Paleoweathering and depositional conditions in the inter-flow sediment units (bole beds) of Deccan Volcanic Province, India: a mineral magnetic approach.

摘要

A total of 54 samples from thirteen different profiles of interflow sediment units occurring in the Deccan Volcanic Province (DVP, India) are studied using an integrated mineral magnetic and field documentation approach. The occurrence and distribution of ferri- and antiferromagnetic oxides associated with these sediments infer depositional conditions dominated by various detrital modes and recycling of baked sediments under limited authigenic environments. The baking of underlying sediments is conditioned by aqueous or dry nature of the substrate vis-a-vis the viscosity of the overlying lava flow that can be identified by a combination of brown/red boles and compact/pahoehoe type flows. The presence of antiferromagnetic superparamagnetic (SP) fraction in the 'red bole capped brown boles' indicates the depth of baking to ~ 20 cm; while the SP fraction also marks infilling, recycling and pigmentation in other occurrences of the red boles studied here. Overall, the mixed magnetic mineralogy and sediment characters depict frequent recycling and re-deposition by surface run-off, infiltration and ponding as the most common processes of bole bed formation in DVP governed by shallow streams or laterally migrating channels. Infiltration of the baked or unbaked sediments into fragmentary topped basalts is frequently shown by the red and brown boles, while infilling into the interstices and cavities is common with green boles. The red boles are also characteristic of detrital mixing of oxidized/partially oxidized ferrimagnets, many times coated with pigmentary hematites. The present results envisage a great scope for the routine mineral magnetic studies (integrated with field observations) for rapid characterization of the extensively occurring bole bed horizons in the DVP and their study as analogs of Martian soils and sediments.Digital Object Identifier http://dx.doi.org/10.1016/j.geoderma.2012.01.034