AbstrakKabupaten Nunukan termasuk wilayah yang signifikan menyumbang cadangan batubara di Indonesia dengan cadangan hipotetik mencapai sepuluh juta ton. Salah satu data yang dibutuhkan dalam tahapan eksplorasi lanjut batubara adalah informasi lingkungan pengendapan. Penelitian ini bertujuan untuk menentukan lingkungan pengendapan batubara Miosen di Kabupaten Nunukan, Kalimantan Utara. Metode yang dilakukan dalam penelitian yaitu analisis petrografi mencakup analisis maseral dan mineral, pengukuran vitrinite reflectance, plotting Tissue Preservation Index (TPI) terhadap Gelification Index (GI). Komposisi batubara di daerah penelitian tersusun dari dominasi vitrinit (68%-91%) juga dijumpai mineral pirit (0,9%-6,6%). Berdasarkan hasil analisis, batubara di daerah penelitian adalah lignit (Ro= 0,39%-0,44%). Plot Tissue Preservation Index (TPI) dan Gelification Index (GI) menunjukkan bahwa pada saat mengendapkan gambut, daerah penelitian berada pada lingkungan lower delta plain, lahan gambut wet forest swamp dan clastic marsh, serta pada kondisi lingkungan pengendapan telmatic dan limno-telmatic. Kehadiran pirit framboidal mengindikasikan formasi pembawa batubara mengalami reduksi sulfat, yang berasal dari lingkungan anoxic, dengan ion besi pada saat pembatubaraan. Kata kunci :Maseral; Nunukan; Reflektansi Vitrinit; TPI-GI. AbstractNunukan Regency, North Borneo, significantly contributes coal reserves in Indonesia with hypothetical reserves reaching ten million tons. One of the data required in the next stage of coal exploration is information of depositional environment. This study aims to determine the Miocene coal depositional environment in Nunukan Regency. The method used in this research are petrographic analysis including observation of minerals and minerals, measurement of vitrinite reflectance, plotting tissue preservation index (TPI) of Gelification Index (GI). The composition of coal in the study area composed of vitrinite dominance (68% -91%), pyrite minerals are also identified (0.9% -6.6%). Based on the analysis, coal in the study area is lignite (Ro = 0.39% -0.44%). Tissue Preservation Index (TPI) and Gelification Index (GI) plot shows that the study area is in the lower delta plain environment, wet forest swamp and clastic marsh peatlands, and in the telmatic and limno-telmatic depositional environment during peat accumulation. The presence of ramboidal pyrite indicates the coal bearing formation experienced reduction of sulfates, from anoxic environment, with iron ions during coalification.

Kei Islands are known to have hydrocarbon potentials in shallow rock layers, trapped by folds and faults. This potential is characterized by the amount of gas seepage found in Kei Kecil, Kei Besar and Tayandu Island. The study was conducted in central and southern part of Kei Besar Island through outcrop observations and stratigraphic measurements aim to recognize the physical characteristics of rock. Kei Besar Island located in the easternmost part of Australian continental passive margin separated by the extension of Aru Through. Digital Elevation Model of Kei Besar Island shows that the northern part of research area has a steeper morphology than the southern. The stratigraphic characteristic in the central part of research area dominated by clastic limestone showing a shallowing-up stacking pattern. While in the southern part, the lithology dominated by coralline limestone contains many fragments of coral and large foraminifera. Stratigraphic analysis shows that lithology in the study area was formed in carbonate submarine fan which formed Elat Formation. This formation underlained by shallow carbonate rock which contain large foraminifera from Tamangil Formation. Tamangil Formation interfingered with lower part of Weduar Formation. Based on the analysis of surface data above, concluded that subsurface exploration is necessary to reconstruct the petroleum system in research area.

Kabupaten Bantul, Provinsi Daerah Istimewa Yogyakarta (DIY) mempunyai banyak kekayaan sumberdaya alam dengan potensi keindahan dan keanekaragaman geologi yang merupakan hasil dari proses  masa lampau yang mempunyai potensi untuk menjadi kawasan geowisata. Penelitian ini dilakukan untuk mengidentifikasi potensi situs geologi (geosites), dengan mencari dan memetakan situs geologi yang tersebar di kawasan ini. Penelitian dilakukan menggunakan metode studi pustaka, observasi lapangan, analisis laboratorium, analisis penilaian situs geologi. Analisis penilaian situs geologi menggunakan metode penilaian menurut Kubalíková, 2013 digunakan untuk memberikan penilaian mengenai kelayakan dari lokasi situs geologi. Hasil analisis kuantitatif dari metode penilaian yang dilakukan, menunjukkan hanya 8 (delapan) situs geologi yang memungkinkan untuk dikembangkan menjadi objek geowisata. Berdasarkan semua situs yang ditemukan, maka dibuat 2 (dua) jalur Geotrack wisata yaitu jalur rute barat dan rute timur.

Silicified coal is formed by the enrichment of mineral in the coal seam. Due to the very hard form, silicified coal interferes with the effectiveness of mining causing more time for excavation. The purpose of this study was to determine the characteristics and distribution of silicified coal in PT. Mitrabara Adiperdana Tbk, which is used as a reference for selective mining. This research has conducted mapping which includes surface and subsurface data collection and laboratory tests. Surface data includes geological structure, stratigraphy, distribution patterns and observations of megascopic characteristics of silicified coal inseam 3. Subsurface data include drill point and coal seam cross-sections in Sector Y. Laboratory analysis is carried out from the outcrop coal sample and overburden of seam 3. Silicified coal inseam 3 has two types, which are type A, which is more fragile, and type B which is harder. In general, silicified coal in the research area was formed on the coal layer that has direct contact with the tuffaceous sandstones. In fault areas, silicified coals are found along the fracture zone where coal seams come in contact with tuffaceous sandstones. Thus, the recommended mining area is based on the silicified coal distribution map.

Wonosegoro is part of western Kendeng Zone, the depocenter of North East Java Basin that is mainly filled with thick pelagic and volcaniclastic sediments. Sandstones lithofacies is presence within the research area and may act as a useful tool to reach the aim of this research, which is to determine the provenance. The research has conducted field observation, petrographic analysis on seven thin sections of sandstones from the field, and bathymetry interpretation from benthic foraminifera. Overall, the sandstones are predominantly composed of lithic components (72.73%-88.05%) and significant matrix (25%-50%), thus classified as lithic greywacke. The combination of quartz-feldspar-lithic (QFL) and the heavy minerals composition suggest that the sandstone provenance in research area is a product of Oligo-Miocene volcanic of southern mountain range.