u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

sedimentological and palaeoecological integrated analysis of a miocene channelized carbonate margin matese mountains southern apennines italy abstract lower middle miocene temperate marine carbonates occur in the matese mountains southern apennines italy these carbonates formed in an open shelf depositional system with an uneven margin 10 km long and up to 6 km wide shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans two main channel networks pietraroia and regia piana channels with their sedimentary bodies were analysed the studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate shallow water rhodalgal skeletal debris from moderately re mobilized up to significantly re worked built up the complex channel system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified the early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting the rhodoliths dominated by melobesioid coralline algae are sub discoidal and sub spheroidal in shape with a characteristic loosely packed inner arrangement these sediments whose latter portion underwent submarine diagenetic processes incipient to evoluted hard grounds were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone rudstone their rhodoliths constituted by melobesioids mastophoroids and subordinate lithophylloids and sporolithaceans are mainly spheroidal sub spheroidal in shape with subordinate sub discoidal specimens with massive and laminar inner arrangements the lack in early lithification can be drawn back to the physiography of the channelized shelf margin to the active tectonic as well as to the temperate type carbonate dominant biogenic components the depositional surface profile and local hydrodynamic conditions were the major factors controlling sedimentary facies which differ in their relative proportions of dominant components their internal structures and sedimentary body geometries

holocene late pleistocene non tropical carbonate sediments and tectonic history of the western rift basin margin of the southern gulf of california abstract using high resolution seismic reflection profiling and dating of 1 shallow marine vibracores and 2 sediments collected from uplifted marine terraces we reconstruct the tectonic history and sediment accumulation patterns of holocene to late pleistocene warm temperate to subtropical carbonates in the southern gulf of california mexico the study was conducted in the vicinity of la paz where carbonates form along the fault bounded narrow western shelf of the tectonically active gulf of california rift basin the non tropical nature of the setting is responsible for 1 poor cementation of the bioclastic carbonates and 2 a composition which is dominated by rhodoliths coralline red algae corals and mollusks unrimmed carbonate flats forming in small pocket bays and a rhodolith bioherm which has a surface area of more than 20 km2 and is up to 16 m thick constitute the major carbonate factories holocene carbonate accumulation rates were deduced from seismic and core data and are highest on the rhodolith bioherm 260 cm ka and in subtidal zones of pocket bays 210 cm ka and lowest on the inner and middle shelf 100 cm ka taken together rates of carbonate accumulation are intermediate in magnitude between higher rates recorded in fully tropical carbonate settings and lower rates typical of cool water carbonates seismic reflection profiles demonstrate that isla espiritu santo in the center of the study area is a west dipping fault block which is tectonically influenced by two distinct faults the la paz and espiritu santo faults the latter fault accommodates at least 700 m of east side down normal offset and forms a steep eastern escarpment leading into the la paz slope basin some of the sediments produced in the shallow carbonate factories of the narrow la paz shelf are transported across this escarpment and are redeposited in the slope basin at a water depth of 750 m uranium series dates of marine terraces exposed on isla espiritu santo indicate that late pleistocene uplift along the eastern side of the island could be as high as 310 mm ka whereas downdropping along the western side of the island occurred at a rate of up to 15 mm ka isla espiritu santo therefore constitutes part of the uplifted shoulder of the western margin of the gulf of california rift basin patterns of vertical tectonic movements of isla espiritu santo together with fault offsets on the surrounding seafloor and slump features on steep submarine slopes point to continuous activity of the la paz and espiritu santo faults results of this study will assist in recognizing and interpreting similar settings along ancient non tropical rift basin margins worldwide and especially in the neogene of the gulf of california

