred to as the "Yunguilla Formation", grade upwards into continental, volcanogenic red beds. From the "Yunguilla Formation", [START_REF] Bristow | Ecuador. Lexique Stratigraphique International[END_REF] reported one Inoceramus sp. and an unidentified ammonite, and [START_REF] Pratt | Geology of the Cordillera Occidental of Ecuador between 3°00' and 4°00[END_REF] collected the ammonites Hoploscaphites sp. and Baculites sp. of Maastrichtian age. From the overlying fine-grained red beds, [START_REF] Bristow | Ecuador. Lexique Stratigraphique International[END_REF] collected Paleocene molluscs, and [START_REF] Pratt | Geology of the Cordillera Occidental of Ecuador between 3°00' and 4°00[END_REF] collected Pterotrigonia sp., known in the Maastrichtian of Peru.

In the Cuenca area, the "Yunguilla Formation" is overlain by Middle Eocene volcanics (Chinchín Formation, approximately 43 Ma) and unconformable continental volcanogenic red beds of Mid to Late Eocene age (Quingeo Formation, 42-34 Ma) [START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF][START_REF] Hungerbühler | Neogene stratigraphy and Andean geodynamics of southern Ecuador[END_REF]. [START_REF] Pratt | Geology of the Cordillera Occidental of Ecuador between 3°00' and 4°00[END_REF] correlated the continental volcanogenic red beds of the Cumbe area with the Quingeo Formation (Fig. 2), defined and dated further northeast by [START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF].

Stratigraphy and depositional interpretation of the Late Cretaceous-Paleocene rocks of the Cuenca area

Based on geological surveys and study of stratigraphic sections, combined with exhaustive fossil collecting, we have subdivided the rock succession formerly ascribed to the "Yunguilla Formation" into four formations ranging in age from the mid or late Campanian to the Paleocene (Fig. 3). We here introduce the Yunguilla Group, which comprises the middle (?) to upper Campanian Jadán Formation, the conglomeratic Quimas Formation, and the lower Maastrichtian Tabacay Formation. The Yunguilla Group is overlain by the Paleocene Saquisilí Formation, formerly included in the "Yunguilla Formation".

Jadán Formation (middle(?) to upper Campanian) Although it corresponds to the lithologic unit 2 described above, the Jadán Formation is the lowest unit of the Yunguilla Group. It consists mainly of shales and marls, with thin limestone and arkosic sandstone beds. The base of the formation is not exposed. Since metamorphic rocks crop out just east of the Yunguilla Group, the latter most probably overlies unconformably the continental margin [START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF], as observed further north [START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF]. The lowermost part of the Jadán Formation is strongly deformed and probably acted as a décollement level.

The Jadán Formation is best exposed along the El Descanso-Jadán road (Loma Tunasloma), which is proposed as the type section, and East of Azogues (Santa Bárbara). It is also exposed southeast of Santa Ana, northeast of El Descanso and around Cumbe (Fig. 2). The 500-800 m thick formation can be subdivided into three lithologic units ("members"). -The lower part of the formation is made up of loose, silty shales and marls with thin beds of dark micritic limestones and arkosic to lithic, fine-to medium-grained sandstones. The limestones are locally nodular and sandy. The sandstones are locally rich in micas, and cementation is generally calcareous. Local bioclastic limestones are interpreted as distal turbidites. The succession is composed of 100-200 m thick, coarsening-, thickening-and shallowing-upward sequences. Abundance of the bivalve Pinna sp. indicates a moderate paleodepth ( 100 m), whereas common wood fragments suggest proximity to land. Ammonites ≤ collected along the El Descanso-Jadán road were indentified as Diplomoceras sp. (upper Campanian-Maastrichtian) (sample [02.C.52], Table 1) and Glyptoxoceras sp. (Santonian-Maastrichtian) or Neoglyptoxoceras sp. (lower-middle Campanian) ([02.C.53, 02.C.G1, 03.Cu.05], Table 1). -The middle part of the formation includes, in addition to the former lithologies, massive interbeds of black siliceous silts, thin-bedded calciturbidites, thin limestones interbedded with thin sandy laminae, and thick sandstone beds with coarsening-upward trends and progressive unconformities reflecting synsedimentary tectonic activity. The lower part of this unit yielded the Campanian ammonite Nostoceras (Nostoceras?) sp. (upper Campanian) ([03.Cu.03], Table 1).

-The upper part of the formation (Fig. 4) consists of shales, marls and limestones rich in ammonites, gastropods, oysters, inoceramids and other bivalves. This unit is composed of prograding, thickeningupwards sequences, of external, distal shelf environment, and is interpreted as representing a transgressive pulse. Toward the top, the limestones become progressively more sandy and eventually grade into conglomerates. We collected the ammonites Libycoceras sp. 1). In addition, a loose inoceramid found by D. Iza was identified as Cataceramus cf. pseudoregularis [START_REF] Sornay | Etude d'une faune d'inocérames du Sénonien supérieur des Charentes et description d'un espèce nouvelle du Sénonien supérieur de Madagascar[END_REF], which is known from the uppermost Campanian of Tercis, France (lower part of the Nostoceras hyatti Zone, [START_REF] Walaszczyk | Inoceramids from the upper Campanian and lower Maastrichtian of the Tercis section (SW France), the Global Stratotype Section and Point for the Campanian-Maastrichtian boundary; taxonomy, biostratigraphy and correlation potential[END_REF]. East of Azogues (Santa Bárbara), the upper part of the formation yielded Glyptoxoceras sp. (Santonian-Maastrichtian) or Neoglyptoxoceras sp. (lower-middle Campanian) [03. Cu.35,03.Cu.36], and a pachydiscid, probably Menuites sp. [03.Cu.34] of Santonian to Maastrichtian age (Fig. 5). Thus, the weight of evidence suggests that the upper part of the Jadán Formation is upper Campanian. Within their lithology 2, [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF] identified, among others, the planktic foraminifers Globotruncana [= Gansserina] gr. gansseri [START_REF] Bolli | The genus Globotruncana in Trinidad, BWI[END_REF], Plummerita hantkeninoides (Brönnimann, 1952), Rugoglobigerina macrocephala Brönnimann, 1952, R. cf. reicheli Brönnimann, 1952, R. gr. rugosa [START_REF] Plummer | Foraminifers of the Midway Formation in Texas[END_REF], and the benthic foraminifers Rzehakina epigona var. lata Cushman & Jarvis, 1929, Siphogenerinoides cf. bramlettei Cushman, 1929, S. cretacea Cushman, 1929, and S. reticulatus Stone, 1946 (det. J. Sigal). South of Santa Ana, in the Quebrada Salada, we collected Platyceramus sp., of late Coniacianearly Maastrichtian age, from undifferentiated Jadán Formation. Near Cumbe, shales and marls with limestone nodules and arkosic sandstone interbeds ascribed to the Jadán Formation yielded planktic and benthic foraminifers; the association of Bulimina midwayensis [START_REF] Cushman | Notes on some Cretaceous species of Buliminella and Neobulimina[END_REF]) (Campanian-Paleocene), Haplophragmoides aff. horridus [START_REF] Grzybowski | Die Microfauna der Karpathenbildungen; III -Die Foraminiferen der Inoceramenschichten von Gorlice[END_REF]) (Campanian-Paleogene), Hedbergella holmdelensis Olsson, 1964 (Late Cretaceous), Nodosaria cf. longiscata d'Orbigny, 1846 (Maastrichtian-Eocene), Praebulimina reussi [START_REF] Morrow | Foraminifera and Ostracoda from the Upper Crretaceous of Kansas[END_REF]) (Late Cretaceous) and Turrilina carseyae [START_REF] Plummer | Some Cretaceous foraminifera in Texas[END_REF] (Campanian-Maastrichtian) indicates a Campanian-Maastrichtian age for these outcrops.

