sedimentary impacts of anthropogenic alterations on the yeongsan estuary south korea abstract over the last half century coastal zones within the republic of korea s korea have experienced a wide range of engineered coastal modifications including construction of seawalls extensive land reclamation and installation of estuarine dams the yeongsan estuary has experienced all of these modifications and provides an ideal case study on how sedimentation changes within a macrotidal estuary in response to these alterations combined these alterations have considerably modulated the timing and intensity of river discharge prevented natural tidal exchange modified the shoreline profile and altered the transport of sediment and organic matter within the coastal zone these impacts have been investigated using 30 gravity cores analyzed for 210 pb radioisotope geochronology laser diffraction particle size analyses 13 c and 15 n isotope ratio mass spectrometry and x radiography average sediment accumulation rates range from 0 9 0 6 cm yr 1 to 10 0 2 9 cm yr 1 with the highest rates proximal to the downstream side of the dam and some areas determined to be either actively eroding or recently dredged these results are supported by comparison of multiple bathymetric surveys and chirp seismic data suggest an order of magnitude increase from average holocene sediment accumulation rates side scan sonograms collected adjacent to the dam reveal distinctive scouring transitioning to areas accumulating fine grained sediments shifts in the organic matter source inputs are apparent in pre post dam sediments and reflect the occluding of tidal influence above the dam resulting in increasingly terrestrial dominated signatures additionally a time series of cores collected during periods of limited and high discharge analyzed for 7 be indicates sediment deposition occurs episodically corresponding to high discharge dam releases our observations record a shift in depositional environments as a response to an extensive array of anthropogenic alterations ultimately land reclamation and dam construction have severely altered the fate and transport of sediment within the estuarine system as a consequence sedimentation rates have increased dramatically and depositional events are primarily controlled by discharges from the estuarine dam

response of sedimentation processes in the minjiang river subaqueous delta to anthropogenic activities in the river basin abstract sedimentary processes in the subaqueous deltas of small mountainous rivers are very sensitive to environmental variation within the river basin and hydrodynamic conditions near the estuarine environment through radiometric dating and sediment grain size analysis of core sediments collected in the subaqueous delta area of the minjiang river mjr we studied the sedimentary processes in this area since the 1950s and revealed their responses to human activities within the mjr basin the dry density of core sediments in the mjr subaqueous delta varied from 0 81 to 1 32 g cm3 the mean sedimentation rate was 0 61 cm yr 0 68 g cm2 yr before 1963 and has increased to 1 04 cm yr 1 05 g cm2 yr between 1963 and 1986 and then decreased to 0 46 cm yr 0 41 g cm2 yr between 1986 and 2014 the core sediments were composed primarily of silt and the main sediment type was clayey silt the mean grain size varied from 5 1 to 22 3 m with a mean value of 10 3 m with increasing anthropogenic activity within the mjr catchment the land use pattern changed markedly soil erosion intensified and the sediment flux discharged by the mjr to the sea clearly increased consequently the sedimentation rate in the subaqueous delta also increased however owing to dam construction large quantities of sediment were trapped within reservoirs decreasing the sediment flux discharged by the mjr to the sea affecting the sedimentation rate in the subaqueous delta and also changing the sediment frequency curve from a bimodal pattern to a single peak pattern

subaqueous delta of the ganges brahmaputra river system abstract the ganges brahmaputra is among the world s three largest river systems in terms of sediment load but until now no high resolution seismic data have been obtained to document the nature of the sediment deposit seaward of the rivers mouths the other two amazon huanghe discharge into energetic coastal environments and form subaqueous deltas with characteristic clinoform stratigraphy high resolution seismic reflection profiles of the bengal shelf reveal similar stratigraphy topset beds dip gently 0 036 and diverge offshore more steeply dipping foreset beds 0 190 converge farther seaward and relatively thin gently dipping bottomset beds 0 022 extend across the outer shelf overlying an erosional surface presumed to be of late pleistocene age sediment accumulation rates are highest in the foreset region 5 cm year and reduced in the bottomset region

a ductile extensional shear zone at the contact area between hp lt metamorphic units in the talea ori central crete greece deformation during early stages of exhumation from peak metamorphic conditions we report on an extensional ductile shear zone in central crete at the contact area between the high pressure low temperature hp lt metamorphic phyllite quartzite unit sensu stricto pq s str and the talea ori group plattenkalk unit mapping and microscopic analysis along the 20 km long contact reveal extensional shear bands shear band cleavages c type and associated quartz veins in both units occurring over a width of up to a kilometer the shear offset along the shear bands is systematically perpendicular to the contact with the hanging block pq s str being downfaulted abundant discordant quartz veins are associated to shear band boundaries asymmetric boudinage and foliation boudinage forming m wide vein networks these mesoscopic deformation structures together with related microstructures such as strain shadows growth rims of albite porphyroblasts and stylolites indicate dissolution precipitation creep as main deformation mechanism accompanied by vein formation temperatures during deformation are indicated to be close to peak metamorphic temperatures 300 350 c by the growth rims of albite porphyroblasts and micas present in the shear band cleavages which are consistent with quartz vein microstructures showing subgrains and sutured high angle grain boundaries peak metamorphic temperatures inferred by the degree of graphitization of carbonaceous material are similar in the hanging wall and the footwall of the shear zone which is consistent with fast and nearly adiabatic exhumation our study demonstrates the importance of ductile shear zones with high strain rate dissolution precipitation creep and vein formation in hp lt metamorphic rocks for the early exhumation history

u pb zircon and biostratigraphic data of high pressure low temperature metamorphic rocks of the talea ori tracking the paleotethys suture in central crete greece inherited deformation microfabrics of detrital quartz grains and u pb laser ablation la icpms and id tims ages of detrital zircons separated from the phyllite quartzite unit s l of the talea ori central crete suggest strikingly different source rocks albite gneiss of the lower rogdia beds includes cambrian and neoproterozoic rounded zircons with main u pb age peaks at 628 and 988 ma these and minor paleoproterozoic and archean peaks together with the lack of variscan aged and mesoproterozoic zircons are similar to the age spectra obtained from the phyllite quartzite unit s str of the peloponnesus and eastern crete and from the taurides all of these zircons should be derived from the northeastern passive margin of gondwana cimmeria metatuffites of the uppermost rogdia beds and metasandstone of bali beach on the other hand include euhedral detrital zircons displaying a variscan u pb age spectra at ca 300 ma with concordia ages at 291 3 300 1 ma rogdia and 286 3 300 3 313 2 ma bali both types of metasediments and their zircons are similar to those of the pre alpine basement and overlying tyros beds of eastern crete revealing a provenance at the southern active margin of laurasia thus in central crete the paleotethys suture should be situated inside the rogdia beds magmatic zircons separated from a rhyolite boulder of the lower achlada beds yielded a concordant u pb zircon age at 242 2 ma placing a maximum age for the deposition of the meta conglomerate from which the boulder was collected this age is compatible with an olenekian early anisian age of the underlying vasilikon marble suggested by new findings of the foraminifera meandrospira aff pusilla both the achlada beds and the vasilikon marble can be attributed to the lower tyros beds of eastern crete the alpine deformation led to a pervasive mylonitic foliation which is affecting most of the studied rocks this foliation results from d2 top to the north shearing which post dates the growth of blue amphiboles crossite

