late pleistocene sea level change in the bahamas from mass spectrometric u series dating of submerged speleothem abstract the dating of sea level events by a method independent of orbital tuning techniques and the marine foraminiferal isotopic record provides a test of both the dating of the marine record and the strength and nature of the relationship between climatic change sea level change and milankovitch cycles dating of fossil corals and submerged speleothem provides such independent information results of thermal ionization mass spectrometric u series dating on layers of flowstone speleothem from lucayan caverns grand bahama island indicate that multiple sea level events have passed through a depth of 10 to 15 m below modern sea level during the last 300 000 years these data are used to constrain the magnitude and timing of sea level fluctuations during the late pleistocene the new sea level curve constructed from these data correlates closely with the marine isotopic record sea level peaks occurred at around 233 215 125 and 100 ka bp there is no evidence at the depth from which this speleothem was retrieved of any high sea stands at 195 or 80 ka corresponding to the foraminiferal 7a and 5a oxygen isotope peaks there is also no evidence of a double rise around the 125 ka 5e peak although such an oscillation could have occurred above 10 m leaving no record in the lucayan caverns speleothem

the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

geochemical facies analysis of fine grained siliciclastics using th u zr rb and zr rb sr ratios abstract abundance of the trace elements zr rb sr th and u may provide insight into the sedimentological origin of fine grained siliciclastic sediments provided that the units are derived from similar source areas as demonstrated here with suites of the fine grained jurassic and cretaceous rocks from the barents sea and svalbard zr rb ratios can be interpreted to indicate grain size variations while zr rb sr values reflect variations in the siliciclastic versus carbonate contents the th u ratio can be applied as an indicator of the redox conditions in 3d plots such as presented here the interplay between these geochemical factors can be interpreted in terms of the sedimentological evolution of the depositional basin the geochemical facies analyses show that similar depositional conditions existed on the jurassic shelf in the two studied localities the succeeding prodeltaic cretaceous beds were generally coarser grained and deposited in ventilated depositional conditions

south carolina interglacial sites and stage 5 sea levels abstract amino acid and other studies have been made on the 30 km pleistocene sections of the intracoastal waterway between myrtle beach and little river south carolina our ratios differentiate the long established waccamaw oldest canepatch and socastee formations the ratios from the four laboratories that have worked in this area agree very well and apparent conflicts with u series dates may merely reflect an abundance of reworked corals our amino acid correlations with u series coral dates in south carolina bermuda and the mediterranean all argue that the classical canepatch and its horry clay date from isotope stage 5e and not as has been implied from stage 7 9 11 or 13 excavations and erosion have increased position fixing problems along the waterway and canepatch amino acid ratios and u series dates 460 000 100 000 yr b p at icw5 may be from an older unit the canepatch shows the double marine transgression visible in many stage 5e deposits pollen shows that the second transgression occurred late in the interglaciation and stratigraphic studies show that it reached 14 m it therefore fits very well antarctic ice surge models of stage 5 sea level and climate the socastee adds to the evidence for one or more sea levels above 0 m late in stage 5

synchronization of late glacial vegetation changes at crystal lake illinois usa with the north atlantic event stratigraphy abstract late glacial 17 11 cal ka bp pollen records from midwestern north america show similar vegetation trends however poor dating resolution wide interval pollen counts and variable sedimentation rates have prevented the direct correlation with the north atlantic event stratigraphy as represented in the greenland ice core records thus preventing the understanding of the teleconnections and mechanisms of late quaternary events in the northern hemisphere the widespread occurrence of late glacial vegetation and climates with no modern analogs also hinders late glacial climate reconstructions a high resolution pollen record with a well controlled age model from crystal lake in northeastern illinois reveals vegetation and climate conditions during the late glacial and early holocene intervals late glacial crystal lake pollen assemblages dominated by picea mariana and fraxinus nigra with lesser amounts of abies and larix suggest relatively wet climate despite fluctuations between colder and warmer temperatures vegetation changes at crystal lake are coeval with millennial scale trends in the ngrip ice core record but major shifts in vegetation at crystal lake lag the ngrip record by 300 400 yr this lag may be due to the proximity of the laurentide ice sheet the ice sheet s inherent slowness in response to rapid climate changes and its effect on frontal boundary conditions and lake effect temperatures

