Reef Sequence Research Articles

Neogene carbonate platform development in the southern South China Sea: Evidence from calcareous microfossils

Biogenic reefs are unique geologic bodies that are the products of biological activity in tropical and subtropical oceans and critical to global carbon cycling. The South China Sea (SCS) has developed largest carbonate platforms in the Western Pacific. The fully-cored Well NK-1, which is drilled through the reef complex on the Meiji Atoll, Nansha Islands, offers good opportunity for assessing the long-term evolutions of biogenic reefs in the SCS. The stratigraphic ages based on palaeomagnetic and Sr isotopic data are controversial in some intervals of core NK-1. To reveal the evolution history of Nansha Islands and their controlling factors, more credible age constraints on core NK-1 are needed. This research presents new records of calcareous microfossils (calcareous nannofossil and foraminifer) abundances and diversities in the biogenic reef carbonates of core NK-1. Based on the assemblages of the calcareous microfossils, seven biostratigraphic datums are recognized from the sequence of core NK-1, revealing a general continuous succession of the earliest Miocene to Pleistocene age. By combining with the magnetostratigraphic data, the development and evolution of carbonate platform in Nansha Islands are reconstructed. The bottom age of the biogenic reef sequence of NK-1 is estimated for 23.03 ± 1.06 Ma, close to the Oligocene/Miocene boundary. The new chronology highlights three short hiatuses of 3.6–2.4 Ma, 11.1–10.0 Ma, and 13.5–11.9 Ma, which are well correlated with the prominent exposed surfaces at 210.3 m, 464.6 m and 561.6 m, respectively. It reveals remarkably similar evolution history of carbonate platforms in the SCS since Neogene by comparing with records of stratigraphy and growth rate from deep drilling cores on isolated coral reefs in Nansha and Xisha Islands. The results showed that the SCS carbonate platform developments, which go through Late Oligocene / Early Miocene initiation phase, Early-Middle Miocene rapid growth phase, Middle-Late Miocene erosion phase, Miocene-Pliocene stable development phase and Quaternary growth phase, are mainly influenced by global sea level changes, environmental factors and regional tectonism such as the SCS basin spreading, Sabah Orogeny Movement and Dongsha Movement.

Refining patterns of melt with forward stratigraphic models of stable Pleistocene coastlines

Abstract. The warmest peak of the Last Interglacial (ca. 128–116 ka) is considered a process analogue and is often studied to better understand the effects of a future warmer climate on the Earth's system. In particular, significant efforts have been made to better constrain ice sheet contributions to the peak Last Interglacial sea level through field observation of paleo relative sea level indicators. Along tropical coastal margins, these observations are predominantly based on fossil shallow coral reef sequences, which also provide the possibility of gathering reliable U-series chronological constraints. However, the preservation of many Pleistocene reef sequences is often limited to a series of discrete relative sea level positions within the interglacial, where corals suitable for dating were preserved. This, in turn, limits our ability to understand the continuous evolution of paleo relative sea level through an entire interglacial, also affecting the possibility of unraveling the existence and pattern of sub-stadial sea level oscillations. While the interpretation of lithostratigraphic and geomorphologic properties is often used to overcome this hurdle, geological interpretation may present issues related to subjectivity when dealing with missing facies or incomplete sequences. In this study, we try to step back from a conventional approach, generating a spectrum of synthetic Quaternary subtropical fringing reefs for a site in southwestern Madagascar (Indian Ocean). We use the Dionisos forward stratigraphic model (from Beicip-Franlab) to build a fossil reef at this location. In each model run, we use distinct Greenland and Antarctica ice sheet melt scenarios produced by a coupled ANICE–SELEN glacial isostatic adjustment model. The resulting synthetic reef sequences are then used test these melt scenarios against the stratigraphic record. We propose that this sort of stratigraphic modeling may provide further quantitative control when interpreting Last Interglacial reef sequences.

