Four new species of larger benthic foraminifera are described from lower–middle Campanian inner-platform carbonates of the island of Brač, Croatia: Bakhtiarella minima sp. nov. (family ...Bakhtiarellidae), Biconcava brattiana sp. nov. (family Mayncinidae), Paravanneauina campaniana gen. et sp. nov. and Calveziconus pygmaeus sp. nov. (family Orbitolinidae). The latter two taxa are also reported from time-equivalent strata of the Gavrovo–Tripolitza Platform, southwestern Greece. The new taxa provide further evidence for the pronounced Campanian diversification within the Late Cretaceous Global Maturation Cycle of larger benthic foraminifera in the inner platform facies of the Mediterranean Adriatic Carbonate Platform.
New findings of numerous levels with scleractinian corals and layered domical and bulbous growth forms (calcified sponges?) within the upper Maastrichtian–lowermost Palaeocene shallow marine ...carbonates from the Adriatic islands Brač and Hvar (Croatia) are described. They indicate the existence of patch reefs developed on the Adriatic Carbonate Platform in the western Tethys area shortly before and after the Cretaceous/Palaeogene (K/Pg) boundary mass extinction event. Studied sections comprise reef remains preserved in situ with the remains of reef organisms in growth positions, but intense neomorphic alteration and weathering prevented determination to generic or species level. Observed coral morphology can be compared to the columnar coral growth form of modern scleractinian corals. Both the larger and smaller digitate corals described, have built small coral knobs scattered in the shallow waters of the inner carbonate platform. Layered micritic domical and bulbous growth forms that appear either as individual forms or sheet-like crusts around coral colonies are tentatively designated as possible calcified sponges. The in situ preserved fossil association reflects the once-living community and reveals palaeoecological succession within the thicker reef levels. Layered domical and bulbous growth forms prevail in the lower parts, while both corals and layered domical and bulbous growth forms in the middle and upper parts of reef levels indicate similar, but somewhat different palaeoecological requirements for the two groups. Many reef levels in the Brač sections overlie subaerially exposed limestones, following their irregular morphology, implying patch reef development during relative sea-level rise after subaerial exposure. Fossil remains described from the uppermost Maastrichtian and lowermost Danian reef levels on the island of Brač are very similar, indicating that despite the biotic crisis related to the K/Pg boundary events the reef biota from the latest Maastrichtian crossed the K/Pg boundary into the early Danian.
•In-situ preserved patch reefs in uppermost Maastrichtian–lowermost Danian strata.•Reef biota composed of corals and layered bulbous growth forms (calcified sponges?).•Coral remains similar to columnar coral growth form of modern scleractinian corals.•Described reef biota shows vertical succession within some reefs.•Evidence of reef biota recovery soon after the Cretaceous/Palaeogene boundary
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.
•Detailed reconstruction of environmental changes around the K/Pg transition.•Refined litho- and biostratigraphy of the youngest Cretaceous and oldest Palaeogene deposits.•K/Pg contact preserved in shallow-marine carbonates influenced by storms.•Firmground recognized between the uppermost Cretaceous and lowermost Palaeogene strata.•Coral–stromatoporoid patch reefs recognized in Cretaceous and Palaeogene deposits.
•Palaeosol associated with Upper Jurassic unconformity hosts glauconite.•Glauconite formed by halmyrolysis of a palaeosol.•Formation of glauconite was microbially mediated.•Glauconite may mark ...initial flooding of subaerially exposed terrain.•Glauconite as an indicator of paleolandscape and paleoenvironment.
Glauconite formation is generally perceived as a process occurring in deep-marine environments, but in the last few decades its formation in shallow-marine environments is progressively more recognised and utilized for palaeoenvironmental reconstructions. One such example is the lower Kimmeridgian to upper Tithonian Zlatni Rt palaeosol, which is especially unique since the glauconite occurrence is hosted within the palaeosol material. Micromorphological, mineralogical, and chemical characterisation of the palaeosol was followed by the detailed analysis and description of glauconite using SEM-EDS, XRPD and FTIR. In addition, lithofacies and micropalaeontological analyses have been carried out on the carbonate succession under- and overlying the palaeosol in order to better understand the stratigraphic framework. The palaeosol formed in hydromorphic conditions, in contact with brackish to marine porewater, and is composed of mixed-layer illite–smectite, illite, kaolinite, vermiculite, pyrite, marcasite and titanium oxides. The glauconite was formed after the formation of the palaeosol, predominantly through fixation of potassium and iron into illite and mixed–layer illite–smectite, while part of the glauconite formed authigenically, with evidence for microbial influence. The glauconite is present in a more oxidised and more reduced form, which alternate together with pyrite in veins, indicating fluctuations in the redox potential. This can be connected to the variations in the supply of organic matter and sea-level oscillations during the initial stages of the transgression. Glauconite formation was locally followed by the formation of transgressive breccias and a complete drowning of the area. During this phase lagoonal Kirmenjak limestone was deposited throughout the area, while in the palaeosol coarse pyrite crystals precipitated. Presented study documents a unique glauconite occurrence and proposes that it can be successfully used for the detailed palaeoenvironmental reconstruction of the initial flooding of subaerially exposed terrains.
