weichselian and holocene growth of the northern high latitude lofoten contourite drift on the continental slope of norway abstract the weichselian and holocene sediments in the lofoten drift comprise six lithofacies brown sandy mud olive grey mud olive grey laminated mud dark brown mud massive sand and dark grey sandy mud during the weichselian the sediment input to the lofoten drift was from two main sources i e glacimarine sedimentation and ocean current winnowing during the holocene the sediment input was only from winnowing the sediment source area was the voring margin and the continental margin further south the sedimentation rate was 190 cm ka during the late weichelian and 9 cm ka during the holocene the weichselian rates are high compared with the deep sea contourite drifts comprising highly bioturbated sediments and probably explain why bioturbation is less pronounced in these slope drift sediments drifts on glaciated margins as exemplified by the lofoten contourite drift represent areas of high sedimentation rate during glacial maxima sediment input was not restricted to glacial maximum periods for sediments also accumulated during other stadial and interstadial periods

sediment fluxes along the northeastern european margin inferring hydrological changes between 20 and 8 kyr abstract in an attempt to delineate past hydrographic conditions on the northeastern atlantic ocean margin along a latitudinal transect 37 63 n and link the eastern north atlantic ocean with the norwegian sea we have investigated planktonic and benthic stable oxygen isotopes as well as abundances and fluxes of planktonic and benthic foraminifera calcium carbonate organic carbon and detrital grains in six sediment cores studied by the enam project in our joint approach we focused on the major climatic events of the last 20 kyr that is the last glacial maximum lgm the heinrich event 1 h1 the younger dryas yd and the holocene climatic optimum hco simmax temperature estimates suggest glacial ssts off portugal similar to holocene values contradicting the proposed polar front position of climap project members 1976 besides increased planktonic and benthic foraminiferal fluxes in the norwegian sea and the faeroe islands cores point to nordic seas partially ice free with seasonally productive polynas multiple ird spikes observed at the faeroe islands and norwegian sea sites coeval with h1 suggest multiple pulses of the fenno scandian ice sheet at the same time the presence of ird on the portuguese margin cores confirms the southward influence of icebergs the increase in foraminiferal abundances and fluxes that parallel ird spikes at all sites suggests that times of increased productivity either succeed or occur simultaneously with the iceberg surges in the open north atlantic productivity conditions similar to those observed during h1 are also registered during the yd even though planktonic foraminiferal assemblages suggest less cold conditions

use of dipmeter data in clastic sedimentological studies resistivity curves from he eight measuring electrodes of schlumberger s stratigraphic high resolution dipmeter tool tm shdt can be processed to give a detailed reservoir characteriation that includes electrofacies and sedimentary dip data this conclusion is supported by evaluation of processed shdt data compared with information from over 1 000 m 3 280 ft of cores covering fluvial and eolian sedimentary environments based on three examples we give general guidelines for processing of and noise removal from shdt data to obtain satisfactory geological information foreset dips in sets as thin as 20 cm 8 in can be reliably calculated by using side by side processing options with a correlation interval of 10 cm 4 in and a step distance of 7 5 cm 3 in in many formations spurious dip readings cause serious problems these readings originate from irregularities in the formation or from processing artifacts have no directional implication and produce unsatisfactory signal to noise ratios however criteria have been defined to select relevant dips from such noisy data structural dips must be measured with a sufficient degree of confidence to accurately subtract them from sedimentary dips reliable data can be obtained by large scale interval correlation particularly when the interpretation is concentrated on suitable intervals laminated shales and horizontally bedded heterolithic sequences the shdt tool also can provide detailed information on reservoir characteristics particularly on small scale heterogeneities that escape the resolution of conventional logs boreholewide resistivity displays from interpolation of shdt traces enable the recognition of resistivity distribution patterns and may give a new scope to facies recognition from logs

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

interaction between aeolian fluvial and playa environments in the permian upper rotliegend group uk southern north sea the permian upper rotliegend group in offshore uk quadrants 42 43 47 and 48 comprises a sequence of mixed aeolian fluvial playa deposits these deposits are up to 300 m thick and contain a record of the interaction between desert fluvial systems and adjacent aeolian and playa environments the relative dominance of water vs wind transport and deposition in this stratigraphic package was a function of fluctuations in the discharge of ephemeral fluvial systems and changes in water table playa level driven by a combination of climatic change and syndepositional tectonics the rotliegend sedimentary record is punctuated by numerous surfaces recording erosion by wind and water the origin of these surfaces is mostly climatic with periods of increased runoff resulting in fluvial incision especially near active faults during periods of reduced runoff wind erosion of fluvial deposits occurred with fluvially derived sand being reworked into expanding aeolian dune fields wind erosion also occurred as a rising water table isolated dunes from their sediment supply resulting in deflation of dunes down to the water table these surfaces formed in a basin that was subsiding thus even in a background of overall increasing accommodation space climatically driven falls in the water table allowed for periods of erosion the occurrence of significant erosion especially near syndepositional fault zones resulted in a sedimentary record that shows pronounced lateral as well as vertical facies variations

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

structural control of jurassic sedimentation in alabama and florida the extent and thickness of jurassic strata in alabama and florida were mapped as part of a u s geological survey regional geohydrologic study rocks equivalent to the werner louann norphlet smackover haynesville and cotton valley sequences of mississippi and arkansas have been recognized and except for the werner equivalent are herein extended into panhandle florida the predominantly fluvial jurassic sequence in alabama and florida was interrupted at least twice by barred basin conditions that resulted in the deposition of extensive evaporite deposits and at least once during deposition of the smackover formation by a major marine transgression the updip limits and isopach map trends of the jurassic units mapped appear to have been controlled by a major nort west trending right lateral wrench fault the dominant master shear in a regional wrench fault system active throughout jurassic time

