selective alteration of sargassum lipids in anoxic sediments of the orca basin abstract the orca basin represents a unique depositional environment where sediments are overlain by several hundred meters of anoxic brine layers of the seaweed sargassum are found as discrete layers within the sediments and appear intact by visual examination to examine lipid diagenesis in this environment major lipid classes sterols fatty acids and alcohols in plants collected in the water column were compared to those of plants found in sediments and dated at 380 years old by 14 c measurements plant fronds stipes and air bladders were analyzed separately to compare the preservation of lipids among major sargassum tissues all lipids showed significant changes in distribution and abundance in preserved plants with a general loss of unsaturated components the concentration of several saturated fatty acids however remained unchanged or increased in older plant tissues suggesting that thet were more resistant to decomposition and that reduction of unsaturated acids to saturated forms may have occurred over time sterols showed contrasting results with nuclear saturated sterols stanols decreasing in abundance by an average of 62 in preserved tissues while nuclear unsaturated sterols stenols showed only a mean decrease of 41 two major sterols cholest 5 en 3 ol and cholesta 5 24 dien 3 ol were reduced on average by 92 2 and 93 5 respectively while the major sterol in all sargassum tissues 24 ethylcholesta 5 24 28 e dien 3 ol showed no significant change in concentration over time results of lipid analysis for preserved and fresh sargassum suggests that selective degradation may occur in anoxic marine environments counter to pathways typically seen in other systems

organic geochemical characteristics of sediments from the anoxic brine filled tyro basin eastern mediterranean abstract soxhlet extractable organic compounds of sediments from the anoxic brine filled tyro basin eastern mediterranean were analyzed by gas chromatography and gas chromatography mass spectrometry cholesterol and 22 29 30 trisnorhopan 21 one are the major compounds identified the occurrence of this triterpenoid ketone as well as 22 29 30 trisnorhop 6 en 21 one and diplopterol both tentatively identified is ascribed to an input of microbiota living at the brine seawater interface

clay mineral provinces in tidal mud flats at germany s north sea coast with illite k ar ages potentially modified by biodegradation abstract mineralogical studies chemical analyses and k ar dating were carried out on clay fractions from tidal mud flats along the lower saxony coast and its bays to identify material sources and sedimentary processes at this dynamic interface between air land and sea from the coast into the bays sediments are enriched in fine grained smectite relative to the coarser grained illite chlorite and kaolinite due to the weakening of the tidal current energy in the bays in addition the study area can be divided into two provinces on the basis of the illite k rb ratios and mg contents to the west schiermonnikoog dollart ley bay up to norderney island longshore currents carry suspensions from the belgian and dutch coasts to the east from langeoog island jade bay to the helgoland mud area suspensions from the elbe and weser rivers are mixed with submarine reworked glacial sediments whereas the portion of longshore current suspensions from the west decreases becoming negligible in the helgoland mud area off the elbe and weser estuaries the illite k ar data vary considerably and fail as source indicators due to differential settling and mixing of the clay material and probably to ar loss from illite by biodegradation during digestive processes only further offshore outside the zone of dynamic sediment dispersion do the k ar data fit provenance patterns

comment on depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington by james e evans

stratigraphy age and paleogeography of the eocene chuckanut formation northwest washington the eocene chuckanut formation of washington s north cascades comprises as much as 6000 m of alluvial strata and is one of the thickest nonmarine sequences in north america it is exposed in several disconnected outcrop belts that are remnants of what was probably an extensive fluvial system in western washington in this study seven stratigraphic members are defined in the main outcrop belt of the chuckanut formation near the town of bellingham their ages based on fission track zircon dates palynologic studies and correlation by mapping extend from the early to the late eocene three types of fluvial systems contributed to the chuckanut formation and are distinguished on the basis of their lithology sedimentology and petrology the first comprises fine load meandering river deposits of the lower eocene bellingham bay member and the middle eocene slide member sandstones are arkosic and had their main source in rapidly uplifted high grade metamorphic terranes in eastern washington the second type

the newport fault eocene listric normal faulting mylonitization and crustal extension in northeast washington and northwest idaho the newport fault is a spoon shaped shallowly dipping fault zone across which a proterozoic to tertiary sedimentary suprastructure is juxtaposed above an infrastructure of basement gneiss and granitic batholiths as a result of eocene normal faulting and crustal attenuation chloritic microbreccia occurs at the top of the newport fault zone below which a zone of mylonitization as much as 500 m thick is developed in footwall rocks including the eocene silver point quartz monzonite detailed kinematic analysis of fabric and structures in the mylonite and microbreccia establishes that displacement was normal in sense on both sides of the u shaped fault trace the direction of extension was 74 254 as shown by consistently oriented mylonitic lineation crustal attenuation across the newport and adjacent purcell trench faults may have reached as much as 68 km 120 and in any case it exceeded 35 km 40 during faulting the footwall moved up and out to the east and west relative to the hanging wall forming two flanking footwall culminations or crustal scale boudins tectonic denudation of the footwall infrastructure is shown by eocene k ar cooling ages for granitic rocks within it chrontours that increase in age outward from the newport fault record abrupt cooling of the infrastructure as it was drawn away from the hanging wall the silver point quartz monzonite was emplaced into the dilatant zone between the footwall infrastructural culminations during displacement hanging wall strata were rotated down the listric fault surface the footwall rotated upward and the fault surface flattened probably as a consequence of isostatic adjustment to mass redistribution caused by normal faulting a roll over anticline developed in the hanging wall as it moved into the zone of attenuation between the footwall culminations syntectonic eocene extrusive rocks and coarse clastic deposits accumulated in a growth fault basin on the west flank of the hanging wall anticline crustal extension and normal displacement on the newport fault are compatible with a regional eocene strain regime that crossed northern idaho washington and southern british columbia and produced dextral transcurrent faulting core complex development and clockwise rotation of crustal blocks throughout that area

sedimentation and tectonics of the lower and middle eocene swauk formation in eastern swauk basin central cascades central washington the swauk basin lies between the straight creek and entiat leavenworth fault systems in the central cascades of washington and is one of several early tertiary strike slip basins in the pacific northwest in this paper seven informal stratigraphic units are recognized in the lowest portion of the basin fill the lower and middle eocene swauk formation in the eastern part of the basin these units have a stratigraphic thickness of more than 4800 m and were deposited in alluvial fan braided river meandering river lacustrine deltaic and lacustrine environments rapid facies changes and reversals in paleocurrent directions indicate numerous tectonically controlled drainage reorganizations sediments were mainly derived from crystalline rocks to the east north and west and sediment accumulation rates were high about 64 cm 1000 years the leavenworth fault has a complex history and periodically formed the eastern margin of swauk basin during the final phases and shortly after deposition of th

