a novel multiproxy approach to reconstruct the paleoecology of extinct cephalopods abstract reconstructing marine paleoenvironments from the skeletal hardparts of nektic organisms is often hampered by their unknown migrational pathways involving different water masses and their corresponding physico chemical parameters despite significant progress over the last years the reconstruction of migration patterns of extinct ammonoids is difficult because both vertical and horizontal ones lead to an intricate combination of reconstructed seawater temperatures paleonvironmental data retrieved from exceptionally well preserved lower albian douvilleiceras mammillatum ammonite zone uppermost cc8a nannofossil zone 110 5 111 0 ma cephalopod shells from madagascar mahajanga basin 40 42 southern latitude are reconstructed based on a novel multi proxy approach here we combine and contrast i nacre tablet paleobathymetry ii westermann morphospace and iii shell isotope geochemistry analysis results obtained allow for a robust reconstruction of habitat depth paleo seawater temperatures and paleoecology of extinct cephalopod taxa the discocone nautiloid cymatoceras is regarded as vertical migrant with a maximum habitat depth of 250 m and a mean habitat water temperature of 20 21 c all three ammonoid taxa cleoniceras desmoceras and eogaudryceras share a platycone to planorbicone shell shape suggesting a demersal life habit at maximal water depths of 450 500 m and temperatures of 19 21 c for cleoniceras and desmoceras and the deepest 525 m and coolest 14 c habitat for eogaudryceras circumstantial evidence from benthic mollusk shells from the same stratigraphic interval as well as sedimentological and paleopathological data provide further support for habitat reconstructions reconstructed paleotemperatures shown here provide well constrained evidence for the thermal structure of past oceanic water masses and have significance for cretaceous paleoceanography in general

wave attenuation over coastal salt marshes under storm surge conditions salt marshes protect coastlines against waves wave flume experiments show that marsh vegetation causes substantial wave dissipation and prevents erosion of the underlying surface even during extreme storm surge conditions

mississippi river subaqueous delta is entering a stage of retrogradation abstract the subaqueous delta of the mississippi river the largest river system in the conterminous u s has entered a stage of retrogradation caused by multiple natural and anthropogenic activities since the 1950s the suspended sediment load of the mississippi river has decreased by 50 due primarily to the construction of 50 000 dams in the mississippi basin the impact of this decreased sediment load has been observed in subaerial environments but the impact on sedimentation and geomorphology of the subaqueous delta front has yet to be examined to identify historic trends in sedimentation patterns we compiled bathymetric datasets including historical charts industry and academic surveys and national oceanic and atmospheric administration hydrographic data collected between 1764 and 2009 the progradation rate measured at the 10 m depth contour of southwest pass which receives 69 of the suspended sediment load reaching head of passes has decreased from 67 m yr between 1874 and 1940 to 26 m yr between 1940 and 1979 with evidence of further deceleration from 1979 to 2009 at south pass and pass a loutre the delta front has entered the destructive phase with the 10 m contour retreating at rates 20 m yr at both passes since 1979 advancement of the delta front also decelerated in deeper water in some areas out to 180 m depth except locally where mudflow lobes are advancing deeper contours show a pattern of decreasing progradation rate between 1874 1940 and 1979 2005 time periods furthermore based on differences measured between available bathymetric datasets the sediment accumulation rate across the delta front decreased by 73 for the same period the retention rate of mississippi river sediment on the delta front ranged from 67 to 81 for the time periods assessed with total sediment load stored on the delta front equal to 317 54 mt yr from 1874 to 1940 145 25 mt yr from 1940 to 1979 and 87 15 mt yr from 1979 to 2005 we document for the first time that the mississippi river delta front has entered a phase of retrogradation which will likely be accelerated by future upstream activities that divert a portion of the sediment load to the upper delta for coastal protection and restoration projects the decline of the subaqueous mississippi river delta has critical implications for biogeochemical cycling subaqueous mass wasting and sediment dispersal to the coastal ocean

an attempt to reconcile subsidence rates determined from various techniques in southern louisiana abstract subsidence rates determined from geodetic releveling observations since 1920 in southern louisiana are consistently higher than subsidence rates determined from radiocarbon data in the same region over holocene timescales radiocarbon based subsidence rates are similar to numerically modeled shallow sedimentary compaction rates at similar timescales while recent geodetic observations are an order of magnitude higher possible explanations for the dramatic recent increase in regional subsidence rates suggested by the geodetic data that are considered here include 1 a recent increase in regional contributions from faulting 2 the recent contribution of a regional high impact process such as fluid withdrawal 3 accuracy in one or more of the datasets and 4 a strong dependence of subsidence rates upon the time frame over which different techniques are used faulting and regional groundwater withdrawals appear insufficient to explain the high regional geodetic rates the contribution of regional depressurization from deep fluid withdrawals remains unknown estimate errors are likely smaller than the magnitude of the discrepancies between rates from different datasets observations of subsidence rates may be biased by measurement duration

coupling instrumental and geological records of sea level change evidence from southern new england of an increase in the rate of sea level rise in the late 19th century 1 we construct a high resolution relative sea level record for the past 700 years by dating basal salt marsh peat samples above a glacial erratic in an eastern connecticut salt marsh to test whether or not the apparent recent acceleration in the rate of sea level rise slr is coeval with climate warming the data reveal an average slr rate of 1 0 0 2 mm year from about 1300 to 1850 a d coupling of the regional tide gauge data 1856 to present with this marsh based record indicates that the nearly three fold increase in the regional rate of slr to modern levels likely occurred in the later half of the 19th century thus the timing of the observed slr rate increase is coincident with the onset of climate warming indicating a possible link between historic slr increases and recent temperature increases

relative sea level rise and climate change over the last 1500 years we constructed a detailed relative sea level rise curve for the last 1500 years using a novel approach i e charting the rate of relative sea level rise using microfaunal and geochemical data from a coastal salt marsh sequence clinton ct usa the composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively the resulting sea level rise curve with age control from 14c dating and the onset of anthropogenic metal pollution shows strong increases in the rate of relative sea level rise during modern global warming since the late nineteenth century but not during the little climate optimum ad 1000 1300 there was virtually no rise in sea level during the little ice age ad 1400 1700 most of the relative sea level rise over the last 1200 years in clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years changes from slow to fast rates of relative sea level rise apparently occurred over periods of only a few decades we suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea level rise along the northeastern usa seaboard relative sea level rise in that area is currently faster than the worldwide average which may result partially from an ocean surface effect caused by hydrodynamics our data show no unequivocal correlation between warm periods on a decaal to centennial time scale and accelerated sea level rise one period of acclerated sea level rise may have occurred between about ad 1200 and 1450 which was the transition for the little climate optimum to the little ice age i e a period of cooling at least in northwestern europe local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea level however the second period of accelerated sea level rise occurred during the period of modern global warming that started at the end of the last century

episodic overbank deposition as a dominant mechanism of floodplain and delta plain aggradation the common view that frequent overbank flooding leads to gradual aggradation of alluvial strata on floodplains and delta plains has been challenged by a variety of studies that suggest that overbank aggradation occurs in a strongly episodic fashion however this remains a largely untested hypothesis due to the difficulty in establishing age models with sufficiently high resolution here we use 39 optically stimulated luminescence osl ages from proximal overbank deposits in the mississippi delta to demonstrate for the first time that alluvial aggradation over centennial to millennial time scales is predominantly episodic with aggradation rates of 1 4 cm yr that can persist for centuries osl ages from three separate study areas produce age clusters that are distinctly different yet complement each other these findings suggest that a substantial portion of the continental stratigraphic record consists of patchworks of relatively discrete centennial to millennial scale sediment bodies assembled by autogenic processes

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

deltaic morphodynamics and stratigraphic evolution of middle barataria bay and middle breton sound regions louisiana usa implications for river sediment diversions abstract river sediment diversions have been recognized as a key strategy for offsetting land loss in coastal louisiana recently much attention has been focused on sediment capture from the main stem river and conveyance of that material through diversion outflows yet the performance and long term feasibility of diversions as land building agents also hinges upon the subsurface stratigraphic architecture of receiving basins a concept that has largely been unexplored a major core collection and analysis program was undertaken to study the geological properties of substrates in the middle barataria bay and middle breton sound diversion receiving basins louisiana usa over a region of 200 square kilometers in both basins 50 vibracores up to 5 5 m in length were collected in spring and summer of 2015 cores were logged for bulk density and imaged with a geotek multi sensor core logger split cores were then subsampled for granulometry organic content and 14c dating both receiving basins are characterized by 1 2 m of organic rich surficial strata underlain by 2 m of mineral rich sand and silt beds that display a greater bulk density additionally some cores contain deeper peaty strata intercalated within muds and sands 14c dates of these buried peats range between 1910 and 3203 calendar years before present demonstrating that relatively old deltaic strata exist at shallow depths age comparisons of stratigraphically similar peat beds from this study and previous delta lobe chronological models indicate that the st bernard lobe prograded eastward at a time averaged rate of 75 m yr from a geotechnical standpoint the surficial uncompacted

regurgitalites a window into the trophic ecology of fossil cephalopods fossil oral ejecta that exclusively contain bivalved calcitic lower jaws of ammonites aptychi from late jurassic solnhofen type deposits of southern germany are described based on the symphysis length of aptychi the ammonite shell diameters were reconstructed ranging from 5 to 170 mm to identify the potential ammonite predator published reports on stomach contents coprolites and ammonite palaeopathology were critically assessed implementation of the actualistic approach together with some functional considerations includes the identification of modern cephalopod predators with a focus on the modern nautilus and the distribution of vomiting behaviour among them stomach fluid ph is also important because species with an alkaline stomach ph are unable to dissolve calcareous hardparts and have to orally eject such material herein we regard coleoids with an opportunistic diet as the most likely producers of the aptychi bearing regurgitalites this is based on finds of aptychi in the stomachs of the two coleoids plesioteuthis and trachyteuthis they were likely fast highly manoeuvrable swimmers both share a strong triangular shaped jaw apparatus that could possibly crush ammonite shells as well as arms equipped with suckers to hold their prey circumstantial evidence for coleoids as the producers comes from the alkaline ph of the stomach fluids of modern coleoids supplementary material data for lamellaptychi are available at https doi org 10 6084 m9 figshare c 4695002

climate change record in subsurface temperatures a global perspective analyses of underground temperature measurements from 358 boreholes in eastern north america central europe southern africa and australia indicate that in the 20th century the average surface temperature of earth has increased by about 0 5 degreesc and that the 20th century has been the warmest of the past five centuries the subsurface temperatures also indicate that earth s mean surface temperature has increased by about 1 0 degreesc over the past five centuries the geothermal data offer an independent confirmation of the unusual character of 20th century climate that has emerged from recent multiproxy studies

effects of peat compaction on delta evolution a review on processes responses measuring and modeling abstract peat is most compressible of all natural soils compaction of peat layers potentially leads to substantial amounts of land subsidence peat is common in many distal parts of holocene deltas which are often densely populated it is known that land subsidence due to peat compaction may have serious societal implications in such areas as it may cause damage to construction works and lead to land inundation effects of peat compaction on the natural evolution of deltas are however poorly understood whereas this might be an important control on delta evolution at both local and regional scales the main objective of this paper is to review current knowledge concerning the peat compaction process and its effect on delta evolution in holocene settings and to identify gaps in this knowledge an overview is given regarding 1 the compaction process 2 presumed and potential effects of peat compaction on delta evolution 3 field methods to quantify peat compaction and 4 numerical models to calculate the amount and rate of peat compaction peat compaction and formation influence channel belt elevation channel belt geometry and channel belt configuration last mentioned aspect mostly concerns the influence of peat compaction on avulsion which is one of the most important processes controlling delta evolution interactions between peat compaction peat formation and avulsion have seldom been studied and remain unclear partly because factors such as peat type organic matter content sediment sequence composition and groundwater table fluctuation are so far not taken into account peat compaction and formation potentially influence avulsion as 1 a decrease in accommodation space created by peat compaction underneath a channel causes superelevation and or an increase in lateral migration 2 the high cohesiveness of peat banks inhibits lateral migration which increases bed aggradation decreases sediment transport capacity and hence increases crevassing frequencies which possibly evolve into an avulsion although the low regional gradient in peatlands will hinder this and 3 peat compaction and oxidation in flood basins following groundwater table lowering leads to relief amplification of channel belts at delta scale variations in compaction rates might stimulate the occurrence of nodal avulsions to quantify effects of peat compaction on delta evolution and to determine the relative importance of different factors involved field research should be combined with numerical models describing peat compaction and formation the model should be validated and calibrated with field data

