Authigenic potassium feldspar in cambrian carbonates: evidence of alleghanian brine migration

The shallow-water limestones and dolostones of the Conococheague Limestone (Upper Cambrian) of western Maryland contain large amounts of authigenic potassium feldspar. The presence of halite daughter crystals in breached fluid inclusions, low whole-rock ratios of chlorine to bromine, and thermochemical data suggest that the potassium feldspar formed at low temperature by the reaction of connate brines with intercalated siliciclastic debris. Analyses of argon age spectra indicate that the authigenic feldspar probably formed during Late Pennsylvanian to Early Permian time. These results may indicate mobilization and migration of connate brines brought about by Alleghanian folding. The widespread occurrence of authigenic potassium feldspar in Cambrian and Ordovician carbonate rocks throughout the Appalachians suggests that this may have occurred throughout the entire basin.     

台山市土壤硒来源的研究

[目的]研究台山地区土壤富硒来源,为资源开发利用提供重要科学依据。[方法]从成土母质和大气沉降上,对比分析了硒的含量。[结果]源岩中,上寒武系地层含硒量高,可达1.34 mg/kg;大气干沉降物中,硒年通量平均达285.18μg/(m2.年)。[结论]上寒武统水石组为该区的主要物质来源,而大气沉降为提供丰富物质补充。     

Precambrian sponges with cellular structures

Sponge remains have been identified in the Early Vendian Doushantuo phosphate deposit in central Guizhou (South China), which has an age of approximately 580 million years ago. Their skeletons consist of siliceous, monaxonal spicules. All are referred to as the Porifera, class Demospongiae. Preserved soft tissues include the epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel. Among thousands of metazoan embryos is a parenchymella-type of sponge larvae having a shoe-shaped morphology and dense peripheral flagella. The presence of possible amphiblastula larva suggests that the calcareous sponges may have an extended history in the Late Precambrian. The fauna indicates that animals lived 40 to 50 million years before the Cambrian Explosion.     

Detrital Zircon Link Between Headwaters and Terminus of the Upper Triassic Chinle-Dockum Paleoriver System

New detrital-zircon geochronologic data reveal that a through-going paleoriver connected Texas with Nevada in Late Triassic time. Sandstone from the Upper Triassic Santa Rosa Sandstone (Dockum Group) from northwestern Texas contains a detrital zircon suite nearly identical to that found in western Nevada in the Upper Triassic Osobb Formation (Auld Lang Syne Group, correlative with the Chinle Formation). The Santa Rosa Sandstone was derived in large part from the eroded Cambrian core of the Amarillo-Wichita uplift, as evidenced by abundant zircons with ages of 515 to 525 million years. Other zircon grains in the sandstone are Permian, Devonian, Proterozoic, and Archean in age and, with the exception of the Archean grain, are also matched by the population in the Nevada strata.     

A chronology of Paleozoic sea-level changes

Sea levels have been determined for most of the Paleozoic Era (542 to 251 million years ago), but an integrated history of sea levels has remained unrealized. We reconstructed a history of sea-level fluctuations for the entire Paleozoic by using stratigraphic sections from pericratonic and cratonic basins. Evaluation of the timing and amplitude of individual sea-level events reveals that the magnitude of change is the most problematic to estimate accurately. The long-term sea level shows a gradual rise through the Cambrian, reaching a zenith in the Late Ordovician, then a short-lived but prominent withdrawal in response to Hirnantian glaciation. Subsequent but decreasingly substantial eustatic highs occurred in the mid-Silurian, near the Middle/Late Devonian boundary, and in the latest Carboniferous. Eustatic lows are recorded in the early Devonian, near the Mississippian/Pennsylvanian boundary, and in the Late Permian. One hundred and seventy-two eustatic events are documented for the Paleozoic, varying in magnitude from a few tens of meters to approximately 125 meters.     

Ediacaran (precambrian) fossils from the wernecke mountains, northwestern Canada

Fossil medusoids identified as Cyclomedusa davidi?, Beltanelliformis brunsae, and cf. Sekwia excentrica are reported from Late Precambrian strata in the Wernecke Mountains. They are representatives of the Ediacaran fauna, the oldest assemblage of cosmopolitan metazoans, and are only the third such occurrence in Canada. In addition, specimens broadly resembling the problematic structure Rugoinfractus ovruchensis, previously known only from the Precambrian of the Ukraine, are reported from the Lower Cambrian of the nearby Mackenzie Mountains.     

