Reef Formation Research Articles

A possible link between coral reef success, crustose coralline algae and the evolution of herbivory

Crustose coralline red algae (CCA) play a key role in the consolidation of many modern tropical coral reefs. It is unclear, however, if their function as reef consolidators was equally pronounced in the geological past. Using a comprehensive database on ancient reefs, we show a strong correlation between the presence of CCA and the formation of true coral reefs throughout the last 150 Ma. We investigated if repeated breakdowns in the potential capacity of CCA to spur reef development were associated with sea level, ocean temperature, CO2 concentration, CCA species diversity, and/or the evolution of major herbivore groups. Model results show that the correlation between the occurrence of CCA and the development of true coral reefs increased with CCA diversity and cooler ocean temperatures while the diversification of herbivores had a transient negative effect. The evolution of novel herbivore groups compromised the interaction between CCA and true reef growth at least three times in the investigated time interval. These crises have been overcome by morphological adaptations of CCA.

Composition, distribution and relative abundance of fishes linked to fringing reefs of southern Veracruz, Gulf of Mexico

The biological knowledge of the reef communities of southern Veracruz is fundamental, because, according to the Mexican National Commission for the Knowledge and Use of Biodiversity, they are part of a priority marine zone. This paper describes the ichthyological components of the southern Veracruz fringing reefs, including information on abundance and distribution. 146 random visual censuses were conducted in 5 habitats characterized by the dominant benthic groups and environmental features (structural complexity, transparency, and depth). In each census, fish species were identified and their abundance estimated using 6 ordinal categories. Subsequently, the similarity of the ichthyologic communities with the Jaccard Index was determined. The reef formations of southern Veracruz include 91 fish species, 58 genera, and 31 families. According to their relative abundance, 25 % of the fish species were catalogued as rare, 25 % as uncommon, 23.9 % as occasional, and 22.7 % as common or abundant. The most abundant fish species were: Stegastes adustus, Halichoeres bivittatus, Thalassoma bifasciatum, Bodianus rufus, and Ophioblennius maclurei while, the families: Epinephelidae, Gobiidae, and Scaridae showed a scarce richness and abundance. The benthic attributes (coral cover) and environmental features of habitats were related to the richness, components, and relative abundance of fishes.

Abundance and distribution of the invasive polychaete Ficopomatus enigmaticus in three South African estuaries

Ficopomatus enigmaticus (Fauvel 1923) is a reef-building serpulid polychaete that is found in warm and temperate estuaries across the globe. This ecosystem engineer causes ecological and socio-economic impacts in invaded systems through efficient filtering of the water column and the formation of large calcareous reefs. As such it is important to monitor F. enigmaticus invasions and track changes in distribution and abundance. Although recent genetic studies have highlighted cryptic sympatric species within invasions previously ascribed to F. enigmaticus the genetic status in South Africa remains unresolved. This study provides an assessment of the invasion by this tube worm in three estuaries of conservation importance in the Western Cape, South Africa. Through the use of historical data, the trajectories of these invasions were considered. Zandvlei Estuary supported the largest standing stock (29 194.22 kg) while Berg River Estuary supported only 3.39 kg. It was notable that in both estuaries the worm was almost totally confined to artificial substrata. Despite the presence of large intact reefs in Milnerton Lagoon, no live worms were recorded in 2019. Comparisons with historical data revealed that populations have declined in all three estuaries. These results highlight the need for routine monitoring of Ficopomatus populations. It is suggested that episodic removal of the small reefs from Berg River Estuary could minimise spread within the estuary and prevent the negative impacts known from elsewhere. Strategic removal from Zandvlei Estuary, and Milnerton Lagoon should the worm be detected again, could limit its negative impacts in these systems while retaining the benefit of enhanced water quality associated with this prolific filter feeder.

