response of tide dominated mangrove shorelines in northern australia to anticipated sea level rise the exact response of mangrove shorelines to anticipated sea level rise will depend upon the balance between sedimentation and sea level change within the top end of the northern territory of australia there are extensive relatively unmodified tide dominated mangrove forests where tidal processes redistribute sediment harbours such as darwin harbour and tidal rivers such as the south alligator river with its associated coastal and estuarine plains represent opposite extremes in terms of holocene sedimentary infill and will respond differently to sea level rise in darwin harbour mangrove assemblages can be recognized in geomorphologically defined habitats similar topography within and between creeks implies morphodynamic equilibrium with tidal processes tidal reworking of sediment may maintain an equilibrial profile under gradually rising sea level with resuspension of lower intertidal and subtidal muds and their redeposition within upper intertidal mangrove habitats in contrast the plains along the coast and tidal rivers draining into van diemen gulf developed during the post glacial marine transgression and since sea level stabilized around 6000 years ago coastal plains have prograded these broad plains are presently not extensively influenced by salt water but are often at elevations close to or even below modern high tide levels they may therefore revert to saline conditions particularly rapidly if the sea rises the pattern of change may not be directly analogous to marine incursion experienced in the early holocene because broad plains have been able to prograde during the last 6000 years of relatively stable sea level

holocene climatic and human influences on lakes of the yucatan peninsula mexico an interdisciplinary palaeolimnological approach we used palaeolimnological techniques to examine effects of holocene climate change and human influence on lakes of the yucatan peninsula mexico the three study lakes are located along a west east transect that represents a gradient of increasing modern precipitation and density of former maya settlement at lake coba an 880 cm sediment core yields a complete record of lacustrine sedimentation that began when the lake first filled 8000 bp as groundwater level rose in response to rising sea level and increased precipi tation diatom ostracod and 18o evidence indicate that lake coba was initially shallow and saline coba presently in the region of greatest rainfall showed more episodic water level changes than lake san jose chulchaca or lake sayaucil high lake level and fresh water were evident at 440 cm 2600 bp followed by a decline in water levels and an increase in total ionic salinity to the present time in a 613 cm core from sayaucil in the intermediate precipitation zone total salini

drivers of holocene sea level change in the caribbean abstract we present a holocene relative sea level rsl database for the caribbean region 5 n to 25 n and 55 w to 90 w that consists of 499 sea level index points and 238 limiting dates the database was compiled from multiple sea level indicators mangrove peat microbial mats beach rock and acroporid and massive corals we subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on rsl we account for the local scale processes of sediment compaction and tidal range change using the stratigraphic position overburden thickness of index points and paleotidal modeling respectively we use a spatio temporal empirical hierarchical model to estimate rsl position and its rates of change in the caribbean over 1 ka time slices because of meltwater input the rates of rsl change were highest during the early holocene with a maximum of 10 9 0 6 m ka in suriname and guyana and minimum of 7 4 0 7 m ka in south florida from 12 to 8 ka following complete deglaciation of the laurentide ice sheet lis by 7 ka mid to late holocene rates slowed to

last interglacial reef growth beneath belize barrier and isolated platform reefs we report the first radiometric dates thermal ionization mass spectrometry from late pleistocene reef deposits from offshore belize the location of the largest modern reef complex in the atlantic ocean the results presented here can be used to explain significant differences in bathymetry sedimentary facies and reef development of this major reef area and the results are significant because they contribute to the knowledge of the regional geology of the eastern yucatan the previously held concept of a neotectonically stable eastern yucatan is challenged the dates indicate that pleistocene reefs and shallow water limestones which form the basement of modern reefs in the area accumulated ca 125 130 ka significant differences in elevation of the samples relative to present sea level 10 m have several possible causes differential subsidence along a series of continental margin fault blocks in combination with variation in karstification are probably the prime causes differential subsidence is presumably related to initial extension and later left lateral movements along the adjacent active boundary between the north american and caribbean plates increasing dissolution toward the south during pleistocene sea level lowstands is probably a consequence of higher precipitation rates in mountainous southern belize

paleoecology of mangroves along the sibun river belize abstract this study examines a sediment core sr 63 from a mangrove ecosystem along the sibun river in belize which is subject to both changes in sea level and in the characteristics of the river s drainage basin radiocarbon dates from the core show a decreased sedimentation rate from 6 ka to 1 cal ka bp and a marked change in lithology from primarily mangrove peat to fluvial derived material at 2 5 cal ka bp changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea level and the rate of sea level rise pollen analyses show a decreased abundance of rhizophora red mangrove pollen and an increased abundance of avicennia black mangrove pollen and non mangrove pollen coeval with the decreased sedimentation rates elemental ratios n c a and stable isotope analyses 15 n and 13 c show that changes in the composition of the organic material are also coeval with the change in lithology the decrease in sedimentation rate at the site of core sr 63 and at offshore sites supports the idea that regional changes in hydrology occurred during the holocene in belize influencing both mainland and offshore mangrove ecosystems

holocene sedimentary evolution of a mid ocean atoll lagoon maldives indian ocean based on detailed analyses of cores covering the lagoon of rasdhoo atoll maldives six carbonate facies one soil and one peat facies have been identified the abundance of carbonate and rare opaque grains was quantified with a point counter x ray diffractometry was used to measure mineralogical composition of samples the statistical delineation of facies using cluster analysis was based on point count mineralogical and textural analyses in decreasing abundance the six carbonate facies are classified as mollusk coral algal floatstone to rudstone 30 mollusk coral red algae rudstone 23 mollusk coral algal wackestone to floatstone 23 mollusk coral wackestone 13 mollusk coral mudstone to wackestone 9 and mollusk mudstone 2 the carbonate facies represent lagoonal background sedimentation mostly consisting of fine sediments and event sedimentation depositing transported coarse grained reefal components fifty seven carbonate samples and one peat sample were dated radiometrically covering the holocene transgression from 10 kyrs bp until today comparing the sediment accumulation data of the lagoon with two local sea level curves three systems tracts can be identified 1 a lowstand systems tract characterized by karst and soil deposition 10 kyrs bp 2 a transgressive systems tract with peat and carbonate separated by hiatus 10 6 5 kyrs bp and 3 a highstand systems tract dominated by carbonate sedimentation 6 5 0 kyrs bp and further divided into three stages 6 5 3 3 1 and 1 0 kyrs bp during the holocene transgression sedimentation rates increased continuously to a maximum of 1 4 m kyr during 3 1 kyrs bp modern 1 0 kyrs bp mean sedimentation rates average 0 6 m kyr a simple calculation suggests that two processes background sedimentation and sand apron progradation will probably fill up the accommodation space of the lagoon during the holocene highstand but these processes will not suffice to fill the larger atoll lagoons of the archipelago

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

great blue hole lighthouse reef belize a continuous annually resolved record of common era sea surface temperature atlantic multidecadal oscillation and cyclone controlled run off abstract the holocene 1900 ce is more likely the result of the suess effect anthropogenic impact of the industrial revolution on carbon isotopes composition than another reflection of a tc peak activity interval

bundled turbidite deposition in the central pandora trough gulf of papua since last glacial maximum linking sediment nature and accumulation to sea level fluctuations at millennial timescale since last glacial maximum 23 19 ka earth climate warming and deglaciation occurred in two major steps bolling allerod and preboreal interrupted by a short cooling interval referred to as the younger dryas 12 5 11 5 ka b p in this study three cores mv 33 mv 66 and md 40 collected in the central part of pandora trough gulf of papua have been analyzed and they reveal a detailed sedimentary pattern at millennial timescale siliciclastic turbidites disappeared during the bolling allerod and preboreal intervals to systematically reoccur during the younger dryas interval subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1b the holocene interval was characterized by a lack of siliciclastic turbidites relatively high carbonate content and fine bank derived aragonitic sediment the observed millennial timescale sedimentary variability can be explained by sea level fluctuations during the last glacial maximum siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge although they did not occur during the intervals of maximum flooding of the shelf during meltwater pulses 1a and 1b siliciclastic turbidites reappear briefly during the younger dryas an interval when sea level rise slowed stopped or perhaps even fell the timing of the calciturbidite coincides with the first reflooding of eastern fields reef an atoll that remained exposed for most of the glacial stages

mangrove history during middle and late holocene in pacific south eastern mexico a paleoecological analysis of a 6 m long sedimentary sequence from the la encrucijada biosphere reserve rble from southern pacific mexico provides detailed information about past vegetation chang

quaternary reef response to sea level and environmental change in the western atlantic the tropical subtropical western atlantic realm harbours abundant fringing reefs two major barrier reefs belize florida several atolls and large reef fringed carbonate platforms bahamas data from belize and south florida indicate that major barrier reefs were established during the high sea levels of the long and warm marine isotope stage 11 reefs formed during pleistocene sea level highstands whereas erosion non deposition and the formation of subaerial exposure surfaces prevailed during lowstands of sea level florida bahamas exposed reefs and platforms with siliciclastic hinterlands were characterized by deposition of clays and sands on fluvial plains belize elevated terraces and outcrops of reefs of the last interglacial of marine isotope stage 5e are evidence of higher than present sea level and temperature that sustained large reef fringed carbonate platforms and ramps in the florida bahamas region and central america belize mexico including ooid deposition in warm and shallow waters during the highstands of marine isotope stages 5c and 5a at sea levels several metres lower than today fringing reefs developed in parts of the caribbean for example in south florida outlier reefs data from the island of barbados support the contention that the postglacial sea level rise from about 120 m was rapid and punctuated by two meltwater pulses ia and ib which bracket the beginning and end of the younger dryas respectively after reflooding of shelves in the early holocene reefs developed preferentially on highs of the underlying karstified pleistocene limestone surface and on former river channel bars many reefs in the western atlantic region kept pace with holocene sea level rise whereas some were drowned reasons for reef drowning are debated and include sea level rise elevation of antecedent topography and deterioration of environmental conditions such as high nutrient input apart from sea level and antecedent topography factors such as exposure to waves and currents storms and sedimentation have controlled reef development the historical decline of acroporid corals in the caribbean realm has been attributed to cooling following the holocene thermal optimum however historical die offs of reef building corals and other reef organisms suggest that some if not all recent declines were unprecedented during the holocene rising temperatures decreasing carbonate saturation increased frequency of major storms high nutrient concentrations and sedimentation overfishing and disease certainly played a role in decline but systematic studies relating these environmental factors to holocene reef building are only in the early stages

