reply to the discussion on carbon and oxygen isotope systematic of a paleoproterozoic cap carbonate sequence from the sausar group central india by anupam chattopadhyay 2015 published in palaeogeography palaeoclimatology palaeoecology 433 156 157 abstract the discussion on our paper on paleoproterozoic glaciation arises out of the failure of previous geological mapping in the sausar belt to identify many features which were reported earlier and to examine the outcrops critically for evidence of volcanism and glaciation in central india the details of these are given in this reply

role of fluid mixing and wallrock sulfidation in gold mineralization at the semna mine area central eastern desert of egypt evidence from hydrothermal alteration fluid inclusions and stable isotope data abstract the semna gold deposit is one of several vein type gold occurrences in the central eastern desert of egypt where gold bearing quartz veins are confined to shear zones close to the boundaries of small granitoid stocks the semna gold deposit is related to a series of sub parallel quartz veins along steeply dipping wnw trending shear zones which cut through tectonized metagabbro and granodiorite rocks the orebodies exhibit a complex structure of massive and brecciated quartz consistent with a change of the paleostress field from tensional to simple shear regimes along the pre existing fault segments textural structural and mineralogical evidence including open space structures quartz stockwork and alteration assemblages constrain on vein development during an active fault system the ore mineral assemblage includes pyrite chalcopyrite subordinate arsenopyrite galena sphalerite and gold hydrothermal chlorite carbonate pyrite chalcopyrite and kaolinite are dominant in the altered metaggabro whereas quartz sericite pyrite kaolinite and alunite characterize the granodiorite rocks in the alteration zones mixtures of alunite vuggy silica and disseminated sulfides occupy the interstitial open spaces common at fracture intersections partial recrystallization has rendered the brecciation and open space textures suggesting that the auriferous quartz veins were formed at moderately shallow depths in the transition zone between mesothermal and epithermal veins petrographic and microthermometric studies aided recognition of co 2 rich h 2 o rich and mixed h 2 o co 2 fluid inclusions in the gold bearing quartz veins the h 2 o co 2 inclusions are dominant over the other two types and are characterized by variable vapor liquid ratios these inclusions are interpreted as products of partial mixing of two immiscible carbonic and aqueous fluids the generally light 34 s of pyrite and chalcopyrite may suggest a magmatic source of sulfur spread in the final homogenization temperatures and bulk inclusion densities are likely due to trapping under pressure fluctuation through repeated fracture opening and sealing conditions of gold deposition are estimated on basis of the fluid inclusions and sulfur isotope data as 226 267 c and 350 1100 bar under conditions transitional between mesothermal and epithermal systems the semna gold deposit can be attributed to interplay of protracted volcanic activity dokhan volcanics fluid mixing wallrock sulfidation and a structural setting favoring gold deposition gold was transported as au bisulfide complexes under weak acid conditions concomitant with quartz sericite pyrite alteration and precipitated through a decrease in gold solubility due to fluid cooling mixing with meteoric waters and variations in ph and f o 2

