closure of a seaway stratigraphic record and facies guadix basin southern spain during the late tortonian upper miocene the guadix basin in s spain formed one of the betic corridors that connected the mediterranean sea with the atlantic ocean the closure of this connection occurred in a series of steps documented by three sedimentary units a lower unit consisting of basinal marls shallow water calcarenites and sands records the formation of a wide seaway during deposition of the following unit this narrowed to a strait no more than 2 km in wide triggering an intensification of currents that caused migration of submarine dunes preserved as giant cross beds in bioclastic sands and conglomerates current flowed from the mediterranean to the atlantic the third unit constitutes the youngest marine episode of the filling of the guadix basin at this stage the connection between the mediterranean sea and the atlantic ocean was broken and a system of coastal coral reefs was established in the northern part of the basin

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

mean currents and sediment transport in a rip channel measurements of hydrodynamics and suspended sediment transport were carried out along a cross shore transect in a rip channel a tidally induced threshold for rip flow initiation was found this threshold depended upon the degree of wave energy dissipation and could be identified through a critical value of the ratio of significant wave height to water depth s in the rip neck with normally incident waves rip current velocities were well correlated with velocities predicted from a simple model involving the onshore mass transport in asymmetric breaking waves crossing the bar hydrodynamics and sediment transport were tidally modulated with strong offshore directed rip currents and associated offshore sediment transport due to the mean flow at low tide at high tide when the rip was inactive the tendency was for weak onshore directed mean flows and or oscillatory incident waves transporting smaller amounts of sediment landward the net result was a gradual lowering of the topographic relief along the rip channel with net deposition seaward of the rip outside the surf zone transport was mainly landward due to oscillatory incident waves

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

downslope migrating large dunes in the chattian carbonate ramp of the majella mountains central apennines italy abstract this work is the result of detailed geological mapping and stratigraphic analysis of the lepidocyclina limestone in the northern sector of the majella mountains central apennines the lepidocyclina limestone represents an informal member of the bolognano formation chattian to messinian in age four main lithofacies have been recognized planar cross bedded grainstone fa moderate angle cross bedded grainstone to packstone fb sigmoidal cross bedded grainstone fc and bioturbated marly packstone to wackestone fd a detailed description of the recognized lithofacies and facies association of the lepidocyclina limestone is given in this work together with an interpretation of the corresponding depositional setting and a discussion of the related larger scale processes in summary the depositional profile of the lepidocyclina limestone is consistent with a carbonate ramp where most of the sediments appear to be parautochthonous in the middle ramp environment and autochthonous dominated in the outer ramp environment palaeocurrent patterns indicate a strong generally north west basin ward direction that affected the middle ramp environment and developed a wide down slope migrating dune field considering that the warm oligocene climate of the mediterranean area was favorable to tropical cyclone development both in terms of frequency and intensity it is suggested that return currents generated by strong winds or storms were common on the lepidocyclina carbonate ramp thus favoring the development of the observed dune field

temperate carbonate platform drowning linked to miocene oceanographic events maiella platform margin italy carbonate platform drownings are frequent often synchronous global occurrences yet explanations for these world wide events remain unsatisfactory in the central apennines lower and middle miocene carbonate rocks deposited on a temperate ramp in the maiella platform margin record two episodes of platform drowning followed by hemipelagic sedimentation dated as latest oligocene aquitanian 26 23 ma and as burdigalian langhian 20 16 ma a high resolution stratigraphy based on strontium isotopes allows us to correlate key phases of platform evolution with events recorded in deep water ocean sediments this paper suggests that high weathering rates and nutrient input in the mediterranean during the early and middle miocene possibly linked to the uplift of the tibetan region set the preconditions for platform drowning which were ultimately caused by rapid eustatic sea level rises

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

orbitally paced phosphogenesis in mediterranean shallow marine carbonates during the middle miocene monterey event during the oligo miocene major phases of phosphogenesis occurred in the earth s oceans however most phosphate deposits represent condensed or allochthonous hemipelagic deposits formed by complex physical and chemical enrichment processes limiting their applicability for the study regarding the temporal pacing of miocene phosphogenesis the oligo miocene decontra section located on the maiella platform central apennines italy is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting of particular interest are the well winnowed grain to packstones of the middle miocene bryozoan limestone where occurrences of authigenic phosphate grains coincide with the prominent carbon isotope excursion of the monterey event this unique setting allows the analysis of orbital forcing on phosphogenesis within a bio chemo and cyclostratigraphically constrained age model la icp ms analyses revealed a significant enrichment of uranium in the studied authigenic phosphates compared to the surrounding carbonates allowing natural gamma radiation gr to be used as a qualitative proxy for autochthonous phosphate content time series analyses indicate a strong 405 kyr eccentricity forcing of gr in the bryozoan limestone these results link maxima in the gr record and thus phosphate content to orbitally paced increases in the burial of organic carbon particularly during the carbon isotope maxima of the monterey event thus phosphogenesis during the middle miocene in the mediterranean was controlled by the 405 kyr eccentricity and its influence on large scale paleoproductivity patterns rare earth element data were used as a tool to reconstruct the formation conditions of the investigated phosphates indicating generally oxic formation conditions which are consistent with microbially mediated phosphogenesis

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

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

heterozoan carbonates in oligotrophic tropical waters the attard member of the lower coralline limestone formation upper oligocene malta abstract photozoan and heterozoan skeletal assemblages are controlled by their trophic requirements i e light based photosynthesis versus other sources and temperature photozoan associations tend to dominate tropical and subtropical waters whereas heterozoan carbonate systems tend to occur in cooler waters and in localised areas that are affected by nutrient rich upwelling or terrestrial runoff because of the wide climatic spectrum in which heterozoan carbonates are found their interpretation is often problematic we present a high resolution analysis of the attard member of the lower coralline limestone formation upper oligocene malta the biotic associations and palaeolatitudinal reconstructions suggest that carbonate sedimentation took place in tropical waters under oligotrophic conditions an important factor controlling the spread of heterozoan assemblages in the late oligocene of malta seems to be related to the palaeoecology and evolution of zooxanthellate the limited capacity of corals to thrive in high light conditions and to form a wave resistant reef promoted the diffusion of heterozoan assemblages

diversity of magma types in a lower paleozoic island arc marginal basin system eastern klamath mountains california u s a abstract a trace element investigation has been conducted on ordovician to devonian volcanics of the eastern klamath mountains spatially associated to the siluro ordovician trinity peridotite and gabbros all the studied volcanics low k tholeiites and calc alkaline volcanics present strong island arc geochemical features low tio 2 contents negative nb zr and ti anomalies mild lree enrichment and depletion some volcanics from lovers leap and copley exhibit strong immature island arc geochemical affinities very depleted lree patterns and very low nb contents suggesting that they were formed by high degrees of partial melting 20 of a residual lithosphere diminution of the partial melting degree and addition of sediments to the source will explain the occurrence of less depleted or slightly lree enriched volcanics the grey rocks basaltic pillow lavas thrust onto the trinity peridotitic sheet probably represent the extrusive member of the ophiolitic sequence their strong island arc geochemical affinities suggest that the ophiolite was formed during the first stages of a back arc basin development differentiation took place in the arc by melting of the deeper basaltic layers leading to the formation of abundant rhyolitic and trondhjemitic magmatism representing the first stages of continental accretion

from fracture analysis to flow simulations in fractured carbonates the case study of the roman valley quarry majella mountain italy abstract this work assesses the impact of the stratigraphic and structural heterogeneities on the fluid distribution and migration within a deformed carbonate reservoir analogue the study was carried out in the abandoned roman valley quarry majella mountain central italy well known for its historical bitumen extraction the studied rocks consist of ramp carbonates of the lower member of the bolognano formation oligocene miocene in age mainly composed of grainstones and secondary packstones and wackestones in the quarry the exposed rocks are crosscut by two high angle oblique slip faults striking wnw ese with up to 40 m of throw with the aim of deciphering the contribution of both matrix and fracture pore space on the fluid storage and migration both laboratory measurements and field based discrete fracture network dfn models cubes with 4 m per side have been carried out the obtained dual porosity permeability model which includes the lithological and the structural heterogeneities observed at the location was used to run flow simulations under different scenarios of well locations the fluid distribution in the matrix resulting from these flow simulations is consistent with field observations where bitumen localizes within the most permeable lithofacies grainstones in the fault zones the fracture network causes an important fluid flow anisotropy enhancing the flow in a direction subparallel to the faults the flow orthogonal to the fault zones is controlled by type and lateral continuity of fault rocks where fault breccias represent conduits and cataclasites localized barriers

the oligocene miocene stratigraphic evolution of the majella carbonate platform central apennines italy abstract the stratigraphic architecture of the bolognano formation documents the evolution of the majella carbonate platform in response to global and local changes that affected the mediterranean area during the oligocene miocene interval the bolognano formation consists of a homoclinal ramp that developed in a warm subtropical environment five different lithofacies associations have been identified lepidocyclina calcarenites cherty marly limestones bryozon calcarenites hemipelagic marls and marly limestones and lithothamnion limestones each association corresponds to a single lithostratigraphic unit except for the lepidocyclina calcarenites that form two distinct lithostratigraphic units lepidocyclina calcarenites 1 and 2 these six units reflect alternation of shallow water carbonate production and drowning specifically two of the three stages of shallow water carbonate production regard the development of wide dune fields within the middle ramp one stage dominated by red algae and a sea grass carbonate factory whereas the two drowning phases are represented by marly cherty limestones and calcareous marls a new biostratigraphic framework for bolognano formation is presented based on high resolution analysis of calcareous nannofossil assemblages which proved to be very useful for biostratigraphic constraints also in shallow water settings using this approach we have linked the first drowning phase late chattian aquitanian p p in age to western mediterranean volcanism and the mi 1 event and the second drowning phase late burdigalian serravallian in age to the closure of the indo pacific passage and the occurrence of the global monterey event these results permit a new deciphering in terms of sequence stratigraphy of the bolognano formation that is interpreted as a 2nd order super sequence that can be subdivided into 3 transgressive regressive sequences

tectonic setting of the southern cascade range as interpreted from its magnetic and gravity fields we have compiled and analyzed aeromagnetic data from the southern cascade range and compared them with residual gravity data from the same region in order to investigate regional aspects of these young volcanic rocks and of basement structures beneath them various constant level aeromagnetic surveys were mathematically continued upward to 4 571 m and numerically mosaicked into a single compilation extending from lat 40 10 n to lat 44 20 n these data were reduced to the pole upward continued an additional 10 km and compared with a magnetic topographic model and with residual gravity data upward continued to the same level several intriguing regional features are suggested by these data 1 the trinity ophiolite complex that is exposed west of mount shasta probably dips at a shallow angle to the east and continues in the subsurface at least 10 km east of mount shasta 2 mount shasta lassen peak and medicine lake volcanoes are located in a widespread magnetic low possibly caused by an upwarp of the curie temperature isotherm 3 crater lake caldera is located at the intersection of various linear anomalies interpreted to be related to structure in basement rocks below the cascade range 4 three sisters volcanoes and newberry crater are connected to each other by an arcuate magnetic source 5 the high cascades from lat 40 10 n to at least lat 44 30 n are marked by a residual gravity low which includes the three sisters volcanoes mount shasta medicine lake volcano mount mcloughlin and crater lake we believe this gravity feature represents a major structural depression beneath the high cascades 6 except for newberry crater every major volcano of the study area is located on the perimeter of a local gravitational low we suggest that the gravity lows reflect subsidence of low density volcanic material relative to denser country rock and that the major volcanoes have developed over structures at the perimeters of their respective depressions

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

correlating carbon and oxygen isotope events in early to middle miocene shallow marine carbonates in the mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy during the miocene prominent oxygen isotope events mi events reflect major changes in glaciation while carbonate isotope maxima cm events reflect changes in organic carbon burial particularly during the monterey carbon isotope excursion however despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions the decontra section on the maiella platform central apennines italy however allows to resolve them for the first time in such a setting during the early to middle miocene the present study improves the stratigraphic resolution of parts of the decontra section via orbital tuning of high resolution gamma ray gr and magnetic susceptibility data to the 405 kyr eccentricity metronome the tuning allows within the established biostratigraphic sequence stratigraphic and isotope stratigraphic frameworks a precise correlation of the decontra section with pelagic records of the mediterranean region as well as the global paleoclimatic record and the global sea level curve spectral series analyses of gr data further indicate that the 405 kyr orbital cycle is particularly well preserved during the monterey event since gr is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the decontra section it follows the same long term orbital pacing as observed in the carbon isotope records the 405 kyr gr beat is thus correlated with the carbon isotope maxima observed during the monterey event finally the mi events can now be recognized in the 18o record and coincide with plankton rich siliceous or phosphatic horizons in the lithology of the section

timescales of orogeny jurassic construction of the klamath mountains an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 94ycj2454 timescales of orogeny jurassic construction of the klamath mountains b r hacker m m donato c g barnes m o mcwilliams and w g ernst diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order classical interpretations of orogeny were based on relatively imprecise biostratigraphic and isotopic age determinations that necessitated grouping apparently related features that may in reality have been greatly diachronous isotopic age techniques now have the precision required to resolve the timing of orogenic events on a scale much smaller than that of entire mountain belts forty five new 40ar 39ar ages from the klamath mountains illuminate the deformation metamorphism magmatism and sedimentation involved in the jurassic construction of that orogen leading to a new level of understanding regarding how preserved orogenic features relate to ancient plate tectonic processes the new geochronologic relationships show that many jurassic units of the klamath mountains had 200 ma or older volcanoplutonic basement subsequent formation of a large 170 ma arc was followed by contractional collapse of the arc collision with a spreading ridge may have led to large scale nw se extension in the central and northern klamaths from 167 to 155 ma coincident with the crystallization of voluminous plutonic and volcanic suites marked cooling of a large region of the central klamath mountains to below 350 c at 150 ma may have occurred as the igneous belt was extinguished by subduction of colder material at deeper structural levels these data demonstrate that the klamath mountains and perhaps other similar orogens were constructed during areally and temporally variant episodes of contraction extension and magmatism that do not fit classical definitions of orogeny

genesis and evolution of a permian jurassic magmatic arc accretionary wedge and reevaluation of terranes in the central klamath mountains investigation of key areas of the central klamath mountains demonstrates that genetic relationships connect several regionally significant lithologic units that were previously considered to be separate tectonostratigraphic terranes the rocks embody an intraoceanic tholeiitic to alkaline magmatic arc and contiguous accretionary wedge formed in permian to middle jurassic time the eastern hayfork and st claire creek units comprise permian jurassic oceanic sedimentary rocks deposited nearby and coeval with eruption of the north fork salmon river volcanoplutonic arc the more inboard st claire creek unit consists of stratigraphically coherent chert and minor argillite probably deposited in a back arc setting whereas the more outboard eastern hayfork sedimentary rocks were disrupted during formation of an accretionary wedge the volcanoplutonic north fork salmon river arc extends for 200 km in the central klamath mountains and was active episodically or continuously from permian through middle jurassic time alkalic members of the mafic igneous suite may have erupted following subduction of a spreading center a varied heating history has produced an amalgam of submarine and regional low pressure moderate temperature metamorphism overprinted locally by contact metamorphism geochronology of weakly metamorphosed mafic dikes sills 10 new 40ar 39ar analyses suggests that significant heat was retained regionally into early cretaceous time

tertiary palaeogeography and tectonostratigraphic evolution of the northern and southern peri tethys platforms and the intermediate domains of the african eurasian convergent plate boundary zone abstract the increasing effects of african eurasian convergence during the tertiary resulted in the uplift and emergence of the northern and southern peri tethys platforms palaeogeographic maps covering six selected time slices including the middle eocene late early oligocene late early miocene early middle miocene early late miocene and middle to late pliocene illustrate that environmental and depositional differentiations on the northern platform and along the bordering domains of the convergence zone were more pronounced than on the southern platform and its adjacent areas the tectonic evolution of the northern platform included an overall eastward directed trend in the onset of basin uplift and emergence which started at about the eocene oligocene transition at 34 ma tectonostratigraphic analyses indicate a striking contemporaneity of the events which defined the temporal and spatial development of both the domains of the convergent plate boundary zone and the bordering platforms five episodes of major regional change in palaeogeographic and tectonic setting are distinguished they occurred in the late eocene 37 34 ma early late oligocene 30 27 ma latest early to earliest middle miocene 17 15 ma early late miocene 9 8 ma and late early to early middle pliocene 4 3 ma these episodes encompassed changes which were most probably induced by geodynamic events primarily related to the relative motions of the african arabian and eurasian plates in turn the plate motions are assumed to have triggered discrete steps in the regional kinematics and geodynamics that governed the palaeogeographic evolution of the peri tethys platforms and the intermediate domains of the african eurasian plate boundary zone

stratigraphic sedimentology of tertiary cool water limestones se australia abstract mid tertiary limestones exposed as sea cliffs along the coast of victoria southeastern australia accumulated on the inner part of a cool water distally steepened ramp or open shelf all sediments are bioclastic dominated by particles of bryozoans echinoderms benthic foraminifers brachiopods and molluscs shallow grainy facies also contain coralline algae quartz and glauconite while deep muddy facies include ahermatypic corals ostracodes sponge spicules planktic foraminifers and terrigenous clays the fundamental depositional unit is a meter scale subtidal cycle or rhythm shallow shelf cycles are shallowing upward cross bedded or burrowed grainstone capped by a marine cemented hardground or quartz granule lag while mid shelf cycles are upward coarsening and thickening proximal to distal tempestites such cycles are interpreted to form by eustatically driven climatically controlled oscillations in abrasion wave base and swell wave base deep shelf rhythms are interbedded bryozoan marl and calcareous clay thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution lowstand systems tracts are depositional or erosional sequence boundaries are complex multigeneration mostly submarine surfaces condensed cycle boundaries that can be traced offshore into multiple omission surfaces and conformable contacts basinward facies shifts result in deposition of condensed lowstand wedges of stacked shallowing upward grainstone cycles transgressive systems tracts are thick bryozoan marl calcareous clay rhythms associated with facies backstepping and abrupt deepening such rhythmites typically grade stratigraphically upward into tempestite cycles highstand systems tracts are highly progradational wedge shaped rock bodies of shallowing upward grainy cycles these limestones provide the critical link of stratigraphy between modern cool water carbonate shelf deposits and the older mesozoic and paleozoic record of similar sediments

the messinian salinity crisis in the adriatic foredeep evolution of the largest evaporitic marginal basin in the mediterranean abstract the recent release of a large number of subsurface geological data by the italian minister of economic development including boreholes and seismic profiles provided the occasion for a new assessment of the deposits associated with the messinian salinity crisis msc in the adriatic foreland basin system and a new integration with the outcropping successions of the apennines in particular the study of the messinian evaporites allowed to reconstruct a new detailed palaeogeographic and palaeobathymetric framework for all the stages of the crisis we identified the largest evaporitic marginal basin ever described for the mediterranean hosting the precipitation of the primary shallow water gypsum deposits plg primary lower gypsum during the first stage of the crisis during the second and third stages of the crisis the plg basin underwent uplift and erosion and the evaporite accumulation moved to the deeper part of the basin and was characterized by the deposition of the resedimented lower gypsum unit including clastic evaporites recycling the plg ones primary halite and terrigenous deposits the distribution of the different evaporitic facies was the basis for an improved reconstruction of the upper miocene tectonic evolution of the apennines thrust belt our results show a clear separation between shallower depocenters located in the wedge top and in the adriatic foreland basins and characterized by msc stage 1 plg deposition and deeper water ones located in the adriatic foredeep and close to the calabrian arc where msc stage 2 terrigenous and gypsum bearing clastic deposits and primary halite accumulated

sub wavebase cross bedded grainstones on a distally steepened carbonate ramp upper miocene menorca spain cross bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines shoals or shelf breaks in contrast on the early tortonian carbonate platform of menorca balearic islands coarse grained cross bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase excellent exposures along continuous outcrops on the sea cliffs of menorca reveal the depositional profile and three dimensional distribution of the different facies belts of the tortonian ramp depositional system basinward from the palaeoshoreline fan deltas and beach deposits pass into 5 km wide gently dipping bioturbated dolopackstone inner and middle ramp then into 12 20 dipping dolograinstone rudstone clinobeds ramp slope and finally into subhorizontal fine grained basinal dolowackestone to dolopackstone outer ramp in this miocene example coarse grained grainstones exist in five different settings other than beach deposits 1 on the middle ramp where cross bedded grainstones were deposited by currents roughly parallel to the shoreline at 40 70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones 2 on the upper slope where clinobeds are composed mostly of in situ rhodoliths and red algae fragments 3 on the lower slope as small scale bedforms small three dimensional subaqueous dunes migrating parallel to the slope 4 at the transition between the lower slope and the outer ramp where mollusc rich and rhodolithic rudstones and grainstones interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera infill slide slump scars as upslope backstepping bodies backsets 5 at the toe of the slope where coarse skeletal grainstones indicate bedform migration parallel to the platform margin induced by currents at more than 150 m estimated water depth this late miocene example also illustrates how changes in intrabasinal environmental conditions nutrients and or temperature may produce changes in stratal patterns and facies architecture if they affect the biological system two depositional sequences compose the miocene platform on menorca where a reef rimmed platform prograded onto an earlier distally steepened ramp the transition from the ramp to the reef rimmed platform was effected by an increase in accommodation space caused by ecological changes promoting a shift from a grain to a framework producing biota

cryptic tectonic domains of the klamath mountains california and oregon abstract numerous fragments of oceanic crust and island arcs make up the klamath mountains province these fragments were joined together amalgamated in an oceanic setting during paleozoic and mesozoic collisional events and were accreted to north america as a composite unit during latest jurassic or earliest cretaceous time the roughly arcuate and concentric distribution of the terranes of the klamath mountains does not now seem to be a result of simple oroclinal bending as earlier believed although commonly described as a west facing arcuate structure the province is cut diagonally by a vaguely defined nw trending zone of discontinuity or hinge line that divides the province into ne and sw tectonic domains the zone of discontinuity is marked by a number of lithic and structural anomalies and particularly by the distribution of a remarkable series of belts of plutonic rocks the terranes regional structures and plutonic belts of the ne domain trend ne and are generally wider and more coherent than the narrow nw trending terranes and plutonic belts of the sw domain most plutonic belts of the ne domain do not have equivalents in the sw domain paleomagnetic evidence suggests that all the plutonic belts except possibly the youngest the earliest cretaceous shasta bally belt were emplaced before the klamath mountains terranes finally accreted to north america

large scale fluid flow in the middle devonian presqu ile barrier western canada sedimentary basin saddle dolomite cements are regionally extensive in the middle devonian presqu9ile or keg river barrier and are spatially associated with mississippi valley type mineralization at pine point northwest territories from northeastern british columbia to pine point over a lateral distance of 400 km these dolomite cements show general trends of decreasing 87 sr 86 sr ratios 0 7106 to 0 7081 and homogenization temperatures 178 to 92 c with some increase in 18 o values 16 to 7 pdb these regional trends suggest that hotter and more radiogenic basinal fluids moved eastward updip along the presqu9ile barrier and mixed with cooler ambient formation waters these movements of basinal fluids were probably related to tectonic thrusting and compression sedimentary loading and tectonic uplift on the western margin of the western canada sedimentary basin which began to form during late jurassic to early cretaceous time and climaxed during the late cretaceous to paleocene the middle devonian presqu9ile barrier appears to have acted as a deeply buried regional conduit system that played an important role in focusing and channeling these basinal fluids these regional fluid flows appear to have been responsible for extensive burial dolomitization secondary migration of hydrocarbons and local mississippi valley type mineralization in the western canada sedimentary basin

sulfuric acid speleogenesis in the majella massif abruzzo central apennines italy abstract many active and inactive hypogene sulfuric acid cave systems are known along the apennines italy the cavallone bove cave system is located in the external part of the central apennine chain in the majella massif and opens at 1470 m asl along the taranta gorge south of chieti the presence in these caves of peculiar geomorphological features such as feeders rising channels megacusps cupolas and replacement pockets offers evidence of rising acidic fluids the secondary mineral deposits including meter size white gypsum deposits alunite jarosite black layers of iron manganese oxides and hydroxides along with a rare association of authigenic rutile ilmenite minerals indicate a sulfuric acid origin stable isotope analyses of sulfates further confirm a sulfuric acid speleogenetic sas origin of these minerals and in general of the whole cave system with h2s coming from the bacterial sulfate reduction of deep seated triassic evaporites interacting with hydrocarbons alunite dating demonstrates this water table sas cave to have been active at least until 1 52 0 28 ma all the evidence suggests that cavallone bove is an ancient sulfuric acid karst system that was uplifted

