shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

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

spatial analysis of thickness variability applied to an early jurassic carbonate platform in the central southern alps italy a tool to unravel syn sedimentary faulting early jurassic syn sedimentary extensional tectonics in the central southern alps controlled patterns of deposition within the calcari grigi carbonate platform we used variogram maps to gather model independent information on the spatial distribution of thicknesses of selected platform units and investigated whether major syn sedimentary faults outlined subsiding domains during platform growth thicknesses display a spatial organization that suggests that large fault belts often coincident with exposed jurassic extensional structures transected large parts of the platform the network of four fault systems trending nnw sse and ne sw displays orthorhombic symmetry suggesting non andersonian faulting and a true triaxial strain field with n100 e maximum extension or transfer shear zones connecting major nnw sse trending extensional faults in both cases inherited structures of permian to triassic age may have played a primary role in jurassic faulting if confirmed throughout the south alpine domain this arrangement could shed new light on early jurassic rifting mechanisms in the southern alps

el chichon the genesis of volcanic sulfur dioxide monitoring from space the 1982 eruption of el chichon inspired a new technique for monitoring volcanic clouds data from the total ozone mapping spectrometer toms instrument on the nimbus 7 satellite were used to measure sulfur dioxide in addition to ozone for the first time precise data on the sulfur dioxide mass in even the largest explosive eruption plumes could be determined the plumes could be tracked globally as they are carried by winds magmatic eruptions could be discriminated from phreatic eruptions the data from el chichon are reanalyzed in this paper using the latest version of the toms instrument calibration v8 they show the shearing of the eruption cloud into a globe circling band while still anchored over mexico in three weeks the measured sulfur dioxide mass in the initial march 28 eruption was 1 6 tg the april 3 eruption produced 0 3 tg more and the april 4 eruptions added 5 6 tg for a cumulative total of 7 5 tg in substantial agreement with estimates from prior data versions toms aerosol index absorbing aerosol data show rapid fallout of dense ash east and south of the volcano in agreement with advanced very high resolution radiometer avhrr ash cloud positions

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

stability and instability on maya lowlands tropical hillslope soils abstract substantial lake core and other evidence shows accelerated soil erosion occurred in the maya lowlands of central america over ancient maya history from 3000 to 1000 years ago but we have little evidence of the wider network of the sources and sinks of that eroded sediment cascade this study begins to solve the mystery of missing soil with new research and a synthesis of existing studies of tropical forest soils along slopes in nw belize the research aim is to understand soil formation long term human impacts on slopes and slope stability over time and explore ecological implications we studied soils on seven slopes in tropical forest areas that have experienced intensive ancient human impacts and those with little ancient impacts all of our soil catenas except for one deforested from old growth two years before contain evidence for about 1000 years of stable tropical forest cover since maya abandonment we characterized the physical chemical and taxonomic characteristics of soils at crest shoulder backslopes footslopes and depression locations analyzing typical soil parameters chemical elements and carbon isotopes 13 c in dated and undated sequences four footslopes or depressions in areas of high ancient occupation preserved evidence of buried clay textured soils covered by coarser sediment dating from the maya classic period three footslopes from areas with scant evidence of ancient occupation had little discernable deposition these findings add to a growing corpus of soil toposequences with similar facies changes in footslopes and depressions that date to the maya period using major elemental concentrations across a range of catenas we derived a measure ca mg al fe mn of the relative contributions of autochthonous and allochthonous materials and the relative age of soil catenas we found very low ratios in clearly older buried soils in footslopes and depressions and on slopes that had not undergone ancient maya erosion we found high ca mg al fe mn values on slopes with several lines of evidence that suggest relative youth soils possibly formed since maya abandonment carbon isotopes 13 c also provide some evidence of past vegetation change on slopes we found strong evidence for maize or other alien c 4 species in an ancient terrace soil and additional evidence in buried footslopes but only evidence for c 3 species like tropical trees on the backslopes and other crest shoulders the fact that steep slopes preserved no evidence of c 4 species inputs may mean that the ancient maya maintained forests here alternatively ancient maya land uses eroded slopes with the 13 c signatures detected today being the result of more recent soil development under forest over the last millennium additional evidence that these soils are recent in age includes elevated ca mg al fe mn values skeletal soil profiles and low soil magnetic susceptibility besides the evidence for truncating backslopes and aggrading footslopes the ancient maya built agricultural terraces that accumulated soils and altered drainage all these ancient maya slope alterations would have influenced modern tree distributions because many tree species in the modern forest show strong preferences for different soil types and topographic situations that the ancient maya changed

