Exclusive governance of the 1st and 2nd order sequence framework by regional extensional tectonics as demonstrated on the Gondwanian Tethyan margin

• Autorzy: Krishna J.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

Krishna et al. (2000) invoked the role of extensional tectonics to explain the explicit discordance of the 1st order MFS of the Jurassic-Cretaceous depositional sequences on the two margins of the Tethys, respectively i. e. above the Late Kimmeridgian Eudoxus Zone on the European Tethyan margin, and above the Middle Oxfordian Schilli Subzone in Kachchh (India). By way of further demonstration of the exclusing role of the regional extensional tectonics is here interpreted the basal SB of the sequence near the Pliensbachian/Toarcian boundary in different basins of the Gondwanian Tethyan margin from East Africa and Madagascar in the west to Indonesia and Australia in the east inclusive of the entire Tethyan margin of the Indian subcontinent. The so determined basal SB is again found unambiguously discordant with the corresponding SB on the European Tethyan margin. The interpretation of the basal SB is based on the presence of tectonically induced marked change of environment and litho-biofacies along with subaerial stratigraphic gap of varying duration between the Triassic-Liassic stratigraphic units below, and Toarcian or younger units above with or without ammonoids in Somalia, Ethiopea, Kenya, Tanzania, Madagascar; Baluchistan, Attock and Hazara regions of Pakistan; Kachachh, Jaisalmer, Malla-Johar and Spiti regions of India; areas of Nepal; Indonesia and Australia. These facies changes and subaerial stratigraphic gaps are also evident in the intra-cratonic non-marine Gondwana basins, as also in the exposed and onshore/offshore well sections on the Indian East coast. Igneous activity is also manifested in a few regions of the Gondwanian Tethyan margin. In the East African countries, Madagascar and Baluchistan the non-marine Triassic sands are uncoformably overlain by marls and limestones with basal Toarcian Bouleiceras. In Kachchh the late Late Bajocian Leptosphinctes bearing sediments are underlain by several hundred meters of sediments before reaching the Precambrian basement. In Spiti the marine ammonoid devoid Liassic limestones are overlain by marls with Early Toarcian Alocolytoceras. In the Indian intra-cratonic non-marine successions too, there is evidenced a large stratigraphic gap between Triassic-Liassic and Late Jurassic - Early Cretaceous stratigraphic units. In the Indian East coast Krishna-Godavari and other basins the non-marine Triassic units are overlain by Late(?) Jurassic - Early Cretaceous marine units. To conclude, the 1st and 2nd order sequence stratigraphic framework on the two margins of the Tethys is exclusively governed by the respective highly differing regional/basinal extensional tectonics and so is highly discordant. In contrast the agreement at the 3rd order is solely guided by the global sea-level changes. Further, the tectonically governed high magnitude and low frequency 1st and 2nd order framework is unable to distort the eustatically guided low magnitude high frequency 3rd order framework.

Słowa kluczowe

EN

sequence stratigraphy; tectonics; eustatics; Gondwanian; Tethys; sequence boundary; SB; maximum flooding surface; MFS

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 51--51
• Opis fizyczny: Bibliogr. 1 poz.

Twórcy

autor

Krishna J.

• Department of Geology, Banaras Hindu University, Varanasi-221005, India,

Bibliografia

• 1. Krishna J., Pathak D. B., Pandey B. and Ojha J. R. 2000. Transgressive sediment intervals in the Late Jurassic of Kachchh, India. GeoResearch Forum, 6: 321-332.