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Sedimentologic, stratigraphic, and structural data indicate that the Fountain Formation at Manitou Springs consists of three tectonostrarigraphic units, herein termed the lower, middle, and upper Fountain Formation. Both the lower and middle Fountain Formation were deposited in a fan-delta setting adjacent to the active ancestral Ute Pass fault. The lower is thin and predominantly characterized by deposirional stability as recorded by abundant well-developed, deeply rooted paleosols. The middle Fountain Formation reflects fan progradation and highland rejuvenation as a result of increased activity of the ancestral Ute Pass fault. This activity was likely the result of a basin-ward splay of the ancestral Ute Pass fault with reverse dip-slip motion as indicated by (1) exhumation of the lower Paleozoic Sawatch Formation and (2) fault-parallel folding. The upper Fountain Formation reflects deposition in a NW-SE-trending, braided-river system and appears to postdate movement on the ancestral Ute Pass fault. Lithostratigraphic correlation allows for a Latest Pennsylvanian-Early Permian age for the upper Fountain Formation, thus constraining cessation of the ancestral Ute Pass fault to Middle to Late Pennsylvanian time. The Fountain Formation was deposited within a NW-SE--oriented structural trough (i.e., Woodland Park trough) that separated the ancestral Front Range into a northern block (i.e., ancestral Front Range block) and a southern block (i.e., Ute Pass uplift). The Woodland Park trough was bounded on its southern margin by the ancestral Ute Pass fault, which was active throughout deposition of the lower two Fountain tectonostratigraphic units, during which time sediments were shed northward across the ancestral Ute Pass fault into a marine environment. By the rime of deposition of the upper Fountain Formation, movement on the ancestral Ute Pass fault had ceased or dramatically decreased. During this time, the Fountain Formation records predominantly axially oriented, braided-stream deposition. Comparison of the timing and kinematic history of the ancestral Ute Pass fault with other documented reverse and strike-slip faults of the ancestral Rocky Mountains suggests that: (1) cessation of faulting within the ancestral Rocky Mountains displays a slight east-to-west younging, but the crude age resolution of adjacent basin fill also allows for the possibility of relatively synchronous cessation of faulting, and (2) kinematics of all faults examined are consistent with a NE-SW--oriented maximum horizontal compressional stress field. These inferences contrast with the proposed Laurentian-Gondwanan diachronons closure models for the ancestral Rocky Mountains, which require rotation of the maximum horizontal stress orientation through time and pronounced east-to-west younging of faulting. Rotation of the horizontal stress field may be recorded in multistage, kinematic histories of faults, but multiple faults require study to assess this model. Age constraints on post-tectonic units of the ancestral Rocky Mountains, such as the upper Fountain Formation tectonostratigraphic unit defined herein, are poor and further refinement would greatly aid understanding of the kinematic riming and tectonic driving force of these ancient mountains. doi: 10.1130/B26554.1

Ocean-plate stratigraphy (basalt, chert, clastics) of the Balcreuchan Group in the Ballantrae complex is repeated by layer-parallel thrusts to form duplex structures south of Bennane Head, ~5 km north of Ballantrae. Five tuff beds, all in chert, have similar U-Pb zircon ages of ca. 470 [+ or -] 10 Ma. The geometrical polarity of the duplexes and the zircon ages provide new constraints on the tectonic evolution of the accretionary wedge of the Ballantrae complex. Northwestward thrusting of the duplexes suggests that subduction was from the northwest to the southeast, and this polarity at the leading edge of the main ophiolite body is consistent with the northward younging of the volcanic arc rocks of the Ballantrae complex. doi: 10.1130/B26329.1

A long-standing hypothesis links the increased prominence of meandering rivers in the middle Paleozoic to the colonization of terrestrial environments by vegetation. This hypothesis is tested using a data set of Cambrian to Devonian fluvial literature and field examination of key stratigraphic units. According to some researchers, Cambrian to mid-Silurian river systems were braided in planform, with a sharp increase in the abundance of meandering rivers during the Silurian--Devonian. Although meandering systems were largely identified on the basis of thick mudstones and organized channel deposits, the data set record of lateral accretion sets appears to be a robust proxy for the abundance of meandering river point bars. Lateral accretion is first recorded from Pridolian--Lochkovian strata, but is noted in nearly 40% of fluvial case studies by the Famennian. This trend matches the known record of rooted vegetation, suggesting that vegetation progressively stabilized river banks and promoted single-thread channels. However, the presence of Precambrian and extraterrestrial meandering systems indicates that vegetation is not essential for meandering, and the lack of evidence for Cambrian to Silurian (Ludlow) point bars is surprising. If originally present, they may largely have been destroyed by extreme floods, chute cut-offs in coarse-grained meandering systems, and eolian activity. doi: 10.1130/G30443

The collision between the Eurasian and Arabian plates along the 2400-km-long Bitlis-Zagros thrust zone isolated the Mediterranean from the Indian Ocean and has been linked to extension of the Aegean, rifting of the Red Sea, and the formation of the North and East Anatolian fault systems. However, the timing of the collision is poorly constrained, and estimates range from Late Cretaceous to late Miocene. Here, we report the first apatite fission-track (AFT) ages from the Bitlis-Zagros thrust zone. The AFT samples are distributed over the 450 km length of the Bitlis thrust zone in southeast Turkey and include metamorphic rocks and Eocene sandstones. Despite the disparate lithology and large distance, the AFT ages point consistently to exhumation between 18 and 13 Ma. The AFT ages, along with a critical appraisal of regional stratigraphy, indicate that the last oceanic lithosphere between the Arabian and Eurasian plates was consumed by the early Miocene (ca. 20 Ma). The results imply that Aegean extension predated the Arabia-Eurasia collision. doi: 10.1130/G30234.1

The late Wenlock Series (Homerian Stage) of the northern Midland Platform (central England) comprises silty mudstones and limestones of the upper part of the Coalbrookdale and overlying Much Wenlock Limestone formations. Based on outcrop studies and borehole data, the sequence stratigraphical interpretation developed for the inliers of the West Midlands is slightly revised, and extended to the stratotype sections along Wenlock Edge. A single third-order cycle of sea-level change is identified, punctuated by a regressive--transgressive episode associated with a higher-order glacioeustatic cycle, allowing the upper Wenlock Series of the area to be divided into two subsequences (A and B). Subsequence A and the early transgressive systems tract began with regression associated with the basal sequence boundary in late Cyrtograptus lundgreni Biozone times. This was followed by a period of slow transgression or stillstand, allowing shallower water carbonate environments to prograde. A minor phase of regression followed, resulting in the generation of the shallowest water deposits of both the Lower Quarried Limestone and Farley members (of the Much Wenlock Limestone and Coalbrookdale formations, respectively). The overlying Subsequence B and the late transgressive systems tract are marked by transgression and a period of rapid sea-level fluctuation and are likely contained within the Gothograptus nassa Biozone. A minor highstand is widely recognizable at this time. The rest of Subsequence B consists of an initial phase of weak progradation (highstand systems tract), followed by a marked regression (falling stage systems tract) culminating in an erosive upper sequence boundary at or close to the top of the Monograptus ludensis Biozone, but within the uppermost Much Wenlock Limestone Formation. Above Subsequence B is a marked transgression into the Lower Elton Formation and the Ludlow Series. Both late Wenlock lowstands and the succeeding flooding events have been recognized on other palaeocontinents, reflecting the eustatic nature of sea-level changes reported here. Keywords: Much Wenlock Limestone Formation, sequence stratigraphy, Silurian, Wenlock Series. doi: 10.1017/S0016756809990197

ABSTRACT Regional mapping and petrological studies have led to revision of the Cambrian-Ordovician stratigraphy in southwestern Nova Scotia. The Goldenville and Halifax formations have been elevated to groups, and formations [...]

