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Abstract <p>Siliciclastic sediments archive vital information on source rock composition, palaeoclimatic conditions, and evolving tectonic settings. The present study investigates the petrography and geochemistry of these clastic sediments to reconstruct these parameters for the Late Palaeocene–Early Eocene Tura Formation, a key siliciclastic unit in the Upper Assam Basin, India. Petrographic analysis reveals texturally submature to mature sandstones dominated by quartz (<i>Q</i> = 74.2%), with minor feldspar (<i>F</i> = 8.1%) and lithic fragments (<i>R</i> = 17.7%), including interbedded volcaniclastics indicative of syn-depositional magmatism. Diagenetic features include mechanical compaction, authigenesis of cements and clays, dissolution, and alteration of unstable clastic grains. Geochemical data confirm a provenance dominated by felsic to intermediate igneous rocks, with a minor mafic component. This is evidenced by discriminant diagrams and chondrite-normalized REE patterns showing LREE enrichment, flat HREE, and a negative Eu anomaly, comparable to UCC and PAAS. Weathering indices (CIA, PIA, CIW, ICV) and geochemical signatures reflect moderate to intense chemical weathering in the source region, consistent with geochemical proxies for a shift toward more humid conditions during deposition. Tectonic setting discrimination diagrams yield a mixed model, integrating passive margin sedimentation with active margin inputs. We interpret this as a record of the basin’s dynamic tectonic evolution during the India-Eurasia convergence, with sediment derived from the Indian Craton, recycled orogens, and contemporaneous volcanic sources. Our integrated approach provides a model for resolving complex, multi-source sedimentary systems in convergent margin settings.</p> Research highlights: <p><OrderedList> <ListItem> <ItemNumber>1)</ItemNumber> <ItemContent> <p>LREE enrichment, negative Eu anomalies and elemental ratios suggest felsic provenance.</p> </ItemContent> </ListItem> <ListItem> <ItemNumber>2)</ItemNumber> <ItemContent> <p>Indo-Asian collision transitioned Indian passive margin to active margin.</p> </ItemContent> </ListItem> <ListItem> <ItemNumber>3)</ItemNumber> <ItemContent> <p>Early Himalayan uplift and tectonic reworking influenced the depositional history.</p> </ItemContent> </ListItem> <ListItem> <ItemNumber>4)</ItemNumber> <ItemContent> <p>Volcanic tuff in the basal Tura Formation likely linked to Mikir Traps.</p> </ItemContent> </ListItem> </OrderedList></p>

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Deciphering provenance, tectonic history and palaeoweathering conditions from siliciclastic sediments: a petrographic and geochemical approach of the Tura Formation, NE India

  • 期刊论文

  • 发表日期：

    2026年4月13日

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  • Nishanta Sahariah,
  • Abhijit Gogoi,
  • Pramathesh Bhattacharyya

摘要

Abstract

Siliciclastic sediments archive vital information on source rock composition, palaeoclimatic conditions, and evolving tectonic settings. The present study investigates the petrography and geochemistry of these clastic sediments to reconstruct these parameters for the Late Palaeocene–Early Eocene Tura Formation, a key siliciclastic unit in the Upper Assam Basin, India. Petrographic analysis reveals texturally submature to mature sandstones dominated by quartz (Q = 74.2%), with minor feldspar (F = 8.1%) and lithic fragments (R = 17.7%), including interbedded volcaniclastics indicative of syn-depositional magmatism. Diagenetic features include mechanical compaction, authigenesis of cements and clays, dissolution, and alteration of unstable clastic grains. Geochemical data confirm a provenance dominated by felsic to intermediate igneous rocks, with a minor mafic component. This is evidenced by discriminant diagrams and chondrite-normalized REE patterns showing LREE enrichment, flat HREE, and a negative Eu anomaly, comparable to UCC and PAAS. Weathering indices (CIA, PIA, CIW, ICV) and geochemical signatures reflect moderate to intense chemical weathering in the source region, consistent with geochemical proxies for a shift toward more humid conditions during deposition. Tectonic setting discrimination diagrams yield a mixed model, integrating passive margin sedimentation with active margin inputs. We interpret this as a record of the basin’s dynamic tectonic evolution during the India-Eurasia convergence, with sediment derived from the Indian Craton, recycled orogens, and contemporaneous volcanic sources. Our integrated approach provides a model for resolving complex, multi-source sedimentary systems in convergent margin settings.

Research highlights:

1)

LREE enrichment, negative Eu anomalies and elemental ratios suggest felsic provenance.

2)

Indo-Asian collision transitioned Indian passive margin to active margin.

 3)

Early Himalayan uplift and tectonic reworking influenced the depositional history.

 4)

Volcanic tuff in the basal Tura Formation likely linked to Mikir Traps.