Jurassic mountain building and Mesozoic-Cenozoic geodynamic evolution of the Northern Calcareous Alps as proven in the Berchtesgaden Alps (Germany)

New data from the Berchtesgaden Alps result in a reconstruction of the Mesozoic-Cenozoic geodynamic history of the Northern Calcareous Alps. The closure of the western part of the Neotethys Ocean started in the late Early Jurassic and is evidenced by the onset of thick clay-rich sediments in the outer shelf area (=Hallstatt realm). The Middle to early Late Jurassic contraction is documented by the migration of trench-like basins formed in front of a propagating thrust belt. Due to ophiolite obduction, these basins propagated from the outer shelf area, forming there the Bajocian to Oxfordian Hallstatt Mélange, to the Hauptdolomit/Dachstein platform area, where the Oxfordian Rofan and Tauglboden Mélanges were formed. The basins were separated by nappe fronts forming structural highs. This scenario mirrors syn-orogenic erosion and deposition in an evolving thrust belt. Active basin formation and nappe thrusting ended around the Oxfordian/Kimmeridgian boundary, which was followed by the onset of carbonate platforms on structural highs prograding towards the former basins in latest Oxfordian to Early Tithonian time. Underfilled basins remained between the platforms. Rapid deepening around the Early/Late Tithonian boundary was induced by extension due to mountain uplift and resulted in the reconfiguration of the platforms and basins related to normal and probably strike-slip faults. Erosion of the uplifted nappe stack including obducted ophiolites caused final drowning and demise of the platforms in the Berriasian. The remaining Early Cretaceous basins were filled up with molasse sediments including siliciclastics until Aptian. Around the Early/Late Cretaceous boundary again extension and strike-slip movements started, followed by Eocene thrusting and Miocene strike-slip movements with block rotations. These younger tectonic movements destroyed the Triassic to Early Cretaceous palaeogeography and arranged the modern block configuration. The described Jurassic to Early Cretaceous history corresponds with that of the Western Carpathians, the Dinarides, and the Albanides, where (1) age dating of the metamorphic soles prove late Early to Middle Jurassic inneroceanic thrusting followed by late Middle to early Late Jurassic ophiolite obduction, (2) Kimmeridgian to Tithonian shallow-water platforms formed on top of the obducted ophiolites, and (3) latest Jurassic to Early Cretaceous sediments show postorogenic character. Therefore, we correlate the Jurassic geodynamic evolution of the Northern Calcareous Alps with the closure of the western part of the Neotethys Ocean.     

Bioerosional structures and pseudoborings from Late Jurassic and Late Cretaceous-Paleocene shallow-water carbonates (Northern Calcareous Alps, Austria and SE France) with special reference to cryptobiotic foraminifera

Examples of bioerosional processes (boring patterns) are described from shallow-water limestones of the Late Jurassic Plassen Carbonate Platform (PCP) and the Late Cretaceous to Paleocene Gosau Group of the Northern Calcareous Alps, Austria. Some micro-/macro-borings can be related to distinct ichnotaxa, others are classified in open nomenclature. In the Alpine Late Jurassic, bioerosional structures recorded from clasts in mass-flows allow palaeogeographical conclusions concerning the source areas. In particular, these are borings of the Trypanites-ichnofacies detected from clasts (Barmstein limestones) of the PCP or special type of bored ooids of unknown source areas or restricted autochthonous occurrences. In the Lower Gosau Subgroup, Gastrochaenolites macroborings occur in mobile carbonate clast substrates of shore zone deposits (“Untersberg Marmor”). Different types of borings are recorded from rudist shells and coral skeleton, some of which are referable to the ichnotaxon Entobia produced by endolithic sponges. In the present study, special attention is paid to the occurrences of the cryptobiotic foraminifera Troglotella incrustans Wernli and Fookes in the Late Jurassic and Tauchella endolithica Cherchi and Schroeder in the Late Cretaceous. The latter is so far only known to be from the Early Cenomanian of France and is reported here for the first time from the Late Turonian-Early Coniacian stratigraphic interval where it was found in turbulent carbonate deposits within borings penetrating bivalve shells or coralline algae. The records of cryptobiotic foraminifera from the Northern Calcareous Alps are supplemented by a single finding from the Middle Cenomanian of SE France. A palaeoenvironmental interpretation of the occurrences of the cryptobiotic foraminifera is provided.     

