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Abstract: The Coulon deposit is a volcanogenic massive sulphide (VMS) system in the James Bay area, Superior craton, Quebec, that was metamorphosed to amphibolite-facies conditions. The chemistry and mineralogy of [...]

Both spilitic and non-spilitic metabasaltic sills are hosted by greenschist-facies metasediments in the SW Scottish Highlands. Spilitization is mainly characterized by enrichment in [Na.sub.2]O, elevated modal plagioclase and epidote segregations. Mapping of the spatial distribution of spilitic metabasalts reveals an ancient sub-sea-floor fluid cell centred on the extrusive Tayvallich Volcanics. Fluid circulation was most extensive at shallow levels where most sills were spilitized. We attribute this to pervasive flow of saline fluid, which was thermally driven by the cooling suite of lava flows and sills. Spilitization below this lithostratigraphic depth was restricted to only a few sills. Their spilitization is largely unrelated to specific properties of these sills (e.g. width, chemistry or host lithology). We conclude that fluid channelling was an intrinsic property of sub-sea-floor fluid flow either at deeper levels or earlier during fluid circulation. By profiling of the size distributions of relic phenocrysts in a partly spilitized sill, we conclude that spilitization proceeds with the symmetric propagation of a spilitization front from the sill margins towards the sill interior. Based on chemical profiling across the margin of an epidote segregation, we conclude that spilitization is associated with chemical transport on scales ranging from 0.1 to 10m. doi: 10.1144/0016-76492009-130.

This paper aims to separate different snow regions over the terrestrial ice sheets based on their measured microwave signatures. It takes advantage of coregistered data from passive and active sensors on the Environmental Satellite (Envisat) to directly derive a snow facies indicator in a point-by-point basis. This paper represents the first attempt of this kind in exploiting nadir-viewing and dual-frequency data from both altimeter and radiometer sensors. The approach is based on a clustering method. Such representation of the data by means of fewer clusters necessarily loses fine details but achieves simplification in geographical representation and eases the description of the condition of the ice sheets in 2004. Our approach broadens the description of the snow pack by taking into account characteristics such as surface roughness, grain size, stratification, and snowmelt effects, whereas the latter has often solely been considered in most previous work. Such partition of the ice sheets might help to better understand relationships between microwave signatures and snow morphology. It could also be useful for estimating elevation uncertainty in altimeter data, which, in turn, is essential to correctly interpret the significance of the rates of elevation change in a changing climate and to convert elevation change to snow mass change. Index Terms--Pattern classification, radar altimetry, snow.

Most tide-dominated estuarine and deltaic deposits accumulate in the fluvial-to-marine transition zone, which is one of the most complicated areas on earth, because of the large number of terrestrial and marine processes that interact there. An understanding of how the facies change through this transition is necessary if we are to make correct paleo-environmental and sequence-stratigraphic interpretations of sedimentary successions. The most important process variations in this zone are: a seaward decrease in the intensity of river flow and a seaward increase in the intensity of tidal currents. Together these trends cause a dominance of river currents and a net seaward transport of sediment in the inner part of the transition zone, and a dominance of tidal currents in the seaward part of the transition, with the tendency for the development of a net landward transport of sediment. These transport patterns in turn develop a bedload convergence within the middle portion of all estuaries and in the distributary-mouth-bar area of deltas. The transport pathways also generate grain-size trends in the sand fraction: a seaward decrease in sand size through the entire fluvial--marine transition in deltas, and through the river-dominated, inner part of estuaries, but a landward decrease in sand size in the outer part of estuaries. A turbidity maximum (i.e., a zone of significantly elevated suspended-sediment concentrations) is developed within estuaries and the delta-plain region of deltas as a result of flocculation and density-driven water-circulation patterns. This leads to an area within the estuary or delta plain where the abundance and thickness of the mud drapes are greatest, including the potential for the development of fluid-mud deposits (i.e., structureless mud layers more than 0.5-1 cm thick that were deposited in a single slack-water period). A monotonic seaward increase in salinity characterizes both estuaries and deltas. The brackish-water conditions in the transition zone, accompanied by the high turbidity and physically harsh conditions, produce a biologically stressed environment, in which bioturbation is generally not pervasive. The ichnofossil assemblage in this zone is characterized by the low diversity of ichnogenera, small size of the individual burrows (typically smaller than their open-marine counterparts), and highly variable population densities, ranging from unbioturbated to very high-density mono-specific assemblages in local areas. This review begins with a survey of how and why each depositional process varies through the fluvial-to-marine transition and then examines the sedimentological responses to these processes, focussing on the observable, longitudinal variations in the development and/or abundance of each deposit characteristic (e.g., sand grain size, paleocurrent patterns, mud drapes, and biological attributes). The review ends with a summary of the characteristics of each major facies zone through the transition, with separate discussions for both estuaries and deltas. It must be noted that any attempt to generalize, as is done here, will undoubtedly contain statements that are inappropriate for individual deposits or systems. Exceptions must be expected and the concepts must be applied with due consideration for the local context. Keywords: tide-dominated; proximal-distal facies trends; fluvial--marine transition; delta; estuary

