tectono stratigraphy of the cankiri basin late cretaceous to early miocene evolution of the neotethyan suture zone in turkey the cankoro basin straddles the izmir ankara erzincan suture zone which demar cates the former position of the northern branch of the neotethys it includes more than 3 km of pre middle miocene in fill related to late cretaceous to pre middle miocene evolution of the region the basin has developed on the upper cretaceous subduction complex and arc related basins of the neotethys ocean the basin fill includes an upper cretaceous forearc sequence over lain by paleocene with a local unconformity the upper cretaceous configuration of the cankoro basin is interpreted as a part of a forearc basin the paleocene and younger history is interpreted as a foreland sequence dominated by progressively southwards migrated depocenters in front of southward migrating thrust faults upon which a series of piggy back basins were developed ter mination of the forearc setting and beginning of foreland basin conditions indicates complete sub duction of the neotethyan oceanic crust and onset of collision between the pontides laurasia and the taurides gondwana in the paleocene thrusting and related sedimentation continued until the aquitanian early miocene

miocene sea level falls related to the geologic history of midway atoll a period of atoll emergence results in the development of a karst surface on the atoll upon resubmergence this surface is preserved as a subsurface solution unconformity that can be identified by petrographic characteristics and a distinctive stable isotope signature imprinted by subaerial or phreatic diagenesis determination of the magnitude of miocene sea level falls by considering subsidence rates and depths to solution unconformities must take into account the lowering of the emergent atoll surface by dissolution previously the depth to a miocene solution unconformity below midway atoll was assumed to record a maximum highstand of sea level that preceded a period of island emergence however because of surface dissolution the solution unconformity must represent some elevation between a past highstand and a subsequent lowstand the subsurface stratigraphy of midway atoll shows that a late miocene sea level fall of 75 125 m below present sea level took place the magnitude of this fall is greater than that previously determined on the basis of stable isotope data from midway atoll but approximates miocene sea level falls determined by seismic stratigraphic methods

reservoir implications of modern karst topography tropical karst landscapes exhibit a predominance of positive relief features relative to the negative relief features i e sink holes dolines etc of temperate karst areas and yet paradoxically have never been observed in the subsurface on seismic sections to understand why this is the case topographic profiles were made over the positive karst relief features of china java and jamaica and were used to construct synthetic seismic sections the results indicate that in most instances the magnitude of the topographic relief is sufficient to be seen on seismic sections a possibility of misinterpreting karst highs as reefs seems clear but more important in explaining the paradox is the fact that the magnitude of modern karst relief expression is largely attributable to uplift over an extended period the probability of preservation of these positive relief solution residuals is dependent on the karstification process being aborted by the deposition of overlying sediment an event not likely to occur in an uplift area uplift of well lithified carbonate minimally results in an areally extensive runoff surface that controls the development of positive karst landforms uplift also commonly induces faulting and fracturing that further control the distribution of karst land forms hydrocarbon production from the resulting karst is geared to matrix porosity the higher the matrix porosity the greater the rate of deliverability of matrix oil to produced fracture and karst conduit oil in contrast the lowering of the base level of erosion due to a fall in sea level is generally less than that induced by uplift and consequently minimizes positive karst relief development relative to that of uplift subaerial exposure induced by passive sea level fall also minimizes the potential for the related occurrence of fracturing and faulting which of itself mitigates against the general development of positive karst relief the subaerial consequences of passive sea level fall are commonly preserved in the geologic record and result in karst reservoirs dominated by extensive moldic and vuggy porosity interconnected by solution channels these reservoirs lack the production problems commonly attending fractured karst reservoirs with little matrix porosity

a revised pliocene record for marine 87sr 86sr used to date an interglacial event recorded in the cockburn island formation antarctic peninsula abstract we present a revised 87sr 86sr curve for marine sr in the interval 2 5 4 5 ma using analysis of orbulina universa from the middle pliocene type section in sicily punta piccola section and a mixed assemblage of planktonic foraminifera from odp site 758a and b the new calibration is used together with new 87sr 86sr analysis of pectenid calcite from cockburn island antarctica to confirm an age of 4 7 ma for the pectenids of the cockburn island formation formerly the pecten conglomerate a unit important in marking a period of warmth and possible glacial retreat in antarctica finally to aid interlaboratory comparison of 87sr 86sr data we calibrate a value of 0 709174 for en 1 against a value of nist 987 of 0 709248

paleoseismology of the palu lake hazar segment of the east anatolian fault zone turkey the east anatolian fault zone eafz is among the most important active continental transform fault zones in the world as testified by major historical and minor instrumental seismicity the first paleoseismological exploratory trenching study on the eafz was done on the palu lake hazar segment plhs which is one of the six segments forming the fault zone in order to determine its past activity and to assess its earthquake hazard the results of trenching indicate that the latest surface rupturing earthquakes on this segment may be the ms 7 1 1874 and ms 6 7 1875 events and there were other destructive earthquakes prior to these events the recurrence interval for a surface rupturing large m 7 earthquake is estimated as minimum 100 35 and maximum 360 years estimates for the maximum possible paleoearthquake magnitude are mw 7 1 7 7 for the palu lake hazar segment based on empirical magnitude fault rupture relations an alluvial fan dated 14 475 15 255 cal years bp as well as another similar age fan with an abandoned stream channel on it are offset in a left lateral sense 175 and 160 5 m respectively indicating an average slip rate of 11 mm year because 127 years have elapsed since the last surface rupturing event this slip rate suggests that 1 4 m of left lateral strain has accumulated along the segment ignoring possible creep effects folding and other inelastic deformation a 2 5 ma age for the start of left lateral movement on the segment and in turn the eafz is consistent with a slip rate of 11 mm year and a previously reported 27 km total left lateral offset the cumulative 5 6 mm year vertical slip rate near lake hazar suggests a possible age of 148 178 ka for the lake our trenching results indicate also that a significant fraction of the slip across the eafz zone is likely to be accommodated seismically the present seismic quiescence compared with the past activity paleoseismic and historic indicate that the eafz may be locked and accumulating elastic strain energy but could move in the near future

