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Serravallian (middle Miocene) coralline algal assemblages at the southern margin of the Guadalquivir Basin (southern Spain) occur as rhodoliths preserved in situ or very close to their growth habitats (autochthonous–parautochthonous assemblages) and also as reworked remains (allochthonous assemblages). The former assemblages consist of spherical rhodoliths built up by encrusting to warty plants and also of large fragments of branches, whereas the latter are mostly unrecognizable small fragments occurring in channeled packstone–grainstone beds. In both cases, the most abundant components are members of the order Hapalidiales (Mesophyllum roveretoi, Mesophyllum sp., Lithothamnion ramosissimum, and less frequently Phymatolithon group calcareum and Lithothamnion group corallioides). Laminar growths of Lithoporella minus and branches of Spongites group fruticulosus and Sporolithon sp. occur very rarely. There are also anecdotal records of Subterraniphyllum thomasii, extending its upper stratigraphic range up to the Serravallian in the western Tethys. The autochthonous–parautochthonous coralline algal assemblages formed in a middle ramp, at several tens of meters of water depth, as suggested by the dominance of Hapalidiales. The allochthonous assemblages represent fragments of coralline algae derived from the middle ramp and redeposited in deeper settings, most likely the outer ramp, due to storm-generated currents.

The late Miocene is a crucial interval for global climate evolution as well as for the regional geodynamic evolution of the Central Mediterranean area. It spans the transition from the warm Mid Miocene Climatic Optimum, associated with the major Monterey Carbon Isotope Excursion, to the cooler Pliocene, characterized by a bipolar glaciation. Within this climatic transition, during the early Tortonian, a positive carbon isotope excursion related to a global carbon cycle perturbation is recorded, named Carbon Maximum 7 (CM7). In this study, two upper Serravallian–lower Tortonian carbonate ramps of the Central Mediterranean have been analysed: the Latium‐Abruzzi and the Apula ramps (Central Apennines, Central Italy). Carbon isotope ratios have been coupled with facies and microfacies analyses with the aims: (1) to identify the CM7 in the Central Mediterranean carbonate ramp successions; (2) to evaluate potential carbonate factory changes or demises related to the CM7; and (3) to discriminate the role of global vs regional factors in affecting the Mediterranean carbonate ramps. The two studied ramps show different evolutions due to regional geodynamics causes. The Latium‐Abruzzi ramp drowns in the Tortonian, while the Apula shows a regressive trend, with upper Tortonian middle ramp facies overlying the lower Tortonian outer ramp. Despite the complex geodynamic setting, a positive carbon isotope shift has been identified in both ramps and correlated with the CM7. This positive carbon isotope shift may be linked to the strengthening of the global ocean circulation during the late Miocene cooling. This strengthening of the circulation enhanced the coastal upwelling, bringing nutrient‐rich waters to the surface and triggering an enhanced primary productivity consistent with the CM7. [ABSTRACT FROM AUTHOR]

is a characteristic trace fossil in the Mississippian in the Alborz Basin deposits of north Iran, and is described for the first time in the Mobarak Formation. The vertical distribution of the carbonate deposits bearing Zoophycos provided the basis for distinguishing three distinct types of sedimentary sequences including Zoophycos (type A, B, and C) in shallow marine sediments of Mobarak Formation. Type A is composed of rare to common density of small to medium lobed Zoophycos. Type B is characterized by common density of medium lobed Zoophycos. This ichnogenus in type A and B is associated with Palaeophycus. The low diversity and bioturbation of the trace fossils would be the result of a stressful environment characterized by optimal water circulation and high-energy conditions. Type C consists of abundant density of large lobed Zoophycos. Type C is associated with Chondrites and planolites. The high diversity and bioturbation of the trace fossils in type C than type A and B would be the result of a calm environment characterized low-energy conditions. Under low sedimentation rate, stable paleoenvironment, dysaerobic conditions, and high amount of benthic food, the size of Zoophycos is the biggest, whereas in the high sedimentation rate, unstable paleoenvironment, aerobic conditions, and shortage of benthic food, the size of Zoophycos is small. [ABSTRACT FROM AUTHOR]