Geodynamic control on Pleistocene coral reef development: Insights from northwest Sumba Island (Indonesia)

AbstractThe fossil record of Quaternary reef systems, as expressed in uplifted regions by sequences of stacked terraces, has been extensively used either to understand their morphodynamics or to unravel sea level variations. Yet, because these two aspects are intimately linked, Quaternary reef analysis is often underdetermined because the analysis often focuses on single sequences, along one‐dimensional profiles. Here, we take advantage of the lateral variations of coral reef sequences by documenting the morphological variations of the reef sequence on Sumba Island. Near Tambolaka, northwest Sumba, we analysed a reef transect, topography, and associated sedimentological record to obtain a precise coral reef stratigraphy and geomorphic patterns that can be compared with the well‐documented eastern counterpart. In Tambolaka, the reef sequence displays four lower layers of bedded chalky limestone units with a weakly cemented sandy matrix, which we attribute to the Middle Miocene to Pliocene Wakabukak formation based on calcareous nannofossils and planktonic foraminifers. The uppermost layer is a calcretized reefal limestone unit with a well‐lithified sandy matrix, which we attribute to the Plio–Pleistocene reef sequence of the Kalianga formation. Seven marine terraces imprint the regional morphology, four of which we correlate with Marine Isotope Stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c terraces of Cape Laundi, northeast Sumba. When scrutinized at the light of numerical models of reef development, these results indicate that the morphodynamics of reefal sequences is strongly impacted by the tectonic evolution. The geodynamic context sets both the extrinsic conditions of reef development, such as the morphology of the basement and hydrodynamics, and the intrinsic properties, in particular reef growth rate. While the morphodynamic evolution of the sequence is at first‐order representative of the interplay between uplift rates and sea level oscillations, the detailed assemblage of the reef units drastically varies along the coastline.

New insights on the Late Quaternary evolution of Abrolhos reefs, Eastern Brazilian Shelf

The Abrolhos shelf, in the eastern Brazilian margin, encompasses the largest reef province in the South Atlantic, characterised by low coral diversity and a high level of endemism. Knowledge gaps about how the Abrolhos coastal reefs evolved, during the post LGM and MIS 6/MIS 5, favoured a paradigm that is revisited in the light of new data. Here, new data from two new, long boreholes (20 and 50 m-long) are presented in order to investigate and provide new insights into the evolution of two shallow reefs on the Abrolhos Shelf during the late Pleistocene and Holocene epochs. Results show that Holocene and Pleistocene reefs grew on highly turbid waters with a significant terrigenous sediment input. Corals and CCA assemblages were identified as main framework builders of Abrolhos inner-shelf reefs since the Pleistocene. No clear shallowing upward sequence of reef builders was observed, which differs from other reef sequences all over the world. In terms of Holocene reef growth, Pedra Grande and Coroa Vermelha reefs turned on roughly coevally at different depths and with different coral assemblages. Pedra Grande reef started growing circa 6.8 kyr BP in a water depth approximately 10 m deeper than Coroa Vermelha, which started growing around 6.4 kyr BP, but Coroa Vermelha turned off at around 4 kyr BP, while Pedra Grande kept growing until around 1.2 kyr BP. This novel reef stratigraphy data provided a new insight on the evolution of the Abrolhos coastal reefs, showing that different environmental and topographic controls could have acted spatially in different ways. Coroa Vermelha reef seems to have started its growth as a result of a topographic high control. Pedra Grande reef seems to be connected to a broader submerged reef setting and started to grow in deeper water depths. The presence of three reef arcs in Abrolhos is proposed, including a submerged reef arc.

Facies character and geochemical signature in the late Quaternary meteoric diagenetic carbonate succession at the Xisha Islands, South China Sea

The late Quaternary shallow-water carbonates have been altered by a variety of diagenetic processes, and further influenced by high-amplitude global and regional sea level changes. This study utilizes a new borehole drilled on the Yongxing Island, Xisha Islands to investigate meteoric diagenetic alteration in the late Quaternary shallow-water carbonates. Petrographic, mineralogical, stable isotopic and elemental data provide new insights into the meteoric diagenetic processes of the reef limestone. The results show the variation in the distribution of aragonite, high-Mg calcite (HMC) and low-Mg calcite (LMC) divides the shallow-water carbonates in Core SSZK1 into three intervals, which are Unit I (31.20–55.92 m, LMC), Unit II (18.39–31.20 m, aragonite and LMC) and Unit III (upper 18.39 m of core, aragonite, LMC and HMC). Various degrees of meteoric diagenesis exist in the identified three units. The lowermost Unit I has suffered almost complete freshwater diagenesis, whereas the overlying Units II and III have undergone incompletely meteoric diagenesis. The amount of time that limestone has been in the freshwater diagenetic environment has the largest impact on the degree of meteoric diagenesis. Approximately four intact facies/water depth cycles are recognized. The cumulative depletion of elements such as strontium (Sr), sodium (Na) and sulphur (S) caused by duplicated meteoric diagenesis in the older reef sequences are distinguished from the younger reef sequences. This study provides a new record of meteoric diagenesis, which is well reflected by whole-rock mineralogy and geochemistry.

