Outcrop and core-based studies of clinothems provide valuable archives basin-margin evolution. However, published quantitative grain character data (including grain size, grain shape, sorting, and sand-to-mud-ratios) are limited, and grain character variation across complete clinothem systems remains poorly constrained. Novel quantitative grain character datasets are presented here for core (Miocene intrashelf clinothems, offshore New Jersey) and outcrop (Eocene clinothems, Sobrarbe Deltaic Complex, Spain) case studies, which target quasi-coeval topset, foreset and bottomset deposits of prograding clinothems.
Grain character datasets reveal that basin-scale and intraclinothem variations in sedimentary fabric are dependent on the dominant process-regime in operation at the shelf-edge. At basin-scales, shelf process-regime plays a more important role than clinoform trajectory in determining the location and timing of coarse-grained sediment delivery; river-dominated clinothems effectively convey coarse-grained sediment downdip under both rising and falling clinoform rollover trajectories. At intraclinothem scales abrupt stratigraphic changes in process-regime significantly impact the distribution of grain character across the complete depositional profile, forming observable and quantifiable intraclinothem chronostratigraphic surfaces.
The grain-character dataset has been used to: i) compile unique databases of grain size, grain shape, and sorting statistics, which can be applied to test and refine numerical forward models of sediment distribution, which seek to improve prediction of lithology distribution; ii) quantitatively define intraclinothem surfaces at a higher resolution than is possible using chronostratigraphic techniques; iii) refine the placement of sequence boundaries, and iv) develop a model of clinothem evolution, in which the nature of the flows, and dominant process-regime in the shelf, control the downdip and vertical distribution of sand and mud. This study challenges widely held paradigms that link accommodation, sediment supply, and clinoform rollover trajectories to the distribution of sediment on basin margins. The results highlight the critical role played by the shelf process-regime in determining how and when sediment of different calibre and maturity is transported downdip.
