Tidal flat deposits of the Lower Proterozoic Campbell Group along the southwestern margin of the Kaapvaal Craton, Northern Cape Province, South Africa

Lower Proterozoic stromatolites and associated clastic carbonate deposits of the Campbell Group, from the southern margin (Prieska area) of the Kaapvaal Craton, northern Cape Province, are described. Contrary to previous interpretations (Beukes, 1978; 1980a) shallow subtidal to supratidal facies are recognised and discussed in regional context. An alternative model for the facies development of the Campbell Group is proposed

Stratigraphy and development of the Late Miocene-Early Pleistocene Hawke’s Bay forearc basin

A Late Miocene-Early Pleistocene mixed carbonate-siliciclastic sedimentary succession about 2 500 m thick in the Hawke’s Bay forearc basin is the focus of a basin analysis. The area under investigation covers 3 500 km2 of western and central Hawke’s Bay. The stratigraphy of Hawke’s Bay Basin is characterised by dramatic vertical and lateral facies changes and significant fluxes of siliciclastic sediment through the Late Miocene and Pliocene. This project aims to better understand the character and origin of the sedimentary succession in the basin. Geological mapping has been undertaken at a scale of 1:25000, with data managed in an ARCINFO geodatabase, following the database model employed in the IGNS QMap programme. Along the western margin of the basin there is progressive southward onlap of late Cenozoic strata on to basement. The oldest units are of Late Miocene (Tongaporutuan) age and the youngest onlap units are of latest Pliocene (Nukumaruan) age. Geological mapping of the basin fill places constraints on the magnitude (about 10 km) and timing (Pleistocene) of most of the offset on the North Island Shear Belt. Lithofacies have been described and interpreted representing fluvial, estuarine, shoreface and inner- to outer-shelf environments. Conglomerate facies are representative of sediment-saturated prograding fluvial braidplains and river deltas. These units are dominated by greywacke gravels and record the erosion of the Kaweka-Ahimanawa Ranges. Sandstone facies typically comprise very well sorted, clean non-cemented units of 10-50 m thickness that accumulated in innershelf environments. Siltstone facies probably accumulated in relatively quiet, middle- to outer-shelf water depths, and comprise well-sorted, firm non-cemented units with occasional tephra interbeds. Limestone facies represent examples of continent-attached cool-water carbonate systems that developed in response to strong tidal currents and a high nutrient flux during the Pliocene. These facies are examples of mixed siliciclastic-bioclastic sedimentary systems. Of these facies the widespread distribution and thickness of sandstone and limestone units present the most potential for hydrocarbon reservoirs. Similarly, the distribution of siltstone and mudstone beds provides adequate seal rocks. Mangapanian limestone facies have already been targeted as potential petroleum reservoirs (e.g. Kereru-1). Geological mapping suggests that potential hydrocarbon reservoir and seal rocks occur extensively in the subsurface

Origin and significance of 'dispersed facies' basal ice: Svínafellsjökull, Iceland

Dispersed facies basal ice - massive (i.e. structureless) ice with dispersed debris aggregates - is present at the margins of many glaciers and, as a product of internal glacial processes, has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment. The origin of dispersed facies is poorly understood, with several hypotheses having been advanced for its formation, and there is disagreement as to whether it is largely a sedimentary or a tectonic feature. We test these established hypotheses at the temperate glacier Svfnafellsjokull, Iceland, and find that none fully account for dispersed facies characteristics at this location. Instead, dispersed facies physical, sedimentological and stable-isotope (5180, 8D) characteristics favour a predominantly tectonic origin that we suggest comprises the regelation and straininduced metamorphism of debris-rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall. Further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening. Lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation, including the preservation of dispersed facies. Despite the relatively low sediment content of dispersed facies (~1.6% by volume), its thickness (up to 25 m) and ubiquity at Svfnafellsjokull results in a significant contribution to annual sediment discharge (1635-3270 m3 a"1) that is ~6.5 times that contributed by debris-rich stratified facies basal ice

J-Block Triassic Well Performance & Reservoir Heterogeneity

Imperial Users onl

How to Model Condensate Banking in a Simulation Model to Get Reliable Forecasts? Case Story of Elgin/Franklin

Imperial Users onl

Facies Modelling of Mishrif Formation in Selected Wells of Tuba Oil Field, Southern Iraq

The current study includes building a 3D geological facies model of the Mishrif Formation (Cenomanian-Early Turonian) in Tuba oilfield, southern Iraq. Microfacies study and core samples examination reveals the occurrence of six facies associations within Mishrif succession represented by; Basin, deep marine, rudist biostrome, shoal, back- shoal, and lagoon. Each reservoir unit is characterized by distinct facies distribution that controls their quality. High reservoir quality is predominantly developed in rudistid facies that are productive from units MB1 and MB2. The 3D facies model shows that these units have greater continuity and thickness along Tuba anticline and control the structural and stratigraphic trapping. Units MA and Mishrif have lower reservoir quality due to the dominance of mud-dominated facies. The unit CR2 consists of non-reservoir facies, and can be captured along the oilfield structure

Establishing the Imperial Oilfield Case Study: Part 1 - Reservoir Appraisal and Characterisation

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On the peritidal cycles and their diagenetic evolution in the Lower Jurassic carbonates of the Calcare Massiccio Formation (Central Apennines)

This paper shows the environmental changes and high-frequency cyclicity recorded by Lower Jurassic shallow- water carbonates known as the Calcare Massiccio Formation which crop out in the central Apennines of Italy. Three types of sedimentary cycle bounded by subaerial erosion have been recognized: Type I consists of a shallowing upward cycle with oncoidal floatstones to rudstones passing gradationally up into peloidal packstone alternating with cryptoalgal laminites and often bounded by desiccation cracks and pisolitic-peloidal wackestones indicating a period of subaerial exposure. Type II shows a symmetrical trend in terms of facies arrangement with peloidal packstones and cryptoalgal laminites present both at the base and in the upper portion of the cycle, separated by oncoidal floatstones to rudstones. Type III displays a shallowing upward trend with an initial erosion surface overlain by oncoidal floatstones to rudstones that, in turn, are capped by pisolitic-peloidal wackestones and desiccation sheet cracks. Sheet cracks at the top of cycles formed during the initial phase of subaerial exposure were successively enlarged by dissolution during prolonged subaerial exposure. The following sea-level fall produced dissolution cavities in subtidal facies, while the successive sea-level rise resulted in the precipitation of marine cements in dissolution cavities. Spectral analysis revealed six peaks, five of which are consistent with orbital cycles. While a tectonic control cannot be disregarded, the main signal recorded by the sedimentary succession points toward a main control related to orbital forcing. High frequency sea-level fluctuations also controlled diagenetic processes