Slope Facies Research Articles

Stratigraphy, facies and geodynamic settings of Jurassic formations in the Bükk Mountains, North Hungary: its relations with the other areas of the Neotethyan realm

AbstractJurassic mélange complexes related to the subduction of the Neotethys Ocean occur in the Bükk Mountains, North Hungary. This paper characterizes the sedimentary sequence of basin and slope facies that occur in the southwestern part of the Bükk Mountains, placing special emphasis on the redeposited sedimentary rocks (olistostromes, olistoliths: Mónosbél Group) in order to obtain information on the provenance of the clasts, and the mode and time of their redeposition. The series of formations studied shows a general coarsening-upwards trend. Based on radiolarians and foraminifera, the Mónosbél Group formed in Early to Late Bathonian time. The lower part of the complex is typified by a predominance of pelagic carbonates, shale and radiolarite with andesitic volcaniclastic intercalations. The higher part of the succession is characterized by polymictic olistostromes. Large olistoliths that are predominantly blocks of Bathonian shallow marine limestone (Bükkzsérc Limestone) appear in the upper part of the sequence. Based on the biostratigraphic and sedimentological data, results of analyses of the redeposited clasts and taking into consideration the concepts of the development of the western Neotethys domain, the evolutionary stages of the sedimentary basins were defined. The onset of the compressional stage led to initiation of nappe stacking that led to the formation of polymict olistostromes and then to the redeposition of large blocks derived from out-of-sequence nappes of the former platform foreland.

Anatomy of carbonate mounds from the Middle Anisian of Nakhlak (Central Iran): architecture and age of a subtidal microbial-bioclastic carbonate factory

The Anisian succession of Nakhlak (in Central Iran) is characterized by a siliciclastic succession with minor carbonate units, with massive carbonate mounds up to 50 m thick in its upper part. The mounds, constrained in age to the late Bithynian (Ismidicus Zone) by ammonoids and conodonts, are characterized by a flat top and a lateral pinch-out marked by clinostratified slopes (about 15° in dip). Stratigraphic and microfacies analyses document an inner part of the mound characterized by massive microbial carbonates with open-space structures (stromatactis) filled with fine-grained internal sediments and marine cements. Isolated sponges (up to 5 cm), serpulids and bryozoans are present, which grew on the calcimicrobial limestone. A narrow bioclastic margin (mainly with crinoids and brachiopods) produces most of the slope facies (consisting of bioclastic grainstone and packstone, with intraclasts from the inner part of the mounds) which interfinger basinward with volcaniclastic sandstones. The demise of carbonate productivity is marked on the top of the carbonate mounds by a condensed surface, rich in ammonoids, glaucony grains, and articulated crinoids, documenting a rapid drowning. Paleolatitude data support deposition in a tropical setting, and sedimentological constraints indicate deposition close to the fair-weather wave base, within the photic zone. The late Bithynian Nakhlak carbonate mounds developed before the appearance (documented since the Pelsonian in different parts of the world) of scleractinians which, despite the favorable environmental conditions, are absent at Nakhlak. The Nakhlak mounds thus represent one of the last occurrences of the microbial factories (which developed after the Permo-Triassic extinction event and persisted for most of the Middle Triassic, but with a gradually increasing role played by scleractinians) before the first appearance of the Mesozoic corals.

Cambrian sponge spicules and Chancelloriid sclerites from the Argentine Precordillera: A Review

Spicules of sponges and sclerites of chancelloriids have been collected from in situ Cambrian sections of the La Laja Formation (San Juan Precordillera). They have also been collected from carbonate olistoliths, which were emplaced from the Cambrian units in the Early Ordovician Los Sombreros Formation (San Juan Precordillera) and Empozada Formation (Mendoza Precordillera). The Cambrian La Laja Formation sequences were deposited in a shallow carbonate platform in the eastern part of the Precordillera. The Cambrian carbonate rocks, which make up the olistoliths in the Los Sombreros and Empozada Formations, record deposition in the slope environments which developed in the western Precordillera. Cambrian Porifera and sponge-like chancelloriid assemblages are known mainly from fragments of skeletal nets, dissociated spicules and sclerites, which enable us to define two assemblages. The first assemblage of spicules was defined from the upper Lower to Middle Cambrian sequences of the La Laja Formation. This assemblage consists of a variety of stauractines and sclerites of Chancelloria WALCOTT. The family Protospongiidae is represented by triradiate prodianes, pentactines and hexactines, all belonging to Kiwetinokia WALCOTT. The second assemblage, which consists of isolated hexactines, pentactines, monaxons and skeletal nets, was defined in the Cambrian derived olistholiths of the Los Sombreros and Empozada Formations. Early hexactinellid Protospongiidae with body preservation (Diagoniella ? and Kiwetinokia) also occur. Demosponges have a very limited record in the Cambrian of the Precordillera. Anthaspidellid sponges had been reported from the La Laja Formation and now from the San Martin olistolith (Empozada Formation). The occurrences of these two assemblages of spicules and sclerites in both the Cambrian platform and slope facies of the Precordillera contribute additional data for a better understanding of the relationships between the eastern and the western facies assemblages, which developed in the Precordillera during the Cambrian. Therefore, they are useful for paleoenvironmental and paleogeographical interpretations of the Cambrian depositional framework.

