late quaternary palaeoenvironment of northern guatemala evidence from deep drill cores and seismic stratigraphy of lake peten itza long sediment cores were collected in spring 2006 from lake peten itza northern guatemala in water depths ranging from 30 to 150 m as part of an international continental scientific drilling program project the sediment records from deep water consist mainly of alternating clay gypsum and carbonate units and in at least two drill sites extend back 200 kyr most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes a revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin from ca 200 to ca 85 ka sediments are dominated by carbonate clay silt often interbedded with sandy turbidites indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate at ca 85 ka an exposure horizon consisting of gravels coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation indicating dry climate conditions from ca 85 to ca 48 ka transgressive carbonate clay sediments overlain by deep water clays suggest a lake level rise and subsequent stabilization at high stage from ca 48 ka to present the lithology is characterized by alternating clay and gypsum units gypsum deposition correlates with heinrich events i e dry climate whereas clay units coincide with more humid interstadials

climate forcings on vegetation of the southeastern yucatan peninsula mexico during the middle to late holocene abstract climate and vegetation history from the yucatan peninsula southeastern mexico are inferred from a mangrove sediment core deposited between the middle and late holocene 5600 1700 cal yr b p in the rio hondo delta fossil pollen and concentrations of ca and fe and ca fe ratio in sediments are used to record changes in vegetation and climate palaeoecological and palaeoclimatic interpretations obtained from pollen abundances and associations and fe ca ratio coincide with dynamics of major global forcings of climate change like itcz enso and global cooling mesic conditions enabled tropical forest expansion during the middle holocene 5600 3650 cal yr b p although there were periodic dry episodes at 5200 cal yr b p and at 4300 cal yr b p that caused disturbance and enabled herbaceous vegetation to expand changes in sedimentation and a gradual change from semi evergreen to dry tropical forest occurred at 3650 cal yr b p with increasing enso activity and southward migration of the itcz during transition of the middle to late holocene the driest period and lowest forest cover occurred between 2600 and 2000 cal yr b p data show that over the last two millennia influence of the enso on southeastern mexico is stronger compared to other proxy records of climate variability from the caribbean region

climate change in the lake valencia basin venezuela 12600 yr bp to present we present a palaeoclimate record for northern south america extending from the latest pleistocene 12600 14c yr bp to present climate reconstruction for the valencia basin venezuela was base

holocene vegetation change in the northern peten and its implications for maya prehistory an 8400 cal yr record of vegetation change from the northern peten guatemala provides new insights into the environmental history of the archaeological area known as the mirador basin pollen loss on ignition and magnetic susceptibility analyses indicate warm and humid conditions in the early to mid holocene evidence for a decrease in forest cover around 4600 cal yr b p coincides with the first appearance of zea mays pollen suggesting that human activity was responsible the period between 3450 cal yr b p and 1000 cal yr b p is characterized by a further decline in forest pollen types includes an abrupt increase in weedy taxa and exhibits the highest magnetic susceptibility values since the early holocene all of which suggest further agricultural disturbance in the watershed a brief drop in disturbance indicators around 1800 cal yr b p may represent the preclassic abandonment of the area changing pollen frequencies around 1000 cal yr b p indicate a cessation of human disturbance which represents the late classic collapse of the southern maya lowlands

late quaternary vegetation and climate of the sahel abstract pollen and phytogeographic evidence provides a vegetational history of the sahel for the period 0 18 000 yr b p the zonal vegetation fluctuated latitudinally and its most extreme positions occurred at 18 000 and 8500 yr b p the first involved a southward shift of the sahelian wooded grassland to 10 n under the arid conditions of the last glacial maximum the second change shows a rapid northward migration of humid vegetation guinean elements reach 16 n and sahelo sudanian elements extend to the southern margin of the modern sahara 21 n when the atlantic monsoon flux increased in the middle holocene the extensive spread of sudanian elements into the modern sahelian zone suggests the appearance of a markedly dry season the modern sahelian semiarid conditions appeared abruptly at 2000 yr b p

a late holocene vegetation history from the maya lowlands lamanai northern belize a 3 m core from the new river lagoon adjacent to the maya city of lamanai northern belize contains a continuous record of vegetation change between c 1500 bc and ad 1500 inferred changes in forest abundance and plant community assemblage build on previous palaeolimnological analysis of the same core reported by metcalfe et al 2009 a near complete abundant record of zea mays grains provides a detailed account of field based agriculture local to lamanai in the context of a regional record obtained from a large lake 13 5 km2 with a substantial catchment three periods c 170 bc ad 150 c ad 600 980 and c ad 1500 of extraction of pinus from pine savannas adjacent to the east of the new river lagoon can be distinguished from clearance of seasonal broadleaf forest for agriculture an increased palm signal is observed during c 1630 1150 bc and 100 bc ad 1100 and may be indicative of maya cultivation this record shows that during the late classic period the maya actively managed the vegetation resources using a combination of field based agriculture arboreal resources and perhaps palm cultivation there is no evidence from the vegetation history of drying during the late classic coincident with the maya collapse and this is consistent with the palaeolimnological and archaeological records of continuous occupation of the maya at lamanai both the decline in palms c ad 1400 and the increase in pinus extraction c ad 1500 are consistent with changes in vegetation associated with european arrival however further analysis of material from the last 1000 years will enable a better understanding of vegetation change pre and post european encounter

