LINGKUNGAN PURBA FORMASI JATILUHUR BERDASARKAN KUMPULAN FOSIL FORAMINIFERA PADA DAERAH DESA JATILUHUR DAN SEKITARNYA, KECAMATAN JATILUHUR, KABUPATEN PURWAKARTA, JAWA BARAT

ABSTRACTThis research was conducted to determine environmental changes in the study area based on the abundance of foraminifera fossils and the lithology of the emerging rocks. The research area is in Jatiluhur District, Purwakarta Regency, West Java Province. Rock samples taken during the Advanced...

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Bibliographic Details
Main Authors: Osvaldus, Rodrigo, Jurnaliah, Lia, Muljana, Budi
Format: Article in Journal/Newspaper
Language:Indonesian
Published: Fakultas Teknik Geologi Universitas Padjadjaran 2021
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Online Access:http://jurnal.unpad.ac.id/bsc/article/view/33366
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Summary:ABSTRACTThis research was conducted to determine environmental changes in the study area based on the abundance of foraminifera fossils and the lithology of the emerging rocks. The research area is in Jatiluhur District, Purwakarta Regency, West Java Province. Rock samples taken during the Advanced Geological Mapping activity were then used as a composite log, divided into 15 rock samples representing any changes in lithological characteristics. The number of small foraminifera fossils found from the 15 samples was 120,912 individuals with 75,840 individual planktonic foraminifera fossils and 45,072 individual benthonic foraminifera fossils. The abundance of small foraminifera fossils varies in number in each sample and the number is more abundant in the younger layers than in the older layers. The P / B ratio analysis was performed using a comparison calculation between planktonic and benthonic foraminifera. From the P / B ratio analysis, it was found that four bathymetric zones had occurred in the study area. From the results of the P / B ratio analysis and associated with rock lithology, it can be concluded that the environment of the study area is in a shallow sea where there have been several times of local deepening and silting of the water column. The analysis of environmental changes is strengthened by drawing the age which is determined based on the appearance of the fossil index in the layers. Referring to Bolli & Saunders (1985) and Boudagherfadel & Banner (1999), the results of this analysis indicate that the study area was deposited at an age not older than the Middle Miocene.Keywords: Foraminifera, Abundance, Environment, Lithology, Middle MioceneABSTRAKPenelitian ini dilakukan untuk mengetahui perubahan lingkungan pada daerah penelitian berdasarkan kelimpahan fosil foraminifera dan litologi batuan yang muncul. Daerah penelitian berada pada Kecamatan Jatiluhur, Kabupaten Purwakarta, Provinsi Jawa Barat. Sampel berupa batuan yang diambil ketika kegiatan Pemetaan Geologi Lanjut yang kemudian dijadikan sebuat composite log terbagi menjadi 15 perconto batuan mewakili setiap perubahan karakteristik litologi. Jumlah fosil foraminifera kecil yang ditemukan dari 15 sampel tersebut adalah 120.912 individu dengan fosil foraminifera planktonik 75.840 individu dan foraminifera bentonik 45.072 individu. Kelimpahan fosil foraminifera kecil bervariasi jumlahnya pada masing-masing sampel dan jumlah tersebut lebih melimpah pada lapisan yang lebih muda dibandingkan dengan lapisan yang lebih tua. Analisis P/B ratio dilakukan menggunakan perhitungan perbandingan antara foraminifera planktonik dan bentonik. Dari hasil analisis P/B ratio didapatkan empat zona batimetri pernah terjadi pada daerah penelitian. Dari hasil analisis P/B ratio dan dikaitkan dengan litologi batuan, dapat ditarik kesimpulan bahwa lingkungan dari daerah penelitian berada pada laut dangkal dimana terjadi beberapa kali pendalaman serta pendangkalan kolom air secara setempat. Analisis perubahan lingkungan diperkuat dengan penarikan umur yang ditentukan berdasarkan kemunculan indeks fosil pada lapisan. Mengacu pada Bolli & Saunders (1985) dan Boudagherfadel & Banner (1999), hasil analisis tersebut menunjukkan bahwa daerah penelitian diendapkan pada umur tidak lebih tua dari Miosen Tengah.Kata Kunci : Foraminifera, Kelimpahan, Lingkungan, Litologi batuan, Miosen Tengah.