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The Kerek Formation in Sojomerto, Kendal, Central Java is the westernmost part influenced by the Kendeng zone. The presence of sandstone lithofacies in the study area can be a useful tool for determining composition and the provenance. This study involved field observation and analysis of eight thin sections of sandstone from the field. There is no notable petrographic difference across the sandstone succession in the study. the sandstones are predominantly composed of lithic components (48%-63%), matrix (2%-16%), and quartz (1%-24%) thus classified as lithic arenite and lithic wacke. The combination of quartzfeldspar-lithic (QFL) diagram indicates that the sandstone in research area was the result of volcanic activity which is in the southern part of the study area.

Analysis of foraminifera in geology,usually being used to find the age of rocks/ sediments and depositional environment. In this study, recent foraminifera was used not only to determinethe sedimentary environment,but also to estimate the ecological condition of the water through a statistical approach.Analysis was performed quantitatively in 10 surface seabed sediment samples in Weda Bay North Maluku. The analysis includes dominance (Sympson Index), diversity and evenness (Shannon Index), and the ratio of planktonic -benthic. The results were shown in the plotting diagram of M-R-T (Miliolid-Rotalid-Textularid) to determine the depositional environment. Quantitative analysis was performed using Past software (paleontological version Statistic 1:29).The analysis result showed there was no domination of certain taxon with a moderate degree of evenness and stable communities and considerably a moderate diversity. The results of this analysis indicated that research area had a stable water conditions with the optimum level of carbonate content, oxygen supply, salinity, and temperature. The ratio of planktonic and benthic indicate the relative depth, which was deeper the water increased the percentage of planktonic foraminifera. Based on M-R-T diagram showed the distribution of sediment deposited on exposed carbonate (carbonate platform) environment with normal saline.

Sentolo formation that is included in the Kulon Progo stratigraphic series has a wide distribution. Although there have been a number of studies on it, more detailed research is needed, as there are still many unexplored outcrop locations. Moreover, there are still a lot of questions about the stratigraphic relationship between Sentolo Formation and Oligocene-Miocene volcanic series of Kulon Progo. Based on this background, this study is focused on the existence of foraminifera fossil in Sentolo Formation as an indicator of palaeoecological conditions at the time Sentolo Formation was deposited. This research is very important to get a detail understanding about the indicators that are influential at the time of deposition process of Sentolo Formation in research area. Based on palaeoecological analysis, the palaeoecology at the time Sentolo Formation deposited was normal marine continental slope waters. Meanwhile, the community structure of foraminifera indicates a stable water conditions in a marine environment that was not disrupted by volcanism, so it becomes a good factor for the growth of foraminifera. Whereas the presence of volcaniclastic material mixed with carbonate which is occurred in the lower part of Sentolo Formation were interpreted as reworked of older volcanic rock.

The Eocene Lower Ngimbang carbonaceous shales are geochemically proven hydrocarbon source rocks in the East Java Basin. Sedimentary facies of source rock is important for the source evaluation that can be examined by using biomarkers and carbon-13 isotopes data. Furthermore, paleogeography of the source sedimentation can be reconstructed. The case study was conducted on rock samples of Lower Ngimbang from two exploration wells drilled in Cepu area, East Java Basin, Kujung-1 and Ngimbang-1 wells. The biomarker data include GC and GC-MS data of normal alkanes, isoprenoids, triterpanes, and steranes. Carbon-13 isotope data include saturate and aromatic fractions. Various crossplots of biomarker and carbon-13 isotope data of the Lower Ngimbang source samples from the two wells show that the source facies of Lower Ngimbang shales changed from transitional/deltaic setting at Kujung-1 well location to marginal marine setting at Ngimbang-1 well location. This reveals that the Eocene paleogeography of the Cepu area was composed of land area in the north and marine setting to the south. Biomarkers and carbon-13 isotopes are powerful data for reconstructing paleogeography and paleofacies. In the absence of fossils in some sedimentary facies, these geochemical data are good alternatives.

The Sunda Basin and Asri Basin are two adjacent basins located to the east of the South Sumatra Basin and north of the North West Java Basin. Several geochemical studies have been conducted in these two basins, indicating different depths of the oil window. Some research even mentions variations in the depth of the oil window in the Sunda Basin. The purpose of this study is to compare the differences in maturity depth in these two basins and compare their organic material characteristics. The research methods used involve conducting Source Rock Potential analysis and Biomarker analysis. This study involves 99 wells scattered across both basins. Wells in the Sunda Basin have Total Organic Carbon (TOC) values ranging from 0.04% to 16.03% wt, with the top oil window estimated at vitrinite values around 0.55-0.6%. The Banuwati formation has an average TOC value of about 1.946% wt with a maturity level of around 0.682%. The Lower Zelda formation has an average TOC value of about 1.387% wt with a maturity level of around 0.568%. The Sunda Basin is a mixture of Kerogen types II and III, where type III tends to produce gas when mature. In contrast, the Asri Basin contains Kerogen types I and II, which tend to produce oil when mature. Wells in the Sunda Basin generally reach maturity phase at a depth of 6000 feet, while those in the Asri Basin reach maturity at around 7000 feet.