Basins in which turbidity currents are completely or partially trapped are common in many tectonically active, deep-water settings. Field study of an Eocene-Oligocene turbiditic system in the Peira Cava area, a sub-basin of the Alpine foreland in southeastern France, allows spatial characterization of a ponded basin fill on the basis of a correlation framework derived from measured outcrop sections and photomosaics. The basin-fill architecture comprises a sand-rich, proximal scour-and-fill facies and a downstream transition to mud-rich, basin-plain turbidite sheet facies. The proximal facies is interpreted to have formed directly downstream of a slope break, where currents were highly erosional during some periods and highly depositional during other periods, as a result of the interacting effects of turbulence enhancement and rapid deceleration. Both the proximal facies and the downstream transition to distal basin-plain facies occur in progressively landward positions at higher stratigraphic levels. The landward shift in depositional facies is likely to have resulted from the basin-floor aggradation and a landward migration of the slope break. This 'back-stepping' process may be expected to occur in many ponded turbiditic basins and to produce a similar type of sedimentary architecture.

Abstract: The Selbaie Cu-Zn deposit is located in the northeastern portion of the northern Archean Abitibi volcanic belt. It is one of the most important base metal deposits in Canada. [...]

Abstract: The Carillon Formation underlies the Ottawa Embayment, a craton-interior extension of the regional Laurentian paleoshelf, defined today by the Ottawa-Bonnechere Graben. Facies within the embayment during the Middle Ordovician [...]

Quantifying the facies architecture of flood basalt provinces is important as it can be used to understand the physical volcanology and rock property variations throughout the lava sequence. The 3D facies architecture and internal heterogeneity of the Skye Lava Field, for example, provides important insights into the evolution of the British Tertiary Igneous Province, and valuable information to aid in the exploration of potential offshore reservoirs underlying significant flood lavas along the North Atlantic margin. The volcanic stratigraphy of the Talisker Bay area of Skye comprises: (1) lower compound-braided lavas (flow lobes Keywords: Skye Lava Field, flood basalts, 3D modelling, rock properties, structure.

The Upper Cambrian Deadwood Formation of north-central Montana is composed mainly of fine-grained calcareous sandstone and intercalated silty shale, and contains scattered intraclastic flat-pebble conglomerate. These rocks, typical of many mixed carbonate-siliciclastic, subtidal shelf successions of Proterozoic through Early Ordovician age, are distal storm deposits in which the conglomerates are conventionally thought to record occasional, very high energy events that scoured incipiently cemented layers. In the Deadwood Formation, most sandstone beds have a linear to crudely reticulate pattern of vertical cracks filled with injected silt and clay. The cracks exhibit a consistent northwest-southeast trend, and are very shallow burial deformation structures caused by the passage of seismic waves possibly originating from strong earthquakes in Idaho. Most conglomerates are composed of angular to subangular sandstone intraclasts, the polygonal plan view of which is similar in outline to the areas between cracks in the sandstones. The deformation implied by the cracks, sporadic distribution of conglomerates, high degree of scouring indicated, and angularity of the intraclasts argue that, rather than storms, the conglomerates were generated by occasional tsunamis. The sweep of these tsunamis, across the shallow intracratonic sea created extraordinarily strong oscillating bottom currents at the deeper reaches of storm wave base. 'Tsunamites' are therefore identified with confidence virtually for the first time in shallow subtidal shelf deposits. Keywords: storms, earthquakes, tsunami, facies, flat-pebble conglomerates, Cambrian, Precambrian, Proterozoic, Montana.

Sedimentologic, geotechnical, geochemical, and accelerator mass spectrometer (AMS) radiocarbon data from two marine geologic cruises in the Ross Sea have allowed us to constrain facies relationships and temporal changes in the West Antarctic Ice Sheet. The selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality (CHIRP) subbottom reflection system. A complex but consistent succession of facies documents a number of environments from subglacial to open marine. Massive, mud-rich diamictons have low water contents, contain (in places) a calcareous microfossil assemblage, show minimal textural variation, and contain low and uniform total organic carbon values. This reflects a subglacial setting. This unit passes upward into a stratified, thin, granulated facies consisting of pelletized, sandy, muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble-sized clasts. This facies reflects the lift-off zone or thin water film between the basal debris and sea floor. Overlying this unit are silty clays that contain a well-sorted, very fine-grained sand component. There are no coarse grains within this unit. This facies is, in part, laminated and reflects deposition beneath an ice shelf, near and away from the grounding-line zone. The ice-shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open-marine setting. A sandy, volcaniclastic-rich subfacies marks the transition from ice shelf to open-marine environments found at the calving line. The 86 AMS radiocarbon dates on organic matter provide an accurate chronology for 19 cores. Ice-shelf conditions were established in the outer Drygalski Trough by 11 +/- 0.25 ka and perhaps earlier. This transition took place in the JOIDES Basin by 10-8 ka. The calving front of the Ross Ice Shelf passed over the Drygalski Trough at 74 degrees S by 9.5 +/- 0.25 ka. The timing of deglaciation of the Ross Sea calls into question current models for the contribution of Antarctic glacial ice to Holocene sea-level rise and suggests that recession was relatively gradual and more closely aligned with Northern Hemisphere deglaciation and its associated eustatic pulse.

