Grain size distribution analysis of sediments containing Younger Toba tephra from Ghoghara, Middle Son valley, India

The Toba super-eruption in northern Sumatra ∼74 ka was the largest eruption of the Quaternary period. Terrestrial deposits of distal Toba tephra have been found across the Indian subcontinent, although few localities have been adequately described with respect to stratigraphy and sedimentary history. This study provides the first detailed description of the Ghoghara 1A ash section, Middle Son Valley, India. The sediment analyses provide insights into the depositional processes in the valley before and after the initial period of ash deposition. Grain size distribution analysis of sediments from Ghoghara 1A indicates that 4–5 cm of primary air-fall ash was laid down at the time of the Toba super-eruption. This study has implications concerning previous isotopic studies in the Middle Son Valley, concluding that reconstructions demonstrative of dramatic ecological changes are questionable.