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

,• ELS EV IER

Review of Palaeobotany and Palynology 92 (1996) 329-350

REVIEW OF PALAEOBOTANY AND PALYNOLOGY

Palynology and paleobotany of the Early Pliocene section Rio Frio 17 (Cordillera Oriental, Colombia)" biostratigraphical and chronostratigraphical implications Vincent M. Wijninga Hugo de Vries-Laboratory, Department of Palynology and Paleo/Aetuo-ecology (The Netherlands Centrefor Geo-ecological Research, ICG), Universityof Amsterdam, Kruislaan 318, 1098 SM Amsterdam, The Netherlands Received 9 May 1995; revised and accepted 13 October 1995

Abstract

Organic-rich sediments of section Rio Frio 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 Rio Frio 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 Rio Frio 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 Rio Frio 17 should be placed in Biozone II, instead of Biozone I of the biostratigraphical zonation for the high plain of Bogotd as suggested by Helmens and Kuhry (1990). The arrival of Hedyosmum in the pollen record and the final uplift of the high plain of Bogot~i 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.

I. Introduction

The N e o g e n e - Q u a t e r n a r y sediment sequence in the area o f the high plain o f Bogot~t (Cordillera Oriental, C o l o m b i a ) was palynologically studied by e.g. Van der H a m m e n and Gonz~lez (1960), Van der H a m m e n (1961, 1966), Van der H a m m e n et al. (1973), H o o g h i e m s t r a (1984), Helmens 0034-6667/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0034-6667(95)00102-6

(1990), H o o g h i e m s t r a and R a n (1994), and H o o g h i e m s t r a and Cleef (in press). These studies record the vegetational history o f the area since the Neogene. Pollen f r o m strata rich in organic material suggest sediment deposition at increasing higher elevations when c o m p a r e d to the m o d e r n altitudinal vegetation distribution (Van der H a m m e n et al., 1973). Pollen assemblage changes

330

~ M. W(]ninga/Review o f Palaeobotany and Palynology 92 (1996) 329 350

correlated with depositional conditions suggest a transition from warm tropical to cool Andean (upper montane vegetation) and are taken as evidence for the final uplift of the Cordillera Oriental in the Pliocene.

The present study contributes to the understanding of the development of the Andean flora during the Miocene and Pliocene as it reflects the uplift of the Cordillera Oriental. The exposed sediments of the section Rio Frio 17 form part of the

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V.M. Wijninga/Review of Palaeobotany and Palynology 92 (1996) 329-350

Neogene-Quaternary sediment sequence in the area of the high plain of Bogot~i. The section is located in the Rio Frio valley in the northwestern part of the high plain of Bogotfi (Fig. 1), where its sediments are exposed along the main road from Bogotfi to Pacho in a depression on the western main water divide at 3165 m elevation. Based on pollen and macrofossil data, the environmental conditions prevailing around 5.3+ 1.0 Ma are deduced and discussed, and the altitude of sediment deposition. During this period, the chronostratigraphical and biostratigraphical consequences for other Neogene sediments on the high plain of Bogotfi are evaluated.

II c..o o ][ STRATIGRAPHY

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STRATIGRAPHY-

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vii VI

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upper subandean

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2. Geology, biostratigraphy and chronostratigraphy The geological and tectonic history of the area of the high plain of Bogot~i has been studied by Btirgl (1957), Hubach (1957), Van der Hammen (196!), Julivert (1961, 1963), Van der Hammen et al. (1973), Fabre (1983), Helmens (1990), and Helmens and Van der Hammen (1994); for details the reader is referred to these studies. An overview of the chronostratigraphy, lithostratigraphy, and biostratigraphy of the Neogene-Quaternary sediment sequence is shown in Fig. 2. Temperate arboreal taxa from North America (Myrica, Alnus, and Quereus) and the southern South American taxa (Weinmannia, Hedyosmum) immigrated into the area of the present-day high plain of Bogotfi during the Neogene and Quaternary (Van der Hammen et al., 1973). These taxa are prolific pollen producers and their pollen is well dispersed, making these taxa excellent biostratigraphical markers. The presence of these taxa and the general composition of the pollen assemblages in the sediments from the high plain of Bogotfi prompted Van der Hammen et al. (1973) to propose a biostratigraphical framework of 7 biozones for the late Tertiary-Quaternary sediments (Fig. 2). Time control for the sediment sequence in Fig. 2 is provided by fission-track datings on zircon from intercalated tephras (Andriessen et al., 1993). The following section gives a concise description of the distinguished biozones.

