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Diethard Sanders - One of the best experts on this subject based on the ideXlab platform.
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Shell disintegration and taphonomic loss in rudist Biostromes
Lethaia, 2007Co-Authors: Diethard SandersAbstract:Radiolitid Biostromes in the Upper Cretaceous of Austria and Italy record a marked taphonomic loss controlled mainly by the composition of the biocoenosis, by the density of rudist colonization, by the style of radiolitid shell disintegration and by early diagenetic processes. Radiolitid shells consisted of a calcitic ostracum and an originally aragonitic hypostracum. The attached valve of most radiolitids was built of (1) an outermost ostracal layer of delicate calcite lamellae, (2) a thick layer of ‘boxwork ostracum’ built of radial funnel plates and cell walls, (3) a thin, inner ‘ostracal layer 3’ of thick-walled boxwork, and (4) the hypostracum that formed the innermost shell layer. The attached valve disintegrated by spalling of radial funnel plates of layer 2, and by selective removal of the boxwork ostracum. In the free valve, the ostracum consisted of two layers: (a) an inner, lid-shaped layer of dense calcite, and (b) an outer layer composed of calcite lamellae. The free valve disintegrated by spalling into ostracal and hypostracal portions, by spalling of the ostracum into layers a and b, and by disintegration of layer b into packages of calcite lamellae and individual lamellae. The specific style of disintegration of the radiolitids was aided or induced by discontinuities in shell structure. Lamellar fragments from the ostracum of the upper valve and from the radial funnel plates of the lower valve locally are abundant in free-valve-funnel-plate floatstones that comprise the matrix of or occur in lenses within radiolitid Biostromes. In Biostromes with an open parautochthonous fabric, selective removal of the boxwork ostracum of the attached valve occurred by mechanical spalling and, most probably, by early diagenetic dissolution. Complete removal of the boxwork ostracum yielded thin, relict shells composed of the ‘ostracal layer 3’ and the hypostracum. During early diagenesis, the hypostracum was replaced by blocky calcite spar, or was dissolved and became filled by internal sediments. The combination of both selective removal of boxwork ostracum and early diagenetic dissolution of aragonite locally resulted in the formation of ghost Biostromes that entirely or largely consist of faint relics of radiolitids. The syndepositional formation of radiolitid shell relics and the presence of radiolitid ghost Biostromes produced by bios-tratinomic and early diagenetic processes show that rudist Biostromes can undergo marked taphonomic loss during fossilization. The presence of ghost Biostromes with a burrowed, open parautochthonous rudist fabric indicates that the final preservation of a rudist Biostrome was directly influenced by the characteristics of the biocoenosis, including unpreserved burrowing taxa. Rudist Biostromes may be of markedly different taphonomy as a result of the taxonomic composition of the entire assemblage and the density of colonization by the rudists.
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Burrow-mediated carbonate dissolution in rudist Biostromes (Aurisina, Italy): implications for taphonomy in tropical, shallow subtidal carbonate environments
Palaeogeography Palaeoclimatology Palaeoecology, 2001Co-Authors: Diethard SandersAbstract:Abstract In Upper Cretaceous rudist Biostromes at Aurisina, Italy, marked taphonomic loss of radiolitids by burrow-mediated dissolution and mechanical disintegration illustrates the relation between synecology and early diagenesis in the fossilization of tropical shallow-water bioconstructions. The studied platform succession accumulated in a prevalently open lagoon with bioturbated carbonate sand, rudist thickets, bioclastic dunes, and areas with shelly lime ooze. Rudist Biostromes consist of radiolitids and hippuritids, or of radiolitids only, and have an open, parautochthonous rudist fabric with a matrix of bioclastic, bioturbated wackestone. “Swirly” disorientation of bioclasts records early softground bioturbation. Later firmground burrows comprise an irregular network of tunnels and chambers filled with bioclastic packstone to grainstone. The size, geometry and sediment fill of the firmground burrows suggest that they were produced by crustaceans. Radiolitid preservation ranges from complete to relictic. Radiolitid relicts formed by (a) spalling and/or dissolution of the cellular boxwork ostracum of the attached valve, leaving “calcite-tubes” built by a distinct, thin ostracal shell layer, or (b) dissolution of the entire shell, leaving the sedimentary fills of the intertabular spaces of the attached valve as a diagnostic vestige, or (c) shell dissolution within the firm sediment, with subsequent filling of the biomould by bioclastic wackestone to packstone to grainstone. Loss of radiolitids produced a taphonomic bias towards rudists with non-cellular ostracum. Locally, taphonomic loss produced “ghost Biostromes” composed nearly entirely of faint radiolitid relicts. Shell dissolution resulted from chemical gradients in the sediment within and near the burrows, and from enhanced microboring and microbial infestation. Dissolution of radiolitids was favoured by the combined effects of chemical instability of hypostracal aragonite and by the structure of the calcitic boxwork ostracum of thin-walled cells. Some Biostromes are intercalated with, or are capped or overlain within a short vertical distance, by a hardly recognizable emersion surface, as a consequence of the shallow depth of Biostrome accumulation. Taphonomic loss by dissolution is widespread in open, parautochthonous rudist fabrics, and confirms actuogeological results of other authors that bioturbation mediates carbonate dissolution also under shallow tropical waters supersaturated for calcium carbonate. The amount of carbonate dissolved upon burrowing of the Biostrome matrix is hardly quantifiable but, by analogy to Recent carbonate environments, may have been large. Within bioconstructions, deep-tiered burrowing occurred at least since the Carboniferous. Taphonomic loss by dissolution thus may have been active in the fossilization of tropical shallow-water mounds and Biostromes over much of Phanerozoic times.
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Carbonate deposition in mixed siliciclastic–carbonate environments on top of an orogenic wedge (Late Cretaceous, Northern Calcareous Alps, Austria)
Sedimentary Geology, 2000Co-Authors: Diethard Sanders, R. HöflingAbstract:Abstract In the Middle Turonian to Lower Campanian (Lower Gosau Subgroup; LGS) of the Northern Calcareous Alps, Austria, in the highstand systems tract of mixed siliciclastic–carbonate depositional sequences, small carbonate shelves locally developed that were mainly controlled by a differentiated morphology of the substratum and siliciclastic input onto a storm-dominated shelf. The LGS was deposited above thrust nappes of the Alpine orogen. The transgressive systems tracts of depositional sequences consist of local fan delta or fluvial deposits, overlain by a succession mainly of siliciclastics that records deepening from paralic to outer shelf environments. Locally, rudist Biostromes and coral–rudist mounds accumulated in lagoonal/bay to inner shelf environments, but were buried by paralic siliciclastics. Along coastal sectors of low siliciclastic input, because of a high-relief truncation surface at the base of the LGS, the transgressive systems tracts consist of an upward-deepening succession of clastic carbonates deposited from gravelly to rocky carbonate shores. The highstand systems tracts are dominated by siliciclastics, and record shoaling to inner shelf depths and, near the basin margins, to lagoonal to marsh environments. During highstand conditions, delta progradation combined with shoreline compartmentalization by headlands locally led to establishment of inner shelf compartments of low siliciclastic input. In these compartments, carbonate shelves developed. Along strike, the carbonate shelves were up to more than 10 km in length (beyond limits of larger outcrops), and about 1 km to, possibly, 10 km wide down dip. The carbonate shelves consisted of (a) an inner shelf belt with coral–rudist mounds, rudist Biostromes and bioclastic sand bodies, (b) a dissipative shore zone of bioclastic sand bodies, (c) open lagoons/bays with radiolitid Biostromes, and (d) narrow, micro-tidal flats or lithoclastic/bioclastic beaches. Up-section, inner shelf to shore zone carbonate parasequence tracts consist of a coral–rudist mound, a rudist Biostrome, and of shore zone bioclastic limestones. Parasequence tracts deposited in lagoons/bays commonly shoaled incompletely, and mainly consist of more-or-less marly limestones deposited in shallow subtidal environments with radiolitid Biostromes, substrata of bioclastic sand or lime mud, and with local mass accumulations of gastropods or of epibenthic non-rudist bivalves. The carbonate shelf successions are up to 100 m thick and, in vertical section, consist of stacked parasequence tracts that become thinner up-section and record a shoaling of mean depositional water depth. Carbonate deposition was confined to the actual inner shelf to tidal flat/beach compartment. Down dip, the coral–rudist mounds scattered along the seaward fringe of the carbonate shelves graded into small haloes composed mainly of disoriented, fragmented rudists and corals. Larger carbonate slope depositional systems were not individuated, and the carbonate shelves interfingered with and pinched out into inner shelf siliciclastics. The development of larger carbonate slopes was prevented by the low relief of the coral–rudist mounds, combined with high input and effective dispersal of siliciclastics ahead. Carbonate shelf progradation over a possible distance of up to a few kilometres was linked with aggradation of shelf siliciclastics.
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Rudist formations in mixed siliciclastic-carbonate depositional environments, Upper Cretaceous, Austria: stratigraphy, sedimentology, and models of development
Palaeogeography Palaeoclimatology Palaeoecology, 1999Co-Authors: Diethard Sanders, Josep Maria PonsAbstract:Abstract The upper Turonian to lower Campanian succession (Lower Gosau Subgroup) of the Northern Calcareous Alps, Austria, provides a model for the development of rudist formations on wave-dominated, mixed siliciclastic-carbonate shelves that were situated on top of an accretionary wedge. The rudist formations are present either within parasequences or in non-cyclic transgressive successions, and include (a) skeletal mounds up to about 20 m thick that are composed of corals, rudists and, locally, skeletal sponges; and (b) rudist Biostromes of less than a metre to several meters in thickness. In the coral–rudist mounds hippuritids and radiolitids thrived together with scleractinians, skeletal sponges and diverse encrusters. The mounds are topped by a hippuritid Biostrome. We distinguish hippuritid Biostromes, radiolitid Biostromes and `composite Biostromes' with a vertical succession from hippuritids to radiolitids. The Biostromes are less than a metre to a few meters thick and show autochthonous rudist fabrics, parautochthonous rudist fabrics, and vertical combinations thereof. Autochthonous rudist fabrics had a simple trophic structure composed of epifaunal suspension feeders, whereas parautochthonous rudist fabrics had a more complex trophic structure. The rudist Biostromes were either terminated by frequent toppling and fragmentation of rudists, by burial with sediment, or by environmental restriction. Hippuritids and radiolitids could both colonize and persist in siliciclastic depositional environments. Overall, however, the presence/abundance of rudists and of intervals of shallow-water limestones correlate. Because the Late Cretaceous rudists thrived together with hermatypic corals as well as in environments precluded to the latter, a larger number of rudist formations and a smaller number of coral–rudist formations results. In siliciclastic-dominated depositional sequences, both in the transgressive and in the highstand systems tract, coral–rudist mounds and rudist Biostromes locally accumulated in areas of intermittently reduced siliciclastic input in open lagoons and in the shoreface to inner shelf environment. Transgression of rocky coasts or of gravelly carbonate beaches is recorded by a basal interval either of cliff talus breccia or of beachface and shoreface conglomerates, overlain by a coral–rudist mound and/or a rudist Biostrome with associated bioclastic limestones. Where siliciclastic input was persistently low, the highstand systems tract developed as a regressive carbonate shelf succession that consists, in its lower part, of coral–rudist mounds, hippuritid Biostromes and bioclastic packstones to grainstones deposited from bioclastic sand bodies, whereas the upper part consists of radiolitid Biostromes and bioclastic wackestones to packstones. The regressive carbonate shelves were narrow and included, on a reconstructed internal-to-external transect, micro-tidal flats, an open lagoon with radiolitid Biostromes, a dissipative shore zone with bioclastic sand bodies, and an inner shelf facies belt with coral–rudist mounds and hippuritid Biostromes. In the contemporaneous mid- to outer shelf environment, siliciclastics were deposited.
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Coral-rudist bioconstructions in the Upper Cretaceous Haidach section (Gosau Group; Northern Calcareous Alps, Austria)
Facies, 1997Co-Authors: Diethard Sanders, Rosemarie C. Baron-szaboAbstract:In the area of Haidach (Northern Calcareous Alps, Austria), coral-rudist mounds, rudist Biostromes, and bioclastic limestones and marls constitute an Upper Cretaceous shelf succession approximately 100 meters thick. The succession is part of the mixed siliciclasticcarbonate Gosau Group that was deposited at the northern margin of the Austroalpine microplate. In its lower part, the carbonate succession at Haidach comprises two stratal packages that each consists, from bottom to top, of a coral-rudist mound capped by a rudist Biostrome which, in turn, is overlain by bioclastic limestones and, locally, marls. The coral-rudist mounds consist mainly of floatstones. The coral assemblage is dominated by Fungiina, Astreoina, Heterocoeniina and Agathelia asperella (stylinina). From the rudists, elevators ( Vaccinites spp., radiolitids) and recumbents ( Plagioptychus ) are present. Calcareous sponges, sclerosponges, and octocorals are subordinate. The elevator rudists commonly are small; they settled on branched corals, coral heads, on rudists, and on biolastic debris. The rudists, in turn, provided settlement sites for corals. Predominantly plocoid and thamnasteroid coral growth forms indicate soft substrata and high sedimentation rates. The mounds were episodically smothered by carbonate mud. Many corals and rudists are coated by thick and diverse encrustations that indicate high nutrient level and/or turbid waters. The coral-rudist mounds are capped by Vaccinites Biostromes up to 5 m thick. The establishment of these Biostromes may result from unfavourable environmental conditions for corals, coupled with the potential of the elevator rudists for effective substrate colonization. The Vaccinites Biostromes are locally topped by a thin radiolitid Biostrome. The Biostromes, in turn, are overlain by bioclastic limestones; these are arranged in stratal packages that were deposited from carbonate sand bodies. Approximately midsection, an interval of marls with abundant Phelopteria is present. These marls were deposited in a quiet lagoonal area where meadows of sea grass or algae, coupled with an elevated nutrient level, triggered the mass occurrence of Phelopteria . The upper part of the Haidach section consists of stratal packages that each is composed of a rudist Biostrome overlain by bioclastic wackestones to packstones with diverse smaller benthic foraminifera and calcareous green algae. The Biostromes are either built by radiolitids, Vaccinites , and Pleurocora , or consist exclusively of radiolitids (mainly Radiolites ). Both the Biostromes and the bioclastic limestones were deposited in a low-energy lagoonal environment that was punctuated by high-energy events. In situ -rudist fabrics typically have a matrix of mudstone to rudistclastic wackestone; other biogens (incl. smaller benthic foraminifera) are absent or very rare. The matrix of rudist fabrics that indicate episodic destruction by high-energy events contain a fossil assemblage similar to the vertically associated bioclastic limestones. Substrata colonized by rudists thus were unfavourable at least for smaller benthic foraminifera. The described succession was deposited on a gently inclined shelf segment, where coral-rudist mounds and hippuritid Biostromes were separated by a belt of bioclastic sand bodies from a lagoon with radiolitid Biostromes. The mounds document that corals and Late Cretaceous elevator rudists may co-occur in close association. On the scale of the entire succession, however, mainly as a result of the wide ecologic range of the rudists relative to corals, the coral-dominated mounds and the rudist Biostromes are vertically separated.
Steve Kershaw - One of the best experts on this subject based on the ideXlab platform.
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Palaeoecology of corals and stromatoporoids in a late Silurian Biostrome in Estonia
2016Co-Authors: Steve Kershaw, Mari-ann MotusAbstract:Kershaw, S. and Mõtus, M.-A. 2016. Palaeoecology of corals and stromatoporoids in a late Silurian Biostrome in Estonia
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Middle Viséan (Mississippian) coral Biostrome in central Guizhou, southwestern China and its palaeoclimatological implications
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Le Yao, Steve Kershaw, Xiangdong Wang, Wei Lin, Wenkun QieAbstract:Abstract A middle Visean (Mississippian) coral Biostrome is reported for the first time from the Shangsi Formation in Yashui area, central Guizhou Province, southwestern China (palaeogeographically located in eastern Palaeotethys). The Biostrome, which is about 500 m across and 2.5–3.9 m thick, is laterally variable and composed of rugose and tabulate corals with low taxonomic diversity comprising 4 rugose and 1 tabulate coral species belonging to 5 genera. Three growth stages of the Biostrome are distinguished, based on different compositions of coral taxa. Average coral contents of the Biostrome increase from 38.7% to 72.0% upward and the main builders are Siphonodendron pentalaxoidea, Syringopora sp. and Kueichouphyllum sinense. Associated fossils include abundant brachiopods, crinoids and common foraminifers together with rare calcareous algae, bryozoans, gastropods and ostracods. Relative sea-level changes are interpreted to have controlled growth and demise of the Biostrome, which grew continuously during sea-level rise and decreasing water energy, as evident from the gradually increasing of micrite content and in situ coral colonies. However, the Biostrome declined and died as the sea level fell and hydrodynamic energy strengthened, indicated by an increase of bioclasts and sparry calcite cement (indicating lack of micritic matrix due to higher energy) overlying the Biostrome. This coral Biostrome has similar biotic composition to middle to late Visean coral Biostromes in Europe and North Africa (western Palaeotethys). The approximately coeval occurrence of coral Biostromes in both eastern and western Palaeotethys suggests that a relatively global warm episode existed during the Visean Stage.
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Paleobiology, Ecology, and Distribution of Stromatoporoid Faunas in Biostromes of the Mid-Ludlow of Gotland, Sweden
Acta Palaeontologica Polonica, 2008Co-Authors: Olof Sandström, Steve KershawAbstract:Six well exposed mid-Ludlow stromatoporoid-dominated reef Biostromes in four localities from the Hemse Group in southeastern Gotland, Sweden comprise a stromatoporoid assemblage dominated by four species; Clathrodictyon mohicanum, “Stromatopora” bekkeri, Plectostroma scaniense, and Lophiostroma schmidtii. All Biostromes investigated in this area (of approximately 30 km2) are interpreted to belong to a single faunal assemblage forming a dense accumulation of fossils that is probably the best exposed stromatoporoid-rich deposit of the Silurian. The results from this comprehensive study strengthen earlier interpretations of a combination of genetic and environmental control on growth-forms of the stromatoporoids. Growth styles are similar for stromatoporoids in all six Biostromes. Differences in Biostrome fabric are due to variations in the degree of disturbance by storms. The uniformity of facies and the widespread low-diversity fauna support the view that palaeoenvironmental conditions were similar across ...
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Ludlow (Silurian) stromatoporoid Biostromes from Gotland, Sweden: facies, depositional models and modern analogues
Sedimentology, 2002Co-Authors: Olof Sandström, Steve KershawAbstract:Stacked stromatoporoid-dominated Biostromes of the Ludlow-age Hemse Group (Silurian) in eastern Gotland, Sweden, are 0.5-5 m thick and a few tens of metres to >1 km in lateral extent. They form one of the world's richest Palaeozoic stromatoporoid deposits. This study compiles published and new data to provide an overall facies model for these Biostromes, which is assessed in relation to possible modern analogues. Some Biostromes have predominantly in-place fossils and are regarded as reefs, but lack rigid frameworks because of abundant low-profile non-framebuilding stromatoporoids; other Biostromes consist of stromatoporoid-rich rudstones interpreted here as storm deposits. Variation between these two 'end-members' occurs both between interlayered Biostromes and also vertically and laterally within individual Biostromes. Such variation produces problems of applying established reef classification terms and demonstrates the need for the development of terminology that recognizes taphonomic destruction of reef fabrics. An approach to such terminology is found in all four categories of a recent Biostrome classification scheme that are easily recognized in the Hemse Biostrome facies: autoBiostromes (>60% in place); autoparaBiostromes (a mixture of in-place and overturned reef-building organisms, 20-60% in place); paraBiostromes (builders are overturned and damaged,
Caleb Izdepski - One of the best experts on this subject based on the ideXlab platform.
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Biostrome communities and mercury and selenium bioaccumulation in the great salt lake utah usa
Science of The Total Environment, 2011Co-Authors: Wayne A. Wurtsbaugh, Jodi Gardberg, Caleb IzdepskiAbstract:The Great Salt Lake has a salinity near 150 g/L and is habitat for over 200 species of migratory birds. The diet of many of these birds is dependent on the food web of carbonaceous Biostromes (stromatolites) that cover 260 km(2) of the lake's littoral zone. We investigated the Biostrome community to understand their production processes and to assess whether they are a potential vector for bioconcentration of high mercury and selenium levels in the lake. The periphyton community of the Biostromes was >99% colonial cyanobacteria. Periphyton chlorophyll levels averaged 900 mg m(-2) or nine times that of the lake's phytoplankton. Lake-wide estimates of chlorophyll suggest that their production is about 30% of that of the phytoplankton. Brine fly (Ephydra gracilis) larval densities on the Biostromes increased from 7000 m(-2) in June to 20000m(-2) in December. Pupation and adult emergence halted in October and larvae of various instars overwintered at temperatures <5°C. Mean total dissolved and dissolved methyl mercury concentrations in water were 5.0 and 1.2 ηg L(-1). Total mercury concentrations in the periphyton, fly larvae, pupae, and adults were, respectively, 152, 189, 379 and 659 ηg g(-1) dry weight, suggesting that bioconcentration is only moderate in the short food web and through fly developmental stages. However, common goldeneye ducks (Bucephala clangula) that feed primarily on brine fly larvae at the Great Salt Lake had concentrations near 8000 ηg Hg g(-1) dry weight in muscle tissue. Data from a previous study indicated that selenium concentrations in periphyton, brine fly larvae and goldeneye liver tissue were high (1700, 1200 and 24,000 ηg g(-1), respectively) and Hg:Se molar ratios were <1.0 in all tissues, suggesting that the high mercury concentration in the ducks may be partially detoxified by combining with selenium. The study demonstrated that the high mercury levels in the Great Salt Lake are routed through the Biostrome community resulting in invertebrate prey that may provide health risks for birds and humans that consume them.
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Biostrome communities and mercury and selenium bioaccumulation in the Great Salt Lake (Utah, USA).
The Science of the total environment, 2011Co-Authors: Wayne A. Wurtsbaugh, Jodi Gardberg, Caleb IzdepskiAbstract:The Great Salt Lake has a salinity near 150 g/L and is habitat for over 200 species of migratory birds. The diet of many of these birds is dependent on the food web of carbonaceous Biostromes (stromatolites) that cover 260 km(2) of the lake's littoral zone. We investigated the Biostrome community to understand their production processes and to assess whether they are a potential vector for bioconcentration of high mercury and selenium levels in the lake. The periphyton community of the Biostromes was >99% colonial cyanobacteria. Periphyton chlorophyll levels averaged 900 mg m(-2) or nine times that of the lake's phytoplankton. Lake-wide estimates of chlorophyll suggest that their production is about 30% of that of the phytoplankton. Brine fly (Ephydra gracilis) larval densities on the Biostromes increased from 7000 m(-2) in June to 20000m(-2) in December. Pupation and adult emergence halted in October and larvae of various instars overwintered at temperatures
Markus Aretz - One of the best experts on this subject based on the ideXlab platform.
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Upper Viséan coral Biostrome in a volcanic-sedimentary setting from the Eastern Tianshan, Northwest China
Palaeogeography Palaeoclimatology Palaeoecology, 2019Co-Authors: Xing Huang, Markus Aretz, Xionghua Zhang, Tengfei LuanAbstract:Abstract For the first time, a Mississippian coral Biostrome is described from the Eastern Tianshan, Xinjiang Province, Northwest China. Rugose corals and foraminifers show that the Biostrome developed during the late Visean in one of the rare carbonate levels in the mainly volcanic-siliciclastic succession of the Yamansu Formation. A single fasciculate coral, Siphonodendron irregulare, dominates (>80%) this Biostrome. Of the 22 coral genera found in the Yamansu Formation, 5 colonial and 6 solitary dissepimented corals are recorded in the Biostrome. The Biostrome can be divided vertically into two parts. In the main thick part dominate large patches of in situ Siphonodendron irregulare colonies. In the thinner uppermost part, Siphonodendron irregulare and Lithostrotion formed locally isolated small patches in a capping bed. The initial growth of the coral patches was related to slight topographic irregularities in the underlying volcano-sedimentary rocks. Siphonodendron irregulare appears to have been the best adapted species to the environmental pressures in the unstable tectono-sedimentary environment of the Yamansu Formation. It flourished and outnumbered the other corals when volcanic activity ceased and carbonate production became active for a short time. The development of the Siphonodendron Biostrome ceased due to increases in sea-level and volcanic activity. Compared to Siphonodendron Biostromes in the western and eastern Paleotethys, the Siphonodendron Biostrome in Yamansu is unique for having developed in an island arc setting. To date, the Yamansu Biostrome is the only documented coral bioconstruction at similar latitudes in the Central Asian Orogenic Belt (CAOB). Formation of this coral Biostrome was controlled by extrinsic factors, such as changes in global climate and ocean currents, and intrinsic factors, such as the pioneering nature of the fast-growing Siphonodendron irregulare. Both sets of factors are responsible for the expansion of the tropical reef belt into previously more temperate environments.
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brachiopods and rugose corals in an upper serpukhovian mississippian Biostrome preliminary results from the djebel arhlal bechar basin algeria
Boletín geológico y minero, 2016Co-Authors: Khireddine Faiceyle Tewfik Atif, Markus Aretz, Marie Legrandblain, Aman Bouzid, M AimoucheAbstract:espanolDjebel Arhlal es el afloramiento mas meridional de los estratos serpukovienses en la cuenca Bechar. En esta zona el Miembro Djenien de la Formacion Djenien ha sufrido tres etapas de plegamiento y contiene en su unidad media un biostroma de coral de 10 m de espesor y formado por Siphonodendron, Diphyphyllum y Lithostrotion. Las distancias in situ entre las colonias son del orden de varias decenas de decimetros y el espacio entre ellas esta relleno de caliza bioclastica que contiene restos de coral. Se han encontrado pocos braquiopodos y corales solitarios como residentes dentro del biostroma, aunque si son abundantes en los estratos por debajo y por encima del mismo. Esto es especialmente cierto para los braquiopodos, los cuales llegan a alcanzar una diversidad de mas doce especies en horizontes especificos; y pertenecen a los ordenes Productida, Spiriferida y Athyridida. Las facies generales que se encuentran en el Miembro Djenien en Djebel Arhlal son las que corresponden a ambientes energeticos de plataforma interior marina abierta o margen de plataforma. Los datos de campo incluyen conchas de braquiopodos y muchos fragmentos de braquiopodos y corales, tal y como se ha confirmado por analisis de microfacies. Sin embargo, el biostroma coralino registra un ambiente mas tranquilo en la interfase entre ambientes de rampa media y externa, como se ha visto en la coexistencia del crecimiento del coral in situ, la entrada de material retrabajado, la deposicion de lodo carbonatico y las texturas espaleriticas. Este autoparabiostroma en Djebel Arhlal es comparable con otros biostromas del Serpukhoviense superior de bastante espesor y con una extension horizontal excepcional (de unos pocos kilometros). EnglishThe Djebel Arhlal is the southernmost outcrop of upper Serpukhovian strata in the Bechar Basin. Here the Djenien member of the Djenien Formation is three-folded and it contains a 10 m-thick coral Biostrome in its middle unit formed by Siphonodendron, Diphyphyllum and Lithostrotion. Distances between in situ colonies are in the order of several decimetres and the space between them is filled with bioclastic limestone containing coral rubble. Few brachiopods and solitary corals are found as dwellers within the Biostrome, but these groups are much more common in the strata below and above the coral Biostrome. This is especially true for the brachiopods, which reach diversities of more than a dozen species in specific horizons. They mainly belong to the orders Productida, Spiriferida and Athyridida. Agitated open-marine platform interior or platform margin settings are the general facies encountered in the Djenien member at the Djebel Arhlal. The field data, including brachiopod coquinas and many fragmented brachiopods and corals, are confirmed by microfacies analysis. However, the coral Biostrome records a quieter setting at the interface of middle and outer ramp settings, as seen in the co-existence of in situ coral growth, input of reworked material, deposition of carbonate mud, and sparitic textures. This autoparaBiostrome at Djebel Arhlal is compared to other rather thick and of exceptional horizontal extension upper Serpukhovian Biostromes (few kilometres).
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Habitats of colonial rugose corals: the Mississippian of western Europe as example for a general classification
Lethaia, 2010Co-Authors: Markus AretzAbstract:Aretz, M. 2010: Habitats of colonial rugose corals: the Mississippian of western Europe as example for a general classification. Lethaia, DOI: 10.1111/j.1502-3931.2010.00218.x. Colonial rugose corals are a major constituent of shallow-water marine benthic communities in Mississippian times. The study of western European rugose coral habitats from the base of the Tournaisian stage to the Serpukhovian stage allows the recognition of four basic habitat types, which can be divided into a total of 11 subtypes. The classification is mainly based on field data, and thus rapidly applicable. Level-bottom communities in which large colony distances are characteristic (type A) represent the most basic community type; polyspecific (subtype A1) and monospecific (subtype A2) subtypes occur. Reduced colony distances result in the formation of coral meadows (type B), which either show homogenous coral distribution (subtype B1) or the development of patches (subtype B2). Coral Biostromes (type C) represent a spectrum between hydrodynamically controlled Biostromes (nothing in place, subtype C1) and biologically constructed and controlled Biostromes (subtype C2). The bulk of the Biostromes represent mixtures of those two subtypes (subtype C3). Colonial rugose corals are widely encountered in Mississippian bioherms where they are dwellers (subtype D1), form capping beds (subtype D2), support framework building along with other organisms (subtype D3) and form coral framework (subtype D4). The latter is probably the most uncommon of all subtypes in Mississippian times. The classification is widely applicable to other groups. □Classification, habitats, Mississippian, palaeoecology, palaeoenvironment, rugose corals.
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Rugose coral Biostromes in the late Viséan (Mississippian) of NW Ireland: Bioevents on an extensive carbonate platform
Palaeogeography Palaeoclimatology Palaeoecology, 2010Co-Authors: Markus Aretz, Hans-georg Herbig, Ian D. Somerville, Pedro CózarAbstract:Abstract The extensive upper Visean (Asbian) platform carbonates in NW Ireland (Bricklieve Limestone Fm, Glencar Limestone Fm and Dartry Limestone Fm) contain distinctive rugose coral Biostromes, which are dominated by different species of the genus Siphonodendron. These are in stratigraphic sequence: pauciradiale Biostrome (oldest), martini Biostrome and several junceum Biostromes (youngest). They represent bioevents caused by special short-lasting ecological conditions and can be used as approximately synchronous horizons to correlate within the region. The pauciradiale Biostrome is the thickest, laterally most persistent and most variable in facies and biotic composition of all Biostromes. It formed on a tectonically influenced platform with a landward–seaward zonation from northwest to southeast, mainly above storm wave-base and below fair-weather wave-base. The northwestern Streedagh facies is characterized by the presence of clusters of large sheet-like colonies of S. pauciradiale. The intermediate O'Donnell's Rock facies is unique for the predominance of the fasciculate genus Solenodendron. The southeastern Bricklieve facies represents the amalgamation of autochthonous and allochthonous coral debris and bioclastic debris with localized small patches of coral boundstone. Mass occurrences of fasciculate rugose corals re-appear in the martini Biostrome. This Biostrome developed in a shallower water setting, just above fair-weather wave-base on a levelled carbonate platform. The junceum Biostromes are thinner, decimetre to some metres thick, and less persistent. They formed in deeper water mostly below storm wave-base, except for the composite 2nd junceum Biostrome of the Bricklieve Mountains, which records a period of shallowing. According to facies and coral morphologies, which were compared with modern scleractinian growth forms, sea-level variation exerted one of the strong controls on the rise and decline of the Biostromes. The pauciradiale Biostrome formed during an extended shallowing-upward cycle in a depth interval leading to the climax of Siphonodendron pauciradiale. The cycle ended with the development of the martini Biostrome in shallow water. Its demise is probably caused by drowning during the late Asbian sea-level rise. During that time slice the junceum Biostromes flourished in deeper water on the platform. Coral growth ceased almost completely after formation of the junceum Biostromes during the falling sea level of the latest Asbian. Siliciclastic input and resulting turbidity, as well as turbulence formed a complex cascade of ecological constraints. In addition to the local tectonic influences, they combined to result in the “depth” factor which controlled the distribution of predominating coral populations and the succession of the different Biostromes in the Asbian of NW Ireland.
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Deep shelf Biostrome of Late Permian in South China and its implications for the adaptability of calcisponges to water depth
Palaeogeography Palaeoclimatology Palaeoecology, 2014Co-Authors: Zheng Meng, Yongbiao Wang, Adam D. Woods, Wei LiaoAbstract:Abstract The Yangtze platform of South China was an area of extensive carbonate accumulation during the Late Permian, with abundant benthic fossils and reef buildups. Its northern margin has long been considered to be bordered by deep shelf sediments rich in radiolarians and ammonoids. However, recent investigations found a sponge Biostrome in deeper shelf settings in the uppermost Permian. The Biostrome is about 0.45 m thick with an organic framework formed by autochthonous calcisponges. In contrast to more diverse shallow marine reef communities at this time, the Biostrome was almost entirely constructed by the sponge genus Peronidella as the only frame-building organism. This low biodiversity reflects a relatively deep-water environment. Peronidella individuals in the Biostrome are apparently larger than the same genus in shallow platform settings, including the diameters of both the sponge bodies and the central tubular spongocoel, as well as the thicknesses of the body walls. This increased size may be related to the low biodiversity and therefore to reduced competition, with sponge individuals having increased space in which to develop. Biostrome development was terminated by volcanic clay deposition.