the quaternary evolution of the gulf of corinth central greece coupling between surface processes and flow in the lower continental crust abstract the gulf of corinth in central greece is an active normal fault zone with particularly clear evidence of isostatic footwall uplift constrained by quaternary marine terraces and hanging wall subsidence and sedimentation it is bounded to the south by a pliocene to early pleistocene sedimentary basin which is now eroding into the gulf previous work has suggested that the relief across this region has increased dramatically since the early pleistocene due to the isostatic response to increased rates of footwall erosion and hanging wall sedimentation it is indeed assumed here that incision accompanying the draw down of global sea level at 0 9 ma during the first major pleistocene glaciation initiated the erosion of the basin south of the gulf of corinth and so abruptly increased the sedimentation rate in the gulf the resulting transient thermal and isostatic response to these changes is modelled with the subsiding depocentre and eroding sediment source coupled by flow in the lower continental crust the subsequent enhancement of relief involving an increase in bathymetry from near zero to 900 m and 500 m of uplift of the eroding land surface in the sediment source is shown to be a direct consequence of this change the model is sensitive to the effective viscosity of the lower crust and can thus resolve this parameter by matching observations a value of 6 1019 pa s is indicated suggesting a viscosity at the moho no greater than 1018 pa s similar transient topographic effects caused by increased rates of sedimentation and erosion are likely to be widespread within the geological record suggesting that this coupling process involving flow in the weak lower crust may be of major geological and geomorphological importance

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

rheological differences between archaean and younger crust can determine rates of quaternary vertical motions revealed by fluvial geomorphology surface uplift is widely observed in subaerial regions of continental crust that are distant from plate boundaries often revealed by river terrace staircases with altitude ranges of several hundred metres which typically span the quaternary this characteristic geomorphology has been explained by forcing of flow in the weak lower crustal layer by surface processes non steady state erosion and cyclical loading by ice sheets and sea level fluctuations this study tests this interpretation by showing that analogous river terrace staircases are absent in archaean crust which lacks the weak lower crustal layer found elsewhere

stratigraphy and magnetic polarity of the high terrace remnants in the upper ohio and monongahela rivers in west virginia pennsylvania and ohio abstract a synthesis of previous work and new data on the stratigraphy of high terraces of the ohio and monongahela rivers upstream from parkersburg west virginia indicates a correspondence between terrace histories in the ancient teays and pittsburgh drainage basins four terraces are identified in each sediments of the lower three alluvial and slackwater terraces correlated with illinoian early wisconsin and late wisconsin glacial deposits have been traced along the modern ohio river through the former divide between the teays and pittsburgh basins sediments in the fourth terrace the highest well defined terrace in each basin were deposited in two ice dammed lakes separated by a divide near new martinsville west virginia some deposits of the highest slackwater terrace in both the teays and pittsburgh basins have reversed remanent magnetic polarity this and the stratigraphic succession in the two basins suggests that both were ponded during the same glaciation reversed polarity in these terrace sediments restricts the age of the first ice damming event for which stratigraphic evidence is well preserved to a pre illinoian early pleistocene glaciation prior to 788 000 yr ago in contrast slackwater sediments in the monongahela river valley upstream from an outwash gravel dam at the allegheny monongahela confluence have normal remanent magnetic polarity corroborating correlation with an illinoian ponding event

comparative precambrian stratigraphy and structure along the mid continent rift the mid continent rift is a geophysically identified tectonic structure that has been traced from kansas northeastward into the lake superior district a related arm has been identified by gravity as extending from eastern lake superior southeastward into the lower peninsula of michigan this rift is of precambrian keweenawan age and began developing approximately 1 1 b y b p for most of its extent this continental class rift system is buried below phanerozoic strata outcrops are found only in east central minnesota northwestern wisconsin and the upper peninsula of michigan the most accepted tectonic model of the mid continent rift is that of a central horst partly covered by clastic rocks bounded by high angle faulting and flanked by basins filled with clastic rocks this model was developed in conjunction with field studies in the southwestern lake superior area and generally has been adopted for minnesota iowa nebraska and kansas a comparable model has yet to be presented for the related arm extending into southern michigan in the lake superior outcrop belt the oldest recognized rifted rocks are layered basalts of middle keweenawan age overlying these basalts is an upper keweenawan thick sedimentary sequence composed of the oronto older and bayfield younger groups these sedimentary rocks are almost entirely clastic with texture ranging from conglomerate to shale mudstone rock colors are principally reds and browns with secondary shades of green and white the oronto group is more immature mineralogically and texturally and more complex structurally than the bayfield group the oronto group also is differentiated by one of its units the nonesuch formation which contains organic shales that bleed liquid hydrocarbons from subsurface fractures and vugs in a michigan copper mine conditions of eposition for both groups are closely allied with an aquatic continental environment specific paleogeography ranged from alluvial fan and plain to deltaic flood plain fluvial and lacustrine southwest and southeast of the lake superior outcrop belt stratigraphic relationships are known principally from fewer than a dozen significant wells drilled into the precambrian within the mid continent rift trend analysis of the proposed upper keweenawan red clastic sedimentary rock column within these wells suggests that the lake superior stratigraphy can be provisionally correlated throughout the mid continent rift trend

