lethal sandslides from eolian dunes fossil vertebrates entombed within the upper cretaceous djadokhta formation of southern mongolia bear testimony to a heretofore unknown geologic phenomenon mass wasting of eolian dunes during heavy rainstorms evaporation of shallow penetrating rainwater led to progressive calcite accumulation in a thin layer of sand about 0 5 m below the surface of dune lee slopes during rare heavy rainstorms a perched water table developed at the top of calcitic zones positive pore water pressure led to translational slides and fast moving sediment gravity flows that overwhelmed animals on the lee slopes of large dunes and in interdune areas

gravel ripples on the inner scotian shelf abstract sidescan sonar and photo video surveys have revealed the presence of symmetrical gravel bedforms interpreted as wave generated ripples with wavelengths of 1 3 to 3 0 m occurring in patches and narrow ribbons in depths of 15 to 65 m on the inner scotian shelf direct observations and sediment sampling from the pisces iv submersible have been used to ground truth surface based survey dam and to quantify relationships between the bedforms and the processes responsible for their formation the ripples are formed in polymodal sandy gravels with modal sizes ranging from 0 1 to 45 mm evaluation of threshold criteria for coarse sediments together with an 11 year record from a nearby wave rider buoy suggests that existing models for wave entrainment of gravel on rippled surfaces ove estimate the critical velocity by a factor of approximately 2 and that conditions suitable for transport of the coarsest 45 mm size mode sampled in the ripple crests occur on average 43 hr yr analysis of gravel ripples on the inner scotian shelf and of other examples noted in the recent literature extends the range of empirical data for oscillation ripple wavelengths by a factor of 3 and for ripple grain size by a factor of 5 the gravel ripples display a linear scaling to wave orbital diameter similar to that reported for orbital ripples in sand use of such relations for paleoenvironmental interpretation of gravel ripples preserved in the rock record is complicated by the difficulty of selecting appropriate grain size and wave parameters conditions suitable for potential formatio of large scale symmetrical ripples in coarse sediments extend from the outer continental shelf to shallow shore face settings with possible fetch lengths as short as 20 km under intense storms

morphodynamic evolution self organisation and instability of coarse clastic barriers on paraglacial coasts abstract beaches and barriers on many mid to high latitude coasts comprise mixtures of fine and coarse clastic materials forming a distinctive morphodynamic environment in many cases the sediments are derived primarily from limited glacigenic deposits and the coasts are considered paraglacial over relatively long time scales decades to centuries coarse clastic barriers on such coasts show evidence of self organisation through large scale morphological evolution and facies differentiation this process involves gradual reworking partitioning and textural sorting of material toward transport minima long intervals of slow evolution are punctuated by episodes of rapid reorganisation involving breakdown of stable barrier structures and facies patterns remixing of sediment and accelerated migration of transgressive systems drift aligned systems develop longshore cell structure sometimes leading to breaching and segmentation and may evolve toward progressively greater swash alignment under appropriate circumstances swash aligned systems may experience catastrophic transformation when appropriate environmental triggers lead to threshold exceedance in the morphodynamics of the shore system adjacent barriers may show quite different behaviour depending on the antecedent states of individual coastal cells while appropriate parameterisations and sediment budget formulations allow us to model the long term evolution of some barrier structures the non linear dynamics that appear to dominate large scale behaviour may limit predictability the identification of stability threshold criteria remains an important research priority

refined chronostratigraphy of the late mesozoic terrestrial strata in south china and its tectono stratigraphic evolution abstract the late mesozoic terrestrial strata in numerous basins in s south china provide important sedimentary archives to understand the tectonic evolution of s china and east asia however establishing regional stratigraphic framework within a basin and precisely correlating strata among basins remain challenging due to limited chronological constraints in this study we report zircon u pb ages of 21 samples and a compilation of 132 reliable age data from 15 type sections of the volcanic sedimentary basins in s china the synthesized geochronology allows us to establish a refined chronostratigraphy for the late mesozoic terrestrial strata new calibrated results indicate that most of the lithostratigraphic units are diachronic laterally stacking and or interfingering six stacking styles are classified for the relationship of lithostratigraphic units analysis of the refined chronostratigraphy and the stratal stacking styles together with lithological composition reveals three episodes of tectono stratigraphic evolution episode i 145 125 ma is characterized by intense volcanism as evidenced by widespread occurrence of volcanic strata and 137 120 ma a type granites and was probably related to the rollback of the subducting paleo pacific plate the strata deposited during episode ii 125 100 ma are composed of variegated sediments associated with without volcanic intercalations in sedimentary faulted depression basins indicating the waning of volcanism and tectonism attributed to the ending of the izanagi kula plate subduction in episode iii

fluid compartmentalization of devonian and mississippian dolostones western canada sedimentary basin petrologic and geochemical evidence from fracture mineralization1 integrated petrographic geochemical and fluid inclusion study of fracture mineralization and associated host rock in selected mississippian and devonian carbonates extending from southeastern alb

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

a model for drowned terrestrial habitats with associated archeological remains in the northwestern gulf of maine usa abstract marine geophysical techniques and geological measurement of sea level change allow detailed mapping of seafloor archeological sites and development of models in the northwestern gulf of maine the lowstand of sea level is only at 60 m depth but a prolonged stasis during the late quaternary sea level rise herein termed the slowstand occurred between 11 500 and 7500 calibrated years before present cal yr bp at depths of 15 25 m this slowdown caused substantial erosion of glacial deposits and formed terrestrial beaches wetlands and lakes these landforms attracted people whose tools were later discovered during present day scallop fishing activities our study areas at the green islands and bass harbor are within the lowstand and slowstand depth ranges but at highly exposed and sheltered sites respectively the green islands site has lost most of its former terrestrial sediment and there is no longer any context for recovered artifacts at the protected bass harbor site the remains of eroded moraines are associated with drowned spits and a former lacustrine estuarine basin cores at the bass harbor location encountered freshwater peat deposits and numerous shallow subtidal shell and plant fossils all deposited during the slowstand the two most important controls on the preservation of terrestrial landforms and associated human artifacts in the northwestern gulf of maine are the rate of sea level rise and degree of shelter of the site from waves

morphology and seismic stratigraphy of the inner continental shelf off nova scotia canada evidence for a 65 m lowstand between 11 650 and 11 250 c14 yr b p abstract nova scotia s position near the margin of large pleistocene ice sheets makes the scotian shelf region critical for evaluation of glaciation models and sea level change the sea floor of the inner scotian shelf was mapped using multibeam bathymetry a combination of conventional seismic and sonar techniques and sampling multibeam bathymetry provides an areal image of the sea floor combining this unique image with sub bottom seismic imaging the relationships between sea floor topography and the underlying strata were explored the inner continental shelf of nova scotia can be subdivided into five major terrain zones these are the 1 truncation zone 2 morainal zone 3 outcrop zone 4 basin zone and 5 scotian shelf end moraine complex the scotian shelf end moraine complex and basin zone are glacial depositional zones at the seaward edge of the inner shelf landward of these zones is a region of high relief bedrock with ridges and valleys largely devoid of surficial sediments extending from 80 to 120 m water depth outcrop zone this zone is interpreted as a relict bedrock surface preserved under frozen bed glacier conditions to the east of the outcrop zone in similar water depths are unmodified till ridges overlying bedrock morainal zone the truncation zone is a region of the inner shelf from 90 m to the present shoreline characterized by muted acoustic topography and planar erosional surfaces truncating bedrock and surficial sediments the truncation zone is subdivided into the valley subzone the transition subzone the platform subzone and the estuarine subzone the valley subzone is typified by sediment infilled valleys occurring in 75 to 90 m water depths these valleys contain seismic facies with a ponded style of deposition planed off at the sea floor or by erosional unconformities near the sea floor the transition subzone is marked by a relatively steep ramp and terraces the ramp at the type section extends from 75 to 65 m water depth the surface of the ramp can be either an erosional unconformity or a depositional surface formed by clinoform beds the 65 m former shoreline is interpreted as the top of the transition subzone ramp surface at one ramp locality clinoform beds form part of a progradational sequence called the sambro delta a mussel valve fragment mytilus edulis was obtained from a core in the foresets and radiocarbon dated an age of 11 650 110 yr b p was obtained adjusted for isotopic fractionation above 65 m the sea floor forms a low relief gently sloping erosional surface platform subzone estuarine deposits have been found above 50 m the new sea level curve constructed with the dated 65 m shoreline and recently published data is at variance with calculated rsl curves based on geophysical models primarily in the amplitudes and rates of rsl change reasons for the discrepancies may be late melting ice and regional variations in lithospheric strength and thickness