Coral Record of Younger Dryas Chronozone Warmth on the Great Barrier Reef

AbstractThe Great Barrier Reef (GBR) is an internationally recognized and widely studied ecosystem, yet little is known about its sea surface temperature (SST) evolution since the Last Glacial Maximum (LGM) (~20 kyr BP). Here, we present the first paleo‐application of Isopora coral‐derived SST calibrations to a suite of 25 previously published fossil Isopora from the central GBR spanning ~25–11 kyr BP. The resultant multicoral Sr/Ca‐ and δ18O‐derived SST anomaly (SSTA) histories are placed within the context of published relative sea level, reef sequence, and coralgal reef assemblage evolution. Our new calculations indicate SSTs were cooler on average by ~5–5.5°C at Noggin Pass (~17°S) and ~7–8°C at Hydrographer's Passage (~20°S) (Sr/Ca‐derived) during the LGM, in line with previous estimates (Felis et al., 2014, https://doi.org/10.1038/ncomms5102). We focus on contextualizing the Younger Dryas Chronozone (YDC, ~12.9–11.7 kyr BP), whose Southern Hemisphere expression, in particular in Australia, is elusive and poorly constrained. Our record does not indicate cooling during the YDC with near‐modern temperatures reached during this interval on the GBR, supporting an asymmetric hemispheric presentation of this climate event. Building on a previous study (Felis et al., 2014, https://doi.org10.1038/ncomms5102), these fossil Isopora SSTA data from the GBR provide new insights into the deglacial reef response, with near‐modern warming during the YDC, since the LGM.

Neogene–quaternary magnetostratigraphy of the biogenic reef sequence of core NK–1 in Nansha Qundao, South China Sea

Neogene–quaternary magnetostratigraphy of the biogenic reef sequence of core NK–1 in Nansha Qundao, South China Sea

Morphology of fore-reef slopes and terraces, Takapoto Atoll (Tuamotu Archipelago, French Polynesia, central Pacific): The tectonic, sea-level and coral-growth control

A dataset of 41 bathymetric profiles detected by satelline imagery and echo-sounding to a maximum depth of 38 m along the fore-reef slopes of Takapoto Atoll (Tuamotu Plateau, French Polynesia, central Pacific) were qualitatively and quantitatively analyzed in order to identify the main geomorphological features. In addition, scuba-diving investigations from a selected site resulted in defining coral composition and cover rate. Six distinct fore-reef sectors were morphologically differentiated on the basis of seaward extension and slope gradient. Only the north end, and a restricted area of the mid-south-east side extend seawards over an average distance of 150 m, with a relatively low gradient (23°–38°). Most of the outer-slope areas are narrow (<100 m on average) and steep (average slope equals to 45° to up to 70°). Geomorphic features include spur-and-groove systems, sub-horizontal to gently dipping terraces (23–45 m wide) ending seawards in vertical steps (<10 m high) and drop-offs (>10 m high), outer-reef crest-like reliefs (0.5 m–1.5 m high), pinnacles (2 m–17 m high), coral heads (<2 m high), trenchs and concave scars. The recognized seven terrace levels occur at the respective depths of about −5 m, −10 m, −15 m, −20 m, −24 m, −30.5 m and −38 m. Based on comparison with subsurface chronostratigraphy of drilled reef sequences from some other Pacific atolls, the terraces are interpreted as remnants of reef tracts formed during Pleistocene interglacial, high sea-stands, respectively during MIS substage 5e (about −125 ka), MIS substages 7a (about −195 ka), 7c (about −210 ka), 7e (about −240 ka) and 9e (−330 ka). After depth correction of ground lowering during periods of emergence and subsidence effects, terrace elevations were expected to indicate eustatic sea-level positions at each identified high sea-stand, at approximately 7 m (MIS 5e) and 2.2 m (MIS 7a) above present sea level and 9.5 m (MIS 7c), 11 m (MIS 7e) and 8.6 m (MIS 9e) below present sea level. During the post-glacial sea-level rise, from about 9.5 ky, the studied portions of fore-reef slopes were re-flooded. It was assumed that coralgal deposits in the form of thin veneers, coral heads, outer-reef crest-like reliefs and pinnacles have simply overlapped pre-existing structures. Locally, the fore-reef zones are carved by trenchs, i.e. incipient detachment faults, and scars, i.e. imprints of former landslides. Similarly, some drop-offs may be regarded as fault walls. The prevailing direction of faulting–collapsing surfaces is consistent with the SW–NE orientation of the main axis of the atoll and submarine ridges rising up from the north-western floor of the Tuamotu Plateau. Analysis of the composition and distribution of coral communities to −30 m depth revealed high, downslope-increasing coral coverage (24% to 67% on average) and the sharp replacement of robust-encrusting Pocillopora by sub-massive to plate-like Porites from depths greater than −10 m. Significant inter-regional differences were detected with atolls in west Pacific, probably due to local ecological constraints.

