Sedimentary stasis in a Jurassic lagoonal delta system: the Lastres Formation of Asturias, northern Spain

The Jurassic Lastres Formation hosts a suite of well exposed deltaic facies, rendering it an ideal case study to understand the record of sedimentary stasis and true substrates within this broad depositional setting. With novel sedimentological and ichnological field data combined with existing literature, we discuss how durations of sedimentary stasis differ throughout the stratigraphy, ranging from years to centuries on floodplains, to hours to days in interdistributary bays, to instants within distributary channels. The likelihood of true substrates from any given environment being observed in the rock record increases with the recurrence frequency of stasis and preservation potential of the strata, and depends on a sufficiently long colonization window for signatures to be imparted. Intermediate durations lead to the best conditions for preservation of true substrates, as a relatively high recurrence frequency lines up with a sufficiently long colonization window and preservation potential. However, short stasis durations can provide informative snapshots of short-timescale events, and long stasis durations can provide broader palaeoenvironmental context that cannot otherwise be inferred.