an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

phosphatised limestones and associated sediments from the western continental shelf of india abstract the phosphatised limestones and associated sediments of the outer continental shelf of the west coast of india between goa and ratnagiri at depths of between 70 and 120 m have been studied the highest p 2 o 5 content 9 ranging from 2 to 9 depending on location occur in the algal nodules polished and thin sections show that the algal nodules grew with the occasional microbial mat these mats apparently formed by trapping and binding of sediment particles which were subsequently phosphatised phosphate also occurs as pellets and rounded structures high magnesium calcite and carbonate fluorapatite are the major minerals aragonite low magnesium calcite and quartz are also present in some samples microprobe geochemistry of the phosphatised material of the algal nodules reveals the presence of land derived siliciclastic detritus and the possibility of more than one source for ca and p phosphate also occurred as cavity fillings in coral and bryozoan limestones but not in oolitic limestones regardless of their occurrence at the same depths and in the vicinity of the other limestones the associated sediments are mostly sandy and show smaller concentrations of p 2 o 5 average 0 3 and organic carbon average 0 93 as compared to the regions of upwelling where phosphorites are forming the correlation exhibited between the p 2 o 5 and the organic carbon is negative the environmental conditions for the formation of phosphatised limestones and possible sources of phosphate are discussed sheath organic matter associated with filaments appears to be the major source for phosphorus the phosphatisation is a microbial process which takes place at shallow depths the impact of present day upwelling is insignificant in the phosphatisation of the limestones

a possible earthquake triggered mega boulder slide in a chilean mio pliocene marine sequence evidence for rapid uplift and bonebed genesis the type area of the bahia inglesa formation north central chile is structurally complex as a result of active margin subduction at the peru chile trench inliers of subaerially exposed mesozoic igneous basement are unconformably overlain by a mid miocene to late pliocene marine siliciclastic sequence which has become known for its abundance of fossil vertebrates found concentrated in a phosphatite on an omission surface mega boulders derived from one of the largest inliers occur exclusively within this bonebed which appears to have formed after major localized uplift caused removal of a significant thickness of unconsolidated sediment the mega boulders were probably dislodged by a high magnitude earthquake event that accompanied tilting of the sea floor and their emplacement was an integral part of the processes involved in genesis of the bonebed

omission surface incipient phosphate crusts on early diagenetic calcareous concretions and their possible origin upper campanian southern israel abstract flattened calcareous concretions enveloped by a 2 4 mm thick phosphate bearing crust occur in a single level in the lower part of the phosphorite unit upper part of mishash formation in nahal zinim southern israel negev the crust is associated with various ichnofossils penetrating an originally incompletely lithified surficial zone at the periphery of the hardened part of the concretions in thin section the phosphate fraction appears structureless scanning and backscattered electron microscopy shows that this fraction occurs as walls and envelopes of polyhedral cell like units of about 5 m in diameter these structures are interpreted as synsedimentary phosphate coated possible remnants of chasmolithic and epilithic colonial unicells which colonized the pre hardened surficial zone around the concretions during exposure on the sea floor this thin microbially constructed phosphate coat is believed to be an incipient equivalent of more intensely developed phosphate crusts on many omission surfaces in the geological record

late paleoproterozoic extension and a paleostress field reconstruction of the north china craton abstract mafic dyke swarms and aulacogens are major anorogenic extensional events in the late paleoproterozoic north china craton ncc the n nnw mafic dyke swarms are widespread in the ncc whose ages span between 1 83 and 1 77 ga the similar ages and orientations of 1 8 ga dyke swarms in the ncc demonstrate that the amalgamated ncc experienced widespread extension at this time based on the width statistics of dyke swarms on ten survey lines an average crustal extension ratio of 0 35 was found for the ncc the small magnitude of overall extension suggests that the mafic dyke swarms were emplaced into the elastic fractures and indicates that the ncc had become a brittle plate prior to the emplacement of the mafic dyke swarms precisely dated mafic dyke swarms when used as paleostress indicators can be employed in the paleostress field reconstruction of precambrian cratons two dimensional finite element modeling 2 d fem of the ncc in which the various blocks were assigned densities and elastic constants shows that north south compression favors dyke intrusion along generally n nw lines and that deviations in dyke trends can be explained by the effects of boundary constraints and the physical properties of the crust the best fitting model can be considered a plausible representation of the tectonic force acting on the ncc that produces the intraplate stress field that is most consistent with the observed orientation of dyke swarms the results of modeling of the late paleoproterozoic stress field suggest a common tectonic setting for the emplacement of mafic dyke swarms in the central orogenic zone western and east blocks of the ncc the results also show that the north south tectonic forces play an important role in determining the paleostress field in the ncc the widespread extension of the ncc resulted from the north south tectonic forces which may be related to the break up of the late paleoproterozoic supercontinent the paleostress field modeling provides a possible approach to consider the supercontinent paleostress reconstruction and to reveal the mechanisms of the supercontinent break up

petrography chemistry and genesis of phosphorite concretions in the eocene umm rijam chert limestone formation ma an area south jordan abstract phosphorite concretions are recorded for the first time within the lower part of the umm rijam chert limestone formation eocene in the ma an area southern jordan the phosphorite concretions are typically hosted and encountered as individual layer in moderately lithified sediments of marl chalk and chalky marl the phosphorite concretions are present in thin layer 10 30 cm thick they are localized on a hardground surface that formed as a result of cementation of soft ground by bioclastic materials light grey and brownish to black colors are encountered with isometric ellipsoid elongated subangular to subrounded phosphorite concretions up to 6 cm in length most of the phosphorite concretions preserve bioturbation structures they also include fecal pellets of various sizes the main biogenic components are fragments of macrofossils bivalves and microfossils planktonic foraminifera in different proportions petrographic examinations reveal that the phosphorite concretions are composed of cryptocrystalline apatite that characteristically appears in cross polarized light almost as isotropic phosphate and minor anisotropic phosphate apatite and calcite are the main mineral constituents of the phosphorite concretions identified by xrd the apatite is identified as francolite carbonate flour apatite chemical analyses of the phosphorite concretions using x ray florescence indicate that the p2o5 content ranges from 18 8 to 31 19 whereas sem eds analyses indicate that the phosphorus proportion is around 14 by volume it could be argued that the phosphorite concretions were transported after being reworked or were derived from carbonate and chalk pebbles that were later phosphatized and subjected to erosion forming residual lag deposit along the hardground surface

phosphatized soft tissues in bivalves from the portland roach of dorset upper jurassic phosphatized soft tissues are preserved in abundance in the trigoniids bivalvia laevitrigonia gibbosa and myophorella incurva from the portland roach upper jurassic of dorset cellular structures are preserved and fossilization is almost exclusively the result of a dense coating of mineralized microbes phosphatized soft tissues are restricted entirely to those trigoniids whose valves remained tightly closed after death only in these specimens was sufficient phosphorus concentrated by the decay of their most labile soft tissues to trigger the precipitation of apatite in and around microbes infesting their more refractory soft tissues the absence of fossilized soft tissues in the rest of the fauna implies that phosphatization was very taxon specific

prediction of tensile fractures in ks2 trap kuqa depression nw china abstract tectonic fractures that generally controlled by tectonic stress field especially tensile fractures are crucial for tight reservoirs that are characterized by low porosity and low permeability prediction of fracture distribution is extremely important for further exploration and development of such reservoirs tensile fractures are developed in the upper bashijiqike formation in kuqa depression in northwest china the subject of this study was the ks2 faulted fold and the characteristics of the tensile fractures were analyzed in detail a three dimensional finite element elastic model of the faulted fold was constructed and the two factor method was applied to predict the distribution of tensile fractures in the upper bashijiqike formation in the faulted fold distributions of predicted tensile fractures reveal that positions relative to the fold axis and faults in the hinge zone both have significant influence on the distribution of tensile fractures the predicted tensile fractures are developed in the hinge zone in the faulted fold particularly in the area around fault tips which is the region with the most potential for oil and gas exploration in faulted folds

an integrated stratinomic model for the genesis and concentration of small shelly fossil style phosphatic microsteinkerns in not so exceptional conditions abstract carbonate fluorapatite filled millimeter scale microsteinkerns are a key element of the small shelly fossil ssf fauna generally associated with the late proterozoic cambrian the purported disappearance of these fossils and this style of phosphatic preservation during the cambrian stage 2 botomian extinction has been linked to changes in ocean chemistry and or changes to the physical environment due to the evolution of metazoans as well to the changing role of metazoans in the marine environment through a qualitative meta analysis of existing literature we document a broader temporal distribution for ssf style preservation than previously recognized we examine these occurrences for common patterns of depositional conditions and we offer a conceptual model for both the origin of the phosphatic microsteinkerns and their eventual concentration in certain sediments based on known biogeochemical diagenetic processes of authigenic calcium fluorapatite precipitation phosphogenesis and subsequent concentration of phosphatic sedimentary particles this polycyclic phosphogenic condensation ppc model makes predictions as to how and where this form of preservation might occur in cambrian and non cambrian marine strata alike