Stratigraphy and sedimentology of the Pennsylvanian Grande Anse Formation, Cumberland Basin, eastern Canada: its relationship to salt tectonics and coeval strata of the Joggins World Heritage Site

The Cumberland Basin is one of several sedimentary basins composing the late Paleozoic Maritimes Basin complex of eastern Canada. Pennsylvanian salt tectonics in the Cumberland Basin caused two salt mini-basins to evolve on either side of the Minudie Anticline, a salt wall. South of the wall (Athol Syncline), along the Joggins World Heritage shoreline, an ∼3000 m succession of strata (Little River, Joggins, Springhill Mines, and Ragged Reef formations) accumulated conformably on the Boss Point Formation. North of the wall (Black Point sub-basin), the biostratigraphically equivalent, but mostly unstudied, ∼600 m thick succession of Grande Anse Formation lies in angular unconformity on folded and faulted Boss Point and basal Little River formations. Grande Anse Formation sedimentology indicates four lithofacies associations: floodplain (LA1), braided channel (LA2), sheet flood (LA3), and debris flow deposits (LA4). One possible model has the Black Point sub-basin with its own hydrological system, completely separated from the Athol Syncline. A low subsidence rate combined with the low sedimentation rate produced the ∼600 m thick sand- and mud-prone succession that was contemporaneous with the ∼3 km succession to the south. The second model proposes that north of the salt wall was exposed to erosion during accumulation of Joggins and Springhill Mines formation strata to the south. Subsequently, the sediment of the lithologically similar Ragged Reef and Grande Anse formations either (i) onlapped to the north, unconformably on the folded Boss Point; or (ii) unconformably–disconformably on the underlying strata after a period of time indistinguishable in the biostratigraphic record.

Facies and sequence stratigraphic architecture of the Mural Limestone (Albian), Arizona: Carbonate response to global and local factors and implications for reservoir characterization

AbstractThis study documents the detailed facies and sequence stratigraphic architecture of a multi‐cyclic patch‐reef and its associated ramp interior facies that formed during Oceanic Anoxic Event 1b in the Mural Limestone, Arizona, USA. Ramp interior facies are comprised of bedded wackestone/packstone, rudist build‐up and coral–algal patch‐reef facies located north of Bisbee, Arizona, at the Grassy Hill locality. The larger multi‐cyclic patch‐reef that developed coevallyca5 km to the south of Grassy Hill consists of a high‐angle windward margin with a narrowca70 m long reef frame containing vertically zonatedMicrosolena, Actinastrea, diverse branching coral and rudist assemblages, and an 870 m long low‐angle leeward margin comprised of reef debris rudstone and grainstone shoal facies. Similar reef geomorphology and orientation is documented across the Gulf of Mexico and reflects the shelf‐wide north to north‐east‐trending prevailing wind and current energies. Controls affecting reef formation and growth patterns include changes in accommodation space associated with low‐amplitude global sea‐level rise and regional thermotectonic subsidence, local accommodation space and nutrient fluctuations associated with the inner shelf depositional setting within a humid and siliciclastic‐rich environment. Four aggradational to retrogradational high‐frequency sequences are documented in Arizona: High‐frequency sequences 1 and 2 represent the first pulse of patch‐reef development in an overall second‐order marine transgression over the Sonora/Bisbee Shelf. These sequences correlate to δ13C signatures associated with Oceanic Anoxic Event 1b across the Gulf of Mexico and suggest that carbonate reefs persisted on the ramp interior during this time. High‐frequency sequences 3 and 4 record a second brief transgression and backstepping of reef facies followed by the final regression of shallow shelf carbonates that correlates to more robust patch‐reef development in Sonora, Mexico. The patch‐reef at Paul Spur is an excellent outcrop analogue for productive patch‐reefs in the Maverick Basin (Comanche Shelf) of Texas. Detailed facies mapping of this outcrop analogue shows that the greatest reservoir potential is contained within the backreef grainstone shoals where primary porosity of up to 15% is observed.

