the pliocene and quaternary of the high plain of bogota colombia a history of tectonic uplift basin development and climatic change abstract the high plain of bogota in the eastern cordillera of colombia represents a large tectonic basin that is filled with hundreds of metres of lacustrine and fluvial sediments in the centre of the basin the sediment sequence attains a thickness of nearly 600 m and covers a time span of the last 3 ma late pliocene quaternary still older sediments of mainly fluvial origin cover the adjacent mountain slopes the age of these sediments reaches back into the late miocene to 6 ma and older the sediment sequence of the bogota area has been the subject of extensive stratigraphical and palynological studies for decades the results of these studies have provided a unique picture of the pliocene quaternary geological history of a tropical montane region three main factors have influenced the evolution of the landscape sedimentation and vegetation development these are the tectonic uplift of the andes between ca 5 and 3 ma the development of the large tectonic sedimentary basin of bogota after ca 3 5 ma and the quaternary climatic fluctuations and glaciations starting shortly after ca 2 7 ma

paleoelevation records from lipid biomarkers application to the tropical andes new results from two novel lipid biomarker based proxies help to constrain the late cenozoic surface elevation history of the eastern cordillera in the tropical northern andes of colombia previous well known studies have suggested rapid latest miocene pliocene 6 3 ma uplift on the basis of an abrupt shift in pollen species assemblages within sedimentary basin fill of the elevated bogota plateau from resampling of these original study localities we provide a revised chronology based on magnetic polarity stratigraphy and we evaluate paleotemperatures using the mbt cbt indices methylation of branched tetraethers cyclization of branched tetraethers and hydrogen isotopic composition d of leaf waxes as two independent proxies of past surface elevation reconstructed paleotemperatures from the mbt cbt proxy show a more gradual cooling trend from ca 7 6 ma to present consistent with less than 1000 m of elevation gain since latest miocene pliocene time and in agreement with geologic evidence for accelerated shortening and exhumation at this time the leaf wax isotopic data on the other hand lack a systematic trend potentially due to fractionation changes associated with uplift induced turnover in floral populations such changes could obscure isotopic variations in meteoric water suggesting that leaf wax isotopic compositions may not provide a direct proxy for elevation in this particular situation involving uplift in a heterogeneous tropical environment more promising in this case is the mbt cbt proxy which may offer a suitable alternative to carbonate based paleoelevation proxies in tropical regions where year round high precipitation rates prevent formation of soil carbonates

pollen based biome reconstructions for the past 450 000 yr from the funza 2 core colombia comparisons with model based vegetation reconstructions abstract the 586 m funza 2 sequence from the high plain of bogota colombia has provided one of the longest pollen based vegetation reconstructions in the world affinity scores to seven biomes are compared to the record of co2 fluctuation from the vostok ice core for the period spanning from approximately 25 000 to 450 000 yr before present bp results are compared to output from the biome 3 vegetation model run under different environmental scenarios at regional and local scales the model is run with temperature and precipitation reductions relative to the present values of up to 10 c and 700 mm yr 1 respectively for this particular investigation we are interested in the role of co2 as a forcer of vegetation change we run the model with concentrations of atmospheric co2 co2 atm within the range of 170 to 340 ppmv during glacial periods the cool grass shrubland biome is highly dominant less so during interglacial periods when the cool evergreen and cool mixed forest biomes become co dominant in addition to this climate driven altitudinal oscillation of the vegetation there is also a signal that indicates longer term evolution of the vegetation the cool grass shrubland and cool evergreen and cool mixed forest biomes become co dominant for the first time over the 450 000 yr record at approximately 170 000 yr bp become completely anti phase during a period of extreme low co2 atm and then become co dominant from approximately 120 000 yr bp until the core top just prior to the last glacial maximum the model results for the funza area indicate that changes in co2 atm temperature and precipitation are inter linked by the vegetation response a shift of 5 5 c is required to lower the cool grass shrubland biome to altitudes about the funza catchment where the andean forest biome dominant at low co2 atm concentrations particularly below 180 ppmv the composition of the high latitudinal tropical vegetation about the funza catchment changed it is suggested that this low co2 atm combined with a period when the climate was characterised by extreme cooling and drying caused a readjustment of the tropical high altitudinal vegetation zonation and the formation of plant communities that are presently recorded

