crustal structure of the western part of the southern granulite terrain of indian peninsular shield derived from gravity data abstract the southern granulite terrain sgt is composed of high grade granulite domain occurring to the south of dharwar craton dc the structural units of sgt show a marked change in the structural trend from the dominant north south in dc to east west trend in sgt and primarily consist of different crustal blocks divided by major shear zones the bouguer anomaly map prepared based on nearly 3900 gravity observations shows that the anomalies are predominantly negative and vary between 125 mgal and 22 mgal the trends of the anomalies follow structural grain of the terrain and exhibit considerable variations within the charnockite bodies two dimensional wavelength filtering as well as zero free air based zfb analysis of the geoid corrected bouguer anomaly map of the region is found to be very useful in preparing regional gravity anomaly map and inversion of this map gave rise to crustal thicknesses of 37 44 km in the sgt crustal density structure along four regional gravity profiles cutting across major shear zones lineaments plateaus and other important geological structures bring out the following structural information the bavali shear zone extending at least up to 10 km depth is manifested as a plane separating two contrasting upper crustal blocks on both sides and the gravity high north of it reveals the presence of a high density mass at the base of the crust below coorg the steepness of the moyar and bhavani shears on either side of nilgiri plateau indicates uplift of the plateau due to block faulting with a high density mass at the crustal base the bhavani shear zone is manifested as a steep southerly dipping plane extending to deeper levels along which alkaline and granite rocks intruded into the top crustal layer the gravity high over palghat gap is due to the upwarping of moho by 1 2 km with the presence of a high density mass at intermediate crustal levels the gravity low in periyar plateau is due to the granite emplacement mid crustal interface and the thicker crust the feeble gravity signature across the achankovil shear characterized by sharp velocity contrast indicates that the shear is not a superficial structure but a crustal scale zone of deformation reaching up to mid crustal level

paleomagnetic study of cambrian potsdam group sandstones st lawrence lowlands quebec abstract we report paleomagnetic results from oriented drill core samples collected at 10 sites 80 samples from the covey hill and 19 sites 96 samples from the overlying fossiliferous cha teauguay formations of the gently dipping late cambrian potsdam group sandstones exposed in the st lawrence lowlands of quebec stepwise thermal demagnetization analyses ave revealed the presence of two predominant groups of coherent magnetizations c 1 and c 2 after simple correction for bedding tilt the c 1 group magnetization is a stable direction d 332 i 18 with unblocking temperatures t ub between 550 and 650 c present in the older covey hill formation this direction is probably a chemical remanence acquired during the covey hill diagenesis and carried predominantly by hematite the c 2 group magnetization d 322 i 9 is present at 13 sites of the younger cha teauguay formation this is probably carried by magnetite and represents a penecontemporaneous depositional drm characterized by t ub spectra 400 550 c we believe that c 2 is relatively younger than c 1 based on a combination of arguments such as the presence of opposite polarities internal consistency similarity and common occurrence of c 1 and c 2 respectively in the covey hill and cha teauguay members the corresponding paleomagnetic poles c 1 46 n 149 e dp dm 3 5 and c 2 37 n 156 e dp dm 2 5 are not significantly different from most of the other late cambrian dresbachian franconian poles derived from sediments exposed in the southern region texas of the north american craton which are also believed to have been deposited during croixian sauk sea transgression similar to the potsdam sandstones although adequate faunal control is lacking in particular for the covey hill formation this comparison with the cratonic poles suggests a late cambrian age to the potsdam poles the agreement between the results also gives the evidence for internal consistency of cratonic poles at least for late cambrian the incoherent c 3 group remanence d 250 i 15 is commonly present at 7 sites in both the formations this may not correspond to a reliable paleomagnetic signal the other remanence c 4 d 180 i 10 is found only at 3 sites located in the uppermost stratigraphic levels of the cha teauguay formation the corresponding paleomagnetic pole 40 n 107 e does not differ significantly from the ordovician and some late cambrian poles the present data are insufficient to resolve a problem in apparent polar wander for middle and late cambrian time posed by the existence of high latitude poles for some strata of middle cambrian age and low latitude poles for some strata of late cambrian age