gulf of mexico tectonic history hotspot tracks crustal boundaries and early salt distribution a late jurassic mantle plume may have generated hotspot tracks on the north american plate and the yucatan penninsula tectonic block as the gulf of mexico opened ca 150 ma the tracks are identified from deep basement structural highs that have been mapped by integrating seismic refraction and gravity data they are associated with high amplitude distinctive gravity anomalies that provide the basis for a kinematic reconstruction that restores the western ends of the hotspot tracks with a 20 clockwise rotation of the yucatan block or almost one half the total rotation required to open the gulf of mexico basin the duration of track generation is estimated to have been about 8 10 m y or almost one half the total time required to open the gulf of mexico basin prior to this rotation extension of continental crust over a 10 12 m y interval was the result of approximately 22 of counterclockwise rotation and crustal thinning autochthonous salt appears to be confined to the continental flanks of the hotspot tracks confirming that salt was deposited during continental extension and not after ocean floor had begun to form a prominent gravity anomaly along the western boundary of the basin is interpreted to be produced by a marginal ridge which was created along the ocean continent transform boundary as the basin opened the eastern flank of this marginal ridge and the northernmost easternmost and southernmost terminations of the hotspot tracks are interpreted to coincide with the oceanic continental crustal boundary in the basin dale e bird consults in the oil and gas exploration industry as a potential fields specialist since 1981 his experience in the industry includes acquisition processing interpreting and marketing geophysical data including positions with aerodat world geoscience marathon oil company digicon and aero service he earned a ph d from the university of houston in 2004 and his research interests are regional geology and tectonics and the integration and interpretation of gravity and magnetic data he is a member of several local and international geological and geophysical societies kevin burke has been a professor of geology in the university of houston since 1983 having previously lived and worked in several parts of the world his main research is in tectonics the large scale evolution of planetary lithospheres his current interests include african and asian geology and the derivation of large igneous provinces from the core mantle boundary stuart a hall is a professor of geosciences specializing in the study of gravity and magnetic fields he received a b sc honors degree in physics from the university of birmingham united kingdom 1968 and a ph d in geophysics from the university of newcastle upon tyne united kingdom 1976 his current research interests are mainly focused on the use of geophysical data to investigate the development of small ocean basins and orogenic belts he is a member of the society of exploration geophysicists american geophysical union royal astronomical society and sigma xi research society john f casey is a professor of geology and chair of the department of geosciences at the university of houston specializing in structure tectonics and geochemisty he received a b a degree in geology from the university of pennsylvania in 1975 and a ph d in geology with honors from the state university of new york albany in 1980 his research has focused on the tectonics and geochemistry of midocean ridges transform faults and ophiolite bearing orogenic belts

late mesozoic gravity sliding and oxfordian hydrocarbon reservoir potential of the northern yucatan margin abstract the stratigraphy and structural evolution of the western florida margin is much better understood than its northern yucatan conjugate because previous hydrocarbon exploration has been more extensive on the florida margin in the deep water northeastern gom the post salt section records late jurassic cretaceous gravity sliding of rafted blocks along a basinward dipping layer of callovian salt this study uses approximately 31 000 line km of 2d seismic data to describe a coeval area of widespread gravity sliding along the less studied northern yucatan margin we define three structural domains based on their distinctive salt structures and associated deformation 1 a region in the northeastern study area consists of relatively undeformed late jurassic cretaceous section underlain by 0 300 m thick salt 2 areas in the central and southwestern study area contain late mesozoic gravity slides defined by 300 600 m thick salt rollers and normal faults rooted onto a 1 4 basinward dipping salt detachment and 3 the distal margin of the western and central study area exhibits large salt diapirs up to 6 km tall that deform quaternary stratigraphic units in the central yucatan study area containing late mesozoic gravity slides a stratigraphic unit equivalent to the productive oxfordian norphlet sandstone of the deep water northeastern gom is identified based on its similar seismic character reconstructing the extent of this norphlet equivalent unit along the yucatan margin to its location during oxfordian deposition places it adjacent to an extensive area of norphlet sandstone mapped in the deep water northeastern gom by previous authors our reconstruction suggests a 48 000 km2 fairway of potential aeolian late jurassic reservoirs on the yucatan and campeche margins that includes productive reservoirs in the southeastern bay of campeche which previous authors correlated with the norphlet formation

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

late glacial to recent paleoenvironmental changes in the gulf of cadiz and formation of sandy contourite layers planktonic foraminifera and coccoliths were analyzed from six gravity cores obtained on a deep terrace located on the upper continental slope of the gulf of cadiz between 400 and 700 m water depth the lithology of these cores consists mainly of muds with some interbedded sandy or silty foraminifer rich layers that have been reported as contourites originated by the action of the mediterranean outflowing waters mow sweeping the sea bottom today after the last glacial characterized by muddy sedimentation sandy contourites start to deposit in the gulf of cadiz during the bolling allerod 14 11 14c kyr bp climatic optimum this trend was broken during the younger dryas 11 10 14c kyr bp and started again after the end of the younger dryas this pattern is recorded in most of the cores by a single sandy contourite layer formed during the first deglaciation stage bolling allerod time and a sandy contourite interval that initiates immediately after the end of the younger dryas during the second stage of the deglaciation and continues during the holocene the stratigraphy and climatic reconstruction was based on the evolution of the calcareous plankton assemblages during the last climatic transition from the last glacial to the recent holocene the sharp reduction of sinistral n pachyderma along with the reduction of g quinqueloba mark the base of bolling allerod time this is also related to a prominent peak of the subtropical species g sacculifer and g ruber the younger dryas is identified by a reduction in abundance of the subtropical species that again increase just after this period the second step of deglaciation is marked by a sharp decrease in the relative abundance of dextrally coiled n pachyderma in previous papers the sequence of sandy contourites has been related to sea level rise greater gibraltar sill depth and enhanced energy of the mow in this work we suggest that the individual sand layer episodes are condensed layers originating during times of rapid warming and relative sea level rise within the last deglaciation during these times the coastline migrated more rapidly landward and the terrigenous input decreased as it began to be trapped on land and on the shelf resulting in a major drop in sedimentation rate on the upper continental slope in times of low sedimentation rate the particles would have a longer residence time within the upper mixed layer of the near surface sediment and therefore the energy of currents would act longer producing a more efficient winnowing of the sediment at the same time more generations of benthic organisms would rework the mixed layer favoring this winnowing

constraints on the tectonic development of the eastern gulf of mexico provided by magnetic anomaly data boundaries between oceanic and transitional crust in the eastern gulf of mexico have been delineated using detailed accurately navigated high quality aeromagnetic data these data indicate that considerably more oceanic crust may be present than previously suggested by other geophysical data especially seismic reflection data the n s extent of oceanic crust substantially increases westward from approximately 280 km near 87 w to roughly 390 km near 90 w indicating the proximity 10 of the pole of rotation variations in the amount of oceanic crust together with discontinuities in the magnetic anomaly patterns interpreted as the traces of fossil transform faults or fracture zones have been used to obtain a rough estimate of the location of the pole of rotation 24 n 81 5 w for the seafloor spreading phase of opening the magnetic data have been used to develop a model for the opening of the gulf and to identify some geometrical relationships between its conjugate continental margins based upon the estimated pole position the eastern gulf is interpreted to have opened in an approximately nne ssw direction with the counterclockwise rotation of yucatan away from north america the seafloor spreading phase of movement accounts for about 25 of the counterclockwise motion of yucatan rotating the yucatan block clockwise by this amount to restore it to its predrift position places the campeche bank adjacent to the mississippi trough louisiana shelf further clockwise rotation of yucatan by an additional 30 35 about this pole restores extended crust to its original thickness and is consistent with rotations of yucatan predicted from paleomagnetic data from chiapas

paleoceanographic significance of sediment color on western north atlantic drifts ii late pliocene pleistocene sedimentation abstract color variations were interpreted in paleoceanographic terms for the late pliocene pleistocene sediments recovered by odp leg 172 on deep sea drifts at blake bahama outer ridge and northeastern bermuda rise the color derived parameters used in interpretation included predicted carbonate content terrigenous fluxes and hematite content abundance of upper carboniferous spores indicates that the hematite is probably derived from the permo carboniferous red beds of the canadian maritimes in the last 800 kyr sedimentation pattern changes on the blake bahama outer ridge were determined by the sediment delivery to the deep basin as well as circulation changes sediment delivery increased during glacials especially during the last 500 kyr and particularly since stage 6 a fundamental change in the thermohaline circulation occurred at about 500 ka corresponding to the end of the mid pleistocene transition period at the onset of the predominant 100 kyr climate cyclicity sedimentation related to wbuc had intensified at that time and had become more focused at depths below 3000 m changes in hematite content and sedimentation rate show a pulse of sediment via the st lawrence outlet at the pliocene pleistocene boundary suggesting that a likely change in the hydrography physiography of the laurentide ice sheet could have been involved in the climatic and ocean circulation changes at that time

