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The Continental Shelf as a Conveyor or Filter: Sediment Character Analysis From Coeval Topset, Foreset, and Bottomset Deposits


The continental shelf can act as both a conveyor and a filter during sediment transfer from the continents to the deep oceans. However, the updip controls on the character of sediment deposited in deep-water are poorly understood due to poor sampling of coeval deposits along depositional profiles. Miocene clinothems from offshore New Jersey are used to study the role of the continental shelf as a staging-area for sediment delivery to the deep-sea, due to the preservation of complete, stratigraphically-linked clinothem sequences, which can be tied to the eustatic sea-level curve. Here, we present data collected from three cores (M27, M28 and M29) recovered during IODP Expedition 313. The stratigraphic intervals targeted are quasi-coeval shallow- and deep-marine sandstones, spanning the major Miocene seismic sequence boundaries m5.2-m5.7. A total of 560 m of core was sampled at c. 50cm intervals and grain size and shape analysis conducted on 967 sediment samples. Grain size and shape data have been collated according to the assigned sedimentary facies. Each topset facies has been grouped with its stratigraphically-linked counterpart foreset and bottomset facies. Multivariate statistical analysis has been used to test for associations between variability in topset facies and patterns of downdip sediment dispersal. Results indicate that topset facies has a quantifiable effect upon sediment bypass and grain-character partitioning. We see (a) a departure from the traditional ‘Lowstand Bypass Model’ as predicted by the sequence stratigraphic paradigm and (b) a longitudinal sorting profile that is dependent on the process regime during topset deposition. The results can be used to evaluate the extent to which the topset process regime impacts sedimentary character downdip and contribute to a generic model for such variations in passive margin settings. As facies analysis is a building block of the sequence stratigraphic framework, the detailed sedimentary characterisation of facies relationships is essential. The results of this investigation represent a move away from interpretative facies analysis, to a more quantitative methodology. The approach may aid identification of stratigraphic intervals in which reservoir quality sands are most likely to occur by improving understanding of shelf-sand preservation potential and the character of sand bypassed to deep-water basins.