Palorbitolina Lenticularis Research Articles

Stratigraphic updating and correlation of Late Barremian–Early Aptian Urgonian successions and their marly cover, in their type region (Orgon-Apt, SE France)

Comparing the stratigraphy of the rudist bearing limestones of Orgon (the type locality for the Urgonian stage of d'Orbigny) with that of the Urgonian limestones of the Monts de Vaucluse-Apt region, where the stratotype of the Aptian sensu d'Orbigny is located, shows that the corresponding platform carbonates have distinctive ages, late Barremian (Gehrartia sartousiana zone), and Bedoulian (Deshayesites oglanlensis to the middle part of the Deshayesites deshayesi zone) respectively. Nevertheless the Upper Barremian Orgon limestones are still present in the western part of the Monts de Vaucluse where they are capped by a Palorbitolina lenticularis–Heteraster oblongus (Pa1) guide level, ascribed to the Imerites giraudi zone. The overlying rudist beds are characterized by the presence of Caprinidae (Offneria-Pachytraga-Praecaprina assemblage), and spread over the Monts de Vaucluse-Apt region; they also extend to the Mont Ventoux, and to the eastern Languedoc too. These latter beds, assigned to the early Bedoulian, i.e. the D. oglanlensis–D. weissi zones, are interrupted by a drowning discontinuity capped by Palorbitolina beds (Pa2) overlain by bioclastic or coral limestones of early late Bedoulian age (lower part of the D. deshayesi zone). The succeeding marly cover, including marly limestones and the lowermost part of the “Gargas marls”, which marks the regional demise of shallow carbonates, is ascribed to the late Bedoulian (Deshayesites grandis subzone and Dufrenoyia furcata zone) and represents the lowermost part of the “Aptian”sensu d'Orbigny.

Sedimentary succesion of the Lower Cretaceous deposits from the north-western part of Pădurea Craiului (Apuseni Mountains, Romania)

Within the general succession of the Lower Cretaceous deposits from the Vârciorog-Dobreşti area (Pădurea Craiului Mountains), carbonate and terrigenous deposits were identified. The limestones were assigned to two distinctive lithostratigraphic units: the Valea Măgurii and Vârciorog formations. Based on the orbitolinids Palorbitolina lenticularis and Mesorbitolina texana their ages are assigned to the early Aptian, and respectively late Aptian–Albian. The terrigenous facies mainly include fine grained deposits (clays, siltites, marls) and, to a lesser extent, coarser ones (glauconitic sandstones and conglomerates), and they are attributed to the Ecleja and Vârciorog formations. The marls of the Ecleja Formation have been observed in a single section. The lack of fossils prevents assigning an age to this marl succession. Based on their relative location, i.e., at the base of the late Bedoulian Valea Măgurii Limestones, they may be assigned to the early Aptian (early Bedoulian). The siliciclastic deposits of Vârciorog Formation cover the largest areas in the region. Their late Aptian–Albian age is established based on the presence of Mesorbitolina texana. Additional arguments are represented by an ammonite fauna assigned to the terminal Bedoulian–early Gargasian. This fauna is located at the base of the Vârciorog Formation. The Lower Cretaceous deposits cropping out in this area have been investigated in seven geological sections. The data interpretation allowed a synthetic reconstruction of the succession and of the depositional environments.

New data on the Upper Jurassic-Lower Cretaceous limestones from Bihor Mountains: case study of Gârda Seacă-Hodobana region, Romania

This study refers to some problems regarding the lithological succession, facies and carbonate microfacies, and to biostratigraphic markers of the Upper Jurassic-Lower Cretaceous carbonates from Bihor Mountains. Three types of facies (external marginal facies, subtidal and peritidal facies) were separated for the Upper Jurassic, and two (coastal-peritidal and open shelf facies) for the Lower Cretaceous carbonates. The micropaleontological assemblages identified contain species that allow the separation of the two formations of different age: Labyrinthina mirabilis, Kurnubia palastiniensis, Neokilianina rahonensis, Clypeina sulcata (Kimmeridgian-Lower Tithonian) and Parakoskinolina? jourdanensis, Montseciella arabica, Palorbitolina lenticularis, Falsolikanella danilovae (Barremian – Lower Aptian). Field observations and data obtained from studies on thin sections and polished slabs indicate that a large part of the Triassic (Ladinian-Lower Carnian) and Lower Cretaceous limestones from Gârda Seacă-Hodobana region, delimited on the geological maps 1:50 000 scale, sheets 56b (Poiana Horea) and 56d (Avram Iancu) (Bleahu et al., 1980; Dimitrescu et al., 1977), belong in fact to the Upper Jurassic carbonate succession.