stable δ13c δ18o and strontium isotopes through the paleocene at gebel aweina eastern tethyan region abstract stable 13 c 18 o and strontium 87 sr 86 sr isotopic records have been established through the paleocene section at gebel aweina in the eastern desert egypt the section has been formed in a shelf upper bathyal environment and spans the interval from planktonic foraminiferal zones p1d to p6a or p6b integrated evaluation of isotopic results and scanning electron microscope observations suggest that strontium and whole rock 13 c records reflect primarily original isotopic trends whereas 18 o and foraminiferal 13 c values have been severely affected by diagenesis the whole rock 13 c record exhibits a continuous increase of 4 from the early paleocene to middle late paleocene the increase is followed by a stepwise 13 c decrease of the same magnitude through the late late paleocene and onwards the gross trends of this 13 c record have earlier been registered in many coeval deep sea sections but there are also some significant disparities at aweina for example the paleocene carbon isotopic changes have a higher amplitude in the deep sea the mid to late paleocene 13 c increase has been interpreted to reflect high biological productivity and or changes in the global carbon mass balance the 13 c decrease in the upper part of the aweina section can be identified as the paleocene eocene transitional long term 10 3 kyr negative 13 c shift which may reflect a major reorganisation in global oceanic circulation patterns the well known latest paleocene deep sea benthic foraminiferal extinction event has been found in the upper part of the aweina section and coincides with a distinct and rapid 13 c decrease of 1 5 the benthic extinction event and the associated 13 c anomaly thus represent important stratigraphic markers also in more shallow environments the gebel aweina 13 c record shows considerably lower values compared to the global 13 c record during early and early late paleocene and in the latest paleocene in the early late paleocene foraminiferal zones p3a to the base of p4 the aweina 13 c values increase rapidly by 1 5 and converge with the global record thereafter the two records covary up to the benthic extinction event after which they diverge the convergence between the records may reflect sea level rise and more open water mass exchange between the eastern tethys and the world ocean the similarity of pilot 13 c records from greece and tunisia with the aweina record support this interpretation diagenetic processes however cannot be ruled out and further studies are required to determine the significance of the 13 c depletions in the eastern tethyan sediments the 87 sr 86 sr ratios through the paleocene at gebel aweina are remarkably invariable close to a value of 0 7077 this is the same trend that has been reported in some earlier detailed studies conducted on well preserved calcitic material from the paleocene indicating original sr isotopic signatures at gebel aweina the homogeneity of sr isotopic ratios throughout the paleocene contrasts with the prominent changes observed in the carbon isotope record indicating a decoupling of the mechanisms regulating the mass fluxes of these elements the invariable sr isotopic ratios suggest stable conditions as regards to relative changes in mass fluxes of riverine and or hydrothermal sr during the paleocene

the migif hafafit gneissic complex of the egyptian eastern desert fold interference patterns involving multiply deformed sheath folds abstract the wadi hafafit complex whc is an arcuate belt of orthogneisses migmatites and other high grade metamorphic rocks which marks the boundary between the central eastern and the south eastern deserts of egypt in the whc gneissic meta gabbro outlines macroscopic fold interference patterns characterized by elliptical to irregular culminations cored by gneissic meta tonalite to meta trondhjemite the five main culminations of the whc have previously been labeled a most northerly b c d and e most southerly a detailed structural investigation of b c d and e reveals that these structures are a result of the interference of four macroscopic fold phases the first three of which may represent a single deformation event the first folding involved sheath like fold nappes which were transported to the n or nw assisted by translation on gently dipping mylonite zones the regional gneissosity and mineral extension lineations formed during this folding event the fold nappes were deformed by mainly open upright small macroscopic and mesocopic folds with approximately ne trending hinges as a probable continuation of the latter folding the sheaths were buckled into large macroscopic folds and monoclines with the same ne trends the fourth macroscopic folding resulted from shortening along the ne sw direction producing mainly nw se trending upright gently plunging folds gravitative uplift is disputed as a component of the deformation history of the whc the peculiarities of the fold interference pattern result from the interesting behaviour of sheath folds during their refolding

gneiss cored interference dome associated with two phases of late pan african thrusting in the central eastern desert egypt abstract structural analysis of the wadi um had area in the central eastern desert ced of egypt reveals the presence of another nw trending elliptical gneissic and migmatitic domal structure west of gabal meatiq outlined by a thick schistose and mylonitized carapace the sheared carapace formed during a nw nnw ward thrusting event which emplaced thrust slices of ophiolitic melange dokhan volcanics and hammamat group sediments over the higher grade gneisses the gneisses are subdivided by retrograde shear zones of this event the sheared carapace is interpreted as the roof thrust of an imbricate stacked antiformal duplex a second thrusting and folding event associated with ne sw shortening deformed the earlier structures producing the dome and re thrusting low grade units against it as sw and ne dipping thrusts the features of this gneiss dome are inconsistent with it being a metamorphic core complex caution must be exercised in the recognition of transcurrent shears in the eastern desert since folded low angle thrust related mylonite zones may be steepened by folding producing steep shear zones with low pitching slip lineations extension bi directional thrusting and najd faulting in the ced may be explained in an escape tectonic deformation regime involving extrusion of material away from the pivotal collision zone in the mozambique belt to the south