geology of new providence island bahamas contrary to the popular notion that the bahama islands are built of eolianite deposits at least new providence island consists principally of elevated marine sand flat and protected lagoon deposits narrow eolianite ridges separate such deposits from reef tract deposits capped by prograding beach deposits on the northern bank margin side of the island all exposed depositional phases are quaternary the most extensively exposed deposits we correlate with the 125 000 yr high sea level recognized world wide elevations of keystone vugs in beach deposits of that depositional phase indicate paleo mean sea levels of as high as 10 m deposits of an earlier depositional phase suggest that there was then no island but only a barrier sand shoal and reef tract holocene additions to the island9s area have been minor and in the form of prograding beach deposits classical superpositional stratigraphy has limited value in the elucidation of new providence geology due to the nature of the deposits which are partially overlapping thin facies sheets and lenses therefore we have also used a morphostratigraphic approach and as paleontological markers species of cerion a very rapidly evolving genus of land snail limited radiometric dating is reported islands on bahama type banks of earlier geologic periods were probably built almost entirely of beach deposits rather than the eolianites and elevated marine deposits of which new providence is built

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

fuzzy based spatial modeling approach to predict island karst distribution a conceptual model previous studies have shown that island karst could successfully indicate paleoclimate change in the quaternary period however because of the relative inaccessibility of carbonate islands and their rural settings the exploration of island karst features has been limited to enhance future research remote sensing and geospatial modeling were used in this study to improve the island karst exploration record the results showed that fuzzy based spatial modeling could successfully predict the island karst distributions on a simple carbonate island the accuracy of the model was above 90 this method could apply to other coastal karst regions and carbonate islands in the future

paradigms and proboscideans in the southern great lakes region usa abstract thirteen new chronometric dates for illinois proboscideans are considered in relation to well dated pollen records from northeastern and central illinois these dates span an interval from 21 228 to 12 944 cal bp when compared to pollen spectra it is evident that mammut americanum inhabited spruce picea and black ash fraxinus nigra forest during the bolling allerod 14 700 12 900 cal bp and early younger dryas 12 900 11 650 cal bp chronozones both mammuthus jeffersonii and mammuthus primigenius inhabited spruce dominated open woodland during the oldest dryas chronozone while m primigenius persisted in a forest of predominantly black ash during the allerod chronozone a newly discovered specimen from lincoln il clarifies the taxonomic distinction between m primigenius and m jeffersonii hitherto a paradigm of proboscidean succession during the full to late glacial periods was based on the vegetation succession of steppe tundra like vegetation to spruce forest to spruce deciduous forest the presumed proboscidean succession was that of cold dry steppe adapted m primigenius succeeded by more mesic tolerant m jeffersonii that in turn was succeeded by the wet forest adapted m americanum reported data do not support this view and indicate a need for re evaluation of assumptions of proboscidean ecology and history e g the environmental tolerances and habits of m primigenius in regions south of 55 n and its dynamic relationship with other proboscidean taxa

the magnitude of error in conventional bulk sediment radiocarbon dates from central north america abstract although the carbon reservoir problem with bulk sediment radiocarbon dates from lakes has long been recognized many synoptic studies continue to use chronologies derived from such dates for four sites in central north america we evaluate chronologies based on conventional radiocarbon dates from bulk sediment versus chronologies based on accelerator mass spectrometry ams radiocarbon dates from terrestrial plant macrofossils the carbon reservoir error varies among sites and temporally at individual sites from 0 to 8000 yr an error of 500 2000 yr is common this error has important implications for the resolution of precise event chronologies

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

latest pleistocene paleoecology of jefferson s ground sloth megalonyx jeffersonii and elk moose cervalces scotti in northern illinois abstract new records of jefferson s ground sloth megalonyx jeffersonii and elk moose cervalces scotti from lang farm provide the first precise temporal correlation of these taxa with the specific environments inhabited by them near the time of their extinction six ams 14c measurements establish an age of 11 405 50 14c yr b p for lang farm cervalces and an age of 11 430 60 or 11 485 40 14c yr b p for the megalonyx these measurements represent the youngest 14c dates for these two genera based on direct dating comparison of the dates with pollen data from northern illinois indicates that these species inhabited a nonanalog environment that was transitional from mid latitude tundra to mixed conifer and deciduous woodland although spruce picea sp was dominant it was less abundant than prior to 12 500 14c yr b p the presence of black ash fraxinus nigra and fir abies sp indicates a wet climate and heavy winter precipitation this may have been the preferred habitat for cervalces because of its narrow geographic range however this habitat type was only one of many occupied by megalonyx as indicated by its broad geographic distribution

