Carbonate Platform Succession Research Articles

Stratigraphy and Depositional History of the Middle–Upper Jurassic Platform Carbonate Succession in Kıraç Mountain (Western Central Taurides, S Turkey)

Stratigraphy and Depositional History of the Middle–Upper Jurassic Platform Carbonate Succession in Kıraç Mountain (Western Central Taurides, S Turkey)

Salt-rich versus salt-poor structural scenarios in the central Northern Calcareous Alps: implications for the Hallstatt facies and early Alpine tectonic evolution (Eastern Alps, Austria)

One of the most remarkable features of the central Northern Calcareous Alps (Eastern Alps, Austria) is the widespread presence of Upper Triassic deep-water carbonates (the Hallstatt facies) and Permo-Triassic evaporites resting on deep-water Middle Jurassic strata and their underlying Upper Triassic shallow-water carbonate platform successions. The Hallstatt facies and accompanying evaporites have been classically interpreted to originate either from a location south of the time-equivalent carbonate platforms, or to have been deposited in deeper water seaways within the broad platform domain. To date, this dispute has been addressed mostly through the analysis of Triassic and Jurassic facies distribution in map view, which, however, is subject to some degree of ambiguity and subjectivity. In this contribution we present, for the first time, sequentially restored regional cross-sections through the central Northern Calcareous Alps to understand the implications of the contrasting paleogeographic models. We present (a) an interpretation based on a highly allochthonous origin of the Triassic deep-water units and (b) an interpretation based on their relative autochthony in which we incorporate the potential influence of salt tectonics in the central NCA. The restored cross-sections provide a framework within which the alternative scenarios and their paleogeographic implications can be better understood. Through this analysis we propose that salt tectonics in the central NCA can provide a valid explanation for apparent inconsistencies in the relative autochthony scenario and thus constitutes a reasonable alternative to the currently accepted allochthony scenario.Graphical abstract

The Turonian–Campanian rudist bivalve succession in the Central Iberian Basin

Four rudist assemblages: lower Turonian, upper Turonian, upper Coniacian, and Santonian–?Campanian, are distinguished in the shallow water carbonate platform successions of the Iberian Basin, nowadays Iberian Range, a Mesozoic intra-continental basin in the western margin of the Mediterranean Tethys. Because of the depositional evolution of the Iberian Basin, the occurrence, abundance, taxonomic diversity, diagenetic processes, and shell preservation, for each assemblage, is linked, both, to the shallow character of these carbonate platform successions, and the successive high and low frequency sea level falls. Twenty identified rudist taxa are described and figured: Hippuritidae, six species of two genera; Radiolitidae, ten species of six genera, one new, Hoyosites tozoi gen. et sp. nov; Requieniidae, one genus. The knowledge of the shell characters of some taxa has been improved and the taxonomic, biostratigraphic, and palaeobiogeographic significance of most of them increased. The precise positioning of the first three rudist assemblages in high-frequency depositional stacking pattern (parasequence sets) and their correlation and calibration with ammonite biozones provide biostratigraphic datums of great importance. This fact notably improves the chronostratigraphic framework of the Cretaceous sedimentary successions of the Iberian Basin, especially towards the coastal margins, and allows the accurate quantification of the hiatuses associated with the parasequence sets boundaries, so enabling their precise hierarchization.

Aptian major changes in accommodation. New sedimentary evidence from the Maestrat Basin (E Iberia)

Global sea-level fluctuations with amplitudes of tens of metres and durations between 0.5 and 3 Myr are well-known oceanographic events of the Cretaceous Period. During recent years, major Cretaceous changes in accommodation recorded in different basins have been mainly interpreted as eustatically driven. Two episodes of major relative sea-level fall and rise of late early and early late Aptian age were investigated in the Maestrat Basin (E Iberian Peninsula). Previously documented in eight outcrops, these Aptian records of major changes in accommodation have now been identified in five additional localities within the basin, suggesting at least a basin-wide significance of these relative sea-level fluctuations. The records of relative sea-level fall analysed are associated with the local development of incised valleys and forced regressive wedges. Two upper lower Aptian incised valleys, which are downcutting highstand platform carbonates dominated by rudists and corals, were studied and show depths of approximately 10 and 80 m. The incision depths measured indicate amplitudes of relative sea-level variations in the order of tens of metres. During subsequent base-level rise, the lower part of these incised valleys was respectively infilled with orbitolinid limestones and high-energy carbonate deposits influenced by tides. Further evidence of major relative sea-level drop and rise during the late early Aptian includes a detached backstepping carbonate platform of reduced extension, underlain and overlain by basinal marly deposits, which flourished basinwards of a highstand platform margin. Although incised valleys or smaller-scale incisions are local features, evidence for relative declines in sea level can be identified from other evidence. For example, by the development of palaeokarst or by the presence of sharp or slightly erosive stratigraphic surfaces covered by deposits of higher energy influenced by tides, as observed in the late Aptian examples investigated herein. Comparable Aptian sedimentary features of subaerial exposure and subsequent transgressive genetic types of deposits have been observed in other basins across different tectonic plates, indicating that eustasy likely played a role in controlling accommodation changes during this stage. The discovery of new evidence for major relative Aptian sea-level fluctuations in various outcrops within the Maestrat Basin calls for further investigation in other underexplored Aptian platform carbonate successions in this basin. These investigations would contribute to a more accurate understanding of oceanographic dynamics during the Aptian Stage along the western margin of the Alpine Tethys.

Orbital forcing of Upper Jurassic (Tithonian) shallow-water carbonates, Tethyan Adriatic Platform, Croatia evaluated using synthetic vs. real data sets

A continuing debate surrounds the relative dominance of random vs. Milankovitch (astronomical) forcing of the stratigraphic record, particularly in the genesis of shallow-water carbonate platform successions. Using time series analysis, we examined a ∼ 7 myr duration, 700 m thick, internally conformable Upper Jurassic (Tithonian) section from the Adriatic Platform, southern Croatia. The Tithonian succession has a lower interval of dominantly subtidal parasequences and an upper interval of oolitic, laminite-capped peritidal parasequences. We combined this investigation with an analysis of synthetic data sets of water depth derived from numerical models of carbonate sedimentation containing differing amounts of random variance with superimposed Milankovitch forcing. Average Spectral Misfit (ASM) was calculated for each synthetic time series of preserved water depth and our Tithonian data to determine the most likely sedimentation rates and significance levels for rejection of the null hypothesis of no astronomical forcing. The ASM-determined sedimentation rates could then be compared to known long-term rates to again reject or accept the null hypothesis of no astronomical forcing. Using this approach, random synthetic data series showed considerable difference from astronomically-forced synthetic data sets. Multitaper method (MTM) spectral analysis of the Tithonian Dunham rank series tuned to the 100 kyr eccentricity cycle shows variable forcing by short (100 kyr) eccentricity, obliquity, and precession. The Tithonian parasequence thickness series was examined using wavelet analysis for bundling of parasequences and showed that long- (405 kyr), short-eccentricity and obliquity, plus obliquity modulation (∼200 kyr) influenced parasequence bundling. The results indicate that the ASM analysis can differentiate between successions dominated by random processes and those strongly influenced by Milankovitch processes.

Revisiting the upper Visean mud mounds from Derbyshire (UK): the role of brachiopods in their growth

Several brachiopod-rich mud mounds occur in the upper Visean (Brigantian) of the Derbyshire Carbonate Platform succession in UK. The re-evaluation of the lithofacies architecture of a Derbyshire mud mound complex, developed in an intraplatform middle-ramp environment, led to the recognition of three lithofacies associations: (a) a 10 m thick basal unit of automicrite boundstone with siliceous sponge spicules and brachiopod–bryozoan packstone to wackestone beds; (b) a 10 m thick, 250 m wide, lens-shaped, convex-up massive core of clotted peloidal micrite and fenestellid bryozoan boundstone with sponge spicules; (c) inclined brachiopod–bryozoan–crinoid packstone flank beds. In the mud mound complex core, most of the carbonate mud with clotted peloidal and structureless micrite fabric is the result of biologically induced and influenced in-situ precipitation processes (automicrite). Brachiopods are not, as previously thought, limited to storm-scoured “pockets” in the mud mound complex core but are abundant and diverse in all lithofacies and lived on the irregular mud mound complex surface concentrating in depressions sustained by automicrite boundstone and the growth of bryozoans and sponges. The upper Visean Derbyshire mud mounds are, thus, representatives of a newly defined fenestellid bryozoan–brachiopod–siliceous sponge mud mound category, occurring in various middle–upper Visean Western European sites, a sub-type of the fenestellid bryozoan–crinoid–brachiopod Type 3 buildups of Bridges et al. (1995). These mud mounds, and other types of brachiopod-rich buildups, developed in carbonate platform settings between fair-weather and storm wave base, in dysphotic environments with dispersed food resources during the Visean. Brachiopod mud mound colonisation was favoured by moderate water depth, availability of food resources, and diverse substrates.

