late proterozoic lavas of the central arabian shield evolution of an ancient volcanic arc system a petrological assessment of 11 volcano sedimentary belts in the central arabian shield cas using 118 new analyses is presented the same samples have been used in a rb sr dating programme also reported in this volume the oldest volcano sedimentary belts sequence c 900 ma are chemically immature bimodal suites of low k tholeiites and sodic dacite rhyolite depleted in lithophile elements these lavas have chemical characteristics similar to immature island arcs such as the tonga kermadee and lesser antilles arcs younger lavas of sequence b 900 700 ma are slightly more mature in composition being predominantly calc alkaline and low k arc tholeiite series with higher lithophile element contents they are comparable with pacific island are averages the youngest voluminous lavas sequence a 700 570 ma are generally calc alkaline or high k calc alkaline series lavas with moderately high lithophile element abundances they are comparable to volcanic arcs such as central america and indonesia which are transitional between island arcs and continental margin volcanic arcs the cratonization process in the cas thus involved the superimposition of three volcano sedimentary sequences formed in progressively maturing volcanic arcs early formed immature island arcs were succeeded by chemically more mature island arc deposits and then by deposits formed in volcanic arc s transitional between island arcs and continental margins the evolution ceased at this stage and probably did not advance to the equivalent of an andean continental margin

identification of permian palaeowind direction from wave dominated lacustrine sediments lodeve basin france lacustrine environments are an excellent indicator of continental palaeoclimate in particular the sedimentary record of waves in lakes may be used to constrain atmospheric palaeocirculation wave ripples have been identified in a permian lacustrine basin the salagou formation 260 250 ma lodeve basin located in the southern french massif central part of the western european hercynian mountain chain wave ripple patterns are interpreted with regards to hydrodynamics and water palaeodepth it is shown that in the case of the salagou formation wave ripple orientations were controlled by the direction of the prevailing palaeowind the late permian wind blew from between north and 20 east of north possibly over several millions of years and certainly throughout the period of deposition of about 2000 m of strata in the lodeve basin permian lacustrine sedimentation is widespread and well preserved on the earth s surface and so wave ripple data may help constrain numerical modelling of the earth s past climates especially with regards to permian times outside of desert regions

penetration of atlantic westerly winds into central and east asia abstract the geographical position of the convergence zone where the western atlantic climate system meets the asian winter monsoonal system depends on their relative strength these individual strengths are determined by the intensities of the air pressure gradients over the north atlantic and the siberian high pressure cell respectively since the factors that forced those gradients varied throughout glacial interglacial cycles the location of the convergence zone should have moved accordingly both the grain size characteristics of wind blown sediments and climate modelling prove that the atlantic influence extended remarkably far eastward at times the northeastern tibetan plateau was at the cross road of western and monsoonal influences during the last glacial this region was dominated by an atlantic signal with millennial scale climatic oscillations that are similar to the north atlantic marine and greenland ice core records in contrast that same region was only under monsoonal influence during the last interglacial it implies that the atlantic winds penetrated more vigorously eastward in full glacial conditions than in interglacial conditions

late precambrian crustal accretion rates in northeast africa and arabia apparent late precambrian growth rates for continental crust in the arabian nubian craton are implausibly high for simple arcaccretion models if correct these rates imply that some special non uniformitarian process occurred to rapidly produce continental crust assuming that the dominant mechanism for continental growth is by arc magmatism roughly 100 of global island arc production at current rates would have had to accrete in this region from 900 to 600 ma one solution to this paradox is that large amounts of preexisting sialic basement have so far gone undetected and should not be included in the estimate for crustal growth during late precambrian time published radiometric data indicate that older continental material makes up the eastern and western margins of the exposed shield we interpret these and other data to suggest that the larger part of the arabian nubian craton including the platform obscured by phanerozoic cover east and west of the exposed shield is older continental crust in this case a growth rate approximately 20 of the modern global rate is required and nonuniformitarian crustal growth is not necessary to explain late precambrian accretion of the arabian nubian craton

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

coastal lagoons and beach ridges as complementary sedimentary archives for the reconstruction of holocene relative sea level changes coastal lagoons and beach ridges are genetically independent though non continuous sedimentary archives we here combine the results from two recently published studies in order to produce an 8000 year long record of holocene relative sea level changes on the island of samso southern kattegat denmark the reconstruction of the initial mid holocene sea level rise is based on the sedimentary infill from topography confined coastal lagoons sander et al boreas 2015b sea level index points over the mid to late holocene period of sea level stability and fall are retrieved from the internal structures of a wide beach ridge system hede et al the holocene 2015 data from sediment coring georadar and absolute dating are thus combined in an inter disciplinary approach that is highly reproducible in micro tidal environments characterised by high sediment supply we show here that the commonly proximate occurrence of coastal lagoons and beach ridges allows us to produce seamless time series of relative sea level changes from field sites in sw scandinavia and in similar coastal environments

predicting the crest height of a gravel beach the beach crest is a common morphological feature formed by the deposition of sediment carried up slope by wave swash the elevation to which waves can pile gravel is a function of the size and density of the material relative to the hydraulic components of swash velocity wave frequency and runup height two equations 17 and 21 that predict the height of the beach crest to the wave forces and the beach material are derived the first derivation compares the wave force acting to move a stone up the beach face with a weight force acting to hold the stone in place the second derivation relates the potential energy per unit area of the beach crest to the total wave energy that lifted and deposited the material above a given sea level datum as a test of the derived equations the actual crest height of one natural gravel beach was accurately estimated by both equations derived further research and testing on other natural beaches are needed to fully verify eqs 17 and 21 a comparison of other equations eqs 2 3 and 4 that predict crest height is also made the poor fit of the other equations are a result of using values for the coefficients that were established in wave tank experiments another shortcoming of eqs 3 and 4 is that they do not include variables related to the beach material hence they predict that all particle sizes from sand to boulders would be piled to the same elevation by the same wave forcing eq 2 includes a particle size variable but predicts increasingly higher beach crests for larger particles more realistic results for all three equations eqs 2 3 and 4 would be expected with field tested values for the coefficients but a range in values for each different beach would be necessary the advantage of eqs 17 and 21 is that equations are not dependent on coefficients whose values come from correlation with other data sets

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

middle to late jurassic tectonic evolution of the klamath mountains california oregon the geochronology stratigraphy and spatial relationships of middle and late jurassic terranes of the klamath mountains strongly suggest that they were formed in a single west facing magmatic arc built upon older accreted terranes a middle jurassic arc complex is represented by the volcanic rocks of the western hayfork terrane and consanguineous dioritic to peridotitic plutons new u pb zircon dates indicate that the middle jurassic plutonic belt was active from 159 to 174 ma and is much more extensive than previously thought this plutonic belt became inactive just as the 157 ma josephine ophiolite which lies west and structurally below the middle jurassic arc was generated late jurassic volcanic and plutonic arc rocks rogue formation and chetco intrusive complex lie outboard and structurally beneath the josephine ophiolite u pb and k ar age data indicate that this arc complex is coeval with the josephine ophiolite both the late jurassic arc complex and the josephine ophiolite are overlain by the galice formation a late jurassic flysch sequence and are intruded by 150 ma dikes and sills the following tectonic model is presented that accounts for the age and distribution of these terranes a middle jurassic arc built on older accreted terranes undergoes rifting at 160 ma resulting in formation of a remnant arc back arc basin island arc triad this system collapsed during the late jurassic nevadan orogeny 150 ma and was strongly deformed and stacked into a series of east dipping thrust sheets arc magmatism was active both before and after the nevadan orogeny but virtually ceased at 140 ma

