geochemistry of the ungrouped carbonaceous chondrite tagish lake the anomalous cm chondrite bells and comparison with ci and cm chondrites i have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the tagish lake carbonaceous chondrite fall along with bulk samples of the ci chondrite orgueil and of several cm chondrites tagish lake has a mean of refractory lithophile element cr ratios like those of cm chondrites and distinctly higher than the ci chondrite mean tagish lake exhibits abundances of the moderately volatile lithophile elements na and k that are slightly higher than those of mean cm chondrites refractory through moderately volatile siderophile element abundances in tagish lake are like those of cm chondrites tagish lake is distinct from cm chondrites in abundances of the most volatile elements mean ci normalized se co zn co and cs co for tagish lake are 0 68 0 01 0 71 0 07 and 0 76 0 02 while for all available cm chondrite determinations these ratios lie between 0 31 and 0 61 between 0 32 and 0 58 and between 0 39 and 0 74 respectively considering petrography and oxygen isotopic and elemental compositions tagish lake is an ungrouped member of the carbonaceous chondrite clan the overall abundance pattern is similar to those of cm chondrites indicating that tagish lake and cms experienced very similar nebular fractionations bells is a cm chondrite with unusual petrologic characteristics bells has a mean ci normalized refractory lithophile element cr ratio of 0 96 lower than for any other cm chondrite but shows ci normalized moderately volatile lithophile element cr ratios within the ranges of other cm chondrites except for na which is low iridium co ni and fe abundances are like those of cm chondrites but the moderately volatile siderophile elements au as and sb have abundances below the ranges for cm chondrites abundances of the moderately volatile elements se and zn of bells are within the cm ranges bells is best classified as an anomalous cm chondrite

origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

lithospheric processes and products in the southern canadian cordillera a lithoprobe perspective analyses of lithoprobe and other data from southwestern canada provide new insights on how this portion of the cordillera formed during plate convergence along the western margin of north america crustal rocks are detached from their mantle lithosphere which must have been consumed during subduction detachment occurred at or near the base of the crust beneath the intermontane and or omineca belts probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool mechanically rigid north american craton during the late cretaceous and early tertiary rotation of detached rocks caught between the north american craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western cordillera and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern cordillera during the same time interval transpression assoc

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

stratigraphy and paleoenvironmental analysis of the frasnian famennian upper devonian boundary interval in tioga north central pennsylvania abstract two pulses of extinction in the late frasnian late devonian the lower and upper kellwasser lkw and ukw events coincided with the deposition of organic rich strata in many parts of the world including the appalachian basin here we describe two stratigraphic sections from tioga north central pennsylvania that span the frasnian famennian f f boundary interval the f f boundary and ukw equivalent strata are probably located in the covered interval between the two sections but the lkw equivalent pipe creek formation is well exposed we propose several stratigraphic revisions including raising the lock haven formation to group status and dividing it into formations as well as redefining the base of the canaseraga formation and subdividing it into members paleoenvironments at tioga range from offshore outer shelf to middle shoreface a regression follows the lkw transgression as evidenced by the sharp superposition of middle shoreface sands on outer shelf mudstones similar to large facies changes associated with the lkw in other settings the lkw is typically interpreted as representing deposition under dysoxic anoxic conditions and trace and body fossil content suggest that the pipe creek formation represents dysoxic but not permanently anoxic conditions these stratigraphic revisions and records of environmental change will provide the framework for more detailed studies of the lkw and ukw extinction events in the appalachian basin

geologic evidence for chaotic behavior of the planets and its constraints on the third order eustatic sequences at the end of the late paleozoic ice age abstract high resolution 948 samples measurements of anhysteretic remanent magnetization arm were performed on the 200 m thick early middle permian maokou formation of the shangsi section south china the arm variations are quasi periodic and the wavelengths of significant cycles collectively present a ratio of 20 5 2 1 throughout the formation corresponding to long orbital eccentricity short orbital eccentricity obliquity and precession cycles a strong obliquity 44 and 33 kyr signal suggests that waning and waxing of the ice sheet in eastern australia at the end of the late paleozoic ice age lpia exerted a significant influence on global climate and sea level a floating astronomical time scale ats is developed using the 405 kyr orbital eccentricity cycle as an astronomical calibration target this results in estimation of the roadian and wordian stages duration as 3 7 0 4 myr and 2 9 0 4 myr respectively prominent 2 myr cycles likely originated from earth and mars secular frequencies g4 g3 and 1 myr cycles from s4 s3 these periodicities are shorter than those observed in the cenozoic era which may be due to the chaotic behavior of the planets but still reflecting 2 1 secular resonance between earth and mars third order eustatic sequences are linked to the s4 s3 obliquity term which suggests a glacioeustatic controlling mechanism during this transitional stage from paleozoic icehouse to mesozoic greenhouse

continental transform tectonics great slave lake shear zone ca 1 9 ga northwest canada great slave lake shear zone gslsz is a northeast trending dextral mylonite zone across which the coeval north trending thelon and taltson magmatic zones on the west margin of the churchill province are offset 300 700 km it is proposed that the gslsz is a continental transform structure related to oblique collisional indentation of the active margin of the churchill province by the microcontinental slave province this accounts for geologic and geophysical differences between the thelon and taltson zones and explains the localization of a tibetan type queen maud uplift north of the gslsz and the abrupt loss of slip on the gslsz east of the uplift it also provides a new model for the athapuscow aulacogen analogous to the modern bay of bengal indo burman ranges sagaing transform andaman sea situation

early oligocene stratigraphic turnover on the west africa continental margin a signature of the tertiary greenhouse to icehouse transition the post rift stratigraphy on the west african margin is characterized by aggradation of a carbonate ramp during late cretaceous to eocene epochs and progradation of a terrigenous wedge from oligocene to the present such first order structure has been attributed in the past to geodynamic forcing however comparison of the stratigraphic record of the margin with eustasy 18o and 87sr 86sr curves shows a close temporal relationship with the tertiary climate cooling an increase of continental weathering and a long term lowering of sea level we suggest that the transition from low amplitude high frequency sea level changes during the greenhouse period to high amplitude high frequency sea level changes during the icehouse period may account for i the switch from an aggrading carbonate ramp to a prograding clastic wedge and ii the enhanced continental weathering and increased terrigenous influx to the margin

lower and lower middle pennsylvanian fluvial to estuarine deposition central appalachian basin effects of eustasy tectonics and climate interpretations of pennsylvanian sedimentation and peat accumulation commonly use examples from the appalachian basin because of the excellent outcrops and large reserve of coal 100 billion metric tons in the region particularly controversial is the origin of lower and lower middle pennsylvanian quartzose sandstones beach barrier marine bar tidal strait and fluvial models all have been applied to a series of sand bodies along the western outcrop margin of the basin interpretations of these sandstones and their inferred lateral relationships are critical for understanding the relative degree of eustatic tectonic and climatic controls on early pennsylvanian sedimentation cross sections utilizing 1000 subsurface records and detailed sedimentological analysis of the livingston conglomerate rockcastle sandstone corbin sandstone and pine creek sandstone an informal member of the breathitt group were used to show that each of the principal quartzose sandstones on the margin of the central appalachian basin contains both fluvial and marginal marine facies the four sandstones are fluvially dominated and are inferred to represent successive bed load trunk systems of the appalachian foreland base level rise and an associated decrease in extra basinal sediment at the end of each fluvial episode led to the development of local estuaries and marine reworking of the tops of the sand belts each of the sand belts is capped locally by a coal regardless of whether the upper surfaces of the sand belts are of fluvial or estuarine origin suggesting allocyclic controls on deposition peats were controlled by a tropical ever wet climate which also influenced sandstone composition through weathering of stored sands in slowly aggrading braidplains recurrent stacking of thick coarse grained fluvial deposits with extra basinal quartz pebbles dominance of bed load fluvial lowstand deposits over mixed load estuarine transgressive deposits thinning of sand belts around tectonic highs and along faults cratonward shift and amalgamation of successive sand belts on the margin of the basin and truncation of successive sand belts toward the fault bound margin of the basin are interpreted as regional responses to alleghenian tectonism inferred to have been the dominant control on accommodation space and sediment flux in the early pennsylvanian basin

suppression of dominant topographic overprints in gravity data by adaptive filtering southern wyoming province in areas of the world with a protracted tectonic history the gravity field may be dominated by anomalies due to individual structural features developed during the latest tectonic event these individual tectonic features often have a topographic expression adaptive filtering techniques can be used to suppress the gravity effects of such features iterative space domain techniques are particularly well suited to these types of problems one such technique the stochastic gradient algorithm allows easy updating of filter coefficients at each spatial step through the data this approach eliminates windowing and spectral estimation problems associated with cross spectral admittance schemes in this study adaptive filtering of bouguer gravity and topography in the southern wyoming province was successful in suppressing gravity signatures of laramide structural features the regional gravity trends due to isostatic effects were significantly absent from the residual anomaly map a large continuous positive gravity anomaly stretching from the southern wind river range to the northern end of the laramie range was another outstanding feature observed in the residual anomaly this positive anomaly is about the same magnitude size and shape as anomalies due to greenstone belts observed in other archcan cratonal areas scattered occurrences of greenstone lithologies are known throughout the area of the anomaly but a continuous feature is absent in outcrop due to the unusual structural history of the area it is possible that such a continuous belt does exist but was buried at shallow crustal levels by laramide thrusting or later collapse of a laramide uplift due to a change in the regional stress field