Hedyosmum

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tropical lowland

Fig. 2. Compilationof the chrono-, litho-, and biostratigraphy of the Neogene-Quaternarysedimentsin the area of the high plain of Bogot~i (Cordillera Oriental, Colombia) (after Helmens, 1990). The sediments belonging to Biozone I were deposited under tropical lowland conditions during the Middle (?) Miocene (Wijninga, 1996a). The palynological biomarkers Hedyosmum, Myrica, Alnus and Quercus are absent from Biozone I sediments, although sporadic occurrences of Hedyosmum were reported in the Salto de Tequendama sections I and II (Wijninga, 1996a). The start of the Hedyosmum pollen record and plant assemblages characteristic of lower subandean to tropical lowland conditions and Andean to subandean climatic conditions characterize Biozone II (Van der Hammen et al., 1973; Wijninga and Kuhry, 1990; Wijninga, 1996b). Biozone II includes two fission-track dates of 5.3+ 1.0 and 3.7+0.5 Ma. Biozone III is characterized by the first occurrence of Myrica pollen, and upper subandean to lower Andean plant

332

V.M. Wijninga/Reviewof Palaeobotany and Palynology 92 (1996) 329-350

assemblages (Van der Hammen et al., 1973; Wijninga and Kuhry, 1993). Biozone III represents the last phase of the uplift. The lower part of Biozone IV is characterized by Andean pollen assemblages and includes a fission-track date of 2.7_+0.6 Ma. Biozones IV (upper part) to VII are characterized by alternating paramo and Andean forest assemblages, reflecting Pleistocene climatic change (Van der Hammen et al., 1973; Hooghiemstra and Ran, 1994; Hooghiemstra and Cleef, in press). Biozone VI begins with the first occurrence of Alnus in the pollen record, around 1 Ma ago. The base of Biozone VII is characterized by the first occurrence of the record of Quercus at approximately 340,000 yr BP.

RIO FRIO 17 o~ depth (cm) 0

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3. Present vegetation The present-day vegetation in the Cordillera Oriental was studied by Cuatrecasas (1934, 1958), Van der Hammen and Gonzfilez (1960), Cleef (1981) and Sturm and Rangel (1985), among others. Cuatrecasas (1958) described for the first time the altitudinal vegetation belts in Colombia. In 1967 1968, Van der Hammen, Jaramillo and Murillo studied the phytosociology and floristics of the vegetation belts in the Colombian Cordilleras by means of vegetation transects. Based on their data, Cleef and Hooghiemstra (1984) described several vegetation types in the Cordillera Oriental. Fig. 4 shows a schematical cross-section of the Cordillera Oriental and the altitudinal distribution of the vegetation belts. The tropical lowland belt extends from sea level up to approximately 1000 m altitude. The mean annual temperature in this belt ranges from 24 to 30°C. Rain forest is present if mean annual precipitation exceeds 1500 mm and edaphic conditions are favourable. If these conditions are not met, xerophytic, savanna or dry tropical woodland are found instead. Rain forest includes arboreal representatives of taxa such as Acalypha, Alchornea, Amanoa, Anacardium, Annona, Apocynaceae, Astrocaryum, Bactris, Bombacaceae, Cecropia, Cedrela, Clusia, Combretaceae, Croton, Euterpe, Faramea, Ficus, Flacourtiaceae, Guarea, Iriartea, Lauraceae, Lecythidaceae, Leguminosae, Malpigh-

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iaceae, Mauritia, Miconia, Moraceae, Myrtaceae,

Paullinia, Pouteria, Protium, Sacoglottis, Sapium, Solanaceae, Sterculiaceae, Symphonia, Tiliaceae, Vantanea, Virola, Vochysia and Warszewiczia. Savanna vegetation includes arboreal taxa such as Bowdichia, Byrsonima, Curatella, and Palicourea and ground cover consists principally of representatives of the Gramineae. The subandean forest belt lies between c. 1000 and 2300 (2500) m altitude. The annual precipitation is between 1200 and 4000 mm, the average annual temperature is from 16 to 24°C. Common taxa in the subandean forest include Acalypha,

