u pb and th pb whole rock isochrons from metavolcanic rocks of the carolina slate belt felsic volcaniclastic rocks and massive pyrite of a part of the carolina slate belt in south carolina referred to as the haile brewer block seem to have remained closed systems with respect to u th and pb since 465 ma u pb and th pb whole rock isochrons indicate ages of 466 40 2 and 462 53 ma respectively the pb pb secondary isochron age of the volcaniclastic rocks is 455 ma because of the divergent ways in which u th and pb have behaved during the various alteration events that have affected the haile brewer block metamorphism post tectonic intrusion weathering the isochronous relationships most likely represent the emplacement age of the rocks the preservation of u pb and th pb isochrons is thought to be due to the originally glassy nature of the volcaniclastic rocks and to the relatively impermeable character of the rocks which may have been aided by the sealing of pore space by infiltration of penecon temporaneous silica rich hydrothermal fluids the u pb and th pb whole rock ages are considerably younger than the 550 ma age inferred from u pb zircon ages and ediacaran fossil assemblages for the slate belt in north carolina the younger ages agree however with the presence of sponge spicules no older than middle cambrian in the haile brewer block the younger age of the haile brewer block with respect to other parts of the carolina slate belt indicates that the belt is more complex than has been thought

is the central piedmont suture a low angle normal fault in the crystalline southern appalachians the carolina are terrane is in fault contact with the piedmont terrane along a seismically reflective surface dipping toward the hinterland and called the central piedmont suture the central piedmont suture may be interpreted as a thrust but existing data also support a silurian devonian normal slip origin 1 there are lower grade rocks in the hanging wall than in the footwall 2 a normal fault solution allows simultaneous metamorphism of the piedmont terrane and carolina terrane prior to their juxtaposition along the central piedmont suture 3 mineral ages in the piedmont terrane are older in the west than in the east consistent with an eastward progressive unroofing 4 along the western edge of the carolina terrane a linear belt of devonian subalkalic to alkalic granitoids and gabbro norites with low initial 87sr 86sr ratios may represent mantle derived magmas along the axis of rifting that are contemporary with major crustal extension the westernmost piedmont terrane includes the chauga belt the chauga belt comprises metavolcanic and metaplutonic units similar in rock type and age to those of the western carolina terrane chauga belt rocks are interpreted to be the westernmost exposures of the carolina terrane translated west on the lower plate by extension the piedmont and carolina terranes may thus compose a single lithotectonic element the piedmont terrane would represent the basement on which the arc was constructed the terrane was uplifted during extension along a major low angle normal fault recognized today as the central piedmont suture

the carolina terrane in northwestern south carolina u s a late precambrian cambrian deformation and metamorphism in a peri gondwanan oceanic arc the carolina terrane comprises an exotic volcanic island arc in the hinterland of the southern appalachian orogen the western portions of the carolina terrane consist of zoned mafic ultramafic plutonic complexes intruded into a pile of basalts and basaltic andesites this sequence of rocks has been interpreted to represent an episode of intra arc rifting prior to regional metamorphism and deformation new u pb zircon ages from the mean crossroads complex in northwestern south carolina along the central piedmont suture confirm relative ages inferred from detailed mapping two foliated metadiorites yield u pb dates of 579 4 and 571 16 ma interpreted to be crystallization ages a foliated metaquartz diorite yields a u pb date of 538 5 ma interpreted to be a crystallization age an undeformed unmetamorpbosed diorite intruding these metamorphosed zoned complex intrusive rocks yields an age of 535 ma hence we believe that intra arc rifting and regional metamorphism and foliation development both occurred between 580 and 535 ma while petrographic and ar ar studies support subsequent middle to late paleozoic regional metamorphic overprint s or at least static recrystallization and or uplift through hornblende biotite muscovite blocking temperatures for ar the 535 ma undeformed unmetamorphosed intrusion suggests late precambrian early cambrian regional metamorphism and deformation was the event responsible for the regional metamorphic fabric in this area of the piedmont these observations contradict the idea that this metamorphism and fabric development are related to presumed early paleozoic accretion of the carolina arc to laurentia as well as correlations with middle ordovician fabric elements in the eastern piedmont instead this fabric is interpreted to record a changing plate kinematics e g migration of triple junction or change in relative motion vectors during semicontinuous diachronous development of an island arc on the gondwanide margin