Lower Jurassic Bahamian-type facies in the Choč Nappe (Tatra Mts,West Carpathians,Poland) influenced by paleocirculation in the Western Tethys

The Lower Jurassic (upper Sinemurian) of the Hronicum domain (Tatra Mts., Western Carpathians, Poland) represents typical tropical shallow-water carbonates of the Bahamian-type. Eight microfacies recognized include oolitic-peloidal grainstone/packstone, peloidal-bioclastic grainstone, peloidal-lithoclastic-bioclastic-cortoidal grainstone/packstone, peloidal-bioclastic packstone/grainstone, peloidal-bioclastic wackestone, spiculitic wackestone, recrystallized peloidal-oolitic grainstone and subordinate dolosparites. The studied sediments were deposited on a shallow-water carbonate platform characterized by normal salinity, in high-energy oolite shoals, bars, back-margin, protected shallow lagoon and subordinately on restricted tidal flat. Some of them contain the microcoprolite Parafavreina, green alga Palaeodasycladus cf. mediterraneous (Pia) and Cayeuxia, typical of the Early Jurassic carbonate platforms of the Western Tethys. The spiculite wackestone from the upper part of the studied succession was deposited in a transitional to deeper-water setting. The studied upper Sinemurian carbonates of the Hronicum domain reveal microfacies similar to the other Bahamian-type platform carbonates of the Mediterranean region. Thereby, they record the northern range of the Lower Jurassic tropical shallow-water carbonates in the western part of the Tethys, albeit the thickness of the Bahamian-type carbonate successions generally decrease in a northerly direction. The sedimentation of the Bahamian-type deposits in the Hronicum domain, located during the Early Jurassic at about 28°N, besides other specific factors (i.e., light, salinity, and nutrients) was strongly controlled by the paleocirculation of warm ocean currents in the Western Tethys.     

Analysis of Late Jurassic to Early Cretaceous algal debris-facies of the Plassen carbonate platform in the Northern Calcareous Alps (Germany,Austria) and in the Kurbnesh area of the Mirdita zone (Albania): a tool to reconstruct tectonics and palaeogeography of eroded platforms

A characteristic microfacies of the Late Jurassic to Early Cretaceous allodapic Barmstein Limestone of the Northern Calcareous Alps are clasts of wackestones with numerous fragments of calcareous algae (“algal debris-facies”). According to dasycladale palaeocoenoses, several subtypes comprising different associations can be distinguished. One association is characterized by the debris of an unknown large dasycladalean alga reported as dasycladalean alga indet. sp. 1 from different localities in the Northern Calcareous Alps, typically forming a monospecific assemblage. Another microfacies type contains star-like calcitic bodies tentatively referred to the morphospecies Coptocampylodon pantici Ljubović-Obradović and Radoičić, originally described as being from the Turonian of NW-Serbia. Other Coptocampylodon-like bodies represent the calcified tufts of the laterals of Selliporella neocomiensis (Radoičić). The occurrence of Coptocampylodon pantici-like microfossils in the Late Tithonian to Early Berriasian, shows that obviously different species of dasycladaleans display identical to similar shaped tufts of laterals in transverse sections when becoming fragmented. Coptocampylodon pantici Ljubović-Obradović and Radoičić was observed only from different occurrences of Barmstein Limestone, but not from the autochthonous platform carbonates of the Plassen carbonate platform. The Coptocampylodon algal debris-facies is also reported from the Late Jurassic of Albania, Mirdita zone. Occurrences of different types of algal debris-facies in components of mass-flow deposits can be used as a tool to reconstruct eroded carbonate platforms and tectonics, as demonstrated in the Northern Calcareous Alps and the Albanides. Finally, the general occurrences of algal debris-facies in both settings—intra-Tethyan mostly isolated platforms (Alps, Albanides) vs. extended epeiric platforms (Middle East)—are compared and discussed.     

Sedimentary environment of Devonian pelagic limestones in the Southern Alps

Primary sedimentary structures combined with the geometry of Devonian and Lower Palaeozoic lithosomes in the Southern Alps (Austria and Italy) suggest many doubts about the published environmental and bathymetric interpretation of some Lower to Middle Devonian pelagic nodular limestones as 'deep-water' abyssal deposits. Every graded bed is not necessarily aturbidite; a single or some turbiditic beds are not necessarily deep-water or abyssal deposits; carbonate dissolution does not necessarily take place only below the carbonate compensation depth (CCD). Data show that graded allodapic beds, like those of the Lower to Middle Devonian of the Alps, may have been deposited as storm layers at a depth not exceeding some hundreds of metres. Accordingly the margins between Lower Devonian shallow-water platform and basins were characterized by low gradient and transitional sedimentary conditions. They became very steep only at the Devonian–Carboniferous transition because of synsedimentary block faulting.     