Sequence lithofacies paleogeography and reservoir potential of the Maokou Formation in Sichuan Basin

Abstract Based on multidisciplinary analyses of outcrops, core description and log data, two types of sequence boundary are identified, including a partially exposed unconformity surface and a drowned unconformity surface. The Maokou Formation in the Sichuan Basin is divided into three third-order sequences, each lasting 3.3 Ma on average. In this study, system tracts are used as mapping unit to reconstruct systematically the lithofacies paleogeography map within the sequence framework, and to describe paleogeographic features. The results indicate that the Sichuan Basin is dominated by shallow, open marine carbonate platform deposits during the Middle Permian Maokou stage, in which a range of sedimentary facies developed, such as shallow water open platform, deeper water open platform, platform margin bank, and platform front slope facies. Physical property analysis indicates that shallow calcsparite granular limestone has good reservoir qualities, especially after the reservoir rock is reworked by dolomitization and epigenetic karstification. Thus, dolomite reservoir, paleokarst reservoir and shallow bank reservoir make up the main reservoirs of the Maokou Formation. The study on reservoir distribution patterns within the sequence framework indicates that HST reservoirs are relatively well developed, especially the shallow bank sedimentary regions of SQ2-HST in the western-southwestern Sichuan Basin and the paleokarst development area of SQ3 are the most favorable.

From outcrop to 3D modelling: a case study of a dolomitized carbonate reservoir, Zagros Mountains, Iran

ABSTRACT Outcrop data derived from fieldwork, remote sensing satellite and LiDAR-derived 3D models were used to build an integrated dual porosity-permeability static reservoir model which captured stratigraphic, diagenetic and structural heterogeneities. The study focuses upon the Mishrif-Mauddud/Sarvak interval, one of the most prolific reservoir units in the Middle East. The study area is exceptionally well exposed in deep gorges which cut transversally across anticlines of the Simply Folded Belt of the Zagros Mountains. The outcrops reveal volumetrically significant dolomitization of the latest Albian to Turonian carbonates of the Lower and Upper Sarvak formations. Three different dolomite bodies, which are spatially connected and genetically linked to the same fluid flow event, were recognized and mapped: (1) a thick dolomite body replacing the Lower Sarvak and forming a massive dolomite core; (2) horizontally extensive stratabound dolomite bodies (sheets), emanating laterally from the massive dolomite; and (3) vertically elongated dolomite pipes, rooted in the massive dolomite and typically replacing slope facies of the Upper Sarvak Formation. The widespread development of tight, non-planar dolomite textures (a typical feature of high temperature dolomitization) drastically reduces the reservoir potential of the dolomitized geobody in the study area. In particular, this is present in the massive dolomitized body. Vuggy porosity seems to increase porosity only locally and to a limited extent, developing a non-connected pore network. The dominant porous dolomite textures are more abundant in the peripheral part of the geobody (dolomite sheets), where they are strongly controlled by precursor facies and diagenesis. Three main dolomite pore types were identified (intercrystalline, interparticle and mouldic), linked to the depositional environment of the precursor limestone. These pore types were used for petrophysical modelling. The approach adopted in this study allowed the distribution of rock properties in the dolomitized geobody to mimic the main depositional facies architecture. The study area is characterized by a simple fracture network. Two main fracture sets and two major sets of conjugate normal faults were recognized in the field and mapped on 3D virtual outcrop data. Non-stratabound fracture density varied according to stratigraphic unit and/or dolomite body type (pipes/massive/sheets), showing a general increase from precursor limestone to dolomite. Fracture density also varied according to distance from faults (fault damage zone). This was particularly true in the limestone. The data also showed a prominent increase in fracture height from limestone to dolomite bodies, indicating that the dolomitized geobodies are likely sites for high production and early water breakthrough.

Barra Honda (Upper Paleocene- Iower Eocene) and el Viejo (Campanian-Maastrichtian) carbonate platforms in the Tempisque Area (Guanacaste, Costa Rica)

