Shelf Biofacies Research Articles

Systematic paleontology and biostratigraphy of upper Eocene larger benthic foraminifera from Fanari (Thrace Basin, Greece)

Paleogene sedimentary deposits are exposed in several localities along the extended Thrace Basin in the Greek territory. One of the best sites in terms of preservation, richness and type of sediment occurs along the coastline of Fanari village (SW ofKomotini city). Two outcrops, which consist of upper Eocene shallowmarine clastic sediments, were sampled to analyze the full spectrum of larger benthic foraminifera (LBF) that comprises a rich and diverse assemblage of orthophragmines (Discocyclina, Orbitoclypeus and Asterocyclina), nummulitids (Nummulites, Assilina, Operculina, Heterostegina and Spiroclypeus), and other benthic taxa (e.g., Silvestriella, Pellatispira, Fabiania, Sphaerogypsina, etc.).Adetailed systematic description of LBF from Fanari is presented,which refines the biostratigraphic age of SBZ (Shallow Benthic Zone) 20 corresponding to the late Priabonian for the whole sequence. Twenty-four taxa among which six at (chrono)subspecies level belonging to twelve genera were identified and morphometrically analyzed for the first time from Greece. The LBF assemblage is characterized by the constant presence of Nummulites fabianii almost throughout the whole sequence. The most abundant species are Pellatispira madaraszi and Spiroclypeus carpaticus, though they occur in the upper part of the sequence along with orthophragmines. The foraminiferal distribution in the sequence enables paleoenvironmental observations and the reconstruction of the evolution of the Fanari area. Three main depositional marine shelf facies are distinguished at the shallow upper foreslope of the carbonate platform, making the Fanari section a key area not only of latest Priabonian but also of outer shelf biofacies.

Albian to Turonian agglutinated foraminiferal assemblages of the Lower Saxony Cretaceous sub-basins – implications for sequence stratigraphy and paleoenvironmental interpretation

Abstract. Albian to Turonian carbonate deposits at three different locations of the Lower Saxony Cretaceous and thereby of the European mid-Cretaceous epeiric shelf sea were investigated for their fossil agglutinated foraminiferal fauna. In this study, 71 samples from two quarries and three drill cores were treated with formic acid, which enabled the study of agglutinated foraminiferal assemblages even in highly lithified limestones. In total, 114 species were determined and classified as belonging to nine morphogroups. In general, four agglutinated foraminiferal assemblages are distinguished: (1) an uppermost Albian–lowermost Cenomanian assemblage from the Wunstorf drill cores, with the dominant taxa Bathysiphon spp., Nothia spp., Psammosphaera fusca, Reophax subfusiformis, Bulbobaculites problematicus, Tritaxia tricarinata, Flourensina intermedia, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (2) a Cenomanian assemblage from the Baddeckenstedt quarry and Wunstorf drill cores, with Ammolagena clavata, Tritaxia tricarinata, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (3) an assemblage related to the Cenomanian–Turonian Boundary Event in Wunstorf and Söhlde dominated by Bulbobaculites problematicus; and (4) a Turonian assemblage in the Wunstorf and Söhlde sections with high numbers of Ammolagena contorta, Repmanina charoides, Bulbobaculites problematicus, Gerochammina stanislawi, and Spiroplectammina navarroana. The latest Albian–earliest Cenomanian assemblage consists of tubular, globular, and elongate foraminiferal morphogroups which are typical for the low- to mid-latitude slope biofacies. All other assemblages are composed of elongate foraminiferal morphogroups with additionally globular forms in the proximal settings of Baddeckenstedt and Söhlde or flattened planispiral and streptospiral forms in more distal settings of Wunstorf. For these assemblages, a new agglutinated foraminiferal biofacies named “mid-latitude shelf biofacies” is proposed herein. Changes in the relative abundance of different morphogroups can often be referred to single features of depositional sequences. Furthermore, classical macro-bioevents, which are often depositional-related, of the Lower Saxony Cretaceous seem to have a micro-bioevent or acme equivalent of the agglutinated foraminiferal fauna.

