depositional controls on glacial facies associations in a basinal setting late proterozoic amadeus basin central australia abstract diamictites many established as being glacial in origin are globally distributed in late protezoic rocks their widespread occurrence is important in that it implies that significant climatic events occurred during the period between 900 and 600 ma however because of the age of the rocks correlations are poor and it is difficult to establish in a convincing manner whether these sediments were deposited synchronously during a major global ice age or if each occurrence of diamictite relates to local climatic or tectonic events since the biostratigraphy of these rocks is limited and only a small number of radiometric ages are available an alternative approach to correlation is necessary the most promising approach currently available appears to be the application of sequence stratigraphy and the careful evaluation of facies associations on a site by site basis before attempting global correlations late proterozoic diamictites occur in a number of intracratonic basins in a broad belt across the ancient australian craton two late proterozoic diamictite units both previously identified as glacial in origin are exposed in the intracratonic amadeus basin of central australia the areyonga formation the older of the two units forms the basis of this study the areyonga formation is contained within a major depositional sequence the areyonga sequence the bounds of which were determined by basin dynamics and eustatic sea level changes induced by an ice age of global dimensions during deposition of this sequence three major sedimentological systems were in operation along the northern margin of the basin glaciation dominated sedimentation in the south large volumes of sediment were deposited in a shallow marine setting whilst to the west braided streams supplied sediment to a major coastal plain and delta system all three systems operated within the same sea level and basinal constraints but each contributed sediment to the basin independently the glacial sediments of the areyonga sequence were deposited from a relatively small ice cap lying between the amadeus basin and the ngalia basin to the north sediments were deposited from two tongues of ice that extended about 100 km into the northeastern corner of the amadeus basin glacial sedimentation occurred in three stages determined by the initial fall and subsequent rise in eustatic sea level as the ice sheet grew and declined initially thick massive basal till units were deposited on an erosion surface intersected by subglacial and ice marginal channels they were then followed by thinner till units separated by channel like sandstone and conglomerate with associated boulder surfaces or concentrations that were deposited by an extensive subglacial drainage network finally the subglacial deposits grade into ice proximal and ice distal shallow marine sediments deposited in part by mass movement sedimentation appears to have been terminated by a major sea level fall in the ooraminna sub basin to the east rocks originally thought to have been deposited during a second glaciation appear to be part of a lowstand wedge formed during a sea level low following the areyonga glaciation a record of the second glaciation probably does not exist in the amadeus basin similarly diamictites in the inindia beds and originally correlated with the areyonga formation have been shown to belong to the non glacial lowstand wedge of the following sequence preservation of glacial sediments is most likely to occur in a basinal setting where depositional space is being actively created in the amadeus basin depositional space was created prior to deposition of the areyonga formation by subsidence following crustal extension that occurred approximately 150 m y previously the distribution of sequence boundaries and the succession of facies associations identified in the areyonga sequence provide the basis for a depositional model for glacial sedimentation during an ice age to be successful correlation of late proterozoic glacial sediments must be based on an understanding of these facies associations and their bounding depositional surfaces associations similar to those found in the amadeus basin have been documented in other proterozoic basins suggesting that the facies associations and relationships recorded in the areyonga sequence may form the basis for a generalized model for basinal sedimentation from an ice age of global significance if this is so it should be possible to determine if a sequence containing glacial sediments is part of a global climatic event or simply due to local conditions from a single site evaluation

glacial advance and retreat sequences in a permo carboniferous section central transantarctic mountains episodes of glacial advance and retreat can be recognized through analysis of vertical facies sequences in the permo carboniferous pagoda formation of the beardmore glacier area antarctica the formation includes a remarkably complete record of continental sedimentation near the terminus of a temperate glacier facies sequence is pre eminent for inferring glacial advance and retreat other important criteria are abundance and geometry of sandstone interbedded with diamictite diamictite character and nature of bed contacts using these characteristics advance and retreat sequences 5 60 m thick are recognized a sharp contact with a striated surface and erosional relief overlain by structureless diamictite lodgement till is typical of grounded ice advance grounded ice retreat is characterized by structureless diamictite lodgement till overlain by crudely stratified diamictite melt out till and then by diamictite interbedded with sandstone and conglomerate flow till and glacio fluvial or glacio lacustrine deposits gradational contacts between shale overlain by diamictite and diamictite overlain by shale characterize advance and retreat respectively in subaqueous settings pauses in sediment accumulation minor fluctuations of the ice margin and or changes in subglacial dynamics are indicated by specific features within diamictite units such as probable frost wedge casts single layer boulder beds sharp sedimentary contacts and changes in diamictite character these minor events are superimposed upon the main advance retreat cycles study of both the overall facies sequence and of individual diagnostic structures albeit in an incomplete stratigraphic record permits a distinction between major and minor advance retreat events as many as six major advance retreat cycles exist in some pagoda sections but the number of cycles present varies in different sections

strong motion records and synthetic isoseismals of the pyrgos peloponnisos southern greece earthquake sequence of march 26 1993 in this work several seismological observations are presented in order to explain characteristic features of the earthquake sequence which occurred in march 1993 in southwestern greece very close to the city of pyrgos fault plane solutions of the largest fore and aftershocks and the main shock as well as the directions at which the maximum ground accelerations were recorded suggest that this earthquake sequence has been developed by rupturing three distinct focal planes with different focal mechanisms the first focal plane located in the off shore area strikes nw se dips se and includes most of the foreshock activity the foreshock activity migrated to the northeastern part of the city of pyrgos and took place on planes with a predominant direction ne sw the main shock ofm x 5 5 occurred in a focal plane located between the two above mentioned areas strong motion records of significant shocks of the sequence show peak acceleration values on components consistent with the relevant fault plane solutions furthermore the observed macroseismic field has been compared with synthetic isoseismals computed by using a certain velocity model and the focal mechanism parameters of the main shock

controls on early permian shelf deglaciation in the karoo basin of south africa abstract the late carboniferous to early permian glacigene dwyka group has at its top three types of transitions from diamictite to postglacial mudrock in the southern karoo the type 1 transition sequence consists of clast poor carbonate rich diamictite having a sharp contact with the overlying mudrocks this diamicton accumulated slowly by rain out and sediment gravity flow processes during sedimentation the polar ice front was stabilised by a possible ice shelf collapse of the ice shelf caused rapid ice margin retreat the type 2 transition sequence consists of clast poor diamictite with sandstone bodies overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites deposition of the diamictite facies occurred during oscillations of a subpolar ice front with short stable periods of surface melting of the ice resulting in the formation of small subaqueous outwash fans the type 3 transition sequence consists of bouldery diamictite interbedded with massive or sandstone bearing diamictite overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites the sequence represents highly unstable ice front conditions and fluctuating sea levels with periods of rapid deposition probably by collapsing ice streams climatic conditions may have alternated between polar and subpolar the type 1 transition sequence is predominant in the western part and the type 3 sequence in the eastern part of the karoo basin long term controls on deglaciation was climatic warming as gondwana drifted over the pole as well as changes in land sea configuration superimposed on these were local controls such as relative sea level changes presence of deformable substrate and meltwater production

subglacial sedimentary features in late palaeozoic sedimentary rocks central victoria australia abstract a section of late palaeozoic diamictite in the bacchus marsh formation in central victoria southeastern australia contains 1 1 striated boulders with long axes tilted up glacier 2 2 layers of pebbles lacking evidence of water sorting 3 3 thin sheets and lenses of sandstone 4 4 slab like and contorted sandstone bodies cut by closely spaced step fractures 5 5 thin slabs of rhythmically bedded siltstone and claystone the boulders indicate that the diamictite was deposited by lodgement beneath moving wet based glacial ice the sandstone sheets and lenses indicate periods of rapidly increasing subglacial water pressure and the deformed sandstone bodies indicate flow of some of the newly deposited diamicton in response to shear imparted by the overlying ice the pebble layers probably formed as a moving carpet of clasts close to the controlling obstacle size of the glacier during deposition from a layer of mobile subsole debris which then halted these features indicate changes in subglacial conditions that may have led to surging behaviour by the glacier the model of pebble layer formation allows an estimate of ice sliding velocity during layer formation and thus provides a method of quantifying one aspect of ice behaviour for a pre pleistocene glacier

inter and intratill boulder pavements in the carboniferous hoyada verde formation of west argentina an insight on glacial advance retreat fluctuations in southwestern gondwana abstract two glacially abraded surfaces have been identified in the glaciomarine section of the carboniferous hoyada verde formation calingasta uspallata basin in west argentina the glacial erosion surfaces ges found in the hoyada verde section are boulder pavements one is an intertill boulder pavement developed as a single boulder layer resting on massive diamctites dmm and overlain by thick to thin bedded diamictites with ice rafted debris ird the second surface identified in recent field work can be described as an intratill boulder pavement it is also a single boulder layer but under and overlain by massive diamcitites dmm the intratill boulder pavement consists of a laterally discontinuous planar concentration of large clasts with faceted and striated upper surfaces it lies approximately 10 m below the intertill boulder pavement and is exposed on the southern closure of the hoyada verde anticline in both pavements the upper surfaces of the clasts are polished and striated the striae are parallel and subparallel to the a axes of the boulders and indicate similar paleoflow ice directions toward the s and s sw both pavements were probably originally laid down as residual gravel lag surfaces formed by the erosion of underlying diamict when wave and or tidal reworking was strong during a low stand and were subsequently abraded by advancing glaciers although both boulder pavements can be considered to be equivalent to glacial erosional surfaces ges caused by abrasion during a glacial advance and hence sequence boundaries form the sequence stratigraphic viewpoint their hierarchies are different the intertill boulder pavement demarks the demise of the mid carboniferous glacial episode in west argentina whereas the underlying intratill boulder pavement can be interpreted as the product of a minor fluctuation during the same glacial episode

glaciogenic coarse clastics in a permo carboniferous bedrock trough in india a sedimentary model abstract physical aspects of sedimentation particularly of coarse clastics within a bedrock trough in the basal 28 5 m of the permo carboniferous talchir formation in west bokaro india have been addressed herein the trough fill facies assemblage bearing abundant signs of glacial activity was eventually buried under wave agitated open nearshore and shelf sediments analysis of several sedimentary characteristics and their interrelationship help to recognize various types of glacial sediments and their frequent resedimentation through various mass flow processes it brings to light plausible transportational and depositional mechanism facies patterns in relation to the various morphometric parts of the trough reveal a changing pattern of sedimentation whereas available palaeocurrent data indicate palaeoflows converging from the flanks and turning axis parallel on the floor of the trough trough filling through fan progradation initially from single but subsequently from multipoint sources failed to impart systematic changes in bed thickness clast size and composition in the sequence this continued till the major coastal onlapping attributed to rapid deglaciation a model with predictive generalization has been proposed for coarse clastic sedimentation in fjord like coastal glacier fed troughs on the basis of observations made herein

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

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

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

a systematic classification of glacial and periglacial environments facies and deposits abstract several aspects of the deposits formed in the glacial and periglacial environments are presented in order to establish a framework that can be used in various disciplines dealing with sedimentation under glacial and periglacial conditions the almost unlimited number of different deposits are grouped into 37 types that are all described briefly most of them are also illustrated by field examples mainly from poland these 37 types are grouped within 23 facies belonging to 3 continental glacial 3 continental periglacial and 3 marine periglacial subenvironments all environments subenvironments facies and deposits are defined and presented with a hierarchic code that enables unambiguous definition attention is paid to both the general characteristics of the various deposits as they have been described by previous investigators and to specific deposits that have been studied by the present authors the factors influencing peri glacial sedimentation are discussed briefly

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

boulder beds in the glaciogenic permo carboniferous dwyka formation in south africa single layer and massive boulder beds which include boulder pavements are sporadically distributed in the glaciogenic permo carboniferous dwyka formation these matrix supported beds consist of moderately to poorly sorted rounded boulders cobbles and pebbles with a clast composition similar to those in the underlying or overlying diamictite alternatively the clasts are composed of monolithic basement rock types the clasts show a long axis orientation which in the case of the boulder pavements is parallel to the striae on the pavements the various types of boulder beds have a similar mode of deposition and their subglacial origin is evidenced by the clast orientation clasts with stoss and lee sides stacking of clasts and the development of a cleavage in the matrix due to horizontal stresses exerted by the boulders in the subglacial sediment subglacial streams kame mounds subaqeously winnowed till or boulder beaches supplied the coarse debris which was entrained in the basal ice by plastic flow and regelation selective lodgement of the transported boulders occurred down glacier when the basal thermal conditions changed from cold freezing to warm melting the formation of the different types of boulder beds is thought to depend primarily on the concentration of coarse debris in the basal ice

on subglacial stone pavements in till four pavements from central and western canada display uneven pavement surfaces abundant tilted and inverted stones reversed lee ends fine crossing striae in various directions weak striae around curves worn facets distributed evenly on rounded stones and till fabric girdles collectively inconsistent with the popular concept of stones firmly held in till being abraded by overriding ice based on these data new models are offered that involve stone rotation in viscously deforming till to produce deformation pavements in the specific model increased pore water pressure under moving ice locally mobilizes previously formed lodgment and or erosional pavements into deformation pavements in the more general model stones released from the sole of a wet based glacier rotate interact and settle into a viscous suspension zone in deforming till according to velocity density and viscosity gradients stone axes and striae settle into various orientations following dewatering and till stiffening conceptu

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

intertidal boulder pavements in the northeastern gulf of alaska and their geological significance abstract striated boulder pavements consisting of planar concentrations of clasts having striated upper surfaces are a common feature of glacigenic deposits but their origin is not well understood laterally extensive pavements are currently forming in the intertidal zone west of icy bay in the gulf of alaska pavements comprise armoured layers of interlocking boulders one clast thick that have been eroded from underlying outcrops of late cenozoic glaciomarine diamictites they originate essentially as lag surfaces along a high energy storm dominated mesotidal shoreline boulder pavements are either flat or show a nucleated plan form where successively smaller boulders have been accreted around a large core boulder nucleation imparts a hummocky surface topography to the pavements and suggests that some form of size sorting of clasts has occurred packing is promoted by repeated tamping of the clast lag by floating masses of glacier ice which become grounded across the intertidal zone at low tide repeated abrasion of the pavement surface by debris contained within ice blocks produces smooth flattened clast upper surfaces and short randomly oriented striations data from icy bay can be used to constrain the origin of laterally extensive boulder pavements exposed in late cenozoic glaciomarine sediments on middleton island the significance of such pavements in the geologic record is that they form along erosional unconformities and may identify sequence boundaries

the upper paleozoic pebbly mudstone facies of peninsular thailand and western malaysia continental margin deposits of paleoeurasia reply the phuket group in peninsular thailand and the singha formation in nw malaysia are of devonian to lower permian age these approximately 3000 m thick strata which are part of the se asian pebbly mudstone belt stretching from southern tibet to sumatra have been interpreted as continental margin deposits mitchell et al 1970 in contrast recent papers bunopas et al 1978 stauffer 1983 propose a glaciomarine origin these authors follow the scenario that parts of mainland se asia shan thai craton rifted away from gondwana during the lower carboniferous and collided with eurasia during the late triassic after crossing the tethys ocean under clockwise rotation of more than 180 degrees in this paper the arguments of these authors will be discussed and a sedimentological description will be given which shows that the pebbly mudstones are not glaciomarine sediments but rather of continental margin origin the investigations on phuket and langkawi islands when compared with newest results from central and north thailand clearly show that the shan thai craton was a part of or closely connected with palaeoeurasia indosinia during carboniferous and permian times comp helmcke 1985 the pebbly mudstones were deposited on the southern continental margin of this continent northern margin of tethys

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

fracture patterns in clasts of diamictites tillites fracture patterns in some of the clasts of the gowganda formation ontario are inconsistent with aqueous deposition and suggest that locally the diamictites are tillites similar fracture patterns have been found in the clasts of modern tills in the cascade mountains rare examples were also seen on the garvellachs scotland laboratory experiments indicate that such patterns can be developed by the impaction of one clast against another while surrounded by a compliant matrix the stresses which induced cracking were of the same order of magnitude as those which can be expected to occur in a sub glacial environment

mechanisms of autocorrelation the phenomenon of autocorrelation of major physical chemical and biological processes which underlies the recognition of geological rhythms and cycles in the outer earth deserves further study study of the mechanisms which link driving changes with responding changes will be particularly important 3 main drives are identified 1 sea level change 2 calcium sulphate deposition and 3 carbon dioxide injection all other changes are thought to be direct or indirect responses brief consideration is given to the significance of stable carbon isotopes oceanic sedimentation and magnetic reversal sea level variations in elucidating the operation of autocorrelation mechanisms in the past

the major asperities of the 1999 mw 7 4 izmit earthquake defined by the microseismicity of the two decades before it

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

ice margin influence on glaciomarine sedimentation in the permo carboniferous dwyka formation from the southwestern karoo south africa a persistent sedimentary unit interbedded in massive diamictite over a distance of almost 400 km near the top of the permo carboniferous dwyka formation in the southwestern karoo consists of stratified diamictite rhythmite lonestone argillite and black shale the stratified diamictite facies association is interpreted as ice marginal debris flow the diamictite lonestone argillite facies association as proximal to intermediate debris flow debris rain and suspension settling and the shale diamictite facies association as distal debris flow and suspension settling deposits an analysis of the mudrock and diamictite facies relationships suggests deposition from a rapidly calving oscillating ice margin in the east and at a consistently retreating grounded ice margin with few icebergs in the west sediment sources volume of ice rafting resedimentation processes ice marginal recession and advance and configuration of the ice margin influenced the distribution of debris flow deposits and bergstone mud in the east and resulted in a near random facies arrangement due to a lack of icebergs in the west debris flow deposits and bergstone mud were poorly developed which reduced the number of facies transitions and variation resulting in a more systematic upward fining sequence

paleomagnetism of permian sedimentary rocks from tanzania and the permian paleogeography of pangea abstract we report new paleomagnetic results from karoo permian rocks in tanzania k1 and k3 redbeds and k5 siltstones and limestones from the songwe kiwira basin ndeke redbeds from the mikumi basin and group viii redbeds from the nyakatitu basin were sampled and thermally demagnetized palynologic data and lithologic correlations suggest that the k1 redbeds are lower permian and that the k3 ndeke and group viii redbeds as well as the k5 siltstones and limestones are upper permian stable magnetic directions were obtained from the k3 ndeke and group viii redbeds yielding an upper permain pole at 26 n 267 e characteristic remanence directions were also obtained from the k5 siltstones and limestones however because these directions define a pole 66 n 269 e that is very close to the upper cretaceous pole for africa and significantly different from the upper permian redbed poles these rocks may have been remagnetized the k1 redbeds did not yield stable results using our new results together with published permian poles for africa and the other gondwanan continents we revise the mean lower and upper permian poles for africa west gondwana and gondwana and investigate whether or not these revised poles can discriminate between the various pangea reconstructions proposed for the permian with any greater certainty than previous unrevised mean poles when compared to the mean lower and upper permian poles for laurussia we find that our revised west gondwanan and gondwanan poles do not necessarily provide stronger support for any particular pangea reconstruction than the previous poles therefore even though this study improves the paleomagnetic data base for gondwana for the permian it is not clear that the combination of our results with other paleomagnetic data from the gondwanan continents yields significant new insights about the permian configuration of pangea as suggested previously strong non dipole fields during the permian may provide an explanation for why it is not easy to discriminate with certainty between the various permain pangea reconstructions even with new paleomagnetic results