Open Shelf Environment Research Articles

Biostratigraphic analysis of a Late Pleistocene to Holocene section from Punta Pescador, eastern Venezuela

A biostratigraphic study was undertaken on a shallow borehole drilled to 90 meters in the easternmost Orinoco Delta, Venezuela. Twenty-eight samples were analyzed for palynomorphs and foraminifera. Palynomorphs were recovered in all except one sample consisting of 178 entities. Foraminifera assemblages of low diversity were recovered in 17 of the 28 samples. The analysis provides some insight into the vegetation, climate, and depositional history allowing comparisons with other Late Pleistocene to Holocene studies in the northern South America region. The Late Pleistocene to Early Holocene transition is marked by an unconformity, where the vegetation changes from a diverse flora of Mauritia flexuosa, grasses (Poaceae), ferns, and mangroves (Rhizophora, Avicennia) to one dominated by Rhizophora around 10,000 years BP. This transition also contains reworked palynomorphs and abundant black wood (inertinite), indicative of erosion and oxidation. The absence of foraminifera suggests an exposed continental shelf and lowering of sea level. The Early Holocene mangrove flora is replaced by vegetation dominated by Mauritia flexuosa, with Symphonia globuliflora, grasses, and ferns. The palynological signature for the upper 42 m of the section compares favorably with a previous study of the Holocene in the Orinoco Delta. Radiocarbon dating indicates there is an unconformity or condensed section at the vegetation change, representing as much as 5500 ± years. Foraminifera indicate an open shelf environment immediately above this horizon followed by a significant shallowing to nearshore transitional environments near the top of the section. Local climate and/or human influence may have been a factor in the abundance of Mauritia flexuosa as suggested by other studies.

Microfacies analysis and Depositional Basin Model of the Upper Cretaceous, Kurdistan Region, Northern Iraq

This study focuses on the Upper Cretaceous system in the Zagros fold and thrust belt in the Kurdistan Region / Iraq. The impression of this study is created by the variety of formations, facies change, and age of the Cretaceous formations, as well as the different consequences of the contact situation between the formations, particularly the Qamchuqa-Bekhme and Kometan-Shiranish contacts formations. Through investigation, evaluation, and combination of results from Lithostratigraphy and Microfacies of seven sections in various locations of KRI/ Iraq, new paleogeography of the Late Cretaceous of Northern Iraq is constrained. The microfacies of entire Late Cretaceous formations in different sections outcome 16 sub-microfacies types demonstrating open marine deep shelf environment of Shiranish Formation, the entire reef (back-reef, fore-reef, reef body) environment of Bekhme Formation and pelagic open marine ramp depositional environment of Kometan Formation. The output results of stratigraphy and microfacies of Late Cretaceous depositional successions in the Kurdistan Region are paleogeography maps reconstruction. During the Turonian to Early Santonian periods, the Kurdistan Region and northern Iraq were pre-subduction basins due to the presence of open marine outer ramp carbonate of the Kometan Formation in the east (Sulaimaniyah province exceeding Hizop area) and inner shelf of Tanuma and Khasib formations in the center and west (Erbil province). Major regression and unconformities covered the West of the study region during the Middle-Late Santonian; the result of this regression degraded the entire inner shelf facies that deposited during Turonian-Early Santonian periods. During the Early-Middle Campanian, a foreland basin emerged in the extreme northeastern and the Kurdistan Region, which was covered by open marine of the Shiranish Formation and reef platform of the Bekhme Formation. The Kurdistan Region was an active foreland basin margin in the Upper Campanian-Maastrichtian, with a greatly expanded Tanjero Formation, an Aqra reef in the north, and an open marine Shiranish Formation in the center and west.

Bio-sequence stratigraphy of the Neogene: an example from El-Wastani gas field, onshore Nile Delta, Egypt

Abstract. Due to modern hydrocarbon development and exploration activities throughout the onshore Nile Delta of Egypt, a high-resolution biochronologic sequence stratigraphy of the Neogene sequence was conducted to illustrate the gas-bearing reservoirs' depositional sequences. Our study used a multidisciplinary approach comprising biostratigraphy, facies analysis, geophysical logs, and seismic data to shed light on the Neogene stratigraphic framework. The biostratigraphic analysis of planktonic foraminifera and calcareous nannofossils allowed the recognition of six zones and/or subzones and nine zones, respectively. An open-shelf environment was suggested for the Middle–Upper Miocene Sidi Salem Formation, while the Upper Miocene Qawasim and Abu Madi formations were deposited under stressed environmental conditions interpreted as estuary facies. The Lower Pliocene (Zanclean) succession deposited in the middle to outer shelf domains, including the upper-bathyal environments. Seven depositional sequences bounded by six major sequence boundaries were recognized from Serravallian to Zanclean times. These boundaries significantly influenced changes in reservoir properties and architecture of the incised valley fills. The sea-level oscillations are interpreted by correlating the sequence boundaries and flooding surfaces with global eustatic charts.

