Depositional Environment of Mio-Pliocene Siwalik Sedimentary Strata from the Darjeeling Himalayan Foothills, India: A Palynological Approach.

Sandip More,Tapan Chakraborty,Subir Bera,Dipak Kumar Paruya,Suchana Taral,Cheng–Sen Li

doi:10.1371/journal.pone.0150168

Sandip More, Tapan Chakraborty + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0150168

Copy DOI

Journal: PloS one	Publication Date: Mar 1, 2016
Citations: 18	License type: CC BY 4.0

Affiliation: University of Calcutta, Indian Statistical Institute

Abstract

A rich and diverse palynoassemblage recovered from the Churanthi River section (26°53' 59.3" N, 88°34' 17.2" E), Darjeeling foothills Eastern Himalaya, has yielded 87 species assigned to 69 genera. The palynoassemblage is rich in angiosperm taxa (45.63%) followed by gymnosperms (0.45%), pteridophytes (18.49%) and fungal remains (23.88%). Based on their nearest living relatives, a wet evergreen to semi-evergreen forest under a humid tropical to sub-tropical environment during the Mio-Pliocene age has been suggested. A lot of angiosperms such as Palaeosantalaceaepites, Araliaceoipollenites, Malvacearampollis, Zonocostites, Neocouperipollis, Dicolpopollis, Palmidites, Palmaepollenites, isolated salt glands of mangrove plant leaves (Heliospermopsis) and Mediaverrunites type of fungal spores, along with ichnofossils like Planolites, Palaeophycus, Skolithos, Rosselia, Ophiomorpha and Teichichnus associated with rippled mudstone-siltstone suggest an environment strongly influenced by brackish water. Primary sedimentary structures in the associated strata indicate strong wave agitation common in shallow marine setting. Some high elevation components (5.14%) such as Alnipollenites, cf. Corylus (Betulaceae), Juglanspollenites, Engelhardtioipollenites (Juglandaceae), Quercoides, Cupuliferoidaepollenites, Lithocarpus, Castanopsis (Fagaceae), Abietineaepollenites (Pinaceae) represent hinterland vegetation possibly transported to the prograding deltaic coastline by the rivers. Reworked palynotaxa (Striatopodocarpites sp., Striatites sp., Faunipollenites sp., Circumstriatites sp., Crescentipollenites sp., Cuneatisporites sp., Parasaccites sp., Scheuringipollenites sp., Rhizomaspora sp., Marsupipollenites sp., Lophotriletes sp.) of Permian age have also been recorded in the palynoassemblage (11.55%) indicating the abundance of Permian Gondwana strata in the source area.

Highlights

The study of paleovegetation and paleoclimate from the sedimentary rocks of the Siwalik Group through the recovery of micro plant remains is well known from western to central Himalayan sectors [1,2,3,4,5,6,7,8,9,10,11]
The Siwalik fossiliferous localities of eastern Himalaya have been proved as important sites recording a variety of mega-fossils [12,13,14,15,16,17,18,19,20], systematic study of the palynological records for the stratigraphic correlation, paleoclimate reconstruction and depositional setting are scanty [21]
In this article we combine our data from palynological study with stratigraphic, sedimentologic and ichnofossil data to evolve a clearer understanding of the climatic and depositional setting of the Mio-Pliocene Siwalik rocks of eastern Himalaya [22,23,24]

Summary

Introduction

The study of paleovegetation and paleoclimate from the sedimentary rocks of the Siwalik Group through the recovery of micro plant remains is well known from western to central Himalayan sectors [1,2,3,4,5,6,7,8,9,10,11]. The Siwalik fossiliferous localities of eastern Himalaya have been proved as important sites recording a variety of mega-fossils [12,13,14,15,16,17,18,19,20], systematic study of the palynological records for the stratigraphic correlation, paleoclimate reconstruction and depositional setting are scanty [21]. This paper examines paleovegetation pattern from the middle Siwalik deposits exposed in the southern part of the Churanthi River (26°53'59.3" N, 88°34'17.2" E) in the Jalpaiguri District, West Bengal. In this article we combine our data from palynological study with stratigraphic, sedimentologic and ichnofossil data to evolve a clearer understanding of the climatic and depositional setting of the Mio-Pliocene Siwalik rocks of eastern Himalaya [22,23,24]. The deposits of the Siwalik succession have traditionally been inferred as representing continent-interior channel-floodplain successions that were part of large megafans, similar to the Kosi megafan in the present-day Gangetic alluvial plain. [28,29,30]

Methods

Results

Discussion

Conclusion