diameters and albedos of satellites of uranus the five known satellites of uranus are too small and distant to permit direct measurement of their diameters consequently products of the masses of the satellites and estimates of their bulk densities and surface albedos have been used in discussions of their probable dimensions in the absence of measurements the presence of water ice on the surfaces of ariel umbriel titania and oberon has been established spectrophotometrically1 4 and the brightnesses of the satellites have been measured photoelectrically5 determination of the masses of the uranian satellites depends on observations of perturbations of the satellite orbits and results chiefly in upper limits to the products of the masses of various pairs of satellites6 7 the new diameter measurements reported here were made using the photometric radiometric technique of diameter determination this widely used technique has enabled the measurement of the diameters and albedos of approximately 250 asteroids and many planetary satellites a recent recalibration of the technique using independent measurements of the diameters of three solar system objects results in absolute accuracies of better than 5 our new albedo measurements show that umbriel titania and oberon are similar in albedo to j4 callisto while ariel is very similar in albedo to s7 hyperion the diameters of all four satellites are similar to those of the large icy saturnian satellites s5 rhea and s8 iapetus

a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

hierarchal genetic stratigraphy a framework for paleoceanography a detailed genetic stratigraphic framework for paleoceanographic studies can be derived by describing correlating interpreting and predicting stratigraphic sequences relative to a hierarchy of their constituent time stratigraphic transgressive regressive units t r units t r unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data but correlations can be enhanced or checked tested to confirm or deny with objective biostratigraphic magnetostratigraphic or chemostratigraphic data such chronostratigraphies can then be bracketed by radiometric ages so that average periodicities for t r units can be calculated and a hierarchal geochronology derived t r units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening shallowing units because the latter are noncorrelative intrabasinally boundaries between t r units are conformable or unconformable genetic surfaces of two types transgressive surfaces and climate change surfaces the latter are useful for correlating minor transgressive phases through nonmarine intervals thereby deriving information linking paleoclimatic and paleoceanographic processes permo carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic t r units having periodicities of 225 300 m y first order 20 90 m y second order 7 13 m y third order 0 6 3 6 m y fourth order 300 500 10 years fifth order and 50 130 10 years or less sixth order paleogeographic maps for the time of maximum transgression transgressive apex of successive fifth order t r units 5 25 m thick in the glenshaw formation upper pennsylvanian northern appalachian basin delineate delta lobes embayments islands and linear seaways relative extent of marine inundation on the fifth order maps was used to delineate fourth order t r units and the fourth order t r units constitute the transgressive half of a third order t r unit this third fourth and fifth order hierarchy is correlated more than 1200 km 750 miles to the western interior basin and is confirmed with limited objective biostratigraphy

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

ichnology of a paleopolar river dominated shallow marine deltaic succession in the mackellar sea the mackellar formation lower permian central transantarctic mountains antarctica abstract the lower permian mackellar formation in the beardmore glacier area of the central transantarctic mountains antarctica was deposited between 80 and 85 s paleolatitude previous studies suggest that mackellar formation strata were deposited in either a large glacial lake or inland sea our study identified 30 ichnogenera from turnabout ridge and buckley island of which 1 none are exclusively freshwater forms 2 20 ichnogenera are found in freshwater brackish and marine settings and 3 10 ichnogenera are exclusively found in marine settings combining ichnologic evidence with sedimentologic observations suggests that the mackellar formation was deposited in a river dominated delta in a fully marine to brackish marine setting trace fossil associations are grouped into the arenicolites phycodes lingulichnus arenicolites planolites kouphichnium phycodes teichichnus arenicolites and planolites teichichnus phycodes ichnocoenoses of a mixed skolithos cruziana ichnofacies these associations are characteristic of epi and endobenthic worms arthropods and mollusks with the vast majority of the traces being diminutive in diameter and length and exhibit shallow 10 mm penetration depths these ichnocoenoses occur in paleoenvironments that include the prodelta distal to proximal delta front including mouth bars and subaqueous terminal distributary channels the diminutive morphology shallow penetration depth low bed ichnodiversity high overall ichnodiversity and sedimentologic characteristics are indicative of benthic organisms in a marine deltaic environment with short lived communities composed of small bodied organisms stressed by high freshwater input and high sedimentation rates

ichnology of the late carboniferous hoyada verde formation of western argentina exploring postglacial shallow marine ecosystems of gondwana abstract the postglacial interval of the upper carboniferous hoyada verde formation of western argentina contains an ichnofauna dominated by psammichnites plummeri and psammichnites implexus with minor occurrences of ptychoplasma vagans treptichnus bifurcus lingulichnus verticalis protovirgularia isp lockeia isp palaeophycus isp scarce arthropod trackways and some bilobate structures the particular features of this association indicate a depauperate expression of the cruziana ichnofacies and suggest a context that differs from the expected in normal shallow marine settings i e archetypal cruziana ichnofacies integration of sedimentologic ichnologic sequence stratigraphic and paleontologic data points to a prograding deltaic system influenced by wave action trace fossils have been extensively used to recognize stressed brackish water environments in the late paleozoic of gondwana however the recognition of stressed settings needs to take into consideration the specific paleogeographic context of glacially influenced gondwanan settings a postglacial open sea adjacent to a paleotopographic high is considered as a possible scenario for the hoyada verde formation in this particular setting coastal biotas could have been influenced to some degree by the salinity gradient triggered by freshwater release near to melting ice masses stored in highlands and also by freshwater plumes due to longshore currents regional factors e g proximity to highlands and climate may have played an important role in controlling the characteristics of gondwanan ichnofaunas this suggests that the distinction between normal marine and brackish water settings in glacially influenced environments using trace fossils may not be as straightforward as in non glacial settings

the control networks of the satellites of uranus abstract control networks of the five large satellites of uranus have been established photogrammetrically from pictures taken by the voyager 2 spacecraft the control networks cover the illuminated southern hemisphere of each satellite coordinates are listed for 103 points on miranda 52 points on ariel 43 points on umbriel 46 points on titania and 34 points on oberon some points are identified on the u s geological survey maps of these satellites miranda is ellipsoidal in shape with radii of 241 235 and 232 km mean radii are 579 km for ariel 586 km for umbriel 790 km for titania and 762 km for oberon

namurian uplift in australia and south america triggered the main gondwanan glaciation the permo carboniferous glacigenic sediment at the base of the gondwanan basins reflects the culmination1 2 of the glacial episode that started in australia and southern south america in the namurian after two local episodes in northern south america and adjacent africa in the visean and latest devonian3 fig 1 here we show that the start of each episode was associated with orogenic uplift of the bordering regions northern south america and adjacent africa in the latest devonian and visean and southern south america and eastern and central australia in the namurian all areas except southern south america in the namurian were at mid and not high latitudes thus we show that whereas the first order control of glaciation was the configuration of the continents and oceans during the closing of palaeo tethys orogenesis provided a second order control by the accumulation of ice about bordering uplifts during the three glacial episodes

glaciations preservation of their sedimentary record and sea level changes a discussion based on the late precambrian and lower palaeozoic sequence in norway abstract terrestrial glacial sediments have a low preservation potential in the sedimentary record tillites and other glacial sediments of pre quaternary age are often found to represent marginal facies in subsiding marine basins or continental rift environments continental rifting provides an ideal tectonic setting for both accumulation of ice and preservation of glacial sediments in the rapidly subsiding rift basins uplifted horsts along the rifts may be sites for mountain glaciations at relatively low paleolatitude the late precambrian sparagmite basin of south norway may be an example of this major pre quaternary glaciations should be expected to be accompanied by eustatic sea level changes records of sea level changes in tectonically stable areas may provide some constrains on the timing and magnitude of ancient continental glaciations the upper ordovician sequence in the oslo region presents a continuous shallow marine carbonate environment which is sensitive to sea level changes the records here suggest that the ordovician glaciations in west africa were either very minor glaciations compared to the quaternary glaciation causing less than 20 m of eustatic sea level changes or that the glaciations occurred in periods marked by tectonic unconformities

coexistence of brachiopod and bivalves in the late paleozoic of western argentina abstract the relationship between brachiopods and bivalves has been widely discussed in previous studies based on analyses at different temporal and spatial scales several authors have argued either for the indifference or the interaction between the two clades in this contribution we evaluate brachiopod and bivalve coexistence at two different spatial scales in a siliciclastic shelf developed during the late paleozoic in western argentina at regional scale bivalves were more diverse than brachiopods although both had a similar total number and comparable distribution of occurrences at local scale however multivariate analyses indicate that brachiopods and bivalves were segregated null models reinforce this pattern confirming the non random co occurrence pattern and that the coexistence of brachiopods and bivalves was significantly low in addition multivariate analyses indicate that the biotic gradient neither followed the bathymetrical nor a geographical or temporal gradient the possibility that such segregation would have been caused by taphonomic storm reworking was also disregarded considering multivariate analyses together with taphonomic evidence the lack of environmental segregation between brachiopods and bivalves coupled to analyses taking into account ecological guilds indicates that possible factors controlling the segregation such as turbidity substrate or productivity were not relevant as a whole these results suggest a possible competitive interaction between brachiopods and bivalves at local scales interestingly brachiopod bivalve coexistence at regional scale did not foster local coexistence indicating that the processes acting at these two scales are at least partially decoupled finally the regional coexistence pattern suggests that the major transition between brachiopod and bivalve dominated communities was most probably related to processes acting at regional to biogeographic scales rather than to competition