reprocessing and reinterpretation of cocorp southern appalachian profiles abstract reprocessing of cocorp southern appalachian data was focused on basic seismic evidence for continuation of sediments beneath a master decollement the most important evidence is a nearly continuous series of subhorizontal reflections extending from the valley and ridge province into the piedmont province continuity of subhorizontal reflections becomes tenuous in the inner piedmont careful reprocessing has yielded evidence for termination of strong reflections beneath the allochthon and the beginning of a relatively weak and complex series of events termination of sedimentary rocks beneath the piedmont is interpreted from true amplitude seismic data a zone of detachment continues southeast of the sediment termination as far as the master decollement root zone research on stacking velocities has indicated that complex velocity structures could create apparent low stacking velocities this phenomenon may occur in the charlotte belt of georgia bouguer gravity can be modeled as a former craton of normal density with an accreted margin of very slightly higher density variation in crustal thickness also contributes to the bouguer gravity gradient no continuous large scale overthrust is needed southeast of the interpreted master decollement root zone located beneath the kings mountain belt and charlotte belt

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

rotation of fabric elements in convergent shear zones with examples from the southern appalachians plane strain shear zones between rigid walls which do not rotate but which converge and move laterally relative to each other are here in referred to as convergent shear zones analysis of the deformation in convergent shear zones indicates the existence of two flow apophyses one parallel to the shear zone wall and the other inclined to the wall modeling of the development of fabrics in convergent shear zones indicates the occurrence of stable orientations in which s and c do not rotate and are oppositely inclined to the shear zone boundary the stable c orientation is parallel to the inclined flow apophysis and also is parallel to the approach velocity vector of the opposing walls of the shear zone if it can be demonstrated from field relationships that the walls of a shear zone were rigid and remained parallel then the occurrence of a flow apophysis inclined in the direction of shear is diagnostic of convergent shear s and c fabrics in the ridge road and gundy creek shear zones of the southern appalachian piedmont are interpreted to indicate a convergent shear regime with an approach velocity vector oriented 10 13 clockwise from the strike of the zones

ages of regional metamorphism and ductile deformation in the central and southern appalachians abstract a summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation the ca 480 435 ma taconic event affected most of the piedmont and blue ridge provinces the ca 380 340 ma acadian event was milder and was centered in the west central piedmont and eastern blue ridge the 330 230 ma alleghanian event exhibits an abrupt ductile deformation front in the eastern piedmont and extends an unknown distance eastward below the atlantic coastal plain

new field evidence for an exposure of the appalachian decollement at the east end of the pine mountain terrane georgia detailed field mapping at the east end of the pine mountain terrane in central georgia indicates that the box ankle fault is an 4 km thick ductile shear zone separating grenvillian basement of laurentian affinity in the footwall from allochthonous accreted terranes in the hanging wall fabric data from the box ankle fault indicate that it is a gently southeast dipping northwest vergent thrust fault recently discovered structural relations together with geochronological data indicate that the box ankle fault is of late paleozoic age we argue that the box ankle fault is a surface exposure of the appalachian decollement the east end of the pine mountain terrane may be the only place in the entire orogen where this fundamentally important structure is exposed for study

the geometrical relationship between the stretching lineation and the movement direction of shear zones abstract the geometrical relationship between foliations and lineations in shear zones is considered quantitatively assuming that the internal structures of shear zones have monoclinic symmetry the common practice of directly correlating the pitch or plunge of the stretching lineation with the obliquity of the shear direction is challenged it is the orthogonal projection of the stretching lineation on the shear zone boundary that is parallel to the shear direction a shear zone is parallel to a plane containing both the pole to the symmetry plane and the strike of the shear zone and the shear direction is parallel to the intersection of the symmetry plane and the shear zone boundary the symmetry plane is determined by the stretching lineation and the poles to the s foliation the implications of this study for the interpretation of shear zones are discussed with reference to an actual example

