Gsc2011 Paper Gprg

8/3/2019 Gsc2011 Paper Gprg

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Name Isnianto Saputra and Rian Cahya RohmanaSchool/CollegeUPN Veteran Yogyakarta

Address of School/College Jl. SWK 104 (Lingkar Utara) Condongcatur

Himpunan Mahasiswa Geofisika (HMGF)

Fakultas Matematika dan Ilmu Pengetahuan Alam

Universitas Gadjah MadaSekip Utara Unit III F-MIPA UGM PO BOX BLS 21Yogyakarta 55281

STRATIGRAPHY SEQUENCE BASED ON OUTCROP DATA APPROACH ON

INTREPERTATING DUKUH-FORMATIONS DEPOSITIONAL

ENVIRONTMENT (STRATIGRAPHY)

STRATIGRAPHY SEQUENCE BASED ON OUTCROP DATA APPROACH

ON INTERPRETATING DUKUH-FORMATIONS DEPOSITIONAL

ENVIRONMENT

Isnianto Saputra*,**

Rian Cahya Rohmana*,**

ABSTRACT

Dukuh Formation is a Late Oligocene Formation belongs to the southern mountain

range. The study area is located in Samigaluh and Kalibawang district, Kulonprogo,

Yogyakarta. The paper emphasizes the study of depositional environment utilizing the

concept of sequence stratigraphy. Field observation and measuring section method has

been done at the two different location which is supported by sedimentological,

paleontological and petrographical analysis. Based on the observation and analysis it is

revealed that the deposit on the first measuring section is characterized by the

occurrence of mPSm, csGu, vcSs, cSo, mSl, csGs, csmSs, cSfu, csGs, fSl, csGi lithofacies,

whereas, the second measuring section are characterized out by csGm, Gs, tmSs, Lv, Cs,

csmSm, csGm, cscPSs, Gic, Cs, csmSvb, csGsc, mSs, vcSh, csGg, csSs, csSl, csGa, Pcs, csGs,

fSr, csmSvb lithofacies. Interpretation using facies model is merely unsatisfied because

the lacks of appropriariety so, sequence stratigraphy is prefered. Based on it, lower

Dukuh Formation was interpreted as early lowstand system tract is deep marine. Dukuh

Formation was interpreted as late lowstand system tract is shallow marine, whereas

transgressive system track was representated by Limestone of Jonggrangan Formation.

Keywords: Dukuh, depositional environment, lowstand

INTRODUCTION

The study area was located at Samigaluh district, kulonprogo regency, D. I.

Yogyakarta province. The trevel time to get to the study area is around 45 minutes from

Yogyakarta, and it can be through by the motorcycle and car with good asphalt

condition.

Stratigraphicaly, in the early study dukuh Formation was involved within old

andesit Formation by Van Bemmelen (1949), the processes which occurred has a

relationship with the volcanic activity event at the java island at oligosen-miosen. But, in

further study Pringgoprawiro and Riyanto (1987) did the revision to the classification of

Van Bemmelen. They devided old andesit Formation and introduced two new Formation

both Kaligesing Formation and Dukuh Formation. Kaligesing Formation is characterized

by the rock unit in land deposit, it is composed by intercalation volcanic breccias, lava,

tuffaceous sandstone, and lahar deposit. whereas Dukuh Formation is characterized by

the deep marine deposit which is composed by intercalaton polymic breccias,

tuffaceous sandstone, claystone, and interbedded by carbonate rocks.

* Geological Engineering Dept. UPN Vet eran Yogyakarta

* Geopangea Research Group (GPRG) Indonesia


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BASIC THEORY

Facies is defined as sum of physical, biological, and chemical aspect of rock unit in

time and space framework. Facies can be subdivided more specifically depends on need,

just to mention lithofacies, that has a meaning physical and chemical aspect of rock.

Facies and litofacies were significant aspect to deciphering rock strata into more

meaningful and useful unit based on the purpose intended. Intrepertation of

depositional environtment can be supported by the detail descripstion of litofacies, and

after it more advance method, litofacies assemblage, can be done to attain the

information about the depositional environment. The present of facies model become

significant both as a norm and also as a comparation. However this method, which was

regarded as conventional method, simultaneously could become unsatisfied since facies

model usualy cant accommodate sedimentological interpretation on deposit which

founded on different location compared to the deposit that has been extracted to

generate those facies model.

Several alternative method could be utilize, one of those is sequence stratigraphy.

Sequence stratigraphy, branch of stratigraphy which was accepted as formal

stratigraphy unit in SSI since 1996, has basic unit called sequence. Its defined as a

stratigraphic unit composed of a relatively conformable succession of genetically related

strata bounded at its top and base by unconformities and their correlative conformities.

