geology and tectonic development of the bras d or suspect terrane cape breton island nova scotia the bras d or terrane is defined in cape breton island and consists of four distinctive components i low pressure regionally metamorphosed aluminous and calcareous gneiss of the proterozoic bra

late precambrian u pb ages for the brookville gneiss southern new brunswick tonalitic orthogneiss from the brookville gneiss in southern new brunswick has an igneous protolith age of 605 pm 3 ma based on u pb dating of zircon metamorphic titanite from the same sample gives a minimum age of 564 pm 6 ma for upper amphibolite facies metamorphism of the unit based on u pb analyses of single detrital zircons a maximum sedimentary protolith age of about 641 ma is suggested for associated paragneiss these ages indicate that the igneous protolith of the orthogneiss was at most 35 ma younger than the sedimentary rocks it intruded and that the brookville gneiss is younger than the green head group to which it was previously considered basement both orthogneiss and paragneiss in the brookville gneiss contain proterozoic and archean detrital zircon grains suggesting an old heterogeneous continental source we conclude that the brookville gneiss does not represent the basement to the avalon terrane

assessment of multiple and interacting modes of soil loss in the karst critical zone southwest china swc abstract in southwest china swc soil loss is becoming a serious threat to the sustainable development of resources and the health of the environment a large number of studies have been conducted to investigate the causes e g environmental factors and human activities and impacts e g karst rocky desertification of soil loss however the following are some important problems related to soil loss in the karst of swc 1 although soil loss is caused by chemical weathering gravity and water interaction in karst the mechanisms by which soil loss takes place in the swc and their interaction are still not clear 2 subsurface soil loss varies under different geological and hydrological conditions and there is still no consensus on the common the ratio between surface soil erosion and underground soil loss 3 traditional methods for soil loss risk assessment are difficult to apply over the whole of swc and 4 a large number of studies have been published only in chinese and remain inaccessible to the international science community therefore a review paper is needed to address this gap and introduce the contributions of chinese researchers to soil loss in karst this paper proposes a novel modelling approach for the grouped soil loss styles and presents a comprehensive discussion for the mechanism causes and risk assessment of the various soil loss styles in swc karst

phytoliths indicators of grassland dynamics during the late holocene in intertropical africa abstract the reconstruction of african tropical grassland history during the late holocene can be carried out using phytolith analysis fossil phytolith assemblages from lake guiers in the sahelian region of senegal and from lake sinnda in the guineo congolian region of congo were investigated the results are interpreted on the basis of modern phytolith assemblages from the same regions and compared to pollen data previously obtained tall or short grass associations are discriminated by their phytolith index iph saddle cross dumbel saddle while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytoliths the phytolith data emphasize that in the guineo congolian region around lake sinnda the driest phase of the late holocene occurred between 4000 and 1200 yr b p commencing with the opening of the dense forest and its replacement by a short grass savanna from ca 1000 yr b p wetter climatic conditions developed as represented by the setting up of a tall grass savanna woodland the modern shrub and tall grass savanna was developed ca 700 yr b p in the sahelian region around lake guiers the driest phase occurred after about 2000 yr b p and has not been followed by moister conditions a tall grass savanna woodland was gradually replaced by a shrub and short grass savanna which still occurs a short period of development of swampy vegetation which can be related to a lake level change interrupted the semi arid adaptation of the vegetation between about 2000 yr b p and the present

northeastern extension and crustal expression of terranes from cape breton island nova scotia based on geophysical data the narrowest section of the appalachian orogen in atlantic canada from grenville age basement in the west to the avalon terrane in the east is preserved in cape breton island where components of four terranes display distinctive stratigraphic igneous metamorphic aeromagnetic and gravity characteristics the blair river complex of northwestern cape breton island is a fragment of grenvillian rocks that is similar to units in western newfoundland the aspy terrane is characterized by mid paleozoic granitic rocks and high pressure paragneisses and appears to continue across the cabot strait as the gander terrane of the hermitage flexure in newfoundland the bras d or terrane is composed of hadrynian to early cambrian low pressure metasedimentary units and dioritic to granitic plutonic rocks as indicated by aeromagnetic anomalies this terrane continues across the laurentian channel to the south coast of newfoundland where it may be terminated by the hermitage fault the avalon terrane of southeaster

tectonic implications of 40ar 39ar hornblende ages from late proterozoic cambrian plutons in the avalon composite terrane nova scotia canada the avalon composite terrane in nova scotia mainly represents a late proterozoic rifted cratonic magmatic arc complex the geo chemistry of the volcanic rocks indicates that most of southeastern cape breton island is underlain by a volcanic arc whereas the antigonish and cobequid highlands expose intra arc rift sequences in cape breton island late proterozoic rocks are both volcanic and plutonic south of the macintosh brook fault transecting the boisdale hills whereas they are mainly plutonic rocks north of the fault these igneous units are unconformably overlain by subaerial to shallow marine cambrian ordovician sedimentary sequences containing an atlantic fauna that are interbedded with early to middle cambrian within plate continental rift volcanic rocks 4o ar 39 ar plateau ages recorded by hornblende from plutons spatially associated with these volcanic rocks correspond to three groupings 1 ca 600 635 ma in cape breton island south of the macintosh brook fault 2 ca 525 555 ma in cape breton island north of the macintosh brook fault boisdale hills north mountain and creignish hills 3 ca 600 625 ma in the antigonish and cobequid highlands based upon the low metamorphic grade of the late proterozoic and early paleozoic rocks and the low pressures recorded in contact aureoles and plutons it is inferred that these plutons were emplaced at relatively shallow crustal levels and therefore the 40 ar 39 ar plateau ages probably closely date their emplacement interpretation of the age data suggests that plutonism in nova scotia associated with the rifted magmatic arc lasted from ca 635 600 ma igneous activity continued between ca 555 525 ma and may have been related to the cambrian within plate rift volcanism

the erosional response of calcareous soils along a climatological gradient in southeast spain abstract the erosional response of calcareous soils along a climatological gradient in alicante se spain was studied the erosional response was defined in terms of indicators obtained from field rainfall simulation experiments and laboratory studies of soil aggregation measurements were made at seven sites on limestones and marls between benidorm with an annual average rainfall of 400 mm yr 1 and coll de rates annual rainfall 900 mm yr 1 the sites were on matorral vegetation affected to varying intensities by grazing and fire at the seven locations soil aggregation was studied by sieving by the single water drop test and by a microscan particle sizer rainfall simulation experiments were made on circular 55 cm diameter target area plots using the calvo simulator at an intensities between 35 and 59 mm h 1 on limestone it was found that on bare surfaces the coarse soil aggregation increases with depth at the highest sites and decreases at the lower sites the benidorm surface soil has the highest erodibility the least stable soils are at the lower intermediate sites on marls the aggregate stability is generally high in contrast to those under cultivation simulated runoff from the wetter limestone sites is very low the driest areas have the highest runoff and sediment yields trends with climate suggest that the erosional responses of the soils indeed increase with aridity and temperature but local factors have a large effect particularly at intermediate altitudes a clear relationship like that found in israel by lavee on a similar lithology does not exist