The Minjera bauxites are the first analysed and mined bauxites in the world. They are a group of pyritised bauxites situated in northern Istria, developed during the subaerial exposure phase which ...marked a major part of the Late Cretaceous and Palaeocene in northern Istria. In this study, the morphology, petrography, mineralogy, geochemistry as well as stable sulphur isotopes of the D-1 and D-15 deposits from Minjera were studied, as well as the evolution of their bedrock and cover. This study found that those two deposits differ in morphology, mineralogy and geochemistry as a consequence of their different palaeotopographical positions, with the D-1 deposit located at a higher position at the time of its formation compared to D-15, which led to the higher degree of leaching and desilicification in the D-1 deposit. The pyritisation in the studied deposits was a multi-phase process, which began with the deposition of framboidal pyrite and micrometre-sized anhedral pyrite, over which colloform pyrite was precipitated. This indicates that the solutions were initially supersaturated with iron sulphide, saturation of which subsequently changed, as finally euhedral, dendritic and acicular pyrite were deposited, indicating undersaturated conditions. The final stage was marked by deposition of pyrite veins. This formational sequence of pyrites is also supported by stable sulphur isotopes, as the δ34S values exhibit a wide range from -40.86 to 2.32 ‰, where lower values indicate an open system with an unrestricted sulphate supply in which supersaturated conditions could have been achieved, while the higher values indicate a change towards a closed system with limited sulphate supply. The organic matter necessary for microbial sulphate reduction was derived from the marshy environment established atop of the bauxite. The initial flooding started in the Palaeocene, with the first part of the sequence being deposited under lacustrine conditions, which changed towards fully marine with the deposition of Foraminiferal limestones.
Carbonate deposits from Zrin in the Mt. Zrinska Gora were deposited in the SW part of the Central Paratethys Sea during the Middle Badenian (Middle Miocene). The studied section contains a rich ...fossil community of non-geniculate coralline red algae (Subfamily Melobesioideae), bryozoans, benthic and planktonic foraminifera, echinoderms, ostracods, molluscs, and calcareous nannoplankton. Based on lithological variations and changes in the biogenic components, four facies associations (FA) are distinguished. Their distribution points to skeletal production and sedimentation on a middle to proximal outer carbonate ramp. The main lithological feature of the section is an alternation of two lithofacies: fully lithified grainstone–rudstone and packstone, and semi-lithified rudstone–floatstone with a carbonate sandy matrix. Depositional environments on the ramp were periodically influenced by minor high-frequency sea-level changes and/or changes of hydrodynamic conditions, which are suggested as the driving mechanisms causing the alternation of the two lithofacies. Vertically in the succession, the two lithofacies alternate to give three thinning- and fining-upward units. The lower part of each unit is formed of a rhodolith and coralline algal FA, which passes upwards into a bryozoan-coralline algal FA and/or FA of bioclastic packstone-grainstone. Based on the vertical upward change in FAs, each unit can be interpreted as a deepening-upward sequence. Patterns in the relative abundance of bryozoan colony growth form (vinculariiform, cellariiform, adeoniform, membraniporiform, celleporiform, and reteporiform), size and abundance of rhodoliths and coralline branches, and benthic foraminifera are interpreted by comparison with data from modern and fossil environments. Based on these data, a water depth range for each FA is interpreted, providing evidence of low-frequency relative sea-level changes. It is hypothesized that relative sea-level fluctuated in the water depth range from 30 to 80 m, and in the uppermost part of the section, rich in planktonic foraminifera and calcareous nannoplankton, possibly deeper. Causes of the low-frequency relative sea-level fluctuations and the general deepening trend observed within the succession cannot be interpreted based on one section; however, they may be related to the subsidence of the depositional basin. The benthic biotic communities are a vertical alternation of rhodalgal and bryorhodalgal associations, and this is attributed to relative sea-level fluctuations. These biotic associations gave rise to warm-temperate carbonates of the Middle Badenian N9 planktonic Zone (
Orbulina suturalis
,
O. universa
) and NN4–NN5 nannoplankton Zones (
Sphenolithus heteromorphus
).
