integrated loessite paleokarst depositional system early pennsylvanian molas formation paradox basin southwestern colorado u s a abstract mississippian paleokarst served as a dust trap for the oldest known paleozoic loessite in north america the early pennsylvanian molas formation consists of loessite facies sorted angular coarse grained quartz siltstone infiltration facies loess redeposited as cave sediments within paleokarst features of the underlying mississippian leadville limestone colluvium facies loess infiltrated into colluvium surrounding paleokarst towers and fluvial facies siltstone rich fluvial channel and floodplain deposits with paleosols the depositional system evolved from an initial phase of infiltration and colluvium facies that were spatially and temporally related to the paleokarst surface to loessite facies that mantled the paleotopography and to fluvial facies that were intercalated with marine deltaic rocks of the overlying pennsylvanian hermosa formation this sequence is interpreted as a response to the modification of the dust trapping ability of the paleokarst surface loess was initially eroded from the surface transported and redeposited in the subsurface by the karst paleohydrologic system maintaining the dust trapping ability of the paleotopographic surface later the paleotopographic surface was buried when loess accumulation rates exceeded the transport capacity of the karst paleohydrologic system these changes could have occurred because of 1 increased dust input rates in western pangaea 2 rising base levels and or 3 porosity loss due to deposition within paleokarst passageways

mud capped dredge pits an experiment of opportunity for characterizing cohesive sediment transport and slope stability in the northern gulf of mexico abstract mud capped dredge pits mcdps defined as sand borrow sites from paleo river channels with cohesive sediment capped walls are used for northern gulf of mexico ngom coastal restoration projects due to lower cost than more distal restoration resources mcdp evolution including infilling and pit wall slope stability is poorly understood in relation to sandy borrow areas we present and interpret bathymetric data from sandy point mcdp which was constructed in 2012 about 20 km northwest of southwest pass the most active mississippi river distributary in water depths of 11 m repeat bathymetric surveys show the pit is infilling 54 cm or volumetrically 200 000 m3 per year which is on the same order as seasonal scale and an order of magnitude higher than the decadal scale vertical accretion rates observed seaward of southwest pass this infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate sediment starved settings mcdp infill is volumetrically dominated by far field here defined as river plume or shelf bed resuspension sediment with only 9 of pit infill from pit wall failure geomorphic comparison of sandy point mcdp walls with southwest pass mudflow gully walls shows that the mcdp is oversteepened relative to natural depression features in this setting the convergence of mcdp and mudflow gully gradients towards a common value 4 5 may represent an angle of repose in lieu of decadal scale forcings findings from this experiment of opportunity show that mcdps 1 are effective sediment traps 2 have steep but relatively laterally stable walls 3 do not represent significant risk to infrastructure in a 3 year time scale and 4 are predicted to infill within about 2 decades provided a proximal sediment source exists

a double vortex along the california coast a double vortex was observed at the entrance to the santa barbara channel california with sequential ir imagery from the noaa 7 satellite during may 1984 while the wind blew strongly to the southeast the double vortex moved westward with a velocity greater than that estimated for the mutual interaction of two idealized vortices the effect of the double vortex on incoming pacific swell is calculated by numerical integration of the ray equations this calculation shows areas of focusing of the rays near the entrance to the channel which suggests elevated wave energy there with reduced wave energy nearby the pattern of wave refraction by mesoscale features such as a double vortex can help detect them and estimate their velocity distribution from remotely sensed surface wave imagery the similarities and differences between refraction patterns produced by double vortices and by eddies is outlined the double vortex and its generation by an episodic or tidal flow is investigated using kashiwai s 1984 approach an example of the related generation of a single vortex in the alboran sea by tidal flow in the strait of gibraltar is briefly discussed