Phanerozoic-cryptozoic and related transitions: new evidence

The fossil Pteridinium, a distinctive component of a worldwide early metazoan (Ediacaran)assemblage, is provisionally recorded from probable early Cambrian strata in eastern California. In context with other evidence, this finding implies a Cambrian age for the Ediacaran fauna and approximate coincidence of limits between Phanerozoic-Cryptozoic, Paleozoic-Precambrian, and Cambrian-Precambrian.     

A search for iridium abundance anomalies at two late cambrian biomere boundaries in Western utah

Iridium concentrations have been measured in samples taken across two Late Cambrian biomere boundaries (crisis zones) in search of evidence for possible elemental abundance anomalies similar to the one observed at the Cretaceous-Tertiary boundary. Sampling was performed in uplifted marine limestone deposits in the House Range of western Utah. Although the two trilobite-brachiopod extinction boundaries could be assigned to +/-4 millimeters of vertical section by laboratory examination of the rocks, only background amounts of iridium (2 x 10(-12) to 17 x 10(-12) gram per gram of whole rock) were observed.     

Cambrian river terraces and ridgetops in central australia: oldest persisting landforms?

Fluvial sediments in paleovaileys cut in the Ashburton surface of the Davenport province of central Australia form terrace remnants that appear to retain their original depositional tops and have probably existed as subaerial landforms since their inception. Marine fossils in sediments conformable with the fluvial sediments near the southeast margin of the province give a Cambrian age for the terraces; the Ashburton surface forming the ridgetops between the paleovalleys is Cambrian or older.     

Late Pleistocene Desiccation of Lake Victoria and Rapid Evolution of Cichlid Fishes

Lake Victoria is the largest lake in Africa and harbors more than 300 endemic species of haplochromine cichlid fish. Seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the Late Pleistocene, before 12,400 carbon-14 years before the present. These results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid.     

Triassic vertebrates of gondwanan aspect from the richmond basin of virginia

A new locality of early Late Triassic age in the Richmond basin of east-central Virginia has yielded abundant remains of a diversified assemblage of small to medium-sized tetrapods that closely resembles Southern Hemisphere (Gondwanan) assemblages in the predominance of certain synapsids. Associated palynomorphs indicate an early middle Carnian age for the fossiliferous strata. The discovery suggests that previously recognized differences between tetrapod assemblages of early Late Triassic age from Gondwana and Laurasia at least in part reflect differences in stratigraphic age, rather than geographic separation.     

Kom ombo: preliminary report on the fauna of late paleolithic sites in upper egypt

A Late Pleistocene fauna comprising 3 fish, 1 reptile, 22 birds, and 14 mammals is identified from sites containing Sebilian, Sebekian, Silsilian, Menchian, and Halfan industries. It is remarkable for its variety, especially of birds, and gives evidence for year-round occupation of these sites.     

Application of carbon isotope stratigraphy to late miocene shallow marine sediments, new zealand

A distinct (0.5 per mil) carbon-13/carbon-12 isotopic shift in the light direction has been identified in a shallow marine sedimentary sequence of Late Miocene age at Blind River, New Zealand, and correlated with a similar shift in Late Miocene Deep Sea Drilling Project sequences throughout the Indo-Pacific. A dated piston core provides an age for the shift of 6.2 +/- 0.1 million years. Correlations based on the carbon isotopic change require a revision of the previously established magnetostratigraphy at Blind River. The carbon shift at Blind River occurs between 6.2 and 6.3 +/- 0.1 million years before present. A new chronology provides an age for the evolutionary first appearance datum of Globorotalia conomiozea at 6.1 +/- 0.1 million years, the beginning of a distinct latest Miocene cooling event associated with the Kapitean stage at 6.2 +/- 0.1 million years, and the beginning of a distinct shallowing of water depths at 6.1 +/- 0.1 million years. The Miocene-Pliocene boundary as recognized in New Zealand is now dated at 5.3 +/- 0.1 million years. Extension of carbon isotope stratigraphy to other shallow Late Miocene sequences should provide an important datum for international correlation of Late Miocene shallow and deep marine sequences.     

Early cambrian foraminifera from west Africa

Agglutinated foraminifera have been recovered from siltstones in the Walidiala Valley, Taoudeni Basin, West Africa. Associated faunas suggest an Early Cambrian age for these strata. These now earliest known unequivocal foraminifera help constrain hypotheses concerning the origin of skeletalization at the beginning of the Phanerozoic.     

Paleozoic sedimentary rocks in oaxaca, Mexico

Fossiliferous Cambrian, Ordovician, Mississippian, and Pennsylvanian rocks, never before found in southern Mexico, have been discovered in the Nochixtlán region. Superjacent unfossiliferous sedimentary rocks may be Permian in age. Early Paleozoic and late Paleozoic intervals of marine sedimentation were bounded by intervals of positive tectonism and erosion.     

The early evolution of the tetrapod humerus

A tetrapod humerus from the Late Devonian of Pennsylvania has a novel mix of primitive and derived characters. A comparative analysis of this fossil and other relevant humeri from the Devonian shows that the role of the limb in propping the body arose first in fish fins, not tetrapod limbs. The functional diversity of the earliest known limbs includes several different kinds of appendage design. This functional diversity was achieved with a humeral architecture that was remarkably conserved during the Devonian.     

Conodont pearls?

Conodonts are zoologically enigmatic, toothlike phosphatic microfossils occurring in marine sedimentary rocks ranging in age from Cambrian to Triassic. Dimpled spheres of less than 1 millimeter in diameter are sporadic associates of conodonts and have identical chemical composition and microstructure. Mineralogy, morphology, and occurrence of these spheres suggest that they are pearls secreted by the conodont-bearing animal.     

洞庭湖鱼类资源研究进展

参阅了近50年对洞庭湖鱼类研究的文献资料,对洞庭湖鱼类资源的研究进行了综述。洞庭湖鱼类物种数一般稳定在110～120种,但是近10年来有减少的趋势;洞庭湖的鱼类区系属于长江鱼类区系的一部分,洞庭湖鱼类区系是以第三世纪现代中国平原复合体为主体;洞庭湖鱼产量有逐年下降的趋势,洄游型和半洄游型鱼类数量和所占鱼获物比重急剧下降;洞庭湖主要经济鱼类个体低龄化、小型化。最后,分析了鱼类资源衰退的主要因素并提出保护对策。     

Evidence for monophyly and arthropod affinity of cambrian giant predators

The Chinese Early Cambrian Chengjiang fauna includes three different anomalocaridids, a globally spread, extinct marine group including the largest known Cambrian animals. Anomalocaridids were active predators, and their presence implies that a complex ecosystem appeared abruptly in the earliest Phanerozoic. Complete specimens display several sets of characters shared only with some other exclusively Cambrian forms. This evidence indicates that anomalocaridids, Opabinia, and Kerygmachela form a monophyletic clade. Certain features indicate arthropod affinities of the lade, and for this group an unnamed (sub)phylum-level taxon within an arthropod (super)phylum is proposed.     

Calibration of the great american interchange

From radioisotopic (potassium-argon) age determinations of tuffs and magnetostratigraphy of Late Tertiary mammal-bearing beds in Catamarca Province, northwest Argentina, refined estimates have been obtained for the durations and boundaries of beds of Chasicoan (Middle Miocene) through Chapadmalalan (Pliocene) age. An age of 9.0 million years is tentatively accepted for the Chasicoan-Huayquerian boundary, 5.0 million years for the Huayquerian-Montehermosan boundary, and 3.0 million years for the Montehermosan-Chapadmalalan boundary. Procyonids (raccoons and their allies), a group of North American origin, are first recorded in South America in a level immediately below a unit dated at 6.0 million years. Cricetine rodents of the tribe Sigmodontini are first recorded in South America in beds of Montehermosan age in Argentina. Ground sloths, a group of South American origin, first appear in North America in Early Hemphillian time in beds dated between 9.5 and 9.0 million years. The Panamanian land bridge was established by 3.0 million years ago, and an interchange of the terrestrial faunas was well under way by Late Blancan time (around 2.5 million years before present) in North America and by Chapadmalalan time in South America.