Preliminary comparison of ancient bole beds and modern soils developed upon the Deccan volcanic basalts around Pune (India): Potential for palaeoenvironmental reconstruction

Relict weathering mantles are frequently preserved in the form of paleosols, which generally document the long-term evolution of earth-surface processes. Bole beds occur as prominent horizons composed of fine-grained clayey or earthy material having colors in shades of red to chocolate brown, green, purple or gray, often marking the flow contacts of Deccan basalts, which date to approximately 65 Ma. Bole beds preserved between two successive lava flows can be studied relative to soils developed into the same basalts during the Holocene. The bole beds have slightly lower pH but significantly lower electrical conductivity values and organic matter contents compared to modern soils. They also have higher SiO2 and lower Al2O3 and H2O+ (crystal lattice water) content than modern soils. Results indicate that the bole beds may not have been subjected to intense weathering and long-term pedogenesis, but nonetheless formed under uniform rainfall with surface runoff exceeding evaporation. Weathering chemistry suggests different types of protolith for red and green boles. The high stratigraphic frequency of bole beds throughout the Deccan Volcanics makes them an important source of information about the frequency and environment of inter-eruption intervals.