oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

multidecadal oceanographic changes in the western pacific detected through high resolution bomb derived radiocarbon measurements on corals high resolution measurements of radiocarbon 14c in corals can be used to reconstruct past variability in ocean conditions here we report seasonal 14c changes in coral from ishigaki island japan and compare with previously reported data from palau and guam our data clearly indicate a significant increase in 14c from 1947 to 1998 related to atmospheric nuclear bomb testing the three early 14c spikes related to the atmospheric nuclear bomb tests in the us proving grounds at bikini and enewerak atoll conducted in 1954 1956 and 1958 were detected from the ishigaki coral after 1976 variability in the mindanao dome region related to north equatorial current nec bifurcation latitude migration affected the 14c difference between palau and guam whereas the difference between ishigaki and guam was not correlated with the bifurcation latitude the 14c difference between ishigaki and guam may be due to mesoscale eddies in the kuroshio area on the decadal scale the northward shift of nec bifurcation latitude after 1976 the year as known as pacific decadal oscillation regime shift from negative to positive was concurrent with the abundant westward propagating mesoscale eddies in the subtropical countercurrent region and stronger kuroshio transport off the east taiwan which may be represented by a smaller 14c difference between ishigaki and guam after 1976

quaternary glaciations in the northern andes venezuela colombia and ecuador abstract the nature and distribution of glacial drift in the high andes of venezuela colombia and ecuador suggest that deposits of only the last two quaternary glaciations isotope stages 6 and 4 2 are present the penultimate glaciation in ecuador may be represented by deeply weathered drift that is beyond the range of radiocarbon dating in colombia and venezuela subdued moraines covered with loess may be of equivalent age in places this drift extends 1000 m lower in altitude than the limits of the last glaciation which comonly reach 3400 3600 m radiocarbon dated organic deposits 33 43 ka bp lying between tills composing superposed terminal moraines suggest that andean glaciers may have been as extensive during isotope stage 4 as during isotope stage 2 a relatively long interstadial from 43 33 ka bp preceded the glacier advance that culminated during the interval ca 28 15 ka bp two late glacial stadials are marked by moraine complexes at 3900 4200 m altitude they are partly constrained by radiocarbon ages of 12 9 ka bp and 12 10 ka bp moraines apparently deposited during neoglacial advances of the last ca 5 ka lie in front of most of the glaciers remaining in the northern andes

energetic subthermocline currents observed east of mindanao abstract two cruises of the jamstec ship kaiyo during october 1999 and september 2000 included lowered acoustic doppler current profiler adcp measurements to 2000 m depth on zonal sections extending east from the mindanao coast on the second cruise the lowered adcp profiles were augmented by profiles to 1000 m from a 38 khz shipboard adcp all zonal ladcp sections 7 n 8 10 showed southward flow along the coast extending to at least 2000 m depth although the mindanao current in the upper 500 m forms a continuous narrow stream along the coast the deeper southward flow appears to be part of a set of subthermocline eddies within 300 km of the coast northward flow was found 100 200 km offshore during both cruises currents mapped by the shipboard adcp on the second cruise indicate that cyclonic eddies were centered near 7 5 n 128 e and 10 2 n 127 e maximum speeds of 0 6 m s 1 were observed at 800 m depth on the 10 n section and speeds of 0 2 0 3 m s 1 were found below 1500 m on all sections

process of slip surface development and formation of slip surface clay in landslides in tertiary volcanic rocks japan abstract once landslide movement has been initiated the sliding mass tends to move toward a more stable position however landslides that have occurred in some tertiary volcanic rocks in japan show recurrent movement a possible reason for this behavior is that the mineral composition and properties of slip surface materials results in better lubrication along the slip surface as movement continues in order to determine the causes five landslides in japanese tertiary volcanics with different movement histories were studied based on geological investigation the results presented in this paper were obtained by studying the development process and formation of slip surfaces and clays in landslides in these volcanics for rocks of similar types and mineralogies the clay content of slip surface materials can be directly related to the displacement and history of slide movement this study indicates that the type of slip surface ranges from 1 striation type showing only striations on bedrock without clay to 2 brecciated type clayey breccia 3 mylonite type clay with breccia and to 4 clay type clay without breccia if the slip surface occurs in tuff or tuffaceous materials and is subjected to increasing slide movement the smectite content in the slip surface clay increases while the silicate mineral content decreases furthermore the smectite content is observed to increase within the same landslide from the head to the toe portion of the landslide direction of groundwater flow the groundwater along the slip surface above the impervious zone contains an increased concentration of ca ions as the concentration of hco3 ions exceeds 40 mg l an environment is created that promotes the formation of smectite this process indicates that there is an active ion exchange within the groundwater near the slip surface that forms smectite thus the formation of smectite in the slip surface requires the presence of tuff and a sufficient concentration of hco3 ions in the groundwater the study results presented here indicate that frictional resistance decreases as clay content increases the reason for repeated movement of japanese landslides in tertiary tuffs or tuffaceous rocks at or in the immediate vicinity of the slip surface is attributed to 1 an increase in clay materials along the slip surface as the slide movement is repeated and 2 the presence of groundwater that promotes the formation of smectite as is commonly known smectite is one of the clay minerals that has lowest frictional resistance

a new paradigm for the north pacific subthermocline low latitude western boundary current system abstractsubthermocline western boundary circulation along the low latitude north pacific ocean 2 25 n is investigated by using profiling float and historical ctd expendable ctd xctd data and by analyzing an eddy resolving global ogcm output in contrast to the existing paradigm depicting it as a reversed pattern of the wind driven circulation above the ventilated thermocline i e depth 26 8 the subthermocline western boundary circulation is found to comprise two components governed by distinct dynamical processes for meridional scales shorter than 400 km the boundary flows along the philippine coast exhibit convergent patterns near 7 10 13 and 18 n respectively these short scale boundary flows are driven by the subthermocline eastward zonal jets that exist coherently across the interior north pacific basin and are generated by the triad instability of wind forced annual baroclinic rossby waves for meridional scales longer than 400 km a time mean mindanao undercurrent muc is obs

