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.

POST-COLLISIONAL TECTONIC ESCAPES IN INDONESIA : FASHIONING THE CENOZOIC HISTORY

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

POST-COLLISIONAL TECTONIC ESCAPES IN INDONESIA : FASHIONING THE CENOZOIC HISTORY

Awang Harun Satyana^1
1BPMIGAS
ABSTRACT

Post-collisional tectonic escape refers to the lateral escape or extrusion of fault-bounded geological blocks as a result of collision or compression away from the collision zone and towards free edge of oceanic margin. While the collision zone is represented by fold-thrust belts, the tectonic escape is accommodated by large strike-slip faults and rifting and spreading of basement.

There are five significant collisional events fashioning the Cenozoic tectonics of Indonesia. The first was collision of India to Eurasia started at 50 or 45 Ma (early-middle Eocene). The collision resulted in the Himalayan Fold-Thrust Belt and was followed by the escape of the Sundaland southeastwards through major strike-slip faults and the formation of sedimentary basins in the Sundaland as well as the opening of marginal seas of the South China Sea and Andaman Sea. The faults occupied and reactivated Mesozoic sutures within the Sundaland. The faults are Red River Fault-Sabah Shear, Tonle-Sap-Mekong (Mae Ping) Fault, Three Pagoda Fault-Malay-Natuna-Lupar Line-Adang Fault, and the Sumatran Faults.

The second collision occurred at about 25 Ma (late Oligocene) when an oceanic island arcs constructed on the southern margin of the Philippine Sea Plate collided with the northern margin of Australia Continent. The collision resulted in fold-thrust belt of the Papua Central Ranges and was followed by tectonic escapes of strike-slip faults and basin formation. The faults are Sorong-Yapen Fault, Waipoga Fault, Gauttier Offset, and Apauwar-Nawa Fault. Opening of the North Irian Basin in northern Papua also shows the post-collision tectonic escapes.

The third collision was the collision of the Bird’s Head microcontinent with Papua at 10 Ma (late Miocene). The Lengguru Fold-Thrust Belt marks the collision zone. Strike-slip faults away from the collision zone like the Tarera-Aiduna, Sorong, Waipoga, and Ransiki Faults may demonstrate the post- collision tectonic escape. The Bintuni Basin located just to the west of the Lengguru Fold-Thrust Belt is a foreland basin developing as a response to post-collision extensional structure.

The fourth collision occurred from 11 to 5 Ma (late Miocene to earliest Pliocene) when the Buton-Tukang Besi and the Banggai-Sula microcontinents collided East Sulawesi ophiolite. The microcontinents were detached from the Bird’s Head of Papua and escaped westwards by the Sorong Fault. The collision has formed Batui Fold-Thrust Belt and was followed by post-collision tectonic escapes in forms of rotation of arms of Sulawesi, formation of major strike-slip faults of Palu-Koro, Kolaka, Lawanopo, Hamilton, Matano, and Balantak Faults, and the opening of the Gulf of Bone. More recent transtensional movement is responsible for the opening of pull-apart basins of Poso, Matano and Towuti Lakes, as well as the Palu Depression.

The last collision commenced at about 3 Ma (mid-Pliocene) when northern margin of Australia Continent collided Banda Island Arc. The collision resulted in foreland fold-thrust belt from Timor, Tanimbar to Seram. Lateral extension is observed to follow the arc-continent collision indicating a tectonic escape. Major strike-slip faults were formed sub-paralleling the Timor Island and may relate to the escape of the Sumba Island westwards. Extensional crustal collapse followed the arc-continent collision and has resulted in the formation of the Weber Deep, Savu Basin, and opening of the Banda Sea. The cases in Indonesia show that tectonic escape is a widespread process and may have been very important in the evolution of convergent region like Indonesia. The concept of tectonic escape can contribute to the understanding of the process by which continents are assembled and slivered

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

APPLICATION OF INTERFEROMETRIC SYNTHETIC APERTURE RADAR (IFSAR)
DATA FOR GEOLOGICAL MAPPING

Ipranto¹, Tony Said²

¹Pusat Penelitian dan Pengembangan Geologi (P3G), Jl.Diponegoro No.57 – Bandung Indonesia
ipranto@yahoo.com
²PT. ExsaMap Asia, Plaza 89 Jl.HR Rasuna Said No.6 Jakarta Indonesia
tsaid@exsamap.com

ABSTRACT

Geology mapping process requires three dimension accurate data. In most cases of high mountain and steep hill terrain, none optical remote sensing technique can provide stereo images. The advantage of radar in cloud penetration should be the only alternative of data source for geology mapping. High resolution Interferometric Airborne Synthetic Aperture Radar (IFSAR) produces image with appearance close to panchromatic optical image. Merge data IFSAR with color optical satellite data give more beneficial in interpretation some geological features. Geology mapping method is visual interpretation of radar image called ORI – Orthorectified Radar Image that display in three dimension and superimpose with contour line and color optical satellite image. Digital processing equipment is workstation computer with socet set system, desktop computer with ER Mapper and Mapinfo.

Radar acquire the data in side look model has advantage in expose image for geological features such as drainage pattern, rivers, shaded relief which indicate geology structure and lithology. Contour line as one important part of geology map can generate from DSM (Digital Surface Model) IFSAR. Contour line pattern show terrain model and give significant support in interpretation. Type III of IFSAR Data is adequate to generate geology map up to scale 1:25.000.

The purpose of this paper presents some new geology features have been found from IFSAR data compare with the original geology data in scale 1:250.000. The research was using IFSAR Data merge with Landsat TM. Research area is Makasar – South Sulawesi Province that covers in Bakosurtanal Map tile #2011. The new features have been found still need validation ground survey in the future.

Keywords: IFSAR, DSM, ORI, mapping.

A GIS APPROACH ON PROSPECT EVALUATION AND MINERAL TARGETING IN BATU HIJAU AREA OF INTEREST

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

A GIS APPROACH ON PROSPECT EVALUATION AND MINERAL TARGETING IN
BATU HIJAU AREA OF INTEREST

Dibiansyah Hamid & Elang Soeriaatmadja
PT Newmont Nusa Tenggara, Batu Hijau Mine, West Sumbawa, NTB
ABSTRACT

Series of intensive and extensive exploration works, in various phases, have been carried out within the PT Newmont Nusa Tenggara Contract of Work since the early CoW application in 1986. These include the data set that has led to the discovery of the world class Batu Hijau porphyry copper-gold mine in May 1990, with ore reserve of 1,197 metric tonnes grading 0.43% copper and 0.33 g/t gold. The exploration data consisted of packages of geological, geochemical and geophysical data set which were taken in various exploration stages from early regional reconnaissance, prospect definition to deposit delineation stages. Prior to the construction of copper and gold mine in Batu Hijau in 1997, the exploration work in the area surrounding, Batu Hijau Areas of Interest (AoI) had also been intensely carried out but with a different goal namely to search ‘additional reserves’ within the current mine project.

Following digital map data conversion into GIS Map-Info format of all exploration mapping data, a fully GIS-based digitally processed area rating has been applied to rank the prospect in term of main target ‘porphyry Cu-Au’ type of deposit and based on basic concept exposed ‘classical porphyry’ analogue to Batu Hijau mine. The method is mainly based on the compilation of all geological, geochemical and geophysical datasets which were converted into eight ‘digital’ ‘exploration aspects’ as rating criteria.

Weighting as the most important process in the rating were defined for each polygon clusters within each layers based on the basic concept and target that already been set up. The layer of polygon, representing each aspect, then will be overlaid each other, and the total weight of the combined polygons will be digitally calculated using map-info based GIS operation.

The rating has produced final prospectivity image for porphyry copper and gold target that showing the rank of exploration target based on the total weight and it is confirmed to be still referred and analogue to Batu Hijau mine in where the highest total weight and rank outline is located. It also successfully drives the area of Naga Emas, Arung Ara and West Nangka in northwest of Batu Hijau as the high priority targets. The high total weight has also occurred at Katala Prospect, east of Batu Hijau, eventhough the area is closed to Batu Hijau mine facility – Katala east dam.

This area rating method is conclusively highly applicable in ranking and defining priority target in areas or block that data collection has been performed in a similar proportion. Best practices can be applied to do the same process in rating the similar area using a different basic concept and/or target. In this case, weighting will be the critical aspect to produce accurate rate and rank.

DIAMOND CORE SAMPLING ERROR AND IMPLICATION TO RESERVE

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

DIAMOND CORE SAMPLING ERROR AND IMPLICATION TO RESERVE

Kusuma, Nusa^'
'Dept. Geology, PT Newmont Nusa Tengara

ABSTRACT

Sampling is one of significant factor to determine an economic of a deposit. Batu Hijau is one of largest porphyry disseminated and vein control copper gold deposit. Sampling performed during exploration to development periods contribute a bias. The bias occurred due to the nature of deposit, drilling and sampling technique.

The significant economic mineral occurred as dissemination, vein control or along the fracture as fracture filling. The usage of excessive water during drilling washed the economic mineral. Manual carelessly sampling results the economic minerals is not sampled. Those factors results the bias in resource and reserve estimation.

An improvement of sampling and drilling technique is developed based on grade bias study. The new technique prove to reduce the bias significantly.

Mineralogical type, lithological characteristics combine by recorded geotechnical parameters is investigated to quantify the bias. The developed bias adjustment formula is a function of lithology, grade and RQD.

Validation of developed bias adjustment through production shows the bias adjustment is valid to be implemented for resource and reserve estimation. The grade bias adjustment factor implemented to the block model estimation increase metal content which worth to one year production.