aeolian sand sea development along the mid cretaceous western tethyan margin spain erg sedimentology and palaeoclimate implications the existence of a mid cretaceous erg system along the western tethyan margin iberian basin spain was recently demonstrated based on the occurrence of wind blown desert sands in coeval shallow marine deposits here the first direct evidence of this mid cretaceous erg in europe is presented and the palaeoclimate and palaeoceanographic implications are discussed the aeolian sand sea extended over an area of 4600 km2 compound crescentic dunes linear draa and complex aeolian dunes sand sheets wet dry and evaporitic interdunes sabkha deposits and coeval extradune lagoonal deposits form the main architectural elements of this desert system that was located in a sub tropical arid belt along the western tethyan margin sub critically climbing translatent strata grain flow and grain fall deposits pin stripe lamination lee side dune wind ripples soft sediment deformations vertebrate tracks biogenic traces tubes and wood fragments are some of the small scale structures and components observed in the aeolian dune sandstones at the boundary between the aeolian sand sea and the marine realm intertonguing of aeolian deposits and marine facies occurs massive sandstone units were laid down by mass flow events that reworked aeolian dune sands during flooding events the cyclic occurrence of soft sediment deformation is ascribed to intermittent marine flooding of aeolian dunes and associated rise in the water table the aeolian erg system developed in an active extensional tectonic setting that favoured its preservation because of the close proximity of the marine realm the water table was high and contributed to the preservation of the aeolian facies a sand drift surface marks the onset of aeolian dune construction and accumulation whereby aeolian deposits cover an earlier succession of coastal coal deposits formed in a more humid period a prominent aeolian super surface forms an angular unconformity that divides the aeolian succession into two erg sequences this super surface formed in response to a major tectonic reactivation in the basin and also marks the change in style of aeolian sedimentation from compound climbing crescentic dunes to aeolian draas the location of the mid cretaceous palaeoerg fits well to both the global distribution of other known cretaceous erg systems and with current palaeoclimate data that suggest a global cooling period and a sea level lowstand during early mid cretaceous times the occurrence of a sub tropical coastal erg in the mid cretaceous of spain correlates with the exposure of carbonate platforms on the arabian platform during much of the late aptian to middle albian and is related to this eustatic sea level lowstand

the relationship between shellbed type and sequence architecture examples from japan and new zealand abstract examples of lithology fossil content and taphonomic features of shellbeds and intervening less fossiliferous intervals are presented from four plio pleistocene successions shimosa group boso peninsula omma formation hokuriku area japan and okehu kai iwi and shakespeare groups in wanganui and the rangitikei group along the rangitikei river in new zealand as for pre pliocene 3rd and 4th order depositional sequences plio pleistocene 5th to 7th order depositional sequences contain a variety of shellbeds which are often associated with surfaces or intervals that are characterized by sedimentary condensation omission or erosion e g sequence boundaries ravinement surfaces downlap surfaces and condensed sections stratigraphic patterns of shellbed type tend to be similar and repetitive within a basin and a locality this demonstrates that a specific palaeogeography played an important role in determining the nature of shellbeds for example shellbeds formed in the context of toplap are common only in the shimosa group which was deposited in a moderately sheltered sea the palaeo tokyo bay toplap shellbeds are rare in other sequences formed in more open conditions despite the variability resulting from such basin characteristics common styles of shellbeds can be recognized that formed under conditions of marine onlap backlap downlap and toplap each type of shellbed has a characteristic fossil composition and taphonomy onlap and toplap shellbeds contain low diversity macrobenthic associations including glycymeris mercenaria paphies or other bivalves having robust shells which are often abraded or fragmented backlap shellbeds which are equivalent to the condensed section formed at the maximum transgression are characterized by dominance of epifaunal macrobenthos such as bryozoa brachiopoda pectinid and ostreid bivalves preserved in a slightly cemented glauconitic muddy matrix in contrast to fossils in such condensed sections the shell density and species diversity of downlap shellbed associations are rather low and in a few examples the macrobenthic association was buried rapidly in a lower unit of the highstand systems tract hst stratigraphically located above the condensed sections variations in the stratigraphic distribution of shellbed types are reflected in symmetrical and asymmetrical sequence architectures symmetrical sequences have roughly the same thickness of transgressive systems tracts tst and highstand systems tracts hst and have well segregated shellbeds that were formed during marine onlap and backlap asymmetrical cycles have very thin tsts and much thicker hsts and are characterized by the amalgamation of condensed onlap and backlap shellbeds such contrasting cycle architectures are interpreted to reflect inner symmetrical and outer asymmetrical shelf palaeodepositional settings the amalgamated onlap backlap shellbeds appear to be common in plio pleistocene sequences owing to the short duration of glacio eustatic sea level changes with dominant frequencies of 20 000 40 000 or 100 000 years shellbeds in the plio pleistocene are relatively simple and thin compared to those formed in ordinary third order depositional sequences infauna dominated benthic associations are generally more common than in third order cycles and epifaunal associations facilitated by taphonomic feedback on sediment starved shell gravel substrates occur only in the condensed section corresponding to maximum transgression in most plio pleistocene sequences

criteria for stratigraphic correlation using aerial photographs examples from the south central pyrenees photostratigraphy a new method of aerial photo interpretation establishes local photostratigraphic correlation frameworks with relative chronostratigraphic significance this method is based on the analysis of strata geometry their relationships and the photographic aspect of the rocks for identification and hierarchic organization of photostratigraphic units the definition of these units does not presuppose any a priori genetic implications the units represent volumes of rocks bounded by surfaces with chronostratigraphic significance photostratigraphic units contain time transgressive photofacies and photofacies units which record lithologic and depositional characteristics of the strata the procedure for establishing photostratigraphic correlation frameworks is illustrated through examples from the south central pyrenees direct integration with field data allows the comparison of photostratigraphic frameworks with frameworks based on other stratigraphic criteria photostratigraphy is proposed as an independent and relatively rapid preliminary approach to the study of a basin

burrows dug by large vertebrates into rain moistened middle jurassic sand dunes abstract in south central utah eolian cross strata of the escalante member of the entrada sandstone contain inclined cylindrical burrows up to 63 cm in diameter and 305 cm long of the 14 large tunnels located during this study 12 descend from second and third order bounding surfaces that formed on the lee slopes of large dune ridges well above the water table the tunnels are inclined 15 22 one tunnel ends in an expanded chamber eolian cross strata fill proximal portions of four of the tunnels and indicate that after abandonment sand drifts migrated as much as a meter into the open shafts structureless sand and breccia blocks that were generated by roof collapse fill other tunnels animals dug the tunnels in rain moistened cohesive sand the burrows may have served as temporary shelters from severe diurnal conditions in the shadeless subtropical entrada dune field