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

accretionary tectonics of the north american cordillera continental geology stands on the threshold of a change that is likely to be as fundamental as plate tectonic theory was for marine geology ongoing seismic reflection investigations into the deep crustal structure of north america are verifying that orogenic zones are underlain by low angle faults of regional extent brown et al 1981 the growing body of regional field relations is likewise delineating numerous orogenic sutures that bound discrete crustal fragments paleomagnetic and paleobiogeographic studies are revealing major latitudinal shifts and rotations within and between suture bounded fragments particularly within the north american cordillera such interdisciplinary studies are leading to a consensus that the cordillera has been built by progressive tectonic addition of crustal fragments along the continent edge in mesozoic and early cenozoic time such crustal growth is referred to as accretionary tectonics in this paper we review some of the important concepts in accretionary tectonics discuss the nature of the materials accreted between central alaska and southern california in jurassic and cretaceous time and consider the general relations between cordilleran accretion and the movement of lithospheric plates the concept of continents growing by peripheral accretion through geologic time has long been a topic of great interest with the advent of plate tectonics a number of different mechanisms for crustal accretion have arisen along with mechanisms for crustal attrition accretion mechanisms include the growth of imbricated sedimentary prisms along inner trench walls slicing off of submarine topographic irregularities within subducting plates and collision of continents and volcanic arcs by ocean basin closure tectonic attrition mechanisms include rifting transform faulting and strike slip or underthrust removal of inner trench wall materials coincident with or in place of accretionary prism growth growth of intraorogenic ocean basins by seafloor spreading is an additional important mechanism for creating accretionary materials as well as displacing crustal fragments an important implication of plate kinematic theory is the likelihood for accretionary and attritionary mechanics to operate in series both in time and space along continental margins since attrition by nature leaves little material evidence of having operated one of the major problems confronting cordilleran geologists lies in the recognition of such attrition within the ancient record particularly when interspersed with accretionary events the spectrum of accretion and attrition mechanisms viewed at cm yr 1 plate transport rates over time scales of 100 m y leads one to suspect a highly mobile history for continental margin orogens the serial arrangement of subducting transform and rifting links along the modern cordillera plate juncture system and both serial and parallel arrangements in the western pacific systems show the complex interplay of such mechanisms through space similar arrangements overprinted through time are suggested by the rock assemblages and structural patterns within the cordillera which presently resemble a collage of crustal fragments davis et al 1978 recognition of the structural state of this collage geologic field mapping and geophysical investigations will bring about a new level of understanding in the growth of continental crust and the reading of stratigraphic records within the fragments and future palinspastic restorations will lead to a new level of understanding in paleogeography and earth history the first problem to be considered is the recognition of native north american crust from exotic fragments that have been accreted to its edge

new evidence for crustal accretion in the outer mariana fore arc cretaceous radiolarian cherts and mid ocean ridge basalt like lavas new age determinations on radiolarian cherts foraminifers and volcanic rocks document the presence of allochthonous fragments of cretaceous oceanic plate suggesting accreted terrane in the outer mariana fore arc more than 50 km from the trench three dredges from 3km 2 area along a steep scarp recovered a diverse assemblage of rocks representing an ophiolite suite chert mafic and intermediate lavas and intrusive rocks trace element patterns of the lavas suggest at least three tectonic associations island arc ocean island and oceanic plate the cherts contain two deep water assemblages of radiolaria of middle to late valan ginian 131 138 ma and albian 97 112 ma age foraminifers recovered with the chert are aptian to albian in age the lavas record a wide range of k ar ages 85 ma for a metabasalt with trace element signatures of mid ocean ridge basalt 71 ma for a highly metamorphosed alkalic basalt and 39 ma for a fresh glassy boninite these ages imply multiple volcanic events and at least two tectonic settings for magma genesis the cherts and metabasalts are too old to have formed in situ or to be part of trapped west philippine basin crust the mix of old oceanic plate with younger are rocks requires complex tectonic relations we suggest that one or more fragments of cretaceous oceanic plate chert mid ocean ridge basalt and alkalic lavas were accreted to the mariana fore arc and have been extensively faulted and probably intruded by arc lava island arc tholeiite and boninite

morphology and paleoclimatic significance of pleistocene lake bonneville spits abstract pleistocene lake bonneville of western utah contains a variety of spits associated with shorelines and other features that formed between 21 000 and 12 000 14 c yr bp field studies in the low lying mountain ranges of the central portion of lake bonneville identified 17 spits of various types the spits are connected to small mountain ranges and islands vary in size from 0 02 to 0 5 km 2 and are composed of coarse grained well rounded poorly sorted sedimentary material sixteen of the 17 spits have a northeasterly to southwesterly orientation implying that winds were from the northwest to northeast approximately 180 out of phase with modern winds in the eastern great basin lake bonneville spit orientation is best explained as the result of persistent northerly winds caused by the high atmospheric pressure cell of the continental ice sheet and passage of low pressure extratropical storms south of the lake similar strong persistent winds are a common feature of modern continental ice sheets and passing low pressure systems if so the north american jet stream tracked south of lake bonneville as recently as 12 000 14 c yr bp well past the height of the last glacial maximum

assumed holocene highstands gulf of mexico basic issues of sedimentary and landform criteria discussion record high mid and late holocene relative sea levels significantly above the current sea level have been widely documented in certain areas of the australo pacific region brazil lessa et al 2000 and parts of africa and india that were not characterized by tectonic uplift and or glacio isostatic rebound such elevated sea levels are yet to be reliably identified on our gulf and atlantic shores radically departing from traditional gulf of mexico sea level curves morton et al 2000 now suggest recurring highstands throughout the entire second half of the holocene epoch their findings echo earlier ideas in the same vein see otvos 1995 1997 1999 however a detailed analysis of several lines of evidence presented by morton et al raises serious doubts about these conclusions morton et al accept the position of beach ridge summits as indicative of higher than present elevations thus seaward declining beach ridge summits on bolivar peninsula galveston island and other coastal areas of texas in their view reflect late holocene sea levels that fell from their highest elevations although beach ridges are of wave constructed berm ridge foredune or composite origins otvos 2000 morton et al fail to distinguish adequately among these categories by sediment and landform analysis the problem is that under favorable circumstances wave built berm ridges may be accurate markers of ancient sea levels or lake levels foredunes on the other hand aggrade to varying supratidal elevations rising several meters above the associated high tide level for this reason summit elevations of relict foredunes can not provide precise data on corresponding sea level otvos 1995 foredune ridges foredune ridges often overlie mask and bury wave built berm ridges beal and shepard 1956 because sand is usually readily available for wind transport on most gulf shores the upper interval in most beach ridges tends to be of eolian origin except when wave built

textural and compositional variability across littoral segments of lake tanganyika the effect of asymmetric basin structure on sedimentation in large rift lakes lake tanganyika part of the east african rift system represents one of the most widely cited modern analogs for interpreting ancient rift lakes to date few published detailed sedimentologic studies of the modern sediments allow for comparisons to outcrop and well bore scale observations within ancient strata four recurrent structural margin types exist along the alternating half graben structure of the lake hinged margins axial margins accommodation zone margins and escarpment margins the hinged margin consists of a series of structurally controlled benches over which long continuous tracts of bioclastic lag deposits predominate clastic sands are limited to moderate size silty deltas and long narrow shoreface sands the axial margin is dominated by a wave dominated silt rich delta system accommodation zone margins consist of bioclastic lag deposits atop structural highs whereas carbonate and clastic mud accumulates farther offshore escarpment margins contain small fan delta deposits alternating along shore with talus deposits offshore carbonate and clastic mud is present away from active gravity flow deposition total organic carbon toc and pyrolysis data from fine grained samples subtly reflect the contrasts in margin types but these values are controlled more directly by water depth although facies are similar among all margin types their spatial distribution in particular the degree to which facies tracts trend parallel to shore best discriminates among the different margin types these data suggest that unique but predictable associations of reservoir seal and source facies exist along each of the different margin types

