Isotope Stratigraphic Curves of Devonian Marine Carbonates in Ganqi Profile

Ganqi profile with a length of 13 km is located by a road from Mianyang to Pinwu .Started at Guixi grain depot and ended at limekiln of Shawozi. The Devonian of Longmenshan belongs to shallow sea and shallow water deposits .The clastic rocks of lower part of low一Devonian overlay unconformly on the lightly metamorphic siltstone and silty slate of lower一middle Silurian. Middle part of low一Devonian to lower part of mid一Devonian are charcteraized by interbedded clastic and carbonate rocks. Upper part of mid一Devonian and up一Devonian are entirely carbonate deposits. The marine carbonates of Devonian from Ganxi profile are determined serially for Sr, C, O isotopes and Na,Sr,Mn、Al、Fe, Mn trace elements as well as cathodolumines feature. Sr and C isotope stratigraphic curves of marine carbonates of Devonian are first set up some conclusions are as follows. 1. Based on studies of trace element and C,O isotopes most samples of marine carbonate and brachiopods fossil have the same strorium and carbon isotopic features as they deposited. 2. Sr and C isotope stratigraphic curves of Devonian marine carbonates and fossils from Ganxi profile are familiar with the function curves of geological age (B. N. Popp et al 1986;W. H. Barke, 1982;L. R. Kump and Garrets.1986).They implicates that Sr and C isotopic compositions of marine carbonates and fossil are controlled by globe factors(but C isotopic composition is superimposed influence of regional geological process)and have significance on statigraphic correlation. 3. C and O isotopic components of marine carbonates vary obviously at geological boundaries and can be used as subsidiary criteria for stratigraphic division. 4. When deposited,marine carbonates formed by organism or non一organism have no detectable fractionation of strontium isotope.