soils in the mediterranean region what makes them different mediterranean climates are characterized by winter rains with some months of excess rainfall over evatranspiration warm and dry summer months with moisutre deficits drying out soils and their annual vegetation xeric moisture regime they are found on western parts of all continents between the cooler temperature zone and the hot dry desert zone the largest mediterranean region surrounding the mediterranean sea extends over 4 300 000 km2 and exhibits a wide variety of soils and geo ecosystems characteristics landscape attributes are the high proportion of mountains with sleep slopes significant additions of saharan desert dust to practically all soils of the region and a large proportion of limestone and other calcareous rocks as soil parent materials characteristics soil behavior features are moderate weathering with pervection leaching lessivage of mostly 2 1 clays into b horizons xeralfs luvisols hematite induced reddening of the clays due to summer dehydration of free iron oxyhydroxides carbonate dissolution and reprecipitation with prevalence of calcic horizons xerolls calcisols in semiarid regions and development of vertisols mostly in lowlands where deep layers of swelling cracking clays have sedimented shallows soils on nearly bare slopes mostly a result of erosion subsequent to deforestation are frequent leptosols cambiosols inceptisols entisols red or brown mediterranean soils are no longer used as a separate classification group in modern well defined soil property controlled taxonomies soil taxonomy fao system but were partially replaced by duchaufour s term fersiallitic soils in some classification systems terra rossa continues to be used in some classification for hard limestone derived red soils mostly shallow the effects of man s past and current interference with the lanscape are pervasive in most regions and predictions for possible future effects on the soils and ecosystems due to greenhouse gas induced warming and rainfall change are partly negative partly still too uncertain

long period multiple suppression by predictive deconvolution in the x t domainl1 there are two forms of systematic error in conventional deconvolution as applied to the problem of suppressing multiples with periodicities longer than a hundred milliseconds one of these is the windowing effect due to the assumption that a true autocorrelation function can be computed from a finite portion of data the second form of error concerns the assumption of periodicity which is strictly true only at zero offset for a 1d medium the seriousness of these errors increased with the lengthening of the multiple period this paper describes and illustrates a rigorous 2d solution to the predictive deconvolution equations that overcomes both of the systematic errors of conventional 1d approaches this method is applicable to both the simple or trapped system and to the complex or peg leg system of multiples it does not require that the design window be six to ten times larger compared to the operator dimensions and it is accurate over a wide range of propagation angles the formulation is kept strictly in the sense of the classical theory of prediction the solution of normal equations are obtained by a modified conjugate gradient method of solution developed by koehler in this algorithm the normal equations are not modified by the autocorrelation approximation as with all linear methods approximate stationary attitude in the multiple generating process is assumed this method has not been tested in areas where large changes in the characteristic of the multiple generating mechanism occur within a seismic spread length

calcite raft geochemistry as a hydrological proxy for holocene aquifer conditions in hoyo negro and ich balam sac actun cave system quintana roo mexico abstract two cores from calcite rafts deposits located in cenote ich balam and hoyo negro were dated and analyzed for 87sr 86sr 18o 13c sr ca and cl ca the geochemical records show changing aquifer salinity spanning the last 8 5 cal kyrs bp and interrelationships with holocene climate trends wet and dry periods during the wet mid holocene the salinity of the meteoric water mass wm at 7 8 8 3 cal kyrs bp was relatively high at 1 5 2 7 ppt and then became less saline 1 0 1 5 ppt during the last 7000 yrs as climate became progressively drier high salinity of the meteoric wm during the wet mid holocene is attributed to increased turbulent mixing between the meteoric and underlying marine wm increased precipitation in terms of amount frequency and intensity e g hurricanes causes higher flow of meteoric water towards the coast and mixing at the halocline a phenomenon recorded with recent instrumental monitoring of the aquifer conversely during dry periods reduced precipitation and flow in the meteoric wm would result in lower salinity karst properties and holocene sea level rise also seem to have an effect on the aquifer when the regionally extensive network of shallow cave passages 10 12 m water depth are flooded at 8000 cal yrs bp there is a rapid shift in salinity this study demonstrates that calcite raft deposits can be used as paleo environmental recorders documenting the effects of sea level and climate change on aquifer condition

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

red mediterranean soils in some karstic regions of taurus mountains turkey abstract red soils are found along fractures and between bedding surfaces in karstic regions of both mediterranean and aegean regions of turkey these soils are very unique and information on pedogenesis in karstic regions are rather limited detailed field works were carried out at 17 locations soil profiles were examined at 14 sites and 7 of these were reported here soil samples from thea and b horizons of these soils are used to detailed characterization analyses in the laboratory occurrence of normal soil profiles were unusual in the study regions the fractured structure of limestone leads to unusual water and air circulation when water penetrates into rock fissures and holes and diffuses into sedimentary layers in situ weathering processes take place rock fissures and holes may also be filled in by the transport of soil materials from higher elevations sedimentary petrology and mineralogy of limestones are the factors that control the course of the pedogenesis oxidation of fe especially sulfides pyrite accelerates the soil formation in limestones soils are not present on massive an fractured or fissured limestones and thin and stony red soils are common only at the bottom parts of v shaped dolines however soils are thick and common within the materials that have alternating marl and sandy silty layers vertical movement of soil particles towards the deeper parts of te limestone tkes place as a result of the widening of the lapies which are mostly formed along the fractures most of the red soils in the studied karstic regions were likely developed during the tertiary and ot and humid periods of the quaternary epochs large body of soils which are found in deep limestones suggest their formation under paleochimatic environments

