comparative stratigraphy and subsidence history of mesozoic rift basins of north atlantic mesozoic rift basins around the north atlantic all possess many of the following upper jurassic to lower cretaceous oxfordian to albian stratigraphic elements 1 an early oxfordian hiatus 2 backfill deposits in upper jurassic paleovalleys 3 multiple tithonian transgressive regressive sequences 4 early berriasian regressive sequences 5 a sub valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates 6 valanginian to hauterivian fining upward sequences 7 condensed barremian sequences and 8 prominent aptian unconformities more local features include abrupt kimmeridgian deepening lusitanian basin portugal albian deepening cantabrian and aquitaine basins northern spain and southern france and late albian early cenom nian source rejuvenation cantabrian basin northern iberia decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence relatively high rates 50 100 m m y characterize onset of rift phases in the triassic and the kimmeridgian locally in the lusitanian basin of portugal kimmeridgian rates reach about 250 m m y in the cantabrian and aquitaine basins a third phase of rapid subsidence characterizes the aptian albian interval after the main phase of continental breakup around iberia this phase may be due to transtensional stresses as iberia continued to rotate relative to europe tensional intraplate stresses or gravity driven partial collapse of the new continental marg n the north atlantic mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of europe and north america pulses of extension generally are reflected in the stratigraphy of all of the basins superimposed on this record are the effects of eustatic sea level variations the main difference between the canadian jeanne d arc basin and iberian basins is the significantly greater early and middle jurassic basement subsidence rate in the former about 40 m m y vs 0 10 m m y this difference may result from prolonged extension on the canadian side perhaps due to northward transfer of shear stress from left lateral transform motion between the grand banks and northwestern africa

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

stratigraphy and facies architecture of the fluvial aeolian lacustrine sergi formation upper jurassic reconcavo basin brazil abstract the sergi formation encompasses an upper jurassic fluvial eolian lacustrine succession deposited within a wide intracratonic basin its sand bodies represent the largest and more important reservoirs in the reconcavo basin hosting 362 million m 3 of oil in place the main goal of this paper is to provide a detailed stratigraphic analysis of the sergi formation based on core and outcrop data it was achieved through the recognition and correlation of regional surfaces that have allowed the subdivision of this unit into distinct depositional sequences and the reconstruction of its depositional history the studied succession can be subdivided into three unconformity bounded sequences sequence i is composed of lacustrine mudstone at its base which is overlain by fine to medium grained sandstone related to aeolian dune and sand sheet and ephemeral fluvial stream deposits fluvial strata indicate northeastward flowing streams whereas aeolian dune deposits suggest the action of southwestward blowing winds the regional unconformity bounding sequences i and ii denotes both a climate change and tectonic rearrangement of the basin this surface delineates a change in the depositional style from fluvial aeolian lacustrine sequence i to entirely fluvial sequence ii the latter includes coarse grained to conglomeratic sandstone deposited within northwestward flowing braided channel belts changes in fluvial palaeocurrent from sequence i to ii indicate rearrangement of the drainage system related to basin tectonism furthermore a change in the fluvial discharge regime took place as a result of a change from a drier to a wetter climate fluvial deposition in sequence i was related to ephemeral streams whereas fluvial facies architecture of the sequence ii deposits indicates perennial braided streams with significant discharge variation another regional unconformity this time related to a stratigraphic base level fall and consequent widespread basinwide aeolian deflation separates the braided fluvial facies of sequence ii from the fine to medium grained sandstones ascribed to sheet floods aeolian dunes and aeolian sand sheets of sequence iii the resumption of aeolian sedimentation indicates a return to drier conditions in the basin the abrupt change from fluvial aeolian deposits to the lacustrine deposits of the overlying itaparica formation suggest a rapid rise of the water table and consequent basinwide flooding

quaternary alkalinity fluctuations recorded in rock varnish microlaminations on western u s a volcanics abstract rock varnish contains an alternating micron scale layering of manganese rich and manganese poor microchemical laminations holocene varnishes have lower mn fe ratios when exposed to alkaline environments and higher mn fe ratios when exposed to less alkaline environments this is consistent with abiotic and biotic mechanisms of varnish formation as alkalinity inhibits the concentration of manganese in both models mn fe variations with depth in varnishes in the western u s are interpreted as fluctuations in alkalinity or local microenvironmental influences if enough varnishes are sampled from different rocks in a region local effects can be ruled out k ar dating of volcanics in the coso cima lunar crater and crater flat volcanic fields in the western basin and range provide numerical age control throughout the quaternary and allow the number of alkalinity fluctuations to be assessed for given periods of time alkalinity fluctuations in varnishes are likely tied to fluctuations in the abundance of alkaline aerosols which are in turn related to fluctuations in the cover of water over playas and the cover of vegetation over soils microchemical laminations in varnish therefore have the potential to serve as an indicator of environmental fluctuations for the entire quaternary

hoanib river flood deposits of namib desert interdunes asanalogues for thin permeability barrier mudstone layers inaeolianite reservoirs abstract the ephemeral braided hoanib river of nw namibia ows for a few days ayear and only high discharges enable the river to pass through interdunaldepressions within the northern namib desert dune eld to the atlantic thedune eld comprises mainly large transverse dunes resulting frompredominant ssw winds river ood deposits between aeolian dunes areanalogous to mudstone layers conformably interbedded with ancientaeolianite dune foresets deep oods pond laterally to considerable depths metres to 10 m in adjacent interdunes depositing mud layers 1 50 cm toconsiderable heights on avalanche and stoss faces of bounding dunes fairlypassive ooding only disturbs aeolian strati cation minimally floodwaterclay in ltrates and settles as an impermeable seal with a ood pond on top perched above regional groundwater flood ponds evaporate slowly for longperiods 3 years early emergence desiccates higher parts of a mud layer subsequent oods can re ll a predecessor pond bene ting from the existingimpervious seal potential preservation of such mud layers is lower on thestoss face but high on the avalanche face after burial by subsequent dunereactivation and migration the leeward right hoanib bank a dune stoss face is river and wind eroded to exhume fossil interdune pond mud layers of anearlier hoanib channel the highly inclined layers are interbedded with duneavalanche foresets and represent the edges of two successive fossil pondsexposed in plan ancient ood pond mudstones occur in the permian triassichydrocarbon reservoir the sherwood sandstone group of the cheshire basin kinnerton formation and irish sea basin and were previously usederroneously to argue against the aeolian origin of cross bed sets hoanibstudies show that primary river interaction with a dune eld might preserveonly localized erosional omission surfaces in ancient aeolianites with littlesandy barform preservation prone to aeolian reworking around the main uvial channel locus however ood pond mudstone layers should form apredictable halo within which uid permeability will decrease keywords aeolian dunes aeolianite reservoir ash ood interdune namibdesert namibia permeability introductionhigh discharge oods of the hoanib river occa sionally break through the skeleton coast dune eld which forms part of the extensive namibdesert that parallels the western margin of thesouthern african subcontinent this arid regionis 140 km wide and over 2000 km long fromsouth western angola to the northern capeprovince south africa the northern namib dune eld termed the skeleton coast dune eld bywilson 1973 lancaster 1982 and ward sedimentology 2002 49 719 736

sedimentology of an ancient erg margin the lower jurassic aztec sandstone southern nevada and southern california the lower jurassic aztec sandstone is an aeolian deposited quartzose sandstone that represents the western margin of the southerly migrating navajo nugget sand sea or erg vertical and lateral facies relations suggest that the erg margin encroached upon volcanic highlands alluvial fan wadi and sabkha environments in southern nevada 700 m thick facies successions record the arrival of the aztec sand sea initial erg sedimentation in the valley of fire consists of lenticular or tongue shaped aeolian sand bodies interstratified with fluvially deposited coarse sandstone and mudstone above evaporite rich fine sandstone and mudstone are overlain by thick cross stratified aeolian sandstone that shows an upsection increase in set thickness the lithofacies succession represents aeolian sand sheets and small dunes that migrated over a siliciclastic sabkha traversed by ephemeral wadis these deposits were ultimately buried by large dunes and draas of the erg in the spring mountains a similar facies succession also contains thin lenticular volcaniclastic conglomerate and sandstone these sediments represent the distal margin of an alluvial fan complex sourced from the west thin aeolian sequences are interbedded with volcanic flow rocks ash flow tuffs debris flows and fluvial deposits in the mojave desert of southern california these aeolian strata represent erg migration up the eastern flanks of a magmatic arc the westward diminution of aeolian deposited units may reflect incomplete erg migration thin accumulation of aeolian sediment succeptible to erosion and stratigraphic dilution by arc derived sediment a two part division of the aztec erg is suggested by lithofacies associations the size and geometry of aeolian cross strata and sediment dispersal data the leading or downwind margin of the erg here termed the fore erg is represented by a 10 100 m thick succession of isolated pods lenses and tongues of aeolian deposited sediment encased in fluvial and sabkha deposits continued sand sea migration brought large dunes and draas of the erg interior into the study area these 150 500 m thick central erg sediments buried the fore erg deposits the trailing upwind margin of the erg is represented by back erg deposits in northern utah and wyoming

effect of precessional insolation changes on cretaceous climate and cyclic sedimentation the often striking presence of cyclical beddings has frequently been noted in cretaceous marine sediment deposits in many instances these beddings appear to have periodicities similar to those of the earth s orbit i e its precession obliquity and eccentricity variations in the primary deposition of ocean sediments are strongly linked to atmosphere land ocean interactions we report a set of numerical experiments using an atmospheric general circulation model that are designed to examine the sensitivity of mid cretaceous climate to insolation changes due to the precessional cycle we restrict attention to a single orbital parameter because most limestone black shale bedded sequences were deposited at low latitudes where precessional insolation variations predominate we varied systematically the precessional index between the maximum positive and negative values calculated over the last 2 m y and used mid cretaceous paleogeographic and paleotopographic reconstructions and zonally symmetric sea surface temperatures based on earlier work by barron and washington surface wetness and albedo values appropriate for grassland were prescribed uniformly over all land regions to capture the seasonality of precession we employed both perpetual january and perpetual july simulations changes in surface heating due to the imposed insolation anomalies resulted in a strong basically linear response of monsoonal circulations dominated by changes over the northern hemisphere the hydrologic cycle shows a significant response over many regions the low latitude proto south atlantic region varies from a strong net sink for water vapor excess precipitation to a strong source excess evaporation over the precession cycle this variation is consistent with an alternation between a stagnant stratified ocean basin with anoxic bottom water and an evaporative basin that produces bottom water that is warm saline and oxygenated the portion of the tethys ocean that overlays the limestone black shale sequences now found in present day italy does not exhibit comparable behavior but the reconstruction of orography and basin boundaries in this region is less known the simulations show however that as the monsoonal flow over south proto asia intensifies water vapor evaporated in this part of tethys is prevented from crossing the proto alps into the interior of the continent thereby remaining in the tethian drainage basin as a result central proto asia shifts between arid and moist conditions with precessional variations the water vapor budget over northeast africa varies systematically from zero seasonality to a marked wet dry seasonal cycle the deposition of eolian material can be inferred from a combination of continental aridity favorable mean wind directions and significant wind variances in our experiments the mean surface and upper winds often show a systematic response to precession but surface wind variances show a systematic response only in isolated regions our simulations do not provide a simple mechanism to explain the cyclicity in eolian deposition that has been reported for north central tethys

