age of the peach springs tuff southeastern california and western arizona sanidine separates from pumice of the early miocene peach springs tuff are concordantly dated at 18 5 0 2 ma by two isotopic techniques the peach springs tuff is the only known unit that can be correlated between isolated outcrops of miocene strata from the central mojave desert of southeastern california to the western colorado plateau in arizona across five structural provinces a distance of 350 km thus the age of the peach springs tuff is important to structural and paleogeographic reconstructions of a large region biotite and sanidine separates from bulk samples of the peach springs tuff from zones of welding and vapor phase alteration have not produced consistent ages by the k ar method published ages of mineral separates from 17 localities ranged from 16 2 to 20 5 ma discordant 40ar 39ar incremental release spectra were obtained for one biotite and two of the sanidine separates ages that correspond to the last gas increments are as old as 27 ma the 40ar 39ar incremental release determinations on sanidine separated from blocks of peach springs tuff pumice yield ages of 18 3 0 3 and 18 6 0 4 ma laser fusion measurements yield a mean age of 18 51 0 10 the results suggest that sanidine and biotite k ar ages older than about 18 5 ma are due to inherited ar from pre tertiary contaminants which likely were incorporated into the tuff during deposition sanidine k ar ages younger than 18 ma probably indicate incomplete extraction of radiogenic 40ar whereas laser fusion dates of biotite and hornblende younger than 18 ma likely are due to postdepositional alteration laser fusion ages as high as 19 01 ma on biotite grains from pumice suggest that minerals from pre tertiary country rocks also were incorporated in the magma chamber

effects of multipropped excavation on an adjacent floating pile abstractdeep excavations inevitably induce stress relief and soil movement which may affect the safety and serviceability of nearby existing pile foundations although the effects of excavation on

the silurian qusaiba hot shales of saudi arabia an integrated assessment of thermal maturity abstract the lower silurian qusaiba hot shales qhs are proven source rocks for oil within the paleozoic and possibly some of the mesozoic reservoirs in saudi arabia moreover these shales have oil shale potential where they are immature and shallow enough for mining as well as unconventional shale oil and shale gas potential in areas where they are within oil maturity and gas maturity levels respectively the qhs were deposited in relatively shallow marine environments under anoxic water conditions resulting in accumulation of amorphous kerogen organic walled graptolites and acritarchs across the arabian basin organic matter quality does not show much variation for the qhs but the maturity varies greatly as a result of varying burial history thermal maturity assessment of shale source rocks that lack vitrinite such as the qusaiba hot shales continues to be challenging especially where conflicting measurements are obtained from different sources this paper presents an integrated assessment of qhs thermal maturity parameters based on cores from 13 carefully selected boreholes that based on regional basin models are believed to cover a wide maturity range ca 0 5 to 2 0 ro we conducted some analyses on kerogen maceral petrography graptolite reflectance uv fluorescence whole rock pyrolysis raman spectroscopy of graptolite and other analyses on bitumen extracts gc and gc ms of saturate and aromatic fractions and ftir spectroscopy of the asphaltene fraction we show that using many thermal maturity parameters reduces uncertainty significantly and we therefore recommend that graptolite reflectance analyses should be conducted in support of other maturity indicators proper reflectivity measurements of the graptolites set the reference for comparison of other maturity parameters obtained from petrographic geochemical and spectroscopic techniques our work provides a template by which qusaiba thermal maturity can be more accurately estimated when only a limited set of maturity parameters is available

age inheritance and uplift history of the old woman piute batholith california and implications for k feldspar age spectra ion probe u pb zircon analyses yield a crystallization age of 74 pm 3 ma for both peraluminous and metaluminous plutons within the old woman piute batholith these analyses reveal that about 50 of the zircons from the peraluminous sweetwater wash granite are restitic inherited zircons from this batholith yield ages ranging from older than 1800 ma to 1100 ma and most are similar in age to proterozoic igneous rocks in the eastern mojave desert 40 ar 39 ar hornblende ages from the metaluminous granodiorite are 73 pm 2 ma and mica ages from both plutonic series are 70 pm 2 ma k feldspar age spectra yield age gradients with initial steps between 60 and 67 ma and rise to plateau ages of 70 pm 2 ma several k feldspars from the granodiorite yield elevated plateau ages after 50 39 ar released that result from excess argon uplift rates as high as 4 mm yr between 74 and 70 ma are required by the narrow age range for all minerals

mapping the piute mountains california with thermal infrared multispectral scanner tims images thermal infrared multispectral scanner tims data were acquired in 1990 over the piute mountains california to evaluate their usefulness for lithologic mapping in an area of metamorphosed structurally complex igneous and sedimentary rocks the data were calibrated and atmospherically corrected and emissivity variations in the form of alpha residuals were extracted from which color composite images were made there was an excellent visual correlation between the units revealed in the color composite image and the lithologic units mapped in the eastern side of the area it was also possible to correct improve and extend the recent map for example several areas mapped as granodioritic gneiss had tims alpha residual spectra consistent with mafic rocks and were subsequently mapped as amphibolite the presence of a swarm of mafic dikes of which only a few had previously been identified was also revealed the images also showed color variations in granitoid plutons that correlated with compositional variations previously determined by extensive field and geochemical work the western piute mountains is an area that has proven to be especially difficult to map with field and air photographic methods due to heterogeneous nature of certain units and various levels of desert varnish the images permitted the extremely heterogeneous proterozoic schists gneisses and granites to be easily mapped because the small scale compositional variability was averaged to the tims pixel size 12 m 12 m square areal measurements from the images show that the proterozoic rocks in the piute mountains consist of granitoids 50 biotite gneiss 15 pelitic gneiss 15 quartzite 10 and amphibolite 10 tims data can dramatically increase the efficiency and the quality of geologic mapping in well exposed heterogeneous areas with minimal vegetation cover where detailed mapping of lithologic contacts by traditional methods is unusually difficult

synmagmatic deformation patterns in the old woman mountains se california abstract synmagmatic structures within granitic plutons may provide insight into the interplay between plutonism and regional deformation at mid crustal levels within the late cretaceous old woman pluton mojave desert se california synmagmatic structures include magmatic fabrics parallel to wall rock foliations melt filled shear zones folded gneissic xenoliths and schlieren with axial planar magmatic fabric deformation continued below granite solidus temperatures in shear zones on the pluton margins these structures permit reconstruction of a sheet like pluton that was emplaced under regional extension taken together with published thermochronometric data the synmagmatic structures constrain the role played by magmatic events in the collapse of a thickened crustal section the post plutonic cooling history suggests rapid uplift and denudation ending by 65 ma we argue that extensional deformation overlapped and post dated pluton emplacement and may have contributed to tectonic unroofing we suggest that magma emplacement can trigger subsequent extensional collapse in overthickened crustal blocks

mid tertiary structural evolution of the old woman mountains area implications for crustal extension across southeastern california investigations in the old woman mountains area provide insights into mid tertiary extensional tectonism in southeastern california the old woman mountains area is a moderately extended region that lies between two highly extended terranes the central mojave extensional complex and the colorado river extensional corridor two normal faults and a high angle fault that we interpret to be a transfer structure divide the area into four distinct structural blocks these blocks correspond to the four mountain ranges of the area the old woman piute little piute and ship mountains other major faults involved in tilting are inferred to be buried beneath alluvium in surrounding valleys deformation occurred in part before but primarily after deposition of the peach springs tuff an 18 5 ma regional stratigraphic marker transport directions of hanging walls are westward on the west side of the old woman mountains area and east southeastward on the east side we suggest that the old woman mountains area is a less extended portion of a continuous extensional terrane that stretches from the central mojave desert across the colorado river to the transition zone of the colorado plateau lower strain in the old woman mountains area than in most of the colorado river extensional corridor and central mojave extensional complex and age relations across the terrane can be explained by a model in which the principal locus of upper crustal breakaway to an east dipping low angle simple shear zone shifted at about 18 20 ma from a position far to the west to just east of the old woman mountains area