geophysical investigations and crustal structure of the north american midcontinent rift system abstract geophysical investigations have had a prominent role in studying the 1100 ma midcontinent rift system because of limited surface exposures and deep drilling of the rift rocks gravity and magnetic anomaly data delineate the rift system its central volcanic filled graben and overlying and adjacent post rift sedimentary basins and the major faults of the system over its 2000 km length in central north america crustal seismic studies indicate a high velocity crust that is thickened to as much as 55 km along the rift deeply penetrating seismic reflection data obtained across the rift show that the crust was thinned to less than one half of its original thickness during rifting and the present crust has been thickened by addition of up to a total of 30 km of mantle derived volcanic rocks within grabens and clastic sediments deposited in overlying sag basins as well as by intrusions into the crust and crustal underplating these data also confirm the occurrence of a post rift regional compressional event that locally caused broad folding of the rift rocks and reactivation of the graben normal faults as high angle reverse faults with vertical throws of several kilometers geophysical data indicate that the rifting event had a profound effect on the entire vertical range of the crust and that structures and thus the tectonic evolution are similar along the entire length of the rift

pliocene pleistocene incision of the green river kentucky determined from radioactive decay of cosmogenic 26al and 10be in mammoth cave sediments cosmogenic 26al and 10be in sediments washed into mammoth cave kentucky record the history of 3 5 m y of water table position governed by incision and aggradation of the green river a tributary of the ohio river upper levels of the cave formed during a period of slow river incision and were later filled with sediment due to river aggradation at 2 3 2 4 ma a brief surge of river incision ca 2 ma was followed by river stability and cave passage formation at a lower level rapid incision through 15 m of bedrock ca 1 5 ma was prompted by repositioning of the ohio river to its present course along an ice sheet margin renewed incision ca 1 2 ma and aggradation at 0 7 0 8 ma correlate with major ice advances in the ohio river basin measurements of 26al and 10be also indicate that sandstone capped uplands have maintained slow erosion rates of 2 7 m m y for the past 3 5 m y despite accelerated pleistocene river incision rates of 30 m m y

rivers and valleys of pennsylvania revisited abstract the 1889 paper by william morris davis on the rivers and valleys of pennsylvania is a landmark in the history of geomorphology it was in this manuscript that he set forth what came to be known as the davisian system of landscape it is important to understand that davis interpretation of landforms was restricted by the geologic paradigms of his day uniformitarianism was strongly entrenched and darwin s theory of evolution had become popularly accepted the concept of the landmass appalachia and then current theories on mountain building affected the approach that davis took in hypothesizing the origin and development of the folded appalachian drainage all of these geologic precepts influenced the formulation and explanation of his theories in his exposition he adapted synthesized and embellished on ideas he derived from fellow geologists such as gilbert dutton powell and mcgee a number of the concepts he proposed in the 1889 paper quickly became the bases for geomorphic studies by others the cycles of river erosion and landscape evolution and the peneplain here called base level erosion the cycle of erosion became the model for subsequent geomorphic analyses and peneplain hunting became a popular sport for geomorphologists davis hypothesis of the origin and development of pennsylvanian drainage stimulated subsequent discussion and further hypotheses by others in fact many of the later theories were refinements and or elaborations of ideas mentioned in this paper of davis he proposed the origin of the drainage as consequent streams then antecedence superposition headward extension of divides by piracy erosion along lines of weaknesses faults easily erodible beds through resistant ridges and normal fluvial erosion thus the hypotheses of regional superposition johnson extended consequents ruedemann consequents and local superposition meyerhoff and olmstead the utilization of structural weaknesses in development of transverse drainage thompson meyerhoff oberlander among others and migration of divides thompson all had been suggested by davis in 1889 although the concepts of erosion cycles and peneplaination have waned in popularity in recent geomorphic research the principles of formation of water and wind gaps headward migration of divides stream piracy and adjustment to streams to structure so clearly and minutely explained in his 1889 publication are still viable today

accelerated uplift resulting from anglian glacioisostatic rebound in the middle thames valley uk evidence from the river terrace record abstract a relatively simple analysis of the terraces of the middle thames valley reveals a complex sequence of responses to late anglian late middle pleistocene drainage disruption a decrease in the amounts of vertical incision separating the later post anglian terraces strongly suggests a major change in the rate of incision in the middle thames area in the post anglian a late anglian and early post anglian incision rate of 1 45 m ka 1 was quickly replaced by incision at a rate of 0 089 m ka 1 in the later post anglian period the lower incision rate of the later post anglian compares favourably with previous estimates of regional uplift two plausible explanations for the enhanced incision in the late anglian and early post anglian are recognized one related to ponding of the river by anglian ice and the other to glacio isostatic rebound in the latter case the mismatch between expected and actual heights of late anglian deposits would suggest glacio isostatic uplift of the order of 22 25 m

