Geochemistry of Neoproterozoic cap carbonate of banded iron-formation of the Rizu serie in Jellal abad Zarand
الموضوعات :
Mehdi Kianian
1
(Department of Geology, Faculty of Basic Sciences, Sciences & Research Branch, Islamic Azad University, Tehran, Iran)
Ahmad Khakzad
2
(Department of Geology, Faculty of Earth Science, Shahid Beheshti University, Tehran, Iran)
Iraj Rasa
3
(Department of Geology, Faculty of Earth Science, Shahid Beheshti University, Tehran, Iran)
Mansor Abedini
4
(Department of Geology, Faculty of Earth Science, Shahid Beheshti University, Tehran, Iran)
الکلمات المفتاحية: Global glaciations, Carbon isotope, Diamictite, Dropstone, Glacial,
ملخص المقالة :
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 δc13 ,δo18 values of carbonates in area are low , ranging From- 2.65 to -6.79 per mil versus (PDB), and- 6.48 to – 15.21permil (PDB), respectively, whereas the excursion wide range of 18-oxygen isotope reflect the alteration and diagenetic processes. The high concentration of iron and manganese and high index of alteration (Fe/Sr=720 or Mn/Sr=52) is associated by decreasing 13-carbon isotope. The δc13 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.
