taphocoenoses and diversification patterns of calcimicrobes and calcareous algae ordovician tarim basin china despite the crucial role of epibenthic primary producers cyanobacteria green and red algae no diversity curves for calcimicrobes and calcareous algae are available to assess the pyramiding paleoecology characterizing the ordovician biodiversification episode a total of 24 taxa of calcimicrobes and calcareous algae are identified from a dapingian to lower katian succession of carbonate sedimentary rocks exposed at the leyayilitag ridge bachu uplift tarim basin northwest china calcimicrobes 14 taxa dasycladales seven taxa bryopsidales one taxon and cyclocrinales two taxa contribute to five distinct taphocoenoses characterizing a suite of carbonate mounds in stratigraphic order these are calathid sponge mounds algal calcimicrobial mounds algal mounds algal reefs and calcimicrobial mounds within the lower katian belodina confluens zone the diversity increases substantially from around 5 to more than 20 taxa per 2 ma this increase in diversity is based on new calcimicrobes bija o

lake devlin and pinedale glacial history front range colorado abstract glacial lake devlin was an ice margin lake that formed during pinedale time when the north boulder creek valley glacier blocked the mouth of a tributary near the downvalley limit of glaciation the lake was about 2 km long and as much as 60 m deep and was fed by meltwater from small valley glaciers it accumulated sediment apparently without interruption for about 10 000 yr the inception of lake devlin between 23 500 and 21 000 yr b p provides a limiting date for the maximum expansion of pinedale ice because the lake could not form until the north boulder creek glacier had advanced to within 2 km of its downvalley limit the maximum lowering of timberline which occurred about 19 000 yr b p is assumed to coincide with the pinedale glacial maximum apparent timberline elevations determined from picea pinus pollen ratios suggest that ice front positions during the time between 23 000 and 19 000 yr b p may have been only slightly less extensive than at the pinedale maximum lake devlin drained catastrophically about 13 000 yr b p which was after ice had receded from the outlet area pinedale glaciation in the front range began about or after 30 000 yr b p and final deglaciation occurred between 15 000 and 12 000 yr b p

the impact of depositional events and burial rate on carbonate silica diagenesis in a middle jurassic stromatactis carbonate mud mound sainte baume massif se france abstract understanding the processes and conditions of chertification in carbonates is a challenging problem to assess the marine silica cycle this contribution highlights parameters of internal silica recycling processes from their biogenic source to quartz cementation by describing a unique case of carbonate silica diagenesis in a mesozoic mud mound stromatactis carbonate mud mounds exposed in the sainte baume massif basse provence france developed in an outer shelf environment during the late aalenian concavum ammonite zone middle jurassic they form part of a cherty succession punctuated by hardgrounds and stratigraphically condensed intervals interpreted to record deepening episodes these mud mounds rich in siliceous sponge spicules and stromatactis are similar to their widespread paleozoic counterparts but are particular in being extensively silicified carbonate silica paragenesis forms a polymud fabric including four microcrystalline carbonates m1 to m4 all low mg calcite lmc five spar cements c1 to c5 c1 with high mg calcite hmc precursor mineralogy and four silica phases s1 to s4 s1 to s3 replacive chalcedony after opal ct s4 euhedral quartz cement m1 assumedly related to the degradative calcification of siliceous sponges forms a labyrinthine network into which m2 to m4 were infiltrated spar cements c1 to c3 include a successive decrease of 18 o at fairly invariable 13 c interpreted to represent marine to shallow burial conditions suggesting burial and successive transformation of marine bottom waters temperature estimation based on the average 18o value of c4 18o 7 9 indicates a temperature of around 50 c at a maximum burial depth of about 1000 meters replacive chalcedony s1 to s3 occurs between calcite cementation c3 and c4 in combination with traces of corrosion on c3 mg calcite was preferably replaced particularly the precursor of cement c1 that surrounds peloids of m2 and preserved some ghost structures corrosion and substrate selectivity suggest that acidification mg hydroxyl complexes and surface area are the triggers for flocculation of a silica gel because dissolution of opaline sponge spicules started almost contemporaneously with c1 the dissolved silica was retained in a connate fluid as phases c1 to c3 were precipitated and stagnant conditions prevailed for around 1 ma bulk 18o d values s1 s3 below the marine chert line together with the range of s1 s3 18o 18o smow 28 3 1 0 suggest silica flocculation in a shallow burial environment at temperatures of 25 30 c the establishment of acidic conditions might have been favored by sulfide oxidizing micro organisms numerical simulation of early diagenetic silica flux in such marine sediments is consistent with the interpretation that small grain size changes and fluid barriers that create diffusion controlled conditions such as those induced by stratigraphic condensation are key parameters to retain pore water dissolved silica over geologic time inversely paleozoic stromatactis carbonate mud mounds typically form part of large scale coarsening and shallowing upward successions that correspond to rapid burial these conditions support convergent pore water flux and drainage of pore water dissolved silica in the shallow burial realm hence spicule rich mounds should tend to silicify if they form part of a condensed section

foreslope stromatoporoid renalcid bioherm with evidence of early cementation devonian ancient wall reef complex rocky mountains a small mound 4 x 23 m in size on the fore reef slope of the ancient wall reef complex at mouni haultain alberta consists of fenestral renalcid micrite and wac kestone stroniatoporoids are the most abundant skeletal component but do not form an organic framework renalcids together with early micrite cementation performed a supporting and stabilizing role but only rarely directly encrusted skeletal material many of the primary shelter voids interparticle voids and fenestrae were filled with internal sediments and submarine micrite cements a considerable proportion of the micrite matrix appears to be cement the location and development of the bioherm was controlled by a local hard substrate and suitable environmental conditions the mound developed on and around a large block within an underlying megabreccia bed soon after it was deposited in a debris flow on the fore reef slope it formed near wave base in about 30 50 m water depth and was subject to gentle current action laminar stromatoporoids grew on the flanks and top of the mound and fenestral renalcid micrite and wackestone accumulated in the central part deepening water and increased rates of mud accumulation terminated further build up of the bioherm and it was buried by basin mud fenestral renalcid micrite occurs in a number of devonian and lower palaeozoic organic mounds this study suggests that early submarine cementation was a significant factor in the developmen and preservation of this distinctive lithotype

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

depauperate skeletonized reef dwelling fauna of the early cambrian insights from archaeocyathan reef ecosystems of western mongolia abstract reef dwelling organisms in the early cambrian include typical members of the cambrian fauna such as trilobites chancelloriids and hyoliths however in comparison to later ordovician reefs cambrian reefs often do not appear as diverse here we investigate early cambrian microbial archaeocyathan reefs of the salaagol formation in the zavkhan basin of mongolia as well as perform a literature survey of 40 early paleozoic reefs to understand the timing of reef biodiversity by using point count analysis we can quantify the carbonate contribution of framework builders and reef dwelling organisms in these ecosystems we find that mongolian reefs contained several genera of framework building archaeocyaths 5 0 by volume and associated microbial forms 5 4 but are unevenly distributed through the formation archaeocyathan contribution increases are potentially concurrent with negative shifts in carbon isotopic composition similar to other localities in gondwana however reef dwelling biota was minimal 0 3 throughout the salaagol formation and did not correlate to changes in framework builders or geochemical proxies such as u v and carbon isotopes a literature survey of ediacaran through ordovician reefs suggests that there is a trend of increasing reef dweller abundance functional richness and skeletonization through time the changes in abundance 17 9 to 28 8 considered frequent and functional richness 3 7 to 6 0 functional groups could be due to an increase in productivity in the oceans during the cambrian thereby expanding the base of the food web during the lead up to the ordovician radiation the trend of increasing skeletonization could be due to the evolution of more robust skeletons among reef dwellers in order to protect themselves from increased predation in reef environments these trends suggest that at least during the early paleozoic increases in biological diversity are not necessarily concurrent with the establishment of a framework reef

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

early cambrian microbial reefs archaeocyathan inter reef communities and associated facies of the yangtze platform abstract a sedimentological and paleoecological study of part of the northern yangtze platform of china was conducted three sections of the early cambrian atdabanian botomian stage xiannudong formation where studied and reveal that stromatolite and thrombolite reefs flourished in close association with an inter reef community of archaeocyaths and other organisms adjacent to the reef environment were migrating ooid shoals oncoids peloids and silty sandy lime mud no archaeocyathan reefs were observed in any of the measured sections but irregular archaeocyaths were found in some microbial reefs and archaeocyaths form the bulk of the debris in float rudstone that was deposited between microbial reefs we interpret the archaeocyath rich float rudstone to represent a storm churned inter reef deposit typically regular type archaeocyaths dominated the float rudstone while irregular type archaeocyaths were found in abundance dwelling within the microbial reefs this trend changed upsection as irregular type archaeocyaths dominated both the float rudstone and in the microbial reefs the oncolite and peloidal mudstone are interpreted as representing a quiet water lagoonal environment created by the presence of the microbial reefs and ooid shoals during large storms material from the ooid shoals or microbial reefs would wash into the lagoon the silty sandy micrite represents a quiet water setting which could either be a deep subtidal environment or a restricted lagoonal environment the facies associations of these three sections along with other published data indicate that the yangtze platform at least during the early and middle cambrian was a carbonate platform and equatorially located

stratigraphic context of old crow tephra holitna lowland interior southwest alaska abstract a thick deposit of old crow tephra was discovered in a bluff exposure along the middle holitna river near the kulukbuk hills 61 20 n latitude 157 10 w longitude in interior southwest alaska this locality is the southwesternmost known deposit of old crow tephra in alaska thickness and grain size data from this site support a source volcano in the eastern aleutian arc pleistocene stratigraphic sequences in the lowland are dominated by upward fining eolian sand sheet deposits and loess separated by organic silt these deposits record at least two episodes of regional glaciation and an intervening nonglacial period marine oxygen isotope stage 3 stage 5 or both old crow tephra crops out near the top of the lower upward fining eolian unit indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation the sequence of eolian deposits that contain old crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6 whereas the overlying eolian sequence formed during the last glaciation stage 2 this stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission track and thermoluminescence ages of ca 140 000 10 000 yr b p

