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<p>A thin sequence of Paleocene–Eocene rocks, usually termed the Yinkiong Group, has been recorded in the Eastern Himalayan syntaxis. Our present study focuses on the Early to Middle Eocene Dalbuing Formation of this Yinkiong Group exposed along the Pasighat-Mariyang road section as well as the Dalbuing village of Arunachal Pradesh. This litho unit is largely composed of limestone, shale and sandstone, in which the limestones are characterised by fossils, micrite and coarse calcite cement as well as terrigenous constituents. The fossils present in these limestones include <i>Nummulites</i>, <i>Linderina sp.</i>,<i> Rotaliid sp.</i>,<i> Assilina sp.</i>,<i> Ranikothalia sp.</i>,<i> Lockhartia sp.</i>,<i> Rotalia trochidoformis and Ranikothalia nuttali</i>, which indicate an Early to Middle Eocene age for Dalbuing Formation. Six lithofacies (LFA-1 to LFA-6) and four microfacies (MFT-1 to MFT-4) have been identified. The various geochemical proxies show both positive and negative correlation amongst SiO<sub>2,</sub> Fe<sub>2</sub>O<sub>3</sub>, CaO, P<sub>2</sub>O<sub>5</sub>, Na<sub>2</sub>O, TiO<sub>2</sub>, K<sub>2</sub>O as well as Na<sub>2</sub>O, inferring high rate of terrigenous influx into the basin during the deposition of the limestones. Further, the HREE enrichment and positive Eu/Eu* anomaly, as well as both positive and negative Ce/Ce* anomalies suggest different degrees of detrital input and a dynamic environment alternating between oxic and anoxic conditions during their deposition. The present study reveals that the rocks of the Dalbuing Formation are associated with an inner to outer carbonate ramp setting and experienced varying degrees of detrital influx and rapid changing environmental conditions during deposition.</p>

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Larger benthic foraminifera bearing limestones of Early to Middle Eocene Dalbuing Formation, Yinkiong Group, Eastern himalaya: insights into depositional condition and diagenesis

  • 期刊论文

  • 发表日期：

    2026年1月8日

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  • Anannya Bordoloi,
  • Chaitra Dhar Taye,
  • Ananya Chutia

摘要

A thin sequence of Paleocene–Eocene rocks, usually termed the Yinkiong Group, has been recorded in the Eastern Himalayan syntaxis. Our present study focuses on the Early to Middle Eocene Dalbuing Formation of this Yinkiong Group exposed along the Pasighat-Mariyang road section as well as the Dalbuing village of Arunachal Pradesh. This litho unit is largely composed of limestone, shale and sandstone, in which the limestones are characterised by fossils, micrite and coarse calcite cement as well as terrigenous constituents. The fossils present in these limestones include Nummulites, Linderina sp., Rotaliid sp., Assilina sp., Ranikothalia sp., Lockhartia sp., Rotalia trochidoformis and Ranikothalia nuttali, which indicate an Early to Middle Eocene age for Dalbuing Formation. Six lithofacies (LFA-1 to LFA-6) and four microfacies (MFT-1 to MFT-4) have been identified. The various geochemical proxies show both positive and negative correlation amongst SiO2, Fe2O3, CaO, P2O5, Na2O, TiO2, K2O as well as Na2O, inferring high rate of terrigenous influx into the basin during the deposition of the limestones. Further, the HREE enrichment and positive Eu/Eu* anomaly, as well as both positive and negative Ce/Ce* anomalies suggest different degrees of detrital input and a dynamic environment alternating between oxic and anoxic conditions during their deposition. The present study reveals that the rocks of the Dalbuing Formation are associated with an inner to outer carbonate ramp setting and experienced varying degrees of detrital influx and rapid changing environmental conditions during deposition.