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

effects of internal structure and local stresses on fracture propagation deflection and arrest in fault zones the way that faults transport crustal fluids is important in many fields of earth sciences such as petroleum geology geothermal research volcanology seismology and hydrogeology for understanding the permeability evolution and maintenance in a fault zone its internal structure and associated local stresses and mechanical properties must be known this follows because the permeability is primarily related to fracture propagation and their linking up into interconnected clusters in the fault zone here we show that a fault zone can be regarded as an elastic inclusion with mechanical properties that differ from those of the host rock as a consequence the fault zone modifies the associated regional stress field and develops its own local stress field which normally differs significantly both as regard magnitude and orientation of the principal stresses from the regional field the local stress field together with fault rock heterogeneities and interfaces discontinuities fractures contacts determine fracture propagation deflection along discontinuities interfaces and arrest in the fault zone and thereby its permeability development we provide new data on the internal structure of fault zones in particular the fracture frequency in the damage zone as a function of distance from the fault core new numerical models show that the local stress field inside a fault zone modelled as an inclusion differ significantly from those of the host rock both as regards the magnitude and the directions of the principal stresses also when the mechanical layering of the damage zone due to variation in its fracture frequency is considered the numerical models show abrupt changes in local stresses not only between the core and the damage zone but also within the damage zone itself abrupt changes in local stresses within the fault zone generate barriers to fracture propagation and contribute to fracture deflection and or arrest also analytical solutions of the effects of material toughness the critical energy release rate of layers and their interfaces show that propagating fractures commonly become deflected into and often arrested at the interfaces generally fractures propagating from a compliant soft layer towards a stiffer one tend to become deflected and arrested at the contact between the layers whereas fractures propagating from a stiff layer towards a softer one tend to penetrate the contact thus it is normally easier for fractures to propagate from the host rock into the damage zone than vice versa similarly it is easier for fractures to propagate from the outer stiffer parts of the damage zone to the inner softer parts and from the stiff host rock to the outer damage zone than in the opposite directions these conclusions contribute to increased understanding as to how fractures propagate and become arrested within fault zones and how the fault zone thickness is confined at any particular time during its evolution

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

microbial processes in the negev phosphorites southern israel microscopic and sem observations indicate that cyanobacterial activity was important during the formation of the campanian negev phosphorites one aspect of such activity is the development of phosphorites through the binding of phosphate particles these sediments often demonstrate a conspicuous smooth cryptalgal lamination the algal binder was fossilized as intertwined phosphatic sheaths that coat and seal off the phosphate grains different types of sheaths representing the remnants of an algal community were found thick apatite overgrowth commonly deforms the microbial fossils converting them into barely recognizable forms fabrication of phosphate particles is another aspect of the microbial activity phosphate algal coated grains are a common constituent of the negev phosphorites the algal coating consists of stacked phosphatic tubes and colonies of coccoid unicells with an apatite infilling fragmented phosphatic sheath bundles form another type of phosphate particle produced by algae obliteration of algal structures is common resulting in undifferentiated groundmasses of cryptocrystalline apatite the extremely close connection between microbial structures and phosphatization processes suggests cyanobacterial participation in phosphorus enrichment

mechanics of the giant radiating mackenzie dyke swarm a paleostress field modeling 1 the 1 27 ga mackenzie dyke swarm of the canadian shield is a giant radiating dyke swarm that gradually swings in orientation from n s in the focal area to nw se trends in peripheral areas in this paper we propose a new model the plug model that accounts for the paleostress contribution to the mechanism of emplacement for the mackenzie dyke swarm in the canadian shield the 1 27 ga stress field on the canadian shield calculated by the plug model explains the radiating nature of the mackenzie dyke swarm around the coppermine river lava field by local stress concentrations the parallel nature of the dyke swarm at distance more than 1000 km from the focal source can be explained by the existence of a regional tectonic stress field created by ridge push acting on the southeast margin of the canadian shield from the grenville ocean the thin elastic plate and two dimensional cross section modeling suggest that the interaction between stresses from a mantle upwelling and the grenville ocean spreading play an important role in the intrusion mechanism of the mackenzie dyke swarm the change in dyke orientation from n s trending to nw se trending is caused by coupling between resistance from the focal area plug area and a grenville ocean ridge push

microbial dolomite crusts from the carbonate platform off western india the occurrence of late pleistocene dolomite crusts that occur at 64 m depth on the carbonate platform off western india is documented dolomite is the most predominant mineral in the crusts in thin section the crust consists of dolomitized microlaminae interspersed with detrital particles under scanning electron microscopy these laminae are made up of tubular filaments or cellular structures of probable cyanobacterial origin dolomite crystals encrust or overgrow the surfaces of the microbial filaments and or cells progressive mineralization obliterates their morphology well preserved microbial mats sulphide minerals pyrrhotite and marcasite and the stable isotope composition of dolomite in the crusts indicate hypersaline and anoxic conditions during dolomite formation the crusts are similar to dolomite stromatolites and biogeochemical processes related to decaying microbial mats under anoxic conditions probably played an important role in dolomite precipitation the dolomite is therefore primary and or very early diagenetic in origin the dolomite crusts are interpreted to be a composite of microbial dolomite overprinted by early burial organic dolomite the results of this study suggest that a microbial model for dolomite formation may be relevant for the origin of ancient massive dolomites in marine successions characterized by cryptalgal laminites the age of the crusts further suggests that the platform was situated at shallow subtidal depths during the last glacial maximum

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model reply abstract fault planes propagate radially from a point source and this failure propagation process is very similar to the movement of a dislocation through a crystal lattice an elastic strain represented by an extra half plane is necessarily imparted to the lattice at an edge dislocation and this is equivalent to the ductile bead which accompanies the propagating tip of a thrust fault this ductile bead migrates with the fault tip and imparts a characteristic internal strain to the thrust sheet a two dimensional model is presented to illustrate the inter relationship between fault plane slip fault tip propagation and internal strain in multilayered sequences internal strain is usually represented by asymmetric folds verging in the thrust transport direction a simple technique the displacement distance plot utilizes the fact that displacement dies out towards the fault tip this plot can be used to quantify the relative stretch measured parallel to the fault movement which is dependent on the slip propagation rate and it may be used to define exactly the position of the fault tip on a cross section examples of fold thrust structures from devon england and pembrokeshire wales are used to illustrate the technique

open shear fractures at depth in anticlines insights from the kuqa foreland thrust belt tarim basin shear fractures that close under compressive stress regime were described by previous workers here we show the existence of hinge parallel shear opening mode fractures at a certain depth within an anticline structure through core observations formation micro imager fmi log interpretations and production data studied reservoir is a tight sandstone body of cretaceous age which is emplaced in ks2 anticline with depth ranging between 6000 and 8100 m we explore the mechanism of hinge parallel shear fractures by stereographic technique and backtilting as well as show field evidences for opening displacements these shear fractures mainly consist of vertical tension set moderate dipping shear set steeply dipping shear set and sub horizontal shear set crosscutting relationships and surface textures suggest that although the moderate dipping shear set is older and maybe sealed by cements it may have been opened by local stress due to outer arc extension through folding calcite bridges with rhombohedral structures may support fracture walls helping them to remain open in case of compressive stress our work documents shear fracture openings in the anticline at depth and fluid flow in subsurface reservoirs

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

numerical simulations of parasitic folding in multilayers we use the finite element method to simulate slow viscous newtonian flow in two dimensions without gravity and to model asymmetric sand z shaped and symmetric m shaped parasitic folds during multilayer folding during multilayer folding the matrix between stiffer layers shows a deformation close to pure shear in the hinge area and a combination of pure and simple shear in the limb areas thinner layers placed between thicker layers develop symmetric parasitic folds in the hinge and eventually asymmetric parasitic folds in the limbs of the larger fold our results verify numerically the theory that asymmetric parasitic folds develop from symmetric buckle folds that are sheared by the hingeward relative displacement of the thick layers in the limbs of the first order fold to develop asymmetric shapes the amplitudes of the parasitic folds must exceed a critical value before the first order fold begins to amplify otherwise the parasitic folds are unfolded during flattening that takes place in the limb area between the thick layers more than five thin layers are necessary to generate distinct asymmetric parasitic folds for the applied model setting more layers generate higher amplification rates in the thin layers and hence higher amplitudes 2006 elsevier ltd all rights reserved

fracture zones constrained by neutral surfaces in a fault related fold insights from the kelasu tectonic zone kuqa depression abstract stress variation associated with folding is one of the controlling factors in the development of tectonic fractures however little attention has been paid to the influence of neutral surfaces during folding on fracture distribution in a fault related fold in this study we take the cretaceous bashijiqike formation in the kuqa depression as an example and analyze the distribution of tectonic fractures in fault related folds by core observation and logging data analysis three fracture zones are identified in a fault related fold a tensile zone a transition zone and a compressive zone which may be constrained by two neutral surfaces of fold well correlation reveals that the tensile zone and the transition zone reach the maximum thickness at the fold hinge and get thinner in the fold limbs a 2d viscoelastic stress field model of a fault related fold was constructed to further investigate the mechanism of fracturing statistical and numerical analysis reveal that the tensile zone and the transition zone become thicker with decreasing interlimb angle stress variation associated with folding is the first level of control over the general pattern of fracture distribution while faulting is a secondary control over the development of local fractures in a fault related fold

late holocene estuarine phosphogenesis in raglan harbour new zealand a unique instance of holocene estuarine phosphogenesis has been investigated in raglan harbour on the west coast of north island new zealand nodular calcareous concretions which formed within surficial estuarine muds between 6500 and 3600 years bp were superficially impregnated by carbonate fluorapatite between 3600 and 1600 years bp the phosphatized nodules lie beneath a late quaternary shore platform which is reinforced by a mass of intertwined bioturbation structures and tubular rootlet casts impregnated by limonite and goethite large polygonal cracks indicative of a desiccatory regime are locally conspicuous on the platform surface and in the immediately subjacent muds the phosphogenesis in raglan harbour is here related to an episode of lowered sea level during which a paludal environment succeeded the estuarine to be followed in turn by a positively and interlude the subsequent rise of sea level to its present position over the last 1600 years or so has reinstated the shore platform in its present intertidal situation

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

fractures in the low porosity and ultra low permeability glutenite reservoirs a case study of the late eocene hetaoyuan formation in the anpeng oilfield nanxiang basin china the naxiang basin located within the qin and dabie mountains orogenic belt in central china is a small intermountain faulted basin in which the late eocene hetaoyuan formation in the anpeng oilfield is the low porosity and ultra low permeability glutenite reservoirs the large scale fractures are mainly developed in the thick bedded conglomerates and gravel bearing gritstones the small scale jointed fractures bounded by layer are mainly developed in the medium granular and fine sandstones between the conglomerates or gravel bearing gritstones there also developed three kinds of micro fractures namely intergranular fractures intragranular fractures and transgranular fractures in the tight glutenites the fractures in the glutenite reservoirs are of chiefly high dip angles they assume chiefly the e w strikes next are the ne sw and nw se strikes on the log curve fractures usually show such responses as a decrease of the deep and shallow lateral resistivities an increase of the acoustic time difference a reduction of the density an increase of the compensation neutrons an occurrence of middle and high gamma ray and an expansion of the calipers fractures make contributions to the low porosity and ultra low permeability glutenite reservoirs by improving the permeability and then porosity micro fractures are the important channels connecting intergranular and intragranular solution pores thereby making better the connectivity within the tight glutenite reservoirs the small and medium scale fractures serve as the flow channels within the layers of fine and medium granular sandstones while the large scale fractures serve as the main flow channels for the whole reservoir under the impact of the present day stress the ne sw fractures perpendicular to the minimum principal stress assume a tensile state and have good connectivity large apertures and high permeability and are the major direction for fluid flow thereby providing a major basis for a further development

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

insights into the damage zones in fault bend folds from geomechanical models and field data abstract understanding the rock mass deformation and stress states the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development and geothermal reservoir characterization and management geomechanical modeling can be used to simulate the forming processes of faults and folds and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses this approach enables the development of forward models that incorporate realistic mechanical stratigraphy e g the bed thickness bedding planes and competence contrasts include faults and bedding slip surfaces as frictional sliding interfaces reproduce the geometry of the fold structures and allow tracking strain and stress through the whole deformation process in this present study we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault bend folds and discuss the mechanical controls e g the slip displacement ramp cutoff angle frictional coefficient of interlayers and faults that are able to influence the development and distribution of fractures during fault bend folding a linear relationship between the slip displacement and the fracture damage zone the ramp cutoff angle and the fracture damage zone and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results these mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault bend folds

bacterial origin of east australian continental margin phosphorites many models of the origin of marine phosphorites require a sediment rich in organic matter which by decomposition releases phosphorus for the precipitation of carbonate fluorapatite1 7 this concept is useful in explaining contemporary phosphorite in areas of very high productivity off the coasts of peru chile and south west africa8 10 where there are high organic matter fluxes to the sea floor4 7 11 it does not explain the origin of marine phosphorite deposits which formed in regions of limited oceanic upwelling and productivity12 14 the east australian continental margin an area of phosphogenesis throughout the late pleistocene and holocene13 14 is a modern analogue of an east coast phosphogenic province15 17 with low productivity over the upper slope region where the most recent phosphorites have been found18 evidence is reported here for the carbonate fluorapatite in the east australian phosphorites being located within bacterial cellular structures and a model proposed for the origin of these deposits through the slow bacterial assimilation of phosphorus from seawater in an area of restricted sedimentation

possible microbial origin of phosphorites on error seamount northwestern arabian sea abstract petrographical mineralogical and microprobe analysis of phosphorites from error seamount in the northwestern arabian sea demonstrates that microbial processes played an important role in the early diagenetic formation of the phosphorites during subaerial exposure of the seamount the phosphorites on error seamount occur as laminated crusts and massive slabs low magnesium calcite and carbonate fluorapatite are the major minerals of the phosphorites with goethite being important only in the massive slab phosphorites elemental sulphur pyrrhotite gypsum and chlorite are the mineral phases present in the acid insoluble residues of the phosphorites elemental sulphur which is exclusively formed by microbial processes occurs as submicrometre sized granules on gypsum surfaces the laminated crust phosphorites consist of organic rich and organic poor laminae interlayered with ghost pellets index fossils of oligocene to lower miocene age peloids and coated grains massive slab phosphorites are fine grained and consists of goethitic and non goethitic zones non goethitic zones comprise mainly microsphorite with oligocene to lower miocene fossils and microfossils goethitic zones contain abundant quaternary skeletons microprobe analyses of the error seamount phosphorites indicate that the geochemistry of these phosphorites is similar to that of the tertiary seamount phosphorites in the atlantic and pacific ocean and that they are enriched in ca and depleted in p compared to other seamount and island phosphorites in the indian ocean microbial activity is evident in both types of phosphorites and occurs in the form of microborings in peloids and on skeletal fragments encrustation of phosphate crystals on hollow globular microstructures and phosphate sheaths enclosing organic filaments the presence of calcite rim cements microspar filled patches and recrystallised grains indicates exposure of the seamount under subaerial conditions during which phosphatisation took place

mobile hinge kinking in layered rocks and models abstract an unresolved question in structural geology is whether kink folds grow by the gradual rotation of the fold limbs about a fixed hinge by the nucleation of kink bands that grow by fold hinge migration or by some combination of these mechanisms the importance of mobile hinge kinking has previously been recognized in experimentally deformed slate and phyllite as well as decks of paper cards but its importance in the folding of multilayers consisting of alternating competent and incompetent layers has been uncertain this study shows that mobile hinge kinking can be an important folding mechanism in both natural and experimental multilayers the natural folds are in pelagic limestones from the umbria marche apennines of italy the geometrical properties of these folds as well as the small scale structures in the rocks indicate that these folds formed by the nucleation and expansion of kink bands with mobile hinges not by a fixed hinge folding mechanism the experimental folds were produced by the deformation of multilayered models consisting of layers of lead separated by layers of wax impregnated cloth the progressive growth of these folds by the nucleation and expansion of kink bands was directly observable a rough estimate of the rate at which fold hinges migrated through the apennine limestones was obtained indirectly using the displacement history recorded by calcite fibers on a fault which cuts a kink fold and was active during the formation of the fold it appears that the rate at which fold hinges migrated was approximately 100 times greater than the displacement rate along a fault that was moving by pressure solution slip

geometric tests and their application to fault related folds in kuqa abstract for brittle rock deformation there are two main types of fault related folds found in foreland thrust belts i e fault bend folds and fault propagation folds the predicted angular function for the quantitative geometric relationships between fault shapes and fold shapes in fault bend folds and fault propagation folds have been tested in seismic profiles i e deep bashijiqike tugeerming kashangtokai east qiulitage deep east qiulitage and yakelike fault bend anticlines and bashijiqike yiqikelike and south yiqikelike fault propagation anticlines in the kuqa rejuvenated foreland thrust belt test results for the transformation from seismic time section into seismic depth section using the seismic velocity spectrum can be used to identify whether the interpreted structures are reasonable with geometric analysis and testing of the subsurface structures it is possible to predict the existence of the fault bend folds and fault propagation folds in the kuqa area this study provides convincing proof that the kuqa basin is a rejuvenated foreland basin

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

phosphogenesis and organic carbon preservation in the miocene monterey formation at naples beach california the monterey hypothesis revisited the middle part of the miocene monterey formation at naples beach west of santa barbara california is predominantly composed of organic rich mudstone interstratified with phosphatic laminae minor lithologies include volcanic ash dolomite porcelanite and chert and condensed phosphatic beds sediments dated as 14 3 13 5 ma have average total organic carbon toc values around 8 5 wt and organic carbon oc accumulation rates are around 565 mg cm2 k y sediments dated as 13 5 13 ma are characterized by average toc values of 12 6 wt and oc accumulation rates of around 1130 mg cm2 k y the interval between 13 and 10 6 ma is marked by condensation average toc values are around 8 6 wt and oc accumulation rates diminished to around 55 mg cm2 k y the last interval studied is dated as 10 6 9 4 ma and average toc values are around 6 wt whereas oc accumulation rates rose again to 320 mg cm2 k y the presence of erosional surfaces angular unconformities and reworked clasts and nodules suggests that bottom current activity and gravity flow deposition have been instrumental in sediment accumulation the phosphatic laminae were precipitated at a very early stage of diagenesis during periods of nonsedimentation they formed less permeable sedimentary lids and may as such have contributed to enhanced oc preservation between 13 and 10 6 ma the thus formed phosphatic laminae were frequently subjected to subsequent sediment winnowing and reworking resulting in the formation of condensed phosphatic beds calculated p c molar ratios suggest that 1 the measured section is highly enriched in phosphorus p relative to oc 2 regeneration of organic p from organic matter decomposition was negligible and 3 the source of p was external likely upwelled bottom water rich in inorganic p in spite of good preservation conditions and correspondingly high toc contents the overall oc accumulation rates are moderate in comparison to those of actual high productivity areas which is mainly due to the episodic character of depositional processes and the intervening long periods of nondeposition and sediment reworking they preclude this section and by extrapolation the monterey formation in general from being an important oc sink during the middle miocene alternatively large oc sinks were probably created on the continent lignite deposits and in sedimentary depocenters which received increasing amounts of detrital sediments due to a combination of climate change spreading of grasslands and the increasing importance of mountain chains such as the himalaya the associated high nutrient fluxes may have been involved in the backstepping and drowning of carbonate platforms and in the generation of widespread phosphat rich deposits during the late early and early middle miocene

microbially influenced formation of phosphate nodules and megafossil moulds negev southern israel abstract phosphate nodules and megafossil moulds occur at the top of the late cretaceous mishash formation in southeastern israel their palaeogeographic distribution as well as the microstructure of the moulds and the nodules suggests that the former represent rapid lithification of the infilling sediment by apatite precipitating bacteria before the dissolution of the calcareous skeletons the nodules on the other hand are partly lithified portions of microbial mats formed in a lagoonal environment disrupted rolled and embedded in granular phosphorite carbonate replacement by apatite does not seem to be involved in the formation of this pebbly phosphate

quaternary phosphorites from the continental margin off chennai southeast india analogs of ancient phosphate stromatolites abstract pleistocene phosphorites occur on the continental margin off chennai abundantly in the depth range of 186 293 m they are associated with outer shelf glauconites and carbonate skeletals including large shells of molluscs and rhodoliths these are primary phosphate deposits and are similar to phosphate stratiform stromatolites this is the first report of phosphate stratiform stromatolites during the quaternary and modern times and they provide a quaternary analog for ancient phosphorites thin sections of phosphorites exhibit laminated phosphatized microbial mats consisting of mechanically deposited clastic particles or of phosphatic molds clay particles are scattered throughout the matrix sem studies reveal that the laminated phosphate matrix is made of thin sheets of tightly packed apatite globules densely packed intertwined microfilaments or filament molds phosphate with obscured laminae is composed of phosphate tubules cell like structures resembling coccoid cyanobacteria or their botryoidal aggregates are common carbonate fluorapatite and low magnesium and high magnesium calcites are the major mineral phases the structural co2 content of apatite ranges from 4 to 5 5 quartz feldspar and goethite are accessory minerals the microbial mats were formed on the outer shelf most probably during conditions of low sea level in the quaternary and microbial processes played a major role in direct phosphatization of these mats the primary phosphorus source seems to have been the continental supply and degradation of organic matter associated with benthic microbial communities the phosphate stratiform stromatolites thus formed were subsequently reworked into a shelf margin depression and resulted in the occurrence of condensed phosphorites

cambrian phoscrete profiles coated grains and microbial processes in phosphogenesis georgina basin australia abstract middle cambrian phoscrete profiles occurring within phosphatic carbonates that surround the phosphate deposits of the georgina basin australia are described in detail the profiles occur within a mixed mineralogy suite of rocks and are characterized by fabrics and textures identical to those developed in calcretes phoscrete profiles are subdivided into an overlying laminar phoscrete crust and an underlying phoscrete modified substrate diagenesis in the substrate results in the elimination of primary structures producing a coated to vaguely pelleted texture micritic phosphate cements dominate the phosphate profiles these cements occur as irregular coatings on 1 grains and 2 thread like structures which criss cross interparticle spaces scanning electron microscope examination f these cements indicates that they are coatings on tubular structures herein interpreted as chasmolithic and epilithic filaments the preferential occurrence of phosphate on organic substrates suggests that organic matter plays a dual role in phosphogenesis it provides both a source of phosphate to the pore waters via bacterial degradation and it also provides a substrate on which phosphate preferentially nucleates phosphate particles derived from the erosion of phoscrete profiles vary from friable aggregates and lumps to peloids and coated grains whereas the composite particles were unlikely to survive sediment transport peloids and coated grains were coherent particles able to survive transport and sorting this suggests that some of these particles may occur in the phosphate d posits

phosphorites hardgrounds and syndepositional solution subsidence a palaeoenvironmental model from the miocene of the maltese islands abstract two major phosphorite conglomerate horizons occur throughout the central mediterranean maltese islands within the lower middle miocene globigerina limestone formation the lower conglomerate lies directly upon a hardground and both conglomerates include lithoclasts of hardground material variation in clast size and bed thickness indicates a source area to the west and north of the present day islands of malta and gozo particularly thick phosphorite conglomerates occur in solution subsidence structures in western gozo being developed as a result of synsedimentary seafloor collapse these structures indicate that phosphorite clasts were deposited during several discrete pulses of turbulence punctuated by periods of non depositional hardground formation or normal marine pelagic sedimentation geochemical analysis of the contained phosphorite clasts within the conglomerates shows that p 2 o 5 generally is concentrated around the outer margins of the pebbles and contributes up to 17 by weight of some samples some 654 580 m 3 and 837 870 m 3 of phosphorite bearing strata are contained within the xlendi and qawra subsidence structures respectively the maltese islands represent part of a miocene carbonate shelf whose margin lay nearby to the west and which was subject to periodic erosion by strong currents transporting phosphorite pebbles eastwards to their present sites these currents further contributed phosphorus to semi autochthonous phosphorite developments located within the present maltese area the maltese phosphorites are related to other phosphorite areas in sicily a major province of miocene phosphogenesis is proposed to account for these occurrences it extends along the western margins of the malta ragusa rise

early diagenetic phosphate cements in the albian condensed glauconitic limestone of the tatra mountains western carpathians early diagenetic phosphate cements are described from the albian condensed glauconitic limestone of the tatra mountains western carpathians with regard to their macro and micromorphology distribution classification and genesis the cements occur within stratigraphically condensed semi pelagic foramini feral glauconitic layers and are associated with mature hardgrounds within the tatra albian limestone phosphate cement fabrics consist of crypto to microcrystalline carbonate fluorapatite and they occur as i rim envelopes ii infillings of intraparticle porosity iii rim cement iv multiple rim cement v palisade fabric and vi cluster cement micromorphological variability of the cement fabrics results from varying texture of the cemented sediment the nature of original porosity as well as from presence of associated microbial fabrics the microbial fabrics are interpreted as fossilized coccoid cyanobacteria phosphate cementation developed under peculiar early diagenetic conditions within semi closed microenvironments rich in organic matter in the marine phreatic environment the cementation contributed to the formation of phosphatic fossils and hardgrounds the accretion of the cements was due to concentration of biologically uptaken phosphorus near the sediment water interface enrichment of pore fluids with respect to phosphate and its precipitation within restricted microenvironments phosphate cementation post dated seafloor formation of pelletal glauconite but predated partial decomposition of organic matter as well as dissolution or neomorphism of aragonite and high mg calcite phosphate cementation occurred on a carbonate platform following the submersion of urgonian reefal build ups episodes of phosphate cementation were repeated during the sedimentation of the tatra albian limestone as a response to rapid relative sea level rises and increased influence of nutrient rich tethyan waters

