palynofacies and stable c and n isotopes of holocene sediments from lake macuco linhares espirito santo southeastern brazil depositional settings and palaeoenvironmental evolution particulate organic matter in sediments constitutes a valuable proxy for paleoenvironmental reconstructions a 192 cm lacustrine sediment core 7521 cal yr b p from the northern coast of the state of espirito santo southeastern brazil was radiocarbon dated and then analyzed for palynofacies stable isotopes c and n and grain size the values for total organic carbon toc 1 91 to 20 89 total nitrogen tn 0 08 to 1 1 13c 27 10 to 29 01 15n 1 92 to 5 09 and c n 12 87 to 50 11 suggest predominance of c3 plants and changing mixtures of terrestrial and aquatic organic matter in the sediments palynofacies and cluster analyses were used to identify four palynofacies associations that reflect different phases in the lake macuco evolution palynofacies 1 192 to 106 cm 7521 cal yr b p to 7054 cal yr b p interpolated age is characterized mainly by amorphous organic matter aom non opaque phytoclasts nops mangrove pollen grains rhizophora sp l 1753 and avicennia sp l 1753 and foraminiferal test linings palynofacies 2 106 to 65 cm 7054 cal yr b p interpolated age to 4847 cal yr b p is dominated by nops and aom with an increase in the values of mangrove pollen grains relative to palynofacies 1 both palynofacies reflect marine and fluvial influences in a depositional environment related to the development of an estuarine system during the mid holocene transgressive stage palynofacies 3 65 to 27 cm 4847 cal yr b p to 3800 cal yr b p interpolated age comprises high abundances of fluvial elements nop and opaque phytoclasts op and low values of aom the depositional environment is interpreted as being an estuary during the marine regression with the displacement of the estuarine basin and mangroves towards the sea palynofacies 4 27 to 0 cm 3800 cal yr b p is characterized by the predominance of aom and nop increase in the values of freshwater algae and no evidence of marine influence this last phase reflects the beginning of the establishment of lake macuco and floodplain of the barra seca river under conditions similar to the present day

a nearly complete skeleton of a new troodontid dinosaur from the early cretaceous of the ordos basin inner mongolia people s republic of china an articulated skeleton of a 1 m long theropod from early cretaceous strata in inner mongolia is clearly referrable to the troodontidae representing the most complete specimen known of this group of small carnivorous dinosaurs the tail and neck of the animal were curled next to its body upon burial the upper surface of the skeleton was badly damaged by erosion previously unknown details of troodont morphology include a quadratic contact with the braincase wall forming part of a channel leading to the lateral depression a presacral vertebral count possibly similar to that of most theropods absence of ossified caudal tendons presence of a rod like clavicle and absence of sternal ossifications a new genus and species sinornithoides youngi n gen n sp is established for the specimen on the basis of its short skull laterally directed orbital rim of the frontal and elongated hind limb a reassessment of character distributions in other small theropods and primitive birds must be completed befor

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

late pliocene quaternary evolution of redox conditions in the western qaidam paleolake ne tibetan plateau deduced from mn geochemistry in the drilling core sg 1 abstract manganese mn in lake sediments reacts strongly to changes of redox conditions this study analyzed mn concentrations in oxides carbonates and bulk phases of the calcareous lacustrine sediments of a 938 5 m long core sg 1 taken from the western qaidam basin well dated from 2 77 ma to 0 1 ma comparisons of extractions from diluted hydrochloric acid acetic acid and citrate bicarbonate dithionite demonstrate that variations of mn concentrations from acetic acid leaching mnhoac are mostly responsible for mn ii fluctuations in the carbonate phase taking into account the relevant processes during weathering transportation deposition and post deposition of mn bearing rocks we conclude that mn input from catchment weathering and paleolake redox condition provide the primary controls on variations in the mn records of carbonate and oxide phases we propose mnhoac as a new sensitive indicator of paleolake redox evolution and catchment scale climate change the mnhoac variations show a long term upward decreasing trend indicating a long term decrease of mn input from catchment weathering associated with increasing oxygen content in the paleolake bottom water the great similarities of the mnhoac record with other regional and global records suggest that paleolake redox changes and climatic drying in the qaidam basin may be largely related to global cooling

middle to late holocene environmental changes in the depositional system of the tropical brackish bolgoda lake coastal southwest sri lanka abstract the tropical bolgoda lake is one of the largest lagoonal estuaries in sri lanka organic constituents in this lake were investigated using 28 surface sediments three cores from the lake and four short cores from mangrove mud elemental and molecular compositions of sediments and living organic matter om were determined using cns elemental analysis and gas chromatography mass spectrometry respectively chronology of events was determined using accelerated mass spectrometry ams 14 c data for bulk oms woods and mollusk shells the history of bolgoda lake can be divided into two major chrono stratigraphic divisions namely a lower sedimentary succession from ca 7 0 cal ky b p to 2 5 cal ky b p and an upper sedimentary succession from ca 2 5 cal ky b p to the recent according to the sapropelic depositional system concentrations of the mangrove biomarker taraxone increased significantly at ca 7 0 cal ky b p the lower part of the sediment sequence had moderate productivity and was mainly deposited under marine terrestrial influence in oxygen poor anoxic conditions during mid holocene sea level highstands a drastic increase in total organic carbon toc content reaching 29 was found in one of the bolgoda cores this increase occurred because of sea level regression at about 2 5 cal ky b p this change was probably caused by development of a beach rock sandbar and the estuary system changed to a semi closed lake due to the sea level regression as a result aquatic vascular plants predominate in this depositional system after ca 2 5 cal ky b p toc content decreased slightly but relatively high toc contents were maintained in the muddy sediments in moderately sized and shallow 1 2 m tropical estuaries lagoons such as bolgoda lake drastic changes in toc contents may be the most sensitive indicator of sea level variations increase in higher plant om with higher n c 29 n c all and n c 37 n c all alkane ratios also suggest a climatic transition from wetter to somewhat drier after the middle holocene accumulations of pyrogenic polycyclic aromatic hydrocarbons pahs in the modern sediments record anthropogenic activity after european settlement in the 15th century

