internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

imaging the structure and reconstructing the development of a barchan dune using ground penetrating radar abstract the formation mechanism and development processes of aeolian landforms are significant research topics of aeolian environment the analysis of the sedimentary structure and stratigraphic sequence of sand dunes is the key content of this study ground penetrating radar gpr has been widely used in investigations of aeolian landforms to help detect underground sediment structures early studies using gpr to investigate dune sands were aimed at studying sedimentary structures and establishing the cause of gpr reflections but seldom displayed the complete dune structures in this study gpr techniques were used to reveal sedimentary structures and reconstruct the development process of a barchan sand dune in the mu us sandy land from the perspective of three dimensional space through reasonable arrangement of gpr survey lines in grids based on the analysis of 41 gpr profiles this study identified five major dune radar facies and three radar surfaces the results showed the following 1 the dune structures were mainly sets of low to high angle crossbedding with and low angle superposition surfaces which could be divided into modern and old deposition 2 the modern deposition was dominated by trough cross bedding distributed in the centre of the barchan dune and the old deposition was dominated by tabular cross bedding and lateral accretion bedding in dune wings the leeward slope form was a significant factor impacting the formation of the dune structure 3 the sedimentary structure showed the barchan dune experienced two major episodes in the early stage parabolic dunes migrated over fixed sand dunes and were subsequently covered by the upwind barchan dune due to the impacts of wind erosion the oldest age preserved in modern and old deposition can be approximately 1997 and 1970s respectively the sedimentary structures imaged by gpr can reveal these geomorphologic processes which can help better understand the formation mechanisms and development processes of sand dunes

radar reflections from sedimentary structures in the vadose zone ground penetrating radar gpr is a suitable technique for imaging sedimentary structures in the vadose zone because small texture related capillary pressure variations lead to changes in water content and electromagnetic properties to study exactly how gpr reflections are generated by sedimentary structures gpr profiles of an aeolian sedimentary succession are combined with measurements of textural electromagnetic and water retention characteristics from a trench time domain reflectometry indicates that small variations in texture in the high angle dune sediment are associated with changes in water content synthetic modelling shows that these changes cause clear gpr reflections in an experimental approach to estimate the radar response of structures below the wave resolution i e features smaller than 4 variations in grain size distribution and porosity in a thin section were used to reconstruct water retention curves and impedance models of the thinly layered sediment synthetic radar records calculated from the impedance models show that reflections from the studied subcentimetre scale structures are composites of interfering signals although these low amplitude interfering signals will commonly be overprinted by more prominent reflections they may cause reflection patterns that change with frequency and do not represent primary bedding

sedimentology of coarse clastic beach ridge deposits essex southeast england abstract the distinction of cheniers from other types of beach ridge can often be problematic the stratigraphy sedimentology and geomorphological development of sand and gravel rich beach ridges at three sites on the northern essex coast england were determined using ground penetrating radar gpr ground truthing trenches and auger holes and historical aerial photograph analysis the 900 mhz gpr system used achieved a maximum vertical resolution between 0 02 and 0 06 m there was good correspondence between the radar stratigraphy obtained from time migrated radar reflection profiles and the nature and form of bounding surfaces sets of lamination beds and bedsets observed in trenches data for one of the study sites colne point illustrate a complex beach ridge stratigraphy and sequence of development that confirms they are not true cheniers instead the ridges form part of both retrogradational and progradational barrier spit sequences chenier designation at the other two study sites foulton hall and stone point is more straightforward as the beach ridges lie at the junction between actively eroding mudflat and saltmarsh however despite the distinction between the barrier spit beach ridges and the cheniers the same types of deposit are recognised in both indicating similar formative processes washover sheet deposits consist of low angle

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

influence of relative sea level change and tidal inlet development on barrier spit stratigraphy sandy neck massachusetts abstract sandy neck is a 10 km long sheltered mesotidal barrier spit along the southeastern new england coast bordering cape cod bay its stratigraphy contains evidence of relative sea level rsl rise and tidal inlet development and enables reconstruction of accretion and progradation of this barrier through time core trench and ground penetrating radar gpr data show that the lower boundary of the uppermost eolian facies climbs about 9 m from the proximal to the distal part of the spit away from the mainland anchor point this change is thought to be related primarily to a comparable rise in rsl the same boundary also shows a shallowing trend in a seaward direction indicating net spit progradation through time the absence of inlet channel facies in the stratigraphy of the proxima part of the barrier spit in contrast to the presence of inlet facies in more distal parts of the spit indicates that some time elapsed after barrier initiation before an inlet thalweg developed in its earliest stages this thalweg was poorly defined wide and shallow but its characteristics changed as the barrier spit lengthened in the central part of sandy neck the assemblage of inlet channel facies becomes markedly thicker reflecting thalweg deepening in response to paleotopographic and substrate lithologic factors the stratigraphy of the distal part of the spit shows the effects of continued but more gradual inlet deepening that may be tied directly to increasing barrier length the process controlled stratigraphy presented here differs from current facies models because i accounts for temporal changes in coastal environmental processes and parameters it suggests a high preservation potential for proximal eolian facies in the spit sequence underneath a cover of fine grained and organic back barrier sediment once reliably dated the new stratigraphic data will help to improve the regional rsl curve for the southern cape cod bay area

emeishan basalts sw china reappraisal of the formation s type area stratigraphy and a discussion of its significance as a large igneous province the late permian emeishan basalt formation of sw china is one of earth s lips large igneous provinces yet its basic geology remains poorly documented recent work on sections close to the type area in sichuan province enable us in part to rectify this descriptions of the formation and associated units at two areas one on the lower flanks of mt emei and another from a series of outcrops in ebian county 50 70 km to the sw are presented the basalt pile is 180 270 m thick and in both areas comprises 12 flows that were erupted in relatively quick succession it rests conformably upon shallow marine limestones lignites suggesting emplacement close to sea level the upper half of the youngest basalt was intensively weathered but not eroded prior to it being conformably succeeded by complex body of rocks c 30 m thick that includes thin basalts pyroclastic rocks tuffs and organic rich terrestrial sediments this unit which has previously been described as a sedimentary package presumably because intense weathering has obscured the primary lithological fabric in key outcrops is considered to mark the volcanic waning phase uppermost permian and triassic terrestrial sediments conformably overlie the terminal volcanic rocks the sub regional stratigraphy is compared as best it can be with that described from two sections 400 km to the se one section matches reasonably well the other does not indicating that regional correlations need to be developed carefully the information is discussed in the context of lip generator models several key features of the emeishan basalt terrain are at odds with those commonly encountered in lip s the most important conclusion is that the unit marks a prematurely terminated system in which full bloodied rifting leading to the development of an ocean basin never started