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

fluorapatite in the paleoproterozoic thelon basin structural stratigraphic context in situ ion microprobe u pb ages and fluid flow history fluorapatite cements have been documented at more than 18 localities in the thelon basin canada occupying stratigraphic positions from the paleosol below the unconformity to well within the upper parts of depositional sequence of the fluvial siliciclastic thelon formation ion microprobe analyses targeted using cathodoluminescence images to areas of higher uranium content on petrographically characterized cements provide the most precise pin on the timing of mesodiagenesis in the northeastern part of the thelon basin at 1667 5 ma expulsion of phosphate rich basinal brines was associated with development of faults and local breccias in the lower strata where extensive quartz cementation took place before the apatite event the new data do not support previous interpretations for multiple episodes of fluorapatite cementation within the basin despite the wide range of stratigraphic positions and variations in style of occurrence the tectonic cause remains speculative as does the relationship of the fluorapatite cements to the unconformity style uranium mineralization thelon fluorapatite cements are older than those reported in the athabasca basin suggesting distinct fluid flow histories occurred within the two basins the difference in timing indicates that the basinwide events that generated the fluids with the chemistry capable of producing fluorapatite cement took place independently but under similar conditions within the thelon and athabasca basins

synsedimentary lacustrine phosphorites from the pliocene glenns ferry formation of southwestern idaho abstract numerous laterally extensive thin fresh water lacustrine phosphatic horizons characterize nearshore facies of the pliocene glenns ferry formation in southwestern idaho these units are restricted to and formed on hiatal surfaces in coarse sandstone and oolite which now crop out in a narrow northwest trending belt along 50 km of the southwestern shoreline of pliocene lake idaho these hiatal surfaces developed during periods of transgression when sites of nearshore deposition migrated landward phosphatization occurred through the replacement of calcareous ooid and oncoid cortices and through the precipitation of fibrous isopachous cements around both terrigenous and coated grains francolite a carbonate fluorapatite is the primary phosphate phase present phosphatization was a synsedimentary diagenetic event it occurred just below the sediment water interface as a consequence of high phosphate concentrations in interstitial waters which resulted from intergranular decay and dissolution of organics during periods of low terrigenous sedimentation

quartz arenites of the cambro ordovician kamouraska formation quebec appalachians canada ii eolian sands in deep sea sedimentary gravity flow deposits the kamouraska formation is a quartz arenitic unit of latest cambrian earliest ordovician age in the quebec appalachians that was deposited by hyperconcentrated to concentrated density flows in a meandering submarine canyon on the continental slope bordering the iapetus ocean as outlined in a companion paper detailed petrographic study of the quartz arenites of the kamouraska formation combined with scanning electron microscopy of grain surface textures suggests that the quartz sands are of eolian origin having been derived from an inland desert or less likely a barrier beach dune system transport of the mature quartz arenitic sand onto the shelf and deposition into the deep sea was not accompanied by substantial mixing with material from other sources thus preserving the inherited eolian characteristics a modern analogue for the eolian interpretation of the deep sea quartz arenite beds is as follows thick late pleistocene eolian sand beds on a modern abyssal plain in the east atlantic referred

stratigraphie framework for the cambrian ordovician rift and passive margin successions from southern quebec to western newfoundland the taconian humber zone stretches from western newfoundland to southern quebec the early cambrian slope succession in newfoundland is found in the curling group whereas in quebec various units were deposited during that first time slice biostratigraphic data allow correlation of the curling group with the labrador group in newfoundland and with the newly time constrained slope succession in quebec the end of the rift drift transition is marked by a sea level lowstand at the end of the early cambrian the middle cambrian to latest early ordovician passive margin history recorded five cyclic sea level fluctuations three of these cycles are recorded in the shallow marine middle to late cambrian platform port au port group and slope sediments preserved in the cow head and northern head groups in newfoundland the biostratigraphic information assists correlation with cambrian passive margin units in quebec major sea level lowstands are recognized along the continental margin in early middle late camb

