Abstract Mixed siliciclastic–carbonate successions provide crucial stratigraphic archives for reconstructing depositional processes and basin evolution, though the Precambrian examples remain underexplored compared to the Phanerozoic. The lower part of the Mesoproterozoic Kurnool Group, Cuddapah Basin, southern India, preserves such a mixed siliciclastic-carbonate succession between the Banaganapalle Formation and the Narji Limestone. Through detailed field mapping, lithostratigraphic logging, and correlation across multiple sections, we document the laterally persistent approximately ~10 m thick heterolithic succession, which is best exposed near Ujjalawada, Andhra Pradesh. On the basis of lithological distinctiveness, stratigraphic position, thickness, and mappability, this mixed succession is formally defined as the Ujjalawada Member within basal part of the Narji Limestone. This transitional heterolith records both strata-and compositional mixing, comprising interbedded glauconitic sandstone-siltstone, calcareous shale, and carbonate-clast conglomerates that reflect variable siliciclastic supply, simultaneous carbonate precipitation, and relative sea-level oscillations. This mixed siliciclastic-carbonate heterolith refines lithostratigraphic framework of the Kurnool Group and capture evolutionary transition from the rift-controlled Banaganapalle siliciclastic sedimentation to passive-margin carbonate deposition of the Narji Limestone. Formal definition of the Ujjalawada Member establishes a revised lithostratigraphic framework that provides essential reference for future lithostratigraphic correlation, basin analysis, and comparative studies across the Mesoproterozoic Purana basins in the Southern Indian Block. Research highlights <UnorderedList Mark="Bullet"> <ItemContent> Formal proposal of the Ujjalawada Member within the basal Narji Limestone, representing a ~10 m thick Mesoproterozoic mixed siliciclastic–carbonate heterolithic succession. </ItemContent> <ItemContent> Revision of the lithostratigraphic framework of the lower Kurnool Group, resolving ambiguities at the Banaganapalle–Narji transition. </ItemContent> <ItemContent> The Ujjalawada Member records both strata and compositional mixing, reflecting tectonic influence, sediment supply variations, and relative sea-level changes. </ItemContent> <ItemContent> The revised lithostratigraphic framework will provide a robust basis for regional correlation and future integrative studies on the South Indian Mesoproterozoic Purana basins. </ItemContent> </UnorderedList>

Introducing “Ujjalawada Member” in the Mesoproterozoic Kurnool Group: a record of siliciclastics to carbonate platform transition in a mixed siliciclastic-carbonate platform

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发表日期：

2026年6月29日

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Damayanti Choudhury,
Arijit Debnath,
Amlan Banerjee

摘要

Abstract

Mixed siliciclastic–carbonate successions provide crucial stratigraphic archives for reconstructing depositional processes and basin evolution, though the Precambrian examples remain underexplored compared to the Phanerozoic. The lower part of the Mesoproterozoic Kurnool Group, Cuddapah Basin, southern India, preserves such a mixed siliciclastic-carbonate succession between the Banaganapalle Formation and the Narji Limestone. Through detailed field mapping, lithostratigraphic logging, and correlation across multiple sections, we document the laterally persistent approximately ~10 m thick heterolithic succession, which is best exposed near Ujjalawada, Andhra Pradesh. On the basis of lithological distinctiveness, stratigraphic position, thickness, and mappability, this mixed succession is formally defined as the Ujjalawada Member within basal part of the Narji Limestone. This transitional heterolith records both strata-and compositional mixing, comprising interbedded glauconitic sandstone-siltstone, calcareous shale, and carbonate-clast conglomerates that reflect variable siliciclastic supply, simultaneous carbonate precipitation, and relative sea-level oscillations. This mixed siliciclastic-carbonate heterolith refines lithostratigraphic framework of the Kurnool Group and capture evolutionary transition from the rift-controlled Banaganapalle siliciclastic sedimentation to passive-margin carbonate deposition of the Narji Limestone. Formal definition of the Ujjalawada Member establishes a revised lithostratigraphic framework that provides essential reference for future lithostratigraphic correlation, basin analysis, and comparative studies across the Mesoproterozoic Purana basins in the Southern Indian Block.

Research highlights

Formal proposal of the Ujjalawada Member within the basal Narji Limestone, representing a ~10 m thick Mesoproterozoic mixed siliciclastic–carbonate heterolithic succession.

Revision of the lithostratigraphic framework of the lower Kurnool Group, resolving ambiguities at the Banaganapalle–Narji transition.

The Ujjalawada Member records both strata and compositional mixing, reflecting tectonic influence, sediment supply variations, and relative sea-level changes.

The revised lithostratigraphic framework will provide a robust basis for regional correlation and future integrative studies on the South Indian Mesoproterozoic Purana basins.