Fluvial trace fossils in the Middle Siwalik (Sarmatian-Pontian) of Darjeeling Himalayas, India

Journal of Earth system science

Harendra Nath Bhattacharya3¹  Bhaskar Ghosh1³  Stephen T Hasiotis2²  Abhijit Chakraborty1³ 

[1] Department of Geological Sciences, Presidency University, 86/1 College Street, Kolkata 700 073, India.$$;Department of Geology, The University of Kansas, 1475 Jayhawk Blvd., rm. 120, Lindley Hall, Lawrence, KS 66045-7594, USA.$$;Department of Geology, Jogamaya Devi College, 92 S.P. Mukherjee Road, Kolkata 700 026, India.$$

关键词: Trace fossils;    Cenozoic;    fluvial;    molasse deposits;    Middle Siwalik;    Geology;    biogeosciences.;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

Trace fossils that record animal and plant activity are described for the first time from the Middle Siwalik, Neogene deposits of Darjeeling Himalaya. Sedimentary facies association attests to a channel–interchannel floodplain fluviatile setting. The intimate association of the burrows with phytoliths, rhizoliths, leaf compressions and coal lenses suggest that the tracemakers dominated a floodplain habitat. Point bar deposits host a low diversity Planolites-Naktodemasis-Macanopsis-Cylindricum equilibrium ichnocoenosis in the heterolithic fine sandstone-siltstone-shale facies that alternates with dense, monospecific colonization of Planolites as opportunistic pioneers relocating under stressed condition. Interlayered floodplain deposits in the fluvial successions preserve enigmatic large diameter, vertical tubes within thin to thick-bedded, dark silty shale facies. These tubes bear mixed characters assignable to both crayfish burrows and large-diameter rhizoliths. Further work on these tubes is necessary to make more accurate interpretations of those structures. Shallow to moderate burrow depths; intermittent, short-lived colonization events and preservation of rhizoliths and rhizohalos under fluctuating moisture content indicate short-term fluctuations of a relatively high water table (close to the paleosurface) in an imperfectly drained proximal floodplain setting. Ichnotaxa distribution and their inferred ethology provide significant faunal data that may put constraints on the reconstruction of Middle Siwalik depositional environment.

【 授权许可】

Unknown