provenance of pliocene sediments and paleoenvironmental changes in the southern north sea region using samarium neodymium sm nd provenance ages and clay mineralogy abstract an 800 m thick sedimentary succession from the late pliocene north sea has been investigated on the provenance of the sediments and on changes of the source regions related to transport processes and climate changes the lower zanclean to piacenzian part of the succession from 1250 to 1050 m depth and the middle early gelasian part from 1100 to 700 m depth belong to one distributory system with at least two contributing source areas provenance ages calculated on basis of sm nd content indicate one old archean and one young

quantitative clay mineralogy as provenance indicator for recent muds in the southern north sea abstract the origin of recent mud deposits as well as the coastal turbidity maximum in the french belgian dutch nearshore area of the southern north sea is still under debate in the literature some models favor the erosion of the cretaceous chalk cliffs along the english channel and subsequent ne ward directed transport other models focus on the erosion of eocene to earliest oligocene and pleistocene to holocene clays outcropping on the seafloor off the belgian coast in order to validate these hypotheses the detailed qualitative and quantitative clay mineral composition of these sediments was used as a provenance indicator by comparing the clay mineral composition of the mud deposits and the associated suspended particulate matter spm with the composition of potential nearby and more remote sources such as the present day marine environment estuaries and rivers coastal erosion areas and the geological substratum the origin of the mud deposits and the spm could be traced results showed that only the clay composition of the scheldt estuary coincides with those of the mud deposits and the coastal turbidity maximum and that all other potential sources could be excluded our data suggest that the clay mineral composition of the mud deposits has a similar composition since at least about 100 000 years indicating that these deposits originate from a paleo scheldt river rather than from the recent river system as the present day scheldt estuary is not source of fine grained sediments the present day spm in the belgian dutch nearshore area originates mainly from the erosion and resuspension of the existing mud deposits situated in the belgian nearshore this study demonstrates the value and suitability of quantitative bulk and clay mineralogy techniques in sediment provenance studies and highlights the importance of incorporating the recent geological history in hydrodynamic studies of sedimentary basins

trace metal distributions in seawater and anoxic brines in the eastern mediterranean sea abstract the vertical distribution of dissolved and particulate trace metals mn fe ni cu cd is reported for seawater and the anoxic brines of tyro and bannock basins in the eastern mediterranean in normal mediterranean seawater the distribution of dissolved trace metals is governed by water mass circulation as well as by local input sources for cd and possibly cu steady state behaviour is not a viable assumption probably as a result of anthropogenic sources in agreement with previous reports no correlation was observed between dissolved ni cu cd and the major nutrients at the seawater brine interface all trace metals show dramatic changes in concentration in the brines the concentrations of dissolved fe and mn are strongly elevated compared to overlying waters yet probably limited by formation of solid sulfide and or carbonate phases the distributions of dissolved fe and sulfide show a remarkable mirror image of those found previously in the orca brine gulf of mexico and the ionic concentration products are approximately the same in all three basins the difference in absolute fe and sulfide concentrations is thought to be caused by a high supply of fe to orca basin concentrations of dissolved ni cu and cd in the brines are at least one order of magnitude lower than in overlying waters most likely due to formation of solid sulfide phases we believe these data provide the first indication of substantial nickel sulfide co precipitation within an anoxic basin particulate metal concentrations are elevated at the seawater brine interface and are probably associated with the presence of solid sulfide phases in addition the extreme density gradient at the interface will slow the sinking rate of particles and lead to accumulation of particles at the interface due to accumulation

paleodepositional conditions in the orca basin as inferred from organic matter and trace metal contents abstract the orca basin located in the gulf of mexico is a highly stratified basin that collects sedimentary particles of clastic origin supplied by the mississippi river and of biogenic origin marine surface productivity the strong pycnocline induces anoxic bottom conditions that are expected to be favorable to organic matter om accumulation and prone to enrichment of sediments in redox sensitive trace metals here we report on om and trace metal contents in the upper 750 cm below sea floor cmbsf of core md02 2552 mostly holocene and deposited under permanently stratified bottom conditions the organic content is dominated by marine derived amorphous om contrary to expectations sedimentary om in the basin is highly degraded probably due to a long residence time of organic particles at the basin s basin s halocline at 2240 m also unexpected is the limited sedimentary enrichment of redox sensitive trace metals we suggest that the non enrichment in u and v could be explained by the so called basin reservoir effect that is limited metal availability because of low rates of water renewal in a strongly restricted subpycnoclinal water mass the non enrichment in cu could have the same cause plus the fact that the relatively degraded om may not readily form organometallic complexes however a marked enrichment is observed for mo and a moderate one for ni and cr which could be accounted for by sporadic presence of h 2 s in bottom waters such occurrences of h 2 s would not be sufficient to promote a detectable fes to fes 2 conversion but they would induce the capture of mo in the form of thiomolybdate and accessorily ni cr as ni cro 4 complexes

cenozoic evolution of the eastern pamir implications for strain accommodation mechanisms at the western end of the himalayan tibetan orogen detailed field mapping geochronologic and thermochronologic analyses and petrologic investigations conducted along the southern segment of the late cenozoic kongur shan extensional system provide new information on the cenozoic tectonic evolution of the eastern pamir at the western end of the himalayan tibetan orogen field relations and cooling age patterns in the hanging wall and footwall of the active faults show a southward decrease in the magnitude of east west extension along the southern kongur shan extensional system from 20 km or less along the muztaghata massif in the north to l3 km along the tashkorgan fault in the south these results in conjunction with previously published work on the northern segment of the kongur shan extensional system show a general southward decrease in east west extension along the entire length of the extensional system consistent with models of extension primarily driven by oroclinal bending or radial thrusting of the pamir petrologic data 40 ar 39 ar cooling ages and monazite th pb ages from schists and gneisses in the footwall of the southern kongur shan normal fault along the muztaghata massif record two tectonic events that immediately preceded late miocene initiation of east west extension 1 high grade schists and gneisses experienced upper amphibolite facies metamorphic conditions 9 10 kbar 700 750 c dated as late oligocene to middle miocene by in situ ion microprobe analyses of monazite inclusions in garnet and 2 high grade schists and gneisses were subsequently rapidly exhumed to shallow crustal levels in the late miocene with 40 ar 39 ar biotite cooling ages of 7 5 9 ma rapid exhumation was accommodated in part by the east west striking south dipping shenti normal fault field relations and regional geologic correlations indicate that this exhumation event was related to the formation of the central pamir gneiss domes and the antiformal muztaghata massif is the eastward continuation of the sares dome of the central pamir these observations suggest that the antiformal gneiss domes of the central pamir have not been offset across the karakorum right slip fault from the qiangtang anticlinorium in tibet instead we propose that the development of the central pamir gneiss domes may have been related to oligocene miocene northward underthrusting and thickening of crust beneath the pamir

