Investigation of depositional fabric and its impact on the geomechanical behavior of limestones

This study presents detailed petrographic and physico-mechanical analyses of five textural varieties of limestone from the Upper Indus Basin, Pakistan: bioclastic grainstone, ooidal grainstone, bioclastic packstone, bioclastic wackestone, and neomorphosed mudstone. Comprehensive tests were conducted on the samples, including specific gravity, water absorption, porosity, Ultrasonic Pulse Velocity (UPV), Schmidt Hammer Test (SHT), Unconfined Compressive Strength (UCS), and Point Load Test (PLT). Additionally, Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) were used to characterize the microstructure and elemental composition of the studied carbonate rocks. The study highlights the impact of depositional fabric and diagenetic processes on geomechanical behavior of limestones. The results reveal (a) an inverse relationship between allochems and strength properties such as in wackestone and packstone, (b) micrite content shows a direct correlation with strength, and (c) sparite content exhibits an inverse correlation with strength properties. The bioclastic wackestone yielded the highest strength due to high micrite content, while the neomorphosed mudstone displayed the lowest strength due to microspar formation and increased porosity from aggrading neomorphism. Linear regression analysis showed weak correlations between allochems, micrite, and strength due to heterogeneity of the matrix and diagenetic alterations. However, sparite content had a strong correlation with strength properties. This research provides critical insights into the geological diversity and potential applications of limestones from the region.