determination of basinwide paleocurrent patterns in a shale succession from anisotropy of magnetic susceptibility ams a case study of the mid proterozoic newland formation montana abstract in shales of the mid proterozoic newland formation magnetic fabrics can be used as indicators of paleoflow direction the long axis of the anisotropy of magnetic susceptibility ams ellipsoid parallels paleoflow and is inclined in the upcurrent direction schieber and ellwood 1988 to apply the ams paleocurrent method to shales on a basinwide scale oriented samples from the two members of the newland formation and its lateral equivalents were collected over the entire southeastern belt basin for the lower member of the newland formation the data show a parallel bipolar and north south oriented paleoflow pattern the pattern for the upper member of the newland formation is more complex it indicates the presence of a northern and southern shoreline from where sediment is transferr d deeper into the basin parallel unimodal pattern as well as a central zone of overlap with a parallel bipolar pattern the results of the study show that ams based paleocurrent patterns support paleogeographic reconstructions based on stratigraphic and sedimentologic studies and that tectonic deformation did not significantly alter primary fabrics in the upper member of the newland formation shore normal vs shore oblique sediment transport for sandy and muddy storm deposits respectively is in agreement with a recently proposed depositional model for storm deposits duke et al 1991

the eastern jura relations between thin skinned and basement tectonics local and regional the thesis area of hans cloos in the eastern jura straddles the boundary between the paleogene structures of the tabular jura a part of the southeastern end of the rhine graben and the neogene folds and thrusts of the folded jura a recent reflection seismic survey in the area adjacent to the east provides new information on the subsurface structure and the relation between three superposed tectonic events the main boundary fault zones of a deep and complexly faulted late paleozoic trough trending ene were reactivated in the early tertiary faulted flexures and small folds rooted in the basement and paleozoic with an amplitude of usually 100 to 300 m were produced rather than the normal faults typical for the extensional fields of the rhine bresse graben system in the west and the bavarian molasse basin in the east this suggests their being part of a transform zone between these extensional fields during jura decollement in the neogene these inherited deeply rooted sub decollement structures remained passive their small size is kinematically incompatible with the intense subsequent thrusting and folding of the thin mesozoic tertiary skin however thrust ramps were apparently nucleated at the respective southern foot of these paleogene flexures and folds the best defined and simplest of these composite structures is the mandach structure within the tabular jura a south facing flexure of about 300 m relief developed in the paleogene by reactivation of the northern border fault zone of the paleozoic trough in the neogene a north vergent decollement thrust which is connected with the regional jura decollement in the middle triassic evaporites was initiated at its site

current scattered detrital remanence directions in the zn rich pennsylvanian stark black shale usa summary palaeomagnetic results are reported from the metalliferous stark black shale in the upper pennsylvanian missourian kasimovian kansas city group palaeomagnetic analysis of 400 specimens from 28 sites gives a characteristic remanent magnetization in 17 sites of the shale that yields a late mississippian to middle pennsylvanian palaeopole at 32 2 n 128 5 e dp 4 7 and dm 8 8 the observed palaeomagnetic age is slightly older than the host rock indicating that the mineralization of the stark shale has excluding recent alteration a primary sedimentary or syngenetic origin the reason for the slightly older age is likely due to trace modern hematite that slightly steepens the remanence inclination the large oval of 95 per cent confidence is interpreted to be caused by clay magnetite aggregates that formed during sediment transport and the biasing effect of the gentle palaeocurrent at each site acting on the large aggregates therefore the scattered distribution of the site mean remanence declinations found for the stark shale is evidence of a detrital remanent magnetization that is formed by primary sedimentary processes with an enriched metallic content and not remagnetization with mineralization by secondary hydrothermal processes