Discontinuity surfaces of different types and scales are common in successions of shallow-marine carbonate platforms because sediments there are deposited close to the sea level and therefore are ...sensitive to any significant physico-chemical changes of environmental factors. Discontinuity surfaces indicate breaks in sedimentation under subaqueous or subaerial conditions. Most discontinuities in shallow-marine carbonate successions are on a bed-scale, and can be determined only by analysis of sedimentologic, diagenetic, taphonomic, and ichnologic features of the rock. The study of small-scale discontinuities has been carried out on two Lower Jurassic successions of the Velebit Mt. Depending upon their common features and environment of formation, three groups of discontinuities are distinguished on simple bedding planes: subaerial exposure surfaces, erosion surfaces, and omission surfaces. The distribution of discontinuity types in both successions is evaluated. Exposure surfaces prevail in both sections, and four units (relatively thin intervals of the sedimentary record) with abundant subaerial exposures are recognized. Dated by biostratigraphy, these units are of earliest Sinemurian, middle Early Sinemurian, earliest Pliensbachian, and late Early Pliensbachian age. Omission surfaces are the least common type of discontinuity. Thickness variations of high-frequency peritidal and shallow subtidal shallowing-upward cycles, highlighted by the Fischer plots show a very similar long-term trend for the two sections. The units with common subaerial exposure surfaces coincide with the falling limb of the Fischer plots and the section with common omission surfaces coincides with the rising limb of the plots. The studied discontinuities are formed by autocyclic and/or allocyclic processes operating on the shallow platform, but the units with abundant subaerial exposures invoke allogenic forcing of the sedimentary record. The use of the units with abundant discontinuities instead of a single surface has proven useful for the correlation of the studied shallow-platform deposits because one type of discontinuity may change laterally into another type or features of different discontinuity types can be superimposed.
The upper part of the Middle Coniacian/Santonian-Middle Campanian deep-water Dol Formation of the island of Brač is composed of countless fine-grained allodapic intercalations deposited in an ...intraplatform trough. Within the studied section 13 beds can be distinguished, each defined by its lower part built up of dark grey limestone with abundance of branched, horizontally to subhorizontally oriented burrows, and the upper part, in which the light grey to white limestone contains larger burrows, rarely branched, showing no preferential orientation. The lower, dark grey, intensively bioturbated levels are interpreted as intervals formed during high-frequency sea-level highstands, while the upper, light grey-to-white levels are interpreted as intervals formed during the high-frequency sea-level lowstands. Cyclic alternation of these two intervals within the fine-grained allodapic beds is interpreted as the interaction between the amount of carbonate production on the platform margin and the periodicity and intensity of shedding and deposition in the distal part of toe-of-slope environment, which is governed by Milankovitch-band high frequency sea-level changes.
The Triassic carbonate platform succession of the Karst Dinarides was deposited at the southern Tethyan realm. The facies analysis and distant correlation suggests that a regional terrestrial phase ...occurred in that area during the Triassic. Due to its regional extent, this terrestrial phase has been viewed as a product of tectonically induced uplift of the huge platform area, causing an extensive emersion and distinct disruption in depositional regime when disconformity and/or various types of terrestrial depositional intervals were formed. Two geodynamic scenarios are presented; a) regional, contemporaneous tectonic uplift scenario; and b) diachronous and differential tectonic uplift scenario. During Norian, the uplifted, exposed platform area was flooded and covered by tidal flat-dominated shallow-water carbonates, marking the beginning of wide and long-lasting isolated platform regime.
Trijaski karbonatni slijed Krških Dinarida istaložen je na prostranstvu južnog Tetisa. Facijesna analiza i prostorna korelacija tog slijeda naslaga upućuje na regionalnu kopnenu fazu koja je tijekom ...Trijasa zahvatila ovaj prostor. Svojim regionalnim pružanjem, ova kopnena faza se sagledava kao posljedica tektonski izazvanog izdizanja prostranog platformnog područja, a što je uzrokovalo izrazito okopnjavanje i izrazit prekid dotadašnjeg taložnog režima, čime su nastali taložni diskonformiteti i/ili različiti tipovi kopnenih taložnih slijedova. Predstavljena su dva geodinamska scenarija; a) scenarij regionalnog, istovremenog izdizanja prostranog platformnog područja; i b) scenarij vremenom i intenzitetom različitog izdizanja prostranog platformnog područja. Tijekom Norika, to dotad izdignuto i izloženo platformno područje bilo je preplavljeno i prekriveno plitkovodnim karbonatima plimne zone, označavajući početak prostranog i dugotrajnog taložnog režima izolirane karbonatne platforme.
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