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

concordant paleolatitudes for neoproterozoic ophiolitic rocks of the trinity complex klamath mountains california 1 new paleomagnetic results from the eastern klamath mountains of northern california show that neoproterozoic rocks of the trinity ophiolitic complex and overlying middle devonian volcanic rocks are latitudinally concordant with cratonal north america combining paleomagnetic data with regional geologic and faunal evidence suggests that the trinity complex and related terranes of the eastern klamath plate were linked in some fashion to the north american craton throughout that time but that distance between them may have varied considerably a possible model that is consistent with our paleomagnetic results and the geologic evidence is that the trinity complex formed and migrated parallel to paleolatitude in the basin between laurasia and australia east antarctica as the rodinian supercontinent began to break up it then continued to move parallel to paleolatitude at least through middle devonian time although the eastern klamath plate served as a nucleus against which more western components of the klamath mountains province amalgamated the klamath superterrane was not accreted to north america until early cretaceous time index terms 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 5475 planetology solid surface planets tectonics 8149 8157 tectonophysics evolution of the earth plate motions past 3040 9350 information related to geographic region north america 9619 information related to geologic time precambrian

sedimentology and palaeoenvironment of the southeast sicilian tertiary platform carbonates abstract a thick succession of shelf and shelf slope carbonates is developed in southeastern sicily sedimentological aspects of the oligocene to tortonian sequence including distribution and palaeoenvironmental factors are considered a new formation and four new members are proposed in the upper part of the succession the region comprises a western half typically exhibiting the principal deeper water planktonic facies including marls and an eastern area displaying typically inner shelf carbonates and an attenuated succession coralline algal limestones and calcarenites are more typical of this latter region but there are also some volcanic intercalations an attempt is made to relate the hyblean succession to that of the maltese islands which lie at the southern end of this tertiary carbonate platform

components facies and ramps redefining upper oligocene shallow water carbonates using coralline red algae and larger foraminifera venetian area northeast italy abstract chattian mixed carbonate siliciclastic deposits from two palaeogeographic units of southern alps the lessini shelf and venetian foreland basin of northeast italy are studied with respect to facies distributions and controlling ecological factors on dominant biogenic components these ramp depositional systems are located in the western southern alps on the lessini shelf and in the eastern southern alps in the venetian foreland basin the successions show an extensive geographic distribution of at least 150 km 40 km at the southern margin of the southern alps palaeoenvironments are inferred following microfacies characteristics and floral and faunal indicators especially those of coralline red algae and larger foraminifera an inner to middle homoclinal ramp morphology is reconstructed based on facies distributions and taxonomic and coralline algal growth form proxy data the distribution along depositional strike shows variation from thinner carbonate dominated sequence in the west monti berici and monti lessini to a more variable mixed carbonate siliciclastic dominated environment to the east vittorio veneto alpago facies character and occurrence are controlled by local hydrodynamic conditions and varying water turbidity of the studied ramp depositional system the general facies succession shows a transgressive sequence from the proximal inner to proximal middle ramp a shoal belt of trough cross bedded sandstones occurs in a proximal inner ramp position in all of the studied areas in a gentle dipping homoclinal ramp most benthic organisms inhabited the relatively quite environments off these shoals in a distal inner ramp setting basinward environments proximal middle ramp constitute areas of maximal carbonate production and consist primarily of larger foraminiferal facies and rhodolith pavements larger foraminifera represented by two larger foraminiferal assemblages are most diversified in the shallower settings near the fair weather wave base distal inner proximal middle ramp whereas coralline algae predominate in deeper areas proximal middle ramp constructing extensive rhodolith pavements rhodolith pavements are distinguished with respect to rhodolith shape size growth forms and coralline algal taxonomic composition larger foraminifera are interpreted with respect to shell structures shell architectures and comparable recent counterparts the analysed benthic communities thrived in a mesotrophic regime within trophic gradients constrained by fluvial influence coralline algal dominance and a moderately diverse larger foraminiferal assemblage suggest a tropical warm temperate transition the considerable stability imposed on sediments by the rhodolith pavement must also have significantly contributed to the maintenance of a middle ramp profile bulge this study will contribute to a better understanding of oligocene carbonates which have received less attention than their eocene or miocene counterparts

regional three dimensional seismic velocity model of the crust and uppermost mantle of northern california 1 we present a three dimensional 3d tomographic model of the p wave velocity vp structure of northern california we employed a regional scale double difference tomography algorithm that incorporates a finite difference travel time calculator and spatial smoothing constraints arrival times from earthquakes and travel times from controlled source explosions recorded at network and or temporary stations were inverted for vp on a 3d grid with horizontal node spacing of 10 to 20 km and vertical node spacing of 3 to 8 km our model provides an unprecedented comprehensive view of the regional scale structure of northern california putting many previously identified features into a broader regional context and improving the resolution of a number of them and revealing a number of new features especially in the middle and lower crust that have never before been reported examples of the former include the complex subducting gorda slab a steep deeply penetrating fault beneath the sacramento river delta crustal low velocity zones beneath geysers clear lake and long valley and the high velocity ophiolite body underlying the great valley examples of the latter include mid crustal low velocity zones beneath mount shasta and north of lake tahoe

downslope migrating sandwaves and platform margin clinoforms in a current dominated distally steepened temperate carbonate ramp guadix basin southern spain during the late tortonian platform margin prograding clinoforms developed at the south western margin of the guadix basin large scale wedge shaped deposits here comprise 26 rhythms of mixed carbonate siliciclastic bedset packages and marl beds these sediments were deposited on a shallow water temperate carbonate distally steepened ramp a downslope migrating sandwave field developed in this ramp with sandwaves moving progressively down the ramp to the ramp slope where they destabilized folded and occasionally collapsed downslope sandwave migration was induced by currents flowing basinwards during the late tortonian the guadix basin was open north to the atlantic ocean via the dehesas de guadix strait and connected east to the mediterranean sea through the almanzora corridor according to the proposed current circulation model for the guadix basin for this time surface marine currents from the atlantic entered the basin from the northern seaway these currents moved counter clockwise and shifted the sediment on the ramp forming sandwaves that migrated downslope the development of platform margin prograding clinoforms by the basinward sediment transport mechanisms inferred here is known relatively poorly in the ancient sedimentary record moreover these wedge shaped geometries are similar to those found in some shelves in the western mediterranean sea and could represent an outcrop analogue to sub recent platform margin clinoforms revealed by high resolution seismic studies

stratigraphic lithologic and major element geochemical constraints on magmatic evolution at lassen volcanic center california the lassen volcanic center is the most recent of several long lived volcanic centers in the southernmost cascade range these centers have erupted products ranging from basaltic andesite to rhyolite and are superimposed on a background of regional basaltic to andesitic volcanism the evolution of the lassen volcanic center is described in three stages stages i and ii comprise the brokeoff volcano and 80 km3 andesitic stratocone active from 600 to 400 ka brokeoff volcano is compositionally equivalent to the regional basaltic andesite to andesite volcanism in the lassen region and is the result of structurally controlled focusing of the diffuse regional mafic magmatism stage iii comprises a silicic dome field and adjacent area of hybrid andesites and has a total volume of about 100 km3 volcanism during stage iii was episodic and is subdivided into four sequences of lithologically and temporally distinct lavas stage iii began at 400 ka with a rhyolitic caldera forming pyroclastic eruption and chemically related lavas additional sequences of dacite erupted between 250 200 ka and 100 0 ka hybrid andesites erupted adjacent to the silicic dome field between 300 and 0 ka porphyritic andesite and dacite with high al2o3 low tio2 medium k2o and feo mgo ratios of 1 5 2 0 are the most abundant rock types in the lassen volcanic center however the single most voluminous unit is sparsely phyric rhyolite pumice in general the lavas of lassen volcanic center form a single coherent trend on major element variation diagrams and in pseudo quaternary phase space consistant with an origin either by fractional crystallization or magma mixing in detail however the lack of systematic temporal change in silica and subtly crossing trends indicate a complex origin a variety of statistically successful fractional crystallization models can be constructed that derive brokeoff andesites from regional magmas an important conclusion of the modeling is that if fractional crystallization is the process responsible for generation of brokeoff andesite then the parent magma must be low to medium k in geochemical affinity in order to explain the variation in k2o however although major element variation can be modeled by fractional crystallization petrographic and stratigraphic evidence indicates that magma mixing is an important but subtle process in brokeoff lavas and suggests that lavas evolved in small independent batches lavas erupted during stage iii while predominantly silicic range from 53 to 75 sio2 disequilibrium mineral assemblages in the stage iii lavas indicate that they are not directly derived from brokeoff andesite by fractional crystallization mixing of silicic magma with regional mafic magma and disaggregation of andesitic quenched magmatic inclusions play dominant roles in the compositional diversity of stage iii lavas

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

facies analysis and sequence stratigraphy of a miocene warm temperate carbonate ramp montagna della maiella italy abstract the uppermost oligocene lower miocene to upper miocene ramp carbonates from montagna della maiella italy form a supersequence bounded by deeply incised truncation surfaces this supersequence is subdivided into four sequences each sequence is composed of skeletal limestones in its lower part and marly limestones in its upper part the lower parts of the sequences are foramol limestones which suggest deposition in the warm temperate climate zone changes in climate oceanography and relative sea level combined to control sedimentation in the four sequences in the lower parts of the two older sequences the skeletal sands built dunes suggesting high energy conditions the dominant skeletal grains in the oldest sequence are larger foraminifers and in the next sequence they are bryozoans this change reflects cooling around the time of the aquitanian burdigalian boundary in the lower parts of the two younger sequences of middle and late miocene age sediment sheets with red algal bryozoan oncoids suggest deposition under calmer conditions transgressive and highstand systems tracts are recognized in all sequences a shelf margin systems tract may be exposed in the second oldest sequence in contrast to the situation that exists when warm water carbonates are deposited sedimentation of the foramol limestones on this isolated ramp was unable to balance accommodation during sea level rise this led to hemipelagic sedimentation during sea level highstands conglomerates resulted from reworking along flooding surfaces

the lower rupelian cluster reefs of majella platform the shallow water record of eocene to oligocene transition abstract the eocene oligocene transition is a key interval in the evolution of the modern climate representing the last greenhouse icehouse transition faced by the earth shallow water carbonate systems hold essential information of the global changes related to the e o transition in this work we focus on the majella mountain carbonate ramp to identify the shallow water sedimentary expression of the oceanographic and sea level changes related to the e o transition and to compare it with the deep marine records and the coeval shallow water successions field observations coupled with the study of thin sections to identify textural characters and of the larger benthic foraminiferal associations for biostratigraphic purposes allowed reconstructing the depositional model and the stratigraphic distribution of the examined ramp the lower rupelian ramp outcropping in the majella mountain is characterized by seagrass meadows in the euphotic inner ramp corals developed in the middle ramp building mounded cluster reefs in the mesophotic zone below wave base in high hydrodynamic conditions produced by rip currents induced by storm events or by the breaker zone of internal waves the outer ramp consists of alternating bioturbated wackestone rich in planktonic foraminifera bioclastic packstone and skeletal rudstone to floatstone the depositional model of the oligocene ramps is the result of the major changes that occurred during the greenhouse icehouse transition in the majella platform the e o transition corresponds to an unconformity developed on the priabonian substrate where the cluster reefs grew and expanded the unconformity results from the sea level drop of tens of meters recorded also in the outer ramp related to the oi 1 event the cluster reefs started to develop when the priabonian ramp was flooded and continued to grow during the following highstands forming an extensive coral unit that prograded basinwards interfingering with the outer ramp deposits

extensional faulting in southern klamath mountains california large northeast striking normal faults in the southern klamath mountains may indicate that substantial crustal extension occurred during tertiary time some of these faults form grabens in the jurassic and older bedrock of the province the grabens contain continental oligocene or miocene deposits weaverville formation and in two of them the oligocene or miocene is underlain by lower cretaceous marine formations great valley sequence at the la grange gold placer mine the oligocene or miocene strata dip northwest into the gently southeast dipping mylonitic footwall surface of the la grange fault the large normal displacement required by the relations at the la grange mine is also suggested by omission of several kilometers of structural thickness of bedrock units across the northeast continuation of the la grange fault as well as by significant changes in bedrock across some northeast striking faults elsewhere in the central metamorphic and eastern klamath belts the trinity ultramafic sheet crops out in the eastern klamath terrane as part of a broad northeast trending arch that may be structurally analogous to the domed lower plate of metamorphic core complexes found in eastern parts of the cordillera the northeast continuation of the la grange fault bounds the southeastern side of the trinity arch in the eastern klamath terrane and locally cuts out substantial lower parts of adjacent paleozoic strata of the redding section faults bounding the northwestern side of the trinity arch generally trend northeast and juxtapose stacked thrust sheets of lower paleozoic strata of the yreka terrane against the trinity ultramafic sheet geometric relations suggest that the tertiary extension of the southern klamath mountains was in nw se directions and that the redding section and the southern part of the central metamorphic terrane may be a large tertiary allochthon detached from the trinity ultramafic sheet paleomagnetic data indicate a lack of rotation about a vertical axis during the extension we propose that the trinity ultramafic sheet is structurally analogous to a metamorphic core complex if so it is the first core complex to be described that involves ultramafic rocks we infer that mesozoic terrane accretion produced a large gravitational instability in the crust that spread laterally during tertiary extension

cross stratified calcarenites from new zealand subaqueous dunes in a cool water oligo miocene seaway cross bedded cool water bioclastic limestones of the te kuiti group on the north island of new zealand are composed primarily of bryozoans echinoderms and benthic foraminifers their prominent large scale unidirectional cross stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50 100 km wide north east trending seaway in water depths of 40 60 m these dunes are thought to have developed in response to strong seaway parallel tidal currents combined with a north east directed set up or oceanic current cross stratification is organized into four hierarchical levels 1 cross lamination 2 first order sets 3 second order sets and 4 cross stratified successions the levels are based on increasing degrees of internal complexity distinct attributes such as internal organization cross set thickness foreset shape and lower bounding surface shape are used to describe and interpret the cross stratification all these attributes are here integrated in a new and expanded classification of unidirectional cross stratification that emphasizes flow and bedform dynamics rather than overall set shape individual cross stratified successions are interpreted to have formed by dunes with varying sinuosity superposition and flow history under conditions of different current strength but constant sediment production horizontally bedded successions are the result of robust active dune fields that grew during times of vigorous sediment transport formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport these decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment formset cross stratified successions are most likely to develop in carbonates where the sediment is produced in place than in terrigenous clastics where the sediment is imported

late cenozoic volcanism subduction and extension in the lassen region of california southern cascade range hundreds of short lived small to moderate volume mostly mafic volcanoes occur throughout the lassen region of ne california and surround five longer lived large volume intermediate to silicic volcanic centers younger than 3 ma volcanic rocks older than 7 ma are scarce in the lassen region we identify 537 volcanic vents younger than 7 ma and we classify these into five age intervals and five compositional categories based on sio2 content maps of vents by age and composition illustrate regionally representative volcanic trends by 2 ma the eastern limit of voicanism had contracted westward toward the late quaternary arc late quaternary volcanism is concentrated around and north of the silicic lassen volcanic center the belt of most recent volcanism 25 0 ka has been active since at least 2 ma most mafic volcanism is cakalkaline basalt and basaltic andesite however lesser volume of low potassium olivine tholeiite lkot a geochemically distinctive basalt type found in the northern basin and range province also has erupted throughout the lassen segment of the cascade arc since the pliocene thus models of the mantle source and tectonic control of lkot magmatism should be applicable both within and behind the subduction related arc normal faults and linear groups of vents are evidence of widespread crustal extension throughout most of the lassen region nnw alignments of these features indicate nnw orientation of maximum horizontal stress ene extension which is similar to the stress regime in the adjacent northwestern basin and range and northern sierra nevada provinces the large long lived volcanic centers developed just west of a zone of closely spaced nnw trending normal faults within that zone of faulting pervasive ene extension has precluded growth of large long lived crustal magma systems we interpret the western limit of the zone of nnw trending normal faults as the western boundary of the basin and range province where it overlaps the lassen segment of the cascade arc in our view the lassen volcanic region occurs above the subducting gorda north plate but also lies within a broad zone of distributed extension that occurs in the north american lithosphere east and southeast of the present cascadia subduction zone an episode of ene extension that began in the late miocene in the northwestern basin and range province appears to have triggered widespread late miocene to quaternary mafic volcanism in the lassen region the scarcity of volcanic rocks older than 7 ma suggests that a more compressive lithospheric stress regime prior to the late miocene extensional episode may have suppressed volcanism even though subduction probably was occurring beneath the lassen region

geological analysis of aeromagnetic data from southwestern alaska implications for exploration in the area of the pebble porphyry cu au mo deposit aeromagnetic data are used to better understand the geology and mineral resources near the late cretaceous pebble porphyry cu au mo deposit in southwestern alaska the reduced to pole rtp transformation of regional scale aeromagnetic data shows that the pebble deposit is within a cluster of magnetic anomaly highs similar to pebble the iliamna kijik and neacola porphyry copper occurrences are in magnetic highs that trend northeast along the crustal scale lake clark fault a high amplitude short to moderate wavelength anomaly is centered over the kemuk occurrence an alaska type ultramafic complex similar anomalies are found west and north of kemuk a moderate amplitude moderate wavelength magnetic low surrounded by a moderate amplitude short wavelength magnetic high is associated with the gold bearing shotgun intrusive complex the rtp transformation of the district scale aeromagnetic data acquired over pebble permits differentiation of a variety of jurassic to tertiary magmatic rock suites jurassic cretaceous basalt and gabbro units and late cretaceous biotite pyroxenite and granodiorite rocks produce magnetic highs tertiary basalt units also produce magnetic highs but appear to be volumetrically minor eocene monzonite units have associated magnetic lows the rtp data do not suggest a magnetite rich hydrothermal system at the pebble deposit the 10 km upward continuation transformation of the regional scale data shows a linear northeast trend of magnetic anomaly highs these anomalies are spatially correlated with late cretaceous igneous rocks and in the pebble district are centered over the granodiorite rocks genetically related to porphyry copper systems the spacing of these anomalies is similar to patterns shown by the numerous porphyry copper deposits in northern chile these anomalies are interpreted to reflect a late cretaceous magmatic arc that is favorable for additional discoveries of late cretaceous porphyry copper systems in southwestern alaska

global dominance of coralline red algal facies a response to miocene oceanographic events rhodoliths free living coralline red algae can thrive under a wide range of temperatures reduced light and increased nutrient levels and often form a distinct so called rhodalgal lithofacies that is an important component of cenozoic shallow water carbonates global distributions illustrate that from the late early to early late miocene burdigalian early tortonian rhodalgal facies reached peak abundances and commonly replaced coral reef environments accompanied by a decline in other carbonate producing phototrophs we argue that the dominance of red algae over coral reefs was triggered in the burdigalian by enhanced trophic resources associated with a global increase in productivity as evidenced by a long term shift toward higher carbon isotope values rhodalgal lithofacies expanded further in the middle miocene when strengthened thermal gradients associated with the establishment of the east antarctic ice sheet led to enhanced upwelling while climate change generated increased weathering rates introducing land derived nutrients into the oceans globally cooler temperatures following a climatic optimum in the early middle miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs the global shift in nearshore shallow water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow water carbonate facies as indicators of past oceanographic conditions

a genetic classification of carbonate platforms based on their basinal and tectonic settings in the cenozoic abstract this paper reassesses the usefulness of the morphological classification of carbonate platforms into rimmed shelves and ramps whilst the existing classifications have value in describing platform margin morphology at any one time the terms rimmed shelf and ramp are less successful at categorising the entire morphology and stratigraphy of carbonate platforms research on cenozoic carbonate platforms from a range of different tectono stratigraphic settings indicates that the basinal and tectonic setting of a platform can be used to erect a first order genetic classification of carbonate platforms the basinal and tectonic setting of carbonate platforms is shown to control their occurrence the overall 3 d platform morphology the large scale stratigraphic features and depositional sequences climate ocean chemistry and biological evolution control grain types facies and some elements of platform margins but not the larger scale features considered in this new classification from a review of well exposed outcropping and seismically imaged cenozoic platforms it is proposed that eight types of carbonate platform can currently be recognised and characterised based on their basinal and tectonic setting fault block salt diapir subsiding margin offshore bank volcanic pedestal thrust top delta top and foreland margin carbonate platforms these eight types are described using information from cenozoic platforms worldwide and the controls on their development are discussed many platform types e g subsiding margin offshore bank salt diapir thrust top and foreland margin are typical of particular classes of sedimentary basins others e g fault block volcanic pedestal and delta top are more widespread in their occurrence and occur in a range of basin types the value of this classification is that it is genetic rather than morphological the classification reflects the entire morphology and large scale stratigraphy of the platform and the controls on its development in addition the platform models can be used to understand the details of less well exposed or seismically imaged platforms so that they can be characterised and understood in terms of tectono sedimentary processes conversely the classification also provides valuable information on basin evolution as carbonate platforms house information on palaeoenvironments sea level change and are sensitive recorders of the tectonic environment

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

paleozoic and lower mesozoic magmas from the eastern klamath mountains north california and the geodynamic evolution of northwestern america abstract the paleozoic to early mesozoic geology of the eastern klamath mountains n california is characterized by three major magmatic events of ordovician late ordovician to early devonian and permo triassic ages the ordovician event is represented by a calc alkalic island arc sequence lovers leap butte sequence developed in the vicinity of a continental margin the late ordovician to early devonian event consists of the 430 480 ma old trinity ophiolite formed during the early development of a marginal basin and a series of low k tholeiitic volcanic suites lovers leap basalt keratophyre unit copley and balaklala formations belonging to intraoceanic island arcs finally the permo triassic event gave rise to three successives phases of volcanic activity nosoni dekkas and bully hill represented by the highly differentiated basalt to rhyolite low k tholeiitic series of mature island arcs the permo triassic sediments are indicative of shallow to moderate depth in an open warm sea the geodynamic evolution of the eastern klamath mountains during paleozoic to early mesozoic times is therefore constrained by the geological petrological and geochemical features of its island arcs and related marginal basin a consistent plate tectonic model is proposed for the area consisting of six main stages 1 1 development during ordovician times of a calc alkalic island arc in the vicinity of a continental margin 2 2 extrusion during late ordovician to silurian times of a primitive basalt andesite intraoceanic island arc suite which terminated with boninites the latter suggest rifting in the fore arc followed by the breakup of the arc 3 3 opening and development of the trinity back arc basin around 430 480 ma ago 4 4 eruption of the balaklala rhyolite either in the arc or in the fore arc ending in early devonian time with intrusion of the 400 ma mule mountain stock 5 5 break in volcanic activity from the early devonian to the early permian and 6 6 development of a mature island arc from the early permian to the late triassic the eastern klamath mountains island arc formations and ophiolitic suite are part of the cordilleran suspect terranes considered to be gondwana margin fragments that have undergone large northward translations before final collision with the north american craton during late mesozoic or cenozoic times these eastern klamath mountains island arcs could be associated with the paleo pacific oceanic plate that led to accretion of these allochthonous terranes to the american margin

gravity model studies of newberry volcano oregon newberry volcano a large quaternary volcano located about 60 km east of the axis of the high cascades volcanoes in central oregon has a coincident positive residual gravity anomaly of about 12 mgals model calculations of the gravity anomaly field suggest that the volcano is underlain by an intrusive complex of mafic composition of about 20 km diameter and 2 km thickness at depths above 4 km below sea level however uplifted basement in a northwest trending ridge may form part of the underlying excess mass thus reducing the volume of the subvolcanic intrusive a ring dike of mafic composition is inferred to intrude to near surface levels along the caldera ring fractures and low density fill of the caldera floor probably has a thickness of 0 7 0 9 km the gravity anomaly attributable to the volcano is reduced to the east across a north northwest trending gravity anomaly gradient through newberry caldera and suggests that normal perhaps extensional faulting has occurred subsequent to caldera formation and may have controlled the location of some late stage basaltic and rhyolitic eruptions significant amounts of felsic intrusive material may exist above the mafic intrusive zone but cannot be resolved by the gravity data

on the minimum amplitude of regional sea level fluctuations during the flandrian the mathematical form of a time height sea level curve representing intermediate frequency fluctuations superimposed on an underlying upward trend yields a simple method for estimating the minimum amplitude of fluctuations from field measurements of the thickness of silt peat couplets drawing on data from the thames estuary and the fenland basin fluctuations of relative sea level with minimum amplitudes between 0 08 m and 0 91 m seem to have occurred in the southeast british region during the mid flandrian 1997 john wiley sons ltd

larger foraminiferal and coralline algal facies in an upper eocene storm influenced shallow water carbonate platform colli berici north eastern italy abstract facies analysis of priabonian shallow water carbonate successions in the outcrops near mossano eastern colli berici north eastern italy and the subsequent integration of palaeoecological data have been used to produce a detailed palaeoenvironmental model the facies distribution and the processes which controlled the larger benthic foraminiferal and coralline algal assemblages in the study priabonian storm influenced carbonate ramp are discussed in detail in the middle ramp trough cross bedded small nummulites and rhodolith packstones pass laterally into coralline algal crust wackestones these rhodoliths exhibit two well differentiated growth phases the first occurring during low water energy periods followed by a second developed during high energy events during which they were reworked and partially destroyed these facies pass laterally into orthophragminid rudstones and packstones characterised by orthophragminid tests and channel structures the latter were formed by storm induced return currents which swept the middle ramp creating distal middle ramp channel structures further toward the distal part of the middle ramp the return currents decreased in energy and discharged nutrients allowing the coralline crustose pavement to develop this is characterised by rhodoliths typically discoidal in shape up to 10 cm in diameter with a loose inner arrangement consisting of encrusting to foliose growth forms the occurrence of the channel structures in orthophragminid rudstones and in the coralline crustose pavement appears to be unique in upper eocene carbonate ramp depositional systems during the erosive events associated with the return currents these shallow water carbonates were unlithified or only weakly lithified and were therefore easily transported into deeper water ramp settings the model suggests that the significant changes of the middle ramp benthic communities with depth could have formed at least in part by offshore return currents which played an important role in both controlling substrates and in supplying nutrients

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

a model for the palaeoenvironmental distribution of larger foraminifera based on late middle eocene deposits on the margin of the south pyrenean basin ne spain abstract on the margin of the south pyrenean basin the late middle eocene sediments represent a well preserved regressive system permitting determination of the distribution of larger foraminifera along the depth gradient eocene deposits are compared with distribution patterns of recent larger foraminifera based on taxa occupying comparable positions along similar ecological gradients eocene taxa reveal by their test morphology a similar response to specific ecological conditions to that recorded for recent foraminifera four assemblages characterise an open marine shelf they range from the lower limit of the photic zone to the lower part of the upper photic zone two assemblages characterise the upper part of the upper photic zone and indicate respectively two different substrates firm or soft below the photic zone no larger foraminifera exist and the foraminiferal assemblages are dominated by smaller benthic foraminifera

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

differential compaction as a control on depositional architectures across the maiella carbonate platform margin central apennines italy abstract the role of differential compaction as a control in the creation of accommodation and on compaction modified depositional features and stratal geometries across the maiella platform margin has been investigated through a combined analysis of seismic scale outcrops porosity evaluation and modeling geologic evolution and large exposures make the platform margin of the maiella an ideal place to investigate the effects of differential compaction a high relief cemented carbonate platform a deep basin filled with highly compactable deposits and a prograding grain rich succession sealing morphologic differences across the platform margin represent suitable features for promoting differential compaction stratal relationships across the platform margin exhibit evidence of differential compaction induced effects such as basinward divergence and thickening of strata updip pinch out of wedge shaped stratal packages and an anticline hinge porosity analysis and modeling indicate that through progressive loading mechanical and chemical processes act in concert to destroy most of the depositional porosity mechanical compaction appears to have played the greatest part in the total budget of compaction however chemical compaction seems to have played a prominent role in the formation of geometrically consistent depositional profiles during progradation due to differential compaction across the platform margin a compaction hinge formed concomitantly with the beginning of progradation producing a basin facing monocline characterized by the progressive steepening of basinward stratal dips the resulting compaction induced stratal deformation together with sea level changes controls the distribution and depositional timing of wedge shaped stratal packages during late cretaceous and paleocene and the distribution of coral algal reef buildups during the late eocene early oligocene the development of the compaction hinge usually follows the progressive increase of loading but a decrease in compaction dissipation may be caused by overburdening of compactable deposits this will cause a delayed compaction induced subsidence whose effects will be produced after deposition i e during loading interruption this mechanism is thought to have an important role in the timing of compaction induced subsidence throughout the end of cretaceous and the early tertiary and it is considered together with sea level as the main controlling process of the occurrence and distribution of downslope sediments during a long lasting period of platform emersion

short paper a standardized model for tethyan tertiary carbonate ramps low latitude carbonates in massive and clinoform bedded sheets termed ramps occur throughout the tertiary tethyan realm and are characterized by recurring biofacies usually including large foraminifera rhodolithic algae coralgal patch reef and gastropod dominated sequences all can be interpreted broadly within a standardized tertiary carbonate ramp model biota can be used to define precise palaeobathymetric zones which have a predictive utility in palaeoenvironmental modelling especially where data are limited the carbonate ramp model of earlier authors has been elaborated by read 1982 and ramp formation occurs mostly in passive margin and extensional tectonic settings ramps are characterized by slope gradients of less than 1 degree and once established are conservative to change much use has been made of the ramp model for palaeozoic and mesozoic lithofacies modelling in contrast published work on cenozoic ramps is limited however tethyan ramps are particularly widespread and extend tens to hundreds of kilometres along strike and occupy tens of kilometres of slope many studies have dealt with cenozoic ramp associations and sequences e g pedley 1983 reiss hottinger 1984 purser 1973 and have demonstrated the diversity of biotal and sediment detail but without ascribing them to a ramp model biota were quick to adapt to the tertiary environments left vacant after the k t boundary extinction events new genera of foraminifera mollusca bryozoa and echinoder mata rapidly replaced the extinct forms in bursts of innovative opportunism codiacean algae rhodophyta and marine angiosperms were equally adaptive colonizers of the carbonate platforms novel biofacies associations were derived from

oxygen isotope geochemistry of the lassen volcanic center california resolving crustal and mantle contributions to continental arc magmatism this study reports oxygen isotope ratios determined by laser fluorination of mineral separates mainly plagioclase from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the lassen volcanic center lvc northern california plagioclase separates from nearly all rocks have o values 6 1 8 4o higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back arc regions of the southernmost cascades during the late cenozoic most lvc magmas must therefore contain high o crustal material in this regard the o values of the volcanic rocks show strong spatial patterns particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust rhyodacitic magmas erupted from vents located within 3 5 km of the inferred center of the lvc have consistently lower o values average 6 3o 0 1o at given sio2 contents relative to rocks erupted from distal vents 47 0 km average 7 1o 0 1o further magmas erupted from vents situated at transitional distances have intermediate values and span a larger range average 6 8o 0 2o basaltic andesitic to andesitic composition rocks show similar spatial variations although as a group the o values of these rocks are more variable and extend to higher values than the rhyodacitic rocks these features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas followed by mixing or mingling with silicic magmas formed by partial melting of initially high o continental crust 9 0o increasingly hybridized by lower o 6 0o mantle derived basaltic magmas toward the center of the system mixing calculations using estimated endmember source o values imply that lvc magmas contain on a molar oxygen basis approximately 42 to 4 isotopically heavy continental crust with proportions declining in a broadly regular fashion toward the center of the lvc conversely the o values of the rhyodacitic rocks suggest that the continental crust in the melt generation zones beneath the lvc has been substantially modified by intrusion of mantlederived basaltic magmas with the degree of hybridization ranging on a molar oxygen basis from approximately 60 at distances up to 12 km from the center of the system to 97 directly beneath the focus region these results demonstrate on a relatively small scale the strong influence that intrusion of mantle derived mafic magmas can have on modifying the composition of pre existing continental crust in regions of melt production given this result similar but larger scale regional trends in magma compositions may reflect an analogous but more extensive process wherein the continental crust becomes progressively hybridized beneath frontal arc localities as a result of protracted intrusion of subduction related basaltic magmas

storm related sedimentation influenced by coastal configuration in the stratigraphic record of a tectonically active shelf upper pleistocene le castella terrace italy abstract analysis of patterns of coastal circulation and sediment dispersal is an essential step for the study of controlling factors influencing the long term dynamics of coastal systems modern settings offer the possibility to monitor relevant parameters over relatively short time spans however geological examples complement this perspective by providing a time averaged record where longer trends and stratigraphically significant processes can be evaluated this study investigates the shallow marine deposits of le castella terrace upper pleistocene southern italy to document how patterns of circulation influenced by coastline configuration can affect the preserved millennial scale depositional record of a progradational shoreline system the regressive portion of the le castella terrace deposits developed during a relative sea level highstand and falling stage consists of a progradational wedge mainly composed of redistributed skeletal particles of a coeval shallow water carbonate factory preservation of the morphology of the paleocoastline and abundant current related sedimentary structures allow reconstruction of the predominant sediment dispersal dynamics responsible for the formation of this sedimentary wedge facies and paleocurrent analysis indicate offshore and alongshore sediment transport modes consistent with coastal circulation driven by storms normally incident to the shoreline and a sharp change in coastline orientation this coastal inflection influenced circulation patterns causing flow separation and eddy formation in the lee of the curved coastline syndepositional tectonic deformation also affected the architecture of the preserved deposits controlling the nucleation and development of a clinostratified body and determining localized lateral stratigraphic variability this study illustrates how transient but recurrent circulation patterns associated with changes in coastal orientation and related to high energy storm events can leave a predominant signature in the stratigraphic record of microtidal shallow marine successions

facies partitioning and stratal pattern in salt controlled marine to continental mini basins examples from the late oligocene to early miocene of the sivas basin turkey the sivas basin turkey records a complex interaction between sedimentation salt tectonics and regional shortening leading to the formation of numerous mini basins the segmentation into mini basins was initiated during the oligocene by the deposition of the fluvio lacustrine karayun fm this continental succession is overlain abruptly by an oligo miocene shallow marine succession karacaoren fm which comprises two main sub environments i mixed deltaic and carbonate ramp ii coastal plain and lagoon the karacaoren fm forms a marine succession more than 1500 m thick that passes vertically upwards into a continental succession the fluvial dominated benlikaya fm these two formations are the focus of the present study during the period of marine sedimentation the competing accumulation of carbonates and clastics is related not only to the topography inherited from salt tectonics but also to relative sea level variations expressed by two large scale transgressive regressive cycles we analyse these complex facies and stratal relationships to illustrate the modifications induced by salt tectonics this study is based on extensive fieldwork and mapping making use of numerous measured stratigraphic sections and aerial photos over a large area comprising more than fifteen adjacent outcropping mini basins the aim of this study is to provide a detailed description of the stratigraphic relationships correlations and sedimentary systems distribution in mini basins during deposition of the oligo miocene shallow marine and continental successions we first clarify the vertical stratigraphic succession of the oligo miocene marine and continental deposits and establish correlations between the studied mini basins these correlations then allow us to characterize and assess the local effects of salt withdrawal in relation to the regional forcings associated with flexural subsidence tectonic shortening and relative sea level changes an improved understanding of the complex interactions of these variables provides a framework to distinguish the mechanisms that control facies distribution and stratal geometry in salt basins

longshore bar and trough systems in a microtidal storm wave dominated coast the ebro delta northwestern mediterranean abstract the ebro delta coast is a microtidal sandy shoreline affected by a low energy mean wave climate consecutive topographical and bathymetrical surveys during the years 1990 and 1991 have allowed us to identify nine major longshore bar and trough systems as the main morphological feature of the ebro coast bar systems show high mobility both cross shore and longshore the cross shore migration of these systems may be landward or seaward with mean migration rates of up to 0 25 m day the longshore migration is produced by the longitudinal growth of the bar systems in the downdrift direction with rates of up to 11 m day the major morphological changes in the nearshore zone occurred during storm periods when the nearshore profile is modified as a consequence of shoreline erosion and the cross shore migration and longshore growth of the bar systems produced by these events the modifications in the nearshore profile may continue during some months after the storm before attaining a new equilibrium profile a descriptive model relating the shoreline displacement with the cross shore migration and the longshore growth of the bar and trough systems is proposed

global versus regional influence on the carbonate factories of oligo miocene carbonate platforms in the mediterranean area abstract the oligocene miocene is a key interval that was characterized by a cooling trend associated with a progressive decrease of atmospheric co2 concentrations that ends in the present days in the central mediterranean area during this interval three main carbonate platform domains developed in the foreland zone of the apennines the latium abruzzi campana and apulia domain in the central and south eastern sectors of the chain and the hyblea and pelagian carbonate platforms in the south and south western sectors this work analyzes the impact and interplay of global and regional factors controlling the development of different carbonate factories and facies associations over the chattian and the early messinian time interval three well studied examples of the central mediterranean will be used the chattian ramp of malta the latium abruzzi ramp and the bolognano ramp within the northern portion of the apulian carbonate platform outcropping on majella mountain the malta ramp represents the reference model for the heterozoan oligo miocene carbonate factory since it developed far from terrigenous input in persistent oligotrophic conditions and within a tropical climate in contrast the evolution of the central apennine ramps is strictly related to the geodynamic evolution of the apennines and simultaneously to global oceanographic changes the chattian apennine ramps are affected by a basin conformation that favored the development of dominant currents and related dune fields successively these ramps were exposed to strong aquitanian volcanism that induced a shift towards an aphotic dominated carbonate factory since the burdigalian the development of the apennines has affected the evolution of the investigated ramps through the eastward migration of foredeep systems and related nutrient input this influence becomes more evident between the tortonian and messinian during which reef rimmed platforms developed in the rest of the mediterranean while red algae still dominated in the apennine ramps amongst the global events the c cycle perturbation occurring between the late burdigalian and serravallian monterey event leaves a clear sign on the two apennine ramps

sedimentologic and diagenetic controls on pore network characteristics of oligocene miocene ramp carbonates majella mountain central italy this article addresses the controls exerted by sedimentologic and diagenetic factors on the preservation and modification of pore network characteristics porosity pore types sizes shapes and distribution of carbonates belonging to the bolognano formation this formation exposed at the majella mountain italy is composed of oligocene miocene carbonates deposited in middle to outer ramp settings the carbonates consist of 1 grainstones predominantly composed of either larger benthic foraminifera especially lepidocyclina or bryozoans 2 grainstones to packstones with abundant echinoid plates and spines and 3 marly wackestones to mudstones with planktonic foraminifera the results of this field and laboratory based study are consistent with skeletal grain assemblages grain sizes sorting and shapes all representing the sedimentologic factors responsible for high values of connected primary macroporosity in grainstones deposited on the high energy middle to proximal outer ramp cementation responsible for porosity reduction and overall macropore shape and distribution in grainstones to packstones deposited on the intermediate outer ramp was mainly dependent on the following factors 1 amount of echinoid plates and spines 2 grain size 3 grain sorting and shapes and 4 clay amount differently in the wackestones to mudstones laid down on the low energy distal outer ramp matrix is the key sedimentologic factor responsible for low values of scattered macroporosity and dominance of microporosity the aforementioned results may be useful to improve the prediction of reservoir quality by means of mapping simulating and assessing individual carbonate facies with peculiar pore network characteristics

depositional geometries and facies associations in an upper cretaceous prograding carbonate platform margin orfento supersequence maiella italy abstract although progradation of platform margins is a well documented process its timing with respect to sea level cycles is controversial this outcrop study was designed to test the relation between prograding stratal patterns and sea level cycles using a sequence stratigraphic analysis and direct investigation of the sedimentological facies associations the upper campanian maastriehtian orfento supersequence in the maiella platform margin is an outstanding outcrop example of a large scale prograding carbonate wedge composed of smaller scale vertically and laterally stacked sequences the evolution of the orfento supersequence was characterized by an initial phase of aggradation followed by progradation at the scale of the supersequence basinal aggradation preceded progradation of hallower water facies because excess relief had to be buried prior to progradation seven depositional facies were distinguished on the basis of depositional geometries stratal patterns and sedimentary features these facies record different depositional environments on a low angle ramp ranging from deep water pelagic wackestones to wave dominated upper shoreface grainstones facies distributions record the overall transition from pelagic sediments turbidites and megabreccias into progressively shallower water shoreface complexes the prograding units consist of shingled offlapping sigmoidal complexes composed of rudstones and grainstones deposited in shallow wave dominated environments and their deeper water equivalents sigmoidal sequences are separated by erosive unconformities which bring upper shoreface facies into direct contact with underlying lower shoreface or outer shelf facies indicating a sea level fall forced regression meteoric diagenesis associated with the unconformities also supports lowering of relative sea level depositional facies patterns within sequences record a relative rise and highstand of sea level repetitive downward shifts bring the shoreline successively farther basinward indicating long term lowering of sea level during the late stages of progradation producing downstepping progradation our data suggest that changes in relative sea level acting on a low angle ramp control the overall architecture of sequence distribution whereas changes in sediment supply con rol changes in facies association within each sequence