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

production of subtidal tubular and surficial tempestites by hurricane kate caicos platform british west indies abstract storm infilling of deep open callianassa burrows with molluscan to peloidal packstone was the dominant style of preservable sedimentation produced by the passage of hurricane kate across caicos platform british west indies on 18 november 1985 this moderate hurricane was the first to affect an actively studied portion of the carbonate platform environments of the south florida bahama region in 19 years a time during which many of our concepts of storm sedimentation have evolved prior to hurricane kate much of the shallow platform interior peloidal packstone to grapestone grainstone had a sparse seagrass cover and a highly irregular bottom caused by abundant callianassa mounds hurricane kate flattened the mounded bottom of the platform interior and caused minor smothering and erosion of the seagrass beds a thin surficial tempestite though deposited over much of the platform was difficult to identify because it lacked a coarse base instead much of the reworked surface sediment poured down the large callianassa burrow entrances and filled the vast burrow networks with either a coarse molluscan packstone or peloidal skeletal packstone storm burrow filling tubular tempestites effectively removed the coarse fraction from contributing to a surficial storm layer ten percent of the upper 75 cm of platform interior sediment consists of tubular tempestites from hurricane kate

development of a pliocene mixed carbonate siliciclastic reef limon costa rica the miocene to pleistocene limon group of costa rica is a mixed carbonate siliciclastic succession that formed in association with the emergence of the central american isthmus our study focuses on a lower late pliocene reef unit the newly excavated contact cut which is located at the contact between the siliciclastic sediments of the rio banano formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the quebrada chocolate formation the siliciclastic sediments were deposited in a thick deltaic setting sourced by erosion of the cordillera de talamanca deposits of the limon group preserve a sequence of progressively shallowing near shore sediments that were exposed by uplift during the early to middle pleistocene the contact cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of caribbean coral reef predominance in the neogene it shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea level highstand three stages of reef evolution are recognized based on faunal diversity the contact cut reef complex is comparable to the time equivalent reef of the las islas roadcut situated west of limon which shows a rapid burial of the corals by siliciclastics both reefs document a distinct facies diversification during the final stages of the closing of the central american seaway the reefs developed in an environment stressed by siliciclastic input which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs the biotic composition of the patch reefs that occurred during the sea level rise las islas and contact cut did not differ from the reefs that developed during the final highstand in sea level the reefs of the overlying moin formation limon group differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs with a very fast give up scenario for las islas reef and a catch up followed by a give up phase for contact cut reef

reefal coralline algal build ups within the arctic circle morphology and sedimentary dynamics under extreme environmental seasonality abstract carbonate frameworks secreted by phototrophic organisms within the arctic circle are not well documented underwater surveys of the inner shelf off troms northern norway 70 n reveal extended fixed algal build ups which are fringed by rhodolith belts affected by storms reefd growth by coralline algae under temperature and light regimes of extreme seasonality is made possible because of a decoupling of carbon fixation during summer and utilization of stored carbon during the period of winter darkness although the annual growth of the framework constructing algae is comparatively low the annual carbonate production rate is similar to subtropical tropical counterparts because of a remarkably high standing stock early diagenetic alteration is restricted to intraparticle cementation processes which start in vivo bioerosional destruction is the dominant control on the preservation of high latitude build ups preservation of holocene autochthonous coralline algal biostromes is enhanced by rapid burial during storm events redeposition during storms is the most important process in forming a distinct sedimentary facies zonation

the environments of production and deposition of calcareous sediments on the shelf west of scotland the dominant calcareous organisms and sediment characteristics are described for eight different physical settings on the shelf west of scotland each having a different depth substrate and degree of hydrodynamic exposure the principal sites of carbonate production are on shallow rocky substrates where barnacles molluscs echinoderms and serpulids are the dominant calcareous organisms in sheltered shallow sandy zones molluscs echinoderms and benthic foraminiferans are the active producers though the sediments are commonly barnacle rich where tidal currents are enhanced between islands and the waves are suppressed calcareous red algae phymatolithon calcareum and mussel shells build localised banks in deep open shelf water molluscs are the major skeletal contributor to the sediment though on rocky sea beds bryozoans serpulids and echinoderms are important the major sites of deposition are where persistent hydro and aero dynamic conditions sweep together grains from active production sites e g sand ribbons or beaches and dunes adjacent to shallow rocky platforms or in sinks where the physiographic configuration favours the deposition and retention of locally produced sediment or sediment derived from suspension the well sorted cross bedded beach and dune sands commonly contain 75 caco3 in sheltered depressions bioturbated muds accumulate with up to 30 calcite silt which is probably the breakdown product of barnacles and benthic foraminiferans

