isotope geochemistry sr nd pb and petrogenesis of leucite bearing volcanic rocks from colli albani volcano roman magmatic province central italy inferences on volcano evolution and magma genesis the colli albani composite volcano is made up of strongly silica undersaturated leucite bearing rocks magmas were erupted during three main periods but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs the most alkali rich magmas restricted to the caldera forming period pre caldera are extremely enriched in incompatible trace elements and display more radiogenic sr 87sr 86sr 0 71057 0 71067 with slightly less radiogenic pb with respect to those of the post caldera period post caldera volcanic activity was concentrated in three different volcanic environments external to the caldera along the caldera edge and within the caldera the post caldera magmas produced melilite to leucitite bearing plagioclase free leucitites in contrast to the pre caldera lavas they are characterised by lower incompatible trace element abundances and less radiogenic sr 87sr 86sr 0 71006 0 71039 magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre caldera period the multiple caldera collapses dissected and partially obliterated the early magma chamber during the post caldera stage magmas were channelled through several pathways and multiple shallow level magma reservoirs were established a lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab derived component is suggested as the mantle source of colli albani parental magmas two different parental magmas are recognised for the pre and post caldera stages the differences may be related to the interplay between smaller degrees of melting for the pre caldera magmas and more carbonate rich recycled subducted lithologies in the post caldera magmas

concentrated and lean oolites examples from the nubia formation at aswan egypt and significance of the oolite types in ironstone genesis

aptian albian palaeogeography of neo tethyan domain abstract the aptian albian interval 124 5 97 0 ma was a critical time both globally and for the tethyan domain in the tethyan domain it was the time when a united neo tethyan subduction zone became established between the future site of the alps and southeast asia and greatly accelerated the rate of north south convergence throughout the tethyan region a consequent widespread transgression on both laurasian and gondwanian margins deposited orbitolina limestones and associated clastics on wide continental shelf areas on the sea floor of the neo tethys ocean organic rich siliceous black shales radiolarites and turbidites with minor amounts of carbonates were deposited siliceous black shales accumulated under euxinic conditions of restricted small ocean basins of the neo tethyan realm and along their margins these areas received large amounts of organic debris from deltaic areas and coastal plains of the neighbouring continental shelves following the establishment of the north dipping subduction zone the laurasian passive margin was largely converted to an active one fringed by a large number of magmatic arcs that greatly influenced the sedimentation on the margin land areas and continental basins were widespread on this margin in northern tibet china and indo china this was a consequence of the late triassic to early jurassic continental collissions and accompanied intracontinental convergence that lasted well into the cretaceous a detailed aptian albian facies map and a crude palinspastic palaeogeographic map of the entire tethyan realm are prepared in order to express the contrasts in sedimentation on laurasian and gondwanian margins and to show the compatibility of the presented data with the most recent and reliable reconstructions of the major tectonic elements in tethysides

search for milankovitch patterns among oolitic ironstones the stratigraphic record of about 175 oolitic ironstones is sparse yet it portrays several meaningful patterns repeated ironstone episodes occurred in only about 10 major sedimentary basins which were marked by relative tectonic stability or subdued orogeny intervals between episodes varied but were mostly a few to several million years long repetitions on this scale are commonly construed as global rise and fall of sea level the pattern persisted for a few tens of million years in fore deeps several tens of million years on unstable cratons and microcontinents and more than 100 m y in intracratonic basins within the congenial habitats an ironstone developed locally between each of several successive shallow marine upward shoaling detrital sequences these asymmetric units normally a few meters to a few tens of meters thick recurred on average every 250 to 500 kyr commonly fewer than 10 ironstone bearing sequences are involved during a very long lapse in normal sedimentation between such sequences stacked ironstones accumulated on the same short time scale speculation about short time scale patterns is poorly constrained but several other repetitive stratigraphic successions with a several hundred thousand year cadence have been attributed tentatively to the 400 000 year milankovitch climate cycle it is unclear how this would exert a eustatic control without the waxing and waning of continental glaciers

petrology and geochemistry of potassic and ultrapotassic volcanism in central italy petrogenesis and inferences on the evolution of the mantle sources major trace element sr isotopic and mineral chemical data are reported for mafic volcanic rocks mg value 65 from the northern central sector of the potassic volcanic belt of central italy the rocks investigated range from potassic series ks and high k series hks to lamproitic lmp and kamafugitic kam through a transitional series trans thus covering the entire compositional spectrum of potassic and ultrapotassic magmas kam rocks are strongly silica undersaturated and compared with the other rock series have low sio2 al2o3 na2o sc and v and high cao k na na k al ks and hks have high al2o3 cao and variable enrichment in k2o and incompatible elements lmp rocks are saturated in silica and have high sio2 k2o k2o na2 mgo ni and cr and low al2o3 cao na2o sc and v trans rocks display intermediate compositional characteristics between lmp and ks all the rocks under study have fractionated hygromagmaphile element patterns with high lil hfs element values and negative anomalies of ti ta nb and ba negative sr anomalies are observed in the lmp and trans rocks lil elements show overall positive correlations with k2o whereas different trends of sr and hfse vs k2o are defined by lmp trans and ks hks kam 87sr 86sr range from about 0 710 to 0 716 ks hks and kam rocks have similar 87sr 86sr values clustering around 0 710 lmp and trans rocks have the highest 87sr 86sr values geochemical and isotopic data reported for the most primitive italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of italian potassic magmatism simple mass balance calculations exclude however an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of central italy volcanics underwent contamination with fluids and or melts released by upper crustal material previously brought into the mantle by subduction processes different trends of incompatible elements vs k2o observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of lmp rocks fluids or melts rich in ca sr and with high lile hfse value and sr isotopic composition around 0 710 are the most likely contaminant of the source region of ks hks and kam volcanics variations in cao na2o and ferromagnesian element abundances and ratios suggest that in some zones the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism

petrology and mineralogy of wollastonite and melilite bearing paralavas from the central apennines italy small outcrops of wollastonite and melilite bearing pyrometamorphic rocks paralavas are found along the apennine chain in central italy at the localities of colle fabbri and ricetto these rocks have coarse to fine grained crystalline spotted and glassy textures the colle fabbri rocks have abundant and ubiquitous wollastonite with plagioclase clinopyroxene melilite is found only in the most ca rich and silica poor samples garnet perovskite quartz leucite silica rich glassy mesostasis and ocelli filled by calcite are present locally the ricetto rock is made up of wollastonite and melilite with minor clinopyroxene set in a glassy matrix with a few crystals of restitic quartz these rocks have variable contents of sio2 43 to 64 wt and cao 37 to 3 7 wt the latter decreases with increasing mgo al2o3 fe2o3 tot tio2 k2o sio2 and most trace elements excluding sr peculiar parageneses e g coexisting melilite and anorthite in the most silica poor samples abundance of wollastonite mineral compositions gehlenite rich melilite al ti and fe3 rich clinopyroxene al ti rich but fe poor garnet and major and trace element geochemistry suggest that the colle fabbri and ricetto rocks are not ultimately mantle derived but are the result of melting devolatilization and recrystallization of marly sediments 50 60 to 5 10 calcite with clay minerals quartz likely due to coal fires the 87sr 86sr and 143nd 144nd range from 0 70772 to 0 71190 and from 0 51223 to 0 51219 respectively again suggesting sedimentary protoliths of a mixed nature substantial chemical and isotopic differences between these samples and those from the roman magmatic province are highlighted

paleozoic metasomatism at the origin of mediterranean ultrapotassic magmas constraints from time dependent geochemistry of colli albani volcanic products central italy abstract the major processes that control the genesis of potassic volcanic rocks like the timing of multi stage mantle metasomatism remain largely unclear in an attempt to clarify the timing of the metasomatic process a detailed geochronologic and geochemical study has been conducted on the ultrapotassic rocks of the colli albani volcanic district central italy new 40 ar 39 ar data coupled with literature and newly performed 87 sr 86 sr 143 nd 144 nd and chemical data allow us to precisely delineate the time dependent geochemical variations of the magmas erupted at the colli albani volcanic district and to better define mantle source processes responsible for their genesis the temporal geochemical variations observed in the colli albani magmas indicate that i the ultrapotassic magmas originated from a metasomatized mantle source in which phlogopite is the potassium bearing phase ii the partial melting of the mantle source involved mainly phlogopite and clinopyroxene olivine whereas the role of accessory phases was less significant and iii the metasomatic process that led to the formation of the phlogopite in the mantle can be reasonably related to events that have occurred during the paleozoic era

