Submarine gravity flows are a key process for transporting large volumes of sediment from the continents to the deep sea. The location, volume, and character of the sediment bypassed by these flows dictates the areal extent and thickness of the associated deposits. Despite its importance, sediment bypass is poorly understood in terms of flow processes and the associated stratigraphic expression. We first examine the relationships between the physical parameters that govern bypass in flows, before assessing the variable stratigraphic expression of bypass from modern seafloor, outcrop, and subsurface datasets. Theoretical and numerical approaches distinguish grain size, slope, flow size, and sediment concentration as parameters that exert major controls on flow bypass. From field data, a suite of criteria are established to recognize bypass in the geological record. We identify four bypass-dominated zones, each of which is associated with a set of diagnostic criteria: slope-channel bypass, slope-bypass from mass wasting events, base-of-slope bypass, and basin-floor bypass. As the expression of bypass varies spatially and is dependent on the scale of observation, a range of scale-dependent criteria are required for robust interpretation of these zones in the field or subsurface. This synthesis of deep-water sediment bypass highlights the challenge in quantitatively linking process with product. The establishment of criteria to recognize sediment bypass, qualitatively linked with flow processes, is an important step towards improving our understanding of submarine flow dynamics and resultant stratigraphic architecture.

The processes within deep-sea sedimentrouting systems are diffi cult 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 fi ll in outcrop (Cretaceous Tres Pasos Formation, southern Chile) in order to evaluate the geological evidence of the full channel cycle, from inception to terminal infi ll 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 fi lls are typically represented by sandstoneor conglomerate-dominated deposits that defi ne 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 fi ne-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 fi lling and abandonment.

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Counter point bar deposits in the meandering Peace River, North-central Alberta, Wood Buffalo National Park, are distinct from point bar deposits in terms of morphology, lithofacies and reservoir potential for fluids. Previously referred to as the distal-most parts of point bars, point bar tails and concave bank-bench deposits, counter point bar deposits have concave morphological scroll patterns rather than convex as with point bars. The Peace is a large river (bankfull discharge 11 700 m 3 sec )1 , width 375 to 700 m, depth 15 m, gradient 0AE00004 or 4 cm km )1 ) in which counter point bar deposits are dominated by silt (80% to 90%), which contrasts with sanddominant (90% to 100%) point bar deposits. Beginning at the meander inflection (transition from convex to concave), counter point bar deposit stratigraphy thickens as a wedge-like architecture in the distal direction until the deposit is nearly as thick as the point bar deposits. The low permeability silt-dominant lithofacies in counter point bar deposits will limit reservoir extent and movement of fluids in both modern and ancient subsurface fluvial deposits. In the exploration and extraction of bitumen and heavy oil in subsurface fluvial rocks, identification and mapping of reservoir potential of point bar deposits and counter point bar deposits is now possible in the fluvial-dominated tidal estuarine Lower Cretaceous Middle McMurray Formation, North-east Alberta. Recent geophysical advances have facilitated imaging of some ancient buried point bar deposits and counter point bar deposits which, on the basis of morphological shape of sedimentary bodies observed from seismic amplitude, can be interpreted and mapped as depositional elements or blocks that contain associated sandstone or siltstone dominant lithofacies, respectively. As counter point bar deposits exhibit poor permeability and thus limit reservoir potential for water, natural gas, light crude, heavy oil and bitumen, counter point bar deposits should be avoided in resource developments. Geophysical imaging, interpretation and mapping of point bar deposit and counter point bar deposit elements provide new opportunities to improve recovery of bitumen and heavy oil and reduce development costs in subsurface cyclic steam stimulation and steam-assisted gravity drainage projects by not drilling into counter point bar deposits.

Submarine channels have been important throughout geologic time for feeding globally significant volumes of sediment from land to the deep sea. Modern observations show that submarine channels can be sculpted by supercritical turbidity currents (seafloor sediment flows) that can generate upstream-migrating bedforms with a crescentic planform. In order to accurately interpret supercritical flows and depositional environments in the geologic record, it is important to be able to recognize the depositional signature of crescentic bedforms. Field geologists commonly link scour fills containing massive sands to crescentic bedforms, whereas models of turbidity currents produce deposits dominated by back-stepping beds. Here we reconcile this apparent contradiction by presenting the most detailed study yet that combines direct flow observations, time-lapse seabed mapping, and sediment cores, thus providing the link from flow process to depositional product. These data were collected within the proximal part of a submarine channel on the Squamish Delta, Canada. We demonstrate that bedform migration initially produces back-stepping beds of sand. However, these back-stepping beds are partially eroded by further bedform migration during subsequent flows, resulting in scour fills containing massive sand. As a result, our observations better match the depositional architecture of upstream-migrating bedforms produced by fluvial models, despite the fact that they formed beneath turbidity currents.

An integrated provenance analysis of the Upper Cretaceous Magallanes retroarc foreland basin of southern Chile (50°30′–52°S) provides new constraints on source area evolution, regional patterns of sediment dispersal and depositional age. Over 450 new single‐grain detrital‐zircon U‐Pb ages, which are integrated with sandstone petrographic and mudstone geochemical data, provide a comprehensive detrital record of the northern Magallanes foreland basin‐filling succession (>4000‐m‐thick). Prominent peaks in detrital‐zircon age distribution among the Punta Barrosa, Cerro Toro, Tres Pasos and Dorotea Formations indicate that the incorporation and exhumation of Upper Jurassic igneous rocks (ca. 147–155 Ma) into the Andean fold‐thrust belt was established in the Santonian (ca. 85 Ma) and was a significant source of detritus to the basin by the Maastrichtian (ca. 70 Ma). Sandstone compositional trends indicate an increase in volcanic and volcaniclastic grains upward through the basin fill corroborating the interpretation of an unroofing sequence. Detrital‐zircon ages indicate that the Magallanes foredeep received young arc‐derived detritus throughout its ca. 20 m.y. filling history, constraining the timing of basin‐filling phases previously based only on biostratigraphy. Additionally, spatial patterns of detrital‐zircon ages in the Tres Pasos and Dorotea Formations support interpretations that they are genetically linked depositional systems, thus demonstrating the utility of provenance indicators for evaluating stratigraphic relationships of diachronous lithostratigraphic units. This integrated provenance dataset highlights how the sedimentary fill of the Magallanes basin is unique among other retroarc foreland basins and from the well‐studied Andean foreland basins farther north, which is attributed to nature of the predecessor rift and backarc basin.

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