ALBERT

Description: The processes within deep-sea sediment-routing systems are difficult to directly monitor. Therefore, we rely on other means to decipher the sequence and relative magnitude of the events related to erosion, sediment bypass, and deposition within channels that crosscut the seascape, and in particular, continental slopes. In this analysis, we examine the nature of slope channel fill in outcrop (Cretaceous Tres Pasos Formation, southern Chile) in order to evaluate the geological evidence of the full channel cycle, from inception to terminal infill with sediment, and we attempt to provide insight into the enigmatic deep-sea processes that are critical for a comprehensive understanding of Earth surface dynamics. In the stratigraphic record, slope channel fills are typically represented by sandstone- or conglomerate-dominated deposits that define channelform sedimentary bodies tens of meters thick and hundreds of meters across. Despite the prevalence of coarse-grained sediment, key information is recorded in the fine-grained deposits locally preserved within the channelform bodies, as well as a breadth of scours or internal channelform stratal surfaces. These characteristics preserve the record of protracted sedimentary bypass and erosion. In many instances, the life of a slope channel is dominated by sedimentary bypass, and the stratigraphic record is biased by the products of shorter-lived channel filling and abandonment.

Description: Stratigraphic rule-based modeling methods approximate sedimentary dynamics to generate numerical descriptions of reservoir architecture and the spatial distribution of petrophysical properties. A few intuitive rules included in a reservoir model construction workflow are shown to render realistic reservoir heterogeneity, continuity, and spatial organization to petrophysical property distributions that are difficult to obtain using conventional reservoir modeling methods. These rules may be inferred from mature reservoirs, surface and subsurface datasets, and process-based models. Examples include confinement, meander, compensation, and healing rules. By incorporating stratigraphic rules that relate to the underlying geological processes in temporal sequence, rule-based modeling methods offer more realistic representation of inferred reservoir heterogeneity beyond conventional geostatistical reservoir modeling approaches. These include variogram-based, multiple point-based and object-based approaches that rely on a limited set of spatial statistics to describe the products of geological processes. Moreover, since these methods operate within a geostatistical framework, uncertainty can be explored by varying geologically meaningful parameters over multiple scenarios and realizations whilst maintaining consistency with input data constraints and applied to reservoir modeling studies within standard workflows. Rule-based modeling methods enable a variety of applications, including use: directly as reservoir models, as a source of reservoir model input statistics such as variograms and training images, and as a numerical analog laboratory to explore relationships between data, model choices and forecasts. Challenges remain, such as reliability of emergent features, alignment to grid framework, and feasibility for broad application. Despite challenges, rule-based methods can offer uplift when the natural facies continuity patterns and their corresponding petrophysical properties are critical to support decisions in reservoir modeling projects.

Description: Submarine channels are often thought of as having relatively simple geometries, with significant along-channel morphologic and stratigraphic continuity. Using high-resolution seismic reflection data from offshore Angola and a kinematic model of channel evolution, we present evidence that channels on the seafloor can develop slope variability as a result of meander cutoff events. When cutoffs develop, the shortened flow paths produce locally steep gradients, thus initiating knickpoints. Waves of knickpoint retreat and the related channel incision explain the occurrence of terraces and associated remnant channel deposits above the youngest channel thalweg. The simple processes of meander cutoff followed by knickpoint retreat are intrinsic to submarine channels and result in significant morphologic variability, erosion, and stratigraphic complexity, without any external forcing. These insights highlight the early evolution of submarine channels, a phase with a record that is commonly fragmented or completely absent as a result of subsequent erosion, and allow a better understanding of the autogenic controls on deep-marine stratigraphy.

Description: Submarine channels are often thought of as having relatively simple geometries, with significant along-channel morphologic and stratigraphic continuity. Using high-resolution seismic reflection data from offshore Angola and a kinematic model of channel evolution, we present evidence that channels on the seafloor can develop slope variability as a result of meander cutoff events. When cutoffs develop, the shortened flow paths produce locally steep gradients, thus initiating knickpoints. Waves of knickpoint retreat and the related channel incision explain the occurrence of terraces and associated remnant channel deposits above the youngest channel thalweg. The simple processes of meander cutoff followed by knickpoint retreat are intrinsic to submarine channels and result in significant morphologic variability, erosion, and stratigraphic complexity, without any external forcing. These insights highlight the early evolution of submarine channels, a phase with a record that is commonly fragmented or completely absent as a result of subsequent erosion, and allow a better understanding of the autogenic controls on deep-marine stratigraphy.

Description: Continental-scale drainages host the world’s largest rivers and offshore sediment accumulations, many of which contain significant petroleum reserves. Rate of sediment supply in these settings may be a signal of external controls (e.g., tectonics) on landscape evolution, yet deciphering these controls remains a major challenge in interpreting the ancient stratigraphic record. Integration of new and published detrital zircon U-Pb ages from the United States Rocky Mountain region and Gulf of Mexico (GOM) sedimentary basin demonstrates profound changes in the U.S. continental drainage divide that controlled the rate of sediment delivery to the northern GOM during Paleocene–Eocene time. Sedimentation rate increased dramatically during deposition of the lower Wilcox Group, reaching approximately three times the Cenozoic average, accompanied by pronounced shoreline regression and delivery of a large volume of sand to the basin floor. We hypothesize that this increase in sediment delivery to the GOM resulted from drainage capture of a significant portion of the Sevier-Laramide structural province (~900,000 km 2 ) that included the headwaters of the California and Idaho Rivers. Capture of the California River drainage may have occurred in the vicinity of the Hanna Basin of eastern Wyoming that previously emptied northward into a shallow seaway, but was subsequently diverted southward to the Rockdale delta, which accumulated within the Houston embayment during the time of deposition of the lower Wilcox Group. Detrital zircon U-Pb ages from Wilcox samples within the Rockdale delta show a remarkable similarity with contemporaneous Laramide synorogenic units, including enrichment in detritus derived from the Cordilleran arc and basement terranes of western North America relative to older and younger units in the Houston embayment. A subsequent order of magnitude decline in sedimentation rate to the GOM can be partly attributed to well-documented drainage closure (~800,000 km 2 ) that accompanied lake formation in interior Laramide basins (ca. 53–51.8 Ma). Our results demonstrate that tectonically induced drainage migration in the high-relief segments of continental-scale drainages can have a pronounced effect on the rate of sediment transfer to continental margins.

Description: A bstract :  Turbidity currents, and other types of submarine sediment density flow, redistribute more sediment across the surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The deposits of these flows are of societal importance as imperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understanding field observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than ~ 0.6°. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low (〈 0.1%) volume concentrations. This could have important implications for flow evolution and deposit geometries. Better quantitative constraints are needed on what controls flow capacity and competence, together with improved constraints on bed erosion and sediment resuspension. Recent advances in understanding dilute or mainly saline flows in submarine channels should be extended to explore how flow behavior changes as sediment concentrations increase. The petroleum industry requires predictive models of longer-term channel system behavior and resulting deposit architecture, and for these purposes it is important to distinguish between geomorphic and stratigraphic surfaces in seismic datasets. Validation of models, including against full-scale field data, requires clever experimental design of physical models and targeted field programs.