ocmulgee fault the piedmont avalon terrane boundary in central georgia the ocmulgee fault is a fundamental boundary within the piedmont of central georgia separating north american piedmont terrane rocks from exotic rocks of the avalon carolina terrane contrasts in stratigraphy metamorphic grade and aeromagnetic signature coincide with the fault trace the fault comprises a broad zone ca 2 km of foliation dipping steeply southeast and containing localized syn and post thermal peak right lateral strike slip shear zones oblique dextral convergence between the avalon and peidmont terranes most likely around 350 ma produced the steep zone and its attendant dextral shear zones steep foliation within the fault zone resulted in its predisposition to later faulting

generation segregation ascent and emplacement of alleghanian plutons in the southern appalachians the carboniferous permian alleghanian orogeny in the southern appalachians produced a distinctive 45 m y long intrusive event that formed a ne trending band of dispersed composite plutons covering 10 500 km 2 of these plutons 75 are metaluminous biotite or amphibole biotite granitoids with lower crustal sources and 20 are peraluminous biotite muscovite garnet or cordierite biotite granitoids with more evolved crustal sources the remaining 5 are gabbroids intermediate rocks and possible alkaline granitoids the granitoid to gabbroid intermediate rock area ratio is 180 1 the exposed intrusive rocks were produced at a relatively slow rate of 2 km 3 linear km m y along the orogen indicating an inability of the source to produce much melt inefficient melting mechanisms or difficulty of magma segregation and ascent the absence of spatial trends in rock composition and age of emplacement the small amount but relative abundance of the granitoids and coincidence with con

confirmation of the carolina slate belt as an exotic terrane an assemblage of middle cambrian atlantic faunal province trilobites has been found in the rocks of the carolina slate belt near batesburg south carolina geologic and paleomagnetic data suggest that the carolina slate belt and the adjacent charlotte belt constitute an exotic terrane that was accreted to north america in early to middle paleozoic time

the association of folds and veins in shear zones abstract paired hook shaped asymmetric folds with shared limbs cut by axial planar veins dikes or fractures are common in glaciers and rocks the sense of offset across the vein or fracture is characteristically opposite to that expected from the sense of fold asymmetry the kinematics of development of the folds and the relationship of the folds to the fractures or veins can be understood by considering the nature of glacial flow and by utilizing simple clay experiments in zones of simple shear dilational fractures may form at about 45 to the shear zone boundaries the perturbation of strain around such a fracture during its development and subsequent rotation and closure under continued deformation causes layers or pre existing foliation cut by the fracture to become folded thus folding is a consequence of the fracturing and not vice versa the precise shape of the fold depends on the nature of the perturbation and particularly whether or not the fracture remains for a time open or fluid filled and thus has walls unable to sustain a shear stress during vein rotation paired hook folds provide evidence for non coaxial strain and are good sense of shear indicators however not all folds with veins parallel to their axial surfaces form in the way described in this paper in some cases vein emplacement occurs late during fold development or post dates folding in these cases offsets along the veins are consistent with fold asymmetry

character of the alleghanian orogeny in the southern appalachians part iii regional tectonic relations geological and geochronological studies in the eastern piedmont of the southern appalachians have documented a polyphase late paleozoic deformational chronology d 2 d 4 that is contemporaneous with the alleghanian orogeny recorded in the western appalachian foreland the scale and vergence of d 3 anticlinoria in the eastern piedmont are similar to those of anticlinoria in the western appalachians which are related to ramping of underlying thrust surfaces we suggest that the appalachian decollement extends southeastward beneath the entire piedmont province and that all of the piedmont rocks were displaced at least 175 km northwestward relative to north america during the alleghanian orogeny late paleozoic deformational effects in the eastern piedmont thus are considered cogenetic with alleghanian foreland deformation we interpret the alleghanian orogeny to be the result of oblique dextral convergence and collision of gondwana and laurentia