structure and development of shell cheniers in essex southeast england investigated using high frequency ground penetrating radar abstract the stratigraphy and internal structure of contemporary shell cheniers on the southern essex coast england were investigated using a high frequency 900 mhz ground penetrating radar gpr system the cheniers lie on the seaward edge of laterally eroding saltmarshes at the junction with the tidal flats four main types of chenier are recognised each with a characteristic morphology and dynamic status migrated radar reflection profiles obtained from each of the chenier types achieved a sub decimetre vertical resolution ground truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified these have resulted from overwashing overtopping sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface each chenier is characterised by a different spatial arrangement of these four basic depositional units the results from the gpr surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms however a simple model involving a linear progression through chenier types 1 4 with time appears inappropriate instead two main evolutionary pathways are proposed with the sequence of development being principally controlled by the nature of the cheniers longer term sediment budgets

sedimentary structures of cold climate coastal dunes eastern hudson bay canada a study of sedimentary structures of cold climate coastal dunes along eastern hudson bay canada showed that in areas of very sparsely vegetated surfaces tractional sedimentary processes are dominant while in partly and well vegetated areas grainfall deposition is the dominant sedimentary process alternating fine and coarse sand strata are characteristic of the vegetated foredune ridge coarse strata are interpreted to be mainly related to niveo aeolian deposition in poorly vegetated areas deformed strata associated with the melting of snow were preserved a vaguely stratified strata interpreted as a dimpled surface as well as coarse lenses with irregular basal contact were found such distinctive sedimentary structures may represent good indicators of cold climate conditions and could serve as criteria to identify aeolianites that may have been deposited in similar cold climate environments in palaeoenvironmental reconstructions

surface subsidence caused by mantle plumes and volcanic loading in large igneous provinces abstract large igneous provinces form with massive flood basalts being erupted over a large region within a few million years a prevailing model for their formation is a mantle plume model in which a plume head originates from the core mantle boundary ascends through the mantle and produces topographic uplift and eventually massive melting at the surface however many geological observations indicate surface subsidence in the central region before or during flood basalt eruptions in this study we demonstrate that a plume head temporarily ponding below the 660 km phase change boundary causes significant subsidence at the earth s surface over an extended period before the eruption and that the loading from erupted basalts causes surface subsidence at the periphery of the eruption area that affects the environment for subsequent episodes of basalt eruptions our studies therefore demonstrate that the observed subsidence history in many flood basalt provinces is characteristic of the dynamics of mantle plumes and may be used as diagnostics for identifying plume induced flood basalt events

facies analysis and sea level change at the guadalupian lopingian global stratotype laibin south china and its bearing on the end guadalupian mass extinction abstract the guadalupian lopingian boundary stratotype at penglaitan and the nearby tieqiao section near laibin south china record a series of major environmental changes within the jiangnan basin during a mid permian biotic crisis the sequence stratigraphic petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea level fall that led to the establishment of mid ramp conditions laibin limestone in settings that were previously dominated by radiolarian mudstones the regression also coincides with a low point of 87 sr 86 sr ratios the lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the emeishan flood basalt province 800 km to the west of laibin thus unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event subsequent environmental changes included transgression spread of dysoxic waters indicated by populations of small pyrite framboids and a major negative c isotope excursion all these phenomena have been previously related to the end guadalupian extinction but they in fact post date the crisis because a post extinction fauna of foraminifers is encountered at this time

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

sedimentation and lithofacies paleogeography in southwestern china before and after the emeishan flood volcanism new insights into surface response to mantle plume activity abstract investigations into permian sedimentation and reconstruction of paleogeography in sw china are aimed at characterizing sedimentary responses to the emeishan mantle plume in addition to erosional features on the sediments underlying the uplifted emeishan basalts unusual depositions of permian age are also present in the emeishan large igneous province lip specifically carbonate gravity flows and submarine incised canyon fillings were developed in the western margin of the postulated uplifted area and rifting trenches were developed along the eastern margin alluvial fan deposits occur at the boundary between the inner and intermediate zones these depositions all rest on the maokou formation and are in turn covered by the emeishan basalts implying synchronism between crustal uplift and depositional events these deposits and the associated extension and normal faulting along the margin of and within the lip represent sedimentary features resulting from dynamic behavior of mantle plume com

sedimentary evidence for a rapid kilometer scale crustal doming prior to the eruption of the emeishan flood basalts biostratigraphic and sedimentologic investigations in 67 sections have been carried out for the middle permian maokou formation that immediately underlies the emeishan flood basalts in southwest china the results suggest a domal crustal thinning before the emplacement of the emeishan large igneous province variably thinned carbonates in the maokou formation are capped by a subaerial unconformity which is generally manifested by karst paleotopography paleoweathering zone or locally by relict gravels and basal conglomerates provenance analysis indicates that these gravels and conglomerates were mainly derived from the uppermost maokou formation therefore the stratigraphic thinning likely resulted from differential erosion due to regional uplift iso thickness contours of the maokou formation delineate a subcircular uplifted area in accordance with the crustal doming caused by a starting mantle plume as predicted by experimental and numerical modeling the duration of this uplift is estimated to be less than 3 myr and the magnitude of uplift is greater than 1000 m the sedimentary records therefore provide independent supporting evidence for the mantle plume initiation model for the generation of the emeishan flood basalts