Many basins are filled under the influence of tectonics and variable climatically driven processes. Unravelling the relative contributions of these is generally easier in fossiliferous sequences if faunal diversity patterns are considered in conjunction with lithofacies analysis. This approach has been successfully applied to Late Miocene strata of Sicily, where progressive restriction and desiccation within the Sicilian Caltanissetta region occurred under a semi-arid climate during the Messinian Stage. This restriction was partly due to Antarctic cooling which produced Palaeo-Mediterranean sea-level oscillations during the Early Messinian, as a prelude to closure of the Atlantic connections. In addition, regions within this Afro-European plate collision zone were also subjected to syndepositional tectonic deformation associated with progressive perched basin development above foreland (south) verging thrust sheets. The relative impacts of climatic (eustatic) versus tectonic control on sedimentation patterns within these perched basins has been debated at length. However, progress towards resolving this problem by a combined approach involving lithofacies analysis, and faunal phase analysis provides clues for separating the effects of the controlling factors. Faunal phase analysis identifies general faunal associations with minimal emphasis on species diversity. The resulting 'phase' plots for Early Messinian strata appear to be transgression skewed when controlled by eustatic cyclicity, and regression skewed when driven by regional tectonics associated with perched basin tectonics. Keywords: Messinian, Sicily, faunal phase analysis, tectonics, eustasy.

Palynofacies analysis of marine Jurassic sedimentary successions in France and the United Kingdom demonstrates the pervasiveness of regular cycles in qualitative and quantitative aspects of the microscopic particulate organic content of the rocks, especially that part which is ignored during routine palynology. The cycles are attributed to precession, obliquity, and eccentricity forcing. Most of the palynofacies cycles are independent of lithology, whether it be cyclic, irregular, or uniform. Terrestrially derived organic particles record the effects of orbital cyclicity on land, which may be controlled by orbital cycles different from those controlling marine sediment deposition. The majority of studies on orbital cyclicity in the sedimentary record concentrate on cyclicity in lithology. This study demonstrates that sections lacking regular lithological cycles may still record evidence of orbital forcing of both the depositional environment and sediment source and transport.

Hydration reactions associated with eclogite-facies metamorphism of granulites in the Norwegian Caledonides led to the formation of saline brines with exceptional compositions. Primary omphacite- and garnet-hosted fluid inclusions from Norwegian eclogites formed by hydration of granulites contain a plethora of solid phases. A total of 18 different minerals have been identified in multiphase brines, and 12 of these occur at the Badsholmen locality in Sunnfjord. Fluid inclusions from this locality are characterized by a high Br/Cl mass ratio (0.03) and extreme Pb enrichment as demonstrated by the presence of Pb-bearing daughter minerals including galena, a Pb-Cl-bearing phase, and a Pb-Cl-Br-bearing phase. The fluid compositions may reflect enrichment of elements incompatible with the silicate structure during consumption of [H.sub.2]O by eclogite-forming hydration reactions. Pb is believed to have been scavenged from the parent granulite by the increasingly saline brine during K-feldspar breakdown.

The influence of clay units on ground-water composition was investigated in a heterogeneous carbonate aquifer system of Miocene age in southwest Florida, known as the Intermediate aquifer system. Regionally, the ground water is recharged inland, flows laterally and to greater depths in the aquifer systems, and is discharged vertically upward at the saltwater interface along the coast. A depth profile of water composition was obtained by sampling ground water from discrete intervals within the permeable carbonate units during coring and by squeezing pore water from a core of the less-permeable clay layers. A normative salt analysis of solute compositions in the water indicated a marine origin for both types of water and an evolutionary pathway for the clay water that involves clay diagenesis. The chemical composition of the ground water in the carbonate bedrock is significantly different from that of the pore water in the clay layers. Dissolution of clays and opaline silica results in high silica concentrations relative to water in other parts of the Intermediate aquifer system. Water enriched in chloride relative to the overlying and underlying ground water recharges the aquifer inland where the confining clay layer is absent, and it dissolves carbonate and silicate minerals and reacts with clays along its flow path, eventually reaching this coastal site and resulting in the high chloride and silica concentrations observed in the middle part of the Intermediate aquifer system. Reaction-path modeling suggests that the recharging surficial water mixes with sulfate-rich water upwelling from the Upper Floridan aquifer, and carbonate mineral dissolution and precipitation, weathering and exchange reactions, clay mineral diagenesis, clay and silica dissolution, organic carbon oxidation, and iron and sulfate reduction result in the observed water compositions.

