Concave and convex raindrops. El Pueblo early Permian, NM, USA.

Description

Because of its hydrological variance the El Pueblo early Permian swamp often exposed smooth clayey surfaces, especially after rain water receded from the shore area. The tail end of rain showers recorded on such surfaces. Successive rainfall deposited a thin layer of clay that recorded convex mold impressions of previous raindrop impressions. Note: I recently received information from a collector that some convex "rainfall impressions" can be from gas bubbles emanating from decaying organic matter. A valid theory, since there was a lot of that going on. I have many times detected a faint carbonic odor from trapped gas between rock layers. Gas bubble emissions would have recorded upward, opposite of raindrop impact. Collapse of gas bubbles conceivably could have created concave impressions. Very interesting theory and I will look for more clues. One constant remains: moist soft clayey soil (redbeds) modernly recreates tail-end raindrops identical to the early Permian. That's because muddy red water deposits a thin last layer of fine clay (H. Ortiz 2021).