Estuaries of the past and present: A biofacies perspective     

Claudia Schrder-Adams 《Sedimentary Geology》2006,190(1-4):289-298

Estuaries are complex sedimentary and ecological systems, where controlling factors are variable largely depending on wave vs. tidal dominance and fluvial processes. Paleoenvironmental reconstruction of their ancient counterparts in the form of coastal valley deposits in the subsurface or outcrop requires a multidisciplinary approach. Microfossils can play an integral part in identifying estuarine subenvironments. Foraminifera can be abundant in modern estuaries and resemble characteristics of brackish ichnofaunal communities in featuring low species diversity, but high abundances of opportunistic species, different feeding strategies and common infaunal species. Whereas sediment distribution is highly controlled by energy regimes, foraminifera seem to respond to salinities and tidal exposure. Whereas individual taxa can widely range bathymetrically, the combination of certain taxa becomes diagnostic for estuarine environments. Fossil marginal marine assemblages are dominated by agglutinated species due to taphonomic loss of the calcareous component that is often dominant in modern estuaries. When comparisons between fossil and modern assemblages are undertaken it is advisable to compare with Recent subsurface or remnant assemblages for a more accurate basis of paleoenvironmental interpretation. More integrated research with detailed taphonomic observations is needed on ancient coastal valley deposits to find the paleoecological requirements of extinct taxa and their link to sedimentary facies and ichnofacies.  相似文献   

Stable isotope analysis of the Cenomanian–Turonian (Late Cretaceous) oceanic anoxic event in the Crimea     

Jodie K. Fisher  Gregory D. Price  Malcolm B. Hart  Melanie J. Leng 《Cretaceous Research》2005,26(6):853-863

Carbon and oxygen isotope data from Cenomanian–Turonian sediments from the southwest of the Crimea are presented. The sediments consist of limestones, marls and organic-rich claystones, the latter with total organic carbon values up to 2.6 wt. %, representing Oceanic Anoxic Event 2. A shift to more negative δ¹⁸O values through the uppermost Cenomanian into the lowermost Turonian may be the result of warming; however, petrographic analysis shows that the samples have undergone a degree of diagenetic alteration. The carbon isotope data reveal a positive excursion from 2.7‰ to a peak of 4.3‰ at the Cenomanian/Turonian boundary; values then decrease in the early Turonian. This excursion is comparable to those of other Cenomanian–Turonian sections, such as those seen in the Anglo-Paris Basin, and is thought to be due to global changes in the oceanic carbon reservoir. On this curve are a number of negative δ¹³C excursions, just below the Cenomanian/Turonian boundary. It is suggested that these negative excursions are associated with the uptake of light carbon derived from the oxidation and deterioration of organic material during localised exposure of the sediments to oxic or meteoric diagenetic conditions, possibly during sea-level fluctuations.  相似文献   

Lagoon subsidence and tsunami on the West Coast of New Zealand     

S.L. Nichol  J.R. Goff  R.J.N. Devoy  C. Chagu-Goff  B. Hayward  I. James 《Sedimentary Geology》2007,200(3-4):248-262

Sediment core and trench data from a coastal lagoon on the West Coast of the South Island, New Zealand are used to investigate evidence for co-seismic subsidence and associated tsunami inundation. Physical data are used to document a salt marsh soil buried  80 cm below the modern sediment surface that is locally covered by a gravelly sand bed. The sediment record also contains geochemical and biological (diatom and foram) evidence for abrupt changes in salinity of lagoon waters that link to subsidence, tsunami flooding and to the open versus closed state of the lagoon tidal entrance. At the local scale, these relationships allow for separation of tsunami evidence from other agents of environmental change in the lagoon. We also propose a conceptual connection between these local changes and regional drivers of landscape development, most notably major earthquakes and resultant pulses in sediment supply to the coast.  相似文献   

