Reef slope geometries and facies distribution: controlling factors (Messinian,SE Spain)

Sea-level fluctuations and changes in sediment grain size are widely thought to be the main factors controlling carbonate platform slope geometries. Two successive clinoform bodies from the Upper Miocene Cariatiz carbonate platform (SE Spain) were selected to analyze geometry and facies distribution in relation to sea-level oscillations. Facies occurring in these clinoform bodies are from top to bottom reef-framework, reef-framework debris, Halimeda breccia, Halimeda rudstone, and bioclastic packstone, as well as siltstone and marl. Slope geometry and facies, composition, and distribution, are significantly different in each clinoform body. These differences are the result of the interaction of several factors such as coral growth, in situ slope carbonate production, rockfalls and sediment gravity flows, hemipelagic rain, reworking of reef-slope facies and siliciclastic input. Changes in accommodation were related to sea-level fluctuations and controlled the relative impact of these factors. A sea-level fall took place in the time between deposition of the selected clinoform bodies and changed the hydrographical conditions of the basin. These changes influenced the presence of Halimeda and the grain-size distribution, and consequently the slope geometries. Reef-slope geometry is not exclusively controlled by changes in grain size. The stabilization by organic binding is proposed to be a significant factor controlling the slope deposition.     

前科迪勒拉（阿根廷）寒武─奥陶纪牙形刺和沉积演化

阿根廷前科迪勒拉区寒武─奥陶系地层发育。中晚奥陶世时,前科迪勒拉东部与中部山区为浅水陆棚相,西部山区为斜坡─盆地相。牙形刺的分布主要与平静的暖水大洋有关。寒武纪仅发现晚寒武世Ｐｒｏｃｏｎｏｄｏｎｔｕｓ带,此期间有一次海侵事件。在奥陶纪发现了牙形刺并可识别出四次海侵事件三次海退事件和二次缺氧事件。     

滇东,黔西和桂北不同相区的三叠纪牙形刺

本文描述了采自滇东、黔西和桂北不同相区２８个剖面的三叠纪牙形刺共２２属７９种。由于不同相区的牙形刺动物群具有不同的特征,因此不同性质的牙形刺动物群的分布与岩相和古沉积环境关系非常密切。本区三叠纪牙形刺可明显分为两大类型,即“台地型”和“盆地型”。本文论述了牙形刺动物群的分布与岩相相带之关系,组建了不同相区的牙形刺序列,同时讨论了二叠－三叠系界线。     

On quantitative and semiquantitative analysis of the paleozoic-mesozoic nonmarine paleoecosystems

Quantitative analysis of taphocoenoses allows the recognition of dominants and codominants of the main associations and reconstruction of the taph, i.e., simplified skeletal structure of the lower units of the paleocatena, which is a reconstructed sequence of benthic communities on the slope of a sedimentary basin (Zakharov and Shurygin, 1985; Krassilov, 2003). Only aquatic and riparian associations are connected with the lithological characteristics of the taphocoenosis. The composition of zootaphocoenoses allows the hydrological mode of basins to be determined. The frequency ratio of basin and lowland associations is determined by the watering of the bottom of valleys and depressions. The frequency ratio of lowland and slope associations is determined by the ripeness of valleys. The frequency ratio of herbaceous and arborescent slope associations is determined by the ruggedness of terrain adjacent to the basin.     

Silurian carbonate platforms and extinction events—ecosystem changes exemplified from Gotland, Sweden

Recent and ancient carbonate platforms are major marine ecosystems, built by various carbonate-secreting organisms with different sensitivity for environmental change. For this reason, carbonate platforms are excellent sensors for changes in contemporaneous marine environments. A variety of ecosystem changes in carbonate platforms have previously been recognised in the aftermath of mass extinction events. This paper addresses how two Silurian extinction events among graptolites, conodonts, and pentamerid brachiopods can be related to changes in the style of carbonate production and general evolution of low latitude carbonate platforms in a similar way as previously reported from the major five mass extinctions of the Phanerozoic. Strata formed on Gotland during the Mulde and Lau events share remarkably many similarities but are strikingly different in composition compared to other strata on the island. The event-related strata is characterised by the sudden appearance of widespread oolites, deviating reef composition, flat-pebble conglomerates, abundant micro- and macro-oncoids, stromatolites, and other microbial facies suggesting decreased bioturbation levels in contemporaneous shelf seas. Importantly, these changes can be tied to high-resolution biostratigraphic frameworks and global stable isotope excursions. The anomalous intervals may therefore be searched for elsewhere in order to test their regional or global significance.     

