Reef Deposits Research Articles

A Middle Ordovician (Darriwilian) Calathium reef complex on the carbonate ramp of the northwestern Tarim Block, northwest China: A sedimentological approach

Middle Ordovician carbonates are exposed for 25km along the Lianglitag Mountains in the Tarim Basin, northwest China. They reflect platform carbonate and reef deposition along the ancient Central Tarim Uplift. The Darriwilian Yijianfang Formation, ~70m thick, was deposited in a shallow carbonate ramp setting, deepening seaward to the north in current geography. Reefal and biostromal units are constructed primarily by sessile Calathium of possible sponge affinity in the Middle Member of the formation. Patch reefs, ~10m in thickness and tens of meters in diameter, are common in the northern region. Associated shelly faunas, including trilobites, bivalves, and brachiopods, are diverse and preserved as coarse bioclastic materials together with intraclasts. Towards the south, patch reefs are smaller, <1m in thickness and with low relief. A biostrome formed by in situ Calathium framework is interpreted to act as a baffle for fine sediments, with smaller amounts of bioclasts and intraclasts. The biostrome is only ~3m thick in the southernmost section suggesting a calmer leeward setting initially. Tempestite beds composed of Calathium and nautiloid floatstones are abundant through the section, with monospecific brachiopod layers in the tempestite beds. This work demonstrates previously unrecognized paleogeographic variations of the Darriwilian Calathium reef complexes, which have larger patch reefs generally developing in the north area, smaller patch reefs dominating southward, and biostromes occurring in the southernmost locations. The reef complex was drowned due to sea-level rise, which is recorded in the upper Yijianfang Formation.

Post-rift sequence architecture and stratigraphy in the Oligo–Miocene Sardinia Rift (Western Mediterranean Sea)

Rift basins provide important sedimentary archives to reconstruct past tectonic and climatic conditions. Understanding their sedimentary history is, however, largely hampered by the competing influence of tectonic versus climatic forcing. The aim of this study is to comprehend the effects of local to regional tectonic and global climatic/eustatic changes on shallow marine depositional systems in the Sardinia Rift (Western Mediterranean Sea). For this purpose the stratigraphic and depositional relations of a mixed siliciclastic-carbonate ramp at the Porto Torres Basin margin were studied along extensive proximal to distal transects. Three depositional sequences (DS1 to DS3) of late Burdigalian to early Serravallian age have been identified, which are separated by erosional unconformities. Each contains a lower transgressive part and an upper regressive part. The former includes shoreface sandstone (DS2) or coral reef (DS3) deposits on the proximal ramp and channelized sheet sandstone (DS1) or basinal mudstone (DS2, DS3) deposits on the distal ramp, typically recording an upsection trend of sediment starvation. The latter is represented by basinward-prograding coralline red algal carbonate wedges due to enhanced shallow water carbonate production rates. In the long term, the depositional evolution from DS1 to DS3 reveals basin margin progradation associated with decreasing siliciclastic supply. Integrated calcareous nannoplankton-foraminiferal-pectinid biostratigraphy links the depositional sequences to third-order sea-level cycles and allows to correlate the erosional unconformities at the top of DS1 and DS2 with the Bur 5/Lan 1 and Lan 2/Ser 1 sequence boundaries. The improved sequence stratigraphic framework enables better regional and global correlations. This shows that rhodalgal carbonate slopes started prograding in the western branch of the Sardinia Rift during the late Burdigalian because (1) of a worldwide bloom of rhodalgal facies, and (2) decreasing tectonic activity at the transition from the syn-rift to the post-rift stage caused a continuous reduction of the siliciclastic sediment input.

