Introduction stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering (stratification). Stratigraphy, from Latin stratum + Greek graphia, is the description of all rock bodies forming the Earth's crust and their organization into distinctive, useful, mappable units based on their inherent properties or attributes in order to establish their distribution and relationship in space and their succession in time, and to interpret geologic history. Stratum (plural=strata) is layer of rock characterized by particular lithologic properties and attributes that distinguish it from adjacent layers.

History of stratigraphy begin by Avicenna (Ibn Sina) with studied rock layer and wrote The Book of Healing in 1027. He was the first to outline the law of superposition of strata:^[1] "It is also possible that the sea may have happened to flow little by little over the land consisting of both plain and mountain, and then have ebbed away from it. ... It is possible that each time the land was exposed by the ebbing of the sea a layer was left, since we see that some mountains appear to have been piled up layer by layer, and it is therefore likely that the clay from which they were formed was itself at one time arranged in layers. One layer was formed first, then at a different period, a further was formed and piled, upon the first, and so on. Over each layer there spread a substance of differenti material, which formed a partition between it and the next layer; but when petrification took place something occurred to the partition which caused it to break up and disintegrate from between the layers (possibly referring to unconformity). ... As to the beginning of the sea, its clay is either sedimentary or primeval, the latter not being sedimentary. It is probable that the sedimantary clay was formed by the disintegration of the strata of mountains. Such is the formation of mountains."

The theoretical basis for the subject was established by Nicholas Steno who re-introduced the law of superposition and introduced the principle of original horizontality and principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment.

The first practical large scale application of stratigraphy was by William Smith in the 1790s and early 1800s. Smith, known as the Father of English Geology, created the first geologic map of England, and first recognized the significance of strata or rock layering, and the importance of fossil markers for correlating strata. Another influential application of stratigraphy in the early 1800s was a study by Georges Cuvier and Alexandre Brongniart of the geology of the region around Paris.

In the stratigraphy you can find term of

- Stratigraphic classification. The systematic organization of the Earth's rock bodies, as they are found in their original relationships, into units based on any of the properties or attributes that may be useful in stratigraphic work.

- Stratigraphic unit. A body of rock established as a distinct entity in the classification of the Earth's rocks, based on any of the properties or attributes or combinations thereof that rocks possess. Stratigraphic units based on one property will not necessarily coincide with those based on another.

- Stratigraphic terminology. The total of unit-terms used in stratigraphic classification.It may be either formal or informal.

- Stratigraphic nomenclature. The system of proper names given to specific stratigraphic units.

- Zone.Minor body of rock in many different categories of stratigraphic classification. The type of zone indicated is made clear by a prefix, e.g., lithozone, biozone, chronozone.

- Horizon. An interface indicative of a particular position in a stratigraphic sequence. The type of horizon is indicated by a prefix, e.g., lithohorizon, biohorizon, chronohorizon.

- Correlation. A demonstration of correspondence in character and/or stratigraphic position. The type of correlation is indicated by a prefix, e.g., lithocorrelation, biocorrelation, chronocorrelation.

- Geochronology. The science of dating and determining the time sequence of the events in the history of the Earth.

- Geochronologic unit. A subdivision of geologic time.

- Geochronometry. A branch of geochronology that deals with the quantitative (numerical)measurement of geologic time. The abbreviations ka for thousand (103), Ma for million (106), and Ga for billion (milliard of thousand million, 109) years are used.

- Facies. The term "facies" originally meant the lateral change in lithologic aspect of a stratigraphic unit. Its meaning has been broadened to express a wide range of geologic concepts: environment of deposition, lithologic composition, geographic, climatic or tectonic association, etc.

- Caution against preempting general terms for special meanings. The preempting of general terms for special restricted meanings has been a source of much confusion.

GUMAI SHALES OF JABUNG AREA: POTENTIAL SOURCE ROCKS IN JAMBI SUB-BASIN AND THEIR CONTRIBUTIONS TO THE NEW PETROLEUM SYSTEM

PROCEEDINGS PIT IAGI RIAU 2006
The 35^th IAGI Annual Convention and Exhibition
Pekanbaru – Riau, 21-22 November 2006

GUMAI SHALES OF JABUNG AREA: POTENTIAL SOURCE ROCKS IN JAMBI
SUB-BASIN AND THEIR CONTRIBUTIONS TO THE NEW PETROLEUM SYSTEM

Lambok P. Marpaung¹, I Nyoman Suta¹, Awang H. Satyana²

¹PetroChina International Jabung Ltd.
²BPMIGAS

ABSTRACT

Jabung area has been proven as prolific hydrocarbon producer. It is well known that oils and gas have been sourced from terrestrial to fluvio-deltaic shales and coals of Talang Akar Formation. In addition to this, based on geochemical and geologic data, shales of Gumai Formation display characteristics and capability of both potential and generating source rocks.

Source potential of Gumai shales is indicated by TOC value of 0.79-8.00 %, potential yield of 0.3-24.83 mg HC/g TOC and T-max of 426-445 ^oC. Kerogen type II and III predominate the Gumai source shales. Biomarker parameters show that the shales were deposited in anoxic to suboxic environment, indicating a good preservation of organic materials. Geologic setting determines that the Gumai shales were deposited in more marine setting than those of the Lower Talang Akar. However, inputs from higher land plants still influence the source facies. Available maturation data and modeling from well located in the kitchen area reveals that the Gumai source section is within immature to early mature window. Hence, the Gumai source from the existing data analysis is basically the potential source rocks.

However, some oils in Jabung area show close correlation to the Gumai shales, showing that the shales have been generating oils. Knowledge of Gumai as both potential and generating source rocks will create new petroleum systems of Gumai shales-Gumai sands (.) or Gumai shales-Air Benakat sands (.). These systems will make migration routes from source to reservoirs to be much simpler. The new petroleum systems will significantly influence the future exploration strategy in the Jabung area.

SEDIMENTOLOGY OF MALLAWA CLASTICS AND ITS IMPLICATION TO HYDROCARBON OCCURRENCES IN WESTERN PART OF WEST ARM SULAWESI

PROCEEDINGS PIT IAGI RIAU 2006
The 35^th IAGI Annual Convention and Exhibition
Pekanbaru – Riau, 21 – 22 November 2006

SEDIMENTOLOGY OF MALLAWA CLASTICS AND ITS IMPLICATION TO HYDROCARBON OCCURRENCES
IN WESTERN PART OF WEST ARM SULAWESI

Johnson Achmad Paju¹ ,Yudi Satria Purnama¹ ,Bayu Nugroho¹ ,Andang Bachtiar² , & Fatma Peera³

¹GDA Consultant
²Exploration Think Tank Indonesia
³Geology Postgraduate Program, ITB

ABSTRACT

A Paleogene clastic sediment package of Mallawa Formation has been recognized by several previous researcher in southern part of West Arm of Sulawesi. It’s unconformably overlying Flysch deposit of Balangbaru and Marada Formation and overlied by Tonasa Limestone and a thick volcanic sequence series of Camba Formation. Mallawa Formation also interfingering with volcanic sequence of Langi Formation to the east. The Mallawa distribution has N – S trend with covered area 4448 km² and from the regional cross section the thickness can reach 400 m. Several previous study and paper has indicated a Paleogene Basin which covered where Mallawa Formation deposited.

To figure out some opportunities of Mallawa Formation, several fieldworks has been done by author especially with Mallawa Sediment outcrops which have objectives to arrange a better tectonic setting and sedimentary response processes understanding of southern part of West Arm Sulawesi especially about sedimentology, stratigraphic correlation, lateral distribution and also hydrocarbon potential of Eo­Oligocene deposit of Mallawa Formation.

Sedimentology observation in 5 Mallawa outcrops (Watangmallawa, Gattareng, Padanglampe, Doi-doi and Siloro) result a widespread depositional environment. Mallawa location type outcrops in Watangmallawa consist of medium – fine sandstone, mudstone and coal interbedded with up to 40 m vertical thickness. The Location Type of Mallawa Formation in Watangmallawa unconformably overlied by Tonasa Limestone. The marine influx dominated such as shoreface bar complex also observed in three other location Padanglampe, Doi-doi and Gattareng with various lateral dimension. Meanwhile, observation in Siloro outcrop dominated by tidal – meandering/floodplain – braided sequences.

Hypothetically, Mallawa Formation has a complete petroleum system components. The type II and III of source rock can be provided by intraformational Mallawa shale and coal and reservoirs by its fluvio­deltaic clean sandstone facies, mean while the seal developed by younger tight limestone facies of Tonasa Formation.

It believed that Eo-Oligocene fluvio-deltaic Lower Toraja sediment which situated to the north of West Arm of Sulawesi is equivalent with Mallawa Formation to the south. To predict the hydrocarbon potential, some of geochemical parameter like Maturity and Hydrocarbon Index that adopted from Lower Toraja could be applied to Mallawa and build-up some model and probable reserves estimation.

An integration research should be establish to get further information about the potential yield of Mallawa source rock and maturation model, reservoirs quality and distribution, and also the multiple volcanics event which can affected the reservoirs quality and the geophysical subsurface data.

REAPPRAISAL OF KEROGEN TYPING ON LOW RANK COAL FROM SOUTH SUMATRA BASIN, INDONESIA

PROCEEDINGS PIT IAGI RIAU 2006
The 35^th IAGI Annual Convention and Exhibition
Pekanbaru – Riau, 21 – 22 November 2006

REAPPRAISAL OF KEROGEN TYPING ON LOW RANK COAL FROM SOUTH SUMATRA BASIN, INDONESIA

Hendra Amijaya

Department of Geological Engineering, Gadjah Mada University
Jalan Grafika 2, Yogyakarta 55281, Indonesia, Tel./Fax: +62-274-513668
Email: hamijaya@ugm.ac.id

ABSTRACT

The low rank coals from Tanjung Enim Area, South Sumatra Basin, Indonesia have a mean random huminite reflectance between 0.35-0.46% and are dominated by huminite (34.6-94.6%). Less abundant are liptinite (4.0-61.4%) and inertinite (0.2-44%) Minerals are found only in small amounts (max. 2.6%); mostly as iron sulfide. Rock Eval pyrolysis shows that the coals indicate lowest Hydrogen Index (HI) values of 171 mg HC/g TOC. Sample with high liptinite content even indicates HI values of 507 mg HC/g TOC. The Oxygen Index (OI) values are considered low (<25 mg CO2/g TOC). The mean value of Tmax is 420 °C. As depicted in HI – OI diagram, the samples are located at the conjugation line of the coalification paths of kerogen type I and II. Rock Eval analysis result shows that low rank coals from South Sumatra Basin do not generally respond as expected, where humic coal is considered as type III kerogen. However, from organic petrographic point of view, the kerogen type of the studied coals is mainly type III. In the sense of kerogen typing, coal should not be treated in the same way as dispersed organic matter.

Keywords: low rank coal, kerogen type, Rock Eval pyrolysis, organic petrography, South Sumatra Basin, Indonesia.

FACIES DETERMINATION OF Mg-BREARING CARBONATES, A CASE STUDY FROM GUNUNG BODAS, CIAMPEA, BOGOR

PROCEEDINGS PIT IAGI RIAU 2006
The 35^th IAGI Annual Convention and Exhibition
Pekanbaru – Riau, 21 – 22 November 2006

FACIES DETERMINATION OF Mg-BREARING CARBONATES, A CASE STUDY FROM GUNUNG BODAS, CIAMPEA, BOGOR

Adam D. Zeiza¹ , Heri Tanjung¹ , Krishna P. Laya^1
1Department of Geology, Padjadjaran University
ABSTRACT

The observed area is the limestone member of Bojongmanik Formation and it is occurred as lenses within the Bojongmanik Formation which is Middle Miocene in age. It is interesting that limestone from this area has been used extensively in steel industry. Further more it is discovered from the chemical analysis of MgO content.

From the field observation of this limestone hill, the eastern side of the hill is concluded as a reef build up and comprised of a more rigid body of carbonate rather than the western side. The eastern reef build up is considered to be developed in high energy environment and this is assumed to be related with the enriching distribution of MgO from western to eastern side of the carbonate body. The bedding trend with orientation N 265^o E/65^o that occured adjacent to the western side of the first mentioned reef build up give us explanation that the sediment is dumped at the confluence of the opposing sets of waves refracted around the reef front to form less rigid and finer grain carbonate sediment, which in this case is the carbonate on the western side that derived from the the eastern side.

All the statements above are strenghtened by the observation of carbonate body from the eastern part of the area which shows texture of reefal carbonate and finer grain size to the west. In conclusion, the reef build up on the eastern side developed at the seaward and high energy environment and eroded to form another carbonate sediment on the western side.

This study suggest that from the field observation combine with geochemical analysis, Gunung Bodas hill contain sufficient Mg-bearing carbonate which is assumed to be usefull in steel industry as steel fluxing agent for example. By this study, it is expected that the area with sufficient Mg content such as on the western side of Gunung Bodas Hill could be recognized as an eligible source of limestone to be used in steel industry.