A eustatically driven calciturbidite sequence from the Dinantian II of the Eastern Rheinisches Schiefergebirge

Summary The Gladenbach Formation is an approximately 30 m thick, well-segregated calciturbidite sequence, restricted to the H?rre belt of the eastern Rheinisches Schiefergebirge. It is middle Tournaisian in age (lowerPericyclus Stage, lower cd II of the German Culm zonation) and is an equivalent of the Liegende Alaunschiefer. The sequence is composed predominantly of minor turbiditic fining-upward cycles. Cycles start with massive calciturbidite beds. They are composed of fine-grained intraclastic-bioclastic grainstone/packstone, more or less ooid-bearing in the top of the formation, and/or radiolarian-rich packstone. Cycles continue with platy, dense limestones consisting of radiolarian-rich wackestone/packstone and microlithoclastic-microbioclastic wackestone/packstone. Different types of shales finish the fining-upward development. Minor cycles can be grouped into several 4th order cycles, composing a single 3rd order cycle. Towards the top, abundance of resedimented platform components, like ooids, calcareous smaller foraminifers, echinoderms, brachiopods, bryozoans and critical conodont genera, increases. Simultaneously, the thickness of the minor cycles decreases. This indicates a transgressive phase, characterized by increasing over-production of carbonate on platform realms and a correlated increase in the frequency of resedimentation events in the basin. The transgression corresponds to the well-documented global eustatic transgression of the Lowercrenulata andisosticha-uppercrenulata Zone of the conodont chronology. Thus, the Gladenbach Formation is interpreted as a transgressive systems tract/highstand systems tract. The Liegende Alaunschiefer is the time-equivalent, starved basin facies. Predominating hemipelagic calciturbidites of the lower Gladenbach Formation derive from the deeper shelf slope or from an intrabasinal swell, which might constitute a flexural bulge in front of the shelf slope. Turbidite sediments from the upper part of the formation derive from shelf-edge sands and the upper shelf slope. The source might be related to the ancient Devonian reef complex of Langenaubach-Breitscheid in the southwest.     

Robust sequential Factor Analysis of geochemical data from the Permian-Triassic Gartnerkofel-1 core (Southern Alps): the geochemical response to changing paleo-oceanographic conditions in shallow-marine carbonate platforms

The Gartnerkofel-1 core provides a high-quality multi-element dataset that characterizes an Upper Permian to Lower Triassic shallow-marine carbonate sequence (Bellerophon and Werfen Formations) of the Carnic Alps (Southern Alps). Based on the well-known sedimentological evolution, robust sequential Factor Analysis is explored as a multivariate statistical technique to understand geochemical processes in carbonate platforms. The results demonstrate that 93% of the whole-rock compositional variability of the Gartnerkofel-1 core can be explained by the detrital input that is diluted by the carbonate production and the early diagenetic redox state. Two stages of anoxia, one at the Permian/Triassic boundary and one in the Mazzin Member of the Werfen Formation, are related to indicative factor scores. The factor scores within this interval suggest an enhanced dolomitization of shales and marls, a mobilization of manganese, and an accumulation of syndiagenetically precipitated pyrite.     

Facies and biota of Anisian to Carnian carbonate platforms in the Northern Calcareous Alps (Tyrol and Bavaria)

Summary During the Middle and early Late Triassic carbonate ramps and rimmed platforms developed at the northwestern margin of the Tethys ocean. In the Northern Calcareous Alps, Anisian stacked homoclinal ramps evolved through a transitional stage with distally steepened ramps to huge rimmed platforms of Late Ladinian to Early Carnian age. Middle Triassic to early Late Triassic facies and biota of basin, slope and platform depositional systems are described. Special emphasis is given to foraminifers, sponges, microproblematic organisms and algae. The Ladinian to early Carnian reef associations are characterized by the abundance of segmented sponges, microproblematica, biogenic crusts and synsedimentary cements. Among the foraminifers, recifal forms likeHydrania dulloi andCucurbita infundibuliformis (Carnian in age) are reported from the Northern Calcareous Alps for the first time. Some sphinctozoid sponges likeParavesicocaulis concentricus were known until now only from the Hungarian and Russian Triassic.     

