fishes and palaeogeography of the african drainage basins relationships between chad and neighbouring basins throughout the mio pliocene article i nfo keywords miocene pliocene palaeobiogeography africa the neogene african fossil record of two fishes i e semlikiichthys perciformes indet and calarius siluriformes ariidae is reviewed including new material from chadian outcrops their distribution confirms the existence of a nilo sudan ichthyological province during an early part of the miocene an east west waterway is demonstrated to have crossed africa allopatric speciation in the chadian and east african areas suggests that a split occurred in this system prior to 7 ma moreover our data support the existence of hydrographical connections between the chadian basin and the syrte basin after 7 ma at about the mio pliocene boundary finally our study also demonstrates that connections between the niger and chad basins

an observational search for carbonates on mars a search for carbonates and other salts exposed on the surface of mars was undertaken by observing areas of the surface in the 2 6 m to 4 2 m spectral region using the university of hawaii 2 2 m telescope at the mauna kea observatory hawaii observations of four mars areas syrtis major hellas arabia and an area northeast of hellas were made on the night of september 19 1986 the reflectance spectra for two partially overlapping areas show a weak absorption band in the 3 8 m to 3 9 m region which is in the spectral region where carbonate absorptions appear 3 8 m to 4 0 m the mars area of overlap contains syrtis planum the spectral feature from about 3 76 m to 3 95 m is clearly shortward of and broader than the calcium carbonate band about 3 9 m to 4 0 m and is at a slightly shorter wavelength position than magnesium carbonate magnesite bands about 3 8 m to 3 96 m as measured in this study positive identification of this band cannot be made by us at this time measurements for two other mars areas show no evidence of carbonate or other bands if the band is due to absorptions in the mars surface material spectrum and if it is due to carbonates then the results imply about 3 to 5 wt of a carbonate such as magnesite on average in the upper few millimeters of the mars surface material over the two areas where the weak spectral feature appears we can place an upper limit of 3 to 5 wt calcium carbonate and about 5 wt magnesite for all areas observed the interpretations are based on laboratory measurements of the reflectance spectra of calcite and magnesite and their mixtures with palagonite effects of thermal emission on the detection of carbonates were also explored for a wide range of temperatures thermal effects are not sufficient to mask the presence of calcite in the 3 to 5 wt range theoretical reasoning strongly supporting the presence of carbonates as a component of the mars surface is reviewed these and earlier observations do not rule out carbonates below the surface in other locations as small outcrops or in concentrations of less than 3 to 5 of the areas observed

local geoelectrical models of the martian subsurface for shallow groundwater detection using sounding radars received 15 february 2002 revised 20 july 2002 accepted 28 august 2002 published 6 march 2003 1 low frequency sounding radars should be able to probe the martian subsurface layers down to varying depths depending on the geoelectrical properties of the sounded sites we present in this work four frequency dependent geoelectrical models of the martian subsurface in the 1 20 mhz frequency band based on laboratory electromagnetic characterization of martian soil analogues those models correspond to local martian sites that we considered to be of particular interest in the search for water using mainly the ground penetrating radar gpr instrument of the netlander mission results and discussion are also valid for both sounding experiments marsis and sharad the four models of the martian subsurface are designed to represent terrains where recent fluviallike features suggest the presence of near subsurface ground ice and probably liquid water we performed measurements on volcanic and sedimentary materials that may be present on these sites under the appropriate geophysical conditions that may exist in those terrains we then simulated the backscattered radar echo arising from each site in the 2 mhz frequency band using the finite difference time domain fdtd algorithm in order to evaluate the instrument performances to probe the subsurface stratigraphy of each site our results confirm that the near subsurface rich iron oxide mineralogy controls the instrument performances in terms of penetration depth and signal to noise ratio in the 2 mhz frequency band we finally discuss the geophysical and geoelectrical sounding conditions that could lead to an ambiguous detection of shallow subsurface water on mars for the netlander gpr index terms 3210 mathematical geophysics modeling 1794 history of geophysics instruments and techniques 5144 physical properties of rocks wave attenuation 5109 physical properties of rocks magnetic and electrical properties keywords mars hydrology gpr sounding simulation fdtd

microwave remote sensing of physically buried objects in the negev desert implications for subsurface martian exploration 1 we report the remote detection of a physically buried specular reflecting object using microwave radar at ashalim in the northern region of the negev desert israel such detection provides an important terrestrial analogy for the potential detection of specularly reflecting subsurfaces under the desiccated regolith on mars such as ground ice and liquid water at ashalim a scatterometer operating in the p band 441 mhz 68 cm was mounted on a cherry picker truck at a height of 8 m and used to detect two triangular aluminum mesh reflectors forming a one meter square area reflector buried down to a depth of 8 cm in dry sand the decrease in measured backscattered power with increasing burial depth of the reflector is clearly evident the experimental results compare well with a theoretical model that incorporates radar absorption effects arising in the sandy subsurface layer and radar interference effects arising from phase differences between reflections from the surface and buried reflector this experiment and the associated modeling approach is the first of a series of planned experiments which we outline for the detection and the theoretical evaluation of buried reflectors using remote microwave and vhf radar we identify many potential subject areas for subsurface remote sensing in the martian domain particularly groundwater ground ice

the pragmatic roots of american quaternary geology and geomorphology abstract h l fairchild s words from the 1904 geological society of america bulletin remain appropriate today geologists have been too generous in allowing other people to make their philosophy for them geologists have quietly followed a methodological trinity involving 1 inspiration by analogy 2 impartial and critical assessment of hypotheses and 3 skepticism of authority prevailing theoretical constraints or paradigms these methods are described in classical papers by quaternary geologists and geomorphologists mostly written a century ago in recent years these papers have all been criticized in modern philosophical terms with little appreciation for the late 19th century american philosophical tradition from which they arose recent scholarly research however has revealed some important aspects of that tradition giving it a coherence that has largely been underappreciated as 20th century philosophy of science pursued its successive fads of logical positivism critical rationalism relativism and deconstructivism for all of which science is synonymous with physics nearly all this ideology is geologically irrelevant as philosophy of science in the late 20th century has come to be identical with philosophy of analytical physics focused on explanations via ideal truths much of geology has remained true to its classical doctrines of commonsensism fallibilism and realism in contrast to the conceptualism and the reductionism of the analytical sciences geology has emphasized synthetic thinking the continuous activity of comparing connecting and putting together thoughts and perceptions the classical methodological studies of geological reasoning all concern the formulation and testing of hypotheses analysis does not serve to provide the ultimate answers for intellectual puzzles predefined by limiting assumptions imposed on the real world rather analysis in geology allows the investigator to consider the consequential effects of hypotheses the latter having been suggested by experience with nature itself rather than by our theories of nature these distinctions and methods were described in g k gilbert s papers on the inculcation of scientific method by example 1886 and the origin of hypotheses 1896 portions were elaborated in t c chamberlin s method of multiple working hypotheses 1890 and his method of the earth sciences 1904 in w m davis s value of outrageous geological hypotheses 1926 and in d johnson s role of analysis in scientific investigation 1933 american quaternary geology and geomorphology have their philosophical roots in the pragmatic tradition enunciated most clearly by c s peirce now recognized as the greatest american philosopher and considered by sir karl popper to be one of the greatest philosophers of all time quaternary geology and geomorphology afford numerous examples of peirce s method of science which might be termed the critical philosophy of common sense the most obvious influence of pragmatism in geology however has largely been conveyed by the tradition of its scientific community the elements of this tradition include a reverence for field work a humility before the facts of nature a continuing effort to discriminate the phenomena observed from the observer s inference in regard to them a propensity to pose hypotheses and a willingness to abandon them when their consequences are contradicted by reality

geomorphological understanding of floods abstract the summer 1993 flooding of the upper mississippi river valley reminds us that floods are the most globally pervasive environmentally diverse and continually destructive of all natural hazards the fact that flood damages continue to rise raises commonsense questions about conventional flood science like much modern environmental science conventional flood science has followed the model of theoretical physics it advanced from early emphasis on streamflow measurement to the use of simple formulae and finally to the abstract theoretical sophistication of modern modeling studies two approaches are now used to predict flood phenomena 1 beginning with the conventional database of measured properties of small common floods a conceptual generalization is made to the idealized properties of the large rare floods from which society is assumed to be at risk and 2 explanation of detailed specific flood phenomena is achieved through theoretical generalization models based on first principles which are assumed to apply to the entire class of phenomena unfortunately both approaches devote almost all their attention to methodology increasingly mathematical without questioning basic underlying assumptions increasingly it is the assumptions often unstated that serve to embody the understanding of floods as real world particular phenomena rather than as conceptual generalities such trends lead to an unease that it is not floods that are being researched by much of conventional flood science rather such flood science is increasingly becoming the mathematical manipulation of idealized parameters that are assumed to have flood like properties these idealizations of flood attributes are generalized and the resulting predicted consequences are imposed upon society through engineering designs flood hazard zonations and the like geomorphological understanding of floods derives a from along geological tradition of studying indices of real processes operating in the past in contrast to the conceptual theoretical treatment of floods as classes or generalizations geomorphologists study particular floods revealed as a natural experience that is recorded in the sediments landforms and erosional scars of past floods the strength of this approach is in its affinity to the commonsense perceptional basis that underpins human action geomorphological flood studies including recent advances in paleoflood hydrology are needed as a complement to conventional hydrological approaches the resulting complementarity will allow the predictions of the conventional approach to be grounded in the concrete particulars of experience without such grounding flood science risks continuing as an empty quest for universal ideals while humanity paralyzed by inaction continues to suffer from the reality of particular floods

