Carbonate Platform Setting Research Articles

Hybodont dentition from the Upper Jurassic of Monte Nerone Pelagic Carbonate Platform (Umbria‐Marche Apennine, Italy) and its ecological implications

Here we describe a number of articulated teeth of a hybodont shark from Upper Jurassic deposits of the Monte Nerone Pelagic Carbonate Platform, in the Umbria‐Marche‐Sabina Palaeogeographic Domain (Northern Apennines, Central Italy). The material has been referred to asAsteracanthuscf.A. magnus, a quite well‐known taxon already reported from Middle to Upper Jurassic deposits of Europe. Teeth indicate an extreme crushing feeding behaviour, suggesting as putative prey both infaunal and epifaunal hard‐shelled invertebrates dwelling the sea‐floor, such as large bivalves, brachiopods, gastropods as well as vagile crustaceans. The finding represents, to date, the first formal report of hybodont shark in the Umbria‐Marche‐Sabina Domain, throwing further light on the ecology within Pelagic Carbonate Platform settings, and on the occurrence ofAsteracanthusin the Late Jurassic of the Western Tethys.

STRATIGRAPHY OF THE LOWER OLIGOCENE NUMMULITIC LIMESTONES, NORTH OF SONQOR (NW IRAN)

The lower Oligocene hyaline and porcellaneous larger foraminifera of a carbonate platform setting, north of Sonqor, were studied for high-resolution biostratigraphy in the context of European standard zonation (Shallow Benthic Zones). According to the geological map of Kermanshah, these beds were previously ascribed to the Miocene. The identified larger foraminifera include Nummulites fichteli Michelotti, Nummulites vascus Joly & Leymerie, Operculina complanata (Defrance), Asterigerina rotula (Kaufmann), Planorbulina bronnimanni Bignot & Decrouez, Discogypsina discus (Goes), Gypsina mastelensis Bursch, Halkyardia maxima Cimerman, Stomatorbina concentrica (Parker & Jones), Praerhapydionina delicata Henson, Penarchaias glynnjonesi (Henson), Austrotrillina aff. paucialveolata Grimsdale, and Haddonia heissigi Hagn, associated with the coralline alga Subterraniphyllum thomasii Elliott. The foraminiferal association characterises the SBZ 21 Zone (early Rupelian).

A missing link in the peri-Gondwanan terrane collage: the Precambrian basement of the Moroccan Meseta and its lower Paleozoic cover

This article provides stratigraphic and geochronological data from a central part of Gondwana’s northern margin — the Moroccan Meseta Domain. This region, located to the north of the Anti-Atlas area with extensive outcrops of Precambrian and lower Paleozoic rocks, has hitherto not received much attention with regard to its Precambrian geology. Detrital and volcanic zircon ages have been used to constrain sedimentary depositional ages and crustal affinities of sedimentary source rocks in stratigraphic key sections. Based on this, a four-step paleotectonic evolution of the Meseta Domain from the Ediacaran until the Early Ordovician is proposed. This evolution documents the transition from a terrestrial volcanic setting during the Ediacaran to a short-lived carbonate platform setting during the early Cambrian. The latter then evolved into a rifted margin with deposition of thick siliciclastic successions in graben structures during the middle to late Cambrian. The detritus in these basins was of local origin, and a contribution from a broader source area (encompassing parts of the West African Craton) can only be demonstrated for postrifting, i.e., laterally extensive sandstone bodies that seal the former graben. In a broader paleotectonic context, it is suggested that this Cambrian rifting is linked to the opening of the Rheic Ocean, and that several peri-Gondwanan terranes (Meguma and Cadomia–Iberia) may have been close to the Meseta Domain before drifting, albeit some of them seem to have been constituted by a distinctly different basement.