pin stripe lamination a distinctive feature of modern and ancient eolian sediments abstract pin stripe laminations are a distinctive feature of modern and ancient eolian sediments in sets of eolian ripple or translatent strata they represent deposition of silt and very fine sand in the troughs of the advancing wind ripples in sets of avalanche strata they probably result from the downward settling of fine sand and silt within the moving avalanche to the interface of moving and unmoving sands wind tunnel experiments suggest that pin stripe laminations can also form in grainfall deposits the textural segregation associated with deposition of the fine layers in most cases leads to early cementation along and near the finest sand and silt comprising the pin stripe lamination the pin stripe effect seen in outcrops is usually due to resistance to weathering along such cemented zones the cementation of the pin stripe laminations can occur early in the history of diagenesis and thus may provide clues to the post depositional history of the rock pin stripe laminations in many instances represent the sequestering of the small population of ultrafine sediment present in most eolian depositional systems they may prove useful in the recognition of ancient eolian sediments

lithostratigraphic hydrothermal and tectonic setting of the boundary volcanogenic massive sulfide deposit newfoundland appalachians canada formation by subseafloor replacement in a cambrian rifted arc the boundary volcanogenic massive sulfide vms deposit 0 5 mt 3 5 cu 4 zn 1 pb 34 0 g t ag in the tally pond group central newfoundland represents one of the best preserved subseafloor replacement style vms deposits in the northern appalachian orogen the deposit is hosted within a late cambrian 510 ma volcanic sequence consisting predominantly of rhyolitic flows and associated volcaniclastic rocks footwall strata are dominated by rhyolitic lapilli tuff tuffs lesser rhyolite flows and in situ rhyolite breccias the hanging wall consists of massive quartz bearing flow banded lobe and breccia facies rhyolite the deposit occurs at and below the contact between these two units and comprises pyrite chalcopyrite and lesser sphalerite and other minerals massive mineralization contains abundant clasts of the surrounding host rocks including chlorite sericite quartz altered rhyolite lapilli and ash hydrothermally altered rocks consist of variably intense chlorite with lesser sericite and quartz chlorite alteration occurs in a discordant geometry likely representing hydrothermal upflow zones and chlorite sericite quartz occur as blankets that are parallel to the volcanic stratigraphy likely representing alteration associated with replacement the hanging wall rhyolite flows also contain moderate to intense pervasive quartz and sericite alteration both the hanging wall and footwall are characterized by strong na2o sr depletions k2o mgo fe2o3 ba enrichments high alteration index values e g ba sr chlorite carbonate pyrite index ccpi alteration index ai and enrichments in base metals and volatile metals e g cu zn pb hg the presence of abundant remnant wall rock and host rock clasts within the ore intricate sulfide replacement of laminated porous tuff and sand dikes replacement fronts in host lithofacies and intense alteration in both the footwall and hanging wall where the hanging wall is preserved are all features consistent with formation of the bulk of the boundary deposit via subseafloor replacement the deposit likely formed as a result of cooling of metal bearing hydrothermal fluids mixing with ambient seawater and pore water entrained seawater within the volcanic rocks at a permeability interface between young unlithified highly permeable footwall volcaniclastic rocks and relatively impermeable hanging wall rhyolitic flows in our model this permeability boundary was an important feature that promoted subseafloor replacement within the deposit immobile element systematics of rhyolitic rocks from the boundary deposit lack major differences in primary petrochemistry between hanging wall and footwall strata all rocks from the deposit area are subalkalic with transitional zr y ratios 2 8 4 5 la sm ratios 1 normalized to upper crust and primitive mantle normalized signatures with slightly light rare earth element lree enriched patterns with flat heavy ree hree and negative nb ti and eu anomalies these geochemical features coupled with existing nd pb isotope data zircon inheritance patterns and geologic information are consistent with rhyolitic rocks at the boundary deposit having formed by re melting of arc basement with continental crust or recycled continental crust present in the source region it is likely that the deposit and its associated rhyolitic host rocks formed within a cambrian continental or pericontinental rifted arc along the margin of ganderia within the iapetus ocean

magnetic record of milankovitch rhythms in lithologically noncyclic marine carbonates rock magnetic variations record cyclicity within lithologically homogeneous basinal lime mudstones of the lower cretaceous san angel limestone northeastern mexico variations in ferromagnetic mineral concentrations as measured by anhysteretic remanent magnetization arm occur at frequencies consistent with milankovitch orbital rhythms magnetic mineral compositions grain size distributions and grain shapes from digested samples are congruent with far traveled atmospheric dust prevailing winds and the proximity of the cretaceous basin to an african eolian source support the encoding of orbitally modulated changes in wind intensity or source area aridity arm measurements offer great potential to calibrate the pace of depositional processes in carbonates and to investigate high frequency orbitally driven climate change in basinal strata throughout geologic time

fluvial response to late quaternary climate changes western india we review here the fluvial response to late quaternary climatic changes in the semi arid regions of western india i e the thar desert and its margins and maharashtra the rivers in the thar desert show a spectrum of environments from gravel bedload braided to ephemeral sand bed streams to sheet flows and sheet floods while those in the thar margin and maharashtra show dominantly two modes i e braided and meandering rivers the streams became defunct and aeolian sands were deposited during periods of relatively greater aridity in the thar desert and its margins incisions occurred during the wet phases in ois 1 it is inferred that changes in the monsoon precipitation led to relative changes in the discharge and sediment supply which were routed through those in the vegetation cover and played a key role in determining the fluvial style an inter comparison of the late quaternary alluvial deposits in the semi arid regions of western india suggests a continuum of fluvial environments interrelated through a precipitation gradient further a global comparison indicates that the response of semi arid western indian rivers was synchronous with the rivers in other climatic settings

reply sulphur isotope composition of the brunswick no 12 massive sulphide deposit bathurst mining camp new brunswick implications for ambient environment sulphur source and ore genesis the brunswick no 12 massive sulphide deposit occurs within a middle ordovician bimodal volcanic and sedimentary sequence that is thought to have formed in a continental back arc rift covered with a thick succession of carbonaceous hemipelagic and turbiditic sedimentary rocks the deposit consists of three en echelon lenses that are zoned from vent complex to bedded ore and bedded pyrite facies the bedded ore facies has the lowest average 34s values 14 2 but are only slightly less positive than laminated pyrite in footwall sedimentary rocks 34smean 15 1 34s values for the bedded sulphides show an upward increase from 14 2 in bedded ore to 16 5 in bedded pyrite average 34s values for vent complex 15 8 and underlying stringer sulphides 16 1 are consistently more positive than those for bedded ore in carbonaceous shales and siltstone of the patrick brook formation that underlie the deposit 34s values that range between 13 8 and 25 6 and the similarity of these values to those of the bru

jet efflux deposits of a subaqueous ice contact fan glacial lake rinteln northwestern germany abstract the coarse grained ice contact porta subaqueous fan delta complex was deposited in glacial lake rinteln at the margin of the saalian ice sheet that advanced south of the weser chains nw germany the ice proximal depositional system was up to 15 km long and 10 km wide the present study deals with ice proximal subaqueous fan deposits which are interpreted as products of a subcritical plane wall outflow jet that periodically passed into a supercritical jet with hydraulic jump the proximal facies assemblage consists of the coarse clast supported gravelly deposits of a hyperconcentrated high density effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment the intermediate facies assemblage attributed to the outflow jet proximal zone of flow transition is dominated by normally graded and cross stratified gravels with scour structures at their bases these gravels were deposited by a high density effluent capable of forming mouthbar like features these deposits pass downcurrent into an assemblage of planar parallel stratified and planar and trough cross stratified sands and pebbly sands partially interpreted as antidunes with abundant scour structures and intercalated layers of fine sand silt and silty mud attributed to the jet distal zone of flow transition the distal facies assemblage consists of trough cross stratified sands and pebbly sands and is attributed to the outflow jet proximal zone of established flow the sedimentary succession as a whole has wedge shape geometry with a gentle fan shaped inclination of the bedding from the southeast to the southwest repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow whereas the overall upward fining of the succession indicates a net decline of meltwater discharges

sulphur and lead isotope geochemistry of sulphide minerals from the zn pb cu ag au lemarchant volcanogenic massive sulphide vms deposit newfoundland canada abstract the lemarchant zn pb cu ag au volcanogenic massive sulphide vms deposit in the newfoundland appalachians canada is an important example of a precious metal bearing vms deposit the deposit contains vms and sulphosalt rich mineral assemblages which are paragenetically distinct initial zn pb sulphosalt mineralization was deposited from low temperature 300 c less oxidized hydrothermal fluids with lower sulphur activity in situ microanalyses of pyrite chalcopyrite and galena yield a wide range of 34s values 6 4 to 15 1 sulphides from paragenetically early lower temperature zn pb sulphosalt assemblages have the lowest average 34s values 4 6 whereas the highest 34s values occur in the late stage high temperature cu rich sulphide assemblages variability in 34s occurs in all styles of mineralization and is consistent with s derived from thermochemical reduction of seawater sulphate igneous leaching and potentially disproportionated magmatic so2 although it is difficult to distinguish explicitly between leached igneous and magmatic sources of sulphur mineralogical and geochemical data from lemarchant suggest a possible contribution of magmatic so2 during the deposition of epithermal style mineralization at the earlier stages of deposit formation lead isotope compositions of galena show little variability with style of mineralization suggesting similar pb sources throughout ore deposition most pb at lemarchant is derived from underlying neoproterozoic sandy brook group volcanic rocks with potential input of juvenile pb from the lake ambrose basaltic rocks of the tally pond group and or from more juvenile neoproterozoic basement rocks

complex holocene lunette dune development south africa implications for paleoclimate and models of pan development in arid regions closed depressions pan or playa basins are very common landscape features in arid or formerly arid regions many have associated downwind dune assemblages lunettes that have been explained in terms of deflation of sediments from the basin these widespread features have also been used as proxies of late quaternary rainfall and atmospheric circulation change we use a detailed program of optically stimulated luminescence dating at witpan south africa to show that lunette construction may be rapid and spatially complex this study presents 33 ages from 9 sample sites on the dune that show how accumulation of the present dune largely occurred over the past 2 k y but with marked sectoral variability in accumulation rates and timing variability is attributed largely to local sediment supply factors geochemical analysis shows that primary deflation from the pan has not contributed significantly to the construction of much of the current lunette most sand is derived from recycling of older lunette sediments preserved today at only a few locations and from neighboring linear dunes these findings if representative of lunettes in other localities have marked implications for the types of paleoclimatic information that these features may yield