E M. WUninga/Rev~w of Pa&eobomny and Pa~no&gy 92 (1996) 329-350

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Alchornea, Araliaceae, Billia, Cecropia, Cedrela, Clusia, Coussapoa, Croton, Eugenia, Ficus, Freziera, Hyeronima, Leguminosae, Malpighiaceae, Melastomataceae, Nectandra, Ocotea, Palmae, Proteaceae, Quercus, Solanaceae, Vismia and Warszewiczia. The Andean forest belt is found between 2300 (2500) and 3300 (3500) m altitude. Precipitation ranges from 1000 to 2500 mm/yr, and the average annual temperature is 9 to 16°C. C o m m o n taxa in this belt include Alnus, Bocconia, Clethra,

Clusia, Daphnopsis, Drimys, Escallonia, Eugenia, Freziera, Hedyosmum, Hesperomeles, Ilex, Melastomataceae, Myrica, Myrsine (formerly Rapanea), Oreopanax, Palmae, Podocarpus, Quercus, Solanaceae, Symplocos, Vallea, Viburnum and Weinmannia. The paramo belt occurs between 3300 (3500) and 4700 m elevation. The average temperature is between 0 and 9°C. The annual precipitation is 1000 to 3000 ram. The lower paramo, i.e. subparamo, is characterized by dwarf trees and shrubs. D w a r f shrub and bunchgrass vegetation is found in the grassparamo. In the superparamo belt, between 4200 and 4700 m elevation, the vegetation cover is scanty due to solifluction as a result of

frequent night frosts. Common taxa found in the subparamo, paramo and superparamo belts include representatives of Acaena, Aragoa, Arcythophyllum, Caryophyllaceae, Compositae (e.g. Diplostephium, Espeletia, Senecio), Ericaceae, Escallonia, Gramineae (e.g. Calamagrostis and representatives of Bambusoideae), Hypericum, Miconia, Myrica, Polylep& and Scrophulariaceae.

4. Material and methods

The three silty sand layers of section Rio Frio 17 were sampled; one sample was taken for pollen and macrofossil analyses from each of these layers. Large macrofossils were collected separately. In the laboratory pollen samples each with a volume of 4 cm 3 were treated with a boiling 10% aqueous Na-pyrophosphate solution, followed by acetolysis and gravity separation by means of a b r o m o f o r m alcohol mixture (specific density 2.0). Exotic Lycopodium spores were added to the sample to calculate pollen concentrations in the sediment. Two of the three pollen samples taken turned out to be barren. A volume of of 100cm 3 for the macrobotanical samples was treated with a 5% aqueous Na-pyrophosphate solution and subse-

334

ld M. Wijninga/Review of Palaeobotany and Palynology 92 (1996) 329 350

Table 1 List of taxa included in the pollen sum arranged after their ecological preference, reflecting the altitudinal vegetation belts in the Cordillera Oriental. Macrofossil taxa are arranged in groups reflecting their modern habitat preference Gramineae Andean forest belt Hedyosmum Ilex Symplocos Andean--subandean forest belt Melastomataceae Myrtaceae Podocarpus Proteaceae Subandean-tropical lowland forest belt A h'hornea Palmae Urticales Tropical lowland forest belt Amanoa Astrocaryum Bombacaceae lriartea cf. Macoubea (610) Macrolobium Mauritia Spatiphyllum Forest components Cecropia (T366) Cyatheaceae Freziera (T365) Sacoglottis (T377) Swamp taxa Compositae (T376) Cyperaceae cf. Evodianthus (T370) cf. Juncus (T375) Ludwigia Aquatic taxon Azolla Taxa with wide ecological range Melastomataceae (T367, T368, T369) Polypodiales

quently rinsed with water through a 150 ~m sieve. Percentage calculations and plotting of the diagrams were performed on an Apple Macintosh computer using POLLEN DIAGRAM (Duivenvoorden, 1992).

The results of the palynological and macrobotanical analysis of the sediments are shown in the pollen diagram (Fig. 5) and the macrofossil diagram (Fig. 6). The pollen diagram includes a cumulative diagram, a simplified lithological column and seperate counts for the recovered taxa. The cumulative diagram consists of ecological groups that reflect as accurately as possible the main composition of the regional vegetation in terms of altitudinal belts. The frequency of all pollen taxa was calculated as a percent of the pollen sum. The macrofossils were counted and expressed as absolute numbers per sample volume of 100 cm 3. Macrofossil taxa were grouped according to their modern ecological preference.