Silicon isotopic compositions of dissolved silicic acid in pre- and post-diatom oceans

Silicon (Si) isotopic compositions of marine authigenic and biogenic silica deposits are valuable proxies for reconstructing Si cycling in the Earth’s oceans. Recent studies predict that pre-diatom-controlled oceans would have Si isotopic compositions of dissolved silicic acid (δ30SiDSi) that were enriched in heavier isotopes, ranging from +1.9‰ to +4.6‰, relative to NBS28 silica. This predicted range is based on calculations that assume a fractionation factor between sponges and silicic acid (Δ30Sis) in ancient (or modern) ocean waters of −3.8‰. Recently published data on sponge silicon isotopic compositions (δ30Si) and Δ30Sis, indicate that a Δ30Sis value for ancient sponges is more accurately calculated by applying corrections based on Michaelis–Menten enzyme kinetics. Predicted Δ30Sis values for pre-diatom sponges using the Michaelis–Menten enzyme kinetics corrections are −4.6 ± 0.1‰, roughly 0.9‰ lower than previous predictions. The new Δ30Sis value, applied to silicon isotopic compositions of silicified mid-Paleozoic and mid-Cenozoic coral fossils, allows for the calculation of δ30SiDSi between +2.0‰ and +2.3‰ for a Paleozoic open shelf environment. Applying the model to silicified mid-Cenozoic coral fossils, using Δ30Si values based on diatoms (−1.1‰) and sponges (−3.0 to −3.5, corresponding to DSi of 10 to 20 µM), resulted in an estimation of ocean’s δ30SiDSi of +0.8 to +2.9‰. The mid-Cenozoic samples highlight the strong control of Δ30Si on the calculated values for δ30SiDSi. The results show the promise of these approaches in understanding the ocean water δ30SiDSi from Si isotope abundances measured in abiotic precipitates where DSi and Δ30Si are accurately known.

Lithological-genetic features of Starorusskaya, Vasileostrovskaya and Siverskaya formations of the Upper Vendian-Lower Cambrian Baltic-Ladoga Monocline

Research subject. Sections of the Upper Vendian-Lower Cambrian, opened at the beginning of the XXI century by wells Avloga-12R, Utkina Zavod - 1 and Thais-2 with a depth of 150-370 m, in the north and in the central part of the Leningrad region. Methods. The analysis of the structural and textural features of the rocks of the contact layers, the distribution of allotigenic (quartz, feldspar) and autigenic (pyrite, siderite, glauconite) minerals in them allowed us to supplement the characteristics of the Old Russian, Vasileostrovsky and Siverskaya formations previously isolated in these wells. The use of the structural-genetic method made it possible to clarify the volumes and boundaries of the formations, to prove the absence in the section of the Lomonosov formation, previously isolated in the well Thais-2. Results. Based on the reconstruction of sedimentation conditions and settings, the development of sedimentation processes over time, three transgressive-regressive sequences of layers - cyclothemes were established in sections. The first corresponds to the Old Russian, the second - Vasileostrovskaya, and the third - Siverskaya formation. It is shown that in the studied part of the paleobasin at the end of the Vendian-the beginning of the Cambrian, there were open shelf environments (an area of mobile shallow water with underwater shafts (zone Y), an area of relative deep water with background and storm sedimentation (zone X) and a transitional zone of patchwork sands between X and Y with a variable hydrodynamic regime. The maxima of transgressions corresponding to the development of the deepest water environments occurred in the middle of the Old Russian, Vasileostrovsky and Siversky time, and the maxima of regressions marked by shallow water deposits belong to the end of these time intervals. According to isochronous levels - maxima of transgressions and regressions, correlation of well sections was performed.

