testing the sensitivity of geomorphic indices in areas of low rate active folding eastern betic cordillera spain abstract active deformation structures have an incidence in topography that can be quantified by using geomorphic indices most of these indices have been checked in faulted regions with high deformation rates the application of several geomorphic indices hypsometric curve analysis normalized stream length gradient and valley width to valley height ratio to the drainage network of the southern limb of the sierra de las estancias antiform internal zones eastern betic cordillera where low rate active folding has been recognized allows us to investigate the suitability of these indices to identify active structures in such a scenario hypsometric curves clearly identify regions with recent uplift and young topography but they do not provide any constraint on the location of active folds local valley width to valley height index variations have been detected just coinciding whit the position of ene wsw active folds normalized stream length gradient index serves to locate active folds in areas of hard rock substratum but not in those areas with soft sediments neogene quaternary sedimentary basins this is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors in view of these results we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low rate uplift related to active folding with the best results obtained in hard rock areas

seismicity rate change before the irpinia m 6 9 1980 earthquake the stability of seismicity rate in central and southern italy was examined in two data sets from 1975 0 to 1995 0 with m 3 4 and from 1987 5 to 1996 0 with m 2 5 these are the approximate minimum magnitudes of complete reporting for the respective periods the first set was used to evaluate the possibility that the 23 november 1980 irpinia m 6 9 earthquake was preceded by precursory seismic quiescence the second was used to evaluate the conditions under which a current seismic quiescence could be detected in central or southern italy during the years before the irpinia earthquake the seismicity rate in the northern half of the rupture area and north of it was low whether this was a case of precursory quiescence or not is subject to interpretation because the background rate cannot be established for the years before 1975 if we accept the relatively constant seismicity rate in the irpinia volume during the decade after the mainshock as representative for the background rate we have a clear case of precursory quiescence lasting at least 1 3 yr up to the mainshock alternatively it can be postulated that the seismicity rate during the decade following this shock was elevated regionally because of the stress redistribution and that the low rates seen before it represent the normal background rate even if this reasoning is accepted the fact remains that a volume including the northern part of the rupture produced no m 3 4 earthquakes during 1 3 yr before the irpinia earthquake but produced 10 earthquakes during the 4 7 previous yr given these facts we favor the interpretation that the irpinia 1980 earthquake was preceded by precursory seismic quiescence in the entire data set there are three other cases of quiescence of higher significance without a mainshock following since no other mainshock with m 6 exists in the data set no missed event exists we propose that in italy precursory seismic quiescence may precede mainshocks and that it may be detected in the future by the improved catalog of the modern data set beginning in 1987 5 major magnitude scale changes give the mistaken appearance that fewer large magnitude earthquakes occur in italy now than in years before 1987 we postulate that the rate of earthquakes has not changed and that the magnitude scale should be adjusted

geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

the summit erosion surfaces of the inner betic cordillera their value as tools for reconstructing the chronology of topographic growth in southern spain erosion surfaces at the top of mountain ranges have suggested to geomorphologists that the earth s crust can undergo rapid pulses of uplift during which rates of denudation fail to balance with rates of crustal uplift thereby preserving much of the initial plateau topography as it rises to greater elevations here we analyze a regionally extensive population of mappable planar surfaces which crown several major tectonically active sierras of the inner south eastern betic cordillera se spain based on a synthesis of long term landscape evolution involving landform reconnaissance dem based morphometric analysis structural geology sediment provenance analysis and field stratigraphy we conclude that the summit surfaces are a mosaic of discrete post orogenic erosion surfaces that each developed in relation to mediterranean marine base levels at a time when the sierras formed a series of low elevation islands they are not therefore fragments of a once regionally continuous paleoplain the summit surfaces were partly the result of shallow angle detachment faulting during the middle miocene in response to lithospheric slab detachment where evidence exists that the resulting low relief topography was reworked by marine abrasion during the tortonian sea level rise the terminal age of the surfaces is latest miocene age bracketing based on stratigraphic correlations among the many depocentres of the region and on published thermochronological data indicates that some erosion surfaces locally formed in less than 3 million years 8 ma 5 7 ma they were subsequently uplifted to their current elevations 1 7 to 2 km by pliocene to quaternary neotectonics in at least two major pulses

palaeoflood estimates of pleistocene coarse grained river terrace landforms rio almanzora se spain abstract a series of palaeoflood estimation techniques are applied to an inset sequence of middle to late pleistocene river terrace landforms associated with the rio almanzora se spain the study area is a 7 km long transverse reach where 4 terrace levels level 1 highest and oldest level 4 lowest and youngest document some 200 m of incision across an uplifted basement block during the pleistocene for the broader region river terrace aggradation is attributed to increased sediment supply during glacial to interglacial transitions level 1 marine oxygen isotope stages mois 12 11 l2 10 9 l3 8 7 and l4 6 5 within the transverse reach terrace levels 2 3 and 4 are characterised by coarse boulder rich gravels d max 2 5 m organised into 3 5 m high cross beds level 4 is characterised by a series of km scale abandoned meander loops with levels 2 and 3 showing evidence for similar degraded high sinuosity forms the fluvial setting is interpreted as a braided river environment with lateral and longitudinal gravel barforms using field derived sedimentary boulder size etc and morphological width slope etc features flow competence and regime based methods were applied palaeoflood estimates varied from 40 to 2859 m 3 s with mean maximum discharges showing an increase through time l2 278 l3 413 l4 1361 m 3 s palaeoflood estimates were compared to flood events associated with the ephemeral modern rio almanzora catchment 2500 km 2 to establish whether palaeoflood values were reasonable estimations a 46 year 1963 2009 modern flood gauge record shows infrequent flood events with discharges typically 3 s a rare flood event in 1973 5680 m 3 s provides an upper value for comparison with the palaeoflood estimates although estimates appear reasonable they should be considered as minimum values due to 1 some disparities between flow depths derived from the palaeoflood equations 0 7 4 m and field based evidence 3 5 m high cross beds 2 issues related to field sampling of boulders from sections and 3 uncertainties as to the relationship between flood hydrology and transportation of boulders formation of 3 5 m high cross beds and the position of the terrace remnants in the river valley the palaeoflood estimates suggest that relatively large discharges occurred during valley floor aggradation in the glacial interglacial transitions periods characterised by low vegetation cover and high sediment yield discharge increases through time can be explained by the long term drainage evolution of the rio almanzora characterised by an expanding catchment area linked to river capture driven by regional uplift patterns the 3 5 times larger discharge estimates recorded in terrace level 4 are coeval with large and rapid changes in precipitation or elevated seasonal discharge linked to the mois 6 5 glacial interglacial climate transition overall within tectonically active regions affected by river capture fluvial systems could be responding to loss or expansion of catchment areas long term palaeoflood records from inset flights of river terraces could store such signals and may mask complicate any climate palaeoflood relationships

1 fβ fluctuations and self similarity in earthquake dynamics observational evidences in southern italy abstract recently it has been determined that many statistical features of earthquakes are scale invariant with universal values for exponents the analysis of scaling laws has led to the development of a wide variety of physical models of seismogenesis involving nonlinear dynamics and it can be used to better characterize the seismicity pattern in this work the presence of scale invariance properties in the seismicity of a selected area of the southern appennine chain is revealed 1 f fluctuations are detected from the analysis of earthquake sequences using the counting statistics and at the spatial scale a self similar structure in the epicentre aggregate is determined by the estimation of its fractal dimension finally correlations between temporal exponent fractal dimension and b value variations are described

calcrete fossilisation of alluvial fans in se spain the roles of groundwater pedogenic processes and fan dynamics in calcrete development abstract dryland alluvial fans developed along the northern flanks of the sierra lisbona in the north western vera basin almeria region southeast spain display negligible amounts of incision despite distal base level lowering of 30 m by the modern drainage network the fans are of early middle quaternary age and are graded to a coeval river terrace now isolated from the modern drainage network the negligible incision is due to the encasement and fossilisation of the alluvial fans by calcrete this paper explores the reasons for such fossilisation and assesses the relative importance of pedogenic and groundwater mechanisms for calcrete formation within an alluvial fan setting a single fan was selected for detailed examination the geomorphological and sedimentological features of the fan its catchment area and their relationship to the distal river terrace were documented qualitative and semi quantitative petrographic and scanning electron microscope analyses of calcrete samples collected from transects across the fan surface and within its distal top river terrace surface enabled the style pattern and relative timing of calcrete development to be assessed calcrete fabrics comprised initial micritic grain coating cements pellets and glaebular carbonate nodules with interstitial spaces infilled by equant sparite and microsparite mosaics it is proposed that the early phases of calcrete development were dominated by pedogenic processes with increasing groundwater calcretisation over time point count data indicated increased quantities of interstitial sparite and microsparite cement within near surface proximal fan calcretes and at depth across the fan suggesting that groundwater processes played a more important role in calcrete formation in these locations the contribution of groundwater to calcrete development can be best explained by the intrinsic funnelling of groundwater from the catchment through the proximal fan head area a zone where the fan gravels are thinnest calcrete fossilisation appears to have followed a reduction in the fan catchment area as a result of rockfalls and watershed stream capture which reduced water and sediment supply to the fan and enabled surface stabilization and calcrete development to take place the reduced sediment water supply combined with calcrete fossilisation appears to have protected the alluvial fans from regional base level lowering the implications of these results for existing pedostratigraphic models of calcrete development in alluvial fans are subsequently explored

interaction between the controls on fluvial system development tectonics climate base level and river capture rio alias southeast spain fluvial systems in uplifting terrain respond to tectonic climatic eustatic and local base level controls modified by specific local factors such as river capture the rio alias in southeast spain is an ephemeral transverse to structure fluvial system the river drains two interconnected neogene sedimentary basins the sorbas and almeria basins and crosses two major geological structures the sierras de alhamilla cabrera and the carboneras fault zone regional epeirogenic uplift resulted in sustained fluvial incision during the quaternary punctuated by major climatically driven periods of aggradation and dissection which created a suite of five river terraces the river terrace sequence was radically modified in the late pleistocene by a major river capture itself a response to regional tectonics localized tectonic activity and eustatic base level change the rio alias is defined by four reaches within each the climatically generated region wide fluvial response was modified by tectonics base level change or river capture to varying degrees in the upper part of the basin lucainena reach climate was the dominant control on river development with limited modification of the sequence by uplift of the sierra alhamilla and local drainage reorganization by a local river capture downstream of the sierra alhamilla in the polopus reach the climatic signal is dominant but its expression is radically modified by the response to a major river capture whereby the alias system lost up to 70 of its pre capture drainage area in the reach adjacent to the carboneras fault zone argamason reach modification of the terrace sequence by local tectonic activity and a resultant local base level fall led to a major local incisional event propagating c 3 4 km upstream from the area of tectonic disturbance at the seaward end of the system el saltador reach quaternary sea level changes modified the patterns of erosion and incision and have resulted in steep incisional terrace profiles the signals generated by regional tectonics and the quaternary climate change can be identified throughout the basin but those generated by ongoing local tectonics river capture and sea level change are spatially restricted and define the four reaches the connectivity of the system from the headwaters to the coast decreased through time as incision progressed resulting in changes in local coupling characteristics copyright 2012 john wiley sons ltd