Strontium isotope stratigraphy and paleomagnetic age constraints on the evolution history of coral reef islands, northern South China Sea

Abstract Understanding the history of the response of coral reefs to past climate changes can provide valuable information for predicting the future response of modern reefs. However, dating such ancient biotic carbonate is still challenging because of its sensitivity to diagenetic alteration processes, scarcity of well-preserved fossils, and low magnetic mineral content. There have been a long debates about the origin and evolutionary history of coral reefs in the northern South China Sea, mainly due to the lack of direct and reliable age constraints. This provides us with a good opportunity to verify the practicability of different dating approaches, especially the strontium (Sr) isotope analysis of bulk carbonate. Here, we retrieved a 972.55-m-long core from the Xisha Islands to provide a credible chronologic constraint on the carbonate platform evolution. The lithostratigraphy, strontium isotope stratigraphy, and magnetostratigraphy were analyzed throughout the whole reef sequence. The lithostratigraphic results show that the 873.55 m reef sequence developed on an ancient volcaniclastic basement and experienced multiple evolutionary phases. The 87Sr/86Sr results of all 100 bulk carbonate samples vary from 0.708506 to 0.709168 and show a monotonic increase with decreasing depth, except for a few outliers. Trace-element criteria and stable isotope (δ18O and δ13C) methods were applied to these bulk carbonate samples, and results imply that the primary or near-primary seawater 87Sr/86Sr values were likely preserved, although different degrees of diagenetic alteration occurred. In addition, the paleomagnetic results indicate 10 normal polarity and eight reversed polarity magnetozones. Based on the 87Sr/86Sr ratios of the selected 58 samples and paleomagnetic reconstruction of polarity reversals, the bottom of the reef sequence is dated to 19.6 Ma, and the observed polarity chronozones extend from chron C6 (19.722–18.748 Ma) at 866.60 m to present at the top. Based on the new data, we propose a new chronologic framework for the evolutionary history of the reef islands, where: (1) the reefs initiated in the early Miocene (19.6 Ma) and were drowned until 16.26 Ma; (2) during 16.26–10.66 Ma, lagoon to lagoon slope environments prevailed; (3) the lagoon environment progressively transformed into a reef crest environment from 10.66 to 4.36 Ma and 4.36 to 1.59 Ma; and (4) the reef started to be drowned again during 1.59–0 Ma. Our study provides a new and reliable chronologic constraint on the general evolutionary history of the reef islands in the northern South China Sea. Furthermore, the 87Sr/86Sr results from bulk carbonate indicate that strontium isotope stratigraphy is a powerful dating tool only when rigid sample selection, sequential leaching procedures, and strict trace-element and isotopic criteria are applied.

PGE reefs of the West-Pana layered intrusion, Kola Region, Russia: plagioclase composition as an indicator of the economic potential

The paper summarizes the present time available data on plagioclase composition through PGE reef sequences in the West-Pana intrusion, Kola Peninsula, NW Russia. The intrusion hosts two PGE-enriched levels with a strongly different economic potential. A lower level is known as “North Reef” and contains several deposits of low-sulfide Pt-Pd ores discovered in past decades whereas an upper “South Reef” level showing high-grade mineralization in some places does not have ore bodies. Comparing the variations of anorthite content in plagioclase through the North Reef with sharp changes from An63 in the underlying unit to An86 in the reef sequence with those in the South Reef (An75 with no significant changes) it is suggested that the formation of the former directly corresponds with an early-magmatic process while the latter has a distinct late-magmatic genesis. Thus plagioclase can be considered as an indicator of the economic potential of PGE reef within the West-Pana intrusion and probably in other layered intrusions when it is necessary to choose the most promising mineralized level in the stratigraphy.

