Geochemistry of Neoproterozoic cap carbonate of banded iron-formation of the Rizu serie in Jellal abad Zarand

In the study area, the various of cap carbonates include medium to coarse (saddle dolomite) grains of dolomites, are situated uppermost of sequence of Rizu Formation. The sequence of Rizu serie contains of various lithology, quartzite sandstone, turbidities (Greywacke) with association of ore minerals(Magnetite- Hematite- Jasper) , in the form of Banded iron- Formations, (BIFs) .The existence of dropstones with heterogeneous grains (Diamictite) within fine matrix of carbonate are the indicators for glaciations episodes, which are located under the cao carbonate. Chemical analyses of carbonates showed that the δc۱۳ ,δo۱۸ values of carbonates in area are low , ranging From- ۲.۶۵ to -۶.۷۹ per mil versus (PDB), and- ۶.۴۸ to – ۱۵.۲۱permil (PDB), respectively, whereas the excursion wide range of ۱۸-oxygen isotope reflect the alteration and diagenetic processes. The high concentration of iron and manganese and high index of alteration (Fe/Sr=۷۲۰ or Mn/Sr=۵۲) is associated by decreasing ۱۳-carbon isotope. The δc۱۳ depleted carbonates reflect climate changes from glacial (Icehouse) to greenhouse conditions that deposited during sea- level rise after retreating and deglaciation after math global glaciations snowball earth.

Keywords:

Global glaciations , Carbon isotope , Diamictite , Dropstone , Glacial