lithic tools from arago cave tautavel pyrenees orientales france behavioural continuity or raw material determinism during the middle pleistocene abstract arago cave at tautavel pyrenees orientales france is one of the earliest known middle pleistocene sites in the pyrenees the cave contains a long stratigraphic sequence including over twenty archaeological levels which have yielded abundant bone and lithic remains including nearly 100 hominid remains the vast quantity of lithic material is comprised of diverse raw materials including quartz quartzite and flints from both local and distant sources this raw material diversity makes it possible to establish links between the mechanical properties of the different rock types the distances separating the sources from the site technological behaviour and tool types moreover the long chronological sequence reflecting climatic fluctuations and different assemblage types makes arago cave a privileged site for assessing the influence of environmental factors and assemblage types on certain aspects of prehistoric man s behaviour during the middle pleistocene through a detailed lithological technological and typological study of one aspect of the lithic assemblage the flake tools this paper aims to bring to light the factors determining stone tool production at arago cave during the middle pleistocene

evolution of cupido and coahuila carbonate platforms early cretaceous northeastern mexico the cupido and coahuila platforms of northeastern mexico are part of the extensive carbonate platform system that rimmed the ancestral gulf of mexico during barremian to albian time exposures of cupido and coahuila lithofacies in several mountain ranges spanning an 80 000 km 2 area reveal information about platform morphology and composition paleoenvironmental relations and the chronology of platform evolution new biostratigraphic data integrated with carbon and strontium isotope stratigraphy significantly improve chronostratigraphic relations across the region these data substantially change previous age assignments of several formations and force a revision of the longstanding stratigraphy in the region the revised stratigraphy and enhanced time control combined with regional facies associations allow the construction of cross sections isopach maps and timeslice paleogeographic maps that collectively document platform morphology and evolution the orientation of the cupido barremianaptian shelf margin was controlled by the emergent coahuila basement block to the northwest the south facing margin is a highenergy grainstone shoal whereas the margin facing the ancestral gulf of mexico to the east is a discontinuous rudist coral reef a broad shelf lagoon developed in the lee of the cupido margin where as much as 660 m of cyclic peritidal deposits accumulated during middle to late aptian time a major phase of flooding forced a retrograde backstep of the cupido platform shifting the locus of shallow marine sedimentation northwestward toward the coahuila block this diachronous flooding event records both the demise of the cupido shelf and the consequent initiation of the coahuila ramp the backstepped coahuila ramp aptianalbian consisted of a shallow shoal margin separating an interior evaporitic lagoon from a low energy muddy deep ramp more than 500 m of cyclic carbonates and evaporites accumulated in the evaporitic lagoon during early to middle albian time restriction of the platform interior dissipated by middle to late albian time with the deposition of peloidal miliolid rich packstones and grainstones of the aurora formation the coahuila platform was drowned during latest albian to early cenomanian time and the deep water laminites of the cuesta del cura formation were deposited this study fills in a substantial gap in the cretaceous paleogeography of the eastern gulf of mexico coast improving regional correlations with adjacent hydrocarbon rich platforms the enhanced temporal relations and chronology of events recorded in the cupido and coahuila platforms significantly improve global correlations with coeval economically important platforms worldwide perhaps con

last interglacial mis 5 ungulate assemblage from the central iberian peninsula the camino cave pinilla del valle madrid spain the fossil assemblage from the camino cave corresponding to the late mis 5 constitutes a key record to understand the faunal composition of central iberia during the last interglacial moreover the largest iberian fallow deer fossil population was recovered here other ungulate species present at this assemblage include red deer roe deer aurochs chamois wild boar horse and steppe rhinoceros carnivores and neanderthals are also present the origin of the accumulation has been interpreted as a hyena den abundant fallow deer skeletal elements allowed to statistically compare the camino cave fossils with other pleistocene and holocene european populations the morphological comparison of the dentition and morphometrical analyses of the metapodials suggest that the fallow deer from the camino cave are closer to the subspecies dama dama geiselana and dama dama tiberina than to the recent dama dama dama estimations of the age at death in several fallow deer young individuals provided information on seasonality suggesting that the cave was occupied by the hyenas almost all year round the ungulate composition provides a clear example of an interglacial faunal complex which agrees with the published pollen charcoal and small vertebrate data that indicate a continental mediterranean climate this interglacial character was also registered at other iberian mis 5 sequences coming from the mediterranean margin