late cretaceous aeolian dunes and reconstruction of palaeo wind belts of the xinjiang basin jiangxi province china the tangbian formation k2t the middle part of the upper cretaceous guifeng group in the xinjiang basin jiangxi province southeastern china is usually regarded as an aqueous sediment however based on our study it is now attributed to an aeolian origin this new interpretation is supported by considerable evidence including purple red well sorted and round grained medium to fine grained pure sandstone with little suspension load such as clay silt and mica well developed thick large scale and high dip tabular planar cross beddings characterized by aeolian dune foresets wind ripple lamination typical aeolian grain surface textures such as dish shaped impact scars crescent shaped impact scars and frosted surfaces our palaeo current reconstruction proved that the dominant prevailing winds were westerlies and the secondary prevailing winds were northeasterlies with a small amount of south southeasterlies and north northwesterlies based on the palaeogeography and the global wind belt model the studied area was located within the westerlies and northeast trades of the northern hemisphere and possibly influenced by the south southeast and north northwest monsoons during the late cretaceous

oil reservoirs in grainstone aprons around bryozoan mounds upper harrodsburg limestone mississippian illinois basin several oil pools have been discovered recently in the upper harrodsburg limestone middle mississippian of the illinois basin a depositional model for bryozoan mound complexes has allowed more successful exploration and development in this play in the johnsonville area of wayne county illinois three lithofacies are dominant in the upper harrodsburg 1 bryozoan boundstones 2 bryozoan grainstones and 3 fossiliferous wackestones bryozoan boundstones occur as discontinuous mounds and have low porosity although bryozoan boundstones are not the main reservoir lithofacies they are important because they influenced the distribution of bryozoan grainstones and existing structure bryozoan grainstones have intergranular porosity and are the main reservoir rock bry zoan fragments derived from bryozoan boundstone mounds were concentrated in grainstones around the mounds fossiliferous wackestones are not porous and form vertical and lateral seals for upper harrodsburg grainstones fossiliferous wackestones were deposited in deeper water adjacent to bryozoan grainstone aprons and above grainstones and boundstones after the mounds were drowned upper harrodsburg oil reservoirs occur where grainstone aprons are structurally high the harrodsburg is a good example of a carbonate mound system where boundstone cores are not porous but adjacent grainstones are porous primary recovery in these upper harrodsburg reservoirs is improved by strong pressure support from an aquifer in the lower harrodsburg unfortunately oil production is commonly decreased b water encroaching from that underlying aquifer

mid cretaceous aeolian desert systems in the yunlong area of the lanping basin china implications for palaeoatmosphere dynamics and paleoclimatic change in east asia abstract the mid cretaceous constitutes a period of worldwide atmospheric and oceanic change associated with slower thermohaline circulation and ocean anoxic events possible polar glaciations and by a changing climate pattern becoming controlled by a zonal planetary wind system and an equatorial humid belt during the mid cretaceous the subtropical high pressure arid climate belt of the planetary wind system controlled the palaeolatitude distribution of humid belts in asia as well as the spatial distribution of rain belts over the massive continental blocks at mid low latitudes in the southern and northern hemispheres additionally the orographic effect of the andean type active continental margin in east asia hindered the transportation of ocean moisture to inland regions with rising temperatures and palaeoatmospheric conditions dominated by high pressure systems desert climate environments expanded at the inland areas of east asia including those accumulated in the mid cretaceous of the simao basin the sichuan basin and the thailand s khorat basin and leading the late cretaceous erg systems in the xinjiang basin and jianghan basin this manuscript presents evidences that allow to reinterpret previously considered water laid sediments to be accumulated as windblown deposits forming part of extensive erg sandy desert systems using a multidisciplinary approach including petrological sedimentological and architectural observations the mid cretaceous albian turonian nanxin formation from the yunlong region of lanping basin formerly considered to aqueous deposits is here interpreted as representing aeolian deposits showing local aeolian fluvial interaction deposits the palaeowind directions obtained from the analysis of aeolian dune cross beddings indicates that inland deserts were compatible with a high pressure cell hpc existing in the mid low latitudes of east asia during the mid cretaceous compared with the early cretaceous the mid cretaceous had extremely lower temperatures and pressure gradients more arid climate which is in accordance with the existing morphology of hpc and the hpc was stable with little movement simultaneously the deserts controlled by the mid cretaceous hpc were closer to the equator indicating the shrinkage of the hadley cell relative to the early cretaceous

mechanisms associated with the erosion of sand dune cliffs magilligan northern ireland a fifteen year history of coastal dune recession at magilligan northern ireland has revealed both time and space contrasts in processes and morphology since 1968 storm frequency has increased while dune retreat reached a peak 5 4 m in 1978 1979 three types of dune eroding events are noted resulting from particular wave wind tide combinations the spatial variability in dune scarping is associated with vegetation and soil development and slope failures range from granular avalanches to retrogressive rotational slumps

the postglacial relative sea level lowstand in newfoundland relative sea level in coastal regions of newfoundland fell from late glacial maximum levels to postglacial minima in several phases i an early period of high relative sea level when late wisconsinan ice was at the coast and discharging meltwater plumes into the ocean ii a period of rapidly falling relative sea level during which glaciers retreated inland and iii a period without glacier ice during which relative sea level continued to fall but at decreasing rates falling relative sea level caused fluvial incision of glacial deposits in some coastal embayments and culminated with the construction of lowstand marine deltas these deltas were submerged during the subsequent holocene transgression seismic reflection data from selected deltas show that they comprise wedges of sediment with prograded seaward dipping foreset style internal reflections the depth of the relative sea level lowstand varies spatially and it was diachronous it occurred relatively early and deep in peripheral regio

archean to recent aeolian sand systems and their sedimentary record current understanding and future prospects the sedimentary record of aeolian sand systems extends from the archean to the quaternary yet current understanding of aeolian sedimentary processes and product remains limited most preserved aeolian successions represent inland sand sea or dunefield erg deposits whereas coastal systems are primarily known from the cenozoic the complexity of aeolian sedimentary processes and facies variability are under represented and excessively simplified in current facies models which are not sufficiently refined to reliably account for the complexity inherent in bedform morphology and migratory behaviour and therefore cannot be used to consistently account for and predict the nature of the preserved sedimentary record in terms of formative processes archean and neoproterozoic aeolian successions remain poorly constrained palaeozoic ergs developed and accumulated in relation to the palaeogeographical location of land masses and desert belts during the triassic widespread desert conditions prevailed across much of europe during the jurassic extensive ergs developed in north america and gave rise to anomalously thick aeolian successions cretaceous aeolian successions are widespread in south america africa asia and locally in europe spain and the usa several eocene to pliocene successions represent the direct precursors to the present day systems quaternary systems include major sand seas ergs in low lattitude and mid latitude arid regions pleistocene carbonate and holocene modern siliciclastic coastal systems the sedimentary record of most modern aeolian systems remains largely unknown the majority of palaeoenvironmental reconstructions of aeolian systems envisage transverse dunes whereas successions representing linear and star dunes remain under recognized research questions that remain to be answered include i what factors control the preservation potential of different types of aeolian bedforms and what are the characteristics of the deposits of different bedform types that can be used for effective reconstruction of original bedform morphology ii what specific set of controlling conditions allow for sustained bedform climb versus episodic sequence accumulation and preservation iii can sophisticated four dimensional models be developed for complex patterns of spatial and temporal transition between different mechanisms of accumulation and preservation and iv is it reasonable to assume that the deposits of preserved aeolian successions necessarily represent an unbiased record of the conditions that prevailed during episodes of earth history when large scale aeolian systems were active or has the evidence to support the existence of other major desert basins been lost for many periods throughout earth history

