a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

late ordovician glacial record of the anti atlas morocco abstract late ordovician glaciogenic deposits are exposed intermittently along an 800 km long outcrop belt in the anti atlas mountains of southern morocco these deposits are of economic significance as potential oil bearing sandstones in the tindouf and boudenib basins and thus are here re examined as analogues to subsurface hydrocarbon reservoirs glaciogenic deposits of the upper second bani formation rest unconformably upon underlying shallow marine clastic deposits the unconformity is characterised by a series of palaeovalleys some 0 5 1 0 km wide and up to 100 m deep which may have been cut under elevated hydrostatic pressures as tunnel valleys beneath a late ordovician ice sheet the valleys and intervalley areas are filled with glaciogene sediments categorized into five facies associations namely 1 a tabular sandstone association shallow marine shoreface deposits 2 a massive sandstone and conglomerate ice contact debrites 3 meandriform sandstone deposits ice proximal sandur 4 stratified diamictites ice rafted debris and 5 sigmoidally bedded sandstones intertidal sandstones deformation in these sediments is ubiquitous and includes soft sediment striated pavements metre scale duplex systems thrust and fold belts of deformation affecting some tens of metres of sediment and pervasive lineations these features are interpreted to record the complex nature of deformation processes operating beneath a late ordovician ice sheet including sliding at the ice bed interface folding and deformation within the sediment column and a series of complex ramps detachments and shear zones within an unconsolidated pile of sediment beneath the ice sheet

submarine landforms in the fjords of southern chile implications for glacimarine processes and sedimentation in a mild glacier influenced environment abstract chilean fjords are the lowest latitude at which glaciers reach the sea today high accumulation and mass throughput sustain tidewater glacier margins in this relatively mild climatic and oceanographic setting 27 000 km 2 of swath bathymetry allow mapping of sea floor landforms and inferences on glacimarine sediments and sedimentation tidewater glaciers are present in several fjords beyond retreating tempano glacier a terminal moraine marks the limit of probable little ice age advance with smaller transverse ridges closer to the glacier beyond advancing pio xi glacier there are few signs of organised submarine landforms older moraine ridges along several fjords formed at still stands during deglaciation elsewhere meltwater fed braided rivers connect the glacial and marine sedimentary systems swath imagery shows glacifluvial and fluvial deltas with small channels and chutes that develop into long and sinuous turbidity current channels few iceberg ploughmarks and submarine slope failures were observed but several fields of pockmarks were present the fjords of chile are dominated by sediment delivery from turbid meltwater which distributes fine grained debris widely producing sorted and laminated fine grained ice proximal wedges and draping ice distal seismic architecture to give a predominantly smooth sea floor turbidity currents also transfer sediments to some ice distal environments the chilean fjordlands represent the mildest climatic and oceanographic end member of a continuum of glacier influenced marine settings similar to south east alaska in the northern hemisphere components of a landform assemblage model for climatically mild meltwater dominated fjords include ice contact moraine ridges glacifluvial and fluvial deltas and turbidity current channels full glacial and deglacial streamlined subglacial landforms are likely to have been buried in many areas by subsequent glacimarine sedimentation

lenticular shale fabrics resulting from intermittent erosion of water rich muds interpreting the rock record in the light of recent flume experiments lenticular lamination is a fabric that is known from shales of all ages but its origin and paleoenvironmental significance is poorly understood we have successfully reproduced this fabric in flume experiments beds of water rich mud were eroded in a flume and yielded sub millimeter to centimeter size fragments that can be transported in bedload for distances of ten kilometers or more upon redeposition and compaction these deposits have the same textural qualities as lenticular laminated shales from the rock record although accumulation of fecal pellets or abundant burrow tubes in a shale may produce comparable fabrics upon compaction these can be distinguished from erosion produced lenticular lamination via petrographic criteria lenticular lamination in shales that is due to deposition of water rich mud fragments most likely records intermittent erosion and transport of surficial muds by currents

a punctuated late ordovician and early silurian deglaciation and transgression evidence from the subsurface of northern saudi arabia abstract the lower section of the lower silurian qusaiba member qalibah formation is characterized by regionally developed organic rich shales that have sourced many of the large paleozoic petroleum systems of saudi arabia in northern saudi arabia these high total organic carbon toc horizons are being assessed for their unconventional shale gas potential the initial phase of exploration drilling which resulted in a quadrupling of the number of penetrations in northern saudi arabia had the dual purpose of 1 assessing the high toc horizons as an unconventional resource play and 2 acquiring the fundamental data required to understand the geologic development of the zones of interest within the lower qusaiba the availability of numerous new cores from across northern saudi arabia enabled an extensive refinement of the existing biostratigraphy and enhanced integration between graptolite and palynomorph biozonation systems in cores from the study area four distinct sedimentary facies are recognized 1 pyritic siltstone 2 black mudstone 3 black chert and 4 gray shale representing distinct paleoenvironmental conditions related to the stepped latest ordovician and early silurian gondwanan deglaciation the failure of the gondwanan ice sheet was not a simple short lived consistent melting and associated flooding of a flat continental shelf this study highlights the complex interplay of sea floor topography ocean currents sediment supply and variations in the rate of melting of the ice sheet with the associated rising ambient temperatures there are 1 increasing clay concentrations associated with intensifying chemical weathering of the exposed land mass and 2 progressive lowering of the carbonate compensation depth as water temperatures rise enabling the preservation of carbonate shell material

the magnitude and cause of short term eustatic cretaceous sea level change a synthesis abstract no consensus currently exists regarding the magnitude of cretaceous short term less than 3 ma in duration eustatic sea level change the lack of a consensus limits the ability to predict sedimentary facies and architecture and to assess the potential drivers of eustasy during a period of earth history considered as significantly warmer than today consequently this review documents weighs synthesises and summarises records of short term relative sea level change and evaluates the observed trends in magnitude within the context of potential climatic drivers and their eustatic expression although cretaceous sea level change is addressed in many publications estimates of absolute values are relatively limited often cover short time intervals and use different methods based upon integrated geological and statistical analyses four broad episodes of magnitude change have been identified three of these episodes reflect trends of increasing magnitudes of sea level change from the berriasian to early hauterivian late hauterivian to aptian and santonian to maastrichtian the fourth episode reflects a decreasing magnitude trend from the albian to coniacian in addition the maximum magnitude of sea level change at an approximate stage level has been identified and categorised as slight less than 10 m modest 10 to 40 m or significant 41 to 65 m significant magnitudes are inferred for the valanginian aptian albian and maastrichtian exclusively slight magnitudes are restricted to the berriasian such an assessment casts doubt on the repeated and stratigraphically widespread episodes of very large magnitudes more than 75 m advocated by some workers and instead defines distinct periods and magnitudes of sea level change that should be globally reflected in sedimentary facies patterns for example intervals of sea level fall of significant magnitude are commonly associated with the increased delivery of sediment into basinal settings including the marked progradation of shallow marine sediments whilst up systems tract there can be enhanced development of karst and erosional features because climatically driven eustasy is the likely cause of short term sea level change an assessment of the characteristic maximum magnitude limits of the principal climatic drivers thermo aquifer and glacio eustasy has been made such a comparison argues for glacio eustasy as the driver of significant short term sea level change in addition climate proxy data demonstrates that the valanginian aptian albian and maastrichtian are intervals of cooling within the cretaceous thereby supporting the link between significant magnitudes and glacio eustasy

repetitions and cycles in stratigraphy abstract stratigraphic sections show repetitions of similar or identical conditions on all scales from millimeters to many hundreds of meters representing time intervals from possibly seconds to many millions of years any such repetitions have been called cycles to understand the reason why cycles occur a time scale is essential beds can be with or without time information the latter are known as event stratifications the event which triggers the formation of beds or any succession of sediments could be a random effect or it could be part of a mechanism in which cyclic behaviour is due to an oscillating physical system such systems are dynamic systems which means that they involve the transport of masses over distances and in definite time intervals cycles generated by such systems can be used as time units a special example is the earth solar system which can generate cycles from daily periods to orbital variations of thousands and millions of years orbital variations are known as milankovitch cycles and they are the subject of cyclostratigraphy proper the recognition of milankovitch cycles or of any other cycle associated with oscillating systems rests on the regularity or time periodicity of such patterns the correct ways of analysing such cycles are the methods of time series analysis repetition patterns representing time intervals of millions and possibly many hundreds of millions of years are known from sequence stratigraphy we know as yet very little about the mechanisms which generate such long periods of repetition it has been suggested that the earth s crust has reached a state of self organized criticality bak p 1996 how nature works springer new york 212 pp in which case sequence formation could be part of the complexity which undoubtedly is an attribute of the earth s crust and history

the milankovitch fingerprint on the distribution and thickness of bedding parallel veins beef in source rocks bed parallel mineralized fractures are common in source rocks and generally consist in mm to cm thick veins developed parallel to bedding known as beef or bedding parallel veins considering they can form a dense network of mechanical discontinuities the prediction of beef distribution is a major issue impacting shale reservoir production beef distribution is predominantly controlled by the lithological characteristics of source rocks and we here decipher the relation between mineralogical and chemical proxies controlled by orbital parameters and distribution of the beef along a late jurassic section of the well known vaca muerta formation source rock in the neuquen basin using multiple proxies collected along the beef rich huncal section we show that milankovitch cycles rule the mineralogical evolution and beef distribution in these organic rich mudrocks cycles inferred from the statistical treatment of sedimentary magnetic susceptibility elemental and mineralogical ratios biogenic total organic carbon and diagenetic beef distribution and thickness signals revealed indeed the influence of an astroclimatic fingerprint in sediments and on processes controlling mineralized fracture generation and distribution the astroclimatic memory recorded in many source rocks worldwide is therefore envisaged as a suitable proxy for the prediction of mineralized fracture distribution

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

calibrating the late ordovician glaciation and mass extinction by the eccentricity cycles of earth s orbit a process based sedimentological analysis of upper ordovician glacial marine rocks in africa suggests that full glaciation of the continental shelf started in the late extraordinarius zone of the hirnantian two cycles of ice sheet growth are represented during full glaciation initial terrestrial ice sheet growth in the early extraordinarius zone influenced the first event of the late ordovician mass extinction retreat of the ice sheet from the shelf ended by the persculptus zone when the second event of the late ordovician mass extinction began eccentricity controlled ice sheet growth is assumed periodicity 0 1 m y hence two cycles of full glaciation lasted 0 2 m y the duration of the extraordinarius zone is estimated as 0 5 m y therefore the minimum duration of the first extinction event was 0 3 m y

lower cretaceous calcareous nannoplankton from the neuquen basin argentina abstract we present nannofossil analyses from five new sections of the neuquen basin which together provide a relatively continuous stratigraphic succession ranging from tithonian to hauterivian vaca muerta to agrio formations the sections provide an opportunity to study nannofossils from a relatively little studied area which nevertheless represents an important marginal basin and a relict of the single largest mesozoic marine habitat the pacific ocean our aims were firstly to generate biostratigraphic data in order to test existing ammonite based age models and ultimately to improve stratigraphic correlations between the argentinian sections and global chronostratigraphic standards and secondly to collect palaeogeographic information in order to improve our understanding of mesozoic nannoplankton distributions and ecology the sections yielded a continuous nannofossil succession with assemblages of moderate preservation abundance and diversity although many standard biostratigraphic index species of both boreal and tethyan affinities were absent we were able to use age diagnostic taxa to provide a relatively robust stratigraphic framework the first and last occurrences of clepsilithus maculosus cruciellipsis cuvillieri eiffellithus primus eiffellithus windii eiffellithus striatus lithraphidites bollii and nannoconus ligius throughout the sections there is remarkably good agreement between the correlation suggested by the nannofossils based largely on globally distributed species and ammonites which are largely endemic to the basin the vaca muerta and upper agrio member correlations are identical or within one or two ammonite zones the lower agrio member correlations are similarly close but the occurrence of wide canalled nannoconids suggests slightly younger latest valanginian to early hauterivian ages for much of the member the neuquen nannofossil assemblages are rather low in diversity and suggest that the basin supported a restricted nannoflora dominated by shelf adapted taxa watznaueria micrantholithus nannoconus biogeographically distinctive taxa whether tethyan or boreal austral are limited to a few rare and sporadically distributed examples but two new species of crucibiscutum may prove to be austral in affinity the presence of nannoconids consistently from the late valanginian indicates the presence of a good shallow marine connection with tethys via the hispanic corridor seaway but their low abundance and rather sporadic occurrence suggests they were probably at the limits of their ecological ranges four new nannofossil species are described crucibiscutum trilensis crucibiscutum neuquenensis calculites suturus and nannoconus quadricanalis

astronomical frequencies for pre quaternary palaeoclimate studies the sensitivity of the earth s orbital frequencies involved in the astronomical theory of palaeoclimates to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth has been investigated for the last billion years the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for the obliquity and the precession a shortening which is larger for the longer periods these periods of precession and obliquity influenced by the changing earth moon distance length of the day and dynamical ellipticity of the earth have been recomputed for the last 440 million years

upper jurassic lower cretaceous depositional environments and evolution of the bilecik sakarya zone and tauride carbonate platforms turkey abstract three late jurassic early cretaceous carbonate platform stratigraphic sections have been studied in central western turkey bilecik carbonate platform at bilecik and saricakaya and in the taurides in southern turkey tauride carbonate platform at beysehir by using sedimentological and cyclostratigraphical methods one section was analyzed by detailed magnetic susceptibility measurements peritidal carbonates on both platforms display cyclic patterns throughout the sections and do not contain any siliciclastic material this cyclicity is generally expressed as shallowing upward cycles and interpreted as records of short term sea level changes magnetic susceptibility ms analysis revealed that small scale changes in the ms values can be followed by cyclic alternation of facies and may indicate that varying detrital input during wet and dry climate alternation can be one of the controlling factors for short term sea level changes the large scale ms evolution records an increase just around the jurassic cretaceous boundary interval and a decrease above the boundary this curve pattern can be correlated with some european ms sections and seems to indicate a consistent ms pattern around this critical interval consequently this study implies that sea level variations on studied shallow carbonate platforms were on the order of few meters pelagic equivalents of these sea level records can be traced along the margins short term climatic control can be seen as one of the controlling factors for small scale sea level changes the large scale changes can be associated with oceanographic climatic third order sea level changes and the influence of regional tectonics

tidal rhythmites in a deep sea environment an example from mio pliocene misaki formation miura peninsula japan abstract the mio pliocene misaki formation miura peninsula japan is characterized by alternation of mafic scoriaceous pebbly sandstone pumiceous sandstone and siltstone and mudstone formed in a fore arc basin in an arc arc collisional zone the qualitative as well as quantitative evidences of tide during the misaki sedimentation in the jogashima area miura peninsula are presented here the lunar synodic period of 28 days lunar month extracted from the misaki tidal rhythmite agrees well with the published miocene tidal rhythmite data the couplet series of the misaki tidal rhythmite however is often interrupted by downslope resedimentation via turbidity currents intense penecontemporaneous deformation and bioturbation association of deep sea turbidites mass flow deposits and tidal rhythmite suggest misaki sedimentation in the miura peninsula took place in a submarine canyon setting

deep sea submersible survey in the suruga sagami and japan trenches preliminary results of the 1985 kaiko cruise leg 2 abstract nine submersible dives were made in three trenches off central japan between 2990 and 5900 m of water depth our observations confirm the interpretation that daiichi kashima seamount is a cretaceous guyot formed on the pacific plate that has traveled into the japan trench we also confirmed the previous interpretation of a large normal fault that splits the seamount in two halves the lower one being now subducting beneath the japan margin compressional deformation was identified within the lower part of the inner slope in front of the seamount the pattern of deformation that affects quaternary sediments is in agreement with the present kinematics of the convergence between the pacific plate and japan deep water 5700 m clam colonies are associated with advection of fluids driven by the subduction related overpressures in the northern slope of the boso canyon along the sagami trough system philippine sea plate japan boundary the deformation affecting a thick upper miocene to lower pliocene sequence indicates two directions of shortening a n175 e direction which is consistent with the present relative motion along the sagami trough n285 n300 e and a n30 e direction which could be related to a more northerly direction of convergence that occured during the early quaternary and earlier

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

geohazards in coastal areas near the northernmost sagami trough central japan review of neotectonic activity in onshore and offshore areas of the izu island arc collision subduction zone

stacking pattern of cyclic carbonate platform strata lower cretaceous of southern apennines italy detailed sedimentological analysis of aptian albian shallow water carbonate platform strata from monte faito southern italy reveal composite sea level change the organization of the lithofacies and their related diagenetic overprint have allowed the identification of 50 elementary cycles they often show exposure related diagenetic features superimposed on subtidal deposits suggesting drops of relative sea level elementary cycles are grouped into 16 bundles forming six superbundles the hierarchical organization of the cycles are interpreted to be related to composite eustatic sea level fluctuations driven by the earth s orbital perturbation in the milankovitch frequency band moreover the systematic variation of superbundle thickness and the general evolution of the lithofacies reflects variations of accommodation potential defining longer term environmental changes different lithofacies forming elementary cycles are frequently separated by bedding planes that when viewed in a sequence stratigraphic context are interpreted as transgressive surfaces maximum flooding surfaces or sequence boundaries this allows the recognition of lowstand transgressive and highstand deposits in the cyclic units considering both the bundle superbundle ratio and the sequence stratigraphic interpretation of the superbundles a chronostratigraphic diagram illustrating both gaps at bundle level and their expected location along the section was created it establishes that the section developed over about 2 4 ma

new constraints on the jurassic cretaceous boundary in the high andes using high precision u pb data abstract the jurassic cretaceous j k boundary is poorly constrained and is the only phanerozoic system boundary that lacks an internationally accepted reference stratigraphic section gssp precise radio isotopic u pb data are unavailable for the earliest stage of the cretaceous the berriasian the age of the jurassic cretaceous boundary was based on several assumptions including the relative duration of ammonite zones the constant spreading rates of magnetic anomalies and the extrapolation of rb sr or k ar isotopic data this paper discusses a site in an andean basin of western gondwana showing the j k boundary interval with geographically widespread nannofossil markers which are here uniquely combined with precise radiometric dates the recent finding of a sequence of marine black shales in the high andes of argentina interbedded with ash fall tuffs provides important constraints on this boundary this succession bears calcareous nannofossils and ammonites which allow correlation with well established tethyan floras and faunas in the northern hemisphere the tithonian berriasian transition in the andes was recognized on the basis of ammonite zones and nannofossil bioevents for the first time in the southern hemisphere the new ages obtained are 137 9 0 9 ma by sensitive high resolution ion microprobe shrimp and 139 55 0 09 0 18 ma by chemical abrasion isotope dilution thermal ionization mass spectrometry tims near the base of the berriasian these new ages can be interpreted in two different ways the first alternative would indicate that the present geological time table is correct and the fossil levels should be late berriasian the second alternative is that the j k boundary is 5 ma younger than the recently published geological time scale the authors support the last alternative and propose that the j k boundary should be close to 140 ma

