Abstract:

  Based on the C and O isotopic profile of 114 analytic results obtained by the standard method of phosphorolysis, we have discussed the compositions and evolution of δ13C and δ18O recorded in the carbonates in the Yanshan area during the interval of 16 10 Ga and their geological implications. The C and O isotopic profile reveals a secular cyclic evolutionary trend in ascending order of carbonates, i.e., δ13C shows a shift from -3‰ to +30‰ and δ18O shows a range from -20‰ to -80‰. An elevation of δ13C correlated with the relative variation from intertidal to subtidal sedimentary environments, the sea level rising, the flux of fresh water and the high organic productivity, whereas a decreasing shift corresponded to a transition from supratidal to intertidal facies or sedimentary boundaries in term of sequence stratigraphy. The nodular limestone or shalestone has negative δ13C excursion, representing the maximum sea flooding sediments from Gaoyuzhuang and Hongshuizhuang Formations respectively. The O isotopic composition and evolution suggests that a salted water paleoenvironment was prevailing over the research area during the synsedimentary period from the Upper Yangzhuang to Lower Wumishan Formations, i.e., the more salted interval, which recovered later in Upper Wumishan Formation. The current study and C and O isotope evolution are consistent with the previous research results, which provides isotopic evidence supporting the existence of an aulacogen basin alone, and furthermore are highly concordant with the C and O isotope evolutions in Belt Supergroup in North America and MidRiphean in Ural, Russia, which suggests a response to a global paleoocean geochemical setting.

Key words:

Key words: Yanshan area; MesoNeoproterozoic; carbonates; C and O isotope; implications