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

shallow marine response to global climate change during the paleocene eocene thermal maximum salisbury embayment usa the paleocene eocene thermal maximum petm was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale here we examine the sediments flora and fauna from an expanded section at mattawoman creek billingsley road mcbr in maryland and explore the impact of warming at a nearshore shallow marine 30 100 m water depth site in the salisbury embayment observations indicate that at the onset of the petm the site abruptly shifted from an open marine to prodelta setting with increased terrestrial and fresh water input changes in microfossil biota suggest stratification of the water column and low oxygen bottom water conditions in the earliest eocene formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites this proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12c enriched co2 we conclude that the mcbr site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming

understanding fine grained river sediment dispersal on continental margins studies of fine grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies based on the pattern and nature of sediment accumulation for twenty three case studies we propose there are five basic types of dispersal systems and these are related to river wave tide and margin characteristics data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load mean significant wave height tidal range and continental shelf width at a river mouth and from these a hierarchical decision tree is developed analysis of the dispersal system type of more than 100 river mouths reveals that proximal accumulation dominated pad and marine dispersal dominated mdd systems are most abundant but estuarine accumulation dominated ead systems also are anticipated to be numerous globally research quantifying marine sediment dynamics in these system types is needed although less common the size and nature of subaqueous delta clinoform sdc and canyon captured cc systems also warrant future attention to their study strong correlations between physical characteristics i e significant wave height and tidal range and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types the process related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon

historical changes in terrestrially derived organic carbon inputs to louisiana continental margin sediments over the past 150 years 1 major rivers and associated deltaic environments provide the dominant pathway for the input of terrestrial derived organic carbon in sediments toct to the ocean natural watershed processes and land use changes are important in dictating the amount and character of carbon being buried on continental margins seven core sites were occupied on the louisiana continental margin aboard the r v pelican in july 2003 along two major sediment transport pathways south and west of the mississippi river mouth lignin profiles in these age dated cores 210pb geochronology indicate artificial reservoir retention as a primary control on organic carbon quantity and quality reaching the margin post 1950 whereas pre 1950 sediments may reflect soil erosion due to land clearing and farming practices lignin 8 concentrations range 0 2 to 1 7 also indicate that toct delivery rates decay processes have probably remained relatively consistent from proximal to distal stations along transects the down core profile at the canyon station seems to be temporally linked and connected to inner shelf deposition suggestive of rapid cross shelf transport sources of terrestrially derived organic carbon were reflective of mixed angiosperms over the last 150 years in cores west and south of the mississippi river delta the lignin phenol vegetation index lpvi range 130 0 to 510 proved to be a sensitive indicator of source changes in these sediments and eliminated some of the variability compared to c v range 0 01 to 0 4 and s v range 0 9 to 2 1 ratios stochastic events such as hurricanes and large river floods have a measurable albeit ephemeral effect on the shelf toct record burial of toct on the river dominated louisiana continental margin is largely driven by anthropogenic land use alterations in the last 150 years land use changes in the mississippi river basin and river damming have likely affected carbon cycling and toct burial on the louisiana continental margin over a large spatial extent as observed by similar trends in cores from across and along the margin

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

contrasting modes of shelf sediment dispersal off a high yield river waiapu river new zealand abstract recent studies of continental margins suggest that small high yield rivers are capable of generating shelf sediment gravity flows an idea that fundamentally alters our understanding of material flux from the continents to the ocean discharge measurements indicate that the waiapu river north island new zealand reaches hyperpycnal concentrations 36 kg m 2 on a yearly basis this study contrasts shelf edge basins with a broad trough along the shelf edge off the waiapu river testing whether there is evidence that shelf sediment gravity flows propagate to topographic lows observations and measurements through geochemical and sedimentological analyses of sediment cores em1002 swath bathymetry and chirp sub bottom profiles suggest differing transport modalities on the outer shelf in general a southern trough shaped region exhibits high terrigenous inputs and non steady state 210pb profiles whereas the northern basins contain steady state 210pb profiles and increased marine influence sediment gravity flows dominate accumulation in the southern region whereas within the northern portion surface plume sedimentation is indicated overall this study suggests that sediment gravity flows could be bypassing the northern basins perhaps a result of oceanographic influences and bathymetric steering as they seek a more direct route across the shelf

non steady state 210pb flux and the use of 228ra 226ra as a geochronometer on the amazon continental shelf the recovery of quasi cyclic 210pb profiles from the foreset region of the amazon subaqueous delta has raised questions concerning the non steady state flux of 210pb to this region of the shelf radioisotopic profiles 210pb 234th 228ra 226ra 137cs from seven kasten cores along with the analysis of grain size organic carbon and clay sized mineralogy are used to investigate the time scale and the controlling mechanisms of the 210pb cyclicity a common assumption used in 210pb geochronology is that the initial specific activity is constant with time an assumption that is invalid in this region variations of particle affinity for 210pb have been shown to affect the initial specific activity reaching the seabed in various other studies however investigations of grain size organic carbon and mineralogy have revealed no relationship with the fluctuating 210pb activity in this area a new geochronometer 228ra 226ra is used to determine sediment accumulation rates over a 30 year time scale which range from 10 to 60 cm yr in the study area spectral analysis of the 210pb cyclicity has revealed that the major component of 210pb cyclicity has a frequency of approximately 2 3 years in addition components of the 210pb cyclicity occur on annual and semi annual frequencies the controlling mechanism for the 210pb cyclicity on these time scales appears to be the seaward transport and accumulation of low activity fluid muds from the topset region

modern accumulation rates and a sediment budget for the eel shelf a flood dominated depositional environment the northern california continental margin is periodically impacted by geologically significant storms which have a marked influence on terrigenous sediment supply flood deposition and long term accumulation of fine grained sediment on the eel shelf accumulation of eel river muds on the adjacent shelf was investigated using 210pb and 137cs geochronologies in order to understand the fate of sediment discharged by the eel river and to relate patterns of net sediment accumulation 100 yr time scale to sediment dynamics 210pb data demonstrate that modern accumulation of river mud occurs from the 50 m isobath seaward across shelf accumulation rates decrease from maximum mid shelf values of 0 6 1 7 g cm 2 yr 1 to values of 0 2 0 4 g cm 2 yr 1 at the shelf break with a spatially weighted mean of 0 5 g cm 2 yr 1 0 4 cm yr for the entire shelf 210pbxs sediment depth profiles from the region of highest accumulation rate are characterized by subsurface intervals of low and uniform activity which are produced by flood deposition in some cores particular 210pbxs activity intervals may be associated with major eel river floods of 1955 1964 and 1974 it is postulated that because of the coincidence of high river flow events and southerly winds during cyclonic winter storms net northward transport allows for preferential deposition of fine grained sediment north of the river mouth over the past 100 years fluvial sediment input combined with marine dispersal processes have produced a mid shelf depocenter evident by both the spatial distribution of 210pb accumulation rates and by clay rich flood layers partially preserved in shelf deposits a fine grained sediment budget for the dispersal system based on hydrological data and 210pb geochronologies demonstrates that a maximum of 20 3 109 kg yr of the mean annual supply of fluvial mud 14 109 kg yr is trapped on the shelf the results of this study demonstrate that 1 short term sedimentation processes associated with floods can influence sediment accumulation on longer time scales and 2 a major fraction of fine grained sediment supplied to tectonically active margins by flood prone mountainous rivers bypasses narrow continental shelves

comments on the paper of yokoyama et al 2000 entitled timing of the last glacial maximum from observed sea level minima abstract in their analysis of relative sea level observations from the j bonaparte gulf of northern australia the authors interpret the raw observations of the last glacial maximum lgm lowstand of the sea by invoking the notion that there is a significant difference between the spatially averaged change in sea level at any time and what is referred to as ice equivalent eustatic sea level in peltier on eustatic sea level history last glacial maximum to holocene quaternary science review 21 2002 in press companion paper this notion is incorrect as it violates the principle of mass conservation the implications of this error of interpretation to the primary conclusion of the yokoyama et al nature 406 2000 713 716 analysis that the ice volume equivalent sea level at lgm lies between 135 and 130 m is discussed herein it is concluded on the basis of this discussion that although the argument presented in this paper for such a deep lgm depression of sea level relies upon this invalid notion it may nevertheless be true that the lgm low stand was greater than the 120 m conventionally assumed

