Late Barremian Research Articles

Time contrasting palaeobiogeographies among Hauterivian–Lower Aptian rudist bivalves from the Mediterranean Tethys, their climatic control and palaeoecological implications

From the Mediterranean Tethys, the Hauterivian−Barremian rudist genera Lovetchenia, Agriopleura, Pachytraga and Offneria simplex, show contrasting palaeobiogeographies through time. Lovetchenia is a western European form in the Hauterivian whereas it is an Eastern European and Apulian form in the late Barremian and early Aptian. Agriopleura is also a western European form in the late Hauterivian and Barremian p.p., whereas in the early Aptian this genus is only found on the Southern Tethyan margin. Pachytraga documented from the Hauterivian of both the European and Southern Tethyan margins, disappeared during the Barremian and re-occupied Western Europe and some parts of Africa during the early Aptian. Offneria simplex, a Barremian form from the Caribbean Province, is recorded in the uppermost Lower Barremian of SE France. The regional disappearance of these taxa is not linked to platform or rudist community demise, whereas community changes reflect the resulting modifications in biodiversity. There is a good correspondence between the regional disappearance of western European taxa, cooling events documented by oxygen isotope studies, and biological interchanges between the Boreal and Tethys realms. The regional disappearance of Lovetchenia and possibly Pachytraga are coeval with the Pseudothurmannia ohmi cooling episode whereas that of Agriopleura is coeval with the Ancyloceras vandenheckii cool episode. By contrast the intrusion of Offneria simplex in Western Europe coincides with the Coronites darsi warm peak. Thermal shifts between cool and warm episodes fluctuate from 3 to 5 °C, and the thermal threshold assumed to control the demise of western European taxa is in the range of 18 to 20 °C, a value similar to those controlling the geographic distribution of modern coral reefs, or the boundary between tropical and subtropical seas. The southward displacement of the rudist biomes also accounts for the migration of climatic belts and a decreasing of 3 to 5 °C in palaeotemperatures. Spatial contractions of Lovetchenia and Agriopleura biomes, and the O. simplex intrusion, suggest that these rudists were more sensitive than others to the thermal regime. This observation shows that rather than considering rudists in general as “tropical”, some of them may have been both tropical and subtropical and others tropical. For Pachytraga other factors than temperature, possibly oceanographic changes, may have been responsible for the overall Mediterranean disappearance of this genus in the Barremian.

The Eastern Carpathians “ophiolites” (Romania): Remnants of a Triassic ocean

Mesozoic ophiolitic and related rocks in the Eastern Carpathians occur in three areas, from north to south: Rarău, Hăghimaş and Perşani Mts. They are found as blocks ranging from few metres to a few kilometers in size and as centimetre-sized in breccias, most likely embedded in the Late Barremian–Early Albian Wildflysch formation. Compositionally, they range from lherzolites and harzburgites to mafics such as FeTi gabbros, dolerites, basalts, and to andesites. The volcanics comprise highly-depleted basalts/andesites to enriched-type mid-ocean ridge basalts; additionally they include ocean island basalts and calc-alkaline basalts/andesites and trachytes. Based on paleontological evidence, their age is Middle to ?Late Triassic. They can be clearly compared with remnants of the Meliata–Hallstatt Ocean in the Western Carpathians, but do not match the Jurassic ophiolites and island arc volcanics in the Mureş Zone of the Southern Apuseni Mts. We propose a Triassic ocean connected with the Meliata–Hallstatt Ocean, between (a) the Bucovinian/Sub-Bucovinian continental crust, (b) the Infrabucovinian and finally (c) the Northern Apuseni microcontinents. This ocean closed in the Late Triassic to Early Jurassic causing close juxtaposition of all three microcontinents. An ophiolite complex together with ocean island basalts and calc-alkaline basalts/andesites remained from this ocean and was subsequently eroded and transported as blocks of different size into the Lower Cretaceous Wildflysch basin, together with blocks and clasts of limestones similar to the Mesozoic sedimentary sequences in the Northern Apuseni realm. The Wildflysch formation was thrust as an independent unit during the Albian over the Bucovinian Nappe in the Eastern Carpathians and the Northern Apuseni continental crust, respectively.