Orbitolinid foraminifers in the Northwest Pacific: Their taxonomy and stratigraphy

Orbitolinid foraminifers supply important information for the understanding of Cretaceous marine biogeographic and paleoclimatic conditions. A pre-requisite for these palaeoenviromental interpretations is a sound taxonomy. The taxonomy of the orbitolinids from the Northwest Pacific has been controversial, and this paper aims at a taxonomic and stratigraphic revision of this group. Four orbitolinid species ("Palorbitolina lenticularis", Praeorbitolina cf. wienandsi, Mesorbitolina parva, and M. texana) have been recognized. Orbitolinids occurred almost continuously from the Late Hauterivian to the late Early Albian. Species belonging to the Praeorbitolina cormyi–Mesorbitolina aperta evolutionary lineage are most common, while dictyoconids are missing in the Northwest Pacific. Following the last occurrence ofM. parva in the Douvilleiceras mammilatum Zone of the Early Albian, no orbitolinids have been recognized in the Northwest Pacific. It is possible that provincialism in orbitolinid foraminifers occurred during the Early Cretaceous of the North Pacific.

EXPRESSION OF AN OCEANIC ANOXIC EVENT IN A NERITIC SETTING: LOWER APTIAN CORAL RUBBLE DEPOSITS FROM THE WESTERN MAESTRAT BASIN (IBERIAN CHAIN, SPAIN)

Abstract A singular lower Aptian lithofacies from the western Maestrat Basin (Iberian Chain) highlights the reaction of carbonate platform paleocommunities to natural disturbances of regional to global significance. It is composed mainly of sand- to cobble-sized coral rubble rigidly bound by Lithocodium aggregatum and is coeval with the early Aptian Oceanic Anoxic Event (OAE1a) and the intensified greenhouse conditions connected with this event. Severe storms induced by high atmospheric concentrations of CO2 had a recurrent catastrophic impact on coral populations, giving rise to sub-basin–wide coral rubble levels. Physical responses to elevated atmospheric CO2 levels, such as increased nutrient fluxes, together with low sedimentation rates, and the presence of a hard substratum, favored the mass occurrence of Lithocodium crusts, large flattened Palorbitolina lenticularis, and bioeroders such as lithophagid bivalves and endolithic sponges. These encrusted coral rubble deposits are here interpreted as reco...

Sedimentary evolution of an Aptian syn-rift carbonate system (Maestrat Basin, E Spain): effects of accommodation and environmental change

We report an integrated study of an expanded and relatively complete syn-rift continental to epeiric marine succession of Aptian age, cropping out in the western Maestrat Basin (eastern Iberian Chain). Four transgressiveregressive sequences are recognized throughout this mixed carbonate-siliciclastic succession, with excellent age control provided by ammonite biostratigraphic data. The transgressive systems tracts consist mainly of alternations of marls and limestones rich in orbitolinids. The regressive systems tracts are essentially characterized by wave- and tidally influenced siliciclastic and carbonate deposits, and by the development of carbonate platforms with rudists, corals, orbitolinids and green algae. Carbon and oxygen isotope curves were established in order to identify the global d13C perturbations related to the Early Aptian Oceanic Anoxic Event (OAE1a). These perturbations commence with a horizon of coral rubble encrusted by Lithocodium aggregatum and Bacinella irregularis with widespread large-sized discoidal Palorbitolina lenticularis. Associated d18O values indicate high-frequency cooling-warming climatic cycles. The fault-controlled rapid syn-rift subsidence recorded during this stage was the most important factor in producing accommodation. However, the major transgressions, sea level falls and biotic changes recorded in the eastern Iberian Chain are in agreement with those registered in other contemporaneous basins of the Tethys. Thus, the resulting sedimentary succession faithfully reflects the major oceanographic and climatically-driven global changes that characterized this stage albeit within a context established by regional tectonics. Hence, this well-documented record of the evolution of an Aptian epicontinental sea provides a useful comparative case study for the analysis of other Aptian epeiric sedimentary successions.