Benthic foraminiferal distribution and biofacies in the shelf part of Bay of Bengal, east coast of India

The environmental conditions that determine the benthic foraminiferal biofacies in the shelf part of Bay of Bengal are identified in the present study. The possible variables such as water depth, nature of sediments and substrate, salinity, dissolved oxygen and hydrodynamic factors are evaluated. A total of 23 surface sediment samples were collected at different water depth from the study area and were subjected to foraminiferal analysis and sediment characterisation. Altogether, 147 species belonging to 59 genera and 6 orders are identified, only 22 species are abundant. Cluster (Q-mode and R-mode) analysis of the abundant species resulted in the identification of four distinct biofacies which are correlated with environmental variables. The shallowest biofacies from 0 to 38 m water depth is represented by Ammonia beccarii, Amphistegina radiata, Asterorotalia pulchella and Elphidium crispum, which are associated with sandy sediment. The second biofacies from 38 to 83 m water depth is characterised by Cibicides wuellerstorfi, Quinqueloculina seminula, Quinqueloculina lamarckiana, Quinqueloculina vulgaris, Quinqueloculina agglutinans, Rotalinoides compressiuscula and Textularia agglutinans and the nature of sediments varies from slightly muddy sand to muddy sand. The third middle shelf biofacies from 83 to 150 m water depth is composed of Asterorotalia dentata, Cassidulina laviegata, Cibicides subhaidingerii and Lenticulina thalmani that are found in muddy sand sediment. The fourth outer shelf biofacies consisting chiefly of Bolivina ordinaria, Brizalina spathulata, Bulimina aculeata, Cancris communis, Siphouvigerina proboscidea and Uvigerina parvula exists from the depth of 150–200 m and related to sandy mud sediment. Two Paleo strandlines are identified at the depths of 49 m and 105 m, respectively, from the occurrence of relic forms along with soft coral sclerites. The shallower part of the seafloor up to 30 m depth is dominated by sandy sediments, reflecting the prevalence of high-energy conditions. On the other hand, the deeper part contains sediments with more mud content formed in low-energy conditions. The spatial distribution of benthic foraminifera in this shelf region is chiefly controlled by the nature of sediments and the bathymetry. However, another factor, such as dissolved oxygen, salinity, temperature and hydrodynamic conditions, seems to have an influence on the composition of benthic foraminiferal biofacies.

Distribution of Foraminifera of the Poverty Continental Margin, New Zealand: Implications for Sediment Transport

ABSTRACT Foraminiferal assemblages were used to investigate the nature of sedimentation on the tectonically active Poverty continental margin (PCM) of New Zealand. Recent research around the world has been focused on understanding the sedimentary functioning of small mountainous rivers to the global sediment budget, and this study is part of a greater effort to define the processes that link sediment source and sink of such a system in New Zealand. Fifty-five surface samples from box, gravity, and multi-cores from the shelf and slope of the PCM were used to document the distribution of modern benthic foraminifera. Also, twenty samples from two gravity cores retrieved from Poverty Canyon, a hypothesized conduit of sediment to the deep ocean, were analyzed to evaluate the record of down-slope sediment transport. Seven biofacies, recognized by cluster analysis of benthic foraminiferal abundance data from surface and core samples, are strongly related to water depth and continental margin morphology: inner-shelf biofacies (26–43 m), shelf biofacies (~30–130 m) (this biofacies contained all samples from a canyon-head core taken at 359-m water depth), outer-shelf biofacies (60–250 m), upper-slope biofacies (230–350 m), shallow lower-slope biofacies (870–1255 m), Lachlan Anticline biofacies (40–63 m on the PCM shelf), and a mid-canyon thalweg biofacies from a core taken at 891-m water depth. Foraminiferal assemblages of the Lachlan Anticline biofacies are characterized by the largest foraminifera (mostly inner-and mid-shelf species), the most diverse assemblages, and the highest percentage of reworked planktonic tests in the dataset. Many planktonic and benthic specimens have probably been derived from the outcropping Miocene-Pliocene rock of the anticline. A high percentage of reworked (fossil) planktonic foraminifera at the mouth of Poverty Bay likely results from sediments shed from rapidly uplifting Plio-Pleistocene strata within the Waipaoa River drainage basin. Assemblages throughout the canyon-head (359 m) and mid-canyon (891 m) cores from Poverty Canyon contained higher percentages of shallower-water indicator taxa than other samples at similar depths outside the canyon, thus supporting the hypothesis that Poverty Canyon is channeling sediment from the shelf and upper slope to the deep ocean. However, different patterns of down-core distributions between the canyon head and mid-slope thalweg sites indicate that the nature of sedimentation varies down canyon. Abundances of shallower-water foraminifera suggest that shelf taxa are being supplied from a more consistent source to the canyon head, while shelf and upper-slope taxa are more variably supplied to the deeper-canyon thalweg. The effects of bioturbation appear to be greater in the canyon head.

