Site 1127 is located on the upper slope adjacent to the Eucla Shelf in 479.3 m of water (Fig. F1). It was the deepest site of a depth transect of three sites (Sites 1127, 1129, and 1131) designed to sample an impressive set of progradational sigmoidal clinoforms constituting Sequence 2 as defined by Feary and James (1998, reprinted as Chap. 2) and projected to be Pliocene-Pleistocene in age (Fig. F2). This seismic sequence forms a thin succession over the outer shelf (70-90 m), reaches peak thickness at the present shelf edge (350-550 m), and thins as a wedge farther seaward beneath the modern slope. The sequence occurs across the entire width of the Eucla Basin (~350 km), and reaches its thickest extent in the vicinity of Site 1127. This site, in conjunction with Sites 1129 and 1131, offers the opportunity to develop an in-depth understanding of shelf edge and upper slope depositional and progradational processes and to understand the extent to which complex reflection onlap and erosional truncation patterns within the clinoform package reflect hiatal or erosional episodes. Site 1127 intersected the lowest, most condensed portion of this clinoform facies as well as an expanded record of the youngest clinoforms.
Such clinoforms seem to be a signature of cool-water carbonate platforms and ramps and are undoubtedly a product of shelf-to-slope transport. However, little is known about the accumulation dynamics in relation to storm events and sea-level fluctuations. Additionally, little is known about the composition of these deposits. How much material is produced in place as compared to that transported in? Is sediment produced by enhanced biogenic production along the shelf edge, or are these clinoforms simply made up of fine-grained material produced on the shelf and swept offshore and downslope to accumulate below wave base?
In addition, seismic data indicated the presence of mounded seismic facies that have been interpreted as possible deep-water biogenic features. Although Site 1127 does not intersect any of these mound features, possible biogenic mounds located upslope may have acted as a nearby source of sediment shed downslope to Site 1127.
The principal objective along this transect of sites was to collect a detailed, high-resolution profile through an upper Neogene shelf edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment to determine the response of such a depositional system to Pliocene-Pleistocene sea-level fluctuations.
Additional objectives were to
In addition to providing a detailed understanding of seismic Sequence 2 depositional dynamics, we also sought to recover an incomplete Sequence 3 record at Site 1127 before drilling to target depth in the upper Miocene Sequence 4.
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