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Patricia A Whalen - One of the best experts on this subject based on the ideXlab platform.
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global radiolarian Zonation for the pliensbachian toarcian and aalenian
Palaeogeography Palaeoclimatology Palaeoecology, 2010Co-Authors: Elizabeth S. Carter, Luis Odogherty, Paulian Dumitrica, Rie S Hori, Atsushi Matsuoka, Patrick De Wever, Jean Guex, Špela Goričan, Patricia A WhalenAbstract:Abstract Jurassic radiolarians from 220 samples in Queen Charlotte Islands, B.C., Williston Lake, B.C., east-central Oregon, Baja California Sur, southern Spain, Austria, Slovenia, Turkey, Oman, Japan and Argentina were studied in order to construct global Zonation for the Pliensbachian, Toarcian and Aalenian stages. Well-preserved faunas from continuous stratigraphic sections in Queen Charlotte Islands provide the most detailed record for this time interval, and all collections are tied to North American ammonite zones or assemblages. Collections from nearly all other areas lack independent dating except for early Toarcian carbon-isotope dating in Slovenia and late Aalenian ammonites in Spain. A database of 197 widely distributed updated taxonomic species was used to construct a Unitary Association (UA) Zonation for the interval. A global sequence of 41 UAs was obtained for the top of the Sinemurian to the base of the Bajocian. The first and the last UAs represent the Late Sinemurian and the Early Bajocian respectively. The remaining 39 UAs were merged into nine zones (four Early Pliensbachian, one Late Pliensbachian, one Early Toarcian, one Middle–Late Toarcian, and two Aalenian) according to prominent radiolarian faunal breaks and ammonite data. The new zones are the Canutus tipperi – Katroma clara Zone (latest Sinemurian/earliest Pliensbachian); Zartus mostleri – Pseudoristola megaglobosa, Hsuum mulleri – Trillus elkhornensis and Gigi fustis – Lantus sixi zones (Early Pliensbachian); Eucyrtidiellum nagaiae – Praeparvicingula tlellensis Zone (Late Pliensbachian); Napora relica – Eucyrtidiellum disparile Zone (Early Toarcian); Elodium pessagnoi – Hexasaturnalis hexagonus Zone (Middle and Late Toarcian); Higumastra transversa – Napora nipponica Zone (early Aalenian); and Mirifusus proavus – Transhsuum hisuikyoense Zone (late Aalenian). These zones can be correlated worldwide and link previously established UA Zonations for the Hettangian–Sinemurian and the Middle to Upper Jurassic. The new Zonation allows high-resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of Jurassic radiolarians.
Claudia Bremec - One of the best experts on this subject based on the ideXlab platform.
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Zonation of macrobenthos across a mesotidal sandy beach: Variability based on physical factors
Journal of Sea Research, 2017Co-Authors: M. Cecilia Carcedo, Sandra Marcela Fiori, Claudia BremecAbstract:Abstract The dynamic and unstable nature of sandy beaches results in a highly variable distribution of macroinfauna inhabiting the intertidal fringe. Storm-induced sediment movement on the beaches could alter the distribution of organisms, leading to an indistinct Zonation scheme. In this context, the Zonation pattern of macroinfauna was studied monthly during 2010 in an exposed mesotidal sandy beach on the SW Atlantic coast of Argentina (39°S). Faunal samples were collected with a plastic core (0.02 m2) at 10 to 12 levels along five replicated transects extending from above the drift line to the low tide swash zone. Sand samples were also taken at each level. Wave height and period were measured in situ and data of wind speed and direction were provided by the National Weather Service (SMN). The relationship between the formation of Zonation schemes, meteorological data and the physical features of the beach were explored. The results show some significant trends: the supralittoral zone was characterized by the absence of organisms on all sampling occasions. During most of the year the Zonation scheme comprised two zones, both within the littoral zone; during winter months, no Zonation schemes were found. This contrasting pattern could have been determined by the harsh wind-driven waves, leading to sand movements and thus promoting variations in faunal distribution. Sedimentological changes driven by storms could therefore be the cause of a hidden Zonation scheme occurring during winter months, highlighting the importance of a climatic variable in the detection of macrofaunal Zonation patterns.