natural fractures in a united kingdom shale reservoir analog cleveland basin northeast england faults and fractures within the well exposed lower jurassic cleveland ironstone and whitby mudstone formations may provide insights into the tectonic history of gas prospective mississippian shale in northern england subvertical opening mode fractures occur throughout the cleveland basin bed parallel fractures some of which contain blocky calcite fills occur preferentially within well bedded clay rich mudstones of the cleveland ironstone and whitby mudstone formations at jet wyke and port mulgrave subvertical fractures display abutting or curving parallel relationships with under and overlying bed parallel fractures together these observations suggest that bed parallel fractures at times acted as free surfaces some bed parallel fractures curve toward and branch from calcite filled fault slip surfaces indicating that bed parallel fracturing and normal faulting were synchronous occurring within a regional stress field with vertical maximum principal stress this apparent paradox can be explained by normal compaction followed by cementation and coupling between pore pressure and minimum horizontal stress driven by poroelastic deformation or incipient slip along critically stressed normal faults causing elevation of horizontal stress in excess of the vertical stress within clay rich units propagation of bed parallel fractures was enhanced by dilatational strains adjacent to normal fault planes bed parallel fractures have not been observed within more rich units at the top of the whitby mudstone formation at whitby east cliff or within well bedded clay rich shale at saltwick nab this observation is consistent with the lack of normal faulting at saltwick nab and the whitby mudstone formation having been drained by structural and or stratigraphical juxtaposition against permeable middle jurassic sandstones at both these localities

correlation of the peach springs tuff a large volume miocene ignimbrite sheet in california and arizona the peach springs tuff is a distinctive early miocene ignimbrite deposit that was first recognized in western arizona recent field studies and phenocryst analyses indicate that adjacent outcrops of similar tuff in the central and easten mojave desert may be correlative this proposed correlation implies that outcrops of the tuff are scattered over an area of at least 35 000 km2 from the western colorado plateau to barstow california and that the erupted volume allowing for posteruption crustal extension was at least several hundred cubic kilometres thus the peach springs tuff may be a regional stratigraphic marker useful for determining regional paleogeography and the time and extent of tertiary crustal extension

characteristics of type iii kerogen in coal bearing strata from the pennsylvanian upper carboniferous in the ruhr basin western germany comparison of coals dispersed organic matter kerogen concentrates and coal mineral mixtures abstract quality quantity and maturity of coal and dispersed terrigenous organic matter were studied on six coal bearing intervals in duckmantian strata pennsylvanian upper carboniferous of the ruhr basin western germany between 10 and 40 samples were collected from fresh drill cores of each interval typically consisting of a coal seam as well as clastic roof and floor strata sandstone siltstone claystone coal seams constitute about 8 vol of the succession studied the samples were analysed by organic petrological methods and rock eval pyrolysis maturity expressed in terms of vitrinite reflectance is between 0 75 and 1 0 for the six successions studied the total amount of dispersed organic matter in clastic rocks is about half of that stored in coal seams both containing predominantly vitrinite significant differences between rock eval parameters determined on whole rock samples and kerogen concentrates were observed especially with respect to hydrogen index hi values thus the hi of the coal is about twice as high as that of the dispersed organic matter although the maceral composition is similar the effects of minerals were further examined by rock eval pyrolysis of artificial mixtures of coal lignite powder and different minerals reduced hi values are partly explained by the retention of generated hydrocarbons on mineral surfaces and partly by reactions of generated fluids with pyrite in kerogen concentrates

large magnitude miocene extension in the central mojave desert implications for paleozoic to tertiary paleogeography and tectonics this is the published version copyright 1990 american geophysical union all rights reserved

independence of geostatic stress from overconsolidation in some beaufort sea clays reply since 1982 extensive use has been made of the self bored pressuremeter in arctic offshore site investigations one finding of this work is that the in situ geostatic stress ratio k0 of beaufort sea clays is apparently unrelated to the overconsolidation ratio ocr the procedures and data to support this finding are documented and the finding is discussed in light of the present geological understanding for the area it is concluded that the independence of k0 from ocr may be quite widespread a finding that contradicts the widely held tenet regarding the existence of a single valued function relating k0 and ocr if k0 is regarded as important then it should be measured in situ key words self bored pressuremeter geostatic stress ratio k0 beaufort shelf geologic history overconsolidation ratio

application of hyperbolic stress strain models for sandstone and shale to fold wavelength in the mexican ridges foldbelt abstract the mexican ridges foldbelt on the continental slope east of mexico has major folds with wavelengths averaging 7 km locally there are also small amplitude near surface folds with wavelengths of 2 km initial dominant wavelength is modelled by the finite element method using the hyperbolic stress strain relationship originally derived for soils hyperbolic stress strain models for sandstone and shale are calibrated using field porosity depth relationships for shale and laboratory one dimensional consolidation data for sand and clay effective tangent young s modulus calculated from hyperbolic stress strain models is generally higher for sandstones than for shales and for both rock types modulus increases substantially with depth the finite element models of dominant wavelength duplicate the two orders of folds observed in the mexican ridges and match their wavelengths in the models fold wavelength is nearly constant for large variations in both sandstone fraction in the folded section and pore pressure magnitude in the overpressured basal shale below the folded section but fold amplification is increased by high pore pressure in the basal shale and by high sandstone fraction in the folded section fold wavelength is affected more by depth distribution of high pore pressure than by pressure magnitude and on the lower continental slope where grain size may be smaller a thicker zone of high pressure would partly explain the modest downslope increase in fold wavelength

petrographic examination of low rank coals from saskatchewan and british columbia canada including reflected and fluorescent light microscopy sem and laboratory oxidation procedures the response to oxidation of eight coals of lignite and subbituminous rank from saskatchewan and hat creek british columbia was studied by means of maceral distribution fluorescence and scanning electron microscopy sem the oxidizing agent used was schulze s solution with some modification of reaction time from that normally employed in palynological maceration these eight samples were chosen to represent different macroscopically described lithotypes maceral analysis indicates that the huminite macerals behave differently when oxidized densinite seems to be the most susceptible to destruction along with gelinite humotelinite eu ulminite and texto ulminite is more resistant and in four of the eight samples shows a slight increase in concentration oxidation increases the relative content of liptinite along with some of the inertinite macerals fusinite and semifusinite among the liptinite macerals resinite appears to be preferentially concentrated suggesting that the modified oxidation pr

liquefaction resistance evaluation of pleistocene age south carolina coastal plain sands with the cone penetrometer test abstractthree pleistocene age sand deposits from 100 000 to 1 2 million years old in the south carolina coastal plain were characterized with the cone penetrometer test and samples were tested in a

rheological control on the initial geometry of the raft river detachment fault and shear zone western united states the strain exhumation history and field orientation of a well exposed shear zone and detachment fault in the raft river mountains of northwestern utah a cordilleran metamorphic core complex have been studied to determine the kinematics of ductile shearing and initial orientations of the shear zone and detachment fault mapping and strain and kinematic analysis indicate that the top to the east raft river shear zone initially developed parallel to an unconformity separating archean rocks from overlying proterozoic quartzite and schist for at least 24 km in the shear direction experimental rock deformation data from lithologies similar to the archean and proterozoic rocks suggest the unconformity represented a significant rheological boundary at the deformation temperatures the base of the shear zone was localized along the boundary between relatively weak quartzite above and stronger monzogranite below an extensive thermochronological database is used to reconstruct the position of the basement unconformity in temperature lateral distance coordinates the initial average dip of the shear zone and basement unconformity is estimated between 7 and 30 assuming subhorizontal isotherms and geothermal gradients of 20 40 c km the east dip of the unconformity at the onset of miocene extension is interpreted to have resulted from late eocene unroofing and flexure beneath a top to the wnw extensional shear zone in the western raft river grouse creek and albion mountains the observations from the raft river shear zone suggest that the orientation of some midcrustal shear zones may not reflect the predicted orientation for ductile faults according to ductile failure criteria but rather the orientation of rheological boundaries along which deformation is localized furthermore detachment faults that are superimposed on mylonite during progressive displacement and footwall unroofing may use an inherited mechanical anisotropy from the mylonite and their orientations may not reflect the predicted orientation of shear fractures in isotropic rock the common parallelism between detachment faults and mylonitic foliation may indicate a mechanical and kinematic preference for localization of throughgoing brittle faults parallel to preexisting mylonitic foliation because of this preference studies restricted to detachment faults which lack footwall mylonite or restricted to structural levels between the breakaway and mylonitic front have more bearing on the question of the initial dip of normal sense shear fractures faults within the seismogenic crust