palynological palynofacies paleoenvironmental and organic geochemical studies on the upper cretaceous succession of the gptsw 7 well north western desert egypt abstract the present study of the abu roash and bahariya formations in well gptsw 7 refines our understanding of the subsurface cretaceous of the north western desert of egypt our investigations are based on the palynological analyses of 71 cuttings samples of which 24 have also been analyzed for geochemistry in addition to 3 sidewall cores analyzed for vitrinite reflectance r o four palynological zones and three subzones in addition to a poorly fossiliferous interval ranging in age from coniacian santonian to early cenomanian are proposed these include a poorly fossiliferous interval coniacian santonian dinogymnium vozzhennikovae interval zone late to middle turonian ephedripites ambiguus ephedripites multicostatus foveotricolpites giganteus foveotricolpites gigantoreticultus assemblage zone early turonian classopollis brasiliensis interval zone late to middle cenomanian and afropollis jardinus interval zone early cenomanian the succeeding subzones are afropollis kahramanensis interval subzone elaterosporites klaszii interval subzone and cretacaeiporites densimurus interval subzone all of early cenomanian age total organic carbon toc and rock eval pyrolysis and palynofacies analyses indicate that the bahariya formation and the abu roash g member are primarily of kerogen iii type and hence gas prone suggesting a strong influence of hydrogen enriched organic matter the abu roash a c e members may also be gas prone type iii kerogen and appear to contain highly oxidized terrestrial organic matter in contrast the abu roash f member has very high toc and hi values and contains a very high proportion of amorphous organic matter aom indicating a highly oil prone facies while this finding is not unexpected for anoxic black shale it contrasts with earlier studies that suggest a gas prone nature r o measurements show that the bahariya formation represents an immature early genesis dry gas phase this is also true for all investigated samples from the abu roash and bahariya formations based on their low thermal alteration index tai quantitative and qualitative analyses of both the palynoflora and palynofacies show that the abu roash a and c members b is missing both of coniacian santonian age represent oxic proximal and distal shelf environment the abu roash d and e members dated as turonian represent oxic proximal shelf whereas the cenomanian abu roash f member was deposited in a distal suboxic anoxic basin the cenomanian abu roash g member and the bahariya formation were deposited in a shallow marine and shallow marine to fluvio deltaic setting respectively the senonian palmae province is recognized in the palynoflora by the presence of proteacidites auriculiidites reticulatus ariadnaesporites gabonisporis vigourouxii on the other hand the albian cenomanian elaterates province is characterized by the presence of steevesipollenites gnetaceaepollenites elaterocolpites elaterosporites elateroplicites senegalosporites sofrepites afropollis and cretacaeiporites

post collision a type granites of homrit waggat complex egypt petrological and geochemical constraints on its origin abstract the homrit waggat complex hwc is a ring complex which belongs to the younger granite province of the nubian shield it comprises a central biotite granite encircled by an intermediate ring of mylonitized pink granite both of which have been emplaced by cauldron subsidence in a granodiorite body the mylonitized pink granite is locally cut across by hypersolvus coarse grained red granite the mylonitized pink granite is characterized by fully developed mylonitic fabrics and suffered inflation and flattening due to a ballooning effect which suggests that it has experienced stronger ductile deformation than the granodiorite and biotite granite the hw granites are mildly peraluminous highly fractionated and enriched in rb nb y ree except eu and f with corresponding depletion in mg fe ti ca sr and ba ree fractionation patterns and eu eu values decrease from granodiorite la yb n 6 24 6 69 eu eu 0 95 1 56 to biotite granite la yb n 2 48 4 68 eu eu 0 25 0 75 the mylonitized pink and red granites display flat patterns and large negative eu anomalies la yb n 0 33 1 09 eu eu 0 01 0 07 respectively although accessory minerals e g apatite allanite and fluorite exerted some control on ree concentrations volatile transfer largely controls ree abundances particularly hree heavy rare earth element geochemical data indicate that the granites of hwc are post collision a types the less fractionated granodiorite has an i type and volcanic arc geochemical signature least squares analyses of major elements and modelling of rees indicate that the hw a type granites were formed through two stages of differentiation a first stage crystalmelt fractionation was dominated by the removal of plagioclase biotite quartz and apatite from the granodiorite magma to yield the biotite granite further crystal fractionation of the biotite granite liquid with k feldspar as a dominant separating phase in addition to plagioclase biotite and quartz gave rise to the mylonitized pink granite second stage volatile phase transfer occurred during the second stage of fractionation in the magma chamber the red granite represents the last crystallizing granite type from a residual volatile rich fluids which accumulated and emplaced as ring dykes in the solidified part of the mylonitized pink granite