Quimas Formation (uppermost Campanian-lowermost Maastrichtian)

The Quimas Formation consists of thick beds of coarse to microconglomeratic arkosic and lithic sandstones, poorly sorted conglomerates, and subordinate lithic arenites and limestone nodules containing benthic foraminifers. The base of the Quimas Formation is defined at the base of the first erosional conglomerate bed. However, the lithologic change from the upper Jadán Formation to the lower Quimas Formation is progressive, and mainly expressed by the increase in conglomerates and erosional surfaces (Fig. 4 and5). The Quimas Formation is best exposed along the Cumbe-Quingeo road, notably in the Quebrada Quimas and in Loma Huairapungu. This section is proposed as the type section. Other outcrops occur north of Santa Ana and east of the El Descanso-Azogues road.

The conglomerates contain subangular to well-rounded clasts up to 10 cm in size. The clasts consist dominantly of quartz, metamorphic and sedimentary rocks, and scarce volcanic rocks. The sandstones are commonly turbidite beds, which contain quartz (30-50%), feldspar (20-35%), lithic fragments (30-40%) and scarce detrital micas. [START_REF] Steinmann | The Cuenca Basin of southern Ecuador: tectono-sedimentary history and the Tertiary Andean evolution[END_REF] reports a heavy mineral assemblage (34% zircon, 21% tourmaline, 20% apatite, 20% garnet, ...) typical of crystalline, plutonic and metamorphic source zones. In the Quebrada Tabacay, north of Azogues, conglomerates with well-rounded quartz and metamorphic clasts contain gastropods and bivalves. In Loma Tunasloma, marine bivalves, plant remains and bone fragments indicate a locally shallow-marine depositional environment. Fine-grained sediments show bioturbation, laminae and ripples, suggesting a shelf environment.

The formation contains numerous synsedimentary unconformities, folds and slumps, as well as debris flows, which indicate contemporaneous tectonic activity and/or a steep slope. Conglomerate beds are commonly lens-shaped and channelized, indicating the proximity of fluvial systems that fed fan deltas prograding on the shelf. The formation appears to reach a thickness of 1000 m in the Cumbe-Quingeo area, and grades northwards into much thinner (approximately 500 m) and finer-grained deposits, near Azogues. This suggests that the feeding alluvial system (alluvial fan and fan delta) was located in the Cumbe area. As a whole, the Quimas Formation is interpreted as a fan delta deposit prograding on a steep shelf.

East of Antonio Borrero (Fig. 6), [START_REF] Bristow | Ecuador. Lexique Stratigraphique International[END_REF]and pers. comm., 2003) reported Sphenodiscus peruvianus [START_REF] Gerth | Neue Faunen der oberen Kreide mit Hippuriten aus Nordperu[END_REF] and Solenoceras sp. of early Maastrichtian age (determined by M.K. Howarth, Natural History Museum, London). In the same area (Fig. 6), we found ammonite fragments, which may be either Glyptoxoceras sp. (Santonian-Maastrichtian) or Neoglyptoxoceras sp. (lower-middle Campanian) ([02.C.G2, 03.Cu.38], Table 1). East of Azogues, the base of the formation yielded unidentifiable ammonites [03.Cu.54-55], which directly overlie the upper Campanian species mentioned above (Fig. 5). Based on the above evidences, the Quimas Formation is considered of latest Campanian to earliest Maastrichtian age.

Tabacay Formation (lower Maastrichtian)

The Tabacay Formation corresponds to the lithologic unit 1 of [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF]. The base of the formation is not exposed, except to the east of Azogues (Santa Bárbara), where it is faulted (Fig. 5), and north of Azogues, where it unconformably overlies both the Quimas Formation and undated metamorphic rocks [START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF]. North of Santa Ana and in the Quebrada Tabacay, the formation seems to rest disconformably on the Quimas Formation. However, no suitable type section has been found so far. Although the stratigraphic contact is not visible, the Tabacay Formation seems to rest unconformably on the Quimas Formation, since dip orientations and deformation styles are slightly different.

The Tabacay Formation is made up of a succession of dark, laminated cherts, alternating with variably thick, fine-grained polygenetic conglomerates, volcanogenic greywackes and arkosic lithic arenites. The clasts dominantly consist of volcanic rocks, associated with arkoses, lithic arenites, and chert fragments, as well as locally abundant white quartz. Nodules or irregularly bedded intercalations of micritic black limestones are common, whereas scarce calciturbidites with volcanic or feldspathic fragments are locally observed. The detrital beds are interpreted as turbidites, on account of their erosional bases, presence of flat pebbles and upward fining bedding. The detrital components of the Tabacay Formation indicate a dominantly volcanic source area and a subordinate crystalline basement provenance. The detrital fragments were deposited in a dysaerobic pelagic environment, in which autochtonous, fine-grained, siliceous mud was laid down. Although outcrops are scarce, the thickness of the Tabacay Formation seems to reach a few hundred meters. [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF] recorded Maastrichtian foraminifers (buliminids, arenaceous, Robulus sp., Globigerinella sp.) and scarce indeterminable bivalves, inoceramids and ammonites, within their lithologic unit 1. In the Quebrada Tabacay, [START_REF] Bristow | Guide to the geology of the Cuenca Basin, southern Ecuador[END_REF] found a diplomoceratid ammonite. Further north, in the Pallatanga area near Huangupud, we collected Exiteloceras sp. of Campanian age (or Glyptoxoceras sp., Santonian-Maastrichtian?) and a Hypophylloceras (Neophylloceras) sp., of probably early Maastrichtian age, from a comparable lithology [START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF].

Saquisilí Formation (Paleocene)

In the Quebrada Tabacay, although the contact is not visible, the Tabacay Formation is geometrically overlain by grey to black shales, dark siltstones, sandstone layers, and thicker beds of dark, micaceous and arkosic sandstones. North of Tabacay, the basal contact is an unconformity [START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF]. Beds or nodules of micritic dark limestones, and thin bedded sandy turbidites are locally observed. The beds of fine-grained sandstone show ripples, lamination, hummocky cross stratifications and load structures; they contain plant remnants and Glossifungites or Skolithos burrows. These features suggest deposition in a clastic distal shelf environment, above the storm wave base. The thickness of this unit may reach 500 to 1000 m.

The rocks referred to here as the Saquisilí Formation were formerly included in the "Yunguilla Formation". They have yielded, among others, the benthic foraminifers Bathysiphon gerochi Myatlyuk, 1966 (Paleocene), Bulimina midwayensis [START_REF] Cushman | Notes on some Cretaceous species of Buliminella and Neobulimina[END_REF]) (Campanian-Paleocene) and the palynomorph Tricolporopollenites? sp., indicating a Paleocene age. Due to a similar lithology with abundant detrital white micas, these beds are now referred to the Saquisilí Formation, which, in the type locality, has been dated as Early to Mid Paleocene [START_REF] Mccourt | Mapa geológico de la Cordillera Occidental del Ecuador entre 1°-2° S., escala 1/200.000[END_REF][START_REF] Hughes | Mapa geológico de la Cordillera Occidental del Ecuador entre 0°-1°S, escala 1[END_REF]. A sample from the water divide between Cuenca and Quingeo yielded the benthic foraminifers Dorothia cylindracea (Bermudez, 1963) (Paleocene-Early Eocene) and Haplophragmoides cf. eggeri (Cushman, 1926) (Paleogene), thus suggesting that the Saquisilí Formation also crops out east of Cuenca.

Further north, graded-bedded conglomerates are observed along the Azogues-Ingapirca road [START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF]. These coarser-grained deposits are correletable with the Gallo Rumi Member of the Pallatanga area, which is assigned to the Upper Paleocene [START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF]. [START_REF] Bristow | Ecuador. Lexique Stratigraphique International[END_REF] assumed that the "Yunguilla Formation" of the Cumbe area progressively grades upward into Paleocene variegated, fine-grained subaerial deposits. In the same area, [START_REF] Pratt | Geology of the Cordillera Occidental of Ecuador between 3°00' and 4°00[END_REF] assumed a progressive change from the marine "Yunguilla Formation" to Maastrichtian red beds, and then to the Eocene Quingeo Formation. However, the deformation of the Maastrichtian deposits includes tight folds, the axis of which varies from E-W to N-S, whereas the continental deposits ascribed to the Quingeo Formation only exhibit NNE-trending gentle folds. Therefore, it is probable that a major unconformity separates upper Maastrichtian-Paleocene fine-grained subaerial deposits from the coarser-grained, Eocene Quingeo Formation.