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

jurassic evolution of the gulf of mexico salt basin we present a new hypothesis for the jurassic plate tectonic evolution of the gulf of mexico basin and discuss how this evolution influenced jurassic salt tectonics four interpretations some based on new data constrain the hypothesis first the limit of normal oceanic crust coincides with a landward dipping basement ramp near the seaward end of the salt basin which has been mapped on seismic data second the deep salt in the deep water gulf of mexico can be separated into provinces on the basis of position with respect to this ramp third paleodepths in the postsalt sequence indicate that salt filled the gulf of mexico salt basin to near sea level fourth seismic data show that postsalt sediments in the central louann and the yucatan salt basins exhibit large magnitudes of late jurassic salt detached extension not balanced by equivalent salt detached shortening in our hypothesis callovian salt was deposited in preexisting crustal depressions on hyperextended continental and transitional crust after salt deposition ended rifting continued for another 7 to 12 m y before sea floor spreading began during this phase of postsalt crustal stretching the salt and its overburden were extended by 100 to 250 km 62 155 mi depending on location sea floor spreading divided the northern gulf of mexico into two segments separated by the northwest trending brazos transform the eastern segment opened from east to west leaving the walker ridge salient in the center of the basin as the final area to break apart in some areas salt flowed seaward onto new oceanic crust first concordantly over the basement as a parautochthonous province then climbing up over stratigraphically younger strata as an allochthonous province

biogenic carbonate and ice rafted debris heinrich layer accumulation in deep sea sediments from a northeast atlantic piston core abstract biogenic carbonate mass accumulation rates show distinct quaternary glacial interglacial changes in a mid latitude northeast atlantic deep sea core during the last 208 kyr these were generally higher during interglacials averaging 2 2 g cm 2 kyr than during glacial periods with a maximum average of 1 2 g cm 2 kyr intervals containing high ice rafted debris have very low biogenic carbonate accumulation rates paleo primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gc m 2 yr than during glacials which average 49 gc m 2 yr maximum estimate short intervals with possibly reduced primary productivity correspond to heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the north atlantic we identified thirteen heinrich layers in isotopic stages 7 to 2 they have calendar ages of about 201 189 182 183 164 167 146 149 142 128 131 64 67 52 54 40 43 29 31 21 and 15 kyr these heinrich layers contain large amounts of ice rafted debris including detrital carbonate low amounts of coccoliths and planktic foraminifera mainly neogloboquadrina pachyderma sinistral the upper five heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera the virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs considering the limited use of other proxies such as organic carbon diatom and benthic foraminifera due to their very low content abundance in the sediments biogenic carbonate mass accumulation rates offer a workable paleo primary productivity proxy in open ocean sediments of the carbonate dominated northeast atlantic

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

prediction of deep reservoir quality using early diagenetic process models in the jurassic norphlet formation gulf of mexico we have developed process based models for early grain coats and their impact on deep reservoir quality in the jurassic eolian norphlet formation alabama with implications for exploration and development in other conventional and tight gas continental reservoirs the norphlet a major gas reservoir to depths of 21 800 ft 6645 m and temperatures of 419f 215c displays contrasting intervals of high and low reservoir quality within compositionally similar cross bedded eolian sands study results show that grain coats formed soon after deposition are responsible for differences in deep norphlet porosity of up to 20 and permeability up to 200 md three types of grain coats were identified in norphlet dune sands each formed in a different part of a shallow groundwater system and each with distinctive impact on deep reservoir quality diagenetic chlorite coats formed where dunes subsided into shallow hypersaline groundwater preserve good deep porosity to 20 and permeability to 200 md continuous tangential illitic coats formed in the vadose zone of stabilized dunes exposed to periodic fresh water influx preserve good deep porosity to 15 associated with poor permeability 1 md due to linked formation of later high temperature diagenetic illite discontinuous grain coats formed in active dunes where grains were abraded by eolian transport are associated at depth with tight zones of pervasive quartz cement low porosity 8 and low permeability 1 md these concepts plus data from 60 wells were used to derive bay wide predictive tight and porous zone isopachs that can be used for well placement geologic models and field development

wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison panfish j t and peterson f 1988 wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western united states a comparison in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 261 282 wind directions for middle pennsylvanian through jurassic time are predicted from global circulation models for the western united states these predictions are compared with paleowind directions interpreted from eofian sandstones of middle permsylvanian through jurassic age predicted regional wind directions correspond with at least three quarters of the paleowind data from the sandstones the rest of the data may indicate problems with correlation local effects of paleogeography on winds and lack of resolution of the circulation models the data and predictions suggest the following paleoclimatic developments through the time interval studied predominance of winter subtropical high pressure circulation in the late pennsylvanian predominance of summer subtropical high pressure circulation in the permian predominance of summer monsoonal circulation in the triassic and earliest jurassic and during the remainder of the jurassic influence of both summer subtropical and summer monsoonal circulation with the boundary between the two systems over the western united states this sequence of climatic changes is largely owing to paleogeographic changes which influenced the buildup and breakdown of the monsoonal circulation and possibly owing partly to a decrease in the global temperature gradient which might have lessened the influence of the subtropical high pressure circulation the atypical humidity of triassic time probably resulted from the monsoonal circulation created by the geography of pangaea this circulation is predicted to have been at a maximum in the triassic and was likely to have been powerful enough to draw moisture along the equator from the ocean to the west