A new marrellomorph arthropod from southern Ontario: a rare case of soft-tissue preservation on a Late Ordovician open marine shelf

AbstractOrdovician open marine Lagerstätten are relatively rare and widely dispersed, producing a patchy picture of the diversity and biogeography of nonmineralized marine organisms and challenging our understanding of the fate of Cambrian groups. Here, for the first time, we report soft-bodied fossils, including a well-preserved marrellomorph arthropod, fragmentary carapaces, and macroalgae, from the Late Ordovician (Katian) Upper Member of the Kirkfield Formation near Brechin, Ontario. The unmineralized elements and associated exceptionally preserved shelly biota were entombed rapidly in storm deposits that smothered the shallow, carbonate-dominated shelf. The marrellomorph, Tomlinsonus dimitrii n. gen. n. sp., is remarkable for its ornate, curving cephalic spines and pair of hypertrophied appendages, suggesting a slow-moving, benthic lifestyle. Reevaluation of marrellomorph phylogeny using new data favors an arachnomorph affinity, although internal relationships are robust to differing outgroup selection. Clades Marrellida and Acercostraca are recovered, but the monophyly of Marrellomorpha is uncertain. The new taxon is recovered as sister to the Devonian Mimetaster and, as the second-youngest known marrellid, bridges an important gap in the evolution of this clade. More generally, the Brechin biota represents a rare window into Ordovician open marine shelf environments in Laurentia, representing an important point of comparison with contemporaneous Lagerstätten from other paleocontinents, with great potential for further discoveries.UUID: http://zoobank.org/884589d0-08f7-4398-ab42-1f5d459be9e9

The Rigelj Formation, a new lithostratigraphic unit of the Lower Permian in the Karavanke Mountains (Slovenia/Austria)

Abstract The Rigelj Formation is a new lithostratigraphic unit of the Lower Permian Rattendorf Group in the Karavanke Mountains. The Formation is up to 105 m thick and mainly composed of siliciclastic and fossiliferous carbonate sediments that are entirely of shallow-marine setting. Conglomerates are interpreted as shoreface deposits, sandstones as deposits of the upper to lower shoreface, and fossiliferous siltstones as offshore deposits. Fossiliferous limestones were deposited in a shallow, open-marine shelf environment of moderate to low energy (wackestone, floatstone) and strong water turbulence (packstone, rudstone). The siliciclastic and carbonate lithotypes form some well-developed backstepping cycles starting with conglomerates, overlain by sandstones, siltstones and fossiliferous limestones that formed in an open shelf environment without siliciclastic influx. Similar sedimentary cycles are developed in the Grenzland Formation of the Carnic Alps. The fusulinid fauna indicates that the Rigelj Formation ranges in age from the late Asselian to the middle Sakmarian. In the western Karavanke Mountains and near Trögern, the Lower Permian lithostratigraphic succession is very similar to the succession in the Carnic Alps with Tarvis Breccia resting on the Trogkofel Limestone and the Goggau Limestone. Unlike this, in the central part of the Karavanke Mountains (Dovžanova Soteska–Mt. Pleschiwetz/Plešivec area) the Rigelj Formation is erosively overlain by the Tarvis Breccia. The stronger diversification of the sedimentary environments within the Karavanke-Carnic Alps in the Lower Permian after the uniform sedimentation in the Upper Carboniferous can be attributed to block-faulting.

Cambrian stratigraphy (Series 2 to Miaolingian) of the El Sahuaral area in central Sonora, Mexico: Biostratigraphic implications