Correlations with neighbouring areas

Celica-Lancones Basin (southwestern Ecuador) and Paita area (northwestern Peru)

The unconformable, transgressive Campanian-Maastrichtian sequence in the Celica-Lancones Basin, appears to rest on the Albian volcanic arc in the east, on deformed Cretaceous sediments in the central part, and on Paleozoic basement or Albian transgressive limestones in the west [START_REF] Olsson | Contributions to the Paleontology of northern Peru. The Cretaceous of the Amotape region[END_REF][START_REF] Kennerley | Geology of the Loja Province, Southern Ecuador[END_REF][START_REF] Morris | Sedimentation and tectonics of middle Cretaceous Copa Sombrero formation in northwest Peru[END_REF][START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF]. The uppermost Cretaceous sequence comprises, from base to top (Fig. 7): (1) a middle to upper Campanian prograding sequence of marls, limestones and arkosic sandstones, overlain by transgressive marls (Naranjo and Zapotillo formations); (2) coarse-grained conglomerates derived from either a volcanic source in the east (Casanga Formation) or a crystalline source in the west (Monte Grande, or Tablones Formation); and (3) lower Maastrichtian dark shales interbedded with quartzose sandstones (Cazaderos Formation) (Jaillard et al., 1996[START_REF] Jaillard | Stratigraphy and evolution of the Cretaceous forearc "Celica-Lancones Basin" of Southwestern Ecuador[END_REF]. The latter are unconformably overlain by Paleocene marine shales, with sandstone and limestone interbeds (Balcones Formation) [START_REF] Jaillard | Stratigraphy and evolution of the Cretaceous forearc "Celica-Lancones Basin" of Southwestern Ecuador[END_REF].

In the Paita area (northwestern Peru, Fig. 1,7), the Paleozoic basement is unconformably overlain by a middle-upper Campanian sequence of transgressive marine marls and sandy limestones, which ends with shallowing-upward, rudist-bearing carbonate shelf deposits (La Mesa Formation) [START_REF] Olsson | Contributions to the Paleontology of Northern Peru. Part VII: The Cretaceous of the Paita region[END_REF][START_REF] Palacios | Geología de los cuadrángulos de Paita, Talara, Sullana, Lobitos, Quebrada Seca, Zorritos, Tumbes y Zarumilla[END_REF][START_REF] Jaillard | Revisión estratigráfica del Cretáceo superior del Noroeste peruano y Suroeste ecuatoriano. Datos preliminares y consecuencias tectónicas[END_REF]. The latter formation is overlain by upper Campanian transgressive sandy marls, which rapidly grade upwards into quartz-rich conglomerates. Further to the west, the Paleozoic basement is directly overlain by a 3500 m thick upper Campanian-lower Maastrichtian succession of fan delta breccias (La Tortuga Formation) [START_REF] Jaillard | Revisión estratigráfica del Cretáceo superior del Noroeste peruano y Suroeste ecuatoriano. Datos preliminares y consecuencias tectónicas[END_REF][START_REF] Taipe | Estratigrafia y evolución sedimentológica de la serie del Cretáceo superior de la Península de Paita[END_REF], thus indicating that a deep sedimentary basin was created between the late Campanian and the early Maastrichtian. These breccias are disconformably overlain by lower Maastrichtian transgressive shoreline sandstones, which grade into shallow clastic shelf breccias and sandstones (Cenizo Formation). Paleocene marine marls unconformably overlie the Maastrichtian sandstones [START_REF] Taipe | Estratigrafia y evolución sedimentológica de la serie del Cretáceo superior de la Península de Paita[END_REF][START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF].

The upper Campanian marls, limestones and arkoses of the Jadán Formation in the Cuenca area are lithologically comparable and stratigraphically correlatable with the transgressive Naranjo, Zapotillo and La Mesa formations of southwestern Ecuador and northwestern Peru. The conglomerates of the Quimas Formation are stratigraphically correlatable with those of the Casanga and Monte Grande (or Tablones) formations of the Celica-Lancones area and with the La Tortuga breccias of the Paita area. Although their source areas and depositional environments were different, the lower Maastrichtian cherts and volcanogenic turbidites of the Tabacay Formation can be correlated with the quartz-rich Cazaderos Formation of southwestern Ecuador and with the transgressive Cenizo Formation of northwestern Peru [START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF].

It follows that the sedimentary successions of the Paita, Celica-Lancones and Cuenca areas represent a three-fold evolution: (1) a mid to late Campanian transgressive prograding sequence, followed by a renewed transgression; (2) a significant tectonic event, with deposition of thick, shallow-marine to continental, coarse-grained conglomerates or breccias in the latest Campanian-earliest Maastrichtian; and (3) a new transgression and clastic-shelf or deeper turbiditic deposition in the early Maastrichtian. The latter sequence closes with a regional hiatus in the late Maastrichtian-earliest Paleocene, which reflects a significant tectonic event.

Western Cordillera of central and northern Ecuador

In central Ecuador (0-2°S) the Yunguilla Group is tectonically associated with basalts, dolerites and greywackes, which are interpreted as an accreted oceanic terrane (part of the Pallatanga terrane of [START_REF] Mccourt | Mapa geológico de la Cordillera Occidental del Ecuador entre 1°-2° S., escala 1/200.000[END_REF][START_REF] Kerr | The nature and provenance of accreted terranes in Western Ecuador: Geochemical and tectonic constraints[END_REF][START_REF] Spikings | Thermochronology of allochtonous terranes in Ecuador: unraveling the accretionary and post-accretionary history of the Northern Andes[END_REF]; San Juan terrane of [START_REF] Mamberti | The Early Cretaceous San Juan plutonic suite, Ecuador: a magma chamber in an Oceanic Plateau[END_REF][START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF]. To the west, the late Campanian-Maastrichtian interval is represented by radiolarian-rich black cherts, which overlie red or green radiolarites (Fig. 7). In northern Ecuador, the radiolarian-bearing red mudstones were dated as Santonian-early Campanian [START_REF] Boland | Mapa geológico de la Cordillera Occidental del Ecuador entre 0°-1°N, escala 1/200.000[END_REF][START_REF] Kerr | The nature and provenance of accreted terranes in Western Ecuador: Geochemical and tectonic constraints[END_REF] and constitute the sedimentary cover of basalts, ankaramites and picrites, representing an accreted oceanic terrane (part of the Pallatanga terrane of [START_REF] Mccourt | Mapa geológico de la Cordillera Occidental del Ecuador entre 1°-2° S., escala 1/200.000[END_REF][START_REF] Kerr | The nature and provenance of accreted terranes in Western Ecuador: Geochemical and tectonic constraints[END_REF]Guaranda terrane of Mamberti et al., 2003;[START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF]. Thus, the Yunguilla Group was deposited only on the eastern San Juan oceanic unit.

The Yunguilla sediments of central Ecuador are highly deformed, and it is difficult to ascribe them to any of the formations defined in the Cuenca area. However, their quartz content is low ( 20%, Toro and Jaillard, ≤ 2005), available paleontological data suggest an early Maastrichtian age [START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF], and there are no quartz-rich conglomerates similar to the Quimas Formation. For these reasons, the Yunguilla sediments of the Quito-Pallatanga area are tentatively referred to the Tabacay Formation (lower Maastrichtian). If this is correct, the Tabacay Formation postdates the accretion of the eastern San Juan oceanic terrane [START_REF] Hughes | Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador[END_REF][START_REF] Kerr | The nature and provenance of accreted terranes in Western Ecuador: Geochemical and tectonic constraints[END_REF] and predates the accretion of the western Guaranda oceanic terrane [START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF]. Therefore, the deposition of the coarse-grained conglomerates of latest Campanianearliest Maastrichtian age ( 75-70 Ma) are interpreted as the sedimentary response to the accretion of the ≈ San Juan oceanic terrane.