The network of prior streams and palaeochannels common across the Riverine Plains of the Murray--Darling Basin act as conduits for the redistribution of water and soluble salts beneath the root-zone. To improve scientific understanding of these hydrological processes there is the need to better represent and map the connectivity and spatial extent of these physiographic and stratigraphic features. Groundbased electromagnetic (EM) instruments, which measure bulk soil electrical conductivity ([σ.sub.a]), have been used widely to map their areal distribution across the landscape. However, methods to resolve their location with depth have rarely been attempted. In this paper we employ a 1-D inversion algorithm with 2-D smoothness constraints to predict the true electrical conductivity (σ) at discrete depth increments using EM data. The EM data we use include the root-zone measuring EM38 and the deeper sensing EM34. We collected EM38 data in the vertical (EM38v) and horizontal (EM38h) dipole modes and EM34 data in the horizontal mode and coil spacing of 10, 20, and 40 m (respectively, EM34-10, EM34-20, and EM34-40). In order to compare and contrast the value of the various EM data we carried out multiple inversions using different combinations, which include: independent inversions of (i) EM38 (root-zone) and (ii) EM34 data (vadose-zone), and in combination using (iii) EM38v, EM38h, and EM34-10 (near-surface), and (iv) all 5 EM datasets (regolith) available. The general patterns of σ are shown to compare favourably with the known pedoderms, physiographic, and stratigraphic features and soil particle size fractions collected from calibration cores drilled across the lower Macquarie Valley study area. In general we find that the EM38 assists in resolving root-zone variability, specifically duplex soil profiles and physiographic features such as prior streams, while the use of the EM34 assists in resolving the stratigraphic nature of the vadose-zone and specifically the likely location of palaeochannels and subsurface anomalies that may indicate the location of good quality groundwater and/or clay aquitards. In this case, our potential to use σ to predict clay content is limited by the non-linearity of the cumulative functions. In order to improve on the non-linearity of our inversion we need to develop a full solution of the forward problem. Additional keywords: EM38, EM34, clay content, prior stream channel, palaeochannel, EM inversion., Introduction Across the Murray Darling Basin salt has accumulated naturally (primary salinity) in the regolith via cyclical deposits, aeolian processes, and connate stores. The redistribution of primary salts is attributed [...]

A 1284.87-m-long sediment core (AND-1B) from beneath the McMurdo sector of the Ross Ice Shelf provides the most complete single section record to date of fluctuations of the Antarctic Ice Sheets over the last 13 Ma. The core contains a succession of subglacial, glacimarine, and marine sediments that comprise ~58 depositional sequences of orbitalscale duration. These cycles are constrained by a chronology based on biostratigraphic, magnetostratigraphic, and [sup.40]Ar/[sup.39]Ar isotopic ages. Each sequence represents a record of a grounded ice-sheet advance and retreat cycle over the AND-1B drill site, and all sediments represent subglacial or marine deposystems with no subaerial exposure surfaces or terrestrial deposits. On the basis of characteristic facies within these sequences, and through comparison with sedimentation in modern glacial environments from various climatic and glacial settings, we identify three facies associations or sequence 'motifs' that are linked to major changes in ice-sheet volume, glacial thermal regime, and climate. Motif 1 is documented in the late Pleistocene and in the late Middle Miocene intervals of AND-1B, and it is dominated by diamictite of subglacial origin overlain by thin mudstones interpreted as ice-shelf deposits. Motif 1 sequences lack evidence of subglacial melt-water and represent glaciation under cold, 'polar'-type conditions. Motif 2 sequences were deposited during the Pliocene and early Pleistocene section of AND-1B and are characterized by subglacial diamictite overlain by a relatively thin proglacial-marine succession of mudstone-rich facies deposited during glacial retreat. Glacial minima are represented by diatom-bearing mudstone, and diatomite. Motif 2 represents glacial retreat and advance under a 'subpolar' to 'polar' style of glaciation that was warmer than present, but that had limited amounts of subglacial meltwater. Motif 3 consists of subglacial diamictite that grades upward into a 5- to 10-m-thick proglacial retreat succession of stratified diamictite, graded conglomerate and sandstone, graded sandstone, and/or rhythmically stratified mudstone. Thick mudstone intervals, rather than diatomite-dominated deposition during glacial minima, suggest increased input of meltwater from nearby terrestrial sources during glacial minima. Motif 3 represents Late Miocene 'subpolar'-style glaciation with significant volumes of glacially derived meltwater.

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 [...]

Our understanding of the geologic evolution of the Himalaya remains incomplete, particularly in regard to structural and geochronologic details of the Proterozoic-Paleozoic Lesser Himalayan Sequence. We conducted an integrated field mapping, geochronological study, and geochemical analysis of the Lesser Himalayan Sequence strata in the Kumaun and Garwhai Himalaya of NW India (78[degrees]00'-80[degrees]30'E). Structural observations reveal a systematic change in deformation styles from lower to higher structural levels in the Main Central Thrust footwall. In the south, and at lower structural levels, the Main Central Thrust footwall is characterized by parallel folding and sparse development of axial cleavage. Quartz microstructures indicate that deformation occurred at temperatures below 350[degrees]C. In contrast, in the north and at higher structural levels close to the Main Central Thrust, deformation is characterized by replacement of original bedding, the development of penetrative cleavage, and schistosity locally. Folds are tight, in places isoclinal and overturned. The corresponding quartz microstructures indicate that deformation occurred above 350[degrees]C. Dating of detrital zircons from Lesser Himalayan Sequence metasedimentary units, and igneous zircons from schistose gneisses throughout the Lesser Himalayan Sequence allow refinements to the stratigraphic framework. First, unlike what has been observed in western Nepal immediately west of our study area, U-Pb zircon dating suggests the absence of Paleoproterozoic strata in the Ramgarh Thrust hanging wall. This suggests that the thrust cuts upsection laterally along strike. Second, U-Pb detrital zircon dating suggests that metasedimentary strata in the Ramgarh Thrust hanging wall are correlative with basal units of the Outer Lesser Himalayan Sequence, removing the necessity that the Ramgarh Thrust hanging wall was allochthonous with respect to its footwall Lesser Himalayan Sequence units. Schistose gneisses with U-Pb ages of ca. 1850 Ma are older than Lesser Himalayan Sequence units in the area, suggesting that they are Lesser Himalayan Sequence basement. We conclude that the Ramgarh Thrust is an out-of-sequence thrust postdating a folding event in its footwall. The earlier proposal that Neoproterozoic-Cambrian Lesser Himalayan Sequence strata are the southern extension of the Tethyan Himalayan Sequence requires that the Tons Thrust, which separates the distal and proximal facies of the Lesser Himalayan Sequence, be a major, south-directed structure with a slip magnitude of >50-100 km.

