ABSTRACT Utilizing a basin-wide data set of three-dimensional seismic volumes and the application of principles of seismic stratigraphy and seismic geomorphology allowed identifying numerous depositional elements within the Vaca Muerta–Quintuco system, a set of clinoforms whose topsets belong to the Quintuco Formation, whereas the bottomsets and foresets belong to the Vaca Muerta Formation. Within the topsets, small circular geobodies clustered near the prograding shelf margin, averaging 200–800 m (656–2625 ft) in diameter and up to 75 m (246 ft) in height. These features comprise small carbonate buildups defining carbonate factories trending strike parallel. Identification of intervals where these geobodies are abundant is important because wells drilled through them have experienced either drilling mud admission or gas influx. In addition to these biogenic carbonate mounds, the topsets show elongated oolitic grainstone shoals oriented orthogonal to coeval shelf margins, in some cases measuring up to 22 km (14 mi) long and 5 km (3 mi) wide. The foresets (slope deposits) become progressively enriched in total organic carbon (TOC) and porosity downdip—key variables for a self-sourced unconventional reservoir. These deposits commonly comprise mudstone and marlstone, interbedded with limestones. In the lower foresets to toesets, strike-parallel, high–seismic-amplitude, and high-energy calcareous deposits are embedded in organic-rich mudstones. In some instances, these amplitude anomalies, drilled and cored by a few wells, show both well-defined linear geobodies along the toeset and evidence of bottom currents in cores (thicker limestone beds, ripples, bioturbation, and occasional centimeter-scale soft-sediment deformation). Identification of such geobodies is critical, as there is evidence from ongoing development drilling that these may act as hydraulic-fracture barriers and can also affect well performance as evidenced by increased water production. The bottomsets consist of low–amplitude-parallel, “railroad track” reflections that extend for tens of kilometers, characterizing the classic basin center Vaca Muerta play. Within these deposits, no major mappable geobodies are observed other than localized compressional ridges of mass-transport deposits (MTD) near the toesets. In some areas of the basin, the Vaca Muerta Formation was deposited directly on top of a preexisting non-marine paleo-aeolian dune topography which had a direct impact on the stratal geometries and the bottomset facies of the Vaca Muerta Formation. Acoustic impedance (AI) from seismic inversion show well-defined Vaca Muerta low-impedance seismic facies, which relate to the presence of predominantly fine-grained, organic-rich (~5%), porous (~11%) mudstones and marlstones. Within the high-TOC Vaca Muerta interval, most AI three-dimensional (3-D) volumes throughout the basin show an average of five to six seismic facies with discrete AI values that can be directly correlated to rock types, depending on their position within the clinoform (i.e., topset, foreset, bottomset). These seismic facies correlate to facies associations with distinct petrophysical and geomechanical properties at core/outcrop scale, as measured by lab studies. Understanding this relationship and its distribution in space is critical to predicting optimum horizontal well landing zones and sweet spots.

ABSTRACT The Vaca Muerta Formation consist of outer ramp to basinal facies in a mixed siliciclastic–carbonate creating an organic-rich section up to 500 m thick. This chapter documents stratal terminations, main bounding surfaces, and stacking patterns of the Vaca Muerta–Quintuco system as a means to establish a new sequence stratigraphic framework. The data set comprises more than 500 wells and a basin-scale seismic coverage that spans 30,000 km 2 Regional seismic interpretations and well correlations were calibrated with well geochemical data and acoustic impedance seismic sections. Twelve high-frequency depositional sequences (HFS) with variable combinations of systems tracts were defined and grouped in three low-frequency depositional sequences (LFS). Within this sequence stratigraphic framework, the Vaca Muerta Formation includes organic-rich (total organic carbon, TOC > 2wt. %) and organic-poor intervals (TOC < 2wt. %) At a high-frequency scale, the organic-rich intervals with the highest concentration of TOC belong to transgressive systems tracts and the lower sections within clinoform bottomset and foreset of highstand systems tracts. These condensed sections usually show the best reservoir properties in the self-sourced unconventional play. Conversely, organic-poor intervals are found in the foresets of falling-stage systems tracts and lowstand systems tracts. Condensed sections of each sequence allow subdivide the unconventional play in a stacking of 12 organic-rich Vaca Muerta units (OVM, TOC ≥ 2wt. %). The lowermost eight OVM units correspond to the main tested landing zones. Moreover, a detailed map of shelf breaks reveals a strong three-dimensional (3-D) spatial variability, which is summarized in four groups of plan-view geometries. The 3-D spatial variability of the organic-rich intervals is analyzed at local scale in two cases with different plan-view geometries. At regional scale, thickness maps of the main OVM units allow infer stratigraphic controls (e.g., systems tracts, previous clinoform paleo-topography) and tectonic controls, both regional (morphostructural domains) and local (subsidence axes and paleo-highs), active during the deposition of the Vaca Muerta Formation. The proposed sequence stratigraphic framework provides a predictive understanding of 3-D spatial distribution of the organic-rich intervals in subsurface assessments for the Vaca Muerta play and is applicable to the exploration of other analogous (mixed siliciclastic-carbonate systems) self-sourced unconventional resources.

