The influence of Deccan volcanism on climate: insights from lacustrine intertrappean deposits, Anjar, western India

Abstract

A sedimentary succession from Anjar sandwiched between basaltic flows records what transpired as continental India passed from Cretaceous to Tertiary times in the immediate vicinity of the Deccan Trap Province. The deposits consist of interlayered peloidal cherty limestones and shales. The shales are dominated by the mineral sepiolite. Chert occurs as three varieties. These include an amorphous cement, microcrystalline quartz and chalcedony. The last two usually fill gastropodal chambers and peloids. These sediments are interpreted as being deposited in an alkaline closed-basin lake that periodically received silica-saturated hydrothermal solutions. The lake in spite of having fluctuating shorelines was perennial. This wave-dominated lake was highly productive biogenically which is evident in the abundance of molluscan shell debris. Based on the sedimentological characteristics the site appears to be located proximal to the palaeo-shoreline. The palaeolatitude position of India during the Maastrichtian would suggest a sub-humid to humid, seasonal climate in Kachchh. A semi-arid climate is inferred on the basis of the lake deposits for Anjar. This apparent contradiction is believed to be due to `mock aridity'. This term is used to explain volcanically influenced climates that mimic characters of xeric semi-arid climates. Similar signatures of semi-aridity in the Indian Peninsula are observed in calcic palaeosols of the contemporaneous Lameta Formation sediments around Jabalpur.