Meteoric diagenesis of carbonate ramps is often difficult to interpret and can commonly be confused with other coinciding diagenetic processes. The Middle Triassic Upper Muschelkalk of Switzerland provides an insightful case in which the effects of several overprinting diagenetic environments, including matrix dolomitization, can be clearly unravelled. Previous studies suggested that diagenesis took place in connate marine waters, with later meteoric waters being invoked to explain recrystallization of dolomite. In this study, diagenetic analyses (C–O stable isotope ratios, thin-section point counting, cathodoluminescence and UV-fluorescence microscopy) of calcitic bioclastic samples have revealed that early diagenesis (pre-stylolitization) and the accompanying porosity evolution did not occur exclusively in the presence of marine fluids. Five sequential stages of diagenesis have been identified: marine, shallow burial, mixing-zone, meteoric and dolomitization. Marine diagenesis induced precipitation of bladed and inclusion-rich syntaxial cements that fluoresce strongly under UV-light. Both cements account for a mean 7.5 vol% reduction in the porosity of bioclastic beds. Shallow burial diagenesis likely induced mouldic porosity and associated fluorescent dog-tooth cementation. Based on light oxygen isotope and elevated strontium isotope ratios, matrix aragonite–calcite neomorphism is interpreted to have occurred in a mixture of marine and meteoric fluids. The combination of shallow burial and mixing-zone processes reduced porosity on average by 4.8 vol%. Evidence for subsequent meteoric diagenesis is found in abundant dog-tooth and blocky calcite cements that have mean δ 18 O VPDB of − 9.36‰ and no signs of recrystallization. These meteoric cements reduced porosity by a further 13.4 vol%. Percolation of meteoric water through the ramp was driven by hydraulic gradients on an adjacent basement high, which was exposed by a cycle of early Ladinian regressions. Following meteoric diagenesis the Upper Muschelkalk was dolomitized by refluxing brines. This complex history of diagenesis resulted in moderate porosities in dolomitized rocks (up to 20%), and low porosities (< 5%) in calcitic bioclastic beds. These results are used to show that the present-day reservoir properties of non-dolomitized carbonate rocks, particularly bioclastic beds, can be largely attributed to early diagenetic processes. Thus, knowledge of the early diagenetic history and its regional controls provides a means to predict reservoir properties over wide areas between and beyond well sites. [ABSTRACT FROM AUTHOR]

Detailed study on the Lower Ordovician Mungok Formation in the mideastern part of the Korean peninsula has led to recognition of seven lithofacies which can be grouped into seven facies associations (FAs): FA1 ( lagoon), FA2 ( shoal), FA3 ( shoreface), FA4 ( inner to mid-ramp), FA5 ( inner to outer ramp), FA6 ( mid- to outer ramp), and FA7 ( outer ramp). Spatio-temporal organization of the FAs represents homoclinal ramp environments with fringing ooidpeloid shoals. Correlation and lateral thickness variation of the FAs suggest that deep part of the basin might have been located toward the northern part of the study area. The relative sea-level curve inferred from the facies analysis suggests that the Mungok Formation evolved through three depositional stages in accordance with 3rd-order sealevel change. The organization of the facies succession indicates that the inner ramp facies associations (FA1 to 3) of the Mungok Formation are characterized by non-cyclic facies succession whereas the midand outer ramp facies associations (FA 4 to 7) have distinct cyclicity except non-cyclic FA 7. The difference in the facies successions between the inner ramp and the mid- to outer ramp area may result from the various depositional regime across a ramp. A non-cyclic facies successions of inner ramp facies (e.g., packstone to grainstone and lime mudstone) are suggestive of mosaic-type distribution that is controlled mostly by wave, storms, tides, currents, and local geomorphology. In contrast, cyclic facies successions (e.g., pebbly limestone conglomerate, limestone-shale alternation, and calcareous shale) represent a simple belt-type distribution of mid- to outer ramp facies that seems to reflect shifts of facies belt caused by sea-level changes. The partitioning of inner and mid- to outer ramp facies is appropriate for understanding the facies development of the Mungok Formation and similar ramp successions with distinct inner and mid- to outer ramp facies. [ABSTRACT FROM AUTHOR]

