Abstract In analytical models of salt diapirism, the initial salt-layer thickness and the post-deformation spacing of salt structures are key parameters. Here, 3D seismic data from The Netherlands offshore has enabled these parameters to be measured over large areas which can then be compared with model predictions. Estimates of the original salt-layer thickness were obtained by spatially filtering present thickness, using filters with varied spatial scales that remove local effects. Loss of evaporite minerals by dissolution or erosion during exposure, cannot be ruled out and, as such, thicknesses are minima. Spacing estimates were derived in two dimensions by locating the minimum separation of lines representing ridgelines of diapirs/walls. Because the length scale of spatial filtering was chosen based on the dependent variable, diapir spacing, the results are non-unique. Nevertheless, choosing an apparently optimal filter length of 50 km, a ratio between diapir spacing and original thickness from 12 to 20 is defined. This ratio is greater than has been reported for the pillow province of the UK North Sea Quadrant 44, which is as expected if pillows evolve into diapirs with progressive halokinetic deformation. This work is key to understanding the evolution of salt displacement, a necessity for unlocking remaining hydrocarbon resources.

Abstract Far less is known of the processes involved in erosion of submarine channels compared with channels eroded subaerially by water runoff, but geometrical properties derived for canyons of the USA Atlantic continental slope reveal some intriguing similarities. Slope-confined canyons are concave-upwards, displaying decreasing channel gradient with increasing contributing area, as observed in many bedrock-eroding rivers. Tributaries join principal channels at the same elevation (without intervening waterfalls), in effect obeying Playfair's law, as do many river networks. Gradient and contributing area data for channels at confluences also reveal a tendency for tributaries to have steeper gradients than their associated principal channels, reflecting their smaller drainage areas. The concavities of bedrock-eroding rivers are often explained by a balance between river discharge, which increases with increasing rainfall catchment area, and gradient, which declines to offset the erosive effect of the discharge. It is unclear, however, if such a balance can be invoked for submarine canyons because erosion is probably caused when sedimentary flows are active only in individual canyon branches, originating from isolated slope failures. Instead, the frequency of sedimentary flows experienced by canyon floors may increase downstream simply because the area of unstable canyon walls available to source sedimentary flows increases, and this effect becomes compensated by declining gradient. Knickpoints created by faults in tectonically active slopes provide a further way to infer the form of erosion by sedimentary flows. Such knickpoints typically lie upstream of the faults that probably generate them, implying that detachment-limited erosion is enhanced where sedimentary flows become more vigorous on steep gradients, leading to knickpoint migration.

Abstract Banner tidal sandbanks in the Bristol Channel have been repeatedly surveyed with a multibeam sonar to study the geometry and migration patterns of superimposed dunes. The data presented in this paper constitute one of the first studies concerned with sediment transport around a banner sandbank (Helwick Sands in the Bristol Channel) using repeated swath-bathymetry. The data reveal that the dunes maintain their shapes over a period of 11 months, and that they migrate in opposite directions on the alternate sides of the bank. Curiously, dunes connect over the crest of the bank despite opposing sediment transport directions on the flanks. Dune height increases with water depth as found in similar environments. We suggest how the morphology of the dunes results from the complex interaction between surface waves and tidal currents that occurs within the proximity of the headland.

Abstract Important hydrocarbon accumulations occur in platform carbonates of the Lower Cretaceous Kharaib (Barremian and early Aptian) and Shuaiba (Aptian) formations (upper Thamama Group) of Abu Dhabi. The Kharaib and Lower Shuaiba formations contain three reservoir units separated by three low-porosity and low-permeability dense zones. From base to top, the thickness of the reservoir intervals range from approximately 80, 170, to 55 ft (24, 51, to 16 m), respectively, for the Lower Kharaib, Upper Kharaib, and Lower Shuaiba Reservoir Units. Core and well-log data of a giant oil field of Abu Dhabi, as well as outcrop data from Wadi Rahabah in the Emirate of Ras Al-Khaimah were used to establish a sequence-stratigraphic framework and a lithofacies scheme, applicable to all three reservoir units and the three dense zones. The Lower and Upper Kharaib Reservoir Units, as well as the lower, middle, and upper dense zones are part of the late transgressive sequence set of a second-order supersequence, made up of two third-order composite sequences. The overlying Lower Shuaiba Reservoir Unit belongs to the late transgressive sequence set and the early highstand sequence set of this second-order supersequence and is made up of one third-order composite sequence. The three third-order composite sequences are composed of 19 fourth-order parasequence sets that show predominantly aggradational and progradational stacking patterns, typical of greenhouse cycles. Conventionally, composite sequence boundaries are placed at or near the base of the three dense zones. As an alternative scenario, the possibility that the major composite sequence boundaries actually occur on top of these dense zones is discussed. On the basis of faunal content, texture, sedimentary structures, and litho-logic composition, 13 reservoir lithofacies and 8 nonreservoir (dense) lithofacies are identified from core. Similar lithofacies are identified in time-equivalent rock exposures studied in Wadi Rahabah. Depositional environments of reservoir units range from lower ramp to shoal crest to near-back shoal open-platform deposits. Dense zones were deposited in an inner-ramp, restricted shallow-lagoonal setting. Intensively bioturbated wackestone and packstone, and interbedded organic- and siliciclastic-rich limestone, characterize the dense zones. Locally, mud cracks, blackened grains, and rootlets are observed. Outcrop analogs of subsurface reservoirs allow for a detailed investigation of facies architecture and structure of carbonate bodies. Integration of subsurface and outcrop data (e.g., low-angle clinoforms that cannot be seen in core data) leads to more insightful and realistic geological models of subsurface stratigraphy. Geological model realizations based on core, outcrop, well-log, and seismic data constrain fluid flow-simulation models. Results mimic known behavior in analogous producing fields, and the process of going from rock data to simulation provides a useful training tool for reservoir characterization methods and techniques.

Abstract A new sequence-stratigraphic framework is proposed for the Burgan and Mauddud formations (Albian) of Kuwait. This framework is based on the integration of core, well-log, and biostratigraphic data, as well as seismic interpretation from giant oil fields of Kuwait. The Lower Cretaceous Burgan and Mauddud formations form two third-order composite sequences, the older of which constitutes the lowstand, trans-gressive, and highstand sequence sets of the Burgan Formation. This composite sequence is subdivided into 14 high-frequency, depositional sequences that are characterized by tidal-influenced, marginal-marine deposits in northeast Kuwait that grade into fluvial-dominated, continental deposits to the southwest. The younger composite sequence consists of the lowstand sequence set of the uppermost Burgan Formation and transgressive and highstand sequence sets of the overlying Mauddud Formation. This composite sequence is sand prone and mud prone in southern and southwestern Kuwait and is carbonate prone in northern and northeastern Kuwait. The lowstand sequence set deposits of the Burgan Formation are subdivided into five high-frequency depositional sequences, which are composed of tidal-influenced, marginal-marine deposits in northeastern Kuwait that change facies to fluvial-dominated deposits in southwestern Kuwait. The transgressive and highstand sequence sets of the Mauddud Formation are subdivided into eight high-frequency, depositional sequences. The Mauddud transgressive sequence set displays a lateral change in lithology from limestone in northern Kuwait to siliciclastic deposits in southern and southwestern Kuwait. The traditional lithostratigraphic Burgan-Mauddud contact is time transgressive. The Mauddud highstand sequence set is carbonate prone and thins south- and southwestward because of depositional thinning. Significant postdepositional erosion occurs at the contact with the overlying Cenomanian Wara Shale. The proposed sequence-stratigraphic framework and the incorporation of a depositional facies scheme tied to the sequence-stratigraphic architecture allow for an improved prediction of reservoir and seal distribution, as well as reservoir quality away from well control.