towards a better understanding of the influence of basement heterogeneities and lithospheric coupling on foreland deformation a structural and paleomagnetic study of laramide deformation in the southern bighorn arch wyoming integrated structural anisotropy of magnetic susceptibility ams and paleomagnetic analyses of sedimentary cover rocks along variably oriented major faults and en echelon fold systems in the southern bighorn arch wyoming were undertaken to test kinematic and mechanical models of laramide thick skin deformation the laramide foreland is characterized by an anastomosing network of basement cored arches and associated cover folds that trend overall nw se but in detail are curved range from n s to e w trending and form both right and left stepping en echelon systems development of variably trending laramide arches has been variously attributed to temporal changes in stress directions wrench faulting and localization of deformation related to basement heterogeneities during regional sw ne shortening within the southern bighorn arch widespread but limited layer parallel shortening lps was accommodated mostly by minor faults with conjugate wedge and strike slip geometries early in the deformation history lps directions vary from perpendicular to acute with local fold structural trends consistent with a single shortening episode although internal strain is limited weak ams lineations defined by kinked and rotated phyllosilicates are widely developed and consistently perpendicular to lps directions structurally restored paleomagnetic declinations record only limited non systematic vertical axis rotations indicating that wrenching was not an important component of the deformation field during development of the southern bighorn arch and that curvature of the arch was a primary feature palinspastically restored lps directions are on average wsw ene but display local deflections related to heterogeneities of underlying basement blocks and proximity to major faults some of which were localized along precambrian shear zones and igneous dikes crustal shortening patterns across the laramide foreland are interpreted to reflect deformation partitioning in response to a single far field shortening direction partly related to flat slab subduction along with effects of pre existing basement weaknesses and strain softening during progressive faulting

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

continuous gps and broad scale deformation across the rhine graben and the alps in order to study the ongoing tectonic deformation in the rhine graben area we reconstruct the local crustal velocity and the strain rate field from gps array solutions following the aim of this work we compile the velocities of permanent gps stations belonging to various networks euref agnes regal and rgp in central western europe moreover the strain rate field is displayed in terms of principal axes and values while the normal and the shear components of the strain tensor are calculated perpendicular and parallel to the strike of major faults the results are compared with the fault plane solutions of earthquakes which have occurred in this area a broad scale kinematic deformation model across the rhine graben is provided on the basis of tectonics and velocity results of the gps permanent stations the area of study is divided into four rigid blocks between which there might be relative motions the velocity and the strain rate fields are reconstructed along their borders by estimating a uniform rotation for each block the tectonic behaviour is well represented by the four block model in the rhine graben area while a more detailed model will be needed for a better reconstruction of the strain field in the alpine region

paleomagnetism of the borden dykes of baffin island and its bearing on the grenville loop northern baffin island is intersected by spectacular swarms of predominantly northwesterly trending diabase dykes cross cutting relationships k ar ages and paleomagnetic contact tests indicate that these dykes represent at least two major episodes of hadrynian igneous activity the borden dykes were emplaced during the earlier of these episodes they are about 950 ma old and have a paleomagnetic pole position of 153 3 e 26 7 s m 8 6e p 6 1 the later episode saw the emplacement of the previously defined franklin dykes which are about 750 ma old the newly defined borden pole lies at the southern extremity of the grenville loop and has an age consistent with poles of similar position that were derived from rocks of the grenville province all of the dykes probably reflect tension acting in an east northeast west southwest direction the directions of thick northwest trending dykes which form a considerable angle to that expected from east northeast tension are thought to have been controlled

flow path of the 1993 hokkaido nansei oki earthquake seismoturbidite southern margin of the japan sea north basin inferred from anisotropy of magnetic susceptibility summary a magnetic fabric analysis has been carried out on standard cube samples from one gravity and three multiple cores extracted from the shiribeshi trough and okushiri basin in the southern margin of the japan sea north basin it is aimed at tracing the flow path of turbidites that are assumed to have deposited in response to the 1993 hokkaido nansei oki earthquake magnetic remanence was used for reorientation to the geographic coordinates magnetomineralogical investigations including low temperature magnetometry magnetic hysteresis loops and isothermal remanent magnetization irm acquisition experiments indicate that pseudosingle domain to multidomain magnetite is the principal magnetic carrier and is therefore capable of providing reliable anisotropy of magnetic susceptibility ams palaeocurrent direction estimates a well developed near horizontal magnetic foliation and minimum susceptibility axes lying close to vertical are recorded at all sites reflecting an original depositional fabric clearly defined magnetic lineation was observed at all sites and is considered to reflect the palaeocurrent direction down core changes of susceptibility and key ams parameters show good correspondence to occurrences of turbidite layers marking the increase of input of influx materials in agreement with results from recent marine surveys and izanagi side scan sonar images an nne transportation trend has been estimated for sediments at sites from the shiribeshi trough with a possible depositing path initiating from the slope bounding the south and southeastern margin down to the trough floor similarly a sse palaeocurrent direction has been estimated for sediments from the okushiri basin with evidence for a relatively strong transporting current flowing through the canyons along the steep slope bounding the north and northeastern margins of the basin the present results agree with the view that slope failure is the most probable mechanism for the down slope transport of the sand from the shelves and upper slopes down to floors of basins and troughs in the southern margin of the japan sea north basin they further support the ongoing assumption that the 1993 hokkaido nansei oki and other strong historical earthquakes together with associated tsunamis are the principal triggering forces for the down slope mass gravitational transport and formation of turbidites in this seismically active area

balanced sections and the propagation of decollement a jura perspective 1 the propagation of thrusting is an important problem in tectonics that is usually approached by forward kinematical modeling of balanced sections although modeling techniques are similar in most foreland fold thrust belts it turns out that in the jura there are modeling problems that require modifications of widely used techniques in particular attention is called to the role of model constraints that complement the set of observational constraints in order to fully define the model in the eastern jura such model constraints may be inferred from the regional geology which shows a peculiar noncoaxial relation between thrusts and subsequent folds this relation implies changes in the direction of translation and the mode of deformation in the course of the propagation of decollement these changes are conjectured to be the result of a change in partial decoupling between the thin skinned fold thrust system nappe and the obliquely subducted foreland as a particularly instructive case in point a cross section through the weissenstein range is discussed a two step forward kinematical model is proposed that uses both local observational constraints as well as model constraints inferred from regional data as a first step a fault bend fold is generated in the hanging wall of a thrust of 1500 m shortening as a second step this structure is transferred by flexural slip into the actual fold observed at the surface this requires an additional 1600 m of shortening and leads to folding of the original thrust thereafter the footwall is deformed so as to respect the constraint that this deformation must fit into the space defined by the folded thrust as the upper boundary and the decollement surface as the lower boundary and that in addition should be confined to the area immediately below the fold in modeling the footwall deformation a mix of balancing methods is used fault propagation folds for the competent intervals of the stratigraphic column and area balancing for the incompetent ones further propagation of decollement into the foreland is made possible by the folding process which is dominated by a sort of kinking and which is the main contribution to structural elevation and hence to producing a sort of critical taper of the moving thin skinned wedge

tectonics of the central swiss molasse basin post miocene transition to incipient thick skinned tectonics in this paper we investigate the tectonics of the central swiss molasse basin smb situated between the central european alps and the jura fold and thrust belt based on re interpreted 2d reflection seismic data and geological 3d modeling we present new insights into the structural configuration and evolution of the central smb during the thin skinned main deformation phase of the jura fold and thrust belt 12 4 ma the central smb was riding passively above a major detachment horizon within triassic evaporites which roots beneath the external crystalline massifs of the central alps in the smb low amplitude detachment folds and detachment rooted wsw ene striking thrust and reverse faults are related to this event younger major nne ssw and nnw sse trending strike slip fault zones cross the basin over a length of several kilometers affecting the cenozoic and mesozoic cover units and extending into the pre mesozoic crystalline basement in cases the fault zones apparently reactivate inherited permo carboniferous trough pct bounding paleozoic normal faults seismic data further reveals mild inversion of wsw ene striking pcts these structures clearly cut the basement cover contact thus postdating the main deformation phase of the jura fold and thrust belt present day earthquake focal mechanisms and epicenter distribution show strike slip faulting and basement seated seismicity respectively thus corroborating our observations from seismic interpretation our data suggests a change from late miocene thin skinned to pliocene to present day incipient thick skinned tectonics this major change reflects the establishment of a mid crustal detachment and may be related to changes in slab dynamics of the subducting european lithosphere

the control of cathodoluminescence in dolomite by iron and manganese variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese mn2 as the most important activator and iron fe2 as the main inhibitor of luminescence interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages cambrian to cretaceous and a wide geographical distribution north america and europe iron and manganese are positively correlated in the dolomites with the former showing a greater range of variation very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm mn2 is present in highly luminescing samples the intensity of luminescence is not proportional to the manganese concentration iron begins to quench luminescence as its concentration reaches 10 000 ppm above that level luminescence is rapidly lost and total extinction occurs among samples containing more than 15 000 ppm fe2 regardless of the manganese concentration

plio pleistocene transpressional reactivation of paleozoic and paleogene structures in the rhine bresse transform zone northern switzerland and eastern france pliocene to recent uplift and shortening in the southern rhinegraben is documented by deformation of pliocene fluvial gravels deposited on a nearly planar surface as well as by progressive deflection and capture of rivers this deformation is suggested to result from thick skinned tectonic movements as evidenced by ob servations on seismic records which demonstrate a spatial coincidence between en chelon anticlines at the surface and faults located in the crystalline basement these findings contradict the often invoked thin skinned tectonism in the recent tectonic history of the rhine graben in particular the transfer zone between the rhinegraben and the bressegraben is very suitable for reactivation under the present day stress field thick skinned reactivation of faults in the basement is also expressed by focal plane mechanisms of recent earth quakes showing strike slip rather than reverse faulting characteristics this is of importance for the densely populated and industrialised southern rhinegraben pre viously affected by large earthquakes in historical times e g basel 1356

upper rhine graben role of preexisting structures during rift evolution 1 the evolution of the cenozoic upper rhine graben was controlled by a repeatedly changing stress field and the reactivation of a complex set of crustal discontinuities that had come into evidence during permo carboniferous times a comparison of the spatial and temporal thickness distribution of synrift deposits with preexisting fault patterns permits to infer a sequence of distinct basin subsidence phases that can be related to changes in the ambient stress field reactivation of a system of late palaeozoic fault systems outlining troughs and highs controlled the nucleation of initially separated middle and late eocene basins the depocenters of which coincided with a preexisting wsw ene trend during oligocene crustal extension the individual basins coalesced resulting in the development of the ssw nne striking upper rhine graben during the late oligocene chattian change in stress field the upper rhine graben was probably reactivated as a dextral strike slip system with the central graben segment forming a releasing bend during the early miocene aquitanian a major reorientation of the regional stress field is held responsible for the main subsidence phase of the northern parts of the upper rhine graben this is reflected by a counterclockwise rotation and northeastward shift of the depocenter axis and later by the middle miocene uplift and erosion of the southern parts of the upper rhine graben during the plio quaternary the upper rhine graben was reactivated as a sinistral strike slip system with the central graben segment forming a restraining bend

100 years jura decollement hypothesis how it affects steinmann s 1892 schwarzwaldlinie steinmann then professor of geology at freiburg germany more than a 100 years ago wondered about the southern end of the extensional rhinegraben and proposed that elements of the graben penetrated the contractional jura in particular he recognized the schwarzwaldlinie in the southern prolongation of the eastern border of the southern rhinegraben a line up of topographic as well as structural irregularities he conjectured that it was caused by normal faults of the rhinegraben system subsequently 100 years ago buxtorf 1907 proposed the hypothesis that the jura was a thin skinned nappe sheared off on triassic evaporites in the autochthonous basement underneath the wrinkled skin the schwarzwald line is difficult to define it probably consists of a gentle flexure punctuated by faults that approximately coincides with steinmann s original projection although he sought to identify its constituent faults in the badly deformed allochthonous skin current data place the thin skin elements of the schwarzwald line in a more westerly allochthonous position where most of them were reactivated into sinistrally transpressional structures

plate interactions at the southern end of the rhine graben abstract the southern end of the rhine graben in the basel area originated in the early tertiary as an extensional structure it is the site of a transfer zone that connected the rhine graben with the bresse rhone grabens this transfer zone is located in an area into which a late paleozic trough projects which apparently was reactivated from the beginning of miocene to recent times three distinct phases of slight compression were superimposed on the southern end of the rhine graben the first one in the aquitanian early burdigalian is coeval with the development of the helvetic nappes and the insubric fault zone in the alps the second one in the langhian tortonian interval occurred when the external massifs and an important part of the lombardic fold thrust belt in the southern alps developed and the third pliocene to recent one is contemporaneous with the inactivation of this belt and its incorporation into the foredeep of the northern apennines in the aquitanian the forebulge of the alpine orogen is recognizable as a system of flexures that developed preferably on the margin of the late paleozoic trough the middle late miocene one gave rise to uplift of the black forest vosges domain and a river system flowing from this high to the south in the pliocene to recent one alpine rivers made their appearance flowing first to the west into the rhone system and then as the rhine to the north the pliocene to recent phase seems to be decoupled from the body of the central and southern alps

multistage dolomitization in the society cliffs formation northern baffin island northwest territories canada dolostones of the upper proterozoic society cliffs formation on northern baffin island are host to the nanisivik lead zinc sulfide deposits two distinct stages of dolomitization have occurred distinguished by their petrographic cathodoluminescence and isotopic characteristics 1 massive dolomitization of precursor carbonates and 2 late stage cementation sabkha facies of the lower member of the formation and laminated algal stromatolitic to massive dolostones of the upper member are isotopically similar 18o ranges from 1 5 to 6 5 13c from 1 7 to 3 1 pdb and 87sr 86sr averages 0 70761 petrographic and geochemical evidence indicates that these dolostones formed chiefly by seawater thermal convection beneath shale of the overlying victor bay formation although mixing of meteoric and marine water also could have occurred later fracture filling dolomitic cements have consistently lower 18o but 13c is similar to that in the host dolostones microtraverses of single fractures filled wit