A detailed study of the geochemical and isotopic characteristics of the volcanic rocks of the Hidden and Louis formations, which make up the hanging wall to the volcanogenic massive sulphide deposits at Flin Flon, Manitoba, was carried out on a stratigraphically controlled set of samples. The stratigraphy consists of the lowermost, dominantly basaltic, Hidden formation, and the overlying, dominantly basaltic, Louis formation. Of importance petrogenetically, is the 1920 unit a basaltic andesite with Nb/[Th.sub.mn] = 0.54-0.62, ζ[Nd.sub.(1.9Ga)] = +3.6-+5.9, ζ[Hf.sub.(1.9Ga)] = +8.5-+9.6, and [sup.204]Pb/[sup.206]Pb = 23.9. The basaltic flows that dominate the Hidden formation have Nb/[Th.sub.mn] = 0.16-0.29, ζ[Nd.sub.(1.9Ga)] = +1.7-+4.4, ζ[Hf.sub.(1.9Ga)] = +7.0-+11.8 and [sup.204]Pb/[sup.206]Pb = 16.9-18.6). The Carlisle Lake basaltic-andesite (top of Hidden formation) is characterized by Nb/[Th.sub.mn] = 0.16-0.14, and [sup.204]Pb/[sup.206]Pb = 21.4. The rhyodacitic Tower member (bottom of Louis formation) has Nb/[Th.sub.mn] = 0.23, ζ[Nd.sub.1.9Ga] = +4.6, ζ[Hf.sub.1.9Ga] = +9.3, and [sup.204]Pb/[sup.206]Pb = 22.2. The basaltic flows that dominate the Louis formation have Nb/[Th.sub.mn] = 0.18-0.25, ζ[Nd.sub.(1.9Ga)] = +3.6-+4.2, ζ[Hf.sub.(1.9Ga)] = +8.4-+11.3 and [sup.204]Pb/[sup.206]Pb = 17.9. The Hidden and Louis formations show dominantly transitional arc tholeiite signatures, with the 1920 unit having arc tholeiite characteristics. It is interpreted to have formed through extensive fractional crystallization of differentiated magmas at shallow levels in oceanic crust. Given the geological, geochemical, and isotopic characteristics of the Hidden and Louis formations, they are interpreted to represent subducted slab metasomatism with minor contamination from subducted sediments. Une etude detaillee des caracteristiques geochimiques et isotopiques des roches volcaniques des formations de Hidden et de Louis, lesquelles forment l'eponte superieure des gisements de sulfures volcanogenes massifs a Flin Flon, Manitoba, a ete effectuee sur un ensemble d'echantillons controles par la stratigraphie. La stratigraphie comprend, tout a la base, la formation de Hidden, principalement basaltique et la formation de Louis sus-jacente, principalement basaltique. L'unite 1920, une andesite basaltique, est importante d'un point de vue petrogenetique; elle possede les valeurs suivantes : Nb/[Th.sub.mn] = 0.,54-0,62, ζ[Nd.sub.(1.9Ga)] = +3,6 a +5,9, ζ[Hf.sub.(1.9Ga)] = +8,5 a +9,6, et [sup.204]Pb/[sup.206]Pb = 23.9. Les coulees basaltiques qui dominent la formation de Hidden ont les valeurs suivantes : Nb/[Th.sub.mn] = 0,16-0.29, ζ[Nd.sub.(1.9Ga)] = +1,7 a +4,4, ζ[Hf.sub.(1.9Ga)] = +7,0 a +11,8 et [sup.204]Pb/[sup.206]Pb = 16,9-18,6). L'andesite basaltique Carlisle Lake (sommet de la formation de Hidden) est caracterisee par Nb/[Th.sub.mn] = 0,16-0,14 et [sup.204]Pb/[sup.206]Pb = 21,4. Le membre Tower (bas de la formation de Louis) a les valeurs suivantes : Nb/[Th.sub.mn] = 0,23, ζ[Nd.sub.1.9Ga] = +4,6, ζ[Hf.sub.1.9Ga] = +9,3 et [sup.204]Pb/[sup.206]Pb = 22,2. Les coulees basaltiques qui dominent la formation de Louis ont les valeurs suivantes : Nb/[Th.sub.mn] = 0,18-0,25, ζ[Nd.sub.(1.9Ga)] = +3,6 a +4,2, ζ[Hf.sub.(1.9Ga)] = +8,4 a +11,3 et [sup.204]Pb/[sup.206]Pb = 17,9. Les formations de Hidden et de Louis presentent des signatures surtout d'arc tholeiitique de transition ou l'unite 1920 a des caracteristiques d'arc tholeiitique. Cette unite se serait formee par la cristallisation fractionnee a grande echelle de magmas differencies a de niveaux de faible profondeur dans la croute oceanique. E tant donne les caracte ristiques geologiques, geochimiques et isotopiques des formations de Hidden et de Louis, elles representeraient un metasomatisme de plaque subductee avec une contamination minime par les sediments subductes. [Traduit par la Redaction], Introduction Volcanogenic massive sulphide (VMS) deposits occur in extensional environments within a variety of tectonic settings, including oceanic, fore-arc, arc, back-arc, continental-margin, or continental settings (Franklin et al. 1981, 2005; [...]

The Lower Ordovician St. George Group of western Newfoundland consists mainly of shallow-marine-platform carbonates (~500 m thick). It is formed, from bottom to top, of the Watts Bight, Boat Harbour, Catoche, and Aguathuna formations. The top boundary of the group is marked by the regional St. George Unconformity. Outcrops and a few cores from western Newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation. The δ[sup.13]C and δ[sup.18]O values of well-preserved micrite microsamples range from -4.2‰ to 0‰ (VPDB) and from -11.3‰ to -2.9‰ (VPDB), respectively. The δ[sup.13][C.sub.carb] profile of the St. George Group carbonates reveals several negative shifts, which vary between ~2‰ and 3‰ and are generally associated with unconformities-disconformities or thin shale interbeds, thus reflecting the effect of or link with significant sea-level changes. The St. George Unconformity is associated with a negative δ[sup.13][C.sub.carb] shift (~2‰) on the profile and correlated with major lowstand (around the end of Arenig) on the local sea-level reconstruction and also on those from the Baltic region and central Australia, thus suggesting that the St. George Group Unconformity might have likely had an eustatic component that contributed to the development-enhancement of the paleomargin. Other similar δ[sup.13][C.sub.carb] shifts have been recorded on the St. George profile, but it is hard to evaluate their global extension due to the low resolution of the documented global Lower Ordovician (Tremadoc--middle Arenig) δ[sup.13][C.sub.carb] profile. Le Groupe de St. George (Ordovicien inferieur) de fouest de Terre-Neuve comprend surtout des carbonates de plate-forme marine peu profonde (epaisseur ~500 m). De la base au sommet, il comprend les formations suivantes : Watts Bight, Boat Harbour, Catoche et Aguathuna. La limite superieure du groupe est marquee par la discordance regionale de St. George. Des affleurements et quelques carottes provenant de l'ouest de Terre-Neuve ont ete echantillonnes a haute resolution et les roches micritiques extractes ont ete etudiees pour leurs criteres petrographiques et geochimiques afin d'evaluer leur degre de preservation. Les valeurs δ[sup.13]C et δ[sup.18]O de micro-echantillons de micrites bien preservees variaient respectivement entre -4,2 [por millar] a 0 [por millar] << VPDB >> et entre -11,3 [por millar] a -2,9 [por millar] (VPDB). Le profil δ[sup.13][C.sub.carb] des carbonates du Groupe de St. George montre plusieurs changements a des valeurs negatives; ces changements varient entre ~2 [por millar] a 3 [por millar] et ils sont generalement associes a des discordances ou a de minces interlits de shale, refletant ainsi l'effet des changements importants de niveau de la mer ou ayant un lien avec ces changements. La discordance de St. George est associee a un changement negatif δ[sup.13][C.sub.carb] (~2 [por millar]) du profil et elle est correlee a un important bas niveau dans une reconstruction locale du niveau de la mer (vers la fin de l'Arenigien) ainsi qu'a des bas niveaux dans des regions de la Baltique et du centre de l'Australie, portant ainsi a croire que la discordance du Groupe de St. George avait une composante eustatique qui a contribue au developpement--rehaussement de la paleobordure. [Traduit par la Redaction], Introduction The stable isotope signatures encrypted in preserved marine carbonates have been successfully utilized to understand the evolution of the Earth's system and correlation of sedimentary sequences from different depositional [...]