a 4000 year lacustrine record of environmental change in the southern maya lowlands peten guatemala a 4000 yr sediment core record from lake salpeten guatemala provides evidence for maya induced forest clearance and consequent soil erosion between 1700 cal yr b c and 850 cal yr a d radiocarbon ages of wood seeds and charcoal support an age depth model with average errors of 110 cal yr relatively low carbonate 18o values between 1300 and 400 cal yr b c coincide with pollen evidence for forest loss consistent with increased surface and groundwater flow to the lake minimum 18o values between 400 cal yr b c and 150 cal yr a d suggest a high lake level as do 14c dated aquatic gastropods as much as 7 5 m above the present lake stage high lake levels resulted from reduced evaporation to precipitation ratios increased hydrologic input caused by anthropogenic deforestation or both the preclassic abandonment 150 a d and early classic late classic boundary 550 a d are marked by relatively high 18o values indicating reduced lake levels oxygen isotope composition increased further coincident with the terminal classic maya demographic decline between 800 and 900 a d this period of high 18o may have been caused by the greater aridity that has been documented in northern yucatan lakes or by decreased hydrologic input to the lake as a consequence of forest recovery reduced soil erosion after 850 cal yr a d coincided with the terminal classic maya demographic decline and permitted forest recovery and resumption of organic sedimentation

a 3400 year paleolimnological record of prehispanic human environment interactions in the holmul region of the southern maya lowlands abstract the timing magnitude and drivers of late holocene environmental change in the holmul region of the southern maya lowlands are examined by combining paleoenvironmental and archeological data environmental proxy analyses on a 3350 cal yr lacustrine sediment record include pollen charcoal loss on ignition magnetic susceptibility and elemental geochemistry archeological evidence is derived from extensive settlement surveys conducted near the study site results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr bp the fire history shows a dramatic increase in burning during the classic period possibly reflecting changing agricultural strategies a distinct band of carbonate deposited from 1270 to 1040 cal yr bp suggests decreased hydrologic input associated with drier conditions abrupt changes in proxy data around 940 cal yr bp indicate a cessation of human disturbance and local abandonment of the area

the arid humid transition in the sahara and the sahel during the last deglaciation at the time of the last glacial maximum the sahara and sahel regions of north africa were extremely dry new records of rainfall show that during the subsequent deglaciation the transition from arid to humid conditions in these regions occurred synchronously in two main steps comparison with other records of palaeoclimate in europe and the north atlantic ocean shows that certain common factors controlled changes in ocean and atmosphere dynamics during the deglaciation

holocene precipitation changes in the maya forest yucatan peninsula mexico abstract holocene fossil pollen samples n 38 from lake silvituc in mexico were analyzed with the analog technique using modern pollen samples n 98 of the yucatan peninsula mexico calculated dissimilarity indices allow us to reconstruct the vegetation and to develop a precipitation record for the last 7900 years the middle holocene shows a gradual increase of precipitation and a marked drop in reconstructed precipitation around 4200 bce during the late holocene two phases were identified phase i 2500 bce 1 ce shows the greatest increase in precipitation with four peaks around 1200 bce 650 bce 200 bce and 1 ce also a period of increased precipitation resulted for the period between 200 and 500 bce periods of reduced precipitation were detected at 900 1100 bce 500 600 bce and 100 190 bce phase ii 1 2000 ce encompasses several strong dry events during the following periods 150 300 ce 750 900 ce 1050 1180 ce and 1530 1580 ce a strong reduction of 32 in precipitation in the late preclassic period 100 300 ce was detected non analogs of phase ii are associated with periods of reduced precipitation and fall into time periods of extended droughts related to the maya late classic and the little ice age a limiting factor on the use of analogs for tropical forests is that a combination of different analogs for the same fossil pollen signal exists interpretation under these circumstances requires good knowledge of the ecology of the taxa and a priori characterization of the modern samples