Depositional environment and sequence stratigraphy of the Oligo-Miocene Asmari Formation in SW Iran

The Asmari Formation, a thick carbonate succession of the Oligo-Miocene in Zagros Mountains (southwest Iran), has been studied to determine its microfacies, paleoenvironments and sedimentary sequences. Detailed petrographic analysis of the deposits led to the recognition of 10 microfacies types. In addition, five major depositional environments were identified in the Asmari Formation. These include tidal flat, shelf lagoon, shoal, slope and basin environmental settings and are interpreted as a carbonate platform developed in an open shelf situation but without effective barriers separating the platform from the open ocean. The Asmari carbonate succession consists of four, thick shallowing-upward sequences (third-order cycles). No major hiatuses were recognized between these cycles. Therefore, the contacts are interpreted as SB2 sequence boundary types. The Pabdeh Formation, the deeper marine facies equivalent of the Asmari Limestone is interpreted to be deposited in an outer slope-basin environment. The microfacies of the Pabdeh Formation shows similarities to the Asmari Formation.     

Spatial and temporal development of siliceous basin and shallow-water carbonate sedimentation in Oxfordian Northern Calcareous Alps

The Late Jurassic succession of Mount Rettenstein (central Northern Calcareous Alps, Austria) is unique in comparison to all other sections known in the Northern Calcareous Alps because it provides the oldest coexistence of radiolarite basin sedimentation with contemporaneous shallow-water carbonate intercalations. An up to 3.5-m-thick debris flow made up of shallow-water carbonate detritus with a radiolaritic matrix is overlain by thin (calcareous) radiolarite, followed by several hundreds of meters of shallow-water carbonates of the Plassen Formation. Benthic foraminifers (Labyrinthia mirabilis Weynschenk and Alveosepta aff. jaccardi) and the radiolarian associations indicate a depositional age of both the debris flow and the basal Plassen Formation around the boundary of Middle/Late Oxfordian resp. in the Late Oxfordian. This is as yet the first unambiguous evidence of Oxfordian shallow-water sedimentation in the Northern Calcareous Alps. This early neritic stage with the settlement of ooid bars and coral-stromatoporoid-reefs, evidenced by the debris flow resediments in siliceous basin sedimentation, is followed by the definite, rapid progradation of the actual Late Oxfordian/Kimmeridgian–Berriasian Plassen Carbonate Platform with its steep slope configuration. Assumably, this evolution was steered by a mixture of both global environmental and regional tectonic constraints.     

CARBONATE DEPOSITIONAL ENVIRONMENTS, SEQUENCE STRATIGRAPHY AND EXCEPTIONAL SKELETAL PRESERVATION IN THE MUCH WENLOCK LIMESTONE FORMATION (SILURIAN) OF DUDLEY, ENGLAND

Abstract:  The Much Wenlock Limestone Formation of the Dudley inliers, West Midlands, contains one of the world's richest and most exquisitely preserved Silurian marine biotas. However, for most museum specimens, little is known of their exact provenance and mode of preservation. Detailed comparisons between outcrops and museum collections allow the identification of five faunal-lithological associations and numerous horizons of exceptional skeletal preservation. The associations are interpreted as a series of transient carbonate mid-platform environments extending from below storm wave-base to above fair-weather wave-base. Erosive surfaces, condensed sections, flooding surfaces and the stacking patterns of genetically related bed-sets (parasequences) have allowed the formation to be interpreted as a single third-order sequence stratigraphic cycle of sea-level change. The articulated preservation of taxa such as pelmatozoan echinoderms and trilobites can be attributed to either rapid burial by obrution deposits close to fair-weather wave-base or smothering by storm sequestered muds in slightly deeper-water settings. Such intervals of exceptional preservation are commonly associated with flooding surfaces, presumably reflecting reduced likelihood of reworking once rapid burial had taken place.     