optically stimulated luminescence dating of late quaternary loess deposits in the coastal region of north china provenance and paleoclimatic implications abstract the aeolian deposits in the coastal region of north china are important for reconstructing paleoclimate in this paper chronology climatic proxies and chemical compositions of four loess sections were studied optically stimulated luminescence osl dating results indicate that the coastal loess was accumulated during late quaternary with ages ranging from the penultimate glacial period to the latest holocene both granulometric characteristics and geochemical properties indicate that the dust provenance of the coastal loess is partially different from that of the chinese loess plateau characterized by more proximal contributions except distal dust transported by northwesterly winter winds from the inland gobi and sand deserts the coastal loess also contains proximal local coarse particles which were derived from the exposed shelf as well as neighboring hills multiple climatic proxies including color magnetic susceptibility and particle size parameters correlate well with the marine specmap 18o record indicating that climatic changes in the coastal region of north china during the late quaternary was mainly controlled by variations of the east asian monsoon driven by changes in global ice volumes

the ecology of lower cambrian buildups from zuune arts mongolia implications for early metazoan reef evolution reefal buildups in western mongolia of mid early cambrian late atdabanian age flourished during a period when shelf seas were globally widespread the succession at zuune arts records the transition from shallow marine siliciclastic sediments bayan gol formation to shallow marine but still clastic influenced carbonates salaany gol formation the salaany gol formation is interpreted as having been deposited as a series of shallowing upwards cycles on a shallow gently inclined shelf in a rapidly subsiding epicontinental sea cycles commenced with the growth of subtidal metazoan calcimicrobe aggregative communities on an open shelf the resultant buildups were commonly engulfed by extensive massive microbial stromatolites when they grew in agitated intertidal conditions latterly they were smothered by ooid shoals in response to rapid sea level rise four types of reefal buildup are distinguished 1 green coloured calcimicrobe tarthinia epiphyton gordonophyton and renalcis boundstones 2 red or green coloured cambrocyathellus tarthinia epiphyton bafflestones 3 red coloured okulitchicyathus bindstones and 4 red coloured radiocyath archaeocyath cribricyath bioherms each is interpreted as having grown at increasing depths and possibly sedimentation rates the buildups are commonly enclosed within graded and planar bedded bioclastic grainstones and packstones and are best developed towards the top of the formation when sea level was high thickets of large solitary archaeocyaths are also inferred in the deeper interbiohermal areas these buildups had synoptic relief and constructed porous structures with growth framework cavities housing diverse coelobiontic communities extensive synsedimentary cements are present including pseudomorphed aragonitic fans and possible pseudomorphed aragontic botryoids these early reefs thus have geological fabrics similar to later phanerozoic representatives it is proposed however that this ecosystem was largely composed of generalist and opportunistic filter and suspension feeders which were dependent upon a far higher input of nutrients than modern day reefal developments bacteria were probably the main primary producers from both planktic and benthic cyanobacterial communities the diversity of each buildup assemblage appears to be controlled by primary cavity size the richest fauna belonging to the highly tiered radiocyath dominated community inferred to have lived in the deepest waters the communities at zuune arts can be compared with other buildups from the early cambrian and with lower ordovician receptaculid calcimicrobe solitary sponge bioherms known from the usa and siberia

early cambrian chronostratigraphy and geochronology of south australia abstract the most successful chronostratigraphic correlation methods enlist multiple proxies such as biostratigraphy and chemostratigraphy to constrain the timing of globally important bio and geo events here we present the first regional high resolution shelly fossil biostratigraphy integrated with 13c chemostratigraphy and corresponding 18o data from the traditional lower cambrian terreneuvian and provisional cambrian series 2 of south australia the global zhuce shice positive excursions ii and iii and the care are captured in lower cambrian successions from the arrowie and stansbury basins the south australian shelly fossil biostratigraphy has a consistent relationship with the 13c results bolstering interpretation identification and correlation of the excursions positive excursion ii straddles the boundary between the kulparina rostrata and micrina etheridgei zones and the care straddles the boundary between the m etheridgei and dailyatia odyssei zones peaking in the lower parts of the latter zone new ca tims zircon dates from the upper hawker group and billy creek formation provide geochronologic calibration points for the upper d odyssei zone and corresponding chemostratigraphic curve embedding the lower cambrian successions from south australia into a global chronostratigraphic context this multi proxy investigation demonstrates the power of integrated methods for developing regional biostratigraphic schemes and facilitating robust global correlation of lower cambrian successions from south australia part of east gondwana with coeval terranes on other cambrian palaeocontinents including south and north china siberia laurentia avalonia and west gondwana

dendroid morphology and growth patterns 3 d computed tomographic reconstruction abstract this paper analyzes the growth patterns of dendrolite in the zhangxia formation middle cambrian shandong province china using the technique of 3 d computed tomographic reconstruction dendroids are classified into v dendroids columnar dendroids and arborescent dendroids based on morphological characteristics the means of interconnection between dendroids are classified into trunks nodules shoots and fingers stacking and tiering control the gross morphology and structural framework of dendrolite stacking is a process of vertical growth in which v dendroids create a staircase like structure tiering occurs when a layer of dendroids is covered by sediment and then partially eroded allowing a new layer of dendroids to form a comprehensive blueprint of the structural divisions of dendrolite is presented according to scale being divided into micro meso macro and megastructures the mesostructure which includes individual dendroids and their combined structures is subsequently divided into primary v dendroid secondary columnar and arborescent dendroid and tertiary stair and tier structures and a basic growth model is provided for v dendroids the stages of v dendroid growth are 1 trunk extension and base expansion 2 divergence 3 expansion and convergence followed by repetition of stages 2 and 3 until 4 growth completion followed by the subsequent emergence of a new dendroid by either stacking or tiering this development of systematically ordered structures is suggestive of the reaction of microbial colonies to external environmental conditions

enigmatic chambered structures in cryogenian reefs the oldest sponge grade organisms abstract previously undescribed chambered structures are common and widespread in the cryogenian post sturtian glacial carbonates of the oodnaminta reef complex adelaide geosyncline south australia the rasthof berg aukas formation namibia and the gauss formation namibia these carbonate structures have millimetre to centimetre scale chambers separated by well defined and generally thin micritic walls chamber walls now consist of dolomite but were probably originally aragonitic the chambers may have a lobate polygonal or dendritic morphology and are often further divided into smaller chambers chambered structures occur as reefal growth frameworks as cavity fillings in neptunean dykes and growth cavities and as intercolumnar material within stromatolite frameworks in the oodnaminta reef complex these structures are only present in the sub photic deep water framework these structures probably represent the calcified remains of an organism or community of organisms that was globally distributed and widespread for a significant time period following the sturtian glaciation no precisely analogous structures have been previously described from modern or ancient settings but the complexity and degree of organization suggests a significant evolutionary advance over older proterozoic fossils the closest morphological analogues for the structures are a some types of reef dwelling sponges and b some complex microbialites from archaean and paleoproterozoic carbonates the structures lack spicules and ostia found in sponges ruling out a true poriferan origin however it is plausible that they are proto sponges sponge grade organisms or complex microbial precursors to sponge grade organisms whatever their affinity we suggest these structures record a significant evolutionary event on the path towards organic complexity

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

late devonian carbonate margins and foreslopes of the lennard shelf canning basin western australia part a development during backstepping and the aggradation to progradation transition abstract carbonate reefal margin and foreslope settings are characteristically heterogeneous and difficult to predict due to a spectrum of sediment source factories resedimentation processes resultant deposit types and controlling parameters in particular the effects of changes in long term accommodation on the composition architecture and sediment distribution patterns of carbonate margin foreslope basin systems are poorly understood upper devonian frasnian outcrop exposures along the lennard shelf northeast canning basin western australia were investigated to assess the development of reefal margin and foreslope settings during long term 1 platform backstepping with aggradational pulses and 2 across the transition from platform aggradation to progradation measured sections tied to interpreted photomosaics and detailed mapping using aerial photographs were collected from the south lawford range and windjana gorge areas the exposures reveal distinctive differences in foreslope grain composition deposit characteristics and proportions margin morphology and stratigraphic expression 1 during platform evolution between backstepping events and 2 depending on position within the long term accommodation setting between backstepping events aggradational margins can be classified as growth escarpments with associated grain dominated onlapping foreslope deposits margins across the long term transition from aggradation to progradation evolved from erosional escarpments with onlapping debris deposits to accretionary interfingering configurations development of growth escarpments between backstepping events was a function of vertical reefal growth from sustained high accommodation conditions during the long term transgressive systems tract coupled with a frasnian reefal assemblage that responded to light and tracked relative sea level this net vertical reefal growth also resulted in relative margin stability and the deposition of grain dominated foreslopes conversely margins were highly unstable and underwent repeated failure across the long term aggradation to progradation transition reflecting a lack of underlying substrate to support basinward advance and resulting in debris dominated foreslopes these observations provide relationships that predict margin and foreslope associations of facies scale heterogeneity and seismic scale geometry within a low frequency sequence stratigraphic framework

source regions and formation of the loess sediments on the high mountain regions of northwestern china loess on the high mountains of northwestern china is largely controlled by the topographic features distributed mainly on the northern slopes of the tianshan and kunlun mountains as well as in the ili valley between the northern and central tianshan ranges loess distributed in different regions has different ages with the oldest early pleistocene loess occurring in the ili valley geochemical mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance the loess on the northern tianshan and kunlun mountains is mainly derived from the junggar and taklimakan deserts respectively whereas the loess in the ili valley is derived mainly from the sary ishikotrau desert located in the republic of kazakhstan however these deserts serve mostly as holding areas for the silts rather than original source regions the production of the silt sized particles is mainly associated with glacial abrasion and tectonic induced rock denudation thus the loess in the studied regions can be described as mountainous loess rather than simply glacial loess or desert loess it is unlikely that the mechanisms of loess formation are the same in different regions given their dependence on specific geomorphological conditions and associated processes

