Dolomitic Sandstone Research Articles

Natural stones of the Saale–Unstrut Region (Germany): petrography and weathering phenomena

Dimension stones of the central German Saale–Unstrut Region were investigated with regard to petrographic and petrophysical properties as well as their weathering behaviour, onsite and in laboratory. To evaluate the suitability of building stones in this region, different buildings (the Rudelsburg Castle, Memleben Monastery, and vineyard walls) and one rock relief (Steinerne Bibel), made of different types of sandstone or limestone were studied concerning the damage situations. Laboratory measurements include characterisation of pore space properties, water uptake or water vapour diffusion analyses and strength tests. Weathering simulation tests, such as hygric swelling and salt weathering resistance were performed and compared with on-site building observations. In general, the limestones investigated here are classified with a higher construction suitability due to their lower porosity and ability for water uptake, as well as their higher tensile strength, which again is proven by the weathering tests in laboratory. Laboratory analyses reveal for sandstone samples higher porosities and unfavourable pore radii distributions (high content of capillary pores/micropores), resulting in high rates of water uptake, and low resistance against mechanical stress. This behaviour is attributed mainly to the petrographical/diagenetical properties of sandstones investigated, where, e.g. low compaction or cementation (e.g. due to the presence of clay coatings) prohibit a reduction in intergranular volume and create high amount of capillary pores and, in some cases, a high content of micropores. In deviation to this, one dolomitic sandstone sample shows low porosity and water absorption, as well as high strength properties, making them, at a first glance, highly suitable for building purposes. The limestones predominantly exhibit, due to their micritic fabric, low porosity and water absorption but high strength, and, in consequence, hold a relatively high resistance against salt weathering and therefore a high weathering resistance during laboratory tests and onsite. The generally low hygric dilatation is also a favourable characteristic. Contrary, also limestones with low tensile strength or high porosity occur, which is explained with internal crack structures and loss of components (ooids), respectively. However, together with favourable pore radii distributions (e.g. few capillary/micropores), the construction suitability is evaluated to be better than for the sandstones. These findings on construction suitability are also reflected/supported by studies onsite. Observations at the, e.g. rock relief “Steinerne Bibel” confirm that the unfavourable petrophysical properties of the fluvial, immature sandstones lead to low resistance against salt weathering and together with hygric dilatation, to a poor condition of the rock relief. Additionally, the investigation of the rock relief “Steinerne Bibel” has shown that the preservation of the reliefs within the Solling Sandstone and Chirotheria Sandstone is a great challenge, since the rock interacts with pore water which is enriched by salts of the Rot saline unit. A direct interaction between the cement of natural stones and mortar could also be observed (Bernburg Formation, Memleben Abbey), which emphasises that the application of mortars should only be performed by the existing knowledge of the material properties. Moreover, the intensity and type of deterioration depends mainly on different rock properties and on the exposition.

Reservoir zonation, rock typing and compartmentalization of the Tortonian-Serravallian sequence, Temsah Gas Field, offshore Nile Delta, Egypt

The present study aims to evaluate the petrophysical properties and to discriminate the Tortonian Wakar and the Serravallian Sidi Salem formations in the offshore Temsah gas field, north Egypt into distinctive rock types. The measured conventional core data includes helium and summation fluids porosities, grain and bulk densities, horizontal and vertical permeabilities as well as the water saturation. Also, the Reservoir Quality Index (RQI), Flow Zone Indicator (FZI) and Reservoir Potentiality Index (RPI) were calculated to establish a successful reservoir zonation. In the Temsah field, The Tortonian- Serravallian sequence has been discriminated into four reservoir rock types (RRTs) which are described based on its lithologic composition as 1) Sandy to argillaceous carbonates (RRT1), 2) Siliceous Pebbly sandstones (RRT2), and 3) Argillaceous to Calcareous sandstones (RRT3), and 4) Calcareous to Dolomitic Sandstones (RRT4). Based on the petrophysical interpretation and ranking for the studied samples, samples of RRT2 have very good rank due to presence of very good porosity, excellent permeability, and good to very good RQI and FZI values which are assigned as the best reservoir rock type in the Tortonian-Serravallian sequence. The petrophysical behavior of RRT4 shows the lowest reservoir quality (impervious RQI and poor FZI). The examined sequence has been sliced into reservoir zones; each zone has its hydraulic flow unit range that represents the studied rock types in each zone. Based on the applied pressure tools, including Repeat Formation Tester (RFT) and the Modular Formation Dynamic Tester (MDT), both the Wakar and Sidi Salem reservoirs represent completely isolated compartments. Therefore, ranking both reservoirs and estimating their hydrocarbon potential must be done separately for each reservoir.