hidden tectonism on miranda s elsinore corona revealed by polygonal impact craters abstract we mapped the spatial distribution and orientations of polygonal impact craters pics on the classical uranian satellite miranda to gain insight into the complex tectonic history of this moon pic straight rim segments in regions without visible fractures can be used to infer sub regolith and or sub resolution fracture orientations we identified and analyzed 14 pics on miranda nine of which are located on its trailing hemisphere overprinting elsinore corona and the nearby cratered terrain these pics do not follow the e w orientations of the ridges within elsinore s bounding terrain indicating that these ridges are not underlain by deep rooted at least as deep as the crater bowl sub vertical normal or strike slip faults instead the ridges may be contractional features consisting of folds and possibly thrust faults or cryovolcanic features without fault structures furthermore the pics in this region indicate that a previously undetected nw oriented fracture system is present over much of miranda s trailing hemisphere another pic somewhat distal from elsinore on miranda s anti uranus hemisphere might be associated with the nw fractures as well additionally three pics are present proximal to verona rupes on miranda s uranus facing hemisphere these pics exhibit n s orientations consistent with the surrounding fractures that make up miranda s global rift system one other pic is proximal to arden and might be associated with the arden bounding terrain identification of the nw fracture system provides new information on miranda s complex geologic history based on cross cutting relationships with miranda s ancient subdued crater population the nw fracture system is older than elsinore however this fracture system also overprints elsinore suggesting reactivation of the nw fractures after this corona had formed along with discussion of miranda s geologic history we consider the possibility that miranda has undergone true polar wander and we compare its terrains and geologic features to similar features on the saturnian satellite enceladus

high s n keck and gemini ao imaging of uranus during 2012 2014 new cloud patterns increasing activity and improved wind measurements abstract we imaged uranus in the near infrared from 2012 into 2014 using the keck nirc2 camera and gemini niri camera both with adaptive optics we obtained exceptional signal to noise ratios by averaging 8 16 individual exposures in a planet fixed coordinate system these noise reduced images revealed many low contrast discrete features and large scale cloud patterns not seen before including scalloped waveforms just south of the equator and an associated transverse ribbon wave near 6 s in all three years numerous small 600 700 km wide and mainly bright discrete features were seen within the north polar region north of about 55 n two small dark spots with bright companions were seen at middle latitudes over 850 wind measurements were made the vast majority of which were in the northern hemisphere winds at high latitudes were measured with great precision revealing an extended region of solid body rotation between 62 n and at least 83 n at a rate of 4 08 0 015 h westward relative to the planet s interior radio rotation of 20 88 h westward near equatorial speeds measured with high accuracy give different results for waves and small discrete features with eastward drift rates of 0 4 h and 0 1 h respectively the region of polar solid body rotation is a close match to the region of small scale polar cloud features suggesting a dynamical relationship the winds from prior years and those from 2012 2014 are consistent with a mainly symmetric wind profile up to middle latitudes with a small asymmetric component of 0 09 h peaking near 30 and about 60 greater amplitude if only prior years are included suggesting a declining mid latitude asymmetry while winds at high southern latitudes 50 90 s are unconstrained by groundbased observations a recent reanalysis of 1986 voyager 2 observations by karkoschka karkoschka 2015 icarus 250 294 307 has revealed an extremely large north south asymmetry in this region which might be seasonal greatly increased activity was seen in 2014 including the brightest ever feature seen in k images de pater et al 2015 icarus 252 121 128 as well as other significant features some of which had long lives over the 2012 2014 period we identified six persistent discrete features three were tracked for more than 2 years two more for more than 1 year and one for at least 5 months and continuing several drifted in latitude towards the equator and others appeared to exhibit latitudinal oscillations with long periods we found two pairs of long lived features that survived multiple passages within their own diameters of each other zonally averaged cloud patterns were found to persist over 2012 2014 when averaged over longitude there is a brightness variation with latitude from 55 n to the pole that is similar to effective methane mixing ratio variations with latitude derived from 2012 stis observations sromovsky et al 2014 icarus 238 137 155

fluid volcanism on miranda and ariel flow morphology and composition several types of volcanic units have been recognized on the icy uranian satellites miranda and ariel on miranda ridges characterized by crest grooves are up to 10 km wide and 500 m high a continuous flat topped flow band also 10 km wide and 500 m high forms the outer southern margin of elsinore corona elsinore coronae at least appears to comprise coalesced flow bands and ridges on ariel in addition to at least one ridge unit similar to these on miranda flood plains material has covered the floors of deep chasmata grabens and an irregular depression flows on both satellites are characterized by linear vent geometries and distinct topographic margins which indicate extrusion of a relatively viscous material the topography of the flows can be used to estimate flow viscosity or yield strength using a bingham plastic model extrusion viscosity estimates incorporating plausible volcanologically based emplacement time scales and a rigid crust correction range from 107 to 109 p 1013 p in the unlikely absence of a chilled crust viscosity estimates are dependent on the assumed emplacement time scale however and could be as high as 1016 p if a solid stale based time scale is assumed bingham models indicate that it is yield strength that controls the final flow width and thickness that we see yield strength estimates are probably more reliable because of uncertainties in the viscous flow time scale yield strength estimates range from 10 1 to 10 2 bars consistent with yield strengths of partially crystallized silicate melts on other planets nevertheless both the viscosities and yield strengths are well within the range of and in some cases lower than silicate flows silicate compositions are not possible for these flows because of the ice rich composition of these satellites measured properties of ammonia water liquid crystal mixtures are consistent with the observed and estimated flow rheologic properties however and extrusion of such material s is a viable alternative to solid state extrusion for the origin of these flow features

large impact features on middle sized icy satellites abstract all of the large impact features of the middle sized icy satellites of saturn and uranus that were clearly observed by the voyager spacecraft are described new image mosaics and stereo and photoclinometrically derived digital elevation models are presented landforms related to large impact features such as secondary craters and possible antipodal effects are examined and evaluated of the large impacts odysseus on tethys appears to have had the most profound effect on its target satellite of any of the impact features we examined our modeling suggests that the odysseus impact may have caused the prompt formation of ithaca chasma a belt of tectonic troughs that roughly follow a great circle normal to the center of odysseus although other hypotheses remain viable we identify probable secondary cratering from tirawa on rhea we attribute a number of converging coalescing crater chains on rhea to a putative possibly relatively fresh 350 km diameter impact feature we examine the antipodes of odysseus the putative 350 km diameter rhean impact feature and tirawa and conclude that evidence from voyager data for damage from seismic focusing is equivocal although our modeling results indicate that such damage may have occurred we propose a number of observations and tests for cassini that offer the opportunity to differentiate among the various explanations and speculations reviewed and evaluated in this study

postglacial transgressions in late paleozoic basins of western argentina a record of glacioeustatic sea level rise the areas marginal to main glaciated centers are appropriate sites to distinguish the record of glacioeustatic sea level fluctuations the late paleozoic basins of western argentina show a marginal position with respect to the glaciated areas of eastern south america brazil in three of these basins tarija calingasta uspallata and central patagonian widespread glacial marine diamictites and their gravity reworked counterparts pass upward to open marine fine clastics mudstones shales and scarce fine sandstones with fossils of the levipustula zone of middle carboniferous late namurian westphalian age the presence of fine grained marine sequences capping the diamictitic deposits is interpreted as the sedimentary response to a glacioeustatic sea level rise expressed as a transgression in stratigraphic terms the glacioeustatic nature of this sea level rise is confirmed by the interbasinal facies based correlation of the transgressive episode and the paleolatitudinal positioning of this portion of gondwanaland during carboniferous times

radii shapes and topography of the satellites of uranus from limb coordinates abstract limb coordinates are used to find the radii shapes and local topography of the five large satellites of uranus the technique provides a direct measure of ellipsoidal shapes of satellites and fixes radii to subpixel accuracy umbriel titania and oberon are best fit by spheres miranda and ariel are ellipsoids whose equatorial bulges are consistent with published mean densities limb topography on miranda shows substantial deformation of both old cratered terrain and the younger coronae and complex faulting and uplift at the margins of the coronae the maximum deformation is about 10 km umbriel s limb shows a basin of undetermined origin about 500 km across and 6 km deep

ganymede and callisto complex crater formation and planetary crusts new depth diameter d d rim and peak height and width measurements of fresh craters on ganymede and callisto are utilized to explore not only crater mechanics on icy satellites but intersatellite crater scaling and crustal properties and composition significant systematic differences in crater morphology on icy and rocky planets are confirmed simple to complex transition diameters on icy satellites including ganymede and callisto are much lower than those on rocky planets also complex crater depths and rim heights on ganymede and callisto are inherently 60 70 shallower than lunar complex craters despite similar surface gravity hence viscous relaxation is not as important as is generally assumed central peaks on most icy satellites are 1 2 km higher and considerably wider with respect to diameter than for similar sized lunar craters terracing and rim slumping is also rare in these craters central peaks in craters on ganymede and callisto larger than 15 km however are relatively small in both width and height however correlating with the occurrence of rim slumping thus central peak dimensions are an indirect indicator of the degree of rim slumping transition diameters for the occurrence of central peaks and rim slumps and for d d curve inflections for icy satellites scale approximately with the inverse of surface gravity except possibly at very low g the transition diameters for central peaks and for rim slumping differ however by 5 15 km on ganymede and callisto but by 50 or more km on the smaller icy satellites these large differences suggest that d d curves on icy satellites are comprised of three segments of decreasing slope one for smaller simple craters a second for central peak craters and a third for larger true complex craters with both central peaks and rim slumping the shallow slopes of d d curves on ganymede and callisto resemble that of the moon consistent with the occurrence of both central peaks and rim failure the high slopes of d d curves on the middle sized icy satellites indicate that they are middle segments consistent with the dominance of central peaks in those craters complex crater depths on icy satellites in general scale with the inverse of surface gravity the depths of all the observed large basin scale craters on these small satellites when scaled to ganymede gravity are very similar to those of complex craters on ganymede and callisto these large craters including odysseus 425 km diameter on tethys are probably true complex craters that have not undergone significant viscous relaxation ithaca chasma on tethys probably formed during the prompt collapse of the transient odysseus crater crater morphology is clearly controlled by both gravity and by large variations in material properties i e composition and should be useful in constraining bulk crustal composition i e ice rock ratios the similarity of various morphological transition diameters and complex crater depths on ganymede and callisto two geophysically very similar but geologically divergent large icy satellites indicates that the crusts of both bodies are dominated by water ice with only a minor rocky component

solid state ice volcanism on the satellites of uranus voyager images of the uranian satellites ariel and miranda show flow features with morphologies indicating that ice has been extruded to the satellites9 surfaces in the solid state these images provide the first observational evidence for solid state ice volcanism in the solar system topographic profiles have been measured across a number of flow features on ariel with a simple model of extrusion spreading and cooling of a viscous flow the initial viscosity of the flow material is found to have been no more than about 10 16 poise far lower than expected for h 2 o ice at the ambient surface temperatures in the uranian system sharply reduced viscosities may have resulted from incorporation of ices like nh 3 or ch 4 in the uranian satellites

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

glacial cirques as palaeoenvironmental indicators their potential and limitations abstract glacial cirques are armchair shaped erosional hollows typified by steep headwalls and often overdeepened floors they reflect former regions of glacier initiation and their distribution is therefore linked to palaeoclimate because of this association cirques can be analysed for the information they provide about past environments an approach that has a strong heritage and has seen resurgence over recent years this paper provides a critical assessment of what cirques can tell us about past environments and considers their reliability as palaeoenvironmental proxies specific focus is placed on information that can be obtained from consideration of cirque distribution aspect altitude and morphometry the paper highlights the fact that cirques potentially provide information about the style duration and intensity of former glaciation as well as information about past temperatures precipitation gradients cloud cover and wind directions in all cirques are considered a valuable source of palaeoenvironmental information if used judiciously particularly as they are ubiquitous within formerly glaciated mountain ranges globally thus making regional or even global scale studies possible furthermore cirques often occupy remote and inaccessible regions where other palaeoenvironmental proxies may be limited or lacking

evidence for temporal change at uranus south pole abstract analysis of hubble space telescope images of uranus taken between 1994 and 2002 shows evidence for temporal changes in zonal brightness patterns in the south polar region between 1994 and 2002 a relatively bright ring developed near 70 s the pole itself which was the brightest area of the southern hemisphere in 1994 has become relatively dark the polar collar at 45 s has also become brighter relative to the rest of the southern polar region comparison of images through different filters suggests that the change is occurring at pressures of 2 4 bars in the atmosphere a change at this depth is consistent with radio measurements which indicate seasonal variability in uranus deep atmosphere disk integrated photometry at visible wavelengths also exhibits variability on seasonal decades timescales the observed changes are not predicted by existing dynamical models of uranus atmosphere

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

sedimentation in glacial environments and the identification of tills and tillites in ancient sedimentary sequences abstract tills and tillites are defined and subdivided into primary tills comprising lodgement tills melt out tills and sublimation tills and secondary tills comprising flow tills and deformation tills they are defined on the basis of their mode of deposition which endows them with their distinctive properties another category of till that of supra till is defined on the basis of its debris source derived supraglacially from valley sides and nunataks which gives these tills a coarse grained character the processes of till deposition and of outwash sedimentation are associated in several recurrent combinations which allow the definition of three principal glacial sediment associations and land systems which define the character of the sequences within which tills tend to occur the criteria which allow tills of different genesis to be identified and to be distinguished from non till diamictons are reviewed there are several features which are uniquely characteristic of till but unfortunately these are few it has been found generally necessary to employ an array of characteristics which though not individually unique to till when taken together can be strong evidence for particular till types the recognition of several typical and repetitive facies sequences which form in the major glacial sedimentary environments can also be important indicators of till genesis

long term variations in the microwave brightness temperature of the uranus atmosphere we present a self consistent 36 year record of the disk averaged radio brightness of uranus at wavelengths near 3 5 cm it covers nearly half a uranian year and includes both equatorial and polar viewing geometries corresponding to equinox and solstice respectively we find large greater than 30 k changes over this time span in agreement with analyses made of more limited microwave data sets our observations suggest the changes are not caused by geometric effects alone and that temporal variations may exist in the deep uranian troposphere down to pressures of tens of bars our data also support an earlier suggestion that a rapid planetary scale change may have occurred in late 1993 and early 1994 the seasonal record presented here will be useful for constraining dynamical models of the deep atmosphere and for interpreting observations made during uranus 2007 equinox passage as part of a multi wavelength observing campaign for this event the goldstone apple valley radio telescope gavrt project will continue to make frequent single dish observations near 3 5 cm

depositional models for the glaciomarine sequences of andean late paleozoic basins of argentina abstract diamictite bearing late paleozoic sequences of probably glacial origin crop out in three basins of western argentina 1 the tarija basin 2 the calingasta uspallata basin and 3 the central patagonian basin the tarija section shows clear evidence of soft sediment deformation in a shallow marine environment slump overfolds and hook like and pull apart structures are common in lenses of well sorted sandstones within a sequence mostly composed of massive matrix supported pebbly mudstones the overall shallowing upward trend of the section suggests alluvial progradation underlying fine grained rocks represent quiet water prodelta deposits the diamictites suggest a delta slope position and the overlying red mudstones with cross bedded sandstones and conglomerates correspond to delta plain deposits in the calingasta uspallata basin the hoyada verde formation represents the best example of an ice contact glaciomarine depositional system with minor gravity flow deposits massive matrix supported sandy diamictites associated with a boulder pavement together with sandstone and conglomerate channels represent grounded ice deposits grading to subglacial flow tills thin bedded matrix supported muddy diamictites with dropstones are the product of a process of gravity resedimentation debris flows and ice rafting pebbly shales represent shelf sedimentation with local deposition from floating ice the ansilta formation shows characteristic features of low and high turbidity current dominated environments basal diamictites resemble debris flow deposits and are associated with thickening upward sequences of bouma tb c turbidites and massive sandstones with fluid scape structures these two sections described above represent the end members of a continuum from glaciomarine rocks to gravity induced deposits formed by subaqueous reworking of glacial debris fine grained rocks associated with diamictites contain marine fossils belonging to the livipustula zone of westphalian age middle carboniferous the central patagonian diamictites appear to be clearly associated with classical turbidites with bouma sequences resedimented conglomerates and high density turbidity current sandstones the conglomerates and sandstones form composite channels with common amalgamation and internal scour surfaces the depositional models proposed for the diamictite bearing sequences of the three basins can be placed in a broader model which embraces several types of complex interactions among glaciomarine nearshore and gravity flow dominated environments

tidal heating in icy satellite oceans abstract tidal heating plays a significant role in the evolution of many satellites in the outer solar system however it is unclear whether tidal dissipation in a global liquid ocean can represent a significant additional heat source tyler tyler r h 2008 nature 456 770 772 tyler r h 2009 geophys res lett 36 doi 10 1029 2009gl038300 suggested that obliquity tides could drive large scale flow in the oceans of europa and enceladus leading to significant heating a critical unknown in this previous work is what the tidal quality factor q of such an ocean should be the corresponding tidal dissipation spans orders of magnitude depending on the value of q assumed to address this issue we adopt an approach employed in terrestrial ocean modeling where a significant portion of tidal dissipation arises due to bottom drag with the drag coefficient o 0 001 being relatively well established from numerical solutions to the shallow water equations including nonlinear bottom drag we obtain scalings for the equivalent value of q as a function of this drag coefficient in addition we provide new scaling relations appropriate for the inclusion of ocean tidal heating in thermal orbital evolution models our approach is appropriate for situations in which the ocean bottom topography is much smaller than the ocean thickness using these novel scalings we calculate the ocean contribution to the overall thermal energy budgets for many of the outer solar system satellites although uncertainties such as ocean thickness and satellite obliquity remain we find that for most satellites it is unlikely that ocean tidal dissipation is important when compared to either radiogenic or solid body tidal heating of known satellites triton is the most likely icy satellite to have ocean tidal heating play a role in its present day thermal budget and long term thermal evolution

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

fault geometries on uranus satellite miranda implications for internal structure and heat flow abstract miranda a 470 km diameter uranian icy satellite has a surface that exhibits evidence of a complex tectonic history tectonic structures are mostly localized in three regions termed coronae but also form a rift system inferred to be global in extent ridges within the boundary of arden corona and those that make up the 340 chasma part of the global rift system have been interpreted as normal fault blocks using voyager data we test the hypothesis that these arden corona faults as well as those at the northern edge of the 340 chasma are listric in geometry for this testing we use four geometric criteria for listric faults 1 progressive down dip decrease in fault scarp dip 2 progressive down dip increase in back tilted face slope 3 concavity of the exposed scarp surface and 4 presence of a rollover structure results of this analysis support the hypothesis that the faults within the arden corona boundary are listric in geometry but do not strongly support the hypothesis for the faults within the 340 chasma by analogy with terrestrial structures the listric character of faults within the arden corona boundary suggests the presence of a subsurface detachment this detachment likely occurred at miranda s brittle ductile transition zone at the time of faulting measurements of the arden corona fault system geometry are used to estimate depths to the proposed brittle ductile transition zone at the time of faulting resulting in values of 6 7 9 0 km those depths in turn are used to estimate a thermal gradient of 6 25 k km 1 and a surface heat flux of 31 112 mw m 2 the weaker evidence of a listric geometry for the faults of the 340 chasma suggests that those faults did not interact with a brittle ductile transition at the time of their formation our estimated thermal gradient of the arden corona region is consistent with a previous heating event on miranda that was as significant as europa s current resonance induced tidal heating this heating event may be associated with a hypothesized previous tidal resonance of miranda with umbriel and or ariel

a critical appraisal of allometric growth among alpine cirques based on multivariate statistics and spatial analysis when considering the morphometric attributes of a glacial cirque imbalances between length width and amplitude have been deemed relevant tools for discriminating between two possible pathways of cirque growth downwearing by glaciers or backwearing by freeze thaw processes based on a sample of 1071 cirques in the french pyrenees we reframe the concern for climatic variables by also granting systematic consideration to cirque lithology insight into the factors that control cirque shape is gained from principal component analysis where maps of eigenvalues assigned to six classes of bedrock display spatial patterns of cirque form as a function of position along the regional climatic gradient among crystalline rocks granite gneiss migmatite cirque form is predominantly determined by climatic controls this is highlighted in the contrast between the elevated core of the pleistocene icefield where cirque isometry prevails and the more peripheral areas external sierras of the atlantic precipitation zone and high sierras of the drier mediterranean zone where the lighter imprint of glaciation on the landscape has failed to erase through glacial deepening the allometric signature of pre pleistocene topographic features such as shallow valley heads and etch basins as a result wide and shallow cirques occur in these settings among schist outcrops in contrast cirque form appears randomly distributed suggesting that bedrock characteristics e g structure rather than climate are the key controls on cirque growth patterns given the importance of geological structure and preglacial topographic inheritance cirques are complex landforms for which assumptions of allometric growth may be spurious it follows that form is not always a reliable guide to process

laurentian fan morphology sediments processes and growth pattern thick sediment accumulations in deep water provide a new target in the search for oil and require an innovative approach to hydrocarbon exploration the laurentian fan is a large deep sea 2 000 to 5 000 m fan in the western north atlantic and has been the major depocenter off nova scotia since at least the early tertiary the main development of the present depositional and erosional fan morphology in the past 2 to 3 m y was closely related to onshore glacial history the slope above the fan has been the site of rapid sedimentation and consequent slumping a network of tributaries on the upper fan appears to feed three main channel systems incised up to 800 m between broad asymmetric levees these channels meander widely across the lower fan then die out abruptly and pass into a lobate suprafan differences between the laurentian fan and typical fan models result in part from the muddy nature of the sediment and the supply system the channels contain thick coarse gravels which probably grade distally into sandy lobes both should produce good reservoir bodies with suitable source and trapping mechanisms fine grained sediments were more important in fan construction interbedded turbidites contourites and hemipelagites are present in the late quaternary holocene sequence the distribution of these sediments and in particular the recognition of structural sequences textural trends and fabric types in the fine grained turbidites can be used to characterize particular parts of the fan environment the development of this approach should prove useful in future hydrocarbon exploration

periglacial weathering and headwall erosion in cirque glacier bergschrunds glaciers produce cirques by scouring their beds and sapping their headwalls but evidence to constrain models of these processes has been elusive we report a suite of environmental measurements from three cirque glacier bergschrunds including the first temperature series recorded at depth throughout most of an annual cycle compared to the ambient air the bergschrunds were colder in summer and warmer in winter freeze thaw cycles were rare and relatively stable subfreezing temperatures persisted from november until may using a model for rock fracturing driven by ice segregation we demonstrate that favorable conditions for fracturing occur not only on the headwall above the glacier but also within the bergschrund where periglacial weathering and glacial transport can act together to drive cirque headwall retreat a small 3 c year round decrease in temperatures to conditions more typical of the pleistocene would likely intensify the weathering process though so far ignored in all glacial landscape evolution models the bergschrund likely plays an essential role in the sculpting of alpine landscapes

direct observation of frost wedging in alpine bedrock width and temperature of rock joints were automatically monitored in the japanese alps three years of monitoring on a sandstone rock face shows two seasonal peaks of joint widening in autumn and spring the autumn events are associated with short term freeze thaw cycles and the magnitude of widening reflects the freezing intensity and water availability the short term freezing can produce wedging to a depth of at least 20 cm the spring events follow a rise in the rock surface temperature to 0 c beneath the seasonal snowcover and likely originate from refreezing of meltwater entering the joint some of these events contribute to permanent enlargement of the joint two other joints on nearby rock faces experience only sporadic widening accompanying freeze thaw cycles and insignificant permanent enlargement observations indicate that no single thermal criterion can explain frost weathering the temperature range at which wedging occurs varies with the bedrock conditions water availability and duration of freezing copyright 2001 john wiley sons ltd

evidence from voyager ii photometry for early resurfacing of umbriel the uranian satellite umbrieps dark heavily cratered surface is remarkable for its apparent uniformity in voyager ii images1 its most conspicuous geological feature is a comparatively high albedo annulus shaped deposit which covers the floor of the 40 km diameter crater wunda1 here we present new voyager ii albedo maps of umbriel which reveal that its surface is subdivided into low contrast crudely polygonal areas ranging in size from tens to hundreds of kilometres fig 1 the largest polygons are elongate with systematically trending northeast southwest boundaries some of the polygonal areas form topographic depressions several kilometres in depth we suggest that this newly discovered global albedo pattern is a relic of the early tectonic disruption of umbriel s surface

voyager 2 in the uranian system imaging science results voyager 2 images of the southern hemisphere of uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere the alignment of the cloud bands is similar to that of bands on jupiter and saturn but the zonal winds are nearly opposite at mid latitudes 70 degrees to 27 degrees where winds were measured the atmosphere rotates faster than the magnetic field however the rotation rate of the atmosphere decreases toward the equator so that the two probably corotate at about 20 degrees voyager images confirm the extremely low albedo of the ring particles high phase angle images reveal on the order of 10 2 new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings as well as a broad diffuse low optical depth ring just inside the main rings system nine of the newly discovered small satellites 40 to 165 kilometers in diameter orbit between the rings and miranda the tenth is within the ring system two of these small objects may gravitationally confine the e ring oberon and umbriel have heavily cratered surfaces resembling the ancient cratered highlands of earth s moon although umbriel is almost completely covered with uniform dark material which perhaps indicates some ongoing process titania and ariel show crater populations different from those on oberon and umbriel these were probably generated by collisions with debris confined to their orbits titania and ariel also show many extensional fault systems ariel shows strong evidence for the presence of extrusive material about halfof miranda s surface is relatively bland old cratered terrain the remainder comprises three large regions of younger terrain each rectangular to ovoid in plan that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials perhaps suggesting some exotic composition

planetary cratering 2 studies of saturation equilibrium a realistic computer model has been developed to display images of imaginary cratered surfaces taking into account empirically measured input size distributions of primary and secondary craters ejecta blanket morphology including feathering with distance obliteration due to ejecta from outside the imaged area lighting effects etc the model allows us to track surface evolution of morphology as new craters are added using the model as well as lunar photos we have studied the approach to saturation equilibrium defined as a condition when no further proportionate increase in crater density occurs as input cratering increases we find that an identifiable saturation equilibrium occurs close to a level previously identified for this state hartmann 1984 typically fluctuating around a crater density from 0 4 to 2 times that level this result is fairly robust vis a vis the range of model parameters we have chosen flooding basin ejecta blankets and other obliterative effects can introduce structure and oscillations within this range even after saturation equilibrium is achieved these findings may constrain or revise certain earlier interpretations of satellite and planet surface evolution and impactor populations which were predicated on the assumed absence of saturation equilibrium in our fourth experimental run we found that suppression of sandblasting by subresolution impacts allows the smallest secondaries to rise above the saturation equilibrium line a result that might be relevant to a similar situation on gaspra and perhaps some other asteroids

late paleozoic paleoclimatology of central west argentina abstract based on sedimentologic and paleontological characteristics present in the sedimentary record of the calingasta uspallata and paganzo basins a model of paleoclimatic evolution for the late paleozoic of central west argentina is proposed additional evidence is also provided by data from other basins of southern san rafael and tepuel basins and northern tarija basin west argentina five paleoclimatic stages have been defined paleoclimatic stage i tournalism visean early carboniferous is characterized by temperature and humid preglacial conditions as evidencedin the el raton and maliman formations calingasta uspallata basin plant remains of archeosigillaria and lepidodendropsis zone are present in both units the paleoclimatic stage ii namurian early westphalian middle carboniferous comprises widespread glacial deposits including glaciomarine sequence in the westernmost basins calingasta uspallata western paganzo san rafael and tepuel and terrestrial tillites and glaciolacustrine fine clastics in some areas of the paganzo basin fossils of the levipustula fauna are distinctive in the glaciomarine deposits of this stage and in the overlying postglacial fine clastics of the basal portion of stage iii substage iiia the paleoclimatic stage iii of middle carboniferous late westphalian age corresponds to postglacial transgressions that flooded the previously glaciated shelves in the calingasta uspallata and tepuel basins terminal glaciolacustrine deposits substage iiia indicate of the demise of glacial conditions and coal measures of fluvial affinity in the paganzo basin substage iiib probably this postglacial stage was characterized by high humidity and moderate temperatures this stage is paleobiologi defined by a floral assemblage known as nbg nothorhacopteris botrychiopsis and ginkgophyllum the paleoclimatic stage iv late carboniferous stephanian early permian corresponds to a time interval characterized by seasonally dry climates and a progressive amelioration in humidity clear evidence of these climatic conditions is present in several localities in the paganzo basin the first astherothecae and glossopteris leaves are found finally paleoclimatic stage v middle late permian is dominated by red beds thick eolian sequences and saline lake facies deposited under arid to semi arid conditions coeval volcanism derived from the west is expressed by interbedded tuffs and agglomerates calingasta uspallata paganzo and san rafael basins

extensional tilt blocks on miranda evidence for an upwelling origin of arden corona subparallel ridges and troughs in the outer belt of arden corona on the uranian satellite miranda are interpreted as tilt blocks formed by extension and normal faulting fault scarps generally face outward from the corona exposing dark material in the subsurface reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of 50 local extension reaches 70 extremely high in comparison to previous estimates of strain on icy satellites a rise adjacent to the rift zone is modeled as flexural and indicates an effective elastic lithospheric thickness of 2 km at the time of flexure the assumption that faulting has significantly weakened the lithosphere suggests a mechanical lithosphere thickness of 5 to 10 km corresponding thermal gradients in a frictionally controlled ice lithosphere are 8 to 20 k km 1 and lithospheric tensional strength is 0 4 to 1 8 mpa normal faulting in arden corona indicates that internal upwelling likely formed the corona and the outward facing direction of faults is consistent with such a model an upwelling origin of miranda s coronae eliminates the need to invoke catastrophic breakup and reaccretion of the satellite as an explanation for its surface geology

tectonic rotations in the late palaeozoic continental margin of southern south america determined and dated by palaeomagnetism summary detailed palaeomagnetic studies of late palaeozoic rocks exposed in the uspallatacalingasta valley region located at about 32 s 69 5 w in the argentine andean chain have been recently accomplished previous results are discussed in valencio vilas 1985 and rapalini et al 1989 the most recent studies were carried out mainly on the thick sequences of late early permian to late permian rhyolites and ignimbrites assigned to the tambillos and horcajo formations both formations yielded palaeomagnetic pole positions p15 319 6 e 78 9 s7 n 16 k 33 5 ags 6 5 and p17 264 8 e 72 4 s n 26 k 6 4 ag5 12 respectively concordant with the late palaeozoic path of south america preliminary palaeomagnetic results from the middle carboniferous hoyada verde formation exposed in the same region suggest that these rocks carry a synfolding magnetization acquired during the late carboniferous as the palaeomagnetic pole position computed from partially corrected remanence directions c6 356 2 e 41 9 s d1 8 3 02 6 0 agrees with the late carboniferous poles from cratonic areas of south america this concordant position of c6 definitely rules out the possibility of a late palaeozoic allochthony of this section of the argentine andean chain the discordant positions previously found in late carboniferous and early early permian rocks of this region are interpreted as caused by large clockwise crustal block rotations that occurred not later than the late early permian a tectonic model is proposed to explain these rotations which suggests that they were associated with strike slip displacements parallel to the western continental margin of south america caused by an oblique subduction of the proto pacific plate during the early permian many tectonic and geologic observations fit this model the concordant position of c6 also suggests that a complex pattern of crustal block rotations should have developed in this continental margin other palaeomagnetic data suggest that similar rotations may have taken place in other areas of the argentine andean chain in the early permian

sinker tectonics an approach to the surface of miranda images of the uranian moon miranda show three areas of complex terrain trapezoidal to ovoid in shape with no previously known counterpart these features called coronae are characterized by an inner core of intersecting ridges and troughs surrounded by a series of subparallel and concentric bands two of the proposed explanations for these tectonic features involve mantle convection driven by density anomalies the present study determines the surface stresses induced by such density anomalies and their expected surface expression miranda is modeled as having a rigid core surrounded by a mantle capable of viscous flow which is overlain by a thin elastic lithosphere the density anomaly is modeled as a point mass representing the sinker or riser the model is developed in a spherical coordinate system having axial symmetry about a 0 axis passing through the sinker the flow field set up by the sinking or rising mass is expressed in terms of a stream function using legendre sums streamlines are functions of the position of the mass anomaly and the radii of the core mantle and mantle lithosphere boundaries only magnitudes of the stream function depend upon the size of the mass anomaly its local gravitational field and the mantle lithosphere radius the stresses on the base of the lithosphere are then determined from the equations of motion the viscosity of the mantle material has no effect on the stresses produced at any given time but does control the velocity of the anomaly expressions for displacements and stresses in the elastic shell are developed as legendre sums and coupled to the viscous mantle solution with appropriate boundary conditions the stresses derived yield a pattern of expected tectonic expression this tectonic style varies with the radius of the body for a small body surface stresses are dominant in the area above the mass anomaly while farther away stresses at the base of the lithosphere control the tectonics directly over a sinker and extending outward 15 is a zone of both latitudinal and longitudinal surface compression which produces folding and thrust faults with no preferred orientation beyond 15 longitudinal stresses at the base of the lithosphere are extensional while latitudinal stresses are compressional producing a zone of folding and thrusts concentric about the sinker stresses induced by a riser are opposite in sign and predict extensional features with the same orientation as the compressional features predicted for a sinker stress magnitudes generally decrease with distance from the sinker and also decrease with both increasing sinker depth and lithosphere thickness the predictions of the sinker model are in good agreement with the tectonic styles of the banded and ridged terrains of miranda as determined from the topography as imaged by voyager 2 this agreement supports the idea that the coronae on miranda were produced by dense masses originally located near the surface that sank into miranda s interior for larger bodies the stresses at the surface and base are nearly equal longitudinal stresses are greater than latitudinal stresses resulting in compressional features with a preferred orientation radial to the sinker location the changeover in tectonic styles occurs at a planetary radius of approximately 1500 km

the dark side of iapetus abstract this paper presents new photometric and spectrophotometric observations of the dark leading hemisphere of saturn s satellite iapetus spectrophotometry from 0 3 1 0 um may 1979 shows the dark hemisphere to be very red similar to a few asteroids and the moon but with no spectral features attributable to olivine or pyroxene near infrared spectrophometry in the regions 1 4 2 5 um may 1981 and 3 0 3 8 um february 1981 reveals water ice absorption bands probably resulting from the polar caps intruding onto the dark hemisphere the reflectance of iapetus is unlike that of carbonaceous chondrites or c type asteroids and most closely resembles the reflectance and low albedo of carbonaceous organic residue from the murchison c2 carbonaceous chondrite the murchison material has the same red slope and a probable spectral feature near 0 6 um seen in iapetus data three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data the favored hypothesis is that debris from phoebe or other unknown outer satellites of saturn impacts the dark hemisphere of iapetus as poynting robertson drag causes the debris to spiral toward saturn the high velocity impacts preferentially remove ice from the satellite s surface causing enrichment of included carbonaceous material intrinsic to iapetus the reflectance of phoebe itself is significantly different from that of iapetus suggesting that relatively little phoebe debris lies on the dark hemisphere there remains the possibility that the impacting debris originates from another body of composition similar to the murchison residue and that this material is exposed on the surface of iapetus

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

red material on the large moons of uranus dust from the irregular satellites abstract the large and tidally locked classical moons of uranus display longitudinal and planetocentric trends in their surface compositions spectrally red material has been detected primarily on the leading hemispheres of the outer moons titania and oberon furthermore detected h2o ice bands are stronger on the leading hemispheres of the classical satellites and the leading trailing asymmetry in h2o ice band strengths decreases with distance from uranus we hypothesize that the observed distribution of red material and trends in h2o ice band strengths results from infalling dust from uranus irregular satellites these dust particles migrate inward on slowly decaying orbits eventually reaching the classical satellite zone where they collide primarily with the outer moons the latitudinal distribution of dust swept up by these moons should be fairly even across their southern and northern hemispheres however red material has only been detected over the southern hemispheres of these moons during the voyager 2 flyby of the uranian system subsolar latitude 81 s consequently to test whether irregular satellite dust impacts drive the observed enhancement in reddening we have gathered new ground based data of the now observable northern hemispheres of these satellites sub observer latitudes 17 35 n our results and analyses indicate that longitudinal and planetocentric trends in reddening and h2o ice band strengths are broadly consistent across both southern and northern latitudes of these moons thereby supporting our hypothesis utilizing a suite of numerical best fit models we investigate the composition of the reddening agent finding that both complex organics and amorphous pyroxene match the spectral slopes of our data we also present spectra that span l l bands 2 9 4 1 m a previously unexplored wavelength range in terms of spectroscopy for the uranian satellites and we compare the shape and albedo of the spectral continua in these l l band data to other icy moons in the jovian and saturnian systems additionally we discuss possible localized enhancement of reddening on titania subtle differences in h2o ice band strengths between the southern and northern hemispheres of the classical satellites the distribution of constituents on miranda and the possible presence of nh3 hydrates on these moons in closing we explore potential directions for future observational and numerical modeling work in the uranian system

evidence for a neoglacial advance of the boundary glacier banff national park alberta direct evidence for an early neoglacial advance in the canadian rocky mountains is presented radiocarbon dates from buried peat and tree remains at boundary glacier suggest limiting dates for this advance of between 3800 and 4200 years bp these data from boundary glacier are consistent with previously published dates for the onset of the neoglacial and an early neoglacial advance

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

characteristics of the bergschrund of an avalanche cone glacier in the canadian rocky mountains etude sur le terrain de la rimaye d un petit glacier dans les rocheuses canadiennes en particulier on analyse les effets de la topographie du lit rocheux les effets de la fonte des ecoulements et des taux de depot et de metamorphisme de la neige

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

terrestrial or waterlain glacial diamictites three case studies from the late precambrian and late ordovician glacial drifts in west africa abstract three examples of extensive diamictites within glacial sequences well exposed in the sedimentary cover of the west african cratonic platform are described they belong to the late precambrian and upper ordovician glacial periods and the paleogeography is summarized the late precambrian diamictites of the jbeliat group in adrar of mauritania displays characteristics of tillite deposited as lodgement or melt out till detail studies on structure clast shape nature and fabric texture in thin section clay mineralogy and carbonate content are given and discussed in order to delimitate useful criteria for tillite identification compared to this first example the two other diamictites from the late precambrian bakoye group in western mali and from the upper ordovician tichit group in southeastern mauritania have obviously been deposited in an aquatic environment waterlain glacial diamictites by the action of ice rafting bottom current and flow processes these examples show that for such ancient deposits sedimentological interpretations are partly solved by broad scale stratigraphical relationships however detailed sedimentological analyses remain essential for precise facies identification especially structural and petrographic studies must be encouraged in the lights of modern glaciodynamic processes

central pit and dome craters exposing the interiors of ganymede and callisto central pit craters on the large icy satellites ganymede and callisto are an unusual crater class perhaps related to the unusual properties of water ice the detailed morphology and dimensions of pit crater features differ from those of smaller normal complex craters on these two satellites pit crater depths appear to be constant regardless of diameter rim collapse is also restricted relative to that in lunar craters or smaller ganymede craters the floors of pits in craters larger than 60 km are occupied by smooth bright domes pit to crater and dome to crater diameter ratios increase linearly with crater diameter and are indistinguishable on ganymede and callisto and with terrain type or surface longitude the floors and central structures of young bright rayed pit craters such as osiris are covered by a thin uniformly bright impact melt or frost deposit thus domes and pits form rapidly on the time scale of the impact itself rather than by long term postimpact intrusion or extrusion the bright domes in pit craters are most simply explained as the uplift and exposure of relatively ice rich material from depths of 3 5 to 5 km during impact this process is almost directly analogous to the uplift and exposure of anamolous deep seated material observed in terrestrial and lunar craters the unusual pit morphology on icy satellites may be the result of impact into crust that is mechanically much weaker at shallow depth than on rocky bodies such as the moon because crater morphology is strongly dependent on ice rock composition the similarity of pit and dome dimensions on ganymede and callisto indicates that the structure and rheology of the crusts of these bodies down to depths of 10 km are very similar and have been for several b y pit crater morphology indicates that the crusts of both satellites are probably ice rich and differentiated

the shapes of small satellites abstract improved measurement techniques allow quantitative testing of the physical significance of the shapes of small satellites such as the possible occurrence of equilibrium ellipsoid forms shapes of the small satellites of mars jupiter saturn and uranus have been measured using limb coordinates from spacecraft images limb derived ellipsoidal models can measure volumes of irregular objects accurately ellipsoidal models of phobos and deimos derived from limb coordinates are nearly identical to those obtained independently from stereogrammetry duxbury and callahan 1988 these ellipsoidal approximations however are incomplete descriptions of the shapes of small satellites in that average residuals are much larger than measurement errors ellipsoidal models of eight small satellites compared with equilibrium ellipsoids show that shapes of even moderately irregular satellites are poor predictors of mean densities icy satellites smaller than mean radius r m 150 km are irregularly shaped and have limb roughnesses of several percent of mean radius rms residuals 03 08 r m there is no trend in roughness with size below r m 150 km larger icy satellites are ellipsoidal and have limb roughness below 0 01 r m rocky satellites of r m 6 110 km are also irregularly shaped the only larger rocky satellites are the moon and io r m 1740 and 1820 km which have roughnesses well below 0 01 r m data on rocky satellites combined with published data for ceres and juno millis et al 1981 1987 suggest a gradual transition from irregular to ellipsoidal rocky objects limb topography and images suggest that the small satellites retain impact scars of diameter of up to 1 7 times the satellite mean radius these large indentations are the primary difference in shape between small and large satellites

the marine upper palaeozoic in patagonia tepuel genoa basin chubut province argentina 85 years of work and future prospects abstract argentina is a special place to study late palaeozoic life and environmental change because of the excellent exposures of late palaeozoic sedimentary sequences in particular patagonia has an almost continuous late palaeozoic succession containing well preserved faunal assemblages characterized by both strong endemism and distinctive palaeobiogeographic links to australia and northeast asia in this contribution an overview of the current knowledge of the invertebrate faunas of patagonia and their biostratigraphic and palaeobiogeographic significance are presented along with comments on the future prospects of research in the light of new findings the late palaeozoic outcrops in central western patagonia belong to the tepuel genoa basin chubut province argentina then located in southwestern gondwana during the late palaezoic in this basin the succession is 6000 m thick and constitutes a continuous and complete succession from the lower carboniferous to lower permian as such it has the potential to serve as an important reference section for regional and intercontinental correlations the marine late palaeozoic of patagonia has yielded abundant and well preserved representatives of most invertebrate groups brachiopods bivalves gastropods cephalopods hyolithids pelmatozoans ostracods and cnidarians recently studies of the patagonian faunas have resulted in different opinions on the ages of the faunas biostratigraphic correlation is complex due to strong faunal provincialism for this reason there are several hypotheses concerning the biostratigraphic zonation in the basin since 1920 when studies of late palaeozoic strata in patagonia were first carried out numerous papers on stratigraphic palaeogeographic and taxonomic subjects have been published but our knowledge of carboniferous permian fossils from the tepuel genoa basin is still incomplete at present we are attempting to integrate and calibrate the different faunal associations with a view to achieving a unified biostratigraphic biozonation scheme and hence a much improved understanding of the palaeobiogeographic relationship of patagonian faunas with those from western argentina and other continents currently detailed stratigraphic and palaeontological research is being done in the type section of the tepuel genoa basin the aim of our studies is to integrate all partial sequences exposed throughout the basin and to propose a biostratigraphic chart based on key invertebrate taxa once this goal is achieved a global correlation can be conducted especially with other sections in gondwana and the arctic

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

coordinates of features on the galilean satellites control nets of the four galilean satellites have been established photogrammetrically from pictures taken by the two voyager spacecraft during their flybys of jupiter in 1979 coordinates of 504 points on io 112 points on europa 1547 points on ganymede and 439 points on callisto are listed selected points are identified on u s geological survey maps of the satellites measurements of these points were made on 234 pictures of io 115 pictures of europa 282 pictures of ganymede and 200 pictures of callisto the systems of longitude were defined by craters on europa ganymede and callisto preliminary solutions have been found for the directions of the axes of rotation of the galilean satellites new mean radii have been determined as 1815 5 km for io 1569 10 km for europa 2631 10 km for ganymede and 2400 10 km for callisto

solar cycles recorded in carboniferous glacimarine rhythmites western argentina relationships between climate and sedimentary environment abstract a carboniferous glacial episode has been widely known in the western part of argentina since ca 1910 in some sections it is associated with rhythmic sedimentation one of those rhythmite successions is interpreted as composed by varves annually deposited sedimentary cycles accumulated in a glacimarine environment it is further analyzed as a time series searching for cyclic signals several localities show varve like successions but only a few of them are not disturbed by reworking of bottom currents the rio francia section san juan argentina is well suited for varve counting as no current produced structures are recognized through the rhythmite interval and outcrops are good enough for counting directly in the field five varve types which show differences mainly in thickness grain size and dropstone frequency are recognized internally they are mostly symmetric distinguishing them from traditional normally graded varves a feature that has also been observed in holocene glacimarine varves the different varve types indicate varying positions with respect to the ice front because of disturbances or lack of well defined textural or colour contrasts only the three varve types with intermediate thicknesses were counted three units including 1028 690 and 465 varves were measured and then analyzed as time series in order to detect cyclic signals some differences in the quality of the cyclic signals can be seen in spectral analyses depending on the main type of the varve that composes the unit however a peak around 12 yrs can be seen in most of the spectra and is interpreted as the sunspot cycle record a secondary peak near 24 26 yr also may be related to this phenomenon hale cycle four major cycles recognized in the field but not in the spectra that represent major glacial advances and retreats can also be related to a solar periodicity of 2500 3000 yr the recognition of sunspot cycles in these carboniferous varves is not unusual as they are found in other ancient varve successions random processes typified by the distribution of dropstones played an important role in disturbing the climatic signal in this sedimentary environment the random process of sediment transport and deposition by ice rafting disturbs the cyclic climatic signal mainly in proximal varve successions increased water motion and distance to the source of sediment toward the open sea tend to produce more homogeneous very fine grained distal varves eventually causing the loss of varve like appearance the remaining varves located at intermediate positions with respect to the glacio related sediment source seem to be the best suited for recording climatic cyclicity as shown by spectral analyses

paleomagnetism of the carboniferous tepuel group central patagonia argentina samples of the carboniferous glaciogenic sequences of the tepuel group western central patagonia argentina were collected from 23 sites in two localities sierra de tepuel 43 7 s 70 5 w and las salinas 43 2 s 70 3 w most were fine sandstones to siltstones of late visean to westphalian age a characteristic remanent magnetization was determined in most sites by alternating field and or thermal cleaning at sierra de tepuel all samples were partially overprinted by a secondary magnetization apparently related to mesozoic magmatic activity in this area however site mean directions of the characteristic remanence from both localities passed a tilt test indicating a pretectonic pre early permian magnetization isothermal remanent magnetization experiments showed magnetite as the main and often the only magnetic carrier while thin section analyses indicated a detrital origin for this mineral suggesting a depositional or postdepositional magnetization the paleomagnetic pole for the tepuel group namurian westphalian at 316 1 e 31 7 s number of sites n 16 minor and major semi axes of confidence p 15 0 m 16 0 is considered a key pole for the middle carboniferous of south america and gondwana confirming the apparent polar wander path for the supercontinent for which the pole moved from central to southern africa in the early carboniferous followed by a rapid motion from southern africa to antarctica during the late westphalian the agreement of the tepuel pole with this gondwanan path confirms that patagonia was already part of south america by the middle carboniferous

facies and architecture of a carboniferous grounding line system from the guandacol formation paganzo basin northwestern argentina abstract new outcrops of middle carboniferous glacigenic deposits found in the guandacol formation western paganzo basin are described in this paper the study locality of los pozuelos creek northwestern argentina includes coarse grained diamictites rhythmites laminated pebbly mudstones and shales that represent an expanded column of the gondwanic glaciation in this region thirteen lithofacies recorded at the measured section have been grouped into three facies associations facies association i is composed of coarse grained massive and stratified diamictites lithofacies dmm dms dmg dcs laminated siltstones with dropstones fld and interstratified sandstones and mudstones fl sr these rocks represent both tillites and resedimented diamictites closely associated to small water bodies where laminated siltstones with dropstones and stratified sandstones and mudstones were deposited facies association ii comprises couplets of matrix supported thinly bedded diamictites dmld and laminated mudstones with dropstones fld this facies association results from the combination of three different processes subaqueous cohesionless debris flows coeval rainout of ice rafted debris and settling of fine grained particles from supension finally facies association iii is made up of laminated mudstones without dropstones thin marl levels and scarce fine to very fine grained sandstones this assemblage clearly suggests sedimentation in a deep marine environment below the wave base the architecture of the glacigenic deposits has been investigated using photomosaic panels the geometry of the depositional bodies and facies suggest that los pozuelos creek outcrops exhibit a well preserved three dimensional example of a grounding line system in particular three different subenvironments of a morainal bank were interpreted a bank front a bank core and a bank back the bank front assemblage is characterized by coarse grained mainly resedimented diamictites grading laterally to prograding clinoforms composed of interbedded matrix supported thinly bedded diamictite and mudstones the bank core assemblage is formed by a stacking of coarse grained diamictites where at least five major erosional surfaces bounding four multistory diamictite bodies can be recognized finally the bank back assemblage corresponds to discontinuous intervals of striated lodgement till and coarse grained resedimented diamictites showing important post depositional deformation the retrogradational stacking of the morainal banks indicate an overall glacial retreat and a glacioeustatic sea level rise erosional surfaces at the base of each morainal bank suggest intervening short term episodes of ice advance the new data presented here confirm the existence of true tillites in western paganzo basin and suggest several at least four pulses of glacial advance and retreat during the namurian glaciation in the region and permit a more refined interpretation of the glacial deposits in the huaco area

geological terrains and crater frequencies on ariel the southern hemisphere of ariel a satellite of uranus can be divided into several terrain types data on the size frequency distribution of craters for those different terrain types indicate that these terrains formed over a relatively short period of time much information on ariel s geological history can be gained from these data

stratigraphy and palynology of a late paleozoic glacial paleovalley in the andean precordillera argentina fil limarino carlos oscar consejo nacional de investigaciones cientificas y tecnicas oficina de coordinacion administrativa ciudad universitaria instituto de geociencias basicas aplicadas y ambientales de buenos aires universidad de buenos aires facultad de ciencias exactas y naturales instituto de geociencias basicas aplicadas y ambientales de buenos aires argentina

environmental controls on alpine cirque size pleistocene alpine cirques are emblematic landforms of mountain scenery yet their deceptively simple template conceals complex controlling variables this comparative study presents a new database of 1071 cirques the largest of its kind located in the french eastern pyrenees it is embedded in a review of previous work on cirque morphometry and thus provides a perspective on a global scale first order cirque attributes of length width and amplitude were measured and their power as predictors of climatic and lithological variables and as proxies for the duration of glacier activity was tested using anova simple and multiple linear regression and their various post hoc tests conventional variables such as cirque aspect floor elevation and exposure with respect to regional precipitation bearing weather systems are shown to present some consistency in spatial patterns determined by solar radiation the morning afternoon effect and wind blown snow accumulation in the lee of ridgetops this confirms in greater detail the previously encountered links between landforms and climate a special focus on the influence of bedrock lithology a previously neglected nonclimatic variable highlights the potential for spurious relations in the use of cirque size as a proxy of past environmental conditions cirques are showcased as complex landforms resulting from the combination of many climatic and nonclimatic variables that remain difficult to rank by order of importance apart from a few statistically weak trends several combinations of different factors in different proportions are shown to produce similar morphometric outcomes suggesting a case of equifinality in landform development

oberon color photometry from voyager and its geological implications abstract three primary terrains are exposed at the surface of oberon average cratered terrain bright crater rays and prominent dark deposits often seen on but not restricted to crater floors we have applied hapke s 1986 icarus 67 264 280 photometric model to voyager imaging and earth based observations to determine photometric properties and colors of oberon s terrains and compare the results with those for the other uranian satellites all terrains on oberon exhibit photometric roughnesses 21 that are lunar like and similar to average global photometric roughnesses of titania and umbriel the asymmetry factors are backscattering for all terrains 0 35 g 0 20 and fall within the observed range for other uranian satellites at visual wavelengths g becomes more backscattering with decreasing single scattering albedo 0 25 0 0 61 the brightest materials on oberon are relatively neutral in color typical of materials covering other uranian satellites but the violet clear and green clear albedo ratios for the darkest terrains on oberon are atypically large for uranian satellites the variation can be modeled in terms of a binary mixture of low albedo and high albedo materials having slightly different colors oberon s leading hemisphere is dominantly covered with dark surface materials identical in color to dark deposits on crater floors while materials on the trailing hemisphere are richer in a spectrally neutral icy component with dark materials occurring in small irregular patches bright ray craters appear to have excavated into a relatively cleaner spectrally neutral icy crust dark materials at the surface may be effusive flood deposits a dark layer below the icy crust which is more exposed on the leading hemisphere due to preferential erosion by impacts or possibly exogenic in origin

breaking up is hard to do global cartography and topography of pluto s mid sized icy moon charon from new horizons abstract the 2015 new horizons flyby through the pluto system produced the first high resolution topographic maps of pluto and charon the most distant objects so mapped global integrated mosaics of the illuminated surface of pluto s large icy moon charon have been produced using both framing camera and line scan camera data including four color images at up to 1 47 km pixel scales showing the best resolution data at all areas of the surface digital elevation models dems with vertical precisions of up to 0 1 km were constructed for 40 of charon using stereo imagery local radii estimates for the surface were also determined from the cartographic control network solution for the lorri framing camera data which validate the stereo solutions charon is moderately cratered the largest of which is 250 km across and 6 km deep charon has a topographic range over the observed hemisphere from lowest to highest of 19 km the largest topographic amplitude of any mid sized icy body including ceres other than iapetus unlike saturn s icy moons whose topographic signature is dominated by global relaxation of topography and subsequent impact cratering large scale tectonics and regional resurfacing dominate charon s topography most of charon s encounter hemisphere north of the equator oz terra is broken into large polygonal blocks by a network of wide troughs with typically 3 6 km relief the deepest of these occur near the illuminated pole and are up to 13 km deep with respect to the global mean radius the deepest known surfaces on charon the edge of this terrain is defined by large tilted blocks sloping 5 or so the crests of which rise to 5 or 6 km above charon mean the highest known points on charon the southern resurfaced plains vulcan planitia consist of rolling plains locally fractured and pitted that are depressed 1 km below the mean elevation of the disrupted northern terrains of oz terra that comprise much of the northern hemisphere but 2 2 5 km below the surfaces of the blocks themselves these plains roll downward gently to the south with a topographic range of 5 km the outer margins of vulcan planitia along the boundary with oz terra form a 2 3 km deep trough suggesting viscous flow along the outer margins isolated massifs 2 4 km high also flanked by annular moats lie within the planitia itself the plains may be formed from volcanic resurfacing of cryogenic fluids but the tilted blocks along the outer margins and the isolated and tilted massifs within vulcan planitia also suggest that much of charon has been broken into large blocks some of which have been rotated and some of which have foundered into charon s upper mantle now exposed as vulcan planitia a history that may be most similar to the disrupted terrains of ariel

topography and geology of uranian mid sized icy satellites in comparison with saturnian and plutonian satellites newly processed global imaging and topographic mapping of uranus s five major satellites reveal differences and similarities to mid sized satellites at saturn and pluto three modes of internal hea

radiometric performance of the voyager cameras the voyager imaging experiment provided high quality data of jupiter and the galilean satellites with the two flyby trajectories in march and july of 1979 moderately accurate radio metric measurements have been made using these data this paper evaluates the radiometric results and describes the inflight and ground geometric and radiometric correction factors the radiometric quantities of intensity i and geometric albedo i f are derived and scaling factors for each of the filters are tabulated for correcting the calibrated data from the image processing laboratory at jpl in addition the key characteristics of both voyager 1 and voyager 2 cameras are tabulated

patterns of late paleozoic glacial sedimentation on the southeast side of the parana basin brazil abstract during the late paleozoic glaciation glaciers moved from southern africa over a platform composed of crystalline and sedimentary rocks into the subsiding parana basin of southeastern brazil in each successive glacial advance the platform was eroded and is marked by crescentic gouges striae roches moutonnees grooves and glacially modified valleys the glacial sediments which are found on the platform in southeastern brazil and margins of the parana basin were deposited from grounded ice and are termed terrestrial these sediments which are best exposed in the northern part of the study area are composed of supraglacial deposits such as layers of diamictite flow tillite interbedded with sandstones and minor amounts of lodgement tillite the supraglacial deposits are frequently faulted and the sandstones show pull apart structures and abnormal dips these features and others suggest that ice retreat in the terrestrial environment was primarily by down wasting the glaciogenic sediments found within the subsiding parana basin are termed basinal even though it is not certain that they were all deposited in a subaquatic environment they are composed primarily of sandstones siltstones shales and mudstones interbedded with massive and laminated diamictites it is suggested that the massive diamictite was deposited from the base of the advancing glaciers by basal melting during ice retreat from water filled parts of the basin unstable masses of glaciogenic debris flowed down slope resulting in layered debris flows and in some instances chaotic debris flows which may have been triggered by subaquatic slupms and slides as the ice continued to retreat to the margin of the basin a complex of subaquatic outwash including deltaic sands was deposited minor varvites were deposited in shallow restricted embayments in the shoreline which were flooded with fresh glacial meltwaters deposits of retreat including the varvites interfinger with marine fossiliferous sediments which suggests that the water level in the basin was rising during deglaciation it is not known how may times glaciers advanced into the parana basin but recent studies show that there were at least nine glaciations in the northern part of this study area covering a time span of from 10 to 35 million years

the uranian satellites water ice on ariel and umbriel abstract new near infrared reflectance spectra are presented for ariel and umbriel water ice on the surface of ariel and umbriel is verified from spectral signatures in the 2 m region however the weaker bands in umbriel s spectrum indicate that its surface is significantly different from ariel either in degree of contamination with dark material or in microstate umbriel may have a lower albedo than ariel titania and oberon and therefore may have a diameter comparable to that of titania

facies and preservation of glaciogenic sequences from the varanger ice age in scandinavia and other parts of the north atlantic region abstract thickness and facies variations and state of preservation of varangerian glacial sequences are related to the geotectonic settings of the depositional environments from stable continental platform sites only thin remnants of a single glacial advance retreat sequence are preserved in fault basins thickness and lithofacies vary in response to fault movements in the continental platform to shelf region the sequence ranges from thin beds of one single glacial event on the craton to up to some hundred meterswith several glacial advance retreat cycles from shelf sites the stable and slowly subsiding shelf environment has given rise mainly to a thin sequence of diamictite overlain by mudstone in more rapidly subsiding shelves several glacial advance retreat units are preserved together with interstadial and interglacial sediments with total thickness up to several hundred meters the shelf slope environment is probably represented by up to 3000 m thick diamictites the preservation potential during the glacial epoch is primarily controlled by the property of glacier ice sheets to be either erosive or depositional the long term preservation is determined by various factors controlling relative sea level changes the state of preservation during orogenic processes generally decreases from sequences on platform sites to those on distal shelves and shelf slopes

global resurfacing of uranus s moon miranda by convection miranda an icy moon of uranus is one of the most visually striking and enigmatic bodies in the solar system three polygonal shaped regions of intense deformation dubbed coronae dominate the surface of miranda here we use numerical methods to show that sluggish lid convection in miranda s ice shell powered by tidal heating can simultaneously match the global distribution of coronae the concentric deformation pattern and the estimated heat flow during formation the expected rheological conditions in miranda s ice shell lead to the development of low order convection that produces surface deformation patterns similar to those observed we find that satellite core size strongly controls convection geometry and that loworder convection patterns are much more stable for core radii less than half the satellite radius

crater formation and modification on the icy satellites of uranus and saturn depth diameter and central peak occurrence depth diameters d d for fresh craters on the intermediate sized icy satellites of uranus and saturn have been determined using photoclinometry and shadow lengths and are compared with similar measurements on the terrestrial planets simple bowl shaped craters on icy satellites including those on miranda for which the highest resolution data are available are systematically 20 40 shallower than on the terrestrial planets this pronounced difference between crater depths on icy and rocky surfaces indicates that differences in impact velocity or surface gravity are not as important as the differences in mechanical properties between ice and rock in controlling simple crater morphology experimental impact studies indicate that differences in material properties such as angle of internal friction can control crater depth alternatively breccia lenses may be thicker in icy satellite simple craters complex craters on the icy satellites become significantly deeper with increasing crater diameters unlike complex craters on terrestrial planets which are nearly constant in depth central peaks and hence floor rebound are also volumetrically and morphologically more prominent than wall slumping rim collapse on the icy satellites the magnitude of viscous relaxation of very large craters e g herschel and odysseus on the icy satellites can be estimated from extrapolation of the d d fits at smaller crater diameters the transition diameter from simple to complex morphology is inversely correlated with gravity as it is on the terrestrial planets but at significantly smaller diameters than would be expected from a simple extrapolation of the terrestrial trend thus crater modification especially floor rebound is easier to initiate on icy satellites estimated effective cohesions for shocked icy material are lower by a factor of 10 20 relative to rock although estimated effective viscosities are similar the distinct systematic differences between crater morphology on icy and rocky worlds indicate that gross material property differences between rock and ices play a key role in crater formation and modification but gravity is still the primary driving force

carboniferous permian palynostratigraphy of west australian marine rift basins resolving tectonic and eustatic controls during gondwanan glaciations abstract the longest interval of cold climate in earth s phanerozoic history spanned some 55 million years from the namurian late carboniferous to the kungurian early permian when glaciation affected much of high latitude gondwana uncertainty surrounds the timing of glaciation s and the frequency of interglacial episodes ice volumes and the location of ice centres this is because the glacial record is preserved predominantly within marine strata deposited in intracontinental rift basins marginal to onshore ice centres on uplifted basement highs the direct stratigraphic record of glaciation is meagre on adjoining basement highs and extremely difficult to date many basins contain broadly similar threefold lithostratigraphic successions of lowermost glaciomarine diamictite facies middle shales and uppermost carbonate and sandstone rich commonly coal bearing deltaic strata in the absence of absolute age control and infrequent presence of macrofossils such deglaciation sequences are widely assumed to be correlative from basin to basin recording gondwanan deglaciation s and a world wide glacioeustatic sea level rise a newly compiled biostratigraphic database for west australia using first appearance datums of spore pollen types allows correlation of late palaeozoic siliciclastic successions between seven basins bonaparte canning carnarvon collie gunbarrel northern and southern perth basins these extend some 3800 km along australia s western continental margin adjacent to the west australian shield all but the gunbarrel basin contain tripartite glacially influenced successions diamictite shale sandstone biostratigraphic data reveal sharp differences in ages and stratigraphic distributions and marked variations in the thickness of coeval units diamictite shale sandstone successions accumulated diachronously from basin to basin recording a dominant tectonic control on subsidence and relative sea level middle shale units are not exact correlatives between basins and thus are unlikely to simply represent widespread climatically controlled glacioeustatic events instead they are argued to record high relative sea levels during times of maximum synrift subsidence this tectonostratigraphic model can be applied to other intracontinental rift basin successions across gondwana