deepwater carbonate deposition in response to re flooding of carbonate bank and atoll tops at glacial terminations the late quaternary has experienced large glacial interglacial climatic variations and related 10 s to 100 meters high amplitude sea level fluctuations at milankovich frequencies from 10 s to 100 kyr during which carbonate platform tops have been exposed and re flooded in many occasions this study focuses on the accumulation of calci turbidites the aragonite onset sharp increase in fine sediments and their timing in deep basins adjacent to carbonate platforms a particular emphasis is developed on the occurrence of the first gravity flow event and aragonite onset sharp increase and their linkage to the initial re flooding of the platform tops during deglaciations three basins adjacent to isolated platforms in the bahamas the northern nicaragua rise and the gulf of papua were selected to represent pure carbonate versus mixed systems in quiescent versus tectonically active settings and various carbonate bank top morphologies ranging from atoll to relatively deeply and narrowly flooded flat top banks in spite of these differences each record illustrates a clear relationship between the timing of platform top re flooding and initiation of significant carbonate export by gravity flows and low density plumes into the surrounding basins the concept of re flooding window is introduced to characterize the prolific period of time during which bank and atoll tops are flooded enough to produce large export of bank derived aragonite and of calci turbidites in adjacent basins according to our datasets the main re flooding windows have occurred mainly on the last part of the sea level rise at each glacial termination t those periods being marked by some of the highest rates of sea level rise the analysis of a long piston core from the earthquakes prone walton basin northern nicaragua rise demonstrates that sea level not seismic activities played a major role as trigger mechanism for the initiation of gravity flows since the last four glacial interglacial transitions and supports the existence of an extra glacial termination during the early portion of the transition from mis 7 4 to mis 7 3 tiiia

sedimentological evolution of north sound grand cayman a freshwater to marine carbonate succession driven by holocene sea level rise abstract north sound grand cayman contains up to 4 m of sediments that accumulated under the influence of the holocene rise in sea level originally north sound was a dish shaped depression formed by the erosion of the miocene dolostone and pleistocene limestone bedrock at that time a sill along the northern margin isolated the area from the open ocean sedimentation from 5 000 to 3 800 yr b p which took place in a fresh water to brackish water regime resulted in deposition of the composite grain gastropod and bivalve facies as sea level rose above the sill no later than 2 500 yr b p marine waters began to invade north sound and open connections with the caribbean sea were established peats which developed in mangrove swamps were deposited during this transitional phase fully marine sedimentation ongoing for at least the last 2 500 years resulted in the deposition of the halimeda halimeda benthic foraminifera bivalve and bivalve halimeda facies sediment which accumulated at an average of 85 cm 1000 years did not keep pace with sea level which rose at an average of 160 cm 1000 years as a result accommodation space in north sound has progressively increased a sea level curve derived from basal peats and bivalves found in the sediments of north sound is comparable to sea level curves derived for barbados reefs for the last 2 500 years however the north sound curve is 3 m lower than a sea level curve that was derived from peats on barkers peninsula which forms the northwest boundary of north sound this discrepancy attributed to original differences in elevations of the samples highlights some of the problems associated with the construction and interpretation of sea level curves the sedimentary succession in north sound which is similar to that found in the bight of abaco in the bahamas is a record of transient depositional environments that evolved in response to the holocene rise in sea level

palynological reconstruction of environmental changes in coastal wetlands of the florida everglades since the mid holocene abstract palynological loss on ignition and x ray fluorescence data from a 5 25 m sediment core from a mangrove forest at the mouth of the shark river estuary in the southwestern everglades national park florida were used to reconstruct changes occurring in coastal wetlands since the mid holocene this multi proxy record contains the longest paleoecological history to date in the southwestern everglades the shark river estuary basin was formed 5700 cal yr bp in response to increasing precipitation initial wetlands were frequently burned short hydroperiod prairies which transitioned into long hydroperiod prairies with sloughs in which peat deposits began to accumulate continuously about 5250 cal yr bp our data suggest that mangrove communities started to appear after 3800 cal yr bp declines in the abundance of charcoal suggested gradual replacement of fire dominated wetlands by mangrove forest over the following 2650 yr by 1150 cal yr bp a dense rhizophora mangle dominated mangrove forest had formed at the mouth of the shark river the mangrove dominated coastal ecosystem here was established at least 2000 yr later than has been previously estimated

holocene lagoonal development in the isolated carbonate platforms off belize abstract thirty one vibracores were taken in interior lagoons of glovers reef lighthouse reef and turneffe islands three isolated carbonate platforms offshore belize central america holocene facies successions overlying the pleistocene limestone bedrock begin with soils followed by mangrove peats and marine carbonate sediments of lagoonal origin the soils formed on top of subaerially exposed pleistocene limestone before the holocene transgression mangrove peats developed during initial flooding of the platforms glovers ca 8 5 ky lighthouse ca 7 ky turneffe ca 6 ky bp as water depths increased reefs colonized platform margins lagoonal circulation improved thereby promoting carbonate production the basal lagoonal carbonate sediments are characterized by shell beds and or halimeda packstones grainstones mollusk dominated wackestones and packstones follow upsection in glovers and lighthouse reefs at present open circulation prevails in glovers and lighthouse lagoons in contrast organic rich halimeda wackestones and packstones dominate the turneffe islands holocene succession the main lagoon area of turneffe is enclosed by mangroves and restricted circulation prevails factors that explain the differences in geomorphology circulation and facies are variations in depth of antecedent topography and degree of exposure to waves and currents the thickness of holocene lagoon sediments may exceed the maximum core length of 6 m in all atolls holocene sedimentation rates average 0 6 m ky with highest rates in turneffe 0 82 m ky followed by lighthouse 0 53 m ky and glovers 0 46 m ky like in many other isolated carbonate platforms and atolls lagoon floor sedimentation did not keep pace with rising sea level leading to unfilled accommodation space at present glovers has an 18 m deep lagoon while lighthouse and the main turneffe lagoon are 8 m deep it is unlikely that the lagoons will be completely filled during the holocene sea level highstand cycle this observation should be kept in mind when using cycle thickness as a proxy for eustatic sea level change in fossil carbonate platforms

a multiproxy peat record of holocene mangrove palaeoecology from twin cays belize the extent and function of coastal mangrove ecosystems are likely to be influenced by future changes in sea level multiple proxies of past mangrove ecosystems preserved in a 780 cm long peat core tcc2 taken from twin cays belize record palaeoecological changes since 8000 cal yr bp the proxies included pollen and the stable isotope c n and o compositions of mangrove leaf fragments rhizophora mangle red mangrove has been dominant at this site on twin cays for over 8000 years variations in 13 c and 15n suggest past changes in stand structure between dwarf transition and tall r mangle through the holocene marked changes in the 18o up to 4 of mangrove leaf fragments throughout tcc2 most likely record variations in the proportion of seawater versus precipitation taken up by past mangroves reflecting the degree of inundation of the site with seawater resulting from changes in the rate of holocene sea level rise notably a decline in peat accumulation rate at 7200 cal yr bp correlate

a critical review of mid to late holocene sea level fluctuations on the eastern brazilian coastline abstract the eastern coast of brazil is 7000 km long and has been the subject of systematic paleo sea level investigations for more than 35 years more than 1000 samples have been radiocarbon dated and paleo sea level trends have been determined for 14 coastal sectors these trends have in common a mid holocene sea level maximum pmt above present sea level and a subsequent fall to the present time the time and elevation of the pmt the time when relative sea level rose above present mean sea level and the nature of late holocene sea level fall can however differ significantly discrepancies are observed not only between neighboring coastal sectors but also between different studies in a same coastal sector this paper discusses all the key radiocarbon dated samples used to establish regional trends in relative sea level on the eastern coast of brazil it is concluded that although many of the key sea level indicators are imprecise in time and space there is widespread evidence 30 of the data set for a progressive decline possibly with uneven rates of relative sea level since the end of the pmt

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

holocene development of the belize barrier reef previously knowledge of the holocene development of the belize barrier reef bbr the largest reef system in the atlantic ocean was limited to one location carrie bow cay we present new data from 11 rotary drill cores taken at 9 locations and 36 radiometric ages that indicate that the bbr was established from 8 26 to 6 68 ky bp on pleistocene reef limestones presumably deposited during oxygen isotope stage 5 the nonsynchronous start of holocene reef growth was a consequence of variation in elevation of antecedent topography largely controlled by underlying nne trending structures from north to south pleistocene elevation decreases along these structural trends probably reflecting differential subsidence and variations in karst topography reef anatomy is characterized by three facies in order of decreasing abundance these facies are represented by corals mainly acropora palmata and members of the montastraea annularis group by unconsolidated sand and rubble and by well cemented coral grainstones rudstones holocene reef accumulation rates average 3 25 m ky the degree of reef consolidation is negatively correlated with holocene thicknesses indicating that slowly growing reefs are better cemented than fast growing ones we present a holocene sea level curve for belize based on 36 dates from this study and 33 dates from our previous studies in the area

production of subtidal tubular and surficial tempestites by hurricane kate caicos platform british west indies abstract storm infilling of deep open callianassa burrows with molluscan to peloidal packstone was the dominant style of preservable sedimentation produced by the passage of hurricane kate across caicos platform british west indies on 18 november 1985 this moderate hurricane was the first to affect an actively studied portion of the carbonate platform environments of the south florida bahama region in 19 years a time during which many of our concepts of storm sedimentation have evolved prior to hurricane kate much of the shallow platform interior peloidal packstone to grapestone grainstone had a sparse seagrass cover and a highly irregular bottom caused by abundant callianassa mounds hurricane kate flattened the mounded bottom of the platform interior and caused minor smothering and erosion of the seagrass beds a thin surficial tempestite though deposited over much of the platform was difficult to identify because it lacked a coarse base instead much of the reworked surface sediment poured down the large callianassa burrow entrances and filled the vast burrow networks with either a coarse molluscan packstone or peloidal skeletal packstone storm burrow filling tubular tempestites effectively removed the coarse fraction from contributing to a surficial storm layer ten percent of the upper 75 cm of platform interior sediment consists of tubular tempestites from hurricane kate

carbon and sediment accumulation in the everglades usa during the past 4000 years rates drivers and sources of error 1 tropical and subtropical wetlands are considered to be globally important sources of greenhouse gases but their capacity to store carbon is presumably limited by warm soil temperatures and high rates of decomposition unfortunately these assumptions can be difficult to test across long timescales because the chronology cumulative mass and completeness of a sedimentary profile are often difficult to establish we therefore made a detailed analysis of a core from the principal drainage outlet of the everglades of south florida in order to assess these problems and determine the factors that could govern carbon accumulation in this large subtropical wetland accelerator mass spectroscopy dating provided direct evidence for both hard water and open system sources of dating errors whereas cumulative mass varied depending upon the type of method used radiocarbon dates of gastropod shells nevertheless seemed to provide a reliable chronology for this core once the hard water error was quantified and subtracted long term accumulation rates were then calculated to be 12 1 g m 2 yr 1 for carbon which is less than half the average rate reported for northern and tropical peatlands moreover accumulation rates remained slow and relatively steady for both organic and inorganic strata and the slow rate of sediment accretion 0 2 mm yr 1 tracked the correspondingly slow rise in sea level 0 35 mm yr 1 reported for south florida over the past 4000 years these results suggest that sea level and the local geologic setting may impose long term constraints on rates of sediment and carbon accumulation in the everglades and other wetlands