Gold Run tephra has been found at Thistle Creek, Sixtymile River, and the Klondike goldfields of west-central Yukon, Canada. It is a hornblende-bearing rhyolitic tephra with thicknesses of up to 10 cm at each site, suggesting a widespread distribution across interior Alaska and the Yukon Territory, given the long distance to the nearest volcanic centre. Old Crow, Flat Creek, and TA tephra beds are stratigraphically associated with Gold Run tephra at our study sites and have distinctive compositions. Gold Run tephra is not accommodated by the current classification scheme for late Cenozoic distal tephra beds in Alaska and the Yukon Territory--a scheme based on the physical and chemical attributes so that its provenance is unknown. An early-Middle Pleistocene age is supported by a glass fission-track age of 0.74 ± 0.06 Ma, a normal remanent magnetic polarity for the enclosing loess, and the presence of a late Irvingtonian faunal assemblage in the associated organic-rich silts at Thistle Creek. Hence, Gold Run tephra was deposited during the very early part of the Brunhes Chron, at which time a shrub tundra environment prevailed across west-central Yukon. Le tephra Gold Run a ete trouve a Thistle Creek, a la riviere Sixtymile et dans les champs auriferes du Klondike du centre-ouest du Yukon, Canada. Il s'agit d'un tephra rhyolitique a hornblende et les epaisseurs atteignant 10 cm a chaque site suggerent une vaste distribution a travers f interieur de f Alaska et du Territoire du Yukon en raison de la grande distance au centre volcanique le plus pres. Les lits de tephra Old Crow, Flat Creek et TA sont stratigraphiquement associes au tephra Gold Run de nos sites d'etude et ils ont des compositions propres. Le tephra Gold Run n'a pas sa place dans le systeme de classification actuel des lits de tephra distaux du Cenozoique tardif en Alaska et dans le Territoire du Yukon--une classification basee sur les caracteristiques physiques et chimiques; sa provenance est done inconnue. Un age Pleistocene moyen-precoce de 0,74 ± 0,06 Ma est soutenu par un age obtenu par traces de fission sur du verre, une polarity magnetique remanente normale pour le loess encaissant et la presence d'un assemblage faunique datant de flrvingtonien tardif dans les silts riches en matieres organiques qui sont associes a Thistle Creek. Le tephra Gold Run a done ete depose durant la toute premiere partie du Chron de Brunhes alors qu'un environnement de toundra arbustive prevalait a travers le centre-ouest du Yukon. [Traduit par la Redaction], Introduction Numerous, thin distal tephra beds are preserved in late Cenozoic sediments across Alaska and Yukon Territory, with the source volcanoes located in the Aleutian arc--Alaska Peninsula and Wrangell volcanic [...]

Carbon-isotope stratigraphy is a useful tool for stratigraphic correlation, especially for strata deposited during major perturbations of the carbon cycle that affected the marine, terrestrial and atmospheric reservoirs. For the Triassic--Jurassic boundary, effectively defined by a first-order mass extinction, major fluctuations in carbon-isotope values have been well documented, but these datasets have generally been derived from bulk-rock samples. Hence, the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained. Here, carbon- and oxygen-isotope data are presented from well-preserved oyster shells (Liostrea) comprising low-magnesium calcite, a mineral species relatively resistant to diagenetic alteration. Samples were obtained from Lavernock Point, Glamorgan, Wales, a coastal section close to a candidate stratotype for the base of the Jurassic at St Audrie's Bay, Somerset, England. The carbon-isotope signature from St Audrie's Bay, previously defined on the basis of analysis of bulk organic matter, is confirmed by our new data. Major features are (1) the upper part of an 'initial' negative isotope excursion in the lowest part of the section, followed by (2) a pronounced positive excursion, and (3) an extended 'main' negative isotope excursion in the highest part of the section. The data confirm that the carbon-isotope stratigraphy previously documented from bulk organic matter in SW England records the chemical composition of the contemporaneous seawater. Bulk carbonates sampled over the same interval near Lyme Regis, England, show similar trends to those from oyster calcite in the lower part of the study section, but there are more [sup.13]C-depleted values up-section. These lower values probably result from an admixture of primary and diagenetic carbonate. Palaeotemperatures calculated from oxygen-isotope values from Lavemock Point oyster shells are relatively cool at the beginning of the positive carbon-isotope excursion, and increased by up to 10[degrees]C during the main negative carbon-isotope excursion. The new results are compatible with the view that positive carbon-isotope excursions correspond to times of low atmospheric carbon dioxide content, whereas negative carbon-isotope excursions correspond to times of high atmospheric carbon dioxide content, as is also found to be the case during the Early Jurassic (Toarcian) Oceanic Anoxic Event. The Mg/Ca and Sr/Ca ratios and [delta][sup.18]O of investigated Liostrea hisingeri show no correlation, supporting data from modern bivalves that indicate that incorporation of Mg and Sr is controlled mainly by factors other than temperature.

Adetailed study of the middle--late Cenomanian Belle Fourche Formation in southern Alberta helps to elucidate the evolution of the Cordilleran foreland basin during the middle Cretaceous. By combining isopach data from the study area with previously published research on middle Cretaceous stratigraphy in adjacent areas of northern Alberta and Montana, it is possible to define the position of the proximal foredeep, forebulge, and backbulge depozones from late Albian to Cenomanian time. The foredeep probably lay to the west of the present fold-thrust belt in western Montana from the late Albian to middle Cenomanian, with the forebulge extending northwestward through the northwest corner of Wyoming and curving northeastward through the present-day location of Calgary. Thick Dunvegan deposits (middle Cenomanian) of northwestern Alberta are interpreted as foredeep deposits. Palinspastic reconstruction of the southern Rocky Mountains of Alberta is consistent with a location of the foredeep within the area of the present fold-thrust belt. At the end of the middle Cenomanian the forebulge retreated westward within Alberta, defining a nearly straight northwest-southeast trend through the present position of the Foothills and Front Ranges of Alberta and northwestern Montana. The change in trend of the foreland basin at the end of the middle Cenomanian may reflect the change of convergence vectors along the western margin of North America during the middle Cretaceous. Keywords: Cordilleran tectonics, foreland basin, middle Cretaceous, Alberta, Montana.

The depositional age and stratigraphic correlations of metamorphosed and variably deformed rocks of Mount Everest are poorly known because of limited recovery of diagnostic fossils. Detailed study of Cambrian and Ordovician strata from along the length of the Himalaya has produced a coherent stratigraphy that stretches from northern India to Tibet. Our work also demonstrates that the North Col Formation rocks (= Everest series), between the Qomolangma and Lhotse detachments of the South Tibetan detachment system, still locally preserve sedimentary textures and primary stratigraphy that match those within Cambrian strata ~1100 km to the west in northern India. This demonstrates a coherency of depositional systems and stratigraphic architecture for Cambrian deposits along much of the Himalaya Tethyan margin. It also allows, for the first time, identification of precise depositional ages of several units in the Everest region, in particular, the Yellow Band carbonate and directly underlying siliciclastic strata, which are both shown to be late Middle Cambrian in age. Detrital zircon data presented herein for a sample from these siliciclastic strata contain a similar age spectrum to those from Middle Cambrian strata in northern India, as well as grains as young as ca. 526 Ma, both of which support the depositional age and continuity of depositional systems along the length of the Himalaya. Highly fractured rocks of the Ordovician lower Chiatsun Group in the hanging wall of the South Tibetan detachment system in Nyalam, 75 km to the west of Everest, correlate with Ordovician strata of the Mount Qomolangma Formation on Mount Everest. Our correlations indicate that the base of the summit pyramid of Everest, the foot of the 'Third Step,' is composed of a 60-m-thick, white-weathering thrombolite bed. The top of this ancient microbial deposit crops out only 70 m below the summit of Mount Everest. Keywords: India, Himalaya, Parahio Formation, Cambrian, Tethyan, Everest.

