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1.
High-resolution carbon isotope stratigraphy of the upper Campanian-Maastrichtian is recorded in the Boreal Realm from a total of 1968 bulk chalk samples of the Stevns-1 core, eastern Denmark. Isotopic trends are calibrated by calcareous nannofossil bio-events and are correlated with a lower-resolution δ13C profile from Rørdal, northwestern Denmark. A quantitative approach is used to test the reliability of Upper Cretaceous nannofossil bio-events and provides accurate biohorizons for the correlation of δ13C profiles. The Campanian-Maastrichtian boundary (CMB) is identified through the correlation of dinoflagellate biostratigraphy and δ13C stratigraphy between Stevns-1 and the Global boundary Standard Stratotype-section and Point at Tercis les Bains (SW France), allowing the identification of new chemical and biostratigraphic markers that provide a precise placement of the stage boundary on a regional scale. The boundary interval corresponds to the third phase of a stepwise 0.8‰ negative δ13C excursion, lies in calcareous nannofossil subzone UC16dBP, and encompasses the last occurrence of nannofossil Tranolithus stemmerikii and first occurrence of nannofossil Prediscosphaera mgayae. Fifteen δ13C events are defined and correlated to sixteen reliable nannofossil biohorizons, thus providing a well-calibrated standard high-resolution δ13C curve for the Boreal Realm.  相似文献   

2.
The Upper Barremian to Aptian Almadich Formation (Inner Prebetic Domain of the Betic Cordillera) is composed of hemipelagic sediments deposited on a distal carbonate ramp in the southern Iberian Palaeomargin. Within this facies we have found a thick interval of blue to black shales and marls that is interpreted as deposited under oxygen-depleted conditions. We think that this interval, dated as early Aptian, represents the local record of Ocean Anoxic Event 1a. The integrated biostratigraphic analysis of a section in the Almadich Formation, by means of planktonic foraminifera, calcareous nannofossils and ammonites, enables us to recognize most of the biostratigraphic units based on these three fossil groups and to correlate between them. The Sartousiana, Sarasini, Weissi, Deshayesi and Furcata (ammonite) Zones were identified for the Upper Barremian–Lower Aptian interval. By means of calcareous nannofossil biostratigraphy the Micrantholithus hoschulzii, Hayesites irregularis and Rhagodiscus angustus Zones, plus several additional biohorizons, were identified. A quantitative study performed on a set of 27 Lower Aptian samples has enabled the precise identification of the ‘nannoconid crisis’, the lower limit of which clearly precedes the main anoxic event, and its correlation with other bioevents. Planktonic foraminifera occur consistently throughout the Lower to Upper Aptian of the Cau section and are moderately well preserved. This fact allows us to use the most recent taxonomic framework, based on wall texture, to identify the Blowiella blowi, Schackoina cabri, Globigerinelloides ferreolensis, Globigerinelloides algerianus, Hedbergella trocoidea andTicinella bejaouaensis Zones. Coincident with the anoxic episode, the planktonic foraminiferal assemblages are composed of a significant number of forms with elongated chambers and/or tubulospines assigned to the genera Claviblowiella,Lilliputianella , Leupoldina and Schackoina. Most of the planktonic foraminiferal and nannofossil taxa are illustrated.  相似文献   

