Permian Ecca Group Research Articles

Geochemistry and organic petrology of the permian whitehill formation, Karoo Basin (RSA) and the Devonian/Carboniferous shale of the Appalachian Basin (USA)

Globally, there is significant economic interest in shale gas as a hydrocarbon resource. The success of unconventional shale gas exploration in the United State of America (USA) has raised interests for potential shale gas development in the Karoo Basin of South Africa. The Karoo Basin technically recoverable shale gas resource is estimated to be 13 Tcf, with 19–23 Tcf recoverable free gas. Due to the potential importance of the South African resource, this study characterized the Lower Permian Ecca Group shale and compared its geochemical and organic petrology properties with those of Devonian/Carboniferous shales of the Appalachian Basin, USA. The comparison of research data will aid in the understanding of shale gas potential of the Karoo Basin. Horizons from two boreholes (KZF-01 and KWV-01) drilled in the southern and southeastern Karoo Basin were evaluated and compared with samples of the Late Devonian Ohio and Early Carboniferous Sunbury Shales from the central Appalachian Basin, USA. Total organic carbon (TOC), total sulphur (TS), and organic petrology (bitumen and vitrinite reflectance, and maceral analysis) were used to assess organic richness and thermal maturity of the shale samples. In addition, the samples were evaluated for mineralogical content using X-Ray Diffraction (XRD). Data indicates that the Whitehill Formation of the Karoo Basin has good to excellent shale source potential, with an average TOC of 4.35 wt%. However, thermal maturity data of the Whitehill Formation shows the organic matter to be overmature, with vitrinite reflectance equivalent values greater than 3% RoV. Total sulphur data for the Whitehill Formation and the Devonian/Carboniferous shales suggests that both were influenced by marine environments. Both the KWV-01 and Ohio/Sunbury shale samples contain high amounts of quartz, with clay mineral contents greater than 40% being observed in borehole KWV-01 samples. Collectively, this research study provides valuable data for shale gas exploration and development in the Karoo Basin, South Africa.

Exhumed lateral margins and increasing flow confinement of a submarine landslide complex

AbstractSubmarine landslides, including the basal shear surfaces along which they fail, and their subsequent infill, are commonly observed in modern seabed and seismic reflection data sets; their resultant relief impacts sediment routing and storage patterns on continental margins. Here, three stacked submarine landslides are documented from the Permian Ecca Group, Laingsburg depocentre, Karoo Basin, South Africa, including two superimposed lateral margins. The stratigraphic framework includes measured sections and correlated surfaces along a 3 km long, 150 m high outcrop. Two stacked 2·0 to 4·5 km wide and 90 m and 60 m deep erosion surfaces are recognized, with lateral gradients of 8° and 4°, respectively. The aim of this study was to understand the evolution of a submarine landslide complex, including: evolution of basal shear surfaces/zones; variation of infill confinement; and location of the submarine landslides in the context of basin‐scale sedimentation and degradation rates. Three stages of formation are identified: (i) failure of submarine landslide 1, with deposition of unconfined remobilized deposits; (ii) failure of submarine landslide 2, forming basal shear surface/zone 1, with infill of remobilized deposits and weakly confined turbidites; and (iii) failure of submarine landslide 3, forming basal shear surface/zone 2, with infill of remobilized deposits and confined turbidites, transitioning stratigraphically to unconfined deposits. The expression of basal shear varies laterally, from metres thick zones in silt‐rich strata to sharp stepped surfaces in sand‐rich strata. Faulting and rotation of overlying bedding suggest that the shear surfaces/zones were dynamic. Stacking of landslides resulted from multi‐phase slope failure, increasing down‐dip topography and confinement of infilling deposits. The failure slope was probably a low supply tilted basin margin evidenced by megaclast entrainment from underlying basin‐floor successions and the lack of channel systems. This study develops a generic model of landslide infill, as a function of sedimentation and degradation rates, which can be applied globally.

Diagenesis and Reservoir Properties of the Permian Ecca Group Sandstones and Mudrocks in the Eastern Cape Province, South Africa

Diagenesis is one of the most important factors that affects reservoir rock property. Despite the fact that published data gives a vast amount of information on the geology, sedimentology, and lithostratigraphy of the Ecca Group in the Karoo Basin of South Africa, little is known about the diagenesis of the potentially feasible or economically viable sandstones and mudrocks of the Ecca Group. This study aims to provide an account of the diagenesis of sandstones and mudstones from the Ecca Group. Twenty-five diagenetic textures and structures were identified and grouped into three stages that include early diagenesis, burial diagenesis and uplift-related diagenesis. Clay minerals are the most common cementing materials in the sandstones. Smectite, kaolinite, and illite are the major clay minerals that act as pore lining rims and pore-filling materials. A part of the clay minerals and detrital grains was strongly replaced by calcite. Calcite precipitates locally in the pore spaces and partially or completely replaced clay matrix, feldspar, and quartz grains at or around their margins. Precipitation of cements and formation of pyrite and authigenic minerals occurred during the early diagenetic stage. This process was followed by lithification and compaction which brought about an increase in tightness of grain packing, loss of pore spaces, and thinning of bedding thickness due to overloading of sediments and selective dissolution of the framework grains. Mineral overgrowths, mineral replacement, clay-mineral transformation, dissolution, deformation, and pressure solution occurred during burial diagenetic stage. After rocks were uplifted, weathered and unroofed by erosion, this resulted in decementation and oxidation of iron-rich minerals. The rocks of the Ecca Group were subjected to moderate-intense mechanical and chemical compaction during their progressive burial. Intergranular pores, secondary dissolution, and fractured pores are well developed in the sediments of the Ecca Group. The presence of fractured and dissolution pores tend to enhance reservoir quality. However, the isolated nature of the pore linkage makes them unfavorable producers of hydrocarbons, which at best would require stimulation. The understanding of the space and time distribution of diagenetic processes in these rocks will allow the development of predictive models of their reservoir quality, which may contribute to the reduction of risks involved in hydrocarbon (oil and gas) exploration.

Palinspastic restoration of an exhumed deepwater system: A workflow to improve paleogeographic reconstructions

The Permian Laingsburg depocenter, Karoo Basin, South Africa, is the focus of sedimentological and stratigraphic research as an exhumed analog for offshore hydrocarbon reservoirs in deepwater basins. Thin-skinned thrust tectonics during the Permo-Triassic Cape Orogeny result in postdepositional deformation of the Permian basin fill. Regional-scale cross sections reveal two structural domains: a southern domain in the Laingsburg depocenter comprising 8–11-km wavelength north-verging fault-propagation folding, driven by buried low-angle ([Formula: see text]) reverse faults that coalesce at depth as part of a megadetachment below the Lower Paleozoic Cape Supergroup; and a northern domain to the north of the Laingsburg depocenter of short-wavelength, low-amplitude, asymmetrical folding facilitated by a detachment within the Permian Ecca Group. Five detailed structural cross sections permit the palinspastic restoration, and a calculation of the amount of shortening, across a [Formula: see text] area in the Laingsburg depocenter. Average shortening across the study area is −16.9% (5.8 km), and it decreases south to north. Shortening estimates from the Upper Ecca Group increase from 4.3 km near Matjiesfontein in the west to 10.4 km near Prince Albert in the east. Three-dimensional restorations of stratigraphic surfaces are consistent with these figures (−17%), and they allow paleogeographic and isopach thickness maps to be resorted to their configuration at the time of deposition. Structural restoration can be routinely used in outcrop studies to improve the accuracy of dimensions (e.g., volumetrics) and reconstructions (e.g., sediment dispersal patterns) derived from ancient sedimentary systems. The workflow presented here will add value to exhumed basin analogs by presenting prekinematic configurations at the frontal margins of fold-thrust belts.

Comment on the paper “Palynological records of the Permian Ecca Group (South Africa): Utilizing climatic icehouse-greenhouse signals for cross basin correlations” by K. Ruckwied, A. Götz and P. Jones (PPP, 413, 167-172, 2014)

Comment on the paper “Palynological records of the Permian Ecca Group (South Africa): Utilizing climatic icehouse-greenhouse signals for cross basin correlations” by K. Ruckwied, A. Götz and P. Jones (PPP, 413, 167-172, 2014)

Palynological records of the Permian Ecca Group (South Africa): Utilizing climatic icehouse–greenhouse signals for cross basin correlations

The Permian formations of the South African Karoo Basin play a crucial role in understanding Gondwana's climate history during this time of major global changes. In this paper we present two data sets, one from the coal-bearing Vryheid Formation (Witbank Basin) and one from the Whitehill and Upper Prince Albert formations of the DP 1/78 core (NE Karoo).Our main goal was to study the vegetation changes during this period of global warming and test if the climatic signals could be used to correlate the basinal Ecca group facies with the fluvio-deltaic coal-bearing strata of the Witbank Basin. The palynological record of the No. 2 Coal Seam of the Vryheid Formation indicates a cold climate, fern wetland community, characteristic of lowland alluvial plains, and an upland conifer community in the lower part of the coal seam. Up section, these communities are replaced by a cool-temperate cycad-like lowland vegetation and gymnospermous upland flora. The data set of the DP 1/78 core is interpreted to represent a cool to warm temperate climate represented by a high amount of Gangamopteris and Glossopteris elements.Both data sets are very different in their composition, which can be explained by the differences in depositional environment; however, our findings reveal a different age of the studied assemblages and thus also suggest that both data sets represent different stages in the transition from icehouse to greenhouse during Permian times. As the stratigraphic correlation between the Main Karroo Basin and the peripheral basins is still under discussion, this paper provides new data to underpin the stratigraphic placement of the Whitehill Formation relative to the coal-bearing Vryheid Formation.

Distribution of soft-sediment deformation structures in clinoform successions of the Permian Ecca Group, Karoo Basin, South Africa

The stratigraphic distribution of two groups of soft-sediment deformation structures (SSDS) – detached (dominated by lateral movement forming slides and slump deposits, and debrites) and in situ (dominated by vertical movement forming flame structures, pseudonodules, and ball-and-pillow structures) – are compared in two Permian successions in the Tanqua and Laingsburg depocentres of the Karoo Basin. SSDS occur in a series of well-exposed 40 to 55 m thick sedimentary cycles. Cycle thicknesses decrease upwards and the proportion of deformed strata is around 30% in both successions. Each flooding surface-bounded cycle is characterized by a lower unit dominated by thin-bedded turbidites, overlain by an intermediate section dominated by soft-sediment deformed facies, above which are undeformed thick-bedded mouthbar and shoreface sandstones. The upper part of each cycle fines upwards into thin-bedded turbidites, which are overlain by the cycle-bounding flooding surface. The cycles, and the distribution of SSDS, are the response to delta outbuilding and retreat over a clinoform rollover and onto a clinoform slope. Repeatable trends in the distribution of SSDS during the evolution of clinoforms in both depocentres indicate a level of stratigraphic organisation and predictability in the otherwise complicated record of processes around the clinoform rollover.

Stratigraphic evolution of the upper slope and shelf edge in the Karoo Basin, South Africa

ABSTRACTThe Permian Ecca Group of the Karoo Basin, South Africa preserves an extensive well‐exposed siliciclastic basin floor, slope and shelf‐edge delta succession. The Kookfontein Formation includes multiple sedimentary cycles that display clinoform geometries and are interpreted to represent the deposits of a slope to shelf succession. The succession exhibits progradational followed by aggradational stacking of deltaic cycles that is related to a change in shelf‐edge trajectory, and lies within two depositional sequences. Sediment was transferred to the slope via overextension of deltas onto and over the shelf edge, resulting in failure and re‐adjustment of local slope gradients. The depositional facies and architecture of the Kookfontein Formation record the change from a bypass‐ to accretion‐dominated margin, which is interpreted to reflect a decrease in sediment transport efficiency as the slope gradient decreased, slope length increased and shelf‐edge trajectory rose. During this time the delivery system changed from point‐sourced basin‐floor fans fed by slope channels to starved basin‐floor with sand‐rich slope clinoforms. This is an example of a progradational margin in which the younger slope system is interpreted to be of a different style to the older slope system that fed the underlying sand‐rich basin floor fans.