technical microwear and residues in identifying bipolar knapping on an anvil experimental data the functional study of the stone tool artefacts from the middle pleistocene site of isernia la pineta molise central italy revealed microtraces that display certain features that did not fit in with what we know as use wear traces the suspicion that these microtraces may be technical traces derived from bipolar flaking which is prevalent at this site led us to initiate an experimental programme to check our hypothesis the experiments conducted allowed us to identify residues associated with bipolar flaking on an anvil and to characterise the microscopic traces derived from this production technique our results proved very useful in identifying the artefacts produced by bipolar flaking as well as in determining the basic lithological features of the anvil moreover these experiments allowed us to assess the possible interferences that these kinds of technical traces can cause when performing the functional analyses of lithic assemblages produced by the bipolar technique

a close ridge small scale atmospheric flow field and its influence on snow accumulation the rough steep and complex terrain in the alpine environment causes a variety of flow patterns such as blocking speed up or flow separation which influence precipitation snow deposition and ultimately snow distribution on the ground cloud terrain interactions flow particle interactions and snow transport affect snow accumulation patterns but the relative importance of these processes is not fully understood in particular in complex mountainous terrain a unique combination of measurements and model simulations is used in a local case study during a two day snowfall event to demonstrate the current understanding of snow accumulation in very steep alpine terrain doppler wind lidar measurements show an eddy like structure on the leeward side of the sattelhorn ridge in the dischma valley near davos switzerland which could partly be replicated by advanced regional prediction system arps flow simulations snow deposition measurements with a terrestrial laser scanner tls show a complex deposition pattern which is only partially captured by alpine3d deposition simulations driven by the arps flow fields this shows that additional processes such as avalanches may play a role or that a more refined simulation of flow or flow particle interactions is required to fully understand snow distribution in very steep mountainous terrain

how flakes shatter a critical evaluation of quartz fracture analysis despite its worldwide use as a stone tool raw material quartz is known to be a difficult material for archaeologists the main reason for this is the tendency of quartz flakes to fragment during detachment which complicates the use of traditional lithic analyses in this article we present an experimental study of quartz flake fragmentation we evaluate the method called fracture analysis that has been developed and used explicitly for the study of quartz assemblages the method assumes high predictability of quartz flake fragmentation but our experiments show that there is significant variation in fragmentation that fracture analysis does not take into account our results indicate that this variation is partly explained by indenter hardness the relative thickness of the detached flake as well as individual knapper related factors these results undermine the applicability of quartz fracture analysis in its current form in addition we discuss the effects of flake fragmentation on the technological organisation of prehistoric quartz users and suggest that it has affected reduction strategies as well as blank and tool dimensions we also suggest that there should be mobility related differences in archaeological assemblages in terms of the quality of the quartz raw material and that the curation of quartz should be low in relation to better quality raw materials used parallel with it

vein quartz in lithic traditions an analysis based on experimental archaeology abstract worldwide vein quartz was a commonly used raw material for stone tools but this material has proved difficult for archaeologists to analyse because many quartz assemblages appear to be comprised of amorphous pieces not easily recognised as humanly modified or forming tools this paper discusses the analysis of the debitage focusing on the debitage fragmentation rate the debitage break and fragment types and the quantitative analysis of the complete flakes resulting from experimental knapping of quartz which formed part of a project which investigated the use of quartz in irish prehistoric lithic traditions the results have highlighted the complexity involved in analysing quartz assemblages and the significant differences between the debitage products of quartz and chert knapping assemblages while bipolar knapping is generally easy to differentiate from direct percussion it is harder to differentiate between soft and hard hammer percussion

