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1.
László Kocsis Anouar Ounis Fredj Chaabani Neili Mohamed Salah 《International Journal of Earth Sciences》2013,102(4):1111-1129
Fossil shark teeth and coprolites from three major phosphorite occurrences in the Gafsa Basin (southwestern Tunisia) were investigated for their geochemical compositions to improve local stratigraphy and to better assess paleoenvironmental conditions. 87Sr/86Sr isotope ratios of shark teeth from the Early Maastrichtian El Haria Formation and from the Early Eocene Métlaoui s.s. Formation yielded Sr isotope ages of 68 ± 1 and 47.9 ± 1.3 Ma, respectively, which accord with the expected stratigraphic positions of these sediments. Conversely, shark teeth from the Paleocene–Eocene Chouabine Formation have large variation in Sr isotope ratios even within individual layers. After statistical treatment and then elimination of certain outlier samples, three age-models are proposed and discussed. The most reasonable solution includes three subsequent Sr ages of 61.8 ± 2.2 Ma, 57.2 ± 1.8 and 54.6 ± 1.6 for layer IX, layers VIII–V and layers IV–0, respectively. Three scenarios are discussed for explanation of the presence of the outliers: (1) diagenesis, (2) re-working and (3) locally controlled seawater Sr isotope ratio. The most plausible account for the higher 87Sr/86Sr ratios relative to the global ocean in some fossils is enhanced intrabasinal re-working due to low sea level. Conversely, the sample with lower 87Sr/86Sr than the global seawater may link to diagenesis or to seawater influenced by weathering of Late Cretaceous marine carbonates, which latter is supported by model calculation as well. The εNd values of these fossils are very similar to those reported for Paleogene and Late Cretaceous Tethyan seawater and are compatible with the above interpretations. The relatively low oxygen isotope values in shark teeth from the topmost phosphate bed of the Chouabine Formation, together with the Sr isotope results, point toward recovering better connections with the open sea. These δ18O data reflect elevated ambient temperature, which may link to the Early Eocene Climatic Optimum. 相似文献
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西藏南部晚白垩世厚壳蛤的锶同位素年龄标定 总被引：11，自引：0，他引：11
沉积岩样品年龄的直接标定是沉积学与地层学研究的难点之一.由于锶在海水中的残留时间(≈106a) 大大长于海水的混合时间(≈103a), 因而同一时间全球海水的锶元素在同位素组成上是均一的, 并造成地质历史中海水的锶同位素组成是时间的函数, 这是锶同位素地层学(SIS) 的基本原理和利用锶同位素地层学进行海相地层定年的理论基础.本文根据锶同位素地层学的基本原理, 测试了西藏南部岗巴剖面上白垩统宗山组上段地层中厚壳蛤化石的锶同位素组成, 尝试对这些化石进行了年龄标定, 4个样品分别位于剖面累计厚度381, 362, 358和296m处, 其87Sr/86Sr比值分别为0.707832, 0.707769, 0.707768和0.707695, 年龄的标定结果分别是65.68, 69.34, 69.39和72.32Ma, 定年的平均误差为±1Ma左右.研究结果表明, 锶同位素地层学在海相地层定年方面具有潜在价值. 相似文献
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大兴安岭北部甲乌拉铅锌银矿床Rb-Sr同位素测年及其地质意义 总被引：11，自引：3，他引：8
甲乌拉铅锌银矿床位于内蒙古自治区满洲里市南西150km。矿床产于中蒙古-额尔古纳兴凯造山带南东缘之得尔布干断裂北西侧。本文在甲乌拉矿床选取7件闪锌矿和6件黄铁矿样品开展了Rb-Sr定年。获得闪锌矿的Rb-Sr等时线年龄为143.0±2.0Ma(MSWD=3.2),锶同位素初始值I Sr=0.71265;黄铁矿的Rb-Sr等时线年龄为142.0±3.0Ma(MSWD=5.7),锶同位素初始值ISr=0.71267;闪锌矿与黄铁矿的Rb-Sr等时线年龄为142.7±1.3Ma(MSWD=3.8),锶同位素初始值ISr=0.71266。上述定年结果表明,甲乌拉矿床形成于早白垩世初期。甲乌拉矿床硫化物的Rb和Sr含量分别介于0.1034×10-6～7.367×10-6和1.301×10-6～7.148×10-6之间,Sr同位素初始比值(87Sr/86Sr)i介于0.71238～0.71277之间,平均值为0.71264,暗示甲乌拉矿床的成矿物质主要来源于地壳。甲乌拉矿床形成于蒙古-鄂霍茨克造山过程的后碰撞阶段。 相似文献
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Anselm Loges Thomas Wagner Thomas Kirnbauer Susanne Göb Michael Bau Zsolt Berner Gregor Markl 《Applied Geochemistry》2012
