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The Sulphur Mountain Formation in the Wapiti area is subdivided into the Phroso, Meosin Mountain (new), and Vega members, which collectively span much of the Lower Triassic. The Smithian conodont faunas are particularly well developed and form the basis of three partly new conodont zones and two new subzones: the lachrymiformis Zone, meeki Zone, and mosheri Zone, with the last subdivided into the phryna and milleri Subzones. An informal lowermost Smithian nepalensis interval is introduced, although it has yet to be found in the area. The Phroso Member is latest Griesbachian, Dienerian, and, in its uppermost part, Smithian, specifically the lachrymiformis and meeki zones: these are shown to be equivalent to the Euflemingites romunduri ammonoid Zone. The Meosin Mountain Member is assigned to the meeki Zone in its lower part and the phryna Subzone of the mosheri Zone in its upper part: at least, the upper part of the mosheri Zone is equivalent to the Anawasatchites tardus ammonoid Zone. The Mackenzie Dolomite Lentil is at least partly older than the Meosin Mountain Member, and age equivalence of subsurface turbidite units in the Montney Formation should not be assumed. The lowermost Vega Member is also assigned to the phryna Subzone, and higher parts of that member span both the milleri Subzone of the Smithian and the entire Spathian. The following new conodont taxa are described: Neogondolella? joanae, Novispathodus latiformis, Scythogondolella lachrymiformis, Sc. phryna, and Sc. rhomboidea; several other new species are kept in open nomenclature. La Formation de Sulphur Mountain dans le secteur de Wapiti est subdivisee en quatre membres : Phroso, Meosin, Mountain (nouveau) et Vega qui, ensemble, recouvrent une grande partie du Trias inferieur. Les faunes conodontes du Smithien sont particulierement bien developpees et forment la base de trois zones a conodontes partiellement nouvelles, soit la zone a lachrymiformis, la zone a meeki et la zone a mosheri; cette derniere zone est subdivisee en deux nouvelles sous-zones, la sous-zone a phryna et la sous-zone a milleri. Un intervalle informel, a nepalensis, le plus bas du Smithien, est introduit bien qu'il reste encore a le decouvrir dans le secteur. Le membre Phroso est dans le Griesbachien le plus tardif et dans le Dienerien; sa partie superieure est dans le Smithien, surtout dans les zones a lachrymiformis et a meeki : il est demontre que ces zones sont equivalentes a la zone ammonoide a Euflemingites romunduri. La partie inferieure du membre de Meosin Mountain est assignee a la zone a meeki et, dans sa partie superieure, a la sous-zone a phryna de la zone a mosheri : au moins la partie superieure de la zone a mosheri est l'equivalent a la zone ammonoide a Anawasatchites tardus. Le Mackenzie Dolomite Lentil est au moins partiellement plus age que le membre de Meosin Mountain et les equivalences en age des unites turbidites sous la surface dans la Formation de Montney ne devraient pas etre presumees. Le membre Vega le plus bas est aussi assigne a la sous-zone a phryna et les parties superieures de ce membre chevauchent la sous-zone a milleri du Smithien et tout le Spathien. Les nouveaux taxons de conodonte suivants sont decrits : Neogondolella? joanae, Novispathodus latiformis, Scythogondolella lachrymiformis, Sc. phryna et Sc. rhomboidea; plusieurs autres nouvelles especes sont gardees en nomenclature ouverte. [Traduit par la Redaction] doi: 1139/E09-051, Introduction The Lower Triassic Sulphur Mountain Formation in the Wapiti Lake area (Fig. 1) is well known for its exceptional fossil fish fauna (Schaeffer and Mangus 1976; Mutter and Neumann [...]