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

a cooling event during the younger dryas chron in costa rica abstract a fossil pollen record from the costa rican cordillera de talamanca presents the first ams radiocarbon dated evidence of a temperature decrease during the younger dryas chron this cooling event is named la chonta stadial after the bog at 2310 m altitude located at the actual lower to upper montane forest boundary high resolution pollen analysis revealed that between 11 070 130 ams 14c age and 10 400 yr b p interpolated age vegetation comparable to present day subalpine forest occurred about 300 400 m lower than in the previous warmer interval and 600 to 700 m lower than at present time the radiocarbon dates are close to the earlier estimated ages of 11 080 10 500 yr b p for this interval based on interpolation and pollen concentration rates hooghiemstra et al 1992 the downslope shift of the upper forest line indicates an estimated temperature drop of 2 3 c during the la chonta stadial the local vegetation development is indicative of a drier climate from 10 400 to 9800 120 yr b p ams 14c age subalpine rain forest was replaced by upper montane forest a transitional period to holocene environmental conditions

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

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

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

an 8000 year record of vegetation climate and human disturbance from the sierra de apaneca el salvador abstract an 8000 cal yr stratigraphic record of vegetation change from the sierra de apaneca el salvador documents a mid holocene warm phase followed by late holocene cooling pollen evidence reveals that during the mid holocene 8000 5500 cal yr b p lowland tropical plant taxa were growing at elevations 200 250 m higher than at present suggesting conditions about 1 0 c warmer than those prevailing today cloud forest genera liquidambar juglans alnus ulmus were also more abundant in the mid holocene indicating greater cloud cover during the dry season a gradual cooling and drying trend began by 5500 cal yr b p culminating in the modern forest composition by 3500 cal yr b p a rise in pollen from weedy plant taxa associated with agriculture occurred 5000 cal yr b p and pollen from zea first appeared in the record at 4440 cal yr b p human impacts on local vegetation remained high throughout the late holocene but decreased abruptly following the tierra blanca joven tbj eruption of volcan ilopango at 1520 cal yr b p the past 1500 years are marked by higher lake levels and periodic depositions of exogenous inorganic sediments perhaps indicating increased climatic variability

man and climate in the maya lowlands abstract a 15 m sedimentary core from lake salpeten provides the first complete holocene sequence for the lowlying peten district guatemala today lake salpeten is a brackish calcium sulfate lake near saturation surrounded by tropical semievergreen forest the basal pollen record depicts sparse juniper scrub surrounding a lake basin that held ephermal pools and halophytic marshes the lake rapidly deepened to 27 m in the early holocene and may have been meromictic because nearly 2 m of gypsum mush was deposited mesic forests were quickly established and persisted until the maya entered the district 3000 yr ago and caused extensive deforestation any climatic information contained in the pollen record of the maya period is thus masked but a regional pollen sequence linked to the archaeological record is substantiated because environmental disturbance was pervasive local intensification of occupation and population growth are seen as an increased deposition of pollen of agricultural weeds and colluviation into the lake while the classic maya collapse is marked by a temporary decline in compositae pollen effects of perturbations induced by the maya persist in the pollen and limnetic record 400 yr after the spanish conquest

ages of quaternary pluvial episodes determined by uranium series and radiocarbon dating of lacustrine deposits of eastern sahara abstract as documented by radiocarbon dating and geoarchaeological investigations the now hyperarid northwestern sudan and southwestern egypt experienced a period of greater effective moisture during early and middle holocene time about 10 5 ka we have used the uranium series technique to date lacustrine carbonates from bir tarfawi bir sahara east wadi hussein oyo depression and the great selima sand sheet localities results indicate five paleolakeforming episodes occurred at about 320 250 240 190 155 120 90 65 and 10 5 ka four of these five pluvial episodes may be correlated with major interglacial stages 9 7 5e and 1 the 90 65 ka episode may be correlated with substage 5c or 5a our results support the contention that past pluvial episodes in north africa corresponded to the interglacial periods farther north ages of lacustrine carbonates from existing oases and from the sand sheet fail to indicate pluvial conditions between about 60 and 30 ka age results and field relationships suggest that the oldest lake and ground water deposited carbonates were much more extensive than those of the younger period and that carbonate of the latest wet periods were geographically localized within depressions and buried channels

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

a late holocene paleoenvironmental reconstruction from agua caliente southern belize linked to regional climate variability and cultural change at the maya polity of uxbenka abstract we report high resolution macroscopic charcoal pollen and sedimentological data for agua caliente a freshwater lagoon located in southern belize and infer a late holocene record of human land use climate interactions for the nearby prehistoric maya center of uxbenka land use activities spanning the initial clearance of forests for agriculture through the drought linked maya collapse and continuing into the historic recolonization of the region are all reflected in the record human land alteration in association with swidden agriculture is evident early in the record during the middle preclassic starting ca 2600 cal yr bp fire slowly tapered off during the late and terminal classic consistent with the gradual political demise and depopulation of the uxbenka polity sometime between ca 1150 and 950 cal yr bp during a period of multiple droughts evident in a nearby speleothem record fire activity was at its lowest during the maya postclassic ca 950 430 cal yr bp but rose consistent with increasing recolonization of the region between ca 430 cal yr bp and present these data suggest that this environmental record provides both a proxy for 2800 years of cultural change including colonization growth decline and reorganization of regional populations and an independent confirmation of recent paleoclimate reconstructions from the same region

a 2860 year high resolution pollen and charcoal record from the cordillera de talamanca in panama a history of human and volcanic forest disturbance late holocene vegetational disturbance by human and volcanic activity in the lower montane rain forest region of cordillera de talamanca province of chiriqui in panama have been studied on the sedimentary archive from laguna volcan 1500 m elevation the pollen and charcoal record dated by four radiocarbon ams dates provides evidence of amerindian occupation and strong impact on the lower montane rain forest region since the beginning of the record at 2860 14c yr bp there is evidence of at least three eruptions of volcan baru which affected the study region at 1800 1000 and 500 14c yr bp the first two events had apparently relatively little effects while the latest volcanic eruption which deposited a 20 cm thick tephra layer in the studied lake had a catastrophic impact amerindian life and culture of the study area was destroyed after the last eruption the montane rain forest recovered markedly fires were rare and agriculture activity stopped in the surroundings of the lake suggesting that

palynological record of climate change during the last deglaciation from the song hong red river delta vietnam abstract the palynological sequence from core nd 1 on the song hong delta in the northern vietnam reveals the climate change during the last deglaciation the identified pollen in the core is dominated by castanopsis lithocarpus elaeocarpus ficus piperaceae and quercus high percentages of temperate taxa including the conifers dacrydium podocarpus pinus cupressaceae txodiaceae and cryptomeria and broad leaved taxa of carpinus alnus juglans carya ulmus fagus ilex castanea quercus which have a mainly upland distribution is possibly associated with a lowering of the montane vegetation boundary on the other hand intensified river influence can also result in an increase in the temperate allochthonous taxa after analyzing the magnitude of river influence on pollen assemblages during the sedimentary environment evolution we extracted the climate information and used this to reconstruct climate change during the last deglaciation a cooler climate during 14 5 10 9 cal kyr bp than at present is indicated by higher percentage of temperate types than at present under a similar river influence on the floodplain the younger dryas cooling event is recognized by widely developed grasslands between 12 9 and 11 6 cal kyr bp adding to the evidences for this period from both terrestrial and marine records in regions influenced by the east asian monsoon two other cooling periods 9 4 9 0 cal kyr bp and 6 5 5 2 cal kyr bp are indicated by increases of temperate pollen taxa such as cryptomeria alnus quercus and castanea

remnants of a cretaceous intra oceanic subduction system within the yarlung zangbo suture southern tibet extensive field investigations along the yarlung zangbo suture zone in southern tibet reveal the presence of now fragmented remnants of a south facing intra oceanic subduction system this system developed within tethys during the cretaceous the associated arc forearc ophiolite and subduction complex were emplaced onto the leading edge of india at the end of the cretaceous rapid sedimentation in oblique slip basins and disruption of water saturated sediments into melange was widespread and concomitant with ophiolite emplacement we describe the tectonic entities that developed during this previously unrecognized phase of tethys tibet evolution and present a new model for the evolution of this portion of tibet

diatom response to changes in palaeoenvironments of the northern south china sea during the last 15 000 years changes in palaeoenvironments over the last 15000 years have been documented by a high resolution diatom record of core 17940 from the northern slope of the south china sea four diatom assemblage zones each characterized by different diatom components are distinguished by cluster analysis t nitzschioides var parval t nitzschioides t nitzschioides var parva tnp tnp tn and the brackish littoral species used as the proxies for temperature and salinity are compared with previously published sea surface temperature fp 12e sstw and sea surface salinity sss data from the same core and with the dongge cave delta 18 o record the bolling allerod warm phase the younger dryas cold event the holocene climate optimum and three holocene cooling events 7150 6250 4150 3450 and 1800 1350 cal yr bp are clearly distinguished by changes in the abundance of the brackish littoral species and or in tnp tnp tn data a marked increase in the abundance of the coastal species paralia sulcata during the interval 11150 8050 cal yr bp indicates a strong coastal water influence probably due to both enhanced freshwater discharge from the pearl river and the opening of the taiwan strait this palaeoceanographic change might be caused partly by climate induced sea level lowering during the late pleistocene and the early holocene the palaeoceanography during most of the holocene appears to be primarily controlled by fluctuations in the east asian summer monsoon intensity c 2009 elsevier b v all rights reserved

holocene vegetation zonation in the eastern sahara recent discoveries of fossil bearing holocene lake sediments from the eastern sahara have brought further confirmation and detail to earlier indirect evidence that a major pluvial episode occurred between 9 500 and 4 500 yr bp1 3 the botanical results mainly palynological show that savanna and desert grassland occupied regions that today are plantless hyperarid deserts we present here the first evidence from the entire saharan region of a latitudinal zonation of holocene vegetation extending across a 500 km wide belt in north west sudan we have completed detailed pollen analyses of three of the several sites discovered so far and the salient features from two the northernmost and the southernmost are presented here to demonstrate a steep gradient of past vegetative cover

the northern suture pakistan margin of a cretaceous island arc the northern suture is a fault separating the cretaceous kohistan island arc terrain northwest himalayas from palaeozoic sediments of the asian plate to the north the kohistan arc includes volcanic and sedimentary rocks andesitic lavas tuffs volcaniclastics slates and limestones metamorphosed to greenschist facies and intruded by the two phase kohistan batholith asian continental margin sediments are mainly of shelf type are variably metamorphosed and intruded by the karakoram batholith the northern suture is a zone of melange from 150 m to 4 km wide and contains blocks of volcanic greenstone limestone red shale conglomerate quartzite and serpentinite in a slate matrix it has a strong planar fabric but in many places bedding is preserved in blocks and matrix and depositional rather than tectonic contacts are seen between the two the melange is inferred to be an olistostrome largely derived from the kohistan arc formed in a small back arc basin between kohistan and asia limestone blocks in the melange are dated as aptian albian post tectonic intrusions yield radiometric ages from 111 to 62 ma the northern suture therefore probably formed in the early late cretaceous during closure of the back arc basin the tethys ocean lay south of kohistan where the main mantle thrust represents the westward continuation of the indus tsangpo suture

a 6000 year record of ecological and hydrological changes from laguna de la leche north coastal cuba abstract laguna de la leche north coastal cuba is a shallow 3 m oligohaline 2 0 4 5 coastal lake surrounded by mangroves and cattail stands a 227 cm core was studied using loss on ignition pollen calcareous microfossils and plant macrofossils from 6200 to 4800 cal yr bp the area was an oligohaline lake the period from 4800 to 4200 cal yr bp saw higher water levels and a freshened system these changes are indicated by an increase in the regional pollen rain as well as by the presence of charophyte oogonia and an increase in freshwater gastropods hydrobiidae by 4000 cal yr bp an open mesohaline lagoon had formed an increase in salt tolerant foraminifers suggests that water level increase was driven by relative sea level rise the initiation of laguna de la leche correlates with a shift to wetter conditions as indicated in pollen records from the southeastern united states e g lake tulane this synchronicity suggests that sea level rise caused middle holocene environmental change region wide two other cores sampled from mangrove swamps in the vicinity of laguna de la leche indicate that a major expansion of mangroves was underway by 1700 cal yr bp

effects of syn pandemic fire reduction and reforestation in the tropical americas on atmospheric co2 during european conquest abstract a new reconstruction of late holocene biomass burning in the tropical americas is consistent with the expansion of fire use by mesoamerican and amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years bp the marked reduction of biomass burning after 500 years bp a unique feature of the fire history of the tropical americas relative to other regions of the globe is synchronous with the collapse of the american indigenous population during pandemics accompanying european conquest we predict that fire reduction contemporaneous with pandemics in the tropical americas was associated with massive forest regeneration on 5 105 km2 of land and sequestration of 5 10 gt c into the terrestrial biosphere which contributed to the 2 global reduction in atmospheric co2 levels and the 0 1 increase in 13c of atmospheric co2 from 1500 to 1750 a d this study 1 builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14c dates to resolve features of the late holocene biomass burning record in the tropical americas and 2 corroborates the hypothesis advanced by ruddiman ruddiman w f 2003 the anthropogenic era began thousands of years ago climatic change 61 261 293 ruddiman w f 2005 plows plagues and petroleum princeton university press princeton new jersey that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric co2 concentration during the past millennium

a 43 ka record of paleoenvironmental change in the central american lowlands inferred from stable isotopes of lacustrine ostracods we present a continuous ostracod isotope 18o and 13c record from lake peten itza peten guatemala in the northern lowland neotropics that spans the last 43 cal ka bp variations in oxygen and carbon isotopes closely follow lithologic variations which consist of alternating gypsum and clay deposits that were deposited under relatively dry and wet climate respectively during the last glacial period the greatest 18o and 13c values coincide with gypsum deposited during lake lowstands under arid climate conditions that were correlated previously with north atlantic heinrich events in contrast interstadials and the entirety of the last glacial maximum 24 19 cal ka bp are marked by clay deposition and lower 18o and 13c values reflecting higher lake levels and relatively moister climate isotope results and pollen data along with independently inferred past water levels show the early deglacial period 19 15 cal ka bp was the time of greatest aridity and lowest lake stage of the past 43 ka this period occurred during heinrich stadial 1 hs 1 when an extensive tropical megadrought has been postulated stager et al 2011 heinrich stadial 1 is represented by two episodes of gypsum precipitation and high 18o and 13c values in peten itza interrupted by an intervening period of lower 18o and 13c and clay deposition centered on 17 cal ka bp the two periods of inferred maximum cold and or arid conditions at 17 5 and 16 1 cal ka bp coincide approximately with two pulses of ice rafted debris ird recorded off southern portugal bard et al 2000 at 15 cal ka bp coinciding with the start of the bolling allerod period 18o and 13c decrease and gypsum precipitation ceases indicating a transition to warmer and or wetter conditions gypsum precipitation resumed while 18o and 13c increased at the start of the younger dryas at 13 1 cal ka bp and continued until 10 4 cal ka bp near the onset of the holocene precipitation changes during the last glacial period in the northern hemisphere neotropics were closely linked with freshwater forcing to the high latitude north atlantic and sensitive to changes in the location of meltwater input climate was coldest driest when meltwater directly entered the high latitude north atlantic permitting sea ice expansion and weakening of atlantic meridional overturning circulation amoc which resulted in a more southerly position of the intertropical convergence zone itcz upon deglaciation when meltwater was directed to the gulf of mexico at 17 ka and during the bolling allerod period 15 13 ka precipitation increased in the northern hemisphere neotropics as north atlantic sea ice retreated and the itcz shifted northward results from lake peten itza offer some support for the meltwater routing hypothesis of clark et al 2001

recovery of the forest ecosystem in the tropical lowlands of northern guatemala after disintegration of classic maya polities we employed paleolimnological methods to investigate tropical forest recovery and soil stabilization that followed abandonment of agricultural systems associated with disintegration of classic maya polities ca a d 800 1000 we used lithological geochemical magnetic and palynological data from sediment cores of lake peten itza in the maya lowlands of northern guatemala sediment core chronology was developed using radiocarbon dates on terrestrial wood and charcoal fragments our results indicate that in the absence of large human populations and extensive farming activities peten forests recovered under humid climate conditions within a span of 80 260 yr soil stabilization postdates pollen evidence of forest regrowth stratigraphically and required between 120 and 280 yr we conclude that the tropical forest ecosystem in the watershed of lake peten itza had been reestablished by the early postclassic period a d 1000 1200

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

terrestrial impact structures impact structures are the dominant landform on planets that have retained portions of their earliest crust the present surface of the earth however has comparatively few recognized impact structures this is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere both of which serve to obscure and remove the impact record although not generally viewed as an important terrestrial as opposed to planetary geologic process the role of impact in earth evolution is now receiving mounting consideration for example large scale impact events may have been responsible for such phenomena as the formation of the earth s moon and certain mass extinctions in the biologic record the importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate impact is a highly transient high energy event it is inherently difficult to study through experimentation because of the problem of scale in addition sophisticated finite element code calculations of impact cratering are gen erally limited to relatively early time phenomena as a result of high com putational costs terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared these structures provide information on aspects of the third dimen sion the preand postimpact distribution of target lithologies and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave they also provide data for cratering rate estimates and in some cases on the nature of the impacting body in this review emphasis is placed on the nature of terrestrial impact structures the criteria for their identification and their contribution to

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

impacts of the ancient maya on soils and soil erosion in the central maya lowlands abstract many studies across the central and southern maya lowlands of belize guatemala honduras and mexico have produced records of land degradation mostly sedimentation and soil erosion during the ancient maya period from before 1000 bc to the maya collapse of c ad 900 this paper provides new data from two sites blue creek and cancuen synthesizes more than a decade of the authors research in guatemala belize and mexico and synthesizes other findings from this region these research projects analyzed more than 100 excavations in upland and depression sites cored lakes and wetland sediments and studied sediments in the field and laboratory using radiocarbon dating a battery of soil chemistry tests stratigraphic analysis magnetic susceptibility elemental analyses and artifact identification our objective was to date when sedimentation and soil erosion occurred identify stable surfaces and correlate them with the state of knowledge about past land use these findings indicate three general epochs of accelerated soil erosion and identified two major paleosols the three waves of soil erosion occurred in the preclassic period c 1000 bc to ad 250 the late classic ad 550 to 900 and in the last several decades the major paleosol eklu um in these sites is a well developed mollisol or vertisol that started forming in the early holocene and was buried in either the preclassic or classic periods ad 250 to 900 at some sites the eklu um paleosol lies beneath sediments with a fainter paleosol which in turn lies buried below classic period and later sediments this picture shows higher than expected soil erosion linked to the region s first pioneer farmers in the preclassic and less than expected soil erosion in the late classic when population peaked and land use was the most intensive in other regions like cancuen guatemala however most soil erosion occurred during the maya late classic ad 550 830 erosion here was intense but short lived depressions record 1 3 m of aggradation in two centuries a third epoch of accelerated soil loss and aggradation arose with the rapid land use changes brought by new pioneers during the last several decades

ancient maya impacts on the earth s surface an early anthropocene analog abstract the measure of the mayacene a microcosm of the early anthropocene that occurred from c 3000 to 1000 bp comes from multiple late quaternary paleoenvironmental records we synthesized the evidence for maya impacts on climate vegetation hydrology and the lithosphere from studies of soils lakes floodplains wetlands and other ecosystems maya civilization had likely altered local to regional ecosystems and hydrology by the preclassic period 3000 1700 bp but these impacts waned by 1000 bp they altered ecosystems with vast urban and rural infrastructure that included thousands of reservoirs wetland fields and canals terraces field ridges and temples although there is abundant evidence that indicates the maya altered their forests even at the large urban complex of tikal as much as 40 of the forest remained intact through the classic period existing forests are still influenced by ancient maya forest gardening particularly by the large expanses of ancient stone structures terraces and wetland fields that form their substrates a few studies suggest deforestation and other land uses probably also warmed and dried regional climate by the classic period 1700 1100 bp a much larger body of research documents the maya impacts on hydrology in the form of dams reservoirs canals eroded soils and urban design for runoff another metric of the mayacene are paleosols which contain chemical evidence for human occupation revealed by high phosphorus concentrations and carbon isotope ratios of c 4 species like maize in the c 3 dominated tropical forest ecosystem paleosol sequences exhibit maya clays a facies that reflects a glut of rapidly eroded sediments that overlie pre maya paleosols this stratigraphy is conspicuous in many dated soil profiles and marks the large scale maya transformation of the landscape in the preclassic and classic periods some of these also have increased phosphorous and carbon isotope evidence of c 4 species we synthesize and provide new evidence of maya period soil strata that show elevated carbon isotope ratios 13 c indicating the presence of c 4 species in typical agricultural sites this is often the case in ancient maya wetland systems which also have abundant evidence for the presence of several other economic plant species the mayacene of c 3000 to 1000 bp was thus a patchwork of cities villages roads urban heat islands intensive and extensive farmsteads forests and orchards today forests and wetlands cover much of the maya area but like so many places these are now under the onslaught of the deforestation draining and plowing of the present anthropocene

paleoenvironmental evidence for first human colonization of the eastern caribbean abstract identifying and dating first human colonization of new places is challenging especially when group sizes were small and material traces of their occupations were ephemeral generating reliable reconstructions of human colonization patterns from intact archaeological sites may be difficult to impossible given post depositional taphonomic processes and in cases of island and coastal locations the inundation of landscapes resulting from post pleistocene sea level rise paleoenvironmental reconstruction is proving to be a more reliable method of identifying small scale human colonization events than archaeological data alone we demonstrate the method through a sediment coring project across the lesser antilles and southern caribbean paleoenvironmental data were collected informing on the timing of multiple island colonization events and land use histories spanning the full range of human occupations in the caribbean from the initial forays into the islands through the arrival and eventual domination of the landscapes and indigenous people by europeans in some areas our data complement archaeological paleoecological and historical findings from the lesser antilles and in others amplify understanding of colonization history here we highlight data relating to the timing and process of initial colonization in the eastern caribbean in particular paleoenvironmental data from trinidad grenada martinique and marie galante guadeloupe provide a basis for revisiting initial colonization models of the caribbean we conclude that archaeological programs addressing human occupations dating to the early to mid holocene especially in dynamic coastal settings should systematically incorporate paleoenvironmental investigations

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

shock metamorphic features in quartz grains from the saarijarvi and soderfjarden impact structures finland shock metamorphic features at the saarijarvi d 2 km and soderfjarden d 6 5 km structures in finland have so far only been studied tentatively although both are considered to be proven impact structures this work presents the first detailed universal stage study of planar deformation features pdfs feather feature lamellae ffl and planar fractures pfs in quartz grains from a polymict impact breccia dike from soderfjarden and from sedimentary crater fill rocks from saarijarvi planar microstructures particularly pdfs are very rare and poorly developed or preserved in saarijarvi whereas in soderfjarden they are much more common and well defined miller bravais indices of the planar microstructures in both saarijarvi and soderfjarden are indicative of relatively low shock pressure but high shear conditions only compatible with an impact origin for these structures although a proterozoic age for saarijarvi cannot be ruled out the observations of shock features throughout the sedimentary crater fill sequence and a brecciated sedimentary dike below the crater floor are more consistent with a lower cambrian or younger impact age

biochronological continuity of the paleogene sediments of the himalayan foreland basin paleontological and other evidences abstract the paleontological and field evidences presented in the paper demonstrate a biochronological continuity from the marine subathu late thanetian to middle lutetian through the passage beds late lutetian to middle bartonian to the dagshai and equivalent formations late bartonian to rupelian of the himalayan foreland basin east of hazara kashmir syntaxis a similar continuity has also been demonstrated in the sulaiman range based on an assignment of oligocene age to the bugti vertebrate fauna hitherto considered to be of early miocene age thus the concept of a 10 ma hiatus in the foreland basin based on 40 ar 39 ar dates of single detrital muscovite grains from the supposed basal dagshai arenite is no longer tenable while the occurrence of cr spinel and k t boundary nannoplanktons in the subathu formation and passage beds indicate a westerly northwesterly provenance that of the radiolarian chert in the dagshai and coeval formations indicates a northerly provenance from the indus suture zone coinciding with the first influx of the himalayan detritus around 40 ma

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

a holocene vegetation history from lowland guatemala a 5 45 m core from lake peten itza lowland guatemala contains a near complete record of holo cene sedimentation the age depth relationship for the core is based on ams 14c dating of terrestrial wood fragments and provides a reliable chronology in this karst region where hard water lake error has typically confounded sediment geochronology in the basal part of the sequence pollen of the moraceae urticaceae group dominate indicating the presence of widespread tropical forest during the early holocene c 8600 5600 yr bp relative abundance of pollen of high forest taxa declined beginning as early as 5600 yr bp indicating climatic drying or perhaps initial land clearance deforestation by prehistoric mayan inhabitants is documented clearly in the pollen record beginning about 2000 yr bp 106 cal bc 122 cal ad 95 4 2 sigmas by the appearance of disturbance taxa e g ambrosia and poaceae and presence of zea forest regrowth occurred following the classic maya collapse c ad 900 as reflected by

late holocene human impact and environmental change inferred from a multi proxy lake sediment record in the loja region southeastern ecuador abstract late holocene human impact and environmental changes were reconstructed from a sediment core of the laguna daniel alvarez 2200 m asl located on the outskirts of the city of loja southeastern ecuador palaeoenvironmental changes were investigated by pollen spore algae and charcoal analysis in combination with x ray fluorescence xrf scanning and element analysis of 13c total organic carbon toc total nitrogen tn and radiocarbon dating this multi proxy study provides in detail the settlement history in the inner andean dry valley in southern ecuador over the last ca 1400 years between 630 and 1470 ad zea mays was intensively cultivated around the studied lake by the native palta culture in the loja region after ca 1470 ad z mays cultivation collapsed accompanied by an increase in fallow vegetation such as mimosa and poaceae probably as a result of the inca invasion and occupation from 1463 to 1531 ad in southern ecuador after ca 1570 ad amaranthaceae chenopodiaceae markedly increased reflecting the beginning of the spanish conquest in 1531 ad loja became spanish and during the first ca 100 years of the spanish regime loja developed into the fortified capital of the province in the 17th century crop growing strongly declined due to the diminished indigenous population that probably suffered from new diseases introduced by the spanish invaders pinus and eucalyptus as well as plantago lanceolata were introduced in the loja region about 220 years ago

sensitivity of bulk sedimentary stable carbon isotopes to prehistoric forest clearance and maize agriculture the stable carbon isotope compositions d 13 c of tropical lake sediments and soils have been used to reconstruct the occurrence of prehistoric maize cultivation and its relative importance through time this study assesses some of the possible variables affecting the response of lake sediment bulk organic carbon isotope d 13 ctoc values to variations in the scale of prehistoric maize cultivation and the potential of this proxy to yield quantitative estimates of the scale of prehistoric maize agriculture in small tropical watersheds high resolution analyses of d 13 ctoc values maize pollen concentrations and mineral influx were conducted on sediments deposited during a w220 year period of prehistoric maize agriculture in the watershed of laguna castilla a small lake in the mid elevations of the cordillera central dominican republic close correspondence between d 13 ctoc values and maize pollen concentrations in the laguna castilla sediment record indicates a close relationship between the isotopic values and the scale of prehistoric maize cultivation correlations between the d 13 ctoc signature and mineral influx indicate that the isotope record is also sensitive to variations in allochthonous carbon delivery this study establishes that sedimentary d 13 ctoc values can provide a highly sensitive proxy of the spatial scale of prehistoric maize agriculture in small tropical watersheds but

an 8700 year paleoclimate reconstruction from the southern maya lowlands abstract analysis of a sediment core from lago puerto arturo a closed basin lake in northern peten guatemala has provided an 8700 cal year record of climate change and human activity in the southern maya lowlands stable isotope magnetic susceptibility and pollen analyses were used to reconstruct environmental change in the region results indicate a relatively wet early to middle holocene followed by a drier late holocene which we interpret as reflecting long term changes in insolation precession higher frequency variability is more likely attributable to changes in ocean atmosphere circulation in both the north atlantic and the pacific oceans pollen and isotope data show that most of the period of prehispanic agricultural settlement i e 5000 1000 cal yr bp was characterized by drier conditions than previous or subsequent periods the presence of zea corn pollen through peak aridity during the terminal classic period 1250 1130 cal yr bp suggests that drought may not have had as negative an impact as previously proposed a dramatic negative shift in isotope values indicates an increase in precipitation after 950 cal yr bp hereafter bp