Provenance of the Late Quaternary sediments in the Andaman Sea: Implications for monsoon variability and ocean circulation

Abstract

We present a geochemical and Sr-Nd isotopic study on a sediment core collected from the Andaman Sea in an attempt to reconstruct the Late Quaternary weathering and erosion patterns in the watersheds of the river systems of Myanmar and understand their controlling factors. Age control is based on nine radiocarbon dates and d18 O stratigraphy. The rate of sedimentation was strongly controlled by fluctuations of the monsoon. We identify three major sediment provenances: (1) the Irrawaddy catchment, (2) the western slopes of the Indo-Burman-Arakan (IBA) mountain ranges and the Andaman Islands, and (3) the catchments of Salween and Sittang and the Bengal shelf, with the first two contributing 30-60% of the material. Enhanced contributions from juvenile sources and corresponding positive shifts of d 18 O are observed at seven time periods (11-14, 20-23, 36, 45, 53, 57, and 62 ka) of which five are synchronous with cooling of the northern hemisphere, suggesting a link between the changes in sediment provenances and the shifting of the locus of the summer monsoon, southward from the Himalayas, without substantial reduction in intensity. Our data, and that from other cores in the region suggest that an eastward moving surface current disperses sediments, derived from the Bengal shelf and western margin of Myanmar, from the eastern Bay of Bengal into the western Andaman Sea and that its strength has increased since the LGM. The existence of this current during the LGM implies that the Andaman Sea and the Bay of Bengal were well connected during the last glacial period.

Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

“…The possibility of addition of material from Andaman islands to the CAT is ruled out due to absence of major rivers on islands and the presence of coral reefs which grew since LGM21. Two other records from the western part of Andaman Sea2223 (Fig. 1) have reported high radiogenic Nd.…”

“…Given that the basic and ultrabasic materials tend to weather more quickly than the high crystalline rocks because of textural differences41, the IBR region which is characteristic of recent volcanic dykes, ophiolites, mud volcanoes, flysch1722424344 could have weathered preferentially. It is probable that the increased catchments due to intensified monsoon might have energized the supply of radiogenic Nd to the total sediment discharge of Irrawaddy River.…”

“…Location map (generated by using GMT68 (v4.5)) of ( a ) elevation contours and river paths of Myanmar, bathymetry of the Andaman Sea along with; ( b ) Alcock and Sewell seamount complex; ( c ) shelf sediments of Arakan (SK175/3), river mouths off Irrawaddy (SK175/38), Sittang (SK175/48), Salween (SK175/52), gravity core SK168 (all from this study); ( d ) published records MD77-169, MD77-176, RC12-34412; SK234/6022; NGHP01-17A23.…”

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.…”

“…The major lithologies these rivers drain are presented in Figure 3. The Irrawaddy River flows, in its upper reaches, through the Gangdese batholith, metamorphic rocks and ophiolites of FIGURE 3 | The lithology map of the drainages of the Irrawaddy, the Salween and the Tanintharyi River basins falling in the Tibet, China, and the Myanmar, modified after (Awasthi et al, 2014;Chapman et al, 2015). possible eastern continuation of the Indus Tsangpo Suture Zone, the volcanics from a Cretaceous arc and sediments produced during the collision (Stephenson and Marshall, 1984;Maury et al, 2004;Najman et al, 2004;Szulc et al, 2006;Allen et al, 2008), associated post-collision intrusive igneous rocks (Darbyshire and Swainbank, 1988) and basic/ultrabasic rocks of the eastern syntaxis of the Himalaya.…”