where is my sink reconstruction of landscape development in southwestern africa since the late jurassic abstract quantifying the rates and timing of landscape denudation provides a means to constrain sediment flux through time to offshore sedimentary basins the late mesozoic evolution of drainage basins in southern africa is poorly constrained despite the presence of several onshore and offshore sedimentary basins a novel approach has been developed to calculate the volume of material eroded since the late jurassic at different time steps by constructing structural cross sections and extrapolating thicknesses of eroded material using different assumptions the calculated volumes of material eroded from southwestern africa range from 2 52 106 km3 11 3 km of vertical thickness removed to 8 87 105 km3 4 0 km of vertical thickness removed for the southward draining systems alone the calculated removal of 7 81 105 2 60 105 km3 of material is far greater than the volumes of sediment recorded in offshore sedimentary basins 268 500 km3 reconstruction of the drainage systems using geomorphic indicators and clast provenance of the uitenhage group as well as extrapolated surface exposure ages indicate the southern draining systems were active from the late jurassic with coeval activity in axial and transverse drainage systems the calculated volumes are tied to published apatite fission track aft dates to constrain the changes in exhumation rate through time using multiple scenarios which indicate a significant amount of early cretaceous exhumation up to 1 26 106 km3 equivalent to 5 70 km of vertical thickness for the first time this has permitted long term landscape evolution to be used to support the interpretation that some of the missing sediment was deposited in sedimentary basins on the falkland plateau as it moved past southern africa during the early cretaceous this implies that in this instance the sinks are separated from their source areas by 6000 km

results from the mars global surveyor thermal emission spectrometer the thermal emission spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase together with about a 35 percent dust component provides the best fit to the spectrum qualitative upper limits can be placed on the concentration of carbonates 10 percent olivine 10 percent clay minerals 20 percent and quartz 5 percent in the limited regions observed limb observations in the northern hemisphere reveal low lying dust hazes and detached water ice clouds at altitudes up to 55 kilometers at an aerocentric longitude of 224 degrees a major dust storm developed in the noachis terra region the south polar cap retreat was similar to that observed by viking

elevation modelling and palaeo environmental interpretation in the siwa area egypt application of sar interferometry and radargrammetry to cosmo skymed imagery abstract digital elevation models produced from cosmo skymed imagery were used to delineate palaeo drainage in a wide area surrounding the siwa and al jaghbub oases of the western sahara desert egypt and libya this new generation of synthetic aperture radar imagery is suitable for this purpose because of its high spatial resolution and capacity to penetrate dry surface sediments different techniques such as radar interferometry and radargrammetry were used to produce digital elevation models these were assessed for accuracy and then combined to produce a single elevation model of the area the resulting elevation model was used to support the geological study and palaeo environmental interpretation of the area it revealed buried features of the landscape including inactive palaeo drainage systems drainage features were extracted from the elevation model using geographical information systems results were combined and assessed with respect to geological field data as well as data from the literature previous studies in the area suggest that a wide river probably the old nile river flowed into the libyan palaeo sirte before the late messinian drawdown of the mediterranean sea during the late messinian lowering of the sea the fluvial system changed shape and carved deep canyons throughout north eastern africa the reported findings on the key siwa area were used to precisely delineate the physiography of the modern drainage network and to confirm findings from our previous geological research in the area

image resolution and evaluation of genetic hypotheses for planetary landscapes the spatial resolution of image data tends to constrain the horizontal length scale of genetic hypotheses that are addressable by those data no simple formula exists when image resolution is sufficient to test a given geomorphic process which is dependent on what characteristics are diagnostic of the particular process genetic hypotheses should be formulated along the lines of the multiple working hypotheses concept as described in a classic paper by chamberlin j geol 5 1897 837 an essential element of a viable working hypothesis is a clear indication of the characteristics predicted by or a consequence of the hypothesis an untestable hypothesis is not an effective working hypothesis the history of the study of lunar sinuous rilles is outlined as an illustration of the influence of image resolution and the formulation of genetic hypotheses on the subsequent advancement of understanding of the problem sinuous rilles on venus and mars and controversial sinuous ridges on mars are also reviewed in the lunar case the three order of magnitude improvement in spatial resolution provided by lunar orbiter photographs over earth based telescopic photographs did not result in definitive examination and elimination of published hypotheses for the formation of sinuous rilles topographic data obtained from cartographically controlled apollo orbital photographs along with important observations and samples obtained by the astronauts on the lunar surface did test and exclude several hypotheses the formulation of a genetic hypothesis including testable consequences of that hypothesis is a greater determinant of its ultimate utility to the scientific community than is the image resolution available at any given time

the modern evolution of geomorphology binghamton and personal perspectives 1970 2019 and beyond abstract the annual binghamton geomorphology symposia bgs began in 1970 initiated by professors donald r coates and marie morisawa of the state university of new york at binghamton the 50 bgs meeting topics through 2019 can be organized into five general themes as follows 1 applications 2 methods 3 process and form 4 history philosophy and theory 5 systems my own geomorphological research can be divided among these themes though it has not always been in tune with any prevailing paradigm the experience of the bgs meetings suggests that the immediate future of geomorphology will follow current trends involving technological advances in such areas as geochronology geospatial analysis lidar mapping computer simulation and systems based predictive modeling for the longer term it may be that the research frontiers will lie in outer and inner space with the former involving the discovery and analysis of the surfaces of earth like planets within and beyond our own solar system the challenges of inner space may be even more profound as they are imposed against the background of rapidly accelerating advances in artificial intelligence

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

the educational value of the history of geomorphology abstract the history of geomorphology can be a valuable tool for educating students of geomorphology the largest and most available record of what geomorphologists thought and did in the past is their original published work also available are some fine papers on the history of geomorphology that review and analyze primary sources and past events in the discipline in order to generalize explain trends and reveal historical associations interest in the history of the discipline varies widely of course among geomorphologists nevertheless several educational benefits in addition to explaining the academic affiliation of geomorphology with two separate disciplines can be derived from incorporating the history of geomorphology into university level geomorphology courses history is a popular subject and presenting some geomorphic concepts using a historical approach can help to maintain or stimulate student interest because of the tendency for older literature to contain more qualitative description and methodological detail than more recent literature undergraduate students may comprehend some concepts better from older papers by reading the original literature students determine for themselves what previous practitioners accomplished rather than relying solely on the interpretations of others reading original literature also helps students realize that older does not mean less intelligent and that like the critical reading of recent geomorphic literature the critical reading of historic geomorphic papers can provide a wealth of new research ideas a thematic set of the historic literature can be used to demonstrate to students the scientific method the origin testing and evolution of hypotheses how explanations develop in this field and that science proceeds through individuals working in a sociological context including history of geomorphology in the curriculum helps to place contemporary research in the perspective of the past as well as the perspective of the future

a survey of transverse drainages in the susquehanna river basin pennsylvania abstract although large scale transverse drainages tds such as those of the susquehanna river above harrisburg pa have been recognized since the nineteenth century only two systematic surveys have been published of tds ver steeg 1930 oberlander 1965 a topographic and statistical analysis of tds in the susquehanna river basin using google earth and associated overlays identified 653 tds in the study area 95 of which contain streams with discharges of

subsurface imaging in south central egypt using low frequency radar bir safsaf revisited we present the capabilities of low frequency radar systems to sound the subsurface for a site located in south central egypt the bir safsaf region this site was already intensively studied since the sir a and sir b orbital radars revealed buried paleodrainage channels our approach is based on the coupling between two complementary radar techniques the orbital synthetic aperture radar sar in c and l bands 5 3 and 1 25 ghz for imaging large scale subsurface structures and the ground penetrating radar gpr at 500 and 900 mhz for sounding the soil at a local scale we show that the total backscattered power computed from l band sar and 900 mhz gpr profiles can be correlated and we combined both data to derive the geological structure of the subsurface gpr data provide information on the geometry of the buried scatterers and layers while the analysis of polarimetric sar data provides information on the distribution of rocks in the sedimentary layers and at the interface between these layers the analysis of 500 mhz gpr data revealed some deeper structures that should be detected by lower frequency sars such as a p band system

rivers and valleys of pennsylvania revisited abstract the 1889 paper by william morris davis on the rivers and valleys of pennsylvania is a landmark in the history of geomorphology it was in this manuscript that he set forth what came to be known as the davisian system of landscape it is important to understand that davis interpretation of landforms was restricted by the geologic paradigms of his day uniformitarianism was strongly entrenched and darwin s theory of evolution had become popularly accepted the concept of the landmass appalachia and then current theories on mountain building affected the approach that davis took in hypothesizing the origin and development of the folded appalachian drainage all of these geologic precepts influenced the formulation and explanation of his theories in his exposition he adapted synthesized and embellished on ideas he derived from fellow geologists such as gilbert dutton powell and mcgee a number of the concepts he proposed in the 1889 paper quickly became the bases for geomorphic studies by others the cycles of river erosion and landscape evolution and the peneplain here called base level erosion the cycle of erosion became the model for subsequent geomorphic analyses and peneplain hunting became a popular sport for geomorphologists davis hypothesis of the origin and development of pennsylvanian drainage stimulated subsequent discussion and further hypotheses by others in fact many of the later theories were refinements and or elaborations of ideas mentioned in this paper of davis he proposed the origin of the drainage as consequent streams then antecedence superposition headward extension of divides by piracy erosion along lines of weaknesses faults easily erodible beds through resistant ridges and normal fluvial erosion thus the hypotheses of regional superposition johnson extended consequents ruedemann consequents and local superposition meyerhoff and olmstead the utilization of structural weaknesses in development of transverse drainage thompson meyerhoff oberlander among others and migration of divides thompson all had been suggested by davis in 1889 although the concepts of erosion cycles and peneplaination have waned in popularity in recent geomorphic research the principles of formation of water and wind gaps headward migration of divides stream piracy and adjustment to streams to structure so clearly and minutely explained in his 1889 publication are still viable today

mars aeolian sand regional variations among dark hued crater floor features different regions on mars appear to have low albedo intracrater deposits that have distinct regional thermophysical and or aeolian dune characteristics thermal inertia derived from a carefully selected set of viking infrared thermal mapper observations of the dark features obtained in 1977 1978 supports this conclusion the observed similarities and differences among dark intracrater features on mars is probably a function of the combined influences of sand availability and regional wind conditions