The lower and middle Cambrian strata exposed in the state of Sonora, Mexico, consists of sequences of quartzarenite, limestone, shale and dolomite exposed in several localities, mainly in the northwestern and central regions of Sonora. Approximately 800 m interval of Cambrian marine sedimentary rocks are exposed in the El Sahuaral area, a new Cambrian locality in central Sonora. The sedimentary succession of these marine facies is divided into five lithostratigraphic units previously documented in Mexico: Proveedora, Buelna, Cerro Prieto, El Gavilán and El Tren formations. The Proveedora Formation is the oldest sequence of Cambrian strata in the region and consists of a 168 m thick sequence of bioturbated, fine-grained quartzarenite. The Buelna Formation conformably overlies the Proveedora Formation in the El Sahuaral and adjacent areas and consists of 70 m of interbedded limestone and shale, with abundant fragments of olenellid trilobites from either the Bristolia mohavensis or Bristolia insolens zones (Series 2, Stage 4). The overlying Cerro Prieto Formation is composed of a 70 m thick sequence of recrystallized oolitic limestone with possible fragments of Amecephalus arrojosensis, suggesting the Amecephalus arrojosensis Zone (uppermost Series 2, Stage 4). The El Gavilán Formation conformably overlies the Cerro Prieto Formation with a thickness of 225 m; it is composed of interbedded limestone and shale deposited in a marine open shelf environment, with abundant fauna of the upper Ehmaniella Zone (Altiocculus Subzone), Ptychagnostus praecurrens - Ptychagnostus gibbus Zone (Miaolingian Series, Wuliuan Stage). The El Tren Formation, reported by the first time in central Sonora, conformably overlies the El Gavilán Formation and consists of 250 m thick sequence of dolomitic limestone with unidentified trilobite fragments. The Cambrian deposits of central Sonora present marine facies that vary from the littoral zone to open marine shelf, accumulated in the western part of the North American craton and contains an abundant and diverse biota comprised by cyanobacteria, poriferans, brachiopods, trilobites, and echinoderms.

El registro más austral de la Fauna Aseptella-Tuberculatella / Rhipidomella-Micraphelia (Serpukhoviano tardío-Bashkiriano) en la cuenca Calingasta-Uspallata, Argentina

The Agua del Jagüel Formation crops out in the southernmost part of the Calingasta-Uspallata basin, in central western Argentina. The lower part of the unit is characterized by a glacigenic sequence with diamictites and mudstones with dropstones. In the latter, elements of the Aseptella-Tuberculatella/Rhipidomella-Micraphelia Fauna (AT/RM Fauna), such as the brachiopods Rhipidomella discreta Cisterna, Micraphelia indianae Simanauskas and Cisterna and Orbiculoidea? sp., the gastropods Murchisonia? sp., and Glabrocingulum (Stenozone)? sp., the bivalve Nuculanidae indet., rugose corals, and indeterminate fragments of nautiloids and hyolithids, have been identified. The importance of this fauna mainly resides in its paleoenvironmental and biostratigraphic implications. AT/RM Fauna is characteristic of restricted environments with relatively low concentrations of oxygen and nutrients in the seafloor, which is consistent with the glaciomarine sequences in fjord-type coasts suggested for the Agua del Jagüel Formation. The relatively low diversity of the fauna in this unit compared to that defined in the El Paso Formation, located further north in the basin, might suggest more restricted sectors for benthic colonization, related to the paleovalle’s isolation from oceanic waters. The postglacial mudstones with marine invertebrate faunas of late Serpukhovian-Bashkirian age would have been deposited in relatively restricted (palaeofjord) part of the Uspallata-Calingasta basin as well as in open shelf environments. The marine flooding over drastically different coast configurations and the availability of nutrient and oxygen in the water column would have propitiated the development of faunas with important differences in the taxonomic composition and the paleoecological structure (AT/RM and Levipustula Faunas) occurring at the same time interval. Radiometric data in Agua del Jagüel Formation and paleontological records in the glacial-postglacial sedimentary succession in the basin (marine invertebrate faunas, palynomorphs and plants) are the most important tools to adjust the timing of the postglacial transgression. This information herein presented complements the scheme proposed for the Carboniferous sequences throughout the central western of Gondwana but is not sufficient to assign a more precise age of the fauna studied within the late Serpukhovian-Bashkirian interval.

Glaucony authigenesis, maturity and alteration in the Weddell Sea: An indicator of paleoenvironmental conditions before the onset of Antarctic glaciation

Three types of glaucony grains were identified in the late Eocene (~35.5–34.1 Ma) sediments from Ocean Drilling Program (ODP) Hole 696B in the northwestern Weddell Sea (Antarctica). The grains are K2O-rich (~7 wt%) and formed by smectite-poor interstratified ~10 Å glauconite-smectite with flaky/rosette-shaped surface nanostructures. Two glaucony types reflect an evolved (types 1 and 2 glaucony; less mature to mature) stage and long term glauconitization, attesting to the glaucony grains being formed in situ, whereas the third type (type 3 glaucony) shows evidences of alteration and reworking from nearby areas. Conditions for the glaucony authigenesis occurred in an open-shelf environment deeper than 50 m, under sub-oxic conditions near the sediment-water interface. These environmental conditions were triggered by low sedimentation rates and recurrent winnowing action by bottom-currents, leading to stratigraphic condensation. The condensed glaucony-bearing section provides an overview of continuous sea-level rise conditions pre-dating the onset of Antarctic glaciation during the Eocene-Oligocene transition. Sediment burial, drop of O2 levels, and ongoing reducing (postoxic to sulphidic) conditions at Hole 696B, resulting in iron-sulphide precipitation, were a key limiting factor for the glauconitization by sequestration of Fe2+.

