The Yacoraite Formation (Salta rift, Argentina) consists of Maastrichtian–Danian lacustrine carbonate and siliciclastic deposits with interbedded volcanic ash layers, organized in four third‐order stratigraphic sequences. It offers the exceptional opportunity to jointly apply in situ zircon and carbonate U‐Pb geochronology that resulted in two distinct depositional age depth models. Ages of the youngest zircon population from ash layers were linearly interpolated to derive a zircon depositional age depth model. A carbonate depositional age depth model was instead obtained from dated carbonate phases including microbialites, ooids, oncoids of calcitic and dolomitic mineralogy as well as early lacustrine calcite cements. Mean ages were defined from different carbonate phases belonging to the same layer and then linearly interpolated. Sedimentation rates were calculated from both depth models between pairs of dated samples and used to estimate the age of sequence boundaries, as well as the duration of the four stratigraphic sequences. The zircon and carbonate depositional age depth models agree with biostratigraphic constraints and exhibit excellent consistency. The onset and end of sedimentation were estimated at 68.2 ± 0.9 Ma and 62.3 ± 0.6 Ma (duration ca 5.7 Ma) via zircon geochronology and at 67.9 ± 1.7 Ma and 61.9 ± 1.3 Ma (duration ca 6.0 Ma) via carbonate geochronology. Results from this study show that with suitable samples and a newly implemented working strategy, in situ U‐Pb dating of depositional and early diagenetic carbonates represent a valuable chronostratigraphic tool for estimating sedimentation rate and duration in poorly time‐framed depositional systems.

/pdf/depositional-age-models-in-lacustrine-systems-from-zircon-1b3f5855.pdf

Depositional age models in lacustrine systems from zircon and carbonate U‐Pb geochronology

Evolution of Ordovician YJ1X ultra-deep oil reservoir in the Yuecan oilfield, Tarim Basin, NW China

Multiple fluid flow events and diversity of hydrothermal minerals in Neoproterozoic to lower Paleozoic carbonate reservoirs, Tarim Basin, NW China

The complexity of diagenesis and hydrocarbon accumulation in the deep reservoirs in southern Junggar Basin restricts hydrocarbon exploration in the lower reservoir assemblage. The lithofacies and diagenesis of reservoirs in the Cretaceous Qingshuihe Formation in the Gaoquan structure of the Sikeshu Sag, southern Junggar Basin were analyzed. On this basis, the thermal history was calibrated using calcite in-situ U-Pb dating and fluid inclusion analysis to depict the hydrocarbon accumulation process in the Gaoquan structure. The results show that the Qingshuihe reservoir experienced two phases of calcite cementation and three phases of hydrocarbon charging. The calcite cements are dated to be 122.1±6.4 Ma, 14.4±1.0 Ma –14.2±0.3 Ma. The hydrocarbon charging events occurred at around 14.2–30.0 Ma (low-mature oil), 14.2 Ma (mature oil), and 2 Ma (high-mature gas). The latter two phases of hydrocarbon charging contributed dominantly to the formation of reservoir. Due to the S-N compressive thrust activity during the late Himalayan period since 2 Ma, the traps in the Gaoquan structure were reshaped, especially the effective traps which developed in the main reservoir-forming period were decreased significantly in scale, resulting in weak hydrocarbon shows in the middle-lower part of the structure. This indicates that the effective traps in key reservoir-forming period controlled hydrocarbon enrichment and distribution in the lower reservoir assemblage. Calcite U-Pb dating combined with fluid inclusion analysis can help effectively describe the complex diagenesis and hydrocarbon accumulation process in the central-west part of the basin. 

Restoration of reservoir diagenesis and hydrocarbon accumulation process by calcite in-situ U-Pb dating and fluid inclusion analysis: A case study on Cretaceous Qingshuihe Formation in Gaoquan Structure, southern Junggar Basin, NW China

The absolute timing of carbonate cement formations can provide insights into porosity evolution and hydrocarbon accumulation in reservoirs. In this study, scanning electron microscopy‐based cathodoluminescence (SEM‐CL), quantitative mineralogical analysis and laser ablation inductively coupled plasma‐mass spectrometry U–Pb dating were performed on calcite cements from sandstones in the fourth member of the Upper Triassic Xujiahe Formation in the western Sichuan Basin. Two samples yielded U–Pb ages of 149.5 ± 31.1 Ma and 190.0 ± 180.5 Ma (2σ), suggesting late diagenetic precipitation of calcite cements. The backscattered electron and SEM‐CL images indicated that the cements precipitated after feldspar dissolution. Combined with palaeo‐temperature evolution, these results suggest that the timing of calcite cement precipitation occurred between the Late Jurassic to Early Cretaceous. Rapid accumulation of sediment in the western basin in response to the Yanshanian Orogeny may have caused stratum overpressure, resulting in geofluid activity and calcite precipitation in the Xu4 sandstone.

LA‐ICP‐MS U–Pb dating of calcite cement in Upper Triassic tight‐gas sandstone reservoirs, western Sichuan Basin, SW China

Direct dating Paleo-fluid flow events in sedimentary basins

The invention discloses an ancient oil-water interface recognition method and application thereof in the reestablishment of a crude oil charging history. According to the ancient oil-water interface recognition method, an ancient oil-water interface of oil and gas reservoirs can be rapidly and accurately recognized, and therefore, the crude oil charging history is reestablished. The ancient oil-water interface recognition method comprises the following steps: sampling different depth positions of a reservoir targeted formation of a single well in a research area so as to obtain reservoir samples, and recording corresponding depths of sampling points; acquiring adsorbed hydrocarbon extracts on the surfaces of reservoir sample particles, and determining the contents of trace elements in the adsorbed hydrocarbon extracts; drawing a distribution profile map of the content of the trace elements along the depthaccording to the depths of the sampling points and the data of the trace element content of adsorbed hydrocarbon on the surfaces of the corresponding reservoir sample particles; and recognizing an inflection point where the trace element content starts to continuously deviate from a base line in the map along the depths of the sampling points from large to small according to the distribution profile map, wherein the depth corresponding to the inflection point is the depth of the ancient oil-water interface of the oil and gas reservoirs.

Ancient oil-water interface recognition method and application thereof in reestablishment of crude oil charging history

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Direct dating Paleo-fluid flow events in sedimentary basins

Ancient oil-water interface recognition method and application thereof in reestablishment of crude oil charging history