reconstructing the formation and land use history of the mound 2 depression at rio viejo oaxaca mexico archaeological and geoarchaeological work in the lower rio verde valley oaxaca mexico reveal a varied spatial relationship between the prehistoric inhabitants and this dynamic floodplain region over the last 3000 years significant demographic expansion occurred by the late formative period following floodplain aggradation resulting from a change in stream hydrology and morphology during the classic and postclassic periods major shifts in settlement and land use occurred primarily from the productive floodplain to the piedmont the archaeological site of rio viejo has played a pivotal role in the political and social history of the valley archaeological data indicate the site was occupied from the middle formative to the early postclassic and was an urban center and the political seat of the region during the terminal formative and again in the late classic four large depressions are associated with mounded architecture at the site we collected paleoenvironmental and geoarchaeological data from the mound 2 feature a synthesis of this multi proxy data has enhanced our understanding of site formation occupation and land use from the late formative to postclassic times the analysis indicates that the depression associated with mound 2 was originally a borrow pit on the floodplain that was enhanced and augmented by monumental mound building the area around mound 2 was the focus of domestic and agricultural use during the terminal formative an apparent cessation of activity around mound 2 occurred during the early classic which is consistent with a significant contraction in population at the site at this time activity resumed at mound 2 in the late classic and continued until at least the early postclassic these changes in occupation history appear to have resulted from political developments within the valley

thermal consequences of mantled gneiss dome emplacement abstract bodies of rock within the crust that have higher thermal conductivities than surrounding rocks serve as conduits for the diffusive flow of heat the resultant focusing of heat creates an apparent contact metamorphic aureole in the surrounding rocks without the high conductivity rocks being a heat source themselves two dimensional thermal models of mantled gneiss domes are used to consider these effects and their role in the thermal histories of metamorphic belts the complex metamorphic histories and patterns observed around gneiss domes may be the result of the emplacement of relatively high thermal conductivity rocks dome cores into lower thermal conductivity metasediments mantling strata the degree of the thermal anomaly is primarily affected by the conductivity contrast but is also dependent upon the velocity of emplacement crustal level and heat flux many of the metamorphic isograd features and pressure temperature time paths that are observed around mantled gneiss domes can be explained merely by the emplacement of high conductivity rocks into low conductivity rocks without invoking additional heat sources or significant post metamorphic deformation

archaic settlement in el tebernal veracruz first insights into paleoenvironmental conditions and resource exploitation abstract we present first results about an archaic 9000 4000 bp site el tebernal in the eastern part of mexico at el tebernal a set of lithic artifacts was found associated with a paleosol lower paleosol and buried by an upper paleosol and a modern soil the artifacts are made from local limestone and chert selected paleosol properties were evaluated total organic carbon grain size distribution carbon stable isotope composition magnetic susceptibility and micromorphology that provide information about paleoenvironmental conditions the lower paleosol is composed of the following horizons 3e 3eb 3be 3btg1 3btg2 3c while the upper paleosol only has a 2a horizon the lower paleosol is very well developed with in situ clay coatings moderate weathering of primary minerals and a matrix free of carbonates although the alluvium in the lowermost part of the profile contains a mixture of limestone and volcanic materials the entire sequence is covered by the modern soil mantle which is formed by an a horizon radiocarbon ages determined on soil organic matter from the 3btg1 and 2a horizons were 5580 to 5320 cal bp and 2350 to 2320 cal bp respectively we interpret the age of 3btg1 as close to the final stage of soil formation because the organic matter content in this horizon is illuviated pedogenesis likely began sometime prior to the reported age in the early holocene the paleosol properties indicate a long period of landscape stability n 10 3 10 4 years under humid and temperate conditions it is probable that volcanic events from pico de orizaba located several kilometers from el tebernal affected this stability one of the last eruptions produced a block and ash flow of dacitic composition dated at 4100 bp that contributed to the end of pedogenesis the upper paleosol 2a horizon as well as the modern soil contain ceramics from the post classic period ad 900 1521 the profile is cut by a channel and infilled by a dark material that dates to 1140 to 970 cal bp ad 810 980 in consequence the area has been strongly affected by human occupations during the holocene we suggest these ceramic societies caused erosion and activation of geomorphic processes

