Deep-water Facies Research Articles

Changhsingian (latest Permian) deep-water brachiopod fauna from South China

This paper describes 45 brachiopod species (including 15 undetermined species) in 23 genera belonging to seven orders (Productida, Spiriferida, Athyridida, Orthida, Orthotetida, Rhynchonellida and Lingulida) from the Talung Formation (Changhsingian, latest Permian) of the marine deep-water facies of South China. Two new genera are proposed: Chaohochonetes and Parapygmochonetes; along with nine new species: Tethyochonetes rectangularis, Tethyochonetes? sinuata, Chaohochonetes triangusinuata, Neochonetes (Zhongyingia?) liaoi, Neochonetes (Huangichonetes?) wufengensis, Paryphella majiashanensis, Paryphella minuta, Parapygmochonetes parvulus and Meekella sparsiplicata. The taxonomic composition, significant morphological features and palaeoecological implications of this deep-water brachiopod fauna are summarized, and the fauna is compared with the Permian–Triassic boundary (PTB) mixed brachiopod fauna of South China. The Changhsingian (latest Permian) deep-water brachiopod fauna of South China shares some common features with the PTB mixed brachiopod fauna, especially in terms of taxonomic composition and certain apparent morphological adaptations. This commonality is interpreted to indicate a time and a broad marine environment of widespread low oxygen supply and/or reduced trophic resources during the end-Permian life crisis in South China.http://zoobank.org/urn:lsid:zoobank.org:pub:744771BB-7377-4239-8A29-89183ECEBE09

Integrated middle–upper Homerian (Silurian) stratigraphy of the Viduklė-61 well, Lithuania

Integrated lithostratigraphical, cyclostratigraphical, graptolite and conodont biostratigraphical and chemostratigraphical (δ13C) data are presented from the upper Jaagarahu, Gėluva and Dubysa regional stages, including the lundgreni Event (middle Homerian) in the Viduklė-61 well, Lithuania. The Viduklė-61 well is located in the west of Lithuania in the deep-water facies zone. Because of its completeness, this section is the “keystone” for middle–upper Homerian stratigraphy that allows us to combine different kinds of data into a coherent picture of large-scale biotic and environmental turnover. Three formations are distinguished: the upper part of the Riga Formation, with the Ančia Member in the uppermost part, the Siesartis Formation and the lower part of Dubysa Formation. The Grötlingbo bentonite is in the upper part of Ančia Member. In the Gėluva regional stage, two 4th-order and six 5th-order cycles have been distinguished. In the studied interval of the Viduklė-61 core, the following graptolite biozones were recognized: lundgreni (upper part), parvus, nassa, praedeubeli, deubeli, ludensis and nilssoni (lower part). Conodonts enabled recognition of the bohemica longa Biozone. A single find of Ctenognathodus murchisoni Pander in the nassa graptolite interzone indicates an earlier than previously thought origin of this species.

Biostratigraphy and lithostratigraphy of the Mid-Carboniferous boundary beds in the Muradymovo section (South Urals, Russia)

AbstractThe uninterrupted succession of the Mississippian–Pennsylvanian boundary beds in the Muradymovo section in the South Urals contains diverse fossils and has a high correlative potential. The Muradymovo section is located in the Zilair Megasynclinorium (ZM), which belongs to the West Uralian Subregion and displays carbonate-siliciclastic deep-water facies of the Bukharcha Formation, which is partly Serpukhovian (Kosogorian, Protvian and Yuldybaevian) and partly Bashkirian (Syuranian). In the southern ZM, the lower part of the formation contains argillaceous carbonates with beds of shale and siltstone, subordinate clastic limestones and limestone breccia, while the upper part is mostly limestone with cherty interbeds. In the north of the ZM, the formation mainly consists of limestone. The Muradymovo succession contains no identifiable gaps in the Mid-Carboniferous Boundary (MCB) portion and has a succession of foraminiferal, conodont, ammonoid and ostracod zones. The MCB in this section coincides with the base of the Bogdanovkian and is defined by the entry ofDeclinognathodus noduliferus.This level falls within the upper part of the foraminiferalMonotaxinoides transitoriusZone, is near the base of the ammonoidHomoceras–HudsonocerasGenozone and can be correlated worldwide.