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

beach ridge development in lake michigan shoreline behavior in response to quasi periodic lake level events abstract strandplains of arcuate beach ridges are common in coastal embayments in parts of the great lakes similarities in beach ridge development and geomorphology are recognizable in many of the embayments in the lake michigan basin despite differences in size and shape available sediment type and supply predepositional slope and topography and hydrographic regime between the embayments these similarities are primarily a product of three scales of quasiperiodic lake level variation ranging in time from 30 to 600 years and in water level change from 0 5 to 3 7 m the interaction of these three lake level variations can be represented on a curray 1964 diagram rate of water level change versus rate of sediment supply the position of any shoreline on the diagram and the type of behavior the shoreline is experiencing is a product of the interaction of the three variations two large strandplains of late holocene beach ridges occur at opposite ends of lake michigan toleston beach and thompson embayment the two areas exhibit similar patterns of beach ridge development for the past 2600 calendar years that is both areas form beach ridges about every 30 years groups of 4 to 6 beach ridges reflect a longer term lake level variation of about 150 years only during the largest variation of about 600 years in duration do the two areas differ the rise to the 1700 cal yr b p high caused the erosion of beach ridges back to 2800 cal yrs b p in northern lake michigan in southern lake michigan no erosion occurred during this lake level high differences in shoreline development between the two areas are related to the rate of sediment supply to the shorelines as the sediment sink for the southern half of lake michigan the southern strandplain received a greater sediment flux than the northern strandplain during the latter part of the late holocene and produced a continuous record of beach ridge development

continental detrital zircon in carboniferous ensimatic arc rocks bragdon formation eastern klamath terrane northern california new u pb isotopic data for detrital zircon populations from the upper devonian and lower carboniferous bragdon formation add constraints to the nature of source areas for epiclastic rocks in the ensimatic eastern klamath arc terrane bragdon clastic units include lithic rich sandstone containing quartz chert and sedimentary lithic clasts volcanic lithic rich sandstone and crystal rich tuffaceous sand stone these three compositions reflect a composite source that contained sedimentary and low grade metasedimentary rocks volcanic rocks and penecontemporaneous volcanic debris u pb isotopic data from detrital zircon indicate an ultimate precambrian continental source for components of the bragdon formation and corroborate the previous suggestion that lower paleozoic rocks of the shoo fly complex yreka terrane or related rocks may have been the immediate last cycle sources in modern convergent margins a complex and ongoing relationship between ensimatic arc volcanism and continental sediment sources may be expected from the pattern of oceanic subduction zones that generally dip toward continents and intervening marginal basin systems providing a context for understanding the presence of continent derived detritus in an ancient ensimatic arc

tropical westerlies over pangaean sand seas cross equatorial westerly winds are key features of tropical circulation in monsoonal regions although prominent in numerical climate models of pangaea the supercontinent straddling earth s equator late palaeozoic to early mesozoic such flow has not been confirmed previously by migration directions of ancient dunes wind blown sandstones that span 100 million years of earth history are widely exposed in south western usa if recent palaeomagnetic data from the colorado plateau are used to correct mesozoic palaeogeographic maps the plateau is placed about 10 further south than previously assumed and the prevailing north westerly surface winds recorded by dune deposited sandstones are explicable as cross equatorial westerlies the hallmark of modern monsoon circulation permian to early jurassic dunes were driven by north westerlies produced by a steep pressure gradient spanning the supercontinent during december january february although winds are light in most modern near equatorial settings the east african jet accounts for more than half the cross equatorial flow in june july august the thicknesses of annual depositional cycles within the navajo sandstone indicate that the near equatorial north westerly winds that drove these particular dunes were stronger than the modern east african jet the early jurassic dunes that deposited the thick cycles were positioned west of the dominant southern hemisphere thermal low and against highlands to the west a setting very similar to the east african jet the mountains along the western coast of pangaea not only enhanced wind strength but also cast a rain shadow that allowed active dunes to extend very close to the palaeoequator

paleowind 11 000 bp directions derived from lake spits in northern michigan we report on the characteristics of several previously unstudied late pleistocene spits in northern lower michigan each spit developed as strong waves eroded a headland or island within the main and or later stages of glacial lake algonquin most have ese to wnw orientations with prominent recurved hooks at their ends some are as long as 20 km sedimentologically the spits contain thick several meters or more sequences of sand and well rounded gravel we suggest that summertime winds during the spits formation 11 800 to 10 500 bp were both very strong and dominantly from the e and se based on the following data 1 their ese source or head of the spit to wnw orientation 2 the presence of steep wave cut bluffs on the east sides of the islands and headlands and 3 spit locations on the northeastern shore of michigan s lower peninsula coupled with their absence on the northwestern shore just 100 km away wind direction data provided by these spits agree with paleoclimatic models that suggest that the laurentide ice sheet had developed a strong anticyclonic circulation the near lack of archeological sites from this time period in the northern lower peninsula which was surrounded by lake algonquin at that time supports the notion that the climate of northern lower michigan was inhospitably cold and very windy in the late pleistocene

the najd fault system revisited a two way strike slip orogen in the saudi arabian shield abstract the najd strike slip fault system extends over the northeastern arabian shield in a zone 1200 km in length and 300 km wide faults trend nw se with strike lengths 500 km but small sinistral displacements of 240 km najd faults were active in the late proterozoic and post date cratonization of the shield associated secondary structures include grabens thrust faults folds and dike swarms in the southwest of the najd system near zalm initial faulting was dextral and began earlier than formerly thought emplacement of a plutonic complex was controlled by najd fractures of dextral geometry and displacements the same fractures were active before and after deposition of a group of volcanosedimentary rocks in grabens orientated consistently with development in a dextral strike slip regime graben deformation was controlled by sinistral motion along the same fractures responsible for graben development and also by younger fractures of sinistral geometry and displacement dike swarms in the area are also consistent with early dextral and later sinistral shear of najd trend structures in the zalm area occur throughout the najd system and the consistent chronology of older dextral structures dislocated and deformed by younger sinistral faults suggests a reversal in the sense of motion of the najd system as a whole

influence of air temperature on a glacier s active layer temperature seasonal temperature variations occur in the glacier layer about 15 20 m below the surface while at greater depths the glacier temperature depends on the long term surface conditions it is generally accepted that for glaciers without surface melting the temperature at 10 m depth t10 i s close to the mean annual air temperature at standard screen level ta i e t10 ta we found that this relationship is not valid for ta above 178c and below 558c the goal of our investigation is to find a better temperature transfer function ttf between ta and temperature at the boundary of the active layer in accumulation areas of polar and tropical glaciers low precision t10 temperatures from boreholes obtained at 41 sites are compared with air temperatures ta measured in the vicinity of these sites for at least a 1 year period we determine that when ta falls into the temperature range 60 to 78c empirical values can be approximated as t10 1 2ta 6 7 analysis of these data suggests that high t10 occurs in the areas of the glacier that collect meltwater

measurements of morphodynamic and hydrodynamic overwash processes in a large scale wave flume overwash is an important process that controls short term barrier dynamics as well as long term barrier migration but this process is difficult to study in the field due to its rare occurrence and the challenging conditions under which it occurs this paper uses data collected during the bardex ii experiment in the delta flume the netherlands where a proto type barrier was subjected to a range of wave and water level conditions the objectives of this research are to 1 compare the morphologic response to overwash on a gravel barrier bardex 2008 experiment with that on a sandy barrier bardex ii 2 understand the influence of wave period on overwash characteristics and sediment transport and 3 improve current knowledge of overwash hydrodynamics the comparative analysis shows that barrier overwash can be affected by negative feedback that stabilises the barrier through barrier crest accretion on gravel barriers and by submerged bar development on sandy barriers an increase in the wave period induced a reduction in overwash frequency over the crest but no significant relation was found between wave peak period and overwash discharge nevertheless overall water discharge during an overwash episode significantly correlates with overall overwash sediment transport rate overwash flow depths during the experiment were relatively shallow and velocities were similar compared to those measured during previous studies and reported in the literature despite the controlled laboratory conditions collection of reliable and accurate measurements of overwash velocities remains challenging