High-Frequency Rhythmicity in a Mixed Siliciclastic-Carbonate Shelf (Late Miocene, Guadix Basin, Spain): A Model of Interplay Between Climatic Oscillations, Subsidence, and Sediment Dispersal

Abstract Rhythmites in pelagic sediments can include information on paleoclimate and with orbital cycles. This paper documents and interprets an unusual rhythmic succession from a cool-water shallow-marine shelf that includes features of Mediterranean-type ramps and open-ocean-type ramps. In the subsiding southwestern margin of the Guadix Basin (southern Spain, Betic Cordillera), during the late Tortonian, a 640-m-thick succession was deposited over a short period (7.8–7.2 Ma). This succession contains 30 sedimentary packages or rhythmites, each defined by two facies associations: a mixed cross-stratified siliciclastic–skeletal sandstone and a homogeneous marl rich in planktonic foraminifera. Sandstones ranging in thickness from 3 m to 20 m contain coralline algae, bivalves, bryozoans, benthic foraminifera, echinoids, and brachiopods (typical temperate-water shelf biofacies). These units exhibit cross-strata sets up to four meters high, interpreted to have been produced by strong unidirectional currents. The marly deposits range in thickness from 2 to 17 m and contain an association of cold-water planktonic foraminifera as well as thin sandstone layers that exhibit normal grading corresponding to typical incomplete Bouma sequences or a lower division with planar lamination and an upper division of very fine- to fine-grained sandstone with hummocky and swaly cross-stratification. On the basis of the sedimentary structures, the sandstone layers are interpreted as sporadic turbidity flows and storm ebb–surge deposits. On the basis of the sedimentary structures, the hydrodynamic conditions during deposition of the mixed siliciclastic–carbonate interval were high-energy. Based on sedimentary and biogenic features of the rhythmites and their temporal durations (ca. 20 ka), rhythmicity is interpreted to reflect alternating cool-wet and cold-dry climate episodes driven by precession orbital cycles. This occurrence of alternating mixed carbonate–siliciclastic sedimentation and pelagic sediments represents a unique occurrence in the geologic record.

Brachiopod biofacies in the Barr and Ardmillan groups, Girvan: Ordovician biodiversity trends on the edge of Laurentia