pluvial conditions in the eastern sahara following the penultimate deglaciation implications for changes in atmospheric circulation patterns with global warming during the transition from the penultimate glacial to the last interglacial period isotope stages 6 5e or terminal ii large freshwater lakes abruptly infilled sandy depressions in arid regions of the eastern sahara geochemical and mineralogical studies of samples from lacustrine sequences in the western desert of southern egypt indicate 1 the sediments are chalk composed of authigenic chemical precipitates predominantly low mg calcite with carbonate contents averaging about 80 the low dilution of the chemical precipitate by detrital input implies that physical erosion and transport of detrital grains were minimized by extensive vegetation cover in the catchment area the fauna and flora associated with the lake deposits and middle paleolithic occupation sites on the paleo shorelines attest to a more amenable environment 2 vastly different rainfall or atmospheric circulation patterns than at present must have existed based on consistently negative 18opdb values for the chalk as low as 9 5 which would require precipitation from lake waters significantly more depleted in 18o than the modern local spring water 18osmow 1 8 3 the lakes were stable perennial water bodies with relatively long residence times sufficient to produce isotopic covariant signals in the chalks apparently the lakes disappeared as abruptly as they appeared without going through a terminal phase of evaporative enrichment extremely arid conditions again prevailed during the transition from the last glacial to the present interglacial terminal i a similar change from arid to pluvial conditions occurred thus it is proposed that during transitions from glacial to interglacial climates rapid global warming can lead to temporary alteration to atmospheric circulation with an intersification of the southwest monsoons bringing large quantities of isotopically light moisture to the eastern sahara

continental tectonics selected topics cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the mesozoic and cenozoic terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution deep crustal thrust systems with large lateral transport and vertical stacking of slices of crystalline basement were documented in the cordillera and appalachians new geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic rather than gravitational stresses lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts resulting in extension within the upper part of the lithosphere coeval with shortening at depth

canons revisited and reviewed lester king s views of landscape evolution considered 50 years later fifty years after its publication lester king9s canons of landscape evolution is reviewed and is considered in light of subsequent trends and actual developments some of his ideas such as the role of scarp recession and the antiquity of some surfaces remain current his broad view of the world and his interest in major relief anticipated trends that are now fashionable some of his interpretations however and in particular his downgrading of the importance of structural factors and his linking of scarp retreat and pedimentation have not stood the test of time other concepts such as the etch or two stage origin of forms which were mooted but not fully appreciated in king9s day have come to the forefront and technological advances in dating and survey particularly of the ocean floors have signaled new perspectives in landscape interpretation nevertheless king9s was a courageous attempt to provide guidelines for landscape study

contributions to the history of geomorphology and quaternary geology an introduction this special publication deals with various aspects of the histories of geomorphology and quaternary geology in different parts of the world geomorphology is the study of landforms and the processes that shape them past and present quaternary geology studies the sediments and associated materials that have come to mantle much of earth s surface during the relatively recent pleistocene and holocene epochs geomorphology with its concern for earth s surface features and processes deals with information that is much more amenable to observation and measurement than is the case for most geological work quaternary geology focuses mostly but not exclusively on the earth s surficial sedimentary cover which is usually more accessible than the harder rocks of the deeper past institutionally geomorphology is usually situated alongside or within academic departments of geology or geography in most english speaking countries its links are more likely to be with geography but in the united states these connections are usually shared between geography and geology although rarely in the same institution in leading institutions everywhere strong links exist between geomorphology and such cognate disciplines as soil science hydrology oceanography and civil engineering although nominally part of geology quaternary geology also has strong links with geography and with those disciplines such as climatology botany zoology and archaeology concerned with environmental change through the relatively recent past given that geomorphology concerns the study of the earth s surface i e landforms and their origin evolution and the processes that shape them and that the uppermost strata are in many cases of pleistocene and holocene age it is unsurprising that this special publication should deal promiscuously with topics in both geomorphology and quaternary studies this particular selection has been developed from a nucleus of papers presented at a conference on the histories of geomorphology and quaternary geology held in the baltic states

overview of results of spaceborne imaging radar c x band synthetic aperture radar sir c x sar the spaceborne imaging radar c x band synthetic aperture radar sir c x sar was launched on the space shuttle endeavour for two ten day missions in the spring and fall of 1994 radar data from these missions are being used to better understand the dynamic global environment during each mission radar images of over 300 sites around the earth were obtained returning over a terabit of data sir c x sar science investigations were focused on quantifying radar s ability to estimate surface properties of importance to understanding global change and focused studies in geology ecology hydrology and oceanography as well as radar calibration and electromagnetic theory studies in addition the second flight featured an interferometry experiment where digital elevation maps were obtained by interfering data from the first and second shuttle flight and from successive days on the second flight sir c x sar data have been used to validate algorithms which produce maps of vegetation type and biomass snow soil and vegetation moisture and the distribution of wetlands developed with earlier aircraft data

basement cover relationships in the appalachian caledonian variscan orogen mid devonian end of acadian orogeny to end of permian

book reviewthe geomorphology of egypt landforms and evolution volume 1 the nile valley and the western desert nabil s embabi ed the egyptian geographical society special publication cairo egypt 2004 447 pp hardbound us 60 available from egyptian geographical society 109 qasr el aini street p o box mohamed farid cairo egypt isbn 977 5821 04 5

geomorphology and quaternary geology of the dakhla oasis region egypt abstract dakhla oasis 25 5 n 29 e occupies a structurally localized depression at 90 140 m above sea level 1200 km 2 in area below a 300 m escarpment bordering the libyan plateau western desert of egypt semi arid intervals of the quaternary period generated eight sedimentary formations separated by erosion during hyper arid intervals sediments comprise three generations of colluvial fluvial fanglomerates two generations of tabular spring laid clastic and chemical sediments two generations of mound springs and basinal sediments of fluvio lacustrine evaporitic pluvio aeolian and aeolian origins discussion of these sediments is organized according to geomorphic region from north to south plateau scarp and piedmont lowland and cuesta plain chronological evidence is restricted to many radiocarbon dates of holocene cultural material associated with playa sediments 9 4 5 ka a th u isochron age of 62 0 7 6 ka for basinal evaporites and two th u ages of 176 and 170 ka for a boulder of derived travertine the regional quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces it is broadly similar to sequences earlier reconstructed in the topographically similar kharga oasis region 150 km to the east and kurkur oasis 400 km to the south southeast speculations on chronology and driving mechanism are offered in conclusion

evaluation of carbonate abundance in putative martian paleolake basins abstract carbonate deposits have not been found so far on mars although there appears to have been sufficient water to have supported their formation many hypotheses have been proposed in order to explain this in the present work we explore the possibility that the missed detection of carbonate deposits on the martian surface could be simply due to the fact that the concentration of carbonates when mixed with other materials present in the sedimentary deposits may be below the detection limit of the various instruments used so far in this search in the present study we consider 21 putative paleolacustrine basins and use a sediment transport model to estimate the abundance of carbonates which could be present in the sediments deposited on the basin floor in this way we find that for all the selected basins the estimated carbonate abundances are in general less than a few percent and such values are below or at best comparable to the detection limits of the spectrometers flown around mars during the recent space missions furthermore applying the sediment transport model to the well studied eberswalde crater we conclude that the fluvio lacustrine activity in this basin should have lasted for a period on the order of 10 3 10 4 years in good agreement with previous work our results suggest that a hydrological cycle able to move large volumes of water and to create relatively stable lakes could have been active intermittently on mars in the past producing carbonate deposits that could escape detection by the instruments that have flown to date

subsurface valleys and geoarcheology of the eastern sahara revealed by shuttle radar the shuttle imaging radar sir a carried on the space shuttle columbia in november 1981 penetrated the extremely dry selima sand sheet dunes and drift sand of the eastern sahara revealing previously unknown buried valleys geologic structures and possible stone age occupation sites radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand and alluvium filled valleys some nearly as wide as the nile valley and perhaps as old as middle tertiary the now vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat hyperarid region underfit and incised dry wadis many superimposed on the large valleys represent erosion by intermittent running water probably during quaternary pluvials stone age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation the presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present day oases which have been centers of episodic human habitation radar penetration of dry sand and soils varies with the wavelength of the incident signals 24 centimeters for the sir a system incidence angle and the electrical properties of the materials which are largely determined by moisture content the calculated depth of radar penetration of dry sand and granules based on laboratory measurements of the electrical properties of samples from the selima sand sheet is at least 5 meters recent september 1982 field studies in egypt verified sir a signal penetration depths of at least 1 meter in the selima sand sheet and in drift sand and 2 or more meters in sand dunes

the importance of sar wavelength in penetrating blow sand in northern arizona abstract multifrequency and polarimetric air borne s ynthetic a perture r adar airsar images of a sand streak in northern arizona demonstrate the ability of c 6 cm wavelength l 24 cm and p band 68 cm radar signals to backscatter respectively from increasingly greater depths reaching 2 m or more in active blow sand the studied sand streak located on a salient of ward terrace at lat 35 48 4 n and long 111 15 0 w is sourced in the normally dry little colorado river channel and migrates northeastward toward the moenkopi plateau scarp the sand streak is radar dark compared to the radar bright surface of ward terrace on all c band images it is however penetrated completely at p band and is invisible on these images the sand streak is recognizable on the lhh image but is poorly defined on the lhv image high resolution airsar images constitute the primary data set analyzed in addition a c band radar image acquired by the european remote sensing ers satellite is also presented the spaceborne image data confirms the results of the aircraft data at c band

uranium series dated authigenic carbonates and acheulian sites in southern egypt field investigations in southern egypt have yielded acheulian artifacts in situ in authigenic carbonate deposits caco 3 cemented alluvium along the edges of nowaggraded paleovalleys wadi arid and wadi safsaf uranium series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45 141 and 212 ka thousand years ago most of the carbonate appears to have been precipitated from groundwater which suggests that these three episodes of deposition may be related to late pleistocene humid climates that facilitated human settlement in this now hyperarid region carbonate cements from sediments containing acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

geological assessment of sir b imagery of the amadeus basin n t australia when sir b imagery of the arid margin of the simpson desert of central australia is combined with landsat mss principal component data regional geological structures are clearly defined a variety of sedimentary lithological units are mapped on the basis of outcrop morphology and mss spectral variations on the color composite image relative backscatter power from sir b digital imagery is observed to correlate with surface roughness for a variety of lithological terrains