Paleoecology of cambrian communities of central Sonora, Mexico: Paleoenvironmental and biostratigraphic considerations

Cambrian marine ecosystems in Mexico are constituted by diverse taxonomic groups, including trace fossils, poriferans, brachiopods, hyolithids, trilobites, echinoderms and other problematic fauna. The present research aims to identify and analyze the paleoecological characteristics of the marine ecosystems of central Sonora, Mexico; specifically, in the San José de Gracia area where the Proveedora, Buelna, Cerro Prieto and El Gavilán formations are exposed. In this study some ecological indices have been applied, such as Simpson's dominance and evenness, Shannon H′ diversity, Menhinick species richness and Chao total species richness. Guilds and adaptive strategies show how different environments were occupied through time. The present work constitutes the first paleoecological work for the marine ecosystems of Cambrian strata in Mexico.The Proveedora Formation consists of fine-grained quartzarenite with high bioturbation and trace fossils, it shows a low species richness (4) and evenness, where suspension feeders are dominating. The paleoenvironmental analysis of this unit indicates a sandy environment, such as a coastal and sublittoral areas, sandbars or delta front. The Buelna Formation is composed of limestone interbedded with shale, containing algae, brachiopods, salterellids, hyolithids, trilobites and echinoderms. Mostly it possesses a medium species richness (9) and intermediate evenness. Functional groups are dominated by primary producers and suspension feeders. The paleoenvironmental analysis of this unit indicates a shallow marine environment. The Cerro Prieto Formation consists of an oolitic limestone strongly recrystallized with few fossils, mainly brachiopods and trilobites. It has a low species richness (2) distributed in an unevenness way since only one species occupies the whole site. It indicates a shallow marine environment of high energy. The El Gavilán Formation consists of a thick sequence of shale interbedded with limestone, having abundant fossils like poriferans, brachiopods, hyolithids and trilobites, with a species richness (16) and with a high evenness, exhibiting a great variety of functional groups, dominating the suspension feeders and nektobenthic forms. The paleoenvironmental analysis of this unit shows an open shelf environment.

Earliest Triassic Conodonts of Gua Panjang, Merapoh, Pahang and their Bearing towards Permian-Triassic Mass Extinction in Malaysia

A single sample from the logged section at eastern side of Gua Panjang limestone hill, southwest of Kampung Kubang Rasa Village, Merapoh, has yielded 5 very important conodont species. They are Hindeodus parvus erectus, Hindeodus parvus parvus, Hindeodus latidentatus latidentatus, Hindeodus latidentatus praeparvus, Hindeodus postparvus, Hindeodus eurypge and Isarcicella staeschi. These Early Triassic conodonts were obtained in a bioclastic dolostone sample, located 2.5 m above bioclastic grainstone which yielded Late Permian foraminifera. The conodonts found were given Conodont Alteration Index (CAI) scale of 5, consistent with the heating of Main Range granitoid during Indosinian Orogeny. Limestone harbouring basal Triassic conodonts in Gua Panjang is interpreted to be deposited in an open shallow marine shelf environment.

Devonian–Carboniferous brachiopods and biostratigraphic findings from the Kangal Phyllite–Slate Formation (greenschist), Sivas, Turkey

