• Arka Rudra

      Articles written in Journal of Earth System Science

    • Molecular composition and paleobotanical origin of Eocene resin from northeast India

      Arka Rudra Suryendu Dutta Srinivasan V Raju

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      The molecular composition of fossil resins from early to middle Eocene coal from northeast India, has been analyzed for the first time to infer their paleobotanical source. The soluble component of fossil resin was analyzed using gas chromatography–mass spectrometry (GC–MS). The resin extracts are composed of cadalene-based C_{15} sesquiterpenoids and diagenetically altered triterpenoids. The macromolecular composition was investigated using pyrolysis gas chromatography-mass spectrometry (Py-GC–MS) and Fourier transform infrared (FTIR) spectroscopy. The major pyrolysis products are C_{15} bicyclic sesquiterpenoids, alkylated naphthalenes, benzenes and a series of C_{17}–C_{34} 𝑛-alkene-𝑛-alkane pairs. Spectroscopic analysis revealed the dominance of aliphatic components. The presence of cadalene-based sequiterpenoids confirms the resin to be Class II or dammar resin, derived from angiosperms of Dipterocarpaceae family. These sesquiterpenoids are often detected in many SE Asian fluvio-deltaic oils. Dipterocarpaceae are characteristic of warm tropical climate suggesting the prevalence of such climate during early Eocene in northeast India.

    • Palynological and organic geochemical studies of the middle Eocene Siju Formation of Garo Hills, Meghalaya, India

      Y RAGHUMANI SINGH ARKA RUDRA SH PRIYOKUMAR SINGH SURYENDU DUTTA M SAPANA DEVI N RESHMA DEVI

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      Detailed palynological and organic geochemical analysis of middle Eocene marlstones from the Siju Formation, Garo Hills of Meghalaya, were undertaken. All marl samples contained abundant organic wall dinoflagellate cysts and a few number of spores-pollen grains, foraminiferal linings and calcareous foraminifera. The palynological assemblage consists of 21 genera and 35 species with fungal remains. The occurrence of palynofloral assemblage indicates the prevalence of tropical–subtropical with humid climatic conditions. The deposition environment of the Siju Formation has been interpreted as the neritic setting. Organic matter is thermally immature representing type III–type IV kerogen with low total organic carbon (${\le}$0.72%). The biomarkers suggest microbial degradation of both reworked and terrestrial organic matter. Occurrence of polycyclic aromatic hydrocarbons indicate charred biomass transported from the land.

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