palaeoenvironmental interpretation of fluvial red beds by statistical analysis of palaeocurrent data examples from the buntsandstein lower triassic of the eifel and bavaria in the german basin middle europe abstract palaeocurrent data from parts of the upper buntsandstein lower triassic of both the western eifel kyllburg schichten and eastern bavaria plattensandstein margin of the german triassic basin middle europe have been interpreted by circular directional statistics eigenvalue and eigenvector analysis autocorrelation analysis and vector trend analysis examination of current roses histograms of normalized vector magnitudes and plots of circular skewness of the distribution vs circular kurtosis together with the palaeocurrent plots indicate bimodal palaeocurrent distributions with bipolar orientations within long short and very short sedimentary sequences subset i of the directional data is interpreted to represent larger more continuous flows in a high energy regime of probably perennial type whereas subset ii may represent smaller partially episodic flows of probably ephemeral type with larger variability in direction and flow regime transport and sedimentation rates being significantly smaller than during deposition of subset i a part of the bimodal palaeocurrent distributions within short sedimentary sequences fits rather well into the general transport pattern other bipolarities are primarily interpreted as effects of superimposition of channels of different orientations as well as of main channels and crevasse splay channels and condensation of deposition from discontinuous or episodic flows the main mechanism creating the vertical succession of various directions is stacking of different substratum members to multistorey complexes by primary depositional restriction of formation and or secondary erosional removal of topstratum sediments the occasional occurrence of herring bone cross stratification representing bipolarities within very short depositional sequences testifies to probably episodic and random changes in water surface slopes allowing currents to reverse locally examination of long sedimentary sequences by autocorrelation analysis reveals changes of transport directions with time in a sinusoidal manner indicating a conformable environmental development of the alluvial watercourses which reflects a time cyclic trend of sedimentation by spatially continuous and time concordant shifting of the channel system the results of the statistical analysis enable an enhanced palaeoenvironmental reconstruction of the alluvial network which fits best to a transitional meandering thalweg braided channel pattern comparison of the statistical results especially in the light of vector trend surface analysis clearly reflects the different palaeogeographic positions of both investigated areas but rules out only minor influences of regionally different palaeoslopes on the alluvial depositional environment with the basic principles of fluvial style at the western margin eifel generally matching those at the eastern margin bavaria of the german basin

compressive and tensile failure of inclined well bores and determination of in situ stress and rock strength in this paper we investigate the occurrence of compressive and tensile failures of arbitrarily inclined well bores under a wide variety of stress conditions the principal assumptions in this analysis are that the rock is isotropic and that it deforms elastically to the point of failure as has been shown by previous investigators for a given stress state and well bore orientation it is straightforward to predict the orientation of the failures around the well bore as well as whether failure is likely to occur depending on such parameters as rock strength and borehole fluid pressure however as the stress state is almost never known in situ we demonstrate how observations of compressive and tensile wall failures in inclined holes can be used to constrain in situ stress orientations and magnitudes if there are independent data on the magnitude of the least principal stress from either leak off or microfrac tests and on the formation pore pressure we further demonstrate how once the stress state is determined it is possible to assess both an upper bound on the effective in situ rock strength and the degree to which increasing the borehole fluid pressure or mud weight can reduce the likelihood of borehole failure through application of this methodology to an inclined well bore in an area of complex faulting in the gulf of mexico we illustrate how it is possible to utilize observations of borehole failures to determine the magnitude and orientation of the stress tensor in areas such as offshore sedimentary basins where drilling inclined well bores is quite common

the colli albani mafic caldera roma italy stratigraphy structure and petrology new results for the colli albani volcano roma italy surveyed for the geological map of italy at 1 50 000 scale carg project integrated with previous data provide insights on caldera evolution the colli albani a quiescent volcano became active at 600 ka eruptive compositions are consistently mafic 50 km 3 deposits forming the villa senni eruption unit ignimbrites at ca 355 ka two edifices were built within the caldera 1 the horseshoe shaped tuscolano artemisio ta composite edifice or lithosome consists of coalescing peri caldera fissure related scoriae cones interbedded with lava flows the fissure system forms two segments controlled by regional fractures 2 the steep sided faete stratovolcano 949 m a s l filled the caldera the ta and faete lithosomes partly interfinger and were emplaced at 350 260 ka their products indicate reduced eruption rates relative to the vl period and a change to effusive and mildly explosive eruptions the most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano collectively named via dei laghi composite lithosome the colli albani caldera is poly phase 1 a piecemeal caldera is associated with large volume ignimbrites of the vl edifice the present shape of the caldera is related to the villa senni eruption 2 the ta composite edifice erupted from peripheral caldera fissures is unrelated to explosive phases of caldera collapse the ta final products cover a morphologically stable caldera wall the peripheral fractures feeding the ta composite edifice are interpreted as volcano tectonic structures activated during the late stage downsag of the caldera reduced eruption rates during the ta and the faete stages 10 1 km 3 1 ka respect to 10 0 km 3 1 ka for the vl edifice suggest a reduced recharge of the magma chamber that may have induced prolonged deflation and downsagging of the caldera floor and the opening of outward dipping peripheral fractures by this interpretation the ta edifice represents the surface expression of ring dykes at depth the absence of similar fissure structures along the western caldera rim may relate to the deep geometry of the ring faults dipping inward in those areas and therefore not favourably oriented for magma intrusion during a period of general subsidence by contrast the following and still active phreatomagmatic phase that has emplaced the via dei laghi composite edifice is located right on the western side of the caldera and may therefore relate to resurgent conditions classical petrological and pers pearce elements ratios analyses indicate that lavas are co genetic and show a differentiation trend up through stratigraphy driven by

cretaceous nubia formation and correlative deposits eastern egypt major regressive transgressive complex early to mid late cretaceous nubia formation in and around the natash basin in southeastern egypt incorporates a lower regressive nonmarine sandy facies 1 as much as 100 m thick a middle transgressive paralic to marine facies 2 several tens of metres thick and an upper prograding nonmarine to paralic sandy facies 3 about 120 m thick these deposits extend northwestward across the kharga arch into the large dakhla basin in central and southwestern egypt where facies 1 is several hundred metres thick and has an aptian marine tongue the nubia formation also has correlative lithofacies along the gulf of suez lowland in northeastern egypt there facies 1 is of varying thickness and is an important petroleum reservoir early cretaceous to early cenomanian facies 1 was deposited by high energy low sinuosity braided streams during a low stand of sea level that persisted with only minor interruption for about 50 m y sandy fining upward fluvial sequences record intermittent aggradation and repeated development of paleosols deposits in the dakhla basin were dispersed northward from the deeply weathered nubian shield those in southeastern egypt and in the gulf of suez lowland were dispersed southwestward and westward from uplands on the eastern desert and arabian platforms southward thinning late cenomanian turonian marine facies 2 marks the climax of the first major late cretaceous tethyan transgression waning of northward dispersed detritus fostered development of three extensive beds of oolitic ironstone in the vicinity of aswan as well as a few thin lenses of ironstone in central northern and northeastern egypt distinctive tabular planar cross bedded facies 3 reflects renewed uplift of the nubian shield in late turonian coniacian time and essentially continuous influx of quartzose sand for only a few million years facies 3 was spread across a prograding alluvial plain in migrating sand waves and channel bars in closely spaced non sinuous distributary systems the older regressive facies 1 was succeeded rather abruptly by marine facies 2 as a result of waning detrital influx followed by low energy transgression that developed only minor strand line sand bodies prograding nonmarine facies 3 is separated from overlying transgressive late cretaceous marine deposits by a gradational ripple bedded facies probably produced by gradual waning of detrital supply during continuing high stand of sea level the nubia formation and its correlatives in eastern egypt reflect uplands and irregular topography along the red sea suez tract that had been a broad zone of deformation in late precambrian time the pattern of distribution of early cretaceous facies 1 in the gulf of suez lowland suggests that there may have been very little spreading along the suez graben during cenozoic opening of the red sea