the dynamics of the mississippi river plume impact of topography wind and offshore forcing on the fate of plume waters 1 high resolution numerical simulations of the northern gulf of mexico region using the hybrid coordinate ocean model hycom were employed to investigate the dynamical processes controlling the fate of the mississippi river plume in particular the conditions that favor cross marginal transport the study focuses on the effects of topography wind driven and eddy driven circulation on the offshore removal of plume waters a realistically forced simulation nested in a data assimilative regional gulf of mexico hycom model reveals that the offshore removal is a frequent plume pathway eastward wind driven currents promote large freshwater transport toward the shelf break and the desoto canyon where eddies with diameters ranging from 50 to 130 km interact with the buoyant plume and effectively entrain the riverine waters our estimates show that the offshore removal by eddies can be as large as the wind driven shelf transport the proximity of eddies to the shelf break is a sufficient condition for offshore removal and shelf to offshore interaction is facilitated by the steep bottom topography near the delta strong eddy plume interactions were observed when the loop current system impinged against the shelf break causing the formation of coherent narrow low salinity bands that extended toward the gulf interior the offshore pathways depend on the position of the eddies near the shelf edge their life span and the formation of eddy pairs that generate coherent cross shelf flows this study elucidates the dynamics that initiate a unique cross marginal removal mechanism of riverine low salinity nutrient rich waters allowing their export along connectivity pathways induced by a large scale current system

multiple dipole eddies in the alaska coastal current detected with landsat thematic mapper data seventeen dipole eddies including five large well formed ones three second generation eddies and two double eddies were observed in the alaska coastal current near kayak island in one single scene of the landsat thematic mapper tm on april 22 1985 the digital landsat tm satellite data were computer analyzed to extract details in the near coastal circulation in the northern gulf of alaska enhancement techniques were applied to the visible and thermal ir bands the features are evident only in the visible bands because of the ability of these bands to detect the distribution of sediments in the near surface these eddies did not have a significant thermal signature the sources of these sediments are the glacial streams found throughout the gulf of alaska coast eddies of this configuration and frequency have never been observed here previously however the oceanographic and meteorological conditions are typical for this time of year these eddies should be important to the cross shelf mixing processes in the alaska coastal current and are an indicator that the flow here can be unstable at certain times of the year

shelf currents near the mouth of the mississippi river abstract a year long current meter mooring near the mississippi river delta with meters at four levels suggests that minimal flow occurs around the front of the delta during normal conditions the observed currents exhibit variations on time scales of days to months much of this variability is attributed to an intrusion of the loop current into the northern gulf of mexico during the deployment

sea surface flow estimation from advanced very high resolution radiometer and coastal zone color scanner satellite imagery a verification study a refined technique for estimating surface currents from the displacement of features in sequential advanced very high resolution radiometer avhrr and coastal zone color scanner czcs images is presented it is used to calculate flow fields in two regions along the california coast and the results are compared to concurrent drifter drogue observations there is overall agreement to within approximately 6 cm s with somewhat better agreement at velocities less than 40 cm s the poorer performance of the technique at high velocities was due to difficulties in identifying and tracking features in areas of rapid flow the accuracy of the measurements is primarily affected by the analyst s precision in tracking each feature which in turn depends on how well the 2 to 6 km features preserve their identity from one image to the next a 12 to 24 hour interval yielded the best results in this study the directional component of the satellite derived flow field was representative of subsurface flow patterns down to at least 100 m although velocities obtained from avhrr infrared and czcs visible images may not always represent flow at the same depth the measurements were practically identical with the data used

satellite observations and modeling of meanders in the california current system off oregon and northern california abstract infrared satellite images from the west coasts of oregon and northern california are used to identify meander patterns in sea surface temperature which appear as large cold tongues extending offshore two relatively long series of images from 1982 and a few examples from 1980 and 1983 demonstrate the evolution of the cold tongues from an initial variety of scales 60 200 km to the fastest growing waves 110 130 km and then finally to tongues with longer wavelengths 400 km this is observed to occur over periods of about three months in summer and fall when the coastal circulation is composed of a southward surface current over a northward undercurrent the initial shorter scale features are believed to be excited by the interaction between the mean current and the coastal topography baroclinic instability associated with the vertical shear between the surface current and the undercurrent is found to be responsible for the growth of the features observed in the satellite imagery a nonlinear