early holocene soil cryoturbation in northeastern usa implications for archaeological site formation abstract the study of buried soil archives in alluvial settings can be used to characterize floodplain and terrace habitats and complement other paleoenvironmental and archaeological archives this study examines the early holocene alluvial paleopedology along the delaware river valley in the northeastern usa chronological and alluvial stratigraphic data show that a widespread loam alluvial paleosol formed from 10 7 to 9 3 ka herein referred to as the jennings lane pedocomplex jlp the jlp at the jennings lane locality along the delaware river nj is a loam to silt loam soil that formed on mixed alluvium and windblown and or reworked dust likely sourced from nearby periglacial fines this finding supports previous interpretations of late quaternary dust deposition and reworking in the region fragic properties e g firm peds with brittle manner of failure and rapid slaking in water and cryogenic micromorphological features lenticular pores stone jacking and shattered grains present within the jlp suggest cryoturbation soil mass balance modeling suggests that the strain in immobile elements ti and zr show a dilation collapse profile these data indicate that organic matter and or dust addition and freeze thaw created soil dilation at the jlp paleosurface mass balance additions in fe k and mg are consistent with illuviated fe rich clay coatings present in thin section the x ray diffraction results show that these clays are illite vermiculite and kaolinite paleosol data presented here suggest that the jlp was overprinted by later pedogenic processes during the middle holocene ti na shows minimal loss throughout much of the profile although rapid thaws may have promoted downward translocation of fines the cold environment impeded base loss through either minimal release of cations from primary minerals or negligible water flux as suggested by ti na profiles and gains in ti k and ti mg this silt rich jlp pedofacies experienced minimal chemical depletion over the course of 1200 3500 years this cold climate weathering coincides with rapid temperature fluctuations 10 5 9 3 8 2 ka during the early holocene in northeastern usa this soil cryoturbation evidence has archaeological implications as well the cryoturbation in this early holocene pedocomplex suggests that vertical and lateral artifact redistribution is possible archaeologists should use caution when interpreting archaeological stratigraphy and intrasite artifact patterns at mid to high latitude archaeological sites

geoarchaeology and paleoenvironmental context of the beacon island site an agate basin paleoindian bison kill in northwestern north dakota usa abstract a geoarchaeological investigation that included soil stratigraphic and paleoecological analyses was conducted at beacon island located in the flood pool of lake sakakawea in northwestern north dakota beacon island is a multi component archaeological site that includes an agate basin paleoindian component consisting of the butchered remains of at least 29 bison antiquus along with projectile point fragments and other artifacts the bison bonebed is a product of a single kill at ca 10 300 b p and is buried in a shallow kettle basin the basin formed around 16 000 15 000 b p and initially trapped loess comprising the mallard island member of the oahe formation other members of the oahe formation subsequently filled the basin conditions probably were relatively dry when the mallard island member aggraded but by ca 10 300 b p paludal deposits comprising the aggie brown member began to accumulate in the basin indicating a shift to wetter conditions based on phytolith and stable carbon isotope data cool season c 3 prairie species dominated the site at the time of the bison kill and the micromammal faunal assemblage suggests that this boreal grassland may have been punctuated by stands of shrubby vegetation slight warming and drying occurred soon after ca 10 300 b p indicated by relatively higher 13 c values determined on soil organic matter and a significant increase in concentrations of microscopic particulate charcoal and drought resistant stipa type phytoliths but paludal deposits continued to aggrade resulting in deep burial of the bonebed sedimentation was relatively slow in the basin allowing soil development to keep up with deposition this cumulization process resulted in the formation of an overthickened a horizon in the aggie brown member typical of the leonard paleosol aggradation of the aggie brown member ceased by ca 8000 b p and loess comprising the pick city member began accumulating soon after that time likely marking the initiation of the warm dry altithermal climatic episode isotope and phytolith data also point to a warmer and probably drier climate after 8000 b p indicated by higher 13 c values and the appearance of warm season c 4 chloridoids at the site hence the agate basin occupation coincided with the coolest and perhaps the wettest climatic episode recorded in the sampled deposits however it is likely that the people associated with the agate basin culture at beacon island did not experience environmental conditions dramatically different from the modern conditions at the site

