Demise Of Carbonate Platforms Research Articles

Climate-driven hydrological change and carbonate platform demise induced by the Paleocene–Eocene Thermal Maximum (southern Pyrenees)

The Campo section in the Spanish Pyrenees is classical for shallow-water Paleocene-Eocene Thermal Maximum (PETM) studies. Despite extensive work in the last decades, the stratigraphic location of the onset of the negative carbon isotope excursion (CIE), and hence the Paleocene/Eocene (P/E) boundary, remains a matter of considerable debate in the Campo section. Here we present new biostratigraphic, sedimentological and carbon-isotopic data across the late Paleocene to Eocene strata to constrain the precise stratigraphic position of the P/E boundary and investigate environmental changes across the PETM. Foraminiferal assemblages of biozone SBZ4 found below the Claret Formation are replaced by SBZ6 assemblages above. Detailed microfacies analysis indicated that the pre-PETM upper Navarri Formation represents transgressive inner-ramp deposits, overlain unconformably by mixed carbonate-siliciclastic deposits of the syn-PETM Claret Formation, overlain unconformably in turn by renewed carbonate-ramp deposition in the post-PETM lower Serraduy Formation. The temporary demise of the carbonate ramp during the PETM is ascribed to increased siliciclastic supply associated with a significant change in regional hydrology driven by an increase in magnitude and frequency of extreme rainfall and runoff events.

Eustatic, Climatic, and Oceanographic Influences on Geomorphology and Architecture of Isolated Carbonate Platforms: Miocene, Northwest Shelf, Australia

Abstract The Miocene represents an interval of marked global change, and this evolution is reflected in carbonate platforms from this epoch. Seismic stratigraphic characterization of high-resolution (ca 60 Hz) 3D seismic data from the Browse Basin, offshore Australia, reveals a middle to upper Miocene three-part seismic stratigraphic subdivision. Each unit consists of several seismic sequence sets and their component sequences. Seismic stratal geometries and seismic facies define a prograding shelf (Langhian and older), a barrier-reef complex with scattered platforms (upper Langhian–early Tortonian), and aggrading and prograding isolated platforms (early Tortonian–Messinian). The data permit description and interpretation of high-fidelity stratigraphic details of the initiation, expansion, termination, and geomorphology of over 100 platforms in this interval. The results reveal that the isolated platforms initiated following the Middle Miocene Climatic Optimum. The succession includes major seismic stratigraphic boundaries and overall patterns of platform growth and demise that correspond roughly with periods of pronounced eustatic change associated with initiation of eastern Antarctic ice sheets. Although invoking a eustatic control for coarse trends may be tempting, mismatch between the numbers and ages of sequences, as well as the variable stacking patterns among contemporaneous platforms regionally, precludes such an interpretation; conversely, some globally recognized eustatic changes do not have a pronounced manifestation in this area. Thus, it appears that the eustatic signal combined with dynamic physical regional processes such as waves, currents, and variable subsidence creates the complex architecture and geomorphology of platforms. These results illustrate how global changes can interact with local controls to create diverse patterns of birth, growth, and demise of carbonate platforms and drive local stratal heterogeneity.

Two types of hyperthermal events in the Mesozoic-Cenozoic: Environmental impacts, biotic effects, and driving mechanisms

A deeper understanding of hyperthermal events in the Earth’s history can provide an important scientific basis for understanding and coping with global warming in the Anthropocene. Two types of hyperthermal events are classified based on the characteristics of the carbon isotope excursion (CIE) of the five representative hyperthermal events in the Mesozoic and Cenozoic. The first type is overall characterized by negative CIEs (NCHE) and represented by the Permian-Triassic boundary event (PTB, ~252 Ma), the early Toarcian oceanic anoxic event (TOAE, ~183 Ma), and the Paleocene-Eocene Thermal Maximum event (PETM, ~56 Ma). The second type is overall characterized by positive CIEs (PCHE) and represented by the early Aptian oceanic anoxic event (OAE1a, ~120 Ma) and the latest Cenomanian oceanic anoxic event (OAE2, ~94 Ma). Hyperthermal events of negative CIEs (NCHE), lead to dramatic changes in temperature, sedimentation, and biodiversity. These events caused frequent occurrence of terrestrial wildfires, extreme droughts, acid rain, destruction of ozone layer, metal poisoning (such as mercury), changes in terrestrial water system, and carbonate platform demise, ocean acidification, ocean anoxia in marine settings, and various degree extinction of terrestrial and marine life, especially in shallow marine. In contrast, hyperthermal events of positive CIEs (PCHE), result in rapid warming of seawater and widespread oceanic anoxia, large-scale burial of organic matter and associated black shale deposition, which exerted more significant impacts on deep-water marine life, but little impacts on shallow sea and terrestrial life. While PCHEs were triggered by volcanism associated with LIPs in deep-sea environment, the released heat and nutrient were buffered by seawater due to their eruption in the deep sea, thus exerted more significant impacts on deep-marine biota than on shallow marine and terrestrial biota. This work enriches the study of hyperthermal events in geological history, not only for the understanding of hyperthermal events themselves, large igneous provinces, marine and terrestrial environment changes, mass extinctions, but also for providing a new method to identify the types of hyperthermal events and the inference of their driving mechanism based on the characteristics of carbon isotopic excursions and geological records.

An Early Cretaceous mesophotic coral ecosystem built by platy corals (middle Aptian, Southern Carpathians, Romania)

A low relief middle Aptian (Gargasian) reef built by platy corals is described from the Lower Cretaceous succession of the Reşiţa–Moldova Nouă zone (Southern Carpathians, SW Romania). Two coral-bearing units, 16–17 and 38–42 m thick, discontinuously cover ca. 1100 m. This is an unusually thick fossil reef to be built by platy corals. The coral units are underlain by bioclastic limestones interlayered with thin rudist-chaetetid biostromes, separated by a 15–30 m thick interval of bioclastic limestones and overlain by upper Aptian conglomerates. Mostly dense, rarely sparse, platestones are composed of a low diversity coral assemblage mainly represented by the suborder Microsolenina. Small, branching corals are very rare. The matrix mainly consists of fine bioclastic-peloidal packstones and wackestones. Dominance of microsolenine corals, their flattened morphology, the presence of epibionts on coral undersurfaces and occurrence of red algae Sporolithon rude and Polyastra alba indicate that low-light was the main factor controlling reef growth. As with most fossil reefs dominated by platy corals (e.g., Upper Jurassic microsolenid reefs), the Reşiţa reef can be considered an analogue of modern reefs from mesophotic coral ecosystems (MCEs) in relatively deep water settings. The mesophotic or perhaps oligophotic environment was characterised by low background sedimentation, and high nutrient level as evidenced by abundant bioerosion traces. Matrix sediment and rare fragmentation of coral skeletons indicate moderate water movement. In contrast with common Barremian–lower Aptian coral reefs, younger Lower Cretaceous reefs in Romania are very rare. This reflects the general demise of carbonate platforms in the northern Tethyan domain during the early Aptian Oceanic Anoxic Event (OAE1a).

The palaeoceanographic crisis of the Early Aptian (OAE 1a) in the Vocontian Basin (SE France)

The Vocontian Basin (SE France) which presents lower Aptian expanded successions characterized by major lithological changes, is particularly suitable to determine palaeoenvironmental changes occurring across the OAE 1a. A multidisciplinary study (sedimentology, CaCO3, TOC, carbon and oxygen stable isotopes, micropalaeontology, cyclostratigraphy) was carried out in the Notre-Dame-de-Rosans section in order to establish a detailed chronological framework of these changes. The OAE 1a corresponds to carbon isotope segments C3–C6, and it lasted for 1.2 Myr. A first drop in the carbonate production occurs 500 kyr before the OAE 1a (upper part of the carbon isotope segment C2), and could result from both onset of “Urgonian” carbonate platform demise and associated reducing export of platform-derived sediments into the basin, and nannoconid crisis. A second drastic drop (crash) in the carbonate production is recorded within the lower part of the OAE 1a (latter part of segment C3 to C5) and is explained by a strong dissolution. This study then shows that the onset of the major carbonate crisis, that occurs before the OAE 1a, could be due to both rise in sea-level and in marine surface water fertility, whereas its “acme” that occurs within the OAE 1a, could be related to CO2-induced ocean acidification. Black shales of the “Niveau Goguel” occur in the upper part of the OAE 1a and represent the lower part of segment C6. Surface-waters primary producers are principally represented by cyanobacteria, whereas nannofossil primary productivity is reduced, and deep-water anoxia prevailed during the deposition of “the Niveau Goguel”. The last 300 kyr of the OAE 1a are characterized by a partial recovery of both nannofossil primary productivity and pelagic carbonate production, which sharply increase just after the end of the event. This study also shows that organic-rich layers associated to the OAE 1a are diachronous in the Tethyan realm.

