The vegetation and climate of a Neogene petrified wood forest of Mizoram, India

Abstract

Eleven fossil woods belonging to seven families are described from a petrified wood forest of Mizoram. This fossil assemblage is derived from sediments belonging to the Tipam Group considered to be Late Miocene–Early Pliocene in age. The modern counterparts of the identified taxa are: Gluta L., Mangifera L. (Anacardiaceae), Bursera Jacq. ex L. (Burseraceae), Terminalia L. (Combretaceae), Shorea Roxb. (Dipterocarpaceae), Cynometra Linn., Dalbergia L. f., Millettia Wight et Arn.–Pongamia Vent, Ormosia Jacks. (Fabaceae), Artocarpus Forst. (Moraceae) and Madhuca Gmelin. (Sapotaceae). The genus Dalbergia is described for the first time from India. The modern environmental tolerances of the above taxa indicate the existence of a tropical warm and humid climate in Mizoram during the depositional period. The reconstructed climate data using Coexistence Approach (CoA) based on palaeoflora database of Mosbrugger and Utescher, along with other published data sets indicates an MAT (mean annual temperature) of 26.1–27.7°C, a mean temperature of the warmest month (WMT) of 25.4–28.1°C, a mean temperature of the coldest month (CMT) of 25.6–26°C, and a mean annual precipitation (MAP) of 3180–3263mm. These climatic interpretations are congruent with the data obtained from the anatomical features of all the fossil taxa. As all the fossil taxa possess diffuse porous wood, they further indicate a tropical climate with little seasonality. The majority of the taxa in the fossil assemblage generally have large vessels and simple perforation plates which indicate high precipitation. The present study provides vital evidence of floral exchange or migration between India and southeast Asia.