facies and architectural element analysis of a meandering fluvial succession the permian warchha sandstone salt range pakistan abstract the 30 to 155 m thick early permian artinskian warchha sandstone of the salt range pakistan is a conglomerate sandstone and claystone succession within which seven lithofacies types gt st sp sr sh fl and fm occur in a predictable order as repeated fining upward cycles common sedimentary structures in the conglomerates and sandstones include planar and trough cross bedding planar lamination soft sediment deformed bedding compound cosets of strata with low angle inclined bounding surfaces and lags of imbricated pebbles structures in the finer grained facies include desiccation cracks raindrop imprints caliche nodules and bioturbation groups of associated facies are arranged into nine distinct architectural elements channels gravel bars sandy bedforms downstream and laterally accreting barforms sand sheets crevasse splays levees floodplain units and shallow lakes which is consistent with a fluvial origin for the succession the types of architectural elements present and their relationship to each other demonstrate that the warchha sandstone preserves a record of a meandering river system that drained the northern margin of gondwanaland the dominance of fine grained floodplain facies over gravel grade channel base facies and the widespread occurrence of large scale lateral accretion elements supports the interpretation of a high sinuosity meandering fluvial system in which channel bodies accumulated via the lateral accretion of point bars but in which the active channels covered only a small part of a broad floodplain at any time instant although the regional and temporal distribution of these deposits is complex in broad terms the lower part is dominated by stacked multistorey channel bodies whereas single storey channel elements isolated in abundant fine grained floodplain deposits dominate the middle and upper parts of the formation

zircon xenocrysts from the kambalda volcanics age constraints and direct evidence for older continental crust below the kambalda norseman greenstones abstract the hangingwall basalt at kambalda western australia contains zircons that have been shown by ion microprobe analyses to have very high u and th contents and a wide variety of crystallization ages nearly all of these zircons certainly are xenocrysts a few might relate to intrusive veinlets the age of the youngest xenocrysts 2693 50ma 2 shows that the eruptive age of the basalt cannot exceed 2743 ma this confirms that the apparent sm nd isochron giving 3200 ma 1 2 for kambalda mafic and ultramafic rocks is a mixing line 2 between unrelated components enriched and depleted in light rare earth elements mixing probably occurred at depth by erosion of 3200 3500 ma old felsic crust from the walls of the hwb conduits the zircon xenocryst ages are the first direct evidence for the presence of very old felsic crust in the eastern yilgarn block the latter implies that the kalgoorlie norseman greenstone sequences were formed in a continental rather than an oceanic environment

late palaeozoic gondwana glaciation in oman late carboniferous early permian sediments belonging to the haushi group in oman have been considered to be partly of glacial origin1 3 however conclusive evidence of a continental glaciation has been lacking and the extension of the late palaeozoic gondwana glaciation into the arabian peninsula has not been generally accepted4 during recent visits to outcrops of the haushi group in the al khlata area of the huqf massif fig 1 we have found good exposures of striated pavements of precambrian dolomite which are directly overlain by diamictites of the haushi group fig 2 this occurrence forms the strongest evidence so far for the presence of a continental glaciation in oman during the late palaeozoic

structural setting and geochemistry of archaean i type granites in the bardoc coolgardie area of the norseman wiluna belt western australia abstract regional structures in the bardoc coolgardie area of the archaean norseman wiluna greenstone belt in western australia developed during early large scale thrusting followed by a transpressional regime characterized by enewsw shortening and large scale sinistral strike slip faults structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history emplacement mechanisms include solid or liquid state diapirism forceful dilation of country rocks and passive stoping i type granites are common and include early and late tectonic intrusions the widespread occurrence of i type granodiorite and monzogranite probably derived by partial melting of lower continental crust or subducted oceanic crust suggests a continental margin setting for the belt alkalic quartz diorite occurs as rounded enclaves in granodiorite and is enriched in ba rb sr ce la p and f which suggests a mantle derived volatile component these quartz diorite melts may have formed by partial melting of metasomatized mantle or alternatively mantle degassing may have lowered solidus temperatures in the source region and thus induced melting emplacement of hot volatilerich quartz diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite recent models for archaean gold mineralization suggest that auriferous fluids contained co 2 derived from lower crustal or mantle sources in the bardoc coolgardie area co 2 may have been flushed out during partial melting of the lower continental crust however the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late stage event and took place over a considerably shorter time interval than the formation and emplacement of i type granites