Sequence was defined by unconformities based on Exxon group, whereas Galloway

prefer maximum flooding surface. Sequence consist of system tract, which has definition

linkage of contemporaneous depositional system. There are at least three different

types of system tract. Those are transgressive system tract, highstand system tract, and

lowstand system tract.

METHODS

The study based on outcrops observation and after that continued with somelaboratory analysis. The outcrops observation encompasses sampling of lithological

data, sedimentary structures, outcrops log, measuring section, and geological map.

After that, it was continued with laboratory analysis such as petrography, calsimetry,

paleontology, and outcrops log analysis. At the end, all datas and analysis has been

collaborated to get the interpretation of depositional environment and system tract unit

of Dukuh Formation.

RESULT AND DISCUSSION

- Facies AnalysisIn this study of facies analysis, Tuckers facies classification has been used. From the

result of the analysis there were some lithofacies which can be used to determine the

depositional environment and as basic concept to explain the system tract unit of

Dukuh Formation. Two measuring section has been combined to get one set

stratigraphical assemblage completely. Several lithofacies could be obtained to give the

information about the depositional environment. Precisely there were thirty one

lithofacies occurred in this section. Several keys lithofacies will be explained respectively

below :


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csGi(Inverse graded bedded calcareous Breccia). This lithofacies wasinterpretated as the result of high density turbidity current deposit on traction

carpet phase.

fSl(pararel laminated fine Sandstone) which was deposited by density currentvia traction current on lower flow regime.

vcSu(slumped very coarse Sandstone) which was deposited by density current inwhich rapid sedimentation play an important role.

cSfu (slumped very coarse Sandstone) which was deposited by resedimentationprocess triggered by seismic process or other process.

mSo(ripple cross laminated medium Sandstone) which was deposited by tractioncurrent so possibly generates ripple bedform and the migration as well.

mPsm(massive medium Pebbly Sandstone) which was deposited by high densityturbidity current resembling debris flow in which gravel can be deposited

alongside sand material.

Lv (vertical bioturbated siltstone) was interpreted as a offshore mud depositedat shelf area, the changing of lower current energy to the higher current energyhas been indicated by a vertical bioturbated.

Gic (inverse graded bedded and scour cast Breccia) was interpreted as the resultof high density turbidity current deposit at the traction carpet phase.

csmSvb (vertical and horizontal bioturbated calcareous medium Sandstone) wasinterpreted as the result of a traction mechanism in wave current at the early

sedimentation phase.

vcSh (hummocky cross bedded very coarse Sandstone) was interpreted as theresult of a traction mechanism deposit in a wave current at the shelf area.

csGs (gradded bedded calcareous Breccia) was interpreted as the result of highdensity turbidity current at the suspense phase.

csGsc (stratified and scoured calcareous Breccia) was interpreted as the result ofhigh density turbidity current at the shelf area in traction mechanism.

fSr (cross ripple fine Sandstone) was interpreted as the result of debris flowdeposit which occurred at the shelf area.

Generally Dukuh Formation can be divided into two different depostional

environment based on lithological facies properties. In the upper of Dukuh Formation,

the presence of hummocky cross bedded, symmetrical ripple and vertical bioturbation

(skolithos), those sedimentary structures generally can be the key to explain that Dukuh

Formation was formed by the fair weather wave and storm wave at the shallow marine

area ( shoreface to offshore ).

At the lower of Dukuh Formation turbidity current deposit has been found. It is

characterized by the presence of slumped bedded, inverse graded, and ripple cross

laminated bed which is interpreted as deep marine deposit (in this case as the upper

fan channel fill, walker, 1984) . the upper part becomes problem if the same approach

to interpreted the lower part of Dukuh Formation is conducted. The problem occurred

since there are no facies model that can explain the occurrence of thick breccias deposit

in this section. Almost all breccias on the facies model have thin thickness because of it

is accepted breccias occur only as a gravel lag deposit. Due to this fact sequence analysis


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will be conducted to unravel the problem of upper part of Dukuh Formation depositional

environment.

-

Sequence Analysis

The analysis is being conducted to the complete measuring section. First of all

the parasequence is determined based on its bed or bedsets stacking patern wether it is

coarsening, fining, thickening, or thinning. After that the parasequence set is

determined by combining the patern of the parasequence. From this method more

complete depositional linkage system, well known as system tract, can be described.

There are 2 system tract that can be identified from this measuring section, lowstand

system tract and transgressive system tract. Lowstand system tract encompasses the

lower part of Dukuh Formation in which turbidity current deposit is visible. This can be

formulated from the fact that thick submarine fan deposit only possible in condition

where lot of sedimen influx was injected until it reach the shelf margin. This influx

usually accompanied by minor rate of subsidence. This condition happen at lowstand

system tract where the sea level is stable at low level relatively. In this conditionagradation stacking patern is very obvius. This can be seen from the lower part of Dukuh

Formation where the parasequence shown agradation overall patern. The parasequence

set itself consist of several parasequence which show both thining and thickening

stacking pattern. Thining typified channel of the submarine fan whereas thickening

typified the lobes of the submarine fan.

