Montney Formation (MF) source rock located in northeastern British Columbia (BC), Canada, was analyzed to determine its depositional conditions and organic matter source input other than to determine their level of thermal maturity. The high total sulfur (TS) (2.23-20.86 wt.%) and good to very good total organic carbon (TOC) content (0.3-5.87 wt.%) in the analyzed samples give good evidence that the deposition of MF source rock was in a marine environment under reducing conditions. A mixed marine-terrestrial derived organic matter (OM) for the Montney source rock that was deposited in a marine dysoxic environment is deduced from the composition and distribution of different biomarker traces. Thus, the previous result is supported by the high short-chain n-alkanes ratio, accompanied by carbon preference index (CPI) around unity, high concentration of tricyclic terpanes, high C24 tricyclic/C24 tetracyclic, hopane/sterane ratios ranging from low to moderate, as well as the relationship between regular sterane compositions. During deposition of the MF source rock, it can be noticed that more land organic materials this was deduced according to the high waxiness index. From maturity ratios of Ts/(Ts + Tm), C32 22S/(22S + 22R) homohopane, moretane/hopane and 20S/(20S + 20R) and ββ/(ββ + αα) C29 it can give a conclusion that the source rock is mature to postmature of hydrocarbon generation.
This study investigates marginal marine deposits found in the Tanjong and Sandakan formations from the Early to Late Miocene in Northeast Sabah. It examines sedimentology, trace elements (TE), rare earth elements (REE), hydrocarbon generation potential, and palynology to understand provenance, depositional environments, and paleoenvironmental conditions. Facies analysis identified four associations in the Tanjong and three in the Sandakan Formation, ranging from fluvial-deltaic to shallow marine environments. Mangrove-associated taxa, herbaceous and tree ferns typical of freshwater swamps, and coastal plants indicate a transition zone between terrestrial and marine environments. Siliciclastic deposits in the Northeast Sabah basin show varying redox conditions, ranging from dysoxic to oxic, as indicated by the Ni/Co, V/Cr, and U/Th ratios. These fluctuations may be linked to the tectonic evolution of the Sulu Sea and related sea-level lowstands. The low abundance of marine dinoflagellate cysts, along with high levels of rainforest and peat swamp pollen, suggests periods of subaerial exposure that contributed to the redox conditions. C-values and Sr/Cu ratios in the mudstone samples indicate semihumid to humid and warm conditions during the Miocene. Additionally, the distribution patterns of rare earth elements (REE) and the (La/Yb)N and Th/U ratios reveal consistent sedimentation rates in marginal marine environments. Palynofacies analysis indicates water column fluctuations, leading to oxidation during transport, resulting in low TOC values and kerogen types III and IV. Ternary diagrams of immobile TEs indicate that mudstone samples originate from active continental margins, linked to the rifting of the Sulu Sea during the Early to Middle Miocene. In contrast, sandstone samples exhibit characteristics of passive margins, likely due to recycled sediments from the early "Rajang Group Accretionary Complex." The plots for immobile TEs in the mudstones suggest intermediate and mafic sources, supporting the idea of uplift and erosion from deepwater sediments, as well as volcanic activity from the Cagayan and Sulu Arc systems. Sandstone samples may be sourced from acidic rocks associated with felsic intrusions in the Segama Valley, indicating a significant continental basement beneath the ophiolite. Keywords: Marginal marine, trace element, provenance, palynology, tectonic setting, Northeast Sabah.
Carbonaceous shales of the Early Eocene Dharvi/Dunger Formation in the onshore Barmer Basin, northwest India were studied for the first time by integrating geochemical and organic petrological analyses. The carbonaceous shales of the Early Eocene Dharvi/Dunger Formation are characterized by a higher organic carbon content (TOC) of >10 wt % and consist mainly of a mixture of organic matter of types II and III kerogen, with exhibited hydrogen index values ranging between 202 and 292 mg HC/g TOC. The dominance of such kerogen is confirmed by the high amounts of huminite and fluorescent liptinite macerals. Consequently, the carbonaceous shales of the Early Eocene Dharvi/Dunger Formation are promising source rocks for both oil and gas generation potential, with oils of high wax contents, according to pyrolysis-gas chromatography results. The chemical and optical maturity results such as low values huminite/vitrinite reflectance, production index, and T max show that most of the examined carbonaceous shale rocks from the outcrop section of the Kapurdi mine have entered the low maturity stage of oil generation, exhibiting a range of immature to the very early-mature. Therefore, as highlighted in this study, the substantial abundance in hydrocarbon generation potential from these carbonaceous shales in the Dharvi/Dunger Formation may represent future conventional petroleum exploration in the southern part of the Barmer Basin, where the Dharvi/Dunger Formation has reached deeper burial depths.