structural evolution of the tuzgolu basin in central anatolia turkey abstract the central anatolian segment of the alpine himalayan orogen contains interior basins the largest of which is the tuzgolu salt lake basin 20 000 km2 it is bounded on the east by the tuzgolu salt lake fault zone and on the west by the yeniceoba and cihanbeyli fault zones structural stratigraphic and sedimentologic evidence suggests that the tuzgolu basin started as a fault controlled basin during late maastrichtian tectonism when the present day northwest trending faults that bound the basin were initiated these faults may have been formed as normal faults suggesting extension or strike slip faults with a normal component of movement indicating a large transtension at the time of their initiation the late maastrichtian faults were reactivated as strike slip faults in response to late eocene compression in the region that produced the central anatolian thrust belt to the north and the late eocene south dipping thrust faults of the ulukisla basin to the south this reactivation is su

melange genesis and ophiolite emplacement related to subduction of the northern margin of the tauride anatolide continent central and western turkey the tauride anatolide continent stretching for c 900 km across western and central turkey is one of the world s best example of a subducted exhumed passive margin within a collisional orogen twelve widely separated areas were studied and correlated to develop a new plate tectonic model a metamorphosed rifted continental margin of triassic lower cretaceous age tauride anatolide platform is overlain by upper cretaceous cenomanian lower maastrichtian pelagic sediments and then by both tectonic melange subduction complexes and sedimentary melange foredeep gravity complexes the melanges are overthrust by unmetamorphosed ophiolitic rocks commonly peridotites with swarms of diabase gabbro dykes and are underlain by metamorphic soles new geochemical evidence from basaltic blocks in the melange indicates predominantly subduction influenced within plate and mid ocean ridge type settings the dykes cutting the ophiolites were probably intruded during early stage intra oceanic arc genesis the metamorphosed continental margin melanges and ophiolites in the north anatolides are correlated with unmetamorphosed equivalents in the taurides further south e g beysehir and lycian nappes oceanic crust of triassic late cretaceous age formed between the gondwana related tauride anatolide continent in the south and the eurasia related sakarya microcontinent in the north following late triassic early cretaceous passive margin subsidence the continental margin was covered by cenomanian turonian pelagic carbonates c 98 90 ma ophiolites formed in an intra oceanic subduction zone setting in response to northward subduction probably within a two stranded ocean with the inner tauride ocean in the se and the izmir ankara erzincan ocean in the north nw metamorphic soles relate to intra oceanic subduction c 95 90 ma oceanic sedimentary igneous rocks accreted to the advancing supra subduction oceanic slab the tauride anatolide continental margin then underwent diachronous collision with the trench c 85 ma deeply subducted and metamorphosed at hp lt c 80 ma accretionary ophiolitic and exhumed hp lt rocks were gravity reworked into a southward migrating flexural foredeep and progressively overridden c 70 63 ma slices of the upper part of the platform and its margin detached and were thrust southwards as the tauride lycian and beysehir nappes together with regional scale ophiolites the continental margin and melange were simultaneously exhumed during maastrichtian early paleocene 70 63 ma and transgressed by shallow water sediments beginning in the late maastrichtian in the east c 64 ma and the mid late paleocene c 60 ma further west remnant oceanic crust was consumed during early cenozoic time followed by mid eocene 45 40 ma diachronous continental collision and a second phase of regional deformation rather than being progressive there were two stages of collision first upper cretaceous ophiolite emplacement driven by continental margin subduction trench collision and secondly eocene collision of the tauride and sakarya eurasian continents

tectono stratigraphy of the orhaniye basin turkey implications for collision chronology and paleogene biogeography of central anatolia abstract located along the izmir ankara erzincan suture iaes the maastrichtian paleogene orhaniye basin has yielded a highly enigmatic yet poorly dated paleogene mammal fauna the endemic character of which has suggested high faunal provincialism associated with paleogeographic isolation of the anatolian landmass during the early cenozoic despite its biogeographic significance the tectono stratigraphic history of the orhaniye basin has been poorly documented here we combine sedimentary magnetostratigraphic and geochronological data to infer the chronology and depositional history of the orhaniye basin we then assess how our new data and interpretations for the orhaniye basin impact 1 the timing and mechanisms of seaway closure along the iaes and 2 the biogeographic evolution of anatolia our results show that the orhaniye basin initially developed as a forearc basin during the maastrichtian before shifting to a retroarc foreland basin setting sometime between the early paleocene and 44 ma this chronology supports a two step scenario for the assemblage of the central anatolian landmass with incipient collision during the paleocene early eocene and final seaway retreat along the iaes during the earliest late eocene after the last marine incursion into the foreland basin our dating for the orhaniye mammal fauna 44 43 ma indicates the persistence of faunal endemism in northern anatolia until at least the late lutetian despite the advanced stage of iaes closure the tectonic evolution of dispersal corridors linking northern anatolia with adjacent parts of eurasia was not directly associated with iaes closure and consecutive uplifts but rather with the build up of continental bridges on the margins of anatolia in the alpine and tibetan himalayan orogens

an example of an accretionary forearc basin from northern central anatolia and its implications for the history of subduction of neo tethys in turkey deformed sedimentary sequences of late cretaceous middle eocene age located between the sakarya continent and the anatolian complex have been interpreted as the fill of a forearc basin the history and structure of this basin are critical for understanding the evolution of the neo tethyan subduction in the middle east i test and elaborate upon this interpretation on the basis of three basic outcrop areas of upper cretaceous lower tertiary sedimentary sequences confined to a northeast southwest trending belt in north west ankara these are the alci kinik and orhaniye areas they expose two different sedimentary sequences called alci and orhaniye in the alci area the sequence starts at the base with the continental red clastic rocks on the erosional surface of an underlying ophiolitic melange and continues upward into the shallow marine reefal buildup of the late maastrichtian age the upper half of the alci sequence is separated from its lower half by a local disconformity and dominated by the continental debris flow deposits composed mostly of volcanic material by contrast both the kinik and orhaniye areas are characterized by a thick continuous and coarsening upward sequence overlying conformably the underlying ophiolitic melange the lower half of the orhaniye sequence is dominated by a deep marine flysch its middle part by continental clastic material and the topmost part by the shallow marine reefal buildup lower contact relationships lithologic composition facies distribution internal structures and the regional tectonic settings of both sequences strongly suggest that the above mentioned three outcrops preserve the remnants of a peripheral accretionary forearc basin forming the north northwestern margin of the haymana polath accretionary forearc basin during middle campanian middle eocene time this peripheral basin is here named orhaniye accretionary forearc basin