Refinements in the Upper Permian to Lower Jurassic stratigraphy of Karakorum, Pakistan

New sampling on critical intervals of the uppermost Permian and Triassic successions of the Northern Karakorum Terrain in the Karakorum Range (Pakistan) has refined the stratigraphy. Two types of successions may be distinguished in the Karakorum Range: a carbonate platform succession, spanning the whole interval from Upper Permian to Upper Triassic, possibly with several gaps; and a basinal succession, deposited from the Middle Permian to Early Carnian (Late Triassic), when the carbonate platform prograded into the basin. With the approaching and later docking of the Karakorum Block against the Asian margin closing the Paleo-Tethys, a portion of Karakorum emerged while another part subsided as a fore-deep, receiving clastics from the emerging Cimmerian Range. Molassic sediments filled the basin, whilst shallow-water carbonates transgressed over the emerged carbonate platform sometime between the latest Triassic and the Pliensbachian (Early Jurassic), with Cimmerian deformation occurring to the north. The age control is provided by conodonts, with assemblages of late Wuchiapingian, Changhsingian, Induan (Griesbachian and Dienerian), late Olenekian, early Anisian, late Ladinian, and early Carnian ages, respectively. Some information on the section around the P/T boundary is provided by palynology and isotopic C¹³ values. The dating of the Norian/Rhaetian platform is provided by foraminifers.     

Depositional sequences in the Kimmeridgian of the Vocontian Basin (France) controlled by carbonate export from shallow-water platforms

Detailed sedimentological analyses and sequential and cyclostratigraphic interpretations in the Kimmeridgian of the Swiss Jura and the Vocontian Basin lead to a high-resolution correlation from the platform to the basin where the biostratigraphy is well established. Several orders of depositional sequences are defined. Their duration is estimated from the time frame given in the sequence-chronostratigraphic chart of Hardenbol et al. (1998). It is suggested that an elementary sequence formed in tune with the 20 ky precession cycle. Small-scale and medium-scale sequences correspond to the 100 and 400 ky eccentricity cycles, respectively. The platform-to-basin correlation shows that the composition of the hemipelagic and pelagic deposits depends to a large part on cyclical variations of carbonate production in shallow-marine environments and subsequent export to the basin. The distribution of thick versus thin marl-limestone alternations and carbonate-dominated versus marl-dominated intervals observed in the basinal sections is explained by the superposition of high- and low-frequency sea-level changes that controlled the carbonate productivity on the platform and the export potential of carbonate mud to the basin.     

Charophyte-rich microfacies in the Barremian of the Eastern Iberian Chain (Spain)

Non-marine carbonate microfacies based on charophytes are a useful palaeoenvironmental tool that has been poorly developed to date. In the Barremian of the Maestrat Basin (Eastern Iberian Chain), five such microfacies are described and interpreted in terms of sedimentology and palaeoecology: (1) Microfacies of clavatoracean remains are mudstones and wackestones rich in utricles and well-preserved charophyte thalli of the genus Clavatoraxis, representing in situ deposition of clavatoracean meadows. (2) Microfacies of filamentous algae and clavatoraceans are mudstones with a high proportion of calcified filaments attributed to cyanobacteria and green algae. This facies may correspond to the open lake benthos. (3) Microfacies of Intraclasts and Charophyte remains are packstones formed on the shores of freshwater lakes or brackish swamps that underwent subaerial desiccation and wave reworking. (4) Microfacies of Porocharacean remains are wackestones and packstones with abundant gyrogonite fragments of genus Porochara. They are related to the reworking of a porocharacean meadow in shallow brackish marshes. (5) Microfacies of Munieria grambasti Bystricky 1976 fragments are grainstones attributed to the reworking of Munieria-dominated meadows. In consequence to these results, a palaeoecological model based on charophyte remains is proposed as a useful tool in carbonate facies analysis.     

湘西北晚二叠世-早三叠世早期牙形石古生态

通过对牙形石器官的对称性、相分布和地球化学特征的研究,探讨湘西北晚二叠世至三叠纪初牙形动物的生态分布.按器官所包括不同对称型分子的比例,牙形动物器官的对称性可分为4级,器官的对称性越高,动物运动能力越强.湘西北晚二叠世一三叠纪初地层可分为6种沉积相,即盆地相、盆缘-台坡相、开阔台地相、边缘浅滩相、局限台地相和泥坪相.具不同对称级器官的属种在6种沉积相中的差异分布,反映了牙形动物的3种生态类型:自由游泳型、浮游型和底栖型.牙形石地球化学组分的变化与当时环境演变相吻合.随水深增加,化石中的P含量升高,而Ca、s、sr的含量降低;Al、Fe和Ba在近岸浅水环境的牙形石中富集;而Mg的富集指示高盐环境.基于上述研究,划分了4个牙形石相,建立了一个组合横向替代的牙形动物生态分布模式.     

The oldest Ordovician foraminifers (Oepikodus evae conodont Zone, Floian) from South America

The oldest occurrences of the monothalamous foraminifer species Amphitremoida longa Nestell and Tolmacheva and A. laevis Nestell and Tolmacheva are found in the San Juan Formation together with conodonts of the Oepikodus evae Zone of the Floian (Lower Ordovician), in the Salagasta 2 section, southern Precordillera, Argentina. These discoveries represent the oldest record for foraminifers in South America. The foraminifers, species of which were originally described from the Lower Ordovician of northwestern Russia, are found in shallow high energy carbonate platform deposits in the Precordillera, together with a North Atlantic province conodont fauna. The carbonate sequence of the San Juan Formation in the Salagasta region is interpreted as a succession ranging from shallower tidal deposits to carbonate crinoidal shoaling bar deposits.     

Longitudinal Distribution of the Functional Feeding Groups of Aquatic Insects in Streams of the Brazilian Cerrado Savanna

We demonstrate that the distribution of the functional feeding groups of aquatic insects is related to hierarchical patch dynamics. Patches are sites with unique environmental and functional characteristics that are discontinuously distributed in time and space within a lotic system. This distribution predicts that the occurrence of species will be based predominantly on their environmental requirements. We sampled three streams within the same drainage basin in the Brazilian Cerrado savanna, focusing on waterfalls and associated habitats (upstream, downstream), representing different functional zones. We collected 2,636 specimens representing six functional feeding groups (FFGs): brushers, collector–gatherers, collector–filterers, shredders, predators, and scrapers. The frequency of occurrence of these groups varied significantly among environments. This variation appeared to be related to the distinct characteristics of the different habitat patches, which led us to infer that the hierarchical patch dynamics model can best explain the distribution of functional feeding groups in minor lotic environments, such as waterfalls.     

Stratigraphic modelling of carbonate platform-to-basin sediments (Maastrichtian to Paleocene) in the Eastern Desert, Egypt

In the Galala Mountains of the Eastern Desert, Egypt, carbonate platform and basin deposits have excellent exposure. These exposures show a late Campanian–early Paleocene rimmed platform evolving into a late Paleocene distally steepened ramp. We modelled the evolution of the platform–basin transition from the Maastrichtian to Selandian (68.7–59 Ma) with the 2-D stratigraphic simulation program PHIL and compared the modelled results with outcrop sections. Stratigraphic, facies, and environmental data are summarized and operate as input and control parameters for the computer simulation. The most important parameters that control the depositional geometries of the late Cretaceous mixed carbonate siliciclastic platform and the Paleogene carbonate platform are changes in relative sea level, sediment flux and initial topography. The simulation provides an understanding of platform growth and slope to basin deposition, particularly in areas of the platform that are poorly exposed or have been eroded. Moreover, the simulated geologic parameters like lithology, overall thickness and palaeowater depth closely resemble field and laboratory measurements of the individual sections. In an earlier study, the Maastrichtian slope angle was calculated to be 5–8° and this was confirmed in this study. In this earlier study also the timing of the transition from a rimmed platform to a distally steepened ramp was established to be during latest Maastrichtian–early Paleocene. The present study shows that the rimmed platform persisted at least until the late Paleocene (59 Ma), as indicated by the relatively high slope angle of 6°.     

