the carbonate factory revisited a reexamination of sediment production functions used to model deposition on carbonate platforms there are two widely used models of sediment production on carbonate shelves 1 production varying with depth and 2 production as a function of depth and distance from the platform margin here we recalculate carbonate production on great bahama bank west and northwest of andros island using broecker and takahashi s 1966 pioneering geochemical study in the calculations residence time and depth are used to calculate yearly carbonate production based on equilibrium thermodynamics of caco3 loss from water over the banks whereas broecker and takahashi assumed a uniform depth of 4 5 m in their work here we use realistic depths and residence times interpolated over the bank our results suggest that sediment production is on the order of 4 5 kg m2 y on the bank margins and that production rapidly drops off into the platform approaching zero in the shallowest innermost parts of the platform thus for a large platform such as great bahama bank with long residence times the shallowest areas of the platform may become sinks not sources of sediment

the longest delay re emergence of coral reef ecosystems after the late devonian extinctions abstract reefs are an excellent tool for tracking marine ecosystem changes especially through mass extinction transitions although metazoan reefs proliferated during the phanerozoic prolonged metazoan reef recovery intervals often occurred after extinction events here we document and review the reef recovery interval following the late devonian frasnian famennian kellwasser and end famennian hangenberg mass extinctions which eliminated the largest area of metazoan stromatoporoid coral reefs of the phanerozoic previous reports of the late visean coral bioconstructions from western palaeotethys ocean may mark the first metazoan reef proliferation after the hangenberg extinction in this study abundant coral reefs coral frameworks and coral biostromes were described in detail for the first time from the late visean strata on the south china block eastern palaeotethys ocean the occurrence of these coral bioconstructions further suggests that the late visean coral reef recovery may have been a widespread phenomenon based on the high resolution reef database constructed in this study three sub intervals of the mississippian metazoan reef recovery were distinguished which are 1 metazoan reef gap phase mrg without metazoan reefs during the tournaisian 2 metazoan reef re establishment phase mrr containing a few metazoan reefs from early visean to early part of the late visean and 3 metazoan reef proliferation phase mrp with global coral reef flourishment during the middle part of the late visean late asbian to early brigantian substages hence coral reef ecosystems proliferated and became dominant in marine ecosystems during the late asbian to early brigantian indicating a prolonged metazoan reef recovery of about 12 ma and 23 ma until the mrr and mrp respectively coral reef proliferation at this time shows that the mississippian was not solely a period dominated by microbial reefs late visean coral reef development coincided with increased nektonic and benthic diversity showing that metazoan reef recovery closely tracked overall marine ecosystem evolution even compared with other slow reef recovery intervals such as the middle late cambrian and early middle triassic with the intervals until the mrr and mrp of 5 ma and 2 ma and 15 ma and 9 ma respectively the mississippian metazoan reef recovery was the longest in reef history harsh climatic and oceanic conditions were present during the mississippian mainly including the widespread marine anoxia during the middle part of tournaisian and the following recurrent glacial and interglacial climatic episodes with frequent changes in sea level sedimentary facies and sea water surface temperature which may have stymied metazoan reef recovery during this time during the late visean marine communities flourished during a phase of relative warm conditions and high sea level and coincided with the long delayed re emergence of coral reef ecosystems after the late devonian extinctions

the evolution of a thrust fault system processes of rupture initiation propagation and termination in the 1980 el asnam algeria earthquake summary we discuss work completed to date on the 1980 algerian earthquake and introduce a description of the earthquake in terms of rupture propagation using the nomenclature of fracture mechanics field and teleseismic studies have shown the earthquake fault to be divided into three major thrust segments rupture began at the sw end of the system and propagated along successive segments geological sections reveal that different fault segments have suffered different amounts of displacement in the past the amount of geological displacement increases systematically from almost zero at the sw end of the fault to several hundred metres further ne faulting at the sw end is very young and appears to be extending the thrust system along strike the aftershock data of ouyed et al reveal that strike slip aftershocks occur beyond the sw end of the thrust fault these are accommodating compression by conjugate strike slip faulting on north and west trending planes this network of conjugate faults plays a crucial role in the initiation of major eathquakes on the thrust system and may be regarded as a plastic zone beyond the end of the thrust fault increasing horizontal stress causes the strike slip system to evolve into a zig zag network of thrusts which is partly controlled by the pre existing strike slip faults finally a through going thrust can develop and leads to catastrophic rupture along the main fault plane to describe the propagation of the main shock we extend aki s concept of geometric barriers and divide these into two types in conservative barriers the slip vector is common to both fault planes whereas in non conservative barriers the slip vectors are different on the two fault planes that meet at the barrier although both types of barrier arrest dynamic rupture only nonconservative barriers need produce aftershocks as off fault deformation is required to accommodate the difference in slip vectors by considering the aftershock zones as areas of distributed deformation we show that fracture toughness in the earth is not a material constant but is related to fault geometry and therefore changes as fault systems evolve the current south westwards growth of the el asnam thrust system can be seen as the latest phase in an evolution consisting of periods of along strike extension alternating with periods of increasing net displacement during which no fault growth occurs these two types of behaviour allow a segmented fault system to be produced

the early carboniferous courceyan arundian monsoonal climate of the british isles evidence from growth rings in fossil woods the british isles lay at a palaeolatitude of 4 s during the early carboniferous courceyan arundian period this paper examines fossil gymnosperm wood from ten localities in western ireland and southern scotland in order to analyse palaeoclimate fifty two percent of the 77 fossil wood specimens studied exhibit growth rings that possess subtle discontinuous ring boundaries and ring increments of narrow but variable width these growth rings are qualitatively and quantitatively analysed and are shown to bear a close similarity to growth rings in modern araucarian conifer woods these araucarian growth rings are formed in response to tropical rainfall seasonality linked to monsoonal circulation the findings of this study therefore support earlier palaeoclimatic interpretations based on sedimentological evidence which suggest that the british isles experienced a monsoonal climate during the early carboniferous courceyan arundian period

simulations of permian climate and comparisons with climate sensitive sediments abstract we use a climate model to simulate two intervals of permian climate the sakmarian ca 280 ma at the end of the major permo carboniferous glaciation and the wordian ca 265 ma we explore the climate sensitivity to various levels of atmospheric co2 concentration and to changes in geography and topography between the two periods the model simulates large seasonality and high aridity in the continental interiors of both hemispheres for both periods the northern summer monsoon weakens and the southern monsoon strengthens between the sakmarian and the wordian owing to changes in geography and topography the northern middle and high latitudes cool in winter between the sakmarian and wordian associated with northward shift of the continents this high latitude cooling strengthens the winter westerlies and shifts the maximum storm track precipitation south in the southern hemisphere the winter westerlies weaken from the sakmarian to the wordian starting the simulations with no permanent i

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

crystal fabrics and element impurities sr ca mg ca and ba ca in shells of arctica islandica implications for paleoclimate reconstructions sr ca mg ca and ba ca values are heterogeneously distributed in shells of arctica islandica these patterns are largely associated with crystal fabrics size habit and orientation of crystals or the processes controlling them the outer sublayer of the outer shell layer oosl homogenous and irregular simple prismatic crystal fabrics contained element ca values up to 62 higher than the inner sublayer iosl crossed acicular crossed lamellar fine crossed lamellar and irregular simple prismatic crystal fabrics a gradual decrease in sr ca and mg ca values was observed from the outer portions of the oosl toward the oosl iosl transition zone this chemical shift was accompanied by a gradual transition from homogenous crystal fabrics into crossed lamellar acicular crystal fabrics near annual growth lines irregular simple prisms i e during periods of slow growth sr and mg seemed to be deposited in equilibrium with the ambient environment because the sr ca and mg ca values approached values typical for seawater during the remainder of the growing season sr ca and mg ca remained far below values expected for thermodynamic equilibrium ba ca peaks however occurred erratically at different times of the year without any noticeable changes in crystal fabrics likely the environmental information contained in these peaks was less severely filtered by vital effects than in sr and mg the findings of the present study can help to develop new techniques with which extract environmental signals from the metal to calcium ratios of bivalve shells

structures in segment boundary zones of the lost river and lemhi faults east central idaho geologic mapping and structural analysis of the lost river and lemhi normal faults in east central idaho suggest that many rupture segment boundaries previously inferred from geomorphic data coincide with two classes of structural complexities 1 zones of distributed faults and steps or jogs in the range front faults and 2 intersections with preexisting eocene to oligocene cross faults at 10 15 km depth segment boundaries contain as many as 13 fault splays and are as much as 13 km long and 5 6 km wide in plan view in contrast simple fault traces characterize the range front faults in the interiors of segments thus segment boundaries of normal faults are broad zones of intersecting faults not discrete points the structural data further imply that segment boundaries contain large volumes of fractured and faulted rock and that zones of distributed normal faults have influenced rupture propagation and arrest along these two normal faults intersections of preexisting cross faults and range front faults may also have influenced the locations of rupture boundaries along the lost river and lemhi faults downdip projections of preexisting eocene to oligocene normal faults in the footwall of the lost river and lemhi faults may coincide with four or five segment boundary zones at about 15 km depth the depth at which large earthquakes nucleate in the basin and range province structural analyses also show that some cross faults which coincide with segment boundary zones at the surface are distant from these zones at depth conversely some potentially significant structures present at depth are far removed from the segment boundary zone at the surface thus a close spatial relationship between cross faults and segment boundary zones at the surface cannot prove or disprove a genetic relationship between these features because the near surface geometry of segment boundary zones may differ dramatically from the subsurface geometry of the zones where cross faults define segment boundaries the enhanced fracture toughness of preexisting fault planes and their damage zones may impede or arrest rupture on younger crosscutting faults

