Abstract We illustrate how sediment budgets can be used to understand the relationships between tectonics and sedimentation and to estimate the partitioning of sediment in shelf, slope, and basin-floor fan compartments within ancient shelf-margin strata. The studied Lewis-Fox Hills shelf margin represents the early Maastrichtian infill of the Laramide-type Washakie-Great Divide basin of southern Wyoming. The shelf margin shows an evolution in two stages. In Stage 1, the shelf margin is characterized by rising shelf-edge trajectory associated with increasing clinothem volumes, widening marine topsets, and increasing clinoform heights; a relatively large fraction of the sediment budget is stored on the shelf compartment through Stage 1. In Stage 2, the shelf-edge trajectory becomes more progradational and is associated with decreasing clinothem volumes, wide coastal-plain topsets, and stable to decreasing clinoform heights; a larger fraction of the sediment budget is stored within deep-water compartments. We interpret that the evolution from Stage 1 to Stage 2 is driven chiefly by tectonic uplift of the adjacent mountains and associated basin subsidence: increasing in Stage 1 and stable to possibly decreasing in Stage 2. Sediment budget calculations suggests that average sediment supply to the basin was 4-16 × 10 6 ton/y, yield was within 200-2000 ton/km 2 /y, and hinterland maximum relief was 1000-3000 m. Integration of sediment budget estimates within source-to-sink evolution represents a powerful tool to build improved tectono-stratigraphic models, and develop predictive models for sediment storage across shelf-margin compartments.

Abstract Shelf-edge deltas are the main driver for the delivery of sediment to the deep water lowstand systems tracts. However, the mere presence of deltas at the shelf margin does not guarantee accumulation of deep-water sands. The two main reasons for this are: (1) deltas that develop at the shelf edge during relative sea-level fall generally need to be significantly incised by their own distributaries for sand delivery to be focused down to a basin-floor fan system, and (2) deltas that develop when sea level is rising (late lowstand) tend to be inefficient sand-delivery systems, and disperse sand mainly onto the slope as sheet-like turbidite lobes, with few or no basin-floor fans. Thus, given the presence of deltas at the shelf-edge, both the likely magnitude and direction of sea-level change at the shelf edge needs to be estimated, before significant time-equivalent, deep-water sand can be predicted on the basin floor. Shelf-edge deltas are generally thicker, significantly more unstable, and markedly more turbiditeprone than inner/or mid-shelf deltas. These major differences are due to longer run-out slopes (greater water depths), steeper mud-prone slopes, and greater accommodation at the shelf margin compared to deltas in more proximal shelf settings. There are four main types of shelf-edge deltas that have been documented from a database developed mainly from the Eocene shelf margin on Spitsbergen and the Miocene shelf margin of the Carpathian Foredeep: Type A deltas develop on the outer shelf/shelf-margin transition but without significant progradation beyond the shelf edge onto the slope. These deltas usually form during the falling stage of a fall-to-rise cycle on the shelf. Type B deltas develop at the shelf margin but are significantly cannibalized by fluvial-feeder erosion. Such deltas also form during falling stage, but base level falls below the shelf edge. The deltas are fairly sharp based on the outer shelf, are sand prone, and are deeply eroded by their own river distributaries. Because of the fluvial incision, only remnants of these deltas are preserved. However, their main significance and legacy is their time-equivalent, downslope suite of deep water, lowstand deposits including basin-floor fans. Type C deltas develop at the shelf edge, produce significant basinward growth of the shelf margin but rarely link down to basin-floor fans. They form during a late, rising stage of the fall-to-rise cycle, as they overlie earlier cannibalized deltas and older basin-floor fans of the same sequence. They are many tens of meters thick and consist of stacked, well-developed upward-coarsening and thickening units.. Type D deltas are progradational to aggradational delta complexes at the shelf margin, without underlying shelf-edge erosion, and only rare, linked basin-floor fans. Type A and C deltas simply amalgamate during a fall-to-rise cycle to become a single, thick (many tens of meters) deltaic wedge that is perched at the shelf margin and drapes far out onto the slope.

Abstract Storvola is a Spitsbergen mountainside outcrop (1 km x 10 km [0.6 mi x 6 mi]) that exposes the coastal plain, shelf, slope, and basin-floor reaches of a series of lower Eocene clinoforms (Figure 2B, C). The clinoforms have decompacted amplitudes of some 300–350 m (984–1148 ft) reflecting basin water depths of this magnitude at times of relative sea level lowstand (from shelf edge to basin floor). Type 1 shelf margins typically have relatively deep incision of river distributary channels on their shelf-edge reaches, turbidite channels, and large-scale disruption (growth faults, rotated blocks, and large slump complexes) on their mud-prone slopes, and sand-rich fans on their proximal basin-floor reaches. In contrast, Type 11 shelf margins (see Plink-Bjorklund and Steel, chapter 70, this volume) have their sediment budget partitioned differently in the clinoform. They have limited incision at the shelf edge, and strike-extensive, sand-rich upper and middle slopes, but have no basin-floor fans. The contrasts between Type I and Type II margins are summarized in Figure 2A. Clinoform 14 on Storvola, illustrated here as our Type 1 shelf-margin example (Figure 2B), consists of a regressive delta phase on the shelf platform, a falling-stage and lowstand phase of sandy sediment gravity flows in deep-water channels of the shelf margin (below the shelf edge) and deep-water basin floor, and a transgressive estuarine phase back on the shelf platform. These three phases can be further subdivided into seven segments:

Abstract Høgsnyta is one of the l-by-5-km (0.6-by-3.0-mi)-scale mountainside outcrops that expose shelf-margin clinoform complexes in the Eocene Central Basin of Spitsbergen. The shelf-margin clinoforms have been documented in two approximately 30-km (18-mi)- long transects: Grøndalen-Reindalen transect and Van Keulenfjorden transect. The Høgsnyta shelf margin at Reindalen is exposed on a dip-parallel, steep mountainside as a wedge-shaped turbidite sandstone body. It is 70 m (230 ft) thick at the shelf edge, thins downslope, and pinches out above the base of slope, approximately 5 km (3 mi) from the shelf edge. The height of the clinoform complex of approximately 200 m (656 ft) gives a direct estimate for the paleowater depth. The outcrop also exposes older marine mudstones below the studied shelf-margin clinoform complex. The shelf includes younger clinoform complexes, as well as a younger coastal-plain succession above the shelf-margin complex. The Høgsnyta turbidite system is a slope-turbidite apron, attached to a fluvial, shelf-edge delta system. Fluvial distributary channels fed into delta-front sheets or into slope channels; the slope channels terminated with slope lobes on the upper and middle slope, or with turbidite sheets on the lower slope. The internal architecture of the Høgsnyta shelf-margin clinoform complex reflects deposition in a fourth-order sea-level cycle that includes: (1) shelf-margin progradation during the falling stage, (2) lower slope aggradation during the early lowstand, (3) intralowstand flooding back onto the shelf edge, and (4) shelf-margin progradation during the late lowstand. The Spitsbergen data shows that sands were distributed beyond the shelf edge during falling stage

Abstract The 1 km x 15 km scale mountainside outcrops in Van Keulenfjorden, Spitsbergen, provide an excellent dip-direction exposure of linked coastal-plain, shelf, slope, and basin-floor facies tracts along Early Eocene basin-margin clinoforms. The topsets of these clinoforms form an apparently aggradational coastal-plain succession. This paper focuses on the documentation of three incised valleys within this coastal-plain succession. Because dip-direction exposures cannot show the typical V-forms of incised valleys, these valleys have been recognized by documenting (1) regional unconformities with local segments dipping up to 3 degrees, which can be “walked out” across the exposed coastal plain and onto the coeval paleo shelf and shelf edge, (2) correlation of these erosional unconformities into probable interfluve paleosols, and (3) landward and oblique onlap of subhorizontal fluvial and estuarine deposits onto these regional unconformities. The measured downcutting, across the exposed coastal plain, on these regional unconformities is 43, 18, and 67 m, respectively, and the calculated depth of downcutting, using the thickness of valley fills, is 57, 26, and 67 m, respectively. This is compared to depths of individual fluvial channels of only 3–8 m. Description of valleys of this type, cutting into or sited near to the lowstand shorelines, and near the edge of the preexisting shelf, are rare. The valleys were incised by rivers during fourth-order relative sea-level falls, as the rivers extended seawards and cut into the deposits of the deltas that had crossed the shelf immediately before. Although there are preserved remnants of falling-stage and lowstand river deposits in the valleys, the main volume of sediment supplied by the rivers at this time was preferentially partitioned farther into the basin, as indicated by the presence of coeval basin-floor fans. The main fill of the incised valleys are landward-onlapping, transgressive macrotidal estuary deposits. In two of the valley fills there are also progradational estuarine deposits that mark the final in situ infilling of the estuaries, an aggradational to progradational phase that occurs related to the “turn-around” to highstand progradation. “True” highstand progradation occurred when estuaries were filled and shelf deltas prograded seawards. Erosional remnants of such deltas are preserved below the regional unconformities, close to their coeval lowstand paleoshorelines. Two of the documented incised valleys are deeply cut (57 and 67 m, respectively), whereas the third valley cuts down only ca. 26 m. Despite this difference the depositional facies of all valley fills are similar. The main differences lie in the total thickness of valley fills, the ratio of aggradation to landward shift, the associated tidal ravinement in the transgressive deposits, and the depth of total (and local) incision at the valley base. The two deeply cut valleys are associated with relative sea-level falls below the shelf edge and development of coeval basin-floor fans. Erosion of the third valley occurred during a sea-level fall that did not reach the shelf edge, and no sands were partitioned beyond the outer shelf.

Abstract Shelf-margin transects across the Eocene Central Basin of Spitsbergen provide seismic-scale (1 km x 15 km) outcrops of shelf- margin clinothem complexes with and without basin-floor fans (Type I and Type II respectively). Type I and Type II shelf margins reflect broadly similar timing of deposition in a sea-level cycle: (1) shelf-margin progradation or basin-floor aggradation during the falling stage, (2) lower-slope or basin-floor aggradation during the early lowstand, (3) intra-lowstand flooding back onto the shelf edge, and (4) shelf- margin progradation during the late lowstand. The Spitsbergen database strongly suggests that the sediment budget was partitioned largely onto the shelf and coastal plain during the development of transgressive and highstand systems tracts, whereas sands were distributed beyond the shelf edge during falling stage and lowstand. The conventional explanation for the differences in architectural and sediment-volume partitioning between Type I and Type II margins is that the magnitude or duration of sea-level fall was greater in the case of Type I. We argue here for a possible alternative explanation, that higher rates of sediment fallout at the shelf edge and upper slope during the falling stage can damp incision and prevent deep channeling at the shelf margin. Type I shelf-margin complexes show severe erosion of the falling-stage shelf-edge deltas by the delta’s own distributary channels. Time- equivalent basin-floor fans can be “walked out” and linked to the eroded falling-stage deltas in these clinothem sets. The late-lowstand part of this type of shelf margin consists of prograding shelf-edge deltas, causing a prominent late episode of shelf-margin accretion. These late- lowstand deltas are generally more muddy than those of the Type II margins. Heterolithic, thin-bedded turbidites dominate the delta-front succession, along with slumped units. In contrast, Type II shelf margins accreted with an amalgamated succession of falling-stage, early lowstand, and late lowstand deltas, and have no basin-floor fans. The falling-stage deltas are highly progradational, fluvially dominated, and have a sandy turbidite-prone delta front that reaches the base of slope. The tops of these deltas are severely eroded by a subaerial to subaqueous unconformity that is overlain by amalgamated channels. This unconformity is the sequence boundary that formed during the entire fall to the lowest sea-level position. Despite the documented sea-level fall below the shelf edge, no sand was partitioned onto the coeval basin floor. All the sandy sediment was trapped in the shelf-margin deltas, causing significant shelf-margin progradation. The falling-stage deltas are succeeded by an aggradational and landward-onlapping succession of turbidites, covered by a widespread intra-lowstand flooding surface. No coeval deltas at the shelf edge, or coeval basin-floor fans, were documented. The flooding surface is overlain by deltas that formed late in the lowstand. These late lowstand deltas prograded onto the slope, but they have a strong aggradational component; their distributaries and mouth bars are wave-reworked, and delta-front turbidites become muddy as high as on the middle slope. These deltas represent an important second episode of shelf-margin progradation. Although the latter deltas were deposited during the rising limb of the sea-level cycle, they are still overlain by a transgressive systems tract and maximum flooding surface.

Abstract Sedimentary prisms build out from the margins of most types of sedimentary basin where there is significant differential subsidence. Clinoforms are the large-scale (hundreds of meters), time-line expressions of discrete phases of aggradation and accretion within these prisms. The sigmoidal clinoforms are surfaces of dynamic equilibrium that are created and maintained by sediment aggradation to form topsets and then sediment by-pass through the topsets onto the accreting deepwater slope and beyond ( Swift and Thorne, 1991 ). It is argued, on this basis, that the topset surface of such large-scale clinoforms is referred to as a morphological ‘shelf’ and that the upper rollover of the clinoform is referred to as the ‘shelf-slope break.’ Such features form at the supply margins of many types of basin where there is a water depth of at least several hundred meters and are not restricted to continental margins. The geometry and internal architecture of individual clinoforms, or groups/sets of clino-forms, can be used to predict how sediment budgets have been partitioned between the shelf and deepwater areas beyond the shelf break. The architecture of individual clinoforms (time scale of several 100ky), mainly the degree of shelf-edge incision and the degree of slope disruption, can indicate whether or not significant volumes of sand have been delivered beyond the shelf margin. Another method of prediction makes use of the ‘trajectory’ of the shelf margin on time scales of 1Ma or more; i.e. , how the break-of-slope of successive clinoforms stack with respect to each other. High-angle trajectories generally imply preferential sediment storage on the shelf and coastal plain, whereas low-angle or falling trajectories involve erosion and sediment by-pass to the deepwater slope and basin floor. These concepts are illustrated from well-exposed clinoforms and clinoform sets within a shelf margin that has migrated and accreted some 30 km during an interval of some 6 Ma, in the Central Basin of Spitsbergen.

Abstract The Svalbard margin evolved to its present rifted configuration through a complex strike-slip history of both transtension and transpression. Because the Paleogene plate boundary, the De Geer Line, lay just west of Spitsbergen, many of the details of this structural evolution are contained in a narrow fold and thrust belt, and within a series of sedimentary basins, on Spitsbergen. The early to mid-Paleocene Central Basin was of extensional (possibly transtensional) origin, and contains more than 800 m of clastic deposits. It evolved from a series of partly connected coal basins to a single, open-marine basin. The late Paleocene to early Eocene Central Basin, of transpressional origin, was infilled by more than 1.5 km of clastic sediments from deltas, which prograded out from the rising orogenic belt. The fold and thrust belt of western Spitsbergen, mainly of late Paleocene to Eocene age, was also a product of transpression. Forlandsundet Graben, infilled by as much as 5 km of alluvial and marine elastics, probably formed from late Eocene collapse of the crest of the orogenic belt, or from extension adjacent to a curved fault zone. Rift basins, up to 7 km deep, developed west of Svalbard as the continental margin changed, beginning in the early Oligocene, from a strike-slip to a rifted regime.