Status of corals along the Sindh coast of Pakistan: Prevailing environmental conditions, their impacts on community structure and conservation approaches

Reef system across the globe is facing serious anthropogenic threats and impacts. The present study describes the status of corals, prevailing stresses and their impacts on community structure along the Sindh coast of Pakistan. In the current study, 21 species of hard corals were recorded. All together, 50 live coral species recorded from the coastal waters of Pakistan. High diversity occurred at Churna Island (15 species). A little bit patch reef formation was observed at Churna Island (dive sites 2 and 3) while scattered colonies were recorded in coastal habitats. Porites species were found dominating both in coastal and offshore environments. Overall, temperature and nutrient concentrations were found to be fluctuating than what corals prefer, however, pH concentrations were found in normal ranges. Calcium, carbon and oxygen were recorded as major elements incorporated in coral skeletons. Possible causes of limited coral fauna and a confined distribution pattern appeared to be linked with local factors (strong wave action, high nutrient concentrations, temperature fluctuations, past geological events, reversal monsoon and overfishing) rather than global changes. Other impacts, for example diving tourism, coral mining or collection for ornaments or sale are minor. Prevailing stresses, increase in the construction of local infrastructure in coastal areas and unmanaged tourism indicates that in future, the level of pollution will further increase in coastal areas. As a result, a further shift in community structure will occur and it appears that only Porites will survive in the coastal waters of Pakistan. Future protection efforts should focus on regular monitoring and establishing of an effective Marine Protected Area at least around the shallow habitats of the Churna Island.

ASYNCHRONOUS DEVELOPMENT OF REEFS AND REEF-BUILDING BIOTA. PALEOZOIC

This work analyses the development of reefs, which represent thick morphologically expressed carbonate massifs created by the activity of frame-forming organisms. Major stages in the development of reefs include the periods of Early Cambrian, Ordovician, Silurian-Devonian, Late Visean-Serpukhovian and Permian, the upper boundaries of which are generally determined by mass extinction events. The main reef builders during the Early Cambrian were archaeocyatha and epiphytaceans, while Ordovician reefs were created by sponges, stromatoporoids, tabulata and bryozoans. Stromatoporoid, tabulata, rugose and, to a lesser extent, bryozoans were the reef builders during the longest Silurian-Devonian period. Bryozoans and corals served as the frame-forming organisms for Upper Visean-Serpukhovian reefs. However, during the Permian, reefs were built primarily by sponges and, to a lesser extent, by bryozoans and corals. It is shown that there is no strict correspondence between the termination of reef formation and the beginning of extinction events. During extinction periods, potential reef builders did exist, although beyond the reef biocoenosis structure. Similarly, the beginning of reef formation occurs somewhat later than the appearance of the corresponding frame-forming organisms. Apparently, it takes time for organisms to develop such a biocoenosis that could trigger the formation of reef ecosystems. Reef ecosystems are stable under relatively constant external conditions, changes in which cause first the degradation of the biocoenosis and then the extinction of its constituent organisms. Therefore, the process of reef formation is terminated before the actual extinction of organisms.

Trends in Oyster Populations in the Northeastern Gulf of Mexico: An Assessment of River Discharge and Fishing Effects over Time and Space

AbstractWithin the Big Bend region of the northeastern Gulf of Mexico, one of the least developed coastlines in the continental USA, intertidal and subtidal populations of eastern oyster Crassostrea virginica (hereafter referred to as “oyster”) are a critical ecosystem and important economic constituent. We assessed trends in intertidal oyster populations, river discharge, and commercial fishing activity in the Suwannee River estuary within the Big Bend region using fisheries‐independent data from irregular monitoring efforts and publicly available environmental data. We used generalized linear models to evaluate counts of oysters from line‐transect surveys over time and space. We assessed model performance using simulation to understand potential bias and then evaluated whether these counts were related to freshwater inputs from the Suwannee River and commercial oyster fishing effort and landings at different time lags. We found that intertidal oyster counts have declined over time and that most of these declines are found in inshore intertidal oyster bars, which are becoming degraded. We also found a significant relationship between oyster counts and a 1‐year lag on mean daily Suwannee River discharge, but including commercial fishery trips or landings did not improve model fit. It is unclear whether declines in intertidal oyster bars are offset by formation of new oyster reefs elsewhere. These results quantify rapid declines in intertidal oyster reefs in a region of coastline with high conservation value that can be used to inform ongoing and proposed restoration projects in the region.

