Abstract The Katakturuk Dolomite records an unsurpassed history of Neoproterozoic passive-margin cyclic sedimentation in Arctic Alaska and offers new insights into the evolution of Precambrian carbonate platforms in response to interpreted eustatic sea-level changes. The Katakturuk depicts a south-dipping, low-angle, distally steepened carbonate ramp complex with a complete spectrum of facies types, from proximal, updip tidal-flat complexes to distal, downdip, sub-wave-base allodapic turbidites, debates, and rhythmites. The ramp margin is marked by thick stacks of amalgamated grainstone shoal complexes separating distally steepened downdip facies from ramp-interior facies. Using analysis of cycle stacking patterns, the 2500-m-thick Katakturuk can be subdivided into four second-order supersequences (of roughly equal thickness), each of which is made up of two to four third-order sequences (average a few hundred meters thick). The high-frequency cyclic architecture of a single third-order depositional sequence (lower gray craggy dolomite member) provides an example of systems-tract development in the Katakturuk Dolomite. On the basis of physical bounding surfaces, two types of cycles are recognized: cycles bounded by marine flooding surfaces across which subfacies deepen, termed “subtidal cycles”, and “peritidal cycles”, that are bounded by subaerial exposure surfaces (e.g., peritidal lamjnites). The systematic vertical variation in cycle type (peritidal vs. subtidal) and cycle thickness, combined with vertical subfacies trends and the recognition of significant subaerial exposure surfaces (karsts, stacked tepees or peritidal breccias) define the transgressive and highstand systems tracts of thirteen third-order depositional sequences. The third-order sequences in tum stack to build larger second-order accommodation cycles. Coinciding second-order and third-order rises in relative sea level resulted in two major backstepping events, which were recorded in the deposition of outer-ramp slope facies directly on peritidal facies. The top of the Katakturuk is marked by a complete spectrum of karst facies, representing a supersequence lowstand superimposed on a third-order late highstand.

Abstract Superb sections of submarine fan deposits within the Late Permian Ecca Group are exposed within the Tanqua Karoo basin. Five discrete fan systems are capped by shales and deltaic deposits of the Kookfontein and equivalent Koedoesberg formations. Progradation of the deltaic deposits across the basin was in response to a decrease in accommodation space created by relatively high rates of sedimentation within the foreland basin setting. Evidence for the transition from submarine fans to deltaic deposition has been enigmatic, with limited evidence of sediments representative of slope deposition. The sedimentology and sequence stratigraphy of the Hangklip Fan represents a slope fan and channel complex that shallows up into deltaic deposits, coincident with decresing accomodation space. Erosional slump scars, cutting into laminated shale with chaotic infill of sand intraclasts, point toward slope depositional processes that are not in evidence in the underlying submarine fan deposits. Wave ripples and the trace fossil Gyrochorte suggest substantially shallower depositional conditions than either the submarine fan or slope fan deposits, which are devoid of such features.

Abstract Stacking-patterns analysis is defined as the identification, interpretation, and correlation of chronostratigraphic units from vertical patterns in facies, diagenetic attributes, and the thickness of high-resolution depositional cycles (parasequences). Such analysis has been widely used in outcrop and subsurface studies of shallow-marine carbonate strata to establish a stratigraphic hierarchy and erect a sequence stratigraphic framework. Recent debate about the levels of order and randomness preserved in the record of cyclic platform-carbonate strata, however, points to the likelihood that a broad spectrum of stratigraphic behavior exists, ranging from nearly random (stochastic) to highly ordered (deterministic). To evaluate the levels of order versus randomness inherent in different depositional systems and to detect secular variations in stratigraphic style, we have constructed a digital database of high-quality stratigraphic data from diverse settings and ages ranging across the Phanerozoic; we have analyzed these data (1) by employing statistical tests (Markov chain analysis, runs test, Durbin-Walson test, entropy analysis) and (2) through visual and analytical comparison of normalized stratigraphic plots. The results of our analysis indicate that six empirical classes of stratigraphic style are recognizable. The classes are grouped by age and consist of (1) Proterozoic through Early Ordovician, (2) Silurian-Devonian, (3) Pennsylvanian, Early Permian, Late Triassic, and Neogene, (4) middle to Late Permian, (5) Early to Middle Triassic, and (6) Jurassic to Cretaceous. Differences in stratigraphic style between classes are interpreted to have resulted from differences in the amplitude of eustatic sea-level signatures between icehouse climates (with high-amplitude glacio-eustasy) and greenhouse climates (with low-amplitude eustasy) as well as differences in levels of autocyclicity dictated by tectonic setting and platform configuration. Secular variations in amplitudes of sea-level fluctuation have resulted in differences in the strength of allocyclic forcing and are reflected in the stratigraphic record by the degree to which sediment fill accurately recorded accommodation space. Icehouse platforms (Pennsylvanian, Early Permian, and Neogene) contain stacks of fifth- or fourth-order high-frequency sequences capped with subaerial exposure surfaces, relatively chaotic vertical thickness distributions, and high lateral continuity. High lateral continuity of individual fifth- or fourth-order sequences is interpreted to result from the strong allocyclic forcing potential during icehouse periods. Third-order composite sequences are best identified from regional retrogradational to progradational patterns of platform-margin facies. Chaotic vertical thickness distributions and long-term stationarity (i.e., lacking in long-term directional change) in facies patterns of high-frequency sequences, resulting from incomplete recording of accommodation space, however, hamper the identification of the composite sequences on the basis of individual vertical sections in the platform interior. Greenhouse platforms contain broad transgressive-regressive (or landward-stepping to seaward-stepping) sequences characterized by (1) long-term systematic change in parasequence thickness and facies proportions, (2) gross shallowing and deepening shifts in facies tracts defining maximum regressive and transgressive intervals, and (3) in some cases, a capping surface with extensive subaerial diagenetic modification (e.g., karst). Proterozoic through Ordovician sequences record long-term systematic changes in parasequence thickness and facies proportions. Jurassic and Cretaceous sequences tend to be represented as gross shallowing and deepening shifts in facies tracts with high levels of randomness at the parasequence scale due to greater levels of autocyclicity and the development of facies mosaics. Potential for greater discontinuity at the parasequence scale results from weaker allocyclic forcing by diminished fourth- and fifth-order amplitudes. The superposition of low-amplitude, high-frequency sea-level fluctuations on higher-amplitude fluctuations of lower frequencies, however, sets up the potential for the accurate recording of long-term accommodation and a full expression of the stratigraphic hierarchy (i.e., third-, fourth-, and fifth-order stratigraphic cycles).

Abstract Superimposed short-term and long-term eustatic sea-level fluctuations directly controlled Latemar platform stratigraphy and influenced the deeper water facies and overall buildup geometry. Deposition of deeper water sediments (foreslope and toe of slope) was linked to alternating submergence (highstand shedding) and subaerial exposure (lowstand lithification) of the platform top and thus recorded a periplatform signal of the eustatic fluctuations. The Latemar consists of a platform core (3–4 km wide, 700 m thick) with a narrow margin (tens of meters wide), flanked by foreslope (30°-35° dips), toe of slope, and basinal deposits. The platform sequence is interpreted to record a long-term (about 10 Ma) third-order eustatic sea-level oscillation with an amplitude of about 60 m. The lower 250 m of the platform section marks the initial third-order rise (subtidal carbonates), and the upper 450 m marks the subsequent highstand and is characterized by meter-scale cyclic carbonates. These cycles record platform submergence and exposure interpreted to be caused by short-term (10 4 –10 5 yr) Milankovitch eustatic oscillations superimposed on the long-term trend. The short-term platform submergence and exposure conditions result in alternating styles of foreslope deposition. During highstands, platform-derived sands bypass the foreslope, accumulating as toe-of-slope graded beds and basinal turbidites. During lowstands, sand supply ceases, producing basin hardgrounds. Marginal boundstones supplied clasts to the foreslope breccias during both highstands and lowstands, with only minor amounts of platform-derived sands (highstands) and lithified clasts (lowstands). Since the platform margin/foreslope contact is nearly vertical, a progressively increasing volume of foreslope breccia was needed to maintain the depositional geometry. This coincided with increasing amounts of exposure in the platform section related to the long-term sea-level change, suggesting that increasing clast production (at sea-level highstand and subsequent fall) was the basic control on the depositional geometry.