pedosediments of karstic sinkholes in the eolianites of ne yucatan a record of late quaternary soil development geomorphic processes and landscape stability abstract the pedogenetic and geomorphic processes controlling soil development in tropical karstic landscapes are still poorly understood we have discovered and studied thick pedosediments in karst pockets developed in late pleistocene lithified calcareous dunes eolianites in the ne coast of the yucatan peninsula the morphological geochemical and mineralogical characteristics of the pocket fills were interpreted as a record of pedogenesis and geomorphic dynamics that shaped the soil mantle during the holocene sand fraction mineralogy and the zr ti ratio indicated a mixed origin of the soil parent material volcanic and granitic metamorphic components redeposited in the lithoral and coastal environments were identified within the soil matrix primary minerals were transformed by weathering and caused desilicification accumulation of clay hydroxy interlayered vermiculite and kaolinite and dithionite citrate bicarbonate extractable iron oxides fed reworked pedofeatures indicative of clay illuviation and redoximorphic processes were observed this set of processes points to a continuous phase of humid pedogenesis several thousand years long in the early middle holocene however the development of thick recalcified pedosediments in the pockets contrasting with the thin background rendzinas requires active soil redeposition during a late phase of geomorphic activity the available accelerator mass spectrometry ams radiocarbon date indicates that the switch of the erosion sedimentation processes could be related to ancient maya land use impact

geoarchaeology and tropical forest soil catenas of northwestern belize new research on soil catenas under old growth tropical forest in nw belize aims to understand soil formation long term human impacts and slope stability over time we studied areas with intensive ancient maya impacts from 3000 to 1000 years ago and those with little ancient impact to compare how ancient land use influenced slopes after about 1000 years of stable tropical forest cover we characterized the physical chemical and chronological characteristics of soils at crest shoulders backslopes footslopes and depression locations analyzing typical soil parameters and carbon isotopes 13c in dated and undated sequences several of the footslope and depressions sites preserved evidence of buried paleosols with increased 13c dating by four new ams dates and three others we reported earlier from the maya classic period with high amounts of soil organic matter from c4 species in ecosystems where only a few c4 species occur today most crest shoulders and backslopes had no evidence for increased 13c though some crests and mid slope sinks preserved evidence of ancient maya impacts the observation that steep slopes preserved no evidence of c4 species inputs may mean that ancient maya land use maintained forest reserves here alternatively ancient maya land uses caused slope erosion with the 13c signatures detected today resulting from more recent soil development under forest and soil re formation over the last millennium additional evidence that these soils are recent in age includes elevated caco3 sr and low soil magnetic susceptibility showing less leaching compared with older soils in our study other human impacts on soils include increased concentrations of fe and mn terracing and further evidence of substantial topsoil erosion in antiquity

terra rossa catenas in wisconsin usa abstract the soils in the unglaciated part of wisconsin have a loess cover over sedimentary rock mostly dolostone of ordovician age the dolostone has weathered and produced layers of red clay or terra rossa we have sampled 144 pedons of 16 catenas with different slope aspects and curvatures in a 70 km 2 area half of all the pedons had a red clay subsoil mostly 5yr 3 4 and had on average over 40 clay the mean thickness of the loess above the red clay was 50 cm but it ranged from 7 to 130 cm the thickness of the red clay ranged from 4 cm to 60 cm with an average thickness of 25 cm the red clay was found in every part of the landscape except the valley bottoms it was present in soils on summits shoulders backslopes and footslopes the red clay is only found over dolostone but not present on all dolostone ridges it was concluded that there is large variation in the terra rossa soilscapes of wisconsin and this variation can only partly be explained by topography

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

sequence development in an isolated carbonate platform lower jurassic djebel bou dahar high atlas morocco influence of tectonics eustacy and carbonate production six sequences each with a distinct shape stratal anatomy bounding surfaces lithofacies composition and stacking patterns were identified in the djebel bou dahar isolated carbonate platform which developed in a half graben in the high atlas marine rift basin during the early jurassic sequences are believed to have a complex multi process origin as the result of tectonic processes regional subsidence and fault block rotation overprinting the eustatic signal in addition changing carbonate producers with shifting centres of deposition and relative accumulation potential influenced the filling and anatomy of the accommodation space that had been created by the hybrid tectonic and eustatic processes sequences i and ii are tabular in shape and interpreted to primarily reflect the combined processes of uniform tectonic subsidence and eustacy which resulted in a ramp to shelf carbonate system with lagoon and tidal flat lithofacies onset of a rifting episode around the base of the lotharingian and fault block rotation were responsible for the development of the angular unconformity with the underlying sequence ii and the progressive development of a shallow water isolated platform and the wedge shaped depositional sequences iii to vi during the lotharingian and pliensbachian concurrent variations in palaeoceanographic conditions and in the carbonate factory caused a shift towards a flat topped platform geometry with high energy coated grains and sub photic sponge microbial deposition around the margin the aggradational to retrogradational character of sequences iii iv and vi is inferred to be a result of the combined effect of in situ carbonate production coupled with high rates of creation of accommodation space in the hanging wall environmental effects on carbonate production were the most probable cause for drowning of the djebel bou dahar platform during the toarcian but also influenced the filling and geometry of sequences iv to vi this study suggests that the commonly accepted model of pulse driven sequence development in half grabens may not be fully applicable for the djebel bou dahar where a more continuous rotation at sequence scale associated with subsidence pulses of the djebel bou dahar block seems to have interacted with eustacy and carbonate production to generate sequences continuous rotation is suggested by the presence of regular patterns of diverging strata and numerous minor exposure surfaces in lagoonal deposits of sequences v and vi in addition this study demonstrates that eustacy and variations in the carbonate factory might be as significant as tectonics in sequence development and platform drowning in carbonate platforms within rift basins this observation could imply that the effects of eustacy and the carbonate factory might not have been correctly recognized in other similar carbonate platforms due to a tectonic biased interpretation