a deglacial and holocene record of climate variability in south central alaska from stable oxygen isotopes and plant macrofossils in peat we used stable oxygen isotopes derived from bulk peat d 18 otom in conjunction with plant macrofossils and previously published carbon accumulation records in a w14 500 cal yr bp peat core ht fen from the kenai lowlands in south central alaska to reconstruct the climate history of the area we find that patterns are broadly consistent with those from lacustrine records across the region and agree with the interpretation that major shifts in d 18 otom values indicate changes in strength and position of the aleutian low al a semi permanent low pressure cell that delivers winter moisture to the region we find decreased strength or a more westerly position of the al relatively higher d 18 otom values during the bolling allerod holocene thermal maximum htm and late holocene which also correspond to warmer climate regimes these intervals coincide with greater peat preservation and enhanced carbon c accumulation rates at the ht fen and with peatland expansion across alaska the htm in particular may have experienced greater summer precipitation as a result of an enhanced pacific subtropical high a pattern consistent with modern d 18 o values for summer precipitation the combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation a strengthened al relatively lower d 18 otom values is most evident during the younger dryas neoglaciation and the little ice age consistent with lower peat preservation and c accumulation at the ht fen suggesting less precipitation reaches the leeward side of the kenai mountains during periods of enhanced al strength the peatlands on the kenai peninsula thrive when the al is weak and the contribution of summer precipitation is higher highlighting the importance of precipitation seasonality in promoting peat accumulation this study demonstrates that d 18 otom values in peat can be applied

man and climate in the maya lowlands abstract a 15 m sedimentary core from lake salpeten provides the first complete holocene sequence for the lowlying peten district guatemala today lake salpeten is a brackish calcium sulfate lake near saturation surrounded by tropical semievergreen forest the basal pollen record depicts sparse juniper scrub surrounding a lake basin that held ephermal pools and halophytic marshes the lake rapidly deepened to 27 m in the early holocene and may have been meromictic because nearly 2 m of gypsum mush was deposited mesic forests were quickly established and persisted until the maya entered the district 3000 yr ago and caused extensive deforestation any climatic information contained in the pollen record of the maya period is thus masked but a regional pollen sequence linked to the archaeological record is substantiated because environmental disturbance was pervasive local intensification of occupation and population growth are seen as an increased deposition of pollen of agricultural weeds and colluviation into the lake while the classic maya collapse is marked by a temporary decline in compositae pollen effects of perturbations induced by the maya persist in the pollen and limnetic record 400 yr after the spanish conquest

a new coral reef province in the gulf of carpentaria australia colonisation growth and submergence during the early holocene abstract multibeam sonar mapping drill cores and underwater video data have confirmed the existence of a previously unknown coral reef province in the gulf of carpentaria australia seven reefs comprised of coral limestone that support living corals have been mapped so far and as many as 50 other reefs may exist in the region u th ages show that reef growth commenced shortly after limestone pedestals were submerged by rising sea level around 10 5 kyr bp making them the oldest holocene reefs known in australia reef growth persisted for 2 0 kyr but it had ceased at most locations by 7 0 kyr bp measurements of reef growth rates 0 95 to 4 m kyr 1 indicate that the reefs were unable to keep pace with contemporaneous rapid sea level rise 10 m kyr 1 which is consistent with a give up reef growth history core samples from reef platforms demonstrate that pleistocene limestone is exposed at depths of 27 and 30 m below present mean sea level these depths represent regionally significant phases of reef growth during a prolonged sea level still stand we conclude that the reefs are therefore mostly relict features whose major phase of growth and development relates to an earlier pre holocene sea level still stand

calibrated density profiles of caribbean mangrove peat sequences from computed tomography for assessment of peat preservation compaction and impacts on sea level reconstructions oceanic mangroves accumulate peat with sea level rise without terrestrial sediment inputs but fossil peat s elevation as a tide range limited sea level indicator is assumed to be affected by compaction despite assumption of decomposition compression and dewatering pure rhizophora mangle peat appears coarse water saturated and loose even at depth calibrated peat densities from computed tomography ct and petrologic analysis allow quantitative assessment of compaction in continuous peats from florida 6 m thick belize 12 m thick and panama 3 5 m thick pure peat exhibits voids at all depths and 80 water contents ct density does not increase with depth bulk densities are low minimally variable and trend free higher ct density intervals coincide with compositional changes sediment coral ct of peat buried under sediment shows a shift to higher densities ct of air dried continuous peat shows uncompressed fine and coarse roots and voids with negative densities indicative of air in place of interstitial water peat s high water content and hydraulic conductivity prevent dewatering and compaction hypothetically maintaining original sea level indicative elevations at intermediate depths non compacted sediment free offshore peats can provide a continuous proxy for reconstructing the record of sea level rise at any site if depositional disturbance and geochemical and biotic processes affecting 14 c ages are also assessed

palustrine deposits on a late devonian coastal plain sedimentary attributes and implications for concepts of carbonate sequence stratigraphy abstract palustrine deposits in coastal environments can cover thousands of square kilometers and are stratigraphically important palustrine deposits that originated in supratidal marshes can be used to track shifts in the shoreline position whereas palustrine deposits that formed in marshes above the peritidal realm are indicative of subaerial unconformities despite the importance of these deposits there are few documented examples of ancient coastal palustrine deposits and their sedimentary attributes remain poorly understood misinterpretation of coastal palustrine deposits as marine deposits or calcrete may partly explain this situation the upper devonian alexandra formation exposed in the northwest territories of canada is formed of two reef complexes that are separated by a type i sequence boundary at the landward part of the platform this boundary is marked by a succession of coastal plain deposits that is 50 cm thick the most distinct aspect of this succession are palustrine deposits characterized by charophytes skeletal rivularia stromatolites and various pedogenic features including complex crack networks root traces and authigenic kaolinite karst features and calcrete generally regarded as typical indicators of subaerial exposure are not found this study highlights the sedimentary attributes that can be used to identify ancient palustrine deposits in marine coastal regions distinguish these deposits from calcrete and demonstrates their sequence stratigraphic significance when found in marine limestone successions it clearly demonstrates that palustrine deposits like those found in the alexandra formation should be considered indicative of subaerial unconformities and sequence boundaries in the same manner as karst and calcrete

early middle holocene relative sea level oscillation events recorded in a submerged speleothem from the yucatan peninsula mexico geomorphological and biological archives of relative sea level change in the western north atlantic caribbean region following the last glacial maximum have traditionally supported the hypothesis o

studies on holocene mangrove ecosystem dynamics of the braganca peninsula in north eastern para brazil abstract three sediment cores from the braganca peninsula located in the coastal region in the north eastern portion of para state have been studied by pollen analysis to reconstruct holocene environmental changes and dynamics of the mangrove ecosystem the cores were taken from an avicennia forest bosque de avicennia bda a salt marsh area campo salgado cs and a rhizophora dominated area furo do chato pollen traps were installed in five different areas of the peninsula to study modern pollen deposition nine accelerator mass spectrometry radiocarbon dates provide time control and show that sediment deposits accumulated relatively undisturbed mangrove vegetation started to develop at different times at the three sites at 5120 14c yr bp at the cs site at 2170 14c yr bp at the bda site and at 1440 14c yr bp at the fdc site since mid holocene times the mangroves covered even the most elevated area on the peninsula which is today a salt marsh suggesting somewhat higher relative sea levels the pollen concentration in relatively undisturbed deposits seems to be an indicator for the frequency of inundation the tidal inundation frequency decreased probably related to lower sea levels during the late holocene around 1770 14c yr bp at bda around 910 14c yr bp at fdc and around 750 14c yr bp at cs the change from a mangrove ecosystem to a salt marsh on the higher elevation around 420 14c yr bp is probably natural and not due to an anthropogenic impact modern pollen rain from different mangrove types show different ratios between rhizophora and avicennia pollen which can be used to reconstruct past composition of the mangrove in spite of bioturbation and especially tidal inundation which change the local pollen deposition within the mangrove zone past mangrove dynamics can be reconstructed the pollen record for bda indicates a mixed rhizophora avicennia mangrove vegetation between 2170 and 1770 14c yr bp later rhizophora trees became more frequent and since ca 200 14c yr bp avicennia dominated in the forest

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

depositional cycles composite sea level changes cycle stacking patterns and the hierarchy of stratigraphic forcing examples from alpine triassic platform carbonates carbonate platform deposits record a complex interplay of numerous geodynamic variables of which eustasy subsidence and sediment accumulation are prime factors in determining both the kilometer scale depositional sequence scale and meter scale depositional cycle scale stratigraphic packaging in this study we looked particularly at composite eustasy that is superimposed sea level fluctuations with different frequencies defined as orders and different amplitudes and the role it plays in the linkage between meter scale cyclic stratigraphy and kilometer scale sequence stratigraphy specifically we have investigated the relationship between low frequency third order 1 10 m y period depositional cycles and their component high frequency fourth 0 1 1 m y and fifth 0 01 0 1 m y order cycles through detailed stratigraphic analyses of alpine triassic platforms complemented by computer modeling on the basis of our results we suggest that in general there exists a hierarchy of stratigraphic forcing driven by composite eustasy that results in organized stacking patterns thickness subfacies character early diagenetic attributes of high frequency typically fourth and fifth order shallow water carbonate cycles dictated by low frequency third order relative sea level effects we suggest that systematic vertical changes in stacking patterns of high frequency cycles across a larger depositional sequence are due to systematic and predictable differences in depositional space available during the rising and falling stages of a relative third order sea level change we also suggest that these systematic variations in cycle stacking patterns will exist regardless of the mechanism responsible for generating the high frequency cycles be it an autocyclic or allocyclic mechanism this approach has major implications for the use of high frequency fourth and fifth order cycle characteristics to identify third order cycles in outcrops and cores of shallow water carbonates where stratigraphic control may be less than desirable this would constitute a valuable bridge between cyclic stratigraphy at the meter scale and sequence stratigraphy at the seismic scale we present two examples from triassic buildups of the alps the ladinian latemar buildup and the norian dolomia principale where a systematic succession of high frequency cycle stacking patterns and early diagenetic features exists within an overriding third order cycle sequence reflecting the interplay of short term high frequency fourth fifth order eustasy and long term low frequency third order eustasy in accordance with the hierarchy of stratigraphic forcing central to the interpretation of these examples is the demonstration that true eustatic rhythms are recorded in the high frequency cyclicity as verified by time series analyses and the use of fischer plots these examples can be modeled by computer under conditions of lag depth constrained sedimentation uniform subsidence and composite eustasy we also present two examples one from the alpine triassic the norian lofer cyclothems and one from the pleistocene of south florida that lack both a systematic succession of high frequency cycle stacking patterns and identifiable composite rhythms in the stratigraphic record despite the existence of composite high frequency eustasy in these examples we call upon 1 local tectonic forcing in the form of short term deviations in subsidence via faulting lofer example and 2 large differences in the relative amplitudes of different orders of high frequency sea level oscillations pleistocene example to explain the lack of composite rhythms and we present computer simulations to illustrate the concepts an understanding of composite relative sea level changes and the potential for a hierarchy of stratigraphic forcing provides the link between cyclostratigraphy and sequence stratigraphy and also has important implications regarding the stratigraphy of early diagenesis