depositional dynamics in a river diversion receiving basin the case of the west bay mississippi river diversion abstract river deltas are a globally distributed class of sedimentary environment that are highly productive ecologically diverse and serve as centers for population and commerce many deltas are also in a state of environmental degradation and the mississippi river delta mrd stands out as a particularly iconic example plans to restore the mrd call for partially diverting the mississippi river which should reinitiate natural deltaic land building processes while the basic physical underpinnings of river diversions are relatively straightforward there exists a considerable controversy over whether diversions can and do deliver enough sediment to the coastal zone to build sub aerial land on restoration dependent time scales this controversy was addressed through a study of crevasse splay dynamics at the west bay mississippi river diversion the largest diversion in the mrd that was specifically constructed for coastal restoration we found that most sediments were distributed over a 13 5 km area with the maximum deposition occurring at the seaward end of this field these results indicate substantial sediment deposition downstream of project boundaries and run counter to simple sedimentary models which predict that maximum sediment deposition should occur closest to the riverbank despite this most sediments appear to be retained in the nearshore zone suggesting that the sediment retention efficiency was at the higher end of the 30 70 range suggested by some sediment budgets

the stable isotopic records of fossils from the peterborough member oxford clay formation jurassic uk palaeoenvironmental implications carbon and oxygen isotopic compositions of calcareous nekton aragonite kosmoceras and calcite belemnites and benthos aragonite nuculacean bivalves and calcite gryphaea from the peterborough member of the oxford clay formation vary considerably at any one horizon but show no obvious trend with time this suggests that the temperature and isotopic composition of ambient seawater may have varied considerably over short time intervals but did not change systematically during deposition of the unit thus short term fluctuations were superimposed on longer term 9stability9 in this shallow shelf environment the overlap in carbon isotopic compositions between calcareous nekton and benthos suggest a well mixed water column oxygen isotopic palaeotemperatures suggest thermal stratification provided that kosmoceras 16 28 c inhabited near surface waters and belemnites 12 19 c indistinguishable from the range for benthic bivalves were nektobenthic oxygen isotopic compositions of phosphate from both shallow and possible deeper dwelling vertebrates reptiles bony fish and sharks yield the same range of palaeotemperatures 20 29 c suggesting that all vertebrate taxa may have lived predominantly in warm shallow waters

combined chronological and mineral magnetic approaches to reveal age variations and stratigraphic heterogeneity in the yangtze river subaqueous delta abstract delta deposits show large spatial heterogeneity in terms of depositional rate and age which is critical to the study of delta erosion in response to the declining fluvial sediment load observed at many river mouths in the world in this study we show that the magnetic susceptibility can be an indicator to reveal age variations and stratigraphic heterogeneity in the yangtze river subaqueous delta ages of three short sediment cores 1700 years the cores at shallow water depths are younger than those from deeper sites modern deposits i e 800 a show lower and uniform values due to the reductive dissolution of ferrimagnetic minerals while younger sediments

a revised chronology for mississippi river subdeltas radiocarbon measurements by accelerator mass spectrometry relating to three of the four late holocene mississippi river subdeltas yielded consistent results and were found to differ by up to 2000 carbon 14 years from previously inferred ages these geological dataare in agreement with archaeological carbon 14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework which has implications for prehistoric human settlement patterns coastal evolution and wetland loss and sequence stratigraphic interpretations

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

sea level climate correlation during the past 1400 yr we present a new mean high water curve for hammock river marsh clinton connecticut obtained by improving the age model for an existing record of relative marsh elevation based on foraminiferal analysis of a 1 8 m long peat core unlike the earlier curve the new curve confirms trend changes in mean high water rise during the past 1400 yr as noted for salt marshes 15 km farther west suggesting a regional cause these trend changes and century scale mean high water variations in the clinton record correlate positively with large scale regional variations in sea surface and summer air temperature indicating a link between sea level and the climate ocean system on the basis of the clinton mean high water curve we conclude that real sea level oscillated centimeters to decimeters on a century time scale over the past 1400 yr was 25 25 cm higher ca a d 1050 medieval warm period than ca a d 1650 little ice age and rose at a mean rate of 1 mm yr 1 over the past 350 yr there was little or no rise during the cool 1800s

magmatic and structural characteristics of the ca 3440 ma theespruit pluton barberton mountain land south africa the archean crust in the barberton area on the eastern side of the kaapvaal craton south africa consists of a variety of granitic rocks ranging in age from ca 3600 to 2500 ma a suite of tonalite trondhjemite granodiorite ttg intrusions has been divided into an older group ca 3400 ma and a younger group ca 3200 ma and form a set of domal plutons or cells that have similar petrological geochemical and structural characteristics the theespruit pluton one of the older trondhjemite cells dated between 3443 and 3437 ma displays a number of unique features that distinguishes it from others in the region these features include transgressive as well as concordant contact relationships with the enveloping ca 3530 ma amphibolite facies metavolcanic rocks of the lower part of the onverwacht group sandspruit and theespruit formations of the barberton greenstone belt the trondhjemites further display a variety of textures ranging from homogeneous cumulate rocks to foliated lineated and banded gneissic granitoids amphibolite xenoliths occur commonly throughout the pluton and in many cases show little or no effects of strain thereby contributing to the interpretation that these rocks represent roof pendants stoped from the overlying supracrustal volcanic rocks some xenoliths and pluton contact areas have experienced hydraulic fracturing accompanied by brittle deformation brecciation and agmatite development locally the breccias have experienced additional transformation to dioritic rocks following assimilation metasomatism and hybridization resulting from trondhjemite magma injection and late stage hydrothermal activity in the apical portion of what is interpreted to be a high level granitic intrusion at the level exposed the pluton is geochemically and mineralogically uniform throughout consisting of plagioclase quartz biotite rocks trondhjemite with only minor plagioclase quartz biotite hornblende rocks tonalites diorites developed near assimilated amphibolite xenoliths views on the emplacement style of the pluton are considered and processes akin to diapirism are favored over alternate views suggesting that the barberton ttg plutons formed as a consequence of horizontal thrust accretionary processes