Carbonate platform crisis in the Carnian (Late Triassic) of Hanwang (Sichuan Basin, South China): Insights from conodonts and stable isotope data

During the Carnian, the Hanwang area in the northwestern Sichuan Basin (South China) was characterized by shallow water carbonate sedimentation that underwent an abrupt demise associated to a sudden input of terrigenous sediments. This major facies change was considered to be the expression of the onset of the Carnian Humid Episode, a most remarkable environmental crisis in Late Triassic that is well recognized in northwestern Tethys margins and coincides with a major global perturbation of the carbon stable isotope record. However, the lack of detailed biostratigraphic constraints have so far prevented a precise dating of the carbonate platform demise in western Sichuan Basin.In this work, the Qingyan Gou (HWQ) section, cropping out in Hanwang, was investigated for its facies and microfacies, carbonate carbon and oxygen isotopes on brachiopods, microbial grains and bulk matrix. Facies analysis shows a marine transgression from inner ramp oolitic shoal to middle ramp siliceous sponge mound, then overlain by shale and calcareous siltstone with interbedded silty mudstones. Refined biostratigraphic data from HWQ and Guanyin Ya (HWG) sections imply that the demise of sponge mounds occur in the late Tuvalian or later.A negative carbon isotope perturbation was found in the bulk matrix immediately below the sponge mounds demise, but it was not found on the isotope record from brachiopods. This suggests that the negative shift in the bulk carbonate was probably related to diagenesis. Given the late Tuvalian (last substage of Carnian) age attributed to the demise of the sponge mounds and the absence of a carbon isotopic excursion, we infer that the carbonate platform crisis and strong terrigenous input in Hanwang cannot be related to the onset of the Carnian Humid Episode. These the demise of the carbonate platform and the facies deepening trend could be rather due to the interplay between accelerating subsidence rates, environmental chants and enhanced siliciclastic input related to the formation of a foreland basin during Indosinian orogenesis.

Carbonate-platform response to the Toarcian Oceanic Anoxic Event in the southern hemisphere: Implications for climatic change and biotic platform demise

The Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Ma) was a profound short-term environmental perturbation associated with the large-scale release of 13C-depleted carbon into the global ocean–atmosphere system, which resulted in a significant negative carbon-isotope excursion (CIE). The general lack of characteristic T-OAE records outside of the northern hemisphere means that the precise environmental effects and significance of this event are uncertain. Many biotic carbonate platforms of the northern hemisphere western Tethys drowned or shifted to non-skeletal platforms during the early Toarcian. However, southern hemisphere records of Toarcian carbonate platforms are rare, and thus the extent and significance of biotic platform demise during the T-OAE is unclear. Here we present high-resolution geochemical and sedimentological data across two Pliensbachian–Toarcian shallow-water carbonate-platform sections exposed in the Tibetan Himalaya. These sections were located paleogeographically on the open southeastern tropical Tethyan margin in the southern hemisphere. The T-OAE in the Tibetan Himalaya is marked by a negative CIE in organic matter. Our sedimentological analysis of the two sections reveals an abundance of storm deposits within the T-OAE interval, which emphasizes a close link between warming and tropical storms during the T-OAE event, in line with evidence recently provided from western Tethyan sections of the northern hemisphere. In addition, our analysis also reveals extensive biotic carbonate-platform demise by drowning or changing to non-skeletal carbonates coincident with the onset of the CIE. Taken together, our results suggest that rapid and pervasive seawater warming in response to carbon release likely played a significant role in sudden biotic carbonate platform demise, and suppression/postponement of biotic platform re-development along the whole tropical/subtropical Tethyan margin.

Taxonomy and stratigraphy of Early Cretaceous species of Debrunia Masse and Fenerci-Masse (Hippuritida, Monopleuridae) of the Mediterranean region