paleopedologic and geomorphic evidence for holocene climate variation shortgrass steppe colorado usa abstract radiocarbon dates of paleosols in northeastern colorado indicate distinct periods of stability and soil formation with intervening periods of instability resulting in soil truncation or burial a combination of pedologic and geomorphic indicators were used to resolve the duration of and prevailing climate during these periods five sites each having a paleosol were examined using both traditional soil analyses and grain size statistics the latter to decipher the mode of parent material deposition twenty local stream dune and bedrock deposits were analyzed using grain size statistics to establish benchmarks for comparison with soils field investigation supported by grain size frequency statistics indicate early holocene middle holocene and contemporary soils all formed in alluvium organic c and phytolith data suggest the early and middle holocene climatic conditions were more favorable for plant productivity than the present climate soil development in early and middle holocene paleosols suggests wetter soil moisture regimes than present low parent material carbonate contents suggest an eolian source for the carbonate in the bk and btk horizons the presence of paleosol btk horizons suggests a decrease in precipitation at the end of soil forming intervals followed by drought and subsequent soil burial

hydrological changes related to the variability of tropical south american climate from the cabo frio lagoonal system brazil during the last 5000 years from west to east the fluminense coastline composed of two series of lagoons presents an aridity gradient induced by a local upwelling that is controlled by trade winds coming from the south atl

lu hf zircon and sm nd whole rock isotope constraints on the extent of juvenile arc crust in avalonia examples from newfoundland and nova scotia canada avalonia the largest accreted crustal block in the appalachian orogen consists of neoproterozoic magmatic arc sequences that represent protracted and episodic subduction related magmatism before deposition of an ediacaran ordovician cover sequence including siliciclastic rocks zircon crystals were obtained from arc related magmatic rocks and from clastic sedimentary sequences and analyzed in situ for their hf isotope composition the majority of magmatic and detrital zircons are dominated by initial 176hf 177hf values that are more radiogenic than chondritic uniform reservoir chur with calculated crust formation hf tdm model ages that range from 0 84 to 1 30 ga these results suggest formation by partial melting of juvenile mantle in a neoproterozoic continental arc some zircons have hf tdm model ages ca 1 39 3 09 ga with ehf values of 33 9 to 0 5 and more clearly indicate involvement of older lithosphere in their petrogenesis whole rock sm nd isotopic compositions from felsic volcanic rocks are

origin and evolution of avalonia evidence from u pb and lu hf isotopes in zircon from the mira terrane canada and the stavelot venn massif belgium laser ablation inductively coupled plasma mass spectrometry u pb and lu hf isotope analyses of detrital zircon from neoproterozoic cambrian clastic sedimentary rocks in the mira terrane cape breton island nova scotia canada west avalonia and the stavelot venn massif east belgium east avalonia support deposition on an originally coherent microcontinent crustal evolution trends defined by hf t values varying with age reflect juvenile magma production in the source continent at 1 2 2 2 and 2 4 3 1 ga mixing of juvenile and recycled crust in continental magmatic arcs is recognized at 0 5 0 72 1 4 1 7 1 8 2 2 and 2 4 2 7 ga these results concur with the crustal evolution in amazonia the likely parent craton crustal evolution in avalonia is recorded in detrital and magmatic zircon from neoproterozoic arcs 680 550 ma positive hf t values suggest juvenile input and mixing with recycled crust most negative hf t values represent recycling of predominantly mesoproterozoic underlying crust avalonian arc magmatism was followed by late neoproterozoic early cambrian sedimentation in various belts in west avalonia these belts were juxtaposed by strike slip during late early cambrian deposition in a rift basin the youngest detrital zircon population c 517 ma probably represents synrift magmatism before break up of avalonia migmatization at 406 2 ma in a xenolith from the east avalonian crust reflects post collisional heating supplementary materials details of sample locations and analytical results are available at www geolsoc org uk sup18641

silurian u pb zircon intrusive ages for the red river anorthosite northern cape breton island implications for the laurentia avalonia boundary in atlantic canada abstract current interpretations of the geology of cape breton island suggest that it exposes a complete cross section of the appalachians from laurentia across iapetan vestiges to avalonia crucial to this view is the presence of ca 1 ga plutons including anorthosites which have been regarded as correlatives of grenvillian basement a correlation that overlooks the fact that avalonia is also underlain by a ca 1 ga basement we analyzed zircons from the red river anorthosite blair river complex northwestern cape breton island previously dated as ca 1 1 ga they yielded 421 3 ma intrusive ages with older ages between 865 18 ma and 1044 20 ma inferred to be either xenocrysts derived from the country rock or from the source implications of these data suggest that the accompanying low pressure granulite amphibolite facies metamorphism of the blair river complex is either the root of a 440 410 ma magmatic belt produced during slab break off or relict ca 1 ga basement the blair river complex occurs in a nne ssw sinistral positive flower structure that progresses upwards from a neoproterozoic rifted arc through a low grade upper ordovician silurian overstep sequence to amphibolite facies fault slices capped by the low pressure granulite facies rocks blair river complex the correlation of neoproterozoic rifted arc units across most of cape breton island suggests it represents the deformed northwestern margin of avalonia intruded by a silurian lower devonian magmatic belt as the geological record in the blair river complex is similar to both grenvillian and avalonian basements its provenance is equivocal however pb isotopic data suggest the blair river complex has amazonian avalonia affinities thus cape breton island rather than representing a complete cross section of the appalachian orogen is part of pristine deformed avalonia with a positive flower structure exposing a cross section of avalonian crust

the role of the subcutaneous zone in karst hydrology abstract the subcutaneous zone is the upper weathered layer of rock beneath the soil but above the permanently saturated phreatic zone it is of particular hydrological importance in karst because of its high secondary permeability arising from the considerable chemical solution in this zone however corrosional enlargement of fissures diminishes with depth thus permeability decreases in the same direction with the result that percolation is inhibited except down widened master joints and faults storage of water consequently occurs in this zone particularly after storms the upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table which slopes towards points of rapid vertical percolation the potential induces lateral water movement converging on the most permeable areas such as beneath dolines leakage from the subcutaneous store sustains slow percolation in the vadose zone cross correlation of rainfall with percolation rates in caves in new mexico u s a and new zealand reveal response lags of 2 14 weeks with no apparent relationship to depth below the surface other percolation sites show no correlation with rainfall interpreted as being a consequence of considerable friction in tight fissure networks the recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers the importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised as must the contribution of subcutaneous water to flood hydrographs methods of estimating the volumes of subcutaneous and phreatic components of karst spring flood hydrographs are presented the paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology the desirability of explaining karst landform evolution in terms of hydrologic processes is stressed