sulfur and organic carbon contents in sediment cores from the tyro and orca basins abstract the tyro and orca basins are two small deep water euxinic depressions in the eastern mediterranean and the northern gulf of mexico respectively anoxic bottom waters are known to be nearly saturated with nacl sediment accumulation in the basins has been complicated by episodic slumping and or redeposition analyses of sediment total reduced sulfur and organic carbon and resulting s c ratios are used to test the feasibility of using these parameters as indicators for the mode of sediment deposition in the basins sediments originally deposited in the basin are as expected enriched in sulfur and carbon content as compared to sediments that originated from areas beyond the limit of the anoxic brine pool and were redeposited later inside the basin however values of the s c ratios of these primarily deposited sediments are less than those of sediments of redeposited origin and indicate a low rate of sulfide conversion during bacterial sulfate reduction this inconsistency is interpreted to be due to the high salinity basin waters inhibiting the overall activity of sulfate reducers and their associated heterotrophic microorganism communities and or the reactivity of initially deposited organic matter this study also demonstrates that variations of sulfur and carbon contents and their s c ratios together can be used as a geochemical tool to delineate the origin of sediments accumulated in hypersaline euxinic basins however the feasibility of the s c method requires a further check as to whether the rate of sulfate reduction could have been constrained even in environments of normal salinity

changes in clay mineral content of tidal flat sediments resulting from dike construction along the lower saxony coast of the north sea germany the clay mineral content of the 2 m fraction in tidal flat sediments in the former harle bay on the lower saxony coast has changed considerably since the thirteenth century up to the present time the proportion of smectite has decreased from 29 to 11 wt whereas the proportion of illite has increased by about 10 wt and those of chlorite and kaolinite by about 3 wt each the chemical composition of the major clay mineral illite has also changed al2o3 has decreased by about 2 wt k2o by about 1 5 wt and sio2 by about 3 wt it can be concluded that the changes in the clay mineral content are mainly influenced by dike construction and sea level rise modifying flow pattern submarine morphology sedimentation and tidal range these processes cause smectite to settle less rapidly because of its small grain size and low density resulting from interlayer water so that the sediment becomes impoverished in this mineral

sulfur and oxygen isotopic compositions of dissolved sulfate in the orca basin implications for origin of the high salinity brine and oxidation of sulfides at the brine seawater interface abstract analysis of sulfur and oxygen isotopic compositions of dissolved sulfate from a vertical water profile in the anoxic hypersaline orca basin provides important constraints upon the provenance of the sulfate results support a dissolution origin of the brine from a jurassic evaporitic salt however mass balance considerations and the observed minima in the vertical 18o sulfate profile at the brine seawater interface are not reconcilable with only a simple two box brine seawater mixing model instead the data imply contributions from the oxidation of sulfides

uranium geochemistry of orca basin orca basin an anoxic brine filled depression at a depth of 2200 m in the northwestern gulf of mexico continental slope has been studied with respect to its uranium geochemistry uranium concentration profiles for four cores from within the basin were determined by delayed neutron counting uranium concentrations ranged from 2 1 to 4 1 ppm on a salt free and carbonate corrected basis the highest uranium concentrations were associated with the lowest percentage and 13c organic carbon values for comparison cores frm the brine filled suakin and atlantis ii deeps both in the red sea were also analyzed uranium concentrations ranged from 1 2 to 2 6 ppm in the suakin deep and from 8 0 to 11 0 ppm in the atlantis ii deep no significant correlation was found between uranium concentrations and organic carbon concentrations and 13c values for these cores although anoxic conditions are necessary for significant uranium uptake by non carbonate marine sediments other factors such as dilution by rapidly depositing materials and uranium supply via mixing and diffusion across density gradients may be as important in determining uranium concentrations in hypersaline basin sediments

the anatomy of a pull apart basin seismic reflection observations of the dead sea basin the dead sea basin dsb located along the african arabian plate boundary constitutes a good example of a pull apart basin because of its large dimensions its structural simplicity and its active subsidence a coherent three dimensional picture of the dsb has been constructed on the basis of analysis of seismic stratigraphy together with the interpretation of previously published geological and geophysical data despite the large known vertical offsets across the basin deformation takes place mainly along the transverse and longitudinal faults and the intervening sediments are relatively undeformed and are hardly tilted comparison between e w seismic lines indicate that the basin has widened by the collapse and tilting of arcuate blocks from the western margin but that its original shape is a full graben the southern and central parts of the basin are divided into equidistant segments 20 30 km long by transverse faults activity along these faults commenced only during the pleistocene long after the dead sea strike slip fault system was formed and migrated northward with time a likely scenario for the development of the dsb is one in which the basin grows northward with time by a simultaneous propagation of the southern strand of the dead sea fault and a retardation of the northern strand

ages and stratigraphy of lower and middle tertiary sedimentary and volcanic rocks of the central cascades washington application to the tectonic history of the straight creek fault in the central cascade range of washington three structural blocks of early tertiary sedimentary and volcanic rocks help to define the position and history of the southern segment of the straight creek fault east of the fault in the teanaway river block the early eocene fluviatile feld spathic sandstone of the swauk formation is interbedded with largely dacitic volcanic rocks of the silver pass volcanic member zircon fission track ages on the silver pass are about 52 m y overlying the tightly folded swauk and silver pass is the teanaway formation a gently dipping accumulation of basalt andesite rare dacite and rhyolite that yields middle eocene about 47 m y whole rock k ar ages conformably overlying the teanaway is the roslyn formation a coal bearing fluviatile feld spathic sandstone of probable middle to late eocene age the late eocene and oligocene naches formation exposed west of the straight creek fault in the cabin creek block is rich in fluviatile feldspathic sandstone and rhyolite flows and tuffs in its lower part but grades upward into a sequence dominated by basalt but with some andesite the basal guye sedimentary member of the naches formation underlies and is interbedded with the mount catherine rhyolite member in the snoqualmie pass area on the basis of zircon fission track ages on silicic tuffs and whole rock k ar ages on basalt the basal part of the naches is about 40 to 44 m y old the formation is tightly folded and complexly faulted along the straight creek fault the straight creek fault intersects the olympic wallowa lineament in the strongly deformed manastash river block in this block fluviatile coal bearing feldspathic sandstone of the manastash formation is overlain by principally dacitic volcanic rocks of the taneum formation overlying the taneum is the basalt of frost mountain we correlate this threefold sequence feldspathic sandstone dacite basalt with the sequence in the teanaway river block small patches of rhyolitic ash flow tuff dated at 33 m y late oligocene and interbedded feldspathic sandstone overlie the roslyn and teanaway formations in the teanaway river block and are probably correlative with the late oligocene wenatchee formation exposed in the chiwaukum graben east of the teanaway river block as well as with the late oligocene volcanic rocks 30 m y along the cascade crest to the southwest these latter rocks are little deformed and unconformably overlie the naches formation the ages and depositional record in the three blocks indicate a tertiary history of dominantly vertical movement along the straight creek fault and its southeasterly splays that merge with the olympic wallowa lineament the horst and graben structure of the blocks as well as enechelon fold axes in the swauk formation suggests some post early eocene right lateral shear along the fault although there is no direct evidence of lateral offset vertical movement significant since early eocene swauk deposition followed late eocene naches deposition but tapered off by late oligocene time and ceased by miocene time when the fault was intruded by the 25 m y old snoqualmie batholith and other plutons however structures with olympic wallowa lineament trends appear to have influenced folding of the miocene yakima basalt subgroup