paleowind velocity and paleocurrents of pluvial lake manly death valley usa pluvial lake deposits are found throughout western north america and are frequently used to reconstruct regional paleoclimate in death valley california usa we apply the beach particle technique bpt of adams 2003 sedimentology 50 565 577 and adams 2004 sedimentology 51 671 673 to lake manly deposits at the beatty junction bar complex bjbc desolation canyon and manly terraces and calculate paleowind velocities of 14 27 m s these wind velocities are within the range of present day wind velocities recorded in the surrounding area sedimentary structures and clast provenance at desolation canyon and the manly terraces indicate sediment transport from north to south lake level based on the elevation of constructional features indicates that the hill west of the bjbc was an island and that the bjbc spits formed during simple lake regression the data are consistent with the hypothesis that the present wind regime velocity and direction formed the pluvial lake manly features

structural and litho tectonic controls on neoproterozoic base metal sulfide and gold mineralization in north hamisana shear zone south eastern desert egypt the integrated field structural landsat 7 etm and aster data approach abstract the hamisana shear zone hsz is an excellent example of high strain shear belt of the neoproterozoic arabian nubian shield ans situated in a position between three major pan african terranes se desert gabgaba and gebeit terranes the north hamisana shear zone area nhsz cuts across sequences of island arc related metasediment metavolcanic which are structurally overlain by ophiolitic nappes and intruded by a number of granitoids and gabbroic rocks although it is interesting geological tectonic setting for base metal sulfide and gold ores there is a lack of detailed studies on structure geology and mineralization in this area which considered as poorly mapped remote region not only in egypt but also in sudan for these reasons we integrated image transformation methods include principal components analysis pca band ratios br false color composite fcc and filtering on the spectral bands of two distinct datasets etm and aster for detailed mapping of the nhsz area spectral data fusion with structural data analysis and field observations provide a better understand of the temporal and spatial relationships between the litho tectonic units and regional tectonic setting in the course of controls on base metal sulfide and associated gold mineralization merging these different data sources in the study area suggests that the base metal sulfide and associated gold mineralization are restricted to quartzites member of island arc related metasediments and mostly controlled by d3 deformational event main hsz deformational event this event characterized by transpressional stress regime with 1 trending e w and 3 trending n s activated conjugate nnw sinistral and nne ssw dextral strike slip faulting likely during syn tectonic granodiorite emplacement

spatial pattern of grain size in the late pliocene red clay deposits north china indicates transport by low level northerly winds abstract the confirmation of an eolian origin of the tertiary red clay from north china would make it a valuable terrestrial paleoclimatic record however it is still controversial as to which wind primarily transported the dust forming the red clay onto the loess plateau careful consideration of this question is a prerequisite for better understanding the history of atmospheric circulation in central and east asia during the miocene and pliocene epochs in this paper the grain size distributions of bulk samples and chemically isolated quartz grains of the late tertiary red clay were investigated to explore the potential transportation mechanisms of the dust as well as the atmospheric circulation at the time of deposition the samples were taken from six localities spanning across 550 km on the loess plateau the results show that the mean grain size of both bulk and quartz samples decreases southward as does the coarse fraction content 42 m these data not only give new evidence for the eolian origin of the red clay but also indicate that the red clay was probably transported mainly by northerly low level winds or the winds at least had a strong northerly component therefore the spatial distribution of grain size of the red clay is comparable to that of the overlying quaternary eolian loess which demonstrates a remarkable northwest southeast decrease in grain size sedimentation rate and thickness during the last glacial coinciding with the dominant wind direction of the northwesterly east asian winter monsoon however the grain size of the red clay is generally finer than the corresponding loess this indicates that the red clay may have been transported by a weaker winter monsoon associated with stronger pedogenic modification and or the dust source area was not extensive compared to that during the quaternary moreover the high content of grains coarser than 19 m transported mainly by energetic low level winds over short distances suggests that the dusts were not transported by upper level westerly

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

review of late proterozoic sutures ophiolitic melanges and tectonics of eastern egypt and north east sudan the distribution structural relations and ages of ophiolites and ophiolitic melanges in the eastern deserts of egypt and north east sudan and their relation to arc and post arc magmatism are used to infer the probable positions of sutures and the directions of obduction and subduction the ages of the successive tectonic stages in the terranes decrease northwards by about 100 ma in the region discussed obduction was north westwards the obducted sheets of ophiolite and ophiolitic melange extending about 500 km north from the onib sol flamed suture may all represent a single back arc basin the direction of subduction is still not clearly proved more geochemical evidence of arc magmatic polarity is needed the late tectonic north westward thrusting the nw se stretching lineation the transpressional north south hamisama shear zone and the nw se sinistral najd faults are all attributed to north westward movement present coordinates of terranes towards the older craton west of the nile the najd faults are interpreted as intracontinental transform faults

the ophiolitic north fork terrane in the salmon river region central klamath mountains california the north fork terrane is an assemblage of ophiolitic and other oceanic volcanic and sedimentary rocks that has been internally imbricated and folded the ophiolitic rocks form a north trending belt through the central part of the region and consist of a disrupted sequence of homogeneous gabbro diabase massive to pillowed basalt and interleaved tectonitic harzburgite u pb zircon age data on a plagiogranite pod from the gabbroic unit indicate that at least this part of the igneous sequence is late paleozoic in age the ophiolitic belt is flanked on either side by mafic volcanic and volcaniclastic rocks limestone bedded chert and argillite most of the chert is triassic including much of late triassic age but chert with uncertain stratigraphic relations at one locality is permian the strata flanking the east side of the ophiolitic belt face eastward and depositional contacts between units are for the most part preserved the strata on the west side of the ophiolitic belt are more highly disrupted than those on the east side contain chert argillite melange and have unproven stratigraphic relation to either the ophiolitic rocks or the eastern strata rocks of the north fork terrane do not show widespread evidence of penetrative deformation at elevated temperatures except an early tectonitic fabric in the harzburgite slip fiber foliation in serpentinite phacoidal foliation in chert and mafic rocks scaly foliation in argillite and mesoscopic folds in bedded chert are consistent with an interpretation of large scale anti formal folding of the terrane about a north south hinge found along the ophiolitic belt but other structural interpretations are tenable the age of folding of north fork rocks is constrained by the involvement of triassic and younger cherts and crosscutting late jurassic plutons deformation in the north fork terrane must have spanned a short period of time because the terrane is bounded structurally above and below by middle or late jurassic thrust faults the north fork terrane appears to contain no arc volcanic rocks or arc derived detritus suggesting that it neither constituted the base for an arc nor was in a basinal setting adjacent to an arc sediment source details of the progressive accretion and evolutionary relationship of the north fork to other terranes of the klamath mountains are not yet clear

an expanded view of jurassic orogenesis in the western united states cordillera middle jurassic pre nevadan regional metamorphism and thrust faulting within an active arc environment klamath mountains california basaltic to basaltic andesitic volcaniclastic rocks and their contemporaneous mafic ultramafic intrusive complexes delineate a middle jurassic arc terrane within the klamath mountain province of northern california exposures of the supracrustal volcaniclastic rocks are restricted to a single fault bounded terrane but the deeper level intrusive complexes were emplaced into most if not all the pre late jurassic terranes of the klamath mountain region the pre late jurassic terranes thus constitute the basement of the middle jurassic arc u pb zircon analyses of 39 zircon fractions from 12 intrusive complexes plus k ar dating of the volcaniclastic strata demonstrate magmatic activity over the interval of 177 159 ma the active arc and its basement were imbricated by a compressive deformational event the signature of which included thrust faulting isoclinal folding and regional metamorphism several diverse lines of evidence including k ar dating of metamorphic rocks crosscutting relations of dated intrusive complexes to thrust faults and u pb dating of synmetamorphic intrusive complexes establish a distinctly pre nevadan middle jurassic age ongoing at 169 ma and over by at least 161 ma for this compressive deformational episode outboard and structurally beneath the middle jurassic arc and its basement are several terranes that collectively comprise the western jurassic belt these terranes were deformed and regionally metamorphosed during the late jurassic nevadan orogeny which occurred within the time interval of 157 150 ma as upper jurassic plutons with 150 to 142 m y old zircon ages have contact aureoles that overprint the nevadan fabric and the 157 m y old rogue formation was deformed in the nevadan event the middle and late jurassic compressive deformational events were thus distinct and separated by as much as 15 20 m y the relation between middle and late jurassic magmatism and deformation suggests that the klamath mountain province records the evolution of a considerably long lived arc system that evolved above an east dipping subduction zone in addition we suggest that this are system may represent an oceanic continuation of the long recognized early mesozoic arc terrane of the western u s cordillera