influence of mississippi river induced circulation on the deepwater horizon oil spill transport 1 the 2010 deepwater horizon oil rig explosion caused 7 105 m3 of oil gushing from the northern gulf of mexico bottom the close proximity of the rig to the mississippi delta raised early questions from disaster managers about possible influence of river induced circulation on oil patch evolution in particular it was hypothesized that the high mississippi river mr discharge in may 2010 might have helped to initially keep oil from reaching coastal marshes we have explored this intriguing hypothesis quantifying similar and connecting patterns in the evolution of riverine and oil covered waters we used numerical simulations satellite and in situ data to show the unique influence of a large river plume on a surface oil patch resulting from a deep oil release the mr induced circulation modified by shelf and slope flows was found to substantially influence the near surface transport of oil the mr plume buoyancy driven effects on oil transport had different aspects east and west of the mississippi delta anticyclonic circulation within the upstream plume region east of the delta extending over the mississippi alabama florida shelf created a front that restrained onshore transport conversely the shoreward tendency within the downstream plume region west of the delta dominated by the westward buoyancy driven narrow coastal current guided oil transport along the louisiana texas shelf periods of low discharge reduced the dominance of buoyancy driven effects but an interval of sustained downwelling favorable winds combined with river induced stratification resulted in a strong westward current and surface oil patch extension along the louisiana coast

evolution and structure of a coastal squirt off the mississippi river delta northern gulf of mexico in early october 1992 satellite derived sea surface temperature data revealed a 200 km long and 10 to 30 km wide stream of cool water flowing toward the southwest from the mississippi river delta region satellite imagery and in situ measurements have enabled a detailed study of the squirt s kinematics and subsurface characteristics over a 2 week period in its early stages the squirt appeared as a narrow high speed 75 cm s jet of water which flowed westward over the mississippi canyon forcing a semi submersible drilling rig to suspend operations from october 2 to 4 after crossing back onto the shelf the squirt spread laterally yielding a mushroom shaped feature 75 km wide which consisted of counter rotating vortices northeasterly wind forcing averaging 10 15 m s and water level setup east of the delta appear to have been the primary mechanisms for evolution of the high velocity currents satellite and in situ measurements demonstrate that the dipole eddy was comprised of a cool low salinity low density water mass at least 26 m deep in the center and 16 m deep along its margins this event demonstrates that strong northeasterly winds over the northern gulf of mexico can initiate along shelf and off shelf flows of cooler coastal waters contributing significantly to seasonal cooling and freshening of the continental shelf and to shelf slope exchanges of water during this event approximately 100 km3 of inner shelf and river water was transported off the continental shelf a volume equivalent to 17 of the average annual discharge of the mississippi and atchafalaya rivers

sea surface motion over an anticyclonic eddy on the oyashio front abstract noaa 6 avhrr 11 m band satellite images for 20 and 21 may 1981 have been used with an interactive computer algorithm to calculate surface flow components from displacement of surface pattern features and elapsed time the results give estimates of speed and direction for motion along the oyashio front and over an anticyclonic eddy between the first and second oyashio intrusions speeds of 54 cm s were detected along the oyashio thermal ridge on the periphery of the eddy speeds in the order of 25 cm s were present while nearer the center motion at 14 cm s was indicated a composite picture of flow vectors overlayed on the image for 20 may infers streamline flow characteristics for the surface motion and shows surface isolation of the eddy from the tohoku area to the south

satellite observations of the circulation east of the mississippi delta cold air outbreak conditions abstract examination of 12 years of landsat multispectral scanner images shows a recurrent pattern of westward flow immediately south of the mississippi alabama barrier islands under northerly winds such flow patterns are also seen under similar conditions in imagery from the advanced very high resolution radiometer avhrr of the noaa series satellites the flow enters chandeleur sound between ship island and the northern end of the chandeleur islands it appears to be driven by northerly winds which force water south through the chandeleurbreton sound drawing water in from the shelf region south of the mississippi alabama barrier islands these observations on circulation can be simply explained assuming linear dynamics these two operational satellite systems are accumulating valuable records of coastal circulation patterns under clear sky conditions

the separation of the yucatan current from the campeche bank and the intrusion of the loop current into the gulf of mexico data collected in the eastern gulf of mexico during 1974 1975 and 1976 show that the penetration of the loop current into the gulf is strongly correlated with the location of the yucatan current on the campeche bank the loop does not penetrate far into the gulf when the yucatan current separates from the bank in the vicinity of the catoche tongue i e the eastern campeche bank deep loop penetrations are correlated with separations farther west on the bank the angle of the yucatan current at separation is also correlated with the location of separation i e smaller angles relative to due east are correlated with separations from farther east on the bank thus small angles at separation are correlated with shallow intrusions of the loop historical temperature data collected in the eastern gulf are reviewed and support these correlations simple conservation of potential vorticity considerations can explain the correlation between the angle at separation and the penetration of the loop

seasonal circulation on the western shelf of the gulf of mexico using a high resolution numerical model 1 the seasonal circulation on the western shelf of the gulf of mexico is studied using a high resolution numerical simulation historical hydrographic data sea level data and satellite images three regions are distinguished the tamaulipas veracruz tave shelf the louisiana texas latex shelf and the western campeche bank on the tave shelf there is a swift reversal of the along shelf current downcoast from september to march and upcoast from may to august when there is upwelling due to offshore ekman transport circulation on the western campeche bank is upcoast throughout the year the latex shelf has a cyclonic circulation except during summer months when the flow is eastward during spring summer the upcoast current on the tave shelf reaches the southern texas shelf where it encounters a downcoast coastal current favoring offshore transports in the fall winter the downcoast current reaches the southern bay of campeche where it meets an opposing along shelf current generating seasonal offshore transports during fall and winter cool low salinity water from the mississippi and atchafalaya rivers is advected westward along the latex shelf onto the tave shelf developing along shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break the main forcing over the western shelf of the gulf is the along coast wind stress component the existence of the cross shelf transports in the confluence regions is supported by chlorophyll a data up to 80 of the seasonal sea level variability is explained by the along shelf currents and the low frequency variability of the atmospheric sea level pressure

drifting buoy observations of a loop current anticyclonic eddy the loop current penetrated deep into the gulf of mexico in early 1989 after several eddy formation and reattachment cycles a southwestward propagating anticyclonic eddy was formed during the summer the loop current and subsequent eddy produced strong currents over widespread areas on the louisiana continental slope prompting a series of current measurement programs because of the lack of satellite infrared coverage in the gulf of mexico during the summer the trajectories of 53 argos tracked drifting buoys deployed in the gulf of mexico in 1989 were assembled to determine the synoptic history of the loop current and anticyclonic eddy during this event ten of the most critical summertime buoy trajectories are discussed here in addition the trajectories of three of the buoys simultaneously deployed at different radii in the eddy were chosen for analysis with a kinematic feature model the model assumes the looping buoy motion is generated by an elliptical orbit around a translating eddy center the buoy trajectories were used to determine time series of the feature model parameters including eddy center shape and circulation characteristics the time series results indicate that the eddy actually propagated in a series of short sprints separated by longer stalls during the sprints the eddy propagated as an elliptical but otherwise symmetric solid body during the stalls significant asymmetries developed the asymmetries are consistent with attachment to the loop current during the first stall the effects of topographic rossby wave dispersion during the second and the effects of planetary rossby wave dispersion during the third the results provide both a framework for the interpretation of in situ observations and a detailed evolutionary history for numerical modelers