an early thrust duplex in the kalgoorlie kambalda greenstone belt eastern goldfields province western australia abstract extensive regional mapping of the stratigraphic sequence throughout the kalgoorlie kambalda greenstone belt in western australia has outlined the geometry of early subhorizontal thrust faults these thrusts stacked and repeated the stratigraphy to form a major thrust duplex south of kambalda the roof thrust to the duplex becomes a major thrust flat to the north at kalgoorlie later transpressional deformation f2 upright folds d3 sinistral shear zones and folding has rotated and displaced the d1 thrusts both sub horizontal deformation and subsequent transpression indicate that compressional tectonics rather than vertical tectonics involving solid state granitoid diapirs were crucial in the development of this granite greenstone terrain

late archean convergent margin tectonics and gold mineralization a new look at the norseman wiluna belt western australia on a world scale the most important hydrothermal gold deposits occur either in late archean ca 2700 ma greenstone belts or at late paleozoic to quaternary convergent plate boundaries in the latter environments epithermal and porphyry hosted deposits form during subduction related magmatism in volcanic arcs and deep level meso thermal deposits form during deformation in continental margin orogenic belts the mesothermal deposits are similar to archean gold deposits in greenstone belts such as the norseman wiluna belt in western australia we here suggest that this similarity exists because the norseman wiluna belt is an orogenic belt with a tectonic history similar to that of younger mineralized convergent margins such as the north american cordillera it is most likely that the norseman wiluna belt resulted from the interaction of lithospheric plates during the major period of continental growth and stabilization that occurred in the late archean the distribution of gold mineralization being controlled by convergent margin tectonics

tethyan oceanic currents and climate gradients 300 m y ago we reconstruct the oceanic circulation pattern of the tethys ocean 300 m y ago by placing late carboniferous early permian climate sensitive biotic associations from gondwana and laurasia on a pangea paleogeography constrained by selected paleomagnetic data warm climate fossils and facies from iran located at that time along the gondwanan margin of arabia are compatible with the existence in the tethys ocean of a warm subtropical surface current gyre whereas cold surface currents swept the glaciated gondwanan margin at higher southern latitudes redistributing cold biota toward the tropics this tethyan surface current system and the associated narrow zonal barrier show similarities to recent glacial climate patterns when placed on a large scale paleogeographic reconstruction of pangea of the b type it neatly explains the otherwise problematic observation that the carboniferous permian biota of iran and northern arabia is dominated by warm euramerican and or russian taxa that are strikingly different from typical cold gondwanan associations

gneiss domes and extensional deformation in the highly mineralised archaean eastern goldfields province western australia abstract the recognition of large areas of gneiss within granitic complexes of the northeastern part of the eastern goldfields province of western australia based on analysis of regional aeromagnetic data has resulted in a re evaluation of the structural data for that region five magnetic domains have been established in the granitic complexes which are marginal to the main greenstone belts at least two of these domains have a distinctive domal form and also have internal domeshaped regions the ballard and laverton domains have extensive areas of layered gneissic and migmatitic rocks which flank the internal domes boundary relationships at the laverton and ballard domains show that the domes are concordant sheets and the metamorphic conditions of the boundary rocks imply that the sheets were intruded at a middle crustal level strain conditions in the boundary zones indicate that emplacement of the gneiss domains to the crustal level of the surrounding lower grade greenstones was initially along relatively gently dipping shear zones which were active during uplift structural relationships around both the domal granitic complexes and the later granite batholiths however show that regional shortening deformation events were not caused directly by the emplacement of any of the granitic rocks the tectonic hypothesis presented for the eastern goldfields is similar to that proposed for the formation of cordilleran metamorphic core complexes the uplift event responsible for the crustal extension required to allow the emplacement of the gneiss may have been driven by the same thermal input responsible for the generation of the voluminous granites intrusive into both the gneiss complexes and the surrounding greenstone belts

structural geology across a proposed archaean terrane boundary in the eastern yilgarn craton western australia abstract the eastern goldfields province of the archaean yilgarn craton western australia can be divided into several nw se trending terranes with different stratigraphic signature at least two main phases of penetrative ductile deformation affect the terranes d1 is a phase of nappe type transport mainly to the north along gently dipping ductile shear zones it is interpreted as a phase of regional extension contemporaneous with intrusion of massive granitoid plutons and possibly contemporaneous with deposition of felsic volcanics and metasediments in the greenstone belts terrane boundaries were probably formed during d1 d2 gave rise to steep nw se to n s trending foliations and upright folds d2 is strongly partitioned over the area for strain and vorticity the pattern of partitioning seems to be dependent on the position of granitoid plutons which give rise to development of d2 strain shadows d1 structures have been preserved mainly in these strain shadows terrane boundaries are transected by boundaries of d2 structural domains minor intrusion of granitoids continued during and after d2 d1 is possibly associated with arrival of a mantle plume below the yilgarn craton and d2 may be a phase of regional shortening in a thinned lithosphere weakened by the thermal event