pervasive subsurface dolomitization of the nisku formation in central alberta abstract the nisku formation in the subsurface of central alberta canada contains pervasive dolomites that occur mainly as a replacement of reefal limestones the degree of pervasive dolomitization increases downdip along a structural homocline from about 25 to 100 vol and associated replacive anhydrites increase from about 5 to 20 vol pervasive dolomites occur as two types one type consists of almost non porous and impermeable mosaics of cloudy crystals that have diameters of 5 300 microns the other type has significant intercrystalline porosity and permeability and consists of cloudy and clear crystals ranging in size from 100 500 microns cathodoluminescence zonation is rare but modulated structures observed with tem are common both types of dolomite have strong xrd ordering refl ctions and are nearly stoichiometric sr concentrations 25 125 ppm increase and mn concentrations 20 400 ppm decrease upwards in several cores the boron contents of both dolomite types 20 50 ppm are enriched relative to other diagenetic phases 18 ppm the sr isotope ratios vary from 0 7089 0 7107 and are enriched relative to devonian and younger seawater oxygen and carbon isotope ratios cluster around 5 8 permil pdb and 2 0 permil pdb respectively and are similar to those of remnant calcites from the combination of stratigraphic petrographic petrophysical and geochemical data it is inferred that both types of matrix dolomite formed contemporaneously from the same fluids in a flow regime with predominantly upward fluid movement at temperatures between about 40 50 c and at burial depths of about 300 1 000 m most anhydrites formed originally as gypsum during the advanced stages and after matrix dolomitization and later recrystallized to the anhydrites now present based on all accumulated data and on mass balance calculations at least two types of subsurface flow could have caused pervasive dolomitization and gypsification anhydritization 1 expulsion of burial compaction water i e chemically modified seawater with or without additional contributions of m bearing formation waters from deeper parts of the basin e g middle devonian brines and 2 thermal convection of formation fluids originally underlying and or overlying the nisku

the coincidence of macroscopic paleocurrent indicators and magnetic lineation in shales from the precambrian belt basin abstract paleocurrent flow direction in shale sequences can be inferred from sedimentary structures of associated lithologies from orientation of fossils from alignment of silt and sand sized particles in shales from mapping of scalar properties of a shale sequence and from the orientation of concretions not all of these methods relate to shale properties directly and most of them are very time consuming and may even require fortuitous circumstances to be applicable consequently even though shales constitute about 60 of all sediments paleocurrent data from shale sequences are sparse thus in order to improve our understanding of the evolution of sedimentary basins it would be beneficial to have an accurate and conveniently applicable method of paleocurrent determination for shales p the anisotropy of magnetic susceptibility ams of a number of shale samples from the precambrian belt supergroup carries a fabric related magnetic lineation that coincides with paleocurrents indicated by cross laminated silt beds within the shales magnetic foliation decreases as dolomite content increases because of diagenetic dolomite growth but magnetic lineation is only slightly affected these data indicate that primary flow direction as represented by ams measurement of these samples is preserved and therefore the ams method can provide a rapid and accurate way to determine current flow systems in shale dominated sedimentary basins

strontium isotopic evolution of oil field waters from carbonate reservoir rocks in bindley field central kansas u s a abstract oil field waters produced from mississippian carbonate reservoir rocks in bindley field kansas had an average salinity of about 42 8 mg l they were enriched in ca sr na k rb and li and depleted in mg relative to sea water at the same level of either cl or br concentration the average abundances of different elements are as follows na 13 460 mg l k 325 mg 1 rb 0 9 mg l li 12 mg l ca 1 515 mg l sr 42 mg l mg 430 mg l cl 23 000 mg l so4 2 630 mg l br 32 mg l the 87 sr 86 sr values of the waters ranged between 0 7221 and 0 7230 whereas the values of the host carbonate rocks were between 0 7090 and 0 7093 the very high 87 sr 86 sr values of the waters probably occurred as a result of their reaction with alkali feldspar minerals in buried precambrian crystalline rocks to the east of the bindley field the study demonstrates that despite their residence in carbonate reservoir rocks oil field waters can retain sufficiently distinct isotopic memory that may provide important dues about mineral water interactions in the chemical evolutionary history of the waters the study further indicates that very late diagenetic reactions in many carbonate rocks are of minor extent difference in the sr isotopic data among the oil field waters suggests that the sr isotopic data can be used as a reliable guide in recognising existence of separate pools in an oil field