The genus Debrunia is characterized by its myophoral organisation: the left valve posterior myophore is an erect plate, the anterior is a bulge or a crest, myophores of right valve are on shell wall, the ligament groove is inconspicuous and the cardinal apparatus tends to be shifted posteriorly. Shell habit varies from low conical to elongated cylindrical, and the shape of the left valve ranges from capuloid to flat. The taxonomic revision of Debrunia species of the Mediterranean regions reveals the presence of thirteen species, among which seven are described as new. Multiple Component Analysis and Cluster Analysis document the existence of five groups of species in correspondence with the height of the left valve and the commissural diameter. The longevity of Debrunia is high, 32 Myr, whereas its species have shorter durations which account for a significant biostratigraphic potential within the Valanginian–Albian time span. Debrunia has its FO (First occurrence) in the lower Valanginian and its LO (Last occurrence) in the Albian. Its developmental phase starts in the Hauterivian, marked by an increasing species diversity and a biogeographic expansion; and peaks in the late Barremian, followed by a collapse in diversity and a specific turnover, coeval with the “Agriopleura extinction event”. The mid-Aptian crisis is expressed by a drastic decline in species diversity, controlled by the overall restriction or demise of carbonate platforms in European regions. As elevators, Debrunia species tend to build dense monospecific aggregations and some of them possess a remarkable bioconstructional potential. The contribution of Debrunia to rudist communities is significant throughout the history of the genus.

New drilling of the early Aptian OAE1a: the Cau core (Prebetic Zone, south-eastern Spain)

Abstract. The Cretaceous was punctuated by several episodes of accelerated global change, defined as Oceanic Anoxic Events (OAEs), that reflect abrupt changes in global carbon cycling. The Aptian Oceanic Anoxic Event (OAE1a; 120 Ma) represents an excellent example, recorded in all major ocean basins, and associated with massive burial of organic matter in marine sediments. The OAE1a is concomitant with the "nannoconid crisis", which is characterized by a major biotic turnover, and a widespread demise of carbonate platforms. Many studies have been published over the last decades on OAE1a's from different sections in the world, and provide a detailed C-isotope stratigraphy for the event. Nevertheless, new high-resolution studies across the event are essential to shed light on the precise timing and rates of the multiple environmental and biotic changes that occurred during this critical period of Earth history. Here we present a new drill core recovering an Aptian section spanning the OAE1a in southern Spain. The so-called Cau section was drilled in the last quarter of 2015. The Cau section is located in the easternmost part of the Prebetic Zone (Betic Cordillera), which represents platform deposits of the southern Iberian palaeomargin. The lower Aptian deposits of the Cau section belong to a hemipelagic unit (Almadich Formation), deposited in a highly subsident sector of the distal parts of the Prebetic Platform. Previous work on the early Aptian of the Cau succession has focused on stratigraphy, bioevents, C-isotope stratigraphy, and organic and elemental geochemistry. A more recent study based on biomarkers has presented a detailed record of the pCO2 evolution across the OAE1a (Naafs et al., 2016). All these studies reveal that the Cau section represents an excellent site to further investigate the OAE1a, based on its unusually high sedimentation rate and stratigraphic continuity, the quality and preservation of fossils, and the well-expressed geochemical signatures.

Carbon-isotope anomalies and demise of carbonate platforms in the Sinemurian (Early Jurassic) of the Tethyan region: evidence from the Southern Alps (Northern Italy)

AbstractDespite its global impact on ecosystems, the Triassic/Jurassic boundary event had only a modest effect on the carbonate depositional systems of the Southern Alps, whereas a fundamental reorganization of the same palaeogeographic area took place during the Sinemurian Age. This paper investigates whether or not the well-documented demise of Sinemurian carbonate platforms in the Tethyan region was a response to a global event by examination of carbon-isotope anomalies in successions of different facies that record this interval of time. A chemostratigraphic transect from Lake Garda up to the eastern Italian border is illustrated by four stratigraphic sections; high-resolution (20 cm over key intervals) chemostratigraphic sampling allowed detection of a major negative δ13C anomaly of ~ 1.5‰, preceded by a positive excursion, both in shallow- and deep-water successions, over the stratigraphical range of the ammonite genusArnioceras. A comparison with sections from the UK suggests that the positive excursion belongs to theturneriZone and the succeeding negative excursion falls within theobtusumZone. In the deep-water Belluno Basin, the negative anomaly occurs in a biogenic chert-rich unit recording the onset of mesotrophic conditions in the basin. In the platform-carbonate successions, this major negative carbon-isotope excursion is developed within a calcarenitic unit corresponding to the lowest occurrence of the foraminiferPaleomayncina termieri. This evidence for deepening and transgression across the carbonate platform suggests pre-conditioning for drowning. Hence, rather than tectonic subsidence alone, environmental factors may have aided the demise of Tethyan carbonate platforms during the Early Jurassic Sinemurian Age.