stratigraphy petrography and correlation of late cenozoic middle atlantic coastal plain deposits implications for late stage passive margin geologic evolution regional chronostratigraphic correlation of middle atlantic upper coastal plain and fall zone fluvial deposits long thought to represent the updip proximal facies of a well dated post oligocene marine sequence in the salisbury embayment remains incomplete in part because of the paucity of biostratigraphic data petrography based lithostratigraphic correlations provide an opportunity to extend age control present in downdip marine deposits updip to fluvial deposits thus establishing the means for a regional chronostratigraphic correlation previous stratigraphic studies in new jersey delmarva southern maryland virginia and the central appalachian piedmont are linked by a crucial sequence of fluvial deposits at the head of chesapeake bay here petrography based lithostratigraphic correlations demonstrate 1 late oligocene late miocene susquehanna river dominated polygenetic quartzose fluvial aggradation bryn mawr formation 2 pliocene heterolithic but quartz dominated fluvial terrace and alluvial fan deposition perryville formation 3 pliocene early pleistocene paleo delaware hudson river dominated lithic and feldspathic rich fluvial aggradation pensauken formation and 4 the initiation of estuarine conditions turkey point beds by early pleistocene time these results are synthesized to propose a new late cenozoic regional chronostratigraphic correlation and depositional history for the salisbury embayment the correlation elucidates a complex interaction between passive margin isostasy tectonics eustasy and sediment source

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

development of east asian summer monsoon environments in the late miocene radiolarian evidence from site 1143 of odp leg 184 abundant radiolarians are preserved in the relatively complete upper miocene section of odp site 1143 three radiolarian zones rn6 rn7 and rn8 are recognized on the basis of diartus petterssoni total range in rn6 6 7 ma variations in the abundance of radiolarians especially pyloniid forms radiolarian flux and species diversity are good proxies of upwelling which similar to today s was likely driven by summer monsoons these radiolarian paleomonsoon proxies indicate that the east asian summer monsoon first initiated close to the middle late miocene boundary at similar to 12 11 ma and reached a maximum strength at similar to 8 24 ma therefore the initiation of the east asian summer monsoon was likely earlier than the first indian monsoon which appeared similar to 8 myr ago c 2003 elsevier b v all rights reserved

early pleistocene glacial lake lesley west branch susquehanna river valley central pennsylvania abstract laurentide glaciers extended into north central pennsylvania repeatedly during at least the last 2 million years early pleistocene glaciation extended farther south into central pennsylvania than any subsequent glaciation reaching the west branch susquehanna river wbsr valley early pleistocene ice dammed the northeast flowing west branch susquehanna river at williamsport forming glacial lake lesley a 100 km long proglacial lake in this paper we present compelling evidence for the lake and its age maximum lake volume 100 km 3 was controlled by the elevation of the lowest drainage divide 340 m above sea level at dix pennsylvania stratified deposits at mcelhattan and linden are used to reconstruct depositional environments in glacial lake lesley a sedimentary section 40 m thick at mcelhattan fines upward from crossbedded sand to fine wavy to horizontally laminated clay consistent with lake deepening and increasing distance from the sediment source with time at linden isolated cobbles interpreted as dropstones locally deform glacio lacustrine sediment we use paleomagnetism as an age correlation tool in the wbsr valley to correlate contemporaneous glaciofluvial and proglacial lacustrine sediments reversed remanent polarity in finely laminated lacustrine clay and silt at mcelhattan i 20 4 d 146 7 95 17 7 and in interbedded silt and sand at linden i 55 3 d 175 2 95 74 6 probably corresponds to the latter part of the matuyama reversed polarity chron indicating an age between 770 and 970 ka at mcelhattan a diamicton deformed the finely laminated silt and clay by loading and partial fluidization during or soon after lake drainage as a result the deformed clay at mcelhattan lacks discrete bedding and records a different characteristic remanent magnetism from underlying undeformed beds this difference indicates that the characteristic remanent magnetism is detrital an electrical resistivity survey and drill borings define a buried bedrock channel at bald eagle near the drainage divide that is the proposed spillway for glacial lake lesley the highest terrace at bald eagle qt1 be was truncated by the spillway channel age of qt1 be is estimated as at least middle middle pleistocene to early pleistocene by correlation of soil physical properties on qt1 be to soil chronosequences developed for susquehanna river alluvial terraces further downstream this age is generally consistent with the age estimated from paleomagnetism