u pb geochronological constraints on the evolution of the aspy terrane cape breton island implications for relationships between aspy and bras d or terranes and ganderia in the canadian appalachians new u pb zircon ages from nine samples of igneous and sedimentary rocks in the aspy terrane cape breton island show that neoproterozoic rocks form a major part of the terrane and confirm that the terrane was affected by a major silurian devonian tectonothermal event a rhyolitic crystal tuff a leucotonalite pluton and a felsic sheet yield ages of 618 8 0 6 ma 619 7 0 9 ma and 573 5 2 7 ma respectively a metasedimentary unit contains zircon ranging in age from ca 546 to ca 1520 ma a diorite has an age of 428 6 1 9 ma and another diorite unit and a quartz porphyry also have probable late silurian ages a third diorite yields an age of 373 0 0 5 ma part of a widespread bimodal igneous event represented by both volcanic and plutonic rocks throughout the aspy region geochronological results and field relationships indicate that the neoproterozoic rocks are similar to those in the bras d9or terrane and form the basement to the ordovician silurian rocks in the aspy terrane and that the aspy terrane is probably correlative with rocks in the hermitage flexure of southern newfoundland where silurian metasedimentary and metavolcanic rocks lie unconformably on similar neoproterozoic rocks likely correlative rocks also occur in the kingston terrane of southern new brunswick the results of this study support the idea that the aspy kingston terrane is part of ganderia and that neoproterozoic rocks in the bras d9or terrane and correlative rocks in southwestern newfoundland and elsewhere represent exposed basement to ganderia in the canadian appalachians

geochemistry of late proterozoic basaltic rocks from southeastern cape breton island nova scotia late proterozoic volcanic rocks of the fourchu group from the avalon zone in southeastern cape breton island nova scotia are composed predominantly of mafic and felsic types with subordinate inte

the cheticamp pluton a cambrian granodioritic intrusion in the western cape breton highlands nova scotia the cheticamp pluton consists of biotite granodiorite locally megacrystic in the north and museovite biotite granodiorite in the south in probable faulted contact these two rock types especially the biotite granodiorite show a broad range in modal and chemical compositions they are interpreted to be cogenetic with the museovite biotite grandiorite derived from the biotite granodiorite by crystal fractionation involving mafic minerals plagioclase and sphene the overall peraluminous composition of the suite resulted from the fractionation process probably enhanced by alteration rather than from derivation from peraluminous source rocks a seven point whole rock rb sr isochron indicates an age of 525 40 ma the pluton intruded dioritic rocks and quartzo feldspathic gneisses thus indicating precambrian ages for these units it probably also postdates the western highlands volcanic sedimentary complex a major undated stratigraphic unit in the cape breton highlands although the age overlaps t

an 40ar 39ar study of the cape breton highlands nova scotia thermal histories and tectonic implications forty new 40ar 39ar age spectra on micas and amphiboles from both granitic and metamorphic rocks show that two geologically distinct terranes in the cape breton highlands nova scotia have had contrasting thermal histories some plutons in the bras d or terrane in the southeastern highlands apparently cooled through the hornblende or muscovite closure temperature immediately following precambrian to cambrian intrusion other rock units in this terrane particularly in the west have been variably overprinted by a silurian tectonothermal event probably associated with juxtaposition of the bras d or terrane with the aspy terrane to the northwest gneisses at kellys mountain in the southeastern bras d or terrane apparently were not overprinted by this event argon data from the aspy terrane suggest that silurian deposition deformation and metamorphism were followed by rapid cooling through hornblende and biotite closure temperatures in the middle devonian this probably resulted from uplift and exhumati

u pb zircon titanite and monazite ages in the bras d or and aspy terranes of cape breton island nova scotia implications for igneous and metamorphic history new u pb ages from zircon titanite or monazite separates from 12 units in the aspy and bras d or terranes nova scotia range from late precambrian to devonian and generally support the interpretation that the 2 terranes had differing histories until juxtaposition in the devonian five plutons of dioritic tonalitic and granodioritic compositions in the northern bras d or terrane yielded zircon ages between 575 maximum and 556 4 m y younger titanite ages of 548 2 and 521 2 m y from two of these plutons may indicate younger metamorphism previously undocumented early ordovician plutonism 493 2 ma zircon and metamorphism 496 5 ma titanite also occurred in the bras d or terrane in the aspy terrane a zircon age of 433 7 4 m y was obtained for a rhyolite unit in the upper part of a widespread metavolcanic metasedimentary sequence which together with higher grade probably correlative units is characteristic of the terrane the age is interpreted to indicate that most metamorphic rocks in the terrane are ordovician to early silurian in age in contrast to precambrian ages in the bras d or terrane devonian plutonism was widespread in the aspy terrane whereas devonian plutonism in the bras d or terrane appears restricted to the vicinity of the boundary with the aspy terrane zircon titanite or monazite ages from 4 plutonic and orthogneissic units in the aspy terrane and in the bras d or terrane adjacent to the terrane boundary range from 403 3 to 375 5 4 m y

current perspectives on the environmental impacts and hazards in karst karst geo ecosystems are highly fragile environments that are suffering a progressive degradation caused by human activities in many regions of our planet the interactions between man and karst environments have been relevant since greek and roman times nicod et al 1997 but the resulting detrimental effects became particularly significant from the industrial revolution despite the long history of human induced impacts on the karst environments and damage caused by hazardous karst processes these problems were largely overlooked by the scientific community till the beginning of the 90s fortunately both the perception of the importance of the karst systems and the scientific efforts devoted to their understanding have increased considerably in recent times ford and williams 2007 the results of some investigations have been published in several special issues catena supplement environmental geology oklahoma geological survey circular geological society of london special publication engineering geology williams et al 1993 burri et al 1999 johnson and neal 2003 parise and gunn 2007 gutierrez et al 2008c parise et al 2008 and conference proceedings sauro et al 1991 beck 2003 subsidence related to sinkhole activity is the most important hazard in karst landscapes beck 2003 waltham et al 2005 in many regions financial losses caused by sinkholes are raising considerably due to the humaninduced increase in the probability of occurrence of sinkholes and the development of hazardous areas gutierrez et al 2008a some approaches including mechanical hydrogeological and predictive modelling salvati and sasowsky 2002 he et al 2004 geophysical surveys ardau et al 2007 speleological studies klimchouk et al 2002 and palaeokarst investigations gutierrez et al 2008b have provided enlightening insights on the processes involved in the subsidence phenomena other typical environmental problems in karst terrains are related to water quality and quantity drew and hotzl 1999 goldscheider and drew 2007 ravbar 2007 construction of infrastructures dams highways tunnels milanovic 2002 mining and quarrying gunn 2004 and other human activities such as agriculture waste disposal or urbanisation this special issue of environmental geology contains a selection of peer reviewed articles presented at the symposium on natural and anthropogenic hazards in karst areas held in vienna austria on 16 april 2007 within the framework of the natural hazards programme of the european geosciences union general assembly the symposium was co sponsored by the international union of speleology uis and by the international geographical union igu commission of karst hydrogeology and speleogenesis out of the 35 contributors to the session 22 accepted the invitation to submit a full paper and finally 15 peerreviewed articles have been accepted and included in this special issue they cover many different geographical areas where the interaction between karst systems and human activities results in significant environmental impacts and hazards europe austria bosnia m parise national research council irpi bari italy e mail m parise ba irpi cnr it

effects of fluid flow cooling and deformation as recorded by 40ar 39ar rb sr and zircon fission track ages in very low to low grade metamorphic rocks in avalonian se cape breton island nova scotia canada 40ar 39ar in situ uv laser ablation of white mica rb sr mineral isochrons and zircon fission track dating were applied to determine ages of very low to low grade metamorphic processes at 3 5 0 4 kbar 280 30 c in the avalonian mira terrane of se cape breton island nova scotia the mira terrane comprises neoproterozoic volcanic arc rocks overlain by cambrian sedimentary rocks crystallization of metamorphic white mica was dated in six metavolcanic samples by 40ar 39ar spot age peaks between 396 3 and 363 14 ma rb sr systematics of minerals and mineral aggregates yielded two isochrons at 389 7 ma and 365 8 ma corroborating equilibrium conditions during very low to low grade metamorphism the dated white mica is oriented parallel to foliations produced by sinistral strike slip faulting and or folding related to the middle late devonian transpressive assembly of avalonian terranes during convergence and emplacement of the neighbouring meguma terrane exhumation occurred earlier in the nw mira terrane than in the se transpression was related to the closure of the rheic ocean between gondwana and laurussia by nw directed convergence the 40ar 39ar spot age spectra also display relict age peaks at 477 465 ma 439 ma and 420 428 ma attributed to deformation and fluid access possibly related to the collision of avalonia with composite laurentia or to earlier ordovician silurian rifting fission track ages of zircon from mira terrane samples range between 242 18 and 225 21 ma and reflect late palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid absent conditions during rifting prior to opening of the central atlantic ocean

geological correlations between cape breton island and newfoundland northern appalachian orogen geological correlations between cape breton island and newfoundland are apparent both in surface geology and at deeper crustal levels based on similarities in sm nd isotopic signatures the mira terrane of southeastern cape breton island is part of the avalon terrane sensu stricto and is composed of neoproterozoic volcanic sedimentary plutonic belts and overlying cambrian rocks directly comparable to those in the western part of the newfoundland avalon terrane the bras d or terrane is also mainly of neoproterozoic age but shows lithological and isotopic contrasts with the mira terrane small areas of similar neoproterozoic rocks occur in southern newfoundland and to the north as inliers in the exploits terrane the bras d or terrane and similar rocks in newfoundland are interpreted to represent a peri gondwanan terrane where rocks of the gander terrane were later formed hence this area is part of the central mobile belt and distinct from avalon terrane sensu stricto the aspy terrane is a complex area

geochemistry and tectonic setting of late precambrian volcanic and plutonic rocks in southeastern cape breton island nova scotia late precambrian volcanic sedimentary belts in the mira avalon terrane of southeastern cape breton island display differences in rock types petrochemistry and age showing that they did not form contemporaneously above a single northwest dipping subduction zone as proposed in earlier models the oldest rocks are 680 ma mafic and felsic flows and tuffs and abundant mainly tuffaceous sedimentary rocks in the stirling belt they are interpreted to have formed in a trough within or peripheral to a volcanic arc complex northwest of the stirling belt the east bay hills coxheath hills and sporting mountain belts consist of ca 620 ma mafic to felsic subaerial pyroclastic rocks and flows and contemporaneous dioritic to granitic plutons both volcanic and plutonic rocks are calc alkalic to high k calc alkalic suites formed in a continental margin volcanic arc a correlative 620 ma plutonic suite intruded the western margin of the stirling belt suggesting that subduction may have been toward the prese

employing contact metamorphism to assess the conditions of pluton emplacement and timing of recrystallization in southwestern kellys mountain cape breton island nova scotia at kellys mountain cape breton island nova scotia the late neoproterozoic glen tosh formation a low grade metapsammite metapelite unit of the george river metamorphic suite has been intruded by diorite granodiorite and granite plutons and the diorite hosts a narrow contact metamorphic aureole new mapping and sampling in the contact aureole reveals that the metasedimentary rocks have reached amphibolite facies metamorphism resulting in the development of neoformed biotite muscovite cordierite ilmenite garnet andalusite sillimanite monazite and spinel within the meta pelite a mineral assemblage also found in the kellys mountain gneiss as a result of low pressure regional metamorphism neoformed minerals and the disappearance of foliation defines a contact metamorphic aureole within 300 m of the pluton contacts petrographic and microprobe analyses of equilibrium assemblages in metapelitic units of the contact aureole yielded metamorphic pressures of 250 mpa implying an intrusion depth of 9 km with temperatures ranging from 365 to 590 c the presence of earlier formed andalusite and garnet indicates the rocks may have initially undergone a low pressure regional metamorphic event prior to contact metamorphism monazite in the contact aureole was dated using in situ u pb methods and yielded an age of 480 9 3 7 ma interpreted as the time of formation of the contact metamorphic aureole

a hafnium isotopic record of magmatic arcs and continental growth in the iapetus ocean the contrasting evolution of ganderia and the peri laurentian margin abstract we test the sensitivity of combined u pb hf isotopic analyses of detrital and magmatic zircon to document complex processes in accretionary orogens using ganderia from the canadian appalachian orogen as an example ganderia hosted a long lived magmatic arc that began at least by 650 ma and continued until 450 ma during which time it drifted northward from the amazonian margin its isotopic record suggests arc activity began earlier possibly at 750 ma proto ganderia within an oceanic domain the u pb hf zircon isotopic array suggests that ganderia formed on a sliver of paleoproterozoic mesoproterozoic basement tdmc 2 2 1 1 ga a transition towards more evolved hf isotopic compositions between 650 and 600 ma is interpreted to coincide with its accretion to the amazonian margin of gondwana consistent with other geological evidence accretion was followed by increasing amounts of juvenile crustal inputs between 550 and 500 ma which is interpreted to reflect subduction roll back and the onset of drift from the gondwanan margin trench retreat culminated in the separation of the ganderia arc and formation of the exclusively oceanic 510 450 ma penobscot popelogan victoria arcs on ganderia accretion of ganderia to the active notre dame subzone along the laurentian margin occurred in the late ordovician and is marked by the abrupt termination of ganderian arc magmatism the notre dame arc evolved along the laurentian margin between 515 and 425 ma and was built on paleoproterozoic archean t dm c 2 9 2 5 ga crust supra subduction zone magmatism occurred at 490 460 ma during the closure of the taconic seaway and was dominated by the recycling of laurentian crust with progressive mixing of evolved and juvenile arc magmas over time the preservation of very evolved notre dame arc zircon in ganderian overstep sequences confirms the arrival of the leading edge of ganderia to laurentia by 450 ma the hafnium isotopic method is proven here to be a powerful tool when used in conjunction with geological constraints and is able to identify the changing nature of magmatism during the evolution of complex accretionary systems

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

low pressure cordierite bearing migmatites from kelly s mountain nova scotia the kelly s mountain gneiss complex of cape breton island nova scotia is a migmatitic paragneiss dominated by biotite and cordierite bearing assemblages metamorphic grade throughout the complex is in the upper amphibolite facies with garnet absent and only retrograde muscovite present in the high grade core of the complex the reaction biotite andalusite quartz cordierite k feldspar sillimanite ilmenite h2o is preserved the pelitic migmatites contain cordierite and k feldspar rich leucosomes and biotite rich melanosomes minor clinopyroxene bearing amphibolite in the complex does not show migmatitic textures the migmatites are interpreted as in situ peraluminous partial melts on the basis of phase relations and textural criteria retrograde metamorphism under conditions of high fluid pressure locally produced muscovite after k feldspar and muscovite green biotite chlorite after cordierite in paragneiss and sphene after ilmenite in amphibolite peak metamorphic conditions of 1 3 5 kb and 580 700 c are estimated the high geothermal gradient inferred from these conditions was probably caused by the intrusion of diorites associated with the gneiss complex the kelly s mountain complex represents a rare example of migmatites formed in the low pressure facies series and illustrates some of the reactions involving melting in high grade pelitic rocks

till geochemistry and its implications for mineral exploration southeastern cape breton island nova scotia canada abstract till samples were collected across southeastern cape breton island nova scotia canada at a reconnaissance scale 3 5 km spacing to define regional background levels of base and precious metals in drift and to identify anomalous areas that may indicate mineralization in the underlying bedrock till samples were also collected from detailed sampling grids 100 500 m spacing over three known mineral occurrences to document the nature of glacial dispersal from mineralized sources i e the directions and distance that successive ice flow events have dispersed material and the variation in trace element concentration in till around the bedrock source several areas contain elevated levels of base and precious metals elevated pb and zn concentrations occur along the salmon river valley and are related to glacial dispersal from pb zn mineralization in carboniferous sandstone down northeastward the valley elevated au values in the region up to 78 ppb overlie fourchu group felsic volcanic rocks at a local scale mo and cu have been dispersed at least 500 m to the east of the deep cove pluton by an older eastward ice flow event in the blue mountain area dispersal of sandy metal rich till was mainly northward at stirling exotic red till masks the underlying mineralized bedrock and dilutes the locally derived glacial debris so that there is little geochemical response in the till

u pb geochronological constraints on precambrian stratified units in the avalon composite terrane of nova scotia canada tectonic implications concordant u pb ages of detrital zircons in several proterozoic units in the avalon composite terrane of nova scotia along with previously published data indicate that deposition of low and high grade stratified units in the cobequid highlands gamble brook formation and central cape breton island variously assigned to the george river group or george river metamorphic suite and the bras d or gneiss started after 977 ma extended through a period of volcanic activity between 694 and 637 ma and ended before the 629 612 600 ma volcanic activity associated with deposition of the georgeville and jeffers groups in the antigonish and cobequid highlands and the east bay hills and coxheath groups in southern cape breton island these age data along with u pb analyses of metamorphic and igneous zircon and monazite also constrain three late proterozoic tectonothermal events i oblique sinistral ductile shear deformation and greenschist amphibolite facies metamorphism probably occurred between 694 an

detrital zircon geochronology of a conglomerate in the northeastern cape breton highlands implications for the relationships between terranes in cape breton island the canadian appalachians cape breton island has been interpreted as consisting of four zones of pre carboniferous rocks but the relationships among them are controversial to help resolve the controversy we have dated detrital zircons from a conglomerate part of the cheticamp lake gneiss in the aspy terrane in the northeastern cape breton highlands using the u pb method the following ages were obtained 462 2 ma middle ordovician 492 488 ma 6 ages early ordovician 552 3 ma latest precambrian early cambrian 620 13 and 687 4 ma cadomian and 809 17 1423 10 1462 12 1605 14 1644 4 and 1911 5 ma proterozoic the middle ordovician age sets a maximum age limit for deposition of the conglomerate and supports an ordovician silurian age for the cheticamp lake gneiss the early ordovician latest precambrian early cambrian and cadomian ages match published ages from the bras d or terrane and its correlatives and the mira terrane and its correlatives and indicate provenance of the conglomer

vegetational history of a site in the central amazon basin derived from phytolith and charcoal records from natural soils abstract analysis of phytoliths and macroscopic charcoal from natural soils near manaus brazil shows that the central amazonian terra firme forest has not been stable during the holocene phytolith taxonomic composition and radiocarbon ages indicate that a closed forest has continuously existed in the area since at least 4600 yr b p but that forest composition and species abundance changed significantly sometime during the holocene epoch there is no evidence that the vegetation experienced swidden cultivation the distribution and dates of the charcoal in the soils indicate that forest fires between 1795 and 550 yr b p burned an area of about 200 hectares vegetational changes and fires appear to be a result of climatic drying that may have affected large areas of the amazon basin over the past 5000 to 7000 years soil phytolith analysis is a promising tool for the study of environmental history in the humid tropics and may reduce the previous dependence on lake and swamp sediments at least for the holocene epoch

late holocene phytolith and carbon isotope record from a latosol at salitre south central brazil abstract the reliability of paleovegetation records inferred from soil phytolith assemblages and som soil organic matter carbon isotope analysis was examined in light of previous pollen and charcoal reconstructions the sampled latosol is located in south central brazil salitre at a boundary between forest and cerrado the derived mean age of phytoliths and som at each level is the result of a balance between continuous translocation and selective dissolution it increases with depth in a regular quantifiable fashion that allows paleoenvironmental interpretation phytoliths and som tracers first record a savanna phase associated with the last holocene long dry period occurring between ca 5500 and 4500 yr b p two periods of tree community development followed between ca 4000 and 3000 and after ca 970 yr b p leading to the present cerrado forest association the dry spell interrupted this trend about 970 60 yr b p the second development of woody elements was contemporaneous with an increase in anthropogenic fires therefore climate was more important than fires and human activities in constraining the growth of vegetation during the last nine centuries at salitre more generally despite pedogenic processes soil phytoliths and 13c values of the som may be accurate tracers of vegetation changes

phytoliths as paleoenvironmental indicators west side middle awash valley ethiopia phytolith assemblage analysis offers the potential to refine our knowledge of paleoecosystems where grasses and sedges predominate in this work holocene and pleistocene sediments from an arid tropical region in ethiopia have been analyzed for their phytolith content presented as detailed counts and diagrams according to the twiss classification the aim is to test the usefulness of phytolith assemblages to indicate paleoenvironments at middle awash where fossil pollen grains are poorly preserved in sediments that yielded abundant archaeological remains the vegetation in the middle awash subdesertic valley is currently a shrub steppe dominated by c4 grasses adapted to arid conditions with a narrow riparian forest limited to the awash river our results show that modern surface samples holocene and pleistocene sediments contain well preserved and different phytolith assemblages and therefore that no translocation processes from modern soil to geological strata seem to occur fossil records and modern assemblages are interpreted using phytolith ratios to estimate the density of the tree cover the aridity and the proportion of c3 versus c4 grasses as applied to phytolith assemblages from north america and west africa the phytolith assemblages from modern soil samples correctly reflect the proportion of trees and shrubs versus grasses different in the riparian vegetation and the shrub steppe modern phytolith assemblages appear to be a mixed signature of local and regional vegetation phytolith analysis of the holocene sample suggests a grassland where the grass community is constituted by the chloridoideae subfamily adapted to warm and dry conditions and where c3 pooideae cover the highlands phytolith analysis of the pleistocene sample evidences grassland formation with scattered woody elements where c4 panicoideae grasses adapted to warm and humid conditions dominate the grass cover however these conclusions need to be confirmed by more complete study on phytolith assemblages from modern vegetation from ethiopia

soil erosion rates in two karst peak cluster depression basins of northwest guangxi china comparison of the rusle model with 137cs measurements reliable estimation of erosion in karst areas is difficult because of the heterogeneous nature of infiltration and subsurface drainage understanding the processes involved is a key requirement for managing against karst rock desertification this study used the revised universal soil loss equation rusle to estimate the annual soil erosion rates on hillslopes and compared them with cs 137 budget in the depressions at two typical karst peak cluster depression basins in northwest guangxi southwestern china runoff plots data were used to calibrate the slope length factor l of the rusle model by adjusting the accumulated area threshold the rusle model was sensitive to the value of the threshold and required dems with 1 m resolution due to the discontinuous nature of the overland flow the average annual soil erosion rates on hillslopes simulated by the rusle were 0 22 and 0 10 mg ha 1 y 1 2006 through 2011 in the partially cultivated gz1 and the undisturbed gz2 basins respectively the corresponding deposition rates in the depressions agreed well with the cs 137 records when recent changes in precipitation and land use were taken into consideration the study suggests that attention should be given to the rusle l factor when applying the rusle on karst hillslopes because of the discontinuous nature of runoff and significant underground seepage during storm events that effectively reduces the effects of slope length c 2015 elsevier b v all rights reserved

precise u pb dating of meguma basement xenoliths new evidence for avalonian underthrusting u pb zircon and monazite dates for granulite facies basement xenoliths from the popes harbour dyke on the eastern shore of nova scotia provide strong evidence that the meguma terrane overlies avalo

late proterozoic tectonic model for the avalon terrane in maritime canada the avalon terrane in maritime canada extends from cape breton island through northern nova scotia antigonish and cobequid highlands to southern new brunswick the terrane contains abundant late proterozoic volcanic rocks 570 680 m y old the geochemistry of the volcanic rocks of southern cape breton island and southern new brunswick indicates that they were erupted in a volcanic arc environment in both regions the mafic rocks display a remarkably similar compositional zonation which resembles the across arc variations observed in modern volcanic arcs the progressive compositional changes that include a transition from island arc tholeiites along the southeastern coasts to calc alkaline rocks inland to the northwest are probably due to a northwest dipping subduction zone with a trench located to the southeast in the antigonish and cobequid highlands continental tholeiites and calc alkaline volcanic rocks are interbedded and overlain by turbidites that have probably been deposited in a back arc or intra arc environment the superimposed positive gravity and magnetic anomalies that may be traced discontinuously from the grand banks through nova scotia collector anomaly and along the northern side of the gulf of maine to near boston probably represent late proterozoic ophiolitic remnants preserved by incomplete suturing along a late proterozoic plate boundary northeast trending segments are inferred to mark subduction zones and the e w portions could correspond to transform faults thus the present geographical distribution of the late proterozoic volcanic rocks is explained by a tectonic model involving a single subduction zone offset by two late proterozoic transform faults located approximately along the minas fault and the scatarie ridge

effects of land use land cover and rainfall regimes on the surface runoff and soil loss on karst slopes in southwest china abstract surface runoff and soil loss from 2007 to 2010 related to land use and rainfall regimes in karst hill slopes in guizhou province southwest china were analyzed using the hierarchical clustering method sixty one rainfall events under the subtropical monsoon climate condition were classified into 5 types of rainfall regimes according to the depth maximum 30 min intensity and duration of rainfall in our study we first demonstrated that the amounts of surface runoff and soil loss on the karst hill slopes were very small compared to the non karst areas because the dual hydrological structure in the karst region including ground and underground drainage systems could influence the processes of rainfall recharge and runoff generation most rainfall water was transported underground through limestone fissures and fractures while little was in the form of surface runoff second the runoff and soil loss were affected by land use management and vegetation cover soil loss was intensified in a descending order to five types of land uses pastureland burned area cropland combination vegetation land young forestland third the runoff and soil loss exhibited remarkable variances among different rainfall regimes large runoff and soil loss were mainly created by heavy rainfall storms with a rainfall depth of more than 40 mm and a maximum 30 min rainfall intensity of over 30 mm h 1 in addition rainfall storms with large antecedent precipitations could also produce large runoff and soil loss these observations indicated that limestone fissures and fractures play important roles in surface runoff generation on karst limestone slopes due to their large storage capacity and high infiltration rate lastly the soil erosion risk in the karst pure limestone slope is quite high and should be paid particular attention especially in regards to over grazing because the soil loss created by a single heavy rainstorm in pastureland was 5 times the annual soil loss tolerance

changes in holocene tree cover density in cabo frio rio de janeiro brazil evidence from soil phytolith assemblages the coastal region of cabo frio in the brazilian state of rio de janeiro is characterized by xeric vegetation surrounded by humid forest it is considered as a phytogeographical enclave the vegetation is adapted to the dry conditions which are present locally mainly due to the cabo frio coastal upwelling although quaternary changes in the intensity of the upwelling were reconstructed from coastal lagoons and oceanic sediment records the lack of continental deposits has precluded vegetation reconstructions the objective of this study was to investigate the pedogenic features of two soil profiles developed under patches of dry forest in the cabo frio area and to assess their potential for inferring past changes in tree cover density from their phytolith assemblages for this purpose field and petrographical observations c content c n ratio phytolith content and phytolith assemblages were investigated soil phytolith assemblages were compared to modern phytolith assemblages the deepest soil organic carbon soc samples were analyzed in c 14 ams related c 14 mean age values were interpreted as the youngest ages of the oldest soc these data suggest a first soil development phase occurring after 13 ka cal bp followed by erosive and depositional episodes and by a second soil development phase given the complexity of the studied soil sequences an attempt to quantify the sources of soc and phytoliths would require investigation of many more soil samples than the ones collected this prevents interpretation of the phytolith sequences as continuous chronological sequences however for both profiles phytolith indices d p from a ab and bottom horizons can be compared assuming a bicompartmental distribution of phytoliths in relation with each of the soil development phases d p values range from 0 8 to 4 in agreement with what would be expected for dry forest d p values and do not substantially change in both profiles this comparison suggests that the tree cover density of the successive vegetation sources did not suffer considerable change over the period under analysis last 13 ka for profile a and never reached the tree density of the humid forest currently widespread in the rio de janeiro state c 2012 elsevier ltd and inqua all rights reserved

runoff and erosion processes on bare slopes in the karst rocky desertification area underground pore fissure and bedrock bareness are the main factors that lead to complicated mechanisms of soil erosion in karst regions the objectives of this study were as follows a to measure runoff and sediment generated from the surface and underground in the karst bare slope and b to analyse the impacts of underground pore fissures and bedrock bareness rates on soil erosion to achieve these objectives we designed an experiment in which underground pore fissure degrees and bedrock bareness rates were varied and their impacts on soil erosion were measured the results showed that runoff and sediment yields from the surface and underground increased with increasing rainfall intensity and the surface runoff was much more easily generated when the rainfall intensity was greater ii surface runoff yield first increased and then decreased with increasing bedrock bareness rates while the runoff yield in underground pore fissures increased with increasing bedrock bareness rates thus sediment production on the surface and in underground pore fissures showed the same pattern i e first decreased and then increased iii the surface runoff and sediment generally decreased with increasing degrees of underground pore fissures while that of underground pore fissures presented a different pattern and iv rainfall intensity bedrock bareness rates and underground pore fissure degrees were the important factors affecting soil erosion processes in karst bare slopes because the bedrock bareness rates and underground pore fissure degrees were the main factors causing the uneven distribution of runoff and sediment on soil surfaces and underground therefore soil and water loss in underground pore fissures was the special pattern and main difference in soil erosion processes in the karst region compared with other regions these results have theoretical and practical significance for understanding soil erosion mechanisms and controlling soil and water loss in karst regions

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

assessment of sediment and erosion rates by using the caesium 137 technique in a chinese polygonal karst depression karst depressions comprise geomorphologically important sources and sinks for sediments and associated pollutants yet the sedimentology of many depressions is not well understood in the world in this paper the 137cs technique was employed to estimate recent sedimentation rates in a chinese polygonal karst depression the results indicate that the sediment deposition rates ranged from 0 91 to 1 97 mm year 1 from 1963 to 2007 and the average sediment deposition rate and specific deposit yield were estimated to be 1 47 mm year 1 and 20 t km 2 year 1 respectively these results are consistent with the local monitoring data of runoff fields which confirms the validity of the overall approach this shows that the soil loss rate is very low in some karst areas of southwest china above all the approach appears to offer valuable potential to study surface erosion by estimating sediment deposition rates of karst depressions rather than the assessment of complicated soil erosion in stony soils of carbonate rock slopes in addition the space distribution of surface soil and 137cs inventories are affected remarkably by the inhomogeneous dissolution of limestone under the soil it may be an important phenomenon which exists widely in karst areas and it is significantly different from other places

the evolution of the avalonian plate abstract the avalon platform of newfoundland is the type locality of the avalonian plate that is characterized by late precambrian volcanic and clastic rocks marine at the bottom and terrestrial at the top all are intruded by 650 550 ma granites late precambrian rocks in the southern british isles are similar in both areas northeastern parts of the belt are affected by deformation and metamorphism that have orogenic aspects the orogeny is referred to as the avalonian in newfoundland and monian in britain to the southeast of the avalonian rocks in europe lies another late precambrian cadomian orogenic belt of rocks as a part of the pan african orogenic belt the cadomian and avalonian belts extend into north africa morocco since these belts are ophiolite bearing it is suggested that the plate was bordered by oceanic domains it is therefore proposed that a microcontinental volcanic arc that was generated in the late precambrian was orogenically deformed by collision with north america europe and africa and survived as a coherent terrain until the late carboniferous

u pb age constraints on the stratigraphy and tectonic history of the avalon terrane new brunswick canada six new u pb ages for avalonian plutonic and volcanic rocks from the eastern caledonia highlands southern new brunswick indicate that magmatic activity occurred between 625 600 ma ago with another probably separate major episode at ca 550 ma this gap in igneous activity is consistent with differences in the metamorphic and deformational character of rocks from the two episodes the 625 600 ma activity was calc alkalic and probably occurred in an andean type magmatic arc it correlates with most volcanism and plutonism in the type avalon terrane of newfoundland the ca 550 ma activity formed bimodal volcanic rocks and high level plutons probably in an extensional setting u pb ages of xenocrystic zircons from avalonian igneous rocks indicate both archean and proterozoic components at depth in avalonian basement an observation consistent with pb isotopic signatures which suggest an old radiogenic crustal source the african craton for the magmatic products

contrasting u pb ages from plutons in the bras d or and mira terranes of cape breton island nova scotia u pb dates from zircon titanite and monazite in plutons of the bras d or and mira terranes of southern cape breton island combined with 40ar 39ar and other radiometric age data indicate that th

40ar 39ar mineral ages from kellys mountain cape breton island nova scotia implications for the tectonothermal evolution of the avalon composite terrane hornblende from a diorite stock within the kellys mountain plutonic complex within the avalon composite terrane and hornblende muscovite and biotite from amphibolite and gneiss within the contact aureole record similar 40ar 39ar plateau ages of 493 498 ma these data indicate relatively rapid cooling through the contrasting temperatures appropriate for intracrystalline retention of argon in the different minerals this is consistent with the relatively high level of intrusion of the pluton 3 10 km suggested previously from the study of mineral assemblages developed in the contact aureole these relationships suggest that intrusion of the kellys mountain complex took place at approximately 500 ma indicating an age close to the cambro ordovician boundary the complex may have formed in the same within plate rifting regime as the middle cambrian bourinot group volcanic sequences exposed within the avalon composite terrane

the acadian fold belt in the meguma terrane nova scotia cross sections fold mechanisms and tectonic implications 1 structural data and cross sections from the eastern part of the devonian carboniferous fold belt of the meguma terrane give insight into its structural development and crustal tectonics the sandy goldenville formation the active competent member during buckling formed a multilayer several kilometers thick that lay beneath the denser softer muds and silts of the halifax formation cross sections reveal 2 orders of folds 11 18 km wavelength folds are interpreted as resulting from buckling under the influence of gravity 4 6 km wavelength folds reflect the thickness of the multilayer with buckle shortening in the range 32 44 depth to detachment derived from the sections 11 13 5 km below present erosion surface is such that given the depth of the detachment below the paleosurface during the main phase pre devonian granite of folding it would likely have been a relatively soft and thick shear zone that would have influenced profile geometry of the main phase folds at this stage of fold belt development granite production that may have been triggered by mantle delamination during continuing convergence accompanying terminal pangean assembly and ocean basin closure was followed by rapid exhumation later localized deformation late devonian carboniferous in the fold belt took place as the meguma terrane was displaced along the terrane bounding cobequid chedabucto fault system the characteristic asymmetric cross sections of structures of this phase are attributed to cooling and strengthening of the detachment that was a consequence of the postgranite uplift and exhumation

dynamics of soil organic carbon and nitrogen following agricultural abandonment in a karst region agricultural abandonment is regarded as a major driver of soil organic carbon c dynamics but the mechanisms underlying the direction and magnitude of soil c dynamics following agricultural abandonment are poorly understood here dynamics of soil c and n contents during postagricultural succession were investigated in areas underlain by dolomite or limestone by using a space for time substitution approach in a karst region southwest china one hundred twenty five sites from cropland grassland shrubland and secondary forest were selected to represent different succession stages overall soil c and n contents were greater p 0 05 over limestone than over dolomite mainly due to significantly greater contents of soil c and n in the cropland and grassland underlain by limestone both soil c and n contents were lowest in the cropland while highest in the forest further analysis indicated that the patterns of soil c and n dynamics differed between the two lithology types soil c and n contents increased significantly from cropland to forest over dolomite while varied insignificantly among succession stages over limestone exchangeable calcium explained most of soil c and n variance we proposed that higher dissolution rate of limestone could replenish the lost calcium so that the calcium levels and in turn soil c and n contents were stable from the cropland to the forest nevertheless due to relatively low dissolution rate for dolomite the calcium level was depleted in the cropland following agricultural abandonment calcium level recovered due to decreased loss which in turn resulted in recovery of soil c and n

ice flow history and glacial dispersal patterns southeastern cape breton island nova scotia implications for mineral exploration regional till sampling and stratigraphic studies were completed in southeastern cape breton island nova scotia in 1990 and 1991 to document the directions and distances that successive ice flow events have dispersed material and to document regional till geochemical patterns to aid mineral exploration in this heavily drift covered area three major wisconsinan ice flow events affected the area an early eastward flow followed by a northeastward flow and finally a southward flow the shape and magnitude of dispersal trains in the area are the net result of the three ice flow events which are variable from north to south in the north the northeast ice flow was the dominant erosive and depositional event producing a large northeast trending drumlin field salmon river porphyry clasts and pb and zn rich till from the yava pb mine were dispersed more than 15 km to the northeast in the south eastward ice flow was the dominant erosive and depositional event producing large east trending till ridges dispersal in this area is difficult to detect because exotic red silty till in the giant till ridges masks underlying mineralized bedrock and dilutes the locally derived glacial debris many precious and base metal anomalies and dispersal trains were identified in the regional till samples several of which are related to unknown mineralized sources

40 ar 39 ar mineral ages from the southern cape breton highlands and creignish hills cape breton island canada evidence for a polyphase tectonothermal evolution 40 ar 39 ar ages for hornblende and muscovite from plutons and metamorphic country rocks in the southern cape breton highlands and creignish hills together with previously published u pb rb sr and 40 ar 39 ar ages document a complex tectonothermal history that included 1 episodes of plutonic activity at ca 600 565 560 555 500 490 470 and 410 395 ma all of which cooled through 500 400 c within ca 20 m y and 2 deformation in the late precambrian 550 ma and the late silurian middle devonian 415 380 ma the latter was associated with evelopment of a positive flower like structure during maintenance of medium pressure greenschist amphibolite facies regional metamorphic conditions that may be traced northward along the length of the cape breton highlands it may be correlated with the kingston complex and associated mylonite zone exposed in the avalon composite terrane of southern new brunswick northward it merges with a major high grade poly deformed belt within the gan

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

role of rock dip angle in runoff and soil erosion processes on dip anti dip slopes in a karst trough valley abstract due to the great difficulty of monitoring surface and underground runoff and sediment yield directly the surface and underground hydrological processes associated with soil leakage loss in karst trough valleys remain unknown the objective of this study was to analyse the role of the rock dip angle in the water and soil leakage loss processes to assess the characteristics of surface and underground runoff and soil erosion and to investigate their conversion relationships using rainfall experiments the results showed the following i at a steep rock dip angle 60 the underground runoff yield had a shorter stabilization time than the surface runoff yield and that the underground runoff coefficient of the dip slope exceeded 0 5 ii the surface sediment yield could be divided into the suspended load and the bed load and the underground sediment yield included only the suspended load on the anti dip slope the surface erosion modulus was 0 83 2 50 times the underground erosion modulus iii the surface and underground cumulative runoff was linearly correlated with the cumulative sediment yield the rock dip angle had a significant quadratic relationship with the surface and underground runoff and sediment yield these results improve the understanding of the surface underground runoff and soil erosion processes and have significance for preventing water and soil leakage loss on the slopes of karst trough valleys

assessing soil redistribution in a complex karst catchment using fallout 137cs and gis abstract caesium 137 derived from nuclear testing in the past century has been widely used as a sediment tracer of soil redistribution providing information on medium term 40 50 years erosion rates to date most studies have focused on individual fields of limited extent but estimated rates and patterns of soil redistribution require upscaling to catchment level an attempt to assess soil redistribution processes with strong geomorphic control on complex terrain such as an internally drained karst catchment is presented in this work a comprehensive geomorphological survey of the estanya lake catchment spanish pyrenees enabled the main geomorphic elements to be identified with a grid resolution of 5 5 m which was the basis for the terrain analyses a detailed dem was constructed and improved after field identification of the drainage system and point measures on gentle slopes with total topographic station a 100 100 m sampling grid was established to derive point data of 137 cs inventories across the catchment geostatistical interpolation of point samples of 137 cs inventories in soil was carried out to identify and assess the areas of sediment gain and loss by comparing with 137 cs reference inventories profile activity models were used to calibrate 137 cs data and to derive estimates of soil redistribution gis was used to provide spatially distributed erosion and deposition rates in the landscape for the whole catchment the median values of soil erosion and deposition of 4 7 and 3 1 mg ha 1 year 1 respectively showed a large variability and reveal coupling between erosional and depositional forms in the catchment the highest erosion and deposition rates were found in cultivated fields at the southern sector of the catchment the spatial analysis of the results supports the importance of taking into account geomorphological features in karst catchments as relevant controlling factors in soil redistribution processes

grenvillian basement in the northern cape breton highlands nova scotia the northernmost cape breton highlands are underlain by the blair river complex a distinctive assemblage of basement rocks including felsic and mafic gneisses foliated gabbroic to granitic rocks

runoff generation sediment movement and soil water behaviour on calcareous limestone slopes of some mediterranean environments in southeast spain abstract an interpretation of soil hydrology and erosion data obtained from limestone areas in southeast spain is presented in the framework of recent hypotheses on runoff generation mechanisms in mediterranean environments the main objective is to synthesise and harmonise the data in theoretical concepts or behavioural models of hydrological functioning of mediterranean limestone slopes for this purpose data were collected in a typical limestone area with climatic characteristics ranging from subhumid to semiarid several sites were chosen with comparable slopes vegetation and soils along a transect of 20 km to carry out several research projects the data discussed in this paper consist of information on water redistribution within the soil profiles obtained from long duration up to 5 h rainfall simulation experiments with continuous monitoring of soil moisture at different depths runoff and sediment concentration data were obtained i from rainfall simulation experiments with different antecedent soil moisture conditions and ii as natural results from open gerlach plots on runoff and sediment movement over 4 years three conceptual models of water redistribution during the infiltration process could be observed two of them imply nonuniform water redistribution within the soil profile due mainly to macropore flow caused by specific soil surface characteristics at the plot scale runoff generated in bare patches is mainly hortonian in plots with previously wetted soils or soils with high infiltration capacities the generated runoff implies the saturation of the upper soil both types of runoff are discontinuous through time and space the runoff generation mechanisms at the slope scale have been synthesised into two conceptual models a hortonian discontinuous runoff model that takes place in the most degraded slopes or during high intensity rain events and a mixed runoff generation model in less degraded slopes or in previously wet soils where infiltration excess runoff as well as saturation excess runoff can happen on the same slope in both cases slopes behave as a patchwork of runoff and runon areas the size of the runoff or runon patches is dependent on the climatological conditions these control the hydrological disconnection between different parts of the slopes hortonian and saturation runoff can both be generated and infiltrated downslope

interpreting the 137cs profiles observed in several small lakes and reservoirs in southern england abstract the depth distribution of bomb derived 137cs has been studied in cores collected from five small lakes and reservoirs with high sediment accumulation rates in southern england an empirical approach was employed to demonstrate the influence of the catchment derived 137cs input and the post depositional redistribution of 137cs on the 131cs profiles of the sediment cores by incorporating the remobilisation of 137cs and deposited sediment a catchment related 137cs lake deposition model has been used to interpret the 137cs inventories and concentrations in the lake and reservoir sediments in terms of sediment sources a clear linkage between the 137cs concentration in the lake sediment and that in catchment source soils has been established for the five water bodies estimates of the proportion of the total 137cs inventory of individual sediment cores derived from the catchments ranged between 57 and 97 these values emphasise the importance of the catchment derived contribution to the overall 137cs inventory of sediments in small lakes and reservoirs receiving significant sediment inputs from their catchments the estimates of sedimentation rates for the water bodies provided by the cores were also used to estimate the sediment yields from their respective catchments