Palynology and palynofacies analysis of the Subathu Formation (Early Ypresian-Middle Lutetian) of Morni Hills, Haryana, India

Abstract

Palynofossils and sedimentary organic matter recovered from two well exposed stratigraphic sections of the Subathu Formation (early Ypresian to middle Lutetian) outcropping in the Morni Hills, Haryana (Lesser Himalayas) are evaluated to interpret the depositional environment. The Morni Hills’ palynofloral assemblage consists of dinocysts, spores, pollen grains, fungal spores and ascostromata, and freshwater algae. Among these the significant palynotaxa are Pediastrum diffusus, P. angulatus Achomosphaera ramulifera, Adnatosphaeridium multispinosum, A. vittatum, Areoligera senonensis, Cleistosphaeridium diversispinosum, Cordosphaeridium fibrospinosum, C. gracile, Glaphyrocysta exuberans, Homotryblium abbreviatum, H. pallidum, H. tenuispinosum,  Hystrichokolpoma salacium, Hystrichosphaerdium tubiferum, Lingulodinium machaerophorum, Operculodinium centrocarpum, Thalassiphora pelagica, Lygodiumsporites lakiensis, Todisporites major, Pteridacidites sp., Podocarpidites couperi and Neocouperipollis brevispinosus, etc. Five assemblage zones along with one barren zone are recognized on the basis of restricted species and variable abundance data of the examined palynofossils. Dinoflagellate cyst associations show a remarkable change from the older to younger horizons in the present succession. Variation in the composition of the assemblages from lower to upper horizons of the present succession might have been governed by several factors, viz. change in salinity concentration, decrease in water depth, and increase in proximity to the shoreline.  Different types of organic matter types were also characterized, whose relative proportions in a vertical succession in both the sections, show changing depositional environmental gradients in this area. The study indicates that the basal carbonaceous shales seem to have been deposited in a freshwater swamp environment. Later, an open lagoon followed by closed lagoon and tidal flat environments are interpreted during the progradational sequence of the regressive phase.