large scale stabilized dunes on the high plains of colorado understanding the landscape response to holocene climates with the aid of images from space principal component analysis of landsat thematic mapper images from eastern colorado reveals stabilized dune fields that are composed of single and compound parabolic dunes some longer than 10 km these dunes have been reactivated at least four times in the past 10 000 yr at ca 9500 to 5500 yr b p 5500 to gt 4800 yr b p 4800 to gt 1000 yr b p and lt 1000 yr b p during droughts that probably exceeded the dry conditions during the 1930s dune orientations indicate that these landforms were molded by winds from the northwest which now dominate during the winter and spring with the passage of pacific air masses this study underscores the sensitivity of the landscape of the high plains to drought conditions which may become more prevalent because of the anticipated effects of greenhouse warming

spatial and temporal patterns of late quaternary eolian deposition eastern colorado u s a abstract eolian sediment covers about 60 of colorado east of the rocky mountains about 30 of the sediment is sand and 70 is loess initially flood plains were the principal sources of eolian sediment but during the holocene dunes formed from older eolian sand and alluvium on uplands since latest pleistocene time dominant dune forming winds have been northwesterly in the northern part of the region and southwesterly in the southern part at present sand sheets and dunes mainly parabolic types are stable and covered with vegetation in dunes sand is commonly 20 30 m thick but elsewhere averages

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

stratigraphic evidence for late quaternary dune activity near hudson on the piedmont of northern colorado stabilized dune fields are common features near hudson on the piedmont of northern colorado exposures in dune and interdune sites expose a sequence of eolian sediments and paleosols that record a complex history of eolian activity during the late quaternary radiocarbon and thermoluminescence age estimates on a horizons buried by eolian sand indicate that dunes were reactivated sometime between 7 and 9 ka on the basis of morphology of surface soils the dunes were most recently stabilized 3 ka at present there are no data to indicate if there were multiple periods of dune movement and stabilization during the holocene the penultimate pre holocene dune forming episode probably terminated ca 13 ka and may be coincident with the pinedale glaciation the stratigraphy at interdune sites shows at least two eolian depositional events prior to the penultimate event they were separated by periods of pedogenesis one of which may have exceeded 40 ka this analysis indicates that dunes in northern colorado were active during both cold arid and warm arid periods in the late quaternary

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

deep water stratigraphic cyclicity and carbonate mud mound development in the middle cambrian marjum formation house range utah usa in mid middle cambrian time shallow water sedimentation along the cordilleran passive margin was abruptly interrupted by the development of the deep water house range embayment across nevada and utah the marjum formation 330 m in the central house range represents deposition in the deepest part of the embayment and is composed of five deep water facies limestone argillaceous limestone rhythmites shale thin carbonate mud mounds bioturbated limestone and cross bedded limestone these facies are cyclically arranged into 1 5 to 30 m thick parasequences that include rhythmite mound rhythmite shale rhythmite bioturbated limestone and rhythmite cross bedded limestone parasequences using biostratigraphically constrained sediment accumulation rates the parasequences range in duration from 14 to 270 kyr the mud mounds are thin 2 m closely spaced laterally linked symmetrical domes composed of massive fenestral peloidal to clotted microspar with sparse unoriented poorly sorted skeletal material calcitized bacterial filaments tubes and abundant fenestrae and stroma tactoid structures these petrographic and sedimentological features suggest that the microspar peloids clots and syndepositional micritic cement were precipitated in situ from the activity of benthic microbial communities concentrated growth of the microbial communities occurred during periods of decreased input of fine detrital carbonate transported offshore from the adjacent shallow water carbonate platform in the neighbouring wah wah range and throughout the southern great basin coeval mid middle cambrian shallow water carbonates are composed of abundant metre scale upward shallowing parasequences that record high frequency 104 105 years eustatic sea level changes given this regional stratigraphic relationship the marjum formation parasequences probably formed in response to high frequency sea level fluctuations that controlled the amount of detrital carbonate input into the deeper water embayment during high frequency sea level rise and early highstand detrital carbonate input into the embayment decreased as a result of carbonate factory retrogradation resulting in the deposition of shale base of rhythmite shale parasequences or thin nodular rhythmites followed by in situ precipitated mud mounds lower portion of rhythmite mound parasequences during the ensuing high frequency sea level fall lowstand detrital carbonate influx into the embayment increased on account of carbonate factory pro gradation towards the embayment resulting in deposition of rhythmites upper part of rhythmite mound parasequences reworking of rhythmites by a lowered storm wave base cross bedded limestone deposition or bioturbation of rhythmites by a weakened lowered o2 minimum zone bioturbated lime stone deposition this interpreted sea level control on offshore carbonate sedimentation patterns is unique to palaeozoic and earliest mesozoic deep water sediments after the evolution of calcareous plankton in the jurassic the presence or absence of deeper water carbonates was influenced by a variety of chemical and physical oceanographic factors rather than just physical transport of carbonate muds

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

pollen diagram from the nebraska sandhills and the age of the dunes abstract radiocarbon dates of organic alluvium beneath as much as 40 m of dune sand along the dismal river have led to the suggestion that the nebraska sandhills date from the holocene rather than the last glacial period on the other hand the basal layers of lake and marsh deposits in interdune depressions at three localities date in the range of 9000 to 12 000 yr b p implying a pre holocene age for the sand dunes a pollen diagram for one of these sites swan lake indicates prairie vegetation throughout the last 9000 yr with no suggestion that the landscape was barren enough to permit the shaping of the massive dunes characterizing the area sand was not transported across the site during the holocene either during the marsh phase which lasted until 3700 yr b p or during the subsequent lake phase the sand that buries the alluvium along the dismal river may represent only local eolian activity or it may indicate that the younger of the two main dune series identified by h t u smith 1965 journal of geology 73 557 578 is holocene in age and the older one late wisconsin in age

sequence stratigraphy of the middle cambrian daegi formation korea and its bearing on the regional stratigraphic correlation abstract the sediments that comprise the middle cambrian daegi formation in eastern central korea are interpreted to have been deposited in a carbonate ramp setting the daegi formation consists of nine lithofacies argillaceous rock ribbon rock oolitic limestone skeletal limestone microbial limestone intraclastic limestone micritic limestone bioturbated limestone and crystalline limestone which are grouped into three facies associations presenting from base up outer ramp grain shoal and inner ramp facies associations two depositional sequences can be distinguished in the daegi formation sequence 1 in the lower part of the daegi formation comprises a lower transgressive systems tract tst and an upper highstand systems tract hst the tst consists of terrigenous deposits with subordinate limestones while the hst contains various types of limestone sequence 2 comprises the upper half of the daegi formation and was deposited during a tst the sequence stratigraphic analysis of the daegi formation suggests that the sediments were deposited during one 3rd order sea level change during the middle to late middle cambrian the sequence stratigraphic framework of the daegi formation can be excellently correlated with coeval deposits in north china the zhangxia and the lower part of the overlying gushan formations which belong to the same tectonic block as the korean peninsula the sino korean block skb the almost identical sequence stratigraphic frameworks in two separate basins suggest that the sequence stratigraphic development on the skb was mainly influenced by eustatic changes during the middle cambrian

megablocks of calcified algae in the cow head breccia western newfoundland vestiges of a cambro ordovician platform margin slope and basin deposits in the cow head group of early paleozoic age contain a wide variety of carbonate clasts among the most common largest and most persistent middle middle cambrian to lower middle ordovician are blocks of fine grained white limestone the origin of these clasts is unknown as no limestones of similar lithology have been found in contemporaneous shallow water carbonate deposits anywhere in the northern appalachians petrographic study of these enigmatic limestones reveals that no matter what their age they are of similar composition calcified algae cement and fine grained sediment the predominant algae are epiphyton spp occurring as numerous masses of tiny shrublike and clumplike growths and girvanella spp developed as numerous thin strands and arcuate sheets renalcis spp and stromatolitic algae although locally common are not persistent the algae are surrounded by fibrous calcite cement interpreted to be synsedimentary while the numerous small cavities between algae are partly filled with geopetal marine sediment these blocks are interpreted to be redeposited fragments of reef mounds and buildups which grew along the shallow submerged margin of the north american craton during early paleozoic time these buildups are now probably buried beneath the allochthonous cow head strata the mounds were composed of calcareous algae because there were no large reef building metazoans during this time in geologic history recognition of similar clasts in analogous settings in the quebec and southern appalachians as well as in the cordillera suggests that this facies was both widespread and persistent for more than 70 m y

facies phosphate and fossil preservation potential across a lower cambrian carbonate shelf arrowie basin south australia abstract the effects of sedimentological depositional and taphonomic processes on preservation potential of cambrian small shelly fossils ssf have important implications for their utility in biostratigraphy and high resolution correlation to investigate the effects of these processes on fossil occurrence detailed microfacies analysis biostratigraphic data and multivariate analyses are integrated from an exemplar stratigraphic section intersecting a suite of lower cambrian carbonate palaeoenvironments in the northern flinders ranges south australia the succession deepens upsection across a low gradient shallow marine shelf six depositional facies sequences are identified ranging from protected fs1 and open fs2 shelf lagoonal systems high energy inner ramp shoal complex fs3 mid shelf fs4 mid to outer shelf fs5 and outer shelf fs6 environments non metric multi dimensional scaling ordination and two way cluster analysis reveal an underlying bathymetric gradient as the main control on the distribution of ssfs unlike groups that produced primary organophosphatic biominerals taxa that built calcareous skeletons are more taphonomically controlled which is further exacerbated by sampling and processing biases a strong facies association with condensed and reworked horizons suggests the stratigraphic occurrence of calcareous groups reflects conditions conducive to preservation phosphogenesis and phosphatization rather than true stratigraphic ranges consequently organophosphatic taxa should take precedence in the erection of biostratigraphic zones for subdivision of lower cambrian successions

origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry muhs d r bettis iii e a aleinikoff j n mcgeehin j p beann j skipp g marshall b d roberts h m johnson w c benton r 2008 origin and paleoclimatic significance of late quaternary loess in nebraska evidence from stratigraphy chronology sedimentology and geochemistry gsa bulletin 120 11 12 1378 1407

biomarker and isotopic signatures of an early cambrian lagerstatte in the stansbury basin south australia abstract the lower cambrian series 2 emu bay shale biota found at big gully on the north coast of kangaroo island south australia is by far the richest burgess shale type bst fauna in the southern hemisphere while the trace element geochemistry of the host shale shows it accumulated beneath an oxic water column this appears difficult to reconcile with the exceptional preservation of organs such as gut glands muscles and eyes in some of its fauna micro scale sealed vessel mssv pyrolysis of kerogen isolated from a solvent extracted sample of fossiliferous emu bay shale provided independent confirmation of its redox status and also implicated cyanobacteria in the preservation of its fauna thermal extraction and pyrolysis each yielded alkanes displaying a low ratio of pristane to phytane pr ph 1 and n alkanes with a marked odd even predominance in the 20 range the latter molecular signature is diagnostic of gloeocapsomorpha prisca and is the first indication that mats of this or a similar coccoid cyanobacterium were involved in the taphonomy of a bst deposit hopanes including 2 methylhopanes are far more abundant than steranes and the shale s bulk organic matter has 13 c values in the range 32 to 28 providing further evidence of the cyanobacterial affinity of its microbial biomass thus mat forming cyanophytes rather than sulfur oxidising bacteria may have played a key role in maintaining a sharp redox boundary at the sediment water interface during deposition of the emu bay shale lagerstatte thereby enabling the survival of soft body parts within its fossil fauna for long enough to permit inorganic replication of their fine detail during late diagenesis

archaeocyathan buildups within an entirely siliciclastic succession new discovery in the toyonian lalun formation of northern iran the proto paleotethys passive margin of northern gondwana abstract meter scale buildups constructed exclusively by archaeocyaths have been recognized within the uppermost lower cambrian siliciclastic succession of eastern alborz in northern iran they are the only known toyonian reefs in iran and adjacent countries and occur in the lower part of the shale unit of the lalun formation the reefs are of limited lateral extent reach a maximum thickness of 2 5 m and consist of several reef complexes containing cabbage or sack shaped buildups surrounded by well bedded colored shale each reef complex in the main reef zone consists of meter scale individual and kalyptrate compound buildups that are overgrown by laminated stromatolite the individual buildups are 12 to 75 cm thick and 5 to 50 cm in diameter but the compound buildups are up to 2 m thick and their diameter ranges from 75 to 120 cm in contrast to most lower cambrian reefs these compound buildups demonstrate a complete ecological succession including pioneer and climax phases archaeocyaths in the buildups are solitary and colonial types showing great diversity of growth forms with vase bowl and cup shaped and cylindrical forms present the cups range from less than 1 mm to 1 5 cm in diameter and are up to 4 cm tall in the majority of the skeletons but they may reach up to 4 cm in diameter in the massive colonial forms or in the branching forms of the upper outer part of the compound bioherms the limited lateral extent of the reef horizons and lateral facies changes in the colored shale toward various reefs supports deposition in drowned tidal channels in an estuarine depositional environment a change of the individual bioherms to larger compound buildups suggests lateral depth variation of the tidal channels partial infilling of the primary inter biohermal cavities by large reef clasts and cross laminated siltstone to very fine sandstone suggests occasional disturbances by storms and periodic influx of coarse siliciclastics in striking contrast to other lower cambrian reefs the archaeocyathan buildups of the alborz flourished in a completely siliciclastic setting and lack the skeletal calcimicrobes which dominated the lower cambrian reefs abrupt lateral and vertical facies changes to colored shale and fluvial red beds the presence of infiltrated shale between the skeletons and in central cavities and the intervallum of the archaeocyaths suggest highly turbulent and turbid incoming water with abnormally high concentrations of fine siliciclastic material during reef development high concentrations of fine suspended siliciclastics could well have prevented the light penetration which was necessary for calcimicrobial growth in addition the relatively small size of the archaeocyaths and absence of reef dwellers is very likely a consequence of the high terrigenous mud content and perhaps below normal salinity of the ambient sea water in the absence of calcimicrobes and suspension feeder metazoans in the dark and muddy water of the mid estuarine setting archaeocyathans became the only bioconstructors of the iranian buildups abnormally high concentration of nutritious fine siliciclastics suggests that photosymbionts and oligotrophic conditions were not needed by archaeocyaths particular hydrodynamic conditions along with high nutrient flux rather than light were essential for archaeocyathan communities

eolian sand transport pathways in the southwestern united states importance of the colorado river and local sources geomorphologists have long recognized that eolian sand transport pathways extend over long distances in desert regions along such pathways sediment transport by wind can surmount topographic obstacles and cross major drainages recent studies have suggested that three distinct eolian sand transport pathways exist or once existed in the mojave and sonoran desert regions of the southwestern united states one hypothesized pathway is eolian sand transport from the eastern mojave desert of california into western arizona near parker and would require sand movement across what must have been at least a seasonally dry colorado river valley we tested this hypothesis by mineralogical geochemical and magnetic analyses of eolian sands on both sides of the colorado river as well as sediment from the river itself results indicate that dunes on opposite sides of the colorado river are mineralogically distinct eastern california dunes are feldspar rich whereas western arizona dunes are quartz rich derived from quartz rich colorado river sediments because of historic vegetation changes little new sediment from the colorado river is presently available to supply the parker dunes based on this study and previous work the colorado river is now known to be the source of sand for at least three of the major dune fields of the sonoran desert of western arizona and northern mexico on the other hand locally derived alluvium appears to be a more important source of dune fields in the mojave desert of california although many geomorphologists have stressed the importance of large fluvial systems in the origin of desert dune fields few empirical data actually exist to support this theory the results presented here demonstrate that a major river system in the southwestern united states is a barrier to the migration of some dune fields but essential to the origin of others published by elsevier science ltd

provenance of aeolian sediment in the taklamakan desert of western china inferred from ree and major elemental data abstract to identify the provenance of aeolian deposits in the extensive dune field in the taklamakan desert is of great importance for understanding the formation of this the largest sand sea in china the opinions from earlier studies are quite dipolar and are as follows a local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages and b strong homogenization of the sands in the entire taklamakan on the basis of geochemical data from whole rock samples by separately examining the ree characteristics and major elemental composition in coarse and fine fractions of the samples from aeolian deposits this paper provides new data for interpreting sources of aeolian deposits in the taklamakan the sampling sites are distributed in four different fluvial systems i e the areas of the keriya river niya river and cele river in the southern part and the northern margin near the tarim river fig 1 our results show that there are some significant differences in concentrations of trace elements and in ree features between the coarse and the fine fractions of the aeolian sediment the major elemental and ree data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin the fine fractions mainly silts are more homogenized the regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin this confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east west direction it should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea in addition little variation is found between old and young sands in two sediment sequences in the central part of the desert indicating consistency of sand sources in a given site during the last 40 ka

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

cretaceous oceanic red beds corbs different time scales and models of origin abstract the cretaceous oceanic red bed corb is a newly opened window on global oceanic and climate changes during the cretaceous greenhouse world as a result of the international geoscience programmes 463 494 and 555 2002 2010 corbs have been documented in many places by numerous publications the principle goal of this paper is to summarize scientific advances on corbs including chronostratigraphy sedimentology mineralogy elemental and isotopic geochemistry and their relationship to oceanic anoxic events oaes palaeoclimate and palaeoceanography we propose a new geochemical classification of the corbs using cao al 2 o 3 and sio 2 values which lithologically refer to marly clayey and cherty corbs respectively detailed mineralogical studies indicate that hematite goethite and mn 2 bearing calcite are the minerals imparting the red color of corbs hematite clusters of several to tens of nanometers in the calcite structure are the main cause of the red coloring of limestones and the mn 2 bearing calcite gives additional red color goethite was thought to form originally with hematite and was subsequently transformed to hematite during late diagenesis chronostratigraphic data allow the distinction of two groups of corbs by their durations short term corbs are generally less than 1 myr in duration and seem to be on the scale of milankovitch cycles during the deposition of cretaceous reddish intervals from odp cores 1049 and 1050 low primary productivity and relatively high surface temperature resulted in low organic carbon flux into the sediments which reduced oxygen demand and produced oxidizing early diagenetic conditions in such an oxic environment iron oxides formed imparting the reddish color the long term corbs depositional events lasted longer than 4 myr and may be a possible consequence of the oaes enhanced amounts of organic carbon and pyrite burial during and after the oaes would have resulted in a large and abrupt fall in atmospheric co 2 concentration which probably induced significant global climatic cooling during and after the oaes global cooling would have enhanced formation of cold deep water increasing its oxidizing capacity due to the greater content of dissolved oxygen and would promote formation of oceanic red beds sedimentological mineralogical and geochemical data indicate that corbs were deposited under highly oxic oligotrophic conditions probably at a low sedimentation rate the cretaceous red and white limestones from italy have similar compositions of terrestrial input sensitive elements al ti k mg rb zr higher contents of fe 2 o 3 and depleted redox sensitive elements v cr ni and u and micronutrient elements cu zn indicating similar provenance sources but red limestones were deposited under more oxic conditions at the sediment water interface than white limestones the cretaceous red shales such as those from the north atlantic and tibet have similar mineralogy and geochemistry as the late cenozoic red clays in the pacific ocean and the environment where both are formed was well oxidizing at a very low sedimentation rate we compiled seventeen published stratigraphic examples of phanerozoic oceanic red beds including the late cenozoic red clays in the pacific different hypotheses explain the origin of red pigmentation of limestones and shales including 1 detrital origin of iron derived from continental weathering 2 iron bacterial mediation at the time of sedimentation and 3 iron oxidation in oligotrophic highly oxic environment additional research on phanerozoic oceanic red beds is needed in order to better document their origin and palaeoceanographic and palaeoclimatic significance