The Paleocene Saquisilí Formation in the Cuenca area exhibits similar lithologies and is coeval with that in central and northern Ecuador. In the latter area, it unconformably overlies both the Maastrichtian Tabacay Formation (San Juan Terrane), and the Campanian-Maastrichtian black cherts (Guaranda Terrane), thus concealing the accretion of the latter terrane to the former [START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF]. Therefore, the accretion of the Guaranda terrane occurred in the late Maastrichtian-earliest Paleocene ( 68-65 Ma; Fig. 7). ≈

Oriente Basin of Ecuador

The Cretaceous, fine-grained, shallow-marine sediments in the Oriente Basin (Napo Group) record the arrival of significant detrital input in the Santonian, which predates a major hiatus of late Santonian to early Campanian times [START_REF] Jaillard | Síntesis estratigráfica y sedimentológica del Cretáceo y Paleógeno de la cuenca oriental del Ecuador[END_REF][START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF]. These deposits are disconformably overlain by a 5 to 20-m-thick middle to upper Campanian transgressive sequence of sandstones and thin marine shales (M-1 Sandstones, [START_REF] Raynaud | Equateur, Bassin de l'Oriente : Etude palynologique d'un intervalle Crétacé supérieur sur 20 puits[END_REF][START_REF] Rivadeneira | La Arenisca «M-1» en la cuenca ecuatoriana[END_REF]. However, in the western part of the Oriente Basin and in the Subandean Zone, Campanian sediments are absent. There, lower Maastrichtian sandstones unconformably overlie the eroded marine shales and limestones, which are dated as Turonian to Santonian, depending on the region [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF][START_REF] Jaillard | Síntesis estratigráfica y sedimentológica del Cretáceo y Paleógeno de la cuenca oriental del Ecuador[END_REF]. Therefore, in the western part of the Oriente Basin a late Campanian hiatus coincides with the accretion of the eastern San Juan terrane [START_REF] Hughes | Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador[END_REF][START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF].

The early Maastrichtian transgression (Basal Tena Formation) is overlain by prograding, fine-grained red beds (Lower Tena Formation) [START_REF] Faucher | Sedimentary formations in Ecuador. A stratigraphic and micropaleontological survey[END_REF][START_REF] Jaillard | Síntesis estratigráfica y sedimentológica del Cretáceo y Paleógeno de la cuenca oriental del Ecuador[END_REF][START_REF] Ruiz | Detrital thermochronology -a new perspective on hinterland tectonics, an example from the Andean Amazon Basin, Ecuador[END_REF]. These are, in turn, disconformably overlain by a succession of Paleocene coarser-grained fluvial red beds [START_REF] Mills | A review of micropaleontological evidence from the Ecuadorian Oriente. Anglo-Ecuadorian Oilfields Ltd[END_REF][START_REF] Jaillard | Síntesis estratigráfica y sedimentológica del Cretáceo y Paleógeno de la cuenca oriental del Ecuador[END_REF]. Thus, a hiatus occurred some time after the early Maastrichtian and before part of the Paleocene, coinciding with the accretion of the western Guaranda unit [START_REF] Mamberti | Accreted fragments of the Late Cretaceous Caribbean-Colombian Plateau in Ecuador[END_REF][START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF].

It should be noted that the Paleocene Upper Tena Formation is in turn eroded and unconformably overlain by coarse-grained fluvial conglomerates of the poorly dated Lower Tiyuyacu Formation [START_REF] Christophoul | Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times[END_REF]. Although poorly constrained, this major unconformity would correlate with the accretion of the Piñón Terrane of southern coastal Ecuador in the Late Paleocene ( 58-55 Ma;[START_REF] Jaillard | Basin development in an accretionary, oceanic-floored forearc setting : southern coastal Ecuador during late Cretaceous to late Eocene times[END_REF]. These observations demonstrate that the accretion of oceanic terranes coincides with important sedimentary hiatuses in the Subandean Zone and Oriente Basin and therefore, with uplift and erosion of those areas.

Geodynamic interpretations and discussions

The middle to late Campanian Jadán Formation represents the oldest Cretaceous sediments exposed in the Cuenca area. Although the stratigraphic contact is not visible, we assume that it was unconformably deposited onto the metamorphic basement of the Andean margin. A similar unconformable contact of transgressive mid to late Campanian resting on deformed, Albian to Paleozoic rocks of the Andean margin is known from the forearc zones of southwestern Ecuador and northwestern Peru (Jaillard et al., 1996;1998;1999 ;[START_REF] Taipe | Estratigrafia y evolución sedimentológica de la serie del Cretáceo superior de la Península de Paita[END_REF]. This suggests that a strong subsidence affected the western edge of the Andean continental margin of southern Ecuador by mid Campanian times. Since this subsidence event followed the compressional « Peruvian phase », we suggest that the latter was responsible for a strong tectonic erosion of the forearc continental edge, which accounts for the subsequent subsidence of the forearc zones [START_REF] Jaillard | The Cretaceous to Early Paleogene tectonic evolution of the northern Central Andes and its relations to geodynamics[END_REF].

The Cuenca succession exhibits four distinct lithological units, which reflect distinct paleogeographic settings and geodynamic events (Fig. 7).

The Jadán and Quimas formations are separated by a significant, though progressive coarsening of the detrital input, evidencing a significant rejuvenation of the eastern reliefs in the late Campanian. Therefore, the accretion of the San Juan terrane provoked the incipient uplift and erosion of the Eastern Cordillera and the ongoing coarse, quartz-rich detrital input (Quimas conglomerates). The significant change from a crystalline source area in the Jadán and Quimas formations to a mainly volcanic source area in the Tabacay Formation reflects the onset of erosion of the newly accreted San Juan oceanic terrane. The abundance of feldspars suggests that erosion mainly affected volcanic arc rocks. However, in southwestern Ecuador (Cazaderos Formation), the volcanic clastic input is less significant.

Accretion of oceanic terranes and related uplift and erosion of the Andean continental margin is classically admitted to have begun in the Campanian (e.g. [START_REF] Lebrat | Geochemistry and tectonic setting of pre-collision Cretaceous and Paleogene volcanic rocks of Ecuador[END_REF][START_REF] Daly | Correlations between Nazca/Farallón plate kinematics and Forearc basin evolution in Ecuador[END_REF][START_REF] Reynaud | Oceanic plateau and island arcs of southwestern Ecuador: their place in the geodynamic evolution of northwestern South America[END_REF][START_REF] Kerr | The nature and provenance of accreted terranes in Western Ecuador: Geochemical and tectonic constraints[END_REF][START_REF] Hughes | Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador[END_REF][START_REF] Jaillard | Stratigraphy of the Late Cretaceous-Paleogene deposits of the Western Cordillera of Central Ecuador : Geodynamic implications[END_REF][START_REF] Toro | Provenance of the Upper Cretaceous to Upper Eocene clastic sediments of the Western Cordillera of Ecuador: Tectonic and geodynamic implications[END_REF]Vallejo et al., 2006;[START_REF] Luzieux | Origin and Cretaceous history of the coastal Ecuadorian forearc between 1°N and 3°S: paleomagnetic, radiometric and fossil evidence[END_REF]. Based on thermochronological studies, [START_REF] Spikings | Along-strike variations in the thermal and tectonic response of the continental Ecuadorian Andes to the collision with heterogeneous oceanic crust[END_REF][START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF] proposed that (1) uplift of the Andean continental margin is older in southernmost Ecuador (75-65 Ma) than in the rest of the country (65-60 Ma), although Late Cretaceous ( 75 Ma) cooling of continental basement is recorded ≈ by Paleocene sediments in central Ecuador [START_REF] Spikings | Thermochronology of allochtonous terranes in Ecuador: unraveling the accretionary and post-accretionary history of the Northern Andes[END_REF], and (2) uplift of the Andean margin began earlier to the West than to the East. On the other hand, the Eastern Cordillera became a source area for deposits of the Oriente basin by early Maastrichtian times ( 70 Ma; [START_REF] Baldock | Geología del Ecuador. Boletín de Explicación del Mapa geológico de la República del Ecuador[END_REF][START_REF] Jaillard | Síntesis estratigráfica y sedimentológica del Cretáceo y Paleógeno de la cuenca oriental del Ecuador[END_REF][START_REF] Ruiz | Detrital thermochronology -a new perspective on hinterland tectonics, an example from the Andean Amazon Basin, Ecuador[END_REF]. These dates are consistent with the latest Campanian age (75-70 Ma). for the accretion of the San Juan terrane, inferred from the sedimentary record in the Cuenca area. The Tabacay and Saquisilí formations differ from each other by quite distinct clastic sources, different deformation styles, and are separated by a probable unconformity, interpreted as the result of the accretion of the Guaranda terrane, during the late Maastrichtian (to earliest Paleocene ?; 68-65 Ma). The change from a mainly volcanic source in the Maastrichtian to a crystalline source in the Paleocene would reflect the renewed uplift and erosion of the Eastern Cordillera, related to the Guaranda terrane accretion. This interpretation is in agreement with recent studies [START_REF] Spikings | Along-strike variations in the thermal and tectonic response of the continental Ecuadorian Andes to the collision with heterogeneous oceanic crust[END_REF][START_REF] Vaca | Sedimentología, petrología y tectónica de las secuencias cretácicas entre Ingapirca y Pindilig, provincia de Cañar[END_REF][START_REF] Jaillard | Late Cretaceous marine transgressions in Ecuador and northern Peru: a refined stratigraphic framework[END_REF]Vallejo et al., 2006).