3d aquifer mapping employing airborne geophysics to meet india s water future with the growing dependence on groundwater escalating demand and increasing depletion of aquifers the government of india has accorded special emphasis to management of groundwater resources through precise aquifer mapping we have carried out hydrogeophysical surveys including airborne electromagnetic aem in six hydrogeologically divergent areas comprising sedimentary basins basalts weathered and fractured granite gneisses and schists desert and costal alluvium with the objective to establish suitability of aem for a countrywide aquifer mapping in india efficacy of the dual moment aem surveys in mapping the shallow and deep aquifers is evaluated in conjunction with geologic geophysical and borehole data it is found that the aem surveys provide reliable images of the subsurface resistivity distribution defining the 3d geometrical and electrical attributes of aquifers in different areas the surveys helped identify the suitable zones for managed artificial recharge mar subsurface structur

diagenetic fluorapatite and aluminum phosphate sulphate in the paleoproterozoic thelon formation and hornby bay group northwestern canadian shield in the northwestern part of the canadian shield fluorapatite and a rare earth element bearing hydrated aluminum phosphate sulphate mineral aps occur as cements in continental successions near the base of the paleoproterozoic thelon formation thelon basin and hornby bay group hornby bay basin these minerals occupy interstitial sites form euhedral crystals display micro scale zonation make up part of an unmetamorphosed paragenetic assemblage and are distributed in correlative units across thousands of square kilometres suggesting a diagenetic origin stratigraphy geochronology and other lines of evidence suggest that the thelon formation and hornby bay group containing these phosphatic cements as well as the ellice formation and athabasca group are correlative and may have been originally interconnected the evidence suggests that the basal thelon formation and the hornby bay group underwent similar and approximately coeval diagenetic mineral paragenesis furthermore the diagenetic fluid

a modern terrestrial phosphorite an example from sri lanka abstract at eppawala in central sri lanka a thick weathering profile is mined for use as phosphate fertilizer recent tropical subaerial weathering processes have produced a phosphate enriched horizon in the weathering profile which has developed on a precambrian apatite marble formation the enriched horizon with p2o5 compositions ranging from 10 to 40 is formed essentially of laminar phoscretes occurring in a network of sinkholes detailed examination of the laminar phoscretes reveals that primary metamorphic apatite crystals occur in association with phosphatic allochems such as coated grains ooids pisoids and intraclasts in a finely layered groundmass it has been observed that the primary apatite grains released from the parent apatite marble due to tropical weathering processes have been deposited in sinkholes where nutrient rich percolating meteoric waters were precipitating secondary apatite subsequent diagenetic processes active in such sinkhole sedimentary environments have produced the phosphatic allochems characteristic of secondary phosphate mineralization the allochems together with their mineralized groundmass and the associated primary apatite grains have given rise to the eppawala phosphorite deposit

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

regional tectonic interpretation of image enhanced gravity and magnetic data covering the mid norwegian shelf and adjacent mainland abstract gravity and magnetic field data covering mid norway and the norwegian sea were processed in order to enhance tectonic features on various scales the local features were subjected to an unconventional processing technique involving a non linear adaptive wallis filter designed to enhance the smallest wave lengths when compared with recent structural information derived from seismic data the processed gravity and magnetic maps show the main structural trends major fault zones and basin boundaries thus proving their worth for regional tectonic mapping previously undetected nw se trending offshore crustal lineaments are revealed a landward prolongation of the bivrost lineament appears to continue subparallel towards proterozoic shear zones below the caledonian nappes in the rana area either along the western margin of the transscandinavian granite porphyry belt or the nw se trending mala skelleftea tectonic zone a large lineament is also observed as a landward prolongation of the surt lineament indicating a relationship with the storsjon edsbyn deformation zone a major deep crustal shear zone in the precambrian of sweden a slightly increased seismic activity which is possibly related to the present ridge push force is observed along parts of the previously unknown transfer zones combined gravity and magnetic modelling indicates a low crustal thickness in the northwesternmost part of the voring basin between the surt and the jan mayen lineaments the lack of correlation between the gravity and the magnetic patterns observed on the residual field maps suggests the presence of a shallow curie isotherm situated above or within the uppermost basement