syn tectonic sedimentation in a neogene strike slip basin containing a stacked gilbert type delta se spain abstract the pliocene sedimentation in the cerro blanco ei barranquete subbasin cbb subbasin that forms part of the larger almeria nijar carboneras basin anc basin is controlled by a releasing overstep and a restraining zone in the ne trending serrata strike slip fault zone the sedimentary development of this subbasin can be considered in three stages of a fault kinematic model during stage i a wave influenced shoaling zone was present in front of an emergent serrata cape to the ne with a basin to the sw and w uplift of the shoaling zone in a restraining n080e trending cerro blanco fault zone cb fault zone is evidenced by the following syn tectonic sedimentary phenomena a a rotational unconformity towards the nw b four deepening pulses in the shallow water zone c massflow deposits originating from a near coastal zone possibly triggered by tectonic pulses during stage ii the uplifted zone became increasingly shallow and finally emerged quartz pebbles in the sediments that indicate a land connection between the serrata cape and the metamorphic basement in the north differentiate this stage from the previous one prograding shoreline deposits marked the outbuilding of the serrata cape towards the sw an episodically subsiding zone due to a releasing overstep between the sinistral n040e trending nw serrata boundary fault nwsb fault and b fault during stage ila is indicated by a southwestward outbuilding fandelta during this stage there was only one depocentre during stage ilb the depocentre of the subsiding zone split up this shifting of depocentres is explained according to the releasing overstep model by an increase of the overlap between the nwsb fault and the b fault during stage iii the cbb subbasin became continental and was inverted as demonstrated by its present day relief the area was severely faulted by n040e trending r and y shears on a metre scale which led to an estimated cumulative sinistral displacement of 2 km since fandelta deposition the present day activity of the nwsb fault is shown by sinistrally deflected stream courses and pressure ridges

living foraminiferal assemblages in two submarine canyons polcevera and bisagno of the ligurian basin mediterranean sea abstract living rose bengal stained benthic foraminifera were investigated in eleven stations sampled along transects following a depth gradient from polcevera and bisagno canyons and the adjacent open slope ligurian sea in a depth interval ranging from 200 to 2000 m in order to understand which environmental factors influence the abundance and taxonomical composition of the foraminiferal assemblages in these two domains canyon and open slope qualitative and quantitative foraminiferal data were correlated to the sediment biochemical composition in terms of phytopigments proteins lipids carbohydrates and biopolymeric carbon grain size and the main hydrological characteristics salinity temperature dissolved oxygen the cluster analysis and canonical correspondence analysis allowed us to detect two sectors coastal and offshore characterized by contrasting trophic conditions the coastal sector reflects spread meso eutrophic conditions in both physiographic domains being possibly more impacted by the river inputs and sediment transport processes from land in fact the narrow continental shelf of the ligurian sea favors the deposition of sediment transported by riverine processes on the immediately adjacent coastal areas as a result homogenization of sea bottom conditions occurs leading to an unclear differentiation between open slope and canyon foraminiferal assemblages conversely the offshore sector is less affected by physical disturbance due to the sedimentary flows decreasing in relation to the larger distance from the coastline consequently the lower organic matter content and lower food quality expressed in terms of contribution of the primary material to the biopolymeric carbon pool lead to a more oligotrophic condition which favors the development of peculiar assemblages dominated by glomospira charoides ammolagena clavata and epifaunal taxa the first finding ever of a warm tropical species amphistegina lessonii in the ligurian sea sediments at 500 m depth can be considered the first evidence of upward expansion of tropical species to the northern portion of the mediterranean sea which is experiencing an evident water warming linked to the ongoing global climate change

neogene coralline algal growth forms and their palaeoenvironments in the almanzora river valley almeria s e spain abstract the almanzora river valley is an elongate e w depression containing mainly neogene sediments during the late tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts a on coastal platforms and talus slopes b on fan deltas and c associated with corals in patch reefs growing at the furthermost extremes of coastal fan deltas in the former two cases the predominant growths are as rhodoliths associated with mobile substrates in the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths with depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself the massive crusts and columns which mark the limit of development of the shallow water rhodoliths in the deeper examples are covered by branching and thin leafy laminar growths in the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones in the patch reefs the specific composition of the algal associations changes somewhat and the growths developed on a stable substrate under low energy conditions are mainly vertical branches arising from thin crusts

live rose bengal stained and dead benthic foraminifera from the oxygen minimum zone of the pakistan continental margin arabian sea live rose bengal stained and dead benthic foraminiferal communities hard shelled species only from the pakistan continental margin oxygen minimum zone omz have been studied in order to determine the relation between faunal composition and the oxygenation of bottom waters during r r s charles darwin cruises 145 and 146 12 march to may 28 2003 11 multicores were taken on the continental margin off karachi pakistan two transects were sampled constituting a composite bathymetric profile from 136 m above the omz in spring 2003 down to 1870 m water depth cores surface area 25 5 cm2 were processed as follows for stations situated above and in the upper part of the omz sediment slices were taken for the 0 0 5 and 0 5 1 cm intervals and then in 1 cm intervals down to 10 cm for the lower part of the omz the second centimetre was also sliced in half centimetre intervals each sample was stored in 10 borax buffered formalin for further processing onshore the samples were wet sieved over 63 m 150 m and 300 m sieves and the residues were stained for one week in ethanol with rose bengal after staining the residue was washed again the stained faunas were picked wet in three granulometric fractions 63 150 m 150 300 m and 300 m down to 10 cm depth to gain more insight into the population dynamics we investigated the dead unstained foraminifera in the 2 3 cm level for the fractions 150 300 m and 300 m the fractions 300 m and 150 300 m show nearly the same faunal distribution and therefore the results are presented here for both fractions combined i e the 150 m fraction live foraminiferal densities show a clear maximum in the first half centimetre of the sediment only few specimens are found down to 4 cm depth the faunas exhibit a clear zonation across the pakistan margin omz down to 500 m water depth uvigerina ex gr u semiornata and bolivina aff b dilatata dominate the assemblages these taxa are largely restricted to the upper cm of the sediment they are adapted to the very low bottom water oxygen values ab 0 1 ml l in the omz core and the extremely high input of organic carbon on the upper continental slope the lower part of the omz is characterized by cosmopolitan faunas containing also some taxa that in other areas have been described in deep infaunal microhabitats

reporting history of the central aleutians seismograph network and the quiescence preceding the 1986 andreanof island earthquake the earthquake catalog of the central aleutian seismic network casn was searched systematically for significant rate changes in the period from 1976 through 1985 the magnitude signatures for the nine changes were modeled by synthetic signatures by this method six of the rate changes could be identified as artificial based on the criteria that the rate change was confined to small magnitude events and that magnitude shifts were present for each of these changes an artificial cause existed that affected the network within one to two months of the time of change as estimated from the catalog analysis one of these cases was a rate decrease by a factor of 2 associated with a storm that had put out of operation two thirds of the network another change coincided with the introduction of digital data processing the four remaining cases were artificial reporting rate increases due to installation of several new stations or to repair of several stations that had failed the three rate changes that could not be identified unambiguously as artificial or natural on the basis of magnitude signatures were all rate decreases by factors of approximately 2 two of these were clearly due to disasters that had put out of operation more than half of the network the third was the proposed precursory quiescence to the 1986 andreanof island m 7 9 earthquake from this we conclude that without knowledge of the network history many of the artificial reporting rate changes in earthquake catalogs can be identified as artificial and that their onset time can be estimated to within one to two months an earthquake count independent from the adak catalog was obtained from the helicorder records of the station adak for the years 1978 through 1985 for the vicinity of adak island of a total of 1831 events 335 were not in the adak catalog and 981 were located within the 1986 aftershock area the helicorder earthquake count showed a pronounced decrease by about 50 per cent similar in amount to that in the adak catalog however the decrease started in 1980 at a time when in the central subregion covered by the adak catalog only m 2 9 events decreased while the smaller magnitude bands show a maximum decrease in 1982 we conclude that the possibility could not be ruled out that electronics changes contributed to the reporting rate decrease starting in the years 1980 to 1982 however it seems very unlikely that a network that was at its healthiest during the precursor time would be reduced by an improvement in the electronics to a detection level approximately equal to that in two short periods when only one third of the stations were operating therefore the seismic quiescence reported and interpreted as a precursor by kisslinger et al 1985 was most likely a natural phenomenon

precursory seismic quiescence seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromml 4 7 toms 8 0 are summarized the amount of rate decrease ranges from 45 to 90 the significance of these changes varies between 90 and 99 99 the assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied all quiescence anomalies seem to have abrupt beginnings and the rate during the anomalous period is fairly constant the duration of the precursors ranges from 15 to 75 months and it is not clear what factors determine that time at least three successful predictions have been based on seismic quiescence these cases have shown that mainshocks can be predicted based on quiescence but they have also shown that the interpretation of the data in real time is difficult and nonunique if a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area then we estimate based on searches in four areas that the false alarm rate may be on the order of 50 failure to predict may be expected in perhaps 50 of mainshocks even in carefully monitored areas quiescence cannot be used as a precursor in tectonic environments with low seismic activity most characteristics of the phenomenon are still poorly defined but data exist which probably permit at least a doubling of the presently available data on case histories

3d modelling of the sorbas basin spain new constraints on the messinian erosional surface morphology abstract the scenario of the messinian salinity crisis msc remains one of the most debated topics in the mediterranean realm and especially in the sorbas basin which is one of the type localities of msc related deposits after a recently improved chronostratigraphic framework of the miocene and pliocene deposits of the basin this work is an attempt to image the morphology of the messinian erosional surface mes at depth we built a basin scale 3d model of the miocene and pliocene series that confirms the erosional character of the messinian pliocene boundary solving a long standing and debated question we tentatively also suggest that the fluvial system developed during the peak of the msc was exiting the basin toward the south this new geometrical model showing a robust internal consistency can be used as a basis for interpreting the messinian salinity crisis in other sedimentary basins around the mediterranean sea the return of marine conditions in the early pliocene on an erosional surface interferes with the continuous formation of the sorbas basin asymmetrical syncline subsidence of the hinge uplift of the limbs and gravitational sliding the irregular shape of the mes is superimposed in the southern part of the basin by small scale box type folds with two oblique nne ssw and wnw ese fold axes directions the architecture of these folds suggests gravitational sliding of post evaporitic marine sediments during the progressive deformation of the basin during the zanclean

criteria for the recognition of salt pan evaporites layered evaporites can accumulate in 1 ephemeral saline pans 2 shallow perennial lagoons or lakes and 3 deep perennial basins criteria for recognizing evaporites deposited in these settings have yet to be explicitly formulated the characteristics of the ephemeral saline pan setting have been determined by examining eight holocene halite dominated pans salt pans and their deposits marine and non marine from the u s mexico egypt and bolivia these salt pans are typified by alternating periods of flooding resulting in a temporary brackish lake evaporative concentration when the lake becomes saline and desiccation which produces a dry pan fed only by groundwater the resulting deposits consist of alternating layers millimetres to decimetres of halite and mud the layers of halite are characterized by 1 vertical and horizontal cavities rounded crystal edges and horizontal truncation surfaces due to dissolution during flooding 2 vertical chevrons and cornets grown syntaxially on the bottom during the saline lake stage 3 halite cements overgrowths and euhedral cavity linings and disruption of layering into metre scale polygons produced during the desiccation stage the muddy interbeds are characterized by displacive growth of halite during the desiccation stage immediately below the surface of the pan the halite layers are matured by repeated episodes of dissolution and diagenetic crystal growth this results in porous crusts with patches of chevron and cornet crystals truncated by dissolution clear diagenetic halite cement and internal sediment these layers of mature halite closely resemble the patchy cloudy and clear textures of ancient halite deposits holocene salt pans are known to cover thousands of square kilometres and cap halite deposits hundreds of metres thick so they are realistic models for ancient evaporites in scale e g permian salado formation of new mexico texas which preserves many primary salt pan features

benthic foraminifera associated with cold methane seeps on the northern california margin ecology and stable isotopic composition release of methane from large marine reservoirs has been linked to climate change as a causal mechanism and a consequence of temperature changes during the quaternary and the paleocene these inferred linkages are based primarily on variations in benthic foraminiferal stable isotope signatures few modern analog data exist however to assess the influence of methane flux on the geochemistry or faunal characteristics of benthic foraminiferal assemblages here we present analyses of the ecology and stable isotopic compositions of living rose bengal stained and dead fossil foraminifera 150 mm from cold methane seeps on the slope off of the eel river northern california 500 525 m and discuss potential applications for reconstructions of methane release in the past and present calcareous foraminiferal assemblages associated with calyptogena clam bed seeps were comprised of species that are also found in organic rich environments cosmopolitan paleoceanographically important taxa were abundant these included uvigerina bolivina chilostomella globobulimina a ndnonionella we speculate that seep foraminifera are attracted to the availability of food at cold seeps and require no adaptations beyond those needed for life in organic rich reducing environments oxygen isotopic values of the tests of living foraminiferal assemblages from seeps had a high range up to 0 69 as did carbon isotopic values up to 1 02 many living foraminiferal isotope values were within the range exhibited by the same or similar species in non seep environments carbon isotopic values of fossil foraminifera found deeper in the sediments 18 20 cm however were 4 10 u peregrina and 3 60 b subargentea more negative than living d 13 c values these results suggest that d 13 c values of foraminiferal tests reflect methane seepage and species specific differences in isotopic composition and can indicate temporal variations in seep activity a better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo seep recognition and improve interpretations of climatic and paleoceanographic change 2000 elsevier science b v all rights reserved

rapid late quaternary denudation of the karacasu graben in response to subsidence in the buyuk menderes corridor insights from morphotectonics and archaeogeology abstract the timing and geomorphological consequences of high angle normal faulting in the buyuk menderes graben w anatolia is an essential yet poorly studied issue that has been evaluated mostly regarding detachment faulting in the central menderes core complex however this subject has direct concerns related to ongoing debates regarding the level of seismic risk and the response of surface process to active tectonics in the most rapidly extending region in the world to approach this problem an integrated scheme was followed that involves the study of late quaternary stratigraphy terraces and ancient and modern civic structures in the karacasu graben located on the southern uplifted block of the buyuk menderes graben our stratigraphic observations coupled with the existing micro mammalian fossils demonstrate the widespread occurrence of terrestrial coarse red clastics karacasu formation before the appearance of the narrow faulted corridor the onset of high angle normal faulting started with gradual denudation through the axial dandalas creek and its confluences southward while alluvial sedimentation remained active in the more southern areas of the karacasu graben ages from surface dating techniques mainly osl and cosmogenic radionuclides show that previous knickpoints determined by the incision accumulation threshold reached the vicinity of the antique greek city of aphrodisias 30 km from the buyuk menderes valley with a headward erosion rate of 75mky 1 by the end of last glacial maximum lgm incision rates derived from terraces and roman aqueducts in the middle and upper reaches of the basin increased from 1 mmy 1 background average geological rate for the last 65 ka to 3 mmy 1in the last 2 3 ka presumably due to increased population pressure in and around the vicinity of the city of aphrodisias at the centre of the graben modern civic structures such as aqueducts and bridges constructed after the 1970 s demonstrate the second wave of incision increased to as much as 10 mmy 1 likely due to increasing human pressure and the mechanisation of farming on the other hand inverse extrapolation of the knickpoint progression rate yields a surprisingly younger age of 400 ka for the birth of the new narrow tectonic corridor this morphotectonic transformation exposed large depositional areas such as karacasu and bozdogan grabens to erosion and should have resulted in a significant increase in the sediment supply to buyuk menderes river however seismic investigations in the aegean sea have yet to identify the sedimentary record of this tectonic transformation

the palomares brittle ductile shear zone of southern spain the palomares shear zone is a major neogene quaternary strike slip zone which transects the crust of the betic cordillera in se spain the shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology it is emphasized that the formation of the palomares shear zone was not an isolated tectonic event but part of a complex neogene tectonic history the neogene evolution of the betic rif orogen and its central alboran basin is characterised by the following events 1 emplacement of the alboran diapir with resulting nappe shedding from the overlying crust between 25 and 20 ma ago 2 onset of the subsidence of the alboran basin between 20 and 15 ma ago due to cooling of the alboran diapir and the overlying crust 3 formation of the cabo de gata volcanic chain between 15 and 8 ma ago and 4 refolding of the nappe sheets in the betic rif orogen into a basin and range structure about 7 ma ago continuous activity of the crevillente fault of southern spain may have occured over a period from 20 ma ago up to the present the interrelated palomare fault in se spain was probably formed between 15 and 8 ma ago and seem to be active still the palomares shear zone affects a rock volume 44 km wide at least 80 km long and 30 km deep a shear strain distance diagram constructed across the palomares shear zone and its axial palomares fault involves a new method to estimate or constrain the shear strain magnitude along brittle ductile shears the typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the palomares fault are of the order 10 13 10 14 s 1 the tensor shear strain rate along the palomares fault itself is of the order 10 12s 1 and the time averaged relative displacement rate of its walls is about 2 mm a 1 the range of strain rates within the palomares shear zone are interpreted to be due to a combination of various flow softening mechanisms geometric structural thermal and strain rate softening these softening mechanisms might explain the difference in vertically averaged viscosities of 1020 pa s and 1025 pa s or lower suggested for the crustal rocks in the palomares fault proper and that of the relatively rigid boundaries of the palomares shear zone respectively

neotectonics and plio quaternary landscape development within the eastern huercal overa basin betic cordilleras southeast spain abstract the huercal overa basin is one of a series of neogene sedimentary basins located within the betic cordillera of southeast spain its geological and geomorphological history has been controlled by tectonic activity culminating in basin inversion during the plio quaternary deformation of the huercal overa basin is associated with left lateral strike slip faulting in relation to its position within the trans alboran shear zone in this paper we focus upon the eastern portion of the huercal overa basin and make the first attempt to reconstruct the long term landscape development during the plio quaternary this is done through integration of geological and geomorphological data obtained through field observations and gis and remote sensing techniques in particular this paper provides a case study that contributes to the understanding of landscape development within tectonically active shear zones within the eastern part of the huercal overa basin the main tectonic activity is associated with the left lateral strike slip lorca alhama fault oriented ne sw during the late pliocene and early pleistocene the interaction of this fault with older miocene ene wsw to e w orientated structures formed a subsiding area with pull apart basin characteristics termed the cubeta del saltador subsidence within the cubeta del saltador enabled sedimentary infilling by braided rivers with sediment being derived from the sierra de las estancias to the north and the sierra de almagro to the south sedimentary deformation has resulted in the development of a series of progressive unconformities angular unconformities and faulting within the alluvial sediments towards the end of this stage of landscape development an increase in tectonic activity resulted in the creation of elevated tectonic highs in the north alto de la garita del diablo and east loma de garcia of the cubeta del saltador from the middle pleistocene onwards a progressive decrease in tectonic activity is recorded alluvial sediments infilled the cubeta del saltador these were dominated by braided river sediments that formed part of a fan shaped alluvial distributary system derived from the sierra de las estancias to the north in contrast smaller debris flow dominated alluvial fans were derived from the sierra de almagro along the southern margin currently the study area presents an asymmetric configuration reflecting the different topographic characteristics of the northern and southern limiting mountain fronts

long term control mechanisms of stream piracy processes in southeast spain the guadix basin developed as an endorheic depression during the upper miocene upper pleistocene its principal palaeogeographical characteristics are a large lake in the eastern sector an axial fluvial system and two fluvial systems transverse to it in the western sector the uplift of a central sector of the betic cordillera during the upper pleistocene affected the study area causing northward tilting from the internal zone of the cordillera sierra nevada and sierra de baza step faulting of the plio pleistocene infill of the ancient basin leaving more northern sectors in a lower topographical position alteration of fluvial current profiles and displacement of the ancient axial system to a position very close to the divide between the ancient endorheic guadix basin and the guadalquivir basin this facilitated capture of the endorheic basin by the headward erosion of a tributary of the guadalquivir river the region then began to be rapidly eroded as the new base level was now some 500 m lower than that of the ancient basin the present drainage network is similar to that of the ancient endorheic basin as regards the location of the main streams and the distribution of drainage patterns and fluvial styles although flow reversal is found in some stretches and a barbed drainage pattern appears locally as a result of the inheritance of drainage from the ancient basin fluvial superimposition is found in some stretches of the main streams 1997 by john wiley sons ltd

inadvertent changes in magnitude reported in earthquake catalogs their evaluation through b value estimates a simple procedure is presented for analyzing magnitudes and seismicity rates reported in earthquake catalogs in order to discriminate between inadvertently introduced changes in magnitude and real seismicity changes we assume that the rate and the frequency magnitude relation of the independent background seismicity do not change with time observed differences in the frequency magnitude relation a and b values between data from two periods are modeled as due to a transformation of the magnitude scale the transformation equation is found by a least squares fitting process based on the seismicity data for earthquakes large enough to be reported completely and by comparing the linear relation of one period to the other for smaller events an additional factor accounting for increased decreased detection is allowed this fitting technique is tested on a data set from parkfield for which two types of magnitudes amplitude and duration were computed for each earthquake we found that the b value fitting technique yielded virtually the same result as a linear regression assuming the same errors in the two magnitudes the technique is also applied to interpret the nature of reporting rate changes in a local guerrero mexico and a regional italy earthquake catalog in guerrero a magnitude change in 1991 37 can be modeled about equally well by m new m old 0 5 or by m new 1 02 m old 0 38 but residuals with the latter transformation are smaller in italy a magnitude change in 1980 21 cannot be modeled satisfactorily by a simple magnitude shift but is well described by a compression of the magnitude scale given by m new 0 67 m old 1 03 the proposed b slope fitting method provides a means to interpret quantitatively and in some cases correct for artificial reporting rate changes in earthquake catalogs

seismic quiescence before the landers m 7 5 and big bear m 6 5 1992 earthquakes the landers earthquake of 28 june 1992 was preceded by a seismicity rate decrease of 75 in a volume approximately 11 by 23 by 15 km located adjacent to and north of the epicenter this anomaly started for all magnitude bands in january 1988 lasting 4 5 yr up to the mainshock a smaller volume 7 by 14 by 15 km to the south of the epicenter showed a seismicity rate decrease of 75 starting in november 1989 the big bear earthquake of the same day was preceded by a 100 decrease of the seismicity rate within a volume of approximately 13 by 22 by 15 km around the hypocenter this volume contained 192 earthquakes of m 1 6 during the background period of 9 yr but none during the 1 6 yr from december 1990 to 27 june 1992 the standard deviate z values characterizing these rate changes are very high 6 3 and 12 3 respectively and the anomalies are unique not surpassed in significance by any other rate decrease in portion of the southern california earthquake catalog examined 117 06 w to 115 40 w and 33 45 n to 35 10 n no seismicity rate change was found in the vicinity of the m 6 1 joshua tree earthquake of 23 april 1992 based on magnitude signatures and frequency magnitude analyses we conclude that the two quiescence anomalies could not have been due to a shift or a compression of the magnitude scale and we interpret them as precursor anomalies this analysis was carried out using the declustered earthquake catalog for the landers area with corrections of 0 2 and 0 1 august 1985 and may 1990 for two suspected magnitude shifts with a new visualization technique we can investigate the stability and changes of the seismicity rate as a function of time and space by mapping z values for rate changes at every time interval and in volumes centered on a dense grid of points latitude longitude this computer code furnishes an almost continuous sequence of smooth contour maps of the degree of rate changes any anomalies artificial or real may thus be defined accurately

a non stationary epidemic type aftershock sequence model for seismicity prior to the december 26 2004 m 9 1 sumatra andaman islands mega earthquake 1 we study temporal changes in seismicity in sumatra andaman islands region before the m 9 1 earthquake of december 26 2004 we applied the epidemic type aftershock sequence etas models to the seismicity the two stage non stationary etas model with a single change point provides a better statistical fit to the seismicity data than the stationary etas model throughout the whole period we made further change point analysis of data sets by dividing into two sub regions the best fitted models suggest that the seismic activation relative to the etas rates started in the middle of july 2000 about 4 5 years before the m 9 1 earthquake this includes an increase in the background seismicity rates particularly in the southern part of the seismogenic zone near the epicenter a space time etas model also suggests that the background seismicity throughout the entire sumatra andaman islands area had increased after the change point time

response of plio pleistocene alluvial systems to tectonically induced base level changes vera basin se spain tectonics are perceived to be a major control on the positioning and long term evolution of alluvial systems by increasing slope gradients through uplift and tilting or by changing local base level incision can be stimulated leading to a switch in the active area of sedimentation an example of such a sedimentary response to tectonic activity is provided by well exposed late pliocene early pleistocene alluvial sediments of the salmeron formation from the western margins of the vera basin se spain early stage palaeogeographic reconstructions demonstrate the occurrence of two alluvial fan bodies with distinct palaeocurrent and provenance signatures that suggest sediment source areas from the north sierra lisbona and south sierra de bedar of the study area late stage reconstructions suggest fan abandonment and indicate the occurrence of a braided river system sourced from the sierra de bedar in the south proximal parts of this braided river are incised by up to 100 m into underlying fan sediments sourced from the sierra de bedar in distal areas incision is negligible and the braided system forms a conformable sedimentary succession with underlying fan sediments sourced from the sierra lisbona the switch from alluvial fan to braided river sedimentation and the spatially variable patterns of incision into the alluvial fan bodies can be accounted for by a phase of deformation which affected the vera basin during the early pleistocene extensional faulting resulted in uplift and subsidence leading to localized tilting of depositional surfaces in distal areas of the southern fan increased stream power resulted in headward incision through mid and proximal fan areas once the system became fully trenched distal base level controls became effective in generating an enlarged catchment area and continuing incision the resultant changes dramatically increased both sediment and water discharge to the alluvial system and a switch to braided river sedimentation

landscape response to strike slip faulting linked to collisional settings quaternary tectonics and basin formation in the eastern betics southeastern spain abstract neotectonic behaviour of the eastern betics southeastern spain has been controlled by the presence of a large left lateral shear zone this is an intraplate transcurrent zone probably decoupled by a mid crustal detachment horizon the morphological expression of this crustal structure is a sigmoidal corridor in which the main quaternary basins are located three types of morphostructural domains can be distinguished in the sigmoidal corridor the central segment and the northern and southern terminal splays the central segment is characterized by wrench tectonics whilst the southern and northern terminal splays are controlled by transtensional and transpressional tectonics respectively the quaternary morphostructural pattern is only the more recent picture of the tectonic processes that have controlled the late orogenic evolution of the eastern betics the indentation of the aguilas arc accompanied by thin skinned thrusting and tectonic escape in its easternmost sector and extensional collapse accompanied by thin skinned stretching in its westernmost sector

direct response of small non glaciated headwater catchments to late quaternary climate change the valle de la fueva southern pyrenees abstract topographic depressions in mountain regions function as sediment traps and their morpho sedimentary archives provide important insight into erosion and sediment dynamics in mountain ranges in order to establish the direct drivers and timing of erosion phases in the southern central pyrenees small non glaciated headwater catchments in the highly erodible valle de la fueva drainage basin were investigated as to their morphogenetic development geomorphic mapping revealed three morphogenetic complexes associated with the valle de la fueva drainage basin development i high lying talus plateaus and lateral slopes ii extensive glacis and pedimentation surfaces and iii deeply incised ravines with late stage fluvial cut terraces the talus slopes are the oldest preserved geomorphic units of the valle de la fueva and potentially denote the initial drainage basin topography talus bedrock and boulder exposure ages cluster yet between 21 and 40 10be ka indicating that the carbonate dominated talus surfaces were rejuvenated during the last glacial cycle mis 4 mis 2 the younger morphogenetic complexes ii iii point to successive basin erosion stages from diffusive surface pedimentation under cold climate conditions ii to rapid linear fluvial dissection and late stage terrace formation iii denoting the abandonment of pediments as actively eroding surfaces 10be depth profiles of glacis cover sediments yielded consistent late mis 2 exposure ages the abandoning of pediments marks the onset of rapid fluvial downcutting of deep ravines iii around the holocene climate transition which involved substantial sediment routing and basin scale erosion lower fluvial cut terraces denote the termination of intense catchment erosion at around 14 8 10be ka and minor fluvial incision during middle late holocene this research shows that small non glaciated mountain catchments feature valuable high resolution morpho sedimentary archives that are useful for assessing the direct impact of major climate transitions on surface processes and landscape transformation in mountain regions improvements in quantifying the timing and rates of paleo surface processes are vital for enhancing regional glaciofluvial chronologies and large scale basin erosion models that are possibly afflicted with time averaging biases

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

patterns and average rates of late neogene recent uplift of the betic cordillera se spain abstract the facies distribution in the sedimentary units infilling a series of neogene basins has been used to reconstruct the relief generation and uplift across the internal zone of the betic cordillera in southern spain uplift amounts and average rates can be estimated using the current elevation of the outcrops of well dated deposits indicative of ancient sea level positions coral reefs and coastal conglomerates record the initial development of emergent betic relief during the langhian continental and marginal marine deposits indicate the existence of a large island centred on the present sierra nevada sierra de los filabres chain by the end of the middle miocene the precursor of the sierra nevada sierra de los filabres chain originally part of this large island remained emerged whilst the surrounding areas were re invaded by the sea during the early tortonian at the end of the tortonian the inland basins granada and guadix basins became continental while the sierras de la contraviesa sierra de gador and sierra alhamilla emerged separating the alboran basin from the alpujarra tabernas and sorbas basins which became narrow passages of the mediterranean sea in contrast the sierra cabrera emerged during the late messinian suggesting a progressive uplift from west to east of the sierras south of the sierra nevada sierra de los filabres chain during the pliocene only the low areas closest to the present day coast remained as marine basins and progressively emerged throughout this stage the highest average uplift rate recorded is 280 m ma for the sierra de gador although the average uplift rates of upper neogene coastal marine rocks since depositon have maximum values of approximately 200 m ma most of the uplift of the betic mountains took place before the early pliocene the recorded uplift of neogene rocks was highest at the margins of western sierra nevada where peaks higher than 3000 m occur the average rates of uplift were lower to the east of this major relief the main sierras and depressions in the present day landscape correspond respectively to the emergent land in which uplift was concentrated and to the marine basins that existed before the final emergence of the region the altitude of the sierras reflects the time at which they became emergent the highest mountains being the first to rise above sea level

plio pleistocene drainage development in an inverted sedimentary basin vera basin betic cordillera se spain abstract the vera basin is one of a series of interconnected neogene quaternary sedimentary basins located within the internal zone of the betic cordillera southeast spain since the pliocene the vera basin has been subjected to low uplift rates 11 21 m ma 1 and inverted via compressive tectonics that are related to the ongoing oblique collision between the african and iberian plates within this paper the sedimentary and geomorphic response to basin inversion is explored sedimentary processes and environments are established for key stratigraphic units of the pliocene plio pleistocene basin fill and pleistocene dissectional landscape these data are subsequently utilised to reconstruct an evolving basin palaeogeography fault and uplift data are employed to discuss the role of tectonically driven basin inversion for controlling the resultant palaeogeographic changes and associated patterns of drainage development during the early mid pliocene the vera basin was characterised by shallow marine shelf conditions cuevas formation a major palaeogeographic reorganisation occurred during the mid late pliocene strike slip movement along the eastern basin margin coupled with uplift and basin emergence created a protected partially enclosed marine embayment that was conducive for gilbert type fan delta sedimentation from fluvial inputs along the northern and eastern basin margins espiritu santo formation the vera basin then became fully continental and internally drained through the development of a consequent drainage network that formed following the withdrawal of marine conditions during the late pliocene to early pleistocene alluvial fans developed along the northern and western basin margins grading to a bajada and terminating in a playa lake in central basin areas salmeron formation during the early mid pleistocene a switch from basin infilling to dissection took place recorded by alluvial fan incision a switch to braided river sedimentation and fluvial incision into the underlying basin fill sediments and basin margin mountainous topography fluvial incision headwards erosion expansion and modification of the consequent drainage network is documented within a series of up to four major inset river terrace levels and associated landforms fluvial incision and drainage network expansion are attributed to differential uplift and the creation of regional gradients between adjacent basins the relatively low plio pleistocene uplift rate of the vera basin 11 21 m ma 1 in comparison to adjacent basins sorbas 80 160 m ma 1 huercal overa 50 m ma 1 resulted in a switch from internal to external basin drainage ancestral forms of the principal drainage systems within the vera basin the rios almanzora aguas and antas captured basins and mountain catchment areas to the north huercal overa basin southwest sorbas basin and west sierra de los filabres range the switch from basin infilling to fluvial dissection is coincident with a phase of early mid pleistocene compressional tectonics expressed by extensional faulting this deformation is probably linked to accelerated strike slip movement along the palomares fault zone the faulting is superimposed onto the longer term pattern of plio pleistocene uplift and basin inversion

an integrated field and numerical modelling study of controls on late quaternary fluvial landscape development tabernas southeast spain the variability of quaternary landforms preserved in the tabernas basin of southeast se spain raises numerous questions concerning the roles of external forcing mechanisms e g tectonics and or climate and internal landscape properties e g lithological controls in the evolution of the basin wide fluvial system over late quaternary timescales in this study we apply the fluver2 numerical model to investigate the significance of these landscape controls upon patterns of landscape evolution we highlight the complications of generating realistic input datasets for use in the modelling of long term landscape evolution e g discharge and runoff datasets model outputs are compared to extensive field mapping of fluvial terraces their sedimentary architecture and optically stimulated luminescence dating results of the terraces the results demonstrate the significance of non linear rates of flexural tectonic uplift towards the west of the tabernas basin which have controlled base levels throughout the quaternary and promoted the formation of a series of diverging fluvial terraces our numerical model results further highlight the importance of climate cycles upon river terrace formation basin wide aggradation events were modelled during the transition from marine isotope stage mis 6 to 5 and the last glacial maximum lgm as supported by field evidence this aggradational pattern supports the regional hypothesis of terrace formation during global glacial cycles and cold to warm stage transitions and supports the use of sea surface temperature climate proxy data in the modelling exercise the availability of sediments derived from the surrounding hillslopes and adjacent alluvial fans explains the generation of substantial terrace aggradations copyright 2015 john wiley sons ltd

foraminiferal and palynological biostratigraphy and biofacies from a santonian campanian submarine fan system in the voring basin offshore norway abstract foraminiferal assemblages from a santonian campanian submarine fan system in the northwestern voring basin offshore norway were investigated with the primary objectives to document the stratigraphic ranges of foraminiferal taxa calibrated with dinoflagellate cysts and to interpret foraminiferal biofacies of different fan sub environments previously proposed based on the analysis of ichnofossils the assemblages are composed of deep water agglutinated foraminifera dwaf without carbonate cemented taxa dwaf taxa of high biostratigraphic value are absent but the complete agglutinated nature of the assemblages and the presence of gerochammina stanislawi and rectogerochammina eugubina are similar to those of the lower campanian fenestrella bellii zone of the norwegian sea more reliable dating was provided by palynology and the age of the interval is estimated to be santonian to campanian the inner to middle fan assemblages contain small numbers of specimens and consequently the species diversity and relative abundance of morphogroups are inconsistent deep infaunal forms may be more common in this sub environment but because the abundance is low this observation should be treated carefully in contrast the abundance and diversity of the assemblages of the overbank fringe and basin plain sub environments are fairly high their morphogroup composition is also similar and comparable to each other when the assemblage size is large the assemblage from the interval with suggested hydrothermal activity is similar to those from outside the channel sub environment the presence of bottom water currents possibly in the form of a western boundary current in the basin is suggested based on the abundant occurrence of tubular forms in the overbank fringe and basin plain sub environments

benthic foraminiferal distribution at middle valley juan de fuca ridge a northeast pacific hydrothermal venting site fourteen benthic foraminiferal bearing surface samples collected from the area of active venting aav in middle valley at a depth of 2430 m at the northern end of juan de fuca ridge northeast pacific ocean yielded 156 identifiable taxa sample sites were selected near active or recently active vents where temperatures up to 274 c have been measured the sea floor beyond hydrothermal mounds is characterized by unaltered soft hemipelagic mud and is dominated by a calcareous foraminiferal assemblage which includes numerous allochthonous species derived from the shelf via turbidite flows into the valley within the aav agglutinated foraminifera dominate with proximity to hydrothermal vent activity species of the family hormosinidae subfamily reophacinae dominate in the hydrothermal habitat because of their success at colonization attached agglutinated foraminifera densely colonize the indurated sediment in close proximity to vent sites however like the macrofauna observed near hydrothermal vents foraminifera do not venture into the extreme habitats where temperatures are greater than 20 c where clam beds are found in association with active hydrogen sulphide venting benthic foraminifera occur rarely these beds occur in loose pyritic mud that is toxic to all but species e g the clam culyp ena that co exist symbiotically with sulphur oxidizing bacteria the sparse distribution of calcareous benthic foraminifera in the vent areas is caused by enhanced carbonate dissolution at ph values of 5 2 low foraminiferal abundance and species diversity at the immediate site of active venting is attributed to rapid changes in physical and chemical conditions caused by circulating hydrothermal vent waters

quantifying long term catchment changes of alluvial fan systems in mountain areas affected by uplift significant reorganization of drainage networks can occur through river capture this modification can dramatically affect sediment flux and routing into adjacent sedimentary basins it is thus important to obtain information on rates and direction of changes in catchment areas in such environments this can be achieved where the original precapture catchments can be compared with the postcapture scenario this paper examines three modern mountain catchments from southeast spain that were affected by river capture and that fed relict pliocene pleistocene alluvial fan systems morphometric data have been collated for complete quaternary mountain catchment piedmont fan systems these data are used to establish regressions to determine catchment area and basin relief from a combination of fan characteristics area and gradient these relationships are then used to predict the original catchment characteristics for the three pliocene pleistocene relict fans and compared with the modern catchments to quantify the magnitude and direction of changes which have affected the drainage basins since fan abandonment in the early pleistocene the figures suggest that the catchment areas are responding to regional uplift most significantly by drainage net expansion facilitated by river capture rather than lowering of surface relief as a result sediment routing into the sedimentary basins has been radically altered

reversal of the middle upper songhua river in the late early pleistocene northeast china abstract the study of drainage evolution in the songnen plain northeast china is essential for understanding the interactions between tectonics topography climate drainage evolution in the region despite this it remains unclear whether the paleo songhua river upper middle reaches of the songhua river once flowed westward into the songnen plain and what forcings influenced the drainage development of the songnen plain in this contribution we provide insight into drainage development on the songnen plain using an integrated approach of magnetic susceptibility geochemical elemental and sr nd isotopic and heavy mineral composition recovered from a 102 m sediment core sediments extracted from the eastern edge of the songnen plain with sedimentological and topographic archives our results show that a dramatic provenance shift occurred at the depth of 62 2 m 0 94 ma in the core sediments it is proposed that the songhua river was separated by the jia yi jiamushi yilan divide into two segments before 0 94 ma the west flowing proto songhua river and the east flowing proto sanjiang river lower reach of the songhua river however the proto songhua river reversed direction at 0 94 ma when the jia yi divide was cut through by headward erosion of the proto sanjiang river marking the birth of the songhua river as a single eastward flowing river system tectonics is suggested as the first order control on the evolution of the songhua river before 1 20 ma whereas climate changes may be responsible after 1 20 ma

seismic quiescence before the m 7 1988 spitak earthquake armenia a detailed analysis of the 35 yr of seismicity between 1962 and 1997 using a gridding technique shows that the m7 spitak earthquake of 1988 december 7 was preceded by a quiescence anomaly that started at approximately 1984 0 5 and lasted about 5 0 5 yr up to the main shock this quiescence anomaly had a radius of about 20 3 km estimated from circular areas with 75 per cent rate decrease centred at the point of maximum significance of the anomaly the quiescence was clearly present in the aftershock volume during the 5 yr before the 1988 main shock but its statistically strongest expression was located 30 km nw of the epicentre this anomaly fulfills the association rules between precursory quiescence anomalies and main shocks even for a tight definition and is therefore proposed as a case of precursory quiescence the largest value of the standard deviate z found by random selection of samples by gridding was z 14 for a time window of tw 3 yr using a sample size of n 300 events this makes this anomaly the strongest observed so far and it is the first documented in an environment of continental collision there are no false alarms exceeding in significance the precursor the armenian earthquake catalogue used for this study had 4600 earthquakes with m mmin 2 2 in the area bounded by 39 5 to 42 n 42 5 to 47 e from the point of view of homogeneous reporting this is the best catalogue we have analysed so far the limits of the data used and the density of the grid are dictated by the data and have no influence on the results the choice of free parameters does not influence the results significantly within the following limits 100 n 500 2 tw 7 2 2 mmin 2 8

a seismic quiescence before the 2017 mw 7 3 sarpol zahab iran earthquake detection and analysis by improved rtl method abstract a major earthquake with magnitude mw 7 3 struck sarpol zahab kermanshah province iran on november 12 2017 causing extended damage and casualties the epicenter was located in the northwestern part of the zagros mountain range an active belt originated by the arabia eurasia collision we explore seismicity preceding this earthquake by using the iranian seismological center instrumental earthquake catalog igtu with the aim to identify possible anomalies in background seismicity that can be related with this and other future large events for this purpose we used a method for intermediate term forecasts of large earthquakes namely the region time length rtl algorithm which analyzes declustered catalogs and is sensitive to quiescences that may precede major earthquakes rtl has been progressively refined and has been applied in several regions worldwide during the last decades to decluster the earthquake catalog we used a quite novel approach based on the nearest neigbour distances between events in the space time energy domain a method that preserves the background seismicity while removing the clustered component the retrospective application of rtl algorithm to the area surrounding the mainshock epicenter highlights two significant quiescences one preceding the sarpol zahab mw 7 3 earthquake and the other occurring before a mw 5 7 earthquake which struck the same region on november 2013 the quiescences duration ranges from few months to one year and is compatible with earlier results from different regions of the world in addition we applied an enhanced variant of rtl algorithm which allows us drawing maps for the whole study region and that shows only quiescences consistently detected for different choices of the free parameters and hence more stable the resulting map for northwestern iran calculated for the time span 1 june 2017 11 november 2017 evidences two broad quiescence regions oriented nw se along the zagros belt one located to the north evidences a significant seismic anomaly corresponding to the sarpol zahab earthquake which disappeares immediately after the event the second one located in the southeastern part of the study region persists up to the end of the available catalog october 4 2018

an incision wave in the geologic record alpujarran corridor southern spain almeria abstract the term incision wave was coined in the 1990s to describe wave like patterns of stream incision propagating through numerically modeled bedrock channel river systems an incision wave consists of a crest where available stream power is greatest and where vertical incision is most rapid the crest is flanked by limbs where there is less available stream power and where vertical incision rates are slower farther away from the crest available stream power is less and incision rates are slower than in the limbs modeling results suggest tectonically induced base level fall triggers incision waves that propagate upstream through bedrock stream networks however it has recently been postulated that the equation underpinning incision wave models cannot realistically simulate river systems this paper provides field geological evidence supporting the hypothesis that tectonically induced base level fall triggers incision waves that propagate through bedrock stream networks for tens of kilometers mid and late pleistocene alluvial morphostratigraphy in the rio andarax drainage basin southeast spain is interpreted to indicate that patterns of paleo stream power were controlled by an incision wave in the conceptual model proposed in this paper the signature of an incision wave in the rio andarax drainage network is recorded by the contrasting morphostratigraphy of oxygen isotope stage 8 ois8 time landforms at the crest of the incision wave during ois8 there is no record of a paleoalluvial level because available stream power exceeded critical stream power and streams were incising vertically the crestal area is flanked by ois8 time strath terraces which record the position of the two limbs of the incision wave farther upstream ois8 time alluvial fills mark an area unaffected by the incision wave during oxygen isotope stage 2 ois2 and or oxygen isotope stage 1 ois1 sediment availability in the rio andarax catchment was low and the pattern of relative stream power was threshold like rather than wave like differences in the manifestation of the incision wave during ois8 vs during ois2 and or ois1 indicate that climate and sediment availability can control how incision waves propagate through fluvial systems

mapping seismic quiescence in california the decrease of microearthquake activity is a controversial possible precursor for mainshock prediction the calculation of seismic quiescence is a convenient tool to quantify this decrease however the actual size of an anomaly significantly depends on the calculation parameters the necessary averaging over space and time acts as 3d lowpass filter the sliding statistics windows introduce highpass behavior and the magnitude threshold shall ensure catalog completeness but also biases the data selection to argue on any claimed anomaly the only conclusive solution would be an exhaustive search over all parameters over an area significantly larger than just the epicenter region and against a test of the null hypothesis qmap is a new mapping approach to process full catalogs that is some twenty years of data for areas of one million km 2 with one fixed set of parameters it utilizes fractil statistics to avoid errors otherwise induced by clusters of aftershock series qmap features two different scaling modes one to display absolute decrease and a second for weighted anomalies by erosion filtering applied to california one can recognize quiescence anomalies of regional scale prior to the coalinga and loma prieta earthquakes but there are more and greater anomalies distributed all along the san andreas fault system without further criteria to understand these patterns the additional anomalies degrade seismic quiescence to an observation with high false alarm rate for earthquake prediction

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

tectonic controls for transverse drainage and timing of the xin ding paleolake breach in the upper reach of the hutuo river north china abstract the upper reach of the hutuo river flows along the xin ding basin and cuts a transverse drainage through the xizhou mountain and the taihang range into the north china plain previous studies showed that the xin ding basin was occupied by a lake during the early middle pleistocene however the timing of the paleolake breach and the mechanism for the creation of the transverse drainage are unknown we constructed the fluvial terrace sequence in the upper reach of the hutuo drainage combined with thermoluminescence tl and optically stimulated luminescence osl dating as well as the timescale of the overlying loess paleosol sequence our results reveal that 1 five terraces t5 t1 developed along the upper reach of the hutuo river amongst which terraces t4 t1 were formed synchronously at 600 120 130 20 26 and 6 7 ka respectively 2 the creation of the transverse drainage and breach of the xin ding paleolake occurred between 600 and 130 ka and 3 the mechanism for the creation of the transverse drainage is via river piracy of paleostreams on both sides of the drainage divide localized differential uplift and associated tilting of the xizhou mountain block during the middle pleistocene result in the formation of the transverse drainage and breach of the xin ding paleolake

two current seismic quiescences within 40 km of tokyo summary two highly significant seismic quiescence anomalies that started in 1993 0 exist currently within about 40 km of tokyo they are located in central saitama province at 35 99 n 139 56 e and in tokyo bay south of funabashi at 35 59 n l39 94 e the radii of the anomalous volumes are approximately 15 km centred at about 25 and 20 km depth respectively the seismicity rate during the quiescence was less than 10 per cent background rate in both cases the significance of these quiescences measured by the standard deviate z test comparing the rate of the last three years to the backgound rate is higher than for any other rate changes present in the catalogue zmax 7 5 and 7 2 respectively however episodes of highly significant quiescences which could have been interpreted as precursors but were not followed by main shocks also exist in the data set a third seismic quiescence was found to be in progress since 1993 3 0 5 in nw saitama province at 36 18 n 139 22 e it has a radius of 14 km and is less significant than the other two anomalies zmax 6 8 in a polygon that covers the areas of all three quiescences defined above the seismicity rate since 1994 is only 30 per cent of the previous background rate i e 100 earthquakes that would normally have occurred did not this analysis is based on the earthquake catalogue of the national institute for earth science and disaster prevention for the years 1980 1996 2 and mmin 1 0 as well as for the years 1986 2 1996 2 with mmin 0 1 the anomalies are equally clear in the clustered and in the full catalogues to avoid contamination by explosions only nighttime data 19 00 to 7 00 hours local time were used the frequency magnitude distributions in the quiescent volumes at central saitama nw saitama and funabashi have b values of 1 3 1 5 and 1 1 respectively based on the hypothesis that crustal volumes with high b values may not be capable of m6 earthquakes these three quiescent volumes may be ruled out as source volumes for main shocks of these magnitudes using lilt seismic quiescence hypothesis alone it is a reasonable interpretation to suggest that m 6 5 0 5 earthquakes are expected to terminate each of the three quiescences within 1 year 1 year from now with a 50 per cent probability each the interpretation that all three quiet volumes could rupture together in a large earthquake seems less likely however based on the information that the quiescences are located in volumes with b values above the average b 0 8 it can be argued that the three current quiescences are false alarms the fact that these two lines of evidence allow opposing interpretations in these cases shows that neither hypothesis is sufficiently tested thus the quiescence hypothesis is not advanced enough for issuing earthquake predictions nevertheless it is important that scientific tests of prediction scenarios are formulated in real time so we can learn how to modify our hypotheses to make them useful for prediction in the future

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

tectonic origin and evolution of a transverse drainage the rio almanzora betic cordillera southeast spain abstract the rio almanzora forms one of the larger drainage systems within the betic cordillera southeast spain in its distal reaches prior to joining the mediterranean sea the rio almanzora cuts across a major topographic barrier the sierra almagro forming drainage that is transverse to the regional geological structure the long term drainage evolution of the rio almanzora and its creation as a transverse drainage across the sierra almagro has been examined by reconstruction of an evolving basin scale drainage network using a combination of the geological and geomorphological record the early stages of drainage evolution late miocene pliocene and plio pleistocene reveals the emergence of marine basins to the north and south of the sierra almagro and the development of unconnected drainage systems this emergence records the development of the proto rio almanzora on the south side of the sierra almagro as a prograding fan delta and alluvial fan system expansion of this drainage network via incision and headward erosion across the sierra almagro took place during the pleistocene during the early mid pleistocene the proto rio almanzora became fully transverse across the sierra almagro and linked the endorheic almanzora huercal overa basin with the vera basin a tectonically induced lowering of regional base level is proposed for the incision headward erosion and drainage network expansion that has resulted in the creation of the rio almanzora as a transverse drainage differential uplift between the huercal overa almanzora and vera basins has resulted in southwards tilting and the creation of a regional gradient the fluvial response to tilting was for incision into the steepened regional surface gradient via an increase in stream power the incision headward erosion and drainage network expansion by the proto rio almanzora and its creation as a transverse drainage appears to be part of a regional response by fluvial systems to differential uplift recorded throughout the betic cordillera of southeast spain during the plio pleistocene

the linking of the upper middle and lower reaches of the yellow river as a result of fluvial entrenchment abstract the upper middle yellow river flows through the fenwei graben a structure resulting from extensional tectonism that was formed and repeatedly extended during the cenozoic the drainage system within this graben was formerly isolated from the lower reaches of the yellow river system by the xiaoshan mountains an actively growing nw se trending range the modern course of the yellow river takes it through this range along the sanmen gorge the formation of which was of great significance in that it initiated through going drainage between the upper middle and lower reaches of the system the timing of this event which was clearly a critical point in the evolution of the yellow river can be established by dating the terraces in the gorge intermittent deepening of this gorge by the yellow river from a high level planation surface capping the mountain range has resulted in the formation of five terraces magnetostratigraphic records from aeolian deposits accumulated on these surfaces provide a geochronological sequence for this geomorphic archive in which the ages of the planation surface and of terraces t5 t4 t3 t2 and t1 have been determined as 3 63 ma 1 24 ma 0 86 ma 0 62 ma 129 ka and 12 ka respectively under the constraint of this chronological framework a model for landscape evolution is proposed here uplift of the inner fenwei graben and of the surrounding mountain ranges led to dissection of the 3 63 ma old planation surface in conjunction with the formation of the sanmen gorge drainage of the lake previously occupying the basin would have promoted incision into the fluvio lacustrine graben sediments indeed gorge formation through the xiaoshan may have been initiated or intensified by lake overflow the ages obtained for the planation surface and uppermost terrace suggest that the formation of the sanmen gorge and the initiation of the through going eastward drainage of the yellow river occurred between 3 63 and 1 24 ma before the start of gorge entrenchment the products of erosion in the modern upper catchment of the yellow river were unable to reach the sea the dramatic increase in deposition rates in the bohai gulf at the mouth of the modern yellow river in the east china sea 1 0 ma ago thus resulted from the initiation of an integral enlarged yellow river catchment drainage through the sanmen gorge it does not imply an increase in erosion rates at that time

quantitative mapping of a precursory seismic quiescence to the izu oshima 1990 m6 5 earthquake japan a highly significant seismic quiescence with a standard deviate z 10 1 corresponding to a 99 per cent confidence level lasted from 1987 7 up to the 1990 february 20 izu oshima m 6 5 earthquake the quiescent volume had dimensions of 30 km n s and 10 km e w and was centred below 14 km depth within the recently upgraded seismograph network of the earthquake research institute eri this main shock was the only one with a magnitude m 5 8 in the upper 30 km of the crust for which the precursory quiescence hypothesis could be tested within a radius of 50 km and during the observation period 1983 5 1995 9 there were no other 1 5 yr or longer periods of quiescence that were rated z 6 5 in the declustered earthquake catalogue except one that was associated with volcanic activity the total space time covered by alarms including the volcanic one was less than 1 per cent at the z 6 5 level the rarity of highly significant episodes of quiescence and the correlation in space and time suggest that a precursory seismic quiescence started 2 5 yr before the izu oshima 1990 earthquake in its source volume and to the north of it and that it can be recognized with an alarm level of z 6 0 generating no false alarms during the 1 5 yr quiescence window only 10 earthquakes occurred in the quiet volume whereas 50 events were expected based on the rate seen at other times in randomly selected volumes containing 50 100 and 200 events the anomaly scored z 6 1 to 10 1 on the basis of the data from may 1983 to 1995 there is no highly significant quiescence currently present in the izu oshima area

sedimentary basin inversion and intra plate shortening abstract sedimentary basin inversion the shortening of formerly extensional basins is accommodated mainly by compressional reactivation of extant faults and fractures across a wide range of scales as such inversion is a large scale manifestation of byerlee friction the dynamic criterion for fault reactivation governing the effective shear strength of the shallow crust basin inversion generates distinctive deformational architecture and it is implicated strongly in sedimentary basin exhumation as a principal source of horizontal stress inversion drives significant sedimentary porosity reduction and resultant fluid flow upper crustal deformation is critically dependent on fluid overpressure i e pore fluid pressures greater than would be calculated from a hydrostatic gradient and perhaps more than in any other tectonic setting overpressures are potentially large during sedimentary basin inversion this review therefore includes discussion of the role of fluid overpressure in inversion and the evidence for it collectively inversion has profound implications good and bad for the prospectivity of many petroliferous sedimentary basins thus recognizing the evidence for basin inversion quantifying its magnitude and understanding the mechanisms that accommodate inversion and other phenomena affected by it have become essential components of the basin analyst s remit

sedimentary processes vertical stratification sequences and geomorphology of the roaring river alluvial fan rocky mountain national park colorado abstract the roaring river alluvial fan formed on 15 july 1982 in rocky mountain national park colorado by a catastrophic flood that was generated by a dam failure the fan covers an area of 0 25 square km has a radial length of 0 7 km and is up to 14 m thick sedimentation occurred in three phases each producing a distinct fan lobe initial sedimentation was by a noncohesive sediment gravity flow which deposited two levees on the proximal boundaries of lobe i the levees consist of a poorly sorted mixture of logs sand pebbles cobbles and boulders the first two lobes were built primarily by sheetflooding which deposited imbricated boulders in trains behind obstacles that formed as jams between boulders or logs and upright trees horizontally laminated granule and sand sedimentation took place down fan from the boulders due to deceleration of the expanding sheetflood thin to medium interbedded sand and cobble pebble gravel couplets were deposited by sheetflooding on the third lobe gravel was transported as bedload by supercritical flow and deposited locally where antidunes broke sand was transported as suspended load and deposited where flood velocity locally decreased due to destruction of antidunes increased roughness or flow separation around the low amplitude gravel bed forms the flood rechannelized at the distal end of lobe iii due to constriction between the fan and the valley margin deposits in the upper rechannelized reaches consist of crudely bedded cobble and pebble gravel and interstratified pebble gravel and backset bedded sand deposition was by supercritical flow in the lower reaches planar cross bedded sandy pebble gravel and climbing ripple horizontal trough cross bedded and backset bedded sand were deposited by supercritical and subcritical flow the flood deposit was modified during waning flood stage and during the three years following the flood by noncatastrophic discharge events these events formed braided distributary channels by erosion into the top of the sheet flood deposits fan building took place mostly by catastrophic unconfined discharge whereas much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge

benthic foraminifera from a recent shallow water hydrothermal environment in the aeolian arc tyrrhenian sea benthic foraminiferal assemblages from sediments around active or recently active hydrothermal vents in the aeolian arc have been investigated in four areas with different hydrothermal mineralization and seafloor exhalative activity at depths between 60 and 300 m active hydrothermal spots were distinguished from the surrounding sediments by direct observations by a remotely operated vehicle rov and subsequent seafloor sampling samples were taken at different water depths and are characterized by a number of mineralogies reflecting the changing temperature of the hydrothermal fluids overall benthic foraminifera are absent from sites with high temperature hydrothermal emissions and their distribution at sites of low temperature emissions is very patchy depending on the physical and or chemical conditions reflecting differences in temperature and composition of the emitted fluids in the secca del capo area which is free from recent emission activity the benthic foraminiferal population is indicative of a normal marine environment with globocassidulina subglobosa cassidulina crassa and gavelinopsis lobatulus in the basiluzzo secca dei pesci and panarea areas which are characterized by different degrees of hydrothermal activity three distinct assemblages have been recognized the first assemblage is dominated by ammodiscus catinus glomospira charoides and glomospira gordialis and indicates hydrothermal influence the second assemblage with lobatula lobatula asterigerinata mamilla rosalina globularis and quinqueloculina spp as main constituents indicates a seagrass environment influenced by diffuse emissions the third assemblage with abundant a catinus ammoglobigerina globigeriniformis g gordialis and haplophragmoides canariensis suggests low ph conditions resulting from acidic hydrothermal emissions leading to the dissolution of calcium carbonate tests d 2005 elsevier b v all rights reserved

fluvial terrace formation in the eastern fenwei basin china during the past 1 2 ma as a combined archive of tectonics and climate change abstract the key to understanding the fluvial response to climate change and surface uplift is a thorough distinguishing between their roles in terrace formation previous studies have tended to attribute the fluvial behavior of deposit incision alternation to climate cyclicity a preliminary explanation is proposed here for terrace formation in the eastern part of the fenwei basin china the observed fluvial terrace sequence was developed by the yellow river deeply downcutting into the emei platform which was uplifted within the eastern fenwei basin and therefore it probably records the tectonic history of this platform on the basis of the magnetostratigraphy and optically stimulated luminescence osl dating a ca 1 2 ma chronology was established for this terrace sequence pedostratigraphic analysis of the loess deposits accumulated on each tread reveals that the terrace deposits are overlain immediately by a paleosol bed suggesting that the abandonment of these terraces due to fluvial incision occurred at the transitions from glacial to interglacial climates the glacial interglacial climate cycle probably has a temporal control on the fluvial behavior of deposit incision alternation even though the yellow river develops in the subsiding fenwei basin the terrace generation may be sporadic and in the form of unusual stacked pattern before the emei platform was uplifted within the eastern fenwei basin the terrace staircases however formed in synchrony with glacial interglacial climate cycles since this platform began to uplift in the late middle pleistocene this result indicates that uplift may be necessary in large terrace staircase genesis it can force the river system to downcut deeply enough during climatic transitions to separate terrace levels adequately favoring the generation and subsequent preservation of the terrace treads the terrace sequence of the yellow river in the eastern fenwei basin therefore can be considered as a combined archive of climate change and local tectonic activity

influence of strike slip fault segmentation on drainage evolution and topography a case study the palomares fault zone southeastern betics spain abstract the palomares fault zone pfz is one of the main sinistral strike slip faults in the betics se spain with approximately 16 km of north south displacement the pfz initiated during the tortonian messinian as a transfer structure linking areas subject to nw se shortening during the plio quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of sierra almagrera sierra almenara these sierras which show moderate uplift rates of 0 05 0 15 m ka formed in response to the oblique slip regime of the pfz the drainage system in the vicinity of the pfz is asymmetric with respect to a main axial valley that runs parallel to the pfz on the downthrown fault block in this block the drainage density is lower and the streams are longer than in the uplifted block furthermore west of the main axial valley the streams describe eastward directed deflections indicating the progressive eastward migration of the main axial valley during the pleistocene the drainage system on the uplifted ranges shows a consequent pattern indicating recent uplift and folding under nnw sse convergence recent activity along segments of the pfz has increased topographical gradients favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

an analysis of the process of acceleration of seismic energy emission in laboratory experiments on destruction of rocks and before strong earthquakes on kamchatka and in italy abstract the time to failure model is a technique in which a failure function is fitted to a time series of accumulated benioff strain before a large earthquake we analyze the relation of the time to failure model to the hypothesis of fractal structure of seismicity a power law failure function varnes 1989 bufe and varnes 1993 and its log periodic generalization sornette and sammis 1995 are discussed the results of application of the log periodic time to failure model to the analysis of the process of acceleration of seismic energy emission in the laboratory experiments on rock destruction and before strong earthquakes on kamchatka and in italy are presented

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

the coupling status of alluvial fans and debris cones a review and synthesis alluvial fans and debris cones link two zones of the fluvial system e g hillslope gully systems to stream channels mountain catchment sediment source areas to main river systems or to sedimentary basins and therefore have important coupling or buffering roles these roles may be both functional and preservational the functional role includes debris cone coupling which controls sediment supply from hillslope gully systems to stream channels influencing channel morphology coupling through larger alluvial fans expressed by fanhead trenching causes a distal shift in sedimentation zones or when expressed by through fan trenching causes complete sediment by pass the preservational role stems from the fact that fans and cones are temporary sediment storage zones and may preserve a record of source area environmental change more sensitively than would sediments preserved further downsystem fan coupling mechanisms include distally induced coupling basal scour toe cutting marginal incision and proximally induced coupling fanhead and midfan trenching these mechanisms lead initially to partial coupling either extending the immediate sediment source area to the stream system or shifting the focus of sedimentation distally complete coupling involves transmission of sediment from the feeder catchment through the fan environment into the downstream drainage or a sedimentary basin the implications of coupling relate to downstream channel response fan morphology sedimentation patterns and vertical sedimentary sequences temporal and spatial scales of coupling are related and with increasing scales the dominant controls shift from storm events to land cover to climatic and base level change and ultimately to the relationships between tectonics and accommodation space finally future research challenges are identified modern dating techniques and sophisticated analysis of remotely sensed data can greatly improve our understanding of fan dynamics and should lead to better cross scale integration between short term process based approaches and long term sedimentological applications while maintaining high quality field based observations copyright 2011 john wiley sons ltd

seismicity rate variations and systematic changes in magnitudes in teleseismic catalogs abstract seismicity rate variations are commonplace in teleseismic catalogs these changes have two possible causes they could be real or they could be related to changes in the networks used to detect the events it is clearly important to differentiate between these two possibilities we demonstrate a technique for making this differentiation using uniform data generated with known rates and magnitude shifts we then apply this technique to data from large regions of the world all of these regions show significant variations in seismicity rates for sets with magnitude cutoffs of 5 0 and 5 5 we show that most of these changes have distributions in the magnitude domain which are consistent with systematic changes in magnitudes of between 0 1 and 0 2 units these results suggest that most observed rate variations in teleseismic sets with high magnitude cutoffs are related to systematic changes in magnitudes and are therefore not real this result has important implications for earthquake prediction and tectonic studies which interpret these variations

the influence of tectonics sea level fluctuations and river capture on the quaternary morphogenesis of the semi arid pulpi basin southeast spain abstract the semi arid pulpi basin is located within a 250 km long left lateral shear zone between alicante and almeria the pulpi basin itself is crossed by the n20e striking palomares fault active during the neogene and quaternary in the upper pliocene a major epeirogenic uplift occurred which caused emergence of the basins simultaneously a change from marine to terrestrial sedimentation started and the development of the present landscape began the quaternary relief development in the pulpi basin has been particularly influenced by tectonic disturbances and river captures which have had contrasting effects on different parts of the basin in the southern basin tectonically induced dissection of the oldest quaternary glacis level was accompanied by the influence of the fluctuations in sea level both factors have caused continuing erosion in the central pulpi basin mid quaternary fluvial capture processes were important for the morphogenesis since the loss of the catchment areas in the neighbouring huercal overa basin the fluvial activity of the rivers in the western part has been limited the transition from the distal end of the mid quatemary glacis to the present valley floor takes place without a noticeable step no younger fluvial terraces are missing in the eastern part the catchment area of the main river has hardly changed since its establishment during the upper pliocene besides the relics of the oldest glacis level no further glacis accumulation developed during the mid quaternary only a fluvial terrace was deposited

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

origin of a toarcian manganese carbonate silicate deposit from the križna unit tatra mountains poland abstract a mn bearing sequence of the kri na unit in the western tatra mountains occurs locally between shallow water crinoidal tempestites lower toarcian and pelagic red nodular limestones middle toarcian aalenian the mn bearing sequence forms a lens shaped body up to 2 m thick extending for a few hundred meters it consists of several distinctive facies fe rich layer 15 cm thick jasperite up to 0 5 m thick x ray amorphous mn oxide layer 10 cm thick shale 510 cm thick and mn rich bed up to 1 1 m thick minerals in the mn rich bed such as braunite caryopilite mn bearing calcite and rhodochrosite are distributed in two distinctive zones carbonate and silicate dominated the most important geochemical characteristics of these deposits are high mn contents up to 62 8 wt mno low concentrations of transitional elements co ni cu

seismic quiescence preceding the 2016 central italy earthquakes abstract a complex multiple mainshocks sequence 24 08 2016 mw 6 0 26 10 2016 mw 5 4 and 5 9 30 10 2016 mw 6 5 occurred in central italy causing the death of nearly 300 people and widespread destruction of entire villages the region time length rtl method is used to analyze the seismicity preceding the first mw 6 0 amatrice mainshock this analysis is performed using the earthquake catalogue maintained by the istituto nazionale di geofisica e vulcanologia ingv after a preprocessing which includes the declustering of aftershocks a well evident quiescence that preceded the sequence was detected the quiescence extended throughout a broad region north of the epicenter the largest event of the sequence and the aftershocks covered most of the quiescence region except for a small area to the west the quiescence started from the beginning of september 2015 and lasted for approximately 1 year up to the amatrice mainshock

response of quaternary fluvial systems to differential epeirogenic uplift aguas and feos river systems southeast spain the geomorphic expression of two fluvial systems the rio de aguas and the rambla de los feos in southeast spain reflects their adjustment to differential epeirogenic uplift and local tectonic activity during the quaternary regional uplift of a depositional marine surface resulted in the development of a southward flowing drainage network during late pliocene early pleistocene time disruption of this consequent drainage began as the alhamilla cabrera sierras and the sorbas basin were differentially uplifted relative to the surrounding basins the ancestral feos drainage responded by incision across the uplift through a combination of superimposition and antecedence differential uplift of the sorbas basin enhanced headward erosion of strike oriented drainages and promoted capture of the ancestral feos drainage by the rio de aguas during the late pleistocene stratigraphic relations and soil development indicate that epeirogenic uplift and local tectonics together with climatic fluctuations have influenced the development of the drainage systems throughout the quaternary

teleseismic detection in the aleutian island arc recently it has become apparent that teleseismic detection has decreased substantially in many regions of the world the major decrease was related to the closure of the vela arrays in the united states during the late 1960 s this detection decrease has been recognized in south and central america mexico the kuriles the caribbean tonga and the new hebrides in this paper the effect of the closure of these arrays on the reporting of events in the aleutian island arc is examined in the aleutians the detection history is complicated by the short term installation of a local network on and near amchitka island during the early 1970 s the temporal coincidence of the installation of this network and the closure of the vela arrays delayed the detection decrease in the central aleutians until the amchitka network was closed in early 1973 reporting in the eastern aleutians was unaffected by the installation of the amchitka network in that region the detection decreased between 1968 and 1970 the time of the closure of the vela arrays new techniques have been developed which make it possible to determine the effect of station installation or closure on the reporting in some regions these techniques rely on plots which show the distribution of an observed seismicity rate change in the magnitude domain these plots make it possible to recognize probable detection changes and to determine quantitatively magnitude cutoffs which avoid these changes the magnitude level at which these cutoffs are made is termed the minimum magnitude of homogeneity mmin h the reporting of events with mb 4 6 in the aleutians decreased substantially during the mid 1970 s so mmin h in this region is 4 7 this is different from the magnitude of completeness mmin c which is mb 5 0 0 1 if one is interested in examining seismicity rates for changes which may be precursors to earthquakes then awareness of detection related changes and magnitude cutoffs which avoid these changes are essential for meaningful results

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

massive sulfides in a sedimented rift valley northern juan de fuca ridge a number of mounds each several hundred meters across and up to sixty meters high have been observed with seamarc ii acoustic imagery and seabeam bathymetry in the sediment filled axial valley at the northern end of the juan de fuca ridge the mounds are located a few kilometers west of the eastern valley bounding normal fault scarp where the local sediment fill is approximately 300 m thick all of the mounds are believed to be of hydrothermal origin and one is associated with anomalously high heat flow in excess of 1 w m 2 a piston core collected from that mound comprises coarse clastic sulfide units interbedded with sulfidic muds hydrothermal minerals present in the 2 3 m section include pyrrhotite pyrite marcasite sphalerite chalcopyrite iss intermediate solid solution in the cufezns system chalcopyrrhotite galena talc barite and amorphous silica mineral fabrics of the clasts indicate that the material was precipitated at or near the sea floor by mixing of hot hydrothermal fluids with cold seawater low concentrations of zn cu cd and ag relative to those found in unsedimented ridge hydrothermal deposits and the presence of pyrrhotite as an early phase mineral indicates that the vent fluids have been modified by reaction with sediments beneath the mound rapid sedimentation in a rift valley is clearly conducive to the formation of large hydrothermal mineral deposits like those believed to be present within and beneath these mounds the relatively impermeable sediment cover insulates the crust inhibits groundwater recharge promotes long lived discharge at a restricted number of sites provides a substrate for the efficient subsurface precipitation of minerals and through continued sedimentation protects surficial deposits from the corrosive effects of seawater no reliable estimate of the bulk composition of the mounds can be made with existing data but their size is comparable to major hydrothermal mineral deposits found on land ancient settings in which many land deposits formed are in many ways similar to the one in which the features described here are currently forming

stream capture and piracy recorded by provenance in fluvial fan strata abstract stream capture and piracy in tectonically active regions have been described in geomorphic systems worldwide however few studies show the influence stream capture has on the rock record we present an analysis of fluvial fan stratigraphy that developed as a result of multiple stream capture events building a complex stratigraphic succession beneath the lawrence livermore national laboratory llnl california the llnl site is located in the southeast portion of the tectonically active livermore basin a transpressional basin in the california coast ranges geomorphic evidence for this stream capture include 1 the arroyo seco enters the basin from the south through an uplifted fault block 2 south of this fault block lies an abandoned arroyo seco fluvial fan 3 north of the fault block in the livermore basin arroyo seco built a 7 km2 fluvial fan apparently forcing the arroyo las positas a smaller stream that enters the basin from the east northward around the arroyo seco fan and 4 a knickpoint exists near the point of capture on arroyo seco stratigraphic evidence reflecting this shift in the arroyo seco position into the livermore basin was evaluated through a provenance study of 215 gravel units from 34 boreholes spaced evenly over the 2 6 km2 llnl site the arroyo seco derives its sediment from both the jurassic cretaceous franciscan assemblage and the altamont hills which are comprised of mesozoic great valley group and tertiary continental sediments the arroyo las positas drains only the altamont hills and thus lacks the franciscan assemblage derived clasts the origin of the individual gravel units was determined by the percentage of franciscan assemblage indicator pebbles red chert green chert and blueschist in the samples through this analysis we determined that high percentage franciscan assemblage derived clasts were present below a depth of approximately 35 m below the surface low percentage franciscan assemblage derived clasts were present at depths between 35 m and 18 m and high percentage franciscan assemblage derived clasts were present from depths of approximately 18 m to the surface of the fluvial fan these results indicate that the arroyo seco flowed north and deposited sediments at the llnl site then was later absent from the basin at which time it formed a fan south of the fault block during this absence of the arroyo seco the arroyo las positas a westerly flowing stream dominated the sediment supply at the llnl site the arroyo seco was then captured by a gully headward eroding through the uplifted fault block redirecting the arroyo seco into the basin once again this history of multiple stream captures created three stratigraphic units with alternating overall channel and paleoflow orientations

spatial characteristics of the pliocene to modern alluvial fan successions in the uplifted sedimentary basins of almeria se spain review and regional synthesis