Three-dimensional stratigraphic-sedimentological forward modeling of an Aptian carbonate reservoir deposited during the sag stage in the Santos basin, Brazil

Stratigraphic-sedimentological forward modeling is a useful technique to test the role of parameters that may act in the depositional processes of sedimentary rocks. The technique was applied to the Santos basin, Brazil, using the software program DIONISOS to test possible depositional scenarios for an Aptian section of a lacustrine carbonate platform developed during the late sag stage (uppermost pre-salt section) of the basin. Different parameters were tested in a set of numerical simulations with the aim of reproducing the carbonate facies spatial distribution and the overall stratigraphic stacking pattern of the platform, as observed in the available well data. Several models were simulated, and four of them are discussed in this paper. Based on the available descriptive data from 10 wells, Model 3 is considered to produce the best fit to explain the development of the 100-m thick Aptian carbonate platform, occurrences of grainstones and stromatolites as proximal and intermediate facies, respectively, and the overall carbonate stacking pattern. Thus, based on 3D stratigraphic-sedimentological forward modeling, the best set of environmental conditions able to explain the pattern of carbonate deposition observed in the study area are (1) a slow carbonate depositional rate (0.08 mm/y over an interval of 2.4 My), which is indicative of a larger microbial contribution, and (2) lake-level oscillations, which were essentially induced by arid climatic conditions. These results also enable new perspectives for the application of stratigraphic-sedimentological forward modeling as a predictive tool for hydrocarbon exploration in carbonates and for the development of depositional models of other sag carbonate platform settings.

Micropalaeontology and sedimentology of an inter-evaporite Arab-C carbonate exposure, Riyadh, Saudi Arabia

Alternating carbonate and evaporite successions of strata characterise the Late Jurassic, Kimmeridgian–Tithonian, Arab Formation of Saudi Arabia. Outcrops of the Arab Formation are poorly exposed and are mostly studied from subsurface samples, due to dissolution of the evaporites and the collapse of intervening carbonate strata. The type section for this formation is in the subsurface, where a more complete succession is available for study where four carbonate and evaporite members, namely D, C, B and A in ascending stratigraphic order, have been identified. The Arab has important hydrocarbon associations, due to its excellent porosity, permeability and proximity to underlying source rocks and overlying evaporite seals. This study provides new insights into the internal palaeo environment and depositional cyclicity of the Arab C, with implications to improve understanding of microfacies and porosity variations of the reservoir equivalent. The studied section provides a rare datapoint for the proximal palaeoenvironment of the Arab C carbonates that are mostly studied in the subsurface far to the east. Arab Formation carbonates are exposed along road cuts in the city of Riyadh. One recent exposure, 27 ft (8.2 m) thick, provides new micropalaeontological, sedimentological and palaeoenvironmental information for this stratigraphic unit that is otherwise elusive as an exposure. The new section is located next to the flanks of a sinkhole within gently folded strata and implies that the exposure must represent one of the supra-Arab D evaporite members, for which regional mapping indicates assignment to the C member of the Arab Formation. The Arab C consists of a succession of low diversity microfossiliferous wackestones and packstones, in which the red alga Permocalculus cf. iranae and rhaxellid sponge spicules are well represented. The exposure extends the stratigraphic range of Bramkampella arabica from the Sulaiy Formation down section into the older Arab C. Arab C microfacies are interpreted to represent deposition in a normal marine salinity, carbonate platform setting, probably within a shelf lagoon, mostly below fair-weather wavebase and within storm wavebase. Within the succession is a distinctive grainstone bed containing the benthonic foraminifera Everticyclammina kelleri, Kurnubia jurassica, Nautiloculina oolithica, Pseudocyclammina lituus and Redmondoides lugeoni and is considered to represent the top of one high frequency sequence (HFS). Immediately above the grainstone additional strata in the measured section form the base of a second HFS.

Gradients in the carbon isotopic composition of Ordovician shallow water carbonates: A potential pitfall in estimates of ancient CO2 and O2

The carbon isotopic composition of the global dissolved inorganic carbon (DIC) reservoir is best estimated from open ocean pelagic carbonate sediments (δ13Ccarb). However, this is not practical for most of geologic time because seafloor subduction has removed the pre-Jurassic record and these time periods may have lacked planktonic calcifying organisms, and therefore shallow water carbonate platform or periplatform sediments are utilized. Shallow water deposits are susceptible to a wide range of post-depositional alteration processes and syn-depositional controls on δ13Ccarb that include carbonate mineralogy, water mass restriction, and a host of related variables (e.g., pH, temperature, organic decomposition, evaporation and CO2 solubility) that can produce local gradients in DIC. The degree to which shallow water δ13C curves diverge from open marine deposits may be critical to understanding how well global carbon cycle isotope mass balance models can predict organic carbon burial rates, but documentation of such divergence is often hindered by factors that limit chronostratigraphic correlation in restricted water masses (e.g., endemic faunas). Here we integrate strontium isotope (87Sr/86Sr) stratigraphy and biostratigraphy to compare δ13C curves in a case study along a depth transect in Middle–Late Ordovician carbonate platform settings. The restricted tidal flat and more open marine deposits are offset by a maximum of ∼2‰ during sea level drop and ∼0‰ during highstand flooding of the platform. Global carbon cycle models such as GEOCARBSULF use published δ13Ccarb curves to drive organic carbon burial rates under the assumption that δ13Ccarb reflects a global seawater signal. We show here the potential pitfalls of using a published δ13Ccarb curve that violates this global assumption. For the 460 million year Middle–Late Ordovician time bin in GEOCARBSULF, improper usage of our locally depleted δ13C curve to drive global organic carbon burial would result in erroneous atmospheric O2 (∼10.8% O2, equal to about a 30% reduction from what it should be at ∼15.2% O2 using global δ13C) and CO2 (∼400 ppm too high, equal to about a 13% increase from what it should be at 2570 ppm CO2). With detailed sedimentologic analysis, it may be possible to identify and exclude δ13C samples that record the influences of local carbon cycling from global carbon cycle models such as GEOCARBSULF.

Upper Devonian reefs and microbialite at Maoying, South China—implications for paleoenvironmental changes

Reefal carbonate deposits in South China preserve a record of community structure and environmental change across the Frasnian-Famennian boundary and through the Late Devonian, detailing a regional response to one of the largest mass extinction events in Earth history. The Upper Devonian (Frasnian to Famennian) limestone outcrops in the Maoying area of northern Ziyun County, South China, record a carbonate platform depositional setting with some patch reef development. The Upper Devonian carbonate deposits in Maoying area are distinctive from those in correlative sections in Dushan County with rare argillaceous limestone and dolomitic limestone as well as less dolostone. Exposures to the south in the Guilin area of northeastern Guangxi Province are similar to those seen in the study area. Upper Devonian carbonates in the Maoying area are divided into two lithologic groups, reef limestones or dolostone beds, composed of five lithologically distinctive intervals. The Upper Devonian strata have a cumulative thickness of 530m. The Upper Devonian reefs in the Maoying area were developed on a shell pavement of brachiopod- and bivalve-shell shoal packstones and evolved into patch reefs in the interior of the carbonate platform. Patch-reef development was limited to early Frasnian time. Reef-building organisms are dominated by massive and tabular stromatoporoids, Amphipora sp., Stachyodes sp., and coral Thamnopora sp., while brachiopods and algae accumulated between stromatoporoid skeletal frameworks. Three evolutionary stages of the Frasnian patch reefs, including an initial development stage, maturity stage and demise stage, can be recognized according to sedimentary structures and fossil assemblage characteristics. The Frasnian strata overlying the patch reefs represent a well-bedded back-reef depositional setting and are mainly composed of Amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals. Famennian strata are characterized by laminated limestone and fenestrate limestone that are interbedded with infrequent mudstone and argillaceous limestone horizons. A prominent microbialite bed developed in the laminated limestone of the Famennian carbonate platform consists of stromatolite and thrombolite framestone. This bed can be correlated, in horizon and age, with microbial reefs and mounds in the Famennian offshore carbonate platform in the Huanan Epeiric Sea (such as Famennian microbial reefs and mounds in Guilin). This represents a biogenic carbonate formation characterized by microbial fabrics that accumulated in a nearshore carbonate platform setting after the global Frasnian/Famennian biotic extinction event, which promoted the growth of microbialites during the latest Devonian in South China.