sponge spicules silicification and sequence stratigraphy abstract early diagenetic silica is distributed unevenly in phanerozoic sponge spicule rich carbonate mounds in paleozoic mounds replacive silica occurs principally at the microscopic scale whereas in mesozoic strata it is frequently present as nodular chert this paper explores the possibility of advective dispersive loss of dissolved pore water silica for explaining the contrasting styles of silica cycling in mounds four examples of spicule rich mounds were transcribed into hydrogeological conceptual models two weakly silicified paleozoic mounds with stromatactis silurian carboniferous and two strongly silicified jurassic mounds one stromatactis mound one sponge mound monte carlo fluid flow simulations utilized literature derived ranges of effective porosity while hydraulic conductivity of component hydrostratigraphic units provided quantitative constraints for the paleozoic examples the strata aggrade and prograde which creates shallowing upward trends mesozoic examples aggrade and retrograde resulting in deepening upward trends and stratigraphic condensation and fluid baffling interpreted from hardgrounds and black shale for the silurian and the jurassic stromatactis mound models simulations of advective dispersive silica mass transport were performed by applying different compaction driven fluid fluxes based on stratigraphic data the silurian mound displays vertical flushing but high silica concentrations prevail in off mound and flank deposits the jurassic case maintains a stratiform like silica distribution over tens of thousands of years the two other cases carboniferous jurassic used an identical low fluid flux the simulations which match field observations silica depleted mound versus stratiform chert occur at different time scales realistic for the jurassic case but unrealistic for the carboniferous case because it lacks the required degree of stratigraphic condensation to establish a silica depleted mound the results suggest that the variation of fluxes of dissolved pore water silica in phanerozoic spicule rich mounds is controlled by mass accumulation or sediment burial rate during the paleozoic mound formation is commonly associated with shallowing upward trends high to intermediate accumulation rates whereas mesozoic mound formation more commonly extended into condensed sections with low mass accumulation and respective low rates of compaction driven fluid flow the mesozoic extension of spicule rich carbonate mounds into the condensed section might be related to an intensification of benthic pelagic coupling established during the mesozoic marine revolution

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

a revised classification of limestones abstract the most widely used classifications of limestones are now thirty years old and our appreciation of the diagenetic effects on limestone textures is now much greater a revision of the classifications of dunham 1962 and embry and klovan 1971 is offered and new diagenetic categories are proposed the confusing term lime mudstone is replaced by calcimudstone two categories of diagenetic textures are recognized non obliterative and obliterative the former contains limestones which are almost wholly composed of diagenetic cement cementstones and those whose fabric is the result of intergranular pressure solution condensed and fitted grainstones obliterative categories include limestones and dolomites whose original fabric has been destroyed sub categories include sparstones or dolosparstones crystals 10 m in size and microsparstones dolomicrosparstones crystals 4 10 m in size and dolomicrostones crystals m in size many diagenetic processes can produce fabrics which mimic depositional ones and these are reviewed

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

early cambrian reefs reef complexes and associated lithofacies of the shackleton limestone transantarctic mountains the shackleton limestone formed a carbonate platform that bordered part of the greater antarctic craton in middle and late early cambrian time in the holyoake range of the central transantarctic mountains this unit records deposition on a stable shelf on which flourished ecological reefs composed of microorganisms and archaeocyathans burrow mottled lime mudstone wackestone and packstone with patch reefs represent accumulation in shelf areas of relatively low to moderate energy thick ooidal grainstone units reflect deposition in higher energy shoals and as sand sheets that were associated with extensive reef complexes the framework of these reefs was principally the product of micro organisms by inference mostly cyanobacteria archaeocyathans constitute as much as 30 of some reefs but commonly they form less than 10 and are absent from some on the basis of microbial composition three reef types are recognized the first type is a renalcis boundstone that lacks archaeocyathans within these abundant upward directed thalii of renalcis formed a framework that trapped fine grained sediment the second type which forms the core of some larger reefs is composed of stromatactis bearing microbial boundstone the third yet most common reef type is variable in composition it is characterized by the presence of abundant epiphyton but may include archaeocyathans and the microbial microfossils girvanella and renalcis as well as cryptomicrobial clotted micrite in this type of reef frame building organisms typically constructed highly porous structures that had small interparticle and fenestral pores and large growth framework cavities as well as rare metre sized caverns within these spaces epiphyton and less commonly renalcis encrusted framework elements fine grained sediments accumulated and pervasive sea floor cements were precipitated boundstone fabrics in the shackleton limestone are highly complex with fabrics analogous to younger more metazoan rich reefs as well as deep water stromatactis bearing mud mounds the epiphyton girvanella archaeocyathan frameworks and stromatactis bearing boundstones both of which seemingly first appeared in the middle early cambrian are regarded as the precursors in structure composition and preferred hydrologic setting of the more extensive reefs and complex framework styles of later phanerozoic time

genesis of stromatactis cavities between submarine crusts in palaeozoic carbonate mud buildups it is concluded that the sedimentary structure stromatactis is a calcite cement fill of a swarm of labyrinthine cavities developed in marine carbonate muds of palaeozoic bioherms commonly with geopetal sediment field and petrographic evidence is examined from the ordovician of dalarna sweden the devonian of the canning basin australia and of belgium and the carboniferous of lancashire u k in all four occurrences the host microspar encloses masses of radiaxial fibrous calcite with sub horizontal floors following other workers radiaxial fibrous calcite is regarded as an altered marine cement a conclusion supported by the presence of overlying geopetal sediments with marine fossils widespread evidence of early submarine cementation in palaeozoic mud mounds isotopic analyses and the presence of microdolomites the stromatactis masses are separated from each other by laminae of host biomicrospar which show discontinuities resembling fractures which are healed with the early marine cement or filled with marine internal sediments the fractures are therefore of submarine origin the evidence points to episodic submarine lithification of the carbonate muds yielding successive crusts between which cavities were eroded and then filled the crusts were broken and rotated during bioturbation differential compaction or shearing during burial

stratigraphic evidence of desertification in the west central great plains within the past 1000 yr stratigraphic and geomorphic relations archeological data and eight radiocarbon ages at five widely scattered localities in northeastern colorado indicate that eolian sand was mobilized over broad areas within the past 1000 yr the mobilization began after 1 ka was episodic and ended at some as yet undetermined time prior to the latter part of the nineteenth century given that climate model simulations suggest only slight variation in average surface temperature and annual precipitation in this region during the past 1000 yr this part of the great plains evidently is near the threshold of widespread eolian sand transport under the present climate

the precambrian cambrian boundary seawater chemistry ocean circulation and nutrient supply in metazoan evolution extinction and biomineralization this paper reviews the evidence for changes in the global environment from the late precambrian into the cambrian against which the evolution of many metazoan groups and the development of biomineralization should be seen with higher carbon dioxide levels precambrian seawater was more supersaturated with respect to caco 3 than phanerozoic seawater and carbonates were precipitated easily from the late precambrian to the early cambrian there was a decrease in the mg ca ratio and an increase in the a co 2 of seawater changes in global climate icehouse to greenhouse and increased plate tectonic activity resulted in major changes in ocean circulation and nutrient levels a rise in global temperature and the formation of extensive shallow seas the vendian cambrian radiation events and onset of biomineralization must have been strongly influenced if not driven by these global environmental changes

a new lower cambrian shelly fossil biostratigraphy for south australia abstract definition of early cambrian chronostratigraphic boundaries is problematic with many subdivisions still awaiting ratification integrated multi proxy data from well resolved regional scale schemes are ultimately the key to resolving broader issues of global correlation within the cambrian in australia early cambrian biostratigraphy has been based predominantly on trilobites phosphatic shelly fauna have great potential as biostratigraphic tools especially in pre trilobitic strata because they are widespread and readily preserved but they have remained underutilised here we demonstrate their value in a new biostratigraphic scheme for the early cambrian of south australia using a diverse shelly fauna including tommotiids brachiopods molluscs and bradoriids biostratigraphic data are derived from ten measured stratigraphic sections across the arrowie basin targeting hawker group carbonates including the wilkawillina wirrapowie and ajax limestones and the mernmerna formation the stratigraphic ranges of shelly fossils are predictable and repeatable across the arrowie basin allowing three discrete shelly biozones to be identified spanning terreneuvian stage 2 to series 2 stages 3 4 the kulparina rostrata zone new and part of the overlying micrina etheridgei zone new are pre trilobitic predominantly terreneuvian the cambrian series 2 stage 3 dailyatia odyssei zone new features a very diverse shelly fauna and will be described in detail in a separate publication these zones provide robust means to correlate terreneuvian series 2 successions in neighbouring coeval basins in australia particularly the stansbury basin wider correlation is possible throughout east gondwana and especially with south china

sequence stratigraphy of the frasnian famennian transitional strata a comparison between south china and southern belgium the sedimentological evolution of the frasnian famennian transitional strata in south china and southern belgium has been investigated a similar trend in the deepening and shallowing of the sedimentation environment occurs in the two palaeogeographically distinct areas the stratigraphic succession has been subdivided into depositional sequences a general deepening occurs in the palmatolepis rhenana conodont zone during the most rapid rise in sea level a transgressive systems tract formed this transgressive systems tract is followed by a highstand systems tract in the late p rhenana zone a major sequence boundary within the latter zone is indicated by an unconformity in intraplatform and platform areas and by a conformity in the basinal area the uppermost sediments within the late rhenana zone correspond to a lowstand systems tract a rapid flooding took place near the base of the palmatolepis linguiformis zone and dark shales and limestones formed a second sequence boundary coincides with or is very close to the frasnian famennian boundary base p triangularis zone the global extinction event at the frasnian famennian boundary coincides with an important eustatic fall in sea level the proposed stratigraphic subdivision should allow worldwide correlations of shallow and deep water deposits