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

relating eolian bounding surface geometries to the bed forms that generated them etjo formation cretaceous namibia the cretaceous etjo formation is a 200 m thick eolian and fluvial sandstone succession exposed in the huab basin of northwestern namibia eolian sedimentation was terminated abruptly by the emplacement of flood basalts of the etendeka igneous province across much of the basin at 132 1 ma the lavas drowned the dunes and in doing so preserved bed forms with heights and wavelengths of up to 100 m and 1 3 km respectively subsequent erosion has resulted in the exposure of these bed forms and provides a rare opportunity to accurately reconstruct the three dimensional geometry of an ancient eolian system and to relate bed form morphology to bounding surface geometries some bed forms lacked a single active slipface but instead were characterized by a dome form over which smaller transverse dunes migrated other bed forms were characterized by an active slipface and a stoss slope over which smaller superimposed bed forms migrated one bed form records a transitional evolution between these two end member types preserved bed sets exhibit a positive but stoss erosional angle of downwind bed form climb of 1 bed forms of the etjo formation provide an opportunity to directly relate bed set thickness to original bed form height via the angle of climb

why deposits of longitudinal dunes are rarely recognized in the geologic record dunes that are morphologically of linear type many of which are probably of longitudinal type in a morphodynamic sense are common in modern deserts but their deposits are rarely identified in aeolian sandstones one reason for non recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long term sand transport direction thereby depositing cross strata that have unimodal cross bed dip directions and consequently resemble deposits of transverse dunes dune parallel components of sand transport can be recognized in ancient aeolian sands by examining compound crossbedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along crest direction over the large dunes

application of simple shear model to the evolution of passive continental margins of the gulf of mexico basin the asymmetrical distribution of different crustal types under the gulf of mexico basin and sharp differences in the sedimentary record between the northern and southern parts of the gulf are the main arguments used to invoke the lithospheric simple shear model in interpreting the evolution of the basin9s conjugate passive margins in the framework of this model we interpret the northern and southern gulf margins as proximal and distal margins respectively

sediment source regions and paleotransport of the upper jurassic norphlet formation eastern gulf of mexico the upper jurassic norphlet formation is an eolian sandstone and important hydrocarbon reservoir that overlies the louann salt in the gulf of mexico gom because the sand was concentrated into dunes formed by late jurassic winds determining the source areas and paleotransport direction of the sand can improve predictions of the distribution of the dune facies around the gom paleo wind blown sediment transport into the proto gom was controlled by wind direction and magnitude and the extant topography of the basin and adjacent uplands analysis of the norphlet formation in the eastern gom shows that wadis and alluvial fans controlled by the location of highs were the primary route for introducing sediment of varied provenance into the eolian erg eolian transport directions interpreted from dip log analyses are south directed in southern alabama and west to northwest directed in western florida interpretations of regional two dimensional prestack depth migrated seismic data show that erosional incision of the middle ground arch occurred prior to and during the time of norphlet deposition this as well as preexisting lows in the basement topography may have facilitated basinward sand transport of sediment that fed the norphlet formation erg preserved in the deep water subsurface eastern gom

a model for the development of a carbonate mound population in the rockall trough based on deep towed sidescan sonar data a large carbonate mound population is identified on deep towed tobi towed ocean bottom instrument sidescan data along the eastern margin of the rockall trough west of ireland individual mounds are circular to elliptical in plan view varying from 50 to 850 m in width and up to about 200 m in height strong ne flowing contour currents at 800 m water depth are inferred from large scale sedimentary bedforms smaller mound arrays are spatially associated with slope parallel escarpments produced by mass wastage while around the largest mounds the sharp escarpments may have been smoothed by the vigorous contour currents current streamlining effects control the shape of the mounds which become more elliptical as their size increases thereby minimising the hydraulic drag force the frequency distribution of mound size follows a general power law which is determined by the growth rate of the framework building coral species and the rate at which they colonised the substrate initially bottom currents support mound growth until the mounds become so large that hydraulic drag forces retard their growth a model for the evolution of the population predicts that increased hydraulic drag forces on the larger mounds cause a sharp decrease in their number in agreement with the observations the model also allows an age structure for the population to be determined and correlations between the growth of the mound population and palaeoclimatic variations in the ne atlantic to be attempted

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

deep sea drilling project leg 77 southeastern gulf of mexico in january 1981 r v glomar challenger drilled five holes in the southeastern gulf of mexico to provide ground data for extensive seismic surveys and to document the pre tertiary history of the gulf holes 535 and 540 were drilled in a basinal terrane for maximum penetration of the cretaceous tertiary sequence rhythmic alternations of light bioturbated and dark laminated carbonaceous limestone represent the early cretaceous interval some of the dark layers are rich but immature oil source rocks the limestones resemble the blake bahama formation in the north atlantic but their stratigraphic age overlaps in part with the hatteras shale late cretaceous rocks are almost totally missing in the basin sites and the cenozoic section consists of chalk and marly carbonate ooze holes 536 537 and 538a were drilled on high standing fault blocks hole 537 recovered phyllite that records 40 ar 39 ar plateau ages of about 500 m y and is overlain by an early cretaceous deepening sequence of alluvial to littoral elastics and oolitic oncolitic limestones capped by a thin sequence of cretaceous and cenozoic pelagics in hole 538a basement consists of mylonitic gneiss and amphibolite intruded by several generations of diabase dikes that is transitional crust 40 ar 39 ar dates of hornblendes and biotite from the regional metamorphic rocks suggest a 500 m y pan african age with mild late paleozoic thermal overprint 40 ar 39 ar whole rock dates from the dikes suggest intrusions between 190 and 160 m y ago basement is covered by a thin layer of pelagic chalk followed by early cretaceous skeletal oolitic limestones and finally cretaceous tertiary pelagics the oolitic oncolitic limestones at both sites represent either parts of a shallow water carbonate platform or platform talus deposited in deep water hole 536 bottomed in shallow water dolomite jurassic or permian overlain by middle cretaceous skeletal limestones with shallow water biota and intercalations of pelagic chalk interpreted as cretaceous talus at the foot of the campeche bank cretaceous tertiary chalk and carbonate ooze cap the sequence among the most significant results of the leg are 1 recovery of transitional crust with early paleozoic pan african metamorphic rocks 2 recovery of early cretaceous deep water limestones with immature petroleum source beds 3 recovery of mid cretaceous platform talus resembling the reservoirs in the poza rica and probably some of the reforma fields of mexico and 4 discovery of a late cretaceous hiatus of 30 m y that corresponds approximately to the mid cretaceous unconformity recognized widely on seismic records in the gulf of mexico

desert stream sequences in the sinai peninsula abstract desert sedimentary sequences of late quaternary age mainly subrecent were studied in several stream segments of wadi el arish northern sinai egypt morphologically these stream systems can be divided into three types confined open and terminal floodplains the confined and open floodplain sequences consist of repeated flood originated sedimentation units each around 50 cm thick an idealized sequence begins with mud clasts or either sand or pebble bearing plane beds reflecting the upper flow regime during peak flow stage of the flood these are overlain by cross bedded sands and climbing ripples lower intensities of the flow result in sequences beginning with cross stratified sands cracked mud layers represent the final desiccation stage of the flood in comparison with th confined floodplain units the open up to thousands of meters wide floodplain units are thinner 20 50 cm the horizontal strata are less developed and the mud layers are thicker the terminal floodplain which in the modern examples is a flat a few kilometers wide is the area where the remaining flood energy dissipates and therefore the resultant sedimentation units axe very thin usually less than 20 cm and consist of either finely laminated massive mud or cross laminated fine sand the wadi systems studied are in close geographic relationship with eolian dune fields nevertheless the wadi sequences consist of waterlaid units only