the effect of seasonal rainfall on nutrient input and biological productivity in the yax chen cave system ox bel ha mexico and implications for μxrf core studies of paleohydrology abstract lakes and speleothems from mexico s yucatan peninsula have been used extensively over the past decades for paleoclimate studies however aquifer condition and its response to climate change has received little attention cenotes sinkholes and coastal caves have been shown to record the paleohydrology of the aquifer but there is little information on sedimentation in these cave systems and its response to climate change newly developed xrf instrumentation for the analysis of cores can achieve subannual resolution due to small measurement increments but short period studies examining weathering inputs and rainfall have not yet been undertaken hindering paleoenvironmental interpretations of lake and cave sediment records this study examines the spatial and temporal relationship of cave sediment geochemistry in the anchialine cave system of yax chen quintana roo mexico sediment traps n 51 were placed at seventeen stations along the 2 7 km flooded cave system which transitions from mangrove to upland forest terrain with cenotes of variable size and frequency along its length sediment traps were collected every 6 months from may 2013 may 2017 along with rainfall and groundwater level data there are distinct responses of lithogenic fe ti sr limestone weathering and biogenic influenced si k s phytoplankton and mangrove sediment elements in the sediment samples associated with seasonal rainfall and hurricanes while lithogenic elements ti k show a direct relationship seasonal rainfall the sedimentation of biologically influenced si ti elements exhibit a 6 12 month lagged response with large rainfalls such as hurricane ingrid in 2013 and other tropical storms throughout the study period

margin for error anthropogenic geomorphology of bajo edges in the maya lowlands abstract many early maya cities developed along the edges of large structural or karst depressions bajos this topographic position aided growing populations to more effectively capture and store rainwater a necessity for year round occupation of interior portions of the maya lowlands of mexico and central america ancient maya forest clearance on sloping terrain led to accelerated soil loss and the aggradation of the bajo margins these newly created margins of colluvial lands became a focus of subsequent intensive agriculture and helped underwrite further urban expansion we document this long term landscape transformation with data derived principally from field investigations at tikal guatemala and yaxnohcah mexico but with reference to other maya centers in the elevated interior region eir data are derived from field investigations interpretation of lidar imagery and laboratory analyses we present a model of three variants of bajo margin landscape change with differences attributable to topography lithology hydrology and cultural processes we present preliminary data on crops that were cultivated on bajo margin soils we further describe how agriculture was adapted to evolving bajo margins as evidenced by systems of field walls terraces and ditches

carbonate platform evidence of ocean acidification at the onset of the early toarcian oceanic anoxic event abstract the early toarcian oceanic anoxic event early jurassic 183 myr ago is associated with one of the largest negative carbon isotope excursion cie in the whole phanerozoic 3 7 estimates of the magnitude and rate of co 2 injection in the ocean atmosphere system are compatible with a scenario of ocean acidification many carbonate platforms drowned in the pliensbachian well before the early toarcian event in this paper we test the hypothesis of surface water ocean acidification by presenting data from a resilient carbonate platform the apennine carbonate platform of southern italy the studied sections document a dramatic shift of the carbonate factory from massive biocalcification to chemical precipitation lithiotis bivalves and calcareous algae palaeodasycladus mediterraneus which were the most prolific carbonate producers of pliensbachian carbonate platforms disappear during the first phase of the early toarcian cie before the most depleted values are reached we discuss the local versus supraregional significance of this shift and propose a scenario involving abrupt decline of carbonate saturation forced by co 2 release at the beginning of the early toarcian cie followed by a calcification overshoot driven by the recovery of ocean alkalinity attribution of the demise of carbonate platform hypercalcifiers to ocean acidification is supported by palaeophysiology and reinforced by experimental data on the detrimental effects of ocean acidification on recent shellfishes and calcareous algae

