Sedimentation in the Vicinity of the Sigsbee Escarpment during the Last 25,000 yrs

Self Cite

A large number of slope failures (slumps or submarine slides) have occurred in the geologic past along the Sigsbee Escarpment between the Atlantis and Mad Dog Developments. A multidisciplinary study was conducted to define the risk of submarine slide activity in the context of the past historical activity that created 35 large scale slumps. Large diameter piston cores were obtained at 95 sites and deep soil borings were drilled at 8 locations to define the physical and engineering properties of the sediments and to determine the estimated time that these mass movements occurred along the Escarpment.Age dating ( 14 C and δ 18 O) on the cores and biostratigraphic analyses on borehole samples provided stratigraphic age control required to understand the time scales associated with the structural evolution of the Sigsbee Escarpment, the sequence and timing of the major slump events, and the relative activity and occurrence interval of the smaller debris and turbidity flows.The steep slope angles and upward and lateral movement of the underlying salt mass has resulted in slope instabilities producing gravity-driven slides. This study confirmed that each major "slump feature" is typically the product of a large number of individual soil mass failure events. A total of 79 age dates were measured by C-14 techniques on 95 cores taken within and around the slumps to give an historical account of the level of activity. The age dating and core results were correlated with the geophysical data to assess: (1) the state of seafloor activities and processes, (2) historical account of the slide events, and (3) ground truth the geologic/geotechnical properties within each slump area.A significant level of submarine slide activity has occurred along the Sigsbee Escarpment in this region over the last 25,000 years. The soil mass failures have reduced in number, magnitude, and level of activity in the last 8,000 years. The rates of sedimentation accumulation were higher during the sea level low stand and are now lower during the sea level high stands. Thus, the large slide events and the attendant debris flows creating the slumps occurred primarily during the periods of rapid lowering of the sea level. The most recently active slump event occurred in the Atlantis area about 2,970 years ago. Some slumps have not been active in the last 10,000 to 16,000 years.

Section: Multi-sensor Core Logger (Mscl)mentioning

confidence: 99%

Section: Multi-sensor Core Logger (Mscl)mentioning

confidence: 99%

Section: Multi-sensor Core Logger (Mscl)mentioning

confidence: 99%

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Age Dating of Past Slope Failures of the Sigsbee Escarpment within Atlantis and Mad Dog Developments

Young¹,

Bryant

Slowey³

et al. 2003

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“…External factors determine the volume and type of sediment input to the GoM and include continental glacial cycles, drainage area size, and eustasy. From the Pleistocene last glacial maximum low stand to the present Holocene high stand, sedimentation rates decreased, resulting in the deposition of fine-grained hemipelagic sediments over a large area of the modern continental slope (Slowey et al, 2003). deltas and canyons), and distance from the shelf margin.…”

Section: Geologic Settingmentioning

confidence: 99%

SS: MODU Anchor-Regional Analysis of Seafloor and Near Surface Sediments for MODU Anchors

Berger¹,

Harper²,

Oyebode³

2009

A significant challenge of predicting Mobile Offshore Drilling Unit (MODU) anchor performance is the lack of detailed sediment information. There are several proprietary and non-proprietary sources of seafloor and shallow sediment information. The various sources of sediment information can be merged into a comprehensive regional database. A regional model can be developed for use in the planning of MODU anchors prior to drilling. This paper will document the methodology of the various types and format of sediment information, and the use of that information for planning MODU anchors prior to drilling. In addition, this paper will demonstrate similarities and discrepancies between the regional model and site-specific data. The sources of sediment information originate from academic universities, government databases, joint industry projects, and individual companies. Regional studies include sediment classification with some chemical and physical characteristics. Site-specific samples are often collected as box cores, drop cores, piston cores, and rotary soil borings. The properties of the samples can be geographically represented in a Geographic Information System (GIS). The application of available sediment data can facilitate improved predictions of MODU anchor performance. Regional information can be classified within a site-specific area. Generalities can be inferred from the regional data, and the results can be supplemented by available seismic data. In areas without site-specific geotechnical data, the regional information correlated with seismic data can provide more detail when planning MODU anchor layouts prior to drilling. The use of readily available regional information can be a very cost-effective approach when designing a MODU anchor layout. The regional model can also be used to refine a site-specific geotechnical field program. Additional site-specific information can be analyzed and compared to the regional geologic model and refined accordingly.

“…15) and the last major event to effect this area occurred about 20,000 years ago (Ref. The idea was to back-analyze this geometry with the current soil modeling principles.…”

Section: Stability Of Surficial (Shallow) Sedimentsmentioning

confidence: 99%

Deterministic Slope Stability Analyses of the Sigsbee Escarpment

Nowacki

Solhjell²,

Nadim

et al. 2003

The paper describes the slope stability analyses carried out for BP's planned developments of the Mad Dog and Atlantis prospects. Both prospects are located along the Sigsbee Escarpment in areas where extensive slumping has taken place. The approach was based on combining geological, geophysical and geotechnical data from field and laboratory testing to develop models for slope stability evaluation. Examples of results are presented, including a brief discussion on how sensitive the results are to the variables in the analytical models.The examples demonstrate how an interdisciplinary approach to the geological and geotechnical modeling renders possible extrapolation and interpolation of geotechnical soil data, and that slopes of heights up to 150 -230 m and slope angles of more than 22° have safety factors in the range 1.1 to 1.5 based on best estimate of soil parameters.