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

the mesozoic la mula island coahuila mexico granitic rocks at potrero de la mula and sierra del fuste coahuila mexico are the only known exposures of a late triassic pluton that by the late jurassic stood as a topographically high area until it was inundated by the cretaceous sea the principal igneous rock at potrero de la mula is a two feldspar biotite hornblende i type granite that is cut by comagmatic dikes of six ages and by several shear zones a rb sr age of 213 14 m y and an initial ratio of 0 705 0004 were obtained from nine whole rock samples a shallow depth of emplacement is inferred from textural and mineralogical evidence mineralogy chemistry and isotopes suggest emplacement above a subduction zone which is consistent with the hypothesis that a late paleozoic earliest mesozoic convergent plate boundary existed in northern mexico after being unroofed the pluton contributed sediment to the adjoining sabinas gulf until the mid neocomian by the hauterivian the pluton supported a deeply weathered terrain of moderate relief flanked on its northeastern side by lagoonal environments oballos member padilla formation farther south uplift by faulting along the northern flank of the coahuila island produced a clastic wedge the finer grained paralic components of which la mula formation prograded northeastward and eventually covered la mula island subsequent deposits at potrero de la mula beginning with gypsum reflect gradually deepening water and include the la virgen cupido la pena and tamaulipas formations

possible effects of thermal degradation of organic matter on carbonate paragenesis and fluorite precipitation in mississippi valley type deposits heating of organic matter to progressively higher temperatures causes a sequence of chemical changes in which carbonate minerals are first dissolved then precipitated and then again dissolved the initial carbonate dissolution is related to the production of organic acids as heating continues organic acids begin to decompose to carbon dioxide and methane this addition of carbon dioxide to a solution with an organic acid ph buffer causes carbonates to precipitate eventually a temperature is reached at which any remaining organic acids quickly decompose addition of carbon dioxide to a solution in which carbonate species rather than organic acids now control the ph lowers the ph and causes renewed carbonate dissolution the similarity of this sequence to the carbonate paragenesis of mississippi valley type deposits suggests that the carbonate paragenesis in these deposits may be related to the thermal alteration of organic matter by competing with fluoride for magnesium bicarbonate ions from decarboxylation off organic matter and dissolution of carbonates may break the mgf complex form the mghco3 complex and thereby liberate fluoride to trigger the precipitation of fluorite

a use wear interpretation of the most common raw materials from the olduvai gorge naibor soit quartzite abstract this paper presents for the first time an experimental protocol for the assessment of use wear produced when using precambrian and metamorphic white naibor soit quartzite nq flakes nq is the most recurrent raw material from the archaeological sites of the olduvai gorge during the early stone age esa the objective of this study is to provide a preliminary description of the experimentally produced use wear traces that can be applied to the analysis of sites like the acheulean site of thiongo korongo tk olduvai gorge tanzania or other sites from olduvai where nq was used to tool production this experimental protocol incorporates a broad range to tasks including plant processing underground storage organs usos wood herbaceous plants and canes and carcass processing butchery and bone processing the most novel activity of this experimental protocol is the processing of usos for this we have replicated different steps of tuber processing including the cutting peeling and scraping of five varieties of usos beta vulgaris daucus carota ipomoea batatas pastinaca sativa and zingiber officinale with differences in hardness fibrosity water content and peel regularity after analysing micro and macro wear traces on the experimental flakes several criteria for distinguishing between different activities scraping cutting peeling sawing cutting butchery and the different materials being processed were identified these criteria are based on the presence continuity and morphology of macro scars along with the presence distribution nature and intensity of different micro traces micro scars attrition striations pits rounding polish additionally we have identified several processes that limit the formation of traces including the tendency of some activities to weaken nq edges and shorten the duration of use

lidar measurement of snow depth a review laser altimetry lidar is a remote sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications recently lidar has seen a dramatic widening of applications in the natural sciences resulting in technological improvements and an increase in the availability of both airborne and ground based sensors modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies typical vertical accuracies for airborne datasets are decimeter scale with order 1 m point spacings ground based systems typically provide millimeter scale range accuracy and sub meter point spacing over 1 m to several kilometers many system parameters such as scan angle pulse rate and shot geometry relative to terrain gradients require specification to achieve specific point coverage densities in forested and or complex terrain additionally snow has a significant volumetric scattering component requiring different considerations for error estimation than for other earth surface materials we use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions this paper presents a review of lidar mapping procedures and error sources potential errors unique to snow surface remote sensing in the near infrared and visible wavelengths and recommendations for projects using lidar for snow depth mapping

