Macrofossil Evidence Research Articles

No snow in the mountains: Early Eocene plant fossils from Hotham Heights, Victoria, Australia

An Early Eocene plant assemblage from near the summit of Mt Hotham, Victoria, is described, using a combination of macro- and microfossils, especially cuticles. This is important since no other Australian macrofossil sites from this time, when environmental conditions are believed to have been the warmest of the Cenozoic, have been described in detail. The nature of the flora and vegetation supports geological evidence that the site was upland (approximately 800 m above sea level) at this time, with climatic conditions similar to those now experienced in regions such as the Atherton Tablelands in Queensland and mid-montane Papua New Guinea. The vegetation was probably a form of rainforest dominated by mesotherm elements, with abundant ferns including Gleicheniaceae and the tree ferns Cnemidaria, Cyathea and Dicksonia. Gymnosperms included Araucariaceae (Agathis) and Podocarpaceae (at least Acmopyle and Dacrydium). Angiosperms were diverse in Lauraceae (at least nine species including probably Cryptocarya, Endiandra and Litsea) and Proteaceae (at least nine species including probably Musgravea and Darlingia). Other angiosperms included Cunoniaceae, Gymnostoma (Casuarinaceae), Diospyros-like Ebenaceae, and the vine Cissocarpus (Vitaceae). Nothofagus was rare or absent from the Mt Hotham region at this time, as no macrofossil evidence was found, and pollen percentages were very low.

Late Glacial and early Holocene environment in the middle Lahn river valley (Hessen, central-west Germany) and the local impact of early Mesolithic people?pollen and macrofossil evidence

The Late Glacial to early Holocene river valley landscape of the middle Lahntal in Hessen, central-west Germany, is reconstructed by means of pollen and macrofossil analyses. AMS 14 C dating combined with pollen, macrofossil and geomorphological mapping pro- vide a detailed chronology of the floodplain sediments of the river Lahn. Archaeological evidence for early Mesolithic settlements in the middle Lahntal is backed up by pollen and macrofossil evidence, which indicates an increase in light demanding plants, together with ones indicating nutrient-rich and disturbed environments and more macroscopic charcoal and charred pieces of pine. Different phases of human impact were dated; a first phase was dated at ca. 9,270 uncal b.p. and a second phase at ca. 9,120 uncal b.p. Comparison of the palynological data from different fluvial channel fills demonstrates that during this second phase, between ca. 9,120-8,700 uncal b.p., there were several cycles of woodland clearance. The outcome of combined archaeological, palynological and macrofossil data is discussed in terms of the impact of early Mesolithic people using fire on the vegetation during the early Holocene in the middle Lahntal.

The importance of plant macrofossils in the reconstruction of Lateglacial vegetation and climate: examples from Scotland, western Norway, and Minnesota, USA

Lateglacial and early Holocene (ca 14–9000 14C yr BP; 15–10,000 cal yr BP) pollen records are used to make vegetation and climate reconstructions that are the basis for inferring mechanisms of past climate change and for validating palaeoclimate model simulations. Therefore, it is important that reconstructions from pollen data are realistic and reliable. Two examples of the need for independent validation of pollen interpretations are considered here. First, Lateglacial-interstadial Betula pollen records in northern Scotland and western Norway have been interpreted frequently as reflecting the presence of tree-birch that has strongly influenced the resulting climate reconstructions. However, no associated tree-birch macrofossils have been found so far, and the local dwarf-shrub or open vegetation reconstructed from macrofossil evidence indicates climates too cold for tree-birch establishment. The low local pollen production resulted in the misleadingly high percentage representation of long-distance tree-birch pollen. Second, in the Minnesotan Lateglacial Picea zone, low pollen percentages from thermophilous deciduous trees could derive either from local occurrences of the tree taxa in the Picea/Larix forest or from long-distance dispersal from areas further south. The regionally consistent occurrence of low pollen percentages, even in sites with local tundra vegetation, and the lack of any corresponding macrofossil records support the hypothesis that the trees were not locally present. Macrofossils in the Picea zone represent tundra vegetation or Picea/Larix forest associated with typically boreal taxa, suggesting it was too cold for most thermophilous deciduous trees to grow. Any long-distance tree pollen is not masked by the low pollen production of tundra and Picea and Larix and therefore it is registered relatively strongly in the percentage pollen spectra. Many Lateglacial pollen assemblages have no recognisable modern analogues and contain high representations of well-dispersed ‘indicator’ taxa such as Betula or Artemisia. The spectra could have been derived from vegetation types that do not occur today, perhaps responding to the different climate that resulted from the different balance of climate forcing functions then. However, the available contemporaneous plant-macrofossil assemblages can be readily interpreted in terms of modern vegetation communities, suggesting that the pollen assemblages could have been influenced by mixing of locally produced pollen with long-distance pollen from remote vegetation types that are then over-represented in situations with low local pollen production. In such situations, it is important to validate the climate reconstructions made from the pollen data with a macrofossil record.

