International Geologiical Congress - Oslo 2008


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MPV-01 General contributions to volcanology - Part 1


Deccan Trap's degassing and climate changes during the late Maastrichtian: Insight from the sulfur cycle


Cédric Pellan, Université Paris VI - Pierre et Marie Curie (France)
Annachiara Bartolini, Museum National d'Histoire Naturelle (France)
François Baudin, Université Paris VI - Pierre et Marie Curie (France)
Silvia Gardin, Université Paris VI - Pierre et Marie Curie (France)
Eric Humler, Université de Nantes (France)


Flood Basalt eruptions may have played a key role in past climatic changes by releasing huge amount of volcanic gazes in the atmosphere. Continental Flood Basalt provinces consist of an accumulation of single-lava flows covering a surface of 1 Mkm2 corresponding to a volume of 1Mkm3 over a short-lived period that lasts about 1 Ma typically. Along fissures from tens to hundreds of km long, large amounts of gas (CO2, SO2, H20, HF...) are injected in the upper troposphere and lower stratosphere at the vents, while the lava flows covered huge areas.
We focused on the ∼65Ma Deccan Province degassing in sulfur. To estimate the pre-eruption sulfur concentration, we used an empiric Fe0/S ratio based on 335 samples fresh MORB glass analysis. Thus, we can predict the initial S content of Deccan Trap's magmas, ranging from 933 ppm (Neral Fm) up to 1879 ppm (Mahabaleswhar Fm). Remaining sulfur in the lavas was also measured by pyrohydrolysis and ion chromatography. The difference between these two values may represent amount (in ppm) of sulfur degassed during eruptions. Consequently, the sulfur cycle should record such a massive injection over a short geological period.
Samples of Maastrichtian and Paleocene chalk from DSDP site 217 were pyrohydrolysed and the sulfur content was measured by ion chromatography.
Thus, the amount of sulfur structurally substituted in carbonate (Carbonate Associated Sulfate) is known. Samples also underwent isotopic data (ä13C and ä18O) acquisition, in order to access to climatic changes recorded during this period. Large inputs of sulfur due to volcanic activity in the external cycle should lead to severe perturbations.


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