Late glacial to deglacial variation of coralgal assemblages in the Great Barrier Reef, Australia

Abstract Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1–5) that span the last 30,000 years. Here we examined the variation in coralgal assemblages and their paleoenvironmental settings in late glacial to deglacial sequences from 23 holes cored seaward of the modern GBR in water depths from 46 to 131 m along four transects at three localities: Hydrographers Passage (HYD-01C and HYD-02A), Noggin Pass (NOG 01B), and Ribbon Reef (RIB-02A). We identified three coralline algal assemblages and eight coral assemblages indicating a broad range of reef settings from the shallow reef crest (0–5 m) to the deep forereef slope (>20 m). We document in detail for the first time the distribution and composition of reef communities that grew in the GBR during the LGM from 22,000–19,000 years ago. They included coral taxa that are major reef builders today: Isopora, Acropora gr. humilis, Dipsastraea gr. pallida, Porites, and Montipora. Prior to the fall in sea level to the maximum extent of the LGM, late glacial reef communities developed more proximally (landward) to the modern GBR along the shelf edge. Their distribution and composition reflect influences of the older Pleistocene basement depth and possible terrigenous sediment inputs. Post-LGM deglacial reef growth was vigorous in proximal sites and characterized by the accretion of a very shallow high-energy coralgal assemblage composed of medium to robustly branching Acropora, including A. gr. humilis, and thick algal crusts of Porolithon gr. onkodes associated with vermetid gastropods. More distally, reef growth was variably impacted by terrigenous input following deglacial reflooding of antecedent reef terraces. The coralgal succession and sedimentary facies in Noggin Pass indicate that an early drowning trend was linked to increased turbidity that was likely controlled by shelf morphology (narrow shelf, steep slope) and/or proximity to a paleo-river mouth. The deglacial succession in Ribbon Reef lacks typical shallow-water indicators, which may reflect influences of the particularly steep slope of the northern GBR shelf edge on reef zonation. A major sea-level jump at the onset of the Younger Dryas displaced reef habitats further upslope, forming a barrier reef system mainly composed of robustly branching acroporids distinct from the more distal sites. Our results highlight the importance of sedimentation and shelf morphology in addition to relative sea-level changes in controlling variations in reef community over centennial to millennial timescales.

Late Quaternary uplift across northwest Luzon Island, Philippines constrained from emergent coral reef terraces

AbstractEmergent coral reef terraces in northwest Luzon Island, Philippines are studied to understand relative sea level (RSL) changes and uplift along the Manila Trench forearc region during the Late Quaternary. Coral reef sequences in Currimao, Badoc, and Badoc Island were mapped and were described based on geomorphological characteristics, elevation patterns, and ages. The lower emergent coral reef terraces, which are dated Holocene, are subdivided into three to possibly four terrace steps (TI–TIV in ascending order) with the highest terrace (TIII–TIV) rising up to ~7–9 m amsl. The well‐preserved staircase morphology and meter‐scale terrace risers possibly imply episodes of abrupt RSL changes that resulted from coseismic uplift during the mid‐Holocene. Around 6.8 kyr BP, ~3 m of rapid uplift (possibly coseismic) is inferred to account for the vertical separation of TI (6.2 kyr BP at 3.5 m amsl) and TII (6.8 kyr BP at 6.6 m amsl) in Currimao site. A subsequent episode of RSL fall occurred at 6 kyr BP, based on dated coral samples, and has emerged the lowest terraces in the study sites. New geomorphic and radiometric data suggest that the mid‐Holocene sea level highstand in northwest Luzon occurred at around 7–6 kyr BP. From the elevation and thorium‐230 age of dated terrace surfaces, we estimated Holocene uplift rates from 0.17 ± 0.12 to 0.82 ± 0.15 mm/yr across the three study sites. The estimated uplift rates of northwest Luzon are relatively lower than the uplift rates reported in similar tectonically active regions of the west Pacific such as Papua New Guinea, Taiwan, New Zealand, and Japan. The geomorphological characteristics and age of emergent coral reef terraces reported in this study offer insights on the preservation of long‐term deformation along the northwest Luzon coastal plain that is bordered by a subduction zone and upper‐plate faults. © 2018 John Wiley &amp; Sons, Ltd.

AMS Carbon-14 dating of microbial carbonates in Holocene coral reefs, Western Luzon, Philippines

Microbial carbonates (microbialites) occurred in the Holocene coral reefs at Paraoir, the Philippines. These microbialites appeal grayish to buff in color with a stromatolitic to thrombolitic structures, and encrust on corals directly or on a thin layer of calcareous red algae or encrusting foraminifera that covered the corals first. The microbialites only occur in the lower (earlier) parts of the Holocene reef sequence where Heliopora coerulea dominated. No microbial carbonates were observed in the upper (younger) part of the Holocene reefs that is interpreted to grow in water depth shallower than 6 m on the basis of coral community. Samples of microbial carbonate and associated coral were dated by AMS 14C. The results show that the microbialites formed about 10 to 7.5 kyr BP, nearly coeval to or a few hundred years younger than the corals on which the microbialites encrusted. AMS 14C ages of samples recovered at reef margins are consistent to 230Th ages of corals associated with the microbialites, but those recovered in the back reef are much older that the previously published 230Th ages of corals and interpreted to be reworked into the backreef. It is proposed that the microbialites at Paraoir formed in early Holocene on reef slope when the deglacial sea level was rising rapidly. After 7.5 kyr BP when the sea-level rise slowed down and coral reefs caught up with sea level, the condition became favorable to corals prospered in shallow water, and no longer suitable for microbialite formation.

Geomorphology and late Holocene accretion history of Adele Reef: a northwest Australian mid-shelf platform reef

The mid-shelf reefs of the Kimberley Bioregion are one of Australia’s more remote tropical reef provinces and such have received little attention from reef researchers. This study describes the geomorphology and late Holocene accretion history of Adele Reef, a mid-shelf platform reef, through remote sensing of contemporary reef habitats, shallow seismic profiling, shallow percussion coring and radiocarbon dating. Seismic profiling indicates that the Holocene reef sequence is 25 to 35 m thick and overlies at least three earlier stages of reef build-up, interpreted as deposited during marine isotope stages 5, 7 and 9 respectively. The cored shallow subsurface facies of Adele Reef are predominantly detrital, comprising small coral colonies and fragments in a sandy matrix. Reef cores indicate a ‘catch-up’ growth pattern, with the reef flat being approximately 5–10 m deep when sea level stabilised at its present elevation 6,500 years BP. The reef flat is rimmed by a broad low-relief reef crest only 10–20 cm high, characterised by anastomosing ridges of rhodoliths and coralliths. The depth of the Holocene/last interglacial contact (25–30 m) suggests a subsidence rate of 0.2 mm/year for Adele Reef since the last interglacial. This value, incorporated with subsidence rates from Cockatoo Island (inshore) and Scott Reefs (offshore), provides the first quantitative estimate of hinge subsidence for the Kimberley coast and adjacent shelf, with progressively greater subsidence across the shelf.

The reef platform of Martinique: Interplay between eustasy, tectonic subsidence and volcanism since Late Pleistocene

Reef positions record the interaction between eustasy and tectonics, and have been used worldwide to characterize vertical deformations of upper-plates at different time-scales and constrain the seismic behavior of megathrusts. Along the Lesser Antilles volcanic arc, high-resolution marine geophysical data were collected on the 2–20 km wide eastern Martinique reef platform to reconstruct its stratigraphic and morphologic history, and understand the influence of local normal faulting, volcanism and plate-scale subduction processes on Holocene and Late Pleistocene reef development. The subsiding Martinique platform's stratigraphy is composed of multiple superimposed sea-level highstand deposits separated by subaerial exposure surfaces of sea-level low stands. The carbonate platform consists of two laterally-extensive carbonate units (unit U2 overlying unit U3) that extend to the platform edge to a depth of − 95 m MSL (mean sea level), and form two morphologic terraces, M2 and M3 respectively. The landward portion of unit U2 is partially overlain between 0 and − 60 m MSL by the living reef tract U1. The current reef is composed of a landward fringing reef, a lagoon and a seaward barrier reef, the latter forming a double-bank barrier around the Caravelle Peninsula. In near-shore multi-channel seismic profiles, a distinct reflector at ~− 35 m MSL, probably a subaerial exposure surface E1, separates the reef sequence formed during the last transgression from a Pleistocene fossil reef tract forming unit U2. Offshore of Mount Pelée volcano (Late Pleistocene), the Holocene reef did not develop above unit U2, whose upper surface is incised by channels and apparent sinkholes. During the Holocene transgression, the possibility of excessive turbidity due to volcanic activity may have inhibited reef development in this area. The un-dated unit U2 probably developed 120–130 ka ago during the last interglacial (MIS 5.5) + 6 m MSL highstand as thick, extensive reefs deposited all along the Lesser Antilles arc. Due to subsidence, MIS 5.5 reefs are not represented by onshore facies, except along the southern Sainte Anne Peninsula where normal faulting and uplift balances island-scale subsidence. Based on unit U2's present elevation and assuming an MIS 5.5 age and + 6 m MSL sea level, Martinique has subsided at maximum 0.3 m/ky, likely due to subduction processes that question the coupling state of the megathrust.