Orbital-scale climate change and glacioeustasy during the early Late Ordovician (pre-Hirnantian) determined from δ18O values in marine apatite

Research Article| July 01, 2013 Orbital-scale climate change and glacioeustasy during the early Late Ordovician (pre-Hirnantian) determined from δ18O values in marine apatite M. Elrick; M. Elrick 1Earth & Planetary Sciences Department, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar D. Reardon; D. Reardon 1Earth & Planetary Sciences Department, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar W. Labor; W. Labor 1Earth & Planetary Sciences Department, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar J. Martin; J. Martin 1Earth & Planetary Sciences Department, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar A. Desrochers; A. Desrochers 2Department of Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada Search for other works by this author on: GSW Google Scholar M. Pope M. Pope 3Geology and Geophysics Department, Texas A&M, College Station, Texas 77483, USA Search for other works by this author on: GSW Google Scholar Geology (2013) 41 (7): 775–778. https://doi.org/10.1130/G34363.1 Article history received: 03 Jan 2013 rev-recd: 13 Feb 2013 accepted: 19 Feb 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. Elrick, D. Reardon, W. Labor, J. Martin, A. Desrochers, M. Pope; Orbital-scale climate change and glacioeustasy during the early Late Ordovician (pre-Hirnantian) determined from δ18O values in marine apatite. Geology 2013;; 41 (7): 775–778. doi: https://doi.org/10.1130/G34363.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract This study focuses on the ∼10 m.y. before the latest Ordovician (Hirnantian) glaciation; we test whether orbital-scale climatic fluctuations controlled the growth and melting of continental glaciers, resulting in glacioeustatic sea-level changes and the development of widespread marine sedimentary cycles. δ18O values of conodont apatite from 14 Late Ordovician (Katian) cycles range from ∼17‰ to 21‰. Isotopic values decrease and are lowest in the deepest water facies and increase and are highest in shallow-water facies, supporting the hypothesis that glacioeustasy was the dominant control on water-depth changes. Measured intracycle δ18O changes of 0.7‰–2.5‰ were controlled by changes in ice volume (<60 m sea-level changes), sea-surface temperatures (<5 °C), and potentially local increases in seawater evaporation during drier and/or windier glacial stages. These interpreted orbital-scale climate changes and resultant large glacial ice-volume changes support recent interpretations of a dynamic and prolonged Ordovician greenhouse to icehouse transition. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Carbon isotopes and lipid biomarkers from organic‐rich facies of the Shuram Formation, Sultanate of Oman

The largest recorded carbon isotopic excursion in Earth history is observed globally in carbonate rocks of middle Ediacaran age. Known from the Sultanate of Oman as the 'Shuram excursion', this event records a dramatic, systematic shift in δ(13) Ccarbonate values to ca. -12‰. Attempts to explain the nature, magnitude and origin of this excursion include (i) a primary signal resulting from the protracted oxidation of a large dissolved organic carbon reservoir in seawater, release of methane from sediment-hosted clathrates, or water column stratification; and (ii) a secondary signal from diagenetic processes. The compositions and isotope ratios of organic carbon phases during the excursion are critical to evaluating these ideas; however, previous work has focused on localities that are low in organic carbon, hindering straightforward interpretation of the observed time-series trends. We report carbon isotope data from bulk organic carbon, extracted bitumen and kerogen, in addition to lipid biomarker data, from a subsurface well drilled on the eastern flank of the South Oman Salt Basin, Sultanate of Oman. This section captures Nafun Group strata through the Ediacaran-Cambrian boundary in the Ara Group and includes an organic-rich, deeper-water facies of the Shuram Formation. Despite the high organic matter contents, the carbon isotopic compositions of carbonates - which record a negative δ(13) C isotope excursion similar in shape and magnitude to sections elsewhere in Oman - do not covary with those of organic phases (bulk TOC, bitumen and kerogen). Paired inorganic and organic δ(13) C data only display coupled behaviour during the latter part of the excursion's recovery. Furthermore, lipid biomarker data reveal that organic matter composition and source inputs varied stratigraphically, reflecting biological community shifts in non-migrated, syngenetic organic matter deposited during this interval.