Franco Vaccari - One of the best experts on this subject based on the ideXlab platform.
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seismic wave propagation in laterally heterogeneous anelastic media theory and applications to seismic Zonation
Advances in Geophysics, 2001Co-Authors: G F Panza, Fabio Romanelli, Franco VaccariAbstract:Publisher Summary The ability to estimate accurately seismic hazard at very low probability of exceedance may be important in protecting special objects in the built environment against rare earthquakes. The deterministic approach, based upon the assumption that several earthquakes can occur within a predefined seismic zone, represents a conservative definition of seismic hazard for preevent localized planning for disaster mitigation, over a broad range of periods. Computation of realistic synthetic seismograms, using methods that take into account source, propagation, and site effects, and utilizing the huge amount of available geological, geophysical, and geotechnical data provides a powerful and economically valid scientific tool for seismic Zonation and microzanation. First-order Zonations can be made at regional scale, considering average structural models and a set of sources with damaging potential distributed within the identified seismogenic areas. Seismic microZonations of urban areas can be performed even more accurately when the required geotechnical data are available, so that local site effects can be effectively modeled.
Brian Rosen - One of the best experts on this subject based on the ideXlab platform.
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Quantitative approaches to palaeoZonation and palaeobathymetry of corals and coralline algae in Cenozoic reefs
The Geological Society London Special Publications, 1995Co-Authors: Christine Perrin, Dan Bosence, Brian RosenAbstract:The value of quantitative surveys of ancient reef slopes for palaeobathymetric analysis is reviewed. Reefs are selected for palaeobathymetric analysis because they are characterized by in situ preservation of benthic communities which are often depth related. In addition, if the reef crest and slope are preserved then ancient water depths can be measured. The Zonation of living reefs has been measured using semi-quantitative phytosociological methods as well as a range of plot and plotless techniques, but there is little agreement as to a single best method. For this study a modified line intercept transect method is selected as it may be used on both living reefs and on various types of outcrops of fossil reefs. This method minimizes problems arising from outcrop conditions, is faster than quadrat methods, can be used to assess different frame-building taxa, matrix, cement and porosity along ancient reef surfaces, and is also frequently used in studies of living reefs. The Zonation of corals and coralline algae on living and fossil reefs can be characterized by three parameters: framework density, diversity and species abundance. The framework density of reef corals is normally greatest on external reef slopes between 1 and 30m and decreases into shallow reef crest environments, and towards shorelines. Coralline algal frameworks are highest in reef crest environments and may also replace coral frameworks in deeper reef-slope environments. Variations in diversity are complex and relate to biogeographieal constraints as well as local variations of physical factors and biological factors. The distribution of reef-building assemblages is often expressed as a Zonation which may relate to depth but also to hydraulic energy. Examples of coral and coralline algal Zonation are presented and discussed from Indo-Pacific and Caribbean reefs. Three case studies are presented based on the authors' work on reef Zonation. The Seychelles reefs (Indian Ocean) are used to illustrate depth and water energy related Zonation of present-day living corals. CoraUine algal Zonation is illustrated from present-day St Croix reefs (Caribbean), together with preserved zones in sections through these reefs. Coral and coralline algal Zonation on fossil reefs are characterized using our modified line intercept transect technique on exposures from late Miocene reefs of Mallorca (Spain). This review of reef Zonation and introduction of a new technique for surveying ancient reef communities to establish depth related zones has important advantages over previous qualitative approaches. Direct measurements of palaeodepths in the field make subjective palaeobathymetric interpretations unnecessary and avoids the problems of assuming uniformitarianism. In situ organism assemblages are sampled which minimizes the effects of taphonomic changes on community composition. The technique allows the quantification of framework density, diversity, species abundance and Zonation to be compared between different fossil reefs and between living and fossil reefs for the first time.
Elizabeth S. Carter - One of the best experts on this subject based on the ideXlab platform.
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mesozoic radiolarian biochronology current status and future directions
Revue de Micropaléontologie, 2018Co-Authors: Špela Goričan, Luis Odogherty, Elizabeth S. Carter, Peter Baumgartner, Atsushi MatsuokaAbstract:Abstract Mesozoic radiolarian biochronologic scales have been developed since the 1970s and most of them reached their present day status in the 1990s. The degree of temporal resolution, on average, corresponds to substage level and is sufficient to provide a meaningful framework for general geological studies. The great majority of zonal schemes were elaborated in low-latitude sections but are applicable in high latitudes as well because an adequate number of species occur worldwide. This paper presents a short historical review and a synthesis of currently used Zonations developed in North America, Europe and Asia. The advantages and the shortcomings of the existing Zonations are discussed. As a general rule, the Zonations including a high number of taxa in each zone have a much greater applicability for global correlations than those defined exclusively with marker taxa. In the forthcoming years, particular studies will focus on zonal division of under-explored time intervals and on improved calibration to chronostratigraphy. Two joint objectives for future research are briefly introduced. The first objective, achievable in a relatively short time, is to compile a composite Mesozoic Zonation that would provide a single reference standard for radiolarian dating at a global scale. The second objective is to refine the radiolarian zonal schemes, which, in certain intervals, have already attained the resolution comparable to that of the standard ammonite zones. To increase the degree of precision and accuracy to this level through the entire Mesozoic is a long-term goal that requires additional high-resolution sampling and emphasis on detailed documentation of evolutionary first and last appearances in different phylogenetic lineages.
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global radiolarian Zonation for the pliensbachian toarcian and aalenian
Palaeogeography Palaeoclimatology Palaeoecology, 2010Co-Authors: Elizabeth S. Carter, Luis Odogherty, Paulian Dumitrica, Rie S Hori, Atsushi Matsuoka, Patrick De Wever, Jean Guex, Špela Goričan, Patricia A WhalenAbstract:Abstract Jurassic radiolarians from 220 samples in Queen Charlotte Islands, B.C., Williston Lake, B.C., east-central Oregon, Baja California Sur, southern Spain, Austria, Slovenia, Turkey, Oman, Japan and Argentina were studied in order to construct global Zonation for the Pliensbachian, Toarcian and Aalenian stages. Well-preserved faunas from continuous stratigraphic sections in Queen Charlotte Islands provide the most detailed record for this time interval, and all collections are tied to North American ammonite zones or assemblages. Collections from nearly all other areas lack independent dating except for early Toarcian carbon-isotope dating in Slovenia and late Aalenian ammonites in Spain. A database of 197 widely distributed updated taxonomic species was used to construct a Unitary Association (UA) Zonation for the interval. A global sequence of 41 UAs was obtained for the top of the Sinemurian to the base of the Bajocian. The first and the last UAs represent the Late Sinemurian and the Early Bajocian respectively. The remaining 39 UAs were merged into nine zones (four Early Pliensbachian, one Late Pliensbachian, one Early Toarcian, one Middle–Late Toarcian, and two Aalenian) according to prominent radiolarian faunal breaks and ammonite data. The new zones are the Canutus tipperi – Katroma clara Zone (latest Sinemurian/earliest Pliensbachian); Zartus mostleri – Pseudoristola megaglobosa, Hsuum mulleri – Trillus elkhornensis and Gigi fustis – Lantus sixi zones (Early Pliensbachian); Eucyrtidiellum nagaiae – Praeparvicingula tlellensis Zone (Late Pliensbachian); Napora relica – Eucyrtidiellum disparile Zone (Early Toarcian); Elodium pessagnoi – Hexasaturnalis hexagonus Zone (Middle and Late Toarcian); Higumastra transversa – Napora nipponica Zone (early Aalenian); and Mirifusus proavus – Transhsuum hisuikyoense Zone (late Aalenian). These zones can be correlated worldwide and link previously established UA Zonations for the Hettangian–Sinemurian and the Middle to Upper Jurassic. The new Zonation allows high-resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of Jurassic radiolarians.