Palynostratigraphy, palynofacies and depositional environment of a lignite-bearing succession at Surkha Mine, Cambay Basin, north-western India

Abstract

The paper reports palynology and palynofacies studies of lignite-bearing sediments exposed in an opencast mine succession at Surkha, Bhavnagar District, in the coastal region of Gujarat, India. The study examined the relationships between the palynoflora, sedimentary organic matter and environment at the time of deposition of lignite and associated sediments. Based on dinoflagellate cyst biostratigraphy, the sedimentary succession is dated as early Eocene (Ypresian). Palynofacies studies helped reveal the palaeoenvironmental fluctuations. The dominance of angiosperm pollen grains, freshwater algae, microthyraceous fungi and a large share of land debris in the lower part of the succession suggests a freshwater swamp environment of deposition for the basal lignite facies. Two cenozones - Matanomadiasulcites maximus and Lakiapollis ovatus - were identified in the lower lignite facies, determined from the dominance of these pollen grains in the palynological assemblages. The presence of angiosperm pollen grains and pteridophyte spores in the carbonaceous shale horizon above the lignite facies indicates a change in the depositional regime from freshwater swamp to lagoonal. This was identified as the Arecipites wodehousei cenozone due to its numerical abundance in the assemblage. Dinoflagellate cyst abundance and diversity, and microforaminiferal test linings along with well-sorted terrestrial debris in the mudstone in the upper part of the succession suggest a more open marine estuarine type of depositional environment. The Homotryblium complex along with Cordospheridium fibrospinosum, Kenleyia sp., and Thalassiphora pelagica dinoflagellate cysts are the main representatives of this zone, determined as the Homotryblium tenuispinosum cenozone. The changing depositional settings (freshwater swamp-lagoonal-estuarine) along the vertical succession indicate a marine transgression in this region. Results from palynological studies of early Palaeogene successions of the Cambay and Kutch basins correlate well with the present findings.

Assembly and division of the South and South-East Asian flora in relation to tectonics and climate change

“…The early Eocene flora is well documented from the palynological analysis of coal-bearing successions across India (Monga et al 2015, Prasad et al 2009, Samant & Phadare 1997. The pollen flora suggests a setting with a perhumid climate, and tall, dense, closed-canopy rain forests of modern aspect.…”

Late Miocene-Pleistocene evolution of India-Eurasia convergence partitioning between the Bhutan Himalaya and the Shillong Plateau: New evidences from foreland basin deposits along the Dungsam Chu section, eastern Bhutan

“…Brownlowia may also occur in tidally influenced freshwater swamps along the coastal plain [ Morley , ; Tomlinson , ]. In addition, several single occurrences of palm tree‐type pollens such as Nypa and the extinct Neocouperipollis representing palms from the coastal environment, and extending toward tidally influenced rivers and freshwaters swamps further inland [ Giesen et al ., ; Monga et al ., ], are observed along the entire section (Table S3).…”

Character evolution of modern fly‐speck fungi and implications for interpreting thyriothecial fossils

“…Thyriothecia with a papillate ostiole and a lower wall are characteristic of Trichothyriaceae. Anisotomous At present, T. setifer (Monga et al, 2015), from the early Eocene (56-47.8 Ma), represents the oldest convincing evidence of the clade including Microthyriales and Venturiales.…”

“…Analysis of fossils-We selected three fossils reported as thyriothecial from the literature that were well enough illustrated to be coded for morphology. These include the oldest dispersed thyriothecium-like structure (Mishra et al, 2018), a dispersed Lichenopeltella-like form (Monga et al, 2015) for which cell patterns could be analyzed, and Asterina eocenica found on a leaf associated with mycelium (Dilcher, 1965). As for extant taxa, we coded character states from the illustrations (Appendix S4).…”

“…Microthyriaceous fossil-Trichothyrites setifer (Cookson) Saxena & Misra, a fossil from the early Eocene (Ypresian, 56-47.8 Ma) sediments of India is illustrated by Monga et al (2015) (Fig. 6B).…”