determination of slip sense along a fault in an unlithified sediment abstract it is usually difficult to measure slip sense along a fault in unlithified sediments due to the lack of mesoscopic indicators such as slickenlines in this paper scanning electron microscope sem images of fault surfaces in mudstone at the sandstone mudstone contacts are used for measuring the microscopic slickenlines formed by the scratching of sand grains the lineations are subparallel to the presumed slip direction deduced from a conjugate fault set therefore even in the case of no mesoscopic slickenlines a microscopic scratching by a sand grain on the fault surface where sandstone and mudstone are juxtaposed by the fault is useful as an indicator of slip sense along a fault in sediments lithified subsequent to faulting

evidence for an increase in cosmogenic 10be during a geomagnetic reversal reversals in the geomagnetic field which occur every few hundred thousand years represent a dramatic change in the earth s environment although there is no satisfactory theory for such reversals it is generally accepted that the dipole field intensity decreases to 20 of its normal value for a few thousand years during the change in direction1 because the galactic and solar cosmic rays which impinge on the earth s atmosphere are charged a significant fraction about half of them are deflected by the geomagnetic field2 at the time of a reversal this magnetic shielding is greatly reduced and it has been suggested that the increased flux of high energy particles could have effects on evolutionary3 or climatic4 processes for example the statistically significant coincidence in levels of some marine faunal extinctions and reversal boundaries in ocean sediments5 could be caused directly or indirectly by the decreased geomagnetic intensity during the reversal we report here evidence in marine sediments for an increase in cosmogenic 10be production in the earth s atmosphere during the brunhes matuyama reversal 730 000 yr ago in addition to confirming an increase in cosmogenic isotope production the results provide information on the magnitude and duration of the geomagnetic intensity decrease during such an event and the depth at which rmanent magnetism is acquired in marine sediments

slickenside kinematic indicators abstract a new classification of slickenside kinematic indicators is presented based on 61 criteria these slickensides have been subdivided into eleven major groups v or crescentic markings steps fractures trains of inclined planar structures trailed material asymmetric elevations deformed elements mineralogical crystallographic orientations asymmetric plan view features asymmetric cavities and asymmetric folds this classification constitutes a useful tool for geologists interested in the determination of the shear sense in fault surfaces bearing slickensides examples of application of this classification to natural fault surfaces at different scales are presented

on the formation dynamics of the north equatorial undercurrent abstractbased on a physics oriented modeling study we investigate the underlying forcing processes of the north equatorial undercurrent neuc made up of large scale 90 and mesoscale 10 c

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

paleoelevation records from lipid biomarkers application to the tropical andes new results from two novel lipid biomarker based proxies help to constrain the late cenozoic surface elevation history of the eastern cordillera in the tropical northern andes of colombia previous well known studies have suggested rapid latest miocene pliocene 6 3 ma uplift on the basis of an abrupt shift in pollen species assemblages within sedimentary basin fill of the elevated bogota plateau from resampling of these original study localities we provide a revised chronology based on magnetic polarity stratigraphy and we evaluate paleotemperatures using the mbt cbt indices methylation of branched tetraethers cyclization of branched tetraethers and hydrogen isotopic composition d of leaf waxes as two independent proxies of past surface elevation reconstructed paleotemperatures from the mbt cbt proxy show a more gradual cooling trend from ca 7 6 ma to present consistent with less than 1000 m of elevation gain since latest miocene pliocene time and in agreement with geologic evidence for accelerated shortening and exhumation at this time the leaf wax isotopic data on the other hand lack a systematic trend potentially due to fractionation changes associated with uplift induced turnover in floral populations such changes could obscure isotopic variations in meteoric water suggesting that leaf wax isotopic compositions may not provide a direct proxy for elevation in this particular situation involving uplift in a heterogeneous tropical environment more promising in this case is the mbt cbt proxy which may offer a suitable alternative to carbonate based paleoelevation proxies in tropical regions where year round high precipitation rates prevent formation of soil carbonates

the relationship between slickenside surfaces in fine grained quartz and the seismic cycle abstract well polished or reflective fault surfaces with or without linear striae indicating the sliding direction are commonly referred to as slickensides this study examines the development of slickensides which are now exposed along the surface trace of a large seismically active normal fault zone in dixie valley nevada u s a geologic and mineralogic constraints indicate the slickenside surfaces formed at depths of less than 2 km and temperatures less than 270 c the slickenside surface material is composed of greater than 98 quartz with less than 2 kaolinite and iron oxide transmission electron microscope tem observations reveal that the slickenside surface material has an extremely fine yet variable grain size 0 01 1 m and an unusual nonequilibrium texture characterized by irregular grain boundaries and low dislocation density angular fragments in the cataclasite to either side of the slickensides provide clear evidence of cataclasis crystallographic preferred orientation in the slickenside surface material indicates that non brittle continuous deformation occurred within 0 1 10 mm of the fault surfaces in many areas non brittle continuous deformation must have alternated with cataclasis because some fragments in the cataclasite have strong preferred orientations we suggest that in the dixie valley slickensides continuous deformation and the development of crystallographic preferred orientations occurred at relatively low strain rates during the interseismic period while cataclasis occurred at higher strain rates associated with seismic events the wide range of strain rates occurring within a fault zone during the earthquake cycle may be an essential element in the formation of fine grained glassy slickensides both at dixie valley nevada and many other areas