why is stromatactis so rare in mesozoic carbonate mud mounds the sedimentary diagenetic structure stromatactis is widespread in palaeozoic spiculitic carbonate mud mounds but occurs only sporadically in mesozoic sponge carbonate mud mounds comparative analysis of palaeozoic and mesozoic stromatactis limestones suggests that this variation results from the degree of siliceous sponge skeletal rigidity and the amount of internal sediment accumulation in the original cavity network partial to entire filling by internal sediment resulted in a continuum from a small amount of internal sediment and large amount of cement stromatactis common in the palaeozoic to only internal sediments aborted stromatactis common in the mesozoic these observations match independent lines of evidence concerning the siliceous sponge evolution and sediment recycling e g bioerosion across the palaeozoic to mesozoic biotic revolution

geochemistry of synsedimentary cements in early cambrian reefs abstract synsedimentary fibrous calcite cements in reefs representing different periods of early cambrian time from eastern siberia southern australia and eastern canada were analyzed to determine whether they retained information about the chemical and isotopic compositions of the seawater from which they precipitated although petrographically similar the sr o and c isotopic compositions as well as the sr and mg contents of the cements from the three areas are different such differences can be attributed to varying degrees of diagenesis of the cements that correlate with the tectonic history of each area cements from the siberian craton are the least altered cements from near the appalachian orogen are partially altered and cements from the flinders fold and thrust belt are extensively altered strontium contents of the fibrous cements generally increase with mg contents although the correlation among these two elements is more variable than that reported for devonian or holocene cements those cements with sr mg ratios near 0 04 which include clear fibrous calcite have the lowest 87 sr 86 sr ratios and have been least altered strontium isotopic ratios in the least altered cements are lower than whole rock ratios and probably approach the original values of early cambrian seawater 18o values in the cements are variable because of exchange with diagenetic fluids whereas 13c values exhibit local variations that do not match temporal curves constructed from whole rock data for the same regions thus most of the original chemical and isotopic compositions of these cements have been variably changed through diagenesis although limited information about the composition of early cambrian seawater such as sr and c isotopic compositions have been retained in some samples

early cambrian bioconstructions in the zavkhan basin of western mongolia the neoproterozoic cambrian succession in the zavkhan basin of western mongolia preserves early cambrian bioconstructions of nemakit daldynian to botomian age as elsewhere siberia morocco the nemakit daldynian bioconstructions in the upper tsagaan oloom formation to lower bayan gol formation interval were purely calcimicrobial spectacular calcimicrobial patch reefs of presumed tommotian age are present in the lower bayan gol formation in contrast late atdabanian early botomian bioconstructions are varied and well developed in the upper salaany gol formation including in addition to calcimicrobial bioherms gordonophyton razumovskia crusts radiocyathan archaeocyathan bioherms and thickets of the ramose archaeocyath cambrocyathellus these latter zavkhan basin buildups show some ecological and sedimentological features in common with coeval bioconstructions in south australia which also developed under a tectonically active regime

marine red staining of a pennsylvanian carbonate slope environmental and oceanographic significance abstract red stained platform facies are a common feature of many carbonate settings throughout the geological record although the mechanisms involved in red staining of subaerially exposed or argillaceous peri platform limestones are reasonably well understood the environmental and oceanographic significance of red carbonates often remains uncertain here sedimentological sequence stratigraphic geochemical paleontological and quantitative bathymetric data from pennsylvanian red intervals across a well exposed carbonate platform top and slope are documented and interpreted in a process oriented context on the upper slope 80 350 meters below the shelf break red intervals alternate with gray mainly microbial algal boundstones on the lower slope 350 600 meters below the shelf break redeposited red stained mud builds matrix supported breccia tongues interbedded with predominantly redeposited clast supported carbonate debris the presence of large volumes of fibrous calcite biocementstones as well as firmgrounds point to low sedimentation rates or omission in terms of sequence stratigraphy red intervals occur within maximum flooding intervals and reflect near platform drowning elevated 18o values 2 3 and an essentially cool water heterotrophic biotic association in red intervals on platform top and slope suggest deposition during sea level highs associated with colder water masses and high nutrient levels the most likely drivers are an elevated thermocline and upwelling the red staining is the result of iron oxidation which occurred during early diagenesis likely by iron bacteria these red intervals provide an important bathymetric benchmark against which other mainly paleozoic red facies can be tested and calibrated

growth patterns of the cambrian microbialite phototropism and speciation of epiphyton abstract microbes started constructing shallow marine stromatolitic bioherms in the archean but they transferred their role as a major buildup maker to metazoans in phanerozoic microbial buildups often recovered their predominance in the carbonate platform when reefal metazoan communities collapsed epiphyton an extinct taxon of calcified microbe that possessed branching filamentous trichomes was an important reef builder in the shallow marine carbonate platform during middle cambrian aftermath of an extinction of archaeocyath sponges which were major reef building sessile organisms in the early cambrian here we present direct evidence of phototropism of epiphyton found from fossilized behavior in micro and macro structures of meter scale microbial bioherms of the zhangxia formation middle cambrian north china platform shandong province china the bioherms consist of stacked growth layers with the inner and outer divisions divided by distinct boundary the inner division of growth layers of the epiphyton bioherm is dominated by dense uniform bush shaped epiphyton thalli whereas the curved outer division has layered texture normal to the surface comprised of elongated and chambered thalli it suggests that photosynthetic epiphyton reacted actively to the spatial changes in intensity of sunlight controlled by angle of illumination on the curved growth surface of the bioherm the inner and the outer divisions comprise different morpho types of epiphyton the spatial distributions of different morpho types in variously illuminated divisions of epiphyton might have caused further speciation of epiphyton

questioning the microbial origin of automicrite in ordovician calathid demosponge carbonate mounds calathid demosponge carbonate mounds are a feature of early to middle ordovician shallow marine carbonate depositional environments of tropical to subtropical palaeolatitudes these mounds contain an important amount of autochthonous non skeletal microcrystalline calcium carbonate automicrite conventionally considered microbial in origin here the automicrite of calathid demosponge carbonate mounds tarim basin north west china is broken down into five distinct fabrics an in situ peloidal spiculiferous fabric am 1 an in situ peloidal fabric am 2 an aphanitic microtubular fabric am 3 a minipeloidal fabric am 4 and a laminoid cerebroid fabric am 5 type am 1 occurs with am 2 being succeeded by an assemblage of am 3 and am 4 types am 4 and am 5 are separated by an erosional disconformity a good correlation of fluorescence and cathodoluminescence of automicrites indicates that induced and supported organomineralization produced automicrite probably via the permineralization of non living organic substrates adsorbing dissolved metal humate complexes using a spreadsheet with six parameters and 17 characters am 1 to am 4 turn out to be non microbial in origin instead these automicrites represent relics of calcified metazoan tissues such as siliceous sponges non spiculate sponges or the basal attachment structures of stalked invertebrates fabric am 5 is a microbial carbonate but is post mound in origin forming a drape within a reefal framework established by am 4 the five automicritic fabrics individually or as an assemblage are a common element of ordovician calathid demosponge carbonate mounds in general the reassessment of the origins of these automicritic fabrics holds consequences for understanding of the great ordovician biodiversification event in terms of community structure reef ecology and reef evolution episodically these fabrics are also present in other carbonate build ups stretching from the neoproterozoic over the entire phanerozoic eon the massive calcification of metazoan soft tissue am 1 to am 4 characterizes episodes and conditions of enhanced marine calcification and might be of value to refine secular trends of pco2 ca concentration and mg ca ratio at the scale of individual sedimentary basins

late quaternary eolian sand depositional record for southwestern kansas landscape sensitivity to droughts abstract eolian deposits and landforms are ubiquitous in western kansas particularly south of the arkansas river with the presence of a stabilized dune field stratigraphic studies and associated optical dating reveal a complex depositional history for this dune field spanning the late quaternary the oldest eolian deposits from ca 16 to 12 ka completely or partially bury high terraces with ages of ca 16 and 33 ka it is unknown whether these eolian deposits reflect regional aridity and or a change in sediment availability with the transition of the arkansas river from a single channel to a braided system there is pervasive evidence for episodic eolian erosion and deposition ca 9 8 to 6 3 ka generally coincident with loess deposition on upland surfaces olson c g nettleton w d porter d a brasher b r 1997 middle holocene aeolian activity on the high plains of west central kansas holocene 7 3 255 261 and thus it is inferred to reflect regional aridity sites within the dune field show a sequence of eolian sands and weak buried soils reflecting either dune migration or sand sheet accretion at ca 1490 430 380 320 180 and 70 yr ago which correspond well with continental scale droughts in the tree ring record eolian sand in the arkansas river dune field may be derived principally with variability in fluvial activity and in climate during the late pleistocene to the middle holocene with substantial reactivation of eolian systems during decadal scale drought variability in the past 2000 yr

latest middle cambrian metazoan reef from northern iran middle and late cambrian reefs were built mainly by cyanobacterial communities a few reefs with a metazoan as well as an algal component however are known from this interval a middle cambrian reef formed primarily by spicular demosponges is described here from the mila formation in the elburz mountains northern iran the reef is enclosed within calcareous grainstones which contain terminal middle cambrian late mayan trilobites the mila formation reef was constructed by sponges of the family anthaspidellidae and bacterial algal sheaths and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges the reefal community is typical of subsequent reefal communities of early middle ordovician age the ordovician examples differ only by the incorporation of additional metazoan elements