5. Results

5.1. Lithology Section Rio Frio 17 was described previously (Helmens, 1990). The main lithological characteristics of the sediments are repeated here (Fig. 3). The exposed sediments overlie steeply dipping bedrock of the Guaduas Formation of Maastrichtian Paleocene age. The lower part of the exposure consists of a graded fine gravel at the base with several brown silty sand layers above. The silty sand layers, which contain plant macrofossils, are overlain by two whitish clay layers with a greenish diatom-rich clay in between. The lower whitish clay and the diatom-rich clay layers are separated by a thin green silty volcanic ash layer. Gravels, up to c. 40cm in diameter, in a coarse sandy matrix overlie the upper whitish clay layer. The size and the number of the gravels gradually decrease towards the top of the exposure.

5.2. Description of the diagrams The pollen spectrum (Fig. 5) shows a dominance of subandean-tropical lowland taxa (35%). The proportion of taxa belonging to the tropical lowland, subandean and Andean forest belts is more or less equal (10 15%). Fern spores, including monolete psilate, monolete verrucate, and Cyatheaceae, are abundant with frequencies between 40 and 70%. Palmae psilate type, Palmae

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V.M. Wijninga/Review ~?/"Palaeobotany and Palynology 92 (1996) 329-350

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V.M. Wijninga/Review of Palaeobotany and Palynology 92 (1996) 329-350

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preticulate type, Iriartea, Gramineae, and Hedyosmum have moderate percentages. Other taxa, such as Amanoa, Spatiphyllum, Podocarpus, Ilex, and cf. Macoubea represented by low percent-

Palms, including Iriartea and Astrocaryum, and Cyatheaceae were important elements of the forest surrounding the site. Other arboreal components included Freziera, Cecropia, Bombacaceae,

ages, in general less than 5%. The macrofossil diagram (Fig. 6) is dominated by Freziera, and Ceeropia. Cf. Juneus, Compositae, and several types of Melastomataceae are recorded in low numbers. The two recorded endocarps of Saeoglottis are not included in the macrofossil diagram, because they were not found in one of the three macrofossil samples.

Hedyosmum, Podocarpus, Alehornea, Sacoglonis, cf. Macoubea, Macrolobium, and Mauritia. The numerous seeds of Cecropia and Freziera point to

6. Reconstruction of depositional environment and paleovegetation The rounded gravels and silty sand layers suggest deposition during periods of different stream flow regimes, whereas the clays, particularly the diatom-rich clay, indicate of deposition in a lacustrine environment. The lithofacies of the sampled interval of section Rio Frio 17 suggests that the recovered plant assemblages are most probably allochthonous, i.e. organic material was transported.

the local presence of these two genera close to the deposition site, although transportation over some distance is likely to have occurred. Polypodiales were also abundant and may have comprised the understory of the forest. Palmae, Cyatheaceae, Cecropia and Freziera include species with pioneer qualities, which are important constituents of secondary forests on disturbed sites, such as landslides (Tryon and Tryon, 1982; Gentry, 1993; KappeUe et al., 1994; Weitzman, pers. commun., 1993). The presence of cf. Juncus, Azolla, and Cyperaceae is evidence for the swamp vegetation that surrounded the deposition site.

