The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders. Stratal stacking patterns combine to define trends in geometric character that include upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing of key sequence stratigraphic surfaces. Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphic approach to another. Construction of this framework ensures the success of the method in terms of its objectives to provide a process-based understanding of the stratigraphic architecture. The purpose of this paper is to emphasize a standard but flexible methodology that remains objective.

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Sequence stratigraphy: methodology and nomenclature

http://research.eas.ualberta.ca/catuneanu/files/Papers_PDF%20files/2005_Catuneanu%20el%20al_Karoo_JAES.pdf

The Karoo basins of south-central Africa

Turbidite channel reservoirs—Key elements in facies prediction and effective development

Sea floor and shallow seismic data sets of terminal submarine fan lobes can provide excellent planform timeslices of distributive deep-water systems but commonly only limited information on cross-sectional architecture. Extensive outcrops in the Tanqua depocentre, south-west Karoo Basin, provide these three-dimensional constraints on lithofacies distributions, stacking patterns, depositional geometries and the stratigraphic evolution of submarine lobe deposits at a scale comparable with modern lobe systems. Detailed study (bed-scale) of a single-lobe complex (Fan 3) over a 15 km by 8 km area has helped to define a four-fold hierarchy of depositional elements from bed through to lobe element, lobe and lobe complex. The Fan 3 lobe complex comprises six distinct fine-grained sandstone packages, interpreted as lobes, which display compensational stacking patterns on a 5 km scale. Between successive lobes are thin-bedded, very fine-grained sandstones and siltstones that do not change lithofacies over several kilometres and therefore are identified as a different architectural element. Each lobe is built by many lobe elements, which also display compensational stacking patterns over a kilometre scale. Thickness variations of lobe elements can be extremely abrupt without erosion, particularly in distal areas where isopach maps reveal a finger-like distal fringe to lobes. Lobe deposits, therefore, are not simple radial sheet-dominated systems as commonly envisaged.

Evolution, architecture and hierarchy of distributary deep-water deposits: a high-resolution outcrop investigation from the Permian Karoo Basin, South Africa

Tectonic evolution of the Cape and Karoo basins of South Africa

The Tanqua area of the Karoo basin, South Africa, contains five Permian deep-water turbidite fan systems, almost completely exposed over some 640 km2. Reconstruction of the basin-fill and fan distributions indicates a progradational trend in the 450 m+ thick succession, from distal basin floor (fan 1) through basin-floor subenvironments (fans 2, 3 and 4) to a slope setting (fan 5). Fans are up to 65 m thick with gradational to sharp bases and tops. Facies associations include basin plain claystone and distal turbidite siltstone/claystone and a range of fine-grained sandstone associations, including low- and high-density turbidite current deposits and proportionally minor debris/slurry flows. Architectural elements include sheets of amalgamated and layered styles and channels of five types. Each fan is interpreted as a low-frequency lowstand systems tract with the shaly interfan intervals representing transgressive and highstand systems tracts. All fans show complex internal facies distributions but exhibit a high-frequency internal stratigraphy based on fan-wide zones of relative sediment starvation. These zones are interpreted as transgressive and highstand systems tracts of higher order sequences. Sandy packages between these fine-grained intervals are interpreted as high-frequency lowstand systems tracts and exhibit dominantly progradational stacking patterns, resulting in subtle downdip clinoform geometries. Bases of fans and intrafan packages are interpreted as low- and high-frequency sequence boundaries respectively. Facies juxtapositions across these sequence boundaries are variable and may be gradational, sharp or erosive. In all cases, criteria for a basinward shift of facies are met, but there is no standard ‘motif’ for sequence boundaries in this system. High-frequency sequences represent the dominant mechanism of active fan growth in the Tanqua deep-water system.

Anatomy, geometry and sequence stratigraphy of basin floor to slope turbidite systems, Tanqua Karoo, South Africa

Six individual turbidite systems, informally called Fans A-F, were deposited in the Laingsburg area of the southwestern Karoo Permian foreland basin. This study concentrates on the lowermost, 300 m thick "Fan A" system. Facies associations include channel fills and correlative lateral overbank deposits consisting of thin sheet-like and rippled sandstones. Massive- and thin-bedded frontal sheet sandstones form down-dip extensions to channel systems. Identification and correlation of mudstone-dominated intervals from field mapping and oblique aerial photostratigraphy delineates a high-resolution internal stratigraphy of the fan system which, coupled with 4000 m of logged section, allows detailed geometrical and architectural analysis. Seven individual depositional units have been mapped within Fan A, and these are interpreted as the deep-basin sedimentological expressions of high-frequency lowstand systems tracts, separated by high-frequency transgressive and highstand condensed intervals. Stacking patterns of the seven lowstand fan units that make up Fan A record early progradation (units 1 to 3), a backstep (unit 4), followed by further progradation (units 5 and 6). Retrogradation during unit 7 records abandonment of the whole Fan A deposystem. Coupled with facies analysis, paleocurrents reveal unusual paleotransport patterns that are interpreted as a consequence of structural deformation of the basin floor. Paleotransport indicators reveal that sediment pathways are strongly parallel to the structural grain, while some point to sediment pathways that crosscut the dominant structural grain.

Anatomy and Stratigraphic Development of a Basin Floor Turbidite System in the Laingsburg Formation, Main Karoo Basin, South Africa

Deepwater basin floor/slope deposits of the Laingsburg Depocenter, Karoo Basin, South Africa

Fine-grained, Submarine-fan Growth and the Distribution of Lithofacies and Architectural Elements: An Example (Fan 4) from the Skoorsteenberg Formation Basin, South Africa

H. De Ville Wickens

Papers

Anatomy, geometry and sequence stratigraphy of basin floor to slope turbidite systems, Tanqua Karoo, South Africa

Anatomy and Stratigraphic Development of a Basin Floor Turbidite System in the Laingsburg Formation, Main Karoo Basin, South Africa

Deepwater basin floor/slope deposits of the Laingsburg Depocenter, Karoo Basin, South Africa

Fine-grained, Submarine-fan Growth and the Distribution of Lithofacies and Architectural Elements: An Example (Fan 4) from the Skoorsteenberg Formation Basin, South Africa