geoarchaeological dating of holocene stream terraces along the san pedro river southeastern arizona usa three pleistocene and four holocene floodplain terraces were differentiated along the san pedro river in southeastern arizona during a geological mapping project conducted by the arizona geological survey we used archaeological chronometric data to refine age estimates for the holocene surfaces that had been initially based on only geomorphic and pedologic criteria eight archaeological sites deeply buried in the fill of the most extensive holocene terrace map unit qy2r yielded 10 radiocarbon dates and temporally diagnostic san pedro complex 3150 1900 cal bp artifacts twenty sites recorded on the surface of qy2r terrace treads contained numerous temporally diagnostic hohokam 1950 500 cal bp ceramic sherds and features the age constraints provided by these archaeological materials suggest that the qy2r terrace fill was deposited primarily between 4500 and 1000 cal bp with only a thin veneer of flood deposits added between 1000 and 100 cal bp this late holocene to historical 4500 100 cal bp age estimate is consistent with other alluvial histories in the greater gila river drainage basin and supplants our initial geologically based latest holocene to historical 2000 cal bp qy2r age estimate the archaeologically derived maximum age estimate for qy2r also provides a minimum age for the topographically higher and older qy1r terrace prompting us to revise our original early to late holocene age estimate for qy1r to an early to middle holocene age range of 11 500 4500 cal bp the post a d 1850 historical age we originally proposed for the qy3r terrace deposits inset into qy2r however is consistent with the presence of four historical period surface sites and a concordant absence of surface and buried prehistoric sites

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

late quaternary landscape evolution soil stratigraphy and geoarchaeology of the caprock canyonlands northwest texas usa abstract in northwest texas usa between the southern high plains to the west and the central lowlands to the east lies a geographic boundary known as the escarpment breaks or caprock canyonlands the canyonlands contain abundant springs lithic resources shelter and plant and animal food sources that attracted hunter gatherer groups a geoarchaeological study was conducted in the canyonlands to determine the effects of late quaternary landscape evolution especially intensive erosion on the region s archaeological record geomorphic and stratigraphic field research and a total of 95 new radiocarbon age determinations 94 of which were determined on paired samples aid in reconstructing an understudied dynamic and erosive landscape and explain how the landscape has changed the pattern is similar to reported data from the central plains and western rolling plains but dissimilar to the southern high plains high rates of erosion and geological controls on the south fork of the double mountain fork of the brazos river a 4th order stream have hindered the discovery of deeply buried soils and in situ paleoindian artifacts and features but a late holocene pedocomplex is relatively intact in valley fills beneath remnants of the t 2 terrace of the south fork the eroding slopes near the edge of the caprock escarpment exposed a record of in situ archaic to protohistoric aged materials the eroding slopes should be targeted for future quantification of erosion and archaeological preservation bias for the canyonlands

the timescale and mechanism of granulite formation at kurunegala sri lanka incipient charnockite formation at kurunegala in sri lanka is characterized by the growth of orthopyroxene at the expense of amphibole and biotite in an originally homogeneous gneiss mineral equilibria in the charnockite assemblage record pressure temperature p t conditions of 738 60 c and 6 9 1 2 kbar at 17 0 1 2 log fo2 and ah2o 0 18 0 16 wholerock trace element and isotopic measurements show that charnockite formation was accompanied by a systematic depletion of sm rb pb u sr nd with a fractionation of rb sr sm nd and th u ratios and crystallization of the charnockite assemblage at 535 5 ma major element fe mg ca and sm nd equilibration between minerals occurred at 524 9 ma whereas pb and rb sr underwent continued exchange to 501 5 ma and 486 1 ma respectively trace element data for both amphibolite and charnockite minerals show that depletion on a whole rock scale can be accounted for either by changes in mineral modes or trace element abundances within the immediate area of dehydration the fractionation of sm nd on a whole rock scale is controlled by the breakdown of amphibole without the growth of a major new host phase for sm in the charnockite rubidium and sr are dependent on the relative behaviour of biotite plagioclase and alkali feldspar modelling of dehydration melting involving the breakdown of amphibole biotite and alkali feldspar reproduces the observed sm nd and rb sr fractionation and indicates the loss of small melt fractions on a cm scale from the charnockite these observations suggest that partial melting is the most plausible means of effecting both the dehydration and depletion that accompanies charnockite formation