Platform-induced clay-mineral fractionation along a northern Tethyan basin-platform transect: implications for the interpretation of Early Cretaceous climate change (Late Hauterivian-Early Aptian)

High-resolution clay-mineral analyses were performed on upper Hauterivian to lower Aptian sediments along a platform-to-basin transect through the northern Tethyan margin from the Neuchâtel area (Switzerland), to the Vocontian Trough (France) in order to investigate links between climate change, carbonate platform evolution, and fractionation patterns in clay minerals during their transport. During the Hauterivian, the northern Tethyan carbonate platform developed in a heterozoan mode, and the associated ramp-like topography facilitated the export of detrital material into the adjacent basin, where clay-mineral assemblages are dominated by smectite and kaolinite is almost absent, thereby suggesting dry-seasonal conditions. During the Late Hauterivian Balearites balearis ammonite zone, a change to a more humid climate is documented by the appearance of kaolinite, which reaches up to 30% of the clay fraction in sediments in the Vocontian Trough. This prominent change just preceded the Faraoni Oceanic Anoxic Event and the onset of the demise of the Helvetic Carbonate Platform, which lasted to the late early Barremian. From the Late Barremian onwards, the renewed growth of the northern Tethyan carbonate platform in a photozoan mode and the associated development of a marginally confined platform topography fractionated the clay-mineral assemblages exported into hemipelagic settings: kaolinite particles were preferentially retained in proximal, platform settings, due to their size and their relatively high specific weight. In the inner platform environment preserved in the Swiss Jura, an average of 32% of kaolinite in the clay fraction is observed during the latest Barremian–earliest Aptian, whereas clay-mineral assemblages of coeval sediments from deeper depositional settings are dominated by smectite and show only minor amounts of kaolinite. This signifies that besides palaeoclimate conditions, the morphology and ecology of the carbonate platform had a significant effect on the distribution and composition of clay assemblages during the Late Hauterivian–Early Aptian along the northern Tethyan margin.

On the Validity of Two Lower Cretaceous Non-marine Ostracode Genera: Biostratigraphic and Paleogeographic Implications

Abstract The taxonomic status of the Lower Cretaceous non-marine ostracode genera Hourcqia Krommelbein and Pattersoncypris Bate is discussed. From a detailed analysis of the type species of these genera, and several other species attributed to them, it was possible to conclude that both genera are invalid. Hourcqia africana Krommelbein, the type species of this genus, has an antero-ventral beak, and it is in all other respects identical to Cypridea Bosquet, and therefore should be transferred to this genus. The subspecies originally referred to as Hourcqia africana confluens Krommellbein and Weber, 1971 is subsumed within Cypridea africana. Secondly, the genus Pattersoncypris, as the result of a study of its type species, P. micropapillosa Bate, is shown to be a junior synonym of Harbinia Tsao. Both, Hourcqia and Pattersoncypris must therefore be suppressed. Cypridea africana (Krommelbein) occurs in Brazil, Congo, and Gabon in strata deposited during the rift stage, restricted to the late Barremian to ear...

Charophytes from the Barremian-lower Aptian of the Northern Subalpine Chains and Jura Mountains, France: correlation with associated marine assemblages

Interdigitation of shallow marine limestone containing orbitolinids (benthic foraminifera), echinoids and dasycladales with lacustrine limestone and marl with charophytes in the Northern Subalpine Chains and Jura Mountains, France, enables us to improve the correlation between Early Cretaceous continental and marine biozonations. Early Barremian charophytes were found in marlstones intercalated in the Urgonian Limestone at Pas du Frou (Chartreuse Massif). This flora belongs to the Triquetra charophyte biozone (European Charophyte Biozonation) and is interlayered with rocks containing a characteristic assemblage of orbitolinids and dasycladales of the mid- to early Barremian (uppermost Hugii, Nicklesii and lowermost Caillaudianus ammonite biozones). Younger charophyte associations occur in the overlying Urgonian Limestone and Lower Orbitolina Beds above the major regional unconformity Δ 1 from the Chartreuse Massif, Vercors Massif and Southern Jura Mountains. They are formed by a charophyte association that belongs to the charophyte biozone Cruciata. The flora is interlayered with marine layers rich in orbitolinids and echinoids which enables us to redefine the Cruciata biozone as Cruciata-Paucibracteatus zone, ranging from the late Barremian (Vandenheckii ammonite biozone) to the early Aptian (ammonite biozone Weisii). An interval of uncertainty occurs in the beginning of the Cruciata biozone, which is equivalent to the upper part of the Caillaudianus ammonite biozone.