ABSTRACTLocally abundant and diverse brachiopod faunas, associated with unstable outer shelf and slope environments, occur throughout the Barr and Ardmillan groups (middle Llanvirn–upper Ashgill) in the Girvan district of SW Scotland. A dataset of 350 brachiopod species from 30 horizons through the Middle–Upper Ordovician succession forms the basis for a description of brachiopod diversity through the succession and comparison with global patterns and trends through this time interval. The Middle Ordovician Barr Group incorporates shallow water carbonate and clastic facies, characterised by Valcourea confinis, with deeper-water facies. The trilobite-dominated Albany Group preserves outer shelf biofacies. Deep-water facies occur in the Balclatchie Formation of the lower Ardmillan Group, including an early occurrence of a Foliomena-type species. High diversity brachiopod faunas occur in clastic facies, though many of the biofacies have a transported component to them. Representatives of the deep-water Foliomena fauna occur intermittently throughout the Upper Ardmillan Group, appearing in both the Whitehouse and Drummuck subgroups. This distinctive assemblage of small, thin-shelled brachiopods, including Dedzetina, Christiania, Cyclospira and Foliomena itself, is interbedded with a variety of other less cosmopolitan deep-water assemblages, including the Onniella–Skenidioides and Lingulella–Trimurellina associations. Shallower-water environments in the middle Ashgill Lower Drummuck Subgroup hosted the Fardenia–Eopholidostrophia association in sands, and the Christiania–Leptaena association in muds and silts. The remarkable Lady Burn Starfish Beds in the upper part of the group contain a variety of brachiopod-dominated assemblages, including the Eochonetes and Plaesiomys–Schizophorella associations, transported from various shelf locations, within a very diverse mid Ashgill biota. The upper Ashgill High Mains Formation contains abundant elements of the terminal Ordovician Hirnantia fauna, including Eostropheodonta, Hindella and Hirnantia itself, but also some taxa more typical of the Laurentian Edgewood Province. As a whole, the changing brachiopod biodiversity biofacies reflect environmental fluctuations, on this part of the Laurentian margin, driven by mainly eustatic and tectonic events against a background of global biotic radiation.

Distribution of recent benthic foraminifera on the Sunda Shelf (South China Sea)

In this study we investigate the species composition and spatial distribution patterns of Rose Bengal stained and unstained benthic foraminifera from the central part of the Sunda Shelf in the south-western South China Sea in relation to environmental factors. The uppermost centimetre of the surface sediments (> 150 μm) from 45 sites from inner (60 m) to outer shelf (226 m) water depths revealed 584 species including 443 stained species. The univariate analyses of individual species abundances and community parameters and next canonical correspondence analysis were used to relate the faunal data to a set of measured environmental parameters. Four biofacies recognised on the Sunda Shelf are most strongly correlated to water depth, primary production and sediment type of the habitat. The inner shelf biofacies (CCA cluster A), defined by Ammomassilina alveoliniformis and Asterorotalia pulchella, occurs in fine grained sediments classified as modern terrigenous mud in the region with the highest primary production values. The high-energy inner shelf biofacies (CCA cluster B), defined by Heterolepa dutemplei and Textularia lythostrota, occurs in modern terrigenous sand and silt dominated sediments, northeast from the Natuna Island. The high-energy outer shelf biofacies (CCA cluster C), defined by Cibicidoides pachyderma and Textularia bocki, is sandwiched between assemblages of biofacies D. It occurs in the region characterised by neritic relict sand. In the shallow-waters on the Sunda Shelf the relationship of benthic foraminiferal faunal composition to grain size of sediments indirectly signals the prevailing bottom hydrodynamic conditions. The dominance of the epibenthic foraminifera attached to bigger particles (e.g. Cibicides lobatulus, Planulina arimiensis) and much higher abundances of empty tests suggest greater current velocities northeast of Natuna Island. The outer shelf biofacies (CCA cluster D) is defined by Facetocochlea pulchra and Bulimina marginata. It occurs in an area covered with modern terrigenous silt and mud and is characterised by lower annual primary production, but seasonally influenced by weak upwelling.

The Recent temperate foraminiferal biofacies of the Gippsland Shelf: an analogue for Neogene environmental analyses in southeastern Australia