microwave remote sensing of physically buried objects in the negev desert implications for environmental research we report remote detections of physically buried specularly reflecting objects using microwave radar at two sites ashalim and tseelim in the northern region of the negev desert israel these detections provide confirmation that microwave subsurface remote sensing is a genuine phenomenon at ashalim a scatterometer operating in the p band 441 mhz 68 cm was mounted on a cherry picker truck at a height of 8 m and used to detect two triangular aluminum mesh reflectors forming a 1 m square area reflector buried down to a depth of 8 cm in dry sand at tseelim the same scatterometer was mounted on an airplane flying at an altitude of 70 m and used to detect 1 m square aluminum reflectors each one submerged at a different location along the airplane flight path buried down to a depth of 20 cm the experimental results compare favorably with a theoretical model that incorporates radar absorption effects arising in the sandy subsurface layer and radar interference effects arising from phase differences between reflections from the surface and buried reflector the theoretical modeling also predicts the detection of a subsurface reflector down to a depth of about 4 4 m this experiment and the associated modeling approach is the first of a series of planned experiments which we outline for the detection and the theoretical evaluation of buried reflectors using remote microwave and vhf radar we identify potential subject areas for environmental research

development of the mars microbeam raman spectrometer mmrs 1 raman spectroscopy is a powerful tool for mineral characterization and for detection of water and organic and inorganic forms of carbon the mars microbeam raman spectrometer mmrs is designed for close up analysis of rocks and soils in planetary surface exploration the mmrs consists of a probe in a flight unit to be deployed by a robotic arm and a spectrograph laser source and electronics in a flight unit to reside on a rover or lander the raman probe has a scanning optical bench that enables a 1 cm linear traverse across a target rock or soil both on target materials as encountered and on fresh surfaces of rocks exposed by abrasion or coring from these spectra one can identify major minor and trace minerals obtain their approximate relative proportions and determine chemical features e g mg fe ratio and rock textural features e g mineral clusters amygdular fill and veins one can also detect and identify organic species graphitic carbon and water bearing phases extensive performance tests have been done on a brassboard model of the mmrs using a variety of geological materials minerals rocks martian meteorites etc these tests show that a raman spectrometer can be built that is suitably miniaturized sufficiently robust and low enough in power usage to serve as an on surface planetary instrument yet the spectrometer can retain high detection sensitivity and yield near laboratory quality spectra over a broad wavelength range these features are essential to provide definitive mineralogy in a planetary exploration

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

archean inheritance in zircon from late paleozoic granites from the avalon zone of southeastern new england an african connection abstract in southeastern new england the narragansett pier granite locally intrudes carboniferous metasedimentary rocks of the narragansett basin and yields a monazite u pb permian emplacement age of 273 2ma zircon from the narragansett pier granite contains a minor but detectable amount of an older inherited component and shows modern loss of lead zircon from the late stage aplitic westerly granite exhibits a more pronounced lead inheritance permitting the inherited component to be identified as late archean such old relict zircon has not been previously recognized in proterozoic to paleozoic igneous rocks in new england and may be restricted to late paleozoic rocks of the avalon zone we suggest that the archean crustal component reflects an african connection in which old archean crust was underplated to the avalon zone microplate in the late paleozoic during collision of gondwanaland with avalonia

use of optical and radar remote sensing satellites for identifying and monitoring active inactive landforms in the driest desert in saudi arabia abstract observing earth from the space is key for monitoring land surface dynamics and probing near surface geomorphic and geological features including those obscured by sand sheets dunes and human activity the hyper arid area of the arabian peninsula was selected for detecting and extracting obscure paleohydrological systems and modeling the spatio temporal dynamics of sand dunes using synthetic aperture radar sar and optical high resolution remote sensing images interferometric synthetic aperture radar insar coherence change detection ccd using sentinel 1 imagery was performed revealing subtle changes in the surficial landforms of the study area these images also discriminated between active and inactive geomorphic features in addition low frequency l band advanced land observing satellite phased array type l band synthetic aperture radar alos palsar and shuttle radar topography mission srtm data revealed the details of paleochannels in the basins that drain into the arabian gulf these ephemeral rivers are the source of sand that was later reshaped into dunes by aeolian processes the results also revealed that the morphology and extension of dunes were clearly influenced by topography slope and wind velocity and direction rather than human activities knowledge gained by exploring desert features is essential for planning settlements and development and integrated approaches using a variety of remote sensing datasets are key for enhancing earth observation across a range of spatial and temporal scales

laboratory and field measurements of the modification of radar backscatter by sand abstract over the last two decades the use of synthetic aperture radar sar to address geologic problems has expanded as new applications for radar have been developed one of the earliest and perhaps most surprising results from orbital sar images of the sahara was that under certain conditions radar signals penetrated up to several meters of sand to reveal subsurface features such as ancient river channels subsequent studies of radar penetration of arid sand deposits have dealt with factors that govern the ability of radar to penetrate a sand cover this paper presents results from a laboratory experiment in which radar backscatter from a surface of rocks was measured under controlled conditions as a function of frequency polarization incidence angle and sand cover thickness the sand used in the experiment had a moisture content of 0 28 vol and caused calculated average attenuations of 4 2 1 db m for c band and 11 2 db m for x band results from the experiment were compared to field measurements of sand thickness during acquisition of airborne radar images in airsar images the extent of dry sand in a dune field appears best in c band because longer wavelength l and p band signals penetrate thinner sand deposits images of wet sand 4 9 vol suggest that l band was able to penetrate thin sand even though that sand was wet together these laboratory and field measurements contribute towards a better understanding of how a sand cover modifies the radar backscatter of a surface

spaceborne radar subsurface imaging in hyperarid regions imaging data acquired with the shuttle imaging radar sir a over the hyperarid region of egypt sudan clearly show surface penetration through the sand cover even though absorption does occur in the sand layer surface refraction leads to a steeper incidence angle at the sand bedrock interface resulting in a stronger backscatter a simple backscatter model shows that for a low loss thin sand layer the presence of the covering layer enhances the capability to image the subsurface interface particularly at large incidence angles and hh polarization

a wetter climate in eastern sudan 2 000 years ago within the past 15 years accurate radiocarbon dating and plant microfossil analysis of tropical lake sediments in africa and elsewhere have revealed that the early holocene 11 7 kyr was generally wetter than today throughout the tropics1 4 in contrast to last glacial maximum 18 2 kyr which was cool dry and windy5 6 desiccation beginning 4 5 kyr ago forced neolithic herders to abandon previously habitable old world deserts7 9 less well known is the climate of proto historic times 2 kyr ago when iron smelting became important in africa10 here we present the first evidence that the red sea hills were somewhat wetter at this time and suggest that this was also true of much of northern africa

shuttle imaging radar physical controls on signal penetration and subsurface scattenng in the eastern sahara sir a signal penetration and subsurface backscatter within the upper meter or so of the sediment blanket in the eastern sahara of southern egypt and northern sudan are enhanced both by radar sensor parameters and by the physical and chemical characteristics of eolian and alluvial materials interpretation of sir a images by mccauley et al 1 2 dramatically changed previous concepts of the role that fluvial processes have played over the past 10000 to 30000000 years in shaping this now extremely flat featureless and hyperarid landscape in the present paper we summarize the near surface stratigraphy the electrical properties of materials and the types of radar interfaces found to be responsible for different classes of sir a tonal response the dominant factors related to efficient microwave signal penetration into the sediment blanket include a favorable distribution of particle sizes b extremely low moisture content and c reduced geometric scattering at the sir a frequency 1 3 ghz the depth of signal penetration that results in a recorded backscatter here called radar imaging depth was documented in the field to be a maximum of 1 5 m or 0 25 of the calculated skin depth for the sediment blanket radar imaging depth is estimated to be between 2 and 3 m for active sand dune materials diverse permittivity interfaces and volume scatterers within the shallow subsurface are responsible for most of the observed backscatter not directly attributable to grazing outcrops

neotectonism along the atlantic passive continental margin a review abstract an extensive body of geologic data including the modern state of stress historical seismicity surface and subsurface stratigraphy numerical models of crustal deformation surficial geomorphic systems and historical precise leveling and tidal gauge records constrain the style and rate of neotectonic deformation for the appalachians and atlantic passive continental margin there are two major styles of neotectonism in the eastern united states the northeastern united states is dominated by isostatic uplift and northward migration of peripheral bulge collapse in response to deglaciation this locally rapid but decreasing rate of deformation is superimposed upon slower long term deformation along the atlantic margin most of the long term continental margin deformation is attributed to lithospheric flexuring in response to sediment loading in sedimentary basins especially the baltimore canyon trough and carolina trough isostatic deformation in response to continental denudation and water loading of the shelf and stress from far field plate tectonic sources significant deformational features include an uplift anomaly near cape fear n c northward and southward tilting of the coastal plain into the salisbury and southeast georgia embayments respectively seaward tilting of the coastal plain piedmont and a complex pattern of postglacial uplift and later subsidence in the northeast estimates of vertical crustal velocities for similar locations vary over several orders of magnitude measurement interval bias and systematic leveling errors may account for some of the discrepancies evidence for periodic deformation in the eastern united states in substantial and it is possible that historic data indicate a period of accelerated deformation along the atlantic continental margin

petrology and geochemistry of ordovician k bentonites in new york state constraints on the nature of a volcanic arc altered volcanic ashes k bentonites in the late ordovician caradocian utica shale of new york state are the product of explosive arc volcanism most of the 30 k bentonites examined in this investigation contain fragmental crystals and rock fragments microliths up to 600 mu m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts the dominant phases are garnet two groups gr sub 15 20 alm sub 45 75 py sub 35 0 sp sub 2 5 gr sub 2 5 alm sub 55 85 py sub 10 40 sp sub 1 plagioclase feldspar an sub 80 10 alkali feldspar or sub 99 0 clinopyroxene wo sub 50 40 en sub 50 30 fs sub 0 30 and orthopyroxene wo sub 1 2 en sub 77 32 fs sub 32 66 accompanied by lesser quantities of hornblende aluminosilicate quartz sphene fe ti oxides apatite and zircon most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths which possess minerals with similar compositions both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the ordovician arc was constructed they became entrained in the volcanic plume during explosive eruptions a precambrian age acquired on k feldspars from one k bentonite using the sup 40 ar sub 39 ar method shows that these xenocrysts were derived from depths of less than 5 10 km in the microcontinent at the time of late ordovicianmore volcanism the occurrence of xenocrysts and xenoliths in these k bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks e g isotopic age determinations regional stratigraphic correlations of k bentonites based upon chemical compositions less