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

hydraulic back flood model for the archaeological stratigraphy of the connecticut river alluvial lowland central connecticut usa abstract state mandated archaeological investigations associated with urban renewal in downtown hartford led to the development of a mechanistic model for holocene floodplain sedimentation in central connecticut our model is based on historic flood hydrometeorology and geomorphologic mapping the lithologic magnetic pollen and archaeological stratigraphy exposed in sixteen deep boreholes and 24 hydraulic push cores the chronology provided by sixteen ams radiocarbon ages and diagnostic historic artifacts ranging from 10 030 cal bp to the present we conclude that the alluvial stratigraphy in this part of the lowland resulted from bottom up changes in hydraulic ponding at a bedrock outlet rather than from top down responses of the watershed to changes in climate vegetation or human activity our model provides a geologically based time space framework for the distribution of known archaeological sites and carries implications for future research

response of leaky aquifers to earth tides interpreted with numerical simulation abstract the response of aquifers to earth s solid tides earth tides has increasingly been used as a tool for monitoring the hydraulic properties of groundwater systems recent studies of the tidal response of the arbuckle aquifer opened to a usgs deep well in oklahoma wang et al 2018 barbour et al 2019 which has been injected with an enormous amount of toxic wastewater showed evidence that this aquifer may be leaking quantitative interpretation of the tidal response of this aquifer was made with a one dimensional analytical solution wang et al 2018 that showed that substantial leakage is occurring however the analytical model has inherent simplifications such as conductivity isotropy small aquifer thickness absence of aquitard storage and no basement leakage in this study we revisit the tidal response of leaky aquifers with a finite element multi layered model where such simplifications are removed we found that the simplifications in the analytical model lead to overly conservative estimates of leakage we revisit the tidal response of the arbuckle aquifer in oklahoma with the numerical simulation and estimate an average vertical hydraulic conductivity of 2 10 6 t o 7 10 5 m s for the aquitard overlying the arbuckle thus the aquitard above the arbuckle is not confining at this location but is as conductive as the aquifer itself given the fast rise of fluid level in many arbuckle wells in response to the injection of hundreds of millions of barrels of wastewater into this aquifer across oklahoma and kansas the present result calls for vigilant monitoring of leakage of wastewater from the arbuckle aquifer into the overlying freshwater reservoirs and the surface environment plain language summary earthquakes can damage the confinement of groundwater aquifers and thus can cause seismic hazard by letting freshwater in some aquifers to be contaminated or stored toxic wastewater in other aquifers to leak out into the environment thus it is important to monitor possible leakage of aquifers in earthquake countries analysis of the aquifer response to earth s solid tides in a usgs deep well in oklahoma wang et al 2018 barbour et al 2019 which has been used as the repository of an enormous amount of injected toxic wastewater shows that the aquifer may be leaking an analytical solution wang et al 2018 that contains several simplifications was used to quantify the aquifer leakage from the tidal response here we use a two dimensional multilayered numerical simulation without these simplifications to explore the limitations of the analytical model we find that aquitard storage and basement leakage have important effects on the tidal response of aquifers and the omission of these factors in the analytical solution may have caused underestimation of the aquifer leakage we then apply the numerical model to interpret the tidal response of water level documented in a usgs deep monitoring well installed in the arbuckle aquifer in oklahoma where an enormous amount of toxic wastewater has been stored with reasonable estimates of the aquitard storage our simulations yield an estimate of 2 10 6 t o 7 10 5 m s for the vertical hydraulic conductivity of the aquitard thus the aquitard is not at all confining but is as conductive as the aquifer itself given the fast rise of fluid level in many arbuckle wells in response to the injection of hundreds of millions of barrels of wastewater into this aquifer across oklahoma and kansas the present result calls for vigilant monitoring of leakage of wastewater from the arbuckle aquifer into the overlying freshwater reservoirs and the surface environment

holocene mississippi river floods and geoarchaeological site formation processes in the sny bottom western illinois usa abstract holocene alluvial deposits are well represented in the sny bottom a reach of the mississippi river in western illinois characterized by the presence of a long anabranch channel the sny prior to its engineered confinement the flood stage mississippi functioned as an anastomosed system comprised of many secondary landscape elements hierarchically arranged to distribute water out across a broad floodplain radiocarbon dated stratigraphic sequences are used to reconstruct the geological history of this river reach as it metamorphosed from a sandy late pleistocene braided floodplain into a system dominated by mud by 7400 cal bp the mississippi migrated to its present position and began to build the natural levee it would use for the remainder of the holocene major subsequent geomorphological adjustments to the system resulted from large floods at ca 6900 4900 3300 and 2000 cal bp valley fill is a complex arrangement of individual sedimentary bodies that accumulated at highly variable rates vertical accretion by sedimentation and soil upbuilding acted together to preserve numerous buried archaeological sites of all ages

