The enigmatic black mat sediment complex in the northern Andes, previously considered the product of a high-grade lightning strike and low grade brush fire, has been upgraded recently to a conflagration resulting from incoming asteroid/comet impact over the Laurentide Ice Sheet at approximately
12.9 ka. Previous evidence from the black mat beds of disrupted quartz and orthoclase grains and intense firing from incoming C-rich ejecta is further supported by new SEM/EDS and FIB analyses of fine grain silt and clay spherules (10-∼2 μm dia.) of C, Fe and Mn composition,
a mixed material of partly ejecta and partly country rock. Because the environment at the time of ejecta impact was in the initial stage of seral vegetative development as wet tundra, part of the clay/organic balls, classic 'house of cards' form, which constitute a portion of the sediment
complex, may be of cosmic origin. Evidence of cyanobacteria and fungal filaments on and within grain coatings are probably post depositional and therefore of terrestrial origin.
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