tectonic significance of potential field anomalies in western canada results from the lithoprobe snorcle transect potential field anomalies within the lithoprobe snorcle slave northern cordillera lithospheric evolution transect area provide geometrical constraints for regional crustal and lithospheric structures as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections and forward modelling provides tests of different interpretations of deep crustal and upper mantle density structures in a key result from modelling a paleoproterozoic subduction zone beneath the wopmay orogen probably consists of high density rocks such as eclogite within the upper mantle this result supports the concept of moderate to low angle intra lithospheric sutures on an even larger scale applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus

phyllosilicates in the matrix of the unique carbonaceous chondrite lewis cliff 85332 and possible implications for the aqueous alteration of ci chondrites abstract the fine grained matrix of the unique unequilibrated carbonaceous chondrite lewis cliff lew 85332 has been studied by scanning electron microscopy sem electron probe microanalysis epma and transmission electron microscopy tem compositionally lew 85332 has a matrix that is more fe rich than typical ci chondrites but has elemental abundance ratios that appear to be closer to ci matrices than to cm or cr chondrites the mineralogy of the matrix is dominated by phyllosilicate phases that are predominantly interlayered fe rich serpentine saponite anhydrous silicate phases such as olivine and pyroxene are rare minor magnetite troilite and ferrihydrite also occur associated with the phyllosilicates despite the high degree of weathering in lew 85332 the phyllosilicates appear to have an extraterrestrial origin but the highly variable mg fe ratios of saponite may be the result of partial terrestrial oxidation of fe rich saponite to a more mg rich saponite and ferrihydrite alternatively some of the ferrihydrite may have formed as a result of terrestrial weathering of fe ni metal the compositional and mineralogical data suggest that the matrix of lew 85332 may represent a very early stage in the type of aqueous alteration experienced by the ci chondrites although it is improbable that lew 85332 was a precursor to the ci chondrites because of its high abundance of chondrules the absence of carbonates the high fe content of the matrix and phyllosilicate phases and relatively low abundance of magnetite all indicate that the degree of oxidation and leaching of lew 85332 matrix was significantly less than that experienced by the ci chondrites the absence of clear evidence for alteration of chondrules suggests that either the formation of the hydrous phases in the matrix occurred prior to accretion or that alteration occurred on a parent body and involved limited amounts of fluid such that the reactions took place preferentially and exclusively within the fine grained anhydrous matrix materials

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

incompletely transformed serpentine type phyllosilicates in the matrix of antarctic cm chondrites abstract recent hrem high resolution electron microscopy investigation has shed light on the characterization of matrix phyllosilicates in cm chondrites in examining the antarctic cm chondrite yamato 793321 by hrem mineral grains which show an ed electron diffraction pattern consisting of both olivine and serpentine spots show disordered and defect structures in patchy hrem images these data are interpreted as representing an intermediate phase in the transformation from serpentine to olivine this is the first description of such an intermediate phase in belgica 7904 phyllosilicates seem to have been almost completely transformed to olivine it is suggested that it formed by heating of matrix phyllosilicates preliminary heating experiments on murchison also a cm chondrite showed that the matrix phyllosilicates transformed to a phase which gave an ed pattern and hrem image similar to those for yamato 793321 the results of these heating experiments support the formation of the intermediate phase by transformation from phyllosilicate to olivine during a heating event at a late stage

shallow marine sedimentary processes in the late devonian catskill sea new york state shallow marine strata of the upper devonian west falls group in south central new york comprise centimetre to decimetre thick sheetlike to lenticular beds of sandstone and siltstone interbedded with mudstone unidirectional current scour marks and tool marks occur on the basal erosion surfaces of the sandstones their internal structures are hummocky cross strata of various styles planar laminae and wave ripple cross laminae with characteristic vertical and lateral transitions among them vertical burrows of the skolithos ichnofacies dominate upper portions of sandstone beds whereas mudstones and silt stones contain mainly horizontal burrows of the cruziana ichnofacies transported and in situ shelly fossils occur throughout in places concentrated in coquinite lenses large scale 15 to 30 in bedding sequences are characterized by upward thickening and coarsening of sandstone beds increase in amalgamated hummocky cross strata coquinites plant debris and bivalves followed by abrupt fining and thinning of beds the depositional environment is interpreted as a shallow marine shelf episodically influenced by intense tropical storms hurricanes individual sandstone beds were deposited by spatially decelerating combined flows where an initially strong offshore directed flow component decreased in time relative to the oscillatory flow component large scale bedding sequences reflect changes in storm combined current intensity and deposition rate strong eustatic control is unlikely and there is no evidence of changing wave climate instead these sequences may be associated with delta lobe progradation and or offshore bar development

light element geochemistry of the tagish lake ci2 chondrite comparison with ci1 and cm2 meteorites we have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the tagish lake carbonaceous chondrite by high resolution stepped combustion mass spectrometry and compared the results with data from the orgueil ci1 eet 83334 cm1 and murchison cm2 chondrites the small chip of tagish lake analysed herein had a higher carbon abundance 5 81 wt than any other chondrite and a nitrogen content 1220 ppm between that of ci1 and cm2 chondrites owing to the heterogeneous nature of the meteorite the measured carbon abundance might be artificially high the carbon inventory and whole rock carbon isotopic composition 13c 24 4 of the chip was dominated by 13c enriched carbon from the decomposition of carbonates between 1 29 wt and 2 69 wt 13c 67 and 18o 35 in the proportions 4 1 dolomite to calcite in addition to carbonates tagish lake contains organic carbon 2 6 wt 13c 9 1033 ppm n 15n 77 a level intermediate between ci and cm chondrites around 2 of the organic material is thermally labile and solvent soluble a further 18 of the organic species are liberated by acid hydrolysis tagish lake also contains a complement of presolar grains it has a higher nanodiamond abundance 3650 4330 ppm than other carbonaceous chondrites along with 8 ppm silicon carbide whilst carbon and nitrogen isotope geochemistry is not diagnostic the data are consistent with classification of tagish lake as a ci2 chondrite

three dimensional structure across the tintina strike slip fault northern canadian cordillera from seismic refraction and reflection tomography accepted 2006 june 5 received 2006 june 3 in original form 2005 september 4 summary the development of the northern canadian cordillera involved major strike slip displacement of accreted terranes relative to north america along faults such as the tintina which has experienced 425 km of dextral motion since the palaeocene the snore seismic refraction wideangle reflection experiment was carried out in 1997 as one component of lithoprobe s slavenorthern cordillera lithospheric evolution snorcle transect in addition to four 2 d profiles two sets of broadside recordings were acquired to image the 3 d structure across the tintina fault tf in areas centred at about 59 5 n and 62 n simultaneous and independent refraction and reflection traveltime tomography were applied to the combined inline and broadside data set for each region to establish the range of lower crustal velocity moho depth and upper mantle velocity structure consistent with the data our preferred models are the average of the simultaneous and independent models since they represent the robust features required by the data the preferred 3 d models are generally consistent with the 2 d models obtained from the inline data in previous independent studies there are along strike variations across the tf perhaps due to the change in strike direction or the amount of motion along the fault in the north compared to the south in the lower crust the only correlation with the tf that is required by the data is a 0 1 km s 1 drop in velocity to the southwest of the fault in the northern study area the absence of a strong correlation with the tf in the lower crust is consistent with the interpreted continuity of lower crustal units across the fault in the snorcle reflection data the moho is relatively flat throughout the study area 34 35 km depth but there is broad crustal thickening of a few kilometres centred 50 km southwest of the tf in the northern and southern study areas this thickening may be the result of a period when there was a component of compression along the tf there is strong evidence for a 0 3 0 4 km s 1 drop in upper mantle velocity to the west of the tf in the south and weak evidence for 0 1 km s 1 drop to the southwest in the north the upper mantle variations in the south indicate that the tf is the boundary between cooler and or more refractory ancestral north american mantle to the east and warmer and or more fertile mantle beneath accreted north america to the west in the north the mantle appears to be more intermediate in its properties on both sides of the tf

late frasnian sedimentation cycles in the appalachian basin possible evidence for high frequency eustatic sea level changes abstract during the late frasnian 11 fourth order progradational retrogradational marine sedimentation cycles were deposited in the appalachian foreland basin mapping based primarily on subsurface data demonstrates the continuity of these cycles over a distance of 700 km cyclicity in distal facies occurs as alternations of organic rich and organic poor shales two of the organic shales can be correlated with the transgressive kellwasser beds of europe in more proximal facies recurring lobes of siltstone and sandstone were deposited based on lithologic indices the temporal pattern shows significant variation in the strength of relative facies change during deposition in particular two times of particularly pronounced progradation correspond to previously recognized eustatic sea level falls the correlation of portions of appalachian basin depositional cyclicity with global sea level events suggests that the entire sequence of 11 cycles with estimated average duration of around 100 150 ka were the result of high frequency eustatic sea level changes this in turn would be consistent with a brief period of late frasnian glaciation as others have previously suggested

geometric test for late cretaceous paleogene intracontinental transform faulting in the canadian cordillera the tintina trench northern rocky mountain trench tt nrmt fault zone and the fraser river straight creek fr sc fault zone are separate en echelon concentric small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the canadian cordillera from the outboard part of a tectonic collage of accreted foreign terranes in the south into the north american preaccretionary continental margin in the north most of the 450 km of right hand slip on the tt nrmt fault zone was transformed southward during the late cretaceous and paleocene into oblique convergence in the southern canadian rockies the remainder probably comprising less than 100 km was transformed southwestward during early and middle eocene time via a zone of distributed shear and east west crustal stretching into right hand slip on the en echelon fr sc fault zone these interpretations based on regional systematic mapping of geologic structures are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post mid cretaceous right hand displacement along the general locus of the tt nrmt fault zone involving foreign terranes and the parts of north america to which they had been accreted this paradox must be resolved