Isotopic signatures (δO and δC) of bivalve shells from cold seeps and hydrothermal vents

The oxygen and carbon isotopic compositions of 108 modern shells of various bivalve species collected from cold seeps and hydrothermal vents were investigated in order to evaluate whether these parameters can provide information on environmental geochemical variability as well as on bivalve species and on the type of symbiotic bacteria present in their gills. The results show that the carbonate of bivalve shells from hydrothermal vents is characterized by abnormal positive δ¹³C values due to kinetic isotope effects, whereas the carbonate of bivalve shells from cold seeps exhibits positive as well as negative δ¹³C values suggesting that oxidized methane emitted by the seeping fluids may be incorporated in the shell. Comparison of the δ¹⁸O and δ¹³C values of bivalve shells hosting different chemosymbiotic bacteria suggests that each type of symbiosis is associated with a specific environment and bivalve species, indicating that there is a strong physiological/metabolic control on the incorporation of stable isotopes during the biomineralization process.     

Jurassic radiolarites in a Tethyan continental margin (Subbetic, southern Spain): palaeobathymetric and biostratigraphic considerations

A region of the pelagic Subbetic basin within the Southern Iberian Continental Margin is studied in lithostratigraphical and biostratigraphical detail. Jurassic radiolarites (Jarropa Radiolarite Formation, Bathonian–Oxfordian) interbedded with shallow-water marine limestones have been recognized. Underlying the radiolarites (Camarena Formation, Bajocian) are oolitic limestones showing shallowing-upward cycles with karstic surfaces on the top, corresponding to deposition on an isolated carbonate platform on volcanic edifices. The Milanos Formation (upper Kimmeridgian–Tithonian), overlying the radiolarites, contains calciclastic strata with hummocky cross-stratification, which indicate outer carbonate ramp deposition. In the Jarropa Radiolarite Formation some calcisiltite strata with hummocky cross-stratification have been found. The bathymetry of the Subbetic Jurassic pelagic sediments, including the radiolarites, is considered as moderate or shallow in depth. We suggest that the pelagic character of the Jurassic sediments in this margin and their equivalents in other Alpine domains is a consequence of distance from the continent (beyond the pericontinental platform) but not necessarily of depositional depth.     

The demise of the rudist-bearing carbonate platforms at the Cenomanian/Turonian boundary: a global control

The demise of the rudist-bearing carbonate blatforms at the Cenomanian/Turonian boundary is tudied in different ways through examples from the Vestern Mediterranean Province. During the Late Cenonanian, North and South Tethyan carbonate platforms xtened widely and were subjected to different climatic and oceanographic conditions. The onset of the demise of the carbonate platforms occurred during Upper Arphaeocretacea and Helvetica biozone times and was boeval with the Global Oceanic Anoxic Event (OAE₂). A major biologic turnover affected the benthic organisms i.e. rudists and large foraminifera. The rudists underwent a severe extinction event, leading to the disappearance of the dominantly aragonite secreting rudists, while the dominantly calcitic forms were less affected. The major development of the carbonate platforms occurred during the Latest Cenomanian — Earliest Turonian, involving a transgressive highstand system tract and a keep-up carbonate organization. During the Early Turonian the carbonate sedimentation was disturbed; hard-grounds, condensed beds, terrigenous inputs developed and a gap in the carbonate platform deposition occurred. A combination of several sequentially linked factors, could explain the demise of the carbonate platform and the major change on the benthic ecosystem at the Cenomanian-Turonian boundary.     

Late Triassic, Early and Middle Jurassic Radiolaria from ferromanganese-chert ‘nodules’ (Angelokastron, Argolis, Greece): evidence for prolonged radiolarite sedimentation in the Maliac-Vardar Ocean

In the Argolis, the Basal Sequence, constituting the eastern Pelagonian margin which bordered the Maliac-Vardar oceanic domain, includes shallow-water carbonates of Late Triassic-Early Jurassic, condensed pelagic limestones of Early-Middle Jurassic, radiolarian cherts of late Middle-Late Jurassic age and siliceous mudstones and sandstones rich in ophiolite fragments. Up-section, coarse breccias, including clasts of boninites derived from the ophiolite obducted onto the Pelagonian margin in Late Jurassic times crop out. Near Angelokastron a small quarry exposes pervasively sheared dark reddish-brown, radiolarian-bearing cherty shales with disrupted fragments of chert and chert nodules impregnated by ferro-manganese oxides. These shales occur in the footwall of a thrust bringing them into contact with the Pantokrator Limestone of the Basal Sequence. We collected more than 30 samples of the chert fragments and the shaly matrix. Thirteen nodules and one matrix sample yielded determinable radiolarians. Low to non-detectable concentrations of trace metals such as Co, Cr, Cu, Ni, Zn, and Pb indicate a hydrothermal origin of the ferro-manganese mineralization. The radiolarian taxa found indicate four age groups for the nodules that are embedded in the siliceous shale matrix that yielded a Middle Jurassic age (middle Bathonian). The first group includes a nodule of Late Triassic age (late Norian to Rhaetian); the second group nodules of Early Jurassic age (late early to late Pliensbachian and probably middle-late Toarcian); the third group nodules of early Middle Jurassic age (Aalenian–Bajocian); the last group finally includes nodules of late Middle Jurassic age (Bajocian–Bathonian). The presence of Upper Triassic to Middle Jurassic Mn-impregnated chert nodules in a Middle Jurassic matrix indicates a deep oceanic environment of deposition outside the Pelagonian realm (easternmost Adria Plate), which at that time was a shallow-water carbonate platform with a thin pelagic limestone cover. The chert nodules are with all certainty derived from the oceanic Maliac-Vardar domain and were, together with their host formation, tectonically emplaced onto the Pelagonian margin. We speculate that these nodules, more lithified than their matrix, were exhumed on the slope of an intra-oceanic accretionary wedge and were redeposited in the Middle Jurassic siliceous mudstones on the floor of the subducting Maliac-Vardar Ocean.     

A new species of <Emphasis Type="Italic">Pelekysgnathus</Emphasis> (Conodonts) from the Famennian of the east Russian Platform

A new conodont species, Pelekysgnathus aristovi sp. nov., from the Middle Famennian shallow-water carbonate deposits of the South Tatar Dome in the eastern Russian Platform is described.     

Jurassic reef events in the Moroccan Atlas: A review

In the Moroccan Atlas, sedimentary deposits provide important data on reef events that characterize the Jurassic period. Recent work allows us to enhance knowledge of the Jurassic reefs in the Atlas, in particular their age, character and palaeogeographic distribution. Numerous localities with sponge-microbial mud mounds, coral reefs, and lithiotid bioherms are recorded from the Middle and High Atlas regions. These different biogenic constructions occupy different palaeogeographic settings: on the top of tilted blocks within the basin center; in slightly deeper positions, at the basin platform junction; and on adjacent platforms in the middle of the coastal area. The main episodes of reef building span nearly 30 million years, as follows: (1) Sinemurian, (2) early Pliensbachian, (3) late Toarcian, (4) Aalenian–early Bajocian (pars), and (5) late Bajocian. These five distinct reef events can be linked with general fluctuations of sea level and tectonism, and have palaeoclimatic implications.     

Le Lias et le Dogger du sud du Bassin parisien (France) : rôle de la tectonique syn-sédimentaire et reconstitutions paléogéographiques à l'échelle de la biozone d'ammonite

The Lias and Dogger series in the southern Paris Basin outcrops are precisely dated following the ammonite biozonation scale. In these series, the depositional environment context is accurately identified and thus various isopic zones can bee recognized. From the outcrop study, the depositional sequence and the tectonics events are also distinguished. The poorly dated subsurface data should be not anymore interpreted as diagraphic signatures, with the traditional peak to peak correlation. They now need to be analysed according to the geodynamic evolution of each isopic zone. The Liassic transgressive series (in the Armorican continent) and the Dogger platforms numerous carbonate bodies are correlated at biostratigraphic scale, throughout the whole southern Paris Basin. Subsequently, paleogeographic maps are established and based on depositional sequences. The basin evolution image changes radically. This shows clearly that the complexes carbonate bodies layout prohibits any depositional environment interpretation and any isopach mapping at geological stage level. If not, the carbonate platforms of different age would be amalgamated, without any connection with the reality. Over the time, paleogeographic maps show syn-sedimentary short wavelength deformations, more or less well expressed according to the local sedimentary context. During the Lias and the Dogger, three steps can be distinguished in the southern Paris Basin. Hettangian to Lower Aalenian, the progressive increase in accommodation drives to total immersion of the continental areas; the maximum of accommodation during the Middle Toarcian entails uniform sedimentary conditions. However, short wavelength deformations persist. The major accidents defining the isopic zones are mainly North-South oriented. Middle Aalenian to Middle Bathonian, isopic zones are contrasted, controlled by the North-South accidents but also the North West-South East ones ; the variable accommodation allowed the development of regional sedimentary gaps and shallow limestone progradations on a marly area (so called “Sillon marneux”) ; tectonics events correspond to the Tethyan and the North Sea riftings influences. Upper Bathonian to Upper Oxfordian, the North West-South East tectonics accidents are particularly active; this tectonic phase could be associated to the thermal event, described in the Paris Basin and announcing the Malm depositional environment.     

Middle and Upper Jurassic bivalve associations from the Iberian Range (Spain)

The four sections richest in bivalves from the Middle and Upper Jurassic of the Iberian Range (Spain) were selected for a quantitative palaeoecological analysis of the bivalve fraction of the macrobenthos. Five bivalve associations and two assemblages were recognized with the help of a Q-mode hierarchical cluster analysis (Ward method). The main environmental factors controlling bivalve associations are thought to be substrate, water energy and distribution of organic matter. The bivalves exhibit a distinct spatial and temporal distribution pattern within the Aragonian Branch of the Iberian Range. Four of the bivalve associations occur in the Upper Oxfordian (Sot de Chera Fm) and one association in the Lower Callovian (Chelva Fm). In the Sot de Chera and Loriguilla formations, the abundance of bivalves decreases from NW to SE i.e., from relatively close to the shore line towards the distal-most part of the carbonate platform. In the Chelva Fm, bivalves are abundant in the Ariño region, interpreted as a palaeogeographic high. The spatial distribution of bivalves might have been largely controlled by the availability of nutrients.     

A sequence stratigraphic approach to a Middle Triassic shelf-slope complex of the Ligurian Alps (Ligurian Briançonnais,Monte Carmo-Rialto unit,Italy)

The Mesozoic sedimentary cover belonging to the Monte Carmo-Rialto unit of the Ligurian Briançonnais domain is composed of Scythian clastics and Anisian to Carnian carbonate rocks over 300 m thick. This paper focuses on the stratigraphy of this carbonate complex, its environmental significance, and its evolution in light of dynamic stratigraphy. Our facies analysis of limestones and dolomites of the Triassic complex allowed us to reconstruct an environmental model. Data support a distally steepened carbonate ramp of Anisian age evolving to a more diversified Ladinian platform with an oolitic sand-bar belt separating the lagoon from the slope. The Monte Carmo-Rialto slope facies are the only witnesses of deep sedimentation in the Triassic terrains of the Ligurian Briançonnais domain, otherwise represented by shallow-water carbonate deposits. On the basis of facies succession, we have identified nine medium-scale cycles (third-order sequences) in the study area, comparable to those evidenced in the Briançonnais s.s. domain by the French authors. Small-scale cycles analysis evidenced mainly shallowing-upward trends in the examined sequences; although a few evidences of transgression-related deposits (deepening upward cycles) have been found at the base three sequences, they have been mostly obliterated by dolomitization and masked by local tectonics. For this reason, we can undoubtedly distinguish only the part of each sequence belonging to HST, while the TST, though present, still remains a partition that cannot be precisely characterized. In the same way, LSTs are not present in the Monte Carmo-Rialto unit, due to the original relative landward position of the examined area. Sequence stratigraphy analysis indicates different long-term dynamics for the two evolutionary stages of the Triassic Ligurian platform: a general landward backstepping to moderate progradation during the Early Anisian and true progradation during the latest Anisian and Ladinian. In addition, a good fit with the sequences proposed by the SEPM chart has been found, indicating a correspondence for the third-order sequences of the Middle Triassic.     

The Frasnian-Famennian mass extinction: insights from high-resolution sequence stratigraphy and cyclostratigraphy in South China

Two sequences (SFr, SFa), each 1-1.2 Myr in duration, are recognised in the strata across the Frasnian-Famennian (F-F) transition both in carbonate platform and interplatform basinal successions in South China. The sequence boundary between the two sequences is placed a little below the top of the Frasnian. The sequences are basically composed of coarsening-upward/bed-thickness increasing-upward cycles and shallowing-upward cycles (parasequences) in basinal and platform deposits respectively, which stack into cycle-sets (typically six to eight cycles). 10 and 12 cycle-sets are identified in sequences SFr and SFa respectively. These cycle-sets can be further grouped into larger-scale composite cycle-sets (herein termed mesocycle- and megacycle-sets with two and four cycle-sets respectively). This vertical cycle-stacking pattern and the hierarchy of cyclicity suggest a Milankovitch style of forcing such that the cycles and cycle-sets were formed in response to the orbital perturbations of precession (16-18 kyr) and eccentricity (∼100 kyr in duration), respectively. In the basinal cycles, smaller-scale rhythmic stratification beds (typically six to eight beds in a cycle) are extensive, and were likely caused by millennial-scale climatic forcing. In the lower sequence, SFr, the latest highstand deposits consist of calciturbidites and debrites in deep-water strata and fenestral limestones in shallow-water strata, representing a major (third-order) sea-level fall. Within these deposits, four cycle-sets are further identified in both coeval deep-water and platform successions. Succeeding deeper-water organic-rich facies, within which three cycles occur, are the transgressive deposits of the overlying Famennian sequence (SFa). These cycles represent three higher-frequency (16-18 kyr) sea-level fluctuations and accompanying anoxia, superimposed on a major third-order sea-level rise. The F-F boundary is placed at the top of the first cycle, based on conodont data. Thus, a major sea-level fall and then a rise occurred in the F-F transitional period. Faunal and sedimentological data reveal a massive biotic decline in concert with the major sea-level fall, and a further biotic demise coinciding with the major sea-level rise and its three superimposed higher-frequency sea-level fluctuations and accompanying anoxia. The F-F biotic crisis was therefore characterised by two episodes of step-down extinction. On the basis of Milankovitch orbital rhythms, the first major biotic extinction took place over ∼400 kyr, and the subsequent event was ∼50 kyr in duration, i.e. ∼450 kyr for the entire event. At the same time as the massive decline of normal-marine fossils during the latest Frasnian sea-level fall, there was widespread cyanobacterial growth and a thriving of planktonic calcispheres, suggesting eutrophic conditions. This situation could have caused a severe biotic loss, as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over-consumption of oxygen through respiratory demands and decomposition by the cyanobacteria and phytoplankton. The subsequent rapid sea-level rise with superimposed higher-frequency sea-level fluctuations and accompanying anoxia could have caused rapid elevation of anoxic bottom waters and expansion of eutrophic surface waters over shallow-water platforms due to enhanced upwelling ocean currents and improved ocean circulation. This situation would have exerted further stresses upon the already-weakened biota, leading to a further biotic demise. However, a small number of organisms such as pelagic tentaculitids, small mud-adapted brachiopods and gastropods did survive into the Famennian, although with very low diversity.     

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.     

First occurrence of the Ichnogenus Selenichnites from the Middle Jurassic Strata of the Skoura Syncline (Middle Atlas,Morocco); Palaeoecological and palaeoenvironmental context

Mesozoic strata of North Africa yield the first occurrence of the ichnogenus Selenichnites. The trace fossils occur on the top surface of a sandy carbonate deposit in the axis of a Middle Atlas syncline (Skoura Syncline, NE Morocco). The ichnofossil-bearing horizon belongs to the Late Bajocian–Early Bathonian Ich Timellaline/Bou Akrabene Formation. The trace fossils are crescent-shaped and the best preserved exhibits a posterior central axial impression (possible telson tail impression). They are interpreted as feeding burrows (fodinichnia) or hiding depressions of Xiphosurids or Limulids (horseshoe crabs) on a sandy carbonate substrate beneath a veneer of muddy deposits. The sedimentological character suggests a relatively protected shallow water subtidal palaeoenvironment preceding the Bathonian regression of the Atlas domain. This discovery provides the first evidence of xiphosurans or xiphosuran-like organisms inhabiting the southern shores of the Tethys in the Middle Jurassic.     

Factors controlling upper Jurassic ammonite assemblages in north-central Mexico

Lower Kimmeridgian to Lower Tithonian (Upper Jurassic) sections studied at Sierra de Palotes (Durango) and Sierra de Catorce (San Luis Potosí), Mexico, show low-energy deposits in which the composition of fossil macroinvertebrate assemblages, including megabenthos, reflects biostratinomic control. Monotonous siltstones provide continuous records of ammonite assemblages and reflect dominant deposition of shells in living areas; meanwhile, discontinues records were forced by episodic post-mortem transportation of shells, which was especially accentuated under storm influence. Rhythmic marly-silty limestones and marls illustrate a fossil record probably determined by minor transgressive-regressive pulses. The major changes in lithofacies are reflected by condensed silty and phosphatic mudstones deposited during significant floodings affecting areas under dominant terrigenous sedimentation. These changes determined more or less significant variations in the composition of fossil assemblages according to their relation to changing ecological conditions. However, shifting ecospaces exhibit no direct relationship to changes in lithofacies. Post-mortem transportation, operating in relation to both marine floodings and changes in the pattern of upper-water currents, was the main biostratinomic factor affecting the areal distribution of ammonite populations. Shell transportation and sedimentation rate controlled preservation and ultimately influenced diversity in recorded ammonite assemblages. The post-mortem behaviour (interpreted from shell structure and preservation), and therefore distribution, of ammonite shells points to shallow-water environments during the Kimmeridgian - Early Tithonian in areas (such as SE Durango and San Luís Potosí) close to the changing boundary between dominant carbonate and terrigenous sedimentation. No reworking affecting ammonite biostratigraphy has been identified in the sections studied.     

Sedimentary development of a continuous Middle Devonian to Mississippian section from the fore-reef fringe of the Brilon Reef Complex (Rheinisches Schiefergebirge, Germany)

The Brilon-reef complex is one of the biggest Devonian carbonate buildups (~80 km²) of the Rheinisches Schiefergebirge. The Burgberg section is located in the southeastern fore-reef area of the Brilon Reef Complex and exposes a succession of strata (117 m thick), which extends from the Middle Givetian (middle varcus conodont Zone) to the Viséan (bilineatus conodont Zone). Field and microfacies observations led to the definition of nine microfacies that are integrated into a sedimentary model divided into off-reef, intermediate fore-reef, and proximal fore-reef sedimentary domains (SD). The off-reef domain (SD1) is the most distal setting observed and is characterized by fine-grained sediments, dominated by pelagic biota and the local occurrence of gravity-flow deposits. The intermediate fore-reef (SD2) is characterized by a mixture of biota and sediments coming from both deeper-water and shallow-water sources and is influenced by storm and gravity-flow currents. In this domain, Renalcis mound-like structures developed locally. Finally, the proximal fore-reef (SD3) corresponds to the most proximal setting that is strongly influenced by gravity-flow currents derived from the Brilon Reef Complex. The temporal evolution of microfacies in the fore-reef setting of the Burgberg section show five main paleoenvironmental trends influenced by the onset, general development, and demise/drowning of the Brilon Reef Complex. Fore-reef to off-reef lithologies and their temporal changes are from the base to the top of the section: (U1)—fine-grained sediments with large reef debris, corresponding to the initial development of the reef building upon submarine volcaniclastic deposits during the Middle Givetian (middle varcus Zone) and first export of reef debris in the fore-reef setting; (U2)—high increase of reef-derived material in the fore-reef area, corresponding to a significant progradation of the reef from the Middle Givetian to the Early Frasnian (maximum extension of the Brilon Reef Complex to the south, disparilis to the falsiovalis conodont biozones); (U3)—progressive decrease of shallow-water derived material and increase of fine-grained sediments and deep-water biota into the fore-reef setting, corresponding to the stepwise withdrawal of the reef influence; from the Middle to the Late Frasnian (jamieae conodont Zone); (U4)—development of a submarine rise characterized by nodular and cephalopod-bearing limestones extending from the Late Frasnian to the Late Famennian corresponding to the demise and drowning of the Brilon Reef Complex as a result of the Late Frasnian Kellwasser events (upper rhenana and triangularis conodont biozones); (U5)—significant deepening of the Burgberg area starting in the Late Famennian, directly followed by an aggrading trend marked by pelagic shales overlying the nodular limestone deposits.