the geochemical evolution of clinopyroxene in the roman province a window on decarbonation from wall rocks to magma abstract we present results from magma carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the roman province central italy atmospheric pressure experiments were performed at 1140 1160 and 1180 c under nno mh and air oxygen buffering conditions the starting materials were a shoshonite and a phonotephrite doped with different amounts of cao and cao mgo whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite respectively the results show that clinopyroxenes spinels and residual glasses are ubiquitous phases in all run products calcite doped runs crystallize more clinopyroxene than dolomite doped runs at the same conditions this leads to the formation of strong desilicated cao rich melts showing compositions comparable to those of magmatic skarns during magma carbonate interaction the content of fe3 in clinopyroxene increases with increasing fo2 promoting the substitution of al for si in tetrahedral site local charge imbalances are also compensated by the incorporation of highly charged cations such as ti into the crystal lattice according to this cation substitution al ca fe3 ti rich clinopyroxenes of the skarn environment testify to continuous co2 fluxes produced by the thermal decomposition of carbonate wall rocks nevertheless the oxidative capacity of co2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of si fe2 mg rich clinopyroxenes

anisotropic damage mechanics as a novel approach to improve pre and post failure borehole stability analysis anisotropic damage distribution and evolution have a profound effect on borehole stress concentrations damage evolution is an irreversible process that is not adequately described within classical equilibrium thermodynamics therefore we propose a constitutive model based on non equilibrium thermodynamics that accounts for anisotropic damage distribution anisotropic damage threshold and anisotropic damage evolution we implemented this constitutive model numerically using the finite element method to calculate stress strain curves and borehole stresses the resulting stress strain curves are distinctively different from linear elastic brittle and linear elastic ideal plastic constitutive models and realistically model experimental responses of brittle rocks we show that the onset of damage evolution leads to an inhomogeneous redistribution of material properties and stresses along the borehole wall the classical linear elastic brittle approach to borehole stability analysis systematically overestimates the stress concentrations on the borehole wall because dissipative strain softening is underestimated the proposed damage mechanics approach explicitly models dissipative behaviour and leads to non conservative mud window estimations furthermore anisotropic rocks with preferential planes of failure like shales can be addressed with our model

primary magmatic calcite reveals origin from crustal carbonate abstract we have investigated lava flows representative of the whole eruptive history of the colli albani ultrapotassic volcanic district central italy one of the most intriguing features concerning some of these lava flows is the occurrence of primary magmatic calcite in the groundmass the primary magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i interstitially associated with clinopyroxene nepheline and phlogopite ii in spherical ocelli associated with nepheline fluorite and tangentially arranged clinopyroxene and iii in corona like reaction zones around k feldspar xenocrysts these microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass implying that the temperature of the system was above the solidus of the hosted lava flow 850 c geochemical features of calcite crystals i e stable isotope values and trace element patterns corroborate their primary nature and give insights into the origin of the parental carbonate melt the trace element patterns testify to a high temperature crystallization process not hydrothermal involving a carbonate melt coexisting with a silicate melt the high 18o around 27 smow and wide 13c 18 to 5 pdb values measured in the calcites preclude a mantle origin but are consistent with an origin in the crust in this framework the crystallization of calcite can be linked to the interaction between magmas and carbonate bearing wall rocks and in particular to the entrapment of solid and or molten carbonate in the silicate magma the stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn eruptive time scales

the villa senni eruption alban hills central italy the role of h2o and co2 on the magma chamber evolution and on the eruptive scenario abstract the villa senni eruption unit vseu belongs to the tuscolano artemisio phase of volcanic activity in the alban hills volcanic district the closest to rome of the recent or active volcanoes of central italy the most important products of this eruption are represented by pyroclastic flow deposits named lower and upper flow unit lfu and ufu respectively three main rock types form vseu as follows 1 juvenile k foiditic scoria clasts of the lfu 2 juvenile phonotephritic scoria clasts of the ufu and 3 holocrystalline phonotephritic lithic inclusions italites in the ufu on the basis of the chemistry mineralogy and petrography of the three studied rock types their phase relations have been discussed other petrologic constraints from laboratory melting experiments are presented and used to investigate the role of volatiles on the evolution of the magma chamber system some broad implications on withdrawal pattern are also presented it has been verified the lfu rock type can be obtained from a parental melt of ufu composition by a co2 controlled crystal liquid fractionation of a solid assemblage close in composition to that of italites because it can be proved that the storage of magma occurred at shallow depth within the mesozoic carbonate country rocks it is proposed that co2 diffusion originating from thermal decomposition of wall rock carbonates controlled the evolution trend of the melt at the periphery of the magma chamber whereas the inner part of the magma body retained the volatile component essentially h2o of the original melt the corresponding eruption model is therefore comprehensive of an early eruptive phase lfu rock type involving the more differentiated central magma bulb whereas the late eruptive phase ufu rock type tapped the more mafic peripheral magma the italite xenoliths are believed to represent the chilled margins of the magma chamber

volatiles in alkaline magmatism abstract gases extracted during fusion of volcanic glasses substantiate other sources of evidence that alkaline magmatism is distinguished from calc alkaline by higher co2 so2 contents with relatively smaller proportions of h2o in addition to higher c and s activity alkaline magmas are characterised by high cl and f which are released with alkalis during fusion experiments in a graphic reminder that alkalis should be regarded as mobile elements in magmatism the association of c s and halogens in alkaline magmatism is well shown in some high temperature residua characterized by assemblages such as calcite vishnevite calcium is an important cation in many aspects of alkaline magmatism and the links with carbonatite further emphasize the key position of c s cl and f throughout and the subordinate role of h2o

mixed fluvial systems of the messak sandstone a deposit of the nubian lithofacies southwestern libya abstract the messak sandstone is a coarse grained to pebbly tabular crossbedded deposit of the widespread nubian lithofacies it was deposited during late jurassic and or early cretaceous time at the northern edge of the murzuq basin in southwestern libya although the sedimentary record is predominantly one of braided fluvial systems a common subfacies within the formation is interpreted to record the passage of straight crested sand waves across laterally migrating point bars in sinuous rivers similar to parts of the modern ganga and yamuna rivers because the sand waves were larger on the lower parts of the point bar lateral migration created diagnostic thinning upward cosets of tabular crossbeds as well as fining upward grain size trends common thick interbedded claystones deposited in associated paludal and lacustrine environments and high variance in crossbed dispersion patterns also suggest the local presence of sinuous fluvial systems within the overall braided regime the messak sandstone contains some of the features that led to the proposal of an unconventional low sinuosity fluvial environment for the nubian lithofacies in egypt and the continuously high water levels of this model may explain channel scale clay drapes and overturned crossbeds in the messak however most of the messak characteristics are incompatible with a low sinuosity model suggesting instead that the fluvial channels in the murzuq basin alternated between braided and high sinuosity channel patterns

carbonate assimilation at merapi volcano java indonesia insights from crystal isotope stratigraphy recent basaltic andesite lavas from merapi volcano contain abundant complexly zoned plagioclase phenocrysts analysed here for their petrographic textures major element composition and sr isotope composition anorthite an content in individual crystals can vary by as much as 55 mol an