Thermal water samples and related young and fossil mineralization from a geothermal system at the northern margin of the Upper Rhine Graben have been investigated by combining hydrochemistry with stable and Sr isotope geochemistry. Actively discharging thermal springs and mineralization are present in a structural zone that extends over at least 60 km along strike, with two of the main centers of hydrothermal activity being Wiesbaden and Bad Nauheim. This setting provides the rare opportunity to link the chemistry and isotopic signatures of modern thermal waters directly with fossil mineralization dating back to at least 500–800 ka. The fossil thermal spring mineralization can be classified into two major types: barite-(pyrite) fracture filling associated with laterally-extensive silicification; and barite, goethite and silica impregnation mineralization in Tertiary sediments. Additionally, carbonatic sinters occur around active springs. Strontium isotope and trace element data suggest that mixing of a hot (>100 °C), deep-sourced thermal water with cooler groundwater from shallow aquifers is responsible for present-day thermal spring discharge and fossil mineralization. The correlation between both Sr and S isotope ratios and the elevation of the barite mineralization relative to the present-day water table in Wiesbaden is explained by mixing of deep-sourced thermal water having high 87Sr/86Sr and low δ34S with shallow groundwater of lower 87Sr/86Sr and higher δ34S. The Sr isotope data demonstrate that the hot thermal waters originate from an aquifer in the Variscan crystalline basement at depths of 3–5 km. The S isotope data show that impregnation-type mineralization is strongly influenced by mixing with SO4 that has high δ34S values. The fracture style mineralization formed by cooling of the thermal waters, whereas impregnation-type mineralization precipitated by mixing with SO4-rich groundwater percolating through the sediments. 相似文献
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87Sr/86Sr ratios of fourteen unaltered limestone and six fossil samples show a range of 0.7066-0.7118 for the depositional water of the Middle to Upper Pennsylvanian Madera Formation. The variation of these 87Sr/86Sr ratios may be due to the restricted depositional basin and nature of the source of the Madera Formation.While fossil and limestone samples are equally good for determination of strontium isotopic composition of depositional waters, leaches of calcareous shales contain significant amount of 87Sr leached from the noncarbonate fraction during acid treatment. 相似文献
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Omkar Verma Guntupalli V.R. PrasadAnjali Goswami Varun Parmar 《Cretaceous Research》2012,33(1):183-188
Although a very high invertebrate faunal diversity is known from the outcrops of the Ariyalur group in the Cauvery Basin, southern India, little is known about its vertebrate fauna. Recent fieldwork in the badland exposures of the Karai Formation (Upper Cenomanian-Lower Turonian) near Garudamangalam in the basin has yielded two teeth belonging to the Late Cretaceous shark Ptychodus decurrens (Ptychodontidae). The fossil record of Ptychodus decurrens from the southern continents is very poor, being known from a single Late/Middle Albian occurrence in Australia. This finding documents the first record of fossil P. decurrens in India and second from a Gondwanan landmass, and provides the first evidence of a cosmopolitan, Pangaean, distribution of the species during the Albian-Turonian and additional insights into the palaeoecology of the Cauvery Basin during the deposition of the Karai Formation. 相似文献
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Daniel Herwartz Thomas Tütken Klaus Peter Jochum P. Martin Sander 《Geochimica et cosmochimica acta》2011,75(1):82-5970