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

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

mesozoic seafloor spreading between iberia europe and north america abstract a new earliest cretaceous palaeogeographic reconstruction for the iberian north american and european plates is proposed which attempts to clarify some of the outstanding reconstruction problems in the region from the time of initial opening to the time of magnetic anomaly 34 the instantaneous motion of iberia can be described by a single rotation about a pole off the southwest coast of france in contrast to many previous proposals the new reconstruction places galicia bank east of flemish cap but satisfies all the constraints imposed by palaeomagnetic studies deep sea drilling project results and magnetic anomaly and ocean continent boundary identifications

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

a cratonic middle jurassic paleopole callovian oxfordian stillstand j 2 cusp rotation of the colorado plateau and jurassic north american apparent polar wander 1 paleomagnetic results have been obtained from two sequences of the upper middle jurassic upper callovian summerville formation which are located on the north american craton north central new mexico the thicker of the two sections trujillo exhibits a well defined dual polarity remanence forming a magnetostratigraphy of at least 12 relatively short polarity intervals the high reversal frequency is consistent with that recorded by the oceanic crust at this time the second section romeroville is thin gypsiferous and poorly indurated consequently only a short interval 5 m was successfully sampled the characteristic magnetization was wholly normal polarity in the rapid reversals of the thicker section that thickness of normal polarity is unique and thus forms the basis of magnetostratigraphic correlation between the two sections a cratonic late middle jurassic paleomagnetic pole at 148 2 e 57 3 n k 30 3 95 6 0 was obtained from the larger trujillo sequence despite large confidence limits the small sample population of the romeroville sequence displayed the same pole throughout the western united states the summerville formation is overlain with little or no discordance by the morrison formation although the two stratigraphic units are commonly reported to be separated by an unconformity designated j 5 the new mexico paleopoles of the summerville and overlying lower morrison formations are statistically identical at the 95 confidence level a similar situation exists between summerville and lower morrison paleopoles of the colorado plateau the presence of the same geomagnetic field direction in both the summerville and the lower morrison formations suggests that the j 5 unconformity which separates them may encompass little time perhaps representing only a minor break in deposition the two newly investigated summerville sites are located east of the rio grande rift hence representative of the north american craton their paleopoles are displaced counterclockwise relative to those of the colorado plateau and in amounts consistent with other coeval craton colorado plateau pole pairs together six coeval paleopoles indicate that the colorado plateau has rotated clockwise by about 9 0 3 since late pennsylvanian time the cratonic summerville paleopole also removes the uncertainty over the jurassic north american apparent polar wander path the statistically identical summerville and lower morrison paleopoles form a substantial data set five paleopoles which indicate that na apw traced a path roughly along 60 latitude the five paleopoles stand in stark contrast to the paleopole from the slightly older 5 8 ma moat volcanics spreading rates in the central atlantic do not allow na plate motion that would include both paleopoles positions because the weight of the data five paleopoles from widely spaced localities and different tectonic blocks the moat volcanics pole cannot be representative of north america in the middle jurassic

links between orogenic wedge deformation and erosional exhumation evidence from illite age analysis of fault rock and detrital thermochronology of syn tectonic conglomerates in the spanish pyrenees abstract we present new geochronologic data illuminating the tectonic and erosional history of the orogenic wedge exposed in the south central pyrenees spain we interpret illite age analyses from four fault gouges that record thrust belt development and document the importance of out of sequence thrusting fault activity occurs in pulses with slip occurring contemporaneously on multiple faults throughout the wedge new apatite fission track data from syn orogenic sediments of the sis conglomerate body reveal ages of 48 to 42 ma with no consistent variation upsection in strata deposited from 41 to 30 ma we interpret these data as well as thermal modeling of track length distributions to imply rapid cooling in the interior of the pyrenean wedge during the middle eocene the record of fault activity and erosion suggests that orogenic wedges may not evolve in a steady fashion but generally exhibit significant changes in rates of deformation and exhumation the observed correlation in the timing of tectonism and erosional exhumation provides evidence for links between tectonic and surface processes

paleocene coralgal reefs of the western pyrenean basin northern spain new evidence supporting an earliest paleogene recovery of reefal ecosystems abstract the rate of recovery of photic reefal ecosystems after the cretaceous tertiary crisis is controversial most reports from earlier authors concluded that paleogene reef systems did not completely recover from that crisis at least until oligocene miocene times several other authors however have pointed out that such conclusion was biased by poor preservation and or inaccessibility of many early paleogene successions and that the recovery of reefs might have been a faster process the latter possibility is here strongly supported with data from the pyrenean basin where paleocene shallow water carbonate deposits are thickly developed and outcrop widely five growth phases of reef development have been recognized and age dated with calcareous nannofossils which together define a complete sequence of expansion reduction of reef ecosystems during the paleocene epoch reef growth phase 1 early danian lower middle np3 calcareous nannofossil zone the initial step of that sequence demonstrates that coral dominated reef systems came back into existence less than 2 ma after the k t boundary a comparatively short time considering the magnitude of the end cretaceous biological crisis the climax of the sequence is recorded by growth phase 3 late danian np4 zone when a thick barrier reef complex was developed which was at least 200 km in length but probably much larger and made up by a well diversified coralgal assemblage reef growth phases 4 and 5 early and middle thanetian np6 to np8 zones were characterized by low relief reef banks dominated by encrusting calcareous algae and had less well diversified coral assemblages features that point to a deterioration of environmental conditions tentatively interpreted in terms of a climatic cooling reef bioconstruction almost disappeared in the pyrenean basin during late thanetian times although in all likelihood this is a regional effect of no evolutionary relevance the new data suggest that the cenozoic recovery of reefs was rapid but punctuated with a phase of important reef expansion already in the late danian

