Palynological and Geochemical study of the Dalbuing Formation of Eastern Himalaya: Implications for Palaeoredox, Palaeosalinity, Palaeoproductivity and Palaeoclimatic conditions of the depositional basin

We present here the results and interpretation of the palynological and geochemical studies of the early to middle Eocene Dalbuing Formation of Arunachal Pradesh of the Eastern Himalayan region. Data of palynological organic matter, along with primary and trace element analysis, are taken into consideration for unveiling the palaeoenvironmental condition during the time of deposition of the rock unit. The palynological organic matter includes a relatively higher abundance of amorphous organic matter (AOM), followed by opaque and non-opaque phytoclasts, a smaller amount of palynomorphs, as well as lepidopteran wing scales. The AOM, palynomorph and phytoclast (APP) ternary diagram suggests proximal suboxic-anoxic shelf to marginal dysoxic-anoxic settings of deposition mostly in brackish water conditions. However, the average V/Cr, Ni/Co, U/Th, and Ce anomaly values of the studied sandstone and shale samples suggest an oxic palaeoredox condition. The palaeosalinity proxy Sr/Ba ratio infers the prevalence of brackish water conditions in the depositional basin. The [P] organic , [Ba] biogenic , and UCC normalised enrichment factor (EF) of redox-sensitive elemental palaeoproductivity proxies such as Ni, Cu and Zn indicate negative or low palaeoproductivity due to prevailing oxic palaeoredox conditions or less nutrient availability. The paleoclimate indicators, C-value [Σ (Fe + Mn + Cr + Ni + V + Co)/Σ (Ca + Mg + Sr + Ba + K + Na)], Sr/Cu and Sr/Ba ratios reveal a warm, humid palaeoclimate during the deposition of the lithounit.