Paper No. 5
Presentation Time: 9:00 AM
NEW U-PB SHRIMP AGES AND THE STRATIGRAPHY OF THE CHHATTISGARH BASIN, BASTAR CRATON, CENTRAL INDIA: SIGNIFICANCE FOR GLOBAL STUDIES OF MESOPROTEROZOIC SEDIMENTARY ASSEMBLAGES
BASU, Abhijit1, BICKFORD, Marion E.
2, MUKHERJEE, Arunangshu
3, PATRANABIS-DEB, Sarbani
4, SCHIEBER, Juergen
5, GUHEY, Rajeeva
6, RAY, Ranjan
7, BHATTACHARYA, Purbasha
8 and DHANG, Pratap
4, (1)Department of Geological Sciences, Indiana Univ, 1001 E 10 Street, Bloomington, IN 47408, (2)Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244-1070, (3)Central Ground Water Board, Bhujal Bhawan NH-IV, Faridabad, India, (4)Geological Studies Unit, Indian Statistical Institute, 203, Barrackpore Trunk Road, Kolkata, 700108, India, (5)Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405, (6)Department of Geology, Government Science College, Raipur, India, (7)Central Ground Water Board, Reena Apartment, Pachpedi, Raipur, Chhattisgarh, India, (8)Geological Studies Unit, Indian Statistical Institute, 203, B.T.Road, Kolkata, 700108, India, basu@indiana.edu
Newly determined SHRIMP U-Pb ages of magmatic zircons from two tuff beds in the Tarenga Formation near the top of the sedimentary succession in Chhattisgarh basin are 996 +/-14 and 993+/-10 Ma. The tuff beds occur near Dhamda (N21
Î31’06.3” E81
Î19
’45.6”) of the main western (sub-)basin. Earlier we dated similar tuff units from the eastern sub-basin (Sukhda and Sapos tuffs) at 980-1020 Ma and another tuff near the base of the succession, showing that the latter was not older than 1405 Ma. Together these data confirm that the Chhattisgarh basin, consisting of >2 km of unmetamorphosed, mostly marine sedimentary rocks, was filled essentially during the Mesoproterozoic. The sedimentary succession, with thick units of carbonates and shale, including some that are bituminous, offers an almost unique opportunity to study ocean chemistry, including C, O and Sr isotopic compositions, in this period of major significance in the evolution of world oceans and the development of living organisms.
More locally, the new data demonstrate that the Dhamda tuff near the top of the main basin and the Sukhda-Sapos tuffs in the eastern sub-basin, are coeval, representing a single major volcanic event. Previously, the Sukhda tuff was placed in a sandstone member of the Gunderdehi Formation, about 800m below the stratigraphic position of the coeval Dhamda tuff. The new results require a major revision of the stratigraphy of the Chhattisgarh basin. What was considered stratigraphically below the carbonates of the Chandi Formation (~670m thick) must be near or at the top of the Tarenga Formation (~180m thick) overlying Chandi. An unconformity above the Sukhda tuff underlies the volcaniclastic Sarnadih Formation in the east; no unconformity has been observed above the Dhamda tuff or the Tarenga Formation in the main basin. The conformity in the main basin is thus correlative with the Sukhda-Sarnadih unconformity, and constitutes a sequence boundary. Complete sequence-stratigraphic remapping of the Chhattisgarh basin appears necessary.