3.
Recognition of the Campanian stage on the Brazilian Continental Margin, using calcareous nannofossils, has been historically problematic. This paper constitutes an overview of earlier works, showing how nannofossil biostratigraphic ideas have evolved since Troelsen & Quadros provided the first biozonation of this region in 1971. Recent studied have provided data which have helped to clarify these apparent biostratigraphic problems, and allows this region to be placed in a global biostratigraphic context.The earliest researchers identified the Santonian/Campanian boundary by the last occurrences of ‘Lithastrinus grillii’ andPetrobrasiella venata. P. venatawas later abandoned as an index species due to its rarity and, instead, the last occurrences ofMarthasterites furcatusand ‘Lithastrinus grillii’ became the most-used markers. However, the stratigraphic age of these biohorizons diverged from those quoted in the literature. In the Brazilian basins, these extinctions, rather than having occurred in the Campanian as was recorded elsewhere, were considered to mark the top of the Santonian, as suggested by correlations with other microfossil groups (primarily foraminifera and palynomorphs). To explain this phenomenon, the existence of a condensed sequence was postulated for most of the Brazilian marginal basins, where the uppermost Santonian deposits were apparently indistinguishable from those of the lowermost Campanian. In line with current correlations presented in the nannofossil literature, and with new information obtained from core and side-wall samples, it is now believed that the extinction of these speciesdidoccur in the Campanian in the Brazilian basins, whilst the last occurrence ofLithastrinus moratus(previously misidentified asLithastrinus grillii) has become a useful Santonian marker. Thus the Santonian/Campanian boundary in Brazil lies in a stratigraphic position similar to elsewhere in nannofossil terms, that is below CC18.The Campanian/Maastrichtian boundary was initially characterised in nannofossil terms in Brazil by the last occurrence ofBroinsonia parca constricta, and later by the last occurrence ofEiffellithus eximius. Recently acquired data has shown that the sequence of events in the Brazilian marginal basins is similar to that of the Sissingh/Perch-Nielsen standard biozonation scheme through this interval. Again, correlations in the literature with the recently defined boundary (in macrofossil terms) thus allow the boundary to be determined between the last occurrences ofBroinsonia parca constrictaandUniplanarius trifidus, that is, in CC23b.  相似文献   

4.
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5.
苏新  郭宪璞  丁孝忠 《现代地质》2003,17(4):370-377
库车前陆盆地是中国大型油气基地之一,盆地中的白垩系及古近系为盆地油气的主要储层。对本区白垩系的时代划分和沉积环境的精确确定直接关系到对油气田的规模、储量和分布范围的正确评价。本研究在前人划分为陆相下白垩统巴什基奇克组的顶部首次发现了由10属15种组成的晚白垩世海相钙质超微化石组合Arkangelskiellacymbiformis—Quadrumgartneri。此外,在由前人定为古新统—始新统的塔拉克组下段也发现了晚白垩世Arkangel skiellacymbiformis—Quadrumgartneri组合,在该组上段发现了古新世化石Biantholithussparsus。该成果既为准确确定这两个岩组的地质时代提供了可靠的古生物证据,又为本区存在晚白垩世地层和海相沉积提供了佐证,表明巴什基奇克组顶部存在晚白垩世的海相沉积,塔拉克组下段属于上白垩统,上段属于古新统。  相似文献   

6.
Calcareous nannofossil assemblages at Site 641C (Galicia Margin, North Atlantic) were investigated in order to determine changes in fertility and temperature of surface waters. Taxa such as Zeughrabdotus spp. <3.5 μm, Biscutum constans, Discorhabdus rotatorius and Diazomatolithus lehmanii, which thrived in higher fertility conditions, are particularly abundant across the CM0 interval as opposed to those with oligotrophic affinities such as Watznaueria spp. and Nannoconus spp., which are generally reduced in abundance. The abundances of nannoconids are much lower than those observed in Tethyan sections, indicating higher fertility conditions. Slumpings and low recovery prevent the identification of the onset of the “nannoconid crisis”, but a sharp drop in nannoconid abundances, observed prior to the CM0 interval, correlates with the “nannoconid decline” observed in several Tethys sections.The normalized ratio between low and high fertility taxa (Fertility Index) was used to characterize the nannofossil assemblages in terms of productivity changes. The highest values of the Fertility Index were observed across magnetic chron CM0. The paucity of cold water taxa such as Seribiscutum spp. and Repagulum parvidentatum suggests warm water conditions throughout the deposition of upper Barremian–lower Aptian sediments on the Galicia Margin.  相似文献   

