Decoding paleoenvironment through pedogenic and diagenetic characteristics of pre-volcanic Maastrichtian paleosols of the Lameta Formation, Central India

Abstract

This study presents a detailed micromorphological investigation of Maastrichtian-aged (65Ma) paleosols from the Lower Limestone (LLM) and Mottled Nodular Bed (MNB) units of the Infratrappean Lameta Formation in Central India. Positioned directly beneath the Deccan Traps—one of the main contributors to the K-Pg mass extinction—the Lameta Formation provides crucial insights into pre-volcanic environmental conditions just before the K-Pg extinction event. The morphological and micromorphological features of the paleosols were analyzed from exposures in the Cantonment area and along the Narmada River in Jabalpur, Madhya Pradesh, India. Thin-section analysis played a critical role in distinguishing pedogenic and diagenetic features in these lithified paleosols, offering valuable insights into the paleoenvironment of the Lameta Formation. Major diagenetic alterations identified in the studied paleosols include coarsening of pedogenic calcite to sparitic calcite, remobilization of Fe oxides leading to Fe oxide cementation on coarse grains and ped boundaries, distortion and overprinting of illuvial iron-rich clay and fine silty-clayey intercalations and coatings, sutured quartz grains, and microcrystalline silica in the form of chalcedony. Despite these diagenetic alterations, the paleosols retain well-preserved evidence of paleopedogenic processes, observed through a variety of matrix and intrusive pedofeatures such as clay coatings, calcite hypo-/quasi-coatings, micritic nodules, Fe/Mn hypo-/quasi-coatings, Fe oxide nodules, and partially decomposed organic matter. Based on these pedogenic and diagenetic features, the study identifies a spectrum of paleosol developmental stages, ranging from weakly to well-developed paleosols. These variations are attributed to differences in hydrological conditions and landscape topography. A comprehensive paleolandscape model has been proposed for the Lower Limestone (LLM) and Mottled Nodular Bed (MNB) units, grounded in the micromorphological characteristics. This model suggests that the Lower Limestone region predominantly hosted poorly drained habitats, indicative of more humid climatic conditions. In contrast, the Mottled Nodular Bed litho-unit reflects drier paleoenvironments. This contrast highlights environmental variations within the Lameta Formation, enhancing our understanding of ancient environmental dynamics and providing a glimpse into the climatic variances that shaped the pre-Volcanic terrain.