Biofacies Model Research Articles

The conodont biofacies model of shallow paleoenvironments in Frasnian (Late Devonian)

The article considers various criteria of the conodont biofacies distinguishing, and principles of conodont paleoecological models reconstructing. The proposed conodont biofacies model is based on conodont distribution in the Frasnian (Upper Devonian) of the Voronezh anteclise (Central regions of Russian Platform).

The Conodont Biofacies Model of Shallow Paleoenvironments in the Frasnian (Late Devonian)

The Conodont Biofacies Model of Shallow Paleoenvironments in the Frasnian (Late Devonian)

The Berriasian–Aptian of the Western Gydan Peninsula (West Siberia): Biofacies and Lithofacies Models

Abstract —Well logs and core analyses of Berriasian–Aptian petroliferous sediments from the western Gydan Peninsula are used to model their biofacies and lithofacies and to reconstruct the respective sequence stratigraphy. The sedimentological and palynological data, along with logging results, provide constraints on the history of transgressive and regressive events and make a basis for paleogeographic reconstructions for the Lower Cretaceous deposition of reservoir sand beds.

Latest Devonian (Famennian, expansa Zone) conodonts and sponge-microbe symbionts in Pinyon Peak Limestone, Star Range, southwestern Utah, lead to reevaluation of global Dasberg Event

We document the signature of the late Famennian (Early expansa Zone) multi-phase Dasberg Event, previously termed ALFIE, in Utah and Colorado. The Dasberg was a major event, not a crisis, because it resulted from a eustatic rise that introduced the Etroeungt fauna, consisting of large solitary rugose corals and unusually large brachiopods, from an as yet undiscovered refugium. This “Lazarus” fauna was short-lived; it disappeared within a few million years, as a result of the more intensely studied end-Devonian (D—C) Hangenberg Extinction Event. Our research centers on a meter-thick sponge-microbe symbiont bed at the top of the lower member of the Pinyon Peak Limestone at Elephant Canyon, Star Range, southwestern Utah, USA, which formed during an early phase of the Dasberg Event. This “disaster” bed is well dated by conodont faunas in beds just below and just above. Superficially resembling stromatolites, the meter-thick symbiont bed contains microscopically interlayered sponges and microbialites. Occurring with the symbionts are bryozoans, brachiopods, and megascopic stromatoporoid sponges. This is arguably the first reported occurrence of late Famennian stromatoporoids in North America. Mounds at the top of the biostrome represent the last growth stage of the biostrome, which was arrested by development of a bored hardground. The mounds, which contain the same biota as the symbiont bed, were bored by unknown organisms. By combining our findings at Elephant Canyon with known data on Devonian ∂13C positive excursions, we determined that the biostrome developed at a time of warming during the otherwise cool late Famennian. The presence of a stromatolite-like symbiont bed is suggestive of an extinction event, especially as the environment of deposition represents shallow water, but with normal salinity, allowing growth of a diverse biota. Conodont faunas of the Pinyon Peak Limestone in the Star Range were pivotal in development of a late Famennian conodont biofacies model. Our re-dating of conodont faunas enables an improved correlation of the ∂13C curve between localities in Utah and Colorado.

Conodont biofacies and watermass structure of the Middle Pennsylvanian North American Midcontinent Sea