the thermotectonic evolution of a proterozoic low pressure granulite dome west uusimaa sw finland three fold generations have been recognized in svecofennian rocks 1 800 ma from west uusimaa sw finland the first one f1 might be related to thrusting and imbrication tectonics at plate collision contacts the main generation f2 is due to a n s horizontal crustal shortening which created at first e w trending upright folds in the whole region and later tightened these f2 folds in the western part of the belt whereas conjugate shear zones and tectonic lenses of competent rock bodies developed in the eastern part simultaneously the metamorphic conditions rose from amphibolite to granulite facies in this eastern part which is known as the west uusimaa complex the amphibolite to granulite facies transition zone along the western boundary of the granulite facies complex is studied in detail a number of prograde mineral reactions are telescoped in this transition zone the breakdown of biotite and amphibole to ortho clino pyroxene in metaigneous rocks the appearance of garnet in cordierite bearing metapelites and the appearance of scapolite in calcareous rocks distinct mineralogical changes also occur in this zone which cross cuts all major structures and rock units and are only affected by late f3 folding open disharmonic folds with approximately n s trending axial planes and young shear zones associated with pseudotachylite generation the absence of any evidence of block faulting and tilting of the crust that could be associated with the granulite complex suggests that the whole region represents one crustal level

short term occupation surfaces in the lower ohio river valley exposing more of the late holocene hidden record as in other larger river valleys holocene alluvial deposition in the lower ohio river valley created a sampling bias towards certain prehistoric archaeological sites by burying them too deep to be accessed by conventional archaeological methods alternatively archaeological site types that do not leave a large signature i e a large sample of artifacts may also be obscured since they are not associated with recognizable geomorphic or soil development features such as a buried a horizon this obscuration has led to an incomplete record of the region s prehistory to better understand the age and type of prehistoric sites that may be buried within this alluvial landscape it is necessary to understand the structure and history of the alluvium in the valley this can be done by reconstructing the chronological development of alluvial deposits and the soils that formed in them regional models for the age and development of ohio river valley alluvium and the cultural deposits they may contain have been previously developed but must be continuously reviewed and revised as to their applicability to all and any alluvial packages found within the lower ohio river valley this study tests and expands some of these models through the investigation of an alluvial landscape near the confluence of the ohio and great miami rivers in indiana an age based landscape reconstruction which focuses on late holocene alluvium is presented cultural deposits can be linked to brief stability periods within alluvial packages stability periods that were too brief to have formed an a horizon this study shows that short term or ephemeral prehistoric occupations may co occur with periods where the surface of an alluvial landscape or landform was geomorphically stable for a brief period identifying these short term stable surfaces could likely lead to the better identification of underrepresented prehistoric cultural components or archaeological site types and help to reduce sampling bias in the regional prehistoric record

thermobarometry in granulites pitfalls and new approaches abstract computer models of cooling granulite facies rocks with the assemblage garnet biotite sillimanite k feldspar plagioclase quartz are presented that incorporate simultaneous reaction net transfer and exchange and multicomponent diffusion in garnet in models where cooling is accompanied by exchange reactions plus diffusion only the calculated garnet core matrix biotite temperature is always lower than the metamorphic peak by an amount that depends on the cooling rate the size of the garnet and the volumetric ratio of garnet to biotite maximum calculated core temperatures of approximately 700 750 c are to be expected from typical granulite facies garnet biotite assemblages and calculated core temperatures can easily be as low as 600 c in models where both net transfer and exchange reactions are possible calculated garnet core matrix biotite temperatures are typically higher than the metamorphic peak temperatures by more than 150 c for large garnets r 2 mm but may be lower than the metamorphic peak for small garnets r the composition of matrix plagioclase in equilibrium with garnet is very sensitive to the amount of modal plagioclase that reacts and hence calculated p t trajectories are very sensitive to the petrologic interpretation of this recrystallization history for models in which all the modal plagioclase reacts the core and rim pressures may be faithfully recovered provided that the temperature estimate for the core is reliable for models in which only a small percentage of the modal plagioclase reacts very small modal amounts of plagioclase may be in equilibrium with garnet rim which if incorrectly interpreted may lead to grossly erroneous p t path interpretations a method to test an inferred p t path model is presented that involves attempting to match the observed garnet and plagioclase zoning information with a forward model that involves simultaneous reaction and diffusion an example from western new hampshire usa is presented that closely matches the measured profile