Reservoir assessment and quality discrimination of Kareem Formation using integrated petrophysical data, Southern Gulf of Suez, Egypt

Abstract The middle Miocene Kareem Formation represents one of the most important reservoirs in the Gulf of Suez, Egypt. Six boreholes locating throughout different structural trends in the Southern province of the Gulf of Suez, Egypt, were selected to study the reservoir properties of the Kareem Formation. The study depends on integrated data of well logs and routine core analysis as well as seismic data. The present study is an integrated study aims to study and discriminate the reservoir quality of the Kareem sequence using various statistical techniques. Testerman statistical approach and stratigraphic modified Lorenz (SML) plot were used in reservoir zonation. Principal Component Analysis (PCA) and cluster analysis were used to identify the electrofacies distribution within the studied formation. The well log data enabled characterizing the reservoir sequence into 6 electrofacies. The available core analyses data and core description for the Kareem Formation (850 feet cored interval) in Morgan oil field enabled more accurate discrimination for the reservoir sequence into 13 hydraulic flow units (7 of them are potential flow units). The studied sequence is differentiated into five lithologic-petrophysical facies; siltstone, dolomitic siltstone, dolomitic sandstone, sandstone and friable sandstone. The sandstone and friable sandstone facies are the best petrophysical facies. The dolomite content is the main key factor for reducing the reservoir quality of the studied Kareem sequence. From the core data, a total net pay thickness of 180 feet (mostly composed of sandstone with some siltstone intercalations) was assigned of fair quality (∅He = 14.7%, kH = 89.1 md, So = 28.8%, reservoir quality index ‘RQI’ = 0.60 μm, flow zone indicator ‘FZI’ = 3.81 μm, reservoir potential index ‘RPI’ = 2) with few streaks of good to very good potential. However, the siltstone samples have less petrophysical potential than the sandstones.

The Lower Miocene Nukhul Formation (Gulf of Suez, Egypt): microfacies and reservoir characteristics

The Lower Miocene Nukhul Formation was deposited during early stages of Gulf of Suez rifting. Outcrop of this formation at Gebel el Zeit, Egypt is up to 100 m (328 ft) in thickness and consists of lower sandstone-dominated and upper carbonate-dominated units. Samples were collected from the Nukhul Formation outcrop in order to describe the lithofacies, mineralogy, and petrographic characteristics to better understand the hydrocarbon reservoir potential of the unit. The investigations showed that the lower part of Nukhul Formation at North Gebel el Zeit consists of poorly sorted, dolomitic sandstone and sandy dolomite which were deposited in a shallow-marine setting. The presence of polycrystalline and crushed quartz grains in Nukhul strata indicates that these strata were sourced by recycled sediments associated with local uplift tied to rifting. The upper Nukhul consists of dolomitized carbonates with preservation of original textures; primary limestone depositional textures include intraclast packstone, rudstone, and coral-algal boundstone, wackestone, and grainstone with minor floatstone. Carbonate rock strata were deposited in shallow marine, peritidal to subtidal environments that developed on fault-block highs. The presence of zoned saddle dolomite suggests some component of fault-controlled fluid flow. Reservoir characteristics of the Lower Miocene Nukhul Formation at the Gebel el Zeit indicates favorable properties for reservoir development in both the lower siliciclastic-dominated dolomite and the upper dolomitized carbonate portions of the formation.

Sedimentology and reservoir characterization of the Upper Miocene Qawasim Formation, El-Tamad Oil Field onshore Nile Delta, Egypt

The Upper Miocene Qawasim Formation is an important hydrocarbon reservoir in the Nile Delta Province. This paper presents the diagenetic features and the reservoir characteristics of this formation based on conventional core analysis performed on the El-Tamad-2 well. The Qawasim Formation is consisted of low compacted, poorly cemented, massive, and laminated sandstones with gradual upward facies change to tightly cemented bioclastic and dolomitic sandstones. The sandstones are capped by shallow marine bioclastic limestones followed by the open marine Globigerina wackestone and mudstone facies of the Pliocene Kafr El-Sheikh Formation. The channel-fill massive and laminated sandstones are classified as subarkose arenites with well-preserved primary intergranular porosity and good secondary porosity due to the dissolution of feldspars. In addition, they have low clay volume, well-connected pore spaces, and hence very good reservoir quality. On the other hand, the bioclastic and dolomitic sandstones were affected by the diagenetic alterations. Dolomite cement blocked the intergranular pores and reduced the primary porosity, while the dissolution of bioclasts and feldspars increased the secondary porosity. The reservoir quality decreases dramatically with increasing the marine influence from the channel-fill sandstones to dolomitic and bioclastic sandstones, shallow marine bioclastic limestone, and marine mudstone facies. The massive sandstones at the bottom of the upper part of the Qawasim Formation represent the best reservoir quality interval with excellent porosity and permeability values and have proven to be the main target for future exploration activities.

Mapping subsurface geological structure using TEMPEST data, McArthur Basin, Northern Territory

