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The Tertiary development of the Porcupine and Rockall basins is compared in terms of stratigraphy and sedimentation. Four main unconformities are correlated between the basins and these are interpreted as being of Paleocene (C40), latest Eocene-Early Oligocene (C30), latest Early Miocene (C20) and Early Pliocene (C10) age. Seismic stratigraphic analysis of both basins suggests a greater similarity in post-Eocene deposition than in the Paleocene to Eocene stratigraphy. During Early Tertiary time a regressive succession, punctuated by minor transgressions, marks a major interruption in the general post-rift thermal subsidence pattern of the region. This regression, possibly triggered by lithospheric thermal effects and/or ridge-push stresses, resulted in deltaic and submarine fan deposition in the Porcupine Basin, with submarine channel trends indicating that sediment was sourced mainly from the Porcupine High to the north and west. Sand deposition in the Porcupine Basin occurred principally during Mid- to Late Eocene times. In contrast, Early Eocene sand input is postulated in the Rockall Basin, whereas deposition during the Mid- to Late Eocene times was more mud-prone. In Oligocene and Mio-Pliocene times, sediment build-ups, interpreted as contourites, developed towards the margins of both basins, with sedimentation principally influenced by oceanographic circulation patterns at this time. During Neogene to Recent times limited marginal sediment influx occurred in the Porcupine Basin whereas sediment input continued locally, during Neogene time, in the Hebrides region of the Rockall Basin.

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The margins of the deep-water sedimentary basins west of Ireland contain a number of large clusters (provinces) of spectacular carbonate mounds and build-ups. These basins have a complex development history involving the interplay of rift tectonics, thermal subsidence, igneous activity and oceanographic variations. The Porcupine and Rockall basins both rest upon thin continental crust, the consequence of major rift episodes in Permo-Triassic, Late Jurassic and Early Cretaceous times. Phases of volcanism occurred in the Early Cretaceous and especially in the Early Cenozoic. Fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems, stratal surfaces and unconformities. A number of regional unconformities, controlled by both basin tectonic and regional oceanographic effects, can be mapped and correlated throughout the Porcupine and Rockall basins. The youngest of these unconformities (C10: Early Pliocene) can be traced throughout much of the NW European Atlantic margin. It forms the horizon on which virtually all the carbonate mounds in the basins develop, suggesting a geologically instantaneous mound nucleation and growth event. Although the control on their development is uncertain, the mound clusters show a spatial association with lithified strata, buried contourite and deltaic deposits, slope failure features and with the basin margins. Analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth.

Detachment surfaces have important implications for structural restoration, burial-history and thermal modeling, hydrocarbon migration, and diagenesis.We present criteria to distinguish salt welds from shale detachments based on geophysical data from the innerTexas shelf. Here, the Paleogene detachment has been variously interpreted as salt or shale by di¡erent people. A newly reprocessed 8200 km 2 (3200 mi 2 ) 3D seismic volume provides excellent imaging of this detachment, which separates growth-faulted Oligocene^Miocene strata from the underlying, gently folded Cretaceous^Eocene section. Key criteria to evaluate detachment origins include seismic amplitude response, geometry, and relationship to supradetachment and subdetachment re£ections.We argue that the detachment is a salt weld because (a) it is imaged as a high-amplitude, discrete re£ection; (b) it has a ramp-£at geometry, cutting across underlying re£ections; (c) it locally forms bowl-shaped depotroughs interpreted as former diapiric salt feeders; (d) it is overlain by seismically incoherent pods having high-amplitude tops and bases interpreted as remnant salt; and (e) in the depotroughs associated with former diapiric salt feeders the detachment has hints of upturned strata just beneath (possible halokinetic sequences).The inferred weld represents the evacuated remains of a patchy salt canopy emplaced across the study area during the Late Eocene to Early Oligocene. Preliminary examination beyond our study area suggests that this discontinuous canopy may have extended across most of the modern Texas shelf. Most of the salt was expelled from the canopy by loading from prograding Oligo^Miocene deltaic deposits.

He has published more than 100 articles and abstracts on subjects ranging from clastic sedimentology, sequence stratigraphy, petroleum geology and resource evaluation, hydrogeology, and uranium geology. He is currently the principal investigator on the Gulf Basin depositional synthesis industry consortium, which is in its 13th year.

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