beach ridge development and lake level variation in southern lake michigan abstract the most accurate source of information on lake level fluctuations in the great lakes is the historical record from lake level gauges although it can be semiquantitatively extended back into the late 1700 s the historical record is too short to recognize long term patterns of lake level behavior to extend the historical record information must be obtained from the great lakes geologic record such information includes the elevation and age of geomorphic features and stratigraphic sequences one of the longest geologic records of late holocene lake level variation is preserved in a beach ridge complex along the southern shore of lake michigan called the toleston beach this strandplain contains over 150 beach ridges that arc across northwestern indiana and fan out into northeastern illinois each ridge was formed during the fall from a high lake level and the elevation of the foreshore deposits in each ridge provides information on the upper physical limit of lake level over the past 4000 years three scales of quasi periodic lake level variation were determined by radiocarbon dating basal peats of wetlands between the ridges and by measuring the elevation of foreshore swash deposits within ridges these three scales are 1 a short term and small scale fluctuation of 25 to 35 years with a range of about 0 5 to 0 6 m 2 an intermediate term and meso scale fluctuation of 140 to 160 years and a range of about 0 8 to 0 9 m and 3 a long term and large scale fluctuation of 500 to 600 years and a range of 1 8 to 3 7 m the short term and intermediate term fluctuations are reflected in the historical record an increase in the rate of shoreline progradation from east to west across indiana s shoreline causes differential preservation of the lake level fluctuations that is groups of four to six ridges in the western part of the strandplain that formed in response to the small scale fluctuations combine eastward into single ridges and groups of ridges representing the meso scale fluctuations the large scale fluctuations produced the most dramatic response in the western part of the toleston beach here following each high stand individual spits prograded southward off of a bedrock headland the successive spit extensions created several small lakes landward of the spits and started the 20 km eastward stream mouth deflection of the grand calumet river across indiana s western lakeshore

origin of beach ridges and swales abstract sandy beach ridges occur in four main categories 1 swash built 2 settling lag 3 eolian 4 storm surge ridges in the first two classes are geometrically regular only a few tens of centimeters above adjacent swales and commonly in ridge sets and systems tens to hundreds of ridges each individual sets of 5 25 ridges tend to stand 0 5 m to 2 m above or below adjacent sets ridges in the third and fourth classes do not have these characteristics do not occur in sets and are generally not suitable for detailed historical studies no one of these ridges is the same as the storm built berm which is almost never preserved swash built sandy beach ridges have diagnostic 1 map spacing 2 accretion rate 3 periodicity 4 crossbedding and 5 granulometry the last two indicate fair weather waves on a sandy beach in contrast with settlinglag ridges postma style which have the same external geometry but which were deposited without important wave work and in contrast with storm built berms generally seen on eroding coasts but rarely or never in beach ridge plains the grain size kurtosis of beach sand is an excellent index to near shore wave energy density changes in kurtosis at ridge set boundaries mark changes in long term wave energy density hence in sea level the latter can be deduced also from set height differences and from spacing differences periodicity is typically 30 60 years map spacing 25 50 m and accretion rate fairly close to 1 m yr a few ridge sets with intervals of 3 7 10 12 or 18 19 years have smaller spacings this is not what can be done if each ridge is built by one storm if each ridge had been built by one storm wide beach ridge plains like one in denmark dating from about 11 700 yr b p would have been formed in the last 30 50 years at accretion rates of hundreds of meters per year instead each swash type sandy beach ridge was made by a sea level rise and fall couplet amplitude 5 30 cm the swale marks the lower position this mechanism reflects the fact that the transverse profile from beach to sea is gently concave upward with maximum curvature close to shore this is a shape which is out of adjustment with the shoaling wave system shortly after a small sea level change settling lag ridges were built without waves hence the ridge and swale sequence in this case cannot be attributed to waves either fair weather or storm these ridges show the same historical pattern as do swash built ridges this fact suggests that both were controlled by the same mechanism sea level change

significance of xenocrystic precambrian zircon contained within the southern continuation of the josephine ophiolite devils elbow ophiolite remnant klamath mountains northern california the josephine ophiolite of the western jurassic belt klamath mountain province of california and oregon is the expression of a well documented late jurassic suprasubduction zone rift basin that formed between an active late jurassic arc to the west and a remnant middle jurassic arc to the east the devils elbow ophiolite remnant deo exposed along the south fork of the trinity river represents the southernmost continuation of the josephine ophiolite and provides important new constraints on the early history of this rift basin the deo consists of pillow lavas and breccias and a well developed sheeted dike complex that are depositionally overlain by a clast supported breccia derived almost exclusively from ophiolitic detritus dikes and irregular pods of plagiogranite are conspicuous elements of the deo and exhibit mutually crosscutting relations with mafic dikes thus they are interpreted as genetically related elements of the dike complex zircon separates from two widely separated plagiogranite dike localities yielded two distinct zircon populations a clear euhedral magmatic population and a reddish rounded xenocrystic population the isotopic systematics of four zircon fractions from these two dike localities indicate a crystallization age for the deo of 164 1 ma and an age of 1 7 ga for the xenocrystic zircon component the occurrence of a xenocrystic precambrian zircon component within the plagiogranites of the deo provides unequivocal evidence that rifting occurred within preexisting zircon bearing crustal rocks of the klamath mountains as there is no precambrian crust within the klamath mountains the xenocrystic zircon population must have been derived from supracrustal sedimentary sequences the most likely source for the older zircon component is a terrigenous metasedimentary sequence contained within the rattlesnake creek terrane which formed part of the structural basement of the rifted middle jurassic arc the incorporation of xenocrystic precambrian zircon from the rifted basement of the middle jurassic arc could only have occurred during the earliest stages of rifting thus the deo must represent a fragment of an initial rift that ultimately formed the late jurassic basin now floored by the josephine ophiolite in support of the zircon data dikes and lavas of the deo have geochemical characteristics transitional between island arc and mid ocean ridge magma series as would be expected within an initial rift setting of a suprasubduction zone ophiolite

reconstruction of paleo wave conditions during the late pleistocene from marine terrace deposits monterey bay california the santa cruz coastal terrace fringes much of the northern monterey bay region california it consists mainly of a regressive sequence of high energy barred nearshore marine sediments deposited during the last sangamonian highstand of sea level this sequence can be sub divided into several depth dependent facies on the basis of paleo current data and vertical sequence of sedimentary structures these include a lower shoreface facies deposited in 10 16 m water depth an upper shoreface facies including both a storm dominated assemblage and a surf zone assemblage deposited in 0 10 m water depth and a foreshore facies deposited in the swash zone up to 3 5 m above high tide the magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo wave heights using a variety of criteria e g critical threshold equations breaker depths berm heights in addition the climate and paleogeography during the deposition of these sediments were essentially the same as today allowing the use of present day wave statistics to estimate the frequency of these storm events the largest storms formed offshore flowing currents e g rip wind forced and possibly storm surge ebb currents that resulted in the deposition of approximately 30 of the sediments seaward of the surf zone however the magnitude and frequency of these events are unknown the remaining 70 of the sediment beyond the surf zone was deposited in response to smaller storm waves which were on the average at least 1 6 m high such waves presently occur no more than 15 of the time sediments deposited during fairweather conditions i e the remaining 85 of the time have a low preservation potential and are generally not preserved in this facies in contrast surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably 2 2 m such waves presently occur up to 92 of the time sediments within the swash zone were deposited by waves up to 3 m high the largest of which presently occur approximately 2 of the time most of the sediments were deposited by storms of intermediate magnitude and frequency different facies however appear to preferentially record events of different recurrence intervals in particular surf zone sediments were deposited under relatively small storm and post storm conditions whereas sediments deposited farther offshore record increasingly larger less frequent storm events relatively rare events e g the 100 or 1000 yr events do not appear to have significantly affected sedimentation in these nearshore environments

age and chemical characteristics of some pre pan african rocks in the egyptian shield abstract u pb ages on zircons from several types of sialic rocks together with a variety of geochemical data on one sample of early plutonic activity within the egyptian shield are presented the earliest autochthonous granitic rocks in the egyptian shield are probably quartz diorites tonalites emplaced just prior to the main peak of pan african igneous activity 550 650 ma the studied example has an age of 711 ma 7 ma and is characterized by very low initial sr ratio 87sr 86sr 0 7026 and very low abundances of k2o and related large ion lithophile trace elements ree contents are low less than 20 chondritic abundances abundance patterns show only moderate light rare earth enrichment la yb 4 5 these characteristics are inconsistent with any models requiring fractional fusion of pre existing continental crustal material granitic and arkosic cobbles occur in rare conglomerate beds within volcanoclastic and greywacke sedimentary sequences the cobbles show a wide range in ages 1 1 2 3 ga and have no obvious source within the egyptian shield it is suggested that they are not indicative of any sialic plutons in the egyptian shield which might predate deposition of the enclosing immature sediments more probably they were derived from adjacent continental areas such as the uweinat region to the west and were deposited in an evolving arc ocean basin complex

reconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

on the thermal regime of an arctic valley glacier a study of white glacier axel heiberg island n w t canada from 1974 to 1981 a total of 32 bore holes was drilled on white glacier and vertical ice temperature profiles measured the data obtained allowed the construction of three longitudinal and four transverse profiles of the two dimensional temperature distributions thus an extensive layer of temperate or near temperate ice was discovered close to the bedrock in the lowest part of the glacier tongue it was also found that the temperature distribution cannot be in a steady state since there is a temperature minimum 100 150 m below the glacier surface in the accumulation area a simple numerical model calculation shows that this minimum can be mostly explained by the general climatic warming since 1880 the 10 m temperatures show diffuse relations to climatic conditions and balance zones a simple scheme for extrapolating surface temperatures is discussed

wave runup and overwash on a prototype scale sand barrier abstract accurate methods to predict wave runup are of critical importance to coastal engineers extreme runup during storm conditions can present a danger to coastal infrastructure and lead to dune overtopping and erosion overwash of barrier beaches and is an essential design parameter for certain coastal protection works this paper uses data obtained during the unique bardex ii prototype scale laboratory experiment on a reflective sand barrier to investigate wave runup and overwash runup measurements were acquired using ultrasonic altimeters 2d scanning lidar and camera systems under controlled wave and water level conditions it was found that extreme runup r 2 scaled well with the deepwater irribarren number where the beach slope was taken to be the beach face gradient the lower limit of the swash zone defined by the 2 wave rundown limit was also found to be a function of the irribarren number and was consistently below the swl in all tests the high resolution free surface measurements obtained using the ultrasonic altimeters and lidar enabled an analysis of the dynamics of individual swash events it was found that the vertical runup excursion of each swash correlated strongly with the height of the bore at collapse and could be predicted based on the assumption of a conversion of potential to kinetic energy at bore collapse

use and abuse of crustal accretion calculations recent attempts to calculate the average growth rate of continental crust for the late proterozoic shield of arabia and nubia are subject to large geological uncertainties and widely contrasting conclusions result from dissimilar boundary conditions the four greatest sources of divergence are 1 the extent of 620 920 ma arc terrane crust beneath phanerozoic cover 2 the extent of pre 920 ma continental crust within the arc terranes 3 the amount of postaccretion magmatic addition and erosion and 4 the aggregate length and average life span of late proterozoic magmatic arc systems that formed the arabian nubian shield calculations restricted to the relatively well known arabian segment of the arabian nubian shield result in average crustal growth rates and arc accretion rates comparable to rates for modern arc systems but we recognize substantial uncertainty in such results critical review of available geochemical isotopic and geochronological evidence contradicts the often stated notion that intact pre 920 ma crust is widespread in the eastern arabian shield instead the arc terranes of the region apparently were contaminated with sediments derived in part from pre 920 ma crust available geologic and radiometric data indicate that the arabian nubian shield and its pan african extensions constitute the greatest known volume of arc accreted crust on earth that formed in the period 920 620 ma thus the region may truly represent a disproportionate share of earth9s crustal growth budget for this time period

the geology and geochemistry of upper proterozoic granitoids from the red sea hills sudan granitoid plutons are common throughout the late proterozoic basement complex of north east sudan frequently accounting for 60 of the outcrop geological petrological and isotopic studies indicate that two distinct types of granitic plutonism can be recognized an older diorite to granodiorite assemblage was emplaced between c 815 and 724 ma and a younger predominantly alkali feldspar granite assemblage consisting of numerous discrete high level intrusions was emplaced between c 717 and 555 ma these granitoids have a calc alkaline character similar to the volcanic rocks of the basement complex to which they are spatially and temporally related the geochemical and isotopic data suggest a destructive plate margin rather than a within plate palaeotectonic association it is suggested that the granitoids represent an evolutionary trend from early diorite to granodiorite intrusions emplaced above a late proterozoic subduction zone to later post tectonic intrusions emplaced during a late stage of volcanic arc development the magmas of the early granitoids were probably mantle derived while the later post tectonic intrusions may have been derived from magmas produced by partial refusion of the volcanic arc protolith

dispersed remnants of a northeast pacific fringing arc upper paleozoic terranes of permian mccloud faunal affinity western u s two fragmentary subparallel belts of terranes within the western north american cordillera contain upper paleozoic rocks and are characterized by contrasting lithotectonic assemblages and contrasting permian faunal affinity these two belts are a volcanic arc related successions of permian mccloud faunal affinity mccloud belt and b subduction related accretionary complexes of permian tethy an faunal affinity cache creek belt this paper supports the hypothesis that the fragmentary terranes of the mccloud belt once constituted parts of a northeast pacific fringing arc system and in constrast to some earlier interpretations concludes that the volcanic arc evolved above an eastward dipping subduction zone the absolute distance between this arc and western north america during the late paleozoic cannot be constrained however there is little evidence to suggest closure of a major 10 km ocean basin or protracted periods of westward dipping subduction parts of devonian to permian volcanic island arc sequences of the western u s cordillera are represented in the northern sierra eastern klamath bilk creek grindstone and chilliwack terranes these scattered volcanic arc remnants share several fundamental characteristics 1 the sequences were constructed across continental affinity basement assemblages 2 they underwent similar tectonic evolution during late paleozoic time such as coeval pulses in volcanism and related depositional histories 3 they contain early permian mccloud type fauna of distinctive biogeographic affinity 4 mccloud belt terranes are spatially and possibly genetically related to westward lying accretionary complexes of the cache creek belt which contain fragments of upper triassic blueschist and permian limestone blocks bearing tethyan permian fusulinids and corals based on the presence of distinctive early permian mccloud fauna the island arc remnants discussed in this paper are referred to as the mccloud belt the similarities between mccloud belt terranes suggest that they were once parts of a long lived late paleozoic volcanic arc complex the stratigraphy of these terranes records the tectonic evolution of the volcanic arc volcanism within the paleozoic arc began as early as the early devonian and was succeeded or accompanied by carbonate and epiclastic sedimentation during the middle and late devonian an influx of detritus derived from sedimentary and metasedimentary rocks during the late devonian and mississippian records the uplift and erosion of arc basement sequences an event that was at least locally accompanied by ongoing volcanism a pulse in volcanism during the pennsylvanian and coeval uplift led to the establishment of shallow marine and deltaic volcanogenic and carbonate sedimentation and locally subaerial exposure which persisted into the early early permian elsewhere during the early permian shallow water carbonate deposition was established with only minor influx of volcanogenic debris during the late permian and locally as early as late early permian a major pulse in volcanism occurred and is now represented by voluminous sequences of volcanogenic debris and lavas most of these sequences are overlain by upper triassic carbonate platformal sequences arc volcanism was recorded at least locally until the middle jurassic paleomagnetic data are used to constrain a schematic pre cretaceous reconstruction of these volcanic arc sequences and their associated subduction assemblages the inferred paleogeography of island arc sequences and the adjacent accretionary terranes suggests that volcanism occurred above an east dipping subduction zone with a long lived paleogeographic relation to north america the current structural position of these terranes is largely the result of mesozoic and locally younger deformation

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

microbialites in a modern lagoonal environment nature and distribution tikehau atoll french polynesia abstract microbialites including stromatolitic structures gelatinous masses and mats develop in tikehau lagoon tuamotu french polynesia on the flanks and slopes of numerous pinnacles and motu islets between 0 and 25 m deep on coral colonies algal tufts or on lagoonal sediments individual stromatolitic structures consist of hemispherical domes and are produced by monospecific populations of filamentous cyanobacteria belonging to three distinctive phormidium species symploca and possibly to one new species of schizothrix gelatinous masses hanging from the ceiling of caverns are produced by phormidium laysanense microbial mats are well developed at all depths on pinnacle slopes and are produced by either monospecific or mixed cyanobacterial populations the study of micro and ultrastructure of stromatolites reveals that they result both from trapping and binding of sediments and from carbonate precipitation in addition to phototrophic biomineralization pervasive carbonate precipitation occurred in association with decaying organic matter the basic constructional elements of the precipitated carbonate consist of 0 1 0 2 m rounded bodies that form very fine anhedral to subhedral micrite their surfaces comprise extremely small carbonate granules 20 50 nm gradual changes ageing in the ultrastructure of carbonate precipitates include the precipitation of successive euhedral calcite layers around these grains widespread development of microbialites in this pristine lagoonal environment results from rapid blooms of microbial benthic communities possibly induced by temporary and local nutrient pulses nutrients seem to undergo a restricted circulation between the sediment and pinnacle reef frameworks pinnacles and reef islets are repeatedly affected by catastrophic storm events which cause redistribution of sediments and nutrients

the upper proterozoic ophiolite melange zones of the easternmost arabian shield the arabian nubian shield was produced by the episodic cratonization and accretion of intra oceanic arc systems over the period 1100 500 ma bp the easternmost part of the arabian shield is dominated by the n s al amar fault zone long believed to represent an easterly inclined upper proterozoic suture between either two island arc systems or oceanic and continental lithosphere in the area studied there are two n s ophiolitic melange zones which separate a central belt of metamorphosed trench sediments abt schists from flanking granitoid zones that represent the plutonic cores of arc systems the melange blocks are of layered gabbro chromitite homogeneous gabbro with dykes plagiogranite sheeted dykes and pillow lavas set in a sheared serpentinite matrix the blocks are large c 1 km and gabbroic in the western zone and smaller 1 100 m and of fine grained basic rocks in the eastern zone all are compositionally similar and petrographically typical of rock types found in ophiolite complexes elsewhere however the zr ti and nb content of all these rocks is too low even for the back arc marginal basin setting commonly invoked for ophiolite genesis to explain the unusually low high field strength element abundances it is suggested that either these rocks were generated in or near a transform fault zone and then deposited in an oceanic trench when they began to be subducted or that their boninitic character identifies them as the products of fore arc igneous activity and by analogy with the tectono magmatic evolution of the w phillipine mariana region in the w pacific they mark the site of arc separation prior to back arc sea floor spreading the latter explanation is preferred

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

arabian shield ophiolites and late proterozoic microplate accretion fragments of late proterozoic ocean crust and mantle ophiolites occur within six major fault zones that mark sutures between crustal blocks microplates that were accreted between about 630 and 715 ma to form the arabian shield we report new u pb zircon ages for ophiolitic gabbro diorite and plagiogranite that range from 840 to 700 ma and establish these complexes among the oldest proven ophiolites by dating the ophiolitic rocks we are able to monitor the magmatic ages of sea floor spreading events during accretion of the arabian shield comparison of the ophiolitic dates with the ages of the adjacent crustal blocks provides a more complete basis for plate tectonics reconstruction of the shield than has previously been possible our new zircon ages confirm earlier sm nd mineral isochrons for ophiolites of the northwestern arabian shield show that the ophiolites are among the oldest oceanic rocks in each terrane support near or within arc tectonic settings for the ophiolites suggest that the bir umq suture extends north along the nabitah mobile belt into the northern shield and suggest that older 1250 ma continental crustal material is locally present in the dominantly oceanic western shield we suggest that indonesia and alaska provide phanerozoic analogues for stages in the accretion history

geological characteristics and distribution patterns of hydrocarbon deposits in the bohai bay basin east china abstract the bohai bay basin in east china is a meso cenozoic continental fault bounded basin with abundant petroleum resources based on analyses of sedimentation history and tectonic and thermal evolution the vertical and horizontal distribution patterns of oil and gas are discussed in this paper the basin has characteristics of multiple cycles of depression and uplift and each depression has its own sedimentary system and pattern of oil generation the main source rocks are of lower tertiary sediments characterized by multi cyclic sedimentation multiple source reservoir caprock associations were developed abrupt changes of sedimentary facies and the development of numerous faults caused the formation of various types of oil and gas reservoir that constituted multiple oil and gas accumulation zones based on individual structure zones these accumulation zones are mainly distributed around the centre of source rock deposits and are restricted in the areas where source rocks are distributed

stratigraphy and palaeogeography of the siham group direct evidence for a late proterozoic continental microplate and active continental margin in the saudi arabian shield the presence of ancient continental crust in the afif terrane of the arabian shield has been indicated by radiometric data detailed mapping in the central shield reveals a volcano sedimentary succession older than one of the final cratonizing events of the shield and unconformable upon high grade paragneisses providing direct evidence for a western continental margin to the afif terrane in late proterozoic times the basement gneisses were metamorphosed to almandine sillimanite amphibolite facies and preserve evidence of a deformation not seen in any other rocks of the area the siham group unconformable upon this basement was metamorphosed to upper greenschist facies it has been divided into six formations which provide an e w section through the group the lower members are volcanic and are absent in the easternmost formation their clastic content increases eastward a carbonaceous shale with exhalative chert and marble tuffs and associated volcanogenic massive sulphides is associated with the volcanics it is absent in the east where shallow marine marbles and quartzites lie unconformably upon basement rhyolite and conglomerate complete the succession in the west the base of the group is not seen but the shale is associated with numerous sheet like bodies of mafic and ultramafic rock emplaced in an extensional tectonic setting other plutonic rocks are calc alkaline and are emplaced mainly in the west deep water oceanic conditions prevailed in the west and a shallow marine continental shelf environment existed in the east with deposition of the group across this continental margin the stratigraphy of the siham group is particularly akin to the mesozoic of peru magmatic arc and marginal basin were coincident in space and time and the marginal basin was probably extensional there is some limited evldence that it was ensialic the siham group is bounded to the west by a n s suture zone formed in one of the final collisional events in the cratonization of the shield this event caused the deformation of the siham group and marked the termination of the magmatic are

late proterozoic evolution of the northern part of the hamisana zone northeast sudan constraints on pan african accretionary tectonics new structural data from the red sea hills northeast sudan add constraints to accretionary tectonic processes that acted in the arabian nubian shield during the late proterozoic geometric constraints provided by field data are used together with landsat thematic mapper imagery to interpret the regional distribution and structural relations of spectrally and lithologically distinctive rock assemblages in contrast to interpretations reported elsewhere these studies indicate that the hamisana zone a prominent structural feature in the northern red sea hills post dated terrane accretion it is characterized by east west crustal shortening and by steep folds and thrust faults calc alkaline magmatism was contemporaneous with and outlasted main phase deformation thus deformation occurred in an intra arc setting thrust faults were reactivated after east west contraction compromising their usefulness in delineating 9sutures9 or as piercing points across older faults pan african accretionary processes may have been analogous to phanerozoic ophiolite and island arc accretion in the western north american cordillera where penetrative deformation occurred in response to periodic intra plate shortening events rather than an ultimate collision of unrelated crustal fragments such an analogy implies a mechanism for crustal thickening by structural as well as igneous processes during evolution of an accretionary belt in a long lived convergent margin setting consistent with the long standing observation that pan african magmatism became more evolved with time this view emphasizes that an interplay of deformation and magmatism resulted in protracted accretion and crustal thickening in contrast to models where crustal shortening results directly from collision of a volcanic arc microcontinent or other buoyant features

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

orientation of late precambrian sutures in the arabian nubian shield recent tectonic models have resulted in conflicting descriptions of how the late precambrian sutures of the arabian nubian shield extend into northeast africa the hamisana shear zone in northeastern sudan is critical to this discussion because it truncates and disrupts two sutures the allagi heiani and the onib sol harried analysis of field structural data thematic mapper imagery and rb sr and u pb geochronology suggests that the allagi heiani suture is the western extension of the onib sol harried suture and that both make up the exposed parts of a far traveled polydeformed ophiolitic nappe complex subsequent deformation localized in the hamisana shear zone disrupted this nappe and displaced the suture between 660 and 550 ma during regional deformation associated with the najd fault system these results indicate that at least one suture extends westward into the interior of northern africa

evidence of episodic coastal change during the late holocene the dungeness barrier complex se england plater a j stupples p roberts h m 2009 evidence of episodic coastal change during the late holocene the dungeness barrier complex se england geomorphology 104 1 2 47 58

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

analytical method for estimating palaeowave climate and water depth from wave ripple marks analytical expressions are developed for evaluating palaeodepth and palaeowave conditions from wave ripple marks palaeodepth and palaeowave climate estimates can be extremely powerful predictors in reconstructions of vertical movements related to basin subsidence local and regional ancient wave climate trends and the basin shape the analytical expressions developed herein are applied to wave ripple marks preserved in the lower marine molasse of switzerland western austria and southern germany the results suggest that in contrast to traditional concepts of an eustatic sea level change the lower marine molasse regression was a result of mainly depositional processes the subsidence rate greatly exceeded the rate of sea level fall over a wide geographical area furthermore the widening of the lower marine molasse basin to the ene is well documented by the increase of the ancient wave period and wave power calculated from wave ripple marks found in storm deposits

u pb isotopic evidence for the accretion of a continental microplate in the zalm region of the saudi arabian shield the area covered by this work includes three of the main tectonic units of the arabian shield the afif continental terrain the nabitah suture with its associated mobile belt and the asir ensimatic arc terrain the geology of the zalm area is well understood and this geochronologic and isotopic study confirms that the southern afif terrain was a continental microplate in the late proterozoic the study also provides a time frame for the crustal evolution of this part of the shield the kabid formation is the oldest in the region and comprises pelitic arkosic and felsic high grade paragneisses u pb zircon data from a pelitic garnet sillimanite gneiss show that this part of the continental basement in the southern afif terrain may be as old as 1770 ma isotopic nalyses indicate that lead from the kabid gneiss resided in the upper continental crust for a long period before 1770 ma and consequently archaean source rocks may be present within the southern afif terrain pb and rb sr isotopic data in the zalm region reveal a change in the nature of the underlying crust from continental basement in the northeast to less radiogenic marginal arc rocks in the southwest this change is coincident with both aeromagnetic data and a facies change within a pre collision marginal basin miogeosynclinal continental shelf facies of the siham group lie unconformably over the kabid formation and are in the area of continental lead signatures eugeosynclinal deep water sediments and volcanics in association with ultramafic rocks occur in the area of marginal arc signatures u pb zircon age determinations show that this 9andean9 continental margin developed before about 720 ma and emplacement of calc alkaline plutonic rocks continued until about 690 ma during the period 685 640 ma the continental afif microplate collided with the asir terrain as part of the nabitah orogeny at approximately 640 ma ago the najd strike slip faulting commenced with a dextral phase that controlled the emplacement of granitic plutons as well as the development of a series of large pull apart grabens some of these grabens were floored by new oceanic crust and were filled with volcanosedimentary rocks of the bani ghayy group subsequently the najd fault system changed to sinistral strike slip motion at about 620 ma ago

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

geochronology of the late precambrian hamisana shear zone red sea hills sudan and egypt the hamisana shear zone hsz is a broad zone of deformation approximately 50 km wide and at least 300 km long making it one of the largest basement structures in ne africa it has been interpreted as a precambrian suture as a zone of strike slip displacement or as a zone of crustal shortening the results of new rb sr and u pb zircon geochronological studies indicate that the northern hsz was thermally active during the pan african event until c 550 mg ago initiation of the structure may have begun 40 110 ma earlier all units have low initial 87 sr 86 sr ratios indicating juvenile derivation the timing of activity in the hsz is 50 150 ma younger than collisional suturing and terrane assembly in the arabian nubian shield but is similar to the 655 540 ma najd fault system of egypt and arabia deformation and metamorphism along the hsz clearly post date terrane accretion and probably are closely related to the najd tectonic cycle the most important deformation of the hsz is unrelated to suturing and at least one late precambrian suture must extend west from arabia into the interior of n africa

the late proterozoic ophiolite of sol hamed ne sudan abstract the sol hamed complex a sequence from ultramafics through gabbros thin sheeted dykes to pillow lavas is an ophiolite it was obducted tilted nearly to vertical eroded and covered unconformably by the nafirdeib series this is a volcaniclastic series dated at 712 58 ma the lower part of which includes conglomerates with ophiolitic clasts olistostromes one with large oolitic limestone slabs felsitic and dacitic tuffs turbidites and black shales with andesites above some of the structures in the ophiolite are attributed to sub oceanic deformation deformation after the deposition of the nafirdeib series produced folds and cleavage trending about ne sw and more locally a cleavage trending nw in a shear zone where the ophiolite was thrust northeastwards over the nafirdeib series the ophiolite and the nafirdeib series were intruded by the batholithic granite dated elsewhere at ca 669 ma the ophiolite is thought to occur on a suture with the nafirdeib series representing part of an island arc sequence

estimating palaeowind strength from beach deposits abstract the geological record of past wind conditions is well expressed in the coarse gravel cobble and boulder beach deposits of quaternary palaeolakes in the great basin of the western usa and elsewhere this paper describes a technique using the particle size distribution of beach deposits to reconstruct palaeowind conditions when the lakes were present the beach particle technique bpt is first developed using coarse beach deposits from the 1986 87 highstand of the great salt lake in utah combined with instrumental wind records from the same time period next the bpt is used to test the hypothesis that wind conditions were more severe than at present during the last highstand of lake lahontan 13 ka which only lasted a decade or two at most the largest 50 beach clasts were measured at nine beach sites located along the north west and south sides of antelope island in the great salt lake all of which formed in 1986 87 at these sites the largest clast sizes range from 10 to 28 cm b axis and fetch lengths range from 25 to 55 km nearshore wave height was calculated by assuming that the critical threshold velocity required to move the largest clasts represents a minimum estimate of the breaking wave velocity which is controlled by wave height shoaling transformations are undertaken to estimate deep water wave heights and ultimately wind velocity wind estimates for the nine sites using the bpt range from 6 5 to 17 4 m s 1 which is in reasonable agreement with the instrumental record from salt lake city airport the same technique was applied to eight late pleistocene beaches surrounding the carson sink sub basin of lake lahontan nevada using the bpt estimated winds for the eight sites range from 9 7 to 27 1 m s 1 the strongest winds were calculated for a cobble boulder beach with a fetch of 25 km instrumental wind records for the 1992 99 period indicate that wind events of 9 12 m s 1 are common and that the strongest significant wind event 9 m s 1 for 3 h reached an average velocity of 15 5 m s 1 based on this preliminary comparison it appears that the late pleistocene western great basin was a windier place than at present at least for a brief time