potential misidentification of love wave phase velocity based on three component ambient seismic noise people have calculated rayleigh wave phase velocities from vertical component of ambient seismic noise for several years recently researchers started to extract love waves from transverse component recordings of ambient noise where transverse is defined as the direction perpendicular to a great circle path or a line in small scale through observation sensors most researches assumed rayleigh waves could be negligible but rayleigh waves can exist in the transverse component when rayleigh waves propagate in other directions besides radial direction in study of data acquired in western junggar basin near karamay city china after processing the transverse component recordings of ambient noise we obtain two energy trends which are distinguished with rayleigh wave and love wave phase velocities in the frequency velocity domain using multichannel analysis of surface waves masw rayleigh waves could be also extracted from the transverse component data because rayleigh wave and love wave phase velocities are close in high frequencies 0 1 hz two kinds of surface waves might be merged in the frequency velocity domain rayleigh wave phase velocities may be misidentified as love wave phase velocities to get accurate surface wave phase velocities from the transverse component data using seismic interferometry in investigating the shallow geology our results suggest using masw to calculate real love wave phase velocities

protactinium 231 dating of carbonates by thermal ionization mass spectrometry implications for quaternary climate change measurement of protactinium 231 231pa in carbonates by thermal ionization mass spectroscopy yields 231pa ages that are more than 10 times more precise than those determined by decay counting carbonates between 10 and 250 000 years old can now be dated with 231pa methods barbados corals that have identical 231pa and thorium 230 230th ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the astronomical theory two devils hole calcite subsamples record identical 231pa and 230th ages suggesting that the chronology of this climate record is accurate

modern carbonate and terrigenous clastic sediments on a cool water high energy mid latitude shelf lacepede southern australia the wide lacepede shelf and narrow bonney shelf are contiguous parts of the south eastern passive continental margin of australia the shelves are open generally deeper than 40 m covered by waters cooler than 18 c and swept by oceanic swells that move sediments to depths of 140 m the lacepede shelf is proximal to the delta of the river murray and the coorong lagoon shelf and upper slope sediments are a variable mixture of holocene and late pleistocene quartzose terrigenous clastic and bryozoa dominated carbonate particles bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m they can be grouped into four depth related assemblages coralline algae the only calcareous phototrophs are important sediment producers to depths of 70 m active benthic carbonate sediment production occurs to depths of 350 m but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions the shelf is separated into five zones the strandline is typified by accretionary sequences of steep shoreface beach and dune carbonate siliciclastic sediments similar shoreline facies of relict bivalve limestone cobble ridges are stranded on the open shelf the shallow shelf c 40 70 m deep is a wide extremely flat plain with only subtle local relief it is a mosaic of grainy quartzose palimpsest facies which reflect the complex interaction of modern bioclastic sediment production dominated by bryozoa and molluscs numerous highstands of sea level over the last 80 000 years modern mixing of sediments from relatively recent highstands and local introduction of quartz rich sediments during lowstands the middle shelf c 70 140 m deep is a gentle incline with subtle relief where holocene carbonates veneer seaward dipping bedrock clinoforms and local lowstand beach complexes carbonates are mostly modern uniform clean coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes the deep shelf edge c 140 250 m deep is a site of diverse and active bryozoa growth resulting accumulations are characteristically muddy and distinguished by large numbers of delicate branching bryozoa the upper slope between 250 and 350 m depth contains the deepest platform related sediments which are very muddy and contain a low diversity suite of delicate branching cyclostome bryozoa this study provides fundamental environmental information critical for the interpretation of cenozoic cool water carbonates and the region is a good model for older mixed carbonate terrigenous clastic successions which were deposited on unrimmed shelves

holocene sediment dynamics on a cool water carbonate shelf otway southeastern australia the otway shelf is covered by cool ocean waters and veneered by bryozoan dominated carbonate sediments radiocarbon dating and stratigraphy of shelf vibracores and slope gravity cores document late pleistocene holocene deposition shelf sediments of the late pleistocene highstand 60 26 ky are rare either never having been deposited or having been removed during the following sea level fall 26 17 ky during the subsequent lowstand the shelf was exposed facies shifted basinward and beach dune complexes were constructed near the shelf edge the deep shelf was characterized by nondeposition and hardground formation and the shelf margin became locally erosional upper slope bryozoan sponge assemblages continued to grow actively and lower slope foraminifera and nannofossil ooze was increasingly enriched in hemipelagic terrigenous mud swept off the wide shelf coarse shelf debris and lowstand dune sands were erosively reworked and transported onto the upper slope and redistributed to deep slope aprons during early transgression 17 10 ky this event locally terminated shelf edge bryozoan and sponge growth continued erosive shoreface retreat formed a bored and cemented ravinement surface mantled by bivalves and lithoclasts across the open shelf base level rise reduced the amount of terrigenous material reaching the continental slope slower transgressive flooding from 10 to 6 5 ky allowed infilling of shallow embayments on the shelf and outer shelf sediment accumulation began by 7 ky sea level stabilized near its present level by 6 5 ky and the area is now partitioned into three zones by an energetic wave and swell regimen 1 inboard protected embayments and or beach dune complexes with high sediment accumulation rates about 100 cm ky 2 an open shelf where although sediment production is active accumulation is patchy 3 5 cm ky to nonexistent within the zone of wave abrasion and minimal about 23 cm ky between maximum abrasion depth and swell wave base and 3 a deep shelf edge and upper slope where sediment is accumulating at rates of 2 50 cm ky interpreted deep water 100 m bryozoan sponge mounds are growing at rates of 105 cm ky accumulation decreases progressively down slope with deep slope pelagic carbonate sedimentation at rates of 5 cm ky the late quaternary shelf record resembles that of flat topped warm water platforms with holocene sediment overlying pleistocene tertiary limestone but for different reasons much of this high energy shelf is still within lag depth more than 10 ky after flooding the steady state deep water shelf margin bryozoan factory has been largely unaffected by 50 100 m eustatic changes in sea level and has contributed to slow but continuous platform progradation the slow growth potential uniform profile of sediment production and distribution and inability of constituent organisms to construct rigid frameworks favor maintenance of a shallow ramp profile and makes the cool water carbonate system an excellent modern analog for interpretation of many ancient ramp successions

active continental rifting in southern baja california mexico implications for plate motion partitioning and the transition to seafloor spreading in the gulf of california three major earthquake series have occurred during the past 30 years on fault systems that are spatially and kinematically distinct from oceanic spreading centers and transform faults in the southern gulf of california focal mechanism solutions for earthquakes of the april 1969 and june 1995 series indicate nearly pure normal displacement across nnw striking planes this seismicity falls along different strands of a major system of normal faults that extends at least 300 km along strike and defines the western limit of the gulf extensional province the dominant normal faults control distribution of neogene basins and have been active since middle to late miocene time epicenters of the august 1969 earthquake series lie south of the baja california peninsula and focal mechanism solutions indicate strike slip displacement this seismic activity is likely related to active wnw striking faults in the continental borderland which isolate baja california as a microplate within the pacific north american plate boundary therefore modern pacific north america plate motion is partitioned into at least three distinct fault systems oceanic spreading centers and transforms in the gulf of california normal faults along the western margin of the gulf of california and faults along the pacific margin of the baja california peninsula kinematic partitioning of plate motion is required to accommodate the strongly three dimensional strain of transtensional rifting continental rifting and seafloor spreading have overlapped in time for the past 3 6 myr which also is likely attributed to the highly oblique kinematics of rifting

heterozoan carbonates from the equatorial rocky reefs of the galapagos archipelago strongly influenced by seasonal and interannual i e el nino southern oscillation upwelling the equatorial setting of the galapagos archipelago is divided into well defined temperature nutrient and calcium carbonate saturation aragonite regions to understand the relationship between oceanographic properties and sediment grain associations grain size carbonate content and components from sea floor surface samples were analysed representing the main geographical regions of the galapagos archipelago the shallow water rocky reefs of the galapagos archipelago are characterized by mixed carbonate siliciclastic slightly gravelly sands despite minor differences in carbonate content major differences exist in the distribution and composition of key carbonate producing biota halimeda is absent and benthic foraminifera occur in extremely low abundance the western side of the galapagos archipelago is strongly influenced by nutrient rich low aragonite subtropical water which generates a heterozoan carbonate biofacies in a tropical realm resembling cold water counterparts i e serpulid echinoderm gastropod barnacle and bryozoan rich facies the central east region is composed of a transitional heterozoan biofacies biofacies observed in the northern region have an increased occurrence of tropical corals albeit with a minor overall contribution to the carbonate components although the temperature gradient would allow for a broader distribution of photozoan biofacies the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories mimicking cool water deeper or higher latitude environments the recent sedimentary record of the galapagos archipelago presents a range of tropical heterozoan carbonate communities responding to more than simply latitude or temperature but a much more complex mixture of physical evolutionary and geological processes

mixed carbonate siliciclastic sedimentation on a tectonically active margin example from the pliocene of baja california sur mexico bioclast rich coarse grained deposits in the pliocene loreto basin provide a record of mixed carbonate and siliciclastic sedimentation at the steep hanging wall margin of this small fault controlled basin sedimentary facies consist of sand to gravel sized carbonate debris mixed with volcaniclastic sand and gravel in a proximal to distal facies tract that includes matrix rich and matrix poor shelly conglomerate impure calcirudite and calcarenite mixed composition turbidites and bioturbated calcarenitic sandstone carbonate material was produced by mollusks and other benthic organisms on a narrow high energy shelf and mixed with volcaniclastic sand and gravel in cross shelf channels these mixtures were transported down a steep subaqueous slope by debris flows grain flows and turbidity currents forming foresets and bottomsets of marine gilbert type deltas this style of mixed carbonate siliciclastic sedimentation has not been documented in detail elsewhere but should be locally abundant in the stratigraphic record of fault bounded basins particularly those with cool or nutrient rich waters that support relatively few binding and framework building faunas recognition of similar facies in other settings can provide useful insights into ancient conditions of carbonate production oceanography climate and tectonics

heterozoan carbonates in subtropical to tropical settings in the present and past water temperature has received considerable attention as steering factor for the genesis of different types of marine carbonate sediments however parameters other than temperature also strongly influence ecosystems and consequently the carbonate grain associations in the resulting carbonate rock among those factors are biological evolution water energy substrate water chemistry light penetration trophic conditions co2 concentrations and mg ca ratios in the seawater increased nutrient levels in warm water settings for example lead to heterotrophic dominated associations that are characteristic of temperate to cool water carbonates failure to recognize the influence of such environmental factors that shift the grain associations towards heterotrophic communities in low latitudes can lead to misinterpretation of climatic conditions in the past modern analogues of low latitude heterozoan carbonates help to recognize and understand past occurrences of heterozoan warm water carbonates careful analysis of such sediments therefore is required in order to achieve robust reconstructions of past climate

shelf to basin resedimented carbonates of the southern margin of the jurassic central high atlas trough morocco abstract the central high atlas mountains occupy the site of an early to middle jurassic east west trending seaway known as the central high atlas trough late triassic early jurassic continental rifting combined with a transtensional structural regime formed a system of pull apart basins comprising the trough a thick sequence of carbonate shelf to basin plain deposits filled the trough and were later uplifted and exposed during the oligocene alpine orogeny stratigraphic analysis of 50 km sup 2 located along the trough s southern shelf margin reveals a 1 200 m thick wedge of slope and basin plain deposits these deposits are divided into four lithostratigraphic units 1 pelagic mudstones 2 channel deposits composed of grainstones and packstones interbedded with marls and mudstones 3 turbidite deposits composed of grainstones packstones and wackestones cyclically interbedded with marls and mudstones and 4 cyclically interbedded marls and mudstones this laterally continuous thick wedge of resedimented deposits suggests that a line source of platform margin sediments fed coalescing base of slope aprons these aprons probably accumulated in an actively subsiding half graben parallel to the shelf margin while tectonics played the major role in basin evolution sea level fluctuations and climate influenced the influx of carbonate and terrigenous sediments rapid cessation of mid sinemurian shallow water platform deposition and regionally transgressive domerian toarcianmore marls indicate eustatic sea level rises affected basin sedimentation periodic climate changes perhaps related to the milankovitch effect may have led to systematic variations in carbonate sediment supply resulting in cyclic sedimentation less

the baja california peninsula borderland structural and sedimentological characteristics abstract structural and sedimentological data from three oceanographic cruises define the peninsular margin of the gulf of california as a borderland similar to the california continental borderland bathymetric and high resolution seismic profiles show some active normal faults with a lateral strike slip component which are parallel and oblique at low angle to the peninsular coast and delimit horst and graben structures preliminary conclusions are that active faults are related to the movement of the peninsular block towards the northwest as part of the opening of the gulf circa 6 5 my ago grabens and half grabens separated by highlands islands and banks have formed some of the basins are now inland such as santa rosalia loreto and san jose del cabo and are filled with pliocene and possibly miocene marine rocks other basins are modern shallow bays like concepcion 30 m deep others are slope basins with a range of depths such as alfonso and cochimie basins at about 400 m and la giganta and la paz basins at 500 and 700 m respectively sedimentation in these basins is varied inland basins pliocene are filled with shallow marine sedimentary rocks clastics and evaporites concepcion is a starved basin filled with some terrigenous but mainly biogenic sediments the modern deep basins alfonso la giganta and la paz are filled with terrigenous sediments on their peninsular margin biogenic if they are limited by islands and laminated sediments if they are stagnant or have slopes or sills intersecting the oxygen minimum layer of the water column

seagrass meadow sedimentary facies in a mixed siliciclastic carbonate temperate system in the tyrrhenian sea pontinian islands western mediterranean abstract the paper presents the characteristics of surface sediments in a seagrass dominated environment of the inner shelf of the pontinian islands tyrrhenian shelf central mediterranean the aims of this work are to characterize the carbonate production and sedimentary processes of a representative high latitude temperate posidonia oceanica dominated area to discuss the role of seagrass in the siliciclastic carbonate mixing processes which provide analogs for interpreting the occurrence and importance of these types of deposits in the rock record the majority of sediments are poorly sorted siliciclastic skeletal sand based on grain type and abundance and carbonate content these deposits include six subfacies the different subfacies reflect environmental changes within the seagrass environment associated with variations in light penetration and hydrodynamic conditions additionally the seagrass facies range from purely carbonate to mixed carbonate siliciclastic depending on the amount of siliciclastic input and on the capacity of seagrasses to trap allochthonous sediments while hosting carbonate producing biota the type of substrate and the erosion and transport processes control the siliciclastic input in these pontinian seagrass meadows sedimentary facies contain abundant siliciclastic grains produced by erosion of the volcanic substrate and trapped by seagrass blades and rhizomes this pontinian example illustrates that in heterozoan dominated seagrass settings mud producing green algae are not present or are not calcifying and consequently seagrass deposits are much more grainy than photozoan counterparts ancient heterozoan tropical seagrass deposits likely will be discriminated from their temperate or subtropical counterparts only by careful taxonomic analysis of skeletal grains

model intercomparison for the present day the mid holocene and the last glacial maximum over western europe 1 the focus of this paper is an evaluation of the performance over western europe of an ensemble of general circulation models gcms used to simulate climates at the present day the mid holocene and the last glacial maximum lgm experiments are considered from the palaeoclimate modeling intercomparison project pmip and from more recent sensitivity studies for the same time slices surface air temperature and precipitation are compared between models and with observed and proxy data sets using evaluation measures such as correlation coefficients and root mean squared errors hierarchical and k means cluster analysis are used to quantitatively assess relative model performance comparisons are made for western europe for a gridded domain between 38n13w south west corner and 65n30e north east corner and for four transects within this domain inter experiment comparisons reveal that the ranges of results from the sensitivity studies are within those of the pmip models there is no month to month or time slice to time slice consistency in the clustering patterns produced although one clear characteristic is that experiments performed with models from the same institution tend to cluster inter model agreement at past time slices is considerably reduced when we consider differences from the present day rather than absolute values and this is particularly the case for mid holocene temperature when the insolation forcing only represents a small departure from modern values statistical comparisons of the models with observed and proxy data sets demonstrate a lack of consistency in model performance between months transects and time slices

modern non tropical mixed carbonate siliciclastic sediments and environments of the southwestern gulf of california mexico abstract modern mixed carbonate siliciclastic warm temperate environments were studied in the southern gulf of california goc mexico the combined heterozoan and photozoan character is defined by the absence of true coral reef structures calcareous green algae and non skeletal grains and the dominance of rhodoliths unattached coralline red algae mollusks and small coral patch reefs the major carbonate producing environments are pocket bays a shallow carbonate bioherm high energy rocky and sandy shorelines and mid shelf settings sediments characterizing the pocket bays display heavily bioturbated bioclastic wackestone and grainstone textures the rhodolith dominated bioherm is composed of coarse sediments exhibiting grainstone and rudstone textures with fine material being winnowed away by tidal currents rocky and sandy shorelines are characterized by erosion and mixing of up to boulder size granitic and volcaniclastic material with coralline red algal and molluskan carbonates the mid shelf settings are defined by a silt and fine sand sized non carbonate matrix mixed with abundant molluskan fragments and foraminifera peak carbonate production takes place between 10 and 15 m water depth below 40 m production significantly decreases combined with a steep increase in the amount of siliciclastics this is in contrast to many temperate and cool water mixed carbonate siliciclastic systems where most carbonate production occurs in mid to outer shelf settings a full spectrum of sediments from pure carbonates 90 100 carbonate allochem carbonates 50 90 carbonate and allochemic mud or sand

tidal flat sedimentation from hurricane kate caicos platform british west indies abstract hurricane generated thinly bedded grainstones are the dominant style of stratification on the carbonate tidal flat complex on caicos platform british west indies this is in dramatic contrast to the winter storm generated millimeter thick laminae which dominate stratification on the northwest andros tidal flats and have become the general criteria for recognizing ancient carbonate tidal flat sequences hurricane kate which passed directly across the caicos tidal flats on 18 november 1985 provided an opportunity both to document the character and distribution of a specific storm sediment layer and to evaluate the role of hurricanes in molding the geometry of the tidal flat system though moderate in strength and producing only incomplete flooding hurricane kate deposited a layer of fine to very fine peloidal grainstone 0 5 2 cm in thickness across significant portions of the extremely broad low relief shore and channel levees and the inland algal marsh these storm layers are interbedded with organic rich layers which represent prolonged periods of growth of scytonema algal mat between hurricanes recognition that centimeter thick grainstone layers dominate entire tidal flat complexes necessitates both a thorough modification of criteria for defining ancient carbonate tidal flat deposits and a reevaluation of supposedly subtidal thinly bedded limestones

topographic controls on production and deposition of tidal cool water carbonates uzes basin se france we document an example of a cool water carbonate deposit interpreted as a flood tidal delta formed during sea level fall in the uzes basin french miocene foreland basin in the miocene it was a peripheral basin connected to the open sea by a narrow 15 km long seaway the studied uzes formation is a 50 m thick tidal bioclastic carbonate body formed at the junction between the uzes basin and the seaway it is composed dominantly of rhodalgal packstones that are interpreted to have been produced inside the basin however most of the deposit was built out by bidirectional hydraulic dunes suggesting that accumulation of carbonate grains was not controlled by production but rather by tidal currents the deposit is thickest and coarsest grained and exhibits the larger dunes at the inlet of the seaway where currents are expected to have been fastest the deposit is thinner finer grained and more bioturbated away from the inlet toward the basin that is interpreted as a result of a decrease of current velocity due to flow expansion the main deposit exhibits a general upward increase in thickness and grain size of cross beds together with a decrease of faunal diversity from bivalve rich to rhodalgal facies consistent with progressive tidal flow acceleration in the seaway resulting from sea level fall lime mud is pervasive in the matrix of even the highest energy facies this suggests that one cannot draw any average correlation between permeability and architecture of the deposit also this could favor the observed early marine diagenesis of the deposit and give it a high preservation potential in the stratigraphic record

pleistocene sea levels and tectonic uplift based on dating of corals from sumba island indonesia we collected and dated fossil corals from the uplifted reef tracts of sumba island mass spectrometry tims and ams was used to obtain reliable and precise radiochronological results it is possible to identify outcrops corresponding to major sea level high stands isotope stage 1 starting at 7 1 kyr bp 5a c a 86 kyr bp 5c c a 105 kyr bp 5e between 119 and 132 kyr bp and 9 c a 305 kyr bp the radiochronological data are thus broadly consistent with the timing of sea level fluctuations predicted by the astronomical theory of paleoclimates comparison with similar data from other terrace sequences and from benthic 18o records indicates that the average tectonic uplift rate at cape laundi sumba is on the order of 0 2 0 5m kyr the lowest values 0 3m kyr lead to the build up of polycyclic topographic terraces in which it is possible to find corals grown during different interstadial or even interglacial times

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

late quaternary evolution of coral reefs on a cool water carbonate margin the abrolhos carbonate platforms southwest australia late quaternary coral reefs have developed on the southwestern australian margin which has otherwise been characterised by cool water carbonates since the eocene the houtman abrolhos coral reefs are at the limits of existence extending with the assistance of the leeuwin current a poleward flowing warm water stream into a region dominated by more temperate communities coring in the easter group reefs supported by high precision dating by both view the mathml source tims and 14 c methods has shown vigorous coral growth with reefs over 26 m thick in the holocene and over 15 m thick in the last interglacial each of the three abrolhos platforms consists of a central platform composed of last interglacial reefs about which windward and leeward holocene reefs developed asymmetrically reef peritidal and eolian facies comprise the emergent last interglacial limestones which are extensively calcretized with reef facies up to 5 m above msl the last interglacial high stand lasted for at least 10 ka from 130 to 120 ka and possibly 15 ka from 132 to 117 ka holocene reef facies are also emergent by 0 5 m and are overlain by peritidal and storm ridge facies in an upward shallowing sequence windward 10 m thick and leeward 26 m thick holocene reefs in the easter group show contrasting lithofacies the wave exposed windward reefs consist of a slow growing association of coralline algal bindstones and coral framestones whereas fast growing coral framestones dominate the more protected leeward reefs the leeward reefs commenced growth 10 000 years ago and grew to the present sea level by 6500 years ago generating holocene constructional topography consisting of blue hole terrain in the leeward parts of the platforms

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california