Carbon isotope (δ13Ccarb) and facies variability at the Wenlock–Ludlow boundary (Silurian) of the Midland Platform, UK

The Wenlock–Ludlow series boundary (Silurian) has been recognized as a time of pronounced sea-level rise and the end of a globally recognized Late Homerian Stage (Mulde) positive carbon isotope excursion (CIE). However, the precise timing and synchronicity of the end of the excursion with respect to the Wenlock–Ludlow boundary is debated. Within the type Wenlock and Ludlow areas (UK), high-resolution δ13Ccarb isotope data are presented across the Wenlock–Ludlow boundary, and within a range of carbonate platform settings. Correlation between sections and depositional settings has been based upon the characteristics of high-order sea-level fluctuations (parasequences). Comparisons between parasequence-bounded δ13Ccarb values reveal clear spatial variations, with lighter values recorded from more distal settings and heavier values from shallower settings. Temporal variations in the δ13Ccarb values are also documented and appear to reflect local variations in carbonate provenance and productivity in response to sea-level rise. While δ13Ccarb values converge in all sections towards the Wenlock–Ludlow boundary, the apparent end of the Mulde CIE appears diachronous and is progressively older within more distal settings.

High-resolution SIMS oxygen isotope analysis on conodont apatite from South China and implications for the end-Permian mass extinction

Understanding the interplay of climatic and biological events in deep time requires resolving the precise timing and pattern of paleotemperature changes and their temporal relationship with carbon cycle variations and biodiversity fluctuations. In situ oxygen isotope analyses of conodont apatite from South China enables us to reconstruct high-resolution seawater temperature records across the Permian–Triassic boundary (PTB) intervals in the upper slope (Meishan), lower slope (Shangsi), and carbonate platform (Daijiagou and Liangfengya) settings. Constrained by the latest high-precision geochronological dates and high-resolution conodont biozones, we can establish the temporal and spatial patterns of seawater temperature changes and assess their potential connections with the carbon cycle disruption and biodiversity decline. We find a rapid warming of ~10°C during the latest Permian–earliest Triassic that postdated the onset of the negative shift in δ13Ccarb by ~81kyr (thousand years), the abrupt decline in δ13Ccarb by ~32kyr and the onset of mass extinction by ~23kyr, which contradicts previous claims that the extreme temperature rise started immediately before or coincided with the onset of mass extinction. Our new evidence indicates that climate warming was most likely not a direct cause for the main pulse of the end-Permian mass extinction (EPME), but rather a later participant or a catalyst that increased the pace of the biodiversity decline. In addition, a prominent cooling is recorded in the earliest Changhsingian, with the main phase (a drop of ~8°C in ~0.2Ma) confined to the lower part of the Clarkina wangi zone and synchronous with the positive limb of the carbon isotope excursion (CIE) around the Wuchiapingian–Changhsingian boundary (WCB) in Meishan and Shangsi. Further long-term and high-resolution studies from other sections are needed to confirm the full contexts and underlying dynamics of the WCB “cooling event”.

Tectono-sedimentary evolution of the Permian–Triassic extension event in the Zagros basin (Iran): results from analogue modelling

Since the 1970s, the largest oil and gas reservoirs have been discovered in the Permian–Early Triassic formations in Saudi Arabia. Thus, this time period is important for the discovery of new oil reserves in Iran. The Arabian passive continental margin has undergone lithospheric extension during the Permian–Triassic, which led to the formation of the Neo-Tethys. The aim of this paper is to describe the development of the continental rift basin in the Zagros region based on the tectono-sedimentological evolution. We have studied well-log data to specify the distribution of synrift deposits in the Zagros and have related this information to the modelling. Environmental changes indicated by various sedimentary sequences, from a siliciclastic basin to a carbonate platform setting, are described. The Cambrian Hormuz salt, which overlies the metamorphosed Precambrian basement, becomes effective as a basal detachment layer influencing the style of overburden deformation during the Permian–Triassic extension event. We have investigated the formation of various structures linked to the presence or absence of the Hormuz layer by analogue modelling and relating these structures to the Late Palaeozoic sedimentation. Based on results of the analogue modelling, we argue that the basal detachment layer (Hormuz series) has contributed to the various structural styles of the extensional basin development in the Fars domain and the Lorestan domain.

