heterogeneity in geochemical expression of subaerial exposure in limestones and its implications for sampling to detect exposure surfaces abstract replicate sampling along stratigraphic horizons in one outcrop of ordovician limestones of the nashville dome reveals considerable variation in 13c 18o and sr concentration among seemingly identical samples ten vertical transects were sampled each consisting of samples taken at 10 cm intervals from 2 m below to 1 m above the m4 m5 sequence boundary of holland and patzkowsky 1997 1998 the 10 transects were each 2 m apart the resulting 10 replicate and thus seemingly interchangeable samples from each horizon have ranges of 13c as great as 2 4 and ranges of 18o as great as 2 8 and sr concentrations that vary by as much as a factor of four variance is great both just below and just above surfaces of subaerial exposure as a result maxima in variance in 13c as well as or in some cases instead of minima in mean 13c can be used to test such surfaces for exposure maxima in variance and minima in mean 13c may be found either below a surface of subaerial exposure in the meteorically altered sediment or above that surface in the transgressive lag where reworked pre exposure sediment is mixed with unaltered post exposure sediment the large variances and ranges found in this study and the dissimilarity of geochemical profiles from the 10 vertical transects indicate that single samples of stratigraphic horizons and thus single vertical transects can yield misleading characterizations of stratigraphic variation of geochemical parameters instead replicate sampling along horizons better characterizes isotopic and elemental variation through stratigraphic sections than does existing single sample strategies and it will be more useful in future testing of surfaces of subaerial exposure for example the replicate geochemical data used in this project confirm the presence of three surfaces of subaerial exposure whereas only two had been recognized as exposure surfaces before data from replicate samples also make unnecessary the use of arbitrary criteria for inferring exposure such as the predetermined numerical cutoffs used by railsback et al 2003

lithostratigraphy of the upper turinian lower chatfieldian upper ordovician foreland succession and a u pb id tims date for the millbrig volcanic ash bed in the ottawa embayment three stages of carbonate platform development are preserved in the upper turinian lower chatfieldian succession of the ottawa group in the ottawa embayment and represent deposition along the late ordovician taconic foreland interior of paleo southern laurentia compared with contemporary stratigraphy in the adjacent northern appalachian southern ontario new york state and western quebec basins the intermediate stage 2 succession which brackets the turinian chatfieldian boundary preserves embayment specific stratigraphic patterns these include i dramatic west to east thickening of the upper turinian watertown formation that defines differential subsidence along the present axis of the embayment ii post watertown base level fall defined by appearance of shoreface siliciclastics iii early chatfieldian marine transgression represented by the proposed l orignal formation that is coeval with but lithologically distinct from the selby formation in the northern appalachian basin and iv platf

high resolution sequence stratigraphy of lower paleozoic sheet sandstones in central north america the role of special conditions of cratonic interiors in development of stratal architecture well known difficulties in applying sequence stratigraphic concepts to deposits that accumulated across slowly subsiding cratonic interior regions have limited our ability to interpret the history of continental scale tectonism oceanographic dynamics of epeiric seas and eustasy we used a multi disciplinary approach to construct a high resolution stratigraphic framework for lower paleozoic strata in the cratonic interior of north america within this framework these strata proved readily amenable to modern sequence stratigraphic techniques that were formulated based on successions along passive margins and in foreland basins settings markedly different from the cratonic interior parasequences parasequence stacking patterns systems tracts maximum flooding intervals and sequence bounding unconformities can be confidently recognized in the cratonic interior using mostly standard criteria for identification the similarity of cratonic interior and foreland basin successions in size geometry constituent facies and local stacking patterns of nearshore parasequences is especially striking this similarity indicates that the fundamental processes that establish shoreface morphology and determine the stratal expression of retreat and progradation were likewise generally the same despite marked differences in tectonism physiography and bathymetry between the two settings our results do not support the widespread perception that paleozoic cratonic interior successions are so anomalous in stratal geometries and constitute such a poor record of time that they are poorly suited for modern sequence stratigraphic analyses the particular arrangement of stratal elements in the cratonic interior succession we studied is no more anomalous or enigmatic than the variability in architecture that sets all sedimentary successions apart from one another thus paleozoic strata of the cratonic interior are most appropriately considered as a package that belongs in a continuum of variable stratigraphic packages reflecting variable controls such as subsidence and shelf physiography special conditions of exceptionally slow subsidence rate shallow bathymetry and nearly flat regional shelf gradient are manifest mostly by the presence of individual systems tracts of relatively long duration that extend for much greater distances across depositional strike than those that characterize successions deposited in more dynamic tectonic and physiographic settings these results suggest that if other cratonic interior successions are as anomalous as reported a low sediment supply may have played a primary role in development of their apparently condensed stratal architecture the results also lead us to suggest that a nonvegetated lower paleozoic landscape played a relatively insignificant role in the development of what are commonly perceived to be enigmatic stratigraphic features of sheet sandstones particularly their widespread yet thin geometry and a scarcity of shale and siltstone