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

fluvial terraces of the lower susquehanna river abstract fluvial terraces of the lower susquehanna river offer a unique opportunity to investigate the late stage geologic and geomorphic evolution of the u s atlantic passive margin petrography and elevation distinguish and provide a basis for correlation of two groups of terraces the upland terraces and lower terraces through the piedmont newark basin and great valley downstream correlation to dated upper coastal plain and fall zone fluvial deposits relative weathering and soil profile development characteristics establish terrace age upland terraces tg1 tg2 and tg3 middle to late miocene strath terraces 80 to 140 m above the present channel occur only along the piedmont reach they are underlain by unstratified texturally mature quartz dominated roundstone diamictons lower terraces qtg qt1 qt6 pliocene and pleistocene strath and thin aggradational terraces within 45 m of the present channel are underlain by stratified and unstratified texturally and compositionally immature sand gravel and pebbly silt terrace age and longitudinal profiles suggest complex interactions among relative base level long term flexural isostatic processes climate and river grade our model for terrace genesis requires the susquehanna river to attain and maintain a characteristics graded longitudinal profile over graded time for the u s atlantic margin we propose that straths are continually cut along this graded profile during periods of relative base level stability achieved by slow steady isostatic continental uplift acting in concert with eustatic rise change in an external modulating factor such as eustatic fall or climate change results in fluvial incision and subsequent genesis of strath terraces longitudinal profiles of lower susquehanna river terraces which converge at the river mouth diverge through the piedmont and reconverge north of the piedmont contrast with their hypothesized original concave up profiles progressive and cumulative flexural upwarping of the atlantic margin accounts for terrace profile deformation suggesting flexural isostasy as a first order regional deformation mechanism these results offer new interpretations of terrace age correlation and geologic significance that require modification of previous studies suggesting uplifted or anticlinically warped peneplains on the u s atlantic margin

dependence of active normal fault dips on lower crustal flow regimes two key questions are raised by the presence in the basin and range province of subhorizontal normal faults which were active in and around the miocene first how did they develop when their existence seems to be precluded by elementary rock mechanics arguments second if they did slip in the recent geological past why do normal faults now active in the brittle upper crust have steeper dips both in the western usa and elsewhere one may now answer both questions by considering the stress field in regions where the isostatic response during extension involves horizontal flow in the plastic lower crust this stress tensor will have inclined principal axes making it possible for normal faults to form with either very steep or subhorizontal dips depending on the sense of flow this can be controlled by environmental conditions which influence rates of hanging wall sedimentation and footwall erosion and thus determine lateral variations in lithostatic pressure in the lower crust regional scale lateral variations in the geothermal gradient caused by subduction can also influence lower crustal flow regimes in adjacent zones of continental extension enabling extension to occur on low angle normal faults dipping away from the active continental margin

early proterozoic central plains orogen a major buried structure in the north central united states a major early proterozoic orogen central plains more than 1000 km long and at least 500 km wide has been delineated in the subsurface of nebraska kansas and missouri as a result of a new compilation of precambrian basement drill data in the northern midcontinent the orogen is composed of metamorphic and granitoid rocks in the ringe 1 63 1 80 ga and it is interpreted on the basis of isotopic ages rock types and structure as reflected by magnetic and gravity anomalies as being the eastward extension of the early proterozoic foldbelt exposed in basement uplifts in colorado and southeastern wyoming it truncates the southern margin of the superior archean craton and its marginal early proterozoic orogens the penokean 1 83 1 90 ga and the trans hudson 1 85 1 95 ga the pattern of intersecting proterozoic mobile belts marginal to archean cratons is comparable to that in other continents such as western australia and southern africa

uplift mechanisms of pipes buried in sand reliable design against upheaval buckling of offshore pipelines requires the uplift response to be predicted this paper describes a model scale investigation into the mechanisms by which uplift resistance is mobilized in silica sand and illustrates how the observed mechanisms are captured in prediction models a novel image based deformation measurement technique has been used the results show that peak uplift resistance is mobilized through the formation of an inverted trapezoidal block bounded by a pair of distributed shear zones the inclination of the shear zone is dependent on the soil density and therefore dilatancy after peak resistance shear bands form and softening behavior is observed at large pipe displacements either a combination of a vertical sliding block mechanism and a flow around mechanism near the pipe or a localized flow around mechanism without surface heave is observed depending on the soil density and particle size

early paleozoic transform margin structure beneath the mississippi coastal plain southeast united states a geophysical transect across the central gulf of mexico coastal plain shows that the early paleozoic continental margin of southern laurentia is preserved in a nearly pristine state beneath younger strata that were emplaced during the late paleozoic ouachita orogeny and formation of the modern gulf of mexico coastal plain the thickness of the crystalline crust decreases abruptly across the margin over a distance of 50 km from 35 km beneath the black warrior foreland basin to 10 km beneath the ouachita fold and thrust belt this abrupt decrease in crustal thickness is similar to modern transform margins but very different from most rifted margins which display much more gradual transitions in crustal thickness the geophysical data indicate an absence of synrift intrusive and volcanic rocks underplated mafic rocks at the base of the crust and abnormally thick oceanic crust adjacent to the margin the lack of these features is also characteristic of modern transform margins combined with transects across the margin farther west the data confirm previous suggestions that the central gulf of mexico coastal plain overlies an 800 km long transform segment of the late proterozoic early paleozoic southern laurentian continental margin that extends continuously from western arkansas to southeast alabama

