an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

late cretaceous cenozoic fracturing in lofoten north norway tectonic significance fracture mechanisms and controlling factors abstract the lofoten ridge is a fault controlled basement horst residing between mesozoic basins on the north norwegian passive margin this major horst and the adjacent offshore basin bounding normal faults formed during stages of rifting from the permian jurassic to the early cenozoic well exposed heterogeneous nw se striking brittle fracture sets have been studied onshore at moskenes in the western lofoten islands this area provides an excellent frame for understanding onshore offshore fault fracture correlations and passive margin evolution as inferred from high quality offshore seismic data the fracture sets at moskenes exhibit geometric and kinematic variability i e systematic bisecting conjugate fractures parallel extensional fractures and anastomosing relay stepping shear fractures an incremental nw se oriented 1 compressive stress axis and a ne sw oriented 3 was inferred from the attitudes of the conjugate fracture sets the different fracture sets are interpreted to have formed in isolation and or in a progression through time as precursory parallel mode i or conjugate fractures mode ii and or more complex anastomosing shear fracture sets mode iii due to varying boundary stress conditions as controlling factors and not by mechanical weaknesses in the host rock whether parallel conjugate or anastomosing fractures formed depended on the initial spacing of precursory fractures the timing of development of complementary fractures and on the evolving strain stress conditions in terms of a north atlantic passive margin stress field the nw se trend of the heterogeneous fractures in western lofoten is roughly parallel to the late cretaceous early cenozoic regional extension directions but oblique to that of the permian jurassic a switch of the extension direction from wnw ese in the permian jurassic to nnw sse in the late cretaceous may have initiated multiple reactivations and e g right lateral shearing along ene wsw striking master faults producing a block internal nw se 1 in western lofoten alternatively the fractures formed by reactivation of transfer fault zones between nne ssw right stepping normal faults a third possibility is origin by cenozoic ridge push forces creating neotectonic fractures as a substitute to inversion structures and arc shaped domes on the mid norwegian margin farther south

cenozoic tectonism in the central basin and range magnitude rate and distribution of upper crustal strain a wealth of pre cenozoic geologic markers across the central basin and range province defined mainly by thrust faults developed within a miogeoclinal wedge makes it one of the best areas on earth to reconstruct large scale continental extension we use this 100 000 km 2 region bounded by the southern sierra nevada on the west and the colorado plateau on the east to illustrate the concepts of correlation and misalignment for regional strain markers and of strain compatibility and kinematic viability in palinspastic reconstructions the results indicate 250 to 300 km of west northwest motion of the sierra away from the plateau accommodated by both crustal thinning and north south shortening tertiary intermontane basin deposits and mineral cooling ages of deeply exhumed rocks constrain the overall kinematics of motion most of the westward motion occurred between 16 and 5 ma at rates near 2 cm yr slowing to 1 to 1 5 cm yr in the last 5 ma we have quantified the partitioning of strain between vertical crustal thinning via normal faults and map view plane strain via conjugate strike slip faults by placing a grid of 10 x 10 km elements on a retrodeformed map of the region and measuring the increase in area of grid elements between the undeformed and present day grids this analysis yields a maximum finite elongation of the basin and range at 36 n to 37 n of 3 4 oriented n73 w map view area balance shows that 20 percent of this elongation is compensated by north south shortening and 80 percent by crustal thinning this yields an average thinning factor for the upper crust of 2 7 between the sierra and plateau inconsistent with the hypothesis that neogene deformation in the central basin and range is predominantly dextral shear plane strain these results in concert with the observation that the southern sierra nevada has similar crustal thickness to the central basin and range support the hypothesis of large scale eastward flow of sierran deep crust during extension

closely spaced fractures in layered rocks initiation mechanism and propagation kinematics spacings of opening mode fractures joints and veins in layered sedimentary rocks often scale with the layer thickness field observations reveal that the ratio of fracture spacing to the thickness of the fractured layer s tf ranges from less than 0 1 to greater than 10 there is a critical spacing to layer thickness ratio that defines the condition of fracture saturation and explains the observed spacing ratios between 0 8 and 1 2 values of s tf 1 2 are explained as the results of the fracturing process having not reached the saturation level to explain ratios of s tf 0 8 we study the possibility for further fracture infilling by considering flaw distributions between adjacent fractures loaded by extension of the layer results show that infilling fractures grow more easily from flaws located near the interface than from those in the middle of the fractured layer the propagation of a flaw located in the middle of the fractured layer is unstable but for the flaw to propagate toward the interfaces its height has to be greater than a critical size this critical size decreases with increasing s tf the propagation behavior of a flaw with one of its tips at the interface depends on s tf the propagation is unstable when s tf is greater than a critical value when s tf is less than this critical value the propagation is first unstable then stable and then unstable again an infilling fracture can cut through the fractured layer only if s tf is greater than another critical value otherwise the infilling fracture can only partially cut the fractured layer for models with the same elastic constants for the fractured layer and the neighboring layers this critical value is 0 546 and the minimum spacing to layer thickness ratio of fractures formed by the in filling process under extension is 0 273

the concept of joint saturation and its application two of the major joint driving mechanisms are joint normal stretching and poroelastic shrinkage and these lead to joint sets commonly associated with structural bending and natural hydraulic fracturing respectively regardless of joint driving mechanism joint infilling is a nonhomogeneous poisson process in the presence of stress shadows through probability modeling we show that in all cases joint spacing is best fit with gamma distributions the shape parameter of the best fit gamma distribution to joint spacing data is a quantitative means to assess the extent of saturation which is represented in a new parameter the joint saturation ratio jsr to test the utility of jsr we call upon published structural bending joint data elk basin lilstock and rives plate bending experiment the shape parameters for these well developed structural bending joints are equal to around three corresponding to a jsr of approximately 30p using the same analysis on the spacing of natural hydraulic fractures collected from outcrops in the gas prone devonian sections of the appalachian basin we find that natural hydraulic fractures differ in two aspects from structural bending joints first the joint spacing is proportional to bed thickness in bedded rocks but not in gas shale sections second the joint saturation of natural hydraulic fractures is generally lower than in well developed structural bending joints thus the jsr is a means to distinguish the joint driving mechanism and to represent joint saturation level independent of bed thickness effects it can be used to distinguish natural fractures from drilling induced fractures and to improve the fracture network modeling

raising the colorado plateau comment and reply kilty s main objection to raising the colorado plateau via crustal flow is what he might call the failure of a crucial test verifying the predicted implications of the model for the upper crust we welcome the opportunity to defend the necessity of the tests we proposed and also to explain how the

joint development normal to regional compression during flexural flow folding the lilstock buttress anticline somerset england alpine inversion in the bristol channel basin includes reverse reactivated normal faults with hanging wall buttress anticlines at lilstock beach joint sets in lower jurassic limestone beds cluster about the trend of the hinge of the lilstock buttress anticline in horizontal and gently north dipping beds j3 joints 295 2858 strike are rare while other joint sets indicate an anticlockwise sequence of development in the steeper south dipping beds j3 joints are the most frequent in the vicinity of the reverse reactivated normal fault responsible for the anticline the j3 joints strike parallel to the fold hinge and their poles tilt to the south when bedding is restored to horizontal this southward tilt aims at the direction of s1 for alpine inversion finite element analysis is used to explain the southward tilt of j3 joints that propagate under a local s3 in the direction of s1 for alpine inversion tilted principal stresses are characteristic of limestone shale sequences that are sheared during parallel flexural flow folding shear tractions on the dipping beds generate a tensile stress in the stiffer limestone beds even when remote principal stresses are compressive this situation favors the paradoxical opening of joints in the direction of the regional maximum horizontal stress we conclude that j3 joints propagated during the alpine compression caused the growth of the lilstock buttress anticline q 2001 published by elsevier science ltd

a new palaeolithic discovery tar hafted stone tools in a european mid pleistocene bone bearing bed two stone flakes partly covered in birch bark tar and a third without tar on it were discovered in fluvial gravel and clay in central italy in association with the bones of a young adult female elephas palaeoloxondon antiquus and several micromammals the probable chronology of the stone flakes is compatible with the late middle pleistocene suggested by the site s small mammals and geological context the fauna indicates a cool stadial episode before isotope stage 6 that age means the flakes are the oldest ever found hafted with tar and indicate a greater capacity for late middle pleistocene hominins to utilize raw materials available during cold phases

the active southwest margin of the colorado plateau uplift of mantle origin during cenozoic time the colorado plateau was raised about 2 km above sea level the most recent and best documented uplift of the plateau 1 km has been concentratedatitssouthwestmarginbetween6 and 1 ma whereas the eastern colorado plateau may have been at high elevations sinceeocenetime tobetterunderstandthe recent tectonic activity at the southwest marginofthecoloradoplateau wecompile detailed crustal thickness and density informationfromseismicandgravitydatafor a region that includes northwest arizona and the southern tip of nevada this information is used to isolate the mantle contribution to uplift wefind that there is relatively low density mantle underlying the southernmarginoftheplateauinnorthwest arizona which could result from about 60 80 km of thinning of the dense mantle lithosphere combined with about 100 cof heating through a 100 km thick mantle layer the available estimates from earthquake source seismology in or near the studyareaarecompatiblewiththisestimate of lithospheric thinning we speculate that uplift may result from subduction related thinning of the continental lithosphere

a functional analysis of the lgm microblade assemblage in hokkaido northern japan a case study of kashiwadai 1 abstract topics currently debated in the northeastern asian prehistory include the emergence and spread of microblade technology during the last glacial maximum lgm on these issues hokkaido the northernmost japanese island provides one of the earliest evidences of microblade technology the present study reports results of functional analysis on the lgm microblade assemblage from the kashiwadai 1 site hokkaido and preliminary comparisons with other upper paleolithic up assemblages in japan results indicate that microblades may have been slotted into and served as lateral edges of composite points use wear traces on burins and burin spalls show a strong correlation with antler bone or ivory abi processing end scrapers were used chiefly for hide working a blade may have been employed for sawing or cutting hides and flesh furthermore the comparison suggests that developed abi polishes exclusively observed on burins and burin spalls highlight the lgm microblade assemblage and are rarely found from the other up assemblages until the appearance of the lgm microblade assemblages this implies that the technology and concept to shape abi implements with burins seem to have emerged coincidently with the earliest microblade technology and may not have had roots from previous up technologies in both of the southern paleo sakhalin hokkaido kurile peninsula and paleo honshu island besides the microlithization investigating sophisticated abi technologies will also illuminate the first appearance and spread of the lgm microblade technologies in northeast asia

raising the colorado plateau shallow marine rocks exposed on the 2 km high 45 km thick colorado plateau in the western united states indicate that it was near sea level during much of the phanerozoic isostatic calculations however illuminate the difficulty in maintaining a 45 km thick crust at or near sea level we propose that an isostatically balanced 30 km thick proto colorado plateau crust was thickened during the late cretaceous to early tertiary by intracrustal flow out of an overthickened sevier orogenic hinterland this plateau would have been supported by a thick 70 km crustal root which is proposed to have been the source region for hot and weak mid crustal material that flowed eastward from the plateau toward the low elevation proto colorado plateau

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

a techno functional perspective on quartz micro notches in sibudu s howiesons poort indicates the use of barbs in hunting technology abstract in this paper we present the results of a use wear study of quartz micro notches identified during a technological analysis of lithics from the howiesons poort layers of sibudu cave building on the technological analysis and preliminary functional screening of the archaeological material a series of experiments was designed to evaluate different hypotheses for notch formation blank production intentional notching hafting projectile use and trampling the experimental reference collection was compared with archaeological micro notches and a large sample of other archaeological quartz pieces including bladelets bipolar blanks flakes and retouched pieces this allowed us to evaluate the causes of micro notch formation in the studied assemblage results indicate two novelties in the howiesons poort hunting technology at sibudu the use of quartz barbs and non retouched quartz blanks it seems that in addition to backed pieces segments obliquely backed points etc unretouched pieces were mounted as elements in hunting weapons during the howiesons poort techno tradition seven probable and 29 tentative barbs were identified we thus present one of the strongest and oldest bodies of evidence for the use of barbs as projectile elements

composite projectiles and hafting technologies at ohalo ii 23 ka israel analyses of impact fractures morphometric characteristics and adhesive remains on microlithic tools abstract this study focuses on the correlation between the production of backed microliths in the levant during the late upper palaeolithic and their use as side elements of composite projectile weapons the investigation is based on assemblage sample of microliths from ohalo ii a 23 000 years old submerged campsite and involves analyses of diagnostic impact fractures location of adhesive remains and morpho metric characteristics of the tools two distinct adhesive materials have been also analyzed and the preliminary results indicate the use of both calcareous and organic substances the use of backed microliths as side elements of composite projectiles has been followed for scalene triangles a microlithic type unknown from the earlier upper palaeolithic in the levant the reconstruction of their use has been established based upon all the three evidence lines i e patterns of impact fractures as well as the location of adhesive remains and the morpho metric characteristics of the microliths the results of the study show an upper palaeolithic epipalaeolithic continuity in the approach to the design of hunting weapons and hafting technologies it is also suggested that the origins of composite projectiles in the levant may be found in the earlier phases of the upper palaeolithic

wound ballistics the prey specific implications of penetrating trauma injuries from osseous flaked stone and composite inset microblade projectiles during the pleistocene holocene transition alaska u s a abstract research in the field of wound ballistics has identified three major types of penetrating trauma injuries that will affect wound severity of a projectile point into hard or soft tissues puncture incised and lacerated in this study we report on dual ballistics experiments conducted to better understand the wounding mechanisms of three prehistoric projectile point classes made respectfully of polished bone bifacially flaked stone and composite antler inset with microblades each class of projectiles was launched into ballistics gelatin and into the carcass of a reindeer to explore the relative performance characteristics of each class in terms of tool durability and wound infliction our methods of evaluation included a detailed measurement of projectile attributes before and after penetration of both gelatin and carcass that were then compared using tip metrics penetration depth and total interior wound area our results strongly suggest that the wounding potential differed significantly between projectile point classes and in turn strongly influenced wound severity we suggest that point mechanics may implicate a prey specific hunting strategy and propose that such analyses can help us better understand prehistoric hunter gather behavior and technological variability

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

aspects of three dimensional strain at the margin of the extensional orogen virgin river depression area nevada utah and arizona the virgin river depression and surrounding mountains are neogene features that are partly contiguous with the little strained rocks of the structural transition to the colorado plateau province this contiguity makes the area ideally suited for evaluating the sense magnitude and kinematics of neogene deformation analysis along the strain boundary shows that compared to the adjacent little strained area large magnitude vertical deformation both uplift and depression locally exceeding 10 km greatly exceeds extensional deformation and that significant amounts of lateral displacement approximately parallel the province boundary extensional kinematics the directions of lateral displacements and the position and orientation of uplifts and one major depression are such that isostatic rebound following tectonic denudation is an unlikely direct cause of the strong vertical structural relief adjacent to the strain boundary instead the observed structures are first order features defining a three dimensional strain field produced by approximately east west extension vertical structural attenuation and extension normal shortening all major structural elements of the strain boundary strain field are also found in the adjacent basin and range especially evident is a discontinuous and inhomogeneous distribution of vertical structural relief resulting from uplift and tilting of the footwalls on convex upward normal faults combined with formation of extension parallel folds deformation resulted in a bewilderingly complex mixture of coeval folds normal faults strike slip faults and in some areas reverse faults thrust faults and thrust faults reactivated as extensional detachment faults these complexly mixed structures exhibit a tectonically important aspect of scale independence ranging from micro structures to mountain range scale many intensely extended domains appear to reflect a process of surface relief minimization above uplifted and tilted blocks some intensely extended zones are depth limited by relatively undeformed rocks above and intact tilted blocks below and are best viewed as subhorizontal zones of accommodation for the uplift and tilt of subjacent blocks whether or not the intense deformation extends to the surface its depth distribution commonly reflects lithologic or paleostructural controls whatever the cause for the concentration of extensional strain many gently dipping zones are more accurately viewed as local features recording small to moderate extension parallel translations than a regionally interconnected detachment faults recording enormous extension parallel translations although the total neogene strain field in the nevada utah arizona tricorner area has unique aspects other parts of the basin and range contain generally similar structures that presumably formed from similar processes these processes include lateral mass transfer probably by viscoelastic flow of the material needed to inflate areas of strong uplift and to translate blocks laterally by tectonic rafting directions of mass transfer vary but are commonly both parallel and normal to the direction of extension or parallel to the boundaries of extended areas much of the strong vertical structural relief probably reflects boundary condition or localized perturbations in the form of restraints or releases of the lateral flow system these conclusions are consistent with modern concepts of the flexural strength and rheological stratification of the crust in regions undergoing extension

raising the colorado plateau comment and reply comment mcquarrie and chase 2000 1 proposed three tests for their novel model first that it is possible to account for the elevation of the colorado plateau in their model by reasonable variation of crustal thickness second that mechanical parameters required of their model assume reasonable values

structural analysis and fault segment boundary identification along the hurricane fault in southwestern utah abstract long normal fault zones are common in extending regions and can be divided into segments with different geometries and faulting histories based on surface observations the boundaries between fault segments are important because they may be the sites of significant strain may impede rupture propagation and may greatly influence the locations of earthquakes because large geometric bends exist at some fault segment boundaries throughout the history of the boundary we suggest that such bends can last throughout much of the life of the fault we use fault segmentation concepts to define a segment boundary and parts of two fault segments along the active hurricane normal fault southwestern utah u s a we use fault geometry slip direction shortening structures in the hanging wall and footwall and fault scarp morphology to identify the fault segments and segment boundary the fault strikes n13 w south of the boundary and n21 e north of the boundary stratigraphic separation of geochemically identical quaternary basalt in the footwall and the hanging wall suggests that the slip vector of quaternary displacement trends between n70 w and s18 w and slickenlines earthquake rakes and dip analysis on syndeformational basalt further constrains the slip direction to n75 85 w relative motion on the northern segment termed here the ash creek segment is purely dip slip and on the southern anderson junction segment is dominantly dip slip with a small dextral slip component fault scarps along the ash creek segment compared with offset gravels lacking scarps along the anderson junction segment suggest that the two segments have different late quaternary faulting histories which is indicative of discrete fault segments the ash creek segment is about 24 km long and the anderson junction segment is 19 45 km long although the non adjacent segment terminations remain poorly defined the segment boundary zone consists of 1 a small scale hanging wall anticline that trends roughly normal to the fault 2 a small offset footwall thrust fault and 3 space filling imbricate normal faults in the hanging wall secondary structures suggest the segment boundary is a non conservative boundary

regional joint sets in the arabian platform as indicators of intraplate processes the eastern part of the saudi arabian craton is a platform underlain by gently tilted and horizontal mesozoic cenozoic sedimentary rocks everywhere more than 250 km distant from the zagros deformation front despite its tectonic simplicity the platform contains several laterally extensive but subdued structures and lineaments belonging to more than one system of fault zones and flexures new microtectonic observations of dominant sets of extension and conjugate hybrid joints permit regionally significant extension directions to be inferred and the origin of the macrostructures to be assessed the central arabian arch the e w crest of which coincides with an axis of mesozoic subsidence developed during the late cretaceous to eocene when the basin inverted as a consequence of the emplacement of ophiolite bearing nappes on the zagros and oman margins during arching there was strike parallel elongation of beds at the same time as the arch amplified the central arabian graben system evolved as a result of the northward displacement of an east arabian block or sheet that became detached across an arcuate separation zone which in the south is coincident with the crest of the arch an important neogene response in the arabian platform to ne sw shortening in the zagros ranges was the formation of a swarm of ne striking master joints and lineaments these structures reflect the diffuse and peripheral expansion of the foreland beyond the zagros deformation front

projectile impact fractures and launching mechanisms results of a controlled ballistic experiment using replica levallois points abstract identifying the use of stone tipped projectile weapons in prehistory is important for understanding hominin strategic behavior and cognitive capacities such identifications are based on diagnostic impact fractures difs assumed to form as a result of collisions between the tips and organic materials in the prey body however demonstrating weapon use requires documenting an impact speed and or kinetic energy beyond those likely to occur accidentally or as a by product of other tasks we present a new experiment aimed at investigating the influence of speed on impact fracture formation in controlled conditions using an air gun we fired 234 nearly identical spears tipped with copies of a levallois point cast in soda lime glass into a composite target made of polyurethane bone like plates ballistic gelatin and leather the impact speed ranged from 7 to 30 m s and the impact angle ia varied in increments of 15 from 90 to 45 we show that realistic difs can be produced under these controlled conditions the frequency of longitudinal tip macrofractures is directly proportional to the impact speed but inversely proportional to the ia the relationship between the tip fracture type and the type of damage left on the target explains the contact conditions for the formation of different difs no relationship between either initiation or termination type and speed could be established therefore we conclude that step terminating bending fractures should not be considered diagnostic of weapon use without further supporting evidence further although fracture length increases with speed when ia is held constant a great deal of overlap exists between trials with different ias given the expected high variance in ia in real hunting situations large longitudinal macrofractures on the tips of archaeologically recovered lithics should not automatically be interpreted as resulting from the use of high speed projectiles we discuss the study s implications for the differentiation of prehistoric weapon delivery systems especially regarding recognizing stonetipped weapon use by neandertals

experimental use and quantitative performance analysis of triangular flakes levallois points used as arrowheads the invention and widespread use of projectile weaponry is a characteristic presumed to exist only with homo sapiens however as finds of wooden material during the early development of projectile weapons are extremely rare this remains a contentious topic recent work has proposed a series of ballistically significant morphological characteristics of stone points that yield information about their potential use here we report on initial experimental approaches to quantifying the performance of relatively simple stone points as arrow armatures two experimental trials were performed using a series of 51 levallois points the first against a uniform density target was designed to give an overall indication of performance the second against a simulated animal carcass demonstrated the durability of these points the results of this study suggest that small levallois points could have functioned as arrowheads albeit ones likely to break after limited use they also suggest that these points penetrating power is strongly controlled by their morphometric characteristics most notably their perimeter this latter finding refines a method for assessing hypothetical paleolithic stone points on the basis of tip cross sectional area previously proposed by others

unweaving the joints in entrada sandstone arches national park utah u s a abstract on the southwest limb of salt valley anticline arches national park utah three sets of joints are developed in the entrada sandstone covering an area of about 6 km2 within the 20 m thick moab member a single joint set is is found in three distinct areas separated by a second set of joints at a 35 angle to the first set joint interaction features show that the second set is younger than the first this illustrates that joints of a single set do not have to fill the entire area across which the stresses that formed the joints were acting the underlying slickrock member contains a third set of joints which is at an angle of 5 35 to joints in the moab member the slickrock set nucleated from the lower edges of joints of all orientations in the overlying moab member thus the fracture pattern evolved both horizontally within the same unit and vertically between units the sequence of jointing is determined by establishing the relative ages of each joint set each joint orientation is best interpreted as representing a direction of maximum compression ruling out the possibility that the joints are a conjugate set the joints and an earlier set of deformation bands record a 95 counterclockwise rotation of the direction of maximum compression

structural and microstructural evolution of the rattlesnake mountain anticline wyoming usa new insights into the sevier and laramide orogenic stress build up in the bighorn basin the rocky mountains in western us provide among the best examples of thick skinned tectonics following a period of thin skinned tectonics related to the sevier orogeny the compressional reactivation of basement faults gave birth to the so called laramide uplifts arches the bighorn basin located in wyoming is therefore a key place to study the transition from thin to thick skinned tectonics in orogenic forelands especially in terms of microstructural and stress strain evolution our study focuses on a classic laramide structure the rattlesnake mountain anticline rma wyoming usa a basement cored anticline located in the western part of the bighorn basin stress and strain evolution analysis in folded sedimentary layers and underlying faulted basement rocks were performed on the basis of combined analyses of fractures fault slip data and calcite twinning paleopiezometry most of the fractures are related to three main tectonic events the sevier thin skinned contraction the laramide thick skinned contraction and the basin and range extension serial balanced cross sections of rma and displacement profiles suggest that all thrust faults were coeval evidencing strain distribution in the basement during faulting the comparison of rma with another structure located in the eastern edge of the bighorn basin i e the sheep mountain anticline sma allows to propose a conceptual model for the geometric and kinematic evolution of laramide related basement cored anticlines finally the stress evolution is reconstructed at both the fold scale and the basin scale we show that the evolution of stress trends and magnitudes was quite similar in both structures rma and sma during laramide times thick skinned tectonics in spite of different stress regimes during sevier thin skinned tectonics and post laramide times stress trends and fracture patterns were different in these two structures these results suggest that the distance to the orogenic front influenced the fracture patterns but not the foreland stress magnitudes which were likely controlled by the structural style

estimated pay mapping using three dimensional seismic data and incremental pay thickness modeling better estimates of hydrocarbon pay thickness and reservoir distribution are achieved if forward modeling is combined with crossplot cluster analysis before the seismic amplitude and isochron data are converted into estimates of pay thickness to facilitate this process an enhanced convolutional modeling technique that incorporates petrophysical data and equations into the synthetic seismogram generation process was developed these incremental pay thickness ipt forward models provide the pertinent seismic and petrophysical values required for crossplot analysis the crossplot analyses then define which seismic variables trough amplitude peak amplitude time structure isochron etc are most uniquely related to a pay thickness parameter gross thickness net thickness net porosity thickness or hydrocarbons in place work to date mostly in offshore gulf coast gas sands has shown significant variation in the crossplot transforms required to convert seismic data to estimated pay maps as such an interactive model based interpretive approach is recommended as an appropriate means to integrate petrophysical geologic and 3 d seismic data in the creation of reservoir pay maps

space time patterns and tectonic controls of tertiary extension and magmatism in the great basin of the western united states structural and stratigraphic relations in the great basin indicate widespread pre middle miocene crustal extension that appears to define two north trending belts most extension in these belts was oligocene age but locally it began earlier or lasted into early miocene time the eastern belt straddles the nevada utah border and includes the snake range nevada area with its southern end near 37 5 n and its western edge at the seaman butte mountains breakaway the southern boundary of the eastern belt is occupied by the 26 15 ma caliente caldera complex and approximately coincides with the present east west trending margin of the great basin north of saint george utah crust north of this boundary extended approximately east west before volcanism began at 30 32 ma but to the south extension began after about 15 ma this boundary may have been a rooted zone of left slip faults that allowed the footwall of the stampede detachment to move west relative to unextended terrain to the south the eastern margin of the eastern belt is probably located near the present eastern edge of the great basin but its northern end is poorly defined the western belt runs from the funeral and grapevine mountains california to the ruby mountains nevada and north northeast to the albion range idaho tens of kilometers of crustal extension occurred at least locally in both belts but magnitude of extension is poorly known for large areas of each tertiary volcanism in the great basin began in the north in eocene time with predominantly effusive volcanism and swept southward ending with voluminous oligocene miocene ignimbrite eruptions from calderas in an irregular discontinuous belt between marysvale utah and reno nevada a result of the south ward migration of volcanism is that the onset of extension in both belts was syn or post volcanic in the north but was pre volcanic in the south late paleogene extension and crustal magmatism coincided in both time and space only locally where south migrating magmatism overlapped active north south trending extensional belts most calderas in the southern great basin formed in previously extended belts or on their margins southward migration of ignimbrite sources was apparently blocked by unextended crust to the south in contrast volcanism north of the ignimbrite province was dominated by nonexplosive effusion of lava prior to or during crustal extension this is consistent with observations in the southern basin and range where volcanism and crustal extension were generally synchronous and volcanism was dominantly effusive thus caldera formation may be controlled by the distribution of upper crustal extension although the physical mechanism for this control remains speculative the space time patterns of late paleogene extension in the great basin are consistent with extension being triggered by thermal weakening of subducted oceanic lithosphere rather than by effects transmitted from the plate margin but being driven by gravitational collapse of thick crust space time patterns of tertiary volcanism in the basin and range also appear to conform to patterns of thermal weakening or destruction of the subducted slab both active and passive rifting mechanisms are inapplicable on the scale of the extensional belts because both predict close spatial and temporal association of extension and magmatism which is not generally observed

hard core and cutting edge experimental manufacture and use of magdalenian composite projectile tips the technology of the european upper palaeolithic yielded abundant evidence of the use of composite projectile heads in the form of osseous points on the side of which one or several micro lithic elements are attached yet little experimental work has been devoted to testing and assessing the parameters of use of this type of composite tips in this paper we present a pilot experiment with replicas of magdalenian composite spear tips made of an antler point with one or two rows of flint backed bladelets two series of replicas were manufactured after the lithic and osseous record of respectively the lower magdalenian from southwest france c 20 18 ky cal bp and the upper magdalenian of pincevent in the paris basin c 15 14 ky cal bp the 34 experimental composite heads were hafted to spears that were then shot with a spearthrower at the carcasses of two young deer the results provide some insight into the performance characteristics of the osseous and lithic components both in efficiency and durability finally possible improvements of the experimental protocol are discussed as well as the implications of our results for the understanding of projectile point variability in the upper palaeolithic

kinematic implications of joint zones and isolated joints in the navajo sandstone at zion national park utah evidence for cordilleran relaxation 1 at zion national park znp the landscape is a consequence of differential weathering of the navajo sandstone where closely spaced vertical joints constitute joint zones that erode to form regularly spaced half kilometer slot canyons striking 351 between these joint zones is a set of isolated joints striking 339 fracture interaction and horsetail wing crack development indicate that the 339 striking joint set is younger than the 351 striking joint zones despite the lateral extent of stress reduction shadows in the vicinity of the large scale joint zones in addition to an older less pervasive 020 joint set this sequence of jointing records a counterclockwise rotation of the regional extension directed from wnw to wsw in the navajo sandstone at znp znp is located at the western margin of the colorado plateau 100 km east of the major normal faults of the northeastern central basin and range subprovince extension within the eastern central basin and range initiated during the miocene and exhibited a wsw extension direction anderson 1971 wernicke et al 1988 snow and wernicke 2000 the correlation between nearby basin and range extension and the extension direction for the 351 tending joint zones of znp is so close that the jointing at znp is interpreted as evidence for modest yet pervasive basin and range extension in the western margin of the colorado plateau

technological evolution of hunting implements among pleistocene hunter gatherers osseous projectile points in the middle and upper magdalenian 19 14 ka cal bp abstract the middle and upper magdalenian have yielded rich and diverse assemblages of osseous hunting technology including projectile points barbed or not foreshafts and spearthrowers within the magdatis project the evolution of this technology at french sites was reassessed by building an extensive dataset of 14c dates on magdalenian hunting implements selecting assemblages with good archeological homogeneity and taking into account questions of manufacture hafting and use a finer four stage chronology was established in coordination with lithic studies a steady evolution was identified marked by the intensification of antler exploitation and the increasing diversity and complexity of osseous armatures this evolution is the continuation of a long term trend that began in the badegoulian and lower magdalenian and that culminated in the late middle early upper magdalenian showing a special emphasis on composite projectile tips and evidence of the long distance circulation of osseous materials and objects a simplification process then takes place with much of the technical innovation now centered on barbed implements to the detriment of the rest of the weapon kit a trait that may announce the azilian

formation of regional cross fold joints in the northern appalachian plateau abstract fold axis parallel elongation associated with the development of arcuate fold and thrust belts is proposed as a causal mechanism for syn orogenic cross fold joints such a mechanism can be coupled with other joint propagation models providing a widely applicable resolution to the enigmatic origin of regional systematic joints the fold axis parallel elongation model is compatible with kinematic indicators as recorded by a sequence of cross fold joints and related deformational fabrics in the central and northern appalachian plateau modeling of an arcuate tectonic boundary subjected to normal compressive loading demonstrates that tangential tensile stress can be large enough to initiate cross fold joints on the convex side of the tectonic boundary simulated stress trajectories from boundary element modeling bear a strong resemblance to the stress trajectories inferred from the regional cross fold joint patterns in the central and northern appalachian plateau modeling also displays a cratonward decrease in both the tangential stress and the tangential strain such a decrease is consistent with the deformation styles observed in the central and northern appalachian plateau

chapter 6 mesozoic and cenozoic tectonics of the sevier thrust belt in the virgin river valley area southern nevada

migration of deformation fronts during progressive deformation evidence from detailed structural studies in the pennsylvania anthracite region u s a abstract detailed study of selected outcrops in the pennsylvania anthracite region has resulted in identification of five at least partly continuous stages of alleghanian progressive deformation these structural stages are in sequence a layer parallel shortening and top to the foreland layer parallel shear b a second episode of layer parallel shortening c flexural slip and flexural flow folding d fold modification and late thrust faulting and e late veining and fracturing at each outcrop an average shortening direction was determined for each observed structural stage the mean regional shortening direction for each structural stage was calculated and maps showing the spatial distribution of the shortening directions for each stage were constructed the mean regional shortening directions for the five structural stages successively rotated 25 30 clockwise during the evolution of the fold and thrust belt shortening directions for structural stages b and c over the region show a systematic clockwise change in orientation from hinterland to foreland indicating that these structural stages of progressive deformation were time transgressive on a regional scale

fringe cracks key structures for the interpretation of the progressive alleghanian deformation of the appalachian plateau vertical joints in devonian clastic sedimentary rocks of the finger lakes area of new york state are ornamented with arrays of fringe cracks that reveal the complex deformational history of the appalachian plateau detachment sheet during the alleghanian orogeny three types of fringe cracks were mapped gradual twist hackles abrupt twist hackles and kinks gradual twist hackles are curviplanar en echelon fringe cracks that propagate with an overall vertical direction within the bed hosting the parent crack and are found in all clastic lithologies of the detachment sheet abrupt twist hackles propagate as planar features in thick shale beds above or below the siltstone beds hosting parent joints kinks propagate horizontally as planar surfaces from the tips of parent joints in siltstone beds the breakdown of the parent joint into either gradual or abrupt twist hackles depends on the orientation and magnitude of the remote stress field internal fluid pressure and the elastic properties of the bed the twist angle of gradual twist hackles is larger in coarser clastic beds indicating that stress and internal pressure are more important parameters than elastic properties in controlling breakdown assuming that the vertical stress axis s v equals 78 mpa at 3 km burial depth the difference in twist angle between sandstone and shale beds is used to estimate the maximum horizontal stress difference in the shale beds as s h s h 2 5 mpa when s h s h 12 mpa in sandstone beds the twist angle of the fringe cracks and the abutting relationships of parent joints give an indication of the overall change in stress field orientation within the detachment sheet during alleghanian tectonics these parent joints indicate a regional clockwise stress rotation of alleghanian age concordant with the twist angle of fringe cracks throughout the western part of the study area a counterclockwise twist angle in the eastern portion indicates a local stress attributed to drag where no salt was available to detach the eastern edge of the plateau sheet the clockwise change in stress orientation is consistent with the rotation in stress orientation found in the anthracite belt of the pennsylvania valley and ridge but is opposite to the sense of rotation in the southwestern portion of the detachment sheet western pennsylvania and west virginia the two regional rotation domains are separated by the juniata culmination

late paleogene extensional collapse of the cordilleran foreland fold and thrust belt the cordilleran foreland fold and thrust belt collapsed and spread to the west during a middle eocene to early miocene ca 49 20 ma episode of crustal extension the sedimentary and structural record of this event is preserved in a network of half grabens that extends from southern canada to central utah extensional structures superposed on this allochthonous terrain are rooted to the physical stratigraphy structural relief and sole faults of preexisting thrust fold structures the sole faults dip 3 6 west above an undeformed precambrian crystalline basement and accommodated tectonic transport of a thick up to 20 km eastward tapering hanging wall during regimes of crustal shortening and extension the chronology of tectonism for the foreland fold and thrust belt is established here by dating latest thrusting and initial normal faulting and is best defined where thrusts and normal faults are linked by common detachment surfaces dated movement on two extensionally reactivated thrusts the lewis thrust of northwest montana and southeast british columbia and the medicine butte thrust of southwest wyoming and northeast utah suggests that the hiatus between the end of crustal shortening in the early or early middle eocene and the start of extension in the early middle eocene was brief lateral spreading and extensional basin formation in the cordilleran foreland fold and thrust belt were partly concurrent with formation of metamorphic core complexes and regional magmatism conceptually linking extensional processes that were simultaneously deforming both the hinterland and foreland of the late paleogene cordilleran orogenic wedge is accomplished by applying the extensional wedge coulomb critical taper model the rapid drop in north america pacific plate convergence rate and or steepening of the subducted oceanic slab at ca 50 ma resulted in a large reduction in east west horizontal compressive stress in the cordillera as a result the cordilleran orogenic wedge was left unsupported and it gravitationally collapsed and horizontally spread west until a new equilibrium was established at ca 20 ma subsequently crustal extension and magmatism during the basin and range event ca 17 0 ma overprinted much of this earlier phase of extension

formation and growth of extensional fracture sets naturally occurring extension fractures including some joints and veins form sets consisting of numerous subparallel fractures each with well defined ends in order to correctly interpret these fractures in the field it is necessary to determine which factors control the geometries of fracture sets this requires consideration of the conditions leading to both the initiation and the cessation of fracture propagation a fracture begins to propagate when the crack extension force reaches a critical value which is a property of the rock and of environmental conditions after propagation initiates the crack extension force varies owing to 1 increase in crack length 2 change in remote strain 3 elastic interaction with nearby cracks 4 change in internal fluid pressure and 5 stress relaxation due to growth of cracks in the surrounding rock each fracture continues to propagate as long as its crack extension force exceeds the critical value and terminates when this condition is no longer met neglecting fluid effects the final geometry of the fracture set is a function of the remote strain history and the initial crack geometry which can be characterized by the initial crack density for low initial densities large increases in crack length occur with little or no increase in remote strain however for large initial densities crack lengths increase only if the applied strain increases this analysis is used to estimate the variation in remote strain during formation of a fracture set in granitic rock from observations of the final fracture geometry