magnetic signature of river sediments drained into the southern and eastern part of the south china sea malay peninsula sumatra borneo luzon and taiwan abstract magnetic properties of 22 river samples collected in the malay peninsula sumatra borneo luzon and taiwan have been investigated in order to magnetically characterize the sediments drained and deposited into the south china sea the geological formations as well as the present climatic conditions are different from one region to another laboratory analyses include low field magnetic susceptibility anhysteretic arm and isothermal irm remanent magnetizations acquisition and decay back field acquisition thermal demagnetization of three axes irm hysteresis cycles and low temperature magnetic measurements the magnetic properties indicate that the sediments are a mixture of hematite magnetite and pyrrhotite in different proportions depending on the region combined with results previously reported for the three main asian rivers pearl red and mekong rivers the new data indicate that in general hematite rich sediments are delivered to the southern basin of the south china sea while the northern basin is fed with magnetite and pyrrhotite rich sediments in addition to this general picture some variability is observed at smaller geographic scales indeed the magnetic assemblages are closely related to the geology of the various catchments while clay minerals previously reported for the same samples are more representative of the climatic conditions under which the parent rocks have evolved within each catchment the magnetic fraction now well characterized in the main river sediments drained into the south china sea can be used as a tracer for changes in precipitation on land and in oceanic water mass transport and exchange

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

organic control on shoreface stacking patterns bogged down in the mire in ever wet climates raised mires that are elevated several metres above flood levels can cover significant portions of coastal plains because peat accumulation may keep pace with moderate rates of base level rise the development of raised mires may reduced the areal extent of marine transgressions thick low ash coals are present immediately landward of many vertically stacked shoreface parasequences in cretaceous state of the western interior of north america we suggest that these coals formed in raised mires that stabilized shorelines for long periods of time in such settings the rate of sediment supply including peat accumulation to the coastal environment is partly a function of the rate of change in base level

climate and vegetation changes 180 000 to 345 000 years ago recorded in a deep sea core off portugal a new high resolution combined marine proxy pollen sequence from the portuguese margin md01 2443 enables direct comparison of ocean and ice volume changes with vegetation development in south west iberia during marine isotope stages mis 7 8 and 9 changes in sea surface conditions on both orbital and millennial time scales are closely mirrored by forest extent indicating a coherence of climate variability between the north atlantic and south west iberia deglacial warming at the start of mis 7 and 9 was interrupted by incursions of subpolar water masses at the site accompanied by reversals in tree population expansion during mis 7e and 9e the close relationship in timing and amplitude between vegetation and offshore conditions broke down early forest collapse points to pronounced cooling and aridification on land which although not accompanied by a change in water masses at the portuguese margin appears to have coincided with abrupt decreases in atmospheric methane concentration recorded in antarctic ice cores the most extreme glacial conditions of mis 8 occurred during the early part followed by an interval of warmer conditions and tree population expansion similar to 263 ka this has sometimes been considered as indicating an early deglaciation but the data presented here show that it was distinct from termination iii which occurred later in line with milankovitch forcing a sub orbital oscillation in both isotopic and pollen records is observed at the end of mis 7 ca 184 ka which appears to be coeval with a recently identified sea level high stand c 2006 elsevier b v all rights reserved

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

equatorial carbonates an earth systems approach the hypothesis here is that an earth systems processes to products approach can be used to better develop predictive models for the recognition and assessment of under evaluated equatorial carbonate systems warm temperatures together with common clastic fresh water and nutrient influx as well as basinal settings in the equatorial tropics all have a major impact on carbonate deposition and diagenesis specific features of equatorial carbonate systems resulting from the combination of processes acting in the region include common occurrence of photoautotrophs and heterotrophs aragonitic and or calcitic dominant mineralogies lack of coated grains or aggregates common associations with clastics lack of associations with evaporites and diversity of platform types including oligophotic ones additional diagenetic characteristics include common micritization and bioerosion paucity of marine cements extensive vadose dissolution and concomitant phreatic cementation there is also significant replacement of aragonite by calcite in regions of meteoric groundwater flow common burial compaction and leaching as well as localized massive dolomitization via sea water or continental derived groundwater flow although equatorial carbonates fall into the warm water photozoan association many of the features described above are at odds with models derived from their warm water arid zone counterparts instead a range of the equatorial carbonate features show some similarities with those formed in cool waters and there have been difficulties separating carbonates from these two very different climatic regimes recommendations for the recognition of phanerozoic regional equatorial carbonate development are i a diversity of calcitic and or aragonitic photoautotrophs plus ii common elements of the heterozoan association plus iii independent for example isotopic evidence for warm temperatures 22 c additional indicators towards a humid equatorial setting are iv situation in appropriate palaeolatitudes v lack of association with sedimentary evaporites coated grain or aggregates and vi geochemical evidence for reduced marine salinity and or nutrient upwelling the aim is that this work will lead to greater awareness and understanding of equatorial carbonate systems and contribute to the development of globally predictive models to better understand past and likely future environmental change

the role of tidal velocity asymmetries in the deposition of silty tidal rhythmites carboniferous eastern interior coal basin u s a abstract laminated to thin bedded siltstones directly overlie carboniferous coals at several localities in the eastern interior coal basin because lamina thicknesses show cyclical variations the siltstones have been termed tidal rhythmites the rhythmites commonly show a repetitive thick thin pairing of the laminae and these two lamina rhythmites have been interpreted as the result of the asymmetry of flood and ebb velocities that affected sedimentation in a diurnal paleotidal system alternatively the pairing has been interpreted to be related to a pronounced difference in height between successive high tides in a semidiurnal system this explanation suggests deposition in a mixed predominately semidiurnal system with a marked diurnal inequality in addition to the two lamina rhythmite described originally subsequent examination of drill cores indicates the occurrence of relatively rare more complex three and four lamina rhythmites a variety of mathematical techniques are used herein to analyze lamina thickness data extracted from these rhythmites processing techniques include 1 comparing the linear relationship between the thicknesses of the thinner and thicker laminae and comparing these relationships to modern tidal systems 2 analyses of thickness periodicities and comparison with modern neap spring tidal cycles and 3 extraction of lamina thickness inequalities and comparison to the diurnal inequalities that occur in semidiurnal tidal systems these tests indicate that reasonable conclusions can be made for the type of originating paleotidal system for the cases analyzed herein the paleotidal signature suggests a mixed predominantly semidiurnal system with a marked diurnal inequality

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

development and carbon sequestration of tropical peat domes in south east asia links to post glacial sea level changes and holocene climate variability abstract tropical peatlands of se asia represent a significant terrestrial carbon reservoir of an estimated 65 gt c in this paper we present a comprehensive data synthesis of radiocarbon dated peat profiles and 31 basal dates of ombrogenous peat domes from the lowlands of peninsular malaysia sumatra and borneo and integrate our peatland data with records of past sea level and climate change in the region based on their developmental features three peat dome regions were distinguished inland central kalimantan borneo kutai basin borneo and coastal areas across the entire region with the onset of the holocene the first peat domes developed in central kalimantan as a response to rapid post glacial sea level rise over the sunda shelf and intensification of the asian monsoon peat accumulation rates in central kalimantan strongly declined after 8500 cal bp in close relation to the lowering rate of the sea level rise and possibly influenced by the regional impact of the 8 2 ka event peat growth in central kalimantan apparently ceased during the late holocene in association with amplified el nino activity as exemplified by several truncated peat profiles peat domes from the kutai basin are all younger than 8300 cal bp peat formation and rates of peat accumulation were driven by accretion rates of the mahakam river and seemingly independent of climate most coastal peat domes the largest expanse of se asian peatlands initiated between 7000 and 4000 cal bp as a consequence of a holocene maximum in regional rainfall and the stabilisation and subsequent regression of the sea level these boundary conditions induced the highest rates of peat accumulation of coastal peat domes the late holocene sea level regression led to extensive new land availability that allowed for continued coastal peat dome formation until the present the time weighted mean holocene peat accumulation rate is 0 54 mm yr 1 for central kalimantan 1 89 mm yr 1 for kutai and 1 77 mm yr 1 for coastal domes of sumatra and borneo the mean holocene carbon sequestration rates amount to 31 3 g c m 2 yr 1 for central kalimantan and 77 0 g c m 2 yr 1 for coastal sites which makes coastal peat domes of south east asia the spatially most efficient terrestrial ecosystem in terms of long term carbon sequestration

peat accumulating depositional systems of sarawak east malaysia many coal deposits originate in deltaic estuarine and coastal plain settings and a knowledge of interrelationships between the tectonic and depositional elements active at the time of sediment deposition is necessary to formulate basin scale models the prograding coastal depositional systems of sarawak all contain domed peat accumulating environments in which low ash low sulfur peats are being deposited in areas of active clastic siliciclastic sedimentation these depositional systems are as large as 11 400 km2 and individual peat deposits within systems are in excess of 20 m thick and 1000 km2 in area the geographic positions and drainage basin areas of each depositional system are controlled by fault and fold systems although prograding into the same receiving basin individual system geomorphology is variable and ranges from a wave dominated microtidal delta to a wave dominated meso to macro tidal delta coastal plain system to a tide dominated macrotidal estuarine embayment along a 450 km stretch of coastline system variation is a function of sediment supply shelf and embayment geometry wave climate and tidal range these factors which control depositional system geomorphology also control the resulting long axis orientation of the thick domed peat deposits the surface vegetation and internal characteristics of most domed peat deposits however are similar internal characteristics consist of basal high ash high sulfur degraded peats overlain by low ash low sulfur well preserved peats in vertical profile these systems demonstrate variable responses to late pleistocene holocene sea level rise and in these instances the variation is most attributable to local differences in siliciclastic sediment supply which is a function of the drainage basin area

spatial variability in modern tropical peat deposits from sarawak malaysia and sumatra indonesia analogues for coal petrographic and chemical variability in two tropical low ash domed peat deposits of similar age and physiographic setting but different external morphology were examined as modern analogues for coal both occur in microtidal alluvial to deltaic plain settings support similar arborescent vegetation and have accumulated in the past 5 000 years one deposit is an extremely convex mature done with a surface that rises 10 m above river level the other is a low gradient dome rising only 3 m above river level but with a concave base up to 6 m below both deposits have been eroded by adjacent rivers yet peat in the mature dome has accumulated remote from persistent flooding and exhibits distinctive internal stratigraphy decomposed sapric peat floors the deposits and is overlain by increasingly better preserved woody hemic and a cap of coarse fibrous peat derived from less arborescent vegetation consistent flooding in the low gradient dome has maintained conditions for the accumulation of predominantly woody hemic peat which interfingers with and is overlain by oxidised sapric peat and levee derived clastic sediments peat types in both deposits exhibit distinctive polymodal textures and organo chemical signatures that correspond to botanical input and degree of decay due to the abundance of pre huminite vitrinite macerals in all peat types from these deposits megascopic and microscopic texture is a better discriminator for comparison to ancient coal types it is suggested that the upward vertical sequence of decreasing woodiness and increasing lightness in colour observed in the mature dome might best be compared to sequences observed in tertiary brown coals this typical sequence can be modified or overprinted due to flooding in the burial process

palaeoclimate chronology and vegetation history of the weichselian lateglacial comparative analysis of data from three cores at lago grande di monticchio southern italy abstract palynological and chronological data are presented for the lateglacial from three cores taken at different locations in the basin of lago grande di monticchio plant macrofossil data from one core provide complementary evidence of the palaeovegetation quantitative palaeoclimate reconstructions are made from the pollen data using pollen climate response surfaces the chronological framework for late glacial events as well as the palaeoclimate are compared with other sources of evidence of lateglacial palaeoenvironments surface conditions in the north atlantic appear to be more directly linked to climatic conditions in italy than is the temperature in greenland nonetheless the palynological record exhibits high frequency variability that reflects high frequency climatic changes paralleling those seen in the ice core records from greenland

neotropical vegetation response to rapid climate changes during the last glacial period palynological evidence from the cariaco basin we present new palynological information from the anoxic cariaco basin off venezuela that provides insight into the response of northernmost south american vegetation to rapid climate changes between 68 and 28 ka specifically during north atlantic heinrich events hes and dansgaard oeschger cycles we defined three different vegetation modes 1 an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi deciduous and evergreen forests 2 a stadial mode characterized by increases of salt marshes herbs and montane forests and 3 a heinrich event mode characterized by the lowest pollen concentrations abrupt increases of salt marshes and decreased forest abundance similarly indices of c4 c3 plants show increases during stadials with clear peaks during the onset of hes though grasslands did not become dominant during these periods we alternatively propose that these expansions of c4 plants are associated with the expansion of coastal salt marshes our vegetation record suggests the prevalence of humid conditions during interstadials dry and cold conditions during stadials and dry and cold conditions together with changes in sea level during hes this new palynological evidence supports previous interpretations that main environmental changes in northernmost south america were driven by latitudinal displacements of the intertropical convergence zone and sea level changes

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

provenance and sediment dispersal in the rajang river delta coastal plain system sarawak east malaysia preliminary sedimentologic investigations were conducted in the rajang river delta coastal plain system in sarawak east malaysia to determine the processes and timing of siliciclastic transport and sedimentation in tropical peat dominated systems methods involved depth profiling and collection and analysis of bottom and suspended sediment load samples from channels and offshore areas and coring and trenching of subaerial channel shoreline and backswamp features the rajang delta occurs in an embayment formed by the folded mesozoic and cenozoic sediments of the central borneo massif it covers an area of 11 000 km2 and is physiographically separated into an alluvial valley floodplain an abandoned tidally flushed delta plain and an actively accreting rectilinear delta coastal plain from 50 to 80 of the surface area is covered by peat 1 to 20 m thick during the dry season of july august 1992 river channels varying from 2 to 45 m deep with discharge rates from 100 to approximately 3550 m3 s were carrying suspended sediment loads ranging from 0 to 2281 mg l at present approximately 8 2 x 10 10 kg yr of fine grained sediment is supplied to the system and areal accretion rates are over 1 0 km2 yr the structural configuration of the uplands receiving basin and subsequent drainage patterns and tidal influence results in a contradictory distribution of mature fine grained sediments in the channels of the active delta coastal plain and immature coarse grained angular sands and gravels in the channels of the abandoned delta lobe the contemporaneity of the peat and clastic accumulation is evidenced by the margins of the thick domed low ash peat deposits interfingering with and being overlain by root penetrated siliciclastic sediments much of the fine grained sediment however bypasses the delta plain due to in channel density gradients delta coastal plain accretion occurs by distributary mouth bar buildup sand bar welding and ridge and runnel accretion all subaerially exposed surfaces are quickly vegetated the aberrant depth and configuration of some channels suggest that drainage is in part controlled by contemporaneous faulting

the geology botany and chemistry of selected peat forming environments from temperate and tropical latitudes abstract peat has been studied in several geologic settings 1 glaciated terrain in cold temperate maine and minnesota u s a 2 an island in the atlantic ocean off the coast of maine where sea level is rising 3 the warm temperate u s atlantic and gulf coastal plains where sea level has changed often and 4 the tropical coast of sarawak malaysia and the tropical delta of the batang hari river sumatra indonesia most of these deposits are domed ombrotrophic or partly ombrotrophic bogs in which peat accumulation continued above the surface of the surrounding soil however the bogs of the u s atlantic and gulf coastal plains are comparatively not as domed and many have almost level surfaces in some bogs aquatic or semi aquatic plant materials accumulated replaced water in the depressions and formed a surface on which marsh or swamp vegetation could subsequently live die and accumulate in others the plant materials accumulated initially on level silt or sand surfaces supporting marshes or swamps as the peat dome formed plants growing on it changed from luxuriant ones near the base of the dome where nutrients were brought into the bog by surface and ground water to stunted ones at the top of the dome where the raised bogs are fed by nutrient poor precipitation the physical and chemical changes that take place in the sequence of environments from the pond stage of deposit development through the grassy marsh stage through the forested swamp stage and finally through the heath dome stage can be measured in terms of acidity and ash volatile matter carbon hydrogen nitrogen sulfur and oxygen contents as well as in the kind and distribution of trace elements the organic and inorganic contents of the deposits relate to geomorphology and geomorphology relates to their settings as models of coal formation some domed peat deposits may help in solving problems of distribution and character of ancient coal beds but clearly not all peat deposits are precursors of coal most holocene peat deposits are subject to destruction by erosion fire and decomposition through microbial and chemical oxidation before burial the best environments for coal precursors have biomass accumulation a continuously rising water table within the mass and minimum influx of clay and silt until preservation by burial the most suitable settings for future economic coal deposits are domed bogs that accumulate thick widespread peat having low ash and low sulfur contents the ombrotrophic peat deposits of tropical sarawak and sumatra are thick and extensive contain low ash and low sulfur peat and have high heating values they are considered to be the best tropical coal analogs because of their extent and chances of preservation the base of the peat is below adjacent river levels and chemical and structural conditions are favorable for accumulation

persistence of late carboniferous tropical vegetation during glacially driven climatic and sea level fluctuations abstract the late carboniferous glaciation reached its peak during the latter part of the westphalian late desmoinesian in the tropical illinois basin this was the time of deposition of the carbondale and lower modesto formations characterized by the cyclic repetition of major coal deposits black shales limestones gray shales and sandstones these lithological changes evidence repeated major fluctuations in climate and sealevel fossil floras from the tropical ever wet to seasonally wet terrestrial lithofacies coals and shales above coals remain compositionally similar throughout the 1 1 5 m y time interval floras from coals known from coal balls and palynology characteristically were composed of three major plant communities the wettest sites were dominated by monocarpic lycopsids intermediate sites were dominated by polycarpic lycopsids and areas subject to fires and intermittent flooding were dominated by medullosans and the small lycopsid paralycopodites clastic substrate environments were dominated by ferns and pteridosperms and conform to a single biozone indicating their compositional unity and distinctness from earlier and later assemblages the composition of lowland floras is poorly known from times between the deposition of coals and associated terrestrial rocks intervals during which most of the lowlands were flooded and marine rocks were being deposited consequently the temporally intermittent recurrence of lowland floras despite repeated widespread environmental disruption may be explained either by vegetational persistence and migration of floras or repeated disruption and reassembly several lines of evidence suggest persistence as a likely explanation

late quaternary vegetational and climate dynamics in northeastern brazil inferences from marine core geob 3104 1 abstract late quaternary paleoenvironments from northeastern ne brazil have been studied by pollen analysis of marine sediment the studied core geob 3104 1 3 40 s 37 43 w 767 m b s l from the upper continental slope off ne brazil is 517 cm long and 42 000 14 c yr bp old chronological control was obtained by 12 radiocarbon ams dates from individuals of the foraminiferal species globigerinoides sacculifer modern pollen analogs were received from 15 river lake and forest soil surface samples from ne brazil marine pollen dates indicate the predominance of semi arid caatinga vegetation in ne brazil during the recorded period between 42 000 and 8500 14 c yr bp the increased fluvial input of terrigenous material with high concentrations of pollen and specially fern spores into the marine deposits about 40 000 33 000 and 24 000 14 c yr bp and between 15 500 and 11 800 14 c yr bp indicate short term periods of strong rainfall on the ne brazilian continent the expansion of mountain floodplain and gallery forests characterize the interval between 15 500 and 11 800 14 c yr bp as the wettest recorded period in ne brazil which allowed floristic exchanges between atlantic rain forest and amazonian rain forest and vice versa the paleodata from core geob 3104 1 confirm the in general dry pre last glacial maximum lgm and lgm conditions and the change to wet lateglacial environments in tropical south america the annual movement of the intertropical convergence zone over ne brazil the strong influence of the antarctic cold fronts and changes of the high pressure cell over the southern atlantic may explain the very wet lateglacial period in ne brazil the documented ne brazilian short term signals correlate with the documented dansgaard oeschger cycles and heinrich events from the northern hemisphere and suggest strong teleconnections

peat or no peat why do the rajang and mahakam deltas differ abstract coastal and deltaic holocene peat accumulations around the equatorial island of borneo southeast asia have served as models for economic coal bearing sequences in the stratigraphic record although climatic conditions vegetational communities and sedimentary regimes are comparable peat accumulations are not found on both the western and eastern sides of the island the rajang river delta and coastal plain sarawak east malaysia are covered in areally extensive thick peat deposits that have attained at least a thickness of 13 m in ombrogenous peat domes marudi baram river peat swamp biomass began to accumulate over pleistocene podzols when sea level stabilized 7 5 ka and delta progradation was initiated the mahakam river delta and coastal plain east kalimantan indonesia also began progradation at this time but there is no evidence in any part of the coastal region for peat accumulation rather poorly developed organic rich gleysols occur throughout the delta plain both the rajang river and mahakam river deltas are tidally influenced fine grained systems with a sediment provenance in the central massif sediment transported through the rajang river delta differs in that as much as 60 of the clay minerals deposited in the system are mixed layer i s and expandable k e clays that act to restrict pore water flow in the tidal and overbank deposits that comprise the delta plain these result in the development of an aquiclude above which paludal conditions develop promoting accumulation of organic matter in contrast there is a low proportion of mixed layer and expandable clays transported in the mahakam river system this precludes the development of a stilted water table within the delta allowing for organic matter recycling without peat accumulation the presence of a high proportion of expandable clay minerals on the western side of borneo is a reflection of the weathering and eroding source rocks on this side of the central borneo massif

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

some observations regarding the potential effects of doming of tropical peat deposits on the composition of coal beds abstract several important concepts relative to the origin of coal beds can be gleaned from studies of modern domed and planar peat deposits in tropical subtropical settings these are 1 laterally some portions of a single continuous peat deposit may be domed and some portions may be planar 2 domed deposits are most often found to have begun as planar deposits 3 domed formed peat facies may be overridden by planar formed peat facies due to such factors as sea level rise and or increased rate of local and basinal subsidence 4 domed peat facies tend to have less mineral matter and contain fewer inorganic splits than planar facies 5 sulfur intrusion from marine waters can be retarded by doming allowing low sulfur peats to form relatively near to the coastline 6 marine transgression can cause high sulfur marine influenced planar peat facies to override freshwater domed or planar facies resulting in enrichment of the upper parts of these underlying facies in sulfur and ash 7 dome formed peat facies tend to be thicker and more uniform in composition than planar formed facies with dome formed peat facies having the potential to produce the more uniform bright coal types clarains and vitrains and planar formed peat facies often producing duller coal types and or alternating durainic inertinite rich and vitrainic wood derived bands 8 actively developing peat domes in wet settings often exhibit no appreciable increase in inertinitic material toward their tops although the tops of either domed or planar peat deposits can be enriched in inertinitic material if the water table is lowered by either local or regional changes in hydrology or climate

the changuinola peat deposit of northwestern panama a tropical back barrier peat coal forming environment abstract a large 82 km 2 thick 8 m low ash low sulfur peat deposit has formed on the northwestern coast of panama its low ash and low sulfur contents can be attributed partly to 1 doming 2 the occurrence of a relatively continuous marine blocking beach barrier shoreline feature and 3 leaching of the mineral matter this deposit is roughly rectangular in shape and oriented with its longest axis parallel to the beach barrier shoreline it would produce an economic coal bed that is bright and finely banded in its thickest central region and more coarsely banded at its margins its northwestern margin would be characterized by interfingering of coal with sandstone and siltstone of the changuinola river flood plain whereas its southeastern boundary would be characterized by truncation of the upper part of the seam by marine to brackish shales siltstones and carbonates that were derived from almirante bay total sulfur was found to be very low less than 0 2 dry wt except in a few places in these rare cases nearly all of the sulfur was pyritic and the total sulfur content was anomalously high 14 although the general tendency was for total sulfur to increase wherever the deposit was influenced by marine conditions one case was found where sulfur was high at the base of an inland freshwater peat core which suggests either a hidden marine influence or the need for some new mechanism to explain sulfur enrichment in such an anomalous case differences in inherent fixed carbon contents and calorific values due to changes in peat type and analytical uncertainties tended to mask seamwide trends in these parameters however fixed carbon contents and calorific values showed a slight tendency to increase with depth especially if plotted for single peat types vitrinite reflectance within the hypothetical changuinola coal bed would be expected to increase as follows 1 toward the margins of the deposit 2 toward the bottom and top of the bed and 3 toward stream channels or tidal inlets

holocene evolution of the western orinoco delta venezuela the pristine nature of the orinoco delta of eastern venezuela provides unique opportunities to study the geologic processes and environments of a major tropical delta remote sensing images shallow cores and radiocarbon dating of organic remains form the basis for describing deltaic environments and interpreting the holocene history of the delta the orinoco delta can be subdivided into two major sectors the southeast sector is dominated by the rio grande the principal distributary and complex networks of anastomosing fluvial and tidal channels the abundance of siliciclastic deposits suggests that fluvial processes such as overbank flooding strongly influence this part of the delta in contrast the northwest sector is represented by few major distributaries and overbank sedimentation is less widespread relative to the southeast sector peat is abundant and occurs in herbaceous and forested swamps that are individually up to 200 km 2 in area northwest directed littoral currents transport large volumes of suspended sediment and produce prominent mudcapes along the northwest coast mapping of surface sediments vegetation and major landforms identified four principal geomorphic systems within the western delta plain 1 distributary channels 2 interdistributary flood basins 3 fluvial marine transitional environments and 4 marine influenced coastal environments coring and radiocarbon dating of deltaic deposits show that the northern delta shoreline has prograded 20 30 km during the late holocene sea level highstand progradation has been accomplished by a combination of distributary avulsion and mudcape progradation this style of deltaic progradation differs markedly from other deltas such as the mississippi where distributary avulsion leads to coastal land loss rather than shoreline progradation the key difference is that the orinoco delta coastal zone receives prodigious amounts of sediment from northwest moving littoral currents that transport sediment from as far away as the amazon system 1600 km late holocene progradation of the delta has decreased delta plain gradients increased water levels and minimized overbank flooding and siliciclastic sedimentation in the northwest sector these conditions coupled with large amounts of direct precipitation have led to widespread peat accumulation in interdistributary basins because peat forming environments cover up to 5000 km 2 of the delta plain the orinoco may be an excellent analogue for interpreting ancient deltaic peat deposits

8000 years of vegetation dynamics and environmental changes of a unique inland peat ecosystem of the jambi province in central sumatra indonesia abstract despite their importance as global carbon sinks peatlands of southeast asia have been rarely studied and our current knowledge of the dynamics and ecology of these ecosystems remains incomplete paleoecological and palynological multi proxy analyses including analysis of pollen spores charcoal testate amoebae and sediments were carried out on a 733 cm long core taken from the air hitam peatland in the jambi province central sumatra indonesia the radiocarbon chronology reveals that peat formation started ca 7800 years ago the site was covered by dipterocarp swamp mixed rainforest during the first 2000 years after which freshwater swamp taxa became more important in particular durio trees this lasted until ca 4500 years ago when the swamp vegetation shifted to a pole forest with abundant pandanus thickets in response to a system change from minerotrophic to ombrotrophic conditions for this period macro charcoal analysis reveals that fire frequency increased possibly as a consequence of climate change linked to the onset of the modern el nino southern oscillation enso in the late holocene the ombrogenous pandanus pole forest phases were characterized by lower water table fluctuations and higher peat accumulation rates the area of air hitam has been for thousands of years a highly effective carbon sequestering peatland natural climate variability in the past did not affect the carbon storage function as suggested by the general increase in peat accumulation during relatively drier phases and increasing enso variability in the late holocene however the recent changes caused by selective logging drainage and conversion to oil palm plantations have caused a decline in the peat swamp forest communities changing the ecological functions of the peatland it is likely that the accumulated carbon will be released in the atmosphere due to exposure to aerobic conditions and its function will be lost unless a better management of the watershed is applied

a new estimate of the holocene lowstand level of lake titicaca central andes and implications for tropical palaeohydrology new evidence from piston cores and high resolution seismic reflection data shows that water levels in lake titicaca were as much as 100 m below the present level during the early to mid holocene between 6 and 3 8 14c kyr bp climatological and modelling studies indicate that lake titicaca rainfall depends on convective activity in upwind amazonia the lake level data therefore suggest a drier amazon basin during this time this view is bolstered by an excellent match between the titicaca lake level curve and decreased methane concentrations in greenland ice previously ascribed to drying of low latitude wetlands blunier et al 1995 the postglacial history of lake titicaca fits a global pattern of lake level change in the tropics characterized by opposite phasing between the southern and northern hemispheres this pattern is most likely the result of orbital controls over the intensity of summer insolation

a mechanism to explain the preservation of leaf litter lenses in coals derived from raised mires abstract leaves and other non woody canopy parts are rarely preserved in coals although the ph of pore waters within peat swamps is usually relatively low 3 5 providing geochemical conditions that would promote preservation after burial shed canopy parts may remain at the air soil interface for periods of up to several months prior to burial by additional organic detritus leaf half life in tropical forests has been reported to range from several weeks to months depending upon species histology during this time of exposure on the forest floor catabolic internal enzymatic fungal bacterial and root degradation as well as saprophagous scavenging act upon the least resistant parts to promote decay into hemic and sapric macerals it is unusual then to find well preserved leaves in peats or coals when such accumulations are encountered either permineralized in coal balls or duripartically preserved in lignites the bedded leaves generally are spatially isolated several explanations have been proposed to account for such fossil lagerstatten that require temporal changes in accumulation or degradation rates neither of these mechanisms is required to account for such accumulations bedded leaves showing minimal evidence of subaerial exposure and degradation have been recovered at depth from a vibracore taken 1 km into the interior of a peat swamp in the rajang river delta sarawak east malaysia evidence is provided to indicate that such accumulations form within peat substrate depressions resulting from the displacement of rootstocks as trees either die and fall over or are blown down in severe storms these localized acidic water filled pools act as a natural buffer to the degradation of fallen canopy parts that accumulate therein

effects of the crustal stress on the growth of dikes conditions of intrusion and extrusion of magma dike growth is analyzed on the basis of the fluid dynamical behavior of incompressible newtonian magma in a spatially uniform fissure of temporally variable width the length and width of the dike vary with the magma pressure at the dike entrance connected to the magma chamber and with the mean stress working normal to the dike walls the mean stress consists of the regional crustal stress and the mean elastic stress which is approximately evaluated using an analytic solution of the crack with a constant aperture the length and width of the dike are determined as a function of time by simple ordinary differential equations the dike can grow when the initial pressure of the entering magma is above the lithostatic pressure and high enough to suppress compression of the crustal stress the assumed size of the initial crack affects the growth only in the duration needed for an initial adjustment stage after this stage the width and length first grow exponentially and then the growth slows as magma is released from the chamber the growth in the later stage is classified into two types when the initial magma pressure is high enough the dike elongates unlimitedly while the width finally decreases this extrusive growth is likely to lead to eruptions the other intrusive growth in which the dike finally stops its growth with a finite length and width occurs when the crustal stress component normal to the fissure is of sufficiently strong extension buoyancy of magma is not very effective in the earlier growth stage but it shifts the marginal condition separating the extrusive and intrusive growths the extrusive and intrusive events that recently happened in izu oshima volcano and izu tobu volcano group japan are interpreted as the examples of these two growth types

coal quality controls of the danville coal in indiana illinois basin central usa abstract the danville coal member dugger formation upper desmoinesian pennsylvanian is a significant economic coal resource in the illinois basin central usa deposition of the danville coal peat was in coastal environments varying distances from the coastline and in turn variable influences from saline waters the purpose of this study is to examine the coal quality and petrography of the danville coal and to discuss their relationship with depositional environment as it relates to the final coal product a medium sulfur 1 0 1 5 wt danville coal reserve area northern indiana coalfield was compared to a low sulfur 3 m of finer grained clastic sediments atop the danville the sulfur and trace elements contents are significantly lower

rapid climate change from north andean lake fuquene pollen records driven by obliquity implications for a basin wide biostratigraphic zonation for the last 284 ka this paper compares a new super high resolution pollen record from a central location in lake fuquene 4 n with 3 pollen records from marginal sites from the same lake basin located at 2540 m elevation in the eastern cordillera of colombia we harmonized the pollen sum of all records and provided previously published records of climate change with an improved age model using a new approach for long continental pollen records we dissociated from subjective curve matching and applied a more objective procedure including radiocarbon ages cyclostratigraphy and orbital tuning using the new 284 ka long fuquene basin composite record fq bc as the backbone groot et al 2011 we showed that a common 9 m cycle in the arboreal pollen percentage ap records reflects obliquity forcing and drives vegetational and climatic change the ap records were tuned to the 41 kyr component filtered from standard benthic 18o lr04 record changes in sediment supply to the lake are reflected in concert by the four records making frequency analysis in the depth domain an adequate method to compare records from the same basin we calibrated the original 14c ages and used where necessary biostratigraphic correlation i e for records shorter than one obliquity cycle pollen records from the periphery of the lake showed changes in the abundance of alnus and weinmannia forests more clearly while centrally located record fq 9c shows a more integrated signal of regional vegetation change the revised age models show that core fq 2 reflects the last 44 ka and composite record fq 7c the last 85 5 ka marginally located core fq 3 has an age of 133 ka at 32 m core depth and the lowermost 11 m of sediments appear of older but unknown age the longest record fq bc shows 60 yr resolution over the period of 284 27 ka all pollen records are in support of a common regional vegetation development leading to a robust reconstruction of long series of submillennial climate oscillations reflecting dansgaard oeschger do cycles reconstructed climate variability in the tropical andes since marine isotope stage mis 8 compares well with ngrip 18o based epica dome c d based and the mediterranean sea surface temperature record md01 2443 44 uk 37 based underpinning the global significance of the climate record from this tropical andean lake a basin wide biostratigraphy is presented and we concluded although with varying robustness that each core is representative of regional vegetational and climatic change

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

late pleistocene and holocene development of the interior peat accumulating basin of tropical tasek bera peninsular malaysia the stratigraphy of holocene peat deposits from an interior lowland basin of tropical peninsular malaysia provides insight into the hydrological ecological and climatic controls on tropical peatland development interpretations about vegetation and climate dynamics including storm intensity over the past 5000 years are integrated with regional and global climatic and eustatic changes to serve as a proxy for past ecology and climate tasek bera basin tbb is a lowland dendritic basin in tropical peninsular malaysia accumulation of organic matter occurred in local lakes during the last glacial maximum lgm but widespread peat deposition did not start until 5300 bp when climatic changes led to the evolution of a wetland system peat accumulation progressively expanded with terrestrialisation of channels and subbasins to paludification of the riparian part of the lowland forest zone lithofacies can be distinguished despite the highly diverse peat and organic rich sediment composition as a result of the climatic and hydrologic changes over the past 5300 years peat accumulation rates ranging from 0 7 to 2 5 mm year are highest in pandanaceae environments and lowest in high ash swamp forests and environments dominated by cyperaceae transects of peat cores across the mire system show the stratigraphic complexities of the peat is the result of hydrological variations and thus plant successional changes ash yield shows that periods of high mineral matter input into the drainage system occurred since the mid holocene indicating rapid and cyclic changes in frequency and magnitude of runoff events and by inference storms stratigraphic analysis of peat and ash yield are tools that provide a proxy for development of holocene hydrologic events in topogenous peat deposits

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics

sediment trapping in deltas of small mountainous rivers of southwestern taiwan and its influence on east china sea sedimentation abstract taiwan s setting of high mountains steep gradients frequent earthquakes erodible lithology and heavy rainfall represents an ideal site to focus on sedimentary processes of the deltas of small mountainous rivers smrs several smrs in southwestern taiwan have deposited a thick sedimentary succession in the composite southwest taiwan delta swtd since the middle holocene evidence from the swtd can help to determine its trapping efficiency and assess the role of smrs in sediment transport to the sea we used historical nautical charts bathymetric data satellite radar data and 14c dates to calculate the sediment volume of the swtd on millennial and decadal scales the 14c dates of core samples indicate deposition of thick deltaic sediment in subsiding areas since the time of the maximum flooding surface about 7 cal ka bp the paleo shoreline changes of the swtd suggest a steady westward progradation since 7 cal ka bp in contrast the nautical charts suggest minor volume reduction of the offshore part of the swtd with a deepening trend and retreating shorelines during the last seven decades the results show that at least 201 72 13 90 km3 3 23 105 mt of sediment has been trapped in the swtd since 7 cal ka bp and that the delta has shifted to a destructive phase during the past seven decades as human influences such as construction of reservoirs dams and weirs in the hills have reduced the sediment supply the birth of the taiwan warm current and following continuous sediment supply from the western rivers of taiwan to the east china sea since 7 3 cal ka bp have played a crucial role in the sedimentation of the east china sea particularly in the okinawa trough and the japan sea through the tsushima warm current