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Depositional environments of the Carboniferous-Permian Taiyuan Formation (southern North China Block) as deduced from trace elements and from carbon and oxygen isotopes

Lv Dawei, Hu Guangqing, Van Loon Antonius Johannes, Wu Dun

Geological Quarterly

2021

Vol. 65, No. 1

art. no. 1

Limestone layers are extensively developed in the continental/ocean transitional Taiyuan Formation. This formation accumulated on the southern North China Block. The precise environmental conditions of the Taiyuan Formation are still controversial. More information about these topics is presented here on the basis of the analysis of trace elements (Mo, V, Cd, Cr, U, Th), which can be used to determine characteristics of the depositional environment, and of carbon and oxygen isotopes (δ13C and δ18O) in limestone samples from the Huainan Coal Basin. Samples were taken for the purpose from cores of all 13 limestone levels, obtained from a coal-exploration borehole (code P2) in the Huainan Coal Basin. It was found that the δ18O values show a decreasing trend, suggesting a gradual rise of the sea level in a warm climate. Three negative shifts of δ13C appear in a lower, a middle and an upper limestone layer, accompanied by relative enrichment of the redox-sensitive elements (Cd, Cr, Mo and V). These three layers are thus deduced to have been deposited in a warm climate with a high sea level and with more terrigenous input than during deposition of the other limestone layers. The redox elements and elemental ratios (V/Cr, Th/U) in the limestones suggest deposition in an oxygen-rich sea with high salinity.

Sedimentological distinction in glacigenic sediments between load casts induced by periglacial processes from those induced by seismic shocks

Van Loon Antonius Johannes, Pisarska-Jamroży Małgorzata, Woronko Barbara

Geological Quarterly

2020

Vol. 64, No. 3

626--640

Loading processes and the resulting load structures induced by processes related to periglacial conditions are compared to those induced by seismic shocks. The load structures themselves are relatively easily recognizable but the responsible trigger mechanism is, though depending on the geological context, commonly difficult to establish. Load structures like load casts, pseudonodules, ball-and-pillow structures and flame structures are commonly ascribed to instable density gradients within sediments and to differential loading, but their formation always requires liquefaction. In glacigenic sediments, deformation structures have most commonly been ascribed to periglacial processes (as a type of cryoturbations), but it becomes ever more clear that glacigenic sediments can, particularly during ice-front fluctuations, be affected by faulting-related earthquakes (due to glacio-isostatic adjustment), and the thus triggered seismic shocks may result in deformations, including - most commonly - load structures. We inventory the evidence that may help to distinguish, on the basis of textural and structural features, load structures with a seismic origin from those that result from periglacial processes, taking into account that truly diagnostic criteria do not exist.