Friday, July 21, 2017

Highlights: Cambrian Cratonic Carbonates

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.

Wednesday, July 12, 2017

Highlights: Seismic Expression of Fluvial Channels

Fluvial channels are inherently three-dimensional features; although challenging to study on two-dimensional outcrops, seismic data provide unique perspectives on their architecture. Alqahtani and others evaluate the geometry, dimensions, distribution and evolution of fluvial channel systems from a humid-tropical climatic setting through detailed analysis of high-resolution 3D seismic reflection data from the Malay Basin. The interpretations reveal eight depositional units that include systematic changes in six types of fluvial channels defined based on cross-sectional and planform geometries. The data provide input for reconstructions of the palaeo-hydrological conditions during Pleistocene sea-level cycles that affected the Sunda Shelf Sea. The manuscript further evaluates the roles that sea-level variations, climate, and sediment supply play on controlling the formation and evolution of fluvial systems, including incised valleys and associated tributary channels.