tropical westerlies over pangaean sand seas cross equatorial westerly winds are key features of tropical circulation in monsoonal regions although prominent in numerical climate models of pangaea the supercontinent straddling earth s equator late palaeozoic to early mesozoic such flow has not been confirmed previously by migration directions of ancient dunes wind blown sandstones that span 100 million years of earth history are widely exposed in south western usa if recent palaeomagnetic data from the colorado plateau are used to correct mesozoic palaeogeographic maps the plateau is placed about 10 further south than previously assumed and the prevailing north westerly surface winds recorded by dune deposited sandstones are explicable as cross equatorial westerlies the hallmark of modern monsoon circulation permian to early jurassic dunes were driven by north westerlies produced by a steep pressure gradient spanning the supercontinent during december january february although winds are light in most modern near equatorial settings the east african jet accounts for more than half the cross equatorial flow in june july august the thicknesses of annual depositional cycles within the navajo sandstone indicate that the near equatorial north westerly winds that drove these particular dunes were stronger than the modern east african jet the early jurassic dunes that deposited the thick cycles were positioned west of the dominant southern hemisphere thermal low and against highlands to the west a setting very similar to the east african jet the mountains along the western coast of pangaea not only enhanced wind strength but also cast a rain shadow that allowed active dunes to extend very close to the palaeoequator

sequential evolution and diagenesis of pleistocene coral reefs south sinai egypt abstract the uplifted pleistocene coral reefs in south sinai represent two major depositional sequences they generally form two morphological terraces which locally are tilted and offset by still active faulting the major reef sequences are composed of several small scale sequences corals grew rapidly when accommodation space was created by eustatic sea level rise or fault block subsidence as the accommodation decreased coral rubble and siliciclastic sands prograded over reefal and lagoonal sediments thus creating a shallowing upward sequence terrigenous input was further stimulated by a more humid climate during interglacial times 230 th 234 u dating places the older reef cycle between 350 000 and 270 000 years b p which corresponds to the interglacial period of isotope stage 9 the younger reef cycle has been dated between 140 000 and 60 000 years b p isotope stage 5 an intermediate relic sequence found in only one outcrop can be attributed to isotope stage 7 correlation of the small scale sequences is difficult age dating is not precise enough and local tectonic activity in many cases overruled the smaller eustatic fluctuations the younger reef sequence commonly exhibits marine cements whereas the older sequence was exposed to freshwater dissolution and cementation an important feature is the locally pervasive dolomitization especially of the older reef oxygen and carbon isotope values suggest that the dolomite formed in a seawater dominated mixing zone multiple phases of dissolution cementation and dolomitization point to a very complex diagenetic history

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

long term behaviour of the late quaternary normal faults in the straits of messina area calabrian arc structural and morphological constraints abstract the calabrian arc is located in the peri tyrrhenian orogenic belt of southern italy and is characterised by intense post collision dynamics this consists of rapid regional uplifting combined with active normal faulting affecting the tyrrhenian side of calabria and the ionian coast of sicily the siculo calabrian rift zone the effects of the two combined processes are well exposed in the straits of messina area that represent a major transfer zone located between two opposing sets of normal faults characterising the southern calabria and the northeastern sicily branches of the rift in the straits of messina region the distribution and elevation of the upper quaternary marine terraces suggest a southward propagation of the normal fault belt from calabria to sicily it occurred at about 125 ka after a long period of tectonic quiescence and was triggered by huge elastic releases in southern calabria the long term behaviour recorded on the distinct fault segments of the rift is to relate to the presence of a crustal barrier that influenced both the geometry and the fault propagation along the rift zone

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

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

annual monsoon rains recorded by jurassic dunes pangaea the largest landmass in the earth s history was nearly bisected by the equator during the late palaeozoic and early mesozoic eras modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality1 2 3 but direct evidence for annual rainfall periodicity has been lacking4 in the mesozoic era about 190 million years ago thick deposits of wind blown sand accumulated in dunes of a vast low latitude desert at pangaea s western margin5 6 7 these deposits are now situated in the southwestern usa here we analyse slump masses in the annual depositional cycles within these deposits which have been described for some outcrops of the navajo sandstone8 twenty four slumps which were generated by heavy rainfall appear within one interval representing 36 years of dune migration we interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains with the other four having been the result of winter storms the slumped lee faces of these jurassic dunes therefore represent a prehistoric record of yearly rain events

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

synapsid burrows and associated trace fossils in the lower jurassic navajo sandstone southeastern utah u s a indicates a diverse community living in a wet desert ecosystem abstract enigmatic structures in the lower jurassic navajo sandstone near moab utah occur at three localities below carbonate beds that record interdune lake deposits these structures are interpreted as mammal and therapsid burrows based on their architectural and surficial burrow morphologies type i large diameter and type ii mega diameter burrows type i burrows include sinuous tunnels y and t branched tunnels sinuous ramps and chambers and weather into mounds averaging 33 m 22 m and extend 1m above the surface type i burrows are dorsoventrally flattened in cross section averaging 9 3 cm wide and 4 2 cm high and are sand filled and structureless type i burrows mostly have smooth walls though some have scalloped walls type ii burrows are simple inclined tunnels 35 cm wide and 20 cm high and exhibit well preserved bilobate morphology along the underside of the tunnel the walls preserve a series of 3 or 4 thin 4 8 mm inclined scratch marks from the upper part of the wall and along the floor the great complexity and high density of type i burrow systems is best explained by multiple individuals living together in social groups these burrows are more complex than early triassic therapsid burrows from south africa and are most similar to burrows of extant social e g voles and eusocial mammals e g naked mole rats type ii burrows were likely constructed by therapsids based on burrow size and comparison to permian and triassic therapsid burrows from south africa and antarctica

palaeoecological implications of an upper cretaceous tetrapod burrow bauru basin peiropolis minas gerais brazil abstract we describe a globally rare example of a tetrapod burrow from the upper cretaceous bauru group bauru basin from peiropolis minas gerais state brazil the sedimentary succession containing the burrow includes a rich vertebrate assemblage comprising fish podocnemid turtles mesoeucrocodylians saurischian dinosaurs among others the burrow is composed of an oblique tunnel 30 oval in cross section with a horizontal and sub oval terminal chamber it is 1 3 m long from the midpoint of its inferred entrance to the midpoint of the bottom of the chamber it occurs in the upper portion of a sandstone succession interpreted as a braided channel deposit and the burrow fill comprises medium grained sandstone with mudstone intraclasts derived from fluvial floodplain facies it is overlain by other fluvial channel deposits analyses suggest that the burrow was dug after the filling of the braided channel and during the pedogenesis of its exposed upper surface based on burrow morphology and size the most plausible producer of this burrow is a notosuchian mesoeucrocodylian such as small to mid sized notosuchians e g sphagesaurids the bauru group has an extensive fossil record of notosuchians with disparate morphologies and it is noteworthy that the small sized notosuchian labidiosuchus amicum comes from the same unit as the burrow moreover arid to semi arid conditions have been inferred for fossil bearing rocks of this unit and as such the data here presented add to our palaeoecological knowledge of cretaceous mesoeucrocodylians in gondwana moreover it constitutes a new cretaceous record of a tetrapod burrow during a period when such ichnofossils are globally rare

tyrrhenian coastal deposits from sardinia italy a petrographic record of high sea levels and shifting climate belts during the last interglacial isotopic substage 5e abstract detailed petrographic and sedimentological analysis of tyrrhenian coastal deposits from four sites in sardinia provides new data about climate and sea level changes during the early part of the last interglacial isotopic substage 5e and shows that facies analysis is not only useful for the identification of ancient depositional environments but also represents a powerful tool for evaluating past climatic conditions and sea level forcing mechanisms two shallowing upward sequences sensu ward w c brady m j 1979 strandline sedimentation of carbonate grainstones upper pleistocene yucatan peninsula mexico am assoc pet geol bull 63 362 369 commonly separated by an erosion surface and displaying complex geometric relationships occur above modern sea level at several locations along the shorelines of sardinia these sequences include upper shoreface to backshore deposits and were formed during separate sea level highstands attributed to isotopic substage 5e our recent revision of these deposits indicates that each sequence presents distinctive petrographic characteristics the older succession essentially contains mixed calcarenites rich in quartz grains and lithic fragments whereas the younger sediments are dominated by carbonate bioclasts such as red algae coral and mollusk fragments both units apparently accumulated in a similar depositional setting but during different climatic regimes the petrography of the lower unit reflects a temperate humid period characterized by increased weathering and continental erosion whereas the composition of the upper one suggests a dryer and possibly warmer climate favoring active carbonate production the disparity in petrographic composition between sequences probably records the migration of atmospheric circulation cells i e a shift of climate belts before and after the 128 ka insolation maximum our climatic data are coherent with the calculated insolation curves for isotopic substage 5e and thus support the milankovitch hypothesis for the origin of pleistocene climates in contrast our sedimentological data clearly show the occurrence of two distinctive highstands of sea level during this time period which does not agree with the hypothesis it follows that the relation between orbitally induced insolation variations climate and sea level is not necessarily straightforward

the influence of variable progradation to aggradation ratio and facies partitioning on the development of syndepositional deformation in steep walled carbonate platforms abstract one of the remaining questions in carbonate geology and reservoir studies is the origin of steep walled carbonate platform margins and the role of gravity versus other structural processes in controlling the distribution of fracture networks and failure surfaces this study is an attempt to document the role of gravity interacting with stratigraphic architecture in controlling fracture patterns and margin collapse we employ finite discrete element models to illustrate that progradation aggradation p a ratio and facies tract partitioning in steep walled carbonate platforms affects the development distribution and intensity of syndepositional deformation all models are under the influence of only gravitational loading where pore pressure is held constant we utilize a modified mohr coulomb constitutive law with a rankine rotating crack tensile corner to capture both tensile and shear brittle failure our results illustrate that p a ratio affects the distribution and intensity of discrete fractures that form in steep walled carbonate platforms our results suggest that deformation is more extensive in a progradational carbonate platform where shelf edge angles are greatest and the clinoform is thickest alternatively aggradational carbonate platforms experience localized deformation in front of the antecedent shelf edge where the clinoform is thickest and steepest the introduction of mechanical heterogeneity associated with facies tract partitioning affects the intensity of fracturing in both progradational and aggradational models with the greatest number of fractures developing in reef facies in both scenarios development of brittle deformation under the sole application of gravity and lack of seaward lithostatic confinement is consistent with the syndepositional nature of deformation in these settings this work illustrates the interplay between carbonate platform geometry facies distribution and the resulting syndepositional deformation

integrated ichnofacies models for deserts recurrent patterns and megatrends abstract although it is commonly assumed that the trace fossil record of eolian dunes and associated environments is invariably poor a systematic review of the available information indicates that this is not necessarily the case a model involving five main phases of colonization of desert environments through the phanerozoic is proposed in this paper the first phase cambrian silurian involved animal incursions into coastal dune fields directly from the sea although it is unlikely that these animals would have remained for long periods of time in coastal deserts the second phase devonian reflects the activities of dune pioneers that left their fluvial habitat to enter temporary or permanently into inland deserts the third phase carboniferous permian involved the colonization of deserts by tetrapods the fourth phase triassic cretaceous involved a major exploitation of the infaunal ecospace as reflected by the appearance of more varied behavioral patterns in sub superficial structures the fifth phase paleogene recent reflects the appearance of the ecological dynamic that characterizes modern desert communities the invertebrate ichnofacies for eolian dunes is re named herein as the octopodichnus entradichnus ichnofacies honoring the seminal work of previous workers who simultaneously tackled the issue of eolian dune ichnofacies the chelichnus ichnofacies is retained for vertebrate trace fossil assemblages in eolian settings both ichnofacies occur in mobile and temporary stabilized sandy substrates subject to frequent erosion and deposition and to strong seasonality desert settings consist of complex mosaics of habitats or physical units associated with organism activity trace fossil distribution can be understood as reflecting the partitioning of desert settings in a mosaic of landscape units characterized by water content and its temporal fluctuations nutrient availability nature of the substrate and the dominant organisms present in turn desert systems are dynamic entities that change as a response to regional climate landscape units such as eolian sand seas salt flat and playa lake systems ephemeral rivers and alluvial fans interact in response to regional scale climate variations in hyper arid arid and semiarid climatic settings ancient deserts completely developed under hyper arid climatic conditions rarely preserve trace fossils due to the absence of moisture near the surface however the alternation of wet periods may represent windows for life development and thus preservation of biogenic structures arid deserts display complex patterns of dunes combined with dry wet and flooded interdunes dry desert elements e g dunes interdunes sand sheets typically record the entradichnus octopodichnus and chelichnus ichnofacies slight rises in regional precipitation produce elevation of the water table and increase of fluvial discharges that provide water and sediment to the system these processes may result in the local concentration of trace fossils in wet interdunes and ephemeral fluvial systems illustrating the scoyenia and chelichnus ichnofacies in semiarid systems playa lakes expand by the addition of freshwater evolving into freshwater lakes and fluvial systems may become more common lake margins and fluvial overbanks typically contain trace fossil assemblages that may be ascribed to the scoyenia ichnofacies

gravity modelling to assess salt tectonics in the western end of the south pyrenean central unit a new gravity survey almost 900 new sites and more than 4000 sites from previous studies reveals the existence of pyrenean oriented long wavelength residual gravity anomalies ranging from 18 to 28 mgal associated with frontal structures and short wavelength gravity lows up to 16 mgal distributed along an oblique zone in the western sector of the south pyrenean central unit of the spanish pyrenees these clearly correlate with the occurrence of several bodies and diapirs of triassic evaporites and mudstones the subsurface geometry and regional location of these evaporitic bodies is derived from four 2 5d gravity models that tie data from field geology rock density analysis seismic reflection profiles boreholes and our gravity survey gravity constrained cross sections allow us to distinguish between vertically well developed and poorly developed diapirs that belong to the sierras marginales unit and to characterize the relationships between thrusting and diapirism during eocene oligocene time

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

remagnetization of lower cretaceous limestones from the southern pyrenees and relation to the iberian plate geodynamic evolution paleomagnetic study 34 sites of thick cretaceous 5000 m marine carbonate strata from the organya basin ob in the southern pyrenees reveals a uniformly normal polarity characteristic remanence with varying declination d berriasian barremian d 295 o aptian albian d 348 o upper cretaceous d 354 o that resides in magnetite and predates late cretaceous tertiary folding the lack of reverse polarity magnetizations in the berriasian barremian series together with their distinct hysteresis properties that are typical of remagnetized carbonates elsewhere are taken as evidence for a secondary overprint in the lower part of the succession a hypothesized age of remagnetization near the barremian aptian boundary fits with a major tectosedimentary event in the basin that changed deposition from platform to basinal conditions and increased subsidence during the aptian the angular difference 53 o between declination from the remagnetized strata and the mean for aptian albian strata indicates that a counterclockwise rotation occurred between the two acquisition times part of this rotation is interpreted to be local and due to slip variation along strike of a normal fault that bounded the basin and tilted the pre aptian series this cretaceous extensive phase is framed in the rift evolution of the northern margin of the iberian plate the inferred remagnetization age within the ob falls within the range of previously inferred widespread cretaceous remagnetization events affecting the iberian plate in the ob remagnetization is speculated to have taken place through chemical burial diagenetic origin rather than simple thermoviscous resetting

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

depositional setting and early diagenesis of the dinosaur eggshell bearing aren fm at bastus late campanian south central pyrenees the late cretaceous aren fm exposed north of bastus in the tremp basin south central pyrenees preserves an excellent record of dinosaur eggs laid in a marine littoral setting different from other cases reported in literature at the bastus site the preferential nesting ground was original beach sand the coastal deposits of aren fm can be grouped into four facies assemblages representing respectively shoreface beachface beach ridge plain and backbarrier lagoon environments shoreface deposits include fine to coarsegrained hybrid arenites and subordinate quartz dominated conglomerates with ripple structures of wave and wave current origin beachface deposits are mainly storm beach conglomerates but parallel laminated foreshore arenites locally occur backbarrier lagoon deposits comprise of washover sandy conglomerates that grade laterally into sandy lime mudstones biomicrites and marls beach ridge sediment wherein the bulk of dinosaur eggs and eggshell debris occurs predominantly is a reddish hybrid arenite that has undergone a complex early diagenetic evolution including marine and meteoric cementation followed by soil development the reddish arenites overlie wave dominated shoreface deposits and in places pass laterally into lagoonal deposits they originally formed shore ridges that became stabilized during progradational episodes by pedogenesis beach ridge sensu otvos e g 2000 beach ridges definitions and significance geomorphology 32 83 108 which also affected the dinosaur eggs the eggshell bearing beach ridge arenites are typically preserved at the top of parasequences forming the systems tracts of a third order sequence thick packages of this facies resulted from aggradation of barrier beach ridge deposits whose preservation below surfaces of transgressive erosion was favoured by incipient lithification

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

mesozoic carbonate platforms and banks of the eastern north american margin abstract the jurassic lower cretaceous carbonate platforms and banks form a discontinuous belt extending over distance of 6000 km from the grand banks up to the bahamas six types of carbonate buildups are recognized and document the variability of depositional paleo oceanographic and tectonic processes on the eastern north american margin the composition of the carbonates closely resembles the recent deposits of the western great bahama bank since oolitic shoals were present near to the shelf edge and skeletal peloid wackestones and biomicrites were deposited in the inner part of the platform coralstromatoporoid and sponge bioherms were only rare constituents of the carbonate banks the thickness of carbonate buildups progressively increases southward along the margin attaining a thickness of more than 5 km on the bahamas the carbonate platforms also become younger southwards which is thought to reflect the northward movement of the north american plate of less than 1 5 cm yr the carbonate platforms were seeded over the continental basement following the taphrogenic period of plate tectonics building of carbonate ramps which characterized the early jurassic has began during the transitional period between continental rifting and early drift the second stage in construction of the carbonate platforms and offshore banks proceeded mainly after separation of the continental plates

the impact of milankovitch scale climatic forcing on sediment supply abstract stratigraphy is the main technique to predict the occurrence of potential reservoirs and seals in the oil industry stratigraphic tools used are stratigraphic observations from drilled wells rock samples and wireline logs and seismic interpretation nowadays computer modelling allows scenario forecasting of the sequence to be expected application of these tools indicates that the key input parameters are initial basin topography subsidence eustasy and sediment supply the first three parameters are usually well constrained or can readily be deduced from well and seismic data however the fourth sediment supply is loosely defined and because of that it is used to calibrate the model in the present article the controls on sediment supply are reviewed and the impact of in particular milankovitch scale climatic forcing on sediment supply is tested on the neogene of the niger drainage and delta system sediment supply is controlled by a complex interplay of geographic and climatic factors such as 1 relief or mountain height 2 the size and temporal storage capacity of the drainage area 3 overall climate 4 amount and seasonality of precipitation and 5 vegetation cover studies in geomorphology have indicated that although complex computer models can be made to predict erosional product for the present a large scale sediment supply prediction should be based on the combination of palaeogeographical palaeoclimatological and erosion potential maps more detailed sediment supply predictions should include milankovitch scale variations the climatic impact of these variations is mainly felt when we are in a transition between two climates then the area will experience regular climatic changes from e g wet rainforest to dry monsoonal climate or low to high sediment supply respectively this concept was tested in the forward modelling package stratagem on the neogene of the niger delta four scenarios were evaluated using various combinations of large and milankovitch scale sediment supply curves combined with global or milankovitch scale eustatic sea level curves the results confirm the impact of both large scale and milankovitch scale climatic forcing on sediment supply however in an icehouse world the various scenarios also suggest that the effect of eustatic sea level fluctuations overshadows the impact of milankovitch scale sediment supply by contrast in a greenhouse world the impact of milankovitch scale sediment supply is expected to be more significant in the absence of significant sea level fluctuations

the vertebrate track record a renaissance in the study of fossil footprints has been driven by a multitude of discoveries and the realization that vertebrate ichnology makes important contributions to our understanding of terrestrial vertebrates more striking is the insight the track record gives us into bias and incompleteness in the vertebrate fossil record

application of vertebrate trace fossils to palaeoenvironmental analysis abstract this is a review of the main uses of vertebrate trace fossils ichnofabrics and ichnofacies in the palaeoenvironmental analysis of sedimentary sequences the article accounts for the significant developments produced in the last three decades including the application of the ichnofacies concept to vertebrate trace fossils recognition of footprints in cross sectional view and their distinction from inorganic structures and burrow fills is first discussed the response of different substrates showing contrasting water content and imprinted by different animals or devices is compared in terms of the morphology of the resultant footprint trackways with sand crescents are typical of aeolian cross strata and are absent in associated flat lying to low angle deposits thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margins of fossil ponds and lakes including onshore shoreline and shallow subaqueous zones abundant flamingo like footprints and flamingo nest mounds are good indicators of alkaline and or saline lake waters hippopotamus trails are found closely associated with modern and fossil freshwater wetlands dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth turtle crocodile amphibian hippopotamus and fish swim traces allow one to infer a subaqueous substrate certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as palaeocurrent indicators the preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed vertebrate trace fossils can help to infer discharge variability in fluvial channels the descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates and to a few examples of ichnofabrics with discrete trace fossils the nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in palaeoenvironmental analysis the distinction of a potential vertebrate burrow ichnofacies in carbonate bearing palaeosols is proposed to represent well drained soils developed under arid or semiarid climate

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

sedimentology and high frequency sequence stratigraphy of a forearc extensional basin the miocene caleta herradura formation mejillones peninsula northern chile abstract facies and sequence stratigraphic interpretation for the 380 m thick caleta herradura formation miocene are presented based on detailed and comprehensive outcrop data from the caleta herradura half graben mejillones peninsula northern chile the caleta herradura formation contains an array of lithofacies comprising sandstones sandy mudstones diatomites and breccio conglomerates that are interpreted as the products of inner shelf to non marine depositional settings complete exposure allows for recognition of a number of distinct and laterally persistent key stratal surfaces that permitted the identification of twenty five high frequency meter to tens of meters scale sequences based on their internal organization two main motifs of such unconformity bounded depositional packages can be distinguished deepening and deepening to shallowing upwards transgressive and highstand systems tracts were resolved based on such facies stacking patterns the origin of sequences is difficult to decipher and remains somewhat uncertain however several lines of direct and indirect evidence constrain interpretations for both the sequence architecture and bounding unconformities and help to discriminate between the various mechanisms that may have driven their development in essence these demonstrate that neither tectonically driven sea level oscillations nor climatically induced changes in sediment supply can adequately explain the distinctive features of unconformities and the facies architecture of sediments they delimit instead these high frequency changes in relative sea level are best explained as a consequence of glacio eustatic oscillations the contemporaneous deep ocean proxy records appear to support a causal link between the observed stratigraphic cyclicity and glacio eustatic changes in sea level due to modulation of short term milankovitch scale events by longer period astronomical variations however the type of astronomical forcing remains elusive hindered by lack of adequate age controls and a poor understanding of pacing mechanisms of high frequency climate changes during the middle to late miocene

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

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

eolian origin of upper paleozoic sandstones southeastern utah abstract throughout its outcrop in southeastern utah the permian cedar mesa sandstone contains large scale crossbedding and is devoid of marine fossils except for sand size skeletal fragments although this rock unit has been interpreted by several recent workers as shallow marine stratification identical to that documented in modern eolian dunes is ubiquitous in the cedar mesa thin inversegraded laminations within crossbeds represent the unique product of climbing wind ripples this type of stratification is the best evidence for an eolian origin of the cedar mesa such an interpretation is strongly supported by other evidence vertebrate trackways and simple small cylindrical burrows constitute a distinctively nonmarine ichnofauna rhizoliths root casts are abundant at many stratig aphic levels in the underlying rico and hermosa formations sandstones with physical and biogenic sedimentary structures identical to those in the cedar mesa are interbedded with crossbedded limestones with abundant megafossils and marine traces contacts between sandstones and limestones are sharp gradational relationships would be expected if both sandstones and limestones accumulated subaqueously siliciclastic pebbles are present in some of these carbonate rocks suggesting that the well sorted nature of the sandstones cannot be attributed to the unavailability of coarse clasts palcocurrent data from the sandstones and limestones show significantly different vector means and variance southward pinchout of marine carbonates indicates that winds were onshore winnowing of silicicla tics from coarser carbonate detritus created a strong dichotomy in bulk mineralogy between marine and eolian sediments reinterpretation of the sandstones necessitates reappraisal of ideas concerning the mineralogical maturity of these sediments the relative importance of eolian and shallow marine transport processes to the destruction of labile siliciclastics is unknown

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

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

large vertebrate burrow from the upper mississippian mauch chunk formation eastern pennsylvania usa abstract a burrow of probable amphibian origin was discovered in the upper member of the mississippian mauch chunk formation in eastern pennsylvania facies analysis of the upper member indicates that deposition occurred in an ephemeral braided stream setting the burrow is housed in a mudstone and is filled by two graded beds of conglomerate to sandstone it is characterized by a flared opening leading into a narrower slightly helical tunnel that ends in an inflated ovate chamber approximately 51 to 60 cm in diameter with a maximum height of 20 cm the flared opening is stratigraphically higher than the elevation at the base of the chamber the tunnel has a semicircular base the geometries abrupt angle changes inflated termination width to height ratios of the terminal chamber and graded fill indicate that the structure was an open void prior to sedimentation the geometry and size of this structure are incompatible with known invertebrate burrows and erosional features palaeosauropus primaevus an amphibian footprint ichnotaxon recovered from the mauch chunk formation was made by an amphibian of sufficient size to create such a large burrow this type of burrowing was most likely a response to seasonal droughts as local water sources evaporated

the chronostratigraphic framework of the south pyrenean maastrichtian succession reappraised implications for basin development and end cretaceous dinosaur faunal turnover abstract the evolution of the end cretaceous terrestrial ecosystems and faunas outside of north america is largely restricted to the european archipelago the information scattered in this last area can only be integrated in a chronostratigraphic framework on the basis of robust age constraints and stratigraphy therefore we have revisited the puzzling age calibration of the sedimentary infilling from the isona sector in the tremp syncline south central pyrenees an area renowned for its rich maastrichtian dinosaur fossil record aiming to shed light to existing controversial age determinations we carried out a new magnetostratigraphic study along the 420 m long orcau and nerets sections of that area our results reveal that most of the succession correlates to the early maastrichtian mostly chron c31r in accordance to ages proposed by recent planktonic foraminifera biostratigraphy the resulting chronostratigraphic framework of the entire maastrichtian basin recorded in the tremp syncline shows that a significant sedimentary hiatus of about 3 my characterizes most of the late maastrichtian in the study area this hiatus related to an abrupt migration of the basin depocenter is temporally close to similar hiatuses decreases in sedimentary rates and facies shifts recorded in other southwestern european areas the present chronologic framework sets the basis for a thorough assessment of end cretaceous terrestrial faunal turnover and extinction patterns and the establishment of a more rigorous pyrenean basin evolution analysis

burrow architecture and burrowing dynamics of ctenomys in foredunes and paleoenvironmental implications abstract ctenomys sp also known as tuco tuco is a solitary subterranean small rodent that inhabits sandy soils in south america we studied burrow system architecture of ctenomys flamarioni communities from the foredunes of the southern brazil coastal plain by inserting plaster of paris and excavating the tunnels the structure of the burrow system is complex with interlinked tunnels one occasionally open entrance multiple chambers and turnarounds blind laterals varying slopes t junctions bifurcations and two different levels a specific isolated chamber is used as a latrine while another is used as a nest the burrow entrance is open only when the rodent is taking out sand or feeding the tunnels have an average depth of 35 cm deepest at 55 cm and the most superficial at 15 cm near the entrance the average burrow length ranges from 190 to 500 cm the tunnels have different heights and widths varying from 5 5 9 3 cm wide to 6 11 cm high the entrance is inclined 28 the central part of the burrow system has a steeper slope with an inclination of 38 the plaster molds preserve claw marks of four digits of up to 4 mm in depth collapsed burrows are rapidly sealed to avoid the entrance of predators ctenomys sp burrows provide a suitable microhabitat which is used by the animals as protection from adverse environmental conditions particularly during the winter when wind impacts the coastal area the extensive interlinking tunnels provide underground routes to escape from predators ctenomys burrows in coastal dune environments are appreciably more complex than those excavated in arid environments which are shallower with no chambers and a slope of up to 20 such difference in the architecture of the burrows can be used as a criterion to reconstruct the paleoenvironment of burrow systems in the rock record

mid depth calcareous contourites in the latest cretaceous of caravaca subbetic zone se spain origin and palaeohydrological significance abstract deep marine carbonates of late campanian to early maastrichtian age that crop out in the subbetic zone near caravaca se spain contain a thick succession of dm scale levels of calcareous contourites alternating with fine grained pelagites hemipelagites these contourites characterised by an abundance and variety of traction structures internal erosive surfaces and inverse and normal grading at various scales were interpreted as having been deposited under the influence of relatively deep ocean currents based on these contourites a new facies model is proposed the subsurface currents that generated the contourites of caravaca were probably related to the broad circumglobal equatorial current system the strongest oceanic feature of cretaceous times these deposits were formed in the mid depth 200 600 m hemipelagic environments at the ancient southern margin of iberia this palaeogeographic setting was susceptible to the effects of these currents because of its position close to the narrowest oceanic passage through which the broad equatorial current system flowed in the westernmost area of the tethys seaway regional uplift related to the onset of convergence between iberia and africa probably favoured the generation of the contourites during the late campanian to the early maastrichtian

distribution and geometry of facies and early diagenesis the key to accommodation space variation and sequence stratigraphy upper cretaceous congost carbonate platform spanish pyrenees abstract through only moderate structural deformation the upper cretaceous carbonates of the tremp region in the spanish pyrenees can be studied in the form of a platform to basin cross section comparable in scale to that of a seismic section this study examines the upper turonian to mid coniacian congost platform and its associated basinal succession the sedimentology facies geometries and cycle stacking patterns along with evidence of exposure of the platform are interpreted in terms of fluctuations in relative sea level and variations in accommodation space differences in the facies and early diagenesis of carbonates from different parts of the congost platform suggest two separate phases of platform development an earlier more land ward platform was dominated by clinoforms prograding on to a sloping basin floor with a thin lagoonal sand bank facies upon the platform itself supplying abundant excess sediment to the clinoforms a later more basin ward platform has a more complex internal geometry of depositional units and marginal rudist coral buildups the interpretations are used to propose a new sequence stratigraphic architecture for the congost platform involving two sequences the second produced through dynamic forced regression sequence boundaries are characterised by subaerial exposure on the platform top that can be correlated with hardgrounds and or glauconitic horizons within the more basinal locations overlain by deeper water facies the presence of a submarine onlap surface and down slope slide deposits immediately above the sequence boundary suggests that the major transgressive event that followed sequence boundary development was brought about by local extensional tectonic activity the small scale cyclicity within the sequences and the major falls in sea level that produced the sequence boundaries are interpreted to have resulted largely from eustatic processes probably with tectonic enhancement

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

the last 140 ka in the afro asian arid semi arid transitional zone abstract during the last ten years a great number of geological or other proxy records provided radiocarbon u th or tl dated information on the past climatic oscillations in the arid semi arid zones extending between the atlantic and the pacific comparisons and a synthetic view of these results can now be attempted for the last 140 ka and compared with global changes as registered in oceanic or ice cores and with palaeomonsson models for this purpose wide spatial and time scales have to be used on the whole arid humid alternations roughly fit global changes cold phases corresponding to an extension of the arid areas to the south warm phases corresponding to the shrinking of the same to the north the last interglacial is associated with an increase of precipitation throughout the area considered isotopic stage 4 brings no evidence whatsoever of humid conditions two wetter episodes are registrated during stage 3 a major rainfall decrease is everywhere associated with the last glacial maximum 21 15 ka in most regions the arid or semi arid zones extending several hundred kilometers southwards relative to the present day pattern the two abrupt deglaciation steps and the younger dryas are recorded in all of the most sensitive regions at the margins of the present day monsoonal range during the holocene the precipitation increases everywhere by 100 400 mn relative to the present day values the optimum being at 8 5 6 5 ka a climatic deterioration follows with an irregular pattern of dry wet episodes according to the different geographic conditions the humid phase terminates at 3 5 3 ka in the whole transitional zone the major southward shift of the monsoonal precipitation range since its optimum some 8000 years ago fits the astronomical neoglacial trend and may possibly be correlated with past stage 5d although its rapidity and spatial importance may just reflect one of the sharp successive cold warm variations registered by grip during the whole stage 5

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

cay sal bank bahamas a partially drowned carbonate platform abstract recent high resolution seismic reflection profiling sediment sampling scuba observations and landsat imagery show that cay sal bank csb has very limited reef development no active sand shoals few islands a thin to non existent sedimentary cover and a relatively deep margin 20 30 m and shelf lagoon system 10 20 m windward and leeward margins can be discerned but their general development is poor when compared to the shallower more active margins of little bahama bank lbb and great bahama bank gbb windward margins facing north and east along csb are generally deep rocky sediment barren terraces supporting limited low relief relict reefs leeward margins have small sand bodies maximum thickness 10 m covering reef structures at the bank edge indicating that offbank transport of sands has occurred however these marginal sand bodies are limited in areal extent suggesting that this transport system was not ubiquitous along the south and west facing margins seismic and grab sample data from the deep 200 500 m slopes seaward of the leeward margins show a thin discontinuous unit of periplatform sand containing halimeda molluscs and non skeletal components derived from shallow water the limited basinward extent no deeper than 300 m of this unit recognized by its reflection free seismic facies also indicates that sand production and transport off the bank were never prolific this is in stark contrast to new seismic data from the leeward margins of gbb which clearly show thick 20 m sand bodies covering high reefs 12 15 m along the outer margin and multiple reflection free units extending to great depths 600 m all along the adjacent slope the apparent immature development of normal bank top processes and facies and the absence of key modern depositional environments on csb may be related to the rate at which this platform was submerged due to its comparatively low elevation the initial holocene flooding occurred at approximately 8 10 ka when sea level rise was rapid 6 m ka 1 by comparison the higher lbb gbb were flooded later at a much slower rate 1 5 m ka 1 the relatively rapid flooding of csb provided little time for the shallow depositional environments to start up the continued rapid rate of sea level rise after drowning and offbank transport of sediment and the export of chilled waters formed during winter months prevented the resulting facies from catching up consequently csb appears to be partially drowned particularly when compared to the other healthier rimmed bahamian platforms drowned carbonate banks are very common in the ancient record and potentially provide excellent stratigraphic traps for hydrocarbons csb provides a modern example of a bank that may be in the very early stages of termination final drowning of carbonate platforms may occur as a result of frequent higher order sea level fluctuations superimposed on initial stage of a lower order sea level cycle

life in a sand sea biota from jurassic interdunes interdune deposits in the navajo sandstone of arizona are identified as the source of most fossils known from the formation they provide information on terrestrial life in a poorly known interval of the north american jurassic the biota includes sphenophytes ostracodes and four species of vertebrates including a skeleton of the geologically youngest tritylodontid synapsid from western north america fossils and sedimentary rock localized in interdunes indicate areas of greater available moisture and therefore greater carrying capacity than surrounding dune deposits that compose the bulk of the formation environmental conditions in interdunes favor fossil preservation and thus provide a focus for future studies the diversity and adaptations of fossils from navajo interdunes support models of climatic amelioration during sand sea evolution when wet interdunes were deposited

facies and cycle architecture of a pleistocene marine terrace crotone southern italy a sedimentary response to late quaternary high frequency glacio eustatic changes abstract cyclic late pleistocene shallow marine deposits such as those forming the sedimentary cover of some marine terraces allow a detailed study of the architecture of nearshore to offshore cycles deposited under the influence of high amplitude glacio eustatic changes the capo colonna marine terrace located near crotone southern italy is composed of two cycles recording a low frequency retrogradational trend which is thought to be the result of a generalized base level rise during a late pleistocene interglacial stage superimposed on regional uplift cycles of the capo colonna marine terrace are composed of coarse grained lags siliciclastic shoreface deposits and mostly carbonate shelf deposits and their general stratigraphic architecture evidences relatively thin transgressive and thick regressive intervals the latter can be top truncated due to wave ravinement during a subsequent erosional transgression the architectural style of the capo colonna marine terrace cycles is thought to be linked to very rapid base level rises related to the late pleistocene high amplitude glacio eustatic changes climatic variations controlling the sediment supply rate are considered less effective in the present context present results allow a comparison with other cyclic successions developed under icehouse climatic regimes showing a discrete variability in their stratal architecture

long lived pluvial episodes during deposition of the navajo sandstone abstract the navajo sandstone of the american southwest was deposited at approximately 190 ma in a giant subtropical dune field near the western margin of pangea from this unit we report thick intervals of dune cross strata that were churned by insects and trampled by reptiles although dunes continued to migrate freely the distribution of trace fossils shows that plant life in wet interdune areas sustained high levels of animal activity on the dunes for many thousands of years we interpret this suite of structures as the record of a pluvial episode climatologically similar to the period of greening in the sahara 4000 10 000 yr ago a high percentage of the rainfall on the navajo erg recharged the water table and led to the development of highly dilute local groundwater flow systems that discharged into interdune areas

carbonate platform depositional sequences upper cretaceous south central pyrenees spain abstract the upper cretaceous cenomanian maastrichtian of the south central pyrenees shows five carbonate platform sequences where the major parameters are tectonism relative sea level fluctuations and inherited depositional profile depositional geometries and basin analysis permit an understanding of the depositional history five depositional sequences have been recognized 1 the santa fe sequence middle upper cenomanian a ramp to a skeletal rimmed shelf with an escarpment bypass margin the lower boundary is an angular unconformity and the upper one records a sea level drop the platform location of the margin was determined by a listric normal fault 2 an abrupt sea level rise drowned the former platform the congost sequence turonian lower coniacian a distally steepened ramp with erosional distal deep slope the depositional model was largely controlled by pre existing basin morphology cessation of platform development was due to a relative sea level drop 3 the sant corneli sequence upper coniacian lower santonian a mixed terrigenous skeletal homoclinal ramp with upright margin deep slope and dysaerobic basin the slope results from the backstepping by 24 km of the previous margin and gentle basin tilting the platform margin remained more or less at the same position and relief between platform and slope increased indicating continuous relative sea level rise the upper boundary is an angular unconformity at the platform margin produced by an abrupt sea level rise and platform drowning and by listric normal faulting 4 the vallcarga sequence upper santonian campanian a distal steepened skeletal homoclinal ramp erosional escarpment and turbidite basin which corresponds to the mesozoic maximum marine expansion a listric normal fault created two depositional areas a more or less flat footwall block with a north northwest prograding carbonate ramp