Late‐Quaternary miliolite (biogenic carbonate) deposits and their implications for sea‐level fluctuations and climatic variability

Abstract

The western coast of India (Kachchh) has ubiquitous preservations of Quaternary carbonate deposits popularly known as "miliolites". Field-based detail documentation of the nature and distribution of miliolites supported by sedimentology and scanning electron microscopy (SEM) microtextural studies indicates that the miliolites were primarily deposited by wind as aeolinites and are termed "primary miliolites (PM)". These were subsequently fluvially eroded and deposited and such deposits are termed "secondary miliolites (SM)". The PM are dated between 28 ka to 16 ka largely clustering around the Last Glacial Maxima (LGM). In comparison, the fluvially reworked SM occurs as valley-fill deposits and were deposited episodically during 23 ka to 10 ka before present. Climatically, the deposition of PMs suggests enhanced aridity whereas SMs represent episodic strengthening of the Indian Summer Monsoon (ISM). The bedding attitudes of the PMs indicate that they were deposited predominantly by the northeasterly winds whereas the presence of the deflation lag deposits suggests downwind migration of sands during the equilibrium condition (reduced sediment supply). The aeolian parameters (based on the grain size and wind velocities) for PMs indicate high shear velocity ($23 to 48 cm −1 ) and high transport rate (< 0.1 to 0.2 g/cm s). The short average flying distance implies that the biogenic sands were transported in multiple pulses (from coast to inland) at rates varying from $200 m/h to $1 km/h. Comparing our data with related occurrences along the biologically productive coasts in the mid-latitudinal belt indicates that the regional/global aridity during the lowered sea level was responsible for inland occurrences of aeolinites, particularly during the LGM. The strengthened northeast monsoon winds during the LGM was conducive to upwelling and production of biogenic carbonates along the coasts. The subsequent reworking of the aeolinites were mainly the results of local variability in precipitation.

Introduction to Geology of the Kachchh (Kutch) Basin, Western India

“…Thakkar et al (1999Thakkar et al ( , 2001 reported the Quaternary sequences within the rocky mainland in the form of three major episodes as alluvial and colluvial fan deposits as Early Pleistocene, sandy sheets of miliolites with boulders and pebbles as middle Pleistocene and fluvial sand silt and clay with some aeolian deposits of late Pleistocene and Recent age. Later on, various episodes of Late Pleistocene and Holocene sedimentation along various river courses in Kutch Basin are documented and are exploited for reconstructing the history of sea-level changes, climate and tectonics events spanning the last 100 (Maurya et al 2003a(Maurya et al , b, c, 2008(Maurya et al , 2013Khonde et al 2011Khonde et al , 2017aChowksey et al 2010;Das et al 2016aDas et al , b, 2017Das et al , 2020Prizomwala et al 2014aPrizomwala et al , b, 2016aPrizomwala et al , b, 2019Patidar et al 2007Patidar et al , 2008Kundu et al 2010;Bhattacharya et al 2013aBhattacharya et al , b, 2019Ngangom et al 2012Ngangom et al , 2017Ngangom and Thakkar 2016;Thakkar et al 2020a;Durga Prasad et al 2021).…”

The Unique Geoheritage of the Kachchh (Kutch) Basin, Western India, and its Conservation

“…The various episodes of Late Pleistocene and Holocene sedimentation that took place along various river courses in Mainland Kachchh, the Island belts, and Wagad have been documented and are important for reconstructing the history of climate and tectonics spanning the last 100 ka (Figs. 11 and 18c, d) (Maurya et al 2003a(Maurya et al , 2003b(Maurya et al , 2003c(Maurya et al , 2008(Maurya et al , 2013Khonde et al 2011Khonde et al , 2017aKhonde et al , 2017bChowksey et al 2010;Das et al 2016aDas et al , 2016bDas et al , 2017Prizomwala et al 2014aPrizomwala et al , b, 2016aPrizomwala et al , 2016bPrizomwala et al , 2019Patidar et al 2007Patidar et al , 2008Kundu et al 2010;Bhattacharya et al 2013aBhattacharya et al , b, 2019Ngangom et al 2012, Ngangom and Thakkar 2016Makwana et al 2019;Sane et al 2020;Durga Prasad et al 2021).…”

Geomorphic diversity of the Indian sub‐continent: Progress and updates

“…The Kachchh peninsula in western India has patches of these aeolinites, which are primarily bioclastic carbonate deposits termed as ‘miliolites’ (Bhatt, 2003; Carter, 1849; Lele, 1973). Durga Prasad et al (2021) have studied the primary and secondary miliolites in the Kachchh mainland. The primary miliolites were deposited during the Last Glacial Maximum (LGM) period (26–16 ka) in response to enhanced aridity and lowered sea level.…”