relationships between chamber margin accumulates and pore liquids evidence from arrested in situ processes in ejecta latera caldera italy biotite and clinopyroxene rich mafic nodules occur together with syenite ejecta in ca 235 to 155 ka tuffs surrounding the latera caldera clinopyroxenites and leucite monzosyenites crystallized along the lower margins of a crustal magma system and record complex crystallization histories of potassic magmas that were parental to a range of lava and tuff compositions the mafic nodules have the mineral assemblage clinopyroxene biotite anorthite orthoclase leucite hauyne titanite apatite amphibole olivine phlogopite and comprise mesocumulate and orthocumulate layers that commonly alternate on the scale of several centimeters despite the apparently ultramafic nature of the early cumulate assemblage the common occurrence of intercumulate orthoclase leucite hauyne salitic clinopyroxene and vesicular glass indicates that interstitial liquids underwent late stage differentiation at relatively shallow depths but under highly variable conditions of volatile saturation many of the mafic nodules exhibit pronounced variations in the type and abundance of mineral reaction textures these range from unreacted assemblages to nodules in which cumulate megacrysts are surrounded by well developed symplectite halos the textural variability indicates strongly localized disequilibrium between cumulate frameworks and vapor saturated pore fluids and is attributed to convective fractionation of liquids through permeable crystal mush lithologic discontinuities exhibited by the xenolith suite and host magmas are best explained by variable communication between a compositionally stratified magma reservoir and its partly crystallized lower chamber margins periodic replenishment of this system by less evolved magmas subsequently promoted mixing and hybridization that are characteristic features of many latera lavas and tephra

oxygen isotope geochemistry of pyroclastic clinopyroxene monitors carbonate contributions to roman type ultrapotassic magmas the oxygen isotope geochemistry and chemical composition of clinopyroxene crystals from alban hills pyroclastic deposits constrain the petrological evolution of ultrapotassic roman type rocks volcanic eruptions in the 560 35 ka time interval produced thick pyroclastic deposits bearing clinopyroxene phenocrysts with recurrent chemical characteristics clinopyroxenes vary from si mg rich to al fe rich with no compositional break indicating that they were derived from a continuous process of crystal fractionation based on the 18o and trace element data no primitive samples were recovered monomineralic clinopyroxene cumulates set the oxygen isotope composition of primary magmas in the range of uncontaminated mantle rocks 5 5 but their ree composition resulted from extensive crystal fractionation departing from these mantle like 18ocpx values the effects of crustal contamination of clinopyroxene o isotope composition were identified and used to monitor chemical variations in the parental magma 18o values in si mg rich clinopyroxene are slightly higher than typical mantle values 5 9 6 2 and the low ree contents are representative of early stages of magmatic differentiation 18o values as high as 8 2 are associated with al fe3 rich clinopyroxene showing high ree contents these 18o values are characteristic of crystals formed during the late magmatic stages of each main eruptive phase geochemical modelling of 18o values vs trace element contents indicates that these ultrapotassic magmas were derived from fractional crystallization plus assimilation of limited amounts of carbonate wall rocks starting from a primary melt and from interaction with co2 derived from country rocks during crystal fractionation

non pelletal glauconite from the campanian qusseir formation egypt implication for glauconitization abstract glauconitization processes proposed in the literatures include the layer lattice theory in which glauconite formed through k uptake by a detrital smectite precursor and the neoformation theory that does not require a smectite like precursor the non pelletal glauconite bed in the uppermost part of the campanian qusseir formation at the abu tartur area and the underlying smectite rich beds provided a potential example for the glauconitization process the glauconite occurs as fine clayey moderately hard and homogeneous bed ranges in thickness from 2 to 3 m under the optical microscope glauconite occurs in a unique morphology as very fine green clayey matrix which differs from the typical pelletal shape of many glauconites under the scanning electron microscope it appears as dense uniform and very fine flakes that are composed of si al fe and k x ray diffraction analysis of both bulk samples and clay fractions indicates that the glauconite bed is composed entirely of glauconite geochemical analysis suggested that the investigated glauconites belong to the 2nd stage of the maturity scale i e moderate maturity or they can be alternatively ranked as evolved chondrite normalized ree patterns exhibit lree enrichment relative to hree la yb n ratios vary from 5 to 8 and slightly negative eu anomalies eu eu from 0 7 to 0 8 clay beds that underlie the glauconite bed are composed of two types of smectites smectite of low k 2 o and fe 2 o 3 contents and smectite of high k 2 o and fe 2 o 3 contents smectite of low k 2 o and fe 2 o 3 contents is considered in this study as the initial precursor of glauconite while smectite of high k 2 o and fe 2 o 3 represents the transitional phase between smectite and glauconite this in turns supports the layer lattice theory in which glauconite formed by k diffusion to a detrital smectite precursor from the sea water due to transgression absence of mixed layer minerals suggests that the diffusion process was active and continuous until reaction completion was reached i e formation of glauconite maturity and ree patterns suggest the possible formation of the studied glauconite probably at shelf environment at approximately 100 m water depth the occurrence of glauconite indicates a marine invasion of the upper part of the qusseir formation which was considered previously as non marine sediments

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

facies analysis and sequence stratigraphy of the cenomanian turonian mixed siliciclastic carbonate sediments in west sinai egypt abstract the unconformity bounded cenomanian turonian succession in west sinai is subdivided into three formations the raha abu qada and wata these rock units were deposited in a mixed siliciclastic carbonate system on a ramp setting the studied ramp only includes inner and mid ramp facies whereas the outer ramp facies occurs in northern sinai four sequence boundaries sb were recognized in the studied formations due to the presence of subaerial exposure or flooding events in the facies stacking pattern the first and last sequence boundaries sb1 and sb4 might be considered as type 1 sequence boundary attributable to the presence of widespread erosion it is difficult to determine type of the second and third sequence boundaries sb2 and sb3 because of their minor unconformity and minimal erosion determination of systems tracts within the wata formation is debatable owing to the action of dolomitization that has destroyed both original components and sedimentary structures the lowstand systems tracts of the recorded sequences are characterized by sandstones siltstones and sandy shales while fossiliferous shale and limestone with oysters prevailed during sea level rise the highstand systems tracts are generally characterized by shallow intertidal and subtidal deposits that are made up of abundant oyster wackestones with benthic foraminifera and ostracods

magma chambers emplaced in carbonate substrate petrogenesis of skarn and cumulate rocks and implications for co2 degassing in volcanic areas crystal rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage cooling and fractionation of magmas in pre eruptive volcanic systems these clasts represent snapshots of the magma chamber host rock interface before eruption and provide information on crystallization differentiation and degrees of interaction between magma and wall rock in this study we have focused on the petrology of clasts of cumulate and skarn rocks from the colli albani volcanic district with the aim of shedding light on magma carbonate interaction and co2 emission in volcanic areas by means of phase relations bulk rock chemistry mineral compositions and isotope data we have identified different types of cumulates and skarns cumulates containing either clinopyrox

variations in trace element partition coefficients in sanidine in the cerro toledo rhyolite jemez mountains new mexico effects of composition temperature and volatiles trace element partition coefficients have been measured for one plagioclase and five sanidine mineral separates from the cerro toledo rhyolite new mexico sanidine partition coefficients vary substantially and systematically within the cerro toledo rhyolite partition coefficients for ca sr zn la and eu are lowest in the most evolved rhyolites whereas sm and hree partition coefficients are highest rubidium partition coefficients remain constant while those for ba ce and th are variable variations of the sr zn la and eu partition coefficients are correlated with the ca contents and partition coefficients of the sanidines calcium may have controlled the distribution of these elements in the sanidine by modifying the feldspar structure the low ca partition coefficients in sanidines for the most evolved rhyolites may be the consequence of modification of the melt structure possibly due to increased volatile contents at the top of the magma chamber s during evolution of the cerro toledo rhyolite the zn and la partition coefficients between sanidine and melt also may have been controlled by this change in melt structure modelling using major elements and the constant rb partition coefficient for sanidine indicates 70 crystallization of magma during cerro toledo rhyolite time by removal of 68 sanidine and 32 quartz estimates of the volume 1 of initial parental magma and 2 of the magma that crystallized during this period are 11 670 km3 and 8170 km3 respectively the average intrusion rate of silicic magma during cerro toledo rhyolite activity was 35 10 3 km3 a

