Carbon isotopic compositions of Cretaceous-Palaeogene boundary (K-PgB) sections in Indian subcontinent: Implications for paleoenvironments

Carbon isotopic compositions of Cretaceous-Palaeogene boundary (K/PgB) sections in Indian subcontinent: Implications for paleoenvironments

Pal, S (1), Jayananda, M (1)

(1) Centre for Earth, Ocean and Atmospheric Sciences (CEOAS), University of Hyderabad, India

Abstract:

Significant fluctuations in climatic conditions and organic matter productivity across the K/PgB is hypothesized in relation to the Deccan volcanic activity. These changes were driven by the episodic release of large amounts of volatiles into the atmosphere. Direct impact of volcanism on the carbon cycle and ecosystem are poorly constrained. To evaluate environmental perturbation induced by the Deccan volcanic activity across K/PgB, isotopic compositions of bulk organic carbon were determined from sedimentary profiles at Mahadeo-Cherrapunji (MCR) shelf section, Um-Sohryngkew (USR) shallow marine section, brakish-marine Jhilmili, terrestrial eastern Deccan volcanic province bole bed (EDVP) sections. Overall, depleted δ13Corg values found in the USR, Jhilmili, and EDVP bole beds suggest low primary productivity linked burning of terrestrial biomass. The depletion of the δ13Corg value of the ocean carbon reservoir was perhaps due to increased organic carbon transfer from continents to the ocean. The average δ13Corg value of MCR section clays is -24.85‰. However grey calcareous shale pre-K/PgB layer (MC-12A) in biozone CF1 is showing δ13Corg value -28.91‰ which is significantly (~4‰) lower than the above and below layers. These unusual low δ13Corg values can be explained by extremely anoxic oceanic environment during K/PgB transition. This negative excursion in δ13Corg value matching well with the major incidences of the Deccan volcanic episodes and convergence of the Indian-plate with the Eurasian plate occurred at 66 Ma and with the Burmese-plate during Maastrichtian. The high CO2 level can be achieved by a warm greenhouse gas emissions. Thus, a combination of extra-basinal and tectono-thermal influence together with the greenhouse effects of volcanism led to an increase of temperature and frequent local sea-level changes that may have resulted in biotic stress and faunal crisis.