evidence of a tectonically driven sequence succession in the middle ordovician taconic foredeep the late mohawkian through early cincinnatian ordovician trenton group carbonates and coeval siliciclastic succession of the central mohawk valley new york state were deposited in a foreland basin during the taconic orogeny development of this facies mosaic records changes in stacking patterns that took place during episodic basin deepening and simultaneous carbonate ramp shallowing along a ramp to basin transect located on the distal slope of the foreland basin differential rates of subsidence across the region produced accommodation rates that increased by an order of magnitude from west to east high rates of siliciclastic sediment supply and even higher subsidence rates resulted in a thick deep water succession in the eastern part of the study region the coeval trenton group succession in the west formed under conditions of moderate sediment supply and lower subsidence rate resulting in a net shallowing upward succession these relationships suggest that active margin tectonism was the proximate cause of the mohawk valley facies architecture

seismic velocity model of the central united states version 1 description and simulation of the 18 april 2008 mt carmel illinois earthquake abstract we have developed a new three dimensional seismic velocity model of the central united states cusvm that includes the new madrid seismic zone nmsz and covers parts of arkansas mississippi alabama illinois missouri kentucky and tennessee the model represents a compilation of decades of crustal research consisting of seismic aeromagnetic and gravity profiles geologic mapping geophysical and geological borehole logs and inversions of the regional seismic properties the density p and s wave velocities are synthesized in a stand alone spatial database that can be queried to generate the required input for numerical seismic wave propagation simulations we test and calibrate the cusvm by simulating ground motions of the 18 april 2008 m w 5 4 mt carmel illinois earthquake and comparing the results with observed records within the model area the selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 10 to 430 km from the epicenter the results based on a qualitative and quantitative goodness of fit gof characterization indicate that both within and outside the mississippi embayment the cusvm reasonably reproduces 1 the body and surface wave arrival times and 2 the observed regional variations in ground motion amplitude cumulative energy duration and frequency content up to a frequency of 1 0 hz in addition we discuss the probable structural causes for the ground motion patterns in the central united states that we observed in the recorded motions of the 18 april mt carmel earthquake online material simulated and observed waveforms and response spectral acceleration ground motion prediction equation comparison

the use of a high resolution 3d chirp sub bottom profiler for the reconstruction of the shallow water archaeological site of the grace dieu 1439 river hamble uk the remains of henry v s flagship the grace dieu currently lie buried within the inter tidal sediments of the river hamble s england previous archaeological investigations have been hindered by difficult excavation conditions resulting in a poor understanding of the dimensions shape and degradation state of the hull s deeper structure this study therefore aimed to image characterize and reconstruct the buried remains of this vessel using a high resolution 3d acoustic sub bottom chirp system with rtk gps positioning capability the accurate navigation and high resolution data that were acquired enabled the construction of a full 3d image of the site that not only identified the remains of the wooden hull but also features buried within it in addition the degradation state of these buried wooden remains were investigated by calculating reflection coefficients while a hypothetical larger reconstruction of the grace dieu s hull was achieved through the use of the shipshape ship design software package the results of this project demonstrate that i acoustic data can be used to successfully image buried wooden shipwrecks ii artefacts are buried within the hull of the grace dieu iii there is variation in the degradation state of the buried timbers as calculated from the acoustic data with the shell of the vessel being moderately well preserved and iv the grace dieu was a very large ship for its time possibly over 60 m long and 16 m wide the outcomes of this research not only have considerable implications for the management and monitoring of submerged and buried archaeological sites but also for planning intrusive surveys should they be required