This lowstand deposit continued further upward untill it changes into shallower sea

environment, the upper part of the Dukuh Formation. In this part overall agradation

stacking patern still dominates the section. The deposit in this part is unique since fair

amount of gravel sediment occurred. In first glance its relatively easy to interpretated

this deposit as deep sea deposit because of it. However the occurrence of shallow sea

deposite feature such as hummocky cross bedding, highly bioturbated bed resembleskolithos, coal fragment inside the sandstone bed, etc could obscure that interpretation.

Its more likely a shelf deposit, supported by the paleontological data that has been

obtained from this part of section(more benthonic fossil than planktonic fossil). In this

part the stacking patern of the parasequence set still depicts agradation patern. After

series of intercalation of limey breccias and sandstone a corraline limestone and its

flank was occurred. This is interpretated as the transgressive surface, a surface which

characterize no deposition or in other word the transition from lowstand system tract to

transgressive system tract. This low rate of sedimentation condition allowed corral and

its symbiotic organism to burgeon. Intensive growth in further time generates those

limestones.

Transgressive system tract deposit overlies this transgressive surface. The early

part of the transgressive system tract consist of litology that somewhat similar type of

litology with the upper lowstand system tract deposit. But the overall stacking patern of

the parasequence set is different, where in this part retrograde is the dominant stacking

pattern. In this early transgressive system tract the sediment influx is be still even

though not really significant. The deposition of coralline limestone belongs to

Jongrangan Formation then really conformise the transgressive system tract. it is

supported by the fact that is coralline limestone succession is very thick.


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Based on this sequence analysis the upper part of Dukuh Formation belongs to

late lowstand deposited in shelf area. Because subsequently after this upper part of

Dukuh Formation is overlied by limestone of Jonggrangan Formation, the transgressive

system tract. The ackwardness of the upper part of Dukuh Formation then can beexplained. The presence of the high area ,the source materials for the sedimentation,

which is very closed to the shoreline might be the approach models to explain about

that. Because the high area is very close, the sediment material undergone relatively

short term transportation. Thus, the materials in gravel size still can be found in shallow

sea environment.

CONCLUSSION

The information based on sequence analysis it could be revealed the upper part

of Dukuh Formation is classified to lowstand system tract deposited in shelf area.

Whereas the ackwardness of this deposit, fair amount of breccia, could be explained by

a model in which the source area is very closed to the shoreline area.

ACKNOWLEDGMENT

The authors would like to particularly thank the Department of Geological

Engineering UPN Veteran Yogyakarta for the support to made this paper. Special

acknowledgement is made to Fery Andika Cahyo and Zaenal Fanani as the fieldwork

team and for the help belongs to the written of this paper, Geopangea Research Group

Indonesia for the discussing, UPN geology laboratories for the sample analysis, and GSC

committee 2011 for publishing this paper.


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REFERENCES

- Boggs Jr., S., 2006, Principle of Sedimentology and Stratigraphy 4th edition,Pearson Education, Inc, New Jersey, 335-342- Bouma, A. H., 1962, Sedimentology of Some Flysch Deposite, A GraphicApproach to Fasies Interpretations. Elevier Co., Amsterdams, Netherlands.

- Friedman, G. M., Reeckmann, A.(1982), Exploration for Carbonate Reservoir,John Wiley & Sons, New York, 85-89

- Koesoemadinata, R. P, 1981, Prinsip-prinsip SedimentasiDepartemen TeknikGeologi, ITB, Bandung, 65-100

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

- Van Bemmelen, R. W., 1949, The Geology of Indonesia, vol IA, 2nd ed, TheHague Martinus Nijhoff, Netherlands.

- Walker, R. G. & James, N. P., 1992, Facies Models: Response Sea LevelChange, Geological Association of Canada, Canada.


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Figure 1. Simplified Geological Map of Kecamatan Samigaluh, the study area are shown in pale orange colour


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U i it G dj h M d



ENVIRONTMENT STRATIGRAPHY

Figure 2. massive coral Framestone (Fc)

Figure 3. platy coral Bindstone (Bp)

Figure 4. massive coarse Floatstone (cFm)

Figure 5. massive calcareous breccia (csGm)

Figure 6. vertical bioturbated Siltstone (Lv)

Figure 7. vertical & horizontal bioturbated

calcareous Sandstone (csmSvb)

Figure 8. hummocky cross bedding very

coarse Sandstone (vcSh)

Figure 9. slumped very coarse Sandstone

(vcSu)

Figure 10. Facies Analysis and Sequence Analysis of Dukuh Formatin

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Gsc2011 Paper Gprg