paleoceanographic constraints on precambrian phosphorite accumulation baraga group michigan usa abstract the palaeoproterozoic baraga group ca 1850 1 ma of northern michigan is a 1200 m thick sedimentary succession of marine clastic iron formation chert and phosphatic sedimentary rocks that accumulated at the peak of the world s first major phosphogenic episode lithofacies stacking patterns are interpreted to record the flooding of the nuna continental margin during two sea level cycles the base of the first sequence is marked by a transgressive lag on archean basement that is transitional into a highstand accumulation of sandstones deposited in peritidal environments the bottom of the second sequence is characterized by a chert and carbonate unit with numerous subaerial exposure surfaces deposited in intertidal to supratidal environments this chert grades upward into subtidal deposits composed of interbedded organic rich mudstone and sandstone the highstand and falling stage systems tracts are composed of progradational deltaic deposits sequences were framed using the newly discovered sudbury impact ejecta horizon as a datum its emplacement approximately coincides with unrelated environmental changes that increased the delivery of river borne sediment to the nuna margin iron bearing minerals ankerite siderite and pyrite show that ferrous iron was present in peritidal to deep marine environments ankerite dominates nearshore settings where pyrite is absent pyrite occurs in deeper progradational deltaic deposits where sulfide was produced by bacterial sulfate reduction phosphorite is restricted to shallow water sediments of the first sequence and the lowstand of the second sequence precipitation is interpreted to be the result of fe redox pumping just below the sediment water interface where photosynthetically produced nearshore oxygen oases impinged on the seafloor such shallow water phosphorite accumulation is in stark contrast to many phanerozoic depositional systems in which phosphogenesis occurs across the shelf this difference likely reflects the dissimilarity in the oxygenation state of the seafloor in the precambrian fe redox pumping and thus phosphogenesis was restricted to shallow water settings with a suboxic seafloor in the phanerozoic phosphorite forms in the full spectrum of shelf environments because the entire seafloor is generally well oxygenated the concentration of bioavailable p in neritic environments during the proterozoic may have played a major role in the development of benthic microbial ecosystems and evolving eukaryotes

composition and architecture of braided and sheetflood dominated ephemeral fluvial strata in the cambrian ordovician potsdam group a case example of the morphodynamics of early phanerozoic fluvial systems and climate change abstract two fluvial facies associations braided and ephemeral fluvial are recognized in strata of the cambrian ordovician potsdam group in the ottawa embayment and quebec basin in northeastern north america braided fluvial sedimentation was dominated by the migration of coarse grained sandy dunes and rare unit bars and local gravels that built up low relief 0 4 5 m thick downstream accreting compound bars in very wide and shallow braided channels rare meter scale confluence scours incision and filling of decimeter thick bypass channels and thin 7 cm overbank deposition also occurred ephemeral fluvial sedimentation was dominated by the progradation of lobate terminal splays most of which were deflated and or reworked into thin 10 95 cm sheets by eolian processes during the long recurrence intervals between floods these strata were locally incised by rare 0 3 1 9 m thick scour filling high energy supercritical bedform strata and decimeter thick bypass channels both braided and ephemeral fluvial deposits consist of meter scale stacked high order stratal units separated by horizontal laterally extensive surfaces recording the recurring buildup avulsion and finally abandonment of channel belts in braided fluvial strata of the potsdam the dominance of thin 2 m elongated compound bars with low relief 5 bar margins and internal accretion surfaces 15 suggest that braided channels and in channel compound bars expanded laterally with negligible increase in flow depth during periods of increased discharge in the absence of bank stabilizing vegetation similar to other examples of the pre vegetated sheet braided style however in areas where bedrock topography inhibited the lateral expansion of channels thicker compound braid bars 1 2 3 5 m with higher relief accretion surfaces up to 35 like those observed in post silurian and modern systems preferentially formed in relatively deep channels ephemeral fluvial deposits here are similar to ephemeral examples throughout geologic history in that they mostly comprise poorly confined sheet like terminal splays that accumulated in topographic lows however compared to several post silurian examples strata in the potsdam exhibit considerably more eolian reworking of splays and preservation of supercritical bedform strata a manifestation of greater rates of surface water infiltration due to a lack of sheltering by rooted plants and propensity for unconfined flooding finally in the upper part of the potsdam two regional ephemeral fluvial units are interstratified with two braided fluvial units providing evidence for shifts in regional climate the sharp areally extensive surfaces that separate these fluvial systems are interpreted to approximate time lines and therein provide a means for relative and absolute chronostratigraphic correlation these changes are correlated with documented late cambrian to earliest ordovician global climate fluctuations with semiarid conditions and related ephemeral fluvial systems corresponding to global cooling events at ca 491 and 487 ma

lithostratigraphic and allostratigraphic framework of the cambrian ordovician potsdam group and correlations across early paleozoic southern laurentia the potsdam group is a cambrian to lower ordovician siliciclastic unit that crops out along the southeastern margins of the ottawa graben from its base upward the potsdam consists of the ausable hannawa falls and keeseville formations in addition the potsdam is subdivided into three allounits allounit 1 comprises the ausable and hannawa falls and allounits 2 and 3 respectively the lower and upper parts of the keeseville allounit 1 records early to middle cambrian syn rift arkosic fluvial sedimentation ausable formation with interfingering mudstone arkose and dolostone of the marine altona member recording transgression of the easternmost part of the ottawa graben rift sedimentation was followed by a middle cambrian climate change resulting in local quartzose aeolian sedimentation hannawa falls formation allounit 1 sedimentation termination coincided with latest middle cambrian tectonic reactivation of parts of the ottawa graben allounit 2 lower keeseville records mainly upper cambrian quartzose fluvial sedimentation with transgression of the northern ottawa graben resulting in deposition of mixed carbonate siliciclastic strata of the marine riviere aux outardes member sedimentation was then terminated by an earliest ordovician regression and unconformity development allounit 3 upper keeseville records diachronous transgression across the ottawa graben that by the arenigian culminated in mixed carbonate siliciclastic shallow marine sedimentation theresa formation the contact separating the potsdam group and theresa formation is conformable except locally in parts of the northern ottawa graben where the presence of localized islands and or coastal salients resulted in subaerial exposure and erosion of the uppermost potsdam strata and accordingly unconformity development

diagenetic apatite character and in situ ion microprobe u pb age keeseville formation potsdam group new york state an occurrence of diagenetic fluorapatite cement is documented within the cambro ordovician keeseville formation potsdam group near chateaugay in new york state the fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites which have been reworked by aeolian processes prior to burial the paragenetic sequence includes the following compaction of dust rimmed grains quartz cementation minor kaolinite fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation the fluorapatite occurs as elongated bladed crystals that characteristically contain ladder like inclusion rich cores running parallel to crystal length surrounded by clearer rims and larger blocky crystals towards the middle of interstices in situ shrimp analyses of blocky fluorapatite crystals yield a u pb age of 486 29 ma indicating that the cement for

age of the richmond gulf group and implications for rifting in the trans hudson orogen canada abstract the aphebian richmond gulf group of the east coast of hudson bay is a fluvial sandstone sequence containing basalt flows it was shed eastward from a rifting related thermal dome situated in the present central part of hudson bay sandstone from the base of the group contains a uraniferous diagenetic apatite cement u pb and pb pb isochron analysis from this material show the age of the apatite haematite cement to be 2025 25 ma old these data provide an older age bracket for the deposition of the richmond gulf nastapoka and belcher groups they also date the formation of the richmond gulf graben an aulacogen related to the initial rifting of the trans hudson orogen

the use of magnetic and geo electrical data to delineate the subsurface structures and groundwater potentiality in southeastern sinai egypt the study area is located in the southern part of sinai peninsula this study was done to delineate the subsurface structure of the basement rocks affecting the groundwater potentiality in the study area and to perform the lateral and vertical variations in the subsurface lithologic properties to achieve these a high resolution total intensity magnetic map and geo electrical survey were acquired two dimensional power spectrum analytical signal and euler deconvolution techniques are applied on magnetic data the geo electric data interpretations concluded that the study area can be classified into five units of sediments arranged as 1 the top surficial layer of dry sand and gravels 2 the second layer of silty sand layer with thickness ranging from 5 to 35 m 3 the third layer of dry sand with thickness ranging from 5 to 130 m 4 the fourth layer composed of saturated sand which was considered as the water bearing zone of the investigated interval its thickness ranges between 50m and more than 200 m 5 the fifth layer is interpreted as basement rocks the depth to the basement surface has an average value of 156 m at the eastern side and 758 m at the western side of the study area this area is characterized by a graben structure bounded by major faults striking in the nw se direction and is considered one of the most promising regions for water resources in sinai

apatite light rare earth element chemistry of the port leyden nelsonite adirondack highlands new york implications for the origin of nelsonite in anorthosite suite rocks

a generalized 3 d geological and hydrogeological conceptual model of granite aquifers controlled by single or multiphase weathering summary the weathered layers of crystalline rocks form aquifers that are of prime interest for water supply in hard rock areas these weathering profiles generally develop under both stable geodynamic conditions weathering rate erosion rate and a hydrolysing climate they are composed of thick stratiform layers that follow the paleo landscape paleotopography and thus present a gently dipping sequence at a regional scale the structure and the hydrodynamic properties of the weathering profile of a granitic area 53 km 2 maheshwaram catchment state of andhra pradesh india were characterized in detail and mapped from observations on outcrops 80 vertical electric soundings and lithologs from 45 borewells in which flowmeter measurements and injection tests were also performed to characterize the hydraulic conductivities of the conductive fissure zones the structure of the weathering profile results from a multiphase process an ancient weathering profile was partly eroded down to its fissured layer it was later re weathered more or less parallel to the current topographic surface this peculiar structure is linked to the geodynamic history of the indian peninsula that underwent alternate weathering and erosion dominated phases the profile is thus composed from top to bottom up to a total depth of 35 m of sandy regolith saprolite 1 3 m 10 15 m of laminated saprolite containing unusual preserved fissures and a 15 20 m thick fissured layer by comparing various case studies in similar terrain a generalized 3 d geological and hydrogeological conceptual model of granite type aquifers granites gneisses etc is proposed in granite type rocks single weathering or multiphase weathering and erosion processes induce similar geological structures a few main geological differences arise from the comparison of single phase and multiphase weathering profiles i in the later the respective thicknesses of the various layers can be deeply modified ii the ancient fissured layer can be re weathered and the resulting new laminated layer may contain quite well preserved and conductive ancient fissures and iii the upper part of the fissured layer is more densely fissured as a result of the same weathering processes the fissures from the fissured layer of single phase or multi phase profiles exhibit very similar hydraulic conductivities and show both a higher density of conductive fissures at the top of the layer the preserved ancient fissures within the laminated layer of a multiphase profile are partly obliterated by the recent weathering their hydraulic conductivity is thus significantly reduced nevertheless they do significantly contribute to borewell yield these weathering induced fissures provide most of the aquifer permeability the use of such a conceptual model for the precise geological mapping of the weathering structure appears to be a prerequisite for groundwater development and management in hard rock areas as it answers to several key issues

groundwater flow modeling of quaternary aquifer ras sudr egypt recently ras sudr the delta of wadi sudr area received a great amount of attention due to different development expansion activities directed towards this area although quaternary aquifer is the most prospective aquifer in ras sudr area it has not yet completely evaluated the present work deals with the simulation of the quaternary groundwater system using a three dimensional groundwater flow model modflow code was applied for designing the model of the ras sudr area this is to recognize the groundwater potential as well as exploitation plan of the most prospective aquifer in the area the objectives were to determine the hydraulic parameters of the quaternary aquifer to estimate the recharge amount to the aquifer and to determine the hydrochemistry of groundwater in the aquifer during this work available data has been collected and some field investigation has been carried out groundwater flow model has been simulated using pilot points method seawat has been also applied to simulate the variable density flow and sea water intrusion from the west it can be concluded that 1 the direction of groundwater flow is from the east to the west 2 the aquifer system attains a small range of log transformed hydraulic conductivity it ranges between 3 05 and 3 35 m day 3 groundwater would be exploited by about 6 4 106 m3 year 4 the estimated recharge accounts for 3 106 m3 year 5 an estimated subsurface flow from the east accounts for 2 7 106 m3 year 6 the increase of total dissolved solids tds most likely due to dilution of salts along the movement way of groundwater from recharge area to discharge area in addition to a contribution of sea water intrusion from the west moreover it is worth to note that a part of tds increase might be through up coning from underlying more saline miocene sediments it is recommended that 1 any plan for increasing groundwater abstraction is unaffordable 2 reliable estimates of groundwater abstraction should be done and 3 automatic well control system should be made

determination of sedimentary cover and structural trends in the central sinai area using gravity and magnetic data analysis abstract the present study is an attempt to determine the sedimentary cover and structural trends in the central part of sinai peninsula egypt this study has been implemented by the integration of gravity and magnetic methods gravity data has been used for 2d modelling along some profiles perpendicular to the main structural trends of the study area magnetic data will be analyzed to determine the depth to the basement surface the depths obtained from magnetic data will be used as a control points in the gravity modelling in order to minimize the error and facilitate the iteration of the suggested models the basement relief map from magnetic and gravity output has been produced this map indicates that the basement depths generally increases from south to north and from east to west direction of the study area the sedimentary cover is about 1 5 2 km in the southern part and increases to more than 4 km in the northeastern and western parts and changes gradually in the other parts of the study area results of structural trend analysis indicate that the study area is greatly affected by several structural trends n s e w nw se and nne ssw directions these trends are associated with the baltim fault trend tethyan trend gulf of suez and aqaba trend respectively

delineation of intra crustal horizon in eastern dharwar craton an aeromagnetic evidence abstract a correlative study of two mutually independent geophysical properties like magnetic susceptibility variations and shear wave velocity structure of the crust has been carried out in a part of the eastern dharwar craton of indian peninsular shield analysis of the aeromagnetic anomaly field over an area of 35 000 km 2 comprising the peninsular gneissic basement complex and a part of cuddapah basin has resulted in identification of two distinct magnetic horizons one at a depth of 2 km and the other at a depth of 12 km correlation of these results with the inferences made by the inversion of rayleigh wave phase velocity and other geophysical studies has confirmed the presence of a crustal layer at a depth of 12 km this horizon has been inferred to be the depth to the lower boundary of the upper crust in this region

epeirogenic transgression near a triple junction the oldest latest early middle cambrian marine onlap of cratonic new york and quebec the discovery of a fossiliferous interval altona formation new unit under the potsdam formation requires a new geological synthesis of a large part of the northeast laurentian craton potsdam sandstones can no longer be regarded as the oldest sedimentary unit on the middle proterozoic grenville orogen in northern new york and adjacent quebec and ontario the thickest potsdam sections to 750 m in the east ottawa bonnechere aulocogen have been explained by deposition with normal faulting possibly associated with ediacaran rifting c 570 ma that led to formation of the iapetus ocean however sparse trilobite faunas show a terminal early cambrian middle middle cambrian age of the altona and indicate much later marine transgression c 510 ma of the northeast laurentian craton altona deposition was followed by rapid accumulation of lower potsdam ausable member sandstone in the middle late middle cambrian the altona ausable succession is probably conformable the altona is a lower transgressive systems tract unit deposited on the inner shelf sandstone reddish mudstone and carbonates followed by aggradation and the deposition of highstand systems tract current cross bedded in part terrestrial feldspathic ausable sandstone unexpectedly late altona transgression and rapid ausable deposition may reflect renewed subsidence in the ottawa bonnechere aulocogen with coeval terminal early cambrian faulting that formed the anoxic franklin basin on the vermont platform thus the oldest cover units on the northeast new york quebec craton record late stages in a cooling history near an ediacaran triple junction defined by the quebec reentrant and new york promontory and the ottawa bonnechere aulocogen

stability of detrital heavy minerals on the norwegian continental shelf as a function of depth and temperature abstract petrographic analysis of 1931 thin sections from sandstones of pliocene to devonian age on the norwegian continental shelf indicate that the heavy minerals zircon tourmaline rutile apatite and spinel survive to depths exceeding 5000 m and to temperatures of around 200 c without showing signs of intrastratal dissolution on the other hand the maximum depth and temperature of occurrence for amphibole are 841 m and 40 c around 1500 m and 55 c for sphene when 0 5 km of probable uplift is taken into account 2231 m and 92 c for kyanite 2559 m and 95 c for epidote 2810 m and 109 c for staurolite and 4589 m and 175 c for garnet initial signs of garnet dissolution occur at around 2000 m depth and all garnets are partially dissolved at depths greater than 3500 m monazite is present down to 4858 m and 182 c and chloritoid to 3811 m and 149 c it is however uncertain whether this is due to the low number of samples deeper than 4858 m and to the rare occurrence of chloritoid or to intrastratal dissolution the same sequence of heavy mineral stability is found when volume of quartz cement is used as a proxy for time temperature exposure quartz cement is not found in samples containing amphibole or detrital sphene a maximum of a fraction of a percent quartz cement is found in samples containing kyanite up to 1 together with epidote up to 6 with staurolite up to 24 with chloritoid up to 25 with garnet whereas maximum values of 25 35 are present together with zircon tourmaline rutile patite spinel and monazite the sequence of persistence of heavy minerals versus depth found in this study is very similar to results from several previous studies although unstable heavy minerals survive to greater depths in very young and rapidly buried sandstones and there are some differences regarding the stability of sphene and epidote heavy mineral dissolution has created secondary pores and possibly has contributed to precipitation of kaolinite illite quartz and carbonates in the studied sandstones but these reactions are of very limited volumetric importance

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types