Deccan volcanic bole beds (Greater Mumbai, India): New insights on their nature and evolution based on micromorphology

Abstract

The globally occurring flood basalt volcanic eruptions consist of interbasaltic layers within successive lava flows, and are commonly referred as red ‘bole beds’ due to their dominantly red colour. These bole beds are in-situ layers within successive lava flows, making them reliable geologic proxy tools. These beds also represent short to prolonged hiatus in volcanic activity and subsequent landscape stability. The Indian Deccan traps comprising several bole bed layers constitute one of the world’s largest flood basalt volcanic provinces. The Deccan bole bed studies have already been done based on geochemistry but researchers reached no consensus on their nature and origin, presumably due to lack of detailed and systematic micromorphology. In this regard, ∼ 100 cm thick buried bole bed profile in Kharghar hill (greater Mumbai, India) has been investigated for detailed morphological and micromorphological studies along-with selective geochemical studies. Pedoplasmation features include development of specific voids and microstructure, b-fabrics, bioturbation features and one or more types of pedofeatures. Systematic micromorphology shows that the investigated buried bole bed profile were mature palaeosols formed on pyroclastic deposits. Significant biodiversity under ustic soil moisture regimes existed and resulted in the formation of ferralsols. A greater impact of andosolization on ferralsols is interpreted before onset of successive basalt lava flow. A combination of morphological, micromorphological and geochemical results indicate presence of oxidizing environment under high temperature and acidic soil conditions during pedogenesis. Thus, systematic bole bed micromorphology is pre-requisite for understanding of surficial conditions during quiescence in volcanism. These results are a first step towards detailed such investigations in future for various exposures of bole beds during different phases of Deccan volcanism. Further, compiled multi-proxy data-set will prove significant to compare similar studies done in global, contemporaneous volcanic bole beds.