Spectral analysis is applied to geochemical data from a deep-water Permian-Triassic Boundary (PTB) section across PTB in Dongpan, Guangxi for high-resolution cyclostratigraphic research. The characteristics of the Milankovitch Cycles have been well recorded in the strata of the Dongpan section. Spectrum on Ce/La records shows especially that the ratios among its three preponderant cycles in the section are 5:2:1, which well displays the phenomenon of the sedimentary cycles driven by orbital force. The Milankovitch theory is further confirmed by the Paleozoic records.
Because literatures about the lipid compositions of modern soils in karst areas are scarce,we have studied the soil horizons overlying the Heshang(和尚) Cave that has provided paleoclimate records from speleothem lipid contents.Our analysis reveals a series of n-alkanes,free fatty acids,n-alkanols and n-alkan-2-ones distribution and relative abundance changing with the depth,and in which the ratios of the lower molecular weight to higher molecular weight n-alkanes,free fatty acids,n-alkanols and n-alkan-2-ones have a peak at a subsurface depth of 5 to 10 cm.An accompanying peak in 17β(H),21β(H)-hop-22(29)-ene(diploptene)and a shift to less negative n-alkane carbon isotopic values also identify this layer in the karst soil.This pattern indicates the existence of a subsurface soil layer in which the microorganisms that produce these compounds are especially abundant.The carbon isotopic values of individual plant wax n-alkanes are about 3‰ greater at the base of the 30-to 40-cm soil profile than in the surface layer,probably as a result of selective microbial degradation of n-alkanes from different primary sources.The lipids and carbon isotopic values of individual plant wax n-alkanes study of the overlying soil show a strong microbial activity in this karst soil and help in interpreting the lipid compositions and specific carbon isotopic value of n-alkanes of the stalagmites of the Heshang Cave for paleoenvironmental reconstructions.
The trace fossil Zoophycos was enriched in the lower part of the Guadalupian Maokou Formation of Permian in Laibin, Guangxi of South China, and characterized by observable lamellae within its spreiten. Associated with these lamellae are the prolific coccus- and spirillum-shaped microbe fossils. These microbes morphologically identified are 0.4―3.0 μm in diameter or length. Molecular fossils, including normal alkanes (dominated by C18, without an odd-over-even predominance), acyclic isoprenoids (such as pristane (Pr) and phytane (Ph)), extended tricyclic terpanes, pentacyclic triterpanes, steranes, al-kylcyclohexanes, dibenzothiophenes, benzonaphthothiophenes, benzobisbenzothiophenes, were in-strumentally identified in the wackestone characterized by the occurrence of abundant Zoophycos (composite ichnofabric indices are 4) and crowded microbial fossils. The value of the Pr/Ph ratio is less than 1, indicative of a dysoxic condition. The identification of abundant sulfur compounds (the thio-phene series) related to the contribution of reductive sulfur favors the occurrence of sulphate-reducing bacteria. The association of abundant microbial colonies with microbial molecular fossils within the spreiten suggests that trace fossils Zoophycos would be a multifunctional garden carefully constructed by the Zoophycos-producer, where different microbial colonies were orderly and carefully planted and cultured in different minor lamellae within spreiten. Hence, it is proposed that the Zoophycos-producer symbiosed with microbial colonies on the mutual basis of food supply and the redox conditions.
GONG YiMingXU RanXIE ShuChengHUANG XianYuHU BinQI YongAnZHANG GuoCheng