tropical rain forest and climate dynamics of the atlantic lowland southern brazil during the late quaternary palynological analysis of a core from the atlantic rain forest region in brazil provides unprecedented insight into late quaternary vegetational and climate dynamics within this southern tropical lowland the 576 cm long sediment core is from a former beach ridge valley located 3 km inland from the atlantic ocean radio carbon dates suggest that sediment deposition began prior to 35 000 14c yr b p between ca 37 500 and ca 27 500 14c yr b p and during the last glacial maximum lgm ca 27 500 to ca 14 500 14c yr b p the coastal rain forest was replaced by grassland and patches of cold adapted forest tropical trees such as alchornea moraceae urticaceae and arecaceae were almost completely absent during the lgm furthermore their distributions were shifted at least 750 km further north suggesting a cooling between 3 c and 7 c and a strengthening of antarctic cold fronts during full glacial times a depauperate tropical rain forest developed as part of a successional sequence after ca 12 300 14c yr b p there is no evidence that araucaria trees occurred in the atlantic lowland during glacial times the rain forest was disturbed by marine incursions during the early holocene period until ca 6100 14c yr b p as indicated by the presence of microforaminifera a closed atlantic rain forest then developed at the study site

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

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

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

late pleistocene glacial forest of humaita western amazonia abstract glacial aged vegetation dynamics of the humaita western brazilian amazonia were studied by pollen sedimentary facies 14 c dating 13 c org and c n molar two sediment cores were taken to a depth of 10 and 8 m from areas covered by grassland and dense open forest respectively the deposits represent a succession of sediment accumulation in active channel 42 600 cal yr b p abandoned channel floodplain 42 600 to 39 000 cal yr b p and oxbow lake sedimentary environments 39 000 cal yr b p to modern the predominance of mud sediments depletion of 13 c org and decrease in c n molar values identify the lake establishment in these settings low energy subaqueous conditions were developed locally favoring preservation of a pollen assemblage representing herbaceous vegetation some modern taxa from amazonia and cold adapted plants from the andes represented by alnus 2 11 hedyosmum 2 17 weinmannia 0 18 podocarpus 0 4 ilex 0 4 and drymis 0 1 at least between 42 600 and alnus with other cold adapted plants from the andes during the late pleistocene indicates that alnus probably penetrated the western amazonia lowland or was growing closer to the study site due to cooler temperatures during glacial times the present study presents the first report of a glacial age forest containing alnus in areas of the brazilian amazonian lowlands in addition to its palaeogeographical importance this work demonstrates the effectiveness of using a combination of proxies for reconstructing sedimentary environments associated with vegetation

palaeodrainage on marajo island northern brazil in relation to holocene relative sea level dynamics a large area in northeastern marajo island northern brazil has been characterized geomorphologically applying information acquired from landsat imagery this study was combined with detailed sedimentologic analysis of continuous cores which provided a record of depositional settings developed in this area through the holocene the results revealed well preserved meandering to anastomosed drainage networks of wide palaeochannels that were superimposed by a narrower palaeochannel system in both cases the sedimentary record consists of sands heterolithic deposits and muds locally rich in plant debris the strata are organized into fining upward successions that reach approximately 18 m thick in the wide channels and 4 m thick in the narrow channels sedimentary features suggestive of a coastal location for the wider palaeochannels and reworking of sediments by tidal currents include the prevalence of well to moderately sorted rounded to sub rounded fine to medium grained sands displaying foreset

ordosemys leios n gen n sp a new turtle from the early cretaceous of the ordos basin inner mongolia ordosemys leios n gen n sp from the early cretaceous luohandong formation zhidan group ordos basin inner mongolia is a primitive aquatic turtle with a reduced fenestrated plastron it shares with the members of the centrocryptodira the presence of well formed articular surfaces on the cervical and caudal vertebrae within the centrocryptodira characters of the cervical vertebrae suggest it is more closely related to the polycryptodira than is the meiolaniidae ordosemys shares with the chelydridae the presence of two procoelous anterior caudals but this character may be primitive for the polycryptodira characters of the basicranial region of the braincase shared by ordosemys and the chelonioidea support a sister group relationship between these two taxa but a sister group relationship between ordosemys and the polycryptodira is more strongly supported by characters shared by the chelonioidea and other members of the polycryptodira