unveiling past aeolian landscapes a ground penetrating radar survey of a holocene coastal dunefield system thy denmark abstract the southern part of the hvidbjerg coastal dunefield and the adjacent part of the lodbjerg coastal dunefield system in northwestern denmark has been mapped using ground penetrating radar coastal cliff exposures and 14 c datings indicate that the presently stabilized dunefield is underlain by a 10 15 m thick succession of holocene aeolian sand deposits and interbedded peaty palaeosols this succession is superimposed on a weichselian till towards the south and a mid holocene beach ridge and swash bar complex towards the north the peaty palaeosols represent preceding periods of dunefield stabilization these palaeosols reveal ages about ad 1100 1200 700 bc and 2100 bc and act as marker horizons in the study area more than 16 km of high resolution gpr data covering an area of 6 km 2 were collected in the near coastal part of the dunefields and enabled a correlation of these marker horizons across the dunefields these data allowed the elaboration of topographic subsurface and isopach maps and enabled an interpretation of the accumulation history of the aeolian system since about 2200 bc this accumulation history tells of alternating periods with a stabilization of the dunefields and periods with high sand accumulation basically a perched ground water level and the morphology of the previous stabilized dunefield made it possible to generate an accumulation space large enough to preserve the sand during periods with stronger winds and marked aeolian activity this 3d mapping of the stabilized dunefield subsurfaces has made it possible to unveil the development of the past aeolian landscape

combining ground penetrating radar surveys and optical dating to determine dune migration in namibia ground penetrating radar gpr profiles across a complex linear dune in the namib sand sea have been used to image sets of cross stratification and their bounding surfaces a combination of radar facies analysis and radar stratigraphy has been used to interpret the radar profiles and define a relative chronology thick sets of cross stratification indicate when the dune was most active whereas thin sets of cross stratification are interpreted to indicate the increased prevalence of wind reversals and lower rates of dune migration with bounding surfaces formed during periods of stabilization non deposition or erosion a drilling and dating campaign was designed on the basis of the dune stratigraphy as defined by the gpr survey sampling was targeted at large sets of cross stratification formed when the dunes were most active and avoiding bounding surfaces formed when the dune was stable or even eroded the results from optical dating give ages between 0 34 0 02 ka and 1 57 0 07 ka indicating a time averaged dune migration rate of 0 12 m a 1 over the past 1600 years

the internal structure of vegetated coastal sand dunes sable island nova scotia abstract new data and a comprehensive analysis of stratification and sedimentation in the complex vegetated dunes of sable island nova scotia are presented the internal structures of the dunes are analyzed using a descriptive legend from an earlier paper byrne and mccann 1990 which was based on three elements grain size stratification and the nature of plant remains analysis of the stratification and sedimentary character of the dunes at three sites along the north shore and at ten sites in the interior of the island involved modifications to the original descriptive legend and a more comprehensive listing of the modes of deposition the sites discussed here represent the evidence that was available during the field season summer 1987 and 1988 without extensive excavations and disturbance of the terrain genetic interpretation of the complete data set indicates that the main dunes of sable island fall into two categories 1 1 primary dunes which have developed in situ through several phases of sedimentation at the back of the north beach three sites 2 2 secondary dunes including various remnant forms which result from the passage of migrational dunes in the interior of the island ten sites three types of secondary dunes are defined these dune types are summarized in a map and as a block diagram that can be used to document the development of the dunes and dune systems on the island

pre eruptive uplift in the emeishan in their correspondence he and colleagues question our conclusion of little or no uplift preceding emeishan volcanism that we reported in our letter1 debate concerns the nature of the contact between the maokou limestone and emeishan volcanics the depositional environment and volumetric significance of mafic hydromagmatic deposits mhds and evidence for symmetrical domal thinning mhds in the daqiao section are separated from the maokou limestone by 100 m of subaerial basaltic lavas but elsewhere mhds previously interpreted as basal conglomerates2 3 directly overlie the maokou2 3 mhds thus feature strongly in basal sections of the emeishan lava succession as also recently shown4 elsewhere in the emeishan an irregular surface at the top of the maokou limestone has been interpreted as an erosional unconformity2 3 but clastic deposits presented as evidence of this erosion2 3 are mhds produced by explosive magma water interaction1 a clear demonstration that this irregular top surface is an erosional truncation of limestone reef facies slope rim flat lagoonal is currently lacking but is critical because reefs and carbonate platforms show considerable natural relief of tens of metres the persistent hot wet climate since the oligocene has produced well developed weathering profiles on exposed palaeozoic marine sedimentary sequences5 but weathering and karst relief of the uppermost maokou limestone underlying the flood basalts have not been properly documented nor shown to be of middle permian age and immediately preceding emplacement of the large igneous province

continental eclogites and the wilson cycle the wilson cycle the repeated opening and closing of oceans commonly along roughly the same lines is here attributed to the presence of eclogite facies roots of partially collapsed orogens we present a finite element thermal model that suggests that such roots will weaken the orogenic lithosphere relative to that of the adjacent foreland for hundreds of millions of years and make it a preferred site for later rifting

why deposits of longitudinal dunes are rarely recognized in the geologic record dunes that are morphologically of linear type many of which are probably of longitudinal type in a morphodynamic sense are common in modern deserts but their deposits are rarely identified in aeolian sandstones one reason for non recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long term sand transport direction thereby depositing cross strata that have unimodal cross bed dip directions and consequently resemble deposits of transverse dunes dune parallel components of sand transport can be recognized in ancient aeolian sands by examining compound crossbedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along crest direction over the large dunes

