Reef-building Communities Research Articles

Analysis on ecological characteristics of Mississippian coral reefs in Langping, Guangxi

Several Late Viséan-Serpukhovian coral reefs were identified in Langping, Tianlin. They provided an opportunity to investigate paleo-environments suitable for the development of reef-building communities and the construction of coral reefs in Langping. In this paper, part of the reef-building environmental and the ecological characteristics of coral reefs then were elaborated by analyzing the development settings, palaeogeography, sedimentation of reefs, the response to hydrodynamic conditions of reef-building corals, effects of disturbance and non-reef-building organism on reef communities, and the influence of coral morphology on reef development. It is considered that the sedimentary environment of Langping in Late Viséan-Serpukhovian is suitable for the development of benthic communities. The current appearance of reefs is determined by both coral populations ecological characteristics and reef-building environment.

Palaeontological and sedimentological characteristics of the Changhsingian (Late Permian) platform−margin sponge reef and intraplatform skeletal mound in NE Sichuan Basin, South China: their palaeoenvironmental implications

Well-preserved fossil reef/mound-building communities and shallow microfacies have been recovered from Changhsingian platform−margin sponge reef at the Panlongdong Section and intraplatform sponge skeletal mound at the Yanggudong Section in NE Sichuan Basin, South China. The present contribution focuses on the palaeoenvironmental implication of the differentiated development processes on the platform−margin reef and intraplatform skeletal mound based on the palaeontology and sedimentology. Precise field assessments and macroscopic/microscopic qualitative observations led to the identification of five reef/mound-building community and 14 reef/mound-related microfacies in the 2 sections of Changxing Formation. In the Panlongdong platform−margin sponge reef, reef-building communities are recognized into Amblysiphonella Community, Preperonidella−Amblysiphonella Community, and Preperonidella–Sollasia Community in ascending order. The reef-related microfacies are mainly classified into calcisphere−pelletoid wackestone to packstone, crinoidal wackestone to packstone of shallow water bank environment, hypercalcified sponge bafflestone, calcareous algae−hypercalcified sponge binding framestone, hypercalcifed sponge−calcareous algae bindstone, and calcareous algae−hypercalcifed sponge rudstone of reef environment, and benthic foraminifera−calcareous algae wackestone to packstone of shallower water lagoon environment. Two mound-building communities can only be found in the Yanggudong intraplatform skeletal mound, including Preperonidella−Intrasporeocoelia Community of lower part and Preperonidella−Sollasia Community of upper part. The mound-related microfacies include calcisphere−calcareous algae wackestone to packstone, crinoidal wackestone to packstone and crinoidal packstone to grainstone of shallow water bank environment, hypercalcified sponge bafflestone and cyanobacteria−hypercalcified sponge binding bafflestone of skeletal mound environment, benthic foraminifera−calcareous algae packstone grainstone of shallower water bank environment and benthic foraminifera−calcareous algae wackestone to packstone of shallower water lagoon environment. These palaeontological and sedimentological analysis results have facilitated the classification of sponge reef and skeletal mound sections corresponding to a solitary shallow benthic zone into multiple microfacies attributed to variable environmental depositional conditions. The differentiated evolutional process of multiple reef/mound-building stages at the Panlongdong and Yanggudong sections clearly demonstrate a general shallowing-upward trend from an inner shelf setting to a supratidal and low energy lagoon environment.

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.

Development of Microsatellite Markers for the Hermatypic Coral <i>Porites lutea</i>

By mining the EST and genomic microsatellite sequence resources of Porites species in GenBank, and using interspecific amplification and resequencing, we developed 20 microsatellite markers for the stony coral Porites lutea , meanwhile, validated and excluded 43 microsatellite markers of its symbiotic zooxanthella. These markers of P. lutea were genotyped in one wild population (n=16) from the southwest of Hainan Island fringing reefs. Nineteen of the 20 markers showed polymorphism. The number of alleles was 2~7 (mean 3.5±1.8), and the observed heterozygosity ( H o ) and expected heterozygosity ( H e ) were 0.06~0.94 (mean 0.34±0.29) and 0.18~0.83 (mean 0.57±0.20), respectively. Four markers remained deviated from the Hardy-Weinberg Equilibrium (HWE) after multiple comparison correction for Bonferroin ( P HWE < 0.05). This is the first set of microsatellite markers of P. lutea . They should be useful for the research on the genetic diversity and connectivity of this species and the conservation of endangered coral reef ecosystems and reef-building coral communities in the Indo-Pacific region.

A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef

The fossil record provides valuable data for improving our understanding of both past and future reef resilience and vulnerability to environmental change. The spatial and temporal pattern of the initiation of the Holocene Great Barrier Reef presents a case study of reef response to rapid sea-level rise. Past studies have been limited by the lack of well-dated and closely spaced reef core transects and have not closely examined the composition of the reef-building communities through time. This study presents 80 new high precision UTh and 5 radiocarbon ages from twelve new cores located along three transects across different geomorphic and hydrodynamic settings of One Tree Reef, southern Great Barrier Reef, to document three distinct stages of Holocene reef development in unprecedented detail. Temporal constraints on changing paleoecological assemblages of coral, coralline algae and associated biota revealed three distinct phases of reef development, consisting of: 1)a fast, shallow and clear-water reef initiation from 8.2 until 8 ka; 2)a shift to slower, deeper and more turbid-water reef growth from 8 to 7 ka; and 3)a return to shallow and rapid branching coral growth in clear-water conditions as the reef “catches up” to sea-level. A minimum lag prior to reef initiation of 700 years was identified, which differs in length depending on reef environment and Pleistocene substrate height. In this new model, reef growth initiated on the topographically lower leeward margin and patch reef, prior to the start of windward margin development, contrary to the traditional reef growth model. While there was a shift to conditions less favorable for reef growth at 8 ka, this did not prevent the slow accretion of more sediment-tolerant coral communities. The majority of the reef reached sea level by ~6 ka. This new conceptual model of Holocene reef growth provides new constraints on changes in paleoenvironment that controlled reef community composition and growth trajectories through sea-level rise following inundation.

Assessing the impacts of phosphate mining on coral reef communities and reef development.

Phosphate mining activities on Christmas Island began in the late 1800's providing a unique, long-term case study in which to assess the impacts of mining on coral reef development. Watershed modelling was used to identify potential "hotspots" of mining runoff on to adjacent reefs. Pollution hotspots were also confirmed by analysis of reef sediment. Phosphate rich mining runoff flowed from local watersheds onto nearshore coral reefs with levels of up to 54,000 mg/kg of total phosphate recorded in reef sediment at the Dryers reef site adjacent to the main phosphate storage facility. Using this combination of watershed modelling and in-situ sediment contamination data we identified six coral reef sites along an environmental impact gradient. In-situ benthic transects were paired with a new rubble-encruster method enabling the analysis to combine large scale transect information alongside fine-scale data on epibenthic and encruster assemblages. Results demonstrate that phosphate rich sediment loading negatively impacted coral reef building communities, in particular, branching corals and calcareous encrusting organisms, critical to the future survival of coral reef ecosystems. These findings highlight the importance of curtailing runoff and pollution from catchment based mining activities and protecting reefs for the future.

Geological and biological reasons for the collapse of reef formation, Paleozoic

Paleozoic reef formation developed cyclically, and its global termination has been caused by the biological reasons — biotic crises and mass extinctions near the borders early and middle Cambrian, Ordovician and Silurian, Frasnian and Famennian, Serpukhovian and Bashkirian, Permian and Triassic. The Early Cambrian reef formation has ended along with disappearance of archaeocyathid. In the later stages reefs were much more difficult ecosystems, and they stopped developing before the full extinction of the reef-building communities. The interruption of reef formations within the separate stages have been connected with the geological and paleogeographic reasons – volcanism, regression, climate aridization etc.

LITHISTID SPONGE-MICROBIAL REEF-BUILDING COMMUNITIES CONSTRUCT LAMINATED, UPPER CAMBRIAN (FURONGIAN) ‘STROMATOLITES'

Laminoid, weakly fused sponge spicule networks are intercalated between convex stromatolitic laminae in an upper Cambrian (Furongian) reef. Sponges are small, millimeter to centimeter-sized lithistids that encrusted automicritic laminae and in turn were encrusted by microbial biofilms, eventually leading to columnar, crudely laminated ‘stromatolites'. Weakly fused desmas, now replaced with fine, blocky calcite, possess an arcuate geometry along the medial to distal ray axes. Minimal decay and separation of sponge tissue from these spicules produced arcuate, filament-like cavities that obscure the former presence of spicule networks when viewed in cross-section. Further deterioration produced peloidal networks and voids. These observations have important implications when reconstructing middle to late Cambrian reef-building communities. Until recently, these periods were assumed to be virtually devoid of calcified metazoan reefal components. An increasing number of recent studies, however, are demonstrating that metazoan reef-builders were more prevalent. This paper adds a unique element to the nature of framebuilding by demonstrating that lithistid sponge-microbial reef-building communities constructed laminated ‘stromatolites,' and thus may have had a flourishing ecology within late Cambrian microbial buildups.

The Carboniferous reefs in China

AbstractThe Carboniferous period was a unique period for reef developments during the Late Paleozoic; however, in past years, studies dealing with the Carboniferous reefs in China were very rare. In recent years, the Carboniferous reefs were studied in detail and diverse types of reefs have been discovered in different areas of China. In these areas, the Mississippian reefs were primarily built of bryozoans and rugose corals, which were associated with various kinds of calcareous algae. During the Pennsylvanian, in South China, the reef builders were composed of the rugose coral Fomichevella and phylloid algae, whereas in North China, the reef builders were composed of Chaetetes, bryozoans and corals. There are two main reef-building communities within Carboniferous reefs in China; an algal reef-building community and a reef-building community dominated by colonial coral. No evolutionary relationships between these two types of communities can be detected, thus indicating that two different linerages of reef-building communities evolved during the Carboniferous; the former community consists of cyanobacteria, bacteria and calcareous algae, while the latter one consists of various skeletal metazoan organisms. Through careful study of the developments of Chinese Carboniferous reefs, the evidence indicates that various communities of organisms played important reef-building functions during this period. The occurrence of these metazoan framework reefs also indicates that, during the Carboniferous, most areas in China would have been dominated by the environments with a tropical or subtropical climate.

Middle Permian sponge–microencruster reefal facies in the mid-Panthalassan Akiyoshi atoll carbonates: observations on a limestone slab

A Murgabian (Middle Permian) reef-core facies in the Akiyoshi Limestone, southwest Japan, which is of mid-Panthalassan atoll origin, is here described from a limestone slab. The reef-core facies is composed mainly of boundstone with submarine cement and matrix. The reef-building community is characterized by a high-diversity biota, including sponges (sphinctozoans, inozoans, and chaetetids), bryozoans (fistuliporids and cryptostomates), crinoids and various microencrusters (Tubiphytes, Archaeolithoporella, reticular and laminar microbialites, encrusting foraminifers and problematic laminar red algae). Among them, sphinctozoan sponges and microencrusters such as Tubiphytes and microbialites are the most abundant. This community is similar to a time-equivalent lagoonal mound (patch-reef) biota on the Akiyoshi atoll in terms of the dominant sponges, Tubiphytes and microbialites, but differs in the additional occurrence of bryozoans, Archaeolithoporella and encrusting foraminifers, which probably preferred higher-energy conditions in the reef-core environment. Among temporally changing reef-building communities on the Carboniferous–Permian Akiyoshi atolls, the sponge-dominated reefal community described here flourished on mid-Panthalassan atolls in a relatively stable warm-water environment during a Middle Permian post-deglacial period.

Recurrent patterns of coral community and sediment facies development through successive phases of Holocene inner-shelf reef growth and decline

Coral community decline and resultant ‘turn-off’ of reef accretion potential are commonly predicted outcomes of the increasing environmental stresses experienced by many coral reefs. The potential for coral reef communities to re-establish once environmental conditions ameliorate or new substrates for colonisation become available are, however, less well understood. Here we discuss data from a fringing reef at Dunk Island, an inner-shelf high island on Australia's Great Barrier Reef (GBR). Although this reef is spatially contiguous, detailed coring and dating reveal it was constructed in two discrete temporal phases. The inner part of the reef flat formed first, during the late stages of the post-glacial marine transgression-early sea level highstand (~ 6.9–4.5 k cal yr B.P.), whereas the outer fringe developed after the late-Holocene sea level regression, from ~ 1.6 k cal yr B.P. to present. A hiatus of almost 3000 years separates the two reef growth phases. Data from this reef thus provide a same-site perspective on the degree of temporal continuity that exists where an actively growing reef slows and eventually ceases to accrete for an extended period, before re-establishing and growing again—a temporal transition equivalent to reef ‘turn-off’ followed by renewed reef ‘turn-on’. The depositional architectures of the two phases of reef growth are very similar, as are patterns of facies and coral assemblage development. This study suggests that reefs, over the timescales at which cycles of reef ‘turn-on’ and ‘turn-off’ operate (the centennial to millennial timescale), can not only re-establish successfully, but also that regrowth may be characterised by the establishment of near identical reef-building communities and the development of near identical depositional structures. These findings thus have direct relevance to the on-going debate about whether, and in what form, reef communities will be able to re-establish themselves following periods of suppressed growth, such as those projected for the near-future.

Late Paleozoic reefs and their significance for tectonics and oil-gas exploration in the Hinggan-Inner Mongolia area

Many reefs of the Late Paleozoic have been discovered recently in the Hinggan-Inner Mongolia area. These reefs clearly are geographically extensive, and possess distinctive features and well-developed reef-facies. They have been found to contain five reef-building communities and were constructed in four periods. Colonial coral-algal reefs at Aohan and Chifeng represent a warm shallow-sea in the Carboniferous. Different reefs in the Xiwu Banner were formed in three periods: early Late Carboniferous, late Late Carboniferous and Early Permian. These reefs were built in warm sea conditions. Their buildup types include colonial coral frameworks, algae-buildings and lime-mud mounds. Bryozoan reefs in the Zhalaite and Dongwu banners were built in the late Middle Permian and thrived in a cold shallow-sea. All reefs grew independently on two kinds of sedimentary platforms, carbonate and carbonate-clastic mixed platforms. Four reef-forming periods occurred later from south to north, along a collisional course between the North China Plate and the Siberian Plate. These reefs can be arranged into three ‘reef-links’ or reef zones that extend along plate margins. Among these, the Aohan-Chifeng reef-link indicates a northern margin of the North China Plate, the Zhalaite-Dongwu reef-link marks a southern margin of the Siberian Plate, and the Xiwu-Beishan reef-link reflects the former existence of some inter-plates. The strata of each reef-facies are thick and contain rich asphalt deposits. Overlapping and heteropic layers are very thick and contain dark oil/gas-rich horizons; TOC analyses verify that most of these are good hydrocarbon source rocks. This study shows that the study area is an excellent candidate for oil-gas exploration.

Microbial mounds prior to the Frasnian-Famennian mass extinctions, Hantang, Guilin, South China

Late Frasnian mounds of the Yunghsien Formation, Guilin, South China, developed as part of the Guilin platform, mostly in reef-flat and platform margin settings. Microbial mounds in platform margin settings at Hantang, about 10 km west of Guilin, contain Frasnian biota, such as Stachyodes and Kuangxiastraea and, thus, occur below the Frasnian-Famennian mass extinction boundary. Platform margin facies were dominated by microbes, algae and receptaculitids. Massive corals and stromatoporoids are not common and rarely show reef-building functions as they did in Givetian time. The margin mounds are composed of brachiopod-receptaculitid cementstone, and a variety of boundstones that contain Rothpletzella, Renalcis, thrombolite and stromatolite. Other microbial communities include Girvanella, Izhella, Ortonella and Wetheredella. Solenoporoid algae are abundant locally. Zebra structures and neptunian dykes are well-developed at some intervals. Pervasive early cementation played an important role in lithification of the microbial boundstones and rudstones. Frasnian reefs of many regions of the world were constructed by stromatoporoids and corals, although a shift to calcimicrobe-dominated frameworks occurred before the Famennian. However, the exact ages of many Frasnian margin outcrops are poorly constrained owing to difficulties dating shallow carbonate facies. The Hantang mounds represent a microbe-dominated reef-building community with rare skeletal reef builders, consistent with major Late Devonian changes in reef composition, diversity and guild structure occurring before the end of the Frasnian. A similar transition occurred in the Canning Basin of Western Australia, but coeval successions in North America, Western Europe and the northern Urals are either less well-known or represent different bathymetric settings. The transition in reef-building style below the Frasnian-Famennian boundary is documented here in the two best exposed successions on two continents, which may have been global. Set in the larger context of Late Devonian and Mississippian microbial reef-building, the Hantang mounds help to demonstrate that controls on microbial reef communities differed from those on larger skeletal reef biota. Calcimicrobes replaced stromatoporoids as major reef builders before the Frasnian-Famennian extinction event, and increasing stromatoporoid diversity towards the end of the Famennian did not result in a resurgence of skeletal reef frameworks. Calcimicrobes dominated margin facies through the Famennian, but declined near the Devonian-Carboniferous boundary. Stromatolite and thrombolite facies, which occurred behind the mound margin at Hantang, rose to dominate Mississippian shallow-water reef frameworks with only a minor resurgence of the important Frasnian calcimicrobe Renalcis in the Visean when well-skeletonized organisms (corals) also became volumetrically significant frame builders again.

Quaternary development of resilient reefs on the subsiding kimberley continental margin, Northwest Australia

The Kimberley region in remote northwest Australia has poorly known reef systems of two types; coastal fringing reefs and atoll-like shelf-edge reefs. As a major geomorphic feature (from 12ºS to 18ºS) situated along a subsiding continental margin, the shelf edge reefs are in a tropical realm with warm temperatures, relatively low salinity, clear low nutrient waters lacking sediment input, and Indo-West Pacific corals of moderate diversity. Seismic architecture of the Rowley Shoals reveals that differential pre-Holocene subsidence and relative elevation of the pre-Holocene substrate have controlled lagoon sediment infill and reef morphology, forming an evolutionary series reflecting differential accommodation in three otherwise similar reef systems. The Holocene core described for North Scott Reef confirms previous seismic interpretations, and provides a rare ocean-facing reef record. It demonstrates that the Indo-Pacific reef growth phase (RG111) developed during moderate rates of sea level rise of 10 mm/year from 11 to about 7-6.5 ka BP until sea level stabilization, filling the available 27 m of pre-Holocene accommodation. Despite the medium to high hydrodynamic energy imposed by the 4m tides, swell waves and cyclones the reef-building communities represent relatively low-wave energy settings due to their southeast facing and protection afforded by the proximity of the South Reef platform. This study demonstrates the resilience of reefs on the subsiding margin whilst linking Holocene reef morphology to the relative amount of pre-Holocene subsidence.

Relationship between species diversity and reef growth in the Holocene at Ishigaki Island, Pacific Ocean

Abstract Coral reefs are influenced by global and local factors, and living corals are currently faced with a potential loss of species diversity. Knowledge of the relationship between species diversity and reef growth during the Holocene is important in terms of accurately reconstructing natural conditions prior to recent disturbances (e.g., human impact, pollution, and over-harvesting) and in predicting future scenarios (e.g., abrupt sea-level rise, coastal change, and economic services). This study seeks to characterize the Holocene and present-day reef at Ishigaki Island in the Ryukyu Islands, focusing on spatial and temporal variations in the relationship between species diversity and reef growth. The analysis is based on a drilling core obtained for the Holocene reefs and quantitative species-diversity data (Shannon and Weaver's diversity index, H ′) obtained for the present-day reef. H ′ was calculated for four coral communities surveyed at the Ibaruma and Fukido reefs. The Holocene sequence was dominated by the corymbose coral community (e.g., Acropora digitifera , A. hyacinthus , Goniastrea retiformis , and Platygyra ryukyuensis ), yielding an H ′ value of 1.6. The encrusting coral community (e.g., Echinopora lamellose and Pachyseris rugosa ) showed the highest diversity at the reef ( H ′ = 2.2); however, this community was not one of the main reef builders during the Holocene. The massive coral community (e.g., Porites lutea and Favites chinensis ) showed the lowest diversity ( H ′ = 0.6). It also made a minor contribution to reef building; this community appeared in a shallow lagoon once sea level had stabilized. The arborescent coral community (e.g., A. formosa and A. nobilis ) was one of the main reef builders, although yielding an H ′ value of much less than 1.0. Species diversity is not a prerequisite in terms of Holocene reef growth. Thus, a few species (e.g., A. digitifera , A. hyacinthus , A. formosa , A. nobilis , G. retiformis , and P. ryukyuensis ) from two main reef-building communities are important for reef growth. These corals that act as reefs are characterized by high growth rates, having an upward reef growth rate of 2–12 m kyr − 1 in the Indo-Pacific during the Holocene.

1200 year paleoecological record of coral community development from the terrigenous inner shelf of the Great Barrier Reef

Increased terrestrial sediment and nutrient yields are regarded as significant threats to coral reef health. Within the central Great Barrier Reef lagoon, where water quality has reportedly declined since European settlement (since ca. A.D. 1850), inner-shelf reef conditions have purportedly deteriorated. However, the link between reef decline and water-quality change remains controversial, primarily because of a lack of pre-European period ecological baseline data against which to assess contemporary ecological states. Here we present a high-resolution record of reef accretion and coral community composition from a turbid-zone, nearshore reef on the inner shelf of the Great Barrier Reef; the record is based on six radiocarbon date–constrained cores, and extends back to ca. 1200 calibrated yr B.P. Results demonstrate not only the potential for coral communities to initiate and persist in settings dominated by fine-grained terrigenous sediment accumulation, but also that a temporally persistent (but low diversity) suite of corals has dominated the reef-building community at this site for at least the past millennium. Furthermore, the coral assemblages exhibit no evidence of community shifts attributable to post-European water-quality changes. While extrapolation of these findings to other turbid-zone reefs must remain tentative, the study raises important questions about the resilience of inner-shelf reefs that are under terrestrial sediment influence and subject to elevated turbidity conditions, and demonstrates the potential to develop detailed, millennial time scale, coral community records from Holocene reef systems.

The role of microbes in reef-building communities of the Cannindah limestone (Mississippian), Monto region, Queensland, Australia

Reefs in the Cannindah Limestone at Old Cannindah Homestead, Monto region, Queensland, are exceptional in Eastern Australian Mississippian (Carboniferous) build-ups because of their largest dimension and differentiated microbial fabrics. Calcimicrobes and microbial carbonates, which represent a marine reefal environment occupied by both corals and sponges, are particularly abundant in the reef framework fabrics compared to other Mississippian build-ups in the world. They contributed significantly to the rigidity of the reefs on a crinoidal bank setting. Metazoans and calcimicrobes coexisted and played different roles in reef construction. Reef-building and cavity-dwelling microbes include Renalcis, Palaeomicrocodium, Girvanella, problematic Aphralysia, Ortonella, Shamovella-like, Rothpletzella-like, Wetheredella-like, and some problematic calcimicrobes, which occur in inter-corallite infillings of fasciculate rugose corals, in thrombolitic textures, in or within deposits between microdigitate stromatolite and laminated microbialites, and in reef cavities. Some reef intervals are entirely formed by Renalcis, Palaeomicrocodium, problematic calcimicrobes, and cement. Girvanella, as an encrusting calcimicrobe, generally bound bioclasts and micrite, or together with cement, formed boundstone. Microbial carbonates, including thrombolites, microencrusters, microdigitate stromatolite, laminated and tabular microbialite, irregular layers of self-encrusting vesicles, and microbial micrite, occur commonly in reef framestone and boundstone. The role of microbes and relevant microbial carbonates in the Cannindah reef limestone highlighted a significant account of microbial facies complexes associated with the Mississippian reefs.

Biologic response to environmental stress in tropical reefs: Lessons from modern Polynesian coralgal atolls and Middle Permian sponge and Shamovella-microbe reefs (Capitan Limestone USA)

Despite prejudices that comparisons of paleoecological patterns in modern and fossil reef communities are of doubtful validity, we compare the biologic response of living coralgal reefs in French Polynesia to environmental stress with an exceptionally well exposed Middle Permian sponge reef and Shamovella-microbial reef of the Capitan Limestone in New Mexico. In the western Tuamotu Archipelago, reef margins are characterized by depth-related changes of biodiversity. The subtidal basic reefbuilding community contains the highest diversity (23 coral and 6 calcareous algal species). With decreasing water depth and increasing environmental stress, diversity reaches a minimum of five taxa on the reef flat. The Capitan consists of two reef stages. Reefbuilders of the lowermost exposed part of Stage 1 formed a cement-rich sponge reef with 42 taxa (28 sponge species). Decreasing water depth along the reef face is accompanied by loss of five taxa, variations in the gross morphology of sponges and changes in framework architecture. Stage 2, dominated by Shamovella obscura, one bryozoan species and microbes, is sandwiched between two unconformities suggesting much shallower water and higher environmental stress. Despite differences in shelf profile and taxonomy, both the modern and Permian reefbuilders respond to increasing environmental stress with diversity impoverishment and dominance of binders.

Unique recovery stage of reef communities after F/F event in a huge coral reef of Carboniferous, Southern Guizhou, China

A huge coral reef occurring in the Triticites belt of the Maping Formation, in Bianping Village, about 4 km west of Houchang Town from Ziyun County, Southern Guizhou, China is described. The coral reef has been well studied and some significant characteristics were dis-covered: the composition of reef-building community is very monotonous; there are only one or two builders in each reef-building stage; the dwellers are also poor in variety; the reef-building process is very simple; the reef has been separately built by various reef-building mechanisms, and there have been few parts built by two coexisting building mechanisms; the process of reef building is often discontinuous and lacks transition. All these characteristics are considered to be unique to the recovery stage of reef communities after F/F event and are representative of a process that reef communities must undergo post the catastrophe.

Early‐Middle Permian Reef Frameworks and Reef‐building Models in the Eastern Kunlun Mountains

AbstractReef frameworks and building models of the Early‐Middle Permian in the eastern Kunlun Mountains have been verified through studies of reef‐building communities, palaeoecology and carbonate facies. The eastern Kunlun reefs are built mainly by 6 reef‐building communities, which include 11 major categories of frame‐building organisms and 6 categories of reef‐associated organisms. Eight types of reef‐frames have been distinguished and eleven kinds of rocks identified to belong to 6 reef facies. Three sorts of reefs classified by previous researchers, namely mudmounds, knoll reefs and walled reefs, are well developed in the study area. Such reef‐facies association and reef distribution show that there are 4 models of reef growth and development, i.e. the tidal‐bank knoll‐reef model, the plateau‐margin wall‐reef model, the composite wall‐reef model and the deep‐water mudmound model. The reefs are mainly constructed by calcareous sponge and calcareous algae, which are similar to all Permian reefs in other areas of South China and the world. Their great scales indicate a secular stable platform‐marginal environment.