relation between carbon isotopes of plants and soils on marajo island a large tropical island implications for interpretation of modern and past vegetation dynamics in the amazon region abstract we assess the relation between the contrasting vegetation types of rainforest open savanna and wooded savanna coexisting in close contact on marajo island at the mouth of the amazon river floristic and carbon isotopic characterizations of modern plants were combined with organic matter carbon isotope and grain size records of soil to characterize vegetation evolution at six locations on southeastern and northeastern marajo island and its relations to climate changes since the late pleistocene c3 plants contribute 100 of the biomass in the rainforest on post barreiras sediments site 1 no significant vegetation changes are evident in these places since at least 7860 cal yr b p rainforests on paleochannels sites 4 and 6 are protected from flooding by slightly elevated sandy levee and have flora very similar to site 1 these forests were formed since the early mid holocene after channel abandonment c3 grasses are predominant in open savanna areas sites 4 5 and 6 with less representation in wooded savannas sites 2 and 3 however c4 grasses despite having fewer species constitute significant biomass in the wooded 60 and open savanna vegetation areas especially during the dry season the reconstructions of past vegetation together with the distributions of modern vegetation allow prediction that climate changes to drier conditions can significantly influence the future marajo island landscape likely enabling expansion of c4 plants in the flooding zone and of trees in the rainforests

southward migration of the austral limit of mangroves in south america abstract temperature influences the global distribution of mangroves and global warming may be causing a poleward mangrove expansion sedimentary features pollen and isotopes data from six sediment cores as well as 14c datings indicated a marine transgression during the holocene and it contributed to the expansion of tidal flats occupied by saltmarshes environmental conditions suitable for mangroves development occurred on the study site during the holocene but according to 210pb and 14c dating the establishment of mangroves mainly represented by laguncularia trees only began between 1957 and 1986 ad on the studied tidal flats spatial temporal analysis based on satellite and drone images revealed a mangrove expansion of 10 ha in the study area between 2003 96 1 ha and 2019 106 1 ha nowadays in the study area saltmarshes mainly characterized by spartina and acrostichum are sharing tidal flats with mangroves represented by laguncularia 5 m tall and avicennia 11 m tall probably the absence of mangroves during the holocene followed by their establishment and expansion during the anthropocene in the subtropical zone is associated with a migration of the austral mangrove limit into the temperate zone caused by the gradual increase in winter temperatures this process may be related to a poleward mangrove migration since the late holocene caused by a natural holocene global warming however the industrial era warming must have intensified the mangrove expansion into temperate zones

millennial scale vegetation dynamics in an estuary at the onset of the miocene climate optimum article i nfo pollen analyses have been proven to possess the possibility to decipher rapid vegetational and climate shifts in neogene sedimentary records herein a c 21 kyr long transgression regression cycle from the lower austrian locality stetten is analysed in detail to evaluate climatic benchmarks for the early phase of the middle miocene climate optimum and to estimate the pace of environmental change based on the coexistence approach a very clear signal of seasonality can be reconstructed a warm and wet summer season with c 204 236 mm precipitation during the wettest month was opposed by a rather dry winter season with precipitation of c 9 24 mm during the driest month the mean annual temperature ranged between 15 7 and 20 8 c with about 9 6 13 3 c during the cold season and 24 7 27 9 c during the warmest month in contrast today s climate of this area with an annual temperature of 9 8 c and 660 mm rainfall is characterized by the winter season mean temperature 1 4 c mean precipitation 39 mm and a summer mean temperature of 19 9 c mean precipitation 84 mm different modes of environmental shifts shaped the composition of the vegetation within few millennia marshes and salt marshes with abundant cyperaceae rapidly graded into taxodiaceae swamps this quick but gradual process was interrupted by swift marine ingressions which took place on a decadal to centennial scale the transgression is accompanied by blooms of dinoflagellates and of the green alga prasinophyta and an increase in abies and picea afterwards the retreat of the sea and the progradation of estuarine and wetland settings were a gradual progress again despite a clear sedimentological cyclicity which is related to the 21 kyr precessional forcing the climate data show little variation this missing pattern might be due to the buffering of the precessional related climate signal by the subtropical vegetation another explanation could be the method inherent broad range of climate parameter estimates that could cover small scale climatic changes

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

late holocene development of a mangrove ecosystem in southeastern brazil itanhaem state of sao paulo abstract most palynological studies of mangroves have been carried out in the indo pacific region but few have investigated these ecosystems along the southern atlantic coast this paper provides information on the palynology of a mangrove at itanhaem state of sao paulo on the southeastern brazilian coast this mangrove occurs on microtidal flats adjacent to a fluvial tidal channel mouth itanhaem river part of an estuarine lagoon system established in the mid holocene pollen samples were collected from the surface and from bromeliad water in order to define the composition of modern pollen rain in the study area the results show a strong presence of rain forest taxa in the mangrove pollen spectra which differ from those obtained from northern brazilian mangroves which are characterized by higher percentages of the mangrove taxa rhizophora and avicennia based on palynological and 14 c chronological analysis of a shallow core measuring 135 cm in depth the itanhaem mangrove already existed by 1300 years bp and began expanding about 1000 years bp reaching its present extent sometime after 300 years bp its evolution is related to the sedimentary filling of the estuarine lagoonal depositional system two factors may have controlled the development of this mangrove the relative increase of intertidal areas due to this sedimentary filling and the decrease in wave action and increase in pelitic deposition in the intertidal zone related to the partial closing of the estuarine lagoonal inlets these processes were favored by the advance of bayhead deltas and by the development of sand spits as a part of the regression of the holocene strandplain

an atoposaurid neosuchian archosauria crocodyliformes from the lower cretaceous of inner mongolia people s republic of china cranial and postcranial remains from the laolonghuoze locality in the ordos basin inner mongolia china represent a previously unrecorded taxon of crocodyliform archosaurs from the lower cretaceous luohandong formation zhidan group several cranial features indicate that this form is referable to the atoposauridae which were previously definitely known only from the upper jurassic and lower cretaceous of europe certain derived characters further indicate that the ordos material is closely related to if not actually referable to theriosuchus the ordos atoposaurid differs from the species of theriosuchus in only a few features in view of its fragmentary nature the new material is identified as cf theriosuchus sp at present

holocene environmental changes from the rio curua record in the caxiuana region eastern amazon basin abstract holocene environments have been reconstructed by multiproxy studies of an 850 cm long core from rio curua dating to 8000 14 c yr b p the low energy river lies in the eastern amazon rain forest in the caxiuana national forest reserve 350 km west of belem in northern brazil sedimentological mineralogical and geochemical dates demonstrate that the deposits correspond to two different environments sediments of an active river before 8000 14 c yr b p and later a passive river system the pollen analytical results indicate four different local and regional holocene paleoenvironmental periods 1 a transition to a passive fluvial system and a well drained terra firme unflooded upland amazon rain forest with very limited development of inundated forests varzea and igapo 7990 7030 14 c yr b p 2 a sluggish river with a local mauritia palm swamp and similar regional vegetation as before 7030 5970 14 c yr b p 3 a passive river forming shallow lake conditions and with still abundant terra firme forest in the study region 5970 2470 14 c yr b p and 4 a blocked river with high water levels and marked increase of inundated forests during the last 2470 14 c yr b p increased charcoal during this last period suggests the first strong presence of humans in this region the atlantic sea level rise was probably the major factor in paleoenvironmental changes but high water stands might also be due to greater annual rainfall during the late holocene

holocene palaeoenvironmental history of the amazonian mangrove belt abstract wetland dynamic in the northern brazilian amazon region during the holocene was reviewed using palynological carbon and nitrogen isotopes records and c n ratio previously published the integration of 72 radiocarbon dates recorded in 34 sediment cores sampled along the marine and fluvial littoral and mainly influenced by the amazon river reveals that marine influence and mangrove vegetation were wider than today on the mouth of amazon river between 8990 8690 and 2300 2230 cal yr bp forming a continuous mangrove belt along the northern brazilian amazon littoral the establishment of this mangrove strip is a direct consequence of the marine incursion caused by post glacial sea level rise possibly associated with tectonic subsidence during the early and middle holocene in the late holocene in areas influenced by the amazon river discharge the mangroves were replaced by freshwater vegetation and the coast morphology evolved from an estuarine dominated into a rectilinear coast due to coastal progradation nevertheless the marine influenced littoral which is currently dominated by mangroves and salt marsh vegetation has persistently had brackish water vegetation over tidal mud flats throughout the entire holocene likely the fragmentation of this continuous mangrove line during the late holocene was caused by the increase of river freshwater discharge associated to the change from dry into wet climates in the late holocene this caused a significant decrease of tidal water salinity in areas near the mouth of amazon river these changes in the amazon discharge are probably associated with dry and wet periods in the northern amazon region during the holocene

tetrapod track assemblages from lower cretaceous desert facies in the ordos basin shaanxi province china and their implications for mesozoic paleoecology tetrapod ichnofaunas are reported from desert playa lake facies in the lower cretaceous luohe formation at baodaoshili shaanxi province china which represent the first asian example of an ichnnofauna typical of the chelichnus ichnofacies brasilichnium sub ichnofacies characteristic of desert habitats the mammaliomorph tracks assigned to brasilichnium represent the first report of this ichnogenus from asia the assemblages also contain three different theropod trackway morphotypes one very wide magnoavipes like morphotype one relatively wide broad toed small eubrontes like form with short steps and strides and wide straddle and an elongate morphotype sarmientichnus with longer steps and narrower straddle representing a didactyl trackmaker the latter being the first example of the enigmatic ichnogenus found outside its type area in argentina the sarmientichnus occurrence the first in asia has important implications demonstrating that the trackmaker was not monodactyl but didactyl with probable affinities to deinonychosaurians which are ichnologically well represented in the lower cretaceous of asia although morphologically distinctive sarmientichnus should be recognized as a form ichnotaxon compromised by suboptimal preservation the combination of brasilichnium isp sarmientichnus isp and tridactyl theropod tracks indicates mammaliomoprhs and small theropods and is comparable to ichnofaunas from similar desert facies on other continents thus cretaceous desert ichnofaunas from china are consistent with global ichnofacies predictions

environmental changes recorded in the holocene sedimentary infill of a tropical estuary abstract early to late holocene sedimentary infill of the potengi jundiai estuary brazil was studied in a 31 5 m long sediment core the borehole was drilled in a mangrove area within the central part of the flood tide delta the sedimentary record encompassing the last 10 kyr was studied for sediment texture and for the n alkanes composition of organic matter om sediments rich in om and bivalve shells accumulated during the period of sea level rise mostly in an intertidal environment of mangrove forest mudflat and subtidal estuarine flood delta the characterization of n alkanes c10 c33 and lignin methoxyphenols by means of direct analytical pyrolysis py gc ms technique allowed determining the sources of the extant om downcore fluctuations were observed in n alkanes and in several n alkane based indices such as long chain carbon preference index cpi c24 c33 long to short chain ratio l s and average chain length acl as well as in the relative proportion of lignin derived compounds the n alkanes distribution points to changing sources of om input to the estuarine sediments over most of the holocene period major inputs of terrestrial vegetation alternated with periods of mixed input from aquatic macrophytes as the rate of sea level rise changed over time the n alkanes distribution and the lignin markers were useful for reconstructing paleoenvironmental conditions particularly during the early holocene when the lower potengi river valley now an estuarine area could accommodate terrestrial forest vegetation before switching to halophytic mangroves as sea levels rose

palaeogeography and dynamics of the deltaic wetland of save river mozambique abstract many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation from river inflows in this paper we use the example of the save river delta to assess the palaeogeographic distribution of mangrove wetlands and to analyze their dynamics to track past occurrences of mangrove wetlands in the study area we have integrated sedimentological data with siliceous microfossil analysis combined with ams radiocarbon and osl dating the results show a fine grained deposit with an approximate thickness of 2 m present at different sampling sites in the upper deltaic plain the deposit is interbedded between sand layers while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position in most of the sampling sites the deposit shows a succession with brackish marine diatoms at the bottom of the sequence while the upper part shows only scattered occurrences based on sedimentological and microfossil characteristics we have interpreted the layer to represent a mangrove wetland deposit the development of the deposit in the study area is suggested to have been initiated around 3100 cal yr bp induced by sea level rise thereafter the development followed the combined effect of a sea level fall and delta progradation processes in some areas particularly in the proximal part of the delta the mangrove deposit has developed progressively on top of the delta front from around 1300 years ago osl onwards massive alluvial sedimentation impacted the mangrove ecosystem however the retreat of mangrove wetland coincided with a regional fall of sea level at the edges of the alluvial deposit the current mangrove ecosystem has reclaimed the habitat in some sectors where gully erosion has exposed the once extinct mangrove habitat

relative sea level and climatic changes in the amazon littoral during the last 500 years abstract an integrated approach focused on sedimentology geochemistry palynology c and n isotopes and radiocarbon dating of a sediment core from an herbaceous plain not flooded by tides of the amapa littoral near the amazon river mouth allowed identification of two phases with marine and terrestrial influences mangroves occurred over tidal mud flats with marine influence between 5610 5470 and 470 310 cal yr bp the absence of mangrove vegetation since 470 310 cal yr was followed by the transition of brackish water organic matter to terrestrial c3 plants also the geochemical data indicate a decrease in sea water influence during this last time interval likely the displacement of mangrove forest to lower surfaces was caused by a relative sea level fall that may be associated with drier conditions with less rainfall during the second part of the last millennium as suggested by this work slight relative sea level fluctuations caused by regional or global climatic change may affect significantly the current mangrove area

mangrove dynamics in the southwestern caribbean since the little ice age a history of human and natural disturbances relatively little is known about the long term response of caribbean mangroves to human and natural disturbances during the little ice age lia we present new palynological information on the dynamics of the bahia honda mangrove from the eastern coast of san andres island in the southwestern caribbean for the late holocene major changes in the bahia honda pollen record show the combined effects of natural events strong storms and sea level rise and human disturbances these changes are supported by 14c dates sedimentological and palynological information a storm most probably a hurricane was recorded around ad 1600 caused sediment reworking and the subsequent loss of about 2000 years of the vegetation record the devastation of tree vegetation by this event allowed the expansion of heliophytic vegetation e g grasses and vines mangroves and coastal vegetation started to recover at ad 1700 reaching their maximum extent within a few decades when microforaminifera shells became abundant at

a multi proxy evidence for the transition from estuarine mangroves to deltaic freshwater marshes southeastern brazil due to climatic and sea level changes during the late holocene abstract the present study investigates a paleo estuary at the doce river delta southeastern brazil through a multi proxy approach that links palynology diatoms sedimentology and geochemistry analyses i e total c total n 13 c and 15 n these analyses temporally synchronized with five radiocarbon ages revealed environmental changes from marine to continental over the last 7550 years the studied sedimentary succession recorded the upward transition from estuarine channel until 7550 cal yr bp to estuarine central basin 7550 to 5250 cal yr bp deposits the latter containing increased mangrove vegetation marine and marine brackish water diatoms the range of geochemical values 13 c 30 10 15 n 2 8 and c n 4 40 also indicate marine estuarine organic matter and c 3 terrestrial plants to that time interval a following period recorded two phases lake ria 5250 to 400 cal yr bp and fluvial channel 400 cal yr bp until modern age during this stage mangroves were replaced by trees shrubs and herbs grasses due to the disconnection with the marine realm as a result the corresponding sediments contain only organic matter sourced from freshwater and c 3 terrestrial plants 13 c 29 26 15 n 0 8 and c n 10 45 the equilibrium between fluvial sediment supply and relative sea level changes during the holocene controlled the morphologic and vegetation changes in the studied littoral the estuary became established during the early holocene as a resulted of a eustatic sea level rise when the fluvial sediment supply to the coast was relatively lower due to a dry period however during the late holocene the climatic force was more significant to the development of coastal morphology due to a wet period that caused an increase in sandy sediment supply to coastal system then the increase of fluvial discharge associated to a relative sea level fall caused a marine regression and shrinkage of mangroves during the late holocene the evaluation of mangrove dynamics according to climatic and sea level changes mainly during the late holocene is essential for the understanding of their survival ability under future scenarios with a probable accelerated sea level rise and intensification of extreme climatic events in southeastern brazil for the next century

late holocene sedimentary and environmental development of the northern mekong river delta vietnam abstract a sedimentological and palynological study of three sediment cores from the northern mekong river delta shows the regional sedimentary and environmental development since the mid holocene sea level highstand a sub to intertidal flat deposit of mid holocene age is recorded in the northernmost core shoreline deposits in all three cores show descending ages from n to s documenting 1 the early stages of the late holocene regression and 2 the subsequent delta progradation the delta plain successions vary from floodplain deposits with swamp like elements to natural levee sediments the uppermost sediments in all cores show human disturbance to varying degrees the most intense alteration is recorded in the northernmost core where the palynological signal together with a charcoal peak indicates the profound change of the environment during the modern land reclamation the sediments from at least one of the three presented cores do not show a true delta facies succession but rather estuary like features as also observed in records from southern cambodia this absence is probably due to lack of accommodation space during the initial phase of rapid delta progradation which impeded the development of true delta successions as shown in cores from the southern mekong river delta

mangrove vegetation changes on holocene terraces of the doce river southeastern brazil article i nfo high resolution sedimentological geochemical and pollen analysis on sediment core from the coastal plain of the doce river southeastern brazil revealed changes in the depositional system and vegetation caused by combined action of oscillations in relative sea level rsl and sedimentary supply during the holocene two main phases were discerned using sedimentary features 13 c 15 n total organic carbon toc total ni trogen n c n and cluster analysis of pollen data temporally synchronized with radiocarbon age dating the data indicates the presence of a lagoon system surrounded by a tidal plain colonized by mangroves and its sedimentary organic matter sourced from c4 plants between 8050 and 7115 cal yr bp however during the mid and late holocene the mangroves shrank and freshwater vegetation expanded c3 plants proba bly due to a marine regression during this phase the development of a lacustrine environment was followed by the colonization of herbs trees and shrubs the continuous sediment infilling into the lake allowed the ex pansion of a herbaceous plain as seen today this geomorphologic and vegetation evolution is in agreement with the mid holocene rsl maximum above present rsl and subsequent fall to the present time

holocenic proxies of sedimentary organic matter and the evolution of lake arari amazon region abstract four sediment cores were sampled from lake arari located on marajo island at the mouth of the amazon river the island s vegetation cover is composed mainly of amazon coastal forest herbaceous and varzea vegetation the integration of data on sedimentary structures pollen carbon and nitrogen isotope records c n ratios and radiocarbon ages allowed the identification of changes in vegetation and the sources of organic matter accumulated in the lake during the holocene the data indicate a relatively high flow energy marine water influence and the presence of mangroves during the lagoon phase between 8990 and 8690 cal yr b p and 2310 2230 cal yr b p between 2310 and 2230 cal yr b p and 1000 cal yr b p the flow energy decreased and the mangroves were replaced by herbaceous vegetation following the decline in marine influence likely due to the increase in freshwater river discharge during the last 1000 years lake arari was established in association with the expansion of herbaceous vegetation and the dominance of freshwater algae

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

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

molecular evidence for lignin degradation in sulfate reducing mangrove sediments amazonia brazil abstract molecular lignin analyses have become a powerful quantitative approach for estimating flux and fate of vascular plant organic matter in coastal and marine environments the use of a specific molecular biomarker requires detailed knowledge of its decomposition rates relative to the associated organic matter and its structural diagenetic changes to gain insight into the poorly known processes of anaerobic lignin diagenesis molecular analyses were performed in the sulfate reducing sediment of a north brazilian mangrove organic matter in samples representing different diagenetic stages i e fresh litter a sediment core and percolating water was characterized by alkaline cuo oxidation for lignin composition element c n and stable carbon isotope analyses on the basis of these results and on a balance model long term in situ decomposition rates of lignin in sulfate reducing sediments were estimated for the first time the half life t 1 2 of lignin derived from mangrove leaf litter mainly rhizophora mangle was 150 yr in the upper 1 5 m of the sediment associated organic carbon from leaf tissue was depleted to 75 within weeks followed by a slow mineralization in the sediment t 1 2 300 yr unlike the known pathways of lignin diagenesis even highly degraded lignin did not show any alterations of the propyl or methoxyl side chains as evident from stable acid to aldehyde ratios and the proportion of methoxylated phenols vanillyl and syringyl phenols aromatic ring cleavage is probably the principal mechanism for lignin decay in the studied environment cinnamyl phenols were highly abundant in mangrove leaves and were rapidly depleted during early diagenesis thus the cinnamyl to vanillyl ratio could be used as a tracer for early diagenesis even under the sulfate reducing conditions syringyl phenols were removed from dissolved organic matter in interstitial water probably by sorption onto the sediment suspended organic matter in a mangrove creek showed a different lignin signature than its source namely sedimentary organic matter or mangrove litter with clear evidence for propyl side chain oxidation this was probably attributable to erosion of aerated thin sediment surface layers during mangrove inundation although particulate and dissolved organic matter in the mangrove creek have a common source their compositional patterns were different because of different pathways of release degradation and transport to the creek

introduction to the special issue commemorating the 30th anniversary of the royal tyrrell museum of palaeontology with a summary of the museum s early history and its research contributions located just west of drumheller in southern alberta canada the royal tyrrell museum of palaeontology rtmp is nestled among outcrops of the upper cretaceous horseshoe canyon formation exposed along the red deer river valley fig 1 since it officially opened on 25 september 19851 the museum has become one of alberta s must see tourist attractions a significant contributor to the local economy and earned an international reputation for the quality of its palaeontological collections and the research conducted by its scientists the rtmp is unique within canada in being the only government supported museum dedicated to palaeontology and it is one of the few such institutions in the world fig 1 the royal tyrrell museum of palaeontology a front of museum and main entrance circa 2010 looking westwards and with horizontal beds of the upper cretaceous horseshoe canyon formation exposed in the walls of the red deer river valley in the distance b aerial photograph oblique angle and looking to the north northeast the museum sits on top of the number 7 coal seam sensu gibson 1977 and at the base of the horsethief member of the horseshoe canyon formation d a eberth pers comm 2015 that stratigraphic position correlates with an age of about 71 5 ma i e late campanian and lies within the upper part of the edmontosaurus regalis pachyrhinosaurus canadensis dinosaur assemblage zone see eberth et al 2013 fig 6 c the iconic running theropod logo that until recently graced the exterior of the museum below a life sized tyrannosaurid sculpture by brian cooley one of many such sculptures by cooley that have been featured at the museum since its opening in 1985 and with the education wing opened in 2003 as the atco tyrrell learning centre in the background d the cretaceous alberta life sized diorama opened in 2007 an example of a rtmp exhibit that relies heavily on discoveries and interpretations by museum researchers in this case work done in the albertosaurus bonebed and at other localities throughout the horseshoe canyon formation all photographs courtesy of the royal tyrrell museum of palaeontology this special issue of the canadian journal of earth sciences presents a collection of papers commemorating the rtmp s 30th or pearl anniversary our rationale for doing a 30th anniversary volume was two fold first it is an opportunity to showcase the breadth of research conducted by current and former museum scientists as well as by some colleagues having a history of collaboration with the rtmp the 13 invited papers included in this volume are a mix of review and original research papers all thematically focused on the geology and palaeontology of alberta to varying degrees each contribution is the result of work supported by the rtmp and relies on specimens housed in the museum s collections second the 30th anniversary is an opportunity to reflect on the rtmp s history and its research program as is typical for most institutions the rtmp has done little to formally document its own history this year likely will be the last major milestone for which the original generation of museum staff are still working and available to share their recollections about the museum fieldwork and research already deaths and departures have winnowed away part of the original

the brazilian sea level curves a critical review with emphasis on the curves from the paranaguaand cananeia regions abstract relative sea level curves for the mid to late holocene have been proposed for eight different sectors along the brazilian coast this paper aims to review the data used to construct the curves proposed for two sectors the paranaguaand cananeia regions in southeast brazil more specifically we analyze the palaeo sea level indicators vermetid tubes shells wood fragments and shell midden deposits related to 1 the sea level maximum of the mid holocene and 2 the two secondary oscillations that would have occurred between 4100 3800 years b p and 3000 2700 years b p the sedimentary deposits of the coastal plain as well as vermetid datings suggest a mid holocene sea level maximum between 3 5 and 4 m the great majority of the indicators used to infer the secondary oscillations in previous studies were derived from shell middens besides being unreliable palaeo sea level indicators these data also showed inconsistencies that undermine the existence of such oscillations the plot of all the data derived from vermetid samples found along the brazilian coast also indicate a rather smoother sea level fall in the last 5100 years

wetland dynamics of marajo island northern brazil during the last 1000 years abstract the wetland dynamics in eastern amazon region during the last thousand years were studied by pollen analysis and ams radiocarbon date three sediment cores were sampled from the marajo island which is located at the mouth of the amazon river marajo island is covered mainly by amazon coastal forest herbaceous and varzea vegetation one core was obtained from lake arari which is surrounded by herbaceous vegetation flooded by freshwater two cores were sampled from an herbaceous plain that lies 45 km southeast from the lake arari the pollen records indicate that the herbaceous vegetation began its development approximately 800 cal yr b p the pollen percentages between 750 and 500 cal yr b p indicate the expansion of mangroves the predominance of herbaceous and varzea pollen occurs between 500 and 200 cal yr b p and the varzea pollen percentage increased during the last 200 years the vegetation changes proposed by the pollen records from the lake arari probably represent the regional vegetation dynamics of the marajo island while the pollen profiles from herbaceous plain present a smaller spatial representativeness of the vegetation the alternation between fresh and brackish water vegetation in the wetlands may indicate changes in the physicochemical characteristics of the sediment during the time interval studied

sunosuchus junggarensis sp nov archosauria crocodyliformes from the upper jurassic of xinjiang people s republic of china a new species of crocodyliformes sunosuchus junggarensis is established on the basis of six individuals from the upper jurassic of the junggar basin xinjiang northwest china it differs from other species of sunosuchus primarily in having a dorsoventrally depressed supraoccipital that in occipital view lacks a median crest a frontal that is ridged anteriorly a distinct depression distal to the foramen aereum on the dorsal surface of the quadrate and an elongate undivided maxillary depression cranial ontogenetic variation in s junggarensis is discussed sunosuchus is probably a goniopholidid crocodyliform it is distinguished from other genera of the goniopholididae by a narrow and elongate snout a small skull table a partially ridged frontal a pair of anteriorly located anterior palatal fenestrae a lateroventrally mediodorsally expanded retroarticular process some enlarged pits on the frontal and an elongate mandibular symphysis with the splenial forming a small part of it sunosuchus

connection between macrotidal estuaries along the southeastern amazon coast and its role in coastal progradation abstract sediment transport in the southeastern amazon coastal zone sacz is substantially affected by tidal asymmetry seasonal variation of the wind and wave regime and especially rainfall i e river discharge the regional climate and geological configuration have resulted in numerous estuaries and large mangrove covered coastal plains that partially divide the estuarine basins which are connected by tidal channels based on the investigation of the furo grande tidal channel we assess the relevance of connectivity on the sediment transport and evolution of the 8000 km2 sacz mangrove belt extensive sedimentologic and bathymetric surveys as well as hydrodynamic measurements including water level water and sediment flow and physical chemical characteristics of the water were undertaken at different seasonal periods water level variation along the channel shows that sediment transport convergence stc tends to be formed within the connecting channel as the tide propagates from both ends morphologic and sedimentologic results show the accumulation trend of fine sediments within the stc zone and this is relevant for mud retention and further delivery to the mangrove plains which may eventually lead to channel connection closure despite the stc results also show that there is an important net flux of suspended sediments between estuaries through the studied channel however the connected estuaries of taperacu and caete have substantial differences regarding riverine discharge and thus estuarine processes tidal propagation and sediment transport bottom sediments and morphology reflect long term trends and show stc migration towards the taperacu as a result of substantially smaller fluvial discharge in that estuary and therefore higher sediment accumulation rates compared to the caete estuary the migration of the stc prevents the closure of the connection and its maintenance preserves these channels as sediment flow conduits between estuaries the connectivity is a key process to redistribute mainly muddy sediments along this coastal sector which helps to explain the evolution and maintenance of the relatively homogeneous and widespread progradation of mangroves along the sacz with uneven mud supply

new geological framework for western amazonia brazil and implications for biogeography and evolution abstract although many of the current hypotheses to explain the origin and distribution of the amazon biodiversity has been based directly or indirectly on geological data the reconstruction of the geological history of the amazon region is still inadequate to analyze its relationship with the biodiversity this work has the main goal to characterize the sedimentary successions formed in the brazilian amazon in the neogene quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap radar image interpretation sedimentological studies and radiocarbon dating allowed the mapping of plio pleistocene to holocene units along the solimoes amazonas river brazil this integrated work led to the characterization of five sedimentary successions overlying miocene deposits of the solimoes pebas formation which include the following ica formation plio pleistocene deposits q1 37 400 43 700 14c yr b p deposits q2 27 200 14c yr b p deposits q3 6730 2480 14c yr b p and deposits q4 280 130 14c yr b p these deposits occur mostly to the west of manaus forming nw se elongated belts that are progressively younger from sw to ne indicating a subsiding basin with a depocenter that migrated to the ne the reconstruction of the depositional history is consistent with significant changes in the landscapes hence the closure of a large lake system at the end of the miocene gave rise to the development of a plio pleistocene fluvial system this was yet very distinct from the modern drainage with shallow energetic highly migrating braided to anastomosed channels having an overall northeast outlet this fluvial system formed probably under climatic conditions relatively drier than today s during the early pleistocene there was pronounced erosion followed by a renewed depositional phase ca 40 000 14c yr b p with the development of prograding lobes and or crevasse splays associated with a lake system i e fan delta and or fluvial flood plain areas after a period of erosion a fluvial system with eastward draining channels started to develop at around 27 000 14c yr b p the fluvial channels were overflooded in mid holocene time this flooding is attributed to an increased period of humidity with a peak between 5000 and 2500 14c yr b p the data presented herein support that rather than being a monotonous area the amazonia was a place with frequent changes in landscape throughout the neogene quaternary probably as a result of climatic and tectonic factors we hypothesize that these changes in the physical environment stressed the biota resulting in speciation and thus had a great impact on modern biodiversity

sea level rise since 8 2ka recorded in the sediments of the potengi jundiai estuary ne brasil abstract we present the first data set on the evolution and holocene infilling of the potengi river estuary at the ne brazilian continental margin near the city of natal the study is based on integrated sedimentological geochemical and palaeontological information from 6 boreholes drilled in the area of estuarine mangroves complemented by radiocarbon dating of the in situ remains of mangrove vegetation four samples taken close to the pre inundation substratum set the baseline of reference points for the sea level reconstruction this palaeoenvironmental reconstruction coupled with a 14 c age model complements previous sea level studies along the rio grande do norte coast which have been based primarily on beach rocks and other on shore exposed sedimentary materials a rapid sea level rise at an averaged rate of approximately 6 1 mm yr 1 occurred between 8300 and 7000 cal yr bp since then the pace of relative sea level rise slowed and non eustatic factors namely terrigenous sediment supply and coastal dynamics became dominant in the evolution of the estuary the post transgression period witnessed the decline of mangroves whose remnants were identified mostly in the initial 2 m of holocene estuarine sediments accelerated sea level rise combined with geomorphological confinement of the studied intertidal zone was probably responsible for the demise of halophyte vegetation which thrived again in the late holocene

mid holocene mangrove succession and its response to sea level change in the upper mekong river delta cambodia abstract middle holocene vegetation and mangrove successions are clearly evident in the palynological records of two cores from the upper mekong river delta in cambodia spanning from 9 4 to 6 3 cal ka bp the cores mainly record a transgressive sequence from floodplain freshwater marsh to tidal flat which was overlain by mangrove corresponding to the decelerated sea level rise at 8 3 cal ka bp pioneer mangrove species sonneratia alba and sonneratia caseolaris appeared in the sediments and then was replaced by regressive mangrove succession containing upward increasing abundances of rhizophora apiculata and bruguiera spp high salinity and flooding tolerant community s alba was developed at the western core site psg at 8 2 cal ka bp and the eastern core site pk at 7 5 cal ka bp the time difference of s alba appearance between the two sites might be resulted from the complexity of sedimentary environment where a higher sediment supply was provided to the western floodplain than to the eastern floodplain after 7 5 cal ka bp aggradational stacking of intertidal sediments of which the thickness is larger than the present maximum tidal range may have resulted from continuous sea level rise during 7 5 7 0 cal ka bp