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

physical modelling to demonstrate the feasibility of screw piles for offshore jacket supported wind energy structures screw piles potentially offer quieter installation and enhanced axial tensile capacity over straight shafted driven piles as such they have been suggested as a possible foundation solution for of

late cenozoic uplift of the eastern united states revealed by fluvial sequences of the susquehanna and ohio systems coupling between surface processes and lower crustal flow abstract fluvial and karstic data sets indicating late cenozoic surface uplift in the eastern united states are modelled for the first time using a technique incorporating coupling between surface processes and flow in the lower continental crust which has been extensively used for modelling similar data sets elsewhere in the world notably in europe distinct phases of lower crustal flow forcing starting in the early middle miocene late pliocene and late early pleistocene are evident as observed elsewhere and relate to combinations of cyclic surface loading by sea level variations and ice loads and to variations in regional erosion rates as elsewhere however the detailed uplift histories inferred are rather different from those indicated in many other regions notably europe primarily because of different properties of the crust in particular in the late proterozoic phanerozoic crust of the appalachians the mobile lower crustal layer seems to be relatively thick causing a prolonged uplift response for each phase of lower crustal flow forcing whereas in the early proterozoic crust of the yavapai crustal province farther west underlain by a thick basal mafic layer this mobile layer is much thinner leading to a very different response consisting of abrupt alternations of uplift and subsidence as is also observed in other regions of early proterozoic crust another important difference relative to western and central europe is the much smaller number of terraces in the eastern us rivers that have been studied the general applicability of this type of physics based modelling technique is thus confirmed

mantle temperature and lithospheric thinning beneath the midcontinent rift system evidence from magmatism and subsidence the tectono magmatic history of the midcontinent rift system can be explained by the presence of a mantle plume bringing elevated temperature mantle beneath the rift system at about 1110 ma huge volumes of extrusive and intrusive igneous rocks were generated as abnormally hot mantle decompressed beneath the lithospheric rift geochemical and isotopic data from the keweenawan volcanics show that the earliest melts were derived from small degree melting of primitive plume mantle coupled with enriched metasomatic melts derived from the continental lithosphere as rifting progressed the main bulk of the volcanics was generated primarily from the plume mantle with the melting starting at depths of about 120 km and extending to as shallow as the base of the stretched lithosphere at 45 km depth elevated mantle temperatures of 1500 1560 c approximately 150 200 c above normal are inferred from the rare earth element concentrations in the volcanic rocks further constraints on the mantle temperature come f

re evaluation of extension across the pearl river mouth basin south china sea implications for continental lithosphere deformation mechanisms abstract the tertiary pearl river mouth basin in the south china sea is one of relatively few localities where independent estimates of extension from upper crustal normal faulting crustal thinning and subsidence have been compared previous work indicates that these methods all support extension factor 1 8 for this basin however the estimate from faulting used the controversial rigid domino method whereas summing normal fault heaves gives only 1 3 instead this study pursues the possibility that the true value for this basin is 1 3 and the published estimates of extension from subsidence and crustal thinning are exaggerated because they do not take account of outflow of lower crustal material from beneath this basin such outward channel flow will occur when the lithostatic pressure at the base of the brittle upper crust is greater beneath a basin than beneath its surroundings in response to such a pressure gradient material lost from beneath this basin has probably flowed to beneath the adjacent chinese landmass where it isostatically compensates the erosion that has supplied much of the basin s sediment

flow in the lower continental crust as a mechanism for the quaternary uplift of south east england constraints from the thames terrace record abstract the sequence of terraces of the river thames in south east england has been shown to date from the early pleistocene onwards and to provide an indication of the quaternary uplift history of the region using this evidence supplemented by altitudes of pliocene and early pleistocene marine sediments we have determined the pliocene and quaternary uplift histories of five representative localities clacton colchester and dartford for the lower thames and cookham and reading for the middle thames these uplift histories have been modelled using a physics based technique which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the earth s surface our results suggest that the late pliocene and early pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at 3 1 ma which marked the start of upland glaciation elsewhere in europe the later increase in uplift rates in the middle pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage ois 22 at 0 87 ma dartford cookham and reading in the interior of south east england are all shown to have begun to uplift quite rapidly at rates of up to 0 1 mm a 1 following the start of forcing at 3 1 ma they have since uplifted by distances which increase gradually westward from 200 to 250 m of which a uniform 70 m has occurred since ois 22 at 0 87 ma in contrast clacton and colchester near the present north sea coastline experienced slow subsidence until the late early pleistocene but have nonetheless uplifted since ois 22 by similar distances to the other sites

palynology of the bryn mawr formation miocene insights on the age and genesis of middle atlantic margin fluvial deposits abstract the ages of fluvial deposits at the head of chesapeake bay thought to be the updip chronostratigraphic equivalents of a well dated late oligocene to quaternary marine sequence in the salisbury embayment are poorly known we present data regarding a new occurrence of a palynoflora recovered from the bryn mawr formation in cecil county maryland the floral assemblage for the bryn mawr formation includes at least 40 taxa at the generic level where quercus cupuliferae ilex carya taxodium and pinus are important elements most of the taxa identified from the bryn mawr formation palynoflora are extant and occur within the modern middle atlantic coastal plain however several important taxa such as alangium engelhardia sciadopitys tricolporopollenites sp and cupuliferoidaepollenites sp are at present either extinct or exotic to the middle atlantic coastal plain comparison of the bryn mawr formation palynoflora to well dated marine deposits of the salisbury embayment suggests a late middle to early late miocene age late serravallian early tortonian for bryn mawr formation phase 2 deposition supporting previously proposed genetic links to the marine deposits of the choptank formation in the subsurface of the delmarva peninsula relative abundances of common extant taxa such as quercus carya pinus and nap the total non arboreal pollen vary considerably throughout late cenozoic deposits of the middle atlantic coastal plain we present data for common extant taxa in a ternary diagram to define discrete palynofacies that discriminate among middle miocene late miocene pliocene and pleistocene palynofloras these results show that relative abunances of common easily identifiable extant pollen may be as diagnostic as exotic taxa in assigning ages to middle atlantic coastal plain deposits the bryn mawr formation palynoflora like other middle to late miocene palynofloras of the middle atlantic coastal plain suggests terrestrial climatic cooling in the larger temporal scale of climate change throughout the cenozoic this change in miocene climate is one of three major events that may have had a significant impact on the rate of sediment yield from the appalachians as recorded in the volume of offshore basin sediments

