A Look Back…50 Years: South Florida Sediment

A lasting paradigm in carbonate sedimentology is that “carbonates are born, not made,” a truism that distinguishes them from the siliciclastic relatives. Fifty years ago, a classic contribution by Swinchatt emphasized the impact of their distinct origins and characteristics of early alteration on composition and texture of sediment of the South Florida reef tract. The results illustrated the complex influences of seagrass, physical process, biological breakdown, and how they vary across this shelf margin. Swinchatt suggested that “interrelationships between various rates of production and breakdown may be extremely complex and their effect on the sediment difficult to evaluate…and that further investigation is needed.”

Significance of constituent composition, texture, and skeletal breakdown in some Recent carbonate sediments by Jonathan P. Swinchatt

Highlights—Crevasse Subdeltas: Small but Important

The geomorphology, stratal architecture, and sedimentologic attributes of a range of deltas have been interpreted in the context of fluvial, tidal, and wave processes and sea-level change. Most studies focus on delta-front regions, whereas finer (and typically less well exposed) delta plain deposits have received less attention. Here, Gugliotta et al. focus on defining and describing tide-influenced crevasse subdelta deposits, an important component of lower delta plain stratigraphy of a river-dominated delta in the Lajas Formation of the Neuquén Basin of Argentina. The study emphasizes the importance of understanding the relative importance of tide and river processes in facies distribution and architecture, and the applications to characterization of interdistributary deposits. The data suggest that some “tidal” deposits interpreted from the rock record may instead be river-dominated, tide-influenced crevasse subdeltas, and that this distinction has important implications for understanding paleogeography and predicting reservoir geometries.

Stratigraphic record of river-dominated crevasse subdeltas with tidal influence (Lajas Formation, Argentina) by Marcello Gugliotta, Stephen S. Flint, David M. Hodgson, and Gonzalo D. Veiga

Highlights—Minibasin Dynamics

Although typically < 10 km wide, intraslope minibasins such as those in the Gulf of Mexico can include rapid subsidence, accumulate thick sediment pile, and ultimately host large hydrocarbon accumulations. Differential sediment loading on a mobile substrate (e.g., salt) can drive accommodation and stratigraphic architectures in intraslope minibasins, but sedimentologic and tectonic processes commonly are evaluated separately. This contribution by Kopriva and Kim experimentally integrates depositional and tectonic processes to investigate the relations of substrate movement and minibasin sedimentation. A silicone polymer model of a viscous mobile substrate provided the basis for a series of 2D experiments to explore the effects of variation in 1) sediment supply rate, 2) depositional style (intermittent sediment supply), and 3) the thickness of the deformable substrate on subsidence patterns and minibasin stratigraphic development. The results highlight the possible role of autogenic processes on minibasin dynamics and fill-and-spill stratigraphy.

Coevolution of mini basin subsidence and sedimentation: experiments by Bryant T. Kopriva and Wonsuck Kim