investigating the record of permian climate change from argillaceous sedimentary rocks oman a standard method for the analysis of carbon isotope composition of bulk organic matter 13 c bulk in palaeoenvironmental and stratigraphic studies of sedimentary basins associated with hydrocarbons is suggested this method includes the removal of interstitial hydrocarbon within the sediments which is shown to have a negative effect on 13 c using the method a 13 c bulk trend c 21 to 24 was found within the lower permian al khlata and lower gharif formations of thuleilat 16 and 42 well sections south oman palaeontological and sedimentological evidence indicates considerable palaeoenvironmental change from a cold climate lowland fern flora and upland primitive conifer flora low in the sequence to a lowland cycad like and upland glossopterid or other gymnospermous flora higher in the sequence the lithologies range from glacial diamictite at the base to calcrete horizons and redbeds at the top it is therefore likely that the 13 c bulk trend is related to palaeoenvironmental change

gondwanan deglaciation and opening of neotethys the al khlata and saiwan formations of interior oman abstract new stratigraphic petrographic and paleontological data from the lower permian of southeastern arabia help to elucidate the still debated timing of neotethys rifting and the climatic evolution following the gondwanan glaciation the transition from the al khlata to the saiwan formation here described in detail is interpreted to record continental break up and onset of neotethyan spreading between northern gondwana and the cimmerian terranes at mid sakmarian times as constrained by brachiopod assemblages the eastern oman arm of the neotethyan rift system instead failed and sea floor spreading of the indo madagascar trough was delayed until final fragmentation of gondwana in the late jurassic petrographic composition of lower permian sandstones documents a distinct change from transitional to dissected rift shoulder provenance and widespread exposure of granitoid basement rocks at a late syn rift to early post rift stage very abundant pore filling celestite at the al khlata saiwan transition may have precipitated from circulating brines related to remobilization of proterozoic salt due to rift tectonics the sharp base of the saiwan formation records a major transgression related to the onset of neotethyan spreading final deglaciation and consequent global sea level rise as indicated by ravinement surfaces associated with lag deposits with tree trunks reworked ferruginous pedogenic concretions and phosphate and by paleoecological analyses the basal bed of the saiwan formation is characterized by the pioneer pachycyrtella paleocommunity with pachycyrtella omanensis 85 suspension feeding rapid rates of reproduction and growth r strategy early maturity high mortality rates in the juveniles the more mature secondary ecological succession developed higher in the saiwan formation records maximum flooding and significant climatic amelioration the saiwan formation at the beginning of the late sakmarian finally sutures the irregular rift related topography in the rim basin of interior oman and records a shift towards warmer temperate conditions after the end of the gondwanan glaciation

deciphering the tectonic evolution of archaean greenstone belts the importance of contrasting histories to the distribution of mineralization in the yilgarn craton western australia abstract the distribution of archaean metallic mineral deposits reflects tectonic controls operating during the evolution of granitoid greenstone terranes tectonic analysis of these terranes not only allows recognition of parameters that may be important in interpreting the tectonic histories of greenstone belts but also the resultant tectonic control on mineral deposit distribution in the yilgarn craton of western australia the late archaean 2 7 ga norseman wiluna belt is most intensely mineralized with both komatiite associated ni cu deposits and epigenetic gold deposits this belt is dominated by 2 7 ga supracrustal successions and its tectonic history is that of an orogenic belt at an obliquely convergent craton or proto craton margin tectonostratigraphic associations preserved resemble younger volcanic arc and back arc basin crust and many represent the remains of a volcanic arc and back arc basin complex developed in response to westward dipping subduction these sequences were deformed metamorphosed and intruded by granitoids relatively soon 30 ma after the major period of volcanism with gold mineralization occurring late in the orogenic event possibly during uplift in contrast greenstone belts in the murchison and southern cross provinces are dominated by older supra crustal successions that contain 2 9 ga volcanosedimentary associations characterized by extensive oxide facies banded iron formations bifs bifs appear to have been deposited in shelf or platform environments in intra oceanic or passive craton margin settings komatiite associated ni cu mineralization and volcanogenic cu zn mineralization are locally hosted by favourable tectonostratigraphic associations the main period of deformation metamorphism and gold mineralization in these provinces was broadly synchronous with that in the norseman wiluna belt as was regional granitoid emplacement during this event strain was probably transmitted from the eastern margin of the craton via a yilgarn wide system of shear zones faults and fold belts gold mineralization is developed best in greenstone belts such as the meekathara mt magnet belt that contain large scale fault systems and internal granitoids similar tectonic controls on the distribution of mineral deposits can also be recognized in other archaean cratons and the heterogeneous distribution of archaean mineral deposits probably reflects a range of tectonic settings as well as different stages in the evolution of individual cratons

warm water carbonates in proximity to gondwanan ice sheets a record from the upper paleozoic of iran abstract sedimentologic and paleontologic proxies recovered from the alborz basin the sanandaj sirjan zone and additional iranian peri gondwanan continental blocks near the arabian margin of northeastern gondwana record the formation of warm water shallow marine carbonates throughout the late pennsylvanian earliest permian this reflects a prevailing favorable climatic and environmental regime that contrasts with the cold conditions of slightly more southerly gondwanan regions that experienced profound glaciations the sedimentologic and paleobiologic properties of these iranian carbonates also differ greatly from coeval cool water carbonates of bolivia that developed at equivalent paleolatitudes along the northwestern margin of gondwana the complex climatic patterns reflected in the dispersal of marine taxa and their colonization of ecosystems relatively remote to their customary habitats and climate zones are interpreted to record the influence of ocean circulation based on these sedimentologic and paleobiologic data we utilized a climate model community climate system model version 3 ccsm3 to help resolve the mechanisms responsible for enabling transport of warm water to higher latitudes in northeastern gondwana these simulations reveal that spatial variations in sea surface temperatures exerted a strong forcing on paleo tethyan oceanic circulation and thereby governed the distribution diversity and abundance of taxa in late paleozoic marine ecosystems based on this outcome we conclude that the climatic contrasts registered across upper pennsylvanian lower permian carbonate platforms of the paleo tethys and panthalassic ocean originated through oceanic circulation driven by geographic differences in sea surface temperature

palynology and detrital zircon geochronology of the carboniferous fenestella shale formation of the tethyan realm in kashmir himalaya implications for global correlation and floristic evolution abstract first palynological data supplemented by detrital zircon u pb ages from the fenestella shale formation near the gund village in the banihal area of jammu and kashmir state india provide new insights into the floristic evolution of gondwana during the late palaeozoic especially in india from where the carboniferous permian macro and microfloral records are impoverished we also present a first approach to the palynological correlation of the carboniferous permian palynoassemblages described from the various gondwana countries the palynomorphs from the fenestella shale formation are fairly well preserved and diversified and include 11 genera and 18 species while the trilete spores and striate bisaccate pollen grains are scarce monosaccate pollen taxa mainly parasaccites plicatipollenites and potonieisporites are dominant the assemblage is most similar to the parasaccites korbaensis palynozone of the lower gondwana basins of the indian peninsula and the stage 2 palynozone of the late carboniferous of east australia besides it is comparable with the known carboniferous assemblages of pakistan yemen and south america carboniferous early permian assemblages of south africa and permian assemblages of antarctica the sediment source of the siliciclastic shelf and delta deposits intercalated in the fenestella shale formation is a hinterland in which precambrian rocks dominantly were exposed and the th u ratios of detrital zircons suggest that most rocks exposed on the erosion level in the hinterland had a felsic composition the youngest u pb zircon age of the investigated fossiliferous strata is 329 16 ma late visean to early serpukhovian providing a maximum age of deposition of the studied succession based on the affinities of the palynofloral assemblage and earlier palaeontological records a warm temperate and arid climate has been inferred for the fenestella shale formation

dynamothermal transition zone between archaean greenstone and granitoid gneiss at lake dundas western australia abstract a 500 m wide shear zone occurs between the base of an archaean greenstone sequence and adjacent granitoid gneiss complex on the shores of lake dundas western australia the dynamothermal margin remains distinguishable due to the preservation of upper amphibolite facies assemblages related granitoid anatectites and mylonitic schistose and gneissose fabrics developed parallel to the contact which itself lies subparallel to the greenstone bedding surface the margin contrasts with less deformed greenschist to low amphibolite facies assemblages which characterize lithologies within the greenstone belt many of which retain igneous textures and relict primary phases structural petrological and textural evidence indicates that the dynamothermal contact originally evolved as a subhorizontal ductile shear zone during juxtaposition of the greenstone pile with granitoid gneiss and that its formation preceded regional folding greenschist facies overprinting and granitoid intrusion which occurred at about 2700 ma the amount of heat generated within the transition zone during thrusting was limited to maximum temperatures of c 650 c due to the buffering effect of granitoid anatexis

