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ETUDE SEDIMENTOLOGIQUE ET GEOCHIMIQUE (ISOTOPES STABLES) DES BASSIN SYN-OROGENIQUES DE L'HYMALAYA DU NEPAL (SIWALIKS ET BASSIN DE KATHMANDU)

Abstract : The work deals with paleo-environmental study of the Siwalik foreland basin (upper Miocene) and the intermountain Kathmandu basin (Plio-Pleistocene). O and C composition of modern mollusks and waters of Ganga Plain and intermountain basins were realized as a reference for paleo-environmental study.
The Δ18O of rivers varies from -18‰ in north of Himalaya to -4‰ in the plain. The Δ18Ocar of modern shell show an equilibrium fractionation with the river waters (20 to 25°C). Both carbonate and river water values are different according to catchment basin extension. The Δ13CDIC of rivers are higher than Δ13Ccar due to organic carbon incorporation in shell.
In the Siwaliks, Δ18Ocar varies from -16.4 to 0.6‰. For the Late Miocene, the Δ18Ocar values are lower than Pliocene and modern values. Therefore, rivers running through the Siwalik plain should show different geometry. The Δ13C show a sharp increase up to 0‰ around 5 Ma, which seems to be linked to the contemporaneous evolution of C4 plant.
The Kathmandu Basin (3-0 Ma) is a transported basin and characterized by fluvio-lacustrine sediments. The evolution of lake is controlled by tectonic, landslide and debris-flow.
The Δ18Ocar older than 1 Ma vary from -11 to -4‰ and are compatible with river water (-10.1 to -7‰) as well as monsoon water (-18 to 2‰) in Kathmandu. In contrast Δ18Ocar of Gokarna Formation (< 50 Ka) is extremely high (-2.4 to 8‰) and is compatible to dry period meteoric water (-6.5 to 7.5‰). Such values are generally associated with diatomite. Two processes could be interacted for diatomite time: reduction in summer precipitation and strong evaporation; both phenomena tend to make a strong concentration in 18O.
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https://tel.archives-ouvertes.fr/tel-00110985
Contributor : Ananta Prasad Gajurel <>
Submitted on : Thursday, November 2, 2006 - 6:26:08 PM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
Long-term archiving on: : Friday, November 25, 2016 - 1:52:37 PM

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  • HAL Id : tel-00110985, version 1

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Ananta Prasad Gajurel. ETUDE SEDIMENTOLOGIQUE ET GEOCHIMIQUE (ISOTOPES STABLES) DES BASSIN SYN-OROGENIQUES DE L'HYMALAYA DU NEPAL (SIWALIKS ET BASSIN DE KATHMANDU). Géochimie. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00110985⟩

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