Abstract: The Neoproterozoic Wynniatt Formation, part of the upper Shaler Supergroup, is exposed in the Minto Inlier of Victoria Island, Canada, and was deposited in the intracratonic Amundsen Basin. The unit consists of a southwest-thickening (480 to 1000m over ~300km) shallowing-upward succession of three carbonate ramp sequences separated by regional unconformities. In ascending order: 1) inner to outer ramp carbonate facies, gradationally overlain by siliciclastic rocks of a pro-delta slope setting; 2) inner to mid-ramp subtidal carbonate facies, including a regional stromatolitic barrier system; and 3) outer ramp carbonate (gravity flow) facies overlain by shallowing-upward subtidal to intertidal, mixed siliciclastic-carbonate inner ramp facies. Spatial arrangements of nineteen lithofacies illustrates that each carbonate ramp sequence represents part of a distally steepened, storm-dominated carbonate ramp, with an interval of deep-water carbonate rocks coincident with oceanic restriction that elevated salinity. Migration of depocentre loci for successive ramp stages reflects changing patterns of subsidence. This may identify far-field extensional effects in this intracratonic basin because ages of the lower (~850Ma) and middle (~761Ma) formation bracket initiation of supercontinent (Rodinia) break-up. Our work offers an improved sedimentary framework for interbasinal correlation with coeval Neoproterozoic basins. It highlights temporal changes in carbonate facies compared to older carbonate successions in the Shaler Supergroup, and it defines depositional context for the Tawuia-Chuaria assemblage zone, providing important interbasinal biostratigraphic correlation. [Copyright &y& Elsevier]

La sedimentación en la cuenca ibérica septentrional durante el Kimmeridgiense tuvo lugar en una extensa rampa carbonatada de bajo ángulo. Las facies de rampa externa, acumuladas por debajo del nivel de base del oleaje debido a tormentas (i.e., C. 50 to 80 m de profundidad), están formadas por una ritmita de margas y calizas (i.e., Fm Loriguilla). Las facies de rampa interna, localizadas por encima del nivel de base del oleaje de buen tiempo (i.e., hasta 10 m de profundidad), están dominadas por bioconstrucciones de corales (i.e .. Fm Torrecilla). Las facies de rampa media están representadas por margas y micritas con niveles de tempestitas bioclásticas y oolíticas que pasan lateral y verticalmente a sandwaves oolíticos de gran amplitud (i.e., Mb. Ricia). La modelización por ordenador ha permitido cuantificar algunos aspectos de esta rampa. Así, la distancia de resedimentación mar adentro del sedimento de grano fino producido en las zonas internas de la rampa, por el efecto de tormentas, puede ser de hasta 40 Km. La producción de carbonato oscilaría entre 8 y 2 cm/l.000 años. en función de la profundidad. Por otra parte, la curva de la variación de la acomodación deducida para el Kimmeridgiense está compuesta por tres elementos: un ascenso lineal de 4 cm/l.000 años. un ciclo de tercer orden de baja amplitud y ciclos de mayor orden. de 20.000 y 100.000 años respectivamente. Tanto el ascenso lineal como el ciclo de tercer orden se han relacionado con causas regionales, mientras que los ciclos de mayor orden se encuentran en la banda de Milanckovich y pueden ser por tanto de origen eustático.

Abstract: A mixed carbonate–siliciclastic succession developed on the southern margin of the Bonifacio Basin (Cala di Labra, SE Corsica) during the Burdigalian, in the margin of a back-arc setting which had formed during the Sardinia-Corsica block rotation. This shallow marine setting was fed by abundant nearshore siliciclastic supply, and substantial carbonate production/accumulation increased from the euphotic to the oligophotic zones. Two third-order depositional sequences (SD1, SD2) corresponding to Bur 3 and Bur4, are recorded in the sedimentary succession. [Copyright &y& Elsevier]

Abstract: High-diversity marine biotic communities characterize the lower Kasimovian (Upper Pennsylvanian) carbonates of the Las Llacerias Formation in the Ándara Massif (Picos de Europa Province, Cantabrian Mountains, Spain). The carbonates accumulated on a small thrust-top ramp system. Within the shallow, low-energy and euphotic realms, biotic communities were characterized by abundant photozoans (calcareous algae and cyanobacteria) and heterozoans including filter and suspension feeders (calcareous and siliceous sponges, bryozoans, brachiopods, crinoids), diverse other metazoans (rugose solitary and colonial corals, tabulate corals, bivalves, gastropods and echinoids), benthic foraminifers including very abundant small incrusting “tubiforms” and conspicuous swarms of cement-filled spheres (calcispheres or Penella). Small-sized buildups of chaetetid sponges, syringoporids, branching rugose corals, Anthracoporella and phylloid algae commonly developed in these shallow-water environments. Meanwhile, mud mounds formed at greater water depths, mostly below the lower limit of the phothic zone. The occurrence of such diverse biotic communities and the grain composition of the shallow-water deposits, not recorded in the platform-top successions of the antecedent Bashkirian–Moscovian carbonate shelf (Valdeteja and Picos de Europa formations) are interpreted as linked to increased nutrient levels (mesotrophic to mildly eutrophic conditions) in the actual sea-surface water. The nutrients are inferred to have resulted from land-derived fluxes from the rivers draining the adjacent growing Variscan Orogenic chain. Nutrients were subsequently transported into the narrowed marine shallowing foreland basin located in the eastern side of Pangea, within the palaeoequatorial humid belt. Comparison to the Pennsylvanian Auernig Group in the Carnic Alps allows the discrimination between the influence of land-derived versus upwelling-derived nutrients, providing a useful tool in the interpretation of biotic assemblages in the fossil rock record. [Copyright &y& Elsevier]

Abstract: The Ediacaran–Early Cambrian Ara Group in the South Oman Salt Basin consists of six evaporite–carbonate cycles (A0/A1 to A6) that record tectono-eustatic sea-level changes. The A4 cycle developed at the Precambrian–Cambrian boundary (∼542 Ma). It forms a single depositional sequence with evaporites deposited in a lowstand systems tract (LST). Overlying carbonates represent an open-marine shallowing-upward ramp succession that developed in transgressive (TST) and highstand systems tracts (HST). The low-energy carbonate ramp occupied a relatively protected site between a large shelf and an exposed paleogeographical high. The TST facies include sulfates, evaporite–carbonate laminites, and organic-rich carbonate laminites that record initial flooding, deepening of the basin, and establishment of an outer ramp depositional environment. Carbonate sediment flux was low and the environment was partly subject to cyclically elevated salinity. Subsequent HST facies comprise mostly fine-grained clastic carbonates and stromatolites that formed in middle and inner ramp settings. These facies show evidence of shoaling and establishment of a carbonate factory that probably operated over most of the middle and inner ramp. Sediment was redistributed in suspension, by muddy turbidity currents, muddy debris flows, storm and shallow-water currents. During the late HST, carbonate facies were affected by elevated salinity and recorded the gradual transition to the overlying LST evaporite unit. A combination of strong tectonic subsidence and transient flooding caused significant shallow-water evaporite deposition to occur not only down dip, but also on top of the former carbonate platform, where several hundreds of meters of evaporites accumulated. The transgressive carbonate laminites are the main reservoir facies and thus represent a relatively unusual reservoir unit. The presence of organic material and the relative scarcity of carbonate mud influenced diagenesis and reservoir properties. Distribution of organic material and carbonate mud can be linked to specific environmental conditions (low physical and biogenic disturbance of sediment and stratified water mass) and the sequence stratigraphic position (low flux of fine-grained carbonate during TST). In contrast, diagenetic evaporite formation has largely degraded reservoir quality in porous shallow-water facies near the top of the A4C. [Copyright &y& Elsevier]

