Intensification of Early Miocene Monsoon Detected Using Cap 47 Record From the Seasonal Growth Bands in the Well Preserved Gastropod shells from the Kachchh Basin, Western India
Abstract
Miocene Climate Optima (MCO) is one of the unique extreme time period in the earth history characterized by global annual temperature excess of 3-8°C compared to the pre industrial level . The atmospheric pCO2 level of 500 ppm was an important factor in driving the temperature; similar or higher than the temperature rise witnessed in the post-industrial era. Thus, MCO is the immediate time period in geological time scale to draw comparison with climatological scenario envisaged today or in the future. The onset of this extreme climate event ( ca. 17-14.7 Ma) took place during early Miocene ~ Burdigalian. The δ18OVPDB records from the benthic foraminifera from the sediment core (IODP site U1337) revealed isotopic excursion of 0.75‰ and 1.5‰ denoting onset and peak of MCO respectively [1], where the lighter isotopic values implies increase in the freshwater influx. Here we report early Miocene seasonal records of temperature and precipitation (/freshwater influx) fluctuations at the coastal Arabian sea region revealed from the simultaneous analysis of stable C, O and clumped isotope across the growth bands Turritella sp. from the Kachchh basin. Four well preserved shell specimens investigated in this study reveal δ13C variability from -1.80 ‰ to -4.83 ‰ with an average of -2.94 ‰ and δ18Ocarb variability from -2.66‰ to -7.06‰ with an average of -4.98‰. Clumped isotope analysis of the carbonate retrieved from the successive growth bands of two shells showed a variability of Δ47 values from 0.66 to 0.75 ‰ in the CDES scale that yielded a range of temperature from 17°-36°C using [2] equation projected into ARF. The estimated δ18Owater composition varies from -0.67 to -4.62‰ in VSMOW scale. A quantitative rainfall variability from 1700 to 2500 mm within a year was reconstructed using the δ18Ocarb- Rainfall equation given by [3]. Comparison with the modern climatological data shows intensification of rainfall or presence of freshwater flux from the glacial melting during Early Miocene, consistent with the palynological data. With the present understanding on the stratigraphy of the basin, we will discuss if the extreme event captured in this study represents a prelude of MCO and is consistent with the paleoclimate models' results.
Ref: [1] Holbourn etal., 2015, Geology; [2] Ghosh et al., 2006, GCA; [3] Chakraborty and Ramesh 1998, PIAS.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP12A..04B
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1626 Global climate models;
- GLOBAL CHANGE;
- 4934 Insolation forcing;
- PALEOCEANOGRAPHY