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

multi proxy evidence of rainfall variability recorded in subaqueous deltaic deposits off the adra river southeast iberian peninsula highlights multi proxy evidence of rainfall variability in subaqueous deltaic deposits low absolute abundances related with rainfall driven periods of increase supply raise of colonizers and opportunistic species during dry periods human activities led to a drastic reduction of sedimentation rates abstract the adra river deltaic system southeast iberian peninsula shows a steep topography and is subjected to strong climatic seasonality this system has been affected by alternating wet and dry periods and it has also undergone numerous anthropogenic activities such as deforestation mining activities river channel deviations and dam construction particularly during the last two centuries two sediment cores were retrieved off the adra river from the western ms v9 and eastern ms v4 lobes of the subaqueous deltaic deposit a multi proxy study was carried out including grain size benthic foraminiferal assemblages magnetic susceptibility and geochemical element analyses in order to understand the sedimentary expression of recent climatic cycles and anthropogenic interventions in the river basin periods of increased deposition of coarse grained sediments low absolute abundance of benthic foraminifera and high elemental ratios indicative of terrigenous contributions were interpreted as periods of increased sediment supply to the shelf four flooding events were recorded in core ms v9 and three events on core ms v4 of which two were observed in both cores they were related to periods with major floods that were documented on the southern iberian peninsula around 1770 1810 and 1860 1870 ad on the other hand sediment core intervals exhibiting increasing proportion of fine grained sediments and higher abundances of foraminiferal species assigned as successful colonizers textularia earlandi and opportunistic species that feed on bacteria or terrestrial organic matter bolivina ordinaria bulimina elongata eggerelloides scaber and ammonia beccarii or tepida indicate the establishment of new environments with new ecological constraints they were related to significant decreases of terrigenous sediment input during low rainfall or dry periods the increase of opportunistic species feeding on fresh phytodetritus nonionella iridea nonionella stella nonionella sp brizalina dilatata epistominella vitrea and bolivinellina pseudopuntata under more stable environmental conditions also point to a stronger marine influence on the prodeltaic environments during these periods the human interventions on the river basin after 1872 ad with the deviation of the main river channel to the east led to a drastic reduction of the sediment exported to the western delta lobe this study showed that the sedimentation on the adra subaqueous deltaic deposit was mainly controlled by rainfall variability from 1663 to 1872 ad and afterwards by anthropogenic interventions

mesozoic extensional history of the southern tethyan continental margin in the se aegean the islands of rhodes alimnia and symi are situated at the eastern end of the hellenic arc well exposed on these islands are a series of nappes composed of mesozoic early tertiary principally carbonate sequences which formed the sedimentary cover of the southern tethyan margin and were stacked during alpine deformation in the late palaeogene the stratigraphy of these sequences is described and interpreted as preserving a transition from a carbonate platform through slope to basin the sequences formed part of the cover of a passive continental margin but this margin differed from typical modern margins in recording several episodes of extension with no clear evidence of ocean crust formation in the se aegean three important episodes of extension are recorded a platform basin topography was initiated by mid late triassic rifting late liassic extension led to platform collapse and development of carbonate slopes and renewed late cretaceous extension further reduced the size of carbonate platforms the late cretaceous extension was probably linked to the formation of ocean crust further east in cyprus and turkey sedimentological evidence indicates that the slope was eastward facing and the platform basin margin was orientated approximately north south this evidence is not consistent with previously proposed palaeogeographic reconstructions of the region based on tracing the isopic zones of the hellenides through the arc a new two dimensional reconstruction of the form of the southern tethyan margin in the se aegean is proposed

the structure and regional significance of the talea ori crete abstract on the basis of detailed geological mapping in the talea ori of crete metamorphic rocks previously interpreted as basement to the plattenkalk series are re interpreted as down faulted parts of the overlying phyllite quartzite series nappe a supposed unconformity separating these two units is shown to be a high angle fault the phyllite quartzite series and overlying nappes were affected by two major deformational phases whereas the plattenkalk series has a simpler structural history and was folded and imbricated by southwards directed overthrusting which emplaced the phyllite quartzite series nappe and other overlying nappes in the oligocene we reject previous models of a huge inversion of the plattenkalk series and we also consider that considerable local inversion by tight to isoclinal folding and thrusting means that the stratigraphic thickness is much less than previously appreciated the differences between the structural and sedimentological histories of the plattenkalk series and the overlying nappes implies that they were separated by a major crustal discontinuity such as a transform or transcurrent fault before the oligocene overthrusting

geochemistry tectonic setting and metamorphism of mid triassic volcanic rocks of greece abstract mid triassic volcanic rocks are preserved in about eight localities in the nappes of the external hellenides and are also widespread in the pelagonian zone of central greece most have suffered low grade metamorphism immobile trace elements from 35 samples 80 major element analyses and pyroxene analyses show that these rocks are the product of an eastward dipping subduction zone the subducted ocean was perhaps analogous to the pennine zone of the alps the othris and pindos ophiolites are probably contemporaneous products of related back arc extension metamorphic mineral assemblages in volcanic rocks of the phyllite series of the external hellenides indicate high pressure low temperature conditions probably related to a second subduction that occurred prior to the main phase of hellenide nappe emplacement in the miocene

an introduction to the geological significance of sediment transport and accumulation on the amazon continental shelf in order to understand the formative processes and resulting stratigraphy on the amazon shelf and adjacent shoreline of amapa geological investigations were undertaken as part of a multidisciplinary amazon shelf sediment study amasseds the design of the study provided results of a multifaceted nature integrated with observations in other disciplines focused on sedimentary processes representative of fluctuating conditions on several time scales and broadly distributed on the shelf including regions not investigated in the past on short time scales most muddy sediment is transported northwest of the river mouth from there it moves seaward as fluid mud to cause rapid accumulation of foreset beds and moves northwestward to prograde the northernmost amapa shoreline and to supply sediment to the guianas fluid muds cover the shelf as far northward as 3 5 n and allow strong tides to propagate to shore where tidal currents cause most of the amapa shoreline to undergo erosion today averaged over decades and centuries about half of the amazon sediment discharge accumulates on the adjacent shelf and another significant fraction one sixth leads to accretion of the northernmost amapa shoreline and northwestward bypassing of sediment the remaining sediment is hypothesized to be trapped in deltaplain deposits of the lower amazon river system the foreset region and shoreline represent the two common loci of sediment accumulation that alternate their predominance on time scales of millennia and lead to a two stage progradation of coastal plain and subaqueous deltaic deposits this muddy regressive sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions future research in the study area should address important considerations that were delineated by the present study including mechanisms of shoreline accretion the holocene history recorded in topset and coastal plain strata the role in local sedimentation played by the large shoal extending from cabo norte and the entrapment of amazon sediment by the delta plain