The Peerless Park Member [Keokuk Limestone, Lower Carboniferous (Visean, Mississippian)], exposed in the St. Louis, MO, area includes a carbonate-filled channel complex with lithology and faunal elements distinct from under- and overlying strata. The complex is confined within a channel of 100-m apparent width that is under- and overlain by cherty, glauconitic crinoid–bryozoan–skeletal wackestone, packstone and grainstone with abundant hardgrounds and little evidence for wave or current energy. Laterally, the valley includes two subchannels separated by a subtle high. The deeper subchannel truncates up to 5 m of strata.The maximum thickness of the channel fill and associated deposits is 6 m. The channel fill includes a matrix-supported conglomerate locally at its base, non-cherty quartz silty–foraminifer–peloid–crinoid–bryozoan–skeletal grainstone with spectacular lateral accretion foresets up to 5 m thick, and cherty skeletal packstone. A capping foraminifer–skeletal grainstone is erosionally overlain by a 10-cm thick quartz siltstone that grades up into glauconitic crinoid–bryozoan–skeletal wackestone and packstone.On the channel flanks, correlative strata of the Peerless Park Member are less than 1 m thick, and include a lower non-cherty crinoid–foraminiferal–skeletal grainstone, a middle cherty packstone and an upper skeletal grainstone. The upper grainstone is in turn erosionally overlain by the thin quartz siltstone that abruptly grades into the crinoid–bryozoan–skeletal wackestone and packstone of the upper part of the Keokuk Limestone.The strata of the Peerless Park Member are interpreted to be the result of a relative fall of sea level that places shallow water, high-energy inner ramp grainstone immediately above deeper water, outer ramp packstone and grainstone. There is no evidence for gradual downward or basinward migration of facies belts. Instead, shallow water facies appear to have abruptly jumped downdip. Likewise, no field or petrographic evidence for subaerial exposure has been recognized, so the relative fall in sea level may not have subaerially exposed the area. This occurrence of an isolated, downdip carbonate grainstone filled channel complex not accompanied by progradational, forced regressive deposits appears to be unique in carbonate ramp depositional systems and the channel includes fill with character different from many previously documented ramp carbonate-filled channels. [Copyright &y& Elsevier]

A study of the paleoenvironmental evolution of the middle Eocene platforms recognized in the westernmost Tethys has been carried out in the well-exposed middle Eocene succession from Sierra Espuña-Mula basin (Betic Cordillera, S Spain). Eight microfacies (Mf1 to Mf8) have been recognized, based mainly on fossil assemblages (principally larger benthic foraminifera), and rock texture and fabric. The fossiliferous assemblage can be assigned to the 'subtropical' heterozoan association or to the low-latitude 'foralgal facies', which are dominated by non-framework building, light-dependent biota such as perforate larger benthic foraminifera, coralline algae, and sometimes green algae and solitary corals. Larger benthic foraminifer assemblages, corresponding from euphotic to oligophotic conditions and the large surface showed, suggest a progressive marine ramp under essentially oligotrophic conditions. Eventually, supply of detrital sediments from the continent and/or upwelling currents increases the nutrients of marine waters. Comparison with other Tethyan sectors allows stating that coral-reef buildups (z-corals) were widespread on shallow platforms of the central and eastern Tethys Ocean, but these were neither of great dimensions nor dominant because of the much more dominant presence of larger benthic foraminifera. Moreover, these coral constructions were completely absents in the westernmost Tethys. The dominance of larger benthic foraminifera and the absence of z-corals in the westernmost Tethys are explained by particular paleogeographic features due to the occurrence of a narrow and deep oceanic branch (i.e., the Maghrebian Flysch Basin) connecting the Tethys with the Atlantic Ocean. The various issues regarding the morphological characters and evolution of larger benthic foraminifera in the study area, such as sizes of tests, specific diversity and/or intraspecific variability, number of appearances and last occurrences during the middle Eocene are analyzed and compared with those appearing in other Tethyan sectors. In addition, the early to late Bartonian boundary is recognized in the study area as critical for the biological change as in other shallow-marine environments along the Tethys margins. [ABSTRACT FROM AUTHOR]