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

origin of sulphur in the quaternary perpotassic melts of italy evidence from hauyne sulphur isotope data abstract hauyne na ca 4 8 alsio 4 6 so 4 s 1 2 is a rare mineral which occurs in ejecta and lavas of perpotassic volcanoes of the roman comagmatic region italy as a high temperature sulphur bearing phase it is a valuable indicator of the sulphur characteristics in the melt therefore sulphur isotope determinations were carried out for the first time on samples from some italian volcanoes on average 34 s values 1 1 to 10 8 are above the normal range 0 to 3 for igneous materials and can be classified into two groups phenocrysts in lavas avg 34 s 4 2 and metasomatic crystals in ejecta avg 34 s 8 3 such data are compatible with the hypothesis that hydrous fluids released from subducted sediments were responsible for the high volatile and lile supply to the mantle region where the magma generating process occurred

limestone assimilation and the origin of co2 emissions at the alban hills central italy constraints from experimental petrology abstract the alban hills volcanic region 20 km south of rome in the roman province emitted a large volume of potassic magmas 280 km 3 during the quaternary chemical interactions between ascending magmas and the 7000 8000 m thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys in this paper we characterize the effect of carbonate assimilation on phase relationships at 200 mpa and 1150 1050 c by experimental petrology calcite and dolomite addition promotes the crystallization of ca rich pyroxene and mg rich olivine respectively and addition of both carbonates results in the desilication of the melt furthermore carbonate assimilation liberates a large quantity of co 2 rich fluid a comparison of experimental versus natural mineral glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different alban hills eruptions a maximum of 15 wt assimilation is suggested by some melt inclusion and clinopyroxene compositions however most of the natural data indicate assimilation of between 3 and 12 wt carbonate current high co 2 emissions in this area most likely indicate that such an assimilation process still occurs at depth we calculate that a magma intruding into the carbonate basement with a rate of 1 2 10 6 m 3 year estimated by geophysical studies and assimilating 3 12 wt of host rocks would release an amount of co 2 matching the current yearly emissions at the alban hills our results strongly suggest that current co 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate hosted reservoir at 5 6 km depth with important consequences for the present day volcanic hazard evaluation in this densely populated and historical area

a criticism of the holm munksgaard oxygen and strontium isotope study of the vulsinian district central italy discussion sur l article de holm p m munksgaard n c paru dans earth planet sci letters nld 1982 60 376 388

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

comparison between analytical and 3d finite element solutions for borehole stresses in anisotropic elastic rock we present a rigorous validation of the analytical amadei solution for the stress concentration around an arbitrarily orientated borehole in general anisotropic elastic media first we revisit the theoretical framework of the amadei solution and present analytical insights that show that the solution does indeed contain all special cases of symmetry contrary to previous understanding provided that the reduced strain coefficients b11 and b55 are not equal it is shown from theoretical considerations and published experimental data that the b11 and b55 are not equal for realistic rocks second we develop a 3d finite element elastic model within a hybrid analytical numerical workflow that circumvents the need to rebuild and remesh the model for every borehole and material orientation third we show that the borehole stresses computed from the numerical model and the analytical solution match almost perfectly for different borehole orientations vertical deviated and horizontal and for several cases involving isotropic transverse isotropic and orthorhombic symmetries it is concluded that the analytical amadei solution is valid with no restriction on the borehole orientation or the symmetry of the elastic anisotropy

correlation of the major late jurassic early tertiary low and highstand cycles of south west egypt and north west sudan the mainly continental deposits of northwest sudan and south west egypt have been correlated with coeval shallow marine and marine deposits in northern egypt along a north south running cross section based on surface and subsurface data the palaeodepth curve of northern egypt illustrates the gradual seal level rise reaching its maximum during the late cretaceous with conspicuous advances during the aptian and late cenomanian a general highstand is also recorded during the campanian maastrichtian in north west sudan a detailed facies correlation is given for the aptian and late cenomanian highstand in western egypt the correlation of the cenomanian bahariya and maghrabi formations displays short term relative sealevel fluctuations the interpretation illustrates the extensiveness of related erosional processes in the hinterland partly intensified by temporarily uplift of the uweinat aswan high in the south regional uplift and constant erosion took place in south west egypt during coniacian and santonian times the regional stratigraphic gaps and uncertain interpretation of the bahariya uplift are induced by the influence of the trans african lineament especially during the late cretaceous low stand fluvial sheet sandstones characterized by non cyclic sequence development and high facies stability occur especially in the neocomian and early turonian during the barremian and albian fluvial architecture changes to more cyclic fluvial sequences and increasing soil formation due to increasing subsidence more humid climatic conditions and the generally rising sea level culminating in the extensive shallow marine abu ballas and maghrabi formations

active skarn formation beneath lascar volcano northern chile a petrographic and geochemical study of xenoliths in eruption products calcsilicate xenoliths occur in large numbers in some lavas and pyroclastic flows of lascar volcano their whole rock major element and ree compositions indicate that the protolith was the upper cretaceous yacoraite formation which crops out extensively in nw argentina the whole rock major element compositions of the xenoliths fall into specific groups suggesting a strong geochemical zonation in the skarn zone three geochemical zones have been identified 1 an outer metamorphic zone rich in wollastonite 2 a middle zone rich in pyroxene and garnet 3 an inner zone rich in pyroxene and magnetite the two innermost zones have developed from the wollastonite zone by infiltration of metasomatic fluids rich in fe mn mg ti and al whole rock ree patterns have not changed significantly during prograde metamorphism and metasomatism indicating ree immobility in the altering fluids retrograde alteration by acid sulphate fluids produced anhydrite skarns and secondary calcite and wilkeite veins in the wollastonite zone the carbon and oxygen isotopic compositions of this calcite indicate that it formed by rayleigh crystallization from a low temperature 200 c fluid containing dissolved h2co3 the calculated 18o of the water in this fluid suggests a magmatic origin whereas the calculated 13c of the dissolved carbonate is consistent with derivation from rocks of the yacoraite formation at 350 c it is suggested that the magmatic acid sulphate fluid was responsible for leaching carbonate from the surrounding carbonate rocks and redepositing it in the skarn zone rees were mobilized during the retrograde acid sulphate and acid carbonate alteration a negative ce anomaly associated with this carbonate and sulphate indicates high oxygen fugacities in the mineralizing fluids

mineralogical and geochemical study of granular xenoliths from the alban hills volcano central italy bearing on evolutionary processes in potassic magma chambers granular xenoliths ejecta from pyroclastic deposits emplaced during the latest stages of activity of the alban hills volcano range from ultramafic to salic ultramafic types consist of various proportions of olivine spinel clinopyroxene and phlogopite they show low sio2 alkalies and incompatible element abundances and very high mgo however cr co and sc are anomalously low at a few ppm level olivine is highly magnesian up to fo 96 and has rather high cao 1 ca and very low ni around a few tens ppm contents these characteristics indicate a genesis of ultramafic ejecta by thermal metamorphism of a siliceous dolomitic limestone probably with input of chemical components from potassic magma the other xenoliths have textures and compositional characteristics which indicate that they represent either intrusive equivalents of lavas or cumulates crystallized from variably evolved ultrapotassic magmas one sample of the former group has major element composition resembling ultrapotassic rocks with kamafugitic affinity some cumulitic rocks have exceedingly high abundances of th 81 84 ppm and light rare earth elements lree la ce 421 498 ppm and extreme ree fractionation la yb 288 1393 not justified by their modal mineralogy which is dominated by sanidine leucite and nepheline finegrained phases are dispersed through the fractures and within the interstices of the main minerals semiquantitative eds analyses show that th and lree occur at concentration levels of several tens of percent in these phases indicating that their presence is responsible for the high concentration of incompatible trace elements in the whole rocks the interstitial position of these phases and their association with fluorite support a secondary origin by deposition from fluorine rich fluids separated from a highly evolved potassic liquid the nd isotopic ratios of the cjecta range from 0 51182 to 0 51217 87sr 86sr ratios range from 0 70900 to 0 71036 with the exception of one sample these values are lower than those of the outcropping lavas which cluster around 0 7105 3 this indicates either the occurrence of several isotopically distinct potassic magmas or a variable interaction between magmas and wall rocks however this latter hypothesis requires selective assimilation of host rocks in order to explain isotopic and geochemical characteristics of lavas and xenoliths the new data indicate that the evolutionary processes in the potassic magmas of the alban hills were much more complex than envisaged by previous studies interaction of magmas with wall rocks may be an important process during magmatic evolution element migration by gaseous transfer often invoked but rarely constrained by sound data is shown to have occurred during the latest stages of magmatic evolution such a process was able to produce selective enrichment of th u lree and to a minor degree ta and hf in the wall rocks of potassic magma chamber finally the occurrence of xenoliths with kamafugitic composition points to the existence of this type of ultrapotassic magma at the alban hills