The airborne TEMPEST electromagnetic (EM) and magnetic survey is a proven tool for mapping geological structure for exploration. This technique was applied at the Bulman project area in the McArthur Basin to identify the geological environment of stratabound carbonate-hosted Pb-Zn mineralisation. The Late Palaeoproterozoic to Early Mesoproterozoic sedimentary fill of the McArthur Basin in the Bulman project area consists of the Dook Creek and Limmen Formations. They are intruded by Early Mesoproterozoic dolerite sills and dykes. The location of the intrusive rocks was mapped using magnetic data while their depth was estimated from EM data. To find the top of the intrusives, depth to resistive basement was mapped using Conductivity Depth Images (CDIs) generated from the TEMPEST B-field Z-component data. Additionally, a voxel model was constructed from the CDIs to show the conductivity distribution in three dimensions. The conductivity pattern indicates that the dolomite sandstone and siltstone of the Dook Creek Formation are more conductive than the overlying coarse sandstone of the Limmen Formation. A disconformable boundary between the formations is shown as a distinct interface in the EM data. There is no marked conductivity contrast between intrusives and other rocks making up the resistive basement. As a result, the picked depth to resistive basement horizon corresponds to the bottom of a surface conductive unit that is interpreted to be the base of the Cenozoic unconsolidated deposits or part of the Dook Creek Formation. In places, the base of a sub-surface conductive zone is interpreted to be the top of the intrusives. The thickness of sediments above the resistive basement is variable, reaching up to 170 metres in the central - eastern part of the study area. Additionally, a 3D geological model has been constructed to image the distribution of the interpreted geological units and the tectonic pattern.

Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia

Research Article| October 01, 2013 Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia C.R. Calver; C.R. Calver 1Mineral Resources Tasmania, PO Box 56, Rosny Park, Tasmania 7018, Australia Search for other works by this author on: GSW Google Scholar J.L. Crowley; J.L. Crowley 2Department of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho 83725-1535, USA Search for other works by this author on: GSW Google Scholar M.T.D. Wingate; M.T.D. Wingate 3Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia 6004, Australia4School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia Search for other works by this author on: GSW Google Scholar D.A.D. Evans; D.A.D. Evans 5Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06520-8109, USA Search for other works by this author on: GSW Google Scholar T.D. Raub; T.D. Raub 6Department of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL Scotland, UK Search for other works by this author on: GSW Google Scholar M.D. Schmitz M.D. Schmitz 2Department of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho 83725-1535, USA Search for other works by this author on: GSW Google Scholar Author and Article Information C.R. Calver 1Mineral Resources Tasmania, PO Box 56, Rosny Park, Tasmania 7018, Australia J.L. Crowley 2Department of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho 83725-1535, USA M.T.D. Wingate 3Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia 6004, Australia4School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia D.A.D. Evans 5Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06520-8109, USA T.D. Raub 6Department of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL Scotland, UK M.D. Schmitz 2Department of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho 83725-1535, USA Publisher: Geological Society of America Received: 14 Mar 2013 Revision Received: 19 Jun 2013 Accepted: 27 Jun 2013 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2013) 41 (10): 1127–1130. https://doi.org/10.1130/G34568.1 Article history Received: 14 Mar 2013 Revision Received: 19 Jun 2013 Accepted: 27 Jun 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation C.R. Calver, J.L. Crowley, M.T.D. Wingate, D.A.D. Evans, T.D. Raub, M.D. Schmitz; Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia. Geology 2013;; 41 (10): 1127–1130. doi: https://doi.org/10.1130/G34568.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract U-Pb zircon data from the uppermost Cottons Breccia, representing the Marinoan glacial-postglacial transition on King Island, Tasmania, provide the first direct age constraint on the Cryogenian-Ediacaran boundary in Australia. Zircons in four samples from the topmost meter of the Cottons Breccia, dated by sensitive high-resolution ion microprobe, exhibit two modes ca. 660 Ma and ca. 635 Ma. The younger component predominates in the uppermost sample, a possibly volcanolithic dolomitic sandstone, apparently lacking glacially transported debris, in the transition to cap carbonate. Chemical abrasion–thermal ionization mass spectrometry (CA-TIMS) U-Pb dating of euhedral zircons from that sample yields a weighted-mean age of 636.41 ± 0.45 Ma. Equivalence to published TIMS ash bed dates from Cryogenian-Ediacaran transitional strata in Namibia (635.51 ± 0.82 Ma, within glacial deposit) and China (635.23 ± 0.84 Ma, 2 m above glacial deposit) supports correlation of those strata to the Australian type sections and globally synchronous deglaciation at the end of the Cryogenian Period. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Modeling CO2–brine–rock interactions in the Knox Group: Implications of a deep carbon storage field test in western Kentucky

The Cambrian–Ordovician Knox Group, a thick sequence of dolostone and minor dolomitic sandstone, is a prospective CO2 sequestration target in the southern Illinois Basin, USA. Thorough evaluation of the Knox Group is critical because the main sequestration target elsewhere in the Illinois Basin, the Cambrian Mount Simon Sandstone, is thin or absent throughout most of Kentucky. A 2477-m-deep carbon storage test well in Hancock County, Kentucky, was drilled, and 626metric tons of CO2 was injected into the Knox saline reservoirs. To understand the long-term fate of CO2 injected into the Knox reservoirs, geochemical reactions between CO2, brine and rock-forming minerals were modeled using TOUGHREACT. The modeling benefited from a robust data set collected from the test well, including core porosity and permeability, petrographic and X-ray powder diffraction mineralogy, brine chemistry, temperature and pressure measurements. Kinetic batch models and 2-D radial reactive transport models were used to evaluate the migration of the injected CO2, changes in brine chemistry, and mineral dissolution and precipitation. Results from the kinetic models suggest that sections of the Knox dominated by dolomite have very limited mineral-trapping capacity for CO2, whereas thin sections of dolomitic sandstone with aluminosilicate minerals such as K-feldspar facilitate mineral trapping. The 2-D model for the CO2 injection test suggests that, because of the presence of thick permeable intervals in the Knox and the small volume of injected CO2 in the test, the radius of influence is less than 11m from the well. The hypothetical long-term injection model indicates, on the other hand, that commercial-scale injection would influence a much larger area and part of the injected CO2 remains in the supercritical/gas phase for a long time. Because of the buoyancy effect, most supercritical/gas-phase CO2 migrates upward and stays in the top of the reservoirs dominated by dolomite with small mineral-trapping capacity.

