Marginal Marine Environments Research Articles

Distribution of dinoflagellate cysts and other aquatic palynomorphs in surface sediments from the Beagle Channel, Southern Argentina

Palynological analyses of 22 surface sediment samples from the Beagle Channel, Tierra del Fuego, Argentina, were performed in order to investigate the distribution of dinocyst assemblages and other aquatic palynomorphs and to explore their relationships with sea-surface conditions, which are regionally characterized by cold and low salinity conditions (4–9 °C and 27–33.5, respectively). Results show relatively low dinocyst concentrations (253 to 5568 cysts/g) and species diversity (19 taxa identified). The assemblages are mostly composed of Protoperidiniaceae and appear typical of a marginal marine environment with surface waters characterized by low to moderate salinity and high nutrient content due to river inputs. The assemblages are thus compatible with the occurrence of freshwater to brackish water taxa Botryococcus braunii , Botryococcus sp., Polyasterias sp., Halodinium sp., and Radiosperma corbiferum . The dinocyst assemblages are dominated by Brigantedinium spp., Echinidinium spp. and Selenopemphix quanta accompanied by cysts of Pentapharsodinium dalei , Islandinium minutum , Votadinium spinosum , Polykrikos kofoidii and Polykrikos schwartzii . The assemblages from the Beagle Channel show similarities with those of high latitude regions of the Northern Hemisphere. However, some taxa, which were exclusively reported from relatively warm environments in the Northern Hemisphere, occur in relatively high percentages in the Beagle Channel (e.g. Echinidinium delicatum and Votadinium spinosum ). The absence of Selenopemphix antarctica in the Beagle Channel is consistent with its known ecological affinities, since it characterizes environments marked by seasonal sea-ice cover. ► First record of dinocyst assemblages are from off the coast of southern South America. ► They are comparable with assemblages from the continental shelf of the Arctic Ocean. ► Include taxa previously reported from temperate to warm climatic domains. ► SST and SSS might not be the most determinant parameters in their distribution.

Incised valleys in marginal-lacustrine depositional environments: a new reservoir analogue from Lake Eyre, central Australia

Incised-valley fill deposits can form important hydrocarbon reservoirs and provide pathways for hydrocarbon migration. Incised-valleys formed in marginal-marine environments are well described, however, marginal-lacustrine incised-valleys have been the focus of extremely few investigations and are poorly understood. This paper provides a new description of incised-fluvial systems that are presently constructing terminal deposits in embayments around the shoreline of Lake Eyre, central Australia. It is anticipated that better awareness of such deposits will assist in the recognition of these depositional environments in the rock record, which should be useful for exploration purposes and for the generation of improved models for continental dryland fluvial-lacustrine reservoir deposits. A classification of all significant river mouth deposits around Lake Eyre (width >300 m; n = 104), from topographic map and satellite image data, found that 54% are incised-valleys presently accreting a terminal deposit in a shoreline embayment (playa lake estuary). The depositional elements of three incised-valley systems have been mapped using satellite imagery in a GIS platform, from which element geometries are described. Controls on incised-valley formation are investigated by comparing these observations with evidence for past lake highstands and neotectonics and observations from satellite images, geological map data, and digital elevation model data. The terminal splay deposits of rivers around Lake Eyre are well-used analogues for dryland reservoirs; however, the focus has been on deposits accreting directly onto the playa. It is likely the incised-valleys and terminal deposits in the embayments described here will be of interest to companies exploring in, and producing from, ancient drylands and other lacustrine depositional environments.

Palinología y palinofacies de una secuencia marina del Holoceno medio-tardío: Albufera Lanushuaia, Canal Beagle, Tierra del Fuego, Argentina