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

last interglacial reef growth beneath modern reefs in the southern great barrier reef studies of modem coral reefs have shown that holocene reef growth is relatively thin and that in many instances it has developed on an older limestone surface1 4 this surface is commonly associated with leaching and pedogenic processes indicative of subaerial exposure and has been termed the solution unconformity5 investigations into reef growth history have interpreted the pre holocene substrate as an older reef surface2 4 6 8 that may or may hot have undergone karst erosion during periods of lower sea level6 9 uranium series dating of corals directly below the uppermost solution unconformity at eniwetok10 and mururoa11 has shown that previous reef growth before the holocene occurred 120 kyr ago we present here 230th 234u dates that confirm a last interglacial age for reefal limestones directly beneath the uppermost solution unconformity in the southern great barrier reef

messinian late miocene karst on grand cayman british west indies an example of an erosional sequence boundary abstract the cayman unconformity which separates the pedro castle formation pliocene from the underlying cayman formation miocene is a sequence boundary that developed during the messinian when sea level was at a lowstand due to glaciation in the southern hemisphere by the end of the messinian grand cayman was an atoll like island that had an elevated peripheral rim that was up to 41 m above the central depression the cayman formation contains paleocaves and paleosinkholes that were linked to the cayman unconformity the topography on the cayman unconformity is attributed to erosional processes because 1 there is no evidence of carbonates that formed by constructional processes i e reefs dunes in the elevated peripheral rim and 2 there is ample evidence of dissolutional fe tures in the cayman formation the topography developed on the interior of grand cayman during the messinian was uneven a deep basin like depression with its base as much as 50 m below the peripheral rim formed on the western part of the island by comparison the floor of the depression on the eastern part of the island was 20 30 m higher the difference in the topography which is a reflection of the amount of bedrock dissolution suggests that the effective rainfall was highest over the western part of the island the relief on the cayman unconformity and associated structures shows that base level during the messinian karst development was at least 41 m below present day sea level this is also provides an estimate of the messinian lowstand position because the base level in oceanic karst settings is usually controlled by sea level

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

coherent noise in marine seismic data three mechanisms that might produce noise patterns on stacked sections are examined direct and trapped waves that propagate outward from the seismic source cable motion caused by the tugging action of the boat and tail buoy and scattered energy from irregularities in the water bottom and sub bottom different noise patterns can be observed on shot profiles and common midpoint cmp gathers these patterns can be diagnostic of the dominant mechanism in a set of data field data suggest that the dominant noise is from waves scattered within the shallow sub bottom this type of noise is enhanced by cmp stacking moreover it can be as strong as surface wave noise on stacked land seismic data as well moveout filtering is best for suppressing the noise while preserving signal since the scattered noise does not exhibit a linear moveout pattern on cmp sorted gathers moveout filtering must be applied either to traces within shot records and common receiver gathers or to stacked traces our data example demonstrates that although it is more costly moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data dependent processing steps of predictive deconvolution and velocity analysis modified journal abstract

stress accumulation and increased seismic risk in eastern turkey abstract unlike the north anatolian fault zone which has produced 11 large earthquakes since 1939 the east anatolian fault zone eafz has been relatively quiescent in the last century when compared to historical records and has therefore accumulated significant stresses along its length determination of the location and likely magnitude of a future probable earthquake along the eafz is of interest both because of this history of large earthquakes m 8 and the density of population in the area here we calculate stress evolution along the fault zone due to both seismic and tectonic loading since 1822 a sequence of 10 well constrained historical earthquakes is selected and the resulting stresses are calculated summed with tectonic loading stresses and resolved onto the mapped active faults we identify two areas of particular seismic risk one of which might be expected to yield a large event our results are sensitive to the previous history of large earthquakes in the region and indicate a need for detailed investigations to constrain the exact rupture geometries of previous earthquakes on these segments

prolonged carbonate diagenesis under an evolving late cenozoic climate nullarbor plain southern australia abstract the nullarbor plain in southern australia the largest areal karst on the globe is a 240 000 km2 uplifted succession of cenozoic marine carbonates whose surface has been exposed for 14 to 15 m y the middle miocene nullarbor limestone forms the upper surface of the plain and hosts a complex and prolonged record of meteoric diagenesis such a complete record offers unique insights into the effects of climate tectonics sea level topography and hydrology on the style and placement of numerous diagenetic events in flat low lying carbonate plains alteration took place during three broad phases comprising eight stages that are interpreted to have formed against a background of dramatic climate change middle miocene phase one diagenesis took place under a humid climate and resulted in rapid mineral equilibration calcite cementation extensive karst development and finally widespread lacustrine and palustrine sedimentation resultant palustrine sediments especially terrestrial ooids are now preserved at the surface and in underlying karst cavities latest middle miocene to middle pliocene phase two diagenesis occurred during a prolonged period 8 m y of temperate climate and resulted in initial deep cave dissolution during low sea levels and later shallow cave development in the course of a high sea level onset of a somewhat more arid climate in the latest pliocene led to the development of the modern desolate landscape of the plain this final phase of diagenesis involved creation of solution pits filled with black limestone pebbles open and closed dolines with associated colluvium fill and pervasive pedogenic calcrete the nullarbor plain demonstrates that low lying carbonate plains can have low surficial erosion rates precisely record relative sea level positions be able to have extensive caves with extended periods of arrested calcite precipitation and finally host extensive terrestrial ooid deposits the importance of this comprehensive paragenetic record is its applicability to not only recognize unconformities in the rock record but to better appreciate the climate in which they formed