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

mafic volcaniclastic deposits in flood basalt provinces a review flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks mostly sills with any pyroclastic rocks limited to silicic compositions however mafic volcaniclastic deposits mvds exist in many provinces and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions the province where mvds are the most voluminous the siberian traps is also the one temporally associated with the greatest phanerozoic mass extinction a lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established but as a first step this contribution reviews in some detail the current knowledge on mvds for the provinces in which they are better known i e the north atlantic igneous province including greenland the faeroe islands the british isles and tephra layers in the north sea basin and vicinity the ontong java plateau the ferrar and the karoo we also provide a brief overview of what is known about mvds in other provinces such as the columbia river basalts the afro arabian province the deccan traps the siberian traps the emeishan and an archean example from australia the thickest accumulations of mvds occur in flood basalt provinces where they underlie the lava pile faeroes n1 km ferrar province z400 m siberian traps 700 m in the faeroes case the great thickness of mvds can be attributed to accumulation in a local sedimentary basin but in the ferrar and siberian provinces the deposits are widespread n310 5 km 2 for the latter on the ontong java plateau over 300 m of mvds occur in one drill hole without any overlying lavas where the volcaniclastic deposits are sandwiched between lavas their thickness is much less in most of the cases reviewed primary mvds are predominantly of phreatomagmatic origin as indicated by the clast assemblage generally consisting of basaltic clasts of variable vesicularity dominantly non to poorly vesicular mixed with abundant country rock debris the accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins east greenland ferrar karoo these underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity in the

flow dynamics and geomorphology of a trough blowout the dynamics and geomorphological development of a trough blowout located at fiona beach in the myall lakes national park in nsw australia are examined wind speeds velocities and flow structure were measured utilizing an array of miniature rimco cup anemometers gill bivane and uvw instruments and wind vanes flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation jets occur both in the deflation basin and along the erosional walls relative flow deceleration and expansion occurs up the depositional lobe jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls maximum erosion and transport occurs up the deflation basin and onto the depositional lobe trough blowout morphologies are explained as a function of these flow patterns when the wind approaches the blowout obliquely the flow is steered considerably within the blowout and the degree and complexity of topographic steering is dependent on the blowout topography the flow is usually extremely turbulent and large corkscrew vortices are common the local topography of a blowout can be very important in determining overall sand transport and blowout evolutionary conditions and paths estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remotely sensed wind data are used

karst development and the distribution of karst drainage systems in dejiang guizhou province china abstract the nature of karstification of two contrasting areas on the north guizhou plateau south china is shown to be controlled by structure lithology geomorphic history and tectonics and causes significant differences to arise in the subsurface drainage systems of the areas the shaqi area lies in a syncline of permo triassic limestones underlain by an insoluble sandy shale which forms the local base level karst landforms are strongly influenced by the presence of four erosion levels corresponding to four periods of rejuvenation of the drainage systems drainage is concentrated along the syncline axis and one system naoshuiyan has been pirating another lengshuiyan by headward retreat cave passages are typically phreatic the dejiang town area lies in an anticline of cambrian dolomite and ordovician limestone three large subsurface drainage systems have developed along parallel faults and have typically vadose cross sections

erosion processes in a dune landscape along the dutch coast abstract the landscape of the dunes along the dutch coast is the result of the interaction of biological and geomorphological processes where the latter prevail new landforms are created blowouts by wind erosion and rills and accumulation footslopes by overland flow spatial extent and rate of the erosion processes have been assessed by mapping and by measuring it appears that dune sand is either sensitive to erosion by wind or erosion by water depending on the presence of organic material clean yellow sand is cohesionless and easily blown away but has no surface runoff grey sand containing organic matter on the other hand will resist wind erosion but it is waterrepellent and will be washed from slopes when rain follows a period of dry weather once the grey surface sand is removed from the surfaces by water erosion wind erosion begins in the underlying yellow sand present day geomorphological processes reshape the slopes of the original parabolic dunes wind is particularly active in summit areas where new blowouts are formed whereasoverland flow creates concave south exposed slopes the stepped surface of the north exposed slopes is due to mass movements following rabbit activity

identifying causes of ground penetrating radar reflections using time domain reflectometry and sedimentological analyses ground penetrating radar gpr is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves however little is known about the exact cause of gpr reflections because few studies have coupled wave theory to petrophysical data in this study a 100 and 200 mhz gpr survey was conducted on aeolian deposits in a quarry time domain reflectometry tdr was used to obtain detailed information on the product of relative permittivity er and relative magnetic permeability lr which mainly controls the gpr contrast parameter in the subsurface combining tdr data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr synthetic radar traces constructed using the tdr logs and sedimentological data from the lacquer peels were compared with the actual gpr sections numerous peaks in erlr which are superimposed on a baseline value of 4 for dry sand are caused by potential gpr reflectors these increases in erlr coincide with the presence of either organic material having a higher water content and relative permittivity than the surrounding sediment or iron oxide bands enhancing relative magnetic permeability and causing water to stagnate on top of them sedimentary structures as reflected in textural change only result in possible gpr reflections when the volumetric water content exceeds 0ae055 the synthetic radar traces provide an improved insight into the behaviour of radar waves and show that gpr results may be ambiguous because of multiples and interference

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

ground penetrating radar stratigraphy and dynamics of megaflood gravel dunes ground penetrating radar was used to elucidate the stratigraphy of late pleistocene gravel dunes in the altai mountains of southern siberia that formed when a lake emptied as a result of ice dam failure survey lines across dunes had a resolution of decimetres with depth penetration of 20 m the reflections identify bounding surfaces and radar facies two classes of unconformities are identified 1 an erosional unconformity at the base of the dunes 2 steeply inclined unconformities that truncate underlying inclined reflections and are downlapped by overlying inclined reflections within the dunes unconformities define six radar facies rf rf 1 basal subhorizontal discordant reflections rf 2 poorly defined discordant reflections rf 3 planar inclined reflections rf 4 sigmoidal inclined reflections rf 5 trough fills rf 6 low angle inclined reflections the basal unconformity represents the flood cut surface across which the dunes migrated the inclined unconformities may be interpreted in two ways 1 erosional surfaces induced by unsteady flow within one flood or 2 erosional surfaces developed by a series of floods reactivating dunes left stranded by previous floods the evidence favours the latter model which is consistent with the occurrence of several dune forming events within the basin the broader implications of the study are considered with respect to investigations of megaflood bedforms worldwide