secular variation in seawater chemistry during the phanerozoic as indicated by brine inclusions in halite analysis of data on the chemical composition of primary fluid inclusions brine inclusions in primary bedded halite from many evaporite formations of northern pangea shows that during the phanerozoic the chemical composition of marine brines was oscillating significantly between the na k mg ca cl type and the na k mg cl so4 type we regard those changes as corresponding to the chemical evolution of the phanerozoic ocean the changes correlate in time with earlier suggested secular changes in the mineralogies of marine nonskeletal limestones and potash evaporites in addition to those secular changes of seawater chemistry the concentrations of k mg ca and so4 ions in marine brines underwent important changes under the influence of local factors including rock water interaction these secondary changes did not influence the principal chemical type of the brine characteristic for a given time interval in the past concentration of the ca ion did not exceed the present concentration in marine water by a

stable isotope mapping in messinian evaporative carbonates of central sicily mapping stable isotope isolines in both modern and ancient evaporative carbonate formations demonstrates that regional variations of 18 o values exist in the case of the messinian central sicilian basin an ancient evaporite basin the distribution pattern of the 18 o isolines can be related to the paleogeometry and paleohydrology of the basin isolines of equal 13 c values also show large regional variations possibly reflecting the domination of different bacterial processes oxidation sulfate reduction or methanogenesis in different regions the potential application for stable isotope mapping in evaporative carbonate formations deposited in both marine and lacustrine environments lies in its ability to predict the location of depositional centers in ancient evaporite basins

strontium isotope evidence on the history of oilfield brines mediterranean coastal plain israel abstract the isotopic composition of sr in oil field brines from the mediterranean coastal plain was determined in 18 drillholes 13 of which are oil producing wells the brines are characterized by salinities ranging from 35 to 93 g l tds sr from 28 to 350 mg l sr ca molar ratios from 0 011 to 0 053 and 87 sr 86 sr ratios from 0 7075 to 0 7090 e a 0 7081 0 0004 2 the brines are classified into two groups 1 a mavqi im group brines with relatively high 87 sr 86 sr ratios 0 7087 and 0 7090 sampled from elastics dolomites and anhydrites of upper miocene age 2 b heletz group brines with relatively low 87 sr 86 sr ratios 0 7075 to 0 7081 sampled from sandstones and dolomites of lower cretaceous age equations were derived to show the relations between 87 sr 86 sr ratio of the brines and the processes through which they evolved dolomitization and dissolution reprecipitation it is suggested that both groups of brines originated from mediterranean evaporated seawater during the messinian desiccation the strontium isotope composition of the seawater is reflected in that of both groups of brines the mavqi im group containing the original 87 sr 86 sr ratio 0 7088 the heletz group evolved later on through exchange reactions of those primary brines with a carbonate sequence of cretaceous age and consequently new 87 sr 86 sr ratios 0 7078 could have been developed the effect of the dissolution reprecipitation reactions on the carbonate rocks is estimated to be very slight only around 1 by weight

late palaeozoic early cenozoic tectonic development of southern turkey and the easternmost mediterranean region evidence from the inter relations of continental and oceanic units

compaction induced inclination shallowing of the post depositional remanent magnetization in a synthetic sediment summary a synthetic sediment comprised of kaolinite distilled water and either equidimensional or acicular magnetite was given a post depositional remanent magnetization pdrm by being stirred in a magnetic field this sediment was compacted under pressures which varied continuously from 0 to 0 14 mpa in a water tank consolidometer and to higher pressure steps 2 53 mpa in a standard soil consolidometer compaction took place in the same magnetic field in which the sample was given its pdrm the compaction caused shallowing of the sample s magnetic inclination this shallowing was found to be a function of the sample s initial magnetic inclination and the degree of sample compaction tan i 1 aav tan lo where ir is the remanent inclination after compaction av is the volume change i is the initial magnetic inclination and a is an empirically derived constant the data show a maximum inclination shallowing of 12 for an initial inclination of 54 in good agreement with the maximum inclination shallowing predicted by the above equation we propose an electrostatic mechanism to be the cause of the inclination shallowing in this model positively charged magnetite grains adhere to the surface of negatively charged clay grains with their long dimension parallel to the clay grain s surface as the clay grains become reorientated due to compaction the easy axes of magnetization are rotated away from the axis of compression alternating field demagnetization data reveal that our samples have shallower characteristic magnetizations than their post compaction nrms implying that the smaller higher coercivity grains are most affected by the compaction process these data support our model since a surface charge mechanism for inclination shallowing would predict that the smallest magnetic grains would be preferentially affected

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

late cretaceous to paleocene oroclinal bending in the central pontides turkey 1 the turkish pontide fold and thrust belt formed since the paleozoic and is an important element in the africa eurasia convergence and the resulting closure of the neo tethys ocean it has a peculiar arc shaped geometry in its central part along the black sea coast which may have resulted from oroclinal bending we have determined the vertical axis rotation history of this area using paleomagnetism on cretaceous to eocene rocks from 47 sites and critically analyzed previously published data we applied the same reliability criteria to all data our results show that late cretaceous sites have clockwise and counterclockwise rotations perpendicular to the structural trend in the central pontides in the eastern pontides they show only local rotations paleocene to eocene rocks in the central and eastern pontides show no rotation we conclude that the central pontide northward arc shaped geometry results from oroclinal bending in latest cretaceous to earliest paleocene times the timing and scale of geological processes that occurred in the region make it likely that orocline formation resulted from neo tethys closure between the pontides and the metamorphic promontory of the anatolide tauride block earlier studies on the southerly located cankiri basin reveal that clockwise and counterclockwise rotations occurred in eocene oligocene times this implies that the entire region underwent continuous deformation from late cretaceous to eocene caused by convergence of the pontides and the anatolide tauride block with a southward moving deformation front deformation was first localized in the northern part of the central pontides until the paleocene resulting in oroclinal bending and from at least eocene times it shifted toward the cankiri basin region

late eocene evolution of the cicekdagi basin central turkey syn sedimentary compression during microcontinent continent collision in central anatolia abstract the central anatolian crystalline complex cacc exposes metasediment rocks overlain by cretaceous ophiolites and intruded by granitoids following late cretaceous exhumation of its high grade metamorphic rocks the cacc started to collide with the central pontides of southern eurasia in the latest cretaceous to paleocene here we present the sedimentary stratigraphic and tectonic evolution of the cicekdagi basin located in the northwest of the cacc magnetostratigraphic dating supported by 40 ar 39 ar geochronology shows a late eocene basin age the basin fill unconformably overlies metamorphic basement in the south and ophiolites of the cacc in the north it consists of red conglomerates sandstones and siltstones which overlie a sequence of nummulitic limestones in the south these limestones are 10 m thick are underlain by a few meters of conglomerate unit unconformably covering the cacc metamorphics in the north the limestones are underlain by a 200 m thick sequence of volcanics and fine grained clastics intercalating with shallow marine black shales the upper eocene sediments of the cicekdagi basin were deformed into a syn anticline pair progressive unconformities in the northern flank and a rapid and persistent 180 switch in paleocurrent directions from southward to northward in the southern flank of the anticline demonstrate syn sedimentary folding we interpret the folding to result from a southward progression of the cankiri foreland basin as a result of ongoing collision between the cacc and the pontides

kinematic stratigraphic evolution of a growth syncline and its implications for tectonic development of the proximal foreland basin southeastern ebro basin catalunya spain in the southeastern ebro basin of spain analysis of sequential fold history in combination with stacking patterns of conglomerate deposited in a growing syncline demonstrates the impact of local uplift attendant upon fold growth on nonmarine depositional systems in a foreland basin the penyagalera syncline is part of a belt of asymmetric folds developed in proximal paleogene foreland basin deposits by foreland directed propagation of a detachment beneath the basin foreland basin strata form a progradational succession of interbedded siltstone sandstone and evaporite overlain by conglomerate stratal stacking patterns and fold history indicate that conglomerate of the syncline marks the transition within the foreland basin succession from foredeep to wedge top depositional zones the conglomerate is divided into three informal members separated by unconformities the members are divided in turn into lithosomes separated by prominent bounding surfaces lithosomes represent depositional elements deposited by episodic progradation of alluvial fan lobes older conglomerate members are more tightly folded than younger members demonstrating that folding accompanied conglomerate deposition the uplift of opposing limbs of the penyagalera syncline was diachronous the asymmetric syncline comprises an overturned interior southeastern limb and a gently dipping exterior northwestern limb the interior limb rotated to a steep to slightly overturned attitude before significant rotation and uplift of the exterior limb took place rotation of the interior fold limb was episodic and punctuated by periods of erosion of older conglomerate uplift rates during rotation events along the interior limb generally were more rapid than sediment accumulation rates and caused sediment bypass to the foreland basin however sediment accumulation rates overtook uplift rates during late limb rotation causing alluvial fan lithosomes to onlap previously formed unconformities offlap signifying a slight excess of uplift over sediment accumulation rates is not observed in the syncline on the exterior limb sedimentation rates exceeded early limb uplift rates but the relationship of later folding and deposition is not preserved most synclinal closure postdated the youngest preserved lithosomes in the fold young lithosomes occupy a paleocanyon incised deeply into the interior limb of the syncline and mesozoic strata of the thrust belt the paleocanyon was backfilled during late aggradation of the ebro basin an event independent of local folding

on the secular variations in the composition of phanerozoic marine potash evaporites in a recent paper l a hardie proposed that the secular changes in the mineralogy of marine nonskeletal limestones and in the mineralogy of marine potash evaporites during the phanerozoic are the result of changes in the composition of seawater caused primarily by fluctuations in the flux of seawater through mid ocean ridges he suggested that even quite small variations 25 in this flux have a profound effect on the composition of seawater we show that the effects of changes in the hydrothermal flux are much smaller than he proposed nevertheless a doubling of the hydrothermal flux could probably alter the composition of seawater sufficiently to affect the mineralogy of marine potash evaporites an alternative explanation for the variations in the mineralogy of these deposits invokes differences in the degree of dolomitization during the evaporation of seawater the apparent near constancy of the k sup content of seawater during the phanerozoic supports this hypothesis it seems likely that during periods of rapid seafloor spreading the rate of seawater cycling is greater than today that sea level is higher that very large carbonate platforms are more abundant and that changes in seawater chemistry together with increases in dolomitization during the evaporation of seawatermore lead to mgso sub 4 free potash deposits the relative importance of these several effects can probably be determined with certainty only when we have analyses of relatively unaltered seawater from the several phanerozoic periods 27 refs 1 fig 1 tab less

reconciling the geological history of western turkey with plate circuits and mantle tomography abstract we place the geological history since cretaceous times in western turkey in a context of convergence subduction collision and slab break off to this end we compare the west anatolian geological history with amounts of africa europe convergence calculated from the atlantic plate circuit and the seismic tomography images of the west anatolian mantle structure western turkish geology reflects the convergence between the sakarya continent here treated as eurasia in the north and africa in the south with the anatolide tauride block atb between two strands of the neotethyan ocean convergence between the sakarya and the atb started at least 95 90 myr ago marked by ages of metamorphic soles of ophiolites that form the highest structural unit below sakarya these are underlain by high pressure low temperature metamorphic rocks of the tavsanli and afyon zones and the oren unit which in turn are underlain by the menderes massif derived from the atb underthrusting of the atb below sakarya was since 50 ma associated with high temperature metamorphism and widespread granitic magmatism thrusting in the menderes massif continued until 35 ma after which there is no record of accretion in western turkey plate circuits show that since 90 ma 1400 km of africa europe convergence occurred of which 700 km since 50 ma and 450 km since 35 ma seismic tomography shows that the african slab under western turkey is decoupled from the african plate this detached slab is a single coherent body representing the lithosphere consumed since 90 ma there was no subduction re initiation after slab break off atb collision with europe therefore did not immediately lead to slab break off but instead to delamination of subducting lithospheric mantle from accreting atb crust while staying attached to the african plate this led to asthenospheric inflow below the atb crust high temperature metamorphism and felsic magmatism slab break off in western turkey probably occurred 15 myr ago after which overriding plate compression and rotation accommodated ongoing africa europe convergence slab break off was accommodated along a vertical ne trending subduction transform edge propagator step fault zone accelerating southwestward slab retreat of the aegean slab the se aegean slab edge may have existed already since early miocene times or before but started to rapidly roll back along the southeastern aegean step in middle miocene times penetrating the aegean region in the pliocene