contrasting styles of taconian eastern acadian and western acadian metamorphism central and western new england the two major early to middle palaeozoic tectonic metamorphic events in the northern appalachians were the taconian middle to late ordovician in central to western areas and the acadian late silurian to early middle devonian in eastern to west central areas this paper presents a model for the acadian orogenic event which separates the acadian metamorphic realm into eastern and western belts based on distinctively different styles we propose that the acadian metamorphism in the east was the delayed consequence of taconian back arc lithospheric modification east of the taconian island arc thick accumulations of late ordovician and silurian sediments coupled with plutons rising along a magmatic arc produced crustal thermal conditions appropriate for anomalously high t low p metamorphism accompanied by major crustal anatexis in this zone upward melt migration was coupled with subsequent e w crustal shortening possibly due to outboard collision with the avalon terrane to produce mechanical conditions that favoured formation of fold and thrust nappes and resultant tectonic thickening to the west and probably to the east as well the basis for the distinction between the eastern and western acadian events lies in the contrasting styles of metamorphism accompanying each evidence for contrasting metamorphic styles consists of 1 estimated metamorphic field gradients mfgs based on thermobarometric studies and 2 petrological evidence for contrasting p t trajectories west of the acadian metamorphic front the taconian zone has an mfg in which peak temperatures of 400 600 c were reached at pressures of about 4 6 kbar with both p and t increasing to the east near its western edge the western acadian metamorphic overprint has a similar mfg to the taconian and is mainly discriminated by 40ar 39ar dating and microtextural evidence east of this narrow zone the western acadian overprint is characterized by progressively higher temperatures 600 725 c and pressures 6 5 10 kbar or more to the east yielding an overall mfg that lies along or slightly above the kyanite sillimanite boundary on a p t diagram there is little or no plutonism accompanying western acadian metamorphism in contrast thermobarometry in the eastern acadian east of the bronson hill belt yields high t intermediate p conditions for the highest grade rocks known in new england t 650 750 c p 4 5 6 5 kbar for granulite facies assemblages which apparently formed along an anticlockwise p t path the bronson hill belt lies geographically between the eastern and western acadian zones and shows transitional petrological behaviour anomalously high temperatures at intermediate pressures but a clockwise path with decompression cooling radiometric dating indicates peak taconian conditions may have been achieved as early as 475 ma in the taconian hinterland and as late as 445 ma in the taconian foreland including the taconic allochthons eastern acadian magmatism may have started as early as 425 ma and most nappe stage deformation and metamorphism in the eastern acadian zone appears to have ended by about 410 ma tectonic thickening in the western acadian including the western counterparts of the nappe stage deformation documented in the eastern acadian must pre date attainment of peak metamorphic conditions dated at 395 385 ma dome stage deformation clearly post dates peak metamorphism and deforms metamorphic isograds the end of western acadian deformation is well constrained by 370 375 ma radiometric ages of late pegmatites and granitoids which cross cut all structures

a 9000 year record of vertical and lateral accretion on the floodplain of the lower thames river southwestern ontario canada and implications for archaeological research abstract results of ground penetrating radar and grain size analysis of sediments from three 5 7 m long cores generally support a classic fining up point bar model of floodplain development on a reach of the lower thames river a single thread meandering channel that flows southwest into lake st clair bankfull discharge 411 m3 s 1 four radiocarbon dates on organic material recovered from cores indicate that floodplain development in this reach occurred over at least the past 9000 years these results are not typical for southern ontario channels previous studies have shown that some other large rivers in southern ontario have low energy cohesive bank channels with floodplains strongly dominated by vertical accretion the distribution of culturally diagnostic archaeological artifacts on the floodplain surface dating back to the middle archaic period but mostly confined to the early woodland period or later suggests that human settlement of the floodplain was restricted to the later holocene the observation that a middle archaic site component is located in what should be a younger part of the floodplain challenges the notion that a simple lateral channel migration occurred with orderly channelward emplacement of sediment by the river there is a possibility that the channel was anabranching in this reach of the river