cambrian series 3 carbonate platform of korea dominated by microbial sponge reefs abstract metazoans have been considered as negligible components of cambrian series 3 and furongian microbial dominated reefs in contrast to their presence in earlier terreneuvian cambrian series 2 microbial archaeocyath reefs however recent discoveries of sponges in cambrian series 3 furongian reefs of australia china iran usa and korea have raised question regarding their contribution in terms of carbonate platform development which have never been assessed this study examines cambrian series 3 deposits of the daegi formation korea to elucidate this question the 100 m thick middle part of the daegi formation is dominated by boundstone facies which occupies 45 of the study interval as well as bioclastic wackestone to packstone bioclastic grainstone and ooid packstone to grainstone facies the daegi reefs are primarily thrombolitic in composition with 90 n 26 29 of the reefs containing an average of 9 sponges in aerial percentage calculated from thin sections lithistid sponges composed of peloidal fabrics some desma spicules and spicule networks commonly occupy the interstitial space in microbial clusters are encrusted by mesoclots and epiphyton and are surrounded by micrite subordinate non lithistid demosponges occur within clusters of microbial elements the middle daegi formation can be largely subdivided into shoal environment dominated by grainstone to packstone facies and shallow subtidal platform interior environment located behind shoal with wackestone to packstone facies the microbial sponge reefs mainly developed around platform interior as patch reefs the current study indicates that metazoans in the form of lithistid and non lithistid demosponges are nearly ubiquitously incorporated in daegi reefs and contributed greatly to the formation of microbial sponge reefs as well as carbonate platform during the time study of these microbial sponge reefs and their distribution within the carbonate platform may help us to understand how carbonate sedimentary environments responded to the extinction of archaeocyaths

middle cambrian siliceous sponge calcimicrobe buildups daegi formation korea metazoan buildup constituents in the aftermath of the early cambrian extinction event abstract numerous decimetre to metre scale carbonate buildups dominated by siliceous sponges and the calcimicrobe epiphyton are reported from the middle cambrian series 3 daegi formation of korea these siliceous sponge epiphyton buildups consist predominantly of grey micritic boundstones with dark clots and or white clumps the boundstones contain sponge spicule networks interpreted as the calcified remains of siliceous sponges the white clumps and dark clots in the boundstones represent variously preserved epiphyton siliceous sponges form constructional pore space and are commonly encrusted by epiphyton the sponges were probably the primary frame builders providing substrates for the attachment and subsequent growth of epiphyton epiphyton is considered to be a binder when covering the surface of siliceous sponges and a subordinate frame builder when filling depositional voids created by siliceous sponges or growing on top of other epiphyton growth bundles the siliceous sponge epiphyton buildups of the daegi formation show similarities to previously described late cambrian furongian anthaspidellid calcimicrobe buildups from iran and the usa together with recently reported examples from the zhangxia formation of eastern china the sponge epiphyton buildups from korea represent some of the oldest metazoan calcimicrobe buildups after the extinction of most archaeocyaths at the end of the early cambrian series 2 this implies that the incorporation of metazoans in middle cambrian series 3 carbonate buildups occurred much earlier than previously known the buildup forming siliceous sponges described in this study demonstrate that their role in early phanerozoic carbonate buildups has been grossly underestimated

timing and origin for sand dunes in the green river lowland of illinois upper mississippi river valley usa abstract the recent increase in dune studies in north america has been heavily focused in the great plains while less attention has historically been given to the dune fields east of the mississippi river here we report ages and suggest a potential sediment source for sand dunes in the green river lowland illinois which may provide a better understanding of the dynamic interactions between eolian glacial lacustrine and fluvial processes that shaped the landscapes of the upper midwest seven coherent optically stimulated luminescence ages osl or optical ages obtained from four sites suggest that major dune construction in the green river lowland occurred within a narrow time window around 17 500 ago this implies either an enhanced aridity or an episodic increase of sediment supply at 17 500 years ago or combination of the both contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the lake michigan lobe retreated from the area we propose that green river lowland dunes sand originated from the green bay lobe through the rock river specifically sediment supply increased in the rock river valley during drainage of glacial lake scuppernong which formed between 18 000 and 17 000 years ago when the green bay lobe retreated from its terminal moraine the lake drained catastrophically through the rock river valley providing glacial sediment and water to erode the preexisting sandy sediments throughout the remainder of the late pleistocene the laurentide ice sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys therefore the dunes in the green river lowland formed only during the catastrophic drainage of glacial lake scuppernong but were stabilized through the remainder of the pleistocene this scenario explains the abrupt dune construction around 17 500 years ago and explains the lack of later dune activity up to the pleistocene holocene transition osl and radiocarbon ages also indicate that dunes were reactivated during the early middle and late holocene some eolian activation occurred within well defined dry intervals in the upper midwest suggesting that increased aridity may have been the primary driver in mobilizing sand however many ages do not correspond to drier periods in contrast to the relative coherency of the pleistocene osl ages from multiple study sites the holocene osl ages do not overlap from one site to another suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the holocene therefore we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the holocene the multiple periods of eolian activity during the holocene suggest a high potential for future sand activation in the region and these results are informative for environmental prediction and potential future mitigation

accelerator dating of a mixed assemblage of late pleistocene insect fossils from the lamb spring site colorado abstract fossil insects from the late glacial deposits at the lamb spring archaeological site near denver colorado are relatively abundant and diverse providing considerable paleoecological data for the site the late pleistocene insect fauna from the site comprises 72 identified taxa principally beetles however the fauna presented an interpretive problem because it contained a mixture of prairie and alpine tundra species this was initially considered to be the result of a mixing of faunal elements during the climatic transition of late glacial times a no modern analog fauna accelerator dating of insect fossil specimens from the two ecological groups helped resolve the paleoecological problem fossil specimens of the prairie associated species were dated at 17 850 550 yr b p while specimens of the tundra associated species yielded an age of 14 500 500 yr b p these dates reveal that what appeared to be an ecological mixing was probably a taphonomic problem wherein full glacial age fossils were probably reworked into latest wisconsin sediments while both faunal assemblages reflect climatic conditions substantially colder than present initial results suggest that the full glacial fauna represents a cold dry grassland or steppe environment while the younger fauna suggests moister and more tundra like conditions

pleistocene periglacial eolian deposits in southwestern alaska sedimentary facies and depositional processes abstract pleistocene periglacial eolian sediments are widespread in the nushagak holitna and upper kuskokwim lowlands of southwestern alaska these sediments comprise mainly sand sheet deposits and sand loess intergrades with subordinate sand dune deposits and loess sand sheet deposits range from 1 sharply defined parallel low angle laminae formed by migrating wind ripples to 2 irregular subhorizontal strata which reflect migration of poorly segregated wind ripples accumulation on a sparsely vegetated surface adhesion on a quasi planar bed and or niveo eolian deposition sand loess intergrades represent alternating bed load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems the dominance of sand sheet deposits over deposits of well formed dunes in the pleistocene eolian record of southwestern alaska reflects the limited availability of loose dry sand in this former periglacial environment immobilization of sand after deposition as low relief sheets resulted from a seasonally variable combination of ice cementation sparse vegetation high water tables and snow cover

biosedimentology of a silurian thrombolite reef with meter scale growth framework cavities a completely dolomitized silurian reef at maumee ohio u s a is uncommon among early paleozoic reefs in that its framework consists of about 95 thrombolite boundstone and 5 corals the reef lithified syndepositonally as evidenced by centimeter to meter scale growth framework cavities within it that are completely filled with internal sediment the largest cavities 2 3 5 m in diameter are prob ably the largest ever recorded in a thrombolite reef four main types of components are distinguished in the reef frame work 1 dense bushy mesoclots 2 dense rounded to subrounded mesoclots 3 saccate microstructures and 4 crusts mostly struc tureless but also containing dense bushy mesoclots the dense bushy components are abundant rounded to sub rounded mesoclots less so and the remaining components are rare the dense bushy and rounded to subrounded mesoclots are interpreted to represent the calcified re mains of what were initially either aggregates of the probable filamen tous cyanobacterum angulocellularia or aggregates of renalcid calci microbes or both and the saccate mesoclots as the calcimicrobe ren alcis sensu stricto it is speculated that syndepositonal lithification of the reef framework was accomplished by impregnation of unlithified protomesoclots by micrite to create mesoclots along with the formation of micritic cement around and between mesoclots that served to fuse together successive generations of mesoclots the direction of branching of bushy mesoclots in the reef indicates that unlithified protomesoclots were able to grow upward laterally and downward this ability along with syndepositional lithification to create mesoclots and to cement them together enabled the protome soclots and mesoclots to create reef knobs and eventually to roof over spaces that were centimeters to three or more meters in width and height to create growth framework cavities features indicative of rap id deposition including graded bedding poor sorting of bioclasts and textural inversion are common in internal sediment in meter size cav ities these features suggest that storms possibly hurricanes were at least as important and probably more so than everyday wave en ergy in transporting sediment into all cavities in the reef regardless of size

stratigraphy of the younger dryas chronozone and paleoenvironmental implications central and southern great plains abstract the great plains of the united states was the setting for some of the earliest research in north america into patterns and changes in the character of late pleistocene environments and their effects on contemporary human populations many localities in the region have well stratified records of terminal pleistocene and early holocene human paleoindian activity and past environments these have proven important in debates over the character of the younger dryas chronozone ydc 11 000 10 000 14c bp 12 900 11 700 cal bp in the continental interior this paper reviews the lithostratigraphic record of the ydc on the central and southern great plains and summarizes paleobiological records largely isotopic the goal is to determine if there is any uniformity in the timing character direction and or magnitude of changes in depositional environments or broader geomorphic systems before during or after the ydc in order to address the question of the character of environments through this time the stratigraphic records of the late pleistocene to early holocene transition and in particular the stratigraphic records of the ydc vary through time and space the data clearly show that a host of geomorphic processes produced the terminal pleistocene and early holocene stratigraphic records of the great plains moreover the ydc is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils the various geomorphic systems of the great plains did not behave synchronously in response to any common climate driver these stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid latitude climates in the terminal pleistocene and early holocene

comment a new lower cambrian shelly fossil biostratigraphy for south australia by marissa j betts john r paterson james b jago sarah m jacquet christian b skovsted timothy p topper glenn a brock

