Abstract:
The Andigama Basin is a pre-rift Gondwana sedimentary basin containing Late Jurassic to Early Cretaceous calcareous
sandstones and carbonaceous shales of varying thickness. This study aims to reconstruct the weathering, tectonic setting, and
paleoenvironment of East Gondwanaland using a 90 m deep drill core. Whole-rock geochemistry and elemental analysis were
carried out using X-ray fuorescence spectrometry and CHNS/O elemental analyzer, respectively. Lithological changes in
the borehole core refect diverse hydrodynamic conditions. X-ray difraction patterns indicate a signifcantly high content of
quartz and kaolinite peaks. Scanning electron microscope images suggest that quartz, carbonate, and aluminosilicate dominant
detrital particles and chemical residues enhanced the cementation by reducing the porosity and permeability of sealing
interfaces. Major oxide and trace element concentrations are approximately similar to the Upper Continental Crust values.
High Chemical Index of Alteration, Plagioclase Index of Alteration, Index of Compositional Variability, and high content
of kaolinite peaks refect intense chemical weathering, suggesting a hot and humid climate during the Late Jurassic–Early
Cretaceous periods. The calculated paleo-land surface temperature (24.7±5 °C) and mean annual precipitation (1120 mm)
values are also consistent with the interpretation of weathering indices and global oxygen isotopic studies. Provenance and
tectonic setting discrimination diagrams suggest the deposition of quartzose and mafc igneous sources under the passive
margin stage. In addition, elemental analysis indicates a nutrient-rich (average total organic carbon=4.67±1.04 wt. %
and total nitrogen=3.13±3.39 wt. %) and oxic to oxygen-poor reducing (average total sulfur=2.13±1.43 wt. %) swamp
environment. Consequently, the Late Jurassic–Early Cretaceous climate was simulated as a prominent deglaciation/hot
and humid climate in the Gondwana supercontinent, based on calculated paleo-land surface temperatures and mean annual
precipitation.