hydrochemical assessment of pond and stream water near abandoned barite mine sites in parts of oban massif and mamfe embayment southeastern nigeria hydrochemical studies were carried out in parts of oban massif and mamfe embayment southeastern nigeria to examine the contributions of barite mining activities on water quality pond and stream water samples were collected from six abandoned barite mines and adjoining streams areas during dry and wet seasons these samples were analysed for physicochemical parameters using standard techniques the results showed that the quality of water samples in the vicinity of barite mine sites was characterized by low ph low mineralization high suspended solids and deep colour sodium na and calcium ca2 are the dominant cations and bicarbonate hco3 and sulphate so4 2 the dominant anions the low concentration of dissolved silica relatively high concentrations of na hco3 and so4 2 suggest a combined influence of silicate carbonate and weathering of mine spoils the total dissolved solids total suspended solids electrical conductivity and major ions except na and k are higher for water draining barite mines from cretaceous sediments while na k ba2 are higher in basement rock areas correlation and factor analyses suggest that the main components of the water samples are related to anthropogenic geogenic mineralization and environmental controls while gibbs diagram plots indicate weathering as the main process controlling the chemistry of water computed values of hardness and some irrigational parameters showed that the pond and stream water samples are generally soft and can be used for irrigation generally the water quality satisfied the who 2008 and nis 2007 standards for domestic agriculture and industrial however there is the need to assess the impact of the pollution on the ecosystem and human health while remediation measures are being considered

discussion on carbon and oxygen isotope systematic of a paleoproterozoic cap carbonate sequence from the sausar group central india by s mohanty a barik s sarangi and a sarkar 2015 published in palaeogeography palaeoclimatology palaeoecology 417 195 209 abstract the recent proposition by mohanty et al 2015 that the lower part of sausar group of rocks in central india has a glacial origin and represents a major paleoproterozoic super glaciation event contradicts some well established geological and geochronological data on these rocks put forward by other workers in recent past the merits of this conclusion are discussed here

the relevance of the sedimentary history of the grand conglomerat formation central africa to the interpretation of the climate during a major cryogenian glacial event the cryogenian grand conglomerat formation 735 ma in age and with considerable thickness variations up to a maximum thickness of about 950 m is an association of interbedded glaciogenic clastic periglacial and non glacial deposits topped by the kakontwe limestone cap carbonate these units occur within the nguba group of the katanga supergroup which was deposited in a rift basin and subsequently deformed as part of the pan african lufilian orogenic belt that separates the congo and kalahari cratons both correlation of regional unconformities and facies distribution suggest that the grand conglomerat sediments were deposited during and after eruption of flood basalts in an asymmetrical rift with a strongly uplifted southern shoulder and a graded shelf defining the northern margin glaciomarine sedimentary rocks along the southern margin of the katangan rift are preserved within fan delta conglomerates supplied from an elevated rift shoulder by contrast the northern margin of the rift was the site of continental glaciation with cross bedded glaciofluvial and marginal marine sandstones and conglomerates associated with massive tills glaciogenic diamictites that pass laterally towards the south into glaciomarine mixtite interlayered with wedges of dolomitic sandstone the kakontwe limestone cap carbonate is present only in the distal parts of the basin its absence in proximal regions is considered to reflect very high rates of sedimentation of fine grained glaciogenic debris derived from deglaciated source areas palaeomagnetic data indicates that the grand conglomerat glaciogenic sediments were deposited close to the equator during the cryogenian this low latitude setting coupled with the absence of a topographical trigger would suggest that glaciation was related to global atmospheric cooling however the presence of water borne glaciogenic on shore sediments and offshore sediments derived from floating glaciers suggests that the ocean during this part of the cryogenian was not completely frozen associations of glaciogenic facies with non glaciogenic sedimentary rocks imply glaciation with interglacial periods and gradual deglaciation instead of severe conditions of permanent sea ice cover and rapid change to the greenhouse environment

carbon and oxygen isotope systematics of a paleoproterozoic cap carbonate sequence from the sausar group central india abstract well preserved sedimentological features of the paleoproterozoic age sausar group of central india indicate glaciogenic origin for the diamictite in the lower part of the unit deglaciation was responsible for a marine transgression and the deposition of proximal glaciomarine facies and a cap carbonate followed by fine clastics with manganese ore analyses of 13 c and 18 o contents in the carbonate unit overlying the diamictite together with sr and ba contents and ree data indicate the preservation of primary geochemical signatures the average 13 c carb content ranges between 3 1 and 0 1 v pdb having peak negative 13 c excursions of up to 7 4 v pdb similar to paleoproterozoic and neoproterozoic cap carbonates elsewhere high sr and ba contents indicate the presence of aragonite and barite precursors similar to well studied neoproterozoic cap carbonates a single continuous carbonate unit shows 13 c excursions from 4 4 to 2 6 v pdb the lithological association and chemostratigraphy are comparable with the carbonate tillite association of the huronian supergroup of canada the snowy pass supergroup of the usa the transvaal supergroup of south africa and the turee creek group of australia

structural framework of deolapar area central india and its implications for proterozoic nappe tectonics abstract a controversial nappe like structure deolapar nappe in the intensely deformed and polymetamorphosed precambrian rocks of the sausar fold belt around the deolapar area of central india has remained the subject of a long standing unresolved debate while some workers interpreted it as the inverted limb of a large scale recumbent fold which has been thrusted onto the adjoining part of the supracrustal sequence sausar group others discounted the very existence of the nappe because of the lack of structural evidence in favour of the recumbent fold thrust structure recent structural study by the present authors around the deolapar area and also in the adjoining parts of the sausar fold belt has looked back into the controversy surrounding the deolapar nappe the study reveals that the deolapar nappe is constituted of an allochthonous block of metasedimentary rocks and crystalline gneiss migmatites placed over the metacalcareous rocks lohangi formation of the sausar group along a low angle thrust plane marked by a sheared fibrolite biotite schist the whole thrust sheet has been folded by later f2 upright folds however careful structural mapping confirmed that there is no evidence of any map scale f1 recumbent fold in the whole area although small scale thrust related reclined f1 folds are occasionally found also there is not enough field evidence suggesting regional inversion of stratigraphic succession so as to indicate the lower limb of a recumbent fold the deolapar nappe can therefore be best interpreted as a thrust nappe details of the existing controversy the new observations and a new tectonic model of the deolapar nappe is presented here

cratonic and foreland early cambrian phosphorites of west africa palaeoceanographical and climatical contexts abstract in western gondwana two types of pan african brasiliano fold belts have been distinguished the first type is characterized by an old long lived tectonic cycle 1000 600 ma and is generally oceanic the closure of these oceans resulted in the aggregation of western gondwana in late neoproterozoic time the second type is characterized by a young short lived cycle about 600 520 ma and is mostly intracontinental fold belts of the second type have various geodynamic significances and represent folded foreland intermontane or impactogen type basins formed during or slightly after the deformational closure of the old long lived cycle phosphorites of west africa are associated with the young short lived tectonic cycle they occur together with the upper member of a distinctive formation known all over west africa this formation is made up of three members and consists from base to top of diamictites generally tillites with detrital intercalations carbonate rocks with barite and bedded cherts with local shale or siltstone intercalations in eastern senegal in the cratonic taoudeni basin the carbonate member is palaeontologically dated as early cambrian deposited during a glacio eustatic transgression it can be considered as a chronostratigraphic marker for the entire west africa phosphorites associated with or immediately following the eustatic transgression are also possibly of early cambrian age they are located either in the lower part of the chert member in the upper part of the carbonate member or sandwiched between these two units in fersiga and namel in the taoudeni basin phosphorites are associated with stromatolites characterizing the initial stage of the transgression they are overlain by evaporites which can be related to an isostatic rebound in the volta foreland basin phosphorites are associated with the chert member there they were deposited on a shelf ramp either on its proximal portion where they are strongly reworked kodjari and arli occurrences or in its distal part where they are interbedded with sediments deposited under anoxic conditions tapoa mekrou and aloub djouana occurrences the depth of marine sedimentation as indicated by the sedimentological characteristics of phosphorites and associated sediments was controlled by the combined effect of glacio eustatic sea level rise subsidence rate and isostatic rebound numerous textural features are similar in the phosphorites from the two basins phosphatic grains occurring as oncolites and stromatolitic fragments together with intraclasts show a noticeable biogenic contribution of microbial origin microbial build ups were formed in submergent emergent environments in the taoudeni basin and in the outer shelf of the volta basin apatites from these basins have similar ree contents which suggest a continental origin for the phosphorus early cambrian phosphorites of west africa were deposited soon after glacially derived sediments according to the available palaeocontinental maps both were laid down at palaeolatitudes of about 40 s west african early cambrian phosphorites thus formed at higher latitudes than their modern analogues which are confined within the inter tropical zone

the kunene complex angola namibia a composite massif type anorthosite complex the c 15000 km2 c 2 ga kunene complex of southern angola and northern namibia is one of the world s largest occurrences of anorthositic rocks rivalled only perhaps by the lac st jean massif of the grenville province in quebec we report here the results of a detailed field and laboratory study of a 100 km2 area in the northern part of the complex coarse grained av 1 2 cm anorthosite and leucotroctolite are the predominant rock types although colour index varies between 0 and 50 averaging about 10 ultramafic rocks are totally absent typical mineralogy is plagioclase an57 76 olivine fo64 71 orthopyroxene en65 74 clinopyroxene fe ti oxides apatite textures are dominantly massive although weak impersistent magmatic lamination with nearvertical dip and unsystematic strike is also present other magmatic features include plagioclase and orthopyroxene megacrysts block structure mortar texture and anorthositic dykes metamorphic effects are minimal or absent all of these attributes are similar to those found in typical massif type anorthosites since comparable features are present over large areas elsewhere in the complex we suggest that kunene should be considered analogous to a large composite massif type anorthositic intrusive complex rather than to a large single or composite mafic layered intrusion such as bushveld as has been previously suggested or assumed this interpretation is supported by satellite imagery which shows the outlines of several individual anorthositic plutons one of which clearly encompasses our field area

the pan african toro complex northern nigeria magmatic interactions and structures in a bimodal intrusion the toro complex is one of the pan african older granites of nigeria first described as a reversely zoned pluton made of a central dioritic mass surrounded by a broad granitic rim it has been thoroughly reinvestigated both from the petrographic and structural points of view with the help of systematic anisotropy of magnetic susceptibility ams measurements the granite main body is a hornblende biotite porphyritic monzogranite characterized by an early submagmatic fabric displaying a concentric pattern of foliations and west plunging lineations stage 1 this fabric is overprinted by a later one due to solid state strain along north south subvertical dextral shear zones stage 2 in the vicinity of the diorite an evengrained granite displays magmatic structures that are contemporaneous with this strike slip event the diorite granite contact is a complex zone where field petrographic and geochemical data enable recognition of the effects of mixing and mingling between a mafic and a felsic magma tonalites cropping out within this contact zone are interpreted as hybrid rocks the reverse zonation of the diorite itself is also the result of some hybridization process magmatic interactions mainly resulted from in situ infiltration of granitic liquid into the dioritic mass the detailed history of this bimodal intrusion began with the emplacement of the granitic magma acquiring a first stage fabric before full crystallization of the granitic core intrusion of the dioritic magma permitted reheating of the granitic magma that then crystallized with specific structural characters the second stage structures whether characterized by magmatic fabric near the diorite or by solid state strain features in north south shear zones elsewhere in the granite are related to late pan african dextral strike slip tectonics in the basement of northern nigeria the bimodal toro complex is therefore considered as a late pan african syntectonic pluton

the cambrian araba formation in northeastern egypt facies and depositional environments abstract the cambrian araba formation exposed in gabal el zeit and in the sinai peninsula unconformably overlies precambrian basement rocks and is in turn overlain unconformably by the ordovician naqus formation the araba formation has been subdivided into three informal lithologic units lower middle and upper from field observations seven sedimentary facies assignable to three facies associations fluvial tidal and coastal to open marine are recognized within the araba formation the lower unit comprises two main facies matrix supported conglomerate facies a in the south gabal araba and wadi feiran and interbeds of granulestone and sandstone facies b in the north gabal dhalal and taba deposited in fluvial conditions the middle unit includes four facies cross bedded sandstone facies c thin laminated sandstone facies d burrowed massive sandstone facies e and rhythmically bedded sandstone mudstone facies f deposited mainly under tidal conditions in the coastal zone the upper unit consists mainly of interbeds of burrowed mudstone siltstone with skolithos probably deposited in open marine environment the sequence records the southward transgression of the tethys ocean over a horst and graben system developed in the late precambrian on the northern margin of the arabo nubian continent

tectonic evolution of the satpura mountain belt a critical evaluation and implication on supercontinent assembly abstract the satpura mountain belt also referred as central indian tectonic zone in recent literature forms an important morphotectonic unit in the central part of india some of the recent workers have reported an orogenic event at 1000 900 ma termed sausar orogeny which led to amalgamation of the north indian block and the south indian block and formation of the satpura mountain belt in this model the stratigraphic relations of two important lithostratigraphic units on either side of the satpura mountain belt the sausar group in the south and the vindhyan supergroup on the north are suggested to be revised from previously held ideas critical analyses of available published work in the region to assess the status of the sausar group vis a vis the vindhyan supergroup was carried out it is found that the ideas proposed by the recent workers stem from an earlier interpretation that the sausar group has monocyclic evolution and the earliest fabric in the sausar group is marked by a schistosity with ew strike re mapping of the gneissic rocks and adjacent matasedimentary rocks of khawasa deolapar and kandri mansar areas revealed presence of gneissic rocks and granulites of two generations and of four phases of superposed deformations in the metasediments and gneisses the older gneisses and granulites constitute the basement over which the rocks of the sausar group were deposited and the younger gneisses developed by metamorphism and migmatisation of the rocks of the sausar group the latter types are found in the khawasa ramakona areas contrary to the belief of the recent workers that no volcanic activity is present in the sausar group volcanic rocks marked by amygdular basic flows and tuffs have been mapped from different parts of the sausar group migmatisation and metamorphism of these volcanic rocks of the sausar group have given rise to amphibolites and granulites in khawasa and ramakona areas therefore the use of fabric patterns in these areas to suggest that the granulite facies metamorphism in the ramakona katangi granulite domain was pre sausar in age is debatable available geochronological data of the satpura mountain belt and its eastward continuation into the chhotanagpur gneiss terrain indicate that the basement and cover rocks of these areas were subjected to multiple deformation and metamorphic episodes of similar style and nature the earliest deformation and metamorphism of the rocks of the sausar group and its equivalent rocks to the east took place at 2100 1900 ma the regional ew trend of the belt developed during the second deformation at 1800 1700 ma and again at 1600 1500 ma this deformation was accompanied by migmatisation and granulite facies metamorphism in the northern domain of the sausar belt and in the chhotanagpur gneiss region late phase low intensity deformations in the region were associated with thermal events at 1100 1000 ma and 900 800 ma the ew trending fabric referred as satpura orogenic trend in indian literature marks a major compressional tectonic event developed during the second deformation of the sausar group this has its counter part in western australia as the capricorn orogeny 1780 1830 ma the development of the satpura mountain belt during the grenvillian orogeny is ruled out from the synthesis of event stratigraphic data of the region and from its comparison with the western australian craton

modeling the baroclinic circulation in the area of the sicily channel the role of stratification and energy diagnostics 1 aspects of the circulation of the sicily channel region are studied with a high resolution primitive equation sigma coordinate model this work is an attempt to study the process governing the purely baroclinic dynamics and its sensitivity to seasonal stratification thus no atmospheric forcing is used two numerical experiments are analyzed using as initial conditions diagnostic velocity fields derived from the winter and summer climatological hydrologies the quasi steady state is characterized by circulation patterns in the depth range of the modified atlantic water maw and the levantine intermediate water liw strongly controlled by mesoscale eddies and topography seasonal difference is found in the surface current which exhibits the major variability on the african side downstream of adventure bank and the ionian slope where the absolute maximum occurs the intermediate circulation instead does not show relevant seasonal differences liw enters through the two passages south of malta plateau and preferentially flows along the sicilian shelf edge exiting over the northern sill its pathway is strongly controlled by subsurface cyclonic and anticyclonic cells the results are in good agreement with observations an energy diagnostics is applied to model results and sheds important light on dynamical characteristics of the mesoscale eddy field and indicates seasonal differences in the energetic exchange with the mean flow the analysis of the mean mke and eddy eke kinetic energy the transfer terms between energy compartments and the eddy momentum flux divergence indicates how eddies are strongly energetic in summer and exchange energy more efficiently with the mean flow in the quasi steady state maw volume transport and mke and eke fluctuations are strongly correlated this result suggests that mesoscale motions can control up to 40 of volume transport variability