nonlinear response of pliocene climate to orbital forcing evidence from the eastern equatorial pacific a high resolution radiolarian record from the eastern equatorial pacific is used to examine paleoceanographic events during the pliocene from 1 8 to 4 9 ma these data provide a means to evaluate the response of the equatorial pacific to the onset of northern hemisphere glaciation near 2 47 ma and to the closure of the isthmus of panama near 3 2 ma responses are recorded both as long term trends and as variations within the milankovitch band 104 to 105 years radiolarian based sea surface temperature sst estimates indicate a mean cooling from lower to upper pliocene but no significant changes occur near the onset of northern hemisphere glaciation and no abrupt changes are observed before or after the closure of the isthmus spectral and cross spectral analyses of this sst time series indicate concentrations of variance within the precession 23 kyr and obliquity 41 kyr bands in several but not all time intervals variance is commonly concentrated at lower frequencies cross spectral analysis of sst time series and calculated orbital variations indicates that the sst record is not coherent with and therefore not linearly related to orbital variations detailed time series analysis of the sst and 18o time series indicates the absence of a direct linear relationship but rather the presence of a strongly nonlinear relationship between pliocene climatic variables and earth s orbit high coherence is seen between the amplitude of the 23 kyr component of sst and the amplitude modulation of precession the amplitude modulation of the 41 kyr component of the sst record is dissimilar to the amplitude modulation of obliquity but is extremely similar to and coherent with the amplitude of the 23 kyr component of sst the amplitude modulations of sst and 18o at a range of frequency bands have the same features features that roughly follow the modulation of precession this suggests a strongly nonlinear response of equatorial pacific sst and planktonic 18o to orbital forcing in the pliocene such a response extending over a number of frequency bands has not previously been seen in a paleoclimatic data set but may be consistent with proposed models describing paleoclimatic variability although the reasons for this response are still unclear it is evident that strong nonlinearities in climate are present during this time

strengthening kuroshio observed at its origin during november 2010 to october 2012 direct measurements of kuroshio at its origin 18 degrees n east of the luzon island are conducted from november 2010 to october 2012 it is found that the depth averaged kuroshio between 200 and 700 m has increased over 15 cm s 1 during the 2 year observational period and it is accompanied by the pronounced southward shift of the north equatorial current nec bifurcation further analysis indicates that the kuroshio s strengthening is confined to the upstream segment east of the luzon island while the kuroshio decreased as it passed the luzon strait due to a dipole like sea surface height ssh trend between 15 degrees n and 23 degrees n it is demonstrated that the 2 year strengthening of the kuroshio as well as the dipole like ssh trend can be adequately reproduced by a 1 5 layer nonlinear reduced gravity model suggesting an important role of upper ocean response to low frequency wind forcing in the western pacific salinity at 500 m depth is also found to increase during the concurrent 2 years this subthermocline salinity increase is a combined outcome of vertical basin scale isopycnal surface movement and horizontal advections i e strengthened kuroshio due to changes in the large scale wind driven ocean circulation

tectonics of the acadian orogeny in new england and adjacent canada paleogeographic analysis of post taconian rocks in new england and adjacent parts of canada has revealed the existence of two volcanic arcs which shut off at the time of the acadian orogeny one was built on arc basement previously accreted to north america during the taconic orogeny the other on precambrian continental basement of avalonia in the intervening merrimack fredericton trough metamorphosed and poly deformed turbidites and black shales record deep water conditions in silurian following mckerrow and ziegler 1971 this tract is interpreted as the site of an ocean which closed in siluro devonian by simultaneous subduction beneath both continental margins in the molucca sea in indonesia a comparable arc arc collision is in an early stage of development moore et al 1982 suggested that an accretionary prism built against one arc is overthrusting its counterpart which developed on the other side of the ocean an identical geometry with an avalonian accretionary prism overriding the conve

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

geologic time series from deep sea sediments time scales and distortion by bioturbation abstract in order to evaluate the time and frequency domain characteristics of geologic time series obtained from deep sea sediments two important problems must be considered first an accurate time scale must be established for the sediment records to be studied an accurate time scale is a basic requirement for such techniques as spectral and cross spectral analysis secondly the distortion of a geologic time series by sedimentation processes such as bioturbation must be considered if inferences are to be made about the mechanisms controlling climatic and oceanographic processes reflected in the geologic record recently it has been suggested that the periodic components in paleoclimatic records which can be related to variations in the earth s orbital parameters can be used as a means for providing very detailed control for late pleistocene sediment sections a time scale is estimated by tuning an individual frequency component in a climate record to an orbital parameter the tuning procedure commonly uses the technique of bandpass filtering which removes all frequency components except the one equivalent to an orbital parameter and then adjusting the geologic time scale so that the filtered record and orbital record align since bandpass filtering will produce a periodic record from any data set a question is raised as to the circularity of this tuning approach a series of numerical experiments using synthetic time series are used to determine if the tuning of a geologic record artificially induces improved correlation and increased periodic character in a climatic record these experiments indicate that the tuning does not artificially induce these effects thus it is suggested that the careful use of orbital tuning provides a powerful means of defining a geologic time scale the degree to which bioturbation distorts a paleoclimatic record is studied by comparing the spectra of oxygen isotopic records obtained from cores with sedimentation rates ranging from 1 to 12 cm 1000 yr 1 it is shown that the systematic change in the variance spectra of these records that is predicted by models of bioturbation cannot be observed for sedimentation rates greater than 2 cm 1000 yr 1 this can be explained in part if bioturbation is a function of sedimentation rates if this is the case then bioturbation must proceed to depth of tens to hundreds of centimeters however it seems likely that the degree to which bioturbation alters the climate signal preserved in deep sea sediment cores has been overestimated

the control of coal bed decollement related slickensides on roof falls in north american late paleozoic coal basins abstract slickensides cause potentially hazardous ground conditions in underground coal mines investigations by the mine safety and health administration s msha roof control division indicate that many slickensides represent bedding plane faults and drag folds that formed during coal bed decollement a style of bedding plane faulting that occurs in shale units above coal seams these slickensides formed in response to regional tectonic stresses rather than by differential compaction and strike parallel to local and regional fold axes and thrust faults this paper relates some slickensides in the appalachian illinois arkoma and black warrior basins to the structural grain developed during the late pennsylvanian permian alleghanian orogeny provides descriptions of slickensides and advocates geologic mapping as a predictive method for identifying adverse ground conditions associated with tectonically formed slickensides