facies and evolution of the modern brazos delta texas wave versus flood influence abstract in order to better define the facies architecture and processes controlling the evolution of wave dominated deltas a detailed sedimentary and geomorphologic study was undertaken on the brazos delta texas the delta has formed since 1929 when the brazos river was diverted by the u s army corps of engineers the brazos delta is composed primarily of fine grained sediments prodelta clay constitutes more than half of the sediment volume thick sands are restricted to the narrow delta front environment whereas back bar lagoonal clays are a significant component of the delta plain sequence the facies architecture is not representative of the classic strandplain model for wave dominated deltas this is due to the strong influence of floods on deltaic evolution in early 1992 statewide flooding gave rise to a major constructional phase of the delta significant quantities of fine grained sediments were deposited in the prodelta one year after the onset of flooding a channel mouth bar emerged offshore of the river mouth and enabled progradation of the delta similar flood events that occurred during 1941 1957 and 1965 were recorded as ridge trough pairs in the delta headland the brazos delta is therefore fluvially influenced during floods and wave influenced during intervening periods

facies analysis of the trypali carbonate unit upper triassic in central western crete greece an evaporite formation transformed into solution collapse breccias the trypali carbonate unit upper triassic which crops out mainly in central western crete occurs between the parautochthonous series plattenkalk or talea ori ida series e g metamorphic ionian series and the tripolis nappe comprising the tripolis carbonate series and including a basal phyllite quartzite unit it consists of interbedded dolomitic layers represented principally by algally laminated peloidal mudstones foraminiferal peloidal and ooidal grainstones as well as by fine grained detrital carbonate layers in which coarse baroque dolomite crystals and dolomite nodules are dispersed baroque dolomite is present as pseudomorphs after evaporite crystals nodules and rosettes which grew penecontemporaneously by displacement and or replacement of the host sediments sabkha diagenesis however portions of the evaporites show evidence of resedimentation pre existing evaporites predominantly consisted of skeletal halite crystals that formed from fragmentation of pyramidal shaped hoppers as well as of anhydrite nodules and rosettes salt crusts all microfacies are characteristic of peritidal depositional environments such as sabkhas tidal flats shallow hypersaline lagoons tidal bars and or tidal channels along most horizons the trypali unit is strongly brecciated these breccias are of solution collapse origin forming after the removal of evaporite beds evaporite related diagenetic fabrics show that there was extensive dissolution and replacement of pre existing evaporites which resulted in solution collapse of the carbonate beds evaporite replacement fabrics including calcitized and silicified evaporite crystals are present in cements in the carbonate breccias brecciation was a multistage process it started in the triassic but was most active in the tertiary in association with uplift and ground water flow telogenetic alteration during late diagenesis in zones of intense evaporite leaching and brecciation solution collapse breccias were transformed to rauhwackes the trypali carbonate breccias trypali unit are lithologically and texturally similar to the triassic solution collapse breccias of the ionian zone continental greece the evaporites probably represent a major diapiric injection along the base of the parautochthonous series metamorphic ionian series and also along the overthrust surface separating the parautochthonous series from the tripolis nappe phyllite quartzite and tripolis series the injected evaporites were subsequently transformed into solution collapse breccias

detrital zircon and micropalaeontological ages as new constraints for the lowermost tectonic unit talea ori unit of crete greece the talea ori unit is the lowermost known tectonic unit of crete and the most external part of the hellenides its stratigraphy ranges from late carboniferous to oligocene and outcrops of the lower part are only known in the talea ori mountains central crete in this area a black sandstone at the base of the galinos beds thought to be the oldest formation contains zircons which were dated using the single grain evaporation method the majority of these grains yielded late carboniferous ages variscan while a small group yielded early proterozoic ages the age distribution of these zircons suggests that at the carboniferous permian boundary not much of the older north gondwanan basement was exposed and that a river system carried detrital material from the variscan belt towards the forming neotethyan rift additionally higher up in the stratigraphy benthic foraminifers miliolids were found in clasts from a conglomerate which was so far thought to be of early triassic age epting m kudrass h r leppig u schaffer a 1972 geologie der talea ori kreta n jb geol palaont abh 141 259 285 these miliolids belong to the species hoyenella inconstans michalik j jendrejakova o borza k 1979 some new foraminifera species of the fatra formation uppermost triassic in the west carpathians geol carpath 30 1 61 91 thus attributing a late triassic carnian norian maximal age to this conglomerate the carbonate platform from which the miliolids bearing clasts come is not known the presence to the north of a continuous hemipelagic record from the carboniferous to the triassic phyllite quartzite and tripali units attributed to the palaeotethys realm allows the talea ori unit and its lateral equivalents the ionian zone to be assigned to the westward continuation of the cimmerian block and therefore to the northern margin of the east mediterranean neotethys ocean

sediment flux and the anthropocene data and computer simulations are reviewed to help better define the timing and magnitude of human influence on sediment flux the anthropocene epoch impacts on the earth surface processes are not spatially or temporally homogeneous human influences on this sediment flux have a secondary effect on floodplain and delta plain functions and sediment dispersal into the coastal ocean human impact on sediment production began 3000 years ago but accelerated more widely 1000 years ago by the sixteenth century societies were already engineering their environment early twentieth century mechanization has led to global signals of increased sediment flux in most large rivers by the 1950s this sediment disturbance signal reversed for many rivers owing to the proliferation of dams and sediment load reduction below pristine conditions is the dominant signal today a delta subsidence signal began in the 1930s and is now a dominant signal in terms of sea level for many coastal environments overwhelming even the global warming imprint on sea level humans have engineered how most water and sediment are discharged into the coastal ocean hyperpycnal flow events have become more common for some rivers and less common for other rivers bottom trawling is now widespread suggesting that even continental shelves have received a significant but as yet quantified anthropocene impact the anthropocene attains the level of a geological climate event such as that seen in the transition between the pleistocene and the holocene

sedimentary impacts of recent moderate earthquakes from the shelves to the basin floor in the western gulf of corinth abstract in seismically active areas long term records of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes in the western corinth rift one of the most active areas in europe in terms of seismicity data about ancient earthquakes are still insufficient despite historical records covering the last two millenia and several studies in onshore paleoseimology in this paper we test the use of offshore sediments from the gulf of corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes two shelves 40 100 m deep one sub basin 180 m and the basin floor 330 m have been sampled by short gravity cores the cores were analyzed in order to identify and characterize event deposits the age control has been provided by 137cs and 210pb activity measurements showing that the cores represent 2 to 4 centuries of sedimentation in each site sandy event deposits are interbeded in the muddy hemipelagic sedimentation the age of event deposits has been compared to the record of historical earthquakes using new and published macroseismic data this comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity vii in the area e g in 1861 ce 1888 ce and 1909 ce in nearshore shallow water settings the record of event deposits does not exactly fit with the historical record of large earthquakes because too few event deposits are present this may be due to the absence of sediment failures or to a lower preservation of the deposits in such settings in the deepest site in the basin floor the correspondence is better a sandy turbidite probably corresponds to each large earthquake since 1850 ce except one aseismic sediment density flow that occurred at the end of the 20th century surprisingly the ms 6 2 june 15 1995 aigion earthquake is only possibly recorded in one nearshore site on the aigion shelf in the form of a tsunami back wash flow deposit this study showed that moderate earthquakes m 5 8 6 5 can significantly impact marine sediments regarding the evaluation of seismic hazard in the area the basin floor is proposed as a promising site for long term paleoseismology in the gulf of corinth while shallower settings need to be considered more carefully