PALYNOLOGY AND PALYNOFACIES OF A MIDDLE-LATE HOLOCENE MARINE SEQUENCE: ALBUFERA LANUSHUAIA, BEAGLE CHANNEL, TIERRA DEL FUEGO, ARGENTINA. Palynological analysis, with emphasis on palynofacial analysis was carried out on Holocene marine deposits located on the northern coast of the Beagle Channel, Argentina. This analysis allowed paleoenvironmental assessments and paleoclimatic inferences. A fossil section from Albufera Lanushuaia (54°52'04.4S-67°60'44.9O), located on the northern coast of the Beagle Channel was analyzed. The set of particulate organic matter indicate the proximity of the area of continental input to the marine environments, with distances and/or times of transport relatively short. The presence of pyrite suggests reducing conditions, probably associated with marginal-marine environments. At the Albufera Lanushuaia, from the ca. 5,800 years 14 C BP, palynological associations reveal the same pattern of regional vegetation with a closed forest of Nothofagus and an assemblage of Peridiniales dinocysts dominated by taxa that suggest marginal-marine environments, with low to moderate salinity and high nutrient concentrations in shallow marine waters, probably due to the contribution of freshwater due to surface runoff. For the past 3,000 years, a decrease in pollen records of Nothofagus and an increase in shrub and herb pollen with a limited occurrence of aquatic palynomorphs were observed. These reflects the development of a more open forest and adjacent areas of herbaceous and shrub with marginal-marine influence, associated to a regressive event.

Vascular Cryptogam Plants of the Khoshyeilagh Formation, Northern Shahrud, Eastern Alborz Ranges

Fragmentary, indifferently preserved, and of low diversity plant remains occur in basal part of the Khoshyeilagh Formation, northern Shahrud, eastern Alborz Ranges. The oldest hitherto reported from Iran, the remains are essentially assignable to lycophytes and psilophytes. Additionally, spores retrieved from the Khoshyeilagh Formation with reference to available data on spore-plant relation-ships denote that Phaeophyta, Rhyniopsida (Rhyniales and Trimerophytales), Zosterophyllopsida, Barinophytopsida (Barinophytales), Filicopsida (Cladoxylales and Zygopteridales), Lycopsida (Drepanophycales), Equisetopsida, and Progymnospermopsida (Aneurophytales and Archaeopteridales) were perhaps the main sources of sporae dispersae. Variations in the samples examined of approximate ratio of land-derived to marine palynomorphs, however, evidently support stabilization of marginal marine environments and noticeable modification in complexion of the contemporaneous coastal vegetation upward in the section investigated. Vertical distribution of the plant remains, associated palynofloras, and available faunal indications collectively permit the host strata to be dated as early Middle Devonian (Eifelian). Poor preservation of the plant remains perhaps conveys accumulation during flooding. A river with alternating floods emasculating its bank overtaken by Protolepidodendron and Dawsonites may be envisaged.

Silurian and Devonian in Vietnam—Stratigraphy and facies

Silurian and Devonian deposits in Viet Nam are present in several zones and regions, including Quang Ninh, East Bac Bo, and West Bac Bo Zones of the Bac Bo Region, the Dien Bien-Nghe An and Binh Tri Thien Zones of the Viet-Lao Region, and the South Trung Bo, and Western Nam Bo Zones of the South Viet Nam Region (Fig. 1). The main lithological features and faunal composition of the Silurian and Devonian Units in all these zones are briefly described.The Silurian consists of deep-water deposits of the upper parts of the Co To and Tan Mai Formations in the Quang Ninh Zone, the upper parts of the Phu Ngu Formation in the East Bac Bo Zone and the upper parts of the Long Dai and Song Ca Formations in the Viet-Lao Region. Shallow water facies Silurian units containing benthic faunas are more widely distributed, including the upper part of the Sinh Vinh and Bo Hieng Formations in the West Bac Bo Zone, the Kien An Formation in the Quang Ninh Zone, and, in the Viet-Lao Region, the Dai Giang Formation and the upper part of the Tay Trang Formation.No Lower and Middle Devonian deposits indicate deep water facies, but they are characterized by different shallow water facies. Continental to near shore, deltaic facies characterize the Lower Devonian Song Cau Group in the East Bac Bo Zone, the Van Canh Formation in the Quang Ninh Zone, and the A Choc Formation in the Binh Tri Thien Zone. Similar facies also occur in the Givetian Do Son Formation of the Quang Ninh Zone, and the Tan Lap Formation in the East Bac Bo Zone, and consist of coarse terrigenous deposits—cross-bedded conglomerates, sandstone, etc. Most Devonian units are characterized by shallow marine shelf facies. Carbonate and terrigenous-carbonate facies dominate, and terrigenous facies occur in the Lower and Middle Devonian sections in some areas only.The deep-water-like facies is characteriztic for some Upper Devonian formations in the Bac Bo (Bang Ca and Toc Tat Formations) and Viet-Lao Regions (Thien Nhan and Xom Nha Formations). These formations contain cherty shale or siliceous limestone, and fossils consist of conodonts, but there are also brachiopods and other benthos. They were possibly deposited in a deep water environment on the slope of the continental shelf.Most Devonian units distributed in the North and the Central Viet Nam consist of self shallow water sediments, and apparently they were deposited in a passive marginal marine environment. The coarse clastic continental or subcontinental deposits are distributed only in some areas of the East Bac Bo and of the Quang Ninh zones of the Bac Bo Region, and in the south of the Binh Tri Thien Zone. This situation suggests the influence of the Caledonian movement at the end of the Silurian period that called the Guangxi movement in South China.

