A squall by the seashore ca 2.3 billion years ago : raindrop imprints in a Paleoproterozoic tidal flat deposit, Kungarra Formation, Western Australia

Abstract

In this contribution, we describe the occurrence of well-preserved Paleoproterozoic raindrop impact imprints on two surfaces of rippled siltstone–mudstone from the uppermost part of the Paleoproterozoic Kungarra Formation, Turee Creek Group, Western Australia. The raindrop imprints appear on the tops of two immediately overlying bedding surfaces in siltstone, near the top of a shallowing upward sequence that progresses from sandstone to mudstone. Imprints are circular to elliptical with an average diameter of 2–3 mm and a maximum length of 6.3 mm when elliptical. Flat ripple crest morphologies, varied ripple crest orientations, and marks of standing water in the ripple troughs indicate very shallow water conditions. When combined with sedimentological data from the underlying Kungarra Formation (shallow marine sandstones and siltstones), and mature quartz arenites of the overlying Koolbye Formation (mixed tidal, beach, fluvial and eolian), the interval examined is interpreted as a tidal flat deposited during a falling stage systems tract.