the use of volcanic materials for the manufacture of pozzolanic plasters in the maya lowlands a preliminary report this paper focuses on the description and characterization of the nature of isotropic and silicon rich particles observed in plaster samples from the maya archaeological sites of calakmul and lamanai based on the composition and morphology of these particles it is proposed that volcanic ash and glass were incorporated into some of the ancient maya plasters in order to produce hydraulic reactions from a technological point of view the intent on the part of the maya to produce such reactions is relevant because it would reflect resource planning and complex knowledge of materials results also confirm previous reports of the presence of volcanic ash layers at the site of calakmul and suggest that there were considerable ash falls in the maya lowlands during prehispanic times which may have made the material available in many areas of the central lowlands if as we propose here volcanic ash was employed in lowland maya plasters then the use of volcanic materials by the lowland maya was more intensive than has been recognized our paper also reviews the literature about the use of volcanic materials in lowland maya materials and suggests future lines of research

mineralogical and geochemical indicators of the polygenetic nature of terra rossa in istria croatia abstract terra rossa in istria is situated on the jurassic cretaceous paleogene carbonate plain and is considered a polygenetic reddish soil which bears typical terra rossa fe oxide characteristics e g fe d and fe d fe t the difference in particle size mineralogy and geochemistry observed between terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in istria terra rossa is clay and silty clay composed of quartz plagioclase k feldspar micaceous clay minerals illitic material and mica kaolinites kl d and kl chlorite vermiculite low charge vermiculite or high charge smectite mixed layer clay minerals other than illitic material hematite goethite and xrd amorphous inorganic compound calcite dolomite and boehmite are sporadically present and are of local importance kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from istria kaolinite which does not form intercalation compounds with dimethylsulfoxide dmso is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock if terra rossa has developed only from the insoluble residue of limestone and dolomite its clay content due to weathering should be higher than that in the insoluble residues which is not the case plagioclase was found only in one insoluble residue while all terra rossa samples contain this mineral moreover insoluble residues do not contain vermiculite which was observed in small amounts in clay fraction of all terra rossa samples na 2 o k 2 o 100 zr nb and zr ti 1000 ratios in the majority of terra rossa samples are much higher than in the insoluble residue of limestones and dolomites which also supports external material influence in the genesis of terra rossa materials other than the insoluble residue of limestones and dolomites which might have contributed to terra rossa are loess sediments whose deposition was very important recurrent process in istria probably since the early middle pleistocene and flysch sediments which extended much more southwards from its present position analyses performed indicate that both loess older than that of the upper pleistocene age and flysch might have contributed in the genesis of terra rossa

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

terra rossa genesis implications for karst and eolian dust a geodynamic thread abstract although terra rossa has long been thought to form by residual dissolution of limestone and or by accumulation of detrital mud ash or dust on preexisting karst limestones we present conclusive new field and petrographic evidence that terra rossa forms by replacement of limestone by authigenic clay at a moving metasomatic front several centimeters wide the red clay s major chemical elements al fe and si probably come from dissolved eolian dust the replacement of calcite by clay exhibits a serrated microstylolitic texture that helps prove that replacement happens not by dissolution precipitation as conventional wisdom has it but by pressure solution of calcite driven by the crystallization stress generated by the growth of clay crystals the acid produced by the isovolumetric replacement of limestone by clay quickly dissolves out additional porosity permeability in an adjacent slice of limestone within the front triggering a reactive infiltration instability that should theoretically

the role of african dust in the formation of quaternary soils on mallorca spain and implications for the genesis of red mediterranean soils abstract african dust additions explain the origin of terra rossa soils that are common on the carbonate platform island of mallorca spain mineralogical and geochemical analyses indicate that quaternary carbonate eolianites on mallorca have a very high purity usually composed of more than 90 carbonate minerals calcite dolomite and aragonite in contrast terra rossa soils developed on these eolianites have lower carbonate contents and contain higher concentrations of quartz and other silicates analyses of immobile trace elements indicate that the non carbonate fractions of the eolianites have distinctive zr hf la yb cr sc and th ta values that differ from the superjacent terra rossa soils these observations indicate that even if sufficient dissolution of the eolianite had taken place to create the soils by residual accumulation immobile element ratios in the soils require an external source however zr hf la yb cr sc and th ta values in the soils fall within the range of values for these element ratios in african dust collected on barbados and mainland spain we conclude that the silicate fractions of terra rossa soils on mallorca are derived mainly though not wholly from far traveled african dust and this process may explain the origin of other terra rossa soils found in southern europe

