Abstract
We present a multi-proxy mineral record based on X-ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western Indus Shelf in order to reconstruct changing weathering intensities, sediment transport, and provenance variations since 13ka. Core Indus-10 is located northwest of the Indus Canyon and exhibits fluctuations in smectite/(illite+chlorite) ratios that correlate with monsoon intensity. Higher smectite/(illite+chlorite) and lower illite crystallinity, normally associated with stronger weathering, peaked during the Early–Mid Holocene, the period of maximum summer monsoon. Hematite/goethite and magnetic susceptibility do not show clear co-variation, although they both increase at Indus-10 after 10ka, as the monsoon weakened. At Indus-23, located on a clinoform just west of the canyon, hematite/goethite increased during a period of monsoon strengthening from 10 to 8ka, consistent with increased seasonality and/or reworking of sediment deposited prior to or during the glacial maximum. After 2ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite/goethite, which we attribute to widespread cultivation of the floodplain triggering reworking, especially after 200years ago. Over Holocene timescales sediment composition and mineralogy in two localities on the high-energy shelf were controlled by varying degrees of reworking, as well as climatically modulated chemical weathering.
Highlights
Understanding how climate change affects continental environments and weathering processes is a key component of quantifying solid Earth–climate interactions
A study of the geophysical properties and clay mineralogy of sediments from the Indus Shelf was conducted at two sites in ~70 m water depths west of the Indus River mouth and canyon
The coherent variation in smectite/ and illite crystallinity with monsoon intensity at Indus-10 is consistent with a climatic control to chemical weathering processes since 14 ka
Summary
Understanding how climate change affects continental environments and weathering processes is a key component of quantifying solid Earth–climate interactions. There has been limited interest in the physical and mineralogical properties of sediments in the Northern Arabian Sea over any timescale, especially during the Holocene to Recent, despite the relatively well-defined variability in climate and sea level known for this period. This lack of data is despite the fact that physical and mineralogical properties have been shown to be effective in tracing sediment transport in several areas worldwide (e.g., Balsam et al, 1995; Liu et al, 2003; Adler et al, 2009). Sediment supply is dominantly from the Himalayas and Karakoram (Clift et al, 2004; Garzanti et al, 2005)
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