Short-stasis signatures in Cambrian and Ordovician shallow-marine sandstones: implications for the ichnological record and time preserved at outcrop

Shallow-marine sandstones are an archetypal facies in the stratigraphic record of the Cambrian Explosion and the Ordovician Radiation but have been considered uninformative owing to erosional signatures, time incompleteness and unfossiliferous outcrops. New analyses of the Carnedd-y-Filliast Grits (Furongian, Wales) and littoral sandstone successions from Baltica and Laurentia reveal that, besides erosion, bedding planes in such outcrops commonly register sedimentary stasis. Most stasis intervals were brief, reflecting (1) a high sedimentation frequency, (2) post-depositional substrate resculpting by wave action during ‘active-layer stasis’, inhibiting infaunal colonization and rendering the surface representative of only the interval immediately preceding burial, and (3) the low preservation potential of longer-stasis surfaces, which mainly occur within heterolithic packages that, in low-subsidence settings, are commonly eroded and replaced by amalgamation surfaces between sandstones. The short-stasis signature of littoral sandstones renders metre-scale architectural elements relatively time-complete but biases their fossil record at outcrop. Short-stasis surfaces are high-resolution snapshots but form incomplete representations of ancient ecosystems compared with surfaces that capture longer intervals. As such, the predominance of short-stasis surfaces contributed to the low ichnodiversity and sparse fossil content of littoral sandstones, implying that early Paleozoic littoral ecosystems were more biodiverse than their known record suggests.