Most accretionary events of oceanic terranes resulted in the uplift and erosion of the Eastern Cordillera. Moreover, accretions of oceanic terranes in western Ecuador (late Campanian, late Maastrichtian, late Paleocene) correlate with significant sedimentary hiatuses in the Subandean Zone and locally in the Oriente Basin (Upper Napo/Lower Tena, Lower/Upper Tena, and Upper Tena/Lower Tiyuyacu unconformities). These observations demonstrate that accretions of oceanic terranes provoked the uplift of the Andean continental margin, this uplift being higher toward the west (Fig. 8). The Oriente Basin of Ecuador, therefore, cannot be considered as a flexural foreland basin at that time. Conversely, deposits in the forearc zone are thick and localised, due to structural sediment traps related to the deformation of both the Andean margin and the oceanic terranes. We propose that accretion of oceanic terranes through subduction jam added relatively buoyant oceanic material beneath the western edge of the continental margin, thus provoking its westward increasing uplift. In this view, accretion and tectonic underplating of oceanic material beneath the continental margin would be a major process in the creation of relief and crustal thickening of the early Andes of Ecuador (Fig. 8).

Conclusions

The uppermost Cretaceous unconformable clastic deposits of the Cuenca area, here referred to as the Yunguilla Group, include from base to top, distal shelf fine-grained marls, arkoses and limestones (Jadán Formation, middle and upper Campanian); coarse-grained, quartz-rich shelf and fan delta conglomerates (Quimas Formation, uppermost Campanian-lowermost Maastrichtian), and unconformable black cherts interbedded with volcanogenic turbidites (Tabacay Formation, lower Maastrichtian). This succession resembles that of the Paita and Celica-Lancones regions, indicating that the Campanian-Maastrichtian basin extended to the south as far as northern Peru. The creation of such a mid Campanian forearc basin evidences a strong subsidence, interpreted as due to a significant tectonic erosion, resulting from the former compressional Peruvian phase (late Santonian-early Campanian). The Yunguilla Group is overlain, probably unconformably, by quartz-rich, micaceous distal shelf sandstones (Saquisilí Formation, Paleocene).

The conglomerates of the Quimas Formation are interpreted as reflecting the accretion of the San Juan oceanic terrane (eastern part of Pallatanga terrane), whereas the Maastrichtian-Paleocene boundary unconformity is interpreted as the result of the accretion of the Guaranda oceanic terrane (western part of Pallatanga terrane). These accretionary events correlate with a rejuvenated erosion of the Eastern Cordillera, and with uplifts and erosional hiatuses in the Subandean Zone and Oriente Basin of Ecuador, indicating that accretion and tectonic underplating of oceanic material beneath the continental margin induced the jerky uplift of a large western part of the continental margin. Therefore, the Oriente Basin of Ecuador cannot be considered as a flexural foreland basin at that time.

Fig. 1 :

 1 Fig. 1: Structural sketch of Ecuador, and location of Figure 2.Bold lines represent sutures bounding oceanic terranes.

Fig. 3 :

 3 Fig. 3: Synthetic lithological succession of the upper Cretaceous-Paleocene series of the Cuenca area.

Fig. 4 :

 4 Fig. 4: Lithological succession of the upper Jadán Formation and contact with the Quimas Formation in Loma Tunasloma. Location on Figure 2.

  [03.Cu.07] (upper Campanian to lower or middle Maastrichtian), Nostoceras (Nostoceras?) sp. [03.Cu.07] (upper Campanian), Glyptoxoceras sp. (Santonian-Maastrichtian) or Neoglyptoxoceras sp. (lower-middle Campanian) [03.Cu.08, 09, 10] and Menuites sp. (Santonian-Maastrichtian) in Loma Tunasloma ([03.Cu.11], location in Table

Fig. 5 :

 5 Fig. 5: Lithological succession of the upper Jadán to Tabacay formations, at Santa Bárbara (East of Azogues). Location on Figure 2.

Fig. 6 :

 6 Fig. 6: Structural section of the Yunguilla Group East of Antonio Borrero. Location on Figure 2.

Fig. 7 :

 7 Fig. 7: Correlations between the upper Cretaceous-Paleocene series of the Cuenca area and other parts of Ecuador and northernmost Peru, and interpretation of tectonic events.

Fig. 8 :

 8 Fig. 8: Interpreted consequences of terrane accretion on syntectonic sedimentation on the Ecuadorian margin. Addition of buoyant material beneath the continental margin provokes the uplift of the western part of the margin, and hiatuses in the Subandean Zone, whereas the deformation of the continental margin and oceanic terrane creates sediment traps in the forearc zone.

Table 1 :

 1

Origin and location of the fossil samples cited in the text.

Acknowledgements. This work was carried out in the frame of a scientific agreement between Petroproducción (filial of Petroecuador) and the Institut de Recherche pour le Développement-IRD. The IRD (UR 154) supported field work and sample expeditions. We are grateful to G. Gastineau, D. Iza and W. Lugo for their participation to field work and fossil findings, to R. Bristow and W. Pratt for fruitful discussions and correspondences, and to R. Campaña and M. Rivadeneira for their constant support of this scientific agreement. R. Spikings and an anonymous referee are thanked for their constructive reviews.


Lingli Ni
email: nilingli520@126.com

Dr Abraham Chemtob
email: abraham.chemtob@uha.fr

Céline Croutxé-Barghorn

Céline Dietlin

Jocelyne Brendlé

Séverinne Rigolet

Loïc Vidal

Alain Dieterlen

Elie Maalouf

Olivier Haeberlé

Photoinduced self-assembly of carboxylic acid-terminated lamellar silsesquioxane: highly functional films for attaching and patterning amino-based ligands

Introduction

Hybrid sol-gel silicates derived from silsesquioxane precursors, R-[Si(OR') 3 ] n (n ≥ 1), where R and OR' are respectively covalently attached organic groups and hydrolyzable alkoxy functions, represent a highly versatile class of nanocomposites. 1,2 In the early development phase, the reported hybrids were amorphous, and their growth was essentially driven by the inexhaustible choice of organic moieties achieved through the Si-C bond molecular scale homogeneity. More recently, research efforts have centred on ways to inhibit the disordering effect of Si-O-Si condensation, in order to create ordered organosilica nanostructures. 3,4 Harnessing silsesquioxanes in a way that the organic and siloxane fragments self-assemble into spatially defined and organized nanodomains has been a very attractive goal to fabricate a wide spectrum of advanced hybrid nanomaterials including membranes, 5 conductive films, 6 absorbents 7 and optoelectronic devices. 8 In fact, unique chemical or physical properties may emerge from hybrid materials when organic moieties form mesoscopically segregated functional domains, both ordered and confined. 9 When the ultimate aim is not the fabrication of mesoporous materials, the major route for synthesizing nanostructured hybrids has been the direct template-free self-assembly of silsesquioxane precursors, usually leading to lamellar structures. Critical to self-organization is the presence of noncovalent binding organic groups (van der Waals forces, π-π stacking) or/and amphiphilic interactions. This has imposed strict constraints on precursor architecture and synthesis conditions, which account for the fact that the long-range molecular ordering of most organosilica hybrids has remained very challenging. 10 Accordingly, self-assembled hybrids rely only on a handful of mono-, bis-or multi-silylated building blocks picked essentially for driving self-assembly. To this end, the suitable organic moieties R must be able to develop hydrophobic interactions (long hydrocarbon chain 11 ) or/and hydrogen bonds (ureido 12 , amide groups 13 ). Notwithstanding the wealth of periodically ordered mesostructures achieved with these precursors, they have actually a narrow application potential due to restricted intrinsic functionality. For hybrids to fully benefit from nanostructuration, there is the need of simple organic groups, not only tolerant or favourable to selfassembly, but also able to confer functionality and specific properties to the final material. There have been very few examples of such 'active' nanostructured silsesquioxanes, containing for example photosensitive (azobenzene, 14 diacetylene, 15 perylenediimide 16 ) or conductive organic groups (crown ether, 17 perylene [18][19][20] ). Recently, Mehdi et al. reported several multi-step routes to yield amino-, thiol-21 , sulfonic acid-21 , carboxylic acid- [22][23][24][25] and phosphonic acid-23 functionalized lamellar hybrids. The high density of reactive and accessible end groups arranged within a robust lamellar mesostructure was exploited for the chelation of transition metals and lanthanides in separation applications. 3 Despite the success of this methodology, all the reported materials lacked uniform morphology control.

In this work, we report an efficient UV-driven approach to COOH-functionalized lamellar organosilica films with longrange molecular ordering and uniform film morphology via a photoacid-catalysed sol-gel process. Using this original approach, we have recently described the formation of 'passive' lamellar alkyl silicate films 26,27 and its mechanism. 28 UV control offers several advantages over conventional sol-gel process such as storable, ready-to-use formulation with no potlife issue since the photocatalyst (superacid) is released on demand. Additionally, photopolymerization helps to make the process faster, solvent-free and energy-saving. Here, a similar UV-mediated methodology is exploited to synthesize, for the first time, functional multilayer silsesquioxane films.

Introduction of carboxylic acid groups into the supramolecular structure is based on a 2-step procedure, as outlined in Figure 1. Scheme 1 shows the structure of the starting ester-terminated trimethoxysilane precursor 1 (H 3 COC(O)(CH 2 ) 10 Si(OCH 3 ) 3 ) derived from a purely aliphatic precursor (H 3 C(CH 2 ) 9 Si(OCH 3 ) 3 , 2). Upon UV irradiation in the presence of photoacid generator (PAG, Scheme 1), this precursor film condenses into a mesoscopically ordered and cross-linked lamellar architecture. Hydrophobic interactions (C 10 H 21 ) combined with hydrogen bonds (CH 2 -C=O, Si-OH) serve to self-assemble precursor 1. Subsequently, the terminal ester groups of this robust structure can be partially hydrolyzed into carboxylic acid groups without undermining the mesostructural order. In our case, we chose precursor 1 because of the high abundance of useful amino-based ligands in chemistry, which can be conjugated in high yield to the resultant carboxylic acid groups. To illustrate the usefulness of the method, we used Safranin O, a fluorescent amino ligand (L, Scheme 1) mimicking for example biologically relevant amino derivative ligands able to bind proteins or promote the adhesion of mammalian cells. [START_REF] Lahiri | [END_REF]30 The first advantage of this prototype system is that ligand's retention and binding onto the lamellar hybrid mesostructure can be readily confirmed by optical and fluorescence imaging. Another key feature of L includes its facile spatially-controlled decomposition when exposed to deep UV light under a photomask, in order to generate precisely defined and easy characterized fluorescent patterns. solution was coated on a silicon wafer using an automatic film applicator (Elcometer 4340) equipped with a wire wound bar to yield a ca. 2 µm thick liquid film. Subsequent ambient UV irradiation was performed, at room temperature and ambient humidity (30-35 %), using a medium-pressure Hg-Xe lamp (Hamamatsu L8252, 365 nm reflector) coupled with a flexible light-guide, at a controlled irradiance of 20 mW/cm 2 (the emission spectrum of the UV lamp is provided in the supplementary information, Fig. S1). The film samples were irradiated during 1800 s to yield transparent solid esterfunctionalized silsesquioxane film (1-P). The as-synthesized coated nanocomposite was immersed in an HCl aqueous solution (50 mL, 2 mol/L) at 65°C without stirring for 18 h to promote the conversion of the ester functions into carboxylic acids. The resultant film (1-PH) was thoroughly rinsed with deionized water until the pH of the washing solution remained within the range of 6 to 7. The as-synthesized film was dried overnight in vacuum at room temperature.

Experimental Section

Coupling of the carboxylic acid-functionalized silsesquioxane film with an amino fluorescent ligand and its deep UV photopatterning

The substrate coated with acid-terminated silsesquioxane (1-PH) was activated by immersion in a solution of acetonitrile (50 mL) with Safranin O (L, 0.01 mol/L). 12 h exposure converted the transparent colourless film into a red film (1-PHL). Several washings of the film with acetonitrile were performed until the characteristic signature of Safranin O (maximum absorption at λ max = 517 nm) became non detectable in UV-vis spectroscopy (1 cm thick quartz cell). The 1-PHL film was rinsed with deionized water and vacuum dried at room temperature for 24 h. Subsequently, a TEM grid was deposited onto the solid film surface, and was eventually exposed during 1 hour to deep UV light provided by a medium-pressure Hg-Xe lamp (Hamamatsu L8252, 254 nm reflector). This lamp was connected to a flexible light-guide generating a focused light beam on the film sample. Under these irradiation conditions, the flux of energetic photons is high enough (irradiance = 80 mW/cm 2 for λ < 300 nm and 600 mW/cm 2 for the whole UV spectrum) to enable the degradation of the organic ligand. Finally, the TEM grid was removed showing a red/transparent micropatterned film indicative of a spatially-controlled photodegradation. The sample was washed several times with ethanol and acetone to remove the organic fragments expelled from the film during photocalcination.