The origin of gullies on Mars is controversial (e.g., catastrophic groundwater release, debris flows, dry granular flows, or meltwater from surface ice and snow) and their ages are difficult to determine due to their small size. We describe a gully depositional fan that contains a unique chronostratigraphic marker (secondary crater clusters) between episodes of gully activity during fan development. This marker can be traced to its source, a 7-km-diameter rayed crater that we have dated as ca. 1.25 Ma. This age links gully activity to the emplacement of dust-ice mantling deposits interpreted to represent recent ice ages on Mars. This association, together with multiple episodes of depositional fan formation, favors an origin for these gullies from top-down melting of snow and ice during multiple favorable spin-axis and orbital variations. This melting mechanism is consistent with the occurrence of gullies in unique steep-sloped, poleward-facing insolation microenvironments that favor the melting of small amounts of surficial snow and ice.

A unique isochronous interval in the Karoo Basin, South Africa, previously has been interpreted to postdate vertebrate extinction at the Permian-Triassic boundary in the Bethulie area, Lootsberg Pass, and elsewhere. It is demonstrated that the laminated beds, or laminites, in the Bethulie region are stratigraphically indistinct. The heterolithic interval exposed on the Heldenmoed farm is ~8 m below the Bethel farm section,

New chitinozoan data are presented from the classical section along the Onny River in the type Caradoc area, and from the deeper-water sections in the Shelve area, including the former British candidate GSSP for the base of the Upper Ordovician Series. The rich and well-preserved chitinozoan fauna of the Onny River has been a standard for 40 years, but new data revise some of the identifications. The assemblages are now attributed to biozones that are more readily applicable for international correlation. The main part of the section can be interpreted as belonging to the originally Baltoscandian Spinachitina cervicornis Biozone, although this is uncertain in the lower part. Within this biozone, the Fungochitina actonica Subzone has been defined. The Onny Formation at the top of the section is equated with the Acanthochitina latebrosa-Ancyrochitina onniensis Biozone; contrary to earlier reports, Acanthochitina barbata is absent. The Lower Wood Brook and Spy Wood Brook section from the Shelve Inlier yielded a great number of moderately to well-preserved chitinozoans, but a low-diversity assemblage. Their ranges have been neatly positioned against the well-known graptolite stratigraphy in the area. A local Eisenackitina rhenana Biozone? has been recognized, allowing us to suggest some international correlations. Keywords: chitinozoans, biostratigraphy, Caradoc, Welsh Borderland, type section.

We report here the discovery of a new end-Cryogenian glacial diamictite and an overlying basal Ediacaran cap carbonate within the Tsagaan Oloom Formation of southwestern Mongolia. The identification of the Cryogenian-Ediacaran boundary, coupled with new [delta].sup.13]C chemostratigraphic profiles, facilitates the integration of the Neoproterozoic stratigraphy of Mongolia with records elsewhere. These correlations indicate that a previously unrecognized, -16%[?] Cryogenian [[delta][.sup.13]C] anomaly is present in the newly defined Tayshir member (informal) of the Tsagaan Oloom Formation. Furthermore, chemostratigraphic and lithostratigraphic relationships suggest an ~35 m.y. depositional hiatus below the phosphorite-bearing Zunne Arts member (informal) of the upper Tsagaan Oloom Formation and that subsidence renewed in the latest Ediacaran-Early Cambrian. We propose that the lower ~1500 m of the Tsagaan Oloom Formation was deposited on a thermally subsiding passive margin after Rodiniaage rifting, whereas the Zunne Arts member and the overlying ~1600 m of Early Cambrian strata were deposited in a foredeep basin that formed as the southern margin of the Dzabkhan terrane was subducted beneath the Khantayshir-Dariv arc.

Geophysical instruments show great potential for the detailed quantification of soil stratigraphy. In this study, two electromagnetic induction sensors were evaluated on their capacity to map small-scale variations of the depth to the interface ([z.sub.in]) in a two-layered soil. On a 2-ha study site, [z.sub.in] between the silty topsoil and the contrasting clayey subsoil was modeled first by relating the two apparent electrical conductivity ([EC.sub.a]) measurements of the EM38DD sensor to observations of [z.sub.in] obtained by augering. A substantial number of these calibration observations was needed, however, to account for the modeling parameters. To avoid this step, an entirely noninvasive procedure was proposed based on one survey with the DUALEM-21S sensor. This sensor simultaneously records four [EC.sub.a] values with different coil configurations. These measurements correspond to four different depth response functions that allow modeling [z.sub.in] without calibration observations. The only assumption was a two-layered soil profile. The [z.sub.in] predictions were validated with 24 independent depth observations. Both procedures resulted in equal correlation coefficients (0.85) between predicted and measured [z.sub.in] and average estimation errors (0.26 m). This indicated that both sensors allowed the accurate mapping of the depth to a contrasting textural layer. With the EM38DD, calibration observations are needed, whereas the four different coil conurations of the DUALEM-21S sensor provided sufficient information to predict the interface depth without angering. Abbreviations: DOE, depth of exploration; [EC.sub.a], apparent electrical conductivity; EMI, electromagnetic induction; RMSEE, root mean squared estimation error.

New magnetostratigraphic data from seven Western Ghats sections in the Deccan Volcanic Province are presented. These are combined with an established geochemically defined stratigraphy, and volcanological logs, to provide a correlated, chronological eruptive framework. We identify two magnetic polarities in five of the sections, and these are assigned to chrons 29r and 29n. Importantly, the reversal boundary represents an identifiable isochronous surface within the volcanic pile. This surface occurs at different elevations, as does the altitude of the geochemically defined formation boundary (i.e. Ambenali-Mahabaleshwar Fms), which defines a second isochronous surface. Inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces. This indicates that there was significant local topography (c. 80 m) across Deccan Volcanic Province lava fields during their development; an interpretation consistent with topographies observed across modern and historical examples (e.g. Hawaii, Iceland). These data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub-regional detail in lava stacking patterns when applied at smaller spatial scales (

The paleoceanographic history of the Pacific Ocean during the mid-Cretaceous is poorly constrained due to the loss of much of the contemporaneous Pacific seafloor to subduction and difficulties in recovering chert-rich sediments by ocean drilling. Pelagic sediments that were originally deposited in the Pacific Ocean but that have been subsequently accreted during subduction potentially provide an alternative paleoceanographic archive. This study presents micropaleontological and carbon-isotope data from the Calera Limestone, part of the classic Franciscan Complex exposed in Permanente Quarry, central California, USA. In the three stratigraphic sections studied, pelagic limestones with low organic-carbon contents are the dominant lithology. However, two stratigraphic intervals are recognized that contain organic carbon, and these date to the early Aptian and late Albian--early Cenomanian. These time intervals correspond to two mid-Cretaceous oceanic anoxic events (OAEs): early Aptian OAE1a (equivalent to the 'Selli level') and late Albian OAE1d (equivalent to the 'Breistroffer event'). It is well established that both of these events were associated with significant carbon-isotope excursions, which are also shown to exist in the Calera Limestone. The record of OAE1a from the Calera Limestone complements ocean drilling records by providing further evidence for variability in the sedimentary and stratigraphic record of this event. The carbon-isotope data from the late Albian--early Cenomanian provide the first detailed chemobiostratigraphic record of this period for the Pacific Ocean, confirming that environmental change occurred at this time in the Pacific, possibly related to OAE1d. Keywords: Cretaceous, oceanic anoxic events, carbon isotopes, Calera Limestone, paleoceanography.

Extreme spatial heterogeneity has emerged as a salient characteristic of groundwater arsenic in many complex fluviodeltaic environments. Here we examine patterns of arsenic heterogeneity in the shallow ( Keywords: arsenic, groundwater, Bangladesh, floodplain, stratigraphy.

We combine surface structural measurements, subsurface seismic imaging, and magnetostratigraphic dating to retrieve, through geometric modeling, the detailed history of fold growth and sedimentation across the Huerguosi anticline, on the northern Tianshan piedmont, taking advantage of a beautifully exposed section of growth strata. The model assumes a fault-bend folding mechanism, consistent with subsurface fold geometry. The shortening history is obtained by least-squares fitting of the measured dip angles of the growth strata. The shortening rate across the anticline is shown to have been remarkably constant: it increased only slightly from 0.84 [+ or -] 0.04 mm/yr between 10 and 4 Ma to 1.14 [+ or -] 0.02 mm/yr over the past 4 m.y. This approach also allows correcting syntectonic sedimentation rates for the effect of the fold growth and shows that the sedimentation rates in the piggyback basin increased abruptly from ~0.4 to ~0.7 mm/yr ca. 4 Ma.

A biomagnetostratigraphy for the Lower Triassic is constructed, using the ammonoid biostratigraphy from Arctic Boreal successions. Combined thermal and alternating field demagnetization determines the Triassic magnetic field polarity in 86% of specimens, with 36% showing linear trajectory line fits and the remainder showing great-circle trends toward the characteristic magnetization. Mean pole directions for the Deltadalen ([lambda] = 50[degrees], [phi] = 159[degrees], dp/dm = 3.9[degrees]/5.1[degrees]), Lusitaniadalen ([lambda] = 56[degrees], [phi] = 163[degrees], dp/dm = 4.4[degrees]/5.4[degrees]), and Vendomdalen ([lambda] = 57[degrees], [phi] = 143[degrees], dp/dm = 4.4[degrees]/5.4[degrees]) members fall close to the European Lower Triassic apparent polar wander path. Mean directions for two of these member-means pass the reversal test. The remanence is predominantly carried by magnetite. The polarity stratigraphy, when integrated with the ammonoid and meager conodont data, is similar to that determined from successions in the Sverdrup Basin (Canada). The Permian-Triassic boundary post-dates a pronounced palynofloral turnover and predates a short duration reverse magnetozone (LT1n.1r). In the correlated Shangsi section (in South China), LT1n.1r occurs after the first appearance datum (FAD) of H. parvus, but in the Arctic is within the Otoceras boreale Zone. The late Griesbachian to early Smithian is mostly reverse polarity, with three normal-polarity intervals, overlain by mid and late Smithian normal polarity. The Spathian contains four reverse-polarity intervals, the oldest one within the early Spathian with the remainder in the late Spathian. The transition into the Anisian is within the uppermost reverse magnetozone, a feature documented in other sections of this age. The polarity pattern is correlated to other marine sections, indicating the robustness of the biomagneto-stratigraphic composite and its utility in calibrating Lower Triassic time. Keywords: boreal, ammonoids, geochronology, magnetostratigraphy, Permian-Triassic boundary, Svalbard.

An integrated, high-resolution chemostratigraphic (C, O and Sr isotopes) and magnetostratigraphic study through the upper Middle Cambrian-lowermost Ordovician shallow-marine carbonates of the northwestern margin of the Siberian Platform is reported. The interval was analysed at the Kulyumbe section, which is exposed along the Kulyumbe River, an eastern tributary of the Enisej River. It comprises the upper Ust'-Brus, Labaz, Orakta, Kulyumbe, Ujgur and lower Iltyk formations and includes the Steptoean positive carbon isotopic excursion (SPICE) studied here in detail from upper Cambrian carbonates of the Siberian Platform for the first time. The peak of the excursion, showing [[delta].sup.13] C positive values as high as +4.6 [per thousand] and least-altered [sup.87] Sr/[sup.86]Sr ratios of 0.70909, is reported herein from the Yurakhian Horizon of the Kulyumbe Formation. The stratigraphic position of the SPICE excursion does not support traditional correlation of the boundary between the Orakta and Labaz formations at the Kulyumbe River with its supposedly equivalent level in Australia, Laurentia, South China and Kazakhstan, where the Glyptagnostus stolidotus and G. reticulatus biozones are known to immediately precede the SPICE excursion and span the Middle-Upper Cambrian boundary. The Cambrian-Ordovician boundary is probably situated in the middle Nyajan Horizon of the Iltyk Formation, in which carbon isotope values show a local maximum below a decrease in the upper part of the Nyajan Horizon, attributed herein to the Tremadocian Stage. A refined magnetic polarity sequence confirms that the geomagnetic reversal frequency was very high during Middle Cambrian times at 7-10 reversals per Ma, assuming a total duration of about 10 Ma and up to 100 magnetic intervals in the Middle Cambrian. By contrast, the sequence attributed herein to the Upper Cambrian on chemostratigraphic grounds contains only 10-11 magnetic intervals. Keywords: Cambrian, Ordovician, carbon, strontium, palaeomagnetism, stratigraphy.

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 [...]

The Cambrian Drumian Carbon Isotope Excursion (DICE) and the Steptoean Positive Carbon Isotope Excursion (SPICE) have been so far reported in subtropical platforms: the DICE event is a large negative excursion in [delta][sup.13][C.sub.carb] record that nearly coincides with the beginning of the Drumian (Cambrian Series 3), whereas the SPICE event is a large positive shift in [delta]13[C.sub.carb] identified close to the base of the Paibian (Furongian Series). The chemostratigraphic excursions have been recognized in carbonate-dominated platforms, and their application to mid- and high-latitude, siliciclastic-dominated platforms has been problematic. This paper offers, for the first time, a high-resolution stratigraphic analysis of this time span in a temperate-water platform (Montagne Noire, France) that recorded episodes of carbonate productivity in nearshore environments. Two sections were analyzed in detail: a complete Cambrian Series 3-Tremadocian succession, devoid of carbonate interbeds and paleogeographically located in the distal part of the platform (Pardailhan nappe), and a Furongian-Tremadocian succession, which has limestone interbeds and represents the proximal part of the platform (Minervois nappe). The lower part of the La Gardie Formation in the Pardailhan nappe displays background [delta]13[C.sub.org] values of -22[per thousand] punctuated by a large negative, middle Languedocian (regional substage) shift, peaking at -24.5[per thousand]. This negative excursion is similar to the DICE event reported close to the base of the Drumian, although the latter is exclusively based on [delta][sup.13][C.sub.carb] values. Stable isotopes of [delta][sup.13][C.sub.carb] and [delta][sup.13][C.sub.carb] org from both sections also indicate a common chemostratigraphic shift at the onset of the Furongian. In nearshore deposits of the Minervois nappe, the [delta][sup.13][C.sub.carb] background values for the interbedded limestone strata of the Val d'Homs Formation gradually increase from -3[per thousand] to -1[per thousand] and are punctuated by a sharp increase in [delta][sup.13][C.sub.carb] values to >3.0[per thousand]. By contrast, in basinal shales of the La Gardie Formation in the Pardailhan nappe, the [delta][sup.13][C.sub.org] background values decrease from -22% to - 27.1[per thousand]. This trend is directly controlled by total organic carbon (TOC) contents and is interpreted to have been initiated by changes in the degree of biodegradation of organic matter, sulfate reduction, and methanogenesis before or soon after burial. Despite this overprinting and the very low degree of metamorphism reached by the shales, the [delta][sup.13][C.sub.org] background trend is also punctuated by a sharp positive shift in [delta][sup.13][C.sub.org] values to >4.0[per thousand], similar to the SPICE event. In addition, the asymmetric shape of the SPICE excursion in the Montagne Noire shows evidence for the HERB event, a late Furongian negative carbon isotope excursion not yet accepted as a worldwide chemostratigraphic anomaly. The recognition of both chemostratigraphic shifts in mixed and clayey strata opens new possibilities of chemostratigraphic correlation in mid- and high-latitude platforms, where carbonate factories did not widely develop, and strata only contain endemic fauna. This implication has a major consequence because the Global Stratotype Section and Point (GSSP) of the Drumian and Paibian stages occurs near the base of both excursions. Keywords: chemostratigraphy, Cambrian, Ordovician, West Gondwana.

Distinct [sup.18]O depletion is characteristic of a large majority of the 620-550 Ma felsic igneous rocks of Avalonia in the northern Appalachian orogen. Neoproterozoic rocks in the Boston Avalon terrane have the lowest δ[sup.18][O.sub.WR] values (≥-3.1‰), followed by the Mira terrane in Cape Breton Island and the Caledonia terrane in New Brunswick (≥-1.2‰), the Avalon terrane in Newfoundland (≥+2.8‰), and the Antigonish Highlands in Nova Scotia (≥+5.3‰). In contrast, this depletion of [sup.18]O is observed in very few of the Paleozoic felsic igneous rocks from these Avalonian terranes, and also in very few of the Neoproterozoic and Paleozoic felsic igneous rocks from the inboard Ganderian terranes. The low-[sup.18]O character of the Neoproterozoic igneous rocks is related to regional pervasive, post-magmatic alteration by predominantly meteoric-hydrothermal fluids (δ[.sup.18][O.sub.H2O] ~ -6‰ to -4‰) at 200-450 °C. The alteration likely occurred during late Neoproterozoic transtensional extension of Avalonia. Large-scale fluid infiltration and circulation within the Avalonian crust accompanied this extension with development of pull-apart sedimentary basins and extension-related magmatism that were the prelude to Cambrian submergence of Avalonia. This regional [sup.18]O depletion provides a geochemical fingerprint by which Avalonia can be distinguished from other peri-Gondwanan terranes. These data suggest that Avalonia existed as a composite terrane on the Gondwanan margin in the Neoproterozoic, separate from Ganderia. Un appauvrissement en [sup.18]O est caracteristique d'une grande partie des roches ignees felsiques, 620-550 Ma, de l'Avalonia dans le nord de l'orogene appalachien. Les roches neoproterozoiques du terrane Boston Avalon ont les valeurs δ[sup.18][O.sub.WR] les plus faibles (≥-3,1 ‰), suivies du terrane Mira dans l'Ele du Cap Breton et le terrane Caledonia au Nouveau-Brunswick (≥-1,2 ‰), du terrane Avalon a Terre-Neuve (≥+2,8 ‰) et dans les terres hautes de l'Antigonish en Nouvelle-Ecosse (≥+5,3 ‰). Par contre, cet appauvrissement en [sup.18]O est observe dans tres peu de roches ignees felsiques paleozoiques de ces terranes d'Avalon et aussi dans tres peu de roches felsiques ignees neoproterozoiques et paleozoiques des terranes interieurs de Gander. La faible teneur en [sup.18]O des roches ignees neoproterozoiques est liee a une alteration postmagmatique regionale penetrante par des fluides hydrothermaux principalement meteoriques (δ[.sup.18][O.sub.H2O] ~ -6 a -4 ‰) a 200-450 °C. L'alteration est probablement survenue au cours de l'extension de tension transverse d'Avalonia au cours du Neoproterozoique tardif. Une infiltration et une circulation de fluides a grande echelle a l'interieur de la croite avalonienne a accompagne cette extension avec le developpement de bassins sedimentaires d'etirement et d'un magmatisme relie a l'extension qui forment le prelude a la submersion d'Avalonia au Cambrien. Cet appauvrissement regional en [sup.18]O fournit une signature geochimique par laquelle le terrane d'Avalonia peut etre distingue d'autres terranes peri-Gondwana. Selon ces donnees, Avalonia aurait existe en tant que terrane composite sur la bordure gondwanienne au Neoproterozoique, separe de Ganderia., [Traduit par la Redaction] Introduction The comparative tectonostratigraphic histories and relationships among the peri-Gondwanan composite terranes comprising Avalonia and Ganderia in the northern Appalachian orogen have been the subject of [...]

The Anatolian Platform, which was a part of the Gondwanan Platform, is mainly characterized by carbonate-dominated deposits ranging in age from Devonian to Permian. The biostratigraphy and systematics of a late Asselian-early Sakmarian fusulinid fauna from the Anatolian Platform including Eastern and Central Taurides have been investigated in three sections: Ozbek Hill, Eskibey and Bademli. Twenty-four fusulinid taxa, belonging to twelve genera, were determined in a single fusulinid zone dated as late Asselian-early Sakmarian. Early-middle Asselian fusulinid faunas have not been observed in any of the measured sections throughout the Anatolian Platform. This indicates that lower to middle Asselian deposits are represented by an interval characterized by quartz sandstone overlying upper Gzhelian strata. Five new species (Pseudochusenella anatoliana, Pseudofusulinoides altineri, Pseudofusulinoides convexus, Pseudofusulinoides subglobosus and Pseudofusulinoides vachardi) are described in this study. The Early Permian fusulinid fauna correlates very well with the fauna of other sections in the Palaeotethyan realm (Southern Alps, Central Asia, Southern China and Japan). Keywords: biostratigraphy, fusulinids, Early Permian, Anatolian Platform, Turkey.

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 [...]

To help calibrate the emerging Upper Ordovician chitinozoan biozonation with the graptolite biozonation in the Anglo-Welsh, historical type basin, the graptolite-bearing CaradocAshgill successions between Fishguard and Cardigan, and at Whitland, SW Wales, have been collected for chitinozoans. In the Cardigan district, finds of Armoricochitina reticulifera within strata referred to the clingani graptolite Biozone (morrisi Subzone), together with accessory species, indicate the Fungochitina spinifera chitinozoan Biozone, known from several Ordovician sections in northern England that span the base of the Ashgill Series. Tanuchitina ?bergstroemi, eponymous of the succeeding chitinozoan biozone, has tentatively been recovered from strata of Pleurograptus linearis graptolite Biozone age in the Cardigan area. The T. ?bergstroemi Biozone can also be correlated with the type Ashgill Series of northern England. Chitinozoans suggest that the widespread Welsh Basin anoxic--oxic transition at the base of the Nantmel Mudstones Formation in Wales, traditionally equated with the Caradoc--Ashgill boundary, is of Cautleyan (or younger Ashgill) age in the Cardigan area. In the broadly time-equivalent, graptolite-rich Whitland section, also in SW Wales, two Baltoscandian chitinozoan biozones and a subzone have been recognized (again using accessory species), namely the Spinachitina cervicornis Biozone?, the Fungochitina spinifera Biozone and the Armoricochitina reticulifera Subzone. The new chitinozoan data provide a more precise means of correlation between the Whitland and Cardigan successions and suggest that the Normalograptus proliferation interval of the Whitland section is at least partly attributable to the Dicellograptus morrisi Subzone of the Dicranograptus clingani Biozone, rather than equating with the overlying Pleurograptus linearis Biozone. Keywords: chitinozoans, graptolites, Ordovician, biostratigraphy, Wales.

The Oligocene represents an important time period from a wide range of perspectives and includes significant climatic and eustatic variations. The pelagic succession of the Umbria-Marche Apennines (central Italy) includes a complete and continuous sequence of marly limestones and marls, with volcaniclastic layers that enable us to construct an integrated stratigraphic framework for this time period. We present here a synthesis of detailed biostratigraphic, magnetostratigraphic, and chemostratigraphic studies, along with geochronologic results from several biotite-rich volcaniclastic layers, which provide the means for an accurate and precise radiometric calibration of the Oligocene time scale. From this study, the interpolated ages for the Rupelian/Chattian stage boundary, located in the upper half of Chron 10n at meter level 188 in the Monte Cagnero section, and corresponding to the 04/05 planktonic foraminiferal zonal boundary, are 28.36Ma (paleomagnetic interpolation), 28.27 [+ or -] 0.1 Ma (direct radioisotopic dating), and 27.99 Ma (astrochronological interpolation). These ages appear to be slightly younger than those reported in recent chronostratigraphic time scale compilations. The Monte Cagnero section is a potential candidate for defining the Chattian Global Stratotype Section and Point (GSSP) and some reliable criteria are here proposed for marking the Rupelian/Chattian boundary according to International Union of Geological Sciences (IUGS) recommendations. Keywords: Integrated stratigraphy, Oligocene, Rupelian/Chattian boundary, Umbria-Marche Apennines, central Italy.

High Resolution Imaging Science Experiment (HiRISE) images of Holden crater, Mars, resolve impact megabreccia unconformably overlain by sediments deposited during two Noachian-age phases of aqueous activity. A lighter-toned lower unit exhibiting phyllosilicates was deposited in a long-lived, quiescent distal alluvial or lacustrine setting. An overlying darker-toned and often blocky upper unit drapes the sequence and was emplaced during later high-magnitude flooding as an impounded Uzboi Vallis lake overtopped the crater rim. The stratigraphy provides the first geologic context for phyllosilicate deposition during persistent wet and perhaps habitable conditions on early Mars. Keywords: Mars, stratigraphy, aqueous, megabreccia.

Abstract: Sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings. In this study, aerial photographs, ground-penetrating radar (GPR), and stratigraphic analysis document the [...]

An exceptionally well-preserved aragonitic coral of the extinct species Goniopora hilli was collected from late Cenozoic sedimentary deposits in the Dominican Republic and dated using U-Pb techniques. Nine coralline subsamples yielded a [sup.238]U/[sup.206]Pb-[sup.207] pb/[sup.206]Pb three-dimensional (3-D) inverse linear concordia age of 5.52 [+ or -] 0.15 (2[sigma]) Ma, which, when coupled with [sup.87] Sr/[sup.86]Sr ratios obtained from the same coral, allows for tighter constraints on temporal variability of marine species diversity prior to closure of the Central American Seaway. The recognition that pre-Quaternary aragonitic corals can be suitable for U-Pb dating creates new possibilities for refining the chronologies of late Cenozoic marine sedimentary sequences. Keywords: coral, U-Pb, Dominican Republic, Miocene, Central American Seaway, Sr chemostratigraphy.

Abstract: Thick, marine clay deposits in valleys along the Norwegian coast are occasionally subjected to large landslides involving quick clay. Detailed mapping of the extent of quick clay is of [...]

Measurements of OH and CI growth zoning in apatite phenocrysts from the Cerro Galan ignimbrite describe the tumultuous volatile history of a magma chamber in the days to months prior to a supereruption. The chemical stratigraphy in these crystals provides a unique relative time scale not otherwise available when studying pre-eruptive volatiles in ancient magma chambers, and it allows us to temporally correlate the data within each crystal, resulting in a 'volatile history.' The five crystals studied show broadly similar volatile histories, but distinctive differences between the various crystals suggest that each recorded a specific perspective on the magma chamber prior to eruption, perhaps correlating to different depths or laterally separated regions within the >1000 [km.sup.3] magma chamber. All crystals are consistent with the interpretation of a multistage magmatic history, including a period of residence in a quiescent magma, and a period of rapid growth under strongly varying conditions. Several apparent 'events' during this period of growth, consistent with two competing processes of [H.sub.2]O degassing and recharge, are recorded by nearly all of these crystals. Such zoning could not have survived for more than ~400 d prior to eruption, suggesting that during the days to months leading up to a supereruption, apatite records key aspects of the processes that directly lead to and influence these catastrophic events. Keywords: magma, volatiles, water, apatite, SIMS, ion probe, Cerro Galan, Argentina, supereruption, supervolcano.

We studied the alluvial histories of eight small ( Keywords: alluvial stratigraphy, valley fills, Younger Dryas, Holocene, millennial scale, climate change, southwestern United States, High Plains. doi: 10.1130/B26034.1

Sediment from landscape disturbance often enters temporary storage in valleys and evacuates over longer times, which in steeplands are poorly delimited. We hypothesize that, across process transitions (e.g., debris flow versus fluvial transport), distributions of sediment transit times also change. We use field surveys and extensive radiocarbon dating to assess the distribution of transit (residence) times through the proxy measurement of ages of bank deposits in two mainstem reaches of a 2.23 [km.sup.2] watershed in the Oregon Coast Range. In the downstream reach, debris fans impound fluvial deposits; debris-flow, fine fluvial, and coarse fluvial deposits compose nearly equal parts of the valley fill; and fluvial erosion evacuates deposits. Transit times have a sample mean of 1.22 x [10.sup.3] [sup.14]C yr and an exponential distribution, indicating uniform probability of evacuation from storage. In the upstream reach, valley-spanning debris jams impound debris-flow deposits composing >95% of the valley fill, which is routinely scoured by debris flows. Transit times have a sample mean of 4.43 x [10.sup.2] [sup.14]C yr and, if >100 [sup.14]C yr, a power-law distribution, indicating preferential evacuation of younger deposits and retention of older deposits. In both reaches, most sediment has short transit times ( Keywords: sediment budget, residence time, debris flows, fluvial transport, radiocarbon dating, stratigraphy. doi: 10.1130/G239365A.1

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 [...]

Radiocarbon-calibrated amino acid racemization ages of 250 individually dated Tellina shells from two sediment cores are used to quantify molluscan time averaging with increasing burial depth in the shallow-water carbonate lagoon of Rib Reel, central Great Barrier Reef, Australia. The top 20 cm of sediment contain a distinct, essentially modern assemblage with a median age of only 5 yr. Sediment between 20 and 125 cm are age-homogeneous and significantly older than the surface sediment (median age 189 yr). Shell age distributions within layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a subcentennial scale. Shell size is an important correlate of shell half-life and an important determinant of the inferred age of sedimentary layers. These results illustrate the importance of bioturbation in these environments, indicate that age estimates in this depositional setting are sensitive to specimen choice, and document a size-dependent bias in death assemblage formation. Keywords: Mollusca, carbonate sediments, size distribution, time averaging, taphonomy, bioturbation.

Contrary to widely used sequence-stratigraphic models, lowstand fans are only part of the turbidite depositional record; our analysis reveals that a comparable volume of coarse-grained sediment has been deposited in California borderland deep-water basins regardless of sea level. Sedimentation rates and periods of active sediment transport have been determined for deep-water canyon-channel systems contributing to the southeastern Gulf of Santa Catalina and San Diego Trough since 40 ka using an extensive grid of high-resolution and deep-penetration seismic-reflection data. A regional seismic-reflection horizon (40 ka) has been correlated across the study area using radiocarbon age dates from the Mohole borehole and U.S. Geological Survey piston cores. This study focused on the submarine fans fed by the Oceanside, Carlsbad, and La Jolla Canyons, all of which head within the length of the Oceanside littoral cell. The Oceanside Canyon-channel system was active from 45 to 13 ka, and the Carlsbad system was active from 50 (or earlier) to 10 ka. The La Jolla system was active over two periods, from 50 (or earlier) to 40 ka, and from 13 ka to the present. One or more of these canyon-channel systems have been active regardless of sea level. During sea-level fluctuation, shelf width between the canyon head and the littoral zone is the primary control on canyon-channel system activity. Highstand fan deposition occurs when a majority of the sediment within the Oceanside littoral cell is intercepted by one of the canyon heads, currently La Jolla Canyon. Since 40 ka, the sedimentation rate on the La Jolla highstand fan has been >2 times the combined rates on the Oceanside and Carlsbad lowstand fans. Keywords: submarine fans, sequence stratigraphy, sedimentation rates, shelf width, California borderland.

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 [...]