Castillo-palacio de La Calahorra, Granada: influencia de los factores climáticos y arquitectónicos en el deterioro diferencial de sus fábricas pétreas

The castle-palace of La Calahorra is a historical building (6th century ) with a dual-function. The exterior is a castle-fortress of late-medieval style, built with rubbles and rough ashlars of a crystalline limestone of great hardness and strength. The interior is a Renaissance palace, made of micritic limestone and dolomitic sandstone ashlars, both stone materials are porous, soft and low strength. The entire building has an orangey colored due to an iron patina that stains its stone masonries as a result of wind action. There is a differential deterioration among its external and internal, depending on the type of stone used factories, the rainwater and wind action and the building defects detected. While the exterior stone is in good state of conservation, the interior stones shows some important deterioration processes , mainly the micritic limestone present in the ornamental and decorative areas of the central courtyard.

Reavaliação paleoambiental e estratigráfica da Formação Nobres do Grupo Araras, Neoproterozóico da Faixa Paraguai, região de Cáceres (MT)

Outcrop-based facies and stratigraphic studies in the region of Cáceres, State of Mato Grosso, Brazil, subdivided the Nobres Formation into: lower member, composed of dolostone, intraclastic dolopackstones, sandy dolostones, stratiform stromatolites and evaporitic molds, interpreted as tidal flat/sabkha deposits; and upper member, constituted of dolostone, dolomitic sandstone, stratiform to domal and wrinkled stromatolites, evaporite molds, sandstones and mudstones, interpreted as mixed tidal flat deposits. The stacking of these deposits up to 200 m thick is composed by meter-thick shallowing/brining upward cycles related to a hot arid climate. The peritidal cycles also suggest continuous and recurrent generation of accommodation linked to tectonic subsidence. The siliciclastic inflow at the end of the deposition of the Nobres Formation that hindered the carbonate sedimentation and is attributed to the uplift of source areas linked to the initial phase of closure of the Clymene Ocean, during the Pampean-Araguaia Orogeny, at the limit Neoproterozoic-Cambrian.

A new actinopterygian fauna from the latest Cretaceous of Quintanilla la Ojada (Burgos, Spain)

We describe a new actinopterygian fauna from the uppermost Cretaceous of Quintanilla la Ojada (Burgos, Spain), in the Villarcayo Sinclynorium of the Basque-Cantabrian Region. It consists mostly of isolated teeth of pycnodontiforms (cf. Anomoeodus sp., Pycnodontoidea indet.), amiiforms (cf. Amiidae indet.) and teleosteans (elopiforms: Phyllodontinae indet., Paralbulinae indet.; aulopiforms: Enchodontidae indet., plus fragmentary fi n spines of Acanthomorpha indet.). Paralbulinae teeth are the most abundant elements in the fossil assemblage. All the remains are disarticulated and show intense post-mortem abrasion. Th e fossil association has been found in dolomite sandstones that are laterally correlated with the Valdenoceda Formation (Lower to basal Upper Maastrichtian) of the Castilian Ramp. Th e observed taphonomic features are coherent with the sedimentological interpretation of the fossiliferous beds as coastal deltaic deposits.

Stratigraphy, Petrography, and Petrophysical Properties of the Subsurface Upper Cretaceous Sediments, Northwestern Desert, Egypt

In this article, 33 core samples and 160 ditch samples of Upper Cretaceous age were studied at different depths from Horus well 1. Stratigraphic, petrographic, and petrophysical studies and well log analysis are used to study and evaluate the rock units. The studied core samples are dolomite (Abu Roash formation), shaly limestone, and argillaceous sandstone (Bahariya formation). The depositional environments of the studied rock units vary from deltaic to deltaic-marine. The effective porosity of the studied core samples is low and may be of secondary origin. The upper part of low Bahariya is considered a high category of reservoir. The stratigraphic significance of some benthonic foraminifera (Thomasinella, Nezzazata, and Nezzatine) furnishes new information on the age determination. Cenomanian-Santonian time is suggested for the studied interval (Bahariya and Abu Roash formations).

The relevance of the sedimentary history of the Grand Conglomerat Formation (Central Africa) to the interpretation of the climate during a major Cryogenian glacial event

The Cryogenian Grand Conglomerat Formation (<765 and >735 Ma in age and with considerable thickness variations up to a maximum thickness of about 950 m) is an association of interbedded glaciogenic, clastic, periglacial and non-glacial deposits topped by the Kakontwe Limestone cap carbonate. These units occur within the Nguba Group of the Katanga Supergroup, which was deposited in a rift basin and subsequently deformed as part of the Pan African Lufilian orogenic belt that separates the Congo and Kalahari cratons. Both, correlation of regional unconformities and facies distribution suggest that the Grand Conglomerat sediments were deposited (during and after eruption of flood basalts) in an asymmetrical rift, with a strongly uplifted southern shoulder, and a graded shelf defining the northern margin. Glaciomarine sedimentary rocks along the southern margin of the Katangan rift are preserved within fan delta conglomerates supplied from an elevated rift shoulder. By contrast, the northern margin of the rift was the site of continental glaciation with cross-bedded, glaciofluvial and marginal marine sandstones and conglomerates, associated with massive tills (glaciogenic diamictites) that pass laterally towards the south into glaciomarine mixtite interlayered with wedges of dolomitic sandstone. The Kakontwe Limestone cap carbonate is present only in the distal parts of the basin. Its absence in proximal regions is considered to reflect very high rates of sedimentation of fine-grained, glaciogenic debris derived from deglaciated source areas. Palaeomagnetic data indicates that the Grand Conglomerat glaciogenic sediments were deposited close to the Equator during the Cryogenian. This low latitude setting coupled with the absence of a topographical trigger would suggest that glaciation was related to global atmospheric cooling. However, the presence of water-borne, glaciogenic, on-shore sediments and offshore sediments derived from floating glaciers suggests that the ocean during this part of the Cryogenian was not completely frozen. Associations of glaciogenic facies with non-glaciogenic sedimentary rocks imply glaciation with interglacial periods and gradual deglaciation, instead of severe conditions of permanent sea ice cover and rapid change to the greenhouse environment.

The geology of the Neoproterozoic Swakop-Otavi transition zone in the Outjo District, northern Damara Orogen, Namibia

Research Article| March 01, 2008 The geology of the Neoproterozoic Swakop-Otavi transition zone in the Outjo District, northern Damara Orogen, Namibia Tom N. Clifford Tom N. Clifford School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa, e-mail: cliffordt@geosciences.wits.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information Tom N. Clifford School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa, e-mail: cliffordt@geosciences.wits.ac.za Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2008, The Clay Minerals Society South African Journal of Geology (2008) 111 (1): 117–140. https://doi.org/10.2113/gssajg.111.1.117 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Tom N. Clifford; The geology of the Neoproterozoic Swakop-Otavi transition zone in the Outjo District, northern Damara Orogen, Namibia. South African Journal of Geology 2008;; 111 (1): 117–140. doi: https://doi.org/10.2113/gssajg.111.1.117 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The Neoproterozoic succession in the Outjo District of northern Namibia is a mainly sedimentary sequence that was deposited in the time-interval of approximately 800 to 600 Ma ago and was deformed and suffered mild greenschist facies regional metamorphism during Damaran times ca. 550 Ma ago. The map area occupies the lithofacies and tectonic transition from the highly deformed more eugeoclinal Swakop Group sequence to the south to the coeval, uniformly southward-dipping, miogeoclinal Otavi Group of the Fransfontein Ridge to the north. The oldest unit is a largely sandstone and biotite-muscovite phyllite succession tentatively equated with the volcanogenic Naauwpoort Formation (Nosib Group) that pre-dates the Swakop Group in the Summas Mountains to the southwest. The overlying Saturn Formation comprises two distinct but coeval lateral carbonate facies: a 300 m thick sequence of bedded dolomite with a 20 m thick median limestone; and massive biohermal dolomite of undetermined thickness. The conformably overlying Landeck Formation comprises a lower succession of interbedded sandstone, phyllite and local carbonate rocks, a distinctive middle iron formation marker horizon with rather rare overlying dolomite, followed by a siliciclastic-carbonate sequence. The combined succession is up to 450 m in thickness, and glacial diamictite is recorded at 30+ localities sited below, within and above the iron formation. However, in the more distal parts of the Landeck Formation in the Saturn Dome, glacial diamictictite has not been identified, the iron formation is overlain by a distinctive dolomite, and the uppermost 200 to 300 m of the Landeck Formation is characterized by four horizons of siliciclastic sediments with three intervening horizons of blue limestone that reflect the concordant transition to the overlying Bergfriede Formation. New chemical analyses are reported for graphitic dolomite, magnetite-calcite schist, iron formation, ferruginous limestone, dolomitic sandstone and biotite-muscovite phyllite of the Landeck Formation. The Bergfriede Formation consists almost entirely of limestone and dolomite and is characterized by major changes in facies and thickness, and five lateral facies end-members are recognized: I. Hankow Facies, a five-fold succession of limestone, dolomite and calcarenite up to 500 m thick; II. Tsuwandes-Zuwitsaub Facies, a three-fold sequence of limestone-dolomite-limestone >300 m thick; III. Uranus Facies, entirely dolomite generally 150 m thick; IV. Belina-Sophienhof Facies, a limestone-dolomite sequence, with a distinctive arenaceous limestone at the top, 100 to 400 m thick; and V. Mooilagte-Mooihoek Facies, largely dolomite-chert-limestone ≥1500 m thick, that is transitional to the dolomite-dominated upper Otavi Tsumeb Subgroup of the Fransfontein Ridge to the north. The overlying Okaua Formation is composed of a >3000 m thick sequence of muscovite-chlorite phyllite and calcareous sandstone that occupy, inter alia, the troughs of the regional Ugab and Uranus-Neuland Synclines; it is most likely correlative with the Mulden Group of the Otavi Mountainland. The Damaran regional structure of area is characterized by: D1 an early phase of southward-directed gravity nappes; D2 the regionally dominant northeast-southwest to east-west trending tight compressional upright or northward-verging folds, and local thrusts; and D3 late strike-slip faulting. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation

Research Article| December 01, 2007 Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation David Chew; David Chew 1Department of Geology, Trinity College Dublin, Dublin 2, Ireland Search for other works by this author on: GSW Google Scholar Christopher Kirkland; Christopher Kirkland 2Laboratory for Isotope Geology, Swedish Museum of Natural History, S-104 05 Stockholm, Sweden Search for other works by this author on: GSW Google Scholar Urs Schaltegger; Urs Schaltegger 3Department of Mineralogy, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland Search for other works by this author on: GSW Google Scholar Robbie Goodhue Robbie Goodhue 4Department of Geology, Trinity College Dublin, Dublin 2, Ireland Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (12): 1095–1098. https://doi.org/10.1130/G23768A.1 Article history received: 01 Feb 2007 rev-recd: 20 Jul 2007 accepted: 23 Jul 2007 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David Chew, Christopher Kirkland, Urs Schaltegger, Robbie Goodhue; Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation. Geology 2007;; 35 (12): 1095–1098. doi: https://doi.org/10.1130/G23768A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Chiquerío Formation in southern Peru records the only documented Neoproterozoic glacial episode in the entire Andean Belt. We present U-Th-Pb secondary ion mass spectrometry (SIMS) detrital zircon ages and C isotopic data from the tillite and its overlying dolomite cap, the San Juan Formation. Two prominent negative C isotopic excursions are documented: an older excursion (δ13C = −2‰) in the cap-carbonate unit overlying the tillite, and a younger excursion (δ13C = −8‰) in a laminated limestone unit 700 m up sequence. In both cases, δ13C values recover to 2‰. U-Th-Pb SIMS detrital zircon results from the tillite (both matrix and interbedded turbiditic sandstones) indicate a restricted age distribution of 950–1300 Ma. Turbiditic dolomitic sandstones overlying the younger (−8‰) carbon isotope excursion yield a similar 950–1300 Ma peak, but also contain grains dated as 1600–2000 Ma and 700–820 Ma. The detrital zircon geochronology and C isotope chemostratigraphy are consistent with the Chiquerío Formation being equivalent to the ca. 700 Ma Sturtian glacial. The younger negative C isotope excursion is delimited by the youngest detrital zircon (697 ± 11 Ma) in overlying strata. A correlation with the 635 Ma Marinoan glacial is inferred, although no unequivocal glaciogenic strata have been identified. The detrital zircon data are consistent with derivation from the Proto-Andean margin, despite the Chiquerío Formation unconformably overlying basement gneisses of the 1800–2000 Ma Arequipa-Antofalla basement (AAB), which is exotic to Amazonia. This implies the Chiquerío Formation and AAB were proximal to the proto-Andean margin during Neoproterozoic glaciation, and supports paleogeographic reconstructions that favor AAB accretion to the Amazonian craton during the 1000–1300 Ma Grenville-Sunsas orogeny. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Sedimentology of the Upper Triassic Charlie Lake, Baldonnel and Pardonet formations from outcrop exposures in the southern Trutch region, northeastern British Columbia

Abstract Upper Triassic strata in the Trutch (94 G) NTS map area consist of the Charlie Lake, Baldonnel and Pardonet formations. These units comprise a mixed siliciclastic-carbonate succession, approximately 350 to 400 m thick. Sediments accumulated along a low gradient continental ramp deposited on the northwestern margin of Pangaea. Twenty-two lithofacies, deposited in distal offshore through supratidal settings are documented. Seven recurrent facies associations are identified in these strata; four reflecting deposition in continental to marginal marine settings, and three reflecting shallow to deep water marine deposition. Facies association 1 (FA1) consists of interbedded dolomitic mudstone/siltstone and dolomitic sandstone that was deposited in an intertidal flat depositional setting. Facies association 2 (FA2) consists of normally graded, trough cross-bedded to current ripple-laminated lenticular beds of mudclast-rich fine- to medium-grained sandstone, and was deposited by a series of small tidal channels. Facies association 3 (FA3) consists of well-sorted fine-grained sandstone beds characterized by high-angle tabular to wedge-shaped cross-beds, low-angle planar cross-beds, low-relief, translatent ripples and inversely graded lamina sets. FA3 is interpreted to represent deposition by a series of elongate, shore-parallel aeolian dunes. Facies association 4 (FA4) consists of a heterogeneous succession of solution collapse breccias, rooted, pedogenically-altered mudstone and siltstone, and wave-rippled very fine- to fine-grained sandstone. It is interpreted as ephemeral lacustrine and/or supratidal sabkha. Facies association 5 (FA5) consists of variably bioclastic quartzose sandstone, crinoidal packstone-grainstone and bivalve-dominated packstone beds. It is interpreted as a wave-dominated shoreface to foreshore on a shallow (inner) ramp. Facies association 6 (FA6) is dominated by very fine-grained calcareous sandstone and thin to thick-bedded bivalve-dominated wackestone, packstone and grainstone. It is interpreted as medial ramp (i.e., offshore transition to proximal offshore). Facies association 7 (FA7) consists primarily of organic-rich calcareous siltstone and mudstone (commonly with abundant carbonate concretions) and variably thick tightly packed bivalve packstone/grainstone beds. It is interpreted as outer ramp (proximal to distal offshore). Siliciclastic sediment in the study area was derived from a variety of sources, including fluvial input from the east-northeast, longshore drift from the north, and aeolian input sourced from marginal marine dune fields. Carbonate sediment in the study interval consists primarily of bioclastic detritus, although non-skeletal grains, particularly faecal pellets, and ooids are locally common. Skeletal carbonate material is dominated by disarticulated mollusc valves and crinoid skeletal debris but also includes ammonoids, articulate brachiopods, gastropods. Vertebrates (fish and reptiles) are also common.

Is the transition impact to post‐impact rock complete? Some remarks based on XRF scanning, electron microprobe, and thin section analyses of the Yaxcopoil‐1 core in the Chicxulub crater

Abstract The transition from impact to post‐impact rocks in the Yaxcopoil‐1 (Yax‐1) core is marked by a 2 cm‐thick clay layer characterized by dissolution features. The clay overlies a 9 cm‐thick hardground, overlying a 66 cm‐thick crossbedded unit, consisting of dolomite sandstone alternating with thin micro‐conglomerate layers with litho‐ and bioclasts and the altered remains of impact glass, now smectite. The micro‐conglomerates mark erosion surfaces. Microprobe and backscatter SEM analysis of the dolomite rhombs show an early diagenetic, complex‐zoned, idiomorphic overgrowth, with Mn‐rich zones, possibly formed by hot fluids related to cooling melt sheet in the crater. The pore spaces are filled with several generations of coelestite, barite, K‐feldpar, and sparry calcite. XRF core scanning analysis detected high Mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements Cr, Co, Fe, and Ni in the clay layer. Shocked quartz occurs in the crossbedded unit but is absent in the clay layer. The basal Paleocene marls are strongly dissolved and do not contain a basal Paleocene fauna. The presence of a hardground, the lack of siderophile elements, shocked quartz, or Ni‐rich spinels in the clay layer, and the absence of basal Paleocene biozones P0 and Pa all suggest that the top of the ejecta sequence and a significant part of the lower Paleocene is missing. Due to the high energy sedimentation infill, a hiatus at the top of the impactite is not unexpected, but there is nothing in the biostratigraphy, geochemistry, and petrology of the Yax‐1 core that can be used to argue against the synchroneity of the end‐Cretaceous mass‐extinctions and the Chicxulub crater.

The Padaeng Supergene Nonsulfide Zinc Deposit, Mae Sod, Thailand

The Padaeng deposit near Mae Sod in western Thailand was the first supergene nonsulfide zinc deposit in the world to be developed as a large modern mining operation. The mine and associated zinc smelter, operated by Padaeng Industry Public Company Ltd. since 1984, went into production with reserves of 4.59 Mt at a grade of 28.9 percent zinc with a 10 percent zinc cutoff. Current resources are 5.14 Mt at a grade of 12.0 percent zinc with a 3 percent zinc cutoff. The Padaeng deposit is hosted by a mixed carbonate-clastic sequence of Middle Jurassic age. The deposit occurs in the hanging wall of the Padaeng fault, a major northwest-trending structure that was active through Cretaceous and Tertiary tectonism and uplift. Nonsulfide zinc ore comprises dominant hemimorphite with minor smithsonite and hydrozincite. Strata-bound ore zones occur within a northwest-dipping, deeply weathered, dolomitic sandstone; steeply dipping and irregular karstic zones in underlying massive, silty dolomite are controlled by north-trending fracture zones. Sulfide zinc-lead mineralization of Mississippi Valley type occured extensively in the vicinity of the Padaeng mine, most notably the small resources at Pha De and Hua Lon. Mineral deposits are typically sphalerite rich with minor galena and pyrite, forming small-scale open-space fillings, veins, and replacements within hydrothermal dolomite. Mineralization is dominantly strata bound within a horizon of intense hydrothermal dolomitization that forms the stratigraphic hanging wall to the nonsulfide ore zones at Padaeng. The only significant sulfide at the Padaeng mine is within this unit. Only trace sulfide occurs peripheral to, or down dip of, strata-bound or steeply dipping, nonsulfide orebodies. Sulfide mineralization is believed to have accompanied Cretaceous uplift and deformation, related to the onset of oblique subduction beneath the western margin of the Shan-Thai terrane. The nonsulfide deposit is believed to have formed when a substantial body of sulfide ore was uplifted on the margin of the Mae Sod Tertiary intermontane basin, commencing in the middle to late Miocene. Zinc-bearing acidic supergene fluids, generated by oxidation of the precursor sulfide body, reacted with carbonate in the underlying stratigraphic section to precipitate hemimorphite and smithsonite. Fluids were channeled by permeable dolomitic sandstones and by steep fracture and fault zones. Acidic fluids promoted deep weathering and karst formation, allowing mineralization to extend down dip in sandstone units for at least 150 m and vertically for a similar distance in steep structural zones. Transport of zinc out of the precursor sulfide body was facilitated by a falling water table, owing to uplift of the Padaeng fault block and a change from wet tropical to monsoonal or semiarid climatic conditions. There is no evidence for significant in situ replacement of sulfide deposits, and the leached remnants of the precursor sulfide body have been removed by erosion. The supergene process of dissolution and reprecipitation of zinc in the host rocks increased zinc grades and separation of zinc from lead, producing an economically attractive deposit. Successful exploration for this type of deposit requires a good understanding of the controls on primary sulfide mineralization and a good knowledge of local neotectonism, uplift history, hydrogeology, climatic evolution, and weathering history.

An eolian facies within the Upper Jurassic Smackover Formation, Tchula Lake field, Mississippi

The Late Jurassic upper Smackover Formation in Mississippi is primarily composed of an overall regressive sequence of marine carbonate ramp deposits. In central Mississippi, however, carbonate deposition was interrupted by a large influx of siliciclastic sediment. Tchula Lake field is unique not only because it produces gas and condensate from dolomitic quartz sandstone deposited in a mixed siliciclastic-carbonate environment but also because it produces from what we interpret to be an eolian dune sand facies. Throughout the Gulf Coast Basin no previous literature has cited an eolian facies within the Smackover Formation. Several characteristics of the producing zone sandstones have led to interpretations of this unit as an eolian coastal dune facies deposited on and around a Jurassic paleohigh. Facies and paleoenvironmental interpretations are based on compositions and textures described in cores and thin sections. The eolian facies consists of fine-grained, dolomitic quartz sandstone with a mean porosity of 10-20% and permeability of 0-800 md. The sand grains are rounded to subrounded and well sorted. The sandstone exhibits a sequence of upward-steepening planar laminations capped at the top by a set of small-scale wedge planar cross-laminations. The sharply defined, parallel lamina are less than 5 mm thick and are commonly inversely graded and contain probable vadose meniscus carbonate cements. This facies is interpreted to have been deposited in a backshore coastal dune environment. The unit is characterized by low-angle (<20 degrees dip) climbing translatent strata commonly produced by the migration of wind ripples along a dune. No fossils or trace fossils are found within this facies. Eolian-deposited sandstone is a potential reservoir rock along the updip limit of the Smackover Formation in west-central Mississippi. Other paleohighs along the Jurassic shoreline may have undergone similar eolian deposition during a regional sea level fall. Eolian-deposited sandstones on these paleohighs should have (Begin page 486) similar reservoir properties as the sandstone at Tchula Lake field. The updip Smackover Formation in west-central Mississippi is an underexplored horizon, and eolian-deposited reservoirs have strong potential as a new exploration target. The sea level fluctuation event associated with deposition at Tchula Lake field also has implications for exploration in Upper Jurassic sedimentary rocks across the entire United States Gulf Coast Basin and prompts a reevaluation of these reservoirs.

Abstract: Reservoir characterization in the San Andres formation of Vacuum field, Lea County, New Mexico - another use of the San Andres Algerita outcrop model for reservoir description

Since its discovery in 1929, Vacuum field, Lea County, New Mexico has produced 361 million bbl of oil and 298 bcf of gas from the Leonardian–Guadalupian (Permian) San Andres Formation. Despite this impressive performance, 65–70% of the estimated original oil in place remains in the ground. Complex variations in the porosity and permeability of reservoir lithologies are the principal causes for incomplete hydrocarbon recovery. Dolomitized oolitic-peloidal and fusulinid-peloidal packstones and grainstones constitute the productive reservoir facies. Interbedded in these porous units are tight, anhydritic or quartzose dolomudstones to mud-rich dolopackstones and dolomitic sandstones. Cores recovered from the nonporous intervals reveal textures, fabrics, and grain types indicative of (1) deposition in tidal-flat (peritidal) environments or (2) diagenetic modification, including collapse breccias, sinkholes, caves, and vertical fractures plugged with quartz sand or anhydrite cement, suggestive of exposure (karst) overprinting. Early geologic models of the Vacuum field were primarily generated from petrophysical data, resulting in lithostratigraphic correlations that crossed time lines and flow units. Application of a chronostratigraphic framework for the San Andres based on outcrop studies results in an updated reservoir model for Vacuum field. Improvements include (1) recognition of localized, tight, tidal-flat cycles in separate horizons in the youngest San Andres high-frequency sequence (HFS) instead of correlating all nonporous, high gamma-ray intervals as a single, regional quartzose sandstone (Lovington sand), (2) identification of bypassed pay in porous, strike-parallel dolopackstones that are stratigraphically equivalent to, but downdip from, the tidal flats, and (3) recognition of the presence of tight karst intervals in older HFSs that compartmentalize the most continuous San Andres pay interval. Deeper, uncored San Andres lithologies can be more accurately characterized by comparing petrophysical information with facies attributes from older San Andres outcrops. An untested reservoir may occur in basal San Andres skeletal dolopackstones that are sealed by dolomudstones.