revised sequence stratigraphy of the upper katian stage cincinnatian strata in the cincinnati arch reference area geological and paleontological implications abstract the upper ordovician cincinnatian series is a critical upper katian reference succession previously six 3rd order depositional sequences c1 to c6 have been recognized and frequently used as regional time slices recent research however indicates a need for revision and additions including the recognition of additional 3rd and 4th order sequences we propose amendments based upon high resolution correlations using a combination of regional disconformities cycle stacking patterns bioevents marker beds and chemostratigraphy several disconformities including a large regionally angular mid richmondian unconformity are newly recognized or reinterpreted in addition distinctive depositional patterns aid in the recognition of systems tracts with a thick proximal laminated peritidal facies representing early transgressive systems tracts tsts or lowstands in part lsts b shell rich limestone packages representing later tsts and overlain by c more shale prone highstand systems tracts hsts themselves overlain locally by d siliciclastic dominated falling stage systems tract fsst deposits that are commonly removed beneath substantial unconformities sequence boundaries at present we recognize eight 3rd order cincinnatian sequences designated c1 through c8 and 16 4th order subdivisions and their component systems tracts a younger hirnantian sequence may be present at some localities as the enigmatic centerville formation and or basal belfast member of the brassfield formation the implications of these new correlations and sequence interpretations include a new standard for relative sea level changes and insights into basin dynamics this framework also permits a more nuanced history of biotic changes that include geologically brief pulses of immigration associated with the transgressions of the c1 lower kope formation c5c clarksville member of waynesville formation and c7a basal whitewater formation

sea level curve for the middle to early late ordovician in the armorican massif western france icehouse third order glacio eustatic cycles abstract this contribution deals with the middle to early late ordovician of the armorican massif western france the aim is to reconstruct a multi order eustatic curve from the stratigraphic record the studied section crozon peninsula area shows sediments deposited in tidal to storm dominated shelf environments a sequence analysis facies and stacking pattern analyses combined with a gamma ray record and a backstripping procedure was carried out chitinozoan assemblages provide the biostratigraphic framework including time calibration the stratigraphic succession is dominated by the stacking of sequences representing different orders of sea level change i e very high formosa and pissotensis biozones of the darriwilian the reconstructed sea level curve reveals that most of the third order cycles comprise three fourth order cycles of assumed 400 kyr duration this 1 2 myr duration of the ordovician third ordersequences suggests that they may be related to long period obliquity cycles an orbital forcing characteristic of icehousesequences in the late cenozoic and the quaternary these results imply that the major part of the middle and early late ordovician was characterized by icehouse conditions and third orderglacio eustatic cycles a time calibration of the chitinozoan biozones was developed from the sequential analysis it suggests that the early darriwilian biozones from henryi to calix biozones have short durations of several 10 to several 100 kyr whereas the pissotensis biozone has a temporal extent of several myr extending into the early sandbian

sequence stratigraphy and relative sea level history of the middle and upper ordovician of the nashville dome tennessee abstract eleven depositional sequences are present in the middle and upper ordovician of the nashville dome all but one lack lowstand systems tracts and many display evidence of subaerial exposure such as paleokarst or regional erosional truncation at their sequence boundaries which are combined with transgressive surfaces features formed during the transgression such as hardgrounds are more prominent at most sequence boundaries than are those features related to subaerial exposure all sequences have maximum flooding zones with aggradational stacking rather than discrete maximum flooding surfaces condensation features are much more common at transgressive surfaces than within the maximum flooding zone the expression of these parasequences and sequences changes with the onset of the taconic orogeny although parasequences from equivalent depositional environments can be recognized before and after the onset of the orogeny their facies composition changes completely sequences following the orogeny display fewer paleokarst features more pyritized and iron stained hardgrounds at flooding surfaces and transgressive surfaces and more phosphatic lags and mineralization at transgressive surfaces than those preceding the orogeny a relative sea level curve for the nashville dome has a long term 5 m y component presumably dominated by subsidence and a short term 1 3 m y component consisting of 10 50 m fluctuations that is primarily the result of eustasy