west antarctic ice sheet grounding events on the ross sea outer continental shelf during the middle miocene abstract new seismic stratigraphic analysis of the ross sea continental shelf suggests that there were a at least five shelf wide grounding events of the west antarctic ice sheet wais during the middle miocene although the number of wais grounding events generally matches the number of extreme 18 o enrichments and eustatic lowstands these results do not support the long standing assumption that west antarctica was substantially ice free instead seismic stratigraphic evidence from the ross sea shelf documents waxing and waning of a well developed wais in the marine environment at least on the pacific sector of the west antarctic continental shelf

correlation of miocene 18 12 ma sequence boundaries in central japan to major antarctic glaciation events abstract using magnetostratigraphy constrained by biostratigraphy and radiometric dating we have investigated whether early to early middle miocene 18 12 ma sequence boundaries in central japan were synchronous with major antarctic glaciation events we have correlated miocene sequence boundaries across three sedimentary basins across central japan representing backarc basin yatsuo area intra arc basin mizunami area and forearc basin kakegawa area environments these boundaries were formed during four time intervals designated as zones jmi1 to jmi4 zone jmi1 correlates with chron c5dn 17 61 17 27 ma zone jmi2 correlates with chron c5br 16 01 15 15 ma zone jmi3 correlates with subchron c5bn1r 15 03 14 88 ma and zone jmi4 ranges from 14 88 to 12 3 1 9 ma the age range of japanese miocene jmi zones represents the range of uncertainty error limits in the age of individual sequence boundary formation we have correlated zones jmi1 3 to positive shifts of 18o in the deep sea cores from odp leg 120 site 747 southern indian ocean where magnetostratigraphic data are available suggesting that the sequence boundaries of zones jmi1 3 were formed by eustatic sea level falls during major antarctic ice sheet developments zone jmi4 age constraints are too poor to test correlation with odp site 747

stratigraphy and correlation of glacial deposits from indiana to new york and new jersey the quaternary glacial history of part of the region from indiana to new york and new jersey fig 1 was outlined in three summaries prepared for the vii congress of the international union for quaternary research wayne and zumberge 1965 goldthwait et al 1965 muller 1965 subsequent regional summaries by white 1969 1982 white et al 1969 ray 1974 and coates 1976 reviewed the entire succession of tills in parts of kentucky northeastern ohio pennsylvania and new york other syntheses and discussions by dreimanis and goldthwait 1973 evenson and dreimanis 1976 dreimanis 1977 fullerton 1980 mayewski etal 1981 and mickelson et al 1983 were concerned only with late wisconsin tills the glacial history of the region fig 2 and chart 1 is much more complex than was assumed in 1965 much of the new information is in unpublished theses and dissertations and other publications of limited distribution and it has not been summarized correlations in chart 1 are based primarily on stratigraphic relationships of tills and paleosols and secondarily on radiometric ages paleomagnetic polarity data and relativeage data this summary serves as an expanded explanation of chart 1 glacial events are discussed within a framework of time divisions from older to younger and by glacial lobes as shown in chart 1 paleomagnetic polarity data in chart 1 are from harrison and terasmae 1961 bleuer 1976 and pers commun johnson 1976 this volume and pers commun hoyer 1977 1983 and pers commun bonnett et al 1978 and teller and last 1981 sources of data related to named tills in indiana ohio pennsylvania new york and new jersey are listed in appendix 1 the term glacial lobe here is applied both to a regional physiographically controlled pattern of ice dispersal and to the geographic region influenced by such movement huron erie lobe glaciation includes ice movement from the georgian bay region ontario into the lake erie basin as well as ice movement through the lake huron basin into the lake erie basin fig 3 illinoian and pre illinoian tills throughout the region have not been well studied and they have no radio

evolution of cenozoic seaways in the circum antarctic region abstract a complete circum antarctic seaway did not open until both the south tasman rise cleared the oates land coast of east antarctica and drake passage opened between the southern tip of south america and the northern end of the antarctic peninsula major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the south tasman rise and antarctica as very close to the eocene oligocene boundary with an unrestricted opening deeper than 2000 m dating from 32 ma timing of the opening of drake passage is more circumstantial because the exact motions of certain micro continental fragments are not known the motion of africa with respect to south america as well as the motion of east antarctica with respect to africa are well constrained for the cenozoic these major plate motions are used with the reasonable assumption of no cenozoic motion of the antarctic peninsula with respect to east antarctica to constrain the location of the antarctic peninsula with respect to the southern tip of south america for the critical period of late eocene to late oligocene uncertainty of motion of the south georgia and south orkney microcontinents and other possible continental fragments make an exact time for opening of drake passage difficult to ascertain even so the early oligocene position of the antarctic peninsula with respect to south america requires a through going deep water seaway to have been open at drake passage prior to 28 ma even given the unconstrained motion of various high standing crustal fragments in the scotia sea with reasonable assumptions concerning motion of the crustal fragments in the western and central scotia sea it is likely that drake passage or passage through powell basin was open to deep water circulation by 31 2 ma

improving the time control of the subboreal subatlantic transition in a czech peat sequence by 14c wiggle matching to achieve an optimal time control for a late subboreal to early subatlantic peat sequence from pancavska louka in the czech republic different strategies are applied to convert a series of radiocarbon dates into a calendar time scale the methods of selection and preparation of the samples for ams 14c dating are presented the results of calibrating single radiocarbon dates are compared with a 14c wiggle match strategy as the accumulation rate of the peat was not constant the concentrations of arboreal pollen are used to estimate the accumulation rate changes and to correct for these changes the resulting time control represents the best solution for this peat sequence with the methods currently available

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

structure and evolution of the central gulf of mexico continental margin and coastal plain southeast united states as in many continental margins mesozoic rifting in the gulf of mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin unlike the situation in most other margins however extension in the gulf of mexico did not involve widespread reactivation of these older tectonic features this difference may be related to the unusual facts that 1 the antecedent passive continental margin was a transform rather than a rift margin and 2 the prior orogeny did not substantially thicken the crust in order to characterize the interaction between mesozoic rifting and prior tectonic events two geophysical transects were constructed across the central gulf of mexico coastal plain and continental shelf the transects show that the early paleozoic passive continental margin buried beneath the late paleozoic ouachita orogen was little affected by compressional tectonism or mesozoic extension during opening of the gulf of mexico the thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km consistent with previous interpretations that this was a transform margin the ouachita fold and thrust belt is shown to be a thin skinned doubly vergent orogen that formed above a well preserved southward dipping subduction system relict cambrian oceanic crust may exist beneath the southern part of the orogen but its presence is not required by the data the thin crust and shallow mantle in the ouachita suture created a zone of relatively high strength that acted as a barrier to mesozoic extension which is restricted to regions south of the orogen extension was initially distributed over a broad area that included the mississippi interior salt basin and regions south of the wiggins arch extension became progressively more focused south of the wiggins arch with time culminating in the onset of seafloor spreading beneath the modern continental rise mesozoic extension factors are 1 4 1 9 beneath the mississippi interior salt basin 2 9 immediately south of the wiggins arch and 4 adjacent to the oldest oceanic crust in the central gulf of mexico

a finite element approach for determining the full load displacement relationship of axially loaded shallow screw anchors incorporating installation effects screw anchors have been recognised as an innovative solution to support offshore jacket structures and floating systems due to their low noise installation and potential enhanced uplift capacity

nd and sr isotope chronostratigraphy of colorado plateau lithosphere implications for magmatic and tectonic underplating of the continental crust nd sr isotopes and major and trace element abundances were measured in lower and upper crustal xenoliths carried in tertiary minettes and kimberlitic diatremes of the colorado plateau the objective was to establish the vertical distribution of mantle extraction ages for an undisturbed precambrian crustal province characterized by normal thickness and low cratonic heat flow and to thereby evaluate the importance of magmatic or tectonic underplating in crustal growth mid proterozoic age 1 7 2 0 ga material is found at all levels of the crust although mafic granulites and amphibolites have major and trace element compositions compatible with an origin as magmatically underplated material nd model ages do not indicate that there has been significant mantle contribution to the lower crust by igneous processes such as magmatic underplating since the main crust forming event ca 1 85 ga ago the meta igneous lower crustal xenoliths have relatively radiogenic nd isotopic compositions and unradiogenic sr compositions there is little variability in nd model ages in spite of large variability in sm nd high and variable sm nd ratios were therefore established early in the history of the protolith during igneous or metamorphic processes coincident with or shortly after extraction from the mantle metapelitic xenoliths tectonically emplaced into the lower crust have the same proterozoic model ages as meta igneous parts of the lower crust these paragneisses are probably arc associated sediments that were underthrust during terrane accretion in the proterozoic the isotopic data indicate that eclogite xenoliths are likely to represent proterozoic lithosphere rather than subducted mesozoic morb as previously proposed a number of the eclogite xenoliths have experienced a metasomatic event which introduced lree sio2 and na2o and shifted the nd and sr isotopic compositions the least altered eclogite xenoliths have major and trace element and radiogenic nd isotopic compositions similar to those of other proterozoic mafic lower crustal xenoliths a more plausible protolith for the eclogites is proterozoic lithosphere that was metamorphosed to eclogite facies conditions either during precambrian continental assembly or in more recent times

quaternary soil chronosequences on terraces of the susquehanna river pennsylvania abstract susquehanna river terraces are used to establish time lines along a 150 km reach of the river from the lower piedmont to the edge of the appalachian plateau this is achieved by generating soil chronosequences at two locations marietta pa in the lower piedmont and muncy pa near the glacial border on the boundary between the valley and ridge province and the appalachian plateau these sites preserve the most complete record of fluvial incision on the susquehanna river with flights of seven quaternary terraces ranging in elevation from 3 m to 51 m above the modern river soil characteristics used to develop the soil chronosequences include complexity of horizonization thickness of b horizon clay content of b horizon soil color cbd extractable fe al and mn total extractable fe and clay mineralogy terrace age constraints are based on soil development correlation to regional glacial stratigraphy correlation to dated fluvial and glaciofluvial deposits and by paleomagnetic analysis of sediments terrace ages at the muncy site range from modern

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

pliocene palaeotemperature reconstruction for the southern north sea based on ostracoda abstract the development of a large northeastern atlantic shelf ostracod database has confirmed that an intrinsic relationship exists between watermass temperature and the spatial latitudinal distribution of benthonic shelf ostracoda a second pliocene ostracod database using assemblages from four boreholes in the netherlands and a number of localities from the east anglian neogene succession has also been constructed a quantitative method of modern analogues and the squared chord distance dissimilarity coefficient has been employed as a means of calculating the level of similarity between recent and neogene assemblages and therefore to aid in the reconstruction of palaeotemperatures in the southern north sea basin during the pliocene the results in the form of contoured dissimilarity values indicate the presence of at least seven palaeoceanographical climatic phases between ca 5 2 and 1 6 ma bp an early pliocene cooling phase ecozone a in which the fauna is dominated by the cryophilic species palmenella limicola norman elofsonella concinna jones robertsonites tuberculatus sars neomonoceratina tsurugasakensis tabuki and acanthocythereis dunelmensis norman supervenes a period of stable subtropical conditions in the miocene a mid pliocene warming phase ecozone b which has been documented throughout the north atlantic can be recognized in the faunal composition of the sublittoral ostracod assemblages of both the netherlands and east anglia a hiatus between the coralline and waltonian crags is thought to be associated with a deterioration in climatic conditions recent analogues to the netherlands faunas of ecozone c first phase late pliocene cooling ca 2 9 ma bp indicate a decrease of approximately 5 6 c in mean summer surface temperatures a return to elevated temperatures of a mauritanian aspect can be seen in the fauna of the fa2 zone and waltonian crag this amelioration of climate occurred prior to the praetiglian cold phase second phase late pliocene cooling ca 2 4 ma bp which again saw the reintroduction of cryophilic species including baffinicythere howei hazel fimarchinella logani brady crosskey and robertson and hemicythere emarginata sars into the southern north sea during the newbournian and butleyan stages the final phase of the latest pliocene third phase late pliocene cooling is only documented in the ostracod fauna of the norwich crag evidence in the covariance of loxoconchidae and norwegian provincial cryophilic species indicates that the polar front may have been as much as 2000 km further south during the deposition of the chillesford sand member norwich crag fm ca 2 0 1 6 ma bp

mechanistic solutions to the opening of the gulf of mexico two mechanistic models which are unlike the traditional plate tectonic landfill models used for most proposed pangea reconstructions of the yucatan block relate the mesozoic opening of the gulf of mexico directly to the movement of the north and south american plates 1 a previous piggyback model in which yucatan moves with south america out of the western gulf and 2 a new edge driven model in which the motion of the yucatan block is caused by forces applied to its margins by the movement of the north and south american plates in the second model yucatan moves out of the northern gulf of mexico as a gear or roller bearing on the basis of magnetic edge anomalies around the gulf this edge driven model predicts that from the bathonian to tithonian 170 to 150 ma yucatan was rotated 60 counterclockwise as a rigid block between north and south america with rift propagation and extension occurring simultaneously in the gulf of mexico and yucatan basin

quimby iowa scientific drill hole definition of precambrian crustal features in northwestern iowa geophysical data and sparse subsurface samples suggest that the spirit lake trend slt in the aeromagnetic fabric of northwest iowa is the southern boundary of the archean superior craton several small diameter positive aeromagnetic anomalies south of the slt have been interpreted as middle proterozoic anorogenic magnetite bearing granites that intruded juvenile early proterozoic crust a scientific drill hole 609 m deep was drilled into a 1200 gamma aeromagnetic anomaly near quimby iowa to test these interpretations precambrian basement was reached at a depth of 510 m and 99 m of undeformed megacrystic magnetite bearing granite core was collected petrographic and chemical data are consistent with derivation of the granite magma by melting of preexisting tonalitic continental crust a u pb zircon age of 1433 4 ma shows that this granite is part of the older anorogenic granite rhyolite suite of the united states sm nd data yield a depleted mantle separation age of 1860 ma which confirms that the source for the pluton magma was early proterozoic crust all data are consistent with the hypothesis that the aeromagnetic anomalies are caused by middle proterozoic anorogenic plutons and with interpretation of the slt as an archean early proterozoic crustal boundary

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression