thermal infrared data analyses of meteor crater arizona implications for mars spaceborne data from the thermal emission imaging system thermal infrared tir data from the advanced spaceborne thermal emission and reflection radiometer aster instrument are used to identify the lithologic distribution of the meteor crater ejecta blanket and nearby within 3 km region this has many applications to the analysis of data from the thermal emission imaging system themis instrument that is currently in orbit at mars aster and themis whereas orbiting different planets have similar spatial and spectral resolutions themis represents the highest spatial resolution 100 m to date of the martian surface thereby allowing small 1km impact craters to be studied in detail for the first time meteor crater serves as an analog for the many similar sized impact sites on the surface of mars these sites are future research targets with themis and aster data of meteor crater provides ideal data and geologic landscape in preparation for future themis investigations fieldwork at meteor crater yielded sample collection of the primary lithologies and an opportunity to validate previously collected high resolution 3 2 m airborne thermal imaging multispectral scanner tims data laboratory thermal emission spectra were obtained for the samples collected deconvolution of aster tir emissivity data were performed with image end members and sample end members comparisons of the spaceborne data to high resolution airborne tims data were used to assess the validity of the aster end member analyses the aster image end member analysis agreed well with the earlier tims end member analysis where the effects of resolution degradation were accounted for laboratory spectra and mineral spectral libraries provided poor fits of deconvolution of multispectral tir data lithologies with similar spectral signatures or with low areal abundances were difficult to identify using the same methodology as that applied to the aster tir data of meteor crater themis tir data of a small 1 km impact crater in syrtis major were analyzed the crater s rim and ejecta blanket was found to contain larger particle sizes than the surrounding ejecta free plain indicating a young fresh impact age and little or no accumulation of dust the composition of the rim ejecta and surrounding plain was determined to be basaltic it is hoped that the work performed here will complement future investigations of fresh impact sites with themis data that may be used to solve geologic questions such as 1 the composition of ejecta blocks that represent pre impact underlying stratigraphy in high albedo dust covered regions of mars 2 the approximate age of impact and 3 regolith dust thickness which appears to be a factor of 2

extinct mountain goat oreamnos harringtoni in southeastern utah the extinct harrington s mountain goat oreamnos harringtoni stock is predominantly known from dry cave localities in the grand canyon arizona in addition to two sites in the great basin nevada and from san josecito cave nuevo leon mexico a dry shelter in natural bridges national monument on the central colorado plateau southeastern utah preserves numerous remains of the extinct mountain goat in addition to pack rat middens remains from a 100 cm stratigraphic profile indicate that o harringtoni lived on the plateau 39 800 yr b p the oldest directly dated find of extinct mountain goat plant macrofossils indicate that engelmann s spruce picea engelmannii limber pine pinus flexilis rose rosa cf woodsii and douglas fir pseudotsuga menziesii grew during the late pleistocene where a riparian and a pinyon juniper pinus edulis juniperus osteosperma community now predominates douglas fir are found only in mesic protected north facing areas limber pine douglas fir bark and grasses were the major dietary components in the dung a springtime diet of birch betula is determined from pollen clumps in dung pellets

lithofacies architecture composition and age of the carboniferous teplice rhyolite german czech border insights into the evolution of the altenberg teplice caldera abstract the teplice rhyolite tr intra caldera deposits of the altenberg teplice caldera atc central europe were investigated by lithofacies analysis stratigraphy and whole rock chemistry as well as laser ablation u pb zircon dating the aim was to demonstrate that the joint application of these methods can discern complex stratigraphy of ancient volcanic successions susceptible to erosion and alteration taking the tr as case study the tr was regarded as a formation and divided into nine members that represent three main eruptions each one separated by periods of volcanic quiescence the first two eruptions mainly portrayed opening and clearing of vents which were dominated by lithic rich ignimbrites with lateral lithofacies changes fiamme rich to crystal rich covered by lava flows domes eruption style was low pyroclastic fountaining alternated with effusive lava outpour a sustained buoyant eruption column was exclusively interpreted at the outset of the second eruption based on the presence of a basal fallout deposit the third eruption recorded three different phases further vent opening a waxing phase and final lava extrusion the vent opening phase was similar to those occurred in previous eruptions the waxing phase produced voluminous massive poorly sorted very crystal rich 50 vol ignimbrites exhibiting progressive increase in crystal contents with height and chemical composition variations that indicate deposition by progressive aggradation low pyroclastic fountaining formed these high particle concentration currents that waxed and reached quasi steady conditions eruption ended with extrusion of a lava flow the tr ignimbrites were emplaced hot and were partially to densely welded as evidenced by eutaxitic texture deformed glass shards spherulites perlitic cracks and microcrystalline to granophyric textures horizontal and vertical lithofacies variations in pyroclastic deposits together with progressive infill and association between tr feeding systems and faulting demonstrate that eruptions developed through several fissure vents or faults a volcanic explosivity index of 7 was estimated according to a minimum ejecta volume of 320 km3 dre volcanic architecture of the tr can be linked to sequential caldera subsidence that occurred synchronously with progressive deposition regional faulting ne sw trending rhyolitic dykes related to atc feeding conduits suggests that progressive subsidence and final trap door caldera collapse possibly with a piece meal component faulted caldera floor originated from post variscan tensional stress regime nnw sse direction the tr formation has a general rhyolitic composition with a type granite affinities and a normal chemical zoning u pb zircon dating yielded ages from 323 to 312 ma which compared to age data from other atc rocks indicate that the tr was generated within a time span of 325 317 ma

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

erosional modification and gully formation at meteor crater arizona insights into crater degradation processes on mars hydrogeological modification of meteor crater produced a spectacular set of gullies throughout the interior wall in response to rainwater precipitation snow melting and possible groundwater discharge the crater wall has an exceptionally well developed centripetal drainage pattern consisting of individual alcoves channels and fans some of the gullies originate from the rim crest and others from the middle crater wall where a lithologic transition occurs broad gullies occur along the crater corner radial faults deeply incised alcoves are well developed on the soft coconino sandstone exposed on the middle crater wall beneath overlying dolomite in general the gully locations are along crater wall radial fractures and faults which are favorable locales of erosion due to preferential rock breakup from faulting and groundwater flow discharge these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow causing erosion and crater degradation channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor caves exposed on the lower crater level point to percolation of surface runoff and selective discharge through fractures on the crater wall in addition lake sediments on the crater floor provide significant evidence of a past pluvial climate when the water table was higher and groundwater may have seeped from springs on the crater wall although these hydrological processes continue at meteor crater today conditions at the crater are much more arid than they were soon after impact reflecting a climatic shift this climate shift and the hydrological modifications observed at meteor crater provide insights for landscape sculpturing on mars during various parts of its history

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

relative age dating of transported regolith and application to study of landform evolution in the appalachians abstract surficial deposits in the appalachians generally are thin discontinuous and difficult to date in the absence of numerical dates particularly for older deposits relative age indices based on degree of weathering and soil development have been used to distinguish and correlate deposits of different ages a favorite locale of relative age studies has been stream terraces where chronosequences have been developed to shed light on the relationship between time and weathering soil development the lack of applicable numerical dating techniques has led some researchers to establish relative chronosequences in which height of stream or fan terraces above modern river level arl serves as a proxy for time approximate incision rates can then be used to estimate numerical ages of the deposits relative age correlations between the weathering indices on the terraces and comparable indices on dated deposits on the coastal plain and in nearby glaciated regions suggest that ages so estimated are the right order of magnitude relative age indices show correlations with height arl that are as high as those with time perhaps because more data sets are available for relative chronosequences than for true chronosequences analogous relative age sequences can be established for alluvial fans and even for hillslope colluvium many weathering indices have been employed but weathering rind thickness on mafic to intermediate clasts has proved to be a particularly consistent and useful parameter in addition to showing how weathering and soil development progress over time relative age dating has shed light on the manner in which landforms evolve along some rivers for example the areal extent of old highly weathered alluvium far exceeds that of younger alluvium suggesting that formerly floodplains and low terraces were much more extensive than at present in addition the manner in which weathering indices on some river terrace sequences vary with height arl suggests that incision rate has changed through time relative age mapping of alluvial fans produces a map pattern of older and younger fan surfaces that allows the sequence of fan development to be inferred in one case suggesting a scenario different from those previously described for fans mapping also shows that the relative abundance of young intermediate and old fan surfaces varies greatly from one area to another several studies have demonstrated clustering of relative age values into a small number of groups suggesting temporal grouping and thus episodic deposition on fans regression of weathering rind thickness against height above modern drainageways of remnant fan surfaces in two areas suggests that fans are being incised more rapidly in one area than in another relative age of hillslope colluvium also aids geomorphic interpretation young brown colluvium is much more common than old red colluvium near the glacier border where red colluvium rarely occurs at the surface but typically is covered by brown colluvium probably mobilized during the late pleistocene distant from the ice margin however red colluvium is extensively exposed on interfluves relatively stable hillslopes can also be distinguished from active ones in this manner for example colluvium on hillslope noses is somewhat more weathered than that on hollow floors and sideslopes

permo carboniferous magmatism of the northeast german basin abstract variscan continent continent collision in central europe was followed by a period of syn to late tectonic magmatism involving the extrusion of large volumes of permosilesian age volcanic rocks particularly in the northeast german basin the volcanic suite up to ca 2000 m thick comprises rhyolites acid and basic andesites and tholeiitic and alkali basalts tectono geochemical analysis in conjunction with volume calculations and petrography reveals changes in volcanic activity over time a total of five eruptive stages are recognised beginning in the stephanian and extending up into the upper rotliegend permian these include the stephanian late carboniferous andesite pre ignimbrite stage i lower rotliegend permian age explosive ignimbrite stage ii post ignimbrite stage iii late rhyolite stage iv and upper rotliegend permian age late basalt stage v in addition several volcanic centres including at least two large caldera like structures are recognised the total calculated volume for the northeast german basin volcanics is ca 48 000 km3 comprising rhyolitic rocks and ignimbrites ca 70 andesitic rocks ca 26 and basalts with cogenetic dolerites ca 4 regional variations in composition and geochemistry are related to diverse crust mantle regimes which correlate with differing positions relative to the heterogeneous basement of the variscan foredeep or within the rhenohercynian orogenic zone the crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre existing subduction influenced basaltic magma source

weathering rinds and the evolution of piedmont slopes in the southern blue ridge mountains the piedmont slopes on the west side of rich and snake mountains in the blue ridge province are composed of dozens of fans and fan remnants of various ages the fans consist of a few meters of flood and debris flow deposits overlying saprolite and deeply weathered bedrock the deposits are rich in amphibolite clasts the weathering rinds of which allowed fan surfaces to be classified into six relative age categories on the basis of rind thickness the presence of reversed remanent magnetism in one old fan deposit indicates an age of at least 780 ka however the magnetization appears to reside in secondary hematite produced by weathering rather than in original magnetite grains so that a minimum age on the order of 1 ma is more likely transverse profiles surveyed across 15 fans and fan remnants show that old surfaces may attain heights as great as 30 m above younger surfaces but that a better index of age is the convexity of the profile young surfaces show only slight transverse convexities but old su

the cosmogenic 21ne production rate in quartz evaluated on a large set of existing 21ne 10be data abstract based on a compilation of published combined 10 be and 21 ne cosmogenic nuclide data sets from quartz samples obtained at eth zurich we assess the 21 ne 10 be p21 p10 production rate ratio with the goal to determine the 21 ne production rate p21 in quartz a variety of sliding erosion islands in a 21 ne 10 be versus 10 be diagram were evaluated to find the one that fits the data best which in turn yields the most probable p21 if the 10 be production rate is known the approach minimizes the influence of samples with a complex exposure history a best fit value for p21 p10 sp sp the 10 be fraction being produced by spallation as opposed to production by muons of 4 23 0 17 is obtained for a 10 be half life of 1 39 ma adopting a p10 sp value in quartz of 4 41 0 52 at g 1 yr 1 this yields a p21 of 18 7 2 3 at g 1 yr 1 it is possible that 2 of the 21 ne is produced by fast muons

cosmogenic chlorine 36 from calcium spallation calcium is a major target element for cosmogenic 36cl production consequently 36cl rapidly reaches detectable levels in minerals such as calcite and calcium feldspar exposed at the earth s surface spallation of calcium isotopes typically accounts for 80 90 of 36cl production in these minerals with subsidiary contributions from negative muon capture by 40ca and thermal neutron capture by 35cl to provide a basis for surface exposure dating we have calibrated cosmogenic 36cl production in calcium feldspar from the 17 300 year old tabernacle hill basalt at an altitude of 1445 m and an effective geomagnetic latitude of 40 9 the calcium spallation rate is 152 11 atoms g ca 1 a 1 the corresponding rate at sea level and high latitude is estimated at 48 8 3 4 atoms g ca 1 a 1 the muon capture rate used to derive these values is 8 8 2 2 atoms g ca 1 a 1 at the tabernacle hill site scaled from a value of 4 8 1 2 atoms g ca 1 a 1 at sea level and high latitude the calcium spallation rate determined in this study is in excellent agreement with previous whole rock calibration measurements at tabernacle hill when these are recalculated with respect to the absolute timescale the calibration of 36c1 production from calcium underpins development of an exposure dating technique for calcite due to its high calcium content the 36cl production rate in calcite is higher than in any other common rock forming mineral measurement of 36cl in calcite with an accelerator mass spectrometric detection limit of 5 103 atoms per gram allows dating of limestone surfaces exposed for periods ranging from 102 106 years alternatively erosion rates from less than 1 to greater than 1000 m per year can be determined in the case of eroding karst surfaces though the 36cl production rate is lower in calcium feldspar than in calcite measurements on this mineral will provide a useful means of dating young basalt lavas

the canyon diablo impact event projectile motion through the atmosphere meteor crater is one of the first impact structures systematically studied on earth its location in arid northern arizona has been ideal for the preservation of the structure and the surviving meteoric material the recovery of a large amount of meteoritic material in and around the crater has allowed a rough reconstruction of the impact event an iron object 50 m in diameter impacted the earths surface after breaking up in the atmosphere the details of the disruption however are still debated the final crater morphology deep bowl shaped crater rules out the formation of the crater by an open or dispersed swarm of fragments in which the ratio of swarm radius to initial projectile radius cd is larger than 3 the final crater results from the sum of the craters formed by individual fragments on the other hand the lack of significant impact melt in the crater has been used to suggest that the impactor was slowed down to 12 km s by the atmosphere implying significant fragmentation and fragments separation up to 4 initial radii this paper focuses on the problem of entry and motion through the atmosphere for a possible canyon diablo impactor as a first but necessary step for constraining the initial conditions of the impact event which created meteor crater after evaluating typical models used to investigate meteoroid disruption such as the pancake and separated fragment models we have carried out a series of hydrodynamic simulations using the 3d code sova to model the impactor flight through the atmosphere both as a continuum object and a disrupted swarm our results indicate that the most probable pre atmospheric mass of the meteor crater projectile was in the range of 4x10 8 to 1 2x10 9 kg equivalent to a sphere 4666 m in diameter during the entry process the projectile lost probably 30 to 70 of its mass mainly because of mechanical ablation and gross fragmentation even in the case of a tight swarm of particles cd 3 small fragments can separate from the crater forming swarm and land on the plains tens of km away from the crater as individual meteorites starting from an impactor pre atmospheric velocity of 18 km s which represents an average value for earth crossing asteroids we find that after disruption the most probable impact velocity at the earths surface for a tight swarm is around 15 km s or higher a highly dispersed swarm would result in a much stronger deceleration of the fragments but would produce a final crater much shallower than observed at meteor crater

morphological dating of cumulative reverse fault scarps examples from the gurvan bogd fault system mongolia morphological dating of cumulative reverse fault scarps

emplacement textures in late palaeozoic andesite sills of the flechtingen roslau block north of magdeburg germany

how do you grade peperites a spectacular graded peperite of volcanic origin from the palaeogene mull lava field of nw scotland the carraig mhor bed cmb consists of a basal facies of pale sub horizontally aligned fluidal shaped clasts of hydrothermally altered basalt set in a brown complexly laminated silt to clay grade host siliciclastic sediment the basal facies of the cmb grades upwards over an interval of 10 m into an upper facies dominated by smaller and more angular clasts of identical composition set in a subordinate proportion of the same sediment matrix the distinctive textural characteristics of the cmb together with its remarkably uniform grading motif may be explained in terms of the mingling of basaltic magma and fluidised siliciclastic sediment resulting in the ductile fragmentation of magma and production of the fluidal clasts which dominate the basal facies cooling of the system led to limited brittle fragmentation yielding the finer grained sediment poor upper facies of the cmb during cooling the larger fluidal shaped clasts settled to the base of the unit through the saturated sediment producing the vertical stratigraphic grading now preserved grading occurred essentially in situ during peperite formation and cannot be attributed to remobilisation mass flow or pyroclastic phenomena

lake deposits of moderate salinity as sensitive indicators of lake level fluctuations example from the upper rotliegend saline lake middle late permian northeast germany abstract the rotliegend saline lake periodically covered wide areas of the southern permian basin in northwest europe during the permian the sedimentology mineralogy and geochemistry of lake deposits were studied to document very high frequency lake level fluctuations and to evaluate their triggers increased precipitation and marine ingressions into the basin resulted in lake extension increased run off is documented by intercalated fluvial deposits in low salinity deposits of the lake because lake deposits reflect mainly deposition in relatively wet climate phases they are not correlatable to halite deposits in other basin areas decreased precipitation is followed by shrinkage of the lake desiccation at its margins and higher lake salinity due to concentration of the brine carbonate and anhydrite contents of lake deposits increased considerably before the areas fell dry but halite is not preserved in the study area falling lake level is also reflected by the occurrence of wave ripples reflecting decreased water depth and finally by desiccation and formation of evaporite crusts not only the mineralogical content but also the colour of lake claystones changes with varying salinity anhydrite and carbonate free red claystones were replaced by violet to green and grey anhydritic and calcareous claystone or marls with increasing salinity the amount of boron adsorbed on illite also corresponds to changes in salinity and can therefore be used as a palaeosalinity indicator rare earth element concentrations within lake deposits do not reflect variations in salinity but different palaeogeographical settings marine ingressions into the lake are neither reflected by the amount of boron adsorbed onto illite nor by rare earth element contents of the lake deposits highly saline deposits are partly characterised by intensive deformation which can be interpreted as seismites or dissolution breccias