estimating aquifer parameters from analysis of forced fluctuations in well level an example from the nubian formation near aswan egypt 3 diffusivity estimates for saturated and unsaturated zones atmospheric pressure variations provide a broadband signal that may force a sympathetic response in well water levels in this paper time series analysis techniques are used to estimate the response as a frequency dependent admittance function which is then modeled to provide estimates of the fluid transport properties of strata the data derive from five cased piezometer wells sampling aquifers in the nubian formation southwest of aswan egypt three shallow wells 100 140 m deep sample a water table aquifer a fourth w3 400 m deep samples a basal aquifer in the same area that behaves in a confined manner up to a period of several years the fifth well samples another basal aquifer and shows evidence of partial blockage nontidal water level variations in the shallow wells are due almost entirely to barometrically driven flow of air and water using a simple model to fit the observed barometric admittance spectra we obtain estimates of horizontal and vertical permeabilities for water in the saturated zone local horizontal permeability is constrained by modeling the effects of flow induced pressure gradients near the screen for the w3 deep well sampling the basal aquifer the resulting values 0 15 0 3 2 are marginally lower than the large scale 5 km estimates 0 32 0 43 2 derived in a previous paper however the values for the three wells sampling the water table aquifer although consistent among themselves 0 2 0 5 2 are significantly lower than the large scale estimate 1 0 1 5 2 this is contrary to what might be expected given that the wells are preferentially screened in clean sandstones vertical permeability estimated by modeling partial confinement effects is constrained for only one well a low value was obtained because of the presence of claystone beds in the diffusion path between screen and water table at this well the effects of air wave diffusion are clearly manifest in the spectra of one well where the water table lay at a depth of about 40 m the form of the spectra was well fit by ascribing a uniform pneumatic diffusivity of 1 75 10 m 3m2 s to the unsaturated zone however it was also necessary to include an apparent attenuation of the air wave at the capillary fringe of about 0 5 we propose that the effect is due not to attenuation but that it reflects compression of the phreatic surface arising from the presence of trapped air pockets in the underlying saturated zone a 40 m rise in the water table at the site during the decade prior to the measurements might explain the presence of significant quantities of trapped air this rise in water table together with the arid climate might be taken to suggest that the moisture content of the unsaturated zone is negligible except within a meter or so of the water table however calculation of the intrinsic rock permeability from pneumatic diffusivity assuming zero moisture content yields an estimate which is considered to be too low the likely explanation is that the assumption of zero moisture content is in error despite conditions which are as favorable as are ever likely to be realized under field conditions

estimating aquifer parameters from analysis of forced fluctuations in well level an example from the nubian formation near aswan egypt 1 hydrogeological background and large scale permeability estimates this is the first of three papers concerning the extraction of aquifer parameters through the application of time series analysis to water level data from boreholes the analysis is performed on data from six wells located in the nubian desert near the shores of lake nasser egypt these wells are ideally suited to this study since they are remote from most sources of hydrological noise and hence respond primarily to forcing functions that can be measured or modeled for four of the wells which were part of a monitoring system installed prior to impoundment of lake nasser monthly at least water level measurements began in 1964 in 1985 two additional wells were drilled and high precision piezometers that sampled data every 0 2 hour were installed in five of the wells thus data are available which span the period band 23 years to 0 4 hour this paper provides background information and stratigraphy relevant to assessing the significance of the aquifer parameters derived using spectral methods a regional scale three dimensional hydrogeological model for the study area is developed based on the 23 year record of water level changes that occurred at the various well sites in response to the changing level of lake nasser the model that best fits the data and is consistent with recent stratigraphic studies of the nubian formation in the area consists of three horizontal units of total thickness 400 m the lowermost unit overlying the granitic basement is an aquifer of fluvial sandstones and has a large scale several kilometer horizontal permeability of 0 32 0 43 m2 the middle unit is an aquaclude that extends unbroken under the lake and leaks at periods longer than several years thus the lower aquifer is confined up to periods of several years the uppermost unit is the water table aquifer which is composed of 25 30 porosity sandstones with interspersed claystone lenses and has a large scale permeability of 1 0 1 5 m2 of the wells studied two are screened in the basal sandstone and four are screened in the water table aquifer analysis of tidally and atmospherically forced fluctuations in five of these wells is presented in the companion papers

origins and energetics of maar volcanoes examples from the ultrapotassic sabatini volcanic district roman province central italy maar volcanoes represent a common volcano type which is produced by the explosive interaction of magma with external water here we provide information on a number of maars in the ultrapotassic sabatini volcanic district svd roman province as young as 90 ka the svd maars are characterised in terms of crater and ejecta ring morphologies eruptive successions and magma compositions in light of the local substrate settings with the aim of assessing magma water interaction conditions eruption energetics and genetic mechanisms feeder magmas spanned the whole svd differentiation trend from trachybasalts shoshonites to phonolites from the ejected lithic fragments from aquifer rocks the range of depth of magma water explosive interaction is estimated to have been mostly at 400 600 m below ground level with a single occurrence of surficial interaction in palustrine lacustrine environment in particular the interaction with external water may have triggered the explosive behaviour of poorly differentiated magmas whereas it may have acted only as a late controlling factor of the degree of fragmentation and eruption style for the most differentiated magma batches during low flux ascent in an incipiently fragmented state crater sizes ejecta volumes and ballistic data allow a reconstruction of the energy budget of svd maar forming eruptions erupted tephra volumes from either monogenetic or polygenetic maars ranged 0 004 0 07 km3 during individual maar forming eruptions with corresponding total magma thermal energies of 8 1015 4 1017 j based on energy partitioning and volume balance of erupted magmas and lithic fractions vs crater holes we consider the different contributions of explosive excavation of the substrate vs subsidence in forming the svd maar craters following available models based on crater sizes highly variable fractions 5 50 of the magma thermal energies would have been required for crater excavation it appears that subsidence may have played a major role in some svd maars characterised by low lithic contents whilst substrate excavation became increasingly significant with increasing degrees of aquifer fragmentation

aggregate scale spatial heterogeneity in reductive transformation of ferrihydrite resulting from coupled biogeochemical and physical processes abstract iron hydr oxides are ubiquitous in soils and sediments and play a dominant role in the geochemistry of surface and subsurface environments their fate depends on local environmental conditions which in structured soils may vary significantly over short distances due to mass transfer limitations on solute delivery and metabolite removal in the present study artificial soil aggregates were used to investigate the coupling of physical and biogeochemical processes affecting the spatial distribution of iron fe phases resulting from reductive transformation of ferrihydrite spherical aggregates made of ferrihydrite coated sand were inoculated with the dissimilatory fe reducing bacterium shewanella putrefaciens strain cn 32 and placed into a flow reactor the reaction cell simulates a diffusion dominated soil aggregate surrounded by an advective flow domain the spatial and temporal evolution of secondary mineralization products resulting from dissimilatory fe reduction of ferrihydrite were followed within the aggregates in response to a range of flow rates and lactate concentrations strong radial variations in the distribution of secondary phases were observed owing to diffusively controlled delivery of lactate and efflux of fe ii and bicarbonate in the aggregate cortex only limited formation of secondary fe phases were observed over 30 d of reaction despite high rates of ferrihydrite reduction under all flow conditions tested ferrihydrite transformation was limited in the cortex 70 85 mol fe remained as ferrihydrite because metabolites such as fe ii and bicarbonate were efficiently removed in outflow solutes in contrast within the inner fractions of the aggregate limited mass transfer results in metabolite fe ii and bicarbonate build up and the consummate transformation of ferrihydrite only 15 40 mol fe remained as ferrihydrite after 30 d of reaction goethite lepidocrocite and minor amounts of magnetite formed in the aggregate mid section and interior at low lactate concentration 0 3 mm after 30 d of reaction under high lactate 3 mm concentration magnetite was observed only as a transitory phase and rather goethite lepidocrocite and siderite were the dominant secondary mineralization products our results illustrate the importance of slow diffusive transport of both electron donor and metabolites concentrations and concomitant biogeochemical reactions within soils and sediments giving rise to heterogeneous products over small spatial m scale

interaction between ultrapotassic magmas and carbonate rocks evidence from geochemical and isotopic sr nd o compositions of granular lithic clasts from the alban hills volcano central italy abstract magma carbonate rock interaction is investigated through a geochemical and sr nd o isotope study of granular lithic clasts ejecta from the alban hills ultrapotassic volcano central italy some samples group 1 basically represent intrusive equivalents of alban hills magmas a few samples group 2 are ultramafic have high mgo 30 to 40 wt and 18o and originated by accumulation of mafic phases that crystallised from ultrapotassic melts during assimilation of dolomitic rocks group 3 ejecta consist of dominant k feldspar and show major element compositions similar to phonolites which however are absent among the alban hills volcanics finally another group group 4 contains corroded k feldspars surrounded by a microgranular to porphyritic matrix made of igneous minerals k feldspar foids clinopyroxene phlogopite plus wollastonite garnet and some cuspidine group 4 ejecta are depleted in sio2 and enriched in cao with respect to group 3 the analysed ejecta have similar 143nd 144nd 0 51204 0 51217 as the alban hills lavas whereas 87sr 86sr 0 70900 0 71067 is similar to lower whole rocks 18o ranges from 7 0 to 13 2 reaching maximum values in ultramafic samples a positive correlation with cao is observed in single rock groups large ion lithophile element lile abundances and ree fractionation are generally high and extreme values of th u and lree are found in some group 3 and group 4 rocks mineralogical petrological and geochemical data reveal extensive interaction between magma and carbonate wall rocks involving both dolostones and limestones these processes had dramatic effects on magma compositions especially on phonolites which were transformed to foidites evidence of such a process is found in group 4 samples in which k feldspar is observed to react with a matrix that represents strongly undersaturated melts formed by interaction between silicate magma and carbonates trace element data also testify to a very important role for f co2 h2o s fluids during magma wall rock interaction fluid transfer was responsible for extreme enrichments in th u and lree especially observed in group 3 and group 4 rocks implications of these processes for potassic magma evolution in central italy are discussed

anatomy and origin of a cretaceous phosphorite greensand giant egypt late cretaceous epicontinental phosphorites porcelanites cherts dark coloured shales glauconitic sandstones and bioclastic and fine grained carbonate rocks in egypt are examined in terms of their overall depositional and diagenetic framework and stable isotopic and organic geochemical characteristics two main depositional realms are interpreted and correlated through sequence stratigraphic analysis 1 a shallow hemipelagic environment accompanying initial stages of marine transgression and conducive to the formation of organic carbon rich shales biosiliceous sediments and thick phosphorites and 2 a relatively high energy depositional regime accompanying sea level fall during which deltas advanced glauconites were reworked seaward and prograding oyster banks became periodically exposed to episodes of fresh water diagenesis thereby promoting solution collapse phenomena in associated cherts lenticular to massive phosphorites are viewed as the result of current winnowing and concentration of authigenic grains initially precipitated in associated reducing shales and biosiliceous sediments in eastern egypt the phosphorites form winnowed lag layers some of which may have been redeposited down slope in structural lows in the west these sands were concentrated into giant phosphorite sand waves built by reworking of penecontemporaneously deposited phosphatic muds during marine transgression carbon isotopic results substantiate interpretations from modern deposits for limitation of phosphate mineral precipitation with depth in sediments as a result of lattice poisoning however direct desorption of phosphorus to pore waters from detrital iron oxyhydroxide phases also may have been important in the cretaceous setting the iron reduced in this process being available for incorporation in glauconites the main locus for authigenic glauconite precipitation appears to be where iron fluxes from regions of lateritic weathering were highest and near the boundary between oxygenated and reduced waters this study suggests a model for the common coexistence of glauconites and phosphorites in the geological record although upwelling is often advocated as the origin of nearly all giant phosphorite deposits we suggest that some of these may have been strongly influenced by fluvially derived phosphorus borne on particulates and desorbed from these compounds upon flocculation and or reduction in bottom waters or pore waters

were springline carbonates in the kurkur dungul area southern egypt deposited during glacial periods the tufa deposits in the kurkur dungul area southern egypt date from marine isotope stage mis 11 to mis 1 springs across the region were active during glacial periods with sea level below 50 m reflecting changed atmospheric circulation over the indian ocean as well as peak interglacial periods during times of low sea level reduced indonesian throughflow promoted formation of an indian ocean warm pool and anomalous rainfall on its western margin we suggest that egypt lies at the intersection of westerly maghrebian and easterly mashriqian rainfall provinces which show different timing with relation to orbital forcing and different source water regions tufa growth periods are therefore not mechanistically linked to humid periods or sapropel events identified elsewhere stable isotope and t 47 data are also inconsistent with these spring systems being part of a larger system spanning northern africa and lack a clear interaction between northern hemisphere heating and mid latitude rainfall we also follow previous researchers in concluding that formation of springline deposit formation was probably delayed compared with rainfall owing to aquifer flow distances this delay is unlikely to be sufficient to explain why rainfall is out of phase with movements of the monsoon belts but may complicate interpretation of these records supplementary material a lithofacies description and supplementary figures and tables are available at https doi org 10 6084 m9 figshare c 5246661

relationships between ultrapotassic and carbonate rich volcanic rocks in central italy petrogenetic and geodynamic implications the pleistocene intra apennine volcanic iav centres occurring east of the potassium rich roman comagmatic province show variable petrological and geochemical composition some rocks have a strongly undersaturated ultrapotassic kamafugitic affinity with k2o na2o 8 20 whereas the rocks from the southern center of mt vulture are still strongly undersaturated in silica but are enriched in both na2o and k2o with k na around unity carbonate rich pyroclastic rocks believed to represent carbonatitic magmas are found in the iav centers kamafugites have high abundances of lile and high lile hfse ratios and their incompatible element patterns resemble closely those of ultrapotassic rocks from the adjoining roman province the vulture volcanics also display high contents of lile but their lile hfse ratios are intermediate between intraplate alkaline rocks and kamafugites the carbonate rich rocks exhibit an exotic mineralogy and high enrichments in lile which speaks for a carbonatitic affinity however they have similar incompatible element patterns but consistently lower abundances of almost all the elements than the associated silicate volcanics these data favour the hypothesis that the iav carbonate rocks may represent mixtures of silicate magmas and geochemically depleted carbonate material the sedimentary carbonates that crop out extensively along the apennine chain may be the source of barren carbonate material overall geochemical data of iav centres and of the rocks from the roman province display strong geochemical and isotopic evidence of being generated in an upper mantle that was modified by addition of upper crustal material brought down by subduction processes a possible exception is represented by mt vulture which however occurs east of the main axis of the apennines on the western margin of the foreland adria plate the occurrence of strongly undersaturated alkaline rocks requires magma generation at high pressures and xco2 this is in agreement with the hypothesis that subduction processes under the apennines occurred by consumption of poorly hydrated thinned or delaminated continental crust

palaeogeography of africa during the cretaceous period abstract a first attempt is made to synchronize the major palaeogeographical events of the african cretaceous where recognizable palaeoclimatological interpretations are given an overview of the nature of the continental margins and the plate tectonic setting for africa during the cretaceous provides a convenient backdrop for presenting the palaeogeographical development of the continent lacustrine deposits occur along the line of south atlantic rifting late jurassic oceanic crust in the south atlantic dates from the valanginian with continental volcanism adjacent to the walvis ridge continuing until the albian locally there was a barremian incursion in southeast africa the falkland plateau and walvis ridge areas created shallow water barriers in the aptian which facilitated the massive accumulation of salt tectono eustatic transgressions took place in the middle to late albian cenomano turonian late turonian to coniacian and campano maastrichtian anoxic conditions prevailed during the late jurassic agulhas bank falkland plateau aptian albian the cenomanian turonian and the coniacian these are relatable to the epicontinental transgressional maxima and the heavy influx of organic debris however there was no campano maastrichtian anoxic event

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

poroelastic response of a borehole in a non hydrostatic stress field abstract this paper deals with the solution of the stress displacement and pore pressure field induced by the drilling and or the pressurization of a vertical borehole the rock which is permeated by fluid is assumed to behave as a poroelastic material with compressible constituents following the biot theory the analytical solution is derived in the laplace transform space and is transformed to the time domain using an approximate numerical inversion technique the solution reveals a full range of coupled poroelastic effects which provide potential mechanisms for delayed borehole instability and shear fracture initiation inside the rock

geological exploration history of the eastern sahara the major contributions to our knowledge of the geological history of the east saharan countries are described much work has been published on the history and progress of geographical socioeconomic and archaeological exploration in north africa little attention however has been paid to the question of how our knowledge of the geology of this vast area was developed thus even though progress in geology is vital to the development of saharan countries little has been recorded of this progress without an understanding of regional geology and without a good knowledge of groundwater mineral and petroleum potentials these countries would be in very different situations today the author has over the last 35 years been involved in scientific research and exploration of petroleum mineral and groundwater resources in libya egypt sudan and chad

evidence for the presence of carbonate melt during the formation of cumulates in the colli albani volcanic district italy abstract fergusite and syenite xenoliths and mafic lapilli from two locations in the villa senni ignimbrite of the colli albani volcanic district show evidence for fractionation of a silicate magma that led to exsolution of an immiscible carbonate melt the fergusite xenoliths are divided into two groups on the basis of their clinopyroxene compositions group 1 clinopyroxene records the crystallisation of a silicate melt and enrichment of the melt in al ti and mn and depletion in si as well as enrichment in incompatible trace elements the second group of clinopyroxene compositions group 2 comes mainly from ba f phlogopite and ti andradite bearing fergusites they have significantly higher si and lower al and ti and like the coexisting phlogopite and garnet are strongly enriched in mn the minerals in the fergusites containing group 2 clinopyroxene are enriched in ba sr cs v and li all of which are expected to partition strongly into a carbonate melt phase relative to the coexisting silicate melt the compositional data suggest that the group 1 fergusites record sidewall crystallisation of co2 rich silicate melt and that once the melt reached a critical degree of fractionation carbonate melt exsolved the group 2 fergusites record continued crystallisation in this heterogeneous silicate carbonate melt system composite xenoliths of fergusite and thermometamorphic skarn record contact times of hundreds to a few thousand years indicating that fractionation and assimilation was relatively rapid

coseismic deformation of the wrights tunnel during the 1906 san francisco earthquake a key to understanding 1906 fault slip and 1989 surface ruptures in the southern santa cruz mountains california the wrights tunnel is an abandoned railroad tunnel that crosses the san andreas fault in the southern santa cruz mountains in the vicinity of the 1989 loma prieta earthquake the tunnel was damaged and deformed during the 1906 san francisco earthquake and a plot showing postearthquake measurements made in the tunnel is given by lawson 1908 the amount of offset shown on this plot 1 5 m has been used in several studies as being representative of the amount of fault offset along this segment of the san andreas fault in 1906 our historical research shows that different observers reported different amounts of fault offset in the tunnel and that the 1 5 m given on the plot is not a surveyed measurement in addition the plot of the tunnel has been interpreted in several previous studies as evidence of a broad 1 5 km zone of faulting beneath summit ridge our analysis shows that this plot need not indicate a broad zone of deformation our historical research and modeling of the tunnel measurements indicate that faulting was confined to a zone less than 400 m wide and that 60 85 of the coseismic slip occurred across a single fault plane there is no evidence for offset across a second shear zone beneath summit ridge in 1906 this implies that surface fractures reported on summit ridge in 1906 were not associated with significant deformation of the tunnel implying that they were shallow surficial features by analogy the very similar fractures that occurred on summit ridge in 1989 were also probably the result of shallow gravitational rather than deep seated tectonic processes our modeling also indicates that total coseismic near surface slip across the san andreas fault zone in the wrights tunnel in 1906 was at least 1 7 1 8 m

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

pervasive assimilation of carbonate and silicate rocks in the hortavaer igneous complex north central norway the intrusive complex at hortav r represents a magma transfer zone in which multiple pulses of gabbroic and dioritic magmas evolved along fe and alkali enrichment trends extreme alkali enrichment resulted in nepheline normative and sparse nepheline bearing monzodioritic and monzonitic rocks more evolved monzonitic and syenitic rocks are silica saturated and in some cases quartz bearing previous and current research recognized an abundance of clinopyroxene and other ca rich phases such as scapolite grossular rich garnet and igneous textured calcite among the mafic and intermediate rocks even the most pyroxene rich samples contain low sc concentrations which suggests early intense fractionation of clinopyroxene these features and the alkali enrichment are consistent with assimilation of carbonate rich host rocks carbon isotope ratios of the igneous textured calcite indicate an origin of the carbon from host rocks rich in calcite consistent with assimilation however low end values 3 4 to 10 2 and moderate initial 87 sr 86 sr values 0 7052 to 0 7099 indicate the need for assimilation of quartzofeldspathic rocks as well models of combined assimilation and fractional crystallization indicate that assimilation of simple end members either carbonate or silicate cannot explain the entire data set instead variable proportions of carbonate and silicate materials were assimilated with the most pronounced assimilation effects in the mafic rocks the reasons for variable degrees of assimilation are as yet uncertain it is possible that assimilation of calc silicate rocks with variable carbonate silicate proportions resulted in the range of observed compositions however the importance of carbonate assimilation in mafic rocks compared to felsic ones suggests that assimilation of carbonates was predominant at high temperature and or mafic magma compositions and assimilation of silicates was predominant at lower temperature and or felsic magma compositions we suggest that the ability of the mafic magma to dissolve higher proportions of carbonate contaminants is the result of the magma s ability to form clinopyroxene as a product of assimilation in any case extensive carbonate assimilation was possible because co2 escaped from the system d 2004 elsevier b v all rights reserved

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

the gulf of suez northern red sea neogene rift a quantitive basin analysis abstract subsidence analysis backstripping was carried out on a series of wells from the gulf of suez and northern red sea region of egypt in order to examine the interplay between tectonic events basin subsidence sedimentation and sea level changes in a young developing ocean basin and continental margin using constraints on chronostratigraphy and paleodepth from various sources combined with stratigraphic and structural information from industry wells and other geophysical sources it has been possible to compile the data necessary to perform geohistory analyses throughout the region major subsidence due to crustal thinning began 25 ma with sedimentation initially occurring in isolated sub basins these earliest sediments record the transition from continental to marine depositional environments subsequently during early and middle miocene times subsidence was rapid and uniform along and across the entire rift basin open marine sedimentation occurred across all structural regimes the mid clysmic tectonic event 16 5 ma resulted in structural rearrangement of the rift basin and uplift of the rift shoulders rapid subsidence continued as global sea level fell producing a series of prograding siliciclastic fan deltas at the rift margins at 15 5 ma opening of the suez rift was terminated tectonic subsidence decreased dramatically in the southern rift and ceased entirely in the northern rift tensional plate motion probably was transferred from the gulf of suez to sinistral strike slip movement on the dead sea transform at this time the quiescence in subsidence combined with a lowered global sea level resulted in the deposition of a thick up to 4 km series of evaporites within the central trough of the rift from the middle to latest miocene the accumulation of such a thick sequence of sediments during a phase of decreased tectonic subsidence is interpreted as a filling in of the rift topography which developed during the earlier period of rapid subsidence and rift shoulder uplift and continued compaction a rapid global sea level rise concomitant with a subsequent pulse of increased tectonic activity in the latest miocene earliest pliocene returned the rift to dominantly marine conditions

genesis evolution and tectonic significance of k rich volcanics from the alban hills roman comagmatic region as inferred from trace element geochemistry trace element data are reported in 21 lava samples from the alban hills one of the most important volcanic complexes of the roman comagmatic region the samples consist mostly of tephritic leucitites with minor phonolitic tephrites and tephritic phonolites emplaced during two distinct phases of activity separated by a caldera collapse