Reconstructing the evolution of the Bengal Fan with physical properties (ReconFan)
Final Report Abstract
Project ReconFan relied on my previous work and publications on different environments of the Bengal Fan and the resulting gaps in knowledge. The focus was on sediment physical and optical property data collected during IODP Expedition 354. General objectives were to (i) unravel the history of turbiditic and hemipelagic deposition on the lower fan as a result of the interplay of Himalayan erosion and Asian monsoon development, (ii) provide high-resolution age control through orbital tuning, biomagnetostratigraphy, and ash identification, and (iii) study the response to climate and monsoon forcing on different time scales. Specifically, sediment physical (wet-bulk density, compressional-wave velocity, and magnetic susceptibility) and optical (LaCie L*, a*, b* reflectance color) properties were processed to assign sediment facies codes for each non-destructive measurement and to determine, through geochemical calibration, the relative proportions of the three major sediment components detritus, biogenic opal, and biogenic carbonate. Also, relative proportions of sand, silt, and clay were determined for the detrital fraction, based on grain-size determinations in turbidites. The ultimate goals was to obtain vital information on the erosional history and the associated amount of fluvial transport via the Ganges Brahmaputra river systems, the depocenter migration with respect to sea-level changes, and the long-term changes in monsoon and climate as documented on the Lower Bengal Fan core transect at 8°N. Given the known response of sediment-physical properties to orbital forcing, I also tested to which extent insolation-based age models can be constructed for all sites with the aid of paleomagnetic and biostratigraphic ground-truth chronological constraints. Orbital tuning of key properties obtained in hemipelagic strata were compared to determine which properties yield the key chronological information. As a result, sediment lightness (L*) proved to be the most reliable tracer of insolation-induced changes in the lower Bengal Fan over the past 1.3 Ma. Both facies assignation and orbital tuning helped testing existing theories of fan growth relative to sea-level rise and fall, and unraveling potential long-term changes in monsoon and climate development at key changes in time.
Publications
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(2016): The last glacial cycle documented on the Lower Bengal Fan – chronological and paleoclimate implications. – AGU Fall Meeting, EOS, Transactions, AGU, San Francisco
Weber, M.E., Dekens, P.S., Reilly, B.T., Lantzsch, H., Selkin, P.A., Das, S.K., Williams, T., Martos Martin, Y.M., Adhikari, R.R., Gyawali, B.R., Jia, G., Fox, L.R., Ge, J., Manoj, M.C., Savian, J.F., Meynadier, L., Spiess, V., France-Lanord, C. and IODP Expedition 354 Scientists
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(2017): Middle to late Pleistocene orbital tuning on the lower Bengal Fan. – IODP Postcruise Meeting, Pokahara, Nepal
Weber, M.E., and Reilly, B.T.
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(2017): Paleoclimate reconstruction on the Lower Bengal Fan for the last 200 ka - Implications for monsoonal development. – AGU Fall Meeting, EOS, Transactions, AGU, New Orleans
Weber, M. E., Lantzsch, H., Dekens, P., Reilly, B.T., Das, S.K., Martos, Y.M., and Williams, T.
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(2017): The Last Glacial Cycle in the Bengal Fan - Chronology and Paleoclimate. – Goldschmidt Conference, Paris, France, abstract volume
Weber, M.E., Dekens, P.S., Reilly, B.T., Lantzsch, H., Selkin, P.A., Das, S.K., Williams, T., Martos Martin, Y.M., Adhikari, R.R., Gyawali, B.R., Jia, G., Fox, L.R., Ge, J., Manoj, M.C., Savian, J.F., and Meynadier, L.
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(2018): 200,000 years of monsoonal history recorded on the lower Bengal Fan - strong response to insolation forcing. – Global and Planetary Change
Weber, M. E., Lantzsch, H., Dekens, P., Das, S.K., Reilly, B.T., Martos, Y.M., Meyer-Jacob, C., Agrahari, S., Ekblad, A., Titschack, J., Holmes, B. and Wolfgramm, P.
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(2018): Bengal Fan depositional history through Pleistocene climate, monsoon, and sea level transitions. – AGU Fall Meeting, EOS, Transactions, AGU, Washington DC
Weber, M.E., and Reilly, B.T.
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(2018): Hemipelagic and turbiditic deposits constrain lower Bengal Fan depositional history through Pleistocene climate, monsoon, and sea level transitions. – Quaternary Science Reviews
Weber, M. E., and Reilly, B.T.
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(2019): Late Pleistocene monsoon history of the lower Bengal Fan (IODP Expedition 354). – 20th Congress of the International Union for Quaternary Research (INQUA) 2019, Dublin, Ireland
Weber, M.E., Reilly, B.T., Dekens, P.S., Lantzsch, H., Das, S.K., Martos, Y.M., and Selkin, P.
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(2020): Middle to Late Pleistocene evolution of the Bengal Fan at 8°N: integrating core and seismic observations for IODP Expedition 354 transect age-depth modeling. – Geochemistry, Geophysics, Geosystems (G3), 1-20
Reilly, B.T., Bergmann, F., Weber, M.E., Stoner, J., Schwenk, T., Spiess, V., and France-Lanord, C.
