sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

the trace fossil thalassinoides bacae in the cambrian zhangxia formation miaolingian series of north china abstract branched complex burrows with thick linings assigned to thalassinoides bacae are abundant in the cambrian zhangxia formation miaolingian series in southern north china these burrows occur in thinly layered micritic limestones which were formed in a restricted marine environment surrounded by oolitic shoals the macromorphological characteristics of the burrows observed in outcrop combined with microscopic burrow characteristics assessed using light microscopy and scanning electron microscopy were used to analyze the ethology of t bacae the complex geometric characters of horizontal branching tubes and subvertical shafts reflect t bacae is an agrichnical burrow system the horizontal tubes were used to cultivate microbes for food while the subvertical shafts provided openings to the sea floor organic material iron minerals and pyrite framboids just present in the margin of the fill indicate a special micro environment in the burrow system with a reducing environment and a high organic content and they may provide evidence for microbial garden the functions of the thick micrite lining may have included maintenancce of environmental conditions within the burrow and provision of suitable conditions for growing microbes dark colored irregular areas around the lining are identified as diagenetic halos the burrowers of t bacae built complex burrows system and thick lining for cultivating microbes to survive in a restricted marine environment that was oxygen poor and with low food availability reflecting adaptive behavioral evolution of the metazoan in the middle cambrian

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

effect of baselevel change on floodplain and fan sediment storage and ephemeral tributary channel morphology navarro river california managed baselevel lowering in tributaries that emerge from small canyons onto forested floodplains affects floodplain and fan sediment storage and small ephemeral tributary channel morphology in the navarro river basin mendocino country california usa numerous small tributaries drainage areas up to several square kilometres flow through culverts under highway 128 across the forested floodplain of the navarro river and one of its major tributaries the north fork excavation significantly deepened and widened these small tributaries upstream and downstream of culverts under the highway following the 1997 flood recurrence interval 12 years that inundated both the floodplain and the highway and culvert system the excavation lowered the local baselevel of the tributary systems within the floodplain this field study documents the effect of the lowered baselevel on floodplain and fan sediment storage and ephemeral tributary channel morphology excavation created defined channels in the floodplain where no channels previously existed additionally the excavation and baselevel change created steps or knickpoints that migrated headward and incised the upstream tributary channels tributary incision decreases the sediment storage potential of the fan and floodplain and reduces the residence time for storage of fine sediment a reduction in fine sediment residence time degrades downstream habitat for anadromous fish and other aquatic organisms in the navarro river large wood influences floodplain and small tributary channel morphology by forming steps and increases sediment residence time by trapping sediment in forested tributary fan floodplain systems although this field investigation is specific to the navarro river basin our findings linking culvert maintenance excavation to geomorphic processes may be extended to other roads on forested floodplains in the pacific northwest or other systems with roads on floodplains

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

tectonic history of northern alaska canadian arctic and spitsbergen regions since early cretaceous the correlation of interregional unconformities structures and magmatic activity suggests tectonic events in the arctic were controlled by the early cretaceous collision and combined interaction of the eurasian and north american plates in northeastern ussr the late mesozoic cenozoic accretion of exotic terranes in the north pacific and north atlantic arctic sea floor spreading contemporaneous with the accretion of exotic terranes in northeastern ussr and interior alaska the brooks range developed as a cordilleran mountain belt at the same time during the cretaceous between 125 and 85 ma the canada basin spread north of alaska about a pole of rotation located southeast of the mackenzie delta the alaskan plate was first a part of the northwestern nose of the north american plate when the canada basin spreading ceased the basin was severed by movement along the kaltag and associated strike slip faults and became a part of the northeasterly moving eurasian plate the kaltag fault system is inferred to extend from the western bering sea at the northern end of the kuril arc through alaska and along the outer margin of the arctic islands to the north of greenland it is postulated to have formed the transform boundary between the north american and eurasian plates with the alaskan plate bonded to the latter since the late cretaceous the late eocene change in the direction of pacific spreading terminated the subduction related laramide orogeny as well as the right lateral displacements of major cordilleran faults such as the tintina and denali faults changing eurasian plate movement may have caused most of the strong middle eocene right lateral displacement along the kaltag fault zone continuing displacement from the southwest caused the development of a late cenozoic foldbelt in coastal northeastern alaska herein named the romanzof disturbance coeval with balancing right lateral movement along the kaltag fault zone the huge undrilled marsh creek anticline is a part of this foldbelt seismic data show evidence of middle eocene compression followed by weak extension east of the kaltag fault zone in the beaufort sea the same activity is evident at the northeastern end of the north american plate at nares strait located between the arctic islands and greenland eocene fault movement along the kaltag nares strait and de geer separating greenland and spitsbergen transforms is regarded as complementary the presence of eocene thrust zones located on the western side of nares strait and in western spitsbergen suggests that northward movement of the greenland plate formed both the transforms and the thrust belts

spatial and temporal patterns of debris flow deposition in the oregon coast range usa patterns of debris flow occurrence were investigated in 125 headwater basins in the oregon coast range time since the previous debris flows was established using dendrochronology and recurrence interval estimates ranged from 98 to 357 years tributary basins with larger drainage areas had a greater abundance of potential landslide source areas and a greater frequency of scouring events compared to smaller basins the flux rate of material delivered to the confluence with a larger river influenced the development of small scale debris flow fans fans at the mouths of tributary basins with smaller drainage areas had a higher likelihood of being eroded by the mainstem river in the interval between debris flows compared to bigger basins that had larger more persistent fans valley floor width of the receiving channel also influenced fan development because it limited the space available to accommodate fan formation of 63 recent debris flows 52 delivered sediment and wood directly to the mainstem river 30 were deposited on an existing fan before reaching the mainstem and 18 were deposited within the confines of the tributary valley before reaching the confluence spatial variation in the location of past and present depositional surfaces indicated that sequential debris flow deposits did not consistently form in the same place instead of being spatially deterministic results of this study suggest that temporally variable and stochastic factors may be important for predicting the runout length of debris flows

