Revised chronology and expanded insights: Geologic perspective on the Luna impact event and its influence on the Harappan Civilization

Luna is a potential impact crater located in the Banni Plains of the Kutch Basin in western India. The suspected impactites, collected from a 1-m deep trench near the vicinity of the Luna structure, possess a range of physical (porosity and magnetism) properties. Petrographic studies reveal that these impactites are dominated by wüstite, kirschsteinite, spinel, olivine, and quartz (in decreasing order of abundance), with a few silica grains exhibiting potential planar fractures (PF). These impactites can be grouped into three distinct melt classes based on their wüstite and kirschsteinite content (classified as Ca-rich, Ca-poor, and transitional type). Spectroscopic analysis indicates a higher concentration of wüstite in magnetic samples, whereas weakly magnetic to non-magnetic samples have an elevated presence of kirschsteinite. Major oxide geochemistry comparison between the impactites and the surrounding Banni Plain sediments show that some Luna impactites have a chemical affinity with a terrestrial or transitional setting, whereas the remaining samples portray a non-terrestrial trend suggesting notable mixing of target rock and projectile material. Optically stimulated luminescence dating of the sediment layer containing the impactites yielded an age of 4045 ± 182 years for the impact, consistent with the earlier proposed age of <6900 years based on radiocarbon dating. The revised age places the Luna impact event much closer to the time frame of the Harappan Civilization's decline, suggesting that it may have had a greater impact on the Harappan Civilization than previously thought.