cathodoluminescene at low fe and mn concentrations a sims study of zones in natural calcites abstract point analyses of natural calcite cements by sims confirm the earlier suggestions that 20 ppm mn is required to activate luminescence whereas fe concentrations in excess of 1400 ppm quench it partly independently of the mn content below this fe threshold luminescence is bright at mn concentrations in excess of 225 ppm in the range 20 225 mn all types of luminescence dull luminescent and nonluminescent can occur this undifferentiated domain is evident also from a compilation of literature data the type of luminescence is not a simple function of fe and mn concentrations other parameters influence cl sinc most diagenetic calcite cements have fe and mn concentrations that place them within the field of mixed cathodoluminescence these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

the 1983 borah peak idaho earthquake and its aftershocks abstract the 28 october 1983 borah peak idaho earthquake m s 7 3 occurred in an area of low historic seismicity within east central idaho along a segment of the lost river fault active during the holocene a dense network of portable short period seismographs up to 45 stations station spacings of 2 to 10 km was installed beginning several hours after the main shock and operated for 22 days in addition to records from the portable instrumentation data from permanent seismograph stations operating in idaho utah montana oregon washington and wyoming provide a good regional data base no foreshock activity above m c coda magnitude 2 0 was detected for the 2 month period preceding the main shock the epicenter of the main shock is 14 km south southwest of the end of the surface faulting this relationship suggests unilateral rupture propagating to the northwest the distribution of 421 aftershocks of m c 2 defines an epicentral pattern 75 km 10 km trending north northwest parallel to the surface rupture but displaced laterally southwest by 5 to 10 km aftershocks extend to depths of approximately 16 km and in the central and southeastern portion of the aftershock pattern define a zone dipping approximately 45 southwest that intersects the surface near the fault scarp the entire aftershock zone as observed during the first 3 weeks was active shortly after the main shock occurred fault plane solutions for 47 aftershocks show predominantly normal faulting with varying amounts of strike slip motion tension axis orientations indicate a dominant extension direction of nne ssw during the aftershock sequence there is considerable diversity among the aftershock focal mechanisms even along the central and southeast portions of the fault where the hypocenters appear to outline the main fault break we therefore interpret most of the aftershocks to represent complex fracturing on subsidiary structures adjacent to the main fault

isotopic records of brachiopod shells from the russian platform evidence for the onset of mid carboniferous glaciation we performed isotopic analyses of carboniferous brachiopod shells from the russian platform to examine global and regional environmental change along the western and eastern margins of laurussia during the formation of pangea and specifically to examine the isotopic evidence for the onset of mid carboniferous glaciation shell preservation was evaluated from shell microstructure cathodoluminescence trace element content and isotopic comparison with matrix material most interior nonluminescent nl prismatic shell appears to be chemically well preserved as indicated by low to undetectable si al fe and mn contents with minor exception nl shell 13c and 18o values are higher than those of corresponding cements and matrix the 13c record for the russian platform clearly shows a 3 increase from 2 4 0 7 to 5 5 0 6 in the serpukhovian or early bashkirian this shift was first reported by popp et al popp b n anderson t f sandberg p a 1986 brachiopods as indicators of original isotopic compositions in some paleozoic limestones geol soc am bull 97 1262 1269 but had not been documented for a single region widespread occurrence of high 13c values in the late carboniferous support the interpretation of popp et al with regard to this shift as a record of increased burial of organic carbon north american sections show a mid carboniferous 13c shift of only 1 5 we hypothesize that the reduced 13c shift reflects enhanced upwelling on the epicontinental seas of north america after the closing of the seaway between laurussia and gondwana the 18o record for the russian platform shows a 1 8 increase in the mid carboniferous correlative with increased occurrence of glacial sediments and a drop in sea level as a first approximation ice volume calculations suggest that 0 7 of the mid carboniferous 18o shift is due to changes in seawater 18o and 1 1 is due to 5 c cooling concurrent positive 13c and 18o shifts provide evidence for a relationship between mid carboniferous glaciation and burial of organic carbon presumably through changes in atmospheric co2 levels

kinematics and timing of three superposed extensional systems east central idaho evidence for an eocene tectonic transition cenozoic crustal extension in east central idaho began about 50 ma and continues at present three distinct episodes characterize one of the longest intervals of cenozoic extension yet documented in the north america cordillera crosscutting relationships between ne striking normal faults and volcanic rocks regional dike trends and slickenline data indicate nw se extension during peak eocene volcanism about 49 48 ma episode 1 ne striking normal faults with at most a few kilometers of offset formed in an intraarc setting during rapid ne subduction of oceanic plates under the pacific northwest north to nnw striking and west dipping normal faults with offsets up to 10 15 km formed during a younger middle eocene to oligocene basin forming event episode 2 this newly documented episode was the most important extensional event in east central idaho and began during the waning phases of challis volcanism wsw ene to sw ne extension during episode 2 was nearly perpendicular to the extension direction during episode 1 and perpendicular to the grain of the idaho montana fold and thrust belt the flip in extension direction between episode 1 and episode 2 is tightly constrained by 40ar 39ar age determinations to have taken place at the end of eocene challis magmatism about 46 48 ma i infer that plate boundary forces controlled the geometry of normal faults and dikes during episode 1 whereas internal stresses within previously thickened crust drove major sw to wsw directed extension during episode 2 a drop in convergence rates between the north american and farallon plates between 59 ma and 42 ma stock and molnar 1988 may coincide with the onset of gravitational spreading during episode 2 and may also explain the abrupt end of eocene magmatism in the pacific northwest miocene and younger sw dipping basin and range faults episode 3 extended the region in a ne sw direction although faults formed during episode 2 and episode 3 are not parallel slickenlines indicate only small changes in slip vector trends suggesting little rotation of the extension direction in east central idaho since 46 ma

immigration and extirpation selectivity patterns of brachiopods and bivalves across a carboniferous glacial to non glacial transition pennsylvanian central western argentina and their influence in building the biotic bathymetric gradient abstract the growth and demise of glaciers during the late paleozoic ice age had profound consequences on the marine biota in central western argentina the transition from glacial to non glacial interval during the pennsylvanian caused a major regional turnover which remodeled the bathymetric diversity gradient in order to understand the nature of the environmental changes related to such turnover event we compared selectivity patterns in extirpation and immigration of bivalves and brachiopods using logistic regression we tested for a wide range of potential drivers of extirpation and immigration namely body size geographic range size environmental breadth preferred depth metabolic rates infaunalism and taxonomic identity while extirpation preferentially hit brachiopods and genera having smaller geographic ranges and smaller body sizes immigration was related to genera with preference for deeper environment and small geographic ranges extirpation selectivity was not uniform along the bathymetric gradient both geographic range and body size selectivity are stronger towards deeper environments each clade on the other hand showed idiosyncratic responses to climate change while brachiopods show extirpation selectivity for smaller geographic ranges small sized bivalves were preferentially extirpated these contrasting selectivity regimes however could be reflecting different faunal responses to the same environmental changing factor namely higher thermal amplitude immigration in both brachiopods and bivalves was related to preference to deep environments confirming previous results however brachiopods also showed preferential immigration of small geographic range genera which is puzzling given the extinction selectivity related to the glacial non glacial transition possible explanations point to a brief time span in which an increase in thermal amplitude occurred the rapid climate changes particularly related to a rise in maximum temperatures lead the ecological response of the benthic faunas differences in extinction and immigration selectivity along the bathymetric gradient suggest that the turnover event also remodeled the bathymetric gradient in body size and biogeographic structure and brachiopod bivalve proportions such changes were driven by extirpation contrasting with the remodeling of the bathymetric diversity gradient that was driven by immigration our results therefore highlight that immigration and extirpation can shape different aspects of the bathymetric biotic gradient

the sou hills a barrier to faulting in the central nevada seismic belt bedrock zones transverse to regional structures may indicate barriers at depth that inhibit the propagation of fault ruptures in the basin and range province the tertiary bedrock of the sou hills separates dixie and pleasant valleys and is transverse to the trends of physiography and historic surface faulting in central nevada four lines of evidence indicate that the sou hills are a barrier to faulting in the seismic belt first total late cenozoic vertical displacement on range bounding faults decreases toward the sou hills second analyses of landforms that reflect rates of relative uplift show that quaternary uplift decreases where range bounding faults meet the sou hills third the most recent prehistoric faulting south of the transverse zone is several thousand years younger than faulting to the north fourth patterns of late quaternary fault scarps in the sou hills are similar to rupture patterns observed at the termination of faults elsewhere

a portable electrical based percussion coring system for use in deep water this article describes a sediment coring system that can be used in deep water 30 to 60 m with no aid from divers the system is light and compact enough to be operated by three persons and transported in a small boat and or in a small airplane a core tube penetrates into sediments with the force caused by percussion of a water proof electric hammer driven by a generator on the boat with this device four sand cores were retrieved from a lagoon floor at depths ranging from 40 m to 58 m a flexible vinyl tube is used as a core liner and it provides an exact measure of core recovery

the pangean ice age studies with a coupled climate ice sheet model application of an ice sheet model developed for the pleistocene to the extensive carboniferous glaciation on gondwana yields an ice sheet which has several features consistent with observations while complete deglaciation is not achieved without co2 changes the milankovich induced fluctuations in ice sheet volume are comparable to pleistocene glacial interglacial signals this result is shown to hold for a large fraction of physically reasonable parameter space the model also exhibits multiple equilibria and sharp bifurcations as infinitesimal changes in the solar constant or precipitation can lead to a qualitatively different climate the success of the model in predicting ice location in an environment quite different from the pleistocene provides additional support for the robustness of the basic model physics and suggests that the model can be applied with some confidence to other pre pleistocene glaciations