impact of atmospheric circulation patterns on coastal dune dynamics nw spain article i nfo dunes in temperate latitudes have experienced a significant stabilization in recent times essentially as a conse quence of the expansion of dense vegetation cover yet the causes for this gradual stabilization as well as the causes promoting antecedent aeolian mobilization remainpoorlyunderstood the traba coastal dune field located in nw spain was examined to explore the causes inducing aeolian activity and subsequent stabilization since 1940 morphological changes were identified through the combination of aerial photographs and geophysical techniques local wind field regimes were simulated using a regional climate model to obtain the variability of the most relevant modes of atmospheric circulation in the north atlantic and european regions north atlantic oscillation nao eastern atlantic ea and scandinavian scand this allows us to identify the impact of these circulation modes over dune dynamics results document an episode of aeolian activity during the 1950s followed by a gradual stabilization and fixation of the dune coincident with a decrease on storm and wind inten sity yet aeolian sand movement remained active insmall areas blowouts occurring mainly during the summer ne winds associated with a negative phase of the ea explain the movement of sand within the dune field under favorable conditions of sand supply on the other hand sand supply to the dune field from the beach was promoted by nw winds coincident with the summer negative phase of nao during winter the negative nao favored frequent sw winds associated with the passage of intense storms which in turn explain sand remobilization from the beach making sediment available for the nw winds to blow inland with this work it is proven that to understand past and future aeolian activity requires critical consideration of the variability and impact of the two principal modes of atmospheric circulation in the north atlantic nao and ea the scand mode explaining alowerpercentageofthelocalwind fieldvariabilitywasalsoincludedtoachievehigher significance levels of explained variance

coastal dune erosion at formby point north merseyside england causes and mechanisms abstract following a period of coastal progradation during the nineteenth century since ca 1900 a 5 km length of dune fronted shoreline at formby point located between the ribble and mersey estuaries in northwest england has been eroding at an average rate of up to 3 m yr although several factors probably contributed to the onset of erosion meteorological records suggest that a high frequency of strong westerly winds and by inference storm waves around the turn of the century played an important role the erosional trend was reinforced by the effects of training wall construction and dredge spoil dumping which changed the bathymetry in liverpool bay and led to greater focussing of wave energy onto the north central part of formby point sand eroded from this part of the shore has been transported by longshore drift northwards and southwards away from the point leading to beach and foredune accretion between ainsdale and southport and at altcar foredune erosion at formby point was also accelerated between 1900 and the mid 1970s by the abandonment of dune and foreshore management which had been extensively practised during the late 19th century and by a significant increase in recreational pressure sand mining and military activities since the instigation of a coastal management scheme in 1977 damage to the dunes from these causes has been greatly reduced but the dune protection and restoration works employed have had little effect on the underlying problem of beach and foredune erosion by waves especially during storm surges

internal structure of a trough blowout determined from migrated ground penetrating radar profiles ground penetrating radar gpr was used to investigate the relationship between the geomorphological development of a large aeolian trough blowout and the stratigraphy and internal sedimentary structure of its associated deposits although analogous many of the data processing techniques routinely applied in seismic reflection are very rarely applied in gpr studies in this study a simple migration program was used that significantly enhanced the quality of gpr images from a large trough blowout at raven meols on the sefton coast northwest england these improvements aided subsequent data interpretation which was achieved through application of the principles of radar stratigraphy gpr shows the pre blowout dunes to have a complex internal structure that suggests they were formed in the presence of at least a partial vegetation cover subsequent to stabilization of these dunes a thin soil developed this dune soil forms an important radar sequence boundary and delineates a complex topography beneath the depositional lobe of the blowout the internal structure of the depositional lobe of the blowout does not conform to a model of simple radial foreset deposition as derived from contemporary process studies reported in the literature instead the pattern of deposition has been extensively modified by the antecedent dune topography and by varying spatial and temporal exposure to important sand transporting winds that is partly controlled by interactions between the regional wind pattern and local dune morphology trough blowout deposits in coastal aeolian sedimentary sequences are likely to be recognized by the presence of laterally continuous packets of relatively high angle cross strata which often display a spatially variable radial dip pattern that is only very poorly or partially developed in addition a soil or other surface representing a significant hiatus in dune deposition is likely to underlie the blowout deposits the topography of which will show a clear relationship to the dip and orientation of the overlying cross strata

influence of grain size shape and compaction on georadar waves examples of aeolian dunes summary many ground penetrating radar gpr profiles acquired in dry aeolian environment have shown good reflectivity inside present day dunes we show that the origin of this reflectivity is related to changes in grain size distribution packing and or grain shape in a sandy material we integrate these three parameters into analytical models for bulk permittivity in order to predict the reflections and the velocity of gpr waves we consider two gpr cross sections acquired over aeolian dunes in the chadian desert the 2d migration of gpr data suggests that dunes contain different kinds of bounding surfaces we discuss and model three kinds of reflections using reasonable geological hypothesis about aeolian sedimentation processes the propagation and the reflection of radar waves are calculated using the 1d wavelet modelling method in spectral domain the results of the forward modelling are in good accordance with real observed data

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

internal structure of a barrier beach as revealed by ground penetrating radar gpr chesil beach uk abstract chesil beach dorset is one of the most famous coastal landforms on the british coast the gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as the fleet the beach links the isle of portland in the east to the mainland in the west despite its iconic status there is little available information on its internal geometry and evolutionary history here we present a three fold model for the evolution of chesil beach based on a series of nine ground penetrating radar gpr traverses located at three sites along its length at abbotsbury langton herring and at ferry bridge the gpr traverses reveal a remarkably consistent picture of the internal structure of this barrier beach the first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr bp the second evolutionary phase involves the bulking out of the beach during continued sea level rise but in the presence of abundant gravel supplied by down drift erosion of periglacial slope deposits this episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole the final phase in the evolution of chesil beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance but during a still stand or slight fall in relative sea level this phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the south coast of britain and dated to between 1 2 and 2 4 k yr bp subsequently the barrier appears to have become largely inactive except for the reworking of sediment on the beach face during storm events the case study not only refines the evolutionary picture of chesil beach but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system in addition it also illustrates the potential of gpr in resolving the evolutionary history of gravel rich coastal landforms such as chesil beach