En este trabajo preliminar se reportan las edades, microfacies, microfósiles y la situación estructural delas calizas de plataforma que afloran en el área del río Tempisque (Guanacaste). Existen dos plataformas carbonata-das: el Viejo, de edad Campaniano Superior-Maastrichtiano, que está representada por facies de talud en los cerrosBallena y Cebollín y, la plataforma de Barra Honda, de edad Paleoceno Superior-Eoceno Inferior, que se extiende des-de los afloramientos típicos, en el sur del área estudiada (cerros Barra Honda), hasta la región de Palo Verde al norte.En el cerro Cebollín, los basaltos del Complejo de Nicoya s.str están sobreyacidos disconformemente por depósitosturbidíticos y de mass. Clastos de caliza pelágica con foraminíferos planctónicos como globotruncanas (Globotrun-canita elevata), macroforaminíferos (Sulcoperculina globosa, Sulcoperculina vermunti, Pseudorbitoides rutteni,Asterorbis, Nummuloculina, Proporocyclina) y abundantes fragmentos de rudistides atestiguan una edad del Campa-niano Superior al Maastrichtiano para esta secuencia. Contenidos variables de clastos de basalto y de serpentinita documentan la erosión de un basamento ultramáfico, como la unidad Ultramáfica de Santa Elena. Interpretamos la secuencia de los cerros Ballena y Cebollín como depósitos de talud que fueron alimentados desde la plataforma somerade la Formación El Viejo, que aflora, tanto al norte de la península de Nicoya, como de la de Santa Elena.En los cerros Barra Honda, Quebrada Honda y otros afloramientos clásicos de la Formación Barra Honda, observa-mos una variedad de microfacies que documentan paleoambientes de plataforma restringida hasta de plataforma abier-ta. Todas las facies se caracterizan por la presencia de algas rojas (coralinaceas) y de Ethelia alba, una alga de la fa-milia Squariamaceae, característica del Paleoceno en las plataformas del Medio Oriente, que se reporta por primeravez en América Central. Ethelia alba aparentemente creció en las zonas de plataforma abierta y fue transportada enfragmentos hacia las zonas restringidas. Las facies micríticas contienen foraminíferos Rotalides, entre los cuales sedestaca Thalmannita madrugaensis, que se conoce hasta ahora únicamente en el Paleoceno de Cuba, además formasde miliólidos y Alveolinides.En la zona de Palo Verde (Fig. 5) las facies típicas de Barra Honda pasan a facies de alta energía, caracterizadas porla presencia de macroforaminíferos del Paleoceno Superior-Eoceno Inferior Ranikothalia catenula, Neodiscocyclinabarkeri asociados a Ethelia alba .En el cerro Espíritu Santo se observa la transgresión de la plataforma de Barra Honda sobre lutitas silíceas alteradasy cubiertas por un posible paleosuelo, estas lutitas descansan sobre basaltos. Las primeras capas de plataforma contie-nen cantos rodados y perforados típicos de la zona costera.En el extremo sur de los afloramientos de Barra Honda, cerca de Pochote observamos una secuencia que documenta el re-trabajo de clastos del Cretácico terminal en un ambiente de mar abierto, están caracterizados por abundantes foraminífe-ros planctónicos del Paleoceno Superior (Morozovella velascoensis) y Pentacrinites sp. (crinoideo de plataforma abierta).La secuencia pasa gradualmente a facies típicas de Barra Honda hacia el techo. Calizas de plataforma somera datados delEoceno Inferior - Medio afloran como pequeños montículos en la región de la Laguna Jicote, en el noroeste de la zona estudiada. Se caracterizan por una microfacies rica en algas rojas (Coralinaceas) y macroforaminíferos (Discocyclina, Eoco-nuloides wellsi, Amphistegina). Por ahora no podemos interpretar el origen de estos afloramientos.La plataforma Barra Honda sobreyace discordantemente a las formaciones deformadas del Cretácico Superior-Paleo-ceno, tanto al oeste del río Tempisque, como en la zona de Palo Verde. Al este del río Tempisque, en la zona del cerroNaranjo, el contacto basal de Barra Honda se caracteriza por la deformación semiplástica intensa de las formacionesdetríticas subyacentes, las cuales pueden ser tan jóvenes como el Eoceno Medio. El emplazamiento de Barra Hondasobre estas formaciones puede ser atribuido a una compactación de las formaciones detritícas y un asentamiento de lascalizas, aunque también puede ser un resultado de una situación transcompresiva, a lo largo de las fallas longitudina-les que han sido señaladas a lo largo del Tempisque.

Biostratigraphic and Chemostratigraphic Correlation for the Base of the Middle Ordovician between Yichang and Western Zhejiang Areas, South China

Abstract:The base of the Middle Ordovician (i.e. Dapingian Stage) has been defined at the first appearance datum (FAD) of conodont Baltoniodus?triangularis at Huanghuachang, Yichang, China, but the precise correlation of the boundary to regions of other facies remain to be resolved. Herein we review the biostratigraphy and chemostratigraphy of the Huanghuachang Global Standard Stratotype‐Section and Point (GSSP) section, and present our latest stratigraphic work on the nearby Chenjiahe section in Yichang, and the Hengtang Quarry section, Jiangshan, Zhejiang, which is regarded as representative of slope facies. The conodont and graptolite biostratigraphy as well as chemostratigraphy of the Chenjiahe section indicate that the base of the Middle Ordovician also falls within the graptolite Azygograptus suecicus Zone, and coincides with a high or maximum δ13C value within a minor positive carbon isotope excursion, suggesting that the base boundary can be readily recognized across the entire Yangtze Gorges area. The integrated graptolite and conodont biostratigraphy and chemostratigraphy of the Hengtang section, Jiangshan, indicates that the basal boundary probably falls within the graptolite Isograptus caduceus imitatus Zone that overlies the Azygograptus suecicus Zone, and coincides with a remarkable drop of δ13C. This difference indicates that a multi‐disciplinary approach is critical to identify the base boundary in those regions where the Baltoniodus?triangularis is absent

Geochemistry, petrogenesis and geodynamic origin of basalts from the Katun' accretionary complex of Gorny Altai ( southwestern Siberia)

