documenting drainage evolution in bir kiseiba southern egypt constraints from ground penetrating radar and implications for mars 1 ground penetrating radar gpr helps to constrain the origin of relict and largely buried fluvial channels in the bir kiseiba region of southern egypt our results indicate that the trunk channel to a tributary system identified in shuttle imaging radar data is incised 10 12 m into bedrock was southwest draining in its final configuration and laterally migrating toward the northwest and accentuated relief along the nearby kiseiba escarpment alluvium partially filling the main channel likely reflects effects of increasing aridity and bed load combined with less frequent flashier precipitation in contrast to defining channel margins radar data do not indicate subtle stratigraphic changes in bedding related to fluvial aggradation but do highlight local reflections likely corresponding to relict alluvial bedforms our results support the contention that an impulse gpr system currently under development could be deployed on a future mars rover and assist in defining the regional evolution of the landscape and specific targets for sampling

performances of ground penetrating radars in arid volcanic regions consequences for mars subsurface exploration a gpr field experiment in the republic of djibouti provides evidence for very low radar penetration in arid volcanic materials in the range 100 500 mhz this phenomenon is attributed to the high iron oxide and evaporite concentration in soils which significantly increases the conductivity thus leading to poor subsurface imaging performances the geologic context in djibouti is shown to provide a good terrestrial analogue to mars geology results of this study show that the future sounding radar missions to mars may not reach the penetration depths previously anticipated

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

open system coral ages reveal persistent suborbital sea level cycles sea level is a sensitive index of global climate that has been linked to earth s orbital variations with a minimum periodicity of about 21 000 years although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing suborbital frequency sea level change has been difficult to resolve primarily because of problems with uranium thorium coral dating here we use a new approach that corrects coral ages for the frequently observed open system behavior of uranium series nuclides substantially improving the resolution of sea level reconstruction this curve reveals persistent sea level oscillations that are too frequent to be explained exclusively by orbital forcing

regional uplift and local tectonic deformation recorded by the quaternary marine terraces on the ionian coast of northern calabria southern italy abstract the setting of a flight of marine terraces along a 65 km long section of the ionian coast of northern calabria is the result of the interaction between interglacial sea levels regional uplift and local fault related elevation changes seven terraces with corresponding palaeoshoreline angles at elevations ranging from 12 m to 420 m were recognised by aerial photo interpretation and field surveying the terraces were correlated to the oxygen isotope stages 1 5a 5c 5e 7 9 15 which correspond to the 7 81 102 124 215 330 and 600 ka highstands of the palaeosea level curve the 600 ka long regional ascent of the terraces took place at an average uplift rate of 0 67 mm yr this value slightly but progressively increases southward along the coastline the elevation of the strandlines is related to the activity of tectonic structures three cases were analysed allowing us 1 to recognise the height anomalies of the terraces on the sibari plain as the result of cumulated coseismic deformation caused by the normal castrovillari fault and on this basis calculate a minimum slip rate and a mean recurrence time for a single event of deformation 2 to exclude the presence of significant vertical deformations and consequently activity on the easternmost section of the normal pollino fault and 3 to hypothesise the presence of an hitherto unknown active fault responsible for the strong vertical displacements of the flight of terraces near the river avena finally we find the ratio of the rate of regional uplift to the average rates of local tectonic deformation to be 2 to 3 1

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

vertical sequence and lateral transitions in the facies of a barred nearshore environment abstract nine tube cores 7 cm in diameter and up to 150 cm long from a nearshore crescentic bar in kouchibouguac bay new brunswick canada reveal the vertical sequence and lateral transitions of facies previously identified only in shallow box cores the facies are a inner shelf shoreface transition bioturbated fine sands and silts with remnant primary structures b seaward slope planar lamination in medium to fine sands dipping gently seaward and composite bed sets of planar to ripple cross lamination in fine sand chevron lamination is rare c bar crest low angle planar lamination dipping both landward and seaward and medium scale trough cross lamination in medium to coarse sands d landward slope planar lamination dipping landward with small scale la dward dipping trough cross lamination occasionally small to medium scale trough cross lamination is found with seaward dips e trough massively bedded lags of coarse gravelly sands with abundant shell fragments contrast with isolated very thin units of massive silt and units of well sorted sands the latter display subhorizontal planar lamination and small to medium scale trough cross lamination polymodal dips indicate bed form migration landward alongshore and offshore vertical sequences and lateral transitions seaward of the bar crest suggest that three wedge shaped units inner shelf shoreface transition seaward slope bar crest interdigitate in an offlap onlap sequence to landward the trough and landward slope facies interfinger complexly while the crest facies forms a simple onlap over landward slope facies total reworking of sediments within the bar trough system is expected every 5 to 6 years and long term preservation is limited to the inner shelf shoreface transition seaward slope and trough facies

the calcarenite di gravina formation in matera southern italy new insights for coarse grained large scale cross bedded bodies encased in offshore deposits excellent outcrops of the upper pliocene lower pleistocene calcarenite di gravina around matera southern italy provide continuous exposure of coarse grained clastic basin margin shoreline to offshore facies among these facies the most conspicuous and volumetrically important are the transition slope deposits that form large scale high angle cross bedded lithosomes these are laterally extensive parallel with the paleoshoreline and show seaward progradation we interpret them to represent avalanches of sediment swept out onto a depositional slope below wave base from the shoreface zone by storm waves and wind driven currents three types of building blocks are recognized based on bedding patterns and facies architecture embryonic parasequences mature parasequences and simple sequences parasequences formed during stillstands of sea level and simple sequences during high frequency cycles of relative change of sea level these building blocks are stacked in a backstepping configuration and onlap onto cretaceous limestone substrate backstepping is believed to be due to a tectonically forced transgression that is punctuated by high frequency cycles of sea level modern analogs for these building blocks are the holocene prograding prisms detected in high resolution seismic lines of the mediterranean shelves the reflection patterns of these seismic units resemble the bedding architecture of the matera simple sequences and parasequences and show similarities of shape size position and orientation of coastal setting and direction of progradation comparison of the holocene prisms and the pliocene pleistocene accretional units in matera indicates that they may represent the same begin page 662 genetic process progradation of clastic prisms below the wave base level the matera accretional units also show similarities with other examples of laterally extensive large scale cross bedded sand bodies encased in offshore deposits such as some sandbanks differentiating between these laterally extensive and seaward prograding cross bedded sand bodies and some coarse grained gilbert type deltas is difficult however if interpretations are based only on two dimensional 2 d outcrops in dip section without high resolution data it is also difficult to distinguish between transition slope and prograding shoreface lithosomes this difficulty may be acute where only seismic or well log data are available however certain other architectural characteristics such as stacking and preservation of facies belts and position of bounding surfaces as well as differences in associated sedimentary structures and fossil content may be used for interpretation the matera example provides a mechanism for emplacement in offshore settings of elongate and strandline parallel sand and gravel deposits that prograde seaward and that preserve a coarsening upward internal succession this article offers an interpretation for other ancient examples of large scale cross bedded lithosomes encased in offshore deposits

the geographical distribution and palaeo ecology of selenopemphix undulata sp nov a new late quaternary dinoflagellate cyst from the pacific ocean abstract detailed palynological studies in the northeast ne pacific strait of georgia bc canada southeast se pacific and northwest pacific dongdo bay south korea resulted in the recognition of the new dinoflagellate cyst species selenopemphix undulata sp nov this species is restricted to cool temperate to sub polar climate zones where it is found in highest relative abundances in highly productive non to reduced upwelling regions with an annual mean sea surface temperature asst below 16 c and an annual mean sea surface salinity asss between 20 and 35 psu those observations are in agreement with the late quaternary fossil records from santa barbara basin odp 893 34 n and offshore chile odp 1233 41 s where this species thrived during the last glacial this period was characterised by high nutrient availability and the absence of species favouring upwelling conditions the indirect dependence of s undulata sp nov abundances on nutrient availability during reduced or non upwelling periods is expressed by the synchronous fluctuations with diatom abundances since the distribution and growth rates of the latter are directly related with the availability of macronutrients in the surface waters

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

the architectural variability of small scale cycles in shelf and ramp clastic systems the controlling factors many sedimentary successions are composed of metre to decametre scale cycles exhibiting various stratal architectures that depend on the complex interplay among several syndepositional controlling factors these controlling factors may produce extremely different stratal and facies architectures along relatively brief distances in the same basin but in contrast they also may form similar architectures in basins that experience a radically different tectonic setting the recognition of factors that controlled the architecture of small scale cycles therefore is very important to reconstruct the depositional history of sedimentary successions these factors include 1 the interplay between the rate of accommodation development and the rate of sediment supply a s 2 the amplitude and shape of the relative sea level curve 3 the position in the shoreface shelf system 4 the basin physiography 5 the shoreline trajectory 6 the climate driven environmental energy 7 the siliciclastic input vs carbonate production shoreface to shelf small scale cycles can be grouped into three main categories r cycles showing a dominant regressive interval t r cycles with transgressive and regressive intervals of similar thickness t cycles showing a dominant transgressive interval although some depositional settings may favour the deposition of a particular type of cycle these cycle motifs appear to be mainly controlled by the interaction of local and wider scale controlling factors for example t cycles may be present in both subsiding and uplifting settings depending on the interplay between the a s and the other factors cited above as a result r t r and t cycles may be recognized within the same depositional system these evidences suggest that care must be taken to apply general models that predict the stratal architecture of cycles mainly in function of the long term a s the correct prediction of the cycle architecture is important also for hydrocarbon researches as the thickness of potential reservoir deposits is the result of the interplay among factors discussed here

early pliocene transgressive coastal lags bajo segura basin spain a marker of the flooding after the messinian salinity crisis abstract the messinian salinity crisis is recorded on the northern margin of the bajo segura basin by lacustrine and fluvial deposits coeval to the evaporites that precipitated in the basin s central areas these syn evaporitic messinian deposits are bounded at the top by an erosional surface caused by a fall in base level end messinian unconformity on which an early pliocene sequence is located the latter begins with a coastal lag consisting of oncoliths and carbonate clasts intensely bored and encrusted by lithobionts that records the installation of beach environments at the beginning of the pliocene transgression a succession of pelagic marls rich in planktonic and benthic foraminifers lies on this basal lag and indicates the complete marine flooding of the basin and the definitive conclusion of the salinity crisis

radar investigation of mars mercury and titan radar astronomy is the study of the surfaces and near surfaces of solar system objects using active transmission of modulated radio waves and the detection of the reflected energy the scientific goals of such experiments are surprisingly broad and include the study of surface slopes fault lines craters mountain ranges and other morphological structures electrical reflectivities contain information about surface densities and to some extent the chemical composition of the surface layers radar probes the subsurface layers to depths of the order of 10 wavelengths providing geological mapping and determinations of the object s spin state radar also allows one to study an object s atmosphere and ionic layers as well as those of the interplanetary medium precise measurements of the time delay to surface elements provide topographic maps and powerful information on planetary motions and tests of gravitational theories such as general relativity in this paper we limit our discussion to surface and near surface probing of mercury mars and titan and review the work of the past decade which includes fundamentally new techniques for earth based imaging the most primitive experiments involve just the measurement of the total echo power from the object the most sophisticated experiments would produce spatially resolved maps of the reflected power in all four stokes parameters historically the first experiments produced echoes from the moon during the period shortly after world war ii see e g evans 1962 but the subject did not really develop until the early 1960s when the radio equipment was sufficiently sensitive to detect echoes from venus and obtain the first doppler strip maps of that planet the first successful planetary radar systems were the continuous wave cw radar at the goldstone facility of the caltech s jet propulsion laboratory and the pulse radar at the mit lincoln laboratory all of the terrestrial planets were successfully studied during the following decade yielding the spin states of venus and mercury a precise value of the astronomical unit and a host of totally new discoveries concerning the surfaces of the terrestrial planets and the moon this work opened up at least a similar number of new questions although the early work was done at resolution scales on the order of the planetary radii very rapid increases in system sensitivities improved the resolution to the order of 100 km but always with map ambiguities recently unambiguous resolution of 100 m over nearly the entire surface of venus has been achieved from the magellan spacecraft using a side looking synthetic aperture radar reviews of the work up to the magellan era can be found in evans 1962 muhleman et al 1965 evans hagfors 1968 see chapters written by g pettengill t hagfors and j evans and ostro 1993 the radar study of venus from the magellan spacecraft was a tour de force and is well described in special issues of science volume 252 april 12 1991 and in the journal of geophysical research volume 97 august 25 and october 25 1992 venus will not be considered in this paper even though important polarization work on that planet continues at arecibo goldstone and the very large array vla in this paper we review the most recent work in earth based radar astronomy using new techniques of earth rotation super synthesis at the vla in new mexico operated by the national radio astronomy observatory and the recently developed long code techniques at the arecibo observatory in puerto rico operated by cornell university note it was recently brought to our attention that the vla software doubles the flux density of their primary calibrators consequently it is necessary to half the radar power and reflectivity numerical values in all of our published radar results from the vla goldstone radar the symbiotic relationship in these new developments for recent advances in our understanding of mercury and mars is remarkable vla imaging provides for the first time unambiguous images of an entire hemisphere of a planet and the long code technique makes it possible to map mars and mercury using the traditional range gated doppler strip mapping procedure which was apparently developed theoretically at the lincoln laboratory by paul green based on a citation in evans 1962 richard goldstein was the first to obtain range gated planetary maps of venus as reported in carpenter goldstein 1963 such a system was developed earlier for the moon as reported by pettengill 1960 and pettengill henry 1962 we first discuss the synthesis mapping technique

marine cements in mid tertiary cool water shelf limestones of new zealand and southern australia large areas of southern australia and new zealand are covered by mid tertiary limestones formed in cool water shelf environments the generally destructive character of sea floor diagenesis in such settings precludes ubiquitous inorganic precipitation of carbonates yet these limestones include occasional units with marine cements 1 within rare in situ biomounds 2 within some stacked cross bedded sand bodies 3 at the top of metre scale subtidal carbonate cycles and 4 most commonly associated with certain unconformities the marine cements are dominated by isopachous rinds of fibrous to bladed spar interstitial homogeneous micrite and interstitial micropeloidal micrite often precipitated sequentially in that order internal sedimentation of microbioclastic micrite may occur at any stage the paradox of marine cemented limestone units in an overall destructive cool water diagenetic regime may be explained by the precipitation of cement as intermediate mg calcite from marine waters undersaturated with respect to aragonite in some of the marine cemented limestones aragonite biomoulds may include marine cement sediment internally suggesting that dissolution of aragonite can at times be wholly marine and not always involve meteoric influences we suggest that marine cementation occurred preferentially but not exclusively during periods of relatively lowered sea level probably glacio eustatically driven in the mid tertiary at times of reduced sea level there was a relative increase in both the temperature and the carbonate saturation state of the shelf waters and the locus of carbonate sedimentation shifted towards formerly deeper shelf sites which now experienced increased swell wave and or tidal energy levels fostering sediment abrasion and reworking reduced sedimentation rates and freer exchange of sediment pore waters energy levels were probably also enhanced by increased upwelling of cold deep waters onto the southern ocean margins of the australasian carbonate platforms where water mass mixing warming and loss of co2 locally maintained critical levels of carbonate saturation for sea floor cement precipitation and promoted the phosphate glauconite mineralization associated with some of the marine cemented limestone units

temporal development of prograding beach shoreface deposits the holocene of kujukuri coastal plain eastern japan abstract prograding beach foreshore deposits with a basal ravinement bed are recognized from detailed ams 14c dating and grain size analyses of holocene deposits of the kujukuri coastal plain facing the pacific coast of japan the holocene deposits are about 20 m thick and consist of an upward shoaling beach foreshore succession that has a basal unconformity overlain by a thin layer of relatively coarse sand the unconformity is a downlap surface which originated from a ravinement surface the overall succession was formed by a prograding beach foreshore system during the highstand in sea level of the last 6000 years poorly preserved fossil shells enclosed in the thin layer of coarse sand at the base of the succession date from the transgressive stage in sea level before 6000 cal yr bp grain size distribution patterns are polymodal in the basal sand layer and unimodal in the remainder of the succession modal classes of the basal part are fine 3 3 2 6 medium 2 3 1 8 and coarse 1 2 1 0 the fine mode and the unimodal grain sizes define an overall upward coarsening trend which correlates with the upward shoaling succession in contrast the medium and coarse modes are restricted to the basal sand and are interpreted as related to the ravinement process the thin basal sand layer an admixture of these modal classes is interpreted as a type of ravinement deposit preserved during sea level highstand no transgressive deposit was preserved on the ravinement surface because sediment supply was so small that the sediment on this surface experienced thorough reworking by storm waves

coralline algal reef frameworks published and unpublished accounts of coralline algal reef frameworks are reviewed the descriptions are divided into frameworks constructed from crustose coralline algae and those constructed from branching corallines crustose frameworks are briefly described and illustrated from the miocene of malta recent coralligene from the mediterranean eocene reefs from spain recent algal reefs of st croix u s virgin is and algal reefs from bermuda branching frameworks are briefly described and illustrated from the recent maerl of the ne atlantic recent mud mounds from florida recent algal reefs from st croix and recent algal ridges on pacific reefs crustose and branching frameworks show an increase in strength of construction early submarine cements and macro borers and a decrease in erodibility from low to high energy environments the occurrence of genera in coralline frameworks is primarily controlled by their geographic and water depth ranges the construction of coralline frameworks is seen as the result of competition for living space on shallow marine hard substrates

burial dominated cementation in non tropical carbonates of the oligocene te kuiti group new zealand abstract cementation of bryozoan echinoid benthic foraminiferal temperate shelf carbonates of the oligocene te kuiti group north island new zealand occurred mainly during subsurface burial the calcite cements in the limestones are dominated by equant and syntaxial rim spar which typically becomes ferroan given an iron supply and compared to the skeletal material with normal marine 18o values from 2 to 1 more depleted in 18o with depth of burial the 18o composition of bulk cement samples ranging from 1 to 7 these trends reflect the establishment in pore waters during sediment burial of reducing conditions and gradually increasing temperatures 20 50 c respectively the 13c values 0 to 3 of the cements remain the same as the host marine shells suggesting the source of carbon in the cements was simply redistributed marine carbonate derived from shell dissolution two gradational burial diagenetic environments influenced by marine derived porewaters are arbitrarily distinguished shallow burial phase and moderate burial phase during the shallow burial phase down to 500 600 m sub bottom depth the carbonates lost at least 25 of their original porosity by mechanical compaction and were selectively cemented by non ferroan or usually ferroan variably luminescent slightly 18o depleted sparry calcite cement 18o 2 to 4 mainly as syntaxial rims about echinoid grains these shallow burial cements form less than about 10 of total cement in the majority of the limestones and their source was probably mainly mild intergranular dissolution of calcitic skeletal fragments accompanying the onset of chemical compaction during the moderate burial phase between about 600 and 1100 m sub bottom depth porosity loss continued typically to about 70 of its original value as a result of pressure solution of calcitic bioclasts associated with more advanced stages of chemical compaction this involved development of a wide variety of non sutured and microstylolitic solution seams including both single and composite wispy or continuous bedding parallel types and non parallel reticulate forms the released carbonate was precipitated as ferroan or non ferroan where iron supply was negligible dull luminescent strongly 18o depleted 18o 4 to 7 mainly equant calcite spar cement occluding available pore space in the limestones

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

nearshore temperate carbonate depositional systems lower tortonian agua amarga basin southern spain implications for carbonate sequence stratigraphy abstract the bryozoan rich lower tortonian carbonates of the agua amarga basin in southern spain province of almeria provide an example of sediments formed in a nearshore non tropical depositional setting based on data derived from logging of sections and from field mapping these lower tortonian carbonates form a depositional sequence which is subdivided into several depositional systems a lowstand systems tract which consists of volcaniclastic fan deltas and washover deposits formed on the leeward side of a basement shoal which delimited the basin towards the south a transgressive systems tract which is characterised by a landward encroachment of deposits is represented by submarine bars and dune deposits a highstand systems tract consists of progradational beach deposits owing to strong reworking and re distribution of the particles by currents and waves microfacies differentiation of the deposits in poor these tortonian non tropical carbonates display a style of deposition similar to siliciclastics suggesting that sequence stratigraphic concepts derived from tropical carbonates do not apply to non tropical carbonates

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

facies partitioning and sequence stratigraphy of cool water mixed carbonate siliciclastic sediments upper miocene guadalquivir domain southern spain during the late miocene the guadalquivir basin and its satellite basin the ronda basin were under atlantic cool water influence the aim of our study is to develop a sequence stratigraphic subdivision of the ronda basin fill and to provide models for the cool water carbonates the upper miocene of the ronda basin can be divided into three depositional sequences sequence 1 is early tortonian sequence 2 late tortonian to earliest messinian and sequence 3 messinian in age the sediments were deposited in a ramp depositional system sequence 1 is dominated by conglomerates and marls in sequence 2 and sequence 3 carbonate deposits dominate in the inner ramp whereas siliciclastics preferentially occur in the middle and outer ramp bryomol carbonate sediments occur in all sequences whereas rhodalgal carbonates are restricted to sequence 3 in bays protected from siliciclastic influx rhodalgal deposits formed under transgressive conditions a bryomol factory occurs in zones of continuous siliciclastic supply this distribution results from facies partitioning during the flooding of the ronda basin which has a rugged and irregular relief embayments were protected from siliciclastic influx and provided regions with less hydraulic energy

integrated micropaleontological study of the messinian diatomaceous deposits of the monferrato arc piedmont basin nw italy new insights into the paleoceanographic evolution of the northernmost mediterranean region abstract the upper miocene diatom bearing section of pecetto di valenza piedmont nw italy represents a unique site for reconstructing the paleoceanographic processes that occurred before the onset of the messinian salinity crisis in the northernmost mediterranean basin the combined analysis of foraminifera calcareous nannofossils diatoms and other siliceous microfossils observed in the marly and diatomaceous sediments allowed us to define four main evolutionary stages of the biogenic sedimentation each stage was typified by specific water column and seafloor conditions tentatively correlated to the precession insolation variability in particular the variation of the benthic assemblages allowed us to distinguish two stages in the evolution of the diatomaceous deposition which would be otherwise impossible from the lithology the accumulation of the diatomaceous sediments was likely controlled by the interplay between riverine runoff water column stratification and convective mixing rather than with upwelling and seafloor anoxia as inferred for the western and eastern sectors of the mediterranean

rare earth element geochemistry of laminated diatom mats from tropical west pacific evidence for more reducing bottomwaters and higher primary productivity during the last glacial maximum rare earth elements ree along with selected major and trace elements were measured in laminated ethmodiscus rex diatom mats and associated sediments diatomaceous clay and pelagic clay in two sediment cores collected from the parece vela basin of the eastern philippine sea ree distributions are characterized by strong enrichment of middle ree mree and heavy ree hree over light ree lree and slight enrichment of mree over hree this distribution pattern suggests that ree compositions of the laminated e rex diatom mats were not the product of e rex blooms an inference also supported by the fact that ti normalized ree concentrations are not clearly different from those in the diatomaceous clay and pelagic clay comparison of ree patterns with the vertical distribution of authigenic phases in the sediment indicates that lree were dominantly associated with detrital materials whereas mree and hree were selectively enriched by mn oxyhydroxides and authigenic phosphates in the pelagic clay a weak negative ce anomaly cannot be linked to oxic depositional conditions but instead is attributed to the retention of a negative ce anomaly associated with authigenic phosphates in the laminated e rex diatom mats a weak positive ce anomaly is consistent with depositional sulfidic anoxic conditions and is interpreted to represent enhanced scavenging of reduced aqueous ce3 by barite in a strongly reducing environment moreover variably negative to positive ce anomalies in the diatomaceous clay may reflect the concurrent operation of the two processes controlling ce accumulation in the laminated e rex diatom mats and pelagic clay the study cores show a ubiquitous positive eu anomaly owing to the presence of volcanic materials the smaller eu anomaly in the laminated e rex diatom mats and diatomaceous clay relative to that in the pelagic clay may be attributed to the release of reduced eu2 from mineral phases to the sediment pore water under strongly reducing conditions previous studies have shown that the advection of lower circumpolar water lcpw strengthened during the last glacial maximum lgm which should have resulted in better ventilation of the deep eastern philippine sea evidence presented here for more reducing bottomwater conditions during the laminated e rex diatom mats formation implicates elevated primary productivity and enhanced organic sinking fluxes as primary controls on redox changes in the eastern philippine sea during the lgm enhanced primary productivity and more reducing bottomwaters during the laminated e rex diatom mats deposition resulted in a larger respired carbon pool in the deep eastern philippine sea which may have been part of a larger scale modulation of atmospheric co2 variation during pleistocene glacial interglacial cycles by deep ocean carbon storage c 2011 elsevier b v all rights reserved

bedforms and depositional sedimentary structures of a barred nearshore system eastern long island new york abstract the depositional sedimentary structures and textures of a single barred nearshore system on the atlantic coast of eastern long island new york were studied along seven shore normal transects data along these transects consisted of textural analysis of 160 sediment samples temporal bedform observations and 42 can cores for the analysis of sedimentary structures six sedimentary subenvironments were observed based on distinct combinations of sediment color and texture bedforms physical and biogenic sedimentary structures and benthic infaunal communities the shoreface environment is divided into the upper shoreface the longshore trough and the longshore bar the divisions of the inner shelf environment are the shoreface inner shelf transition the offshore and the coarse grained deposit the first five subenvironments are arranged in bands parallel to the shoreline whereas the coarse grained deposit occurs in patches across the inner shelf the location of fair weather wave base coinciding with a reduction in slope 3 0 0 3 from the shoreface to the inner shelf is characterized by the cessation of debris surge in the troughs of ripples the formation of a rust layer of microorganisms over the bedform surface and a sediment color change caused by an increase in organic detritus the sequence of bedforms and physical sedimentary structures observed in this system fits well with existing wave generated oscillatory flow regime models these models explain the observed sequences as a response to the degree of asymmetric flow created by shoaling waves distribution of biogenic structures and assemblages of infaunal organisms is influenced by the distance landward or seaward of fair weather wave base the overall relationships of this nearshore system can then be summarized as a hypothetical prograding stratigraphic sequence the entire sequence is underlain by organic rich bioturbated offshore deposits overlying the offshore is the planar laminated sediments of the transition grading upward from the transition are the cleaner planar laminated seaward slope deposits of the longshore bar above this is a distinct erosional surface indicating the base of the massive to cross laminated coarse sediments of the longshore trough capping the sequence are the cross to planar laminated clean sands of the upper shoreface and foreshore

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

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

drastic change in the late pliocene subarctic pacific diatom community associated with the onset of the northern hemisphere glaciation abstract to date there is scarcely clear understanding of the detailed responses of the subarctic pacific phytoplankton communities to the significant climate transition across the initiation of the northern hemisphere glaciation nhg approximately 2 7 million years ago we present more highly resolved evidence of the rapid and drastic change in the phytoplankton biosphere using diatom as a tracer of environmental changes and based on quantitative assemblage analysis of two marine cores from oceanic regions of the north pacific subarctic gyre in the late pliocene subarctic pacific coscinodiscus marginatus and neodenticula kamtschatica were widely dominant but the flora rapidly and drastically shifted to one rich in neodenticula complex n koizumii n seminae at the onset of nhg perhaps due to intense changes in paleoceanographic conditions such as cooling and or a collapse of the previously nutrient regime in the region we also suggest that vertical pumping of biogenic matter by diatoms may have been more efficient in this region earlier than the onset of nhg after the nhg intensification the major primary productivity role in the subarctic pacific shifted from the c marginatus rich flora to the neodenticula complex the drastic decrease of biogenic opaline accumulation reportedly associated with the initiation of nhg would have resulted from not only a decrease of primary production but also from the change in diatom assemblages and consequent effects on their principal role in export flux

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france reply abstract studies of fluvial sequences from the upper jurassic and lower cretaceous of the cameros basin spain and the upper cretaceous of the aquitaine basin france have revealed large numbers of calcrete profiles which have formed wholly or largely through the action of plant root calcification those from spain have formed by the calcification of root mats whereas those from france resulted from the accumulation of calcified root cells microcodium these root related rhizogenic calcretes developed in stages allowing developmental time series chronosequences to be identified contrasting with existing models for calcrete profile growth they provide unique examples where vegetation has been the dominant control on profile development and probably indicate specific vegetation types and palaeoecological settings the role of root activity in forming some quaternary calcretes is also discussed

anomalous south atlantic lithologies confirm global scale of unusual mid pleistocene climate excursion abstract carbonate rich nannofossil oozes are the typical sediments deposited under the low productivity regime of the subtropical gyre in the south atlantic surface productivity has remained virtually constant during the late pleistocene schmiedl and mackensen palaeogeogr palaeoclimatol palaeoecol 130 1997 43 80 increasing slightly only during the most extreme glacial periods recently the puzzling occurrence of thick monospecific diatom layers ethmodiscus rex has been reported within the carbonaceous sequences of two sediment cores in the south atlantic gyre schmieder et al earth planet sci lett 179 2000 539 549 the layers dated 544 534 ka are isochronous and record a period of increased organic carbon flux above them at 530 524 ka unusually high carbonate contents are recorded this double feature of anomalous lithologies is unique in the sediment record of the last 1500 kyr and can be related to the terminal event of the mid pleistocene climate transition mpt the mpt is characterized by reduced thermohaline circulation and stronger carbonate dissolution schmieder et al earth planet sci lett 179 2000 539 549 reduced circulation and a more stratified water column may have trapped nutrients in deep nitrate pools and may have fostered favorable conditions for the development of deep dwelling populations of e rex the onset of more turbid conditions led to the rapid settling of diatom populations subsequently introduced nutrients to the surface layer and improved calcite preservation thus creating a biogenic silica carbonate double peak the carbonate peak is synchronous with an unusual mid pleistocene sapropel observed in the mediterranean which is attributed to a massive odd monsoon over central africa rossignol strick et al nature 392 1998 269 272 since summer insolation was relatively low during this time the formation of this thick sapropel cannot be explained in terms of current understanding of astronomical forcing rossignol strick et al nature 392 1998 269 272 a non linear response to a 400 kyr low frequency climatic cycle as discussed for the mediterranean sapropel is not confirmed by data from our south atlantic core records

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

glacial variability over the last two million years an extended depth derived agemodel continuous obliquity pacing and the pleistocene progression abstract an agemodel not relying upon orbital assumptions is estimated over the last 2 ma using depth in marine sediment cores as a proxy for time agemodel uncertainty averages 10 ka in the early pleistocene 2 1 ma and 7 ka in the late pleistocene 1 ma to the present twelve benthic and five planktic 18 o records are pinned to the agemodel and averaged together to provide a record of glacial variability major deglaciation features are identified over the last 2 ma and a remarkable 33 out of 36 occur when earth s obliquity is anomalously large during the early pleistocene deglaciations occur nearly every obliquity cycle giving a 40 ka timescale while late pleistocene deglaciations more often skip one or two obliquity beats corresponding to 80 or 120 ka glacial cycles which on average give the 100 ka variability this continuous obliquity pacing indicates that the glacial theory can be simplified an explanation for the 100 ka glacial cycles only requires a change in the likelihood of skipping an obliquity cycle rather than new sources of long period variability furthermore changes in glacial variability are not marked by any single transition so much as they exhibit a steady progression over the entire pleistocene the mean variance skewness and timescale associated with the glacial cycles all exhibit an approximately linear trend over the last 2 ma a simple model having an obliquity modulated threshold and only three adjustable parameters is shown to reproduce the trends timing and spectral evolution associated with the pleistocene glacial variability

migration of the antarctic polar front through the mid pleistocene transition evidence and climatic implications abstract the antarctic polar front is an important biogeochemical divider in the southern ocean laminated diatom mat deposits record episodes of massive flux of the diatom thalassiothrix antarctica beneath the antarctic polar front and provide a marker for tracking the migration of the front through time ocean drilling program sites 1091 1093 and 1094 are the only deep piston cored record hitherto sampled from the sediments of the circumpolar biogenic opal belt mapping of diatom mat deposits between these sites indicates a glacial interglacial front migration of up to 6 degrees of latitude in the early mid pleistocene the mid pleistocene transition marks a stepwise minimum 7 northward migration of the locus of the polar front sustained for about 450 kyr until an abrupt southward return to a locus similar to its modern position and further south than any mid pleistocene locus this interval from a 900 ka event that saw major cooling of the oceans and a 13c minimum through to the 424 ka mid brunhes event at termination v is also seemingly characterised by 1 sustained decreased carbonate in the sub tropical south atlantic 2 reduced strength of antarctic deep meridional circulation 3 lower interglacial temperatures and lower interglacial atmospheric co2 levels by some 30 per mil than those of the last 400 kyr evidencing less complete deglaciation this evidence is consistent with a prolonged period lasting 450 kyr of only partial ventilation of the deep ocean during interglacials and suggests that the mechanisms highlighted by recent hypotheses linking mid latitude atmospheric conditions to the extent of deep ocean ventilation and carbon sequestration over glacial interglacial cycles are likely in operation during the longer time scale characteristic of the mid pleistocene transition the cooling that initiated the 900 ka event may have been driven by minima in insolation amplitude related to eccentricity modulation of precession that also affected low latitude climates as marked by threshold changes in the african monsoon system the major thresholds in earth system behaviour through the mid pleistocene transition were likely governed by an interplay of the 100 kyr and 400 kyr eccentricity modulation of precession

paleoecological significance of laminated diatomaceous oozes during the middle to late pleistocene north atlantic ocean iodp site u1304 abstract we examined diatom assemblages in a series of remarkable laminated diatomaceous ooze ldo horizons in the marine sediments from integrated ocean drilling program iodp site u1304 to reconstruct the middle to late pleistocene paleoceanographic evolution of the northern north atlantic ocean four confirmed diatom biohorizons combined with calcareous nannofossil and paleomagnetic stratigraphies established the chronological framework for the material the planktonic araphid needle like species thalassiothrix longissima was the greatest contributor to the ldo facies from the results of a principal component analysis using the percent abundances of 65 significant p 5 diatom taxa except for tx longissima which was extremely dominant in almost all horizons observed we identified two principal component pc axes taxa probably associated with the stratigraphic distribution of the major zonal marker neodenticula seminae ranging from 1 26 to 0 84 ma in this ocean loaded on pc1 with a high value pc2 was related to the ocean surface temperature the stratigraphic variability of the pc2 score indicated that switching between warm and cold water assemblages occurred concurrently with ldo deposition or extreme tx longissima dominance episodes in several horizons particularly after 0 84 ma suggesting that the subarctic convergence sac oceanic front passed over site u1304 during pleistocene glacial interglacial cycles our floral evidence supports the model of nearly monospecific ldo formation caused by the enhanced physical accumulation of particular diatoms such as tx longissima on the other hand nd seminae which probably contributes to spring phytoplankton blooms in the modern ocean was present only between 1 26 and 0 84 ma in this area thus we infer that the main contributor of export flux in the regional annual primary production cycle would have shifted drastically from one of a spring phytoplankton bloom leader nd seminae to minor but mass dump assemblages tx longissima etc in the mid pleistocene

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

the upper miocene diatomaceous sediments of the northernmost mediterranean region a lamina scale investigation of an overlooked palaeoceanographic archive

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

on the occurrence of the giant diatom ethmodiscus rex in an 80 ka record from a deep sea core southeast of sumatra indonesia implications for tropical palaeoceanography environmental changes recognised in a 80 ka record obtained from a deep sea core taken at a water depth of 2542 m offshore southeast sumatra conclusively indicate for the first time that blooms of the giant diatom ethmodiscus rex occurred in the indian ocean during the last glacial period with the largest numbers coinciding with the last glacial maximum previous occurrences of e rex in both the indian and the western pacific oceans could not be dated due to the paucity of foraminifers and contamination by diagenetic carbonate found in association with the diatoms we use a reliable n 18 o record to date the core the interpretation of terrigenous clays and trace metals in the core sediments together with carbon isotopes measured on planktic foraminifers suggests that conditions that favoured the diatomaceous blooms were a combination of changes in hydrological regime in the region caused by a substantial increase in salinity near the surface and coinciding with a rise in nitrate levels near the surface no major upwelling was recorded during glacial times during the glacial period the indonesian archipelago as other tropical regions was much drier thus preventing a low salinity cap to occur at the surface of the oceans in contrast with the holocene in addition monsoonal winds were absent thus permitting the ocean to be permanently stratified with high levels of silica and nutrients near the surface the glacial mode of productivity represented by the blooms of e rex added considerable amounts of biogenic silica to the sediment but is not reflected by classic productivity proxies like biogenic barium therefore we have to distinguish between a classic productivity mode as observed in the photic zone today and a glacial deep productivity dominated by e rex which may have utilised nutrients from a wider depth range 9 2002 elsevier science b v all rights reserved

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

el nino southern oscillation variability from the late cretaceous marca shale of california changes in the possible behavior of el nino southern oscillation enso with global warming have provoked interest in records of enso from past greenhouse climate states the latest cretaceous laminated marca shale of california permits a seasonal scale reconstruction of water column flux events and hence interannual paleoclimate variability the annual flux cycle resembles that of the modern gulf of california with diatoms characteristic of spring upwelling blooms followed by silt and clay and is consistent with the existence of a paleo north american monsoon that brought input of terrigenous sediment during summer storms and precipitation runoff variation is also indicated in the extent of water column oxygenation by differences in lamina preservation time series analysis of interannual variability in terrigenous sediment and diatom flux and in the degree of bioturbation indicates strong periodicities in the quasi biennial 2 1 2 8 yr and low frequency 4 1 6 3 yr bands both characteristic of enso forcing as well as decadal frequencies this evidence for robust late cretaceous enso variability does not support the theory of a permanent el nino in the sense of a continual el nino like state in periods of warmer climate

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

ecological control of sedimentary accommodation evolution from a carbonate ramp to rimmed shelf upper miocene balearic islands abstract stratal patterns and facies architecture develop in response to sediment flux and the available space for sediment accumulation accommodation in siliciclastic systems these two parameters are independent in carbonates however they are highly interdependent 1 sediment input production highly depends on biological systems and consequently on intrabasinal conditions nutrients temperature salinity etc 2 sediment dispersal depends on the production loci and on the interaction between the amount and type of sediment being produced and the hydraulic energy additionally biological processes binding baffling framework construction and even cementation frequently modify it 3 accommodation is not an independent factor with respect to sediment input type efficiency and area of the carbonate factory depend on sea level changes and sea floor morphology the base level for sediment to accumulate accommodation depends on the type and locus of sediment being produced the upper miocene carbonate platforms of the balearic islands illustrate how changes in intrabasinal environmental conditions nutrients and or temperature produce changes in stratal patterns and facies architecture if they affect the biological system during early tortonian carbonate production occurred both in the shallow euphotic zone foramol and in the deeper oligophotic zone rhodalgal originating a distally steepened ramp during late tortonian and early messinian carbonate production mainly occurred in the euphotic zone where framework producing biota coral reefs formed a rimmed platform although deposited under similar conditions of high frequency sea level fluctuations these two types of platforms exhibit different internal facies architecture and distribution of heterogeneities because of differences in base level in carbonates base level for sediment accumulation depends on the type and amount of sediment being produced on the production loci and on the processes controlling sediment dispersal base level for the loose foramol rhodalgal sediment associations of the ramp was controlled by wave and storm base and the associated currents whereas base level for the framework dominated reef complex was sea level furthermore the increase on effective accommodation space to allow the reef rimmed shelf to prograde onto the distally steepened ramp both platforms being depositional sequences resulted from an ecological change rather than significant relative sea level change namely by the shift from grain to framework producing biota the euphotic framework producing biota was able to fill the accommodation space existing between wave and storm base level and sea level that was not previously filled by the loose bioclasts

probing structural elements of small buried craters using ground penetrating radar in the southwestern egyptian desert implications for mars shallow sounding we report results from a field survey performed on a recently discovered impact field in the southwestern egyptian desert using a 270 mhz ground penetrating radar gpr this hyperarid region has significant similarities to the martian heavily eroded mid latitude cratered terrains in terms of crater density size and geomorphology profiles across small buried craters revealed a coherent sequence of tilted layers constituting the cratonic infill resulting from aeolian deposits in the intercrater areas the radargram revealed a poorly defined subsurface stratigraphy and the presence of shallow structural elements associated with potential evidences of the consequences of the shock effects i e faulting fractures and chaotic bedrock the radar penetration depth varied from 2 to 15 m depending mainly on the amplitude of the volume and multiple scattering in the subsurface caused by fractures and debris created by the impacts we conclude that mid frequency gpr onboard future martian rovers can successfully perform similar structural mapping

raised pleistocene marine terraces of the crotone peninsula calabria southern italy facies analysis and organization of their deposits abstract wide marine terraces well known in the italian literature are present in the crotone peninsula ionian calabria they are related to the interplay between pleistocene sea level changes and the progressive uplift of the calabrian arc from the middle pleistocene onwards we present a description of facies organization and stratigraphical characteristics of the terrace deposits along with a new geological map of the area all the marine terraces unconformably overlie a plio pleistocene slope succession known as cutro clay the oldest and highest terrace named cutro terrace is placed between 90 and 200 m of elevation and is gently inclined south eastwards four younger terraces placed at progressively lower elevations and dipping seawards at low angles have been recognized the sedimentary deposits of the terraces are represented by mixed carbonate and siliciclastic bodies up to 10 m thick algal reefs and grainstone to rudstone deposits are common in the south eastern part of the study area whereas mostly siliciclastic sandstone units of shoreface environments are more abundant northwards and westwards the deposits of some terraces are made up of minor cycles bounded by subaerial transgressive and flooding surfaces referred to minor sea level fluctuations nne ene e and wnw trending normal fault systems are present within the study area and dissect the marine terraces specifically the activation of ene trending faults took place after the formation of the oldest terrace but prior to the formation of the younger terraces

the effects of sea level and palaeotopography on lithofacies distribution and geometries in heterozoan carbonates south eastern spain this study utilized three dimensional exposures to evaluate how sea level position and palaeotopography control the facies and geometries of heterozoan carbonates heterozoan carbonates were deposited on top of a neogene volcanic substrate characterized by palaeotopographic highs palaeovalleys and straits that were formed by subaerial erosion possibly original volcanic topography and faults prior to carbonate deposition the depositional sequence that is the focus of this study ds1b consists of 7 10 fining upward cycles that developed in response to relative sea level fluctuations a complete cycle has a basal erosion surface overlain by deposits of debrisflows and high density turbidity currents which formed during relative sea level fall overlying tractive deposits most likely formed during the lowest relative position of sea level overlying these are debrites grading upward to high density turbidites and low density turbidites that formed during relative sea level rise the tops of the cycles consist of hemipelagic deposits that formed during the highest relative position of sea level the cycles fine upward because upslope carbonate production decreased as relative sea level rose due to less surface area available for shallow water carbonate production and partial drowning of substrates the cycles are dominated by two end member types of facies associations and stratal geometries that formed in response to fluctuating sea level position over variable substrate palaeotopography one end member is termed flank flow cycle because this type of cycle indicates dominant sediment transport down the flanks of palaeovalleys those cycles drape the substrate have more debrites high density turbidites and erosion on palaeovalley flanks and in general the lithofacies fine down the palaeovalley flanks into the palaeovalley axes the second end member is termed axial flow cycle because it indicates a dominance of sediment transport down the axes of palaeovalleys those cycles are characterized by debrites and high density turbidites in palaeovalley axes and lap out of strata against the flanks of palaeovalleys where and when an axial flow cycle or flank flow cycle developed appears to be related to the intersection of sea level with areas of gentle or steep substrate slopes during an overall relative rise in sea level results from this study provide a model for similar systems that must combine carbonate principles for sediment production palaeotopographic controls and physical principles of sediment remobilization into deep water

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

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 2 diatom assemblages 1 the distribution of late pleistocene to holocene diatom assemblages from ocean drilling program odp leg 178 site 1098 palmer deep is described and compared using multivariate statistical methods cluster analysis and analysis of variance five assemblages are identified from site 1098 which are correlated with the climatic zones identified previously in the palmer deep domack et al 2001 a thalassiosira diatom assemblage characterizes the deglaciation phase 13 2 11 0 ka and was deposited during glacial retreat at the end of the regional last glacial maximum a well preserved rhizosolenia assemblage was deposited during a climatic reversal 11 0 9 0 ka and indicates periods of seasonally open water with diatom blooms an open water fragilariopsis kerguelensis assemblage characterizes the mid holocene climatic optimum 9 0 3 7 ka in the neoglacial late holocene 3 7 ka climatic cooling increased sea ice cover and increased wind are inferred from a cocconeis assemblage during the climatic optimum neoglacial transition 4 4 1 8 ka laminae characterized by corethron criophilum were preserved it is uncertain whether the laminae represent short lived interannual bloom events with high settling rates or have been deposited over longer time periods

transgressive surfaces of erosion as sequence boundary markers in cool water shelf carbonates abstract although sequence stratigraphy was first conceptualized in and applied to siliciclastic successions its methodology and concepts are applicable to the carbonate regimen provided that potential modifications to the existing models are appreciated that take into account the specificities of carbonate systems we demonstrate that some properties inherent to isolated i e continent detached shallow water temperate carbonate systems including their typical low diagenetic potential due to the prevalance of calcitic mineralogies the critical role exerted by storm waves and tidal currents on sediment dynamics e g shedding of sediments at wave abrasion depth during highstand and lowstand conditions and uneven sea bed topographies cause both the genesis and preservation of subaerial unconformities to be uncommon thereby rendering their use as sequence boundaries inappropriate instead transgressive surfaces of erosion tses that formed as wave base shifts upwards during early rise of relative sea level are readily identifiable in the field extensive and by their very nature are preserved in the rock record typically at the base of upward deepening stacked facies in pliocene cool water carbonate successions from new zealand the tses are characterized by starved sedimentation and burrowed network development and are overlain by coarse bioclastic shoreface sediments and shell beds in most cases the surfaces top truncate shoaling upward deposits but also deepening upward stacking facies in places emersive events rarely correspond to actual physical surfaces but diagenetic evidence preserved beneath tses indicates that occasionally subaerial surfaces had previously developed and were later modified into tses therefore we propose that tses are the most adequate unconformities to define high order depositional sequences 20 250 ka in the studied successions because by contrast with emersion surfaces their formation and preservation are not dependent upon cool water sedimentary facies and mineralogy and are favoured by the dynamics of the setting i e wave base shift and accommodation creation during relative sea level rise

the deep sea microfossil record of macroevolutionary change in plankton and its study the deep sea planktonic microfossil record foraminifera coccolithophores diatoms radiolaria and dinoflagellates provides a unique resource for palaeobiology despite some geographical gaps due to poor regional preservation and intermittant time intervals lost to erosion most time periods for each cenozoic planktonic biogeographical province are preserved vast numbers of specimens and numerous deep sea cores provide abundant material and the opportunity to tightly integrate macroevolutionary and palaeoenvironmental data current documentation of this record is mixed catalogues for foraminifera and coccolithophores offer nearly complete species level clade histories but taxonomy for siliceous microfossils is incomplete published occurrence data is primarily stratigraphic and covers only a fraction of the total preserved diversity age models for some sections are excellent accuracy c 100 kya but for many other sections are still poor taxonomic errors age model errors and reworking displace fossil occurrences in time complicating palaeobiological analysis with additional taxonomic work careful collection of whole fauna floral assemblage occurrence data improved age models and the development of better data filtering and analysis tools to deal with data outliers the deep sea microfossil record can deliver its promise of providing the most complete detailed record of macroevolutionary change available to science

diatom mats in gulf of california sediments implications for the paleoenvironmental interpretation of laminated sediments and silica burial preservation of laminations in hemipelagic and pelagic sediments is routinely attributed to reduced oxygen conditions that inhibited benthic activity as such the degree of preservation of laminae is used commonly as a paleo oxygenation indicator recent evidence from deep sea pelagic sediments in the eastern equatorial pacific and north atlantic however demonstrates that preservation of laminae may occur by rapid deposition of ungrazed thalassiothrix longissima diatom mats that overwhelm the benthos in otherwise oxic bottom waters here we report that similar diatom mat laminae are common in hemipelagic sediments of the guaymas basin in the gulf of california have aided preservation of the laminated sediment sequence and have also enhanced opal burial examples of diatom mats influencing sediment preservation are also described from the northern california margin and from the miocene monterey formation southern california thus even in classical settings of laminated sediment occurrence caution needs to be taken in correlating degree of lamina preservation with paleo oxygen levels such studies must be underpinned by detailed microfabric and micropaleontological analyses

age of settlement and accumulation rate of submarine coralligene 10 to 60 m of the northwestern mediterranean sea relation to holocene rise in sea level morphological and chronological studies have been carried out on coralline algal buildups coralligene situated between 10 and 60 m depth near marseilles and in corsica france despite the presence of occasionally sizeable quantities of iron hydroxide these constructions prove to be a reliable material for radiocarbon dating ages obtained using this method range from 640 120 yrs b p corsica scandola natural reserve 15 m to 7760 80 yrs b p marseilles grand congloue 52 m internal erosion surfaces within the buildups give evidence of discontinuous development the accumulation rate of the coralligene constructions is very low 0 006 0 83 mm yr 1 according to the depth and time period the higher values 0 53 0 83 mm yr 1 were recorded for the deeper constructions they correspond to a period between 8000 and 6000 yrs b p after 6000 yrs b p the only appreciable accumulation rates 0 11 0 42 mm yr 1 were recorded for constructions situated between 10 and 35 m depth whereas the accumulation rates of deep coralligene 50 m appear to be low or zero the age of the large constructions overhang 80 cm in width is positively correlated with depth r 0 95 p 0 005 their development occurred during the flandrian transgression the oldest structures today situated at 50 to 60 m depth started to develop when water depth was probably no greater than 10 to 15 m apart from in strongly shaded fissures on rocky coasts and areas subjected to heavy sedimentation the main framework building algal species was initially mesophyllum lichenoides ellis lemoine a high tolerant species to light hydrodynamic energy and temperature with the rise in sea level the coralligene structure gradually became available to other less tolerant algal species lithophyllum lithothamnion and the crustforming population diversified because of the good preservation of coralligene structures the reliability of radiocarbon dating and the correlation between the age and bathymetric position of the large coralligene structures except in areas of heavy sedimentation and fissures in shallow rocky coasts these buildups are considered to be of use as biological indicators of variations in sea level

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

silica diagenesis porosity evolution and mechanical behavior in siliceous mudstones mowry shale cretaceous rocky mountains u s a quartz in mudstones of the mowry shale cretaceous rocky mountain region takes several forms extrabasinal detrital silt some with transported overgrowths replacement of skeletal debris minor overgrowth on detrital quartz and replaced radiolaria pore filling in the intragranular pores of allochems and authigenic microquartz that is dispersed through the clay size matrix the matrix dispersed microquartz has cl character similar to the overgrowths with which it is intergrown supporting the interpretation that it is authigenic and pore filling radiolaria are widely observed in these mudrocks but are poorly preserved by partial mineral replacement quartz dolomite calcite pyrite we interpret dissolved radiolaria and possibly now cryptic diatoms as the likely source of silica for the overgrowths and microquartz through a reaction pathway that entailed the formation of opal ct lepispheres that subsequently recrystallized to microquartz a newly devised variation of the igv intergranular volume concept a parameter igvm is applied for partitioning the causes of porosity decline in mudstones all of the samples examined contain authigenic microquartz which averages around 40 of the rock volume the large volume of microquartz together with the volumes of surviving intergranular pores and pore filling solid hydrocarbon constrain the porosity to around 50 at the time of initial lepisphere formation despite the exceptional abundance of cement overall porosity decline is compaction dominated the presence of significant volumes of cement has implications for mechanical rock properties in the mowry shale which is expected to manifest brittle behavior where cements are most prominently developed

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom mats in the tropical west pacific paleoproductivity and paleoredox conditions were reconstructed in a sediment core in the parece vela basin of the eastern philippine sea the core consists of three units from youngest to oldest 1 laminated diatom mats ldm formed by ethmodiscus rex during the last glacial maximum similar to 18 28 kyr b p 2 diatomaceous clay dc and 3 pelagic clay pc elevated levels of export productivity during ldm deposition are indicated by high values for excess ba opal content and toc ti ratios estimated rates of organic carbon degradation ca 98 opal mass accumulation average 1322 g m 2 yr 1 and corrected organic carbon flux average 248 g m 2 yr 1 are comparable to high productivity regions of the modem ocean the ldm is also characterized by moderate enrichment of redox sensitive elements such as u mo cd and zn highly s 34 depleted pyrite sulfur isotopic compositions indicating bacterial sulfate reduction in a sulfate unlimited system and c s fe systematics reflecting limitation of pyrite formation by organic matter rather than reactive fe availability these features suggest mainly suboxic conditions in bottom waters but development of sulfidic anoxic conditions at or close to the sediment water interface association of intensified anoxia with productivity maxima indicates that export production was a more important control on bottom water redox conditions than lateral ventilation the dc and pc accumulated under oxic to suboxic conditions our observations suggest that redox environments during deposition of laminated marine sediments are more complicated and varied than previously thought and thus the use of sediment lamination as an indicator of anoxic bottom water conditions must be approached cautiously c 2012 elsevier b v all rights reserved

are the 41 kyr glacial oscillations a linear response to milankovitch forcing abstract the characteristics of glacial oscillations changed drastically 0 8 ma ago at the mid pleistocene transition during the past 0 8 ma the 100 kyr glacial interglacial oscillations were strongly asymmetric i e long glacial intervals of growth followed by rapid intervals of deglaciation the 40 kyr oscillations prior to the mid pleistocene transition were of a smaller amplitude and less asymmetrical looking the smaller amplitude apparently symmetric form and period that matches that of obliquity suggests that these oscillations were a linear response to milankovitch forcing while the 100 kyr oscillations are attributed either to some nonlinear self sustained variability due to a mechanism internal to the climate system itself or to nonlinear amplification of the insolation forcing the significant strengthening of the 100 kyr eccentricity power in the past 800 kyr is one of the intriguing questions of climate history here we show that glacial interglacial oscillations pre mid pleistocene transition are in fact significantly asymmetric this asymmetry may contradict a straight forward linear milankovitch explanation and we therefore suggest that the glacial oscillations before and after the transition may both be explained as self sustained variability although the possibility of nonlinear response to insolation forcing still exists the role of milankovitch forcing is in setting the phase of the oscillations e g time of terminations and their period rather in being the main driving force of the oscillations this is demonstrated using a simple model based on the sea ice switch mechanism of gildor and tziperman paleoceanography 15 2000 605

history of the south java current over the past 80 ka a sediment core located below the present south java current sjc was used to reconstruct paleoclimate and paleoceanography on the basis of biogenic and terrigenic proxy records the core spans the past 80 ka of environmental change and shows considerable contrasts from the glacial to the holocene presently the core site is situated beneath a seasonally varying low salinity tongue which is advected from the java sea via the sunda strait it carries terrigenous matter of a characteristic signature during the last glacial period stage 4 2 when sea level was lower than during the holocene the sunda strait was closed and the terrigenous supply from that source ceased as the core site is close to the equator our results indicate that atmospheric and oceanographic circulation was alternatively dominated by the northern hemisphere east asian monsoon system and the southern hemisphere australian monsoon system between 20 and 12 ka the australian se winter monsoon reached its maximum and intensified the westward flowing sjc increased mixing of the surface waters led to a slight rise in paleoproductivity a similar but much weaker situation prevailed from 74 to 70 ka during most of the glacial period from 70 to 20 ka strong northeasterly winds associated with the east asian winter monsoon intensified the indian monsoon current and the eastward flowing sjc and may have also carried dust across the equator to our core site during this glacial phase populations of the giant diatom ethmodiscus rex were thriving and may indicate a reduced deep and intermediate thermohaline circulation at the site the monsoonal system as we know it today with distinct dry and wet seasons may not have been active before v12 ka 2002 elsevier science b v all rights reserved

bryozoan distribution and growth form associations as a tool in environmental interpretation tasmania australia abstract the cool temperate carbonate sediments of eastern and western tasmania and bass strait composed of 29 50 of bryozoan skeletal grains two hundred and eighty three bryozoan bulk sediments around tasmania were studied to determine the relationship between bryozoan zoarial growth form association and their depth zone bryozoans skeletons are grouped into 11 morphotypes according to architecture and style of disarticulation fragmentation encrusting forms erect flexible cellariiform and erect rigid robust branching adeoniform cheilostomes are consistently the most widespread with delicate branching cyclostomes the next most common growth form associations were grouped into four depth related settings strand line shallow shelf middle shelf and deep shelf this study demonstrates that bryozoan morphotype associations occupying different depth zones are valuable for providing fundamental paleo environmental information morphotype associations are related mainly to water depth water energy sedimentation rate and substrate in the strand line setting encrusting unilaminar and erect flexible articulated branching are abundant while in the shallow shelf erect flexible encrusting multilaminar erect rigid robust fenestrate and delicate branching are major growth forms the above associations indicate high to moderate energy levels moderate to high sedimentation rates and flexible to hard substrates in middle shelf areas erect rigid fenestrate robust and delicate branching cheilostomes and cyclostomes are the most common growth forms these associations indicate decreasing water energy lower sedimentation rate and presence of stable hard to soft substrates in the deep shelf setting the dominance of erect rigid robust fenestrate and foliose forms indicate deep quiet water low sedimentation rate and hard substrate

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

sedimentology and palaeoecology of a miocene coralline algal biostrome from the maltese islands abstract a large coralline algal biostrome 20 km 5 km 16 m thick is well exposed in western malta and eastern gozo the biostrome is composed of limestones largely constructed by in situ coralline algae or transported algal debris some sediments are dominated by rhodoliths and others by crustose coralline frameworks six facies are distinguished crustose algal marl crustose algal wackestone rhodolith pavement algal branch packstone crustose pavement and algal crust packstone each facies is characterised by different rhodolith morphologies and coralline crusts which are constructed mainly bymesophyllum commune the coralline morphogenesis is related to the palaeoenvironmental conditions the biostrome is thought to have developed from a series of relic sand ridges to form a low relief platform of moderate depths containing a mosaic of sedimentary facies the sequence is affected by growth faulting which divides the biostrome into eight units

formation morphology and preservation of high energy carbonate lithofacies evolution of the cool water recherche archipelago inner shelf south western australia cool water carbonate environments are responsible for up to one third of the carbonate sediment produced on continental shelves and are useful modern analogues for many geologically ancient carbonate deposits on modern and ancient high wave energy carbonate ramps it has been suggested that wave abrasion generally limits sediment accumulation to the outer shelf sediment are produced on the modern inner shelf although few studies have investigated processes of sedimentation in these energetic environments the recherche archipelago in the west of the great australian bight gab was examined to better identify processes of carbonate sedimentation and preservation on extremely high energy shelves surficial sediments video traverses multibeam sonar data cores and shallow seismics were analysed these data reveal that the topographically varied environment of the recherche archipelago experienced gradual episodic accumulation of a prograding sediment wedge with substantially thicker deposits located on the lee side of topographic highs modern sediment accumulation is largely restricted to the shoreface and inner shelf where the highly discontinuous storm influenced blanket of holocene sediment comprises a shore attached quartzose sediment prism leeward accretionary wedges and rhodolith beds above a laterally continuous pecten dominated basal transgressive lag storm events play an important role in these environments resulting in a mostly bare shaved middle and outer shelf onshore sediment transport reworking of particles and periodic removal of sediment the modern recherche archipelago is a high energy end member of cool water carbonate environments in which calcareous algae dominate sediment production modern esperance bay provides a useful analogue for the interpretation of high energy palaeoenvironments and demonstrates that in addition to sea level change wave energy and local geomorphology are important considerations for carbonate facies reconstructions this study has presented new information for carbonate inner shelves that differs from classic carbonate ramp models showing that ancient rhodolith bearing carbonate deposits have the potential to form and be preserved in very high energy settings

sedimentary model and high frequency cyclicity in a mediterranean shallow shelf temperate carbonate environment uppermost miocene agua amarga basin southern spain uppermost tortonian to lower messinian temperate carbonates crop out in the agua amarga basin se spain they consist of four units the lower three units can be tentatively assigned to the lowstand systems tract of a fourth order sequence constituting in turn the lowstand megatrough unit transgressive breccia unit and highstand bedded unit stages of a higher order cycle all these materials were deposited in a small pull apart basin related to the sinistral carboneras strike slip fault system the best represented is the bedded unit up to 25 m thick which consists of bioclastic bryozoan bivalve dominated calcarenites calcirudites with abundant fragments of echinoids barnacles benthic foraminifers coralline algae brachiopods and solitary corals facies trends within this unit are roughly arranged in an e w direction with the coastline to the north of the basin the depositional model is that of a gentle ramp with prograding beaches and shoals in its higher parts seaward of the shoals was the factory area where most organisms lived and maximum carbonate production took place from this area some of the skeletons were washed landwards by waves and or currents during storms and incorporated into the shoals and beaches and others moved downslope along the ramp as mass flows accumulating to form the fan bedded zone the factory area and fan bedded sediments intercalate five well defined thick beds of calcarenites fine grained calcirudites they show bar morphologies single or amalgamated or make up sand waves with very consistent tabular cross bedding pointing landwards these beds formed in a very shallow wave current influenced coastal environment the bars and sand waves in the fan bedded zone developed during lowstands while those located higher up in the ramp interbedded with the factory facies are related to transgressive stages prograding beaches shoals factory facies and fan bedded layers developed during the highstands net skeletal production occurred mainly during the highstands sediment accretion values of these sediments are similar to those of present and ancient shallow marine temperate carbonates considering that the whole bedded unit was deposited in a 100 000 year interval equivalent to the short eccentricity cycle the five cycles inside the bedded unit would therefore correspond to the c 20 000 year precession cycles of the milankovitch band

pliocene pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits salento se italy nine discrete metre scale sequences of early pliocene to middle pleistocene age were deposited in the small novoli graben salento peninsula puglia s italy they consist of carbonate and mixed carbonate siliciclastic sediments deposited on a slowly subsiding foreland ramp skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes taphonomic and palaeoecological analyses indicate that storm induced waves and currents reduced sediment input and settling behaviour of components were the main factors controlling the features of the various shellbed types the concentrations were formed below fair weather wave base in low stress inner to outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations hence may result from glacio eustatic sea level changes most sequences are bounded by subaerial karstic unconformities because of the regional setting of low subsidence rate the record of the relative sea level fluctuations is incomplete episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by i diagenetic changes leading to hardening of unconformity horizons ii local subvertical solution pits developed in the vadose zone below unconformity surfaces iii networks of polygonal cracks below unconformities and iv infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity due to superimposition of the diagenetic effects of repeated high amplitude sea level fluctuations

facies and stratigraphic anatomy of a temperate carbonate sequence capo colonna terrace late pleistocene southern italy abstract accurate interpretation of ancient non tropical carbonate systems requires the development of appropriate facies and sequence stratigraphic models these models should account for the marked differences in sedimentation style among non tropical carbonates formed under different energy settings this paper presents data and a conceptual model of the sequence architecture of non tropical carbonates of moderate energy environments based on the late pleistocene deposits of capo colonna marine terrace calabria southern italy these deposits have the advantage of being continuously exposed along a proximal distal transect across the paleo shelf and their geometry has not been disturbed by later tectonic activity they consist of a transgressive regressive t r cycle whose genesis can confidently be related to one of the interstadial glacio eustatic fluctuations of marine isotope stage mis 5 eight different mixed carbonate siliciclastic and carbonate facies are present in the studied sequence of these biogenic dominated facies are invariably made up of skeletal remains of light independent organisms plus or minus red calcareous algae the heterozoan association the relatively young age of the deposits allows calibration of the paleoecological significance of observed facies by direct comparison with modern analogues from the mediterranean sea four laterally persistent discontinuity surfaces were identified along the transect and interpreted from bottom to top as 1 a basal ravinement surface 2 a submarine hardground locally acting as a substrate for algal boundstones 3 a regressive surface of marine erosion and 4 a surface of subaerial exposure sequence stratigraphic analysis indicates that the preserved t r cycle is asymmetric with a thicker regressive portion highstand deposits can be subdivided into a shore connected sandy prism and more distal autochthonous and parautochthonous skeletal accumulations and algal boundstones during forced regression a thin sharp based strongly progradational unit of calcarenites was deposited above the regressive surface of marine erosion the deposits of capo colonna terrace document the response of non tropical moderate energy carbonate ramps to sea level fluctuations during icehouse conditions their architecture can facilitate the interpretation of other successions from similar settings and provide an end member to be compared and contrasted with high wave energy cool water carbonates

comparison of esr and tims u th dating of marine isotope stage mis 5e 5c and 5a coral from barbados implications for palaeo sea level changes in the caribbean abstract electron spin resonance esr dating of coral has become an efficient geochronological tool in supporting morphostratigraphic studies carried out on barbados during the last 10 years the newly developed approach for de determination de dmax plot procedure improves the precision of esr dating of pleistocene coral and therefore permits differentiation between the main marine isotope stages mis 5 7 9 and 11 and also between sub stages 5e c and a this study compares results of esr and tims uranium series dating u th of emergent last interglacial coral reef terraces from barbados and presents some implications for the timing and extent of sea level changes during marine isotope stages mis 5e c and a both dating methods indicate a distinct formation of up to three coral reef terraces during mis 5e at approximately 132 ka esr to 128 ka u th at c 128 ka esr and at c 120 ka u th to 118 ka esr it is also highly probable that three reef terraces were developed during mis 5c between c 103 ka u th and 105 ka esr the formation of two separate coral reefs during mis 5a is recognized for the first time on barbados with an age estimate for the older mis 5a 2 reef of 85 ka esr or 84 ka u th and an age estimate for the younger mis 5a 1 reef terraces of 74 ka esr or 77 ka u th assuming a constant uplift rate of 0 276 m ka at the south coast of barbados sea level reached its maximum during mis 5e 3 and mis 5e 2 between 132 and 128 ka ago after this sea level declined reaching a level of c 11 m below present sea level approx 118 120 ka ago mis 5e 1 during the substage 5c sea level was generally lower than in substage 5e it reached relative maxima at c 13 20 and 25 m during mis 5c approx 105 ka and formed three distinct coral reef terraces probably in relative short time intervals for the first time a double sea level oscillation is recognized on barbados during mis 5a an early mis 5a 2 c 85 ka with a sea level places at approx 21 m and a late mis 5a 1 sub stage c 74 or 77 ka with a sea level at approx 19 m below present sea level

ground penetrating radar geologic field studies of the ejecta of barringer meteorite crater arizona as a planetary analog 1 ground penetrating radar gpr has been a useful geophysical tool in investigating a variety of shallow subsurface geological environments on earth here we investigate the capabilities of gpr to provide useful geologic information in one of the most common geologic settings of planetary surfaces impact crater ejecta three types of ejecta are surveyed with gpr at two wavelengths 400 mhz 200 mhz at meteor crater arizona with the goal of capturing the gpr signature of the subsurface rock population in order to ground truth the gpr characterization subsurface rocks are visually counted and measured in preexisting subsurface exposures immediately adjacent to and below the gpr transect the rock size frequency distribution from 10 to 50 cm based on visual counts is well described by both power law and exponential functions the former slightly better reflecting the control of fragmentation processes during the impact ejection event gpr counts are found to overestimate the number of subsurface rocks in the upper meter by a factor of 2 3x and underestimate in the second meter of depth 0 6 1 0x results attributable to the highly scattering nature of blocky ejecta overturned ejecta that is fractured yet in which fragments are minimally displaced from their complement fragments produces fewer gpr returns than well mixed ejecta the use of two wavelengths and division of results into multiple depth zones provides multiple aspects by which to characterize the ejecta block population remote gpr measurement of subsurface ejecta in future planetary situations with no subsurface exposure can be used to characterize those rock populations relative to that of meteor crater

ground penetrating radar as a tool for probing the shallow subsurface of mars 1 design and testing of an impulse ground penetrating radar gpr for possible rover deployment on mars in 2009 is well underway the gpr has mass power volume and data rate targets of 0 5 kg 3 w peak 3400 cm3 and 0 3 mb d and will possess easily modified bistatic high frequency e g 500 600 mhz and monostatic rat tail e g 100 mhz antennas the gpr should be capable of measuring in situ radar properties on mars to depths of up to 10 20 m thereby helping to constrain near surface geology and structure initial gpr tests at the site of the 2001 fido rover field trials near cronese lake california confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements a rover deployed gpr may enable three dimensional mapping of local stratigraphy which in turn can assist in evaluating the history of aqueous activity and the accessibility of near surface water