text:
Python Programming/Sequences

Sequences allow you to store multiple values in an organized and efficient fashion. There are seven sequence types: strings, bytes, lists, tuples, bytearrays, buffers, and range objects. Dictionaries and sets are containers for sequential data.

Strings
We already covered strings, but that was before you knew what a sequence is. In other languages, the elements in arrays and sometimes the characters in strings may be accessed with the square brackets, or subscript operator. This works in Python too: Indexes are numbered from 0 to n-1 where n is the number of items (or characters), and they are given to the characters from the start of the string: H e  l  l  o ,     w  o  r  l  d  ! 0 1  2  3  4  5  6  7  8  9 10 11 12 Negative indexes (numbered from -1 to -n) are counted from the end of the string: H  e   l   l   o  ,       w   o   r  l  d  ! -13 -12 -11 -10 -9 -8  -7  -6  -5  -4 -3 -2 -1

If the number given in the bracket is less than -n or greater than n-1, then we will get an IndexError.

But in Python, the colon : allows the square brackets to take two numbers. For any sequence which only uses numeric indexes, this will return the portion which is between the specified indexes. This is known as "slicing" and the result of slicing a string is often called a "substring."

As demonstrated above, if the first and second number is omitted, then they take their default values, which are 0 and n-1 respectively, corresponding to the beginning and end of the sequence respectively (in this case). Note also that the brackets are inclusive on the left but exclusive on the right: in the first example above with [3:9] the character at index 3, 'l', is included while the character at index 9, 'r', is excluded.

We can add a third number in the bracket, by adding one more colon in the bracket, which indicates the increment step of the slicing: The increment step can be positive or negative. For positive increment step, the slicing is from left to right, and for negative increment step, the slicing is from right to left. Also, we should aware that

 * the default value of the increment step is 1

 * the default value for the first and second number becomes -1 (or n) and -n (or 0) respectively, when the increment step is negative (same default value as above when the increment step is positive)
 * the increment step cannot be 0

Lists
A list is just what it sounds like: a list of values, organized in order. A list is created using square brackets. For example, an empty list would be initialized like this:

The values of the list are separated by commas. For example:

Lists may contain objects of varying types. It may hold both the strings "eggs" and "bacon" as well as the number 42.

Like characters in a string, items in a list can be accessed by indexes starting at 0. To access a specific item in a list, you refer to it by the name of the list, followed by the item's number in the list inside brackets. For example:

You can also use negative numbers, which count backwards from the end of the list:

The  function also works on lists, returning the number of items in the array: Note that the  function counts the number of item inside a list, so the last item in spam (42) has the index (len(spam) - 1).

The items in a list can also be changed, just like the contents of an ordinary variable:

(Strings, being immutable, are impossible to modify.) As with strings, lists may be sliced:

It is also possible to add items to a list. There are many ways to do it, the easiest way is to use the append method of list:

Note that you cannot manually insert an element by specifying the index outside of its range. The following code would fail:

Instead, you must use the insert function. If you want to insert an item inside a list at a certain index, you may use the insert method of list, for example:

You can also delete items from a list using the  statement: As you can see, the list re-orders itself, so there are no gaps in the numbering.

Lists have an unusual characteristic. Given two lists a and b, if you set b to a, and change a, b will also be changed. This can easily be worked around by using  instead.

For further explanation on lists, or to find out how to make 2D arrays, see Data Structure/Lists

Tuples
Tuples are similar to lists, except they are immutable. Once you have set a tuple, there is no way to change it whatsoever: you cannot add, change, or remove elements of a tuple. Otherwise, tuples work identically to lists.

To declare a tuple, you use commas:

It is often necessary to use parentheses to differentiate between different tuples, such as when doing multiple assignments on the same line:

Unnecessary parentheses can be used without harm, but nested parentheses denote nested tuples:

both produce:

but:

For further explanation on tuple, see Data Structure/Tuples

Dictionaries
Dictionaries are also like lists, and they are mutable -- you can add, change, and remove elements from a dictionary. However, the elements in a dictionary are not bound to numbers, the way a list is. Every element in a dictionary has two parts: a key, and a value. Calling a key of a dictionary returns the value linked to that key. You could consider a list to be a special kind of dictionary, in which the key of every element is a number, in numerical order.

Dictionaries are declared using curly braces, and each element is declared first by its key, then a colon, and then its value. For example:

Also, adding an element to a dictionary is much simpler: simply declare it as you would a variable.

For further explanation on dictionary, see Data Structure/Dictionaries

Sets
Sets are just like lists except that they are unordered and they do not allow duplicate values. Elements of a set are neither bound to a number (like list and tuple) nor to a key (like dictionary). The reason for using a set over other data types is that a set is much faster for a large number of items than a list or tuple and sets provide fast data insertion, deletion, and membership testing. Sets also support mathematical set operations such as testing for subsets and finding the union or intersection of two sets.

Note that sets are unordered, items you add into sets will end up in an indeterminable position, and it may also change from time to time.

Sets cannot contain a single value more than once. Unlike lists, which can contain anything, the types of data that can be included in sets are restricted. A set can only contain hashable, immutable data types. Integers, strings, and tuples are hashable; lists, dictionaries, and other sets (except frozensets, see below) are not.

Frozenset
The relationship between frozenset and set is like the relationship between tuple and list. Frozenset is an immutable version of set. An example:

Other data types
Python also has other types of sequences, though these are used less frequently and need to be imported from the standard library before being used. We will only brush over them here.

 * array: A typed-list, an array may only contain homogeneous values.
 * collections.defaultdict: A dictionary that, when an element is not found, returns a default value instead of error.
 * collections.deque: A double ended queue, allows fast manipulation on both sides of the queue.
 * heapq: A priority queue.
 * Queue: A thread-safe multi-producer, multi-consumer queue for use with multi-threaded programs. Note that a list can also be used as queue in a single-threaded code.

For further explanation on set, see Data Structure/Sets

3rd party data structure
Some useful data types in Python do not come in the standard library. Some of these are very specialized in their use. We will mention some of the more well known 3rd party types.

 * numpy.array: useful for heavy number crunching => see numpy section
 * sorteddict: like the name says, a sorted dictionary

Exercises

 * 1) Write a program that puts 5, 10, and "twenty" into a list. Then remove 10 from the list.
 * 2) Write a program that puts 5, 10, and "twenty" into a tuple.
 * 3) Write a program that puts 5, 10, and "twenty" into a set. Put "twenty", 10, and 5 into another set purposefully in a different order. Print both of them out and notice the ordering.
 * 4) Write a program that constructs a tuple, one element of which is a frozenset.
 * 5) Write a program that creates a dictionary mapping 1 to "Monday," 2 to "Tuesday," etc.

title: Python Programming/Sequences


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User talk:Ethernet2Factory

Page to create a book on Indusrial Ethernet

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: User talk:Ethernet2Factory


text:
19th Century Literature/Frankenstein

Mary Shelley's Frankenstein was first published in 1818, then later revised into the form we know it as today. One of the most notable differences was the change in Elizabeth's personal history from Victor's cousin to adopted orphan.

For more information on Mary Shelley, a plot summary of Frankenstein and its representation in the media check out their Wikipedia pages.

Narrative Structure

The novel is structured as a frame narrative, opening and concluding with a letter written by Captain Walton, an arctic explorer who comes across Victor on the ice. He claims to be transcribing Victor's story as it is told to him, thus switching to Victor's perspective. Half way through Victor's narrative he describes a meeting with his creation, in which the creature tells his own life history to Victor. As Victor recounts this apparently word for word, we change perspectives again, creating a third layer within the narrative.

In this first sentence of letter one the information is that is read about is that the journey or quest that the speaker was on was successful so far. He is writing to someone who did not have a good insight on how this would end up. He is telling them you will rejoice, be happy because he has accomplished what they thought would be evil.

Victor Frankenstein
Despite what Hollywood might have you believe, Victor is not a wholly evil character. The novel follows him from childhood and shows how his keen interest in science developed from studying ancient texts, in particular concerning alchemy. Science was his passion; he even delayed marrying Elizabeth and left his home to attend university and become a doctor. It is during his anatomy classes that he hits upon an idea that could bring life to dead flesh; just as an alchemist might create gold out of lead.

Despite building his creature out of the parts of executed criminals, Victor is so enamored with his own brilliance that he expects it to be beautiful, and envisions himself to be the god of a new race of people, free from the hardships of disease and aging. Victor always has the best intentions in his actions, but he fails to see his own limitations. When the creature is born hideous, instead of celebrating his success at creating life Victor is appalled and abandons it immediately.

From then on Victor is haunted by his creation. He tries to run from it and shuns it at every opportunity, but when it murders he is forced to confront it. The creature tells a sympathetic story of its abandonment and how being so frightening looking means it can never befriend ordinary people. Having no parent to guide it, the creature also has no morals so Victor fears it - sensing this the creature threatens Victor and commands him to build a female to act as wife to the creature.

About to enter a marriage himself Victor is terrified of what the creature might do to further injure his family. He agonizes over his decision, feeling that to create another creature, although within his power, would be an abomination. Victor is as much disturbed by his own power over nature as by the physical strength of the thing he has created. Ultimately his own moral compass takes over and he destroys the partially made female creature, costing him his own wife and future. In an attempt to right his wrongs against nature, Victor vows he will not rest until he has destroyed the monster he created.

The Creature
The creature that Victor creates has frequently been misrepresented in films as a hulking, mute beast. Although initially abandoned by Victor, the creature learns to speak and read from observing a family teaching their children, watching them through a crack in the wall. Seeing his reflection in a river the creature is traumatized by his disfigured face and knows that he should not approach people. As well as reading the creature also plays an instrument, later telling Victor that his hand remembered the notes.

When Victor recounts the creature's monologue the creature is both articulate and sensitive. He feels keenly the abandonment of Victor, effectively his father, who did not even see fit to give the creature a name. In this, the creature can be seen as a symbol for disenfranchised people who are ignored or shunned by the upper class.

title: 19th Century Literature/Frankenstein


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User talk:Ghosthunter893

Come introduce yourself at the new users page. If you have any questions, you can ask there or contact me personally. -- Herby talk thyme 14:14, 8 November 2007 (UTC)

-- Herby talk thyme 14:14, 8 November 2007 (UTC)

title: User talk:Ghosthunter893


text:
User:Whiteknight/gadgets.js

//core script for all gadgets import_script('User:Whiteknight/gadgetscore.js'); //Gadget Scripts import_script('User:Whiteknight/printversion.js'); import_script('User:Whiteknight/designer.js'); import_script('User:Whiteknight/categorize.js'); import_script('User:Whiteknight/remotetalk.js'); import_script('User:Whiteknight/editinsert.js'); import_script('User:Whiteknight/pagetester.js');

title: User:Whiteknight/gadgets.js


text:
User talk:62.171.194.5

-- Herby talk thyme 15:04, 8 November 2007 (UTC)

Blocked
You were warned and are now blocked from editing - thanks -- Herby talk thyme 15:11, 8 November 2007 (UTC)

title: User talk:62.171.194.5


text:
User talk:204.113.112.19

-- Herby talk thyme 15:34, 8 November 2007 (UTC)

Please stop creating pages that are not textbooks and so are outside of the project scope or you will be blocked, thanks -- Herby talk thyme 15:39, 8 November 2007 (UTC)

title: User talk:204.113.112.19


text:
Cookbook:Al Dente

Al dente means "to the tooth" or "to the bite" in Italian. It refers to the need to apply sufficient pressure while masticating so that firmness can be felt.

While the expression is most commonly used to describe pasta that has been served at this degree of firmness – generally considered to be the most widely preferred – it can be used to describe any food for which the al dente sensation is particular, such as rice and tender-crisp vegetables.

The expression al dente should be considered laudatory, and in no way refers to foods being underdone or too hard.

Serving pasta al dente
Pasta is most widely known as a shaped, dehydrated, raw, enriched wheat durum semolina dough and the following deals in the preparation of such. As the pasta enters boiling water, it hydrates and wheat proteins and starches form coherent structures under the influence of heat. The process occurring from the outside-in, the pasta is allowed to retain its shape and the al dente sensation is most often and wrongly procured, in dehydrated pasta, by a slightly less hydrated peripheral core.

Water
The amount of water to bring to a boil greatly varies. While it's possible to cook 500 g of pasta in about 4 L of water, the water will become viscous from the starch that is lost from dissolution and mechanical action of the steam pockets rising from the heat source. The residual starch, at the origin of the viscosity, affects the final dish in its composition, as it contributes to the adhesion of other ingredients – such as spices – to the pasta. This layer of residual starch also absorbs liquids in a superficial manner while partially dissolving into sauces, thereby perceptually blending the taste of the pasta and that of the added liquid ingredients.

Certain dishes, such as pasta pomodoro, will benefit from more residual starch while others, like pasta salads, will benefit from less.

Salt
The addition of salt to the pasta's boiling has two effects: the first is that is increases the boiling temperature, and the second is that the salt will permeate the pasta, imparting it its taste. The use of salt in the boiling water greatly affects overall dish composition; while certain prefer to use a salted sauce over unsalted pasta, others prefer to not salt their sauces – where the addition of sodium would affect consistency, for instance – and to salt the pasta's boiling water. In domestic and in some professional settings, it is also not uncommon for both, the water and the dressing, to be salted.

The boiling temperature, in turn, affects overall pasta density. A lower boiling temperature means more dough is hydrated before it has cooked and is able to exert pressure on the hydrating and cooking core. It is then possible to imagine that al dente pasta should be partially cooked in water containing a fair amount of salt and then finished in a more solute bath, this, to achieve a high density and avoid a sticky, undercooked core that people sometimes mistake for al dente.

Oil
Cooking instructions for dry pasta sometimes call for the addition of oil to the water, most often under the pretext that is prevents pasta from sticking together. The statement is obviously fallacious, as oil's density is lesser than that of water and therefore floats. The addition of oil to the boiling pot may, however, control "boil-overs", this, in being mechanically emulsified by the surfacing bubbles and then affecting the surface tension of air pockets formed under the starchy water's surface, preventing their accumulation.

To prevent boil-overs, it is generally considered more efficient – energetically and in labor – to control temperature than to add oil or surfactants to the water.

Addition of Pasta
Once the water bath has reached its maximum temperature – when it boils – pasta should be added and stirred so as to prevent the individual hydrating dough parts from superficially merging. Once the water returns to boiling temperature, heat should be lowered to maintain the bath at simmering temperature, so as to benefit from the mechanical action of the rising steam pockets while avoiding boil-overs.

Drainage
Drainage should occur slightly before the pasta is considered al dente, this, to allow for continued hydration and cooking during the process, during further processing – such as after adding the pasta to a sauce – and during transition.

Rinsing
In certain dishes – such as cold pasta salads – the pasta does not often benefit from a starch coating and a lighter, fluffier texture is preferred. It then becomes efficient to rinse pasta, to free it of its residual starch and cool it. It is also possible to rinse with hot water to, likewise, control the amount of residual starch and the temperature of the pasta.

Quality Control
Al dente pasta is pasta that is served in this manner and which remains so throughout the meal. It should be firm, without being sticky so as to provide a pleasant experience nor should it be underhydrated, so as to favor proper digestion.

Quality control should occur at the plating level, when the pasta is ready to be served. If the pasta has the proper density and if the dish is served at the right temperature, the pasta should remain edible throughout the entire course.

title: Cookbook:Al Dente


text:
XQuery/Displaying Lists

Motivation
You have a list of items in an XML structure and you want to display a comma separated list of the values in an output string.

Method
XQuery provides the "string-join" function that will take a sequence of items and a separator string and create and output string with the separator between each of the items. The format of the function is: where nodeset is a list of nodes and separator the string that you would like to separate the values with.

Output
= Create a CSV file from XML = We will use two "string-join" functions, one for all rows and one for each row. We will create one large string and then use the "response:stream" function to return the results.

Which returns: Row1 Col1,Row1 Col2,Row1 Col3,Row1 Col4 Row2 Col1,Row2 Col2,Row2 Col3,Row2 Col4 Row3 Col1,Row3 Col2,Row3 Col3,Row3 Col4 Row4 Col1,Row4 Col2,Row4 Col3,Row4 Col4

= Discussion = The "string-join" function takes two arguments, the first is the sequence of strings to be joined and the second is the separator.

title: XQuery/Displaying Lists


text:
Teaching Elementary School Health Education/Injury Prevention and Safety

Injury Prevention and Safety

Injury Prevention and Safety is the area of health that focuses following guidelines to reduce the risk of unintentional injuries. It is an important area of health that teaches young people important life skills to help keep them safe and out of harms way in the future. The over all area of Injury Prevention and safety includes following safety guidelines for the following risk situations:

/Unintentional Injuries/

/Severe Weather, Natural Disasters, and National Alerts/

/Motor Vehicle Safety/

/Violence/

/Respecting Authority and Obeying Laws/

/Physical Violence and Abuse/

/Sexual Violence and Abuse/

/Gangs/

/Weapons/

/First Aid/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Unintentional Injuries

Unintentional Injuries

In the Home:

/Falls/

/Fires/

/Poisoning/

/Airway Obstruction, Suffocation, Choking/

In the Community:

/Drowning/

/Bicycling, Scooter/

In the Workplace

/Laws Providing Protection/

/Repetitive Strain Injury/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Severe Weather, Natural Disasters, and National Alerts

Severe Weather, Natural Disasters, and National Alerts

/Guidelines/

/Landslides/

/Floods/

/Earthquakes/

/Tornadoes/

/Hurricanes/

/Wildland Fires/

/Electrical Storms/

/Winter Storms/

/The Homeland Security Advisory System/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Motor Vehicle Safety

Motor Vehicle Safety

/Obtaining a Valid Driver’s License/

/Being a Defensive Driver/

/Avoiding High-Risk Driving/

/Avoiding Drinking and Driving/

/Avoiding Traffic Violations/

/Wearing Safety Belts/

/Motor Vehicle Violence – Carjacking/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Violence

 Reduce the Risk of Violence

/Bullying/

Elementary School Bullying
/Fighting/

/Assault/

/Homicide/

/Sexual Harassment/

/Rape/

/Child Abuse/

/Domestic Violence/

/Risk Factors for Violence/

/Protective Factors for Violence/

/Using Assertive Behavior to Reduce the Risk of Violence/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Respecting Authority and Obeying Laws

Respecting Authority and Obeying Laws

/Developing a Moral Code/

/Why do some Youth Challenge Authority and Break Laws?/

/Juvenile Offenders/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Physical Violence and Abuse

Physical Violence and Abuse

/Self Defense Strategies/ /Hazing/

/Bullying/

/Child Abuse/

/Physical Abuse/

/Neglect/

/Emotional Abuse/

/Sexual Abuse/

/Child Abuse laws/

/Mental and Emotional Abuse/

/Domestic Violence/

/Dating Violence/

/Recovering from Violence/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Physical Violence and Abuse/Self Defense Strategies

For the Home

For Public Places

Social Situations


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Physical Violence and Abuse/Recovering from Violence

Post-Traumatic Stress Disorder

Secondary Victimization

Victim Recovery

Perpetrator Recovery


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Sexual Violence and Abuse

Sexual Violence and Abuse

/Rape/

/Acquaintance and Date Rape/

/Laws Concerning Date Rape/

/Alcohol and other Drug Use/ Sexual Abuse /Sexual Harassment and Stalking/ /Recovering for Survivors of Sexual Violence/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Sexual Violence and Abuse/Alcohol and other Drug Use

Date Rape Drugs

/Rohypnol/

/GHB/

/Ketamine/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Physical Violence and Abuse/Sexual Abuse

/Incest/

/Laws and Sexual Abuse/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Sexual Violence and Abuse/Sexual Harassment and Stalking

Sexual Harassment and Stalking Laws


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Sexual Violence and Abuse/Recovering for Survivors of Sexual Violence

/Recovery for Rape Survivors/

/Recovery for Perpetrators/


text:
Teaching Elementary School Health Education/Injury Prevention and Safety/Gangs

Gangs

/Recognizing Gangs/

/Risks of Belonging to a Gang/

/Reasons for Membership in a Gang/

/Protection form Gangs/

/Leaving a Gang/


text:
Knowledge Patterns/Stories of Learning

See Lore of Learning/Stories of Learning and consider capturing the stories there - or create a new pool of stories here?

title: Knowledge Patterns/Stories of Learning


text:
User talk:Lteets00

 * I have nominated all your first aid pages for speedy deletion as they contain no content and would duplicate content in First Aid (I haven't deleted them myself because I am the principal author of that book). Please feel free to contribute to that book, and link to it from Injury Prevention and Safety. Thanks. – Mike.lifeguard  | talk 19:15, 8 November 2007 (UTC)

title: User talk:Lteets00


text:
XQuery/Returning the Longest String

Motivation
You want to find the longest string(s) in a sequence of strings.

Sample Program
[/basics/longeststring.xq Execute]

Discussion
This XQuery creates a local function that takes zero or more strings:

and returns one or more strings:

It uses the max XPath function that looks at a sequence of values and returns the highest.

Note that if there are several strings in the input set that each have the same max length, it will return all strings of max length.

If you only want the first returned, add "[1]" to the return expression:

''

title: XQuery/Returning the Longest String


text:
User talk:WikiWhatWikiWho

Come introduce yourself at the new users page. If you have any questions, you can ask there or contact me personally.– Mike.lifeguard  | talk 19:19, 8 November 2007 (UTC)

title: User talk:WikiWhatWikiWho


text:
Talk:Materials in Electronics/Schrödinger's Equation

Time Dependant Schrodinger Equation
Any chance of extending this analysis to include the time dependant Schrodinger equation?


text:
The Geology of Indonesia/Natuna

Contributors: Murti, N., Minarwan, Darman, H.

The Natuna area discussed in this article is Natuna Islands and the surrounding area within the Indonesian territory. The area forms the south-westernmost tip of South China Sea, with Malay Basin, Penyu Basin, Sarawak Basin and Sunda Shelf as its immediate geological neighbours. Natuna area itself is presently configured by two Tertiary basins, namely West Natuna Basin and East Natuna Basin, separated by Natuna Arch (Figure 1).

This article is a result of a comprehensive library study of the available published materials and various unpublished internal studies within the writers' reach. The objective of this article is to explain simply and hopefully clearly the geological facts of this Natuna Area and to expose its geological highlights. The more detailed study, investigations and experiments can be found in the bibliography.

Geological information of the Natuna Area mainly comes from petroleum exploration, which high frequency has resulted in many comprehensive geological study of the area. The availability of these studies does not mean that the geological history of this area is clearly understood. There are still many uncertainties, which need to be addressed, as can be seen in the subsequent text.

Tectonic
The West Natuna Basin is bounded at the north by Khorat Swell, which is a south-dipping monocline basement high. To the south it is bounded by Sunda Shelf and to the east by Natuna Arch. At the north-west it opens to the NW-SE elongated Malay Basin, and at the south-western tip it opens to a smaller E-W elongated Penyu Basin. The Malay Basin is separated from the Penyu Basin by Tenggol Arch, a ridge extruding east to the western part of the West Natuna Basin. In the West Natuna Basin itself several main structural elements can be recognised, i.e. Anoa Graben, South Kakap Graben, Northern Central High, Southern Central High and the Anambas Graben (Figure 2).

The predominant structural orientations in the West Natuna Basin are SW-NE and NW-SE (Wongsosantiko & Wirojudo, 1984), including several big NW-SE wrench faults. The faults are typified by the changes in their sense of movements, from reverse in the shallower horizons to normal in the deeper. The fold styles also change from anticlines at the top to half grabens at depth. The West Natuna Basin is classified by Daines (1985) as an intracontinental failed rift basin. The various structural elements in this basin were formed during two distinct deformation period i.e. Late Eocene-Oligocene period of extension which resulted in graben and half graben formation, and a later compressional phase which resulted in the inversions of the structures. This compressional phase re-activated the existing structures with reversed sense of movements.

The Natuna Arch, which separates the West and East Natuna Basins, is a northern protrusion of Sunda Shelf. Along with Khorat Swell, this ridge was emergent periodically during Tertiary (White & Wing, 1978) and thus provided the source of sediments for the two adjacent basins.

The East Natuna Basin is bounded at the west by Natuna Arch, to the east it opens to Sarawak Basin. The south part is bounded by Sunda Shelf and the northern part by Vietnam Basin. Hutchison (1989) divided the East Natuna Basin into Sokang Sub Basin and North East Natuna Basin. They are separated by the Paus-Ranai Ridge, a feature parallel to the eastern side of Natuna Arch, which also forms the north-eastern boundary of Sokang Sub Basin. To the east both basins open to Sarawak Basin (Figure 2). In a Late Cretaceous - Early Eocene reconstruction for the area, White & Wing (1978) concluded that the East Natuna Basin was part of a large fore-arc basin extending from offshore Vietnam, across Natuna waters to Sarawak.

Unlike in the West Natuna Basin, the main structural trend in the East Natuna Basin is NNW-SSE, only in the northern part SW-NE trending structures exist (Wongsosantiko & Wirojudo, 1984). This SW-NE trending structures are extensional faults and half grabens similar to the ones found in West Natuna Basin, but the rift magnitude is generally less than the ones in the West Natuna Basin. In the East Natuna Basin all the structures are extensional, there seems to be no compressional tectonic phase happened in this area. White & Wing (1978) stated that the structural trend seems to follow the underlying basement fabric, which is formed by the eastward migrating subduction zone.

Stratigraphic
The stratigraphic framework of both West Natuna Basin and East Natuna Basin was first compiled by Pupilli (1973), based on lithostratigraphy. Several companies working in different concession blocks in the West Natuna Basin have since developed various stratigraphic columns for the area with different nomenclatures, as can be seen in subsequent works by Armitage & Viotti (1977), Pollock et al. (1984), Daines et al. (1985), Sutoto (1991), Fahman et al. (1991) and Ginger et al. (1993). The one used in this paper, a generalised stratigraphic framework for the whole area, can be seen in Figure 4.

Underlying the sequences of the West Natuna Basin is the Cretaceous basement, which according to Pollock et al. (1984) is comprised of amphibolites. According to a more detailed recent study the basement actually comprises intrusive acidic-type igneous rocks such as quartz-diorite, granite and phyllite, chlorite-schist, gneiss and amphibolite.

The earliest sediment found in the West Natuna Basin is thought to be older than Early Oligocene, based on the dating of the diabase intrusion found in the basal sediment. Lama Formation of Late Eocene (?) to Early Oligocene is found above the basement. Lama Formation consists mainly of fluvio-deltaic, fluvial and alluvial fan sandstones. Benua Formation conformably overlies Lama Formation. This formation is a sequence of shales interpreted as of lacustrine origin. Both Lama and Benua Formation are mostly barren of fauna, except some palynomorphs that indicate the fresh-water depositional environment. Overlying Benua shales are the interbedded sandstones and shales of Lower Gabus. The sandstone is fine to medium grade sands with plant debris typically form thick, blocky or fining upward units and usually massive in appearance. This sequence is interpreted to be of fluvio-deltaic and fluvial origin, and its age determined from palynomorphs is Oligocene.

Above the Lower Gabus Formation, Keras Shale was deposited in lacustrine environment at Mid Oligocene to Late Oligocene time. This Keras Shale was then gradually replaced by the interbedded sandstone and shale of Upper Gabus Formation. The sandstone of Upper Gabus Formation is fine to very fine grained, in blocky or fining upward units similar to the Lower Gabus. This formation was deposited in braid-delta and lacustrine plain environment at Late Oligocene-Early Miocene time. Palynological data shows that the Oligocene/Miocene boundary is within the topmost part of Gabus interval. Barat Shale was then deposited above Upper Gabus in lacustrine depositional environment with the influences of marine condition at some places in Early Miocene time. This assigned age is based on the non-existence of Oligocene and older markers, and the possible occurrence of Florschuetzia levipoli. After the deposition of Barat Shale, Arang Formation was conformably deposited above it. Palynological evidence gives an Early to Middle Miocene age for this formation. The entire Arang Formation was deposited in shallow marine environment with fluctuations to coal-swamp dominated coastal plain related to basin inversion and relative sea level changes.

Above Arang Formation, Muda Formation was deposited unconformably in shallow marine environment. The Base Muda unconformity is widely recognised at West Natuna basin. The Muda Formation consists of mudstone, shales and sands. This formation is formed from Late Miocene until the present time.

Geological map by Hakim & Suryono (1994) shows that the eastern part of Natuna islands, situated on the Natuna Arch, is comprised of Mesozoic (Early – Mid Cretaceous) melange sediments (Bunguran Formation) and Late Cretaceous granites. Older igneous rocks, mafic and ultramafic rocks from Jurassic time, outcropped in several parts of the islands. In the western and northern part of Natuna islands, sediment sequence consisting of conglomerate, massive sandstones and siltstone outcropped. This sediment is interpreted as the result of fluviatil processes and interpreted to be the equivalent of Oligo-Miocene sediments of the West Natuna Basin. Granites of Late Cretaceous age can also be found in the Anambas Islands, in the Sunda Shelf to the south of the West Natuna Basin (Samodra, 1995).

The stratigraphic framework for the East Natuna Basin does not appear much in published literature, the one used in this paper is a generalised one taken from several published and unpublished work (Figure 4). The oldest sediment found in East Natuna Basin is of Late Oligocene to Early Miocene age (Pertamina & BEICIP, 1985). This sediment comprises a lower sandstone unit followed by a shale unit. The sandstone is the equivalent of Upper Gabus Formation in the West Natuna Basin. This deposit is interpreted to be of alluvial plain and delta plain origin. The shale that overlies it is the equivalent of the Barat Formation of the West Natuna Basin, and consists of greenish and grey marine shales. This sequence represents the maximum transgression of the area. These sequences cannot be seen in the Sokang Sub Basin because they were not reached by any well. The sediments overlying this Barat shale are the sandstones of Lower Arang Formation, which is formed in the regressive phase, terminating the transgression. The regressive phase was immediately followed by a transgression. Both the regressive and transgressive sandstone sequence form the Lower Arang sandstones. The transgression ended by the forming of Lower Arang shale which consists of grey and brown marine shales. In the south, the Lower Arang shale was then followed by the forming of Sokang sandstones. These formations are deposited in Early Miocene through Middle Miocene time.

In the north part, overlying conformably the Lower Arang shales is the Terumbu Formation. Pupilli (1973) divided the formation into a lower member and an upper member. The lower member is termed the platform member, and is characterised by stratified wackestone, packstone and boundstones. The upper member is termed the reef member which consists of highly fossiliferous diagenetic dolomite. The boundary between the lower member and the upper member is unconformable in certain places. This unconformity marked the end of the regression phase. The upper member of this Terumbu Formation is formed of many reefal build-ups, with marine shale and marls filling the depressions between the build-ups. During the Middle Miocene to Late Miocene forming of the Terumbu Formation in the North, in the South a transgression phase deposited the Upper Arang shale (Pertamina & BEICIP, 1985). This shale was followed by an Upper Arang sandstone. The sandstone extends also in the northern part, overlying the Terumbu Formation. The youngest formation Muda overlies unconformably all the oldest sediment, and formed as a transgressive sedimentary section.

Geological History
Natuna Area is part of the Sundaland, consequently the evolution of this area can be traced back to the forming of Sundaland. According to Hutchison (1989) Sundaland is the stable continental core of South East Asia, and it was formed and cratonised in Late Triassic time. Taylor and Hayes (1983) reconstructed that during Mid Jurassic to Mid Cretaceous in the east part of Sundaland a subduction zone was formed by Pacific plate subducting from the east. In the area west of the subduction zone a volcanism activity occurred along with granitic instrusions. The rocks formed by these activities later were metamorphosed and became the basement of the Tertiary basins in Natuna Area as proven by wells (Pupilli, 1973). The subduction activity also resulted in the forming of melange complexes, as is found in parts of Natuna Islands in the Natuna Arch (Hamilton, 1979).

During Late Cretaceous this subduction activity was still continuing and it continuously moving eastward, as postulated by Pupilli (1973) and Hamilton (1979). At this time the subduction zone occurred along a line from SW Borneo through the east of Natuna Island and up north to offshore Vietnam. This subduction still continued in the earliest Paleocene and through Eocene, as according to Taylor & Hayes (1983) the volcanism along Natuna Arch and SW Borneo continued into the earliest Paleocene, and according to White & Wing (1978) it was during Eocene that a melange facies was formed in Paus-Ranai Ridge. To the west of the subduction zone, a shelf deposit was accumulated, forming the basal formations of South Sokang Sub Basin (White and Wing, 1978). Sedimentary record shows that by Oligocene this subduction zone has stopped completely (White & Wing, 1978).

The cessation of the subduction and the forming and subsequent evolution of the West and East Natuna Basins may be explained by several theories on the relative motions of the India, Asia and the Pacific plates. Regional Tertiary tectonic framework proposed by Tapponnier et al. (1982) and by Daly et al. (1991) have been commonly used as the models to explain the tectonic evolution of South China Sea area, because they seem to fit fairly well with developed structural elements on this area. Both papers stated that the indentation of Indian plate into Asia has led into the rotation of Indochina. However, Tapponnier et al. (1982) suggested that the basin evolution of SE Asia is mainly due to major lateral extrusion of Indochina and Eastern China when India and Asia collided each other. Later in 1991 Daly et al. suggested that the major effect of this collision is just in term of clockwise rotation of Indochina and extension along the Sumatran active margin, not in the term of basin evolution of SE Asia.

Using Tapponier et al. (1982) "extrusion" model, Wongsosantiko and Wirojudo (1984) and Daines (1985) explained the structural development in the Natuna area. The south-eastward movement of the Malay Peninsula and Sunda Shelf relative to the Asia mainland resulted in rifts and pull-aparts in the Gulf of Thailand and West Natuna. In Thai and Malay basin, NW-SE orientated grabens were developed as a result of left-lateral movement associated with rifting. Meanwhile, SW-NE grabens which dominate the West Natuna basin were formed by pull-aparts in response to the separation of Sunda Shelf from Indochina (Wongsosantiko and Wirojudo, 1984). This feature, which occurred during Early Oligocene time was called by Daines (1985) as graben development phase in West Natuna basin. However, Daines (1985) suggested that the graben (especially the SW-NE orientated Boundary graben) were developed as a direct result of the collision between India and Asia, not due to a pull-apart.

Using a different approach, Daly et al. (1991) explained that the forming of the West Natuna Basin is connected to the opening of the South China Sea. The Pacific plate, subducting northward below the Eurasia continental plate, stopped the movement in Eocene. This cessation was followed by a gravitational collapse of the crust, due to the rollback of the subducting oceanic plate. The collapse was then followed by a rifting which opened the South China Sea. The change of Pacific plate movement stopped the subduction along the line from SW Borneo through east of Natuna to offshore Vietnam, and it was transformed into a strike-slip fault. Thus according to the concept of Daly et al. (1991), the rifting which formed the West Natuna Basin was caused by a right lateral stress regime, with the initial opening of South China Sea. This Early Oligocene-Mid Oligocene rifting phase in West Natuna Basin resulted in the sedimentation of the Lama Formation, Benua Formation and Lower Gabus Formations.

In East Natuna Basin when the subduction along the line from SW Borneo to offshore Vietnam became inactive during Oligocene, the previous fore-arc basin sediment deposition was followed by the deposition of shallow and deep water facies (White & Wing, 1978). However, the oldest deposits confirmed by well in this basin are the Late Oligocene sediments, which are the equivalent of Upper Gabus and Barat Formation of the West Natuna Basin and it is mostly of alluvial plain and delta plain setting (Pertamina & BEICIP, 1985). These sediments are the result of the rifting phase, which according to Wongsosantiko & Wirojudo (1984) also affected the East Natuna Basin, especially the northern part, forming the SW-NE half grabens. During Early to Middle Miocene, the South China Sea spreading continued and caused the forming of the NNW-SSE structures, following the basement weak zone patterns.

In Mid Oligocene to Early Miocene a period of tectonic quiescence, a post rifting phase, happened (Ginger et al., 1993). The deposition of this period resulted in the Keras and Upper Gabus Formations. Barat Formation which was deposited after them is interpreted to be included in both post-rift and syn-inversion megasequence (Ginger et al., 1993). The boundary between post-rift and syn-inversion megasequence is marked by an onlap surface to lower part of Barat seen on the upper part of the Barat Formation.

After the post rifting phase, a period of compressional stresses during Early Miocene to Mid Miocene caused the inversion of the grabens and the wrench faulting in the West Natuna Basin. In some inverted grabens the Miocene sediments were entirely eroded, causing the Oligocene sediment to be in direct contact with Muda Formation (Figure 5). Using the concept of Daly et al. (1991) the compressional stresses can be explained by the collision of the continental fragments which form the southern tail of South China spreading with Borneo. According to Daines (1985) the compressional stresses, which mostly form SW-NE trending anticline in West Natuna Basin, came from the north-northeastward penetration of Indian plates against Asia. The deposits formed during this inversion period is the Arang Formation.

The effect of these stresses to East Natuna basin is not too significant to form any compressional structures. According to Pertamina & BEICIP (1985) the compressional phases only caused regional uplifting in the East Natuna Basin. During Early Miocene to Late Miocene several cycles of sedimentation in the South Sokang Sub Basin resulted in the Arang Formation and the Sokang Sandstone. In the North East Natuna Basin the formations formed are the Arang and Terumbu Formations.

The period of uplift was ended by a general unconformity in the Late Miocene (Ginger et al., 1993), which formed the boundary between the syn-inversion and the post-inversion products. The formation formed during this post-inversion phase is the Muda Formation. In the East Natuna Basin the last cycle of sedimentation formed the equivalent of the Muda Formation.

Economical Value
The interest people put on Natuna Area is mainly due to its strategic location and its economical value, i.e. its hydrocarbon resources. It is here that the biggest gas field in Indonesia was found (Esso's giant "L" Field), which is unfortunately not developed yet. The value of the area is increasing lately with the advent of the West Natuna Gas Project, which is a project selling gas produced from gas fields in the West Natuna Area owned by Gulf, Premier Oil and Conoco to Singapore. Exploration history of the Natuna Area was started in 1968 when Natuna Sea Block "A" (covering the north part of Natuna Area) and Natuna Sea Block "B" (the south part) respectively were awarded to AGIP and Conoco. In 1974 Conoco succeeded to discover the Udang oil field and AGIP discovered Anoa oil field. Belanak field was then discovered by Conoco in 1975. In 1980s, Conoco discovered some more significant oil fields such as Ikan Pari (1983), Forel (1984) and Belida (1989), and also gas fields such as Bawal (1979) and Tembang (1981). Several other discoveries were made by other companies in the Kakap Block and Natuna Sea Block "A" during the period of 1980s up to 1990s. The most recent one is the Pelikan gas field, which was drilled by Premier Oil in 1999.

Reservoir rocks in the area are mainly the sandstones of Gabus and Arang, and the limestones of Terumbu Formations. Oil is usually found in Gabus and gas in Arang sandstones. The source rock for oil is mainly from the shales of Benua Formation. The gas is mainly biogenic, generated in the Arang Formation. The Keras and Barat Formation act as excellent seals over the Lower and Upper Gabus Formations respectively. In the Arang Formation, the seals are intraformational. The traps in the West Natuna Basin are mostly structural, in the form of inverted anticlines (Figure 5) and wrench-faulted structures. In the East Natuna Basin traps are mainly present in the form of stratigraphic traps such as reefal buildups (Figure 6) or structural traps such as drapes over basement high.

Anoa, Belida and Kakap Fields are the three most prolific oil producer in the West Natuna Basin. The extraordinary thing about the oil produced from these fields is its high quality, which can reach 46-49API, fetching good prices in the market.

Acknowledgement
We would like to thank Pertamina BPPKA and Premier Oil for the permission to use data and publish this paper, and IPA for the permission in using references. Our gratefulness also extends to our colleagues in Premier Oil for their support in the form of encouragement and discussions and to Mr. Wartono Rahardjo and the librarians of Geology Dept. Gadjah Mada University for their willingness to help us in researching.

title: The Geology of Indonesia/Natuna


text:
The Geology of Indonesia/Kalimantan

The island of Kalimantan presently lies upon the southeastern margin of the greater Eurasian plate. It is bounded to the north by the South China Sea marginal oceanic basin, to the east by the Philippine Mobile Belt and the Philippine Sea Plate and to the south by the Banda and Sunda arc systems (Figure 1). It is bounded to the west by the Sunda Shelf and ultimately by Paleozoic and Mesozoic continental crust of the Malay Peninsula. The Greater Kalimantan Block is surrounded to the north, east, and south by plate boundaries and arc systems which are presently active or which have been active during the Tertiary and it is bounded to the west by an underexplored shelf region which possibly conceals a terrane boundary (Fuller & Richter, ?).

Kalimantan can be divided into several roughly E-W trending tectonic provinces (Figure 5.1). The northern portion of the island is dominated by the Cretaceous and Eocene to Miocene Crocker-Rajang-Embaluh accretionary complex. This consists primarily of turbidites which were being shed northeastward (present day coordinates) off of the Schwaner and younger volcanic arcs into a paralic to deep marine trench basin. These sediments were imbricated, deformed, and weakly metamorphosed during Creraceous and Tertiary subduction and finally were intruded by late stage and post subduction intrusions of the Oligo- Miocene Sintang Group.

The Melawi-Ketungau basins and the Kutei basin (Figure 5.1) formed along the southern margin of this complex during the Late Eocene and are separated from it by the Lupar- Lubok Antu and Boyan melange-ophiolitic zones. Scattered exposures of Cretaceous marine sediments adjacent to these basins likely record the Cretaceous fore-arc basin to the Schwaner arc. The Kutei basin developed primarily along an arm of the Makassar rift system while the Melawi-Ketungau basins and the Upper Kutei basins occupy more of a fore-arc to intra-arc position to Tertiary volcanism. Tarakan and Sandakan basins are Tertiary basins developed in the northeast part of Kalimantan. Similar to Kutai basin, these basins are sourced by deltaic system from the Kalimantan mainland. The Barito basin formed at the same time but appears to have formed as a back-arc or continental rift. Pieters et al (1987) have correlated an Eocene basal sandstone/conglomerate and Eocene volcanics throughout all of these basins and it appears that a continuous system of Eocene rifts Formed along the margins of the uplifting and eroding Schwaner Batholith. These developed into separate basins during the Oligocene and Miocene and sedimentation has continued throughout most of the Neogene. The Schwaner Barholith itself is a triangular exposure of Cretaceous granitic rocks which intrude Paleozoic and Mesozoic volcanics, volcaniclastics, and marine sediments. The only region of Kalimantan in which this Paleozoic and Mesozoic section is well preserved is in Northwest Kalimantan and Western Sarawak (the Northwest Kalimantan domain of Williams et al (1988)) although it presumably formed the continental crustal host for Schwaner plutonism. The eastern margin of the Barito Basin is formed by the Meratus ophiolite. This was emplaced during the Middle Cretaceous (Sikumbang, 1986), presumably during northwestward directed subduction (present day coordinates). Arc volcanism in SE Kalimantan then jumped outboard to the Sulawesi arc system. The Meratus ophiolite separates the Barito basin from Asem-asem basin in the southeastern portion of Kalimantan. Asem-asem basin is a Tertiary basin which converted eastward gradually to Paternoster carbonate platform.

For practical convenience and presentation, the tectonic features of Kalimantan are divided into two part: Tertiary Basins and Pre to Early Tertiary Highs.

5.1. TERTIARY BASINS
5.1.1. BARITO BASIN

The Barito Basin is situated along the southeastern margin of the Schwaner Shield in South Kalimantan (Fig. 8). The basin is defined by the Meratus Mountains to the east and separated from the Kutei Basin to the north by a flexure related to the Adang Fault. The basin has a narrow opening to the south towards the Java Sea. The Barito Basin is an asymmetric basin, forming a foredeep in the eastern part and a platform approaching the Schwaner Block towards the west (Fig. 9 and Fig. 14).

The Barito Basin commenced its development in the Late Cretaceous, following a micro-continental collision between the Paternoster and SW Borneo microcontinents (Metcalfe, 1996; Satyana, 1996). Early Tertiary extensional deformation occurred as a tectonic consequence of that oblique convergence. This produced a series of NW – SE trending rifts. These rifts became accommodation space for alluvial fan and lacustrine sediments of the Lower Tanjung Formation, derived from horst areas. In the earliest Middle Eocene, as the result of a marine transgression, the rift sediments becoming more fluviodeltaic and eventually marine, as transgression proceeded during the deposition of the Middle Tanjung Formation. The marine transgression subsequently submerged the rifts in late Eocene – earliest Oligocene time, resulting in the deposition of widespread marine shales of the Upper Tanjung Formation. After a short-lived marine regression in the Middle Oligocene the development of a sag basin caused renewed marine transgression. The Late Oligocene is characterized by the deposition of platform carbonates of the Berai Formation (Figs. 6 and 7). Carbonate deposition continued into the Early Miocene, when it was terminated by increasing clastic input from the west. During the Miocene the sea regressed, due to the uplift of the Schwaner Core and the Meratus Mountains. Clastic input resulted in the deposition of the eastwards-prograding deltaic sediments of the Warukin Formation. In the late Miocene the Meratus Mountains re-emerged, followed by the isostatic subsidence of the basin which was situated in a foreland position in relation to the rising mountains. Sediments shed from this uplift were deposited in the subsiding basin, resulting. in the deposition of thousands of meters of the Warukin Formation. The uplift of the Meratus Mountains continued into the Pleistocene and resulted in the deposition of the molassic-deltaic sediments of the Pliocene Dahor Formation. This struc- tural and depositional regime still exists today. The structural development of the Barito Basin is a consequence of two distinctly separate, regimes (Fig. 6). First, an initial transtensional regime, during which sinistral shear resulted in the formation of a series of NW – SE trending wrench-related rifts, and second, a transpressional regime involving convergent uplift, which reactivated and inverted old tensile structures and resulted in wrenching, faulting and folding. The kinematics and type of Barito tectonic inversion have been discussed by Satyana and Silitonga (1994). Presently, the structural grain of the basin is charac- terized by the concentration of structures in the NNE part of the basin, typified by tight, parallel SSW – NNE trending folds, bounded towards the Meratus Mountains by high-angle easterly-dipping imbricate reverse faults, which involve the basement (Figs. 5 and 9). The presence of major wrench faults is indicated by drag or fault-bend folds and reverse fault traces. The unique concentration of structures in the NE part of the basin was interpreted by Satyana (1994) as the tec- tonic consequence of half-encirclement of the area by the two pre-Tertiary massifs: the northern Meratus Range and the North Meratus Massifs (Fig. 8). The western and southern parts of the Barito Basin was mildly tectonized and show almost no deformation structures. Thin-skinned tectonic manifestations, rep- resented by decollement and ramp anticlines are only vaguely identifiable in this portion of the basin (Satyana and Silitonga, 1993). Along the northern Central Warukin and East Tapian Fields (Fig. 3). All of the fields occur in faulted anticlines dipping to the east. The Tanjung and Kambitin Fields are associated with basement-involved structures. The Warukin and East Tapian Fields occurred in structures developed by thin-skinned tectonics within the Warukin Formation (Fig. 9). Hydrocarbons are reservoired in the Lower and Middle Tanjung Sands (Middle Eocene) and in the Lower and Middle Warukin sands (Middle Miocene) (Figs. 7, 14 and 15). Pre-Tertiary basement rocks and the Berai carbonates (late Oligocene – early Miocene), where they are fractured, have also proved to be good reservoirs, and may trap hydrocarbons if they are well positioned. The hydrocarbons were generated in, and migrated from, Lower and Middle Tanjung coals and carbonaceous shales, and Lower Warukin carbon- acerous shales. The main kitchen is located in the pre- sent basin depocentre. The sealing rocks are mainly provided by the intra-formational shales. Generation, migration and entrapment of hydrocarbons has taken place since the middle Early Miocene (20 Ma). The Barito Basin provides the best example of the effects of tectonic interaction on hydrocarbon habitat (Fig. 9). In this basin, tectonics controlled each com- ponent of the hydrocarbon habitat (petroleum system). Extensional tectonics in the Early Tertiary formed a rifted basin within which the lacustrine Tanjung shales and coals were deposited in graben areas. This lacus- trine environment was responsible for the deposition of the Tanjung source rocks. As subsidence continued and the rifted structures were submerged, widespread shales were deposited, which became an important seal for the underlying reservoir rocks. This condition was also responsible for the deposition of the widely-dis- tributed Middle Tanjung reservoir rocks. Extensional faults became conduits for the migration of hydrocar- bons generated in the deeper graben areas. The role of tectonics in hydrocarbon accumulation in the basin during Neogene and Pleistocene time is indisputable. The implications of basin reversal in the development of the petroleum system in the Barito Basin is discussed in Satyana and Silitonga (1994). During the Late Miocene the basin was inverted, in as- sociation with the Meratus Uplift, to produce an asymmetric basin; the Barito Basin, dipping gently in the NW, towards the Barito Platform, and steeply in the SE against the Meratus Uplift. Consequently the central part of the basin subsided rapidly, due to iso- stasy, causing the Tanjung source rocks to be deeply buried, so that they attained the depth at which hydro- carbons were generated. Restored modelling for the Barito tectonics and pet- roleum generation (Satyana and Silitonga, 1994; Satyana, 1995; Satyana and Idris, 1996) has shown that inversion of the basin resulted from compressional tectonism (Fig. 9). Graben-fill sequences were actively inverted and asymmetric anticlines were generated along the reverse faults. Hydrocarbons generated from the basin depocentre were expelled to fill these struc- tural traps. Structures such as the Tanjung Field were thus favorably positioned for the entrapment of early migrating hydrocarbons. Uplift of the Meratus Mountains was continuous during the Late Miocene, through the Pliocene, and peaked in the Plio – Pleistocene. Tanjung source rocks in the depocentre were already mature by the Late Miocene. Proto- inverted structural traps formed in the early Miocene time were continuously inverted as basin compression developed, resulting in strongly positive features. Hydrocarbons filled these traps through the faults and along permeable sands. It is considered that in the early Pliocene the Tanjung source rocks in this area had exhausted their liquid hydrocarbon generating capability. At this stage gas was generated and migrated to fill the existing traps. Plio – Pleistocene tectonism caused the whole Barito Basin to be strongly inverted (Fig. 9). This tectonic event caused both the formation of new traps and the destruction of existing traps. Entrapped hydrocarbons probably remigrated to the newly-formed structures as old traps were tilted or breached by the Plio – Pleistocene inversion. At this stage the Tanjung source rocks had ceased to generate oil and gas in the depo- centre, since the section was firmly within the dry gas window. The Lower Warukin Shales in the basin depo- centre reached the depth of the oil window in the peak episode of tectonism during Plio – Pleistocene times. Oil was generated and migrated to accumulate in struc- tural traps within the Warukin sands. The Warukin and East Tapian Fields were charged in this period. The foregoing discussion depicts how critical tec- tonics are to the deposition of reservoir and source rocks, the maturation of source rocks, the formation of structural traps and oil field distribution. However, tectonics may also destroy pre-existing traps.

5.1.2. KUTEI BASIN

The Kutei Basin is the largest (165,000 km ) and the deepest (12,000 – 14,000 meters) Tertiary sedimentary basin in Indonesia. The basin is bounded to the north by the Mangkalihat High; to the south the basin hinges on the Adang – Flexure (Adang-Paternoster Fault); to the west it is terminated by the Kuching High – part of the Kalimantan Central Ranges; and to the east the opens into the Strait of Makassar (Fig. 10). The Tertiary stratigraphic succession within the basin commenced with the deposition of Paleocene alluvial sediments of the Kiham Haloq Formation in the inner basin, close to the western border (Figs. 6, 7 and 14). The basin subsided during the late Paleocene – Middle Eocene to Oligocene, due to basement rifting, and became the site of deposition of the Mangkupa Shale in a marginal to open marine environment. Some coarser siliciclastics, the Beriun Sands, are locally associated with the shale sequence, indicating

an interruption of basin subsidence by uplift. The basin subsided rapidly after the deposition of the Beriun Sands, mostly through the mechanism of basin sagging, resulting in the deposition of marine shales of the Atan Formation and carbonates of the Kedango Formation (Satyana and Biantoro, 1996). Subsequent tectonic events uplifted parts of the basin margin by the late Oligocene (Figs. 6 and 7). This uplift was associated with the deposition of the Sembulu Volcanics in the eastern part of the basin. The second stratigraphic phase was contemporaneous with basin uplift and inversion, which started in Early Miocene time. During that time, a vast series of allu- vial and deltaic deposits were deposited in the basin. They comprise deltaic sediments of the Pamaluan, Pulubalang, Balikpapan and Kampung Baru for- mations, prograding eastwards, which range in age from the Early Miocene to Pleistocene times. Deltaic deposition continues to the present day, and extends eastwards into offshore Kutei Basin. At present, the structural style of the Kutei Basin is dominated by a series of tight NNE – SSW trending folds (and subsidiary faults) that parallel the arcuate coastal line, and are known as the Samarinda Anticlinorium – Mahakam Foldbelt (Figs. 5, 10 and 11). These fold belts are characterized by tight, asymmetric anticlines, separ- ated by broad synclines, containing Miocene siliciclas- tics. These features dominate the eastern part of the basin and are also identifiable offshore. The defor- mation is increasingly more complex in the onshore direction. The western basin area has been uplifted, A minimum of 1500 m to over 3500 m of sediments have been removed by a mechanism of inversion (Wain and Berod, 1989; Courteney and Wiman, 1991). Not much is known about the structure of the western basin area and, although large structures are evident, a similarity in structural trend and style is not apparent from the available data (Ott, 1987). In this region, the tectonics may involve the basement (thick-skinned tectonics). Tectonic reversal, in terms of origin and its strain re- sponse, is not as obvious as in the Barito Basin. Prograding deltaic sediments may have contributed to the mechanism of structural inversion, by a mechanism of diapirism or growth-faulting, these mechanisms are very different from those which affected the Barito Basin. The origin of folds and faults in the Kutei Basin remains unresolved and concepts as diverse as vertical diapirism, gravitational gliding ( Rose and Hartono, 1978; Ott, 1987), inversion through regional wrenching (Biantoro et al., 1992), micro-continental collision, detachment folding above overpressured sediments (Chambers and Daley, 1995), differential loading on deltaic sediments and an inverted delta growth fault system (Ferguson and McClay, 1997) have been invoked.

5.1.3. TARAKAN BASIN

The Tarakan Basin encompasses the basinal areas in NE Kalimantan (Fig. 12). Workers in this area usually subdivide the NE Kalimantan basinal areas into four sub-basins: the Tidung Subbasin, the Berau Sub- basin, the Tarakan Sub-basin, and the Muara Sub- basin. The Tarakan Basin of this paper includes all four sub-basins. The boundaries between the sub- basins are not always eA’ective borders, some are only hinges or fault zones. The Tarakan Basin is separated from the Kutei Basin by the Mangkalihat High or Arch (Fig. 12). To the west the basin is terminated by the Sekatak – Berau High of the Central Ranges, the basin hinges on the Semporna High to the north, and opens eastwards and southeastwards into the Straits of Makassar.

Deposition in the Tarakan Basin commenced in the Middle Eocene, simultaneously with the rifting of the Makassar Straits which separates Sulawesi from Kalimantan (Lentini and Darman, 1996) (Figs. 6 and 7). The basin subsided and opened to the east. The sea transgressed westwards and shallow marine shales of the Sembakung Formation were deposited, overlying the older Dannu basement rocks. The. transgression was interrupted by the latest Eocene uplift which resulted in the deposition of coarse clastics of Sujau Formation. During Oligocene times a carbonate plat- form (Seilor Formation) developed and continued into the Early Miocene as the Mangkabua Shales and the. reefal Tabalar Limestone. In the middle Miocene, the western basin margins were uplifted and caused open marine conditions to give way to widespread and rapid clastic deltaic deposition, which successively prograded eastwards with time. Periodic and cyclic regression – transgression during the middle Miocene to Pleistocene time caused sedimentary switching, leaving marine shales and limestones intercalated with coarse clastic deltaic sediments (The Naintupo shales, Meliat – Tabul – Santul – Tarakan – Sajau – Bunyu deltaics and the Domaring – Waru carbonates). The present structural grain of the basin is charac- terized by folds trending NW – SE and by the faults trending NE – SW (Figs. 5 and 13). Structural defor- mation becomes increasingly complex northwards. The regular NE – SW trending faults, which are normal to the direction of sedimentary thickening, suggests that they were developed contemporaneously with depo- sition, and may be the direct result of sediment loading of successive deltaic sediments. All structures in the lower basin formed as the result of thin-skinned tec- tonics (Fig. 14). Involvement of the basement charac- terizes the structures of the upper basin, approaching the Sekatak – Berau High. Tectonic inversion is almost absent in this basin. The tectonic history of the Tarakan Basin com- menced with extensional tectonics in the Middle Eocene, initiating the basin by block faulting, simi- lar to events in the neighbouring basins. In the Middle Miocene, the Sulu Sea, located to the north of the basin, was subducted below the accreted con- tinental crust of North Kalimantan, and this resulted in the extrusion of Neogene volcanics in the Semporna Peninsula and was responsible for the formation of NW – SE trending, SE plunging folds in the Tarakan Basin. These fold axes are now rep- resented by the islands of Sebatik, Bunyu and Tarakan. The folds become increasingly more com- plex towards the north as they approach the con- vergent margin. Some workers (Lentini and Darman, 1996; Biantoro et al., 1996) relate the for- mation of these folds to wrench tectonics in the basin itself. The thick progradation of a deltaic suc- cession during Middle Miocene to Pleistocene time resulted in growth-faulting with rollover structures, aligned perpendicular to the sedimentary flow and subsiding towards the east.

5.1.4. SANDAKAN BASIN

The Sandakan Basin, located in the southern portion of the Sulu Sea, with Tertiary deltaic complex in the south of the basin. It is analogous in many ways to the hydrocarbon-producing Baram and Mahakam deltas, which like the Sandakan, are adjacent to Kalimantan (Figure 1). This affinity with Borneo distinguishes the Sandakan Basin from all other sedimentary basins of the Philippines.

The Sandakan Basin is filled mainly with Mio- Pliocene age fluvio-deltaic sedimentary rocks, up to 15 km thick (Figure 2). The stratigraphic section in the basin has been described by Tamesis (1990). The basin is bounded on the northwest by the Cagayan Ridge and extends southwestward into central and southeastern Sabah. The inactive Sulu Trench and the Sulu Archipelago form the eastern boundary of the basin. To the northeast, sediments are deformed by toe-of-slope compressional folds. Northeast of these folds, the sedimentary succession thins to 2.5 km and downlaps onto the Southeast Sulu Sea oceanic crust, marking the northeastern boundary of the basin (Graves & Swauger, 1997).

The tectonic history of this basin is not agreed upon. Back-arc and intra-arc classifications have been assigned to the Southeast Sulu Sea. In either case, the sea-floor spreading may have been associated with southeast-directed subduction of a proposed proto- South China Sea oceanic crust, under a northeastern extension of the Borneo microcontinent (the Cagayan Ridge), during Middle Miocene time (Hinz, et al., 1991). Further discussion of the basin development is made by Hutchison (1992) and Rangin et al. (1990).

5.1.5. SARAWAK BASIN

The continental shelf offshore East Malaysia belongs to an extensive shallow-water area that connects Borneo with the Asian mainland (Fig. 2). Only the northern part of Borneo is separated from continental Asia by deep water areas of the South China Sea. Along central Sarawak the shelf is extremely broad, generally exceeding 300 km from shelf edge to coast. It becomes narrow toward northern Sabah, where it locally is less than 100 km wide.

Most of the shelf is underlain by a thick upper Tertiary sequence. Magnetic data, locally supported by seismic data, suggest the greatest sedimentary thicknesses are in central and northern Sarawak, close to the present coast (Figs. 3, 4). In Sa- bah, a zone of maximum thicknesses appears to occur 60 km offshore. The main source of these sediments was the orogenic belt that runs along the southern border of Sarawak northward into Sabah. These mountains, that were mainly uplifted in the Eocene, now form the landward boundary of the thick upper Tertiary basin.

In Sarawak, thick upper Tertiary sediments reach tar beyond the shelf edge, covering large deepwater areas (Sarawak basin. Fig. 2). Farther north, in western Sabah, a deep relatively narrow trough (Sabah trough) with mostly undisturbed, horizontal sediments of probably Pliocene age, separates the thick upper Tertiary sequence beneath the shelf from the much thinner Tertiary sequence which underlies the deep water farther offshore (Fig. 3, 4: sections 1, 2). A similarly deep, but shorter graben is found 250 km farther to the west-northwest (Fig. 2). The abyssal plain of the China basin lies 350 km to the northwest of the Sabah trough, at a water depth of 4,000 m, and is underlain by oceanic basement with only a thin veneer of sediments. In this area, crustal extension led to the formation of oceanic basement, probably in middle Tertiary time, whereas in the south rifting never went beyond the initial graben formation. Thick upper Tertiary sediments also underlie part of the shelf in eastern Sabah, extending landward across Dent Peninsula. However, in the deep waters to the northeast, oceanic basement appears to be at shallow depth beneath the Sulu Sea (Fig. 2).

In most areas seismic basement offshore corresponds to indurated Paleogene sediments. Based on projections from onshore western Sarawak and offshore well data from Peninsular Malaysia and Indonesia, basement is expected to consist of Mesozoic metamorphic and granitic rocks, and possibly at least partly of upper Paleozoic rocks similar to those exposed in Vietnam, Peninsular Malaysia, and western Sarawak. Mesozoic metamorphic rocks have been described from surface outcrops in eastern Sabah (Leong, 1974).

While shelf conditions prevailed in western Sarawak, a deep trough developed in central Sarawak during Cretaceous- Paleogene time, extending northward over parts of Kalimantan and western Sabah. Several thousand meters of deepwater shales and turbidites accumulated in this trough, the axis of which appears to have been located 100 to 200 km inland from today’s coast. Paleocene shallow-water limestones found in the subsurface of southwest Luconia indicate the presence of carbonate shoals along the western flank of the Paleogene deepwater trough. The main orogenic belt of the Northwest Kalimantan basin was strongly folded and uplifted during Eocene time, thus becoming an important source for the younger Tertiary sediments.

Mid-Tertiary rifting in the China basin is thought to have exerted extensional stresses that led to the formation of a half graben and graben system in which mostly continental sediments were deposited (Figs. 2-5). At the same time a deep trough developed in front of the Eocene fold belt in Sabah and northern Sarawak. It rapidly filled with a thick shale and turbidite sequence (West Crocker and Temburong formations; Liechti et al, 1960), but carbonate shoals and reef buildups developed along the southwestern flank of the trough (Melinau Lime- stone; Liechti et al, 1960). In central Sarawak a shallower environment prevailed with a mainly argillaceous facies deposited (Kelabit formation, Setap shale, Penian marl; Liechti et al, 1960; partly Miri Zone, Hale, 1973). Deep-marine, predominantly shaly sequences also were de- posited in eastern Sabah, where they contain radiolarites and spilites. These have been interpreted as trench melanges indicative of a late Oligocene-early Miocene northwest to southeast oriented subduction zone (Hamilton, 1976; Beddoes, 1976). Although no blueschist metamorphism has been observed, this zone with its highly contorted shales and the frequent radiolarites and ophiolithes shows more indications of subduction than the southwest to northwest oriented trend of the main North- west Borneo geosyncline, which lacks typical trench melanges. Structurally. Sabah is the most complex area in northwestern Borneo, because of its megatectonic position between the is- land arc system of the western Pacific and the Asian mainland.

During the early Miocene the sea transgressed westward. Deeper marine deposits reached the present northern Sarawak shelf and a shallower marine wedge extended far into Indonesian waters (Fig. 5). Locally carbonate shoals and buildups fringed the basin (e.g. Subis Limestone, Melinau Limestone, Liechti et al 1960). Extensive coastal plain continental deposits formed along the basin margin, with a particularly thick development in the present area off central/western Sarawak. Northwest to southeast oriented horst and graben tectonics affected the area, but large parts of the area off western Sarawak have subsequently become fairly stable, elevated, and extensively eroded. During the middle Miocene strong subsidence began off central Sarawak along a fault system of a general north- northwest to south-southwest orientation. The middle Miocene sea spread into the depressions that formed on either side of a relatively stable, elevated central area, where extensive carbonate buildups began to form (Central Luconia). At the same time gradually outbuilding deltas came into existence in western and northern Sarawak and in northern Sabah (Fig. 5). During the late Miocene, much of the present area off central and southern Sabah underwent strong folding, initiated through basement uplifts and wrench faulting. Large parts of northern Sarawak, both onto and offshore, were also affected by this tectonic phase, though deformation generally has been weaker. Synsedimentary deformation took place in the thick sedimentary sequences that filled the deep depressions on either side of the Central Luconia carbonate platform. Deltaic outbuilding continued in western and central Sarawak and new deltas developed in southern and eastern Sabah (Fig. 5). During the Pliocene, the sea rapidly expanded over the northward tilting shelf, depositing open-marine clays and sands (Fig. 5). On the shelf slope, thrust folds developed far offshore. Synsedimentary deformation continued in the deltaic areas, while another folding phase, probably again triggered by trough basement uplifts and wrench faulting, affected large parts of nearshore northern Sarawak and particularly northern Sabah (Figs. 3, 4).

5.1.6. MELAWI AND KETUNGAU BASIN

The melange and accretionary rocks east of the Northwest Kalimantan domain are unconformably overlain by three sedimentary sequences; the Silat sequence, Melawi Basin sequence and Ketungau/Mandai Basin sequences. The earliest of these is the Silat sequence, which comprises a fluviatile sandstone up to 600m thick overlain by up to 2000m of lacustrine black shale. The sequence thins rapidly to the west and is not present to the west of the Kapuas River (Fig. 2). It is folded into a tight, east plunging syncline, and limbs are in places overturned. The Silat sequence overlies the southern accretionary deposits and is unconformably overlain by rocks of the Melawi Basin. The area of outcrop of the sequence was referred to by Zeybnans van Emmichoven (1939) and Williams et al., (1984) as the Silat Fold Belt. The Silat sequence was folded before the deposition of the Melawi Basin sequence. The nature of the folding suggests the presence of thrust faults at depth (Williams et al., 1984). The Melawi Basin contains up to 5 km of fluviatile, lagoonal and marginal marine sediments. Volcanic detritus is not abundant but van Es (1918) and Williams and Heryanto (1986) recognised many horizons containing air-fall fragments and silicified glass shards indicating distant contemporaneous volcanism. The source for this detritus is probably from the volcanism which produced the Early Tertiary volcanics in the Schwaner Mountains. The Melawi Group unconformably overlies either the Cretaceous shelf sediments or the Silat sequence in the north and onlaps the granitic and metamorphic basement to the south. Age diagnostic fossils are rare in the Melawi Group but a Turonian foraminiferal assemblage has been recovered from near the base (Williams and Heryanto, 1986). It is an asymmetrical basin, with the maximum sediment accumulation closer to the northern margin. The rocks are folded into a gentle syncline, with maximum limb dips of 30. Folds are also asymmetric, the northern limb more steeply dipping than the southern limb. The Ketungau Basin sequence is separated from the Melawi Basin by accretionary rocks and the Boyan Melange. It is also an east- west trending basin and as is the Mandai Basin to the east. The Tertiary sediments in the Mandai Basin are porbably correlates of the Ketungau Basin sequence. The stratigraphy of the basin fill is shown in Fig. 6 (Column 5) and the total sediment thickness in the Ketungau Basin is estimated to be at least 5 km. The lower formation is very similar to the Melawi Group which prompted Zeylmans van Emmichoven (1939) to correlate the two. However fossils from the lowest exposed rocks of the Ketungau Basin are Eocene (Tan, 1979) and it is unlikely that a thick section exists below the fossil horizon (Williams and Heryanto, 1986). In addition the thick (approx. 2000 m) fluviatile sandstone in the middle of the Ketungau sequence (Fig. 6) has no equivalent in the Melawi Basin. Consequently the Ketungau Basin is considered younger than the Melawi Basin. The Ketungau Basins is faulted against the Lubok Antu Melange to the north, and in places onlaps the Boyan Melange to the south. In other places the southern boundary of the Basin is faulted. Like the Melawi Basin, the Ketungau Basin is asymmetrical, units in the south being substantially thinner than their equivalents to the north. It is also folded into a gentle east-trending symmetrical syncline with limb dips generally 250 The Mandai basin sediments onlap Turonian flysch north of the Boyan Melange.

5.2. PRE-EARLY TERTIARY HIGHS
5.2.1. NW KALIMANTAN DOMAIN

The oldest fossiliferous rocks of the North- west Kalimantan domain are Late Carboniferous limestone and marble containing diagnostic fusulinids. These crop out in small areas of both Kalimantan (Zeylmans van Emmichoven, 1939) and Sarawak (Sanderson, 1966). In Kalimantan the limestone and marble flank a unit comprising schist, phyllite and quartzite with garnet grade greenschist facies assemblages (Fig. 2). Small areas of similar schist are present in Sarawak (Pimm, 1965). In Kalimantan the metamorphic rocks are intruded by biotite granite which yields K-Ar ages from Permian to Late Triassic (Table 3, Group 1). Many of the granitic rocks contain a strorig foliation, and the Lhte Triassic ages are obtained from biotites from deformed rock The Permian dates come from hornblende crystals from undeformed regions of the granites or from amphibolite en-claves. The older ages are interpreted as minimum intrusive ages and the Middle to Late Triassic ages as the deformation age of the suite (Fig. 6, col. 1).

Late Triassic shallow marine shales containing Monotis and Halobia were deposited on the Northwest Kalimantan domain, and these prob- ably post-date the main Late Triassic deformation event recorded in the granitic rocks. The shales are not in contact with the schist and granitic rocks, but Tan (1986) indicates that similar rocks in Sarawak contain detritus from the older calcareous rocks and granite, implying an unconformable relationship. Basic and intermediate volcanic rocks are also present which may correlate with the Late Triassic volcanics of Sarawak (Wilford and Kho, 1965; Kirk, 1968; Hon, 1978). Early Jurassic ammonites and bivalves have been identified from several localities west of the metamorphic part of the domain (Wing Easton, 1904). The fossils occur in shallow marine shales, calcareous and nodular siltstone, and feldspathic conglomerate intercalated with biohermal limestone, oolitic and intra-clastic limestone. These appear to form a conform- able sequence with the Late Triassic strata. In the far west spilite appears to overlie the Late Triassic to Early Jurassic sedimentary sequences, which are only middly deformed. Regions of older slate are also present in this area which are affected by the Middle to Late Triassic deformation event. In Sarawak, the sedimentary record from the Late Jurassic to the Late Cretaceous is fairly complete (Tan, 1986). Late Jurassic near-shore detritus and shallow marine limestone form a marginal facies to the north-trending trough containing dominantly Cretaceous sandy turbidites and calcareous mudstone (Fig. 2). Tan (1986) argues that a hiatus exists between the Late Jurassic - Cretaceous strata and the Late Triassic rocks. This is supported by a structural divergence between the two units in Kalimantan. In Kalimantan Late Jur- assic ammonites have also been recovered (Sato, written communication) from localities adjacent to the metamorphic rocks and the north-trending trough, which contains dominantly Cretaceous sandy and calcareous flysch deposits. The trough is 40 km wide in Kalimantan, bounded on the west by Late Triassic sequences and on the east by the metamorphic rocks. The trough sequence is gently to strongly folded; north-dipping thrust faults and folds with a north-dipping axial surface are evident in many road cuttings. These formed prior to the Senomanian, because the rocks are unconformably overlain by undeformed fluvial sandstone of that age (Muller, 1968; Tan, 1983). In the far northwest (area 2 on Fig.l, Fig.6, co1.2) chert, gabbro and ultramafic rocks form isolated outcrops in Kalimantan which occur within a sequence of deformed turbidites and pebbly mud- stone. These have also been mapped in Sarawak (Wolfenden, 1963) where they are Jurassic. The rocks of this area may belong to a Jurassic melange (Hamilton, 1979), but they do not form an east- west trending belt as suggested by hirn or trend to the south across the Northwest Kalimantan do- main (Sengor, 1984, 1986). The relationship between the Northwest Kalimantan domain and the Schwaner Mountains is obscured by the extent of Early Cretaceous batholiths. No equivalent sedimentary sequences are present in the Schwaner Mountains, and no granites equivalent to the deformed Permian granites have been found despite an intensive dating programme. Probably Triassic basic volcanics in the southwest (de Keyser and Rustandi, in press) may be equivalent to the Late Triassic volcanics in Sarawak and low-grade schists in the Schwaner Mountains and the Northwest Kalimantan domain could be equivalent.

5.2.2. SCHWANER MOUNTAINS

Batholiths of tonalite and granodiorite with minor mafic rocks and granite intruding low-grade regional metamorphic rocks underline most of the Schwaner Mountains region (Fig. 5.1). Basic volcanic rocks both older than and younger than the granitoids are also present (de Keyser and Rustandi, in press). The granitoids form a belt 200 km. wide and at least 500 km long. Chemical analyses of typical rocks from the Schwaner Mountains (Table 1) indicates the I-type calc-alkaline nature of the suite. The most mafic rock analysed is a norite, and the most acid rocks are syeno-granite is a gap in composition from 67% Si02 to 72% Si02 which suggests at least two batholiths are present. In the southwest, a third batholith composed dominantly of granite with subordinate riebeckite-bearing alkaline granite and syenite (de Keyser and Rustandi, in press; Table 2), has distinctive geochemical characteristics com- pared to the extensive tonalite and syenogranite suites (Fig. 4).

Age determination on biotite and hornblende from the hornblende from the granitoids has been carried out by Haile et al. (1977) and several new determinations have been made during the recent mapping program. Haile et al. obtained ages ranging from Jurassic (157 Ma) to Late Cretaceous (77 Ma). The current project obtained ages on 33 specimens and ages range from 129 Ma to 87 Ma, falling into four main groups (Table 3). Early Cretaceous ages were obtained from tonalite and granodiorite bodies (Group 2) and the middle to Late Cretaceous ages (Group 3) were obtained from the granite batholith in the southwest. The range of ages from 100 Ma to 120 Ma in the tonalite and syenogranite suite may indicate twomain magmatic episodes over that period, the second corresponding to the intrusion of the more siliceous batholith. Ages obtained on basic-intermediate volcanics in the area indicate Early Tertiary volcanism tookplace in the Schwaner Mountains.

5.2.3. MERATUS MOUNTAINS

The Meratus Mountains or Meratus Range is a Cretaceous subduction complex, located in southeast Kalimantan (Fig. 5.1). This mountain separate Barito Basin in the west from the Asem-asem Basin which lies to the east. The directions of main folding are NNE – SSW (in the northern part) and NE – SW (in the southern part).

Three major units are exposed in the southern part: The Peridotitic Nappe, overthrust (together with its metamorphic thrust sole) on the Alino formation (Koolhoven, 1935). Both units are unconformably overlain by the Manunggul Formation. All these Cretaceous units are then overlain by younger marine and continental deposits. The Peridotitic Nappe is made up mostly of serpentinites. gabbros and plagiogranites. The metamorphic thrust sole of the Peridotitic Nappe is composed of crystalline schists and amphibolites, and is intruded by several gabbroic an basaltic plugs.

The Alino Formation is made up mainly: of volcanic and volcaniclastic rock series: lava flows. dykes. volcanic breccias. greywackes and tuffs. The volcanogenic rocks are interbedded with predominantly sedimentary layer, radiolaria-bearing tuffaceous clays and turbidite. Orbitolina and radiolaria-bearing limestones. ammonite-bearing argillaceous limestones and finally cong1omerates containing pebbles and blocks of the former rocks toward the upper part of the sequence. The corresponding faunistic ages range from Upper Aptian to Cenomanian (Priyomarsono, 1985). The Manunggul Formation is also made up mostly vo1canogenic rocks, but it was deposited after the over thrusting of the Peridotitic nappe: thus it has the geological character of a molasse deposit. Volcanic sediments (tuffs and greywackes) are interbedded with conglomerates, sandstones, tuffaceous c1ays, and Upper Turonian clays near the bottom of the formation. Senonian conglomerates and clay beds occur near the top of this this sedimentary sequence, transitional to the lower units of Eocene detrital Tanjung Formation. The Manunggul formation, as well as the underlying Periodititc Nappe, are intruded both by basaltic and andesitic dyekes and by a number of gabbroic, dioritic, microdioritic and granitic plugs.

5.2.4. RAJANG-EBALUH GROUP FOLD-THRUST BELT

This great flysch belt is the eastwards continuation of the Sibu Zone Belaga Formation of Sarawak (Kirk 1957), which swings north and north-north- east along the eastern margin of the Miri Zone continental margin, to reach its best known localities in the Crocker Range near Mount Kinabalu. In the south it has been mapped as the Late Cretaceous to Eocene Lurah and Mentarang formations (BRGM 1982). These continue northwards into Sabah as the West Crocker and Sapulut formations, respectively (Collenette 1965).

The Rajang – Embaluh Group ranges in age from Late Cretaceous (Santonian) to Early Eocene. Embaluh Group strata contain upper Santonian/lower Campanian nannofossils (Moss & Finch 1998). Middle Eocene larger foraminifera are reported from outcrops of turbidites in east Kalimantan. Ter Bruggen (1935) described Palaeocene to Middle Eocene benthic foraminifera from the headwaters of the Embaluh River in Kalimantan. Picters et al. (1993) suggest a Late Cretaceous to mid-Eocene age for these rocks on the basis of regional correlation, and all available data confirm a Late Cretaceous (Santonian) to Valaeocene/Early Eocene age for the bulk of the sediments. In Sarawak the Rajang Group youngs northward from the Upper Cretaceous Lupar Formation and Layer Member of the Belaga Formation to the Middle Eocene members of the Belaga Formation (Hutchison 1996). The Embaluh Group is unlikely to extend into the Middle Eocene, at least within the study area, because felsic agglomerates, flat-lying lava flows and vent-related intrusions unconformably overlie or intrude the Embaluh Group along the course of the upper Mahakam river. Both the volcanics and lava flows are part of the Nyaan Volcanics suite radiometrically dated using the K – Ar technique at 48.6+ 0.5 Ma (Pieters et al. 1993) and correlative with other felsic intrusives across Borneo in the middle Eocene (Moss et a1. 1997). Middle Eocene rocks of the Kutai Basin also unconformably overlie the Embaluh Group in the study area (Moss & Finch 1998).

In West Sabah, this belt consists of Eocene to Oligocene turbidites, hemipelagics, and associated broken formations (Crocker, Temburong, Trusmadi and other formations) that have been deformed into a thrusted, steeply-dipping sequence. The sequence becomes younger in a seaward direction (northwestward) but bedding tops face southeastward, indicating that the structure must be intricately imbricate (Hamilton, 1979). On seismic (Fig. 5b) the Fold-Thrust Belt can be seen to extend in the offshore area at least up to the Bunbury-St. Joseph Ridge (that is, beneath the Inboard Belt), where it is sharply bounded to the west by a major wrench zone. The uplifted, exposed part of the Fold-Thrust Belt provided the main source of sediments for the Inboard Belt and subsequently for the Baram Delta and Outboard Belt depocentres (Hazerbroek & Tan, 1992).

title: The Geology of Indonesia/Kalimantan