Sedimentology, stratigraphic context, and implications of Miocene intrashelf bottomset deposits, offshore New Jersey
Hodgson, DM; Browning, JV; Miller, KG; et al.Hesselbo, SP; Poyatos-Moré, M; Mountain, GS; Proust, J-N
Date: 7 December 2017
Journal
Geosphere
Publisher
Geological Society of America
Publisher DOI
Abstract
Drilling of intrashelf Miocene clinothems onshore and offshore New Jersey has provided better understand deposition on topsets and foresets, but the sedimentology and stratigraphy of their bottomset deposits have not been documented in detail. Three coreholes (M27-29), collected during Integrated Ocean Drilling Program (IODP) Expedition ...
Drilling of intrashelf Miocene clinothems onshore and offshore New Jersey has provided better understand deposition on topsets and foresets, but the sedimentology and stratigraphy of their bottomset deposits have not been documented in detail. Three coreholes (M27-29), collected during Integrated Ocean Drilling Program (IODP) Expedition 313, intersect multiple bottomset deposits and their analysis helps to refine sequence stratigraphic interpretations and process response models for intrashelf clinothems. At Site M29, the most downdip location, chronostratigraphically well-constrained bottomset deposits follow a repeated stratigraphic motif. Coarse-grained glauconitic quartz sand packages abruptly overlie deeply-burrowed surfaces. Typically, these packages coarsen- then fine-upwards and pass upward into bioturbated
siltstones. These coarse sand beds are amalgamated, poorly-sorted, and contain thin-walled
shells, benthic foraminifera and extrabasinal clasts, consistent with an interpretation of debrites.
The sedimentology and mounded seismic character of these packages support interpretation as
debrite-dominated lobe complexes. Farther updip, at Site M28, the same chronostratigraphic
Sedimentology and stratigraphic context of bottomset deposits
units are amalgamated, with the absence of bioturbated silts pointing to more erosion in proximal locations. Graded sandstones and dune-scale cross-bedding in the younger sequences in Site M28 indicate deposition from turbidity currents and channelization. The sharp base of each
package is interpreted as a sequence boundary, with a period of erosion and sediment bypass
evidenced by the burrowed surface, and the coarse-grained debritic and turbiditic deposits
representing the lowstand systems tract. The overlying fine-grained deposits are interpreted as
the combined transgressive and highstand systems tract deposits and contain the deep-water
equivalent of the maximum flooding surface. The variety in thickness and grain-size trends in
the coarse-grained bottomset packages point to an autogenic control, through compensational
stacking of lobes and lobe complexes. However, the large-scale stratigraphic organization of the
bottomset deposits, and the coarse-grained immature extrabasinal and reworked glauconitic
detritus point to external controls, likely a combination of relative sea-level fall and waxing-and-
waning cycles of sediment supply. This study demonstrates that large amounts of sediment
gravity flow deposits can be generated in relatively shallow (~100-200 m deep) and low gradient
(~1-4°) clinothems that prograded across a deep continental shelf. This physiography likely led
to the dominance of debris flow deposits due to the short transport distance limiting
transformation to low concentration turbidity currents
Camborne School of Mines
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