influence of diel biogeochemical cycles on carbonate equilibrium in a karst river abstract variations in temperature photosynthesis and respiration force diel variations in ph and dissolved co 2 concentrations of surface streams possibly controlling carbonate equilibrium between river water and carbonate stream beds diel cycles of water chemistry and 13 c of dissolved inorganic carbon dic were measured to assess how biogeochemical processes affect dissolution and precipitation of calcite and thus channel development in ichetucknee river a large spring fed river discharge 6 m 3 s flowing over carbonate karst terrain in north central florida usa samples were collected at a 4 h sampling interval during two one week periods and at a 1 h interval during a single 24 h period simultaneously temperature ph dissolved oxygen do and no 3 concentrations were measured using in situ sensors at 15 min or 1 h intervals ca 2 dic and no 3 concentrations decreased during the day and increased at night causing diel changes of in stream specific conductivity these changes were inversely related to diel changes in ph pco 2 and do concentrations this work shows that photosynthesis and respiration of subaquatic vegetation are the dominant processes influencing in stream diel variation during the day a simultaneous increase of 13 c dic and decrease in dic indicates that photosynthesis was the primary control on dic concentrations calcite saturation indices ranged from 0 to 0 5 with the highest value in daylight as a result of co 2 consumption causing carbonate precipitation the water remained saturated with respect to calcite at night and 13 c dic values decreased indicating that co 2 production from ecosystem respiration was the dominant process affecting dic concentrations but was insufficient to induce significant carbonate dissolution at night outgassing maintained in stream dic concentrations lower than the supersaturated dic springs source but a drop in 13 c dic indicates that ecosystem respiration had a dominant influence over outgassing although co 2 outgassing occurs it is shown to be a minor component of the dic mass balance while carbonate precipitation represents 88 of dic loss these results indicate that in stream biological processes influence carbonate mineral diagenesis in large clear water rivers

active mountain building along the eastern colombian subandes a folding history from deformed terraces across the tame anticline llanos basin active crustal shortening and surface uplift are vividly expressed in the foothills of the eastern cordillera of colombia quaternary alluvial fan and terrace deposits are folded and uplifted tens to hundreds of meters above the local base level recording deformation and incision of the landscape we used geomorphic observations and structural analysis from a 300 km 2 three dimensional seismic reflection survey over an actively growing anticline to investigate the relationship between finite shortening and surface uplift and its effects on landscape evolution a quantitative description of finite shortening of the pregrowth strata from excess area and line length calculations were compared with uplift and shortening estimates obtained from geomorphic strain markers dated using in situ 10 be cosmogenic nuclide depth profiles this combined approach provides the first estimates of quaternary surface uplift and horizontal shortening rates along the foothills of the northeastern colombian andes finite shortening for the tame anticline was calculated using two different approaches excess area shortening varies from 530 36 m 2 at its southern end decreasing northward to 404 72 m 2 whereas line length shortening is typically an order of magnitude smaller using the maximum horizontal shortening our results for the tame anticline reveal a quaternary uplift rate of 2 8 1 5 mm yr and a shortening rate of 2 1 1 2 mm yr 2 with the older terraces located at the highest elevations and recording the highest rotation from the horizontal indicating growth by limb rotation based on these rates the initiation of folding is estimated to be 0 25 0 09 0 05 ma 2 we hypothesize that the discrepancy between shortening estimates from line length and excess area calculations can be reconciled by accounting for internal deformation likely developed during the initial stages of folding which can be represented by strain hardening for example the shortening rates we obtain are comparable to geodetically derived shortening rates but are slightly lower than long term geologic shortening rates slower shortening rates and the presence of a youthful structure at the thrust front suggest that the orogen has been migrating eastward since the late pleistocene probably due to reorganization of a supercritical thrust wedge farther west in the hinterland to attain critical taper

last glacial maximum and hypsithermal in the southern hemisphere abstract a synthesis of the two contrasting climates of the upper quaternary in the southern hemisphere based on continental geological indicators suggests that the antarctic anticyclone is the most important climatic system in the hemisphere according to glaciological and oceanographic studies the antarctic anticyclone covered an area in the lgm that was double of that during the hypsithermal this phenomenon produced a consequent shifting of the climatic belts by approximately 10 of latitude to the north in the lgm and a migration to the south during the hypsithermal oceanic and continental anticyclones were active systems in shaping climates in south america australasia and southern africa these structures were enhanced throughout the lgm provoking generalized droughts and weakened at the hypsithermal permitting more rains in tropical latitudes the results presented here were obtained by integrating our own results with regional and continental syntheses of other authors the paleoclimatic proposals are amply validated by more than 1500 dates in the four continents geological and geomorphological features such as dunefields paleosols fluvial terraces and lake levels were the main tools employed in the work

late pleistocene glacial sequence in the area of the high plain of bogota eastern cordillera colombia abstract four main glacial events could be reconstructed on the basis of morphologic and 14c evidence in the parano regions surrounding the high plain of bogota eastern cordillera colombia in the area four distinct morainic levels were recognized between ca 2750 3000 m and ca 3750 m radiocarbon dates in combination with climatological data derived from palynological evidence indicate that morainic complex 4 was formed between ca 13 000 12 400 yr b p complex 3 between ca 18 000 14 000 yr b p complex 2 between ca 22 500 19 500 yr b p whereas complex 1 may be of middle last glacial age or of penultimate glacial age the spatial distribution of moraines throughout the area clearly shows that limits of former glacier systems were strongly influenced by local climatological conditions

chronostratigraphy and correlation of the pliocene and quaternary of colombia abstract names for the chronostratigraphic units of the pliocene and quaternary of colombia are defined and formalized based on studies of outcrops and deep bore holes in the area of the high plain of bogota chronostratigraphic biostratigraphic and lithostratigraphic sequences have been correlated as far as possible a tentative correlation with the marine oxygen isotope stratigraphy is indicated pliocene chronostratigraphic units are provisionally characterized by abundance first appearance in the pollen record of specific floral elements mauritia zone tequendamian ca 5 5 4 2 ma hedyosmum zone facatativanian ca 4 2 3 5 ma myrica zone sisganian ca 3 5 3 1 ma borreria zone chocontanian ca 3 1 2 7 ma and engativanian ca 2 7 2 4 2 2 ma although precise boundaries cannot yet be established the engativanian is a transitional phase characterized by a continuous temperature decrease in successive cold episodes and may include the latest part of the pliocene and the earliest part of the quaternary quaternary chronostratigraphic units are precisely limited by levels of pronounced climatic change these boundaries are near to the first appearance abundance of juglans plantago funzanian ca 2 4 2 2 1 0 ma alnus fuchanian ca 1000 660 ka and cotanian ca 660 335 ka and quercus subanian ca 335 128 ka bacatanian ca 128 73 ka fuquenian ca 73 10 ka and the holocene the relationship with the officially defined position of the base of the quaternary at ca 1 80 ma is shown the last glaciation in colombia is named the cocuy glaciation

absolute chronology of the pliocene quaternary sediment sequence of the bogota area colombia abstract a revised geochronological framework is presented for the sequence of unconsolidated sediments present in the bogota area eastern cordillera colombia this is based on 11 fission track dates on zircons that were obtained both from exposed ash layers and from a series of ashes from the funza ii borehole which reached 586 m below the surface of the high plain the 3 dates obtained from the exposed ash layers provide control for the older part of the sequence 6 2 5 ma the 8 dates from the funza ii core give control for the younger part of the sequence 3 0 ma acceptance of these new fission track dates on volcanic zircons means that many of the tephra dates obtained from the funza i core that included fission track dates on glass shards and k ar dates using the mineral fractions in the ashes published in 1984 are rejected it also confirms earlier climate stratigraphical dating the neogene quaternary sediments of the bogota area span a period of at least the last 6 ma the fluvial lacustrine sediment record registers major tectonic uplift of the eastern cordillera for the period between 5 and 3 ma the development of the large sedimentary basin of bogota after 3 5 ma with an important phase of tectonic adjustment at about 1 ma and a long period of strong climatic fluctuations that started shortly after 2 7 ma