significance of dextral reactivation of an e w transfer fault in the formation of the pennsylvania orocline central appalachians 1 three hypotheses for orocline development including 1 primary plate boundary shape 2 arc rotation and 3 arc overprinting were evaluated for the formation of the pennsylvania orocline maryland usa using foliation intersection inflection axes preserved within porphyroblasts fia the distribution and the timing of sequences of fia data measured from garnet porphyroblasts within the loch raven formation are statistically the same across the pennsylvania orocline suggesting that all subregions of the arc have experienced the same deformation history this may suggest that the geometry of the paleocontinental margin controlled the basic shape of this orocline however if the orocline is treated as three separate regions defined by the sw we ne trending portions of its slightly staircase shaped outline a much higher proportion of the nne ssw trending fias set ii are preserved in the w e trending region than those to either side this geometric relationship could have resulted from wnw ese directed bulk stress causing a zone of dextral shear along what is now the w e trending portion of this orogen it appears that what could have been an early formed w e trending sinistral transform shear zone was preferentially dextrally reactivated during the taconian orogeny

changes in the fine sediment dynamics of the ouse and tweed basins in the uk over the last 100 150 years sediment cores collected from nine headwater lakes and reservoirs in their catchments and adjacent areas and from ten floodplain sites in the middle and lower reaches of the two river systems have been used to reconstruct changes in suspended sediment yields rates of sedimentation and suspended sediment sources for the ouse and tweed catchments in the uk over the last ca 100 150 years in response to recent environmental change for the small lake reservoir catchments in or adjacent to the ouse basin average sediment yields for the recent period 1963 95 were generally found to exceed those for the period prior to 1963 by up to 94 suggesting that sediment yields have increased over time for the equivalent lake reservoir catchments in and adjacent to the tweed basin sediment yields were generally lower in the period since 1963 in both basins sediment yields over the past 100 150 years were characterized by considerable temporal variability which was seen to reflect at least in part the significant changes in land use and land management that occurred within their catchments no clear links between the variability of sediment yields and changes in climate were apparent changes in sediment source reconstructed for one of the lakes appeared primarily to reflect catchment disturbance during afforestation in the 1940s average rates of overbank sedimentation for the ten floodplain sites varied considerably between sites for those cores collected from the ouse basin there was no consistent temporal trend and average sedimentation rates for the period extending from ca 1895 to 1963 were broadly similar to those for the period since 1963 for the tweed basin sedimentation rates for all three cores were higher prior to 1963 reflecting the increased soil erosion and sediment yields associated with the conversion of pasture to arable land in the immediate post world war ii period and the ditching and planting operations associated with afforestation in the 1940s substantial downcore variability in the source of the overbank sediment considered in terms of both source type and spatial location was found in both river basins this was seen to reflect land use change including land drainage the conversion of pasture to arable land afforestation and increased cereal production the evidence provided by the floodplain cores again showed little indication of any influence linked to climate change although the detailed patterns of temporal variation of sediment yield overbank sedimentation rate and sediment source reconstructed from the sediment cores collected from the lake reservoirs and floodplain locations are site specific there is a general consistency between the changes in sediment dynamics reconstructed for the headwater catchments based on the cores collected from the lakes and reservoirs and the equivalent evidence for the middle and lowland reaches of the catchments provided by overbank floodplain deposits despite significant changes in climate and more particularly land use over this time period the general lack of evidence of substantial changes in downstream sediment yield and rates of overbank sedimentation over the last ca 100 150 years in the ouse and tweed basins suggests that their sediment dynamics have been generally insensitive to recent environmental change this finding has important implications when considering the likely response of these and similar uk river basins to future environmental change

the spokane flood debates historical background and philosophical perspective the 1920s 1930s debates over the origin of the channeled scabland landscape of eastern washington northwestern usa focused on the cataclysmic flooding hypothesis of j harlen bretz during the summer of 1922 bretz began leading field parties of advanced university of chicago students into the region in his first paper published in the bulletin of the geological society of america bretz took special care not to mention cataclysmic origins however in a subsequent paper in the journal of geology to the editorial board of which he had recently been added bretz formally described his hypothesis that an immense late pleistocene flood which he named the spokane flood had derived from the margins of the nearby cordilleran ice sheet this cataclysm neatly accounted for numerous interrelated aspects of the channeled scabland landscape and nearby regions nevertheless the geological community largely resisted bretz s hypothesis for decades despite his enthusiastic and eloquent defence thereof resolution of the controversy came gradually initially through the recognition by j t pardee of a plausible source for the flooding ice dammed pleistocene glacial lake missoula in northern idaho and western montana eventually by the 1960s the field evidence for cataclysmic flooding became overwhelming and physical processes were found to be completely consistent with that evidence the controversy is of philosophical interest in regard to its documentation of the attitudes of geologists toward hypotheses which illustrate aspects of geological reasoning that are distinctive in degree from those of other sciences j harlen bretz there can be no period after the j it was the man s entire first name was born in 1882 he initiated one of the great debates in the history of geomorphology while not revolutionary in its implications the debate is nevertheless instructive for how it illustrates the workings of science where the latter is defined not as a sterile collection of facts or even as a logical application of method but rather as the collective workings and attitudes of human beings passionately dedicated to the search for truth the subject of the debate is an unusual landscape in eastern washington northwestern united states described by bretz 1928a pp 88 89 as follows no one with an eye for land forms can cross eastern washington in daylight without encountering and being impressed by the scabland like great scars marring the otherwise fair face to the plateau are these elongated tracts of bare black rock carved into mazes of buttes and canyons everybody on the plateau knows scabland the popular name is a metaphor the scablands are wounds only partially healed great wounds in the epidermis of soil with which nature protects the underlying rock the region is unique let the observer take wings of the morning to the uttermost parts of the earth he will nowhere

late cenozoic uplift of the eastern united states revealed by fluvial sequences of the susquehanna and ohio systems coupling between surface processes and lower crustal flow abstract fluvial and karstic data sets indicating late cenozoic surface uplift in the eastern united states are modelled for the first time using a technique incorporating coupling between surface processes and flow in the lower continental crust which has been extensively used for modelling similar data sets elsewhere in the world notably in europe distinct phases of lower crustal flow forcing starting in the early middle miocene late pliocene and late early pleistocene are evident as observed elsewhere and relate to combinations of cyclic surface loading by sea level variations and ice loads and to variations in regional erosion rates as elsewhere however the detailed uplift histories inferred are rather different from those indicated in many other regions notably europe primarily because of different properties of the crust in particular in the late proterozoic phanerozoic crust of the appalachians the mobile lower crustal layer seems to be relatively thick causing a prolonged uplift response for each phase of lower crustal flow forcing whereas in the early proterozoic crust of the yavapai crustal province farther west underlain by a thick basal mafic layer this mobile layer is much thinner leading to a very different response consisting of abrupt alternations of uplift and subsidence as is also observed in other regions of early proterozoic crust another important difference relative to western and central europe is the much smaller number of terraces in the eastern us rivers that have been studied the general applicability of this type of physics based modelling technique is thus confirmed

the quaternary development of tributary channels to the nile river at kom ombo area eastern desert of egypt and their implication for groundwater resources the dry wadis ephemeral channel constituting the main tributaries to the nile river in kom ombo are structurally and tectonically controlled and exhibit complex drainage pattern this complicated drainage pattern is inherited from the morpho tectonic evolution of the ancestral nile river protonile which drained the eastern desert during the middle pleistocene a digital elevation model derived from shuttle radar topography mission data is used to delineate the contemporary drainage networks and their catchments satellite images acquired during a flash flood event were used to validate the delineated watershed divides and flow pathways particularly where the courses of dry wadis are interlocked currently the westward flow of wadi abu suberah is derived from a small area in the eastern desert as the palaeo upper reaches of this wadi were captured due to tectonic movements along nw se and n s faults by wadis in the kharit and elewa areas the influence of these tectonic movements on groundwater distribution is also shown where the deep nubian aquifer discharges its water into the quaternary aquifer through fault planes the northward flowing protonile main course has tectonically shifted from the gallaba plain in the western desert eastward to the current nile river course this shift has produced several cut off segments of the palaeo tributary drainage that was originally flowing westward towards the old protonile main course in the gallaba plain however these segments have reversed their surface run off flow directions eastward towards the current nile course they could include potential groundwater resources as their alluvium may be still recharged by the nile river copyright 2010 john wiley sons ltd

relict drainages conical hills and the eolian veneer in southwest egypt applications to mars viking images indicate that no single process is sufficient to explain the origin and evolution of martian landforms landforms common to both earth and mars result from a complex interplay of geologic agents including water mass wasting wind and possibly ice the relict wadis of the gilf kebir plateau in southwest egypt strongly resemble fluvial channels on mars particularly those of the fretted terrain like the fretted channels on mars the egyptian wadis are dry flat floored and deeply incised in a plateau surface they have stubby theatre headed wide and deep tributaries that commonly join the trunk valleys at odd angles they apparently lack drainage basins and are separated by areas that appear on most of the available images to be undissected the wadis grade into adjacent low lying smooth plains mantled by eolian debris and dotted with myriads of conical and flat topped inselbergs that have obviously undergone mass wasting the unusual geomorphic characteristics of the gilf region are herein interpreted as the results of an extreme eolian and mass wasting overprint on a landscape originally carved by running water the relict networks of southwest egypt were initiated by streams that drained formerly extensive gilf highlands those highlands are inferred to have been a major tertiary watershed in north africa as quaternary dessication set in these rivers vanished and were replaced by ephemeral gullies cliff sapping wind abrasion and deflation have widened the gilf valleys and reduced many interfluves to clusters of flat topped and conical hills these now rise as inselbergs on the adjacent desert plains on which little evidence of former fluvial activity remains wind has deflated the surface and redistributed the finer particles from fluvial sediments and the debris of mass wasting into eolian sand sheets drifts and dunes dunes are migrating southward through the region along eolian thoroughfares that follow the apparent paths of ancient master streams toward distant basins of sand accumulation in the central sahara the fluvial and mass wasting origin of the particles in the eolian deposits the segregation of these materials according to grain size and the migration of those particles capable of saltation to areas of accumulation in lowland basins of the sahara are suggested as analogs for the formation and accumulation of sand sheets and dunes on the northern plains and in the polar erg on mars outliers of the martian plateau in the fretted terrain appear to have been dissected at least initially by channels whose upstream portions are incised in the uplands the martian wadis have many geomorphic peculiarities similar to those of the gilf wadis and like the egyptian features they have been attributed to mass wasting although basal sapping and removal of debris by wind have almost certainly modified the martian features their deep incision in the plateau and their inferred northward extensions on the northern plains seem to require not only initial downcutting by fairly energetic streams but also prolonged and long distance flow of water on mars as in southwest egypt running water is now nonexistent as suggested by milton 1973 the northern plains may be the most extensive of the landforms produced during a fluvial stage of martian history inferred integrated stream networks in the fretted terrain on mars as in the gilf plateau may be relics of earlier less arid climatic intervals when runoff collected and flowed with sufficient power to carve valleys in bedrock in this interpretation the uplands might once have stood as a watershed on a much less arid mars

origin and tectonic setting of ordovician bentonites in north america isotopic and age constraints the large volume of ordovician bentonites in the eastern and central united states indicates that they originated from a major volcanic system the location and paleotectonic setting of this volcanic source is unknown nd and sr isotopic data were collected from eight samples of primary apatite phenocrysts contained in four ordovician bentonites and u pb data were collected from one bentonite to determine the origin of this extensive volcanism the range in initial isotopic ratios for the four bentonites is nd 3 5 to 5 2 87 sr 86 sr 0 71005 to 0 71200 the age of the deicke bentonite is 457 1 1 0 2 determined by a concordant u pb zircon fraction five other zircon fractions from the deicke bentonite contain an inherited lead component lines drawn through the concordant point and the extremes of the discordant points have calculated upper intercepts with concordia of 1 090 ma and 1 540 ma the nd and sr isotopic data and the u pb age data are consistent with the generation of the volcanic ash by anatexis of evolved continental crust an evolved source region with volcanics of the same age and isotopic composition as the north american bentonites has not been found this source region however may be the same as the source of ordovician bentonites in sweden because the ages of both groups of bentonites are identical the 87 sr 86 sr ratios overlap and zircon phenocrysts from both groups of bentonites contain an inherited pb component an appropriate tectonic setting for the generation of both groups of bentonites was a continental margin volcanic arc or an extensional regime associated with such an arc

infrared stealthy surfaces why tes and themis may miss some substantial mineral deposits on mars and implications for remote sensing of planetary surfaces 1 infrared spectral observations have yielded many important insights into the nature of mars however spectral effects tied to surface roughness and particle size can make mineral deposits substantially more difficult to detect and identify than is generally known including for current investigations the effects hold for mars and other planets but here we focus on the impact on the exploration of mars laboratory spectra of pure smooth surfaced minerals have previously been used to conclude that the 1996 global surveyor thermal emission spectrometer tes and the 2001 mars odyssey thermal emission imaging system themis will detect a mineral deposit that covers 10 of a pixel those laboratory spectra have formed the foundation for modeling and interpretations of tes themis data and for development of the 2003 mars rover minites here for the first time we compare tes themis foundation data to laboratory field and unique airborne spectra of rough surfaces we demonstrate that substantial well crystalline regional mineral deposits including rock outcrops can be 100 exposed and remain undetected at the sensitivity of tes themis we then detail the physics which apply to all geologic materials previous studies have demonstrated the complicating physical effects for solids versus particulates for a range of minerals including oxides sulfates carbonates and each of the seven silicate classes we identify three cases of spectral behavior that can impact interpretations in case 1 physical effects cause a target to be undetectable by a given infrared instrument infrared stealthy in case 2 variations in spectral contrast mimic abundance variations which confounds abundance mapping in case 3 alteration of the spectral band shape impacts compositional interpretations optically smooth materials will be well represented in tes themis minites identifications conversely if a material forms an optically rough surface or sufficiently small particles on mars then it will be comparatively underrepresented or missed surface roughness occurs on three broad scales and roughness at the grain scale can be a primary variable in whether a mineral is detectable nondetection of certain key minerals e g carbonates can significantly impact geologic and climatic interpretations and landing site selection the tes themis detection threshold may be 10 coverage on the basis of specific laboratory samples but for field measurements that prediction represents an idealized lower bound interpretations built on nondetection should be revisited after defining the uncertainties in detection capabilities for specific instruments as applied to expected mineral surface textures on mars including at the grain scale the impact on future measurement strategies including minites should also be assessed

central and southern appalachian water and wind gap origins review and new data abstract the origin and evolution of transverse drainage were stumbling blocks to classical historical geomorphologists and many problems still remain decollements that upramp laterally transported at depth tectonic sheets in the central and southern appalachians have produced structural geomorphic fronts that are prominent features often of regional or subregional extent cf blue ridge north mountain allegheny as these structural geomorphic fronts likely were features that developed significant cover relief during the alleghanian orogeny they may hold clues to incipient landscape development during and soon after orogenesis unless buried by thick sediment cover where these fronts are crossed by transverse drainage lines spectacular water gaps that frequently expose complex structural features are produced there are many other transverse water gaps not located across decollement structures in the region these gaps display complex features that shatter bedrock and must also be accounted for in any comprehensive hypothesis of transverse water gap origin lineaments including both cross strike structural discontinuities and disturbed zones are present in the appalachians and coincide with a number of transverse water gaps the positioning of weakened bedrock zones high on structures where downcutting streams had access to them permits a localizing mechanism such as structural ensnarement to operate local sedimentary patterns may also have played roles in drainage localization major unsolved problems include post alleghanian tectonic effects rates and timings of uplift erosion and deposition whether lithotectonic weaknesses are most pronounced in gap areas and establishing a numerical chronology for drainage development whereas lithotectonic influence upon drainage development is stressed in this chapter the importance of other factors e g climate catastrophic events as documented by others in this volume is fully recognized

surficial geology of the safsaf region south central egypt derived from remote sensing and field data abstract we used a decorrelation stretched image of landsat thematic mapper tm bands 1 4 and 7 and field data to map and describe the main surficial units in the hyperarid safsaf region in south central egypt we show that the near infrared bands on landsat tm which are sensitive to very subtle changes in mineralogy common to arid regions significantly improve the geologist s capability to discriminate geologic units in desert regions these data also provide the spatial and spectral information necessary to determine the migration patterns and provenance of eolian materials the safsaf area was the focus of our post flight field studies using shuttle imaging radar sir data following the discovery of buried paleochannels in north africa most of the channels discernible on sir images are not expressed in tm data but traces of a few channels are present in both the sir and the tm data within the wadi safsaf area here we present a detailed digital examination of the sir and the tm band reflectance and reflectance ratio data at three locations of the more obvious surface expressions of the buried channels our results indicate that the tm expressions of the channels are not purely topographic but are more compositional in nature two possibilities may account for the tm expressions of the buried channels 1 concentrations of windblown iron rich materials that accumulated along subtle curvilinear topograpohic traps or 2 curvilinear exposures of an iron rich underlying unit of the flat sand sheet

evidence for mg rich carbonates on mars from a 3 9 μm absorption feature abstract the origin and nature of the early atmosphere of mars is still debated the discovery of sulfate deposits on the surface coupled with the evidence that there are not large abundances of carbonates detectable on mars in the optically accessible part of the regolith leaves open different paleoclimatic evolutionary pathways even if carbonates are responsible for the feature observed by tes and mini tes at 6 76 m alternative hypotheses suggest that it could be due to the presence of hydrated iron sulfates his carbonates can be discerned from his by investigating the spectral region in which a strong overtone carbonate band is present the planetary fourier spectrometer on board the mars express spacecraft has acquired several thousand martian spectra in the range 1 2 45 m since january 2004 most of which show a weak absorption feature between 3 8 and 4 m a similar feature was observed previously from the earth but its origin could not be straightforwardly ascribed to surface materials and specifically to carbonates here we show the surficial nature of this band that can be ascribed to carbonate mixed with the martian soil materials the materials that best reproduce the detected feature are mg rich carbonates huntite camg3 co3 4 and or magnesite mgco3 the presence of carbonates is demonstrated in both bright and dark martian regions an evaluation of the likeliest abundance gives an upper limit of 10 wt the widespread distribution of carbonates supports scenarios that suggest carbonate formation occurred not by precipitation in a water rich environment but by weathering processes

a gravity interpretation of the benue trough nigeria abstract reconnaissance gravity surveys carried out in the benue trough from 1975 to 1977 have revealed a broad positive regional anomaly over the whole trough attributable to moho uplift superimposed on this regional gravity high in the lower benue trough is an axial positive anomaly this positive anomaly with a maximum width of 100 km and an amplitude of 20 mgal seems to disappear around latitude 9 n and is associated with a basic body of density 2 90 gcm 3 that decreases in width and thickness from the south to the north an axial negative anomaly observed in the upper benue is attributed to sedimentary fill 6000 m thick in the middle and lower benue flanking negative anomalies are attributable to the accumulation in the marginal basins of post deformational sediments up to 5000 m thick

computing applachian geomorphology abstract craig r g 1989 computing appalachian geomorphology in t w gardner and w d sevon editors appalachian geomorphology geomorphology 2 197 207 a computer model is used to represent the stochastic effects of geomorphic processes acting on appalachian structures and to produce the various stages of cenozoic appalachian geomorphic history that model incorporates the uncertainty in our current representation of elevation lithology dependence of slope on lithology structural dip percent of surface lithology uneroded and stratigraphic thickness four theories of appalachian history defined by initial surface relief and adjustment to underlying lithology are analyzed initial surface relief like that proposed by j t hack yields the best fit to the current surface mean elevation 410 m when erosion proceeds from a surface initialized to the modern mean elevation of the ridgetops 760 m

aridity and humidity two aspects of the late miocene climate of north africa and the mediterranean abstract the physiography of north africa is not greatly changed from that of the messinian with the drawdown of the mediterranean in the late messinian the then existing river systems were incised into the landscape and emptied into lake cyrenaica which occupied the substantially drained eastern mediterranean basin the record of incision provides a record of the magnitude of the messinian river systems an analysis of these river systems demonstrates that messinian rainfall a consequence of the zeit wet phase was greatest in east and south central north africa in keeping with the derivation of the water mainly from the indian ocean in central north africa the eosahabi river flowed from messinian lake chad eroding the east tibesti valley and cutting a channel which is especially well preserved near the coast of the gulf of sirt the penetrated sediments of lake cyrenaica and the marginal basins of the messinian transgression are known as the upper evaporites and are generally fine clastics gypsarenites and gypsum anhydrite they were rapidly deposited underlying them is the halite of the lower evaporites this sequence of upper and lower evaporites is much like the lower halite of the tortonian south gharib formation and the overlying clastics and anhydrite of the messinian zeit formation in the gulf of suez red sea area this type of sequence is termed an evaporitic couplet and as has been demonstrated for the gulf of suez red sea is a consequence of a transition from a dry to a more humid climate in a restricted or semirestricted basin this transition occurred at about 7 5 ma in the gulf of suez red sea and at about 5 8 ma in the mediterranean the zeit wet phase manifest in the above events developed in association with the initiation and development of the asian monsoon and the drying of the mediterranean it can be understood in terms of the development of an evolving monsoon desert system the asian monsoon was initiated 8 7 ma in association with the uplift of tibet at this time the north african desert zone was displaced northwards to be over the mediterranean and central and eastern north africa became seasonally humid a concept is advanced in which the early stage of the development of the asian monsoon is seen as having two phases alternating at the precessional ca 21 ka cycle one phase transferred moisture from the indian ocean mainly to southern asia the other phase transferred moisture mainly to north africa with the drawdown of the mediterranean at about 5 8 ma the zeit wet phase intensified a further northward movement of the humid and desert zones occurred at the time of drawdown with the messinian and early pliocene transgressions the wet phase ameliorated but a substantial river system still crossed central north africa at about 4 6 ma north africa became drier probably in response to the developing dominance of the features of the monsoon that transferred moisture mainly to southern asia features of the monsoon that are well recognised today

hydrous carbonates on mars evidence from mariner 6 7 infrared spectrometer and ground based telescopic spectra absorption features at 2 28 and 5 4 m identified in mariner 6 7 infrared spectrometer and terrestrial telescopic spectra are consistent with the spectra of hydrous magnesium carbonates such as hydromagnesite and artinite spectral characteristics of these hydrous carbonates are different from those of the anhydrous carbonates as the former do not have the strong spectral features typically associated with anhydrous carbonates such as calcite and siderite theoretical mixing indicates that depending on the type of hydrous carbonate 10 20 wt can be incorporated into the regolith without contradicting the spectral observations or the viking x ray fluorescence chemical analysis hydrous carbonates form as weathering products of mafic minerals in the presence of h2o and co2 even in the antarctic their formation as evaporite minerals from either original magmas or hydrothermally altered rocks is consistent with the martian environment provided liquid water is or has been at least transiently present on earth formation of hydrous mg carbonates is associated with the production of amorphous iron oxides which is consistent with both the environment and the inferred surface mineralogy of mars these minerals are about 60 wt h2o co3 and oh if they are abundant everywhere at the 10 level then about 6 of the surface weight could be volatiles bound in this type of mineral although the stability of hydrous carbonates in a martian environment is uncertain there may be kinetic factors inhibiting the dehydration of these minerals which may persist metastably in the current environment although the spectroscopic evidence for anhydrous carbonates is scant the possible presence of hydrous carbonates provides an appealing mechanism for the existence of carbonates on mars

evidence for pleistocene lakes in the tushka region south egypt space shuttle radar topography mission srtm data have revealed new details on the extent and geomorphic relations of paleodrainage in southern egypt following a period of late tertiary drainage from the red sea hills south through wadi qena and west across the tushka region the nile river as we now know it established its connections with central africa and the mediterranean in the middle pleistocene oxygen isotope stage ois 7 to ois 5 srtm topography reveals a lake level at 247 m that is coincident with the elevation of middle pleistocene fish fossils 400 km west of the nile and with the termination of shallow runoff channels in northern sudan that were active during the middle pleistocene and holocene pluvial periods an additional lake level at 190 m is based on the current elevation at wadi tushka and is consistent with paleolithic sites at bir kiseiba followed by neolithic sites at lower topographic levels overflow of the nile through wadi tushka during the wetter north african climate of the middle pleistocene coupled with limited local rainfall was the likely source of water for these lakes

presence and detection of carbonates on the martian surface the messages we receive from mars about the presence of carbonates are quite contradictory on the one hand images of the planet clearly show the signatures of past bodies of standing water where the accumulation of sedimentary deposits should have occurred on the other hand the apparent absence of carbonates in the homogeneous fines covering the martian surface raises the question where could carbonates hide now in this paper we discuss the subject and demonstrate that a proposed destruction mechanism the photodecomposition caused by uv radiation cannot account alone for the missing carbonates by means of simulations we show that the difficulties in detecting the carbonates can be ascribed to the low temperatures of the emitting zones observed up to now finally we derive the minimum amount of such minerals that could possibly be detected in future observations of mars and we compare the results of simulations with observed spectra

calcium carbonate and sulfate of possible extraterrestrial origin in the eeta 79001 meteorite abstract two varieties of ca carbonate were found in a total of three interior 2 cm depth samples of glass inclusions from the shergottite meteorite elephant moraine antarctica a79001 two of the samples including the largest deposit around a vug near the center of the meteorite 8 cm depth contained veins of granular calcite with significant magnesium avg atomic mg mg ca 0 14 0 15 and phosphorus avg atomic p ca 0 04 either as mg calcite with dissolved p or as calcite with very finely intergrown mg bearing phosphate the second variety which occurred in a third sample with a previously documented high concentration of trapped gases consisted of disseminated 10 20 m anhedral grains of nearly pure caco3 and was intimately associated with laths and needles of ca sulfate possibly gypsum the coexisting carbonate and sulfate appeared to be partially decrepitated relict grains that were trapped during rapid solidification of quench textured pyroxene and glass for at least the latter occurrence textural relationships clearly indicate a pre terrestrial origin for the salts all evidence considered it is probable that both varieties of cacarbonate and the ca sulfate formed on a planetary body probably mars before the meteorite fell on earth

paleodrainages of the eastern sahara the radar rivers revisited sir a b implications for a mid tertiary trans afnrcan drainage system a complex history of cenozoic fluvial activity in the presently hyperarid eastern sahara is inferred from sir data and postflight field investigations in southwest egypt and northwest sudan sir images were coregistered with landsat and existing maps as a guide to exploration of the buried paleodrainages radar rivers first discovered by sir a field observations explain the radar responses of three types of radar rivers rr 1 rr 2 and rr 3 rr 1 broad aggraded valleys or basins filled with alluvium generally give a dark response relative to the surrounding radar bright tone of the wind roughened discontinuously sand covered bedrock of the remnant interfluves the alluvial fill in some of the rr 1 valleys gives a locally intermediate to bright response where cemented by diagenetic caco3 caliche the rr 2 type braided channels inset in the rr 1 valleys are filled with noncalichified loose sediment and are visible on sir because of the caliche effect the dark response of unconsolidated alluvium in the inset channels contrasts with the brighter response of calichified alluvium in the broad valleys the third type rr 3 narrow long bedrock incised channels which are partly visible on the ground and on landsat in areas where the sand sheet is patchy are conspicuous on sir because the dark response of their unconsolidated channel fill contrasts with the brighter response of the surrounding bedrock disconformably overlying and concealing the rr 1 valleys the rr 2 channels and parts of the rr 3 channels are eolian sand sheet sheet de deposits which in turn are locally overridden by trains of barchan dunes

planetary geomorphology some historical analytical perspectives abstract three broad themes from the history of planetary geomorphology provide lessons in regard to the logic valid reasoning processes for the doing of that science the long controversy over the origin of lunar craters which was dominated for three centuries by the volcanic hypothesis provides examples of reasoning on the basis of authority and a priori presumptions percival lowell s controversy with geologists over the nature of linear markings on the surface of mars illustrates the role of tenacity in regard to the beliefs of some individual scientists finally modern controversies over the role of water in shaping the surface of mars illustrate how the a priori method i e belief produced according to reason can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm

diagenetic control on mineralogical suites in sand silt and mud cenozoic nile delta implications for provenance reconstructions abstract this nile delta case study provides quantitative information on a process that we must understand and consider in full before attempting provenance interpretation of ancient clastic wedges petrographic and heavy mineral data on partly lithified sand silt and mud samples cored from the up to 8 5 km thick post eocene succession of the offshore nile delta document systematic unidirectional trends with increasing age and burial depth quartz increases at the expense of feldspars and especially of mafic volcanic rock fragments heavy mineral concentration decreases drastically transparent heavy minerals represent progressively lower percentages of the heavy fraction and zircon tourmaline rutile apatite monazite and cr spinel relatively increase at the expense mainly of amphibole in pliocene sediments and of epidote in miocene sediments recent studies have shown that the entire succession of the nile delta was deposited by a long drainage system connected with the ethiopian volcanic highlands similar to the modern nile since the lower oligocene the original mineralogy should thus have resembled that of modern delta sand much more closely than the present quartzose residue containing only chemically durable heavy minerals stratigraphic compositional trends although controlled by a complex interplay of different factors document a selective exponential decay of non durable species through the cored succession that explains up to 95 of the observed mineralogical variability our calculations suggest that heavy minerals may not represent 20 of the original assemblage in sediments buried less than 1 5 km 5 in sediments buried between 1 5 and 2 5 km and 1 for sediments buried 4 5 km no remarkable difference is detected in the intensity of mineral dissolution in mud silt and sand samples which argues against the widely held idea that unstable minerals are prone to be preserved better in finer grained and therefore presumably less permeable layers intrastratal dissolution acting through long periods of time at the progressively higher temperatures reached during burial can modify very drastically the relative abundance of detrital components in sedimentary rocks failure to recognize such a fundamental diagenetic bias leads to grossly mistaken paleogeographic reconstructions as documented paradigmatically by previous provenance studies of ancient nile sediments

evidence for a large extended paleolake in the eastern sahara as revealed by spaceborne radar lab images recently processed radar images from the two flights of the space shuttle endeavour by the spaceborne imaging radar c x band synthetic aperture radar instrument in 1994 give a clear view of widely distributed sediments of a palaeolake in today s hyperarid eastern sahara nw sudan although a few of the sites of lacustrine sediments were previously examined in the field their extent now visible on the images yields a new perspective on the early to mid holocene wet phase that affected northern africa freshwater wetlands across an area exceeding 15 000 km2 existed between 8800 and 4500 b p owing to a significant increase in rainfall the phenomenon called the west nubian lake constitutes the largest scale hydrographic evidence in the eastern sahara for a northward shift of the tropical rain belt given that the region now receives less than 15 mm of precipitation per year on average the former open water body and its vegetated catchment may have acted as a modifier of the regional climate in connection with the detection of a buried major palaeodrainage system near kufra se libya the west nubian lake confirms the new multifrequency and multipolarization radar imaging as a powerful tool for the reconstruction of arid land palaeohydrology

thermal emission spectra of mars 5 4 10 5 μm evidence for sulfates carbonates and hydrates we have obtained spectra of the thermal emission from mars in the 5 4 10 5 m wavelength domain at a resolving power of about 60 from the kuiper airborne observatory spectra were obtained for several large spots on mars whose ground temperatures and air masses through the martian atmosphere differed significantly these data were taken at two times during the flight by taking the ratio of the spectral flux from one spot to that of a second spot we obtained results that were independent of uncertainties in the instrument s spectral response and the transmission of the earth s atmosphere these data as well as spectral fluxes of single spots based using the star tau as a calibration standard show a number of emission and absorption features they are present in sets of spectra taken at two different times some of the absorption features are due to gaseous co2 in the martian atmosphere the remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface comparison of the strength of features seen at similar times but with three different air masses and ground temperatures suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere based on comparisons of the observed features with laboratory data for a broad ensemble of minerals spectra of other solar system bodies and relevant compositional information about mars we have made the following tentative identifications of the observed features emission features at 7 8 and 9 7 m are attributed to surface silicates an emission feature at 6 1 m is attributed to a molecular water component of the surface material an absorption band at 8 7 m as well as possibly one at 9 8 m is ascribed to sulfate or bisulfate anions probably located in a distorted crystalline site and an absorption band at 6 7 m is attributed to carbonate or bicarbonate anions located in a distorted crystalline site although we cannot totally rule out a nitrate origin for this feature we have simulated these spectra with radiative transfer programs for the atmosphere and surface these simulations indicate that the sulfate and carbonate bearing minerals are contained in the same particles of the airborne dust as the dominant silicate minerals that the dust optical depth was about 0 6 at a reference wavelength of 0 3 m over the area of the observed spots and that sulfates and carbonates constitute about 10 15 and 1 3 by volume of the airborne dust respectively these results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current mars

an episode of rapid bedrock channel incision during the last glacial cycle measured with 10be we use 10 be to infer when how fast and why the susquehanna river incised through bedrock along the u s atlantic seaboard one of the world s most prominent and ancient passive margins although the rate at which large rivers incise rock is a fundamental control on the development of landscapes relatively few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins exposure ages of fluvially carved bedrock strath terraces preserved along the lower susquehanna river demonstrate that even along a passive margin large rivers are capable of incising through rock for short periods of time at rates approaching those recorded in tectonically active regions such as the himalayas over eighty samples collected along and between three prominent levels of strath terraces within holtwood gorge indicate that the susquehanna river incised more than 10 meters into the appalachian piedmont during the last glacial cycle beginning 36 ka incision rates increased dramatically and remained elevated until 14 ka the northern half of the susquehanna basin was glaciated during the late wisconsinan however similar rates and timing of incision occurred in the unglaciated potomac river basin immedi ately to the south the concurrence of incision periods on both rivers suggests that glaciation and associated meltwater were not the primary drivers of incision instead it appears that changing climatic conditions during the late pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion thus enabling a short lived episode of rapid incision into rock although this study has constrained the timing and rate of bedrock incision along the largest river draining the atlantic passive margin the dates alone cannot explain fully why or by what processes this incision occurred however cosmogenic dating offers compelling evidence that episodes of rapid incision into bedrock are tied to glacial cycles and changes in global climate these results and the methods we employ provide valuable insights into the nature of bedrock channel incision not only along the susquehanna river and passive margins but also across a wide range of settings around the globe because river incision into bedrock transmits the effects of changing climate and tectonics through fluvial networks to hillslopes comprehending when where and why rivers incise has important implications for the evolution of land scapes

reconstruction of ancestral drainage patterns in an internally draining region fars province iran google earth imagery is used here in conjunction with a geographic information system to identify transverse drainages and recreate palaeodrainage in an internally draining region in iran at least 35 water gaps and 34 wind gaps are shown to exist in the region as well as evidence for an integrated palaeodrainage that originated north of the internally draining region and emptied into the mand watershed to the west the topographic characteristics of the transverse drainages suggest a strong control by local topography and support formation of the internally draining region by basin filling and overflow both climatic and tectonic factors may have controlled the loss of external connectivity

hutton to horton views of sequence progression and equilibrium in geomorphology abstract the papers by strahler 1952 and chorley 1962 strongly advocated the adoption of a dynamic as opposed to an historical approach to geomorphology the opinion of some later workers notably simpson 1963 and mayr 1982 is however that any advance in the historical natural sciences depends upon the combined appreciation of immanent and configurational elements simpson s terminology and the view that events may have an essential historical or timebound component is now accepted even in experimental sciences such as chemistry prigogine 1978 in the light of these contrasting approaches to earth science an attempt is made to analyse the mjor lines of thought concerning change progression and equilibrium in the work of six leading precursors of modern geomorphology james hutton charles lyell charles darwin james dwight dana grove karl gilbert and robert e horton despite their perceived general adherence to the uniformitarian tradition it is suggested that the work of the six reveals two contrasting attitudes to ideas of change and of equilibrium it is argued that those authors lyell dana horton who are primarily concerned to demonstrate that the present state of the earth is in some sense the normal or optimum tend at the same time to accept the existence or desirability of some equilibrium state and paradoxically to overstate the role of unusual cataclysmic or catastrophic events in creating and sustaining this equilibrium the views of horton in particular lend themselves to the description punctuated equilibrium in contrast it is contended that hutton darwin and gilbert have no ideological commitment to the present state of the earth as anything other than one moment in time their ideas are considered to focus upon the entire sequence of changes which may be inferred to create the phenomena viewed at any time or place as a consequence the concept of equilibrium has only a minor role in the works of these authors who accept that earth history reveals a mix of events of all physically possible magnitudes and frequencies in the light of this analysis the distinction between dynamic and historical geomorphology advocated by strahler and chorley is felt to be unhelpful a truly historical study of the sequence of phenomena exemplified by chapter iv in gilbert s geology of the henry mountains 1877 necessarily requires consideration of all scales of dynamic processes

gravity study of the central african rift system a model of continental disruption 1 the ngaoundere and abu gabra rifts abstract a regional compilation of published and unpublished gravity data for central africa is presented and reveals the presence of a major rift system called here the central african rift system it is proposed that the junction area between the ngaoundere and abu gabra rift arms in western sudan forms an incipient intraplate triple junction with the as yet unfractured but domally uplifted and volcanically active darfur swell it is only the darfur swell that shows any similarities to the uplift and rift history of east africa the other two rifts arms are considered to be structurally similar to the early stages of passive margin development and thus reflect more closely the initial processes of continental fragmentation than the structures associated with rifting in east africa

a philosophy of rivers equilibrium states channel evolution teleomatic change and least action principle until recently no universal agreement as to a philosophical or scientific methodological framework has been proposed to guide the study of fluvial geomorphology an understanding of river form and process requires an understanding of the principles that govern the behaviour and evolution of alluvial rivers at the most fundamental level to date the investigations of such principles have followed four approaches develop qualitative unifying theories that are usually untested collect and examine data visually and statistically to define semi quantitative relationships among variables apply newtonian theoretical and empirical mechanics in a reductionist manner resolve the primary flow equations theoretically by assuming maximum or minimum outputs here we recommend not a fifth but an overarching philosophy to embrace all four clarifying and formalising an understanding of the evolution of river channels and iterative directional changes in the context of least action principle lap the theoretical basis of variational mechanics lap is exemplified in rivers in the form of maximum flow efficiency mfe a sophisticated understanding of evolution in its broadest sense is essential to understand how rivers adjust towards an optimum state rather than towards some other because rivers as dynamic contemporary systems flow in valleys that are commonly historical landforms and often tectonically determined we propose that most of the world s alluvial rivers are over powered for the work they must do to remain stable they commonly evolve to expend surplus energy via a variety of dynamic equilibrium forms that will further adjust where possible to maximise their stability as much less common mfe forms in stationary equilibrium this paper 1 shows that the theory of evolution is derived from and applicable to both the physical and biological sciences 2 focusses the development of theory in geomorphology on the development of equilibrium theory 3 proposes that river channels like organisms evolve teleomatically progression towards an end state by following natural laws and iteratively one stage forming the basis for the next towards an optimal end state 4 describes lap as the methodological basis for understanding the self adjustment alluvial channels towards mfe 5 acknowledges that whereas river channels that form within their unmodified alluvium evolve into optimal minimum energy systems exogenic variables such as riparian or aquatic vegetation can cause significant variations in resultant river styles we specifically attempt to address luna leopold s lament in 1994 that no clearly expressed philosophy explains the remarkable self adjustment of alluvial channels

great sand sea and selima sand sheet eastern sahara geochronology of desertification the relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the great sand sea active dune formation corresponds with interpluvial periods of hyperaridity dune stability corresponds with semiarid pluvial periods archeological sites associated with truncated paleosols in the selima sand sheet suggest a similar climatic relation and indicate that the isohyets of central sudan shifted at least 400 kilometers northward during the peak of pluvials

multifrequency and multipolarization radar scatterometry of sand dunes and comparison with spaceborne and airborne radar images understanding the unusual radar scattering characteristics of sand dunes is necessary in the analysis of radar images of aeolian landscapes of the earth and of other planets in this paper we report on airborne radar scatterometer data of sand dunes acquired at multiple frequencies and polarizations radar backscatter from sand dunes is very sensitive to the imaging geometry at small incidence angles the radar return is mainly due to quasi specular reflection from dune slopes favorably oriented toward the radar a peak return usually occurs at the incidence angle equal to the angle of respose for the dunes the peak angle is the same at all frequencies as computed from specular reflection theory at larger angles the return is significantly weaker the scatterometer measurements verified observations made with airborne and spaceborne radar images acquired over a number of dune fields in the united states central africa and the arabian peninsula the imaging geometry constraints indicate that possible dunes on other planets such as venus will probably not be detected in radar images unless the incidence angle is less than the angle of repose of such dunes and the radar look direction is approximately orthogonal to the dune trends

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve