Vindhya supergroup
The Vindhya supergroup is a powerful geological system of the Proterozoic in central India . It documents over 1000 million years of geological history , including gaps in the layers .
etymology
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The Vindhya supergroup, English Vindhyan supergroup is, after the Vindhya Range named. Vindhya ( विन्ध्य ) is derived from the Sanskrit word vaindh (lock, block).
Occurrence
The supergroup covers an area of 105,000 square kilometers and extends from the Indian state of Bihar in the east via Chhattisgarh , Madhya Pradesh and Uttar Pradesh to Rajasthan in the west.
Geological background
At the turn from the Archean to the Proterozoic around 2500 million years BP , the Aravalli Kraton (or Bhandara Kraton) was stabilized by post-orogenic granite intrusions . The thickened continental crust of the craton was then reduced again by rift processes . At the beginning of the Proterozoic, the sedimentary sequences of the Bijawar group and the Mahakoshal group were deposited in the trenches created in this way , which - in contrast to the Vindhya supergroup - were later deformed and metamorphosed. After this, towards the end of the Paleoproterozoic, the Vindhya supergroup was sedimented in an east-west rift system. The rift process was accompanied by right-sided shear, which induced secondary northwest-southeast oriented rift systems.
description
The mostly flat sediments of the Vindhya supergroup, up to 4500 meters thick, were deposited in an intracratonic rift basin during the Proterozoic. The basin was oriented in an east-west direction and opened to the sea to the west. The paleo-current generally ran to the northwest, which indicates a continental erosion area to the south. The paleoclimate at that time must have been warm and humid.
The predominantly marine sediments were not sunk very deep and are therefore not overprinted metamorphically. Only on the western edge of the basin were they slightly folded and disturbed. The sedimentation did not occur uniformly, so the supergroup shows great differences in thickness and facies between the eastern edge of the basin (in the Son valley ) and the western edge (in the Chambal valley ).
lithograph
Ripe sandstones , shale clays , intraformational conglomerates (rare), porcelainites (originated from volcanic plastics), limes , dolomites and phosphorites were mainly deposited .
The super group can be divided into four groups . These are from hanging to lying :
The Semri group formed in the period 1800 to 1600 million years BP ( Statherium ) is also referred to as the Lower Vindhya , the following three groups are combined to the Upper Vindhya . The sedimentation ended with the Bhander group in the Neoproterozoic between 700 and 600 million years BP. The lower and upper Vindhya are separated from each other by a discordance . The Lower Vindhya represents a restless rift stage marked by seismic processes, whereas in the Upper Vindhya there were essentially calmer sedimentation conditions and the basin now only slowly sagged ( sag basin ).
The Vindhya supergroup overlays the Bijawar group and the metamorphic basement of the Bundelkhand-granite-gneiss complex discordantly. In turn, it is covered by the Gondwana supergroup (on its southern edge), the sediments of the Lameta group and the basalts of the Dekkan Trapp . Its northern edge is veiled by alluvium of the Ganges plain.
Fossil content
The Vindhya supergroup is characterized by rich stromatolite finds . There are also spores , acritars , algae , primitive brachiopods , vascular plants and ichnofossils .
The sediments of the Lower Vindhya are a spectacular window for biota of the late Paleoproterozoic . In particular, the phosphorites in the Tirohan limestone with their astonishing preservation yielded multicellular eukaryotes (algae filaments) that are 400 to 600 million years older than previously known finds. Like many of the carbonate horizons in the Vindhya supergroup, the formation is very rich in stromatolites and contains, for example, the genera Baikalica , Collenia , Colonella , Conophyton and Kussiella .
Individual evidence
- ↑ Eriksson, PG et al: The 2.7 - 2.0 Ga volcano-sedimentary record of Africa, India and Australia: evidence for global and local changes in sea level and continental freeboard . In: Precambrian Research . tape 97 , 1999, pp. 269-302 .
- ↑ Mazumder, R., Bose, PK and Sarkar, S .: A commentary on the tectono-sedimentary record of the pre-2.0 Ga continental growth of India vis-à-vis a possible pre-Gondwana Afro-Indian supercontinent . In: Journal of African Earth Science . tape 30 , 2000, pp. 201-217 .
- ↑ Bose, PK, Banerjee, S. and Sarkar, S .: Slope-controlled seismic deformation and tectonic framework of deposition: Koldaha Shale, India . In: Tectonophysics . tape 269 , 1997, pp. 151-169 .
- ^ Ahmad, K .: Paleogeography of central India in the Vindhyan period . In: Rec. Geol. Surv. India . tape 87 , 1958, pp. 531-548 .
- ↑ a b Chanda, SK and Bhattacharya, A .: Vindhyan sedimentation and paleogeography: post-Auden developments . Ed .: Valdiya, KS et al., Geology of Vindhyachal. Hindustan Publishing Corporation, Delhi 1982, p. 88-101 .
- ↑ Kumar, S., Schidlowski, M. and Joachimski, MM: Carbon isotope stratigraphy of the Paleo-Neoproterozoic Vindhyan Supergroup, central India: implications for basin evolution and intrabasinal correlation . In: Journal of the Palaeontological Society of India . tape 50 (1) , 2005, pp. 68-81 .
- ↑ Javaux, EJ: Origins and Evolution of Eukaryotic Endomembranes and Cytoskeleton . Ed .: Jékely, G., The early eukaryotic fossil record. Landes Bioscience, Austin, Texas 2007, pp. 1-19 .
- ↑ Bakliwal, PC and Dwivedi, CS: A preliminary note on the occurrence of stromatolites in parts of Sawai Madhopur district, Rajasthan . In: Workshop on Stromatolites: Characteristics and Utility - Volume Abstracts . Geological Survey of India, Udaipur 1978, p. 10 .
- ^ Barman, G .: Importance of Conophyton in Vindhyan Stratigraphy . In: Symposium Vindhyans of Central India, Abstracts . Geological Survey of India, Bhopal, S. 41 .