A distinctive trilobite fauna occurs within condensed staff graphic sections of the Lower Mississippian (Tournaisian) Chappel Limestone of the Llano region of Texas, the Welden Limestone of Oklahoma, and the Chouteau Limestone of Union County, Illinois. The seven species comprising this fauna are interpreted to have inhabited sediment-starved basinal environments. The starved-basin facies existed in the south-central United States throughout the Tournaisian (Kinderhookian to Osagean). Two species from this fauna, Australosutura llanoensis, and Carbonocoryphe planucauda, are new. The remaining five species, Griffithidella doris (Hail), Griffithidella alternata (Girty), Carbonocoryphe depressa (Girty), Thigiffides roundyi (Girty), and Pudoproetus chappelensis (Hessler), are restricted to starved-basin facies.

A study was conducted on several exhumed melange facies in the western Band orogen, Indonesia, to determine the structural and stratigraphic connections between various facies in the region and nearby active melange-forming processes. The approach involved the analysis of block assemblages, clay mineral and microfaunal characteristics of the melange matrix, and offshore seismic reflection profiles. Results showed that melange-forming processes are similar to those in the Sonnebait Disruption Zone and produce distinctive mixed block-in-clay facies melange that is common in most of the hinterland in the Banda orogen.

The petrogenetic grids of the model system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH), which is relevant for several greenschist, blueschist, amphibolite and eclogite facies rocks, were calculated to examine pressure/temperature- (PT) evolution of metabasic rocks from Samos, Greece. Results showed a clockwise PT-path, indicating cooling during exhumation of the rocks. Moreover, the rocks are probably related to high-pressure rocks found in the Menderes Massif in western Turkey.

Accessory monazite crystals in granites are commonly unstable during amphibolite facies regional metamorphism and typically become mantled by newly formed apatite-allanite-epidote coronas. This distinct textural feature of altered monazite and its growth mechanism were studied in detail using backs-cattered electron imaging in a sample of metagranite from the Tauern Window in the eastern Alps. It appears that the outer rims of the former monazites were replaced directly by an aparite ring with tiny thorite intergrowths in connection with Ca supply through metamorphic fluid. Around the apatite zone, a proximal allanite ring and a distal epidote ring developed. This concentric corona structure, with the monazite core regularly preserved in the center, shows that the reaction kinetics were diffusion controlled and relatively slow. Quantitative electron microprobe analyses suggest that the elements released from monazite breakdown (P, REE, Y, Th, U), were diluted and redistributed in the newly formed apatite, allanite, and epidote overgrowth rings and were unable to leave the corona. This supports the common hypothesis that these trace elements are highly immobile during metamorphism. Furthermore, microprobe data suggest that the preserved monazite cores lost little, possibly none of their radiogenic lead during metamorphism. Thus, metastable monazite grains from orthogneisses appear to be very useful for constraining U-Th-Pb protolith ages. On the basis of these findings and a review of literature data, it seems that monazite stability in amphibolite facies metamorphic rocks depends strongly on lithologic composition. While breaking down in granitoids, monazite may grow during prograde metamorphism in other rocks such as metapelites.

Late Pleistocene Heinrich ice-rafting events produced layers rich in ice-rafted debris in major parts of the North Atlantic north of 40 [degrees] N. A high detrital carbonate content points to the Hudson Strait outlet of the Laurentide ice sheet as a dominant source of the icebergs. Heinrich events were coupled with short-term climate fluctuations during the last and penultimate glaciations and provide evidence for cryosphere-hydrosphere-atmosphere interaction in Pleistocene climate change. An unsolved problem with Heinrich layers has been their high concentration of fine-grained detrital carbonate (>80% of the total detrital carbonate), which cannot have been delivered by icebergs alone. We propose combinations of different processes that deposited four sedimentologically different types of Heinrich layers: ice rafting alone for the coarser, sand- to gravel-sized fractions and the fine fractions in distal regions (type IV Heinrich layers), whereas nepheloid flows deposited the bulk of the fine sediment in regions proximal to the Hudson Strait (type I Heinrich layers). On the Labrador slope, turbidity currents spilling over from canyons were also involved in transporting the fine-grained carbonate-rich material, causing an alternation of mud-turbidites and thin laminae of ice-rafted debris in type II Heinrich layers. On the levees of the Northwest Atlantic Mid-Ocean Channel, the thickness relationship is reversed: mud-turbidites deposited by occasional spillover of currents from the channel are thin and alternate with thicker laminae of ice-rafted debris (type III Heinrich layers).

Schistose, upper amphibolite facies, metasedimentary enclaves from granites across the southern Lachlan Fold Belt of southeastern Australia have a common structural history. The middle crustal region, from which the enclaves and their host granites derived, is assumed therefore to be structurally uniform across the fold belt. The uniform nature of the crustal component represented by the metasedimentary enclaves casts doubts on the existence of suspect or Proterozoic microcontinental blocks within the terrane collage. A proposed crustal cross section for the southern Lachlan Fold Belt shows a tectonically thickened Paleozoic section overlying an oceanic substrate. An Ordovician sedimentary component,was involved in the generation of both S- and I-type granites.

A study that establishes the origin of metamorphism in eclogite-facies in north-east Greenland as having started in the Caledonian age is given. Geochronologic, isotopic and petrologic analyses were made on three samples of mafic and ultramafic rocks. Results of the study lend credence to significant thickening of the Laurentian crust during the Caledonian period. These findings challenge current theories about the collision geometries in the Arctic caledonides.

The Flagstone Bench Formation ranges in age from earliest Triassic to Norian (Late Triassic) and is exposed in the Beaver Lake area of the northern Prince Charles Mountains. This sandstone-dominated formation rests conformably on the Bainmedart Coal Measures and represents the upper part of the Permian-Triassic Amery Group. It is divisible into three members: the Ritchie, Jetty and McKelvey members (in ascending order). Nine sedimentary facies assignable to three facies associations (major channel, crevasse/fan and flood-basin deposits) are recognized within the formation. Ritchie Member sedimentation took place during a transition from consistently hygric to seasonally dry conditions and the unit comprises sandstone-dominated, sheet-like channel deposits interspersed with few, thin, mottled, haematite-rich flood-basin siltstones. Deposition took place under fluctuating discharge conditions chiefly within the channel tracts of axially (northwesterly/northeasterly) flowing, low-sinuosity braided rivers. The Jetty Member shows a gross upward-fining profile dominated in the lower part by poorly sorted pebbly sandstones and in the upper part by ferruginous mudcracked siltstones, mottled palaeosols, calcrete and thin massive sandstone sheets. This unit reflects deposition of easterly directed alluvial fans and extensive flood-basin silt under a semi-arid climatic regime. The Upper Triassic sandstone-dominated McKelvey Member shows a return to axial drainage along the Lambert Graben with sedimentation occurring primarily within low-sinuosity braided channel tracts under wetter climatic conditions.

The U-Pb zircon ages for four granulite-facies xenoliths discovered from a Jurassic kimberlite pipe in the south-central Superior craton of the Canadian Shield are studied. Results show that granulite facies anorthositic to mafic xenoliths in a Jurassoc kimberlite pipe have Neoarchean protolith ages. Xenoliths also witnessed Paleoproterozoic metamorphic activity marked by zircon growth at 2416 +/- 30 Ma and 2497 +/- 25 Ma.

The 8-km-thick, Keweenawan metabasaltic, North Shore Volcanic Group in Minnesota shows a continuous zeolite to greenschist facies progression through five zonal divisions. Mafic phyllosilicates are ubiquitous and a well-developed smectite-corrensite-chlorite transition is observed. This sequence provides an excellent framework in which the influence of regional (thermal) as opposed to local scale (lithology: porosity and permeability) factors on this transition, factors that are actively debated, can be comprehensively documented. On a regional scale, at lowest grades (zones 1 and 2; thomsonite-scolecite and heulandite-stilbite assemblages, respectively), tri-smectitic phyllosilicates dominate and, with increase in grade to zone 3 (laumon-tite-albite), there is a marked step and compositional gap to corrensite. With further increase in grade to zones 4 (laumontite-albite [+ or -] prehnite [+ or -] pumpellyite) and 5 (epidote-albite-actinolite), chlorite becomes dominant. Although a spread in the X-ray diffraction and microprobe data suggests that the corrensite to chlorite transition is continuous rather than stepwise, analytically distinct corrensite and chlorite in one flow suggest a clear compositional gap between these two phases. Overall, the data offer some support for a discontinuous smectite-corrensite-chlorite transition. Above the lowest grade (zones 1 and 2; approximately 150 [degrees] C), the phyllosilicates vary on a local, within-flow scale related to morphological contrasts in flow lithology. Smectite is dominant in the massive flow units (low porosity and permeability), whereas corrensite or chlorite is dominant in the amygdaloidal flow tops (high porosity and permeability). These changes provide clear indication that, once above a threshold of approximately 150 [degrees] C, fluid/rock ratios have a strong control on the metamorphic process at low grade. Similarities in [X.sub.MgO] between smectite, corrensite, chlorite, and [X.sub.MgO] of the whole rock show that even though smectite is a relict phase remaining in massive zones, it continues to undergo crystal chemical change with increasing grade. However, contrasts between [Al.sup.IV] in the same minerals are provisional indicators that other factors, perhaps related to kinetic features linked to advective and diffusive modes of fluid transport, may be involved.

The 3.8 [km.sup.3] Osceola Mudflow began as a water-saturated avalanche during phreatomagmatic eruptions at the summit of Mount Rainier about 5600 years ago. It filled valleys of the White River system north and northeast of Mount Rainier to depths of more than 100 m, flowed northward and westward more than 120 km, covered more than 200 [km.sup.2] of the Puget Sound lowland, and extended into Puget Sound. The lahar had a velocity of [approximately equals]19 m/s and peak discharge of [approximately equals]2.5 x [10.sup.6] [m.sup.3]/s, 40 to 50 km downstream, and was hydraulically dammed behind a constriction. It was coeval with the Paradise lahar, which flowed down the south side of Mount Rainier, and was probably related to it genetically. Osceola Mudflow deposits comprise three facies. The axial facies forms normally graded deposits 1.5 to 25 m thick in lowlands and valley bottoms and thinner ungraded deposits in lowlands; the valley-side facies forms ungraded deposits 0.3 to 2 m thick that drape valley slopes; and the hummocky facies, interpreted before as a separate (Greenwater) lahar, forms 2-10-m-thick deposits dotted with numerous hummocks up to 20 m high and 60 m in plan. Deposits show progressive downstream improvement in sorting, increase in sand and gravel, and decrease in clay. These downstream progressions are caused by incorporation (bulking) of better sorted gravel and sand. Normally graded axial deposits show similar trends from top to bottom because of bulking. The coarse-grained basal deposits in valley bottoms are similar to deposits near inundation limits. Normal grading in deposits is best explained by incremental aggradation of a flow wave, coarser grained at its front than at its tail. The Osceola Mudflow transformed completely from debris avalanche to clay-rich (cohesive) lahar within 2 km of its source because of the presence within the preavalanche mass of large volumes of pore water and abundant weak hydrothermally altered rock. A survey of cohesive lahars suggests that the amount of hydrothermally altered rock in the preavalanche mass determines whether a debris avalanche will transform into a cohesive debris flow or remain a largely unsaturated debris avalanche. The distinction among cohesive lahar, noncohesive lahar, and debris avalanche is important in hazard assessment because cohesive lahars spread much more widely than noncohesive lahars that travel similar distances, and travel farther and spread more widely than debris avalanches of similar volume. The Osceola Mudflow is documented here as an example of a cohesive debris flow of huge size that can be used as a model for hazard analysis of similar flows., Avalanches caused by phreomagnetic eruptions at the peak of Mount Rainier during the Holocence epoch resulted in lahar flows that formed the Osceola Mudflow (OM). The OMs have an average age of 5603 and 5491 year B.P. with a calendar age of 5600 year B.P. Analysis of the Tephra layers also indicated a mixture of angular fragments and ash from the lithic Mount Rainier andesite that were produced by laterally directed, phreatic or phreomagnetic eruptions.

Localization of flow in natural quartzo-feldspathic shear zones at granulite-facies temperatures does not occur purely by dislocation creep and dynamic recrystallization. From a review of some natural shear zones, initial faulting focused along a pre-existing shear zone, and/or the boundary of a volume of relatively strong crust or lithosphere, guides emplacement of hot mantle-derived melts into the base of the crust, leading to extensive melting. When crystallized, the sub-solidus plutons represent a focused zone of thermally softened material, capable of deforming readily and developing the full range of crystal-plastic microstructures and fabrics associated with mylonites, contrasting with the intrusion-free wall rocks. Keywords: Shear zones, plutons, granulites, reactivation, faults.

A mineralogical and 40Ar/39Ar study of 13 amphibole samples in the Kamila Amphibolite Belt and Kamila Shear Zone in northern Pakistan has found a correlation between the degree of greenschist facies alteration and quantity of excess 40Ar. Additionally, there is a north-south divide with amphibole samples from the northern region showing larger degrees of greenschist facies alteration, brittle deformation, and excess 40Ar incorporation compared to the predominantly plastically deformed, less altered, amphibole samples from the Kamila Shear Zone in the south. Acid leaching of two amphiboles from the Kamila Amphibolite Belt indicates that a large proportion of the excess 40Ar is correlated with later greenschist facies alteration phases, and can be easily removed by acid etching, thus revealing acceptable regional 40Ar/39Ar plateau ages.

The Permo-Triassic Trinity Peninsula Group is a widespread, regionally metamorphosed metasedimentary sequence in northern Graham Land, Antarctica, which forms the local 'basement' to the mainly Jurassic-Cretaceous Antarctic Peninsula magmatic arc. The metamorphic grade, thermal evolution and pressure series of this major tectono-stratigraphical unit are largely unknown. Determining the nature of the metamorphism has relied hitherto on conventional optical identifications of the major phases, mainly in rare volcanic beds. However, diagnostic mineral parageneses are generally absent and the precise metamorphic grade is unknown or has to be inferred over large areas. Using white mica (illite) crystallinity of interbedded mudrocks, the Trinity Peninsula Group is now shown to have been pervasively altered mainly at anchizonal and epizonal grades. Conditions ranged from upper anchizonal in the northeast to thoroughly epizonal in the southwest. Outwith thermal aureoles near plutonic intrusions, the alteration temperatures ranged mainly from 250 to 325 [degrees] C, exceeding 300 [degrees] C in the highest-grade (epizone/greenschist facies) parts of the sequence. The facies series, K-white mica b cell dimension measurements and mineral phases present are characteristic of an intermediate pressure series altered under moderate geothermal gradients (< 35 [degrees] C/km), corresponding to burial depths of c. 7-10 km. Unroofing and substantial erosion of the Trinity Peninsula Group took place during polyphasal vertical tectonic movements linked to the development of the magmatic arc in northern Graham Land. The geological setting of the Trinity Peninsula Group is ambiguous and could have been a foreland (or back-arc) basin or the mid- to upper levels of an accretionary prism.

In the Katawaz basin, Pakistan, the deltaic and turbidite facies of the Khojak Formation are the Paleogene analogue of the modern Indus River emptying into the Arabian Sea to form the Indus delta-fan system. Facies identified include upper continental slope to prodelta, distal to proximal distributary mouth bar, distributary channel, interdistributary bay, estuary, fluvial channel, natural levee, and flood plains of lower and upper delta plains. The proposed model is a fluvial-dominated, wave-modified delta that axially fed Khojak submarine-fan turbidites, exposed in the southwestern part of the basin. These sediments were eroded from the early Himalayan orogenic highlands and transported southwestward down the axis of the Katawaz remnant ocean basin.

Submarine jet processes are inferred from glaciomarine facies exposed in gravel pits in southwestern coastal Maine. The geometry and distribution of fan facies depend on (1) the proximity to the grounding line and stream effluxes, (2) the angle of jet trajectory from glacier conduits, and (3) sediment re-mobilization processes. Syndepositional glaciotectonic deformation further augments morainal bank formation through pushing and squeezing of fan sediments at the grounding line. Complex process-sediment interactions along the temperate tidewater margin of the Laurentide ice sheet are recorded in the facies architecture of sedimentary sequences in morainal banks. Morainal bank accumulation was governed by rapid fluvial deposition, and outwash jet dynamics that controlled the spatial distribution of sedimentary facies. Near the grounding line, meltwater dynamics change rapidly where sediment-laden fresh water is discharged at or near the sea floor. Turbulent mixing with ambient sea water and discharge fluctuations cause rapid changes in flow competence, accompanied by the dumping of bed-load gravel and sand at the apices of grounding-line fans in the morainal banks. Jet trajectory relative to the morainal-bank slope determines whether a jet will make contact with the morainal bank. Gravel and sand remain in bed-load traction as long as the jet is in contact with the morainal bank. Bed-load dumping and settling of the coarse suspended load occurs where buoyant forces in the jet overcome momentum forces or where the jet is deflected by the morainal bank. Below these buoyant jets, backflow eddies can produce currents that drive ripple migration toward the grounding line. Abrupt facies changes record fluctuations in jet discharge and trajectory and sediment redistribution by sediment gravity flows initiated near the grounding line.

Neoproterozoic-Cambrian rocks of the Zavkhan Basin (Govi-Altay, western Mongolia) comprise large-scale alternations of siliciclastic- and carbonate-dominated units (cf. 'Grand Cycles'). Analysis of such depositional sequences near the base of the Cambrian confirms that the distribution of trace fossils, small shelly fossils and calcimicrobial structures was strongly controlled by ecology and taphonomy, corresponding to specific points in a sea-level cycle. Evolution of the Cambrian biota is thus viewed through a series of narrow time windows, once only for each depositional cycle. Correlation of the Precambrian-Cambrian boundary level on the basis of the first appearance of the Phycodes pedum assemblage is also fraught with difficulty, since stratigraphic resolution may be limited to a single sea-level cycle (c. 1-5 Ma). It is suggested that, in many cases, basin analysis will need to be undertaken before this boundary can be drawn.

A small suite of trace fossils from the Zavkhan Basin (Govi-Altay) includes many of the ichnotaxa typical of the Nemakit-Daldynian, Tommotian and younger Cambrian stages, and other indeterminate forms. The traces are almost entirely from the sandstone intervals of the large-scale alternations of carbonate and siliciclastic sediments, thus emphasizing the facies and taphonomic controls on trace fossil distribution, and hence the inherent difficulties in using trace fossils in detailed global correlation, especially in using first appearances. The assemblage of traces and biofabrics is seen as resulting from the partly non-uniformitarian (non-actualistic) sedimentary environments that pertained over the boundary interval, rather than as evolutionary failures and subsequently vacated environments.

40Ar/39Ar dating of hornblende, muscovite, and orthoclase from southeastern Quebec provides new constraints on the timing, grade, and regional extent of Taconian and Acadian metamorphism in the Canadian Appalachians. Muscovite ages reveal that the Taconic orogeny occurred at ca. 463 Ma throughout the region. Lack of reset amphibole indicates that the metamorphic grade did not exceed greenschist facies. Acadian metamorphism, with a peak of