7.
In the past15 years,the Cenozoic calcareous nannofossilsin the East China Sea were biostratigraphically studied duringthe extensive offshore petroleum exploration in a number ofbasins on the shelf of the East China Sea.A number of Pale-ocene to Quaternary nannofossil zones were recognized basedon the nannofossils from m any offshore wells (SBMGS,1989,1985 ) .These previous studies indicated a lot of biostratigraphicproblems,resulting in difficulties in the understanding of afurther detail…  相似文献   

8.
A high-resolution, biostratigraphic (calcareous nannofossils, calpionellids), chemostratigraphic (C-isotope) and cyclostratigraphic (magnetic susceptibility) study was performed on the marl–limestone alternations of the Upper Berriasian–Valanginian Orpierre section, deposited in the hemipelagic setting of the Vocontian Basin (SE France). The main aims of this study were to detect orbital forcing, to estimate the duration of the Valanginian “Weissert” episode, and to discuss the palaeoenvironmental implications. Detailed calcareous nannofossil biochronology allowed the recognition of Upper Berriasian–Lower Hauterivian biohorizons. The general trends of the δ13C curve and the major positive C-isotope excursion (amplitude of 1.8‰) recorded at the Orpierre section are very similar to those found in other sections worldwide. Spectral analysis applied on high-resolution magnetic susceptibility (MS) variations coupled with frequency ratio method reveals a strong cyclic pattern related to the Earth's orbital parameters (precession, obliquity and eccentricity). The prominent 405 kyr eccentricity cycle in the MS signal and has been used as a geochronometer to time calibrate the section. The duration of the Weissert episode was estimated as 2.08 Myr. This duration is coherent with those obtained from the Umbria Marche Basin (∼2.3 Myr) and from the Angles section (∼2.14 Myr). Durations of more than 2 Myr suggest that a long perturbation in the dynamic of the global carbon cycle that is not compatible with the rapid and intense volcanic activity. Our cyclostratigraphic study indicates a minimal duration of 4.29 Myr for the Valanginian stage. The comparison between the MS signal at Orpierre and the spectral gamma-ray signal recently obtained in two composite sections of the Vocontian Basin allows to propose a revised duration for the Valanginian stage of 4.695 Myr instead of 5.08 Myr.  相似文献   

9.
We present evidence of accumulation of calcareous cyanobacterial “microspheroids” as predominant components of the Cenomanian-Turonian Indidura Formation of northeastern Mexico. The unit at Parras de la Fuente includes a sequence of limestones and marls with well-defined light-dark rhythms at the decimetric to millimetric scale, in which CaCO3 and total organic carbon vary between 43–78% and 0.3–3.6%, respectively.A distinctive feature of the section is the presence of abundant millimeter-scale microlaminae arranged in nearly even-parallel white and dark gray “varve like” dual lamination less than 3 mm thick, in which the darker units contain scattered planktonic foraminifera and radiolaria, whereas the lighter microlaminae are dominated by calcitic microspheroids (20–40 μm). The white laminae are evidently the result of recurring cycles of calcareous cyanobacterial blooms, possibly associated with fluvial dilution of surface waters.The organic carbon-rich laminated marlstones and laminated biocalcilutites of the Indidura Formation document paleoceanographic conditions favorable to unusual cyanobacterial productivity cycles that were also characterized by strong dysoxic/anoxic bottom conditions.  相似文献   

10.
For the first time, the calcareous nannofossils of the chalky limestone of upper Abderaz Formation and lower part of Abtalkh Formation have been studied. In this study, 83 nannoplanktonic species of 45 genera were identified and presented. A biostratigraphic study of calcareous nannofossils from this section has allowed the recognition of five calcareous nannofossil biozones of Sissingh (Geol Mijnbouw 56:37–65, 1977) CC17–CC21. On the obtained calcareous nannofossils, the age of this section is Late Santonian/Early Campanian–Early Late Campanian.  相似文献   

11.
Amino acid enantiomeric (D/L) ratios in the mollusk Mercenaria are compared with recently published biostratigraphic and/or U-series solitary coral data from 22 Quaternary localities on the central and southern Atlantic Coastal Plain. In all cases, local relative aminostratigraphic sequences are consistent with relative ages inferred from U-series or biostratigraphic data, although occasionally more depositional events are recognized by aminostratigraphic than biostratigraphic methods. However, if the U-series data are used as age calibrations for the D/L values, latitudinal trends of “isochronous” D/L values are highly variable and conflict with trends expected from the present temperature gradient, which is smooth and nearly linear between 45° and 25° N. Age estimation can be performed independently of the U-series data using a kinetic model that relies on the assumption that Pleistocene temperature gradients have also been smooth functions of latitude, although significantly steeper than the present temperature gradient. Within the uncertainties of this assumption, kinetic model age estimates for localities in the coastal plain fall into the following groups: 70,000–130,000 yr, 200–250,000 yr, 300,000–400,000 yr, 500,000–600,000 yr, 700,000–800,000 yr, and > 1,000,000 yr. Major conflicts between these model age estimates are observed for localities near Charleston, South Carolina and in central Virginia. These conflicts could indicate that the basic temperature assumptions of aminostratigraphy are incorrect, and that apparent local aminostratigraphic sequences (clusters of different D/L values) could be due to factors other than age difference. Alternatively, some of the U-series dates may be only minimum ages for these localities.  相似文献   

12.
The first detailed biostratigraphic analyses of the Coniacian-middle Campanian shallow-marine carbonate successions exposed in the Mitla Pass, west central Sinai, Egypt have revealed the stratigraphic distribution of diverse calcareous nannofossil and planktonic foraminiferal species. Thirty-six calcareous nannofossils and thirty-two planktonic foraminifera are identified, indicating a Coniacian to middle Campanian age and four Tethyan planktonic foraminiferal and five calcareous nannofossil zones. A comparison of these bioevents from different palaeolatitudes shows considerable variation in age.Three sequence boundaries coincident with the Turonian/Coniacian, Coniacian/Santonian and Santonian/Campanian stage boundaries are recognized. A fourth sequence boundary is marked by a major upper Campanian to early Ypresian (early Eocene) unconformity. These sequence boundaries are primarily related to regional tectonism associated with the Syrian Arc Fold System and secondarily to eustatic sea-level fluctuations.  相似文献   

13.
Stefan Gartner 《Earth》1977,13(3):227-250
Intensive biostratigraphic studies of calcareous nannofossils have been carried out for only about a decade, even though nannofossils have been known for over a century. Although coccoliths have been reported from various Paleozoic deposits, datable assemblages are known only from Liassic (early Jurassic) and younger strata. Today nannofossils are one of the best correlation tools available to the biostratigrapher in marine sediments that contain pelagic constituents. Precise age determinations and correlations can be made in Cretaceous and Cenozoic strata for which numerous reference sections have been studied. The Jurassic nannofossil succession is less completely known mainly because of a lack of good reference material.The very large number of specimens per sample and the minute size of calcareous nannofossils create both advantages and disadvantages in their utilization. Variability of synchronous assemblages may occur latitudinally as well as from the oceanic to the hemipelagic realms.  相似文献   

14.
The Jinshajiang Suture Zone is important for enhancing our understanding of the evolution of the Paleo-Tethys and its age, tectonic setting and relationship to the Ailaoshan Suture Zone have long been controversial. Based on integrated tectonic, biostratigraphic, chemostratigraphic and isotope geochronological studies, four tectono-stratigraphic units can be recognized in the Jinshajiang Suture Zone: the Eaqing Complex, the Jinshajiang Ophiolitic Melange, the Gajinxueshan “Group” and the Zhongxinrong “Group”. Isotope geochronology indicates that the redefined Eaqing Complex, composed of high-grade-metamorphic rocks, might represent the metamorphic basement of the Jinshajiang area or a remnant micro-continental fragment. Eaqing Complex protolith rocks are pre-Devonian and probably of Early–Middle Proterozoic age and are correlated with those of the Ailaoshan Complex. Two zircon U–Pb ages of 340±3 and 294±3 Ma, separately dated from the Shusong and Xuitui plagiogranites within the ophiolitic assemblage, indicate that the Jinshajiang oceanic lithosphere formed in latest Devonian to earliest Carboniferous times. The oceanic lithosphere was formed in association with the opening and spreading of the Jinshajiang oceanic basin, and was contiguous and equivalent to the Ailaoshan oceanic lithosphere preserved in the Shuanggou Ophiolitic Melange in the Ailaoshan Suture Zone; the latter yielded a U–Pb age of 362±41 Ma from plagiogranite. The re-defined Gajinxueshan and Zhongxinrong “groups” are dated as Carboniferous to Permian, and latest Permian to Middle Triassic respectively, on the basis of fossils and U–Pb dating of basic volcanic interbeds. The Gajinxueshan “Group” formed in bathyal slope to neritic shelf environments, and the Zhongxinrong “Group” as bathyal to abyssal turbidites in the Jinshajiang–Ailaoshan back-arc basin. Latest Permian–earliest Middle Triassic synorogenic granitoids, with ages of 238±18 and 227±5–255±8 Ma, respectively, and an Upper Triassic overlap molasse sequence, indicate a Middle Triassic age for the Jinshajiang–Ailaoshan Suture, formed by collision of the Changdu-Simao Block with South China.  相似文献   

15.
In this work, the recently developed “second-order” self-consistent method [Liu, Y., Ponte Castañeda, P., 2004a. Second-order estimates for the effective behavior and field fluctuations in viscoplastic polycrystals. J. Mech. Phys. Solids 52 467–495] is used to simulate texture evolution in halite polycrystals. This method makes use of a suitably optimized linear comparison polycrystal and has the distinguishing property of being exact to second order in the heterogeneity contrast. The second-order model takes into consideration the effects of hardening and of the evolution of both crystallographic and morphological texture to yield reliable predictions for the macroscopic behavior of the polycrystal. Comparisons of these predictions with full-field numerical simulations [Lebensohn, R.A., Dawson, P.R., Kern, H.M., Wenk, H.R., 2003. Heterogeneous deformation and texture development in halite polycrystals: comparison of different modeling approaches and experimental data. Tectonophysics 370 287–311], as well as with predictions resulting from the earlier “variational” and “tangent” self-consistent models, included here for comparison purposes, provide insight into how the underlying assumptions of the various models affect slip in the grains, and therefore the texture predictions in highly anisotropic and nonlinear polycrystalline materials. The “second-order” self-consistent method, while giving a softer stress-strain response than the corresponding full-field results, predicts a pattern of texture evolution that is not captured by the other homogenization models and that agrees reasonably well with the full-field predictions and with the experimental measures.  相似文献   

16.
Edward R. Carr  Brent McCusker   《Geoforum》2009,40(4):568-579
In a previous paper [McCusker, B., Carr, E.R., 2006. The co-production of livelihoods and land use change: Case studies from South Africa and Ghana. Geoforum 37 (5), 790–804], we argued that land use and livelihoods could best be understood as co-produced, where land use and livelihoods are not separate objects of knowledge related to one another through abstract processes, but different manifestations of social processes through which individuals and groups come to understand the challenges facing their everyday lives, the various resources available to them to negotiate these challenges, and the strategies by which they can conduct that negotiation. In this paper, we examine the theoretical basis for “co-production” with the goal of using this approach to inform development interventions.  相似文献   

17.
The Gargano Promontory of southern Italy, located on the eastern margin of the Apulia Platform, represents a peculiar Tethyan area where the transition between carbonate platform and adjacent basins is exposed on land. The Aptian stratigraphic record, represented in shallow-water, slope and deep-water deposits, provides a good opportunity to investigate the regional response to the worldwide documented climatic, biotic and palaeoceanographic changes related to Oceanic Anoxic Event 1a (OAE1a). A synthesis of data previously published (Ischitella and Coppitella sections), together with original data (Val Carbonara and Coppa della Guardia sections), from four stratigraphic sections from different depositional settings (proximal to distal) is provided, using an integrated, high-resolution micropalaeontological (planktonic foraminifera and calcareous nannofossils) and, for one section, geochemical (stable carbon and oxygen isotopes) approach. Organic matter preservation is confined to the more distal areas and consists of two thin intervals of black shales in the Aptian portion of the Marne a Fucoidi Formation. Biostratigraphic data assign the older black shale (5 cm thick) to the Selli Level equivalent (OAE1a, Lower Aptian); this carbon-rich interval is immediately followed by another black shale (7–10 cm thick) of early Late Aptian age.OAE1a is generally interpreted as a high-productivity event during a warming interval, followed by a cooling trend. In the Gargano Promontory, although the oxygen isotope curve indicates the above-mentioned climatic evolution, the micropalaeontological data do not support high fertility of the surface water, whereas micropalaeontological and geochemical data for the younger black shale do record high productivity (radiolarian increase in overall abundance, low nannofossil and foraminiferal species richness, increase in abudance of nannofossil fertility indices) associated with a cooling trend. The carbon and oxygen isotope record is in line with evidence from the curves documented elsewhere, whereas, among the biotic events, only the “nannoconid crisis” preceding OAE1a is revealed to be globally correlable.Environmental models for the two episodes of organic matter preservation are proposed, taking into account both global and local controlling factors.  相似文献   

18.
The aim of this study is to determine calcareous nannofossil species found in Kamar-Kuh area and demonstrate this use for biostratigraphic studies. The Qom Formation is widely distributed in Kamar-Kuh section and has nine members(a–f). In this study, 12 samples were taken and prepared with smear slide. Some of the determined species are listed below, and some of them are photographed by light and scanning microscope. According to obtained nannofossils, 16 species, nine genera, and six families were determined. Obtained nannofossils indicated age of Burdigalian–Serravalian (middle Miocene) for this section.  相似文献   

19.
The calcareous nannofossil genus Eiffellithus is an important taxon of mid- to Upper Cretaceous marine sediments in biostratigraphy and paleoceanography. The definition of species within Eiffellithus have been both broadly interpreted and variably applied by nannofossil workers. This is particularly true for the Eiffellithus eximius plexus. While the taxonomy of mid-Cretaceous Eiffellithus species has recently been well-defined, the remaining 35 m.y. history of the genus has not been closely examined. Our investigation of Cenomanian to Maastrichtian sediments from the Western Interior Seaway, Gulf of Mexico, and Western Atlantic gives rise to six new species of Eiffellithus that can be reliably differentiated. In this paper the hitherto used biostratigraphic markers (E. turriseiffelii and E. eximius) have been redefined in a more restricted sense to increase their utility. These refinements in taxonomy reveal an obvious shift in abundance both within the genus and within the nannofossil assemblage as a whole through the Late Cretaceous. In the Cenomanian and Maastrichtian the genus is composed exclusively of coccoliths bearing an X-shaped central cross, such as E. turriseiffelii, while in the Coniacian through Campanian axial-cross forms such as E. eximius comprise more than 60% of the genus. Within the nannofossil assemblage the genus has low abundances in the Cenomanian but increases to >15% of the assemblage in well-preserved samples in the Santonian. In addition, the pattern of diversification of this genus, whereby a x-shaped, diagonal cross repeatedly gives rise to an axial cross by rotation about the central axis, is an excellent example of iterative evolution that may be related to repetitive shifts in Late Cretaceous climatic and paleoceanographic regimes.  相似文献   

20.
深海钻探计划（ＤＳＤＰ）和大洋钻探计划（ＯＤＰ）实施以来促进了地层学的发展。通过对大洋沉积物的研究，利用生物属，种的始，末现面事件建立起了晚中生代－新生代高精度的钙质超微化石，有孔虫，放射虫以及沟鞭藻的化石带，综合利用这些基准面事件，可使地层划分精度达１０万年以内。使用液压活塞取心技术，建立起了完整，连续的中，新生代磁性地层剖面，加之放射性年龄的测定，确定了数百个生物属，种始，末现面的绝对年龄值，  相似文献   

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