7. Discussion The sediments of section Rio Frio 17 reveal a plant assemblage consisting of taxa from Andean,

340

V.M. Wijninga/Reviewof Palaeobotany and Palynology 92 (1996) 329 350

subandean and lowland forest belts. The altitude at the time of deposition may be inferred from the current altitudinal range of the recorded taxa. Sacoglottis, Astrocaryum, Amanoa, cf. Macoubea, Macrolobium, Spatiphyllum and Mauritia have tropical lowland affinities; the latter four taxa frequently occur under poorly drained conditions (Duivenvoorden and Lips, 1993; Urrego-G., 1994). At present Sacoglottis is restricted to altitudes below c. 1200 m elevation (Cuatrecasas, 1961), whereas the highest altitudinal record of Mauritia is 700 m (Fanshawe, 1952). Subandean and Andean vegetation is suggested by the presence of Hedyosmum, Podocarpus and Symplocos, which at present occur from sea level to approximately 3500 m elevation (Gentry, 1986; Todzia, 1988). These taxa most likely formed part of the montane forest on nearby slopes, and wind or streams carried their pollen to the deposition site. Streams draining elevated areas may carry substantial amounts of pollen of montane taxa to lowland sites (Crowley et al., 1994; Wijninga, 1996a). The macrofossils of Freziera and Cecropia might also have been transported by water, but over a shorter distance. Presumably both genera occurred relatively close to the deposition site. Although Freziera has a present-day altitudinal range comparable to the previous montane taxa, in this case Freziera is thought to have grown at the same elevation as the recorded tropical lowland taxa. At present a few species of Freziera occur in Venezuelan, mainly coastal, cloud forests at low elevation, e.g. 500-1000 m (Weitzman, pers. commun., 1993). The indicator value of Gramineae and Ilex pollen is poor as both taxa have a wide altitudinal range. Species of Ilex occur frequently in the Andean forest belt, but some are also known from swamp forests in the tropical lowlands (Duivenvoorden and Lips, 1993; Urrego-G., 1994). Gramineae are found in grassparamo, savanna and as part of floating meadows in the Amazon Basin. Because no other savanna or grassparamo taxa were recorded, Gramineae pollen might have originated from the swamp vegetation along the deposition site. Primarily, the find of Sacoglottis endocarps and the presence of other tropical lowland taxa show that, compared to present-day climatic and floral

conditions, the fossil pollen spectrum is indicative of a depositional elevation of approximately 1000 m. This elevation is close to the upper limit of the present-day tropical lowland belt and might explain the relative low contribution of tropical lowland taxa to the regional vegetation. Several studies indicate that in the Pliocene average tropical sea temperatures varied with an amplitude of _+3°C from present-day tropical marine temperature (Shackleton, 1982; Crowley and North, 1991; Tiedemann et al., 1994). Using a lapse rate of 6°C/1000 m (Meyer, 1991; Witte, 1994), the maximum altitude for sediment deposition of section Rio Frio 17 was 1500 m. Pollen assemblages from sediments older than those of section Rio Frio 17 show marked differences in composition, notably the dominance of tropical lowland taxa (Wijninga, 1996a). If temperature conditions were then the same as those during sediment deposition of section Rio Frio 17, uplift would have been some hundreds of meters. The substantial presence of pollen, spores, or macrofossils of Palmae, Cyatheaceae, Freziera and Cecropia in the sediments of section Rio Frio 17 suggests that secondary forest made up a considerable part of the regional forest. The presence of secondary forests point to instability of the landscape probably related to the first phase in the final uplift of the area. The coarse nature of the sediments of section Rio Frio 17 would be additional evidence for such an unstable landscape. The combined occurrence of Andean-subandean and subandean-tropical lowland forest taxa in section Rio Frio 17 may also be explained in two other ways. (1) The modern montane taxa, i.e. Freziera, Podocarpus and Hedyosmum, may have formed part of the tropical lowland-lower subandean forest. Under specific conditions, i.e. very wet and/or those found on soils poor in nutrients, these taxa are found below the Andean forest belt in which they occur at present-day (Freziera-Weitzman, pers. commun., 1993; Podocarpus-Torres-R., 1988; Gentry, 1986; Hedyosmum Gentry, 1986; Todzia, 1988). However, no evidence for such specific conditions was found in section Rio Frio 17. Moreover, the low quantities of Hedyosmum and Podocarpus

V.M. Wijninga/Review of Palaeobotany and Palynology 92 (1996) 329-350

pollen suggest that these two taxa stood relatively far away from the deposition site. In other cases, where Hedyosmum and Podocarpus occurred close to the deposition site, relatively high pollen percentages, ranging from 15 to 40%, were recorded (e.g. Wijninga and Kuhry, 1993; Wijninga, 1996b). (2) Possibly, the present-day tropical lowland taxa, e.g. Sacoglottis, cf. Macoubea and Mauritia, formed part of the subandean forest. This possibility cannot be completely ruled out, in which case the plant assemblage of section Rio Frio 17 might represent a subandean forest type. The tropical lowland taxa subsequently may have disappeared from the subandean forest during the course of the Pliocene and Quaternary. These two explanations were also put forward for the composition of the flora of section Subachoque 39 (Wijninga and Kuhry, 1990). The paleoflora of this section shows a predominance of montane pollen taxa and lowland macrofossil taxa. The pollen and macrofossil assemblages of section Subachoque 39 are also suggestive of tropical lowland-lower subandean conditions (Wijninga and Kuhry, 1990). The plant assemblages of sections Subachoque 39 and Rio Frio 17 share characteristic taxa, e.g. Freziera, Mauritia, Hedyosmum, Sacoglottis, Cecropia, and Melastomataceae. In addition, the plant assemblage of section Subachoque 39 included macrofossils of Vantanea, Symplocos, Humiriastrum, and Parinari and a greater proportion of Andean and subandean taxa. This difference may be attributed to the fact that the paleoflora of section Subachoque 39 contains a much higher number of taxa than section Rio Frio 17. Nevertheless, the relative high level of similarity between the two pollen assemblages and the high degree of similarity between the two macrofossil assemblages suggests that sediment deposition of sections Subachoque 39 and Rio Frio 17 occurred at comparable paleoaltitudes.

7.1. Biostratigraphy At first the sediments of section Rio Frio 17 were considered a probable equivalent of the Tequendama Member of the Lower Tilat~i Formation (Helmens, 1990). Although no palyno-

341

logical evidence was available at the time, the sediments of section Rio Frlo 17 were believed to belong to Biozone I (Helmens, 1990). New palynological evidence now reveals the significant presence of Hedyosmum and the absence of Myrica, Alnus and Quercus in the sediments of section Rio Frlo 17. Consequently, the sediments of section Rio Frio 17 belong to Biozone II. Sections Rio Frio 17 and Subachoque 39 belong to the same biozone, despite that the sediments of the latter section are assigned to the Tibagota Member of Lower Tilat~i Formation. Sediments of this member were also present as fluvial terraces in the Rio Frlo valley, where they have incised the sediments to which section Rio Frio 17 belongs. This means that the sediments of section Rio Frio 17 were deposited before those of section Subachoque 39, all during Biozone II. The new biostratigraphical position of the sediments of section Rio Frio 17 has several biostratigraphical and chronostratigraphical implications. (1) The record of Hedyosmum in the area of the high plain of Bogot~i started around 5.3 + 1.0 Ma. (2) The sediments of sections Salto de Tequendama I and II (Biozone I; Van der Hammen et al., 1973) are older than 5.3__+1.0 Ma. This minimum age is in agreement with the suggested Middle? Miocene age of sections Salto de Tequendama I and II (Wijninga, 1996a). (3) The minimum time-span for Biozone II is inferred from two fission-track dates on zircon from section Rio Frio 17, dated at 5.3__+1.0 Ma and section Facatativ/t 13, dated at 3.7___0.5 Ma (Helmens, 1990; Andriessen et al., 1993).

8. Conclusions

(1) Fossil pollen and macrofossil assemblages of section Rio Frio 17 may be compared with the present-day altitudinal distribution and ecological requirements of these same taxa when the nonanalog situation is carefully considered. (2) Despite the relative poor palynological evidence, the presence of Hedyosmum and tropical lowland and lower subandean fossil pollen, spores and fruits, suggest that the 5.3 + 1.0 Ma sediments of section Rio Frio 17 belong to Biozone II.

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PLATEI

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Previously, these sediments were assigned to Biozone I based on lithostratigraphical evidence (Helmens, 1990). The inferred paleoaltitude is estimated at c. 1000 m. Extrapolating from the Pliocene temperature, with an amplitude of c. 3°C compared to present-day temperature, sediment deposition may have been between 500 and 1500 m elevation. (3) Biozone II spans a time interval from 5.3 _+ ! .0 to 3.7 _+0.5 Ma, based on the fission-track dates on zircon of sections Rio Frio 17 and Facatativ~i 13 (Helmens, 1990; Andriessen et al., 1993). This time interval includes the early and later stages of the final uplift of the area of the high plain of Bogota. (4) As a consequence of the fact that section Rio Frio 17 belongs to Biozone II, the sediments of sections Salto de Tequendama I and II (Biozone I) must be older than 5.3_+1.0 Ma. This in agreement with an age of Middle? Miocene for the two sections suggested by Wijninga (1996a).

Description and illustration of macrofossil types The morphological descriptions of the seeds follows mainly the terminology of Berggren (1981). The numbering of the macrofossil types is continuous with that of Kuhry (1988a [T1-T52], 1988b [T53 T165]), Wijninga and Kuhry (1990 [T166-T204], 1993 [T205-T267]) and Wijninga (1996a [T268-T318], 1996b [T319-T364]). Information is given about the ecology and geographical distribution of the fossil taxa where possible. This information is mainly from Van Roosmalen (1985), and Gentry (1993).

Abbreviations used in the descriptions are: h = height, /=length, Iv=length view, sio=shape in outline, ts = transverse section, w = width. T365 Freziera Willdenow (Theaceae). Plate I Seed. sio=reniform to broadly elliptic, ts= obovate, lv = elliptic. Size (n = 9) l x w x h = (1065) 970 (800) x (900) 835 (760) x (600).590 (550) ~tm. Lateral faces concave; ventral marginal face concave. Surface reticulate to subscalariform. Cells pitted, and in some specimens parts of the periclinal cell wall preserved. Cells decreasing in size towards the ventral margin. Seed wall c. 110 ~tm thick and composed of two cell layers, an inner layer with small slightly flattened cells, 10-15 lam thick, and an outer layer with larger more elongated cells, 35-45 ~tm thick. Ecology and distribution: Freziera is a characteristic canopy or subcanopy element of Andean forests. The genus includes some pioneer species in secondary forest, e.g. on landslides (Kappelle et al., 1994). It is found most frequently in the Andean forest belt, but also occassionally in coastal lowlands (Weitzmann, pers. commun., 1993). Remark: Identification based on Wijninga and Kuhry (1990). T366 Cecropia Loefling (Cecropiaceae). Plate I Seed. sio = ovate, ts = elliptic, lv = narrow eliptic. Size (n = 4 ) l x w x h =(1600) 1470 (1265) x (800) 775 (750)x (460) 445 (400)#m. Surface tuberculate; testa provided with small depressions (c. 5 ~tm in diameter) formed by cells of abraded layer. Testa cell walls pitted. Ecology and distribution: Cecropia is an pioneer tree, commonly colonizing tree gaps and sand fiats

PLATE I T365a. T365b. T365c. T365d. T365e. T365~ T366a. T366b. T366c.

Freziera, seed. x 60. ldem. Idem, Idem, Idem, ldem,

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x 61. detail of surface with partly preserved periclinal cell walls. × 460. cross-section of seed, showing chalaza (a), raphe (b), hilum (c), and micropyle (d). x 60. detail of seed wall. x 307. detail of raphe, x 230. Cecropia, seed, with distinct raphe (a). x 35. Idem, detail of surface, x 480. ldem, detail of seed wall with elongated cells (a). x 470.

V.M. Wijninga/Review (~f Palaeobotany and Palynology 92 (1996) 329-350

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PLATE II

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along rivers. The genus is found below 2400 m altitude. Remark: Identification based on Wijninga and Kuhry (1990).

Found especially in second growth vegetation in subandean-Andean cloud forests (Gentry, 1993). Remark: Identification based on Whiffin and Thomb (1972) and Groenendijk et al. (in prep.).

T367 Melastomataceae. Plate II Seed. sio = cuneate, ts = cuneate, lv = cuneate. Size ( n = l ) l × w x h = 8 2 0 x 5 5 0 × 5 4 5 ~ t m . Seed with large lateral raphe and straight faces. Cells of testa slightly rounded to interdigitating to varying degrees. Surface finely striate. On dorsal face impressions of elongated fruit wall cells visible. Ecology and distribution: Melastomataceae, a family consisting mostly of shrubs, but also including herbs, lianas, hemiepiphytes and large trees.

T368 Melastomataceae. Plate II Seed. sio=obconic, ts=broadly elliptic, lv= elliptic. Size (n = 1 ) l x w × h = 4 1 0 x 250 x 230 lam. Seed with large lateral raphe, convex faces and tuberculate. Tubercles formed by testa cells and of variable size and shape, sometimes more than one tubercle per cell. Cells of testa interdigitating to varying degrees. Surface finely striate. Ecology and distribution: See T367. Remark: For identification see T367

PLATE II T367a. T367b. T367c. T368a. T368b. T368c. T369a. T369b.

