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SEDIMENTOLOGICAL SIGNIFICANTS OF DEEP-WATER SEDIMENTS OF PENOSOGAN FORMATION IN KEBUMEN AREA, CENTRAL JAVA
Vicky Widianto1*, Ari Wibowo2 1Universitas Pembangunan Nasional “Veteran” Yogyakarta
2 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 to
understand 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 to
distribute analogue in subsurface geophysical data.
This paper objective is to understand better the heterogenetic deep-water sediments facies by using
outcrops approach, then the conceptual of reservoir characteristic could be identified. The data were
collected in the Penusupan area, Kebumen – Central Java. The primary methods used in this study
were stratigraphic measuring section and field geological mapping. Laboratory analyses were also
added 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 association
represent 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 study
the 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 sediment
deposition 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 this
phase 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 and
stratigraphy 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 to
variety 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 deposition
model (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 fan
It 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 still
must 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.
REFERENCES Asikin, 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
TABLES Table 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 sand Convolute, grey to brown sandstone 10-20
cm average thickness.
MSs Planar Stratified medium
sandstone Coarse - medium sand
Planar stratified beds, gray sandstone with
30 – 50 cm average thickness.
VcSgs Graded bedding very coarse
sandstone Very coarse sand
Graded bedding, brown sandstone, 10 –
30 cm average thickness.
PSo Scour pebbly sandstone Pebble – medium sand Scour, brown sandstone with pebbly
fragmen, 3 m average thickness.
csfSm Massive calcareous fine
sandstone Fine sand
Massive, sandstone that contains
calcareous matter with 1 m average
thickness. Without sedimentary structure
vfSs Planar stratified very fine
Sandstone Very fine sand
Planar stratified beds, brown sandstone
with 10 – 20 cm average thickness.
Someplace association with Fm.
mSo Scour medium Sandstone Medium sand
Scour, grey sandstone with 2-3 m average
thickness. Beds erodes top surface of
other beds.
fSm Massive fine sandstone Fine sand
Massive, grey sandstone with 30 – 70 cm
average thickness without sedimentary
structure
mSw Wavy lamination medium
sandstone Medium sand
Fine layers with wave pattern , grey
sandstone with 20 – 30 cm average
thickness.
Gm Massive conglomerate Gravel
Massive, grey to black conglomerate with
3 – 5 m average thickness without
sedimentary structure
vfSl Slump very fine sandstone Very fine sand
Beds, bright grey sandstone with 50 cm
average 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.