the prina complex in eastern crete and its relationship to possible miocene strike slip tectonics abstract the basal neogene formations in the ierapetra region eastern crete are strongly influenced by a late serravallian tectonic phase which resulted in the breakup of pre existing palaeogeographic patterns important vertical movements caused the southward emplacement of neogene sediments together with parts of the underlying pre neogene nappe pile the resulting chaotic association of exotic blocks and sediments known as the prina complex has the properties of a sedimentary melange it can be traced for more than 15 km from north to south in the north a relatively coherent accumulation of large slide masses overlies deformed neogene coarse clastics and pre neogene rocks distally it comprises a poorly stratified sequence of breccias and intermixed finer grained sediments which locally contains olistostromes and debris flows and interfingers to the south with submarine fan deposits the intricate relation of faulting and gravity sliding in a rapidly subsiding basin can be explained by generation in a strike slip setting it is suggested that the ierapetra basin and its offshore extension the south cretan trough were initiated by sinistral movements along a ne sw oriented fault zone implications of this model for the geodynamic evolution of the south aegean area are discussed

event driven deltaic sedimentation on a low gradient low energy shelf the brazos river subaqueous delta northwestern gulf of mexico abstract the brazos river delta is located in the northwestern gulf of mexico sedimentation on the brazos river subaqueous delta has been largely understudied swath bathymetry data collected across the subaqueous delta reveals a noticeable asymmetry with much deeper water depths and greater cross shelf slopes along the eastern up drift side of the delta than along the western down drift side end member sampling reveals that brazos river derived sediment is red red brown or brown in color exhibits increased bulk density and is enriched in calcium a function of carbonate rich areas of the watershed whereas the gulf of mexico inner shelf muds are gray to black and have a relatively lower calcium content analyses of a series of 33 submersible vibra cores collected across the subaqueous delta reveal alternating beds of brazos river derived sediment and gulf of mexico shelf dominated sediment excess 210pb geochronologies of select cores reveal that sediment accumulation has been a combination of fluvial flood event deposition and deposition of remobilized sediment from the proximal shelf and older portions of the delta rather than steady state accumulation because the brazos river is susceptible to local climatic cycles fluvial flood events that create the event layers are intermittent between prolonged periods where marine processes drive accumulation results also show that the primary depocenter of the subaqueous delta has migrated southwestward over time and the erosion of earlier depocenters and proximal shelf sediment has contributed to accumulation on the delta over the past 50 years the subaqueous delta has reached an equilibrium where flood event beds can be completely remobilized within a year and net accumulation approximates relative sea level rise this study highlights relatively rapid clinoform migration due to natural and anthropogenic changes to the system and demonstrates subaqueous delta growth through a combination of direct fluvial and marine derived sediment input

the influence of a salt wedge intrusion on fluvial suspended sediment and the implications for sediment transport to the adjacent coastal ocean a study of the lower brazos river tx usa abstract the brazos river is second only to the mississippi river in terms of sediment load discharged to the gulf of mexico gom this study focused on the interaction between a salt wedge and suspended sediment in the lower brazos river and the implications for sediment export to the coastal ocean salinity and turbidity optical backscatter sensor data with depth swath bathymetry and chirp sub bottom profiling data were collected from 2007 to 2012 over various river discharge stages sampling locations included the lower most 15 km river reach and the coastal ocean proximal to the mouth results indicated that during low to moderate river discharges a salt wedge was present in the lower river but absent during elevated fluvial discharge quantitative analysis showed the salt wedge within the river modulated sediment export to the gom by trapping sediment along the lower most 9 km reach within this reach the trapped sediment formed a decimeter thick mud layer observed in the chirp and bathymetric data at elevated fluvial discharges the salt wedge was no longer observed in the river and the lower river reach transitioned from depositional to erosional based on the observations and analysis from this study a fluvial discharge threshold where the salt wedge is not present in the river and sediment export to the coastal ocean was maximized was estimated this threshold has been met or exceeded only 10 of time since the 1960s these conditions imply that sediment transport to the coastal ocean is highly variable and occurs during irregular pulsed events this study highlights how estuarine conditions at the river mouth can impact terrestrial material flux to the coastal ocean

climate forcing in a wave dominated delta the effects of drought flood cycles on delta progradation abstract the modern brazos delta is composed of a series of ridge trough pairs reflecting episodic delta growth previous work has shown that these features represent remnants of channel mouth bar and back bar lagoon deposits formed as a consequence of major floods subsequent reworking by wave action welds these units to the western flank of the delta plain forming the next ridge trough set recent work however has brought to light a primary climate component in the development of these facies making development of ridge trough pairs a more complex process than the previous model suggests climate in texas is characterized by extremes many of which can be attributed to el nino and la nina cycles el nino events result in dramatically higher precipitation and flooding and la nina events trigger periods of extreme drought the development of an emergent channel mouth bar is correlated to high sediment yield floods induced by el nino events however only five ridge trough sets exist on the delta plain and an estimated 20 el nino events have occurred since 1929 when the delta began to form indicating that the flood criterion alone is not sufficient to initiate delta progradation each of the five episodes of rapid delta growth occurred when a period of extensive drought preceded an el nino induced flood the droughts associated with la nina events were instrumental in removing vegetation and pre conditioning the drainage basin for erosion without a preceding drought the floods are ineffective in generating sufficient sediment to create a ridge

seabed dynamics of the inner amazon continental shelf temporal and spatial variability of surficial strata the continental shelf southeast and northwest of the amazon river mouth is overlain by a sediment layer of about a meter in thickness characterized by 210pb profiles consisting of one or more segments with nearly uniform excess activity uniform 210pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments however biological activity is minimal in this area hence this surficial layer sl is a result either of physical reworking of the sediments or of rapid possibly episodic deposition of sediment factors controlling the formation of the sl were examined during the amasseds project between august 1989 and october 1991 primarily using 210pb t1 2 22 3 yr activity profiles and x radiography the thickness and character of the sl were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions e g discharge stage wind stress one of these stations was reoccupied during semidiurnal and fortnightly periods additionally replicate sediment cores were obtained at stations in order to assess small scale spatial variability of geochemical and sedimentological characteristics in the seabed the sl thicknesses in replicate sediment cores obtained at each site were found to vary within 5 cm normalized thickness of the sl decreased by an average of 17 cm between august 1989 and february 1990 a period of increasing wind stress during falling to rising river discharge the sl thickness subsequently increased slightly 8 cm from february to may 1990 and increased again 27 cm between may 1990 and october 1991 the maximum sl thicknesses were observed in october a period of low wind stress and minimal river input suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge variations in sl thickness are reflected by changes in suspended sediment mostly as fluid muds as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when sl thickness is at a minimum although a significant sl was present during all of the sampling periods changes in the character of 210pb profiles at two of the stations suggest that substantial perhaps complete removal and redeposition of the sl occurred some time between february and may preserved strata i e below the sl is characterized by greater evidence of bioturbation and increased sand content but otherwise is similar to that of the sl long term preservation of strata is thought to occur through episodic suspension and redeposition of the sl with net accumulation of decimeter thick hiatus bounded layers

evidence of recent flood deposits within a distal shelf depocenter and implications for terrestrial carbon preservation in non deltaic shelf settings abstract extreme episodic events have the capacity to transport large amounts of terrestrial material to the coastal ocean while estuaries and deltas are typically thought to trap most of this material some escapes these coastal features and is transported to distal depocenters along the continental shelf distal shelf depocenters can act as the ultimate sink for event deposits yet event sedimentation and the impact of terrestrial carbon burial within these shelf deposits remains understudied therefore this study investigated event sedimentation within the texas mud blanket tmb a distal shelf depocenter of the brazos river located in the northwestern gulf of mexico using a core that was collected from the tmb during a months long elevated discharge event in late 2015 to early 2016 we applied a multi proxy approach to delineate the event deposit we utilized physical sediment properties fabric texture and bulk density radioisotopes 7be and 210pb and organic geochemical properties 13c c n and lignin phenols to identify a 10 cm event layer at the surface of the core within this 10 cm layer we also distinguished two sub layers associated with separate extreme discharge periods in the winter and spring respectively using these event layer characteristics we identified three other earlier potential event deposits in the core that we have attributed to events in 2010 2007 and 2000 2001 from these results this study has demonstrated that the tmb may be an archive for event deposits over multi decadal time periods in particular the transition from periods of prolonged drought to extreme wetness associated with the brazos river this event dominated sedimentation regime can enhance long term carbon burial potentially increasing current estimates of carbon burial significantly in the tmb and other similar distal shelf depocenters ultimately this study highlights the potential for distal shelf depocenters as organic carbon burial hotspots and postulates that this role may expand in the future as climate change increases the intensity and frequency of extreme events

the deltaic nature of amazon shelf sedimentation despite the annual discharge of more than a billion tons of sediment by the amazon river the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta the river mouth however is not an estuary either these observations raise a major question as to what type of sedimentary environment the amazon river mouth represents seismic stratigraphy has been examined on the continental shelf at the mouth of the amazon river using high frequency 3 5 khz seismic records from about 6 000 km of ship track these records demonstrate three regions 1 the amazon river has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth the feature is prograding seaward and accreting upward and it contains fine scale stratification typical of classic deltas the feature forming at the mouth of the amazon is a subaqueous delta it differs from classic deltas primarily in its lack of subaerial expression subaqueous deltas such as the amazon represent the general case of a major river entering an energetic oceanic regime

changes in clay minerals and potassium fixation capacity as a result of release and fixation of potassium in long term field experiments abstract we investigated to what extent soil k balances resulting from plant off take and k fertilizer application rates had changed the content of illitic 10 a materials as discrete illite and as illitic layers in mixed layer minerals in soil clay fractions we also assessed to what extent different particle size fractions were involved in the processes the study was performed on soil samples from five long term agricultural experiments located on mollisols and inceptisols in south and central sweden each having a range of k fertilizer application rates we analysed x ray diffraction xrd patterns from parallel orientated samples of the following particle size fractions total clay

clinoform sedimentation along the apennine shelf adriatic sea abstract sedimentation along the central adriatic coastline of italy results from a series of small distributed fluvial sources i e a line source draining the apennine mountains these rivers deliver 3 107 t y 1 of sediment contributing to the formation of a shore parallel shelf clinoform that has developed throughout the holocene across shelf sediment accumulation rates calculated from 210pb half life 22 3 years measurements are greatest on the clinoform foreset 1 cm y 1 which is characterized by seafloor crenulations in a few areas however for some cross sections of the clinoform accumulation rates are not significantly higher on the foreset than on the topset and bottomset indicating that the clinoform may not be actively prograding in those areas today accumulation rates increase southward along the shelf and are greatest near the gargano peninsula 1 7 cm y 1 between ravenna and the gargano peninsula 3 1 107 t y 1 of sediment accumulate on the apennine shelf although the amounts of sediment supply and accumulation are about the same additional po river sediment is thought to enter the system from the north and some sediment is transported beyond the gargano peninsula to the south anthropogenic activities particularly dam construction following world war ii have significantly impacted sedimentation in this region changes in 210pb profiles document reduction in sediment accumulation however observations during winter 2002 2003 using the short lived radioisotope 7be half life 53 3 d have indicated that some new sediment is delivered to the shelf during periods of elevated discharge so dam entrapment is not complete

exhumation of high pressure rocks under continuous compression a working hypothesis for the southern hellenides central crete greece combined kinematic structural and palaeostress calcite twinning fault slip data analyses are used to study the exhumation mechanism of the high pressure rocks exposed on the island of crete southern aegean greece our study shows that the evolution of windows in central crete was controlled by two main contractional phases of deformation the first phase d1 was related to the ductile stage of exhumation nnw sse compression during d1 caused layer and transport parallel shortening in the upper thrust sheets resulting in nappe stacking via low angle thrusting synchronously intracontinental subduction led to high pressure metamorphism which however did not affect the most external parts of the southern hellenides subsequent upward ductile extrusion of high pressure rocks was characterized by both down section increase of strain and up section increase of the pure shear component the second phase d2 was associated with the brittle stage of exhumation d2 was governed by nne ssw compression and involved conspicuous thrust related folding considerable tectonic imbrication and formation of a middle miocene basin the major d2 related psiloritis thrust cross cuts the entire nappe pile and its trajectory partially follows and reworks the d1 related contact between upper and lower high pressure tectonic units eduction and doming of the talea window was accompanied by gravity sliding of the upper thrust sheets and by out of the syncline thrusting late orogenic collapse also contributed to the exhumation process therefore it seems that the high pressure rocks of central crete were exhumed under continuous compression and that the role of extension was previously overestimated

clay mineral distributions in and around the mississippi river watershed and northern gulf of mexico sources and transport patterns abstract maps of the distributions of the four major clay minerals smectite illite kaolinite and chlorite in and around the mississippi river drainage basin and in the northern gulf of mexico have been produced using newly acquired data from erodible alluvial terrestrial sediments and marine surface sediments as well as from previously published data east of the rockies north america can be divided into four large clay mineral provinces 1 the north western mississippi river watershed smectite rich 2 the great lakes area and eastern mississippi river watershed illite and chlorite rich 3 the south eastern united states kaolinite rich and 4 the brazos river and south western mississippi river watersheds illite and kaolinite rich the clay mineral distributions in surface sediments of the present day gulf of mexico are strongly influenced by three main factors 1 by relative fluvial contributions the mississippi river delivers the bulk of the clay input to the northern gulf of mexico whereas the apalachicola mobile brazos and rio grande rivers inputs have more local influences 2 by differential settling of various clay mineral species which is identified for the first time in northern gulf of mexico sediments and 3 by oceanic current transport the gulf of mexico surface and subsurface circulation distributes the clay rich sediments from river mouth sources throughout the northern gulf of mexico

new techniques in sediment core analysis an introduction marine sediment cores are the fundamental data source for information on seabed character depositional history and environmental change they provide raw data for a wide range of research including studies of global climate change palaeoceanography slope stability oil exploration pollution assessment and control and sea floor surveys for laying cables pipelines and siting of sea floor structures during the last three decades a varied suite of new technologies have been developed to analyse cores often non destructively to produce high quality closely spaced co located downcore measurements characterizing sediment physical properties geochemistry and composition in unprecedented detail distributions of a variety of palaeoenvironmentally significant proxies can now be logged at decadal and in some cases even annual or subannual scales allowing detailed insights into the history of climate and associated environmental change these advances have had a profound effect on many aspects of the earth sciences particularly palaeoceanography in this paper we review recent advances in analytical and logging technology and their application to the analysis of sediment cores developments in providing access to core data and associated datasets and data mining technology in order to integrate and interpret new and legacy datasets within the wider context of sea floor studies are also discussed despite the great advances in this field however challenges remain particularly in the development of standard measurement and calibration methodologies and in the development of data analysis methods new data visualization tools and techniques need to be developed to optimize the interpretation process and maximize scientific value amplified collaboration environments and tools are needed in order to capitalize on our analysis and interpretation capability of large multi parameter datasets sophisticated yet simple to use searchable internet databases with universal access and secure long term funding and data products resulting in user defined data mining query and display so far pioneered in the usa and australia provide robust models for efficient and effective core data stewardship

exhumation of deep crustal metamorphic rocks and crustal extension in arc and back arc regions we adress the problem of exhumation of metamorphic rocks in arc and back arc positions based on observations of the aegean and tyrrhenian back arc regions in both regions back arc extension has been active for 25 ma at least while convergence and crustal thickening was going on at the thrust front compressional structures are reworked in the back arc domain as extensional flat lying detachments which allow unroofing of the metamorphic pile metamorphic rocks suffer first a dynamic burial during nappe stacking and then fast exhumation when they reach the extensional region we describe a continuous process of burial and exhumation that is contemporaneous with the migration of the thrust front toward external zones the front of extension follows behind at approximately one hundred kilometers at the convergence front continuous subduction of a cold oceanic slab or continuous accretion of continental units keeps a cool p t gradient and hp lt metamorphic rocks are formed at depth the overall cool environment leads to a deep brittle ductile transition and thus to a resistant crust which can sustain its large thickness while the thrust front propagates forward parts of the accretionary wedge which were formed earlier enter the back arc domain which can be already under extension and which is warmer because of a greater distance to the cold slab and the presence of the volcanic arc the brittle ductile transition rises in the thick crust which then becomes unstable and subsequently collapses the exhumation history of metamorphic rocks below detachments is two fold 1 a constantely thickening crust is unroofed by flat lying detachments which rework early thrusts this first period is characterized by a good preservation of hp lt parageneses 2 the second period is when rocks are in the zone of crustal scale extension of the back arc region deep crustal metamorphics are exhumed below flat lying detachements which affect the whole crust

asymmetry in holocene river deltas patterns controls and stratigraphic effects abstract understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture most classifications of deltas have focused on subaerial plan morphology as a simplistic function of river tide and wave energy new work however is revealing the importance of subaqueous deposits and in particular shore parallel sediment redistribution in the shaping of delta planform delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal asymmetry has been described from onshore and offshore environments from several different types of modern deltas but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known this study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic geophysical and geochronological datasets we reviewed 27 deltas using over 100 papers primarily from the past 15 20 years morphological facies and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta we define quantifiable indices of asymmetry describing upcurrent vs downcurrent distribution of sediment volume sediment area sediment caliber and distributary channels most deltas are asymmetrical to some degree with respect to one or more of these parameters many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub environments i e delta plain delta front prodelta some deltas are skewed toward the upcurrent side in one sub environment and toward the downcurrent side in another sub environment sand is preferentially deposited on the downcurrent side of most deltas but distributary channels tend to develop toward the upcurrent side the highest sand mud ratios are often on the upcurrent side in the lower delta plain but in the delta front these ratios are highest on the downcurrent side these complex patterns of asymmetry reflect different combinations of controls including discharge partitioning lobe abandonment and localized transgression plume deflection by coastal currents dominance of longshore current direction variable subsidence and other factors these processes may result in upcurrent downcurrent variations in clinoform geometry rates of progradation and stratal lapping relationships asymmetry has multiple aspects manifestations and controls even within a single delta but the long term preservation potential of these patterns likely varies depending on depositional setting and shoreline trajectory studies of ancient deltas will be better informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry

the metamorphic and structural evolution of the phyllite quartzite nappe of western crete abstract the phyllite quartzite pq nappe constitutes an external allochthonous complex of the hellenides on the island of crete and shows a polyphase structural history a first phase of deformation f 1 produced recumbent isoclinal folds a penetrative schistosity and boudinage under high p low t metamorphic conditions mylonite formation at the top of the pq nappe below the overriding tripolitza nappe further boudinage and schistosity s 2 represent a late tectono metamorphic episode post metamorphic small folds f 3 lineations and a crenulation cleavage were formed synchronously with transport of the pq nappe a last phase f 4 developed small folds a fracture crenulation cleavage and large scale folds after nappe movement it is suggested that high p low t metamorphism in the pq rocks originated during subduction nappe transport of the higher unmetamorphosed units which were thrust over the pq nappe began under waning metamorphic conditions subsequent transport of the pq nappe itself also occurred after the completion of metamorphism and after the formation of the mylonite at its top

late neogene to quaternary contractional structures in crete greece abstract based on geological and tectonic investigations carried out along an n s coast to coast transect across central crete southern aegean greece new meso and macro structural data mainly collected from neogene quaternary deposits are presented and discussed the occurrence of large scale folds and thrusts together with diffuse minor contractional structures as well as the overall geometry of the fault bounded sedimentary basins document the persistence of a tortonian early pleistocene contractional regime characterized by an nnw sse to nne ssw shortening direction and affecting the upper crust this contractional event s was associated with the ongoing hellenic subduction and caused the development of a southwards migrating out of sequence thrust system consisting of both reactivated inherited structures and new ones the new data emphasize the importance and the extent of this contractional event intervening between the early middle miocene exhumation phase and the still active upper crustal extensional regime that was resumed in the island only during pleistocene when the region was affected by diffuse normal faulting while the contractional event was likely due to a stronger coupling along the overall subduction system the onset of the new extensional stress conditions was probably related to a sudden southwards jump of the basal detachment along the lithospheric african subduction that caused a general stress release in the uppermost crust

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

recycling sediments between source and sink during a eustatic cycle systems of late quaternary northwestern gulf of mexico basin abstract the northwestern gulf of mexico basin is an ideal natural laboratory to study and understand source to sink systems an extensive grid of high resolution seismic data hundreds of sediment cores and borings and a robust chronostratigraphic framework were used to examine the evolution of late quaternary depositional systems of the northwestern gulf of mexico throughout the last eustatic cycle 125 ka to present the study area includes fluvial systems with a wide range of drainage basin sizes climate settings and water and sediment discharges detailed paleogeographic reconstructions are used to derive volumetric estimates of sediment fluxes volume accumulation rates the results show that the response of rivers to sea level rise and fall varied across the region larger rivers including the former mississippi western louisiana presumably the ancestral red river brazos colorado and rio grande rivers constructed deltas that advanced across the shelf in step wise fashion during marine isotope stages mis 5 2 sediment delivery to these deltas increased during the overall sea level fall due to increases in drainage basin area and erosion of sediment on the inner shelf where subsidence is minimal and transport of that sediment to the more rapidly subsiding outer shelf the sediment supply from the brazos river to its delta increased at least 3 fold and the supply of the colorado river increased at least 6 fold by the late stages of sea level fall through the lowstand repeated filling and purging of fluvial valleys from 119 22 ka contributed to the episodic growth of falling stage deltas during the mis 2 lowstand 22 17 ka the mississippi river abandoned its falling stage fluvial deltaic complex on the western louisiana shelf and drained to the mississippi canyon likewise the western louisiana delta was abandoned presumably due to merger of the red river with the mississippi river terminating growth of the western louisiana delta the brazos river abandoned its mis 3 shelf margin delta to merge with the trinity sabine and calcasieu rivers and together these rivers nourished a lowstand delta and slope fan complex the colorado and rio grande rivers behaved more as point sources of sediment to thick lowstand delta fan complexes lowstand incised valleys exhibit variable morphologies that mainly reflect differences in onshore and offshore relief and the time intervals these valleys were occupied they are deeper and wider than falling stage channel belts and are associated with a shelf wide surface of erosion sequence boundary during the early mis 1 17 ka to 10 ka sea level rise the offshore incised valleys of the calcasieu sabine trinity brazos colorado and rio grande rivers were filled with sediment the offshore valleys of smaller rivers of central texas would not be filled until the late holocene mainly by highstand mud the lower onshore portions of east texas incised valleys were filled with sediment mainly during the holocene with rates of aggradation in the larger brazos and colorado valleys being in step with sea level rise smaller rivers filled their valleys with back stepping fluvial estuarine and tidal delta deposits that were offset by flooding surfaces in general the sediment trapping capacity of bays increased as evolving barrier islands and peninsulas slowly restricted tidal exchange with the gulf and valley filling led to more shallow wider bays a widespread period of increased riverine sediment flux and delta growth is attributed to climate change during mis 1 between 11 5 and 8 0 ka and occurred mainly under cool wet climate conditions relatively small sea level oscillations during the mis 1 transgression 17 ka to 4 0 ka profoundly influenced coastal evolution as manifested by landward stepping shorelines on the order of tens of kilometers within a few thousand years the current barriers strand plains and chenier plains of the study area formed at different times over the past 8 ka due mainly to differences in sand supply and the highly variable relief on the mis 2 surface on which these systems formed modern highstand deposition on the continental shelf formed the texas mud blanket which occurs on the central texas shelf and records a remarkable increase in fine grained sediment supply this increase is attributed to greater delivery of sediments from the colorado and brazos rivers which had filled their lower valleys and abandoned their transgressive deltas by late holocene time and to an increase in westward directed winds and surface currents that delivered suspended sediments from the mississippi river to the texas shelf collectively our results demonstrate that source to sink analyses in low gradient basin settings requires a long term perspective ideally a complete eustatic cycle because most of the sediment that was delivered to the basin by rivers underwent more than one cycle of erosion transport and sedimentation that was regulated by sea level rise and fall climate was a secondary control the export of sediments from the hinterland to the continental shelf was not directly in step with temperature change but rather varied between different fluvial deltaic systems

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

the modern po delta system lobe switching and asymmetric prodelta growth the modern po delta system comprising five main delta lobes has been investigated by integrating vhr seismic surveys recorded offshore from water depths as shallow as 5 m to the toe of the prodelta in about 30 m with accurate historical cartography extending back several centuries previous studies give sedimentological and geochronological information from precisely positioned sediment cores this combined historical and stratigraphic reconstruction of the modern po prodelta allows volumetric reconstructions indicating an average sediment load of 9 4 10 6 ty r 1 for po di pila and po di goro gnocca lobes this estimate is remarkably consistent with the total sediment load of 11 5 10 6 ty r 1 available for parts of the last century from a gauge station at the apex of the delta plain in pontelagoscuro these integrated stratigraphic studies allow to explain the key characters of the po delta system a the marked asymmetry of the whole delta prodelta system reflecting prevailing sediment dispersal to the south of each individual delta outlet b the shoreparallel overlapping of successive prodelta lobes fed by distinct river outlets of ever changing relative importance c the delta outlets being artificially forced in a fixed position so that natural avulsion is prevented and delta lobes undergo headland retreat leaving a marked erosion on the prodelta d the presence of prodelta lobes showing widespread bcut and fillq features ranging from 100 to 300 m and depths up to 4 5 m filled with massive silt to very fine sand offshore of short lived very active distributary channels e g po di tolle lobe and suggesting that in some particular interval short lived episodes of submarine erosion are induced by catastrophic increases in river discharge of natural origin or induced by human maintenance the seismic stratigraphy of the modern po delta documents that markedly distinct prodelta architectures form when a newly activated lobe is located updrift north in this case or downdrift south of the one that is retreating in the first case the abandoned lobe becomes sheltered by the new rapidly advancing one in the opposite case the retreating lobe is updrift and a substantial portion of the sediment is cannibalized and transported to the new lobe downdrift d 2005 elsevier b v all rights reserved

an evaluation of subsidence rates and sea level variability in the northern gulf of mexico 1 while subsidence is widely recognized as a driver of geomorphic change in the northern gulf of mexico gom there is considerable disagreement over the rates of subsidence and the interpreted variability in these rates which leads to controversies over the impacts of subsidence on surface land area change here we present a new method to calculate subsidence rates from the tide gauge record that is based on an understanding of the meteorological drivers of inter annual sea level change in grand isle la and galveston tx we explicitly show that temporal patterns of subsidence are closely linked to subsurface fluid withdrawal and coastal land loss and suggest changes in withdrawal rates can both increase and decrease rates of subsidence and wetland loss our results also imply that the volume of sediment needed to rebuild gom wetlands may currently fall within the low end of some restoration scenarios

sedimentary evidence from the south mediterranean region sicily crete peloponnese evia used to test alternative models for the regional tectonic setting of tethys during late palaeozoic early mesozoic time

seismic facies architecture and evolution of the bolivar roads tidal inlet delta complex east texas gulf coast abstract the seismic facies facies architecture and stratigraphy of tidal inlet and tidal delta deposits and their relation to the development of adjacent coastal lithosomes are examined using high resolution seismic profiles vibracores and borehole descriptions the bolivar roads tidal inlet delta complex along the east texas gulf coast was formed 3 3 ka by spit accretion across a baymouth following a rapid sea level rise 4 ka an increase in the tidal prism through time and entrenchment of the tidal inlet over the trinity river incised valley stabilized the inlet and intensified tidal processes on the tidal inlet delta complex the tidal inlet facies show channel stacking and cut and fill structures stacked clinoforms dip westward across the inlet the spit facies is characterized by oblique tangential clinoforms that build outward and deepen from the edge toward the center of the valley the flood tidal delta facies has a base that shallows abruptly bayward as the flood tidal delta facies thins bayward it interfingers with bay sediments near the inlet the flood tidal delta shows channel cut and fill with an overall channel stacking pattern on the seaward side the channels have a trough like geometry bayward the channels broaden and shallow the channels show a prograded fill pattern the ebb tidal delta facies exhibits gently inclined clinoforms prograding over a ravinement surface tidal inlet deposits are composed of sand shell and mud interbeds sand and clay interlaminae are ubiquitous in the tidal deltas and sand and shell beds are common near the inlet overall the bolivar roads tidal inlet delta complex is mud dominated as a result of high influx of fine sediment into the bay

static recrystallization of vein quartz pebbles in a high pressure low temperature metamorphic conglomerate abstract microfabrics of quartz pebbles in hp lt c 1 gpa c 350 c metamorphic conglomerates are investigated the conglomerate was deformed by dissolution precipitation creep while the interior of the pebbles remained undeformed the different pebbles display a wide variety of quartz microstructures imported from the source rocks one type of pebble is derived from quartz veins it shows old grains with numerous fluid inclusions subgrains and undulatory extinction which are partly replaced by new grains devoid of inclusions and substructure free dislocation densities are on the order of 1012 m 2 in both grains we conclude that 1 the quartz vein underwent inhomogeneous crystal plastic deformation in the source rock 2 recrystallization took place by strain induced grain boundary migration starting from small crystalline volumes poor in defects 3 recrystallization was purely static and commenced during re burial of the conglomerate which 4 was simultaneously deformed by dissolution precipitation creep at low differential stress insufficient for crystal plastic deformation of quartz 5 fluid inclusions within old grains were eliminated and their fluid content was drained along the migrating high angle grain boundaries and 6 strain induced grain boundary migration ceased once the driving force became too low by static recovery concurrent to recrystallization within the deformed old grains