The Lower Paleozoic rock units in Egypt: An overview

Lower Paleozoic rocks are exposed in various regions of Egypt (south central Sinai, north Eastern Desert and southwest Western Desert), in addition to occurring in the subsurface such as north Western Desert and the Gulf of Suez. The Lower Paleozoic rocks in Egypt include surface and subsurface rock units of formational status. The surface rock units are the Taba, Araba and Naqus formations. The subsurface rock units include the Shifa, Kohla and Basur formations. The Infracambrian Taba Formation has been discovered recently in the outcrops of the southeast central Sinai in the Taba-Ras El-Naqab area. It is missing and/or not recognized in the subsurface. The Taba Formation consists mainly of reddish brown, unfossiliferous gravelly fine- to medium-grained kaolinitic sandstones and subordinate horizons of paleosols. The Cambrian Araba Formation and its subsurface equivalent (the Shifa Formation) are essentially composed of reddish brown, fine-grained laminated sandstone and siltstone with abundant Skolithos and Cruziana sp. In contrast, the Ordovician–Silurian Naqus Formation and its subsurface equivalents (the Kohla Formation and Basur Formation) are mainly composed of white, unfossiliferous, cross-bedded, medium- to coarse-grained sandstones with haphazardly distributed pebbles and cobbles. Sedimentological analysis indicates that the Araba Formation and its subsurface equivalent were deposited in a marginal-marine environment, whereas the Naqus Formation and its subsurface equivalents were laid down in a fluvio-glacial environment. Integrated stratigraphic and sedimentological studies of the Lower Paleozoic rocks permit reconstruction of the paleogeography of Egypt at that time. Egypt has been largely controlled since the Cambrian by the pre-existing structural framework of the pre-Phanerozoic basement rocks inherited from the Late Proterozoic Pan-African event. Additionally, sedimentation processes were controlled during Cambro-Ordovician times by tectonic movements, whereas glacio-eustatic control predominated during the Late Ordovician–Silurian Period. These studies suggest that most areas of Egypt were exposed lands with episodically transgression by epi-continental seas related to the paleo-Tethys. These lands formed a part of a stable subsiding shelf at the northern Gondwana margin.

A Labyrinthodont Amphibian from the Margin of the Pennsylvanian Epicontinental Sea in Kansas

A partial labyrinthodont amphibian skull was collected from the Pony Creek Shale Member of the Wood Siding Formation (Virgilian Stage, Upper Pennsylvanian) in Wabaunsee County, Kansas. The partial skull provides supporting evidence that labyrinthodonts frequented marginal marine environments. The fossil is from an animal that probably was about 1.5 meters long in life and was ecologically similar to an alligator.

Identification of the Icelandic Landnám tephra (AD 871 ± 2) in Scottish fjordic sediment

Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved. This paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the Loch Sunart record (MD04-2831) on the NW coast of Scotland (UK). One tephra horizon (containing both silicic and basaltic shards) is identified within Late Holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the Veidivötn-Bárðarbunga volcanic system. Radiocarbon age estimates and stratigraphic information suggests that the AD 871 Landnám tephra is the most likely candidate. The shards identified within this horizon appear hydrated and indicate the operation of post-depositional weathering processes possibly influenced by the saline conditions of the fjord environment.

Petroleum generation in the southeast Texas basin: Implications for hydrocarbon occurrence at the South Liberty salt dome

Geochemical characteristics of hydrocarbons from the South Liberty field, Liberty County, Texas, were integrated with local stratigraphy, pressure, temperature, seismic data, and formation water chemistry to determine the source, maturity, and migration pathways of hydrocarbons associated with the salt dome in the southeast Texas Gulf Coast. Fourteen crude oil samples from the soft-geopressured Cook Mountain and Yegua (both Eocene) and Frio (Oligocene) reservoirs (989–2886 m [3245–9469 ft]) were analyzed by whole-oil high-resolution gas chromatography (GC) and GC–mass spectrometry. Pressure and temperature data from 36 wells were used to model the thermal maturation history in the vicinity of the dome. South Liberty oils were found to belong to a single genetic family, sourced from rocks with a similar level of maturity. Biomarkers indicate they were formed in a marginal marine environment with notable terrestrial input from a likely lower Tertiary source rock (probably the downdip lower Claiborne and/or Wilcox Group). Oils were generated within the peak oil window (vitrinite reflectance, ~0.6–0.9%) at expulsion temperatures of 125 to 130C. Thermal modeling indicates the lower Claiborne and/or upper Wilcox beds attained optimum maturity in and around the dome between 8 to 20 Ma and 18 to 31 Ma, respectively. Oil migration toward the structure probably occurred through faults breaching the deep-seated lower Claiborne/upper Wilcox source. Two severely biodegraded samples were found, and these were associated with cooler formation water (50 to 55C) with a greater meteoric water component (48–60%). Comparison with Brazoria County oils (100 km [62 mi] to the southwest) indicates that the South Liberty oils belong to the same genetic family, with minor differences resulting from a greater input from terrestrial kerogen.

A new look at modern agglutinated benthic foraminiferal morphogroups: their value in palaeoecological interpretation

Morphogroups offer a way of overcoming taxonomic differences and thereby making comparisons between assemblages of different geological ages. Relating morphogroups to environments has proved useful in palaeoecological interpretations. The model proposed by Jones and Charnock in 1985 has subsequently been adapted and still serves as the main reference for such palaeoecological interpretations. New data from > 400 samples from marsh to deep sea off NW Europe are used here to refine the model by providing the range of abundance of each morphogroup in each environment. It is shown that this range of variation is great so that there is considerable overlap between environments. Nevertheless, the mean values show patterns of distribution. Tubular forms (morphogroup A) are characteristic of slope environments, especially those under the influence of geostrophic currents. Morphogroup B is not common in marginal marine environments but is an indicator of shallow fjord to deep sea. The elongate forms of morphogroup C are widely distributed but C1 is especially common in marginal marine and shelf to upper slope settings. The quinqueloculine coiled C2 subgroup is characteristic of marsh and marginal marine environments in the temperate zone but around Antarctica this form is common down to 2000 m. The plano-convex, low trochospiral trochamminids of morphogroup D are typical of marshes. Therefore, these trends have application to palaeoecology of similar well-oxygenated temperate environments.

Estudio de los foraminíferos de la Formación Pirabas (Mioceno Inferior), estado de Pará, Brasil y su correlación con faunas del Caribe

Las variaciones verticales en el contenido de las asociaciones de foraminíferos, detectadas por medio de estudios cuantitativos y cualitativos, permitieron el reconocimiento de ocho biofacies en la Formación Pirabas, correspondientes a los subambientes de plataforma somera y lagunar. Los sedimentos fueron depositadosen las áreas lagunares en función de las variaciones en la profundidad y la salinidad.La presencia de los foraminíferos planctónicos confirma la edad Mioceno Inferior para la Formación Pirabas. El registro de Globorotalia kugleri Bolli y Globigerinoides primordius Blow & Banner en la base y Globigerinoides altiaperturus Bolli y Globigerinoides trilobus trilobus (Reuss) en el tope del afloramiento puede ser co-rrelacionado con las Zonas Bioestratigráficas Internacionales N4 y N5 de Blow (1969)