The paper presents new data on geochemistry (major and trace elements, isotopes) and petrology (composition of phenocrysts and mineral thermometry) of basalts from the Early Cambrian Katun' accretionary complex of the Kuznetsk–Altai island arc (Gorny Altai). We also discuss the geodynamic settings of the formation of basalts based on petrologic, geochemical and isotope data taking into account their relationships with associated sedimentary rocks of oceanic origin and with terrigenous sedimentary rocks of the accretionary complex. The Late Neoproterozoic basalts associated with siliceous sediments are characterized by medium TiO 2 and Zr/Nb, flat REE patterns and Nb/La pm < 1 (MORB-type oceanic floor basalts). The oceanic floor basalts are represented by high- and low-magnesium varieties. The Early Cambrian basalts (Manzherok Formation) were formed in an oceanic island setting (OIB-type). They occur in sections consisting of paleo-oceanic island basalts alternated with siliceous-terrigenous-carbonate sediments of slope facies. The Manzherok basalts are characterized by high crystallization temperatures (1175 °C), and enriched incompatible elements (LREE, Ti, Nb), whose variations suggest a mantle plume source and variable degrees of partial melting in the spinel and garnet stability fields. The low to high-Mg Middle Cambrian basalts of the Ust'-Sema Formation occur as subparallel dikes and lava flows, which cut and overlap the accretionary complex. The basalts are characterized by low TiO 2, Nb, LREE, high Zr/Nb and, compared to the OIB-type basalts, lower temperatures of crystallization, 1047 °C and 1138 °C for the low- and high-Mg varieties, respectively. Geochemically, the low-Mg basalts of the Ust'-Sema Formation are close to MORB, and the high-Mg basalts—to island-arc tholeiites. Such a combination of geochemical and geological data suggest that the low-Mg basalts of the Ust'-Sema Formation formed during ridge subduction, and the high-Mg basalts formed in a suprasubduction setting, at the crust-mantle boundary.

Evaluating the Pharmacist-Physician MTM Collaborative Relationship Using Patient Outcomes

The Vaca Muerta Formation (early Tithonian–early Valanginian) is a rhythmic succession of marls and limestones, cropping out in the Neuquén Basin, west-central Argentina. This lithostratigraphic unit was traditionally interpreted as basinal to slope deposits. Detailed facies analysis allows to differentiate seven facies associations, representing basinal to middle ramp facies of a homoclinal ramp system prograding westward from the eastern margin, and slope facies attributed to a distally steepened ramp system that progrades eastward from the Andean volcanic arc in the west. Two sequence hierarchies are recognized: five third order depositional sequences, and fifteen fourth order high-frequency sequences. Fluctuations in organic matter content within the Vaca Muerta Formation suggest relationship with depositional sequences, finding the highest values associated with transgressive system tracts. This work represents an important advance in the understanding of the sedimentary and stratigraphic evolution of this exceptional unconventional reservoir. Our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter, facies, and sea-level changes.

Diversity and paleobiogeographic distribution patterns of early and Middle Ordovician graptolites in distinct depositional environments of South China

An analysis of Ordovician graptolite diversity across several distinct lithofacies belts in South China, which represent nearshore, inner-shelf, outer-shelf, slope, and basin environments, indicates that diversity increases progressively from nearshore toward the outer-shelf, acquiring its maximum in the slope facies and thereafter decreases slightly in basinal facies. When scaled against graptolite zones and more equal duration ‘Time Units’, the graptolite diversity patterns of the Early and Middle Ordovician are broadly similar among the distinct environments of South China but exhibit some important differences. A synthesized graptolite diversity curve from the Early Ordovician to the Sandbian Stage of the Late Ordovician in South China displays a step-wise increase with three peaks: 1) middle Floian (Early Ordovician), 2) late Dapingian-early Darriwilian (Middle Ordovician), and 3) latest Darriwilian (Middle Ordovician), which closely coincide with transgressive events in South China, implying a likely correlation. The biogeographic distribution of four graptolites with different ecological preferences, Pseudisograptus, Isograptus-Parisograptus, Undulograptus austrodentatus, and Corymbograptus turgidus, displays a significant parallelism with the coast or shelf margin, suggesting that their distributions may be controlled by water depth, basin morphology, and the distance from the coast.

Distinguishing fluvio-deltaic facies by bulk geochemistry and heavy minerals: an example from the Miocene of Denmark

Interpretations of seismic profiles, gamma-ray logs and sediment descriptions were used to classify seven facies in Miocene fluvio-deltaic deposits of Denmark. An impartial approach was adopted by not including analytical data in the facies definition. This approach allowed identification of significant differences between facies, where each fluvio-deltaic facies can be distinguished by integrating geochemistry and mineralogy through a sedimentary succession. Variations in the heavy mineral assemblage between facies are caused primarily by sorting of hydraulically equivalent grains. Decreasing grain size of quartz and heavy minerals from the channel facies towards the delta shoreface facies and further along the coast to the spit shoreface facies is associated with an increase in sorting and textural maturity. This trend is related to longshore drift. Increasing heavy mineral grain size is found from the delta slope facies offshore to the delta toe and shelf facies. This trend is interpreted as a result of sorting by turbidity currents. The mixed origin of the transgressive lag facies is shown by the poorer sorting in this facies. By indicating the amount of alteration the sediments have been exposed to, the Ti-mineral maturity has proven useful in characterizing the facies. This systematic approach of tying depositional environments to a well-calibrated sequence stratigraphic model has generated analytical results which are valid as reference levels for future facies identifications.