character of the alleghanian orogeny in the southern appalachians part ii geochronological constraints on the tectonothermal evolution of the eastern piedmont in south carolina a nearly concordant u pb zircon age of 550 4 ma is interpreted to closely date crystallization of the epizonal little mountain metatonalite in the southeastern part of the charlotte belt in south carolina this confirms field studies which indicate that the charlotte belt contains a plutonic metaigneous complex that developed as a sub volcanic arc infrastructure contemporaneous with vulcanism manifested in the carolina slate belt both paleontological and geochronological controls indicate that the south carolina slate belt is mostly younger than 570 ma cambrian whereas the slate belt in north carolina and virginia is mostly of late proterozoic age a regionally significant mid paleozoic ca 340 360 ma thermal event is suggested by discordant 40ar 39ar whole rock age spectra of slate phyllite in the northwestern carolina slate belt and from hornblende in the southeastern charlotte belt it is uncertain if this event was associated with deformation in the eastern piedmont however mid paleozoic deformation has been previously documented elsewhere in the western piedmont a slightly disconcordant u pb zircon age of 317 4 ma is interpreted to closely date initial crystallization of the deformed edge field granite and confirms a record of late paleozoic penetrative deformation in the kiokee belt of south carolina u pb isotope data for the lake murray orthogneiss and clouds creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic precam brian source and then emplaced in the eastern piedmont at ca 315 ma prior to or during the early stages of the alleghanian orogeny the thermal maximum of alleghanian regional metamorphism amphibolite facies in the kiokee belt greenschist facies in the southeastern part of the carolina slate belt occurred during ca 295 315 ma during the late carboniferous and early permian the eastern piedmont experienced differential uplift erosion and relatively rapid postmeta morphic cooling isothermal surfaces were folded into an antiform synform antiform configuration corresponding to the kiokee carolina slate and charlotte belts respectively the geochronological data provide the following calibration for the late paleozoic deformational chronology recorded in the kiokee and carolina slate belts d2 lake murray deformation ca 295 315 ma d3 clarks hill deformation ca 285 295 ma and d4 irmo deformation ca 268 290 ma

cold core anticyclonic eddies south of the bussol strait in the northwestern subarctic pacific abstract summer hydrographic surveys from 1993 to 1997 in the area south of the kuril islands in the northwestern subarctic pacific showed the existence of anticyclonic eddies south of the bussol strait at almost the same location but with variable sizes and intensities depending on the year every eddy had a cold low salinity and low potential vorticity core suggesting a strong influence from the okhotsk sea water two formation processes and annual variations were found with satellite data analyses one is the case where eddies are locally formed south of the bussol strait and intensified from summer to fall with the supply of okhotsk sea water as observed in 1993 in the other case kuroshio warm core rings that had translated northeastward are arrested near the bussol strait and amplified with the supply of okhotsk sea water as seen from summer to autumn in 1995 in winter eddies tend to move northeastward with decay the 1992 eddy moved northeastward then northward in winter and was eventually

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

isotopic evidence for a tectonic boundary between the kings mountain and inner piedmont belts southern appalachians concordant u pb zircon ages of 320 ma for the deformed high shoals granite of the kings mountain belt kmb extend the range of known alleghanian late paleozoic deformation and metamorphism in the southern appalachian piedmont isotope systematics in kmb rocks suggest an affinity with terranes to the southeast rather than with the inner piedmont belt to the northwest lead isotope systematics in meta igneous rocks of the kmb suggest direct or indirect mantle derivation with little or no crustal contamination

interactive property of large thrust sheets with footwall rocks the sub thrust interactive duplex hypothesis a mechanism of dome formation in thrust sheets abstract recently acquired appalachian ultradeep core hole adcoh project site investigation seismic reflection data and geologic data from the appalachians and several other orogenic belts suggest an important mutually interdependent relationship exists between emplacement of large crystalline thrust sheets and the deforming foreland rocks beneath this relationship suggests isolated domes beneath crystalline thrust sheets may be produced by passive folding of the sheet as a result of formation of an antiformal stack duplex in the platform sedimentary sequence beneath suggestions that domes in crystalline thrust sheets formed by interference of late open folds is doubtlessly still valid in places but the platform duplex mechanism is probably also valid to explain the late doming of many crystalline and other large thrust sheets the dome beneath the shooting creek and brasstown bald windows in the adcoh site region is imaged as an antiformal stack duplex at depth the tallulah falls dome grandfather mountain and mountain city windows and smokies foothills duplex in the site region and elsewhere in the southern blue ridge are all late isolated domes and all are probably or demonstrably underlain by antiformal stack duplexes beneath the blue ridge piedmont composite crystalline thrust sheet the assynt window and footwall duplex benath the arnabol and moine thrusts in scotland and the engadine window in the alps may be similar structures

did the taconic appalachians continue into southern south america the appalachian mountains now terminating abruptly at the gulf of mexico coastal plain may have formerly continued into southern south america rocks forming the basement of the argentine andes can be interpreted as remnants of an early paleozoic orogen the famatinian belt not unlike the taconic appalachians both orogens are bordered to the west present coordinates by lower paleozoic carbonate platforms bearing the olenellid trilobite fauna that is characteristic of laurentia paleomagnetic and geologic data indicate that they could have formed as one continuous mountain chain possibly extending into antarctica during ordovician closure of an ocean basin southern iapetus between laurentia and gondwana the taconic and famatinian segments of the chain may have been truncated during late ordovician separation of laurentia and gondwana along the preexisting late neoproterozoic to cambrian rift system that initiated formation of the ouachita embayment and the southern margin of north america

paleomagnetism and 40ar 39ar ages from the carolina slate belt albemarle north carolina implications for terrane amalgamation with north america paleomagnetic and sup 40 ar sup 39 ar dating studies of late proterozoic metamorphic rocks from the carolina slate belt were undertaken to gain insight into the history of this suspect lithostratigraphic terrane geochronological data suggest a peak metamorphic age of ca 455 ma and a later thermal overprint at ca 185 ma thermal demagnetization indicates two magnetization components a low temperature component yields a pole close to 180 190 ma segments of the north american apparent polar wander path a high temperature component postdates folding and is inferred to have been acquired at ca 455 ma corresponding paleomagnetic pole is lat 20 sup 0 n long 80 sup 0 e although paleomagnetic data from the carolina slate belt remain too ambiguous for construction of a unique polar wander path consideration of available paleolatitudes suggests that the terrane may have been proximal to cratonic north america after ca 455 ma this result contrasts markedly with high southerly ordovician paleolatitudes inferred from paleomagnetic studies within central and northern appalachian terranes

ordovician docking of the carolina slate belt paleomagnetic data paleomagnetic results from eight sites in argillaceous metasediments from union county north carolina in the central carolina slate belt yield a consistent high blocking temperature magnetization component the precision of the mean declination and inclination of all site means is maximized at 50 tilt correction and the improvement in grouping relative to 0 and 100 tilt correction is significant at the 95 confidence level this tends to indicate that the high blocking temperature component was acquired during folding the metamorphism and deformation in this area are rather well constrained by recent 40ar 39ar data to the late ordovician 450 ma we therefore interpret the computed pole position 29 6 n 122 1 e 95 5 11 as late ordovician in age and note that it lies close to some of the late ordovician poles for cratonic north america the paleolatitude 22 2 s of the sampling site is certainly unlike those derived from armorica and gondwana for this time interval and is rather similar to that proposed for the iapetus coast of laurentia during the late ordovician indeed the magnetization and deformation may be contemporaneous with the docking of the carolina slate belt onto the laurentian continent

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

experimental investigations of the soil water characteristics of a volcanic soil rain induced landslides are common around the world to analyse transient seepage and to predict pore water pressure distribution in unsaturated slopes subjected to rainfall infiltration it is essential to study soil water char acteristics and water permeability functions the soil water characteristic curve swcc is a relationship between suc tion and water content or degree of saturation conventionally only the drying soil water characteristic curve of soil specimens is determined in a pressure plate extractor without the application of any external stress in this paper the influences of initial dry density and initial water content history of drying and wetting soil structure and the stress state upon the desorption and adsorption soil water characteristics of a completely decomposed volcanic soil in hong kong are examined and discussed the experimental results presented are obtained by using a conventional volumetric pressure plate extractor and a newly modified one dimensional stress controllable pressure plate extractor with deforma tion measurements the swcc of a recompacted specimen is very different from that of a natural specimen with the same initial soil density and initial water content the swcc of the recompacted specimen is highly dependent on the history of drying and wetting the rates of desorption and adsorption are substantially higher at the first drying and wetting cycle than at the second drying and wetting cycle the size of the hysteresis loop of the recompacted specimen is considerably larger than that of the natural specimens the swcc of soil is stress state dependent for recompacted specimens subjected to different stress states the higher the applied stresses the lower the rate of desorption and the smaller the size of the hysteresis loops however for natural specimens the size of the hysteresis loops seems to be independent of the stress state under a higher applied stress natural specimens exhibit lower rates of desorption and adsorption

bouguer gravity in northeastern georgia a buried suture a surface suture and granites a bouguer gravity map of an area of northeastern georgia encompassing parts of the inner piedmont charlotte belt and carolina slate belt has been constructed from gravity stations spaced 2 km apart anomalies in the charlotte carolina slate belts are due to metamorphosed mafic rocks in the upper crust depth extent

structural analysis of the carolina inner piedmont terrane boundary implications for the age and kinematics of the central piedmont suture a terrane boundary that records paleozoic laurentia gondwana interactions new field mapping along the carolina inner piedmont terrane boundary in south carolina and eastern georgia reveals preaccretionary synaccretionary and postaccretionary faults the dextral strike slip lowndesville shear zone is adjacent to a 50 km long segment of the terrane boundary however the lowndesville shear zone is correlated eastward with the dextral strike slip beaver creek shear zone which is within the carolina terrane and predates 415 ma the lowndesville shear zone is overprinted by a dextral strike slip phyllonite zone named the deal creek shear zone the deal creek shear zone is correlated eastward with the gold hill silver hill shear zone which is also within the carolina terrane and records dextral strike slip motion between 400 and 325 ma the cross anchor and mulberry creek faults both truncate the lowndesville and the deal creek shear zones and form the terrane boundary the mulberry creek fault probably of triassic jurassic age juxtaposes the lowndesville shear zone adjacent to the carolina inner piedmont terrane boundary west of waterloo south carolina the cross anchor fault is the terrane boundary east of waterloo south carolina and forms the southeastern boundary of the whitmire reentrant crosscutting relationships indicate that the cross anchor fault is the oldest fault which juxtaposes the carolina and inner piedmont terranes in the study area these structural interpretations and available geochronological data indicate that the cross anchor fault is a 325 ma thrust fault and may be the central piedmont suture an early alleghanian suture resolves the problem of inserting the carolina terrane into the western iapetus ocean

analogous tectonic evolution of the ordovician foredeeps southern and central appalachians new stratigraphic data suggest that the diachronous evolution of the ordovician foredeeps in the southern and central appalachians was remarkably similar stratigraphic features that characterize the middle ordovician sevier basin in tennessee and the middle and late ordovician martinsbuirg basin in pennsylvania are in identical ascending order 1 disconformity on the knox group beekmantown group 2 shelf carbonates 3 slope deposits 4 submarine fan turbidites and 5 contourites and muddy turbidites we propose that diachronous attempted subduction of the north american craton beneath southeastern microplates and or volcanic arcs resulted in uplift and erosion of the western shelf followed by its rapid subsidence basinward migration of eastern and northeastern terrigenous source areas and associated submarine fan turbidites resulted from continued convergence and filled the basins finally tectonic stabilization and lowering of the source area is recorded by contourites and muddy turbidites the evolutionary model proposed for the sevier and martinsburg basins closely resembles present day tectonics of the timor foredeep and the adjoining sahul shelf north of australia similar comparisons have also been made for ordovician basins in the northern appalachians analogous tectonic mechanisms therefore appear to have operated diachronously along the eastern margin of north america from tennessee to new england and possibly to newfoundland during ordovician time

biogeographical significance of cambrian trilobites from the carolina slate belt abundant middle middle cambrian trilobites of the ptychagnostus atavus interval zone are described from the upper asbill pond formation informal name near batesburg south carolina the fauna containing at least nine species has strong affinities with cool water faunas of both armorica and baltica but little affinity with warm water shelf faunas of laurentia this is compatible with previous conclusions that the carolina slate belt is an exotic terrane that was accreted to north america during the early or middle paleozoic further evaluation however introduces an alternative possibility that the fauna could have lived in deep cool water environments along the periphery of laurentia and subsequent displacement need not necessarily have been great combined faunal and stratigraphic components of the carolina slate belt do not precisely match those of any known region but may be closest to those of bohemia although a southpolar location in proximity to armorica baltica and gondwana seems likely a definitive placement in a reconstruction of the cambrian world is not yet possible included in the trilobite fauna are the agnostoids hypagnostus mammillatus h parvifrons peronopsis fallax ptychagnostus sp and tomagnostus fissus the polymeroids include agraulos sp paradoxides cf polonicus paradoxides sp and skreiaspis sp