Carbon and oxygen isotope systematics of a Paleoproterozoic cap-carbonate sequence from the Sausar Group, Central India
Authors:
Mohanty et al
Abstract:
Well-preserved sedimentological features of the Paleoproterozoic age Sausar Group of central India indicate glaciogenic origin for the diamictite in the lower part of the unit. Deglaciation was responsible for a marine transgression and the deposition of proximal glaciomarine facies and a cap-carbonate, followed by fine clastics with manganese ore. Analyses of δ13C and δ18O contents in the carbonate unit overlying the diamictite, together with Sr and Ba contents and REE data, indicate the preservation of primary geochemical signatures. The average δ13Ccarb content ranges between − 3.1‰ and + 0.1‰ V-PDB, having peak negative δ13C excursions of up to − 7.4‰ V-PDB, similar to Paleoproterozoic and Neoproterozoic cap-carbonates elsewhere. High Sr and Ba contents indicate the presence of aragonite and barite precursors, similar to well-studied Neoproterozoic cap-carbonates. A single continuous carbonate unit shows δ13C excursions from − 4.4 to + 2.6‰ V-PDB. The lithological association and chemostratigraphy are comparable with the carbonate–tillite association of the Huronian Supergroup of Canada, the Snowy Pass Supergroup of the USA, the Transvaal Supergroup of South Africa, and the Turee Creek Group of Australia.
Contradictory correlations of Paleoproterozoic glacial deposits: local, regional or global controls?
Author:
Young
Abstract:
There is little agreement among recently proposed correlation schemes for Paleoproterozoic glaciogenic rocks scattered thinly around the globe. Correlations are hindered by the dearth of tight geochronological control on the ages of glacial deposits, which are notoriously difficult to date. Most attempts at global correlation are based on comparison to the Huronian Supergroup in Canada, which contains three glaciogenic formations. Although the two lower glacial units were deposited in a rift setting and have a restricted distribution even in North America, they have been used in attempts to effect international correlations. The Gowganda Formation, together with correlatives, comprises the thickest and by far the most widespread Paleoproterozoic glacial deposits in North America. Glacial deposits are also reported from South Africa, Western Australia and elsewhere, where they appear to fall within the time period as the Huronian Supergroup (2.45-2.2 Ga) but attempts to correlate individual diamictite-bearing units to the three Huronian glaciogenic formations have proved difficult. None of the Huronian glacial formations has been precisely dated. Until such geochronological data are available it is practical and prudent to recognize that, during the early Paleoproterozoic, as in the Cryogenian, the Earth was susceptible to glaciations that could be triggered by a variety of local events including uplift, related to rifting and compressional orogeny. Within the 250 million years of the ‘Huronian Glacial Event’ (2.45 - 2.2 Ga) it is commonly assumed that ice sheet fluctuations were globally synchronous but this has not been demonstrated.
Dating Palaeoproterozoic glacial deposits of the Fennoscandian Shield using detrital zircons from the Kola Peninsula, Russia
Authors:
Gärtner et al
Abstract:
New age constraints from detrital zircon U-Pb geochronology from clastic sediments and diamict deposits obtained maximum depositional ages for the Seidorechka and Polisarka Sedimentary formations of the Imandra-Varzuga Greenstone Belt of theKola Province, NW-Russia. These delimit the deposition of Palaeoproterozoic Huronian-age glacial deposits of the Fennoscandian Shield from c. 2430 Ma to less than 2411 Ma. The time constraint allows comparison to the first two of three possible glacial intervals recognized in the Huronian Supergroup, Canada, and South African diamict deposits. Intercontinental comparisons support these constraints, the assumption of a glacial origin of the diamictites and, further, the eventually global extent of the event.Similar age distributions and depositional ages of c. 2400 Ma within the Neverskrukk Formation of the Pechenga Greenstone Belt support a correlation with the Imandra-Varzuga Greenstone Belt succession, which was traditionally based on lithostratigraphic observations.
The detrital zircon age spectra of eight analysed samples show an Archaean dominance and reoccurring peaks around 2800-2750 Ma,which indicate similar origins for the zircons. Such peaks are corroborating with a major global crustal generation event being recorded in detrital zircon spectra worldwide. Additionally, certain age populations around 2440 Ma and 2500 Ma are present andindicate a correlation with intrusive magmatism that affected the region at that time and support a correlation based on overlapping age distributions