Age Controls on the Tanqua and Laingsburg Deep-Water Systems: New Insights on the Evolution and Sedimentary Fill of the Karoo Basin, South Africa

Abstract Improved constraints on the timing of Permian clastic sedimentation in the Karoo basin of South Africa have been revealed by new U-Pb single-grain zircon ages determined using the Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG). Analyses were performed on 180 zircon grains recovered from six ash beds exposed in the southwestern part of the Karoo basin. Samples were collected from two distinct loci of deep-water basin-floor and submarine-slope deposition within the Permian Ecca Group: the Tanqua and Laingsburg depocenters. Previous work constrained depositional ages of the 1800-m-thick deep-water to fluvial succession to 270–255 Ma. This poor chronostratigraphic resolution precluded robust stratigraphic correlation between the depocenters and impeded interpretation of basin evolution. The new data suggest that deep-water siliciclastic deposition began ~ 275 Ma (the lower Permian Collingham Formation), while the youngest ages are latest Permian. The Tanqua and Laingsburg depocenters began sand deposition at different times. Sandstone deposition in the Laingsburg depocenter started sometime after 275 Ma, and deposition of the first thick turbidite-dominated succession (Fan A) is bracketed into a period of less than 20 My. The Tanqua depocenter was sand starved during this interval. Both the uppermost sample from the Laingsburg depocenter and the lowermost from the Tanqua depocenter yield similar maximum depositional ages. This indicates, within the resolution of the age data, synchronous submarine sandstone deposition in the two loci at this time (~ 255 Ma). These data indicate that submarine deposition was still ongoing at a time when fluvial floodplain conditions are interpreted elsewhere in the Karoo basin. All the ash samples contain late Paleozoic zircon-grain age populations, while three samples contain small numbers of early Paleozoic, Proterozoic, and Archean zircon grains. Paleozoic zircon-grain age populations are interpreted as a record of arc activity linked to subduction. Increasing numbers of Precambrian zircons stratigraphically upward provide insight into changing source terranes during deposition into the Karoo basin.

Spirodesmos milanai n. isp.: A Shallow-Water Spiral Trace Fossil from the Cambrian of the Eastern Cordillera, Northwest Argentina

A new ichnofossiliferous locality in Salta Province (northwest Argentina) contains an association with numerous irregular spiral traces assigned to Spirodesmos milanai n. isp., in mature sandstones and quartzites with rippled bedding surfaces, rare wavy lamination and cross-bedded stratification. This record of early spiral behavior is interpreted as a primitive grazing method formed on muddy laminae above sand layers, and is related to a feeding strategy of an annelid-type of organism. Associated traces are Cruziana cf. semiplicata, Diplocraterion isp., Monocraterion isp., Rusophycus isp., Skolithos linearis Haldeman and Skolithos magnus Howell. The ichnoassemblage is similar to a shallow-water ichnoassociation from the Permian Ecca Group of South Africa (Mason et al., 1983).

Éditorial

Globally, there is significant economic interest in shale gas as a hydrocarbon resource. The success of unconventional shale gas exploration in the United State of America (USA) has raised interests for potential shale gas development in the Karoo Basin of South Africa. The Karoo Basin technically recoverable shale gas resource is estimated to be 13 Tcf, with 19–23 Tcf recoverable free gas. Due to the potential importance of the South African resource, this study characterized the Lower Permian Ecca Group shale and compared its geochemical and organic petrology properties with those of Devonian/Carboniferous shales of the Appalachian Basin, USA. The comparison of research data will aid in the understanding of shale gas potential of the Karoo Basin. Horizons from two boreholes (KZF-01 and KWV-01) drilled in the southern and southeastern Karoo Basin were evaluated and compared with samples of the Late Devonian Ohio and Early Carboniferous Sunbury Shales from the central Appalachian Basin, USA. Total organic carbon (TOC), total sulphur (TS), and organic petrology (bitumen and vitrinite reflectance, and maceral analysis) were used to assess organic richness and thermal maturity of the shale samples. In addition, the samples were evaluated for mineralogical content using X-Ray Diffraction (XRD). Data indicates that the Whitehill Formation of the Karoo Basin has good to excellent shale source potential, with an average TOC of 4.35 wt%. However, thermal maturity data of the Whitehill Formation shows the organic matter to be overmature, with vitrinite reflectance equivalent values greater than 3% RoV. Total sulphur data for the Whitehill Formation and the Devonian/Carboniferous shales suggests that both were influenced by marine environments. Both the KWV-01 and Ohio/Sunbury shale samples contain high amounts of quartz, with clay mineral contents greater than 40% being observed in borehole KWV-01 samples. Collectively, this research study provides valuable data for shale gas exploration and development in the Karoo Basin, South Africa.

