Diversification and evolution of Early Cretaceous East Coast flora of India

Abstract

The Early Cretaceous continental sediments in the East Coast of India are characterized by the Ptilophyllum flora. Interplay of tectonism and sedimentation caused plant fossil preservation in different unconnected paralic deposits distributed in Cauvery, Palar, Krishna-Godavari and Mahanadi basins and in the associated Pranhita-Godavari Graben. Plant megafossils assigned to pteridophytes, pteridosperms, cycadophytes, Taxales, Ginkgoales and Coniferales are variously distributed in these basins. Differential preservation of plant parts denotes an incomplete evolutionary pattern. Variation within the basinal flora reflects a localised aspect. Plant fossils preserved in the Cauvery, Palar, Krishna-Godavari and Mahanadi basins reflect a near shore continental sedimentary fill subjected to more dynamic events like marine transgression, which probably did not allow better preservation of plant fossils. Paucity of carbonised/silicified material, abundance of impressions of plant leaf fossils, scarcity of wood and reproductive parts indicate an unfavourable environment for plant fossil preservation in these pericratonic basins. Whereas in the associated Pranhita-Godavari Graben the plant fossils are better preserved in the sub-aerially exposed basinal areas away from the main coast-line. The Early Cretaceous flora of Cauvery, Palar and Krishna-Godavari basins dominated by cycadophytes suggests presence of seaward margins of fluviodeltaic palaeoenvironment. The pteridophyte dominant flora of Mahanadi Basin represents a decreasing marine influence contrary towards the south-eastwards. The evolution and diversification of the East Coast Early Cretaceous flora runs parallel to other intracratonic basinal flora. The uniformity in the floral component supports an equable climate. Conifers being the upland floral elements constitute chief components of intracratonic basinal flora. The fluviomarginal elements like cycadophytes predominate the pericratonic sedimentation with some upland near basinal taxa. Pteridosperms and Ginkgoales are scanty. Presence of leaves with entire margin indicates a favourable growth environment.