The Kangal Phyllite-Slate Formation forms the basement rocks in Kangal-Çetinkaya-Alacahan-Divriği (Sivas). These late Paleozoic phyllite-slate associations occupy a large area, possibly composed of Early Paleozoic sediments in its lower part. The lower levels (Bakırtepe Metaquartzite Member; 0-500 m) and uppermost levels comprise the Düzce Recrystallized Limestone Member (0-25 m). The lower boundary is invisible and the upper boundary is unconformably overlain by the Kıratgediği Limestone (late Jurassic- early Cretaceous). The studied brachiopod fauna, about 400 specimens, was collected from the 150-m-thick uppermost part of the greenschist sequences in the Kulluk Hill area, Elkondu village, 25 km east of Kangal. Some bryozoans, corals, trilobites, and crinoids were also retrieved. Five fossiliferous levels belonging to the lower, middle, and upper Devonian, and the lower Carboniferous stages were assigned as follows: (1) Pragian-Emsian; (2) Eifelian-Givetian; (3) Fransian-Famennian-Etroeungtian (Strunian); the Devonian- Carboniferus boundary; (4) lower Carboniferus: Tournaisian and Viséan stages, based on the brachiopods; and (5) upper Permian: from Roadian to Capitanian stages, based on the foraminifera and algae in the Düzce recrystallized limestone. This level indicates a sedimentary interruption. All of these fossils and fossiliferous beds were correlated with the type localities and related beds. The Kangal brachiopods are similar to those of Şafaktepe, the Gümüşali Formations (middle and upper Devonian), and the Ziyarettepe Formation (lower Carboniferous) of the eastern Taurides. The brachiopod community is closely affiliated with the Mediterranean, northwest European Faunal Provinces, part of the Transcaucasian Region, and microfossils of the Düzce recrystallized limestone belonging to the Tethyan Region. Brachiopod fauna and lithologic characteristics of the formation suggest that the upper (150 m) greenschist sequences were deposited in an open shelf environment under warm sea conditions in the Late Paleozoic era.

Silicificaciones selectivas en <em>Thalassinoides</em> y otras estructuras biogénicas asociadas a calizas de plataforma marina y <em>hardground</em> (Albiense inferior, Sonabia, Cantabria)

El presente trabajo estudia los diferentes tipos de sílex que aparecen en la Formación Calizas de Oriñón (Aptiense superior-Albiense inferior), en un zona concreta de la costa oriental de Cantabria (Liendo-Castro Urdiales), debido a su gran abundancia y espectacularidad. Las rocas que los incluyen son principalmente biocalcarenitas (wackestones/packstones de pellets, fragmentos de equinodermos, ostreidos, foraminíferos y espículas calcáreas o silíceas calcificadas), siendo el ambiente de depósito marino de plataforma abierta, y existiendo un hardground regional, donde las silicificaciones son diferentes. La fuente de la sílice proviene de la calcitización o disolución de las espículas de esponjas silíceas. 
 Se determina que la gran mayoría de sílex (mosaicos de cuarzo micro-microcriptalino y calcedonita principalmente), se forman por la silicificación selectiva de estructuras biogénicas, siendo las galerías de Thalassinoidespreferentemente silicificadas, debido a que en su relleno existe mayor proporción de materia orgánica y mayor porosidad y permeabilidad. En las calizas que soportan el hardground además de las silicificaciones selectivas sobre fósiles (rostros de belemnites, ostreidos y equínidos), la sílice se acumula de forma importante en huellas de alimentación y rellenos de perforaciones, dando lugar a su vez a costras sobre bioturbaciones y perforaciones que a pesar de su importancia no han podido ser clasificadas. 
 La silicificación de todas las estructuras biogénicas, originó inicialmente fases opalinas y tuvo lugar durante la diagénesis temprana cuando la oxidación de la materia orgánica estaba todavía activa, conservándose en los Thalassinoides silicificados formas (filamentos y cocoides) que podrían ser consideradas microbianas. La transformación ópalo-cuarzo fue temprana, preservándose dichas formas. 
 En las galerías silicificadas de Thalassinoides los procesos diagenéticos son diferentes a los de los sedimentos carbonáticos marinos que las incluyen, y al resto de estructuras biogénicas silicificadas, existiendo en estas galerías neoformación de dolomita y calcita, en un microambiente cerrado donde las condiciones cambian de oxidantes a reductoras.

Palynomorphs of the Fezouata Shale (Lower Ordovician, Morocco): Age and environmental constraints of the Fezouata Biota

The present study documents new palynological investigations of the Fezouata Shale from the Anti-Atlas (Morocco). Palynomorphs were extracted from samples collected from both outcrops and drill cuttings. Outcrop samples were taken near Zagora, and include some that were collected during excavation of stratigraphic horizons where exceptionally well-preserved fossils of the Fezouata Lagerstätte occur. Subsurface samples were taken from the AZ-1 (Adrar Zouggar Mountain) borehole, which was extracted some 300km to the southwest of Zagora. The palynological samples yielded acritarchs, chitinozoans, scolecodonts, conodonts and fragments of graptolites. The abundance and quality of preservation of palynomorphs varies greatly, but rich and diverse assemblages were recovered from several samples. The diversity and composition of the assemblages points to an open shelf environment. Generally mixed preservation states suggest resedimentation or differential transport histories. The acritarchs can be assigned to the diagnostic messaoudensis-trifidum acritarch assemblage, which is typical of the Tremadocian/Floian boundary interval of the Gondwanan margin in high southern palaeolatitudes. The acritarch taxa present in some of the lower parts of the Fezouata Shale including levels of exceptional preservation can be attributed to sub-assemblages 1–2 of the messaoudensis-trifidum assemblage and thus point to a late Tremadocian age of the Fezouata Lagerstätte, confirming biostratigraphic data provided by graptolites of the Araneograptus murrayi graptolite biozone. Chitinozoans from the Fezouata Shale are from the E. symmetrica and E. brevis biozones and include various species that are well-known from several localities on the Gondwanan margin and from other palaeocontinents (Baltica, Laurentia, and South China), demarcating broad links between those regions. The coincidence between index fossils of these three groups, hitherto not all found in the same level, suggests that the age assignments of chitinozoan biozones may be in need of revision.

Systematics, age, paleoecology and paleobiogeography of Jurassic foraminifera from Fakirwari Dome, Kutch, Gujarat, India

The studied section of the Chari Formation exposed at Fakirwari Dome, Kutch yielded rich foraminiferal assemblages comprising 54 species, ofwhich 22 are reported for the first time from the Indian region. The foraminiferal species are systematically described and employed for interpretations of age, paleoecology, and paleobiogeography. Although most of the foraminiferal species are rather long ranging, on the basis of a few species characteristic of the Callovian in diffrent parts of the world, a Callovian age is assigned to the studied sequence. Based on the dominance of suborder Lagenina, superfamily Nodosariacea, family Vaginulinidiae, calcareous hyaline forms, genus Lenticulina, wide ranging and fluctuating Fisher index, morphogroup K, and potential deep infaunal life habit group in the present assemblages, a shallow water, near shore, open marine middle shelf environment with frequently fluctuating shoreline having normal salinity and nomal to high level of oxygen is envisaged for the studied assemblages. The Middle Jurassic Fakirwari foraminiferal assemblages are assigned to a separate province of the Antiboreal Realm, the Indo-East African Province, located at the southern margin of the Tethyan Realm and transitional between the Tethyan and the Antiboreal realms.

Jurassic Foraminifera from Jajiya Member, Jaisalmer Formation, Western Rajasthan

Abstract: The Jajiya Member of Jaisalmer Formation yielded a foraminiferal assemblage comprising twenty-three species dominated by the family Vaginulinidae. An Oxfordian age is assigned to the foraminiferal assemblage based on the record of some characteristic Oxfordian species reported from different parts of the world. The foraminiferal assemblage suggests an open marine shelf environment of deposition.

Shallow-marine systems in a wedge-top basin setting: an example from the middle-upper Pliocene deposits of the Southern Apennines mountain front (Basilicata region, South Italy)

Middle-upper Pliocene wedge-top deposits cropping out near San Mauro Forte village (Basilicata region), along the Southern Apennnines chain-front, unconformably overlie deformed, lower Pliocene deposits and the pre-Pliocene substratum, represented by Cretaceous to Miocene allochtonous units. The middle-upper Pliocene sedimentary succession is markedly transgressive, with deltaic sands and gravels, overlain by shallow-marine to shelfal hybrid arenites (panchine Auctt.) and open-shelf hemipelagic deposits. This sedimentary succession was syndepositionally deformed, as shown by growth strata and progressive unconformities. Different ranks of unconformity surfaces separate hierarchically ordered, informal stratigraphic units. Two main units have been recognised: the lower unit (designated as Sequence 1) is mainly represented by siliciclastic deposits; the upper one (Sequence 2), is made of hybrid arenites and the overlying hemipelagites. Growth strata in the hybrid arenites indicate a strong synsedimentary control of a N-S trending anticline-thrust.Siliciclastic deposits of Sequence 1 can be ascribed to coarsegrained delta environments, fed by hyperpychnal flows arising from the chain-front and spreading out towards the foreland areas.Hybrid arenites of Sequence 2 has a mixed carbonate-siliciclastic to pure silicilastic composition and was deposited in storm-driven, shoreface to open-shelf environments. Skeletal grains of Sequence 2 belong to the foramol-type association, in good agreement with other Neogene and Quaternary mixed carbonate-siliciclastic systems of the Mediterranean area. Stratigraphic-sedimentological data suggest that the aforementioned uplift of the anticline-thrust played a leading role in the establishment of favourable conditions for carbonate production. Regional-scale subsidence has brought to the final drowning of these carbonate factories, overwhelmed by hemipelagic sedimentation.

Organic matter–apatite–pyrite relationships in the Botneheia Formation (Middle Triassic) of eastern Svalbard: Relevance to the formation of petroleum source rocks in the NW Barents Sea shelf

The Middle Triassic Botneheia Formation of eastern Svalbard (Edgeøya and Barentsøya) comprises an organic carbon-rich, fine-grained clastic succession (∼100 m thick) that makes the best petroleum source rock horizon in the NW Barents Sea shelf. The succession records a transgressive–regressive interplay between the prodelta depositional system sourced in the southern Barents Sea shelf (black shale facies of the lower and middle parts of the Muen Member) and the open shelf phosphogenic system related to upwelling and nutrient supply from the Panthalassic Ocean (phosphogenic black shale facies of the upper part of the Muen Member and the Blanknuten Member). The relationships between organic matter, authigenic apatite, and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation. The accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing-upward productivity related to early transgressive phase and retrogradation of the prodelta system. The phosphogenic black shale facies deposited in an oxygen-minimum zone (OMZ) of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity, suppressed sedimentation rates, and changing bottom redox. The phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of OMZ, including high input of autochthonous organic matter into sediment, oxic-to-dysoxic (episodically suboxic and/or anoxic) conditions, intense phosphogenesis, and recurrent reworking of the seabed. The massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of OMZ during high-stand of the sea. High input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis. In mature sections in eastern Svalbard, the petroleum potential of the Botneheia Formation rises from moderate to good in the black shale facies, and from good to very good in the phosphogenic black shale facies, attaining maximum in the massive phosphatic mudstone.

The Role of Microbial Activity In the Generation of Lower Cretaceous Mixed FE-Oxide-phosphate Ooids from the Provencal Domain, French Maritime Alps

Abstract Early Hauterivian mixed Fe-oxide–phosphate ooids from the Lower Cretaceous condensed succession of the Alpine Provencal Domain are ellipsoidal, 200–2000 µm in diameter, and the main component of a sedimentary body, 0–100 cm thick, that can be traced laterally for tens of kilometers. Cathodoluminescence, EDS microprobe, backscattered electron imaging, epifluorescence, XRD, and micro Raman spectroscopy reveal that ooid cortices consist of variable proportions of Fe-oxide-rich and Ca-phosphate-rich layers. SEM observations show that phosphate-rich layers are composed of a dense matrix of micrometer-size, rod-shaped, commonly curved phosphate grains, whose size and shape strongly suggest a microbial origin. Conversely, Fe-oxide-rich ooid cortical layers consist of aggregates of micrometer-size, plate-like crystals of hematite that point to an inorganic precipitation. We suggest that the ooidal condensed interval records a long sedimentary history in an open shelf environment subject to a background accumulation of organic-rich, fine-grained sediments. It was periodically interrupted by high-energy, storm-related events that resulted in winnowing, reworking, and oxygenation that favored precipitation of Fe-oxides around nuclei of biogenic origin. Such precipitation was not uniform on the outer surface of ooids and influenced their ellipsoidal shape. After the return to background conditions, Fe-ooids were buried and driven from an oxic to a post-oxic subbottom geochemical environment where rod-shaped Fe-reducing bacteria colonized Fe-ooid outer surfaces. Decomposition of organic matter and release of P bound on Fe-oxides increased pore-water concentration of phosphate, which precipitated at the outer surfaces of the ooids, thus preserving the microbial community. The bimineralic composition of these ooids discloses a complex and prolonged history of cyclic alternations of oxic and post-oxic geochemical conditions, which are in turn related to alternating sediment accumulation and winnowing phases with exposure at the seafloor.