Climatic and glacio-eustatic information for the Late Paleozoic Ice Age is often extracted from cyclothems of the Midcontinent of North America. Although it is recognized that these important archives of global climate and environmental change are the result of waxing and waning of Gondwanan glaciers that produced widespread transgressive-regressive events, the relationships of conodont biofacies to changes in water depth, water chemistry, and other environmental parameters remain in dispute. Here, we investigate environmental gradients within the watermass of the Middle Pennsylvanian North American Midcontinent Sea (NAMS) based on geochemical proxies and conodont abundance patterns. To this purpose, we studied the Excello Shale at three geographically widely separated locations representing a ~500-km transect across the Midcontinent Shelf. We analyzed the organic (total organic carbon, carbon isotopes, and organic matter maturity) and inorganic geochemistry (major and trace elements) of the black and gray shale succession, as well as conodont abundance patterns and oxygen isotopic compositions, at 5–10 cm intervals through each study section.Our results suggest that the standard depth-stratification model of conodont biofacies in Pennsylvanian marine systems needs refinement. Although both Gondolella and Idioprioniodus are regarded as deep-water taxa, they differ in their stratigraphic distributions, with Idioprioniodus present through most of the Excello Shale but Gondolella confined to a narrow zone in the middle part. The Gondolella acme was not accompanied by pronounced changes in δ18O or trace-metal enrichment factors, implying that water depths and redox conditions were not the main controls on its distribution. Rather, the Gondolella acme is associated with the regressive condensation surface (RCS) of the core shale, which marks the onset of eustatic fall (renewed Gondwanan glaciation) and breakdown of the NAMS pycnocline. The latter process led to enhanced vertical overturn, mixing nutrients up into the ocean-surface layer and stimulating marine algal productivity, which was probably the trigger for blooms of Gondolella, suggesting that it was an opportunistic taxon. The upper part of the Excello is characterized by divergent δ18O compositions (~1‰ heavier in proximal areas), greater conodont abundance in offshore areas, and the appearance of Hindeodus exclusively in nearshore areas. This pattern suggests that Hindeodus was tolerant of somewhat more saline conditions, which developed during the climatic drying trend that accompanied the onset of the renewed Gondwanan glaciation. Our refined conodont biofacies model thus takes into consideration the effects of variable nutrient levels and watermass salinities in addition to water-depth controls.

Depositional biofacies model for post-OAE1a Aptian carbonate platforms of the western Maestrat Basin (Iberian Chain, Spain)

Two well exposed platform successions of late Early Aptian age developed in the central part of the Galve sub-basin of the Maestrat Basin: the highstand ‘Camarillas–El Morrón’ platform, and the succeeding ‘Las Mingachas’ small lowstand platform, built out downslope in the former basin. Both platforms had a flat-topped non-rimmed depositional profile, showing similar platform-top to slope biofacies, which are described here in both qualitative and quantitative terms. The proximal platform top succession is characterized by a Toucasia-dominated rudist association. The margins of the two platforms consist of massive limestone characterized by a Polyconites-dominated association, in which clusters of Polyconites hadriani in life position are joined by both branching and domal corals, as well as the oyster-like Chondrodonta and nerineid gastropods. In Las Mingachas platform, where the massive rudist- and coral-rich platform limestones pass laterally into the slightly more marly and recessive clinoforms of the upper slope facies, Polyconites is especially abundant. Basinwards these slope deposits pass into basinal marls with orbitolinids and ammonoids. The distribution of the two distinct rudist associations recognized here is attributed to the different environmental tolerances of the rudists with respect to such factors as current regime and rate of sedimentation. The prevalence of polyconitids, in place of caprinids, in these late Early Aptian platform margin facies makes a striking contrast with older, earliest Aptian platforms.

Chemosymbiont-dominated seafloor communities in modern and Cretaceous upwelling systems support a new, high-productivity variant of standard low-oxygen models

Faunal analysis of modern (Benguela upwelling system, Namibia) and ancient (upper Cretaceous, Israel) sedimentary records rich in organic matter, biogenic silica, carbonate, and phosphate indicates that, contrary to stereotypes of upwelling systems as dead zones, macrobenthic communities are present but highly variable. Biofacies vary with distance from the upwelling core and as a function of both the supply of food to the seafloor and the oxygen demand it creates there: under a high organic supply, large-bodied chemosymbiotic bivalves dominate exaerobic and lower dysaerobic seafloors, and deposit feeders are abundant in upper dysaerobic and aerobic zones. Macrobenthic biofacies under upwelling thus contrast strongly with the overwhelmingly filter feeder–dominated biofacies encountered in the dark siliciclastic shales on which standard oxygen-restricted biofacies models have been based, and argue that, mechanistically, the low-oxygen conditions characterizing those shales reflect ordinary levels of water-column productivity and arise largely from water-column stratification. Our biofacies model requires testing in other upwelling records. However, we expect it to be robust and useful given the long evolutionary histories of the chemosymbiotic and deposit-feeding guilds, providing a new means for discriminating the relative roles of high organic flux and low ventilation in creating low-oxygen conditions at the seafloor.

