The Miocene coastal vegetation of southwestern India and its climatic significance

Abstract

The late early to middle Miocene sediments at Varkala cliff section (SW India) offer a great potential to study paleoenvironmental and paleoclimatic conditions. The succession consists of coastal marine sands alternating with fine grained, organic-rich siliciclastics. Based on several palyno-samples, a mangrove flora could be reconstructed, composed of Rhizophoraceae, Avicennia, Xylocarpus, and Sonneratia. These grew in front of backswamps, followed by evergreen forests in hinterland with many rainforest elements.Despite these similarities between the Miocene and the modern vegetation, differences can be documented, e.g., the abundance of Nypa and the absence of gymnosperm in the Miocene vegetation. Based on the Coexistence Approach, a temperature is reconstructed, which is similar to today's (mean annual temperature 22.2–27.5°C; coldest month temperature 20.6–23.6°C; warmest month temperature 27.5–28.1°C). However, in comparison to today, significantly lower values for the mean annual precipitation are reconstructed (1748–1958mm), although a seasonality pattern was established (wettest month mean precipitation 225–358mm; driest month mean precipitation 18–83mm).Comparison with other localities along the west coast of southern India hints at a similar vegetation and climate throughout the early and middle Miocene. Furthermore, the same results were obtained for SE India. This is in contrast to the strong west-east gradient in rainfall caused by the Indian Monsoon nowadays. Therefore, the paleovegetation of the early and middle Miocene of southern India appears to be more uniform than today. This outlines the complexity of describing the paleoclimatic evolution in the tropics based on plant fossils, but emphasizes the need for further study of this area to understand the early history of the Indian Monsoon.