Birbal Sahni Institute of Palaeosciences

Due to the lack of unambiguous fossils, the biogenicity of early Precambrian microbialites have often been questioned. To address this challenging issue, we conducted petrography, FESEM-EDX, Raman spectroscopy, and stable carbon isotope investigations on the carbonaceous laminae of hemispheroidal microbialites from the Paleoproterozoic carbonate deposits of Bajna Dolomite, Bijawar Group, India. Thin-section petrographic analysis reveals that the carbonate is mainly composed of dolomite, with alternating laminae rich in carbonaceous material associated with early diagenetic silica deposition. The carbonaceous matter is present in the form of sheaths and fragments dispersed in a three-dimensional orientation. The FESEM-EDX investigation of carbonaceous matter and the surrounding matrix demonstrates that the carbonaceous matter contains significant enrichment of cations such as Ca, Mg, K, Na, Al, and Fe, which are rare in the matrix of the immediate vicinity. This association of cations with the carbonaceous matter indicates the possibility that these carbonaceous matters are the remains of microbial communities predominantly comprising extracellular polymeric substance-secreting bacteria and cyanobacteria. The results of Raman spectroscopic analysis reveal minor spatial variations in thermal maturation and the corresponding maximum and minimum organic carbon disorder. These data reasonably indicate a biogenic origin for the carbonaceous material and the absence of any younger organic contamination.

The Indian Monsoon System, an integral part of the Asian Monsoon, is intricately linked to the global climate system through solar forcing, abrupt warming or cold events in the Northern Hemisphere, and deep ocean circulation. This study reconstructs the sedimentation history and its linkages to monsoon seasonality and intermediate-to-deep ocean circulation over the last 50 ka using well-dated sediment core SK-257/02 from the southeastern Arabian Sea (SEAS). Environmental magnetic parameters (concentration, mineralogy, and grain size) combined with the end-member analysis reveal three dominant sedimentary components. The fine-grained fluvial suspension-driven fraction (EM1- mean size 3.46 mu m) reflects intensified Indian Summer Monsoon (ISM) precipitation during the interglacial periods (MIS 3 and 1) and warmer phases of Dansgaard-Oeschger (D-O) cycles, associated with precession-driven changes in solar insolation. In contrast, the Northeast Monsoon (NEM) wind-driven aeolian silt fraction (EM2, mean size 5.59 mu m) dominates during glacial stages (especially the last glacial maximum; LGM) and Heinrich events (HS). The co-occurrence and compensatory depositional behavior of EM1 and EM2 demonstrate the seasonal occurrence of the South West Monsoon (SWM) and NEM during the glacial-interglacial cycle. The fractional abundance of the coarsest fraction (EM3, mean size 15.92 mu m) shows coherence with enhanced southern component waters (SCW)- Antarctic Bottom Water: AABW and/or Pacific Deep Water: PDW), admixed intermediate-to-deep circulation across the Arabian Sea, Equatorial Indian Ocean, and the Bay of Bengal, particularly during glacials and stadials. This signifies that the resuspension of fine-tomedium silt-sized sediment is associated with stronger circulation at intermediate water depths, temporally synchronizing with colder Antarctic and Southern Ocean episodes, promoting the advent of more SCW admixed Circumpolar Deep Water (CDW) into the Northern Indian Ocean. This suggests a teleconnection with the SEAS through altered intermediate and deep-water circulation, linked to the deep-water mass structure and global overturning circulation changes in the glacial deep ocean.

Petroglyphs on Murujuga in northwest Western Australia depict 50,000+ years of the culture and spiritual beliefs of humankind. They are sacred for the indigenous people. These priceless and irreplaceable petroglyphs are threatened by acidic gas and nitrogenous pollutants from natural gas and chemical facilities. Preservation of the rock surface ferromanganese layer is crucial for survival of the petroglyphs. Rock surface pH has fallen from neutral pre-industrialisation to 4.4-5.2 adjacent to industry. We separated surface material from Murujuga rocks, ground it finely, and subjected the powders to increasing concentrations of inorganic compounds emitted by industry and to organic acids from organisms stimulated by pollutants. Statistical analyses revealed the release of elements crucial for maintaining the integrity of the ferromanganese layer commenced at pH values well above rock surface measurements. Preservation of the globally unique petroglyphs on Murujuga requires urgent introduction of available technologies to reduce industrial emissions to zero.

Herbivory plays a crucial role as a long-term driver of ecosystem changes. Understanding the interactions between herbivores and ecosystems is particularly important for shaping conservation policies, especially those focused on re-wilding. Additionally, understanding changes in the abundance of large herbivores over time and assessing the role of key animal species in disturbance regimes, biodiversity dynamics, and ecosystem resilience remains a significant challenge in long-term ecological studies. Spores specific to herbivore dung offer a valuable source of information on past herbivore populations. Sporormiella, a coprophilous fungal spore that grows on herbivore dung, serves as an important proxy for reconstructing the presence and/or abundance of megaherbivores, livestock density, grazing activity (pastoralism), human impact, extinction events, and the effects of husbandry practices on the natural environment over time and across regions. In India, the application of Sporormiella as a proxy for herbivore presence and abundance remains at an early stage and requires further systematic testing. This review article aims to evaluate the potential of Sporormiella in reconstructing herbivore presence and abundance across different temporal and spatial scales in India. The synthesis of Sporormiella records from both modern and the Holocene sediment samples provides insights into past herbivore densities. Additionally, this study discusses various factors influencing the composition of the spores of coprophilous fungi, and the abundance of Sporormiella, potential constraints on their preservation in certain settings, and the limitations of current research. This research review article also outlines broader implications and directions for the future research.

The present study investigates a 1.55 m long lacustrine sediment core from the Central Ganga Plain (CGP), influenced by the Indian Summer Monsoon (ISM), to reconstruct Holocene variations in sedimentary organic matter (SOM) and hydrodynamic changes. Age-depth modelling based on four radiocarbon dates refines the sedimentary sequence to similar to 4610 cal yr BP. Multiproxy analyses, including grain-size distribution, total organic carbon (TOC), total nitrogen (TN), stable isotopes (delta C-13(TOC) , delta N-15(TN)), and palynological records, reveal four major palaeoenvironmental phases. 4610-3480 cal yr BP represents a dry phase associated with a weak monsoon, enriched delta C-13(TOC) values (-21.2 parts per thousand to -17.9 parts per thousand), and dominance of grass pollen, indicating escalated C-4 vegetation linked to the global 4.2 ka arid event. 3480-2830 cal yr BP reflects relatively strengthened monsoon conditions, facilitating agricultural activity and human-climate adaptation under evolving ecosystem processes. 2830-720 cal yr BP broadly corresponds with the Roman Warm Period, marked by hydroclimatic variability and increasing evidence of human adaptability, including manure-use in agricultural practices inferred from coprophilous fungi. 720-60 cal yr BP indicates a warm and moist phase characterized by increased C-3 vegetation (delta C-13(TOC) -25.2 parts per thousand to -20.8 parts per thousand) and the occurrence of palaeoflood deposits. The increased SOM associated with coarser sediment fractions (26.7-66.1 & micro;m) in this period suggests increased runoff during a generally weak ISM phase, likely reinforced by western disturbances (WDs) coinciding with the Little Ice Age. The study provides new insights into Late Holocene monsoon variability, hydrodynamic processes, and anthropogenic impacts on SOM alteration in the Central Ganga Plain.