Abstract. This study describes the foraminiferal biofacies of a temperate stenohaline shelf and associated euryhaline marine lakes of Gippsland in southeast Australia. The study incorporates facies analyses and interpretations of three types of foraminiferal distributional data: forms alive at the time of collection, recently dead forms and relict forms. Four principal biofacies types occur: (1) the euryhaline marine Gippsland Lakes silts and sands; (2) inner shelf medium to coarse quartz-rich sands and bioclastic silty sands; (3) medium shelf bryozoan-rich bioclastic silt and silty sand; (4) outer shelf bryozoan- and plankton-rich silts and fine sands.The euryhaline marine Gippsland Lakes silts and sands contain abundant Ammonia beccarii and Eggerella, with minor Quinqueloculina, Elphidium and Discorbinella. The Gippsland inner shelf biofacies (0–50 m depths) consists of medium to coarse quartz-rich sands and bioclastic silty sand. Abundant living, relict and recently dead miliolids occur in the inner shelf with rare planktonic forms. Common planktonic foraminifera, with Cibicides, Parrellina, Elphidium and Lenticulina and relict forms occur in the bryozoan-rich bioclastic silt and silty sand of the Gippsland middle shelf (50–100 m depth). Bryozoan and plankton-rich silts and fine sand occur in the outer shelf to upper slope facies (100–300 m) below swell wave base on the Gippsland Shelf. A diverse fauna with common textulariids, Uvigerina, Bulimina, Anomalinoides and Astrononion and rare relict forms, occurs in this biofacies. Planktonic foraminifera and Uvigerina are most abundant at the shelf break due to local upwelling at the head of the Bass Canyon.Estimates of faunal production rates from live/dead ratios and full assemblage data suggest that the fauna of the Gippsland Shelf has not been significantly reworked by wave and/or bioturbation processes. Most relict foraminifera occur in the inner shelf, with minor relict forms in the middle to outer shelf. This pattern is similar to other shelf regions in Australia, where shelf areas were exposed during Pleistocene lowstand times, principally reworking pre-existing inner to middle shelf faunas. Correspondence analyses of the foraminiferal data yield a clear depth-related distribution of the faunal assemblage data. Most of the modern Gippsland Shelf fauna are cosmopolitan species and nearly a third are (semi-)endemic taxa suitable for regional palaeo-environmental studies. From biostratigraphic studies it is clear that the modern Gippsland foraminiferal assemblage evolved since Early Miocene times, with most elements present by the Late Miocene. Hence, the Recent Gippsland Shelf foraminiferal biofacies distribution is a good analogue for Neogene palaeo-environmental studies in the region. The longer ranging pre-Miocene mixture of epifaunal and infaunal taxa are deeper shelf cosmopolitan forms and are inferred to be more conservative since they evolved in relatively lower stress environments, typifying mesotrophic to eutrophic conditions compared to inner shelf epifaunal forms with ecological niches markedly affected by sea-level and temperature fluctuations in zones of constant wave action, in oligotrophic environments.The foraminiferal and facies analogues of this study on the Gippsland Shelf can be used for palaeo-environmental analyses of the Gippsland and Otway Neogene sedimentary successions. Such improvements will lead ultimately to a better understanding of the evolution of the neritic realm in southeastern Australia, an area facing the evolving Southern Ocean during the Cenozoic.

Foraminiferal biofacies and palaeoenvironmental evolution of an Oligo-Miocene cool-water carbonate succession in the Otway Basin, southeast Australia

Abstract. This multidisciplinary study integrates fades studies and foraminiferal analyses to assess the palaeoenvironmental evolution of an Oligocene to Miocene cool-water carbonate succession in the Otway Basin, southeastern Australia. The cool-water carbonate succession in the Otway Basin records signals relating to the evolution of the Southern Ocean throughout the Cenozoic. The strata are correlated with the relative coastal onlap curve of Haq et al. (1988) and several sequences can be identified in three formations. The Early Oligocene Narrawaturk Formation (TA 4.5) comprises near the base high-energy, inner shelf biofacies (lowstand systems tracts) and up-section to lower energy mid- to outer shelf marls (TST and maximum flooding surfaces) with storm events and/or minor shallowing intervals. Foraminiferal reworking and post-depositional dolomitization occurs at the top of this unit. The Late Oligocene Clifton Formation (TB 1.1 and TB 1.2.) was deposited in a relatively high-energy inner to mid-shelf environment. The base of this unit preserves evidence of a shift in biofacies that correlates to a major sea-level fall at the Mid/Late Oligocene boundary coincident with a major ice advance in Antarctica, and correlates with other Mid-Oligocene unconformities world-wide. The Late Oligocene Gellibrand Marl Formation (TB 1.2 and TB 1.3) began with low-energy outer shelf cherty marly biofacies (TST and MFS) followed by mid- to outer shelf calcisiltites (HST). High-energy mid- to outer shelf conditions were established after an hiatus in the Late Oligocene. A relative sea-level rise at the base of the Lower Miocene (TB 1.5 and TB2.1) led to the deposition of lower energy outer shelf cherty marls.Four biofacies with distinctive foraminiferal faunas are distinguished. (1) Grey mid- to outer shelf low-energy bryozoal marls with infaunal foraminifera and high plankton values. Two foraminiferal assemblages occur: lagenids and Uvigerina are common in the Narrawaturk marls, whereas bolivinids and Astrononion occur in the Gellibrand marls. The faunal variation in the marls may relate to changes in nutrient supply, anoxia, the presence or absence of organic material and/or changes in depth. (2) Chalky packstone facies with a high epifaunal content were deposited in oligotrophic inner to mid-shelf palaeoenvironments subject to intermittent reworking. (3) Bryozoan-poor inner to outer shelf foraminiferal packstones and grainstones facies enriched in epifaunal forms. (4) Well-sorted coarsegrained regular echinoid and bryozoan-rich packstones to grainstones. Infaunal taxa are absent in this facies, where most preserved foraminifera are robust spherical to discoidal forms. The facies were deposited in inner to mid-shelf palaeoenvironments where reworking by intense wave action (either above normal wavebase or by storms) winnowed out all smaller foraminifera.The stratigraphic and palaeoenvironmental utility of the Cenozoic foraminifera studied is improved greatly by facies analyses. Similar integrated studies will lead to better correlations and palaeoenvironmental interpretations of southeastern Australian sequences and equivalent successions in the southern hemisphere.