Stratal architecture and platform evolution of an early Frasnian syn‐tectonic carbonate platform, Canning Basin, Australia

AbstractFacies architecture and platform evolution of an early Frasnian reef complex in the northern Canning Basin of north‐western Australia were strongly controlled by syn‐depositional faulting during a phase of basin extension. The margin‐attached Hull platform developed on a fault block of Precambrian basement with accommodation largely generated by movement along the Mount Elma Fault Zone. Recognition of major subaerial exposure and flooding surfaces in the Hull platform (from outcrop and drillcore) has enabled comparison of facies associations within a temporal framework and led to identification of three stages of platform evolution. Stage 1 records initial ramp development on the hangingwall dip slope with predominantly deep subtidal conditions that prevented any cyclic facies arrangements. This stage is characterised by basal siliciclastic deposits and a major deepening‐upward facies pattern that is capped by a sequence boundary towards the footwall (north‐west) and a major flooding surface towards the hangingwall. Stage 2 reflects the bulk of platform aggradation, significant platform growth towards the hangingwall and the development of reef margins and cyclic facies arrangements. Thickening of this stage towards the hangingwall indicates that accommodation was generated by rotation of the fault block and overlying platform. Stage 3 records a major flooding and backstep of the platform margin. The Hull platform illustrates important elements of margin‐attached carbonate platforms in a half‐graben setting, including: (i) prominent, but limited, coarse siliciclastic input that does not have a major detrimental effect on carbonate production near the rift margin in arid to semi‐arid settings; (ii) wedge‐shaped accommodation created by syn‐depositional rotation of fault blocks and tilting of the hangingwall dip slope, resulting in shallow‐water facies and subaerial exposure up‐dip of the rotational axis and deeper water facies down‐dip; and (iii) evolution of a ramp to rimmed shelf, coincident with a sequence boundary–flooding surface, that is accelerated by tilting of the hangingwall dip slope during fault‐block rotation.

Island slopes and jumbled shell beds

Shell beds pose questions of provenance, but determining the degree of pre-depositional transport of bioclasts can be speculative. Bioclastic beds deposited on a broad, shallow continental shelf may consist of a minimally transported accumulation. In contrast, islands may have steep shelves and accumulate disharmonious bioclastic assemblages in deeper water. The latter are a signature of the stratigraphic record on many islands. Herein, we contrast differing examples of jumbled shell beds preserved around islands. The Lower Permian Mengkarang Formation of Sumatra preserves deep-water facies at the base of a volcanic section. Nektonic cephalopods overlie a fine-grained ash containing a diverse association of terrestrial pollen. The Lower Miocene Montpelier Formation of Jamaica yields allochthonous packstones and slide blocks of reef limestone embedded in chalk; the ichthyofauna indicates deposition in ≥200 m water depth. Abundant evidence that deposition occurred in a deep-water turbidite basin flanking a volcanic island is found in the Middle Miocene Grand Bay Formation of Carriacou, the Grenadines. Diverse, deeper water taxa are preserved in association with land snails, hermatypic scleractinians, algal balls and planktic pteropods. The famous Upper Pliocene Bowden shell beds, Jamaica, preserve terrestrial, shallow-water, deep-water and planktic taxa.

