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

first cycle quartz arenites in the orinoco river basin venezuela and colombia modern first cycle quartz arenites are forming in the orinoco drainage basin by at least two distinct mechanisms common to both mechanisms is an environment of intense chemical weathering and extended time over which weathering can occur in the llanos andean foreland basin extended time is provided by temporary storage of orogenically derived sediments on extensive alluvial plains in lowland portions of the guayana shield long soil mineral residence times are produced by very low erosion and transport rates resulting from low relief and tectonic quiescence both weathering intensity and the duration of weathering are important in the modification of sand composition first cycle quartz arenites are produced in diverse tectonic settings and cannot be used by themselves to infer paleotectonic settings of ancient sequences furthermore although tectonic setting is of great importance in determining sand composition modifications during transport and deposition can overprint the effects of the tecto

holocene transgression recorded by sand composition in the mesotidal galician coastline nw spain this study confirms several inferences regarding holocene coastal dynamics and climate through a petrographic modal analysis of 60 holocene sand samples recovered in seven sites along the nw coast of the iberian peninsula fluvial sand can be discriminated from more mature intertidal and aeolian sand according to texture and composition fluvial sand contains soil products and coastal sand has significant bioclasts quartzofeldspathic sand appears in the western area produced by the erosion of granite and granitoid and quartzolithic sand occurs in the eastern area produced by the erosion of metasediment changes in sand composition during holocene deposition are manifested by an increase in modern carbonate clasts mc correlated with the holocene transgression episodes of faster sea level rise and subsequent erosion of surrounding cliffs are indicated by the preservation of high proportions of feldspar in intertidal sand in contrast fluvial sand is characterized by greater quartz enrichment these inferences were confirmed by petrographic indices carbonate clasts total clasts mc t total feldspars monocrystalline quartz f qm and plagioclase total feldspars p f the different maturity of intertidal and aeolian sands is revealed by their variable quartz contents despite similar proportions of plagioclase and k feldspar this suggests mechanical abrasion as the main factor controlling maturity in contrast fluvial sand shows depleted plagioclase contents as the result of inland weathering processes intertidal beach and aeolian sands are essentially the products of the erosion of coastal cliffs and head deposits with only the scarce contribution of fluvial drainages the long distance transport of galician coastal sands is discarded based on the close relationship between their composition and that of local sand sources our findings indicate that short distance transport of sediments from the west closed off coastal wetlands and occluded estuarine mouths during the holocene transgression by deposition on sediment trap zones along the irregularly shaped galician coast

holocene vegetation change in the northern peten and its implications for maya prehistory an 8400 cal yr record of vegetation change from the northern peten guatemala provides new insights into the environmental history of the archaeological area known as the mirador basin pollen loss on ignition and magnetic susceptibility analyses indicate warm and humid conditions in the early to mid holocene evidence for a decrease in forest cover around 4600 cal yr b p coincides with the first appearance of zea mays pollen suggesting that human activity was responsible the period between 3450 cal yr b p and 1000 cal yr b p is characterized by a further decline in forest pollen types includes an abrupt increase in weedy taxa and exhibits the highest magnetic susceptibility values since the early holocene all of which suggest further agricultural disturbance in the watershed a brief drop in disturbance indicators around 1800 cal yr b p may represent the preclassic abandonment of the area changing pollen frequencies around 1000 cal yr b p indicate a cessation of human disturbance which represents the late classic collapse of the southern maya lowlands

overlooked sedimentary particles from tropical weathering environments two varieties of sedimentary particles that are common in tropical weathering environments have remained largely overlooked by sedimentary petrologists alterites are grains that have been so thoroughly altered by chemical weathering processes that identification of the precursor grain is impossible they consist of secondary weathering products such as clays zeolites and iron sesquioxides as well as incompletely weathered remains of relatively stable mineral phases alterites that consist of clay sand composites allow the transport and deposition of hydraulically dissimilar constituents under a single hydrodynamic regime and may be important in the production of some graywackes a second class the pedogenic ferruginous particles takes on a variety of forms including laterite fragments soil pisolites and oxidized burrow rinds although these particles are common in modern fluvial sands in the tropics wholesale dissolution of amorphous or poorly crystalline iron sesquioxides during burial diagenesis may help to explain the rarity of such particles in ancient sediments although their potential for preservation is low dissolution of ferruginous particles may be an important source of diagenetic iron which may be redeposited to form ferruginous cements or diagenetic redbeds

annual textural banding in holocene estuarine silts severn estuary levels sw britain patterns cause and implications a high resolution textural study has been made of laminated and banded estuarine silts exposed intertidally at representative localities and horizons in the holocene deposits of the severn estuary levels the laminae on a submillimetre to millimetre scale are sharp based graded couplets formed of a lower silty part overlain by a finer textured clayey element the centimetre to decimetre scale banding is formed of laminae in alternating gradually intergrading sets of relatively coarse and relative fine grained examples at outcrop in the field the banding is recognizable because the coarse sets prove to be recessive to varying degrees under the influence of weathering and current action independent evidence at two localities points toward an annual origin for the banding at a third it arose during part of what appears to have been a relatively short period quantified physical arguments suggest that the textural banding is a response of suspended fine sediment to marked seasonal changes in sea tempe

evolution of holocene coastal environments near robe southeastern south australia abstract coastal robe range and adjacent woakwine range situated 10 15 km inland are the most southwesterly and youngest of a series of parallel low altitude pleistocene beach dune barriers in southeastern south australia in the early holocene the post glacial marine transgression flooded the robe woakwine corridor thus forming a shallow back barrier lagoon open to the southern ocean near the present towns of robe and beachport marine to lagoonal bioclastic carbonate quartz sedimentation prevailed within the corridor from ca 7500 2000 yr bp along the seaward side of robe range transgressive sands were deposited initially as ephemeral sand flats but were mostly redistributed as coastal dunes which today remain active and blanket the pleistocene core of the range sand was also transported along the coast and deposited within the protected embayments of guichen and rivoli bays in the form of prograded beach ridge plains eventually isolating the back barrier lagoon from the open ocean sediment aggradation within the lagoon cessation of marine influence and regional uplift of 0 7 m during the holocene combined to transform the corridor to a lacustrine landscape fossil molluscs foraminifera and ostracods are diagnostic of successive palaeo environments and thus signify stages in the rapid geomorphic evolution of the coastal robe woakwine corridor

identification of the main driving mechanisms in the evolution of a small coastal wetland traba galicia nw spain since its origin 5700 cal yr bp this paper examines the interdependence among the different forcing factors in the evolution of the traba coastal wetland galicia nw spain based on lithofacies and diatom analyses of three cores reaching the basement according to radiocarbon data the wetland originated 5700 cal yr bp a time when similar systems on the atlantic coast of the iberian peninsula were formed diatom assemblage data allow the estimation of the sea level position at 5700 cal yr bp at least 7 m below present day mean sea level attenuation of the sea level rise at that time was a major driving mechanism that permitted the establishment of an incipient beach dune complex causing water logging in the traba basin however the location of this incipient wetland on a basement high which prevented an open connection to the sea made topographic inheritance the main forcing factor in the subsequent evolution of the wetland thus traba was never a coastal lagoon system as it has sometimes been defined the maximum permeability of the beach dune complex enclosing the wetland was recorded after its origin until 2900 cal yr bp when increased stormy conditions affected the galician shelf waters since then the evolution of the wetland has been mainly controlled by more local factors especially the continental sediment supply changes in land use in the basin have accelerated the infilling of the water body since the 19th century this rapid infilling makes the whole system more prone to total encroachment in the short term rather than to sea drowning palaeoenvironmental analyses showing the main trends in the long term evolution of coastal wetlands can be of key importance in any management decisions aimed at preserving these kinds of sensitive coastal environments

8000 years of environmental evolution of barrier lagoon systems emplaced in coastal embayments nw iberia the rocky and indented coast of nw iberia is characterized by the presence of highly valuable and vulnerable small and shallow barrier lagoon systems structurally controlled the case study was se

sand composition in an iberian passive margin fluvial course the tajo river the tajo river the 10th largest river in europe drains part of the western passive margin of europe that includes multiple tectonic elements of the iberian plate modern fluvial sand composition in the tajo river drainage basin reflects the nature of the source region which lies in the central part of the iberian peninsula four fluvial petrographic provinces a b c and d can be established in the tajo drainage basin corresponding well with the four principal structural units drained 1 the iberian range 2 the hesperian massif 3 the tertiary tajo basin and 4 the neogene santarem lisboa basin province a corresponds to the tajo river head and is characterized by quartzolithic sedimenticlastic sands qm67f4lt29 and rs79rg3rm18 these sands have been derived from diverse mesozoic siliciclastics and carbonates of the iberian range province b appears in the upper reaches of the tajo river course and is quartzofeldspathic qm57f34lt9 with diverse rock fragments rs34rg23rm43 sources are hercynian granitoids and metasediments and neogene clastics and minor carbonates of the tertiary tajo basin province c extends along the middle course of the tajo river with quartzofeldspathic metamorphiclastic sand modes qm60f33lt7 rs4rg21rm75 the sources are metamorphic rocks intruded by plutonites of the hesperian massif province d is quartzofeldspathic qm55f39lt6 with a dominance of phaneritic rock fragments rs5rg33rm62 and corresponds to the lower reaches of the tajo river where siliciclastic deposits of the neogene santarem lisboa basin are the main sources sands plot on provenance discrimination diagram qmflt within the recycled orogen field tajo river head and continentalblock fields upper middle and lower course in addition we have proven the usefulness of the rsrgrm diagram to discriminate the defined fluvial provinces originating from heterogeneous parent rock textures and mineralogy climate does not exert any strong influence on the petrogenesis of the tajo river drainage basin sand and erosion in the source areas may be described in terms of weathering limited denudation regime by contrast mixing with tributary supplies is the main process that modifies composition in the tajo river sand the establishment of fluvial provinces related to the main bedrock structural units reflects the great relevance of tributaries from each province in the generation of the tajo river sand and the low significance of inherited sandy load from previous provinces the abundance of granitoid rock fragments rsrgrm rg in fluvial sand of both tributaries and main channel of the tajo river drainage basin faithfully represents the relative abundance of granodiorite monzogranite bedrock exposure in each subbasin metasedimentary and metamorphic bedrock outcrop area is overrepresented by metamorphic rock fragments rsrgrm rm in both sand from tributaries and from the tajo main trunk river this is manifested by differences of 18 23 between means of metasedimentary outcrop area and the rsrgrm rm mean in the sand from provinces b and c d respectively sedimentary mainly carbonate outcrop area is underrepresented or not represented by sedimentary rock fragments rsrgrm rs in sand of the tajo river this underrepresentation causes a difference between means of sedimentary outcrop area and the rsrgrm rs mean of 21 17 1 and 10 7 in sands from province a b and c d respectively this fact confirms the rapid loss of these grains during transport because of their labile nature

an 8000 year record of vegetation climate and human disturbance from the sierra de apaneca el salvador abstract an 8000 cal yr stratigraphic record of vegetation change from the sierra de apaneca el salvador documents a mid holocene warm phase followed by late holocene cooling pollen evidence reveals that during the mid holocene 8000 5500 cal yr b p lowland tropical plant taxa were growing at elevations 200 250 m higher than at present suggesting conditions about 1 0 c warmer than those prevailing today cloud forest genera liquidambar juglans alnus ulmus were also more abundant in the mid holocene indicating greater cloud cover during the dry season a gradual cooling and drying trend began by 5500 cal yr b p culminating in the modern forest composition by 3500 cal yr b p a rise in pollen from weedy plant taxa associated with agriculture occurred 5000 cal yr b p and pollen from zea first appeared in the record at 4440 cal yr b p human impacts on local vegetation remained high throughout the late holocene but decreased abruptly following the tierra blanca joven tbj eruption of volcan ilopango at 1520 cal yr b p the past 1500 years are marked by higher lake levels and periodic depositions of exogenous inorganic sediments perhaps indicating increased climatic variability

the effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the neto river calabria italy implications for provenance studies plutonic and gneissic rocks of the sila massif in the uppermost portion of the neto drainage basin calabria southern italy weather and erode under a humid mediterranean climate during the development of weathering profiles a combination of chemical weathering and granular disintegration processes occurred chemical weathering involves a loss of both plagioclase mainly during grus generation and k feldspar mainly during soil formation this loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of k feldspar sand composition is quartzofeldspathic and nearly homogeneous along the main channel of the neto river even where the river cuts across a blanket of sedimentary cover thus fluvial transport does not alter sand composition within the neto drainage basin petrographic indices are effective in 1 discriminating between contributions from similar granite and gneiss source rocks qm f 2 relating the provenance of plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons qm f q rg and 3 distinguishing between upstream first cycle and downstream multicycle sand q rg this last distinction is further emphasized by considering both aphanitic and phaneritic varieties of rock fragments rgrmrs diagram chemical weathering is the main sand producer within the regolithic environment in northern calabria in addition rapid erosion resulting from steep slopes removes weathered products and rapid and short transport leads to minimal sediment maturation in general the f q index is climate and relief dependent thus it should be used in conjunction with palaeoclimatic and palaeophysiographic evidence for provenance interpretations of ancient quartzofeldspathic sandstones

a palynological study of surface and suspended sediments on a tidal flat implications for pollen transport and deposition in coastal waters this study examines patterns of pollen deposition and resuspension on a tidal flat of the dollard a tidal basin near the mouth of the ems river at the border of germany and the netherlands fig 1 sediment samples were collected during three sequential low tides at the spring stage of the lunar tidal cycle when the greatest area of the flat would be exposed and with the exception of storm events when maximum scour and redeposition would be expected to occur fifteen sample stations were selected along a 5 km transect with paired ripple crest and trough samples collected at three stations water samples were collected hourly during two tidal cycles from a single location on the flat both numbers and condition of pollen and spore taxa were determined for all samples grain size and loi of suspended matter were also determined the same eight types of pollen and spores were important in both water and sediment samples ericaceae alnus betula chenopodiaceae corylus gramineae and polypodiaceae in water samples the lack of a relationship between concentrations of some pollen types and mineral fractions is assumed to be evidence that certain pollen types are preferentially incorporated into floccules suspended in local waters analysis of tidal flat sediments indicates that pollen concentrations increase in troughs between ripples and at lower elevations where finer grain sizes accumulate there is minimal evidence of selective sorting of pollen types ordination using principal components analysis of pollen percentages and concentrations in sediments indicates that both elevation and distance from the estuary mouth influence concentrations of all abundant pollen types these parameters however have minimal influence on pollen percentages incorporation of pollen into fecal pellets which have relatively high settling velocities is assumed to be a critical control on pollen deposition in this environment analysis of stomach contents of locally common bivalves supports this hypothesis transport and deposition of individual pollen types cannot be predicted as floccules and pellets have varying densities and settling velocities some pollen and spores may be deposited in coarser sediments than would be predicted based on the size and density of individual grains but in general display predicted patterns of deposition of fine grained clastic sediments

a review of human and natural changes in maya lowland wetlands over the holocene abstract in the maya lowlands of mexico belize and guatemala two main types of wetlands have played important roles in human history bajos or intermittently wet environments of the upland interior yucatan and perennial wetlands of the coastal plains many of the most important maya sites encircle the bajos though our growing evidence for human wetland interactions is still sparse the deposits of these wetlands record two main eras of slope instability and wetland aggradation the pleistocene holocene transition as rainfall increased and forests eclipsed savannas and the maya preclassic to classic as deforestation land use intensity and drying increased the ancient maya adapted with terraces around these bajo margins but retracted in the late preclassic in some areas the perennial wetlands of the coastal plains have different histories and the first conceptual model of human wetland interaction described intensive wetland agriculture in the preclassic through classic based on raised fields and canals but a second model arose that interpreted the wetland stratigraphy and canals as more indicative of natural aggradation by accelerated erosion and gypsum precipitation that buried archaic and preclassic fields and there was little classic era use we present new data on a third and fourth model in this study the third is a hybrid of the models one and two including the archaic to preclassic aggradation of the second model and the first model s classic period fields and canals as piecemeal attempts by the maya to adapt to these and other environmental changes the fourth conceptual model describes a very late terminal classic preplanned project on a floodplain these wetland fields were short lived aggraded rapidly but with some reoccupation in the postclassic all of these new models display the burgeoning evidence for intricate maya interactions with wetlands and the diversity of evidence from the relatively few studies underscores the infancy of our understanding of maya interaction with tropical wetlands

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

seasonality of modern pollen and sediment deposition in an estuarine context the severn estuary levels southwest england recent sedimentological and palynological research on subfossil holocene banded sediments from the severn estuary levels suggested seasonality of deposition registered by variations in mineral grain size and pollen assemblages between different parts of the bands here we provide data that strengthen this interpretation from sampling of modern sediments and pollen deposition on an active mudflat and saltmarsh on the margin of the severn estuary and comparison with a vegetation survey and contemporary records of climate river and tidal regimes the results of grain size analysis indicate deposition of comparatively coarse grained silts during the relatively cool and windy conditions of winter and comparatively fine grained sediments during relatively warm and calm summer months pollen analysis demonstrates the significance of long term storage of pollen grains and fern spores in the estuarine waterbody superimposed on which seasonal variations in pollen inputs from local and regional vegetation remain detectable copyright c 2007 john wiley sons ltd

extensive evaporation in a modern temperate estuary stable isotopic and compositional evidence estuaries have long been recognized as sites of major compositional fluctuations that can have a range of effects including mineral growth in the water column and in the underlying estuarine sediment we have studied chloride and sodium concentrations and stable isotopes h and o from a suite of estuarine waters from the temperate anllons estuary in nw spain to assess the complexity of estuarine mixing process water samples were collected hourly from in estuary sites over three consecutive days and end member samples were collected on each sampling day evaporative concentration of the estuarine waters is demonstrated by the maximum concentration of geochemically conservative chloride being as much as 17 5 greater in the estuary than in the local seawater relative to chloride concentration both 2h and 18o values of estuary waters tend to be more enriched than would be expected for the simple physical mixing of river water and seawater these patterns can only be plausibly accounted for through evaporation affecting the water concentrating the chloride and causing isotope fractionation we have modelled the effects of evaporation on chloride concentration and the stable isotopes in the estuary the results closely match the distribution of analytical data suggesting that up to 40 evaporation has happened we have demonstrated that two thirds of estuarine water samples analysed underwent between 5 and 40 evaporation this previously unreported degree of evaporation in estuaries has important implications for any processes that is effected by the consequent degree of elevated solute concentration

the influence of climate and topography on rock fragment abundance in modern fluival sands of the southern blue ridge mountains north carolina chemical weathering influences the detrital composition of sand size sediment derived from source areas subject to different amounts of precipitation in the coweeta basin north carolina of the grain types studied rock fragments are most sensitive to chemical degradation therefore their abundance is the best indicator of cumulative weathering effects destruction of sand size rock fragments by chemical weathering is a function of both the intensity and duration of chemical weathering experienced by grains in regoliths of the source area in the coweeta basin the intensity of chemical weathering is directly related to the climate via effective precipitation in individual subbasins whereas the duration of chemical weathering is inversely related to the relief ratio of the watershed therefore soils in watersheds with low relief ratios and high discharge per unit area experience the most extensive chemical weathering and sediments derived from these watersheds contain the lowest percentage of rock fragments the effects of climate alone cannot explain the systematic variation of rock fragment abundance in sediments from the coweeta basin the compositional imprint left on these sediments by chemical weathering is a function of both climate and topographic slope in the sediment source area

detrital modes in sedimenticlastic sands from low order streams in the iberian range spain the potential for sand generation by different sedimentary rocks the composition of modern stream sands derived from sedimentary source rocks in the iberian range has been analyzed in order to evaluate the contributions of the different bedrock types mainly sandstones limestones and dolostones temperate to subhumid climate and short transport conditions promote a weathering limited denudation regime as expected sand composition proved to be essentially quartzolithic with variable amounts of penecontemporaneous carbonates sand compositional data were compared with the exposure areas of the different bedrocks in the drainage sub basins considered for semi quantitative assessment of the sand generation potential of each bedrock type siliciclastic formations sandstones appear to be by far the most significant sand producers with sand generation indices sgis in the medium sand fraction ranging from 4 to 20 i e 4 to 20 times greater than the sgi of carbonate rocks composition and texture are the main factors controlling carbonate sand generation sparitic limestones yield higher sgis 2 8 to 20 when source terrains are constituted exclusively by carbonate rocks high sparite grain content in the sands is enhanced by supplies from additional sources such as calcitized dolostones dolomicrite sources are strongly under represented in the sands analyzed very low sgi whereas the proportion of micritic limestone grains tends to be an accurate reflection of that bedrock at the source even though the results presented here refer to the first stage of sand generation with negligible transport effects we think they may be helpful in the analysis and reconstruction of source terrains in ancient sedimenticlastic deposits

pollen representation source area and basin size toward a unified theory of pollen analysis abstract the concepts of pollen source area and of production and dispersal biases in pollen representation are quantified by means of a simple theoretical model source areas and relative pollen representation are shown to depend on basin size according to functions that describe the amount of pollen remaining airborne at increasing distances from single pollen sources the form of these functions is determined by physical processes standard formulas for elevated sources do not apply but the integrated form of sutton s equation for particle dispersal from a ground level source gives useful approximations applicable to pollen transport over a forest canopy simulations using this equation yielded source areas that increased realistically with basin size showed substantial differences between source areas for pollen grains with different deposition velocities and predicted that lighter pollen grains should become better represented with increasing basin size all of these predictions are qualitatively consistent with present knowledge of the characteristics of pollen assemblages in different depositional environments the model further allows parameters that can be estimated by statistical calibration methods to be predicted from underlying physical quantities this extension suggests procedures for testing the theory with quantitative data on surface pollen and forest composition preliminary results showed reasonable agreement between estimated and predicted values of dispersal indices for the most abundant taxa in pollen spectra from the northern midwestern united states

preliminary results from laguna minucua a potentially annually resolved record of climate and environmental change for the past 5000 years in the mixteca alta of oaxaca mexico abstract despite several decades of research focusing on prehispanic human ecology debate continues over the impact of climatic and anthropogenic landscape change on human populations in mesoamerica one problem in identifying the cause of this change is the lack of high resolution paleo environmental data from many regions the southern mexican highlands in particular have yielded few paleoenvironment data yet have a rich and diverse cultural history the sedimentary record from laguna minucua located within the sierra madre del sur oaxaca offers an exceptional opportunity to address human and environmental interactions in the region minucua is a small 0 25 ha currently shallow pond with no apparent inlets or outlets we retrieved two sediment cores from the site 3 5 m and 5 6 m long the cores are highly laminated core chronology was developed with paleomagnetic secular variation data and compared with couplet counts and limited radiometric measurements these data indicate that the minucua record at least spans the last 4500 100 years we discuss preliminary results that assess long term environmental change for the region through examination of geochemical and magnetic susceptibility data in particular we discuss in more detail a 500 year time slice which encompasses the period known as the classic collapse the record indicates overall dry conditions but with two extended wet periods experienced between 1160 and 1120 cal yr bp and 1060 1000 cal yr bp we place our findings in the context of current archaeological and paleoclimatological research in oaxaca

buried salt marsh edges and tide level cycles in the mid holocene of the caldicot level gwent south wales uk combining stratigraphical sedimentological and biofacial foraminifera approaches a high resolution time constrained study has been made of a mid holocene c 5800 4900 14c yrs bp estuarine su

late holocene vegetation change in the sierra madre oriental of central mexico abstract past vegetation and climate changes reconstructed from a sediment core from laguna atezca molango mexico provide new insights into the environmental and cultural histories of the sierra madre oriental during the last 1700 yr pollen microscopic charcoal sediment chemistry loss on ignition and magnetic susceptibility indicate that three phases of human occupation deforestation and erosion ca a d 280 890 ca a d 1030 1420 and ca a d 1680 present alternate with two phases of abandonment ca a d 890 1030 and ca a d 1420 1680 forest composition of the two abandonment phases differed with cloud forest taxa liquidambar ostrya carpinus ulmus etc dominating the pollen record during the first phase and quercus and pinus pollen characterizing phase two these differences may reflect a climate change in which the second phase was drier than the first alternatively the increase in pinus and quercus may have been caused by a human induced decline in soil fertility the laguna atezca record also differs from several other mesoamerican paleoenvironmental records in that it shows no evidence of drought at the end of the classic period ca a d 900

fossil grass cuticles from lacustrine sediments a review of methods applicable to the analysis of tropical african lake cores the need for alternatives to fossil pollen for the reconstruction of vegetation dominated by grasses has prompted the use of grass cuticles which lack a described method of analysis methods used to analyse sediments for palaeoecological materials allied to grass cuticles including microscopic charcoal phytoliths and plant cuticles are reviewed a simple set of methods and protocols for extracting identifying and quantifying fossil grass cuticles are presented

initial generation of sand across climate zones of the mojave sierra nevada and klamath batholiths in california u s a the generation of modern plutoniclastic sediment across california varies with climate resulting in significant mineralogical and geochemical differences between parent rock weathering profile material and low order stream sand with average precipitation of 15 cm yr in the arid zones and 120 cm yr in the temperate zones feldspar is relatively decreased in stream sand compared to parent rock by 2 and 20 respectively potassium feldspar is more resistant to weathering than plagioclase but is less stable than quartz in temperate climates hornblende and biotite are more easily weathered in temperate than arid climates although their occurrence in medium grained stream sands is affected by hydraulic sorting and comminution during transport temperate climate sands have lower concentrations of cao and na2o compared to k2o and al2o3 reflective of the expected faster loss of plagioclase than potassium feldspar during weathering with the exception of biotite the mineralogy of medium grained stream sand reflects that of medium grained weathering profile material in both climates confirming the findings from constant climate case studies that the composition of proximal sand is largely achieved within weathering profiles and during initial erosion we encourage continued attention to climate as a control on sand composition in provenance and paleoclimate studies where a moderate precipitation shift is capable of producing a significant loss of feldspar the differential response of common minerals to chemical weathering should be considered for studies and modeling related to bedrock erodibility sediment supply and landscape evolution

quartz grain types in holocene deposits from the spanish central system some problems in provenance analysis holocene sands of the spanish central system were exclusively derived from plutonic middle upper grade and low grade metamorphic rocks modal composition of studied sands is mostly controlled by grain size and source area lithology thus sands derived from slates and schists plot near the qr edge on the qfr diagram for ali grain size fractions sands derived from granitic or gneissic rocks have a wide dispersion on the qfr diagram from the r pole to the qf edge depending on sand grain size percentages of quartz types in granitic derived sands are qnu42 qu40 qp2 314 and qp 34 sands of gneissic origin have qnu 51 qu 1 5 qp2 323 and qp 311 sands derived from slates and schists have qnu 20 qu 1 2 qp2 35 and qp 363 quartz types easily discrimina te sands of low grade origin but distinction of sands derived from plutonic rocks from those derived from middle upper grade metamorphic rocks is difficult because of the highly variable qu content of plutonic rocks related to strain history and crystallization conditions thus quartz types mus be used with caution in source discrimination if plutonic rocks are present in the source area

late flandrian holocene tidal palaeochannels gwent levels severn estuary sw britain character evolution and relation to shore abstract the exceptionally well exposed flandrian sediments on the welsh shores of the severn estuary reveal tidal palaeochannel networks uniquely tied to vertically stacked peat silt couplets field relationships show that channels multiplied and were enlarged as each peat organogenic marsh was rapidly transgressed replaced by and buried beneath silt mineralogenic marsh the networks infilled and shrank as the silt marsh later gave way regressively to the next peat marsh simulation and hydraulic models show that this cycle depended on an increase followed by a decrease in the tidal prism imposed on the marsh during a sea level fluctuation coupled patterns of channel width downstream orientation and coarseness of fill suggest that the many networks tied to the final flandrian peat silt couplet cycle iii ranged inland from a marsh edge lying of the order of 2 km seaward from the modern coast

oxygen and carbon isotope study of the holocene oyster reefs and paleoenvironmental reconstruction on the northwest coast of bohai bay china abstract the northwest coast of bohai bay supports large areas of holocene crassostrea gigas oyster reefs their huge size and the fact that the shells are composed of consecutive microgrowth layers consisting of primary calcite make them an ideal object for a stable isotope study the 18o and 13c compositions of the oysters reveal a number of interesting features the most important are annual cycles related to seasonal variations the regional 18o water versus salinity ratio and a stop in shell secretion below a water temperature of 11 5 1 5 c a positive correlation covariance between 18o and 13c values is present in most specimens the 18o and 13c values of single specimens are believed to be mainly controlled by water temperature and the occurrence of phytoplankton blooms and decomposition however correlation among oysters of different ages indicate that the 18o and 13c values are mainly dependant of three variables water temperature salinity and phytoplankton blooms decomposition between ca 6500 yrs cal b p and 2300 yrs cal b p the salinity in bohai bay increased from less than 20 to 30 based on geological data combined with ecological data from c gigas we suggest that precipitation decreased during this period while the input of fluvial sediments increased the sediment load of rivers increased markedly after ca 4000 yrs cal b p possibly due to a change in climate in our study area this resulted in the development of the oyster plain

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

pollen transport through distributaries and depositional patterns in coastal waters abstract in this study we compare seasonal pollen and spore assemblages in river waters from the mississippi river at vicksburg mississippi to those downstream at belle chasse louisiana and in a distributary the atchafalaya river at morgan city louisiana assemblages of pollen in waters at vicksburg and belle chasse are similar to each other but distinctively different from those in the atchafalaya river local pollen inputs are more important in the anastomosing atchafalaya river channel as compared to the meandering main stem mississippi channel which discharges through the bird foot delta riverine pollen and spore assemblages are also compared to those of surface sediments from the louisiana continental shelf in the vicinity of the mississippi river plume in this area the primary source of marine pollen and spore assemblages appears to be the discharge from the main stem mississippi with limited input from the atchafalaya thus pollen deposited in these coastal waters provides a record of vegetation in the mississippi drainage basin rather than local coastal areas pollen assemblages on the continental shelf vary with distance from the river source but not in a systematic manner the pattern is explained by biological controls on fine particle deposition in marine waters i e deposition of pollen in copepod fecal pellets as copepod grazing is dependent upon phytoplankton production pollen deposition from the river plume will be limited by high turbidities proximal to the river mouth we hypothesize that in neritic environments pollen is preferentially deposited in areas corresponding to high phytoplankton production which are characterized by reduced turbidity and high nutrient availability

the holocene pollen record in the villaviciosa estuary asturias north spain new data are provided on the history of holocene vegetation based on pollen records from a coastal sequence on the cantabrian coast a core with a continuous record corresponding to a complex sequence reflecting upward shallowing was studied and two 14 c dates of 6180f40 7030 cal yr bp and 2610f70 2775 cal yr bp were obtained the pollen study highlights the development in the area of an oak forest with corylus the presence of an interesting thermophilous floral assemblage and alder forests that spread around 3000 years ago the latter appears to be related to the availability of large areas of territory close to the villaviciosa estuary main channel and to a high phreatic zone it is interpreted as a response to autocyclic sedimentary discontinuity channel displacement rather than as an episode of sea level fall d 2006 published by elsevier b v

multiproxy paleoecological reconstruction of prehistoric land use history in the western region of the lower rio verde valley oaxaca mexico paleoecological archives from three paleomeander sites and one archeological feature located in the lower rio verde valley oaxaca mexico are used to develop a spatial understanding of the patter

stratigraphic evidence for anthropogenically induced coastal environmental change from oaxaca mexico abstract previous interdisciplinary paleoenvironmental and archaeological research along the rio verde valley of oaxaca mexico showed that holocene erosion in the highland valleys of the upper drainage basin triggered geomorphic changes in the river s coastal floodplain this article uses stratigraphic data from sediment cores extracted from laguna pastoria an estuary in the lower rio verde valley to examine changes in coastal geomorphology potentially triggered by highland erosion coastal lagoon sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene times three distinct storm facies are identified from sediment cores obtained from laguna pastoria which indicate that profound coastal environmental changes occurred within the region and are correlated with increased sediment supplied from highland erosion the chione laevicardium facies was deposited in an open bay while the mytella barnacle facies and sand facies were deposited in an enclosed lagoon following bay barrier formation we argue that highland erosion triggered major geomorphic changes in the lowlands including bay barrier formation by 2500 cal yr b p these environmental changes may have had significant effects on human populations in the region the lagoon stratigraphy further indicates an increase in mid late holocene hurricane activity possibly caused by increased el nino frequencies

seasonal deposition of holocene banded sediments in the severn estuary levels southwest britain palynological and sedimentological evidence abstract banded sediments outcrop widely in the intertidal zone of the severn estuary and have been suggested on the basis of textural analysis to have formed in response to seasonal variations in sea temperature and windiness holocene 14 2004 536 here palynological and sedimentological analyses of banded sediments of mid holocene date from gold cliff on the welsh side of the severn estuary are combined to test and further develop the hypothesis of seasonal deposition pollen percentage and concentration data are presented from a short sequence of bands to establish whether textural variations in the bands coincide with variations in pollen content reflecting seasonal flowering patterns it is shown that fine grained band parts contain higher total pollen concentrations and a higher proportion of pollen from late spring to summer flowering plants than coarse grained band parts pollen in the coarser deposits appears primarily to reflect deposition from the buffering reservoir of suspended pollen in the estuarine water body and from rivers when there is little pollen in the air in winter while the finer sediments contain pollen deposited from the atmosphere during the flowering season superimposed on these background sources the potential of such deposits for refining chronologies and identifying seasonality of coastal processes is noted and the results of charcoal particle analysis of the bands presented as an example of how they have the potential to shed light on seasonal and annual patterns of human activity

pseudomorphic transformation of plagioclases during the weathering of granitic rocks in galicia nw spain abstract microscopic study of twelve weathering profiles developed on granitic rocks in galicia nw spain showed that in most cases the transformation of the parent rock into saprolite occurs with pseudomorphic alteration of the plagioclases it was seen that the transformation and the retention of plagioclases in the alteration profile are directly related to the conservation of the general structure of the rock and this in its turn depends on the mineralogical composition and texture the most unstable constituents in the galician environment are biotites and plagioclases there being a clear difference in the rate of alteration between the plagioclases and the k feldspars this implies that a large part of the fabric of the rock remains unaltered when the plagioclases are completely weathered so that the pores caused by the weathering of the plagioclases are filled by their own alteration products with regard to the influence of the texture it was observed that fine grained rocks are altered more easily than coarse grained ones especially if they are rich in biotites in this study we show various examples in which even with high levels of alteration the morphological features of the original plagioclase crystals are preserved twins original zoning myrmekitic textures and perthites the pseudomorphic transformation of plagioclase is independent of the products to which it gives rise and here we show examples where gibbsite 1 1 dioctahedral phyllosilicate or a mixture of both appear as secondary minerals the mineralogical nature of a newly formed product depends mainly on the intensity of the leaching to which the profile is subjected which is influenced by the rainfall in the area where they are found as well as the size of existing voids in the material

human and natural impacts on fluvial and karst depressions of the maya lowlands abstract this paper begins to differentiate the major drivers and chronology of erosion and aggradation in the fluvial and fluviokarst landscapes of the southern and central maya lowlands we synthesize past research on erosion and aggradation and add new data from water soils radiocarbon dating and archaeology to study the quantity timing and causes of aggradation in regional landscape depressions geomorphic findings come from many excavations across a landscape gradient from upland valleys karst sinks and fans into the coastal plain floodplains and depressions findings from water chemistry show that sources in the uplands have low quantities of dissolved ions but water in the coastal plains has high amounts of dissolved ions often nearly saturated in calcium and sulfate we found significant geomorphic complexity in the general trends in upland karst sinks in a few instances sediments preserve late pleistocene paleosols buried 2 3 m though many more have distinct middle to late holocene paleosols buried 1 2 m after c 2300 bp maya early to late preclassic from 2300 1100 bp late preclassic to classic periods the landscape aggraded from five main mechanisms river flooding climatic instability accelerated erosion ancient maya landscape manipulation and gypsum precipitation from a rise in a water table nearly saturated in calcium and sulfate ions evidence exists for two or three high magnitude floods possibly driven by hurricanes moreover lake core and geophysical studies from the peten lakes region have shown high rates of deposition of silicate clays maya clays starting and peaking during the maya preclassic and continuing to be high through the late classic the main driver on upland karst depressions the peten lakes upland valleys and fans was accelerated soil erosion but water table rise probably driven by sea level rise was the main driver on the wetlands of the coastal plain because the aggraded sediments here are dominantly composed of gypsum precipitated from the groundwater this latter mechanism represents a little recognized mechanism of aggradation over a large region these large scale environmental changes occurred during periods of intensive ancient maya land use and climatic instability both of which may have contributed to erosion by increasing runoff despite these geomorphic changes ancient maya farmers adapted in several key cases