Clim. Past Discuss., 9, 583-613, 2013
www.clim-past-discuss.net/9/583/2013/
doi:10.5194/cpd-9-583-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Cyclone trends constrain monsoon variability during Late Oligocene sea level highstands (Kachchh Basin, NW India)
M. Reuter1, W. E. Piller1, M. Harzhauser2, and A. Kroh2
1Institute for Earth Sciences, University of Graz, Heinrichstraße 26, 8010, Graz, Austria
2Department of Geology and Palaeontology, Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria

Abstract. Important concerns about the consequences of climate change for India are the potential impact on tropical cyclones and the monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as an indicator of tropical cyclone activity along the NW Indian coast during the Late Oligocene warming period (~27–24 Ma). Direct proxies providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system in the Early Miocene. The vast shell concentrations comprise a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deep to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished each recording a relative storm wave base depth. (1) A shallow storm wave base is shown by nearshore mollusks, corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclind foraminifers, Eupatagus echinoids and corallinaceans; and (3) a deep storm wave base is represented by an Amussiopecten–Schizaster echinoid assemblage. Vertical changes in these skeletal associations give evidence of gradually increasing tropical cyclone intensity in line with third-order sea level rise. The intensity of cyclones over the Arabian Sea is primarily linked to the strength of the Indian monsoon. Therefore and since the topographic boundary conditions for the Indian monsoon already existed in the Late Oligocene, the longer-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~26 Ma followed by a period of monsoon weakening during the peak of the Late Oligocene global warming (~24 Ma).

Citation: Reuter, M., Piller, W. E., Harzhauser, M., and Kroh, A.: Cyclone trends constrain monsoon variability during Late Oligocene sea level highstands (Kachchh Basin, NW India), Clim. Past Discuss., 9, 583-613, doi:10.5194/cpd-9-583-2013, 2013.
 
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