late cenozoic cooling history of the central menderes massif timing of the buyuk menderes detachment and the relative contribution of normal faulting and erosion to rock exhumation abstract based on new thermochronological data and 10be derived erosion rates from the southern part of the central menderes massif aydin block in western turkey we provide new insights into the tectonic evolution and landscape development of an area that undergoes active continental extension fission track and u th he data reveal that the footwall of the buyuk menderes detachment experienced two episodes of enhanced cooling and exhumation assuming an elevated geothermal gradient of 50 c km the first phase occurred with an average rate of 0 90 km myr in the middle miocene and the second one in the latest miocene and pliocene with a rate of 0 43 km myr the exhumation rates between these two phases were lower and range from 0 14 to 0 24 km myr depending on the distance to the detachment cosmogenic nuclide based erosion rates for catchments in the aydin block range from 0 1 to 0 4 km myr the similarity of the erosion rates on both sides of the aydin block northern and southern flank indicate that a rather symmetric erosion pattern has prevailed during the holocene if these millennial erosion rates are representative on a million year timescale they indicate that apart from normal faulting erosion in the hanging wall of the buyuk menderes detachment fault did also contribute to the exhumation of the metamorphic rocks

the 40ar 39ar thermochronology of the eastern mojave desert california and adjacent western arizona with implications for the evolution of metamorphic core complexes mesozoic thickening and cenozoic extension resulted in the juxtaposition of upper and middle crustal rocks in the eastern mojave desert southeastern california and western arizona the application of 40ar 39ar thermochronology to rocks in this region provides information about the timing and nature of thrusting plutonism metamorphism denudation and detachment faulting the 40ar 39ar ages of 175 to 125 ma from the clipper piute turtle mohave bill williams and hualapai mountains are interpreted to be the result of a middle mesozoic thermal event s caused by crustal thickening the 40ar 39ar data from the clipper and piute mountains suggest that this thermal event was followed by a period of cooling at rates of 1 5 c m y orogenesis culminated during the late cretaceous when rocks exposed in the old woman piute chemehuevi and sacramento mountains attained temperatures 500 c which reset the k ar systems of minerals from proterozoic rocks high grade metamorphism in the old woman mountains area was caused by the intrusion of the old woman piute batholith at 73 1 ma cooling rates following batholith emplacement in the old woman mountains were 100 c m y between 73 and 70 ma and 5 10 c m y from 70 to 30 ma between 65 and 25 ma the entire eastern mojave desert underwent a period of cooling at a rate of 2 10 c m y by 30 ma rocks exposed in the old woman piute marble ship clipper and turtle mountains were below 100 c the 40ar 39ar ages from the sacramento mountains suggest that mylonitization caused by the onset of regional extension occurred at 23 1 ma when extension started in the chemehuevi mountains rocks exposed in the southwestern and northeastern portions of footwall to the chemehuevi detachment fault were at 180 c and 350 c respectively this suggests that the exposed part of the chemehuevi detachment fault initiated at a dip of 5 30 or as a series of higher angle faults that cut to a depth of 10 12 km and were later rotated to their present dip unroofing of the footwalls to detachment faults in the sacramento and chemehuevi mountains resulted in average cooling rates of 10 50 c m y between 22 and 15 ma

contraction driven shear failure in compacting uncemented sediments shear failure in sediments is universally linked with active boundary conditions such as those imposed by tectonic stresses under conditions of no lateral strain and in the absence of tectonic stress soil mechanics theories predict a simple one dimensional compaction in which sediment particles displace vertically without shear failure during pressure diffusion conflicting with this theory shear failure planes are often found in sediments that formed under near horizontal burial conditions we investigated the effect of particle scale volume contraction as a potential cause of shear failure in uncemented particulate materials and found that loss of particle volume under confined conditions no external loading resulted in pronounced lateral stress reduction often reaching coulomb frictional failure conditions shear strain localization was analytically predicted and modeled numerically due entirely to volume loss at the grain scale we define this mode of internally driven shear failure as contractile to distinguish it from that caused by external loading and show that it can explain many natural fracture systems without invoking regional tectonics

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

organic petrology and rockeval analysis of the lower carboniferous emma fiord formation in sverdrup basin canadian arctic archipelago abstract samples of the lower carboniferous emma fiord formation from two localities in the sverdrup basin of arctic canada were examined using reflected white and fluorescent light the samples from kleybolte peninsula on ellesmere island show a relatively high level of thermal maturity in contrast those from grinnell peninsula on devon island are immature to marginally mature and include subbituminous coals and oil shales two types of oil shales are distinguished on the basis of liptinite content mineral matrix rockeval pyrolysis analysis and concentration of boron one is characterized by a liptinite rich clay carbonate matrix with a relatively high hydrogen index and boron content and the other by a liptinite poor carbonate matrix with a relatively low hydrogen index and boron content hydrogen rich components of these shales consist of alginite matrix bituminite and minor amounts of exsudatinite and sporinite kerogen types iii and iv comprise only minor components of the organic matter thermal maturity of the grinnell peninsula oil shales increases with depth matrix bituminite in these oil shales has seeped into cavities and microfractures in the kerogen types iii and iv forming exsudatinite the distribution and character of the organic constituents and also the concentration of boron in these samples indicate a fresh to brackish water environment

denudation of metamorphic core complexes and the reconstruction of the transition zone west central arizona constraints from apatite fission track thermochronology apatite fission track thermochronologic results from transects across the basin and range and transition zone provinces in west central arizona provide constraints on the denudational history and structural framework of the region apatite fission track ages decrease from 21 to 14 ma in the harcuvar mountains and from 16 to 13 ma in the buckskin rawhide mountains in the slip direction sw ne of detachment faults in the lower plates of the metamorphic core complexes mean lengths of confined fission tracks from the core complexes are all 14 m indicating that the apparent apatite ages record rapid cooling through the apatite partial annealing zone 40 c m y for lower plate rocks apparent apatite ages in the transition zone province generally increase from 25 ma to 100 ma away from the basin and range province this trend of increasing apatite age is disrupted by faulting as many as seven times at the fronts of major mountain ranges and within valleys between the weaver mountains and the colorado plateau gradients of apatite fission track age and confined track length with elevation in the mountain ranges and in the phillips kirkland drill hole reveal parts of denuded mesozoic and cenozoic apatite partial annealing zones these paleopartial annealing zone profiles provide a reference datum for preextension reconstructions of fault blocks the reconstructions indicate that the major faults in the transition zone province have relative displacements of 1 km and that offset on them occurred mostly after 25 ma these data also indicate that most of the rocks now exposed in the transition zone of west central arizona were not exposed until miocene time

vitrinite reflectance anomalies in the high volatile bituminous coals of the gunnedah basin new south wales australia abstract the rank of the permian coals in the gunnedah basin has been analyzed using both petrographic and chemical methods apart from the effects of local igneous intrusions a number of seams in the sequence have vitrinite reflectance values rv max that deviate significantly from the trend expected with a steady downward increase in coalification correlation of these anomalies with interpreted depositional environments suggests that abnormally low vitrinite reflectance values in the sequence occur in seams either overlain by or intimately associated with marine strata the three dimensional distribution of such low reflectance values in part of the section at least can be related either to the lithofacies pattern or post depositional groundwater flow associated with a major fan delta system coals with anomalously high vitrinite reflectance values appear to contain material described elsewhere as pseudovitrinite a component not previously reported in australian permian bituminous coals both low value and high value anomalies need to be taken into account when interpreting maturation patterns from vitrinite reflectance data in some cases other rank indicators such as air dried moisture may be useful to complement vitrinite reflectance in rank studies of high volatile bituminous coals abnormally low vitrinite reflectance values due to environmental factors such as marine influence on the other hand may be used to identify flooding surface sequence boundaries in the basin for stratigraphic and sedimentological investigations

the role of extension in the miocene denudation of the nevado filabride complex betic cordillera se spain the internal zone of the betic cordillera se spain consists of a nappe stack of three complexes the deepest of which is the nevado filabride complex the zone is separated from the overlying alpujarride complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment a suite of 74 new apatite and zircon fission track results have been obtained from the nevado filabride complex and these have been used to define regional cooling patterns for the complex rapid cooling 105 c 200 c ma 1 is spatially related to the tectonic contact with the overlying alpujarride complex cooling to near surface temperatures occurred first in the east sierra de los filabres during the mid serravallian 12 1 ma and was completed by the early tortonian 9 8 ma in the west sierra nevada there is no correlation between fission track age and sample elevation these results are consistent with tectonic unroofing of this complex a finding that favors extension as the mechanism by which the two complexes were brought into contact extension spans the middle and earliest upper miocene 12 8 ma in the study area and therefore lasted much longer than previously documented a hypothesis is advanced which links oblique convergence between the iberian plate and the betic internal zones resulting in crustal contraction at depth with orogen parallel extension in the middle and upper crust

