Geochemical characteristics and correlation of oil and nonmarine source rocks from Mongolia
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New bulk and molecular organic geochemical analyses of source rock and oil samples from Mongolia indicate the presence of lacustrine-sourced petroleum systems in this frontier region. Samples of potential source rocks include carbonate, coal, and lacustrine-mudstone lithologies that range from Paleozoic to Mesozoic in age, and represent a variety of tectonic settings and depositional environments. Rock-Eval and total organic carbon data from these samples reflect generally high-quality source rocks, including both oil- and gas-prone kerogen types, mainly in the early stages of generation. Bulk geochemical and biomarker data indicate that Lower Cretaceous lacustrine mudstone found in core from the Zuunbayan field is the most likely source facies for the East Gobi basin of southeastern Mongolia. Oil and selected source rock samples from the Zuunbayan and Tsagan Els fields (both in the East Gobi basin) demonstrate geochemical characteristics consistent with nonmarine source environments and indicate strong evidence for algal input into fresh- to brackish-water source facies, including elevated concentrations of unusual hexacyclic and heptacyclic polyprenoids. Despite similarities between Zuunbayan and Tsagan Els oil samples, biomarker parameters suggest higher algal input in facies sourcing Zuunbayan oil compared to Tsagan Els oil. Tsagan Els oil samples are also generated by distinctly more mature source rocks than oil from the Zuunbayan field, based on sterane and hopane isomerization ratios.The foreland slope in the south marginal Junggar Basin (SMJB) is geologically favorable for mass lithologic oil and gas reservoir accumulation. Based on outcrops, thin sections, individual-well facies, and cross-well stratigraphic correlation, the stratigraphic distribution and features of the Upper Jurassic Kalazha Formation were investigated in the SMJB. There are two sedimentary sources in the southwest and southeast Kalazha Formation, which thin out from south to north and vanish in the northern slope. Fan deltas occur in the southwest, and braided river deltas occur in the southeast. Kalazha reservoir rocks and sedimentary facies were predicted using joint 2D and 3D seismic impedance inversion. According to the overall analysis, the Kalazha Formation in the foreland slope is favorable for hydrocarbon accumulation, considering structural highs as the destination of long-term hydrocarbon migration and the updip wedge-out zone in the north with potential lithologic traps. The accumulation model was established with source rocks, reservoir rocks, caprocks, and migration systems for the lithologic hydrocarbon reservoirs in the Kalazha Formation in the SMJB. As per the model and regional stratigraphic and structural features, Kalazha lithologic hydrocarbon reservoirs mainly formed in the annular updip wedge-out zone in the foreland slope. Our deliverables may provide useful information for mass lithologic hydrocarbon accumulation in the foreland slope and deep to ultra-deep hydrocarbon exploration in the SMJB.
Lithology
Outcrop
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Protolith
Felsic
Banded iron formation
Greenschist
Basement
Geochronology
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Continental Margin
Red beds
Diachronous
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Yilgarn Craton
Greenstone belt
Hornblende
Arsenopyrite
Dike
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During the last 10 m.y., the Nanga Parbat Haramosh Massif in the northwestern Himalaya has been intruded by granitic magmas, has undergone high‐grade metamorphism and anatexis, and has been rapidly uplifted and denuded. As part of an ongoing project to understand the relationship between tectonism and petrologic processes, we have undertaken an isotopic study of the massif to determine the importance of hydrothermal activity during this recent metamorphism. Our studies show that both meteoric and magmatic hydrothermal systems have been active over the last 10 m.y. We suggest that the rapid uplift of the massif created a dual hydrothermal system, consisting of a near‐surface flow system dominated by meteoric water and a flow regime at deeper levels dominated by magmatic/metamorphic volatiles. Meteoric fluids derived from glaciers near the summit of Nanga Parbat were driven deep into the massif along the transpressional faults causing δ 18 O and δD depletions in the gneisses and marked oxygen isotopic disequilibrium between mineral pairs from the fault zones. The discharge of these meteoric fluids occurs in active hot springs that are found along the steep faults that border the massif. At deeper levels within the massif, infiltration of low δ 18 O magmatic fluids caused δ 18 O depletions in the gneisses within the migmatite zone. These low δ 18 O fluids were derived from the young (<4 Ma), relatively low δ 18 O granites (∼8‰c) that are found within the core of the massif. Geochronological evidence in the form of fission track and 40 Ar/ 39 Ar cooling ages and U/Pb ages on accessory minerals from the granites and gneisses provide a constraint on the timing of fluid flow in the surface outcrops we examined. Fluid infiltration in the migmatite zone rocks located along the Tato traverse was coeval with metamorphism, granite emplacement, and rapid denudation, in the interval 0.8–3.3 Ma. Finally, we infer from the presence of active hot springs that significant flow systems continue to be active at depth within the central portion of the Nanga Parbat‐Haramosh Massif.
Massif
Leucogranite
Migmatite
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