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

hydrothermal and unexpected diagenetic alteration in permian shales of the lodeve epigenetic u deposit of southern france traced by k ar illite and k feldspar dating abstract mineralogical and chemical analyses combined with k ar dating of illite and k feldspars were carried out on bulk samples and different fractions from permian shales around the lodeve u deposit to identify diagenetic and hydrothermal alteration episodes and their timing authigenic 2m1 and 1m illite with k ar ages between 270 and 245 ma are the predominant mineral types in the shales they are of early diagenetic origin relative to deposition and formed apparently directly from pyroclastic materials in a lagoonal to deltaic environment under semi arid conditions albite and a first generation of k feldspar developed by a replacement of analcime the k feldspar growing only in the former lagoonal environment that favored also early diagenetic dolomitization at the expense of calcite the hydrothermally altered shales next to the u deposit contain authigenic quartz fe chlorite neoformed illite and a second generation k feldspar with k ar ages beginning at about 220 ma triassic although jurassic and cretaceous ages were also obtained this younger age spectrum jurassic cretaceous is close to previous u pb isotope data from the u deposit probably reflecting several episodes of u mobilization therefore the hydrothermal activity extended episodically from triassic to cretaceous time within the u deposit the hydrothermal temperatures attained locally 220 c as the k ar system of illite from early permian diagenesis is partially reset triassic hot fluids ascended along faults into the northern area of the lodeve basin during an initial rifting of the nearby western tethys ocean further fluid pulses were recorded at lodeve during the opening of the north atlantic and separation of europe from africa jurassic cretaceous which also caused the peak hydrothermal activities in central and western europe as the lodeve area is located between two independently developing oceans it could have been supplied with hot fluids for a long period of time

delamination of smectite in river borne suspensions at the fluvial marine interface an experimental study abstract fine fractions the variations in fwhm d values and peak intensity of the smectitic material are assumed to be caused by an exchange of na for ca in the interlayer spaces and subsequent delamination of the particles along the na activated interlayers only those smectite particles in which adjacent sheets are still stabilized by the remaining ca are preserved after contact with seawater the experiments show that delamination of smectite and i s mixed layer minerals is likely to occur in the brackish environment at the mouth of a river however formation of these fine laminae is expected to be a transitional stage in the development of clay particle size owing to the formation of flocs and aggregates in the higher salt concentrations of seawater

stable carbon isotope ratio variations of organic matter in orca basin sediments abstract orca basin is a highly reducing basin on the slope of the gulf of mexico stable carbon isotope ratios and total organic carbon percentages were determined for two cores within the basin and one control core outside the basin the results show that the organic carbon content of the basin cores is consistently 2 3 times greater than that of the control core the pleistocene holocene boundary indicated by a break in the 13 c depth profile occurs at a greater sediment depth in the basin cores than in the control core a small sampling interval has made it possible to detect an unexplained fine structure in the 13 c profile not previously observed

mesozoic hydrothermal impact on rotliegende and bunter immature sandstones of the high rhine trough and its adjacent eastern area southern black forest germany abstract the mesozoic hydrothermal and geodynamic evolution of a complex region of the european crust is studied here on immature and highly reactive rotliegende and bunter sandstones of the intramontane high rhine trough southern black forest and its adjacent eastern area bounded by the upper rhine graben and the alpine foreland microscopic observations outline varied degrees of illitization of detrital feldspar grains muscovite flakes and illite particles xrd analysis shows that the clay fractions are dominated by illite with minor illite smectite mixed layered minerals of r3 and r1 ordering the chemical composition of these minerals is controlled by precursor minerals since the illitic material inherited its chemical components from detrital muscovite and illite towards the centre of the trough the sandstones were more strongly affected by the hydrothermal impact showing extensive replacement of feldspar grains by al rich illite k ar dating of the authigenic illite type material points to multiple hydrothermal alteration episodes a late jurassic event at 147 ma seems to have affected extensively the study area especially towards the centre of the trough at the periphery of the trough relics of an early jurassic activity are likely preserved an additional early cretaceous hydrothermal event seems to have occurred locally near schopfheim and next to the rhine graben boundary fault long before its main rifting phase the 147 ma event was obtained also nearby in the previously investigated breisgau schramberg offenburg teinach and baden baden troughs and is characteristic for the black forest and some other areas outside this region it concludes obviously a period of regional hydrothermal activities between 160 and 145 ma whereas the early jurassic and cretaceous signatures are also known throughout central and western europe suggesting repeated fluid pulses the hydrothermal flows were controlled by reactivated basement faults due to periods of extensive reorientation of the tectonic stress during the break up of pangaea illitization was triggered by hot and low saline solutions of about 180 c and eq whereas a later fluid pulse of about 80 c and 20 wt nacl eq caused quartz overgrowth fluid flows delivered by the long lasting orogeny of the nearby alps were probably limited towards the black forest becoming part of the european margin of the tethys in the mesozoic the pre alp area evidently developed a separate fluid flow system

alkali elements na k rb and alkaline earth elements mg ca sr ba in the anoxic brine of orca basin northern gulf of mexico abstract a profile of filtered seawater and brine samples was collected in the summer of 2003 from a depth of 1500 m down to the bottom of the anoxic hypersaline orca basin northern gulf of mexico using ion chromatography and inductively coupled plasma mass spectrometry icp ms these samples were analyzed for alkali cations na k rb alkaline earth cations mg 2 ca 2 sr 2 ba 2 and the major anions chloride cl and sulfate so 4 2 major ion concentrations in the brine are consistent with previous studies confirming that na plus cl make up more than 95 of its composition hence governing its density and hydrodynamic stability binary mixing plots across the interface between deep gulf of mexico seawater and the anoxic brine are generally linear but display substantial deviations from conservative behavior at the steepest part of the pycnocline for all analytes except na cl and ca negative deviations signify localized cation removal by an adsorption or ion exchange process probably associated with the dense layers of particles that are trapped there especially strong mg removal may be indicative of dolomitization whereby the concomitant release of ca counters its adsorption resulting in zero net ca removal a positive deviation for sulfate is attributed to bacterial sulfide oxidation concentrations of rb sr and ba in the homogeneous brine reported here for the first time are enriched by factors of 1 5 1 4 and 9 respectively with respect to the overlying seawater unlike ca and sr ba concentrations in the brine are clearly controlled by the solubility of its sulfate salt barite causing a maximum of 670 nmol kg at the interface several independent lines of evidence suggest that the brine is formed outside the basin most likely by the interaction of seawater with regionally extensive evaporite deposits a simple mass balance shows that the dissolution of about 280 g of halite per kg of seawater can account for the extreme concentrations of na and cl in the orca basin brine the same mass balance was applied to a number of minor constituents k rb mg ca sr so 4 br total iodine in order to calculate what abundances in the halite are required to reproduce their concentrations in the brine as measured in the present work and by others the results are entirely compatible with the composition of the jurassic louann salt specifically with the median of compositions published for a transect spanning early to late stage halites elevated abundances of k and rb point to contributions from bittern facies modified by prior diagenetic contact with seawater