high precision mass spectrometric uranium series dating of cave deposits and implications for palaeoclimate studies calcite deposits in caves known as speleothem can provide valuable palaeoenvironmental information1 4 in particular because speleothem are deposited only in air filled caves gaps in deposition in coastal caves record high stands of sea level here we report the use of isotope dilution mass spectrometry to date speleothem by the uranium series method the use of mass spectrometry in uranium series dating was first applied to corals5 and has greatly improved the precision of this dating method the speleothem dated here a flowstone from 15 m below modern sea level in a bahamian cave records changes in sea level over the past 280 000 years the dated hiatuses in deposition indicate high sea level stands that are in general agreement with data from deep sea oxygen isotope stratigraphy6 and other estimates for the timing of high stands and glacial minima1 3 7

expanded response surfaces a new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues pollen based paleoclimatic interpretations of late glacial to early holocene climates 17 9 ka in midwestern north america are hampered by samples that lack modern analogues unresolved questions include the magnitude and direction of temperature seasonality i e were these climates more or less seasonal than present and the temporal changes in precipitation central to the no analogue problem is the truncation of modern pollen climate relationships for abundant late glacial taxa such as fraxinus here we present a new method called the expanded response surface ers method developed to reconstruct climates from no analogue pollen assemblages and applied to a high resolution late glacial pollen record from crystal lake illinois to test hypotheses about late glacial climates the key assumptions central to the ers method are 1 plant species and pollen abundances follow symmetrical unimodal distributions along climatic gradients 2 taxa with truncated distributions in modern climate space occupy a subset of their fundamental niche and 3 expansion of truncated distributions by mirroring around the distributional mode recovers the portion of the fundamental niche not realized in the modern climate space with the ers method we expanded modern pollen climate relationships by mirroring pollen abundances for each taxon around a mode defined with respect to four climate axes mean winter temperature mean summer temperature mean winter precipitation and mean summer precipitation the ers method reconstructed past temperatures and precipitation during the height of no analogue conditions 14 160 12 370 cal yr bp for 37 of the crystal lake samples where techniques that employed only modern observational data found matches for only 13 of the fossil samples the total climate space of the expanded taxa set allowed analogue matches under more seasonal than present climates with higher than present precipitation the ers climate reconstructions for the height of no analogue conditions indicated cooler than present summer and winter temperatures similar to present seasonal range in temperatures higher than present winter precipitation and similar to present summer precipitation these results thus suggest that high moisture availability helped drive the formation of the midwestern no analogue communities with high fraxinus nigra abundances but do not show higher than present temperature seasonality notwithstanding the higher than present insolation seasonality at this time during the no analogue late glacial interval picea mariana f nigra and larix stands probably grew on low lying poorly drained soils in the crystal lake region whereas abies picea glauca quercus and ostrya carpinus grew on upland positions with better soil drainage

heterogeneous distributions of co 2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution mixing dissolution a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals is commonly considered to form cavernous macroporosity e g flank margin caves and banana holes in eogenetic karst aquifers on small islands macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface suggesting that dissolution processes are decoupled from surface hydrology mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pco2 was assumed to be homogeneously distributed within the phreatic zone here we report data from two abandoned well fields in an eogenetic karst aquifer on san salvador island bahamas that demonstrate pco2 in the phreatic zone is distributed heterogeneously the pco2 varied from less than log 2 0 to more than log 1 0 atm over distances of less than 30 m generating dissolution in the subsurface where water flows from regions of low to high pco2 and cementation where water flows from regions of high to low pco2 using simple geochemical models we show dissolution caused by heterogeneously distributed pco2 can dissolve 2 5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater dissolution resulting from spatial variability in pco2 forms isolated globular chambers lacking initial entrances to the surface a morphology that is characteristic of flank margin caves and banana holes both of which have entrances that form by erosion or collapse after cave formation our results indicate that heterogeneous pco2 rather than mixing dissolution may be the dominant mechanism for observed spatial distribution of dissolution cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings copyright 2015 john wiley sons ltd