Abstract Seismic stratigraphic and seismic geomorphologic observations can yield comprehensive sequence stratigraphic interpretations. When these interpretations incorporate process sedimentological inferences, more robust interpretations are produced. In practice, each informs the other, creating a strong positive feedback loop that results in a more comprehensive interpretation. Moreover, considerations of process sedimentology can lead to extension of interpretations both up-system and down-system of study areas. The end result will be enhanced regional lithologic prediction. Two examples are used to illustrate this work flow: deep-water channels and deep-water terminal fans. In the former, the architecture of channel fills implies an early erosional phase associated with relatively large flows, which commonly characterize early lowstand periods. This early erosional phase, having little to no preserved deposits due to repeated cannibalization, creates the “container” that will ultimately provide the accommodation for sedimentation. Subsequently, this sedimentation occurs during late lowstand, which is characterized by relatively smaller, less energetic flows that result in a net depositional phase. Considerations of process sedimentology shed light both on the genesis of deposits within the channel as well as what has occurred up-system where associated flows originated. In the case of deep-water terminal fans, the succession of depositional systems as documented by seismic stratigraphic and seismic geomorphologic data is interpreted through the lens of process sedimentology, resulting in enhanced understanding of the depositional sequence that is preserved and enhanced lithologic predictability. In this case as well, this integrated work flow results in predictions relevant to both up-system and down-system deposits.

Abstract Linked shelf edge deltas and slope channel systems are observed in the eastern Gulf of Mexico. The slope channels are characterized by deep incision into the substrate and moderate sinuosity nearly to the shelf-slope break. Channelized flows were not fully confined as evidenced by well-developed levees up to 90 m thick. This sinuosity suggests that turbulent flow within the channel was likely nearly from the uppermost slope. With apparent turbulence characterizing these channels nearly to the shelf-slope break, the dominant mode of sediment delivery to the slope and basin beyond probably was in the form of density underflow ( i.e. , hyperpycnal flow) rather than shelf edge slump and/or slide progressively transformed into turbidity flow. The stages of evolution of these slope channels are (1) clustering of small slope gullies on the slope at the initiation of lowstand deposition, (2) dominance of one of these slope gullies and formation of one significant channel, formation of a frontal splay fed by the dominant channel, (3) abandonment of frontal splay deposition in favor of leveed channel deposition across the entire slope, and (4) entrenchment of the leveed channel into the earlier deposited leveed channel and frontal splay.

Abstract Historically, submarine-mass failures or mass-transport deposits have been a focus of increasingly intense investigation by academic institutions particularly during the last decade, though they received much less attention by geoscientists in the energy industry. With recent interest in expanding petroleum exploration and production into deeper water depths globally and more widespread availability of high-quality data sets, mass-transport deposits are now recognized as a major component of most deep-water settings. This recognition has lead to the realization that many aspects of these deposits are still unknown or poorly understood. This volume contains twenty-three papers that address a number of topics critical to further understanding mass-transport deposits. These topics include general overviews of these deposits, depositional settings on the seafloor and in the near-subsurface interval, geohazard concerns, descriptive outcrops, integrated outcrop and seismic data/seismic forward modeling, petroleum reservoirs, and case studies on several associated topics. This volume will appeal to a broad cross section of geoscientists and geotechnical engineers, who are interested in this rapidly expanding field. The selection of papers in this volume reflects a growing trend towards a more diverse blend of disciplines and topics, covered in the study of mass-transport deposits.