sedimentologic and paleoclimatic reconstructions of carbonate factory evolution in the alborz basin northern iran indicate a global response to early carboniferous tournaisian glaciations the lower carboniferous mobarak formation records the development of a storm sensitive pervasive carbonate factory on the southern paleo tethyan passive margin following the opening of the paleo tethys ocean into the alborz basin along the northern margin of gondwana its depositional facies encompass inner ramp peritidal environments peloidal to crinoidal shoals storm to fair weather influenced mid ramps proximal to distal shell beds and low energy outer ramps sedimentological analyses and foraminiferal biostratigraphy reveal four events affecting carbonate platform evolution in the alborz basin during the lower carboniferous 1 a transgression following global temperature rise in the early tournaisian middle hastarian caused the formation of thick bedded argillaceous limestones this interval correlates with early tournaisian nodular to argillaceous limestones in the moravia basin lisen formation czech republic the dinant basin pont d arcole formation belgium and at the rhenish slate mountains lower alum shale germany 2 late hastarian early ivorian glaciations previously identified in southern gondwana but had not yet recognized in northern gondwana were recorded through a sequence boundary 3 during the late tournaisian early visean a differential block faulting regime along the basin s margin caused uplift of the westernmost parts of the alborz basin and resulted in subsidence in the eastern part of the central basin this tectonically controlled shift in depositional regime caused vast sub aerial exposure and brecciation preserved in the top of the mobarak formation in the western portion of the central alborz basin 4 tectonic activity coinciding with a progressive multiphase sea level drop caused indirectly by the visean and serpukhovian glaciations phases ultimately led to the stagnation of the carbonate factory paleothermometry proxies the presence of foraminiferal taxa with a northern paleo tethyan affinity and evidence for arid conditions in the terrestrial hinterland place the alborz basin at lower latitudes than the approximately 45 50 southern paleolatitude reported thus far

character and regional implications of the sheared archaean granite greenstone contact near leonora western australia abstract the boundary between greenstone belt rocks and deformed domal bodies of granite and gneissic granite in the area west and northwest of leonora is marked by a wide zone of high strain within which the dominant fabric elements are parallel to the boundary the high strain zone is arcuate the granitic body is domal in form consistent sense of shear movement indicators show that the greenstones moved down relative to the granite rocks from a continuous core of 1 6 km drilled 4 km southeast of leonora exhibit mesoscale recumbent folding and ductile faulting the upper 900 m of core is characterised by recumbent flexural slip folds with half wavelengths up to 660 m separated by discrete shear zones below about 1200 m rock type and structural character change at this depth greenschistfacies rocks are juxtaposed against amphibolite facies rocks across a major ductile shear thermodynamic data give estimates of 370 c 2 1 kbar for greenschist and 610 c 5 6 kbar for amphibolite facies with high fluid pressures dominated by water in low grade rocks and co 2 in high grade ones several kilometres of section have therefore been lost across this zone the amphibolite hosts broad and narrow shear zones within which movement sense is consistently normal the structural and metamorphic data suggest that emplacement of the domal granitic and gneissic rocks was temporally linked with normal ductile shearing the regional structural setting and juxtaposition of high and low grade rocks across the shear zone with abrupt changes in temperature and fluid composition suggests that the domes were emplaced as uprising hot deep seated rock in a regional extensional tectonic environment comparable to the tectonic setting of metamorphic core complexes

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

permian palynostratigraphy a global overview permian palynostratigraphic schemes are used primarily to correlate coal and hydrocarbon bearing rocks within basins and between basins sometimes at high levels of biostratigraphic resolution up to now their main shortcoming has been the lack of correlation with schemes outside the basins coalfields and hydrocarbon fields that they serve and chiefly a lack of correlation with the international permian scale this is partly because of phytogeographical provinciality from the guadalupian onwards making correlation between regional palynostratigraphic schemes difficult however local high resolution palynostratigraphic schemes for regions are now being linked either by assemblage level quantitative taxonomic comparison or by the use of single well characterized palynological taxa that occur across permian phytogeographical provinces such taxa include scutasporites spp vittatina spp weylandites spp lueckisporites virkkiae otynisporites eotriassicus and converrucosisporites confluens these palynological correlations are being facilitated and supplemented with radiometric magnetostratigraphic independent faunal and strontium isotopic dating

a review of the palynostratigraphy of gondwana sediments from the godavari graben india global comparison and correlation of the permian triassic palynoflora abstract the continental sequences of gondwana deposits from the chintalapudi sub basin of the godavari graben south india have been palynologically investigated to explore the permian triassic palynoflora total 11 distinct palynoassemblages belonging to the asselian sakmarian i ii artinskian iii iv guadalupian v vi lopingian vii viii ix induan x and olenekian xi age have been documented the palynological studies support the existence of the two coal bearing horizons in the chintalapudi sub basin one in the karharbari and barakar formations sakmarian artinskian while other in the raniganj formation guadalupian lopingian the lack of the upper barakar and barren measures roadian palynoflora indicates apparent discordance in stratigraphic sequence in this sub basin presently studied the permian triassic palynofloral transition has been found akin to the palynoflora of the salt range madagascar antarctica australia and south africa the palynofloral correlation supports the presence of guttulapollenites palaeophytogeographic province in the gondwana during the guadalupian lopingian the guttulapollenites palaeophytogeographic province co exists with the glossopteris megafloral province and extends from the salt range in the north to amery basin in the south mid zambesi luangwa basin in the west to satpura wardha godavari basin in the east

palynology and correlation of carboniferous permian glacigene rocks in oman yemen and pakistan palynological assemblages from sections in yemen and pakistan are similar enough to allow the application of biozones based on the pennsylvanian glacigene sediments of interior oman thirty four samples from the upper 84 m of a 125 m thick section of the tobra formation at zaluch nala western salt range pakistan yielded palynomorph taxa including microbaculispora tentula abundant monosaccate pollen including cannanoropollis janakii and plicatipollenites malabarensis converrucosisporites grandegranulatus horriditriletes ramosus and horriditriletes tereteangulatus indicating the late pennsylvanian oman 2165b biozone eleven samples from the yemen kuhlan formation and 22 samples from the underlying akbarah formation from approximately 300 m of a section near kuhlan in northwest yemen suggest a 2165a biozone age also late pennsylvanian this correlation indicates the widespread nature of glacial sediments of a narrow biostratigraphic late pennsylvanian age range the oman p5 unit in basins across part of the north gondwana margin new data from three samples from the tobra formation at the choa road section near khewra in the eastern salt range pakistan are assignable to the earliest permian 2141b biozone indicating a possible correlation between the tobra shale and the rahab shale member of oman which is considered to mark the final deglaciation sequence in oman

evidence for structural repetition in the greenstones of the kalgoorlie district western australia abstract regional mapping and air photographic interpretation of an area of about 20 000 km 2 centred on kalgoorlie provided compelling evidence that some previously published polycyclic stratigraphies cannot be substantiated large areas of rocks formerly proposed as younger cycles represent repetition mainly by faulting of a somewhat simpler stratigraphic sequence the main lines of support are 1 the similarity of older and younger mafic ultramafic successions 2 the tendency of younger sequences to merge with older ones when traced along strike and 3 the abundant evidence of faulting along critical contacts the subtle concordant nature of some of the faulting is consistent with an origin by thrusting at an early stage in the tectonic history especially where repeat sequences are folded around major upright structures later reactivation of sheared contacts and initiation of new ones during upright folding and faulting and transcurrent shearing is believed to have widely occurred gravitational gliding is proposed as a possible mechanism for thrust generation this being consistent with evidence of earlier instability in the sedimentation style of turbidites debris flows and olistostromes however conclusive evidence of a mechanism is lacking due to incomplete field evidence the repetition is viewed as a rearrangement of recognisable elements of the local stratigraphy rather than the result of a major collisional event at a plate margin this tends to favour an intracratonic rather than an oceanic setting for the local greenstones though the characteristic geological features of modern continental rifts have not been observed

age and origin of granitic rocks in the kalgoorlie norseman region of western australia implications for the origin of archaean crust three granites from the norseman area at stennet rocks buldania rocks and east of lake johnston have u pb zircon ages of 2691 8 95 c l 2689 22 and 2661 8 ma respectively one stennet rocks contains 3100 3200 ma cores providing support for oversby s 1975 argument that all three plutons were derived by anatexis of much older basement common leads within the zircons show evidence of having been derived from within the rock and represent mixtures of initial rock leads and radiogenic leads the unusually 208pb rich compositions of the common leads suggest the breakdown of a th rich phase perhaps uranothorite as a major contributor to the radiogenic component available zircon geochemical and isotopic data are used to develop a two stage model for archaean crustal development in this region with formation of primitive crust of broadly andesitic composition from depleted mantle or basalt beginning at 3400 ma followed by extensive thermal reworking and possibly continued growth over the period 3000 3300 ma in the second stage at 2700 ma anatexis resulted in large scale intra crustal differentiation giving a thick upper granitic layer and a lower crust residual from anatexis it is this second major thermal event that is recorded by most geochronometers implicit in the andesitic crustal growth model is that because the sm nd and rb sr ratios of newly formed archaean crust are close to mantle values this process is transparent to the sm nd and rb sr isotope systems until recycling of incompatible element rich sediment becomes important following the late archaean production of a wide spread differentiated upper crust

upper paleozoic glacigenic deposits of gondwana stratigraphy and paleoenvironmental significance of a tillite succession in northern victoria land antarctica abstract late paleozoic glacial deposits are widespread in gondwana in antarctica the best outcrops occur in the central transantarctic mountains ellsworth mountains pensacola mountains and in southern victoria land whereas they are rare and very scattered in northern victoria land which represents a linkage sector with tasmania and eastern australia the aim of the present research is to define the stratigraphic setting and the environmental interpretation of a poorly studied lower permian glacigenic succession located near orr glacier in the lanterman range in northern victoria land it has great importance because it represents the only significant glacigenic succession for this wide area marking and defining time and modality of a glacial postglacial transition during the early permian a critical time interval in the paleoenvironmental evolution of southern gondwana this succession named here as the lanterman formation lies directly on to crystalline basement and is overlain by a thick permian fluvial succession takrouna formation the results provided by sedimentological facies analysis and palynological analysis integrated with a limited petrographic characterization show a correlation framework between two isolated successions outlining their stratigraphic architecture and subdivided into a lower glacial portion and an upper postglacial portion the former asselian in age is dominated by diamictite sandstone mudstone with lonestones and carbonate deposits suggesting repeated advance and retreat of a terrestrial glacier with facies associations indicating environmental changes from subglacial to glaciofluvial to glaciolacustrine the latter is dominated by lacustrine mudstone with decreasing lonestones upward thin bedded sandstone conglomerate and a thick fluvial sandstone and pebbly sandstone succession at the top signalling the transition to a fluvial system through time the overall dataset suggests that the late paleozoic glacigenic deposits of northern victoria land record the evolution from a setting characterized by a terrestrial small ice cap that underwent repeated advances and retreats due to climate cycles in a lacustrine setting into a postglacial paleoenvironmental scenario with a wide fluvial system draining northwards from victoria land towards the tasmanian basin the results contribute to increasing knowledge of the timing and modalities of the late paleozoic ice age in gondwana particularly for polar regions such as antarctica

oil bearing sediments of gondwana glaciation in oman more than 3 5 billion bbl of oil in place have so far been discovered in reservoirs of the al khlata formation of the permian carboniferous lower haushi group in south oman glacially striated pavements and boulders in exposures at al khlata in east central oman confirmed previous interpretations that the formation is at least partly of glacial origin core and wireline log data from some 500 wells that penetrate the formation show that glacial facies are widespread in the subsurface shales with varvelike laminations and dropstones are present in two main layers which extend over the larger part of south oman and are perhaps the most diagnostic facies diamictites are also widespread and some which can be correlated as sheets over thousands of square kilometers are interpreted as true tillites other diamictites are interbedded with shales with varvelike laminations or unbedded siltstones and are interpreted as subaqueous glacial deposits ten sedimentary facies have been described in cores and outcrops an important result of this study is a formal scheme to interpret these facies from wireline logs using quantitative analysis of density and neutron logs and qualitative information from other logs lateral facies relationships are complicated by syndepositional salt withdrawal and dissolution paleorelief on the basal unconformity and intraformational unconformities beneath regionally extensive tillites at least three glacial phases can be recognized an early phase represented only by erosional remnants of diamictites and two later phases the last of which extended over the whole of oman south of the oman mountains deglaciation is represented by a regional shale bed sharply overlying the diamictite sheet of this last glaciation oil occurrence can be related to three northwest southeast striking facies belts 1 in the south oman salt basin deposits consist of sands pebbly sands and diamictites deposited in glaciofluvial environments this sequence lacks good seals 2 in the downdip part of the basin s eastern flank interbedded sands silts shales with varvelike laminations and diamictites represent glaciolacustrine deposition at ice margins and in meltwater deltas this belt contains interbedded reservoirs and seals and includes the largest number of oil accumulations 3 updip in the eastern flank area several hundred meter thick siltstones and claystones with thin turbiditic sandstones represent a belt of persistent glaciolacustrine deposition probably in the axis of a salt dissolution synclin this belt contains few oil accumulations

crustal structure of the mid atlantic ridge south of the kane fracture zone from seafloor and sea surface gravity data seafloor and sea surface gravity data are inverted together to construct a model for the near axis crustal structure of a slow spreading ridge the seafloor data set offers two main advantages it allows us to recover shorter wavelengths signal and to constrain the value of a potential field at two different levels the model we propose here would not have been derived from sea surface data alone it is based on a dense sea surface gravity coverage and on 121 sea bottom gravity measurements collected in the mid atlantic ridge at kane mark area during the hydrosnake 1988 and gravinaute 1993 cruises the primary goal of the seafloor surveys was to test for the presence of a magma reservoir beneath the axial neovolcanic ridge first a forward two dimensional 2 d model of the crustal structure across the axis is fit to observed gravity anomalies using constraints from geological and structural observations bouguer anomalies computed from sea bottom measurements and downward continuation of sea surface measurements both constrain the forward modeling this forward model is the starting point of a 2 d monte carlo inversion of seafloor and sea surface data in addition to the crustal thickness variations along axis our data document the amplitude variations of the crustal thickness and or its density in the across axis direction the model resulting from our inversion exhibits several features of the crustal structure in the mark area 1 the presence of a low density ap 300 50 kg m 3 body beneath the neovolcanic ridge is suggested and could correspond to a magma chamber or more probably to a highly hydrothermally fissured zone 2 both long and short wavelength gravity signals exhibit a difference between the western and eastern sides of the axial domain the mean value and the amplitude of bouguer anomalies are higher on the western part this difference suggests that axial processes in this area are very asymmetric 3 abyssal hills are not associated with a single gravity signature for instance on the west side of the axis one of the explored hills has no bouguer anomaly and is interpreted as a neovolcanic ridge whereas the others are associated with a shifted bouguer anomaly high and are interpreted as having thinner magmatic crust 4 the last feature of the crustal fabric we document here is the asymmetric emplacement of some deep rocks outcrops in the mark area we find that pink hill a topographic high where serpentinized peridotites are outcropping is much more serpentinized on its east flank toward the axial valley than on its west flank alteration occurring mainly by fluid circulation through faulted zones the asymmetric serpentinization suggests that deep origin rocks have outcropped by means of a main fault zone and are not emplaced by diapirism

archaean basin development and crustal extension in the northeastern yilgarn block western australia abstract supracrustal sequences in the northeastern yilgarn block western australia form two contrasting lithotectonic associations most sequences were deposited in subaqueous to subaerial environments in a basin 120 km in width the preserved succession reaches a maximum of e 10 km in thickness in the central part of the basin although there is no record of the basement on which it was deposited in the later stages of its development the basin was intruded by calc alkaline granitoids that are in part comagmatic with calc alkaline volcanic rocks in the upper part of the stratigraphic succession brittle fracture normal strike faults and conjugate cross faults open upright folds and peak low strain metamorphism were coincident with granitoid emplacement the eastern and western margins of the basin were greatly modified during a period of increased crustal extension marked initially by the generation of a mildly peralkaline volcanic plutonic suite the volcanic members of which were deposited in linear faultbounded depressions a major growth fault indicated by thin persistent units of oligomictic and polymictic conglomerate and localized intense metasomatism was probably contemporaneous with felsic volcanic activity subsequent sediments derived largely from granitic source areas were deposited in narrow grabens the youngest felsic plutonic rocks in the area include small bodies of alkali feldspar syenite many of which are found near the margins of the late sediment filled grabens tectonism at the eastern basin margin extended into the proterozoic in contrast to sequences at the centre of the basin those at its margin have undergone isoclinal folding ductile deformation and high strain metamorphism the geological framework of the northeastern yilgarn block emphasizes the importance of crustal extension in the development of younger archaean supracrustal sequences and provides valuable support for extension dependent greenstone belt evolutionary models e g groves and batt