Rediscovery of a classic Middle Triassic fossil site of the Balaton Highland (Transdanubian Range, Hungary): cephalopods, brachiopods and vertebrate remains from the Akol Hill at Barnag

Recent collecting of the classic Middle Anisian fossil site of the Akol Hill at Barnag (Nagyvázsony Plateau, Balaton Highland) yielded a plenty of new palaeontological data.The Middle Anisian platform carbonate succession (Tagyon Formation) is overlain by 1-2 metres thick reddish, nodular, crinoidal limestone (Vászoly Formation) that contains a very rich fossil assemblage with ammonoids, nautiloids and brachiopods. Some vertebrate fossils were also found. Besides fish teeth, remains of marine reptiles are also present in the fauna. Four vertebrae, a piece of a rib, as well as a tooth crown fragment have also been found.Based on the geological buildup and the new biostratigraphic data the active stage of the Barnag Platform was much shorter than that of the other two Middle Anisian platforms of the Balaton Highland (Tagyon Platform, Kádárta Platform). The ammonoid fauna of the lowermost thin limestone bed above the Tagyon Formation contains elements reworked from the Balatonicus Zone. The overlying some beds contain a very rich lower Illyrian ammonoid fauna which is more diverse than the equivalent faunas of the Tagyon Platform and the Kádárta Platform. The ammonites of the Balatonicus Zone in the basal part of the Vászoly Formation prove that the drowning of the Barnag Platform occured even during the Pelsonian, earlier than in the case of the Tagyon and the Kádárta Platforms where the oldest basin sediments are mid-Illyrian (Camunum Subzone of the Trinodosus Zone) above the drowning surface.The Akol Hill locality also provided the first known occurrence of ichthyosaurs like Cymbospondylus, predators that probably dwelled mostly open marine environments but also might have been well adapted for hunting in shallow environments like submarine highs.

A late Asbian (Mississippian) stratotype for England: Trowbarrow Quarry, Cumbria, UK

AbstractA detailed biostratigraphy is established, using the high foraminiferal abundance and diversity at Trowbarrow Quarry, which is also proposed as a stratotype section for the late Asbian (late Visean), a substage not previously formally subdivided. The foraminiferal assemblages suggest that the early Asbian has to be revised, which has implications for the chronostratigraphy of many late Visean outcrops in Britain, which are probably erroneously interpreted. From the upper part of the Park Limestone Formation at Trowbarrow Quarry, near the base of the section, the transition between foraminifers assigned to the early and late Asbian (Cf6α–β to Cf6γ subzones) is identified. The Urswick Limestone Formation contains excellent biostratigraphic records of many important taxa, enabling the subdivision of the formation into five foraminiferal assemblage zones for the late Asbian, namely Cf6γ1a, Cf6γ1b, Cf6γ2a, Cf6γ2b and Cf6γ2c. The last assemblage is currently recognized only in the North Pennines and at Trowbarrow. These assemblages enable revision of the stratigraphic range of many taxa used as biostratigraphic markers in Britain and Ireland. Owing to its excellent foraminiferal record, the late Asbian subdivisions will significantly facilitate the reinterpretation of other well‐known Asbian platform carbonate successions in Britain. Although there are some faunal differences, the base of the late Asbian can be confidently correlated to other European zonal schemes, with its base being equivalent to the base of the former V3bγ or more recent MFZ14 foraminiferal zones of Belgium, and the base of the Mikhailovian Substage in Russia.

Dolomitization of Late Norian carbonate deposits of restricted basin facies in the Keszthely Mts., Transdanubian Range, Hungary

In the Transdanubian Range (Hungary), a wide spectrum of Triassic dolomites is known. Mechanism of dolomitization of the platform carbonate successions was subject of a number of studies but the study of dolomitization of basinal carbonates is very limited. Petrographical and isotope–geochemical characteristics of the Upper Triassic dolomitized carbonate deposits, formed in a fault-controlled intraplatform basin, and interpretation of the dolomite-forming processes are presented in the current paper. From the latest Carnian to Middle Norian under semi-arid climatic conditions density-driven flux of seawater derived mesohaline fluids was the dominant mechanism of the near-surface pervasive dolomitization of the thick platform carbonate succession. In the late Middle Norian incipient rifting of the Alpine Tethys led to establishment of an extensional structural regime and onset of the formation of the Kössen Basin. In the study area, above the dolomitized platform carbonate succession, platform-derived carbonate sediments were accumulated in a fault-bounded, semi-restricted sub-basin of the Kössen Basin, whereas talus breccias and debrites were deposited near a basin-bounding master fault. The basin deposits (lower and upper members of the Rezi Dolomite Formation) were subject of early diagenetic dolomitization in shallow burial setting. Enhanced salinity seawater was the dolomitizing fluid; the synsedimentary fracturing may have promoted the fluid flow and thereby the dolomitization. Thick-bedded carbonates (middle member of the Rezi Dolomite Formation) representing a progradational tongue of the ambient platform are intercalated between the basin deposits. The dolomitization of this unit can be explained by the reflux model.

Bituminous coals on emergent surfaces in an Asbian, lower Carboniferous (Mississippian) limestone succession on the North Wales carbonate platform, UK, and implications for palaeoclimate

Emergent surfaces in the Mississippian (Asbian to Brigantian) carbonate platform succession of North Wales record periods of plant colonization and peat formation that led ultimately to the local development of coals. Examination of bituminous coals on three emergent surfaces within Cefn Mawr Quarry reveals information on palaeoclimate that is not available from study of the limestones alone. Three coal seams in the Asbian Loggerheads Limestone Formation were identified and the lowest one studied in detail. Vitrinite reflectance data from alternating bands of vitrite and duroclarite microlithotypes, the distribution of pyrite within them, and the sharp contacts between them, suggest that there were abrupt changes in marine influence during the development of the peats that formed the coals. It is inferred that local palaeoclimate alternated between periods of high and low rainfall, the amount of rainfall influencing the extent to which seawater encroached into the peats, with higher rainfall suppressing the ingress of saline waters into groundwater. On the basis of modern peat growth rates, the timescale of the alternation indicated by each duroclarite-vitrite couplet is suggestive of an annual cycle, such as would arise in a monsoonal climate. The low proportion of ash in the three coals, the preservation of internal lamination, the low diversity of spore species in the lowest coal compared with the over- and underlying mudrock, and the presence of rhizoconcretions in palaeokarstic limestone beneath the lowest and highest coals, demonstrate that the peat swamps were isolated from the hinterland and autochthonous. This study demonstrates that a wider application of palynology and coal petrology is an important contribution to the study of marine carbonate successions of any age where terrestrial organic matter, formed during emergence, has been preserved.

Valanginian cold/warm climatic oscillation and synsedimentary tectonic interaction for drowning the carbonate platform of Southern Tethys (Sicily)

Valanginian is a deeply investigated time interval due to the climatic, environmental and oceanographic changes that characterised it, globally recorded in sedimentary successions.During the Valanginian, an oscillation between warm and cold climatic phases is generally accepted as causing change in sedimentation, especially along the carbonate platform successions. In this context the so-called “Weissert event” occurred.The analysed stratigraphic interval consists of a Valanginian–Hauterivian package of two black metallic crusts (hardgrounds) and condensed pelagites, interbedded in the Lower Cretaceous carbonate shallow-water succession outcropping in the Palermo Mountains (NW Sicily). Integrating facies, structural, mineralogical and geochemical analysis, including analysis of δ13C and δ18O isotope records, the interaction between synsedimentary tectonics and climatic changes, as causing palaeoenvironmental and palaeoceanographic changes in the Lower Cretaceous Panormide carbonate platform, has been envisaged.A regional extensional tectonic event in the Southern Tethyan margin was detected at the Berriasian/Valanginian boundary, as responsible for the tectonic fragmentation of the Mesozoic Panormide carbonate platform in various fault-blocks. Locally, tectonic subsidence caused drowning of some of the fault-blocks. Before the recovery of the benthic carbonate factory in the Barremian, condensed pelagites and mineralised (Fe–Mn) crusts developed during the alternation of warm and cold climatic pulses.The positive–negative excursions of the Valanginian–Hauterivian δ13C pattern of the Colombrina section provide solid evidence for the chronostratigraphic assignment of the study interval to the drowning of many carbonate platforms that preludes the onset of the “Weissert event”. In detail, the drastic negative shift of δ13C in the late early Valanginian mineralised crust reveals massive release of isotopically light carbon to the atmosphere/hydrosphere reservoirs from a possible excess of volcanogenic CO2 or methane release from clathrate dissociation. Combining sedimentological data with the increase of the δ18O isotope records, two cold climate pulses are envisaged. The first one is assigned to the Berriasian/Valanginian boundary and led to the formation of the lower mineralised crust. The second and more evident positive shift of δ18O is assigned to the earliest late Valanginian, during the sedimentation of the laminated pelagites deposited immediately after the upper mineralisation event. These cold events that are comparable with the coeval cooling pulses recorded at a global scale highlight icehouse interludes during the Lower Cretaceous greenhouse mode.

Reappraisal of Arundian–Asbian successions of the Great Scar Limestone Group across northern England

The correlation of disparate mid- to late Visean platform carbonate successions of the Great Scar Limestone Group across northern England formerly relied heavily upon a coral and brachiopod biozonation scheme erected in the early twentieth century. This subsequently guided the development of a regional chronostratigraphic scheme some sixty years later that continues to be used to the present day, broadly coinciding with development of new lithostratigraphical nomenclatures, different for each distinct structural area. Correlation problems encountered within these lithostratigraphic units from study of their foraminiferal assemblages, as well as critical analysis of the stratotype sections for the Holkerian and Asbian substages, questions the veracity of the long-established coral and brachiopod biostratigraphy. This study appraises the lithostratigraphical and biostratigraphical relationships of late Arundian to late Asbian limestones across the Askrigg and Alston blocks, the Stainmore Trough and flanks of the Lake District Block. It considers the correlation and potential rationalization of lithostratigraphic units, comments on revisions to the definition of the Holkerian and Asbian substage stratotypes and the suitability of the various biostratigraphical guide fossils.

Paleoenvironment, chemostratigraphy, and age of Pennsylvanian carbonate platform succession of the Amazonas basin, northern Brazil, Uruará region

Extensive Pennsylvanian carbonate platforms are the main transgressive successions recorded on Laurasia and Gondwana continents. The western Gondwana was one of the important sites of these transgressive carbonate accumulation exposed on several basins in Amazonia. Carbonate platform successions are exceptionally preserved in the southern border of the Amazonas Basin, northern Brazil, represented by the Pennsylvanian Itaituba Formation, previously interpreted as tidal flat, lagoon, and carbonate subtidal deposits. Microfacies and petrographic analysis of ~32 m-thick succession of core F5 allowed the definition of nine microfacies grouped in three facies associations: lagoon (FA1), bioclastic bars (FA2) and open carbonate platform (FA3). The FA1 is composed by massive lime-mudstones and dolostones with silt to sand-size terrigenous grains, brachiopods, echinoderms, and rare foraminifers. The lagoon deposits represent a low energy environment with intense micrite precipitation, low diversity of fossils, but that indicates a marine connection, mainly because of the presence of echinoderm and brachiopods. The FA2 is composed of massive grainstone with ooids, intraclasts, brachiopods, echinoderms, corals, bivalves, and foraminifers cemented by granular calcite. The bioclastic bars are affected by wave actions and currents that reworked the carbonate substrate. The FA3 is composed of wackestone and lime-mudstone with micritic matrix, terrigenous, pyrite, brachiopods, bivalves, echinoderms, foraminifers, and ostracods. The Itaituba carbonate platform deposits indicate sedimentation under warm climate, normal salinity and were directly connected with the ocean by the record of benthic organisms. δ13C and δ18O, were obtained for these carbonate rocks and the determination of alteration degree was assisted by Rb/Sr, Fe/Sr, Ca/Mg, and Fe/Sr ratios assisted by digenetic indicators. The Ca and Mg become constant between 30 and 40% in the succession while the Si, Al, and Fe contents decrease upward coincident with the transgressive trend of the succession revealing low continental inflow. Diagenetic processes are represented mainly by stylolitization, cementation, micritization, dolomitization, fracturing, and pyritization that partially modify the framework of carbonate rocks, attesting low diagenetic alteration. The δ13C and δ18O range from +1.60‰ to +5.42‰, and −8.73‰ to +0.80‰ respectively. These values show wide dispersion (non-covariance), suggesting the circulation of diagenetic fluids through these rocks was not able to modify the original composition of δ13C. The carbon and oxygen data coincide with values obtained for carboniferous marine deposits, and the positive data of δ13C in FA2 and FA3 indicates intense organic productivity, similar to that recorded in transgressive deposits associated with the Panthalassa Ocean. The strontium ratios values vary from 0. 708466 ± 0. 000011 to 0. 708417 ± 0. 000009 with 30–299 μg/g in the carbonate platform and presents three age intervals of deposition with a range varying between 293 and 303 Ma (Bashkirian to Kasimovian stages). These data are analogous to the palynomorphs and conodonts ages from the Pennsylvanian of the Amazonas Basin positioned the basal part of the Pennsylvanian succession in the Bashkirian stage.

Structural setting and geodynamics of the Kvarner area (Northern Adriatic)

The Kvarner area is located in the Northern Adriatic Sea, between the south-east Istrian Swell, the Rijeka coast and the Croatian sea boundary. It includes several islands, representing the outcropping parts of anticlines produced by the compressional/transpressional deformation of the External Dinaric Chain. An extensive 2D seismic dataset, acquired for hydrocarbon exploration and calibrated by wells, allowed us to reconstruct the time structural maps in Kvarner and unravel its regional fault pattern. The Dinaric compressional phase affected the area in the Late Cretaceous, with both thin- and thick-skinned tectonics related to Adriatic Carbonate Platform (AdCP) succession rigidity. Structural highs facing the Kvarner offshore from the Istrian inland continue through the Kvarner and Rijeka bays and outcrop in the islands. These anticlines, originating from the pre-Messinian Dinaric thrust system, were reactivated by the post-Messinian transpression, as testified by flower structures. Several sharp valleys represent two main low structural lineaments, developed between the anticlines and partially incised during the Messinian. They were observed throughout the entire studied area, specifically in the western part of the bays, where the lineament continues through the valleys and penetrates the SW-Istria land. Data show that the Messinian erosional effect and sedimentation patterns were influenced and driven by the morphology of older structures produced by the Dinaric compressional phase.

Sequence stratigraphy of a Middle to Upper Ordovician foreland succession (Ottawa Embayment, central Canada): Evidence for tectonic control on sequence architecture along southern Laurentia

AbstractThe Middle to Upper Ordovician foreland succession of the Ottawa Embayment in central Canada is divided into nine transgressive‐regressive sequences that defines net deepening of a platform succession over ~15 m.y. from peritidal to outer ramp settings, then a return to peritidal conditions over ~3 m.y. related to basin filling by orogen‐derived siliciclastics. With a backdrop of net eustatic rise through the Middle to Late Ordovician, there are several different expressions of structural influence on sequence development in the embayment. During the Middle Ordovician (Darriwilian), foreland‐basin initiation was marked by regional onlap with abundant synsedimentary deformation across a faulted trailing‐margin platform interior; subsequent craton‐interior uplift resulted in voluminous influx of siliciclastics contemporary with local structurally influenced local channelization; then, a formation of a platform‐interior shale basin defines continued intrabasin tectonism. During the Late Ordovician (Sandbian, early Katian), structural influence was superimposed on sea‐level rise as indicated by renewed local development of a platform‐interior shale basin; differential subsidence and thickness variation of platform carbonate successions; abrupt deepening across shallow‐water shoal facies; and, micrograben development coincident with foreland‐platform drowning. These stratigraphic patterns are far‐field expressions of distal orogen development amplified in the platform interior through basement reactivation along an inherited buried Precambrian fault system. Comparison of Upper Ordovician (Sandbian‐lower Katian) sequence stratigraphy in the Ottawa Embayment with eustatic frameworks defined for the Appalachian Basin reveals greater regional variation associated with Sandbian sequences compared to regional commonality in base level through the early Katian.

Lithostratigraphy and biostratigraphy of the uppermost Cretaceous to lowermost Palaeogene shallow-marine succession: top of the Adriatic Carbonate Platform at the Likva Cove section (island of Brač, Croatia)

The Likva Cove section on the island of Brač (Croatia) represents a rare example within the Adriatic Carbonate Platform (AdCP) succession of the basal Palaeocene limestones overlying the uppermost Maastrichtian shallow-platform limestones with evidence of only a brief stratigraphic hiatus at the Cretaceous/Palaeogene (K/Pg) contact. Detailed study of the 50-m-thick section resulted in the description of eight lithofacies arranged into six lithostratigraphic units: (A) rudist limestones, (B) deposits with coral–stromatoporoid patch reefs, (C) bindstones, and (D) fine-grained limestones with benthic and rare planktonic foraminifera in the uppermost Maastrichtian (comprising microfossil assemblage biozones I and II), and (E) limestones with benthic foraminifera (mostly discorbids), ostracods and rare planktonic foraminifera, and (F) ostracod–discorbid limestones in the lowermost Palaeocene (representing microfossil assemblage biozone III).The K/Pg contact is constrained between the last occurrence of Maastrichtian benthic and rare planktonic foraminifera, and the first occurrence of Danian planktonic and benthic foraminifera. The uppermost Cretaceous bed represents a firmground, but low biostratigraphic resolution precludes defining duration of a probable short-lasting hiatus at the K/Pg contact. Planktonic foraminifera are mixed with benthic forms in a 3.5-m-thick interval comprising the K/Pg contact as a consequence of decreased depositional rate and probable storm influence.Top of the section contains well developed coral patch reefs intensely karstified during a long-lasting regional unconformity, which in the studied part of the AdCP commenced in the early Palaeocene, i.e. later than at most parts of the platform. Therefore, the end of AdCP deposition should be locally extended into the Palaeocene in both its NW and SE parts.

Lower Jurassic benthic foraminiferal assemblages from shallow-marine platform carbonates of Mallorca (Spain): stratigraphic implications

The stratigraphic distribution of larger benthic foraminifera and other microfossils, as analysed in thin-sections, has been investigated in three stratigraphic sections from the island of Mallorca (Son Maina, S’Heretat and Cuevas de Arta). These stratigraphic sections represent deposition in a Lower Jurassic shallow-water carbonate platform succession (Es Barraca Member, Soller Formation) of the Llevant Mountains. The microfossil assemblages contain abundant benthic foraminifera and calcareous algae, including the typical Liassic dasycladalean alga Palaeodasycladus mediterraneus (Pia) and the microproblematica Thaumatoporella parvovesiculifera (Raineri), which provide good age constraint of the succession. Three consecutive biozones have been recognized based on the stratigraphic distribution of foraminifera, including the evolutionary bioseries Mesoendothyra—Lituosepta—Orbitopsella spp., which are documented for the first time in the Balearic Basin: Biozone A (interval Zone) is characterized by the occurrence of small Siphovalvulina spp., Mesoendothyra sp. and rare Lituosepta ancestors. Biozone B (lineage Zone), whose lower boundary is defined by the first occurrence of Lituosepta recoarensis Cati and its top by the first appearance of Orbitopsella aff. primaeva (Henson). The uppermost part of biozone B shows an interval with transitional morphotypes between Lituosepta and Orbitopsella, indicating that the change between biozones B and C1 is gradual (B/C1 transition). This interval is characterized by the presence of very primitive forms of Orbitopsella. Finally, Biozone C1 (lineage Zone) is defined by the first occurrence of Orbitopsella aff. primaeva together with L. recoarensis. The upper boundary of the Biozone C1, which is defined by the first occurrence of O. praecursor s.l., is not recorded in the studied sections of the Es Barraca Member. This biostratigraphic zonation is consistent with a Sinemurian age for the Es Barraca Member with its top most likely not extending into the Pliensbachian. The proposed biostratigraphic scheme is comparable with those established for other western Tethyan margins such as the High Atlas of Morocco, the Southern Italian Alps or the Dinaric Alps of Slovenia and Croatia. The reconstruction of a depositional transect across the studied sections shows the progressive loss of the upper biozones towards the northeast, demonstrating the existence of significant hiatuses in some sections of the Llevant Mountains domain. These hiatuses point to an intra-lower Pliensbachian (Carixian) early stage of platform fragmentation, with areas affected by erosion or non-deposition, and areas with marine marly limestone sedimentation followed by deltaic siliciclastic progradation on the north-western part of Mallorca.

An Albian–Turonian shallow-marine carbonate succession of the Bey Dağları (Western Taurides, Turkey): biostratigraphy and a new benthic foraminifera Fleuryana gediki sp. nov.

The studied Cretaceous succession is exposed at the Toçak Mountain in the southeastern part of the Bey Dağları Carbonate Platform (BDCP). The Alakır outcrop section presents seemingly continuous shallow-marine carbonate sedimentation during the Albian–Turonian times which is known from very few parts of the peri-Mediterranean platforms. Approximately 550 m thick platform carbonate succession is unconformably overlain by carbonate breccia/conglomerate and pelagic limestones of Campanian age. A benthic foraminiferal biostratigraphic zonation scheme is presented. The biozones are tentatively placed into the stages, without chronostratigraphic calibration, based on stratigraphic distribution of common benthic foraminifera in the peri-Mediterranean platforms. Protochrysalidina elongata–Cuneolina pavonia assemblage zone and Coskinolinella bariensis taxon range subzone are assigned to the upper Albian. In the conformably overlying limestones, Sellialveolina gr. viallii taxon range zone (lower–middle Cenomanian), Pseudorhipidionina casertana assemblage zone (upper Cenomanian), Pseudorhapydionina dubia–Pseudolituonella reicheli assemblage zone (uppermost Cenomanian) and Pseudocyclammina sphaeroidea assemblage zone (Turonian) have been distinguished. Two-step pattern of extinction of benthic foraminifera across the Cenomanian–Turonian boundary interval, which was first recorded from the Apennine Carbonate Platform, has been documented also from the BDCP. The tentative Cenomanian–Turonian Boundary is constrained into an interval of one meter between the last occurrence of the Cenomanian larger foraminifera and the first occurrence of the Turonian benthic foraminiferal assemblage comprising morphologically-simple and less-known taxa and other taxa left in open nomenclature. Fleuryana gediki sp. nov. is described from the Turonian.

Facies variability of a lower Aptian carbonate platform succession, Tirgan Formation, eastern Kopet Dagh Basin, northeast Iran

The Lower Cretaceous (Hauterivian-lower Aptian) Tirgan Formation is a carbonate platform succession in the Kopet Dagh Basin and is up to nearly 800 m thick. This study focuses on facies variability and depositional settings of the Tirgan in the eastern part of eastern Kopet Dagh where the formation constitutes the basal part of the lower Aptian deposits. The succession developed during the final stage of evolution of Cretaceous carbonate platform in the southern Eurasian margin and could demonstrate a synchronicity with comparable successions in other areas. In the study area, the Tirgan (48 m thick) overlies Berriasian–Barremian continental strata and underlies the lower Aptian deep marine deposits. Facies analysis of Tirgan determined several facies related to open marine, ooid grainstone shoal, protected lagoon, and lower intertidal facies belts of a carbonate system. Abundant ooids, calcareous green algae, mud size carbonate, lack of evaporite evidence, and the absence of basinal deposits record deposition in warm water shallow marine settings of a carbonate ramp under a relatively humid climate. The Tirgan encompasses a single third-order depositional sequence composed of transgressive and highstand systems tracts. The transgressive package consists of intertidal, lagoon, and open marine facies intercalated with storm and shale layers showing an overall retrogradational trend. However, the highstand package consists mainly of ooid grainstone facies and displays prograding clinoforms. The lowermost lower Aptian Tirgan sequence in the study area corresponds to the basal Aptian global third-order sea level cycle. Contact of Tirgan sequence with the overlying middle to late Aptian deep marine strata is abrupt, suggesting a drowning event, which was likely the result of early Aptian extraordinary global warming.

δ13C stratigraphy of a Turinian-Chatfieldian (Upper Ordovician) foreland succession, Ottawa Embayment (central Canada): resolving local and inter-regional isotope excursions in a tectonically active basin

Positive δ13Ccarb excursions are correlated through an upper Turinian to lower Chatfieldian carbonate-platform succession along the axis of the Ottawa Embayment and into outliers of the northern Ottawa-Bonnechere graben in central Canada. Successive Turinian excursions (E1 and E2) are lithostratigraphically constrained by erosional surfaces and hosted within the Watertown and overlying L'Orignal formations, respectively, the latter coeval with the Selby Formation in the adjacent northern Appalachian Basin. The excursions coincide with periods of regional transgression, but geographic patterns of 13C depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions, respectively. Differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas, with preferential Corg recycling with stratigraphic condensation. By early Chatfieldian time, segmentation of the once regional carbonate platform (L'Orignal Formation) produced a regional mosaic of low-energy muddy carbonate banks (Rockland Formation) and a deeper water platform (lower Hull Formation) settings subject to fluctuating high to low energy current flow. Excursion E3 occurs in both successions, but 13C enrichment is associated only with the bank-top muddy facies. This may identify preferential photosynthetic drawdown of 12C across the bank tops due to limited seawater exchange across the bank-deeper platform boundaries. Excursions E1 to E3, and a younger excursion (E4) in the Hull Formation, are correlated with varying confidence with excursions across southern Laurentia, excursion E3 being the local expression of the Guttenberg δ13C excursion. Our study supports local modulation of regional, if not global, δ13C excursions arising from structurally controlled changes in oceanography and productivity.