Evolution of weathering patterns in the Indo‐Burman Ranges over the last 280 kyr: Effects of sediment provenance on ⁸⁷Sr/⁸⁶Sr ratios tracer

Abstract

[1] A high-resolution study of mineralogy and major element geochemistry combined with Sr and Nd isotopes has been conducted on high sedimentation rate cores collected off the Irrawaddy River mouth in the Andaman Sea and the Bay of Bengal to reconstruct the erosional and weathering history of the Irrawaddy River basin. In both cores, eNd(0) values imply that both glacial and interglacial sediments share a common crustal source: the Irrawaddy River. Strong glacial/interglacial cycles are recorded by 87 Sr/ 86 Sr: interglacial periods yield values between 0.713 and 0.717, whereas glacial periods show higher values between 0.717 and 0.719. Variations of the pedogenic clays (smectite and kaolinite) to primary mineral (feldspar, quartz, illite, and chlorite) ratios show strong precessional cycles, suggesting a control by past changes in the summer monsoon intensity. Each increase in pedogenic clays content is also associated with a net loss of labile elements (Na, K, and Ca) from the detrital minerals under chemical weathering. Sr gives a pseudoisochrons interpreted as a mixing line representing the strength of chemical weathering. During glacial stages, enhanced physical erosion induced by glacier scour and frost action in the highland of the Irrawaddy River basins produced high volumes of unaltered, Rb-rich minerals. The low sea level of glacial times constricted the river to the main channel in the lower reaches and permitted an efficient transport of unaltered Rb-rich minerals with high radiogenic Sr composition from the high relief of the Indo-Burman Ranges and the Tibetan plateau to the Indian Ocean.

Lithology, Monsoon and Sea-Surface Current Control on Provenance, Dispersal and Deposition of Sediments over the Andaman Continental Shelf

“…K is more abundant in feldspar and illite so that the variations in the K/Al ratio may reflect the variations in feldspar and illite abundances present in the sediments due to inherent source signature or due to weathering and transport. Higher K concentration shows more feldspar and illite (Colin et al, 1999;Singh et al, 2008) (Goldstein and O'Nions, 1981;Bouquillon et al, 1990;France-Lanord et al, 1993;Galy et al, 1996Galy et al, , 2010Winter et al, 1997;Pierson-Wickmann et al, 2001;Clift et al, 2002;Singh and France-Lanord, 2002;Banner, 2004;Ahmad et al, 2005Ahmad et al, , 2009Colin et al, 2006;Singh et al, 2008;Viers et al, 2008;Rahaman et al, 2011;Tripathy et al, 2011;Goswami et al, 2012;Awasthi et al, 2014;Ali et al, 2015). These isotope pairs are used as reliable proxies to track the sediment sources, as there are distinct differences in their composition in the different lithologies supplying these sediments.…”

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“…The Andaman Sea drilling sites are within the Nicobar-Andaman Basin, bounded on either side by the Diligent and Eastern Margin Faults. Terrigenous sediment supply to the Andaman Sea is dominantly from the Irrawaddy and Salween Rivers (Colin et al, 1999(Colin et al, , 2006. Analysis of Andaman Sea surface sediments indicates that foraminifers are abundant and well preserved shallower than ~1800 mbsl (>100,000 individuals/gram) and decrease to <100 individuals/gram deeper than 3000 mbsl (Frerichs, 1971).…”

Climate induced temporal change in Sr-Nd isotope ratios in the valley-fill deposits of the Ganga river

“…We also compared Sr and Nd isotopic composition of the Firozpur core sediments with the existing records generated from the Bay of Bengal (France-Lanord et al, 1993;Galy et al, 2008Galy et al, , 2010Colin et al, 1999Colin et al, , 2006 and the Ganga Plain sediments (Rahaman et al, 2009;Agrawal et al, 2013a). France-Lanord et al (1993) investigated variations in the Sr and Nd isotopic ratios in a sediment core from the Bay of Bengal spanning 17 Ma time period and showed that the dominant source of these sediments is the Higher Himalayan Crystallines with lesser contribution from the LH.…”

“…It confirms the stable erosion regime of the Himalaya during millennium and millennial time scale. Colin et al (1999Colin et al ( , 2006 used Sr and Nd isotope composition of sediment core collected from the Bay of Bengal and the Andaman Sea to identify the sources of sediments. On the basis of Sr and Nd isotope Coiln et al (1999Coiln et al ( , 2006 suggested that these basins receive sediments from multiple sources.…”