deglacial hydroclimate of midcontinental north america abstract during the last deglaciation temperatures over midcontinental north america warmed dramatically through the bolling allerod underwent a cool period associated with the younger dryas and then reverted to warmer near modern temperatures during the early holocene however paleo proxy records of the hydroclimate of this period have presented divergent evidence we reconstruct summer relative humidity rh across the last deglacial period using a mechanistic model of cellulose and leaf water 18o and d combined with a pollen based temperature proxy to interpret stable isotopes of sub fossil wood midcontinental rh was similar to modern conditions during the last glacial maximum progressively increased during the bolling allerod peaked during the younger dryas and declined sharply during the early holocene this rh record suggests deglacial summers were cooler and characterized by greater advection of moisture laden air masses from the gulf of mexico and subsequent entrainment over the mid continent by a high pressure system over the laurentide ice sheet these patterns help explain the formation of dark colored cumulic horizons in many great plains paleosol sequences and the development of no analog vegetation types common to the midwest during the last deglacial period likewise reduced early holocene rh and precipitation correspond with a diminished glacial high pressure system during the latter stages of ice sheet collapse

episodes of low dissolved oxygen indicated by ostracodes and sediment geochemistry at crystal lake illinois usa low dissolved oxygen during the summer and early fall controls profundal continental ostracode distribution in crystal lake mchenry county illinois favoring cypria ophthalmica and physocypria globula at water depths from 6 to 13 m these species also thrived in the lake s profundal zone from 14 165 to 9600 calendar year before present cal yr b p during the late bolling allerod and younger dryas chronozones and early holocene characterized by sand cemented tubules large aquatic gastropod shells and littoral ostracode valves thin 1 6 cm tempestite deposits punctuate thicker deposits of organic gyttja from 16 080 to 11 900 cal yr b p the succeeding 2300 yr 11 900 9600 cal yr b p lack tempestites and reconstructed water depths were at their maximum deposition of marl under relatively well oxygenated conditions occurred during the remainder of the holocene until the arrival of europeans when the lake returned to a pattern of seasonally low dissolved oxygen such conditions are also indicated in the lake sediment by the speciation of phosphorus high concentrations of organic carbon and abundant iron and manganese occluded to mineral grains initial low dissolved oxygen was probably caused by the delivery of dissolved p and fe in shallow groundwater the chemistry of which was influenced by spodosol pedogenesis under a spruce forest the triggering may have been regionally warm and wet conditions associated with retreat of the lake michigan lobe south central laurentide ice sheet

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

correspondence regarding atmospheric changes in north america during the last deglaciation from dune wetland records in the midwestern united states by wang h stumpf a j miao x lowell t v 2012 quaternary science reviews 58 124 134

isotope evidence of paleo el nino southern oscillation cycles in loess paleosol record in the central united states abstract the 13 c of soil carbonate in rhizoconcretions collected from aloess paleosol sequence in the central united states indicates that grow ing season c 3 c 4 plant ratio oscillated by 35 on a 900 200 yr timescale during the late wisconsinan glaciation the pattern appears inphase with advance and retreat of the southern margin of the lauren tide ice sheet suggesting influence by paleo el nino southern oscilla tion cycles the 13 c of soil organic matter indicates that the annual av erage c 3 c 4 plant ratio oscillated only by 18 with a periodicity of450 100 yr and closely matched the cyclic pattern of loess paleosollayers it suggests a periodic enhancement of the penetration of thegulf of mexico air over the region during this time keywords carbon isotope loess paleosol glacial phase paleo enso cycle introduction the el nino southern oscillation enso causes global scale climateanomalies the el nino and la nina are two counterparts of enso whichare associated with warming and cooling in surface water in the eastern trop ical pacific on the basis of modeling studies cane 1998 cane andclement 1999 and clement and cane 1999 proposed that frequency in tensity and duration of long term el nino or la nina intervals have oscil lated on a millennial time scale during the past 150 k y they proposed thatduring glacial periods these long term enso cycles might alter the globalclimate via atmospheric teleconnections in which el nino dominant inter vals may cause retreat and la nina dominant intervals may cause advanceof the southern margin of the laurentide ice sheet the enso sensitive re gions currently in north america partially overlap the area that was coveredby the laurentide ice sheet during the last glaciation fig 1 modernla nina conditions cause heavy snowfall whereas el nino conditions re duce winter precipitation in these regions http www ogp noaa gov enso it is reasonable to assume that la nina or el nino dominant intervals mighthave controlled advance and retreat of the southern margin of the laurentideice sheet if these intervals oscillate on a long term time scale in this paper we use stable isotope ratios from a loess paleosol exposure in the centralunited states to seek evidence for millennial scale paleo enso cycles

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

how did the hydrologic cycle respond to the two phase mystery interval abstract lake estancia s transition from a big dry episode during the first half of the mystery interval to a big wet episode during the second half has equivalents in records from across the planet at the time of this transition chinese monsoons experienced pronounced weakening closed basin lakes in both the great basin of the western united states and in the southern altiplano of south america underwent a major expansion mountain glaciers in southern hemisphere middle latitudes had retreated and the rates of increase of co2 and of 18o in antarctic ice underwent a decrease finally the precipitous drop in dust rain over antarctica and the southern ocean terminated as did a similar drop in the 13c to 12c ratio in atmospheric co2 these changes are consistent with a southward shift of the thermal equator the cause of such a shift is thought to be an expansion of sea ice caused by a shutdown in deep water production in the northern atlantic this creates a dilemma because a similar southward shift is an expected consequence of the heinrich event 1 which initiated the mystery interval

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

process like modeling of flank margin caves from genesis to burial evolution abstract a major challenge in groundwater and petroleum modeling is how to represent the diagenesis effect sensu lato and its associated features e g karst cavities porosity and permeability characteristics both geometrical descriptions and genesis are necessary for modeling diagenetic features because they allow the restitution of phenomenon in subsurface settings where they cannot be fully observed this study focuses on flank margin caves developed on carbonate islands as in the case of the bahamian islands over the last twenty years numerous measurements and observations have been carried out on quaternary carbonate islands these together with reasonable hypotheses of genesis fresh water lens dissolution make island karst an appropriate subject for developing concepts and modeling methods which can be then applied to other diagenetic features such as reflux dolomitization and hydrothermal fluid effects the speleogenesis of flank margin caves was modeled following deterministic and stochastic methods to achieve a description of dissolution genesis a fresh water lens surface was built based on the topography of long island bahamas and was then used to simulate virtual development of flank margin caves at several formation phases including uncertainty coefficients applied to both fresh water lens location and stability time by using 3d probability cubes the cave simulations were compared with over sixty bahamian cave surveys in order to substantiate our modeling processes and results finally the model was exposed to a cave collapse situation the likelihood of preservation and the extent of the area affected were measured to provide an evaluation of the spatial distribution of associated petrophysical characteristics e g porosity and permeability the results reveal close resemblance and coherence between modeled and field data including collapse features therefore the optimum method for restituting diagenetic features is by stochastic modeling actively driven by process concepts and most up to date methods

pyrolysis combustion 14c dating of soil organic matter abstract radiocarbon 14c dating of total soil organic matter som often yields results inconsistent with the stratigraphic sequence the onerous chemical extractions for som fractions do not always produce satisfactory 14c dates in an effort to develop an alternative method the pyrolysis combustion technique was investigated to partition som into pyrolysis volatile py v and pyrolysis residue py r fractions the py v fractions obtained from a thick glacigenic loess succession in illinois yielded 14c dates much younger but more reasonable than the counterpart py r fractions for the soil residence time carbon isotopic composition 13c was heavier in the py v fractions suggesting a greater abundance of carbohydrate and protein related constituents and 13c was lighter in the py r fractions suggesting more lignin and lipid related constituents the combination of 14c dates and 13c values indicates that the py v fractions are less biodegradation resistant and the py r fractions are more biodegradation resistant the pyrolysis combustion method provides a less cumbersome approach for 14c dating of som fractions with further study this method may become a useful tool for analyzing unlithified terrestrial sediments when macrofossils are absent

isotopic evidence for younger dryas aridity in the north american midcontinent determining the impact of the younger dryas yd climate event on the unglaciated north american midcontinent has proved difficult due to a scarcity of suitable paleoclimate proxies here we present a well dated carbon isotope 13c record from a buried soil sequence in southwestern missouri which reveals a large isotopic excursion during the yd chronozone in this region of the modern prairie forest border the 13c signature of soil organic matter is a reliable indicator of past climatic change because 13c values are controlled primarily by the relative abundance of c3 and c4 plants which is tied to the environmental setting between ca 13 200 and 11 900 yr ago the abundance of c4 grasses increased by upwards of 50 of the total biomass indicating expansion of grassland most likely driven by increased aridity during this period environmental gradients in the midcontinent must have been very steep because at the same time that a c4 rich prairie existed in southwestern missouri spruce forests grew in iowa illinois and ohio

revised interpretations of stable c and o patterns in carbonate rocks resulting from meteoric diagenesis abstract a positive correlation between the 13c and 18o values of carbonate rocks is a screening tool widely used to identify the overprint of meteoric diagenesis on the original isotopic composition of a sample in particular it has been suggested that systematic change from negative to positive 13c and 18o values with increasing depth in the core is an indicator of alteration within the zone of mixing between meteoric and marine waters in this paper we propose that such covariance is not generated within the traditionally defined mixing zone and that positive correlations between 13c and 18o values in marine carbonates are not necessarily indicators of meteoric alteration this new interpretation is based on data collected from the shallow sub surface of the bahamas a region unequivocally influenced by meteoric waters to depths of at least 200 m below the current sediment water interface the classic interpretation of the diagenetic environments based on changes in the 13c and 18o values would suggest the maximum penetration of freshwater occurs between 65 and 100 m below seafloor below these depths a strong positive covariation between the 13c and 18o values exists and would traditionally be defined as the mixing zone however based upon known changes in sea level the penetration of the freshwater lens extends significantly below this limit we contend that the zone showing covariance of 13c and 18o values is actually altered within the freshwater lens and not the mixing zone as previously proposed the co varying trend in 13c and 18o values is the result of diagenetic processes occurring at the interface between vadose and phreatic zones significantly greater rates of recrystallization and neomorphism are driven by the increased rates of oxidation of organic matter at this transition with progressively less alteration occurring with increasing depth as sea level oscillates the position of this interface moves through the deposit causing cumulative alteration throughout the section hence we propose that the covariation between 13c and 18o values is a consequence of varying degrees of alteration rather than the result of diagenesis occurring within the zone where marine and freshwater fluids mix furthermore within the pervasively altered vadose zone there is little correlation between 13c and 18o values and therefore covariation between 13c and 18o values is not an unequivocal indicator of meteoric diagenesis

terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest ohio usa article i nfo article history received 7 may 2010 available online 21 february 2011 optically stimulated luminescence dated sand dunes and pleistocene beach ridges in northwest ohio are used to reconstruct landscape modification more than 5000 yr after deglaciation four of the osl ages 13 3 11 1 ka cluster around the younger dryas cold event five ages 10 8 8 2 ka cluster around the preboreal one young age 0 9 0 7 ka records more recent aeolian activity and one age of 15 1 13 1 ka dates a barrier spit in lake warren in northwest ohio both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the younger dryas however the climate conditions during the preboreal resulting in aeolian activity are not recorded in the available pollen records from this we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler drier episodes of climate and can complement pollen data younger dryas and preboreal aged aeolian activity in northwestern ohio coincides with aeolian records elsewhere in the great lakes region east of the prairie forest ecotone

intensity gradients and reversals in late glacial environmental change in east central north america abstract radiocarbon dated pollen sites from the allegheny plateau east and the till plains west document significant vegetational and climatic change between 15 000 and 9000 14 c bp south of the great lakes although limited by the problems of no analog vegetation pollen transfer functions tf and response surfaces rs quantify the climatic changes including a cold oscillation chronologically equivalent to the european younger dryas phase i before ca 13 000 14 c bp conditions across the region were similar january 20 to 16 c july 12 c rs or 19 c tf mean annual precipitation 80 to 90 cm year 1 phase iia between ca 13 000 and 11 000 14 c bp n s and e w climate gradients were initiated till plains temperatures increased by ca 8 c in january and by 8 c rs or 2 3 c tf in july plateau increases for january were 3 6 c and for july were 8 c rs or 1 2 c tf precipitation generally increased somewhat phase iib ca 11 000 to 10 000 14 c bp gradients became less pronounced the western sites show a climate reversal january drop of ca 5 to 2 c july drop to ca 1 2 c becoming more like the plateau sites which show a brief small fluctuation this is followed by an abrupt 10 to 20 cm year 1 reduction in precipitation january warming of ca 3 c and continued cooler julys phase iii after 10 000 14 c bp gradients similar to those of today developed the changes in phases iib and iii are probably linked to the drainage history of the great lakes and via that history to the changes on the european continent

atmospheric changes in north america during the last deglaciation from dune wetland records in the midwestern united states reconstructing moisture conditions during the early retreat of the laurentide ice sheet lis may help define the phase relationship of deglacial conditions and atmospheric changes over north america here we report two sediment successions near the concurrent ice margins in the midwest of the u s a to show that dune formation was active from 17 7 to 14 7 and from 12 8 to 11 8 thousand years ago ka and lowland soils formed at 14 7 and wetland sediments developed from 13 5 to 12 8 ka our results suggest that moisture conditions in the midwestern u s a were inversely phased with those in the southwestern u s a during the heinrich event 1 h1 and younger dryas yd stadials the northern area became drier and southern area became wetter whereas during the bolling allerod b a interstadials the northern area became wetter and southern area became drier this pattern is also observed on phase change levels within the h1 interval in detail from 17 7 to 16 5 ka during the h1b phase major aridity in the midwest corresponded to wet conditions in the southwest u s a from 16 5 to 15 0 ka during the h1a phase climate reversed from dry to wet in the midwest whereas conditions went from wet to dry in the southwest from 15 0 to 14 7 ka during the transition to the bolling allerod t b a phase a return of aridity in the midwest corresponded to a return of humidity in the southwest

u series and amino acid racemization geochronology of bermuda implications for eustatic sea level fluctuation over the past 250 000 years abstract bermuda is a stable mid oceanic carbonate platform for which a particularly complete record of late pleistocene eustatic sea level fluctuation has been reconstructed from a detailed study of geological field relationships combined with an extensive programme of u series and amino acid racemization geochronology only twice in the past 250 000 yr has sea level in bermuda been above its present level once at approximately 200 k y when it stood at about 2 m and most recently at 125 4 k y when it stood at 5 1 m these times of interglacial high sea level are characterized by the development of patch reefs and marine calcarenites at elevations above present sea level episodes of lower sea stand onto the bermuda platform at elevations higher than 20 m are observed within the two interglacial periods and are characterized by the deposition of eolianites by contrast glacial periods are times of residual soil formation and deposition of speleothems in caves at elevations below present sea level excellent correlation is observed between the bermuda glacio eustatic sea level record and other marine and terrestrial paleoclimate records

late quaternary u series speleothem growth record from southeastern minnesota southeastern minnesota contains an extensive karst developed in limestones and dolomites ranging in age from early ordovician to middle devonian preliminary results from u series dated speleothems from caves within the karst show cyclic deposition of secondary calcium carbonate that coincides with cycles of late pleistocene glaciation peak intervals of deposition which broadly correlate with interglacial or interstadial climates occur from the present to 13 000 yr b p from 35 000 to 70 000 yr b p from 90 000 to 170 000 yr b p and an undivided interval from 170 000 to 350 000 yr b p intervals of little or no deposition are thought to reflect glacial climates the youngest growth intervals can be interpreted in terms of known glacial records in the midwest but for the older intervals where the glacial record is not well defined and beyond the range of radioactive dating it becomes more difficult to correlate speleothem deposition to glacial cycles although the groups of ages are in general agreement with sea level curves the correlation is not exact local climatic conditions seem to have had as much importance in determining when deposition occurred as did the major climatic cycles recorded in the marine record

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

provenance age and environment of mid wisconsinan slackwater lake sediment in the st louis metro east area usa abstract valleys tributary to the mississippi river contain fossiliferous slackwater lake sediment equality formation deposited in response to aggradation of the mississippi river valley during the last glaciation in the st louis metro east area the lower part of the equality formation is primarily laminated fossiliferous silt and clay deposited from about 44 150 to 24 310 14c yr b p the upper equality formation is primarily very fine sand to silt deposited from about 21 200 to 17 000 14c yr b p among the four cores that sample this succession in the st louis metro east area core mnk 3 38 64en 90 01ew was selected for detailed study three sources are distinguished by the following characteristics 1 gray smectite quartz se rich feldspar poor material of the des moines wadena and james lobes 2 reddish brown kaolinite cu fe rich sediment of the superior and rainy lobes and 3 brown illite dolomite sr rich sediment of the lake michigan and green bay lobes the earliest sediments 44 150 to 41 700 14c yr b p were derived from the central and western provenances and are chronocorrelative with the lower roxana silt a hiatus occurred from about 41 700 to 29 030 14c yr b p when much of the middle roxana silt meadow member was deposited on adjacent uplands the youngest sediment includes evidence of heightened activity of the superior lobe at about 29 000 14c yr b p the lake michigan and green bay lobes from about 25 000 to 24 000 14c yr b p and the wadena des moines james lobes at about 21 000 14c yr b p

highstands during marine isotope stage 5 evidence from the ironshore formation of grand cayman british west indies abstract the ironshore formation on grand cayman is formed of six unconformity bounded packages units a f units a b c and d known from the subsurface in the northeastern part of grand cayman formed during marine isotope stages mis 11 9 7 and 5e respectively unconformities at the tops of units a b and c are highlighted by terra rossa and or calcrete layers strata in core obtained from wells drilled in george town harbour and exposed on the west part of grand cayman belong to unit d and the newly defined units e and f corals from unit e yielded th u ages of 104 ka whereas conch shells from unit f gave ages of 84 ka unit e equates to mis 5c whereas unit f developed during mis 5a th u dating of corals and conchs from the ironshore formation on the western part of grand cayman shows that unit d formed during the mis 5e highstand whereas units e and f developed in association with highstands at 95 110 ka mis 5c and 73 87 ka mis 5a unit e 5 m thick in the offshore cores is poorly represented in onshore exposures unit f which unconformably overlies unit d at most localities is formed largely of fossil poor cross bedded ooid grainstones the unconformity at the top of unit d a marine erosional surface with up to 2 5 m relief is not characterized by terra rossa or calcrete in the offshore cores or onshore exposures unit d formed with a highstand of 6 m asl whereas units e and f developed when sea level was 2 to 5 asl and 3 to 6 m asl respectively thus the highstands associated with mis 5e 5c and 5a were at similar elevations

rapid sea level and climate change at the close of the last interglaciation mis 5e evidence from the bahama islands the geology of the last interglaciation sensu stricto marine isotope substage mis 5e in the bahamas records the nature of sea level and climate change after a period of quasi stability for most of the interglaciation during which reefs grew to 2 5 m sea level rose rapidly at the end of the period incising notches in older limestone after brief stillstands at 6 and perhaps 8 5 m sea level fell with apparent speed to the mis 5d lowstand and much cooler climatic conditions it was during this regression from the mis 5e highstand that the north atlantic suffered an oceanographic reorganization about 118 3 ka ago during this same interval massive dune building greatly enlarged the bahama islands giant waves reshaped exposed lowlands into chevron shaped beach ridges ran up on older coastal ridges and also broke off and threw megaboulders onto and over 20 m high cliffs the oolitic rocks recording these features yield concordant whole rock amino acid ratios across the archipelago whether or not the last interglaciation serves as an appropriate analog for our greenhouse world it nonetheless reveals the intricate details of climatic transitions between warm interglaciations and near glacial conditions

reply to comments by curry et al 2013 on atmospheric changes in north america during the last deglaciation from dune wetland records in the midwestern united states

a dated cave sediment record of pleistocene transgressions on berry head southwest england berry head a limestone headland in torbay southwest england exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms and developed in a marine freshwater mixing zone whose position was controlled by high sea level still stands corbridge cave in berry head quarry lies below the raised beaches in torbay and contains evidence of three marine transgressions in the form of fine grained marine ponding deposits with a marine microfauna uranium series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5 8 m od while an earlier transgression probably during stage 7 reached at least 7 2 m od these findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in southwest britain and a correlation of the unnamed stage of bowen sykes reeves miller andrews brew and hare with oxygen isotope stage 5e is proposed

tectonic uplift sea level changes and plio pleistocene evolution of a coastal karst system the mount saint paul palawan philippines the st paul karst palawan philippines is a tropical coastal karst consisting of towers cones huge depressions and large caves this area hosts the puerto princesa subterranean river ppsr 24 km long whose main entrance is a large spring along the coast and which is one of the largest cave complexes in eastern asia a geomorphological study performed by several field surveys and a morphometric analysis of the digital terrain model dtm and 3d cave models allowed formulation of a first evolutionary framework of the karst system the dtm was extracted from maps and aerial photographs in order to find different generations of relict landforms through the morphometric analysis of topographic surface and karst landforms several features suggest a long and multi stage evolution of the karst whose age ranges from pliocene to present the southern and northern sectors of the area differ in their altimetric distribution of caves in the southern sector some large caves lie between 300 and 400 m asl and were part of an ancient system that developed at the base level of a past river network in the northern sector some mainly vadose caves occur with a phreatic level at 120 130 m asl an important phase of base level cave development is well documented in the inactive passages of ppsr at 50 80 m asl morphological features such as horizontal solution passages and terraced deposits suggest a phase of stillstand of the base level which is recorded in the topography as low relief surfaces at 40 50 m asl the age of this phase is probably early pleistocene on the basis of assumed uplift rates the more recent caves are still active being located at the current sea level but they show more than one cycle of flooding and dewatering with calcite deposition in the ppsr several morphologic features such as two main water level notches at 12 4 and 7 7 m asl and terraced alluvial deposits suggest that the lower and active level passed through more than two high stands of sea level and so it could have formed throughout most of the middle late pleistocene copyright 2010 john wiley sons ltd