Middle Jurassic Monte Fallano Plattenkalk (Campania, southern Italy): first report on terrestrial plants, decapod crustaceans and fishes

A new Jurassic fossiliferous Plattenkalk has been discovered at Monte Fallano (Caserta, Campania, southern Italy). Biostratigraphic analyses indicate a Bajocian/Bathonian age (Middle Jurassic). The fossil assemblage consists of terrestrial plants, invertebrates (bivalves, gastropods, decapod crustaceans, isopods and insect larvae) and vertebrates (fishes). This study takes terrestrial plants, fishes, and decapod crustaceans into account, giving systematic, taphonomic and palaeoenvironmental considerations. The land flora consists of impressions of sterile and fertile shoots of microphyllous conifers; leaves with parallel venation of unknown taxonomy are also present. The genera Cupressinocladus, Brachyphyllum and Araucarites are documented and their microscopical characters are examined. Plant remains possibly represent a stable biotope, as floral composition presents no variation along the section studied. Taphonomic considerations on plant fossils suggest parautochtonous deposition. The study of the rich decapod crustacean fauna includes Acanthochirana liburiaensis n. sp. (Aegeridae Burkenroad, 1963), Casertanus sabellicus n. gen., n. sp. (Sergestidae dana, 1852), Eryma osciensis (Erymidae Van Straelen, 1925) and Tethyseryon campanicus n. gen., n. sp. (Eryonidae de Haan, 1841). Casertanus sabellicus n. gen., n. sp. is the oldest representative of Sergestidae in the fossil record, extending the stratigraphic range of this family into the Middle Jurassic. Tethyseryon campanicus n. gen., n. sp. is the earliest species in which juveniles have been identified within the Eryonidae; the presence of both juveniles and adults in the depositional environment of Monte Fallano suggests that this species was autochthonous or parautochthonous. Preliminary data on fossil fishes sample have lead to the identification of leptolepid, macrosemiid among which Notagogus (Neonotagogus) denticulatus, pleuropholid (Pleuropholis) and pycnodontid fishes; other primitive teleosts and incomplete and indeterminate “ganoid” fishes are also reported. Based on the sedimentological data and the characteristics of decapod crustaceans and fishes, the investigated record of the Monte Fallano section represents the product of depositional process in shallow water carbonate platform settings.

Early Aptian algal bloom in a neritic proto-North Atlantic setting: Harbinger of global change related to OAE 1a?

Pervasive growth of microencrusters ( Lithocodium/Bacinella ) characterizes short-lived stratigraphic intervals in Lower Aptian shallow-water carbonate platform settings of the central and southern Tethys. Although a causal relationship between this peculiar shallow-water facies and the early Aptian oceanic anoxic event (OAE) 1a seems likely, the temporal and spatial distributions of Lithocodium and Bacinella mass occurrences in the rock record point to a rather complex pattern. Possible controls include various global and regional drivers expressed in environmental perturbation of neritic ecosystems. Microencruster blooms have hitherto been reported to occur at the onset and in the aftermath of oceanic anoxic event (OAE) 1a, slightly pre- or postdating the deposition of dark organic-rich black shales in pelagic basins. This study presents evidence for a punctuated and well-expressed early Aptian bloom of the ulvophycean green algae Lithocodium aggregatum observed at the proto-North Atlantic margin, Lusitanian Basin, Portugal. Similar to southern and central Tethyan sections, a Lithocodium -dominated interval temporally replaces the rudist-dominated platform ecosystem. This Lithocodium -rich horizon is composed of oncoidal floatstones and boundstones, including a well-exposed biohermal level, and reaches a thickness of up to 6 m. High-resolution carbon-isotope stratigraphy shown here clearly argues for Lithocodium to represent a biotic harbinger of environmental change in the run-up of OAE 1a. Chemostratigraphy provides evidence that the subsequent carbonate platform breakdown in the proto∼North Atlantic was coeval with an early Aptian carbonate platform drowning episode observed in the northern Tethys prior to OAE 1a. A regionally enhanced nutrient level and a relative sea-level rise are suggested to have triggered the transient mass occurrence of Lithocodium microencrusters, which also may have been influenced by elevated atmospheric CO2 concentrations related to the emplacement of the Ontong Java large igneous province. Upwelling water masses and enhanced terrigenous runoff due to increased weathering may have served as possible sources of the required nutrients, which tentatively diminished and finally interrupted the metazoan carbonate platform factory.