Planktonic foraminifera in the sediment of a western boundary upwelling system off Cabo Frio, Brazil

Abstract The distribution of planktonic foraminifera in box-core tops under the influence of a western boundary upwelling system along the southeastern Brazilian continental margin was examined to evaluate the similarity percentage (SIMPER) and to create a biofacies model for paleoenvironmental applications. Species associated with warm and oligotrophic water were distributed in the Rio de Janeiro sector of the Campos Basin, while productive water species were most abundant in the Rio de Janeiro sector of the Santos Basin, and cold-water species were most abundant in the Cabo Frio Upwelling System (CFUS). Four major biofacies are associated with the oceanographic setting of the CFUS: one from the Campos Basin (A — Brazil Current front), one from the Santos Basin (B — mixture of coastal and oceanic waters), and two associated with the Cabo Frio High in the northern biofacies (C) and southern biofacies (D). The distribution of biofacies C and D was associated with temperature differences. Biofacies C represents a mixture of upwelling and tropical waters, while biofacies D represents a mixture of cold, nutrient-rich and Santos Basin waters. These biofacies were also defined in core CF10-01B, in which six main paleoceanographic phases were characterized during the last 9 cal kyr, predominantly showing alternating dominance between biofacies C and D. From 9.0 to 5.0 cal kyr before the present (BP), the system was dominated by biofacies C. Between 4.0 and 3.5 cal kyr BP, biofacies D was dominant. Between 3.5 and 2.5 cal kyr BP, a strong influence of coastal waters and weakened upwelling activity were indicated by the dominance of biofacies B + C + D. The last 2.5 cal kyr was dominated by biofacies D. The SST in this core was reconstructed using the Modern Analog Technique (MAT), which revealed 0.35 °C of variability, indicating no SST changes during the Holocene. The weak sensitivity of the MAT was due to the interplay among different oceanographic features.

Bioturbation by symbiont-bearing annelids in near-anoxic sediments: Implications for biofacies models and paleo-oxygen assessments

Anoxic or nearly anoxic conditions (<4 μM O 2) have long been associated with the absence of bioturbation and animal traces. This premise has guided interpretation of paleoceanographic conditions from rocks and sediments. We recently observed a high-density, living assemblage of highly mobile, symbiont-bearing, burrowing, phallodrilinid oligochaetes within a nearly anoxic basin (<1 μM O 2 [0.02–0.03 ml l −1]) on the Peru margin (305 m). These observations were made during the most intense part of the 1997–98 El Niño when there may have been slight oxygenation of an otherwise anoxic basin, but oligochaete presence prior to this event is likely. The occurrence of symbiont-bearing gutless oligochaetes mainly within the upper 5 cm of the sediment column coincided with a bioturbated zone overlying distinctly laminated sediments. Our observations redefine the lower oxygen limit of macrofaunal bioturbation to ≪2 μM, and indicate a need to modify currently accepted ideas about the relationship between bioturbation and paleo-oxygen concentration. These results also address an ongoing debate about the lifestyles of bioturbating organisms in oxygen-poor settings.

Variations in bioturbation across the oxygen minimum zone in the northwest Arabian Sea

Oxygen minimum zones are expected to alter substantially the nature, rates and depths of bioturbation along continental margins, yet these effects remain poorly studied. Using excess 210 Pb profiles, sediment X-radiography and box-core samples for macrofauna, we examined bioturbation processes at six stations (400, 700, 850, 1000, 1250 and 3400 m deep) along a transect across the oxygen minimum zone (OMZ) on the Oman margin. Bottom-water oxygen concentrations ranged from ∼0.13 ml l −1 at 400 m to ∼2.99 ml l −1 at 3400 m. 210 Pb mixed-layer depth and bioturbation intensity ( D b) exhibited high within-station variance, and means did not differ significantly among stations. However, the mean mixed-layer depth (4.6 cm) for pooled OMZ stations (400–1000 m depths, 0.13–0.27 ml l −1 bottom-water oxygen) was half that for stations from similar water depths along well-oxygenated Atlantic and Pacific slopes (11.1 cm), suggesting that oxygen stress reduced 210 Pb mixing depth on the Oman margin. Modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom-water oxygen concentration from the edge to the core of the Oman OMZ (Spearman's rho⩾0.89, p⩽0.02), suggesting that these parameters are useful proxies for bottom-water oxygen concentrations under dysaerobic conditions. In contrast, neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen-related patterns along the transect. Reduced 210 Pb mixing depth within the Oman-margin OMZ appeared to result from a predominance of surface-deposit feeders and tube builders within this zone, rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass. The number of burrow types per station was highly correlated with macrofaunal species diversity, suggesting that burrow diversity may be a good proxy for species diversity in paleo-dysaerobic assemblages. We conclude that bottom-water oxygen concentrations of 0.13–0.27 ml l −1 substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins.

Extension of lithofacies and conodont biofacies models of Late Devonian to Early Carboniferous carbonate ramp and black shale systems, southern Canadian Rocky Mountains

Uppermost Devonian and Lower Mississippian strata in the Rocky Mountains of southwestern Canada and northwestern Montana record widespread oceanographic changes during middle to late Paleozoic time associated with the termination of a carbonate ramp system, the onset of a deep-water, low-oxygen event and possible marginal tectonism, and the later reestablishment of a carbonate ramp. Integrated lithofacies and conodont biofacies developed previously for these strata between the Bow Valley and the international border have been extended northward to the Athabasca region of the Alberta Rocky Mountains. During early-middle Famennian time, the southern Canadian Rocky Mountains region was the site of a westward-deepening and westward-thickening carbonate ramp system (Palliser Formation). By late Famennian time carbonate ramp deposition ended and was followed by widespread deposition of organic-rich, low-oxygen facies in shelf to basinal environments (Exshaw Formation and correlative units). The overlying Banff Formation consists of anaerobic to marginally aerobic, starved-basin to deep-ramp lithofacies succeeded by shallower water carbonates; this sequence records basinward (westward) progradation of the Banff ramp in middle to late Tournaisian time. Distinct conodont biofacies representative of shallow-ramp to deep-basin settings that were previously recognized in the southernmost Canadian Rocky Mountains and Montana have also been identified to the north between the North Saskatchewan and Athabasca valleys. Upper Palliser carbonates contain low-diversity conodont faunas of indigenous to transported palmatolepid-, polygnathid-, and apatognathid-dominated assemblages. Exshaw deposits contain indigenous and reworked palmatolepid- and bispathodid-dominated assemblages and reworked or transported polygnathids. Lower Banff biofacies include transported and indigenous assemblages of siphonodellids, polygnathids, and pseudopolygnathids representative of the deep-middle Banff ramp. Polygnathid-hindeodid biofacies of shallower middle-ramp environments occur higher in the Banff Formation in the North Saskatchewan and Athabasca valleys.

Extension of lithofacies and conodont biofacies models of Late Devonian to Early Carboniferous carbonate ramp and black shale systems, southern Canadian Rocky Mountains

Extension of lithofacies and conodont biofacies models of Late Devonian to Early Carboniferous carbonate ramp and black shale systems, southern Canadian Rocky Mountains

Diversity and Species Abundance Patterns in Late Cenomanian Black Shale Biofacies, Western Interior, U.S.

Questions concerning the application of established biofacies models to mid-Cretaceous black shales prompted a study of diversity characteristics in a fauna from the Late Cenomanian Hartland Shale Member, Western Interior basin. Numerical faunal data are used to assess species abundance patterns, and a new method of analyzing diversity is introduced that incorporates species richness, Shannon index, and equitability into a single plot. In addition, numerical simulations designed to emulate the sampling of species-abundance distributions are used to improve data interpretation. The study illustrates how measured diversity results from the combination of primary ecological controls and sampling effects. Proximal offshore assemblages are characterized by high diversity and log series species-abundance patterns, interpreted as truncated (incompletely sampled) log-normal distributions. Primary ecological controls include variable physical/chemical parameters, biological factors such as predation and competition, and intermediate disturbance frequency. Distal offshore assemblages are characterized by low diversity with patterns of species abundance resembling geometric series. These are interpreted as truncated log-series distributions (sampling effect) that reflect dominance of multiple opportunists, abundant resources in a dysoxic environment, and high disturbance frequency. The data are used to develop an ecological model for diversity levels in basinal black shale facies based on the interplay of recruitment, growth rate, tolerance to low oxygen and sulphide, and disturbance frequency (due to fluctuations of the redox boundary). Although certain taxa (chiefly Inoceramidae) evolved highly opportunistic life strategies to exploit basinal paleoenvironments, it was the unpredictable interaction of these four factors that determined diversity patterns. Analysis of Hartland Shale biofacies illustrates the difficulties in applying a strictly linear relationship between paleo-oxygen levels and diversity.

Biofacies Model for Identification of Paleodepth Trends, Maximum Flooding Surfaces and Marine Condensed Sections in Late Carboniferous and Early Permian Fourth-Order Cyclothemic-Scale Depositional Sequences in North America

Biofacies Model for Identification of Paleodepth Trends, Maximum Flooding Surfaces and Marine Condensed Sections in Late Carboniferous and Early Permian Fourth-Order Cyclothemic-Scale Depositional Sequences in North America - Volume 8

An Alternative Benthic Biofacies Model for the Plio-Pleistocene of the Gulf of Mexico: Examples from the Green Canyon Area: ABSTRACT

An Alternative Benthic Biofacies Model for the Plio-Pleistocene of the Gulf of Mexico: Examples from the Green Canyon Area: ABSTRACT

Revision of the Zone 13 graptolite biostratigraphy in the Marathon, Texas, standard succession and its bearing on Upper Ordovician graptolite biogeography

One of the long-standing problems in North American graptolite biostratigraphy is the distinct differences in assemblages of post-Climacograptus bicornis age between the classical graptolite sequences in the New York - Quebec and Marathon, west Texas, regions. These have been attributed either to faunal provincialism or to the presence of a major hiatus between the Woods Hollow and Maravillas formations in Texas. New collections from the key Marathon Picnic Grounds section contain diagnostic Late Ordovician graptolites that confirm the existence of a major stratigraphic gap below the Maravillas Formation. The lower Maravillas Formation (Zone 13) has a Late Ordovician, low-diversity Pacific Province graptolite fauna that includes the biostratigraphically diagnostic species Climacograptus nevadensis, C. tubuliferus, Orthograptus fastigatus and Dicellograptus ornatus. Zone 13 graptolite assemblages from the Marathon region correlate with the C. tubuliferus to D. ornatus zones in the Trail Creek, Idaho, succession, the Ea4-Bo2 interval in Victoria, the O. fastigatus Zone in the Canadian Arctic Islands, the O. quadrimucronatus to D. ornatus zones of the Canadian Cordillera, and the D. complanatus to D. anceps zones in Scotland. The hiatus between the Woods Hollow and Maravillas formations spans an interval corresponding to at least the Eal Ea3 interval in Australia, the C. americanus to upper A. manitoulinensis zones in the New York - Quebec succession, and the D. clingani and P. linearis zones in Scotland. These results agree with the magnitude of the hiatus previously indicated by conodont biostratigraphy. Late Ordovician graptolite distribution patterns in North America can be explained by an extension of Cooper, Fortey & Lindholm's (1991; Lethaia 24) Lower Ordovician graptolite biofacies model into the Upper Ordovician, which incorporates both lateral water-mass specificity and depth stratification. Using this model, we recognize in Laurentia two separate biofacies among tropical-zone Late Ordovician Pacific Province graptolite faunas, a cosmopolitan Oceanic biofacies, and a cratonic Laurentian biofacies. The lower Maravillas Formation graptolite fauna is clearly part of the Oceanic biofacies, whereas the coeval Appalachian faunas represent the Laurentian biofacies. □Graptolites, Ordovician, biostratigraphy, Texas, biofacies, biogeography.

Palaeoecological models, non-uniformitarianism, and tracking the changing ecology of the past

Abstract Palaeoecological models are commonly used by palaeontologists and sedimentary geologists to reconstruct ancient palaeoenvironments. In order to illustrate the ways in which palaeoecological models develop as new information is discovered, four examples are discussed: (1) reefs and fossil cold seeps; (2) biofacies models for strata deposited in ancient oxygen-deficient environments; (3) palaeoenvironmental distributions of post-Ordovician stromatolites; and (4) onshore-offshore trends of trace fossils. The development of physical sedimentological and geochemical criteria that can independently be used for evaluating ancient depositional environments provides a base line with which to assess palaeoecological change through geological time. Thus, the possibility now exists to free palaeoecological models and the study of ancient ecology from traditional uniformitarianism and Lyell’s dictum that the ‘present is the key to the past’, so that palaeoecological models may be developed which are useful for segments of time not anchored in the present. This approach will also be essential for evaluating the changing ecology of the past, which at present is only poorly understood. Future development and independent testing of such palaeoecological models will allow a more complete appreciation of the changing roles of environment, ecology and evolution in the history of life.

Benthic invertebrates of a modern carbonate ramp: a preliminary survey

A preliminary survey of benthic invertebrates off central west Florida provides documentation of modern epifaunal communities on a low-gradient carbonate slope. Three large-scale biofacies occur in soft-sediment carbonate environments between 200 and 2,000 m: an Echinoderm biofacies (200–550 m) dominated by a diverse assemblage of echinoderms, gastropods, and decapod crustaceans; a Penaeid shrimp–conical mound biofacies (550–1,200 m) characterized by large bioturbation structures; and a Microbial mat biofacies (1,200–2,000 m) with only rare epifaunal invertebrates. A fourth, hard-substrate biofacies reflects the presence of localized Miocene and Pleistocene hardgrounds in water depths of 200–600 m. This illustrates that hard-substrate biofacies may be laterally correlative with soft-sediment biofacies in a slope setting, thus producing a mosaic of contrasting faunal associations. All four biofacies have low population densities, presumably as a consequence of relatively low surface productivity. All four biofacies also show biogeographic affinity with other faunas at intermediate depths in the Caribbean region. Depth-related faunal transitions on the west Florida slope correlate with substrate and current velocity. Decreasing species diversity and abundance and a biofacies transition from suspension-feeding to deposit-feeding assemblages correlate with increasing depth, a decrease in mean grain size, and an increase in organic content of the sediment. This biofacies model may provide a modern analogue for faunas of ancient low-gradient slopes such as those of Cretaceous “shelf-sea” chalks of northwestern Europe.

Palaeoecology and sedimentology of the dysaerobic Bedford fauna (late Devonian), Ohio and Kentucky (USA)

Oxygen-deficient biofacies models rely on lithologic and paleontologic attributes to identify distinctive biofacies interpreted to reflect levels of oxygenation in anaerobic, dysaerobic, and aerobic parts of a stratified water column. This study of the Bedford fauna from the Bedford Shale of Ohio and Kentucky and from adjacent black-shale units reports faunal distributions different from those predicted by the accepted models. This study suggests that, although oxygenation was an important factor that determined the taxonomic makeup of the fauna, bacterially mediated nutrient recycling and substrate characteristics were more important than oxygenation in determining faunal distribution in the dysaerobic zone.

Mixed Siliciclastic-Carbonate Deposition in an Early Cambrian Oxygen-Stratified Basin, Chapel Island Formation, Southeastern Newfoundland

ABSTRACT The upper portion of member 3 and member 4 of the uppermost Precambrian (Vendian)-Lower Cambrian Chapel Island Formation represents a large-scale shoaling-up deposit dominated by shelf siliciclastic mudstone. Medium-scale, higher-order shoaling-up cycles at the top of member 3 and in member 4 are capped by peritidal limestones that contain a wide variety of stromatolitic buildups and algal mud mounds. Sedimentation took place in an oxygen-stratified basin with accumulation of gray dysaerobic mudstone offshore and green and red mudstone in shallower, more oxygenated waters. Biofacies models for dysaerobic basins can be applied to this sequence and help in understanding the distribution of trace fossils, skeletal fossils (shells and pyritic steinkerns), and diagenetic features. These da a are important for the understanding of the stratigraphic distribution of shelly fossils within this lowest Cambrian unit. A mixed carbonate-siliciclastic facies model is presented in which carbonate sediments formed in intertidal areas along the shoreline of a siliciclastic muddy shelf. The carbonate shoreline prograded during periods of increasing rate of relative sea-level fall or decreasing rate of relative sea-level rise. Restriction of carbonate sediments to the peritidal environment may have been due to a combination of higher rates of carbonate sediment production and accumulation in the peritidal zone, seaward dilution by siliciclastic mud, and a paleogeographic position near the latitudinal climatic extreme for carbonate production.