beach ridges from the varanger peninsula arctic norwegian coast characteristics and significance the most common coastal sedimentary forms on the arctic coast of the varanger peninsula are raised beach ridge plains the majority of the ridges consist of coarse material but there are also sandy beach ridge areas close to the river mouths of some of the major rivers some bays having the same isostatic rebound and dynamic conditions have been studied to test if the number of beach ridges in each locality is significant to prove climatic changes storminess and rates of sediment accumulation or if the number of beach ridges in each bay is only dependent on their intrinsic characteristics and self organization because the number of ridges varies not only from bay to bay but even within the same bay it has to be accounted for by contrasting internal and local evolution sediment supply offshore gradient and coastal evolution these differences between various bays or parts of the same bay invalidate the explanations that global processes planetary orbital forces relative sea level changes or past climatic condition are responsible for beach ridge development

eolian deposits of the northern margin of the south china jianghan basin reconstruction of the late cretaceous east asian landscape in central china abstract the late cretaceous honghuatao formation includes a succession of thick clastic sedimentary sequences which are widely exposed in northwestern jianghan basin central china here detailed sedimentological and facies architectural analyses are performed allowing to re interpret and identify the controversy for sedimentary environment and to investigate the paleoclimatic condition the honghuatao stratigraphic sequence includes eolian dunes and dry interdunes deposits with fluvial channel deposits at the bottom and top the vertical change between fluvial and eolian systems indicates alternating wet and dry climate at the same time the provenance analysis combined with the paleocurrents from the w nw and ne indicates that huangling dome south qinling belt and dabie orogen supply the main detrital source for the honghuatao formation the late cretaceous first rifting subsidence in the jianghan basin provided accommodation space for the preservation of the aeolian accumulation moreover the existence of the mountain belts around the basin that is the orographic effect precluded the winds from transporting humidity to the interior of the jianghan basin generating the desert system this study shows that the formation of eolian deposits in the honghuatao formation and coeval strata in numerous adjacent basins was a sedimentary response to the prevailing desert climate in the mid to low latitude areas of the northern hemisphere during the late cretaceous which was predominately controlled by the subtropical high pressure system on a planetary scale

submerged early holocene coastal and terrestrial landforms on the inner shelves of atlantic canada coastal and terrestrial landforms that formed with lowered relative sea levels during the early postglacial period in atlantic canada were submerged during the holocene transgression however these landforms are seldom seen on sea floor imagery factors that contribute to their destruction include the brevity of sea level lowstands and high wave energy on shallow modern shelves we identify one situation within which preservation has been relatively good large coastal lakes that existed for many thousands of years before being connected to the ocean by rising sea level in the mid holocene we describe bedford basin near halifax nova scotia and deal more exhaustively with the bras d or lakes an inland sea in cape breton nova scotia the preservation of shore platforms barrier beaches and spits and fluvial systems was due to the rapid onset of the transgression and the relatively low wave energy in the subsequent marine phases the well preserved early holocene coastlines are highly favourable targets in the search for evidence of human occupation in the early to mid holocene

barrier and lagoon coast evolution under differing relative sea level regimes examples from ireland and nova scotia abstract although the coasts of southern ireland and eastern nova scotia possess many basic similarities especially in terms of geology glacial history sediment character resistance to erosion and wave and tide regimes there is a fundamental contrast in holocene sea level history in ireland recent the past 4000 years sea level rise has been limited to less than 1 mm year by contrast the atlantic coast of nova scotia has been experiencing sea level rises up to three to five times greater over the same period under these markedly differing relative sea level rise regimes barrier and lagoon evolution has varied considerably in ireland barrier lagoon form is controlled by local basement expression particularly through the emergence of headlands creating largely closed sediment systems and the requirement to maintain cross shore drainage it is this latter factor that leads to a simple four fold categorization of the irish barriers and lagoons from freshwater seepage to open tidal environments the nova scotian examples are associated with rapidly moving erosional fronts with local basement control relegated to a subordinate role at the expense of rapid changes in sediment supply barriers can both grow and decay under these conditions subject to certain critical but as yet ill defined thresholds simultaneously forcing development and destruction of adjoining lagoons these major differences also find expression in sedimentary sequences

shallow water mud mounds of the early devonian buchan group east gippsland australia abstract the lower devonian rocky camp member of the murrindal limestone buchan group of southeastern australia consists of a series of carbonate mud mounds and smaller lagoonal bioherms the rocky camp mound is the best exposed of the mud mounds and has many characteristics in common with waulsortian carboniferous mounds detailed paleoecological and sedimentological studies indicate that the mound initially accumulated in the photic zone in contrast to most of the previously recorded mud mounds five facies are present in the mud mound a dasycladacean wackestone facies at the base of the mound represents a moderate energy shallow water bank environment within the photic zone a crinioidal wackestone facies was deposited in a laterally equivalent foreslope setting a poriferan crinoidal mudstone facies developed in a quiet deeper water lee side mound setting associated with a minor relative sea level rise a stromatoporoid coralline packstone facies in the upper part of the mound deposited in a high energy fair weather wave base mound front environment the crest of the mound is represented by a crinoidal receptaculitid packstone facies indicative of a moderate energy mound top environment in the photic zone sheltered by the mound front stromatoporoid coral communities a mound flank facies is present on the southern side of the mound and this consists of high energy crinoidal grainstones mud mound deposition was terminated by a transgression that deposited dark gray fossil poor marl of the overlying taravale formation the rocky camp mound appears to have originated in shallow water photic zone conditions and grew into a high energy environment with the mound being eventually colonized by corals and stromatoporoids the indications of a high energy environment during later mound growth growth form of colonial metazoans and grainstones of the flanking facies suggest that the micrite in the mound was autochthonous and implies the presence of an energy damping mechanism probably biological at the mound surface

a drowned holocene barrier spit off cape ann massachusetts seismic profiles and bathymetric contours reveal a drowned barrier spit on jeffreys ledge off cape ann massachusetts seaward dipping internal reflectors indicate that a regressive barrier formed during the early holocene low sea level stillstand preservation of the barrier spit may have been favored by its large size as much as 20 m thick by an ample sediment supply from unconsolidated glacial drift and by the subsequent rapid sea level rise the barrier spit is present in water depths of 50 to 70 m and indicates a low relative sea level stand of 50 m this value confirms the low relative sea level stand of 47 m postulated by oldale et al 1983 for northeast massachusetts and new hampshire on the basis of the submerged delta of the merrimack river and it indicates that the barrier and delta were contemporaneous oldale et al 1983