decimeter resolution 3d seismic volume in shallow water a case study in small object detection the 3d chirp subbottom profiler provides high resolution imaging of coastal and inshore seabed and subseabed structure by combining the known highly repeatable source waveformofchirpprofilerswiththecoherentprocessingand interpretation afforded by true 3d seismic volumes comprising 60 hydrophone groups arranged around a maltese cross of four chirp transducers 3d chirp permits acquisition of a true 3d volume with a horizontal resolution of 12 5 cm providing an excellent base for shallow water engineering archaeological military and geologic studies here we presentresultsfromsurveyinganatidalbasinonthesouthern coastofenglandtomapbedrockprotrusionsandthesizeand distributionofburiedobjects thestudyareaof150250 m provided a series of unique challenges including a large number of discrete objects ranging from tens of centimeters toseveralmetersinsize buriedinathinveneer0 5to1 5 m of unconsolidated silt overlaying a flat bedrock surface that showed high acoustic contrast and short wavelength roughness by comparing comprehensive postsurvey dredging of the entire site with a prestack time migrated 3d volume it is possibletoconfirma100 detectionrateforalldiscreteburied objects larger than 0 300 30 m in an illuminated area although one acoustic anomaly could not be accounted for in thedredgingresults

controls on geochemical expression of subaerial exposure in ordovician limestones from the nashville dome tennessee u s a abstract stable isotope and trace element data from 301 samples in six stratigraphic sections largely support previous inferences of subaerial exposure at third order sequence boundaries in mohawkian and cincinnatian limestones of the nashville dome they also reveal the presence of previously unrecognized surfaces of subaerial exposure for example evidence of subaerial exposure at the tops of parasequences suggests that at least some of the latter are better interpreted as high frequency sequences clusters of surfaces of subaerial exposure near some previously interpreted sequence boundaries suggest that the latter may represent sequence boundary zones some surfaces of subaerial exposure are at neither recognized sequence boundaries nor parasequence boundaries and may represent missed beats in which sea level fluctuations are preserved geochemically but not recognized on stratigraphic criteria recognition of these unexpected surfaces of subaerial exposure may in part depend on the close spacing of samples used in this study different sequence boundaries exhibit different degrees of geochemical alteration and more extensive alteration appears to characterize sequence boundaries of greater temporal significance overprinting of exposure surfaces is controlled by accommodation rate in that meteoric alteration as suggested by low c isotope composition and sr concentration is seemingly pervasive in an interval of slow accommodation but not in an interval of rapid accommodation 18o values show little relationship to exposure surfaces in these strata so that sr 13c plots are more useful than 18o 13c plots in recognizing meteoric diagenesis in aggregated data in this data set 13c excursions interpreted to result from pedogenic processes are at most 2 4 and extend at most only 1 5 meters below exposure surfaces less than the extent of such signatures in younger carbonates such minima are best developed in paleo lowland and paleo coastal settings and they are essentially unrecognizable in paleo inland settings where more section was removed by lowstand and transgressive erosion

isotopic and geochemical characteristics of laramide magmatic systems in arizona and implications for the genesis of porphyry copper deposits major element trace element and nd sm and rb sr isotope data are described from igneous rocks in 11 multiphase magmatic complexes of laramide age in arizona eight complexes contain barren stocks as well as productive plutons associated with the formation of porphyry base metal deposits whereas in three complexes porphyry orebodies have not been recognized most of the complexes evolved through similar stages early dominantly intermediate volcanic rocks were intruded by multiphase complexes temporally characterized by increases in sio 2 changes in the ferromagnesian mineral assemblage increasingly porphyritic textures and a progression from barren to subproductive to productive intrusions within complexes the sequence is independent of both the absolute age of initiation of local magmatism and its duration analytical data and field relationships are combined to show elements of the petrogenetic history of these complexes potential relationships between productive and barren magmas and factors which may have influenced formation of the characteristic magmatic hydrothermal sequence the isotopic composition of laramide igneous rocks forms an array from epsilon ndt and 87 sr 86 sr initial values of 0 and 0 704 to 14 and 0 710 respectively early volcanic rocks have a more primitive signature consistent with retention of a significant mantle component subsequent intrusions were derived predominantly from isotopically heterogeneous precambrian lower crust but probably also contain an undefined amount of mantle component individual complexes do not exhibit any consistent isotopic trends over time and unique types of source rocks are not indicated for productive magmas in contrast rare earth elements ree in several complexes display temporally systematic behavior progressively younger intrusions in a given complex follow a path of decreasing concentration of ree steepening profiles greater upward concavity in heavy ree profiles and changes in the eu anomaly from negative to either markedly less negative or positive the ree data from individual complexes suggest an increasing petrogenetic involvement of amphibole either in the restite of the source region or as a fractionating phase and similar paths of petrogenetic evolution in spite of chronologic and trace element evidence which argues against completely comagmatic development productive and barren intrusions cannot be clearly distinguished by the isotopic data but the systematic ree trends parallel increasing productivity of magmas in individual complexes models which reconcile isotopic variation systematic ree behavior protracted local but largely noncomagmatic magmatism and the increasing development of porphyry mineralization include 1 progressive metasomatism of the crustal component 2 increasing assimilation of amphibolitic crust by mantle basalts and 3 migration of crustal anatexis from deep anhydrous rocks to shallower amphibolites the relative importance of these processes cannot yet be clearly assessed from the data but a plausible metallogenic impact of each would be upon the concentration and possibly the composition of magmatic volatiles in the primary melts and or during subsequent fractionation in this light existing models which propose that the principal control upon intrusion productivity is a balance between crystal fractionation and the timing of saturation and release of magmatic hydrothermal fluids may be strongly influenced by processes operative either in their source regions or during their interaction with the crust initiation of such processes may be a response to abrupt changes in tectonic regime in the volcanic are environment

comparative sequence stratigraphy of two classic upper ordovician successions trenton shelf new york ontario and lexington platform kentucky ohio implications for eustasy and local tectonism in eastern laurentia abstract comparison of the classic upper ordovician mohawkian to lower cincinnatian caradoc to lower ashgill black river and trenton groups in new york state southern ontario with the tyrone lexington formations exposed in the jessamine dome southern cincinnati arch in north central kentucky and southern ohio reveals striking similarities previous emphasis on complex local facies mosaic has obscured widespread regional patterns biostratigraphy and k bentonites provide broad constraints on inter regional correlations however an allostratigraphic approach permits higher resolution correlations and a partial test of eustatic vs strictly local tectonic models to explain stratigraphic patterns upper mohawkian to lower cincinnatian 455 449 ma depositional sequences previously recognized for the jessamine dome and nashville dome areas are correlated between the two main study areas and further refined chatfieldian rocklandian to shermanian or cobourgian of traditional terminology sequences m5 and m6 of previous workers are interpreted to be composite sequences and are each subdivided into three smaller scale sequences which also have counterparts in the new york ontario strata in turn these correlations indicate at least partial allocyclic control on sedimentary cycles complex lateral variations within depositional sequences especially in the late shermanian to edenian indicate that tectonically controlled patterns of basinal subsidence and uplift of crustal blocks perhaps reflecting forebulge migration exerted a strong influence on the local facies and motif of depositional sequences these tectonic features however did not obliterate the underlying allocyclic pattern indeed high resolution sequence stratigraphy enables detailed resolution of shifting patterns of minor uplift and subsidence

record of microendoliths in different facies of the upper ordovician in the cincinnati arch region usa the early history of light related microendolithic zonation abstract this study provides the first documentation of microendolithic borings made by cyanobacteria algae and fungi in invertebrate skeletons from the late ordovician of eastern north america samples from the upper mohawkian to cincinnatian series katian stage caradoc to lower ashgill of traditional usage limestones and calcareous shales of ohio indiana and kentucky were selected for study because of the excellent preservation of fossil shell material the substrates mostly are brachiopods and corals strata of the mohawkian lexington limestone and cincinnatian kope formation maysville and richmond groups have been recently studied in terms of facies sequence stratigraphy and paleoenvironments which facilitates a reliable comparison of the distribution of microborings and inferred environmental settings especially relative paleobathymetry this paper reports the first occurrence of 10 ichnospecies plus various conchocelis traces in late ordovician cincinnatian marine shells these traces have been previously observed in shells from younger geological periods their modern counterparts are produced by species of cyanobacteria green algae red algae and heterotrophic microendoliths considering the bathymetric index ichnocoenoses of microendoliths defined for the later phanerozoic it appears that only one or two light related bathymetric zones can be recognized in a few samples from the upper ordovician cincinnatian of ohio and kentucky but not in all deposits where they might have been expected the shallow euphotic zone iii and with less certainty the deep euphotic zone on the contrary our samples from the underlying lexington formation contain only borings of worms macrotubular form and some forms with unknown producers although they were collected in facies realms comparable to the younger samples given the present state of knowledge the best explanation for the appearance of these 10 ichnospecies and the first bathymetric index ichnocoenoses within the late ordovician is that they represent the early evolution of microendolithic ichnospecies and early emplacement of ichnocoenoses

the middle caradoc facies and faunal turnover in the late ordovician baltoscandian palaeobasin abstract a late ordovician episode of remarkable biotic climatic sea level and facies changes named here as the middle caradoc facies and faunal turnover took place in the baltoscandian area this paper presents an integrated overview of these changes in the critical middle caradoc interval data are given on carbonate rock composition distribution and grain size composition of the siliciclastic material and the carbon isotopic composition of whole rock carbonates in cores of estonia and sweden the middle caradoc facies and faunal turnover can be described as a succession of related environmental changes the turnover began with a positive excursion in carbonate 13c and continued with sea level changes that led to a sedimentary hiatus on the shelf and a change from carbonate dominated to siliciclastic dominated sedimentation in the basin the turnover ended with an extinction event and associated microfaunal crisis the middle caradoc turnover in baltoscandia is comparable to a similar succession of changes in north america the turnover affected two palaeocontinents and reflects a widespread possibly global environmental change onset of glaciation on gondwana and or increased orogenic activity might have initiated the changes in ocean circulation and led to the initial carbon isotope excursion the following sea level rise and faunal changes affected several different continents

an extensive erosion surface of a strongly deformed limestone bed in the gushan and chaomidian formations late middle cambrian to furongian shandong province china sequence stratigraphic implications abstract in order to understand sequence development and sea level fluctuations during the late middle cambrian to early furongian on the north china epeiric platform the present study focuses on a unique subtle erosion surface of an extensive approx 100 km strongly deformed limestone bed in the uppermost part of the gushan formation shandong province china the gushan formation and the overlying chaomidian formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments e g deep subtidal shallow subtidal shoreface shoal subtidal microbial flat and restricted platform interior three third order depositional sequences s1 3 are identified each of which comprises a thin transgressive systems tract tst and a relatively thick highstand systems tract hst each sequence is bounded by a drowning unconformity sb1 a subaerial unconformity sb2 or a surface of submarine erosion sb3 the upper sequence boundary sb2 of sequence 1 s1 is represented by a subtle erosion surface of an extensive deformed limestone bed with a wide variety of soft sediment deformation structures e g lime mudstone breccias chaotic wacke packstone laminae and fragments homogenized oolites and clastic dykes and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed the deformed limestone was formed during early diagenesis by differential deformation processes brecciation liquefaction fluidization and injection which were most likely induced by pore water overpressure during the period of rapid sea level fall despite the lack of subaerial exposure features e g paleokarst paleosol etc the characteristics of the erosion surface cutting well lithified sediment below the missing of a significant geological record the prochuangia biozone and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment the missing of the prochuangia biozone is most likely due to non deposition at a subaerial hiatal surface the erosion surface was submerged as a result of subsequent rise in sea level where sporadic microbial buildups formed under suitable conditions freshly deposited winnowed shell dominated transgressive lag deposits containing chuangia trilobite fragments brachiopod shells and abundant glauconite grains formed with continued rise in sea level which became in turn overlain by shale dominated facies the unique combination of the subtle erosion surface sensu stricto a subaerial unconformity and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms

sequence stratigraphy in the middle ordovician carbonate successions yeongheung formation mid east korea paleogeographic implications for a land detached ramp type platform abstract this study reveals the origin of the stratigraphic discrepancy between the yeongweol and taebaek groups and reconstructs paleogeographic model for the taebaeksan basin on the sino korean craton skc the global sea level fall in the earliest middle ordovician would have subaerially extensively exposed the lower ordovician peritidal successions forming the solution collapsed breccia zones on the sauk tippecanoe bounding surface the successive rise in sea level generated the fine grained siliciclastic successions in the taebaek group during early transgression since the carbonate production of the group was hampered by the strong input of siliciclastic sediments from terrestrial sources however such successions are absent in the yeongweol group because the yeongweol platform was distant from the siliciclastic sources and sustained carbonate production due to isolation from terrestrial influences the yeongweol group is interpreted as a land detached isolated ramp type platform as it responded to sea level fluctuations with restricted terrestrial influence whereas the taebaek group can be described as a land attached ramp type platform affected by a large input of siliciclastic sediments during lowstand and early transgression based on the comparison of stratigraphic patterns and configurations of land attached and detached ramp type successions this study concludes that the yeongweol sequence would have been formed on a land detached isolated carbonate ramp type platform located at the skc along the northeastern gondwana margin

3d seismic imaging of buried younger dryas mass movement flows lake windermere uk abstract windermere is a glacially overdeepened lake located in the southeastern lake district uk using the three dimensional 3d chirp subbottom profiler we image mass movement deposits related to the younger dryas yd within a decimetre resolution 3d seismic volume documenting their internal structure and interaction with preexisting deposits in unprecedented detail three distinct flow events are identified and mapped throughout the 3d survey area package structures and seismic attributes classify them as a small total volume of c 1500 m 3 debris flow containing deformed translated blocks a large inferred total volume of c 500 000 m 3 homogeneous fine grained mass flow deposit and a debris flow inferred total volume of c 60 000 m 3 containing small c 8 0 2 0 m deformed translated blocks geomorphological mapping of their distribution and interaction with preexisting sediments permit the reconstruction of a depositional history for the stratigraphic units identified in the seismic volume

revised stratigraphy of the middle simcoe group ordovician upper sandbian katian in its type area an integrated approach the upper ordovician bobcaygeon formation of southern ontario is a widespread unit that spans the sandbian katian stage boundary and contains exceptionally preserved invertebrate fossil assemblages

the geological hubble a reappraisal for shallow water traditional two dimensional 2d seismic acquisition techniques image the subsurface using a grid of orthogonal lines dips are recorded only in the along track direction limiting migration to a 2d along track approximation of the inherently 3d wavefields this produces profiles that are often complicated by out of plane reflections and with resolution for structural interpretation constrained by the line spacing rather than the source wavelength the acquisition of true 3d seismic reflection data in contrast provides dip information for the reflected wavefields in both along and across track directions this allows a full treatment of the 3d wavefields during migration affording accurate 3d structural reconstruction significantly improved resolution theoretically 1 2 source wavelength and increasing signal to noise ratio snr through more effective noise cancellation

late ordovician glaciation initiated by early land plant evolution and punctuated by greenhouse mass extinctions abstractlate ordovician hirnantian glaciation indicated by periglacial paleosols tillites and glacial pavements in saharan africa has been attributed to advances in weathering and carbon sequestration due to evolution of early land plants in the same way that devonian permian glaciation has been attributed to evolution of forests and quaternary glaciations to evolution of grasslands two problems for carbon cycle explanations of this glaciation are an hirnantian co2 greenhouse estimated at 4035 ppmv from mass balance models and possibly related hirnantian mass extinctions this estimate of high co2 is a 10 m yr average here evaluated against high resolution sequences of paleosols that give estimates not only of co2 but also of paleoclimate and vegetation through the late ordovician katian paleosols of the eastern united states show increases in depth and in degree of carbon consumption and storage comparable with those preceding glaciation of the devonian permian and quaternary early thalloid l

high resolution sequence stratigraphy of a mixed carbonate siliciclastic cratonic ramp upper ordovician kentucky ohio usa insights into the relative influence of eustasy and tectonics through analysis of facies gradients abstract detailed facies analysis and event stratigraphy of an upper ordovician rocklandian edenian cratonic ramp succession in eastern north america yields insights into eustatically driven sequence architecture and localized tectonic instability seven predominantly subtidal mixed carbonate siliciclastic depositional sequences 3rd order are identified and correlated across the length of a 275 km ramp to basin profile within the larger depositional sequences 3rd order at least two smaller orders 4th and 5th of cyclicity are recognizable three systems tracts occur within each sequence transgressive tst highstand hst regressive rst and are considered in terms of their component parasequences 5th order generally tsts are composed of skeletal grainstone rudstone facies hsts are dominated by shaly nodular wacke packstone facies and rsts are mostly calcarenite facies systems tracts sequence boundaries and their correlative conformities maximum flooding surfaces and forced regression surfaces were traced from shallow shelf to basinal settings this high resolution framework also provides insight into the timing of tectonic fluctuations on this cratonic ramp during the taconic orogeny and documents the relative influence of tectonism on lateral facies distributions and eustatically derived cyclicity