Characterization

Infrared spectra obtained by FTIR spectroscopy were recorded with a Bruker Vertex 70. The resolution of the infrared spectra was 2 cm -1 . For all experiments, an effective precursor 1 film thickness of 2 µm was chosen and assessed by profilometry using an Altisurf 500 workstation (Altimet) equipped with a 350 µm AltiProbe optical sensor. X-Ray Diffraction patterns (XRD) were obtained on a PANalytical X'pert Pro diffractometer with fixed slits using Cu/Kα radiation (λ = 1.5418 Å) and θ-2θ mounting. Before analysis, films on silicon wafers were directly deposed on a stainless steel sample holder. Data were collected between 1 and 10 ° 2θ degrees (XRD) with a scanning step of 0.01° s -1 . Morphologies of the samples were characterized by scanning electron microscopy (SEM) (FEI Quanta 400 microscope working at 30 kV). The samples being nonconductive, they have been metalized with gold (15 nm thickness). 1 H (I = 1/2) MAS NMR experiment was performed at room temperature on a Bruker Avance II 400 spectrometer operating at B 0 = 9.4 T (Larmor frequency ν 0 = 400.17 MHz). Single pulse experiment was recorded with a double channel 2.5 mm Bruker MAS probe, a spinning frequency of 25 kHz, a π/2 pulse duration of 3.5 µs and a 10 s recycling delay. 64 scans were recorded. Optical observations of the photopolymerized films were performed using an Olympus BX51 microscope in fluorescence modes. The microscope is equipped with U-LH75XEAPO Argon lamp. Fluorescence excitation is performed through a FITC block filter U-MWIBA2 with an excitation filter BP460-490, a dichroic mirror DM505 and an emission filter BA510-550. Observation was performed at low magnification using 40x NA=0.65 Plan objectives, and at high magnification and high resolution using a 100x, NA=1,4 PlanApo oil-immersion objective. A CoolSnap HO 2 cooled camera is used for recording images. For precise and repetitive sample positioning, a Märzhäuser Wetzlar SCAN 130 x 85 2-D motorized stage is used. Accurate specimen focusing as well as three-dimensional measurements can be performed via motorized focusing controlled by the homemade software developed on ImageJ platform. Image processing (stacking, intensity and dimensional measurements) has been performed using the ImageJ software. As shown in Figure 2, the XRD pattern of the hybrid films 1-P and 2-P derived respectively from 1 and 2 reflect the formation of highly ordered mesostructures. Regardless of the precursor, the long hydrophobic organic chains favoured low curvature mesophases, and the formation of lamellar structures with an intense (001) reflection. Additionally in 1-P, the appearance of new (002) and ( 003) reflections (along with some peak narrowing) indicate a better ordering. This may be induced by additional hydrogen bonding between terminal CH 2 -C=O moieties, which is the only structural difference between both precursors. Higher inter-and intramolecular interactions between organic groups can enhance the enthalpic association forces, and promote self-assembly. The corresponding d 100 values are equal to 3.58 nm for 1-P and 2.78 nm for 2-P. These results are relatively consistent with the bilayer repeating unit distance RSi(OH) 3-x O x ---O x (OH) 3-x SiR (1-P: 3.52 nm and 2-P: 3.14 nm) predicted by molecular models (using ChemDraw 3D calculation). This result therefore confirms the head-to-head bilayer packing of the lamellae, schematically shown in Figure 1. The film is made up of macroscopic multilayered crystallites with no specific orientation in contrast to Self-Assembled Monolayers (SAMs). Typically a few tens to a few hundreds of mesolayers may form spontaneously, but there was no estimate of the crystallite size. Furthermore, altering the aliphatic spacer with an ester end group has not affected the resulting mesophase. Accordingly, a longer hydrophobic pendant chain reduces the surfactant packing parameter, thus maintaining a lamellar organization in the film 2-P. The FTIR spectrum of the nanocomposite derived from 1 (see the supporting information, Fig. S2) shows a quantitative consumption of the band corresponding to methoxysilyl functions (v s (SiOCH 3 ) ≈2840 cm -1 ) within one minute. Moreover, based on the continuous growth of the Si-O-Si antisymmetric stretching band (1000-1260 cm -1 ), we infer that photoinduced condensation reactions take place. However, there is no sign of ester groups' hydrolysis because the band at 1740 cm -1 (v asym of C=O groups) is unchanged (position, intensity) during and even after UV exposure. As a highly efficient reaction, we suggest that the superacid-catalysed hydrolysis of methoxysilyl groups may proceed through the permeation of only traces of atmospheric water. 31 Conversely, the acid-catalysed ester hydrolysis is an equilibrated reaction, which requires generally a much higher water concentration to shift the equilibrium towards products. Furthermore, the ester groups compartmentalized in the hydrophobic channel of the hybrid mesophases may not be accessible to the nucleophilic attack of water molecules, which on the contrary are localized preferentially in the hydrophilic siloxane interlayers. However, heating the as-irradiated film 1-P at 65°C in an acid HCl aqueous solution promotes the slow hydrolysis of the ester functions without damaging the aspect of the resultant film (1-PH). Figure 3 shows the evolution of the IR spectrum in the carbonyl stretching region (1600-1800 cm -1 ) after 18 h immersion. We see a significant decrease of the band assigned to ester groups at 1740 cm -1 (C=O ester symmetric stretch) and the emergence of a neighbouring band at 1710 cm -1 reflecting the concomitant formation of hydrogen-bonded carboxylic acid groups (C=O symmetric stretch of COOH). Based on the relative integrated absorbance of these bands, we infer that the yield of hydrolysis is ca. 40 %. Comparison of the IR spectra of the films 1-P and 1-PH in the CH and OH stretching region (2800-3800 cm -1 ) shows that hydrocarbon chain remains unchanged, while there is no longer band corresponding to residual hydrogen-bonded silanols (3400 cm -1 , stretch of the OH--O bonds), thus indicating further siloxane acid-catalysed condensation. The formation of acid protons and their possible engagement in hydrogen-bonding was investigated by 1 H MAS NMR based on the proton chemical shift. As shown in Figure 4, the spectrum of 1-PH exhibits a distinctive acidic proton signal at ca. 11.2 ppm, assigned to the CO 2 H protons, while absent before hydrolysis (1-P). 32 This resonance is the clear signature of hydrogen-bonded COOH groups, but its broadness may also suggest mixture of different hydrogen-bonded structures and the possibility of some free CO 2 H groups (9 ppm). Furthermore, there is a relative decrease of the resonance attributed to the pendant methyl protons (CH 3 O) of the ester group, slightly shifted downfield from 3.4 to 3.7 ppm after reaction. A hydrolysis degree of ca. 40 % was estimated by comparing the 1-P and 1-PH spectra, which is consistent with FTIR data. The increase in siloxane condensation during the ester hydrolysis step is also noticeable in the 1 H spectrum through the complete disappearance of hydrogen bonded SiOH protons (4.4 ppm). 33 The resonances of the aliphatic protons at ∼1-2 ppm in the hydrolysed film (1-PH) are notably broader than those of the ester-functionalized film (1-P). The larger line width of the methylene protons (CH 2 ) may reflect a more rigid local environment due to higher level of condensation or/and enhanced hydrogen-bonding interactions among the COOH end groups. In contrast to ester groups, the carboxylic acid group can act as both a hydrogen-bond donor through the C-OH groups and an acceptor via the C=O oxygen, leading to a complex array of hydrogen bonds favoured by the head-to-head configuration of the lamellar mesostructure (Figure 2). As a result, the chain mobility of the carboxylic acid terminated silsesquioxane may be quite restricted, and approach that of a rigid crystalline solid. TGA data (see supporting information, Fig. S3) confirm that 1-PH decomposes at higher temperature than 1-P, respectively 520 and 460 °C for a weight loss of 50 %. The presumed H-bonded interactions engaged in the COOH-terminated film could provide the nanocomposite with better thermal stability. Figure 5 shows the result of ester hydrolysis on the XRD pattern of the nanocomposite film assembled from 1, indicating clearly a conservation of the long-range ordered lamellar mesostructure. Nevertheless, hydrolysis caused a slight decrease in the d 001 -spacing from 3.58 to 3.06 nm due to the end group shortening as well as the siloxane interlayer contraction induced by post-condensation reactions. Moreover, the exposure to a concentrated acid solution induced also greater disorder (one order of the 00l peaks was almost lost) along with some peak broadening. Although hydrolysis could be enhanced by a prolonged exposure to HCl solution, these conditions clearly affect the mesostructure stability. The hydrolysis conditions were chosen to ensure a trade-off between conversion and ordering. The SEM images in Figure 6 provide further evidence that the lamellar structure is retained. Even after the acid treatment, one can guess from the blurred images the same plate-like lamellar crystallites in the 1-P and 1-PH films.

Results and discussion

Fluorescent micropattern: direct patterning using deep UV

The COOH-terminated silsesquioxane film (1-PH) represents a highly functional mesostructured support. Although accessibility may be lower than in surface reaction using SAMs, the multilayer structure provides a higher density of reactive groups and an enhanced robustness due to siloxane cross-linking. The reactive carboxylic acid functional groups found in the hybrid film 1-PH allow it to be activated for attachment of amino ligands using standard method as that of 'normal' carboxylic acid group in organic chemistry. After immersion in a solution of a diamino fluorescent ligand (Safranin O, L), the resultant film (1-PHL) was washed several times with ethanol to remove the excess of dye non-specifically anchored to the silsesquioxane network. Binding was first detected straightforwardly by optical and fluorescence microscopy (data not given). Additionally, we used FTIR spectroscopy to assess the yield of coupling. Figure 7 shows the IR spectra of the COOH-terminated hybrid to which the ligand L has been coupled. After activation, there is no band corresponding to residual carboxylic acid groups (C=O symmetric stretch of COOH, ≈ 1710 cm -1 ), which are replaced entirely by another blue-shifted band of similar intensity assigned to NH-C(O) amide groups (C=O amide stretch ≈ 1690 cm -1 ), 33 thus suggesting a quantitative coupling. Another evidence was given by the appearance of the characteristic v(N-H) band at 3440 cm -1 . A benchmark experiment was performed by immersing a nonhydrolyzed film (1-P) in the same fluorescent ligand solution. As expected, the film remained transparent after washing and IR spectra revealed no sign of amide linkages or dye entrapment. We introduced finally a simple method to fabricate a fluorescent pattern based on the use of deep UV light directed through an optical mask deposited onto the 1-PHL film surface. We used energetic photons to promote the spatially-controlled degradation of the organic fragments of the hybrid film exposed to UV light. After irradiation, the film was washed several times with acetone and ethanol, and the pattern was studied by optical and fluorescent microscopy. Figure 8 displays a series of optical images (a-d) of the patterned film prepared with masks of different shapes and sizes. The bright regions correspond to the irradiated areas, where the fluorescent and coloured ligand was degraded. In contrast, the red regions were masked and visibly preserved from calcination. Obviously, this direct photopatterning method allows the generation of precisely defined patterns of any arbitrary shape. Highly resolved micropatterns are achieved, and the smallest features that we have resolved are squares with a 7.5 µm side (Fig. 8c). The FTIR analysis (see supporting information, Fig. S4) of the irradiated areas reveals a complete cleavage of the amido bonds and a significant decrease of the C-H stretching modes (2800 and 3100 cm -1 ) while the broad envelope (1000-1300 cm -1 ) assigned to Si-O-Si antisymmetric stretching modes is unchanged. This result emphasizes a selective and partial removal of the organic components of the hybrid film but sufficient to fully quench the fluorescence. The consequence is a decreased thickness of ca. 400 nm in the exposed areas and the formation of well-resolved wells as evidenced by atomic force microscopy (see supporting information, Fig. S5). Additionally, the photogenerated pattern was investigated by fluorescence microscopy. Figure 9 shows the fluorescence emission image of the sample obtained with the hexagonal-shaped mask (Fig. 8a). Clearly, the honeycomb was successfully replicated. The non-exposed areas (bright yellow regions) outside the hexagons emit strong and uniform fluorescence signal, demonstrating the capacity of this process to access micropatterned fluorescence. The surface patterning of fluorescence molecules has found already a great importance in displays, optical memory devices and molecular switches, as well as in the sensor and imaging industries. [34][35][36]

Conclusions

Carboxylic acid terminated monolayers have already demonstrated their potential as reactive surface in covalent immobilization of biomolecules, electrochemistry, and crystal growth. In this report, we have described a UV methodology to create COOH-functionalized silsesquioxane films possessing a highly ordered multilayer mesostructure. The method required the photoacid-catalysed sol-gel process of ester-terminated alkoxysilane 1. Subsequent ester hydrolysis by HCl treatment allowed their conversion into carboxylic acid terminal groups as demonstrated by FTIR and solid state were achieved using a UV degradation photolithography procedure.

By successfully adapting this technique to the immobilization and patterning of biologically active amino-reactive ligands for instance, there exists significant potential to study cell adhesion and spreading, biofouling mechanism, or the elaboration of bioanalytical devices (biosensors, protein biochips, miniaturization of DNA analyses). 37,38 We believe that micrometer-scale ordered film structure have several advantages over molecular-scale monolayers based on chloroor alkoxysilane including higher functionality, potential applicability on a variety of substrates without particular surface preparation and chemical/mechanical resistance because of the cross-linked siloxane interlayers.

Figure 1 .

 1 Figure 1. Supramolecular structure formed by the photoinduced self--assembly of precursor 1.

Scheme 1 .

 1 Scheme 1. Structures of monosilylated trimethoxysilane precursors (1, 2), photoacid generator (PAG) and fluorescent amino--based ligand (L)

Figure 2 .

 2 Figure 2. XRD patterns for the two nanocomposite films (1--P and 2--P) assembled from 1 and 2.

Figure 4 .

 4 Figure 4. Solid state 1 H MAS NMR spectra of the hybrid films 1--P and 1--PH following ester hydrolysis

Figure 5 .

 5 Figure 5. XRD patterns of the silsesquioxane films 1--P (as--irradiated film derived from precursor 1) and 1--PH (after ester hydrolysis of film 1--P).

Figure 6 .

 6 Figure 6. Representative SEM images of the scratched nanocomposite films 1--P (a) and 1--PH (b).

Figure 7 .

 7 Figure 7. FTIR spectra of the COOH--functionalized hybrid film 1--PH and 1--PHL obtained after immersion in an ethanolic solution of L.

Figure 8 .

 8 Figure 8. Optical microscopy images of the patterned 1--PHL film obtained with different pattern feature size and shape: (a) hexagon; (b), mixed squares; (c), square; (d) bar (scale bar: 50 or 200 µm)

1 HFigure 9 .

 19 Figure 9. Image of the photopatterned 1--PHL film surface obtained with fluorescence microscopy (scale bar = 50 µm).

2.1 Chemicals

	Methyl 11-(trimethoxysilyl)undecanoate (1, 95 mol. %), n-
	decyltrimethoxysilane (2, 98 mol. %) were purchased from
	SIKÉMIA and ABCR, respectively. The bis-dodecyl
	diphenyliodonium hexafluoroantimonate salt (UV1241) PAG
	was provided by Deuteron. Hydrochloric acid (36.5-38
	mol. %), acetonitrile (99.8 mol. %) and Safranin O (L, 85
	mol. %) were supplied by Sigma-Aldrich. Technical acetone
	and ethanol were provided by Carlo Erba and VWR
	respectively. All the chemicals were used as received without
	further purification.

2.2 Synthesis of ester-and carboxylic acid-functionalized silsesquioxane lamellar films

			1
	Ester terminal group	C 10 hydrocarbon chain	Hydrolyzable alkoxy groups
			2
			PAG
			L
	2 wt. % of PAG was dissolved in precursor 1 to form a
	photolatent homogeneous mixture. The resultant nonhydrolysed

FTIR spectra of the silsesquioxane films 1--P and 1--PH obtained after 18

  h immersion time in a 2 mol/L HCl aqueous solution at 65°C. connected to a long C 10 hydrocarbon chain. Such structural combination has recently proven to drive multilayer selfassembly through hydrophobic interactions.28 Additionally, 1 has a tuneable methyl methanoate group (H 3 COC(=O)-), thereby raising the question about the effect of this ester terminal group on supramolecular organization. Both precursors are commercially available, very stable in the open air and nonvolatile when they are in film form at ambient

		(001)
		3.58 nm		(002)
							(003)	1-P
		(001)
		2.78 nm
								2-P
	2	3	4	5	6	7	8	9
				2θ deg ree (C uK α)
	Figure 3.
	3.1 Synthesis of self-assembled ester-and carboxylic acid-
	terminated silsesquioxane films
	1 and 2 are two monosilylated silsesquioxane precursors
	(Scheme 1) having in common one trimethoxysilyl group

conditions. 1-and 2-based liquid films containing 2 wt. % of PAG were coated on silicon wafer substrate. Subsequent UV irradiation converted them into solid silsesquioxane films.