Weathering characteristics of interflow volcanic boles from Mandla lobe, Eastern Deccan volcanic province

Abstract

The Deccan volcanism straddling the Cretaceous–Paleogene boundary resulted into one of the most extensive continental flood basalts in the Western and Central Peninsular India. The interflow sedimentary units (boles) often cited as paleosols are the rare archives of paleoenvironmental conditions existed during successive lava flows. A debate on the origin of boles as true paleosols exists. Therefore, in order to trace out regional extent of such conditions (pedogenic/non-pedogenic) in the context of their paleoenvironmental significance during the Deccan volcanism, we studied here mineral magnetic characteristics of 36 color differentiated bole beds from the Mandla lobe, in the eastern Deccan volcanic province (EDVP) classified into four types (gray, yellow, brown and red) based on their Munsell notations. The gray, yellow and brown boles show dominantly ferrimagnetic composition (chiefly magnetite and titanomagnetite), while red boles characterize mixed ferri- and antiferromagnetic (mainly hematite) mineralogy. The granulometric (domain) parameters suggest larger single domain (SD) and the multidomain (MD) ferrimagnets in the majority of cases, whereas superparamagnetic (SP) particles (with frequency dependent susceptibility χfd~2.6 to 20.3×10−8m3kg−1) are limited to the few red and brown boles only. The significant presence of primary parent magnetic minerals (i.e. coarse SD–MD titanomagnetite and magnetite) in the majority of boles depict incipient to moderate weathering owing to limited time intervals during successive eruptions. The combination of hematite and SP particles present only in the few red and brown boles depicts baking effect rather than pedogenesis. The comparison of magnetic properties of boles from EDVP and western Deccan volcanic province (WDVP) shows significant differences in the concentration of SP ferrimagnetic particles and hematite attributed to variable weathering intensity, duration and heating related alterations from the upper flows. Both EDVP and WDVP boles indicate similar first order paleoenvironmental conditions without any major pedogenesis that can be regionally correlated.