unconformities and porosity development in carbonate strata ideas from a hedberg conference the purpose of this paper is to highlight ideas from a hedberg conference concerning detection of unconformities and associated porosity in carbonate strata many types of information including cores and outcrops seismic data eustatic sea level curves wireline logs biostratigraphic data stable isotope trends cycle stacking patterns and tectonic and basin evolution models can be used to predict and or detect subaerial unconformities all methods of detecting subaerial exposure with these types of information have limits and pitfalls detailed analysis of the stratigraphy sedimentology and diagenetic history of a rock sequence from outcrop or core data is considered the most reliable means of detecting subaerial exposure though an integrated approach using all a ailable information is recommended the relationship between subaerial exposure and subsurface porosity in carbonates is not simple or easily predicted subsurface porosity is the product of many factors operating during deposition subaerial exposure and burial several concepts should be recognized when evaluating porosity associated with subaerial unconformities 1 carbonate diagenesis during subaerial exposure rearranges pore networks but usually does not increase the total porosity near surface dissolution can simply lower a topographic surface without increasing porosity within the host limestone in many cases total porosity in carbonates under unconformities is actually reduced during subaerial exposure 2 permeability is likely to change more than porosity during subaerial exposure increasing in some c ses but decreasing in others 3 pore systems evolve with time during subaerial exposure short periods of subaerial exposure 10 000 400 000 yr are often associated with greater porosity than long intervals of subaerial exposure 1 20 million yr prolonged subaerial exposure may change permeability less than porosity because high permeability karst related conduits can form quickly and persist for millions of years 4 many carbonates subjected to subaerial exposure have little or no porosity in the deep subsurface because compaction cementation and stratal collapse reduce porosity during burial 5 unconformity related diagenesis may enhance reservoir potential by creating pore systems that are resistant to compaction during deeper burial 6 vugs caverns and breccias can fo m in the deep subsurface because of dissolution by basinal fluids independent of subaerial exposure 7 lithologic changes at unconformities like shales overlying carbonates can influence the flow of subsurface fluids during end page 857 deeper burial resulting in deep burial dissolution localized along unconformities if subaerial exposure and exposure surfaces are integrated into a sequence stratigraphic paleogeographic and climatic framework systematic and hopefully predictable patterns will emerge however we do not fully understand the complex interplay between the factors critical to creating and preserving porosity in carbonates additional research is needed to quantify critical processes and products so we can reliably predict porosity associated with subaerial exposure during exploration in frontier basins and on a smaller scale during reservoir analysis

paleostress inversion a multi parametric geomechanical evaluation of the wallace bott assumptions wallace 1951 and bott 1959 were the first to introduce the idea that the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface however this simplified hypothesis is questionable since fault mechanical interactions may induce slip reorientations earlier numerical geomechanical models confirmed that the slickenlines slip vectors are not necessarily parallel to the maximum resolved shear stress but are consistent with local stress perturbations this leads us to ask as to what extent the wallace and bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data here a geomechanical multi parametric study using a 3d boundary element method covering i fault geometries such as intersected faults or corrugated fault surfaces ii the full range of andersonian state of stress iii fault friction iv fault fluid pressure v half space effect and vi rock properties is performed in order to understand the effect of each parameter on the misfit angle between geomechanical slip vectors and the resolved shear stresses it is shown that significant misfit angles can be found under specific configurations invalidating the wallace and bott assumptions even though fault friction tends to minimize the misfit we therefore conclude that in such cases stress inversions based on fault slip data should be interpreted with care

the role of microorganisms in phytokarst development on dolostones and limestones grand cayman british west indies phytokarst is spectacularly developed on the hard finely crystalline dolostones of the oligocene miocene bluff formation and to a lesser extent on the soft limestones of the pleistocene ironshore formation on grand cayman the black weathered surfaces which are a reflection of an organic coating contrast sharply with the white colour of the unaltered host rocks which lack an organic coating on the dolostones this organic coating is formed principally of fungal sporangia and spores associated with mucilage along with lesser numbers of algae and bacteria endolithic and epilithic filamentous microorganisms are rare on the limestones the organic coating is formed principally of endolithic and epilithic filaments and mucilage fungal spores are rare and no sporangia were found the limestones of the ironshore formation are characterized by an intensely bored zone beneath the weathering surface in contrast the dolostones of the bluff formation have relatively few endoliths penetrating from the w

structural analysis of the northern part of the east anatolian fault system abstract the east anatolian fault system eafs is an intra continental strike slip fault associated with the collision of the arabian plate with the anatolian plate in the alp himalaya system in this study the northern part of the eafs was studied we measure more than two hundred fault slip data strike dip striation and slip sense for each fault in eighteen different localities to make paleostress reconstruction of the related area several criteria are taken into consideration in order to reveal chronology of faulting such as superimposed slickenlines age of the affected strata and syndepositional faults our results show three different deformation stages from the middle eocene to today in the study area 1 the nw se extensional tectonic oldest stage became effective in middle eocene middle miocene 2 the nne ssw compressional tectonic become effective in late miocene early pliocene 3 the strike slip tectonic youngest stage has been effective since late pliocene the maximum compressive stress 1 orientation averaged around n25 e and n15 e for stage 2 and stage 3 respectively this ca 100 rotation of the maximum compressive stress 1 orientation may be related to the formation of the strike slip faults concluded changing in the stress orientations between 3 and 2 in the late pliocene

forty years of paleostress analysis has it attained maturity abstract powerful methods of paleostress analysis from fault slip data have been used since the 1970 s and have demonstrated their capacity for reconstructing stress fields with tectonic significance however in some cases these methods have been applied to samples that do not fulfill basic requirements or developed on the basis of unsound conceptual models most methods of fault slip are based on the wallace bott principle dynamic paradigm while others invoke the necessity of remaining within the alternative kinematic paradigm therefore inferring only finite strain or strain rate axes the scientific community shares neither standard procedures for applying these methods nor standard parameters for assessing the quality of results this indicates that paleostress analysis has not attained maturity it is necessary to see back to the conceptual and methological bases following accurate procedures of data collection using additional field observations and critically assessing the results within the tectonic setting spatial and temporal heterogeneity of stress fields over all scales makes the mean stress tensor obtained from site analysis just an abstract notion though indispensable for understanding lithosphere dynamics

the north anatolian fault a new look dedicated to the memory of three pioneers ihsan ketin sirri erinc and melih tokay and a recent student aykut barka who burnt himself out in pursuit of the mysteries of the north anatolian fault abstract the north anatolian fault naf is a 1200 km long dextral strike slip fault zone that formed by progressive strain localization in a generally westerly widening right lateral keirogen in northern turkey mostly along an interface juxtaposing subduction accretion material to its south and older and stiffer continental basements to its north the naf formed approximately 13 to 11 ma ago in the east and propagated westward it reached the sea of marmara no earlier than 200 ka ago although shear related deformation in a broad zone there had already commenced in the late miocene the fault zone has a very distinct morphological expression and is seismically active since the seventeenth century it has shown cyclical seismic behavior with century long cycles beginning in the east and progressing westwa