Reef to island sediment connections on a Maldivian carbonate platform: using benthic ecology and biosedimentary depositional facies to examine island‐building potential

AbstractReef islands are low‐lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate‐producing reef organisms and are therefore perceived as highly vulnerable to environmental change. However, basic elements of island composition are not well described and given their high inter‐ and intra‐basinal variability a better understanding of reef and island sedimentary environments (and the connections between them) are needed to predict future morphological response. Here, we use detailed ecological and sedimentological datasets to delineate key sediment production zones and biosedimentary depositional facies across the surface of Vabbinfaru platform, Maldives. Field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways. Carbonate production was dominated by coral framework (mean: 52%) within a narrow zone on the outer reef rim (22% of platform area) resulting in coral‐rich detrital sediments (reef: 51%, island: 64%) that closely resemble living assemblages. The net transfer of sediment occurred lagoonward by wave‐driven processes leading to a decrease in grain size towards the island (R2 = 0.502) which acts as a major control on depositional facies development within the lagoon. Island sediments were distinct from reefal deposits, comprising a restricted suite of durable sands (mean: 1.34ϕ) throughout long‐term development. Our findings suggest that the production, breakdown and redistribution of coral‐derived sediment by platform currents is fundamental to future island stability at Vabbinfaru, and although alterations away from current ecological states may reduce sediment supply, the timescales over which island morphological response will occur depends upon phase lags between initial coral mortality and the conversion of this material into island‐grade sand. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Oyster Shells As Recorders of Short-Term Oscillations of Salinity and Temperature During Deposition of Coral Bioherms and Reefs In the Miocene Lorca Basin, SE Spain

Abstract: We use δ 18 O and δ 13 C of oyster shells, inferred seawater δ 18 O (δ w ), and temperature tolerance ranges of modern zooxanthellate coral communities to constrain and model paleo-salinities of marginal-marine waters of the Miocene Lorca Basin, Spain. Salinities ranged from 22 to 32 PSU during growth of coral bioherms and carpets of the Soriana and Parrilla formations, and from 35 to 39 PSU during deposition of the Hondo Formation reef complex. The periods with lower modeled salinities correspond with deltaic and alluvial-fan sedimentation in the area. The modeling is supported by 87 Sr/ 86 Sr data and provides new insights into the evolution of the local depositional settings. Departures of Sr-isotope values from the global oceanic curve occur within the intervals with the lowest modeled salinities, and the non-oceanic 87 Sr/ 86 Sr preserved in individual oyster shells was probably sourced from uplifted Aquitanian–Burdigalian limestones. 87 Sr/ 86 Sr values that plot along the global ocean Sr-isotope curve for the late Miocene indicate a Tortonian age for the upper part of the Soriana Formation and the Parrilla Formation, and a Messinian age for the Hondo Formation. More generally, we demonstrate how the chemical analyses of oyster shells provide additional information regarding short-term oscillations of salinity and temperature of seawater beyond what can be obtained by traditional paleoecological methods.

3D textural evidence for the formation of ultra-high tenor precious metal bearing sulphide microdroplets in offset reefs: An extreme example from the Platinova Reef, Skaergaard Intrusion, Greenland

The Platinova Reef in the Skaergaard Intrusion, east Greenland, is an example of a type of layered-intrusion-hosted, precious metal-enriched, stratiform, disseminated sulphide deposit referred to as “offset reefs”. These typically show platinum-group element (PGE) enrichment immediately below a major increase in the abundance of Cu-rich sulphides, with a prominent peak in Au enrichment exactly at that transition between the PGE-rich and the Cu-sulphide-rich zones. The reasons for the relative sequence of offsets in metal peaks, and the occasionally very high metal tenors have been subject to great debate. Here we use an integrated approach of high-resolution X-ray computed tomography (HRXCT), SEM, synchrotron and desktop microbeam XRF mapping, and thin section petrography to comprehensively classify the textural relations of the precious metal-bearing sulphides of the Platinova Reef as an extreme end member example of an exceedingly high tenor offset deposit. Our results show that in the zones of PGE enrichment, precious metal minerals (PMMs) are intimately associated with Cu sulphide globules, mostly located at, or close to, silicate and oxide boundaries. The textures are identical in zones enriched in Pd and Au, and thus we do not see any evidence for different processes forming the different zones. The PMM:Cu sulphide ratio in each globule varies significantly but overall the size of the globules increases from the Pd-rich, through the Au-rich, and into the Cu zone, with a significant corresponding decrease in PM tenor. As such, this records a progression of exceedingly high tenor, microdroplets of sulphide, which progressively get larger up through the section, and decrease in tenor proportionally to their size. Cumulus droplets of Cu sulphide became enriched in metals, and were trapped in situ without significant transport from their point of nucleation. The transition to larger sulphides represents a change from sulphides nucleated and trapped in situ, to larger ones that liquated from magma devoid of crystals, and that were able to grow and sink. This feature is common in all offset reef deposits, and is marked by the major enrichment in Au. Although the metal ratios of PGE to Au in the Pd- and Au-rich offset zones differ, the identical textures and comparable mineralogy show the physical mechanisms of concentration are the same, indicating a similar physical method of concentration. The relative position of the Pd, Au and Cu peaks in the Platinova Reef is essentially the same as that in numerous other offset reefs, suggesting that common overarching processes are responsible for the enrichment in metals, and relative offsets in peak metal concentrations in all such deposits. The most important of these processes are their relative Dsul/sil values and the diffusivities of the metals, which determine the order of offsets and the high tenors of the smallest sulphide droplets. The Platinova Reef therefore records the extreme enrichment via equilibrium and diffusive partitioning into sulphide liquid microdroplets very close to their point of nucleation.

Microbial domes and megaoncoids in Miocene reefs in the Mahakam Delta in East Kalimantan, Indonesia

Coral patch reefs in the Miocene Mahakam delta in East Kalimantan (Borneo, Indonesia) developed in shallow marine turbid waters. These reefs grew in delta front to prodelta environments under fluctuating siliciclastic input. Langhian patch reefs are well exposed in limestone quarries of the Air Putih area, near the city of Samarinda and include two different types of microbial carbonates in two sections, 2km apart. In the northern section, microbialites occur as low-relief domes, up to 2m wide and 0.5m high. The domes show internal lamination and coralline algae and encrusting foraminifers interlayered with microbial micrite. They developed around large coral fragments at the transition from reef deposits to fine-grained siliciclastics. Microbialites in the southern section formed decimetre- to metre-scale nodules (here termed “megaoncoids”) around nuclei of large coral fragments. Microbial micrite with laminated to digitate fabrics intergrew with coralline algae and encrusting foraminifers to form the thick covers of megaoncoids. Small nodules were bound together in larger ones, which are usually strongly asymmetric internally. Megaoncoids accumulated in a carbonate breccia laterally changing into coral boundstones. In both sections, microbialites grew on the flanks of shallow-water, low-relief patch reefs in poorly illuminated, low-energy conditions. Flat-domed microbialites formed on a nearly horizontal, stable seafloor seawards of the patch reef. The megaoncoids in the southern section formed as a result of downslope displacement of coral fragments coated by microbialite/coralline algal/encrusting foraminifer crusts. The slope of the patch reef's flank favoured the falling and rolling of encrusted corals, with the continued growth of microbial crusts on all sides of nodules. In contrast to Quaternary and recent occurrences of microbialites in Indo-Pacific and Caribbean reefs, the Samarinda microbialites are not components of the reef framework nor formed in deep water. Instead, they developed in shallow, turbid waters of the Miocene Mahakam delta in periods of arrested siliciclastic input.

FossilNewhousia imbricata(Dictyotales, Phaeophyceae) from Postglacial Coral Reef Deposits in Tahiti

Abstract. The calcareous brown alga Newhousia imbricata (Dictyotales, Phaeophyceae) was found from postglacial reef deposits collected during Integrated Ocean Drilling Program Expedition 310 from Tahiti. The alga is composed of successive tiers of bilayered laminae, each consisting of a basal cuboid hypodermal cell bearing smaller epidermal cells (one or two in cross-sectional profiles and three or four in long-sectional profiles). The laminae are separated by extracellular cement. Modern N. imbricata is known only from the Hawaiian Islands; this is the first reported occurrence of fossil N. imbricata.

A NEW RECORD OF THE LATE PLEISTOCENE CORALPOCILLOPORA PALMATAFROM THE DRY TORTUGAS, FLORIDA REEF TRACT, USA

Abstract Pocilloporid corals dominated shallow-water environments in the Caribbean during much of the Cenozoic; however, the regional diversity of this family declined over the last 15 My, culminating with the extinction of its final member, Pocillopora palmata, during the latest Pleistocene. Here we present a new record of P. palmata from Dry Tortugas National Park in the Florida Keys and infer its likely age. Although most existing records of P. palmata are from the sub-aerial reef deposits of MIS5e (~ 125 ka), the presently submerged reef in the Dry Tortugas was too deep (> 18 m) during this period to support significant reef growth. In contrast, the maximum water depth during MIS5a (~ 82 ka) was only ~ 5.6 m, which would have been ideal for P. palmata. Diagenetic alteration prevented direct dating of the samples; however, the similarity between the depths of the Pleistocene bedrock in the Dry Tortugas and other reefs in the Florida Keys, which have been previously dated to MIS5a, support the conclusio...

First report of permineralised plants in the Stephanian of Arnao (Asturias, northwestern Spain)

The first record of an anatomically preserved flora from Stephanian outcrops at Arnao beach (Asturias, Spain) is presented. The stratigraphic section is part of a geological heritage site that preserves exceptional Devonian reef deposits. The Carboniferous succession contains coal seams worked by one of the earliest mines in Spain and its plant-fossil assemblages were reported in the 19th century but scarcely revised later. The new assemblages recovered in the beach, during extreme low tides, represent the first record of permineralised trunks in northwestern Spain. Large cordaitalean specimens are referred to a new species of Cordaixylon characterised by non-septate pith, araucarian radial pitting of the tracheids and cross-fields with phyllocladoid pits. Part of the root mantle of Psaronius is preserved in water-worn pebbles, indicating the presence of tree ferns in the palaeoflora. The associated compression/impression assemblage includes lycophytes, sphenophytes, pteridosperms and pteridophytes. A comparison of the assemblage confirms its importance for reconstructing the Late Pennsylvanian floral succession in the region.

Microencrusters from the Upper Jurassic–Lower Cretaceous İnaltı Formation (Central Pontides, Turkey): remarks on the development of reefal/peri-reefal facies

A detailed taxonomical study was carried out for the identification of encrusting micro-organisms. Among these microencrusters, Perturbatacrusta leini, Iberopora bodeuri, Calcistella jachenhausenensis, and Pseudorothpletzella schmidi have been taxonomically revealed for the first time in Turkey. Within the biostratigraphic frame of the Inalti Formation consisting of Mesoendothyra izjumiana zone (Kimmeridgian), Calcistella jachenhausenensis zone (Lower Tithonian–Upper Tithonian) and Protopeneroplis ultragranulata zone (Upper Tithonian–Berriasian), carbonate sedimentation occurred in five depositional environments comprising slope, fore-reef, reef, back-reef and lagoonal environments. The majority of the reefal deposits of the Inalti carbonates can be classified as coral-microbial-microencruster boundstones, which frequently occur in association with back-reef and fore-reef deposits within the Kimmeridgian–Berriasian interval. A shallowing and a subsequent deepening of water depth in the Berriasian have been revealed by the examination of stacking patterns and vertical evolution of the microfacies. Based on the observed microfacies and general features of micro-encrusting organisms, it is concluded that Inalti carbonates share many similarities with the reefal carbonate deposits of Intra-Tethyan domain in terms of microfacies types and microencruster content.

Habitat heterogeneity reflected in mesophotic reef sediments

Modern reef sediments reflect the physical and chemical characteristics of the environment as well as the local reef fauna. Analysis of sedimentary reef facies can thus provide a powerful tool in interpreting ancient reef deposits. However, few studies have attempted to differentiate sedimentary facies in mesophotic coral ecosystems, low light habitats defined as residing 30–150m below sea level. The low-angle shelf mesophotic coral ecosystem south of the northern U.S. Virgin Islands (USVI) consists of reefs with different structural characteristics ideal for studying the relationship between habitat variability and sedimentary facies. Textural, compositional, and geochemical analyses of surface sediments were used to identify mesophotic reef subfacies associated with distinct benthic communities and structural habitats. Sediment grain composition and bulk geochemistry were found to broadly record the distribution and abundance of coral and macroalgae communities, foundational mesophotic reef benthic organisms. Overall, sediment composition was found to be a good indicator of specific reef environments in low-angle mesophotic reef habitats. Sedimentological analyses indicate that hydrodynamic forces do not transport a significant amount of allochthonous sediment or potentially harmful terrigenous material to USVI mesophotic reefs. Episodic, maximum current velocities prevented deposition of most silt-size grains and smaller, but biological processes were found to have a greater influence on subfacies partitioning than hydrodynamic processes. Results provide a new analog for studies of ancient mesophotic coral ecosystem geological history and document the relationship between mesophotic reef subfacies, structural complexity, and habitat heterogeneity. They also demonstrate how mesophotic reefs along the same shelf system do not always share similar sedimentary characteristics and thus record a diverse set of ecological and environmental conditions.

Crustal structure of the eastern Algerian continental margin and adjacent deep basin: implications for late Cenozoic geodynamic evolution of the western Mediterranean

The Karukera spur is an easternmost submerged rise of the Lesser Antilles fore-arc in the Guadeloupe archipelago, culminating about 4000 m above the fore-arc basin 150 km west of the deformation front. The analysis of 3500 km 2D high-resolution multichannel seismic reflection and multibeam bathymetric data, and the study of 14 core samples, allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution. Seven seismic units (US1 to US7) are evidenced, organised into four major depositional sequences separated by erosional surfaces. Units US1 to US4 thicken to the south-southeast on the spur. The sedimentary deposits rest upon a deeply eroded metamorphic basement of the Caribbean Plate as in La Desirade Island. Sequence 1 (units US1 and US2) remains unknown in its lower part because it does not outcrop. Its upper part comprises early Miocene shallow water carbonates. Sequence S2 (Unit US3) only comprises an upper Miocene transgressive systems tract deposited into basinal environment. It is bounded by major erosional surfaces SB2 and SB3. Sequence 3 (US4 to US6) is Zanclean to Pleistocene. It is dominantly composed of shallow water, reefal deposits. Sequence 4 corresponds to recent deposits. The Karukera spur experienced three main extensional episodes with alternations between uplift and subsidence periods. Uplifts are responsible for emersions and erosions. Subsidence severely drowned shallow water deposits. The first extensional episode led to the formation of horsts and grabens in the basement, prior to early Miocene deposits. The second extensional episode occurred during upper Miocene, in accordance with data in surrounding islands. The third tectonic episode developed since Calabrian. Noticeable is the constant reactivation of N130°–N150°, N150°–N180° and N40° trending faults since early Miocene and the neoformation of E–W trending faults since Calabrian. Our results suggest that at the latitude of Guadeloupean archipelago the Lesser Antilles subduction zone is an erosional margin because of the successive sweepings of the Santa Lucia then Tiburon Ridges.

Glowing Seashells: Diversity of Fossilized Coloration Patterns on Coral Reef-Associated Cone Snail (Gastropoda: Conidae) Shells from the Neogene of the Dominican Republic

The biology of modern Conidae (cone snails)—which includes the hyperdiverse genus Conus—has been intensively studied, but the fossil record of the clade remains poorly understood, particularly within an evolutionary framework. Here, ultraviolet light is used to reveal and characterize the original shell coloration patterns of 28 species of cone snails from three Neogene coral reef-associated deposits from the Cibao Valley, northern Dominican Republic. These fossils come from the upper Miocene Cercado Fm. and lower Pliocene Gurabo Fm., and range in age from about 6.6-4.8 Ma. Comparison of the revealed coloration patterns with those of extant species allow the taxa to be assigned to three genera of cone snails (Profundiconus, Conasprella, and Conus) and at least nine subgenera. Thirteen members of these phylogenetically diverse reef faunas are described as new species. These include: Profundiconus? hennigi, Conasprella (Ximeniconus) ageri, Conus anningae, Conus lyelli, Conus (Atlanticonus?) franklinae, Conus (Stephanoconus) gouldi, Conus (Stephanoconus) bellacoensis, Conus (Ductoconus) cashi, Conus (Dauciconus) garrisoni, Conus (Dauciconus?) zambaensis, Conus (Spuriconus?) kaesleri, Conus (Spuriconus?) lombardii, and Conus (Lautoconus?) carlottae. Each of the three reef deposits contain a minimum of 14–16 cone snail species, levels of diversity that are similar to modern Indo-Pacific reef systems. Finally, most of the 28 species can be assigned to modern clades and thus have important implications for understanding the biogeographic and temporal histories of these clades in tropical America.

Tectonic and sedimentary architecture of the Karukéra spur: A record of the Lesser Antilles fore-arc deformations since the Neogene

The Karukéra spur is an easternmost submerged rise of the Lesser Antilles fore-arc in the Guadeloupe archipelago, culminating about 4000 m above the fore-arc basin 150 km west of the deformation front. The analysis of 3500 km 2D high-resolution multichannel seismic reflection and multibeam bathymetric data, and the study of 14 core samples, allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution. Seven seismic units (US1 to US7) are evidenced, organised into four major depositional sequences separated by erosional surfaces. Units US1 to US4 thicken to the south-southeast on the spur. The sedimentary deposits rest upon a deeply eroded metamorphic basement of the Caribbean Plate as in La Désirade Island. Sequence 1 (units US1 and US2) remains unknown in its lower part because it does not outcrop. Its upper part comprises early Miocene shallow water carbonates. Sequence S2 (Unit US3) only comprises an upper Miocene transgressive systems tract deposited into basinal environment. It is bounded by major erosional surfaces SB2 and SB3. Sequence 3 (US4 to US6) is Zanclean to Pleistocene. It is dominantly composed of shallow water, reefal deposits. Sequence 4 corresponds to recent deposits. The Karukéra spur experienced three main extensional episodes with alternations between uplift and subsidence periods. Uplifts are responsible for emersions and erosions. Subsidence severely drowned shallow water deposits. The first extensional episode led to the formation of horsts and grabens in the basement, prior to early Miocene deposits. The second extensional episode occurred during upper Miocene, in accordance with data in surrounding islands. The third tectonic episode developed since Calabrian. Noticeable is the constant reactivation of N130°–N150°, N150°–N180° and N40° trending faults since early Miocene and the neoformation of E–W trending faults since Calabrian. Our results suggest that at the latitude of Guadeloupean archipelago the Lesser Antilles subduction zone is an erosional margin because of the successive sweepings of the Santa Lucia then Tiburon Ridges.

How gold formed in the Vaal Reef deposit

How gold formed in the Vaal Reef deposit

Кореляційна седиментаційна модель верхньоюрських рифогенних відкладів Передкарпатського та Переддобрудзького регіонів України

Кореляційна седиментаційна модель верхньоюрських рифогенних відкладів Передкарпатського та Переддобрудзького регіонів України

Перспективы нефтегазоносности оксфорд-неокомских рифогенных отложений в пределах южного борта Западно-Кубанского прогиба. Часть 2. Историко-генетическое моделирование нефтегазоносности новых выделенных объектов

Перспективы нефтегазоносности оксфорд-неокомских рифогенных отложений в пределах южного борта Западно-Кубанского прогиба. Часть 2. Историко-генетическое моделирование нефтегазоносности новых выделенных объектов

Перспективы нефтегазоносности оксфорд-неокомских рифогенных отложений в пределах южного борта Западно-Кубанского прогиба. Часть 1. Выделение новых объектов

Перспективы нефтегазоносности оксфорд-неокомских рифогенных отложений в пределах южного борта Западно-Кубанского прогиба. Часть 1. Выделение новых объектов

Ископаемые Chlorophyta верхнеюрских рифовых отложений Запада и Юга Украины

Ископаемые Chlorophyta верхнеюрских рифовых отложений Запада и Юга Украины

Pleistocene Coral Assemblages on Irabu-Jima, South Ryukyu Islands, Japan

Abstract. We identified 40 genera and 83 species of scleractinian corals from middle Pleistocene reef limestones on Irabu-jima, located in the South Ryukyu Islands (South Ryukyus); these data were then combined with previously published data sets on Pleistocene coral assemblages on Okinawa-jima (southern Central Ryukyus), and Kikai-jima (northern Central Ryukyus) to perform statistical analyses, including cluster analysis and multidimensional scaling (MDS) ordination of Bray—Curtis (BC) similarity coefficients applied to coral taxa (R-type analysis) and coral assemblages (Q-type analysis). Results of the analyses, combined with field descriptions of the coral assemblages, allowed interpretations of reef paleoenvironments. Outcrops of Quaternary reef deposits in the Ryukyus comprise both shallow- and deep-water coral assemblages. Generally, coral diversity increases southward along the island chain. The statistical analyses highlight differences in the taxonomic compositions of fossil coral assemblages in ...