Genesis of stromatactis in an upper jurassic carbonate buildup (Mlynka,Cracow region,Southern Poland): Internal reworking and erosion of organic growth cavities

Summary The Middle Oxfordian strata in the southern part of the Cracow-Wielun Upland consist of platy and bedded limestones (‘normal facies’), of massive limestones as well as locally of mass flow sediments. Massive limestones, prevailing in the Upper Oxfordian, form commonly carbonate buildups, which are made up predominantly of cyanobacterial allochems and to a minor amount of siliceous sponges. Stromatactis can be best observed in the Mlynka quarry. They occurs in the uppermost part of slope sediments close to a cyanobacterial-sponge buildup. The bedding-plane of the slope sediments is directly overlain by debris-flow and grain-flow sediments. Fragments of a primary laminar framework rich in growth-cavities occur in the uppermost part of the slope sediments as precondition for the formation of stromatactis. The stromatactis cavities were formed by internal reworking and erosion within these organic growth cavities, caused by strong bottom currents due to mass transport from higher parts of the buildup.     

Sedimentary and biofacies records in calciturbidites at the Devonian-Carboniferous boundary in Moravia (Moravian-Silesian Zone, Middle Europe)

Summary At the Devonian/Carboniferous boundary, major climatic and oceanographic changes influenced sedimentation on carbonate platforms and in peri-platfrom asreas. Three deep-water carbonate successions in Moravia, which were selected to represent different paleotectonic settings, have been studied with the aim of testing the influence of eustatic, climatic and tectonic controls on sedimentation and conodont paleoecology and taphonomy. On the slopes of the wide carbonate platforms of the Moravian Karst Development (Lesní lom and Grygov sections), an exemplary highstand shedding systems developed in the upper Famennian (expansa Zone), marked by a pronounced thickness of their respective calciturbidite successions and an abundance of shallow-water skeletal grains.Palamatolepis— andBispathodus-dominated conodont assemblages contain an admixture ofPolygnathus representing a transported, near-shore component. The eustatic sea-level fall in the praesulcata Zone and the lowstand conditions at the D/C boundary resulted in a decline of carbonate platform production and condensed deposition or nondeposition. In the Lesní lom section, a condensed sequence of turrbiditic calcarenites and shales (Middle praesulcata—lowermost sulcata Zone) was followed by lime mud calciturbidites (sulcata and duplicata Zones). In the conodont assemblages, the first event in the Lower praesulcata Zone was associated with the reduction of ‘mesopelagic’Palmatopic and a bloom of epipelagicPolygnathus communis. The second event in the Middle praesulcata Zone corresponds to the onset of polygnathidprotogranthodid biofacies, indicating a carbonate slope environment. In the Grygov section, a pronounced thickening and upward-coarsening succession of tubiditic calcilutites through calcarenites and intraclast breccias, with poor palmatolepid-bispathodid connodont assemblages (expansa Zone), indicates a progradation of the calciturbidite system associated with sea-level highstand. After a break in sedimentation, covering the interval from the Lower praseulcata to the base of Lower crenulata Zone, thick-bedded, fine-grained calciturbidites were deposited in the Lower crenulata Zone, and are associated with poor, mixed assemblages where siphonodellids and polygnathids predominate. At the isosticha-Upper crenulata/Lower typicus boundary, coasre grained, turbiditic calcarenites and breccias rich in clastic quartz grains and mixed conodont assemblages with reworked Frasnian and Famennian conodonts indicate a deep erosion of the source area, presumably due totectonic uplift (relative lowstand). In the Jesenec section, on the flanks of the volcanic seamount (the Drahany Development), a deep-water Upper Famennian condensed succession of calciturbidites and presumably winnowed pelagic limestones is marked by conodont assemblages of palmatolepid-bispathodid biofacies. More proximal calciturbidites with mixed deep-water and shallowwater conodonts prograde at the top of the Upper Famennian succession (Middle to Upper expansa Zone). A striking hiatus, covering the interval from the Early preaesulcata to the base of Lower crenulata Zone, resulted from extreme condensation and submarine bottom current erosion due to sea-level lowstand in the late Famennian and early Tournaisian. The renewed middle Tournaisian calciturbidite sedimentation with strong evidence of erosion at the source area indicates global eustatic rise and tectonic uplift of the Drahany Development seamounts (relative lowstand). The earlier occurrence of the uplift in the Jesenec area, relative to the Grygov section, shows the advance of tectonic processes over time in the Moravian-Silesian basin (orogenic polarity) as a consequence of Variscan orogenic movements.