Abstract Introduction The significance of submarine mass movement on most continental margins is now well established in the scientific literature. The resultant sedimentary deposits have been called by many names, but will be hereafter termed mass-transport deposits (MTDs) for this publication. Such deposits are distinctive in deepwater depositional systems, most commonly due to their large size, distinctive morphology, and chaotic internal character. Recently, regional overviews have identified a number of margins around the world where MTDs are commonly observed on or near the seafloor across much of the continental slope (e.g., Weaver et al., 2000 ; Evan et al., 2005 ; Posamentier and Walker, 2006 , Huhnerbach et al., 2008; Lee, 2009 ; Twichell et al. 2009 ; Boyd et al., 2010 ). Equally as common, but documented mostly on an areally smaller scale, MTDs have been reported to be a substantial component of the near-surface stratigraphic record in at least a few basins (e.g., Newton et al., 2004 ; Moscardelli et al., 2006 ; Posamentier and Walker, 2006 ; Giles et al., 2010 ).

Abstract Extensive deep-water mass-transport deposits are observed in both slope and basin-floor settings. A detailed understanding of mass-transport deposits, in terms of emplacement processes, depositional products, and their stratigraphic and geographic distribution, is vital because they can constitute a significant portion of the stratigraphic section in deep-water settings. In addition, mass-transport deposits can play a significant role in hydrocarbon exploration, inasmuch as they can constitute seal, reservoir, and possibly source facies under the right circumstances. Different data types bring to light different aspects of mass-transport deposits. This paper focuses on insights derived from seismic and outcrop data. Overall geometries and architecture of mass-transport deposits are readily observable in 3D seismic data; however, features below seismic resolution that are vital for process and lithologic understanding need to be observed in outcrop. Integrating observations across a broad range of scales by linking seismic and outcrop observations constitutes an effective way of improving our understanding of when and where mass-transport deposits are likely to form. In addition, this linkage sheds light on details of internal architecture that commonly characterizes these deposits. Mass-transport deposits can comprise sheets, lobes, and channel fills, and can reach 150 m or more in thickness. Greater thicknesses are observed where successive flows are amalgamated. This paper documents both internal architectural or stratigraphic as well as external geomorphic attributes of such deposits, as expressed in outcrop and imaged by 3D seismic data. Recognition of mass-transport deposits in outcrop is based on identification of bedding deformed by synsedimentary processes, with deformation ranging from minimal redistribution of large slide blocks to complete disaggregation typical of debris-flow deposits. On seismic data, mass-transport deposits can be recognized by certain geomorphologic as well as stratigraphic distinguishing characteristics: basal linear grooved and scoured surfaces, hummocky relief at the top, and internal chaotic to transparent seismic facies, with internal thrust faulting common.

Abstract The volume and interplay of mass-transport (MTD) and turbidite-system deposits varies on different continental margins depending on local and external controls such as active-margin or passive-margin tectonic setting and climatic and/or sea-level change. Erosion and breaching of local grabens at the shelf edge of the southern Bering Sea produce giant, gullied canyons and MTD sheets that dominate the basin-floor deposition and disrupt development of turbidite systems. In contrast, external controls of great earthquakes (> 8 M ) along the Pacific active tectonic continental margins of Cascadia and northern California cause seismic strengthening of the sediment, which results in minor MTDs compared to turbidite-system deposits. Messinian desiccation of the Mediterranean Sea caused a deeply eroded Ebro subaerial canyon and an unstable central segment with an MTD sheet, whereas other stable Ebro margin segments have only turbidite systems. In the northern Gulf of Mexico, the delta-fed Mississippi Fan and intraslope mini-basins contain MTDs and turbidites that are equally intermixed from the largest scales with MTD sheets hundreds of kilometers long to the smallest scales with beds centimeters thick. In the Antarctic Wilkes Land margin, global climate cooling caused a late Oligocene to middle Miocene time of temperate continental ice sheets that resulted in massive deposition of MTDs on the margin, whereas later polar ice sheets favored development of turbidite systems. Our case studies provide the following new insights: (1) MTDs can dominate entire margins, dominate segments of a margin, be equally mixed with turbidites, or dominate a margin during some geologic times and not others; (2) on active tectonic margins with great earthquakes, the maximum run-out distances of MTD sheets across abyssal-basin floors are an order of magnitude less (~ 100 km) than on passive-margin settings (~ 1000 km), and the volumes of MTDs are limited on the abyssal sea floor along active margins; (3) where the most precise radiocarbon ages are available, major MTD episodes of deposition are correlated with the most rapid falls or rises of sea level; (4) gullied canyons feeding MTD sheets have irregular and steep axial gradients (5-9°), whereas canyons feeding turbidite systems have a regular graded profile and less steep gradients (1 to 5°). Our examples of MTD and turbidite systems provide analogues to help interpret ancient systems.

Abstract The present study provides an overview of recent sedimentation patterns on the central Algerian continental margin. Recent sedimentation patterns were assessed from morphological analysis, which is based on swath bathymetry and echo-facies mapping. It appears that sedimentation along the Algerian margin is controlled by two processes: (1) gravity-induced processes, including both mass-transport deposits and turbidity currents, and (2) hemipelagic sedimentation. Mass-transport deposits occur on the Algerian margin at the canyon heads and flanks, in the interfluve areas between canyons, along the seafloor escarpments, and on the flanks of salt diapirs. Mass-transport deposits (MTDs) sampled by coring consist of a variety of soft and hard mud-clast conglomerate and turbidite deposits. MTDs are mostly localized at the toes of steep slopes, where thrust faults were previously identified and mapped. Analysis of the spatial distribution of MTDs and their recurrence in time help reconstruct the main predisposing factors and triggering mechanisms, and evaluate their impact on evolution of the Algerian margin.

Abstract Abstract: Deepwater mass-transport deposits (MTDs) are associated with Upper Quaternary seafloor leveed-channel complexes at the mouth of a large canyon at the base of slope of the offshore Niger delta. They make excellent analogs for interpreting older subsurface features and reservoirs, and for geohazard analysis. These leveed-channel complexes and mass-transport deposits are assessed within a 3D seismic survey, using detailed images of seafloor maps and stratal surfaces, artificially digitally colored, and vertically exaggerated to create optimal imaging. A large canyon head incises the present-day shelf margin of the Niger delta and traverses down the upper and lower slope for 45 km towards the southeast. At the canyon mouth, a large apron of leveed-channel complexes covers the slope and basin plain for a distance of 30 km within the seismic survey. Large sediment waves occur on outer levees of channel bends, attaining heights of 200 m. In some areas, synclinal limbs of individual sediment waves have been deformed by numerous rotated blocks along small listric faults to form small mappable MTDs. Other mass-transport deposits occur associated with and above the leveed-channel complexes. Lengths of the MTDs range from 1 km to over 16 km, and thicknesses commonly range from 100 m to 200 m. Headward escarpments are well imaged in both map and cross-section views. Proximal facies of the MTDs includes rotated blocks and large angular glide blocks. These pass distally into smaller glide blocks and chaotic seismic facies inferred to be debrites. Intermediate parts of the MTDs have longitudinal linear features parallel to inferred flow direction. Distal patterns consist of transverse compressive ridges. Other MTDs too large to be completely imaged within the 3D survey show internal facies, consisting of large angular glide blocks in a matrix of seismically visible smaller blocks and chaotic facies inferred to be debrites. Multiple causes of MDTs in this area are probable. In possible order of importance, these include tilting and oversteepening of sediments because of tectonic uplift, high sedimentation rates at the mouth of the canyon, and eustatic falls of sea level.

Abstract Abstract: The characteristics, evolutionary history, and triggering mechanisms of successive siliciclastic mass-transport deposits (MTDs) of late Cenozoic age on the northwestern South China Sea margin were studied using borehole and 2D/3D reflection seismic data. Multiple mass-transport deposits of various scales and morphologies formed from Pliocene to Holocene time in high-slope-gradient and high-sedimentation-rate parts of the Qiongdongnan and Yinggehai basins. In plan view, MTDs documented by 3D seismic data, deposited between 3 and 2 Ma, are 1 to 11 km wide and 4 to 29 km long. Two seismic geomorphologic characteristics of a typical MTD comprise a basal surface and displaced masses of sediments. Internal seismic facies of the displaced mass consist of extensional wedge facies in upslope areas, thrusted facies in intermediate areas, and chaotic or mounded facies in distal downslope areas. These MTDs likely were triggered by a combination of mechanisms. Seafloor oversteepening, rapid accumulation of thick sedimentary deposits, overpressure, and a tectonically active basin setting provide a background favoring formation of MTDs. Additionally, seismicity, abrupt increase of sedimentation rates, rapid slope progradation, and release of gas contributed to triggering mass-transport deposition in the study area.

Abstract Abstract: The stratigraphic evolution of the Quaternary mass-transport deposits (MTDs) in the Mensa and Thunder Horse intraslope basins, Mississippi Canyon, northern deep Gulf of Mexico, was interpreted based on based on 378 square miles (970 square km) of 3-D seismic data in water depths ranging from 5300 to 6500 feet (1617 to 1983 m). Seven depositional sequences were defined in the study area between 1.3 Ma to the present. Allochthonous salt systems had bathymetric expression and influenced sediment thickness and location of depositional systems. Six MTDs are present in five of the depositional sequences. MTDs overlie erosional boundaries—up to 30 m of the underlying section has been eroded at the base of the deposits. These deposits consist primarily of chaotic, rotated, and thrusted seismic reflections. They vary in size and areal distribution from elongated to more equidimensional. The oldest MTD is in sequence 1, overlies the 1.3 Ma condensed section, and underlies a series of five east-trending channels. This MTD has an easterly trend and represents the initial deposition after a major reorganization of the slope system. In the underlying Miocene-lower Pleistocene sequences, channels trended from the northwest to southeast. Sequences 2 and 3 consist of seven additional channels that trend primarily from west to east. The second MTD is present in sequence 3, trends to the southeast, and truncates four channels. A series of stacked condensed sections (ca. 0.6 to 0.08 Ma) form a thin unit and separate sequences 3 and 4. Sequence 4 consists primarily of hemipelagic and overbank deposits. Four MTDs are present in the sequences 5-7. Multiple sets of these deposits have channelized into and stacked on one another. These MTDs appear to have been sourced primarily from the west, similar to the channels in the underlying sequences. This case study illustrates the many variations in MTDs that are present in the same intraslope setting. These variations can occur in their size, shape, thickness, seismic facies, the amount of erosion at their base, and their timing of formation within different positions of sea level.

Abstract A large submarine-slide deposit from the western Scotian Slope off eastern Canada was imaged on a 3D seismic reflection dataset in the Barrington exploration block. The mass-transport deposit (MTD) forms a tongue-shaped body that is 25 km long and 8 km wide, with a run-out distance from the headscarp of 41.5 km and a total volume of 12.5 km 3 . In profile, it consists of a chaotic seismic facies. This facies forms a highly rugose top surface morphology, suggesting that the flow consisted of an abundance of intact angular blocks. Its base reveals evidence of erosion typical of submarine MTDs, with linear downslope-trending gouges and excavation of a pit 50-m-deep. The source area and headscarp of the Barrington MTD are somewhat obscured by postdepositional erosion. Additionally, high-resolution seismic profiles show that the deposit is draped by approximately 30 m of late Pleistocene and Holocene sediment, providing an age estimate of 30 ka for the failure. Despite this drape, the modern seafloor above the MTD still has a highly rugose morphology, echoing the top surface of the deposit. Seismic profile data show a series of stacked MTDs underlying the Barrington MTD, suggesting that mass-failure recurrence is common on geologic time scales. Although it is difficult to attribute mass-failure triggering mechanisms, high sedimentation rates due to proximal shelf glaciers and intense erosion causing oversteepening, and likely established preconditions for instability. Local seismicity, possibly a result of glacial rebound, is the most probable initiating factor.

Abstract Sediment mass transport in the Pacific margin of the Antarctic Peninsula is strongly influenced by its peculiar tectonic and sedimentary evolution. Analysis of swath bathymetry and multichannel seismic reflection data shows that this setting reflects the passage from an active to a passive margin, and the transition from river-dominated to glacier-dominated sedimentation. Only contouritic sedimentation persisted throughout the late Neogene on the continental rise, while rapid progradation of steep wedges composed of glacial diamicton occurs on the slope. Gravitational instability and mass-transport processes, which occur on the continental rise, appear to relate to physical properties of contourite sediments deposited in this high-latitude setting. Other than minor erosional gullies on the upper slope, there is no evidence of major incisions such as channels, canyons, or slide scars on a steep continental slope (averages 13°). This situation results from high shear strength of the slope-forming diamicton delivered by grounded ice sheets. Short-run-out mass failures were the main sediment transport process to the slope. Turbidity currents, most likely originated by downslope evolution of mass flows, were able to generate large deep-sea channel systems at the base of the continental slope. On the continental rise, relatively good sorting and a high accumulation rate of sediments forming sediment drifts favored slope failure even on gentle slopes. Coalescent headscarps that form the drift crest were produced by undercutting of steeper flanks of drifts. This process formed the walls of turbidity-current channels, flowing in low-relief areas between drifts. Failure along stratal weak layers on the gentle sides of sediment drifts produced either relatively small, concave slide scars in the margin-proximal drift or long, rectilinear scars in distal locations.

Abstract This paper uses three-dimensional seismic data to investigate the typologies, genetics, and mechanisms of soft-sediment deformational processes on the Ebro Continental Margin (offshore northeastern Spain). The study focuses on the two major types of soft-sediment deformation in the region: slope failure and fluid-escape structures. Such processes have operated almost continuously throughout the post-Pleistocene history of the Ebro Continental Margin, and have played a critical role in its overall evolution and construction. This study shows that vertical stacking patterns of submarine canyons create preferential pathways for fluid migration and slope failure. In these areas, three-dimensional seismic analysis reveals a potential cause-and-effect relationship between focused fluid migration and repeated slope failure. The proposed model is that focused fluid flow from sands within stacked submarine canyons leads to overpressure generation and reduction of sediment shear strength, making sediment susceptible to failure. The presence of a widespread region of fluid-escape structures and slope failures on the Ebro Continental Margin has important implications for offshore facilities. The relatively high resolution provided by the seismic data has been sufficient to be used for a geohazard assessment study, aimed at exploratory well design and field development. The results from this study have led to a detailed program of seafloor and near-surface evaluation over a proposed area in the area.

Abstract Abstract: Offshore of northwest Borneo, the occurrence of distinct submarine mass failures on the upper continental slope poses a substantial challenge to deepwater operations for the energy industry. These features are part of a complex of mass-transport deposits (MTDs) that occur in the near-surface interval across most of the upper continental slope, including a large area undergoing field development for hydrocarbon production. In the study area, the shallowest and most prominent feature discernible on conventional 3D seismic data is MTD 1, which has a profound influence on the present-day seafloor topography. This feature has a distinctive fan-like outline in plan view, a maximum strike dimension of approximately 6 mi (10 km), a dip extent up to 24 mi (40 km), and a maximum thickness up to 570 ft (176 m). The fan-like external form and the presence of a dip-oriented erosional keel suggest that the depositional process was a less coherent debris flow, with little to no original internal stratigraphy preserved. The less coherent nature of this feature is further supported by a key observation that this MTD overran an area of substantial high bathymetric relief, which is located in the area considered for a field development. Locally overlying MTD 1 are a series of younger near-seafloor features, termed “canyon-to-fairway” corridors that display a confined updip to less confined downdip plan-view morphology. These unique features locally erode and smooth the rugose top surface of the near-surface MTD 1 and can be interbedded with the lower intervals of the usually overlying draped sediments. Development of these late Pleistocene canyon-to-fairway corridors suggests that these features probably formed during a period of sea-level fall or at a lowstand. A blanket of three distinct intervals of draped sediments cap this entire sequence, composed mostly of muddy turbidites grading upward into hemipelagic deposits. The present hummocky seafloor topography mimics the rugose top surface of the shallowly buried MTD 1, except along its northeast lateral margin and where smoothed by canyon-to-fairway corridors. Internally within MTD 1, physical properties probably vary substantially both laterally and vertically, because draped sediments, turbidites, and occasional channelized sediments were incorporated in the failed matrix of this feature. Some of the geohazards, potentially affecting a field development, are a direct a result of the ubiquitous occurrence of MTD 1 in the study area. These potential geohazards include local steep slopes, seafloor scarps, and variable near-seafloor soil conditions. Understanding the impact of each of these potential geohazards, caused primarily by the presence of MTD 1, on a field development is vital input for selection of production well-site locations and placement of subsea infrastructure.

Abstract Abstract: Deep-marine strata of the Windermere Supergroup, which currently are exposed in an area over 35,000 km 2 in the southern Canadian Cordillera, were deposited on the passive margin of Neoproterozoic western North America. In the Isaac Formation at the Castle Creek study area, stratigraphic evidence of slope instability occurs as mass-movement (slump and slide) and cohesive-debris-flow deposits that crop out locally through the 1.5-km-thick succession. These deposits are particularly common in a mass-transport deposit (MTD) up to 110 m thick that occurs sandwiched between two major channel complexes. Interstratified within these deposits are common coarse-grained channel fills that preferentially infilled irregular topography on the seafloor. In many instances, this irregular topography was most probably related to earlier emplacement of debris-flow and slump and slide deposits. Important stratigraphic characteristics in this succession suggest that this particular MTD represents a major change in the nature of sediment supply and transport and depositional processes within the basin. These changes are interpreted to be controlled principally by changes of relative sea level, which had a first-order control on sediment supply, sediment caliber, and sediment composition to the slope and more distal basin floor.