"Lacustrine carbonate clinoforms deposit can reflect ancient lake condition like paleoclimate and lake type. Complex lithofacies of a carbonate-dominated clinoform package in lower Permian Lucaogou low order cycle, Bogda Mountains, NW China, provide clues on clinoform-forming processes in a half-graben lake. The clinoform package is ~5.2 m thick, prograding from S to N for ~200 m with a maximum 15o dip angle, and spans ~4 km laterally. A clinoform consists of a lower siliciclastic-rich and an upper carbonate-rich beds, forming a clinoform cycle. Results of petrographic study of 30 thin sections suggest that the clinoform package is composed of mixed siliciclastic-carbonate rocks. Carbonate-rich bed is composed of diagenetically-altered lithic packstone and wackestone, and siliciclastic-rich clinoform of micritic sandstone. The foundation rock is mainly microbial boundstone, indicating a shallow littoral environment.
The carbonate-rich beds mainly consist of coarse peloids, rip-up intraclasts, aggregate grains, and volcanic lithics. The siliciclastic-rich clinoform is rich in coarse volcanic lithics. Both types of clinoforms contain abundant current laminations, indicating frequent strong current activities. The lack of evidence of unidirectional current flow suggests that the carbonate-dominated clinoform package was probably primarily formed by wave and longshore current processes. Unlike grains in wave-built terrace in the Glenns Ferry Formation (Swirydczuk et al., 1979, 1980), few ooids were observed in the studied strata, which do not have local sediments as nucleus and are often broken. This indicates that the wave was not facing the lake margin directly but was more oblique to the lake margin. The carbonate-dominated clinoform package is thus interpreted as a bar or spit, controlled primarily by lake shoreline morphology and strong wave and current activities. The shift between carbonate and siliciclastic rich clinoform beds within a clinoform cycle suggests high-frequency changes in climatic conditions.
Detrital lithics were mainly derived from northern Tianshan suture zone to the south. The carbonate clasts were transported from a nearby carbonate factory at the lake margin. The Lucaogou lake was a balanced-filled lake in a semiarid, seasonal climate and had persistent longshore currents caused by strong wind and wave activities"--Abstract, page iii.
Wronkiewicz, David J.
Geosciences and Geological and Petroleum Engineering
M.S. in Geology and Geophysics
Missouri University of Science and Technology
ix, 96 pages
© 2016 Yiran Lu
Thesis - Open Access
Geography -- China
Lithofacies -- China
Geology, Stratigraphic -- Permian
Sedimentation and deposition -- China
Electronic OCLC #
Lu, Yiran, "Origin of lacustrine carbonate-dominated clinoforms in the lower-Permian Lucaogou low-order cycle, southern Bogda mountains, NW China" (2016). Masters Theses. 7609.