“Lungs” in Placoderms, a persistent palaeobiological myth related to environmental preconceived interpretations

The presence of an aerial breathing organ in Placoderms is noticed in many textbooks on the history of breathing in Vertebrates. The origin of this interpretation is from a paper published in 1941 dealing with the interpretation of the differential sedimentary infilling of the armour of the antiarch Bothriolepis canadensis from the Late Devonian Escuminac formation of Canada. A revision of this material shows that if some sedimentary structures could be interpreted as traces of some digestive organs, none could be interpreted as putative lungs. The original proposal was based mainly on a presupposed mode of life of Bothriolepis in a freshwater environment of an alluvial plain. Recent studies of the Escuminac Formation environment conclude that it represents a marginal marine environment. Moreover, Bothriolepis has a worldwide distribution, notably in strictly marine environment. Thus, the presence of lungs in Bothriolepis remains highly questionable: it cannot be supported by anatomical, phylogenetic, nor biological arguments.

Miocene climate evolution of northern Europe: A palynological investigation from Denmark

A palynological investigation has been conducted on Lower–Upper Miocene sediments from Jylland, Denmark, corresponding to the time interval of about 19 to 8 Ma. The sediments, derived from the Sdr. Vium drill core, were deposited in marine to marginal-marine environments, as shown by the relatively high abundance of dinoflagellate cysts in all samples. Nevertheless, rich and diverse pollen assemblages occur throughout the succession and the palynological analysis reveals that coastal areas of the study area were during the Miocene dominated by Taxodium swamp forests that also hosted terrestrial angiosperms such as Nyssa, Betula, Alnus and elements of the Myricaceae. Further inland, a mixed deciduous–evergreen forest prevailed. In areas with better drained soils, or on elevated areas, gymnospermous conifer forests prevailed including taxa such as Pinus, Sequoia and Sciadopitys. Overall, the climate in the study area was warm temperate during major parts of the Miocene with mean annual temperatures between 15.5 and 20 °C. By employing the Coexistence Approach combined with the method of allocating taxa into standardized climatic groups, four different climatic Miocene events are detected within the studied succession correlated to the coeval climate record of northwestern Europe. The oldest event is a cooling during the earlier Burdigalian, at approximately 19 Ma, coinciding with the MBi-1 oxygen isotope excursion. At ca. 18.5 Ma (in mid-Burdigalian) a warming phase is reconstructed, characterized by the highest precipitation rates observed in the sedimentary succession. A warming trend, starting in the latest Burdigalian, corresponds to the globally recognized Middle Miocene Climatic Optimum (MMCO) while a longer-term late Neogene cooling was initiated in the mid Serravallian, about 13 Ma.

Iron Ore Deposits Associated with Precambrian Iron Formations

Most large deposits of iron ore are associated with iron formations for the simple reason that they have the highest iron concentrations of any “normal” rock type. Iron formations are found in all Precambrian shields. Iron was preconcentrated in iron formations by surface processes in Precambrian marginal-marine environments, as outlined elsewhere in this issue.

COMMUNITY STRUCTURE: GLOBAL EVALUATION AND THE ROLE OF WITHIN COMMUNITY BETA-DIVERSITY

Community structure is defined as the mathematical statistical distribution of the relative species abundance vector. Consideration of the decomposition equation for species richness, S, evenness, E, and the Shannon estimate of entropy or information, H, plus their respective regressions on the accumulation of the number of individuals, N, in a sample leads to the establishment of three structural types. Each type is defined by the slope, β 1H , of the regression H versus lnN and depends on the accumulation rate of species between samples (beta-diversity) in a community. These types are designated as 1) Type 0, where H is constant with the accumulation of lnN denoting equilibrium or stability (Log series is a special case); 2) Type 1, where the slope of H is positive with the accumulation of lnN denoting growth or expansion (Log normal is a special case); and 3) Type −1, where the slope of H is negative with the accumulation of lnN denoting decline, instability or stress. In this study, 72 communities were analyzed from environments ranging from marginal marine to the abyss. Only 10 communities are identified as type −1 with the majority of these at lower bathyal and abyssal depths. At abyssal depths the average β 1H is −0.057 and data from fossil communities in the Arctic indicate that this unstable, stressed situation has persisted for at least 50 ka. In the Gulf of Mexico at shelf depths, low values for β 1H are registered near the Mississippi delta. In contrast, the open-ocean east of New Zealand has an average β 1H of 0.227, the highest recorded. Among marginal marine environments an average β 1H of −0.030 was recorded in Long Island Sound before the collapse of that community. In contrast, the Indian River Lagoon, Florida had the highest β 1H for a marginal marine environment with an average value of 0.195. No simple invariant pattern between type 0 and type 1 communities is prevalent in any environment. Overall 31 communities are type 0 and 31 are type 1. In marginal marine environments (22 communities) the average value of β 1H is 0.092. In the open-ocean (50 communities) the average value of β 1H is 0.093. Evidently, for any group to remain highly successful on the average a slightly positive value of β 1H is required.

HYDROCARBON POTENTIAL OF THE UPPER CRETACEOUS SUCCESSION AT WELL 16/U‐1, ONSHORE QAMAR BASIN, EASTERN YEMEN

An Upper Cretaceous succession has been penetrated at onshore well 16/U‐1 in the Qamar Basin, eastern Republic of Yemen. The succession comprises the Mukalla and Dabut Formations which are composed of argillaceous carbonates and sandstones with coal layers, and TOC contents range up to 80%. The average TOC of the Mukalla Formation (24%) is higher than that of the Dabut Formation (1%). The Mukalla Formation has a Rock‐Eval Tmax of 439–454 °C and an HI of up to 374 mgHC/gTOC, pointing to kerogen Types II and III. The Dabut Formation mainly contains kerogen Type III with a Tmax of 427–456°C and HI of up to 152 mgHC/gTOC. Vitrinite reflectance values ranging between 0.3 and 1.0% and thermal alteration index values between 3 and 6 indicate thermal maturities sufficient for hydrocarbon generation.Three palynofacies types were identified representing marine, fluvial‐deltaic and marginal‐marine environments during the deposition of the Mukalla and Dabut Formations in the late Santonian — early Maastrichtian.

Los depósitos oxfordiano-kimmeridgianos de la Formación Lotena: nuevas perspectivas en la estratigrafía del Jurásico Tardío de la Cuenca Neuquina, Argentina

The Oxfordian-Kimmeridgian deposits of the Lotena Formation: new perspectives on the Late Jurassic stratigraphy of the Neuquén Basin, Argentina. New micropaleontological and stratigraphical data of the Lotena Formation at Barda Norte locality suggest that the Picún Leufú sub-basin was connected to open marine conditions at least until latest Oxfordian- early Kimmeridgian. These data reinforce the hypothesis of a temporary physical disconnection between the Picún Leufú sub-basin and the Neuquén Basin. The transitional characteristics of the palynological assemblages containing taxa recognized in Argentina since the Late Jurassic and the presence of sporomorphs belonging to the Stereisporites pandoi Zone (late Oxfordian) suggest a latest Oxfordian - early Kimmeridgian age for the analyzed deposits. According to the micropaleontological and stratigraphical analysis, the age of the Lotena Formation in the Picún Leufú sub-basin could span from the middle Callovian to the late Oxfordian-early Kimmeridgian. The microfossils (palynomorphs and foraminifers) suggest a moderate energy marginal-marine environment, located close to the terrigenous source area, and in which salinity varied with changes in freshwater influx.

Quantifying clinothem geometry in a forced-regressive river-dominated delta, Panther Tongue Member, Utah, USA

This study presents a methodology for the quantitative description of small-scale delta clinothems. The quantitative bed-data analysis is based on three-dimensional virtual outcrop models generated by ground-based laser scanning (Light Detection and Ranging). A large number of clinothem bed measurements have been collected from the ancient forced regressive delta system of the Panther Tongue that crops out in Utah, USA. In river-dominated marginal marine environments, clinothems separated by clinoform surfaces represent the former position of the delta front as it prograded. Systematic collection of data from virtual outcrop models has allowed for accurate, spatially constrained measurement of individual bed thicknesses and the compilation of a detailed database on clinothems and associated clinoform geometries. Measurement locations were selected so that each measurement was 10 m down depositional dip from the previous one. The study area covers 5 km2 within which 2376 measurements were made from 50 separate clinothems in 320 different positions within the virtual outcrop. A bed taper parameter permitted the thinning of the clinothems to be described as a single number and thus allowed relative comparison between beds. Combined measurements were also used to calculate the average dip angle of the clinothems. Analysis of the vertical and lateral stacking of the clinothems has revealed a series of stratigraphic cycles which are termed bedsets (stream-mouth bars). The surfaces that bound the bedsets are unremarkable and it is unlikely that their significance would be recognized without this style of detailed analysis. A cyclic depositional pattern, interpreted as related to autocyclic processes and compensational stacking of mouth bars, is proposed as the origin of these packages. Mapped length/thickness trends constrain the spread of these variables, and can be used to constrain subsurface models of analogous hydrocarbon reservoirs.

Non-pollen palynomorphs in the Black Sea corridor

There have been few studies of non-pollen palynomorphs (NPP) in Holocene brackish water environments. The Black Sea is one of the world’s largest and deepest bodies of stable brackish water and a natural laboratory for study of marine carbon cycling to anoxic sediments. The main NPP in the modern sediments of this brackish water sea are dinoflagellate cysts (dinocysts), acritarchs (mainly the prasinophytes Cymatiosphaera, Micrhystridium, Sigmopollis and Pseudoschizaea) and diverse fungal remains. Other NPP include colonial algae, tintinnids, copepod and cladoceran egg covers, testate amoebae and microforaminiferal linings. These NPP assemblages are similar to those in the marginal marine environment of the Pliocene St. Erth Beds (England), but have more abundant NPP, and virtually lack scolecodonts. In the Black Sea corridor, modern assemblages from areas with salinity >22‰ have higher percentages of microforaminiferal linings and fewer prasinophytes, colonial algae and fungal spores. Prasinophytes dominate only in mid-Holocene sediments, during a 2000 years interval of sea level transgression and sapropel deposition. Early Holocene sediments have lower dinocyst diversity, increased fresh–brackish water colonial algae (Pediastrum spp. and Botryococcus braunii), zygnemataceous spores and desmids (including Zygnema, Cosmarium), ostracod linings and fewer foraminiferal linings. These assemblages are similar to those in the Baltic Sea where the annual salinity is about 6–8‰.

Bivalves from the Triassic-Jurassic transition in Northern Spain (Asturias and Western Basque-Cantabrian Basin)

Bivalve mollusks from the Triassic-Jurassic transition collected in eight localities in Asturias and the western Basque-Cantabrian Basin (Palencia province) are systematically revised. Preservation is poor at all localities. The dominant Rhaetian bivalves are Isocyprina concentrica (Moore) and Bakevellia (Bakevelloides) praecursor (Quenstedt). These species, together with Isocyprina cf. ewaldi (Bornemann), Pteromya cf. crowcombeia (Moore), Pseudoplacunopsis alpina (Winkler), and Modiolus? sp. (cf. minimus J. Sowerby), with a specimen of Arcestidae (?), belong to an assemblage similar to that found in the Westbury and Lilstock formations (Penarth Group) in the late Rhaetian of southern England. The most abundant Hettangian species is Isocyprina (Eotrapezium) germari (Dunker). Others are referred to Cuneigervillia rhombica (Cossmann), Sphaeriola? sp., Eomiodon? sp. and Pteromya cf. tatei (Richardson and Tutcher). All Hettangian shell beds examined are monotypic or have very low diversity, a biological indication that they may belong to a restricted marine environment, with high environmental stress levels. Even the more diverse assemblage (Pteromya-Cuneigervillia-Eomiodon) was probably also salinity controlled. The fauna analyzed here clearly belongs to the same facies and environment as those described from Aquitaine (France) and the Pyrenees and is different from coeval bivalve assemblages from other European Hettangian localities. The Triassic-Jurassic boundary cannot be precisely located at the studied sections on the basis of the bivalve faunas alone, but these indicate that the transition beds in Asturias were deposited in a marginal marine environment and the benthic fauna was dominated by shallow burrowing, suspensivorous bivalves.