The physical environment and major plant communities of the Tankwa- Karoo National Park

Apart from Acocks (1988) there are no published descriptions of the vegetation of the greater Tanqua and Doring River drainage basin (Bayer et al. 1993). A botanical and physical description of the Tankwa- Karoo National Park (TKRNP) which occurs in Veldtype 31b (Acocks 1988) is provided. The three dominant geological formations, older glacigenic deposits of the Dwyka Group, followed by the succession of siliciclas-
 tic sediments of the Permian Ecca Group, with flat dolerite sills and dykes, underlie eight distinct plant communities. The plant communities can be divided into large open plains dominated by Galenia africana and Tripteris sp. in the erosion rills, Malephora luteola and Augea capensis common in the low lying areas and Zygophyllum microcarpum, Brownanthus ciliatus and Galenia crystallina common on the more shaly concave plains and low shale hills. Slightly elevated rocky areas are dominated by Ruschia cf. robusta, Ruschia spinosa communities, while crusts of stemless mesembs such as Rhinephyllum macra denium, Hereroa fimbriata and Cheiridopsis acuminata are found on the desert paved areas. Annual Asteraceae covers all the denuded and sparsely vegetated areas after good winter rains while annual mesembs colonise on the more sodic sites. A total of 259 plant species were collected sporadically over a period of eight years, this includes 65 succulents and seven species endemic to the Tanqua Karoo and immediate adjacent area of the Roggeveld Mountain Range and Sutherland. Four Tanqua Karoo endemic species were found in the park.

Characteristics of Some Submarine Fan Channels, Permian Ecca Group, South Africa

The vary well exposed submarine fan complex in the southwestern part of the Karoo basin permits close examination of channel-fills and in places their associated overbank deposits. The complex comprises five arenaceous fan systems some of which attain 60 m in thickness. The fans are vertically stacked and separated by basinal shale deposits; each system with its own direction of growth. The association of channelized sandstone bodies and thin-bedded sandstone and shale packages in an updip position from predominantly stacked lobe deposits suggest preservation of middle fan settings. A 500 m wide, 20 m thick channel-fill consisting massive amalgamated sandstone beds occupying the channel thalweg occurs in a setting dominated by thin-bedded, ripple-laminated sandstone and shale. Gradual thinning of the channel-fill beds toward the channel edges, lack of internal lateral accretion, and a high width to depth ratio suggests a low sinuous to straight channel. The channel-fill is capped by an abandonment facies characterized by ripple-laminated sandstone and shale. Stacked, laterally offset channel-fill deposits with highly erosional contacts and typical well-bedded overbank deposits form channel-overbank complexes and characterize the mid-fan region of the uppermost fan system. Palaeocurrent directions and gradual diminishing of bed-thickness away from the generally massively bedded, amalgamatedmore » channel-fill sandstones confirm a simultaneous channel/overbank origin for these deposits. Levee morphology has not been recognized. Both examples of channel-fills cited reveal part of the complexity of the channelized portions of submarine fans and hence the implications thereof in exploring for hydrocarbon reservoirs.« less

A Passive Margin-type Submarine Fan Complex, Permian Ecca Group, South Africa

A submarine fan complex, comprising five arenaceous fan systems separated by basinal shale units, occurs in the southwestern part of the intracratonic Karoo basin in South Africa. Although basin development is related to a subduction zone bordering the palaeo-Pacific ocean to the south of Gondwanaland and the evolution of the Cape Fold Belt, the entire Lower Permian Ecca Group basin-fill succession reflects depositional characteristics of a passive-margin setting. The submarine fan complex, 250 m thick, originated from sediments supplied by Mississippi-type deltas dominating the Ecca coastline. The fine grain-size and low sand/shale ratio of the submarine fan and deltaic deposits reflect the maturity of the ancient river systems. Outcrops of the fan complex are well exposed and cover an area of 650 km{sup 2}. The strata are not affected by folding, and deep erosion allows three-dimensional viewing of mid-fan to outer-fan deposits. Features of interest include stacked lobe deposits displayed along 2.5 km of a 60 m high cliff section, and a transverse cliff section through channel-fill deposits 500 m wide. Paleocurrent directions reveal that each sequence had its own main source area located to the northwest and south of its present geographic location. The cyclic nature of the fanmore » complex is attributed to relative sea-level changes; deposition took place on the basin floor in water depths that do not exceed 500 m. Shoaling of the basin to wave base depths is reflected in the pro-delta and delta front deposits overlying the uppermost fan sequence. Major factors in controlling direction of fan progradation were delta switching and basin floor topography.« less

Permian Passive Margin Submarine Fan Complex, Karoo Basin, South Africa: Possible Model to Gulf of Mexico

ABSTRACT The tectonic development of the southwestern part of the intracratonic Karoo Basin was related to a subduction zone and an orogenic fold belt. However, the entire Lower Permian Ecca Group basin-fill succession exhibits the depositional characteristics of a passive-margin setting. The subbasins that developed during subsidence accumulated large submarine fan complexes that were succeeded by a river-dominated deltaic system. The subbasin fill in the west-southwestern area (Tanqua Karoo) is approximately 250 m thick and is comprised of six arenaceous submarine fan systems separated by basinal shales. The uppermost fan system is overlain by prodelta shales and siltstones, followed by delta front and delta plain sediments. The fan complex displays middle and outer fan deposits over an area of about 650 km2. The individual fans vary in maximum thickness from 24 to over 60 m. The cyclicity of the fan deposition is believed to have been controlled by fluctuations in relative sea-level with an average periodicity of about 100,000 years. Paleocurrent directions vary between the six units, reflecting changes in deltaic point source locations between SSE and WSW. The sixth fan system is located to the south, downlaps onto the last of the five sequences, and may represent a slope fan with major slumps and channels. The strata are not affected by folding or vegetation, permitting three-dimensional viewing of channel fills and levee overbank relationships, lateral migration of channels, and the transition from channelized to non-channelized lobe and sheet deposits. The sediments of the different subenvironments seem to have their own typical sedimentary structures which makes it possible to start defining the placing of thin-bedded turbidites and their potential relationships to channel-fill deposits. The gentle tectonic development of the southwestern Karoo Basin, as is reflected in the distribution of the lower shale formations, low sand/shale ratio, and overall fine grain size throughout the entire submarine fan/deltaic mega-sequence reflects a passive margin setting. These well-exposed outcrops contain many sedimentary characteristics that can be related to those of the Mississippi Delta and Fan. Therefore, this area can provide important elements that will be useful for the development of models of deep-water sands in the northern margin of the Gulf of Mexico.

Spiral trace fossils from the Permian Ecca Group of Zululand

The presence of spiral trace fossils is reported for the first time from six localities in strata of the Vryheid Formation of the Ecca Group (Lower Permian) in South Africa. These localities are all in the northeast part of the main Karoo basin of sedimentation. The fossils arc assigned to the ichnospecies Spirodesmos archimedeus, representing the spiral trail or burrow of a deposit-feeding organism. In contrast to other reports of spiral trace fossils, the Spirodesmos traces described here were formed in a shallow-water environment. This is established on both sedimentary and ichnofacies evidence. Associated trace fossils include Skolithos, Corophioides and Siphonichnus, all of which arc members of the Skolithos ichnofacies of Scilacher. The occurrence of Spirodesmos in this ichnofacies suggests that these strata were deposited in a marine basin.

Spiral trace fossils from the Permian Ecca Group of Zululand

Spiral trace fossils from the Permian Ecca Group of Zululand