Revision of the orbitolinid foraminiferal genus Praeorbitolinoides Matsumaru 2005 from the Aptian of Hokkaido, Japan

A revision of Praeorbitolinoides japonica, established by atsumaru (2005) as new genus and species from the Aptian of Hokkaido (Japan), reveals that this taxon is identical with transitional forms between Praeorbitolina cormyi and P. wienandsi Schroeder 1964 known from the upper part of the early Aptian (Deshayesites deshayesi and Dufrenoyia furcata ammonite Zones) of the Tethyan realm. Praeorbitolina gr. cormyi-wienandsi and possibly Palorbitolina lenticularis represent at present the oldest orbitolinids found in Japan. The former genus is reported for the first time from the circum-North Pacific regions.

Salpingoporella? popgrigorei, a new species of Dasycladales (calcareous algae) from the Lower Aptian deposits of Pădurea Craiului (northern Apuseni Mountains, Romania)

A new dasycladalean alga Salpingoporella? popgrigorei n. sp. was identified in Pădurea Craiului Mountains (northern Apuseni, Romania) in the Lower Aptian limestone of the Valea Bobdei Member. The new alga was found within the external platform coarse bioclastic facies with fragments of corals, sclerosponges, bivalves (including rudists), gastropods, echinoderms, brachiopods, and bryozoans. The micropaleontological assemblage consists of foraminifera, calcareous algae, rare rivulariacean-type cyanobacteria, and some problematic microfossils. The deposits are Early Bedoulian in age, as clearly indicated by the orbitolinid foraminifera Orbitolinopsis pygmaea, Paracoskinolina sunnilandensis and Palorbitolina lenticularis. Salpingoporella? popgrigorei n. sp. is a medium-sized dasycladalean alga showing funnel-like laterals with an euspondyl arrangement. The laterals consist of two distinctive parts. The proximal part is narrow and flattened. The distal part widens relatively suddenly, and then narrows slightly before the final widening towards the exterior, in the place where the laterals most probably formed an assimilatory cortex. The distinctive features of the new species are represented by the shape of the laterals. The new Salpingoporella best resembles the Upper Hauterivian–Lower Barremian p.p. Salpingoporella genevensis (Conrad), especially due to the quadrangular aspect of the laterals in middle-deep tangential section. However, differences refer to the laterals’ general shape, and to the typical features of the laterals in deep tangential section of Salpingoporella? popgrigorei n. sp.

Palaeoenvironmental and palaeobiologic changes across the Barremian/Aptian boundary interval in the Tethys Realm, Mexico and Romania

Upper Barremian–lower Aptian rock sequences in northeast Mexico and the South Carpathians of Romania display palaeoenvironmental and palaeobiologic similarities. The upper Barremian deposits in both areas studied accumulated in shallow marine environments. A latest Barremian transgression was recorded only in Romania, where it is characterized by the prevalence of marly sequences that include mixed Tethyan and Boreal floras and faunas. In both study areas, late Barremian shallow-marine carbonate platforms were succeeded by deep-marine facies in the early Aptian. This was probably related to the early Aptian global sea-level rise. The Barremian/Aptian boundary in both areas is indicated approximately by the first occurrence of the foraminifer species Palorbitolina lenticularis, a bioevent that is coincident with the acme of the foraminifer group Orbitolina. In the early Aptian, Tethyan faunas and floras characteristic of the late Barremian were replaced by cosmopolitan assemblages, an event coincident with the first appearance in Romania of the ammonite genus Deshayesites.

Development of a Lithocodium (syn. Bacinella irregularis)-reef-mound- A patch reef within Middle Aptian lagoonal limestone sequence near Nova Gorica (Sabotin Mountain, W-Slovenia)

A Middle-Aptian (zone of Palorbitolina lenticularis) „patch reef“ of about 40 m maximum thickness with marked morphology was analyzed at the Sabotin Mountain near Nova Gorica. It is developed above an basal unit of superficial oolites within lagoonal sediments and is overlain by shallow subtidal to intertidal sediments which reveal short time periodically subaerial exposure and early diagenetic freshwater influxes (birds eyes, vadose silt, characeans). Above these sediments within the zone of Salpingoporella dinarica finebedded to platy, laminated bituminous limestones occur. The central part of the reef structure reveals an alternation of individual lenses of Lithocodium-boundstones and of rudist-beds (up to 4 m thickness) which are separated by coarse- to medium-grained, moderately to poorly sorted bioclastic sands. These facies types show also lateral interfingering and are concentrated in the central part of the buildup where the greatest thickness can be observed and where packstones, grainstones and boundstones prevail. The neighbouring lagoonal sediments which consist of mudstones and wackestones predominantly were analyzed in the so-called Sabotin-standardprofile which is located north of the patch reef at a lateral distance of about 300 m. Three vertical profiles (A = 90 m, B = 100 m, C = 64 m thickness) were analyzed. The middle profile B of greatest thickness is taken as reference profile and documents best the vertical facies development within the patch reef directly overlying a basal unit of peloidal packstones with superficial ooids. The patch reef itself is characterized by the faunal associations within the unit rich in Lithocodium and rudists. It is overlain by a subtidal unit of peloidal mudstones with very minor biogenic allochems. An intertidal unit above rich in birds-eyes and vadose silt is followed by fine-laminated black shales which are covering the general seqeunce of interfingering patch-reef - lagoonal sediments. Using different time lines (marker horizons) for correlation it can be shown that already very early differential compaction of fine-grained uncemented sediments in comparison to the core area of the patch reef is of great importance. The greater thickness of the patch reef itself is caused by an intensive early diagenetic marine phreatic cementation within the core zone and by the early fixing of sediment by Lithocodium aggregatum (syn. Bacinella irregularis) resulting in a greater resistivity against compaction. Furthermore a lagoonal side and an more open marine side of the patch reef can be determined. Lithocodium aggregatum is the main constructing organism within the buildup investigated, beginning with the incrustation of varying substrates and biogenic particles. Finally, a dense network of encrustation-sequences is formed interfingering with the general sedimentary textures intensively and resulting in larger „biogenic-cemented“ patches within the sediment. The correlation of the three profiles A, B, and C allows to reveal the history of differential compaction of the associated lagoonal sediments in comparison to the more massive patch reef limestones. It becomes obvious that the main compaction must have occurred within the time span of about 50 m sediment-deposition overlying the patch reef. Differential compaction resulted in differences in thickness of about 10 m from the patch reef (profile B) to the more lagoonal influenced sediments (profile A) within a lateral distance of about 50 m.

Stratigraphic distribution of Valanginian–Early Aptian shallow-water benthic foraminifera and algae, and depositional sequences of a carbonate platform in a tectonically-controlled basin: the Organyà Basin, Pyrenees, Spain

The Early Cretaceous Urgonian platform carbonates of the Organyà Basin are divided into five depositional sequences for which a foraminiferal distribution chart has been plotted. Each depositional sequence is characterised by its faunal content: Zergabriella embergeri, Valdanchella miliani and Pfenderina neocomiensis characterise sequence OR-0, which is Valanginian in age; Cribellopsis neoelongata characterises the upper part of sequence OR-1; Valserina bronnimanni, Eopalorbitolina charollaisi and Palorbitolina lenticularis characterise sequence OR-2; and Neotrocholina friburgensis characterises sequence OR-3, all of which are Late Barremian; andPalorbitolina lenticularis , the rudist species Pachytraga paradoxa and planktonic foraminifera from theGlobigerinelloides blowi Zone characterise sequence OR-4, which is probably Early Aptian. Other species characteristic of the Hauterivian–Early Barremian have not been found in these sediments. There is probably an important sedimentary gap spanning the interval between OR-0 and OR-1 depositional sequences within the Organyà carbonates.

PALORBITOLINA LENTICULARIS FROM THE NORTHERN ADRIATIC REGION: PALEOGEOGRAPHICAL AND EVOLUTIONARY IMPLICATIONS

Samples bearing Palorbitolina were obtained from three localities on the islands of Cres and Losinj in the northern Adriatic. Although a relatively small number (<60) of specimens were studied, the size of the embryonic chamber and test diameters of Palorbitolina lenticularis indicate a Lower Aptian age. This is confirmed for the Adriatic carbonate platform by the presence of Lower Aptian index taxa. Both embryonic chamber and test diameter variation are pronounced. No change was observed concerning the relationship between stratigraphic horizon and the embryonic chamber diameter. A proportional relationship between the size of the embryonic chamber and the test was determined. These data show that before it appeared on the Adriatic carbonate platform, Palorbitolina already colonized the predominantly mixed clastic-carbonate environments of the Mediterranean, as has been suggested by Velic & Sokac (1978). Although an essentially westwards water circulation during the late Barremian and early Aptian probably aided Palorbitolina in colonization of the Tethyan realm, it can neither explain the simultaneous existence of Palorbitolina in different and remote parts of the Tethys nor its dispersal, which must have been very rapid.

Bioecostratigraphy of the Shu’aiba Formation, Shaybah field, Saudi Arabia

ABSTRACT The Aptian Shu’aiba Formation forms a major carbonate reservoir in the Shaybah field of eastern Saudi Arabia. Lack of exposures and poor seismic data have forced the cored intervals to be fully exploited to provide evidence of the depositional environment and layering of the reservoir rocks and associated lithofacies. Rudist, foraminiferal and coccolith evidence indicates an Aptian age for the entire Formation, most of it being early Aptian. A major unconformity at the top of the Shu’aiba separates it from the overlying Nahr Umr Formation. Rapid biofacies variations suggest possible sequence boundaries within the Shu’aiba Formation. Semi-quantitative macropaleontological and micropaleontological analyses indicate significant paleoenvironmentally influenced lateral and vertical bioassemblage variations. Lagoon, rudist-associated back-bank, bank-crest and fore-bank, and upper-ramp depositional environments have been interpreted, of which the bank represents the gradual amalgamation of earlier isolated rudist shoals. Integrating the micropaleontological analyses with rudist assemblages has facilitated the prediction of rudist-associated reservoir facies. Variations in the micro- and macrofacies permit the Formation to be divided into three layers. (1) The “lower Shu’aiba” (without rudists) is dominated by a regionally extensive, moderately deep marine planktonic foraminiferal/algal association of Palorbitolina lenticularis-Hedbergella delrioensis-Lithocodium aggregatum and the benthonic foraminifera Debarina hahounerensis, Praechrysalidina infracretacea, Vercorsella arenata and rotalids. (2) The “middle Shu’aiba” shows the significant lateral and vertical differentiation of a rudist-rimmed shallow carbonate platform typically associated with a marine highstand. A predominance of rudist species Glossomyophorus costatus and Offneria murgensis occurs together with Lithocodium aggregatum, Palorbitolina lenticularis, Trocholina spp. and miliolid foraminifera. (3) The “upper Shu’aiba” represents an expansion of the lagoon (associated with a marine transgression), and a predominance of Agriopleura cf. blumenbachi and A. cf. marticensis rudists, together with Debarina hahounerensis, Praechrysalidina infracretacea and Vercorsella arenata. The localized distribution of the rudist Horiopleura cf. distefanoi in association with corals, is a feature of the eastern flank of the field. A coarse assemblage-based biozonation for the Shu’aiba has been proposed, but a detailed scheme is precluded by rapid diachronous biofacies variations across the Shaybah field. In addition to the major biocomponent assemblages, minor variations reveal high-frequency depositional cycles that may assist in the interpretation of the distribution and correlation of reservoir facies. The identification of bioassemblages, and the paleoenvironmental interpretation of formation micro-imager logs from vertical cores in exploration wells, has assisted the calibration of images from uncored horizontal development wells.

Stratigraphic evidence for an Early Aptian sea-level fluctuation: the Graua Limestone of south-eastern Ethiopia

The occurrence of a thin band of marine limestone (Graua Limestone) within a thick succession of fluviatile sandstones in south-eastern Ethiopia is direct evidence of flooding of part of the East African craton (Horn of Africa). According to the presence of abundant orbitolinid foraminifers (Palorbitolina lenticularis Blumenbach andPraeorbitolina cormyi Schroeder), the age of the Graua Limestone can be referred to the Early Aptian. Stratigraphy and palaeogeographic reconstructions for the Early Cretaceous in the surrounding regions (Kenya, Somalia, Yemen, Socotra, Oman, Syria, Lebanon, Israel, Egypt and Libya) show that the Early Aptian transgression was of regional extent. Our data seem to confirm that this transgression was of relatively short duration. This pulse cannot be related to tectono-eustatic mechanisms, which are too slow. A short-lived event should be invoked: either a regional tectonic pulse or the desiccation of the proto-South Atlantic.

Lower Cretaceous Shallow-Marine Sedimentation and Biota on Dinaric Carbonate Platform between Logatec, Krka and Kolpa (Southeastern Slovenia)

On the basis of detailed biofacies and microfacies analysis of several cross-sections in the southeastern Slovenia the biostratigraphic subdivision of the Lower Cretaceous stratigraphic sequence has been made. In the study area the Lower Cretaceous involves five cenozones and four subzones, namely: Clypeina ? solkani, Salpingoporella muehlbergii, Salpingoporella dinarica, Orbitolina (Mesorbitolina) ex gr. texana and “Valdanchella” dercourti (cenozones) as well as Favreina salevensis + Salpingoporella annulata, Epimastopora ? cekici + Cuneolina tenuis, Orbitolinopsis capuensis and Palorbitolina lenticularis (subzones). The sediments and fossils in the inner part of the Dinaric carbonate platform point at more or less continual sedimentation, chiefly in very shallow water environments from intertidal to shallow subtidal. The continuity of the sedimentation was interrupted by sporadic intensified intertidal movements and short-lasting emersions.

Lower Aptian AmmonitinaPseudohaploceras liptoviense (Zeuschner) in the Cumburindio Formation (Southwestern Mexico)

The presence of Pseudohaploceras liptoviense (Zeuschner) associated to Palorbitolina lenticularis (Blumenbach)permits to interpret an Early Aptian age for the middle part of the lower member of the Cumburindio Formation nearby Turitzio (Michoacan). It is proposed that Böse's species “Desmoceras” aguilerae, “D.” alzatei, “D.” burckhardti, “D.” durangense, “D.” tenuicostatum and “D.” wielandi are younger synonymous of Pseudohaploceras liptoviense (Zeuschner). An alternative interpretation as Mexican colonizers very close to Pseudohaploceras liptoviense (Zeuschner) cannot be conclusively disregarded.

Orbitolina episodes in carbonate platform evolution: the early Aptian model from SE Spain

Among the Orbitolininae, Palorbitolina lenticularis (Blumenbach) is a common facies marker in Upper Barremian-Lower Aptian shallow water Mesogean deposits and was hitherto ascribed to specific, but contrasting paleoenvironments within the carbonate platform facies suites. The Albacete-Prebetic area (SE Spain) illustrates a model in which the Palorbitolina facies spread over the whole platform system. The development of the Palorbitolina sediments coincided with a transgressive trend at the end of an important terrigenous period. This model could also be applied to similar Middle Crotaceous “Orbitolina” facies.

Cretaceous Orbitolinidae (Foraminifera) from Onshore and Offshore South-West England

Abstract. The occurrence of orbitolinids in onshore and offshore South-West England is fully documented for the first time. Palorbitolina lenticularis is known from the Early Aptian — Late Barremian sediments of the offshore Fastnet Basin, and may also occur in the Aptian Farringdon Greensand. Late Albian Orbitolina sefini occurs in the Wolborough Limestone of Devon, whilst at Haldon, Devon, the orbitoline faunas are of Early Cenomanian age and referable to Orbitolina cf. concava. The orbitolinids from the Upper Greensand of the south-east Devon coast and the Fastnet Basin cannot be precisely identified, but belong to the Late Albian — Early Cenomanian O. sefini - O. concava plexus. Previous records of Orbitolina from the Upper Greensand at Wilmington are shown to be mistaken. These records are in fact referable to the sponge Porosphaera. The precise identification of some of the orbitolinids from South-West England supports the ages of the Wolborough Limestone and Haldon Sands suggested by Hamblin &amp;amp; Wood (1976). It is thought that orbitolinids migrated from Iberia to South-West England via the South-West Approaches during the Late Albian.

Microfacies and diagenesis of lower and middle cretaceous carbonate rocks of NW-Yugoslavia (Slovenia, Trnovo area)

A profile of about 1400 m thickness near the village of Trnovo in the Trnovo forest in SW-Slovenia was studied for the microfacies and diagenetic development of the carbonate rocks. Because of the detailed biostratigraphic subdivision being just in improvement, the interval from the problematic Jurassic/Cretaceous to the Tertiary boundary (Berriasian-Cenomanian, fault, Senonian) was subdivided into ten zones and several subzones. These subdivisions are of practical use and can be found in profiles studied in other areas of SW-Slovenia and Istria as well. The data are based on field observations, thin sections and acetate peels. The following development can be recognized: (1) During the Berriasian(?)-Hauterivian a shallow-marine to intertidal restricted environment was established on the coherent Dinaric Carbonate Platform. This is indicated by low faunal diversity and numbers as well as the common occurrence of marine and meteoric vadose cements, birdseyes and algal-layers.Clypeina jurassica, Bankia striata, Favreina salevensis, and trocholinid foraminifera are chacteristic of the lowermost part (Uppermost Jurassic?, Berriasian-Valanginian) of this section. (2) In the Barremian-Aptian a lagoonal environment with patch reefs was established, characterized by normal marine conditions. High faunal and floral diversity and large numbers occur (hydrozoans, corals,Palorbitolina lenticularis, Salpingoporella dinarica). During this time period the platform was divided into smaller tectonic units with different facies development. (3) An open marine ingression from the Slovenian Basin occurred in the Albian, indicated by dolomitic limestones rich in sponge spicules and silica nodules and layers. (4) In the Cenomanian, mainly bioclastic sands (rich inOrbitolina conica) and micritic limestones (withPithonella) were deposited in alternation with micrites rich in ostracods and limestones containing birdseyes, vugs, and microsparite. This indicates a strong interfingering of different facies on a gently dipping ramp, probably due to sea level fluctuations. (5) The Turonian is missing in the section analyzed due to a fault. (6) In the Senonian bioclastic sands rich in fragments ofSabinia sp. were deposited around rudist mud mounds formed in inner shelf areas under normal marine conditions. Eocene flysch overlies the sequence and influences it diagenetically by silica authigenesis in the upper decimeters of the underlying limestones.

Présence d'une association micropaléontologique de la biozone à Praeorbitolina cormyi (Aptien inférieur) dans l'Urgonien de Tanzanie méridionale. Implications paléogéographiques au niveau de la marge indienne de l'Afrique

Outer shelf calcarenites from Urgonian limestones (Kiturika beds) outcropping in the southern coastal basin of Tanzania yield in the localities of Lisongele Hill and Mavudyi Gorges a micropaleontological assemblage from Early Bedoulian (upper part) -Late Bedoulian (lower part) with, particularly, Praeorbitolina cormyi Schroeder, Palorbitolina lenticularis (Blum.), ? Choffatella decipiens Schlumb., Archaeolithothamnium rude Lem. and Marinella lugeoni Pfender. These limestones overlie green silts containing Late Bedoulian Ammonites as Valdedorsella akuschaense Anth. and Cheloniceras cf. cornuelianum d'Orb. The above-mentioned microfauna shows a certain originality within its East-African and Arabian paleobiogeographic context : different from all known the assemblages of Aptian carbonate from Somalia, Ethiopia, Oman and Saudi Arabia where Praeorbitolines never have been observed, it shows South-Iranian affinities. Its migration southward to such meridional latidudes might have traversed marginal parts of the later Indian microplate, still bound to Africa at this time.