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

a late holocene paleoenvironmental reconstruction from agua caliente southern belize linked to regional climate variability and cultural change at the maya polity of uxbenka abstract we report high resolution macroscopic charcoal pollen and sedimentological data for agua caliente a freshwater lagoon located in southern belize and infer a late holocene record of human land use climate interactions for the nearby prehistoric maya center of uxbenka land use activities spanning the initial clearance of forests for agriculture through the drought linked maya collapse and continuing into the historic recolonization of the region are all reflected in the record human land alteration in association with swidden agriculture is evident early in the record during the middle preclassic starting ca 2600 cal yr bp fire slowly tapered off during the late and terminal classic consistent with the gradual political demise and depopulation of the uxbenka polity sometime between ca 1150 and 950 cal yr bp during a period of multiple droughts evident in a nearby speleothem record fire activity was at its lowest during the maya postclassic ca 950 430 cal yr bp but rose consistent with increasing recolonization of the region between ca 430 cal yr bp and present these data suggest that this environmental record provides both a proxy for 2800 years of cultural change including colonization growth decline and reorganization of regional populations and an independent confirmation of recent paleoclimate reconstructions from the same region

the belize margin revisited 2 origin of holocene antecedent topography the importance of antecedent topography in dictating holocene facies patterns has been generally recognized there is however disagreement as to origin or lithology of the antecedent topography particularly with respect to the siliciclastic or carbonate nature of the underlying topography and structural patterns to help resolve these problems published and unpublished information have been compiled to produce a structural fabric map of onshore and offshore belize that includes a new geologic map of the country the map along with illustrated seismic lines demonstrates the occurrence of a number of nne trending transpressional faults in which landward directed thrusting is consistently displayed along with tectonic inversion offshore wells in conjunction with the seismic lines document the inversion as post eocene suggesting a similar age for transpressional fault movement presumably the landward directed thrusting reflects the opposing force of eastward directed subduction along the western margin of central america relative to the westward seafloor spreading of the caribbean cayman ridge the belize faults show little current seismicity but nevertheless the resulting structures have affected quaternary carbonate deposition as evidenced on an illustrated seismic line by both seaward and landward bi directional progradation of the reef margin from an underlying structural high the structural influence on the development of holocene antecedent topography is further suggested by the occurrence of a bouguer gravity plateau in the same shelf area that marks the occurrence of the belize lagoon rhomboid shelf atolls the youngest documented lithology of 12 illustrated offshore exploration wells is miocene carbonate in some wells the carbonate is interpreted as extending into the pliocene and holocene although no age diagnostic criteria are in evidence in other wells siliciclastics of unknown age and thickness are identified as overlying neogene carbonates the regional distribution and age of onshore limestones suggests that unroofing of the cretaceous carbonate cap of the maya mountains siliciclastic sediment source did not occur until late in neogene time perhaps no earlier than late pliocene consequently the maya mountains could not have been a major offshore source of siliciclastics until the quaternary information on the lithology of the immediately underlying pre holocene is provided by limited penetration core data and shallow resolution seismic lines these show that antecedent pleistocene limestones beneath the holocene reefs were deposited around 130 000 b p isotope stage 5e the thickness of the overlying holocene shelf margin reef capped carbonates increases along depositional strike from a few meters in the north to more than 25 m in the south in contrast piston cores and seismic data from the southern shelf lagoon collectively document the occurrence of antecedent siliciclastic topography the southward dip of both carbonate and siliciclastic antecedent surfaces is presumably a reflection of increasing southerly subsidence increasing antecedent erosional relief in the same direction reflects the pronounced southerly increase in paleo rainfall that presumably paralleled that of present day rainfall

climate variability on the yucatan peninsula mexico during the past 3500 years and implications for maya cultural evolution climate variability on the yucatan peninsula during the past 3500 yrs is reconstructed from the measurement of 18o in monospecific ostracods and gastropods in a 6 3 m sediment core from lake punta laguna mexico this late holocene record is divided into three periods based on changes in mean 18o values from 3310 to 178514c yr b p period i low mean 18o values indicate relatively wet conditions i e low evaporation to precipitation ratio e p mean oxygen isotopic values increased 178514c yr b p and the interval between 1785 and 93014c yr b p period ii was distinctly drier than the periods before or after the climate during the latter part of period ii was persistently dry with exceptionally arid events centered at 1171 1019 and 94314c yr b p equivalent to 862 986 and 1051 a d this interval of frequent drought was recorded at several other localities in mexico and central america and coincided with the collapse of classic maya civilization following the last arid event 18o values decreased abruptly at 93014c yr b p beginning of period iii signaling a return to wetter conditions that have generally prevailed to the present with the exception of a dry episode centered at 55914c yr b p 1391 a d the paleoclimatic record from punta laguna provides evidence that multi decadal and millennial scale changes ine poccurred on the yucatan peninsula during the late holocene these wet dry episodes may have influenced cultural evolution in mesoamerica

facies model on the modern isolated carbonate platform in the xisha archipelago south china sea abstract the xuande atoll with a discontinuous reef rim caused by platform drowning is a typical ellipse isolated platform on the northern slope of the south china sea based on the data of drilling holes the analysis of surface sediments and high resolution acoustic data six sedimentary facies are identified in the xuande atoll including reef outer slope reef front reef flat aeolianite sand island back reef slope and lagoon facies map shows that the elevated reef rimmed margins with islands are more noticeable on the windward of the platform with an elevated and discontinuous reef rimmed margin as well as coarse grained sediment in the interior platform xuande can serve as a case of a leaky bucket atoll which is characterized by initially drowning scenarios the facies architecture of the xuande atoll is evidently influenced by complex and interacting parameters including antecedent topography sea level wind driven currents water depth and tectonic subsidence different controlling factors exist in the drowning of the windward and leeward sides of the platform margin the study of modern depositional settings in the xuande atoll will provide insight on predictions for ancient carbonate provinces

contradicting barrier reef relationships for darwin s evolution of reef types the darwinian progressive subsidence model for the evolution of fringing reefs barrier reefs and atolls has been generally accepted following the indisputable proof of subsidence provided by drilling results in the pacific nonetheless there are data that do not fit the expectations of the model such as the similar lagoon depths of barrier reefs and atolls as opposed to the subsidence theory s implicit prediction that atolls should have significantly greater depths in contrast a great deal of evidence supports the influence of meteoric solution on barrier reef morphology for example the maximum lagoon depth of 56 modern barrier reefs is statistically correlated with the lagoon catchment area for modern annual rainfall these modern rainfall patterns would seem to be a reasonable proxy for relative geographic differences in glacial lowstand rainfall even though the absolute amounts of such rainfall are unknown the correlation therefore suggests the importance of pleistocene subaerial solution in contributing to barrier reef morphology further support for antecedent influence occurs in the form of barrier reef passes in which the depth of the reef pass is correlated with onshore drainage volumes on a larger scale the cook island of mangaia provides evidence that solution can produce barrier reef morphology independent of reef development in contrast there are no examples of the subsidence predicted lagoon transition of fringing reefs to barrier reefs to atolls moreover the common occurrence of fringing reefs within barrier reefs negates subsidence as a causal factor in their presumed progressive evolutionary development consequently the evidence to date suggests that a solution morphology template has been accentuated by reef construction to produce the diagnostic barrier reef morphology we see today the importance of subsidence would seem to be in accounting for the overall thickness of the resulting carbonate caps of oceanic examples and in contributing to lagoon depth variation among the larger continental entities

mangrove ecosystem dynamics and elemental cycling at twin cays belize during the holocene existing at the transition between the terrestrial environment and hydrosphere mangroves are sensitive to environmental change e g sea level rise we present pollen and stable isotope data from a core tcc1 of continuous 10 m mangrove peat from twin cays 12 km off of the coast of belize central america radiocarbon dates on fragments of mangrove leaves preserved in tcc1 show that the core provides an 8600 14c year record of mangrove ecosystem changes variation in the stable carbon and nitrogen isotope composition 13c 30 to 25 15n 6 to 2 of mangrove leaves imply that the stand structure and nutrient status of the mangroves at the site have changed during the holocene pollen data from the same core show that the floral composition of the site has changed at points during the holocene most notably a brief 240 years switch at 3860 14c yr bp to dominance by a species of myrsine not currently present at the site our results are consistent with significant environmental changes either marked disturbance from hurricanes or fluctuations in sea level through the holocene copyright 2004 john wiley sons ltd

organic petrology of subbituminous carbonaceous shale samples from chalāw kabul province afghanistan considerations for paleoenvironment and energy resource potential abstract neogene subbituminous carbonaceous shale deposits from chal w afghanistan were investigated through organic petrology techniques and standard coal analyses to determine paleoenvironment and potential for resource utilization the chal w deposit approximately 30 km southeast of kabul currently is exploited for brick making and domestic heating and cooking three multiple bench channel samples of the mined bed at chal w were collected and evaluated the presence of significant huminite ranging from 0 2 to 59 0 vol mineral inclusive basis is suggestive of a terrestrial lignin rich precursor plant material measured reflectance values of 0 38 0 55 indicate subbituminous rank this rank suggests burial depths of approximately 1500 m and maximum temperatures of approximately 50 c structured liptinite macerals generally are absent except for some fluorescing morphologies interpreted to be poorly preserved root cork suberinite sponge spicule bioliths including gemmoscleres and megascleres are common these petrographic observations in addition to high mineral matter content 33 to 95 vol medium to high sulfur content 2 1 11 5 wt dry basis db and the presence of common gastropod shell fragments and an aragonite needle chalk bed are consistent with but not directly indicative of a marginal marine or estuarine mangrove depositional environment however additional data are necessary to confirm this hypothesis and deposition in a freshwater environment cannot be ruled out at this time commercial scale development and utilization of the chal w deposit as a thermal fuel resource may be possible using a fluidized bed combustion system which could accept the low quality mine product currently produced samples examined herein contain high ash yield 45 90 wt db high total moisture content 17 39 wt low calorific value 980 6860 btu lb m mmf and have poor agglomerating properties fsi 0 consistent with fuels utilized in fluidized bed combustors however delineation of the extent of the deposit through field investigation will be necessary to make a quantified resource estimate for mine planning