Drowning events, development and demise of carbonate platforms and controlling factors: The Late Barremian–Early Aptian record of Southeast France

In Provence and Languedoc, SE France, four drowning events were identified in platform carbonates of late Barremian–Bedoulian age; their timing, referred to ammonite zones or subzones, is as follows:(1)Late Barremian (D1), at the Gerhardtia sartousiana–Imerites giraudi boundary,(2)Middle Bedoulian (D2), at the Deshayesites weissi–Deshayesites deshayesi boundary,(3)Mid late Bedoulian (D3) in correspondence with the “Roloboceras hambrovi subzone”, and(4)Late Bedoulian (D4) at the Deshayesites grandis–Dufrenoya furcata transition.Notwithstanding their relatively wide regional, lateral continuity, the depositional hiatus, linkage with exposure, paleobathymetric range and offset, and geographical extent of drowning discontinuities are not uniform.The late Barremian drowning (D1) is marked either by the development of a permanent intra-shelf basin with ammonites associated with the re-organization of platform–basin relationships, or by the wide extent of Palorbitolina–Heteraster facies, which develops to the detriment of the antecedent rudist facies. The drowning event is followed by platform recovery during the early Bedoulian, but the corresponding development of shallow water carbonates is subsequently interrupted by the emergence of an uplifted bulge trending sub-parallel to the Provence–Languedoc margin. The Middle Bedoulian drowning (D2) is concurrent with the sealing of the antecedent paleotopography and the wide development of Palorbitolina facies, then bioclastic and coral facies tend to recover. The Mid late Bedoulian drowning (D3) is characterized by an overall deepening phase, with ammonite-bearing marly facies or cherty limestones, shallow bioclastics being locally present. The late Bedoulian drowning (D4) records the deposition of deep water marls.Evidence is lacking that global sea level changes or transgressive–regressive cycles had a significant impact on drowning events, and some evidence that changes in temperature and productivity of the ocean may have contributed to these phenomena in conjunction with other factors.Though distension fault activity is regarded as a major controlling factor for the origin of the late Barremian deepening event, its associated paleogeographic re-organization, ensuing emergence of the Provence–Languedoc marginal bulge and its subsequent detumescence coeval with the Middle Bedoulian drowning. Associated changes in facies types, from rudist to Palorbitolina, reflect sea-water deepening coupled with trophic modifications.As agents of differential subsidence, tectonic phenomena are also testified by the contrasting regional patterns of paleobathymetric offsets combined with drowning events. They are a clue for understanding thickness changes and coeval modifications in the overall orientation of the progradational polarity of the platform system, towards the adjacent basinal areas.Environmental changes, essentially the two main OAE1a subevents, are regarded as significant agents of the Mid late and late Bedoulian drownings, whereas tectonic processes are also involved in the corresponding deepening. However, the effects of the OAE events on the functioning of the shallow carbonate factory are poorly understood and still need to be investigated.The rise in atmospheric carbon dioxide pressure and, as a consequence, the reduction of the calcification potential of benthic organisms, both reported in the literature, are not clearly reflected in the composition of the biota: aragonite-dominated organisms such as caprinid rudists thrive throughout the Bedoulian. The role of acidification in platform demise is therefore questionable.

A new ammonoid fauna from the Carnian (Upper Triassic) Kasimlar Formation of the Taurus Mountains (Anatolia, Turkey)

AbstractWe describe a new ammonoid fauna from the Taurus Mountains of southern Turkey. The Carnian ammonoid fauna from Aşağiyaylabel is presented for the first time. Ammonoids were obtained from limestone to marl beds of an approximately 35‐m‐thick section, which presents the rare opportunity to investigate ammonoid faunas across the Lower–Upper Carnian boundary. Intense sampling near the village of Aşağiyaylabel led to the recognition of a new Lower Carnian (Julian 2) to Upper Carnian (Tuvalian 1) ammonoid fauna from the Kasimlar Formation. The genus Kasimlarceltites gen. nov. is reported for the first time from the Taurus Mountains, which represents the main faunal element and occurs as huge mass occurrence (n ≫ 1 million). Kasimlarceltites krystyni gen. et sp. nov., Klipsteinia disciformis sp. nov. and Anasirenites crassicrenulatus sp. nov. occur within the Lower Carnian Carbonate member (Units A–B) of the Kasimlar Formation from the Taurus Platform Units. Ammonoids described from the marls of the Tuvalian Marlstone member were deposited during a major, Tethyan‐wide climate crisis – the so‐called Carnian crisis – characterized by a demise of carbonate platforms. Based on the biostratigraphic relevance of certain ammonoid taxa described herein, the age of the analysed parts of the Kasimlar Formation is Julian 2 to Tuvalian 1. The discovery of the new ammonoid assemblages from Aşağiyaylabel substantiates the significance of Upper Triassic faunas within the Taurus Mountains and facilitates the correlation with faunal assemblages from other regions in the Tethyan Realm. The ammonoid fauna and facies indicate a general deepening from open‐platform margins, over deeper shelf settings down to an open marine‐influenced basinal environment. The tentative habitat for Kasimlarceltites gen. nov. is a shallow platform environment to upper mid‐ramp.

Density banding in corals: barcodes of past and current climate change

The predicted sea surface temperature (SST) rise over the next decades is likely hazardous to coral health because precipitation of the calcareous skeleton depends primarily on SST. Temperature modulates vertical growth and density of the skeleton with seasonal SST changes resulting in an alternation of high-density and low-density bands (HDB and LDB). Notably, growth rates and the timing of the HDBs and LDBs relative to the seasons differ on a global scale within geographic regions. In this contribution, we use combined information of skeletal density and seasonally resolved oxygen isotope SST estimates from massive Porites from a Late Miocene (9 Ma) reef in the eastern Mediterranean Sea (Crete, Greece) to understand reef vulnerability over short and geological periods of time. Three types of HDB–SST relationships have been found: (1) coincidence of HDB with summer, (2) winter or (3) autumn and spring. The latter doubles HDBs in a year and implies maximum calcification is coupled to the taxon-specific optimum SST during the transitional seasons and reduced at its respective critical winter and summer SSTs. Modeling with a nonlinear temperature–calcification relationship reproduces the climate barcode of density bands. The model should be relevant for other poikilothermic carbonate producers in reefs and platforms and has implications for judging geographic distributions and causes of extinctions of corals, benthic carbonate communities and entire carbonate systems. With regard to the causes underlying expansion and demise of carbonate platforms and reefs in geological history, we expect the model predictions to help for a deeper understanding of biotic responses during hyperthermals or coolings and possibly also for identifying regions in the modern ocean where corals are endangered or taking advantage of global warming.

High-frequency, moderate to high-amplitude sea-level oscillations during the late Early Aptian: Insights into the Mid-Aptian event (Galve sub-basin, Spain)

This paper presents a field-based stratigraphic architecture research from the Aptian of Spain in which high-frequency (7cycles/Ma), moderate to high-amplitude (8–127m) sea-level oscillations are evidenced by the repeated incision of palaeovalleys in a carbonate platform developed during the late Early Aptian in a rift setting. Global eustacy, tectonic uplift and mantle dynamic topography are considered as potential mechanisms to explain the observed relative sea-level record. Glacioeustacy is interpreted as the most reliable mechanism to drive the observed sea-level oscillations, however, other mechanisms as oscillations of the groundwater capacity of sedimentary basins and sudden flooding of major a basin as the south Atlantic rift are also considered. A major cooling event is proposed to occur during the late Early Aptian as a response to a large-scale episode of ignimbritic volcanism, increased burial of organic carbon during the Aptian OAE-1a, and a significant demise of carbonate platforms. This cooling event is interpreted as the origin for glacioeustatic sea-level oscillations during the Mid-Aptian.

Rudist bivalves and the Pacific in the Late Jurassic and Early Cretaceous

Although rudists of Late Jurassic to earliest Cretaceous age are known from Nova Scotia to Japan, the oldest specimens recovered from Pacific seamounts are Barremian (or possibly Hauterivian). The lack of evidence for disjunct endemism limited to either side of the ocean, then, precludes the inference that earlier rudists might have been present within it. Yet trans-Pacific range expansion of Caribbean-derived taxa, by means of larval ‘island-hopping’, was accomplished by the Early Aptian. Following a mid-Aptian mass extinction, the Pacific then became an important nursery of rudist re-diversification. Late Aptian rudists in Japan and derivative Late Aptian–Albian polyconitids in the Japanese Seamounts and Cebu show affinities with those from the eastern (Himalayan) sector of the northern Tethyan margin. By contrast, the caprinid Caprina mulleri in the Mid-Pacific Mountains is most closely allied with the C. choffati–C. adversa lineage known from the Atlantic–Mediterranean Tethyan region. However, the Pacific species could have been derived from an Early Aptian Caribbean Caprina that survived in some Pacific refuge, later reintroducing the genus to the Tethyan region in the Late Albian. Colonization of Pacific volcanic prominences ceased in the latest Albian, with the demise of carbonate platforms there, and was not resumed until the Campanian–Maastrichtian.

A mechanism for brief glacial episodes in the Mesozoic greenhouse

The Mesozoic, perhaps the longest period of warmth during the Phanerozoic Earth history, has been repeatedly affected by short‐lived cold interludes lasting about one million years. While the origin of these cold snaps has been classically attributed to a temporary atmospheric CO2 drawdown, quantified mechanisms explaining these instabilities of the carbon cycle are still lacking. Based on a climate carbon cycle model, we show that the general demise of carbonate platforms accompanying these short‐lived cold interludes is a powerful mechanism capable of generating a fast atmospheric CO2 decrease and a moderate sea level drop associated with ice sheet buildup. The temporary nature of the carbonate production decline explains the relative short time of these cold events but makes it possible to account for ice sheet waxing and waning.

Strontium and carbon-isotope chronostratigraphy of Barremian–Aptian shoal-water carbonates: Northern Tethyan platform drowning predates OAE 1a

A widely accepted hypothesis proposes that the Early Aptian demise of carbonate platforms in the northern Tethyan realm reflects the impact of environmental changes that eventually led to the deposition of organic-rich basinal sediments during oceanic anoxic event (OAE) 1a. In fact, the temporal correlation of oceanic anoxia and platform drowning has not been rigorously tested and evidence indicating causality is debated. The present paper provides a high-resolution carbon- and strontium-isotope chronostratigraphy combined with detailed sedimentological analysis applied to the Barremian–Aptian Urgonian carbonate platform development at the northern rim of the Tethys (Subalpine Chains, Haute-Savoie, ESE France). A characteristic Barremian–Aptian carbon- and strontium-isotope pattern below the onset of OAE 1a interval permits precise platform-to-basin correlation with the Barremian stratotype locality of Angles (SE France). This chemostratigraphic pattern equally allows for a correlation with well-studied shoal-water and pelagic records of the northern and central Tethys. Strontium-isotope stratigraphy provides a high-resolution numerical age-data set, indicating an earliest Aptian age (< 124.5 ± 0.4 Ma) of platform demise in the Subalpine Chains. The detailed platform-to-basin correlation obtained in France clearly illustrates that shoal-water carbonate production in the Urgonian platform ceased about 300 kyr before the most negative values of the characteristic negative carbon-isotope anomaly, which marks the beginning of OAE 1a black-shale deposition. The stratigraphic results confirm (i) the theory of an Early Aptian northern Tethyan platform drowning episode predating OAE 1a and (ii) document the temporal response of shoal-water carbonate platforms to the environmental perturbations prior to the OAE acme.

Palynological correlation of Carnian humid pulses throughout western Tethys

The Carnian Pluvial Event is an Upper Triassic swing toward increased rainfall best documented in the Tethys tropical belt, and mainly recognized on its effects on sedimentary systems, as the demise of carbonate platforms and the enhanced siliciclastic supply. In some portions of western Tethys, and particularly in the Raibler Schichten of the Northern Calcareous Alps and in the Dolomites, the Carnian Pluvial Event is recorded by four discrete siliciclastic pulses. In the Raibler Schichten, three siliciclastic intervals are documented and take the name of first, second and third shale. In order to correlate these pulses at the basinal scale, the study of the palynological assemblages in a section of the Raibler Schichten near Rubland (Austria), and of the classical succession of the Lunz nappe, have been carried out. More than eighty palynomorph species are recorded. Most of them correspond to typical Carnian morphospecies of the Carnian Pluvial Event in Europe. On the base of their stratigraphic distribution, three different palynomorph assemblages are described: Aulisporites astigmosus assemblage, Lagenella martinii assemblage and Granuloperculatipollis rudis assemblage. A fourth, older assemblage is also informally defined. A palynostratigraphic correlation between the NCA, the Germanic Basin and the Dolomites has been obtained. The four siliciclastic pulses recognized in the Raibler Schichten and Lunz are also found in the Dolomites, and yield the same palynological associations. The base of the Schilfsandstein, that record the Carnian Pluvial Event in the Germanic Basin, is correlated to the second or third siliciclastic pulse (first or second shale of the Raibler Schichten). Siliciclastic pulses are thus correlated throughout western Tethys, and can thus be interpreted as short-lived humid climate wiggles within the Carnian Pluvial Event. A quantitative analysis of the Carnian successions of the NCA highlights a shift toward hygrophytic elements in the uppermost Julian, and an abrupt return to xerophytic associations in the lower Tuvalian. The palynological hygrophytic associations that characterize the Aulisporites astigmosus and Lagenella martinii assemblages are present in many other parts of Europe and Middle East, suggesting that the Carnian Pluvial Event determined a humid climate perturbation in a wide area of the northern hemisphere spanning from tropical to high latitudes.

Drowning history of a Miocene carbonate platform (Zhujiang Formation, South China Sea)

The identification and interpretation of drowning events in the geologic record can aid significantly to the reconstruction of the depositional, tectonic and eustatic history of a study area and often improve reservoir and seal prediction in carbonate rocks. The differentiation between drowned platforms showing a record of continuous deepening and those with a record of exposure followed by rapid deepening remains, however, problematic. The Zhujiang carbonate platform (Liuhua 11-1 field, South China Sea) study shown here provides an example of an integrated approach combining high-resolution geochemistry, microfacies analyses and foraminiferal biostratigraphy in order to improve the reconstruction of environmental conditions prior, during and after platform demise and drowning. The Zhujiang carbonate platform displays the following vertical succession of four facies types i) skeletal grain facies with a miogypsinid/lepidocyclinid-dominated fauna deposited in a moderately deep (< 50 m), oligotrophic back-reef setting; ii) in situ corals in patch-reef facies in an oligotrophic lagoon (< 10 m); iii) rhodoid facies with in situ red algal crusts, dominated by Heterostegina sp. and spiroclypeids, possibly capped by a subaerial exposure surface. Well-rounded rhodoids representing a mesotrophic lagoon dominate the upper portions of the rhodoid facies; iv) pelagic marine shales of the Hanjiang Formation burying the carbonate platform after drowning. This facies succession, in combination with geochemical evidence suggests a deepening-upward trend. This trend might have been interrupted by transient subaerial exposure but no evidence for meteoric diagenesis was found at the drowning unconformity topping the carbonate platform. Instead, microfacies analyses suggest that platform demise may be related to progressive changes in environmental conditions, including increasing nutrient-levels and/or decreasing temperature up-core towards the drowning unconformity. These findings are of significance for those concerned with Miocene carbonate factories and, more specifically, the demise of carbonate platforms in general.

Stratigraphic organisation, spatial distribution, palaeoenvironmental reconstruction, and demise of Lower Cretaceous (Barremian-lower Aptian) carbonate platforms of the Western Pontides (Black Sea region, Turkey)

Barremian-Lower Aptian platform carbonates (“Urgonian limestones”) of the northern margin of the Istanbul zone extend from Zonguldak to the Kurucasile area along the Black Sea coast. New stratigraphic data on the “Inpiri” Formation of the Inpiri-Kurucasile area are based on the identification of calcareous algae, foraminifera, and rudists. They show that this lithostratigraphic unit is stratigraphically and lithologically equivalent to the Öküşmedere Formation from Zonguldak. Some of the biostratigraphic markers are reported for the first time in Anatolia. Foraminifera are represented by several forms with a significant biostratigraphic potential used to distinguish the Barremian from the lower Aptian. Lower Aptian beds also yield relatively advanced caprinid rudists. The Öküşmedere Formation is relatively thin, terrigeneous-rich, and rudist-free or rudist-poor in the Kurucasile sector, and thick, terrigeneous-poor, and rudist-rich from Amasra to Zonguldak, with a set of marker beds including either charophytes or Palorbitolina and capped by a coral unit underlying ammonite bearing marls. Terrigeneous-rich carbonates from the eastern sector are interpreted as marginal marine coastal, infralittoral environments and grade distally, northward, to marly basinal sediments. By contrast “Urgonian type” limestones from the Zonguldak-Amasra region possess a wide extent and no transition to coastal or basinal sediments has been observed. A transition from a typical platform westward to a mixed siliciclastic-carbonate ramp eastward was controlled by both the nature of the adjacent exposed area and tectonic factors affecting the overall continental margin that is a northward downwarping. The exposed area was flanked southward by a belt of coastal siliciclastics grading southward and eastward to deep water sediments of the Ulus basin. In mid-Bedoulian time, carbonate platform demise from the western region was drowned below deeper marly sediments whereas the eastern siliscilastic-carbonate ramp was buried below coastal clastics.