华北寒武纪苗岭世晚期δ13C演化及生态环境特征

豫北和鲁西地区寒武系苗岭统上部δ¹³C演化表现为下降趋势,芙蓉统下部δ¹³C呈上升趋势,并表现出显著正漂移,这次δ¹³C正漂移出现在三叶虫Chuangia带内,可与世界各地芙蓉统排碧阶的δ¹³C正漂移(SPICE)对比。δ¹³C演化趋势与三叶虫、牙形石、浮游植物的繁盛与萧条表现出一定的耦合关系。苗岭世晚期三叶虫大规模绝灭时期,δ¹³C呈逐渐降低趋势,苗岭世末期新的三叶虫科大量出现时期,δ¹³C呈上升趋势。另外,海平面升降对δ¹³C演化具有明显的影响,海侵时期沉积的碳酸盐岩其δ¹³C呈逐渐增大趋势,高水位早期沉积的碳酸盐岩具有较高的δ¹³C值,高水位晚期或海平面下降期沉积的碳酸盐岩的δ¹³C呈逐渐下降趋势。海平面变化是导致生态环境变化、生物群落演化、碳同位素组成演化的关键因素。

Carbon Isotope Evolution and Ecological Environments in the Late Miaolingian Epoch of the Cambrian,Northern China

Studies of carbon isotope records from upper Miaolingian?lower Furongian series in Cambrian in northern Henan and western Shandong, northern China, indicate a falling trend δ13C in upper Miaolingian series followed by a remarkable positive shift in lower Furongian series. This positive shift, which spans the trilobite Chuangia zone in northern China,is comparable to the global Steptoean Positive Carbon Isotope Excursion （SPICE） in the early Furongian. The δ13C trend is covariant with the rise and fall of populations of trilobites, conodonts and phytoplanktons. Mass extinction of trilobites occurred in the upper part of the Guzhangian stage,Where δ13C decreased to low values. However, new trilobite populations flourished at the top of the Guzhangian stage,Where δ13C gradually rose to high levels, exhibiting a strongly positive excursion in the Paibian stage. Carbon isotope evolutions are constrained by changes in sea level and sedimentary environment: for example,gradually increasing values of δ13C are always found in carbonates deposited during a seawater transgression, peaking in the lower part of high-water system tracts；however, carbonates from the upper part of a high-water system tract or formed during the sea-level falling stage usually have a low δ13C record. Therefore, sea-level changes were crucial ininducing changes in ecological environments, biological communities and carbon isotope evolution in the late Miaolingian and early Furongian series in the Cambrian.