statistical methods for describing seafloor topography we present a method for objectively characterizing a swath of digitally sampled seafloor topography our method analyzes the distribution of surface slopes by compiling surface normal vectors into a two dimensional histogram using an equal area projection the direction of maximum variance first principal axis of the histogram is used to determine the azimuth of lineations in the topography and the variance is used as a measure of seafloor roughness we apply the method to short sections of sea beam swath data and find that the histogram parameters are effective in describing the behavior of the topography in particular similar patterns are observed for a sequence of histograms derived from data collected over the mendocino and the surveyor fracture zones in the northeast pacific because the method does not require any data modification and is suitable for irregularly shaped sample regions it lends itself to real time analysis

widespread prolonged late middle to late ordovician upwelling in north america a proxy record of glaciation late middle to late ordovician subtidal ramp carbonates of new mexico texas and oklahoma contain abundant spiculitic chert to 70 chert by volume and phosphate 1 5 wt indicating that these rocks formed in an extensive upwelling zone upwelling began in the late middle ordovician ca 454 ma and persisted until the end of the ordovician late ordovician cherty carbonates also occur along the u s cordilleran margin in board of organic rich graptolitic shale and chert the widespread occurrence of late ordovician cherty and phosphatic carbonates on southern and western laurentia in addition to phosphate rich cool water carbonates over much of the north american midcontinent suggests vigorous thermohaline circulation related to prolonged 10 14 ma gondwana glaciation

early palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms abstract stylophorans cornutes mitrates represent one of the most diverse classes of cambro ordovician echinoderms they were free living benthic non radiate forms closely related to asterozoans and crinoids taphonomic sedimentological and palaeosynecological data provide useful information on key aspects of stylophoran palaeoecology such a combined approach suggests that the rarity of stylophorans in proximal environments above storm wave base was probably original and does not exclusively result from the possession of a loosely articulated polyplated calcitic test conversely stylophorans were relatively abundant in deeper settings below storm wave base where they frequently occur in low diversity dense beds several tens to hundreds of individuals per square metre such assemblages were either largely dominated by stylophorans only middle cambrian darriwilian or by the association of both stylophorans and ophiuroids latest darriwilian silurian comparison with ecological requirements of similar modern and fossil dense populations of ophiuroids suggests that stylophoran beds occurred in well oxygenated oligotrophic waters with low predatory pressure and that sea temperature played a key role in the palaeobiogeographic distribution of stylophorans seven main stylophoran biofacies are identified and described the associated environments and tropical distribution of primitive heavily plated forms suggest that the initial radiation of the class probably took place in warm to temperate shallow settings earliest middle cambrian late cambrian however from this primitive stock stylophorans radiated several times towards deeper and or colder environments possibly because of the lower predation pressure in such settings cothurnocystid cornutes in the middle cambrian mitrates in the late cambrian hanusiids in the tremadocian as a consequence the fact that most cambro ordovician cornutes and mitrates were psychrospheric i e cold water adapted probably explains their relatively wide palaeobiogeographic distribution in high palaeolatitudes cambro ordovician stylophorans were abundant and diverse in shallow to deep environments but they were generally restricted to deep settings in low palaeolatitudes the great caradocian transgression favoured the extension of stylophorans from circum polar regions e g western margin of gondwana towards external settings at lower palaeolatitudes avalonia baltica and eastern margin of laurentia where one group of mitrates underwent a major radiation anomalocystitids and extended towards shallower and warmer palaeoenvironments in contrast all silurian stylophoran assemblages known so far are rare poorly diversified and restricted to shallow warm to temperate environments in tropical regions this distribution partly results from 1 the probable eradication of psychrospheric forms e g cornutes because of the prolonged anoxia of deep environments in the late hirnantian early silurian of west gondwana 2 the radiation of some mitrates anomalocystitids in shallow tropical settings in the late ordovician and 3 of strong taphonomic and or sampling biases numerous ghost lineages

large scale convection patterns observed by dmsp the authors present a comprehensive compilation of the average distribution of the electrostatic potential across the high latitude ionosphere the averages are compiled from potentials along the satellite path calculated from thermal ion drift data from instrumentation on the defense meterological satellite program dmsp flights 8 and 9 satellites data were collected from the dmsp f8 satellite during the period september 1987 to december 1990 and from the dmsp f9 satellite during the period march 1988 to december 1990 the potential distributions are separated by geomagnetic position season and orientation of the interplanetary magnetic field imf and then averages of the distributions are calculated the average potential distributions clearly show the displacement of polar cap convection contours to the dusk or dawk flanks under the influence of the imf b sub y component the cross cap potential decreases as imf b sub z changes from southward to northward the average distributions indicate that the development of more than two convection cells for northward imf is either uncommon or nonexistent for imf b sub z 0 and b sub z vert bar b sub y vert bar a distorted pattern is observed in the average potential distribution not a four cell pattern as some previous studies suggest it should be for allmore orientations of the imf the convection reversal boundary at the poleward edge of the auroral zone is observed in the average distributions to be a rotational boundary it is not a shear boundary as suggested by some previous investigations on average the harang discontinuity convection reversal in the auroral zone near midnight is observed to exist weakly or not at all when examining individual passes a strong eastward flow is present sometimes in the region of the harang discontinuity especially on the poleward boundary but not at all times as implied by the heppner maynard model 39 refs 9 figs 2 tabs less

time specific aspects of facies state of the art examples and possible causes abstract the term time specific facies tsf was introduced to the scientific community by the late otto h walliser to refer to unique facies typical of particular narrow intervals some of which were related to bioevents in some senses however the concept was recognized much earlier and is even engrained in the very names of some geologic periods the concept of time specific facies is expanded slightly herein to include distinctive or unique regional to global characteristics of the sedimentary record that characterize particular intervals of geologic time the recognition of time specific and widespread processes in the sedimentary record is a critical step in unraveling the interplay between processes of differing scale these range from very short term but widespread facies that overlap with event deposits to general facies types that may persist for intervals up to 10s of millions of years in duration this paper briefly summarizes the history of development of the tsf concept provides examples to illustrate a few of the key aspects of time specific facies and offers a few tentative explanations for this phenomenon among the factors that control tsfs abrupt changes in redox conditions and early diagenetic mineralization sedimentary condensation often associated with abrupt sea level change altered climate and paleoceanography and biotic evolution and extinction seem to be most critical and permit a preliminary genetic classification of tsfs inevitably however many tsfs reflect multiple effects and some remain largely unexplained

quantitative topographic method of fault morphology recognition abstract a quantitative method for morphology recognition of topographically expressed faults is developed the method is based on the analysis of digital elevation models dems lineaments revealed on horizontal landsurface curvature map indicate faults formed mostly by horizontal tectonic motion i e strike slip faults lineaments recognized by vertical landsurface curvature mapping correspond to faults formed mainly by vertical motion i e dip slip and reverse faults and thrusting lineaments recorded on both horizontal and vertical curvatures maps indicate as a rule oblique slip and gaping faults the method is tested by processing the dems of an imaginary area with modeled faults and a dem of a part of the crimean peninsula and the adjacent sea bottom for the imaginary area the results obtained mostly correlate with the theoretical basis of the method for the real area a comparative analysis of the results obtained and factual geological data demonstrate that the method actually works to identify individual faults in regions where both topography and tectonic structure are complicated some aspects of the method precision requirements for initial data and further development of the method are discussed

an integrated technique for delineating groundwater contaminated zones using geophysical and remote sensing techniques a case study of al quway iyah central saudi arabia geophysical and remote sensing techniques were carried out to raise the groundwater quality and delineate expected contaminated zones near an open waste disposal site in al quway iyah central saudi arabia an extracted digital elevation model dem from very high resolution vhr satellite images was used to define the surface lineaments and prevailing flow path directions present in the study area remote sensing results indicated that groundwater in the al quway iyah metropolitan area flows through a complex network of interconnected fractures which are controlled by the regional geological and structural settings of the area seismic refraction profiling was applied to delineate the depth to the groundwater table and bedrocks and to locate those faults that may provide pathways to contaminants associated with the open waste disposal site in the survey area the results showed that possible subsurface groundwater contamination zones are mainly associated with weaker fractured zones underlying the surface lineaments this survey suggests that adequate integration of remote sensing and seismic refraction data can be applied to map spatial distribution of contaminants efficiently it can facilitate future studies to be conducted for environment and human health hazard appraisal

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

cherty carbonate facies of the montoya group southern new mexico and western texas and its regional correlatives a record of late ordovician paleoceanography on southern laurentia abstract the upper ordovician montoya group in southern new mexico and westernmost texas records predominantly subtidal deposition on a gently dipping carbonate ramp that was subsequently nearly entirely dolomitized the medial unit of the montoya group the aleman formation is unique because it contains abundant chert 10 70 by volume the chert occurs as 1 thin continuous beds of sponge spicules within mudstone or calcisiltite 2 discontinuous lenses or nodules within skeletal wackestones and packstones or 3 as a replacement of skeletal grains and burrows coeval skeletal grainstones and muddy peritidal facies contain little chert phosphate up to 5 wt occurs within the underlying upham formation and the aleman formation as replacement of fossils and peloids the abundance of chert and phosphate in these subtidal facies indicates they formed within a region of strong upwelling regional correlation with upper ordovician cherty units along the periphery of southern laurentia and other low latitude continents suggests that upwelling was widespread and long lived during the late ordovician the upwelling is interpreted to record vigorous oceanic circulation produced by the onset of glaciation on gondwana during this period late ordovician relative sea level curves around the periphery of laurentia indicate correlative third order 1 3 my duration fluctuations that may provide a means for high resolution global correlations however the mechanism s that produced these long term fluctuations are unclear

role of poleward moving auroral forms in the dawn dusk auroral precipitation asymmetries induced by imf by 1 in a case study we document the detailed spatial temporal structure of the aurora in the 0900 1500 magnetic local time mlt sector during an interval of steady southeast imf orientation emphasis is placed on ground based observations of structure that is often averaged out in large statistical studies a central feature is the phenomenon of poleward moving auroral forms pmafs an ionospheric manifestation of pulsed magnetopause reconnection in the form of flux transfer events ftes whose evolution in both prenoon and postnoon mlts can be monitored under similar interplanetary conditions differences in auroral precipitation associated with pmafs about the noon meridian related to imf by are documented while the prenoon pmafs develop in three stages spanning a latitude range of 500 km the highest latitude stage is absent in postnoon pmafs for by 0 which after the initial intensification progressively fade we suggest that this auroral precipitation asymmetry is closely related to the different field aligned current configuration in pmafs prenoon and pmafs postnoon and the underlying plasma convection pattern we detail the association between the high latitude component of pmafs in the prenoon sector by 0 and a channel of plasma convection located in the dawnside convection cell the latter convection channel located in the regime of old open flux represents an aspect of the svalgaard mansurov effect which is not included in the traditional description the auroral and plasma convection data are placed in the context of recent work on solar wind magnetosphere interconnection topology for a southward pointing imf with a strong by component

molecular indicators of redox and marine photoautotroph composition in the late middle ordovician of iowa u s a abstract saturated and aromatic hydrocarbons were used to evaluate depositional redox conditions and marine photoautotroph contributions to middle caradocian strata of the central united states ia at the base of the spechts ferry member of the decorah formation 13c enriched aryl isoprenoids derivatives of green sulfur bacteria become abundant indicating the development of photic zone anoxia this is coincident with the disappearance of the organic walled microfossil gloeocapsomorpha prisca and a marked decrease in the relative abundances of cyanobacterial biomarkers the development of dysoxic to anoxic conditions and or associated changes in basin circulation potentially affected the distributions and abundances of these organisms in the overlying guttenberg member g prisca derived organic matter becomes dominant but relative cyanobacteria abundances remain low in addition the percentage total organic carbon is greater than 20 even though selected biomarker ratios pristane phytane ratios greater than 3 and homohopane indices less than 0 5 and the presence of bioturbation indicate that bottom waters were oxygenated it is suggested that deposition of g prisca affected both organic matter preservation and depositional redox conditions observed variations in redox indicators and marine photoautotroph contributions are associated with changes in siliciclastic deposition reported macrofauna turnover and with evidence for oceanic cooling and a change in circulation patterns documented in the eastern united states

ordovician metre scale cycles implications for climate and eustatic fluctuations in the central appalachians during a global greenhouse non glacial to glacial transition abstract metre scale shallowing upward cycles in ordovician carbonates of the central appalachian basin record climate and eustatic fluctuations during a transition from early ordovician global greenhouse to late ordovician icehouse conditions peritidal facies and shale abundance suggest a long term trend in this area from semi arid early ordovician to more humid middle to early late ordovician conditions with a return to semi arid conditions during the late ordovician the climatic fluctuations were most likely produced by tectonics uplift and erosion related to taconic orogenesis plate motion of north america and the areal extent of water covering the shelf peritidal cyclic facies indicate that high frequency relative sea level fluctuations were of small amplitude 20 m relative sea level fluctuations that decreased into the later ordovician if these sea level changes are eustatic then the increased amplitude may mark the early initiation of continental glaciation on gondwana in the late middle ordovician followed by waning of ice sheets prior to the latest ordovician glaciation

dynamic cusp aurora and associated pulsed reverse convection during northward interplanetary magnetic field we report a study of ionospheric signatures of plasma entry and momentum transfer at the dayside magnetopause during northward oriented interplanetary magnetic field imf combining ground observations of the dayside aurora and ionospheric ion drift cutlass hf radar with simultaneous particle precipitation data obtained from three overflights by the defence meteorological satellite program dmsp f12 f13 and f14 spacecraft the observations were taken during a 37 min long interval of strongly northward imf bz 7 nt clock angle 10 15 after a rapid northward turning the meridan scanning photometer at the ground station recorded a long stepwise poleward retraction and latitudinal widening of the band of auroral emission in the cusp region thus the activity includes a series of episodes which are characterized by an initial 1 2 min poleward step of the auroral poleward boundary followed by a 3 4 min period of relatively steady auroral latitude the auroral events were accompanied by bursts of reverse two cell convection characterized by equatorward flow across the cusp poleward boundary the three dmsp spacecraft which traversed the poleward boundary of the cusp aurora from north to south entered into a region of auroral precipitation where electrons and ions of magnetosheath origin were present together with equatorward convection the observations are found to be consistent with a theoretical description of a sequence of bursts of lobe reconnection involving both hemispheres this process results in the capture of magnetosheath flux tubes and thereby closed flux is added to the dayside magnetosphere