annual monsoon rains recorded by jurassic dunes pangaea the largest landmass in the earth s history was nearly bisected by the equator during the late palaeozoic and early mesozoic eras modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality1 2 3 but direct evidence for annual rainfall periodicity has been lacking4 in the mesozoic era about 190 million years ago thick deposits of wind blown sand accumulated in dunes of a vast low latitude desert at pangaea s western margin5 6 7 these deposits are now situated in the southwestern usa here we analyse slump masses in the annual depositional cycles within these deposits which have been described for some outcrops of the navajo sandstone8 twenty four slumps which were generated by heavy rainfall appear within one interval representing 36 years of dune migration we interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains with the other four having been the result of winter storms the slumped lee faces of these jurassic dunes therefore represent a prehistoric record of yearly rain events

formation of volcanogenic massive sulfide deposits the kuroko perspective abstract the main objective of this paper is to identify the geochemical hydrological igneous and tectonic processes that led to the variations in the physical size geometry and chemical mineralogy metal ratios and zoning characteristics of volcanogenic massive sulfide deposits with respect to space from a scale of mining district size area to a global scale and time from a all volcanogenic massive sulfide deposits vmsds appear to have formed in extensional tectonic settings such as at mid ocean spreading centers backarc spreading centers and intracontinental rifts and failed rifts all vmsds appear to have formed in submarine depressions by seawater that became ore forming fluids through interactions with the heated upper crustal rocks submarine depressions especially those created by submarine caldera formation and or by large scale tectonic activities e g rifting become most favorable sites for the formation of large vmsds because of hydrological physical and chemical reasons the fundamental processes leading to the formation of vmsds include the following six processes 1 1 intrusion of a heat source typically a 10 3 km size pluton into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton the radius of a circulation cell is typically 5 km the temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350 c and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years the majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity 2 2 reactions between low temperature t 2 4 as disseminated gypsum and anhydrite in the country rocks 3 3 reactions of the modified seawater with higher temperature rocks at depths during the waxing stage cause the transformation of the seawater to metal and h 2 s rich ore forming fluids the metals and sulfide sulfur are leached from the county rocks the previously formed gypsum and anhydrite are reduced by fe 2 bearing minerals and organic matter providing additional h 2 s the mass of high temperature rocks that provide the metals and reduced sulfur is typically 10 11 tons 40 km 3 in volume the roles of magmatic fluids or gases are minor in most massive sulfide systems except for so 2 to produce acid type alteration in some systems 4 4 reactions between the ore forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores 5 5 mixing of the ore forming fluids with local seawater within unconsolidated sediments and or on the seafloor causes precipitation of primitive ores with the black ore mineralogy sphalerite galena pyrite barite anhydrite 6 6 reactions between the primitive ores with later and hotter hydrothermal fluids cause transformation of primitive ores to matured ores that are enriched in chalcopyrite and pyrite variations in the mineralogical and elemental characteristics the geometry and the size of submarine hydrothermal deposits are controlled by the following four parameters 1 a the chemical and physical characteristics of seawater composition temperature density which depend largely on the geographical settings e g equatorial evaporating basins 2 b the chemical and physical characteristics of the plumbing system lithology fractures 3 c the thermal structure of the plumbing system which is determined largely by the ambient geothermal gradient and the size and temperature of the intrusive and 4 d the physical characteristics of the seafloor depth basin topography for example the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in pb and ba compared to those developed in felsic plumbing systems the lower temperature systems are generally poorer in sulfides but richer in iron oxides and sulfates the higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores contrasts in the metal ratios between the noranda type archean vmsds and the younger vmsds reflect the differences in the geothermal gradient of the plumbing systems the submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins the basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history from at least 3 5 billion year ago to the present

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

the duck pond and boundary cu zn deposits newfoundland new insights into the ages of host rocks and the timing of vhms mineralization the duck pond cu zn pb ag au deposit in newfoundland is hosted by volcanic rocks of the cambrian tally pond group in the victoria lake supergroup in conjunction with the nearby boundary deposit it contains 4 1 million tonnes of ore at 3 3 cu 5 7 zn 0 9 pb 59 g t ag and 0 9 g t au the deposits are hosted by altered felsic flows tuffs and volcaniclastic sedimentary rocks and the sulphide ores formed in part by pervasive replacement of unconsolidated host rocks u pb geochronological studies confirm a long suspected correlation between the duck pond and boundary deposits which appear to be structurally displaced portions of a much larger mineralizing system developed at 509 3 ma altered aphyric flows in the immediate footwall of the duck pond deposit contained no zircon for dating but footwall stringer style and disseminated mineralization affects rocks as old as 514 3 ma at greater depths below the ore sequence unaltered mafic to felsic volcanic rocks that occur structurally above the o

the role of granites in volcanic hosted massive sulphide ore forming systems an assessment of magmatic hydrothermal contributions assessment of geological geochemical and isotopic data indicates that a significant subgroup of volcanic hosted massive sulphide vhms deposits has a major or dominant magmatic hydrothermal source of ore fluids and metals this group which is typically characterised by high cu and au grades includes deposits such as those in the neoarchean doyon bousquet laronde and cambrian mount lyell districts these deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones in many of these deposits 34ssulphide is low with a major population below 3 34ssulphate differs from coexisting seawater and 34ssulphate sulphide 20 30 these characteristics are interpreted as the consequence of disproportionation of magmatic so2 as magmatic hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic hydrothermal contribution other characteristics that we consider diagnostic of significant magmatic hydrothermal input into vhms ore fluids include uniformly high 3 times modern seawater values salinities or very 18o enriched 18o 5 ore fluids we do not consider other criteria e g variable salinity moderately high 18ofluid 2 5 34ssulphide near 0 metal assemblages or a spatial association with porphyry cu or other clearly magmatic hydrothermal deposits that have been used previously to advocate significant magmatic hydrothermal contributions to be diagnostic as they can be produced by non magmatic processes known to occur in vhms mineral systems however in general a small magmatic hydrothermal contribution cannot be excluded in most vhms systems considered conclusive data that imply minimal magmatic hydrothermal contributions are only available in the paleoarchean panorama district where coeval seawater dominated and magmatic hydrothermal systems appear to have been physically separated this district which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages is typical of many vhms deposits around the world suggesting that for garden variety vhms deposits a significant magmatic hydrothermal contribution is not required other than deposits associated with advanced argillic alteration assemblages the only deposit for which we ascribe a major magmatic hydrothermal contribution is the devonian neves corvo deposit this deposit differs from other deposits in the iberian pyrite belt and around the world in being extremely sn rich with the sn closely associated with cu and in having formed from high 18o rich fluids 18ofluid 8 5 we consider these characteristics particularly the last as diagnostic of a significant magmatic hydrothermal contribution our analysis indicates that two subgroups of vhms deposits have a major magmatic hydrothermal contribution cu au rich deposits with aluminous alteration assemblages and reduced very sn rich deposits in which sn was introduced in a high temperature ore assemblage comparison with normal vhms deposits suggests that these subgroups of vhms deposits may form in specialised tectonic environments the cu au rich deposits appear to form adjacent to magmatic arcs an environment conducive to the generation of hydrous oxidised melts by melting metasomatised mantle in the wedge above the subducting slab this contrasts with the back arc setting of normal vhms deposits in which relatively dry granites in this contribution we use the term granite sensu latto formed by decompression melting drive seawater dominated hydrothermal circulation the tectonic setting of highly sn rich vhms deposits such as neves corvo is less clear however thick continental crust below the ore hosting basin may be critical as it is in other sn deposits

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

development and environmental significance of an eolian sand ramp of last glacial age central iran abstract a 25 m thick section of mostly eolian sediment is exposed in the stream cut flank of a sand ramp accumulated in a mountain saddle near ardakan playa central iran the well sorted eolian sediments of the ramp contain talus beds and incipient paleosols morphology and bedding structures imply that southeasterly winds were primarily responsible for deposition of the eolian sand optical dating shows that the sand was deposited near the last glacial maximum within about 5000 yr surface stabilization lack of surface scree and the development of a stream cut between the mountain and the ramp show that sediment accumulation ceased after this time the siberian high pressure system may have been established over central iran during the last glacial maximum causing cooler temperatures and a prevalence of southeasterly winds these colder windier conditions would have led to frost shattering and eolian transport both of which are not significant processes today but which are evident as past processes from the ramp sediments

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

eustatic and climatic controls on the development of the wahiba sand sea sultanate of oman aeolian sand sea accumulations can serve as valuable archives of climate change in continental environments the wahiba sand sea is situated at the northern margin of the area presently affected by indian summer monsoon circulation and it records environmental changes associated with this major climatic boundary over the last 160 000 years the internal stratigraphy and evolution of the sand sea is investigated using a combination of outcrop borehole seismic and luminescence data proximity to the indian ocean means that the sand sea succession shows the influence of sea level changes on the sedimentary architecture and composition of the dune deposits during the last two glacial periods low global sea level was associated with a high input of bioclastic grains reflecting the significance of subaerially exposed shelf areas as one of the main sources of aeolian sediment the onset of aeolian sediment transport and deposition was related to the breakdown of stabilizing vegetation during arid periods that equate with sea level lowstands the preservation of aeolian sediments by the formation of supersurfaces and associated palaeosoils took place during times of increased wetness and elevated groundwater tables this interplay of constructive and destructive periods greatly influenced the sedimentary architecture oscillations of wet and dry periods between 160 000 and 130 000 years and 120 000 105 000 years ago are attributed to the evolution of a wet aeolian system younger periods of aeolian deposition around and after the last glacial maximum were characterized by dry aeolian conditions no soil horizons developed during these times

periodic accumulation and destruction of aeolian erg sequences in the permian cedar mesa sandstone white canyon southern utah usa the permian cedar mesa sandstone represents the product of at least 12 separate aeolian erg sequences each bounded by regionally extensive deflationary supersurfaces facies analysis of strata in the white canyon area of southern utah indicates that the preserved sequences represent erg centre accumulations of mostly dry though occasionally water table influenced aeolian systems each sequence records a systematic sedimentary evolution enabling phases of aeolian sand sea construction accumulation deflation and destruction to be discerned and related to a series of underlying controls sand sea construction is signalled by a transition from damp sandsheet ephemeral lake and palaeosol deposition through a phase of dry sandsheet deposition to the development of thin chaotically arranged aeolian dune sets the onset of the main phase of sand sea accumulation is reflected by an upward transition to larger scale ordered sets which represent the preserved product of climbing trains of sinuous crested transverse dunes with original downwind wavelengths of 300 400 m regularly spaced reactivation surfaces indicate periodic shifts in wind direction which probably occurred seasonally compound co sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger slipfaceless draa each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio eustatic origin that characterize many permo carboniferous age successions sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level the main sand supply being former shallow marine shelf sediments that lay to the north west sand sea deflation and destruction would have commenced at or shortly after the time of maximum aridity as the available sand supply became exhausted restricted episodes of non aeolian accumulation would have occurred during humid interglacial phases accumulation and preservation being enabled by slow rises in the relative water table subsidence analysis within the paradox basin together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the cedar mesa erg sequences could be the product of 413 000 years so called long eccentricity cycles by contrast annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the cedar mesa succession was reserved for supersurface development

quaternary sandstones northeast jordan age depositional environments and climatic implications abstract osl dating of weakly consolidated root bound non calcareous quartz arenites in northeast jordan currently assigned to the plio pleistocene azraq formation suggests a middle pleistocene 652 47 ka age the sandstones are up to 15 5 m thick and overlain by a 2 5 m thick holocene gypcrete caprock facies and textural analyses suggest that the sandstones are predominantly aeolian in origin mainly derived from tertiary sediments exposed close to the depositional site the sands were transported by the prevailing nw winds and deposited in a broad relatively flat sand sheet environment rhizoliths occur throughout the sandstones mainly as long downward tapering vertical tap roots rarely branched and with few laterals microscopic examination of root cores replaced by carbonate reveals the presence of alveolar fabrics possible needle fibre calcite calcified organic filaments of fungal root vessel and root hair origins characteristic of low magnesium beta calcretes typical of humid climates morphologically the roots resemble modern shrub like species typical of desert environments where water availability at the surface and in the subsurface was sufficient to support an effective vegetation cover plots of stratigraphic variations in root length root spacing and root frequency reflect temporal variations in the water table level and precipitation during sand deposition all three parameters show a similar crude cyclicity consistent with fluctuations in the level of the water table with the most moist phase beneath the predominantly waterlain holocene gypcrete when trees appeared for the first time the gypcrete signifies a change to temporary wetter conditions and may mark the boundary between the pleistocene and holocene in this area although pedogenic horizonation is poorly developed especially in desert sands the beta calcretes and rhizocretions typically form within active soil zones soils do not form where rainfall is

neoproterozoic and cambrian arc magmatism along the eastern margin of the victoria lake supergroup a remnant of ganderian basement in central newfoundland abstract the eastern margin of the composite and structurally complex victoria lake supergroup has previously been mapped where the silurian rogerson lake conglomeratic rocks unconformably overlie cambrian tally pond volcanic rocks however the recognition that the form of this contact changes between an unconformity and a brittle ductile fault in conjunction with the neoproterozoic age of the crippleback intrusive suite dictate that the above interpretation of the nature of this margin requires revision these discrepancies are resolved by the recognition of a neoproterozoic largely bimodal volcanic sequence sandy brook group which is unconformably overlain by rogerson lake rocks to the east with these combined units in fault contact with the tally pond group to the west the sandy brook group and crippleback intrusive suite form a terrane of ca 563 ma rocks with continental arc like geochemical signatures the distinctly negative nd 563 values for the felsic rocks mean 3 of this terrane imply derivation from a crystalline basement older than the largely pan african crust that underlies contemporaneous volcanic rocks in west avalonia but similar to that inferred for the gander zone thus this terrane is likely to be the leading edge of the peri gondwanan microcontinent ganderia the ca 511 ma tally pond group arc magmatism represent some of the oldest products of iapetean subduction in newfoundland although the tally pond group are only observed to be in fault contact with the ca 50 million year older sandy brook group the high proportion of felsic volcanic rocks sandy brook crippleback age inherited zircons and pb isotopic data all support the inference that the tally pond group was formed on sandy brook crippleback continental crust

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

windblown desert sands in coeval shallow marine deposits a key for the recognition of coastal ergs in the mid cretaceous iberian basin spain introductionthe action of the wind in ancientsedimentary records is commonlybased on the direct observations ofdune and interdune deposits within ahierarchy of aeolian bounding surfa ces a direct observation of ancientaeolian systems is not always possibleas they are prone to erosion and to theremoval of sand into other uvial andmarine systems although the aeoliandeposits may no longer be present their former existence can be inferredon the basis of grain size characteris tics and aeolian features on grainsurfaces aeolian sediments indeedconstitute an important source formarine deposits kukal and saadal lah 1973 fryberger et al 1983 widespread ne grained very well sorted quartz sandstones characterizeshallow marine facies in the mid cre taceous of the eastern spain iberianbasin the good sorting and round ness of the grains hint at the presenceof a nearby erg system suggestive ofan arid climatic zone along the west ern tethyan margin during the mid cretaceous geological settingthe mesozoic iberian basin along thewestern tethyan margin has one ofthe more complete lower middle cre taceous sedimentary records in eur ope the iberian range is a nw sestriking intraplate fold belt generatedby the tectonic inversion of theiberian basin during the palaeogene fig 1a b salas and casas 1993 capote et al 2002 this basin wasformed by crustal thinning duringthe late permian triassic and latejurassic early cretaceous rift stages salas and casas 1993 arche andlo pez go mez 1996 during thesecond rift stage extensional sub basins were formed as part of thelarger maestrazgo basin i e the east ern sector of the iberian basin fig 1b soria 1997 sands of boththe last synrift unit of these sub basins the escucha formation and of the rst post rift unit of the iberian basin the utrillas formation were depos ited across the estuarine deltaic and uvial environments fig 1c quer ol et al 1992 the sands are domi nantly ne grained show excellentsorting and as they consist almostpurely of quartz they are mineralog ically very mature the escucha and the utrillasformationsthe upper aptian middle albian es cucha formation aguilar et al 1971 sole de porta et al 1994 fig 1c was formed during the last phases ofthe second rift stage that a ected theiberian basin salas and casas 1993 it is a tidally in uenced heterolithicunit dominated by very well sorted ne sand and clay with coal bearingdepositsinitslowerpart andlocallyinthe basal part coarse grained siliciclas tic levels it lies upon the limestonesand marls of the urgonian platform aptian and is covered by sandstonesof the utrillas formation fig 1c pardo 1979 querol 1990 the es cucha formation was interpreted as adeltaic estuarine succession querolet al 1992 with a barrier island sys tem in the northern part of the olietesub basin rodri guez lo pez et al 2005 it was deposited in extensionalsub basins bounded by palaeogeo graphic thresholds produced by listricand block rotation faults the utrillasformation overlies the escucha for mation and is late albian early cen omanian in age and represents uvialdeposits pardo 1979 however theabstract

the latitudinal gradient of shell ornament a case study from changhsingian late permian brachiopods abstract although there have been many studies of biological patterns along latitude less attention has been paid on how latitude might affect the large scale spatial patterns of ornament among shelled invertebrate organisms based on a newly designed set of four quantitative metrics of shell ornaments and the measurement and quantification of shell ornaments from 2654 changhsingian late permian brachiopods representing 702 species spanning 80 south to 30 north in paleolatitude this paper analyzes the relationship between the degree of shell ornament development of changhsingian brachiopods and paleolatitude for the first time we report the presence of statistically significant latitudinal gradient patterns in the development of a multitude of brachiopod shell ornament types for the permian generally characterized by the tendency of an increased proportion of brachiopods with more complicated and stronger ornament towards the paleotropics the gradient pattern is manifested not only in the individual types of ornament e g radial ornament body spines but also pronounced when all the studied ornament types are integrated and analyzed together two scenarios are offered to account for the latitudinal gradient of changhsingian brachiopod shell ornaments first in consistency with most previous similar studies the latitudinal gradient of brachiopod shell ornament is explained by g vermeij s escalation theory in that shell ornaments are regarded as defence apparatuses against predation and that shell ornament of changhsingian brachiopods is interpreted to have become stronger and more elaborate in lower paleolatitudes as an adaptive response to the progressively increased predation pressure towards the paleotropics second the latitudinal gradient pattern of changhsingian brachiopod shell ornaments could also be explained by the varied calcification rate in the oceans as a function of the latitudinal temperature gradient the caco3 solubility is known to increase in colder high latitude areas this means it is more difficult for marine organisms to extract calcium carbonate to generate their shells in higher latitudes consequently resulting in less developed ornament for shelled marine benthic organisms living in colder water habitats this second interpretation potentially complements and extends the g vermeij s escalation theory in explaining the observed latitudinal gradients of changhsingian brachiopod shell ornaments but the theory itself requires both experimental and empirical testing with respect to living shelled marine invertebrates and their production of shell ornament

origin of the eskay creek precious metal rich volcanogenic massive sulfide deposit fluid inclusion and stable isotope evidence the eskay creek deposit is an unusual polymetallic au ag rich volcanogenic sulfide sulfosalt deposit located in the iskut river area of northwestern british columbia canada economic concentrations of precious and base metals are contained in the 21 zone which is divided into a number of subzones as of december 31 1998 total production and proven probable reserves are 1 9 million tons mt at 60 2 g t au 2 652 g t ag 3 2 percent pb 5 2 percent zn and 0 7 percent cu the 21b zone which contains the bulk of the reserves began production in 1995 the mineralization occurs mainly as well preserved stratiform clastic beds of sulfide sulfosalt debris and also as discordant footwall quartz sulfide veins the hydrothermal system that formed the eskay deposit was low temperature

preservation of pre vegetational mixed fluvio aeolian deposits in a humid climatic setting an example from the middle proterozoic eriksfjord formation southwest greenland abstract sedimentological studies of a 30 m thick coastal cliff section within the middle proterozoic eriksfjord formation in western south greenland reveals three distinct types of fluvial sand sheet deposits that reflect perennial streams type i semi perennial streams type ii and ephemeral flash floods type iii perennial river sand sheets are characterised by co sets of medium scale trough cross beds interbedded with isolated medium and large scale high angle tabular cross beds indications of desiccation or subaerial exposure are absent semi perennial fluvial sand sheets consist predominantly of low angle cross beds interbedded with isolated sets of high angle tabular cross beds with common reactivation surfaces horizontal lamination and climbing ripple lamination form subordinate structures associated with the sand sheets are adhesion structures and 0 05 0 4 m thick sets of wind ripple lamination indicating periods of subaerial exposure and aeolian reworking high energy ephemeral flash flood sand sheets consist almost exclusively of planar parallel lamination and climbing ripple lamination with some isolated sets of low angle cross bedding scouring and internal truncation surfaces are common the three types of sand sheets are considered to reflect deposition under changing climatic conditions varying from humid to arid or semi arid aeolian deposits are preserved within the sand sheets showing characteristics of dominantly perennial flow punctuated by shorter periods of desiccation type ii while sand sheets showing features typical of arid and or semi arid flow conditions type iii contain no preserved aeolian deposits this selective preservation is interpreted to be a result of the combined effect of groundwater table level and fluvial style which in turn are inferred to have been controlled by the climatic regime the deposits show that during pre vegetational times the preservation of aeolian deposits under certain conditions may be more optimal in fluvial systems formed in a humid climate than in fluvial systems formed under semi arid or arid circumstances the occurrence of aeolian deposits within a precambrian succession of fluvial deposits therefore need not be an indication of the most arid environmental conditions

australian volcanic hosted massive sulfide deposits features styles and genetic models the cambro ordovician period has yielded the major development of volcanic hosted massive sulfide vhms deposits in australia resulting in about 12 million metric tons of contained metal copper lead and zinc concentrated in the mount read volcanics tasmania and the mount windsor volcanics queensland the archean 4 million metric tons of metal and the silurian 3 5 million metric tons of metal constitute the next important episodes while the devonian and permian have produced isolated deposits the deposits range from cu type to zn cu type to zn pb cu type the zn cu type deposits are restricted to the archean and silurian whereas the cu type and zn pb cu type occur sporadically throughout the time span from early archean to permian in general terms the major vhms bearing districts are calc alkaline in character and display a thick basal pile of rhyolitic volcanics 1 3 km thick including lavas epiclastics and subvolcanic intrusions which is overlain by a polymodal sequence containing various proportions of rhyolite dacite andesite basalt and sediments the major deposits are commonly located at the top contact of the rhyolite pile or within the lower part of the overlying polymodal sequence there is a wide range in variability of styles of australian vhms deposits including mounds pipes sheets layered deposits stacked deposits stockwork and disseminated deposits distal reworked deposits and cyclic layered deposits although these various styles show a range of features there is a consistent theme across the spectrum of metal zonation alteration mineralogy alteration chemistry sulfur isotopes macrotextures microtextures and host volcanic relationships which strongly suggests that they all belong to the one genetic group of ore deposit the classic mound style deposits such as hellyer have a series of key features subsets of which are represented in the other deposit styles the mound deposits are considered to form from deposition of metal sulfides on the sea floor immediately around the hydrothermal vent growth of the mound occurs by upward replacement of sulfide assemblages stable at higher fluid temperatures leading to zone refining and lead zinc silver gold enrichment in the outer and upper parts of the mound departure from the classic mound style of deposit is related principally to three key factors the chemistry of the ore fluid salinity temperature f02 and ah2s the nature permeability and chemistry of the volcanic pile and the sea hoor environment sea hoor topography and seawater depth these factors control the aspect ratio of the deposit the extent of stringer zone development the degree of subsea floor replacement mineralization the nature and spatial development of footwall alteration and the development and style of related distal mineralization sulfur isotope studies of australian vhms deposits indicate that reduced seawater sulfate is a major source of sulfur in the deposit whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks this conclusion is supported by the application of various leaching models which demonstrate the availability of an adequate source of both base and precious metals in the footwall volcanic sequences the input of metals directly from volcanic magma chambers is not precluded by the available data and one likely scenario involves the contribution of gold and copper from a magmatic vapor plume rising to mix with convective seawater fluids which contribute lead zinc silver and gold leached from the footwall volcanics and basement rocks the relative importance of the magmatic input compared with the seawater convective input may help to explain the spectrum of deposit styles arid their spatial relationship to volcanic centers or adjacent sedimentary basins

depositional facies paleogeography and palaeoclimatology of the lower jurassic mccoy brook formation fundy rift basin nova scotia the mccoy brook formation is a 230 m sequence of redbeds of early jurassic age that accumulated in the subtropical fundy rift basin the basin was asymmetrical bordered on the northern side by the cobequid fault system and adjacent highlands the formation is a mosaic of terrestrial facies a multi and single storey fluvial sandstones were deposited by rivers that collected drainage from the norhern highlands and flowed southwest across the valley floor b graded bed sequences of sandstone mudstone were deposited by flood events on the fluvial floodplains and the margins of playas c interbedded sandstones and finely laminated to disrupted red mudstones represent deposits of interfingering sandflats at the toes of alluvial fans and playas respectively the fabrics of both lithologies are commonly disrupted by desiccation and intrastratal precipitation of calcite and minor gypsum d plane bedded conglomerate and pebbly sandstone record deposition in shallow channels that traversed alluvial fans e non bedded breccias of basalt boulders up to 8 m in size in a sand to mud matrix formed as talus against palaeocliffs of the lower jurassic north mountain basalt the palaeocliffs resulted from synsedimentary faulting within the basin f basalt conglomerate beds with matrix to clast supported fabrics comprise sequences deposited by debris flows probably generated by remobilization of talus g a thin sequence of limestone siltstone and muddy sandstone containing fish scales and bones formed in a shallow lake on a basalt flow h sandstones containing m scale crossbeds and a three fold hierarchy of erosional surfaces accumulated as barchans and barchanoid transverse ridges that moved southwest in the valley all of these facies occur within an area of 18 km2 located south of the fault bounded highlands synsedimentary faulting within the basin during early deposition of the mccoy brook formation created palaeocliffs of north mountain basalt talus and debris flow deposits accumulated adjacent to these cliffs interfingering with eolian fluvial and lacustrine sediments during later deposition of the mccoy brook formation the early fault controlled topography was buried as alluvial fans prograded southward from the highlands broad sandflats extended basinward from the toes of the fans interfingering with playa mudflats on the valley floor the palaeoclimate was semi arid as evidenced by gypsum bearing playa redbeds eolian sandstones and caliche palaeosols

coastal aeolian dune development solheimasandur southern iceland abstract a coastal aeolian dune field on the distal parts of solheimasandur southern iceland is currently undergoing active construction ongoing sand deflation in the foreshore is demonstrated by the preservation of sand ridges in the downwind lee of obstacles while a backshore sandsheet is characterised by actively accumulating long wavelength wind ripples the main region of aeolian accumulation is in the immediate backshore where sand has accumulated to a thickness of up to 8 m and is largely stabilized by vegetation surrounding interdune areas have undergone repeated flooding by fluvial incursions from the adjacent jokulsa river and are characterised by mud drapes which lap against the lower flanks of neighbouring dunes widespread sand adhesion structures testify to the often damp nature of the substrate over 1200 vegetated and stabilized dunes nebkhas occupy a 5 km 2 area of wind deflated gravel sandur plain downwind from the main site of aeolian accumulation the nebkhas show strong relationships between plan form shape and height indicating that they have attained equilibrium morphology for the prevailing climatic conditions within the nebkha field dunes demonstrate a predictable downwind decrease in height spatial concentration and degree of sand stabilization a time series of aerial photographs documents the temporal evolution of the dune field and demonstrates that aeolian accumulation commenced about 1940 and has been ongoing to the present day prior to 1940 repeated outburst floods associated with catastrophic lake drainage events from the solheimajokull glacier 8 km inland were of sufficient magnitude to repeatedly destroy any incipient aeolian bedforms that developed although strong onshore winds and high rates of sediment supply promote aeolian sediment transport dune field development is rare in humid boreal and sub arctic climates as encountered in southern iceland because the availability of sediment for aeolian transport is usually severely limited by damp substrate conditions thus the airflow tends to be undersaturated with respect to its potential sand transporting capacity and dune construction can only occur because of the stabilizing influence of vegetation

sedimentary record of erg migration the sedimentary record of erg eolian sand sea migration consists of an idealized threefold division of sand sea facies sequences the basal division here termed the fore erg is composed of a hierarchy of eolian sand bodies contained within sediments of the flanking depositional environment these sand bodies consist of eolian strata deposited by small dune complexes zibars and sand sheets the fore erg represents the downwind leading edge of the erg and records the onset of eolian sedimentation basin subsidence coupled with erg migration places the medial division termed the central erg over the fore erg strata the central erg represented by a thick accumulation of large scale cross stratified sandstone is the product of large draa complexes eolian influence on regional sedimentation patterns is greatest in the central erg and most of the sand transported and deposited in the erg is contained within this region reduction in sand supply and continued erg migration will cover the central erg deposits with a veneer of back erg deposits this upper division of the erg facies sequence resembles closely the fore erg region similar types of eolian strata are present and organized in sand bodies encased in sediments of the upwind flanking depositional environment s back erg deposits may be thin due to limited eolian influence on sedimentation or incomplete erg migration or they may be completely absent because of great susceptibility to postdepositional erosion tectonic climatic and eustatic influences on sand sea deposition will produce distinctive variations or modifications of the idealized erg facies sequence the resulting variants in the sedimentary record of erg migration are illustrated with ancient examples from western north america europe southern africa and south america

late cenozoic fluvial successions in northern and western india an overview and synthesis abstract late cenozoic fluvial successions are widespread in india they include the deposits of the siwalik basin which represent the accumulations of the ancient river systems of the himalayan foreland basin palaeomagnetic studies reveal that fluvial architecture and styles of deposition were controlled by himalayan tectonics as well as by major climatic fluctuations during the long 13 ma span of formation the indo gangetic plains form the world s most extensive quaternary alluvial plains and display spatially variable controls on sedimentation himalayan tectonics in the frontal parts climate in the middle reaches and eustasy in the lower reaches close to the ganga brahmaputra delta climatic effects were mediated by strong fluctuations in the sw indian monsoon and himalayan rivers occupy deep valleys in the western ganga plains where stream power is high cut in part during early holocene monsoon intensification the broad interfluves record the simultaneous aggradation of plains fed rivers since 100 ka the eastward increase in precipitation across the ganga plains results in rivers with low stream power and a very high sediment flux resulting in an aggradational mode and little incision the river deposits of semi arid to arid western india form important archives of quaternary climate change through their intercalation with the eolian deposits of the thar desert although the synthesis documents strong variability both spatial and temporal in fluvial stratigraphy climatic events such as the decline in precipitation during the last glacial maximum and monsoon intensification in the early holocene have influenced fluvial dynamics throughout the region

lateral variability of ancient seismites related to differences in sedimentary facies the synrift escucha formation mid cretaceous eastern spain abstract lateral extent and continuity of deformation has been used as criterion for the recognition of a seismic origin of soft sediment deformations particular problems are posed by ancient seismites developed in deposits that show lateral variability of sedimentary facies in such a context the lateral continuity of deformation will depend on the lateral variability of physical properties of sediments that ultimately results in the lateral variability of seismites in a single deformation event a variety of decimetre scale soft sediment deformation structures occurs in the synrift escucha formation late aptian middle albian in teruel spain these structures which include pseudonodules ball and pillow structures slumps water escape structures multi phase deformed structures folds sagging like structures and synsedimentary faults were developed contemporaneous to the formation of dark grey silty mudstones and grey clayey siltstones in a shallow marine environment the soft sediment deformation is constrained to a 1 2 m thick horizon exposed in four outcrops consisting of quiet water mudstones and heterolithic storm deposits the deformed horizon can be sub divided into two parts each reflecting a deformation event that affected both cohesive and granular non cohesive sediments the deformed structures occur in the vicinity of the gargallo normal growth fault which is several kilometres long activity along this fault controlled the facies distribution of the unit bearing soft sediment deformations high energy facies were located in the fault tip while low energy facies developed in both the down tilted hanging wall and footwall blocks in addition fault induced shocks released enough kinetic energy to trigger soft sediment deformation the soft sediment deformation in the escucha formation represents different responses of deformation susceptible sediments to earthquakes which reflect the lateral variability of sedimentary facies

geology mineralogy and lithogeochemistry of metalliferous mudstones associated with the lemarchant volcanogenic massive sulfide deposit tally pond belt central newfoundland the cambrian lemarchant zn pb cu au ag bimodal felsic volcanogenic massive sulfide vms deposit tally pond group central newfoundland canada contains metalliferous mudstones that occur either immediately on top or laterally along strike from massive sulfide mineralization or as interflow mudstones within hanging wall basaltic rocks the mudstones are brown to black graphite rich and locally have intercalations of siliciclastic volcaniclastic and or amorphous chert layers and in some cases fine lamina of organic matter the main sulfide phases are pyrite framboidal and euhedral and pyrrhotite with minor chalcopyrite sphalerite arsenopyrite and galena barite is a common sulfate the metalliferous mudstones occur at various stratigraphic levels and have variable inputs of hydrothermal high fe al and base metal values and detrital components lower fe al and base metal values with positive shale normalized eu anomalies eu eu 1 negative ce anomalies ce ce 1 and an average y ho ratio of 28 3 these signatures suggest precipitation from reduced high temperature hydrothermal vent fluids in an oxygenated water column coupled with the hydrothermal particles having a short residence time within the hydrothermal plume i e a vent proximal setting deposition from an oxygenated water column is also supported by the presence of abundant barite in both the lemarchant massive sulfides and the metalliferous mudstones as well as locally preserved marcasite in the mudstones redox sensitive trace elements as u v mo cr ni and co were scavenged as oxyanions onto fe oxyhydroxides during mudstone formation and these elevated levels of scavenged redox sensitive trace elements cause apparent anoxic signatures immobile element systematics la th zr 10 and th la sc indicate that the detrital components of the lemarchant mudstones were mixtures of both continental and mafic sources most likely deposited within a pericontinental rifted arc environment our research illustrates that the lithogeochemistry of metalliferous mudstones can identify vent proximity and provides insights into the physiochemical conditions of the deposit formation and the ambient environment these results have implications for similar precious metal bearing vms deposits globally

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

large scale low amplitude bedforms chevrons in the selima sand sheet egypt landsat images of the selima sand sheet in southwestern egypt display alternating light and dark chevron shaped patterns that occur downwind from low scarps and major dune fields images acquired between 1972 and 1988 indicate that these features move as discrete bedforms at a rate of up to 500 meters per year extremely long wavelength 130 to 1200 meters low amplitude 10 to 30 centimeters bedforms were measured in the field the light chevrons seen in the orbital data may be thin accumulations of active sand sheet deposits in the lee of these bedforms dark chevrons contain an admixture of coarse granule lag deposits that are continually winnowed by aeolian erosion on the windward sides of the large bedforms sediment transport budgets derived from orbital and field analyses suggest net movement of up to 83 000 cubic meters per year for a single light chevron such measurements can be used as a check on similar calculations from dunes and other smaller scale features to determine sand transport budgets for large areas of the eastern sahara

palaeo yardangs wind scoured desert landforms at the permo triassic unconformity in canyonlands national park south east utah at least 29 partly exhumed aligned sandstone ridges trending generally n20 w occur at the upper unconformable surface of the lower permian leonardian white rim sandstone the ridges are at least 1 5 km long 250 m wide and have up to 14 m of vertical relief mean of 9 m a thin lag of coarse sandstone that contains wind ripple laminae and granule ripples directly overlies the ridges angular blocks of sandstone within the lag and sand filled fissures immediately below the lag within the ridges attest to early cementation of the ridge forming material se dipping aeolian cross strata within the white rim sandstone and within the lag closely parallel the ridge trend the ridges are interpreted as wind sculpted desert landforms yardangs that developed on the lithified upper surface of the white rim sandstone during an extended period of hyperaridity towards the end of the permian

preservation of aeolian genetic units by lava flows in the lower cretaceous of the parana basin southern brazil the lower cretaceous geological record of the intracratonic parana basin in southern brazil comprises a thick succession of aeolian sandstones and volcanic rocks the intercalation between aeolian sandstone and volcanic floods allowed the preservation of distinct aeolian genetic units each genetic unit represents an accumulation episode bounded by supersurfaces that coincides with the base of lava flood events the entire package can be subdivided into a lower genetic unit which corresponds to aeolian sandstones preserved below the initial lava flows botucatu formation and an upper set of genetic units which comprises interlayered aeolian deposits and lava floods serra geral formation the lower genetic unit is up to 100 m thick its base is composed of ephemeral stream and aeolian sand sheet deposits that are overlain by cross bedded sandstones whose origin is ascribed to simple locally composite crescentic and complex linear aeolian dunes aeolian accumulation of the lower unit was possible as a result of the existence of a wide topographic basin which caused wind deceleration and a large sand availability that promoted a positive net sediment flux the upper genetic units comprise isolated sand bodies that occur in two different styles 1 thin lenses 3 m thick formed by aeolian sand sheets and 2 thick sand lenses 3 15 m comprising cross bedded cosets generated by migration and climbing of simple to locally composite crescentic aeolian dunes accumulation of the aeolian strata was associated with wind deceleration within depressions on the irregular upper surface of the lava floods the interruption of sedimentation in the lower and upper genetic units and related development of supersurfaces occurred as a result of widespread effusions of basaltic lava preservation of both wind rippled topset deposits of the aeolian dunes and pahoehoe lava imprints indicates that lava floods covered active aeolian dunes and hence protected the aeolian deposits from erosion thus preserving the genetic units

tectonic signatures in arid continental basins an example from the upper miocene pleistocene calama basin andean forearc northern chile abstract the calama basin a transtensional basin situated within the andean forearc and its extension to the pampa del tamarugal central depression is filled with 700 m of sediments detailed sedimentary logging and 40ar 39ar dates from interbedded volcanic deposits have established a lithostratigraphic and chronostratigraphic framework for the upper 95 m thick upper miocene pleistocene succession five facies associations fluvio lacustrine diatomite palustrine carbonate massive anhydrite fluvial and alluvial fan have been identified within this part of the basin fill the following events are recognised in the basin evolution 1 deposition of diatomaceous lacustrine sediments in two separate depocentres in the pampa del tamarugal and the central calama basin with alluvial fan accumulation along the basin margins at 8 ma 2 localised deformation within the central calama basin between 7 and 6 ma but continuous sedimentation elsewhere 3 palustrine carbonate deposition across the entire area from 6 to 3 ma except in the pampa del tamarugal where diatomaceous sedimentation continued until 5 ma before being replaced by palustrine carbonate deposition 4 widespread folding after 3 ma and entrenchment as the drainage system cut down to reach a new base level caused by the rio loa breaching the coastal cordillera and reaching the sea localised lacustrine deposition in topographic lows or tectonically created dams also occurred during this period comparison with similar age facies elsewhere in northern chile has shown changes such as these to be localised and diachronous indicating that tectonic controls on accommodation space and drainage patterns are the primary influence on sedimentation in this tectonic setting the lacustrine deposits do not appear to be a reliable recorder of low frequency climatic change this is exemplified by the change from lacustrine to palustrine deposition at 6 5 ma which would appear to record a drying of the climate however a synchronous change from ephemeral alluvial fan deposition to more permanent fluvial deposition at the basin margins indicates increased run off

erosion and sediment yields as influenced by coupled eolian and fluvial processes the yellow river china based on data from the middle yellow river a model of erosion and sediment yield is proposed to describe coupled eolian and fluvial processes in a transitional zone from and to sub humid climates and to explain rapid erosion and a high sediment yield in the zone in the study area wind action predominates from march to june which erodes weathered bedrock and transports eolian sand to gullies river channels and floodplains in the following summer especially from july to september rainstorm runoff in gullies and river channels transports large quantities of fine loessic material in the form of hyperconcentrated flow as a result most of the previously stored eolian sand and material supplied by mass wasting of loess can be transported to the major tributaries and the main stream of the yellow river resulting in the high specific sediment yield there exists all optimal grain size composition which maximizes suspended sediment concentration in the study area resulted from the combined wind water processes c 2005 elsevier b v all rights reserved

variations in style of volcanism and massive sulfide deposition in early to middle ordovician island arc sequences of the newfoundland central mobile belt the newfoundland central mobile belt records the early paleozoic birth development and destruction of the iapetus ocean following opening of the ocean in the cambrian a compressional plate margin developed in the early ordovician and an island arc was formed above an east dipping subduction zone volcanism was active at this plate margin from late tremadocian to early caradocian at which time subduction ceased and the products of the volcanism were blanketed by argillite and flysch the pre caradocian island arc volcanic sequences of the central mobile belt are host to numerous volcanogenic massive sulfide occurrences both the volcanic rocks and the associated massive sulfide occurrences show distinct contrasts across the volcanic belt in the northern part of the belt notre dame bay area submarine dominantly mafic volcanic rocks host pyritic cu zn deposits associated with local felsic domes these sequences pass southward into the victoria river area where volcanic rocks are characterized by laterally extensive felsic pyroclastic sheets which host polymetallic zn pb cu deposits in southern newfoundland the hermitage flexure area partially emergent preponderantly felsic volcanic rocks host pb zn ag massive sulfide mineralization formed during the waning stages of volcanism lead isotope ratios in massive sulfide deposits in the hermitage flexure area are consistently more radiogenic than in deposits hosted by more mafic volcanic sequences to the north this coupled with geologic evidence suggests that these sequences formed under the influence of sialic crustal material it is inferred that the early middle ordovician island arc volcanism in the newfoundland central mobile belt occurred in both oceanic and continental margin settings the compositions and geologic environments of the associated massive sulfide deposits reflect these variations in tectonostratigraphic settings time and space relationships within the volcanic arc during the interval of active volcanism are not entirely clear all early to middle ordovician volcanic rocks in central newfoundland may have formed from contemporaneous volcanic activity if this is the case simultaneous volcanism must have occurred both in oceanic environments and at or near the continental margin alternatively the volcanism may have been slightly diachronous with an early episode of ensimatic mafic volcanism followed by migration of the volcanic centers toward the continental margin the massive sulfide deposits of the pre caradocian island arc exhibit lead isotope ratios which are distinctly more radiogenic than those in the buchans roberts arm and post caradocian cutwell groups this appears to support geologically based inferences that the latter sequences are not part of the main phase of island arc activity in central newfoundland

mass and hyperconcentrated flow deposits record dune damming and catastrophic breakthrough of ephemeral rivers skeleton coast erg namibia channel shaped deposits of well sorted sand with only 2 4 fine grained material being either massive and structureless or upward fining with basal lag are found interbedded with aeolian sand in the skeleton coast erg namibia detailed analyses of the channel shaped deposits suggest that they are formed as hyperconcentrated flows within the erg grain size analysis and whole rock geochemical modeling revealed that some of the fluvial sediments contain up to 70 aeolian sand interpreted as a result of dune collapse into the fluvial system in certain cases this instantaneous supply of sand resulted in generation of sandy mass flows with laminar flow behaviour the presence of smectite as dominant clay mineral proved to be of crucial importance in formation of mass flow deposits these mass flows had no erosional capacity and drape the palaeotopography they are comparable to those generated by catastrophic collapse of dunes described in the literature this paper suggests that all these deposits should be termed intra erg mass flows as several of them carry little if any debris based on their origin intra erg mass flows can be divided into two groups

provenance of exhalites associated with the lemarchant volcanogenic massive sulphide vms deposit central newfoundland canada insights from nd isotopes and lithogeochemistry neodymium isotope data on exhalites and tuffs from the cambrian lemarchant volcanogenic massive sulphide vms deposit provide insights into the tectonic environment of the tally pond group canada new data from exhalites from the lemarchant area show evolved values of end 513 6 0 to 1 8 whereas the associated volcanic rocks have end 513 of 0 4 to 1 4 the lemarchant exhalite end compositions overlap the underlying ganderian neoproterozoic sandy brook group end t 6 5 to 1 9 and crippleback intrusive suite end t 5 9 to 5 2 the evolved nd isotopic signatures suggest that the volcanic rocks of the tally pond group were formed upon ganderian arc basement which itself was possibly built upon or proximal to the gondwanan amazonian margin erosion of older crustal material and tally pond group volcanic rocks together with coeval eruption of the volcanic rocks released nd rich detritus into the water column uptake of eroded detrital and scavenged nd resulted in mixed nd sources juvenile and evolved which are archived in the exhalites the results of this study are not only of significance for occurrences of exhalites within the tally pond group but also have exploration implications for vms districts globally

changes in whangaehu river lahar characteristics during the 1995 eruption sequence ruapehu volcano new zealand abstract during the 1995 ruapehu eruptive sequence multiple lahars occurred in the whangaehu river which drains ruapehu s crater lake during the earlier phreatic and phreatomagmatic eruptions lahars were generated by expulsion of waters from the lake but once the lake had emptied lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra four types of lahars occurred during the eruptive sequence 1 initial snow slurry lahars composed of granular snow and ice incorporated by eruptively expelled crater lake waters which left behind frozen deposits with 2 5 20 clastic sediment 2 large dilute lahars generated as the volumes of ejected lake water increased and removed much of the readily available snow at least one third of the pre eruption crater lake volume was expelled during one day producing the largest lahars of the series these lahars were hyperconcentrated flows for up to 84 km from source leaving extensive deposits along the channel margins 3 concentrated lahars smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined these lahars were able to maintain high sediment concentrations measured at 46 52 by volume suspended sediment at 42 km from source their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins 4 remobilised tephra lahars generated following the two largest tephra eruptions of the sequence seasonal snowpack was covered by water saturated tephra warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra producing several lahars in catchments draining eastern ruapehu

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

aeolian architecture bedform climbing and preservation space in the cretaceous etjo formation nw namibia sets of aeolian cross strata within the cretaceous etjo formation of nw namibia are bounded by a hierarchy of surfaces the origin of which are ascribed to one of four processes related to aeolian bedform and erg behaviour the base of the main aeolian succession is characterized by a basin wide erosional supersurface that formed in response to a period of aeolian deflation before the onset of the main phase of erg building interdune migration surfaces formed by draa migration are planar in sections parallel to the palaeowind and are inclined at up to 5 in an upwind direction sw perpendicular to the palaeowind interdune surfaces form 500 m wide troughs signifying crestline sinuosity within the original bedforms superimposition surfaces are inclined at 5 10 in a downwind direction and indicate the migration of crescentic oblique dunes over larger slipfaceless transverse draa reactivation surfaces associated with minor changes in dune slipface orientation are distinct from other bounding surface types because overlying cross strata lie parallel to them rather than downlap onto them analysis of the geometry of these bounding surfaces together with the orientation of the cross strata within the sets that they bound has enabled the detailed morphology of the original bedforms to be reconstructed the maximum preserved thickness of individual aeolian sets varies systematically across the basin from 52 m in the basin depocentre to only 8 m at the basin margin the set architecture indicates that this spatial variation is primarily the result of decreased angles of bedform climb at the basin margin rather than the presence of smaller bedforms similarly a temporal reduction in the angle of climb rather than a reduction in bedform size is considered to be responsible for an upward decrease in preserved set thickness reductions in bedform climb angle reflect progressive loss of accommodation space as the accumulating erg filled the basin

eolian sandstones in upper triassic lower jurassic red beds of the fundy basin nova scotia abstract eolian sandstones occur interbedded with alluvial fan and braided river red beds in the upper triassic wolfville formation and at the base of the lower jurassic mccoy brook formation in nova scotia extensive semiaridity and aridity in the subtropical rift valley favored deposition of eolian sandstones caliche paleosols alluvial fan conglomerates braided river alluvium and playa mudstones in postdrift configuration paleowinds blew to the southwest west and northwest down the valley reflecting the direction of trade winds at 25 n paleolatitude a three step hierarchy of surfaces truncates cross beds first order bedding planes of low relief extend for at least hundreds of meters truncating all eolian structures these surfaces were sculptured by desert flash floods and then deflated to ventifact bearing bimodal regs second order surfaces bound cross bed sets and are mostly concave up and dip downwind recording shifts in migration direction of individual dunes or dunes superimposed on larger dune structures third order surfaces within cross bed sets formed on the lee sides of dunes due to fluctuations in wind direction and strength barchans initially developed on the alluvial fan and braided river alluvium later coalescing into barchanoid transverse ridges as evidenced by the internal geometry of the eolian sandstones p

late quaternary environmental changes in the taklamakan desert western china inferred from osl dated lacustrine and aeolian deposits sediment records from the tarim basin of western china are of great importance for understanding late quaternary climatic variability in central asia a chronology of aeolian and lacustrine deposits from the centre and southern margin of the taklamakan desert central tarim basin has been established using optical dating methods distinct variations in humidity during the last 40 000 a in this extremely arid inland basin have been identified lacustrine sediments were deposited in the centre of the taklamakan during two periods of wetter than present day conditions at around 2000 and 30 000 a ago another humid period is recorded between 40 000 and 30 000 a ago aeolian processes the development of large migrating dune fields dominated during periods of more arid conditions sand wedges at the southern margin of the taklamakan are dated at ca 40 000 a and ca 18 000 a and imply a significant temperature decrease in that area sedimentological evidence for a late holocene humid period are consistent with records in ancient chinese literature wetter environmental conditions in the past within the taklamakan as indicated by the presence of lacustrine deposits are also supported by data from adjacent regions it is assumed that changes of global westerlies and of the mobile polar high triggered the fluctuations of precipitation in the study area however variations in temperature in the taklamakan desert are presumed to be mainly controlled by the intensity of the winter monsoon

generation transport and preservation of armoured mudballs in an ephemeral gully system abstract armoured mudballs have been reported from modern fluvial catchments and preserved in ancient quaternary and older sedimentary sequences despite many descriptions of mudballs in the literature there is little systematic analysis of their physical properties genesis transport and deposition within alluvial sequences this study uses two adjacent catchments developed on identical geology in southeast spain that offer a unique opportunity to examine the key controls on armoured mudball development as one catchment produces armoured mudball whilst the second does not field survey using a total station together with laboratory tests for material composition and aggregate stability were used to examine the catchment and the armoured mudballs the results show that the generation of the armoured mudballs is heavily dependent on the correct sediment supply suitable aggregates to act as mudball seeds and suitable fragments to source the armour and good slope channel coupling within the catchment coupling is facilitated by steep gully sides which deliver the weathered blocks of marl mudball seeds to the gully floor the seeds form the core of the mudballs in the mudball factory zone if the seeds are subjected to sealing by moisture from rainfall the mudball will hold together through negative pore pressures and can be transported by the ensuing gully flow as the mudball rolls it picks up a surface armour which becomes embedded into the mudball with longer transport paths the turbulent nature of the flow creates spherical mudballs which are size sorted downstream by the hydraulics of the flow rather than attrition armoured mudball deposition occurs within unit braid bars in areas of waning flow due to transmission losses within vegetated point or mid channel bars the armoured mudballs are preferentially deposited within the coarser bar head of these depositional units with smaller marl fragments forming the finer bar tail trenching of the bars reveals that the armoured mudballs are preserved in the subsurface although they may become increasingly flattened upon burial at depth and may be difficult to recognise due to disaggregation by roots this study suggests that armoured mudballs recognised in ancient alluvial sequences imply seasonality of climate and good slope channel coupling within the catchment area and that they are capable of transporting delicate flora undamaged making them good targets for pollen recovery in ancient alluvial sequences where armoured mudballs were present but go unrecognised in the ancient record the mode and energy of transportation and deposition of the fine sediment may be misinterpreted as the fines are in fact being transported as bedload rather than suspended load the armoured mudballs have also been noted to transport pristine microfauna such as ostracod shells from the source area material this may provide challenges to palaeoenvironmental interpretations of the mud dominated unit as environmentally significant fauna may not be contemporaneous with the unit

upper cambrian to upper ordovician peri gondwanan island arc activity in the victoria lake supergroup central newfoundland tectonic development of the northern ganderian margin the exploits subzone of the newfoundland appalachians comprises remnants of cambro ordovician peri gondwanan arc and back arc complexes that formed within the iapetus ocean the exploits subzone experienced at least two accretionary events as a result of the rapid closure of the main portion of the iapetus tract the penobscot orogeny c 480 ma which juxtaposed the penobscot arc c 513 486 ma with the gander margin and c 450 ma collision of the victoria arc c 473 454 ma with the annieopsquotch accretionary tract that juxtaposed the peri laurentian and peri gondwanan elements along the red indian line the newly recognized pats pond group forms a temporal equivalent to other lower ordovician intra oceanic complexes of the penobscot arc the pats pond group c 487 ma has a geochemical stratigraphy that is consistent with rifting of a volcanic arc an ensialic setting is indicated by low end values end 0 3 to 0 5 near the stratigraphic base and its abundant zircon inheritance c 560 ma and 0 9 1 2 ga the spatial distribution of tremadocian arc back arc complexes indicates that the penobscot arc is best explained in terms of a single east dipping subduction zone this model is favored over west dipping models in that it explains the distribution of the penobscot arc elements continental arc magmatism and the obduction of back arc penobscot ophiolites without requiring subduction of the gander margin or subduction reversal the newly recognized wigwam brook group c 454 ma disconformably overlies the pats pond group and records the youngest known phase of ensialic arc volcanism end 4 1 in the victoria arc which is also related to east dipping subduction thus the penobscot and the overlying victoria arc are reinterpreted in terms of a single relatively long lived east dipping subduction zone beneath the peri gondwanan microcontinent of ganderia the cessation of arc volcanism towards the top of the wigwam brook group and the subsequent syn tectonic sedimentation in the badger group constrain the arrival of the leading edge of ganderia with the ensialic arc complexes to the laurentian margin to c 454 ma

desert sedimentary environments present and past a summary abstract tropical deserts develop where the potential rate of evaporation exceeds that of precipitation where rainfall is too low or spasmodic to support vegetation these usually occur in the trade wind belts north and south of the equator and in the rain shadow of mountain ranges about half the area of deserts comprise outcrop subject to erosion and deflation the rest consists of sediments of fluvial wadi lacustrine salina paralic coastal sabkha and aeolian origin and of evaporites ephemeral streams deposit sands and gravels over basin margin alluvial fans and over desert plains where sub surface cementation commonly takes place evaporation of basin centre temporary lakes results in a crust of halite inland sabkha fluvial sands are an important source of dune sand the finer fractions are removed from the desert in suspension to become loess and the coarser grain remain as a deflation lag the axes of sand dunes are transverse to moderate winds and parallel to strong winds giant forms of the latter dune type were prevalent during the last ice age and in coastal areas carbonate cemented dune sands extend below present sea level this suggests a causal relationship between polar glaciations and strong desert winds desert fluvial sediments rarely reach the sea so the warm and clear coastal waters are ideal for the manufacture of organic carbonates longshore currents sweep them into offshore bars behind which evaporitic lagoonal conditions develop the lagoons become sabkhas as they are infilled with algally bound marine and wind blown sediment although there are desert sequences as old as about 2000 ma they seem to have occurred only sporadically during the earth s history it seems likely that their occurrence was controlled by the past size of continents their location relative to the equator by the freedom of circulation of global oceanic water and by the presence of ice caps the permo triassic was a time of extensive evaporite deposition and dune activity by implication other known occurrences of evaporites may be marginal to wadi and dune sequences that have yet to be identified

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

erratum to variations of sulphur isotope signatures in sulphides from the metamorphosed ming cu au volcanogenic massive sulphide deposit newfoundland appalachians canada the ming deposit is an early ordovician bimodal mafic cu au volcanogenic massive sulphide vms deposit in the newfoundland appalachians that was metamorphosed to upper greenschist lower amphibolite facies conditions and deformed in the silurian and devonian the ming deposit consists of several spatially proximal ore bodies of which the 1806 zone 1807 zone ming south up plunge and down plunge and the lower footwall zone are the focus of this paper the ore bodies have similar stratigraphic sequences the ore bodies can be divided into 1 a silicified horizon that caps the massive sulphides 2 semi massive to massive sulphides and 3 sulphide mineralization in a rhyodacitic footwall sulphide mineralization in a rhyodacitic footwall includes a sulphide stringers immediately below the semi massive to massive sulphides and b chalcopyrite pyrrhotite pyrite stringers distally from semi massive to massive sulphides in the lower footwall zone pyrite chalcopyrite pyrrhotite arsenopyrite and galena were analysed by in situ secondary ion mass spectrometry sims for sulphur isotope compositions the isotopic signatures of pyrite chalcopyrite pyrrhotite and arsenopyrite fall within a limited range of 2 8 to 12 0 for semi massive to massive sulphides and sulphide mineralization in the footwall the silicified horizon capping the semi massive to massive sulphides has higher 34s 5 8 19 6 especially for pyrrhotite mean 17 2 2 2 n 8 the sulphur isotope composition of galena is more heterogeneous especially within semi massive to massive sulphides and sulphide stringers ranging from 0 8 to 17 3 mean 6 1 4 3 n 35 and 7 6 to 17 1 mean 13 7 5 3 n 3 respectively geothermometric calculations give insufficient formation and metamorphism temperatures for neighbouring mineral pairs because sulphides were not in isotopic equilibrium while deposited in early ordovician or re equilibrated during silurian devonian metamorphism respectively therefore original isotopic compositions of sulphides at the ming deposit have been preserved modelling of the source of sulphur shows that 1 reduced seawater sulphate and 2 sulphur leached from igneous wall rock and or derived from magmatic fluids are the main sources of sulphur in the ming deposit the influence of igneous sulphur igneous wall rock magmatic fluids increases with temperature and is an important sulphur source for the semi massive to massive sulphides and footwall mineralization in addition to a contribution from thermochemical sulphate reduction tsr of seawater it is difficult to distinguish between sulphur leached from igneous rocks and magmatic fluid related sulphur and it is possible that both sources contributed to the ores at the ming deposit in addition to igneous sulphur the heavy isotopes of the silicified horizon are consistent with the sulphur in this horizon being derived only from thermochemical sulphate reduction of early ordovician seawater sulphate

role of metalliferous mudstones and detrital shales in the localization genesis and paleoenvironment of volcanogenic massive sulphide deposits of the tally pond volcanic belt central newfoundland canada the cambrian tally pond volcanic belt in central newfoundland contains numerous volcanogenic massive sulphide vms deposits and prospects associated with exhalative metalliferous mudstones deposits in the belt are bimodal felsic vms deposits that are both base metal bearing e g duck pond boundary and base metal and precious metal bearing lemarchant at the lemarchant deposit metalliferous mudstones are stratigraphically and genetically associated with mineralization in the remainder of the tally pond belt detrital shales occur predominantly in the northeastern part of the belt mostly as unrelated mid ordovician structural blocks in the upper sections of the cambrian volcanic stratigraphy but locally also are intercalated with metalliferous mudstones their relationships to massive sulphides are less obvious with many spatially but not necessarily genetically related to mineralization upper cambrian to lower ordovician black shales from bell island which represent pelagic sedimentation not associated with hydrothermal activity and volcanism are compared with the tally pond belt mudstones and shales exhalative mudstones like those at lemarchant have elevated fe al and base metal values and have shale normalized negative ce and positive eu anomalies indicative of deposition from high temperature 250 c hydrothermal fluids within an oxygenated water column mudstones and shales sampled from other tally pond prospects have more variable signatures ranging from hydrothermal to nonhydrothermal black shales no positive eu anomalies flat rare earth element patterns low fe al and base metal contents to those that have mixed signatures accordingly mudstones from areas with a lemarchant like hydrothermal and vent proximal character are more attractive exploration targets than mudstones and shales with predominantly detrital signatures

genesis of the buntsandstein lower triassic in the western eifel germany abstract the buntsandstein lower triassic of the western eifel germany is composed of sediments of different origin these are alluvial fan fluviatile aeolian lacustrine and deltaic deposits the fluviatile deposits are subdivided into channel lag bar and topstratum deposits alluvial fan deposits occur in local depressions of the pre triassic morphology aeolian sediments build up the main part of the middle buntsandstein locally interfingering with fluviatile deposits paleowind and paleocurrent directions generally coincide the upper buntsandstein consists of fluviatile sediments only which can be subdivided into well developed small cyclothems average thickness of sedimentation units 3 8 m capped by paleosoils the uppermost buntsandstein is of deltaic origin the ingression of the lower muschelkalk sea terminates the terrestrial buntsandstein sequence

palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest permian late triassic solway basin u k abstract the late permian to late triassic sediments of the solway basin consist of an originally flat lying laterally persistent and consistent succession of mature dominantly fine grained red clastics laid down in part of a very large intracontinental basin the complete absence of body or trace fossils or palaeosols indicates a very arid hyperarid depositional environment for most of the sediments at the base of the succession thin regolith breccias and sandstones rest unconformably on basement and early permian rift clastics overlying gypsiferous red silty mudstones very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary and their margins these pass upwards into thick bedded multi storied fine to very fine grained red quartzo felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter above thick trough cross bedded and parallel laminated fine grained aeolian sandstones deposited in extensive barchanoid dune complexes pass up into very thick multicoloured mudstones and gypsum deposited in marginal marine or lacustrine sabkha environments the latter pass up into marine lower jurassic shales and limestones thirteen non marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures the five associations can be compared with the desert pavement arid ephemeral stream sabkha saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as lake eyre and lake chad the accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent caused by climatic change and local variation and this promotes a large scale layer cake stratigraphy as exemplified in the solway basin here the dominant fine grained mature sandstones above the local basal reg breccias suggest water reworking of wind transported sediment as in the northern part of the lake chad basin growth faulting occurs in places in the solway basin caused by underlying evaporite movement but these faults did not significantly affect pre late triassic sedimentation and did not expose pre permian units above the basal breccias there is no evidence of post early permian rifting anywhere during deposition of the late permian to middle triassic british succession although the succession is often interpreted with a rift basin model the arid to hyperarid palaeoclimate changed little during deposition of the solway basin succession in contrast to lakes eyre and chad and this is attributed to tectonic and palaeolatitude stability unlike the later mesozoic cenozoic only limited plate movements took place during the triassic in western europe palaeolatitude changed little and the solway basin remained in the northern latitudinal desert belt from early to mid triassic times however the influence of the early triassic impoverished biota on environmental interpretations needs further study

sheet flow deposits of graded beds and mudstones on an alluvial sandflat playa system upper triassic blomidon redbeds st mary s bay nova scotia the 400 m of blomidon redbeds accumulated in a semi arid rift valley in the subtropics at st mary s bay these redbeds are 64 sandy mudstone playa mudflats 25 graded beds sandflats at the toes of alluvial fans 10 fissile claystone playa lakes and 1 channel sandstone stream channels flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north east as sheet flows on sandflats and playa mudflats deceleration of the sheet flows deposited graded beds 2 83 cm in thickness on the sandflats and thin layers of mud on the playas nine sequences consisting of arrangements of six lithologies compose 90 of the graded beds in order of decreasing abundance these are ripple cross laminated siltstone horizontally laminated mudstone fining upward ripple cross laminated siltstone ripple cross laminated sandstone horizontally laminated mudstone cross bedded sandstone horizontally laminated mudstone ripple cross laminated sandstone ripple cross laminated siltstone rippledrift cross laminated siltstone horizontally laminated mudstone fining upward ripple drift cross laminated siltstone cross bedded sandstone ripple cross laminated siltstone and cross bedded sandstone ripple cross laminated siltstone horizontally laminated mudstone the sheet flows perhaps up to 1 m in depth had a high concentration of suspended load deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration there are 32 thinning and fining up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone the cycles range in thickness from 1 3 to 13 3 m averaging 4 6 m each cycle is initiated by avulsion to a new active channel network on a fan gradual abandonment of the channel network produces the thinning and fining up cycle the cycles are grouped in three 60 70 m fining up megacycles upwards within each megacycle the packages of sandy mudstone compose a progressively larger proportion of the cycles each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor subsequent erosion gradually lowered the relief to yield a fining up megacycle