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

Abstract

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 channelinterchannel 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.

Provenance of the Middle Siwalik sandstones of the Himalayan foreland basin (south central Kumaun, India): Implications for tectonics and paleoclimate of the source area

“…The Middle Siwalik sequences represent fluvial deposits in the western and central Himalaya and deltaic deposits in the eastern Himalaya (Khan & Tewari, ; Kumar & Nanda, ; More et al, ; Nakayama & Ulak, ; Sharma, Sharma, Shukla, & Singh, ; Tandon, ; Taral & Chakraborty, ; Thomas et al, ; Zaleha, ); some studies, however, propose a fluvial palaeoenvironment for the eastern Himalayan Middle Siwalik as well (e.g., Chakraborty, Hasiotis, Ghosh, & Bhattacharya, ; Kundu et al, , 2016). The fluvial sedimentation was in megafan–interfan settings, from large, mainly braided, rivers of Himalayan origin that flowed transverse to the axis of the foreland basin.…”

Deltaic coastline of the Siwalik (Neogene) foreland basin: evidences from the Gish River section, Darjeeling Himalaya

“…The conclusion was, however, not based on systematic facies analysis (sensu Reading and Levell, ; Walker and Posamentier, ; James and Dalrymple, ). Palaeoenvironmental interpretation by the later workers varied from alluvial fan (Kundu et al ., , ) to braided fluvial, point bar and interchannel floodplain facies (Chakraborty et al ., ; Mandal et al ., ).…”

“…In the Siwalik succession of Eastern Himalaya, the presence of thick dark grey mudstone (Karunakaran and Ranga Rao, ), palynoassemblages and trace fossils of brackish water affinity (Mitra et al ., ; More et al ., ), abundance of wave generated structures and a complex polymodal palaeocurrent have been reported (Taral, ). The existing depositional models of upland alluvial fan or fluvial channel–interchannel setting for Siwalik rocks of the Tista valley (Banerjee and Banerjee, ; Kundu et al ., , ; Chakraborty et al ., ; Mandal et al ., ) do not explain any of these peculiarities of the Siwaliks of Eastern Himalaya. A sedimentological analysis of the succession is critical in understanding the pattern of the drainage network, palaeogeographic setting and tectonic evolution of the foreland basin (Bera et al , ; Leeder, ; Chirouze et al , ; Bracciali et al ., ).…”

Biomarker and Carbon Isotopic Evidence of Marine Incursions in the Himalayan Foreland Basin During Its Overfilled Stage

“…The paleo‐depositional interpretation from the invertebrate fossils was further challenged due to their limited occurrence and the possibility of its derivation from the older Himalayan tertiary rocks (Acharyya et al., 1987). Recently, efforts have been made to reconstruct the past environmental conditions using ichnofossils (Chakraborty et al., 2013; More et al., 2018; Taral et al., 2018, 2019; Ulak, 2009). Specific ichnogenera traces in pre‐requisite amounts are considered as important paleo‐environmental markers (MacEachern et al., 2008).…”