spaceborne imaging radar c sir c observations of groundwater discharge and wetlands associated with the chicxulub impact crater northwestern yucatan peninsula mexico analyses of spaceborne imaging radar c sir c data and field data from the northwestern yucatan peninsula mexico demonstrate that spaceborne multifrequency polarimetric radars are excellent tools for characterizing patterns of wetland flooding seasonal flooding can be detected in most types of forest and marsh in the radar backscatter magnitude and phase data of both l and c band field observations made in the wet and dry seasons concurrent with the space missions and chemical analyses of floodwaters confirm that flooding is the product of discharge from the yucatan aquifer which consists of a fresh water lens floating on seawater this discharge controls the distribution of wetlands therefore vegetation and flooding patterns mapped with sir c imagery provide valuable information on the hydrogeology of the region radar image maps of wetlands and flooding indicate that there are three major zones of groundwater discharge that correlate with structures of the buried chicxulub crater zone 1 with the peak ring zone 2 with the crater rim and zone 3 with the exterior ring zone 1 has sulfate poor discharge unlike the sulfate rich discharge in zones 2 and 3 the highest discharge is in zone 3 where the buried crater is closest to the surface this groundwater discharge pattern can be explained by tidal pumping of fresh water to the surface through high permeability zones developed in the tertiary carbonates overlying crater faults and escarpments

relay zone geometry and displacement transfer between normal faults recorded in coal mine plans abstract overlap lengths separations and throw gradients were measured on 132 relay zones recorded on coal mine plans throws on the relay bounding fault traces are usually 2 m and individual structures are recorded on only one seam throw gradients associated with relay zones are not always higher than on single faults but asymmetry of throw profiles is diagnostic of relay zones bed geometries around larger faults in opencast mines are used to assess the displacement accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane three dimensional structure is defined for two relay zones each recorded on five seam plans these relay zones are effectively holes through the fault surfaces and overlap occurs between salients or lobes of the parent fault surfaces lobes initially terminated at tip lines but as the faults grew gradually rejoined the main fault surfaces along branch lines this type of relay zone originates by bifurcation of a single fault surface at a locally retarded tip line and is an almost inevitable result of a tip line irregularity

forest canopy characterization and vegetation penetration assessment with space borne radar synthetic aperture radar sar images from the national aeronautics and space administration s shuttle imaging radar b sir b mission were used to analyze the effects of radar incidence angle on information content and vegetation penetration three sar data sets using incidence angles of 26 46 and 58 were acquired over the mangrove jungles of southern bangladesh the data sets were digitally processed using 3 3 7 7 and 11 11 spatial filters and geometrically registered to a multisource multilevel corraborative data base consisting of landsat data forest map data and in situ acquired forest enumeration and topographic information analyses revealed that significant vegetation penetration was found at all angles and that tree and canopy structural morphology may exert an influence on this phenomenon

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

strike slip relay ramps areas of reorientated bedding at contractional oversteps between strike slip faults are here called strike slip relay ramps metre scale examples are described from the jurassic sediments at east quantoxhead somerset u k larger strike slip relay ramps occur in the rio de peixe basin ne brazil along the newport inglewood trend california and in the bovey basin sw england although the geometry and development of strike slip relay ramps are similar to those of relay ramps in normal fault systems there are differences in the structures which accommodate the transfer of displacement between the overstepping faults whereas strike slip relay ramps are typically transpressional with pressure solution often occurring relay ramps in normal fault systems are dominated by extension or transtension care needs to be taken when interpreting areas of reorientated bedding between overstepping faults particularly when displacement directions are unknown for example when using seismic data this is because relay ramps can occur in both strike slip and normal fault zones

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

carbonate geochemistry and the concentrations of aqueous mg2 sr2 and ca2 western north coast of the yucatan mexico abstract we have measured concentrations of major cations sr 2 and alkalinity in groundwater pore water and surface water samples collected from the western north coast of the yucatan peninsula mexico thermodynamic calculations indicate that almost all water samples from the study area are supersaturated with respect to calcite aragonite high mg calcite hmc and dolomite analysis of the data suggests that the geochemical processes controlling mg 2 sr 2 and ca 2 concentrations differ in different environments mass balance modeling has been used to calculate the amount of dissolution and or precipitation of aragonite low mg calcite lmc and hmc and or dolomite required to produce waters with the observed mg 2 sr 2 and ca 2 concentrations mass balance calculations indicate that hmc and aragonite are dissolving whereas lmc is precipitating from most groundwater and inland surface waters the chemistry of surface waters from an extensive saline coastal swamp suggests that lmc and aragonite in surficial swamp sediments are converted to hmc or dolomite while swamp pore water chemistry suggests that hmc is dissolving and lmc and aragonite are precipitating in deeper swamp sediments the chemistry of pore waters suggests that they are derived from saline surface waters and that fresh to brackish groundwater from the shallow confined aquifer does not flow into swamp sediments

mexican site for k t impact crater research throughout the caribbean suggests that the geophysical anomalies in the yucatan first noted by penfield and camargo 1981 and called the chicxulub crater could be the site of the impact purported to have caused the k t extinctions a semicircular ring of sink holes known locally as cenotes which correlates with the geophysical anomalies has been identified and it is argued that the origin of the cenote ring is related to postimpact subsidence of the chicxulub crater rim if there is indeed a crater the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km if confirmed as a site of impact the chicxulub crater would be the largest terrestrial impact crater known which is consistent with the uniqueness of the k t global catastrophe

chicxulub crater a possible cretaceous tertiary boundary impact crater on the yucatan peninsula mexico we suggest that a buried 180 km diameter circular structure on the yucatan peninsula mexico is an impact crater its size and shape are revealed by magnetic and gravity field anomalies as well as by oil wells drilled inside and near the structure the stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with and overlain by breccias that contain evidence of shock metamorphism the andesitic rocks have chemical and isotopic compositions similar to those of tektites found in cretaceous tertiary k t ejecta a 90 m thick k t boundary breccia also containing evidence of shock metamorphism is present 50 km outside the crater s edge this breccia probably represents the crater s ejecta blanket the age of the crater is not precisely known but a k t boundary age is indicated because the crater is in a thick carbonate sequence shock produced co2 from the impact may have caused a severe greenhouse warming

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

size and structure of the chicxulub crater revealed by horizontal gravity gradients and cenotes it is now widely believed that a large impact occurred on the earth at the end of the cretaceous period and that the buried chicxulub structure in yucatan mexico is the resulting crater24 knowledge of the size and internal structure of the chicxulub crater is necessary for quantifying the effects of the impact on the cretaceous environment although much information bearing on the crater s structure is available diameter estimates range from 170 to 300 km refs 1a 7 corresponding to an order of magnitude variation in impact energy here we show the diameter of the crater to be 180 km by examining the horizontal gradient of the bouguer gravity anomaly over the structure this size is confirmed by the distribution of karst features in the yucatan region mainly water filled sinkholes known as cenotes the coincidence of cenotes and peripheral gravity gradient maxima suggests that cenote formation is closely related to the presence of slump faults near the crater rim

large lateral ramps in the eocene valkyr shear zone extensional ductile faulting controlled by plutonism in southern british columbia abstract a 2 5 km high s facing lateral ramp links northern and southern segments of the ductile eocene valkyr extensional shear zone which defines the upper and outer boundary of the valhalla core complex in southern british columbia canada the evolution of the valkyr shear zone and of the lateral ramp is strongly influenced by the setting and geometry of middle jurassic tonalitic plutons and of paleocene eocene leucogranite aplite and pegmatite middle jurassic plutons were emplaced in the region of the valhalla complex as a series of interconnected flatbottomed laccoliths with the basal surfaces of adjacent bodies at the same structural level however on a large scale the southern portion of the laccolithic complex is structurally 2 5 km lower than the northern portion the lower surface of the laccolithic complex formed the upper limit of injection of gently dipping paleocene eocene leucogranite sheets as a consequence the upper margin of leucogranite is 2 5 km structurally lower in the south than in the north during the eocene extensional shear zones propagated along the interface between the upper plate stiffened by the cool strong middle jurassic tonalite and the lower plate made weak and ductile by voluminous hot paleoceneeocene leucogranite sheets the northern and southern segments of the valkyr shear zone propagated at two different structural levels and a lateral ramp formed in the intervening zone the ramp was localized at a rheological change across a s dipping boundary between hot ductile paleocene eocene leucogranite and an adjacent strong middle jurassic pluton maximum displacement of 15 20 km occurs in the central portion of the northern segment of the valkyr shear zone the southern segment has only 1 3 km of displacement this has left the pre eocene geological relationships of the southern valhalla complex and its surrounding rocks nearly intact and it can be demonstrated that the valkyr shear zone formed with a gentle original dip

crustal structure from deep seismic soundings along the koyna ii kelsi loni profile in the deccan trap area india abstract the crustal depth section obtained from deep seismic soundings along the koyna ii kelsi loni profile which lies near latitude 18 n roughly in the east west direction in that part of the deccan trap maharashtra state india shows a number of reflection segments below the deccan traps down to the moho discontinuity a deep fault below the deccan traps 13 km east of mahad divides the entire cross section including the moho boundary into two crustal blocks the reflection segments show updip towards the west coast in the western block the moho discontinuity which is at a depth of 39 km near the deep fault starts rising towards the coast reaching a depth of 31 5 km at the west coast the eastern block is thrown up by 1 5 km with respect to the western block along the deep fault a structural contour map of the moho discontinuity for the koyna reservoir area has been prepared from the present results and the crustal information obtained along the koyna i profile kaila et al 1979a shows that the deep fault in the koyna area is aligned in the nnw sse direction refraction seismic data analysis by the wave front method reveals that the thickness of the deccan trap increases towards the west coast the deccan trap is 600 700 m thick in the eastern region between nira sp 130 and loni sp 200 and attains a thickness of 1500 m at 10 km east of the west coast the longitudinal wave velocity in the deccan traps along the profile varies from 4 8 to 5 0 km sec and in the crystalline basement from 6 0 to 6 15 km sec a tentative isopach contour map of the deccan traps and a tentative structural contour map of the pre deccan trap contact have been prepared for the koyna reservoir area from the results along the koyna ii and koyna i profiles a flexure aligned in a nnw sse direction in the pre deccan trap contact which is an expression of the deep fault into the basement has been clearly brought out the flexure coincides in general with the orientation of the deccan volcanic scarp in this area

surface expression of the chicxulub crater analyses of geomorphic soil and topographic data from the northern yucatan peninsula mexico confirm that the buried chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the cenozoic has been influenced by the crater late tertiary sedimentation was mostly restricted to the region within the buried crater and a semicircular moat existed until at least pliocene time the topographic expression of the crater is a series of features concentric with the crater the most prominent is an approximately 83 km radius trough or moat containing sinkholes the cenote ring early tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km respectively two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km the low ridge between the inner troughs corresponds to the buried peak ring the moat corresponds to the outer edge of the crater floor demarcated by a major ring fault the outer trough and the approximately 62 km radius inner trough also mark buried ring faults the ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes these interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km but concentric low relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km

ring of cenotes sinkholes northwest yucatan mexico its hydrogeologic characteristics and possible association with the chicxulub impact crater a 180 km diameter semicircular band of abundant karst sinkholes ring of cenotes in northwest yucatan mexico coincides approximately with a concentric ring of the buried chicxulub structure a circular feature manifested in cretaceous and older rocks that has been identified as the product of the impact of a bolide the ring expressed in tertiary rocks marks a zone of high permeability as shown by 1 the sinkholes themselves 2 breaks in the coastal dune system and high density of springs where the ring intersects the coast and 3 water level transects characterized by a decline in water level toward the ring any direct relation that exists between the ring of cenotes and the chicxulub structure bears on regional hydrogeology if the layer or zone responsible for the ring is deeply buried it may act as a barrier to the movement of ground water across the main flow direction shallower zones of horizontal permeability could result in less complete diversion of ground water through its influence on yucatan aquifer characteristics the ring may provide a link between modern environmental problems and astrogeology possible origins for the ring of cenotes are 1 faulting perhaps reactivated by post eocene mid miocene basin loading 2 permeability in a buried reef complex developed in the shallow paleocene sea around the crater rim or 3 breccia collapse occasioned by consolidation or by solution of evaporite components if the ring developed on ancient faults it may outline hydrothermal systems and mineral deposits produced during paleocene cooling of the chicxulub melt sheet

radar scattering from a diffuse vegetation layer over a smooth surface a simple model is presented for the oblique backscatter and bistatic scatter from a smooth surface overlain by a diffuse layer only single scattering in the diffuse layer is taken into account the model analysis shows that the combination of volume scattering and oblique reflection at the surface may increase appreciably the waves scattering the scattering strongly depends on the properties of the smooth surface these results support some of the observations made with the seasat spaceborne imaging radar over flooded regions with heavy vegetation cover

a deep groundwater origin for recurring slope lineae on mars the recurring slope lineae on mars have been hypothesized to originate from snow melting deliquescence dry flow or shallow groundwater except for the dry flow origin these hypotheses imply the presence of surficial or near surface volatiles placing the exploration and characterization of potential habitable environments within the reach of existing technology here we present observations from the high resolution imaging science experiment heat flow modelling and terrestrial analogues which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere at depths of approximately 750 m spatial correlation between recurring slope lineae source regions and multi scale fractures such as joints and faults in the southern mid latitudes and in valles marineris suggests that recurring slope lineae preferably emanate from tectonic and impact related fractures we suggest that deep groundwater occasionally surfaces on mars in present day conditions observations and heat flow modelling suggest that briny groundwater surfacing from fractures forms recurring slope lineae on mars

size and morphology of the chicxulub impact crater the chicxulub impact in mexico has been linked to the mass extinction of species at the end of the cretaceous period from seismic data collected across the offshore portion of the impact crater the diameter of the transient cavity is determined to be about 100 km this parameter is critical for constraining impact related effects on the cretaceous environment with previous estimates of the cavity diameter spanning an order of magnitude in impact energy the offshore seismic data indicate that the chicxulub crater has a multi ring basin morphology similar to large impact structures observed on other planets such as venus

geologic interpretation of space shuttle radar images of indonesia the national aeronautics and space administration nasa space shuttle mission in november 1981 acquired images of parts of the earth with a synthetic aperture radar system at a wavelength of 23 5 cm 9 3 in and spatial resolution of 38 m 125 ft this report describes the geologic interpretation of 1 250 000 scale images of irian jaya and eastern kalimantan indonesia where the all weather capability of radar penetrates the persistent cloud cover the inclined look direction of radar enhances subtle topographic features that may be the expression of geologic structures on the indonesian images the following terrain categories are recognizable for geologic mapping carbonate clastic volcanic alluvial and coastal melange and metamorphic as well as undifferentia ed bedrock regional and local geologic structures are well expressed on the images in the vogelkop region of irian jaya the major tectonic elements tamrau mountains sorong fault kemum block bintuni basin and lengguru foldbelt are readily mapped on the image of the sorong fault geomorphic features offset drainage shutterridges aligned notches provide clear evidence for left lateral strike slip displacement several lineaments on the image correlate with previously mapped faults other lineaments may be the expression of previously unrecognized faults on the image of the mainland of irian jaya a belt of metamorphic and melange terrain marks the zone of collision between the pacific plate and the australian plate the high central range of irian jaya is located south of the metamorphic and melange belt the generally homoclinal structure of the central range is interrupted in the paniai lake region by a series of southward directed thrust plates indicated by belts of carbonate terrain new guinea limestone group that alternate with belts of clastic terrain kembelangan formation in the image of eastern kalimantan several major foldbelts are clearly expressed these limited examples of space shuttle radar images demonstrate their value for geologic interpretation of indonesia it is recommended that future shuttle missions acquire complete radar coverage of the main islands of indonesia for use in geologic mapping and energy exploration shuttle radar images would also be valuable for other cloud covered forested regions

unam scientific drilling program of chicxulub impact structure evidence for a 300 kilometer crater diameter as part of the unam drilling program at the chicxulub structure two 700 m deep continuously cored boreholes were completed between april and july 1995 the peto unam 6 and tekax unam 7 drilling sites are 150 km and 125 km respectively sse of chicxulub puerto near the crater s center core samples from both sites show a sequence of post crater carbonates on top of a thick impact breccia pile covering the disturbed mesozoic platform rocks at unam 7 two impact breccia units were encountered 1 an upper breccia mean magnetic susceptibility is high 55 10 6 si units indicating a large component of silicate basement has been incorporated into this breccia and 2 an evaporite rich low susceptibility impact breccia similar in character to the evaporite rich breccias observed at the pemex drill sites further out the upper breccia was encountered at 226 m below the surface and is 125 m thick the lower breccia is immediately subjacent and is 240 m thick this two breccia sequence is typical of the suevite bunte breccia sequence found within other well preserved impact craters the suevitic upper unit is not present at unam 6 instead a 240 m thick evaporite rich breccia unit similar to the lower breccia at unam 7 was encountered at a depth of 280 m the absence of an upper breccia equivalent at unam 6 suggests some portion of the breccia sequence has been removed by erosion this is consistent with interpretations that place the high standing crater rim at 130 150 km from the center consequently the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias depth and thickness support a 300 km diameter crater model

reinterpretation of the ordovician rotations in nw argentina and northern chile a consequence of the precordillera collision early paleozoic paleomagnetic data from nw argentina and northern chile have shown large systematic rotations within two domains one composed of the western puna that yields very large up to 80 counter clockwise rotations and the other formed by the famatina ranges and the eastern puna that shows 40 clockwise rotations around vertical axes in several locations lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the paleozoic previous tectonic models have explained these rotations as indicative of rigid body rotations of large para autochthonous crustal blocks or terranes a different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of precordillera in the late ordovician this collision should have generated dextral shear zones in the back arc region of the convergent sw gondwana margin where systematic domino like clockwise rotations of small crustal blocks accommodate crustal shortening the western puna block bordering the precordillera terrane to the north might have rotated counterclockwise as an independent microplate due to tectonic escape processes in a fashion similar to the present day relationship between the anatolia block and the arabian microplate

geologic and environmental aspects of surface cementation north coast yucatan mexico the northernmost part of the fresh water aquifer of yucatan mexico is confined near the coast by a thin flat nearly impermeable calcareous layer the authors think it probable that this confining layer is now developing by a process of sedimentation and precipitation of pore filling cement on and near the surface of older limestone at the landward margin of the swamp that extends virtually continuously along the north yucatan coast it is their interpretation that this caco sub 3 cemented layer which is 0 5 to 1 4 m thick developed in the zone of discharge of the fresh water aquifer the presence of sup 14 c 6 0 plus minus 0 4 modern carbon in a sample of aquitard supports the hypothesis that cementation is an ongoing process further support comes from the remarkable regularity between modern mean sea level and the elevation of the landward boundary between the confining zone and normal karst along 250 km of coast confinement of the aquifer produces an elevation of the piezometric surface to about 0 5 m above mean sea level and a concurrent depression of the fresh water salt water interface to an estimated depth of about 18 m below mean sea level at the coast breaching of the confining layer implicit inmore some development schemes for the region could dramatically decrease the thickness of the fresh water lens a valuable water resource the mixing zone beneath the confined part of the aquifer is a chemically active volume that may be vigorously pumped by tides as evidenced by increased salinity of ground water near the coast thus making this zone a likely place for rock water interaction including perhaps dolomite formation less