FASIES DAN LINGKUNGAN PENGENDAPAN FORMASI HALANG DAERAH CIHAUR, SUNGAI CIHAUR, KABUPATEN BANYUMAS, PROVINSI JAWA TENGAH

Abstract

ABSTRAK: Formasi Halang (Tmh) bagian bawah tersusun atas batuan sedimen yang terdiri dari satuan batupasir, batulanau, batulempung, dan batuserpih. Lokasi studi terletak di Daerah Cihaur, Kabupaten Banyumas, Provinsi Jawa Tengah. Studi ini bertujuan untuk mengidentifikasi karakteristik fasies, umur, dan lingkungan pengendapan Formasi Halang berdasarkan analisis litofasies yang didukung oleh data paleontologi yang ditemukan di daerah studi. Metode yang digunakan dalam studi ini adalah pengambilan data lapangan dengan metode Measuring Stratigraphy (MS) untuk menghimpun data geometri lapisan, ketebalan lapisan, tekstur batuan, serta struktur sedimen, dan analisis studio. Analisis litofasies digunakan untuk mengidentifikasi karakteristik litologi dari setiap lapisan batuan serta didukung oleh paleontologi untuk pengamatan lebih lanjut mengenai komposisi fosil yang terdapat didalam batuan. Berdasarkan analisis litofasies Formasi Halang di daerah Sungai Cihaur memiliki karakteristik litologi berupa perselingan yang didominasi oleh satuan batupasir, terdiri dari dua jenis fasies yaitu; Classical Turbidite (C.T.) dan Massive Sandstone (M.S.) coarsening upward succession. Hal tersebut menunjukan bahwa endapan turbidit yang terbentuk dipengaruhi oleh mekanisme arus turbidit, serta ditemukan struktur sedimen yang menjadi penciri dari sikuen Bouma Tb hingga Te. Dijumpai keterdapatan foraminifera plantonik berupa Globorotalia tumida, Globigerinoides immaturus, dan Globorotalia plesiotumida yang menunjukan umur relatif Miosen Akhir-Pliosen Awal (N16-N18), serta foraminifera bentonik berupa Caclymmina cancellate yang menunjukan bahwa lingkungan batimetri lower bathyal zone (2002-3048 m). Lingkungan pengendapan Formasi Halang didaerah studi terletak didalam Sub-marine Fan System, tepatnya dibagian Outer Fan dan Suprafan Lobes.

Kata Kunci: Formasi Halang, fasies, Biozonasi, Turbidit, Submarine Fan

ABSTRACT: The lower Halang (Tmh) Formation is composed of sedimentary rock consisting of sandstone, siltstone, claystone, and shalestone units. located in Cihaur Village, Banyumas Regency, Central Java Province. This study aims to identify the characteristics of the facies, age, and depositional environment of the Halang Formation based on the analysis of lithofacies supported by paleontological data found in the study area. The method used in this study are field data collection with the Measuring Stratigraphy (MS) method to collect data on the geometry of layers, thickness of layers, rock texture, sedimentary structures, and studio analysis. Litofasies analysis is used to identify lithological characteristics of each rock layer and supported by paleontological data for further observation of the composition of fossils. Based on the analysis of the Halang Formation litofasies in the Cihaur River area, lithological characteristics are in the form of interbedded sandstone dominated by sandstone units, consisting of two types of facies; Classical Turbidite (C.T.) and Massive Sandstone (M.S.) with coarsening upward succession. This shows that the turbidite deposits formed are influenced by the mechanism of turbidite currents, as well as various sedimentary structures found to be characteristic of the Bouma Tb to Te sequences. Paleontological analysis found the presence of plantonic foraminifera in the form of Globorotalia tumida, Globigerinoides immaturus, and Globorotalia plesiotumida which indicate the relative age of Late Miocene until Early Pliocene (N16-N18), and bentonic foraminifera in the form of Caclymmina cancellate which indicate that the Halang Formation in the study area was deposited in the deep sea environment of the lower bathyal (2002-3048 m). Halang Formation depositional environment in the study area is located in the Sub-marine Fan System, precisely in the Outer Fan and Suprafan Lobes sections.

Keywords: Halang Formation, Facies, Biozonation, Turbidite, Submarine Fan