a geologic history of the north central appalachians part 2 the appalachian basin from the silurian through the carboniferous the north central appalachians occupy a critical position within the 3000 km long appalachian orogen lying southwest of the boundary between the central and northern appalachians cnab the one billion year long history of tectonic activity in the north central appalachians includes the assembly and breakup of a late proterozoic supercontinent the creation and evolution of the appalachian orogen during the paleozoic and the mesozoic transformation of the active orogen into a passive margin during pangea9s disassembly an important part of the middle and late paleozoic history is the formation and growth of the appalachian basin an enormous elongate continental basin lying cratonward of the active appalachian internides along laurentia9s eastern margin the appalachian basin developed out of the taconic orogeny the second of the four orogenies that formed and modified the character of the appalachian orogen prior to the taconic orogeny the eastern margin of laurentia consisted of a broad carbonate shelf facing the theic ocean the taconic orogeny obduced various theic components including microcontinents magmatic arcs and accretionary prisms onto the carbonate shelf the resulting taconic highlands formed a topographic barrier between theia and the craton9s interior because tectonic activity in the internides continued more or less throughout the remainder of the paleozoic the appalachian basin never had a direct connection with theia the coarse grained molasse from the newly uplifted taconic highland spread westward over most of the basin during the early silurian carbonate deposition gradually encroached eastward over the basin as the siliciclastic input from the southeast waned a resurgence in the earliest late silurian perhaps related to orogenesis in newfoundland and the maritimes expanded the clastic wedge somewhat before long however carbonate deposition once again dominated most of the north central basin for the remainder of the silurian and into the early devonian the early to middle devonian acadian orogeny began introducing siliciclastic material into the eastern part of the appalachian basin thereby ending the largely paralic environment that persisted from the late silurian a number of deltas formed around local sediment input centers during the middle devonian continued uplift and or orogenesis must have continued into the late devonian because a vast amount of terrigenous sediment was introduced into the appalachian basin to form the vast upper devonian catskill delta although the principal tectonic activity appears to have centered in new england the large volume of sediment input suggests that orogenesis may have extended southward to the north central appalachians however direct evidence of actual acadian deformation and metamorphism is lacking at this latitude the north central appalachian basin underwent a significant change during the carboniferous prior to this time the shoreline shifted laterally through transgressions and regressions largely as a function of sediment input and regional subsidence in the carboniferous vertical movements in the basin became more important during the early carboniferous much of the mauch chunk delta was eroded in the central and western parts of the basin at the end of the early carboniferous an unconformity truncated progressively older rocks to the north toward new york new sediment transport patterns and depositional environments within the basin during the late carboniferous probably reflect significant topographic and tectonic changes not only in the hinterland but in the basin itself perhaps in conjunction with climatic changes extensive interfluvial swamps on a lower delta plain accumulated thick organic deposits which would become coal this delta plain graded southwestward into tidal and marine environments the alleghany orogeny in the early permian interrupted deposition in much of the north central appalachian basin and profoundly altered its structure

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

late pleistocene and holocene climates of venezuela abstract the present review accounts for the most important climatic data published until 1992 about venezuela and attempts to correlate them with other results from tropical south america the evidence of climatic changes prior to the last glacial maximum consists of several terrace levels one of which representing an arid oscillation dated isotopic stage 6 older terraces have not been dated and their meaning still remains questioned the late merida glaciation stage began between 19 and 16 ka and ended around 13 ka associated with an arid or semi arid climate in the lowlands the post glacial times after 13 ka were characterized by oscillations of colder and warmer climates in the mountains correlated respectively with drier and wetter ones in the lowlands the early holocene is characterized by a climate similar to the present day one followed by a colder and drier phase around 6 ka present like conditions established again until about 3 ka when a new warm humid phase began with a maximum at 2 5 ka later on the current climat dominated however some minor oscillations occurred the most notable one in the little ice age 14th to 19th centuries these climatic trends agree with those reported for the majority of the south american tropical regions but a certain degree of heterogeneity exists in the holocene attributed to differences in the local climatic patterns and or to the high frequency of changes the intensity and duration of climatic oscillations as well as to differences in biotic responses conditioned by the internal properties of the ecological systems

experimentally produced slickenside lineations in pyrophyllitic clay abstract during shearing of pyrophyllitic clay fault planes bearing slickenlines were generated on previously initiated c and c planes these slickenlines have excess lengths with respect to the measured slip displacement on the fault plane and are of the ridge in groove type with the hangingwall nesting into the footwall and vice versa these features cannot be explained in terms of either frictional asperity ploughing or dissolution reprecipitation but are produced during the development of a complex ductile shear zone that contains the fault plane this initial shear zone nucleates from localized shear bands that link up to form a throughgoing shear plane the nucleation and propagation of the fault post dates the formation of the shear plane and depends on the development of a zone of highly oriented layer silicates within the pyrophyllitic clay the fault is confined to this zone the lineations observed on the fault surfaces are produced while the material behaves plastically prior to the brittle faulting with increasing shear strain the brittle ductile transition is crossed and sliding continues under brittle conditions along the former shear zone

isotopic evidence for cooler and drier conditions in the tropical andes during the last glacial stage documentation of paleoclimatic conditions during the last glacial stage in the tropical andes is sparse despite the importance of understanding past climate changes in the tropics to reconstruct paleoenvironmental conditions in the alpine neotropics we measured the oxygen 18o and hydrogen d isotopic composition of authigenic kaolinite within weathering profiles of the bogota basin colombia because of the strong dependence of isotopic values on both surface temperature and rainfall while kaolinite isotope data from holocene soils in the basin reflect modern mean annual temperature and mean weighted rainwater isotopic composition of the basin kaolinite isotope data from paleosols developed during the last glacial stage suggest 6 2 c cooler temperatures moreover the isotope data indicate higher isotopic values of paleorainwater interpreted to reflect drier conditions the combination of reduced rainfall temperature and p co2 significantly affected the distribution of tropical montane flora during the last glacial stage

effects of late paleozoic foreland deformation on underground coal mine ground instability illinois and appalachian basins abstract slickensides are commonly associated with potentially hazardous ground conditions in underground coal mines investigations by the mine safety and health administration s roof control division indicate that slickensided drag folds in the immediate roof of pennsylvanian age coal seams represent instances of ground instability of various scales from skin control hazards to roof falls that block travelways and belt entries the occurrence of features in the roof of the illinois basin s springfield coal seam that are identical to structures interpreted as drag folds in pennsylvanian age coal measure rocks of the appalachian basin suggests that tectonic stress associated with the late pennsylvanian permian alleghanian orogeny was transmitted into the mid continent this paper relates slickenside occurrences in the pennsylvanian age springfield coal seam to local structural geologic features that are associated with the late pennsylvanian permian alleghanian orogeny because the slickensides discussed are interpreted to have formed in response to regional tectonic stress small scale controls on coal mine ground instability can be related to large scale regional tectonic processes field investigations indicate that mine wide geologic mapping of structural geologic features can be used to project zones of subtle yet problematic structural weakness in advance of face positions by incorporating this style of structural geologic hazard mapping in mine planning and operation miners can be prepared to install appropriate supplemental support or reduce the effects of structural weaknesses with local modifications to mine design

thrust fault nucleation due to heterogeneous bedding plane slip evidence from an ohio coal mine abstract shales often form the roof and floor rocks of coal mines in the appalachian basin from a geologic perspective these mines offer outstanding 3d exposures of fresh rocks otherwise only accessible via boreholes or heavily weathered surface outcrops and present an excellent opportunity to directly observe pristine in situ natural fractures in shale in carroll county ohio small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal shale contacts are steepest causing ground instability we hypothesize that bedding contact surfaces served as natural displacement discontinuities that perturbed the local stress state resulting in localized thrust fault development using borehole and in mine survey data we digitally constrain bedding contact geometry to model slip along this interface and resolve related stress perturbations our modeling results suggest that inherited non planarity of contact surfaces influenced the nucleation of secondary faults simulation results as constrained by the integrated field and modeling approach taken in this study help us to better understand the relationship between subsurface stress perturbations and the formation of secondary fractures for mining purposes recognizing subsurface stress heterogeneities due to variable bedding geometry within a regional stress field can improve our predictive capabilities of underground structural hazards

analysis of roof fall hazards and risk assessment for zonguldak coal basin underground mines the roof fall hazards are frequent problems of underground coal mines which are generally unpredictable due to the associated uncertainties these uncertainties which arise from geological and stress conditions and mine environment make the control of roof fall hazards difficult in underground coal mines the most efficient method for coping with uncertainties in roof fall hazards is the use of risk assessment techniques in this study a risk assessment and management methodology is proposed for roof fall hazards in underground mines of the zonguldak coal basin the annual rates of roof falls obtained from the five mines in the basin are statistically analyzed the components of risk which are the probability of roof fall and consequences of roof fall hazard are identified and quantified the probability of roof fall is computed by fitting a distribution function to the annual roof fall while the consequences of roof falls are quantified based on a cost model then a decision analysis methodology for evaluating the performance of possible alternative action to be taken in order to decrease the risk is developed the results show that the underground coal mines in the zonguldak coal basin have considerably high risk levels and hence require comprehensive risk management schemes

quaternary and upper pliocene glaciations and forest development in the tropical andes evidence from a long high resolution pollen record from the sedimentary basin of bogota colombia pollen analysis of 1230 samples from a 357 m long core of lake sediments from the sedimentary basin of bogota eastern cordillera colombia alt 2550 m above sea level has provided a high resolution record of changes in the andean vegetation belts and long range climatic fluctuations during the last 3 5 ma direct time control is provided by k ar datings and fission track datings of 14 intercalated volcanic ash layers the resulting pollen diagram has been divided into 55 pollen zones representing 27 complete major climatic cycles glacial interglacial cycles a tentative correlation with the marine oxygen isotope chronology and the european stratigraphical climatic subdivision could be established the altitudinal position of the forest line which corresponds with the 9 5 c isotherm shifted between minimal c 1700 1800 m and maximal c 3400 3700 m alt at present situated at c 3100 m alt which rendered the altitudinal position of the high plain of bogota the dry bed of a former lake at 2550 m a sensitive recorder of temperature changes the estimated fluctuations in mean annual temperature at the level of the high plain of bogota are from 15 c a distinct change in the nature of the climatic cycles occurs around 2 5 ma b p the interval of 3 5 2 5 ma b p shows high frequency low amplitude climatic oscillations whereas the last 2 5 ma is characterized by low frequency high amplitude climatic oscillations with a superposed high frequency oscillation it is assumed that these oscillations correspond mainly with the variations in orbital eccentricity and obliquity the major constituents making up the andean forest have been subjected to considerable changes in the course of time in the early pliocene forests vallea and myrica are prominent elements weinmannia was almost absent the role of polylepis in the timberline forests increased markedly around 3 1 ma b p and also migrated by adaptation from the upper andean forest line to higher elevations the closure of the isthmus of panama during the pliocene enabled northern hemisphere elements to migrate into south america alnus reached the area of bogota around 2 7 ma b p and dramatically changed the vegetation especially on the flats around the lake of bogota where alnus swamp forests replaced myrica carr around 2 9 ma b p weinmannia became an important constituent of the upper andean forest but slightly later slope forests of alnus replaced parts of the area which had previously been covered by weinmannia forest the marked role of vallea in the andean forest diminished definitively after 2 5 ma b p quercus migrated more recently to south america and reached the area of bogota 1 ma b p it changed for the last time drastically the aspect of the andean forest all palynologically recognizable elements of the modern andean forest were present from now on and the subsequent adaptation and speciation of quercus and many other elements must have mainly taken place at the species level

mining induced fault reactivation associated with the main conveyor belt roadway and safety of the barapukuria coal mine in bangladesh constraints from bem simulations fault reactivation during underground mining is a critical problem in coal mines worldwide this paper investigates the mining induced reactivation of faults associated with the main conveyor belt roadway cbr of the barapukuria coal mine in bangladesh the stress characteristics and deformation around the faults were investigated by boundary element method bem numerical modeling the model consists of a simple geometry with two faults fb and fb1 near the cbr and the surrounding rock strata a mohr coulomb failure criterion with bulk rock properties is applied to analyze the stability and safety around the fault zones as well as for the entire mining operation the simulation results illustrate that the mining induced redistribution of stresses causes significant deformation within and around the two faults the horizontal and vertical stresses influence the faults and higher stresses are concentrated near the ends of the two faults higher vertical tensional stress is prominent at the upper end of fault fb high deviatoric stress values that concentrated at the ends of faults fb and fb1 indicate the tendency towards block failure around the fault zones the deviatoric stress patterns imply that the reinforcement strength to support the roof of the roadway should be greater than 55 mpa along the fault core zone and should be more than 20 mpa adjacent to the damage zone of the fault failure trajectories that extend towards the roof and left side of fault fb indicate that mining induced reactivation of faults is not sufficient to generate water inflow into the mine however if movement of strata occurs along the fault planes due to regional earthquakes and if the faults intersect the overlying lower dupi tila aquiclude then liquefaction could occur along the fault zones and enhance water inflow into the mine the study also reveals that the hydraulic gradient and the general direction of groundwater flow are almost at right angles with the trends of faults fb and fb1 which could act as barriers to groundwater flow into the mines

direct measurements of the luzon undercurrent abstractthe luzon undercurrent luc was discovered about 20 years ago by geostrophic calculation from conductivity temperature depth ctd data but it was not directly measured until 2010 from november 2010 to july 2011 the luc was first directly measured by acoustic doppler current profiler adcp from a subsurface mooring at 18 0 n 122 7 e to the east of luzon island a number of new features of the luc were identified from the measurements of the current its depth covers a range from 400 m to deeper than 700 m the observed maximum velocity of the luc centered at about 650 m could exceed 27 5 cm s 1 four times stronger than the one derived from previous geostrophic calculation with hydrographic data according to the time series available the seasonality of the luc strength is in winter summer spring significant intraseasonal variability isv 70 80 days of the luc is exposed evidence exists to suggest that a large portion of the intraseasonal variability in the luc is related to the w

carbon isotopic evidence from paleosols for mixed c3 c4 vegetation in the bogota basin colombia abstract pollen reconstructions in the bogota basin colombia indicate the expansion of tropical high altitude grassland paramo at the expense of andean forests during glacial intervals the carbon isotopic composition 13c of soil organic matter som can be a useful indicator of changes in vegetation affecting grasslands because it distinguishes between two groups of grasses c3 and c4 adapted to different ecological environments values of som 13c were determined in four weathering profiles containing both modern holocene soils and paleosols formed during the last glacial stage these profiles are located along an altitudinal transect in the bogota basin extending from 2550 to 3100 m values of som 13c in the topsoil horizons reflect those of the native c3 vegetation that currently dominates the ecosystems in the colombian andes although c4 grasses are currently negligible in the basin elevated som 13c values indicative of c4 plants were found in two holocene soils environmental changes or ancient agricultural activities could explain the increased abundance of these plants in the basin during the late holocene isotopic values in the studied paleosols revealed the presence of a mixed c3 c4 vegetation in the basin during the last glacial stage thus indicating the expansion of c4 grasses we hypothesized that lowered pco2 and possibly reduced rainfall resulted in the colonization of the tropical andes by lowland c4 grasses despite of prevailing cooler temperatures

duplex geometry an example from the moine thrust belt abstract the geometry and microstructure of a small duplex formed in one bed from the moine thrust belt of northwest scotland is reported the structure is seen in oblique section within the cambrian pipe rock in an area of low strain a range of movement direction indicators are present in the structure an early grain shape fabric developed close to the roof thrust is taken as the best estimate of the overall movement direction towards 287 slickensides in the gouge developed on movement planes within the duplex show varied orientations on a given plane and are not considered useful indicators of thrust transport direction branch lines exposed converge and diverge suggesting little lateral continuity of the exposed structure the microstructures present within the structure indicate an increase in localised deformation and in cataclastic behavior as the duplex evolved early layer parallel shear is ubiquitous giving rise to an elongate grain shape fabric close to bedding surfaces in early formed horses a layer parallel oblate grain shape fabric which shows localised slip zones is overprinted by gouge formation later formed horses show only fracturing and gouge development this sequence is attributed to stick slip behavior in the propagation or displacement of the original fault now the floor thrust

intraseasonal variability of the surface zonal currents in the western tropical pacific ocean characteristics and mechanisms abstractthe surface circulation of the tropical pacific ocean is characterized by alternating zonal currents such as the north equatorial current nec north equatorial countercurrent necc south equatorial current sec and south equatorial countercurrent secc in situ measurements of subsurface moorings and satellite observations reveal pronounced intraseasonal variability isv 20 90 days of these zonal currents in the western tropical pacific ocean wtpo the amplitude of isv is the largest within the equatorial band exceeding 20 cm s 1 and decreases to 10 cm s 1 in the necc band and further to 4 8 cm s 1 in the nec and secc the isv power generally increases from high frequencies to low frequencies and exhibits a peak at 50 60 days in the necc sec and secc these variations are faithfully reproduced by an ocean general circulation model ogcm forced by satellite winds and parallel model experiments are performed to gain insights into the underlying mechanisms it is found that large sca

composition of carboniferous sandstones and tectonic framework of southern appalachian ouachita orogen abstract regional stratigraphic and sedimentologic studies in the appalachian fold and thrust belt and black warrior foreland basin in alabama indicate deposition of two converging clastic wedges during carboniferous time a northeastward prograding clastic wedge floyd pride mountain hartselle parkwood reached alabama by late meramecian time progradation continued with deposition of the lower pennsylvanian pottsville formation a southwestward prograding clastic wedge pennington pottsville did not appear in alabama until latest mississippian time the northeastward prograding wedge indicates a source terrain southwest of the black warrior basin and implies orogenesis as a result of convergence along the southern margin of north america petrographic data from 79 sandstone and 6 conglomera e samples from the parkwood and pottsville formations in alabama provide information on the composition of the source rocks and thus on the crustal components and tectonic setting of the convergent margin foliated quartzmica rock fragments unstable polycrystalline quartz pelitic rock fragments and polycyclic monocrystalline quartz suggest that the largest and or most proximal source rock province was a low grade metamorphic and sedimentary fold thrust belt detrital chert suggests derivation from a subduction complex or from bedded chert incorporated in a fold thrust belt andesitic basaltic and dacitic volcanic rock fragments indicate the presence of an arc complex a complex source terrain produced by juxtaposition of a fold thrust belt subduction complex and arc sugge ts collision of the alabama promontory of the southern margin of north america with an arc or with a microcontinent and associated continental margin arc

early holocene aridity in tropical northern australia thermoluminescence ages from a longitudinal dunefield in tropical northern australia suggest that complete dune activation occurred here either continuously or sporadically between approximately 8 2 ka and 5 9 ka this period in australia is normally ascribed to one of increasingly warm and wet conditions towards the holocene climatic optimum however elsewhere this time 8 ka coincides with a brief period of global climate change recognized in 18 o records from antarctica methane records of the greenland summit ice cores changes to deep sea benthic foraminferal composition and atmospheric 14 c variations in tropical africa two distinct phases of aridity have been dated at approximately 8 ka and 6 ka the coincidence of aeolian reacti vation episodes in this north australian dunefield with brief phases of early holocene climate change elsewhere suggests possible global climatic teleconnections at this time

towards a high resolution global deep sea chronology for the last 750 000 years abstract variations in the ratio of 18 o 16 o as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume hence these variations provide a set of global time lines in deep sea sediments it is likely that the timing of major changes in oxygen isotope values is strongly influenced if not controlled by variations in the geometry of the earth s orbit since the variation of orbital parameters can be accurately calculated the opportunity exists for transforming this orbital chronology into a geological chronology through careful correlation of oxygen isotope records in a set of deep sea cores from the sub antarctic south atlantic and equatorial pacific we have assembled a composite isotopic section spanning the last 750 000 years with an average sedimentation rate of 2 3 cm 1000 years a new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300 000 years to the entire 750 000 year record previously identified difficulties in phase locking precession with the filtered isotopic signal between 365 000 and 465 000 years b p have been resolved with the recognition that precessional variations have an average period of 19 000 years and not 23 000 years during this interval since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record we believe that it presents the most accurate chronology yet developed for deep sea sediments with this new age model providing the time control power spectral analyses of south atlantic and sub antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of 100 000 41 000 and 23 000 years

laramide orogeny related controls on coal mine ground instability in cretaceous coal seams southern rocky mountain foreland abstract investigation of ground conditions in nine coal mines located in the structurally complex southern rocky mountain foreland tectonic province suggest that structural compression associated with the late cretaceous eocene laramide orogeny caused deformation of cretaceous aged coal seams structures include low angle bedding plane faults and drag folds that are indicative of bedding plane faulting other structures include high angle joints and faults the pattern of structural geologic features documented during mine mapping is similar to the local trends of regionally extensive thrust faults fold axes and basement cored uplifts that formed during the laramide orogeny this suggests that the observed structural geologic features in mines developed in cretaceous coal seams reflect regional deformation that occurred in response to the laramide orogeny the geologic structures documented in colorado new mexico and utah coal mines were commonly associated with major instances of ground failure the recognition of regional tectonic controls on relatively localized geologic structures has important implications for the prediction of degraded ground conditions in advance of mining because the structural discontinuities observed in coal mine immediate roof strata formed in response to regional stress conditions during orogenic activity they can often be simply characterized as linear zones that are relatively continuous along strike at the mine scale once recognized the structural zones can be projected in advance of mining so that section crews can be forewarned of potentially adverse ground conditions and be prepared to install appropriate supplemental support and local modifications to pillar design can be implemented to enhance long term stability thus geologic hazard mapping that incorporates structural geologic features as part of an integrated geologic characterization should be an appropriate method for ground control planning

the orbital tuned marine oxygen isotope record applied to the middle and late pleistocene pollen record of funza colombian andes abstract assuming that orbital variations are the main external cause of the succession of late pleistocene ice ages deep sea stratigraphers developed an orbital tuned chronology of the marine oxygen isotope record the pollen record of funza eastern cordillera colombia displays in great detail long range altitudinal shifts of the forest line being also an expression of long range fluctuating global temperatures both records of palaeotemperature were visually correlated 48 isotopic events are assumedly reflected in the pollen record this enables an orbital tuning of the initial time frame of the pollen record which was based on 14 dated volcanic ash horizons and provides a detailed record of changes in sediment accumulation in the sedimentary basin of bogota inferences for the time frame of the pollen record of paramo de agua blanca from the same area are discussed

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

absolute chronology of the pliocene quaternary sediment sequence of the bogota area colombia abstract a revised geochronological framework is presented for the sequence of unconsolidated sediments present in the bogota area eastern cordillera colombia this is based on 11 fission track dates on zircons that were obtained both from exposed ash layers and from a series of ashes from the funza ii borehole which reached 586 m below the surface of the high plain the 3 dates obtained from the exposed ash layers provide control for the older part of the sequence 6 2 5 ma the 8 dates from the funza ii core give control for the younger part of the sequence 3 0 ma acceptance of these new fission track dates on volcanic zircons means that many of the tephra dates obtained from the funza i core that included fission track dates on glass shards and k ar dates using the mineral fractions in the ashes published in 1984 are rejected it also confirms earlier climate stratigraphical dating the neogene quaternary sediments of the bogota area span a period of at least the last 6 ma the fluvial lacustrine sediment record registers major tectonic uplift of the eastern cordillera for the period between 5 and 3 ma the development of the large sedimentary basin of bogota after 3 5 ma with an important phase of tectonic adjustment at about 1 ma and a long period of strong climatic fluctuations that started shortly after 2 7 ma

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

the geochemistry and formation of ferromanganese oxides on the eastern flank of the gagua ridge abstract ferromanganese oxides on the eastern flank of the gagua ridge were collected from a water depth of 4071 m by tv grab in 2016 and analyzed for their mineralogical and chemical compositions these oxide fragments were broken from a large poly core crust and can be divided into three parts a dense inner nodule a radial middle crust and a loose outer crust the close proximity of the nodule and crust is similar to that observed in the amalgamated deposits from the shatsky rise nw pacific all samples are mainly composed of fe rich vernadite amorphous feooh and associated quartz plagioclase pyroxene and mg titanomagnetite the mineralogy mn fe ratios rare earth element patterns and slow growth rates with a mean value of 6 2 mm myr of the samples reflect their predominantly hydrogenetic origin co ni cu rey and other critical metals are most enriched in the mn rich inner nodule samples which also have the highest fe contents in contrast the si and al contents in the samples of the middle and outer crusts are very high up to 19 wt and 6 29 wt respectively correlation analysis indicates that li sc cr rb and cs tend to concentrate in detrital silica aluminosilicate phases the gagua ridge samples generally have lower metal contents than the hydrogenetic crusts and nodules from other open ocean regions which can be attributed to their dilution by detritus and the poor development of a mid water oxygen minimum zone however the incorporation of detritus has little effect on the generation of fe mn oxides in the gagua ridge based on their mineralogy textures and chemical variations the accretion of the hydrogenetic fe mn oxides was initiated in the late miocene and the formation of the amalgamated fe mn deposits comprised three stages

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

middle and late quaternary vegetational and climatic history of the paramo de agua blanca eastern cordillera colombia abstract the results of a palynological study of a 13 m deep bore hole of lake deposits from the paramo de agua blanca colombian eastern cordillera 5 n elev 3250 m are reported by means of 14 c dates and an indirect dating method based on pollen densities it was possible to provide the pollen diagram with an approximate time scale the section representing some 465 000 years gives a continuous record of the middle and late pleistocene and holocene vegetational and climatic sequences the sequence of glacial and interglacial periods in combination with their age and duration according to the indirect time determinations could be tentatively correlated with the european chronostratigraphic sequence

eddy transport of heat and thermocline waters in the north pacific a key to interannual decadal climate variability abstract high resolution xbt transects in the north pacific ocean at an average latitude of 22 n are analyzed together with topex poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field based on anomalies in dynamic height 410 eddies are identified in 30 transects from 1991 to 1999 including eddies seen in multiple transects over a year or longer their wavelength is typically 500 km with peak to trough temperature difference of 2 2 c in the center of the thermocline the features slant westward with decreasing depth by 0 8 of longitude on average from 400 m up to the sea surface this tilt produces a depth varying velocity temperature correlation and hence a vertical meridional overturning circulation in the mean 3 9 sv sv 106 m3 s 1 of thermocline waters are carried southward by the eddy field over the width of the basin balanced mainly by northward flow in the surface layer corresponding northward heat transport is 0 086 0 012 pw

structural chronology of the alleghanian orogeny in southeastern west virginia the trend change between central and southern appalachian structures is sharply defined in southeastern west virginia there n30 35 e trends coincident with major central appalachian folds such as the browns mountain anticline end abruptly at n60 e trending southern appalachian structures along the st clair fault analysis of local and regional folds cleavage bedding perpendicular stylolite seams and bedding and fault slickenlines reveals that layer parallel shortening directed n10 30 w occurred in nonfolded greenbrier group mississippian carbonates well into the present appalachian plateau area this structural event is early and is associated with the evolution of southern appalachian folds and faults south of the st clair fault central appalachian folds and mesoscopic structures were superimposed on this early layer parallel shortening fabric this structural chronology indicates that southern appalachian folds and faults predated the development of central appalachian structures in the region

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

morphology and geometry of duplexes formed during flexural slip folding abstract bedding parallel slip on the limbs of chevron style folds during flexural slip folding results occasionally in the formation of small scale duplexes the duplexes described here from upper carboniferous turbidites in sw england generally range in thickness from 0 3 to 30 cm and are up to 2 4 m long they have smooth nearly flat roofs and both the internal thrusts and the slickenfibres on them are commonly oblique to the mean transport direction as indicated by slickenfibres on the floor and roof thrusts the morphology of the duplexes suggests that they developed between active floor and roof thrusts and they show a characteristic lack of hangingwall anticlines on the link thrusts their shear sense always corresponds to that required by flexural slip and the total bedding parallel displacement across each is commensurate with that predicted by the flexural slip model all thrust surfaces in the duplexes are marked by quartz fibre veins a feature which distinguishes them from soft sediment and other pre folding duplexes and carry slickenfibres whose mean orientation and complex variations in slip direction on different fibre sheets on the same slip surface are identical to those on flexural slip movement horizons from the same fold limb the duplexes form either as a result of resistance to thrust propagation by local facies or bed thickness changes or develop as transfer structures between the tips of movement horizons propagating along adjacent slip surfaces late stage duplexes develop from imbricated fibre veins and also form on slip surfaces oblique to the axial planes of major folds