CAPITANIAN (MIDDLE PERMIAN) MASS EXTINCTION AND RECOVERY IN WESTERN TETHYS: A FOSSIL, FACIES, AND 13C STUDY FROM HUNGARY AND HYDRA ISLAND (GREECE)

The Capitanian (middle Permian) extinction and recovery event is examined in carbonate platform settings from western Tethys (Hungary and Hydra, Greece). The age model for these sections is poorly resolved and we have constructed a δ13C chemostratigraphic correlation scheme, supported by conodont and foraminifer data, which attempts correlation with the well-dated events in China. This reveals the timing of events was similar in all Tethyan regions: extinction losses in the middle of the Capitanian produced late Capitanian assemblages in Hungary and Hydra with a distinctive late Permian character (for example, they lack large fusulinaceans). There is no evidence for an extinction event at the end of the Guadalupian (Capitanian) suggesting that previous claims for an end-Guadalupian mass extinction are based on poorly dated records of a mid-Capitanian event. Base level was stable through much of the middle–late Permian transition with the exception of a major regression within the Capitanian Stage. The subsequent transgression established widespread shallow-water carbonate deposition, such as the Episkopi Formation in Hydra and the Nagyvisnyo Limestone Formation in Hungary.

Geology and geochemistry of the Jurassic carbonate hosted barite deposits, Northeast Zakho, Iraq

Barite deposits located in Marsis locality of about 25km northeast of Zakho City were hosted in Jurassic dolomitic rocks. The barite is extending for about 6km and limited within about 38m thickness of dolomitic rocks. The thickness of the barite veins varies between few centimeters to 2.5m which increases downward. The major mode of occurrence of barite is as vein and cavity-filling. The barite and other minerals of vein and cavity-filling deposits are typical of suite precipitated from low-temperature hydrothermal solutions associated with igneous activity. Carbonate-hosted barite deposits contain 0.237% BaO, 103ppm Zn, and 83 ppm Pb. These rocks are deficit in Fe and F. Most of carbonate rocks are dolomitized, which provide appropriate physical and chemical conditions that permitted the passage of mineral-bearing fluids. These deposits are formed in carbonate platform setting and commonly developed in foreland thrust belt.

Tectonostratigraphic framework of Upper Ordovician source rocks, Ottawa Embayment (eastern Ontario)

Abstract Two intervals of Upper Ordovician organic-rich (gas-prone) source rocks are preserved in a regional fault block of approximately 1000 km2 within the Ottawa Embayment (eastern Ontario). They bracket an apparent conformable mid-Katian (late Edenian to early Maysvillian) transition from a relatively shallow-water carbonate platform setting to a deep-water shale basin within the local Taconic foreland basin. The platform succession is represented by the Lindsay Formation, and records deepening and replacement of a once skeletal-rich, productive platform environment by fossiliferous shale and limestone facies association (10 to 18 m thick) comprising the Eastview Member. Nodular and bedded crinoidal lime mudstone is intercalated with fossiliferous (trilobite, brachiopod) organic-rich (2–6% TOC) shale. The upper 2 m of the unit contain shale with dispersed to compacted accumulations of trilobites and brachiopods. The Eastview Member thickens to the southeast, and is overlain with apparent conformity by organic-rich (2–4+% TOC) shale of the Billings Formation. Regionally, this latter unit is approximately 20 m thick, and accumulated in an anoxic to dysoxic deep-water basin. Thin laminae of siltstone to fine-sandstone herald the later, principal, phase of basin fill by sandstone and shale that characterize the overlying Carlsbad Formation. Geophysical (gamma-ray) transects restricted to the western embayment reveal km-scale spacing of high-angle faults and small-scale synsedimentary horsts and grabens that formed after shallow (3–5 m) burial of the Eastview Member. One small-scale graben illustrates a near doubling (<40 m) of the Billings Formation. A tectonostratigraphic framework for source rock accumulation includes a first-order geodynamic control driving regional platform foundering, then a higher-order structural response that enhanced local thickness of organic shale and created faults subject to reactivation in post-Ordovician time.

Reply to the comment on “Sea-level control on facies architecture in the Cenomanian–Coniacian Apulian margin (Western Tethys): A record of glacio-eustatic fluctuations during the Cretaceous greenhouse?” by S. Galeotti, G. Rusciadelli, M. Sprovieri, L. Lanci, A. Gaudio and S. Pekar [Palaeogeography, Palaeoclimatology, Palaeoecology 276 (2009) 196–205

Parente et al. (2010) (hereafter Petal10) (Comment on “Sea-level control on facies architecture in the Cenomanian–Coniacian Apulian margin (Western Tethys): A record of glacio-eustatic fluctuations during the Cretaceous greenhouse?” by S. Galeotti, G. Rusciadelli, M. Sprovieri, L. Lanci, A. Gaudio and S. Pekar [Palaeogeography, Palaeoclimatology, Palaeoecology 276 (2009) 196–205], Palaeogeogr. Palaeoclimatol. Palaeoecol, 2010–this issue) discuss our contribution to the correlation of eustatic sea-level changes observed in the Cenomanian–Coniacian Apulian margin (Western Tethys) to reference records of sea-level fluctuation and the methods implied in constructing such correlation. Their conclusions stem from a fundamental misinterpretation of the method used in our study, particularly as far as the approach used to put the observed sequences, which are interpreted to reflect global sea-level changes, into context. In their comment, Petal10 extensively discuss the pitfalls implied in calibrating records and events in carbonate platform settings to a standard chronostratigraphy on the basis of biostratigraphy. This approach would be an obvious element of concern, but does not form the basis of the calibration in our study, which is based on the following procedure: 1. Biostratigraphy and event stratigraphy-based correlation – not calibration – of the events observed in the carbonate platform to the adjacent base-of-slope Monte Turno record; 2. Calibration of the Monte Turno bio- and chemostratigraphic record to reference (glacio)eustatic and chemostratigraphic records.

Sequence stratigraphy and carbon isotope stratigraphy of an Aptian mixed carbonate-siliciclastic platform to basin transition (Galve sub-basin, NE Spain)

Abstract A 380 m thick Aptian platform to basin transition has been studied along a 16 km long transect of excellent and continuous outcrops in NE Spain. The series has been dated using biostratigraphy (foraminifera and ammonites) and carbon-isotope stratigraphy, and has been subdivided at four scales of depositional sequences. The Aptian marine succession is subdivided into two-large scale sequences separated by a middle Aptian sub-aerial exposure surface. A characteristic trend of the floral-faunal fossil assemblages is present, which evolves from orbitolinid-ooid dominated ramps in Sequence I-1, to a coral-stromatoporoid-microbialite dominated platform in Sequence I-2, to a rudist-dominated platform top in Sequence II-1, and finally to a second episode of orbitolinid-ooid dominated ramp system in Sequence II-2. There was an influx of siliciclastic sediments at the base and at the top of this succession. The detailed carbon-isotope curve measured along the Miravete section and covering almost the complete Aptian succession, is compared with published Aptian curves recorded in both basinal and carbonate platform settings along the northern and southern NeoTethys margins. It shows that the Galve sub-basin curve represents all the major isotope excursions of the lower and upper Aptian, in a dominantly shallow-water succession.

Channelized systems in an inner carbonate platform setting: differentiation between incisions and tidal channels (Natih Formation, Late Cretaceous, Oman)

Abstract The Natih Formation (late Albian–early Turonian, Oman) corresponds to a very broad inner carbonate platform extending over more than 800 km between the Arabian Shield to the south and the Tethys continental margin to the north. Two types of channelized systems have developed recurrently on this inner carbonate platform: incisions corresponding to strictly erosive drainage systems which formed at the top of the sub-aerially-exposed platform during significant drops of relative sea level; tidal channels corresponding to partly erosive but mainly constructive/depositional systems which formed during phases of flooding of the inner platform. The comparative analysis of the basal surface and fill of incisions and tidal channels, based on the study of several outcrops in the Oman Mountains allows the recognition of the similarities and the main differences between these two types of channelized systems which both develop in an inner carbonate platform setting. One of the main criteria of differentiation is the stratigraphic context in which incisions and channels develop. Incisions develop at the top of regressive sequences, whereas the channels analysed here developed during phases of flooding or maximum flooding, during which higher energy processes such as tidal currents developed on the platform. The incision surface is clearly defined, with diagenetic effects such as silicification and dolomitization below, and with the systematic fill of subjacent burrows and cracks by sparitic calcite crystals. The basal erosion surface of channels is often multiple and composite, systematically burrowed, and associated with no significant diagenetic effect. Channels are generally less deep than incisions but their width is very similar. Incisions are longer than channels and present a section that is, on the whole, symmetrical and regular, whereas channels locally have one margin that is steeper and more erosive than the other. Finally, the less diagnostic parameter of differentiation is their fill. Indeed, incisions and channels are similarly filled during phases of flooding of the inner platform. Incisions and channels form significant heterogeneities at the reservoir scale. It is therefore necessary to be able to recognize these two types of channelized systems, in order to predict their geometry, extent and fill type, and the eventual occurrence of associated reservoir bodies in the more distal direction (forced regressive wedges/bioclastic shoals).

Stability of regional brachiopod diversity structure across the Mississippian/Pennsylvanian boundary

The middle Carboniferous was an interval of global change when the climate was transitioning from greenhouse to icehouse conditions. Field collections of paleotropical brachiopod assemblages across the Mississippian/Pennsylvanian boundary reveal a taxonomic turnover event in which the overall diversity structure is conserved, despite an apparent regional extinction of 63% of latest Mississippian genera and an apparent regional origination of 50% of earliest Pennsylvanian. An analysis of the global ranges of the brachiopods encountered in the field reveals that turnover was driven primarily by extirpation and immigration rather than true extinctions and originations. Taxonomic richness and evenness are indistinguishable between the latest Mississippian and earliest Pennsylvanian stages. Additive diversity partitioning shows that the within-collection, between-collections (i.e., within-bed), and between-bed diversity components do not change across the Mississippian/Pennsylvanian boundary for richness or evenness. Rank-abundance plots of genera show the same distribution for both stages, but with no correlation between the Mississippian abundances of range-through genera and their abundance in the Pennsylvanian. Detrended correspondence analysis shows a major change in taxonomic composition across that Mississippian/Pennsylvanian boundary and consistency in the general gradient along which genera were distributed. An estimation of spatio-temporal heterogeneity of taxonomic composition within each stage reveals that the earliest Pennsylvanian was significantly more homogeneous. These results suggest that middle Carboniferous brachiopod assemblages from tropical shallow-water carbonate platform settings were organized by some factor that was independent of the specific taxa present. Furthermore, the increased homogeneity in taxonomic composition in the Morrowan did not affect the overall diversity structure. Strong competitive interactions among taxa do not appear to be important in determining the taxonomic compositions and abundances of brachiopod stage-level assemblages.

SEALEX — Internal reef chronology and virtual drill logs from a spreadsheet-based reef growth model

A reef growth model has been developed using an Excel spreadsheet. The 1D forward model is driven by a user definable sea-level curve. Other adjustable model parameters include maximum coral growth rate, coral growth rate depth dependence and light attenuation, subaerial erosion and subsidence. A time lag for the establishment of significant reef accretion may also be set. During the model run, both, the external shape and the internal chronologic structure of the growing reef as well as the paleo-water-depths are continuously displayed and recorded. We tested the model on fossil reef systems growing in a range of different tectonic settings such as both on slowly subsiding islands like Tahiti (subsidence rates of 0.25 m ka − 1 ) and rapidly subsiding islands like Hawaii (subsidence rate of 2.5 mka − 1 ) as well as rapidly uplifting coastal settings like Huon Peninsula (uplift rates of 0.5 to 4 m ka − 1 ) and more slowly uplifting settings like Haiti (uplift rates of 0.55 mka − 1 ). The model runs show the sensitivity of the resulting overall morphology and internal age structure to different model parameters. Additionally the water depth at the time of deposition is recorded. This allows the constructions of virtual borehole logs with the coral age profiles and the paleo water depth at the time of growth both displayed and recorded. Because the model is implemented as a macro in a popular spreadsheet program, it may be easily adapted or extended to model the growth of different reef and carbonate platform settings. Single model runs take a few minutes on a standard (2 GHz CoreDuo) desktop computer under Windows XP. The model may be used to investigate the effects of different boundary conditions such as maximum reef growth, erosion rates, subsidence or uplift on both, the general morphology of the reefs, and the internal chronologic structure. These results can then be compared to observed data allowing different hypothesis concerning reefs development to be tested. The model may also be used to assist in finding sampling locations in reef bodies that are likely to contain critical information for sea level studies. SEALEX is available online at http://www.rcom.marum.de/English/SEALEX_reef_growth_model.html.