Environmental implications of Gondwana wood studies in India

Abstract

A synthesis of fossil gymnospermous woods from various Gondwana basins of India is presented, and characters of growth rings in the secondary wood, particularly tracheidal cell characters, are evaluated for possible palaeoclimatic signals. Permian fossil woods are mostly recorded from the Damuda, Wardha and Pranhita-Godavari basins. Growth rings are common in many of these species and suggest strong seasonality. Triassic woods are poorly known from the South Rewa Gondwana Basin; the paucity of growth rings suggests a lack of marked seasons. Available evidence on Jurassic woods from the Pranhita-Godavari Graben indicates lack of consistency in the growth ring distribution. Early Cretaceous fossil woods recorded from the Damuda, Pranhita-Godavari, East-Coast and Kutch basins mostly show growth rings, which suggest prevalence of distinct seasons. Ecological factors coupled with phenotypic plasticity, i.e., variation with the same genotype as a function of environmental differences (genetic flexibility) probably dictated wood accumulation patterns in Indian Gondwana woods. However, palaeo-latitudinal and palaeo-physiographic constraints influenced habitats, and subsequent taphonomic processes resulted in incomplete understanding of palaeoclimate. In the absence of contemporary meteorological data during Gondwana times on what is now on the Indian continent, fossil woods constitute an important tool for understanding the past impact of climate on tree growth.