geoarchaeology of the falls of the ohio river quaternary landforms at the falls at the narrowest point in the lower part of its valley the ohio channel falls through a length of rapids between louisville ky and new albany in known as the falls of the ohio below and above the falls area a ridge and swale topography characterizes the late pleistocene to late holocene alluvial landforms recording the shifting pattern of the channel and dictating the location of age based cultural materials this geoarchaeological study looks at four distinct landforms at the falls of the ohio on both the northern and southern banks in order to ascertain the development of holocene alluvial landforms in this area investigations undertaken recently within the falls of the ohio region at the newcomb 12cl2 m kraft 12cl935 and shippingport 15jf702 sites as well as information gained from prior excavations at the old clarkesville site 12cl1 have provided the necessary insight into the development of the individual bars that these four sites where found lying upon texture elevation and temporal comparisons of these four alluvial bars have allowed for a generalized sequence of bar development to be formulated at the falls forming as a mid channel bar the old clarkesville is the oldest landform dating to the early holocene this was followed by the middle holocene m kraft bar forming a side channel bar to the north and the similarly aged shippingport bar on the southern bank of the channel the newcomb bar formed last in the late holocene filling in the swale or channel between the old clarksville and m kraft bars and allowing the formation of a single floodplain surface this study shows a general conformity to other geoarchaeological models and patterns in the region and as such it appears that the falls of the ohio has had little effect on the overall natural and cultural deposition in the region the exploration of these landscapes helps to expand on the regional synthesis of the understanding of the prehistoric cultural period deposits they hold

the cultural nature of tephra problematic ecofacts and artifacts and the baru volcano panama abstract this paper presents data from archaeological stratigraphy and lacustrine core samples containing tephra from the baru volcano in western panama the discussion seeks to refine the understanding of medial tephra deposits near baru in relation to the eruption history indicated by geological palaeoecological and archaeological data a primary goal of this fieldwork is the identification and correlation of tephra from major baru eruptions encountered in archaeological contexts by their lithology stratigraphic position and mineralogy without resorting to geochemical fingerprinting the intention is to develop a cost efficient and reproducible means of utilizing tephra as a chronostratigraphic marker in archaeological contexts and examine the intersection of human life with volcanic events and dynamic environments tephra in archaeological contexts can have ambiguous placement between ecofact and artifact as is the case with a small number of crude tephra sculptures in my excavated material and that of a seminal prior study while the research project utilizes visible tephra layers not cryptotephra by all means the tephra data prove to be cryptic engagement with the imperfection entailed in meshing multidisciplinary data sets and different scientific communities with interests in tephra particularly in lesser studied regions is posited as a total view of tephra

early holocene alluvial stratigraphy chronology and paleoindian early archaic geoarchaeology in the loup river basin nebraska u s a abstract the preservation of alluvium dictates the discovery of archaeological sites in valleys we address two questions in our study of the loup river basin in the midcontinent of north america 1 what is the alluvial chronology of the loup river basin between about 10 300 and 7700 bp and 2 what is the potential for preservation and exposure of paleoindian and early archaic sites cleaned cut banks walls of backhoe trenches and archaeological test units cores collected with a trailer mounted giddings soil probe and bucket auger samples were described buried a horizons organic enriched alluvial strata peat and charcoal were sampled for radiocarbon dating dating was supplemented by temporally diagnostic cultural materials we recognize the absence of 14 000 10 300 bp alluvium in the loup river basin floodplain stability very slow aggradation occurred from 10 300 10 000 bp rapid floodplain aggradation is inferred between 10 000 and 9450 bp between 9450 and about 9250 bp erosion initially produced the kilgore creek terrace the valley floor landscape stabilized from about 9250 to 9100 bp before an episode of rapid aggradation overwhelmed floodplains and alluvial colluvial fans the fans stabilized about 8600 8500 bp while floodplains in larger valleys 5th order stabilized shortly after about 8400 8200 bp renewed valley bottom aggradation after 8200 was interrupted at about 7750 the absence of alluvium dated between 14 000 and 10 300 bp in the loup river basin precludes discovery of early paleoindian sites in valleys and contrasts with the presence of alluvium and buried soils containing clovis and folsom paleoindian sites in other drainage basins in the u s central great plains although the distribution of the kilgore creek terrace is an excellent proxy of preservation of 10 300 9450 bp alluvium in the loup river basin and thus late paleoindian sites very few remnants of this terrace have been preserved two early holocene erosional episodes have been documented in the loup river basin at 9450 9250 bp and again immediately before 8300 8200 bp alluvium deposited between 10 300 and 9450 contains one archaeological site and alluvium deposited 9250 8200 contains five other paleoindian sites five early archaic sites are documented in three alluvial colluvial fans and on a terrace remnant in the north loup river valley but have not been discovered in an alluvial stratigraphic context outside of fans although stable surfaces are much more likely to accumulate a greater density of artifacts than sedimentary units that are deposited rapidly we document three paleoindian components that are in alluvium between buried soils

apparent isobaric cooling paths from granulites two counterexamples from british columbia and new hampshire textural evidence for the reaction histories of pelitic granulites from british columbia and new hampshire shows that pressure temperature paths obtained from thermobarometry on these samples are an artifact of the calculation technique samples from both localities show breakdown of garnet to form cordierite a reaction that occurs during decompression additional reaction textures and fluid inclusion data also imply decompression at high temperatures for both localities however core rim thermobarometry yields nearly isobaric cooling paths similar cooling paths have been used by other authors to argue for a magmatic underplating model for regional mafic granulites we show that mineral homogenization in pelitic granulites can lead to erroneous isobaric cooling paths and hence to incorrect conclusions concerning tectonic similarities between different types of granulites

tectonic controls of metamorphic field gradients abstract we investigate the effects of horizontal variations in tectonic factors heat production and rate amount and duration of erosion on the magnitudes and gradients of pressure p temperature t and cooling ages observed in mountain belts horizontal gradients of p t and cooling ages are largely controlled by two dimensionless parameters 1 the horizontal length scale over which erosion erosion rate or erosion duration varies and 2 the peclet number pe which describes the relative rates of advection and diffusion of heat in contrast the magnitudes of observed p and t depend strongly on the degree of thickening and original burial depth as well as pe and since horizontal heat conduction can usually be ignored do not depend strongly on p and t gradients generally increase with decreasing and pe for calculations in which either but not both erosion rate or erosion duration is horizontally constant p and t gradients are moderate in magnitude and increase in the direction of increasing total erosion in contrast calculations with horizontally constant total erosion but varying erosion rate and erosion duration show small temperature and pressure gradients pressures and temperatures can increase in the same or in opposite directions depending on the magnitude of calculations with horizontally varying crustal heat production show small but non zero temperature gradients and negligible pressure gradients these results indicate that knowledge of temperature pressure and cooling age gradients in individual mountain belts can constrain fundamental quantities such as magnitude and horizontal gradient of the exhumation rate and the average shear strain rate occurring during exhumation on the basis of their metamorphic field gradients most mountain belts can be divided into one of three groups the first and largest group shows strongly positive p and t gradients precambrian orogenic areas comprise the second group and have small t gradients

a geoarchaeological perspective on late holocene puyallup river delta history using lithostratigraphic data from xaxtl abish 1 on the hylebos creek distributary in tacoma wa abstract geoarchaeological data from the pre contact archaeological midden site xaxtl abish 1 45pi974 on the hylebos distributary of the puyallup river delta contribute to understanding local site formation processes and the regional pre contact landscape near what is now tacoma washington the post glacial history of deltaic progradation non seismic deltaic subsidence tectonic subsidence and eustatic sea level rise along the puyallup river delta front provides temporal limitations for late holocene occupation of the delta as well as expectations for past land use of the hylebos creek vicinity the formation history of xaxtl abish 1 was developed by examining the stratigraphy and lithology of the natural and cultural deposits hosting composing and preserving the site using an allostratigraphic approach and considering post depositional alteration and preservation seven strata including intertidal delta delta plain midden peat wetland floodplain and fill were identified at xaxtl abish 1 based on the distribution of 22 discrete lithofacies radiocarbon dates collected from xaxtl abish 1 nearby archaeological sites and other geological contexts across the puyallup river delta allow estimates of late holocene aggradation rates and provide limiting dates for human occupation of the delta front preliminary results show the lower puyallup river delta aggraded at an average rate of about 15 cm a year during the middle to late holocene late holocene archaeological sites may be buried within the upper 11 m of sediment on the delta front and are younger than 3140 cal bp the site formation history of xaxtl abish 1 argues for the presence of other deeply buried archaeological sites in similar sub environments on deltas around puget sound

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated