Distribution of Indus born Mica along Gulf of Kachchh Coast: Implications in Understanding Current Dynamics

Abstract

Indus is one of the major sources of sediments to the Gulf of Kachchh. Yet only its <63 micron fraction is studied in detail with regards to the offshore current dynamics. Hence here we present our study on characteristic signature of the Indus sediment load (i.e. mica minerals) in >63 micron size fraction along the coast of Gulf of Kachchh. The spatial distribution of mica minerals along the Gulf of Kachchh coast was studied which showed in general decreasing trend as we move along the northern and southern coast of the Gulf of Kachchh but, an increase in amount near the southern mouth at Okha. The study shows that the earlier proposed tidal barrier is ineffective in restricting movement of mica across the mouth of the gulf due to its characteristic transport mechanism. Also the presence of mudflats along the gulf of Kachchh coast plays a vital role as sediment receptors in the active sediment transport processes and mica minerals prove to be a promising simple tracer in studying the Indus born sediments in the region.

Understanding the sediment routing system along the Gulf of Kachchh coast, western India: Significance of small ephemeral rivers

“…The southern coast of the inner GoK shows an anomalous decrease in the concentrations of mica minerals probably because of the input from the Saurashtra rivers draining through Deccan Trap basalt source. Further along the sediment transport path a sharp increase at the westernmost end of the southern coast at the mouth of GoK is also interesting to note, as it is supportive evidence to claim that the currents travel directly from north across the mouth of the GoK (Prizomwala et al 2012).…”

“…As shown by figure 1 and the present understanding of current dynamics (Nair et al 1982;Chauhan 1994;Kunte et al 2003;Chauhan et al 2006;Prizomwala et al 2012) the sediments are believed to enter the gulf mouth from the northwest and travel along the GoK coastline before exiting from southwestern part of the mouth. In this scenario the concentration of Indus River sediment (within sand and heavy mineral content) should be highest at the northwestern end and should subsequently reduce along the rest of the pathway towards east.…”

“…The spatial variability in salinity in the GoK exhibits a characteristic feature of an 'inverse estuary' with higher values in eastern part compared to the western part (Vethamony et al 2007). Present understanding (Nair et al 1982Chauhan 1994;Kunte et al 2003;Chauhan et al 2006;Prizomwala et al 2012, figure 1) reveals that currents enter the gulf from the western through long shore current and travel predominantly along the northern coast of GoK until they reach the central part. Because of the shallower depth and the change in orientation of the central GoK, the currents are deflected towards north and thereafter, they are reversed from the head of the gulf.…”

“…The presence of mica minerals (muscovite and biotite) has a special significance in the GoK, owing to its characteristic sediment transport mechanism (Nair et al 1982;Prizomwala et al 2012). Figure 5 shows the spatial distribution of mica minerals in the intertidal sediments of the GoK coast.…”

“…Prizomwala et al (2012) observed the higher concentrations towards west in the northern sandy segment and progressive reduction towards the east (figure 5). Mica minerals are sourced from the Indus River, which drains from the Himalayas and are redistributed along the GoK coast via the alongshore currents (Garzanti et al 2005;Prizomwala et al 2012). In this scenario as the distance from the source (i.e., the Indus River) increases the concentration of mica minerals would be expected to reduce.…”