Mineralogy and geochemistry of fine-grained clastic rocks in the Eocene Huadian Basin (NE China): Implications for sediment provenance, paleoclimate and depositional environment

Abstract

The Huadian Basin is a small fault-controlled basin in northeast China. It is filled by the Eocene Huadian Formation comprising thick lacustrine oil shale-and coal-bearing sediments. Oil shale, mudstone and carbonaceous shale samples have been collected to determine their mineralogical and geochemical (major, trace and rare earth elements) characteristics. These data are used to evaluate sediment provenance as well as paleoclimate and depositional environment. The fine-grained sediments in the Huadian Formation are derived from felsic volcanic rocks and granites, mixed with minor amounts of mafic and sedimentary rocks. Geochemical proxies confirm sediment recycling in the source region. Clay mineralogy and indices of chemical alteration suggest that a subtropical warm and humid climate prevailed during deposition of the fine-grained sediments. The data also suggest climatic changes during deposition of the Huadian Formation, from a stable warm and humid climate causing intermediate chemical weathering (Pyrite Member), to a seasonal dry-wet climate (Oil Shale Member), to a stable warmer and more humid climate causing strong chemical weathering (Carbonaceous Shale Member). Based on inorganic proxies, the fine-grained sediments in the Huadian Formation have been deposited in an anoxic fresh-water environment. Only the sediments of the Oil Shale Member reflect fluctuating freshwater and brackish conditions. The Eocene climatic change controlled lake level variations and water chemistry. A brackish and strictly anoxic environment together with a warm and humid climate was beneficial for the formation of high quality oil shale, whereas fresh-water conditions and warm and more humid climate favored peat accumulation.______________

Organic matter enrichment mechanism of Youganwo Formation oil shale in the Maoming Basin

“…Other evaluation parameters, such as ash and sulfur content, are also influenced by the sedimentary environment [ 36 ]. Several sedimentary factors influence the OM enrichment of oil shale, including sedimentation rate, biological productivity, paleo-redox condition, paleoclimate, changes in water level, detrital matter input, the origin of OM, redox condition and water stratification [ 2 , 18 , 26 , [37] , [38] , [39] , [40] ]. Although the OM enrichment in oil shale has multiple influencing factors, it can be synthetically summarized that bioproductivity, preservation and dilution are the major conditions that control OM enrichment [ 32 ].…”

Geochemistry of the Permian Oil Shale in the Northern Bogda Mountain, Junggar Basin, Northwest China: Implications for Weathering, Provenance, and Tectonic Setting

“…29 Such an elemental enrichment and depletion commonly depend on the intensity of chemical weathering. 30,31 Nesbitt and Young (1982) proposed the chemical index of alteration (CIA) to quantify the degree of weathering CIA = 100 10 In this formula, all values are in molar fractions, and CaO* represents the calcium oxide in silicate minerals. The correction of the carbonate component is not possible because of the lack of data on carbon dioxide.…”

“…During weathering, stable cations (e.g., Al 3+ and Ti 4+ ) form weathered products, whereas unstable cations (e.g., Na + , Ca 2+ , and K + ) tend to be lost in solution . Such an elemental enrichment and depletion commonly depend on the intensity of chemical weathering. , Nesbitt and Young (1982) proposed the chemical index of alteration (CIA) to quantify the degree of weathering CIA = 100 × [Al 2 O 3 /(Al 2 O 3 + CaO* + Na 2 O + K 2 O)] . In this formula, all values are in molar fractions, and CaO* represents the calcium oxide in silicate minerals.…”