shock melting of the canyon diablo impactor constraints from nickel 59 contents and numerical modeling two main types of material survive from the canyon diablo impactor which produced meteor crater in arizona iron meteorites which did not melt during the impact and spheroids which did ultrasensitive measurements using accelerator mass spectrometry show that the meteorites contain about seven times as much nickel 59 as the spheroids lower average nickel 59 contents in the spheroids indicate that they typically came from 0 5 to 1 meter deeper in the impactor than did the meteorites numerical modeling for an impact velocity of 20 kilometers per second shows that a shell 1 5 to 2 meters thick corresponding to 16 percent of the projectile volume remained solid on the rear surface that most of the projectile melted and that little if any vaporized

regolith residence time and the concept of surface age of the piedmont peneplain the common upland weathering profile on foliated metamorphic rocks on the appalachian piedmont between alabama and maryland includes a 50 cm 1 m thick clay rich soil b horizon over 10 20 m of saprolite the saprolite retains the volume fabric and structure of the underlying parent rock but has lost about one third of the mass of the parent rock where the saprolite is thickest beneath upland drainage divides those divides are of loow slope and relief the flatness of the piedmont drainage divides provides the appearance of a planation surface of accordant summits or peneplain i interpret this flatness to be the result of three active processes volume reduction during compaction of saprolite into soil loss of mass in dissolved solids draining the soil b horizon and loss of mass from the soil surface by erosion of clay size particles the cumulative effects of these upland processes are to convert saprolite into soil to limit soil thickness and residence time and to limit the age of the oldest residual soils on the surface this results in a continual lowering of the piedmont peneplain surface this interpretation is corroborated by evidence of topographic inversion of fluvial gravels since the miocene near the fall line study of baseflow dissolved solids draining piedmont basins indicates a minimum rate of saprolite production of about 4 m ma 1 this minimum rate of production near the fall line is less than the estimated rate of surface lowering and saprolite consumption during the late tertiary and quaternary periods of topographic inversion measurement of cosmogenic 10be inventories in two 15 20 mores of piedmont upland regolith indicate a minimum residence time of residual soil and saprolite of about 1 ma this indicates a possible maximum rate of saprolite production and erosion of about 20 m ma 1 using the best available evidence therefore the typical piedmont upland regolith has a residence time of between 1 and 5 ma residence times may not be the same everywhere and ages may vary systematically across the surface the geomorphic evidence of topographic inversion and similar regolith profiles in other humid temperate and tropical regions strongly suggests that production and removal of piedmont saprolite has been an ongoing quaternary process and that most of the piedmont regolith is significantly younger than 5 ma independent geophysical evidence suggests that the rate of uplift probably involving tilting of parts of the piedmont blue ridge and valley and ridge has averaged between 5 and 20 m ma 1 through the cenozoic

sill morphology and comparison of brittle and non brittle emplacement mechanisms magmatic sheet intrusions contribute significantly to the upper crustal magma transport network the emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation previous observations have highlighted the preponderance of brittle structures associated with shallow level sheet intrusions however recent studies have suggested that non brittle host rock behaviour also occurs particularly related to the formation of magma fingers during shallow level sill intrusion here we examine both brittle and non brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems non brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics purely brittle and non brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling incorporation of variable host material behaviours in numerical and analogue modelling tuned using direct field observations may consequently further our understanding of the controls on shallow level intrusion

geometry of laccolith margins 2d and 3d models of the late paleozoic halle volcanic complex germany well data and core samples from the late paleozoic halle volcanic complex hvc have been used to describe the geometry of the rhyolitic porphyritic laccoliths and their margins the hvc formed between 301 and 292 ma in the intramontane saale basin and it comprises mainly rhyolitic subvolcanic bodies 300 km3 as well as minor lava flows and volcaniclastic deposits the major hvc laccolith units display aspect ratios ranging between 0 04 and 0 07 and they are separated by tilted and deformed carboniferous permian host sediments for the margin of the landsberg laccolith a major coarsely porphyritic unit of the hvc an exceptional data set of 63 wells concentrated in an area of 10 km2 reaching to depth of 710 m exists it was used to explore the 3d geometry and textures and to deduce an intrusion model for a 3d visualization of the landsberg laccolith margin geological object computer aided design paradigm software gocad was used curve objects have been derived from the intrusion host contacts automated gocad methods for 3d modelling failed as a result manual refinement was essential a major finding of the 3d modelling is the presence of prolate sediment rafts up to 1 400 m in length and up to 500 m in thickness surrounded by landsberg rhyolite the sedimentary rafts dip away from the laccolith centre the engulfing laccolith sheets reach thickness of 100 300 m for other hvc laccolith units lobejun petersberg brachstedt well data reveal vertical rhyolite sediment contacts or magma lobes fingering into the host sediments hvc laccolith contact textures include small scale shearing of the intruding magma and of the host sediment in addition internal shear zones have been detected inside the rhyolite bodies the present study suggests that the emplacement of successive magma sheets was an important process during laccolith growth in the hvc

in situ weathering rind erosion abstract the use of cosmogenic nuclide dating methods place in doubt the long term future of weathering rinds wrs as a chronometric tool why estimate ages when radiometric control is possible this paper presents evidence that wrs can provide invaluable clues about what particular sample would provide the most accurate cosmogenic age by avoiding inheritance of cosmogenic nuclides and by avoiding boulders undergoing spalling the key to this new use requires testing the occurrence and nature of wr erosion back scattered electron microscopy reveals that ignimbrite andesite basalt and granitic clasts experience wr erosion in all subsurface and surface contexts thus far studied in arizona california hawaii oregon and washington to understand the magnitude of wr erosion we measured wr thicknesses all while controlling the cosmogenic and surface stability ages of clasts by chlorine 36 and rock varnish microlamination dating methods our data reveal that traditional methodologies of sampling cobbles remove two thirds of the true thickness of weathering rinds calling into question many beliefs including the notion that clay minerals are not produced during weathering rind formation comparisons of optical and electron microscope measurements support concerns that measurement of wrs by color changes while useful as a pedagogical tool creates serious biases in underestimating the true dynamics of wrs in the end we found that concordance of wr and rock coating age trends indicates the ideal boulder for cosmogenic nuclide dating offsets reveal either ongoing boulder erosion invalidating zero erosion model ages or a potential problem with inheritance of cosmogenic nuclides

the canyon diablo impact event 2 projectile fate and target melting upon impact abstract despite its centennial exploration history there are still unresolved questions about meteor crater the first recognized impact crater on earth this theoretical study addresses some of these questions by comparing model results with field and laboratory studies of meteor crater our results indicate that meteor crater was formed by a high velocity impact of a fragmented projectile ruling out a highly dispersed swarm as well as a very low impact velocity projectile fragmentation caused many fragments to fall separately from the main body of the impactor making up the bulk of the canyon diablo meteorites most of these fragments were engulfed in the expansion plume as they approached the surface without suffering high shock compression and were redistributed randomly around the crater thus the distribution of canyon diablo meteorites is not representative of projectile trajectory as is usual for impactor fragments in smaller strewn fields at least 50 of the main impactor was ejected from the crater during crater excavation and was dispersed mostly downrange of the crater as molten particles spheroids and highly shocked solid fragments shrapnel when compared with the known distribution model results suggest an impactor from the sw overall every model case produced much higher amounts of pure projectile material than observed the projectile target mixing was not considered in the models however this process could be the main sink of projectile melt as all analyzed melt particles have high concentrations of projectile material the fate of the solid projectile fragments is still not completely resolved model results suggest that the depth of melting in the target can reach the coconino sandstone formation however most of the ejected melt originates from 30 40 m depth and thus is limited to moenkopi and upper kaibab material some melt remains in the target based on the estimated volume of the breccia lens at meteor crater our models suggest at most a 2 content of melt in the breccia finally a high water table at the time of impact could have aided strong dispersion of target and projectile melt

soil development in till of various ages in northeastern pennsylvania abstract eleven well drained soils formed in till parent materials of varying ages in northeastern pennsylvania were studied to determine changes in the soils with time four profiles three lackawanna and one bath were formed in woodfordian till 15 000 yr b p and two leck kill were formed in altonian till 28 000 75 000 yr b p in these soils the extractable iron oxide extractable aluminum oxide and kaolinite contents increase with age as do the total clay and fine total clay ratio with increasing age the maximum accumulation of these constituents is found deeper in the profile the extractable silicon oxide distribution is constant with depth but it decreases in overall amount with time gibbsite is found only in small amounts in the a horizon of altonian soils but occurs throughout the profile of pre wisconsinan soils although only in small amounts in general differences were found in these soils which separated them into three groups representing varying degrees of soil development a regression equation was derived to predict the age of soils formed from the altonian till based on a clay accumulation index value for soils of known woodfordian and holocene ages the equation log y 1 80 0 992 log x best fit the data with an r 2 value of 0 913 using this equation a mean age of 41 000 yr was calculated for the altonian soils this date was used to derive a second equation to predict ages for pre wisconsinan soils the equation with the highest r 2 value 0 934 was log y 1 81 0 998 log x dates for soils developed in the white deer till and the laurelton till of the pre wisconsinan stage were calculated to be 86 000 and 91 000 yr b p respectively these dates fall within ages estimated for the sangamon interglaciation and thus would appear to be too young for pre sangamonian materials the probable reason for the too young age is that the c horizon material of the pre wisconsinan soils was weathered and did not provide an accurate estimate of clay accumulation for the prediction equation

two large meteorite impacts at the cretaceous paleogene boundary the end cretaceous mass extinction has been attributed by most to a single asteroid impact at chicxulub on the yucatan peninsula mexico the discovery of a second smaller crater with a similar age at boltysh in the ukraine has raised the possibility that a shower of asteroids or comets impacted earth close to the cretaceous paleogene k pg boundary here we present palynological and 13 c evidence from crater fi ll sediments in the boltysh impact crater our analyses demonstrate that a post impact fl ora formed on the ejecta layer was in turn devastated by the k pg event the sequence of flrecovery from the k pg event is directly comparable with that in middle north america we conclude that the boltysh crater predated chicxulub by 2 5 k y a time scale that constrains the likely origin of the bodies that formed the two known k pg craters

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

application of in situ produced cosmogenic 10be and 26al to the study of lateritic soil development in tropical forest theory and examples from cameroon and gabon abstract depth profiles of in situ produced cosmogenic nuclides including 10 be t 1 2 1 5 10 6 years and 26 al t 1 2 0 73 10 6 years in the upper few meters of the earth s crust may be used to study surficial processes quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations in this paper we discuss the fundamentals of the method and apply it to two lateritic sequences located in african tropical forests

late paleozoic volcanism in the central part of the southern permian basin ne germany w poland facies distribution and volcano topographic hiati based on facies analysis of more than 5 500 m cores of 45 deep wells three large sub provinces have been defined for the lower rotliegend volcanic rocks in the central southern permian basin spb in northeastern germany and western poland additional data came from unpublished descriptions of more than 200 wells the three sub provinces are a the mecklenburg vorpommern sub province mvsp dominated by silica rich lava domes and subvolcanic intrusions b the eastern brandenburg sub province ebsp dominated by a mg andesite shield volcano complex which extends into western poland and c the flechtingen altmark sub province fasp with prominent ignimbrite sheets punctuated by lava domes and flows whereas in ne germany thickness of up to 2 300 m have been found in places in western poland ignimbrites and other pyroclastic deposits as well as andesitic and silica rich lava complexes accumulated successions of a few hundreds of meters a hiatus of up to 30 ma occurs between the lower rotliegend volcanic and sedimentary rocks asselian sakmarian and upper rotliegend ii sediments upper wordian capitanian upper rotliegend i deposits are known from a few wells and outcrops only previous studies postulated solely intrabasinal tectonics to account for this major unconformity however under semiarid to arid conditions as assumed for the rotliegend of the spb both sio2 rich lava complexes and silica poor shield volcanoes can be expected as being extremely resistant to weathering and erosion most probably these bodies drowned in a regolith formed by physical weathering rarely removed by torrential rain thus the silica rich lava complexes and the shield volcanoes in the central european basin system cebs can be viewed as long living morphological highs with intervolcanic depressions in between in these intervolcanic depressions syn to postvolcanic successions of conglomeratic to sandy alluvial fan sediments and lake to mud flat deposits accumulated during the upper rotliegend i they show numerous pedogenic horizons representing times of non deposition during the upper rotliegend ii the remaining volcano topography was filled up with alluvial eolian and playa deposits in some places in western poland covering was not complete until the zechstein latest permian at the same time soil formation and or erosion in the upper part of sio2 rich complexes and shield volcanoes remained subordinate consequently the volcano topographic hiatus on top of the volcanic complexes comprises the maximum period of time whereas in the intervolcanic depressions this time splits into periods of deposition and numerous minor intraformational hiati intrabasinal tectonic activity cannot be ruled out as one major control of the rotliegend depositional evolution in the subsiding spb however the presence of weathering resistant volcanic edifices led to the formation of long lasting depositional gaps in many regions of the central spb

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

the chicxulub impact event and its environmental consequences at the cretaceous tertiary boundary abstract an impact mass extinction hypothesis for the cretaceous tertiary k t boundary transition has been confirmed with multiple lines of evidence beginning with the discovery of impact derived ir in k t boundary sediments and culminating in the discovery of the chicxulub impact crater likewise a link between the chicxulub impact crater and k t boundary sediments has been confirmed with multiple lines of evidence including stratigraphic petrological geochemical and isotopic data the environmental effects of the chicxulub impact event were global in their extent largely because of the interaction of ejected impact debris with the atmosphere the environmental consequences of the chicxulub impact event and their association with the k t boundary mass extinction event indicate that impact cratering processes can affect both the geologic and biologic evolution of our planet

thermoluminescence measurements on shock metamorphosed sandstone and dolomite from meteor crater arizona 2 thermoluminescence age of meteor crater thermoluminescence tl dating measurements were performed on shock metamorphosed rocks from meteor crater arizona il ages were obtained for eight specimens four coconino sandstone and four kaibab dolomite which experienced sufficient shock heating during the impact to reset their preimpact tl postimpact radiation doses were determined for each shocked fragment from thermoluminescence measurements on quartz mineral separates effective radiation dose rates were calculated from concentrations of uranium thorium potassium and rubidium in the rocks and their burial environment and the distributions of these elements as determined by fission track and microprobe analyses cosmic radiation dose rates were estimated by altitude scaling of sea level data and were corroborated by tl dosimeter measurements at the crater the mean tl ages for the two rock types were reasonably concordant 50 400 2900 and 46 000 3100 years for sandstones and dolomites respectively the overall mean age 49 000 3000 years is significantly older than the 25 000 year age estimate based on the inferred correlation of the oldest pluvial episode at the crater with radiometrically dated 18o maxima

cosmogenic 26al in the atmosphere and the prospect of a 26al 10be chronometer to date old ice abstract cosmogenic radionuclides in the one million year half life range offer unique possibilities for age determinations in geophysics in measurements where the radioactive decay is being utilized as a clock uncertainties in age determinations may be reduced if the ratio of two radioisotopes with different half lives can be used as a chronometer in this work we investigate the atomic ratio of atmospheric 26al t1 2 0 717 ma to 10be t1 2 1 386 ma measured with accelerator mass spectrometry ams and its potential as a chronometer for dating old ice the 26al 10be ratio decreases with an effective half life of t1 2 26al 10be 1 49 ma for its application as a chronometer the atmospheric 26al 10be ratio has to be well characterized however the properties of atmospheric 26al have been understood only poorly so far at the vera ams facility of the university of vienna a first systematic study of the global variations of the 26al 10be ratio in the atmosphere and in surface firn has been carried out and pilot measurements of the 26al 10be ratio in deep antarctic ice have been performed our results indicate that this ratio is globally constant to within 5 in the atmosphere and in surface firn with a mean value of 1 89 10 3 the data also suggest that non atmospheric sources of 26al such as extraterrestrial in situ produced or re suspended 26al do not contribute significantly to the observed 26al 10be ratio in addition atmospheric mixing seems to exert only a minor influence in a first application of the method 26al 10be ratios were measured in chips collected in connection with the drilling of the lowest part of an ice core 2250 to 2760 m in dronning maud land antarctica surprisingly variable 26al 10be ratios ranging between 0 5 and up to 2 times the atmospheric ratio were found at different locations in this deep ice core while the cause for the ratios higher than atmospheric remains unexplained so far the ratios lower than atmospheric may be caused by radioactive decay allowing a first dating attempt using the 26al 10be ratio thus at an ice depth of 2760 m an approximate date of 6 7 2 6 105 years was established

cosmogenic 14c in carbonate rocks abstract the rate of in situ production of cosmogenic 14 co in limestone is 18 3 atom g caco3 year corrected to high latitude and sea level based on measurements of 14 co in limestone associated with the bonneville provo shoreline complex in utah in situ cosmogenic 14 co was separated cryogenically from co2 using 14 c dead co as a carrier for in situ cosmogenic 14 co this rate of production was used to estimate an age of 4360 1220 cal year b p for the last movement on the south oquirrh mountain fault zone in northern utah and an age of at least 10 600 900 years for the penultimate event of the pleasant valley fault in northern nevada

the geochronology of large igneous provinces terrestrial impact craters and their relationship to mass extinctions on earth the relationship between sudden catastrophic events and sudden mass extinctions on earth has attracted a great deal of research effort including measurements of the absolute and relative ages of these events the result has been a rapid improvement in the precision and accuracy of radiometric dates for large igneous provinces lips for which there is now a consensus on the peak eruption times over the last 250 ma in parallel there has been a more gradual improvement in the radiometric dates for craters formed by hypervelocity impacts hvis of asteroids and comets with earth the absolute ages of the largest craters are known to within a few million years but the ages of many smaller craters are poorly constrained in addition whereas relatively few lips have formed in the last 250 ma at least one hvi crater larger than 20 km diameter has formed on earth every million years only 25 such craters have been discovered so coincidence between the ages of hvi crater formation and ages of mass extinctions is related as much to crater preservation as to coincidence of the events the difference in quality of geochronology between hvis and lips is the result of differing availability of samples lips cover large areas and present an array of basalt samples suitable for dating whereas hvi craters are often poorly preserved and present few datable samples the radiometric data for preserved hvis and lips are now sufficiently precise and accurate for us to be confident that there is no one to one correlation between either lips or hvis and global mass extinctions of life on earth however there is a close association between a significant number of lips and sudden environmental change and a very close association between at least one massive hvi crater formation and a mass extinction further there is no apparent correlation between hvis and lips and thus no reason to suggest a causative relationship finally the radiometric dating of hvi craters indicates several clusters in the geological record but the correlation with sudden environmental change is no better than for large craters

carboniferous permian volcanic evolution in central europe u pb ages of volcanic rocks in saxony germany and northern bohemia czech republic nine shrimp u pb ages on zircon and two pb pb single zircon ages have been determined from late paleozoic volcanic rocks from saxony and northern bohemia samples came from the teplice altenberg volcanic complex the meissen volcanic complex the chemnitz basin the dohlen basin the brandov olbernhau basin and the north saxon volcanic complex the teplice altenberg volcanic complex is subdivided into an early namurian phase mikulov ignimbrite 326 8 4 3 ma thus older than assumed by previous studies and a late caldera forming phase teplice ignimbrite 308 8 4 9 ma the age of the latter however is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint the leutewitz ignimbrite product of an early explosive volcanic episode of the meissen volcanic complex yielded an age of 302 9 2 5 ma stephanian a volcanic rocks intercalated in the brandov olbernhau basin bob 302 2 8 ma chemnitz basin cb 296 6 3 0 ma dohlen basin db 296 3 0 ma and the north saxon volcanic complex nsvc c 300 290 ma yielded well constrained stephanian to sakmarian ages the largest late paleozoic ignimbrite forming eruption in central europe the rochlitz ignimbrite has a well defined middle asselian age of 294 4 1 8 ma ages of palingenic zircon revealed that the namurian westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous paleozoic geodynamic phases the precambrian inherited ages support the chronostratigraphic structure assumed for the saxo thuringian zone of the variscan orogen the present results help to improve the chronostratigraphic allocation of the late paleozoic volcanic zones in central europe at the same time the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the variscan orogeny

climatic impact on isovolumetric weathering of a coarse grained schist in the northern piedmont province of the central atlantic states the possible impact of periglacial climates on the rate of chemical weathering of a coarse grained plagioclase muscovite quartz schist has been determined for a small watershed near baltimore maryland the isovolumetric chemical weathering model formulated from the geochemical mass balance study of the watershed shows that the weathering front advances at a velocity of 9 1 m m y if the modern environmental parameters remain the same back through time however recent surficial geological mapping demonstrates that periglacial climates have impacted the area such an impact significantly affects two key chemical weathering parameters the concentration of co2 in the soil and groundwater moving past the weathering front depending upon the assumptions used in the model the rate of saprolitization varies from 2 2 to 5 3 m m y the possible impact of periglacial processes suggested by the chemical weathering rates indicates a need to reconsider theories of landscape evolution as they apply to the northern piedmont province of the mid atlantic states i suggest that from the late miocene to the present that the major rivers have become incised in their present locations this incision has enhanced groundwater circulation and chemical weathering such that crystalline rocks beneath interfluvial areas remain mantled by saprolite and the saprolite mantle has been partially stripped as periglacial conditions alternate with humid temperate conditions

a middle wisconsin pollen record from hay lake arizona abstract the lower part of a 5 m core from hay lake 34 n 109 25 w at 2780 m in east central arizona provides a pollen record for the middle wisconsin identification of fossil pines is based on a key modified from hansen and cushing 1973 geological society of america bulletin 84 1181 1200 pinus edulis and p monophylla are similar in size and morphology but are significantly different from p flexilis haploxylon pines dominate the pollen record the abundance of pinyon pines during the middle wisconsin is interpreted as indicating that this group was widespread at lower elevations the local vegetation was mixed conifer forest consisting of picea p aristata p flexilis and or p strobiformis and with p ponderosa and or p contorta after about 26 000 yr b p tree line was above the elevation of hay lake the middle wisconsin climate is inferred to have been cooler than today and is marked by more available moisture that permitted pinyon pines to grow at low elevations

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

age and effects of the odessa meteorite impact western texas usa the odessa meteorite craters texas united states include a main crater 160 m diameter 30 m deep plus four smaller meteorite craters the main crater was sampled by coring to 22 m depth to better understand its origin and history dating by optically stimulated luminescence indicates that it was produced immediately prior to ca 63 5 4 5 ka sediment filling the crater includes impact breccias produced at the time of impact wind dominated silts with minor amounts of pond sediments deposited ca 63 5 ka probably just after the impact and ca 53 2 ka wind dominated silt ca 38 1 7 ka and playa muds with a wind blown silt component younger than 36 ka the environment was arid or semiarid at the time of impact based on characteristics of soils on the surrounding landscape the impact caused severe damage within 2 km and produced 1000 km hr winds and thermal pulse animals within a 1 1 5 km diameter area were probably killed this is only the second well dated pleistocene hypervelocity impact crater in north america

recent aqueous environments in martian impact craters an astrobiological perspective the discovery of gullies and debris aprons raises the question of the existence of aqueous environments on mars in recent geological times and its astrobiological implications three cases of such environments are surveyed at moc high resolution in the e gorgonum chaos and newton and hale craters the regional setting of these craters suggests that the mechanisms of aquifer destabilization flow discharge and gully formation in these three cases result from local geological triggers that can include impact cratering and tectonic processes rather than climate or insolation factor we take as a working hypothesis that microbial life appeared on mars in ancient geological times probably in a geothermal environment but potentially evolving via infrared detection systems to give photosynthetic communities under the selective pressure of energetic solar radiation we hypothesize that some microbial communities could have survived underground in either dormant or active state or that their biomolecules could be preserved either frozen or desiccated in the subsurface beneath the upper oxidized zone we assess the known environmental constraints for life and what type of potential habitats are provided in these three craters by aquifer discharges using comparison with terrestrial analogues and their associated microbial communities these environments include 1 the release of water on a dry crater floor in e gorgonum and the possibility for microorganisms and preserved biomolecules to be flushed out and mixed in with the sediment exposed at the surface 2 the evidence of a recent lacustrine episode in the newton crater with analogy to antarctic dry valley lakes 3 the exposure on the floor of hale crater of material from a regional subsurface that is likely to have retained traces of one of the oldest martian bodies of water recognized to date parker et al 2000 in the argyre basin we show how the water in argyre 3 8 billion years ago gya was likely to have been alterated by hydrothermal processes and how the subsequent formation of the 150 km hale crater on the northern ring of argyre generated hydrothermal pumping this accounts for the anomalously high location of the springs on the crater crests today with respect to the rest of the regional subsurface distribution finally we envision current impact cratering as a factor for destabilizing aquifers on mars today thus creating new environments we analyze the implications of impacts for two geological types of rock units that could harbor traces of life as a result we compare the potential of astrobiological exploration of crater floors rims and ejecta on future missions to mars

control of geomorphic processes on 10be concentrations in individual clasts complexity of the exposure history in gobi altay range mongolia the dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre deposition inheritance from the post deposition history of the clasts in the studied marker moreover estimating catchment scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local regional relationships between rock exhumation and transport through space and time this is still poorly known for timescales of tens of thousand years in order to document the evolution of clast exhumation and transport rates through time we analyze in situ 10be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in gobi altay mongolia strongly affected by global climatic changes during the pleistocene holocene period samples were collected on bedrock abandoned alluvial deposits active colluvia and alluvia our results show a large 10be scattering in the active river bed consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision on the contrary pre exposure signal within abandoned terraces is much more homogeneous consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport these results show that exhumation transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations the occurrence of abrupt climatic changes during short periods of time recorded by 10be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers on the other hand strong and short erosion events limit and homogenize the pre exposure 10be signal in associated deposits like debris flows making them particularly suitable markers for dating in active tectonic and paleoclimatic studies

the significance of garnet in the permo carboniferous volcanic rocks of the pyrenees garnet occurs within rhyolitic to dacitic lavas ignimbrites and volcaniclastic sediments of the pyrenean calc alkaline permo carboniferous volcanic rocks on the basis of texture and major and trace element composition the garnet is interpreted as having a phenocrystal as opposed to a xenocrystal or restite origin the pyrenean silicic volcanics are strongly peraluminous consistent with derivation as a partial melt from a sedimentary source they were erupted contemporaneously with the hercynian thermal anomaly which produced regional granulite facies metamorphism and anatectic granites the late hercynian granodiorites were also intruded at about this time geochemical data suggest that the petrogenesis of the volcanic rocks differed from that of the granodiorites ree garnet matrix partition coefficients for garnets from a welded rhyolitic ignimbrite are similar to those reported for other phenocrystal garnets in rhyolites ree abundances imply that the garnets crystallized from a hree depleted melt and this is considered to reflect the effects of garnet in the restite experimental constraints suggest that the garnet crystallized at pressures 4 5kb implying that the rhyolites originated from 14 17km depth and were erupted rapidly from these depths in order for the garnet to survive these figures place constraints on the thermal regime prevailing in the late stages of the hercynian orogeny

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

mars chronology assessing techniques for quantifying surficial processes abstract currently the absolute chronology of martian rocks deposits and events is based mainly on crater counting and remains highly imprecise with epoch boundary uncertainties in excess of 2 billion years answers to key questions concerning the comparative origin and evolution of mars and earth will not be forthcoming without a rigid martian chronology enabling the construction of a time scale comparable to earth s priorities for exploration include calibration of the cratering rate dating major volcanic and fluvial events and establishing chronology of the polar layered deposits if extinct and or extant life is discovered the chronology of the biosphere will be of paramount importance many radiometric and cosmogenic techniques applicable on earth and the moon will apply to mars after certain baselines e g composition of the atmosphere trace species chemical and physical characteristics of martian dust are established the high radiation regime may pose a problem for dosimetry based techniques e g luminescence the unique isotopic composition of nitrogen in the martian atmosphere may permit a mars specific chronometer for tracing the time evolution of the atmosphere and of lithic phases with trapped atmospheric gases other mars specific chronometers include measurement of gas fluxes and accumulation of platinum group elements pge in the regolith putting collected samples into geologic context is deemed essential as is using multiple techniques on multiple samples if in situ measurements are restricted to a single technique it must be shown to give consistent results on multiple samples but in all cases using two or more techniques e g on the same lander will reduce error while there is no question that returned samples will yield the best ages in situ techniques have the potential to be flown on multiple missions providing a larger data set and broader context in which to place the more accurate dates

textural variations and fragmentation processes in peperite formed between felsic lava flow and wet substrate an example from the cretaceous buan volcanics southwest korea abstract multiple exposures of peperite within the cretaceous buan volcanics southwest korea have been examined in order to determine variations in their textural characteristics and to investigate their mode of formation along undulating boundaries between rhyolite lava flow and deformed host sediment expressed as a series of load and flame structures exposures commonly contain two distinct types of peperite type 1 peperites are composed mostly of rounded juvenile clasts at their base and polyhedral juvenile clasts at their upper levels interpreted to have formed via a two stage process firstly abrasion of juvenile clasts occurred after their fragmentation due to shear stress imparted by the overlying and still moving lava flow forming rounded juvenile clasts subsequent in situ quenching fragmentation of the lava flow produced clasts with platy to polyhedral shapes immediately after emplacement of the lava flow type 2 peperites laterally extend into the interior of featureless rhyolite as layers that decrease in thickness with increasing distance away from the flame zone these layers exhibit horizontal textural variations ranging from poorly sorted mixtures of ash to block sized angular juvenile clasts in the proximal zone to closely packed polyhedral and tabular juvenile clasts with jigsaw crack textures in the middle and distal zones type 2 peperite are inferred to have formed due to internal steam explosions that resulted from an expansion of heated pore water leading to an increase in pore fluid pressure that had been vertically injected into the interior of the rhyolite from the flame zone the proximal zone composed mainly of poorly sorted mixtures of juvenile clasts represents the explosion sites juvenile clasts in the middle and distal zones are interpreted to have formed due to three separate processes the development of fractures in the rhyolite during the internal steam explosions injection of the host sediment through the fractures and in situ quenching fragmentation deformation of the host sediment exerted an important control on peperite forming processes with the internal steam explosions suggested to have formed the closely packed juvenile clasts with a jigsaw crack texture rather than the clasts that are widely dispersed

dating a small impact crater an age of kaali crater estonia based on charcoal emplaced within proximal ejecta the estimates of the age of the kaali impact structure saaremaa island estonia provided by different authors vary by as much as 6000years ranging from similar to 6400 to similar to 400 before current era bce in this study a new age is obtained based on c 14 dating charred plant material within the proximal ejecta blanket which makes it directly related to the impact structure and not susceptible to potential reservoir effects our results show that the kaali crater was most probably formed shortly after 1530 1450 bce 3237 10 c 14 yr bp saaremaa was already inhabited when the bolide hit the earth thus the crater forming event was probably witnessed by humans there is however no evidence that this event caused significant change in the material culture e g known archeological artifacts or patterns of human habitation on saaremaa

quaternary geochronology and distribution of mammuthus on the colorado plateau there are 41 known localities containing mammoth remains from the colorado plateau 24 in arizona 12 in utah 3 in new mexico and 2 in colorado of the 41 localities 13 32 arizona and utah only have yielded radiometric dates sup 14 c and u th 10 77 of these have been the result of the authors investigations the four youngest radiocarbon dates produce a weighted average date of approximately 11 270 plus minus 65 yr b p the youngest directly aged mammoth remains on the colorado plateau mammoth remains are recovered predominantly in alluvial regimes in addition to alcove cave and spring deposits no direct association of mammuthus and the clovis hunters has been reported from the colorado plateau dietary intake recorded in dung remains included predominantly graminoids in addition to various woody shrubs and trees that currently grow at higher elevations on the colorado plateau

techniques for measuring rock weathering application to a dated fan segment sequence in southern tunisia there are a number of techniques for estimating the amount of weathering a clast has undergone these usually have the objective of establishing an ordinal chronology of geomorphological surfaces or investigation of site specific conditions affecting weathering rates three such techniques are applied to a dated sequence of alluvial fan segments in southern tunisia two of these techniques depend on measuring surface roughness the micro roughness meter and a displacement approach and one uses the structural weakening of the rock fabric schmidt hammer the micro roughness meter enables calculation of standard deviation of surface height variation root mean square roughness and surface autocorrelation function of these techniques schmidt hammer rebound values standard deviation root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0 05 level however the amount of variance in all datasets is very large indicating the need for caution in application of these techniques for relative dating 1998 john wiley sons ltd

alluvial soil chronosequence in the inner coastal plain central virginia abstract a chronological sequence of soils formed on a series of alluvial depositional surfaces ranging in age from late middle miocene to late pleistocene was characterized to clarify soil geomorphic relations and provide a basis for allostratigraphic subdivision of the inner coastal plain on quaternary river terraces ultic hapludalfs containing abundant weatherable mineral species and clast types are estimated to have formed in 60 000 120 000 yr whereas typic hapludults greatly depleted in weatherable minerals and showing strong weathering of clast types are estimated to be 700 000 1 600 000 yr old typic paleudults with incipient plinthite duripan and ferricrete development characterize interfluves that have been little eroded since early pliocene time 3 4 5 3 myr ago typic plinthic paleudults with intense weathering of siliceous clasts and moderate to strong duripan and ferricrete development are found on surfaces that formed near the beginning of late miocene time 10 8 13 0 myr ago chemical weathering in the chronosequence may be classified into three progressive stages 1 decomposition of unstable sand and silt sized minerals into a mixed stable unstable clay mineral suite stable fe al si bulk chemical composition 107 yr not all soil properties show unidirectional development nor is a steady state of pedon development observed even after approximately 107 yr of chemical weathering soil development in the chronosequence is episodic the transition from one phase to the next is marked by a change in rate and sometimes a reversal in the direction of development of one or more soil properties

weathering and soil development on fan surfaces as a function of height above modern drainageways roan mountain north carolina abstract a relative age chronosequence has been established for fan surfaces on the west and south piedmont slopes of roan mountain north carolina based on measurements of weathering and soil development indices at 20 sites in addition to standard soil properties measurements were made of amphibolite clast weathering rind thickness maximum surface boulder size and mean size and sorting of a 10 kg whole sediment sample from the c horizon soils lacking bt horizons occur only at high altitudes at or near the heads of young fans excepting these locations the youngest fan surfaces have soils with bt horizons generally less than 60 cm thick hues of 10 7 5yr maximum clay contents less than 35 percent rind thicknesses less than 1 2 mm and maximum boulder diameters of 1 2 m soils of the oldest fan surfaces have bt horizons 75 200 cm thick hues of 5 2 5yr rind thicknesses of 6 14 mm maximum clay contents of 40 60 percent and maximum boulder diameters less than 0 75 m although the youngest fan surfaces are close to the level of modern drainageways the oldest stand as much as 20 m above these drainageways and are obviously relict features an index of fan height above modern drainageways was devised that combines height above lateral drainageways with height above the main stream of the valley into which the fan debouches many weathering and soil development properties correlate significantly with this height index including weathering rind thickness r 0 86 munsell hue 0 65 maximum percent clay 0 59 graphic mean phi units of whole sediment particle size analysis 0 54 maximum boulder diameter 0 52 maximum percent free iron in b horizon 0 50 and thickness of bt horizon 0 49 a soil weathering soil development index using these parameters shows a 0 82 correlation coefficient with the height index a cluster analysis shows that the 20 sites can be placed into three distinct groups suggesting that the formation of fan surfaces may be episodic on long time scales a comparison of the fan map with a county soils map shows that the oldest fan surface is fairly consistently mapped as dillsboro series but that the younger fan surfaces show no consistent relationship to soils mapping

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

boulder streams debris fans and pleistocene climate change in the blue ridge mountains of central virginia the west slope of the blue ridge mountains in central virginia is a polygenetic landscape containing interglacial and periglacial features this paper proposes a general model relating the distribution and origin of hillslope and toeslope quaternary landforms to climatically influenced geomorphic processes two generations of interglacial debris fans in the study area differ in their degree of soil development and clast weathering boulder streams which clog debris flow chutes for the upper debris fans are interpreted as solifluction features formed during successive periglacial episodes growth of the boulder streams and associated talus slopes can influence the magnitude and frequency of debris flows and fan formation during interglacials

magnetostratigraphy of sediments in mammoth cave kentucky clastic sediment deposits found within the caves of mammoth cave national park have yielded a magnetostratigraphic pattern of magnetic polarity reversals which indicates that they were deposited over a range of at least 1 million and most likely 2 million years

air blast produced by the meteor crater impact event and a reconstruction of the affected environment using scaling relationships determined from nuclear explosions the radial extent of the air blast produced by the meteor crater impact event is estimated the wind velocity at a distance of 5 crater radii 3 km from the point of impact should have exceeded 2000 km h hurricane force winds would have existed as far away as 20 to 40 km depending on the exact explosive energy of the impact event to determine how this event may have affected the environment surrounding the crater the topography vegetation and animal life that existed at the time of the impact are reconstructed for example if the coniferous woodlands were 100 m lower than they are presently and they had moved farther out onto the plains then the air blast would have flattened trees within a 16 to 22 km radius of the point of impact and damaged them over an area of 4100 to 8500 km2 the distance over which the damage occurred may have been up to 2 larger in some directions around the crater because of additional effects produced by the ballistic shock wave unfortunately since the trajectory of the projectile is not well known the direction of the ballistic shock wave effects cannot yet be determined

earth impact effects program a web based computer program for calculating the regional environmental consequences of a meteoroid impact on earth we have developed a web based program for quickly estimating the regional environmental consequences of a comet or asteroid impact on earth www lpl arizona edu impacteffects this paper details the observations assumptions and equations upon which the program is based it describes our approach to quantifying the principal impact processes that might affect the people buildings and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions the program requires six inputs impactor diameter impactor density impact velocity before atmospheric entry impact angle the distance from the impact at which the environmental effects are to be calculated and the target type sedimentary rock crystalline rock or a water layer above rock the program includes novel algorithms for estimating the fate of the impactor during atmospheric traverse the thermal radiation emitted by the impact generated vapor plume fireball and the intensity of seismic shaking the program also approximates various dimensions of the impact crater and ejecta deposit as well as estimating the severity of the air blast in both crater forming and airburst impacts we illustrate the utility of our program by examining the predicted environmental consequences across the united states of hypothetical impact scenarios occurring in los angeles we find that the most wide reaching environmental consequence is seismic shaking both ejecta deposit thickness and air blast pressure decay much more rapidly with distance than with seismic ground motion close to the impact site the most devastating effect is from thermal radiation however the curvature of the earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon

erosion of ejecta at meteor crater arizona new methods for estimating erosion at meteor crater arizona indicate that continuous ejecta deposits beyond 1 4 1 2 crater radii from the rim 0 25r 0 5r have been lowered less than 1 m on the average this conclusion is based on the results of two approaches coarsening ofunweathered ejectainto surface lag deposits and calculation of the sediment budget within a drainage basin on the ejecta preserved ejecta morphologies beneath thin alluvium revealed by ground penetrating radar provide qualitative support for the derived estimates although slightly greater erosion 2 3 m of less resistant ejecta locally has occurred such deposits were limited in extent particularly beyond 0 25r 0 5r from the present rim subtle but preserved primary ejecta features e g distal ejecta lobes and blocks further support our estimate of minimal erosion of ejecta since the crater formed 50 000 years ago unconsolidated deposits formed during other sudden extreme events e g landslides exhibit similarly low erosion over the same time frame the common factor is the presence of large fragments or large fragments in a matrix of finer debris at meteor crater fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse grained ejecta fragments that armor surfaces and slow vertical lowering

late quaternary paleoclimates and biotic responses in eastern north america and the western north atlantic ocean abstract broad scale late quaternary paleoclimatic changes are interpreted from palynological records across eastern north america and from assemblages of marine foraminifera in the western north atlantic ocean quantitative reconstructions of past dominance for major tree taxa at eight fossil pollen sites located south of the maximum glacial extent in the southeastern united states illustrate dramatic responses of tree populations to climatic change during the transition from pleistocene to holocene conditions a series of maps depicting changes in inferred boundaries of predominant airmasses during the late quaternary are based upon paleoclimatic interpretation of paleovegetation maps for eastern north america and climap maps of winter sea surface temperatures for the western north atlantic ocean in the eastern united states at 18 000 b p strong zonal circulation resulted in a fixed position of the atmospheric polar frontal zone along 33 n latitude the pacific airmass extended from 33 n latitude north to the southern margin of the laurentide ice sheet with the maritime tropical airmass dominating south of 33 n across the gulf coastal plain the gulf of mexico and the equatorial atlantic ocean the oceanic polar frontal zone extended northeastward from cape hatteras to 37 n in the western north atlantic ocean late glacial climatic amelioration was first reflected in vegetational changes south of the laurentide ice sheet beginning at 16 500 b p late glacial weakening in zonal atmospheric flow resulted in the penetration of the maritime tropical airmass farther to the north during the summer season increased summer warmth and rain produced substantial melting of the southern flank of the laurentide ice sheet the early holocene interval from 12 500 to 8 000 b p bracketed the time of maximum seasonality of solar radiation ca 11 000 b p during the early holocene enhanced meridional air flows resulted in increased seasonality of temperatures by 10 000 b p the oceanic polar frontal zone was displaced northward from the gulf stream anomalously cold maritime climatic conditions persisted along the central atlantic coast reflecting the position of the cold marine labrador current between the atlantic seaboard and the gulf stream during the mid holocene or hypsithermal interval from 8 000 to 4 000 b p prevailing westerlies expanded the midcontinental region of warmth and aridity for the last 4 000 years the modern climatic regime has been characterized by increased meridional flow

an andesitic sill complex in the southern permian basin volcanogenetic model and stratigraphic implications subvolcanic intrusions are highly variable in shape and structure and occur in nearly all parts of the upper crust as a result of extensive volcanic activity processes of subvolcanics interacting with the host rock are insufficiently understood as they are rarely exposed in the southernmost part of the flechtingen altmark subprovince sub volcanic rocks of the flechtingen volcanic complex fvc are exposed in several quarries it is built up of silicic tuffs ignimbrites and lava flows but also of intermediate lavas and extended sill sheets additionally major granitic intrusions exposed by drillings are associated with the fvc in the mammendorf quarry a sill intruded in between lithified turbiditic series of early carboniferous visean serphukovian age at the base and widely consolidated volcanoclastic deposits of late carboniferous late pennsylvanian age at the top various magma host rock interactions were found indicating brittle and ductile deformation patterns occurring at the basal contact and secondary fluidal mixing predominantly occurring at the top contact most probably caused by fluids accompanying the intruding magma we present an extended volcanogenetic model for the fvc volcanic activity initiated at 302 3 ma with fallout deposits represented by mostly re deposited silicic ashfall deposits of the flechtingen formation and cumulated in depositing major ignimbrite series most likely forming a caldera later the sills intruded at the rheological boundary of the lithified mississippian turbiditic series and the partly consolidated volcanoclastic series finally major granitic intrusions emplaced in the basement rocks at around 298 4 ma the study contributes to clarify stratigraphic constraints of late carboniferous to early permian continental deposits and sheds light on stratigraphy of significant late paleozoic volcanic deposits of the flechtingen altmark subprovince in the southern permian basin

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

the late paleozoic felsic lava dominated large igneous province in northeast germany volcanic facies analysis based on drill cores in the deep subsurface of the northeast german basin products of extensive volcanism are present that formed during the waning phase of the variscan orogeny permian carboniferous boundary large volumes 48 000 km3 of dominantly felsic magma were emplaced in the northern foreland of the variscan mountains in a terrestrial semi arid environment most of these units were inferred by previous authors to represent the products of explosive volcanic eruptions such as ignimbrites however a detailed analysis of the volcanic texture and lithofacies association shows that most units are best interpreted as coherent lavas emplaced either as extrusive units or as shallow intrusions with important implications for the reconstruction of the paleo environment this study shows that detailed textural examination of drill cores provide important observations which can be applied as criteria for the interpretation of the mode of volcanic eruptions furthermore phenocryst logging and geochemical fingerprinting based on immobile element ratios can be employed for the classification and discrimination of individual emplacement units

dating inset terraces and offset fans along the dehshir fault iran combining cosmogenic and osl methods summary be and 36 cl cosmic ray exposure cre and optically stimulated luminescence osl dating of offset terraces have been performed to constrain the long term slip rate of the dehshir fault analysis of cosmogenic 10 be and 36 cl in 73 surface cobbles and 27 near surface amalgamscollectedfrominsetterracesdemonstratestheoccurrenceofalowdenudationrateof 1mm a 1 and of a significant and variable inheritance from exposure prior to the aggradation of these alluvial terraces the significant concentrations of cosmogenic nuclides measured in the cobbles collected within the riverbeds correspond to 72 20 ka of inheritance the mean creageofthesurfacesamplescollectedontheolderterracet3is469 88kabuttheanalysis of the distribution of 10 be concentration in the near surface samples discard ages older than 412 ka the mean cre age of the surface samples collected on terrace t2 is 175 62 ka but the 10 be depth profile discard ages older than 107 ka for each terrace there is a statistical outlier with a younger age of 49 9 3 3 and 235 5 35 4 ka on t2 and t3 respectively the late sediments aggraded before the abandonment of t2 and inset levels t1 b and t1a yielded osl ages of respectively 26 9 1 3 21 9 1 5 and 10 0 0 6 ka for a given terrace the osl ages where available provide ages that are systematically younger than the cre ages these discrepancies between the cre and osl ages exemplify the variability of the inheritance and indicate the youngest cobble on a terrace that minimizes the inheritance is the most appropriate cre age for approaching that of terrace abandonment however the upper bound on the age of abandonment of a terrace that is young with respect to the amount of inheritance is best estimated by the osl dating of the terrace material for such terraces the cre measurements are complementary of osl dating and can be used to unravel the complex historyofweatheringandtransportinthecatchmentofdesertalluvialfans thiscomprehensive set of dating is combined with morphological offsets ranging from 12 2t o 380 20 m to demonstrate the dehshir fault slips at a rate in the range 0 9 mm yr 1 1 5 mm yr 1 t he variable inheritance exemplified here may have significant implications for cre dating in arid endorheic plateaus such as tibet and altiplano

petrographic studies of the impact melts from meteor crater arizona usa we investigated the ballistically dispersed melts from meteor crater arizona usa to determine the stratigraphic extent of its melt zone from the compositional relationship of melts and target rocks most melt particles are crystallized hydrated and oxidized pristine glasses are rare hydration and oxidation occurred at ambient temperatures long after the impact the preserved glasses are generally clear and texturally homogeneous but unlike typical impact melts they have unusually heterogeneous compositions both within individual particles and from sample to sample for example the average sio2 for individual particles ranges from 43 to 65 the projectile content is unusually high and it is distributed bimodally with specific samples containing either 5 10 or 20 30 feo these compositional heterogeneities most likely reflect the high carbonate content of the target rocks and the release of copious co2 that dispersed the melts thereby terminating melt flow and mixing the high projectile content and the co2 depleted residue of purely sedimentary rocks produced mafic melts that crystallized fine grained olivine and pyroxene the melts fall into three compositional groups reflecting variable proportions of the major target formations moenkopi kaibab and coconino least square mixing calculations revealed one group to contain 55 moenkopi 40 quartz rich upper kaibab and 5 meteorite suggesting a source depth of 90 m or 30 m respectively additional studies especially hydrocode calculations are needed to better understand the source depth of these melts and their exceptionally high projectile content

magma traps and driving pressure consequences for pluton shape and emplacement in an extensional regime abstract the level of emplacement and final form of felsic and mafic igneous rocks of the wichita mountains igneous province southwestern oklahoma u s a are discussed in light of magma driving pressure lithostatic load and crustal magma traps deposition of voluminous a type rhyolites upon an eroded gabbroic substrate formed a subhorizontal strength anisotropy that acted as a crustal magma trap for subsequent rising felsic and mafic magma intruded along this crustal magma trap are the a type sheet granites length thickness 100 1 of the wichita granite group of which the mount scott granite sheet is typical and smaller plutons of biotite bearing roosevelt gabbro in marked contrast to the subhorizontal granite sheets the gabbro plutons form more equant stocks with flat roofs and steep side walls late diabase dikes cross cut all other units but accompanying basaltic flows are extremely rare in the volcanic pile based on magmastatic calculations we draw the following conclusions concerning the level of emplacement and the shape of these intrusions 1 magma can rise to a depth at which the magma driving pressure becomes negligible magma that maintains a positive driving pressure at the surface has the potential to erupt 2 magma ascent may be arrested at a deeper level in the crust by a subhorizontal strength anisotropy i e crustal magma trap if the magma driving pressure is greater than or equal to the lithostatic load at the depth of the subhorizontal strength anisotropy 3 subhorizontal sheet intrusions form along crustal magma traps when the magma driving pressure greatly exceeds the lithostatic load under such conditions the magma driving pressure is sufficent to lift the overburden to create the necessary space for the intrusion 4 thicker steep sided stocks or batholiths with flat roofs form at crustal magma traps when the magma driving pressure approximates that of the lithostatic load under these conditions the necessary space for the intrusion must be created by other mechanisms e g stoping 5 subvertical sheets i e dikes form when the magma driving pressure is less than the lithostatic load at the level of emplacement

in situ10be 26al exposure ages at meteor crater arizona a new method of dating the surface exposure of rocks from in situ production of 10be and 26al has been applied to determine the age of meteor crater arizona a lower bound on the crater age of 49 200 1 700 years has been obtained by this method

age and geomorphic history of meteor crater arizona from cosmogenic 36cl and 14c in rock varnish abstract using cosmogenic 36 cl buildup and rock varnish radiocarbon we have measured the exposure age of rock surfaces at meteor crater arizona our 36 cl measurements on four dolomite boulders ejected from the crater by the impact yield a mean age of 49 7 0 85 ka which is in excellent agreement with an average age of 49 3 ka obtained from thermoluminescence studies on shock metamorphosed dolomite and quartz these ages are supported by undetectably low 14 c in the oldest rock varnish sample

magmatic flare up at the carboniferous permian boundary in the ne german basin revealed by shrimp zircon ages shrimp ages of 12 volcanic samples indicate intense magmatic activity to have occurred at the carboniferous permian boundary throughout much of the ne german basin rhyolitic crystal rich samples have been taken from quarries in the halle volcanic complex hvc and in the flechtingen ignimbrite and from drill cores of the kotzen mirow friedland and penkun areas ten samples yielded 206pb 238u ages between 302 and 297 ma 3 ma respectively which indicate that the magmatic activity took place concentrated in a relatively short time span throughout much of the ne german basin two hvc samples have ages of 307 and 294 ma this remarkably synchronous magmatic activity occurred during the initial phase of the basin development considering published volume estimates 48 000 km3 extrusion rates during this time period probably were in the order of 0 01 km3 a 1 implying magma production rates of 0 1 km3 a 1 the calc alkaline sio2 rich volcanic rocks originated from magmas that presumably formed during anatexis and subordinate magma mixing in an intra continental transtensional setting the basaltic magma which must have provided the thermal input into the lower crust probably formed during decompressional melting of lithospheric mantle fertilised by previous magmatic processes the dated volcanic rocks occur in three geotectonic provinces namely the a mid german crystalline rise which forms the northern part of the internal variscides the b external variscides and the variscan foreland which is considered as c eastern avalonia many of the old zircons found in the hvc samples reflect the magmatic activity of the mid german crystalline rise 325 400 ma however cadomian 500 650 ma and older gondwanian elements 1674 2373 ma are also present although the flechtingen and kotzen areas are located within the external variscides it seems more likely that the middle to lower crust that experienced anatexis formed part of the eastern avalonia plate overridden by the variscan front thus the old zircons found in flechtingen 350 and 538 ma and kotzen 345 ma but certainly those present in the penkun drill cores 1483 ma represent eastern avalonia tectonic history the anatectic magmas in the friedland area probably formed partly from baltic crust thrusted below eastern avalonia during the caledonian orogeny among the old zircons from the friedland samples in addition to proterozoic ages 1456 ma we found testimony of caledonian 443 ma and of clearly post caledonian 387 ma magmatism