weathering rates on a caribbean reef limestone results and implications abstract weathering of presently raised reef islands provides an analogue for the behaviour of pleistocene reefs made emergent by glacio eustatic falls in sea level micro erosion meter measurements on grand cayman island west indies have shown that high mean weathering rates 1 00 mm yr 1 are restricted to the marine environment large scale landform development is unlikely to have been the product of the last period of exposure but rather the result of successive phases of weathering and reef growth increasing the differential relief of the reef base throughout the pleistocene

ongoing long term evolution of an unconformity that originated as a karstic surface in the late miocene a case study from the cayman islands british west indies abstract on grand cayman and cayman brac karst development on the upper surface of the cayman formation during the late miocene lowstand produced the cayman unconformity on grand cayman this led to the development of a deep atoll shaped depression on the western part of the island the ensuing lower pliocene transgression buried that unconformity and led to deposition of sediments that now form the pedro castle formation today on grand cayman the dolostones of the cayman formation remain largely buried on the western half of grand cayman but are widely exposed on the central and eastern parts of the island where they have been subjected to extensive weathering over the last 4 3 ma although the situation is similar on cayman brac uplift of the central core led to removal of the pedro castle formation and much of the cayman formation karst development on both islands reflects the interplay between neogene sea level changes climate and tectonic uplift today weathering is further modifying the cayman unconformity on the eastern parts of both islands the cayman unconformity on the central and eastern parts of grand cayman is characterized by karst landforms including a peripheral rim sinkholes solution widened joints and photolineaments surface traces of joints and or faults the westward tilting of cayman brac 4 3 ma to 400 ka led to more severe weathering of the exposed cayman formation that included 1 enhancement of the peripheral rim and karst features on the upslope margin and 2 higher denudation rates than on grand cayman during the messinian the denudation rate on the west end of grand cayman was 0 03 0 10 mm yr 1 in contrast the denudation rate over the an estimated period of 4 9 to 6 2 ma for the eastern half of grand cayman has been about 0 01 mm yr 1 whereas on the east end of cayman brac it has been 0 03 0 04 mm yr 1 on both islands substantial thicknesses of strata have been lost to erosion and the cayman unconformity has been subject to ongoing modification over a period of 4 9 to 6 2 ma

deciphering the impact of sea level changes and tectonic movement on erosional sequence boundaries in carbonate successions a case study from tertiary strata on grand cayman and cayman brac british west indies abstract the stratigraphic architecture of carbonate successions that develop on geographically isolated islands reflects the balance between sea level highstands lowstands and tectonic activity this is readily apparent in the tertiary carbonate sequences on the cayman islands that are formed of the bluff group which includes the brac formation lower oligocene cayman formation middle miocene and pedro castle formation middle pliocene these strata are overlain by the pleistocene ironshore formation the unconformities that define the boundaries between these formations are variable because some developed during one cycle of past erosion others developed through two or more past erosional cycles and some are still developing today some unconformities like the one at the top of the cayman formation are geographically variable because they underwent different developmental histories in different areas the challenge with architectural complex successions like those on the cayman islands is that of deciphering the impact of sea level changes as opposed to tectonic influences during sea level lowstands the older carbonate successions were exposed on land and modified by surface and subsurface karst development at the same time marine erosional processes affected the coastal areas surface karst modification which commonly produced rugged topographies with erosional relief at least 62 m was controlled largely by rainfall runoff and stratal dip weathering on grand cayman at the end of the miocene for example produced a dish shaped topography with elevated peripheral rims in contrast uplift of the east end of cayman brac between the late pliocene 3 6 ma and 400 ka elevated the basal part of the cayman formation 33 m above sea level subsequent karst development which is still ongoing today removed most of the cayman formation on the eastern part of the island and produced peripheral rims that are higher than those on grand cayman during some lowstands like that between the late pliocene and 400 ka coeval coastal erosion led to the development of coastal benches that cut into the older carbonate strata the combination of karst development in the islands interiors and coastal erosion produced complex rugged topographies that strongly influenced patterns of deposition during the following highstand the complex stratigraphic architecture of the carbonate successions on the cayman islands reflects the variable impact of tectonics karst development and coastal erosion that was associated with each lowstand highstand cycle

origin of island dolostones a case study from the cayman formation miocene cayman brac british west indies abstract cayman brac the easternmost of the cayman islands is 19 km long 1 5 to 3 km wide and rises 40 m above sea level at its eastern end geographically isolated by the deep oceanic waters of the caribbean sea this island with its thick succession of pervasively dolomitized tertiary rocks is a natural laboratory for assessing the origin of island dolostones dolostones in the miocene cayman formation 100 m thick with most crystals 55 mol caco3 geochemically they are characterised by 13c values of 1 6 to 3 5 18o values of 2 3 4 0 80 279 ppm sr 52 340 ppm fe and 9 82 ppm mn the inverse correlation between 18o and mol caco3 and positive correlation between sr and mol caco3 largely reflect kinetic effects on oxygen isotope fractionation and the sr partition behaviour between dolomite and water dolomite stoichiometry indicates formation from waters with a high mg ca ratio and 18o values corrected for biases associated with dolomite stoichiometry and phosphoric acid fractionation indicate formation from normal seawater like fluids under near surface conditions the 87sr 86sr ratios point to two phases of dolomitization phase i in the late miocene 6 8 ma caused partial dolomitization of the basal part of the cayman formation phase ii during the pliocene to early pleistocene 1 5 ma completed dolomitization of the cayman formation both phases of dolomitization were mediated by similar fluids although available information suggests that dolomitization was probably linked to sea level fluctuations the timing of dolomitization relative to the transgressive regressive cycle remains open to debate

morphometric analysis of sinkholes in a karst coastal area of southern apulia italy salento the southern portion of apulia region se italy is a narrow and elongated peninsula in carbonate rocks with prevailing low coastlines locally interrupted by high rock cliffs the long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes as observed in many other karst coastal settings worldwide development of sinkholes may be particularly severe along the coasts where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes even influencing the coastline evolution following a previous study where the main features of sinkholes at torre castiglione taranto province were investigated and described and a preliminary susceptibility map produced at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes the main morphometric parameters generally used for sinkhole characterization have been considered in this study shape of the sinkhole azimuth and length of maximum and minimum axes depth elongation ratio and distance from the shorelines each of them is described both as individual parameter and in conjunction with the others in the attempt to identify the main factors controlling development of sinkholes in the area and their evolution as well with regard to this latter aspect beside simple morphometry of the sample of sinkholes at torre castiglione we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities to investigate the matter a three stage analysis has been carried out in this study by means of field measurements of the fractures bounding the sinkholes field measurement of the long axes azimuth of the elongated sinkholes comparison of the previously described sets with the strikes of the main regional geological structures the obtained results show in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays eventually the approach here presented may be applied in other karst coastal sinkhole prone areas to gain new knowledge on the genesis and evolution of coastal sinkholes and to properly evaluate the hazard they pose to the anthropogenic environment

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

karst database implementation in minnesota analysis of sinkhole distribution this paper presents the overall sinkhole distributions and conducts hypothesis tests of sinkhole distributions and sinkhole formation using data stored in the karst feature database kfd of minnesota nearest neighbor analysis nna was extended to include different orders of nna different scales of concentrated zones of sinkholes and directions to the nearest sinkholes the statistical results along with the sinkhole density distribution indicate that sinkholes tend to form in highly concentrated zones instead of scattered individuals the pattern changes from clustered to random to regular as the scale of the analysis decreases from 10 100 km2 to 5 30 km2 to 2 10 km2 hypotheses that may explain this phenomenon are 1 areas in the highly concentrated zones of sinkholes have similar geologic and topographical settings that favor sinkhole formation 2 existing sinkholes change the hydraulic gradient in the surrounding area and increase the solution and erosional processes that eventually form more new sinkholes

oligocene sea level falls recorded in mid pacific atoll and archipelagic apron settings drilling results from mid pacific atoll and archipelagic apron sites in the line islands and marshall islands provinces lead to the conclusion that oligocene sea level falls detected in atlantic passive margin sequences are also recorded in a mid plate tectonic setting in the pacific basin the mid pacific sea level falls are recorded by a the presence of distinct coarse grained graded beds of turbidite origin rich in reef derived skeletal debris of oligocene eocene and cretaceous age that were redeposited in deep water archipelagic apron carbonate sequences of middle and late oligocene age now flanking the atolls and b a marked stratigraphic hiatus and solution unconformity in the subsurface of enewetak atoll which dates an oligocene period of atoll emergence correlative with both the deposition of the turbidites and the coastal offlap events discerned in atlantic passive margins correlation of the subsidence path of enewetak atoll with the development of the oligocene solution unconformity shows that ca 30 ma sea level was as much as 100 m lower than at present

paleostress analysis of the yesilyurt elazig fault zone and its importance for the tectonic evolution east turkey abstract the yesilyurt elazig fault zone yefz located in eastern anatolia is a morphologically distinct ne sw trending left lateral strike slip fault about 150 km long in this study inversion of fault slip data collected from the yefz and tectonic locations of the stratigraphic units are used in order to reveal the tectonic evolution and chronology of faulting from early paleocene to today based on the inversion of about 250 fault slip data four successive deformation phases are defined in the study area since early paleocene the first deformation phase is characterized by n s compression during the early paleocene the second deformation phase is nw se extension related to slab steepening and breakoff in late paleocene early miocene the third deformation phase is a nne ssw compressional one in the middle miocene early pliocene a strike slip phase with nne ssw compression is the fourth and youngest deformation phase in the study area dip slip striations are overprinted by strike slip striations we hence interpret that these faults were reactivated under the later stress field our results are consistent with other published regional studies

improved chronostratigraphic reference curve of late neogene seawater 87sr 86sr we present a reference curve of seawater 87 sr 86 sr variation through the past 7 m y based on 455 samples of planktonic foraminifera from ocean drilling program odp site 758 in the indian ocean this single site curve is superior to extant curves because of several features 1 a continuous sedimentary section free of disturbances 2 a well determined and precise chronostratigraphy that is calibrated to numeric age on the basis of continuous magnetostratigraphy and a refined astronomical time scale 3 a high temporal resolution sample interval averages 15 ka 4 an improved analytical reproducibility and 5 a uniformly high sample quality the gross structure of the site 758 curve is generally similar to that observed in previous work but the increased temporal resolution and decreased analytical scatter of the curve provide improved chronostratigraphic resolution at the 95 confidence level uncertainties on age estimates range from 0 60 m y in the lower pleistocene and upper miocene to 2 03 m y in the middle pliocene moreover this detailed record identifies two periods of steplike increases in seawater 87 sr 86 sr 6 10 to 5 80 ma and 1 46 to 1 13 ma that are characterized by rates of change of 150 10 6 m y these features if verified at other sites indicate abrupt changes in the sr mass balance of the ocean and may be used as precise event markers in late neogene marine sections

absolute magnitude of the second order middle to late miocene sea level fall marion plateau northeast australia the miocene carbonate platform of the marion plateau in northeast australia preserves an excellent record of sea level fluctuations the warm water platform consists of an early to middle miocene second order highstand complex whereas the late miocene platform is a second order lowstand complex analysis of the sea level fall that led to this relation shows that the amplitude of this event was at least 180 m furthermore we suggest a methodology for determining the amplitude of sea level fluctuations based on measurement of sea level falls in structurally simple parts of passive margins or in distal parts of foreland basins

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

discontinuity surfaces on a shallow marine carbonate platform berriasian valanginian france and switzerland discontinuities in sedimentation are commonly expressed as surfaces in outcrop sections and are due to rapid and substantial environmental changes on shallow marine carbonate platforms most such surfaces represent hiatuses below biostratigraphic resolution and detailed analysis is necessary to identify and evaluate the environmental change involved surfaces in nine sections of the lower cretaceous of the french and swiss jura platform are characterized on the basis of eight universally applicable criteria geometry lateral extent morphology biological activity mineralization facies contrast diagenetic contrast and biostratigraphy nine different surface types are distinguished by their common features and environment of formation all of them are related to environmental changes in the form of subaqueous erosion subaerial exposure subaqueous omission or changes in texture and facies the distribution of surface types in the studied sections shows that condensation and exposure related surfaces tend to occur repetitively in certain intervals calibrated by biostratigraphy these surface zones can be correlated across the platform from proximal to distal positions in comparison with the global sequence stratigraphic framework hardenbol et al 1997 most exposure zones correlate with third order sequence boundaries condensation zones fall in between in the studied sections third order eustatic sea level drops appear to be represented rather by zones of small scale discontinuities than by widespread and well marked single sequence boundaries this is explained by the superposition of high frequency low amplitude sea level fluctuations on a larger scale sea level trend under greenhouse conditions the lateral extent of the surface zones varies through time and indicates important changes in platform morphology changes in local subsidence rate indicated by variable thicknesses of the deposits in comparison with second and third order sea level trends suggest an evolution of the french jura platform from a ramp type morphology in the late middle berriasian to a flat topped platform in the late berriasian the early valanginian again is characterized by increased differential subsidence and well marked platform morphology this study demonstrates that 1 small scale and short lived discontinuities can reflect large scale variations of relative sea level 2 on shallow platforms characterized by small topographic variations and lateral facies changes third order sequence stratigraphic surfaces are not necessarily expressed by one widespread single surface but by zones of surfaces indicating repeated environmental changes surface zones can serve as an additional tool for correlation and interpretation of platform evolution and 3 small scale discontinuities form an integral part of the stratigraphic record and should receive the same attention as the sedimentary deposits they delimit

the paradox of tropical karst morphology in the coral reefs of the arid middle east despite differences in reef growth between the arabian gulf and the red sea a common distinctive pattern of polygonal sills surrounding ponded depressions consistently occurs in shallow water viewed from a satellite these seafloors are reticulated and maze like despite little current rainfall this patterning is best explained by karst dissolution of limestone during periods of lower sea level this is a paradox since such fine scale karstification is confined to areas with considerably more precipitation than currently observed in arabia we resolve this apparent contradiction by developing a pleistocene holocene chronology of sea level and climate for the red sea and arabian gulf and through the use of pattern analysis and computer simulation reveal the mechanism of formation for these structures we demonstrate that this patterning can be taken as a quaternary signature of paleohumidity in the now hyperarid red sea and arabian gulf

petrographic and geochemical features of sinkhole filling deposits associated with an erosional unconformity on grand cayman abstract on grand cayman exposures of dolostones belonging to the cayman formation miocene represent an erosional unconformity that has been developing since the late pliocene 3 6 ma sinkholes that developed during this time have remained open or become partly to fully filled with various combinations of rootcrete breccias loose limestone and dolostone lithoclasts and white red and orange limestones these sinkhole filling deposits have different geochemical attributes to the neogene and pleistocene marine carbonates that form the bedrock of the island the deposits in the sinkholes formed in response to the variations of sea level climate exposure and vegetation that developed during the period when the erosional unconformity was developing the rootcrete oncoids red and orange limestones are terrestrial in origin whereas the limestone and dolostone lithoclasts and white limestones are derived from marine deposits on the erosional unconformity intense root activity led to the formation of rootcrete and terrestrial oncoids but also selectively blackening reworked marine carbonates the red and orange limestone matrices which formed under more arid conditions contrast with the other sinkhole filling deposits that formed during periods when the climate was semi arid to humid the distinctive ree signatures of the sinkhole filling deposits which are different from those of the bedrock limestones and dolostones can probably be attributed to trace amount of terra rossa and or airborne saharan derived dust that are present in those deposits

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

age refinement of the messinian salinity crisis onset in the mediterranean we propose a revised age calibration of the messinian salinity crisis onset in the mediterranean at 5 971 ma based on the recognition of an extra gypsum cycle in the transitional interval of the perales section sorbas basin spain and the revision of the magnetostratigraphy of the monticino section vena del gesso basin italy this age re calibration allows to state more accurately that i the interval encompassing the msc onset is continuous thus ruling out any erosional feature or stratigraphic hiatus related to a major sea level fall affecting the mediterranean ii the first gypsum was deposited during the summer insolation peak at 5 969 ma associated with an eccentricity minimum and roughly coincident with glacial stage tg32 iii the msc onset was preconditioned by the tectonically driven reduction of the hydrological exchanges with the atlantic ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern africa

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

stress deflection in a tectonic compressional field a model for the northwestern iberian chain spain by means of fault population analysis using the right dihedra y r diagram and etchecopar s methods the states of stress in a number of sites of the cameras massif northwestern iberian chain spain and nearby areas of the ebro basin have been determined these states of stress have been used as a framework in order to infer a model of the actual stress field in that area during the main stage of the alpine compression oligocene lower miocene the three main compression directions obtained nw se nne ne sw can be explained by a single compression field with horizontal 1 trending nne and vertical 2 whose primary trajectories are deflected due to 1 large scale strike slip faults or lateral ramps of thrusts or 2 frontal ramps of thrusts oblique to the main compressive axis the reliability of this scheme has been checked by means of a two dimensional mathematical model based upon the finite element method and applied on a sheet whose rheological properties are similar to those of a standard limestone this model simulates the main features of the regional stress field and it was constructed after determining the average parameters of the possible external or primary field and simulating the major faults that could deflect the stress trajectories

sea level events in the south pacific linked with the messinian salinity crisis cores drilled through the carbonate cap of niue a mid oceanic carbonate platform in the south pacific contain an unusually well resolved stratigraphic section of the latest miocene at 35 to 140 m depth below sea level intensely leached and chalky intervals associated with pronounced 18 o and 13 c depletions mark the position of dissolution unconformities representing eight episodes of eustatic falls that outstripped the local rate of subsidence we demonstrate on the basis of sr isotope chronostratigraphy that these eustatic changes are correlative with the messinian salinity crisis events in the mediterranean sea level changes of about 10 m amplitude commenced at 6 14 ma and culminated in a large sea level fall that reached at least 30 m at 5 26 ma corresponding to the miocene pliocene boundary evaluation of the sea level history reported here and the contemporaneous mediterranean events supports the model of coupling between tectonic and eustatic factors that caused the onset and demise of the salinity crisis the available evidence suggests that during messinian time glacio eustatic falls and rises are likely to have modulated the connection between the atlantic and the mediterranean and influenced the evaporite deposition and may have contributed significantly to the final phase of isolation and desiccation of the mediterranean and its subsequent refilling during the zan clean deluge

void filling deposits in karst terrains of isolated oceanic islands a case study from tertiary carbonates of the cayman islands caves fossil mouldic cavities sinkholes and solution widened joints are common in the cayman and pedro castle members of the bluff formation oligocene miocene on grand cayman and cayman brac because they have been subjected to repeated periods of karst development over the last 30 million years many voids contain a diverse array of sediments and or precipitates derived from marine or terrestrial environs mineral aerosols and groundwater exogenic sediment was transported to the cavities by oceanic storm waves transgressive seas runoff following tropical rain storms and or in groundwater at least three periods of deposition were responsible for the occlusion of voids in the cayman and pedro castle members voids in the cayman member were initially filled or partly filled during the late oligocene and early miocene this was terminated with the deposition of the pedro castle member in the middle miocene subsequent exposure led to further karst development and void filling sedimentation in both the cayman and pedro castle members speleothems are notably absent the void filling deposits formed during these two periods which were predominantly marine in origin were pervasively dolomitized along with the host rock 2 5 million years ago the third period of void filling deposition after dolomitization of the bluff formation produced limestone various types of breccia terra rossa speleothemic calcite and terrestrial oncoids most of these deposits formed since the sangamon highstand 125 000 years ago voids in the present day karst are commonly filled or partly filled with unconsolidated sediments study of the bluff formation of grand cayman and cayman brac shows that karst terrains on isolated oceanic islands are characterized by complex successions of void filling deposits that include speleothems and a variety of sediment types the heterogenetic nature of these void filling deposits is related to changes in sea level and climatic conditions through time

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

origin of atoll lagoons a database of 301 atolls from the pacific indian and atlantic oceans has been analyzed with respect to factors governing maximum atoll lagoon depth statistically significant correlations between maximum atoll lagoon depth and both atoll area and present day rainfall are viewed as the combined effect of paleorainfall precipitation and catchment area in contributing to overall atoll morphology this interpretation is supported by the gross saucer shaped morphology of several of the lau group of the fiji islands and the subsurface cretaceous golden lane atoll of mexico where evidence of reef rim construction is lacking but evidence for significant solution relief is compelling the contribution of reefs to atoll rim construction appears to be limited generally to 10 m leaving more than 20 m of relief to be explained at most atolls at a number of these the last interglacial highstand surface is 15 20 m beneath holocene rim sediments subsidence rates of even 5 cm k y do not suffice to explain the subsea depth of this unconformity suggesting the dominating influence of solution on relief expression calculations of solution rates relative to the residence time of sea level below given depths during the past 700 k y suggest that the observed atoll relief is in part inherited from more than one pleistocene or perhaps earlier glacial stage whatever the precise time of origin the data available strongly suggest that atoll morphology is solution determined rather than growth predicated

distribution and interpretation of rare earth elements and yttrium in cenozoic dolostones and limestones on cayman brac british west indies abstract the cenozoic carbonate succession on cayman brac a small island 19 km long and 1 5 to 3 km wide located in the caribbean sea has been dolomitized to varying degrees the rare earth element ree and yttrium y concentrations ree y of 134 carbonate samples 127 from cayman brac and 7 supplementary samples from grand cayman vary from 0 2 to 7 5 ppm average 2 8 ppm n 134 the shale normalized ree y patterns of the carbonate samples akin to those of oxygenated seawater are characterized by 1 lree depletion relative to hree average dy n sm n 1 7 n 125 2 positive la anomalies 3 negative ce anomalies average ce ce 0 4 n 133 and 4 superchondritic y ho molar ratios average y ho 85 n 86 the lack of correlation between the dolomite content of the samples and their ree y dy n sm n la n nd n ce ce or y ho indicates that dolomitization did not have a major impact on ree y signatures and that dolomitization was probably mediated by seawater like fluids the shale normalized patterns e g dy n sm n la n nd n ce ce and y ho vary from formation to formation for samples from the cayman formation the pedro castle formation and the ironshore formation there are subtle but gradual changes in dy n sm n la n nd n ce ce with depth in contrast there are marked changes in la n nd n ce ce y ho and sm nd across the brac unconformity which forms the boundary between the lower oligocene brac formation and the overlying miocene cayman formation variations in the ree y patterns reflect diagenetic processes e g dy n sm n and possibly secular changes in the ree y composition of seawater e g la n nd n y ho and sm nd

the east anatolian fault geometry segmentation and jog characteristics a detailed account is given of the fault geometry and segment structure of the east anatolian fault zone as a whole based on mapping of active faults supported by available seismological and palaeoseismological data we divide the east anatolian fault into two main strands southern and northern the main southern strand is c 580 km long between karliova and antakya and connects with the dead sea fault zone and the cyprus arc via the amik triple junction the northern strand termed the surgu misis fault system is c 350 km long and connects with the kyrenia misis fault zone beneath the gulf of iskenderun we infer that slip partitioning between the main and northern strands of the east anatolian fault accommodates 2 3 and 1 3 of the slip rate of the lateral motion between the arabian and anatolian plates respectively in the celikhan adana antakya region taking account of the time elapsed from the latest events on the east anatolian fault we suggest that the pazarcik and amanos segments have the potential to produce destructive earthquakes in the near future

effects of topography on surface fault geometry and kinematics examples from the alps italy and tien shan kazakstan abstract the kinematics and extent of surface faulting are usually determined using observations on morphostructures such as escarpments and measurements of the net displacement of geologic deposits and topographic features such as gullies and ridges the present paper shows that these measurements can be misleading in rugged terrains if one does not take into account the effect of topography to illustrate this effect field data on surface deformations collected along holocene faults of the italian alps and kazakstan tien shan are compared with fault plane geometry and local topography the reverse foscagno fault italy which is also linked to deep seated gravitational slope deformation splays upward at a 50 m high ridge inducing scarps with apparent normal offset the transpressional sate fault tien shan changes its dip near the surface where it intersects ridges at least 50 60 m high here fault inclination changes up to 60 80 with a complete inversion of fault dip a normal fault appearing at the surface the transpressional beskaragai fault tien shan manifests an opposite sense of slip at a 80 m high ridge a detailed measurement of surface displacement along these holocene structures shows that the offset apparently increases at ridges and tends to zero at inter ridge depressions these data are here explained with a new model which considers the greater mobility of the rock mass of the ridge which has unbuttressed sides this produces upward or horizontal downhill expulsion of part of the ridge in a direction perpendicular to the fault strike if faulting has vertical motions while the expulsion direction is parallel to the fault strike when strike slip motions occur this expulsion can be accompanied by tilting which produces oversteepening of the downhill slope and landsliding

open and filled karst features on the cayman islands implications for the recognition of paleokarst the dolostones of the oligocene miocene bluff formation on the cayman islands are characterized by well developed surficial interface and subsurface karst features that are open or filled with speleothems and sediment some of the open caves show evidence of a minimum of two stages of development related to dissolution in the phreatic zone and the vadose zone the development of speleothemic formations e g stalactites stalagmites columns is limited in some caves but extensive in others some of the caves have limited amounts of sediment on their floors in these caves the speleothems and sediments are still formed of caco3 and thus contrast sharply with the dolostone of the bluff formation in which they occur some of the joints sinkholes and caves are filled with breccia caymanite terra rossa terra rossa breccia pisolitic limestone and speleothems although filled such karst features are analogous to the open karst features that occur elsewhere on the islands the filling of joints sinkh

hydrogeology of grand cayman british west indies a karstic dolostone aquifer abstract on grand cayman freshwater bodies present in the bluff formation are typically small and occur as thin lenses floating on top of dense saline water evaluation of the water resource potential of these freshwater lenses is difficult because of their variable hydrological conditions complex paleohydrogeology and aquifer heterogeneity secondary porosity created by preferential dissolution of aragonitic fossil components is common open fissures and joints developed under tectonic stress and karst development associated with sea level fluctuations are however the two most important causes of porosity and permeability in the aquifers on grand cayman fracture and karst porosity control the lens occurrence by 1 acting as avenues for the intrusion of seawater or upward migration of saline water 2 acting as recharge focal points 3 enhancing hydrodynamic dispersion 4 defining lens geometry 5 facilitating carbonate dissolution along joints and fissures a clear understanding of the hydrological and geological conditions is important in developing small lenses in a setting similar to that on grand cayman this pragmatic approach can help identify the optimum location of the well field and avoid areas particularly susceptible to saline water intrusion

sea level highstands over the last 500 000 years evidence from the ironshore formation on grand cayman british west indies abstract the ironshore formation up to 19 m thick in the rogers wreck point area of grand cayman is divided into the unconformity bounded units a b c and d the unconformities are highlighted by caliches and or terra rossa th u dates from aragonitic corals indicate that unit a formed at 400 ka unit b 346 ka unit c 229 ka and unit d 131 ka these ages correlate with the highstands of the last four interglacial periods and probably represent marine isotope stages 5 unit d 7 unit c 9 unit b and 11 unit a the limestones in units a d which have similar biotic and lithologic characteristics represent deposition in shallow water on a narrow coastal shelf unit a has a high faunal diversity and was deposited in open marine conditions whereas units b c and d were deposited in quieter water lagoons that probably had fringing reefs along their sea ward edges although grand cayman is located on the cayman ridge close to an active spreading center and transform fault the island has undergone little or no vertical movement over the last 500 ky available evidence indicates that sea level at the time of deposition of each unit relative to present sea level was unit a 9 0 to 5 5 m unit b 3 0 to 0 5 m unit c 2 5 to 1 1 m and unit d 2 5 to 6 0 m these data are good estimates of eustatic sea level highstands over the last 500 ky

theory of slickenline patterns based on the velocity gradient tensor and microrotation abstract brittle fault zones commonly are characterized by a multitude of lineated shear planes having a wide distribution of orientations in our model we assume the faulted rock comprises an aggregate of rigid blocks whose surfaces are the shear planes we define two independent scales of motion to distinguish the local rigid rotation of the blocks with their shear planes the micromotion from the average deformation of the material on a macroscopic scale the macromotion the macromotion is defined by the macrovelocity gradient tensor which is separated into symmetric and antisymmetric parts the deformation rate and the macrospin tensors respectively the micromotion is defined by a microspin tensor on any shear plane slickenlines form parallel to the direction of the maximum rate of shear which we assume is determined by the direction of the maximum component of the macrovelocity gradient tensor tangent to the shear plane and by a component of the microspin in the shear plane for a restricted kinematic model patterns of slickenline orientations are defined on a uniform distribution of shear plane orientations by the values of d and w d is a ratio of differences in the principal values of the deformation rate tensor and w is a ratio of the net spin to the maximum rate of macroshear we distinguish between instantaneous slickenline patterns and finite deformation patterns the two are different if the shear planes rotate relative to the principal deformation rate axes in which case finite deformation slickenlines form curved or crossing lineations if w 0 the instantaneous slickenline patterns have orthorhombic symmetry 0 d d 1 or 0 if w 0 the instantaneous slickenline patterns have monoclinic symmetry for pure shear in an isotropic body instantaneous slickenline patterns have orthorhombic symmetry w 0 d 0 5 whereas for pure shear accommodated by shear on a planar anisotropy w 1 d 0 5 the pattern is monoclinic for simple shear with the rigid rotation of local shear planes defined by the shear induced spin w 0 d 0 5 the instantaneous slickenline pattern is orthorhombic but the finite deformation pattern is monoclinic for simple shear with no shear plane rotation w 1 d 0 5 the instantaneous pattern is monoclinic special cases of our hypothesis are equivalent to the hypothesis that slickenlines are parallel to the direction of maximum resolved shear stress e g angelier 1979 1984 the slickenline patterns predicted for this case are always of orthorhombic or higher symmetry and are equivalent to our instantaneous patterns for which w 0 and to our finite deformation patterns for which in addition there is no microspin