Temperature controlled deposition of early Cretaceous (Barremian–early Aptian) black shales in an epicontinental sea

A continuous, 103m thick mudstone sequence of Barremian–early Aptian age, recently exposed in northern Germany, has been logged and analyzed with respect to its macrofaunal content and its geochemistry ( δ 13C, δ 18O). Based on common belemnite and rarer ammonite findings a detailed biozonation has been established covering the complete Barremian–early Aptian interval, including the mid early Aptian “Fischschiefer”, the deposition of which occurred during Oceanic Anoxic Event 1a. Quite common throughout the sequence are finely laminated black shales (Blätterton) with high TOC contents of up to 7%. These laminated black shales with CaCO 3 contents of up to 60% are interbedded with dark and carbonate-poor clays on the scale of decimeters to several meters. Oxygen depletion of bottom waters is indicated for the laminated intervals since these are barren of any benthic fossils. A salinity driven stratification of the water column during more humid periods was caused by a more intense run-off from the nearby hinterland. This and increased surface water productivity are seen as a possible cause for the lamination with observations being mainly based on micropalaeontological evidence (dinoflagellates, calcispheres, calcareous nannofossils). Stable isotope studies ( δ 13C, δ 18O) performed on belemnite guards show δ 13C values of 0‰ to 2‰ for the Barremian. A distinctive positive excursion of ~ 4‰ directly above the early Aptian Fischschiefer correlates well with the global positive δ 13C excursion of mid early Aptian age following the Oceanic Anoxic Event 1a. This first record of the δ 13C positive excursion from the Boreal Realm therefore confirms the global nature of the signal. A shift in δ 18O values of about 2‰ in the late Barremian–early Aptian is interpreted as a temperature decrease by ~ 8°C. This cooling goes along with a shift from the thick (up to 6.5m) early Barremian Hauptblätterton to thin (10cm to 20cm) laminites (Blätterton) in the late Barremian. During the deposition of the Hauptblätterton very warm conditions caused a long lasting (> 500kyrs) stable water stratification. The cooler temperatures of the late Barremian reduced the stability of the water stratification resulting in rather short termed alternations of thin laminites and dark clays. These observations suggest a temperature controlled peak of anoxic conditions in the early Barremian Hauptblätterton and subsequently short termed changes from anoxic to suboxic conditions in the late Barremian and early Aptian.

MORPHOLOGY, TAXONOMY AND DISTRIBUTION OF THE CRETACEOUS CORAL GENUS AULASTRAEOPORA (LATE BARREMIAN-EARLY CENOMANIAN; SCLERACTINIA)

The Cretaceous coral genus Aulastraeopora is being revised, mainly on the basis of sample material. This genus of solitary growth form is characterised by medium-sized to large specimens, compact septa in a regular hexameral or tetrameral symmetry and lonsdaleoid septa. Related genera are Preverastraea and Apoplacophyllia , which only differ by their cerioid-astreoid and phaceloid growth forms. There are four species of Aulastraeopora . The genus, which occurred world-wide, is restricted to the period from the Late Barremian to the Late Cenomanian, being most common in the Aptian to Early Albian. Forty-one samples are either known from the literature or have been to hand. This makes Aulastraeopora a rare genus.

Lithostratigraphy and biostratigraphy of some Lower Cretaceous outcrops from Northern Sinai, Egypt

Lower Cretaceous successions of the Risan Aneiza, El Tourkumanyia and Manzour areas (Northern Sinai, Egypt) were studied for biostratigraphic purposes. These successions were subdivided into three rock units, from base upwards: the Malha, the Risan Aneiza and the Halal formations. Each formation included enriched cephalopod horizons. Fifty cephalopod species were identified. The age and stratigraphic distribution of these cephalopods allowed the recognition of eight ammonite zones ranging in age from Barremian to late Albian. These zones are, from base to top: Subpulchellia oehlerti Zone (late Barremian), Barremites difficilis Zone (late Barremian), Deshayesites deshayesi Zone (early Aptian), Aconeceras nisus Zone (early middle Aptian), Epicheloniceras tschernyschewi Zone (late middle Aptian), Acanthohoplites nolani Zone (late Aptian), Knemiceras gracile Zone (early Albian) and Mortoniceras inflatum Zone (late Albian). The identified ammonite zones were correlated with national and standard international ammonite zones as proposed in previous studies of the same time interval.

Radiolarian biostratigraphic constraints on the generation of the Nidar ophiolite and the onset of Dras arc volcanism: Tracing the evolution of the closing Tethys along the Indus – Yarlung-Tsangpo suture

The Nidar ophiolite in Ladakh Himalaya is a substantial fragment of oceanic lithosphere preserved along the western continuance of the Indus - Yarlung-Tsangpo suture zone. It was generated in a supra-subduction zone setting and is linked in development to the Dras intra-Tethyan volcanic arc. Earlier reported Hauterivian - Aptian radiolarians from the volcano-sedimentary succession atop the ophiolite were used to constrain the age of the ophiolite and duration of arc volcanism. Re-assessment of radiolarian taxonomy and biostratigraphy reveals an upper Barremian to upper Aptian range for the Nidar volcano-sedimentary section, the same as for the marine sedimentary cover atop the Dazhuqu ophiolite in the southern Tibet. The lower limit of its stratigraphic range places a minimum temporal constraint on the Nidar ophiolite generation in the late Barremian (ca 126 Ma). This compares well with radiometric age for the ophiolite (124± 1 Ma). The sedimentary successions of both ophiolites bear resemblance in the record of associated arc volcanism. Dras arc volcanism in the Nidar section began in the early Aptian. The Nidar and Dazhuqu ophiolites are interpreted as distal chronological equivalents developed in association with the same intra-Tethyan subduction system. Parallels between the evolution of this Cretaceous intra-Tethyan subduction system and other systems in the region remain uncertain.

Upper Jurassic–Lower Cretaceous stratigraphy in south-eastern Tibet: a comparison with the western Himalayas

Lithostratigraphic studies of the Upper Jurassic–Lower Cretaceous sedimentary successions exposed in the Tingri–Gyangze area, south-eastern Tibet resulted in the establishment of a revised stratigraphic framework. A major crustal fault separates the southern Tibetan sedimentary successions into a Southern Zone and a Northern Zone. The Upper Jurassic–Lower Cretaceous strata of the Southern Zone are subdivided into the Menkadun Formation (Oxfordian, Kimmeridgian, up to lower Upper Tithonian), the Gucuo Formation (Upper Tithonian to Lower Albian) and the overlying Dongshan Formation (Upper Albian). The Gucuo Formation is further subdivided into a quartz arenite unit, which is overlain by a shale unit, in turn overlain by a volcaniclastic sandstone unit. The youngest cluster of detrital zircon absolute age data (127.7 ± 1.8 Ma) from the lower part of the volcaniclastic unit of the Gucuo Formation place the volcanic event before the Late Barremian. In the Northern Zone, the Upper Jurassic–Lower Cretaceous strata have been subdivided into four formations: the Zhera Formation (Upper Jurassic), the Weimei Formation (Tithonian), the Rilang Formation (?Berriasian) and the Gyabula Formation (? post-Valanginian). The appearance of silica cemented quartz arenites in both the quartz arenite unit of the Gucuo Formation and the Weimei Formation in the uppermost Jurassic is considered to provide strong evidence for an eustatic sea level drop affecting the northern margin of Greater India. In contrast the appearance of volcaniclastic sandstones in the Gucuo and Rilang formations are interpreted to represent a rift related volcanic event. The Menkadun–Zhera formations, the quartz arenite unit of the Gucuo Formation–Weimei Formation, the volcaniclastic sandstone unit–Rilang Formation in south-eastern Tibet are lithologically similar and broadly correlative with the Spiti Shale, Takh and Pingdon La formations in Zanskar (India), and Spiti Shale, Dangardzong, Kagbeni and Dzong formations in the Thakkhola area (Nepal). The onset of quartzose and subsequently volcaniclastic deposition becomes progressively younger westward, from the Gucuo region toward Zanskar.

Unlocking paleo-environmental information from Early Cretaceous shelf sediments in the Helvetic Alps: stratigraphy is the key!

The northern alpine Helvetic thrust-and-fold belt includes an Early Cretaceous shallow-water carbonate succession, which was part of an extensive carbonate platform rimming the northern Tethyan margin. The structural architecture of the Helvetic zone allows for the palinspastic reconstruction of proximal-distal transects across the former platform into the outer-shelf realm for distances surpassing 80 km. The Early Cretaceous platform sediments preserved therein provide, therefore, excellent insight into the spatial and temporal evolution of this platform. Furthermore, the presence of ammonites in marker horizons within the Helvetic succession is key to unprecedented time control. During the life span of the Helvetic platform, carbonate build up and build out occurred along two distinct pathways: we discern between a mode including oligotrophic photozoan communities (latest Tithonian – Late Berriasian; Late Barremian; Early Aptian) and a mode dominated by mesotrophic heterozoan communities (Valanginian – Early Barremian; earliest Aptian; late Early Aptian – Late Aptian). The heterozoan mode was frequently interrupted by incipient platform drowning episodes, which materialized either in an important erosive hiatus, or in the deposition of highly condensed, glauconiteand phosphate-rich intervals (Early Valanginian – Early Hauterivian; late Early – early Late Hauterivian; latest Hauterivian – latest Early Barremian; middle Late Barremian; late Early Aptian – early Late Aptian; and latest Aptian – Early Albian). The photozoan mode is interpreted as essentially oligotrophic, whereas the heterozoan and drowning phases were associated with the input of coarser-grained detrital sediments and a correspondingly increased nutrient load, which were both the consequence of intensified chemical weathering on the continent due to warmer and more humid climate conditions. Their onset is signaled by increases in oceanic phosphorus burial rates and major positive excursions in the stable carbon isotope record. Oceanic anoxic episodes occurred during these latter phases. The northern Tethyan platform was not only controlled by climatic, environmental and paleoceanographic change, but changes in platform morphology and the composition of carbonate-producing benthic communities also influenced the quality and quantity of dissolved and particulate material exported into adjacent basins.

Biostratigraphy of the Cretaceous deposits in the Western Transylvanides from Ampoi Valley (Southern Apuseni Mountains, Romania)

The present study is an approach of the issues related to the biostratigraphy of the Western Transylvanides. The research provided exact age data for the Fenes Formation, Valea lui Paul Formation, Bozes Formation and Râmeţi Formation. The age of the formations was established based on the calcareous nannoplankton assemblages in Barremian-Campanian range. The lithological features together with the new age data allowed us to modify the boundaries between formations; accordingly the knowledge on the structure of South Apuseni Mountains required changes, too. The new data also imply the modification of the existent geological maps of the region. Based on the identified calcareous nannoplankton assemblages, the following zones were defined: CC6 - Late Barremian, CC9 - Lower Cenomanian, CC14 - Late Coniacian and CC17, CC18, and CC19 for Campanian.

Changes in sedimentary patterns of coastal and deep-sea successions from the North Atlantic (Portugal) linked to Early Cretaceous environmental change

Coastal mixed carbonate-siliciclastic and carbonate deposits of Late Barremian to Early Aptian age from the Lusitanian Basin (Portugal) are compared with a deep-sea succession (ODP 641) off the coast of Portugal. The coastal deposits show an abrupt cessation of rudist-dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid-rich marls during the Early Aptian. The subsequent development of the carbonate platform during the Late Aptian is masked by a hiatus. For this time interval shallow-water debris deposits of the deep-sea succession ODP 641 indicate that carbonate production in shallow-water areas resume in the early Late Aptian. Carbon-isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the Portuguese with shallow-water successions from Switzerland, France, Oman and the Pacific. The correlation reveals that during the Early Aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon-isotope values associated with the global deposition of organic rich black shales in the deep sea (OAE 1a). In all compared sections rudist-dominated carbonate deposition is stopped and followed either by orbitolinid-rich deposits, the deposition of microbial carbonates or by the drowning of the carbonate platform. The comparison shows that the deterioration for carbonate platform growth conditions during the Early Aptian occurred essentially simultaneously at the various localities. During this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms. Sea level change combined with local effects like elevated nutrient levels and higher temperatures, were probably determining the nature of sedimentary change in shallow-water environments during the carbonate crisis. In the sections studied in Portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late Early Aptian.

Palaeobiogeographic aspects of Late Barremian to Late Albian coral faunas from Northern Mexico (Sonora) and the southern USA (Arizona, Texas)

The taxonomy of Early Cretaceous shallow marine coral faunas from the Bisbee Basin (northwestern Mexico and Arizona, southwestern USA) and the Comanche Platform (Texas, USA) are compared to each other and to coral associations of the same age around the world. The analysis here employs a large, comprehensive computer database on Mesozoic corals. The database is used to develop a uniform palaeogeographic framework for the comparisons (300 palaeo-provinces are distinguished worldwide for the Cretaceous), and a distance matrix cluster analysis of shared presence is performed on the data to correlate coral faunas both within and outside of the study area. The study is based entirely on coral material recently collected in the field and studied in museum collections. Of the 754 coral samples examined, a total of 160 species is identified from 54 sample locations. This large total number is in contrast to the low to moderate number of species found in each locality, with a maximum number of 28 species from one locality in northwestern Mexico. This demonstrates that coral distribution was controlled by regional (even local) factors. Outside of the sample area, the coral faunas show a strong correlation to central Tethyan faunas, with strongest affinities to that of the Iberian Peninsula, and also to eastern Tethys and western Pacific faunas. This argues against the commonly held concept of a distinct New World coral faunal realm, and is explained by a west-to-east orientation of warm oceanic connections and the close proximity of the land masses during the Early Cretaceous.

Palaeoenvironmental significance of Early Cretaceous foraminifera from northern Sinai, Egypt

The Lower Cretaceous section in the El Tourkumanyia area, northern Sinai, is represented lithostratigraphically by the Malha, Risan Aneiza and Halal formations. A number of beds in these formations yielded high numbers of both benthonic and planktonic foraminifera. 157 foraminiferal species, of which 28 are planktonic, have been recognised. The stratigraphical ranges of these species indicate a Barremian–Albian age for this section. Both faunal diversity and cluster analyses have been performed on the smaller benthonic foraminiferal species that occur throughout the studied section. The faunal characters and diversity indices that are relatively low, with relatively high equitability and low dominance, throughout this section suggest shallow marine environments for these sediments, with unstable, fluctuating conditions. Cluster analysis allows the recognition of four faunal assemblages. Assemblage 1 ( Ammobaculites humei– Evolutinella subevoluta) dominates the late Barremian – early Aptian interval, suggesting calm inner neritic conditions within an epicontinental, semi-enclosed sea. Assemblage 2 ( Flabellammina macfadyeni, Haplophragmium aequale, Osangularia schloenbachi and Paleogaudryina textilarioides) dominates the late Aptian – early Albian interval and points to an open marine environment with warm, more or less energetic inner neritic conditions. Assemblage 3 ( Mayncina orbignyi– Choffatella decipiens) is mostly restricted to the late Barremian – early Aptian interval and dominates in intercalated beds where Assemblage 1 disappears, suggesting oscillating conditions towards deeper environments (middle-outer neritic). These deep conditions are also suggested by the contemporaneous occurrence of planktonic forms and Assemblage 4. This assemblage consists mainly of calcareous taxa and continues with irregular frequency to the topmost part of this section.

Early Cretaceous nonmarine bivalve assemblages from the Jehol Group in western Liaoning, northeast China

The Jehol Group in western Liaoning yields 13 species of nonmarine bivalves belonging to seven genera. Three assemblages are identified: Arguniella yanshanensis-Sphaerium anderssoni, Margaritifera ( Mengyinaia) mengyinensis-Nakamuranaia subrotunda and Arguniella liaoxiensis-Musculiopsis yixianensis, their ages ranging from late Barremian to early Albian. The Arguniella yanshanensis-Sphaerium anderssoni Assemblage is shown to be late Barremian–early Aptian in age on the basis of radiometric dating. The other two assemblages range from middle Aptian to early Albian in age according to both marine intercalations and radiometric dating.

Stratigraphy and Palaeobiogeography of Mesozoic Benthic Foraminifera - Part 3

The Adriatic Carbonate Platform (AdCP), was a separate shallowmarine depositional system characterized by a lack of terrigenous input and was connected to Gondwana towards the South via Gavrovo–Tripolitza or Apulia. It existed for approximately 120 MY, from the Early Jurassic Pliensbachian/Toarcian) to the end of the Cretaceous, resulting in a 4000–6500 m thick succession of almost pure carbonates. However, this is part of a thicker (>8000 m) sequence of predominantly carbonate rocks which forms the Karst Dinarides, and was deposited during more than 270 MY – at least from the Carboniferous (Moscovian) to the Late Eocene. Among many different groups of fossil organisms, benthic foraminifera are especially abundant and well preserved, so they, along with calcareous algae (Dasycladales), are the most important fossils used for age determination and stratigraphic subdivision of shallow-marine carbonate deposits. Within the 257 determined taxa belonging to different foraminiferal families which lived through the Mesozoic, numerous different index fossils occur in assemblages indicating various ages: Early Triassic, Anisian, Carnian, Norian–Rhaetian, Late Sinemurian, Early and Late Pliensbachian (Carixian and Domerian), Early and Late Aalenian, Early and Late Bajocian, Early and Late Bathonian, Callovian, Early and Late Oxfordian, Kimmeridgian, Tithonian, Berriasian, Valanginian, Late Hauterivian, Late Barremian, Early and Late Aptian (Bedulian and Gargasian), Early and Late Albian, Early, Middle and Late Cenomanian, Turonian, Coniacian, Santonian, Early and Late Campanian and Early and Late Maastrichtian. A total of 64 biostratigraphic units – biozones of different categories, from subzone to superzone, were defined within the stratigraphic interval from the Carnian to the Late Maastrichtian. This enabled very detailed biostratigraphic subdivision of the carbonate deposits within the Karst Dinarides. This is one of the most precise sequences, not only in this area, but also among former shallow marine deposits of the entire Neotethyan realm in the present Mediterranean region. The palaeobiogeographic characteristics of biotopes and the composition of foraminiferal assemblages during the Mesozoic were controlled by the position of the study area within the Neotethyan bioprovinces. Until the Albian, this area represented part of the Southern Neotethyan bioprovince, while from the Cenomanian to its final disintegration at the end of the Cretaceous it belonged to a separate, Central Mediterranean Neotethyan bioprovince.

Stratigraphy and Palaeobiogeography of Mesozoic Benthic Foraminifera - Part 2

The Adriatic Carbonate Platform (AdCP), was a separate shallowmarine depositional system characterized by a lack of terrigenous input and was connected to Gondwana towards the South via Gavrovo–Tripolitza or Apulia. It existed for approximately 120 MY, from the Early Jurassic Pliensbachian/Toarcian) to the end of the Cretaceous, resulting in a 4000–6500 m thick succession of almost pure carbonates. However, this is part of a thicker (>8000 m) sequence of predominantly carbonate rocks which forms the Karst Dinarides, and was deposited during more than 270 MY – at least from the Carboniferous (Moscovian) to the Late Eocene. Among many different groups of fossil organisms, benthic foraminifera are especially abundant and well preserved, so they, along with calcareous algae (Dasycladales), are the most important fossils used for age determination and stratigraphic subdivision of shallow-marine carbonate deposits. Within the 257 determined taxa belonging to different foraminiferal families which lived through the Mesozoic, numerous different index fossils occur in assemblages indicating various ages: Early Triassic, Anisian, Carnian, Norian–Rhaetian, Late Sinemurian, Early and Late Pliensbachian (Carixian and Domerian), Early and Late Aalenian, Early and Late Bajocian, Early and Late Bathonian, Callovian, Early and Late Oxfordian, Kimmeridgian, Tithonian, Berriasian, Valanginian, Late Hauterivian, Late Barremian, Early and Late Aptian (Bedulian and Gargasian), Early and Late Albian, Early, Middle and Late Cenomanian, Turonian, Coniacian, Santonian, Early and Late Campanian and Early and Late Maastrichtian. A total of 64 biostratigraphic units – biozones of different categories, from subzone to superzone, were defined within the stratigraphic interval from the Carnian to the Late Maastrichtian. This enabled very detailed biostratigraphic subdivision of the carbonate deposits within the Karst Dinarides. This is one of the most precise sequences, not only in this area, but also among former shallow marine deposits of the entire Neotethyan realm in the present Mediterranean region. The palaeobiogeographic characteristics of biotopes and the composition of foraminiferal assemblages during the Mesozoic were controlled by the position of the study area within the Neotethyan bioprovinces. Until the Albian, this area represented part of the Southern Neotethyan bioprovince, while from the Cenomanian to its final disintegration at the end of the Cretaceous it belonged to a separate, Central Mediterranean Neotethyan bioprovince.

Stratigraphy and Palaeobiogeography of Mesozoic Benthic Foraminifera - Part 1

The Adriatic Carbonate Platform (AdCP), was a separate shallowmarine depositional system characterized by a lack of terrigenous input and was connected to Gondwana towards the South via Gavrovo–Tripolitza or Apulia. It existed for approximately 120 MY, from the Early Jurassic Pliensbachian/Toarcian) to the end of the Cretaceous, resulting in a 4000–6500 m thick succession of almost pure carbonates. However, this is part of a thicker (>8000 m) sequence of predominantly carbonate rocks which forms the Karst Dinarides, and was deposited during more than 270 MY – at least from the Carboniferous (Moscovian) to the Late Eocene. Among many different groups of fossil organisms, benthic foraminifera are especially abundant and well preserved, so they, along with calcareous algae (Dasycladales), are the most important fossils used for age determination and stratigraphic subdivision of shallow-marine carbonate deposits. Within the 257 determined taxa belonging to different foraminiferal families which lived through the Mesozoic, numerous different index fossils occur in assemblages indicating various ages: Early Triassic, Anisian, Carnian, Norian–Rhaetian, Late Sinemurian, Early and Late Pliensbachian (Carixian and Domerian), Early and Late Aalenian, Early and Late Bajocian, Early and Late Bathonian, Callovian, Early and Late Oxfordian, Kimmeridgian, Tithonian, Berriasian, Valanginian, Late Hauterivian, Late Barremian, Early and Late Aptian (Bedulian and Gargasian), Early and Late Albian, Early, Middle and Late Cenomanian, Turonian, Coniacian, Santonian, Early and Late Campanian and Early and Late Maastrichtian. A total of 64 biostratigraphic units – biozones of different categories, from subzone to superzone, were defined within the stratigraphic interval from the Carnian to the Late Maastrichtian. This enabled very detailed biostratigraphic subdivision of the carbonate deposits within the Karst Dinarides. This is one of the most precise sequences, not only in this area, but also among former shallow marine deposits of the entire Neotethyan realm in the present Mediterranean region. The palaeobiogeographic characteristics of biotopes and the composition of foraminiferal assemblages during the Mesozoic were controlled by the position of the study area within the Neotethyan bioprovinces. Until the Albian, this area represented part of the Southern Neotethyan bioprovince, while from the Cenomanian to its final disintegration at the end of the Cretaceous it belonged to a separate, Central Mediterranean Neotethyan bioprovince.

Relative importance of the Hercynian and post-Jurassic tectonic phases in the Saharan platform: a palaeomagnetic study of Jurassic sills in the Reggane Basin (Algeria)

SUMMARY In the intracontinental domain of the northwestern Saharan platform, the deformation of the Palaeozoic sedimentary cover is mainly attributed to a far-field effect of the Hercynian orogeny having occurred at the African‐Laurusian plate boundary in the Late Carboniferous to Early Permian times. However, geological observations from different parts of Africa and Arabia provide evidence that several minor but widespread tectonic events occurred later, particularly during the Cretaceous. Contrary to elsewhere in the northwestern part of Africa, in the Reggane Basin, outcropping doleritic sills of Early Jurassic age are intruded in folded Palaeozoic sediments of Devonian to Carboniferous ages deposited before the Hercynian orogeny. In this favourable situation, a palaeomagnetic study of the Liassic dolerite is able to provide information on the tectonic history of the surrounding area independently from geological observations. The present study aims to quantify the relative proportion of tilting related to, respectively, the Hercynian and a post-intrusion phase, using a fold test based on the small circle analysis. This method proved to be very efficient to unravel these tectonic events. It shows that, in the studied area, the folds were initiated during the Hercynian phase, but mainly amplified during the post-intrusion phase which turned out to be the dominant one. In the Reggane Basin, the age of this second event is not geologically well constrained between probably Late Jurassic and Early Cretaceous. It could be the far-field effect of either the Cimmerian phase (∼140 Ma) or more likely the Austrian tectonic phase (Late Barremian, ∼125 Ma). The Late Barremian tectonic episode corresponds to a major event: the break-up of Western Gondwana, which led to the separation of Africa from South America and to the incipient fragmentation of the African plate into three major blocks. The conclusion drawn from the palaeomagnetic study in the Reggane Basin is consistent with the geological observations and representative of the intraplate Cretaceous deformations recorded in many other places in Africa. It emphasizes once again that stresses can be transferred far from the plate boundaries, into the continental plate interiors.