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

the pennsylvanian permian transition in the low latitude carbonate record and the onset of major gondwanan glaciation abstract recent studies suggest a marked expansion of glacial ice across much of gondwana beginning in the earliest permian because expansion of glacial ice results in a lowering of sea level the imprint of ice expansion should be evident worldwide as significant exposure event hiatuses or other evidence for sea level drop at or near the pennsylvanian permian boundary this literature review investigates the signature of an early permian expansion of gondwanan ice through examination of stratigraphic records from eight carbonate dominated palaeotropical regions across pangaea tropical carbonate environments are used because most form in tectonically quiescent regions and are sensitive indicators of eustatic change correlation between stratigraphic sections is achieved using the most current biostratigraphic and absolute time constraints available all studied sections show a sequence boundary or basinward shift in facies at or near the pennsylvanian permian boundary supporting the hypothesis of a significant expansion of glacial ice and global eustatic lowstand beginning in the early permian by contrast a series of mid sakmarian kungurian transgression events in the palaeotropics are interpreted to reflect the asynchronous deglaciation of gondwana the stratigraphic framework developed herein will allow for better correlations among stratigraphic records from gondwana and northern pangaea which will ultimately improve the understanding of how carbonate systems respond to global icehouse conditions such as during the late palaeozoic

petrographic and sims pyrite sulfur isotope analyses of ediacaran chert nodules implications for microbial processes in pyrite rim formation silicification and exceptional fossil preservation abstract the lower ediacaran doushantuo formation in the yangtze gorges area contains exceptionally preserved microfossils including the earliest known animal resting eggs and embryos these fossils are preserved in cm sized chert nodules which typically have a microbial mat fragment in the center a silica cortex a pyrite rim and an outer rim of blocky calcite petrographic analysis indicates that the formation of the blocky calcite rim postdates that of the pyrite rim and silica cortex the pyrite rim grew centripetally during early diagenesis representing a reaction front that was determined by the dynamics between ambient fe2 and h2s the latter of which was derived from bacterial sulfate reduction bsr of mat fragment in nodule center the silica cortex was formed pervasively through replacement of carbonate sediments prior to compaction secondary ion mass spectroscopy sims sulfur isotopes of individual pyrite crystals 34spy sims in pyrite rims and matrices show highly positive values 15 2 39 8 the pyrite rims do not show an isotopic gradient between small crystals formed in outer rim during early diagenesis and large crystals formed in inner rim during subsequent overgrowth although rim pyrite in the same chert nodule has consistent 34spy sims values there are significant spatial and stratigraphic variations in 34spy sims values of both matrix and rim pyrite overall isotopic fractionation between pyrite and carbonate associated sulfate cas is small

depositional and diagenetic c s fe signatures in early paleozoic normal marine shales the degree of pyritisation dop of cambrian silurian normal marine shales is always less than 0 70 similar to that found previously for sediments of devonian to cretaceous ages this indicates that dop can be used as a paleoenvironmental indicator of deposition from normal marine i e oxygenated bottom waters throughout the phanerozoic record although the range in dop is similar significant variations in normal marine cs ratios can occur relatively low cs ratios 1 5 result from lower reactive iron contents which are also independent of organic carbon variations reactive iron contents and hence normal marine cs ratios are able to vary at a regional or basinal level

diagenetic cycling of nutrients in seafloor sediments and the carbonate silica balance in a paleozoic cool water carbonate system sverdrup basin canadian arctic archipelago abstract seafloor processes are often destructive of biogenic remains while at the same time promoting growth of authigenic minerals such as hematite fluorapatite glauconite and chalcedony middle to late permian sedimentary rocks in the sverdrup basin are cool water marine sandstones shales limestones and cherts rich in carbonate and siliceous biotic components the authigenic minerals hematite fluorapatite glauconite and chalcedony are abundant from the interactions of nutrient elements silica phosphorus and iron with carbonate and siliceous biotas in ramp environments of variable energy and sediment accumulation rate these authigenic phases represent in part faunas that are no longer preserved and should not be viewed simply as diagenetic products early middle permian siliciclastic rocks the assistance formation contain carbonate heterozoan biotas with widespread siderite and hematite and local void filling phosphate deposited under moderate sediment accumulation rates sponge spicules were dissolved unless encased in hematite or siderite and incorporated in silica cement in contrast more slowly deposited younger middle permian inboard cherty limestones the lower trold fiord formation underwent frequent physical and biological reworking resulting in dissolution of biogenic silica and precipitation of glauconite and carbonate fluorapatite sediment reworking also excavated and produced rounded glauconite and phosphate clasts much of the glauconite was then oxidized to hematite on the seafloor again unless encased in phosphate sponge spicules were dissolved and the silica precipitated as glauconite or chalcedony coeval deeper water phosphatic cherty limestones the degerbols formation do however contain sponge spiculites reduced sediment reworking led to retention of silica in pore fluids and slowed dissolution of sponge spicules resulting in local preservation of sponge spiculite facies late permian organic rich cherts the lindstrom formation with prolific siliceous sponges and a less plentiful carbonate biota accumulated relatively slowly sponge spicules were preserved and carbonate biota partially dissolved in these organic rich deposits implying that the biota had to be overwhelmingly dominated by siliceous components to overcome ambient silica undersaturation in pore fluids each succession has a distinct composition depending upon the rate of sediment accumulation the original benthic biota and the nature and abundance of silica phosphate and iron in seawater at any given time these characteristics controlled the formation of authigenic minerals and the preservation or dissolution of carbonate and silica biotas

side valley tributary fans in high energy river floodplain environments sediment sources and depositional processes navarro river basin california side valley tributary fans within the main axial valley river floodplain system are integral components of the sediment assemblage characterizing floodplains in the high energy navarro river basin california laboratory analyses of subsurface core and auger samples from four study sites reveal that sediment size distributions within the floodplain are controlled by spatial and temporal variation in sediment sources and depositional processes over 75 of sediment within individual lower fan strata are poorly sorted and include gravel clasts inferred to be contributions from the side valley tributary whereas remaining strata are composed of fine sediment less than 2 mm without gravel high water marks indicate that portions of the side valley tributary fans are episodically inundated by axial valley overbank flow a factor that influences fan relief and profile thus two dominant sources supply sediment to this transitional environment side valley tributaries and the axial valley river the transport and depositional processes that supply sediment to the fans operate under three conditions 1 tributary debris or fluvial flows and selective entrainment of fines by fan surface flows deposit sediment when there is no overbank flow from the axial channel 2 overbank flow deposits sediment derived from the axial valley river when there is no tributary input and 3 tributary flows deposit sediment while the floodplain is inundated by floods from the axial valley river the mixing and interlayering of sediment from these disparate sources within the active floodplain illustrate the significance of both hillslope floodplain and channel flood plain interactions in high energy fluvial systems with floodplains

floodplain evolution in a small tectonically active basin of northern california sediment cores were collected along oodplains in the navarro river basin of coastal northern california to examine the controls on oodplain evolution in a tectonically active setting sedimentary strata were subsampled for organic content bulk density and grain size measurements organic samples were analysed for 14c age which yielded net averaged sedimentation rates for all cores overbank deposition rates decreased at all study sites through time and declined in the downstream direction the ability of intermediary order streams to store sediment in oodplains decreased the ability of highest order streams to record sediment pulse events the effects of anthropogenic disturbance primarily logging on long term overbank deposition rates were minimal climatic variability by affecting sediment loading in the channel network is the principal control on oodplain evolution through the holocene a hypothetical model is proposed to explain overbank deposition rates in the navarro basin which may be extrapolated to the northern coastal california region during the late pleistocene and holocene the complexities observed in sediment storage and routing in this study imply that caution should be made when extrapolating sediment yield measurements obtained at river mouths or coastal shelves to geomorphic events within small tectonically active basins

cretaceous shales from the western interior of north america sulfur carbon ratios and sulfur isotope composition carbon and sulfur abundance and 34 s of pyrite sulfur were studied in cores of selected cretaceous marine shales from the western interior of north america sulfur carbon ratios average 0 67 a value greater than that observed in recent marine sediments and much higher than global values calculated for the cretaceous increased s c ratios probably result from generally low levels of bioturbation and enhanced efficiency of sulfate reduction due to low oxygen levels in the cretaceous seaway isotopic compositions of pyrite sulfur vary systematically with the level of oxygenation of the depositional environment and therefore with organic carbon abundance and type of organic matter samples with organic carbon in excess of 4 wt contain disseminated pyrite that is extremely depleted in 34 s mean 34 s 31 these samples are laminated clay shales that contain hydrogen rich type ii organic matter samples containing less than 1 5 organic carbon display relatively heavy but wide ranging 34 s values 34 s 34 6 to 16 8 mean 34 s 12 4 these samples are highly bioturbated and contain only type iii hydrogen poor organic matter samples containing intermediate amounts of organic carbon contain pyrite with 34 s values averaging 25 9 and contain mixed type ii and type iii organic matter the higher organic carbon content and the preservation of hydrogen rich organic matter generally correlate with slow sedimentation samples rich in organic carbon and containing isotopically light sulfide sulfur accumulated beneath anoxic and perhaps sulfidic bottom waters samples with intermediate organic matter content and intermediate sulfur isotopic compositions accumulated under mainly dysaerobic bottom waters samples with relatively low amounts of organic carbon and wide ranging but less negative sulfur isotopic values were deposited beneath oxygenated bottom waters sulfur isotope data are apparently a sensitive indicator of diagenetic or depositional facies of fine grained cretaceous rocks in the western interior

sediment production from forest road surfaces erosion on roads is an important source of fine grained sediment in streams draining logged basins of the pacific northwest runoff rates and sediment concentrations from 10 road segments subject to a variety of traffic levels were monitored to produce sediment rating curves and unit hydrographs for different use levels and types of surfaces these relationships are combined with a continuous rainfall record to calculate mean annual sediment yields from road segments of each use level a heavily used road segment in the field area contributes 130 times as much sediment as an abandoned road a paved road segment along which cut slopes and ditches are the only sources of sediment yields less than 1 as much sediment as a heavily used road with a gravel surface

abundant and diverse early paleozoic infauna indicated by the stratigraphic record marine benthic animals have lived within the sediment since the late precambrian an abundant early paleozoic infauna is indicated by bioturbated zones and diversity of deposit feeder and suspension feeder trace fossil genera burrow depths extended tens of centimetres below the sediment water interface trace fossil evidence of an abundant early paleozoic infauna conflicts with evidence from the shelled fauna which lacks infauna this requires reinterpretation of early paleozoic community structure and raises new questions about interactions between early paleozoic soft bodied and skeletonized animals

climate and local geomorphic interactions drive patterns of riparian forest decline along a mediterranean basin river abstract dynamic fluvial processes strongly influence ecological communities and ecosystem health in riverine and riparian ecosystems particularly in drought prone regions in these systems there is a need to develop tools to measure impacts from local and regional hydrogeomorphic changes on the key biological and physical processes that sustain riparian ecosystem health and potential recovery we used dendrochronology of populus nigra a riparian tree that is vulnerable to changes in local hydrology to analyze ecosystem response following channel incision due to gravel mining along the drome river a mediterranean basin stream in southern france we cored 55 trees at seven floodplain sites measured ring widths and calculated basal area growth to compare the severity and timing of local growth decline along the river current basal area increment bai growth per tree ranged almost 10 fold among sites 7 7 1 3 to 63 9 15 2 cm 2 year 1 mean se and these differences were significant mean bai was correlated positively with the proportion of healthy trees at a site and negatively with proportion of dead canopy area regime shift analysis of the tree ring series indicates that tree growth declined significantly at four sites since 1978 coincident with documented channel incision in addition patterns of low growth and crown dieback are consistent with stress due to reduced water supply the most impaired sites were not directly adjacent to local mining pits visible on aerial photographs nor did the sequence of growth regime shifts suggest a pattern of channel incision progressing from these areas the initiation of site growth declines was most typically associated with drought years and the most impaired sites were spatially distributed to suggest the influence of local bedrock controls on soil depth climate in the drome basin and in the mediterranean region is trending significantly toward hotter growing seasons with a decrease in summer river discharge and this will increase both chronic and acute water shortage for riparian trees this study shows that drought prone riparian forests are vulnerable to hydrogeomorphological changes but the severity of impacts is conditioned by interactions between drivers at different scales including regional climate variability reach based geomorphic alteration and local lithological controls

large complex burrow systems from freshwater deposits of the monongahela group virgilian southeast ohio usa abstract a large burrow complex is described from the monongahela group upper pennsylvanian in southeastern ohio the burrow complex consists of a branching network of elliptical to circular horizontal tunnels 1 18 cm in diameter occurring on a single horizontal plane the tunnels branch to form x t and y junctions with branch angles between 60 and 130 branching produces multiple polygonal galleries up to 60 cm wide connected by small horizontal tunnels vertical shafts connecting the galleries to the surface are not preserved tunnel surfaces are irregular with circular to elliptical nodes and depressions elongate ridges and grooves and 1 5 4 0 cm wide nodular patches typically located at branch points the occurrence of these burrow complexes in the monongahela group represents one of the largest examples of a branching burrow complex older than the cretaceous the monongahela burrow complexes are preserved within a succession of floodplain and palustrine sediments suggesting a freshwater habitat for the tracemaking organisms potential tracemakers of the monongahela burrow complexes include a variety of pennsylvanian crustaceans and vertebrates the presence of these and similar paleozoic ichnofossils indicate a long and complex evolutionary history of the trace making behaviors associated with the construction of large open burrow networks

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

geomorphic adjustment to hydrologic modifications along a meandering river implications for surface flooding on a floodplain abstract responses of large regulated rivers to contemporary changes in base level are not well understood we used field measurements and historical analysis of air photos and topographic maps to identify geomorphic trends of the lower white river arkansas usa in the 70 years following base level lowering at its confluence with the mississippi river and concurrent with flood control by dams incision was identified below a knickpoint area upstream of st charles ar and increases over the lowermost 90 km of the study site to 2 m near the confluence with the mississippi river mean bankfull width increased by 30 m 21 from 1930 to 2010 bank widening appears to be the result of flow regulation above the incision knickpoint and concomitant with incision below the knickpoint hydraulic modeling indicated that geomorphic adjustments likely reduced flooding by 58 during frequent floods in the incised lowermost floodplain affected by backwater flooding from the mississippi river and by 22 above the knickpoint area dominance of backwater flooding in the incised reach indicates that incision is more important than flood control on the lower white river in altering flooding and also suggests that the mississippi river may be the dominant control in shaping the lower floodplain overall results highlight the complex geomorphic adjustment in large river floodplain systems in response to anthropogenic modifications and their implications including reduced river floodplain connectivity

pyrite and organic matter in normal marine sediments of middle cambrian age southern georgina basin australia normal marine sedimentary rocks of middle cambrian floran undillan age from the southern georgina basin have pyrite sorganic c ratios with a mean value of 0 65 and show a significant positive correlation with an extension of the line of best fit through zero the sc ratio of 0 65 determined in this study is close to the mean ratio for all cambrian sediments of 0 7 but differs markedly from the recently reported sc ratio of 2 for normal marine early palaeozoic rocks mainly from the united kingdom the variations shown by these figures indicate that if the oxidation state of the crust ocean atmosphere over geological time is to be fully understood and related to possible world wide trends further assessment of early palaeozoic sulfur and carbon burial rates is needed furthermore as sc burial rates are known to vary the ages of the sediments being analysed need to be more precisely known

sediment budgets for a sediment laden river the lower wei river in the period 1960 1990 fluvial sediment delivery is the main form of sediment transfer from the land to the sea but this process is currently undergoing significant variations due to the alteration of catchment and base level controls related to climate change and human activities especially the widespread construction of dams using the lower wei river as an example and an integrated approach this study investigates the variation of fluvial sediment delivery as well as the connectivity under the effects of both controls based on hydrological records and channel cross section surveys sediment budgets were constructed for two periods 1960 1970 1970 1990 after the dam was closed in 1960 in the period 1960 1969 due to the elevated base level 327 2 1 62m caused by the dam the aggradation rate was 0 451x10 8 tyr 1 in the channel and 0 716x10 8 tyr 1 on the floodplain indicating that the positive lateral connectivity between these locations was enhanced as a consequence serious sediment storage resulted in a sediment delivery ratio sdr that was smaller than that occurring before 1960 in the period 1970 1990 sweeping soil and water conservation swc measures were implemented resulting in a reduction of the connectivity between the trunk and tributaries and a decrease of similar to 31 in the mean sediment input in addition together with the base level fluctuation in the range of 327 47 0 49m the annual variation in sediment storage was primarily dependent on the water sediment regime affected by the swc the negative lateral connectivity was enhanced between the channel and floodplain via bank erosion consequently the aggradation rate was reduced by 89 on the floodplain and by 96 in the channel sediment output continued to decrease primarily due to the swc practices and climate changes in this period whereas the sdr increased due to the enhanced longitudinal connectivity between the upstream and downstream copyright c 2014 john wiley sons ltd

road surface drainage channel initiation and slope instability field surveys of road drainage concentration at three sites in the western united states are used to test simple models relating channel initiation and shallow landsliding to ground slope and contributing area thresholds the form of boundaries between data for locations where road drainage concentration is associated with either shallow landsliding channel initiation by overland flow or no observable geomorphic effect is consistent with theoretically derived drainage area slope relations comparison of survey data with results of previous studies in these areas indicates that the drainage area required to support a channel head is smaller for road related runoff than for undisturbed slopes contrary to current land management paradigms in the pacific northwest drainage concentration from ridgetop roads may cause both landsliding and integration of the channel and road networks road drainage concentration increases the effective length of the channel network and strongly influences the distribution of erosional processes in each of the study areas the approach of using field reconnaissance to establish thresholds for erosion associated with road drainage provides a useful method to define regional criteria for road design that should reduce impacts on downstream channel systems

a shallow marine volcaniclastic facies model an example from sedimentary rocks bounding the subaqueously welded ordovician garth tuff north wales u k abstract volcaniclastic sedimentary rocks bounding the ordovician garth tuff in north wales were deposited in a shallow marine setting adjacent to a magmatic arc the volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz angular euhedral feldspar and volcanic rock fragments these grains are of a pyroclastic origin but have been reworked to various degrees sedimentary rock fragments rounded quartz muscovite biotite iron rich chlorite and various clay minerals occur in lesser amounts the sedimentary rocks can be divided into a proximal offshore to foreshore facies association poffa and an offshore to lower shoreface facies association olsfa the sand dominated poffa exposed near capel curig is characterized by large wave ripples hummocky cross stratification co sets of trough cross beds reactivation surfaces plane beds and graded turbidite layers in suspension deposited mudstone water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of hummocky cross stratification and by facies association vary from a few meters to around 30 m 45 50 m theoretical maximum in a 45 m thick stratigraphic section beneath the tuff eight kilometers to the southeast the garth tuff is bounded by a thick sequence of suspension deposited laminated mudstone with thin graded beds of siltstone and fine grained sandstone this facies association olsfa represents the introduction of material by distal turbidites and by pelagic sedimentation the olsfa was deposited in water depths well below storm wave base possibly in excess of 200 m no evidence of storm waves or surface generated currents occur until over 40 m above the tuff this study documents marine sedimentary rocks deposited in water depths ranging from foreshore to offshore as the bounding facies of the garth tuff it is thus reasonable to conclude that the garth tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study

pyrite organic matter relationships currant bush limestone georgina basin australia abstract the relationship between the toc total organic carbon and s pyritic sulphur contents of some organic rich toc 3 14 silty limestones and calcareous siltstones from the cambrian currant bush limestone of the georgina basin australia is similar to that of euxinic sediments but could also indicate deposition in a non saline environment however such conditions are not easily reconciled with the shallow equatorial epeiric sea in which the formation is considered to have been deposited the relationship can alternatively be explained by the relatively low fe content of the sediment being the main limiting factor in pyrite generation coupled with a slightly increased degree of pyritization with increased toc the relationship between the toc and s contents of organic poor toc 0 2 2 4 samples from the same formation is similar to that of normal marine sediments but the fe content is probably also the major controlling factor on pyrite generation these interpretations demonstrate that in using toc and s contents to aid in reconstruction of depositional environments it is important to check whether fe content could have been the limiting factor in the formation of pyrite even in sediments with only moderate carbonate contents

a fuzzy gis model to determine confluence morphological sensitivity to tributary inputs at the watershed scale abstract confluences are key nodes of river systems that have the potential of disrupting downstream longitudinal trends in the main river through inputs of water sediment wood or ice delivered from tributaries from a geomorphological perspective confluence zones are particularly active and thus susceptible to increased flooding and bed instability which in turn pose serious threats to infrastructure however not all confluences are active despite major advances in our knowledge of confluence dynamics there has been limited progress in the development of low complexity practical tools that use remotely sensed data to predict the spatial distribution of the main river s sensitivity to tributary inputs we have thus developed a novel semi automated gis model that uses a fuzzy approach to integrate key factors unit stream power valley confinement and sediment connectivity potential in order to map the distribution of the confluence morphological sensitivity cms index at the watershed scale the gis model was tested using digital elevation models of high lidar 1 m and coarser 10 m resolution in the coaticook and gaspesie watersheds quebec canada results indicate that the model is useful for detecting geomorphologically active confluences and the resulting sensitivity of the main channel and thus has potential to be used in diverse river management applications e g hazard reduction and freedom space mapping

geochemistry and mineralogy of marine and non marine namurian black shales from the tansley borehole derbyshire the namurian black shales studied have a good palaeontological control pyrite illite and organic matter are higher in the marine shales and siderite and kaolinite are higher in the non marine shales the distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity the same control could account for the observed clay mineral distribution by differential flocculation the major element geochemistry closely reflects the above mineral variation mn and zr are higher in the non marine shales due to siderite and zircon respectively co cr rb y and ba are not significantly different and a detrital source mainly clay minerals is suggested in the marine shales the elements pb cu v ni sr and zn are significantly higher using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated the present element locations are thought from correlation analysis to be pyrite and organic matter by analogy with experimental work and modern environments the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors the element enrichment cannot be related directly to seawater concentrations unlike some black shales and the accumulation rates for pb and cu are thought to be unusually high

permian and triassic sedimentation in the northeastern brooks range alaska deposition of the sadlerochit group permian and triassic rocks of the sadlerochit group crop out extensively in the northeastern brooks range adjacent to the coastal plain of the arctic national wildlife refuge terrigenous clastic rocks of the sadlerochit group are separated from underlying carbonates of the lisburne group by a regional unconformity marking the pennsylvanian permian systemic boundary lithologic and diagenetic patterns of rocks above and below the sub sadlerochit unconformity vary systematically with substantial paleotopography along the erosional surface within the sadlerochit group nonmarine conglomerate of the basal echooka formation fills erosional channels and valleys and grades upsection into a retrogradational succession of tempestites deposited during episodic storm surge in shal ow marine environments the overlying ivishak formation records an abrupt reversal of environmental migration pattern and the beginning of southerly progradation of a broad suite of deltaic environments depositional units in the ivishak are strongly progradational and cyclic at a variety of scales reflecting alternating episodes of progradation and transgression inherent in delta construction the basal kavik member of the ivishak formation is an upward coarsening depositional assemblage recording initial migration of prodelta environments and evolution of an extensive subaqueous delta platform the overlying ledge sandstone member is organized into three depositional assemblages recording the evolution of delta fringe distributary channel and crevasse splay environments of the lower delta plain the fire creek siltstone member is an aggradational and transgressive assemblage deposited in shallow marine environments that reworked sediment originally deposited on the lower delta plain the depositional assemblage records the final large scale subsidence and drowning of the ivishak delta platform the most favorable reservoir strata are developed immediately above and below the sub sadlerochit unconformity and in distributary mouth bar and distributary channel deposits of the ledge sandstone member

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

recession rates of waterfalls in boso peninsula japan and a predictive equation rates of waterfall recession and major factors that influence the rate were studied using waterfalls in boso peninsula japan the mean rate of waterfall recession was estimated by determining the age and original location the principal factor in determining the rate of waterfall recession is the ratio of the erosive force of stream to the bedrock resistance this is expressed in terms of measurable variables which include the discharge drainage area and precipitation the width and height of the waterfall and the unconfined compressive strength of the bedrock an empirical equation connecting the force resistance ratios and the rates of waterfall recession is derived copyright 2003 john wiley sons ltd

human topographic signatures and derived geomorphic processes across landscapes abstract the earth s surface morphology in an abiotic context is a consequence of major forcings such as tectonic uplift erosion sediment transport and climate recently however it has become essential for the geomorphological community to also take into account biota as a geomorphological agent that has a role in shaping the landscape even if at a different scale and magnitude from that of geology although the modern literature is flourishing on the impacts of vegetation on geomorphic processes the study of anthropogenic pressures on geomorphology is still in its early stages topography emerges as a result of natural driving forces but some human activities such as mining agricultural practices and the construction of road networks directly or indirectly move large quantities of soil which leave clear topographic signatures embedded on the earth s morphology these signatures can cause drastic changes to the geomorphological organization of the landscape with direct consequences on earth surface processes this review provides an overview of the recent literature on the role of humans as a geological agent in shaping the morphology of the landscape we explore different contexts that are significantly characterized by anthropogenic topographic signatures landscapes affected by mining activities road networks and agricultural practices we underline the main characteristics of those landscapes and the implications of human impacts on earth surface processes the final section considers future challenges wherein we explore recent novelties and trials in the concept of anthropogenic geomorphology herein we focus on the role of high resolution topographic and remote sensing technologies the reconstruction or identification of artificial or anthropogenic topographies provides a mechanism for quantifying anthropogenic changes to landscape systems this study may allow an improved understanding and targeted mitigation of the processes driving geomorphic changes during anthropogenic development and help guide future research directions for development based watershed studies human society is deeply affecting the environment with consequences on the landscape therefore establishing improved management measures that consider the earth s rapidly changing systems is fundamental

development of longitudinal profiles of alluvial channels in response to base level lowering degradation of alluvial channels in cohesive sediments was studied in 15 m and 20 m long flumes with a slope of 0 01 cm cm degradation was initiated by lowering base level to a fixed position and the development of the longitudinal profile of the channel is analysed through a model formulated as a heat diffusion equation it is based on the equation of sediment continuity combined with an assumption regarding sediment transport namely that sediment discharge is linearly proportional to the channel slope in accordance with the boundary and initial conditions imposed by the experimental setup and procedure the basic equation is amenable to an analytical solution which defines bed elevation at any distance and time as a function of the amount of base level lowering and a diffusion coefficient additional problems arising from bank erosion and channel armouring are also treated successfully within the framework of the same model the results show that in homogeneous alluvial sediments not subject to armouring the ultimate result of base level lowering by a certain amount is degradation all along the channel by the same amount the main impact of erosion is felt in the early stages after initiation of the process and mainly near the mouth the rate of degradation at any station along the channel reaches a peak and then slowly decreases with time and the peak rate is attenuated with distance from the outlet the model permits the prediction of intermediate stages of profile development at any distance from the outlet and at different times

models of porosity formation and their impact on reservoir description lisburne field prudhoe bay alaska the lisburne field at prudhoe bay alaska produces from shelfal carbonates in the pennsylvanian wahoo formation four major factors control reservoir behavior 1 depositional stratification 2 a fractured permeable subunconformity alteration zone saz 3 multiple episodes of porosity formation and 4 faulting this paper is the first written description of facies cyclicity and diagenetic processes as they apply to porosity formation and reservoir modeling in the lisburne field successive depositional cycles in the wahoo formation pass from ooid skeletal grainstones deposited in shoal complexes to oncolitic packstones and skeletal peloidal wackestones formed in restricted lagoonal environments geochemical data and crosscutting relationships between porosity and unconformities pressure solution features fractures and faults provide evidence of three distinct episodes of porosity formation earliest porosity is probably due to periodic localized exposure during the pennsylvanian a second stage of porosity is associated with shallow burial dolomitization that probably began during permian triassic subaerial exposure reservoir quality in dolomites varies with the degree of neomorphic recrystallization the third stage began in the cretaceous and lasted in o the tertiary and is associated with final burial and hydrocarbon maturation this burial dissolution event also opened existing fault systems creating a complex reservoir most lisburne field effective porosity is of late burial origin due to either dolomitization or dissolution faults and the saz act as giant collectors of oil from low permeability matrix and they have reduced the number of wells needed for field development faults also complicate waterflood implementation and maintenance of uniform reservoir pressure field studies such as these demonstrate the importance understanding the diagenetic history of a reservoir can have for field management and development planning

growth and demise of permian biogenic chert along northwest pangea evidence for end permian collapse of thermohaline circulation abstract the permian chert event pce was a 30 ma long episode of unusual chert accumulation along the northwest margin of pangea and possibly worldwide the onset of the pce occurred at about the sakmarian artinskian boundary in the sverdrup basin canadian arctic where it coincides with a maximum flooding event the ending of high frequency high amplitude shelf cyclicity the onset of massive biogenic chert deposition in deep water distal areas and a long term shift from warm to cool water carbonate sedimentation in shallow water proximal areas a similar and coeval shift is observed from the barents sea to the northwestern usa a landward and southward expansion of silica factories occurred during the middle and late permian at which time warm water carbonate producers disappeared completely from the northwest margin of pangea biotically impoverished and increasingly narrow cold water carbonate factories characterised by non cemented bioclasts of sponges bryozoans echinoderms and brachiopods were then progressively replaced by silica factories by late permian time little carbonate sediments accumulated in the barents sea and in the sverdrup basin where the deep to shallow water sedimentary spectrum was occupied by siliceous sponge spicules by that time biogenic silica sedimentation was common throughout the world silica factories collapsed in the late permian abruptly bringing the pce to an end in northwest pangea the end permian collapse of the pce was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions chert deposition resumed in the distal oceanic areas during the early middle triassic anisian after a 8 10 ma interruption early triassic chert gap the conditions necessary for the onset expansion and zenith of the pce were provided by the thermohaline circulation of nutrient rich cold waters along the northwestern and western margin of pangea and possibly throughout the world oceans these conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area created a nutrient and oxygen rich environment favouring siliceous biogenic productivity established cold sea floor conditions hindering silica dissolution while increasing calcium carbonate solubility and provided conditions adverse to organic and inorganic carbonate production the northwest margin of pangea was for nearly 30 ma bathed by cold waters presumably derived from the seasonal melting of northern sea ice the assumed engine for thermohaline circulation this process started near the sakmarian artinskian boundary intensified throughout middle and late permian time and ceased suddenly in latest permian time it led to oceanic conditions much colder than normally expected from the palaeolatitudes and the influence of cold northerly derived water was felt as far south southern nevada the demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production accumulation and preservation of biogenic silica

substrate control of lower cambrian trace fossils from bornholm denmark abstract a ten meter thick sequence within the lower cambrian succession from snogebaek harbour to broens odde bornholm contains abundant trace fossils throughout the systematics of some of the ichnogenera are briefly discussed in particular buthotrephis and a new form of diplocraterion the trace fossils can be subdivided into four associations the skolithos diplocraterion rhizocorallium and teichichnus buthotrephis associations the recurrence of these associations can be correlated with changes in substrate in particular the diplocraterion association in the middle and upper part of the broens odde member exposed here occurs only in storm deposits

deep burrowing in the early palaeozoic deep sea examples from the cambrian early ordovician meguma group of nova scotia enigmatic and heterogeneously deformed burrows are described from the cambrian early ordovician meguma group of nova scotia because of their morphological variability and the absence of previously defined morphotypes the burrows are unnamed yet do provide a cautionary note to the naming of trace fossils even at the ichnogeneric level by ichnologists the traces record the activity of unknown and mobile deposit feeding organisms that inhabited interchannel or levee areas immediately adjacent to and up to 5 m laterally from a 2 m deep channel developed on a deep sea mid outer submarine fan complex many of the vertically to subvertically oriented systems penetrate up to 40 cm suggesting that existing models on the depth of early palaeozoic benthic boundary layers obtained from shelf environments must be utilized with caution

experimental study of knickpoint and longitudinal profile evolution in cohesive homogeneous material a series of experiments were conducted in homogeneous bedrock to study knickpoint and longitudinal profile evolution knickpoints are created by successive drops in base level which simulate intermittent uplift channel morphology and flow characteristics vary systematically along a knickpoint reach as the knickpoint lip is approached width decreases but depth velocity and bottom shear stress increase as a result knickpoints are rapidly destroyed through the process of 1 knickpoint replacement and 2 subsequent knickpoint inclination knickpoint replacement consists of two morphologically distinct erosional reaches the knickpoint face below the knickpoint lip which decreases in slope and an incising reach above the knickpoint lip which increases in slope knickpoint replacement is a significant process in the evolution of knickpoints in homogeneous bedrock within experimental limits this study supports the notion that knickpoints do not undergo parallel head ward retreat in homogeneous bedrock given intermittent uplift except in those possible cases of extensive and pervasive bedrock jointing only the erosional sediment transport discontinuity above the knickpoint is developed in cohesive sediments below the knickpoint a steep bedrock channel slope low sediment load and rapid decrease in grain size of sediment load preclude development of the aggradational sediment transport discontinuity knickpoint evolution can be characterized by three general models parallel retreat replacement and inclination these models are based on the following criteria within the knickpoint reach 1 relationship between bottom shear stress 0 and critical shear stress needed to initiate motion c 2 nature of the bed load transport discontinuities and 3 spatial variability of bedrock resistance to fluvial erosion

geology and stratigraphy of fluvio deltaic deposits in the ivishak formation applications for development of prudhoe bay field alaska significant remaining reserves in prudhoe bay field are confined within deltaic rocks at the base of the triassic ivishak sandstone the initial stratigraphic characterization of the prudhoe bay reservoir was lithostratigraphically based and it depicted this basal reservoir interval as tabular zones between marine shale and overlying coarse grained fluvial sandstones a reassessment of this interval based on cores and genetic stratigraphic correlations depicts en echelon offlapping fluvially dominated deltaic wedges reservoir quality rocks occur in distributary mouth bar distributary channel and fluvial facies associations a paleogeographic reconstruction of one delta lobe includes an alluvial plain crossed by channels of possibly braided or low sinuosity rivers this alluvial plain graded into a delta plain cut by distributary channels that fed distributary mouth bars on a broad delta front river dominance is inferred from the abundance of unidirectional current structures normally graded beds soft sediment deformation and general absence of wave formed tidal and biogenic structures slumping and growth faulting locally replaced coarsening upward deltaic successions with sharp based overthickened mouth bar and distributary channel deposits mudstones deposited following delta lobe abandonment form laterally extensive flow barriers between lobes compartmentalization is most pronounced distally where deltaic sandstones are overlain by and pass laterally into marine shale proximally fluvial and deltaic sandstones are juxtaposed across erosional contacts improving reservoir continuity this stratigraphic interpretation is corroborated by production and surveillance data plus an interference test locally stratigraphy and poor waterflood performance reflect completions in diachronous sandstones that originated in separate deltaic lobes previously poor well performances were attributed to sandstone pinch outs in some cases production can be enhanced with recompletions rather than infill drilling nonconventional wells planned and completed with the benefit of detailed facies association correlations currently are recovering millions of barrels of previously bypassed oil

geochemical relationships of late paleozoic carbon rich shales of the midcontinent usa a compendium of results advocating changeable geochemical conditions abstract previous studies have shown that pennsylvanian black shales of the midcontinent us possess a more complex geochemical history than was once thought vine and tourtelot econ geol 65 1970 253 and coveney and glascock appl geochem 4 1989 347 note that the widespread nature of metalliferous pennsylvanian black shales and the diverse geological environments across the midwestern us pose the likelihood that metals contained in the black shales are of complex origins detailed geochemical and statistical representations using characteristics of numerous black shale members have shown that water depth may not have been uniformly deep as previously inferred by numerous workers earlier suggestions that these black shales were associated exclusively with anoxic depositional conditions have been challenged by a more realistic theory of multifaceted fluctuating environmental conditions a wide range of major and trace element concentrations combined with widely varying characteristics and diverse types of organic matter indicate the presence of fluctuating geochemical settings the presumption is that numerous associated chemical reactions occurred syngenetically one geochemical index degree of pyritization dop suggests a dysaerobic to aerobic setting for many of the shales whereas some other geochemical proxies i e v v ni indicate punctuated episodes of bottom water anoxia schieber abstr programs geol soc am 33 6 2001 a102 notes that in some black shales pyrite enrichment due to intermittent organic reworking explains the high dop values once thought to equate with extreme euxinic depositional conditions it seems likely therefore that even during apparent euxinic periods as indicated by bulk geochemistry oxygen deprived events were apparently short lived the seemingly euxinic fingerprint as shown by geochemical characteristics may result through time averaging abstr programs geol soc am 33 6 2001 a102 of intermittent euxinic events providing a misleading indication of dominant euxinic conditions thus detailed microstratigraphic sampling is necessary to delineate short punctuated occurrences of intermittent sub oxic episodes the midcontinent pennsylvanian shales may reflect a complex array of bottom water oxygenation variations and water depth fluctuations in response to climatic and localized events hatch j r and leventhal j s 1992 relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas usa in meyers p a pratt l m nagy b eds geochemistry of metalliferous black shales chem geol 99 65 82 complicated by post depositional events appl geochem 4 1989 347 this research examines the previous exclusively anoxic origin for midcontinent pennsylvanian black shales from a geochemical perspective and offers an alternative supported by detailed statistical presentations with the hypothesis that events of anoxia were punctuated by short lived dysaerobic or even near oxic events

fine bed material in pools of natural gravel bed channels natural gravel bed channels commonly contain a fine mode of sand and fine gravel that fills voids of the bed framework of coarser gravel if the supply of fine bed material exceeds the storage capacity of framework voids excess fine material forms surficial patches which can be voluminous in pools during low flow data collected in 34 natural channels in northern california and southern oregon indicate the following 1 fine material on the bed surface can be readily winnowed and transported at high particle velocities much of it in intermittent suspension fine material can dominate the bed material load in gravel bed channels but its abundance on the bed surface is limited by its increasing mobility as hiding places among prominent particles are filled 2 fine material in pools is typically replaced many times per year 3 the proportion v of residual pool volume filled with fine bed material correlates with annual sediment yield in channels whose parent material produces abundant sandy sediment 4 temporal and spatial changes in v appear to correspond to variations in the balance between sediment inputs and water discharge these results suggest that v can be used to monitor and evaluate the supply of excess fine material in gravel bed channels and that samples of fine material in pools can characterize the fine mobile mode of bed material load the sediment load of a stream channel the amount supplied and transported over a period of time can be difficult to evaluate contributions from hillslopes can be quantified with erosion surveys and sediment budgeting but uncertainty in routing makes it difficult to assess the load at any point in a channel network and direct measurement of transport rates is notoriously difficult bed material typically furnishes the bulk of the annual bed load especially in more distal channels but the active volume that contributes to the load is highly variable and difficult to evaluate it may be easier to detect variations in load by examining the mobility of the bed surface of gravel bed channels bed material in gravel bed channels characteristically includes a wide range of particle size and the bed can become

sediment transport and resulting deposition in spawning gravels north coastal california incubating salmonid eggs in streambeds are often threatened by deposition of fine sediment within the gravel to relate sedimentation of spawning gravel beds to sediment transport infiltration of fine sediment 2 mm in diameter into clean gravel beds bed material size distributions scour fill depths and sediment transport during 10 storm flow events were measured in three streams of north coastal california although suspended sediment comprised most 75 94 of the clastic load during storm flows bed load material 0 25 2 mm accounted for most 70 78 of the fine sediment accumulated in experimental gravel implanted in the streambeds sand trapped in the interstices of the top several centimeters formed a seal that impeded deeper deposition of very fine sand and finer material the seal was responsible at least in part for a decrease in the rate of fine sediment accumulation with increasing cumulative bed load transport areas of the streambeds commonly scoured or filled 0 1 m or more during storm flows and thus scour and fill commonly created a sandy layer at least as thick as the seal formed by sediment infiltration scour could erode eggs laid in the bed and expose deeper levels of the bed to infiltration by fine sediment but at the same time could allow fine sediment to be winnowed away great temporal and spatial variation in sedimentation in these streams suggests that individual storms of moderate size pose a threat to eggs in many but not all areas selected by fish for spawning

bioturbation of intertidal quartz rich sands a modern example and its sedimentologic and paleoecologic implications callianassa californiensis is a deep burrowing deposit feeding thalassinid shrimp which is abundant in intertidal areas of mugu lagoon california it occurs in greater densities 170 m 2 and is distributed more evenly to a depth of 50 cm below the sediment surface in quartz rich sands than in muddy sands 78 m 2 where most individuals live 15 to 30 cm below the sediment water interface callianassa californiensis produces extensive unlined burrow networks and deposits excavated material at the sediment surface given published excavation rates the population of c californiensis in the sandy area of mugu lagoon would deposit a layer 1 to 3 m thick each year it is also capable of rapidly reestablishing burrow openings after burial by up to 16 cm of sediment burrows act as conduits for fresh seawater and rapid overturn of sands inhibits compaction this results in flushing of nutrient and oxygen rich waters to considerable depth in the quartz rich sands as reflected by a depressed oxic anox