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

high resolution sequence stratigraphic analysis of the shannon sandstone in wyoming using a template for regional correlation abstract recent interpretations of the lower campanian shannon sandstone in the powder river basin wyoming have suggested that it was deposited in falling stage and lowstand incised shorefaces rather than in stacked shelf ridges up to 160 km from shore despite these detailed studies there is no published correlation of the outcrop deposits at salt creek anticline with the subsurface deposits in the hartzog draw heldt draw hd hd area a complete high resolution sequence stratigraphic analysis of the shannon requires that the outcrops at salt creek be correlated with the subsurface fields at hd hd there is little core control in the approximately 30 km between these areas so correlations are based almost entirely on well logs a template has been constructed in the hd hd area where ther is good core and well log control which embodies data from facies facies successions well log signatures and bounding discontinuities the template consists of a regressive surface of erosion rse that forms the base of an incised shoreface sandbody and a transgressive surface of erosion tse that truncates the top of the sandbody and the rse two cross sections have been constructed and the template has been used to guide correlations between salt creek and the hd hd area from the cross sections six progradational events and six transgressions have been defined during shannon time the positions of the rses and tses allow estimates of between a few meters and 60 m for the magnitude of sea level fluctuations that controlled shannon deposition the proposed correlations confirm and reinforce the interpretation of the shannon as a series of incised shoreface sandbodies separated by transgressive systems tract mudstone deposits

matrices of carbonaceous chondrite meteorites the morphology classification and chemistry of the matrices of carbonaceous chondrite cc meteorites is reviewed based on recent research results the various kinds of ccs are examined in terms of their matrix mineralogy alteration processes in ccs are discussed

accreted terranes of northwestern british columbia canada lithospheric velocity structure and tectonics 1 lithospheric structure beneath the accreted terranes of the northwestern canadian cordillera is interpreted from analyses of p wave refraction and wide angle reflection data the 535 km long profile extends from the deformed and displaced ancestral north american margin across the omineca belt suture zone and intermontane superterrane to the coast belt this region is interpreted to have grown westward through a progression from thin skinned to thick skinned accretionary tectonics large lateral variations of velocities 2 0 6 4 km s within the upper 15 km correlate with the mapped geological and terrane elements fault offsets and the imbricated base of an overlap basin are clearly identified inboard of the stikine accreted terrane a zone of slow upper crustal velocities thins to the east consistent with an interpretation of thin skinned accretion leaving slivers of terranes overlying a wedge of metamorphosed proterozoic continental margin sediments however in the lower crust the proposed underlying cratonic ramp is not distinguished from outboard or overlying accreted crust by lateral p velocity contrasts or wide angle reflections the moho remains nearly horizontal beneath the intermontane and omineca belts gradually thinning to the east from 36 5 to 35 km to the southwest below the coast belt and to the northeast beneath the tintina fault the crust thins to 32 km upper mantle velocities across the coast intermontane and omineca belts are 7 8 7 9 km s the slow upper mantle and lower crustal velocities are indicative of high temperatures that may permit the flat moho or weak lower crust to partially decouple the crust from the mantle reflections in the upper mantle between 50 70 km depth may be related to the base of the lithosphere or to heterogeneities introduced through melting or accretionary subduction events

incised valley fill interpretation for mississippian black hand sandstone appalachian basin usa implications for glacial eustasy at kinderhookian osagean tn2 tn3 boundary abstract lower mississippian strata of east central ohio are predominantly fine grained marine deposits of the cuyahoga and logan formations within these sediments is the black hand sandstone of the cuyahoga formation the black hand sandstone is a multistory crossbedded coarse grained conglomeratic sandstone the contact between the black hand sandstone and the subjacent cuyahoga formation is sharp and scoured with intraclasts of the cuyahoga formation incorporated into the basal black hand sandstone the black hand sandstone was previously thought to represent a distributary channel deposit however the combination of lithofacies and architectural elements indicates deposition in a braided stream setting the cuyahoga formation was deposited in a shallow marine setting the erosional basal contact of the black hand sandstone and the juxtaposition of fluvial and marine sediments suggests a sequence boundary the geographic distribution of the black hand sandstone combined with the evidence for a sequence boundary suggests deposition in an incised valley the age of the black hand sandstone is key to inferring the causes of valley incision the black hand sandstone is nearly devoid of body fossils necessitating a biostratigraphic analysis of the surrounding cuyahoga and logan formations analysis indicates the logan formation is early osagean age data from the cuyahoga formation suggest a kinderhookian age with a possible transition to the osagean in the uppermost cuyahoga formation this constrains the age of the black hand sandstone to the transition at the kinderhookian osagean boundary recent reports indicate late kinderhookian tournaisian tn2 gondwanan glaciation based upon tillites and sharp excursions in stable isotope curves a glacio eustatic fall in sea level is inferred to have caused incision of the cuyahoga formation followed by deposition of the black hand sandstone and logan formation during the subsequent sea level rise the associated unconformity correlates to the sequence boundary at the kinderhookian osagean boundary in the stratotype area of north america and the correlative tn2 tn3 boundary worldwide supporting the hypothesis of a global eustatic event at this time

mineralogy and noble gas signatures of the carbonate rich lithology of the tagish lake carbonaceous chondrite evidence for an accretionary breccia abstract the carbonate rich lithology of the tagish lake carbonaceous chondrite was characterized by noble gas mass spectrometry synchrotron x ray diffraction analysis and transmission and scanning electron microscopy noble gas analysis was performed on two samples and the results showed that primordial noble gases are abundant and solar noble gases are absent in the samples of carbonate rich lithology the concentrations of ne a2 and e in both samples are at the maximum level observed for ci and cm chondrites suggesting high abundances of presolar diamonds and sic graphite respectively the cosmic ray exposure age cannot be determined precisely because the shielding depth of our tagish lake samples is unknown but the minimum exposure age was determined to be 5 5 0 7 myr on the basis of cosmogenic 21ne concentrations and the highest 21ne production rate x ray and electron microscopic study showed that the carbonate rich lithology is dominated by loosely packed porous matrix that consists mainly of fine grained saponite and ferromagenesian carbonate the matrix contains very few chondrules but many fine grained clasts having angular shape with longest dimensions up to 1 mm the clasts differ from host matrix in both texture and mineralogy they are massive compacted material with porosity much lower than matrix and contain abundant magnetite and a coherent intergrowth of serpentine and saponite that is rare in matrix the presence of texturally and mineralogically distinct clasts indicates that the carbonate rich lithology is a breccia but the absence of solar noble gases and impact induced deformational features in host matrix distinguish it from an asteroid regolith breccia our results instead indicate that it is an accretionary breccia formed by simultaneous accretion of diverse objects in a massive dust cloud the clasts often enclose chondrules and anhydrous silicate fragments such as low iron manganese enriched olivines this observation and their highly compacted angular morphology suggests that the clasts derive from earlier formed chondritic materials which have experienced compression and fragmentation due to mild impacts and from which they were excavated and incorporated into the final rock it is thus suggested that in the course of planetesimal formation agglomeration and disagglomeration of small parent bodies occurred repeatedly in a dense dust cloud where solar wind from the infant sun was shielded the fine grained ferromagnesian carbonates must have precipitated from aqueous solutions after the assembly of the tagish lake asteroid from recycled materials from previous bodies because the carbonates coat the surfaces of pores and fill in veins in the clasts

a computational investigation of adsorption of organics on mineral surfaces implications for organics delivery in the early solar system abstract the adsorption of simple organic compounds onto minerals that are known to occur in the early solar nebula such as olivine spinel and water ice is examined using first principles density functional theory the calculations show that electron rich organics and organics containing cyanide amine and carboxylic functional groups can strongly bind to low index surfaces of olivine and spinel based on the surface coverage as obtained from these calculations it can be inferred that an estimated amount of 10 13 kg of organics could have been delivered to early earth via direct adsorption mechanisms thereby providing an endogenous source of planetary organics in addition adsorption of organic compounds on magnesite a carbonate phase believed to have formed via aqueous processes on asteroidal bodies is also studied the adsorption behavior of the organics is observed to be similar in both cases i e for minerals that formed during the earliest stages of nebular evolution through condensation spinel and olivine or other processes and for those that formed via hydration processes on asteroidal bodies magnesite these results suggest that direct incorporation via adsorption is an important delivery mechanism of organics to both asteroidal bodies and terrestrial planets

great slave lake shear zone nw canada mylonitic record of early proterozoic continental convergence collision and indentation abstract great slave lake shear zone in the nw canadian shield is an excellent example of the kinematic magmatic and thermal evolution of a crustal scale shear zone associated with a collisional continental boundary it is a 25 km wide corridor of granulite to lower greenschist facies mylonites and cataclastic fault rocks developed in the deep seated parts of an early proterozoic 2 0 1 9 ga magmatic arc constructed on the upper rae plate at the contact between the archean slave and rae continents the rocks of great slave lake shear zone the thelon magmatic arc and the taltson magmatic zone are all components of the same magmatic arc but their geological histories reflect different aspects of the continental interaction

lithoprobe crustal reflection cross section of the southern canadian cordillera 1 foreland thrust and fold belt to fraser river fault seismic reflection data from the south central canadian cordillera covering the interval from the easternmost metamorphic core complexes near arrow lakes to the fraser river fault system along the fraser river reveal a highly reflective and complex crust the base of the crustal reflectivity interpreted as the reflection moho is clearly delineated by a continuous sharp boundary that is essentially planar and slopes uniformly over a distance of 250 km from about 12 0 s in the east to about 10 5 s in the west this virtual lack of relief at the base of the crust contrasts sharply with surface structures that involve 25 km or more of structural relief some of these surface structures can be readily correlated to structures that are outlined by the reflection data and that can be followed into the middle and lower crust even though part of this area was subjected to large amounts of eocene extension the crust is not divisible into transparent upper and reflective lower layers as it is in parts of the u s cordillera three structural culminations the monashee complex the vernon antiform and the central nicola horst are interpreted on the basis of the reflection configuration and the surface geological relationships to have formed initially during jurassic to eocene compression and then to have been modified and exposed during early and middle eocene extension an example of a compressional structure observed on the profiles is the monashee decollement which can be traced from the surface westward into the lower crust extension is manifested along a variety of normal faults including the regionally extensive low angle okanagan valley eagle river fault system moderately dipping faults such as the columbia river and slocan lake faults and high angle faults such as the quilchena creek and coldwater faults both jurassic to eocene compressional shear zones and early to middle eocene extensional shear zones are listric into the lower crust or moho under the intermontane belt