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

catastrophic flooding of an aeolian dune field jurassic entrada and todilto formations ghost ranch new mexico usa surveyed outcrops of the middle jurassic entrada sandstone at ghost ranch new mexico show the unusual occurrence of preserved aeolian dune palaeotopography buried beneath subaqueous strata the preserved dune remnants have relief up to 35 m trend nnw and show internal scalloped cross strata dipping to the wsw with small sets occurring as both topsets and bottomsets outcrop data are best satisfied in computer models by 50 m high sinuous bedforms that migrated to the wsw while the sinuosity migrated alongcrest to the nnw superimposed small dunes occurred upon the stoss slope and at the basal lee of the main bedform where they migrated alongslope to the nnw remnant dune palaeotopography is buried by onlapping subaqueous largely structureless sandstones believed to be derived by mass wasting of the upper portions of the dunes and deposited as sediment gravity flows that infilled between the dunes preservation of dune palaeotopography beneath mass flow deposits with no evidence for gradually rising water argues that flooding of the entrada dune field was geologically instantaneous the thickness and lithology of the overlying todilto formation conform to slight remnant palaeotopography on the entrada surface the todilto is a laminated limestone and thinnest over remnant dune crestal areas but thickens and increases in gypsum content downslope until it abruptly yields to a gypsum mound positioned over a remnant interdune hollow the todilto laminations are interpreted as seasonal varves deposited below wave base in a density stratified water body the flooding event that gave rise to the controversial todilto water body occurred during entrada time with todilto deposition occurring within an already substantial water body

norphlet geology and 3 d geophysics fairway field mobile bay alabama the upper jurassic norphlet system in the mobile bay area has been the subject of considerable exploration intrigue during the last 20 years fairway field which came on production in december 1991 lies in the restricted access area of the main mobile bay shipping fairway leading to the city of mobile alabama and is comprised of state blocks 113 and 132

abstract mesozoic stratigraphy of near shelf edge deposits southern mississippi adjacent state and federal waters abstract onshore southern mississippi and adjacent state and federal waters were part of a region where basinward shelf edge migration occurred during the jurassic this migration provided a wide range of environments of deposition and did not become stable until the late cretaceous when more widespread environments of deposition were prevalent jurassic sediments attain a thickness of more than 6 000 ft and consist of evaporites clastics and carbonates jurassic sedimentary rocks are thickest in viosca knoll block 117 which represents the basinward facies of these rocks and correlations are difficult in the norphlet and smackover formations a thin norphlet clastic section is present in mobile block 991 and mississippi sound block 57 and extends this facies of the norphlet farther to the west offshore than previously thought in viosca knoll block 117 haynesville sediments are isolated by a gilmer aged ramp whereas in mississippi sound block 57 a clean white quartzose sandstone extends the presence of the frisco city formation into state waters 20 mi southwest of the wiggins arch onshore west of the wiggins arch the haynesville is open marine carbonates cretaceous sediments are 10 000 ft thick and consist of carbonates clastics and anhydrites lower cretaceous lithologies are less diverse than jurassic lithologies because of stabilization of the shelf edge and are more easily correlated from onshore to offshore with clastic hosston rodessa and eutaw formations interfingering with carbonates along the shelf edge the selma tuscaloosa washita fredericksburg paluxy and mooringsport formations all maintain consistent lithologies geographically figure 1 index map of mesozoic shelf edge deposits end of record last page 583

evolution of the philippine and japan seas from the clastic sediment record abstract mineralogical analyses of the heavy coarse silt fraction including microprobe identifications of certain clastic minerals and bulk chemical analyses of 186 sediment samples from dsdp sites 291 299 301 436 447 449 450 453 459 and 460 are compared with similar data for quaternary sediments on a profile across the pacific from central america to the far east as a result new details of the history of the philippine and japan seas suggest that the active marginal complex has a variety of states stages these states differ in terms of 1 the number of associated echelons i e parts of the complex each consisting of a subduction zone island arc and back arc basin situated one behind the other and 2 their orientations changes in state are caused by blocking i e hindering the subduction continental as well as oceanic lithosphere is involved in the system the island arc lithosphere which is more simatic than continental lithosphere and more sialic than oceanic lithosphere is a final product of the development of the marginal complex irrespective of whether the parent was continental or oceanic lithosphere

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

evolution of the destin dome offshore florida north eastern gulf of mexico abstract structural and stratigraphic relationships indicated by seismic reflection data suggest that uplift of the destin dome anticline resulted mainly from salt movement during late cretaceous to early cenozoic time a thick succession of lower cretaceous sediment was deposited in the central part of the basin seaward of the present day destin dome sediment loading squeezed the salt both updip onto the shelf and downdip into the basin a step in the pre salt basement limited movement of salt and controlled the location of the dome vertical movement of salt was accommodated by extensional faulting during the early cenozoic sediment touchdown onto the pre salt basement formed a salt weld between the anticline and the de soto canyon diapir field cut off the supply of salt and stopped growth of the structure the minimum accumulation thickness of the mother salt is estimated to be 760 m and the original volume of salt deposited at the present day location of the destin dome anticline on the florida shelf is estimated to be 1000 km3 the volume of salt in place today is in excess of 2300 km3

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

review of late jurassic depositional systems and potential hydrocarbon plays northern gulf of mexico basin abstract post salt upper jurassic siliciclastic and carbonate rocks in the east texas north louisiana mississippi region record the early post rift evolution of the interior zone rift basins of the northern gulf of mexico basin four major river systems were fixed in space but variable in supply rate they carried sand and mud in from the northwest ancestral red river the north ancestral ouachita river the northeast ancestral mississippi river and the east ancestral alabama river shoal water carbonate deposits formed when siliciclastic inputs were low and shallow water high energy conditions prevailed usually in association with basement highs salt swells and abandoned deltaic shelf margins smackover shoal water carbonates formed within an extensive carbonate ramp from south central arkansas to central texas and were influenced by initial salt movement subsequent haynesville age gilmer carbonate shoals in texas rimmed rift related high blocks as well as highs formed by early salt movement siliciclastic sedimentation progressively dominated east of shreveport and submarine fans developed in association with a lowstand episode during early cotton valley time a major southeastward advance of the ancestral red river delta formed the taylor and bossier sand series while to the east lower terryville shoreline sands began to prograde southward in front of an expanding lagoon during late cotton valley time continued clastic sedimentation formed wave dominated deltas in texas and upper terryville strike fed sandstones in north louisiana at the close of cotton valley deposition in the earliest cretaceous regional transgression allowed knowles carbonates to colonize the abandoned shelf edge and form a thick shelf edge reef complex on its seaward slope the significant calvin lowstand wedge of sandstones was deposited offshore of this edge in louisiana during a subsequent major sea level fall and was then covered by winn carbonates deposited during the subsequent sea level rise high potential exploration plays remain in upper jurassic strata smackover and buckner gilmer shoals have produced over 10 trillion cubic feet of gas tcfg and 750 million barrels of oil mmbo in east texas and north louisiana but large segments of the complex atolls along the sabine uplift have not been defined complex shoals may rim old rift related highs such as the sabine and wiggins highs the gilmer cotton valley lime pinnacle reefs of the robertson leon trend may develop in one form or another over a broad swath of east central texas into westernmost louisiana haynesville age submarine fans may extend eastward into mississippi updip cotton valley is an established 10 tcf tight gas sandstone play in texas and louisiana but its basinward extensions have high untapped potential significant high quality upper cotton valley production similar to the north louisiana blanket sands may still be found in central mississippi the earliest cretaceous knowles calvin winn margin is poorly tested calvin like sandstones of the lowstand wedge should occur in east central texas and in southwestern mississippi

basin architecture salt tectonics and upper jurassic structural styles desoto canyon salt basin northeastern gulf of mexico despite awareness of the importance of continental extension during rifting there are few quantitative studies that show the influence of crustal extension on basin architecture the distribution of salt and late jurassic sedimentation in the desoto canyon salt basin northeastern gulf of mexico application of simplified isostatic principles using a lithospheric buoyancy model allow quantification of total tectonic subsidence crust thickness crustal extension and crust type interpretation of over 4800 km of migrated multifold seismic reflection profiles and well data integrated with computed isostatic relations provide the basis to characterize middle jurassic callovian age salt halokinetic processes and to describe the structural development of overlying upper jurassic strata an average crustal thickness of 25 km and crustal extension s values between 1 4 and 1 8 suggest the sedimentary succession is underlain by moderately stretched and attenuated continental crust the widespread distribution and geometry of dipping subsalt reflectors particularly in the shelfal areas provide evidence for a late triassic early jurassic phase of rifting prior to deposition of middle jurassic salt the distribution of autochthonous salt and the overlying upper jurassic sediments reflect the presalt structural imprint and suggest that the basic architecture of the basin was established by the middle jurassic following significant attenuation of the crust although deposition occurred in a slowly subsiding stable marginal setting salt movement and associated growth faulting are the most significant tectonic elements affecting the stratigraphic and structural development of the overlying strata faults related to growth of salt structures root at the base of salt in what appears to be a common detachment or decollement for salt movement the original distribution of salt is widespread and sheetlike with an estimated minimum thickness of 760 m progressive basinward subsidence of the margin and differential sediment loading by the overburden are the primary mechanisms initiating mobilization of salt and subsequent deformation of sediments during the late jurassic and from the late cretaceous through the early cenozoic

pennsylvanian to jurassic eolian transportation systems in the western united states peterson f 1988 pennsylvanian to jurassic eolian transportation systems in the western united states in g kocurek editor late paleozoic and mesozoic eolian deposits of the western interior of the united states sediment geol 56 207 260 the direction of sediment transport in eolian sandstones of permsylvanian to jurassic age was interpreted from crossbedding resultants vector means obtained from studies of eolian rocks in the western u s supplemented by data from the few eolian units of eastern north america these were compiled from the published or unpublished theses hterature from unpublished fidd data contributed by colleagues or from measurements made for this study in addition new paleogeographic maps were compiled to evaluate the influence of geographic features on the atmospheric circulation patterns that are inferred from the crossbedding studies regionally the crossbedding indicates northeasterly northerly or northwesterly winds present coordinates from pennsylvanian through most of middle jurassic time a rather abrupt change in wind directions occurred in late middle jurassic time late part of the cauovian age when westerly wind patterns developed by the late jurassic the winds shifted to southwesterly calculations of the consistency factor vector mean strength made from region wide analyses of the resultants indicate fairly unidirectional winds from the permsylvanian through the early jurassic middle jurassic circulation was more varied judging from crossbedding studies in the lower part of the entrada sandstone crossbedding in upper jurassic eolian rocks of wyoming and south dakota yielded a random pattern but upper jurassic rocks farther south on the colorado plateau and adjoining areas show a return to a fairly unidirectional pattern comparing the resultants with their reconstructed paleogeographic setting shows surprisingly little influence of major geographic features on overall circulation patterns however the greatest amount of local variation occurred at or near highly indented shorelines where the temperature contrast between land and water produces local wind currents that may vary appreciably from regional circulation patterns although they do not cause noticeable horizontal deflections in wind patterns small and low topographic highs appear to be able to promote the development of a dune field if a source of sand is available and if streams do not enter the growing dune field

on the origin and pathway of the saline inflow to the nordic seas insights from models the behaviours of three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are investigated in order to elucidate the routes and mechanisms by which saline water masses of southern origin provide inflows to the nordic seas an existing hypothesis is that mediterranean overflow water mow is carried polewards in an eastern boundary undercurrent and provides a deep source for these inflows this study however provides an alternative view that the inflows are derived from shallow sources and are comprised of water masses of western origin carried by branches of the north atlantic current nac and also more saline eastern north atlantic water enaw transported northwards from the bay of biscay region via a shelf edge current sec flowing around the continental margins in two of the models the mow flows northwards but reaches only as far as the porcupine bank 53 n in third model the mow also invades the rockall trough extending to 60 n however none of the models allows the mow to flow northwards into the nordic seas instead they all support the hyporthesis of there being shallow pathways and that the saline inflows to the nordic seas result from nac derived and enaw water masses which meet and partially mix in the rockall trough volume and salinity transports into the southern rockall trough via the sec are in the various models between 25 and 100 of those imported by the nac and are also a similarly significant proportion 20 75 of the transports into the nordic seas moreover the highest salinities are carried northwards by the sec these being between 0 13 and 0 19 psu more saline at the southern entrance to the trough than those in the nac derived waters this reveals for the first time the importance of the sec in carrying saline water masses through the rockall trough and into the nordic seas furthermore the high salinities found on density surfaces appropriate to the mow in the nordic seas are shown to result from the wintertime mixing of the saline near surface waters advected northwards by the sec nac system throughout we have attempted to demonstrate the extent to which the models agree or disagree with interpretations derived from observations so that the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

mass and hyperconcentrated flow deposits record dune damming and catastrophic breakthrough of ephemeral rivers skeleton coast erg namibia channel shaped deposits of well sorted sand with only 2 4 fine grained material being either massive and structureless or upward fining with basal lag are found interbedded with aeolian sand in the skeleton coast erg namibia detailed analyses of the channel shaped deposits suggest that they are formed as hyperconcentrated flows within the erg grain size analysis and whole rock geochemical modeling revealed that some of the fluvial sediments contain up to 70 aeolian sand interpreted as a result of dune collapse into the fluvial system in certain cases this instantaneous supply of sand resulted in generation of sandy mass flows with laminar flow behaviour the presence of smectite as dominant clay mineral proved to be of crucial importance in formation of mass flow deposits these mass flows had no erosional capacity and drape the palaeotopography they are comparable to those generated by catastrophic collapse of dunes described in the literature this paper suggests that all these deposits should be termed intra erg mass flows as several of them carry little if any debris based on their origin intra erg mass flows can be divided into two groups