Deglaciation of the Irish Sea Basin: a critique of the glaciomarine hypothesis     

Danny McCarroll 《第四纪科学杂志》2001,16(5):393-404

The glaciomarine model for deglaciation of the Irish Sea basin suggests that the weight of ice at the last glacial maximum was sufficient to raise relative sea‐levels far above their present height, destabilising the ice margin and causing rapid deglaciation. Glacigenic deposits throughout the basin have been interpreted as glaciomarine. The six main lines of evidence on which the hypothesis rests (sedimentology, deformation structures, delta deposits, marine fauna, amino‐acid ratios and radiocarbon dates) are reviewed critically. The sedimentological interpretation of many sections has been challenged and it is argued that subglacial sediments are common rather than rare and that there is widespread evidence of glaciotectonism. Density‐driven deformation associated with waterlain sediments is rare and occurs where water was ponded locally. Sand and gravel deposits interpreted as Gilbert‐type deltas are similarly the result of local ponding or occur where glaciers from different source areas uncoupled. They do not record past sea‐levels and the ad hoc theory of ‘piano‐key tectonics’ is not required to explain the irregular pattern of altitudes. The cold‐water foraminifers interpreted as in situ are regarded as reworked from Irish Sea sediments that accumulated during much of the late Quaternary, when the basin was cold and shallow with reduced salinities. Amino‐acid age estimates used in support of the glaciomarine model are regarded as unreliable. Radiocarbon dates from distinctive foraminiferal assemblages in northeast Ireland show that glaciomarine sediments do occur above present sea‐level, but they are restricted to low altitudes in the north of the basin and record a rise rather than a fall in sea‐level. It is suggested here that the oldest dates, around 17 000 yr BP, record the first Late Devensian (Weichselian) marine inundation above present sea‐level. This accords with the pattern but not the detail of recent models of sea‐level change. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Les formations burdigaliennes de Corse orientale dans leur cadre géodynamique     

Marie-Dominique Loÿe-Pilot  Michel Durand-Delga  Hugues Feinberg  Yves Gourinard  Jean Magné 《Comptes Rendus Geoscience》2004,336(10):919-930

The earliest marine sediments of eastern Corsica, linked to the birth of the Corsica Basin, are represented by granitic breccia of the Saint-Antoine Formation and pelagic marls of the Alzelle Formation. They are dated as Mid-Burdigalian by nannoplankton and planktonic foraminifera (relative age and grade datings between 18.7 and 18.3 Ma). The Aghione Formation (Latest Burdigalian–Langhian) lies upon the Alzelle Formation. A component of the major East-Corsican faults, the Saint-Antoine Fault, underwent extensional activity during the Burdigalian and until the Late Miocene, when occurred the uplift of the Castagniccia antiform. To cite this article: M.-D. Loÿe-Pilot et al., C. R. Geoscience 336 (2004).  相似文献   

The use of deep-water agglutinated Foraminifera in correlating Lower Cretaceous pelagic and flysch sequences: current status and prospects for the future     

Michael A. Kaminski  Stanislaw Geroch 《Cretaceous Research》1992,13(5-6)

Deep-water agglutinated Foraminifera (DWAF) display potential for correlating pelagic (calcareous and non-calcareous) and flysch environments. This is illustrated by an example from Sites 765 and 261 on the Argo Abyssal Plain. A working zonation based on DWAF has been developed for Lower Cretaceous flysch sequences of the Polish Carpathians, but this zonal scheme has not been tested in other areas of the Tethys. No zonation has yet been developed for abyssal oceanic DWAF. The challenge for the future, under the auspices of Project 262, is to test the existing zonation in other regions and develop a widely applicable biochronology for integration into a general Tethyan biochronological correlation scheme.  相似文献   

塔里木盆地北缘早石炭世有孔虫   总被引：3，自引：0，他引：3  

李汉敏 《新疆地质》1991,(2)

塔里木盆地北缘早石炭世干草湖组和野云沟组产有丰富的有孔虫及(竹蜓)科化石,共计32个属,近100个种,其中7个新种.自下而上建立了四个化石组合即:1.Tournayella discoi-dea-Tuberendothyra tuberculata magna;2.Dainella wushiensis-Endothyra Parain-flata;3.Eostaffella hohsiensis-Archaediscus moelleri;4.Eostaffellinella Prot-vae-Climacammiana ferra.第一组合的时代为杜内(岩关)期,其余三个组合属维宪(大塘)期.  相似文献   

The Lenticulina (Astacolus) humilis (Reuss, 1863) “group” and Lenticulina (Astacolus) atherfieldensis (new species) in the lower aptian of the isle of wight (U.K.)     

S. Crittenden   《Cretaceous Research》1983,4(4):349-359

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Multivariate analysis of environmentally controlled variation in Lagena: Late Maastrichtian,Sweden     

J.O.R. Hermelin  B.A. Malmgren 《Cretaceous Research》1980,1(3):193-206

Costate forms of Lagena (benthonic foraminifer) have been studied in an uppermost Maastrichtian bore-hole core sequence (28 levels) from southern Sweden. Analysis of a large sample shows that consistent assignment to previously described “species” of costate Lagena is not possible. This observation is supported by multivariate analysis of five morphologic variables which indicates that there are no distinct clusters of specimens along principal component axes associated with general size, number of costae, and relationships between roundness of test/length and number of costae. Specimens with a basal ring differ from specimens with an apical spine and those with no basal structure with regard to average number of costae. They also differ from specimens with no basal structure with regard to relationships between roundness of test/length and number of costae. These characters grade into each other thus preventing them from being used as taxonomic criteria.Mean ratios of benthonic foraminifers to total benthonic and planktonic formaminifers determined individually for each level are inversely related to mean relative frequencies of costate Lagena and directly related to mean general sizes of costate Lagena. The benthonic/planktonic ratio has been suggested by other workers to represent a paleobathymetric index across a continental slope and shelf when open marine conditions prevailed. If this were so in the Danish basin at the end of the Cretaceous, costate Lagena would have been relatively less frequent and larger at shallower depths.As a result of the study, the analyzed specimens are considered as representing a single morphospecies of the costate species Lagena sulcata. Between-level variation is regarded as ecophenotypic, and within-level variation as natural biologic variation of no taxonomic significance. A total of about 1000 species of Lagena has been described in the literature which is probably many orders of magnitude too great for a genus with such a simple morphology as Lagena. A revision of the taxonomy of Lagena is, therefore, probably necessary on a wide scale.  相似文献   

Nouvelles Données sur le Crétacé Supérieur de la Sardaigne Orientale     

A. Busulini  I. Dieni  F. Massari  D. Pejović  J. Wiedmann 《Cretaceous Research》1984,5(3):243-258

The stratigraphic distribution of the principal Upper Cretaceous facies in Sardinia ispresented, with special reference to the eastern part of the Island. Included are remarks on the mid-Cretaceous tectonic activity, which marks the base of the Upper Cretaceous depositional cycle. The presence of Upper Santonian and Lower Maastrichtian (the latter represented by marls with sparse turbidite interbeds) in the Lanaitto syncline (Oliena) is documented. Both contain outer-shelf assemblages rich in planktic Foraminifera. Recognition of rare detrital glaucophane in the Maastrichtian sandstones suggests a source area affected by high-pressure metamorphism, possibly corresponding to the southward extension of alpine Corsica.The Tertiary conglomerates exposed near Oliena include pebbles of facies (Campanienand Upper Maastrichtian rudistid limestones with larger Foraminifera) unknown in outcrop. A preliminary study of the rudists suggests a faunal exchange between different palaeobio-geographical provinces belonging, respectively, to the West European and Adriatic Plates.A palaeontological appendix contains remarks on some representatives of the family Heterohelicidae and on one species of Gunnarites found in the Lower Maastrichtian.  相似文献