high resolution sequence stratigraphy of the upper ordovician montoya group southern new mexico and western texas outcrop analog of an unconventional chert and carbonate reservoir the upper ordovician montoya group crops out in southern new mexico and westernmost texas and records predominantly subtidal deposition on a gently dipping carbonate ramp that was subsequently almost entirely dolomitized the montoya group is a third order composite sequence composed of six regionally correlative shallowing upward third order depositional sequences m0 m5 sequence m0 has sandstone at its base that is overlain by skeletal packstone grainstone sequence m0 occurs only locally and was likely deposited in a topographic low formed during regional development of the unconformity following el paso group deposition sequence m1 marking the initial widespread transgression over the ellenburger unconformity consists of sandstone updip that passes downramp into skeletal packstone the highstand systems tract hst of m1 consists of a prograding skeletal grainstone that was subaerially exposed upramp sequence m2 which contains the second order maximum flooding surface has abundant subtidal cherty carbonate at its base which shallows upward into a widespread prograding coral packstone grainstone in the hst sequence m3 also contains abundant downramp chert that passes upramp into an aggrading crinoidal shoal and farther upramp into peritidal mudstone sequence m4 records an extensive basinward shift in facies as peritidal burrowed and cryptalgalaminated mudstone prograded over subtidal carbonate sequence m5 is only locally developed downramp and consists of crinoidal grainstone with abundant evidence of subaerial exposure a regional unconformity separates the montoya group from the silurian fusselman dolostone or younger units parasequences meter scale cycles recording low to moderate amplitude relative sea level fluctuations are ubiquituous features at individual outcrops but are difficult to correlate regionally the abundance of syn or early depositional chert in the subtidal facies indicates that the montoya group was deposited within a region of strong regional upwelling along southern laurentia this early formed chert was the reservoir facies in a successful upper ordovician gas play in ward and reeves counties texas

tectonic processes and geomorphological design abstract deep seated geodynamic processes are the cause of the existence of the geotectonic stress field the influence of the latter and therefore of deep seated processes in surface geomorphology is investigated it is noted that the features caused by deep seated geotectonic processes can be distinguished from those caused by exogenic agents weather erosion etc by their statistical characteristics all statistically systematic features are of geotectonic origin random features are of exogenic origin in this paper various types of morphological features are analyzed with regard to their origin it is shown that lineaments seen on air photographs may not be of recent geotectonic origin specific examples of such lineaments being erosion scarps are given next it is shown that the orientation patterns inherent in fluvial and glacial valleys are indeed affected to a large extent by neotectonic processes the same is naturally the case for rift valleys and chains of volcanoes a further interesting subject is presented by the so called tectonic landforms inselbergs cirques the shapes of mountain summits etc are all shown to be directly or indirectly caused by deep seated processes the mass movements on slopes are also of great importance although it is often thought that these are triggered by meteorological conditions it is shown that their basic design is influenced to a large extent by deep seated processes amongst other things this is borne out by a correlation between landslide and earthquake activity finally it is mentioned that the common joints on rock outcrops are also designed by the neotectonic stress field and that the latter can in fact be determined by an analysis of joint orientations in summary it may be stated that although exogenic agents may be responsible for many morphological features deep seated processes have nevertheless a great influence on the fundamental design of such features

large scale imaging of high latitude convection with super dual auroral radar network hf radar observations the hf radars of the super dual auroral radar network superdarn provide measurements of the e b drift of ionospheric plasma over extended regions of the high latitude ionosphere with the recent augmentation of the northern hemisphere component to six radars a sizable fraction of the entire convection zone approximately one third can be imaged nearly instantaneously 2 min to date the two dimensional convection velocity has been mapped by combining line of sight velocity measurements obtained from pairs of radars within common volume areas we describe a new method of deriving large scale convection maps based on all the available velocity data the measurements are used to determine a solution for the distribution of electrostatic potential expressed as a series expansion in spherical harmonics the addition of data from a statistical model constrains the solution in regions of no data coverage for low order expansions the results provide a gross characterization of the global convection we discuss the processing of the radar velocity data the factors that condition the fitting and the reliability of the results we present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field imf in the case of a sudden polarity change from northward to southward imf the convection is seen to reconfigure globally on very short 6 min timescales

digitally processed topographic data for regional tectonic evaluations siting and design of major structures such as nuclear power plants waste repositories dams and so forth require a thorough evaluation of earthquake hazard including an assessment of the tectonic regime in the site region all available data sources such as geologic maps geophysical maps and synoptic remote sensing images should be fully utilized for regional tectonic evaluations nearly all lineaments mapped on synoptic scale images however are expressions of topographic features it seems desirable therefore to include analysis of digital elevation data in regional phases of tectonic evaluations these data have higher spatial resolution than landsat and are less expensive than both landsat and slar digital elevation data are inherently geometrically correct and although of lower resolution than slar are more versatile in accentuating geologic structure with less cultural and vegetation interference digital elevation data in the form of synthetic relief images and stereo pairs provide ideal data bases for guiding aerial reconnaissance and acquisition of large scale images for detailed evaluations

investigating the development of localized neutral density increases during the 24 august 2005 geomagnetic storm we investigate localized thermospheric neutral density increases or density spikes developed during the 24 august 2005 geomagnetic storm and utilize a multi instrument database for monitoring the underlying thermospheric ionospheric magnetospheric and solar wind conditions we study five scenarios occurring under eastward westward b dominations and demonstrating the development of density spikes during various events these scenarios show 1 a northern density spike associated with enhanced antisunward polar flows driven by dayside merging along old open field lines during the initial phase 2 some southern density spikes associated with enhanced sunward auroral flows caused by auroral brightening events during the storm initial phase and main phase 3 two pairs of southern dayside nightside density spike configuration associated with enhanced antisunward polar flows caused by dayside merging and nightside magnetotail reconnections along old open field lines during the underlying substorm activity and 4 a series of enhanced polar sunward flows developed in the polar cap driven by different processes during the recovery phase we provide a detailed analysis of these events including the specification of underlying field aligned current systems flow channel types and auroral forms observational results demonstrate the various density spikes and their associated auroral forms and or flow channels and thus provide a better understanding of their development during this intense geomagnetic storm

biotic response to a middle ordovician paleoceanographic event in eastern north america global paleontological events such as mass extinctions have been the focus of attention in recent years yet regional biotic events account for a greater proportion of extinction in the fossil record and should receive greater attention if we are to fully understand extinction processes over the phanerozoic we use a sequence stratigraphic framework to document a major extinction and migration episode that occurred in the middle and late ordovician of north america this event is characterized in eastern north america by coordinated changes in faunal assemblages carbonate lithologies siliciclastic influx and phosphatization we ascribe these changes to a regional paleoceanographic event brought on by thrust driven flexural subsidence and sea level fluctuations that lowered water temperature and increased turbidity and nutrient input

empirical high latitude electric field models electric field measurements from the dynamics explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn dusk ogo 6 measurements j p heppner 1977 the analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones paralleling the previous analysis the modeling is based on the distinctly different polar cap and dayside convective patterns that occur as a function of the sign of the y component of the interplanetary magnetic field the objective which is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns is met by deriving one pattern model bc for the northern hemisphere with a y interplanetary magnetic field imf and southern hemisphere with a y imf and two patterns models a and de for the northern hemisphere with a y imf and southern hemisphere with a y imf the most significant large scale revisions of the ogo 6 models are 1 on the dayside where the latitudinal overlap of morning and evening convection cells reverses with the sign of the imf y component 2 on the nightside where a westward flow region poleward from the harang discontinuity appears under model bc conditions and 3 magnetic local time shifts in the positions of the convection cell foci the modeling above was followed by a detailed examination of cases where the imf z component was clearly positive northward neglecting the seasonally dependent cases where irregularities obscure pattern recognition the observations range from reasonable agreement with the new bc and de models to cases where different characteristics appeared primarily at dayside high latitudes the analysis of these differences for strong bz conditions using passes through different mlt zones led to finding that the deviations from both the bc and de models could be modeled by extending the evening cell foci toward and beyond noon with a deformation that roughly resembles a rotational twist of the extended evening cell the morning cell accommodation to the model bc deformation produces a narrow tongue of eastward convection near 75 invariant latitude on the dayside the model de deformation compresses the morning cell toward the night hours such that the sunward convection in the morning cell is diverted to polar latitudes in the 0400 to 0700 mlt sector in both cases the deformations of the two cell patterns lead to sunward convection in dayside polar regions while maintaining the integrity of the nightside convection pattern thus the nightside dilemmas that plague three and four cell models designed to explain sunward convection in polar regions under bz conditions do not appear