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PROCEEDING, SEMINAR NASIONAL KEBUMIAN KE-8

Academia-Industry Linkage

15-16 OKTOBER 2015; GRHA SABHA PRAMANA

111

SEDIMENTOLOGICAL SIGNIFICANTS OF DEEP-WATER SEDIMENTS OF

PENOSOGAN FORMATION IN KEBUMEN AREA, CENTRAL JAVA

Vicky Widianto1*

, Ari Wibowo2

1Universitas Pembangunan Nasional “Veteran” Yogyakarta2

HRH Geology

*corresponding author: [email protected]

ABSTRACT Deep-water sediments are commonly associated with turbidity current, results variety of physical sedimentary features. They are currently a major focus of both academic research and industrial

interest related to petroleum play. Several reservoirs in Indonesia’s basin belonged to deep-water products. Comprehensive geological study with good basic sedimentology knowledge is needed tounderstand more about deep-water sediments related to reservoir opportunities. Penosogan Formation, a part of South Serayu Basin, is one of good outcrop data which can be used as a guide todistribute analogue in subsurface geophysical data.

This paper objective is to understand better the heterogenetic deep-water sediments facies by usingoutcrops approach, then the conceptual of reservoir characteristic could be identified. The data werecollected in the Penusupan area, Kebumen – Central Java. The primary methods used in this studywere stratigraphic measuring section and field geological mapping. Laboratory analyses were alsoadded to support the study.

Based on integration of paleontology, petrography, and facies interpretation, Penosogan Formation in study area demonstrate turbidity current products which are divided into three lithofacies association,

namely: very coarse grained facies, coarse grained facies and fine grained facies. These associationrepresent prograding features from outer fan into middle fan. The outer fan facies is characterized by

interbedded very fine – fine grained sandstone with shale (approximately 25 meters), sand-shale

estimation + 40 % net to gross ratio, porosity ( Φ) up to 8,4 %, and permeability up to 129,38 mD.The middle fan is characterized by interbedded medium – coarse grained sandstone and thin layered

shale with pebble to boulder conglomerate (approximately 46 meters), sand-shale estimation + 85 %net to gross ratio, porosity ( Φ) up to 9,5 %, and permeability up to 146,55 mD.

I. INTRODUCTION

Central Java is one of the places of interest in

the search for hydrocarbons at this time.

Which make interesting due to the discovery

of hydrocarbon seepages under thick volcanic

deposits in North Serayu Basin (Satyana,2007).

Formation that become reservoir in that

petroleum system is part of Rambatan and

Halang formation. Rambatan and Halang

formation deposited with turbidite flows

mechanism in deep water submarine fan

sediment (Kertanegara, et al, 1987). In this

case because of the similarity of

environmental development between those

formation and Penosogan formation,

therefore this research main object is to studythe potential reservoir characteristics of

Penosogan formation if there is a petroleum

system exist in South Serayu Basin. Research

taken place in Penusupan area, Kebumen,

Central Java.

Deep-water environment have a different of

sedimentary system compared to other

environment which build a unique of sedimentdeposition and result. Comprehensive

geological study is needed to understand more

about it.

The main objective of this study is to identify

the EOD (environment of deposition) of

Penosogan formation which characterized

turbidite features and its potential for

analogue reservoir. Penosogan Formation is

one of good outcrop data which can be used

as a guide to distribute analogue in subsurface

geophysical data.



II. STRATIGRAPHY REGIONAL OF

SOUTH SERAYU BASIN

Stratigraphic order in South Serayu basin has

the Late Cretaceous – Paleogene Luk-Ulo

Melange Complex. The mélange in Luk-Ulo

consist of ophiolites assemblage in oceanic

plate that have been thrusted onto the edge

of continental plates (Asikin,1974). It covers by

boulder of ultramafic plutonic igneous rock,

pillow lava, chert, red limestone and schist

that all include in wacke matrix. Its overlain

unconformable by Karangsambung, Totogan,

Waturanda and Penosogan formation.

Karangsambung formation formed by

olistostrome deposits composed with scally

greywacke or claystone with concretion of

nummulites limestone, conglomerate and

quartz arenite in Eosen. Entering the

Oligocene, Totogan formation have the similar

characteristic of Karangsambung formation

but top of Totogan formation become a

submarine gravitional process that consist of

gravely claystone with turbidite deposit.

In Early Miocene – Middle Miocene proceed

the Totogan turbidite conditions is Waturanda

formation with more volcanic matter like

volcanic breccia include in this formation

because of the subduction zone of Oligo-

Miocene that created active volcanism

mountain range in Java specially in South

Serayu Mountain (Hall,2012). In Middle

Miocene, South Serayu volcanism began to

decreased in intensity, it marked slowly shift

from Waturanda volcanic breccia to claystone

– sandstone with marls and limestone of

Penosogan formation in turbidite flows still

occur in it and created the deep water

submarine fan. The Late Miocene is

characterized by the development of a double

volcanic arc in Central Java, with the

ractivation of South Serayu volcanism at the

same time, and the onset of North Serayu

volcanism. Generally the volcanic sandstone of

the Halang Formation dominated the

deposition at this period (Asikin,1992).

The Pleistocene in South Serayu still occur the

event of active volcanism with some land

volcanic in North Serayu began to more intens.

Its triggered the isostatic uplift in South Serayu

Zone as the final stage of deformation. In thisphase Peniron Formation form. It consist of

tuff and volcanic breccia with spar in

submarine fan turbidite or channel in

terrestrial deposit when in middle of South

Serayu uplift (Figure 1).

III. RESEARCH METHOD

The data were collected in the Penusupan

area, Kebumen – Central Java. The study was

conducted by field observation andstratigraphy measuring section as primary

methods. Then, it was continued by post field

works such as :

A. Facies identifying (lithofacies & Facies

Association)

B. Laboratory analysis (paleontology,

petrography, and core analysis))

All data is combined to determine the

environment of deposition and its related tovariety of sediment features.

IV. DATA AND ANALYSIS

Based on paleontology data, Reophax

nodulosus, Nodosaria albatrossi, Rheopax

dentaliniformis, and Hippocrepina indivisa

were observed. These presence confirm the

study area was belonged to lower bathial –

abyssal bathimetric zone (2000-4000 m bsl)

(Figure 2).

Petrography analysis of sandstone describes a

characteristic; brown yellowish, grain size

ranged from 0.25 - 1 mm, sorting is relatively

poor, subangular, supported by matrix,

composed of plagioclase, piroxen, opaque

mineral, lithic, calcit, and lime mud.

Less visible porosity could be observed. It is

classified as Calcareous sandstone (Williams,

1954)(Figure 3).

Stratigraphy measuring section produce a

stratigraphical assemblage completely. There






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are several lithofacies which are grouped into

three lithofacies association, namely: very

coarse grained facies, coarse grained facies

and fine grained facies. These association are

used to build the environment of depositionmodel (Table 1).

Environment of Deposition (EOD)

The outer fan

It is characterized by interbedded

calcareous very fine – fine grained

sandstone with marl on approximately 25

meters thickness. Several lithofacies can be

observed which classified on uncomplete

Bouma Sequence (Ta-Tc). Interbedded of

normal graded bedding sandstone with

erosional contact (Ta), Parallel lamination

sandstone (Tb), and Convolute sandstone

(Tc). Reservoir quality of the outer fan is

indicated by several parameter, namely;

estimation of sand-shale ratio is + 40 % net

to gross ratio, porosity (Φ) up to 8,4 %, and

permeability (K) up to 129,38 mD.

The middle fanIt is characterized by interbedded medium

– coarse grained sandstone and thin

layered shale with pebble to boulder

conglomerate on approximately 46 meters

thickness. Bouma sequence also found at

the bottom and at the youngest part on

sandy facies. Stacking pattern show

coarsening upward sequence which

indicated by presence of very coarse grain

facies association. Sand-shale ratio is +

85 % net to gross ratio, porosity (Φ) up to

9,5 %, and permeability up to 146,55 mD.

Sediment stacking pattern represent

prograding features from outer fan into

middle fan. It was triggered by decreasing sea

level base. All integration data are used to

create environment of deposition model

(Figure 6).

V. CONCLUSIONS

We realize that the outcrop has limit in length

and height. Despite that, subsurface data stillmust be validated toward the surface

condition. Penosogan Formation is good

outcrop data that has a various sedimentary

features can be used as a guide to subsurface

data. Reservoir quality of deep-water deposite

indicate low to moderate. Sand facies has a

immature texture but has a thick sand.

Secondary porosity on calcareous muddy

facies and fractures could be considered as a

good potential opportunity.

VI. ACKNOWLEDGEMENT

Authors would like to acknowledge to

Geological Engineering Department UPN

“veteran” Yogyakarta for the support and our

thank to Anselmus arya for conducting the

core analysis.

REFERENCESAsikin, S.,et al. 1974, Peta Geologi Lembar Kebumen, Pusat Penelitian dan Pengembangan Geologi.

Mutti, E., 1992. Turbidite sandstones. Instituto de Geologia, Universita de Farma.

Shanmugam G.2005. Deep-Water Processes and Facies Models: Implications for Sandstone

Petroleum Reservoirs. Department of Earth and Environmental sciences The University of Texas at

Arlington U.S.A.

Tucker, M.E., 2003, Sedimentary Rock In the Field 3rd edition, John Willey & Son, New York, 16.

Walker, R.W. & James, N.P., (1992), Facies Models: Response to Sea Level Change. Geological

Association of Canada, Ontario, h. 239 – 250



TABLESTable 1. Lithofacies identified as result of measuring section.

Fm Massive mudstone Silt - clay

Massive, grey to brown mudstone. 15 –

30 cm average thickness for gray

mudstone or brown mudstone.Someplace association with vfSs.

FSc Convolute fine sandstone Medium - fine sandConvolute, grey to brown sandstone 10-20cm average thickness.

MSsPlanar Stratified medium

sandstoneCoarse - medium sand

Planar stratified beds, gray sandstone with

30 – 50 cm average thickness.

VcSgsGraded bedding very coarsesandstone

Very coarse sandGraded bedding, brown sandstone, 10 – 30 cm average thickness.

PSo Scour pebbly sandstone Pebble –

medium sandScour, brown sandstone with pebblyfragmen, 3 m average thickness.

csfSmMassive calcareous finesandstone

Fine sand

Massive, sandstone that contains

calcareous matter with 1 m averagethickness. Without sedimentary structure

vfSsPlanar stratified very fineSandstone

Very fine sand

Planar stratified beds, brown sandstone

with 10 – 20 cm average thickness.Someplace association with Fm.

mSo Scour medium Sandstone Medium sandScour, grey sandstone with 2-3 m averagethickness. Beds erodes top surface of

other beds.

fSm Massive fine sandstone Fine sandMassive, grey sandstone with 30

– 70 cm

average thickness without sedimentarystructure

mSwWavy lamination medium

sandstoneMedium sand

Fine layers with wave pattern , greysandstone with 20 – 30 cm average

thickness.

Gm Massive conglomerate GravelMassive, grey to black conglomerate with3 – 5 m average thickness withoutsedimentary structure

vfSl Slump very fine sandstone Very fine sandBeds, bright grey sandstone with 50 cmaverage thickness with slump structure

bending the beds.






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FIGURES

Figure 1. Stratigraphy of South Serayu Basin (Asikin, 1987). Penosogan Fm. are shown by red box.

Figure 2. Paleontology analysis result show the presence various foraminifera.



Figure 3. Photograph of calcareous sandstone under optical microscop.






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Figure 4. Sedimentological log of southern part of study area



Figure 5. Sedimentological log of northern part of study area.






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Figure 6. Environment of Deposition Model of Penosogan Fm. at Penusupan area.

geo26 sedimentological significants of deep-water sediments of penosogan formation in kebumen area,...

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