microwear features on vein quartz rock crystal and quartzite a study combining optical light and scanning electron microscopy abstract in general quartz and most of non flint rocks have not been extensively studied from a functional point of view very frequently the definitions of micro features connected with flint surfaces have been used to describe those encountered on non flint tools this circumstance has repeatedly posed serious methodological problems for evaluating the accuracy of functional results when analysing use wear on quartz and quartzite implements this is due to the intrinsic divergences in morphology and distribution of use wear with regard to the different lithic raw materials even though important efforts to systematise use wear features on quartz have been done almost since the beginning of the discipline there continues to be confusion and lack of standardisation regarding terminology in this aspect in this paper we try to contribute to new insights in this research by means of selecting examples from an extensive experimental programme involving different raw materials from rock crystal the purest form of quartz found in nature to vein quartz and quartzite with the latter two materials extensively used for knapping throughout prehistory and still poorly understood in terms of microwear for data recording we preferentially used sequential experiments and resorted to both optical light and scanning electron microscopy we focused our interest on describing the main groups of wear features the results obtained allowed us to assess the different mechanical behaviours under the stressors induced by tool use from a group of raw materials with the same chemical composition but very different in structure furthermore we propose the revision of some terms commonly employed when documenting micro wear on quartz and similar rocks as well as recurring concepts coming from materials and geological sciences e g tribology quartz exoscopy

some preliminary observations on subsurface damage on experimental and archaeological quartz tools using clsm and dye abstract lithic use wear analysis mainly deals with use wear features which can be observed on the surface of stone tools but a major part of the wear of brittle material is found under the surface this wear might also be a clue to the interpretation of archaeological stone tools in this paper we try to examine subsurface damage on experimental and archaeological quartz tools by dying them with fluorescent colour and scanning them with a clsm this method shows that various worked materials cause different subsurface damage which is related to the hardness of the worked material

simulation of extreme new zealand precipitation events part ii mechanisms of precipitation development abstract the extreme precipitation event that occurred on 27 december 1989 over the south island of new zealand was simulated using the dar hydrostatic mesoscale model nested within the ecmwf analyses the model simulated nearly half of the peak observed rainfall for this storm greater than 700 mm and captured the location and timing of the intense precipitation the heavy precipitation developed while a deep layer of moist subtropical air along a cold front ascended the high terrain of the south island the intense orographic ascent was associated with a low level jet core with wind speeds of over 20 m s 1 ahead of the cold front an upper level trough and jet streak entrance region were also present upstream of the south island during the event aiding the ascent over the mountains and deepening the layer of moist air the air crossing the mountain was nearly saturated throughout the troposphere and had only weak moist vertical stability near the cold front almost all of the simulated precipitation f

microwear analysis of mousterian quartz tools from the navalmaillo rock shelter pinilla del valle madrid spain the study of wear marks on palaeolithic quartz tools allows an understanding of how they were used the present work reports a functional study of a sample of mousterian quartz industry from level f of the navalmaillo rock shelter pinilla del valle madrid spain this level a palimpsest preserves the remains of a neanderthal occupation traceological inspection revealed the tools made at the site were very versatile

understanding the ancient habitats of the last interglacial late mis 5 neanderthals of central iberia paleoenvironmental and taphonomic evidence from the cueva del camino spain site the cueva del camino site pinilla del valle madrid represents the most complete mis 5 record from the iberian peninsula away from the mediterranean margin including a large accumulation of fossilized remains of small and large vertebrates and two human teeth the presence of carnivores mainly hyenas and humans suggests that the site should be interpreted as a spotted hyena den a human occupation or both during an earlier phase of excavation undertaken during the 1980s an anthropic origin was suggested for the accumulation at the site however research was resumed in 2002 leading to an increase in the number of vertebrate remains recovered as well as the recognition of new vertebrate species these have now been incorporated into the site s list of fauna in addition new palaeobotanical geochronological and stratigraphic data have been recorded and analysed and the human teeth identified as being of neanderthal origin floristic data pollen and charcoal remains obtained for the north sector of this site indicate an open landscape with pinus sylvestris nigra as the main arboreal taxon the available evidence suggests this accumulation to be the result of spotted hyena activity during a warm phase of marine isotope stage 5 mis 5 in an environment in which fallow deer was the most abundant herbivore