Lower Carboniferous carbon isotope stratigraphy in South China: Implications for the Late Paleozoic glaciation

Studies on carbon isotopes of bulk carbonates from Longan and Baping sections of Lower Carboniferous in Guangxi of China show that the stable carbon isotope compositions in carbonate rocks of the isolated platform and deep slope facies were resistant to the influence of early meteoric diagenesis and late burial diagenesis. Three major positive carbon isotope excursions have been recognized in Lower Carboniferous in South China. The first major positive δ 13 C shift of 4.19‰ occurred in the middle part of Siphonodella isosticha-upper Siphonodella crenulata zone (Tournaisian); the second with an amplitude of 4.65‰ occurred near the Tournaisian/Visean boundary; and the third of 2.23‰ in the lower part of Gnathodus bollandensis zone. The three positive shifts of δ 13 C can be correlated with global carbon isotope excursions and are consistent with the fall in global sea level, indicating that abundant organic carbon burial, lowering of atmospheric CO 2 , and glaciation may have occurred during these time intervals.

Applying classical shale gas evaluation concepts to Germany—Part I: The basin and slope deposits of the Stassfurt Carbonate (Ca2, Zechstein, Upper Permian) in Brandenburg

Organic-rich mudstones of the Stassfurt Carbonate basinal and lower slope facies (Ca2, Zechstein, Upper Permian) occur in the eastern part of the North German Basin (southern Brandenburg, eastern Germany). These source rocks for oil and gas fields have been investigated as a test system for the application of procedures to characterize gas shales. Classic sedimentological investigation methods, including core descriptions and thin section microscopy, were coupled with standardized organic geochemical analysis procedures, such as total organic carbon determination, Rock-Eval pyrolysis, open system pyrolysis-gas chromatography, gas chromatography of aliphatic hydrocarbons, and thermovaporization employing microscale sealed vessels (MSSV). Furthermore, the maceral composition was analyzed and vitrinite reflectance measurements were carried out. Data from these interdisciplinary methods were evaluated to characterize the basinal Stassfurt Carbonate Ca2 utilizing mainly established guidelines for shale gas exploration in North America. The “Stinkschiefer” sediments in southern Brandenburg show a trend of increasing maturity from south to north, favoring the occurrence of gas shales near the basin center. A distinction between basin and lower slope deposits could be made for the investigated suite of samples. The Ca2 basin facies occurs below 3800 m depth. It has reached a minimum thermal maturity of 2.2% R r and is therefore in the dry thermogenic gas zone. In contrast the lower slope deposits occur at depths from 1250 to 3250 m and have oil window maturity, ranging from 0.7% to 1.0% R r. The organic matter is a mixed Type II/III kerogen, the Hydrogen Index ranges from 7 to 105 mg HC/g rock. The low average TOC contents, varying between 0.2 and 0.8 wt%, and its low formation thickness, on average 6 m, are factors limiting the gas shale potential of the Ca2. However, the effective sealing by evaporites below and above the Ca2 may restrict expulsion of generated gas, leading to gas retention within Ca2 black shales.

Sedimentology and paleoenvironments of the La Laja Formation (Cambrian), Quebrada La Laja, Sierra Chica de Zonda, San Juan, Argentina.

The La Laja Formation is a key unit regarding the hypothesis of the Argentine Precordillera as a Laurentia-derived allochtonous terrane in the south central Andes. Together with the Cerro Totora Formation it comprises the oldest unit exposed at the base of the Lower Paleozoic carbonate platform of the Precordillera. According to previous work these units record the rifting-drifting history of this terrane exotic to Gondwana. The La Laja Formation contrasts with the rest of the overlying units of the Cambro-Ordovician carbonate platform by being partly mixed carbonate-siliciclastic. A detailed facies analysis of the five recognized members in the reference section at Quebrada La Laja (Sierra Chica de Zonda, San Juan Province) allow the recognition of 19 microfacies grouped into four main environmentally significant associations: 1) a storm-influenced, deep subtidal environment with variable influx of fine siliciclastic sediments; 2) shallow subtidal, 3) mixed shallow subtidal and 4) shallow subtidal to intertidal occasionally with well developed high-frequency tidal flat cycles. No deeper basinal or slope facies were found. In contrast, the unit largely records shallow-marine facies with some evidence of subaerial exposure. Medium to coarse, calcareous, feldspar-rich sandstones and sandy limestones characterize the El Estero Member. The base of the Soldano Member shows profuse development of cyclicity with capping oolitic shoals. This member and the upper Juan Pobre Member contain deeper subtidal intervals, below the storm weather wave base, with high percentages of fine terrigenous material represented by shaly marls and nodular limestones. Skeletal-rich and oolite-rich storm beds are recorded within them. Relative shallowing to subaerial environments recorded within the Rivadavia and Las Torres members, with the development of ribbon limestones, intraclastic rudstones, microkarstic surfaces and exposure breccias. Herringbone cross-bedded oolite shoals are common at the top of the uppermost Las Torres Member. The transition into the overlying Zonda Formation is represented by an abrupt rearrangement of the depositional systems and development of meter-scale microbial-rich peritidal cycles. Several orders of superposed cyclicity are recorded within the La Laja Formation. Larger-scale cycles ('Grand Cycles') are inferred from alternating members with important amounts of siliciclastics, whereas meter-scale cycles indicate higher frequency superposed mechanisms. Altogether these show a complex depositional history linking environmental and tectono-eustatic signatures.

Presenting seismic stratigraphy and attribute analysis as pioneer techniques for delineation of reservoir quality sand bodies in the Indus Offshore Basin, southwest Pakistan

It is generally believed that various exploration failures in the offshore areas of Pakistan are due to the absence of a mature petroleum system. However, a few recent gas shows and shales with 0.55–3.24% TOC suggest that a Middle-Upper Miocene lowstand systems tract (LST) exists that possesses organic, paleo-environmental, and sequence stratigraphic characteristics of a potential source rock. The objective of this work was to highlight and delineate the slope and basin facies through seismic sequence stratigraphy and seismic attribute analysis as a new approach to the interpretation of the southwestern Lower Indus Basin of Pakistan. Working within a sequence stratigraphic framework, four sequences have been delineated on the basis of reflection termination patterns. A sea-level curve was constructed from the reflection patterns representing coastal onlap. This sea-level curve was compared to a hypothetical sea-level curve generated by a spectral analysis Fourier transform function on the density logs.

Carbon isotope chemostratigraphy and precise dating of middle Frasnian (lower Upper Devonian) Alamo Breccia, Nevada, USA

At Hancock Summit West, Nevada, western USA, uppermost Givetian (upper Middle Devonian) and lower and middle Frasnian (lower Upper Devonian) rocks of the lower Guilmette Formation include, in stratigraphic sequence, carbonate-platform facies of the conodont falsiovalis, transitans, and punctata Zones; the type Alamo Breccia Member of the middle punctata Zone; and slope facies of the punctata and hassi Zones. The catastrophically deposited Alamo Breccia and related phenomena record the ~ 382 Ma Alamo event, produced by a km-scale bolide impact into a marine setting seaward of an extensive carbonate platform fringing western North America. Re-evaluation of conodonts from the lower Guilmette Formation and Alamo Breccia Member, together with regional sedimentologic and conodont biofacies comparisons, now firmly locates the onset of the Johnson et al. (1985) transgressive–regressive (T–R) cycle IIc, which occurred after the start of the punctata Zone, within a parautochthonous megablock low in the Alamo Breccia. Whole-rock carbon isotope analyses through the lower Guilmette Formation and Alamo Breccia Member reveal two positive δ 13C carb excursions: (1) a small, 3‰ excursion, which is possibly correlative with the falsiovalis Event previously identified from sections in Western Europe and Australia, occurs below the breccia in the Upper falsiovalis Zone to early part of the transitans Zone; and (2) a large, multi-part excursion, dominated by a 6‰ positive shift, begins above the start of the punctata Zone and onset of T–R cycle IIc and continues above the Alamo Breccia, ending near the punctata– hassi zonal boundary. This large excursion correlates with the punctata Event, a major positive δ 13C excursion previously recognized in eastern Laurussia and northern Gondwana. Consistent with previous studies, at Hancock Summit West the punctata Event is apparently not associated with any regional extinctions or ecosystem reorganizations. In the study area, onset of the main punctata Event began after the start of both the punctata Zone and T–R cycle IIc, and preceded the Alamo impact by less than 650 k.y., as inferred from conodont biochronologic and regional rock-accumulation rate estimates. Although complicated by the heterolithic, high-energy deposits of the Alamo Breccia, the carbon isotope record of the breccia and post-breccia beds does not indicate a major impact-correlative perturbation to the carbon cycle. This study extends recognition of the punctata Event to western Laurussia, further reinforcing the potential global scale of the event and its potential importance to understanding early to middle Frasnian marine geochemistry and palaeoenvironments. Based on previous models and our observations, increased tectonic activity, increased nutrient flux to oceans, increased marine bioproductivity, widespread anoxia, and increased organic carbon burial were all likely key factors in driving the punctata Event excursion. Furthermore, periodic eustatic and regional relative sea-level rises may have played an important role in promoting organic carbon burial and in maintaining a link between the primary open-marine geochemical signal and that recorded on the shallow-marine, lower Guilmette carbonate platform.

Upper Palaeozoic subduction/accretion processes in the closure of Palaeotethys: Evidence from the Chios Melange (E Greece), the Karaburun Melange (W Turkey) and the Teke Dere Unit (SW Turkey)

During Late Palaeozoic time a wide ocean, known as Palaeotethys, separated the future Eurasian and African continents. This ocean closed in Europe in the west during the Variscan orogeny, whereas in Asia further east it remained open and evolved into the Mesozoic Tethys, only finally closing during Late Cretaceous–Early Cenozoic. Three Upper Palaeozoic lithological assemblages, the Chios Melange (on the Aegean Greek island), the Karaburun Melange (westernmost Aegean Turkey) and the Teke Dere Unit (Lycian Nappes, SW Turkey) provide critical information concerning sedimentary and tectonic processes during closure of Palaeotethys. The Chios and Karaburun melanges in the west are mainly terrigenous turbidites with blocks and dismembered sheets of Silurian–Upper Carboniferous platform carbonate rocks (shallow-water and slope facies) and poorly dated volcanic rocks. The Teke Dere Unit to the southeast begins with alkaline, within-plate-type volcanics, depositionally overlain by Upper Carboniferous shallow-water carbonates. This intact succession is overlain by a tectonic slice complex comprising sandstone turbidites that are intersliced with shallow-water, slope and deep-sea sediments (locally dated as Early Carboniferous). Sandstone petrography and published detrital mineral dating imply derivation from units affected by the Panafrican (Cadomian) and Variscan orogenies. All three units are interpreted as parts of subduction complexes in which pervasive shear zones separate component parts. Silurian–Lower Carboniferous black cherts (lydites) and slope carbonates accreted in a subduction trench where sandstone turbidites accumulated. Some blocks retain primary depositional contacts, showing that gravitational processes contributed to formation of the melange. Detached blocks of Upper Palaeozoic shallow-water carbonates (e.g. Chios) are commonly mantled by conglomerates, which include water-worn clasts of black chert. The carbonate blocks are restored as one, or several, carbonate platforms that collided with an active margin, fragmenting into elongate blocks that slid into a subduction trench. This material was tectonically accreted at shallow levels within a subduction complex, resulting in layer-parallel extension, shearing and slicing. The accretion mainly took place during Late Carboniferous time. Alternative sedimentary-tectonic models are considered in which the timing and extent of closure of Palaeotethys differ, and in which subduction was either northwards towards Eurasia, or southwards towards Gondwana (or both). Terrane displacement is also an option. A similar (but metamorphosed) accretionary unit, the Konya Complex, occurs hundreds of kilometres further east. All of these units appear to have been assembled along the northern margin of Gondwana by Permian time, followed by deposition of overlying Tauride-type carbonate platforms. Northward subduction of Palaeotethys beneath Eurasia is commonly proposed. However, the accretionary units studied here are more easily explained by southward subduction towards Gondwana. Palaeotethys was possibly consumed by long-lived (Late Palaeozoic) northward subduction beneath Eurasia, coupled with more short-lived (Late Carboniferous) southward subduction near Gondwana, during or soon after closure of Palaeotethys in the Balkan region to the west.

Slope and Submarine Fan Turbidite Facies of the Upper Devonian Imperial Formation, Northern Mackenzie Mountains, NWT

Research Article| June 01, 2009 Slope and Submarine Fan Turbidite Facies of the Upper Devonian Imperial Formation, Northern Mackenzie Mountains, NWT T. Hadlari; T. Hadlari Northwest Territories Geoscience Office, 4601-B, 52nd Avenue, Yellowknife, NWT, X1A 2R3 thomas_hadlari@gov.nt.ca 1Current Address: Geological Survey of Canada, 3303 - 33rd Street NW, Calgary, AB T2L 2A7, thomas.hadlari@nrcan-rncan.gc.ca Search for other works by this author on: GSW Google Scholar S.A. Tylosky; S.A. Tylosky University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3 Search for other works by this author on: GSW Google Scholar Y. Lemieux; Y. Lemieux Geological Survey of Canada, c/o Northwest Territories Geoscience Office, 4601-B, 52nd Avenue, Yellowknife, NWT X1A 2R3 Search for other works by this author on: GSW Google Scholar W.G. Zantvoort; W.G. Zantvoort Northwest Territories Geoscience Office, 4601-B, 52nd Avenue, Yellowknife, NWT X1A 2R3 Search for other works by this author on: GSW Google Scholar O. Catuneanu O. Catuneanu University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3 Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2009) 57 (2): 192–208. https://doi.org/10.2113/gscpgbull.57.2.192 Article history received: 18 Aug 2008 accepted: 30 Mar 2009 first online: 02 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 T. Hadlari, S.A. Tylosky, Y. Lemieux, W.G. Zantvoort, O. Catuneanu; Slope and Submarine Fan Turbidite Facies of the Upper Devonian Imperial Formation, Northern Mackenzie Mountains, NWT. Bulletin of Canadian Petroleum Geology 2009;; 57 (2): 192–208. doi: https://doi.org/10.2113/gscpgbull.57.2.192 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 SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract At the front of the Mackenzie Mountains west of Norman Wells, the Upper Devonian Imperial Formation was deposited by a fan-slope complex that prograded southwest from an eastern basin margin. Laterally extensive submarine fan deposits are composed of intercalated sandstone lobe and lobe fringe deposits. Sandstone lobes are composed of thick-bedded turbidites reflecting high sediment fallout rates. Lobe fringe deposits are thin-bedded turbidites deposited under upper flow regime conditions. Slope facies are shale-dominant, but include turbidites deposited by both fine-grained dilute flows and thin-bedded facies deposited under upper flow regime conditions but low sediment fallout rates. Near the eastern edge of the study area, at Imperial River, shallow marine deposits are preserved above and below slope deposits, a relationship interpreted to record local shelf construction at the basin margin during initial stages of subsidence. Near the western edge of the study area, at Flyaway Creek, Imperial Formation is composed entirely of shale, marking the western extent of well developed base-of-slope submarine fan deposits. In the western area Imperial Formation is overlain by Tuttle Formation sandstone, which marks an increase in the grain size of sediment supplied to the southwestward prograding slope system. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Spatial geochemistry of a Carboniferous platform-margin-to-basin transect: Balancing environmental and diagenetic factors