neogene and quaternary development of the neotropical rain forest the forest refugia hypothesis and a literature overview abstract the upheaval of the northern andes in miocene and pliocene time changed the drainage system in northern south america significantly and caused the present day rain forest areas of choco and the lower magdalena valley became separated from amazonas plant diversity may have reached the highest level in the miocene or pliocene and excessive present day phytodiversity may be regarded as a legacy of the tertiary rather than an evolutionary product of the quaternary in the quaternary strong temperature oscillations related to the series of ice ages were superposed on the late tertiary forest dynamics which included river displacement and latitudinal migrations of the equatorial rain belt caloric equator with the rhythm of the precession cycle of orbital climate forcing the hypothesis that claims a permanent rain forest cover all over the amazon basin during the last glacial is in contrast with the forest refugia hypothesis which accepts replacement of rain forest by savanna or savanna forest during dry climatic intervals both scenarios have been evidenced by pollen records in this paper it is suggested that both hypotheses are not necessarily conflicting and apparently did occur in different parts of the amazon basin and in different periods depending on the climatological constraints a compilation of the most important literature concerning the vegetational climatic and environmental history of the rain forest areas of amazonas and choco and surrounding dry ecosystems has been included

quaternary and upper pliocene glaciations and forest development in the tropical andes evidence from a long high resolution pollen record from the sedimentary basin of bogota colombia pollen analysis of 1230 samples from a 357 m long core of lake sediments from the sedimentary basin of bogota eastern cordillera colombia alt 2550 m above sea level has provided a high resolution record of changes in the andean vegetation belts and long range climatic fluctuations during the last 3 5 ma direct time control is provided by k ar datings and fission track datings of 14 intercalated volcanic ash layers the resulting pollen diagram has been divided into 55 pollen zones representing 27 complete major climatic cycles glacial interglacial cycles a tentative correlation with the marine oxygen isotope chronology and the european stratigraphical climatic subdivision could be established the altitudinal position of the forest line which corresponds with the 9 5 c isotherm shifted between minimal c 1700 1800 m and maximal c 3400 3700 m alt at present situated at c 3100 m alt which rendered the altitudinal position of the high plain of bogota the dry bed of a former lake at 2550 m a sensitive recorder of temperature changes the estimated fluctuations in mean annual temperature at the level of the high plain of bogota are from 15 c a distinct change in the nature of the climatic cycles occurs around 2 5 ma b p the interval of 3 5 2 5 ma b p shows high frequency low amplitude climatic oscillations whereas the last 2 5 ma is characterized by low frequency high amplitude climatic oscillations with a superposed high frequency oscillation it is assumed that these oscillations correspond mainly with the variations in orbital eccentricity and obliquity the major constituents making up the andean forest have been subjected to considerable changes in the course of time in the early pliocene forests vallea and myrica are prominent elements weinmannia was almost absent the role of polylepis in the timberline forests increased markedly around 3 1 ma b p and also migrated by adaptation from the upper andean forest line to higher elevations the closure of the isthmus of panama during the pliocene enabled northern hemisphere elements to migrate into south america alnus reached the area of bogota around 2 7 ma b p and dramatically changed the vegetation especially on the flats around the lake of bogota where alnus swamp forests replaced myrica carr around 2 9 ma b p weinmannia became an important constituent of the upper andean forest but slightly later slope forests of alnus replaced parts of the area which had previously been covered by weinmannia forest the marked role of vallea in the andean forest diminished definitively after 2 5 ma b p quercus migrated more recently to south america and reached the area of bogota 1 ma b p it changed for the last time drastically the aspect of the andean forest all palynologically recognizable elements of the modern andean forest were present from now on and the subsequent adaptation and speciation of quercus and many other elements must have mainly taken place at the species level

palaeomagnetic stratigraphy of pliocene continental deposits of the bolivian altiplano abstract fluvio lacustrine post miocene deposits of the bolivian altiplano have been sampled in 400 m of section in the la paz and avo avo basins in order to provide a magnetostratigraphic scheme for chronostratigraphic interpretations stable characteristics components were isolated after stepwise af or thermal demagnetizations the directions of cleaned magnetization were compared to the normal and reverse dipole field directions at the site the plot of the mean directions calculated for each stratigraphic level define successive magnetozones which can be identified on the standard geomagnetic polarity scale with the help of the k ar ages obtained on tuff layers the deposition of the middle and upper part of the la paz formation covers the gauss epoch the gauss matuyama 2 48 ma and the gilbert gauss 3 4 ma limits are located in the top and the middle of the formation the occurrence of the first glacial interglacial oscillation can be placed in the early matuyama ca 2 2 ma in agreement with the oxygen isotopic record from the equatorial ocean

middle and late quaternary vegetational and climatic history of the paramo de agua blanca eastern cordillera colombia abstract the results of a palynological study of a 13 m deep bore hole of lake deposits from the paramo de agua blanca colombian eastern cordillera 5 n elev 3250 m are reported by means of 14 c dates and an indirect dating method based on pollen densities it was possible to provide the pollen diagram with an approximate time scale the section representing some 465 000 years gives a continuous record of the middle and late pleistocene and holocene vegetational and climatic sequences the sequence of glacial and interglacial periods in combination with their age and duration according to the indirect time determinations could be tentatively correlated with the european chronostratigraphic sequence

magnetic polarity and fission track chronology of a late pliocene pleistocene paleoclimatic proxy record in the tropical andes abstract two sections exposing a late pliocene pleistocene sedimentary sequence in the marginal valleys of the bogota basin colombian andes south america were sampled for paleomagnetic analysis magnetostratigraphy and fission track dates of tephra beds provide a detailed geochronologic calibration for the sedimentary basin measurements of magnetic susceptibility complement the regional environmental record provided by lithological and palynological evidence sedimentation in the bogota basin started in the early part of the gauss chron at ca 3 2 myr the oldest recorded sediments belong to the guasca member of the upper tilata formation they were deposited in a lacustrine paludal environment near the end of the tectonic uplift in the bogota area and or under pliocene climatic conditions that were warmer than today repeated climate cooling associated with glaciations in the surrounding mountains resulted in the deposition of a fluvial lacustrine complex referred to as the subachoque formation the first glaciation is placed near the gauss matuyama polarity reversal at 2 6 myr a lithologic change in the subachoque formation marked by coarser grained fluvial deposits and a possible increase in amplitude of the magnetic susceptibility signal occurs near the matuyama brunhes boundary at 0 8 myr indicating a shift toward higher magnitude climate oscillations

a possible submarine volcano near the central part of ninety east ridge indian ocean abstract floating pumice masses have been observed several times near the central part of ninety east ridge indian ocean in 1879 and in 1883 the author is of the opinion that the source of these pumice masses cannot have been the volcano krakatau in the sunda strait as has been suggested earlier by other authors but that they originated in situ examples of floating pumice observed over submarine volcanoes lying at depths of 1500 m or even more are mentioned briefly by other authors suggesting that eruptions in deep water may indeed lead to its formation the suspected submarine volcano may coincide with an elongated but rather flat elevation a little north of the central part of ninety east ridge the center of this elevation is located approximately at 6 05 s 89 10 e a roughly nw se profile of this area shows the presence of this shield like feature very near the site where floating pumice was seen on three occasions the inferred submarine volcanic center is lying within the belt of heat flow anomaly called belt i a particular hot spot with an unusually high heat flow value 7 61 hfu is located southeast of the feature in question the heat flow values measured in belt i are well above the world average this belt may be the result of the presence of linearly arranged magma chambers at a relatively shallow depth probably within the oceanic crust this belt has a length of 1100 km the seismic activity of the area investigated is similarly remarkable numerous powerful shocks have taken place there belt i represents the axis of the seismic zone extending from points b to c fig 5 the seismic belt is regarded as a zone of weakness within which fractures can originate permitting rock melts to emerge from depth towards the surface

the beginning of the ice age in europe and its major subdivisions abstract the time range of the quaternary is discussed in terms of the view that this period is essentially the one in the earth s history in which during certain intervals inland ice developed in the northern hemisphere this process first became evident about 2 3 ma bp since then the quaternary thus defined has witnessed many climatic variations although for practical reasons it is not feasible to assign the status of stage to each distinclty warm or cold phase climatic change is nevertheless the most appropriate basis for world wide correlation it seems possible to use both climatic change and other correlation parameters to arrive at a practicable subdivision of the quaternary period into stages before about 1 ma vegetational succession during interglacials in western europe differed from that seen in later times a possible cause for this divergence is discussed in the later part of the quaternary after about 1 ma two distinct types of warm temperate intervals occurred one associated with high sea levels and an oceanic climate the other showing lower sea levels and a cooler and more continental climate the difference between these two types is shown by comparison of the distribution of abies during these time intervals

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de