Rare earth element (REE) patterns of fossil bones and teeth are widely used as proxies for provenance, taphonomy, and palaeoenvironment. In order to investigate if fossil bones behave as closed systems over geologic time, REE profiles were analysed by LA-ICPMS along cross sections of 54 bones from various well-characterised and well-dated settings. These include terrestrial and marine diagenetic environments, covering Early Triassic to Holocene ages. In general, all fossil bones exhibit the highest REE concentrations at the outer rim, gradually decreasing by up to four orders of magnitude toward the inner bone cortex. Intra-bone REE concentration gradients decrease significantly from Quaternary via Tertiary to Mesozoic specimens, suggesting long term REE uptake and open system behaviour of fossil bone. This view is further corroborated by 176Lu-176Hf dating of selected samples, all yielding significantly younger ages than the known chronostratigraphic ages. Hence, there is clear evidence for long term open system behaviour of fossil bones with respect to REE, which is in marked contrast to currently accepted models suggesting that REE uptake is only early diagenetic. Although unexpected, statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one Upper Triassic Mastodonsaurus tooth with MSWDs ranging from 0.083 to 4.5. Notably, mobility of Lu alone cannot account for the observed age patterns. Assuming constant Lu uptake rates over time, the radiometric ages should only be as low as half of the chronostratigraphic age. However, a six-point isochron defined by subsamples of a single Upper Triassic Mastodonsaurus tooth yields an age of 65.2 ± 1.1 Ma (MSWD = 0.68), much younger than half of the stratigraphic age (ca. 234 Ma). Hence, Hf must also undergo late diagenetic exchange. Likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both REE and Hf are diffusion, adsorption, and dissolution-reprecipitation processes. 相似文献
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A. B. Kuznetsov O. P. Izokh O. S. Dzyuba B. N. Shurygin 《Doklady Earth Sciences》2017,477(2):1408-1413
The belemnite Sr isotope characteristics obtained over an interval from the Upper Volgian Regional Substage to the lower part of the Ryazanian Regional Stage in the section on the Maurynya River (Western Siberia) fills a gap in the 87Sr/86Sr ocean water variation curve over the Jurassic–Cretaceous boundary. The increase in the 87Sr/86Sr values from 0.707172 to 0.707242 revealed in the section coincides with a general rise in this ratio in the Late Jurassic–Early Cretaceous ocean. 相似文献
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The stratigraphic division and sequence of the Upper Cretaceous sediments in eastern Heilongjiang Province,China,have been ambiguous and controversial,mainly due to a lack of biostratigraphically useful fossils and related radiometric dating.A new species of angiospermous fossil plant.Platanus heilongjiangensis sp.nov.,from Qitaihe in eastern Heilongjiang has been found in sediments conformably above which zircons from a rhyolitic tuff has been dated by U-Pb radiometric methods as 96.2± 1.7 Ma.indicating that the Upper Houshigou Formation is of Cenomanian age.This discovery not only provides new data to improve our stratigraphic understanding of the Houshigou Formation,but also shows that Platanus flourished in the early Late Cretaceous floras of the region.This new study also indicates active volcanism taking place in the eastern Heilongjiang region during the Cenomanian of the Late Cretaceous. 相似文献
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黔东北地区MVT型铅锌矿床闪锌矿Rb-Sr定年及其地质意义 总被引：5，自引：1，他引：4
贵州东北部是中国著名的MVT型铅锌成矿带,长期以来,由于缺少精确成矿同位素年代学数据,对该区矿床成矿类型及其成矿作用的争议较大。文章对铜仁市下寒武统清虚洞组中的卜口场铅锌矿床和中寒武统敖溪组中的大硐喇汞锌矿床进行了同位素年代学研究,获得了闪锌矿的Rb-Sr等时线年龄,分别为(349.6±9.1)Ma(MSWD=0.51,n=5)和(349.2±5.2)Ma(MSWD=0.031,n=4),两个矿床闪锌矿的共同Rb-Sr等时线年龄为(348.6±1.9)Ma(MSWD=0.46,n=9),初始值(87 Sr/86 Sr)i为0.7095。Rb-Sr同位素测年结果表明,黔东北地区不同碳酸盐地层中铅锌、汞矿床的成矿时代是一致的,均为后生矿床类型,其成矿物质可能主要来源于包括震旦系碳酸盐岩在内的下伏地层。区内铅锌、汞矿床在加里东运动后期至华力西运动早期,华夏板块与扬子板块后碰撞过程中,可能与保铜玉深大断裂(中元古代末期上扬子古陆与江南古陆结合带,即最重要的控矿因素)的继续活化、扭动、撕裂紧密相关。 相似文献
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Rare earth elements (REE), while not essential for the physiologic functions of animals, are ingested and incorporated in ppb concentrations in bones and teeth. Nd isotope compositions of modern bones of animals from isotopically distinct habitats demonstrate that the 143Nd/144Nd of the apatite can be used as a fingerprint for bedrock geology or ambient water mass. This potentially allows the provenance and migration of extant vertebrates to be traced, similar to the use of Sr isotopes. Although REE may be enriched by up to 5 orders of magnitude during diagenesis and recrystallization of bone apatite, in vivo143Nd/144Nd may be preserved in the inner cortex of fossil bones or enamel. However, tracking the provenance of ancient or extinct vertebrates is possible only for well-preserved archeological and paleontological skeletal remains with in vivo-like Nd contents at the ppb-level. Intra-bone and -tooth REE analysis can be used to screen for appropriate areas. Large intra-bone Nd concentration gradients of 101-103 are often measured. Nd concentrations in the inner bone cortex increase over timescales of millions of years, while bone rims may be enriched over millenial timescales. Nevertheless, εNd values are often similar within one εNd unit within a single bone. Larger intra-bone differences in specimens may either reflect a partial preservation of in vivo values or changing εNd values of the diagenetic fluid during fossilization. However, most fossil specimens and the outer rims of bones will record taphonomic 143Nd/144Nd incorporated post mortem during diagenesis. Unlike REE patterns, 143Nd/144Nd are not biased by fractionation processes during REE-uptake into the apatite crystal lattice, hence the εNd value is an important tracer for taphonomy and reworking. Bones and teeth from autochthonous fossil assemblages have small variations of ±1 εNd unit only. In contrast, fossil bones and teeth from over 20 different marine and terrestrial fossil sites have a total range of εNd values from -13.0 to 4.9 (n = 80), often matching the composition of the embedding sediment. This implies that the surrounding sediment is the source of Nd in the fossil bones and that the specimens of this study seem not to have been reworked. Differences in εNd values between skeletal remains and embedding sediment may either indicate reworking of fossils and/or a REE-uptake from a diagenetic fluid with non-sediment derived εNd values. The latter often applies to fossil shark teeth, which may preserve paleo-seawater values. Complementary to εNd values, 87Sr/86Sr can help to further constrain the fossil provenance and reworking. 相似文献
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Edward G. Purdy 《International Journal of Earth Sciences》2008,97(3):651-664
Sepkoski’s compendium of 28,730 marine genera was analyzed with a view toward comparing taxonomic diversity, strontium isotope
stratigraphy and sea-level changes. The fossil record analyses discriminated between origination, extinction and pass through
genera and collectively delineated changes in number of genera with time at the largely stratigraphic stage level. With notable
exceptions of the Cretaceous and Tertiary, taxonomic diversity generally paralleled both strontium isotope stratigraphy and
sea-level changes. Sampling bias was suggested in the Tertiary where an increase in genera numbers toward the Recent opposed
the downward trends of both strontium isotope and sea level curves. The removal of all Recent genera from the Sepkoski database
confirmed the bias in producing complimentary downward trends in all curves. Regression analysis of taxonomic diversity with
respect to sea level extent and time duration explained 82% of the variability of the remaining data. Sea-level fluctuations
are not always accompanied by significant changes in taxonomic diversity but strontium isotope analyses offers the potential
of constraining the extent to which the magnitude of changes are associated with time duration. 相似文献
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Shallow-water carbonates are invaluable archives of past global change. They hold the record of how neritic biologic communities reacted to palaeoenvironmental changes. However, attempts to decipher these geological archives are often severely hampered by the low stratigraphic resolution attained by biostratigraphy. This is particularly the case for the Upper Cretaceous carbonate platforms of the central Tethyan realm: their biostratigraphy suffers from very low resolution and poor correlation with the standard biochronologic scales based on ammonites, planktic foraminifers and calcareous nannoplankton.In this paper we show how this problem can be tackled by integrating biostratigraphy with isotope stratigraphy. We present a detailed record of the benthic foraminiferal biostratigraphy and carbon and strontium isotope stratigraphy of three upper Cenomanian-middle Campanian sections belonging to the Apennine Carbonate Platform of southern Italy. For the upper Cenomanian-Turonian interval, the carbon isotope curves of the studied sections are easily correlated to the reference curve of the English Chalk. The correlation is facilitated by the matching of the prominent positive excursion corresponding to the Oceanic Anoxic Event 2. For the Coniacian-middle Campanian interval, the correlation is mainly based on strontium isotope stratigraphy. We use the 87Sr/86Sr ratios of the low-Mg calcite of well preserved rudist shells to obtain accurate chronostratigraphic ages for many levels of the three studied sections. The ages obtained by Sr isotope stratigraphy are then used to better constrain the matching of the carbon isotope curves.From the high-resolution chronostratigraphic age-model stablished by isotope stratigraphy, we derive the chronostratigraphic calibration of benthic foraminiferal biostratigraphic events. For the first time the benthic foraminiferal biozones of the Apennine Carbonate Platform can be accurately correlated to the standard ammonite biozonation. This result is of great relevance because the biostratigraphic schemes of other carbonate platforms in the central and southern Tethyan realm are largely based on the same biostratigraphic events. 相似文献
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Seven coleoid jaws recovered from Santonian to lower Campanian (Upper Cretaceous) strata in Hokkaido, Japan were taxonomically studied. Based on the comparison with the jaws of modern and fossil coleoids, six of the seven jaw fossils are referred to the following two genera and three species, including one possible new species: Nanaimoteuthis jeletzkyi and N. yokotai of the order Vampyromorpha, and Paleocirroteuthis sp. nov. (?) of the order Cirroctopodida. The other single lower jaw is seemingly similar to those of modern octopods and teuthids with respect to the shape of the inner lamella, but its order-level assignment could not be determined because of its imperfect preservation. N. jeletzkyi has been described in the Upper Cretaceous fore-arc basin deposits in Hokkaido (Yezo Group) and Vancouver Island, Canada (Nanaimo Group), whereas N. yokotai occurs only in the Yezo Group. These findings, complemented by previous reports of coleoid jaws, gladii, and phragmocones from the Yezo and Nanaimo Groups, demonstrate that a highly diversified, non-belemnitid coleoid fauna including large teuthids had already appeared during the post-Albian Late Cretaceous, in the North Pacific region. 相似文献
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Fresh basalt and metabasalt dredged from the Mid-Atlantic Ridge were studied for Na, K, Rb, Sr, and H2O(+) contents, and strontium and hydrogen isotope ratios. Na, K, Rb, and Sr contents of these samples are within the range
of those of oceanic tholeiite. H2O(+) content, strontium, and hydrogen isotope ratios vary widely. The variation in water content of metabasalt is apparently
related to the chlorite content. The metamorphic temperature was about 550 °C based on the estimated δD value of chlorite.
There is positive linear relationship between water content and strontium isotope ratio. Based on this relationship, the variation
of strontium isotope ratio of the metabasalt was interpreted as follows: complete exchange occurred between strontium in the
chlorite portion of the metabasalt and strontium in sea water (87Sr/86Sr ratio=0.7090), while the original strontium (87Sr/86Sr∼0.7023) was retained in the non-altered portion of the basalts. 相似文献
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Several publications on the environmental control of strontium in carbonate rocks have stimulated this investigation. Samples from three lithologically different units of the marine Upper Jurassic in the Northeastern Alps are analysed for strontium (x-ray fluorescence, atomic absorption, microprobe). Reported data on Sr in Recent carbonate secreting organisms, Recent and fossil carbonate sediments, on partition between calcite, aragonite and seawater have been used for comparison with those of the Upper Jurassic carbonate rocks. Reef sediments predominantly consisting of aragonite and high magnesium calcite lost extreme portions of their original Sr during diagenesis. Some layers (Oberalmer Schichten, St. Koloman) of probable bathypelagic origin are still comparable in strontium with primary marine calcite (about 0,1 % Sr).The pattern of the Sr distribution in the investigated Upper Jurassic limestones is mainly due to different courses of diagenetic change from different primary carbonates into low magnesium calcite. The change in Sr concentrations of diagenetic solutions is a function of the type of the supporting carbonate in an closed or open system of carbonates with porous solutions and is a function of seawater- or freshwater influence on the latter. A small strontium portion of these rocks occurs in apatite crystals with abnormal sulfur contents which could be identified as fragments of fish teeth.
Wir danken Herrn Dr. A. Schkbidbb, (Göttingen) für zahlreiche Mikrosondenuntersuchungen und Herrn A. FENMNGER (Graz) für die quantitative Bestimmung der Tonrückstände in den Kalken. Für einen Teil der analytischen Arbeiten wurde ein Röntgenspektrometer der Deutschen Forschungsgemeinschaft benutzt. 相似文献
Wir danken Herrn Dr. A. Schkbidbb, (Göttingen) für zahlreiche Mikrosondenuntersuchungen und Herrn A. FENMNGER (Graz) für die quantitative Bestimmung der Tonrückstände in den Kalken. Für einen Teil der analytischen Arbeiten wurde ein Röntgenspektrometer der Deutschen Forschungsgemeinschaft benutzt. 相似文献
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We used analyses of the strontium isotope (87Sr/86Sr) ratios of tooth enamel to reconstruct the migration patterns of fossil mammals collected along the Aucilla River in northern Florida. Specimens date to the late-glacial period and before the last glacial maximum (pre-LGM). Deer and tapir displayed low 87Sr/86Sr ratios that were similar to the ratios of Florida environments, which suggest that these taxa did not migrate long distance outside of the Florida region. Mastodons, mammoths, and equids all displayed a wide range of 87Sr/86Sr ratios. Some individuals in each taxon displayed low 87Sr/86Sr ratios that suggest they ranged locally, while other animals had high 87Sr/86Sr ratios that suggest they migrated long distances (> 150 km) outside of the Florida region. Mastodons were the only taxa from this region that provided enough well-dated specimens to compare changes in migration patterns over time. Pre-LGM mastodons displayed significantly lower 87Sr/86Sr ratios than late-glacial mastodons, which suggests that late-glacial mastodons from Florida migrated longer distances than their earlier counterparts. This change in movement patterns reflects temporal changes in regional vegetation patterns. 相似文献