quantification of macroscopic subaerial exposure features in carbonate rocks abstract the macroscopic features that characterize subaerial exposure surfaces in carbonates are well known but their significance has not been quantitatively evaluated this study presents such an analysis in the lower oligocene suwannee limestone of west central florida eleven cores were point counted on a foot by foot basis for the abundance of caliche rhizoliths karst breccia open vugs infiltrated sediment fractures and pedogenic alteration these features occur at and below intraformational exposure surfaces which represent hiatuses estimated at 104 to 105 years and an uppermost sequence bounding unconformity representing 0 5 myr as revealed by sr isotope data statistical analyses of the point count data reveal only a few significant relationships 1 the hierarchy of exposure surfaces and by inference duration of exposure is differentiated only at a marginally significant level by sediment filled vugs preferentially associated with the sequence boundary duration of exposure did not have a significant impact on the relative abundance of all other features 2 proximity 5 ft to both types of surfaces fractures open vugs and infiltrated sediment show no proximal or distal preference for either type of surface 3 depositional texture has no statistically significant affect on the presence or abundance of the exposure features with the exception that rhizoliths and open vugs are preferentially more abundant in packstones relative to grainstones this is interpreted to be the result of a soil moisture effect factor analysis defines four factors that explain 46 to 52 of the total variance in the abundance data relative to the sequence boundary and the intraformational surfaces respectively the loading of each exposure feature on each factor is the same with respect to both types of surfaces which is further evidence that the abundance of exposure features is independent of duration of exposure factor 1 is interpreted to be the amplitude of base level changes and controls the abundance of karst breccia factor 2 is interpreted to be abundance of vegetation and relates to the abundance of rhizoliths and fractures factor 3 is interpreted to be a combination of soil zone pco2 and the availability of water and affects the abundance of pedogenic overprinting caliche and open vugs factor 4 is stratigraphic proximity to the sequence boundary which controls the presence of sediment filled voids the amount of uncorrelated unique variance associated with infiltrated sediments pedogenic overprinting caliche and open vugs is large 60 meaning that feature abundance is also influenced by other unidentified site specific factors these results demonstrate that quantifying the abundance of macroscopic subaerial exposure features in limestones has the potential to yield more insight into the significance of those features than a mere qualitative assessment this is particularly true when assessing the potential role of the many variables that can affect the development of these features

carbonate platform growth and cyclicity at a terminal proterozoic passive margin infra krol formation and krol group lesser himalaya india the infra krol formation and overlying krol group constitute a thick 2 km carbonate rich succession of terminal proterozoic age that crops out in a series of doubly plunging synclines in the lesser himalaya of northern india the rocks include 18 carbonate and siliciclastic facies which are grouped into eight facies associations 1 deep subtidal 2 shallow subtidal 3 sand shoal 4 peritidal carbonate complex 5 lagoonal 6 peritidal siliciclastic carbonate 7 incised valley fill and 8 karstic fill the stromatolite rich peritidal complex appears to have occupied a location seaward of a broad lagoon an arrangement reminiscent of many phanerozoic and proterozoic platforms growth of this complex was accretionary to progradational in response to changes in siliciclastic influx from the south eastern side of the lagoon metre scale cycles tend to be laterally discontinuous and are interpreted as mainly autogenic variations in the number of both sets of cycles and component metre scale cycles across the platform may result from differential subsidence of the interpreted passive margin apparently non cyclic intervals with shallow water features may indicate facies migration that was limited compared with the dimensions of facies belts correlation of these facies associations in a sequence stratigraphic framework suggests that the infra krol formation and krol group represent a north to north westfacing platform with a morphology that evolved from a siliciclastic ramp to carbonate ramp to peritidal rimmed shelf and finally to open shelf this interpretation differs significantly from the published scheme of a basin centred on the lesser himalaya with virtually the entire infra krol krol succession representing sedimentation in a persistent tidal flat environment this study provides a detailed neoproterozoic depositional history of northern india from rift basin to passive margin and predicts that genetically related neoproterozoic deposits if they are present in the high himalaya are composed mainly of slope basinal facies characterized by fine grained siliciclastic and detrital carbonate rocks lithologically different from those of the lesser himalaya