TERTIARY BRYOZOA FROM WESTERN KACHCHH, GUJARAT - A REVIEW

摘要

The Tertiary (Lutetian - Burdigalian) sequences of western Kachchh, Gujarat have preserved rich bryozoan assemblages, ninety-nine taxa of which are the main topic of this review article. The diversity and abundance of colonies are highly variable within and between formations, reaching their maximum during the deposition of the Khari Nadi Formation (Aquitanian). Fifteen fossil species of Thalamoporella Hincks, 1887, recognized in these sequences, have doubled the number of fossil taxa belonging to this genus to thirty, and have added much information on the Tertiary evolutionary history of this common extant genus. Three new genera, Reniporella, Archoporella and Orbiculipora, have considerably enriched our knowledge about their respective families. The presence of three out of five Tertiary steginoporellid genera makes Kachchh one of the main centres of diversity for this family. Therenia indica takes a conspicuous place in the phylogeny of the genus. Analysis of bryozoan growth forms indicates two episodes of deepening in the shallow pericratonic rift basin of Kachchh. The environment that supported a moderately diverse assemblage was restricted during the early Middle Eocene but gradually opened up and reached its zenith during the Early Miocene (Aquitanian) stage