chemostratigraphy of the ordovician sarah formation north west saudi arabia an integrated approach to reservoir correlation abstract late ordovician pre glacial and syn glacial deposits form economically important hydrocarbon reservoirs throughout north africa and the arabian peninsula internal subdivision of the unit is difficult due to the short time span of deposition resulting in coarse biostratigraphic control the arenaceous character of the sediments has also contributed to poor biostratigraphic recovery the present study focuses on the chemostratigraphic correlation of this interval encountered in ten wells across a complex multi phased pro glacial outwash fan dominated by hyperpycnal jet efflux turbidites fed by glacial outburst floods the high resolution reservoir layering scheme presented here utilizes detailed sedimentological core descriptions borehole image derived palaeoflow indicators 3d seismic attributes and chemostratigraphy the inductively coupled plasma optical emission spectrometry icp oes and inductively coupled plasma mass spectrometry icp ms techniques were used to acquire data for 50 elements with the chemostratigraphic scheme based on changes in the following key element ratios zr y zr lu th nb th p ta p cr p p lu th ti cr yb and th ta g may give the impression that there are two principal aims are defined by distinct values of key element ratios with variations in these mainly reflecting changes in source provenance in order to avoid complications relating to changes in grain size lithology separate schemes were proposed for sandstone and mudrock lithologies with the former comprising a hierarchical order of two zones three subzones and seven divisions owing to the lower number of analyzed mudrocks the scheme produced for this dataset is less detailed but nevertheless consists of three principal zones and five subzones at the formation level chemical stratigraphy allowed for consistent identification and correlation of the pre glacial qasim syn glacial sarah and post glacial qalibah formations the earliest post glacial unit referred to as the uqlah formation has an inherited signature from the syn glacial chemozone i e uppermost sarah formation below and represents initial reworking of the post glacial landscape following isostatic rebound evidence for glacial isostasy is recorded in a regional deformed zone at the top of the sarah formation and immediately beneath an isostatic rebound unconformity at the base of the uqlah formation chemical zonation of this unit clearly illustrates significant local truncation in wells located close to nw se trending lineaments it is proposed that chemozones are missing across reactivated fault block highs as a result of increased erosion on the shallow marine post glacial shelf high resolution reservoir layering of the hydrocarbon bearing syn glacial sarah formation highlights a complex depositional system characterized by an initial phase of deeply entrenched pro glacial turbidite channels and younger sheet like depositional lobes cores and image logs from both elements of the outwash fan system record extensive climbing dune cross bedding an unusual sedimentary structure described from many upper ordovician glacial successions in north africa and considered indicative of quasi steady sediment charged flows initiated by glacial outburst floods there is no shared chemical link between the lowest channels and overlying lobes suggesting a large fan system may be found downdip of this deeper channel system integration of the zonation scheme with 3d seismic attribute analysis clearly illustrates a second and even third phase of small channels cross cutting the lower larger vintage that fed the sheet like younger lobe system this is substantiated by a shared chemical signature and provenance between these small channels and their attached lobes

completing the neogene geological time scale between 8 5 and 12 5 ma a much improved high resolution magnetostratigraphy is presented for the interval between 8 5 and 12 5 ma in the deep marine astronomically tuned monte dei corvi beach section in northern italy this section contains the formally designated boundary between the middle and upper miocene defined by the tortonian gssp the natural remanent magnetization is carried by an unusual low temperature component of primary origin according to interpretations of isothermal remanent magnetization irm acquisition curves the palaeomagnetic signal is most probably carried by iron sulphides such as greigite or pyrrhotite the resultant magnetostratigraphy is reliable and can be straightforwardly calibrated to the astronomically tuned neogene time scale atnts2004 showing that the section ranges from chron c5an 2n up to c4 2r 1 the inferred correlation of the tortonian gssp to the older part of chron c5r 2n is confirmed thereby guaranteeing global correlation potential in addition the monte dei corvi beach section has been re tuned to the new numerical solution la2004 for the interval between 8 5 and 12 9 ma this exercise shows that the characteristic cycle patterns are not consistent with a single solution with fixed values for dynamical ellipticity and tidal dissipation for the younger part of the section sedimentary cycles show an excellent fit with intricate details of precession obliquity interference in the nominal la2004 1 1 solution however this solution produces serious mismatches between the sedimentary cycles and the precession obliquity interference in the interval older than 10 2 ma for this interval changes in tidal dissipation value while keeping dynamical ellipticity constant at its present day value are necessary to maintain a perfect fit a detailed visual comparison reveals a very good to excellent fit with la2004 1 1 2 and to lesser extent with la2004 1 0 5 however la2004 1 1 2 is the preferred tuning target for the moment in the interval older than 10 2 ma the astronomical re tuning on precessional scale to la2004 1 1 yielded slightly different astronomical ages for each basic cycle and hence also for the calcareous plankton events and magnetic reversal boundaries with uncertainties ranging within a few thousand years the age of the tortonian gssp turns into 11 625 ma instead of the previously published 11 608 ma our ages should replace existing ages in the astronomically tuned neogene time scale atnts2004

the cyclic hierarchy of the purbeckian sierra del pozo section lower cretaceous berriasian southern spain the lowermost cretaceous berriasian sierra del pozo formation is divisible into metre scale cycles that are bundled in a four tiered hierarchy of cycles and cyclic sequences at the smallest scale sixth order cycles thought to be the product of precessionally forced sea level fluctuations c 20 ka average less than a metre in thickness shallow upward and are bounded by surfaces where deeper facies abruptly overlie shallower facies bundles of sixth order cycles called fifth order sequences are recognized by two types of asymmetric patterns in facies distribution first more pronounced facies changes occur at sixth order cycle boundaries lower in a sequence whereas smaller facies changes occur at cycle boundaries higher in a sequence secondly subtidal marine limestones i e biomicrites and biosparites are the dominant facies lower in a cyclic sequence whereas more restricted or shallower water facies i e mud cracked microbial laminites dolomites shale and clay are more predominant higher in a cyclic sequence the bundling of sixth order cycles is explained as a product of periodic change 100 ka in the eccentricity of the earth s orbit the degree of orbital eccentricity modulates the magnitude of precessional sea level fluctuations which in turn determine the relative facies contrasts at sixth order cycle boundaries larger scale fourth and third order sequences are defined by similar patterns in facies contrast at successive sequence boundaries and by a change in predominant facies type from bottom to top these patterns are explained as the product of 400 ka and 2 ma periodic variations in the eccentricity of the earth s orbit in summary the strength of the precessional signal varies in consort with periodic changes in orbital eccentricity at three time scales producing a stacked hierarchy of cycles and sequences of cycles change in obliquity of the earth s axis may modulate the effects of the precessional signal and thereby modify patterns of preserved cyclic structure this interpretation of cyclicity in the sierra del pozo section is markedly different from that of

depositional cycles composite sea level changes cycle stacking patterns and the hierarchy of stratigraphic forcing examples from alpine triassic platform carbonates carbonate platform deposits record a complex interplay of numerous geodynamic variables of which eustasy subsidence and sediment accumulation are prime factors in determining both the kilometer scale depositional sequence scale and meter scale depositional cycle scale stratigraphic packaging in this study we looked particularly at composite eustasy that is superimposed sea level fluctuations with different frequencies defined as orders and different amplitudes and the role it plays in the linkage between meter scale cyclic stratigraphy and kilometer scale sequence stratigraphy specifically we have investigated the relationship between low frequency third order 1 10 m y period depositional cycles and their component high frequency fourth 0 1 1 m y and fifth 0 01 0 1 m y order cycles through detailed stratigraphic analyses of alpine triassic platforms complemented by computer modeling on the basis of our results we suggest that in general there exists a hierarchy of stratigraphic forcing driven by composite eustasy that results in organized stacking patterns thickness subfacies character early diagenetic attributes of high frequency typically fourth and fifth order shallow water carbonate cycles dictated by low frequency third order relative sea level effects we suggest that systematic vertical changes in stacking patterns of high frequency cycles across a larger depositional sequence are due to systematic and predictable differences in depositional space available during the rising and falling stages of a relative third order sea level change we also suggest that these systematic variations in cycle stacking patterns will exist regardless of the mechanism responsible for generating the high frequency cycles be it an autocyclic or allocyclic mechanism this approach has major implications for the use of high frequency fourth and fifth order cycle characteristics to identify third order cycles in outcrops and cores of shallow water carbonates where stratigraphic control may be less than desirable this would constitute a valuable bridge between cyclic stratigraphy at the meter scale and sequence stratigraphy at the seismic scale we present two examples from triassic buildups of the alps the ladinian latemar buildup and the norian dolomia principale where a systematic succession of high frequency cycle stacking patterns and early diagenetic features exists within an overriding third order cycle sequence reflecting the interplay of short term high frequency fourth fifth order eustasy and long term low frequency third order eustasy in accordance with the hierarchy of stratigraphic forcing central to the interpretation of these examples is the demonstration that true eustatic rhythms are recorded in the high frequency cyclicity as verified by time series analyses and the use of fischer plots these examples can be modeled by computer under conditions of lag depth constrained sedimentation uniform subsidence and composite eustasy we also present two examples one from the alpine triassic the norian lofer cyclothems and one from the pleistocene of south florida that lack both a systematic succession of high frequency cycle stacking patterns and identifiable composite rhythms in the stratigraphic record despite the existence of composite high frequency eustasy in these examples we call upon 1 local tectonic forcing in the form of short term deviations in subsidence via faulting lofer example and 2 large differences in the relative amplitudes of different orders of high frequency sea level oscillations pleistocene example to explain the lack of composite rhythms and we present computer simulations to illustrate the concepts an understanding of composite relative sea level changes and the potential for a hierarchy of stratigraphic forcing provides the link between cyclostratigraphy and sequence stratigraphy and also has important implications regarding the stratigraphy of early diagenesis

sedimentology and sequence stratigraphy of a tithonian valanginian carbonate ramp vaca muerta formation a misunderstood exceptional source rock in the southern mendoza area of the neuquen basin argentina abstract the vaca muerta formation early tithonian early valanginian is a rhythmic succession of marls and limestones cropping out in the neuquen basin west central argentina this lithostratigraphic unit was traditionally interpreted as basinal to slope deposits detailed facies analysis allows to differentiate seven facies associations representing basinal to middle ramp facies of a homoclinal ramp system prograding westward from the eastern margin and slope facies attributed to a distally steepened ramp system that progrades eastward from the andean volcanic arc in the west two sequence hierarchies are recognized five third order depositional sequences and fifteen fourth order high frequency sequences fluctuations in organic matter content within the vaca muerta formation suggest relationship with depositional sequences finding the highest values associated with transgressive system tracts this work represents an important advance in the understanding of the sedimentary and stratigraphic evolution of this exceptional unconventional reservoir our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter facies and sea level changes

earthquake source fault beneath tokyo devastating earthquakes occur on a megathrust fault that underlies the tokyo metropolitan region we identify this fault with use of deep seismic reflection profiling to be the upper surface of the philippine sea plate the depth to the top of this plate 4 to 26 kilometers is much shallower than previous estimates based on the distribution of seismicity this shallower plate geometry changes the location of maximum finite slip of the 1923 kanto earthquake and will affect estimations of strong ground motion for seismic hazards analysis within the tokyo region

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

oblique and near collision subduction sagami and suruga troughs preliminary results of the french japanese 1984 kaiko cruise leg 2 abstract leg 2 of the french japanese 1984 kaiko cruise has surveyed the suruga and the sagami troughs which lie on both sides of the northwestward moving and colliding izu bonin ridge the northernmost part of the philippine sea plate the transition from the nankai trough to the suruga trough is characterized by northward decrease in width of the accretionary prism in good agreement with the increasing obliquity between the through axis and the direction of the convergence as the strike of the convergent boundary changes from ene nne to south north south of the area the southern margin of the zenisu ridge shows contractional deformations this supports the interpretation made by the team of leg 1 who studied the western extension of the area we studied that it is an intra oceanic thrusting of the ridge over the shikoku basin in the sagami trough where the relative motion is highly oblique to the plate boundary active subduction is mostly confined in the east west trending portions of the trough located south of the boso peninsula and along the lower boso canyon near the ttt triple junction in between the present motion is mainly right lateral along the northwest trending boso escarpment however an inactive but recent pliocene to lower pleistocene accretionary prism exists south of the boso escarpment which suggests that the relative motion was more northerly than at present before about 1 ma ago

an assessment of the suitability of individual rhythmic carbonate successions for astrochronological application abstract a manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high resolution stratigraphic applications and orbital dating while the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy caution is required to carefully choose suitable rhythmites for the analysis diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites to keep orbital dating a reliable method the choice of sedimentary successions has to be undertaken with utmost scrutiny here we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites the goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions

collision of the izu arc with honshu and the effects of oblique subduction in the miura boso peninsulas abstract collision of the izu arc in central japan is discussed with a focus on its tectonic effects to the east of the arc in the miura boso peninsulas of honshu the tectonics are the combination of the following events philippine sea plate spreading in the late oligocene to early miocene opening of the sea of japan in the middle miocene obduction of ophiolitic rocks in the northeasternmost corner of the philippine sea plate and forearc sedimentation between the honshu and izu arcs oblique subduction has shifted the plate boundary from northeast to southwest from the present mineoka tectonic belt through the miura fold belt to the sagami trough since the miocene remarkable right lateral transpressional deformation occurred throughout this period of the oblique collision and subduction

earthquake induced soft sediment deformation structures in upper jurassic open marine microbialites neuquen basin argentina penecontemporaneous decimetre scale soft sediment deformation structures are reported from the basal part of the upper jurassic lower cretaceous vaca muerta formation in the malargue las lenas area of the back arc neuquen basin mendoza province central andes the deformed interval amarillas bed is only 0 3 to 0 9 m thick but occurs in a wide area larger than 1500 km2 its age determined by ammonite biostratigraphy is early tithonian the soft sediment deformation structures were generated in finely laminated partially consolidated organicrich carbonate microbialites that were deposited in open marine poorly oxygenated settings apparently devoid of any significant slope those structures include boudins of different sizes and complexity a variety of folds normal listric dm scale faults sub horizontal detachment surfaces and other features which are part of several larger scale complex slump structures deformation was dominantly plastic but near to the ductile brittle field transition on the basis of the observed soft deformation structures their geographic distribution their lateral homogeneity and the geodynamic framework of the basin in which it was generated the amarillas bed can be tentatively attributed to a large intermediate depth earthquake that occurred within the plate that subducted beneath the andean continental margin and the neuquen back arc basin

proximal distal facies relationships and sedimentary processes in a storm dominated carbonate ramp kimmeridgian northwest of the iberian ranges spain abstract facies analysis of the upper kimmeridgian rocks in the outcrops located near ricla zaragoza province northeast spain and the integration of the resultant data in a broader context the northern part of the iberian basin has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the kimmeridgian carbonate ramp using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail model 1 corresponds to the development of a mixed carbonate siliciclastic ramp during a slow rise and stillstand of sea level sequence 1 hst whereas model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level sequence 2 tst carbonate production was higher in the shallow ramp domains coral reefs and oolitic shoals in model 1 and reefs in model 2 than in deeper domains where there is no indication of significant pelagic or benthic production the activity of unidirectional return flows induced by winter storms and hurricanes played an important role in the redistribution of the sediment across the ramp generating different coarse grained deposits in the inner and mid ramp settings dunes lower scale bedforms and tempestites occur in model 1 and storm lobes bars and tempestites in model 2 moreover a significant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents stillstand of sea level in model 1 involved a rapid progradation of the inner and proximal mid ramp carbonate and siliciclastic facies the rapid relative sea level rise of model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep ramp domains the presence of relatively thick sections in the outer ramp settings instead of condensed sections as observed in model 1 during times of sea level rise model 2 can mainly be explained by the increase of the shallow production in the reef dominated areas

seismic evidence for active underplating below the megathrust earthquake zone in japan determining the structure of subduction zones is important for understanding mechanisms for the generation of interplate phenomena such as megathrust earthquakes the peeling off of the uppermost part of a subducting slab and accretion to the bottom of an overlying plate underplating at deep regions has been inferred from exhumed metamorphic rocks and deep seismic imaging but direct seismic evidence of this process is lacking by comparing seismic reflection profiles with microearthquake distributions in central japan we show that repeating microearthquakes occur along the bottom interface of the layer peeling off from the subducting philippine sea plate this region coincides with the location of slow slip events that may serve as signals for monitoring active underplating

the vaca muerta quintuco system tithonian valanginian in the neuquen basin argentina a view from the outcrops in the chos malal fold and thrust belt the vaca muerta quintuco system uppermost lower tithonian lower valanginian is a thick shallowing upward sedimentary cycle consisting of dark bituminous shales marlstones limestones and sandstones cropping out in the neuquen basin west central argentina this paper analyzes three outcrop sections in chos malal area northem neuquen province detailed facies analysis allows us to differentiate six facies associations representing basinal to proximal outer ramp facies of a homoclinal carbonate ramp system vaca muerta formation and basinal to shoreface facies of a mixed carbonate siliciclastic shelf system quintuco formation prograding westward from the eastern margin of the basin two sequence hierarchies were recognized 5 composite depositional sequences third order and 15 high frequency sequences fourth order fluctuations in organic matter content within the vaca muerta formation suggest a relationship with depositional sequences finding the highest values associated with transgressive systems tract whereas the transition to the quintuco formation shows a strong decrease in total organic carbon the x ray diffraction studies show an increase of clay minerals and quartz in the transgressive systems tract of the vaca muerta formation and an increase in the content of calcite in highstand systems tracts this pattern is reversed in the quintuco formation our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter clay minerals facies stacking pattern and relative sea level changes in this exceptional shale oil and shale gas unconventional reservoir this study may be helpful for a better postulate of petrophysical and geomechanical models for unconventional exploration

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

unit stratotypes for global stages the neogene perspective abstract recent developments in integrated high resolution stratigraphy and astronomical tuning of continuous deep marine successions invalidate arguments against the designation of unit stratotypes for global stages the basic building blocks of the standard global chronostratigraphic scale gcs for the late neogene global stratotype section and point gssp sections may also serve as unit stratotypes covering the interval from the base of a stage up to the level that time stratigraphically correlates with the base of the next younger stage in a continuous and well tuned deep marine succession the added value of such sections as unit stratotype lies in the integrated high resolution stratigraphy and astronomical tuning which combined provides an excellent age control with an unprecedented resolution precision and accuracy within the entire stage as such they form the backbone of the new integrated late neogene time scale and provide the basis for reconstructing earth s history in this way a stage is also defined by its content and not only by its boundaries our unit stratotype concept strengthens the importance of time rock units by allowing the introduction of astronomically defined chronozones as formal chronostratigraphic units thereby arguing against the elimination of the dual classification of chronostratigraphy and geochronology extending this concept to older time intervals requires that well tuned continuous deep marine sections are employed thus necessitating the employment of multiple hole i odp sites for defining remaining stages and stage boundaries in at least the cenozoic and cretaceous and possibly the entire mesozoic evidently the construction of the geological time scale including the gcs should be based on the most appropriate sections available while where possible taking the historical concept of global stages into account

architecture of late ordovician glacial valleys in the tassili n ajjer area algeria abstract the architecture of three late ordovician glacial valleys was studied in detail in the tassili n ajjer se algeria outcrops the valleys are oriented south north 2 to 5 km wide and up to 250 m deep the valley fills revealed a very complex sedimentary architecture with significant lateral facies changes several glacial cycles induced the formation of glacial erosion surfaces ges at the base and within the glacial valleys the first type of ges shows a sharp and steep angled contact without striations or associated syn sedimentary deformation suggesting that subglacial meltwater was the dominant erosive agent a second type associated with the deformation of pre glacial and syn glacial sediment suggests that ice was in contact with the valley floor four facies associations are proposed fa1 subglacial tillite fa2 sub to pro glacial ice contact fans fa3 proglacial sub aqueous gravity flows and fa4 outwash fans the stratigraphic architecture of three of the main valleys reveals a complex polyphase infill at least two main cycles of ice sheet advance and retreat can be interpreted from the sedimentary succession of each valley minor glacial cycles by ice oscillations also occur locally ges morphology and the facies sequence suggest that the iherir valleys were initiated by meltwater erosion in subglacial channels whereas the dider and ouarsissen valleys were part of a large ice stream pathway above the valley fill and the interfluves a sand rich unit of stacked lobes and channels is interpreted as submarine outwash fans deposited during final ice retreat a glacial sequence found between two ges comprises fluvio glacial or ice contact fan deposits fluvio glacial eskers and tills these sediments were deposited subglacially or at the glacier front during the ice maximum phase and or the early ice retreat phase during the ice retreat interbedded subaqueous gravity flow deposits and diamictites filled the glacially cut topography as the sea invaded the valleys maximum ice retreat was associated with high water fluxes and sediment discharge causing a sand dominated outwash fan to prograde out over the valleys and interfluves this outwash fan was supplied mainly by flood activity at the ice front involving high density sustained flows the dominant facies consists of giant aggrading climbing dunes filling channels or constructing sandy lobes downstream

structure and development of the sagami trough and the boso triple junction abstract the sagami trough is located at the particular plate margin where the izu forearc is subducted underneath the honshu forearc at its southeastern end the world s only known ttt type triple junction boso triple junction has developed several different kinds of basins occur in different segments along the sagami trough and at the triple junction the bathymetric geologic and geophysical data obtained during the kaiko project and from additional studies are summarized together with our onland studies we suggest that the right lateral oblique plate motion formed an eduction margin in the sagami basin while a normal subduction margin and an oblique subduction margin have been formed in the middle sagami trough basin these tectonic phenomena resulted from the long lasting compressional covergence between the philippine sea plate and eurasian plate since the early or middle miocene the north basin on the northeasternmost margin of the philippine sea plate near the boso triple junction has developed as a stretched basin due to the westward motion of the philippine sea plate with respect to the eurasian plate

late ordovician ashgillian glacial deposits in southern jordan the late ordovician ashgillian glacial deposits in southern jordan comprise a lower and upper glacially incised palaeovalley system occupying reactivated basement and pan african fault controlled depressions the lower palaeovalley incised into shoreface sandstones of the pre glacial tubeiliyat formation is filled with thin glaciofluvial sandstones at the base overlain by up to 50 m of shoreface sandstone a prominent glaciated surface near the top of this palaeovalley fill contains intersecting glacial striations aligned e w and nw se the upper palaeovalley fill comprises glaciofluvial and marine sandstones incised into the lower palaeovalley or where this is absent into the tubeiliyat formation southern jordan lay close to the margin of a late ordovician terrestrial ice sheet in northwest saudi arabia characterised by two major ice advances these are correlated with the lower and upper palaeovalleys in southern jordan interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest thus four ice advances are now recorded from the late ordovician glacial record of southern jordan disturbed and deformed green sandstones beneath the upper palaeovalley fill in the jebel ammar area are confined to the margins of the hutayya graben and have been interpreted as structureless glacial loessite or glacial rock flour petrographic and textural analyses of the deformed sandstones their mapped lateral transition into undeformed tubeiliyat marine sandstones away from the fault zone and the presence of similar sedimentary structures to those in the pre glacial marine tubeiliyat formation suggest that they are a locally deformed facies equivalent of the tubeiliyat not part of the younger glacial deposits deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre existing faults previously weakened by epeirogenesis triggering sediment liquefaction and deformation typical of earthquake generated seismites deformation confined to an area of not more than 4 km wide adjacent to the major fault zone implies earthquake magnitudes of at least 6 mo the high authigenic chlorite content of deformed tubeiliyat sandstones compared to undeformed ones is attributed to a post seismic hydrothermal system driven by compactional dewatering and hydrofracturing of the bedrock which acted as a groundwater recharge area supplied by subglacial meltwater from beneath the ice sheet fluid movement along glacial seismotectonically reactivated faults infiltrated the adjacent tubeiliyat sandstones under pressure and elevated geothermal gradient where chlorite was precipitated from solution d 2005 elsevier b v all rights reserved

the late jurassic tithonian a greenhouse phase in the middle jurassic early cretaceous cool mode evidence from the cyclic adriatic platform croatia well exposed mesozoic sections of the bahama like adriatic platform along the dalmatian coast southern croatia reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding late jurassic tithonian shallow platform interior over 750 m thick ca 5 6 myr duration facies within parasequences include dasyclad oncoid mudstone wackestone floatstone and skeletal peloid wackestone packstone shallow lagoon intraclast peloid packstone and grainstone shoal radial ooid grainstone hypersaline shallow subtidal intertidal shoals and ponds lime mudstone restricted lagoon fenestral carbonates and microbial laminites tidal flat parasequences in the overall transgressive lower tithonian sections are 1 4ae5 m thick and dominated by subtidal facies some of which are capped by very shallow water grainstone packstone or restricted lime mudstone laminated tidal caps become common only towards the interior of the platform parasequences in the regressive upper tithonian are dominated by peritidal facies with distinctive basal oolite units and well developed laminate caps maximum water depths of facies within parasequences estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences were generally 4 m and facies show strongly overlapping depth ranges suggesting facies mosaics parasequences were formed by precessional 20 kyr orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles parasequences are arranged in third order sequences that lack significant bounding disconformities and are evident on accommodation fischer plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position modelling suggests that precessional sea level changes were small several metres as were eccentricity sea level changes or precessional sea level changes modulated by eccentricity supporting a global hot greenhouse climate for the late jurassic tithonian within the overall cool mode of the middle jurassic to early cretaceous

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

soft sediment deformation structures in the mio pliocene misaki formation within alternating deep sea clays and volcanic ashes miura peninsula japan abstract the mio pliocene misaki formation of the miura group miura peninsula japan shows an extremely wide variety of soft sediment deformation structures the most common deformation structures are load casts and associated flame structures dish and pillar structures synsedimentary faults multilobated convolutions chaotic deformation structures sedimentary veins and dykes and large scale slides and slump scars the formation which accumulated in a deep sea environment 2000 3000 m is well exposed in and around jogashima it consists of relative thin commonly dm scale alternations of deep marine fine grained sediments and volcanic ejecta that are as a rule coarse grained since the formation represents fore arc deposits of the izu bonin and the honsu arc collision zone it might be expected that tectonic activity also played a role as a trigger of the soft sediment deformation structures that abound in these sediments this is indicated indeed by the abundance of soft sediment deformations over large lateral distances that occur in numerous beds that are sandwiched between undeformed beds on the basis of their characteristics and the geological context these layers can be explained satisfactorily only by assuming deformation triggered by seismicity which must be related to the izu bonin and honsu arc collision the layers thus form deep marine seismites

late ordovician glaciogenic reservoir heterogeneity an example from the murzuq basin libya in north africa late ordovician glaciogenic reservoirs contain large volume of recoverable hydrocarbon reserves but their heterogeneity and internal complexity means they are poorly understood to improve this understanding this paper presents the case study of the murzuq basin sw libya and a synthesis of the stratigraphic architecture of upper ordovician glaciogenic reservoirs the mamuniyat formation within it particular attention is paid to regionally extensive stratigraphic boundaries and the geometry of sandstone units of potential reservoir quality four disconformity bound units are recognised the bounding surfaces of which are flat or of high relief unit 1 the oldest and unit 3 are mud dominated and tend towards non reservoir in contrast units 2 and 4 the youngest are sand dominated have poor to excellent reservoir quality but distinctly different sedimentological architectures across the basin unit 2 comprises transitions from glaciofluvial intertidal sandstones to offshore turbidites and formed exclusively during glacial retreat the occurrence of a significant palaeotopography affected sandbody geometry with glaciofluvial intertidal deposits concentrating in the lee of these palaeohighs or infilling the bottom of tunnel valleys unit 4 is a compound stratigraphic unit recording the effects of glacial retreat and isostatic rebound in deep marine settings turbidite fans were deposited during retreat but in shallow water settings structural reactivation and sediment reworking had a more profound effect on sedimentation sedimentological architectures are variable at this level and include prograding coarse clastic wedges away from a palaeohigh or the infill of half graben basins during isostatic rebound

geochemistry and petrology of a middle tithonian limestone marl rhythmite in the neuquen basin argentina depositional and burial history

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

late ordovician tunnel valleys in southern jordan theupperordovicianglacialrecordofsouthernjordan ammarfm essentiallycon sists of palaeovalley infills and of a subordinate time transgressive fluvial to shallow marine suc cession overstepping both the palaeovalleys and interfluvial areas valley size depth 60 160 m width 1 3 km steep 20 508 margins internal organization and depositional facies point to an origin as tunnel valleys the tunnel valleys are infilled by either fluvioglacial sandstones or fluvio deltaic coarsening upward successions including fine grained clayey sediments re occupation of previous valleys is evident in places at least three generations of tunnel valleys are inferred from cross cutting relationships although they most probably only reflect temporary standstills and minor re advances related to the overall recession following the main glacial advance recorded in saudi arabia petrophysical measurements indicate that higher permeabilities are located in the glacially related strata 1 5 3 darcy in fluvioglacial infills with a somewhat reduced porosity 22 28 relative to the preglacial sandstones owing to a higher clay content probably of diagenetic origin sandstone amalgamation however gives the fluvioglacial sandstones a high reservoir quality

glaciation and deglaciation of the libyan desert the late ordovician record detailed outcrop studies at the flanks of al kufrah basin libya reveal the nature of glacially related sedimentation and post depositional deformation styles produced in association with the late ordovician glaciation during which ice sheets expanded northward over north africa to deposit the mamuniyat formation at the se basin flank jabal azbah the mamuniyat formation is sand dominated and incises interfingering braidplain and shallow marine deposits of the hawaz formation the glacially related sediments include intercalations of mud chip bearing tabular sandstones and intraformational conglomerates which are interpreted as turbidite and debrite facies respectively these record aggradation of an extensive sediment wedge in front of a stable former ice margin an increase in mudstone content northward is accompanied by the occurrence of more evolved turbidites a widespread surface bearing streamlined nw se striking ridges and grooves punctuates this succession the structures on the surface are interpreted to have formed during a regional north westward ice advance above siltstones bearing arthrophycus burrows and orthocone bearing sandstones beneath tidal bars testify to glaciomarine conditions for deposition of the underflow deposits beneath by contrast the northern basin margin jabal az zalmah is appreciably different in recording shallower water paralic sedimentation styles and major glaciotectonic deformation features although facies analysis also reveals northward deepening here a siltstone wedging from 8 to 50 m toward the north was deposited lower delta plain succeeded by climbing ripple cross laminated sandstones up to 60 m in thickness distal through proximal delta mouth bar deposits with occasional diamictite interbeds these rocks are deformed by thrusts and 50 m amplitude fault propagation folds the deformation locally sealed by a diamictite then overlain by conglomeratic lag during ultimate deglaciation integrating observations from both basin margins a model of fluvial dominated delta systems feeding a pulsed debrite and turbidite fan system in a shallow proglacial shelf is proposed

tectonic evolution of the triple junction off central honshu for the past 1 million years seno t ogawa y tokuyama h nishiyama e and taira a 1989 tectonic evolution of the triple junction off central honshu for the past 1 million years in j p cadet and s uyeda editors subduction zones the kaiko project tectonophysics 160 91 116 we discuss several models of the evolution of the trench trench trench triple junction off central honshu during the past 1 m y on the basis of plate kinematics morphology gravity and seismic reflection profile data available for the area the study area is characterized by large basins 7 8 km deep on the inner lower trench slope on the philippine sea side and the deep 9 km izu bonin trench to the east between the basins and the trench there are 6 7 km deep basement highs the triple junction is unstable due to the movement of the philippine sea plate at a velocity of 3 cm yr in wnw direction with respect to eurasia northeast japan subparallel to the strike of the sagami trough generally we can expect the boundary area between the philippine sea and pacific plates to be extended because the pacific plate is unlikely to follow the retreating philippine sea plate due to the obstruction of the southeastern comer of eurasia the above peculiar morphology of the junction area could have resulted from this lack of stability however there are several possible ways to explain the above morphology our gravity model across the trench basement high basin area shows that the basement highs are made of low density materials 1 8 2 g cm3 thus we reject the mantle diapir model which proposes that the basement highs have been formed by diapiric injection of serpentinites between the retreating philippine sea plate and the pacific plate the stretched basin model proposes that the basins have been formed by stretching of the philippine sea plate wedge we estimated the extension to be about 10 km at the largest basin we reconstructed the morphology at 1 ma by moving the philippine sea plate 20 km farther to the east after closing the basins and thus obtained 8 km depth of the 1 ma trench which is similar to that of the present japan trench to the north although this stretched basin model can explain the formation of the basins and the deep trench other models are equally possible for instance the eduction model explains the origin of the basin by the eduction of the philippine sea basement from beneath the basement high while the accretion model explains the basement highs by the accretion of the in bonin trench wedge sediments in both of these models we can reconstruct the 1 ma trench depth as about 8 km similar to that of the stretched basin model the deformation of the basement of the basins constitutes the best criterion to differentiate between these models the multi channel seismic reflection profiles show that the basement of the largest basin is cut by normal faults in particular at its eastern edge this suggests that the stretched basin model is most likely however the upper part of the sediments shows that the basement high to the east has been recently uplifted this uplift is probably due to the recent 0 5 ma start of accretion of the trench wedge sediments beneath this basement high

evidence of precessional and eccentricity orbital cycles in a tithonian source rock the mid outer carbonate ramp of the vaca muerta formation northern neuquen basin argentina basin to mid ramp cyclic facies of the tithonian vaca muerta formation are exposed in the loncoche creek section of the neuquen basin mendoza province argentina this unit is characterized by a decimeter scale rhythmic alternation of marls shales and limestones and extends from the lower tithonian to the upper berriasian cyclostratigraphic studies based on a detailed facies analysis allowed the identification of cyclic patterns with frequencies within the milankovitch band according to biostratigraphic data the dominant cycle in the studied section has a period of 20 k y which correlates with the earth s axis precession element spectral analysis based on a series of compacted and decompacted cycle thickness identified a subordinate frequency of about 90 to 120 k y which we interpret as the modulation of the precessional cycle caused by the earth s orbital eccentricity the strength of the precession signal together with the absence of a well defined cyclicity attributable to the obliquity orbital cycle i e 40 k y is in agreement with previous data from the northern hemisphere

cyclic nature of lamination in the tithonian solnhofen plattenkalk of southern germany and its palaeoclimatic implications in the tithonian solnhofen plattenkalk malm 2 of southern germany layers of purely micritic limestone are rhythmically interbedded with ones of marly micritic limestone it appears that this alternation was formed under control of the tithonian orbital variations the fourier spectral analysis shows that on a decimetric to metric scale the long term cyclicities in the number of laminae per centimetre are in agreement with those found in the bed thickness series varying from 0 7 to 1 3 m cycles the number of laminae of the solnhofen formation ranges from about 5 800 to about 12 800 laminae per main cycle this indicates that under an assumption that the main cycle of the solnhofen formation corresponds to the tithonian precessional one a single lamina represents a multi year time interval particularly in the short term cyclic domain the laminated sequence contains clearly millimetric cycles consisting of about two to three cyclic components it implies that laminae formation may result from the composite effect of two or three distinct climatic processes

fluvial shallow marine glaciofluvial depositional environments of the ordovician system in jordan abstract the ordovician system cropping out in southern and west central jordan consists entirely of a 750 m thick clastic sequence that can be subdivided into six formations the lower disi formation starts conformably above the late cambrian umm ishrin formation according to cruziana furcifera occurring in the upper third of the disi formation an early ordovician age is confirmed the disi formation consisting mainly of downstream accretion da fluvial architectural element was deposited in a proximal braidplain flowing n ne from the southerly located arabian nubian shield towards the tethys seaway the braidplain depositional environment evolved into a braidplain dominated delta through the middle and upper parts of the disi formation and the lower part of the overlying um saham formation the delta was replaced by siliciclastic tidal flats that in turn evolved into an upper to lower shoreface environment through the upper part of the um saham formation the depositional environment attained the maximum bathymetric depth during the deposition of the lower and central parts of the third unit the hiswa formation where offshore graptolite rich mudstone with intercalated hummocky cross stratified tempestites were deposited the tethys seaway regressed back through the upper part of the hiswa formation promoting a resumption of the lower upper shoreface sedimentation oscillation between the lower to upper shoreface depositional environment characterized the entire fourth unit the dubaydib formation as well as the tubeiylliat sandstone member of the fifth unit the mudawwara formation the depositional history of the ordovician sequence was terminated by a glaciofluvial regime that finally was gradually replaced by a shoreface depositional environment throughout the last unit the ammar formation

stratigraphic evidence for the hirnantian latest ordovician glaciation in the zagros mountains iran abstract high latitude hirnantian diamictites dargaz formation and lower silurian kerogenous black shales sarchahan formation are locally exposed in the zagros mountains the glaciogenic dargaz deposits consist of three progradational retrogradational cycles each potentially controlled by the regional advance and retreat of the hirnantian ice sheet glacial incisions of sandstone packages change laterally from simple planar to high relief

milankovitch 41000 year cycles in lithofacies and molluscan content in the tropical middle miocene nyalindung formation jawa indonesia abstract nine cyclothems based on changes in sedimentary facies and molluscan fossil associations are identified in the middle miocene 12 ma lower part of nyalindung formation cijarian river section sukabumi west jawa province indonesia molluscan associations were studied in 75 blocks collected through the succession 47 species of autochthonous molluscs belonging to 38 genera were separated from the blocks five molluscan associations were recognized through comparison of these species with their closest living analogues a sedimentary cycle consists of two conformable lithologic units in ascending order a gravelly shellbed or gravelly conglomeratic sandstone and a muddy fine to medium grained sandstone the exception is the basal cycle which has an intercalation of limestone the systematic change in the molluscan fossil associations within individual cycles indicates that lithological changes correspond to changes in water depth with an amplitude of about 30 m the short time period represented by the section and the thin units many not more than 2 m thick indicates that the main cause of the cyclicity was orbitally induced climate change representing milankovitch scale cycles of 41 000 years this appears to be the first time milankovitch sea level cycles have been reported from the tropical regions of the earth

large scale channel fill structures in late ordovician glacial deposits in mauritania western sahara abstract late ordovician siliciclastic glacial and related deposits on the north gondwana continental shelf comprise striking incised features referred to as large scale channel fill structures these are described from exposures and aerial photographs in two areas adrar and hodh in mauritania the channel fill structures are up to several kilometres in length and several hundred metres wide they are slightly sinuous narrow sandstone bodies deeply incised into the late ordovician glacial drift and the cambro ordovician bedrock palaeogeographical reconstructions indicate that these structures were located in the ice marginal zone they are preferentially oriented parallel to palaeo ice flow directions sedimentary facies analysis reveals three vertically stacked architectural units infilling a u shaped erosional basal unconformity unit 1 is thin and made up of conglomeratic sandstones of various origins comprising debris flows deltaic like progradational foresets and trough cross stratified sands in adrar architectural unit 2 shows sheet like evenly laminated fine to medium grained well sorted sandstones characteristic of a high energy marine environment in contrast in the hodh area unit 2 displays vertically stacked successions of coarse grained sandstones that indicate high discharge sediment laden flows these are interpreted as meltwater sediments in both adrar and hodh architectural unit 3 is made up of gravelly coarse grained trough cross stratified sandstone emplaced in a braided low sinuosity fluvial environment the three stage infilling history and the palaeogeographic location combined with size and shape criteria make it possible to compare the channel fill structures with pleistocene tunnel valleys found in areas of low relief in cool temperate and low arctic zones such features are incised by high pressure subglacial meltwater and later infilled by proglacial to postglacial deposits based on this comparison architectural unit 1 represents subglacial or proglacial outwash high sediment discharge in unit 2 took place in a proglacial environment in the hodh area while an isostatically downwarped shelf was responsible for a marine incursion in the adrar channels and deposits in unit 3 are fluvial postglacial sediments identification of preserved channel fill structures may be useful in reconstructing late ordovician ice sheet dynamics

the palaeo valley infilling glaciogenic sarah formation an example from rahal dhab palaeo valley saudi arabia the sarah formation is a glaciogenic sedimentary unit deposited along the gondwana margin during the latest ordovician ice age and represents a major hydrocarbon reservoir in northern saudi arabia large scale glacial palaeo valleys cut into the qasim formation and were infilled by the sarah formation post glacial transgression in the earliest silurian resulted in the deposition of the qusaiba shale member and associated organic rich basal source rocks which cap the sarah formation infilled palaeo valleys this unique setting makes the sarah formation an important emerging exploration target in saudi arabia this paper focuses on the facies and depositional architecture in seismic scale outcrops of the sarah formation in north western saudi arabia the rahal dhab palaeo valley provides a 100 km long dip oriented cross section which has been covered by 24 vertical sections sedimentary architectural analyses at metre to kilometre scale and by three cored shallow boreholes in the rahal dhab palaeo valley the sarah formation was deposited in a proglacial setting that ranged from marginal marine to offshore pro delta and is made up of three units i sarah sandstone ii sarah shale and iii uqlah the present study shows the relationships between these three units and architectural controls on reservoir quality in this system this paper contributes to the regional understanding of the sarah formation and the new depositional model of the rahal dhab palaeo valley provides an outcrop reservoir analogue for hydrocarbon exploration in adjacent areas this article is protected by copyright all rights reserved

tectonic record of convergence changes in a collision area the boso and miura peninsulas central japan abstract late cenozoic formations in boso and miura have been affected by several tectonic events tectonic analysis enables us to reconstruct six different paleostress types 1 early extension affecting the oligocene early miocene mineoka group 2 and 3 relatively minor compressional and extensional events probably early pliocene in age 4 major nne ssw compression dominating prior to 2 or 3 ma ago and 5 and 6 more recent major nnw sse compression to the west and wnw ese extension to the east both types affecting the pleistocene and prevailing since 1 2 ma ago the counterclockwise change from nne ssw to nnw sse compression is not accurately dated but very likely occurred between 2 and 3 ma ago it is compared to similar evolutions in other areas of the izu collision zone we conclude that it corresponds to a major counterclockwise change in the direction of plate convergence from sse nnw to se nw the relationships between the directions of convergence and the distributions of plio quaternary compressional paleostresses in and around the collision zone are described through a simple analogy for the two stages of plio quaternary collision this counterclockwise change in stress fields and relative motions also described in the taiwan collision zone along the same philippine sea plate eurasia boundary is interpreted as a major event at the scale of the plate the possible significances of the other paleostress types identified in boso are discussed we conclude that tectonic analysis in and along collision boundaries provides a key for understanding kinematic evolution

cyclostratigraphy of an orbitally driven tithonian valanginian carbonate ramp succession southern mendoza argentina implications for the jurassic cretaceous boundary in the neuquen basin we conducted detailed sedimentological sequence stratigraphic and cyclostratigraphic analyses on four sections of the vaca muerta formation this unit is characterized by a decimetre scale rhythmic alternation of marls and limestones it consists of five facies associations which represent basin to middle carbonate ramp deposits the rhythmic vertical organization shows a well ordered hierarchy of cycles where elementary cycles bundles of cycles and superbundles within the milankovitch frequency band are recognized cyclostratigraphic data allowed us to build a floating orbital scale for the lower tithonian lower valanginian interval in the neuquen basin orbital calibration of these sections is consistent with riccardi s biostratigraphic scheme which places the jurassic cretaceous boundary within the substeueroceras koeneni ammonite zone equivalent to durangites spp jacobi grandis and initial occitanica standard zones

the jurassic succession in west central argentina stratal patterns sequences and paleogeographic evolution abstract jurassic rocks in west central argentina are predominantly marine and marginal marine siliciclastics associated with prominent but volumetrically subordinate carbonates and evaporites facies developments were ruled by paleogeographic persistence within the southern infratropical latitude belt within 40 50 s and by siliciclastic derivation from the patagonian hinterland to the southwest minor volcanic and volcaniclastic supply arrived from the west out of a magmatic belt related to circum pacific convergence timing of the main marine flooding events and general correspondence with the high rank stratal packaging recorded in western north america suggest that global eustasy was also a factor in controlling the local stratigraphic record early jurassic sedimentation occurred within a series of semi isolated depocentres linked to fault bounded triassic troughs the sinemurian toarcian deposits record depocentre expansion and coalescence these trends were coeval with progressively more widespread marine invasions from the northwest and west leading to an elongate marine seaway which connected central patagonia with the pacific domain during the aalenian bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment bathonian and early callovian were times when coarse clastics prograded into the basin while the marine embayment shrank as a result of stepwise forced regressions during late callovian to oxfordian globally rising sea level the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance that promoted cratonward onlap and inception of widespread carbonate deposition ooidal coralline carbonate development was terminated after a relatively sudden messinian style event that desiccated a large tract of the andean basin and favored massive precipitation of anhydrite in the course of the kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat salina complex linked to a widespread erg and to an ephemeral drainage system by the tithonian at a period of peak oceanic stand marine connection was reinstated and recorded as the most widespread jurassic transgression across the neuquen aconcagua embayment shelfal deposition consisted of molluscs and ooid dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations like in other prolific petroleum provinces around the world the tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content

channelized sandstone bodies cordons in the tassili n ajjer algeria libya snapshots of a late ordovician proglacial outwash plain

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

trench triple junction off central japan preliminary results of french japanese 1984 kaiko cruise leg 2 abstract leg 2 of the french japanese 1984 kaiko cruise has surveyed the trench triple junction off central japan where the japan izu bonin and sagami trenches intersect the izu bonin trench is deeper than the japan trench and filled by a thick turbiditic series its anomalous depth is explained by the westward retreat of the edge of the northwestward moving philippine sea plate on the contrary to what happens in the japan trench horst and graben structures of the pacific plate obliquely enters the izu bonin trench suggesting that the actual boundary between these two trenches is located to the north of the triple junction the inner wall of the izu bonin trench is characterized in the triple junction area by a series of slope basins whose occurrence is related to the dynamics of this area the northernmost basin is overthrust by the edge of the fore arc area of the northeast japan plate the plate boundary is hardly discernible further east which makes it impossible to locate precisely the triple junction itself these features suggest that large intra plate deformation occurs there due to the interaction of the plates involved in the triple junction and the weak mechanical strength of the wedge shaped margin of the overriding plates

models for the deposition of mesozoic cenozoic fine grained organic carbon rich sediment in the deep sea the widespread occurrence of organic carbon rich strata black shales in certain portions of jurassic cretaceous and cenozoic sequences has been well documented from deep sea drilling project sites in the atlantic and pacific oceans and from sequences now exposed on land originally deposited in the tethyan ocean these ancient black shales usually have been explained by analogy with examples of modern deep sea sediments in which organic matter locally is preserved by 1 increasing the supply of organic matter 2 increasing the rate of sedimentation and or 3 decreasing the oxygen content of the bottom water however detailed examination of many black shales reveals characteristics that cannot be explained by simple local models including their approximate coincidence in time globally their occurrence in a variety of different environments including open oxygenated oceans restricted basins deep and shallow water their interbedding with organic carbonpoor strata which often dominate a so called black shale sequence their deposition by pelagic hemipelagic turbiditic and other processes and the variations in type and amount of organic matter that occur even within the same sequence a more complex model for the origin of black shales therefore appears most appropriate in which the cyclic preservation of organic matter depends on the interplay of the three main variables namely supply of organic matter sedimentation rate and deep water oxygenation each of which varies independently to some extent the variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea level climate and related changes in oceanic circulation an important and often overlooked factor for the supply of organic matter to deep basin sediments is the frequency and magnitude of redepositional processes the interplay of these variables is discussed in relation to the middle cretaceous and cenozoic organic carbon rich strata in particular which show marked differences in the relative importance of the different variables

controls on cyclostratigraphy of lower cretaceous carbonates and evaporites cupido and coahuila platforms northeastern mexico the lower cretaceous cupido barremian aptian and coahuila albian carbonate platforms of northeastern mexico exhibit thick successions of meter scale cycles deposited in three unique paleoenvironmental settings 1 the cupido shelf lagoon is composed of peritidal carbonate cycles deposited in the protected lee of a reef rimmed to barrier shoal margin 2 the restricted coahuila ramp interior consists of cyclic alternations of subtidal evaporites and peritidal carbonates 3 the deep water parts of both the cupido and coahuila platforms are composed of foraminiferal wackestones and lime mudstones interspersed with firmgrounds and hardgrounds in a cyclic arrangement vertical successions of meter scale evaporitic cycles and peritidal cycles exhibit systematic stacking patterns that build into intermediate scale high frequency sequences tens to hundreds of meters thick and large scale composite sequences hundreds of meters thick that can be correlated across the cupido and coahuila platforms these large scale stacking patterns are interpreted to reflect longterm accommodation events and when combined with the scale independent architecture of all genetic units permit the inference that all three meter scale cycle types on the cupido and coahuila platforms are also governed by relative sea level change the composition thickness and number of meter scale cycles within individual high frequency sequences can be highly variable across the cupido and coahuila platforms however even though the overall upward shallowing patterns are evident the lateral complexity of cycle architecture and distribution is interpreted to be a natural response to fluctuations in regional climate interacting with autogenic processes such as variations in carbonate production and dispersal intensity and frequency of tropical storms and monsoons thermohaline circulation patterns and ambient ocean chemistry and temperature these interacting processes created laterally variable physiographic and oceanographic conditions across the cupido and coahuila platforms complicating the sedimentary record generated by the composite sea level signal well documented evidence from barremian cenomanian pelagic cycles throughout the tethyan seaway strongly indicates that milankovitch driven climatic changes operated during the early cretaceous contemporaneous shallow marine cyclicity in several locations suggests that these climatic changes may have had globally widespread effects in an effort to link the shallow water and deep water realms we propose a model whereby milankovitch driven global climatic changes generated low amplitude high frequency eustatic fluctuations through some combination of thermal expansion and contraction of ocean water waxing and waning of small ice caps and alpine glaciers and changes in the storage capacity of aquifers and lakes to produce meter scale cycles across lower cretaceous shallow marine platforms

sequence stratigraphy and bedding rhythms of an outer ramp limestone succession late kimmeridgian northeast spain facies stratal and spectral analyses of an outer ramp lime mudstone succession aguilon north iberian ranges spain are presented in this work the studied succession is late kimmeridgian eudoxus and beckeri zones in age and comprises the transgressive and highstand deposits of a third order depositional sequence a number of higher order sequences bundles and sets of bundles have been identified based on the comparative analysis of the bedding planes the bundles and sets of bundles show a well defined stratal pattern spectral analysis has provided further independent confirmation of the cyclical nature of the bundles and sets of bundles defined from field analysis the bundles have variable thickness from 1 to 2 m and are formed by up to 10 micritic beds they have been related to sea level changes controlled by the orbital precession cycle affecting the shallow productivity area a significant amount of the lime mudstones accumulated in outer ramp settings were derived from resedimentation of the shallow carbonate production areas many of the bundles show a lower interval with a thinning and fining up trend indicating a progressive decrease of the carbonate production and carbonate export during periods of high frequency sea level rise the late transgressive and highstand deposits show sets of bundles groups of five bundles from 5 to 8 m probably related to sea level changes controlled by the short eccentricity cycle the overall thickness and the stacking pattern observed in the sets of bundles are controlled by the long term sea level variation the sets of bundles located in the late transgressive deposits show thinner micritic beds in their lower or middle part the sets of bundles found in the highstand deposits are thinner and show a thickening up and thinning up trend on the studied carbonate ramp during periods of long term sea level rise the overall carbonate production and carbonate export is high although the superposition of the high frequency sea level rises may result in episodic flooding and drowning of the shallow ramp areas during periods of long term early highstand of sea level the overall carbonate production and carbonate export is more reduced but it has maximum peaks during the transgressive and early highstand intervals of the high frequency sea level cycles sedimentation during the long term sea level fall late highstand was scarce and discontinuous in the outer ramp area and resulted in the overall thickness reduction of the sets of bundles d 2003 elsevier science b v all rights reserved

integrated stratigraphy and astronomical tuning of the serravallian and lower tortonian at monte dei corvi middle upper miocene northern italy an integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy and cyclostratigraphy is presented for the serravallian and lower tortonian part middle upper miocene of the monte dei corvi section located in northern italy the detailed biostratigraphic analysis showed that both the discoaster kugleri acme and the first influx of neogloboquadrina acostaensis are recorded at monte dei corvi these events which passed unobserved in previous studies play an important role in delineating the serravallian tortonian boundary thermal and alternating field demagnetization revealed a characteristic low temperature component marked by dual polarities the resultant magnetostratigraphy for the upper part of the section can be unambiguously calibrated to the gpts ranging from c5n 2n up to c4r 2r unfortunately the lower part of the section including the serravallian tortonian boundary interval did not produce a reliable magnetostratigraphy despite the fact that some short reversed intervals and a single normal interval are recorded using sedimentary cycle patterns in combination with the calcareous plankton biostratigraphy the section can be correlated cyclostratigraphically in detail to the partially overlapping and previously tuned section of monte gibliscemi on sicily the monte dei corvi section is dated astronomically by calibrating the basic small scale sedimentary cycles to the precession and 65 n lat summer insolation time series of the la93 solution following an initial tuning of larger scale cycles to eccentricity an almost perfect fit is found between the cycle patterns and intricate details especially precession obliquity interference in the insolation target between 8 5 and 10 ma the tuning to precession remains robust for most intervals back to the base of the section dated at 13 4 ma and shows that the section is continuous apart from a possible short hiatus in the tortonian it provides accurate astronomical ages for all sedimentary cycles calcareous plankton events polarity reversals and ash layers and marks a significant improvement of the recently proposed astronomical calibrations of the monte dei corvi section and of parallel sections in the mediterranean astronomical ages for the ancona and respighi ashbeds are significantly older than previously reported 40 ar 39 ar biotite ages even if the revised older age for the fct san dating standard of 28 02 ma is applied the astronomical dating of the magnetic reversals in the monte dei corvi section results in the completion of the astronomical polarity time scale for the last 13 myr the monte dei corvi section has recently been proposed as the stratotype section for the serravallian tortonian boundary despite the moderate to

magnetic fabric development in the tertiary accretionary complex in the boso and miura peninsulas of central japan it has been demonstrated that the anisotropy of magnetic susceptibility ams is a sensitive indicator for distinguishing various processes that had acted during and after the deposition of sediments recently much attention has been focused on proving its usefulness in distinguishing early deformation signatures in sediments which show no visible grain scale deformation here we present the ams results of the neogene miura group of central japan which was formed by arc arc collision tectonics with subdivisions of two contrasting tectonic provinces the southern province a highly deformed accretionary prism and slope basin and the northern province a gently deformed forearc basin samples were collected from 21 sites in both tectonic settings we obtained from axes orientations three typical fabric domains considered to represent sedimentary tectonically deformed and their intermediate types the shape parameters of ams also revealed distinctions clearly sedimentary fabrics are more foliated and anisotropic deformed fabrics show a more prolate shape and are closer to being isotropic the sedimentary fabrics predominate in the northern forearc basin sequence whereas the intermediate and deformed fabrics occur predominantly in the southern province the general trend of the shape of the magnetic fabric in studied sediments reveals a clear evolution in the pattern of the isotropic tectonic fabric constructed from foliated sedimentary fabric

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations

ordovician proglacial sediments in algeria insights into the controls on hydrocarbon reservoirs in the in amenas field illizi basin abstract ordovician proglacial deposits form gas reservoirs in the in amenas field illizi basin algeria depositional models were developed to understand the context and disposition of the main reservoirs through an evaluation of core and analogous outcrops from the tassili n9ajjer tunnel valleys initially accumulated sandstones with tractional structures subsequent failures of subaqueous grounding line sediment deposited proglacial debrites comprising poorly sorted argillaceous sandstone with granules these were interbedded with high density turbidity sandstones their fine grain size indicates they were dynamically disconnected from the lithologically varied debrites a lobate geometry has been defined for one subsurface composite turbidite periodic catastrophic outflows possibly evacuating subglacial lakes incised the network of subglacial tunnels and in the process delivered sand to the turbidite outwashes bedforms indicate high energy transcritical to supercritical outflows that were stable for extended periods during ice retreat a period of ice margin stability may have occurred due to grounding over the in amenas granitic palaeohighs outwash fan apices were located along this grounding line with feeder channels developing where the substrate was more easily eroded such as between the palaeohighs following further ice retreat deposition evolved to variably sinuous channels and thence to pelagic fines with dropstones