The Jim Pitts site is a multicomponent Paleoindian locality in the Black Hills of South Dakota, with a rare Goshen residential occupation. All Paleoindian components were comprised in the Leonard paleosol. The deepest component at the site is a Goshen level dated to 10,185 ± 25 B.P. It correlates with a late fall-early winter camp site. Over the course of its use parts of at least five bison were procured and introduced to the site. Above this level an array of point styles, including Goshen, Folsom, Agate Basin, several Fishtail points, James Allen, Cody, and Alberta, have also been found. The following study provides a typological and technological description of the point assemblage and weighs the implications of the chrono-cultural stratigraphy for reconstructing the Paleoindian cultural landscape. It questions the validity of some types, particularly Goshen, as cultural and chronological markers. Ultimately, the evidence presented here reinforces a model in which multiple Paleoindian point types occur simultaneously on the central and northern Great Plains. This in turn challenges a unilineal view of Puleoindian culture history. El sitio Jim Pitts es una localidad multi-componente Paleoindia en los Black Hills de Dakota del Sur, con una infrecuente ocupacion residencial Goshen. Todos los componentes Paleoindios estan comprendidos en el paleosuelo Leonard. El componente mas profundo del sitio es un nivel Goshen fechado en 10,185 ± 25 a.P., el cual se correlaciona con un campamento otohalinvernal durante el cual partes de al menos cinco bisontes fueron procurados e introducidos al sitio. Sobre este nivel, una variedad de puntas de proyectil incluyendo Goshen, Folsom, Agate Basin, varias puntas cola de pescado, James Allen, Cody, y Alberta tambien fueron halladas. El analisis que sigue aporta una descripcion tipologica y tecnologica de los con juntos de puntas y examina las implicaciones de la estratigrafia crono-cultural para la reconstruccion del paisaje cultural Paleoindio. Se cuestiona la validez de algunos tipos, particularmente el tipo Goshen, como un indicador cultural y cronologico. La evidencia presentada fundamentalmente refuerza un modelo donde mtiltiples tipos de puntas Paleoindias ocurren simultaneamente en las Grandes Llanuras centrales y septentrionales, que desafia la perspectiva unilineal de la historia cultural Paleoindia., Questions of chronology have shaped Paleoindian archaeology since the early days of the debate surrounding the antiquity of in North America. Prior to the development of radiocarbon dating, the Paleoindian [...]

Three ophiolites are currently recognized in the southern Quebec Appalachians, from south to north: the MontOrford ophiolite, dominated by tholeiitic to transitional-alkaline basalt and diabase, and the Thetford Mines and Asbestos ophiolites, which are made up of boninites and tholeiitic basalts. This contribution documents the origin, geochemistry, and geodynamic evolution of the Lac-Brompton ophiolite, which was previously interpreted as a diapiric serpentinite melange and genetically attributed to the Mont-Orford ophiolite. Our study of its igneous rocks rather indicates that the Lac-Brompton ophiolite is an exhumed segment of oceanic lithosphere represented by mantle rocks of harzburgitic composition and a discontinuous crust made up of boninitic volcanic rocks and intrusions of gabbro, pyroxenite, and granitoids that, respectively, overlie and crosscut the harzburgite. The ophiolitic mantle and crustal rocks and underlying infra-ophiolitic tectonic sole are overlain by sedimentary rocks belonging to the Saint-Daniel Melange. The internal stratigraphy of the ophiolite and relationships with the Saint-Daniel Melange suggest that the mantle rocks were exhumed to seafloor level prior to boninitic magmatism, and that the mantle and crustal rocks were deeply eroded during or shortly after obduction. The infra-oceanic evolution of the Lac-Brompton ophiolite is believed to have been comparable to the one of ultramafic core complexes exposed along slow-spreading ridge segments. The stratigraphic and geochemical characteristics of the Lac-Brompton ophiolite suggest that it forms, with the Asbestos and Thetford Mines ophiolites, a composite slab of forearc seafloor. Trois ophiolites sont presentement reconnues dans les Appalaches du sud du Quebec, du sud vers le nord ce sont : l'ophiolite du Mont-Orford, constituee de basalte et diabase de composition tholeiitique a transitionnelle-alcaline et les ophiolites de Thetford Mines et Asbestos dont les roches volcaniques sont de composition boninitique a tholeiitique. La presente contribution documente l'origine, la geochimie et l'evolution geodynamique de l'ophiolite du Lac-Brompton, anterieurement interpretee comme un melange ophiolitique diapirique genetiquement attribue a l'ophiolite du Mont-Orford. Nos travaux suggerent que l'ophiolite du Lac-Brompton represente un segment de lithosphere oceanique constituee de roches mantellaires de composition harzburgitique et d'une croute discontinue representee par des roches volcaniques boninitiques et des intrusions de gabbro, pyroxenite et granitoides qui recouvrent ou recoupent respectivement la harzburgite. Les roches sedimentaires du Melange de Saint-Daniel reposent en discordance sur les roches mantellaires et crustales, ainsi que celles de la semelle metamorphique infra-ophiolitique. La stratigraphie de l'ophiolite et la nature de ses contacts avec le Melange de Saint-Daniel suggerent que les roches mantellaires ont ete exhumees au niveau du fond oceanique avant la formation des roches volcaniques. L'ophiolite a ensuite ete soumise a une profonde erosion pendant ou peu apres son obduction. L'evolution infra-oceanique de l'ophiolite du Lac-Brompton est consideree comme comparable a celle des 'core complexes' oceaniques exposes au niveau des rides oceaniques lentes. Les caracteristiques stratigraphiques et geochimiques de l'ophiolite du Lac-Brompton suggerent qu'elle forme, avec celles de Thetford Mines et Asbestos, une nappe ophiolitique composite de lithosphere oceanique d'avant-arc. [Traduit par la Redaction], Introduction The Southern Quebec Ophiolite Belt, historically interpreted as a collage of different segments of an ocean ridge system (Laurent 1975), has been re-interpreted as the vestige of an immature [...]