Comparative paleoecology of Cambrian trilobite extinctions

Analysis of 164 collections from shelf facies of Laurentian North America indicates that three successive trilobite mass extinctions at Late Cambrian stage boundary intervals (“biomere” boundaries) are characterized by a common pattern of change in distributional paleoecology and species diversity. In all cases, the extinction intervals are marked by a shift to biofacies that have broader environmental distributions than those prior to the onset of extinctions, implying a reduction in between-habitat (beta) diversity. Significant declines in within-habitat (alpha) diversity also characterize each extinction and the compositions of shelf biofacies record extensive immigration of taxa from off-shelf and shelf-margin sites. The nature and extent of ecologic disruption of the shelf appears to be comparable to changes associated with major mass extinctions, such as those at the end of the Ordovician and Permian. Unlike major mass extinctions, the Cambrian events are followed by a complete recovery of diversity and biofacies structure within a few million years.

Bathymetric distribution of benthic foraminifera on the Australian-Irian Jaya continental margin, eastern Indonesia

We identified 164 taxa of benthic foraminifera in 35 selected box-core top samples collected on the Australian-Irian Jaya continental margin in waterdepths between 60 and 2119 m, along three systematically sampled transects across the Banda Arc. The bathymetric distribution pattern of the benthic foraminiferal faunas is related to the oceanographic situation of this area, where the watermasses of the Indian Ocean collide with the watermasses of the Pacific Ocean. With the results of cluster analyses and empirical depth-ranges of “isobathyal” taxa, four faunal depth-zones and four subzones can be distinguished: 1.(A) The Outer Shelf Biofacies (60–150 m), corresponding to the photic oxycline-zone of the Indonesian Surface Waters, and inhabited by a benthic foraminiferal association dominated by Amphistegina lessonii, Operculina ammonoides, Heterolepa dutemplei and various miliolids.2.(B) The Upper Bathyal Biofacies (150–400 m), reflecting the aphotic, deeper Indonesian Surface Waters, dominated by Bolivina robusta, Heterolepa mediocris, Hanzawaia nipponica and Lenticulina spp. A major faunal break is situated at the lower boundary of this depth-zone.3.(C) The Middle Bathyal Biofacies (400–1500 m), representing the Indonesian Intermediate Waters with minimum oxygen-contents, dominated by Bolivina robusta, Cassidulina carinata, Gavelinopsis lobatulus and Sphaeroidina bulloides. In this depth-zone many taxa occur with only limited depth-ranges, on which four subzones (C1–4) could be identified, allowing for a local (paleo)bathymetric resolution of a few hundred meters.4.(D) The Lower Bathyal Biofacies (1500–2120 m) corresponds with the Indonesian Deep Waters. It is dominated by Pullenia bulloides and other cosmopolitan deep water indicators, such as Epistominella exigua, Laticarinina pauperata, Oridorsalis umbonatus and Planulina wuellerstorfi.The sample fraction > 250 μm can be used to readily delineate the major faunal trends. Paleobathymetric resolution improves when the sample portion > 125 μm is used.

Distribution of Benthic Foraminifers Across a Middle Miocene Basin Margin, Central California: Paleoenvironmental, Tectonic, and Biostratigraphic Implications: ABSTRACT

End_Page 498------------------------------The quantitative distribution of Miocene benthic foraminifers within the Cuyama basin, central California, demonstrates the relationship between biofacies, key species, and specific environmental factors. During the Miocene, the Cuyama basin occupied an inboard position along an active, convergent to translational, continental margin resembling the modern continental borderland off southern California. Benthic foraminiferal assemblages delineate shelf, slope, and basin plain biofacies. Migration and replacement of these biofacies with time reflect the depositional subsidence history of this Miocene basin. Initially, biofacies are broad and less structured, reflecting the influx of cosmopolitan species during early basin development. Recognizable biofacies are established quickly after the initial marine transgression and basin subsidence. As the basin fills, the number of biofacies decreases and deeper biofacies are excluded, whereas low oxygen and shelf biofacies expand. Bathymetrically displaced species are common, implying downslope transport by turbidity currents, increased sediment input, and/or tectonic activity. Benthic foraminiferal species diagnostic of the standard California Miocene stages and zones occur commonly throughout the Cuyama basin. Among the key biostratigraphic events commonly cited for the early and middle Miocene are the cal. zone (middle Luisian) and the evolutionary succession of valvulinerids and siphogenerinids. Although these events are important stratigraphic markers, some difficulty is encountered in recognizing certain zones and chronostratigraphic sequences are boundaries as presently defined. The bathymetric distribution and biofacies associations for certain key species critically impact on the usefulness of these species for biostratigraphy. Siphogenerinids appear only in slope, lower slope, and basin plain assemblages, and individual species are re tricted to specific parts of these areas. Stratigraphic and evolutionary events based on these species are therefore limited to deeper water environments. Valvulinerids are present in shelf-edge environments as in-situ members of assemblages and as transported specimens in deeper environments. The Valv. cal. flood is obscured in sections dominated by shelf-edge environments where valvulinerids occur in large numbers throughout the middle Miocene, and is confused in lower slope and basin plain assemblages where they are concentrated as transported specimens. Early and middle Miocene fauna distributions are complex. Sedimentary, tectonic, and oceanographic conditions strongly effect in-situ and transported occurrences of key species. These factors must be evaluated for individual basins if benthic foraminiferal zonations are to have regional applicability. End_of_Article - Last_Page 499------------

A cluster analysis interpretation of Middle Ordovician biofacies, southern Mackenzie Mountains

Collections of fossil trilobites, ostracods, bryozoans, and conodonts from Chazyan and Blackriveran strata of the southern Mackenzie Mountains are analyzed in an attempt to define biofacies, in terms of areal extent and faunal composition. Q-mode and R-mode cluster analyses, using Jaccard's coefficient and the unweighted pair-group method of clustering, are employed to delineate five biofacies. The interpretation of sedimentological features and composition of faunal assemblages shows that one nearshore biofacies, three progressively deeper shelf biofacies, and one continental slope biofacies are represented. A plot of biofacies succession through time in each measured section provides added support for the biofacies interpretations.

Recent Arctic Foraminifera: an Overview: ABSTRACT

The quantitative analysis of recent foraminiferal distributions in the Arctic Ocean indicates that major biofacies reflect broad water-mass relations. Shelf biofacies may also be influenced by substrate variability. Shelf biofacies, within the Arctic Ocean surface water layer (0 to 200 m), show the most variability. Marginal marine environments, characterized by extreme variability in physical and chemical factors, are inhabited by low-diversity assemblages (predominantly Elphidium spp.). The permanently ice-covered shelf of the Canadian Arctic contains a dominantly agglutinated fauna while the seasonally ice-free Beaufort shelf is characterized by dominantly calcareous assemblages. These regional differences are basically variations in species abundance and dominance. Slope biofacies are mixed agglutinated and calcareous assemblages lying beneath the Atlantic water layer (200 to 900 m). Agglutinated species generally become less abundant with depth. Lower slope and basin-plain environments are dominated by calcareous assemblages with agglutinated species virtually absent. These assemblages are indicative of the bottom water layer (deeper than 900 m). Planktonic foraminiferal assemblages are overwhelmingly dominated by sinistrally coiled Neogloboquadrina pachyderma. The distribution of planktonic foraminifera in death assemblages also reflects water-mass structure. Tests are absent or rare in sediments deposited beneath the surface water layer and rapidly increase in abundance below about 200 m. Species diversity trends in the Arctic Ocean show rapid increase in diversity across the inner shelf, a leveling off from the outer shelf to upper slope, and a decline in diversity into deeper water. Overall diversity is lower than similar depths at lower latitudes. Carbonate dissolution is not a factor in determining diversity or biofacies trends. Comparison of Arctic Ocean assemblages with foraminiferal faunas in the Gulf of Alaska shows decreasing similarity with depth, reflecting the influence of the Bering Strait as a barrier to faunal migration. End_of_Article - Last_Page 445------------

Environmental Relationships of Recent Ostracoda in Mesquite, Aransas, and Copano Bays, Texas Gulf Coast: ABSTRACT

ABSTRACT Ostracoda from approximately 100 stations in Mesquite, Aransas and Copano Bays, St. Joseph Island and nearby open Gulf of Mexico represent about 50 species distributed in three principal biofacies. (1) Subtropical lake, pond, and river biofacies with a prodelta subfacies; (2) shallow subtropical bay biofacies; (3) open shallow and subtropical open shelf biofacies. A statistical analysis of Ostracoda from Mesquite Bay suggests that some species are more adaptable than others to environmental changes in the bay. Some of the species of this assemblage range back as far as the Miocene and general similarities of environmental distribution of late Tertiary and Quaternary ostracode faunas and Recent assemblages are indicated by the study.

Foraminiferal Biofacies, Santa Monica Bay, California: ABSTRACT

Santa Monica Bay embraces an area extending more than 45 km. between Point Dume on the north and Palos Verdes Point on the south, and from the shoreline out into Santa Monica basin. Principal features are the mainland shelf (0 to 80 meters), the basin slope (80 to about 900 meters), and the basin floor which extends down to about 938 meters. The mainland shelf is a truncated positive feature separating the Santa Monica basin on the west from the filled Los Angeles basin on the east. Exposed Miocene-Pleistocene rocks on the shelf suggest this feature was formed during the Quaternary. Relict upper Pleistocene-Holocene sediments and faunas provide evidence of an episodic transgression of sea-level across the shelf. Analysis of 85 bottom samples indicates that Recent sediments become finer offshore with the exception of relict grains, and nitrogen values generally are higher in the deeper, fine-grained sediments. Echinoderms and mollusks dominate the megafauna near the edge of the shelf. General foraminiferal trends are: foraminiferal abundance increases offshore; live specimens are most abundant in the central shelf area; living species are most abundant in the central shelf area and in the bathyal zone; higher live/dead ratios occur on the central and outer shelf in areas of slow deposition; arenaceous types dominate dead populations on the central shelf; and live hyaline types are more than 8 times as abundant as live arenaceous forms in most areas. Inshore foraminiferal groups are characterized by species of Rotorbinella, Discorbis, and Elphidium. Open shelf biofacies are characterized by Buliminella elegantissima, Eggerella advena, Bulimina marginata denudata, and Trochammina pacifica. Species of Nonionella, normally abundant, are relatively rare, possibly because of ocean pollution. A Bolivina acuminata group of species is characteristic of the shelf edge and the upper basin slope. A deeper water Bolivina argentea basin facies appears at about 400 meters and is dominant on the floor of Santa Monica basin. End_of_Article - Last_Page 1079------------