Permian Reef Research Articles

Carbon isotopic record of a platform-to-basin transect through the Permian Reef Complex (Guadalupian) in the Delaware Basin of Texas and New Mexico

The Guadalupian Permian Reef Complex of the Delaware Basin is one of the most studied carbonate reef systems of the Paleozoic. Despite extensive work on the carbonate sedimentology, sequence stratigraphy, and diagenetic history of the Delaware Basin, a high-resolution carbonate carbon isotope record along a platform to basin transect for the Capitanian (264.3–259.5 Ma, the youngest age of the Guadalupian Epoch) does not yet exist. The carbon isotopic record of the Delaware Basin is important because 1) it allows us to test hypotheses about controls on the carbon isotope proxy, 2) it provides constraints on how well modern carbonate platforms like the Great Bahama Banks serve as analogues for ancient carbonate settings, and 3) these types of restricted basins likely played an important role in Permian carbon cycling and the Capitanian extinctions.In this study we present 493 new Capitanian carbonate carbon isotopic values paired with a detailed sedimentological and sequence stratigraphic framework from the platform, slope, toe of slope, and deep basin of the Delaware Basin. The bulk of the new δ13C values fall within the range of previously reported unaltered carbonates from the basin, suggesting that these results record primary environmental processes and were not significantly altered by diagenetic overprinting. With this dataset, we test hypotheses about sources of carbon isotopic variability in shallow carbonate platforms. Our results indicate that in the Delaware Basin there are no systematic and resolvable depth or lateral gradients in carbon isotopic values, that δ13C values do not vary as a function of grain type, and that there is no resolvable relationship between carbon isotopic composition and sea level change. However, we do document statistically significant differences in δ13C distributions among facies associations which we attribute to the isotopic evolution of an upwelling water mass due to direct precipitation of mud along the slope. Our results support the idea that increasing carbon isotopic values through the Capitanian were driven by increased organic carbon burial in restricted basins.

А New Species of the Genus Lekiskochiton (Mollusca, Polyplacophora) from the Lower Permian Reef Limestones of Shakhtau (Southern Cis-Urals)

А New Species of the Genus Lekiskochiton (Mollusca, Polyplacophora) from the Lower Permian Reef Limestones of Shakhtau (Southern Cis-Urals)

The Earliest Representatives of the Genus Pinna (Bivalvia), from the Early Permian Reef of Shakhtau (Southern Cisuralia, Russia)

The Earliest Representatives of the Genus Pinna (Bivalvia), from the Early Permian Reef of Shakhtau (Southern Cisuralia, Russia)

The Most Ancient Representatives of the Genus <i>Pinna</i> (Bivalvia) in the Early Permian Reef of Shakhtau (Southern Cis-Urals, Russia)

A new and most ancient species of the genus Pinna, P. pacata sp. nov., has been described from the Lower Permian deposits of the Shakhtau reef (southern Urals, Russia). Until now, the most ancient finds of representatives of this genus were known from the Lower Triassic. The new species adds to the list of species ancestral to Mesozoic forms, which makes it possible to consider the Ural Strait as one of the centers of Late Paleozoic mollusk diversification.

Insights into the structural geology and sedimentary succession of the Baltic Basin, Western Lithuania

The geological structure of the sedimentary cover of the Baltic Basin has been investigated since the 1960's. In Western Lithuania, seismic data were acquired during 1995–2015; however, the interpretation results have remained largely unpublished. In this work, the relatively newly acquired 2D and 3D seismic data have been incorporated into a single seismic interpretation. Detailed depth maps for the key seismic reflection horizons, an updated presentation of fault traces, as well as a few representative seismic profiles are made to illustrate the geological structure of the study area, which is in Western Lithuania and spans nearly 360 km2. This area includes Late Caledonian structures, such as the Gargždai Elevation, which contains some of the Lithuanian hydrocarbon fields, and is limited by the Gargždai Fault. This study demonstrates that the Gargždai Fault is not a single continuous fault, but rather it comprises a system of faults. Moreover, the Gargždai Elevation itself contains small-scale structures that are either fault-related, cross-faults, drape structures or combined types. In addition to previously known large separated Precambrian palaeo-topographical features, additional features are mapped as a result of this study. They are interpreted as erosional remnants (inselbergs) on the sub-Cambrian peneplain surface, and form a large group of inselbergs, which is not typical of the Baltic Basin. Several structural features related to Zechstein Basin are mapped as well: the northern edge of Zechstein evaporites and, possibly, Permian reefs.

Massive dolomitization driven by MgSO4-rich seawater and its effects on thermochemical sulfate reduction, Upper Permian Changxing Formation, northeastern Sichuan, China

Massive dolostones replacing build-ups and containing H2S of thermochemical sulfate reduction (TSR) origin occur in the Upper Permian reef and bank deposits, northeastern Sichuan, China, despite the absence of gypsum or anhydrite deposits, which are usually present in TSR cases. Fluid chemistry from fluid incluions and δ13C, δ18O and 87Sr/86Sr values from different diagenetic phases were measured to determine the dolomitization regime, and to assess the relationships between the occurrence of dolomitization and H2S accumulation. Dolomitization was initiated by seawater with slightly increased salinities (penesaline) at shallow depths prior to chemical compaction. The micro- to fine-crystalline cloudy dolomite formed with relatively high Na and Sr contents, and with δ13C, δ18O and 87Sr/86Sr values (2.2‰∼4.8‰, −3.9‰∼-5.0‰ and 0.70724∼0.70746, respectively) inherited from seawater. The evaporation of Permian seawater in back-reef and inter-reef lagoons during sea-level fall and the subsequent seepage reflux into reef-beach bodies led to greater Mg2+ and SO42− concentrations in higher-salinity pore waters. Further massive dolomitization was promoted by compactional flow of hotter residual seawater at shallow to intermediate depths and resulted in the formation of fine- to medium-crystalline clean dolomite with lower Na and Sr contents, more depleted δ18O values (-5.1‰∼-6.0 ‰), andδ13C (2.5‰∼4.8 ‰) and 87Sr/86Sr values (0.70726∼0.70741) similar to those of the coeval seawater. The relatively closed hydrodynamic system during burial facilitated SO42− preservation. The whole dolomitization process enriched porewater SO42−, which have been almost exhausted by subsequent TSR, accounting for the high present-day concentrations of H2S. The output of this study shows that similar scenarios involving dolomitization driven by condensed MgSO4 seawater and H2S accumulations can occur in evaporite-free settings across a broad range and deserves special attention during deep oil/gas exploitation.

Calcilobes wangshenghaii n. gen., n. sp., microbial constructor of Permian\u2013Triassic boundary microbialites of South China, and its place in microbialite classification

Permian–Triassic boundary microbialites (PTBMs) that formed directly after the end-Permian extinction in the South China Block are dominated by one structure, a lobate-form calcium carbonate construction that created extensive very thin (ca. 2–20 m thick) framework biostromes in shallow marine environments, effectively occupying the ecological position of the prior pre-extinction Permian reefs and/or associated carbonates. In the field, vertical sections show the microbialite is dendrolite (branched) and thrombolite (clotted), but because thrombolite may include branched portions, its structure is overall best classed as thrombolite. In the field and in polished blocks, the microbial material appears as dark carbonate embedded in lighter-coloured micritic sediment, where details cannot be seen at that scale. In thin section, in contrast to the largely unaltered micritic matrix, the microbial constructor is preferentially partly to completely recrystallised, but commonly passes gradationally over distances of a few mm to better-preserved areas comprising 0.1–0.2 mm diameter uneven blobs of fine-grained calcium carbonate (micrite to microsparite). The lobate architecture comprises branches, layers and clusters of blobs ca. 1–20 mm in size, and includes constructed cavities with geopetal sediments, cements and some deposited small shelly fossils. Individual blobs in the matrix may be fortuitous tangential cross sections through margins of accumulated masses, but if separate, may represent building blocks of the masses. The lobate structure is recognised here as a unique microbial taxon and named Calcilobes wangshenghaii n. gen., n. sp. Calcilobes reflects its calcium carbonate composition and lobate form, wangshenghaii for the Chinese geologist (Shenghai Wang) who first detailed this facies in 1994. The structure is interpreted as organically built, and may have begun as separate blobs on the sea floor sediment (that was also composed of micrite but is interpreted as mostly inorganic), by microbial agglutination of micrite. Because of its interpreted original micritic–microsparitic nature, classification as either a calcimicrobe (calcified microbial fossil) or a sedimentary microbial structure is problematic, so C. wangshenghaii has uncertain affinity and nature. Calcilobes superficially resembles Renalcis and Tarthinia, which both form small clusters in shallow marine limestones and have similar problems of classification. Nevertheless, Calcilobes framework architecture contrasts both the open branched geometry of Renalcis, and the small tighter masses of Tarthinia, yet it is more similar to Tarthinia than to Renalcis, and may be a modification of Tarthinia, noting that Tarthinia is known from only the Cambrian. Calcilobes thus joins Renalcis, Tarthinia and also Epiphyton (dendritic form) and others, as problematic microbial structures. Calcilobes has not been recognised elsewhere in the geological record and may be unique to the post-end-Permian extinction facies. C. wangshenghaii occurs almost exclusively in the South China Block, which lay on the eastern margin of Tethys Ocean during Permian–Triassic boundary times; reasons for its absence in western Tethys, except for comparable fabrics in one site in Iran and another in Turkey, are unknown.

Palaeoecological features of Lower Asselian (Lower Permian) carbonate skeletal mounds in the Pisanyi Kamen’ section (Un’ya River, Northern Urals)

AbstractAmong the many Upper Carboniferous and Lower Permian reef structures that are known worldwide, a Lower Permian 360 m long succession of reefal rocks in the Urals, interpreted as representing skeletal mounds, stands out for its complexity. The abundance of lime mud material, both in the skeletal mounds and in the adjacent sediments, indicates that they grew below fair‐weather wave base. An important feature of these Lower Permian organic buildups in the Urals is the widespread development of synsedimentary biologically induced cements, which often prevail in the rock volume. One of the most representative (and unique) skeletal mounds sequences in the Northern Urals is the Pisanyi Kamen’ section located on the Un'ya River. This paper aims to identify changes in the character of the palaeocommunity in the Pisanyi Kamen’ section. In the skeletal mounds development in the Lower Asselian interval of the Pisanyi Kamen’ section, seven events are distinguished. These are: (a) stabilisation of a soft sea floor by bryozoans and heterotrophic microbes; (b) colonisation of a hard sea floor by bryozoans and the appearance of abundant bioinduced cements; (c) displacement of bryozoans by a phylloid algae community; (d) appearance of a higher diversity community; (e) the mound top reaching the fair‐weather wave base; (f) collapse of the ecosystem; and (g) recurrent colonisation of a hard sea floor by phylloid algae. This work summarises the current state of knowledge regarding the Lower Permian skeletal mounds structure of the Northern Urals. The description of the ecological succession offers a new tool for the analysis of similar structures.

Tools for uranium characterization in carbonate samples: case studies of natural U–Pb geochronology reference materials

Abstract. Laser ablation U–Pb analyses of carbonate (LAcarb) samples has greatly expanded the potential for U–Pb dating to a variety of carbonate-producing settings. Carbonates that were previously considered impossible to date using isotope dilution methods may preserve radiogenic domains that can be dated using spatially resolved laser ablation geochronology techniques. Work is ongoing to identify reference materials and to consider best practices for LAcarb. In this study we apply standard and emerging characterization tool sets on three natural samples with the dual goal of enhancing the study of carbonates and establishing a new set of well-characterized natural reference materials for LAcarb studies. We start with the existing carbonate reference material WC-1 from the Permian Reef Complex of Texas, building on the published description to offer a deeper look at U and associated trace elements. We consider a tufa sample from the Miocene Barstow Formation of the Mojave Block, California, as a possible secondary calcite reference material due to its well-behaved U–Pb systematics. There are currently no natural dolomite standards. We present an unusual dolomite sample with very well-behaved U–Pb systematics from the Miocene of the Turkana Basin of Kenya as a possible dolomite reference material for LAcarb dating. In addition to using X-ray fluorescence (XRF) mapping and spectroscopy to better understand U in these natural samples, we have analyzed multiple aliquots of each of them for 87Sr/86Sr by thermal ionization mass spectrometry (TIMS). The Sr isotope compositions are analytically homogeneous within petrographically homogeneous regions of all three samples, and thus these materials could be used as Sr isotope standards as well. While not part of the current contribution, this combination could streamline simultaneous LA analyses of 87Sr/86Sr and U–Pb geochronology.

Reef-building red algae from an uppermost Permian reef complex as a fossil analogue of modern coralline algal ridges

Calcareous red algae have been important components in reefal facies since the Mesozoic but their volumetric contribution to Palaeozoic reefs was usually low. Here, we report a reef-building community dominated by Parachaetetes, a genus of solenoporacean red algae, overgrowing uppermost Permian sponge reefs in Cili (Hunan Province, South China). The fossil assemblage in the community consists of about 88% Parachaetetes, 7% rugose corals, and 5% reef-dwelling organisms, including gastropods, brachiopods, foraminifera and Tubiphytes. Although the biodiversity of this community is far lower than that in modern reefs, the association of red algae and rugose corals shares several attributes with the coral–coralline algal communities of modern tropical reefs. Analysis of sedimentary facies indicates that the reef-building Parachaetetes grew in a turbulent setting near the margin of a carbonate platform, perhaps in a reef-crest environment known from modern coralgal reefs. Although calcifying red algae have been recorded from the Cambrian onwards, this is the oldest site where crustose red algae played a dominant role in reef construction.

Sedimentary pattern and exploration significance of Permian reefs and shoals around the Wusheng-Shizhu intra-platform depression, eastern Sichuan Basin, China

There exists the Wusheng-Shizhu and Chongqing-Qijiang intra-platform depressions in the eastern Sichuan Basin during the Late Permian to the Early Triassic. The clear understanding of the sedimentary pattern and evolution of reef-shoal around the depression-margin has a practical significance for guiding the exploration and development of the Permian–Triassic reef and shoal gas fields. Based on observation, the systematic sampling and laboratory analysis of typical outcrops of the Changxing Formation (i.e. Juandong, Juhuaba, Lengshuixi, and Taiyuan) are located in the eastern Sichuan Basin. Combined with drilling data and previous studies, the study area is dominated by a ramp sedimentary environment, except for the Kaijiang-Liangping Trough in the Early Changxingian. The main sediments are micrite-containing chert nodules and micrite. With the regression that took place during the Middle-Late Changxingian, there is a distinct sedimentary differentiation that began to appear. There is a “two depressions–one platform–one trough” sedimentary pattern from south to north in the study area in the Changxingian. In essence, there exists the Chongqing-Qijiang and the Wusheng-Shizhu intra-platform depressions (two depressions), platform-flat (one platform) between the Wusheng-Shizhu intra-platform depression and the Kaijiang-Liangping Trough, and the Kaijiang-Liangping Trough (one trough). The reef-shoal of the northern depression-margin distributes between the 2nd Member and lower part of the 3rd Member. By comparison, the reef-shoal of the southern depression-margin distributes in the upper part of the 3rd Member; this indicates that the deposition of reef-shoal shows “earlier in the north and later in the south.” It is considered that the sedimentary palaeogeomorphology of the Changxingian is characterized by “higher in the north-lower in the south.” The clear understanding of the sedimentary pattern and evolution of reef-shoal around depression-margin reveal a new field for exploration and development of the Permian Changxing reef-shoal gas fields in the eastern Sichuan Basin.

Morphology and Systematics of the Late Paleozoic Gastropods Deseretospira Gordon and Yochelson and Termihabena gen. nov.

A new genus and species Termihabena lirata gen. et sp. nov. is described from the Lower Permian reef limestones of Shakh-Tau (southern Cisuralia). The new genus includes another five species: T. nikitowkensis (Yakowlew, 1899), T. asiatica (Licharew, 1967), T. millegranosa (Girty, 1934), T. pinegensis (Mazaev, 2006), and T. sp. (Batten, 1985). T. pinegensis is re-described based on new, additional material. The morphological similarities and differences between the new genus and Deseretospira Gordon and Yochelson, 1987 are discussed. The diagnosis of the genus Deseretospira is emended and expanded. Deseretospira and Termihabena gen. nov. are assigned to the family Phymatopleuridae. Deseretospira includes D. venustiformis (Licharew, 1967), in addition to the type species. The revision showed that the two species Rhineoderma ferganica Licharew, 1967 and Yunnania semigranulosa Licharew, 1967 are synonymous with Deseretospira venustiformis (Licharew, 1967).

Characteristics and Mechanism of Upper Permian Reef Reservoirs in the Eastern Longgang Area, Northeastern Sichuan Basin, China

Abstract As a typical kind of lithologic reservoirs, reef reservoirs are generally featured by their large single-well reservoir thickness, good reservoir physical properties, and high gas well productivity. The Upper Permian Changxing Formation is an important natural gas exploration target in the Sichuan Basin, which hosts a large reef gas reservoir and is mainly distributed along the Kaijiang-Liangping Trough. Comprehensive analyses are implemented to investigate reservoir characteristics and identify controlling factors of reef reservoirs in Changxing Formation in the Eastern Longgang Area, Northeastern Sichuan Basin, including core, logging, and seismic data analyses. Changxing Formation reservoirs in the study area mainly occur in the reef-shoal complex, which are featured by wide distribution, large thickness and generally good physical properties. Reservoir rocks are dominantly composed of bioclastic dolomite and silty-fine dolomite (with grain phantom structure), while the main reservoir space consists of residual intergranular pores, intergranular dissolution pores, and karst vugs. In the seismic profiles, typical mound-shaped chaotic reflections can be clearly seen. It is suggested by the main reservoir development controlling factor analysis that the distributions of reef reservoirs are typically controlled by sedimentary facies belts, while the scale of the reef-shoal complex is determined by the pene-sedimentary micro-paleo-geomorphology. Dolomitization can not only significantly preserve the primary pores but also enhance the permeability of rocks. Moreover, karstification is the key to high-quality reef-shoal reservoirs.

Верхнепермские рифы Южного Китая – последние рифы палеозоя

Subject of research . The upper Permian reefs of the Yangtze block of southern China are considered. Among them there are two species which differ in location in the basin and the nature of the internal structure. Methods and results. On the basis of geological and lithological methods of research it is shown that the main rift builders were a variety of sponges, whith a lesser extent bryozoans and wide development of non-carcass organisms. Along with relatively simple buildings (biostromes), the reefs in the strict sense of this term are also established. The beginning of reef formation is fixed by the accumulation of detritus of echinoderms with micro-grain cemented material. Reef formation ended until the end of Permian, before bulk biota extinction on the border of Permian and Triassic although potentially reef-building organisms still existed. Conclusion. The events that led to the great mass extinction were preceded by certain changes, which primarily destroyed the system of reef biocenosis, which led to the cessation of the formation of reefs with the continued existence of individual groups of organisms.

A New Species of the Genus Bellazona (Gastropoda) from the Early Permian Reef Limestones of Shakhtau

A new species Bellazona acuta sp. nov., is described from the Early Permian reef limestone of Shakhtau (southern Cisuralia). This find significantly expands the geochronological range of the genus Bellazona, which was formerly believed to be limited to the Mississippian of the southwestern United States. The morphology of Bellazona and a closely related genus Cerithioides is discussed.

Reef Construction in the Second Half of the Permian and Biotic Crisis at the Permian–Triassic Boundary

The Middle–Late Permian reefs were formed in two paleogeographic realms: North Pangaea and Tethyan Realm. The basic reef builders in the first realm were representatives of Calcispongiae and Bryozoa; in the second realm, sphinctozoans, corals, and stromatoporoids. In these realms, various algae and cyanobacteria communities were of importance. Reef construction in the first realm associated with arid climatic conditions, isolation of water basins, and accumulation of salt-bearing sequences came to the end in the early Late Permian. Reef construction in the Tethyan Realm occurred in the Late Permian up to the Permian–Triassic boundary. The termination of reef construction was due to features of the reef ecosystem, which turned out to be unstable against the background of variations in the conditions and mass extinction at the Permian–Triassic boundary and dissociated before the termination of this extinction.

Subsurface Permian reef complexes of southern Tunisia: Shelf carbonate setting and paleogeographic implications

2-D seismic reflection sections, borehole data as well as published and unpublished data have been investigated to reconstruct the paleogeography of southern Tunisia during Middle to Late Permian times. Paleogeographical reconstruction based on the integration of petroleum well data and 2-D seismic facies interpretation shows three main depositional areas with very contrasting sedimentary pile. These are 1) a subsiding basin; 2) an outer shelf carbonate, and 3) an inner shelf carbonate. Based on typical electric responses of reef buildups to seismic wave, we shall urge that during Middle Permian times, the outer carbonate shelf was subject of reef barrier development. Lithology evidences from core samples show that reef framework correspond mainly to fossiliferous limestone and dolomite. The WNW-ESE recognized reef barrier led between latitudes 33° 10′ 00″N and 33° 20′ 00″N. The Tebaga of Medenine outcrop constitutes the northern-edge of this barrier. Westward it may be extended to Bir Soltane area whereas its extension eastward is still to be determined. Biogenic buildups took place preferentially over faulted Carboniferous and lower Paleozoic paleohighs resulting likely from the Hercynian orogeny. The subsiding basin is located north of Tebaga of Medenine outcrop where Upper Permian sedimentary sequence is made entirely of 4000 m deep marine green silty shale facies. These are ascribed to unorganized and chaotic reflectors. Inner carbonate shelf facies succession corresponds to a typical interbedding of shallow marine carbonate deposits, shale, dolomite, and anhydrite inducing parallel-layered of strong amplitude and good continuity reflectors. Also within the inner carbonate shelf patch reef or reef pinnacles have been identified based on their seismic signature particularly their low vertical development as compared to reef complexes. Southward, towards Sidi Toui area, the Upper Permian depositional sequence thins out and bears witness of land influences as entailed by the increase of silicoclastic sedimentary supply and the lack of marine fossil.

Growth characteristics and sedimentary mode of Permian reefs, Lengwu, Tonglu, Zhejiang Province, southern China

Organic reefs are favourable accumulation spaces for hydrocarbons and various mineral resources. A complete Permian organic reef profile about 44 m thick with distribution area no more than 1 km2 is exposed near Lengwu, Tonglu, Zhejiang Province. Examination of outcrops and thin sections revealed that the main reef-building organisms are calcisponges, with inozoans as dominant type. Five types of rocks have been recognized in the reef, and they are calcisponge framestone, calcisponge bafflestone, bindstone, rudstone and bioclastic wackestone. The profile was constructed in three reef-building stages. The thickness of the second stage is largest, followed by the first stage and the third stage is smallest. Each stage started with a framestone or bafflestone, ended as the reef grew near the sea-level, and died because of influx of terrigenous sediments. The development of the Lengwu reef is controlled by biological factors and sea-level changes. Based on the study a reef sedimentary model is established.

Environmental and tectonic significance of Late Permian reefs in the Linxi and adjacent areas in Inner Mongolia of China

Many plateau-edge reefs and reef mounds of the Late Permian have been discovered in Linxi County and adjacent areas of Inner Mongolia, China. These reefs verify that the Hinggan-Inner Mongolia Area was an open and unobstructed sea-trough in Late Permian. Facies and sequences of reef strata in Member 4 and Member 5 of the Linxi Formation were studied for information to reconstruct the closing process of the Linxi-Jiutai chasm in the sea-trough, i.e., to constrain subsidence, uplift, and final closing. Ages of the reef-bearing strata have been determined to be late and end of Late Permian, based on ranges or abundances of diverse fossils. Six reef-building organic assemblages were distinguished, representing different ecologic conditions, according to morphological functions and paleoecological adaptations of organisms including primarily sponges, bryozoans, and calcareous algae. Two types of shelf slopes, the gentle slope and the steep slope, have been interpreted for Member 4 and Member 5 of the Linxi Formation, based on the assemblages. The locations of outcrops, and types of these reefs delineate the north margin of Sino-Korea Platform, and define uplift and final closing of the Linxi–Jiutai chasm at the end of Late Permian.

Equatorial Palaeotethys as the last sanctuary for late Permian metazoan reef-builders: New evidence from the Bellerophon Formation of Slovenia

The rise and demise of warm-temperate Permian reefs and biostromes reflect the complex geologic history of this dynamic period. Environments suitable for reef-builders were devastated by the Guadalupian/Lopingian crisis, and Lopingian reefs have only been recorded at a small number of localities. The uppermost Permian limestones of the Bellerophon Formation, on the Vojsko Plateau (Slovenia), contain small, lenticular biostromes within a bioclastic wackestone/packstone lithofacies. The major biostrome builders are medium-sized coralline sponges (Demospongea and Calcarea), encrusted by smaller sponges, tube worms, sessile foraminifera, calcareous algae (Archaeolithoporella) and Shamovella (i.e., Tubiphytes), all of which are typically covered by microbial crusts. The biostromes are characteristically composed of bafflestone and bindstone, incorporating sporadic framestone. Narrow belts of floatstone surround the buildups, and sponge debris is also present in lenses within the mud matrix between metazoan bafflestones. The fossils are generally well-preserved, although the fine skeletal microstructure has been partially recrystallized. Sponges are heavily calcified, and ontogenic thickening of the skeleton can be observed in some encrusters. Framboidal pyrite, forming thin films on the inner walls of sponge chambers, suggests the presence of sulphate-reducing bacteria. These microbial symbionts may have enabled the sponges to survive in the anoxic marine environments of the uppermost Permian. The Changshingian sponge biostromes of the Vojsko Plateau represent the westernmost known occurrence of contemporary metazoan boundstones in the Palaeotethys.