Abstract: Two Cordilleran and three Laurentide glacial advances are recorded in Quaternary sediments and landforms in the Peace River valley, northeast British Columbia. The advances are inferred from fluvial gravels, [...]

Abstract: Exposures in the Prophet River valley in northeast British Columbia provide a unique glimpse into the Quaternary history of the northwest Canadian Boreal Plains. The region shows evidence of [...]

Abstract: Lac Guillaume-Delisle Estuary and Nastapoka Sound are two sedimentary basins that recorded the late Quaternary deglaciation on the eastern coast of Hudson Bay. Acoustic profiles reveal an average sediments [...]

Abstract: Differential sea-level change in formerly glaciated areas is predicted owing to variability in extent and timing of glacial coverage. Newfoundland is situated close to the margin of the former [...]

Abstract: The 950 m thick Sibley Group is a relatively flat-lying assemblage of siliciclastic and chemical sedimentary rocks exposed from the northwest shore of Lake Superior to the Lake Nipigon [...]

Abstract: Late Neoarchean volcanic belts in the southern Slave Province include (1) in the east, the Cameron River--Beaulieu River belts, which are characterized by stratigraphically thin, flow-rich, classic calc-alkaline, arc-type [...]

Arenig strata in the Napadogan area of the Miramichi Highlands of west-central New Brunswick are similar to those of the Lunksoos anticlinorial area of eastern Maine. Strata from both areas were deposited in a volcanic back-arc setting upon Cambrian-Tremadoc, deep-water, turbiditic quartzose strata on the northwest-facing Gander margin of Gondwana. Tremadoc southeastward obduction of the Penobscot Arc, formed in the Iapetus Ocean to the northwest of the margin, was followed by local uplift, rift faulting, erosion, and finally by local deposition of late Arenig gravel within the early stages of a subsiding back-arc basin that was related to a younger, northwest-facing, early Arenig-Llanvirn Popelogan Arc lying to the northwest. These strata became overlain by late Arenig marine felsic tuff, sandy and silty tuff and mudstone, coarse textured and many hundreds of metres thick in the Lunksoos area but much finer and only a few metres thick farther from the volcanic centres, in the Napadogan area. During Llanvirn, the strata became covered with deep-water, commonly manganiferous, ferruginous shalechert in a basin shielded from currents carrying coarse detritus. Arenig strata of the Napadogan area probably developed to the southeast of the main rift-volcanism zone that perhaps extended between the Lunksoos and northeastern Miramichi Highlands during the Arenig. Brachiopods of the Celtic paleogeographic assemblage colonized newly formed shelves flanking islands along the zone. Shell beds developed upon fresh layers of ash in a nutrient-rich environment between episodes of volcanism. These Celtic brachiopods developed in cool waters of high southern latitudes off Gondwana, different from those on the Laurentian margin in warm waters of low southern latitudes., RESUME Les strates de l'Arenig dans le secteur de Napadogan du massif de Miramichi, dans le centre-ouest du Nouveau-Brunswick, sont semblables a celles du secteur anticlinorial de Lunksoos dans l'Est [...]

A temperature spike is reported in the haloclines of three Yucatan sinkholes along a 1 km NW-SE transect from 5 to 4 km inland from the Caribbean coast. The temperature spike decreases in magnitude from ~3.5°C to 0.2°C, approaching the coast. The anomaly does not vary diurnally and does not extend down into the underlying sea water. These conditions are inconsistent with explanations such as radiation absorption within the halocline, in situ microbialfy mediated sulfate reduction within the halocline and the underlying sea water, and sulfide oxidation by photosynthetic purple and green bacteria within the halocline. One explanation consistent with the shape and halocline location of the temperature spike involves a localized sea water convection cell operating near the coast. Cold sea water from the Caribbean Sea enters the coastal limestone at depths of a few hundred meters and heats up because of the geothermal gradient, buoyantly rising in vertical fractures within the unconfined aquifer. Blocked by the less dense fresh water, the movement stops in the halocline where the warm sea water mixes with brackish water. The convection cycle would be completed by the coastward movement of cooling brackish water. The observed temperature anomalies could possibly be snapshots of this warm layer moving coastward., Introduction The northeastern coastal Yucatan Peninsula, adjacent to the Caribbean Sea, is a region of karst topography (Back and Hanshaw 1970) with numerous sinkholes and some of the longest subaquatic [...]

A study of the differential preservation of the famous Coa engravings, in the light of the site of Fariseu, place the distribution of the art in a chronological setting, which is in turn placed within the context of lithic raw material procurement. Key-words: rock art, Coa Valley, Upper Palaeolithic, differential preservation, climate, resource exploitation, The natural environment The Coa River is a left-bank tributary of the Douro, the major watercourse of the north central Iberian cordillera (FIGURE 1) which crosses Iberia from east to [...]

A three-dimensional model of mantle convection in which the known history of plate tectonics is imposed predicts the anomalous Cretaceous vertical motion of Australia and the present-day distinctive geochemistry and [...]

Fossil shells and paleosol carbonate from ancestral Himalayan river deposits provide a [sup.87]Sr/[sup.86]Sr record of lowland Himalayan river water during the late Neogene. Reconstructed [sup.87]Sr/[sup.86]Sr river values increased sharply in [...]

The Argentine Precordillera is a continental fragment rifted from the Ouachita embayment of the southern margin of Laurentia (North America) during Cambrian time [about 515 million years ago (Ma)] and accreted to the western margin of Gondwana (South America) during Ordovician time (about 455 Ma). Similarities of Cambrian stratigraphic successions and faunas, Grenville basement rocks, and dimensions link the Argentine Precordillera to the Ouachita embayment. Evidence of rifting during Cambrian time and of a wide ocean basin during Ordovician time indicates that the Precordillera traveled as an independent microcontinent to collide with Gondwana., The rifted continental margin of Laurentia (now North America) records continental breakup and the opening of the lapetus Ocean in latest Precambrian to earliest Paleozoic time (1). Collisions during later [...]

In their report, Matti E. Rasanen et al. state that there is a tidal origin for the sedimentary sequences they studied in the western Amazon region (1). Their interpretation of [...]

Oligocene to middle Miocene sequence boundaries on the New Jersey coastal plain (Ocean Drilling Project Leg 150X) and continental slope (Ocean Drilling Project Leg 150) were dated by integrating strontium isotopic stratigraphy, magnetostratigraphy, and biostratigraphy (planktonic foraminifera, nannofossils, dinocysts, and diatoms). The ages of coastal plain unconformities and slope seismic reflectors (unconformities or stratal breaks with no discernible hiatuses) match the ages of global [delta.sup.18]O increases (inferred glacioeustatic lowerings) measured in deep-sea sites. These correlations confirm a causal link between coastal plain and slope sequence boundaries: both formed during global sea-level lowerings. The ages of New Jersey sequence boundaries and global [delta.sup.18]O increases also correlate well with the Exxon Production Research sea-level records of Haq et al. and Vail et al., validating and refining their compilations., Eustatic (global sea level) changes exert one of the primary controls on the stratigraphic record[1, 2], although controversy surrounds the age, magnitude, and mechanism of these changes[3]. Vail et al.[4] [...]

Fission track analyses indicate that the Red Sea initially opened simultaneously along its entire length. Two distinct pulses of uplift and erosion characterized the early stages of rifting in the Red Sea throughout Egypt and in southwestern Saudi Arabia. The first pulse began at -34 million years ago (Ma). The second pulse began in the early Miocene (21 to 25 Ma) and marked the start of the main phase of extension. These data support a rigid plate model for continental extension. These results also indicate that the initiation of rift flank uplift, and therefore rifting, and volcanism occurred nearly simultaneously. This conflicts with classical models of active and passive extension that predict sequential development of these features., The Red Sea, with the Gulf of Aden, is the only young example of the splitting of a continent to create a new ocean basin. At present the mode of [...]

Geologists have long accepted that the Sierra Nevada, California, experienced significant late Cenozoic tectonically induced uplift. A flexural-isostatic model presented here shows, however, that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the Sierra Nevada and deposition in the adjacent Central Valley and therefore requires less tectonic forcing than previously believed. The sum of range-wide erosion and the resultant isostatic rock uplift would have lowered Sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production., For a century, geologists have thought that the Sierra Nevada (Sierra) crest (Fig. 1) has been uplifted about 2000 m by tectonic forces in the late Cenozoic (1-3) This uplift [...]

Paleomagnetic data from the Mid-Cretaceous Mountains suggest that Pacific plate motion during the Early to mid-Cretaceous was slow, less than 0.3 degree per year, resembling the polar standstill observed in [...]

Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. [...]

Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the western Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota., The southwestern Amazonian lowland is currently 100 to 200 m above sea level. The late Tertiary history of the area has been uncertain; a key area is the state of [...]

Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 ± 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de I'Androy in the south of the island marks the focal point of the Marion hot spot at ~88 million years ago and that this mantle plume was instrumental in causing continental breakup., Many of Earth's flood basalt provinces occur at the rifted margins of continents and can be linked to the initiation of oceanic hot spot tracks [1, 2]. Flood basalt provinces [...]

An element in the changing pattern of Australian archaeology has been the filling-in of great blanks on the archoeological map, once survey and excavation has begun to explore them. The [...]

Late Miocene (about 8.65 million years ago) mafic intrusions and lava flows along with remagnetized host rocks from Paiute Ridge, southern Nevada, provide a high-quality paleomagnetic record of a geomagnetic field reversal. These rocks yield thermoremanent magnetizations with declinations of 227° to 310° and inclinations of -7° to a reasonably continuous virtual geomagnetic pole path over west-central Pacific longitudes. Conductive cooling estimates for the intrusions suggest that this field transition, and mafic magmatism, lasted only a few hundred years. Because this record comes principally from intrusive rocks, rather than sediments or lavas, it is important in demonstrating the longitudinal confinement of the geomagnetic field during a reversal., The record of marine magnetic anomaties and terrestrial magnetostratigraphy demonstrates that geomagnetic field reversals have occurred frequently throughout geologic time. Detailed paleomagnetic records are needed to determine the behavior of [...]

The South Tibetan detachment system separates the high-grade metamorphic core of the Himalayan orogen from its weakly metamorphosed suprastructure. It is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front. Geochronologic data from the Rongbuk Valley, north of Qomolangma (Mount Everest) in southern Tibet, demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago, an interval characterized by large-scale crustal thickening at lower structural levels. These data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of Himalayan tectonics in Miocene time., Although the Himalayan orogen is the product of continent-continent collisional tectonics, the Late Miocene to Recent tectonic evolution of Tibet has been characterized by east-west extension [1-3]. This extension has [...]

The properties of microspherules recovered from an Upper Devonian marine limestone immediately overlain by a geochemical anomaly of siderophile and chalcophile elements are similar to those of impact-derived microtektites. These microspherules are glass, have splash-form shapes, contain spherical vesicles and lechatelierite inclusions, and show oxide compositional variations similar to those in known microtektites. These characteristics suggest that these Upper Devonian microspherules have an impact origin. A bolide impact may have occurred about 365 million years ago on the South China Plate and caused a faunal extinction on eastern Gondwana., Recognition of ancient bolide impacts and their influence on biota is important for understanding the evolution of Earth and its biosystem. Signatures of an impact in the pre-Cenozoic rock record [...]

Quartz grains that appear to have been shock-metamorphosed occur within three closely spaced shale beds from the uppermost Triassic ('Rhaetian') Calcare a Rhaetavicula in the Northern Apennines of Italy. The upper shale coincides with the abrupt termination of the distinctive, uppermost Triassic Rhaetavicula fauna and is overlain by the Hettangian (Lower Jurassic) Calcare Massiccio; no extinctions appear to be associated with the two lower layers, which occur 1.2 and 2.4 meters below the boundary shale. Approximately 5 to 10% of the quartz grains within these layers exhibit one or more sets of planar deformational features whose orientations cluster around the rational crystallographic planes (basal, ω, and π) most commonly observed in shocked quartz. Textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the Triassic., THE TRIASSIC-JURASSIC (T-J) boundary represents one of the five most severe marine extinctions in Phanerozoic history [1, 2] and is a time of important terrestrial extinctions [3-7]. Several groups of [...]

Recent research on fossil insect remains from Quaternary deposits (from 1.7 million years ago to recent times) has shed considerable light on the nature of glacial and interglacial environments and [...]

AT LEAST 11 DISTINCT EPISODES OF voluminous volcanism have produced flood basalt provinces covering more than 100,000 [km.sup.3] in the last 250 millions years [1-3]. The eruption of major flood [...]

THE DISCOVERY OF RELIC TEKTITES [1, 2] in K-T boundary rocks near Beloc, Haiti, has opened the door for geochemical studies needed for an understanding of K-T boundary phenomena, including [...]

STUDIES OF LATE PLIOCENE DEEP-SEA sediments [1-3] have shown that 2.3 million years ago an asteroid 0.5 km in diameter impacted the subantarctic South Pacific Ocean in the region 1400 [...]

Estimates of terrigenous fluxes at three different water depths at two sites in the equatorial Atlantic by normalization against excess [230] Th flux indicate that the flux of terrigenous material [...]

Sedimentary 24-n-Propylcholestanes, Molecular Fossils Diagnostic of Marine Algae A SERIES OF [C.sub.30]-STERANE EPIMERS containing 11 C atoms in the side chain has been empirically established as a widespread fossil marker [...]

The vibroseis reflection profiling component of the URSEIS '95 experiment provides a high-resolution crustal-scale image of the unextended southern Uralide orogen. A marked lateral and vertical variation of reflectivity throughout the entire crust differentiates the former margin of the East European craton to the west from accreted terranes to the east. Between these regions is a less reflective zone corresponding to the Magnitogorsk volcanic arc and the crustal root zone. Continuous reflections and reflective domains that correlate at the surface with major tectonic features define a bivergent orogen in which the Paleozoic collisional structure has been largely preserved., The southern Uralide orogen developed from collisional accretion of volcanic arc and microcontinental fragments along the continental margin of the East European craton during the Late Paleozoic (1). The vibroseis [...]

Cataclysmic flooding is a geomorphological process of planetary significance. Landforms of flood origin resulted from late Pleistocene ice-dammed lake failures in the Altay Mountains of south-central Siberia. Peak paleoflows, which [...]

Strontium and neodymium isotopic data for rocks from the voluminous 90-million-year-old Lamarck intrusive suite in the Sierra Nevada batholith, California, show little variation across a compositional range from gabbro to granite. Data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source. Recognition of local involvement of enriched mantle during generation of the Sierran batholith modifies estimates of crustal growth rates in the United States. These data indicate that parts of the Sierra Nevada batholith may consist almost entirely of juvenile crust added during Cretaceous magmatism., Present models for the origin of the Sierra Nevada batholith developed from the strontium isotope studies of Kistler and Peterman (1) and indicate that the isotope systematics of the batholith [...]

Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western United States are commonly interpreted to originate in the subcontinental mantle. In southere California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local disrepancies between tectonic and isotopic vies of the subcontinental mantle., ISOTOPIC VARIATIONS IN BASALTS CAN yield information about the geodynamic history of the mantle. For example, variations in the Sr and Nd isotopic compositions of basalts have been used to [...]

Exceptionally small spheres (nanospheres) of hematite (diameters between 120 and 200 nanometers) occur in the Marra Mamba Iron Formation of the Hamersley Basin, Australia. The nanospheres are clustered into small [...]

Holocene Mean Uplift Rates Across an Active Plate-Collision Boundary in Taiwan TECTONICALLY, TAIWAN IS OF GREAT interest because a major plate boundary, separating the Eurasian and Philippine tectonic plates, runs [...]

Mechanisms responsible for the initiation of major glaciation in the Northern Hemisphere at about 2.75 million years ago are poorly understood. A laminated terrestrial sequence from Pula maar, Hungary, containing about 320,000 years in annual layers between 3.05 and 2.60 million years ago, provides a detailed record of rates of climatic change across this dramatic transition. An analysis of the record implies that climatic variations at sub-Milankovitch frequencies (less than or equal to 15,000 years) were an important driving force during this transitional interval and that, as the threshold was approached, these increased in frequency and amplitude, possibly providing the final trigger for the amplification of Northern Hemisphere ice sheets., The late Pliocene was a time of major climatic cooling resulting in the growth of large terrestrial ice sheets and the onset of Northern Hemisphere glaciation (NHG) at ~2.75 million [...]

Glaciation in the humid tropical Andes is a sensitive indicator of mean annual temperature. Here, we present sedimentological data from lakes beyond the glacial limit in the tropical Andes indicating that deglaciation from the Last Glacial Maximum led substantial warming at high northern latitudes. Deglaciation from glacial maximum positions at Lake Titicaca, Peru/Bolivia (16°S), and Lake Junin, Peru (11°S), occurred 22,000 to 19,500 calendar years before the present, several thousand years before the Bolling-Allerod warming of the Northern Hemisphere and deglaciation of the Sierra Nevada, United States (36.5° to 38°N). The tropical Andes deglaciated while climatic conditions remained regionally wet, which reflects the dominant control of mean annual temperature on tropical glaciation., Maximum late-Pleistocene glaciation in the tropics was associated with an ~800- to 1000-m elevation lowering of glacier equilibrium-line altitudes in response to a 4° to 6°C reduction in mean annual [...]

Early Archean (3.3-Billion to 3.5-Billion-Year-Old) Microfossils from Warrawoona Group, Australia PUTATIVE CELLULARLY PRESERVEDmicrofossils have been reported from at least 28 Archean (>2.5-billion-year-old) geologic units (1-4). However, virtually all have recently [...]

Amphipithecus mogaungensis Colbert was first described 48 years ago (1). Depite the recovery of only one partial jaw of the type, there has been continued debate about whether Amphipithecus was [...]

Terminal Cretaceous Environmental Events Although there is general agreement that the end of Cretaceous time is marked by one of the most significant faunal and floral transitions in the Phanerozoic [...]

The mineralogy and fossil assemblages of lake beds currently provide the only tool for deciphering pre-Mid-Wisconsin paleoclimatic conditions in the Great Basin. Calcitic veins, which mark the sites of paleoground-water [...]

Recent Sedimentation on the New Jersey Slope and Rise The late Quaternary sediment cover on the slope and upper rise off New Jersey is uneven in thickness, disrupted stratigraphically, and [...]

Two papers critical of the impact theory of the Cretaceous-Tertiary (K/T) extinction (1, 2) have recently appeared in Science (3, 4). These two publications, when coupled with similarly oriented articles [...]

The discovery of an apparently worldwide iridium anomaly at the Cretaceous-Tertiary boundary (1,2) has led to a shift in emphasis from the biotic to the geochemical and geophysical aspects of [...]

The Cretaceous-Tertiary (K/T) boundary in the Raton Basin, as defined by fossil pollen, is in the lower part of the Raton Formation, which crops out over a large area in [...]