sedimentation and climate induced sediments on feni ridge northeast atlantic ocean abstract feni ridge has been studied in detail in the area between 54 and 56 n and 12 and 16 w by using high resolution profiling water column sampling with transmissometer and ctd and by piston and box core sampling the crest of feni ridge is absent in the north of the study area but on passing towards the south it begins to take shape and to increase in height its distance from the rockall slope also increases towards the south on the lower southeastern flank a secondary ridge crest has locally developed and sediment waves along the flanks have amplitudes of up to 45 m the highest and steepest waves are found in the south the waves in the north being somewhat lower bottom nepheloid layers of 175 m near the foot of rockall plateau and 125 m near the crest are attributed to a norwegian sea overflow water current with a core at 2100 m bottom nepheloid layers of 75 100 m on the lower flanks of the ridge are thought to have been caused by northeast atlantic deep water piston cores reflect alternations of glacial and interglacial periods interglacials have a high carbonate and corg content a positive eu anomaly and negative ce anomaly and a low rb la ratio they are dominated by a subpolar and transitional foraminiferal assemblage glacials show a low carbonate and corg content a reduced eu anomaly and a high rb la ratio suggesting increasingly continental sediment sources these deposits are dominated by a polar planktonic foraminiferal assemblage characterized by n pachyderma s and g quinqueloba sedimentation rates reflect differential deposition at crestal station na 87 25 rates are 17 1 cm k y for stage 1 14 6 cm k y for stage 2 3 4 cm k y for stage 3 and 5 4 cm k y for stage 4 stage 5a e has a mean sedimentation rate of 6 1 cm k y over the last 125 k y the development of feni ridge has taken place under a relatively low energy current regime

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

the facies distribution of carbonate sediments on porcupine bank northeast atlantic porcupine bank 51 54 n 12 15 w approximately 10 000 km2 in area and 150 500 m deep is effectively removed from present day terrigenous sedimentation by the broad irish shelf to the east and deep water to the north west and south water temperatures range from 10 to 14 5 c carbonate sediments presently accumulate on the bank mixing with relict quartz sands and lithic pebbles cobbles and boulders of glacial origin traction current structures are absent but biogenic hollows pits mounds and trails are prevalent the lithofacies have a crudely concentric zonation with pelagic foraminiferal oozes in the deepest waters 500 m passing to foraminiferal pelagic and benthic glauconitic quartz sands over the bulk of the bank 500 200 m where scattered patches of lophelia pertusa coral branches are found which in turn pass into a narrow zone associated with the lithic boulder field at the bank crest 500 m pelagic foraminiferans 500 200 m benthic foraminiferans plus lophelia coral patches 200 100 m bivalve echinoderm 100 50 m bryozoan bivalve gastropod serpulid 50 m calcareous red algae bivalve gastropod barnacle

two modes for dune orientation earth s sand seas dune fields experience winds that blow with different strengths and from different directions in line with the seasons in response dune fields show a rich variety of shapes from crescentic barchans to star and linear dunes these dunes commonly exhibit complex and compound patterns with a range of length scales and various orientations which up to now have remained difficult to relate to wind cycles here we develop a model for dune orientation that explains the coexistence of bedforms with different alignments in multidirectional wind regimes this model derives from subaqueous experiments which show that a single bidirectional flow regime can lead to two different dune orientations depending on sediment availability i e the erodibility of the bed sediment availability selects the overriding mechanism for the formation of dunes increasing in height from the destabilization of a sand bed with no restriction in sediment availability or elongating in a finger on a non erodible surface from a localized sand source these mechanisms drive the dune orientation therefore dune alignment maximizes dune orthogonality to sand fluxes in the bed instability mode while dunes are aligned with the mean sand transport direction in the fingering mode applied to earth s deserts the model quantitatively predicts the orientation of rectilinear dunes and their superimposed patterns this field study suggests that many linear dunes on earth elongate from sources and are simply aligned with the mean sand transport direction

norphlet formation upper jurassic of southwestern and offshore alabama environments of deposition and petroleum geology upper jurassic norphlet sediments in southwestern and offshore alabama accumulated under arid climatic conditions the appalachian mountains of the eastern united states extended into southwestern alabama to provide a barrier for air and water circulation during the deposition of the norphlet formation these mountains produced topographic conditions that contributed to the arid climate and they affected sedimentation norphlet paleogeography in southwestern alabama was dominated by a broad desert plain rimmed to the north and east by the appalachians and to the south by a developing shallow sea the desert plain extended westward into eastern and central mississippi norphlet sedimentation initiated as a result of basin subsidence accompanied by erosion of the southern appalachians norphlet conglomerates were deposited in coalescing alluvial fans in proximity to an appalachian source the conglomeratic sandstones grade downdip into red beds that accumulated in distal portions of alluvial fan and wadi systems quartz rich sandstones were deposited as dune and interdune sediments on a broad desert plain the principal source of the sand was updip alluvial fan and plain and wadi deposits wadi and playa lake sediments also accumulated in the interdune areas a marine transgression was initiated during the late phase of deposition of the norphlet formation resulting in the reworking of previously deposited norphlet sediments norphlet hydrocarbon potential in southwestern and offshore alabama is excellent six oil and gas fields already have been established petroleum traps discovered to date are primarily structural traps involving salt anticlines faulted salt anticlines and extensional fault traps associated with salt movement reservoir rocks consist primarily of quartz rich sandstones that are eolian wadi and marine in origin porosity is principally secondary dissolution with some intergranular porosity smackover algal carbonate mudstones were probably the source for the norphlet hydrocarbons jurassic oil generation and migration probably were initiated in the early cretaceous

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

a record of fluctuating bottom currents on the slopes west of the porcupine bank offshore ireland implications for late quaternary climate forcing abstract both local and regional controls on slope sedimentation west of porcupine bank are assessed using an array of 25 gravity cores integrated with shallow seismic tobi side scan and high resolution bathymetry data the cores were retrieved from an area of smooth distally steepened slope between 52 and 53 n in water depths of 950 to 2750 m the slope here is unmodified by gravity failures and is swept by bottom currents that flow from s to n along the margin the cores reveal a coherent shallow stratigraphy that can be traced along and between transects at upper mid and lower slope levels ams 14 c dating oxygen isotopes and carbonate profiles suggest the cored record could extend as far back as 500 ka in the longest cores with most cores providing details of the slope response to the last interglacial last glacial and holocene forcing the facies indicate deposition was dominated by a combination of bottom currents ice rafting and hemipelagic settling with carbonate prone deposits during interglacials and siliciclastic deposits during glacials inferred contourites imply that strong currents operated during interglacials with weaker current reworking during glacial conditions a pair of erosion surfaces record significant mid and upper slope scouring during marine isotope stage mis 3 and in the early holocene the lateral facies distribution implies stronger currents at shallower levels on the slope although there is evidence that the core of the current migrated up and down the slope and that sand might locally have spilt down slope the bathymetry influenced both the wider geometry of the condensed contourite sheet and the local thickness and facies variation across the slope a significant result of the study is the identification of a pair of thin sand mud contourite couplets that record enhanced bottom current reworking corresponding to periods of interstadial warming during mis 3 the couplets can be correlated to the terrestrial records onshore ireland and imply that the ne atlantic margin oceanographic and onshore climate records are strongly coupled at interstadial level