Carbon and oxygen isotopic composition and foraminifers of condensed basal Zechstein (Upper Permian) strata in western Poland: environmental and stratigraphic implications

The basinal facies of the Lopingian Zechstein Limestone in SW Poland consists of thin (often less than 1 m thick) limestones and/or dolomites, often containing the Kupferschiefer (few tens of centimetres thick) at their base, and local thick (up to 90 m) reefal carbonates. The δ13C curve of these basal Zechstein deposits strongly suggests that even when the Kupferschiefer is lacking, the thin (condensed) sequences record the entire interval of the Zechstein prior to the onset of evaporite deposition, in contrast to the thick reef sequences which lack the characteristic δ13C curve for the lowermost part of the Zechstein. The calcite samples show considerable ranges of δ18O values. If the maximum δ18O values are considered to be the closest to the pristine original ones and if δ18Owater value = 0 is assumed, then the calculated range of palaeotemperatures for the Kupferschiefer and Zechstein Limestone calcite ranges from 19 to 34 °C. The faunal restriction, common dwarf foraminifers and the predominance of lagenids in the foraminiferal assemblage indicate continual dysaerobic conditions and possibly elevated salinity of seawater during deposition of thin basinal Zechstein Limestone deposits. The mixing of shallow and deeper waters in the stratified Zechstein Basin caused by upwelling could result in prolific carbonate precipitation in reefs located at the slope of the marginal carbonate platform of the Zechstein Limestone and in isolated reefs related to palaeohighs within the basin; however, there is no isotopic record of eventual upwelling. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Topographic and sea level controls on oolite-microbialite-coralgal reef sequences: The terminal carbonate complex of southeast Spain

The terminal carbonate complex of southeast Spain is a Miocene (Messinian) unit of oolite, microbialite, and coralgal reefs deposited in association with glacioeustasy and evaporitic drawdown. The relationship between paleotopography and sea level history is useful for prediction of microbialite and oolite reservoir facies in the subsurface. Four sequences record sea level change with minimum amplitudes of 32–77 m (105–253 ft). Sequences commonly have local basal stromatolites overlain by local thrombolites, ooid grainstone, volcaniclastic-rich planar-bedded ooid grainstone, and fenestral ooid grainstone. At low substrate positions, thrombolite boundstones are thicker and laterally more continuous than at higher positions. At intermediate substrate positions (relative to sea level history), sequences have a build-and-fill architecture, characterized by a relief-building phase and a relief-filling phase, with thin sequences draping paleotopography. Microbialites dominate during the relative sea level rises and build topographic relief. Oolites dominate during the relative sea level falls and fill topographic relief. At higher substrate positions, close to highstand, sequences thicken and yield stratigraphic character that is inconsistent with a build-and-fill model. Apparently, the build-and-fill model requires an intermediate-elevation substrate position and nonoptimal carbonate productivity during rapid sea level change. Sequences progressively show increasing diversity and more normal marine organisms, possibly caused by decreasing aridity. Lithofacies of the La Molata area show evidence of more restricted conditions compared to the La Rellana-Ricardillo area lithofacies, likely because La Molata was in an embayment. These results show that distribution of oolite, microbialite, and reef facies are predictable given known interaction among sea level, paleotopography of the depositional surface (substrate), and coastline configuration.

Impact of environmental parameters on coral reef development and drowning: Forward modelling of the last deglacial reefs from Tahiti (French Polynesia; IODP Expedition #310)

AbstractThe sedimentological and chronological analysis of the last deglacial reef sequences of Tahiti (French Polynesia), drilled during the Integrated Ocean Drilling Program Expedition 310, provide a high‐resolution data set allowing a well‐constrained forward modelling study. This study represents the first attempt to model in three dimensions the coral reef development of Tahiti during the last deglacial sea‐level rise (23 000 to 6000 cal yr bp) using the software dionisos developed by IFP Energies nouvelles. It allows the testing of the reconstructed last deglacial sea‐level curve and the different environmental parameters (for example, wave energy and sediment fluxes) that could have influenced the reef development. These last deglacial reef sequences form two prominent ridges occurring seaward of the living barrier reef that consist of successive submerged reefs. These reefs have been prone to drowning because the window of maximum carbonate production rate is inhibited by high water turbidity (sediment supply from a nearby river), shallow depth of wave action and substrate availability. These factors, combined with rapid sea‐level rise, have driven the growth of retrograding reef pinnacles. Local factors (substratum nature, sediment supply and wave energy) were the main processes that induced the drowning of the inner ridge, whereas interplay of local and global factors (acceleration of the sea‐level rise) was responsible for the drowning of the outer ridge. This particular acceleration of sea‐level rise of 16 m between 14·6 ka and 14 ka bp corresponds to meltwater pulse 1A.

利川花椒坪长兴组生物礁岩层序地层研究&lt;br&gt;Sequence Stratigraphy Analysis and Reservoir Evaluation of Reef of Changxing Formation in Huajiaoping of Lichuan

利川花椒坪位于川东碳酸盐岩台地与鄂西海槽之间的台地边缘相带，晚二叠世长兴期该区水体逐渐由深变浅，发育了一套规模巨大的加积–近积型台地边缘生物礁沉积。通过野外露头剖面精细地质写实研究，对花椒坪生物礁岩层序地层与储层进行了深入分析。研究表明利川花椒坪生物礁礁体主要在Sq1高位体系域和Sq2海侵体系域，内部由4个准层序组成。随着相对海平面不断下降，水动力条件逐渐增强，利川花椒坪经历了生物礁奠基、初期繁盛、最大繁盛和生物礁衰亡等四个演化阶段。 Huajiaoping of Lichuan is located in platform margin facies between carbonate platform facies in eastern Sichuan and Western Hubei Trough. In the study area, the water gradually changed from the deep to shallow in the stage of Changxing Formation of Late Permian, and developed a huge scale of platform margin reef deposition in aggradation- progradation. Through the multidisciplinary analysis of measured profiles, the authors made an in-depth analysis on the Huajiaoping reef sequence stratigraphy and reservoir. The study demonstrated that the body of reef in the Huajiaoping of Lichuan was located in HST of sequence 1 and TST of sequence 2 of Changxing Formation, and internally consti- tuted by the four parasequence sets. As the relative sea level fell gradually and hydrodynamic force improved progres- sively, the reef in the Huajiaoping had experienced four stages of evolution, including the foundation stage, the initial flourishing stage, the prosperous stage, and the organic reef declining stage.

Platinum-group element distribution in base-metal sulfides of the Merensky Reef from the eastern and western Bushveld Complex, South Africa

Base-metal sulfides in magmatic Ni-Cu-PGE deposits are important carriers of platinum-group elements (PGE). The distribution and concentrations of PGE in pentlandite, pyrrhotite, chalcopyrite, and pyrite were determined in samples from the mineralized portion of four Merensky Reef intersections from the eastern and western Bushveld Complex. Electron microprobe analysis was used for major elements, and in situ laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) for trace elements (PGE, Ag, and Au). Whole rock trace element analyses were performed on representative samples to obtain mineralogical balances. In Merensky Reef samples from the western Bushveld, both Pt and Pd are mainly concentrated in the upper chromitite stringer and its immediate vicinity. Samples from the eastern Bushveld reveal more complex distribution patterns. In situ LA-ICP-MS analyses of PGE in sulfides reveal that pentlandite carries distinctly elevated PGE contents, whereas pyrrhotite and chalcopyrite only contain very low PGE concentrations. Pentlandite is the principal host of Pd and Rh in the ores. Palladium and Rh concentrations in pentlandite reach up to 700 and 130 ppm, respectively, in the samples from the eastern Bushveld, and up to 1,750 ppm Pd and up to 1,000 ppm Rh in samples from the western Bushveld. Only traces of Pt are present in the base-metal sulfides (BMS). Pyrrhotite contains significant though generally low amounts of Ru, Os, and Ir, but hardly any Pd or Rh. Chalcopyrite contains most of the Ag but carries only extremely low PGE concentrations. Mass balance calculations performed on the Merensky Reef samples reveal that in general, pentlandite in the feldspathic pyroxenite and the pegmatoidal feldspathic pyroxenite hosts up to 100 % of the Pd and Rh and smaller amounts (10–40 %) of the Os, Ir, and Ru. Chalcopyrite and pyrrhotite usually contain less than 10 % of the whole rock PGE. The remaining PGE concentrations, and especially most of the Pt (up to 100 %), are present in the form of discrete platinum-group minerals such as cooperite/braggite, sperrylite, moncheite, and isoferroplatinum. Distribution patterns of whole rock Cu, Ni, and S versus whole rock Pd and Pt show commonly distinct offsets. The general sequence of “offset patterns” of PGE and BMS maxima, in the order from bottom to top, is Pd in pentlandite → Pd in whole rock → (Cu, Ni, and S). The relationship is not that straightforward in general; some of the reef sequences studied only partially show similar trends or are more complex. In general, however, the highest Pd concentrations in pentlandite appear to be related to the earliest, volumetrically rather small sulfide liquids at the base of the Merensky Reef sequence. A possible explanation for the offset patterns may be Rayleigh fractionation.