exhumation of the rechnitz window at the border of the eastern alps and pannonian basin during neogene extension abstract the rechnitz window is the easternmost penninic window of the alps and the only one that is partly covered by neogene sediments zircon and apatite fission track ages have been measured on the penninic metasediments of the rechnitz series to better understand the exhumation of the window at the alpine pannonian border the zircon ft ages range from 21 9 to 13 4 ma similar to the white mica k ar ages 19 and 23 ma the exhumation rate during the early miocene extension was high 40 c ma apatite samples display ft ages of 7 3 and 9 7 ma thus the cooling rate was significantly less 7 11 c ma during the post rift uplift uplift in late miocene pliocene than in the early miocene escape period zircon ft ages decrease eastward due to the gradual southeastward slide of the austroalpine cover along low angle normal faults the exhumation of the rechnitz metamorphic core complex is younger than the unroofing of the eastern tauern window morphology of detrital zircon crystals of the penninic metasediments was used for the differentiation of tectonic subunits and to trace the internal structure of the window one population was probably derived from undifferentiated calc alkaline granitoids and tholeiitic granitoid sources while the other derived from evolved calc alkaline granitoids and alkaline granitoids of anorogenic complexes the areal distribution of zircon populations is in harmony with the eastward shift of zircon cooling ages these data indicate the exhumation of deep levels of penninic metasediments in the centre of the window

post plutonic unroofing and morphogenesis of the attic cycladic complex aegea greece abstract the attic cycladic complex of greece comprises an eocene high p unit with blueschist occurrences unroofing of this unit took place in oligocene miocene times and was accompanied by a regional low p medium t overprint and miocene granitic plutonism apatite fission track ages of 14 crystalline samples from the islands of tinos mikonos and serifos range between 13 1 and 5 3 ma corresponding to the middle and late miocene the frequency distributions of confined track lengths are characterised by high arithmetic means of 14 2 15 1 m and by standard deviations from 0 9 to 1 6 m thermochronological modelling of the data indicates rapid cooling between 10 and 6 ma and subsequent deceleration of the cooling rates for a short time the miocene plutons of tinos mikonos and serifos experienced maximum cooling rates above 50 c ma these exceptionally high cooling rates cannot be explained by strong vertical uplift and fast regional erosion such a process is disproved by preserved remnants of a former peneplain including inselbergs and kaolinized tropical subsoil on mikonos fast post plutonic cooling of the lower plate was apparently accompanied by simultaneous sedimentation on the upper plate we propose a post plutonic cooling model which assumes strong periplutonic heat flow into much cooler host rocks and fast extensional unroofing

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

tertiary extension in the old woman mountains area california evidence from apatite fission track analysis apatite fission track ages and confined track length distributions from the old woman mountains area southeastern california record evidence for periods of rapid cooling during the late cretaceous following mesozoic orogenesis and during miocene crustal extension apatites from the clipper marble and turtle mountains give fission track ages between 62 and 69 ma as a result of cooling of these upper crustal rocks after regional late cretaceous plutonism and metamorphism in the piute mountains apatite fission track ages decrease from 70 ma with mean track lengths of 13 5 m to 14 m from west to east intermediate aged samples from the piute mountains have mean track lengths between 11 and 13 m due to their extended residence in the apatite annealing zone during the early tertiary this pattern is the result of 20 30 of westward tilting of the piute mountains block as indicated by the dip of tertiary strata the apatite data indicate that tilting occurred after 18 ma and caused rapid cooling of rocks exposed on the eastern side of the mountain range knowing the amount of tilting and the apparent paleotemperatures across the piute mountains allows us to estimate that the synextensional geothermal gradient was 50 20 c km apatites from the northeastern old woman mountains yield fission track ages of 68 ma with mean track lengths of 13 8 m these samples record cooling after batholith emplacement at 73 ma in the northwestern old woman mountains apatite fission track ages decrease to 20 ma and have mean track lengths 15 m indicating very rapid cooling we interpret this age pattern to be the result of minor eastward tilting of the old woman mountains block after 18 19 ma or flexural unroofing of the northwestern old woman mountains due to movement on the ship mountains fault extension in the old woman mountains area occurred between 19 and 16 ma which is coincident with extension in the colorado river extensional corridor and later than major extension in the mojave extensional belt

effective stress vane shear strength correction factor correlations a recent effective stress model of vane shear strength testing in soils can relate measured torques to vane shear strengths using theoretical analysis in terms of effective stress parameters the strength estimates are based on known in situ stresses and soil parameters derived from laboratory testing the model may be applied for example in obtaining theoretical estimates of conventional undrained vane shear strengths for comparison with field data and for use in stability analyses however the model incorporates a correction factor v analogous to bjerrum s field vane shear strength correction factor intended to compensate for pore pressure and shearing rate effects this correction factor must be evaluated before reliable torque or shear strength estimates can be made in any given case to facilitate this the paper presents correlations of v with both liquid limit and plasticity index based on world wide data from clays and silts the correlations are compared with independent data from norwegian clays

comparison of the measured and finite element predicted ground deformations of a stiff lodgement till the use of the finite element method to model excavations and tunnels in dublin black boulder clay has in the past had limited success owing to the failure of the available constitutive models in commercially available software programs to adequately represent the essential features of a stiff soil a stiff soil lodgement till underlies much of the city of dublin ireland consequently the successful prediction of deformations in this soil arising from structural and infrastructural projects is of considerable importance research has shown that the stress strain response of a stiff soil is complex and depends on many factors including stress history stress level and strain direction these important features are included in the hardening plasticity small strain stiffness hss soil model that is incorporated in the plaxis v8 4 finite element code this paper describes the field and laboratory methods that were used to determine the parameters for incorporation in this soil model and the validati

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

regional maturity as determined by organic petrography and geochemistry of the schei point group triassic in the western sverdrup basin canadian arctic archipelago abstract maturity and source rock potential of organic rich beds in the triassic schei point group in the sverdrup basin arctic canada have been investigated using reflected light microscopy and the results are compared with other maturity parameters determined geochemically i e rock eval and biomarker maturation parameters the samples evaluated belong to the eden bay member of the hoyle bay formation and contain a predominance of marine algal material in the form of tasmanales and dinoflagellates along with mixed terrestrial organics the rock matrix is dominantly carbonate with some shaly input indicating that the rocks were deposited in an iron poor highly euxinic environment with few exceptions there is good agreement between parameters determined using microscopy namely r o max and r gq and geochemical parameters t max hi dia c 27 dia c 27 reg c 27 steranes s s r c 29 steranes the ternary diagram showing the abundance of normalized c 27 c 28 and c 29 regular steranes indicates a mostly marine depositional environment for the schei point source rock this is confirmed by the abundance of marine fauna and flora in these samples analytical results from several different techniques indicate that the source rocks become more mature from the margin towards the axis of the sverdrup basin this is due in part to the increase in overburden of sediments in the axis of the basin also the high thermal conductivity of salt has strongly influenced the maturity of schei point source rocks over the crest of the salt cored structures i e well hazen f 54 and the proximity of salt has enhanced maturation levels at well rock point j 43 the sections investigated were also considered to have an excellent gas potential due to their higher than average toc content

interpretation of moduli from self boring pressuremeter tests in sand the pressuremeter is a unique method for assessing directly the in situ shear stiffness of soils however the correct interpretation and application of the measured modulus must account for the relevant stress and strain level acting around the pressuremeter during the test a method to correct the measured unload reload shear modulus from self bored pressuremeter tests in sands is proposed the method has been evaluated using extensive data obtained from 47 tests performed in a large calibration chamber using pluvially deposited silica sand and from 25 tests performed in situ in a natural deposit of relatively clean silica sand at the river po italy a consistent relationship was obtained between the corrected unload reload shear modulus and the small strain shear modulus determined from resonant column tests and field cross hole tests suggestions are given to link the measured moduli with moduli values required for geotechnical design problems the importance of strain level stress strain model yie

in situ lateral stress coefficient k0 from shear wave velocity measurements in soils abstractthe at rest lateral stress coefficient k0 is an important soil parameter in geotechnical design problems and yet it is quite elusive in our ability to assess its value either by laboratory or in situ tests in this study an innovative geophysics approach toward the evaluation of the in situ k0 profile with depth is obtained by using small strain stiffness anisotropy ratio g0 hh g0 vh in soils the newly proposed k0 equation is derived from a database compiled from 12 test sites which have direct k0 measurements as procured from field tests either self boring pressuremeters sbp or total stress cells tsc and or laboratory triaxial tests instrumented consolidometers and or suction measurements the data show a strong relationship between the overconsolidation difference ocd p vo and stiffness anisotropy ratio thus enabling a k0 assessment in clays silts and sands

magnitude and significance of miocene crustal extension in the central mojave desert california the newly recognized waterman hills detachment fault whdf of the central mojave desert california is significant because it provides the first unambiguous evidence for large scale core complex style crustal extension in the central mojave desert and because it has significantly rearranged the pre miocene paleogeography of the mojave desert the whdf places steeply dipping to overturned miocene volcanic and sedimentary rocks upon mylonitic pre tertiary basement the mylonites which apparently formed during extension are predominantly l tectonites which manifest top to northeast shear the whdf dips to the northeast beneath dominofaulted ranges of the central mojave desert and detachment faults of the colorado river trough forming an imbricated early miocene system of detachment faults extension continued in the colorado river trough after extension had ceased in the central mojave desert tentative correlations of mesozoic intrusions suggest about 40 km of slip across the whdf which carries eugeoclinal paleozoic rocks in its hanging wall and cratonal miogeoclinal paleozoic rocks in its footwall restoration of 40 km of slip 1 removes a prominent kink in the boundary between eugeoclinal and cratonal miogeoclinal facies 2 aligns cratonal miogeoclinal strata near victorville more closely with the late paleozoic continental margin farther north 3 places cratonal miogeoclinal rocks structurally beneath eugeoclinal rocks implying that the facies were stacked by thrusting and 4 straightens the western margin of the late jurassic independence dike swarm

implications of low temperature cooling history on a transect across the colorado plateau basin and range boundary west central arizona fission track ages of apatite and zircon from metamorphic plutonic and sedimentary rocks along a 80 km transect across the colorado plateau basin and range boundary in west central arizona show differences in the low temperature cooling histories between the provinces the transect extends from cypress mountain in the colorado plateau transition zone to the eastern buckskin mountains in the basin and range along the northeast margin of the basin and range province metamorphic rocks exposed in the footwall of a major detachment fault system yield zircon and apatite fission track ages of 16 10 ma these ages are similar to k ar fusion ages of biotite and age minima of k feldspar on 40ar 39ar age spectra and collectively indicate rapid cooling one k feldspar age spectrum has an age maximum of about 22 8 ma an age minimum of 11 8 ma and a spectrum whose shape is suggestive of reheating possibly in middle miocene time the heating event was probably related to hydrothermal activity during emplacement of cu and mn deposits in and above the detachment fault zone effects of this heating are only locally detected in rocks above the detachment fault in the poachie range fission track ages of apatite and zircon are 60 50 and 80 70 ma respectively the disparity between the apatite and zircon ages indicates that the rocks cooled slowly in late cretaceous and early tertiary time probably due to gradual uplift and erosion total uplift and denudation in the area of the poachie range since cretaceous time is 6 km or more to the northeast of the range fission track ages of apatite and zircon increase and diverge indicating that apparent uplift decreased in that direction the apatite ages from the poachie range are concordant with early tertiary hornblende ages determined in other studies of lower plate rocks near the southwest end of the transect the ages represent cooling of crystalline rocks after cretaceous regional metamorphism and magmatism near bagdad 20 km northeast of the poachie range 2 km or less of erosion has occurred since intrusion of high level plutons and dikes and caldera formation in late cretaceous time remnants of an erosion surface that developed in middle tertiary time are preserved in the transition zone volcanic and sedimentary rocks at least as old as early miocene were deposited on the erosion surface and filled valleys cut into it dissection of these deposits began about 8 ma we interpret these data combined with those from other studies to indicate that in cretaceous time southward thrusting and later extensive magmatism in the middle crust led to thickening and heating of the crust the cretaceous igneous rocks at bagdad are high level manifestations of this magmatism uplift and slow cooling occurred in late cretaceous and early tertiary time in late oligocene and early miocene time during northeast southwest extension middle crustal rocks moved southwest put from beneath the southwest margin of the transition zone tectonic denudation rapidly exposed the crust that had been brought up from a depth of 10 km or more and rapidly cooled in the eastern buckskin and harcuvar mountains middle miocene reheating occurred locally in the lower plate along the detachment and in nearby parts of the upper plate

the mojave extensional belt of southern california it is proposed that the regional pattern of early miocene low and high angle normal faulting and dike swarm emplacement in the western and central mojave desert is the result of regional extension developed within a roughly east trending zone named here the mojave extensional belt this zone of extension although now disrupted by late cenozoic right slip faulting can be traced from the intersection of the san andreas and garlock faults to the eastern mojave desert near bristol lake and the granite mountains fault restoration of post oligocene movement along the san andreas fault system places the now buried western part of the mojave extensional belt opposite a similar age extended area of west central california surface mapping and limited subsurface data suggest that the dominant tectonic process responsible for development of the mojave extensional belt was low angle normal sense simple shear detachment faulting strain within the mojave extensional belt is partitioned between four domains edwards waterman daggett and bullion terranes that each consist of one or more half grabens each half graben is composed of tilted normal fault bounded blocks that lie above a rooted low angle brittle ductile normal sense shear zone tilting and extension of the upper plate resulted from the superposition of several generations of originally steeply dipping 80 planar to slightly curviplanar normal faults at least one generation of high angle faults postdates the formation of the detachments differential extension between the domains was accommodated by strike slip faults transfer zones similarly the lack of early miocene extensional elements north of the western segment of the garlock fault suggests that the garlock may have been active in the early miocene and served as the northern transfer boundary of the mojave extensional belt the mojave extensional belt initially began to open about 22 m y ago with the major phase of extension occurring between 22 and 20 ma local high angle normal faults cut older detachments and were active between 20 and 17 ma kinematic indicators suggest that the western part of the mojave extensional belt opened in a ne sw direction whereas the eastern portion extended in an ene wsw direction present day reference frame rotation of the region about vertical axes as revealed by paleomagnetic studies suggests that the direction of extension within the mojave extensional belt was originally oriented n s and was rotated as much as 50 clockwise between 20 and 18 ma early miocene

uplift and erosion of the san bernardino mountains associated with transpression along the san andreas fault california as constrained by radiogenic helium thermochronometry apatite helium thermochronometry provides new constraints on the tectonic history of a recently uplifted crystalline mass adjacent to the san andreas fault by documenting aspects of the low temperature 40 100 c thermal history of the tectonic blocks of the san bernardino mountains in southern california we have placed new constraints on the magnitude and timing of uplift old helium ages 64 21 ma from the large big bear plateau predate the recent uplift of the range and show that only several kilometers of exhumation has taken place since the late cretaceous period these ages imply that the surface of the plateau may have been exposed in the late miocene and was uplifted only 1 km above the mojave desert in the last few myr by thrusting on the north and south a similar range in helium ages 56 14 ma from the higher san gorgonio block to the south suggests that its crest was once contiguous with that of the big bear block and that its greater elevation represents a localized uplift that the big bear plateau did not experience the structure of the san gorgonio block appears to be a gentle antiform based on the geometry of helium isochrons and geologic constraints young ages 0 7 1 6 ma from crustal slices within the san andreas fault zone indicate uplift of a greater magnitude than blocks to the north these smaller blocks probably experienced 3 4 km of uplift at rates 1 5 mm yr in the past few myr and would stand 2 5 km higher than the big bear plateau if erosion had not occurred the greater uplift of tectonic blocks adjacent to and within the san andreas fault zone is more likely the result of oblique displacement along high angle faults than motion along the thrust fault that bounds the north side of the range we speculate that this uplift is the result of convergence and slip partitioning associated with local geometric complexities along this strike slip system transpression thus appears to have been accommodated by both vertical displacement within the san andreas fault zone and thrusting on adjacent structures

late stage evolution of the chemehuevi and sacramento detachment faults from apatite u th he thermochronometry evidence for mid miocene accelerated slip the unique low temperature sensitivity of the apatite u th he ahe technique provides valuable new information relating to the late stage thermal evolution of metamorphic core complexes in the southern basin and range province in all the ranges studied the data show greater complexity than previously seen from other thermochronometers in the chemehuevi and northern sacramento mountains a trend of decreasing ages toward the northeast applies only for the structurally shallowest parts of the footwall this is followed by essentially age invariant segments of 15 1 ma reflecting an increase in the rate of detachment fault movement the timing of the change suggested by the data agrees with recently published ahe results from the nearby harcuvar mountains located 125 km to the southeast suggesting that an underlying regional mechanism triggered this change plate reconstructions indicate that the pioneer mendocino fracture zone migrated northward through the area at this time leaving a slab window in its wake we suggest that the additional heat applied to the base of the lithosphere from the slab window resulted in mechanical weakening of the area and that this combined with the extensional strain regime present resulted in an increased rate of slip within the actively extending metamorphic core complexes this agrees well with timing constraints for extension onset in the central basin and range province of southern nevada and suggests that weakening of the southern basin and range province at 15 1 ma was partially responsible for the onset of extension in the central basin and range these findings demonstrate that improved constraints on changes in extension rate within the basin and range province should be possible through the application of the ahe technique to other metamorphic core complex footwalls

an assessment of the earth pressure coefficient in overconsolidated clays the determination of the earth pressure coefficient k0 in a natural clay deposit is a problem of considerable significance in geotechnical engineering while the methods for evaluation of k0 are reliable for normally consolidated soils significant difficulties still exist in evaluating k0 in overconsolidated clays given that it is influenced by the stress history of the material together with the age structure mineralogical composition and depositional environment indeed some of these factors are responsible for the soil becoming anisotropic the existing framework for prediction of k0 in overconsolidated soils does not account for any influences caused by anisotropy the work reported in this paper evaluates the validity of a revised relationship between k0oc and ocr overconsolidation ratio using data obtained from laboratory investigations the tests were performed on reconstituted and undisturbed samples of belfast upper boulder clay london clay and gault clay tests were also performed on re

effect of mineral matrix and seam thickness on reflectance of vitrinite in high to low volatile bituminous coals an enigma abstract the variation of vitrinite reflectance with respect to mineral matrix lithology the thickness of coal seams and coal lenses and the type of organic matter was studied from two cores in a 550 m sedimentary succession from the upper jurassic to lower cretaceous kootenay group the data obtained indicate that reflectance in high to low volatile bituminous coals ro max 0 8 1 35 with depth of burial is affected by the percentage of organic matter in the samples a positive correlation between the vitrinite reflectance and the percentage of organic matter and a negative correlation with the percentage of mineral matter exist and the thicker the coal interval the higher the vitrinite reflectance thick coal seams 1 m with a mineral content 20 vitrinite dispersed in sandstone and to a lesser extent siltstone and carbonaceous shale has the lowest reflectance variations in vitrinite reflectance may be attributed to chemical differences in the organic matter possibly induced by degradation and diagenesis syn or post depositionally and to the effect of some clay minerals present in the sediments which may act as catalysts differences in the thermal conductivity of the strata have demonstratably not accounted for the observed variations in reflectance with lithology the differences in the vitrinite reflectance of organic matter between lithotypes is substantial and is thus an important consideration in resolving the time temperature history and generation of hydrocarbons from a sedimentary succession

south virgin white hills detachment fault system of se nevada and nw arizona applying apatite fission track thermochronology to constrain the tectonic evolution of a major continental detachment fault the south virgin white hills detachment svwhd in the central basin and range province with an along strike extent of similar to 60 km is a major continental detachment fault system displacement on the svwhd decreases north to south from similar to 17 to 6 km this is accompanied by a change in fault and footwall rock type from mylonite overprinted by cataclasite to chlorite cataclasite and then fault breccia reflecting decreasing fault displacement and footwall exhumation apatite fission track aft thermochronology was applied both along strike and across strike to assess this displacement gradient the overall thermal history reflects laramide cooling similar to 75 ma and then rapid cooling beginning in the late early miocene age patterns reflect some complexity but extension along the svwhd appears synchronous with rapid cooling initiated at similar to 17 ma due to tectonic exhumation slip rate is more rapid similar to 8 6 km ma in the north compared to similar to 1 km ma in the south the displacement gradient results from penecontemporaneous along strike motion and formation of the svwhd by linkage of originally separate fault segments that have differential displacements and hence differential slip rates east west transverse structures likely play a role in linkage of different fault segments the preextension paleogeothermal gradient is well constrained in the gold butte block as 18 20 degrees c km we present a new thermochronologic approach to constrain fault dip during slip treating the vertical exhumation rate and the slip as vectors with the angle between them used to constrain fault dip during slip through the closure temperature of a particular thermochronometer aft data from the western rim of the colorado plateau citation fitzgerald p g e m duebendorfer j e faulds and p o sullivan 2009 south virgin white hills detachment fault system of se nevada and nw arizona applying apatite fission track thermochronology to constrain the tectonic evolution of a major continental detachment fault tectonics 28 tc2001 doi 10 1029 2007tc002194

thermochronological constraints on the timing and magnitude of miocene and pliocene extension in the central wassuk range western nevada apatite fission track and u th he thermochronological data provide new constraints on the timing of faulting and exhumation of the wassuk range western nevada where east dipping normal faults have accommodated large magnitude ene wsw oriented extension extensional deformation has resulted in the exhumation of structurally coherent fault blocks that expose sections of preextensional mostly granitic upper crust in the grey hills and central wassuk range these fault blocks display westward tilts of 60 and expose preextensional paleodepths of up to 8 5 km based on the structural reconstruction of tilted preextensional tertiary andesite flows that unconformably overlie mesozoic basement rocks apatite fission track and u th he thermochronological data from the fault blocks constrain the onset of rapid footwall exhumation at 15 ma fission track modeling results indicate rapid fault block exhumation occurred between 15 and 12 ma which is in agreement with miocene volcanic rocks that bracket the tilting history in addition fission track and u th he data suggest reduced rates of cooling following major extension as well as renewed cooling related to active high angle faulting along the present day range front starting at 4 ma thermochronological data from structurally restored fault blocks indicate a preextensional miocene geothermal gradient of 27 5 c km the thermochronological constraints on the timing of extensional faulting and the eruptive history in the wassuk range imply a model for extension where crustal heating and volcanism precede the onset of rapid large magnitude extension and where synextensional magmatism is suppressed during the highest rates of extension

miocene extension in the east range nevada a two stage history of normal faulting in the northern basin and range the east range in northwestern nevada is a large east tilted crustal block bounded by west dipping normal faults detailed mapping of tertiary stratigraphic units demonstrates a two phase history of faulting and extension the oldest sedimentary and volcanic rocks in the area record cumulative tilting of 30 45 e whereas younger olivine basalt fl ows indicate only a 15 20 e tilt since ca 17 13 ma cumulative fault slip during these two episodes caused a minimum of 40 extensional strain across the east range and quaternary fault scarps and seismic activity indicate that fault motion has continued to the present day apatite fi ssion track and u th he data presented here show that faulting began in the east range ca 17 15 ma coeval with middle miocene extension that occurred across much of the basin and range this phase of extension occurred contemporaneously with middle miocene volcanism related to the nearby northern nevada rifts suggesting a link between magmatism and extensional stresses in the crust that facilitated normal faulting in the east range younger fault slip although less well constrained began after 10 ma and is synchronous with the onset of low magnitude extension in many parts of northwestern nevada and eastern california these fi ndings imply that rather than migrating west across a discrete boundary late miocene extension in western nevada is a distinct younger period of faulting that is superimposed on the older middle miocene distribution of extended and unextended domains the partitioning of such middle miocene deformation may refl ect the infl uence of localized heterogeneities in crustal structure whereas the more broadly distributed late miocene extension may refl ect a stronger infl uence from regional plate boundary processes that began in the late miocene

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

thermal evolution of the hengshan extensional dome in central south china and its tectonic implications new insights into low angle detachment formation abstract the hengshan massif is an exhumed mid crustal plutonic metamorphic dome formed during cretaceous crustal extension in the jiangnan orogenic belt central south china multiple thermochronometers mica 40ar 39ar apatite fission track and zircon u th he are applied to its footwall along a slip parallel transect to quantify its thermal history and cooling rate and the slip magnitude rate initial geometry and kinematic evolution of the low angle hengshan detachment fault our thermochronological data in conjunction with previous ages indicate that 1 footwall rocks cooled from 700 c to 60 c in less than 60 myr 136 80 ma at variable rates ranging from 50 c myr to 13 c myr 2 the hengshan detachment fault accommodated 8 12 km of total slip at variable slip rates from 0 14 to 1 mm yr during tectonic exhumation 3 the footwall has been tilted 26 50 to the east since slip began indicating that the low angle hengshan detachment fault initiated at a steep dip and was passively rotated to a more gentle orientation during subsequent normal slip this study provides compelling evidence supporting that the low angle detachment fault in the extensional dome can be generated by the reactivation and passive rotation of an initially steep reverse fault during normal slip in addition our thermochronological data constrain the time of extension in the hengshan dome between 136 and 80 ma which implies that the back arc extension within south china associated with the rollback of the paleo pacific slab might have lasted until at least 80 ma

rapid extension recorded by cooling age patterns and brittle deformation naxos greece the metamorphic core complex exposed as the island of naxos in the aegean sea records an unusually complete sequence of structures developed as a result of continental extension the structures formed during miocene rise and cooling from ductile upper amphibolite facies and anatectic conditions to brittle near surface conditions beneath the naxos detachment fault top to the north ductile fabrics in the footwall which initially developed during amphibolite facies prograde metamorphism were overprinted by a succession of north directed normal sense lower temperature brittle structures as the footwall was tectonically unloaded and unroofed pseudotachylite and cataclasite formation brittle faulting alteration and erosion of the footwall occurred during continued slip and tectonic denudation neogene conglomerate and megabreccia in part derived from exhumation of this footwall lie structurally above the peripheral naxos fault published k ar and 40ar 39ar ages for hornblende white mica and biotite in the footwall decrease northwestward apparent ages 17 50 ma in the southeast correspond to areas of low metamorphic grade where preextension argon was partially retained published ages 16 10 ma in higher grade rocks of the domal core in the north are cooling ages that for each of the three minerals show a component of younging in the nne direction of extension assuming this is the direction of unroofing we interpret the rate of this younging as the fault slip rate as the footwall rocks moved 20 km ssw relative to their hanging wall along the base of the naxos detachment fault the calculated rates of slip average 5 8 mm yr comparable to maximum rates reported in the basin and range province

topographic fingerprints of bedrock landslides bedrock landslides in mountainous regions may be triggered by either storms or earthquakes the dominant mechanism in a region affects both landscape evolution and landslide hazard we describe a simple observational test to distinguish between storm and earthquake triggers based on a probabilistic measure of hillslope morphology in areas that are dominated by storm triggered landslides steep topographic slopes are concentrated on the lowermost parts of the hillslopes storm triggers act primarily on the hillslope toes and landslides preferentially remove material from those locations giving rise to inner gorges areas where most landslides are earthquake triggered have more uniform spatial distributions of steep topographic slopes because coseismic shaking causes failures at both ridge crests and hillslope toes earthquake triggered landslides lead to planar hillslopes and rare or absent inner gorges

fission track analysis of the footwall of the catalina detachment fault arizona tectonic denudation magmatism and erosion new apatite and zircon fission track ages obtained from the footwall of the catalina metamorphic core complex record a complicated cooling history associated with mid tertiary extension zircon fission track ages record the progressive unroofing of the catalina metamorphic core complex along the catalina detachment fault zircon fission track ages range from 31 9 to 19 4 ma generally decrease in the hanging wall slip direction and yield slip rates along the catalina detachment fault ranging from 1 2 to 12 km myr 1 in contrast apatite fission track ages increase in the hanging wall slip direction samples from the main range of the santa catalina mountains yield apatite fission track ages of 20 5 to 14 6 ma samples from the santa catalina mountain forerange located closer to the detachment fault yield apatite fission track ages of 21 4 to 18 8 ma rapid cooling 40 to 60 c myr 1 related to detachment faulting is best recorded by zircon fission track ages and higher temperature thermochronometers in the main range and by nearly concordant zircon and apatite fission track ages in the forerange slower cooling 3 7 c myr 1 of the footwall is recorded by shortened mean confined fission track lengths 14 m and is related to erosional unroofing approximately 2 km of late tertiary erosion played a significant role in the unroofing of the footwall of the catalina metamorphic core complex in contrast to metamorphic core complexes in western arizona where detachment faulting is the dominant unroofing mechanism

cenozoic tectonic evolution of the white mountains california and nevada the white mountains represent the westernmost range of the central northern basin and range province they are situated to the east of the unextended sierra nevada and represent a crustal block that is bounded along its western flank by the high angle white mountains fault zone the fault zone accommodates up to 8 km of total dip slip displacement investigation of the structural and thermal history of the white mountains indicates a two stage cenozoic tectonic evolution preextensional miocene volcanic rocks preserved along the eastern side of the range unconformably overlie mesozoic granitic basement and currently dip up to 25 to the east recording the total cenozoic tilt of the crustal block apatite fission track and u th he thermochronological data indicate that the white mountains underwent rapid exhumation and eastward tilting in the middle miocene starting at ca 12 ma geologic mapping 1 10 000 fault kinematic analysis and dating of younger volcanic sequences show that following middle miocene east west extension the white mountains have been dominated by right lateral transtensional deformation related to the walker lane belt the eruption of late miocene and pliocene volcanic sequences in the eastern white mountains postdates the majority of the uplift of the range as evidenced by infilling of paleodrainages and the presence of east directed flow fabrics fault kinematic indicators from the white mountains fault zone are characterized by apparent overprinting of dip slip fault motion indicators by right lateral slickenfibers and fault striations demonstrating that the range bounding fault system along the western side of the white mountains was reactivated as a dextral strike slip fault system at the northern and southern ends of the range pliocene right lateral transtension along this northwest southeast trending fault systems resulted in the formation of northeast trending pull apart basins that truncate the mountain range and transfer strike slip displacement eastward from the owens valley fault zone to the fish lake valley fault zone the inception of strike slip faulting in fish lake valley occurred at ca 6 ma as constrained by late miocene volcanic units right lateral faulting on the western side of the white mountains occurred at ca 3 ma and is distinctly younger than the faulting in the fish lake valley area indicating a westward migration of transcurrent deformation through time

dolomite fluorescence red green quotient a potential new thermal maturity indicator abstract geochemical and petrographic effects of burial temperature on sedimentary organic matter have long been recognized and used as various thermal maturity indicators i e pyrolysis tmax conodont and spore coloration vitrinite bitumen zooclast reflectance and fluorescent spectrometry i e max and red green quotient this study investigates variations in the fluorescence color spectra in the visible light spectrum of authigenic dolomite over a wide range of thermal maturities two sample sets of calcareous shales siltstones from eastern and western canada with sparse dolomite crystals in the rock matrix were selected to examine the relationship between thermal maturity and fluorescent properties of dolomite results from a range of thermal maturities from the oil window to the dry gas window reveal a strong positive correlation between the red green quotient q of dolomite crystals and equivalent vitrinite reflectance vroeqv values this can be optically described as the color shift in fluorescent properties of dolomite with increasing maturity this strong positive correlation between q and thermal maturity can potentially be used as an alternative thermal maturity indicator in calcareous shales with low organic content compilation of worldwide data is required to understand the relationship trend and conversion equations among dolomite q and other established thermal maturity indicators

tectonic denudation of a late cretaceous tertiary collisional belt regionally symmetric cooling patterns and their relation to extensional faults in the anatolide belt of western turkey t hermochronological data reveal that the late cretaceous tertiary nappe pile of the anatolide belt of western turkey displays a two stage cooling history three crustal segments differing in structure and cooling history have been identified the central menderes metamorphic core complex represents an inner axial segment of the anatolide belt and exposes the lowest structural levels of the nappe pile whereas the two outer submassifs the g ordes submassif to the north and the ci ne submassif to the south represent higher levels of the nappe pile a regionally significant phase of cooling in the late oligocene and early miocene affected the outer two submassifs and the upper structural levels of the central menderes metamorphic core complex in the northern part of the g ordes submassif cooling was related to top to the nne movement on the simav detachment as the apatite fission track ages show a northward younging trend in the direction of movement on this detachment in the ci ne submassif relatively rapid cooling in late oligocene and early miocene times may have been related to top to the s extensional reactivation of the basal thrust of the overlying lycian nappes the second phase of cooling in the anatolide belt is related to pliocene to recent extension resulting in the formation of the central menderes metamorphic core complex in the inner part of the anatolide belt core complex development caused the formation of supra detachment graben which document the ongoing separation of the central menderes metamorphic core complex from the outer submassifs

variation of maturity indicators optical and rock eval with respect to organic matter type and matrix lithology an example from melville island canadian arctic archipelago abstract the variation of maturity indicators with respect to mineral matrix and organic matter types was examined from the mesozoic succession of melville island arctic canada the t max values of non marine deltaic samples show a much greater degree of scattering with respect to vitrinite reflectance whereas the marine samples show a narrow distribution this behaviour is most likely to be a consequence of the differences in the chemical properties of terrestrial versus marine organic matter which is a function of the organic matter type and of the depositional environment the non marine deltaic samples also show higher t max values than their marine counterparts an indication either of the higher degree of oxidation of the non marine deltaic samples or of the fact that type iii organic matter has intrinsically higher t max values than types i and ii organic matter at the same maturity level based on the relationship between hydrogen index hi and vitrinite reflectance ro it appears that marine organic matter is more sensitive high negative correlation to thermal maturity changes than non marine deltaic organic matter no clear correlation between s 2 hydrocarbon yield and ro maturity could be seen in the suite of samples both fluorescence parameters max and r g quotient increase with maturity but the trends have different slopes for the various macerals a function of their marine or non marine origin

effect of maceral subtypes and mineral matrix on measured reflectance of subbituminous coals and dispersed organic matter abstract the variability in reflectance of huminite texto ulminite eu ulminite a and b different types of corpohuminite and liptinite groups of macerals in subbituminous coals was examined using reflected light microscopy all macerals were selected from coal and interbedded carbonaceous shale and carbonate sediment samples from the 515 m thick coal deposit no 2 located in the hat creek valley of south central british columbia the measurements obtained reveal that in addition to burial depth reflectance distribution depends on maceral subtypes and associated mineral matrix huminite in the coals and sediments kerogen consists mainly of humotelinite with eu ulminite b being the dominant maceral sub type reflectance values determined on huminite in coals and type iiib kerogen increase from eu ulminite a and phlobaphinite type 1 through eu ulminite b and phlobaphinite type 2 to gelinite the reflectance of all five huminite maceral subtypes studied increases with depth however the increase of phlobaphinite type 1 and gelinite reflectance with depth is irregular a comparison of the reflectance values obtained for the same maceral subtype eu ulminite b from the interbedded coal shale and carbonate samples records consistent differences implying some dependence of the reflectance and perhaps rate of organic maturation on the mineral matrix generally the highest eu ulminite b reflectance was recorded from carbonate rocks and the lowest from shale whereas coal matrix produced intermediate values at present it is not known whether differences in reflectance of eu ulminite found in the above lithologies are due to differential retention efficiency of reaction products removal thermal conductivity of the lithologies or existence of a calcium carbonate catalyst

at rest lateral stress coefficient in sands from common field methods abstracta new relationship for estimating the in situ at rest lateral stress coefficient k0 in sands consisting predominantly of silica particles is derived in this technical note using the calibration chamber test results reported in the literature variables in the relationship in order of significance are overconsolidation ratio dilatometer horizontal stress index and normalized cone tip resistance values of in situ k0 estimated with the new relationship generally compare well with k0 determined from self boring pressuremeter tests estimates of k0 in pleistocene sands are on average about 10 higher than in holocene sands

early cretaceous uplift and erosion of the northern appalachian basin new york based on apatite fission track analysis abstract the thermal history of outcropping devonian sediments of the northern appalachian basin new york has been investigated using fission track analysis of detrital apatites from 57 sandstone samples based on lengths and apparent age measurements using fission tracks in apatite it is concluded that lower devonian sediments presently at the surface in the catskill region were cooled rapidly from temperatures higher than about 110 c during early cretaceous times 120 140 ma ago in the western part of new york wellsville buffalo data from late devonian sediments are consistent with cooling at the same time as that identified for the catskill region but from lower temperatures in the range of approximately 80 110 c the maximum temperature these sediments experienced since deposition for a pre uplift paleogeothermal gradient of 25 35 c km the confined track length data indicates uplift and erosion of 2 3 km for western new york and greater than 3 4 km for the catskill region a differential uplift pattern which is consistent with the historical stratigraphic data from the region this conclusion is at variance with earlier interpretations put forth by others rapid broad scale uplift and erosion of the scale identified imply that large volumes of sediment could have been supplied from the northern appalachian basin during the early cretaceous this timing for the dominant post devonian cooling phase in the basin is not accounted for by recent models of the tectonic evolution of the appalachian orogen but is compatible with the change from carbonate to siliciclastic deposition in the atlantic coastal plain it is suggested that this style of broad regional uplift without significant deformation is characteristic of a tectonic regime associated with and subsequent to continental rifting apatite fission track analysis is shown to be a basic tool in providing fundamental limits for thermal history assessment in regional tectonic problems

thermal and unroofing history of a thick tilted basin and range crustal section in the tortilla mountains arizona we estimate here a geothermal gradient of only 17 5 c km 1 for the tilted grayback fault block in southeastern arizona when extension began 25 ma this gradient is lower than preextension gradients estimated elsewhere in the basin and range is only about 50 of typical gradients in the basin and range today and needs to be accounted for in models of continental extension the grayback block exposes a 12 km thick crustal section of proterozoic and cretaceous granitoids which was tilted 90 during extension between 25 and 15 ma zircon fission track ages decrease structurally downward westward across the block and were all within a zone of partial track annealing prior to tilting and quenching the zircon age gradient suggests that the 220 240 c isotherm migrated downward 5 6 km during paleogene erosion and regional cooling apatite fission track ages decrease westward from 83 ma in the structurally highest crystalline rocks to 24 ma at 6 km paleodepth and then to 15 ma another 6 km farther west track length analysis confirms that apatites above the break in slope in age at 5 7 km paleodepth resided in a zone of partial annealing prior to tilting and deeper apatites record rapid cooling upon tilting and unroofing beginning 25 ma at that time the 110 10 c isotherm determined by the depth at which tracks in apatite were fully erased was at a basement paleodepth of 5 7 km and the 220 30 c isotherm as estimated from zircon data resided at a pretilting basement depth of 12 15 km from consistent values of paleogeothermal gradient for two depth intervals we estimate the pretilt gradient was 17 5 c km 1 from 25 to 15 ma the rotating grayback block cooled rapidly as higher westward moving blocks unroofed it tectonically at a rate of 1 km m y 1

in situ lateral stress measurement in glaciolacustrine seattle clay using the pressuremeter pressuremeter testing was conducted for the state route sr 99 bored tunnel project in seattle washington to estimate in situ soil stress deformation parameters along the tunnel alignment many of the tests were conducted in a very stiff to hard glaciolacustrine clay known as seattle clay this unit is historically known for deep seated slope failures and many of these failures have been attributed to the release of high locked in lateral stresses estimation in situ lateral stresses along the tunnel alignment was a primary focus of the exploration program due to the hard consistency of this unit and the potential for cobbles neither self boring pressuremeter nor dilatometer testing was feasible therefore prebored pressuremeter testing was used using several lateral stress estimation techniques including a novel in situ creep testing approach the in situ lateral stresses in the seattle clay were estimated to be significantly higher than what would be expected by assuming a simple laterally constrained vertical loading and unloading stress path due to glaciation deformational features commonly encountered in seattle clay indicate its stress history also has included significant lateral shearing the memory of this shearing within the fabric of the clay may influence the in situ stress state and response to lateral unloading

timing rate and magnitude of slip on the buckskin rawhide detachment fault west central arizona we present thermochronologic and geochronologic data that constrain the slip history of the buckskin rawhide detachment fault in west central arizona one of the largest extensional fault systems in the north american cordillera u th he zircon and apatite thermochronology integrated with 40ar 39ar geochronology of postdetachment volcanic rocks indicate that large magnitude extension associated with the detachment fault initiated at 21 20 ma and continued until 12 11 ma in the southwestern portion of the buckskin rawhide metamorphic core complex u th he footwall cooling ages from the breakaway zone in the western bouse hills to upper greenschist facies mylonites in the southern buckskin mountains indicate that the slip rate on the detachment fault was 3 1 5 1 km myr during the early miocene space time patterns of hanging wall tilting suggest that at 17 16 ma a secondary detachment fault breakaway developed 12 km northeast of the primary detachment fault breakaway proximal conglomerates deposited in a supradetachment basin adjacent to the secondary breakaway scarp were displaced 6 11 km northeast in the middle miocene by the buckskin rawhide detachment fault at a slip rate of 1 2 2 7 km myr the total displacement across the detachment fault in the southwestern portion of the core complex is 24 10 km well short of the previous estimate of 66 8 km across the entire core complex based on these data and new observations we propose that total displacement on the buckskin rawhide detachment fault system increases in the slip direction to 40 50 km at the northeastern end of the exposed footwall corresponding to time averaged slip rates that ranged from 2 km myr to 6 km myr across the entire core complex

evaluating the in situ lateral stress coefficient k0 of soils via paired shear wave velocity modes abstractthe utilization of shear wave velocities toward the evaluation of the in situ geostatic horizontal stress state in soils is validated specifically the lateral stress coefficient k0 field shear wave velocities from paired sets of different directional and polarization modes are compiled from 16 well documented test sites involving a variety of geomaterials focus is particularly placed on shear wave velocities measured by downhole tests vsvh crosshole tests vshv and special rotary type crosshole tests vshh at these sites field k0 stress states have been quantified using one or more direct assessment techniques including self boring pressuremeter total stress cells and hydrofracture in field testing as well as suction measurements special consolidometers and or triaxial arrangements on undisturbed samples in the laboratory although the specific delineation of stress induced versus inherent or fabric anisotropy may be difficult it is shown that the ratio of horizontally polarized