palaeointensity studies of a late permian lava succession from guizhou province south china implications for post kiaman dipole field behaviour summary palaeomagnetic results are presented from a volcanic sequence in zhijin county guizhou province southern china the lavas and associated volcanic breccias comprising the sequence represent a southern extension of the emeishan volcanic province biostratigraphic dating of interbedded limestone units and stratigraphic constraints indicate that the section formed during the late permian 263 255 ma and is thus somewhat older than the emei stratotype section in sichuan province and close in age to reported estimates of the termination of the permo carboniferous kiaman reverse superchron rock magnetic analyses and reflected light microscopy indicate that the magnetic mineralogy of the lava units is dominated by fresh primary magnetites containing a significant fraction of single domain grains thermal demagnetization behaviour of the breccia units is poor but most lava samples have one or two components of remanence above 250 c the normal polarity characteristic remanence held by the lavas implies a post kiaman age for this succession and suggests that the termination of the kiaman occurred prior to 263 ma supporting recently published estimates according to standard criteria thellier palaeointensity results from the lavas are of good quality and reveal that the dipole field strength was comparatively low shortly after the termination of the superchron 80 per cent of samples record relative vdm values in the range 42 52 per cent of the present day value supporting recent studies of mid kiaman field intensity this suggests that a low energy dipole existed at least between 300 and 255 ma and does not appear to have been confined to the stable reverse polarity interval

field survey and analysis of hillslopes on tower karst in guilin southern china limestone dissolution in tropical and subtropical humid southern china created residual hills with steep slopes a landform that is referred to as tower karst two types of tower karst landform feature fenglin or peak forest isolated towers and fengcong or peak cluster linked base towers were identified in guilin previous studies proposed two hypotheses regarding their origin and evolution one is the sequential evolution model from peak cluster to peak forest the other is a parallel development model which postulates that both peak cluster and peak forest have developed simultaneously through detailed field survey and analysis of slope forms on tower karst in guilin it was found that the mean slope angle of the towers is very high 62 4 and ranges from 60 to 75 there is no significant difference in mean slope angle and slope angle distribution between towers in the peak cluster basin and peak forest floodplain areas mean slope angle increases with intensified fluvial dissection three levels of caves in the towers of the peak forest in guilin were identified in previous research the isolated towers of the peak forest as well as scattered residuals of peak cluster are generally distributed in the centre of the guilin syncline favourable circumstances of allogenic water concentration indicate that development of the peak forest resulted from the combined effects of subcutaneous and subterranean dissolution as well as subsequent collapse and recession by fluvial erosion after uplifting by contrast peak clusters generally occur on the limbs of the syncline or at the periphery of the guilin basin with relatively higher elevations the thick vadose zone and predominantly vertical flow suggests that peak clusters are mainly formed by the combination of intensive uplifting and the enhancement of original dolines the evidence of slope survey and slope analysis suggests that both isolated towers and linked base towers developed simultaneously but by different mechanisms of formation and different combinations of development processes copyright 2000 john wiley sons ltd

the structure and development of foredunes on a locally prograding coast insights from ground penetrating radar surveys norfolk uk the internal structure of coastal foredunes from three sites along the north norfolk coast has been investigated using ground penetrating radar gpr which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non destructive or geophysical technique combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution the radar profiles show the internal structures which include foreslope accretion trough cut and fill roll over and beach deposits foredune ridges contain large sets of low angle cross stratification from dune foreslope accretion with trough shaped structures from cut and fill on the crest and rearslope foreslope accretion indicates sand supply from the beach to the foreslope while troughs on the dune crest and rearslope are attributed to reworking by offshore winds bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement radar sequence boundaries within dunes have been traced below the water table passing into beach erosion surfaces these are believed to result from storm activity which erodes the upper beach and dunes in one example at brancaster a dune scarp and erosion surface may be correlated with erosion in the 1950s possibly the 1953 storm results suggest that dune ridge development is intimately linked to changes in the shoreline with dune development associated with coastal progradation while dunes are eroded during storms and where beaches are eroding a stable coast provides more time for dune development resulting in higher foredune ridges a model for coastal dune evolution is presented which illustrates stages of dune development in response to beach evolution and sand supply in contrast to many other coastal dune fields where the prevailing wind is onshore on the north norfolk coast the prevailing wind is directed along the coast and offshore which reduces the landward migration of sand dunes

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

geology and geochemistry of three sedimentary rock hosted disseminated gold deposits in guizhou province people s republic of china abstract five sedimentary rock hosted disseminated gold deposits have been discovered since 1980 in southwestern guizhou province prc submicron sized gold is disseminated in silty carbonate and carbonaceous shale host rocks of permian and triassic age arsenic antimony mercury and thallium accompany the gold associated hydrothermal alteration resulted in decarbonatization of limestone silicification and argillization and depletion of base metals barium and many other elements organic material occurs in most host rocks and ores it was apparently devolatilized during a regional heating event that preceded hydrothermal activity and thus was not mobilized during mineralization and did not affect gold deposition the geologic setting of the guizhou deposits includes many features that are similar to those of sedimentary rock hosted deposits of the great basin western united states the heavy element suite that accompanies gold is the same but base metals are even scarcer in the guizhou deposits than they are in u s deposits the guizhou deposits discovered to date are smaller than most u s deposits and have no known spatially associated igneous rocks

emeishan basalts sw china and the end guadalupian crisis magnetobiostratigraphic constraints abstract a magnetostratigraphic investigation of the permian emeishan lip large igneous province was carried out on a composite section in ebian county close to the type area in sichuan sw china the main succession of twelve flows 175 m thick carries a normal polarity whilst the one reliable site from the overlying 30 m thick volcanic waning sequence is marked by a reverse polarity the data enable a correlation to be proposed with an emeishan basalt sequence in western guizhou c 400 km to the se from our knowledge of the geomagnetic field9s reversal behaviour during the permian it suggests that the main lava pile along the eastern half of the emeishan basalt outcrop belt was erupted within a half to one million years using magnetobiostratigraphic data from the adjacent south china platform the normal polarity magnetozone is correlated with the normal polarity chron associated with the upper part of the maokou limestones constrained by conodont data the main emei basalts appear to be at least two biozones older 1 1 5 ma than the mid late permian boundary it is possible however that the emei basalt waning zone sequence which represents an explosive volcanic phase might be coeval with the end guadalupian biotic crisis thus arguments implicating emei basalt volcanism as the causal mechanism behind this major global event have to accommodate the new relative age constraints

