What sediments are preserved during sea-level falls on cratonic passive margins? Raine and Smith explore the concept that on many carbonate platforms, sequence boundaries are represented by a zone of shallower facies and it is difficult to identify a single surface as a sequence boundary. To do so, they start by describing facies that provide evidence of a coastal sabkha, a sedimentary environment commonly not well preserved in Palaeozoic carbonates. At a larger scale, they document stacking patterns and physical features (e.g., karst, sandstone) that record a falling stage systems tract and a well-defined type 1 sequence boundary in a Cambrian succession in Scotland, interpreted to be consistent with the idea that the Sauk II-III boundary represents a major sea-level fall associated with progradation of sabkhas.
Sabkha facies and the preservation of a falling-stage systems tract at the Sauk II–III supersequence boundary in the Late Cambrian Eilean Dubh Formation, NW Scotland by Robert J. Raine and M. Paul Smith