recent sedimentary facies of isolated carbonate platforms belize yucatan system central america abstract distribution of recent sedimentary facies is significantly different in four closely spaced isolated carbonate platforms off the coasts of belize and yucatan se mexico these differences are largely controlled by variations in submarine topography which are likely the result of differential subsidence and karstification from platform to platform a variety of depositional styles and patterns is found in platform interiors that developed during the same holocene sea level rise composition and texture of surface sediment samples were used to define four major sediment types and to distinguish nine depositional environments within the platforms facies maps are based on analysis of 454 sediment samples and high resolution satellite imagery glovers reef is characterized by a circular facies distribution the nearly continuous reef margin is composed of a coral red coralline algae halimeda grainstone mixed nonskeletal peloidal skeletal wackestones and packstones are present in shallow lagoon parts 5 m water depth behind the margin the deep interior from 5 to 18 m water depth is characterized by mollusk foram halimeda wackestones with over 860 patch reefs of coral red algae halimeda mollusk packstones lighthouse reef also has a coral grainstone and coral red algae halimeda grainstone rim but the facies distribution in the interior is strongly asymmetrical the 8 m deep eastern lagoon is floored by mollusk foram halimeda wackestones and packstones the 3 m deep western lagoon has the mixed peloidal skeletal wackestone to grainstone facies a linear trend of coalescing patch reefs and skeletal grainstone facies separates the two lagoons banco chinchorro is similar to lighthouse reef inasmuch as facies distribution patterns of the interior are strongly asymmetrical mollusk foram halimeda wackestones grainstones are present in eastern lagoon areas whereas shallow 5 m western parts of the lagoon are composed of mixed peloidal skeletal grainstones packstones and wackestones most of turneffe islands is protected on the east by lighthouse reef accordingly turneffe has a narrower reef and skeletal grainstone rim than the other two platforms restricted interior lagoons are up to 8 m deep and are enclosed by wide mangrove rims and surface sediments dominated by halimeda rich wackestone rich in organic matter coral patch reefs are absent in contrast the unprotected northernmost part of turneffe has a wide reef and grainstone rim and the open lagoon area consists of mollusk foram halimeda wackestones packstones with abundant patch reefs

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

oxygen isotopes upper ocean salinity and precipitation sources in the eastern tropical pacific westward transport of freshwater across the panama isthmus helps to maintain the salinity s contrast between the atlantic and pacific oceans important in global thermohaline circulation and climate relatively low sea surface salinities in the panama bight reflect high net precipitation we infer sources of this freshwater input to the region based on oxygen isotopes 18o of precipitation p and seawater sw the primary trend of the surface water sw s relationship implies a freshwater endmember 18o of 8 5 0 3 significantly lower than the mean p of rainwater we measured in the region 4 8 1 8 mixing with waters upwelled from the subsurface s 34 9 35 1 psu sw 0 3 0 4 based on limited isotope and salinity data these upwelling waters are a mixture of 60 tropical waters and 40 subtropical mode waters three secondary trends in the surface water sw s distribution point to similar freshwater sources with 18o of 2 5 1 2 4 7 0 5 and 4 8 0 6 consistent with local precipitation sources accounting for the primary surface water trend intermittent cross isthmus transport of moist air masses from the caribbean may introduce relatively 18o depleted rainfall due to a combination of recycling and orographic distillation in addition relatively infrequent but large tropical storms which may contain freshwater of both pacific and caribbean origin deliver rainfall with p of 10 to 14 the primary trend of regional surface seawater data which integrates the different sources over time suggests that about half of the total precipitation reflects local sources and half reflects a combination of cross isthmus transport and large storms the regional sw s distribution is sensitive to the relative contributions of these freshwater sources which may change under different climate regimes

mangrove degradation and response to anthropogenic disturbance in the maowei sea sw china since 1926 ad mangrove derived om and pollen abstract mangrove forests located at the interface between land and sea have been impacted by an increase in intensive anthropogenic disturbance in developing countries or regions in order to study the impact of human activity on mangrove forests mangrove development was reconstructed over the last 130 yr using the contribution of mangrove derived organic matter om and mangrove pollen as proxies from two sediment cores from the maowei sea sw china it is a semi enclosed bay that receives a large amount of terrestrial material from the qinjiang and maoling rivers with average sedimentation rate of 0 63 0 64 cm yr the material accumulates mainly in the coast and its adjacent region owing to weak water exchange through the channel sediment samples had c n and 13 c org values intermediate between mangrove leaves and flood plain sediments indicating that om sources could be apportioned as a mixture from only these two sources based on k mean cluster analysis mangrove development was divided into three stages since 1880 ad i a flourishing period 1880 1926 ad ii a phase of slow degradation 1926 1980 ad and iii a time of rapid degradation 1980 ad to the present the study indicates that anthropogenic activity including reclamation of mangrove swamps for farmland and shrimp ponds is the primary reason for mangrove degradation since 1926 ad rather than climate change temperature and precipitation

quantification of carbonate ramp sedimentation and progradation rates for the late holocene abu dhabi shoreline abstract we utilize new radiocarbon dates and detailed sedimentological logging of the abu dhabi sabkha to produce the first well constrained internally consistent rates for late holocene carbonate ramp sediment accumulation and progradation for the southern shore of the persian gulf these data are applied to test the hypothesis that in low angle carbonate ramp systems ramp geometry is the primary control on sedimentation and progradation rates and therefore estimates acquired from other depositional environments cannot be applied to low angle carbonate ramp systems average calculated progradation rates of 0 75 m yr are higher than progradation rates proposed for other late holocene and recent carbonate settings a relationship that is explained by the lack of accommodation space in the low angle laterally extensive ramp system in the sedimentary record such relatively high progradation rates would produce laterally extensive lithologically uniform units with little or no evidence of progradational features and would appear to be largely contemporaneous across their extent the total average sediment accumulation rate of 0 029 cm yr is lower than those proposed from most other late holocene to recent shallow water carbonate depositional environments again a relationship interpreted to result from the limited accommodation space of low angle carbonate ramp systems calculated sediment accumulation rates show little variation over the past 1 400 years yet the calculated progradation rates exhibit a sharp decline from a maximum of 1 03 m yr before 677 946 cal bp to 0 70 m yr afterwards this is interpreted to reflect a rise in relative sea level or distal steepening of the ramp system applying the progradation rates proposed in this paper the lagoon system in the study area would be completely infilled in less than 4 000 years calculated sediment accumulation rates for syndepositional and early postdepositional interstitial displacive evaporite formation are higher than those for carbonate and microbial mat intervals continued precipitation of evaporite minerals during burial would result in a further increase in their relative contribution to the sediment pile conversely compaction particularly of microbial mat intervals will result in a decrease in apparent sediment accumulation rates for non evaporite intervals these processes need to be considered when modeling the basin evolution of mixed evaporite carbonate sequences in the stratigraphic record during calculation of sedimentation rates it is important to consider both a correction for compaction and a correction for evaporite formation

precessional forced extratropical north pacific mode and associated atmospheric dynamics using transient accelerated simulations of the community climate system model version 3 and an earth system model of intermediate complexity as well as equilibrium experiments of the community earth system model we identified a response of the extratropical air ocean coupled system to the precessional insolation changes at orbital timescales and named this extratropical response pattern as the north pacific mode npm corresponding to the increased decreased boreal winter summer insolation at 22 ka relative to 10 8 ka the npm is characterized by a western warm eastern cold seesaw pattern of sea surface temperature sst over the extratropical north pacific from november to april a weakened winter aleutian low and an anomalous anticyclonic circulation throughout the troposphere this feature forms a barotropic warm ridge response of tropospheric temperature and geopotential height to the precessional insolation at the surface rainfall increases over east asia and the northwest pacific which indicates a weakened east asian winter monsoon while drier conditions appear over the northeast pacific and the western coasts of north america associated with a negative phase of npm is a weaker warming over the equatorial pacific during winter the increased winter insolation at precessional band not only induces the in phase sst warming over the northwest pacific and the tropical pacific but also explains those extratropical atmospheric changes associated with npm the latter might be associated with the warm sst induced tropospheric downstream ridge response through transient eddy activities besides the vital role of air ocean interactions the decreased summer insolation is also essential to the zonal sst seesaw of npm at precessional band

nature and biological composition of the new caledonian outer barrier reef slopes the grande terre of new caledonia is enclosed by one of the longest barrier reefs in the world for the first time the fore reef slopes of this barrier reef have been sampled by dredging from 40 to 320 m deep in order to analyze their sedimentological and biological characteristics the rocks and sediments can be divided into seven sedimentary facies bindstones dominated by coralline algal crusts bindstones dominated by foraminiferal crusts bindstones dominated by bryozoan crusts coral framestones bindstones and interstratified packstones rich in skeletal debris packstones wackestones and grainstones rich in rock gravels radiocarbon dating performed on encrusting organisms coralline algae and acervulinids and corals provide ages relatively young these ages confirm that the encrusting organisms are modern and the corals mainly dated of holocene are reworked due to the instability of the fore reef slopes especially during storms because the biological assemblages are distributed according to a bathymetric range depending on light intensity a model of distribution of modern encrusting calcareous organisms can be proposed from our observations and analyses from the upper reef slopes to approximately 90 m thick coralline algal crusts are dominant and distributed in three groups group c the shallowest parts of the fore slopes is mainly characterized by mastophorids hydrolithon reinboldii h cf munitum lithoporella melobesoides aethesolithon cf problematicum neogoniolithon sp and undetermined species and lithophylloids lithophyllum sp l pustulatum group b composed of lithophylloids lithophyllum sp l cf kotschyanum l cf moluccence l pustulatum mesophyllum sp and peyssonnelia sp occurs from 15 to 40 m group a rich in mesophyllum sp m cf mesomorphum peyssonnelia sp and sporolithon sp is characteristic of deep reef slopes up to 90 m below approximately 90 m when the light intensity decreases the encrusting foraminifera acervulinids progressively replace the coralline algal crusts such a model is particularly useful to interpret and reconstruct the past quaternary reef environments rich in crusts of coralline algae and or foraminifera

effects of antecedent topography on reefal carbonate deposition early middle miocene of the adana basin s turkey abstract early middle miocene reefal limestones and other shallow marine sedimentary sequences were important components of neogene basins especially the adana basin in southern turkey the most important controlling factors of sedimentation were antecedent topography and substratum type clastic input and sea level changes of different scales the effects of these factors can be observed on the southwest extension of the adana basin miocene sediments unconformably overlie the older limestones ophiolite and ophiolitic melange lithological variations and structural properties of pre miocene rocks caused an irregular sea floor topography development that was initially filled by local terrestrial conglomerates during the early miocene transgression these terrestrial clastics transitionally passed into shallow marine clastics and also new pebbly conglomerate sandstone bearing deposits observed in local depressions of pre miocene topography remaining low lying areas were filled by claystones and sandy clayey limestones at the same time reef limestone deposition developed over the higher areas where a hard substratum was available for red algae and other reef builders large shelled organisms in the clastics created a suitable substratum for successive reef level development the carbonate deposition shifted landwards due to continuous transgression intermediate sea level changes causing backstepping reef development small sea level changes in the study area controlled the energy of the environment lithological variations in the clastics and lateral facies changes in each reef body

contrasting responses of two caribbean mangroves to sea level rise in the guajira peninsula colombian caribbean abstract local geomorphology plays an important role in the response of mangrove communities to both sea level rise and precipitation changes mostly because it exerts an important control of the erosion progradation balance here we present contrasting changes in the palynological records of two sediment cores retrieved from locations occupied by mangroves in the northeastern caribbean coast of colombia calancala and navio quebrado sediments were treated with standard procedures used in palynologycal analysis and dated with ams 14 c and 210 pb age depth models of both cores were constructed by linear interpolation between dated samples the main modern differences between the studied sites are fresh water availability and sediment supply throughout the year while calancala located at the rancheria river delta has direct fresh water influence throughout the year coastal lagoon navio quebrado is only sporadically influenced by fresh water sources according to our findings two main factors contributed to mangrove establishment in the colombian caribbean i high and accelerated sea level rise around 6000 cal yr bp originating coastal lagoons that favored mangrove establishment and ii marine still stand and high precipitation around 3000 cal yr bp leading to a second wave of mangrove expansion a drought between about 2850 and 2450 cal yr bp and the strengthening of easterly trade winds caused a change from rhizophora dominated to avicennia dominated stands increased precipitation after 2500 cal yr bp and subsequent increase of fluvial sediment input promoted recovery of rhizophora dominated mangroves sea level rise during the last 150 yr has caused landward mangrove expansions in deltas and progradation of coastal environments however the general pattern shows a net loss of mangrove vegetation as the result of coastal erosion

coastal landforms and accumulation of mangrove peat increase carbon sequestration and storage given their relatively small area mangroves and their organic sediments are of disproportionate importance to global carbon sequestration and carbon storage peat deposition and preservation allows some mangroves to accrete vertically and keep pace with sea level rise by growing on their own root remains in this study we show that mangroves in desert inlets in the coasts of the baja california have been accumulating root peat for nearly 2 000 y and harbor a belowground carbon content of 900 34 00 mg c ha with an average value of 1 130 128 mg c ha and a belowground carbon accumulation similar to that found under some of the tallest tropical mangroves in the mexican pacific coast the depth age curve for the mangrove sediments of baja california indicates that sea level in the peninsula has been rising at a mean rate of 0 70 mm y 0 07 during the last 17 centuries a value similar to the rates of sea level rise estimated for the caribbean during a comparable period by accreting on their own accumulated peat these desert mangroves store large amounts of carbon in their sediments we estimate that mangroves and halophyte scrubs in mexico s arid northwest with less than 1 of the terrestrial area store in their belowground sediments around 28 of the total belowground carbon pool of the whole region

a taphonomic study of δ13c and δ15n values in rhizophora mangle leaves for a multi proxy approach to mangrove palaeoecology abstract the response of mangrove ecosystems to environmental change can be examined with stable isotopic tracers of c and n the 13c and 15n of a taphonomic series of rhizophora mangle l red mangrove leaves were analyzed from twin cays belize to facilitate reconstruction of past mangrove ecosystems on twin cays fresh leaves of dwarf r mangle trees 0 5 m high were found to have more negative 15n values mean 10 and more positive 13c values mean 25 3 compared to tall r mangle trees mean 15n 0 13c 28 3 these isotopic differences can be related to nitrogen and phosphorus availability ecology 83 2002 1065 we investigated three taphonomic stages in the fossilization of r mangle leaves into peat with the following 1 senescent leaves 2 fallen leaves on the surface of the peat and 3 sub fossil leaves found within mangrove peat in addition by examining natural leaf assemblages we established that 13c and 15n of r mangle leaves were not altered during senescence despite a significant 50 decrease in the n modern dwarf and tall trees could still be identified from 13c and 15n analyses of the leaf assemblages found directly below a tree dwarf and tall trees could also be identified from 13c analyses of leaves that had decomposed for four months although dwarf and tall trees could not be statistically separated after four months according to 15n analyses leaves with very negative 15n 7 were only collected below dwarf trees leaf fragments were present in 50 cm long cores of peat from four sites on the island and their isotopic compositions were determined the ranges of 13c 29 to 22 and 15n 11 to 2 values from sub fossil leaves were similar to the ranges from modern leaves 13c 29 to 23 15n 11 to 1 the sub fossil leaf isotopic compositions were independent values in comparison to the uniform values of the surrounding peat because of the stability and persistence of the stable isotopic signals they could contribute significantly to a multi proxy approach to mangrove palaeoenvironmental reconstruction

polygenetic polyphase karsted hardground omission surfaces in lower silurian neritic limestones anticosti island eastern canada abstract exquisitely preserved and well exposed rocky paleoshoreline omission surfaces in lower silurian chicotte formation limestones on anticosti island quebec are interpreted to be the product of combined marine and meteoric diagenesis the different omission features include 1 planar erosional bedding tops 2 scalloped erosional surfaces 3 knobs ridges and swales at bedding contacts and 4 paleoscarps an interpretation is proposed that relates specific styles of omission surface to different diagenetic depositional processes that acted in separate terrestrial peritidal shallow neritic zones such processes were linked to fluctuations in relative sea level with specific zones of diagenesis such as 1 karst corrosion 2 peritidal shallow subtidal erosion 3 subtidal seawater flushing and cementation and 4 shallow subtidal deposition most surfaces are interpreted to have been the result of initial extensive shallow water synsedimentary lithification forming hardgrounds that were as sea level fell planed by inner neritic abrasion successively altered by exposure and subaerial corrosion only to be buried by sediments as sea level rose again this succession was repeated several times resulting in a suite of recurring polyphase omission surfaces through many meters of stratigraphic section synsedimentary cloudy marine cements are well preserved and are thus interpreted to have been calcitic originally aragonite components are rare and thought to have been dissolved just below the silurian seafloor large mollusks that survived such seafloor removal were nonetheless leached and the resultant megamolds were filled with synsedimentary calcite cement these silurian inner neritic strandline omission surfaces are temporally unique they are part of a suite of marine omission surfaces that are mostly found in early to middle paleozoic neritic carbonate sedimentary rocks these karsted hardgrounds formed during a calcite sea time of elevated marine carbonate saturation and extensive precipitation of marine cement the contemporaneous greenhouse atmosphere was supercharged with co2 leading to profound surface karst under strongly acid rain younger peritidal omission surfaces although potentially formed during aragonite sea or calcite sea times would have been subject to very different terrestrial diagenetic process with lower atmospheric pco2 values but increasingly complex biogenic soils producing dissimilar alteration features

use of fischer plots to define third order sea level curves in ordovician peritidal cyclic carbonates appalachians fischer plots in which cumulative cycle thickness corrected for linear subsidence is plotted against time were originally used in the study of triassic peritidal sequences to define short duration departures in relative sea level in the milankovitch range 104 to 105 yr however they also provide a means of assessing magnitude of third order 1 to 10 m y fluctuations in sea level which on the basis of their regional correlatability we ascribe to eustatic events

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

misuse of fischer plots as sea level curves fischer plots are graphic representations of cyclic carbonate deposits showing cumulative departure from average cycle thickness plotted against cycle number and corrected for assumed subsidence during each cycle observed cycle thicknesses in excess of subsidence have been interpreted to represent depositional accommodation space formed by eustatic sea level rise however implicit in this interpretation is the assumption that preserved cycle thickness is a proxy for accommodation to test this assumption a survey of carbonate sediment accumulation patterns i e cycle thicknesses developing during a single transgressive event the holocene postglacial sea level rise was conducted on a shallow carbonate platform great bahama bank where accommodation was created primarily by sea level rise over the platform margin i e subsidence was minimal this survey demonstrates that holocene sediment cycle thickness and accommodation are uncorrelated r 2 0 03 consequently fischer plots constructed by using holocene cycle thicknesses are poor representations of the holocene transgression in extreme examples holocene fischer plots would be interpreted to show relative sea level fall during the holocene on great bahama bank because holocene subsidence currently exceeds sediment thickness in addition a simple sensitivity test shows that eustatic sea level interpretations based on interbasinal correlation of fischer plots are equivocal the gross form of fischer plots appears so overly robust as to be insensitive to broad variations in stratigraphic completeness cycle duration or subsidence because cycle thickness apparently is uncorrelated with accommodation and the gross form of fischer plots is relatively invariant it seems prudent to reevaluate the practice of interpreting fischer plots as sea level curves per se in the analysis of ancient carbonate cycles

mangrove ecosystem changes during the holocene at spanish lookout cay belize abstract mangroves are halophytic plants living at the land sea interface and are therefore natural trackers of sea level multiple proxies of a continuous 8 m mangrove peat core bt 79 from spanish lookout cay belize illustrate mangrove ecosystem changes during the holocene radiocarbon measurements show this site was colonized by mangroves 8000 cal yrs bp with a significant decrease in the peat accumulation rate from 6000 to 1000 cal yrs bp stratigraphic characteristics of this peat core such as bulk density magnetic susceptibility and loss on ignition show relative uniformity inferring an uninterrupted mangrove ecosystem during a majority of the holocene this is supported by pollen data from bt 79 that show that the site has been consistently dominated by rhizophora mangle red mangrove with avicennia germinans black mangrove and laguncularia racemosa white mangrove present as well subfossil r mangle leaves are used for stable nitrogen carbon and oxygen isotope 15n 13c and 18o analyses 15n and 13c values provide a proxy of this plant s past physiology and stand structure showing that dwarf 15n

the middle eocene seeb formation of oman an investigation of acyclicity stratigraphic completeness and accumulation rates in shallow marine carbonate settings abstract the middle eocene seeb formation represents deposition on one of the earliest modern style carbonate platforms i e influenced by seagrasses and mangroves and presents an opportunity to explore controls on the preservation of cenozoic carbonate lithofacies in the study area the seeb fm is dominated by an anomalously thick approximately 250 m and uniform package of shallow marine platform interior sediments these nodular indistinctly bedded shallow subtidal sediments display no evidence for relative sea level change such as subaerial exposure features and lack the shallowing upwards cyclothems that have characterized carbonate sediments deposited in platform interior settings throughout much of the rock record particularly during greenhouse periods we conclude that this is a consequence of thorough bio retexturing of the sediment by burrowing organisms and the roots of marine vegetation which destroyed primary fabrics facies diversity evidence for cyclicity and missing time horizons such as cycle bounding exposure surfaces it seems possible that the remarkable thickness of apparently acyclic seeb fm sediment that built up may reflect increased bio disturbance of the shallow marine environment following the late cretaceous expansion of seagrasses and mangroves a similar lack of peritidal cyclothems may be common to many cenozoic shallow marine carbonate deposits missing time horizons in limestones reflecting erosion or nondeposition have been identified by some authors to explain discrepancies between low calculated accumulation rates of ancient sediments and higher rates measured in comparable modern environments however our studies of the seeb fm suggest that the significance of such missing time horizons in ancient sediments may have been overstated and that apparent differences between modern and ancient accumulation rates are a consequence of the extrapolation of unrepresentative localized high rates of modern sediment production to large platform scale areas our study reinforces the idea that modern sediment production and accumulation rates may be much lower than previously thought because they are typically measured in highly productive areas such as seagrass beds and do not take into account the highly variable nature of carbonate production storage erosion and destruction across platforms therefore far less missing time needs to be inferred for ancient sediments to account for any imbalance between modern and ancient sediment accumulation rates

seismic stratigraphy of the blue hole lighthouse reef belize a late holocene climate and storm archive abstract five seismic units may be identified in the 8 m thick holocene sediment package at the bottom of the blue hole a 120 m deep sinkhole located in the atoll lagoon of lighthouse reef belize these units may be correlated with the succession of an existing 5 85 m long sediment core that reaches back to 1 385 kyrs bp the identification of seismic units is based on the fact that uniform fine grained background sediments show weak reflections while alternating background and coarser grained event storm beds exhibit strong reflections in the seismic profiles the main source of sediments is the marginal atoll reef and adjacent lagoon area to the east and north northeasterly winds and storms transport sediment into the blue hole as seen in the eastward increase in sediment thickness i e the eastward shallowing of the blue hole previous assumptions of much thicker holocene sediment packages in the blue hole could not be confirmed so far close to 6 m long cores were retrieved from the blue hole but the base of the sedimentary succession remains to be recovered the nature of the basal sediments is unknown but mid holocene and possibly older pleistocene sinkhole deposits can be expected the number of event beds identified in the blue hole n 37 during a 1 385 kyr long period and the number of cyclones listed in historical databases suggest that only strong hurricanes categories 4 and 5 left event beds in the blue hole sedimentary succession storm beds are numerous during 1 3 0 9 kyrs bp and 0 8 0 5 kyrs bp

facies variations in response to holocene sea level and climate change on bora bora french polynesia unravelling the role of synsedimentary siderite in a tropical marine mixed carbonate siliciclastic lagoon abstract five mixed carbonate siliciclastic sedimentary facies were identified in the barrier reef lagoon of bora bora using microfacies and statistical analyses of 70 sediment samples taken at high resolution from two vibrocores facies and facies successions were interpreted with respect to holocene sea level and climate changes the windward lagoon core is characterized by sideritic marly wackestones and foraminifera sideritic wackestones deposited around 7700 years bp years before present during the early mid holocene transgression at that time extensive weathering and erosion of iron bearing minerals from the volcanic island due to a wetter climate were expressed in the formation of synsedimentary siderite in lagoonal sediments the enrichment in 18o 0 32 to 0 54 in the siderite grains indicates marine to mixed marine meteoric conditions during precipitation siderite formation resulted from microbial degradation of organic material indicated by depleted 13c values 13 61 to 14 48 that led to reducing conditions in lagoonal sediments and resulted in iron reduction in the presence of dissolved bicarbonate the chemical compositions of the siderites changes upcore from relatively high fe 91 95 mol and low mn 5 6 mol at the core base to relatively low fe 83 88 mol and high mn 11 16 mol at the core top the substitutions of fe by mn ca and mg at grain margins illustrate changes in pore water chemistry towards more oxygenated conditions and reflect sea level rise and elevated rainfall during the early mid holocene a drier climate during the mid late holocene was accompanied by reduced iron input and the proportion of siderite decreased approaching zero in the upper section of the core in the leeward lagoon core siderite is again common in the lower section and decreases in abundance upcore mollusc foraminifera marly packstones and mollusc wackestones accumulated 5400 3500 years bp during the mid holocene in the windward core early in this period rotalid and miliolid foraminifera dominated these are tolerant of environmental stress such as changes in water quality nutrients or salinity from the mid holocene to the present textularid foraminifera are common in both cores and indicate normal marine lagoonal conditions since the mid late holocene sea level highstand and fall to modern level mudstones have dominated in both cores during the last 1000 years coral fragments have increased in abundance in the windward lagoon presumably as a result of lagoonward progradation of fringing reefs in the mid late holocene since the late holocene motus on the windward side of bora bora have hampered sediment transport and lagoonward progradation of sand aprons increasing numbers of peloids largely hardened faecal pellets in the windward core in the last 1000 years may reflect early submarine lithification within the lagoon our study shows that during the holocene sea level and climate change have influenced sediment import composition and distribution in the bora bora lagoon the sensitive response of the environment to external changes demonstrates the potential of tropical reef lagoons as archives of climate and sea level changes

origin of atoll lagoons a database of 301 atolls from the pacific indian and atlantic oceans has been analyzed with respect to factors governing maximum atoll lagoon depth statistically significant correlations between maximum atoll lagoon depth and both atoll area and present day rainfall are viewed as the combined effect of paleorainfall precipitation and catchment area in contributing to overall atoll morphology this interpretation is supported by the gross saucer shaped morphology of several of the lau group of the fiji islands and the subsurface cretaceous golden lane atoll of mexico where evidence of reef rim construction is lacking but evidence for significant solution relief is compelling the contribution of reefs to atoll rim construction appears to be limited generally to 10 m leaving more than 20 m of relief to be explained at most atolls at a number of these the last interglacial highstand surface is 15 20 m beneath holocene rim sediments subsidence rates of even 5 cm k y do not suffice to explain the subsea depth of this unconformity suggesting the dominating influence of solution on relief expression calculations of solution rates relative to the residence time of sea level below given depths during the past 700 k y suggest that the observed atoll relief is in part inherited from more than one pleistocene or perhaps earlier glacial stage whatever the precise time of origin the data available strongly suggest that atoll morphology is solution determined rather than growth predicated

mangrove development and its response to environmental change in yingluo bay sw china during the last 150years stable carbon isotopes and mangrove pollen abstract located at the interface of terrestrial and marine ecosystems mangroves are particularly sensitive to environmental change they provide a sedimentary sink for organic carbon whereby cores can provide detailed records of mangrove species we aimed to trace the history of mangrove development over the past 150 years in yingluo bay sw china sedimentation rates avg 0 32 and 0 37 cm year were calculated on the basis of ln 210 pb ex vs mass depth and offset the rate of relative sea level rise 0 22 0 24 cm year leading to a seaward expansion of new mangrove habitats chemical tracers 13 c org and c n and an isotope mixing model were utilized to trace the contribution of mangrove derived organic matter mom changes in the relative abundance of pollen from mangrove plants was used to compensate for diagenetic alteration of the stable isotope values and potential overlaps in isotope values for different sources of organic matter the result of pearson correlation analysis showed that the mom was moderately positive correlated with total mangrove pollen indicating that stable carbon isotopes and mangrove pollen provide similar information for tracing mangrove ecosystems based on results from this study compositional changes in mangrove communities could be divided into two main stages a degradation period 1870 1930 ad and a flourishing period 1930 2011 ad corresponding to colder temperature and warmer temperature respectively owing to the location being far away from any industrial area and human activity temperature may be a key factor for mangrove development

radiocarbon dating of mangrove sediments to constrain holocene relative sea level change on zanzibar in the southwest indian ocean mangrove sedimentary deposits are sensitive to changes in sea level and can be used to reconstruct mid to late holocene sea level fluctuations in intermediate and far field locations distant to t

a new model evaluating holocene sediment dynamics insights from a mixed carbonate siliciclastic lagoon bora bora society islands french polynesia south pacific abstract mixed carbonate siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition sediment sources include lagoonal carbonate production the marginal reef and the volcanic hinterland mixed carbonate siliciclastic continent attached coastal lagoons have been intensively studied however their isolated oceanic counterparts have been widely disregarded here we present a new model of holocene sediment dynamics in the barrier reef lagoon of bora bora based on sedimentological paleontological geochronological and geochemical data the lagoonal succession started with a pleistocene soil representing the lowstand systems tract as the rising holocene sea inundated the carbonate platform peat accumulated locally 10 650 9400 years bp mixed carbonate siliciclastic sedimentation started ca 8700 5500 years bp and represents the transgressive systems tract during that time sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon siliciclastic content decreases throughout the holocene after the rising sea had reached its modern level sand aprons formed between reef crest and lagoon creating transport pathways for reef derived material leading to carbonate dominated sedimentation ca 6000 3000 years bp during the highstand systems tract however mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron from ca 4500 500 years bp significant variations in grain size total organic carbon as indicator for primary productivity ca and cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen such patterns could indicate event re deposition and correlate with contemporaneous event deposits found in the lagoon of nearby tahaa which are supposed to be induced by elevated cyclone activity correspondingly enhanced erosion and run off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall increased amounts of coarse grained sediment from marginal reef areas would be transported into the lagoon however ti ca and fe ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid holocene also benthic foraminiferal faunas do not validate reef to lagoon transport of sediment alternatively the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher than present sea level which are supposed for the mid late holocene in the south pacific sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity we propose the shift towards coarser grained sedimentation patterns during the mid late holocene to reflect sediment load shedding of sand aprons due to oversteepening of slopes at sand apron lagoon edges during times of stronger trades and higher than present sea level of the highstand systems tract which led to redeposition of sediment even within the lagoon center modern conditions including a sea level fall to modern level were reached ca 1000 years bp and lagoonal infill has been determined to a large part by fine grained carbonate dominated sediments produced within the lagoon and derived from the marignal reef infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons contrary to the commonly supposed assumption that coarse grained sediment layers within fine grained lagoonal successions represent overwash events induced by storms or periods of higher storm activity we postulate a new model of long term lagoonal sediment dynamics including sea level climatic change and geomorphological variation of the barrier reef lagoon

holocene stratigraphy of cobweb swamp a maya wetland in northern belize we investigated the soils and sediments of cobweb swamp adjacent to the archaeological site of colha in northern belize to adumbrate landscape evolution and the impact of the ancient maya on a tropical palustrine wetland the cobweb section exposes a complex and dynamically evolving landscape with a rich interplay between natural and human forces the cobweb depression probably formed as a karstic doline or polje in interbedded limestone and marl of late tertiary or pleistocene age during the latest pleistocene a terrestrial marsh covered most of the depression slope wash and colluviation from adjacent slopes impacted the depression during the early holocene possibly in response to a drier and cooler climate reported to have occurred in the region during this time after ca 5600 b p the cobweb depression was affected by relatively rapidly rising sea levels in the area and a brackish lagoon filled the basin by 4800 b p a peat filled in the lagoon probably because precipitation of a marl in the lagoon coupled with decreasing rates of sea level rise enabled emergent vegetation to encroach the shallowing waters humans first began to affect the landscape when this peat was at the surface massive deforestation resulting in increased runoff and rising water levels is the most likely explanation for a fresh water lagoon that again inundated the cobweb depression between 3400 and 500 b p the maya clay was deposited on the edge of this lagoon as the result of upland erosion almost as soon as deforestation began but the bulk of the deposit was coincident with the sudden collapse of the classic maya civilization ca 1000 b p suggesting that significant environmental degradation was associated with the demise of the classic maya peat began to fill the cobweb lagoon sometime before 500 b p probably the result of shallower water levels from decreasing runoff resulting from reforestation after abandonment by the maya

paleoenvironments and high frequency cyclicity from cenozoic south east asian shallow water carbonates a case study from the oligo miocene buildups of malampaya offshore palawan philippines abstract the combination of core and cuttings analyses and well log data from the late oligocene early miocene carbonate buildup in the malampaya gas field offshore palawan philippines allowed the recognition of shelf depositional paleoenvironments and the definition of high frequency metre scale subtidal cycles usually bounded by exposure surfaces this is amongst the first documentation of short term platform top evolution of oligo miocene carbonates in response to high frequency relative sea level change described in south east asia during the late oligocene the malampaya carbonate buildup is interpreted as an isolated platform rimmed by a barrier reef system that has developed vertically according to the keep up mode with no significant evidence for retardation in reef development during rises in relative sea level during the early miocene the isolated platform was affected by more open conditions in its inner part due to the inability of the reef to catch up with relative sea level rises strontium isotope derived estimations of cycle durations despite a relatively high degree of uncertainty in their calculation are consistent with 4th to 5th order cyclicity 10 1000 ky

composition and morphology of early devonian microbial and metazoan patch reefs qasr member of the jauf formation northwestern saudi arabia abstract late pragian early emsian 405 ma microbial and metazoan reefs in the al jawf area of northwestern saudi arabia occur in the 20 m thick qasr limestone member of the jauf formation within a dominantly fine grained marine siliciclastic sequence deposited on a broad shelf adjacent to the arabian nubian shield microbial reefs composed of stromatolites thrombolites and to a lesser extent leiolites are circular to elliptical in plan and have mounded domical cross sections individual microbial reefs up to 6 m in height and 15 m across are commonly laterally and vertically juxtaposed in composite buildups up to 10 m high and 60 m across metazoan reefs dominated by poorly preserved bryozoans range from small subcircular mounds 10 60 m across through ridges up to 300 m in length to more complex structures and reach 4 m in height the qasr member provides a rare example of well exposed early devonian reefs in plan view satellite images show the spatial arrangement of qasr mounds as hundreds of small patch reefs over a wide area regardless of type the reefs and composite bioherms are generally nne ssw oriented and many are grouped into parallel rows this pattern as in some modern patch reef complexes may reflect direct influence of paleotopography and water circulation patterns the reefs are enclosed and separated by bedded deposits marls siltstones and limestones intraclastic floatstones bioclastic floatstones rudstones and peloidal grainstones the qasr reef complex probably developed in generally low energy environments between normal and storm wave base in turbid to clear water early devonian increase in microbial reefs such as qasr challenges the view that post cambrian stromatolites were common only in normal marine subtidal settings in the wake of metazoan mass extinctions

sequence development on a sediment starved low accommodation epeiric carbonate ramp silurian wabash platform usa mid continent during icehouse to greenhouse transition abstract twelve cored wells through the silurian section of the wabash platform indiana u s a and 2 non cored basinal wells with cuttings were studied to define the sequence stratigraphy of a sediment starved ramp within a low latitude epeiric sea during the latest ordovician icehouse to silurian greenhouse transition the wabash platform approximately 200 000 km2 area was bounded to the north by the michigan basin to the east by the appalachian foreland basin and passed to the southwest into the vincennes basin which was open to the ocean facies developed include platform fringing buildups stromatactis wackestone core stromatoporoid skeletal wackestone caps and crinoidal rudstone packstone flank facies and non buildup crinoid grainstone packstone sheets shoals skeletal wackestone variably cherty between fair weather and storm wave base deep lagoon and deep ramp and carbonate mudstone clean to argillaceous sub storm wave base deep lagoon and deep ramp basin the eleven sequences 2 m to 30 m thick and 1 to 4 m y durations average 2 5 m y generally can be correlated to global sea level cycles the lower three sequences are disconformity bounded reflecting moderate ice sheets but the others are relatively conformable the most easily mapped regional surfaces are the transgressive surfaces because the correlative conformities are cryptic the wide well spacing prevented mapping of lowstand system tracts the transgressive systems tracts are upward deepening upward fining carbonate units that become more argillaceous and silty upward the highstand systems tracts are upward coarsening carbonate mudstone to wackestone packstone and rare grainstone barrier bank complexes and isolated buildups aggraded during deposition of the upper 4 sequences to form a discontinuous raised rim 40 m relief to the ramp while the interior of the platform remained sediment starved subsidence rates in the basin were very low 0 6 to 1 2 cm k y but the low platform accumulation rates 0 2 cm k y to 0 8 cm k y prevented the seafloor from building to sea level in all but the lower three sequences and later over barrier banks accumulation rates 2 cm k y parasequence development in high accommodation settings elsewhere in the silurian in north america records transition from moderate ice sheets to an ice free world this is weakly expressed on the wabash platform due to the dominantly deeper subtidal setting the remarkably low sedimentation rates resulted from the epeiric sea being isolated from the open ocean and they likely are typical of the large epeiric seas of the paleozoic

a holocene vegetation history from lowland guatemala a 5 45 m core from lake peten itza lowland guatemala contains a near complete record of holo cene sedimentation the age depth relationship for the core is based on ams 14c dating of terrestrial wood fragments and provides a reliable chronology in this karst region where hard water lake error has typically confounded sediment geochronology in the basal part of the sequence pollen of the moraceae urticaceae group dominate indicating the presence of widespread tropical forest during the early holocene c 8600 5600 yr bp relative abundance of pollen of high forest taxa declined beginning as early as 5600 yr bp indicating climatic drying or perhaps initial land clearance deforestation by prehistoric mayan inhabitants is documented clearly in the pollen record beginning about 2000 yr bp 106 cal bc 122 cal ad 95 4 2 sigmas by the appearance of disturbance taxa e g ambrosia and poaceae and presence of zea forest regrowth occurred following the classic maya collapse c ad 900 as reflected by

holocene development of three isolated carbonate platforms belize central america abstract locally operating factors such as topography of the reef basement and exposure to waves and currents rather than regionally effective factors such as the post glacial sea level rise in the western atlantic explain the different holocene developments of the three isolated carbonate platforms glovers reef lighthouse reef and turneffe islands offshore belize a series of nne striking tilted fault blocks at the passive continental margin forms the deep basement of the belize reefs glovers and lighthouse reefs are located on the same fault block while turneffe islands is situated west of lighthouse reef on an adjacent fault block the three platforms are surrounded by deep water and have surfacebreaking reef rims significant differences exist between platform interiors glovers reef has only 0 2 of land and an 18 m deep well circulated lagoon with over 800 patch reefs lighthouse reef has 3 of land and a well circulated lagoon area patch reefs are aligned along a nne striking trend that separates a shallow western 3 m and a deeper eastern 8 m lagoon turneffe islands has 22 of land that is mainly red mangrove interior lagoons are up to 8 m deep and most have restricted circulation and no patch reefs surface sediments are rich in organic matter in contrast the northernmost part of turneffe islands has no extensive mangrove development and the well circulated lagoon area has abundant patch reefs holocene reef development was investigated by means of 9 rotary core holes that all reached pleistocene reef limestones and by radiometric dating of corals maximal holocene reef thickness reaches 11 7 m on glovers reef 7 9 m on lighthouse reef and 3 8 m on turneffe islands factors that controlled holocene reef development include the following 1 holocene sea level the margin of glovers reef was flooded by the rising holocene sea ca 7500 ybp that of lighthouse reef ca 6500 ybp and that of turneffe islands between 5400 and 4750 ybp all investigated holocene reefs belong to the keep up type even though the three platforms were flooded successively and hence the reefs had to keep pace with different rates of sea level rise 2 pre holocene topography pleistocene elevation and relief are different on the three platforms this is the consequence of both tectonics and karst different elevations caused successive reef initiation and they also resulted in differences in lagoon depths variations in pleistocene topography also explain the different facies distribution patterns on the windward platforms that are located on the same fault block on lighthouse reef tectonic structures are clearly visible such as the linear patch reef trend that is aligned along a pleistocene fault on glovers reef only short linear trends of patch reefs can be detected because the pleistocene tectonic structures are presumably masked by the higher holocene thickness the lower pleistocene elevation on glovers reef is probably a consequence of both a southward tectonic tilt and stronger karstification towards the south related to higher rainfall 3 exposure to waves and currents glovers reef lighthouse reef and the northernmost part of turneffe islands receive the maximum wave force as they are open to the caribbean sea adjacent lagoons are well circulated and have luxuriant patch reef growth and no extensive mangrove development by contrast most of turneffe islands is protected from the open caribbean sea by lighthouse reef to the east and is only exposed to reduced wave forces allowing extensive mangrove growth in these protected areas

sea level controls sedimentation and environments in coastal caves and sinkholes abstract quaternary climate and sea level research in coastal karst basins caves cenotes sinkholes blueholes etc generally focuses on analyzing isotopes in speleothems or associating cave elevations prior sea level highstands the sediments in coastal karst basins represent an overlooked source of climate and sea level information in the coastal zone but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them in this study we hypothesize that coastal karst basins transition through vadose littoral anchialine and finally into submarine environments during sea level rise because groundwater and sea level oscillate in near synchrony in the coastal zone causing each environment to deposit a unique sedimentary facies to test this hypothesis the stratigraphy in twelve sediment cores from a bermudian underwater cave green bay cave was investigated and temporally constrained with twenty radiocarbon dates the results indicate that we recovered the first succession spanning the entire holocene from an underwater cave 13 ka to present the sediments were characterized with x radiography fossil remains bulk organic matter organic geochemistry 13corg c n and grain size analysis four distinct facies represent the four depositional environments i vadose facies 7 7 ka calcite rafts lithofacies ii littoral facies 7 7 to 7 3 ka calcite rafts and mud lithofacies iii anchialine facies 7 3 to 1 6 ka slackwater and diamict lithofacies and iv submarine facies

holocene palaeosalinity in a maya wetland belize inferred from the microfaunal assemblage abstract a 5 4 m sequence of peat and marl overlying a basal clay in a northern belize wetland was studied to assess salinity changes over the past 7000 yr the distribution of ostracods gastropods and foraminifers revealed initially freshwater conditions in a terrestrial wetland changing to at least mesohaline conditions by about 5600 yr b p the mesohaline conditions corresponded to the formation of an open water lagoon and precipitation of a lacustrine marl that was contemporaneous with rapidly rising sea level in the area a mangrove peat filled the lagoon by 4800 yr b p probably as a result of increasingly shallow waters as sea level rise slowed and marl precipitation continued a new lagoon began to form sometime after 3400 yr b p freshwater ostracods and gastropods found in the marl of this lagoon suggest that it formed under near limnetic conditions freshwater input likely resulted from massive deforestation by the maya that began by 4400 yr b p subsidence of the mangrove peat likely permitted the formation of a lagoon a peat has filled the lagoon since at least 500 yr b p