Controls on sediment supply to the Holocene Thar Desert: Sr and Nd isotopes with bulk-sediment geochemical constraints

Abstract

Abstract Deserts must be supplied with sediment in order to accrete. The Thar Desert, lying east of the Indus River in South Asia, might be expected to be largely supplied with sediment from that drainage. In this study, we use a combination of major and trace element bulk-sediment geochemistry, together with Sr and Nd isotopes, to constrain the provenance of postglacial dune sand. Our data indicate a stronger influence from mafic source rocks in the Sindh Desert compared to that in Cholistan. Nd isotopes imply sediment was largely derived from the lower Indus River during the early and pre-Holocene post-glacial time. The sand is coarser grained in Sindh and retains higher ϵ Nd values in sediment that eroded from mafic rocks in Kohistan and the Karakorum as a result of deflation of deltaic and floodplain areas in the lower reaches by southwesterly summer monsoon winds. The composition of Cholistan dunes, like that in the Eastern Thar Desert, reveals instead more supply from Himalayan sources and more negative ϵ Nd values. The greater Himalayan influence in Cholistan and the Eastern Thar Desert largely reflects finer grain size, a result of the longer transport from the delta source and a preference for more Himalayan supply in the form of finer sediment.