neanderthal settlement in central iberia geo archaeological research in the abrigo del molino site mis 3 segovia iberian peninsula abstract the abrigo del molino archaeological site is located in the valley of the eresma river near segovia in central spain it consists of a shallow cave of fluvio karstic origin which has been completely filled with detrital deposits geo archaeological interpretation of the genesis of these deposits differentiates three groups a lower group with sandy loams and fine sands interbedded with pebble and gravel layers deposited respectively by palaeofloods and slope contributions a middle group with massive silt and grain supported boulders formed by alternating contributions from the overlying slope karst mudflows and rockfalls from the shelter roof and an upper group of silt cemented by carbonates final backfill alteration and degradation of the host rock the techno typological characteristics of the lithic assemblage confirm the existence of mousterian levels at the site and optically stimulated luminescence osl dating of these levels obtains an age range of 31 60 ka for the detrital deposits presenting the occupation by neanderthal groups for the first time in karstic environments in the northern iberian plateau the southern part of the duero basin

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

quantifying the spatial variability of a snowstorm using differential airborne lidar author s brandt w tyler bormann kat j cannon forest deems jeffrey s painter thomas h steinhoff daniel f dozier jeff

the evolution of middle america and the gulf of mexico caribbean sea region during mesozoic time a plate tectonic model for the evolution of middle america and the gulf of mexico caribbean sea region is presented the model which is based upon the existence of the mojave sonora megashear incorporates into the triassic pangea reconstruction three microplates between north and south america thus avoiding the overlap of the bullard fit these plates are the yaqui bounded on the north by the mojave sonora megashear the east and west maya plates bounded on the north by the mexican volcanic zone and on the south by a predecessor of the motagua fault zone and the chortis plate parts of guatemala and honduras during late jurassic time as north america split away from europe africa and south america shear with left lateral sense of displacement occurred along the transform faults that bounded the micro plates if 800 km of left lateral displacement along the mojave sonora megashear 300 km along the mexican volcanic belt and 1 300 km along a proto motagua megashear are restored and if yucatan and cuba are rotated to fit against northern south america then 1 a curvilinear belt of late paleozoic rocks that show lithologic as well as paleontologic similarities extends across the reconstruction and links outcrops in texas eastern mexico nuclear central america and colombia 2 a mediterranean like sea is delineated that was a precursor of most of the present gulf of mexico 3 correlation is implied between the distinctive quartzose san cayetano formation of cuba and the caracas and juan griego groups of venezuela geometric constraints suggest that probably shear initially occurred along the mexican volcanic zone near the end of the middle jurassic subsequently probably about 160 m y ago displacements that total 800 km began along the mojave sonora megashear contemporaneously yucatan and fragments of pre cretaceous rocks that compose parts of central and western cuba migrated northward toward their present positions rotation of yucatan was facilitated by considerable displacement along the proto motagua zone and along a zone that is probably coincident with the modern salina cruz fault accumulation of widespread major salt units of late jurassic callovian to early oxfordian age in the gulf basin probably occurred contemporaneously with the arrival of these blocks at their present positions clastic units that interfinger with some of the youngest salt units and rim the gulf of mexico have not recorded major recognized translations since their accumulation clockwise rotation of south america and the chortis plate occurred during early cretaceous time this movement which was manifested by subduction of jurassic ocean floor against the previously rifted precursor of the island of cuba and under parts of hispaniola and puerto rico is recorded by circum caribbean orogeny abrupt changes in the relative motions between north and south america during late cretaceous time may have resulted in extension and outpourings of basalt upon the jurassic rocks of the ocean floor of the venezuelan basin west of beata ridge sea floor spreading formed the colombian basin related subduction occurred as the chortis plate including part of central america the nicaraguan rise and southeastern cuba was sutured against the maya east plate along the present motagua fault and cayman trench our model is constrained by published geologic data the relative positions of north and south america from atlantic sea floor magnetic anomalies and the requirement that the major transform faults be compatible with the poles of rotation for the appropriate relative motions between north and south america paleomagnetic data from middle america are sparse but do not conflict with the predicted motions of some of the microplates especially chortis

orographic barriers high resolution trmm rainfall and relief variations along the eastern andes 1 quantifying the degree to which tectonic and erosive processes shape landscapes is key to understanding the evolution of tectonically active mountain belts here we explore the interplay of these two processes along the humid eastern flank of the south american andes we use high resolution tropical rainfall measurement mission trmm and srtm data to characterize elevation relief and hillslope angle of peak rainfall at orographic barriers over a distance of more than 3500 km along the eastern flanks we find that peak rainfall 3 5 m yr occurs at a mean elevation of 1 3 0 17 km a mean relief of 0 95 0 08 km and at moderate mean hillslope angles of 18 3 1 7 we suggest that topographic relief is the best first order rainfall predictor and we demonstrate how relief changes along strike south of the andean orocline alter rainfall distribution changes in climatic sedimentary and tectonic processes prevent the formation of high relief amounts at the mountain front and these areas are not characterized by pronounced rainfall peak

cut marks made with quartz tools an experimental framework for understanding cut mark morphology and its use at the middle palaeolithic site of the navalmaillo rock shelter pinilla del valle madrid spain abstract the study of cut marks in archaeological contexts is of great importance for understanding the subsistence strategies of past human groups many authors have indicated differences to exist between the cut marks produced by different tools and when the same types of tool have been made from different raw materials the present work examines the cut marks made during the experimental butchering of a red deer cervus elaphus using simple quartz flakes with those found on fossilised animal remains at the navalmaillo rock shelter site pinilla del valle madrid spain likely to have been made with similar flakes the methodology followed was that of dominguez rodrigo et al 2009 which was originally designed to differentiate between cut marks and trampling marks but which here was tested as a method of distinguishing between the raw materials from which cutting tools were made the results were also compared to those made with other types of tool raw material reported in the literature the present results confirm the above ideas the marks made experimentally by the quartz flakes are very similar to those seen on the faunal remains from the level f of navalmaillo rock shelter site but different to those made by other tools or by flakes made from other materials they also show however that different cut mark morphologies are largely independent of the size of the animal butchered and of the anatomical element on which they appear

evidence for paleoproterozoic grenvillian and pan african age gondwanan crust beneath northeastern mexico abstract a number of previous studies including two recent reconstructions of rodinia have considered the grenvillian basement of mexico to be continuous with the laurentian basement of texas isotopic studies and u pb dating of zircons from precambrian granitoids that occur as cobbles and boulders in a paleozoic conglomerate exposed in the state of coahuila northeastern mexico indicate the region is underlain by gondwanan rather than laurentian basement essentially nothing was known of the basement before this study because the region is blanketed with phanerozoic sedimentary and volcanic deposits nine out of ten analyzed samples have grenvillian crystallization ages 1232 7 to 1214 2 ma this phase of magmatic activity in northeastern mexico was coeval with the construction of volcanic arcs in east central and southern mexico 1220 1150 ma but was later than the arc magmatism of laurentia e g elzevirian arcs 1230 ma in texas and the grenville province a subset of the grenvillian samples contains xenocrystic 1 85 ga zircons which are the first evidence of paleoproterozoic crust south of the paleozoic ouachita suture in mexico the remaining sample has a pan african crystallization age 580 4 ma and this is the first sample of pan african age basement found in mexico the pan african orogeny marked the assembly of gondwana and laurentia was unaffected by that event two lines of evidence argue that some of the grenvillian rocks of northeastern mexico were affected by a pan african age event first two of the grenvillian clasts have u pb lower intercept ages within error of 580 ma second common pb and nd isotopic compositions of the pan african granite strongly suggest that it was derived either by melting of grenvillian basement or by assimilating massive amounts of that basement thus far no other grenvillian terrane is known to have the exact combination of nd pb isotopic compositions and absolute ages as the coahuila samples although there are some similarities with the santa marta massif of colombia and the cordillera de merida of venezuela

microwear polishes on early stone tools from koobi fora kenya the functions of the stone artefacts made and used by early hominids has been a matter for speculation however recent experimental work has demonstrated that microscopically distinct wear polishes form on tools of cryptocrystalline silica when used on different materials and that these microwear polishes survive on ancient implements1 3 we have now examined 54 artefacts from five early pleistocene archaeological sites dated to 1 5 myr ago in the koobi fora region of kenya for microwear polishes and other traces of use wear traces were found on nine artefacts variously resembling traces induced experimentally by cutting soft animal tissue and soft plant material and by scraping and sawing wood these results greatly extend the time range for which microwear polish analysis is applicable and increase the evidence of early hominid adaptation

fluorite deposits at encantada buenavista mexico products of mississippi valley type processes ore geol rev 23 2003 107 124 a reply we very much appreciate the comments of dr spirakis regarding the fluorite deposits of la encan tada buenavista the contribution by gonza lez par tida et al 2003 represents a partial report of thework we are carrying out on the fluorite deposits ofnorthern coahuila state mexico we have subse quently conducted further work on the deposit inorder to complement the information already pub lished addressing controls on the distribution of themineralized bodies and halogen studies of fluid inclu sions we discuss here in light of our new results theproblem of fluorine transport and precipitation at laencantada buenavista new developments in the mine showed that there isa strong structural control on the distribution offluorite bodies the latter are found at the intersectionof low permeability barriers with low angle faults layer parallel slip developed at stratification bound aries with abundant clayey materials precipitation offluorite is preceded by a dramatic increase in perme ability due to the hydraulic fracturing of the host rock enclosing rock fragments included in the newlydeveloped breccias are usually recrystallized andslightly corroded but are also rapidly covered byfluorite the precipitation of which appears to precludethe continuance of carbonate replacement a thincalcite blanket typically a few centimeters to deci meters thick is found at the boundary of the fluoritebody smoothly passing to the slightly recrystallizedenclosing limestone fluorite appears as white tocolorless corrosion free crystals indicative of passivemineral precipitation late cavities are filled up byidiomorphic cubic zoned fluorite crystals with adeep purple color in their outer zones minor idiomor phic calcite scalenoedrons and extremely rare crystalsof barite

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

regional stratigraphy and distribution of epigenetic stratabound celestine fluorite barite and pb zn deposits in the mvt province of northeastern mexico northeastern mexico hosts numerous epigenetic stratabound carbonate hosted low temperature hydrothermal deposits of celestine fluorite barite and zinc lead which formed by replacement of mesozoic evaporites or carbonate rocks such deposits can be permissively catalogued as mississippi valley type mvt deposits the deposits studied in the state of coahuila are associated with granitic and metasedimentary basement highs horsts marginal or central to the mesozoic sabinas basin these horsts controlled the stratigraphy of the mesozoic basins and subsequently influenced the laramide structural pattern the sabinas basin consists of 6 000 m thick jurassic to cretaceous siliciclastic carbonate and evaporitic series the mvt deposits are mostly in barremian and in aptian albian to cenomanian formations and likely formed from basinal brines that were mobilized during the laramide orogeny although earlier diagenetic replacement of evaporite layers barite and celestine deposits and lining of paleokarstic cavities in reef carbonates zn pb deposits is observed fluid inclusion microthermometry and isotopic studies suggest ore formation due to mixing of basinal brines and meteoric water homogenization temperatures of fluid inclusions range from 45 c to 210 c salinities range from 0 to 26 wt nacl equiv and some inclusions contain hydrocarbons or bitumen sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from barremian to cenomanian evaporites regional geology and a compilation of metallogenic features define the new mvt province of northeastern mexico which comprises most of the state of coahuila and portions of the neighboring states of nuevo leon durango and perhaps extends into zacatecas and southern texas this province exhibits a regional metal zonation with celestine deposits to the south fluorite deposits to the north and barite and zn pb deposits mostly in the central part

an overview of seasonal snow metamorphism the grains in seasonal snow undergo rapid and radical transformations in size shape and cohesion these grain characteristics affect all of the basic properties of snow snow is characterized as either wet or dry depending on the presence of liquid water wet snow is markedly different at low and high liquid contents dry snow is characterized as either an equilibrium form or a kinetic growth form that is it is either well rounded or faceted of course many snow grains display either transitional features between two of these categories or features which arise from other processes snow is classified depending on the dominant processes of its metamorphism