riverine dunes on the coastal plain of georgia usa abstract relict eolian dunes on the georgia coastal plain line the north and east sides of many se trending streams and contain important paleoenvironmental information a detailed analysis of four dune fields characterizes dune geomorphology stratigraphy sedimentology and soils georgia s inland dunes range from parabolic to infilled parabolic to irregular in form typically merge to form long chains that parallel source streams and can occur as distinct bands typically the dunes are composed of 95 quartz sand grains with more than half the sand falling in the medium sand fraction dunes overlie flood plain and pointbar sands backswamp and peat deposits fluvial terraces and other dunes in places organic deposits occur on top of dunes cross bedding is observable in dunes more than about 4 m thick and indicates eastward dune migration paleosols found within some dunes indicate holocene reworking conditions favoring dune formation likely included at least seasonal aridity postdepositional modification of the dunes includes a smoothing of the dune surface a clay increase in the c horizon spodic horizon development bioturbation removal of weatherable minerals and fluvial incision

reconstruction of holocene high altitude vegetation cover in the french southern alps evidence from soil charcoal the study presented here from the southern french alps demonstrates the reliability of soil charcoal analysis for the study of holocene past treeline positions the occurrence of charcoal in mineral soils along transects from 1950 m up to 2920 m demonstrates the role of fire in the establishment of the present vegetation patterns the abrupt decrease of charcoal concentration at about 240 0 2 600 m which varies across the study sites corresponds to the modern transition between subalpine forest and alpine tundra charcoal particles formedinsitu providehighspatial resolutiondataforthereconstructionofpastforestandtreelinechanges soil charcoal analysis indicated that 1 treeline was 300 m higher around 6800 cal bp than today and 2 the uppermost forest belt up to 2810 m was colonized by larch larix decidua mill and arolla pine pinus cem bra l thispineispresenttodaybutpatchilydistributed itisabsentfromthethreeareasstudied radiocarbon dates ranging from c 6800 cal bp to the modern period along with historical and archaeological data sug gest that the present pattern of the uppermost forest belt and the patchy distribution of arolla pine in the stud ied area are the results of anthropogenic fire mainly agropastoral activities the question of global warming consequences on treelines in this part of the french alps is discussed

deflation and redeposition of sand dunes in finnish lapland abstract deflation and redeposition of aeolian sands in finnish lapland have been studied by analysis of their sedimentology and stratigraphy by dating buried charcoal layers and by obtaining tl dates the thickness of redeposited sands on buried soils ranges from a few decimetres to more than two metres original dune formation after deglaciation finished around 7000 bp subsequent aeolian activity has been mainly destructive in nature deflation started in some regions about 4800 bp continuing with several breaks until the present some deflation basins have stayed active for at least 1300 years however it is too early to draw general conclusions for the whole area forest fires have been important reactivators of aeolian sand drift but tend to be rather local events change in the ground water table is a basic factor affecting deflation at present human impact and overgrazing by reindeer seem to increase deflation

groundwater lake interactions ii nearshore seepage patterns and the contribution of ground water to lakes in central alberta abstract seepage flux was measured with seepage meters placed along transects from the lake shore to 30 110m offshore in 10 lakes in central alberta during may august 1986 in the study area the predominant surficial deposit is glacial till which is underlain by sedimentary bedrock seepage flux into the lakes ranged from 3 10 10 to 2 10 7 ms 1 seepage out of the lakes was recorded at only one of 92 seepage meter sites at one lake seepage was measured fortnightly along transects at two locations from may to august 1986 seepage patterns were consistent throughout that period in the nearshore region of six of 10 lakes seepage flux to the lakes decreased with distance from shore deviations from that pattern were probably a result of 1 spatial variability of seepage flux within a small area of lakebed 2 intertill sand and gravel lenses near the lake 3 preglacial bedrock channels of sand and gravel underlying some of the lakes ground water was the major source of water 49 of total inflow to one lake at the other lakes ground water was a relatively small component 10 of total inflow

subsurface flow velocities through selected forest soils south island new zealand subsurface flow through soils in tawhai big bush and craigieburn state forests has been studied by applying water at a line source 1 m upslope from a pit in the base of which an intercepting trough is located by measuring lag times between the centres of mass of input and outflow and between the start of input and start of outflow minimum estimates of mean and maximum flow velocity v and vmax at 51 locations were obtained mean values for the tawhai sites were for v 0 3 cm s and for vmax 0 42 cm s but a considerable degree of variability was present with coefficients of variation up to 90 a number of different pathways through the soil are followed by flowing water macropore networks root channels etc are effective transmitters of water and at some sites conveyed up to 40 of the input rapidly to the interception trough variability in flow velocity and the proportion of the input appearing as rapid outflow is a function of antecedent moisture conditions and of the relative importance of the various pathways at a given site which is in turn a function of the characteristics of the soil the macropore network and the parent material at the base of the soil at sites where the soil had an open structure and the parent material was shattered or permeable the macropore network was a less important control upon soil hydrological behavior than where the subsoil had a less open structure and was underlain by impermeable bedrock measurements of flow velocities on undisturbed logged and logged burned planted sites were made at tawhai sf but the spatial and temporal variability was such that no statistically significant differences could be discerned the time lapse since logging may be insufficient for changes in the root systems to be having a hydrological impact but the high variability would require a sample size of over 1000 to show a significant difference in velocity of even 10 for rapid flow through macropores to have a significant influence on streamflow saturation of the soil is necessary before water can enter the macropores soil topographic geologic and climatic conditions in tawhai sf are such that saturation of the lower layers of the soil regularly occurs so that rapid flow through macropores can contribute to storm period streamflow water may reach the channel system from a proportion of the catchment which varies with antecedent moisture conditions and storm duration and intensity but which may attain 100 in moderate to large rain events because of the drier climate and deeper soils subsurface flow contributions to stormperiod streamflow should be less important in the big bush area and particularly in the craigieburn area where the parent materials shattered sandstone or ancient scree deposits do not provide an impermeable layer which diverts flow laterally

precambrian endoliths discovered the earliest known microborings have now been found in late precambrian ooids upper riphean1 vendian2 570 700 myr of the eleonore bay group of eastern greenland the ooids were originally carbonaceous and underwent silicification after boring occurred the finding establishes that the habit of microbial boring evolved before the appearance of skeleton bearing metazoans in the geological record

mid holocene environmental changes in the bay of skaill mainland orkney scotland an integrated geomorphological sedimentological and stratigraphical study a detailed multidisciplinary investigation of intertidal freshwater sediments exposed in the north of the bay of skaill mainland orkney scotland have revealed a complex sedimentary sequence this provided evidence for dynamic coastal environmental changes in the area since the mid holocene freshwater ponds developed on glacial sediments ca 6550 80 yr bp cal bc 5590 5305 from ca 6120 70 yr bp cal bc 5040 4855 these were infilled by blown sand from the distal edge of a dune ridge located to the west thereafter a series of sand blow events alternating with periods of quiescence occurred until ca 4410 60 yr bp cal bc 3325 2900 between ca 5240 160 and 4660 80 yr bp cal bc 4370 3115 pollen and charcoal records show evidence of anthropogenic activities associated with the nearby neolithic settlement of skara brae agriculture was probably affected by recurrent sand movement and widespread deposition of calcium carbonate in the hinterland of the bay machair development between ca 6100 and 5000 yr bp cal bc 5235 3540 corresponds to a mid holocene phase of dune formation recorded elsewhere in northwest europe the more recent and progressive formation of the bay has probably been related to increasing external forcing via storminess long term relative sea level change and sediment starvation within this exposed environment copyright 2000 john wiley sons ltd

charcoal and wood remains for radiocarbon dating upper pleistocene loess sequences in eastern europe and central siberia abstract the present paper concerns long upper pleistocene loess sequences from eastern europe with multiple upper palaeolithic occupations rich in charcoal as well as loess sequences from central siberia with abundant wood remains these complementary records have allowed establishing a high resolution climatic sequence integrating 24 interstadial episodes between ca 42 5 and 10 kyr bp here we discuss the methodology of dating used to fix the chronological framework of this climatic sequence based on a set of 240 available radiocarbon dates mainly produced on charcoal and wood remains special attention is paid to the strategy of sampling charcoal and wood material in strict accordance with stratigraphy as well as to the preparation process in the laboratory for extraction cleaning identification and selection of the best fragments to date careful stratigraphic drawing and detailed positioning of the samples for each geological layer are also considered in order to clarify the relationship of the obtained dates with respect to any sedimentary pedological or archaeological event to be dated the reliability and accuracy of the dates obtained from loess sequences are further controlled by the internal consistency with regard to stratigraphy palaeoenvironmental implications are also discussed

water pathways and chemistry at the groundwater surface water interface to lake skjervatjern norway water pathways and chemistry at the groundwater surface waterinterface to lake skjervatjern norway

plant landscape reconstruction above the current timberline at the monte cimone and corno alle scale mountain areas northern apennines italy during the late holocene the evidence from soil charcoal this paper presents the first pedoanthracological study carried out on two mountains of the northern apennines monte cimone and corno alle scale where the results provided new palaeoenvironmenta

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

lake belau and its catchment northern germany a key archive of environmental history in northern central europe since the onset of agriculture the environmental history since the onset of agriculture was reconstructed from sediments and soils in the catchment area of lake belau schleswig holstein northern germany the established chron

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

groundwater lake interactions i accuracy of seepage meter estimates of lake seepage abstract the use of seepage meters to identify nearshore seepage patterns and to quantify seepage in lakes was evaluated with a monte carlo simulation model the model simulated seepage flux as would be derived from seepage meter measurements along a transect extending from the shore of a hypothetical lake to 40 or 100m offshore along the transect simulated seepage velocities decreased exponentially with distance from shore according to patterns measured at narrow lake alta and lake sallie mn to determine statistical parameters needed in the model seepage flux was measured in situ with closely spaced seepage meters at four different sites in narrow lake seepage velocities within a small area of lakebed were log normally distributed and the variance was positively correlated with mean seepage flux the modeling indicated that the most sensitive parameter affecting the accuracy of seepage meter estimates of seepage patterns and average seepage flux along the transect was the variability in the spatial distribution of seepage flux within a small area of lakebed there was little improvement in the accuracy of estimates of seepage patterns or transect flux when more than ten seepage meters were simulated along the transect when the transect was sampled more than twice or when seepage meters along the transect were simulated to follow a stratified rather than a systematic design

interactions between ground water and wetlands southern shore of lake michigan usa abstract wetlands between and within dune beach complexes along the south shore of lake michigan are strongly affected by ground water the hydrogeology of the glacial drift aquifer system in a 26 km2 area was investigated to determine the effects of ground water on the hydrology and hydrochemistry of cowles bog and its adjacent wetlands the investigation showed that ground water from intermediate and regional scale flow systems discharges to cowles bog from confined aquifers that underlie the wetland these flow systems are recharged in moraines south of the dune beach complexes water from the confined aquifers discharges into the surficial aquifer mainly by upward leakage through a buried till sheet that serves as the confining layer however the till sheet is breached below a raised peat mound in cowles bog allowing direct upward discharge from the confinef aquifer into the surficial sand marl and peat the shallow ground and wetland water in the area influenced by this leakage is a calcium magnesium bicarbonate type with low tritium concentrations consistent with mixing of older ground water and more recent precipitation ground water and wetland water from surrounding areas are less mineralized and have higher tritium concentrations characteristic of precipitation in the late 1970s the results of this study suggest that wetlands in complex hydrogeologic settings may be influenced by multiple ground water flow systems that are affected by geomorphic features stratigraphic discontinuities and changes in sediment types discharge and recharge zones may both occur in the same wetland multidisciplinary studies incorporating hydrological hydrochemical geophysical and sedimentological data are necessary to identify such complexities in wetland hydrology

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

wood charcoal analysis at riwi cave gooniyandi country western australia abstract wood charcoals excavated from archaeological sites provide a useful tool for palaeoenvironmental reconstruction particularly in arid and semi arid zones where suitable catchments for palynological archives are often limited preservation of organic material in northern australia is characteristically poor and wood charcoal analysis provides a viable alternative to understand shifts in woody vegetation in the past the analysis of charcoal from matrix contexts at riwi cave located in the southern kimberley region of northern western australia has allowed a reconstruction of the local woody vegetation during occupation over the last 45 000 years the wood charcoal assemblage from the holocene stratigraphic units reflects the composition of the modern vegetation and illustrates that people were occupying the site during periods of relative humidity the pleistocene stratigraphic units show a shift in vegetation composition from eucalyptus spp to corymbia sp dominated savanna with an understory of secondary shrub associated with a late mis 3 arid event observed in both terrestrial and marine archives suggesting that activities continued at riwi during this arid event further anthracological analysis of other sites in the kimberley will help to build a regional picture of woody vegetation change and will further disentangle local and regional climatic signals particularly in relation to phases of occupation

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

assessing holocene vegetation and fire history by a multiproxy approach the case of stodthagen forest northern germany the woodland history of the forest of stodthagen northern germany was investigated by using complementary palaeobotanical indicators six soil profiles from the study plot were sampled the wood charcoal pieces extracted from the soil samples were quantified taxonomically identified and some were radiocarbon dated peat sequences from a small adjacent mire were also sampled and the pollen microcharcoal and macrocharcoal were analysed the pollen record shows a continuous forestation during the holocene with small indication of a disturbance phase during the late holocene this continuity of the woodland presence is confirmed by the weak quantity of macrocharcoal indicating that fire did not have a serious impact during the holocene in terms of canopy opening despite the identification of three local fire events however large amounts of wood charcoal pieces were found in the soil samples allowing the identification of at least one more fire event dated in the iron age unrecorded in the charcoa

dominance of an 150 year cycle of sand supply change in late holocene dune building along the eastern shore of lake michigan outcrops of buried soils on lake plains and glacial headlands along lake michigan s eastern shore suggest that periodic dunebuilding has occurred there after relatively long 100 yr periods of low sand supply we located described and radiocarbon dated 75 such buried soils that crop out in 32 coastal dune fields beside the lake we assume that peaks in probability distributions of calibrated 14 c ages obtained from wood charcoal and other organic matter from buried a horizons approximate the time of soil burial by dunes plotted against a late holocene lake level curve for lake michigan these peaks are closely associated with many 150 yr lake highstands previously inferred from beach ridge studies intervening periods of lower lake levels and relative sand starvation apparently permitted forestation and soil development at the sites we studied while late holocene lake level change led to development and preservation of prominent foredunes along the southern and southwestern shores of lake michigan the modern dune landscape of the eastern shore is dominated by perched dunes formed during 150 yr lake highstands over the past 1500 yr 2000 university of washington

anthropogenic influence on rates of aeolian dune activity within the northern european sand belt and socio economic feedbacks over the last 2500 years in north western europe pleistocene sand sheets have been reactivated during phases of holocene deforestation and agricultural land use although there are temporal overlaps between anthropogenic activity and sand sheet reactivation the root cause and subsequent feedbacks between aeolian activity and societal response remain largely unknown here we seek to establish cause and effect by examining the detailed co variation in both timing and magnitude of aeolian and anthropogenic activity through the quantification of holocene dune sediments in combination with archaeological and pollen records these records indicate a series of complex phases of aeolian activity followed by landscape stabilization which we attribute primarily to changing patterns of human impact we find that a steady increase in dune deposition rates in the medieval period corresponds to an increase in settlement activity and deforestation ad 1000 1500 at their peak medieval deposition rates were 3 4 times larger than during th

tracing the origin of natural waters in a glacial till slope during snowmelt abstract a study of the origin of water sampled at a set of sampling points in the discharging area of a sloping forested glacial till was performed during the two snowmelts of 1986 and 1987 analyses of a limited number of chemical components and the 18 o content were performed of the sampled water from the snowmelt of 1986 on the basis of the findings from these analyses a tracer experiment was performed during the snowmelt of 1987 when potassium iodide ki was sprayed on top of the snow cover at two surfaces in the discharging area of the slope the results from both snowmelt studies indicate that macropore channels of old root remains can conduct water rapidly through an unsaturated and frozen matrix without displacing the soil bound water alkalinity and ph values of the sampled water from a macropore were similar to the alkalinity and ph values of sampled snow cores even the deeper ground water from a spring site was affected by the acid surge during the peak snowmelt of 1986 giving proof that macrostructures present in the till were promoting preferential water movement through the soil matrix the surge was also detected with the 18 o technique but was not as pronounced as in the values of the chemical components the iodide tracer experiment during the snowmelt of 1987 also indicated the above mentioned findings despite the large amount of tracer that was retained in the unsaturated soil matrix the otherwise conservative tracer subsequently gave no distinguished breakthrough in the discharging water at the v notch where the runoff from the slope was measured it was therefore not possible to determine the tracer turnover time during this snowmelt however one very important conclusion from this experiment is that iodide should be injected below the humus and the leaching horizons of podsols in order to get good saturated conditions and thereby prevent retention in the matrix

wood charcoal from an inland dune complex at joldelund northern germany information on holocene vegetation and landscape changes abstract the charcoal content of an inland dune complex close to joldelund in northern germany was analysed as part of a project which aims to reconstruct holocene aeolian activity in high spatial and temporal resolution the eleven investigated profiles contained numerous charcoal enriched layers providing evidence for the potential of inland dunes as palaeoarchives for anthracology earlier studies have found late roman iron age settlement activity and iron ore productions in the research area and in its vicinity charcoal assemblages date to roman iron age as well as early high and late medieval times according to radiocarbon dating of single species identified charcoal fragments and the stratigraphic correlation of sedimentary units the dominance of quercus oak and significant proportions of ericaceae charcoal probably calluna vulgaris heather especially in the early and high medieval samples indicate the presence of a heathland with quercus trees which was managed by fire in the younger layers of sand a greater diversity of taxa were found including the dominant quercus fagus beech alnus alder betula birch corylus hazel fraxinus ash salix willow populus salix poplar willow type acer maple pinus pine maloideae apple subfamily tilia lime as well as some ericaceae the diversity of species indicates that some charcoals were transported by wind together with the sand from the surrounding areas and do not represent the local vegetation on the dunes but rather a nonspecific regional input the differences in the charcoal assemblages and thus the possible correlation of aeolian units support the stratigraphic correlation of the sedimentary aeolian units the comparison with the available pollen data from nearby mires showed a good agreement of the proportions of woody taxa with only few exceptions

ancient pine forest on inland dunes in the spanish northern meseta abstract we present a new stratigraphic pollen and nonpollen microfossils and charcoal particle sequence with five ams dates covering about the last 9000 yr of a core collected from the spanish northern meseta one of the territories of the iberian peninsula for which little paleobotanical information is available the results support the hypothesis of the permanence of the pine forests in more or less pure masses or large timber stands during the holocene in some iberian continental zones the typical substitution in postglacial dynamics of heliophyllous species such as pines or cupressaceae by broadleaf trees did not occur in this inland region presumably factors linked to the substrate in this case very deep sand dunes covering vast areas may have contributed to the scarce local competitiveness of the broadleaf trees which would account for the hegemony of pines in this region based on the dynamics of aquatic plants and nonpollen microfossils an initial phase previous to 7500 14c yr b p of high levels in the lake can be identified by high percentages of hydrophytes a progressive increase in helophytes and the gradual infilling of the lake over the last 5000 yr appear to indicate a phase of aridification similar to those established for the western mediterranean study of charcoal particles more abundant in the last 2500 yr has given rise to certain hypotheses regarding the incidence of recurring fires of a local or regional nature

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

epipsammic diatoms as borers an observation on calcareous sand grains abstract sem examination of intertidal calcareous sand grains from the inlet of the tidal lagoon anse de kernic located on the northern coast of brittany indicates that some species of epipsammic diatoms are carbonate borers epipsammic diatoms that remain attached to the sand grains after washing are found in cavities and depressions some of them notably of the genus cocconeis are found in characteristically shaped cavities which are interpreted as made by the diatoms themselves the occurrence of the borings indicates that epipsammic diatoms can play a role in the weathering process of calcareous substrates