Efstadalsvatn – a multi-proxy study of a Holocene lacustrine sequence from NW Iceland

Multi-proxy data, both lithostratigraphic and biostratigraphic, are presented from Efstadalsvatn, a lake in NW Iceland. The sequence covers the period 10,000 to 3500 14C yr B.P. The biostratgraphic data include the first Icelandic chironomid-based reconstruction of Holocene mean July air temperatures, using a Norwegian training set in the absence of modern Icelandic data. The results show that deglaciation and ecosystem development probably began before 10,000 14C yr B.P. and that July temperatures were around 4°C at ca. 9500 14C yr B.P. Temperatures then rose to ca. 8°C at the time of the deposition of the Saksunarvatn tephra (9100 14C yr B.P.), reaching ca. 10°C by 8500 14C yr B.P., high enough for the growth of tree birch, although successful birch colonisation did not take place until 6750 14C yr B.P. There is some evidence for cooling immediately preceding 9100 14C yr B.P. There is little firm biostratigraphic evidence for the 8200 cal. B.P. event, although this may be due to a relatively low resolution pollen sampling interval, but there are changes at this time in the total carbon (TC) and mass susceptibility (MS) data. Optimal temperatures and relative vegetation stability may have occurred between 8000–6100 14C yr B.P. but the chironomid assemblages indicate higher temperatures after 5000 14C yr B.P. This latter interpretation may, however, reflect delayed colonisation of thermophilous taxa and requires further investigation. There is evidence in the lithostratigraphy for greater local terrestrial instability after 6100 14C yr B.P. but it seems unlikely that this led to the redevelopment of ice in the catchment. The biostratigraphic records appear to show a degree of resistence to climate forcing throughout the early and middle Holocene. The new chironomid-based temperature reconstruction needs to be refined by further studies in Iceland, particularly the development of an Icelandic training set, but has already demonstrated the problems of paleoclimatic interpretations based on pollen and/or macrofossil evidence alone.

Late Holocene environmental changes inferred from diatoms in a lake on the western Taimyr Peninsula, northern Russia

Changes in the diatom assemblages preserved in a sediment core taken from a small lake located north of arctic treeline on the western Taimyr Peninsula, Russia, were examined in order to investigate late Holocene (i.e., ca 5000 cal yr BP to present) climatic and environmental changes within the region. Early diatom assemblages were dominated by benthic Fragilaria taxa and indicate a transitional phase in the lake history, most likely reflecting lake development and environmental change associated with treeline retreat to the south of the study site. Concurrent with pollen and macrofossil evidence of a vegetation shift to shrub tundra in the catchment basin at ca 4200 cal yr BP, an increase in cold-water taxa, followed by little change in diatom assemblages until ca 2800 cal yr BP, suggests that conditions were relatively cool and stable at this time. The last ∼2000 years of the Middendorf Lake record have been marked by fluctuating limnological conditions, characterized by striking successional shifts between Fragilaria pinnata and Aulacoseira distans var. humilis. Recent conditions in Middendorf Lake indicate an increase in diatom taxa previously rare in the record, possibly associated with twentieth-century climatic warming. The Middendorf Lake record indicates that significant limnological change may occur in the absence of catchment vegetation shifts, suggesting late-Holocene decoupling of aquatic and terrestrial responses to climatic and hydrological change. Our study results represent one of the few paleoecological records currently available from northern Russia, and highlight the need for further development of calibration data sets from this region.

Paleoecology of a Northern Michigan Lake and the Relationship among Climate, Vegetation, and Great Lakes Water Levels

We reconstructed Holocene water-level and vegetation dynamics based on pollen and plant macrofossils from a coastal lake in Upper Michigan. Our primary objective was to test the hypothesis that major fluctuations in Great Lakes water levels resulted in part from climatic changes. We also used our data to provide temporal constraints to the mid-Holocene dry period in Upper Michigan. From 9600 to 8600 cal yr B.P. a shallow, lacustrine environment characterized the Mud Lake basin. A Sphagnum-dominated wetland occupied the basin during the mid-Holocene dry period (∼8600 to 6600 cal yr B.P.). The basin flooded at 6600 cal yr B.P. as a result of rising water levels associated with the onset of the Nipissing I phase of ancestral Lake Superior. This flooding event occurred contemporaneously with a well-documented regional expansion of Tsuga. Betula pollen increased during the Nipissing II phase (4500 cal yr B.P.). Macrofossil evidence from Mud Lake suggests that Betula alleghaniensis expansion was primarily responsible for the rising Betula pollen percentages. Major regional and local vegetational changes were associated with all the major Holocene highstands of the western Great Lakes (Nipissing I, Nipissing II, and Algoma). Traditional interpretations of Great Lakes water-level history should be revised to include a major role of climate.

The Mesolithic and Neolithic landscapes of Barfield Tarn and Eskmeals in the English Lake District: some new evidence from two different wetland contexts

The evidence from two wetland contexts, submerged forests and valley sediments, are described and discussed. The case is made for re-interpretation of aspects of the late Mesolithic site at Eskmeals whilst late Neolithic cultivation in the vicinity of Barfield Tarn is confirmed. Comparison is made between the pollen and macro-fossil evidence and two late Neolithic crops, emmer and flax, are identified, whilst diatoms provide evidence of environment and sediment source. The overall conclusions are that within the study area the period was one of rapid coastal and landscape change and that, because much of the information in this study did not come from traditional archaeological sites, it is necessary to review the type of data held in SMRs and sites evaluated in the planning process.

The earliest archaeological maize (Zea mays L.) from highland Mexico: new accelerator mass spectrometry dates and their implications.

Accelerator mass spectrometry age determinations of maize cobs (Zea mays L.) from Guilá Naquitz Cave in Oaxaca, Mexico, produced dates of 5,400 carbon-14 years before the present (about 6,250 calendar years ago), making those cobs the oldest in the Americas. Macrofossils and phytoliths characteristic of wild and domesticated Zea fruits are absent from older strata from the site, although Zea pollen has previously been identified from those levels. These results, together with the modern geographical distribution of wild Zea mays, suggest that the cultural practices that led to Zea domestication probably occurred elsewhere in Mexico. Guilá Naquitz Cave has now yielded the earliest macrofossil evidence for the domestication of two major American crop plants, squash (Cucurbita pepo) and maize.

The history of Cunoniaceae in Australia from macrofossil evidence

The macrofossil record of the plant family Cunoniaceae in Australia is summarised and reviewed where necessary by using detailed studies of the morphology of extant genera. Eleven of the 26 Cunoniaceae genera are represented in the Australian macrofossil record and include leaves and leaf fragments, foliar cuticle and reproductive structures, and range from Late Paleocene to Quaternary in age. Macrofossils show that some genera had a different or more widespread distribution in Australia during the Cenozoic, with two genera (Weinmannia and Codia) having become extinct from the continent. Changes in climate, including increasing cold, frost, dryness, seasonality, or some combination of these, or a reduction in vegetation disturbance regimes (e.g. volcanism, uplifting, landslips), may be implicated in the regional or continental extinctions demonstrated by the macrofossil record. Many extant genera (Schizomeria, Vesselowskya, Callicoma, Ceratopetalum, Acsmithia, Codia) had evolved by the Early Oligocene or earlier (Eucryphia, Late Paleocene; Ceratopetalum, Middle Eocene), perhaps with generic diversification more or less complete by the end of the Early Cenozoic or earlier. A Cretaceous origin of the family is possible, and may account for its widespread distribution on Southern Hemisphere landmasses, although long-distance dispersal events are required to explain some modern geographic disjunctions.

Last Interglacial and Devensian deposits of the River Great Ouse at Woolpack Farm, Fenstanton, Cambridgeshire, UK

This paper describes Pleistocene fluvial deposits of the River Great Ouse at Woolpack Farm, Fenstanton, Cambridgeshire, UK. These sediments consist of a basal gravel, fossiliferous fluviatile muds, sands and gravels later disturbed and formed into a diamicton, and overlying gravels. The regional climate inferred from palaeobotany, Mollusca, Coleoptera and vertebrates from the diamicton indicates temperate conditions. Coleopteran evidence suggests a mean July temperature of ca. 21°C, 4°C warmer than today in eastern England, and winter temperatures a little colder than at present. Molluscan assemblages indicate a slight brackish influence during deposition of the muds which form the diamicton. The gravel succession is represented by three members which have a broad distribution in the Great Ouse Valley, and which were laid down in a braided river under periglacial conditions. The occurrence of permafrost is indicated by the presence of ice wedge casts in the gravels. The pollen and macrofossil evidence from the diamicton suggests correlation with Ipswichian substage IpII ( Pinus– Quercetum mixtum – Corylus phase). The basal gravel is of pre-Ipswichian age. A Devensian age is proposed for the overlying gravels and their attendant periglacial phenomena.

The Allerød-Younger Dryas pollen zone boundary in an 800-year varve chronology from southeastern Sweden

This is the first pollen stratigraphical investigation of late Weichselian deposits in the area which was situated close to the late Weichselian Fennoscandian ice sheet margin and the Baltic Ice Lake shore during the Allerød-Younger Dryas climatic transition. Pollen analyses were carried out on varved clay sequences, covering a time span of 350 years of an AMS radiocarbon-dated 800-year varve chronology, and on two lacustrine sequences. The Allerød-Younger Dryas pollen zone boundary has been defined at the local varve year 2000. The pollen zone boundary coincides with an apparent drop of AMS radiocarbon ages from c. 11,000 to 10,800-10,600 14C years BP. The Allerød, Younger Dryas, and Preboreal climatic events are distinguished in the pollen records of the lacustrine sites. Pollen and macrofossil evidence and AMS radiocarbon dates at these sites indicate that the area was deglaciated during the Allerød. Soon after the deglaciation Betula pendula/pubescens immigrated. At the Allerød/Younger Dryas transition the vegetation changed to a herb tundra indicating cooler and/or drier conditions. The Younger Dryas/Preboreal boundary is characterised by a vegetation change from a herb tundra to a park tundra with tree birch. Later in the Preboreal the vegetation became more dense and was dominated again by Betula pendula/pubescens.

Non‐analogous tree flora in the Scandes Mountains, Sweden, during the early Holocene ‐ macrofossil evidence of rapid geographic spread and response to palaeoclimate

Early‐Holocene occurrences of broad‐leaved temperate tree species at a site now within the subalpine belt of the Swedish Scandes are reported and analysed. Macrofossil remains (fruits and leaves) of Alnus glutinosa, Corylus avellana, Quercus robur and Ulmu.s glahra were recovered in a peat deposit far beyond and above their modern distributional limits. A previous nearby finding of Tilia cantata adds to this group of Hemiboreal lowland species, the regional presence of which in high‐elevation northern Scandinavia has gone entirely unrecognized by pollen stratigraphical studies. Radiocarbon dates (AMS) range between 8500 and 8000 BP, indicating early and rapid spread, closely following the ice recession. Maximum tree species richness and distributional limits (latitude and altitude) were attained during the earliest part of the Holocene. In a regional perspective, the temperate trees coexisted with a dominant boreal (cold‐climate) element, viz. Pinus sylvestris, Bclulu pubescens ssp. tortuosa, Betula pendula, Alnus incana, Picea ahies and Larix sibirica, which are all identified and dated from macrofossils. This climatically seemingly incompatible assemblage is without modern analogues. Presumably, this diverse tree flora owed its existence to a unique (Holocene perspective) climatic regime, ultimately forced by the Milankovitch cycles of insolation. The results strengthen previous palaeoclimatic inferences based on past tree‐limit positions (Pinus sylvestris) and imply that Holocene summer warmth peaked fairly soon after the regional deglaciation, practically concurrently with the solar radiation maximum. Important questions are raised concerning several palynologically derived postulates within general palaeobiogeography. For example, rates of geographic tree spread are not necessarily individualistic, despite fundamentally different dispersal modes. The emergent efficiency of dispersal suggests that distribution patterns relate to climate and soil factors rather than time. Dispersal steps may have been fairly large, and the resultant geographic spread was epidemic, resulting in a sparse pattern of outlying stands, rather than sequentially following certain routes in the landscape. Rapid geographic expansion is likely to have been relatively unrestrained by physical barriers, e.g. mountain ranges, seas and large lakes. Even in Central Europe, close to the ice margin, there may have been more trees during the latest glaciation than previously realized.

Pre‐mission invasion of Erodium cicutarium in California

Abstract. The California grassland is dominated by alien plant species. It is generally assumed that the invasion of aliens began with the initial introduction of livestock by Spanish missionaries in 1769. In this paper we present pollen evidence which indicates that Erodium cicutarium, a Mediterranean annual, was well established in the Santa Barbara region several years before the founding of the first California mission at San Diego in 1769. Historical evidence shows that it took the Spanish nearly a decade to develop a livestock base in California. Disturbance by livestock was therefore not a necessary prerequisite for invasion by alien plants. Historical and macrofossil evidence indicates that E. cicutarium invaded California from Baja California.

Early-Holocene vegetation of northern Iceland: pollen and plant macrofossil evidence from the Skagi peninsula

Pollen and plant macrofossil records from two lakes on northernmost Skagi peninsula, northern Iceland, reflect a progressive closing of the vegetation cover during the early Holocene. This development was connected with the succession from an initial herb-tundra phase characterized by Oxyria digyna, Poaceae and Caryophyllaceae, through an intermediate dwarf-shrub phase dominated by Salix and Empetrum nigrum,toa shrub and dwarf-shrub phase with Juniperus communis, Betula nana, Salix and Poaceae. This development is similar to that recorded at other sites in northern Iceland, both with respect to the taxa involved and the timing of transitions between successional phases, which suggests that early-Holocene vegetational development in northern Iceland was forced by broad-scale climatic changes. The palaeobotanical data suggest a gradual early-Holocene warming in northern Iceland, which probably was connected with northward displacements of Atlan tic waters and North Atlantic air masses. The deposition of the Saksunarvatn ash at 9000 BP caused a transitory phase of vegetational succession on northernmost Skagi.

The Late Devensian Lateglacial palaeoenvironmental record from Whitrig Bog, SE Scotland. 1. Lithostratigraphy, geochemistry and palaeobotany

This is the first of a series of articles presenting the results of a multi‐proxy investigation aimed at reconstructing changes in the ecosystem and climate of Whitrig Bog, SE Scotland, during the last glacial‐inter‐glacial transition (Devensian Lateglacial, c. 14–10 ka BP). We present here the results from sediment lithology, chemistry, pollen, and plant macrofossil analyses. These data are used to infer the nature of the local catchment soils and both local and regional terrestrial vegetation. The interstadial period (c. 13–11 ka BP) is characterized by a successional sequence developing from a landscape with bare, poorly developed minerogenic soils supporting a sparse herbaceous flora into open birch woodland with juniper scrub and stable organic soils. At c. 11 ka BP the Younger Dryas climatic cooling event caused an abrupt reversion to an open herbaceous arctic/alpine flora (e.g. macrofossil evidence of Silene furcata and Oxyria digyna) and high levels of minerogenic erosion into the basin, indicating environmental response to a cold Arctic climate. In addition to this Younger Dryas climatic reversal, two lesser reversion episodes occurred earlier during the interstadial. The more pronounced of the two, late in the intersladial, is characterized by high levels of erosion and a change from birch/juniper woodland to an open herbaceous flora. The older oscillation occurs approximately mid‐way through the interstadial sequence and is marked by similar pollen changes, albeit shorter lived and more subtle.

Hydrologic and climatic implications of a multidisciplinary study of late Holocene sediment from Kenosee Lake, southeastern Saskatchewan, Canada

Sediment lithology and mineralogy, as well as ostracode, plant macrofossil and stable isotope stratigraphies of lake sediment cores, are used to reconstruct late Holocene hydrologic changes at Kenosee Lake, a relatively large, hyposaline lake in southeastern Saskatchewan. Chronological control is provided by AMS radiocarbon ages of upland and shoreline plant macrofossils. All indicators outline an early, low-water, saline phase of lake history (4100–3000 BP), when the basin was occupied by a series of small, interconnected, sulfate-rich brine pools, as opposed to the single, topographically-closed lake that exists today. A rapid rise in lake-level (3000–2300 BP) led to the establishment of carbonate-rich, hyposaline lake conditions like those today. Lithostratigraphic data and ostracode assemblages indicate peak salinities were attained early in this period of lake infilling, suggesting that the lake-level rise was initially driven by an influx of saline groundwater. Lake-level and water chemistry have remained relatively stable over the last 2000 years, compared to earlier events. Because of a lack of datable organic material in sediments deposited during the last 2000 years, the chronology of recent events is not well resolved. Plant macrofossil, lithostratigraphic and ostracode evidence suggests that lake draw-down, accompanied by slightly higher than present salinites, occurred sometime prior to 600 BP, followed by peak lake-level and freshwater conditions. This most recent high lake stand, indicative of a high water table on the surrounding upland, may also have led to the establishment of an extensive cover of Betula in the watershed, possibly in response to paludification. Ostracode assemblages indicate that peak freshwater conditions occurred within the last 100 years. Since historically documented lake-level fluctuations correlate with decadal scale climatic fluctuations in the meteorological record, and late-Holocene hydrologic dynamics correspond to well documented climatic excursions of the Neoglacial and Little Ice Age, Kenosee Lake dynamics offer insight into the susceptibility of the region's water resources to climate change.

Analysis of pollen contained in middens from the white mountains and volcanic tableland of Eastern California

Abstract The pollen from five packrat middens from the White Mountains region of California were analyzed and compared to previously analyzed macrofossils from the same middens. The middens span the time from ca. 20,000 yr B. P. to the middle Holocene. While there are similarities in the pollen and macrofossil data, there are some subtle differences between the two types of data. The pollen data would support the macrofossil evidence that indicates the arrival of Pinus by the early Holocene. In spite of this general agreement, the pollen evidence suggests that Pinus was not common in the vicinity of the early Holocene midden sites. The results of this study would indicate the importance of using both the macrofossil and pollen evidence from packrat middens.

Distinguishing fossil Betula nana and B. pubescens using their wingless fruits: implications for the late-glacial vegetational history of western Norway

Principal components analysis of 7 size and shape variables measured on 154 modern fruit bodies of Betula species and hybrids shows that B. pubescens and B. nana can be distinguished from each other on the basis of their fruit bodies, and that B. pubescens ssp. tortuosa and hybrids either fall within the range of B. pubescens or have an intermediate position on PCA axes 1 and 2. Passive positioning on the modern PCA axes of fossil fruit bodies from late-glacial sediments at Eigebakken, south-west Norway, shows that only B. nana was locally present in the Allerod. This contradicts earlier inferences from pollen analyses alone of birch woodland development in the Allerod in south-west Norway. There is no macrofossil evidence for tree-birches in the Allerod near Eigebakken. The relatively large amounts of Betula pollen, including B. pubescens, at Eigebakken are thus probably derived by long-distance transport from tree-birches in Denmark, south Sweden, and Britain, whose presence is proved there by macrofossils. Consequently, earlier estimates of mean July temperature during the Allerod in southwestern Norway should be reduced to around 7.5–10°C. In contrast, the PCA shows that fruit bodies from Holocene sediments at Eigebakken and at Krakenes, western Norway, are mostly derived from B. pubescens. Birch trees were able to spread quickly and effectively across Norway in the early Holocene.

Mid-Holocene Hemlock Decline in Eastern North America Linked with Phytophagous Insect Activity

Macrofossil evidence indicates that the mid-Holocene hemlock [Tsuga canadensisL. (Carr.)] decline that occurred over a wide area in eastern North America was associated with phytophagous insect activity.In situhemlock macrofossils and insect remains found in a paludified dunefield at the northern limit of hemlock testify that two defoliation events occurred at 4910 ± 90 and 4200 ± 100 yr B.P., respectively. The sharp coincidence of remains from hemlock needles with chewing damage typical of hemlock looper feeding, head capsules from the hemlock looper (Lambdina fiscellaria) and the spruce budworm (Choristoneura fumiferana), absence of hemlock fruiting remains, and tree-ring anomalies in fossil hemlocks that died prematurely (<165 yr) suggest that defoliation affected hemlock reproductive capacity and pollen productivity, or more likely caused mass mortality. Our findings indicate that defoliation can affect ecosystems for centuries, especially when long-lived tree species are involved.

Palynology and paleobotany of the Early Pliocene section Río Frío 17 (Cordillera Oriental, Colombia): biostratigraphical and chronostratigraphical implications

Organic-rich sediments of section Río Frío 17 (3165 m altitude, Cordillera Oriental, Colombia) were analyzed for pollen and plant macrofossils. Time control is based on fission-track dating of zircon from an intercalated tephra with an age of 5.3 ± 1.0 Ma. Pollen and macrofossil spectra of several outcrops and cores, including section Río Frío 17, reveal gradually cooler depositional environments during the Neogene. Obvious differences between modern and Pliocene Andean vegetation belts are taken into account. The sequence of outcrops reflects the final uplift of the Cordillera Oriental. Pollen and macrofossils of section Río Frío 17 suggest that lower subandean (lower part of lower montane belt) to tropical lowland conditions prevailed in the area during the Early Pliocene: sediment deposition occurred apparently at c. 1000 m elevation. If Pliocene average temperatures were comparable to present-day values with an amplitude of ± 3°C, an altitudinal shift of 500 m maximum is suggested. Hence sedimentation is estimated to have occurred at 1500 m elevation maximally, based on the fossil plants and the present-day ecological requirements of their extant relatives. The remaining difference in elevation is attributed to tectonic uplift by at least 1700 m. The macrofossil evidence and the presence of Hedyosmum pollen suggest that the sediments of section Río Frío 17 should be placed in Biozone II, instead of Biozone I of the biostratigraphical zonation for the high plain of Bogotá as suggested by Helmens and Kuhry (1990). The arrival of Hedyosmum in the pollen record and the final uplift of the high plain of Bogotá is now estimated at c. 5.3 ± 1.0 Ma. The age of the sediments of sections Salto de Tequendama I and II (Biozone I), estimated as Early Pliocene by Van der Hammen et al. (1973), is earlier than that date. Selected plant macrofossils, such as seeds and fruits, are described and illustrated.