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

middle miocene seasonal temperature changes in the styrian basin austria as recorded by the isotopic composition of pectinid and brachiopod shells abstract using the isotope record on pectinid and brachiopod shells we reconstructed middle miocene palaeotemperatures for a shelf environment in the styrian basin austria bivalve shells of macrochlamys sp collected from different horizons of the lower badenian leitha limestone show 18 o values in the range of 3 to 0 peedee belemnite the large intrashell variability of 3 indicates significant seawater temperature fluctuation the results suggest that despite the high geographical latitude ca 40 n the climate in southern austria was warm subtropical with a pronounced seasonality at that time in contrast the 18 o isotopic composition of a pectinid flabellipecten sp and an indeterminate terebratulid brachiopod from the siliciclastic deposits overlying the leitha limestone ranges between 0 and 1 this indicates cooler mean annual temperatures and reduced seasonal variations a 39 ar 40 ar age on fresh volcanic biotites shows a value of 14 2 0 1 ma the tuffs containing the biotites are located below the layer containing the terebratulid and the flabellipecten sp the stable isotope and radiogenic data suggest that the drop in temperature is in direct relationship with the east antarctic ice sheet expansion which started at ca 14 ma due to the variation in temperature the subtropical fauna in the retznei quarry disappeared during the early miocene and the biogenic limestones were replaced by clastic sediments the 18 o isotopic profiles from three pectinids collected from the leitha limestone indicate that these grew within ca 1 5 years growth interruptions occurred during the warm season because during this period the pectinids very likely used their energy for the growth and maturation of gonads carbon isotopic compositions vary between 0 and 2 statistical tests show that for some of the analyzed shells the cyclicity of the 13 c profiles may be explained by the temperature dependent fractionation between air co 2 and dissolved bicarbonate

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

equatorial aridity and climatic oscillations during the early carboniferous southern britain evidence from palaeosols palaeokarsts and styles of meteoric diagenesis shows that the early carboniferous climate of southern britain was dominantly seasonally semi arid this semi aridity occurred while the region was in an equatorial palaeolatitudinal position the cause of the seasonal aridity was possibly the deflection of easterly winds into a major low pressure zone set up over gondwana during the southern hemisphere summer

planar high angle faulting in the basin and range geodetic analysis of the 1983 borah peak idaho earthquake geodetic elevation changes record the broad scale deformation associated with the m 7 0 october 28 1983 borah peak idaho earthquake on the lost river fault the crest of the lost river range rose 0 2 m and adjacent thousand springs valley subsided 1 0 m in relation to reference points 45 km from the main shock epicenter the deformation was modeled by dislocations in an elastic half space a planar fault with uniform dip slip of 2 05 0 10 m dipping 47 o 2osw and extending to a vertical depth of 13 3 1 2 km fits the geodetic data best and is also consistent with the main shock hypocenter and fault plane solution the geodetic moment is 2 6 0 5 x 1019 n m 2 6 0 5 x 1026 dyn cm and the estimated static stress drop is 2 9 0 4 mpa 29 4 bars tests for coseismic slip on listric faults which flatten with depth and on detachments horizontal faults or shear zones showed fits to the geodetic data that are inferior to those for planar high angle faults no detectable coseismic slip occurred on the mesozoic white knob thrust fault although the low angle thrust sheet intersects the south end of lost river fault near the 1983 mainshock epicenter if the high angle lost river fault abuts a flat lying detachment fault or shear zone such a structure must lie at depths of 12 km near the brittle ductile transition where stick slip behavior gives way to creep the depth and geometry of faulting at borah peak is similar to that inferred from seismic and geodetic evidence for the 1954 m 7 2 fairview peak nevada and the 1959 m 7 3 hebgen lake montana events suggesting that if detachments are active at these localities they are deep and most likely slip by creep

late quaternary fault segmentation from analysis of scarp morphology a thorough knowledge of the lateral extent of individual prehistoric ruptures along a fault is necessary to assess the locations and geologic characteristics of boundaries between independent faultrupture segments paleoseismic studies employing only trenching may yield insufficient data to evaluate the lateral extent of individual rupture events systematic mapping of fault scarps and degradation equation modeling of relative scarp ages on the lemhi fault a range bounding normal fault in east central idaho provide a method to assess rupture extent and boundaries between rupture segments the youngest latest quaternary surface ruptures occurred at distinctly different times on adjacent segments of the fault the boundaries between rupture segments differ in characteristics although most are at intersections of the currently active range bounding fault and mid tertiary normal faults several major structural and tectonic discontinuities did not form segment boundaries in the most recent rupture cycle or probably in the previous cycle the lemhi fault illustrates both the importance of preexisting structures in controlling extent of ruptures and the need for detailed analysis along an entire fault zone

assessing the biomineralization processes in the shell layers of modern brachiopods from oxygen isotopic composition and elemental ratios implications for their use as paleoenvironmental proxies abstract fossil brachiopod shells are often used as valuable archives to reconstruct paleoenvironmental conditions in deep time however biomineralization processes can impact their fidelity as geochemical proxies brachiopod shells comprise an outer primary layer a secondary fibrous layer and sometimes a tertiary columnar layer therefore it is essential to assess the potential effects of the biomineralization processes in each of the different shell microstructures of modern brachiopods this study analyses the oxygen isotopic composition together with li ca na ca mg ca and sr ca data at high spatial 20 50 m resolution in seven modern brachiopod species focusing on differences between the primary secondary and tertiary layers in all studied species 18o values of the outer primary layer are consistently out of equilibrium with seawater also this shell layer is enriched in li na mg and sr contrary to the primary layer the innermost secondary layer is near or at oxygen isotopic and elemental equilibrium with ambient seawater the columnar tertiary shell layer if present has the least variable and the heaviest oxygen isotopic composition within the range of equilibrium values with seawater this tertiary layer however is depleted in minor and trace elements relative to the other shell layers thus the tertiary layer is more suitable for oxygen isotopic studies whereas the innermost secondary layer of the most mature parts of the shell is the best target in two layered shells while we do not observe any clear interspecific relationships between mg ca and sr ca ratios on one hand and environmental parameters such as temperature salinity and ph on the other hand there is a positive interspecific relationship between na ca and salinity and a negative interspecific relationship between li ca and temperature suggesting their potential use as proxies of physicochemical parameters of seawater

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

stepwise transition from the eocene greenhouse to the oligocene icehouse the eocene oligocene transition is the largest global cooling in the cenozoic period a comparison of three independent proxies from the continental shelf and deep ocean reveals a three step transition to cold glacial conditions with ice sheets 25 larger than their present size

warm water carbonates in proximity to gondwanan ice sheets a record from the upper paleozoic of iran abstract sedimentologic and paleontologic proxies recovered from the alborz basin the sanandaj sirjan zone and additional iranian peri gondwanan continental blocks near the arabian margin of northeastern gondwana record the formation of warm water shallow marine carbonates throughout the late pennsylvanian earliest permian this reflects a prevailing favorable climatic and environmental regime that contrasts with the cold conditions of slightly more southerly gondwanan regions that experienced profound glaciations the sedimentologic and paleobiologic properties of these iranian carbonates also differ greatly from coeval cool water carbonates of bolivia that developed at equivalent paleolatitudes along the northwestern margin of gondwana the complex climatic patterns reflected in the dispersal of marine taxa and their colonization of ecosystems relatively remote to their customary habitats and climate zones are interpreted to record the influence of ocean circulation based on these sedimentologic and paleobiologic data we utilized a climate model community climate system model version 3 ccsm3 to help resolve the mechanisms responsible for enabling transport of warm water to higher latitudes in northeastern gondwana these simulations reveal that spatial variations in sea surface temperatures exerted a strong forcing on paleo tethyan oceanic circulation and thereby governed the distribution diversity and abundance of taxa in late paleozoic marine ecosystems based on this outcome we conclude that the climatic contrasts registered across upper pennsylvanian lower permian carbonate platforms of the paleo tethys and panthalassic ocean originated through oceanic circulation driven by geographic differences in sea surface temperature

a greenhouse interval between icehouse times climate change long distance plant dispersal and plate motion in the mississippian late visean earliest serpukhovian of gondwana abstract the late paleozoic ice age lpia is the closest example that can be compared with current climate conditions near the beginning of the lpia fossil plants of mississippian late visean to earliest serpukhovian age indicate a widespread frost free climate in a wide belt on gondwana indicating an interval of greenhouse conditions between the earlier visean and later serpukhovian icehouse times this warm temperate floral belt has been named the paraca floral belt after the locality on the peruvian coast where it was first recognized the origin of this particular zono biome was due to the interplay of 1 climate oscillations 2 several kinds of long distance plant dispersal within between or through zono biomes and 3 plate motion the carboniferous age strata on the paracas peninsula in peru serve as an example for an analysis of these large scale patterns through the analysis of local geology paleobotany and paleoecology the processes observed during this time interval can serve as a model for long distance plant dispersal at other times

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

abrupt changes in early holocene tropical sea surface temperature derived from coral records for many high latitude regions of the globe it is now clear that the transition to modern climate following the last glacial maximum was punctuated by a number of rapid and substantial climate oscillations1 2 in contrast relatively little is known about how the tropics responded to the deglaciation because few high resolution records are available from lower latitudes corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated using either 14c or 230th and because past sea surface temperatures can be recovered from the sr ca ratios in coral skeletons here we use this technique to derive several early holocene sea surface temperature records from a coral drill core recovered from espiritu santo vanuatu in the tropical southwest pacific ocean these records indicate that sea surface temperatures in this region were depressed by as much as 6 5 c below modern values at 10 350 calendar years bp but rose very abruptly during the following 1 500 years this temperature increase lags the post younger dryas increase observed in a coral record from the tropical atlantic ocean3by about 3 000 years an unexpected phase shift that may ultimately shed light on the mechanisms of deglacial climate change

constraints on pennsylvanian glacioeustatic sea level changes using oxygen isotopes of conodont apatite conodonts from u s midcontinent cyclothems were studied for oxygen isotopes in order to constrain pennsylvanian glacioeustatic sea level fluctuations pennsylvanian deposits of the midcontinent united states are composed of cyclic alternations of thin transgressive limestones offshore gray to black phosphatic shales and thick regressive limestones a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds glacioeustatic sea level fluctuations are considered the primary cause for the formation of these cyclothems oxygen isotope analyses of conodont apatite from the black 20 1 0 5 vienna standard mean ocean water vsmow and gray shale units 20 5 0 5 vsmow show lowest average 18 o values whereas conodont elements from the regressive 21 0 0 3 vsmow and transgressive limestone units 21 1 0 6 vsmow are enriched in 18 o the maximum change in 18 o of conodonts from the black shale and carbonate units from individual cyclothems is 1 7 the 1 7 c difference in 18 o compares relatively well to pleistocene interglacial glacial changes in 18 o of equatorial surface dwelling foraminifers and suggests that pennsylvanian glacioeustatic sea level changes may have been of comparable amplitude however since the pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record pennsylvanian glacioeustatic sea level changes were probably larger than the 120 m fluctuations recorded for the pleistocene glaciations

brachiopod shell spiral deviations ssd implications for trace element proxies abstract the importance of brachiopod shells as archives of past environmental changes via chemical proxies isotopes and trace elements will increase significantly if the age of specimens can be determined accurately here we evaluate the interpretation of spiral shell deviations throughout the ontogeny of the modern brachiopod species laqueus rubellus collected from sagami bay japan in combination with high resolution biogeochemistry the determination of spiral maxima and minima indicates that there is a different growth rate for ventral and dorsal valves as well as for juvenile and adult specimens and that the anterior shell regions provide a more accurate record of shell growth the combination of trace element proxies p ca and mg ca with shell spiral deviations indicates that the maxima represent prominent periods of shell growth that occurs during the beginning of the autumn by counting the maxima on dorsal valves of fully mature specimens these specimens can record shell growth up to 6 7 years which is confirmed by independent morphological and isotopic studies in the same brachiopod species the integration of statistical measurements of shell morphologies with chemical measurements represents an innovative methodology for specimen age determinations in brachiopods and provides a better understanding of trace element proxies overall the application of this approach to fossil brachiopods may open a new avenue for paleoseasonality and paleoceanography studies

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

localized rotation during paleogene extension in east central idaho paleomagnetic and geologic evidence we collected paleomagnetic data from 137 sites in middle eocene volcanic rocks of the northeastern basin and range province in order to characterize the three dimensional kinematics of continental extension in the lost river and lemhi ranges idaho and to test previous block rotation models statistically significant flattening of directions at three of 10 localities reflects either insufficient averaging of paleosecular variation or erroneous tilt corrections five of the seven remaining locality means are statistically indistinguishable from the middle eocene reference direction this indicates that vertical axis rotation did not accompany post 50 ma normal faulting discordant declinations from two localities in the northern lost river range indicate 30 40 of counterclockwise rotation of a large domain of nnw striking volcanic rocks inclination flattening at one of the two rotated localities is moderate but statistically significant f f 9 9 6 5 in total the paleomagnetic data conflict with earlier predictions of uniform clockwise rotation in response to right lateral transtension adjacent to the eastern snake river plain there is a close correspondence between counterclockwise rotated localities and domains of nnw striking volcanic rocks and between unrotated localities and domains of north striking volcanic rocks new mapping shows that counterclockwise rotated localities are all in the hanging wall of a major west dipping low angle normal fault the donkey fault named for the first time this fault loses displacement southwards was active in eocene oligocene time and is probably a tilted high angle fault the spatial distribution of rotated and unrotated localities is best explained by counterclockwise rotation of the hanging wall of the donkey fault during opening of a southward tapering half graben according to this hanging wall rotation model the footwall of the donkey fault remained fixed relative to its rotating hanging wall our proposed kinematic model is generally applicable to extending continental lithosphere and provides a mechanism for coeval crustal thinning and vertical axis rotation thus vertical axis rotation may occur in the absence of strike slip faults in extensional orogens

brachiopod geochemical records from across the carboniferous seas of north america evidence for salinity gradients stratification and circulation patterns abstract stable isotopic analyses of 100 well preserved carboniferous brachiopod shells representing two time slices from across north america reveal systematic regional changes in environmental conditions for both of the time slices studied the chesterian latest mississippian and the virgilian latest pennsylvanian 18o and 13c show a stepwise decrease moving across the continent from modern day west to east higher 18o in the west reflects greater water depths less freshwater input and more direct upwelling influence from cool open marine waters than in the east modelling based on these regional isotopic data indicates salinity reductions on the order of 1 4 psu in the appalachian basin relative to the midcontinent basin for the virgilian time interval over a range of reasonable thermal gradient and 18ofw assumptions the magnitude of this gradient is similar to those of modern day hudson bay and the panama bight which exhibit permanent haloclines driven by freshwater discharge considering existing paleoecological evidence for freshening the lack of more dramatic benthic freshening suggests that the depth of a regional halocline was shallower than the depths inhabited by thick shelled stenotopic brachiopods although other lines of evidence are necessary to verify the strength of the halocline estimated 18o temperatures for appalachian basin brachiopods are 3 5 c cooler than those of coeval conodonts due to either slightly warmer fresher surface waters or uncertainty in the phosphate 18o paleothermometer despite discrepancies in calculated temperatures the magnitude of the regional isotopic gradient derived from brachiopod and conodont proxies is similar after making appropriate glacioisotopic and water depth corrections a decreasing 13c trend toward the east southern paleolatitude likely reflects greater restriction and terrestrial influence near the sea s tropical shoreline trace element trends are less consistent and are affected by species and metabolism erratic variations in mg ca concentrations even among pristine samples of the same genera with similar 18o values and unrealistic mg ca derived temperatures justify continued caution in applying existing mg ca thermometer equations to paleozoic brachiopods

late pennsylvanian seasonality reflected in the 18o and elemental composition of a brachiopod shell to evaluate the potential for the study of late pennsylvanian seasonality detailed isotopic and elemental analyses were performed on a single specimen of the brachiopod neospirifer dunbari shell preservation was evaluated by petrographic and cathodoluminescence microscopy carbonate powders from 112 spots were collected from the sectioned shell for isotopic analyses and 369 spots on the complementary thin section were analyzed by electron microprobe for chemical composition in the nonluminescent part of the shell mg ca ratios were between 0 001 and 0 012 and na ca and s ca ratios ranged from 0 003 to 0 012 and 0 003 to 0 021 respectively values of 18 o vary between 2 3 and 1 1 contours of 18 o mg na and s concentrations parallel growth bands and reveal a record of 1 to 2 cycles mg s and na contents varied nversely with 18 o this trend is opposite to the expected diagenetic trend and is consistent with the temperature dependences of mg content and 18 o thus implying preservation of shell chemistry the 1 2 range in 18 o values suggests a seasonal temperature variation of 5 to 6 c assuming no change in the 18 o of the water this high seasonality for the tropical epicontinental sea of kansas supports climate model predictions of enhanced continentality in pangean climate detailed stable isotope and element concentration profiles across growth bands of brachiopod shells can provide quantitative records of paleozoic seasonality

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

the mg ca temperature relationship in brachiopod shells calibrating a potential palaeoseasonality proxy brachiopods are long lived long ranging extant organisms of which some groups precipitate a relatively diagenetically stable low magnesium calcite shell previous work has suggested that the incorporation of mg into brachiopod calcite may be controlled by temperature brand et al 2013 here we build upon this work by using laser ablation sampling to de ne the intra shell variations in two modern brachiopod species terebratulina retusa linnaeus 1758 and liothyrella neozelanica thomson 1918 we studied three t retusa shells collected live from the firth of lorne scotland which witnessed annual temperature variations on the order of 7 c in addition to four l neozelanica shells which were dredged from a water depth transect 168 1488 m off the north coast of new zealand the comparison of intra shell mg ca profiles with shell ad18o confirms a temperature control on brachiopod mg ca and supports the use of brachiopod mg ca as a palaeoseasonality indicator our preliminary temperature calibrations are mg ca 1 76 0 27 e 0 16 0 03 t r2 0 75 for t retusa and mg ca 0 49 1 27 e 0 2 0 11 t r2 0 32 for l neozelanica errors are 95 confidence intervals

boron isotope geochemistry of paleozoic brachiopod calcite implications for a secular change in the boron isotope geochemistry of seawater over the phanerozoic abstract boron isotope composition of marine carbonates has been proposed as a paleo ph proxy and potential tool to reconstruct atmospheric pco2 the precise knowledge of the boron isotopic composition of ancient seawater represents the fundamental prerequisite for any paleo ph reconstruction this contribution presents boron isotope values for silurian to permian brachiopod calcite that might be used to reconstruct ph or boron isotope composition of past oceans all brachiopod shells were screened for diagenetic recrystallization by means of cathodoluminescence microscopy trace element geochemistry b fe mn sr as well as sem only nonluminescent shells revealing well preserved microstructures high strontium and boron concentrations as well as low iron and manganese contents were accepted for boron isotope analysis the boron isotope ratios of silurian devonian pennsylvanian and permian brachiopod calcite range from 6 8 to 11 0 7 3 to 14 9 12 4 to 15 8 and 10 1 to 11 7 respectively these 11b values are significantly lower in comparison to 11b values of modern biogenic carbonates and indicate that the paleozoic oceans were depleted in 11b by up to 10 box modeling of the boron geochemical cycle suggests that the significant depletion of 11b in the oceanic reservoir may have been initiated by an enhanced continental boron discharge our data support the earlier made conclusion that boron isotopes may not be used in the geological past as reliable paleo ph proxy unless the boron isotopic composition of ancient oceans can be constrained by further studies

depressed rates of origination and extinction during the late paleozoic ice age a new state for the global marine ecosystem rates of origination and extinction for marine animal genera dropped to low levels in latest mississippian time immediately after massive glaciers formed in the southern hemisphere and a second order mass extinction occurred evolutionary turnover and diversity remained low for 50 m y shifting markedly upward precisely when extensive glaciation ended in early permian time all diverse taxa with good fossil records experienced low rates of origination and extinction during this major ice age such sluggish rates would be predicted for faunas of shallow seas on or adjacent to a heavily glaciated supercontinent such as pangea where cool and highly seasonal thermal regimes should dictate that species have broad ecological niches widespread geographic distributions and large and relatively stable populations

climatic basis for sluggish macroevolution during the late paleozoic ice age rates of origination and extinction for marine invertebrates fell at the onset of the late paleozoic ice age in late mississippian time and remained low until glaciation ended in middle permian time through the use of a database of stratigraphic and geographic occurrences of brachiopod genera these macroevolutionary changes are traced to the loss of genera with narrow latitudinal ranges which had intrinsically high turnover rates at the onset of glaciation in late visean time when glaciation waned in late sakmarian time narrowly distributed genera rebounded abruptly and restored the global fauna to its pre ice age configuration because narrowly distributed brachiopod genera had dominated tropical diversity the major biotic effects of the late paleozoic ice age were felt at low latitudes the climatic regime of this ice age thus altered the marine ecosystem to one characterized by broadly adapted long lived genera

structural and fluid chemical properties of seismogenic normal faults abstract structures in extensional fault zones can be classified using the configuration of fault branch lines and tip lines important classes include the segment bend segment termination segment branch cross fault intersection and segment offset the effect of these structures on rupture history is not necessarily consistent neither between individual earthquakes nor between different fault zones rupture behavior is dependent on several other factors including loading conditions regional and localized rupture tip stress fields fluid mechanical processes and chemical processes fracture toughness is partly controlled by the angular discordance between slip directions on adjacent fault segments greater discordance between slip directions and intersection lines of fault segments results in greater strain incompatibility an internal fracture network generally evolves within a segment boundary to maintain compatibility and transfer slip between the segments the dimensions and structure of this fracture network may also partly control rupture propagation presumably activation of a fault network with large angular discordances between slip directions and intersection lines will generate numerous asperities as the subsidiary faults mutually interact and offset each other the geometry of a segment boundary may change with depth and the three dimensional nature of the structure may be important in controlling rupture history fluids influence rupturing via fluid pressure effects and time dependent chemical processes fracture propagation by stress corrosion may favor instability and chemical alteration may produce minerals of lower strengths allowing time dependent creep sealing and healing of fractures however may remove damage and increase strength elementary computations indicate that representative times for sealing and chemical alteration are between 1 and 1000 years for reasonable physical conditions well within the recurrence intervals of most large earthquakes time to failure for stress corrosion cracking is more highly variable and strongly sensitive to applied stress and fluid pressure

structure of a fault segment boundary in the lost river fault zone idaho and possible effect on the 1983 borah peak earthquake rupture abstract the 1983 borah peak earthquake m s 7 3 initiated within the southern part of the thousand springs segment in the lost river fault zone east central idaho the earthquake rupture propagated unilaterally to the northwest over a distance of 36 km and was accompanied by sinistral normal slip within the fault zone at the surface the southern most part of the rupture zone is marked by a bend in the lost river fault zone at the intersection between the thousand springs segment to the north and the mackay segment of the fault zone to the southeast the intersection between the two fault segments is a lens shaped area that contains numerous nw and ne striking faults that cut the paleozoic bedrock several of the faults within the intersection zone ruptured at the surface during the 1983 earthquake a three dimensional geometrical model of the intersection zone between the thousand springs and mackay fault segments was constructed from geological mapping in conjunction with previously published interpretations of geodetic and seismological data the longitudinal axis of the intersection zone plunges to the southwest where its projected position in the subsurface roughly coincides with the location of the 1983 earthquake9s hypocenter at a depth of 15 to 16 km the intersection zone between the two fault segments may have played a dual role during the borah peak earthquake both marking the site of rupture nucleation but also acting to arrest spread of the rupture to the southeast onto the adjacent mackay segment

chemical variation in pennsylvanian brachiopod shells diagenetic taxonomic microstructural and seasonal effects abstract to improve our ability to use minor and trace element mte variation in biotic carbonates as diagenetic and paleoenvironmental indicators we performed electron probe microanalysis on more than 100 late pennsylvanian brachiopod shells from texas kansas missouri and new mexico texturally preserved specimens of the genera crurithyris composita and neospirifer from all three regions were analyzed as were eridmatus specimens from texas twenty measurements were made in two transects across each shell shell microstructure and cathodoluminescence were described for each spot analyzed three modern shells were analyzed for comparison diagenesis as indicated by cathodoluminescence and or absence of microstructure tends to enrich shells in fe and mn x ca 0 7 mmol mol and deplete shells in na and s mg content shows no consistent trend with diagenesis in fabric retentive nonluminescent shell areas mg na and s contents vary twofold to sevenfold depending on taxonomy microstructure and season overall taxonomy is the dominant factor controlling mte composition na and s concentrations are consistently highest in crurithyris and eridmatus intermediate in neospirifer and lowest in composita in taxa with mixed microstructure composita neospirifer secondary fibrous layer calcite contains 1 5 to 2 times more na than does interlayer prismatic calcite thus whole shell na contents of these taxa depend on the proportion of fibrous and prismatic shell seasonal cycles are revealed in mte transects across growth lines mg na and s contents commonly vary by more than a factor of two between maxima presumably summer and minima winter within the same shell retention of taxonomic microstructural and seasonal effects in shell chemistry argues for preservation of original chemistry in fabric retentive nonluminescent paleozoic brachiopod shells

sedimentological record of the late paleozoic glaciation in queensland australia although much is known of the timing geographical extent and character of the late paleozoic gondwanan glaciation its rec ord in eastern australia is poorly resolved some previous investigations have asserted that large parts of australia were covered by a cold based continental ice sheet during the pennsylvanian late carboniferous new data from queensland in northeast australia reported herein however suggest that the glaciation there was restricted to discrete short lived periods in the namurian 315 ma westphalian 311 ma and sakmarian 289 293 ma thick successions in three widely separated areas indicate that the glaciation was confined in each case to local valley or mountain glaciers and that the mainly proglacial sediments were enclosed in every case by substantial intervals of fluvial lacustrine and shallow marine strata deposited under nonglacial conditions accordingly we submit that the cessation of glacial sediment deposition elsewhere in gondwana during the pennsylvanian to earliest permian was due to the decay of glaciers rather than to a transition to a cold based ice sheet or sheets as has been previously suggested the interpretations presented herein make a significant contribution toward constraining the size and extent of glaciation in gondwana which has major implications for late paleozoic world climate and sea level fluctuations

mg ca temperature calibration for the benthic foraminifer cibicidoides pachyderma 1 the recent development of foraminiferal mg ca as a paleotemperature proxy has enabled the extraction of global ice volume and local salinity from the more traditional paleotemperature proxy 18o the benthic foraminiferal genus cibicidoides is widely used in paleoceanographic reconstructions because of its epifaunal habitat and cosmopolitan distribution and it has received early attention in mg ca work however existing temperature calibrations for cibicidoides rely heavily on c pachyderma core top data from one location little bahamas bank where authigenic processes and or reworking may result in elevated warm water mg ca values here we present new c pachyderma mg ca data from a series of 29 high quality multicore tops collected in the florida straits spanning a temperature range of 5 8 18 6 c in contrast to previous calibrations we find no evidence for a strongly exponential response to temperature the data are best explained by a linear relationship with a sensitivity of 0 12 mmol mol 1 per c

chemostratigraphy of the mid carboniferous boundary global stratotype section and point gssp bird spring formation arrow canyon nevada usa abstract the iugs in 1998 decided that the mid carboniferous mississippian pennsylvanian global boundary stratotype section and point gssp be assigned to a sequence of sedimentary units within the lower bird spring formation in arrow canyon nevada usa with the boundary defined by the first appearance of declinognathodus noduliferus this study represents the geochemical work on brachiopods matrix and cement covering a 35 m interval of the gssp about the mid carboniferous boundary samples were collected wherever brachiopods were noted in the sequence interval and their stratigraphic position was carefully measured using the a markers left by amoco geologists from their detailed biostratigraphic work the mean chemostratigraphic 1000 sr ca value of unaltered brachiopods from the mississippian side of the boundary 1 928 0 575 are similar to their pennsylvanian counterparts 2 141 0 427 and both are within the range of values obtained for recent low latitude brachiopods 1 50 to 5 50 manganese concentrations are similar with mean values of 33 mg kg and 27 mg kg for mississippian and pennsylvanian boundary brachiopods respectively and fall well within the manganese range of recent low latitude representatives 4 to 58 mg kg in contrast mississippian unaltered boundary brachiopods 244 125 mg kg contain significantly more fe p 0 001 than pennsylvanian ones 141 97 mg kg although both of these averages are above there is some overlap in their ranges with that recorded for fe in recent counterparts 10 to 127 mg kg oxygen isotope values of unaltered brachiopods from the mississippian side of the boundary 2 38 0 82 pdb are similar to the pennsylvanian ones 2 19 0 72 pdb and well within the range recorded in recent low latitude specimens 3 04 to 0 40 pdb carbon isotope values for the mississippian boundary brachiopods 2 01 0 81 pdb are dissimilar to those from the pennsylvanian 2 42 0 83 pdb but both are within the range observed in recent low latitude brachiopods 0 94 to 3 11 pdb the 1000 sr ca mn fe 13c and 18o values contents of the unaltered brachiopods reflect oceanographic conditions of the arrow canyon sea and as such are valuable proxies for local and possibly regional basin correlation at this time the 87sr 86sr values of unaltered brachiopods provide the most useful geochemical tool in recognizing and correlating the mid carboniferous boundary on a global scale the frequency and variations of the mississippian 87sr 86sr trend 0 708 082 0 000 040 are pronounced and significantly different p 0 045 from the essentially invariant trend for the post boundary pennsylvanian 0 708 123 0 000 031 brachiopods from the gssp the mid carboniferous boundary 87sr 86sr value based on unaltered brachiopod samples from within 1 m of the boundary is 0 708 056 0 000 021

source parameters of montana earthquakes 1925 1964 and tectonic deformation in the northern intermountain seismic belt waveform modeling and first motion analysis are used to determine the source parameters of six 5 8 m 6 8 earthquakes that occurred between 1925 and 1964 within the northern intermountain seismic belt of montana results of this study suggest that the 1925 clarkston earthquake occurred along an oblique normal fault with a trend similar to the southern end of the clarkston valley fault the two largest earthquakes of the 1935 helena sequence occurred along right lateral strike slip faults with trends similar to the bald butte and helena valley faults the 1947 virginia city earthquake occurred along a northwest southeast trending segment of the madison fault movement at depth was along a fault with strike similar to that of the 1959 hebgen lake main shock a reanalysis of a m 6 0 aftershock of the 1959 hebgen lake sequence suggests the earthquake occurred at a depth of 8 km along a fault that is not seen at the surface an m 5 8 earthquake in 1964 located about 10 km from the 1959 aftershock may have occurred along steeply dipping fault planes 48 to 80 at depths of 8 to 14 km most events could be modeled as simple ruptures

acme and demise of the late palaeozoic ice age a view from the southeastern margin of gondwana abstract palaeoenvironmental reconstructions from across the globe indicate that the climatic and oceanographic changes that accompanied the permian transition from deep icehouse to greenhouse conditions were uneven and asynchronous because of a paucity of well constrained data environmental changes in gondwana remain poorly understood relative to tropical pangaea in this regard the permian system of eastern australia provides a unique record of this transition along a high latitude open marine shelf not only was glaciation protracted here relative to other regions of gondwana but the record also spans temperate to polar palaeolatitudes providing an opportunity to examine environmental changes along a latitudinal transect we integrate proxies for 18oseawater palaeotemperature pco2 and depositional environment to assess the evolution of nearshore conditions through the permian glaciation was not continuous but rather focused into four discrete glacial epochs p1 p4 each several million years in length which alternated with nonglacial intervals of similar duration during the asselian mid artinskian p1 p2 time uniform conditions along the full extent of the margin were maintained by a cold boundary current coupled with oceanic upwelling increased spatiotemporal variability is evident at the end of glacial p2 mid artinskian perhaps due to tectonic changes that impacted the palaeogeography of the margin although glaciers had disappeared by this time elsewhere in gondwana eastern australia saw two additional periods of glaciation p3 roadian earliest captianian and p4 early wuchiagingian continued albeit intermittent glaciation was facilitated by drift toward higher palaeolatitudes orogenic activity that led to the development of areas of high elevation that could serve as nucleation points for glaciers and transient drops in atmospheric pco2 variations in meltwater input exerted a strong effect on local 18oseawater values complicating attempts to reconstruct latitudinal gradients in palaeotemperature results point to atmospheric co2 as the primary driver responsible for the dynamic climate variations evident in the record

neogene mass extinction of western atlantic molluscs there have been many hypotheses for the global mass extinctions that occurred during the phanerozoic history of the earth and although we cannot study the course of such a mass extinction in progress it is possible to evaluate major pulses of extinction that have taken place recently in geological time explanations of the unusually high rates of extinction within late cenozoic marine faunas of the tropical western atlantic have focused on possible blocking of nutrient laden waters by the origin of the isthmus of panama1 2 and on pleistocene cooling2 3 5 6 or regression2 4 5 of seas here we report that major episodes of molluscan extinction occurred at least as far north as virginia and we conclude that these episodes were caused primarily by refrigeration associated with the late pliocene and pleistocene growth of continental glaciers

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

an inexpensive diver assisted percussion coring device abstract mountain lake giles county virginia contains soft sediments from which undisturbed cores are logistically difficult to collect by conventional gravity coring whereas other more expensive types of corers might successfully sample the sediments in this or similar aquatic systems our new diver assisted percussion coring device assembled with hardware costing about 50 00 enabled flawless collection of 7 cores 100 of tries we describe here this percussion coring device its operation and probable application

a model based evaluation of tropical climate in pangaea during the late palaeozoic icehouse abstract the late palaeozoic ice age lpia is the earth s penultimate icehouse climate geological proxies for tropical pangaean climate during the lpia are significantly modulated on 100 400 kyr and sub 100 kyr scales in addition some geological proxies suggest that equatorial continental areas may have been colder and more arid during lpia glacial intervals than during late cenozoic glacial intervals furthermore the relationship between polar and tropical climate variability remains controversial the climate dynamics underlying these phenomena are only partly understood nevertheless past modeling of lpia climate has suggested that precipitation near the equator was modulated by monsoonal circulation that itself was modulated by orbital variability here the earth s climate during asselian sakmarian time 299 284 ma was simulated with the community climate system model version 3 ccsm3 these simulations address model climate sensitivity to direct and indirect effects of glaciation as well as variability in the earth s orbit the results of these simulations suggest that sea level and orbitally forced monsoon variability were the primary controls on tropical precipitation when ice sheets were confined to polar latitudes any impact of orbital forcing on glaciation therefore could have led to aliasing between glacial and monsoonal effects in particular regions perhaps explaining contrasting geologically based interpretations of how tropical climate responded to glaciation glaciation of the central pangaean mountains would have led to widespread cold and aridity in equatorial pangaea but forming these glaciers would have required an unknown additional climate forcing with an unknown impact on tropical precipitation

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

stable isotopes in late pennsylvanian brachiopods from the united states implications for carboniferous paleoceanography stable isotopic analyses have been performed on nearly 500 nonluminescent brachiopod shells from kansas new mexico and texas to evaluate temporal and geographic variability in the carbon and oxygen isotopic record for late pennsylvanian time brachiopod specimens were collected from missourian and virgilian shales and examined in thin section for preservation of microstructure and absence of cathodoluminescence as a primary test for shell preservation regional variations are observed in the 18o and 13c values of nonluminescent brachiopod shells of the same genera average 18o values for the three genera analyzed crurithyris composita and neospirifer are highest in kansas 1 9 intermediate in texas 2 3 and lowest in new mexico 3 6 vital effect on the 18o of these genera appears minimal 18o data and other evidence suggest warmer temperatures for the shallow new mexico localities and slightly higher salinity for the kansas sea relative to the texas sea the 13c values of composita average about 1 higher than those of co occurring crurithyris and neospirifer suggesting microhabitat differences or vital effects preservation of this species effect argues for preservation of original 13c values average 13c values are highest in texas intermediate in kansas and lowest in new mexico although these values range from 2 6 to 4 9 for individual genera the regional variation in 13c averages less than 1 data for nonluminescent brachiopods and marine cements reveal a mid carboniferous 13c increase of 2 in paleotethyan sea water this increase is not seen in samples from the north american epicontinental seas which opened to the panthalassa ocean this regional difference in 13c appears to be due to changes in ocean circulation associated with the closing of the equatorial seaway and formation of pangea

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

carboniferous permian carbon isotope stratigraphy of successions from china yangtze platform usa kansas and russia moscow basin and urals abstract the pennsylvanian and early permian were times of extreme sea level changes of 100 to perhaps up to 200 m for example glacio eustatic sea level changes are well documented from the us midcontinent moscow basin and yangtze platform where more than 100 stacked subtidal to supratidal sequences have been described in contrast carbonates developed in the ural mountains and south guizhou of the yangtze platform were deposited in ramp and slope settings 13c values of whole rock samples from the us midcontinent and moscow basin were intensively affected by diagenesis only well preserved brachiopod shells maintained their original carbon isotope ratios in contrast limestones deposited in the deeper water slope environments were not affected by meteoric diagenesis and are interpreted to have mainly retained their carbon isotope ratios mean 13c values of slope carbonates of the yangtze platform increase from about 3 during the visean and serpukhovian to 5 at the carboniferous permian boundary and decrease to values around 2 in the early kungurian this positive 13c excursion coincides with low 13c values in the yangtze platform successions which were reset by meteoric diagenesis the highest 13c values recorded in the slope succession coincide with the inferred maximum glaciation that caused pronounced sea level lowstands short lived but significant negative 13c excursions in the chinese slope succession are interpreted to reflect changes in ocean circulation due to sea level rises which caused enhanced production and or preservation of organic matter which influenced the subsequent early diagenetic cementation

a global review of the late mississippian carboniferous gigantoproductus brachiopoda faunas and their paleogeographical paleoecological and paleoclimatic implications abstract the gigantic gigantoproductus bearing brachiopod fauna is one of the most distinct marine benthic faunas in the late mississippian early carboniferous in terms of its huge size extremely thick shell and delicate costation a global review of 145 different occurrences throughout the world reveals a total of 57 gigantoproductus species recorded our investigation into their spatial and temporal distributions indicates that gigantoproductus was originated from the moscow basin in the middle visean and then in the late visean migrated southwestward to western europe and north africa and eastward to north china south china and japan the genus reaches its acme stage in species diversity and abundance in the late visean then gradually declined in the early serpukhovian and finally disappeared in the late serpukhovian gigantoproductus and its related genera were distributed mainly in the circum paleotethys region in the tropical and subtropical zones and favored a relatively shallow shelf environment with high energy and warm water condition with little thermal tolerance the absence of the gigantoproductus and its related genera in america suggests the east west rheic seaway was closed before the gigantoproductus fauna appeared in the middle visean the waxes and wanes of the gigantoproductus faunas temporally coincided with the paleoclimatic shift from greenhouse to icehouse stage in the late visean and early serpukhovian and the final extinction of these gigantic brachiopods in the late serpukhovian implies tropical cooling towards the late serpukhovian by the expansion of the lpia glaciers

structure of the warm spring and northern thousand springs fault segments lost river fault zone idaho possible effects on rupturing during the 1983 borah peak earthquake abstract scarps on the warm spring and northern part of the thousand springs segments of the lost river fault zone idaho were surveyed and analyzed to determine fault orientation and near surface fault roughness scarps formed along these two segments during the 1983 borah peak earthquake and the evolution of the rupture appears to have been related to the large scale geometry of the fault segments and to fault roughness the warm spring and thousand springs segments are divided into approximately planar sections that in detail show roughness at varying scales individual fault sections within these main segments have lengths of 2 to 5 km and average dips of about 30 to 50 to the wsw to ssw the boundary between the warm spring and thousand springs segments is marked by the willow creek hills a large ridge of bedrock that extends across the hanging wall basin no surface faulting occurred along the two main segments within this boundary during the 1983 borah peak earthquake although the presence of discontinuous holocene scarps indicates that the boundary has ruptured during previous earthquakes the willow creek hills lie above a large sw plunging ridge in the southern part of the warm spring segment a smaller ridge is located within the northern end of the thousand springs segment within a region of rupture branching between this segment and the arentson gulch fault the scarps and aftershock distributions indicate secondary faulting within the segment boundary as the result of the borah peak earthquake scarps along both flanks of the willow creek hills formed as the hanging walls of the thousand springs and warm spring segments moved downward relative to the boundary which is structurally perched upon the underlying ridge within the lost river fault zone local surface faulting in the willow creek hills and aftershock activity beneath them reflect continuing deformation as the result of the heterogeneous strain field in the segment boundary fault roughness measured as the mean deviation of fault surfaces from a best fit plane continuously increases with distance along a profile at scales from 50 to 500 m mean deviation in amplitude is related to incremental distance along the surface using a power law function with an exponent between 0 6 and 0 8 detailed surveying and three dimensional analysis of fault scarps along the strike of the fault zone augments common paleoseismological methods of scarp profiling trenching and morphological analysis of mountain fronts the procedures developed in this study may be easily applied to fault zones in many parts of world where scarps cut across suitable topography the results have important implications for better defining the structure of fault zones and the influence this structure may have on fault displacement seismiciry and strong ground motion

mechanics of fault junctions a sharp bend in a fault must be part of a triple junction and slip on the three fault segments at the junction must have a vector sum of zero in order to avoid an unphysical 1 r stress singularity accompanying the slip a volume change occurs at the junction either a void opens or intense local deformation is required to avoid material overlap the energy absorbed due to the volume change is proportional to the slip increment times the total past slip accumulated at the junction at a new junction the energy absorbed is a small fraction of the energy released by slip on the fault system but after a number of earthquakes proportional to shear modulus over confining stress the junction becomes a strong barrier to further slip although slip occurs more easily on old rupture surfaces than on fresh fractures the growing barrier strength of junctions requires that there be some fresh fracture in earthquakes perhaps a small fraction of the surface that slips in any earthquake is fresh fracture which could provide the instability needed to explain earthquakes a numerical model in two dimensional static plane strain shows even without accounting for energy absorbed at the junction that a bend in a fault acts as a barrier if slip is impeded on the associated fault spur the stress concentration at the bend will tend to induce slip on the spur slip occurring on the spur unstably with a drop in the coefficient of friction can induce increased slip on the main fault segments with no change in the coefficient of friction a fault junction provides a natural realization of barrier and asperity models without appealing to arbitrary variations of fault strength the location of the fresh fracture that occurs after a junction becomes a strong barrier remains an unanswered question it is likely to be initiated near the stress concentration at the old junction a model simulating the effect of fresh fracture near old junctions might explain earthquakes without appealing to an unstable friction law anywhere

speculations on the geometry of the initiation and termination processes of earthquake rupture and its relation to morphology and geological structure earthquake initiation and termination processes are commonly described in terms of barriers and asperities barriers fall into two classes geometric barriers are associated with places where the orientation of a failure surface changes and relaxation barriers where stress is low because aseismic creep processes outpace tectonic loading geometric barriers fall into conservative and nonconservative subgroups according to whether finite fault motion can proceed without the creation of new structures or whether it demands the creation of new faulting or void space the multiple faulting or fragmentation associated with some nonconservative barriers can disrupt fault planes and form asperities by means of selected examples it is shown that a description in terms of these barriers can help one to visualise the processes of earthquake rupture and its relation to the geological environment

amplitudes of late pennsylvanian glacioeustasy the late paleozoic is well documented as a time of significant continental glaciation but the extents of the glaciation and attendant glacioeustasy are not well constrained because precise amplitudes of eustasy are difficult to extract from the stratigraphic record in this paper we use preserved relief on ancient subaerial exposure surfaces of large algal bioherms to demonstrate directly that late pennsylvanian glacioeustasy reached minimum amplitudes of 80 m and probably exceeded 100 m upper paleozoic algal bioherms accreted predominantly during sea level falls but also during sea level rises and highstands and were capable of remarkably rapid growth rates eustatic amplitudes in excess of 100 m approach amounts documented for the pleistocene and place constraints on models for gondwanan ice volume climate dynamics and potential character and magnitude of glacioclimatic fluctuations

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

effect of ambient mg ca ratio on mg fractionation in calcareous marine invertebrates a record of the oceanic mg ca ratio over the phanerozoic the mg ca ratio of seawater has changed significantly over the phanerozoic primarily as a function of the rate of ocean crust production echinoids crabs shrimps and calcareous serpulid worms grown in artificial seawaters encompassing the range of mg ca ratios that existed throughout the phanerozoic exhibit a direct nonlinear relationship between skeletal and ambient mg ca specimens grown in seawater with the lowest mg ca 1 changed their mineralogy to low mg calcite 4 mol mgco3 suggesting that these high mg calcareous organisms would have produced low mg calcite in the cretaceous when oceanic mg ca was lowest 1 these results support the empirical evidence that the skeletal chemistry of calcareous organisms has varied significantly over the phanerozoic as a function of the mg ca of seawater and that the mg ca of unaltered fossils of such organisms may be a record of oceanic mg ca throughout the phanerozoic mg fractionation algorithms which relate skeletal mg ca seawater mg ca and temperature were derived from these and other experiments they can be used to estimate paleoceanic mg ca ratios and temperatures from fossil skeletal mg ca of the organisms evaluated paleoceanic mg ca ratios recalculated by using the echinoderm mg fractionation algorithm from published fossil echinoid mg ca crinoid mg ca and paleotemperature data are consistent with other estimates and models of oceanic mg ca over the phanerozoic

ontogenetic trace element distribution in brachiopod shells an indicator of original seawater chemistry articulated fossil brachiopod shells have been used extensively to extract primary chemical information of phanerozoic seawater despite the selection of well preserved shells using trace element microstructure and cathodoluminescence criteria there are still concerns as to whether the selected brachiopod shells do indeed contain original seawater signals analyzed in situ by laser ablation inductively coupled plasma mass spectrometry laicpms sr na mg mn b and ba distribute symmetrically in shell transects of the modern brachiopods magellania flavescens and terebratulina septentrionalis symmetry of the trace element distribution pattern is considered an intrinsic and original ontogenetic property of the brachiopod shell chemistry the trace element distribution is symmetrical in a well preserved shell of the devonian brachiopod independatrypa lemma indicating that the selected shell by the conventional criteria has preserved its original seawater signal for 400 ma in another specimen of i lemma that is considered diagenetically altered trace element concentrations are asymmetrically distributed in the shell the agreement between the distribution criteria and the conventional methods indicates the latter can be used to select brachiopod shells with original seawater chemistry the average element concentration in the whole shell of unaltered brachiopods should be a reflection of the seawater chemistry while its change in different part of a shell reflects ontogenetic effect and its high frequent fluctuations in a transect are results of changes in environmental parameters with seasonal or annual characteristics

corals at their latitudinal limits laser ablation trace element systematics in porites from shirigai bay japan the rapid analytical technique of laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure the trace elements b mg sr ba and u in a high latitude coral colony porites lobata taken from shirigai bay japan 32 n a wide range of sea surface temperatures ssts 14 5 28 c and upwelling events influenced this coral cold winter ssts caused a decrease and or cessation of skeletal extension measurements of u ca and sr ca indicate an approximately linear response to ssts above 18 c and a non linear response below 18 c mg ca and b ca measurements both showed annual cycles broadly consistent with sst variations but also exhibited intra annual fluctuations not associated with temperature suggesting that the incorporation of mg and b into the coral skeleton was not simply regulated by temperature it is shown that ba ca ratios provide a proxy for wind induced seasonal upwelling this is inferred from the strong correlations between the strength of zonal winds 1 month prior to the sst minimum and the ba ca maximum secondary upwelling events occurred during the summers of 1982 1987 1991 and 1992 these summers were cooler than average and were associated with el nino southern oscillation events

quaternary tectonic setting of the 1983 borah peak earthquake central idaho the 1983 borah peak earthquake was accompanied by extensive surface faulting along a part of the lost river fault that has abundant evidence of latest quaternary last 15 000 yr offset this fault and two similar range front normal faults along the lemhi range and beaverhead mountains lie in an area of basinand range structure in central idaho that is part of a roughly v shaped belt of latest quaternary surface faulting that extends from the wasatch fault through the yellowstone area to the lost river fault the position of this belt may be related to the outward migration of a thermal front associated with the northeastward progression of late cenozoic silicic volcanism along the yellowstonesnake river plain axis the central segments of the lost river lemhi and beaverhead faults have been active more recently and probably more active throughout quaternary time than the southern and northern segments the main 1983 surface faulting occurred in an area of high structural relief along a central segment of the lost river fault that has ruptured in latest quaternary time which suggests that comparable areas along other range fronts in the area should be regarded as likely sites of future surface faulting other perspective of fault behavior suggest additional possible sites and all segments of the range front faults are regarded as capable of surface faulting

low latitude ordovician to triassic brachiopod habitat temperatures bhts determined from δ18o brachiopod calcite a cold hard look at ice house tropical oceans abstract some researchers have suggested that phanerozoic land based ice sheets extended occasionally into the tropical realm if true the tropical ocean at those times must have been distinctly colder than at the last glacial maximum lgm when northern hemisphere ice sheets did not extend below 38 latitude low latitude ocean temperatures derived from oxygen isotopes of brachiopod shells test this hypothesis by comparing the temperature regime for paleozoic and early mesozoic low latitude settings to the tropical temperature regime of the modern interstadial ocean and to mean temperatures estimated for the tropical ocean at lgm a running mean of ph adjusted brachiopod habitat temperatures bhts shows that paleozoic low latitude oceans were on average cool to cold relative to the modern interstadial tropical ocean at times during pennsylvanian serpukhovian tournaisian and ordovician silurian glaciations these tropical seas were indeed significantly colder on average than at the lgm ice sheets within tropical latitudes can be reasonably predicted at those times abundant and diverse paleozoic brachiopod communities reflect these cool tropical oceans consistent with modern brachiopod ecological preference for colder waters amplified paleozoic temperature oscillations suggest recurring global warming events which episodically drove these cold tropical oceans to temperatures significantly higher than the warmest modern tropical ocean

low seasonality in central equatorial pangea during a late carboniferous highstand based on high resolution isotopic records of brachiopod shells the relationship between permian carboniferous glacial cycles and low latitude climate remains a subject of vigorous debate this study investigated seasonality and regional environmental variability in a portion of central equatorial pangea during a late pennsylvanian highstand using stable isotope and trace element analyses of brachiopod shells from the virgilian ames member of the conemaugh group in the appalachian basin u s a well preserved thick shelled neospirifer dunbari specimens were serially sampled across growth bands to elucidate a record of seasonal variability during the life of the organisms because neospirifer only colonized this marginal basin during near maximum highstands when stable near marine salinities were established these data are a direct proxy for intra annual climate fluctuations during interglacial times neospirifer specimens show remarkably little internal chemical variability with 18 o generally fluctuating by 0 4 or less and 13 c fluctuating by less than 1 5 within a single specimen moreover total 18 o variability between all specimens is only 1 5 this lack of variation reflects a homogeneous nonseasonal to weakly seasonal climate during the ames highstand both 18 o and 13 c are 1 5 lower than those of other virgilian specimens from regions with a more proximal connection to the open ocean suggesting at least moderate freshwater influence in the appalachian basin during this time although salinities remained close enough to marine levels to maintain stenohaline fauna thus brachiopod seasonal records indicate normal moist tropical conditions during this penultimate carboniferous interglacial with no evidence for strong monsoonal variations in temperature or rainfall

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form

tropical marine climate during the late paleozoic ice age using trace element analyses of brachiopods abstract the late paleozoic ice age can be considered an important analogue to the modern ice age but comparisons between the two time intervals have been hampered by the difficulty of resolving climatic changes that occur over short e g seasonal time scales in the paleozoic record as a first step toward overcoming these limitations this study employed mg ca trace element ratios sampled across the growth bands of six specimens of the brachiopod composita to assess differences in tropical marine mean temperature and seasonality in visean and moscovian time these time intervals bracket the onset of the late paleozoic ice age which occurred in mid serpukhovian time and thus provide a snapshot of climate changes from a greenhouse to an icehouse world shells were screened for diagenetic alteration by cathode luminescence and by comparing the values of mn sr na and b to those reported for modern brachiopods in addition a 87sr 86sr value measured for one specimen agreed with a published strontium isotope curve for the late paleozoic era both the mean and range of mg ca values were larger in visean than moscovian time suggesting colder and less seasonal temperatures during the late paleozoic ice age the decline in seasonality was due to a greater proportional reduction of maximum values which presumably represent summer temperatures than minimum values these relative differences between the pre ice age and ice age tropical climate provide a first step toward understanding the broad patterns of seasonal scale changes in temperature during a critical time in earth s history