Conventional (one-dimensional) chemostratigraphy of marine carbonates assesses the chemical archive of individual stratigraphic sections and their correlation in space and time. Whereas this approach has shown to be of value when linking isobathymetric domains, usually characterised by similar facies, more caution is needed when correlations are extended across different physiographic settings and hence different facies belts. Here, the spatial geochemical record of Pennsylvanian platform-margin-to-basin transects across a bathymetric range of about 800 m is documented and discussed in a process-oriented context. Particularly, the presence of layered palaeo-water masses and their potential control on slope facies distribution and geochemical properties requires attention. Whereas Carboniferous thermo- and/or chemo-clines most likely affected depth-related slope facies zonation, it was facies change and hence, variances in porosity–permeability properties, that controlled differential early burial diagenetic alteration. Specifically, the lower-slope related breccia facies is characterised by higher volumes of early burial carbonate cements. This implies that these sediments entered the shallow-burial domain with a considerable open pore space and gave way to an increased rock:fluid ratio. Whereas the δ 13C record is invariant with bathymetry, the more diagenesis-sensitive δ 18O proxy, records pronounced shifts observed across major facies boundaries. From this it is concluded that although the primary controlling factor of slope facies distribution with depth is probably palaeoceanographic in nature, it is differential rock:fluid ratios that control the first-order, spatial shifts in δ 18O composition. These findings show that one-dimensional chemostratigraphy will severely underestimate the complexity of three-dimensional (bathymetric) data sets across platform margins. This is of relevance for the interpretation of the geochemical archive of fossil carbonate platforms in general.

Ordovician metamorphic event in the carbonate platform of the Argentine Precordillera: Implications for the geotectonic evolution of the proto-Andean margin of Gondwana

Research Article| April 01, 2009 Ordovician metamorphic event in the carbonate platform of the Argentine Precordillera: Implications for the geotectonic evolution of the proto-Andean margin of Gondwana Gustavo G. Voldman; Gustavo G. Voldman * 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina *E-mail: gvoldman@efn.uncor.edu Search for other works by this author on: GSW Google Scholar Guillermo L. Albanesi; Guillermo L. Albanesi 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina Search for other works by this author on: GSW Google Scholar Víctor A. Ramos Víctor A. Ramos 2CONICET—Laboratorio de Tectónica Andina, Universidad de Buenos Aires, Buenos Aires C1428EHA, Argentina Search for other works by this author on: GSW Google Scholar Author and Article Information Gustavo G. Voldman * 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina Guillermo L. Albanesi 1CONICET—Museo de Paleontología, Universidad Nacional de Córdoba, Córdoba X5000FCO, Argentina Víctor A. Ramos 2CONICET—Laboratorio de Tectónica Andina, Universidad de Buenos Aires, Buenos Aires C1428EHA, Argentina *E-mail: gvoldman@efn.uncor.edu Publisher: Geological Society of America Received: 27 Sep 2008 Revision Received: 10 Nov 2008 Accepted: 14 Nov 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (4): 311–314. https://doi.org/10.1130/G25540A.1 Article history Received: 27 Sep 2008 Revision Received: 10 Nov 2008 Accepted: 14 Nov 2008 First Online: 02 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 Gustavo G. Voldman, Guillermo L. Albanesi, Víctor A. Ramos; Ordovician metamorphic event in the carbonate platform of the Argentine Precordillera: Implications for the geotectonic evolution of the proto-Andean margin of Gondwana. Geology 2009;; 37 (4): 311–314. doi: https://doi.org/10.1130/G25540A.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 An Ordovician metamorphic event is recorded by means of conodont paleothermometry in the slope sedimentary sequences of the Western Precordillera. Allochthonous conodonts from reworked deposits of the eastern carbonate platform with CAI 4.5–5 and autochthonous conodonts from the olistostrome matrix with CAI 3 allow for constraining the metamorphic age within the Paltodus deltifer and Lenodus variabilis zones (i.e., ca. 480–465 Ma). The conodont data support an Ordovician instead of an alternative Devonian collision for the Cuyania terrane with the proto-Andean margin of Gondwana, which is consistent with the earlier proposed, but still contentious, microcontinent model. In the latter scenario, the collision of the Cuyania terrane caused unroofing and cannibalism of the leading edge of the carbonate succession and basement rocks. The erosion of these rocks supplied detritus and metamorphosed conodonts to the deeper basinal settings of the Western Precordillera. As the deformation front migrated into the peripheral foreland of the Eastern and Central Precordillera, nonmetamorphosed conodonts were eventually incorporated into the west-prograding synorogenic clastic wedge. The occurrence of allochthonous and autochthonous conodonts in the slope facies of the Western Precordillera provides a time constraint for the early accretion of the Cuyania terrane and its transition to an evolving foreland mountain system in the Ordovician period. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.