Evolution of an organic‐rich lake basin – stratigraphy, climate and tectonics: Piceance Creek basin, Eocene Green River Formation

Abstract

The Piceance Creek basin formed as a continental foreland basin ca 53 to 48 Ma in the early to middle Eocene. On a global basis, the basin contains one of the richest oil shale resources known, where the profundal oil shale deposits, kerogen-rich mudstones (clay and carbonate), exist over most of the basin. Despite its economic importance, the evolution of the Piceance Creek basin is still somewhat unclear. Based on facies association analysis, depositional trends, and gamma ray and Fischer assay data, six evolutionary lake stages are recognized: (i) fresh lake; (ii) transitional lake; (iii) highly fluctuating lake; (iv) rising lake; (v) high lake; and (vi) closing lake. Lake stages are composed of depositional units and characterize large-scale changes in sedimentological patterns, depositional trends and fluctuations in the oil shale richness related to changes in climate and tectonics. Lake stage evolution is also consistent with the global Eocene climate trend. Stage 1 formed prior to the Eocene climate optimum. At the beginning of the Eocene climate optimum, a saline-restricted lake formed (Stage 2) and evolved into the highly fluctuating lake (Stage 3) indicating rapid climate changes during the peak of the Eocene climate optimum. This stage was followed by the rising and high lakes (Stages 4 and 5) after the climate optimum and during a change to a more humid climate. The closing of the lake (Stage 6) was caused by increased sand input from the north, indicating the influence of both tectonics and climate. Based on depositional trends and climate evolution, it is suggested that, during the arid climate, laterally heterogeneous highly cyclic depositional units dominate, whereas, during the humid climate, depositional units form laterally continuous sediments that can be traced over long distances.

Lake sedimentological and ecological response to hyperthermals: Boltysh impact crater, Ukraine

“…The presence of wavy to lenticular lamination in this facies association indicates deposition within an environment of elevated energy. Shoreline wave action and long-shore drift of reworked river discharge material probably produced wavy interlaminated sand and mud (Sturm & Matter, 1978;Renaut & Owen, 1991;Schieber, 1999;T€ anavsuu-Milkeviciene & Frederick Sarg, 2012). Grain-size range and lamination style suggest deposition above the fairweather wave base (FWWB) within a shallow lake which is subject to high sediment supply.…”

“…Normal graded grain size and occasional sudden grain-size break indicate waning flow rates in the upper part of the turbidite beds (Talling et al, 2012), In contrast to FA CT , FA FT represent more distal deposition commonly in the deeper parts of the lake (e.g. Sturm & Matter, 1978;T€ anavsuu-Milkeviciene & Frederick Sarg, 2012); they also may be Bouma (1962). See Fig.…”

“…Normal graded grain size and occasional sudden grain‐size break indicate waning flow rates in the upper part of the turbidite beds (Talling et al ., ), In contrast to FA CT , FA FT represent more distal deposition commonly in the deeper parts of the lake (e.g. Sturm & Matter, ; Tänavsuu‐Milkeviciene & Frederick Sarg, ); they also may be associated with periods of increased river discharge and smaller scale slope failure. Beds of ostracod bioclasts, marlstone and carbonate micrite turbidites originated in shallow lake settings characterized by reduced sediment supply, higher pH and temperature conditions (Kelts & Hsü, ).…”

Origin and reservoirs characterization of lacustrine carbonate in the Eocene Dongying Depression, Bohai Bay Basin, East China

“…3). Lacustrine zones defined by energy levels are (i) the littoral zone above fair-weather wave-base; (ii) the sublittoral zone between fair-weather wave-base and storm wave-base; and (iii) the profundal zone below storm wave base (after Cohen, 2003;Renaut and Gierlowski-Kordesch, 2010;Tanavcuu-milkeviciene and Sarg, 2012).…”

Organic-matter accumulation of the lacustrine Lunpola oil shale, central Tibetan Plateau: Controlled by the paleoclimate, provenance, and drainage system

“…A combination of factors controls the deposition of organic matterrich rocks, including tectonics, climate, global anoxic events, watercolumn stratification, and provenance supply (e.g., Bohacs, 1999, 2001;Tanavsuu-Milkeviciene and Sarg, 2012). In this study, we used an approach integrating element geochemistry and stratigraphy to constrain the regional palaeoclimate and drainage system as well as sedimentary provenance of the Lunpola oil shale and to further reconstruct its depositional history.…”