ALBERT

Description: Abstract The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE ‐ WSW trending elongate basins that extend from St George's Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE‐SW trending half‐grabens developed as a result of the reactivation of Caledonian and Variscan faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW‐SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N‐S oriented extension gave rise to E‐W‐striking minor normal faults and reactivation of the pre‐existing basin‐bounding faults that propagated upwards as left‐stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N‐S Alpine regional compression causing basin inversion is dated as Middle Eocene to Miocene by a well preserved syn‐inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near‐orthogonal NW‐SE dextral strike‐slip faults so that compression was partitioned onto two fault sets the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn‐inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.

Description: I do not agree with the conclusion reached by Hodgetts et al. (2001) that a deltaic shoreline in two adjacent growth fault blocks was simultaneously prograding and retrograding, for reasons explained in this article. My principal objection is illustrated in their figure 14. The block diagram and paleoenvironmental map (Hodgetts et al., 2001, figure 14c, d) show the onset of growth faulting. As the fault begins to offset the depositional surface, Hodgetts et al. (2001) argue that the greater subsidence associated with the hanging-wall (downthrown) block caused updip migration of the shoreline, while the shoreline continued to prograde in the footwall (upthrown) block. If, however, offset on the fault yielded no more than several meters of relief on the sea floor, then the delta would merely heal the surface and continue to prograde in the hanging-wall block, where the succession would be thicker than in the footwall block (overall layer thickening). This is what is observed in numerous cases in the northern Gulf of Mexico Basin (e.g., Curtis, 1970; Curtis and Picou, 1978) and the Niger Delta (Weber, 1971). Several examples that I have studied and described in publications include the Paleocene-Eocene Wilcox Group (Edwards, 1980, 1981; Winker and Edwards, 1983); the Oligocene Frio Formation (Edwards, 1995), the Eocene Yegua Formation (Edwards, 1990, 1991), and the lower Miocene (Edwards, 1994, 1995). Shoreline orientation is irrelevant because the …

Description: The Champion field, offshore Brunei Darussalam, comprises a thick middle-upper Miocene succession of shallow marine sediments associated with major growth fault systems and deposited as part of the paleo-Baram delta. The structural evolution of the Champion field has resulted in an unusual situation where growth faults strike perpendicular to the paleoshoreline orientation. Shoreface parasequences and tidal-estuarine complexes are mapped directly from three-dimensional (3-D) seismic data calibrated from wells. The seismic interpretations provide chronostratigraphic correlations that are more robust than some well-based markers because the seismic interpretations have better spatial coverage. Depositional responses to growth faulting are defined by two end-member models, (1) layer thickening and (2) addition of layers in the hanging wall. Layer addition makes correlation across faults problematical. Growth may be accommodated by either or a combination of these processes, and areas of layer addition are related to transgressive events in the hanging wall. Topographic changes thought to be associated with fault movements may fundamentally change shoreline type, sand body orientations, and petrophysical properties for discrete periods of time. These stratigraphic complexities are linked spatiotemporally to accommodation history but cannot be adequately predicted from well data alone. David Hodgetts received his B.Sc. (hons) degree in geology from Durham University in 1991 and an M.Sc. degree (1992) in computing in earth sciences and Ph.D. (1995) in three-dimensional (3-D) numerical modeling of continental lithosphere deformation from Keele University. After a one year postdoctoral fellowship at Keele working on 3-D structural restoration algorithms, he moved to the Stratigraphy Research Group at the University of Liverpool. Since then he has been working on the tectono-stratigraphy of the Champion field, offshore Brunei Darussalam, South China Sea. His other research interests include development of software to aid the building of reservoir models, synthetic seismic modeling from outcrop data, and numerical modeling of sedimentary depositional systems.Jonathan Imber, a B.Sc. degree graduate of Durham University, joined the Fault Analysis Group in 1998 after completing a Ph.D. on fault/shear zone kinematics at Durham. A research fellow with the Fault Analysis Group at University College Dublin, his research mainly concerns analysis of the kinematics of faults from 3-D seismic data and numerical modeling of fault growth using discrete element modeling methods. Conrad Childs is a senior research fellow within the Fault Analysis Group of University College Dublin, formerly of University of Liverpool. Having earned an M.Sc. degree in structural geology from Imperial College London in 1987, he joined the Fault Analysis Group at University of Liverpool, taking up a senior research role and completing a Ph.D. on the structure and hydraulic properties of fault zones. His research concerns many aspects of faults, including their impact on fluid flow. Stephen Flint holds a personal chair in stratigraphy and petroleum geology at the University of Liverpool, United Kingdom. After earning a Ph.D. from Leeds University in 1985 he joined Shell Research, Rijswijk, Netherlands, where he was involved in development of 3-D reservoir geological modeling technology with related outcrop studies and application to fields worldwide. In 1989 he moved to Liverpool University, where he built up and directs the Stratigraphy Research Group (STRAT Group). This industry-supported team of postdoctoral researchers and Ph.D. students is working on stratigraphic prediction in nonmarine, shallow, and deep marine reservoirs and analog outcrops worldwide. New developments in the group include 3-D reservoir modeling and sediment transport modeling. John Howell gained a B.Sc. (hons) degree from Cardiff (1988) and a Ph.D. from the University of Birmingham (1992). He then moved to Liverpool, where he completed postdoctoral studies on sequence stratigraphy of the Upper Jurassic reservoirs in the North Sea and the Book Cliffs of Utah. In 1995 he took a faculty position in Liverpool as part of the Stratigraphy Research Group. He works on sequence stratigraphy in aeolian, coastal plain, and shallow marine systems in Utah, Namibia, Chile, Argentina, and other exotic places and has just completed a three-month reservoir modeling sabbatical at Saga Petroleum. John Kavanagh graduated from the University of Glasgow in 1992. After working for Bullen Consultants as a graduate geologist and site quality assurance engineer, he then went on to join the Earth Science Department of the University of Liverpool as a laboratory technician. He currently works with the STRAT Group as a research technician where his main work involves seismic and well correlation, as well as field data acquisition. Philip Nell, a B.Sc. degree graduate from Nottingham University, completed a structural geology Ph.D. on the Scottish Dalradian from the University of Manchester in 1984. He held postdoctoral structural geology positions at the University of Leeds, British Antarctic Survey, and University of Manchester prior to joining the Fault Analysis Group at Liverpool in 1995. His recent research has been on fault geometry and the development of new software techniques for seismic interpretation and reservoir modeling. He joined Badley Technology Ltd. as a structural geologist in 2000 to continue these developments. John Walsh is on the teaching staff of the Department of Geology at University College Dublin. He gained a B.Sc. degree from University College Dublin in 1980 and a Ph.D. from University College Galway in 1986, prior to becoming a founding member of the Fault Analysis Group at the University of Liverpool. He has been director of the research group since 1996, both within Liverpool and following its relocation to Dublin. This externally funded research group comprises ten mainly postdoctoral researchers, together with additional postgraduates, and carries out basic research on all aspects of faults and other types of fracture and applies the results to practical problems, principally in the field of hydrocarbon reservoir characterization and modeling.