Pliocene-Pleistocene synorogenic deposits of the Upper Siwalik Group in the northwest Pakistan foreland record changes in dispersal patterns, provenance, and sedimentary facies in response to Himalayan contraction. Three depocenters in the northern Pakistan foreland have been studied: the Peshawar and Campbellpore Basins, situated north of the ranges associated with the Main Boundary fault; and the Soan syncline depocenter, situated in the northern Potwar Plateau, south of the Main Boundary fault. In the Peshawar Basin, an early generation of northward-prograding alluvial fans and gravelly braided streams deposited at ca. 3.0 Ma was folded by en echelon pressure ridges bounded by high-angle reverse faults between 1.7 and 1.4 Ma. The alluvial fan and fluvial deposits were entrenched and infilled by a second generation of northward-flowing braidplain deposits. In the Campbellpore Basin, southwestward-directed fluvial and alluvial-fan deposition in response to uplift of the Kawa Ghar hills began at ca. 1.8 Ma. In the Soan syncline depocenter, deposition occurred at ca. 2.0 Ma as southeastward-flowing braided streams emanating from the Khair-i-Murat uplift, and a southwestward-flowing, gravelly, meandering river derived from highlands to the northeast. Previous stratigraphic and structural interpretations of this part of the Himalayan foreland have included north-dipping, imbricated thrust faults and duplex structures to characterize the deformation patterns in the region. Recently acquired seismic and other geophysical and surficial structural data from the western part of the foreland indicate that the foreland has experienced strike-slip as well as contractile deformation. The structures that controlled depositional patterns of the Upper Siwalik Group are localized uplifts bounded by high-angle reverse faults and not regional thrust faults. The pattern of Pliocene-Pleistocene uplift and resultant deposition across the foreland does not indicate a progression of deformation in either the foreland or hinterland directions, typical of fold-and-thrust belts.

The 40Ar/39Ar and Rb-Sr ages on micas and U-Pb ages for sphenes and amphiboles from the upper Pennine Alps were studies and showed that greenschist assemblages developed at circa 44 Ma in the Zermatt-Saas zone of the footwall and at circa 40 Ma in the thrust zone. Rapid cooling inferred for the Zermatt-Saas ophiolites in the mid-Eocene may document either the extensional unroofing of the ophiolite over the underlying Monte Rosa massif or their tectonic emplacement.

Basinward migration of half-graben footwall margins occurs throughout the active Aegean extensional province and has significant implications for facies distributions and preservation potential in synrift fills worldwide. Recognition of this phenomenon is particularly important for predicting the preservation and distribution of hydrocarbon reservoirs in rift basins. Using an example from the Gediz graben of western Turkey, it is shown that basinward migration of footwall margins exhumes proximal facies of lateral sedimentary systems, severely limiting their preservation potential and providing a ready source of easily erodible material. This in turn leads to the generation of extensive footwall-derived depositional systems, which frequently displace axial drainage systems toward the hanging-wall dip slope.

The Middle Ordovician rocks of the Taconic foredeep in the Mohawk Valley, New York, contain numerous altered volcanic ash beds (K-bentonites). These synchronous beds have the potential to link disparate facies in a way that is not feasible with biostratigraphy or sequence stratigraphy alone. Geochemical fingerprinting of glass inclusions within volcanic quartz phenocrysts permits unambiguous matching of the compositionally unique ash layers. The resulting correlations demonstrate that time lines based on the graptolite biozones and transgressive-regressive facies patterns parallel the K-bentonite isochrons. They also demonstrate that much of the upper Trenton Group is older than previously believed and facies relations are markedly different from previous interpretations. Although some facies patterns appear to be synchronous across the region, the likely existence of substantial structural control on facies development in the basin suggests that it is unwise to attribute these patterns to eustatic sea-level changes.

Investigation of sedimentary successions and depositional structures from the post-abandonment phase of the Great Limestone Cyclothem (Upper Carboniferous), Stainmore, UK suggests that deposition occurred in a sand-dominated coastal setting. Recognition of sedimentary structures produced by storms and interpretation of palaeocurrent and palaeowave data indicate that a W-E oriented, southwardly prograding, high-energy shoreline system existed in the Stainmore region. Two equally plausible interpretations suggest that the trough cross-stratified facies lying towards the top of the shoreface succession may either represent: (1) upper shoreface deposits formed by high energy fairweather waves, or (2) the deposits of a tidally influenced deltaic distributary or incised valley fill estuarine system. These interpretations contrast significantly with the N-S oriented, transgressive barrier island model proposed in an earlier study. The sharp contact between lower shoreface and underlying offshore facies suggests that progradation of the shoreline occurred during a relative sea-level fall ('forced' regression). Palaeocurrent evidence indicates that deposition occurred within a system in which sediment was periodically flushed from a contemporary delta lobe and subsequently transported to the Stainmore shoreline by longshore currents.

Mineral assemblages and textures, illite 'crystallinity' indices and fluid inclusion data on dioctahedral smectite, a retrograde alteration product of chlorite in Permian-Triassic red slates of the Malaguide Complex in Sierra de Espuna, suggest sub-greenschist facies conditions that attained a minimum of 180 degrees centigrade in higher-grade tectonic unit, prior to smectite formation. Replacement of trioctahedral smectite is responsible for dioctahedral smectite.