exploring the geological features and processes that control the shape and internal fabrics of late diagenetic dolomite bodies lower khuff equivalent central oman mountains abstract the lower permian carbonate rock succession of the oman mountains represents a stratigraphical surface analogue for middle eastern lower khuff hydrocarbon reservoirs the characteristics of the carbonate rocks are highly variable both laterally and vertically due to the superposition of several episodes of dolomitization a stratabound early dolomitization event affected the well bedded limestones during triassic times subsequently a later burial dolomitization led to the emplacement of several hundreds of meter wide and tens of meter thick dolomite bodies the goal of our study is to understand the distribution and genetic controls on the formation of late diagenetic dolomite bodies field mapping in wordian to capitanian beds was conducted in the jebal akhdar tectonic window in the central oman mountains to determine the shape internal fabrics and associated structures of late diagenetic dolomite bodies the longest extension of late diagenetic dolomite bodies was found to follow predominantly the strike direction of fracture planes bed to bed contacts the precambrian permian unconformity and the bottom rim of early diagenetic dolomite two groups of diagenetic fabrics were observed in association to fractures and bedding planes first vug related fabrics comprise vuggy pores and zebra dolomite second breccia related fabrics consist of either small scale crackle mosaic breccia fabrics and centimeter sized vugs followed by bedding parallel vugs lined up petrographic analysis revealed three types of diagenetic phases referred to as d1 d2 and d3 the matrix replacive phase d1 represents the main diagenetic phase formed during burial coarse crystalline dolomite rhombs phase d2 and saddle dolomite phase d3 were found along stylolites in vugs and in fractures based on the presence of saddle dolomite and zebra dolomite textures late diagenetic dolomite bodies are interpreted to have formed by the circulation of warm dolomitizing fluids of at least 60 c

stratigraphy and petrology of petroleum producing waulsortian type carbonate mounds in fort payne formation lower mississippian of north central tennessee the petroleum producing subsurface mounds of the fort payne formation lower mississippian in north central tennessee represent a facies that is generally absent or poorly developed in surface sections to the west near the cincinnati arch and to the east in the appalachian fold belt the cross section and isopach maps of the fort payne mound unit and submound unit and a structural map of the underlying chattanooga shale provide evidence for predicting undiscovered mounds by interpolating and extrapolating along several northeast southwest mound trends a petrologic study of cores and well cuttings indicates the character of facies microfacies sedimentary structures porosity and morphology of mounds which provide a basis for interpreting sedimentary environments and the history of mound development interpretations are based on subsurface data and they are reinforced by a comparison with the analogous waulsortian mounds and lenses of the same age in europe waulsortian type mounds are widespread on the surface of western europe and north america however differences in morphology porosity development and the emplacement of petroleum in fort payne mounds are related to local paleogeography in a shallow cratonic shelf sea subjected to cyclic regression and transgression due to regional tectono eustatic events fort payne mounds produced more than 5 5 million bbl of oil through 1980 although the source beds have not been identified petroleum may have been derived from the submound or mound units of the fort payne formation or from the underlying chattanooga shale

large dry humid fluctuations in asia during the late cretaceous due to orbital forcing a modeling study abstract cretaceous stratigraphy in the mid to low latitude asia indicates that the climate was overall dry with large variations in aridity in timescales of 1 100 ka different from the present day monsoonal humid climate to identify the possible mechanism for such variation we modeled the late cretaceous climate using a fully coupled atmosphere ocean general circulation model aogcm community earth system model version 1 2 cesm1 2 under different co2 concentrations and orbital configurations the simulation results show that the mid to low latitude asia was generally dry during that time consistent with reconstructions the arid area decreases and the semi arid area increases with the increase of co2 concentration but the change in total area is small even when co2 is increased by 8 folds in contrast the area of dryland can increase by 67 or 500 depending on how dryness is defined when the orbital configuration changes from one in which the northern hemispheric summer receives the most solar insolation to one in which it receives the least solar insolation therefore the mid to low latitude asia was likely going through dramatic dry humid cycles at orbital timescale during the late cretaceous similar to the saharan region during the late miocene pleistocene

late cretaceous climbing erg systems in the western xinjiang basin palaeoatmosphere dynamics and east asia margin tectonic forcing on desert expansion and preservation abstract this study reassesses the terrestrial deposits of the late cretaceous tangbian formation in the western xinjiang basin of the south china block originally considered to be aqueous deposits we reinterpret these strata as representing an extensive aeolian system in a desert environment this paper suggests that the development of aeolian deposits in the tangbian fm represents the culmination of the late cretaceous desertification that followed the relatively humid early late cretaceous epoch in the interior of south china the area was dominated by subtropical high pressure systems on a planetary scale combined with coastal mountains caused by sustained orogenic activity the interaction between subtropical high pressure systems and topographic conditions ultimately caused the development of a tropical desert climate characterized by an extensive dry climbing aeolian dune system we propose that the coastal mountains not only blocked moisture transport from the ocean and led to the aridification of south china interior but also exerted a control and transformed the original prevailing surface wind pattern

coastal changes in the arctic the arctic s climate system is changing air temperatures major river discharges and open water season length have increased and storm intensities and tracks are changing thirteen quantitative studies of the rates of coastline position change throughout the arctic show that recently observed changes have not increased coastal erosion rates which currently range between 0 and 2 m yr when averaged for the arctic shelf seas current data is probably insufficient both spatially and temporally however to capture change at decadal to sub decadal time scales in this context we describe the current understanding of arctic coastal geomorphodynamics with an emphasis on erosional regimes of coasts with ice rich sedimentary deposits in the laptev east siberian and beaufort seas where local coastal erosion can reach 30 m yr we also examine coasts with lithified rocky substrates where geomorphodynamics are intensified by rapid glacial retreat coastlines of svalbard greenland and the canadian archipelago are less frequently studied than ice rich continental coasts of north america and siberia and studies often focus on coastal sections composed of unlithified material as air temperature and sea ice duration and extent change longer thaw and wave seasons will intensify coastal dynamics in the arctic

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

waulsortian like mounds of the mississippian pekisko formation northwestern alberta petrographic and chemical attributes abstract the tournasian age pekisko carbonates in the normandville field northwestern alberta form waulsortian like bryozoan crinoid mounds that developed in fairly deep low energy cool water systems close to the ramp margin three main depositional environments occur 1 crinoidal apron with wackestone grainstone and floatstone facies 2 mound flank with grainstone wackestone packstone and floatstone facies dipping 35 and 3 bryozoan mound core composed of rudstone and floatstone facies with fenestrate bryozoa minor crinoids and carbonate mud local highs due to fault bounded blocks created from the collapse of the devonian peace river high may have controlled the location of mound nucleation diagenesis of the bryozoan crinoid mounds included calcite cementation compaction dolomitization silicification and hydrocarbon emplacement events the mound core facies contains submarine fascicular optic calcite and bladed prismatic calcite cements and later ferroan brightly luminescent pore filling blocky spar cement the crinoid apron facies contains syntaxial cement associated with crinoids and the ferroan blocky spar cement the mounds are dominantly limestone however in one well dolomite dominates the lower section four types of dolomite have been identified partial replacive chemical compaction related pervasive dolomite and saddle dolomite cement all dolomites are non stoichiometric caco3 mole 56 6 62 6 the partial zoned replacive dolomite replaces micrite and syntaxial rim calcite in mound flank and crinoid apron facies the chemical compaction related dolomite is found along dissolution seams and stylolites and has similar cl characteristics to the replacive dolomite the pervasive dolomite is fabric destructive and has dull cores and bright rims in cl saddle dolomite 0 15 mm has brightly luminescent concentric zoning and occurs in vugs and fossil pore spaces chemical and isotopic analysis of the bryozoan crinoid mounds indicate that the original marine signatures in micrite early cements some crinoids and brachiopods have been preserved however carbon isotopic values for some crinoids matrix and dolomite show more positive values compared to known mississippian carbonate values recrystallization during shallow burial has reset the oxygen isotopic composition of some crinoids and micrite oxygen and carbon isotopic compositions of most dolomites overlap with altered crinoids and early calcite cements however saddle dolomites have lighter 18o values similar to saddle dolomites from the devonian wabamun group in this area the isotopic variations in later ferroan calcite cements show an inverted j trend possibly due to variable amounts of water rock interaction while the sr isotopic ratio of submarine calcite cement coincides with that of mississippian seawater the later ferroan calcite cement is more radiogenic indicating a different source of fluids