early pliensbachian early jurassic c isotope perturbation and the diffusion of the lithiotis fauna insights from the western tethys abstract high resolution carbonate carbon isotope stratigraphy of lower jurassic marine shallow water limestones are compared with the distribution of the lithiotis fauna on the trento platform southern alps italy the lithiotis fauna is the first example of globally distributed mound building bivalves in the geological record and experienced global diffusion in the early jurassic a set of carbonate carbon isotope excursions of 2 3 illustrating three distinct negative shifts followed by positive rebounds are recorded in the isotope stratigraphy and can be correlated with the global negative 13 c shift of the sinemurian pliensbachian boundary event s p event and to the subsequent phase of c isotope perturbation that characterized the lower pliensbachian in the studied stratigraphic sections the s p event likely triggered eutrophic conditions illustrated by the presence of organic rich facies and by fossil associations characteristic of poorly oxygenated waters after the eutrophic phase the amelioration of environmental conditions was marked by a positive 3 rebound of the 13 c carb values and by the occurrence of marine stenotypic faunas on the trento platform the stabilization of the 13 c carb values coincided with the appearance of the lithiotis fauna that subsequently became widely distributed in the entire range of platform environments and thrived in the late pliensbachian when metric scale bivalve mounds were generated during the same time the maximum proliferation of the lithiotis fauna is recorded both in the tethyan and panthalassa regions hence the reported relationships between the 13 c carb data and the distribution and ecological characteristics of the genera contained in the lithiotis fauna suggest that the s p event and its aftermath possibly coupled with the undergoing coeval continent reorganization that led to the opening of the hispanic corridor could have set the stage for the rapid diffusion of these unusual bivalves across many parts of the globe

ancient maya impacts on the earth s surface an early anthropocene analog abstract the measure of the mayacene a microcosm of the early anthropocene that occurred from c 3000 to 1000 bp comes from multiple late quaternary paleoenvironmental records we synthesized the evidence for maya impacts on climate vegetation hydrology and the lithosphere from studies of soils lakes floodplains wetlands and other ecosystems maya civilization had likely altered local to regional ecosystems and hydrology by the preclassic period 3000 1700 bp but these impacts waned by 1000 bp they altered ecosystems with vast urban and rural infrastructure that included thousands of reservoirs wetland fields and canals terraces field ridges and temples although there is abundant evidence that indicates the maya altered their forests even at the large urban complex of tikal as much as 40 of the forest remained intact through the classic period existing forests are still influenced by ancient maya forest gardening particularly by the large expanses of ancient stone structures terraces and wetland fields that form their substrates a few studies suggest deforestation and other land uses probably also warmed and dried regional climate by the classic period 1700 1100 bp a much larger body of research documents the maya impacts on hydrology in the form of dams reservoirs canals eroded soils and urban design for runoff another metric of the mayacene are paleosols which contain chemical evidence for human occupation revealed by high phosphorus concentrations and carbon isotope ratios of c 4 species like maize in the c 3 dominated tropical forest ecosystem paleosol sequences exhibit maya clays a facies that reflects a glut of rapidly eroded sediments that overlie pre maya paleosols this stratigraphy is conspicuous in many dated soil profiles and marks the large scale maya transformation of the landscape in the preclassic and classic periods some of these also have increased phosphorous and carbon isotope evidence of c 4 species we synthesize and provide new evidence of maya period soil strata that show elevated carbon isotope ratios 13 c indicating the presence of c 4 species in typical agricultural sites this is often the case in ancient maya wetland systems which also have abundant evidence for the presence of several other economic plant species the mayacene of c 3000 to 1000 bp was thus a patchwork of cities villages roads urban heat islands intensive and extensive farmsteads forests and orchards today forests and wetlands cover much of the maya area but like so many places these are now under the onslaught of the deforestation draining and plowing of the present anthropocene

a new locality of palygorskite rich clay from the southeastern yucatan a potential material source for environmental applications a palygorskite unit was discovered in a road cut of undifferentiated tertiary limestone between the villages of el pariso and san roman 18 49 309n 88 37 861w in the southeastern yucatan peninsula mexico this is the southern most locality of a clay rich sedimentary unit reported in the literature for the tertiary carbonates of the yucatan peninsula this occurrence indicates a much wider range of palygorskite rich clay deposition than previously recognized the lithology is 99 clay and 1 sand to silt size diagenetic quartz grains the clay consists of approximately 85 palygorskite 15 montmorillonite and trace amounts of titanium oxides eds analyses on palygorskite are largely consistent with sedimentary palygorskites from other coastal marine settings however palygorskite has a low total fe content average 0 40 wt expressed as fe2o3 compared to many other sedimentary palygorskites montmorillonite chemical compositions are typical and compared to the palygorskite have substantially higher fe2o3 concentrations average 3 90 wt the low percentage of coarse grains in the lithology combined with a high proportion of palygorskite and lack of detrimental trace minerals suggest the deposit is of industrial grade however it has limited reserves 6 000 m3 the unit could be potentially used in a wide array of environmental applications which are needed in the region including liners for landfills and constructed wetlands the unit is in a geographic location which would serve the expanding economy of the region this resource has the potential to have great impact on the quality of the local environment and the economy of a region under great environmental threat

spatial distribution and development of soils in tropical karst areas from the peninsula of yucatan mexico abstract better understanding of soil formation requires knowing the spatial distribution of the soils that allows constructing models of soil sequences in multiple directions along various types of gradients this approach was applied to comprehend the soil formation from the soil distribution in the tropical karst areas of the peninsula of yucatan mexico for soil mapping a two step methodology was followed first a geomorphic analysis was performed subsequently 382 soil profiles were reclassified and integrated into a geopedologic map additional soil survey was carried out in areas where soil information was lacking 123 soil profiles satellite images were used to identify flooded areas after conducting numerous field verifications and analyses landforms and soils were combined to make a soilscape map based on field observations and the soilscape map soil development was analyzed on soil sequences four geomorphic environments were identified karstic plains and hills with leptosols cambisols luvisols and vertisols coastal plains with arenosols regosols solonchacks and histosols fluvio paludal plains with gleysols histosols leptosols and solonchacks and tectono karstic plains and hills with leptosols cambisols luvisols and vertisols relevant soil forming factors in the peninsula of yucatan include time of emersion of the limestone platforms climate rock type and macro and micro relief other factors such as groundwater level fractures also have an influence on soil formation karst development can be considered as a complex soil and relief forming factor terra rossa soils as leptosols cambisols luvisols nitisols and vertisols in the peninsula of yucatan may be polygenic in some cases the theory of residual origin fits better the data than the theory of allochthonous origin in other cases it is the other way around

trophic regimes of benthic foraminiferal assemblages in lower jurassic shallow water carbonates from northeastern italy calcari grigi trento platform venetian prealps abstract benthic foraminiferal distribution patterns in the lower jurassic rotzo member trento platform northeastern italy are analysed in terms of trophic gradients to provide a better understanding of the benthic communities during the time of the initial diversification of lower jurassic large foraminifera in the southern alps the rotzo member deposited on the trento platform records a complex mosaic of distinct shallow water ecosystems the changes in the foraminiferal assemblages of the rotzo member are considered to be primarily a reflection of gradients in trophic resources and oxygen levels the comparative analysis of benthic foraminiferal assemblages characteristic taxa number of species test size reproduction strategy the associated sediments lithofacies and the macrofossil and microfossil content allow three trophic regimes to be identified during the time of deposition of the rotzo member a eutrophic b mesotrophic and c oligotrophic a the eutrophic regime marked by episodically dysaerobic bottom conditions and high organic matter supply occurs stratigraphically below and within the orbitopsella spp assemblage sinemurian pro parte carixian gradual change in the benthic foraminiferal assemblage may have been caused by a combination of reduced nutrient supply and increased bottom water circulation which led to a mesotrophic regime b the latter which has been recognised in the basal and middle part of the rotzo member alternating with the eutrophic assemblage is characterised by a foraminiferal assemblage dominated by orbitopsella sp a major foraminiferal faunal turnover across the carixian domerian boundary corresponding to the disappearance of orbitopsella spp indicates a significant environmental change an oligotrophic regime c became established towards the upper part of the rotzo member new taxa appeared and diversity of the foraminiferal faunas was higher than in the previous ecosystems this part of the member characterised by the maximum lateral and vertical development of large lithiotis bivalve mounds reflects low and more stable nutrient supply which provided optimal conditions for the more specialised benthic communities evolution of these benthic foraminiferal faunas from the late pliensbachian onwards was obliterated by events that led to the drowning of the trento platform which is marked by a regional unconformity

morphology genesis and classification of three soils over limestone jamaica abstract this paper describes three jamaican soils over limestone that are widely different in their genesis morphology and classification following descriptions of the locations of the profiles the environmental conditions governing their formation are discussed two of the profiles are derived from limestone the third is developed in bauxite in all three profiles intense weathering preceded actual soil formation in profiles 1 and 2 weathering of the limestone rock through dissolution of caco3 resulted in the residual accumulation of clay minerals such as kaolinite and chlorite the bauxite deposit in which profile 3 developed represents a very advanced stage of weathering and desilication the origin of the jamaican bauxites is not clear however soil formation in the two soils over limestone an ultisol and an alfisol is characterized by downward movement of clay iron and organic matter and by the formation of an argillic horizon biological mixing oxidation reduction and formation of nodules are additional processes one of these profiles shows a lithological discontinuity in this soil transformation of rock fragments chert into pseudo iron manganese nodules has contributed to soil formation we postulate that the dominant processes in the profile developed in bauxite an oxisol are desilication and residual accumulation of oxides of aluminium and iron into an oxic horizon other soil forming processes in this profile comprise biological activity some iron segregation and nodule formation the three profiles are classified according to the usda soil taxonomy the legend for the fao unesco soil map of the world and the french soil classification system cpcs rationales for placement in these systems are discussed detailed profile descriptions and laboratory data are presented in an appendix

pedogenic carbonate crusts calcretes in karstic landscapes as archives for paleoenvironmental reconstructions a case study from yucatan peninsula mexico abstract in the northeastern margin of the yucatan peninsula which is located in southeastern mexico three levels of compact carbonate crusts calcretes interlayered with indurated coastal calcareous sediments calcarenites are discernible since both the calcretes and calcarenites form a continuous carbonate sequence a combined methodology macro and micromorphology geochemistry and mineralogy is used to differentiate them additionally the calcrete layers are dated using the uranium thorium method in order to establish a chronological framework the carbonate differentiation and chronology are then used to establish the paleoenvironmental conditions that prevailed during calcrete formation as well as to reconstruct the coastal landscape evolution and its relation to pleistocene sea level changes during marine isotope stages mis 6 and 5 samples of calcrete layers and calcarenites were taken from two sections in the cancun tulum corridor the lowest level of calcrete underlies a sequence of calcarenites and the two younger levels cap the sequence in calcretes the micromorphology provides evidence of the presence of a relict soil with subangular blocky microstructure root traces and needle fiber calcite associated with soil fungi interactions in contrast the micromorphology of the calcarenites shows ooids and bioclasts typical of a coastal environment geochemically calcretes are depleted in 13c compared to calcarenite with values ranging between 2 and 10 and they have a lower proportion of rare earth elements calcrete mineralogy consists mainly of calcite over aragonite with a low proportion of mg calcite u th dating indicates that the oldest calcrete was formed during the penultimate glacial maximum pgm in mis 6 and the two younger calcretes correspond to the last interglacial period in mis 5c the calcarenite formation occurred earlier also during mis 5 soil formation strong karstification and soil erosion have occurred on younger calcretes this study suggests that these processes developed between mis 4 to mis 1

geochemical evidence for african dust and volcanic ash inputs to terra rossa soils on carbonate reef terraces northern jamaica west indies abstract the origin of red or reddish brown clay rich terra rossa soils on limestone has been debated for decades a traditional qualitative explanation for their formation has been the accumulation of insoluble residues as the limestone is progressively dissolved over time however this mode of formation often requires unrealistic or impossible amounts of carbonate dissolution therefore where this mechanism is not viable and where local fluvial or colluvial inputs can be ruled out an external source or sources must be involved in soil formation on the north coast of the caribbean island of jamaica we studied a sequence of terra rossa soils developed on emergent limestones thought to be of quaternary age the soils become progressively thicker redder more fe and al rich and si poor with elevation furthermore although kaolinite is found in all the soils the highest and oldest soils also contain boehmite major and trace element geochemistry shows that the host limestones and local igneous rocks are not likely source materials for the soils other trace elements including the rare earth elements ree show that tephra from central american volcanoes is not a likely source either however trace element geochemistry shows that airborne dust from africa plus tephra from the lesser antilles island arc are possible source materials for the clay rich soils a third as yet unidentified source may also contribute to the soils we hypothesize that older more chemically mature jamaican bauxites may have had a similar origin the results add to the growing body of evidence of the importance of multiple parent materials including far traveled dust to soil genesis

environmental control and dynamics of lower jurassic bivalve build ups in the trento platform southern alps italy abstract bivalve molluscs show a short and peculiar early jurassic evolutionary phase characterized by the lithiotis sensu lato fauna mainly represented by the three monospecific genera lithiotis cochlearites and lithioperna these bivalves with stick like or flattened large shells are mostly restricted to the pliensbachian they have a wide geographical distribution occurring both in tethyan and panthalassian carbonate platforms where considerable biogenic accumulations formed they were common on the trento platform southern alps where they occur in the rotzo formation calcari grigi group this formation was deposited in a tropical lagoon which was closed seawards by oolitic shoals and bars and bordered landwards by marshes the lithiotis s l fauna of the trento platform seems to be restricted to the upper pliensbachian it appeared after a eutrophic phase with recurrent low oxygen and brackish conditions and flourished in meso to oligotrophic waters the stratigraphic and geographic distributions of each genus are compared to the environmental development of the rotzo formation in order to highlight limiting environmental factors and ecological requirements lithioperna occurs throughout the whole formation it is the most eurytopic genus well adapted to dysaerobic habitats and with higher ecomorphic plasticity than the other two genera it frequently occurs in the life position giving rise to densely packed fan like or book like aggregates lithiotis required aerobic and euhaline marine conditions and is common in the middle part of the formation where mesotrophic conditions prevailed this genus is rarely preserved in the theoretical vertical life position probably due to lower shell stability and a less effective attachment modality cochlearites is the most common genus of the rotzo formation this genus inhabited euhaline to slightly hypersaline marine environments occurring in the upper part of the formation prevailing in oligotrophic conditions lithiotis s l fauna gave rise to biogenic accumulations with an elevation of a few decimeters to several meters above the sea bottom and with a lateral extension ranging from ten to several hundred meters therefore these accumulations represent biological build ups which document four developmental phases colonization aggradation progradation and demise the colonization phase is represented by pioneering individuals which were cemented or byssally attached to a bioclastic coarse grained storm layer which constituted the hard substrate for larval attachment the aggradation phase produced the core of the build up and its elevation above the sea bottom the core is mostly represented by individuals which acted as bafflers commonly with an apparently chaotic fabric the lithiotis s s and cochlearites cores are generally mud supported and contain loosely packed to dispersed specimens occasionally preserved in life position the lithiotis s s and cochlearites build ups can be defined as bivalve mounds the cores of the lithioperna build ups are skeletal supported with shells mostly preserved in life position which characterize the bivalve reefs the prograding phase produced lateral additions to the build up flanks of oblique and imbricated articulated individuals the flanks grew centrifugally from the core and represent the most conspicuous part of the build ups ranging from 10 to 20 times the size of the core and occasionally extending over several hundred meters