river mixing rate residence time and subsidence rates from isotopic indicators eocene sandstones of the u s pacific northwest isotopic analyses of eocene sandstones from the tyee formation and related units in the u s pacific northwest provide evidence for short residence time but extensive mixing and indirectly slow subsidence rates within the major river feeder systems that drained the western flank of the north american cordillera bulk isotopic analyses of coarse white mica are remarkably consistent throughout the tyee formation mean k ar 67 3 ma 18o 9 5 of the oregon coast range other tertiary sandstones in the region have similar values despite small scatter about these mean values the 40ar 39ar ages of single grains of white mica from these units range from about 45 to 120 ma showing that long river systems thoroughly mixed and homogenized the transported sand grains in addition overlap of the youngest mica cooling ages and depositional age for the tyee formation show that homogenization of grains took place during a relatively short residence time in the river transport system 2 m y these results require that the sediments were multiply cycled within the active river system this suggests that average subsidence rates along the alluvial system were low and thus sediment could be recycled by temporary storage in and reintroduction from the river flood plain without spending significant time buried the results show that extensive sediment mixing can occur in large rivers on relatively short time scales and that isotopic analyses can provide indirect evidence of subsidence rates for basins no longer preserved

high resolution temporal and stratigraphic record of siletzia s accretion and triple junction migration from nonmarine sedimentary basins in central and western washington the presence of early eocene near trench magmatism in western washington and southern british columbia has led to speculation that this area experienced ridge trench interaction during that time however the effects of this process as they are preserved in other parts of the geologic record are poorly known we present high precision u pb zircon geochronology from paleogene nonmarine sedimentary and volcanic sequences in central and western washington that preserve a record of tectonic events between ca 60 and 45 ma the data reveal that the swauk chuckanut and manastash formations formed a nonmarine sedimentary basin along the north american margin between 59 9 and 51 3 ma this basin experienced significant disruption that culminated in basinwide deformation uplift and partial erosion during accretion of the siletzia terrane between 51 3 and 49 9 ma immediately following accretion dextral strike slip faulting began or accelerated on the darrington devil s mountain entiat leavenworth eagle creek and straight creek fraser fault zones between 50 and 46 ma during this time the chumstick formation was deposited in a strike slip basin coeval with near trench magmatism faulting continued on the entiat eagle creek and leavenworth faults until a regional sedimentary basin was reestablished 45 9 ma and may have continued on the straight creek fraser fault until 35 30 ma this record of basin disruption volcanism and strike slip faulting is consistent with ridge trench interaction and supports the presence of an oceanic spreading ridge at this latitude along the north american margin during the early eocene

biogenic hydrocarbon gases and sulfate reduction in the orca basin brine the composition of light hydrocarbon gases in the orca basin an anoxic hypersaline intraslope depression on the continental slope of the northern gulf of mexico indicates that both methane and ethane are biogenic in nature with a c1 c2 c3 ratio of 730 and a 13c of methane of 73 relative to the pdb standard the concentrations of methane 750 mm and ethane 1300 mm in the orca basin brine are higher than any other marine anoxic basin these high levels result not from high rates of productivity but from the long residence time of the brine in the basin due to its high stability toward mixing with overlying seawater 1 z 3 2m both methane and ethane show well mixed distributions in the brine these distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments methane and ethane maxima above the pycnocline at the brine seawater interface reflect in situ production and or consumption in the aerobic water column concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter reduced rates of anaerobic decomposition including sulfate reduction in the brine sediments are inferred from preserved sargassum fronds in the sediments vertical sulfate profiles in most cores and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal gulf sediments nearby

vertical distributions and speciation of dissolved rare earth elements in the anoxic brines of bannock basin eastern mediterranean sea abstract vertical distributions of dissolved rare earth elements rees are presented for the anoxic highly sulfidic brines of bannock basin in the eastern mediterranean sea ree concentrations at the seawater brine interface are the highest ever recorded in the water column of an anoxic basin and comparable only to ree concentrations at depth in the porewaters of reducing sediments below the seawater brine interface throughout the upper of two chemically distinct brine layers ree concentrations decrease with depth as a result of scavenging while shale normalized ree patterns are characterized by little or no fractionation between the light rees lrees and the heavy rees hrees and by a positive ce anomaly throughout the lower of the two brine layers ree concentrations are constant while ree patterns are characterized by the same lack of lree or hree enrichment as well as by the absence of any ce anomaly a pronounced ree minimum at the interface between the two brine layers is apparently caused by uptake into dolomite that is formed through in situ recrystallization of ca carbonate a process that was previously reported to cause similar minima for mn and fe calculations of ree speciation incorporated into a model of ree scavenging developed by byrne and kim 1990 which uses ree complexation by monocarboxylic acids to represent ree adsorption onto particulate matter are surprisingly successful at reproducing the unusual shape of ree patterns in the brine this suggests that this shape although very different from that of ree patterns in the overlying seawater due to the very high ionic strength of the brine is the result of much the same processes that constitute ree scavenging in the open ocean

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

reply to comment on depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington

light hydrocarbons in red sea brines and sediments abstract light hydrocarbon c1 c3 concentrations in the water from four red sea brine basins atlantis ii suakin nereus and valdivia deeps and in sediment pore waters from two of these areas atlantis ii and suakin deeps are reported the hydrocarbon gases in the suakin deep brine t 25 c cl 85 ch 4 71 1 are apparently of biogenic origin as evidenced by c 1 c 2 c 3 ratios of 1000 methane concentrations 6 8 l l in suakin deep sediments are nearly equal to those in the brine suggesting sedimentary interstitial waters may be the source of the brine and associated methane the atlantis ii deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources the upper brine t 50 c cl 73 ch4 155 l l gas seems to be of biogenic origin c 1 c 2 c 3 1100 whereas the lower brine t 61 c cl 155 ch4 120 l l gas is apparently of thermogenic origin c 1 c 2 c 3 50 the thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine whereas the biogenic gas is produced in situ or at the seawater brine interface methane concentrations in atlantis ii interstitial waters underlying the lower brine are about one half brine concentrations this difference possibly reflects the known temporal variations of hydrothermal activity in the basin

a new angle on the tectonic evolution of the ridge basin a strike slip basin in southern california the ridge basin located in southern california between the san andreas and san gabriel faults contains as much as 14 km of mio pliocene marine and nonmarine sedimentary fill these strata are exposed as a northwest dipping homoclinal sequence that becomes increasingly younger to the northwest pliocene to holocene deformation uplift and dissection of this basin provide an opportunity to study stratal geometry and sedimentary facies in what is commonly cited as a classic strike slip basin newly acquired seismic data from the northern ridge basin provide new evidence for the subsurface basin geometry these data lead us to conclude that the principal northern strand of the san gabriel fault is a listric east southeast dipping oblique slip fault rather than a subvertical strike slip fault the principal san gabriel fault appears to become subhorizontal at the southeastern end of the seismic line at a present day sub surface depth of 4 km this interpretation is consistent with preliminary two dimensional gravity models across the basin and with the homoclinal structure of basin fill subsidence within the ridge basin is explained as the result of northwest southeast extension locally accommodated along the listric right lateral san gabriel and associated late miocene strike slip faults as a consequence of oblique normal slip on the gently dipping san gabriel fault sedimentary strata were continuously tilted and moved southeastward in the hanging wall away from the depocenter this mechanism of basin formation allowed 14 km of sediment to accumulate without deep burial the geometry and displacement history of the san gabriel fault controlled sediment accommodation and resultant stratal geometries within the basin slip along the san gabriel fault and associated subsidence of the ridge basin correspond temporally with regional tectonic events in southern california reflecting both changes in the relative motion of pacific and north american plates and the evolution of strain partitioning across this plate boundary

isotopic provenance of paleogene sandstones from the accretionary core of the olympic mountains washington conventional modal sandstone data from paleogene units of the pacific northwest are not precise enough to pinpoint source areas and constrain displacement histories of accreted sedimentary terranes isotopic provenance study used in conjunction with traditional basin analysis techniques provides a powerful means of identifying source areas analysis of rb sr data in both wholerock and detrital white micas of paleogene sandstones from allochthonous units in the eastern core of the olympic mountains and coeval autochthonous sandstones from coastal pacific northwest shows that the needles gray wolf and grand valley lithic assemblages of the core came from the same source as sandstones of the chuckanut formation and puget group in northern washington the source of these units is isotopically distinct from the source for units farther south such as the tyee formation in oregon chemical compositions conventional k ar age determinations and oxygen and hydrogen isotope compositions of white micas support this conclusion similar analyses of sandstones from the western olympic lithic assemblage and the yakutat terrane of southeastern alaska suggest that these two units have a similar source but that they differ slightly from sandstones of the eastern olympic core and autochthonous washington units the overall composition of sandstones lithic arkosic and the very high initial sr values 0 710 moderately high 18 o values 9 and mesozoic age for detrital white mica of olympic core rocks and sandstone of the yakutat terrane suggest a source in the high rank metamorphic and plutonic rocks from the eastern part of the omineca crystalline belt in southeastern british columbia furthermore rapid uplift of this source area during eocene time is consistent with the depositional age of the olympic rocks sediment derived from this source area was transported westward by major river systems that crossed the low lying north cascade range and supplied the deposits of the autochthonous units of the northern washington coast and the offshore equivalents before the latter were accreted to form the olympic core limited data from the yakutat terrane suggest that it lay offshore of southern british columbia sometime during middle eocene to early oligocene time consistent with paleomagnetic and some paleontologic interpretations and subsequently migrated northward by plate motions

sulfur isotopic trends and iron speciation from the c 2 0 ga pilgujarvi sedimentary formation nw russia abstract sulfide sulfur isotope values and iron speciation data are reported here for sediments from the 2 0 ga old pilgujarvi sedimentary formation pechenga greenstone belt nw russia sulfides are abundant throughout the c 1400 m thick turbiditic sandstone siltstone shale succession and present as pyrite and pyrrhotite a stratigraphic trend is discernible with respect to sulfide mineralogy and sulfur isotopic compositions changing up section from highly to less variable and positive 34 s values the occurrence of pyrrhotite particularly high in the upper part of the section is thought to be the result of decomposition of pyrite during low grade metamorphism this is evidenced by the crystallographic habit and sulfur isotopic composition of the different sulfide minerals the 34 s of both sulfur species is quite variable in the lower part of the formation 9 5 to 18 7 while the upper part displays a smaller fluctuation in 34 s 4 4 13 3 the pyrrhotite is generally depleted in 34 s by approximately 3 6 average isotopic difference between pyrrhotite and pyrite compared to the pyrite this shift in the sulfur isotopic composition results from thermal decomposition of pyrite the overall spread in 34 s is indicative for the microbial reduction of sulfate but 34 s values suggest a sulfate limited environment in the upper part of the formation we note however that the sulfate limitation is restricted to the pore water realm caused by high sedimentation rates that inhibited a sufficiently high sulfate flux from the overlying water column into the sediment based on iron speciation data a previous characterization of the depositional environment as non euxinic can be specified more precisely we note that the siliciclastic succession of the pilgujarvi sedimentary formation was deposited under anoxic and ferruginous water column conditions derived from high ratios of fe hr fe t and low ratios of fe py fe hr

co generation of hydrogen sulfide and methane in marine carbonate sediments sulfate reduction and methanogenesis are considered to be mutually exclusive microbial reactions in marine sediments typically methane does not appear in significant concentrations in sediment pore waters until almost all dissolved sulfate has been reduced to sulfide an exception to this commonly accepted pattern occurs in an approximately 500 meter thick sequence of quaternary carbonates on the continental margin of the great australian bight an unusual combination of geochemical and sedimentological conditions leads to extensive simultaneous sulfate reduction and methane production throughout the 500 m interval a probable explanation for the co production of these reduced gases in this deeper biosphere is the presence of noncompetitive substrates for the two types of microbiota

composition and origin of clay minerals in holocene sediments from the south eastern north sea the distribution of clay minerals varies systematically in sediments from holocene core material taken along a profile from the east frisian coast to the doggerbank the proportion of illite increases with distance from the coast at the expense of kaolinite whereas slight variations are seen in smectite and chlorite abundances the chemical composition changes and the k rb ratio and k ar isotopic age of illite increase seawards this trend results from progressive mixing processes of riverine detritus with pleistocene fluvioglacial material reworked during the holocene transgression however the clay fluvial flux only became dominant during the decreasing rate of sea level rise in the late holocene especially near the shore for example modern sediments in tidal flats contain 75 of river borne holocene supplied clay detritus whereas this amount is only 10 in modern marine sediments at the doggerbank

depositional history of the southeastern outcrop belt of the chuckanut formation implications for the darrington devil s mountain and straight creek fault zones washington u s a the southeastern outcrop belt of the eocene chuckanut formation contains the erosional remnants of a larger depositional system in the study area the chuckanut formation can be split into four units based upon differences in age lithology sedimentology paleocurrents and provenance relationships the coal mountain unit early eocene represents a southwest flowing fluvial system that shows no evidence for fault control of drainage the overlying higgins mountain unit early middle eocene represents a northeast flowing fluvial system east of the devil s mountain fault zone dmfz with lithologies derived from western source areas the sperry peak unit early middle eocene represents a fluvial system with a wide dispersion of paleocurrent azimuths and a possible mixture of sediment source areas we believe the sperry peak unit was deposited in a fault wedge graben at the junction of the dmfz and straight creek fault zone scfz with sediment sources from both east and west the grade creek unit ag

mechanical aspects of pull apart basins and push up swells with applications to the dead sea transform abstract pull apart basins and push up swells are common features at steps along strike slip faults the structure of these features is examined here for two types of rheology perfect brittle and perfect ductile the stress fields derived for the step area predict that fault patterns mode of deformation and vertical displacement are different for the two rheologies these predictions are illustrated for basins and swells developed in laboratory experiments with modelling materials the structure of basins and swells along the dead sea transform is discussed here the pull apart basins display an intensively faulted southern end and a gently dipping flexure at the northern end a consistent dissimilarity appears between the structures of the eastern and western boundary faults of the basins according to the present interpretation these dissimilarities reflect a relatively ductile crust in arabia and a relatively brittle crust in sinai israel

methane in the upper water column of the northwestern gulf of mexico shallow subsurface dissolved methane maxima were commonly observed in the northwestern gulf of mexico during a series of cruises between 1975 and 1977 although there were often several methane maxima at various depths at any one particular station the most prevalent and widespread occurred over a narrow band of t in a range from 24 to 26 and could be traced as layers extending along and outward from the continental shelf these layers generally followed the local stratification and were associated with the upper part of the pycnocline advection was undoubtedly of importance in determining the extent and distribution of these methane maxima layers but in situ production appears to have supported them some vertical profiles revealed associations between methane atp and suspended matter maxima it is postulated that methane forms in situ in reducing microenvironments associated with suspended participates which are advected from the shelf or which have accumulated in the upper pycnocline due to increase in buoyancy forces

sources and flux of natural gases from mono lake california abstract the ability to identify a formation mechanism for natural gas in a particular environment requires consideration of several geochemical factors when there are multiple sources present four primary sources of methane have been identified in mono lake two of these sources were associated with numerous natural gas seeps which occur at various locations in the lake and extend beyond its present boundary the two other gas sources result from current microbiological processes in the natural gas seeps we observed flow rates as high as 160 moles ch4 day 1 and estimate total lakewide annual seep flux to be 2 1 106 moles ch4 geochemical parameters 13ch4 dch4 ch4 c2h6 c3h8 and 14ch4measurements revealed that most of the seeps originate from a paleo biogenic 13ch4 about 70 natural gas deposit of pleistocene age which underlies the current and former lakebed gas seeps in the vicinity of hot springs had in combination with the biogenic gas a prominent thermogenic gas component resulting from hydrothermal alteration of buried organic matter current microbiological processes responsible for sources of natural gas in the lake included pelagic meth anogenesis and decomposition of terrestrial grasses in the littoral zone methanogenesis in the pelagic sediments resulted in methane saturation 2 3 mm at 50 cm 13ch4 about 85 interstitial sulfate decreased from 133 mm at the surface to 35 mm by 110 cm depth indicating that sulfate reduction and methanogenesis operated concurrently methane diffused out of the sediments resulting in concentrations of about 50 m in the anoxic bottom waters methane oxidation in the oxic anoxic boundry lowered the concentration by 98 but values in surface waters 0 1 1 3 m were supersaturated with respect to the atmosphere the 13ch4 range 21 8 to 71 8 of this unoxidized residual methane was enriched in 13c relative to methane in the bottom water and sediments average outward flux of this methane was 2 77 107 moles yr 1 a fourth but minor source of methane 13ch4 55 2 was associated with the decomposition of terrestrial grasses taking place in the lake s recently expanded littoral zone

sedimentation history of the northern north sea margin during the last 150 ka the norwegian channel ice stream ncis is one the defining features of the fennoscandian icesheet still little is known of the detailed dynamics of this ice stream in relation to regional changes in ice cover paleoceanographic and climatic changes sedimentological data from core md99 2283 in combination with seismic data allow a detailed chronological reconstruction of the outbuilding of the margin and the ice extent in southern scandinavia through the last 150 ka an integrated stratigraphy of the margin is presented and compared to the glacial history changes in the regional ice cover are reflected in the accumulation rates the clay mineralogy the coarse chalk fraction and the number of ird 2 mm in core md99 2283 while the sedimentation on the north sea fan as derived from seismic data provides direct evidence for the glacial activity at the shelf edge tentative evidence was found for two early weichselian glacial advances in southern scandinavia and possibly scotland at around 110 and 80 ka bp from 42 cal ka bp the ice cover expanded in southern fennoscandia and led to increased deposition on the margin and the occurrence of local melt water outbursts significantly increased accumulation rates coarse chalk local meltwater output and smectite occur during the ice expansion in the north sea from around 34 cal ka bp the main outbuilding phase of the nsf during the last glacial cycle occurred after 30 cal ka bp from around 24 cal ka bp the ncis became highly active and advanced at least three times prior to the final retreat from the shelf edge around 19 0 cal ka bp

the ophiolitic ingalls complex north central cascade mountains washington the ingalls complex is the largest and most complete of several middle to late jurassic ophiolites in northwestern washington it structurally overlies the skagit metamorphic core of the north cascades and is intruded by the late cretaceous mount stuart batholith the last truncates major structures of the ophiolite and divides it into two outcrop areas a main area south of the batholith and a smaller area in a roof pendant in the main area the internal structure of the ophiolite is dominated by two wide fault zones characterized by steeply dipping serpentinite melange displacement probably was a combination of strike slip and dip slip with the latter apparently related to diapiric rise of serpentinite deformation probably occurred in an oceanic transform fault zone ultramafic tectonites predominate in the main outcrop area including from south to north 1 harzburgites and dunites 2 mylonitic iherzolites and hornblende peridotites and 3 iherzolites unit 2 represents a high temperature shear zone that may record early movement in the deeper levels of the postulated oceanic fracture zone mafites generally occur as tectonic blocks in the southern fault zone they underwent ocean floor type metamorphism but to the north metagabbros experienced dynamothermal amphibolite facies metamorphism prior to incorporation into the serpentinite melange gabbros in the southern fault zone locally intrude ultramafites and in places pass upward into a diabase dike complex gabbros and diabases intrude partly pillowed basaltic flows and pillow breccias with interbeds of argillite chert and ophiolite derived sedimentary breccia another sequence of basalt argillite chert and minor limestone is penetratively deformed and may be exotic in the pendant on the mount stuart batholith the north directed windy pass thrust wpt places the ingalls on the pelitic chiwaukum schist of the skagit metamorphic core the ingalls is imbricated with amphibolite facies metasedimentary and metaplutonic slices that may be a part of the skagit core not exposed in the lower plate imbrication was synchronous with amphibolite facies metamorphism of the ophiolite in the pendant but the postmetamorphic sole thrust wpt truncates both the imbricate slices and fabric elements in the chiwaukum schist thrusting was mid cretaceous apparently postdating high angle faulting within the main portion of the ingalls the wpt marks a major cretaceous boundary between an oceanic and a metamorphic terrane skagit core and its upper plate represents the only rocks preserved above the skagit core the ingalls is similar in age to ophiolites in california oregon and british columbia as well as those in northwestern washington the california and oregon ophiolites coast range smartville josephine apparently originated in small short lived marginal basins whereas the ingalls was deformed in a fracture zone in a wider longer lived marginal basin or large ocean

the newport fault eocene listric normal faulting mylonitization and crustal extension in northeastern washington and northwestern idaho discussion and reply

geochemistry of holocene salt marsh and tidal flat sediments on a barrier island in the southern north sea langeoog north west germany abstract the barrier islands of the southern north sea were formed during the holocenesea level rise these islands form part of a highly dynamic environment whoseevolution continues today subjected to sea level changes tides and stormevents the sedimentary record re ects processes occurring under varyingenergy conditions this article presents geochemical mineralogical anddiatom investigations carried out in the salt marsh of the east frisian barrierisland of langeoog which is re exposed to a rising sea level due tode embankment the major aim of this study is to improve the knowledge ofthe sedimentological and geochemical development of these deposits underthe in uence of sea level rise with a special focus on the geochemistry anddistribution of heavy mineral associated elements correlation diagramsbetween feo tio 2 and mno as well as ternary plots al 2 o 3 sio 2 zr ortio 2 clearly indicate the variable appearance of heavy minerals in differentlithological facies comprising marsh soil mixed and sand at and relocatedbeach sands a dominating abundance of ilmenite followed by zircon garnetsand some other heavy minerals is evidenced by scanning electron microscope energy dispersive x ray measurements the data presented here suggests thatthese geochemical proxies are useful tools for characterizing depositionalenergy conditions increasing depositional energy is evident for the lithologicalunits in the following order marsh soil mixed at sand at and relocatedbeach sand the energetic conditions during sediment deposition as well asthe sedimentary history are con rmed by diatom analyses as an additionalindependent indicator depending on source rock composition thegeochemical parameters used in this study may also help to investigatedepositional energy regimes of other siliciclastic sedimentary systems keywords depositional energy diatoms heavy minerals inorganicgeochemistry north sea salt marsh tidal at introductionthe depositional history of the barrier islands andadjacent tidal at system of the southern northsea coast was directly related to climate changesduring the holocene sea level rise the lasttransgressive cycle started in the weichselianlate glacial and continues today as evidenced bysedimentology 2012 59 337 355

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

varied pathways of river borne clay minerals in a near shore marine region a case study of sediments from the elbe and weser rivers and the se north sea abstract the the results outline significant systematic changes in the proportions of clay minerals in the k rb ratios the k ar data and in the heavy metal contents at the fluvial estuarine transition and towards the marine environment these changes result from a progressive mixing of suspended fluvial material with reworked pleistocene sediments at the bottom of the north sea near shore the proportion of reworked pleistocene sediment amounts only 20 30 the mixture is distributed within a 100 km wide zone mainly by currents parallel to the coast it is also transported during flood tide into the estuaries where it is mixed further with suspended fluvial material the k rb ratios and k ar dates obtained from illite prove to be particularly useful for modeling the mixing of the clay minerals as well as their distribution patterns and origin

anomalous enrichments of iron monosulfide in euxinic marine sediments and the role of h 2 s in iron sulfide transformations examples from effingham inlet orca basin and the black sea it is well documented that sedimentary pyrite formation proceeds through an iron monosulfide fes precursor laboratory studies have tradition ally indicated that intermediate s species such as elemental sulfur s 0 or polysul fides sx 2 are responsible for the transformation of fes to pyrite fes2 recent experimental work however has suggested that h2s may also be responsible for the transformation the present study extrapolates reaction pathways respon sible for pyrite formation in the laboratory to two fundamentally different modern anoxic marine systems we hypothesize that on decadal timescales h2s or hs is responsible for transformations of fes into fes2 in natural systems where intermediate s species are isolated from fes production the possibility of prolonged coexistence of high levels of h2s and fes however challenges recent experimental predictions of extremely rapid transformations that is timescales of hours or less of fes to fes2 via the h2s pathway sediments of effingham inlet a fjord on vancouver island and the orca basin an intraslope brine pool in the northern gulf of mexico are both charac terized by atypically high concentrations of fes but contrasting levels of h2s and fes2 production in both systems fes formation is spatially decoupled from intermediate s species as a consequence of either rapid deposition burial or extreme water column stratification within settings that promote this separa tion h2s may be the principal species responsible for pyrite formation fes to fes2 transformations are favored by the high concentrations of h2s in sediments of effingham inlet additional results from the margin of the anoxic black sea corroborate the effingham model for iron sulfide transformation h2s concentrations are controlled by the amount of bacterial sulfate reduc tion and the availability of reactive fe h2s concentrations will be buffered to low levels via the production of fes in systems with appreciable amounts of reactive fe and therefore be unavailable to transform fes to fes2 under conditions where h2s is the only species available for fes to fes2 transformations some degree of fe limitation may promote pyrite formation by allowing h2 st o accumulate in the pore waters ultimately this balance between h2s production and reactive fe availability may strongly influence the amount of pyrite formed in anoxic systems

depositional history of the eocene chumstick formation implications of tectonic partitioning for the history of the leavenworth and entiat eagle creek fault systems washington the chumstick basin opened as an extensional half graben prior to 51 ma and was subsequently modified by two episodes of tectonic partitioning of drainage prior to basin deformation initially westward flowing fluvial systems formed a unified depositional system with the swauk basin tectonic partitioning of drainage at 51 49 ma and at 44 42 ma was controlled by localized uplift on the leavenworth lfz eagle creek ecfz and entiat efz fault zones and led in each instance to the truncation of regional depositional systems modification and reversal of paleoflow and internal drainage relief on the lfz at 51 49 ma may be the result of isostatic uplift of the extensional footwall producing the swauk and chumstick basins as a pair of west facing half grabens the earliest convincing evidence for the onset of oblique slip in the region is at about 48 ma folding in the swauk basin or about 44 42 ma probable transpressive uplift at left stepping bends of the lfz development of a transtensional step over basin between the ecfz and efz horsetail splays in the ecfz and possible flower structures in the lfz and ecfz in the chumstick basin each episode of tectonic partitioning was followed by proximal onlap and overtopping of fault zones to reestablish regional flow systems the chumstick formation was deformed by dextral transpression between 37 34 ma and is unconformably overlain by the oligocene wenatchee formation the chumstick basin is an example of an extensional basin modified by subsequent strike slip tectonics thus caution should be used in applying idealized basin models