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

cyanobacterial archaeocyathan radiocyathan bioherms in the wirrealpa limestone of south australia the 140 m thick wirrealpa limestone of south australia is an open shelf marine deposit of early middle cambrian botomian or toyonian age bioherms preserved within this unit have a distinctive epiphyton thrombolitic stromatolite framestone core colonized by a low diversity archaeocyathan radiocyathan biota of ajacicyathus sp archaeocyathus abacus n sp and girphanovella gondwana n sp together with other skeletal invertebrates and macroborers the largest bioherm some 3 m in thickness and 36 m in length is enclosed within an interval of thin bedded to nodular silty bioclast limestone but rests directly on a substrate of bioclast intraclast and onkoid packstone floatstone rudstone the archaeocyathan radiocyathan biota represents the youngest known australian occurrence of these groups

late quaternary loess in northeastern colorado part ii pb isotopic evidence for the variability of loess sources a new application of the pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late wisconsin loess in the central great plains of eastern colorado samples of the peoria loess collected throughout the study area contain k feldspar derived from two isotopically and genetically distinct sources 1 glaciogenic material from early and middle proterozoic crystalline rocks of the colorado province and 2 volcaniclastic material from the tertiary white river group exposed on the northern great plains pb isotopic compositions of k feldspar in loess from two dated vertical sections at beecher island and last chance colorado vary systematically implying climatic control of source availability we propose a model whereby relatively cold conditions promoted the advance of front range valley glaciers discharging relatively little glaciogenic silt but strong winds caused eolian erosion of white river group silt due to a decrease in vegetation cover during warmer periods valley glaciers receded and discharged abundant glaciogenic silt while surfaces underlain by the white river group were stabilized by vegetation isotopic data from eastern colorado loess sections record two warm cold warm cycles during late wisconsin time between about 21 000 and 11 000 radiocarbon yr b p similar to results from other studies in the united states and greenland

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

late devonian carbonate margins and foreslopes of the lennard shelf canning basin western australia part b development during progradation and across the frasnian famennian biotic crisis abstract many studies document the occurrence of carbonate progradational successions that are driven by overall accommodation limited conditions and represent periods when substantial volumes of sediment are stored in slope settings however few have reported on the detailed internal anatomy and components of prograding clinothems and furthermore little is known about how environmental parameters affect the development of carbonate margins and slopes when superimposed on the long term low accommodation signal upper devonian frasnian and famennian carbonate outcrop exposures along the lennard shelf northeast canning basin western australia offer the examination of reefal margin and foreslope development in a variety of settings one of which is long term 10 ma progradation during the late frasnian and famennian in the early phases of progradation a global biotic crisis and faunal overturn occurred around the frasnian famennian f f boundary and indications of global climatic cooling are interpreted at points throughout the late devonian these extrinsic and intrinsic controls provide ecologic context and a stratigraphic framework to assess carbonate margin and foreslope architectures and facies distributions in order to better characterize and predict their complex heterogeneity the outcrop dataset collected includes measured sections tied to interpreted photomosaics and detailed mapping using aerial photographs from the south lawford range windjana gorge and dingo gap areas the outcrop observations highlight distinctive changes in margin style foreslope composition stratigraphic packaging and strike variability within the contexts of the f f biotic crisis long term highstand hst progradation and late devonian climatic changes intervals before and after the f f boundary exhibit notable increases in downslope calcimicrobial boundstone encrustation and evidence for waning foreslope contributions from other previously flourishing carbonate factories reflecting stressed ecological conditions and consequent calcimicrobial opportunism during gradual buildup and recovery periods that bracket the extinction the famennian slope post effects related to the f f crisis can be subdivided into a calcimicrobial boundstone dominated upper slope with a highly complex downdip transition into a mixed debris and grain dominated middle slope and a silt dominated lower slope to toe of slope and exhibits a highly complex lateral heterogeneity associated with multiple contributing sediment factories and temporal partitioning of resedimentation a repeated stacking pattern is observable in the famennian middle slope setting consisting of upward successions of debris followed by a gradation from silt dominated deposits into grain dominated deposits we here interpret these as the expression of high frequency sequences superimposed upon the longer term progradation and a function of transitional greenhouse to icehouse climates these findings offer predictive relationships that link the internal depositional heterogeneity of prograding slope systems to the interplay of long term accommodation drivers ecological conditions affecting carbonate sediment factories and climatic conditions that control the development of high frequency sequences

the structure and genesis of weichselian to early hologene aeolian sand sheets in western europe abstract weischselian to early holocene aeolian sands are widespread in the lowlands of western europe to a large extent these deposits occur in the form of sheet like coversands with slipfaced dunes being much rarer whereas the latter type of landform corresponds to a single facies with dune foreset cross bedding aeolian facies 1 two structurally different facies are distinguishable in the sand sheets this paper concentrates on the two sand sheet facies which are referred to as aeolian facies 2 and aeolian facies 3 data on these two types are based on 1 a survey of existing literature and 2 a detailed analysis of lacquer peels and larger scale exposures in england the netherlands and the federal republic of germany aeolian facies 2 is defined by the spatial position of its beds which may be either horizontal inclined or oppositely dipping in the case of structures formed by fluctuating winds horizontal bedding is by far the most common type inclined bedding is related either to small isolated dome dunes or to scoop shaped deflation surfaces the structures resulting from fluctuating winds are rare and do not represent an inherently large measure of directional variability of the wind regime the internal structure of the beds is dominated by aeolian planebed lamination with or without concordantly infilled wind scours degradation of this stratification type because of interference by coarse particles is discussed aeolian facies 3 is uniquely typified by the alternation of coarser and finer grained horizontal thin beds that are either wavy or even in shape depositional models of facies 3 are given at both the local and regional scales in both cases the coarser grained layers result from tractional deposition of saltating and creeping grains whilst the finer grained strata were laid down by settling from suspension periodic changes in surface wind speed the presence of a damp depositional surface and the availability of both sand and silt in the source area are necessary conditions for the working of the models the large scale model is associated with specific environmental conditions of the weichselian upper pleniglacial the local scale model accounts for the fact that facies 3 is also found in units of weichselian late glacial or early holocene age the regional scale model involves stepwise tractional transport over long distances so that grains of distant provenance were mixed with material from sources nearer to the receiving site this process was an important control on the mineralogical composition of the resultant deposits the prevalence of aeolian planebed lamination in both facies 2 and the coarser grained layers of facies 3 is attributed to the interaction of three factors viz the rarity of topographic barriers the sparseness of vegetation cover and a high ratio between wind energy and sand availability during the processes of transport and deposition in the lowlands of europe sand sheets are gradually replaced in an easterly direction by coeval wind dunes the possible causes of this phenomenon are considered

were there framework reefs in the cambrian it is commonly thought that framework reefs did not exist prior to middle ordovician time lower cambrian archaeocyathan algal limestones from several localities suggest that this view may be incorrect in particular limestones in the poleta formation of western nevada and eastern california display a complex branched framework and a biological zonation similar to that described from ordovician and younger rocks these archaeocyathan rich limestones are associated with coarse grained oolite contain tidal channels and are flat topped and laterally continuous rather than biohermal i interpret them to have been wave resistant environment dominating framework reefs

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions

time transgressive archean unconformities underlying molasse basin fill successions of dissected oceanic arcs superior province canada abstract late archean diachronous unconformities underlying tectonically controlled coarse clastic successions are located throughout the superior province of canada examples studied in detail include hiatuses at the base of the timmins and kirkland basins in the abitibi greenstone belt and the crowduck and stormy basins in the wabigoon subprovince the timmins molasse basin fill succession overlies a high angle subaerial unconformity separating deepwater turbiditic deposits from fluvial conglomerates a subaerial erosional unconformity defines the contact between mafic flows and overlying felsic volcaniclastic deposits and fluvial conglomerates of the kirkland basin the crowduck and stormy successions are characterized by shallow water and subaerial unconformities between quartz feldspar porphyry stocks and clastic deposits the pronounced characteristics of the molasse basins which include 1 basal unconformities with older sedimentary volcanic or plutonic rocks 2 bounding fault systems 3 ba

mesozoic lower jurassic red stromatactis limestones from the southern alps arzo switzerland calcite mineral authigenesis and syneresis type deformation the broccatello lithological unit lower jurassic hettangian to lower parts of upper sinemurian near the village of arzo southern alps southern switzerland is a mound shaped carbonate deposit that contains patches of red stromatactis limestone within the largely bioclastic broccatello unit the stromatactis limestone is distinguished by its early diagenetic cavity system a relatively fine grained texture and an in situ assemblage of calcified siliceous sponges various demosponges and hexactinellids a complex shallow subsurface diagenetic pathway can be reconstructed from sediment petrography in combination with comparative geochemical analysis carbon and oxygen isotopes trace and rare earth elements ree y this pathway includes organic matter transformation aragonite and skeletal opal dissolution patchy calcification and lithification sediment shrinkage sagging and collapse partial ree remobilization and multiple sediment infiltration these processes occurred under normal marine essentially oxic conditions and were independent from local recurring syn sedimentary faulting it is concluded that the stromatactis results from a combination of calcite mineral authigenesis and syneresis type deformation the natural stromatactis phenomenon may thus be best explained by maturation processes of particulate polymer gels expected to form in fine grained carbonate sediments in the shallow subsurface conditions favorable for the evolution of stromatactis appear to be particularly frequent during drowning of tropical or subtropical carbonate platforms

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation