carbonate evaporite siliciclastic transitions in quaternary rift sediments of the northwestern red sea abstract the quaternary and recent coastal environments of the egyptian red sea and gulf of suez are characterized by rapid lateral variations carbonates evaporites and siliciclastic sediments exist in close proximity although the climate is exceptionally dry the numerous wadis draining high hinterland relief deliver important quantities of coarse clastics to coastal environments during the rare periods of flash flooding however because this efficient supply is sporadic coastal waters are contaminated for short catastrophic periods which are followed by a rapid return to clear water carbonate sedimentation the warm arid conditions on the other hand favour both carbonate reef production and evaporite mineral precipitation rapid lateral transitions between continental siliciclastic and marine carbonate facies are favoured by a particular morphology closely related to the active distensional tectonic setting within the red sea rift block faulting which began in the early miocene and continues today has resulted in numerous subparallel grabens and horsts situated between the onshore basement relief and the coast the structural depressions grabens tend to trap much of the episodic siliciclastic input favouring permanent carbonate production in the nearby littoral environments

earthquake induced resedimentation in the badenian middle miocene gypsum of southern poland in the badenian middle miocene basin of the carpathian foreland of southern poland gypsum breccias occur associated with laminated gypsum deposits these breccias consist of large clasts of gypsum carbonates marls and clay chips of variable size embedded in a gypsarenitic matrix constituent gypsum grains and clasts commonly appear to be mechanically abraded and chemically corroded crystals or fragments of selenitic laminated and alabastrine gypsum gypsorudites are commonly accompanied by laminated gypsarenites and gypsolutites which show graded bedding a vertical sequence of graded gypsum beds showing bouma sequences may be recognized in borehole sections microfolding is common within the folded laminated gypsum and is closely associated with expressions of extensional strain both are accompanied by pervasive microfaulting suggesting a semi coherent downslope mass movement the stratiform geometry of the breccias together with the intensity of slumping relatively independent of the palaeoslope suggest earthquake shocks as the initial main cause gypsum deposits form a constant laterally extensive sequence of different lithofacies the occurrence of the same lithologies and shallowing up cycles over a wide area reflects thrusting of the carpathians over the carpathian foredeep local tectonism has also played a significant role the tectonic framework favoured activation of dip slip faults promoting shallow focus earthquakes these in turn resulted in the resedimentation of gypsum by slumps debris flows and turbidites a similar basinward resedimentation of clastic material by gravity flows initiated by fault induced earthquakes could be of great importance in the foreland geological setting and may explain some phenomena observed in other evaporite formations from different geological settings especially of rift type

earthquake triggered soft sediment deformation structures seismites in travertine deposits abstract earthquakes related soft sediment deformations seismites are relevant structures to help reconstructing the palaeoseismicity in a region nevertheless although seismites have been described for a large variety of palaeo environments and stratigraphic settings they are rare and in some cases ambiguous structures in this paper we document for the first time impressive seismites affecting a latest quaternary travertine deposit located in southern tuscany serre di rapolano italy these structures are extremely relevant as seismites have been never described for this kind of terrestrial deposits the seismites developed within a 2 5 m thick stratigraphic succession made of alternating terrigenous and carbonate sediments embedded within the travertine deposits earthquake produced liquefaction and fluidization of some terrigenous levels and the injection of fluidized silty sediments dykes and sills into carbonate and terrigenous levels slumped levels and associated decollement surfaces produced highly non cylindrical folds overall induced by the loss of brittle shear strength along the basin slopes the occurrence of these soft sediment deformations implies an important seismic event that took place in a time spam encompassed between 84 8 and 48 92 5 08 ka in an area characterized by low seismicity and scarce knowledge of its seismotectonic setting their spectacular exposition and preservation in saw cuts of an abandoned quarry cava oliviera quarry highlights their relevance and importance

argon 40 argon 39 age spectra of apollo 17 highlands breccia samples by laser step heating and the age of the serenitatis basin we have obtained high resolution 21 63 steps 40ar 39ar age spectra using a continuous laser system on 19 submilligram samples of melt rocks and clasts from apollo 17 samples collected from the pre imbrian highlands in the easternmost part of the serenitatis basin the samples include poikilitic melt rocks inferred to have been formed in the serenitatis basin forming impact aphanitic melt rock whose compositions vary and whose provenance is uncertain and granulite gabbro and melt clasts three of the poikilitic melts have similar age spectrum plateau ages 72395 96 3893 16 ma 2 72535 7 3887 16 ma 76315 150 3900 16 ma with a weighted mean age of 3893 9 ma which we interpret as the best age for the serenitatis basin forming impact published 40ar 39ar age spectrum ages of apollo 17 poikilitic melts are consistent with our new age but are much less precise two poikilitic melts did not give plateaus and the maxima in their age spectra indicate ages of 3869 ma 72558 7 and 3743 ma 77135 178 plateau ages of two poikilitic melts and two gabbro clasts from 73155 range from 3854 16 ma to 3937 16 ma and have probably been affected by the ubiquitous older clasts and by post formation heating impact events plateau ages from two of the aphanitic melt blobs and two granulites in sample 72255 fall in the narrow range of 3850 16 ma to 3869 16 ma with a weighted mean of 3862 8 ma two of the aphanitic melt blobs from 72255 have ages of 3883 16 ma and 3894 ma whereas a poikilitic melt clast of different composition from the serenitatis melts has an age of 3835 16 ma which is the upper limit for the accretion of 72255 these data suggest that either the aphanitic melts vary in age as is also suggested by their varying chemical compositions or they formed in the 72255 accretionary event about 3 84 3 85 ga and older relict material is responsible for the dispersion of ages in any case the aphanitic melts do not appear to be serenitatis products our age for the serenitatis impact shows on the basis of the isotopic age evidence alone that serenitatis is 20 25 ma and probably 55 60 ma older than imbrium 3870 ma and probably 3836 ma dalrymple and ryder 1993 noritic granulite sample 78527 has a plateau age of 4146 17 ma representing a minimum age for cooling of this sample in the early lunar crust so far there is no convincing evidence in the lunar melt rock record for basin forming impacts significantly older than 3 9 ga

the origin and significance of groundwater seepage gypsum from bristol dry lake california usa gypsum and anhydrite fabrics observed in trenches and deep 500 m cores from bristol dry lake california usa exhibit a vertical alignment of crystals similar to the fabric seen in bottom nucleated brine pond gypsum however geochemical and sedimentological evidence indicate that the gypsum formed in bristol dry lake precipitated displacively within the sediment where groundwater saturated with respect to gypsum recharges around the playa margin groundwater seepage gypsum evidence for displacive growth of gypsum is i the geometry of the deposit ii stable isotopic data and the water chemistry of the brine and iii inclusions of matrix which follow twin planes and completely surround crystals as they grow the bulk of the gypsum precipitated in the playa occurs around the edges of the playa in the playamargin facies and completely rings the lake sulphate concentrations in the groundwater increase toward the gypsum zone in the playa margin basinward of this zone sulphate concentrations decrease sharply to trace element levels in the basin centre brine authigenic gypsum is rare in the centre of the playa stable 18o values measured for gypsum waters of crystallization gwc are similar to the values calculated for groundwater in the playa margin and alluvial fan sediments 6 0 whereas measured brine 18o values range from 0 5 to 3 7 0 deuterium values measured for groundwater are 70 0 gwc are 60 to 65 0 and brine values are 57 0 the geometry of the deposit and the chemical data suggest that the water precipitating the gypsum is more closely associated with the groundwater than the brine however some mixing between groundwater and brine is likely within 100 m of the surface the gypsum dehydrates to anhydrite although the same vertically aligned fabric is retained through the diagenetic process the similarity of displacive vertically aligned gypsum and anhydrite fabrics seen in bristol dry lake to subaqueously deposited gypsum in modern brine ponds indicates that the criteria used to define subaqueous fabrics must be better constrained

deep water resedimentation of anhydrite and gypsum deposits in the middle miocene belayim formation of the red sea egypt the middle miocene evaporites in the red sea rift were deposited within a complex system of fault bounded basins that were episodically active during sedimentation such a tectonic framework is known to be highly favourable to resedimentation processes an offshore petroleum well in the north western red sea has cored below a massive salt unit an anhydrite bearing succession which provides an excellent opportunity to study the processes of gravity induced redeposition of ca sulphates in a deep basin anhydrite deposits interbedded with siliciclastic layers and thin halite layers are composed of resedimented facies ranging from fine grained laminated sediments to coarse grained breccias the components derive from the reworking of shelf sediments deposited initially in shallow water to supratidal settings on the surface and edges of structural highs bordering depressions proximal siliciclastic deposits with interstitial anhydrite cement patches nodules or gypsum and dolostones with early diagenetic anhydrite facies nodular chicken wire formed in sabkha conditions interstitially grown gypsum crystals and subaqueous gypsum crusts precipitated in hypersaline ponds and diatom rich oozes formed in marine shallow water conditions the homogeneity of the stable isotope composition and petrography of sulphates argue for the initial crystallization of ca sulphates within brines of the same origin and in closely interconnected sedimentary settings the unconsolidated sediments redeposited as slope foot accumulations were carried both as anhydrite nodules soft masses various fragments individual grains or crystals released by disintegration of large masses and gypsum crystalline aggregates or single crystals later converted to anhydrite during burial layers of chaotic breccia are interpreted as the result of seismic events whereas the fine grained deposits could be related to redistribution by nepheloid layers of suspensions of finer grains released by disintegration of the soft anhydrite masses during downslope transport or of in situ deposits removed by the turbiditic flows

tectonic and sedimentary evolution of the gulf of suez and the northwestern red sea abstract the structural pattern of the gulf of suez and red sea rift is inherited from the basement tectonics n140 faults clysmic direction parallel to the regional elongation of the rift are associated with submeridian aqaba direction and sub e w faults duwi direction that also play an important role in the rifting processes the pre rift sedimentary cover includes cretaceous and eocene platform deposits it was slightly deformed prior to rifting the syn rift sedimentary sequence comprises four major units groups a to d delimited by unconformities group a oligocene to early burdigalian continental to restricted subaquatic deposits group b burdigalian to middle miocene open marine sediments group c middle to upper miocene major evaporitic episode and group d plio pleistocene which returns to an open marine environment four majors stages of structuration are recorded an initial stage of compressive deformation direction of shortening close to nw se characterized by strike slip movements and associated drag folds early group a a tilted block stage late group a corresponding to the period of highest extensional rate a horst and graben stage group b resulting in the cutting out of the tilted blocks by numerous synthetic faults group b corresponds to the period of highest subsidence rate when a flexuration stage of the margin expressed by a centripetal evolution of the subsidence is associated with major periferal uplift

resedimentation of basin centre sulphate deposits middle miocene badenian of carpathian foredeep southern poland abstract the middle badenian anhydrite sections in the central part of the carpathian foredeep consist mainly of interbedded laminated anhydrite and anhydrite breccia these facies display features characteristic of redeposited sediments such as distortions due to slumping erosional boundaries and graded bedded laminae lamination in laminated anhydrite is rarely regular and often accompanied by disruptions the predominance of clasts of laminated anhydrite combined with the observed brecciation of laminated anhydrite indicates that a short distance for transport and even in situ reworking were common a high degree of convolution indicates that some reworked sediments were unconsolidated when they moved but in many cases they were probably at least partly lithified this is evidenced by the anhydrite breccia consisting of clasts of laminated anhydrite as well as the brecciation in situ the resedimentation processes have not been related to regional bathymetrical differences as indicated by minor differences along seismic profiles a great deal of redeposition within the basin centre of the middle badenian evaporite basin combined with the in situ brecciation suggests that the triggering mechanism for redeposition could be earthquakes they generated mass flows and eventually turbidites so that earlier deposited grains could be redeposited this implies that in other evaporite basins the laminar facies might be at least partly related to redeposition and not necessarily to changes of surface brine concentration as usually supposed

evaporitic sedimentation in the southeastern anatolian foreland basin new insights on the neotethys closure abstract we integrate stratigraphic petrographic and geochemical analysis of subsurface data wells together with field surveys to study the sedimentation of a marginal miocene sub basin of the southeastern anatolian foreland basin seafb se turkey this sub basin located in the batman siirt region is characterized by the existence of evaporites carbonates sulphates and chlorides and alluvial detritus which were divided in the following five lithostratigraphic members from older to younger lower and upper yapilar and lower middle and upper sulha these members deposited in an epicontinental mudflat during the early miocene both the bromine content and the sulphur and oxygen isotope composition 34 s v cdt and 18 o v smow of halite and sulphates samples respectively also suggest a marine origin of the precipitation brines however influence of geothermal fluids and dissolution and re precipitation of evaporites from uplifted areas in these brines such as the early miocene members and or triassic units is interpreted comparing and integrating our results with data documented in previous works it is here recognized that the depositional model of the studied sub basin differs from that which explain the coeval sedimentation of units situated in the western part of the seafb moreover our model shows some depositional and paleoenvironmental similarities with miocene evaporites located in the mesopotamian foreland basin this work provides valuable insights on the middle miocene salinity crisis which is related to the evolution of the neotethys closure

facies and depositional environment of the holocene evaporites in the ras shukeir area gulf of suez egypt the holocene evaporite sequence in the ras shukeir area conformably overlies marine shell banks and cross bedded to graded bedded beach sands and gravels the evaporite sequence is represented by gypsum anhydrite layers that are interbedded with mudstone layers field and petrographic investigations of the evaporite deposits revealed two facies types laminated evaporite facies primary and nodular to enterolithic anhydrite facies diagenetic the laminated evaporite facies is subdivided from the bottom to top into regular laminated evaporite chevron gypsum algal micrite laminations and wavy algal laminated evaporite based on their textures and fabrics the regular and wavy laminated evaporite facies are interpreted as primary deposits in a coastal lagoon and salina environment the chevron gypsum algal micrite facies formed by the growth of chevron gypsum at the sediment water interface within a shallow subtidal lagoonal environment that was characterized by extensive benthic algal mats the nodular to enterolithic anhydrite facies is secondary and formed diagenetically within a siliciclastic supratidal sediment some of the laminated evaporite facies have been diagenetically altered in a supratidal sabkha environment as evidenced by the following 1 the partial formation of nodular evaporite instead of laminated evaporite 2 disruption of gypsum laminations by plant roots and rootlets as well as by precipitation of lenticular gypsum on the root wall and 3 partial dissolution of halite laminae and the formation of wavy anhydrite laminae consequently the holocene evaporites in the ras shukeir area were deposited in a shallow semi closed to closed basin that was separated from the gulf of suez trough changing sea level led to progradation of the evaporite facies from subtidal to intertidal lagoon and salina to a supratidal sabkha

estimating transient crater size using the crustal annular bulge insights from numerical modeling of lunar basin scale impacts 1 the transient crater is an important impact cratering concept its volume and diameter can be used to predict impact energy and momentum impact melt volume and maximum depth and volume of ejected material transient crater sizes are often estimated using scaling laws based on final crater rim diameters however crater rim estimates especially for lunar basins can be controversial here we use numerical modeling of lunar basin scale impacts to produce a new alternative method for estimating transient crater radius using the annular bulge of crust observed beneath most lunar basins using target thermal conditions appropriate for the lunar imbrian and nectarian periods we find this relationship to be dependent on lunar crust and upper mantle temperatures this result is potentially important when analyzing lunar basin subsurface structures inferred from the grail mission

thickness of proximal ejecta from the orientale basin from lunar orbiter laser altimeter lola data implications for multi ring basin formation 1 quantifying the ejecta distribution around large lunar basins is important to understanding the origin of basin rings the volume of the transient cavity the depth of sampling and the nature of the basin formation processes we have used newly obtained altimetry data of the moon from the lunar orbiter laser altimeter lola instrument to estimate the thickness of ejecta in the region surrounding the orientale impact basin the youngest and best preserved large basin on the moon our measurements yield ejecta thicknesses of 2900 m near the cordillera mountains the topographic rim of orientale decaying to 1k m in thickness at a range of 215 km these measurements imply a volume of ejecta in the region from the cordillera ring to a radial range of one basin diameter of 2 9 10 6 km 3 and permit the derivation of an ejecta thickness decay model which can be compared with estimates for the volume of excavation and the size of the transient cavity these data are consistent with the outer rook mountains as the approximate location of the transient cavity s rim crest and suggest a volume of 4 8 10 6 km 3 for the total amount

depositional and diagenetic controls on deeply buried eocene sublacustrine fan reservoirs in the dongying depression bohai bay basin china abstract this paper investigates the reservoir potential of deeply buried eocene sublacustrine fan sandstones in the bohai bay basin china by evaluating the link between depositional lithofacies that controlled primary sediment compositions and diagenetic processes that involved dissolution precipitation and transformation of minerals this petrographic mineralogical and geochemical study recognizes a complex diagenetic history which reflects both the depositional and burial history of the sandstones eogenetic alterations of the sandstones include 1 mechanical compaction and 2 partial to extensive non ferroan carbonate and gypsum cementation typical mesogenetic alterations include 1 dissolution of feldspar non ferroan carbonate cements gypsum and anhydrite 2 precipitation of quartz kaolinite and ferroan carbonate cements 3 transformation of smectite and kaolinite to illite and conversion of gypsum to anhydrite this study demonstrates that 1 depositional lithofacies critically influenced diagenesis which resulted in good reservoir quality of the better sorted middle fan but poor reservoir quality in the inner and outer fan lithofacies 2 formation of secondary porosity was spatially associated with other mineral reactions that caused precipitation of cements within sandstone reservoirs and did not greatly enhance reservoir quality and 3 oil emplacement during early mesodiagenesis temperatures 70 c protected reservoirs from cementation and compaction

sodium sulphate deposits of neogene age the kirmir formation beypazari basin turkey the evaporite member of the kirmir formation was deposited in shallow lacustrine environments during the upper miocene the most soluble minerals of this member can be currently observed in the cayirhan mine the evaporite member which is composed of secondary gypsum at outcrop can be subdivided into a bedded lower unit and a massive upper unit in the bedded lower unit most of the gypsum throughout the basin can be identified as having been transformed from glauberite in the glauberite layers of the cayirhan mine some glauberite textures clear glauberite suggest a primary subaqueous free precipitation on a depositional floor more common however are the glauberite textures indicating an interstitial growth within a clayey magnesitic matrix in the thenardite layers accompanying the glauberite in the cayirhan mine some disruption structures can be assigned to synsedimentary dissolution these structures together with the textures of the thenardite suggest that the original sodium sulphate was mirabilite thenardite being a secondary phase which formed during early to moderate burial diagenesis the massive upper unit in which evidence of sodium bearing minerals is absent is characterized by laminated to banded gypsum and nodular gypsum in the marginal areas of the evaporitic basin whereas thick clast supported gypsum breccias prevail in the northern deeper part of the basin the brecciation of these calcium sulphate layers occurred as a result of synsedimentary gravitative slumping under tectonic control although the sulphur isotopic values d 34 s of the sulphates of the kirmir formation suggest a marine derived brine supply the oxygen isotopic values d 18 o and the strontium ratios 87 sr 86 sr do not support such a supply the origin of the mother brines the glauberite genesis the depositional model of the sodium sulphates and the salinity evolution are discussed d 2002 elsevier science b v all rights reserved

mixed carbonate siliciclastic sedimentation on a miocene fault block gulf of suez egypt abstract the miocene sediments at abu shaar red sea egypt include both carbonates and detrital silicates whose distribution is closely related to a pre miocene basement fault block as such they demonstrate the relationships between local distensional tectonics and sedimentation because of the vertical bathymetric relief of the basement block the carbonates include both a spectacular talus and massive platform facies in spite of the presence of scattered corals sedimentation is not truly reefal as deposits consist essentially of muddy bioclastic and silicate sands the most typical ecological elements are numerous spectacular stromatolites rigidity of the sedimentary mass was mainly induced by early marine cementation carbonate siliciclastic transitions on and around the abu shaar platform were determined mainly by basement morphology and related pre miocene tectonics

the case for a younger imbrium basin new 40ar 39ar ages of apollo 14 rocks petrographically and chemically well characterized rocks of the apollo 14 landing site 12 impact melt breccias 3 clast free impact melt rocks 2 granulitic rocks 1 cataclastic noritic anorthosite 1 shocked gabbronorite 1 mare basalt and 1 plagioclase single crystal have been dated by the 40ar 39ar technique the samples represent two different formations at the apollo 14 site 1 small lithic clasts 10 specimens from fragmental breccia 14063 ejected from the 26 ma old cone crater and one clast mare basalt from cone crater soil 14140 and 2 large rock samples 10 specimens collected throughout the regolith of the landing site the first group of samples has exposure ages close to 26 ma and 40ar 39ar ages ranging from 3 86 to 4 09 ga which indicates that breccia 14063 was assembled 3 86 ga ago the second group of samples displays lower 40ar 39ar ages ranging from 3 73 to 3 85 ga we interpret breccia 14063 as part of a nectarian megabreccia unit which was incorporated into the fra mauro formation as a megablock by secondary mass wasting of the ejecta blanket of a local pre imbrian crater the remaining samples are thought to represent clasts of the apollo 14 subregolith basement megabreccia defined as the fra mauro formation consequently the reported ages of these clasts confirm previous suggestions that the fra mauro formation and therefore the imbrium basin is only 3 75 ga old and not 3 85 ga as commonly assumed

osmium isotope and highly siderophile element systematics of lunar impact melt breccias implications for the late accretion history of the moon and earth abstract to characterize the compositions of materials accreted to the earth moon system between about 4 5 and 3 8 ga we have determined os isotopic compositions and some highly siderophile element hse re os ir ru pt and pd abundances in 48 subsamples of six lunar breccias these are apollo 17 poikilitic melt breccias 72395 and 76215 apollo 17 aphanitic melt breccias 73215 and 73255 apollo 14 polymict breccia 14321 and lunar meteorite nwa482 a crystallized impact melt plots of ir versus other hse define excellent linear correlations indicating that all data sets likely represent dominantly two component mixtures of a low hse target presumably endogenous component and a high hse presumably exogenous component linear regressions of these trends yield intercepts that are statistically indistinguishable from zero for all hse except for ru and pd in two samples the slopes of the linear regressions are insensitive to target rock contributions of ru and pd of the magnitude observed thus the trendline slopes approximate the elemental ratios present in the impactor components contributed to these rocks the 187 os 188 os and regression derived elemental ratios for the apollo 17 aphanitic melt breccias and the lunar meteorite indicate that the impactor components in these samples have close affinities to chondritic meteorites the hse in the apollo 17 aphanitic melt breccias however might partially or entirely reflect the hse characteristics of hse rich granulitic breccia clasts that were incorporated in the impact melt at the time of its creation in this case the hse characteristics of these rocks may reflect those of an impactor that predated the impact event that led to the creation of the melt breccias the impactor components in the apollo 17 poikilitic melt breccias and in the apollo 14 breccia have higher 187 os 188 os pt ir and ru ir and lower os ir than most chondrites these compositions suggest that the impactors they represent were chemically distinct from known chondrite types and possibly represent a type of primitive material not currently delivered to earth as meteorites

a seismite in triassic gypsum deposits grabfeld formation ladinian southwestern germany an approximately 1 m thick gypsum bed and its underlying 45 cm dolomite bed with variable soft sediment deformation structures are described from the grundgips member of the grabfeld formation middle keuper ladinian in southwestern germany the deformation structures are mainly convolutions folds cusps domes and off shooting dykes and less common brecciation or faulting these deformation structures are interpreted to be caused by liquefaction and or fluidization of the semiconsolidated sediments by a seismic shock of approximately magnitude 6 7 palaeoseismicity is thought to be related with a nearby wrench fault system associated with a major suture zone of the variscan basement

tectonic signatures in arid continental basins an example from the upper miocene pleistocene calama basin andean forearc northern chile abstract the calama basin a transtensional basin situated within the andean forearc and its extension to the pampa del tamarugal central depression is filled with 700 m of sediments detailed sedimentary logging and 40ar 39ar dates from interbedded volcanic deposits have established a lithostratigraphic and chronostratigraphic framework for the upper 95 m thick upper miocene pleistocene succession five facies associations fluvio lacustrine diatomite palustrine carbonate massive anhydrite fluvial and alluvial fan have been identified within this part of the basin fill the following events are recognised in the basin evolution 1 deposition of diatomaceous lacustrine sediments in two separate depocentres in the pampa del tamarugal and the central calama basin with alluvial fan accumulation along the basin margins at 8 ma 2 localised deformation within the central calama basin between 7 and 6 ma but continuous sedimentation elsewhere 3 palustrine carbonate deposition across the entire area from 6 to 3 ma except in the pampa del tamarugal where diatomaceous sedimentation continued until 5 ma before being replaced by palustrine carbonate deposition 4 widespread folding after 3 ma and entrenchment as the drainage system cut down to reach a new base level caused by the rio loa breaching the coastal cordillera and reaching the sea localised lacustrine deposition in topographic lows or tectonically created dams also occurred during this period comparison with similar age facies elsewhere in northern chile has shown changes such as these to be localised and diachronous indicating that tectonic controls on accommodation space and drainage patterns are the primary influence on sedimentation in this tectonic setting the lacustrine deposits do not appear to be a reliable recorder of low frequency climatic change this is exemplified by the change from lacustrine to palustrine deposition at 6 5 ma which would appear to record a drying of the climate however a synchronous change from ephemeral alluvial fan deposition to more permanent fluvial deposition at the basin margins indicates increased run off

depositional and diagenetic models of some miocene evaporites on the red sea coast egypt abstract the miocene evaporites on the red sea coast egypt are interpreted as a sabkha chenier complex which includes deposition in shallow water as well as in supratidal environments costal sabkhas and shallow subaqueous evaporite sequences are recognised the subaqueous sequence is represented by nodular mosaic and massive crystalline gypsum covered by a surface layer of nodular white dense powdery anhydrite the sabkha sequences are represented by a small mounds overlying the older rock unit gebel el rusas formation composed of fenestral stromatolitic and nodular dolomites overlain by a dolomitic limestone layer b thin layer overlying the subaqueous evaporite sequence and composed of fenestral stromatolitic dolomite overlain by a nodular anhydrite layer the nodular structure in the subaqueous as well as the sabkha sequences is formed diagenetically by transformation and recrystallization process the dolomites in both sabkha sequences a and b are characterised by low na concentrations 143 to 755 ppm and low values of 18 o 1 85 to 8 7 pdb this indicates that the dolomites were formed from saline water mixed with fresh water these dolomites are also characterised by a low 13 c 12 95 to 27 1 pdb this shows that the light carbon produced by the degradation of organic matter through the sulphate reduction process has played a significant role in the formation of these dolomites both microcrystalline and megacrystalline white dolomites are recognised in sabkha sequences relatively high concentrations of lead zinc and copper are associated with the high percent of megacrystalline white dolomite

the beginning development and termination of the middle miocene badenian salinity crisis in central paratethys abstract middle miocene badenian evaporites of the carpathian region are underlain and overlain by deep water deposits the onset of evaporite deposition was sudden but not synchronous in all facies zones and the deposition of evaporites was controlled by the evolution of carpathian orogen in the carpathian foredeep and most probably in other basins the badenian evaporites represent the lower part of the nn6 zone halite and associated deposits in the central part of the badenian evaporite basin show the same facies successions and marker beds can be traced across and between individual basins characteristic marker beds made it possible to correlate various facies zones of the marginal ca sulfate platform these marker beds seem to reflect events that may be related to sudden and widespread changes in water chemistry which in turn imply major changes in basin hydrology the onset of the evaporitic deposition in the carpathian foredeep was clearly diachronous and the evaporites deposited in the basin centre preceded the beginning of evaporite sedimentation in the marginal basin however depositional history in the marginal basin and the basin centre was the same a general transgressive sequence of evaporites found in the carpathian foredeep resulted from the migration of facies zones induced by the nappe movement isotopic studies of badenian foraminifers occurring below evaporites suggest that the interrupted communication of the paratethys with the ocean was a consequence of eustatic sea level fall possibly related to climatic cooling and it was coupled with a tectonic closure of connection with the tethys thus both tectonics and eustacy have contributed to the origin of salinity crisis sedimentological and geochemical data indicate recycling of evaporites throughout most of the evaporite deposition the recycling at the end of gypsum deposition in the marginal sulfate platform was accompanied by a change in the hydrology of the central paratethys that was tectonically driven and possibly related to the block tectonic phase manifested in the marginal part of the carpathian foredeep basin the change in hydrology implied the dilution of brines by inflowing marine water and this terminated the middle miocene badenian salinity crisis the onset of the badenian salinity crisis shows great similarities to the onset of the messinian salinity crisis and the terminations of both crises were different

soft sediment deformation structures related to tectonomagmatic activity a case study from the borate bearing lacustrine deposits of early miocene bigadic basin nw turkey abstract this study documents soft sediment deformation structures in the lacustrine bigadic basin one of the early miocene terrestrial basins in the extensional tectonomagmatic province of northwestern anatolia the focus is on the upper borate unit of the basin fill succession which consists of sedimentary facies including massive conglomerates stratified sandstones siltstones organic rich claystones laminated limestones organic rich limestones marlstones borates and volcaniclastics their deposition including borates occurred in a deep lacustrine environment possible phases of lake shallowing are represented by stratified sandstones facies soft sediment deformation features include small scale folds formed by convolution with occasional basal decollement minor slumps load casts and related flame structures fragmented and mixed beds brecciated by pore water explusion shallow and deep rooted synsedimentary extensional faults with related neptunian dykes and large slump sheets of thick bed packages with recumbent folds these deformation features are interpreted to be of seismo tectonic and seismo volcanic origin related to syndepositional strike slip faulting and volcanic eruptions seismic tremors combined with the basin floor updoming by magma intrusions caused deep rooted normal faults and intra basinal slumps tens of metres thick the study may serve as a guide to similar deformation structures in the underlying part of the bigadic lake fill succession and in the other neogene basins of northwestern anatolia which shared the region s seismo tectonic magmatic palaeogeographic and sedimentation history

the dimensions of the chicxulub impact crater and impact melt sheet the chicxulub impact crater which is the principal source of impact debris in cretaceous tertiary boundary sediments is currently buried by a 1 km thick sequence of carbonate sediments because the crater is not exposed for direct scrutiny its size has remained uncertain and in particular estimates ranging from 100 to 300 km have been made on the basis of gravity and magnetic field data in this study the physical properties of the k t boundary impact ejecta and chicxulub impact melt sheet have been used to test the geophysical estimates of the impact crater s size on the basis of the measured thickness of impact ejecta in haiti and north america the calculated volume of the impact melt sheet and the chemical and isotopic composition of the melt sheet the chicxulub impact crater is inferred to be 180 km in diameter and to contain a 3 to 7 km thick melt sheet and breccia sequence within a centrally located 100 km diameter region that corresponds to the limits of the transient cavity

tectonic control on carbonate platform facies distribution and sequence development miocene gulf of suez abstract mid miocene deposition in the southwestern gulf of suez was governed by an extensional fault block topography shallow marine carbonates and clastics were deposited around the exposed block crests and in marginal half grabens of the rift while central troughs were filled by slope aprons and turbiditic and pelagic mudstones fan deltas developed at points along the fault block escarpments syn rift platform carbonates from one block crest esh el mellaha are described here the platform evolved in three stages generating three sedimentary sequences sequences 1 and 2 were separated by boundary fault reactivation sequences 2 and 3 by sea level drawdown exposure and karstification the sediments comprise six lithofacies associations la 1 6 reef la 1 fore reef la 2 and back reef embayment la 3 sediments form a small reef rimmed platform in sequence 1 at the southern end of the block fringing reefs and reef lagoon systems also developed along the footwall escarpment and on fan deltas which bridged the block bounding fault fringing reefs in sequence 2 generated a carbonate talus veneer la 4 along the whole 80 km length of the esh el mellaha fault scarp carbonate slope and reefal sediments preserved on the footwall exhibit abundant evidence of syndepositional fault movements with truncation of escarpment fringing sequences and repeated generation of reefal wedges minor drowning at the sequence 1 2 boundary caused deepening of lagoons progradation of leeward reefal margins with lagoonal patch reef development and back stepping and vertical accretion of the reefal rim platform development was followed by algal laminated dolomitic sediments la 5 in the area of the old platform interior sequence 3 much of the esh el mellaha ridge remained exposed during platform growth and shed coarse alluvial clastic sediments la 6 into the peripheral marine environments the relationships demonstrated between miocene sedimentation and structural setting have parallels in the modern environments of the zeit bay area

identifying the geologic context of apollo 17 impact melt breccias abstract the origin of the boulders sampled during the apollo 17 mission to the taurus littrow valley has been debated since the completion of the mission four decades ago no consensus has yet been reached whether the sampled boulders originated in material emplaced as a result of the serenitatis impact i e massifs the imbrium impact i e sculptured hills a combination of both impact events or as a result of another pre or post serenitatis impact event i e massifs or superposed deposits on valley floor these on going debates demonstrate the importance of identifying the geologic context of samples collected during the apollo missions using high resolution imagery and topography data we identify boulder tracks that connect sampled boulders with source outcrops these observations verify astronauts impressions that boulders originated in outcrops within massif walls and that they remain uncontaminated by nearby sculptured hills materials this finding can be used with updated ar ar and u pb ages of analyzed samples to constrain the timing and intensity of the lunar cataclysm epoch

extinct 129i in halite from a primitive meteorite evidence for evaporite formation in the early solar system halite crystals from the zag h3 6 chondrite contain essentially pure monoisotopic xenon 129 129xe produced in the early history of the solar system by the decay of short lived iodine 129 129i half life 15 7 million years correlated release of 129xe and 128xe produced artificially from 127i by neutron irradiation corresponds to an initial 129i 127i ratio of 1 35 0 05 10 4 close to the most primitive early solar system value if the 129xe was produced by in situ decay then the halite formed from an aqueous fluid within 2 million years of the oldest known solar system minerals

magnetostratigraphy and sedimentary evolution of the late miocene to early pleistocene sediments quseir region egyptian red sea an integrated sedimentological and magnetostratigraphic study has allowed a detailed understanding of the late miocene to early pleistocene evolution of the sediments in the quseir region of the egyptian red sea coast palaeomagnetic samples were collected from sections in six wadis covering the shagara formation the gabir and samh members of the wardan formation and the abu dabbab formation evaporites remanence properties are carried by magnetite haematite and goethite the characteristic remanence is typically carried by detrital magnetite and haematite with more recent overprints predominantly associated with haematite and goethite produced by the weathering of diagenetic pyrite the magnetostratigraphy has allowed the following detailed age assignments for the lithostratigraphic units the shagara formation ranges in age from late pliocene late piacenzian to middle pleistocene 0 6 2 5 ma the gabir member is latest messinian to earliest piacenzian in age 3 5 5 5 ma and the samh member late tortonian to mid messinian 6 0 7 5 ma the age of the top of the abu dabbab formation is probably mid tortonian 8 ma disconformities occur between all the lithostratigraphic units with a local angular unconformity between the shagara and wardan formations lowstands in global sea level appear to have a strong influence on the timing of these disconformities characteristic mixed alluvial and reef facies of the shagara formation are a response to the ephemeral wetter climate following the initiation of northern hemisphere glaciation at 2 4 ma enhanced by rift margin uplift of basement complexes to the west this tectonic activity was concentrated in the early piacenzian the marine gabir member was deposited during the early pliocene and latest messinian high sea level stands the late tortonian early messinian age and sedimentological character of the samh member indicates this unit was affected by marine flooding events which ultimately produced during drawdown phases the off shore zeit formation evaporites in half graben depocentres

deep water clastic evaporites deposition in the messinian adriatic foredeep northern apennines italy did the mediterranean ever dry out a new genetic facies model for deep water clastic evaporites is presented based on work carried out on the messinian gessoso solfifera formation of the northern apennines during the last 15 years this model is derived from the most recent siliciclastic turbidite models and describes the downcurrent transformations of a parent flow mainly composed of gypsum clasts the model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites representing the most common evaporite facies of the northern apennines and the definition of the genetic and stratigraphic relationship with primary shallow water evaporites formed and preserved in marginal settings due to the severe recrystallization processes usually affecting these deposits petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized gravity driven deposits ranging from debrisflow to low density turbidites almost all the laminar balatino gypsum previously considered a deep water primary deposit is here reinterpreted as the fine grained product of high to low density gravity flows facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the apennine foredeep basin the messinian salinity crisis occurred during an intense phase of geodynamic reorganization of the mediterranean area that also produced the fragmentation of the former miocene apennine foredeep basin in this area primary shallow water evaporites equivalent to the mediterranean lower evaporites apparently only formed in semi closed thrust top basins like the vena del gesso basin the subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins vertical facies sequences of clastic evaporites can be interpreted in terms of the complex interplay between the messinian tectonic evolution of the apennine thrust belt and related exhumation erosional processes the facies model here proposed could be helpful also for better comprehension of other different depositional and geodynamic contexts the importance of clastic evaporites deposits has been overlooked in the study of other mediterranean areas based on the apennine basins experience it is suggested here that evaporites diffused into the deeper portions of the mediterranean basin may consist mainly of deep water resedimented deposits rather than shallow water to supratidal primary evaporites indicative of a complete basin desiccation

palaeogeographic and burial controls on anhydrite genesis the badenian basin in the carpathian foredeep southern poland western ukraine the badenian middle miocene ca sulphate deposits of the fore carpathian basin including the shelf and adjacent salt depocentre have undergone varying degrees of diagenetic change they are preserved mainly as primary gypsum in the peripheral part of the platform whereas toward the centre of the basin where great subsidence occurred during the miocene they have been totally transformed into anhydrite the facies variation and sequence of badenian anhydrites reflect different genetic patterns of two members of the ca sulphate formation in the lower member restricted to the platform anhydrite formed mainly by synsedimentary anhydritization via nodule formation whereas in the upper member distributed throughout the platform and depocentre the various gypsum anhydrite lithofacies display a continuum of distinctive anhydrite type fabrics these fabrics are based on petrographic features and show from the centre to the margin 1 syndepositional interstitial growth of displacive anhydrite 2 early diagenetic displacive to replacive by replacement of former gypsum anhydrite formation near the depositional surface 3 early diagenetic displacive to replacive anhydrite formation during shallow burial and 4 late diagenetic and only partial replacement of gypsum at deeper burial the cross shelf lateral relations of anhydrite lithofacies and fabrics suggest that the diagenesis developed as a diachronous process these fabrics of the upper member reflect both palaeogeographic linked to different parts of the basin and burial controls anhydrite growth started very early in the basin centre presumably related to high salinity pore fluids anhydritization prograded updip toward the shelf landward in a generalized cross section through the basin the intensity of gypsum replacement by anhydrite was progressively attenuated landward by a decrease in the salinity of the pore fluids in each part of the basin the anhydrite fabric was also controlled by the texture and degree of lithification of the fine grained primary gypsum lithofacies recrystallization of these anhydrite fabrics during late diagenesis linked to deeper burial conditions is insignificant allowing reconstruction of the original anhydritization pattern