Spectroscopic characterization of fluorite of Amba Dongar, Gujarat, India: Linking chemical composition with color.

This work addresses the long-standing debate surrounding the origin of color variation in fluorite (CaF2) through a novel quantitative approach. By examining eight carefully selected fluorite samples having different hue of colors from the Amba Dongar mine in Gujarat, India, a rigorous quantitative analysis was conducted. This approach combined chemical compositional data and optical spectroscopic features to elucidate the relationship between elemental composition, concentration, and color variation in fluorite. Precise elemental concentration data for trace transition metals, alkali metals, and rare earth elements (REEs) were obtained through inductively coupled plasma mass spectroscopy (ICP-MS) analysis of powdered fluorite samples. Optical spectroscopic techniques, including UV-visible absorption, emission (photoluminescence and fluorescence), and Raman spectroscopy, were employed to capture characteristic spectral signatures for specific color of the study sample. The work unveils a strong correlation between specific elemental concentrations and observed spectral features, particularly influenced by alkaline metals, transition group elements, and REEs. Fluorite's optical absorption behavior lacks a clear pattern in UV and infrared wavelength ranges but correlates well with transition metal, alkaline element, and REE concentrations in visible wavelength regions, influencing coloration. Luminescent centers in the study fluorite samples correspond to specific REE concentrations, indicating a strong linkage between emission wavelengths with the presence of specific REE. UV-visible and fluorescence in fluorite result from trivalent REE or Eu2+ ions, with emission intensity affected by REE concentration and specific REE or combinations thereof. Raman spectroscopy identifies characteristic modes related to F-substitution and REE impurities, providing insights into fluorite's structural composition. This quantitative correlation between elemental composition and spectroscopic characteristics represents a novel contribution for understanding color variation mechanisms in fluorite. The comprehensive analysis of this present work underscores the intricate interplay of mineral composition, and element concentration particularly alkaline metals, transition group elements, and REEs, for variation in spectral signatures with variation in fluorite's visual attributes.

On the existence of a perennial river in the Harappan heartland.

The legendary river Saraswati of Indian mythology has often been hypothesized to be an ancient perennial channel of the seasonal river Ghaggar that flowed through the heartland of the Bronze Age Harappan civilization in north-western India. Despite the discovery of abundant settlements along a major paleo-channel of the Ghaggar, many believed that the Harappans depended solely on monsoonal rains, because no proof existed for the river's uninterrupted flow during the zenith of the civilization. Here, we present unequivocal evidence for the Ghaggar's perennial past by studying temporal changes of sediment provenance along a 300 km stretch of the river basin. This is achieved using 40Ar/39Ar ages of detrital muscovite and Sr-Nd isotopic ratios of siliciclastic sediment in fluvial sequences, dated by radiocarbon and luminescence methods. We establish that during 80-20 ka and 9-4.5 ka the river was perennial and was receiving sediments from the Higher and Lesser Himalayas. The latter phase can be attributed to the reactivation of the river by the distributaries of the Sutlej. This revived perennial condition of the Ghaggar, which can be correlated with the Saraswati, likely facilitated development of the early Harappan settlements along its banks. The timing of the eventual decline of the river, which led to the collapse of the civilization, approximately coincides with the commencement of the Meghalayan Stage.

Early Middle Palaeolithic culture in India around 385-172 ka reframes Out of Africa models.

Luminescence dating at the stratified prehistoric site of Attirampakkam, India, has shown that processes signifying the end of the Acheulian culture and the emergence of a Middle Palaeolithic culture occurred at 385 ± 64 thousand years ago (ka), much earlier than conventionally presumed for South Asia. The Middle Palaeolithic continued at Attirampakkam until 172 ± 41 ka. Chronologies of Middle Palaeolithic technologies in regions distant from Africa and Europe are crucial for testing theories about the origins and early evolution of these cultures, and for understanding their association with modern humans or archaic hominins, their links with preceding Acheulian cultures and the spread of Levallois lithic technologies. The geographic location of India and its rich Middle Palaeolithic record are ideally suited to addressing these issues, but progress has been limited by the paucity of excavated sites and hominin fossils as well as by geochronological constraints. At Attirampakkam, the gradual disuse of bifaces, the predominance of small tools, the appearance of distinctive and diverse Levallois flake and point strategies, and the blade component all highlight a notable shift away from the preceding Acheulian large-flake technologies. These findings document a process of substantial behavioural change that occurred in India at 385 ± 64 ka and establish its contemporaneity with similar processes recorded in Africa and Europe. This suggests complex interactions between local developments and ongoing global transformations. Together, these observations call for a re-evaluation of models that restrict the origins of Indian Middle Palaeolithic culture to the incidence of modern human dispersals after approximately 125 ka.

Astrobiological implications of dim light phototrophy in deep-sea red clays.

Red clays of Central Indian Basin (CIB) under influence of trace of Rodriguez Triple Junction exhibited chemoautotrophy, low temperature hydrothermal alterations and photoautotrophic potential. Seamount flank TVBC-08, hosting such signatures revealed dominance of aerobic anoxygenic phototroph Erythrobacter, with 93% of total 454 pyrosequencing tags. Subsequently, enrichments for both aerobic (Erythrobacter) and anaerobic anoxygenic phototrophs (green and purple sulphur bacteria) under red and white LED light illumination, with average irradiance 30.66Wm-2, were attempted for three red-clay sediment cores. Successful enrichments were obtained after incubation for c.a. 120 days at 4°± 2°C and 25°± 2°C, representing ambient psychrophilic and low temperature hydrothermal alteration conditions respectively. During hydrothermal cooling, a microbial succession from anaerobic chemolithotrophy to oxygenic photoautotrophy through anaerobic/aerobic anoxygenic phototrophic microbes is indicated. Spectral absorbance patterns of the methanol extracted cell pellets showed peaks corresponding to metal sulphide precipitations, the Soret band of chlorosome absorbance by photosystem II and absence of peaks at Qy transition band. Dendritic nano-structures of metal sulphides are common in these sediments and are comparable with other sulphidic paleo-marine Martian analogues. Significant blue and redshifts have been observed for the experimental samples relative to the un-inoculated medium. These observations indicate the propensity of metal-sulphide deposits contributing to chemiluminiscence supporting the growth of phototrophs at least partially, in the otherwise dark abyss. The effects of other geothermal heat and light sources are also under further consideration. The potential of phototrophic microbial cells to exhibit Doppler shift in absorbance patterns is significant towards understanding planetary microbial habitability. Planetary desiccation could considerably influence Doppler effects and consequently spectral detection techniques exo-planetary microbial life.