Distribution of Ostracoda from Measured Section Data at Cimerang River, Sukabumi, Jawa Barat

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1 Distribution of Ostracoda from Measured Section Data at Cimerang River, Sukabumi, Jawa Barat Mohamad Solihin 1, Prasma Feby Rahmadhani 1, Renanda Sevirajati 1, Hendy Taufik 1, Lili Fauzielly 1 1 Faculty of Geological Engineering University of Padjadjaran, Jl. Raya Bandung Sumedang KM 21, 45363, Jatinangor, Indonesia msoli.geo@gmail.com Abstract Ostracoda was found at Cimerang River, Sukabumi, West Java, Indonesia. Research area was part of Nyalindung member, Cimandiri Formation, and generally regarded as being of Miocene Age. This is the first research of ostracoda distribution in Miocene deposition in this area. The aims is to know the distribution of ostracoda based on measure section and micropaleontology analysis. Based on measure section, there are 9 stratigraphic unit where ostracoda was only found in 6 units of mudstone. From 6 units samples it is found about 15 species with 164Individuals which dominated by Hemicytheridea ornata, Cytherella hemipuncta, Hemicytheridea reticulata,cytherelloidea excavata, Cyherella javaseanse, and Keijella carrie,. From the ostracoda distribution is known that the paleoenvironment in research area is shallow marine. Keywords: Cimerang s River, Ostracoda, Paleoenvironment, Sukabumi Introduction Nyalindung member, Cimandiri Formation is located in Cimerang, Sukabumi, West Java and generally regarded as being of late Middle Miocene age. According to previous research (Sukamto, 1975) this area was deposited in shallow marine environment, it s identify by the presence of mollusca, coral, and foraminifera. The presence of ostracoda in this formation is haven t publish yet. There s a lot of study about ostracoda which related with paleoenvironment because it has wide distribution in water environment. This study is aim to know the distribution of ostracoda in research area which deposited in shallow marine environment. Research area is located in Parubaya, Sukabumi, West Java. claystone, mudstone, and sandy clay stone with grey, blue, and green color with implied sandstone and clay. In some outcrop there s found glauconitic sandstone, layering coal, and trash of plants and resin with massive and layering structure. It also found cross bedding structure which contains a lot of mollusca, coral, and foraminifera. This area generally as being in late Middle Miocene age and deposited in shallow marine environment. (Sukamto, 1975) (figure 1). Regional Stratigraphy Research area is located at Cimerang River, Sukabumi, West Java which consist of Nyalindung member, Cimandiri formation. They include 259

2 Methodology Figure 1. Research area Cimerang River was part of Nyalindung Member, Cimandiri Formation. The data was collected by measure section method from North to South. There are 9 stratigraphic units in this area, every rock sample was taken from each units which dominated with claystone. Every rock sample are do the laboratory analysis. The techniques used to prepare and concentrate samples for examination vary according to rock type (composition and grain size), how hard or resistant the sediment or rock is, how abundant the fossil are, and how they are preserved within the sediment matrix. Firstly, sample were crushed until it has fine grain, then put it on a plastic cup. In order to remove the shell from impurities add some H 2 O 2 and wait for about 6 hours. After soaking the sample, clean the sample with water and sieve it using 50 and 120 mesh sieves. After that dried the sample in the oven within temperature of 60 0 C for 12 hours. Finally, put the sample into plastic bag and its ready for picking and fossil determination needs under binocular microscope. This analysis is using qualitative method based on van Gorsel, The method for determination and classification of ostracoda was based on Brady, Result of Analysis From 9 sample units that was taken from vertical section there are only 6 units that containing ostracoda whichorderedfrom the oldestto the youngest unit, they areunit I, Unit III, Unit IV, Unit V, Unit VI, and Unit VII (figure 2). There are 15 species of ostracoda that was found in research area which spread in every unit that containing ostracoda. Unit I with 1.8 meters of thickness was dominated with greyish claystone. This unit containing 6 species of ostracoda they are Keijella carriei (14,70%), Keijella cf novinularis (1,48%), Cytherella javaseanse (16,18%), Hemicytheridea ornata (16,18%), Cytherella hemipuncta (30,88%), and Hemicytheridea reticulata (20,58%). From the data, it is known that this unit was dominated with Cytherella hemipuncta, Hemicytheridea reticulata, Hemicytheridea ornata, Cytherella javaseanse and Keijella carriei. (Figure 3) Unit III was dominated with claystone, and containing 11 species of ostracoda, they are Keijella cariei (12,24%), Hemicytheridea ornata (34,79%), Hemicytheridea reticulata (4,09%), Cytherelloidea excavata (22,44%), Keijella sp. (4,09%), Loxoconcha lilljeborgii (6,12%), Loxoconcha wrighti (8,16%), Aglaiocypris sp. (2,04%), Argilloecia sp. (2,04%), Cytherella semitalis (2,04%), and Keijella multisulcus (2,04%). From the data it is known that this unit was dominated with Hemicytheridea ornata and Cytherelloidea excavata. Unit IV with 0.63 meter of thicknesswas dominated with claystone and containing 4 species of ostracoda they are Hemicytheridea ornata (37,50%), Keijella sp. (12,50%), Loxoconcha wrighti (12,50%), dan Cytherella incohota (37,50%). There are no dominated fossil in this unit. Unit V with 0,46 meter of thickness was dominated with claystone. This unit containing 3 species of ostracoda, they are Keijella carriei (3,57%),Hemicytheridea ornata (92,86%), and Loxoconcha wrighti (3,57%). It is known that Hemicytheridea ornata was dominated in this unit. Unit VI has 0,13 meters of thickness was dominated with claystone. This unit containing 2 species of ostracoda but the abundance of the fossil is very limited, they are Cytherella javaseaense (50%) dan Loxoconcha wrighti (50%). Unit VII is the youngest unit with 2.13 meters of thickness and containing 4 species of ostracoda, they are Keijella carriei (22,22%), Cytherella javaseanse (22,22%), Hemicytheridea ornata (22,04%), dan Loxoconcha wrighti (33,34%). 260

3 Figure 2. Distribution of Ostracoda in Measured section 261

4 A B C D E F Figure 3. Ostracoda : (3a) Hemicytheridea ornate Mostafawi, (3b) Cytherella hemipuncta Swanson, (3c) HemicytherideareticulataKingma, (3d) Cytherelloidea excavatamostafawi, (3e) Cyherella javaseansedewi, (3f) Keijella carriedewi Discussion From vertical section in Cimerang River, Sukabumi, West Java, the oldest unit with greyish claystone, carbonate, and also presence some macrofossil such as coelenterate, pelecypoda, and gastropods. To the youngest unit there was dominated with implied greenish sandstone with medium to fine grain of size, containing carbonate, - and nodular claystone. It was also found lignite with black color of fresh surface and blackish brown color of weathered surface, with waxy luster, clay grain size, rounded to very rounded, friable hardness, and greyish black streak. From the characteristic of vertical section, it is known that research area in Cimerang River was deposited in shallow marine environment. From the distribution of ostracoda, it is known that the oldest unit from vertical section containing 68 individuals of ostracoda which dominated with Cytherella hemipuncta, Hemicytheridea reticulata, Hemicytheridea ornata, Cytherella javaseanse and Keijella carriei None of the ostracoda was found in unit II (barren unit), then in unit III there are 49 individuals of ostracoda which dominated with Hemychitheridea ornata and Cytherelloidea excavate. Unit IV containing 8 individuals of ostracoda, they arehemicytheridea ornata, Keijella sp., Loxoconcha lilljeborgii, Loxoconca wrighti, and Cytherella incohota. In unit V there are 28 individuals of ostracoda and dominated with Hemicytheridea ornata. The abundance of ostracoda in unit VI is very limited, there are only containing 2 species, they are Cyherella javaseanse and Loxoconcha wrighti. The distribution of ostracoda in unit VII as the youngest unit was containing 9 individuals, they are Keijella carriei, Cytherella javaseaense, Hemicytheridea ornata, and Loxoconca wrighti. 262

5 Generally, it can be seen that the variety changes of species from the distribution of ostracoda from the oldest to the youngest unit. The variety of ostracoda is decrease through the youngest unit. Conclusion From this study, it is known that research area in Cimerang River, Sukabumi, West Java was deposited in late middle Miocene age with shallow marine environment, it s also supported by the presence of lignite. It can be seen that there are 6 species of ostracoda which dominated in Cimerang River, they are Hemicytheridea ornata, Cytherella hemipuncta, Hemicytheridea reticulata, Cytherelloidea excavata, Cyherella javaseanse, and Keijella carrie. Acknowledgement We thank the following people for their assistance and contribution to this study: Kuat Yogiristanto, Raffi Pratista, Rachmanda Anandita Putra, and Ibnar Auliya Zuhdi for their permission to use the data from their geological mapping area; Mrs. Winantris who help and facilitate us in capturing fossil image.this research was conducted in Laboratory of Paleontology in Faculty of Geological Engineering, Padjadjaran University. References Brady, G.S (1880) Report on the Ostracoda dredged by HMS Chalenger during the year , Zoology, Sukamto Regional Geologic map Jampang, Java, 1: scale. Directory of Geology: Bandung Van Gorsel, J.T. (1988) Biostratigraphy in Indonesia: Methods, Pitfalls and New Directions. Proceedings Indonesian Petroleum Association, 17 th Annual Convention, p