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Miocene Planktonic Foraminiferal Biodatum of the Jatiluhur Sectionsin Northwest Java Basin

Vijaya Isnaniawardhani 1 and Nurdrajat 2

1,2Padjadjaran University, Jl. Raya Bandung-Sumedang km. 21 Jatinangor, Sumedang, IndonesiaEmail:vijaya_i@unpad.ac.id

Abstract

Planktonic foraminiferal biostratigraphic was studied in Jatiluhur area, Northwest Java Basin. The succession ofJatibarang Volcanics, Cibulakan, Parigi and Cisubuh Formations unconformably overlies the Pre-Tertiary basinalbasement. These are unconformably covered with Quaternary alluvial deposits. Detail mapping and measuring sectionswere undertaken in order to acquire relations between outcrop, and for establishing a stratigraphic framework. Thefine grained sediment samples were taken from continuous stratigraphic successions along river-side clifts of theCiherang, Cikeo, Cigajah, Cisaray, Cikekep, Cibinbin, Cigaruguy rivers and also outcrops at the Jatiluhur reservoir.On the basis of laboratory analysis, the five planktonic foraminiferal biodatum were defined: datum planes of Orbulinasuturalis, Globigerinoides subquadratus, Globorotalia acostaensis, Globorotalia plesiotumida, and Globorotaliamargaritae. Based on definition of these five datum planes, four interval zones were established are as follow: Orbulinasuturalis-Globigerinoides subquadratus interval zone, Globigerinoides subquadratus-Globorotalia acostaensis intervalzone, Globorotalia acostaensis-Globotoralia plesiotumida interval zone, and Globotoralia plesiotumida-Globorotaliamargaritae interval zone.

Keywords: Miocene, planktonic foraminifera, datum, Northwest Java Basin

Introduction

Establishment of planktonic foraminiferal biodatumin the Indonesia basins was first studied by Bolli(1966) based on the Bojonegoro well no.1 in EastJava. This pioneering study gave a new insight intopaleontologic and stratigraphic studies of theIndonesia basins, in particular for biostratigraphiccorrelation of the Neogene successions in the basin,which had mainly been studied on the basis of largerforaminifera. After Bolli’s planktonic foraminiferalzonation (1966), many paleontologists andstratigraphers have paid more attention to the studyof planktonic foraminifera for long-distanctbiostratigraphic correlations of the Neogenesuccession. The number of scientific reports on theplanktonic foraminiferal biostratigraphy hasincreased during the last four decades. Kadar (1986)noted that Hartono (1960, 1964 and 1969), Bolli(1966), Pringgoprawiro (1968), Wibisono (1971),Kadar (1972, 1975, 1978, 1981, 1986),Pringgoprawiro et al. (1977), Marc & Suminta(1979), and Purnamaningsih & Pringgoprawiro(1981) have studied this biostratigraphy in Javabasins.

The Miocene planktonic foraminiferalbiostratigraphy was studied in Jatiluhur area, thatadministratively belongs to Purwakarta Regency,West Java Province (Figure 1). It was determinedbased on selected datum planes that are defined bythe first appearance or extinction of importantforaminiferal marker species supported by co-appearance of associated taxa.

This study will give an important worth to establishcorrelation level in the surface sections in NorthwestJava Basin.

Figure 1. The locality map of the studied areasituated near Jatuluhur reservoir.

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Stratigraphy

The geology and stratigraphy of the study area havebeen reported elsewhere (e.g. Marks, 1957; Baumanet al., 1972; Sudjatmiko, 1972; Arpandi &Patmosukismo, 1975; Effendi, 1986; andMartodjodjo, 2003), and the followings are the briefsummary of stratigraphic framework of the studiedsuccessions.

The Northwest Java Basin is underlain by a complexof Mesozoic igneous and metamorphic rocks. ThePaleogene Jatibarang Volcanics unconformablyoverlies the Pre-Tertiary basement, and consists ofthe unfossiliferous continental sediments, which arecharacterized by varicolored and molted tuffsinterbedded with porphyry andesite, basalt, and redclaystone. The Jatibarang Volcanics isunconformably overlain by the Lower CibulakanFormation (syn. Jatiluhur Formation, Sudjatmiko,1972). The basal part of the formation consistsmainly of paralic carbonaceous shales with minorsandstones, siltstones, and coal intercalations, andpasses upward to platform-type limestonesintercalated with glauconitic shale, marl anddolomitic limestone with coal and fine glauconiticsand lenses in the middle and upper parts. TheLower Cibulakan Formation gradationally passesupward to the Upper Cibulakan Formation, which isprimarily composed of marine claystone and shale,interbedded with limestone and sandstone.Intercalations of fine-grained deposits becomefrequent in the upper part of the CibulakanFormation. The Parigi Formation (syn.Klapanunggal Formation, Effendi, 1986)conformably overlies the Upper CibulakanFormation, and is composed reveals detritus andreefal limestone intervals. The Cisubuh Formation isthe youngest Neogene sediments, which outcrop inthe studied area, consist of claystone, sandstone andlimestone. This formation becomes more sandy upsection with intercalated coal beds. All basementrocks, Paleogene and Neogene successions areunconformably covered with Quaternary alluvialdeposits (Martodjojo, 2003) (Figure 2).

