Palynology of the teritary sediments in the Cauvery basin. 2. Oligocene-Miocene palynoflora from the subsurface

Abstract

Exploration, Oil and Natural Gas Commission, Dehra Dun

Subsurface sediments occurring in Karaikal, Madanam and Mannargudi wells drilled by the Oil & Natural Gas Commission are studied. Oligocene-Miocene palynological assemblages recorded from the subcrop sequences of Karaikal and Madanam wells are discussed in the present paper. 68 genera and 96 species of spore and pollen and microplankton are recognised in this study, of which 7 genera and 42 species are newly proposed. Detailed descriptive analysis and differential diagnosis are given to exemplify the new taxa. The following three main palynological zones are recognised.

1. Magnastriatites cauveriensis zone.
2. Lacrimapollis pilosus zone
3. Tricollareporites eclzinatus zone.

Zone 3, designated as Tricollareporites echinafus zone is further subdivided into two subzones as follows:

1. Verrucatosporites bullatus subzone.
2. Malavacearumpollis paucibaculatus subzone.

The abundant angiosperm pollen assemblages recovered in the wells studied, point out that the vegetation that provided material to the Oligocene-Miocene deposits in this basin were chiefly angiospermous. Marine phyto-plankton are recorded only in Oligocene-Lower Miocene sediments. Pteridophytic representatives form a sub-dominant group of plants. Fungal remains show a uniform distribution and form 5-10% of the total assemblage. Pollen of arborescent angiosperm families are more in number as compared to the herbaceous ones. Mangrove elements, such as pollen of Rhizophoraceae, Araliaceae, Lecythidaceae as well as Schizaeaceous spores are present in good number. The overall representation of plant families in general point to swampy tropical warm humid climate, deposited under neritic environment. Marine phytoplankton are confined to hystrichosphaerid remains and recorded only in Oligocene and Lower Miocene sediments.