from phytoplankton to oil shale reservoirs a 19 million year record of the late cretaceous tethyan upwelling regime in the levant basin abstract the complexity of sedimentary organic matter formation its source to burial and influence on bottom water communities are addressed in this study of the 19 million years long upper cretaceous tethyan upwelling regime in the levant a multi proxy approach is amalgamated into a model through which the paleoceanographic complexity of an intense and long lasting upwelling system is better understood a shift in primary producer assemblages and reorganization of the bottom water bacterial consortium followed the campanian maastrichtian boundary enforcing conspicuous sedimentological and faunal changes the siliceous and phosphatic bearing sediments of the campanian gave way to maastrichtian uniform and regionally distributed organic rich carbonates accompanied by an increase in sedimentation rates from 1 to 6 cm kyr this has facilitated both the increase in organic matter production and its excellent preservation and through diagenetic pathways affected its elemental composition these paleoceanographic modifications have also affected foraminiferal assemblages from massive blooms of triserial buliminid benthic foraminifera during the campanian which have sequestered diatom chloroplasts to diverse trochospiral forms during the maastrichtian using nitrate instead of oxygen for their respiratory pathways we propose that shifts in the type of primary producers promote a change in the amount and type of preserved organic matter in bottom water communities on the lithological composition of the rock mass and ultimately on the hydrocarbon generation potential of the studied source rock the continued rise of southern tethyan sea level and global highstands during the upper maastrichtian culminating into arabian plate wide maximum flooding surfaces cause the migration of upwelling activity away from the study area terminating the high productivity sequence in the levant

microbial pathways and palaeoenvironmental conditions involved in the formation of phosphorite grains safaga district egypt abstract phosphatic grains of the shallow marine phosphorite deposits of egypt are classified as either phosphatic bioclasts preserving biological structure e g skeletal fragments such as fish bones and teeth or phosphatic peloids and intraclasts this study describes the destructive and constructive microbial pathways represented by bioerosion of bones by endolithic cyanobacteria and accretion of phosphatic peloids by bacteria the palaeoenvironmental conditions and post depositional diagenetic history of these grains have also been considered scanning and transmission electron microscopy showed that the phosphatic peloids under transmitted light microscopy are composed mainly of microspheres 0 5 to 2 5 m similar in shape and size to coccoid like bacteria chemical mapping showed that these microspheres are composed of carbonate fluorapatite cfa and surrounded by degraded carbonaceous matrix these grains are suggested to be reworked from pre existing microbial mats during transgressive regressive cycles affecting the southern tethyan campanian maastrichtian shallow continental shelf the bioerosion of phosphatic bones is characterized by a network of meandering microborings that penetrated inward from the bone surface by endolithic cyanobacteria the bioerosion of bones resulted in a gradual centripetal digestion and conversion of bones into micritic phosphate peloids the bioerosion mechanism is probably started in the acidic sheath surrounding cyanobacteria followed by supersaturation of po 4 and reprecipitation of crystalline cfa as electron dense remineralized rims electron microprobe microanalyses showed that the remineralized microbored areas are higher in cao p 2 o 5 and f and depleted in cl relative to unaltered bones a gradual demineralization of remineralized rims followed by dissolution of cyanobacterial cells is probably occurred during diagenesis and meteoric water alteration leaving behind empty microborings bone exposed to meteoric water alteration is lower in cao and p 2 o 5 and higher in f and cl than the unaltered bones understanding bone bioerosion has significant implications for palaeoenvironmental and taphonomic reconstruction archaeological applications and a regional correlation of the late cretaceous to palaeogene phosphogenic province extending from middle east to north africa

stress evolution during 3d single layer visco elastic buckle folding implications for the initiation of fractures abstract buckle folds of sedimentary strata commonly feature a variety of different fracture sets some fracture sets including outer arc tensile fractures and inner arc shear fractures at the fold hinge zones are well understood by the extensional and compressional strain stress pattern however other commonly observed fracture sets including tensile fractures parallel to the fold axis tensile fractures cutting through the limb extensional faults at the fold hinge and other shear fractures of various orientations in the fold limb fail to be intuitively explained by the strain stress regimes during the buckling process to obtain a better understanding of the conditions for the initiation of the various fractures sets associated with single layer cylindrical buckle folds a 3d finite element modeling approach using a maxwell visco elastic rheology is utilized the influences of three model parameters with significant influence on fracture initiation are considered burial depth viscosity and permeability it is concluded that these parameters are critical for the initiation of major fracture sets at the hinge zone with varying degrees the numerical simulation results further show that the buckling process fails to explain most of the fracture sets occurring in the limb unless the process of erosional unloading as a post fold phenomenon is considered for fracture sets that only develop under unrealistic boundary conditions the results demonstrate that their development is realistic for a perclinal fold geometry in summary a more thorough understanding of fractures sets associated with buckle folds is obtained based on the simulation of in situ stress conditions during the structural development of buckle folds

the model of fracture development in the faulted folds the role of folding and faulting abstract tectonic fractures are otherwise known as joints or fissures the density of tectonic fractures is governed by the lithology layer thickness and structures the distribution and density of tectonic fractures in the kuqa depression in the northern tarim basin of northwest china are dominantly controlled by the regional faulted fold belt our purpose of this paper is to analyze how folding and faulting control the development of tectonic fractures based on outcrop and logs of drill data in the folded tight sandstone reservoirs in the kuqa depression the extensional area transition area and shortening area have been separated by two neutral lines which control the distribution and density of tectonic fractures in the buckle folds from the twelve sites of field measurements six logs of drill core data and analysis of the micro texture of tectonic fractures it can be deduced that the fracture development in the sub salt faulted fold belt is related to the neutral lines and related faults the high density tensile fractures in the vicinity of fold hinges are more developed than in the limbs of the fold folding is thus the first level of control over the general pattern of fracture distribution the fractures in the hanging wall of the thrust faults are more developed than those in the footwall further more the fractures in the hinge zone and steeply tilted limbs of folds close to thrust faults are more developed than the gently tilted limbs which are far from faulting this suggests that faulting is a secondary control over the development of local fractures within the faulted fold belt the development of fractures related to faulted folds in the kuqa depression can be also divided into three episodes pre folding syn folding and post folding which are identified by field observation

correlation and trend studies of the sea ice cover and surface temperatures in the arctic co registered and continuous satellite data of sea ice concentrations and surface ice temperatures from 1981 to 1999 are analyzed to evaluate relationships between these two critical climate parameters and what they reveal in tandem about the changing arctic environment during the 18 year period the actual arctic ice area is shown to be declining at a rate of 3 1 0 4 decade while the surface ice temperature has been increasing at 0 4 0 2 k decade yearly anomaly maps also show that the ice concentration anomalies are predominantly positive in the 1980s and negative in the 1990s while surface temperature anomalies were mainly negative in the 1980s and positive in the 1990s the yearly ice concentration and surface temperature anomalies are shown to be highly correlated indicating a strong link especially in the seasonal region and around the periphery of the perennial ice cover the surface temperature data are also especially useful in providing the real spatial scope of each warming or cooling phenomenon that usually extends beyond the boundaries of the sea ice cover studies of the temporal variability of the summer ice minimum also reveal that the perennial ice cover has been declining at the rate of 6 6 decade while the summer surface ice temperature has been increasing at the rate of 1 3 k decade moreover high year to year fluctuations in the minimum ice cover in the 1990s may have caused reductions in average thickness of the arctic sea ice cover

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

geomechanical modeling of stress and strain evolution during contractional fault related folding abstract understanding stress states and rock mass deformation deep underground is critical to a range of endeavors including oil and gas exploration and production geothermal reservoir characterization and management and subsurface disposal of co 2 geomechanical modeling can predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses this approach enables development of forward models that incorporate realistic mechanical stratigraphy e g including competence contrasts bed thicknesses and bedding planes include faults and bedding slip surfaces as frictional sliding interfaces reproduce the overall geometry of the fold structures of interest and allow tracking of stress and strain through the deformation history use of inelastic constitutive relationships e g elastic plastic behavior allows permanent strains to develop in response to the applied loads this ability to capture permanent deformation is superior to linear elastic models which are often used for numerical convenience but are incapable of modeling permanent deformation or predicting permanent deformation processes such as faulting fracturing and pore collapse finite element modeling results compared with field examples of a natural contractional fault related fold show that well designed geomechanical modeling can match overall fold geometries and be applied to stress fracture and subseismic fault prediction in geologic structures geomechanical modeling of this type allows stress and strain histories to be obtained throughout the model domain

geomechanical modeling of an extensional fault propagation fold big brushy canyon monocline sierra del carmen texas field structural data from the big brushy canyon monocline developed in cretaceous strata of west texas are combined with nonlinear finite element modeling to help bridge the gap between geometric kinematic and mechanical analysis techniques for understanding the deformation history of reservoir scale geologic structures the massive santa elena limestone is offset along a steep normal fault and fault displacement is accommodated upward by the folding of the buda limestone and boquillas formation and the thinning in the intervening del rio clay mesostructures within competent buda limestone beds are concentrated in the monocline limb instead of the hinge and include bed perpendicular veins that accommodate bed parallel extension and bedding plane slip surfaces that offset the veins and accommodate flexural slip finite element models were constructed to reproduce the monocline geometry and deformation distribution as well as to assess the effect of material properties and boundary conditions on structural evolution the initial model configuration replicated the assumed predeformational geometry included frictional sliding surfaces to allow for bedding parallel slip and used a displacement boundary condition at the base of the santa elena footwall to simulate fault motion geometry and strain evolution were tracked so that 1 fold shape 2 cumulative extension and 3 layer parallel shear strain could be compared to field observations iterative model runs successfully matched field data and revealed the importance of benchmarking the model results against monocline geometry layer parallel extensional strain and bedding slip in the natural example our results illustrate the potential use of this modeling approach whereby calibration is performed using available data and is followed by strain measurement throughout the model domain to aid in prediction of subseismic faults and fractures this geomechanical modeling approach provides a powerful tool for site specific subsurface deformation prediction in hydrocarbon reservoirs that incorporates details of the local mechanical stratigraphy and structural setting

volumetric strains in neutral surface folding neutral surface folding is a significant contributor to fold development this mechanism produces contrasting strains in the inner and outer arcs of the folded layer that arise from principal stress orientations that are approximately parallel and perpendicular to the layer we demonstrate that such stress patterns imply significant gradients of mean stress across the folding layer being more tensional on the outer arc and more compressive in the inner arc this could pump fluids towards the outer arc during folding and result in heterogeneous volume changes we conclude that the neutral surface folding model should be adapted to accommodate volumetric strains in order to explain dilatational structures e g open fractures veining on the extrados and volume loss structures e g pressure solution seams stylolitic cleavages on the intrados this dilatation has economic implications as it allows prediction of sites of mineralization and zones of secondary permeability in fold related hydrocarbon traps

phosphatization of calcium carbonate in phosphorites microstructure and importance fabrics of phosphatized calcium carbonate particles in various phosphorites have been studied using scanning electron microscopy coupled with x ray dispersive microanalysis replacement of calcium carbonate by apatite has been observed in bivalve shell fragments and in foraminiferal tests replacement proceeds at constant volume with excellent preservation of the original microtextures in some deposits replacement of carbonate by apatite is the main phosphogenic process however in general the process seems to be far less important than might be believed purely on the basis of thin section observations in many phosphorites internal or external apatite moulds of bioclasts are common including very small particles such as coccoliths in phosphatized chalks apatite precipitation was typically followed by carbonate dissolution later apatite precipitation within the dissolution voids may produce partial or total phosphate pseudomorphs of the original carbonate grain in these examples direct replacement of carbonate by phosphate cannot be demonstrated

sedimentary phosphate and associated fossil bacteria in a paleoproterozoic tidal flat in the 1 85 ga michigamme formation michigan usa abstract phosphorus is a nutrient fundamental to life and when it precipitates in modern environments bacteria are intimately involved in its release concentration and mineralization preserved fossil bacteria in phosphate crusts and grains from the ca 1850 million year old bijiki iron formation member of the michigamme formation michigan provide insight into the longevity and nature of this relationship the michigamme formation accumulated near the end of the earth s initial phosphogenic episode ca 2 2 and 1 8 ga to produce one of the first granular phosphorites phosphatic lithofacies consist of fine to medium sand sized francolite peloids concentrated on bedding surfaces in peritidal facies granular beds are up to 2 cm thick and peloids are often partially to completely replaced by dolomite and chert the grains contain organic matter and pyrite framboids that suggest bacterial breakdown of organic matter and bacterial sulfate reduction the peritidal nature of phosphorite in the michigamme formation is in sharp contrast to phanerozoic phosphogenic environments in deeper coastal upwelling settings peritidal settings were well suited for phosphogenesis under the very low oxygen and low dissolved sulfate levels of the paleoproterozoic as cyanobacteria produced oxygen in shallow water and evaporation led to increased sulfate concentrations such concomitant processes helped establish focused redox interfaces in the sediment that chemosynthetic bacterial communities sulfur oxidizers reducers forms that concentrate p and possibly iron oxidizers could exploit phosphate released from organic matter by heterotrophic bacteria and fe redox pumping was further concentrated by these chemotrophs a process that forms late neoproterozoic to phanerozoic phosphorites but on a much larger scale this early example of a granular phosphorite demonstrates that like their phanerozoic counterparts paleoproterozoic phosphorites are the concentrated indirectly biomineralized products of bacterial communities but unlike younger analogs which accumulated across subtidal shelves and shelf margins these ancient deposits formed only in tidal flat settings where phosphogenic redox processes could be established in the sediment from this early beginning the zone of phosphogenesis likely migrated into deeper water settings as oxygen and sulfate levels rose expanding the zone of chemosynthetic bacterial and associated phosphogenesis across the shelf

ultrastructure of a microbial mat generated phosphorite optical and sem observations of phosphorites reveal that mineralization is concentrated on ooids and micro oncoids the coated grains occur within microbial mats microbial mats represent the formational environment of the ooids and oncoids both coated grains and mats exhibit similar filamentous micro organisms the mat filaments show no fixed orientation and they merge with the concentrically oriented filaments of the coated grains the branching nature and chlamydospore like structures of filaments suggest that both mat and coated grains have been formed by fungi some coated grains appear to have been slightly disturbed and sometimes mobilized from their sites of formation due to separation from the parent mat resulting perhaps from contraction fragmentation the voids so created within the mat had been later filled with either micrite or sparite

nannostructure and genesis of phosphorites from odp leg 112 the peru margin abstract a sem based petrographic study of miocene to quaternary phosphorites recovered during odp leg 112 shows that they contain a variety of apatitic nannostructures in porous types apatite appears as ovoid dumbbell like botryoid micron sized and inframicron apatite particles and flakes these structures are probably due to microbially mediated apatite precipitation in compact varieties diagenesis reduced the porosity obscuring the original apatite microparticles macroscopic aspects of phosphorites colour brightness hardness density are essentially linked to the porosity of apatitic structures but independent of the apatite particles and structures generally they reflect diagenetic stages in evolution the variety and distribution of the apatite particles and structures suggest that phosphorites mainly formed in three different ways phosphatization of 1 fish excrements forming copronodules 2 diatom muds producing nodules and 3 faecal pellets resulting in rounded grains these phosphorite particles formed in low energy conditions many of them were subsequently reworked

fracture systems and petrophysical properties of tight sandstone undergoing regional folding a case study of the cretaceous reservoirs in the kuqa foreland thrust belt tarim basin abstract the kuqa foreland thrust belt of the tarim basin hosts a prolific hydrocarbon system the main reservoirs are characterized by tight sandstone with low porosity and ultra low permeability buried presently at more than 5000 m depth natural fracture systems have a significant impact on reservoir performance and it may form paths for fluid flow in tight sandstone reservoirs and therefore plays an essential role in controlling high production rates with the aim of analyzing the distribution of favorable reservoir we studied subsurface fracture patterns and petrophysical properties of the bashijiqike formation with data collected from dabei structure and keshen structure we document the presence of four fracture systems whose distribution is related to far field stress thrusting and folding in the keshen anticlines higher fracture intensities are observed in the limbs with principal east west hinge parallel fracture system direction the hinge parallel fracture system includes a moderate dipping fracture set and a vertical fracture set crosscutting relationships stress field inversion and fracture surface textures suggest that the moderate dipping fracture set consists of shear fractures and can be explained by intra layer shear caused by thrusting the vertical fracture set may be formed due to the local outer arc extension during folding the oblique fracture system shows scattering in strike and is supposed to be related to a shear event of locally left lateral strike slip whereas in the dabei anticlines the major system is hinge perpendicular fracture system nw se showing a trending of increasing fracture intensity from limbs to hinge the hinge perpendicular fractures system in the dabei anticlines consist of shear fractures and tension fractures stress inversion result shows it corresponds to northwest southeast orientation compression stage besides we analyzed petrophysical properties include porosity permeability young s module poisson ratio and compressive strength of the bashijiqike formation concerning their structural position within folds it indicates that the highest porosity and permeability are associated with dissolution and fracturing the compressive strength of different structural positions also restrict the variations of mechanical properties of rocks the best reservoir quality is suggested in the hinge zone and areas close to thrust the findings have given maybe helpful for providing favorable reservoir targets for prospecting in the compressional basin

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

dynamic thermodynamic sea ice model ridging and its application to climate study and navigation abstract a dynamic thermodynamic sea ice model with the ocean mixed layer forced by atmospheric data is used to investigate spatial and long term variability of the sea ice cover in the arctic basin the model satisfactorily reproduces the averaged main characteristics of the sea ice and its extent in the arctic basin as well as its decrease in the early 1990s employment of the average ridge shape for describing the ridging allows the authors to suggest that it occurs in winter and varies from year to year by a factor of 2 depending on an atmospheric circulation pattern production and horizontal movement of ridges are the focus in this paper as they show the importance of interannual variability of the arctic ice cover the observed thinning in the 1990s is a result of reduction in ridge formation on the pacific side during the cyclonic phase of the arctic oscillation the model yields a partial recovery of sea ice cover in the last few years of the twentieth century in addition to the sea ice cover

karst dissolution along fracture corridors in an anticline hinge jandaira formation brazil implications for reservoir quality abstract folded fractured and karstified structures have been recognized in several carbonate reservoirs however they are rarely fully identified from seismic or well data and have been poorly described the present study investigates the geological and structural controls that regional anticlines may exert on solution enlarged fracture corridors and epigenic karst concentrations in folded fractured carbonate units we performed regional mapping based on 106 2d seismic lines 51 well logs unmanned aerial vehicle uav imagery of four major outcrop sites i ii iii and iv and field investigations to parameterize fracture and karstic features density spacing length and aperture the study area is potiguar basin brazil where we identified the gentle ne trending apodi fold 10 km wide and 20 km long the fold formed along an inverted extensional fault during the latest miocene quaternary stress field and the envelope of the meandering trend of the apodi river coincides with the ne trending fold axis the fracture pattern in the fold hinge zone consists of two orthogonal syn folding fracture sets a ne sw striking hinge parallel set and an orthogonal nw se striking set these fractures and superposed karstification are mostly concentrated in the hinge zone along fracture corridors in an area 1 5 km wide and 20 km long we conclude that fracture corridors in anticline hinges are likely sites to have high fracture densities and wide apertures these corridors provide reservoir spaces that are favorable for the formation of karst cavities with significant increases in permeability and porosity along the fracture sets these features act as important fluid pathways and storage areas where matrix porosity is low the findings can be used for first order prediction in karstified carbonate reservoirs

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

macrobenthic community structure in a high productivity region upper campanian mishash formation israel abstract a paleoecological study of molluscan fossils from the upper campanian mishash formation of southern israel was undertaken to provide new insights into the inference of bottom oxygen levels food availability and bottom water energy on high productivity seafloors quantitative data for molluscan analysis were collected from each of the main lithologies that comprises the high productivity facies mosaic of the mishash sea i e organic rich carbonates thin porcelanite and chert beds and loosely to densely packed shell beds diagenesis has obliterated faunal remains in carbonate layers pollution studies in modern environments have demonstrated the close connection between stressful conditions such as organic load toxicity and water and sediment aeration and benthic community structure as expressed through species richness evenness taxonomic composition body sizes and trace fossil assemblages these connections and behavior patterns were investigated in the varied benthic fossil assemblages of the phosphate member of the mishash formation bivalves and gastropods dominated the macrofauna in all rock types but in varying abundance and taxonomic compositions changing from diverse assemblages 15 22 species per sample to less rich ones 5 7 species and even barren intervals this range of abundance neatly describes the lateral mosaic and heterogeneous nature of the upwelling environment of the upper campanian and is comparable to the mosaic of sub facies that characterize modern upwelling facies belts today e g in the benguela upwelling system the variations shown for the macrobenthic assemblages within the mishash formation high productivity regime are associated with proximity to the high productivity center or to periods of intensified upwelling the inferred variable oxygen levels and organic load changes point up how dynamic these regions really are this is expressed in community structure and composition which vary between two extremes the low oxygen biofacies 1 is characterized by a smaller range of shell sizes infaunal deposit feeders and low species richness while the high oxygen biofacies 3 is characterized by greater ranges in shell size infaunal but also epifaunal suspension feeders and higher species richness the chert and porcelanite beds exhibit a variety of sub environments and seem to represent an intermediate facies that bridges the two extremes of biofacies 1 and 3 the above ecological criteria may provide evidence of the original carbonate environment for the thin chert and porcelanite layers the chert or porcelanite samples that contain a moderately even and rich assemblage of species intermediate to the values of the two end member facies are taken to represent a shallow water carbonate marine environment marginal to the upwelling center whereas layers of chert and porcelanite containing very low species richness and evenness are taken to characterize primary depositional environments proximal to the paleo upwelling cells

magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china abstract magnetostratigraphic and rock magnetic results from 1006 horizons in paleogene and neogene sediments between the upper kumugeliemu formation and the base of the kuche formation within the kuche depression of the tarim basin nw china are used to evaluate postcollisional uplift and deformation in the tian shan range characteristic remanences with both normal and reversed polarity were isolated by thermal demagnetization generally between 300 and 690 c and a composite magnetostratigraphy is constructed from data at 969 accepted levels correlating with polarity chrons c12n to c3r dated between 31 0 and 5 5 ma on the ck95 geomagnetic polarity time scale observed height dependent changes of rock magnetic parameters km and ams ellipsoid parameters indicate that these sediments were influenced by weak deformation with the succession accumulated before 15 ma recording the effects of compressive deformation this finding together with two substantial increases in accumulation rate at 16 17 and 7 ma define a framework for cenozoic uplift and deformation of the tian shan range we argue that thrusting in the south of the range was probably initiated at 20 ma and followed by rapid uplift at 16 17 ma on the assumption that sediment accumulation in western china was still predominately tectonically controlled at 7 ma another later pulse of rapid uplift with a much larger regional influence is also recognized in the tian shan the kuche depression was subjected to two postcollisional phases of rotational deformation with clockwise rotation prior to 12 ma 1 36 ma succeeded by counterclockwise rotation at 1 64 ma after 12 ma and possibly continuing to the present day this rotational deformation is not temporally related to the history of basin formation resolved from the magnetostratigraphy and may be linked to block interactions with adjoining terranes

sedimentology geochemistry and origin of phosphatic chalks the upper cretaceous deposits of nw europe santonian lower campanian and lower maastrichtian phosphatic chalks in northern france southern england and belgium are europe s largest sedimentary phosphatc deposits the stratigraphy sediment ology petrography mineralogy and geochemistry of the lithofacies are reviewed and new data presented depositional and diagenetic models for phosphatic chalk deposits are developed using published experimental work and from observations of modern high and low productivity phosphogenic systems it is concluded that phosphatic chalks were deposited in well oxygenated current swept environments phosphatization required a delicate balance to be maintained between moderate organic carbon and carbonate sedimentation rates reduced bulk sediment accumulation rate and an enhanced rate of bioturbation precipitation of carbonate fluorapatite francolite accompanied the bacterially mediated decomposition of organic matter occurring within centimetres of the sediment seawater interface and taking place preferentially within microbial bodies and coatings in addition to the organically derived component pore water phosphate levels were enhanced by phosphate absorbed on ferric oxyhydroxides which was liberated during iron reduction mineralization was probably a dominantly post oxic process but occurred in a thick sediment mixed layer in which marine organic matter was undergoing intense mixed aerobic and anaerobic microbial degradation phosphogenesis occurred predominantly on the ne margins of the anglo paris basin where shallower sea floors and suitable palaeoceanographic conditions prevailed phosphogenic episodes were limited by sea level fluctuations which controlled the effectiveness of the erosional currents that formed and maintained the phosphatic basins and may have stimulated local productivity

damage and plastic deformation of reservoir rocks part 1 damage fracturing in this series of studies we develop a numerical tool for modeling finite deformation of reservoir rocks we present an attempt to eliminate the main limitations of idealized methods for example elastic or kinematic that cannot account for the complexity of rock deformation our approach is to use rock mechanics experimental data and finite element models abaqus to generate realistic simulations the present numerical rheology incorporates the dominant documented deformation modes of rocks 1 rock mechanics experimental observations including finite strength inelastic strain hardening strength dependence on confining pressure strain induced dilation pervasive and localized damage and local tensile or shear failure without macroscopic disintegration and 2 field observations including large deformation distributed damage complex fracture networks and multiple zones of failure our analysis starts with an elastic plastic damage rheology that includes pressure dependent yield criteria stiffness degradation and fracturing via a continuum damage approach using the abaqus materials library we then use experimental results for berea sandstone in two configurations four point beam and dog bone triaxial to refine and calibrate the rheology we find that damage and fracturing patterns generated in the numerical models match the experimental features well and based on these observations we define damage fracturing the fracturing process by damage propagation in a rock with elastic plastic damage rheology in part 2 we apply this rheology to investigate fracture propagation at the tip of a hydrofracture

fault and fracture systems in a fold and thrust belt an example from bolivia this paper presents an outcrop analog study of fractures in low porosity sandstones in the subandean thrust belt we analyze the evolution of fault and joint systems in these sandstones quantify their density along the structural trend and identify the main factors controlling their variability we show that faults and joints occur at different scales in a hierarchical fashion as a consequence of progressive shearing the first generation is an orthogonal set of joints one parallel and the other perpendicular to the bedding azimuth shearing along these joints transformed them into small faults and created new sets of fractures oblique to the bedding attitude linkage of these small faults facilitated the formation of larger faults with significant strike slip offset shearing along bedding planes created subvertical splay joints that induced the formation of conjugate normal faults in this thrust belt subordinate strike slip and normal faults are concomitant products of compressive deformation this study documents a hierarchical correspondence between spacing of structural heterogeneities and stratigraphic architecture we measured spacings of joints and outcrop scale faults along the backlimb of the abra del condor anticline we subdivided the structural discontinuities into four main groups joints small faults intermediate faults and fault zones spacing of joints small faults and intermediate faults has a lognormal distribution whereas spacing of fault zones shows a normal distribution the mean of these distributions is about the same as the thickness of the confining stratigraphic intervals therefore spacing and dimensions of joints and faults have a first order relationship to the thickness of the confining stratigraphic sequences

interaction of rock and atmosphere patinas on mediterranean monuments this paper analyzes chemically mineralogically and petrolographically the patinas developed on several mediterranean monuments made with different stones siliceous and carbonatic in order to establish their origin and their evolution under the present environmental conditions and to evaluate the environmental parameters controling their development most of the patinas show a common sequence of layers which from the outer to the inner zone are 1 present bioactivity and or biological remains 2 gypsum rich patina and 3 calcitic brown to orange patina each one may exhibit different fabrics from micritic to stromatolitic and may be more or less continuous and homogeneous the main mineral components are calcite and gypsum but ca oxalates and ca phosphates have also been found associated to biological structures as well as quartz and clays the different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem to be related to the biological activity facilitating the growth of different organisms and leading to the development of a deposit with distinct characteristics fabric texture porosity etc the gypsum rich patina has been interpreted as a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the atmospheric dust the mineralogy and texture of the patina is independent of the nature of the underlying rock and only in few cases a micritization process has been observed as interaction between patina and rock recently the penetration of endolithic microflora produced drillings and the development of a fissuration system parallel to the surface and thus the detachment of the crust from the rock and even flackening of the rock itself has been observed consequently under the present climatic conditions in the mediterranean basin erosion is a more active process than deposition and the crusts and patinas show a tendency to disappear from the surface of the monuments

large scale mechanical buckle fold development and the initiation of tensile fractures tensile failure associated with buckle folding is commonly associated to the distribution of outer arc extension but has also been observed on fold limbs this study investigates whether tensile stresses and associated failure can be explained by the process of buckling under realistic in situ stress conditions a 2 d plane strain finite element modeling approach is used to study single layer buckle folds with a maxwell viscoelastic rheology a variety of material parameters are considered and their influence on the initiation of tensile stresses during the various stages of deformation is analyzed it is concluded that the buckling process determines the strain distribution within the fold layer but is not solely responsible for the initiation of tensile stresses the modeling results show that tensile stresses are most dependent on the permeability viscosity and overburden thickness low permeability 10 19 m2 high viscosity 1021 pa s and low overburden pressure can explain tensile failure at the fold hinge tensile stresses in the limb of the fold cannot in general be explained by buckling rather it develops due to a combination of compression and erosional unloading the modeling results show that erosion of high permeability rocks can explain the generation of tensile stresses at significant depths 2 km both at the hinge of the fold and throughout the limb of the fold this study shows that tensile stresses and associated failure within buckle folds is directly dependent on the distribution of material parameters but moreover to the strain history of the geologic system

the neutral lines in buckle folds abstract the neutral line in a buckle fold dividing areas of outer arc extension from areas of inner arc shortening is a fundamental concept in structural geology in the past folds have been constructed kinematically from a given neutral line geometry using the tangential longitudinal strain pattern in this study a mechanical finite element model is used to numerically buckle single layer folds with newtonian and power law viscous rheology two neutral lines can be distinguished the incremental neutral line zero layer parallel strain rate and the finite neutral line zero finite layer parallel strain the former develops first and migrates through the layer from the outer towards the inner arc ahead of the latter both neutral lines are discontinuous along the fold and terminate either at the bottom or top interface of the layer for decreasing viscosity ratio between layer and matrix and for decreasing initial amplitude the neutral lines develop later during folding and for some cases no neutral line develops the dynamical behaviour of the neutral lines is similar for newtonian and power law viscous rheology if the viscosity ratio is large but substantially different for small viscosity ratios the results are discussed in light of fold related structures such as outer arc extension structures and inner arc shortening structures

nannostructure and significance of fish coprolites in phosphorites abstract phosphatic coprolites 0 5 2 cm long occurring in cretaceous eocene phosphorites of tunisia morocco mauritania senegal and egypt were investigated for their petrology by using sem they exhibit a homogeneous porous apatite structure with a few fish remains the nannostructures of the coprolites consist of inframicron sized and botryoid type apatite microparticles spherical cavities and cavity infill cavity infilled inframicron sized apatite globules are typical in the coprolites and are apparently formed by extracellular precipitation of phosphate around microbial organisms we presume that the coprolites studied here may belong to fishes whose excrements contain abundant organic matter and phosphate phosphatization of excrements appears to be a microbial process controlled by the microenvironment the nannostructures observed in the coprolites investigated here differ significantly from the nannostructures of other studied phosphatic grains pellets and coated grains in the same samples which are mostly heterogeneous and consist of ovoid type apatite particles in the case they are not reworked the centimetre to decimetre thick coprolite beds in phosphorites indicate a lack of detrital input and strong bottom water currents at the sediment water interface during deposition and subsequent phosphatization of the excrements

characterization of lowest oxygen environments within ancient upwelling environments benthic foraminifera assemblages abstract the upper campanian mishash formation of southern israel was deposited within the southern tethys upwelling belt with sea floors beneath this system characterized by poorly ventilated sediments approaching anoxia this study was aimed at tracking the oxygen poor gradient using benthic foraminiferal assemblages of organic rich carbonates that are devoid of benthic macro invertebrates and trace fossils quantitative data were gathered on foraminiferal faunas from four sections namely zin saraf qazra ashosh omer and qilt from three basins affected by upwelling four distinct benthic foraminiferal assemblages characterize the organic rich carbonate facies b assemblages a d these assemblages are distinguished by their species richness and composition relative abundance and dominance patterns the low diversity buliminid dominated faunas correlate with high up to 25 wt total organic carbon levels and inferred pore water oxygen levels range from nearly anaerobic to dysaerobic up to 0 1 ml o2 l the zin and qazra ashosh basins in southern israel have representation of assemblages a and b indicative of the most oxygen depleted environments assemblages c and d are more common in better ventilated environments such as the qazra omer basin of southern israel and the qilt basin to the northeast nonetheless all these basins have benthic assemblages indicative of low oxygen pore waters

phosphate stromatolites from condensed cephalopod limestones upper jurassic southern spain upper jurassic phosphate stromatolites of the almola sierra southern spain encrust macrofossils and hardgrounds and form oncoids included within pelagic condensed fossiliferous limestones their accretion was determined by bacterially mediated precipitation of phosphate by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera phosphorous trace elements and rare earth elements were concentrated from degraded organic matter and seawater by stromatolite building communities which mediated the formation of phosphate rich and fe al si rich organic gels under oxic conditions favouring the precipitation of amorphous mineral precursors acp and fe al si oxyhydroxides the observed ce enrichment for some stromatolites is explained by oxidative scavenging of ce4 from seawater by fe mn oxyhydroxides the bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure and later changed to carbonate fluorapatite haematite and poorly crystalline fe rich clays under postoxic conditions phosphatization of trapped carbonate particles also occurred the phosphate stromatolites formed on a sediment starved pelagic swell during periods of no carbonate sedimentation and hardground development stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis sedimentation and erosion suggesting episodic changes in the sedimentary environment although some of the parameters that controlled phosphate precipitation associated with the stromatolites local high organic productivity sediment starvation moderate depth of deposition and physicochemical conditions were similar to those found in modern and ancient phosphogenic settings the palaeogeographical framework and the intensity of sedimentary processes were different to those of the world s major phosphorite deposits

the distribution of deformation in parallel fault related folds with migrating axial surfaces comparison between fault propagation and fault bend folding abstract in fault related folds that form by axial surface migration rocks undergo deformation as they pass through axial surfaces the distribution and intensity of deformation in these structures has been impacted by the history of axial surface migration upon fold initiation unique dip panels develop each with a characteristic deformation intensity depending on their history during fold growth rocks that pass through axial surfaces are transported between dip panels and accumulate additional deformation by tracking the pattern of axial surface migration in model folds we predict the distribution of relative deformation intensity in simple step parallel fault bend and fault propagation anticlines in both cases the deformation is partitioned into unique domains we call deformation panels for a given rheology of the folded multilayer deformation intensity will be homogeneously distributed in each deformation panel fold limbs are always deformed the flat crests of fault propagation anticlines are always undeformed two asymmetric deformation panels develop in fault propagation folds above ramp angles exceeding 29 for lower ramp angles an additional more intensely deformed panel develops at the transition between the crest and the forelimb deformation in the flat crests of fault bend anticlines occurs when fault displacement exceeds the length of the footwall ramp but is never found immediately hinterland of the crest to forelimb transition in environments dominated by brittle deformation our models may serve as a first order approximation of the distribution of fractures in fault related folds