Figure 2. The geological map of the Jatiluhur area inNorthwest Java Basin (Sudjatmiko, 1972; Effendi,1986 with modified)

Isnaniawardhani and Sunardi (2014) concluded thaton the basis of nannofossils assemblages, thesediment successions on Ciherang, Cikeo, Cigajah,Cisaray, Cikekep, Cibinbin, Cigaruguy rivers andnear the Jatiluhur reservoir were deposited duringMiddle Miocene to Early Pliocene.

Methods

Detailed mapping and measuring stratigraphicsections were undertaken in order to acquirestratigraphic relations between the widely spacedoutcrop sections in the studied area, for establishinga stratigraphic framework of key stratigraphiclevels, which can be used for defining detailedstratigraphic positions of paleontologic samples.

Sediment samples for the analyses of foraminiferaand calcareous nannofossil floras were taken fromcontinuous stratigraphic succession from outcropsnear the Jatiluhur reservoir and along river-sideclifts of the Ciherang, Cikeo, Cigajah, Cisaray,Cikekep, Cibinbin, Cigaruguy rivers. In total 8claystone, 5 silt, 25 fine-grained sandstone samples,which are fresh and contain foraminifera andmolluscan shells, were taken.

In the laboratory, we adopted a simple residupreparation method (Haynes, 1981; andPringgoprawiro et al., 1994) to release foraminiferafrom each of 100 gram fine-grained sedimentsamples using hydrogen peroxide. We used theresidual sediment of each sample to observeforaminifera using a binocular microscope. Weadopted some basic methods for the identification offoraminifera (Postuma, 1971; Stainforth et al., 1975;

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Bolli & Saunders, 1985: Kennett & Srinivasan,1983; and Loeblich & Tappan, 1988).

In planktonic foraminifera assemblages, we selectedthe marker species on the basis of several basiccriteria that selected taxa are distinctive and caneasily distinguished within each sample, and thatthey have a wide distribution within the studiedarea. Moreover, we also selected some species,which were already used to mark somebiostratigraphic zonas by the previous studies (e.g.Blow, 1969, 1979; Postuma, 1971; Bolli &Saunders, 1985). On the basis of the first appearanceand extinction of selected marker species, someplanktonic foraminiferal biodatums can bedetermined.

Planktonic Foraminiferal Biodatums

In these stratigraphic successions, a total of fiveplanktonic foraminiferal marker species have beenselected, i.e:

Orbulina suturalis, Globigerinoides subquadratus, Globorotalia acostaensis, Globorotalia plesiotumida, and Globorotalia margaritae

In a stratigraphic ascending order, the following fiveplanktonic foraminiferal biodatums were defined(Table 1):

Orbulina suturalis datum planeThe first appearance of Orbulina suturalisis observed in the lower part of the UpperCibulakan Formation at Jatiluhur reservoir.The Orbulina suturalis datum plane hasbeen considered take place near the base ofthe Middle Miocene by the previousstudies. For example, Blow (1969, 1979)used the Orbulina suturalis datum plane todefine N.9 of his zonal scheme. In contrast,this datum was suggested to define Early-Middle Miocene boundary byPringgoprawiro et.al (1977) in thesubsurface of Northwest Java Basinal areaand Kadar (1986) in South Central Java. Inhis radiometric time-scale, Berggren (1972)dated this datum at about 16 Ma, and thisnumerical age suggests that this datum candefine as Early-Middle Miocene boundary.

Globigerinoides subquadratus datum plane

The extinction of Globigerinoidessubquadratus takes place near the top of theCibulakan Formation at Jatiluhur reservoir.Blow (1969, 1979) recorded the extinctionof this species at near the top of N.13 Zonein Middle Miocene age. Pringgoprawiro etal. (1977), Kadar (1986) and van Gorsel(1988) documented that the extinction ofthis species slightly above the firstappearance of the Sphaeroidinellopsissubdehiscens subdehiscens.

Globorotalia acostaensis datum planeThe first appearance of Globorotaliaacostaensis is observed at near the top ofthe Parigi Formation exposed at theCibinbin River. Blow (1969, 1979) used theGloborotalia acostaensis to marks the baseof N.16 zone, as was done by Bolli (1966)at Bojonegoro-1 well in East Java.Pringgoprawiro et al. (1977), Kadar (1986)and van Gorsel (1988) evaluated that thisdatum represents one of the importantdatum planes near the base of LateMiocene. Berggren (1972) dated this datumat about 10 Ma, and Saito (1977) also madethe same estimation in Pasific region.

Globorotalia plesiotumida datum planeThe first appearance of Globotoraliaplesiotumida is observed in the lower partof Cisubuh Formation, exposed at the CikeoRiver. Blow (1969, 1979) used the firstevolutionary appearance of Globorotaliaplesiotumida from its immediate ancesorGloborotalia merotumida to deliniate thebase of N.17 Zone. Pringgoprawiro et al.(1977), Kadar (1986) and van Gorsel(1988) documented that the appearance ofGloborotalia tumida as a significant datumlevel in Late Miocene. Saito (1977) datedthis datum at about 7.7 Ma in Pasificregion.

Globorotalia margaritae datum planeThe first appearance of Globorotaliamargaritae is recorded in the CisubuhFormation at Cikeo, Cigajah, Cisaray andCikekep rivers. Kadar (1989) consideredthat the Globorotalia tumida datum plane isequivalent to the Globorotalia margaritaedatum plane of Pringgoprawiro et al.(1977). In this study, Globorotaliamargaritae co-occur with Globorotalia

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tumida. Berggern (1972) dated this datumat about 5 Ma, while Saito (1977) estimatedits age at about 4.8 Ma in the Pacific region.The first appearance of Globorotaliamargaritae has been recognized to be veryclose to the Miocene-Pliocene boundary(Pringgoprawiro et al., 1977, and vanGorsel, 1988) or about 5.3 Ma (Salvador,1985).

On the basis of the definition of these five datumplanes, four interval zones were established are asfollow: Orbulina suturalis-Globigerinoidessubquadratus interval zone, Globigerinoidessubquadratus-Globorotalia acostaensis intervalzone, Globorotalia acostaensis-Globotoraliaplesiotumida interval zone, and Globotoraliaplesiotumida-Globorotalia margaritae intervalzone.

These datum planes are known as correlationbenchmark for local and global as well, thuscoincide with the established datum in the adjacentregion. Broadly speaking, the currentbiostratigraphic study will contribute to providebasinal correlation with reference to the NorthwestJava Basin.

Table 1. Planktonic Foraminiferal Biodatums onJatiluhur Sections

Conclusions

Five planktonic foraminiferal datum planes weredetermined on the basis of the first appearance andextinction of selected marker species (Orbulina

suturalis, Globigerinoides subquadratus,Globorotalia acostaensis, Globorotaliaplesiotumida, and Globorotalia margaritae).

In stratigraphic sections at Ciherang, Cikeo,Cigajah, Cisaray, Cikekep, Cibinbin, Cigaruguyrivers and Jatiluhur reservoir, five planktonicforaminiferal biodatums were defined, i.e: Orbulinasuturalis datum plane (Early-Middle Mioceneboundary or N.9); Globigerinoides subquadratusdatum plane (Middle Miocene, near the top of N.13Zone); Globorotalia acostaensis datum plane (nearthe base of Late Miocene or N.16); Globorotaliaplesiotumida datum plane (Late Miocene or N.17);and Globorotalia margaritae datum plane (close toMiocene-Pliocene boundary or N.18).

Four interval zones were established are as follow:Orbulina suturalis-Globigerinoides subquadratusinterval zone, Globigerinoides subquadratus-Globorotalia acostaensis interval zone,Globorotalia acostaensis-Globotoralia plesiotumidainterval zone, and Globotoralia plesiotumida-Globorotalia margaritae interval zone.

Acknowledgments

The deep appreciation in extended to Rector ofPadjadjaran University for encouragement andsupporting to publish this paper. The field studiesare conducted by funding from PadjadjaranUniversity research grant; four months of researchin Chiba University, Japan collaboration with Prof.Makoto Ito made possible by the grant from HigherEducation Directorate, Ministry of NationalEducation to which the authors are grateful. Thanksalso to colleagues and staff at the PaleontologicalLaboratory of Faculty of Geology, PadjadjaranUniversity for assistance during observations.

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