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

formation and alteration of cais in cold bokkeveld cm2 abstract calcium aluminium rich inclusions cais from the carbonaceous chondrite cold bokkeveld cm2 have been located and characterised in situ the textural environment of cm2 cais has been studied for the first time based on their primary mineralogy 345 cais have been classified into four groups 1 1 spinel inclusions 2 2 a hibonite inclusion 3 3 spinel pyroxene sp py inclusions 4 4 spinel pyroxene olivine sp py ol inclusions in addition refractory spherules and spinel bearing isolated olivines are also recognised cais in cold bokkeveld underwent extensive aqueous alteration and contain secondary minerals including calcite and various phyllosilicates these assemblages are similar to those in the chondrules and matrix of the meteorite and it is concluded that all were altered more or less simultaneously within a parent body regolith as is common in cm2s most cais in cold bokkeveld have a rim sequence containing a prominent fe rich phyllosilicate layer this formed early in the alteration sequence by the dissolution of melilite and subsequent precipitation of fe rich phyllosilicates from fluids with a high fe mg ratio cais in cold bokkeveld experienced two stages of deformation an earlier nebula stage predated the formation of the dust mantles that surround most cais and a later stage occurred in an asteroidal regolith the cais in cm2s are smaller than those in cv3 chondrites because of the greater intensity of the earlier fragmentation episode that they experienced aqueous alteration of cais and regolith deformation appear to have been simultaneous phase relations and pyroxene compositional trends in sp py and sp py ol inclusions indicate that they crystallised from liquids most spinel bearing inclusions in cold bokkeveld have a normal mg isotopic composition so they could not have formed by the simultaneous melting and evaporation of primitive dust one inclusion is enriched in the heavy isotopes of mg and may have formed in this way two or more events are required to form most of the inclusions the first produced the refractory compositions either by vapour solid condensation or slow evaporation of primitive dust the second event melted the refractory precursors which later crystallised to form the observed textures and mineral assemblages it has been suggested that refractory spherules with inwardly radiating hibonites formed from molten droplets at temperatures as high as 2135 c however the crystallisation sequences of these inclusions inferred from textural evidence are incompatible with those derived from phase relations and estimates of bulk composition it is concluded that cm2 refractory spherules did not form by crystallisation of molten droplets but were derived by fragmentation of larger inclusions in which they formed by partial melting

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

sandy high energy flood sedimentation some criteria for recognition with an example from the devonian of s w england abstract many modern sand deposits resulting from episodic floods in semi arid zones are dominated by parallel laminations but parallel laminated sands are not a major feature in perennial streams single flood events may deposit over 1 5 m of parallel laminated sand hence ancient parallel laminated sand dominated alluvial deposits may be the product of ephemeral flows the trentishoe formation hangman sandstone group middle devonian of north devon consists in part of laterally extensive beds of parallel laminated fine grained red sandstones that build multistorey sand bodies individual beds are little more than 1 m thick but may extend laterally for hundreds of metres a vertical sequence of erosion surface sparse silt clasts parallel laminations silt drape is often found suggesting high flow stage deposition of plane bedded sand followed by a very rapid waning of flow with silt fallout in the final stages of the flood this sequence bears marked similarity to certain modern ephemeral flow sands

a conceptual model for the preservation of thick transgressive shoreline successions examples from the forearc nanaimo basin british columbia canada abstract sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines excluding incised valleys as recording periods of sediment starvation and are commonly represented as thin 10 m are more likely to be developed in active tectonic settings e g forearc and rift basins which generally experience high sedimentation rates and relatively rapid changes in base level settings with high sedimentation rates and moderate base level rise lead to progradational trends despite overall transgression of the shoreline in settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture e g passive margins thin transgressive successions 1 10 m are more likely to be produced finally in settings defined by relatively slow base level change e g foreland basins the resultant transgressive succession typically comprises a lag 1 m overlain by offshore mudstones this conceptual model highlights the importance of the interplay between sedimentation rates and base level rise and is intended as a guide for the predictive modeling of sedimentary basins

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

the kaidun meteorite mineralogy of an unusual cm1 lithology kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises many kaidun clasts have been intensely altered by aqueous fluids as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate and phyllo silicate filled veins in this report we describe an unusual cm lithology containing many mineralogical features not previously reported from any meteorite including pyrrhotite with exclusive needlelike morphologies and thick mantles of phyllosilicate and complex aggregates of phyllosilicate melanite garnet crosscut by pentlandite veins the latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 c which is significantly higher than that attained during secondary processing from other known cm material

astronomical cycles of middle permian maokou formation in south china and their implications for sequence stratigraphy and paleoclimate abstract high resolution 930 samples magnetic susceptibility ms and anhysteretic remanent magnetization arm analyses were conducted on the 49 m thick middle permian maokou formation at dukou south china spectral analysis of covariant ms and arm series reveal milankovitch cycles with eccentricity obliquity and precession a 5 7 myr floating 405 kyr eccentricity cycle calibrated astronomical time scale was constructed and used as a geochronometer for estimating the durations of the conodont zones the results indicate that the durations of the jinogondolella postserrata j altudaensis j prexuanhanensis and j xuanhanensis conodont zones were 490 kyr 560 kyr 820 kyr and 750 kyr respectively the 405 kyr calibrated ms and arm series also show prominent 1 myr cyclicity which may correspond to the secular frequencies of earth and mars s 4 s 3 in the middle permian the early capitanian time interval was synchronous with the kamura cooling event and the accentuated obliquity cycling may signal ice sheet expansion the modulations of the obliquity have a close relationship with third order eustatic sequences of the wordian and capitanian stages suggesting a glacioeustatic origin during the middle permian

sequence stratigraphic expression of greenhouse transitional and icehouse conditions in siliciclastic successions paleozoic examples from the central appalachian basin usa abstract climates during the paleozoic varied from greenhouse to transitional to icehouse and siliciclastic successions deposited during those times have stratigraphic architectures consistent with magnitudes and frequencies of sea level fluctuations at the time of deposition three central appalachian basin paleozoic successions the early cambrian chilhowee group the late devonian foreknobs formation and the early pennsylvanian breathitt group are compared and contrasted to develop models that relate stratigraphic architectures to greenhouse transitional and icehouse conditions existing on earth within the upper portion of the early cambrian chilhowee group the hampton and erwin formations represent a succession of 2 myr 3rd order sequences consisting of stacked 40 80 kyr 5th order marine parasequences that record low magnitude high frequency sea level changes consistent with greenhouse conditions the late devonian foreknobs formation consists of a series of 0 8 1 0 myr 3rd order composite sequences comprised of stacked unconformity bounded 225 to 450 kyr 4th order sequences each containing 40 to 65 kyr 5th order marine parasequences the bases of the unconformity bounded sequences are marked by erosional surfaces regressive surfaces of marine erosion fluvial deposits or paleosols indicative of sea level drops of 10 to 45 m consistent with a transitional greenhouse to icehouse climate the early pennsylvanian breathitt group consists of stacked unconformity bounded 100 kyr 4th order sequences that lack parasequences unconformity bounded sequences are comprised of from bottom to top lowstand incised valley braided alluvial deposits transgressive tidal estuarine deposits and progradational highstand deltaic deposits depths of incised valleys and vertical transition into estuarine facies imply sea level changes of 50 m consistent with icehouse conditions this study demonstrates that siliciclastic successions preserve a record of sea level changes consistent with greenhouse transitional and icehouse conditions on the paleozoic earth

the density and porosity of meteorites from the vatican collection abstract we have developed a nondestructive technique to measure the densities and porosities of large 50 g to several kilogram meteorite samples and have begun a systematic measurement program starting with meteorites from the vatican observatory collection our technique utilizes a modified archimedean method 40 m glass spheres substituting for the fluid to determine bulk density and an unusually large he pycnometer to determine grain density from these the porosity is calculated we report here our first results for 89 samples nearly doubling the published database on porosities of meteorite hand samples including porosities of 35 different meteorites these include several types not previously reported eight iron meteorites six stony iron meteorites an enstatite chondrite the ci carbonaceous chondrite orgueil and the shergottite nakhlatite chassignite snc meteorite nakhla

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

revised correlation of the frasnian famennian boundary and kellwasser events upper devonian in shallow marine paleoenvironments of new york state abstract the frasnian famennian boundary upper devonian is exposed in a 200 km long outcrop belt in new york state with deeper paleoenvironments to the west and shallower ones to the east geochronology in the eastern end of the outcrop belt has been based primarily on lithostratigraphic correlation with western sections which were dated using conodonts we collected conodonts and brachiopods from several measured sections and numerous other localities and these collections suggest that these east west lithostratigraphic correlations require revision we correlate the wiscoy formation with the upper angola formation and the canaseraga with the upper hanover thus the canaseraga formation contains the frasnian famennian boundary and upper kellwasser event and the dark shale above the wiscoy is equivalent to the pipe creek formation and lower kellwasser event these new correlations imply that the lower kellwasser event had greater impact on the shelly benthos of new york than the upper kellwasser at least for the subset of taxa examined here all strophomenid brachiopods and rugose corals were extirpated at the lower kellwasser along with numerous other brachiopods the final species of atrypid brachiopod persisted to the upper kellwasser

recognition of facies bounding surfaces and stratigraphic patterns in foreland ramp successions an example from the upper devonian appalachian basin u s a abstract a detailed stratigraphic study of the upper devonian lock haven formation in the appalachian basin provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the foreland ramp setting the common occurrence of graded beds hummocky cross stratification and shell lags indicates that storm processes played an important role in deposition gradational based coarsening upward shoreface sequences of interbedded sandstone and mudstone formed during gradual fall in relative sea level in contrast sharp based regressive sequences consist of laminated sandstone facies overlying a submarine erosion surface that developed in response to more rapid fall in relative sea level transgressive sequences become finer grained upward from conglomerate lag which was deposited on a basal transgressive surface to heterolithic facies and mudstone facies a combination of eustasy and tectonic subsidence of the foreland ramp produced changes of relative sea level these fluctuations provided a means for transporting sand onto the ramp and for producing repetition of stratigraphic patterns in the lock haven formation the upper devonian clastic succession which includes both the lock haven formation and the catskill formation represents northwestward progradation of shoreline to nonmarine environments as sediment supply to the foreland ramp exceeded the rate of formation of accommodation compared to passive margin shelves thick fine grained successions such as the lock haven formation are more likely to form in foreland basins where tectonic subsidence provides a mechanism for creating accommodation sediment influx from uplifted areas and absence of a slope break on the foreland ramp results in a higher rate of fine grained clastic sedimentation than occurs on shelves of passive margins

comparison of the trace element composition of tagish lake with other primitive carbonaceous chondrites a meteorite fall on 18 january 2000 was detected by u s defense department satellites which established its pre impact orbit fresh samples were collected from frozen tagish lake in british columbia a week later and some properties of these samples reveal it to be a unique meteorite we characterized tagish lake and 8 other samples using icpms and rnaa data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the orgueil normalized plateaus expected for members of such types trends evident in tagish lake differ from all other carbonaceous chondrites including ci and cm samples of tagish lake collected later show similar patterns affected by weathering

impact of longer term modest climate shifts on architecture of high frequency sequences cyclothems pennsylvanian of midcontinent u s a abstract pennsylvanian glacioeustatic cyclothems exposed in kansas and adjacent areas provide a unique opportunity to test models of the impact of relative sea level and climate on stratal architecture a succession of eight of these high frequency sequences traced along dip for 500 km reveal that modest climate shifts from relatively dry seasonal to relatively wet seasonal with a duration of several sequences 600 000 to 1 million years had a dominant impact on facies sediment dispersal patterns and sequence architecture the climate shifts documented herein are intermediate both in magnitude and duration between previously documented longer term climate shifts throughout much of the pennsylvanian and shorter term shifts described within individual sequences climate indicators are best preserved at sequence boundaries and in incised valley fills of the lowstand systems tracts lst relatively drier climate indicators include high chroma paleosols typically with pedogenic carbonates and plant assemblages that are dominated by gymnosperms mostly xerophytic walchian conifers the associated valleys are small 4 km wide and 20 m deep and dominated by quartz sandstones derived from distant source areas reflecting large drainage networks transgressive systems tracts tst in all eight sequences generally are characterized by thin extensive limestones and thin marine shales suggesting that the dominant control on tst facies distribution was the sequestration of siliciclastic sediment in updip positions highstand systems tracts hst were significantly impacted by the intermediate scale climate cycle in that hsts from relatively drier climates consist of thin marine shales overlain by extensive thick regressive limestones whereas hsts from relatively wetter climates are dominated by thick marine shales previously documented relative sea level changes do not track the climate cycles indicating that climate played a role distinct from that of relative sea level change these intermediate scale modest climate shifts had a dominant impact on sequence architecture this independent measure of climate and relative sea level may allow the testing of models of climate and sediment supply based on modern systems

diagenetic model for carbonate rocks in midcontinent pennsylvanian eustatic cyclothems abstract diagenetic patterns in cyclic midcontinent pennsylvanian carbonates are readily explained in terms of a predictive diagenetic model derived logically from the eustatic depositional model for widespread pennsylvanian cyclothems developed by heckel 1977 1980 transgressive shoal water calcarenites are characterized by pervasive overpacking of grains neomorphism of originally aragonite grains ooids green algae molluscs and ferroan calcite and dolomite cement which indicate movement from the marinephreatic environment of deposition and diagenesis into the low oxygen deeper burial connate zone with substantial compaction before any cementation offshore invertebrate calcarenites associated with offshore core shales also are characterized by pervasive overpacking of grains an ferroan carbonate cements which indicate a similar diagenetic history their lack of discernible neomorphism relates to original absence of shallow water aragonite grains ooids green algae and probable removal of thin shelled molluscs by dissolution during long periods of sediment starvation in cool water which also corroded the edges of many calcite grains regressive shoal water calcarenites show a much greater variety of diagenetic features including early marine cement rims and large scale leaching of originally aragonite grains often with subsequent collapse of micrite envelopes grain fragments and overlying material in samples insufficiently stabilized by early cement rims this was followed by pervasive cementation by blocky calcite before much further compaction then by ferroan calcite and finally ferroan dolomite in remaining voids this pattern indicates replacement of depositional marine phreatic water by meteoric water which dissolved unstable carbonate grains and then deposited stable carbonate cements in environments that eventually became increasingly oxygen depleted and otherwise chemically changed probably as mixing zone and deeper connate water moved back into the rock and replaced the meteoric water during and after the succeeding transgression trends in calcilutites are essentially similar to those in calcarenites of equivalent phase of deposition with evidence of subaerial exposure and meteoric vadose soil formation in strata at the top of many regressive limestones it is apparent that with the regression of the sea and emergence that terminated deposition of a cyclothem meteoric water penetrated the permeable pans of the regressive carbonate and left its distinctive diagenetic patterns of early leaching and cementation before much compaction took place but rarely did meteoric water penetrate the impermeable offshore shale which acted as a seal this allowed associated offshore and underlying transgressive carbonates to become more deeply buried and substantially compacted before cementation took place with unstable grains undergoing slow neomorphism in the absence of meteoric leaching

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

combined flow model for vertical stratification sequences in shallow marine storm deposited beds abstract we develop a model to help explain the wide variety of vertical stratification sequences in shallow marine sandstones this model embodied in a set of vertical sequence cartoons predicts or accounts for vertical stratification sequences in beds of free sandstone deposited from a full range of decelerating combined flows as well as from purely unidirectional and oscillatory flows according to the model vertical stratification sequences in storm deposited sandstone beds are the outcome of the time history of the bed configuration as deposition proceeds the idealized sequences are based on the initial velocities and subsequent deceleration histories of the unidirectional and oscillatory flow components twenty qualitatively different sequences starting with plane bed are generated and an additional 26 sequences result from omitting one or more of the lowermost intervals in succession the model thus accounts for 46 distinct kinds of sequences five major simplifying assumptions are built into the model bidirectional flows linear deceleration of both unidirectional and oscillatory flow components time independent deposition rate time independent sediment size and equilibrium bed configurations owing to these assumptions the model is likely to be applicable to only a small subset of vertical stratification sequences observed in shallow marine sandstones as more information on combined flow bed configurations becomes available these assumptions could be relaxed to provide a more refined and complete representation of vertical stratification sequences since the model generates vertical sequences formed from any kind of decelerating flow the bouma sequence for deposits from purely unidirectional turbidity currents and also sequences resulting from decelerating purely oscillatory flows similar in appearance to many proposed generalized tempestite sequences are end member cases in the model the model is also extended slightly to explain the geometry of the uppermost bedding surfaces of storm generated sandstones by consideration of disequilibrium effects

evidence for long term climate change in upper devonian strata of the central appalachians abstract the highest 1 to 200 m of the upper devonian famennian catskill and equivalent hampshire formations exhibit a noticeable vertical or stratigraphic change in color and a shift in lithologic character the lower part of the unit is characterized by typically red channel phase sandstones and overbank siltstone and mudstone containing thin calcareous paleosols these lithologies give way to greenish gray sandstone containing abundant coaly plant fragments coalified logs and pyrite interbedded with thick intervals of non calcareous paleo vertisols the increase in the prominence of preserved terrestrial organic matter suggests that there was a corresponding increase in the abundance of plants in terrestrial ecosystems the stratigraphic change in lithology within the upper part of the catskill hampshire succession suggests the onset of environmental conditions that became increasingly wet in response to elevated humid climatic conditions during the final stages of catskill alluvial plain deposition the sedimentological signature suggesting increased climatic wetness within the uppermost catskill and hampshire formations is nearly contemporaneous with the initiation of late devonian gondwanan glaciation in the paleo high latitudes the appalachian climate record indicates that this change began during the fa2c and continued through the latest famennian reaching its peak during the fa2d when glacial deposits are recorded in the paleo mid latitudes of the appalachian basin evidence of this late famennian increase in precipitation also is recorded in the adjacent marine environments equivalent age marine units in ohio and kentucky record progressive increases in both total organic carbon and the percentage of terrestrially derived organic carbon this suggests that there was a late famennian increase in terrestrial organic matter productivity and that during the late famennian there were elevated levels of runoff produced by the interpreted increase in precipitation that washed progressively higher amounts of terrestrial organic matter into the local marine environments the late famennian climate changes identified within the appalachian basin strata have been recognizable globally and appear to have had both positive and negative effects on the earth s biota some marine groups exhibit sharp diversity drops or even extinction coincident with the maximum development of the late famennian ice age conversely terrestrial biota appears to have been more positively affected by the late famennian increased wetness that accompanied this progressive climate change marked diversification and evolutionary innovation which appear to coincide with this climatic deviation can be recognized within terrestrial plant communities and early tetrapod amphibians

structure of the crust and upper mantle of the great slave lake shear zone northwestern canada from teleseismic analysis and gravity modelling the great slave lake shear zone gslsz exposes lower crustal rocks analogous to deep seated segments of modern strike slip fault zones such as the san andreas fault extending for 1300 km beneath the western canada sedimentary basin to the southern margin of the slave province the gslsz produces one of the most prominent linear magnetic anomalies in canada from may to october 1999 13 three component portable broadband seismograph stations were deployed in a 150 km profile across a buried segment of the shear zone to investigate its lithospheric structure splitting analysis of core refracted teleseismic shear waves reveals an average fast polarization direction n49 e 19 that is approximately parallel to the shear zone individual stations near the axis of the shear zone show more northerly splitting directions which we attribute to interference between regional anisotropy in the upper mantle fast axis n60 e and crustal anisotropy within the shear zone fast axis n30 e at the location of o

the role of sea level change and marine anoxia in the frasnian famennian late devonian mass extinction johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 proposed one of the first explicit links between marine anoxia transgression and mass extinction for the frasnian famennian f f late devonian mass extinction this cause and effect nexus has been accepted by many but others prefer sea level fall and cooling as an extinction mechanism new facies analysis of sections in the usa and europe france germany poland and comparison with sections known from the literature in canada australia and china reveal several high frequency relative sea level changes in the late frasnian to earliest famennian extinction interval a clear signal of major transgression is seen within the early rhenana zone e g drowning of the carbonate platform in the western united states this is the base of transgressive regressive cycle iid of the johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 eustatic curve this was curtailed by regression and sequence boundary generation within the early linguiformis zone recorded by hardground and karstification surfaces in sections from canada to australia this major eustatic fall probably terminated platform carbonate deposition over wide areas especially in western north america the subsequent transgression in the later linguiformis zone recorded by the widespread development of organic rich shale facies is also significant because it is associated with the expansion of anoxic deposition known as the upper kellwasser event johnson et al s johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 original transgression anoxia extinction link is thus supported although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out conodont faunas suffered major losses during the upper kellwasser event with deep water taxa notably affected this renders unreliable any eustatic analyses utilising changes in conodont biofacies claims for a latest frasnian regression are not supported and probably reflect poor biostratigraphic dating of the early linguiformis zone sequence boundary

precambrian crust beneath the mesozoic northern canadian cordillera discovered by lithoprobe seismic reflection profiling 1 the cordillera in northern canada is underlain by westward tapering layers that can be followed from outcrops of proterozoic strata in the foreland belt to the lowermost crust of the orogenic interior a distance of as much as 500 km across strike they are interpreted as stratified proterozoic rocks including 1 8 0 7 ga supracrustal rocks and their basement the layering was discovered on two new deep seismic reflection profiles in the yukon line 3 650 km and northern british columbia line 2 1245 km in two segments that were acquired as part of the lithoprobe slave northern cordillera lithospheric evolution snorcle transect in the mackenzie mountains of the eastern yukon the layering in line 3 is visible between 5 0 and 12 0 s 15 to 36 km depth it is followed southwestward for nearly 650 km 500 km across strike and thins to less than 1 0 s 3 0 3 5 km thickness near the moho at the yukon alaska international boundary in the northern rocky mountains of british columbia the upper part of the layering on line 2 correlates with outcrops of proterozoic 1 76 1 0 ga strata in the muskwa anticlinorium at this location the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for 700 km 300 km across strike it disappears as a thin taper at the base of the crust 150 km east of the coast of the alaskan panhandle the only significant disruption in the layering occurs at the tintina fault zone a late to postorogenic strike slip fault with up to 800 km of displacement which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles 300 km apart the base of the layered reflection zone coincides with the moho which exhibits variable character and undulates in a series of broad arches with widths of 150 km in general the mantle appears to have few reflections however at the southwest end of line 3 near the alaska british columbia border a reflection dips eastward from 14 0 s to 21 0 s 45 to 73 km depth beneath exposed eocene magmatic rocks it is interpreted as a relict subduction surface of the kula plate our interpretation of proterozoic layered rocks beneath most of the northern cordillera suggests a much different crustal structure than previously considered 1 ancient north american crust comprising up to 25 km of metamorphosed proterozoic to paleozoic sediments plus 5 10 km of pre 1 8 ga crystalline basement projects westward beneath most of the northern canadian cordillera 2 the lateral 500 km by at least 1000 km and vertical up to 25 km extent of the proterozoic layers and their internal deformation are consistent with a long lived margin for northwestern north america with alternating episodes of extension and contraction 3 the detachments that carry deformed rocks of the mackenzie mountains and northern rocky mountains are largely confined to the upper crustal region above the layering 4 accreted terranes include thin klippen that were thrust over north american pericratonic strata e g yukon tanana and terranes such as nisling and stikinia that thicken westward as the underlying proterozoic layers taper and disappear 5 the ages of exposed rocks are not necessarily indicative of the ages of underlying crust a frequent observation in lithoprobe interpretations so that estimates of crustal growth based on surface geology may not be representative

stratigraphic completeness of carbonate dominated records from continental interiors versus continental margins stratigraphic thinning occurs via condensation and omission at multiple scales abstract over phanerozoic time scales stratigraphic records from continental interiors or cratons are dramatically thinner and are generally assumed to be relatively incomplete with more numerous and longer duration hiatuses compared to records from more rapidly subsiding continental margins however this assumption need not be true for the shorter time scales i e several 106 years and shorter over which accumulation of the preserved stratigraphic record on the continental interior actually takes place this study compares carbonate dominated sedimentary records from the devonian continental interior iowa and continental margin nevada to evaluate whether the continental interior record is 1 miniaturized i e thinner but equally complete 2 comparable in thickness and quality where the sedimentary record is preserved but certain portions of the record are notably absent i e omitted or truncated or 3 so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental margin record this study finds that fourth to fifth order cycles in iowa are on average approximately half as thick and half as numerous compared to the continental margin of nevada moreover the stratigraphic record on the continental margin of nevada is dominated by cycles that are composed of tidal flat and shallow subtidal lithofacies capped by simple flooding surfaces and exhibit catch up or keep up depositional styles the continental interior record in iowa is dominated by cycles that are composed of subtidal lithofacies capped by a range of bounding surfaces and exhibit catch down or give up depositional styles these findings suggest that the thin record in iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric sea setting rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record

upper devonian catskill delta margin cyclic sedimentation brallier scherr and foreknobs formations of virginia and west virginia this study documents the applicability of the pac hypothesis to the clastic sediments of the upper devonian catskill delta sequence in virginia and west virginia detailed studies of the type sections of the back creek siltstone member of the brallier formation the minnehaha springs member of the scherr formation and the foreknobs formation show that the deposition of these sequences was strongly influenced by astronomically controlled sedimentary cycles with a dominant 100 000 yr period and superimposed 40 000 and 20 000 yr variations estimated water depths during the deposition of the foreknobs formation vary from 0 50 m and show an over all shoaling trend as average uncompacted sediment accumulation rates increased from 40 to 140 cm 1 000 yr during the 2 m y duration of deposition of the formation deposition of the foreknobs formation appears to have been influenced by 413 000 yr variations due to eccentricity and possibly by a 2 0 m y duration eccentricity cycle all of these variations in turn are superimposed on the pulse of sedimentation and basin filling produced by the third tecto phase of the acadian orogeny

analyses of crustal structure from bandpass and directionally filtered potential field data an example from western canada application of bandpass and directional filtering to potential field data in northwestern canada allows separation of anomalies due to northwest oriented upper crustal sources that are associated w

on the geological significance of clastic parasequences abstract parasequences recognized in clastic sedimentary successions of shallow marine origin are considered by some geologists to be the fundamental building blocks of depositional sequences even though problems in their definition and application have been identified by others who instead advocate their abandonment as formal sequence stratigraphic units to elucidate the geological significance of clastic parasequences and inform the debate on their use in stratigraphy a quantitative characterization of the geometry facies characteristics and timescale of deposition of 1163 parasequences has been undertaken based on a synthesis of data from outcrop and subsurface studies that are available in the scientific literature through a database compilation the attributes of the studied parasequences are analysed with respect to the interpreted geological origin of the units and with consideration of sources of bias and uncertainty particular emphasis is placed on assessing the following i the importance of heuristics and of data types and coverage in the recognition of parasequences ii differences in parasequence characteristics observed across deltaic and shoreface depositional systems and between the quaternary and the ancient rock record iii possible explanations for the range in timescales of deposition of parasequences and iv the role of autogenic dynamics on the development of deltaic parasequences partly based on a comparison with the recent evolution of modern deltas the results demonstrate that parasequence definition and physical correlation suffer from subjectivity and that significant variability exists in the spatio temporal and architectural attributes of clastic parasequences this gives rise to uncertainty that affects the use of parasequences as a framework for comparison of the architecture of packages of strata originating via shoreline regression this uncertainty must be considered when using analogue data for subsurface predictions or when attempting comparative studies of clastic successions

the upper mississippian bluefield formation in the central appalachian basin a hierarchical sequence stratigraphic record of a greenhouse to icehouse transition abstract the upper mississippian chesterian bluefield formation is the basal unit of the predominantly siliciclastic mauch chunk group in the appalachian basin this formation developed in a northeast southwest oriented foreland trough fronting the alleghanian highlands to the southeast regional cross sections and isopach maps of the bluefield formation in southeastern west virginia southwestern virginia and southeastern kentucky define a depocenter in the southeastern part of the study area and a paleovalley system along the basin margin to the northwest at most localities facies that make up the bluefield formation are stacked into 1 15 m thick upward shallowing parasequences each of which is capped by a flooding surface these parasequences are stacked into four regionally correlatable depositional sequences on the margins of the depocenter incised valleys and fewer meter scale parasequences characterize the depositional sequences stacking of parasequences into sequences reflects a hierarchy of greenhouse type fifth order and icehouse type fourth order sea level cycles superimposed on a differential subsidence history related to early alleghanian thrust loading the bluefield depocenter experienced greater total accommodation which prevented incision during lowstands instead lowstands are typified by preservation of fifth order coal bearing parasequences in the depocenter basin margin areas experienced less total accommodation which resulted in development of fourth order lowstand valleys and erosion of parasequences this study demonstrates that both tectonic and eustatic forcing mechanisms controlled stratigraphic evolution of the bluefield formation

cm chondrites exhibit the complete petrologic range from type 2 to 1 we have characterized the most phyllosilicate rich members of the cm chondrite group based upon petrographic and compositional factors we conclude that these particular meteorites have experienced pervasive aqueous alteration far beyond that witnessed by typical cms the lack of anhydrous silicates cai and except as relicts chondrules merits the classification of type cmi for three meteorites eet 83334 alh 88045 and one kaidun lithology still other cms notably alh 83100 eet 90047 and yamato 82042 are clearly intermediate between types 1 and 2 brecciated cm chondrites like cold bokkeveld contain all of these varied lithologies the cm chondrites thus exhibit the complete petrologic range from 2 through 1 our results show that progressive aqueous alteration on the parent cm asteroid s was locally accompanied by significant increases in temperature to a peak of 450 c for the kaidun lithology fo2 and locally degree of chemical leaching all well beyond the conditions recorded by typical cm2s the most altered cms also are commonly deformed displaying a distinct lineation probably due to static rather than dynamic forces

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

a pedotype approach to latest cretaceous and earliest tertiary paleosols in eastern montana a pedotype approach to the study of paleosols emphasizes individual profiles it is an alternative approach to the study of geosols which are laterally extensive suites of paleosols or pedofacies which are pedogenically distinctive sedimentary facies this is the first pedotype study of paleosols across the cretaceous tertiary boundary in eastern montana pedotypes allow assessment of sedimentation and fossilization the sequence of paleosols across the cretaceous tertiary boundary at bug creek is one of high temporal resolution because most available geological time can be accounted for by differing degree of development inferred for each pedotype paleosols at bug creek include pedotypes that preserve plant fossils well but were unfavorable for preservation of fossil vertebrates pedotypes also allow reassessment of ecosystem change despite indications of catastrophe at the cretaceous tertiary boundary the array of paleocene and cretaceous pedotypes are not strikingly different the upper cretaceous hell creek formation includes pedotypes interpreted as gleyed alfisols inceptisols and entisols probably formed under seasonally water logged forest and mean annual rainfall of the order of 900 1200 mm most paleosols of the lower paleocene tullock formation were histosols but some can be interpreted as gleyed inceptisols and entisols probably formed under bald cypress swamps in a humid climate with 1200 mm mean annual rainfall broadly comparable pedotypes were present before and after the cretaceous tertiary boundary although paleocene flood plain forest lived in paleosols chemically a little more oligotrophic than cretaceous paleosols this modest difference supports the idea that change to coaly facies in the earliest paleocene was a local shift in sedimentary environment such local changes do not begin to account for profound disruption in specific composition of plant and animal communities at the cretaceous tertiary boundary in eastern montana

high frequency cycles and sequence stratigraphy of the lower jurassic marrat formation central saudi arabia abstract well exposed stratigraphic sections of the toarcian siliciclastic carbonate deposits of the marrat formation exposed at the khashm adh dhibi area southwest of riyadh city saudi arabia were studied for their facies associations and controls on sequence development seven facies associations from tide dominated deltaic to inner carbonate ramp were recognized inferences based on facies relationships characteristics of the sequence boundary and other characteristics suggest deposition of the marrat formation during three 3rd order sequences these can be further classified into seventeen 4th order shallowing upward small cycle sets correlation of the recorded sequences boundaries within the arabian african plates europe and global schemes reflect a strong eustatic control during the early jurassic age with recognizable tectonic signature of the gondwanland rift effects that caused a long period of regional uplift and non deposition across the triassic jurassic and early middle jurassic unconformities

the frasnian famennian boundary in central and eastern united states abstract the frasnian famennian f f boundary in the northern appalachian basin is found in the hanover shale and equivalent strata where it is locally associated with a black shale interval equivalent to the upper kellwasser interval in europe the boundary is immediately below the dunkirk huron black shale that represents the iie t r cycle transgression in the southern appalachian basin the southern edge of the cincinnati arch and the southeastern illinois basin the f f boundary is at or near the base of the gassaway member of the chattanooga shale or the morgan trail member of the new albany shale or was eroded during the iie t r cycle beginning in the middle triangularis zone in the western illinois basin grassy creek shale michigan basin lachine member of antrim shale and southern continental margin woodford shale the f f boundary is within black shale strata indicative of an earlier development of the iie t r transgression inboard of the appalachian basin or the juxtaposition of the iie t r transgression over the upper kellwasser black shale interval without significant or recognizable lithologic change

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

late devonian glacial deposits from the eastern united states signal an end of the mid paleozoic warm period abstract a late devonian polymictic diamictite extends for more than 400 km from northeastern pennsylvania across western maryland and into east central west virginia the matrix supported unbedded locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter the mostly rounded clasts are both locally derived and exotic some exhibit striations faceting and polish the diamictite commonly is overlain by laminated siltstone mudstone facies associations laminites the laminites contain isolated clasts ranging in size from sand and pebbles to boulders some of which are striated the diamictite laminite sequence is capped by massive coarse grained pebbly sandstone that is trough cross bedded a stratigraphic change from red calcic paleo vertisols in strata below the diamictite to non calcic paleo spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite the diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the late devonian of the appalachian basin these deposits record a late devonian episode of climatic cooling so extreme that it produced glaciation in the appalachian basin evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite overlain by glaciolacustrine varves containing dropstones and capped by sandstone interpreted as braided stream outwash the appalachian glacigenic deposits are contemporaneous with glacial deposits in south america and suggest that late devonian climatic cooling was global this period of dramatic global cooling may represent the end of the mid paleozoic warm interval that began in the middle silurian

a terrestrial origin for sulfate veins in ci1 chondrites white sulfate veins are a very well known petrological feature of the chemically primitive ci1 carbonaceous chondrites sulfate veins were first described in the orgueil meteorite in 1961 almost one century after its fall however we have observed such veins to form easily during typical sample storage we suggest that all ci1 sulfate veins formed during the terrestrial residence of these heavily brecciated porous stones reacting with atmospheric water sulfates originally present in the meteorites dissolved and remobilized and or sulfides oxidised filling the many open spaces offered to them by the very porous rock sulfate veins in ci1 chondrites can no longer be used as evidence of a late stage oxidation event in the ci1 parent body or of centimeter scale fluid transport on the parent asteroid

cross strike potential field anomalies in the canadian cordillera application of bandpass and directional filtering to potential field maps of western canada has led to the discovery of regionally extensive anomalies crossing the northwest strike of cordilleran structures the most prominent of these the steamboat fraser trend is a north south striking feature that projects from the foreland belt in northeastern british columbia where it becomes subparallel to anomalies east of the mackenzie mountains southward to the northern limit of the fraser river strike slip fault a distance of about 600 km within the hinterland of the cordillera the trend appears to spatially correlate with the margins of some tertiary volcanics the northeasternmost and thus most cratonward tertiary volcanics are located on the northern projection of the trend the trend may thus be interpreted as either late post orogenic intrusives e g dikes and related volcanic rocks that are only partially exposed as pre orogenic pre mesozoic features e g faults dikes in the crust that were overridden by the cordilleran thrust sheets or a combination of these although it is not possible to determine which of these pre or post orogenic is appropriate for the trend the eventual choice has important implications for the structure and evolution of this part of the cordillera if the source of the anomalies is pre orogenic a major implication is that precambrian shield rocks would be present at depth beneath the southern canadian cordillera as far west as the fraser river fault alternatively if the source is post orogenic it represents an anomalously linear feature that has no obvious expression on the surface other than a poorly defined spatial correlation with the margins of some tertiary volcanics

electromagnetic images of a strike slip fault the tintina fault northern canadian 1 wideband magnetotelluric mt data were acquired along three profiles crossing the strike slip tintina fault in northwestern canada the mt responses obtained exhibit remarkable similarity from all three profiles implying similar two dimensional 2 d electromagnetic behavior of the fault zone over a strike length of at least 350 km analyses of the mt responses for dimensionality corroborate the validity of assuming regional 2 d structures in interpretation several high conductivity anomalies at different depth scales are present in the models obtained and we suggest that both the shallow structures and the deep crustal scale anomalies are caused by electronic conduction mechanisms in interconnected mineralized zones intriguingly the middle and lower crust beneath the surface expression of the tintina fault is highly resistive in contrast to some other large scale strike slip faults this implies that fault zone processes that result in interconnected conducting phases are not generic in nature but are controlled by local conditions

compound paleovalley fills in the lower pennsylvanian new river formation west virginia usa abstract ancient paleovalley fills are typically interpreted in the rock record using over generalized models without carefully considering modern analogs especially in light of recent discoveries it is now known that many quaternary paleovalleys are compound in origin exhibit considerable stratigraphic complexity contain multiple incisions and can be orders of magnitude larger than their putative ancient counterparts compound paleovalley fills in the lower pennsylvanian new river formation nrf are directly comparable to these quaternary analogs stimulating a paradigm shift in the interpretation of ancient paleovalleys in the nrf multiple laterally and vertically juxtaposed fill successions separated by incision surfaces record high frequency fluvial responses to external controls within lower order sequences lowstand incision and sediment bypass as predicted in sequence stratigraphy is largely discounted by the available evidence and the definition of regional sequence boundaries is not straightforward the identification of genetic sequences may be the most effective approach to understanding the nrf and by inference many other ancient paleovalleys results from this study of the nrf promote a revised model for ancient paleovalleys that incorporates 1 the pre eminence of compound architecture 2 periodic episodes of incision and subaerial exposure occurring in response to high frequency changes in climate or relative sea level 3 fluvial downcutting as the primary cause of paleovalley incision although some sediments are still preserved in a net erosional regime and 4 composite time transgressive sequence boundaries that may be difficult or impossible to correlate regionally

the importance of sea level fluctuations in the formation of linear conglomerate bodies carrot creek member of cardium formation cretaceous western interior seaway alberta canada abstract the raven river member of the cardium formation turonian upper cretaceous in the carrot creek area of alberta contains two coarsening upward sequences of marine mudstones and sandstones the lower sequence coarsens from black mudstones into bioturbated fine grained sandstones and is capped by a gritty siderite horizon which probably indicates a pause in deposition the sandstones of the upper sequence contain hummocky cross stratification suggesting open marine deposition below fairweather wave base the two sequences are scoured to variable depths by a major erosion surface which has a relative relief of up to 20 m a structure map and three dimensional mesh diagrams of this surface suggest four topographic elements a relatively high terrace a bevel at which und rlying beds are truncated and a series of bumps and hollows these are interpreted to represent a remnant erosional topography which gradually fades away into the final topographic element the smooth basin plain the erosion surface is covered with conglomerate assigned to the carrot creek member of the cardium the conglomerate thickness reaches about 20 m against the bevel and in some of the hollows but usually thins to a veneer on the terrace on top of the bumps and on the distal basin floor the conglomerate bodies are relatively long and narrow and trend northwest southeast they are overlain by marine mudstones of the dismal rat member the elongate conglomerate bodies appear at first sight to be another case of western interior seaway offshore bars encased in marine mudstones many tens of kilometers seaward of time equivalent shoreline deposits however the erosion surface indicates that the conglomerates are not genetically part of the underlying coarsening upward sequence we propose a rapid relative lowering of sea level following deposition of the hummocky cross stratified sandstones the shoreline advanced many kilometers northeastward into the basin and during stillstand wave erosion cut a new shoreface profile the bevel during this lowstand incised rivers supplied gravel to the shoreface waves worked the gravel alongshore against the bevel and into the erosional hollows subsequent transgres ion spread some gravel southwestward back across the terrace storms transported gravel stringers into the transgressive muds accumulating in the hollows other erosional surfaces of this type exist in alberta at the cardium viking and bad heart horizons and in new mexico at the gallup tocito horizon suggesting that sea level changes and shoreface incision may be an alternative explanation for other long narrow offshore bars encased in marine shales

sequence stratigraphic hierarchy of the upper devonian foreknobs formation central appalachian basin usa evidence for transitional greenhouse to icehouse conditions abstract the foreknobs formation upper devonian upper frasnian to basal famennian comprises the uppermost marine strata of the progradational catskill clastic wedge of the south central appalachian mountains virginia west virginia usa the foreknobs formation consists of 14 lithofacies arranged in four facies associations which record the following depositional settings 1 storm dominated distal to proximal offshore to shoreface facies association a 2 sharp based conglomeratic shoreface facies association b 3 fluvial redbed facies association c and 4 incised valley fill ivf facies association d vertical juxtaposition and stacking patterns of lithofacies and facies associations permit recognition of a hierarchy of three scales of cyclicity up to 70 short term 5th order cycles each averaging 65 kyr consist of coarsening upward parasequences of storm dominated offshore marine facies in the distal setting which correspond to high frequency unconformity bound sequences hfs of fluvial redbed strata overlain by offshore marine strata in the proximal setting these facies relationships are a consequence of 10 15 m of sea level fluctuations up to 12 intermediate term 4th order cycles each averaging 375 kyr consist of stacked 5th order cycles the 4th order cycles are bounded by regressive surfaces of marine erosion rsme at the base of sharp based conglomeratic shoreface sandstones in the distal setting that correspond with paleosols in the proximal setting in some cases the 5th order cycles within each 4th order cycle exhibit stacking patterns indicative of increasing or decreasing accommodation space these facies relationships are a consequence of 25 35 m of sea level fluctuations three complete and portions of two additional 3rd order cycles each averaging 1 12 myr consist of stacked 4th order cycles the 3rd order sea level trends reflected in the foreknobs formation are nearly identical to published eustatic sea level curves incised valley fills are present at one of the 3rd order cycle boundaries and are a consequence of a 35 45 m sea level fluctuation the amplitudes of the inferred sea level fluctuations are comparable to the expansion and contraction of ice volumes within the current greenland and antarctic ice sheets which suggests glacioeustasy was the primary control on sea level fluctuations and cyclicity within the foreknobs formation such an interpretation is consistent with knowledge of devonian climate transitioning from middle devonian greenhouse to late devonian icehouse as indicated by evidence of glaciation during parts of the late devonian in south america and the appalachians

refractory inclusions in the prototypical cm chondrite mighei abstract refractory inclusions in the mighei cm2 meteorite are very abundant 35 being found in three thin sections of the meteorite the most common are pyroxene rimmed spinel rich inclusions that occur in a range of structural and textural types some inclusions are simple aggregates of crystals or rimmed crystals ranging from loose clusters of spinel grains to distended chains of pyroxene rimmed spinel knots others are more compact and may have experienced recrystallization or melting these include nodular spinel inclusions with polygonal granular textured spinel interiors and pyroxene rims ribbons of spinel in some cases with hibonite and or perovskite that are again rimmed by pyroxene and refractory spherules four inclusions are complex aggregates of several texturally distinct objects each collectively mighei inclusions are similar to those in murchison but appear to be somewhat more altered volatility fractionated and unfractionated trace element patterns similar to those found in refractory inclusions in other carbonaceous chondrites are represented in mighei inclusions and in addition some mighei inclusions have volatility fractionated pattern types not previously found in refractory inclusions in three of the complex aggregates fundamentally different trace element patterns are present within different portions of each inclusion meaning that these objects accreted from genetically different components that never equilibrated with one another subsequent to accretion bulk inclusion magnesium isotopic compositions show minor mass fractionation effects fmg values range from 2 3 to 7 5 but the average fmg value is indistinguishable from normal 1 8 1 2 there are no correlations between magnesium isotopic composition and textural type or trace element pattern type the diverse inclusion types in mighei represent a variety of origins and histories textures suggest that the nodular and banded inclusions may have experienced solid state recrystallization whereas the porous and chain like varieties and complex aggregates have not magnesium isotopic compositions and trace element abundances suggest that the mighei inclusions are unlikely to be evaporation residues and are more likely to be the products of condensation or recondensation processes

fourth order nonmarine to marine sequences middle castlegate formation book cliffs utah the lower part of the campanian castlegate formation one of the best known fluvial sheet sands of the western interior seaway combines with an overlying finer grained unit middle member of the castlegate formation to form an unconformity bounded third order stratigraphic sequence 3 m y duration this sequence contains a mappable muddy zone along the western book cliffs of utah now mapped as contiguous with the open marine parts of the succession buck tongue sego sandstone anchor mine tongue to the east the correlation within the middle castlegate has been refined and the nature of the link between tidally influenced fluvial strata in the west and marine strata in the east has been remapped five high frequency stratigraphic sequences all within the upper part of the larger third order sequence forming a thickness to 160 m have been mapped in the price area southeastward into the time equivalent marine succession near green river individual sequences probably 0 5 m y duration reflecting transgressive to regressive estuary infilling have an internal architecture in which fluvial and tidally influenced distributary channel belts pass up into muddy central basin sedimentary units to bayhead delta deposits and in some places up to more fluvial channel belts the key to the mapping of individual sequences is recognition of the muddy brackish water interval developed during maximum transgression of the time equivalent shoreline the two most proximal marine influenced sequences 2 and 3 are probably broadly time equivalent with the buck and anchor mine tongues to the east the analysis here contrary to recent suggestions shows that the marine sequences in the eastern book cliffs can be traced far into the time equivalent western fluvio estuarine succession

the origin of chondritic macromolecular organic matter a carbon and nitrogen isotope study the n and c abundances and isotopic compositions of acid insoluble carbonaceous material in thirteen primitive chondrites five unequilibrated ordinary chondrites three cm chondrites three enstatite chondrites a ci chondrite and a cr chondrite have been measured by stepped combustion while the range of c isotopic compositions observed is only delta 13c 30 the n isotopes range from delta 15n approximately 40 to 260 after correction for metamorphism presolar nanodiamonds appear to have made up a fairly constant 3 4 wt of the insoluble c in all the chondrites studied the apparently similar initial presolar nanodiamond to organic c ratios and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites suggest that the chondrites all accreted similar organic material this original material probably most closely resembles that now found in renazzo and semarkona these two meteorites have almost m shaped n isotope release profiles that can be explained most simply by the super position of two components one with a composition between delta 15n 20 and 40 and a narrow combustion interval the other having a broader release profile and a composition of delta 15n approximately 260 although isotopically more subdued the ci and the three cm chondrites all appear to show vestiges of this m shaped profile how and where the components in the acid insoluble organics formed remains poorly constrained the small variation in nanodiamond to organic c ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30 the most 15n rich material probably formed in the interstellar medium and the fraction of organic n in renazzo in this material ranges from 40 to 70 the isotopically light component may have formed in the solar system but the limited range in nanodiamond to total organic c ratios in the chondrite groups is consistent with most of the organic material being presolar