DARRIWILIAN (MIDDLE ORDOVICIAN) CARBON ISOTOPE STRATIGRAPHY IN BALTOSCANDIA

摘要

1 INTRODUCTIONFluctuations in the oceanic dissolved inorganic carbon (DIC) stable isotope composition (δ13C) are considered to be indicators of environmental changes.Unless the marine carbonates are diagenetically altered,their carbon isotope composition is expected to reflect original composition of DIC in seawater.Excursions of δ13C in marine carbonates can be explained by changes in carbon circulation in ocean water.Positive excursions have been attributed to increased organic carbon burial in epeiric seas during episodes of high primary productivity，which may have been produced by intense nutrient upwelling associated with glacial times (e.G.，Himantian Excursion；Brenchley et al.，1994).The glacioeustatic sea level drop might increase weathering of carbonate platforms which resulted in increase of δ13C in fluvial input to the ocean (Kump et al.，1999).Alternatively,the increased organic burial in deep oceans during the sea level rise and stratification may be responsible for the increase of δ13C in platform carbonates (e.G.，Ireviken Excursion；Cramer and Saltzman，2007).