Facies architecture of Miocene subaqueous clinothems of the New Jersey passive margin: Results from IODP-ICDP Expedition 313
Proust, J-N; Pouderoux, H; Ando, H; et al.Hesselbo, SP; Hodgson, DM; Lofi, J; Rabineau, M; Sugarman, PJ
Date: 14 June 2018
Journal
Geosphere
Publisher
Geological Society of America
Publisher DOI
Abstract
Understanding the history, causes, and impact of sea-level changes is a
challenge for our societies that face accelerated global sea-level rise. In this
context, improvement of our knowledge of sea-level changes and shoreline
migration at geological time scales is critical. The preserved, laterally correlative
sedimentary record ...
Understanding the history, causes, and impact of sea-level changes is a
challenge for our societies that face accelerated global sea-level rise. In this
context, improvement of our knowledge of sea-level changes and shoreline
migration at geological time scales is critical. The preserved, laterally correlative
sedimentary record of continental erosion on passive margins has been
used to reconstruct past sea level. However, the detailed nature of a basic
clinothem progradational pattern observed on many of these margins is still
poorly known. This paper describes the sedimentary facies and interprets the
depositional environments and the architecture of the clinothems of the New
Jersey shelf (offshore northeastern USA) to depict the origin and controls of
the distribution of the sediment on the margin. We analyze 612 cores totaling
1311 m in length collected at three sites 60 km offshore Atlantic City, New Jersey,
during International Ocean Discovery Program–International Continental
Scientific Drilling Program (IODP-ICDP) Expedition 313. The three sites sampled
the lower to middle Miocene passive margin sediments of the New Jersey
shelf clinothems. We also collected wireline logs at the three sites and tied
the sedimentary architecture to the geometry observed on seismic profiles.
The observed sediment distribution in the clinoform complex differs from that
of current models based on seismic data, which predict a progressive increase
in mud and decrease in sand contents in a seaward direction. In contrast, we
observe that the clinoforms are largely composed of muds, with sands and
coarser material concentrated at the rollover, the bottomset, and the toe of
the slope. The shelf clinothem topsets are storm-influenced mud whereas the
foreset slope is composed of a mud wedge largely dominated by density current
deposits (e.g., low-density turbidites and debrites). The architecture of
the clinothem complex includes a composite stack of ~30-m-thick clinothem
units each made up of four systems tracts (Transgressive, Highstand, Forced-
Regressive,
and Lowstand Systems Tract) building individual transgressiveregressive
sequences. The presence of mud-rich facies deposited during highstands
on the topset of the clinoform, 40–60 km offshore from the sand-prone
shoreface deposit (observed in the New Jersey onshore delta plain), and the
lack of subaerial erosion (and continental depositional environments) point
to a depositional model involving a subaerial delta (onshore) feeding a distant
subaqueous delta. During forced regressions, shelf-edge deltas periodically
overstep the stacks of flood-influenced, offshore-marine mud wedges of
the New Jersey subaqueous delta, bringing sand to the rollover and building
up the large-scale shelf-prism clinothems. The clinothem complex develops
on a gently dipping platform with a ramp-like morphology (apparent dip of
0.75°–0.5°) below mean storm wave base, in 30–50 m of water depth, 40–
60 km seaward of the coastal area. Its shape depends on the balance between
accommodation
and sedimentation rates. Subaqueous deltas show higher accumulation
rates than their subaerial counterparts and prograde three times
further and faster than their contemporaneous shoreline. The increase in the
intensity of waves (height and recurrence intervals) favors the separation between
subaqueous and subaerial deltas, and as a consequence, the formation
of a flat topset geometry, a decrease in flood events and fluvial discharge, an
overall progressive decrease in sediment grain size (from sequence m5.45, ca.
17.8–17.7 Ma, onwards), as well as an increase in sedimentation rates on the
foresets of the clinoforms. All of these are recognized as preliminary signals
that might characterize the entry into the Neogene icehouse world.
Camborne School of Mines
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