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

parabolic dune reactivation and migration at napeague ny usa insights from aerial and gpr imagery abstract observations from mapping since the 19th century and aerial imagery since 1930 have been used to study changes in the aeolian geomorphology of coastal parabolic dunes over the last 170 years in the walking dune field napeague ny the five large parabolic dunes of the walking dune field have all migrated across or are presently interacting with a variably forested area that has affected their migration stabilization and morphology this study has concentrated on a dune with a particularly complex history of stabilization reactivation and migration we have correlated that dune s surface evolution as revealed by aerial imagery with its internal structures imaged using 200 mhz and 500 mhz ground penetrating radar gpr surveys both 2d transect and high resolution 3d gpr imagery image downwind dipping bedding planes which can be grouped by apparent dip angle into several discrete packages of beds that reflect distinct decadal scale episodes of dune reactivation and growth from aerial and high resolution gpr imagery we document a unique mode of reactivation and migration linked to upwind dune formation and parabolic dune interactions with forest trees this study documents how dune dune and dune vegetation interactions have influenced a unique mode of blowout deposition that has alternated on a decadal scale between opposite sides of a parabolic dune during reactivation and migration the pattern of recent parabolic dune reactivation and migration in the walking dune field appears to be somewhat more complex and perhaps more sensitive to subtle environmental pressures than an idealized growth model with uniform deposition and purely on axis migration this pattern believed to be prevalent among other parabolic dunes in the walking dune field may occur also in many other places where similar observational constraints are unavailable

the transition from sedimentation to flood volcanism in the kangerlussuaq basin east greenland basaltic pyroclastic volcanism during initial palaeogene continental break up primary basaltic pyroclastic deposits compose volumetrically c 35 50 of the lower palaeogene vandfaldsdalen mikis and haengefjeldet formations within the lower volcanic series of the east greenland flood basalt province the eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break up and initiation of flood basalt volcanism we present a revised stratigraphy for the pre volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the kangerlussuaq basin east greenland primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds surge deposits and vent sites with cinder cones early volcanism was apparently restricted to localized basins and formed shield volcano structures 30 40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites sediments pyroclastic deposits and lavas the lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the ne paired with continued down dropping of inactive volcanic centres the complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting

morphology dynamics and internal stratification of some established foredunes in southeast australia abstract foredunes are shore parallel dunes formed by aeolian deposition within vegetation modern established foredunes are classified into five morphologic stages and the morphologies and processes of each is described stage 1 foredunes are well vegetated symmetric stable ridges characterised by stoss face and crest deposition stage 2 foredunes display minor erosional patches 75 90 vegetation cover and slight lateral variation in deposition and erosion stage 3 foredunes are hummocky have a 45 75 vegetation cover range and display various scales of blowouts concave stoss faces and steeper lee faces stage 4 foredunes are characterised by large scale erosional features such as blowouts sand sheets and high asymmetry stage 5 foredunes comprise poorly vegetated remnant knobs each stage is characterised by a set of erosional and depositional processes which produce generally distinctive sets of cross strata sedimentary structures within examples of each foredune stage are examined stage 1 and 2 foredunes are dominated by simple large scale convex continuous strata stage 3 and 4 foredunes display increasingly variable sets of cross strata and a greater degree of planar and trough cross stratification wave cut scarps blowout structures and very steep lee slope bedding may be preserved the internal sedimentary structures presented here form the basis of a facies model for foredunes

understanding the offshore flood basalt sequence using onshore volcanic facies analogues an example from the faroe shetland basin flood basalts in associated volcanic rifted margins such as the north atlantic igneous province have a significant component of lavas which are preserved in the present day in an offshore setting a close inspection of the internal facies architecture of flood basalts onshore provides a framework to interpret the offshore sequences imaged by remote techniques such as reflection seismology a geological interpretation of the offshore lava sequences in the faroe shetland basin using constraints from onshore analogues such as the faroe islands allows for the identification of a series of lava sequences which have characteristic properties so that they can be grouped these are tabular simple flows compound braided flows and sub aqueously deposited hyaloclastite facies the succession of volcanic rocks calculated in this study has a maximum thickness in excess of 6800 m down to the top of the sub volcanic sediments the offshore volcanic succession has a thickness of about 2700 m where it can be clearly identified across much of the area with a further 2700 m or more of volcanic rock estimated from the combined gravity and seismic modelling to the north and west of the region a large palaeo waterbody is identified on the basis of a hyaloclastite front apron consisting of a series of clinoforms prograding towards the eastern part of the basin this body was 500 m deep must have been present at the onset of volcanism into this region and parts of the water body would have been present during the continued stages of volcanism as indicated by the distribution of the hyaloclastite apron

reply to comment on paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism by bin he yi gang xu jun peng guan yu ting zhong lithos 119 1 9 2010 we welcome the comments of ukstins peate et al 2011 on our recent paper he et al 2010a which provide us with an opportunity to extend our discussion on paleokarst between themaokou formation and theemeishanbasalts ukstins peate et al 2011 question the existence of karstic surface of the maokou limestone described by he et al 2010a instead theycontend that the earliest emeishanmagmaswereeruptedat or below sea level in the center of the emeishan large igneous province elip rejecting the pre volcanic domal uplift model proposed by he et al 2003 their arguments are largely basedon their interpretations of field observations such as a sedimentary continuity across the guadalupian lopingian boundary g lb in the center of the elip and b the faulted contact between emeishan basalt andmaokou formation however aswewill showbelow wedispute thesefieldobservations and ukstins peate et al s interpretation of the temporal and spatial frameworks of our and others results in this reply we will clarify using specific examples some key aspects of their questions about the paleokarst on the maokou formation and its relationship to plumeinduced uplift in the elip

paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism abstract the 260 ma emeishan large igneous province elip in southwest china has previously been demonstrated to provide compelling evidence for pre volcanic crustal doming in support of the mantle plume hypothesis however this has been questioned by ukstins peate and bryan 2008 by showing hydrothermal magmatic activity at the daqiao section to solve this argument a detailed characterization of the contact between the emeishan basalts and the maokou formation was carried out the contact is shown to be an unconformity which is characterized by paleokarst on top of the maokou formation including paleokarst relief sinkholes caves tower karst and its corresponding rocks such as kaolinite bauxite and ferruginous duricrust and collapsed breccias etc this paleokarst unconformity was in turn covered or infilled by the emeishan basalts and tuffs suggesting that uplift and erosion occurred prior to the eruption of the elip the extent of erosion of the maokou formation indicates the elip can be divided into three roughly concentric zones the inner intermediate and outer zones the paleokarst features on the top of maokou formation vary across the elip in the inner zone a likely sinkhole and an incision valley with 450 m relief in height are found in the intermediate zone various paleokarst landforms such as karst relief sinkholes and tower karsts are well developed some sinkholes that developed in the qixia formation below the maokou formation imply that the paleorelief is more than 350 m in height in the outer zone the paleokarstic surface is a paleo weathering layer with minor karstification and development of caves at 10 50 m this spatial variation of the paleokarst reflects variation of uplift height across the elip the extent of minimal uplift is estimated to be at least 450 m in the inner zone 350 m in the intermediate zone whereas uplift is minor tens 50 m in the outer zone the magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models the paleokarst was formed after the deposition of the maokou formation and the eruption of the emeishan basalts at the end guadalupian and indicates a short duration of uplift thus this study lends further support to domal uplift prior to the emeishan flood volcanism but also to the mantle plume initiation model for the generation of the elip

comment on paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism a department of geoscience 121 trowbridge hall university of iowa iowa city ia 52242 usa b biogeoscience queensland university of technology brisbane queensland 4001 australia c department of earth and environment university of leeds leeds ls2 9jt uk d dougalearth ltd 12 nevilles cross villas durham dh1 4jr uk e department of earth sciences university of hong kong pokfulam road hong kong china

geothermal constraints on emeishan mantle plume magmatism paleotemperature reconstruction of the sichuan basin sw china the middle late permian emeishan large igneous province elip in southwestern china represents a classic example of a mantle plume origin to constrain the thermal regime of the elip and contemporaneous magmatic activity in the northeastern sichuan basin maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance ro and apatite fission track data two heating patterns were identified 1 heating of the overlying lithosphere by magma storage regions and or magmatic activity related to the mantle plume which resulted in a relatively strong geothermal field and 2 direct heating of country rock by stock or basalt borehole ro data and reconstructed maximum paleotemperature profiles near the elip exhibit abrupt tectonothermal unconformities between the middle and late permian the profiles in the lower subsections i e pre middle permian exhibited significantly higher gradients than those in the upper subsections distal to the basalt province high paleo geotemperatures hereafter paleotemperatures were inferred despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes in contrast ro profiles from boreholes without igneous rocks i e late permian contained no break at the unconformity paleotemperature gradients of the upper and the lower subsections and erosion at the middle late permian unconformity revealed variations in the thermal regime the inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic thermal response to the emeishan mantle plume

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

re evaluating plume induced uplift in the emeishan large igneous province numerical and fluid dynamic modelling predicts that mantle plumes should generate a broad domal uplift 1 000 km wide 500 to 1 000 m high preceding volcanism in large igneous provinces the emeishan large igneous province southwest china has been offered as the best example of plume induced uplift where kilometre scale pre and syn volcanic relief was interpreted to develop in response to the impingement of a plume head here we document voluminous mafic hydromagmatic deposits and submarine extrusions that formed during the initiation and early stages of the emeishan large igneous province these deposits were previously interpreted to be alluvial fan sediments shed from a pre volcanic domal high the abundance of such deposits consisting of variable proportions of marine limestone and basaltic fragments strongly suggests that the bulk of this province was emplaced at sea level evidence for dynamic pre volcanic uplift as predicted by plume models is lacking and such a lack may be the more general case any positive relief that developed was more likely the result of the formation of a volcanic edifice and rapid accumulation of the volcanic pile thick alluvial fan sediments from the core of the emeishan large igneous province have been considered as critical field evidence in support of plume induced pre volcanic doming and uplift these sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level precluding dynamic pre volcanic uplift as predicted by mantle plume models

radar facies of paraglacial barrier systems coastal new england usa analysis of a large data base of ground penetrating radar gpr profiles from both natural and developed paraglacial barriers along the coast of new england has allowed identification of eight reflection configurations that characterize this type of mid to high latitude coastal environment bedrock anchor points yield primarily hyperbolic configurations whereas glacial anchor points and sediment source areas are characterized by chaotic parallel and tangential oblique configurations beaches and dunes produce predominantly sigmoidal oblique hummocky reflection free and bounding surface configurations back barrier sediments may yield basin fill configurations but generally include abundant signal attenuating units the gpr data calibrated with information from cores were collected across swash aligned and drift aligned barriers in a variety of wave and tidal energy settings application of a 120 mhz antenna as used in this study enables portrayal of a range of sedimentary units from individual bedforms on single records to entire barrier elements using large numbers of intersecting gpr sections at maximum vertical resolutions that vary between 0 2 m and 0 7 m the most important drawback of gpr in the coastal environment is attenuation of the electromagnetic em signal by layers of salt marsh peat or by brackish or salty groundwater primarily along barrier edges this disadvantage is offset by many benefits data can be collected at rates of several km per day making gpr an excellent reconnaissance tool a core that is used in the calibration of gpr data can be matched with great accuracy to its position on the complementary gpr record allowing detailed correlation between lithostratigraphy and reflection configuration