hydrocarbon potential of the mississippian carbonate platform bechar basin algerian sahara the western bechar basin contains a 1500 2000 m thick mississippian succession of carbonates consisting of superposed shoaling upward sequences whose porosity or diagenesis have never been investigated to establish the reservoir potential of these carbonates in this paper we present a diagenetic and porosity evolution of the visean part of the mississippian carbonate platform that may lead to the development of new exploration fairways in the region a diagenetic model is proposed in which ooid and crinoid grainstones may have a reservoir potential if hydrocarbon migration occurred before the end of the serpukhovian prior to complete occlusion of porosity

sequence development of a mixed carbonate siliciclastic high relief ramp mississippian kentucky u s a abstract the discovery of the supergiant oil fields of the caspian region has focused attention on eustatic tectonic and climatic controls on lower carboniferous facies this paper documents the development of a highly complex mixed carbonate siliciclastic ramp succession of the lower mississippian upper osagean lower meramecian fort payne salem interval kentucky that formed peripheral to an abandoned delta system borden formation following drowning of the paleoshelf during a time of arid climate and tectonic quiescence the antecedent borden deltaic marine paleoshelf stood 100 m above the starved basin plain to the southwest and had marginal slopes of less than 0 5 the succession is a supersequence 0 to 150 m thick approximately 5 to 10 my duration composed of two upper osagean fort payne and two lower meramecian warsaw salem depositional sequences which correlate with the global sea level cycles of ross and ross 1988 the supersequence lowstand systems tract on the basin floor consists of the lower part of a unit of green shale and mounds mound growth appears to have continued during supersequence transgression culminating in some mounds up to 60 m thick on the borden paleoshelf the supersequence transgressive systems tract is a condensed glauconite horizon s the supersequence highstand tract consists of marine quartz sandstone and shale peritidal carbonates high energy crinoidal bryozoan grainstone banks and deep ramp and slope siliceous calcisiltite third order sequences have local lowstand transgressive sand bodies those in sequence 2 are clinoformed strike sand lobes up to 50 m thick while those in the younger sequences are discontinuous sheets dip oriented lobes the siliciclastic units appear to be associated with a paleodrainage system off the borden paleoshelf in upper osagean sequences 1 and 2 third order highstand systems tracts are aggradational on the paleoshelf and prograded to the southwest as a series of clinoforms into the starved basin lower meramecian sequences 3 and 4 highstand systems tracts are relatively layer cake reflecting loss of accommodation during late osagean basin filling and they prograded more to the west into the subsiding reelfoot graben illinois basin the extremely complex facies relations reflect the interaction of the antecedent shelf slope basin topography the mixed carbonate and siliciclastic systems mounded basin floor topography the highly channeled margin morphology eustasy and relatively stable tectonics

diagenesis of fibrous magnesian calcite marine cement implications for the interpretation of δ18o and δ13c values of ancient equivalents fibrous high mg calcite hmc marine cement from the pliocene hope gate formation jamaica occurs as 1 2 mm thick isopachous coatings on skeletal grains in local occurrences of halimeda grainstone and is commonly syntaxially overgrown by clear prismatic low mg calcite lmc interpreted as a mixing zone cement the presence of inclusions at discrete levels in the fibrous marine cement produces internal growth banding wherein clear inclusion free zones alternate with cloudy inclusion rich zones clear zones have uniform mg contents 13 7 0 2 mol mgco3 and stable isotopic compositions 18o 0 8 0 1 13c 3 2 0 1 consistent with a marine origin in contrast inclusion rich zones contain fine scale intergrowths of lmc dolomite and hmc and have carbon and oxygen isotopic compositions that define a linear mixing trend between compositions of inclusion free hmc and prismatic lmc cement overgrowths petrographic observations indicate that the mixing trend defined by isotopic data from inclusion rich zones is related to the addition of large volumes of secondary lmc as cement in primary pore space as intergrowths among fibers of primary hmc marine cement and or as replacements of primary hmc crystallites dolomite is present in inclusion rich zones in volumes generally compatible with amounts predicted to result from the closed system stabilization of hmc to lmc and dolomite in addition isotopic and geochemical data from some areas of inclusion rich zones are consistent with mass balance constraints assuming a closed system which require that bulk isotopic and geochemical compositions are retained these relations suggest that small remnants of hmc in inclusion rich zones of hope gate marine cement have altered to lmc and dolomite while isolated from system pore fluids such that primary marine isotopic signatures were imparted on diagenetic products similar petrographic geochemical and isotopic relations have been noted in ancient occurrences suggesting that 18o and 13c values from some former marine cements should be useful for the determination of isotopic compositions of original marine cements and ultimately for the determination of ocean chemistry in the geologic past

late quaternary sedimentation in st george s bay southwest newfoundland acoustic stratigraphy and seabed deposits shallow seismic reflection data collected in st george s bay southwest newfoundland reveal a complex pattern of subsurface topography and acoustic facies two basins in the inner bay are underlain by glacially overdeepened valleys that extend to depths in excess of 180 m within the thick quaternary sequence in the inner bay we recognize eight acoustic units units 1 ice contact 2 subaqueous outwash and 3 draped glaciomarine record the presence and retreat of a major late wisconsinan ice margin unit 4 postglacial mud has resulted from reworking of glaciogenic sediments in response to changes in relative sea level unit 5 postglacial sand is a shoreface deposit on the seaward front of the former moraine unit 6 postglacial delta was formed by fluvial reworking of glaciogenic sediments during the postglacial lowstand of relative sea level unit 7 postglacial barrier platform comprises seaward fining clinoform prisms that have prograded into the basins and underlie gravel beach ridge pla

construction of the mississippian pennsylvanian and permian seawater 87sr86sr curve abstract the estimated path of seawater 87 sr 86 sr during the mississippian pennsylvanian and permian is based on 228 analyses the samples are largely from the southern interior of the u s a where rocks of this age are widely exposed multiple analyses from single rock units are used to define the seawater ratio for different time periods the seawater 87 sr 86 sr declines from 0 70812 sw 95 mississippian to an estimated low in the early meramecian of near 0 70755 sw 152 the value rises to near 0 70812 sw 95 in latest mississippian the ratio rises to 0 70830 sw 77 in mid pennsylvanian and decreases to near 0 70809 sw 98 during virgilian time the earliest permian value is near 0 70793 sw 114 after rising to 0 70804 sw 103 in the early leonardian the seawater 87 sr 86 sr falls sharply to reach a low of 0 70672 sw 235 in ochoan time the end of the paleozoic is estimated to be near 0 70707 sw 200 based on samples from china analysis of the paleozoic curve shape shows an alternating dominance of oceanic and continental sr contributions the extended and precipitous decline in the 87 sr 86 sr during mid permian is unmatched during the phanerozoic the contrast of the paleozoic seawater sr curve shape to that in the mesozoic and cenozoic indicates a potentially fundamental change in the balance of oceanic and continental sr contributions at the end of the permian

late jurassic fluvial eolian deposits from the tianchihe formation ningwu jingle basin shanxi province china abstract eolian systems were widespread in china in the cretaceous however the reports of pre cretaceous eolian and its related systems are scarce which prohibits studying the construction accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors in this paper we report on fluvial eolian successions from the late jurassic tianchihe formation in the ningwu jingle basin these successions represent the oldest reported inland fluvial eolian systems in china fourteen lithofacies types are recognized in the tianchihe formation and have been grouped into six facies associations including meandering fluvial channel levee and overbank in the lower part and eolian sandsheet eolian dune ephemeral fluvial channel and floodplain in the upper part the fluvial system comprises a series of wetting upward cycles which indicate humid climate culminating in high precipitation and shallow water table level eolian dune deposits composed of grainflow grainfall wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface suggesting compound dunes or draas eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination the association of eolian dune and eolian sandsheet is development of a dry eolian system twelve drying upward cycles mainly composed of eolian sandsheet eolian dune successions and four wetting upward cycles consisting of eolian sandsheet dune ephemeral fluvial channel floodplain successions occur in the eolian system these repeated cycles likely reflect an evolving erg system directly controlled by sediment supply sediment availability and relative water table the vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions which may be related with the uplift of the east china plateau in the late jurassic

diagenesis of a limestone reservoir lower cretaceous abu dhabi united arab emirates comparison between the anticline crest and flanks abstract petrographic stable isotope and fluid inclusion analyses were conducted on a lower cretaceous limestone reservoir onshore abu dhabi united arab emirates in order to compare the diagenetic processes and products in the oil zone i e crest versus water zone i e flanks of a giant oilfield anticline the near seafloor shallow and intermediate burial

mid cretaceous desert system in the simao basin southwestern china and its implications for sea level change during a greenhouse climate abstract paleoclimatic indicators suggest that the mid cretaceous was one of the warmest intervals of the phanerozoic the period of the mid cretaceous super greenhouse also experienced an equator to pole temperature gradient much lower than that of the present day implying greater meridional heat transport by the atmosphere and or oceans however reconstructions of cretaceous atmospheric circulation have been hindered by a lack of relevant datasets based on reliable proxies or direct geological evidence aeolian deposits provide direct information about paleoclimate as well as the direction and intensity of paleo wind in the interiors of continents using petrologic and sedimentologic observations this study reassesses the terrestrial deposits of the mid cretaceous mangang formation in the simao basin of southwestern china originally considered to be aqueous deposits we reinterpret these strata as representing aeolian transport in a desert environment we suggest that the development of aeolian deposits in the mangang formation and coeval strata in adjacent basins was a local response to the prevailing desert climate in the mid to low latitudes of the northern hemisphere during the mid cretaceous which were dominated by subtropical high pressure systems on a planetary scale in addition with the closure of the mesotethys ocean the intermontane basins of the south china simao and indochina blocks became more isolated from atmospheric circulation bidirectional subduction of the bangong nujiang oceanic crust and the izanagi plate beneath east asia led to the development of andean type margins which created a rain shadow effect in continental east asia these factors caused the development of a tropical desert climate characterized by aeolian dunes and evaporite deposition we speculate that the severe depletion of groundwater reservoirs via the desertification of east asia may represent a previously unrecognized trigger for short term sea level changes during the ice free cretaceous greenhouse interval

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

formation of saddle dolomites in upper cambrian carbonates western tarim basin northwest china implications for fault related fluid flow abstract the saddle dolomites occur more intensely in cores closely to fault than that in cores far away from the fault in upper cambrian carbonate of western tarim basin suggesting that formation of the saddle dolomites is likely related to fault controlled fluid flow they partially fill in fractures and vugs of replacement dolomite the saddle dolomites exhibit complex internal textures commonly consisting of core and cortex in comparison with the matrix dolomites the saddle dolomites show lower sr content and 87 sr 86 sr ratios higher fe and mn content and more negative 18 o values combined with high th 100 130 c of primary fluid inclusions it is suggested that the saddle dolomites precipitated from hydrothermal fluid derived from the deep evaporite bearing middle cambrian strata and the magnesium source may be due to dissolution of host dolomite during hydrothermal fluid migration fault activity resulted in petrographic and geochemical difference of the core and cortex of the saddle dolomites the cores precipitated from the formation water mixed by deep brines at the early stage of fault activity and the cortexes precipitated from the deep fluid with higher temperatures through the middle cambrian later in summary the formation of the saddle dolomites implies a hydrothermal fluid event related to fault activity which also resulted in high porosity in upper cambrian carbonate in western tarim basin

waulsortian type bioherm development and response to sea level fluctuations upper visean of bechar basin western algeria abstract an exceptionally well developed and well preserved upper visean succession rich in sponge bryozoan crinoid mounds in the foreland carboniferous bechar basin northwestern algerian sahara is described and discussed the succession is composed of recurrent facies mosaics forming individual superposed members an ideal member is made up of two distinct fades assemblages the lower assemblage forms the actual mounds and is composed of sponge bafflestone wackestone at the base overlain by massive sponge fenestellid bafflestone wackestone and capped by massive crinoid wackestone with bedded flanks of lithoclastic wackestone in contrast to massiveness of the mounds the upper facies assemblage is composed of well bedded crinoid packstone grainstone and ooid grainstone with local rugose coral and algal foraminiferal banks on the basis of benthic assemblages and nature of substrate seven bathymetric zones are defined and indicate that each member of the bioherm rich formations is a shallowing upward parasequence controlled by an asymmetrical transgressive regressive cycle the local curve of relative sea level for the late visean shows 13 cycles interpreted as fourth order eustatic sea level changes each cycle averaging half a million years in duration third order cycles could not be identified the platform model proposed is a distally steepened ramp 15 20 km wide that developed in a rapidly subsiding foreland basin lateral distribution of facies on the ramp depended strongly on local tectonic setting whereas vertical development was controlled by sea level fluctuation the deep water mud rich sponge bryozoan crinoid mounds developed in 100 150 m water depths during phases of sea level highstand whereas deposition of shallow water facies occurred on top of the mounds in less than 70 80 m water depths during regressive phases the bechar mounds share similarities with the classical lower carboniferous waulsortian mounds but they differ in two aspects the abundance of large sponges which is unique and their vertical zonation wherein basal facies consist of sponge dominated assemblages the proposed model can serve as a tool in developing exploration strategies in the search for hydrocarbon reservoirs in the bechar basin because the peculiar architecture of the platform may provide suitable plumbing systems for fluid migration and the depositional signature of the mounds and associated facies is possibly recognizable on seismic profiles

gravel barrier migration and overstepping abstract despite the widespread occurrence of gravel barriers on mid to high latitude coasts understanding of their stability and relationship to gravel deposits on the inner continental shelf remains rudimentary on sand dominated coasts subject to rising relative sea level barrier overstepping has been postulated as a mechanism for preservation of beach deposits on the shelf but direct observation of overstepping events has been lacking observations at a site on the atlantic coast of canada reveal migration of a gravel barrier at 8 m a 1 landward over back barrier mud following abandonment of part of the barrier volume on the shoreface this provides clear evidence for overstepping and suggests that it may play a role in the formation of inner shelf gravel deposits integrity of the migrating stretching barrier depends on continued sediment supply from the headland source to a connecting ridge which must become progressively longer as the landward displacement of the barrier increases

late cretaceous plateau deserts in the south china block and quaternary analogues sedimentology dune reconstruction and wind water interactions abstract plateau deserts are among those continental systems with the most significant examples of clastic deposits associated with the complex combination of the action of ice wind and water the late cretaceous rocks of china contain the record of desert systems migration and partial destruction in a palaeoplateau desert the evolution of the south china block during late cretaceous was characterized by widespread destructive plate margin activity this favoured orogenic uplift and high altitude mountain ranges of which a direct consequence was a widespread rain shadow effect triggering desertification and erg expansion similar to that of quaternary counterparts in the tibetan plateau this work presents a detailed analysis of the sedimentology stratigraphic architecture palaeogeography and palaeocurrent reconstruction of aeolian and associated alluvial depositional systems the reconstruction of aeolian bedforms based on field data analysis indicates that during late cretaceous draas and crescentic dunes accumulated and migrated in extensive intermontane desert systems heavy rains led to partial destruction of aeolian dunes and the reworking of aeolian sands in interdraa corridors the fault controlled subsidence and an increasing input of windblown sediments favoured the long lasting accumulation of the erg system possible monsoonal rains recharged the groundwater system causing the rise of the regional phreatic level that favoured the ulterior long lasting preservation of the aeolian system in the xinjiang basin the dimensions and processes inferred from this cretaceous desert system are similar to those observed today in the linking zone of the taklamakan gobi deserts where meltwater flows from alpine glaciers in surrounding mountain ranges recharge the alluvial and fluvial network of the erg margin the occurrence of striated cobbles in the alluvial facies suggests glacial activity in the catchment areas of the cretaceous plateau

barriers barrier platforms and spillover deposits in st george s bay newfoundland paraglacial sedimentation on the flanks of a deep coastal basin abstract st george s bay and adjacent coastal areas of southwest newfoundland contain thick sequences of late quaternary glaciogenic sediments and have been subject to relative sea level fluctuations over a rang of 70 m during the past 13 5 ka glaciogenic sediments have been mobilized by littoral processes to form two types of deposits these are 1 the prograded barrier beach and spit at stephenville and flat island respectively which are associated with large subaqueous sandy platforms and 2 a wedge of well stratified sand and gravel on the landward flank of the shallow sill which extends across st george s bay at an average depth of about 25 m the subaerial barriers and spits are composed of gravel beach ridges overlain locally by thin aeolian deposits with freshwater and salt marsh peats in swales these barriers developed during the last several thousand years as relative sea level approached its present position from an early postglacial minimum of approximately 25 m the prerequisite for beach ridge formation was the deposition of large sandy subaqueous platforms which appear on shallow seismic reflection records as clinoform wedges prograded into the deep basin of inner st george s bay the barrier platform at stephenville is constructed across a deep submarine valley the flat island barrier platform sits on the flank of a glacially overdeepened trough partly filled by glacial and postglacial sediments and envelops a delta formed during the early postglacial low stand of relative sea level the platform and barrier together constitute a thick coastal sequence coarsening up from sandy mud at the base to gravel at the top the wedge of well stratified coarse sediment up to 50 m thick situated on the landward flank of the shallow sill overlies older glaciogenic sediments and passes laterally into postglacial basin muds steep foreset reflections dipping 10 20 are evident on shallow seismic reflection records suggesting that the wedge was formed by spillover of sediment entrained by wave and current action into the relatively deep basins of the inner bay active gravel ripples testify to the continued mobility of coarse sediment on the sill the formation of the spillover deposits barriers and platforms demonstrates the potential for glacially overdeepened basins to host thick heterogeneous coarse grained coastal and inner shelf deposits

evolution of the barrier islands of southern long island new york three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the holocene transgression in southern long island new york 1 the holocene transgressive stratigraphic sequence behind the present barriers 2 the stratigraphic patterns of the inner shelf and 3 the morphology of the now buried late pleistocene coastal features the extensive preservation of backbarrier sediments radiocarbon dated between 7000 and 8000 yr bp on the inner shelf of southern long island suggests that the barriers have not retreated by continuous shoreface erosion alone but have also undergone discontinuous retreat by in place drowning of barriers and stepwise retreat of the surf zone such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked based on the presence of submerged barrier sand bodies in seismic records it is inferred that about 9000 years ago when the sea stood about 24 m below the present sea level a chain of barriers developed on the present shelf about 7 km offshore of the present barriers with continued sea level rise the 24 m barrier built upward until the sea reached about 15 m msl just prior to 7000 yr bp the barriers were then submerged by the rapidly rising sea and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline the surf zone overstepped to the landward margin of the old lagoon which had become fixed at the steep seaward face of mid wisconsinan or sangamonian coastal barriers during the past 5000 or 6000 years the shoreface has retreated continuously by about 2 km evidence from southern long island and elsewhere in regions of coastal submergence indicates that rapid sea level rise and low sand supply seem to favour the stepwise retreat of barriers whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat stationary upbuilding or seaward progradation of barriers may occur when supply of sand is great and or submergence is slowed or reversed morphologic highs on the pretransgression surface such as old barrier ridges tend to fix the migrating barrier shoreline during either continuous retreat or stepwise retreat of barriers

deltas spits and littoral terraces associated with rising sea level late quaternary examples from northern iceland abstract boomer records from eyjafjordur northern iceland reveal a major fossil delta with associated wave built littoral terraces which formed when contemporary sea level was at about 40 m below the modern level and which post date late weichselian glaciation of the site the structure of these units and a sequence of similar submerged deltas and spits which lie higher on the fjord side are very instructive examples of the evolution of the structure of shallow water sediment units formed on a rising sea level and permit the nature of the transgression to modern sea level to be reconstructed simple approaches to the reconstruction of sea level change from limited evidence are set out in order to produce a sea level of 40 m in eyjafjordur it is necessary that the isostatic component of sea level change should have decayed before early holocene eustatic sea levels rose above 40 m at 9000 10 000 yrs b p this may be explained either by a substantial early reduction in the local glacier load on the crust and associated early decay of the isostatic component of relative sea level change or by a low asthenosphere viscosity beneath iceland permitting an anomalously rapid decay of the isostatic component

organisational controls typologies and time scales of paraglacial gravel dominated coastal systems abstract the fundamental controls on the initiation and development of gravel dominated deposits beaches and barriers on paraglacial coasts are particle size and shape sediment supply storm wave activity primarily runup relative sea level rsl change and terrestrial basement structure primarily as it affects accommodation space this paper examines the stochastic basis for barrier organisation as shown by variation in gravel barrier architecture we recognise punctuated self organisation of barrier development that is disrupted by short phases of barrier instability the latter results from positive feedback causing barrier breakdown when sediment supply is exhausted we examine published typologies for gravel barriers and advocate a consolidated perspective using rate of rsl change and sediment supply we also consider the temporal variation in controls on barrier development these are examined in terms of a simple behavioural model barch for prograding gravel barrier architecture and its sensitivity to such controls the nature of macroscale 10 2 10 3 years gravel barrier development including inherited characteristics that influence barrier genesis as well as forcing from changing rsl sediment supply headland control and barrier inertia is examined in the context of long surviving barriers along the southern england coastline

lithostratigraphy and depositional environments of the upper cretaceous djadokhta formation ulan nuur basin southern mongolia and its paleoclimatic implication abstract non marine upper cretaceous strata are widely distributed in the gobi basin of southern mongolia and record marked paleoenvironmental and paleoclimatic changes the climate in this region is considered to have changed from humid during the cenomanian to santonian to semi arid during the campanian and returned to humid during the early maastrichtian the change from humid to semi arid climate is well recorded in the djadokhta formation as former division in the ulan nuur basin of the central gobi basin in previous studies the djadokhta formation was formally regarded as being characterized by eolian deposits formed under a semi arid climate however the present study revealed that this formation comprises sub humid fluvial lithofacies in the lower part and semi arid eolian lithofacies in the upper part since the djadokhta formation was initially defined as a succession characterized by eolian lithofacies it is proposed here that the lower part showing fluvial lithofacies should be separated from the djadokhta formation and is newly named as the alagteeg formation the alagteeg formation is characterized by alternating beds of horizontally bedded sandstone and mudstone indicating sandy braided river flood plain and ephemeral lake environments under sub humid climate the djadokhta formation revised division is further subdivided into two parts the lower part is composed of large scale cross stratified sandstone in situ and reworked calcretes and thick mudstone lens suggesting desert environments of broad sand dune fields with few inter dune ephemeral river and pond deposits under semi arid climate on the other hand the upper part comprises structureless sandstone with mature in situ calcretes exotic pebbly sandstone and large sized burrows these lithofacies imply steppe environments with calcic soil development under semi arid climate this change from sub humid to semi arid climate during the campanian is recorded not only in the ulan nuur basin but also in other regions of southern mongolia as well as northern china hence the broad aridification in the mid latitudes of the asian interior during the campanian is inferred

estuarine sedimentation on the eastern shore of nova scotia abstract vibracored sedimentary sequences and microfauna foraminifera were studied in lawrencetown lake a small wavedominated estuary with minor fluvial input located on the eastern shore of nova scotia seven lithofacies were identified on the basis of sedimentological characteristics microfaunal assemblages and stratigraphic relationships these lithofacies can be grouped into three associations which define estuarine basin fill channel cut and fill and channel bypass subenvironments within the estuary system facies relationships indicate a cyclic pattern of estuarine sedimentation controlled by fluctuating local sediment supply superimposed upon a regional transgression

sequence stratigraphy and depositional dynamics of carbonate buildups and associated facies from the lower mississippian fort payne formation of southern kentucky u s a abstract carbonate buildups are a common feature in mississippian sections worldwide yet despite intense study questions remain about depositional processes that form such structures and their interrelations if any to each other carbonate buildups located in siliciclastic basins are particularly understudied and poorly understood this study focuses on a new exposure of buildups in the siliciclastic dominated fort payne basin osagean of south central kentucky it represents a first attempt to combine field and petrographic descriptions of facies in the buildup interval of the fort payne with the concepts of sequence stratigraphy to gain better insight into their depositional histories the buildup interval is composed of five distinct facies two of these the fossiliferous green shale and the tabular crinoidal packstone grainstone represent the background sedimentation during buildup nucleation and growth the remaining three facies make up the buildups themselves the shaly packstone marks the inception of buildup growth the massive wackestone represents the core of the buildups and the crinoidal grainstone is a buildup flank facies deposited near the end of buildup growth the buildups of the fort payne formation grew during the transgressive phase of one third order sequence in the early osagean the time at which buildup growth ceased cannot be determined precisely with available data but likely occurred either at the maximum flooding surface or during the early highstand three commonly used depositional models abbreviated as the lithoherm model the baffling model and the microbial model are evaluated with respect to the fort payne buildups none of the models is deemed adequate to explain all of the features of the buildups rather a combination of all three seems to be required to account fully for all of the characteristics noted in this study this multi faceted depositional model compares favorably with other carboniferous buildups worldwide suggesting commonalities that transcend the properties of the basins in which they grew

alluvial fan facies of the yongchong basin implications for tectonic and paleoclimatic changes during late cretaceous in se china abstract late cretaceous continental redbeds the guifeng group of the yongchong basin in se china have been investigated to conduct detailed fan facies description and interpretation tectonic activities determined the alluvial fan development along the basin margin but the alluvial facies was linked with paleoclimate changes the guifeng group is divided into the hekou tangbian and lianhe formations in ascending order the hekou conglomerates are typically polymict moderately sorted with erosional bases cut and fill features normal grading and sieve deposits representing dominant stream flows on alluvial fans during the initial opening stage of the basin infill the tangbian formation however is characterized by structureless fine grained sediments with dispersed coarse clasts and couplets of conglomerate and sandstone or siltstone and mudstone recording a change to a playa and ephemeral lake environments with occasional stream flooding thus indicating a basin expanding stage the hallmark of the lianhe formation is disorganized poorly sorted conglomerates lack of erosional bases and a wide particle size range from clay to boulders together reflect mud rich debris flows accumulating on fans likely related to reactivation of faulting along the northwestern mountain fronts during a post rift stage the depositional system changes from stream flows up through playa with ephemeral streams to debris flows during the accumulation of the three formations are thus attributed to different source rocks and climatic conditions therefore the fluvial dominated fans of the hekou formation recorded a subhumid paleoclimate coniacian santonian age the dominant semiarid climate during the campanian age produced abundant fine grained sediments in the playa and ephemeral lake environments of the tangbian formation a climatic change towards more humidity during the late stage of the guifeng group maastrichtian age probably yielded high deposition rate of coarse clasts in debris flow dominated fans of the lianhe formation thus the late cretaceous climate changes are inferred to have influenced and preserved signals in the alluvial stratigraphy of the yongchong basin

differential preservation of coastal structures on paraglacial shelves holocene deposits of southeastern canada abstract recent work has advanced our understanding of mixed sand gravel littoral systems in glaciated regions new insights include the nature and causes of coastal instability and conditions for preservation of holocene barrier deposits on paraglacial shelves the best preserved relict barrier structures recognized on the inner shelf of southeastern canada are interpreted as postglacial lowstand deposits initiated under stable to slowly rising relative sea level in areas of substantial shelf relief a largely intact early holocene gravel foreland survives at 38 m present water depth its preservation attributed in part to sediment volume and a partially protected location the mechanism by which this structure was abandoned and overstepped is unclear but may be related to accelerating sea level rise in some cases barriers keep pace with sea level rise for some time before being overstepped or reworked landward the duration and extent of preservation depend in part on the deposit volume as smaller accumulations are consumed and reworked more quickly deposit volume is a function of sediment supply accommodation space and headland spacing among other factors where barriers are small and thin beach sediments overtaken by the transgression may be smeared across the shoreface in a thin post transgressive veneer in such settings as along the eastern shore of nova scotia the only coastal units preserved on the shelf are back barrier estuarine facies in flooded valley depressions differential preservation is governed by shelf relief and accommodation space coastal alignment and compartmentalisation sediment supply and barrier volume rate and acceleration of sea level rise wave energy and potential for sediment reworking on the inner shelf

paraglacial barrier lagoon development in the late pleistocene baltic ice lake southwestern baltic abstract marine geological investigations including shallow seismic sedimentological and stratigraphical studies were carried out in fakse bay southwestern baltic seismic sequence analytical methods were used supplemented by detailed lithological descriptions pollen analysis and 14c dating of core material detailed correlations between sediment facies units and seismic sequences resulted in the establishment of four depositional sequences i glacial related deposits ii lagoon pond and freshwater coastal deposits iii lake bog lake deposits and iv marine sub littoral deposits most attention has been paid to sequences ii and iii showing the development of a transgressive freshwater barrier beach ridge and a following regression pollen spectra indicate allerod and younger dryas chronozone ages 11 500 10 000 14c yrs b p for the development of a sheltered lagoon pond basin behind the transgressive freshwater barrier beach ridge the freshwater coastal deposits are interpreted as the southwesternmost marginal deposits of the baltic ice lake and represent the transgression maximum this transgression maximum reached a level of about 13 m below the present sea level the final drainage of the baltic ice lake resulted in the development of a sheltered basin behind the former beach ridge a fluctuating groundwater level here favoured the deposition of alternating lake gyttja and bog peat deposits in the central part of the basin pollen analysis and 14c dating reveal that the lake deposits correspond to high groundwater levels associated with the ancylus lake 9000 yrs b p and the littorina sea 7000 yrs b p transgressions while the bog sediments represent the low water stands in the early holocene

the waulsortian type mound in the lower namurian of the lublin basin se poland abstract a unique waulsortian like mound is recognized in the lower namurian succession of the central part of the lublin basin se poland the carboniferous succession is characterized here by yoredale type cyclothems with carbonate units of relatively constant thickness an unexpected increase in thickness of the carbonate unit in the minkowice 4a well indicates the occurrence of an organic buildup at least 35 m thick sedimentological analysis reveals that its skeletal composition as well as its peloidal matrix abundant stromatactoid cavities and succession of cements indicate close analogies to similar facies in lower carboniferous waulsortian type mud mounds oxygen isotope data indicates that the formation and growth of the described mound were probably stimulated by hot water vents the occurrence of hot water vents in the open marine setting of the lublin basin is interpreted as a consequence of early namurian tectonic activity when a local tectonic compressional regime occurred in some parts of the basin the mound does not function as a hydrocarbon reservoir however its characteristics point to the presence of sedimentary traps which hitherto have not been recognized in this region