Paper No. 85-15
Presentation Time: 4:45 PM
INTEGRATED CHEMOSTRATIGRAPHY OF UPPER VINDHYAN SEQUENCE CARBONATES, CENTRAL INDIA: IMPLICATIONS FOR DEPOSITIONAL AGE AND GLOBAL CORRELATIONS
The Vindhyan Basin is an intracratonic sedimentary basin exposing Proterozoic strata in central India. The age of the Lower Vindhyan Sequence is constrained to ~1600 Ma, whereas the age of the overlying Upper Vindhyan Sequence (UVS) remains poorly constrained despite paleontological discoveries that have direct bearing on the timing of metazoan evolution. Though the onset of sedimentation in the UVS occurred prior to ~1074 Ma—constrained by kimberlite intrusion into the lowermost Kaimur Group—the overlying Rewa and Bhander groups have been assigned to the late Neoproterozoic based on the discovery of an Ediacara-type fossil assemblage and a potential cap carbonate atop glacial sediments in the Lakheri Limestone (Bhander Group). By contrast, recent data—including paleomagnetic similarity between Bhander strata and the ~1074 Ma Majhgawan kimberlite, as well as Pb-Pb ages of 1073 ± 210 and 908 ± 72 Ma for the Lakheri and Bhander limestones, respectively—suggest that the UVS may be as much as 500 Ma older than previously proposed. Fundamental disagreement between geochronologic, paleomagnetic, and paleontological data persists in part because of the lack of an integrated chemostratigraphy for UVS carbonates. Here we present high-resolution carbon isotope and trace element (Sr, Fe, Mn) data from the Lakheri and Bhander limestones. In the Lakheri Limestone, δ13C values are moderately positive (+2.0 to +3.2‰) with minor episodic shifts down to values near +1‰. These results are inconsistent with deposition following Neoproterozoic glaciation—where large shifts to negative δ13C values would be expected—and instead support deposition during the late Mesoproterozoic to early Neoproterozoic, wherein the global δ13C signal is characterized by moderately positive values punctuated by low-magnitude negative excursions. Together with recent geochronology, our data suggest that reinterpretation of purported Ediacara-type fossils in the UVS is required. Furthermore, future study of UVS strata will provide insight into global events during the late Mesoproterozoic to early Neoproterozoic—a critical period in Earth history that remains understudied.