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

diagenesis of eolian and fluvial feldspathic sandstones norphlet formation upper jurassic rankin county mississippi and mobile county alabama norphlet sandstones in seven cores from mississippi and alabama are arkoses and subarkoses deposited in eolian dune interdune and fluvial environments similar to the deeply buried 5 km tertiary feldspathic sandstones of the gulf basin all detrital plagioclase that survived dissolution has been albitized however some k feldspar instead of dissolving was stabilized by k rich brines derived from adjacent evaporites this k feldspar then developed extensive overgrowths fluvial red sandstone lost all initial porosity by the introduction of preburial pedogenic calcite and compaction initial porosity of eolian sands was reduced by compaction to an average of 29 and later by cementation by quartz carbonates anhydrite halite k feldspar and illite quartz and anhydrite cements precipitated between 90 and 100 c approximately 2 3 km deep carbonates and halite cements formed below 120 c 3 km and late stage illite cement formed between 130 and 150 c 4 5 km deep cements are patchy and some especially quartz and anhydrite are texture selective being more abundant in coarser laminae secondary porosity which makes up approximately half the porosity in thin sections formed by dissolution of detrital grains f ldspar rock fragments and cements anhydrite carbonate halite reservoir bitumen records an early phase of oil entrapment reservoir quality is influenced by the abundance of reservoir bitumen and thread like illite both of which bridge pores the radiometric age of illite approximately 55 ma probably reflects its cementation age but may also record a later recrystallization event depleted oxygen and carbon isotopic values for ferroan dolomite reflect the progressive replacement of earlier more enriched carbonate phases by higher temperature phases isotopic data suggest that during the first 30 to 40 m y of burial subsurface diagenesis of the norphlet formation was dominated by deep circulating hot meteoric water this phenomenon may be characteristic of the early diagene ic history of rifted basins

geologic framework of norphlet and pre norphlet strata of the onshore and offshore eastern gulf of mexico area abstract hydrocarbon accumulations have been discovered in the jurassic norphlet formation in the onshore and offshore eastern gulf of mexico area an understanding of the regional geologic framework of the norphlet and pre norphlet stratigraphic succession in the study area is crucial to successful exploration for and development of norphlet hydrocarbon reservoirs in the eastern gulf region these strata include jurassic sedimentary rocks and pre jurassic sedimentary and crystalline rocks of these strata only the norphlet formation has produced economic quantities of hydrocarbons from reservoirs which include eolian dune interdune wadi and marine sandstones however the pre norphlet geology and paleotopography of the area controlled to a large degree norphlet depositional patterns and subsequent structural development especially important were the locations of pre jurassic paleohighs and the distribution and thickness patterns of the underlying jurassic louann salt norphlet hydrocarbon traps are generally associated with structures that have resulted from halokinesis of the louann traps include salt anticlines faulted salt anticlines and extensional faults associated with salt movement in addition to these salt related structural traps traps resulting from pre salt basement paleotopography may exist in the study area these traps might include norphlet structural highs associated with preexisting basement highs and norphlet stratigraphic terminations along the flanks of basement highs where norphlet reservoir facies are present the key factor controlling hydrocarbon accumulation potential is structural setting in the mississippi alabama florida mafla region that is underlain by the norphlet formation four structural settings have been identified types a and b structural settings are characterized by norphlet sediments overlying basement or thin salt no norphlet fields have been established in these settings types c and d structural settings are characterized by structures related to movement of thick louann salt all norphlet fields established in the mafla region occur in these settings four geographic regions have been defined in the study area for the purpose of characterizing norphlet petroleum potential region 1 has excellent potential for future norphlet discoveries region 2 has low to moderate potential and regions 3 and 4 have very little to no potential

the response of the water table in coastal aeolian systems to changes in sea level abstract the water table in some aeolian systems is a control on the type and rate of accumulation and defines the depth to which deflation will occur in the formation of regional bounding surfaces at the basinal scale over time the elevation of the water table may be a function of climate tectonism and or sea level the latter invokes the hypothesis that the water table underlying an arid coastal sand sea without significant recharge adjusts to changes in sea level for tens to hundreds of kilometers inland the simplest physical and mathematical model for this hypothesis states that the water table re equilibrates as an inland directed diffusion wave to each increment of change in sea level model simulations incorporating a range of hydraulic parameters and periods of sea level cycles demonstrate scenarios ranging from one in which the continental water table is essentially unaffected by sea level to one in which the water table exactly mimics the sea level curve using a realistic set of mid range parameters the model produces a suite of water table curves that evolve from the coast to inland because of a diminishing amplitude for all cycles a loss of more minor cycles and a time lag the resulting stratigraphic record from the coast to more inland positions shows a diminishing number of recorded events a thinning of the section removal of previously preserved strata during lowstands and the appearance of new stratigraphic units far inland most of these characteristics are compatible with those of the jurassic page sandstone in regional cross sections in northern arizona and southern utah but are difficult to distinguish from the effects of tectonism

structural framework and fault analysis in the east central gulf of mexico shelf implications for offshore co2 storage abstract a vast co2 storage resource exists offshore in cretaceous through neogene sandstone in the desoto canyon salt basin in the east central gulf of mexico continental shelf understanding the structural styles the likelihood of reactivation and seal properties of the faults in this area is essential for selecting safe carbon storage sites and minimizing the risk of injected co2 migrating beyond the confines of the storage complex the desoto canyon salt basin has variable structural styles in the basin with different insights for co2 storage the mobile viosca knoll shelf contains stable shelf and a large four way structural closure where provide favorable storage opportunities the destin dome region contains three groups of peripheral faults of the destin fault system faults that strike along shmax dip at 60 and steeply dipping faults are predicted to have elevated risk of slip and dilation the w e striking fault group has an overall higher slip and dilation tendency than the other two groups under the same injection conditions fault seal analysis shows that elevated risk along faults occurs at sandstone sandstone juxtaposition zones and zones with high fault throw and low sgr values storage plans should avoid the faults with elevated risk to ensure that the injectate will not flow into or pressurize the fault zones ideal injection sites within the destin fault system in the destin dome region are in hanging wall rollovers that contain low fault throw and shale sandstone juxtapositions future research should focus on geomechanical pressure and flow simulation of the potential reservoirs and associated seals in the area of the peripheral faults

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope