Abstract:
Seven early Palaeocene planktic foraminiferal genera and their fourteen species have been identified using wall texture criterion in combination with test architecture at DSDP Site 237, Western Tropical Indian Ocean. This is a significant improvement over the record of six species in the previous work. The wall texture criterion is included for taxonomy of planktic foraminifers obtained from the siliceous nannochalk, affected by different levels of diagenetic alteration. It has been observed under SEM that diagenesis does not affect the wall texture in smooth wall normal perforate tests; in microperforate pustulose tests the diagenetic overprinting is directed by the original pattern of ornamentation, whereas remains of cancellate texture are recognizable in the specimens affected by dissolution and overgrowth. To differentiate the cancellate spinose from cancellate nonspinose (premuricate wall texture) forms the disposition of ridges is a clue, but for observing the presence or absence of spine holes good preservation is a prerequisite. Based on the assemblages of species, their ranges and FAD/LAD biochrons, biozones P1b-P2 have been demarcated with redefined boundaries. It is inferred that lower Palaeocene rocks underlain by Upper Cretaceous rocks are likely to be present in the unpenetrated interval of strata above the basement at the DSDP Site 237. Globoconusa daubjergensis, earlier recorded mainly from high latitudes, occurs commonly at Site 237.