faulting of rocks in three dimensional strain fields i failure of rocks in polyaxial servo control experiments abstract the dependence of the number of sets of faults and their orientation on the intermediate strain axis is investigated through polyaxial tests reported here and theoretical analysis reported in an accompanying paper in the experiments cubic samples of berea sandstone sierra white and westerly granites and candoro and solnhofen limestones were loaded on their three pairs of faces by three independent mutually perpendicular presses at room temperature two of the presses were servo controlled and applied constant displacement rates throughout the experiment most samples display three or four sets of faults in orthorhombic symmetry these faults form in several yielding events that follow a stage of elastic deformation in many experiments the maximum and the intermediate compressive stresses interchange orientations during the yielding events where the corresponding strains are constant the final stage of most experiments is characterized by slip along the faults

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

observations of the latitude dependence of the location of the martian magnetic pileup boundary 1 we report observations that show the dependence of the altitude of the magnetic pileup boundary mpb at mars on planetary latitude as seen by the mars global surveyor magnetometer electron reflectometer instrument the mpb is further away from mars on average at southern latitudes than at northern latitudes the data are consistent with a mpb distance mapped to the terminator plane that does not vary with latitude in the northern hemisphere but increases with increasing southern latitude in the southern hemisphere we also report increased variability in the mpb distance within the longitude range 90 270 e longitude in the southern hemisphere which is the region that contains the strongest crustal magnetic fields these trends are most obvious in a planet fixed coordinate system indicating a planet fixed driver of the mpb location the proposed mechanism is the local diversion of shocked solar wind flow by crustal magnetic fields

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

structural evolution of connecting splay duplexes and their implications for critical taper an example based on geometry and kinematics of the canyon range culmination sevier belt central utah abstract critical taper in an evolving orogenic wedge can be maintained by structural thickening in the back of the wedge this is often achieved by folding and uplift of pre existing large internal thrust sheets by the continued growth and or reactivation of duplexes in the hinterland the growth of a blind imbricate complex off a lower thrust provides another mechanism for folding a higher thrust individual splays in a blind imbricate complex may have fault propagation folds and or fault bend folds associated with them if the splays reach the overlying thrust they serve as connecting splays between the lower thrust floor and the upper thrust roof thereby forming a connecting splay duplex csd this type of duplex geometry requires periodic reactivation of the pre existing roof thrust the canyon range thrust in central utah is an internal thrust that is folded into an overturned antiform synform pair and overrides its own synorogenic conglomerates the same conglomerates are infolded into the core of the synform and preserve critical timing information regarding the history of folding and thrust reactivation the folding is caused by the development of a footwall antiformal stack in the core of the canyon range antiformal culmination the geometry and timing relationships suggest that the structure grew as a csd regional timing relationships suggest that the growth of the csd and reactivation of the thrust took place during the later part of the evolution of the orogenic wedge and may have helped the wedge maintain critical taper during thrusting in the external fold and thrust belt

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

tectonic implications of mars crustal magnetism mars currently has no global magnetic field of internal origin but must have had one in the past when the crust acquired intense magnetization presumably by cooling in the presence of an earth like magnetic field thermoremanent magnetization a new map of the magnetic field of mars compiled by using measurements acquired at an 400 km mapping altitude by the mars global surveyor spacecraft is presented here the increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the mars crust variations in the crustal magnetic field appear in association with major faults some previously identified in imagery and topography cerberus rupes and valles marineris two parallel great faults are identified in terra meridiani by offset magnetic field contours they appear similar to transform faults that occur in oceanic crust on earth and support the notion that the mars crust formed during an early era of plate tectonics

a spatial statistics approach to the quantification of finite strain variation in penetratively deformed thrust sheets an example from the sheeprock thrust sheet sevier fold and thrust belt utah abstract strain is an important component of the total displacement field in the emplacement of a thrust sheet the finite strain tensor in a penetratively deformed thrust sheet is a spatial variable i describe a method for quantitative estimation of the finite strain variation in thrust sheets by applying spatial statistics analysis on strain data collected from a part of the sheeprock thrust sheet in the southern sheeprock mountains and the west tintic mountains north central utah strain was measured in the quartzites of the sheeprock thrust sheet and the spatial statistics method is illustrated using the x z strain axial ratios the sheeprock thrust sheet was penetratively deformed during sevier age fault propagation folding i quantified finite strain from quartzites using the modified normalized fry method and calculated the three dimensional strain ellipsoid from the quartzites using three orthogonal thin sections from each oriented field sample the variation of finite strain in the sheeprock thrust sheet was best represented by an exponential semivariogram model which i used to predict values of strain from unsampled locations by ordinary kriging cross validation showed that in general the predicted and measured values show good agreement within 1 of each other the sampled space was contoured using the measured and predicted strain values to obtain a detailed finite strain variation pattern in a part of the sheeprock thrust sheet

brittle to ductile transition due to large strains along the white rock thrust wind river mountains wyoming abstract the deformed foreland of the rocky mountain cordilleras is characterized by major reverse faults that bring precambrian basement rocks to the surface the white rock thrust in the wind river mountains of wyoming is one such fault that developed at fairly shallow levels in the crust detailed study of grain size variations and textures within the fault zone provide a framework for discussion of the mechanics of movement along the fault textural criteria are suggested for distinguishing between dominantly brittle and dominantly ductile deformation a transition from brittle fracturing to ductile deformation is seen with increasing strain and resultant decrease in grain size along the fault zone diffusional creep in the final stages of deformation leads to strain softening and may allow large strains to take place along narrow zones at low deviatoric stresses this may be one way of obtaining large displacements along major faults at shallow levels in the crust

overview of the mars global surveyor mission the mars global surveyor spacecraft was placed into mars orbit on september 11 1997 and by march 9 1999 had slowly circularized through aerobraking to a sun synchronous near polar orbit with an average altitude of 378 km the science payload includes the mars orbiter camera mars orbiter laser altimeter thermal emission spectrometer ultrastable oscillator for radio science experiments and magnetometer electron reflectometer package in addition the spacecraft accelerometers and horizon sensors were used to study atmospheric dynamics during aerobraking observations are processed to standard products by the instrument teams and released as documented archive volumes on 6 month centers by the planetary data system significant results have been obtained from observations of the interior surface and atmosphere for example mars does not now have an active magnetic field although strong remanent magnetization features exist in the ancient crust these results imply that an internal dynamo ceased operation early in geologic time altimetry and gravity data indicate that the crust is thickest under the south pole thinning northward from the cratered terrain to the northern plains analysis of altimetry data demonstrates that mars is egg shaped with gravitational equipotential contours that show that channel systems in the southern highlands drained to the north largely to the chryse trough a closed contour in the northern plains is consistent with the existence of a great northern ocean emission spectra of low albedo regions show that basaltic rocks dominate spectral signatures on the southern highlands whereas basaltic andesites dominate the northern lowlands the bright regions show nondiagnostic spectra similar to that of dust in the atmosphere signatures of aqueous minerals e g clays carbonates and sulfates are noticeably absent from the emission spectra high spatial resolution images show that the surface has been extensively modified by wind and that layering is nearly ubiquitous implying that a complex history of events is recorded in surface and near surface materials altimetry data imply that both permanent caps are composed of water ice and dust with seasonal covers of carbon dioxide frost finally the altimetry data coupled with thousands of atmospheric profiles are providing new boundary conditions and dynamic controls for the generation and testing of more realistic dynamic models of the global circulation of the atmosphere

magnetic field and plasma observations at mars initial results of the mars global surveyor mission the magnetometer and electron reflectometer investigation mag er on the mars global surveyor spacecraft has obtained magnetic field and plasma observations throughout the near mars environment from beyond the influence of mars to just above the surface at an altitude of 100 kilometers the solar wind interaction with mars is in many ways similar to that at venus and at an active comet that is primarily an ionospheric atmospheric interaction no significant planetary magnetic field of global scale has been detected to date 2 1021 gauss cubic centimeter but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of mars is reported

paleoenvironmental evolution and prehistoric human environment in the embayment of palamari skyros island greece during middle late holocene abstract palamari bay is located on the northeastern coast of skyros island sporades islands aegean sea at the northern edge of the bay a fortified prehistoric settlement is found dated between 2800 and 1700 bc early bronze age ii middle bronze age i detailed geomorphological mapping of the coastal alluvial plain and paleontological micropaleontological palynological sedimentological and micromorphological studies of the holocene coastal deposits have been conducted in order to reconstruct the palaeoenvironment and the landscape evolution of the broader area of palamari bay three main sedimentary units were recognized a b and c from oldest to youngest the lowermost sedimentary unit a deposited between before 7500 and 3500 cal bp consists of sediment deposited from high to moderate energy fresh water flows with some suspended load fallout in established water bodies the microfauna indicates a shallow fresh water environment however a tendency to oligohaline conditions was established gradually during the same period the palamari area was characterized by open mixed deciduous forests that gradually retreated as a possible consequence of the intensification of anthropic activity associated with the settlement of palamari indications of cultivating and grazing activities in the vicinity of the lagoon were identified pointing to a strong human presence since the neolithic between about 6000 and 3500 cal bp the embayment was a lagoon southeasterly connected to the sea therefore sheltered and protected from northeastern winds the overlying unit b ca 3500 800 cal bp is characterized by the dominance of brackish water microfauna indicating a brackish stagnant shallow water depositional environment which was periodically supplied with fresh water from the surrounding springs as the result of the continuous sea level rise during the late holocene part of the northern headland was submerged the decline of the palamari settlement at the time of the establishment of unit b might be related to the observed changes that rendered the embayment a restricted body of water the uppermost sedimentary unit c corresponds to a backshore environment dominated by aeolian activity modified by fluvial processes

folding by cataclastic flow at shallow crustal levels in the canyon range sevier orogenic belt west central utah abstract folds form by ductile deformation typically involving continuous flow in the elastico frictional regime such deformation may be accomplished by cataclastic flow involving collective movement on a population of fractures and zones the canyon range cr syncline part of the cr thrust sheet in west central utah developed in this regime the cr syncline is composed of thick bedded quartzite units with a small material contrast between layers limiting limb rotation by flexural slip alone thus fracture populations developed to accommodate fold tightening by limb rotation and thinning and the formation of transverse zones across the fold several generations of fracture and deformation zone dz networks are recognized from mesoscopic and microscopic evidence and can be related to stages of folding the net result of the large number of distributed fractures and deformation zones is a continuous deformation that is homogeneous at the scale of the outcrop all these lines of evidence suggest that large scale cataclastic flow accommodated folding by allowing rigid mesoscopic blocks to slide along bounding dzs along its length the cr syncline consists of several segments bounded by transverse zones with different mechanisms accommodating fold tightening in adjacent segments in one segment fold tightening progressed by limb rotation and then out of the core thrusting in contrast fold tightening in the adjoining segments occurred by rotation and thinning of one limb and possible hinge migration with the steeply dipping to overturned limb showing progressive thinning of units on a megascopic scale and progressive increase in the thickness and density of deformation zones at all scales

the low temperature brittle ductile transition in a quartzite and the occurrence of cataclastic flow in nature the paper describes the mechanical and microstructural characteristics associated with the brittle to cataclastic flow transition in an orthoquarzite oughtibridge ganister and compares its microstructural development with features of cataclastic deformation of rocks in nature

large scale paleoceanographic variations in the western mediterranean sea during the last 34 000 years from enhanced cold water coral growth to declining mounds abstract quantitative and qualitative analyses of cold water coral cwc fragments from two sediment cores obtained from the melilla mounds field mmf in the alboran sea western mediterranean sea reveal an alternation of periods dominated by distinct cwc species the lower parts of the cores are dominated by the cwc species lophelia pertusa which is successively replaced in the upper parts by the species madrepora oculata and dendrophyllids the transition in the macrofauna coincides with a characteristic change in the benthic foraminiferal assemblage benthic foraminiferal assemblage bfaglacial in accordance with benthic cibicides lobatulus and planktic globigerina bulloides 13c and 18o values provide evidence for generally high surface productivity cold and well ventilated bottom waters lasting from the end of marine isotope stage 3 33 3 ka bp reaching a maximum at the transition allerod younger dryas together with 13c of the organic carbon and rock eval pyrolysis benthic foraminiferal assemblage bfainterglacial established since the early holocene indicates that the mmf experienced a decrease in bottom water energy that caused an organic carbon enrichment in the sediments and also depleted oxygen waters compared to the pre holocene interval dominated by the planktic foraminifera neogloboquadrina incompta and the benthic foraminiferal assemblage bfaglacial the organic carbon deposited during the holocene in the mmf contains more refractory components in relation to sea level rise and modern oceanographic configuration based on our data we suggest that l pertusa has a higher ecological requirement than m oculata and dendrophyllids especially with regard to oxygen and nutrient availability

foraminiferal assemblages from a transitional tropical upwelling zone in the golfe d arguin mauritania abstract with the growing pressure of eutrophication in tropical regions the mauritian shelf provides a natural situation to understand the variability in mesotrophic assemblages site specific dynamics occur throughout the 1200 m depth gradient the shallow assemblages divide into three types of warm water mesotrophic foraminiferal assemblages which is not only a consequence of high primary productivity restricting light to the benthos but due to low pore water oxygenation shelf geomorphology and sediment partitioning in the intermediate depth approx 500 m the increase in foraminiferal diversity is due to the cold water coral habitat providing a greater range of micro niches planktonic species characterise the lower bathyal zone which emphasizes the reduced benthic carbonate production at depth although due to the strong hydrodynamics within the golf planktonic species occur in notable abundances through out the whole depth gradient overall this study can easily be compared to other tropical marine settings investigating the long term effects of tropical eutrophication and the biogeographic distribution of carbonate producing organisms

benthic foraminifera from the fernando de noronha archipelago northern brazil abstract the aim of this paper is to describe the little studied shallow water benthic foraminiferal fauna of the fernando de noronha archipelago brazil the archipelago is about 15 km in length and is located just north of the equator off the northeastern coast of brazil samples were collected using scuba to depths of 30 m benthic foraminifera were analysed qualitatively and quantitatively about 150 species were identified with the fauna composed of 74 porcelaneous species 64 hyaline species and 10 agglutinated species miliolids comprise more than one third of all species recognized and constitute 40 60 of the individuals in all samples most of the species identified have been previously reported from the caribbean region and the fauna can be assigned to the west indian faunal province

factors controlling the location of the bow shock at mars 1 during the first year of the mars global surveyor mgs mission 553 shock crossings have been identified from a total of 363 orbits the shape of the shock has been determined by examining the mgs spacecraft magnetometer electron reflectometer mag er data the location of the shock was found highly variable the present study shows that the high crustal magnetic sources found in the southern hemisphere do not seem responsible for the bow shock bs variability the present study shows that contrary to many expectations there is no obvious strong one to one correlation between the location of the highest crustal sources and the variability of the shock position on the other hand the shock appears farthest from mars in the hemisphere of locally upward interplanetary electric field consistent with the idea that mass loading play a role in controlling the bs location which confirms previous results

thrust timing growth of structural culminations and synorogenic sedimentation in the type sevier orogenic belt western united states most of the regional shortening in the type area of the sevier orogenic belt in central utah was accommodated by displacement on the canyon range neocomian aptian pavant aptian albian paxton cenomanian campanian and gunnison late campanian paleocene thrust systems inception of each thrust system generated synorogenic sediment associated with frontal thrust tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland the sevier culmination a large antiformal duplex cored by crystalline basement rocks developed during paxton and gunnison thrusting west of and structurally beneath the canyon range and pavant thrusts growth of the sevier culmination was coeval with reactivation of the canyon range and pavant thrust systems and produced a second culmination in proterozoic lower cambrian rocks in the canyon range these structural highs provided much of the sediment to the adjacent foreland basin from late cenomanian to late paleocene time and may have helped to maintain critical taper in the thrust belt