seismically induced soft sediment deformation structures associated with the magallanes fagnano fault system isla grande de tierra del fuego argentina abstract in this paper evidence of paleoearthquake induced soft sediment deformation structures associated with the magallanes fagnano fault system in the isla grande de tierra del fuego southern argentina has been identified well preserved soft sediment deformation structures were found in a holocene sequence of the udaeta pond these structures were analyzed in terms of their geometrical characteristics deformation mechanism driving force system and possible trigger agent they were also grouped in different morphological types sand dykes convolute lamination load structures and faulted soft sediment deformation features udaeta a small pond in argentina tierra del fuego is considered a quaternary pull apart basin related to the magallanes fagnano fault system the recognition of these seismically induced features is an essential tool for paleoseismic studies since the three main urban centers in the tierra del fuego province of argentina ushuaia rio grande and tolhuin have undergone an explosive growth in recent years the results of this study will hopefully contribute to future analyses of the seismic risk of the region

genesis of a gulf of mexico ring as determined from kinematic analyses the kinematics of the loop current are studied using trajectories of drifters in the gulf of mexico during mid june through september 1985 one of the drifters was in the loop current proper while other drifters were in two recently shed loop current rings the drifter in the loop current showed strong anticyclonic motion during the study period this loop current anticyclone first began off the northwest coast of cuba it rapidly moved northward into the gulf of mexico as a ring pinched off from the loop current analysis of the loop current drifter motion showed that the anticyclone became an integral part of the loop current taking on many of the characteristics of the most recently shed ring the results of the analysis suggest a process by which loop current rings can be generated apparently this mechanism can cause the loop current to become reconfigured in 2 3 months for beginning the process of ring separation

the fate of terrigenous dissolved organic carbon in a river influenced ocean margin the mineralization of terrigenous dissolved organic carbon tdoc discharged by rivers can impact nutrient and trace metal cycling biological productivity net ecosystem metabolism and air sea co2 exchange in ocean margins however the extreme heterogeneity of river influenced ocean margins represents a major challenge for quantitative assessments of tdoc transformations and thereby obscures the role of tdoc in biogeochemical cycles here a lignin based optical proxy for tdoc and a shelf wide mass balance approach were used to quantitatively assess the fate of tdoc discharged from the mississippi atchafalaya river system m ars to the louisiana shelf the mass balance revealed that 40 of the tdoc discharged by the m ars during march 2009 2010 was mineralized to co2 on the louisiana shelf with two thirds of the mineralization taking place in the mixed layer a strong seasonality in tdoc mineralization was observed with mineralization rates severalfold higher during summer than during winter independent assessments of specific mineralization processes indicated biomineralization accounted for 94 of the tdoc mineralization on an annual basis and suggest that photochemical transformations of tdoc enhanced biomineralization by 50 in the mixed layer direct photomineralization accounted for a relatively small fraction 6 of the tdoc mineralization on an annual basis this quantitative assessment directly confirms that ocean margins are major sinks of the tdoc discharged by rivers and indicates that tdoc mineralization rates in the shelf mixed layer are sufficiently large to influence whether the louisiana shelf is a net sink or source of atmospheric co2

preservation and paleoclimatic significance of eolian dust in the ancestral rocky mountains province upper paleozoic pennsylvanian permian silty strata of the northern pedregosa basin southern ancestral rocky mountains province exhibit distinctive features that suggest origin of the silt as eolian dust prior to deposition in marine environments studies of mechanisms controlling modern eolian dust accumulation imply that combined marginal marine epeiric sea environments constitute an ideal sink for eolian dust accordingly pedregosa siltstones may reflect the prevalent mode of eolian dust preservation downwind from coeval ergs and significant volumes of eolian dust may be preserved within analogous epeiric strata because eolian dust reflects conditions of aridity and windiness it bears on paleoclimatic and paleogeographic reconstructions recent studies within several basins of the ancestral rocky mountains suggest an eolian derivation for many siltstones and thus corroborate inferences of increasing aridity and concomitant monsoonal conditions for western pangea further regional analysis may provide valuable insights for refining concepts of the zonal to monsoonal transition that accompanied pangean assembly

book review centennial field guide rocky mountain section beus s s editor 1988 the geological society of america boulder colorado u s a 489 pp price 43 50