Shallow coral reef community mapping and update on its ecological units using aerial images at Isla Arena, Colombian Caribbean

ABSTRACT Remote sensing by unmanned aerial vehicles (UAVs) provides for obtaining large amounts of high-resolution data without direct intervention, which can be managed with geographic information systems (GIS). This allow spatial analysis of a habitat based on georeferenced data which is important to understand the structure and ecological distribution that are fundamental to ecosystems. Isla Arena (10°44ʹ20” N, 75°21ʹ10” W) is an inshore small shoal with a well-developed coral reef formation, despite the sedimentary influence of the Magdalena River in the Colombian Caribbean. Twenty years ago, habitat mapping of ecological units (EUs) of the area was carried out as a baseline study. In this study, we applied an analysis of remotely sensed aerial images, coupled with traditional in situ data to evaluate two different objectives. The first objective was to report the current ecological units in the reef formation with their respective distribution using a high-resolution orthophotomosaic to make a supervised classification based on the spectral reflectance of pixels and a spatial analysis of the reef formation. We evaluated 12 substrate components, of which eight were identified at the species level; then, seven EUs were defined in a thematic map. The second objective was to evaluate variations in the structure of the sessile community with underwater video transects to compare with a baseline study. We found that the coral cover remained similar but that seagrasses and zoanthids decreased in abundance, and macroalgae and sponge abundances increased, which could indicate reef degradation. The implementation of remote sensing by UAVs at Isla Arena was successful and provides a high-resolution alternative for describing the attributes of a shallow reef system. The comparison with the baseline study of the island allowed us to estimate the changes in the community structure and to update its EUs.

Warming and acidification threaten glass sponge Aphrocallistes vastus pumping and reef formation

The glass sponge Aphrocallistes vastus contributes to the formation of large reefs unique to the Northeast Pacific Ocean. These habitats have tremendous filtration capacity that facilitates flow of carbon between trophic levels. Their sensitivity and resilience to climate change, and thus persistence in the Anthropocene, is unknown. Here we show that ocean acidification and warming, alone and in combination have significant adverse effects on pumping capacity, contribute to irreversible tissue withdrawal, and weaken skeletal strength and stiffness of A. vastus. Within one month sponges exposed to warming (including combined treatment) ceased pumping (50–60%) and exhibited tissue withdrawal (10–25%). Thermal and acidification stress significantly reduced skeletal stiffness, and warming weakened it, potentially curtailing reef formation. Environmental data suggests conditions causing irreversible damage are possible in the field at +0.5 °C above current conditions, indicating that ongoing climate change is a serious and immediate threat to A. vastus, reef dependent communities, and potentially other glass sponges.

Significance of granite-greenstone terranes in the formation of Witwatersrand-type gold mineralisation – A case study of the Neoarchaean Black Reef Formation, South Africa

Geological characterisation and U-Pb geochronology of detrital zircon grains has proven valuable in finding potential source terranes of siliciclastic sediments. Sediment transport and reworking from gold-bearing Archaean/Palaeoproterozoic granite-greenstone rocks are significant in the formation of conglomerate-hosted (Witwatersrand-type) gold deposits. We further support this link with an example from the Neoarchaean Black Reef Formation, in the Carletonville Goldfield, South Africa. In this study, the detrital and hydrothermal pyrite grains are petrographically distinguishable. Association of gold with solely detrital heavy minerals such as pyrite and not with hydrothermal minerals is similar to other Witwatersrand-type examples, which were formed during reducing atmospheric conditions from granite-greenstone protosource rocks. Textural evidence, together with gold occurrence data, support gradual homogenisation of primary sedimentological and mineralogical features due to post-depositional alteration. Uranium-Pb dating of the Black Reef Formation detrital zircon grains yields an age between 3149 and 3061 Ma, indicating that that the provenance of Black Reef Formation sediments could have been derived from a mixture of the hinterland proto granite-greenstone rocks, and from the reworking of Witwatersrand auriferous conglomerates. We further infer a favourable palaeo-drainage for primary sedimentary gold deposition from an isopach model and palaeocurrent data. The fluvial origin of the Black Reef Formation basal conglomerate provides an ideal setting for gold mobilisation from the sediment-source rocks. Notwithstanding the contribution of hydrothermal activity, sedimentary processes are interpreted to have been primary in the initial concentration of gold through reworking of the Witwatersrand auriferous conglomerates. This has important implications for the genesis of the younger Witwatersrand-type gold mineralisation. The fact that the Witwatersrand-type gold deposits, a target for exploration, occur spatially and temporally within the Archaean/Palaeoproterozoic geological record demonstrates that the Witwatersrand Basin is not unique in terms of composition and paragenesis, but is unique in terms of physical size and magnitude of its gold and uranium endowment.

Zircon U-Pb-Hf isotope systematics of Transvaal Supergroup – Constraints for the geodynamic evolution of the Kaapvaal Craton and its hinterland between 2.65 and 2.06 Ga

The Transvaal Basin in South Africa hosts a 15 km thick pile of sedimentary successions deposited over a period of >600 Ma during the Neoarchean to Paleoproterozoic. Presently, little is known about the source of these sediments, as well as about the tectono-magmatic evolution in the hinterland of the Transvaal Basin, preventing detailed geotectonic correlations of the Kaapvaal Craton (KC) with other cratons worldwide. To solve this problem, we present the first systematic study of combined U-Pb and Lu-Hf isotope data of >2000 detrital zircons from fourteen formations of the Transvaal Supergroup. These reveal that clastic sedimentary rocks were supplied from sources on and off the present-day KC. Detrital zircons in conglomerates of the Wolkberg and Black Reef formations, maximum deposition ages at 2769 ± 8 and 2618 ± 11 Ma respectively, were mainly supplied from surrounding KC, either from Pietersburg Block Basement (PBB), and/or from eroded sedimentary successions of the Witwatersrand, Pongola and/or Ventersdorp Supergroups. In contrast, clastic sedimentary rocks of the Rooihoogte, Duitschland and Timeball Hill formations (maximum deposition ages at 2353 ± 18 Ma, 2342 ± 18 and 2290 ± 8 Ma, respectively) were predominately supplied from a juvenile Neoarchean terrane (JUNAT) formed at 2570–2500 Ma (εHf2500 Ma = +2 to +9) and intensely reworked at 2400 Ma, and to a minor amount from a composite Archean terrane (CAT) emplaced by granitoids between 3540 and 2680 Ma, and affected by crust reworking at 2570–2430 Ma (εHf2.5Ga = −3 to −12) in a Neoarchean to Paleoproterozoic continental arc terrane (NPCAT). Subsequent periodic reworking of JUNAT at 2250–2220 Ma and 2120 Ma is recorded by detrital zircons in sandstones of the overlying Boshoek, Dwaalheuwel, Daspoort, Magaliesberg and post-Magaliesberg formations, having maximum deposition ages at 2243 ± 7, 2242 ± 7, 2240 ± 7, 2080 ± 7, and 2068 ± 7 Ma, respectively. The Archean zircons (age >2650 Ma) in all these formations were mainly supplied from PBB. The new data sets also suggest that the KC was connected to CAT, NPCAT and JUNAT at <2350 Ma. The nearly absence of detrital zircons with ages of 2570–2500 Ma in all formations younger than Boshoek perhaps results from intense reworking of JUNAT during magmatic events at 2400, 2340, 2220, and 2120 Ma, causing loss of the original juvenile character. Paleoproterozoic zircons with ages of 2220 and 2120 Ma in Dullstroom sandstones most likely result from re-deposition of post-Magalisberg sedimentary rocks, and Archean zircons from sources similar to Moodies and Fig Tree sandstones of the Barberton greenstone belt. Comparison of our new data from the Transvaal Basin with such from the Turee Creek and Horseshoe basins in NW-Australia provides no evidence for Kaapvaal-Pilbara Craton connection during the Neoarchean to Paleoproterozoic.

The contribution of publications of the Yorkshire Geological Society to the understanding of the geological development of the Carboniferous Pennine Basin, northern England

The Carboniferous rocks of the Pennine Basin form the topographical spine of the region between the Scottish Border and the Peak District. They provided many of the mineral resources that fuelled the Industrial Revolution and the growth of the great northern English cities. The description of these resources was very much a focus of early papers in the Proceedings , but they went beyond the assessment of their economic importance, providing striking early insights into our understanding of deep time when the Bible still had a strong control on scientific thinking. Over a 180 year history of publication, the Proceedings and Occasional Publications contain an unparalleled description of the rocks of the Pennine Basin of Carboniferous deposition, and they continue to provide great insight into what have been intensively studied successions but of which much still remains to be learned. This review considers the relevance of these publications to our understanding of the sedimentology of Carboniferous strata, the geometries of Carboniferous basins, how these basins constrained the formation of reefs and controlled the movement of rivers and deltas in the process of eventual infill of these basins, and how sea-level variations influenced the development of cyclical successions, the hallmark of much of the Carboniferous succession.

Tectonic and paleogeographic controls on development of the Early–Middle Ordovician Shanganning carbonate platform, Ordos Basin, North China

Lower–Middle Ordovician platform carbonates are important oil and gas reservoir rocks in the Ordos Basin of the North China craton (NCC). In recent years, numerous cores have been recovered from these units, but the depositional environments and facies architecture of this large carbonate platform system have not yet been reported in detail. This study integrates sedimentological and magnetic fabric data collected from outcrops and cores to document variation in microfacies and facies associations within the Shanganning carbonate platform (SCP), infer paleowind directions and the paleogeographic location of the SCP, and evaluate tectonic and paleogeographic controls on platform development. This analysis documented 25 microfacies belonging to 7 microfacies fabric and sediment types: carbonate mudstone, wackestone, packstone–grainstone, evaporite, bindstone–framestone, siliciclastics, and dolostone. Microfacies can be grouped into facies associations that represent tidal-flat, open-platform, restricted-platform, evaporite-platform, platform-margin, slope, and deep-basinal depositional environments. These environments are mainly distributed zonally around the L-shaped Qingyang paleo-uplift on the western and southern margins of the SCP. Anisotropy of magnetic susceptibility measurements at five platform-margin locales yielded paleocurrent directions of (all approximately) 318°–348°, 51°–81°, 42°–72°, 80°–110°, and 54°–84° from paleo-north after correction for a 120°–150° clockwise rotation of the NCC since the Ordovician. The depositional architecture of the SCP depended on a combination of tectonic and paleogeographic (wind) influences. Local tectonic movements controlled the spatial distribution of facies associations around the Qingyang paleo-uplift, which was characterized by open, restricted, and evaporite-platform facies in the platform interior and mainly slope and basinal facies on the outer-platform margin (to the west and south of the Qingyang paleo-uplift). Vertical tectonic movements resulted in cyclic submergence and emergence of the platform over its approximately 20-m.y.-long formation history. Paleo–trade winds influenced aspects of facies zonation across the platform, including growth of metazoan reefs on the windward platform margin and formation of oolitic grainstone and microbial reefs on the leeward platform margin. The facies model for the SCP developed in this study should provide a useful reference framework for future carbonate oil and gas exploration in Lower–Middle Ordovician units of the Ordos Basin. Furthermore, this study makes innovative use of magnetic anisotropy data, in combination with standard petrographic, core, and field data, to discern facies patterns and controls on a paleo-carbonate platform, which is an integrated methodology that may serve as a model for future studies of other carbonate platforms.

A coralline alga gains tolerance to ocean acidification over multiple generations of exposure

Crustose coralline algae play a crucial role in the building of reefs in the photic zones of nearshore ecosystems globally, and are highly susceptible to ocean acidification1–3. Nevertheless, the extent to which ecologically important crustose coralline algae can gain tolerance to ocean acidification over multiple generations of exposure is unknown. We show that, while calcification of juvenile crustose coralline algae is initially highly sensitive to ocean acidification, after six generations of exposure the effects of ocean acidification disappear. A reciprocal transplant experiment conducted on the seventh generation, where half of all replicates were interchanged across treatments, confirmed that they had acquired tolerance to low pH and not simply to laboratory conditions. Neither exposure to greater pH variability, nor chemical conditions within the micro-scale calcifying fluid internally, appeared to play a role in fostering this capacity. Our results demonstrate that reef-accreting taxa can gain tolerance to ocean acidification over multiple generations of exposure, suggesting that some of these cosmopolitan species could maintain their critical ecological role in reef formation. Crustose coralline algae help build coral reef structures through calcification, a process threatened under ocean acidification. Juvenile algae were highly sensitive on initial exposure to ocean acidification, but continued exposure over six generations showed a gain of tolerance.

СИЛУРИЙСКИЙ РИФ ЛЕДЯНСКОГО ПОДНЯТИЯ КАК ПОТЕНЦИАЛЬНЫЙ РЕЗЕРВУАР УГЛЕВОДОРОДОВ НА СЕВЕРЕ СИБИРСКОЙ ПЛАТФОРМЫ

The results of the lithological study of the Silurian sediments drilled in by wells within the Ledyansk uplift in the north of the Siberian platform are presented. It is found that in the early Silurian time on the territory under consideration a large organogenic buildup corresponding to typical Silurian reefs of a stable shelf was formed, the formation stage of its framework was confined to Wenlock. In Late Silurian, against the background of regression, the reef formations were overlain by lagoon-sebkha clayey-evaporite deposits. It is shown that the heterogeneity of the section affected the distribution of reservoir properties. The high primary porosity of the reef framework contributed to the processes of dissolution, stylolization, fracturing and formation of a high-capacity reservoir. The combination of various voids led to the development of a complex reservoir. The saline-sulfate rocks of the Upper Silurian – Lower Devonian act as a seal. The question of the prospects for the oil and gas potential of the Silurian reef deposits is of particular relevance in view of the wholesale development of organogenic buildups on the Siberian platform in the Wenlock time.

Parental magma, magmatic stratigraphy, and reef-type PGE enrichment of the 2.44-Ga mafic-ultramafic N\xe4r\xe4nk\xe4vaara layered intrusion, Northern Finland

About 20 mafic-ultramafic layered intrusions in the northern Fennoscandian shield were emplaced during a widespread magmatic event at 2.5–2.4 Ga. The intrusions host orthomagmatic Ni-Cu-PGE and Cr-V-Ti-Fe deposits. We update the magmatic stratigraphy of the 2.44-Ga Näränkävaara mafic-ultramafic body, northeastern Finland, on the basis of new drill core and outcrop observations. The Näränkävaara body consists of an extensive basal dunite (1700 m thick), and a layered series comprising a peridotitic–pyroxenitic ultramafic zone (600 m thick) and a gabbronoritic–dioritic mafic zone (700 m thick). Two reversals are found in the layered series. The composition of the layered series parental magma was approximated using a previously unidentified marginal series gabbronorite. The parental magma was siliceous high-Mg basalt with high MgO, Ni, and Cr, but also high SiO2 and Zr, which suggests primary magma contamination by felsic crust. Cu/Pd ratio below that of primitive mantle implies PGE-fertility. The structural position of the marginal series indicates that the thick basal dunite represents an older wallrock for the layered intrusion. A subeconomic reef-type PGE-enriched zone is found in the border zone between the ultramafic and mafic zones and has an average thickness of 25 m with 150–250 ppb of Pt + Pd + Au. Offset-type metal distribution and high sulfide tenor (50–300 ppm Pd) and R-factor (105) suggest reef formation by sulfide saturation induced by fractional crystallization. The reef-forming process was probably interrupted by influx of magma related to the first reversal. Metal ratios suggest that this replenishing magma was PGE-depleted before emplacement.

How corals made rocks through the ages.

Hard, or stony, corals make rocks that can, on geological time scales, lead to the formation of massive reefs in shallow tropical and subtropical seas. In both historical and contemporary oceans, reef-building corals retain information about the marine environment in their skeletons, which is an organic-inorganic composite material. The elemental and isotopic composition of their skeletons is frequently used to reconstruct the environmental history of Earth's oceans over time, including temperature, pH, and salinity. Interpretation of this information requires knowledge of how the organisms formed their skeletons. The basic mechanism of formation of calcium carbonate skeleton in stony corals has been studied for decades. While some researchers consider coral skeletons as mainly passive recorders of ocean conditions, it has become increasingly clear that biological processes play key roles in the biomineralization mechanism. Understanding the role of the animal in living stony coral biomineralization and how it evolved has profound implications for interpreting environmental signatures in fossil corals to understand past ocean conditions. Here we review historical hypotheses and discuss the present understanding of how corals evolved and how their skeletons changed over geological time. We specifically explain how biological processes, particularly those occurring at the subcellular level, critically control the formation of calcium carbonate structures. We examine the different models that address the current debate including the tissue-skeleton interface, skeletal organic matrix, and biomineralization pathways. Finally, we consider how understanding the biological control of coral biomineralization is critical to informing future models of coral vulnerability to inevitable global change, particularly increasing ocean acidification.

ESR and U-Th dating results for Last Interglacial coral reef terraces at the northern coast of Cuba

Fossil coral reef terraces at the northern coast of Cuba in the vicinity of the Bay of Matanzas are forming a prominent flight of terraces. These terraces were already studied by several investigators, but a chronological classification based on numerical dating is still missing. In this study we focus on the lowest unit, the Seboruco terrace, which is assumed to be of MIS 5e age. The morphology of the Seboruco terrace and associated sea-level markers (reef crests and notches) were mapped and their altitude was measured over the whole study area in the field and by using remote sensing. The fossil corals building up the terrace were surveyed in numerous natural outcrops. The species of the fossil coral reefs were determined and subdivided in different facies zones. Fossil corals were taken for numerical dating by Electron Spin Resonance (ESR) and Uranium-series (U-Th) to establish a chronology of the MIS 5e coral reef formation. Both dating techniques yielded age results in good agreement with each other and the stratigraphic context. Corresponding to the field evidence, the age data indicates one MIS 5e sea-level highstand around 126 ka. Some younger ESR ages may be explained by the recrystallization of aragonitic corals and/or by U leaching. At one locality east of Matanzas, the radiometric results for an underlying coral reef body suggest an MIS 7 age. The sea-level markers for the MIS 5e highstand range from 5.5 m a.s.l. (reef crest) to a maximum of 7 m (notches) west of the Bay of Matanzas resulting in relatively low uplift rates of 0.003 m/ka and 0.036 m/ka when applying early MIS 5e sea-level estimates from tectonically stable coasts in the Caribbean between +2.5 m and +6.6 m. Inside the Bay of Matanzas itself, the elevation of sea-level markers increases to more than 10 m a.s.l. indicating a stronger uplift rate of 0.027 m/ka to 0.060 m/ka here.

Photo-movement in the sea anemone Aiptasia influenced by light quality and symbiotic association

The relationship between cnidarians and their micro-algal symbionts is crucial for normal animal function and the formation of coral reefs. We used the sea anemone Exaiptasia pallida (Aiptasia) as a model cnidarian–dinoflagellate system to determine the effects of white, blue and red light on photo-movement. In white light, phototropism and phototaxis of Aiptasia were dependent on the presence of symbionts; anemones with symbionts bent and moved toward the light, whereas aposymbiotic anemones (lacking algal symbionts) moved, but without strong directionality. Phototaxis and phototropism also occurred in blue light, but to a lesser extent than in white light, with no apparent response to red light. Phototactic behavior was also sensitive to the specific anemone–symbiont pairing. The ability to sense and move in response to light would presumably allow for selection of favorable habitats. Overall, this study demonstrates that the algal symbiont is required for photo-movement of the host and that the extent of movement is influenced by the different anemone–symbiont associations.