current subsidence rates due to compaction of holocene sediments in southern louisiana 1 relative contributions of geologic and anthropogenic processes to subsidence of southern louisiana are vigorously debated of these shallow sediment compaction is often considered dominant although this has never been directly observed or effectively demonstrated quantitative understanding of subsidence is important for predicting relative sea level rise storm surge flooding due to hurricanes and for successful wetland restoration despite many shallow borings few appropriate stratigraphic and geotechnical data are available for site specific calculations we overcome this by determining present compaction rates from monte carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the holocene of southern louisiana this approach generates distributions of present compaction rates that are not expected to exceed 5 mm yr but may locally locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

a sea level rise curve from guilford connecticut usa abstract high resolution stratigraphic studies based on sediment chemistry lithology macroflora and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at guilford connecticut show that coastal marshes are ephemeral environments marsh wide environmental variations were common and century long episodes of relative submergence alternated with emergence despite about 2 m of relative sea level rise rslr in connecticut over the last 1500 years the marshes have expanded both landwards and seawards and marsh accretion has been outpaced only marginally by rslr we used radiocarbon dating and the level of anthropogenic markers metal pollution as dated with 210 pb in the cores for age control for most of the last 1000 years the rate of rslr was between 1 3 and 1 8 mm yr but over the last 300 400 years it increased to 2 9 3 3 mm yr and has been faster than the accretion rate especially in the middle marsh the net submergence rate or submergence index ratio of the rate of rslr and marsh accretion rate averaged about 1 15 over the last 1000 years and increased to about 1 5 over the last 200 years the rate of rslr was very sluggish during the early part of the little ice age but we found a slightly higher rate during the little climate optimum this excursion is close to the noise level however the most significant observation is that rslr increased strongly around a d 1650 the onset of this acceleration falls in the middle to end of the little ice age and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases

stable isotope data δ18o δ13c of the ammonite genus simbirskites implications for habitat reconstructions of extinct cephalopods abstract the accurate habitats of the extinct ammonites and belemnites are largely unknown most ammonites are thought to have had a pelagic lifestyle while belemnites are often considered to have dwelled in deeper colder waters stable isotope analysis 18o 13c provides a useful method to reconstruct the habitats of these two groups of extinct cephalopods but is at the same time limited by various unknowns including the isotopic composition of the past seawater vital effects and diagenesis in this paper stable isotope data from 12 ammonite shells simbirskites spp from the upper hauterivian of the lower saxony basin northwest germany are presented ontogenetic isotope profiles have been obtained from six of these shells in order to reconstruct habitat changes during their lifetime these new ammonite data are combined with published stable isotope data from belemnites hibolithes jaculoides and tex86 palaeotemperature estimates from the same section the combination of isochronous ammonite and belemnite stable isotope data shows that the resulting values of both groups go along with each other calculated palaeotemperatures of the two groups differ by 5 10 c with belemnites always showing the colder temperatures all juvenile shells show an increase of the 13camm to more positive values throughout their ontogeny they are stable in an adult shell fragment the incorporation of carbon isotopes in the ammonite shell therefore correlates with ontogeny and is influenced by metabolic effects probably linked to the shell growth rate the isotope profiles further suggest vertical habitat changes during the ontogeny of the ammonites indicating that the 13camm values might record a combination of environmental and metabolic signals taking into account studies on oxygen isotope fractionation of recent aragonitic and calcitic mollusc shells a similar pelagic habitat is proposed here for both ammonites and belemnites

recent global sea level acceleration started over 200 years ago 1 we present a reconstruction of global sea level gsl since 1700 calculated from tide gauge records and analyse the evolution of global sea level acceleration during the past 300 years we provide observational evidence that sea level acceleration up to the present has been about 0 01 mm yr2 and appears to have started at the end of the 18th century sea level rose by 6 cm during the 19th century and 19 cm in the 20th century superimposed on the long term acceleration are quasi periodic fluctuations with a period of about 60 years if the conditions that established the acceleration continue then sea level will rise 34 cm over the 21st century long time constants in oceanic heat content and increased ice sheet melting imply that the latest intergovernmental panel on climate change ipcc estimates of sea level are probably too low

chronology of the oldest supracrustal sequences in the palaeoarchaean barberton greenstone belt south africa and swaziland abstract zircon age data for felsic metavolcanic rocks of the sandspruit and theespruit formations the two oldest supracrustal components in the palaeoarchaean barberton greenstone belt show that these two successions are time equivalent and constitute one single volcanic event at ca 3530 ma the sandspruit felsic rocks are ubiquitously metasomatized intensely deformed and intruded by and tectonically interlayered with ca 3450 ma granitoid sills that are probably part of the theespruit pluton one metasomatized sandspruit sample contains abundant metamorphic zircons with a weighted mean 207pb 206pb age of 3220 1 1 6 ma reflecting a widespread metamorphic event in parts of the eastern kaapvaal craton in south africa and swaziland several samples of felsic metavolcanic rocks of the theespruit formation confirm a previously established magmatic emplacement age of ca 3530 ma but slightly older rocks up to 3552 ma were found in the easternmost exposure of the theespruit sequence near the south african swaziland border and may represent a lower lithostratigraphic level than exposed farther west hf in zircon isotopic data for most felsic metavolcanic rocks confirm earlier results suggesting that these rocks predominantly originated from melting of a felsic continental basement possibly related to the oldest ca 3660 3550 ma components of the ancient gneiss complex in swaziland however several sandspruit samples also suggest that a juvenile source was involved in their generation perhaps a mafic underplate we see no evidence in the geochemistry and isotopic signatures of felsic volcanic rocks of the sandspruit and theespruit formations for partial melting of a metabasaltic protolith and for palaeoarchean oceanic crust that formed in connection with subduction we rather favor a plateau type setting on older continental crust

an equilibrium profile model for retreating marsh shorelines in southeast louisiana abstract louisiana s coastal marshes are experiencing the highest wetland loss rates in the u s in part due to subsidence driven relative sea level rise these marshes are also vulnerable to the erosive power of wave attack 1 on the marsh edge adjacent to open water bodies and 2 after the marsh platform is submerged marsh shorelines in barataria bay breton sound and the active balize delta of southeastern louisiana were examined in areas where the subaerial marsh platform had disappeared since 1932 vibracore transects of marsh and adjacent bay surface sediments to 2 m depth were analyzed using geotechnical stratigraphic and radiochemical 137 cs and 210 pb methods and the subaerial to subaqueous transition of the marsh was mapped for elevation using standard stadia rod transit and fathometer measurements results indicate that marsh edge erosion of the platform takes place subaqueously until water depths of 1 5 m are reached this is observed even in interior pond regions but the shoreface elevation profiles are a function of fetch exposed open bay sites display greater incision depth and rate of the marsh platform than protected interior bay or pond sites core stratigraphy reveals that the outer part of the subaqueous platform switches from erosional to depositional as retreat proceeds covering the incised marsh deposits unconformably with estuarine shelly muds 137 cs and excess 210 pb activity indicates that these muds are deposited within a few decades of subaerial marsh loss the consistency of the cross shore profile results suggests that a single profile of equilibrium can approximate the morphology of eroding marsh edges in southeast louisiana platform stratigraphy and resistance to erosion have a limited effect on profile shape this equilibrium profile and remote sensing images of shoreline change are used to estimate the sediment yield to adjacent estuarine areas by this process on average 1 5 m3 of sediment are yielded per m shoreline length annually from both barataria bay and breton sound due to the highly organic nature of the eroded sediment 30 this supply of organic rich material could significantly impact estuarine productivity and hypoxia on the louisiana continental shelf

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

middle and late holocene sea level changes in eastern maine reconstructed from foraminiferal saltmarsh stratigraphy and ams 14c dates on basal peat abstract a relative sea level history is reconstructed for machiasport maine spanning the past 6000 calendar years and combining two different methods the first method establishes the long term 10 3 yr trend of sea level rise by dating the base of the holocene saltmarsh peat overlying a pleistocene substrate the second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long term trend the indicative meaning of the peat the height at which the peat was deposited relative to mean tide level is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages the chronology is determined from ams 14 c dates on saltmarsh plant fragments embedded in the peat the combination of the two different approaches produces a high resolution replicable sea level record which takes into account the autocompaction of the peat sequence long term mean rates of sea level rise corrected for changes in tidal range are 0 75 mm yr between 6000 and 1500 cal yr b p and 0 43 mm yr during the past 1500 years the foraminiferal stratigraphy reveals several low amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr b p and a sea level rise of 0 5 m during the past 300 years

paleoarchean partial convective overturn in the singhbhum craton eastern india abstract analyses of fold superposition structures and kinematics of shear zones along a 120 km long e w corridor across the singhbhum craton eastern india are combined with u pb th chemical ages of texturally constrained monazites in supracrustals gneisses and granitoids to reconstruct the paleoarchean tectonic history of the western part of the craton metamorphic sub greenschist facies shallow marine to platformal sediments of the iron ore group iog and the accordantly deformed jagnnathpur meta lavas were accreted onto a basement composed of 3 4 ga amphibolite facies para amphibolites quartzites muscovite schists older metamorphic group omg and anatectic older metamorphic tonalite gneisses omtg crustal shortening was followed by emplacement ascent of the singhbhum granitoid pluton sgp 3 2 3 3 ga synchronous with sinking of supracrustal screens along n nne trending steep dipping sinistral normal ductile shear zones deformation microstructures indicate the bulk of the pluton responded to exhumation strain by low t 500 c ductile flow of quartz and k feldspar with plagioclase being largely unaffected but granitoids along the western margin of pluton emplaced concurrent with westward retreating exhumation of the thickened crust was deformed at t 650 c since all granitoids in the pluton share the same n nne trending tectonic fabric microstructural features imply phased emplacement of the pluton during exhumation strain the transition from crustal shortening to exhumation interrupted by phased granitoid emplacement between 3 2 and 3 4 ga is explained by a two stage partial convective overturn model involving structures typical of supracrustal down granitoid up sense of movement the tectonic restoration in the western part of the singhbhum craton is new and complements growing evidence that accretion and convective overturn may have operated during the paleoarchean

degradation of the plaquemines sub delta and relative sea level in eastern mississippi deltaic coast during late holocene abstract the stratigraphic architecture of plaquemines sub delta lobe is identified from sedimentary cores and sub bottom seismic data collected at lower breton sound louisiana usa four lithofacies were identified in cores from bottom to top 1 organic poor mud 2 organic poor silty sand 3 massive mud 4 organic rich peat and root rich soft mud overall the lithofacies displays a typical progradational deltaic deposit at bottom with upward coarsening feature and then an upward fining deposit overlying on top stratigraphic position of the organic rich peat facies indicates that it is formed after the fluvial sediment source moves away from this region and it is recognized as a termination of progradation of the plaquemines sub delta dated peat samples show that sub delta progradation stops between 876 and 1384 yr ad during which a 20 70 cm relative sea level rise is detected the geological framework reported in this study provides critical information for future modeling on river diversions the stratigraphic architecture underlying lower breton sound implicates that top three facies of root rich soft mud organic rich peat and massive mud are likely to be eroded away before the development of new crevasse splay or sub delta when sediment diversion is in operation the deeper organic poor silty sand lithofacies however can serve as a firm foundation to build new land

mid to late holocene relative sea level change in southwest britain and the influence of sediment compaction relative sea level changes in southwest britain are poorly constrained because of limitations in the quality and quantity of existing geological data as a consequence in contrast to most other regions in the uk it is not possible to reliably infer rates of land and sea level change during the last few thousand years furthermore geologically based sea level reconstructions from this area display significant misfits with relative sea level predictions based on a recent global model of the glacio isostatic adjustment process this paper presents a new record of relative sea level change for the last 4000 years derived from radiocarbon dated sea level index points in addition to providing information concerning the pattern and rates of late holocene sea level change these data are used to evaluate the suggestion that the apparent misfits between model predictions and geological reconstructions can be satisfactorily explained as a consequence of the lowering of sea level index points by sediment compaction the results indicate that a simple first order method of decompaction based on the stratigraphic position of sea level index points can eliminate much of the misfit between reconstructions and predictions and substantially reduce vertical scatter in geological data they also suggest that the influence of compaction on sea level data from this region may be larger than previously thought the simple addition of reliable stratigraphic data in combination with targeted sampling has the potential to improve our understanding of the compaction process and increase the utility of existing data this is increasingly important as the partnership between geophysical modelling and geological investigation becomes more commonplace in sea level studies around the world

propensity for erosion and deposition in a deltaic wetland complex implications for river management and coastal restoration abstract the mississippi river delta is one of the most rapidly changing area on earth with large areas experiencing land loss and smaller areas experiencing loss while some of the drivers of these changes are well known high rates of relative sea level rise reduced sediment inputs canal dredging debate exists about other drivers one area that has received substantial attention is the role of river diversions areas where sediments and water are diverted from the mississippi river into degrading wetlands with the hope of reinitiating deltaic land building processes some authors have argued that diversions lead to reduced shear strengths of wetland soils that make them more vulnerable to storm driven erosion while other authors have argued that sediments from river diversions will develop stable land this study examined this controversy in the cubits gap subdelta an analogue for a large 1420 m3 s 1 river diversion by testing the hypothesis that areas of land gain and or resilience to erosion occurred in areas that actively received river sediments and as a result had mineral rich soils with high shear strength to accomplish this a normalized difference water index ndwi was developed for landsat 7 enhanced thematic mapper etm and landsat 8 operational land imager oli images the ndwi was calculated from blue swir blue swir where swir is the shorter wavelength and yielded land water boundary maps with 30 m resolution results indicate that land gain occurred predominantly in the riverside section of this subdelta where sediments were imported from mississippi river crevasses and or dredging land loss typically occurred in the distal regions of the subdelta which had lower levels of sediment supply and greater wave exposure sediment geotechnical analyses revealed land loss pixels generally correlated sediments with to high organic contents 9 0 1 9 water contents 54 8 3 7 and salinity 6 5 2 0 psu with low shear strengths 5 7 0 8 kn m 2 and low bulk density 0 6 0 8 g cm 3 whereas land gain pixels generally correlate with low organic content 3 9 0 6 water content 38 1 4 2 high shear strength 10 9 4 1 kn m 2 and bulk density 1 00 0 1 g cm 3 this study suggests plans to restore the region by partially diverting the flow of the mississippi river will be most successful if they carry high loads of sediment and that concerns about the integrity of fresh marsh may be unwarranted if those marshes are sediment rich

700 yr sedimentary record of intense hurricane landfalls in southern new england five intense category 3 or greater hurricanes occurring in 1635 1638 1815 1869 and 1938 have made landfall on the new england coast since european settlement historical records indicate that four of these hurricanes 1635 1638 1815 and 1938 and hurricane carol a strong category 2 storm in 1954 produced significant storm surges 3 m in southern rhode island storm surges of this magnitude can overtop barrier islands removing sediments from the beach and nearshore environment and depositing overwash fans across back barrier marshes lakes and lagoons in a regime of rising sea level accumulation of marsh lake or lagoon sediments on top of overwash deposits will preserve a record of overwash deposition we examined the record of overwash deposition at succotash salt marsh in east matunuck rhode island and tested the correlation with historical records of intense storms aerial photographs taken after hurricanes in 1954 and 1938 show overwash fans deposited at the site analysis of 14 sediment cores from the back barrier marsh confirmed the presence of these fans and revealed that 4 additional large scale overwash fans were deposited within the marsh sediments the four overwash fans deposited since the early seventeenth century at succotash marsh matches the historical record of significant hurricane induced storm surge these fans were most likely deposited by hurricanes in 1954 1938 1815 and either 1638 or 1635 radiocarbon dating of two prehistoric overwash fans indicated that these were deposited between a d 1295 1407 and 1404 1446 and probably represent intense hurricane strikes in the past 700 yr at least 7 intense hurricanes struck the southern rhode island coast and produced a storm surge that overtopped the barrier at succotash marsh

interpreting sea level rise and rates of vertical marsh accretion in a southern new england tidal salt marsh an investigation of marsh accretion rates on a new england type high marsh barn island wildlife management area stonington connecticut reveals that this system is sensitive to changes in sea level and storm activity and the peat can accurately record rates of relative submergence as determined by tide gauge records over intervals of 2 5 decades the results also suggest that the relationship between the accretion deficit and plant community structure is important when utilizing peat records to reconstruct historic sea level curves within stablespartina patenshigh marsh communities in systems where major vegetation changes are prominent over short periods of time 50 years interpretations of sea level rise should be limited to the system in which they are developed unless careful vertical controls can be maintained on the data and multiple datable horizons can be identified within the substrate the results of this investigation further show that in a stablespartina patenscommunity within this particular system there is little vertical translocation of137cs making this isotope a powerful tool for assessing rates of vertical marsh development since 1954

mitigating land loss in coastal louisiana by controlled diversion of mississippi river sand the bonnet carre spillway diverts floodwaters from the mississippi river to lake pontchartrain and was opened for 42 days during the 2011 flood according to measurements of the newly deposited sediments at least 31 46 of the river s sand load was diverted into the spillway at this time suggesting that such diversions can help mitigate coastal wetland loss

dynamic changes and processes in the mississippi river delta research in the modern delta of the mississippi river has revealed short term changes and processes that are of significant magnitude deltaic lobes each lobe covering an area of 30 000 sq km and having an average thickness of 35 km switch sites of deposition on an average of every 1 500 yr through short periods of geologic time this process results in a relatively thick accumulation of stacked deltaic cycles covering extremely large areas within a single delta lobe and operating on an even higher frequency are bay fills and overbank splays bay fills having areas of 250 sq km and thickness of 15 m require only 150 yr to accumulate four major events have taken place in the modern balize delta since 1838 overbank splays are much smaller covering areas of less than 2 sq km and having thicknesses of 3 m but are associated with high floods on the river at the river mouth continued progradation of the distributary channel can form distributary mouth sand bodies that have dimensions of 17 km long 8 km wide and a thickness of 80 m in a period of only 200 yr differential sedimentary loading at the river mouth results in formation of diapirs that display vertical movements in excess of 100 m in a period of 20 yr on the subaqueous delta platform sediment instabilities operate nearly continuously mass moving large quantities of shallow water deposits to deeper water environments via arcuate rotational slides and mudflow gullies and depositional lobes all of these changes and processes operate at differing spatial and temporal scales but all result in deposition of large volumes of sediment over extremely short periods of time

sand as a stable and sustainable resource for nourishing the mississippi river delta dams have starved the lower mississippi river of sediment over recent decades suggesting that the drowning of the delta is inevitable analysis of the rivers suspended sediment load and morphodynamic modelling suggest that the amount of sand essential for land building has not significantly decreased since dam construction with sand remaining available for several centuries

provenance and tectonic implications of the 3 28 3 23 ga fig tree group central barberton greenstone belt south africa abstract sedimentary rocks provide a valuable record of non uniformitarian paleoarchean tectonic processes the rocks of the 3 28 3 23 ga mapepe formation mark the initiation of orogenesis in the barberton greenstone belt south africa however reconstruction of the mapepe basin s is challenging because the rocks occur in fault bounded structural belts that are characterized by lateral heterogeneity and whose correlation remains uncertain we have studied the petrography geochemistry and detrital zircon geochronology from outcrop and drill core samples from two adjacent structural belts the manzimnyama syncline and the eastern barite valley area to evaluate the timing of basin formation correlate between these two adjacent areas and provide constraints on the character of tectonic uplift in the eastern barite valley area sedimentation was initiated at about 3260 ma the section includes a lower deep water unit of mainly mudstone overlain by a shoaling upward sequence of fan delta sandstone and conglomerate the sandstone throughout the formation was derived by erosion of local uplifts of the underlying greenstone belt sequence except at the top of the section where sedimentation was dominated by dacitic volcaniclastic sediments dated at 3239 ma in contrast rocks of the mapepe formation in the manzimnyama syncline area 1 2 km south of the eastern barite valley area record the initiation of sedimentation at about 3277 ma with deposition of a rhyolitic tuffaceous unit followed by persistent deep water sedimentation of banded iron formation banded ferruginous chert and turbiditic sandstone siliciclastic sediments are immature and were derived by erosion of older supracrustal greenstone belt rocks no fig tree age volcanism younger than 3260 ma is recorded in this belt overall mapepe sedimentary rocks record the formation of numerous local uplifts of underlying supracrustal rocks with periodic volcanic activity and the dispersal of debris to form mainly small fan deltas flanked by deep water systems the contrasting ages lithologies depositional settings and provenance of the sedimentary rocks in the now adjacent eastern barite valley and manzimnyama syncline belts suggest that they were deposited in either different parts of a large complex fig tree basin or represent separate basins that have been juxtaposed during post fig tree tectonism and shortening

morphodynamics of the erosional phase of crevasse splay evolution and implications for river sediment diversion function abstract despite being a primarily depositional landform a crevasse splay experiences an initial evolutionary phase that is primarily erosional as sediment laden river water spills from a main river channel and incises a new route through the river banks and levee into an interdistributary basin or floodplain this phase sets the dimensions and the conveyance properties of the crevasse which in turn influences the continued expansion or closure of the crevasse channel however little is known about the controlling morphodynamics or how the erosional processes transition to depositional processes during this phase the objective of this study is to investigate these phenomena at the west bay sediment diversion louisiana usa using coupled field observations and numerical modeling the west bay diversion was cut into a lower mississippi river levee to mimic the function of a crevasse splay i e to divert river water and sediment to an adjacent receiving basin for land building purposes bathymetric measurements show that the diversion channel experienced significant natural morphologic evolution during the initial decade 2004 2014 hydrodynamic and sediment transport modeling suggests that this evolution initially increased the discharge of flow and sediment through the crevasse as the channel became wider and deeper and altered its orientation relative to the main river flow direction after 5 years the model results predict that further evolution led to monotonically reduced diversion discharges during this time natural and engineered sediment deposition in the receiving basin decreased predicted basin flow velocities and promoted a backwater effect that reduced the sediment transport capacity of the diversion channel observations during the final 2 years show that much of the initial erosion around the diversion had abated indicating that diversion morphology may have stabilized a modeling sensitivity analysis confirmed that the observed changes to channel geometry and orientation likely promoted flows of water and sediment through the diversion while increases in basin bed elevation would have had a contrary effect the morphodynamic evolution of the west bay diversion documented in this study presents a model indicative of the erosional phase of crevasse splay evolution in a deltaic distributary fluvial network study results offer an analogue on how an engineered river sediment diversion constructed for coastal restoration may function during its first years of operation and suggest that the desired land building processes may take time to become established

evolution of habitat depth in the jurassic cretaceous ammonoids ammonoids a group of cephalopods with external chambered shells arose in the early devonian and went extinct at the cretaceous paleogene k pg boundary during their 340 million y history ammonoids suffered three major diversity crises at the end of the devonian permian and triassic periods and the terminal extinction event at the k pg boundary because of their rapid morphological evolution and rich fossil record ammonoids have been used to determine the relative age of marine strata and correlation since the dawn of stratigraphy although the morphological analyses of shell materials have provided some insights into ontogeny and evolution their biological nature is poorly understood because of the lack of soft body fossils and close modern relatives for example although one may usually imagine that ammonoids were planktic or nektic organisms within a water column like the nautilus which is the sole surviving cephalopod bearing an external chambered shell there is very little direct evidence showing the habitat depth of ammonoids within an ancient water column

wetland loss and the subdelta life cycle abstract the rapid deterioration of marsh habitat observed during recent years in the modern mississippi river delta is a consequence at least in part of the natural life cycle of subdeltas with life spans typically less than 200 years subdeltas or bay fill deposits are scaled down versions of major delta lobes yet provide through pulses of sediment nearly all the subaerial land in an active delta using maps charts and aerial photographs curves were constructed for rates of change in land area sediment volume and linear progradation in the four subdeltas that have formed on the modern mississippi river delta since the first accurate survey in 1838 results indicate that each subdelta 1 lasted for approximately 115 175 years 2 included both periods of growth and deterioration 3 was initiated by a crevasse or break in the natural levee system 4 showed linear advancement and volumetric growth during subaerial deterioration and 5 displayed a new pulse of subaerial growth during the high discharge decade of the 1970s contrary to popular accounts demise of the mississippi river delta through deterioration of its subdeltas is not a result of the construction of artificial levees upstream or discharge of sediment off the continental shelf edge rather it is attributable to a substantial decrease and fining of sediments being transported downstream to depositional sites within a delta that has developed through natural processes a complex and inefficient channel network for delivering these sediments

organic clastic facies relationships and chronostratigraphy of the barataria interlobe basin mississippi delta plain abstract the lithofacies of barataria basin an interlobe basin of the mississippi delta plain were established from analyses of 115 boreholes five organic lithofacies are distinguished by organic matter content botanical origin and degree of decomposition organic rich facies accumulated in three stages a b and c during two depositional events stage a developed locally but stages b and c developed as blankets over abandoned delta lobes protected from marine influx by a shoreline stage b lasted from 2 300 1 000 yr bp and ended when clastic sediments from renewed deltaic sedimentation blanketed the peats expanding the basin about 50 km seaward peat accumulation of stage c lasted from 900 yr bp to the present and is currently being terminated by subsidence induced transgression high quality stage b peats accumulated beneath herbaceous freshwater floating and emergent marshes mainly above the footwall of a strike oriented reactivated growth fault above the footwall the basin was shallower than on the hanging wall where the deeper basin invited more overbank sedimentation which increased ash content and diluted peats thus both tectonic and sedimentary factors influenced organic facies the quality and quantity of barataria basin peats differ from those of many deltaic coals however these peats accumulated in only 2 300 yr immediately after a rapid sea level rise frequent delta lobe switching increased organic matter preservation potential but did not provide sufficient time for the accumulation of thick low ash peats the geometries of organic and clastic facies are similar to those of some coal bearing strata

demersal habitat of late cretaceous ammonoids evidence from oxygen isotopes for the campanian late cretaceous northwestern pacific thermal structure comparison of oxygen isotope data for exceptionally well preserved cooccurring plankton and benthos from the campanian of hokkaido japan with nine species of ammonoids clearly indicates the demersal nektobenthic habitat of ammonoids unlike nautilus the ammonoids studied did not engage in significant short term vertical migrations in the water column the new foraminiferal isotopic data suggest that sea surface and sea bottom temperatures were 26 and 18 c respectively at 40 n in the campanian northwestern pacific the temperatures were significantly warmer than those in the modern northwest pacific this finding provides the first reliable evidence for the warm late cretaceous mid latitude north pacific isotopic analyses of ammonoids show that the average calcification temperature of all ammonoid shells analyzed was 19 c comparable to those of cooccurring benthos none of these ammonoids display calcification temperatures equivalent to those of planktonic foraminifers

transgressive depositional systems of the mississippi delta plain a model for barrier shoreline and shelf sand development abstract depositional sequences generated in the mississippi river delta plain consist of a regressive and a transgressive component the transgressive component has been considerably less studied but accounts for the majority of the surface area on the lower mississippi river delta plain and up to 50 percent of the total sequence thickness in shallow water deltas the development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat combined with a vertical component of submergence acting to preserve the sequence the evolution of transgressive depositional systems in each of the abandoned holocene mississippi river delta complex s can be summarized in a three stage model beginning with stage 1 an erosional headland and flanking barriers in this stage regressive sand deposits contained within abandoned deltaic headlands are reworked by the eroding shoreface and dispersed longshore into contiguous flanking barriers enclosing restricted interdistributary bays submergence of the delta plain during relative sea level rise generates an intradeltaic lagoon separating the former stage 1 sand body from the shoreline forming stage 2 a transgressive barrier island arc the landward migrating barrier island arc is unable to keep pace with relative sea level rise and the retreating mainland shoreline resulting in submergence and the formation of stage 3 an inner shelf shoal following submergence the former barrier island arc sand body continues to be reworked into a marine sand body on the inner continental shelf during stage 3 this sequence of coastal evolution provides direct evidence of barrier island formation with each stage producing a distinctive stratigraphic signature the current sea level rise models of shoreface retreat and in place drowning developed for the u s atlantic continental shelf do not adequately explain either the morphology or the stratigraphy of transgressive mississippi river delta sand bodies current models of mississippi deltaic stratigraphy emphasize the deep water artificially maintained balize delta which differs considerably from the shallow water shelf phase delta complexes that are the primary depositional constituents of he holocene mississippi river delta plain

crevasse splays versus avulsions a recipe for land building with levee breaches 2018 the authors natural levee breaches can not only initiate an avulsion but also under the right circumstances lead to crevasse splay formation and overbank sedimentation the formative conditions for crevasse splays are not well understood yet such river sediment diversions form an integral part of billion dollar coastal restoration projects here we use delft3d to investigate the influence of vegetation and soil consolidation on the evolution of a natural levee breach model simulations show that crevasse splays heal because floodplain aggradation reduces the water surface slope decreasing water discharge into the flood basin easily erodible and unvegetated floodplains increase the likelihood for channel avulsions denser vegetation and less potential for soil consolidation result in small crevasse splays that are not only efficient sediment traps but also short lived successful crevasse splays that generate the largest land area gain for the imported sediment require a delicate balance between water and sediment discharge vegetation root strength and soil consolidation

earth s earliest granitoids are crystal rich magma reservoirs tapped by silicic eruptions granitoids of the tonalite trondhjemite granodiorite ttg series dominate earth s earliest continental crust the geochemical diversity of ttgs is ascribed to several possible geodynamic settings of magma formation from low pressure differentiation of oceanic plateaus to high pressure melting of mafic crust at convergent plate margins these interpretations implicitly assume that the bulk rock compositions of ttgs did not change from magma generation in the source to complete crystallization however crystal liquid segregation influences the geochemistry of felsic magmas as shown by the textural and chemical complementarity between coeval plutons and silicic volcanic rocks in the phanerozoic eon we demonstrate here that paleoarchean ca 3 456 million years old ttg plutons from south africa do not represent liquids but fossil crystal rich magma reservoirs left behind by the eruption of silicic volcanic rocks being possibly coeval at the million year scale as constrained by high precision uranium lead geochronology the chemical signature of the dominant trondhjemites conventionally interpreted as melts generated by high pressure melting of basalts reflects the combined accumulation of plagioclase phenocrysts and loss of interstitial liquid that erupted as silicic volcanic rocks our results indicate that the entire compositional diversity of ttgs could derive from the upper crustal differentiation of a single tonalitic magma formed by basalt melting and or crystallization at 40 km depth these results call for a unifying model of hadean archean continent nucleation by intracrustal production of ttg magmas the chemical diversity of earth s early continental building blocks can be explained by differentiation of a single melt without complex geodynamic settings according to petrological and geochemical analysis of samples from south africa