Ordovician stratigraphy of the Stumsnäs 1 drill core from the southern part of the Siljan Ring, central Sweden

The Stumsnäs 1 core, drilled in 2011 in the southern part of the Siljan Ring, provides new insights into the stratigraphy of the Ordovician succession in central Sweden. The core section shows evidence of the structural complications caused by the late Devonian meteorite impact in the area. In the core, about 90 m of Tremadocian to Darriwilian strata are sandwiched between Proterozoic igneous basement rocks. At the lower contact, the sedimentary succession starts with glauconitic, fine-grained siliciclastics and carbonates directly resting on the weathered basement. The basal siliciclastic unit is overlain by a ca. 19-m-thick limestone succession, well-known from this part of the Baltoscandian Basin, includes strata corresponding to the Latorp Limestone through the upper Holen Formation. This succession is covered by a limestone–marl alternating sequence, representing some yet unknown deeper water facies, presumably coeval to the topmost Holen Formation through upper Dalby Limestone. The upper third of the sedimentary succession in the core includes numerous slices of partly overturned strata, including relatively thick successions of the Slandrom Formation, Fjäcka Shale and Jonstorp Formation, as well as carbonate and siliciclastic units of yet unknown stratigraphic origin.

Facies analysis and sequence stratigraphy of an Upper Jurassic carbonate ramp in the Eastern Alborz range and Binalud Mountains, NE Iran

Upper Jurassic (Oxfordian-Kimmeridgian-Tithonian?) strata of NE Iran (Lar Formation) are composed of medium- to thick-bedded, mostly grainy limestones with various skeletal (bivalves, foraminifera, algae, corals, echinoderms, brachiopods, and radiolaria) and nonskeletal (peloids, ooids, intraclasts, and oncoids) components. Facies analysis documents low- to high-energy environments, including tidal-flat, lagoonal, barrier, and open-marine facies. Because of the wide lateral distribution of facies and the apparent absence of distinct paleobathymetric changes, the depositional system likely represents a westward-deepening homoclinal ramp. Four third-order depositional sequences can be distinguished in each of five stratigraphic measured sections. Transgressive system tracts (TST) show deepening-upward trends, in which shallow-water (tidal flat and lagoonal) facies are overlain by deeper-water (barrier and open-marine) facies. Highstand systems tracts (HST) show shallowing-upward trends in which deep-water facies are overlain by shallow-water facies. All sequence boundaries in the study area (except at the top of the stratigraphic column) are of the nonerosional (SB2) type. Correlation of depositional sequences in the studied sections show that relatively shallow marine (tidal-flat, lagoonal, barrier, and shallow open-marine) conditions dominated in the area. These alternated with deep-water open-marine wackestone and mudstones representing zones of maximum flooding (MFZ).

Quaternary seismic facies of the atlantic continental rise

High-resolution seismic profiles collected by Parasound and SES-2000 deep profilers during Cruise 26 of the R/V Akademik Sergei Vavilov (2009) along the continental slope base of South America, NW Africa, and West Europe are correlated with the deep-sea drilling boreholes. Lithofacies interpretation of the Quaternary deep-water seismic facies of hemipelagites, bottom current deposits (contourites), and gravitites (turbidites, mud flow deposits) is presented. The data obtained reveal the domination of contourites in the accumulation of continental rise apron under conditions of relatively scarce terrigenous material supply. It is shown that acoustically stratified seismic facies under these conditions commonly reflect interbedding of the terrigenous clay and biogenic calcareous ooze related to the Pleistocene glacial/interglacial cycles.

Systematics and palaeoecology of Changhsingian (Late Permian) Ambocoeliidae brachiopods from South China and implications for the end-Permian mass extinction

Weihong He, G.R. Shi, Yang Zhang, Tinglu Yang, Fei Teng.& Shunbao Wu, December 2012. Systematics and palaeoecology of Changhsingian (Late Permian) Ambocoeliidae brachiopods from South China and implications for the end-Permian mass extinction. Alcheringa 36, 515–530. ISSN 0311-5518. Four Ambocoeliidae brachiopod species including one new species (Crurithyris tazawai sp. nov., Crurithyris sp., Paracrurithyris pygmaea and Attenuatella mengi) are described from the Changhsingian (Late Permian) deep-water facies of South China. Analysis of the morphology, palaeoecology and palaeogeographical and temporal distributions of these species revealed that the presence of a delthyrium and/or the micro-ornaments among three of the four species (Crurithyris tazawai sp. nov., Paracrurithyris pygmaea and Attenuatella mengi) favoured an epifaunal (epiphytic) lifestyle. Morphological differences suggest that Paracrurithyris pygmaea may have been more effective metabolically in forming the shell compared with Attenuatella mengi and Crurithyris tazawai. The temporal and palaeogeographical distribution of Attenuatella suggests that A. mengi inhabited cool or cold deep waters. Both Crurithyris tazawai and Attenuatella mengi disappeared earlier in the stratigraphic record than Paracrurithyis pygmaea during the Permian–Triassic mass extinction. These differences in timing of extinction, morphology and palaeogeographical distributions suggest that oxygen deficiency and trophic resource limitation (a consequence of the changing composition of marine phytoplankton in the seas) may have contributed to the end-Permian mass extinction.

Controls On Focused-Flow and Dispersed-Flow Deepwater Carbonates: Miocene Agua Amarga Basin, Spain

Abstract Common models for carbonate slope or basin-margin sedimentation emphasize the contrasts between linear sediment sources and point sediment sources. Geologic mapping and high-resolution stratigraphic study of a set of Miocene outcrops, exceptional for their three-dimensional exposure and preservation of paleotopography, demonstrates that paleotopographic focus (or lack thereof) may be a dominant control on geometries and sediment character of sediment-gravity-flow deposits in line-sourced systems. In the Agua Amarga basin, SE Spain, basin topography is initially modified by subaerial exposure and erosion of volcanic basement to form paleovalley systems. After late Miocene marine inundation, topography is partially modified by infilling of high-energy, shallow-water heterozoan deposits (Units 1 and 2) that subdued topography in one area to produce a ramp-like surface, but did not significantly infill a large paleovalley located in another area. Further relative rise in sea level resulted in an extensive reefal platform that formed along a paleo-high adjacent to both features (La Rellana platform). Subsequent sediment-gravity-flow deposits shed from this reefal platform followed two pathways: down the ramp-like surface (dispersed flow), or into the large flooded paleovalley (focused flow). Deposits within each system display contrasting lithofacies architectures. These deepwater deposits (Units 3–7 in this study) consist of carbonate breccia facies (coarse facies), graded skeletal packstone facies (coarse facies), and planktonic foraminifera-rich facies (fine facies) that are interpreted as sediment-gravity-flow deposits and pelagic sediments. Relative sea-level fluctuations resulted in deepwater facies variations in the large paleovalley as a result of significant backstepping and progradation of the Rellana reefal platform on a gently sloping surface. Fining of basinal deposits and shelfward migration of the locus of deposition for sediment gravity flows is associated with sea-level rise. Coarsening of basinal deposits and basinward migration of the locus of deposition for sediment gravity flows is associated with stillstand and relative fall in sea level. Both relationships demonstrate a direct link between the locus of reefal platform growth and style of basin sedimentation. Early parts of relative rises in sea level, late parts of highstands, and falling stages led to transport of abundant coarse sediment into the basin. Focused-flow deposits were line-sourced and funneled into the axis of a large, margin-parallel paleovalley, and confined to a channel. Volume ratio of coarse facies to fine facies is estimated at 0.7. Deposits in proximal paleovalley locations display compensation geometries around positive relief on debrites, channelization, erosional truncation, lapout against paleovalley walls, and some drape as a result of lateral confinement and proximity to the sediment source. Deposits in distal paleovalley locations display increasingly tabular geometries as a result of decreasing lateral confinement and concentration of coarse-grained sediment gravity flows down depositional dip. Dispersed-flow deposits were line-sourced into the basin along a gently inclined ramp-like surface that lacked paleotopographic focus. Volume ratio of coarse facies to fine facies is estimated at 0.1. The less complex sheet-like depositional geometries and locations of these deposits result from the absence of lateral confinement and subtle changes in substrate slope. Focused-flow sediment-gravity-flow deposits that are confined by topographic elements such as channels are most likely to form sizeable accumulations of coarse facies with characteristics most appropriate for conventional oil and gas exploration. There are many paleotopographic configurations that can lead to focusing of flows, so this deepwater carbonate system may be more common than previously recognized.

Chemostratigraphic constraints on early Ediacaran carbonate ramp dynamics, Río de la Plata craton, Uruguay

C- and Sr-isotope data for marine carbonates can provide a detailed record of isotopic variations in seawater through time and have proven to be a valuable tool for interpreting biogeochemical events and correlating Neoproterozoic sedimentary successions worldwide. Negative carbon isotope excursion to values as low as −4.5‰ in the Ediacaran Polanco Limestones Formation, Uruguay has been interpreted as recording the aftermath of a post-Gaskiers glacial event occurred elsewhere on southwest Gondwana. The record of both deep- and shallow-water settings in the Polanco Limestone Formation provides an opportunity to examine δ13C variability across the platform and to evaluate whether the carbon isotope values reflect local or global processes. Herein we provide high-resolution δ13C-chemostratigraphy and Sr-isotope data from stratigraphic sections comprising proximal and distal settings on the carbonate platform. Carbon isotopic values are negative in deep-water facies but progressively rise towards positive values in shallow-water settings. This previously unrecognized trend suggests that deposition of Polanco carbonates occurred in a stratified marine basin where degradation of organic matter below the redox boundary led to lower δ13C values at greater depths. The negative δ13C excursion is restricted to specific horizons in shallow-water facies and is interpreted as being originated due to higher levels of reworking under storm-dominated conditions, which produced a strong local oxidation of organic matter and ultimately, the negative carbon isotope signatures. 87Sr/86Sr and δ13C chemostratigraphy coupled with new radiometric data allow us to revise the previously proposed age for the unit. This new data support an age between 590 and 560Ma for the deposition of the Polanco Limestones Formation.

Facies development along the tide-influenced shelf of the Burdigalian Seaway: An example from the Ottnangian stratotype (Early Miocene, middle Burdigalian)

Herein, we report quantitative micropaleontological (benthic foraminifers, dinoflagellate cysts, calcareous nannoplankton), sedimentological (grain-size analysis) and geophysical (background gamma radiation) analyses from Ottnang–Schanze, the stratotype for the regional Ottnangian stage (Central Paratethys; Lower Miocene, middle Burdigalian). The revealed trends in bathymetry, primary productivity, bottom-water oxygenation and water energy allow exemplary insights into the paleoenvironment of the terminal Burdigalian Seaway. Several facies of a eutrophic environment are distinguished that reflect a transition from a suboxic outer neritic to upper bathyal towards a better oxygenated middle neritic setting under the influence of storm events and currents. A comparison with available data from Upper Austria and Bavaria consistently shows the regressive trend during the late early Ottnangian. In Upper Austria, the deep-water facies from the lower part of the stratotype represents the most distal sediments. The upper part together with localities closer to the northern coast records inner to middle neritic environments that are heavily affected by tidal currents. The facies distribution results from the progradation of a tide-influenced environment along the northern shelf of the North Alpine Foreland Basin, heralding the closure of the Burdigalian Seaway. The available age estimate for the stratotype constrains the onset of the regressive phase to 18 Ma. ► We present a detailed facies analysis of the Ottnangian stratotype. ► Microfossil and lithological data indicate a eutrophic environment. ► A shallowing water depth resulted in increasing water-energy and oxygenation. ► The revealed trends reflect the final regressive phase of the Burdigalian Seaway. ► The beginning of the regression can be dated to c. 18 Ma.

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.

Productos de erosión de las rocas intrusivas y plagio- granitos del complejo ofiolítico de Nicoya, Costa Rica

En este estudio se describe por primera vez la existencia de detrito plutónico en areniscas cretácicasdel noroeste de Costa Rica. Los fragmentos de rocas plutónicas son partículas accesorias, comúnmente presentes enlas areniscas piroxénicas que sobreyacen al Complejo Ofiolítico de Nicoya. Con base en el análisis modal de los granos del esqueleto, se analizan tres unidades de areniscas turbidíticas y neríticas de las Formaciones Rivas y El Viejo, respectivamente, cuya edad data del Campaniano Tardío-Maastrichtiano. Considerando los componentes prima-rios, estas areniscas muestran una composición muy similar a aquellas provenientes de arcos magmáticos. Se introducen dos parámetros modales para evaluar las contribuciones plutónicas. Éstos se definen como el índice de granos plutónicos con respecto al total de líticos (Lp+intercrec.QF/Lt) y el índice de piroxeno uralitizado con respectoal piroxeno total (uralPx/Px). Los valores modales del índice Lp+intercrec.QF/Lt indican, que los fragmentos plutó-nicos constituyen hasta un 9% del total de líticos. La relación relativamente proporcional entre ambos parámetrossugiere, que el piroxeno uralitizado también se deriva de la erosión de las rocas plutónicas. Las rocas-fuente de de-tríto plutónico corresponden con rocas intrusivas básicas hasta intermedias: gabros, doleritas y dioritas. Dos compo-nentes en particular - los intercrecimientos micrográficos de cuarzo y albita y el piroxeno uralitizado - son considerados como productos específicos de la erosión cretácica de las rocas intrusivas, principalmente plagiograníticas. Lasunidades de areniscas con detríto plutónico registran una erosión incipiente de los niveles inferiores de la secuenciaofiolítica de Costa Rica durante el Campaniano Tardío y Maastrichtiano. En este sentido, los fragmentos plutónicosy los granos de pedernales radiolaríticos asociados pueden ser usados como indicadores paleotectónicos del levan-tamiento vertical del orógeno de Costa Rica en el Cretácico Tardío. Este evento tectónico se correlaciona con el inicio de la Orogénesis Laramídica. Observaciones de campo evidencian que las rocas intrusivas del Complejo de Nicoya aún hoy día son una fuente miscelánea de sedimento en el noroeste de Costa Rica.

Larger foraminifera distribution and strontium isotope stratigraphy of the La Cova limestones (Coniacian–Santonian, “Serra del Montsec”, Pyrenees, NE Spain)

The Upper Cretaceous La Cova limestones (southern Pyrenees, Spain) host a rich and diverse larger foraminiferal fauna, which represents the first diversification of K-strategists after the mass extinction at the Cenomanian–Turonian boundary. The stratigraphic distribution of the main taxa of larger foraminifera defines two assemblages. The first assemblage is characterised by the first appearance of lacazinids ( Pseudolacazina loeblichi) and meandropsinids ( Eofallotia simplex), by the large agglutinated Montsechiana montsechiensis, and by several species of complex rotalids ( Rotorbinella campaniola, Iberorotalia reicheli, Orbitokhatina wondersmitti and Calcarinella schaubi). The second assemblage is defined by the appearance of Lacazina pyrenaica, Palandrosina taxyae and Martiguesia cyclamminiformis. A late Coniacian-early Santonian age was so far accepted for the La Cova limestones, based on indirect correlation with deep-water facies bearing planktic foraminifers of the Dicarinella concavata zone. Strontium isotope stratigraphy, based on many samples of pristine biotic calcite of rudists and ostreids, indicates that the La Cova limestones span from the early Coniacian to the early-middle Santonian boundary. The first assemblage of larger foraminifera appears very close to the early-middle Coniacian boundary and reaches its full diversity by the middle Coniacian. The originations defining the second assemblage are dated as earliest Santonian: they represent important bioevents to define the Coniacian-Santonian boundary in the shallow-water facies of the South Pyrenean province. By means of the calibration of strontium isotope stratigraphy to the Geological Time Scale, the larger foraminiferal assemblages of the La Cova limestones can be correlated to the standard biozonal scheme of ammonites, planktonic foraminifers and calcareous nannoplankton. This correlation is a first step toward a larger foraminifera standard biozonation for Upper Cretaceous carbonate platform facies.

Immature oils of deep-water facies: Physicochemical properties and hydrocarbon and trace-element composition

Immature oils of deep-water facies: Physicochemical properties and hydrocarbon and trace-element composition

Precise position of the Basal Choteč event and evolution of sedimentary environments near the Lower–Middle Devonian boundary: The magnetic susceptibility, gamma-ray spectrometric, lithological, and geochemical record of the Prague Synform (Czech Republic)

The Basal Choteč Event, slightly above the Lower–Middle Devonian boundary in the Prague Synform, is significant not only for its faunal and lithological changes but also for its distinct and widely correlatable magnetic susceptibility (MS), gamma spectrometric (GRS), and geochemical patterns. The upper part of the Třebotov Limestone was composed of calcisiltic material deposited from distal storm or turbidite currents, which alternate with slowly deposited and condensed hemipelagic material. The lower part of the overlying Choteč Limestone was also composed of turbidite deposits. A more proximal depositional environment is recorded in the Na Škrábku Quarry whereas the Prastav Quarry represents a more distal environment. A decrease in the proportion of pelagic components was observed toward the event datum and an increase in the amount of recycled lithoclastic-skeletal detritus carbonate material. A similar trend is displayed by the shallow-water stratigraphic equivalents in the Červený Quarry. The MS record across the studied interval produces a smooth curve below the first event-related beds (Třebotov and Suchomasty Limestone), a drop in MS values at the event base (base of the Choteč and Acanthopyge Limestone), and a rapid increase in MS values with high-magnitude and high-amplitude oscillations above the first event-related dark beds. The GRS record shows a reversal in the Th/U ratio at the event base from Th/U ≫ 1 to Th/U < 1. The upper part of the event-related interval is characterized by a GRS-U peak. REE distributions show very uniform patterns both in the deeper-water facies and shallow-water open ocean facies, indicative of their origin by aeolian atmospheric deposition. Light and heavy mineral assemblages are dominated by paramagnetic (kaolinite, muscovite, chlorite, feldspars, pyroxene and amphiboles, apatite, and barite) and ferromagnetic minerals (mostly Fe oxides or oxyhydroxides). The MS and GRS records, together with the lithological character of the sediments, suggest the sea-level rise at the Basal Choteč event interval.

The fossil record of cnidarian medusae

Fossils of cnidarian medusae are extremely rare, although reports of fossil “medusoids,” most of which do not represent medusae, are rather common. Our previous inability to distinguish these fossils has hampered attempts to investigate patterns and processes within the medusozoan fossil record. Here we describe criteria for the recognition of bona fide fossil medusae and use them to assess the evolutionary, paleoenvironmental, and taphonomic history of the Medusozoa. Criteria include distinctive sedimentologic and taphonomic features that result from transport, stranding, and burial of hydrous clasts, as well as unequivocal body structures comparable to those of extant animals. Because the latter are uncommon, most fossil medusae remain in open nomenclature; many are assigned to stem-group scyphozoans. The majority of described medusae are associated with coastal depositional environments (such as tidal flats or lagoons). They rarely occur in oxygen-poor deeper-water facies. All medusan groups have long geologic histories. Scyphozoa are known from the Cambrian, but more derived scyphomedusae were not demonstrably present until the Carboniferous; Mesozoic scyphozoans are rather diverse. Hydromedusae are known from the Ordovician but may extend back to the Cambrian. The record of cubozoans is shorter and sparser; the oldest definite cubozoan is Carboniferous in age.