mechanisms of sulfate removal from subsurface calcium chloride brines heletz kokhav oilfields israel abstract the evolution of the ca chloride brines in the heletz formation lower cretaceous in the southern coastal plain of israel was reconstructed through the study of its sulfate concentration and isotopic composition particular emphasis was given to the brine oil interaction in the oilfields and to the sulfate depletion and lower so4 cl ratio in brines in contact with hydrocarbons oil brines relative to oil free from dry wells in the same oilfields a method is presented for a calculation of the amount of sulfate removed from the original seawater in the various stages of its evolution to ca chloride brine these stages include evaporation dolomitization and sulfate reduction in different stages of its evolution from early diagenetic processes to the contact with crude oil in the present study based on the 34sso4 and so4 cl ratio it was found that in the heletz brines most of the sulfate 80 94 was removed from the original seawater prior to their interaction with the hydrocarbons and only a negligible fraction of few percent of the sulfate was removed during the crude oil water contact the ca chloride brines evolved from messinian upper miocene seawater that underwent evaporation during the desiccation of the mediterranean sulfate was removed from messinian lagoon s during gypsum precipitation due to evaporation and dolomitization bacterial sulfate reduction further depleted the brine in sulfate and changed its isotopic composition from its original miocene seawater composition of 34sso4 20 o 26 o overall some 50 of the original sulfate as normalized to chloride was removed from the original lagoon through the above processes mostly by gypsum precipitation eastward migration of the messinian ca chloride brine into the heletz formation was accompanied by dolomitization of the country rock final depletion of sulfate from the brines took place and possibly still occurs in the presence of crude oil in the oilfields the two oil producing fields heletz and kokhav occupy different areas on a rayleigh distillation diagram sulfate depletion in both fields is accompanied by an increase in 34sso4 which reaches a maximum value of 59 o the above correlation is explained by bacterial sulfate reduction facilitated by the contact with the crude samples collected from the same boreholes at time intervals of several months show two opposing trends sulfate concentration decrease accompanied by increase in 34sso4 and vice versa while the first can be explained as in situ bacterial sulfate reduction the latter attest to subsurface brine migration as would be expected in oil producing fields

the impact of topography on isotopes in precipitation across the central anatolian plateau turkey paleoelevation reconstructions of mountain belts and orogenic plateaus based on stable isotope climate and precipitation records benefit greatly from present day calibrations that relate the fractionation of hydrogen d and oxygen 18o isotopes in precipitation to orographic rainfall here we establish a first order template of d and 18o of modern meteoric waters across the central anatolian plateau cap and its bordering pontic and taurus mountains we identify key regions in the plateau interior and along the plateau margins that have the potential to reliably record topography related paleotemperature and paleoprecipitation changes as recovered from stable isotope paleosol fossil teeth or lipid proxy data based on d and 18o data of more than 480 surface water samples from small catchments and springs we characterize moisture sources affecting the net isotopic budget of precipitation over the cap and analyze how orographic rainout and plateau aridity shape modern patterns of d and 18o in precipitation the taurus mountains bordering the cap to the south act as a major orographic barrier for transport of predominantly winter moisture and exhibit isotopic lapse rates of approximately 20 km for d and 2 9 km for 18o across an elevation range of nearly 3000 m the pontic mountains at the northern margin of the cap force perennial moisture to ascend and condensate revealing lapse rates of 19 km for d and 2 6 km for 18o the difference in the predominant moisture source for the southern and northern margins of the cap north african versus atlantic air masses is manifested in systematic north south differences in near sea level meteoric water compositions of dn s 20 permil and 18on s 3 permil in a swath across the central part of the plateau stable isotope data from the semi arid plateau interior with rainfall as low as 300 to 500 mm yr and mean summer temperatures attaining 23 c provide clear evidence for an evaporative regime that drastically affects surface water and runoff compositions and results in a local meteoric water line for the plateau interior that follows d 4 0 18o 29 3 strongly evaporitic conditions contrast rainfall patterns along the plateau margins including their immediate leeward flanks where d and 18o elevation relationships are reliable predictors of modern topography

cyclicity in the middle eocene cayraz carbonate formation haymana basin central anatolia turkey abstract the haymana basin in central anatolia turkey developed on a fore arc accretionary wedge during the late cretaceous and the middle eocene turbidite deposits fill the center of the basin and grade northwestward into shallow marine clastics and carbonates which in turn pass into lacustrine and fluvial deposits toward the margin the middle eocene cayraz formation represents the youngest paleotectonic unit of the haymana basin it is composed of two shelf systems ss each formed by a package of nummulitic banks and intervening calcareous mudstones 150 250 m thick overlying 70 100 m thick monotonous mudstones within each of the two shelf systems two orders of coarsening upward and shallowing upward sequences are recognized the smaller order sequences 3 10 m thick are termed basic units bu four types of basic units have been distinguished these are made up of either calcareous mudstone overlain by a nummulitic bank or silty mudstone overlain by sandy to conglomeratic beds each basic unit represents a specific depositional environment ranging from quiet lagoon or open marine to more energetic bank or sandy bar basic units are vertically associated to form three types of 15 35 m thick basic sequences bs which represent the time and space evolution of the shelf systems owing to their small scale their lateral association and the condensed nature of their bounding surfaces basic units are considered to be allocyclic transgressive regressive cycles tuned to milankovitch bands at the scale of basic sequences bs and shelf systems ss the lateral and vertical distribution of the sequences and the presence of onlap structures strongly suggest sea level changes the sequential organization thicknesses of basic units and basic sequences and an estimated sedimentation rate favour sea level changes controlled by milankovitch climatic cycles amalgamation or condensation of basic units in basic sequences and the existence of locally accentuated onlaps suggest a coupled effect of discontinuous subsidence

sulfur isotope constraints on the formation of mgso4 deficient evaporites in the qarhan salt lake western china abstract the qarhan salt lake qsl in the qaidam basin in western china is the largest brine potash deposit in the world the formation of mgso4 deficient evaporites in the qsl whether from the evaporation of river waters with high na and cl levels bacterial sulfate reduction bsr in brines resulting in so42 depletion or the mixing of the river and spring waters remains controversial the 34s values of 33 intercrystalline brines and 10 gypsum samples from a sediment core isl1a collected in the qsl were presented in this study combining these results with previously reported major ionic concentrations total dissolved solids tds and 34s values of different waters and 87sr 86sr ratios of sediments it was concluded that 1 34s values of the intercrystalline brines 6 7 to 12 1 and gypsum 8 1 to 10 1 suggested that the bsr was insignificant in the qsl these values were dominated by those of inflowing waters and the evaporation process 2 river waters with high na and cl levels were unable to form mgso4 deficient evaporites in the qsl a strong positive correlation of na and cl equivalents coupled with high na cl tds ratios suggested that the large amount of solutes in golmud river waters results from the dissolution of halite rather than the chemical weathering of rocks and 3 the flowing system of the river and spring in the past 50 kyr was similar to the modern supplying system and mixing of river and spring waters was responsible for the precipitation of evaporites in the qsl

comparative analysis of sulfur isotope behavior in the basins with evaporites of chloride and sulfate types abstract the pripyat trough and the caspian depression are examples of basins with chloride and sulfate type evaporite formations respectively patterns of sulfur isotope distribution in these basins are essentially different sulfur isotopic composition of sulfate minerals in the caspian depression becomes lighter from the gypsum stage 34 s 13 9 0 3 toward the chloride stage 12 7 0 2 an opposite isotopic trend occurs in the pripyat trough 34s are respectively 22 8 1 0 and 25 3 0 5 pyrite formed in the chloride stage in the caspian depression is significantly depleted in 34s with respect to the initial sulfate of the basin 34 s sulfate py 22 5 2 1 34s sulfate py in the pripyat trough is lower 17 6 1 2 diagenetic anhydrites from the intersaliferous and subsaliferous formations are enriched in 34s relative to the sulfur isotope values measured from the anhydrites in the main salts this enrichment is higher in the pripyat trough average 34s 2 7 5 2 than in the caspian depression 0 9 2 1 the above differences are well explained in the terms of chemical systems that are limited or unlimited with respect to sulfur during the sulfate reduction process brines act as sulfur limited systems in chloride type basins and as sulfur unlimited systems in sulfate type ones

metamorphism of the central anatolian crystalline complex turkey influence of orogen normal collision vs wrench dominated tectonics on p t t paths the central anatolian crystalline complex cacc is a microcontinent in the alpine himalayan belt it has previously been considered as a coherent structural entity but although the entire cacc is comprised of similar rocks primarily metasedimentary rocks and granitoids it consists of at least four tectonic blocks characterized by different p t t paths these blocks are the kirsehir north west akdag north east nigde south and aksaray west massifs the northern massifs experienced thrusting and folding during collision and were slowly exhumed by erosion metamorphic rocks are characterized by clockwise p t paths at moderate p t and local low p high t lp ht overprinting in the highest grade rocks apatite fission track ages are eocene to oligocene 47 32 ma the aksaray block represents the hot shallow mid crust of a late cretaceous early tertiary arc it is dominated by intrusions rare metapelitic rocks record low p 4 kbar regional metamorphism overprinted by lp ht contact metamorphism apatite fission track ages are 50 45 ma the nigde massif is different from the other cacc blocks because it evolved as a core complex in a wrench dominated setting it is characterized by clockwise p t paths at moderate p t followed by widespread lp ht metamorphism apatite fission track ages are miocene 12 9 ma significantly younger than those in the northern massifs nigde rocks resided in the mid crust at a time when the rest of the cacc was at or near the earth s surface variations in p t t and tectonic histories especially timing of exhumation between the northern and southern cacc reflect the difference between head on collision vs mid crustal wrenching

modelling the oxygen isotope distribution of ancient seawater using a coupled ocean atmosphere gcm implications for reconstructing early eocene climate one of the motivations for studying warm climates of the past such as the early eocene is the enhanced understanding this brings of possible future greenhouse conditions traditionally climate information deduced from biological or chemical proxies have been used to test computer model simulations of past climatic conditions and hence establish some of the uncertainties associated with model based predictions however extracting climate information from proxies is itself an interpretative process and discrepancies between climate information inferred from different types of proxy undermines the assumption that model data conflicts automatically mean that the model is inherently flawed a new approach which both acknowledges and reduces the uncertainties associated with both model and data is required although the oxygen isotopic ratio 18o preserved in calcareous marine fossils has been used to reconstruct past seawater temperature for several decades significant uncertainties associated with this method persist these include assumptions about past seawater 18o for which no proxy exists and which is a key control on the temperature inferred from fossil carbonate here we present the results of an early eocene simulation made using a state of the art general circulation model gcm hadcm3 with co2 set at six times pre industrial values and which has oxygen isotopes incorporated into the full hydrological cycle and hence simulates the 18o of past seawater this allows us to explore the implications of the different seawater 18o correction factors commonly used for 18o based temperature reconstruction it also allows us to focus model data comparison on 18o rather than interpret ocean temperature an approach that reduces uncertainties in model data comparison since the effects of both the temperature and the isotopic composition of ocean water on 18o of carbonate are accounted for the good agreement between model and data for both modern and well preserved early eocene carbonate increases confidence in climate reconstructions of this time

apatite fission track data from central anatolian granitoids turkey constraints on neo tethyan closure 1 apatite fission track age versus elevation profiles and temperature time path modeling indicate an early to middle paleocene 57 62 ma rapid exhumation of the middle to late cretaceous granitoids in central anatolia and an oligocene 28 30 ma rapid exhumation of the eocene kosedag batholith in the ne sivas region part of eastern central pontides the early to middle paleocene rapid exhumation is thought to result from a regional compressional regime following the collision of the eurasian plate and the tauride anatolide platform at the closure of the izmir ankara erzincan branch of the northern neo tethys the oligocene accelerated exhumation of the kosedag batholith is contemporaneous with the oligo miocene closure of the southern neo tethys which juxtaposed the amalgamated eurasian and tauride anatolide platform and the african arabian plate along the bitlis zagros suture in southeast anatolia the compressional regime due to this collision affected a large area between the greater caucasus in the north and northern african arabian plate in the south

s isotope studies of shallow water laminated gypsum and associated evaporites upper permian east greenland abstract three types of primary subaqueous gypsum occur in the karstryggen formation upper permian of east greenland 1 planar laminated gypsum having a narrow 34 s range of 10 2 to 10 4 cdt 2 algal laminated gypsum 9 2 to 12 0 and 3 bottom nucleated gypsum crystals 11 6 to 11 7 type 3 was deposited from a residual brine in the basin while types 1 and 2 consist of seawater or mixed fresh water seawater derived sulphate with varying contribution of reoxidized sulphur originally deposited as sulphide or organic sulphur diagenetic nodular gypsum 7 3 to 10 8 was formed by redistribution of marine or mixed fresh water seawater derived brines which precipitated the laminated gypsum with contribution of sulphate originally precipitated as sulphide or organic sulphur in the organic rich sediments

high pressure metasediments in central turkey constraints on the neotethyan closure history 1 the distribution of oceanic domains and continental blocks in central anatolia remains a challenge in understanding the alpine geodynamic evolution of the tethys realm the consumption of a neotethys oceanic branch at the mesozoic cenozoic boundary welded the central anatolian crystalline complex in central turkey and the anatolide tauride block in western turkey with the northerly eurasian margin whether those two regions constituted a single or two distinct continental masses is still matter of debate high pressure metamorphism has been locally evidenced in the afyon zone which was however defined as a greenschist facies metamorphic zone of the anatolide tauride block since the afyon zone composes a metamorphic equivalent of a continental margin exposed far south of the izmir ankara suture zone this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central turkey our investigations reveal that the high pressure minerals fe mg carpholite and glaucophane are present in the entire afyon zone which we reconsider as a blueschist facies zone we additionally present a tectonic reconstruction stripping off the postcollisional tectonics it reveals that today s bending of the high pressure belt is consistent with an eocene collision of the anatolide tauride block around the southern edge of the central anatolian crystalline complex we argue that the central anatolian crystalline complex and the anatolide tauride block were two distinct continental masses separated by a neotethyan oceanic stripe the closure of which engendered subduction related metamorphism in the latter and arc volcanism and high grade metamorphism in the former by late cretaceous to early cenozoic

rayleigh taylor instability as a mechanism for corona formation on venus abstract in this study we explore the idea that coronae have formed on venus as a result of gravitational rayleigh taylor instability of the lithosphere the lithosphere is represented by a system of stratified homogeneous viscous layers low density crust over high density mantle over lower density layer beneath the lithosphere a small harmonic perturbation imposed on the base of the lithosphere is observed to result in gravitational instability under the constraint of assumed axisymmetry topography develops with time under the influence of dynamic stress associated with downwelling or upwelling and spatially variable crustal thickening or thinning topography may therefore be elevated or depressed above a mantle downwelling but the computed gravity anomaly is always negative above a mantle downwelling in a homogeneous asthenosphere the ratio of peak gravity to topography anomaly depends primarily on the ratio of crust to lithospheric viscosity average observed ratios are well resolved for two groups of coronae 40 mgal km 1 consistent with models in which the crust is perhaps 5 times stronger than the lithosphere group 3a rim surrounding elevated central region coronae are inferred to arise from a central upwelling model whereas group 8 depression coronae are inferred to arise from central downwelling observed average coronae radii are consistent with a lithospheric thickness of only 50 km an upper low density crustal layer is 10 20 km thick as inferred from the amplitude of gravity and topography anomalies

structure evolution and tectonic activity of the eastern sunda forearc indonesia from marine seismic investigations forearc structures of the eastern sunda arc are studied by new multichannel reflection seismic profiling we image a high along strike variability of the subducting oceanic plate the interface between subducting and overriding plate the accretionary wedge the outer arc high and forearc basins we highlight ongoing tectonic activity of the entire outer arc high active out of sequence thrust faults connecting the plate interface with the seafloor slope basins showing tilted sedimentary sequences on the outer arc high vertical displacement of young seafloor sediments and tilted sedimentary sequences in the lombok forearc basin while frontal accretion plays a minor role the growth of the outer arc high is mainly attributed to oceanic sediments and crustal fragments which are attached to the base of the upper plate and recycled within the forearc we image ongoing large scale duplex formation of the oceanic crust the incoming oceanic crust is dissected by normal faulting into 5 10 km wide blocks within a 50 70 km wide belt seaward of the deep sea trench these blocks determine the geometry and evolution of duplexes attached to the base of the overriding plate landward of the trench long lasting and ongoing subsidence of the lombok basin is documented by distinct seismic sequences in the lombok basin we image mud diapirs fed from deeply buried sediments which may have been mobilized by rising fluids we propose a wrench fault system in the eastern lombok forearc basin that decouples the subduction regime of the sunda arc from the continent island arc collision regime of the western banda arc the observed tectonic activity of the entire forearc system reflects a high earthquake and tsunami hazard similar to the western part of the sunda arc

paleozoic fluid history of the michigan basin evidence from dolomite geochemistry in the middle ordovician st peter sandstone abstract the isotope sr and o and elemental mg ca mn fe and sr compositions of the various dolomites in the middle ordovician st peter sandstone in the michigan basin are determined and the variations are modeled in terms of fluid rock interaction or as mixing relations these geochemical models combined with the paragenetic sequence of the dolomites and late anhydrite cement suggest the existence of at least four distinct diagenetic fluids in the st peter sandstone during the paleozoic fluid 1 sr 30 10 ppm sr ca 0 019 87sr 86sr 0 7093 1 has a composition consistent with a modified older pre middle ordovician seawater origin which indicates that the flow path for this fluid had a major upward component this fluid resulted in th first and volumetrically most important burial dolomitization event producing dolomite in both carbonate and quartz sandstone lithofacies in the st peter sandstone fluid 2 sr 30 10 ppm sr ca 0 019 87sr 86sr 0 7084 1 low fe has a composition consistent with a modified middle to early late ordovician seawater origin suggesting a major downward component for fluid flow fluid 2 produced dolomite cement in the carbonate lithofacies that postdates fluid 1 dolomite the composition of fluid 3 sr 50 ppm sr ca 0 044 0 110 87sr 86sr 0 710 0 711 high fe is best interpreted to reflect a heated deep basinal brine that had previously interacted with the k feldspar rich rocks near the cambrian precambrian unco formity in the michigan basin indicating a major upward component for fluid flow fluid 3 produced dolomite cement in quartz sandstone lithofacies that postdates fluid 1 dolomite fluid 4 87sr 86sr 0 7085 1 resulted in precipitation of late anhydrite in fractures the 87sr 86sr ratio of the anhydrite is consistent with fluid 4 originating as a dilute fluid that interacted extensively with silurian gypsum in the michigan basin this indicates that the flow path of fluid 4 had a major downward component the st peter sandstone was an important migration pathway for many different types of fluids in the michigan basin and the proposed fluid origins indicate that both upward and downward cross formational fluid flow occurred during the paleozoic older and younger modified seawater produced most of the burial dolomite in the st peter sandstone

carbon and oxygen isotopic composition of carbonates from saliferous deposits of the pripyat trough belarus abstract 18o and 13c in accessory calcite and dolomite from salt rock and in intrasalt carbonate beds of the upper frasnian and upper famennian evaporite formations of the pripyat trough vary over a wide range within all the intrasalt carbonate interbeds four distinct groups of rocks have been recognised on the basis of their isotopic composition the ranges of variation of 13c pdb and 18o smow within these groups are respectively a 0 7 to 0 8 and 35 4 to 36 4 b 4 5 to 0 9 and 30 0 to 32 2 c 7 0 to 2 8 and 19 8 to 25 5 d 17 5 to 9 7 and 20 9 to 26 4 the isotopic composition of accessory carbonates is more uniform the main body of values falls within the range 11 to 3 for 13c and 18 to 25 for 18o the carbonate matter with the observed combinations of 13c and 18o could have been formed during sedimentation and diagenesis in sabkhas on subaetially exposed islands on evaporite depression slopes washed by sea water and freshwater and in stagnant zones with hot brines the carbon isotopic composition of intrasalt carbonate rocks is on the average lighter than that of accessory carbonates from the salts this shows that the organic matter was most readily accumulated in evaporite basins during non salt sedimentation

the role of excess co2 in the formation of trona deposits abstract the prevailing theory for the formation of trona na3 co3 hco3 2 h2o relies on evaporative concentration of na hco 3 water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments given the abundance of closed drainage basins dominated by volcanics it is puzzling that there are so few trona deposits and present day lakes that would yield dominantly na co3 minerals upon evaporation groundwater in the san bernardino basin southeastern arizona usa and northeastern sonora mexico would yield mainly na co3 minerals upon evaporation but waters in the surrounding basins would not analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology but the injection of magmatic co2 many major deposits of trona and na co3 type lakes appear to have had excess co2 input either from magmatic sources or from the decay of organic matter it is proposed that along with the presence of volcanics addition of excess co2 is an important pre condition for the formation of trona deposits

role of permeability barriers in alluvial hydromorphic palaeosols the eocene pondaung formation myanmar this study examines the lateral distribution of hydromorphy in the fine grained alluvial deposits of the eocene pondaung formation central myanmar through detailed outcrop analysis and using a combined sedimentological and pedological approach this study proposes a reconstruction of pondaung overbank floodplain palaeoenvironments the variations of hydromorphic features in the different overbank sub environments are then discussed and used to build a model of hydromorphic variability in alluvial deposits two main architectural associations with distinctive lithofacies and pedogenic features were identified corresponding to different sub environments heterolithic deposits and extensive mudstone successions the heterolithic deposits display variegated fine grained lithofacies and contain poorly developed palaeosols with gley and vertic features which are interpreted to reflect a seasonal wetlands landscape developed in actively aggrading avulsion belts extensive mudstone successions with vertisols that locally exhibit mukkara style pseudogley features are interpreted to represent a distal open forested environment the palaeosols of both sub environments display dense local hydromorphic variations they are also characterized by a gradual shift from gley dominated to pseudogley dominated features with increasing distance from the avulsion belt the clay dominated lithology of the floodplain parent material which forms numerous subsurface permeability barriers is shown to have acted as a fundamental control in limiting water table dynamics in coarse grained parts of the succession thereby favouring hydromorphic variability palaeosol sequences of the pondaung formation contrast with the soil landscape associations described in other studies and provide an alternative model with which to account for the hydromorphic variability in poorly drained alluvial soils the model proposed as an outcome of this study demonstrates that hydromorphic variations can be dramatic in floodplains where permeability barriers are numerous further the model stresses the importance of undertaking detailed lateral palaeosol analyses prior to making interpretations regarding hydromorphic variability

palaeostress inversion in a multiphase deformed area kinematic and structural evolution of the cankiri basin central turkey part 1 northern area the kinematic and structural evolution of the major structures affecting the cankiri basin central turkey has been deduced from a palaeostress inversion study four palaeostress tensor configurations indicative of four phase structural evolution have been constructed from the fault slip data collected from the cankiri basin the first two phases indicate the dominant role of thrusting and folding and are attributed to the collision between the pontides and the taurides the proposed interface of which is straddled by the cankiri basin phase 1 occurred in the pre late palaeocene and phase 2 in the late palaeocene pre burdigalian the third phase is dominated by extensional deformation in the middle miocene the latest phase has been active since then and is characterized by regional transcurrent tectonics

asian monsoons in a late eocene greenhouse world the strong present day asian monsoons are thought to have originated between 25 and 22 million years myr ago driven by tibetan himalayan uplift however the existence of older asian monsoons and their response to enhanced greenhouse conditions such as those in theeocene period 55 34myrago are unknownbecause of the paucity of well dated records here we show late eocene climate records revealing marked monsoon like patterns in rainfall and wind south and north of the tibetan himalayan orogen this is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from myanmar and by aeolian dust deposition in northwest china our climate simulations support modern like eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhancedgreenhouse conditions counterbalanced the negative effect of lowertibetanrelief onprecipitation these strong monsoons later weakened with the global shift to icehouse conditions 34myr ago

late cretaceous early eocene tectonic development of the tethyan suture zone in the erzincan area eastern pontides turkey six individual tectonostratigraphic units are identified within the izmir ankara erzincan suture zone in the critical erzincan area of the eastern pontides the ayikayasi formation of campanian maastrichtian age is composed of bedded pelagic limestones intercalated with polymict massive conglomerates the ayikayasi formation conformably overlies the tauride passive margin sequence in the munzur mountains to the south and is interpreted as an underfilled foredeep basin the refahiye complex of possible late cretaceous age is a partial ophiolite composed of 75 by volume serpentinized peridotite mainly harzburgite 20 diabase and minor amounts of gabbro and plagiogranite the complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone unusual screens of metamorphic rocks e g marble and schist locally occur between sheeted diabase dykes the upper cretaceous karayaprak melange exhibits two lithological associations 1 the basalt radiolarite serpentinite association including depleted arc type basalts 2 the massive neritic limestone lava volcaniclastic association that includes fractionated intermediate composition lavas and is interpreted as accreted neotethyan seamount s the several kilometre thick karadag formation of campanian maastrichtian age is composed of greenschist facies volcanogenic rocks of mainly basaltic to andesitic composition and is interpreted as an emplaced upper cretaceous volcanic arc the campanian early eocene sutpinar formation 1500 m thick is a coarsening upward succession of turbiditic calcarenite sandstone laminated mudrock volcaniclastic sedimentary rocks that includes rare andesitic lava and is interpreted as a regressive forearc basin the late paleocene eocene sipikor formation is a laterally varied succession of shallow marine carbonate and siliciclastic lithofacies that overlies deformed upper cretaceous units with an angular unconformity structural study indicates that the assembled accretionary prism supra subduction zone type oceanic lithosphere and volcanic arc units were emplaced northwards onto the eurasian margin and also southwards onto the tauride gondwana related margin during campanian maastrichtian time further mainly southward thrusting took place during the eocene in this area related to final closure of tethys our preferred tectonic model involves northward subduction supra subduction zone ophiolite genesis and arc magmatism near the northerly eurasian margin of the mesozoic tethys

tectonostratigraphic evolution of the upper cretaceous cenozoic central anatolian basins an integrated study of diachronous ocean basin closure and continental collision

geomagnetic secular variation and the statistics of palaeomagnetic directions in this study we examine the role of palaeosecular variation psv in the use of statistics for palaeomagnetic studies and we provide new reliability criteria for palaeomagnetic poles or directions we first conclude that fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole vgp distributions instead secondly we strongly advocate that typical properties of geomagnetic field behaviour are taken into account in the assessment of palaeomagnetic data sets the latitude dependent properties e s k provide useful guidelines for the reliability of a palaeomagnetic data set a reliable assessment of these properties depends on the sufficient number of palaeomagnetic samples being taken therefore as an additional instrument of assessing data sets we provide a n dependent a95 envelope bounded by an upper limit a95max and a lower limit a95min that helps to ascertain whether or not a distribution has sufficiently well sampled psv and therefore geomagnetic field behaviour applying these criteria is indispensable for studies of geomagnetic behaviour or for studies aiming at using tk03 gad for inclination error correction through the elongation inclination e i method for palaeomagnetic studies aimed at geological reconstructions they form helpful guidelines and increase the confidence in the rocks having faithfully recorded the field an analysis of published eastern mediterranean data shows that the vast majority of studies do not conform to the van der voo criteria in particular with respect to n and a95 we have provided criteria that are on the one hand more lenient lower n may still provide relevant information and on the other hand more strict for high n the criterion of a95 16 should be adapted to a requirement of lower a95 e g a95 80

reconstructing the geometry of central anatolia during the late cretaceous large scale cenozoic rotations and deformation between the pontides and taurides the central anatolian crystalline complex cacc exposes metamorphic ophiolitic and igneous rocks that were formed and deformed during closure of the neotethyan ocean the cacc is located in central turkey between the pontides in the north and the taurides in the south separated by major fault zones composite plutons intruded the meta sedimentary and ophiolitic units between 95 and 75 ma and form linear magmatic belts 100 km long along the western and northern margins of the cacc exhumation of the metamorphic and igneous complex was finalized by the paleocene time in this study we paleomagnetically study fifteen plutons spanning the entire non deformed upper cretaceous granitoid belt to test whether the initial configuration of the cacc was modified by vertical axis rotations after its exhumation our results show three internally coherent domains with significantly different vertical axis rotations 1 in the north east the akda block ayb records 151

recent investigations of the 0 5 ma geomagnetic field recorded by lava flows we present a synthesis of 0 5 ma paleomagnetic directional data collected from 17 different locations under the collaborative time averaged geomagnetic field initiative tafi when combined with regional compilations from the northwest united states the southwest united states japan new zealand hawaii mexico south pacific and the indian ocean a data set of over 2000 sites with high quality stable polarity and declination and inclination measurements is obtained this is a more than sevenfold increase over similar quality data in the existing paleosecular variation of recent lavas psvrl data set and has greatly improved spatial sampling the new data set spans 78 s to 53 n and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the time averaged field taf and paleosecular variation psv for the brunhes and matuyama chrons and for the 0 5 ma interval combined the brunhes and matuyama chrons exhibit different taf geometries notably smaller departures from a geocentric axial dipole field during the brunhes consistent with higher dipole strength observed from paleointensity data geographical variations in psv are also different for the brunhes and matuyama given the high quality of our data set polarity asymmetries in psv and the taf cannot be attributed to viscous overprints but suggest different underlying field behavior perhaps related to the influence of long lived core mantle boundary conditions on core flow psv as measured by dispersion of virtual geomagnetic poles shows less latitudinal variation than predicted by current statistical psv models or by previous data sets in particular the brunhes data reported here are compatible with a wide range of models from those that predict constant dispersion as a function of latitude to those that predict an increase in dispersion with latitude discriminating among such models could be helped by increased numbers of low latitude data and new high northern latitude sites tests with other data sets and with simulations indicate that some of the latitudinal signature previously observed in vgp dispersion can be attributed to the inclusion of low quality insufficiently cleaned data with too few samples per site our matuyama data show a stronger dependence of dispersion on latitude than the brunhes data the taf is examined using the variation of inclination anomaly with latitude best fit two parameter models have axial quadrupole contributions of 2 4 of the axial dipole term and axial octupole contributions of 1 5 approximately 2 of the octupole signature is likely the result of bias incurred by averaging unit vectors