Abstract Slope to Basin-floor Evolution of Channels to Lobes, Jurassic Los Molles Formation, Neuquén Basin, Argentina Nataleigh Kristine Vann, MS Geo Sci The University of Texas at Austin, 2013 Supervisor: Ronald J. Steel and Cornel Olariu The relatively steep and short-headed Neuquén Basin margin provides an excellent laboratory for demonstrating down slope changes in sediment gravity flow bed thickness, grain size and facies, as well as channel to lobe transitions. Approximately 400m high clinoformal, shelf-slope-basin-floor deposits of Jurassic Los Molles Formation outcrops are evaluated for reservoir scale definition of facies and architectures in the La Jardinera field area, Neuquén Basin. Slope deposits represent the accretionary front of the prograding shelf margin that were fed by a coarse grained shelf (Lajas Formation). Mapping of a high-resolution satellite images draped on digital elevation model resolved a sub-meter stratigraphic framework. Thirty-three measured sections from outcrops exposed along a 5km transect characterize the evolution of sand body architectures from the shelf edge to the basin floor. The Neuquén Basin margin is typified by four main depositional environments that transition from shelf edge incisions filled with conglomerates, to confined channels in upper- to middle-slope reaches, to weakly confined channels on the lower slope to sheet-like lobes and distributary channel complexes that drape onto both the lower slope and basin floor. Along the slope to basin floor profile the depositional architecture changes by overall decrease in grain size, amalgamation of beds and degree of erosion. Confined slope channels are up to 25m deep, isolated within muddy slope deposits and have complex multistory fills marked by basal and internal erosive contacts lined with mud-clast and/or pebble conglomerates. Channel axes contain amalgamated, medium to coarse sandstones that thin and fine towards channel margins over 100m. Down dip, lower slope channels are up to 400m wide and less than 10m thick. A marked reduction in mud clasts and conglomeratic material at basal erosional surfaces in weakly confined channels represent a downslope decrease in flow energy. However, distinct meter scale erosion surfaces continue to be recognizable where thin ripple laminated sands are truncated on channel margins by amalgamated structureless sands. Erosional surfaces are absent in laterally extensive (>5km), sheet-like lobes of basin-floor fans that are generally finer grained than lower or upper slope channel fills. There are lenticular debrites and thin micro-conglomerates associated with basin-floor fans. / text

Deep-water strata of the Neoproterozoic Kaza Group and Isaac Formation (Cariboo Group) in the southern Canadian Cordillera (B.C.) were deposited in a passive-margin basin during the break-up of supercontinent Rodinia. At the Castle Creek and Mount Quanstrom study areas, a remarkably continuous stratigraphic interval throughout these units preserves a record of basin-floor overlain by strata deposited in the lowermost part of the slope. Although similar stratal intervals have been described from ancient and modern deep-marine settings, they still remain poorly understood. Three main stratal units are recognized within the study areas. The lower unit consists of three channel-lobe systems formed in the basin floor to slope transition. Uniquely, siliciclastic-dominated strata here consist of a variety of small- and few large-scale scour elements, indicating transport bypass along the channel-lobe transition zone, in addition to detached or attached depositional lobes composed mostly of distributary channels, fine-grained deposits, and uncommon splays, and a rare slope leveed channel complex. The middle unit is a siliciclastic-dominated succession of stacked, km-scale mass-transport deposits (i.e. debrites and slides), which indicates the more frequent emplacement of increasingly larger mass failures on a prograding slope, and are overlain by fine-grained, splay deposits that are successively overlain by channel, ponded and fine-grained deposits. In contrast, the upper unit is a mixed siliciclastic-carbonate slope succession of the first Isaac carbonate, a regional marker horizon that comprises mostly carbonate-rich and siliciclastic-rich fine-grained strata intercalated with channel and gully complexes that are mostly filled with coarser-grained strata. Abrupt changes in facies trends, stratal stacking patterns and depositional styles throughout these units are largely linked to long-term changes in relative sea level and its control on sediment supply, namely sediment caliber, volume and mineralogy. Notably, in the upper unit, small-scale changes in sediment source and supply are related to shorter sea-level variations superimposed on the long-term eustatic change.

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Ce travail présente une analyse de la morphologie et de la dynamique sédimentaire des systèmes turbiditiques actuels du Cap-Ferret et de Capbreton (sud du Golfe de Gascogne). La reconnaissance effectuée sur le système de Capbreton est la première à le considérer dans son ensemble. Ce travail se base sur des données acoustiques de subsurface (sondeur multifaisceaux, sondeur de sédiments Chirp) et de carottages issues de la campagne océanographique Sargass menée par l’Université de Bordeaux. L’analyse morpho-bathymétrique révèle l’organisation amont-aval des géométries sédimentaires dans ces systèmes et, couplée aux données sédimentaires, de préciser les processus de dépôts liés aux écoulements gravitaires. Le fonctionnement holocène du canyon de Capbreton montre des processus gravitaires haute fréquence, révélant son rôle de dépôt-centre pour le sud du golfe de Gascogne. Dans le système du Cap-Ferret, la zone de transition chenal-lobe a été investiguée à fine échelle, documentant ainsi des structures sédimentaires rarement identifiées avec ce niveau de détails dans les systèmes turbiditiques modernes. La dynamique sédimentaire de chacun de ces systèmes est soumise à des forçages auto-cycliques et glacio-eustatiques qui affectent chacun des systèmes de façons différentes. Ces informations ont permis de proposer un modèle régional de fonctionnement sédimentaire au cours des derniers 50 000 ans. / This work presents an analysis of the morphology and sedimentary dynamic of the Cap-Ferret and Capbreton turbidite systems (south Bay of Biscay), containing the first recognition of the whole Capbreton turbidite system. The dataset comprises subsurface geophysical data (multibeam bathymetric and imagery, Chirp sub-bottom profiler) and piston cores, acquired during the oceanographic cruise Sargass conducted by the Bordeaux University. Studied by morpho-bathymetric analyses, the upstream-downstream evolution of the sedimentary bodies joined to the sedimentological data help to understand the active gravity processes of the systems. In the Capbreton system, a special focus is made on its Holocene gravity deposits occurring at high frequencies. In the Cap-Ferret system, the channel-lobe transition zone has been investigated at high resolution and revealed sedimentary structures poorly documented at this scale of details in recent turbidite systems. The glacio-eustatic and autocyclic forcing are expressed in different ways in each turbidite sytem. A regional sedimentary dynamic model is proposed for the last 50,000 years.