Melastomataceae, seed. x 77. Idem, detail of surface with finely striated interdigitating testa cells, x 456. Idem, detail of surface on dorsal side, surface cells showing imprints of abraded layer, x 763. Melastomataceae, seed, showing valve (a). x 153. Idem, detail of surface with finely striate tuberculate and interdigitating cells. × 454. Idem, detail of valve, x 600. cf. Melastomataceae, seed. x 77. ldem, detail of tuberculate cells. × 231.

PLATE III (see p. 346) T370. cf. Evodianthus, seed. × 40. T371a. Seed. x 45. T371b. Idem, detail of surface. × 153. T372a. Seed. x 23. T372b. Idem, detail of surface. × 157. T373a. Fruit, x 14. T373b. Idem, showing the five locules. × 15. T373c. Idem, detail of locules, x 50.

PLATE IV (see p. 347) T374a. T374b. T374c. T375a. T375b. T376a. T376b. T377a. T377b.

Seed. x 38. Idem, detail of surface cuticle with stomata, x 610. Idem, detail of seed wall with pitted cells, x 770. cf. Juncus, seed. x 60. Idem, detail of surface showing periclinal cell walls. × 306.

Compositae, achene fragment, remnants of periclinal cell walls visible, x 159. Idem detail o f outer surface of achene fragment, x 470.

Sacoglottis, endocarp, x 1.1. Idem, x 1.1.

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PLATE

II1

(for description see p. 345)

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PLATE IV

T377a (for description see p. 345)

T377b

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T369 cf. Melastomataceae. Plate II Seed. sio = depressedly ovate, ts= obovate, Iv = elliptic. Size ( n = l ) l x w x h = l O O O x 6 5 0 x 5 4 5 . Seed tuberculate and with straight side faces. Tubercles formed by more than one cell, and varying in size and shape. Surface smooth. Ecology and distribution: See T367 Remark: For identification see T367 T370 cf. Evodianthus Oersted (Cyclanthaceae). Plate III Seed. sio=elliptic. Size (n= 1) Ix w = 1425 x 730. Hyaline; seed remains consisting of two cuticlelike layers. Outer layer provided with isodiametric cell pattern and a more elongated cell pattern along the margins. Ecology and distribution: This monotypic genus is found from Central America to Ecuador, including the Amazon basin. Its altitudinal range is restricted to low elevations, although one subspecies occurs up to 1500 m elelevation. Evodianthus is a nonwoody plant with a preference for wet to humid and usually shady habitats (Harling, 1958). Remark: Identification based on Harling (1958) and Wijninga (1996a). T371. Plate III Seed. sio=obovate. Size ( n = l ) lxw= 1390 x 770. Hyaline; seed remains consisting of two cuticle-like layers. Cell imprints on outer layer longitudinally arranged. Taxonomic affinity: Recent seeds of Sphaeradenia (Cyclanthaceae) and Philodendron (Araceae) are more or less morphological similar to T371. Remark: A similar fossil seed type (T270) was found in sections Salto de Tequendama I and II (Wijninga, 1996a). T372. Plate III Fruit. sio = rounded, ts = elliptic, lv = elliptic. Size ( n = l ) l x w x h = 2 . 2 x 2 . 1 xc. 1.2mm. Fruit bivalved, tuberculate and provided with conspicuous smooth rim. Tubercles c. 450~tm high. Surface pitted. Remark: An identical type (T345) was found in section Facatativfi 13 (Wijninga, 1996b). T373. Plate III Endocarp, woody, sio = unknown, ts = elliptic, Iv=elliptic. Size ( n = l ) Ixw×h=4.4x3.4x

2.4 mm. Fruit 5-1ocular, locules between 570 and 850 gm in diameter. Probably 5 rims present, one conspicuous. T374. Plate IV Seed. sio=broadly ovate, ts=circular, lv= broadly ovate. Size ( n = l ) lxwxh=l.5x 1.2 x 1.2 mm. Stomata? present on the seed surface. Seed wall consisting of pitted cells and is c. 55 gm thick. T375 cf. Juncus L. (Juncaceae). Plate IV Seed. sio = elliptic. Size (n = 1) I x w= 1220 x 870 pm. Hyaline; seed remains consisting of two cuticle-like layers. Testa cells longitudinally arranged in c. 18 rows; periclinal cell walls pitted with toothed projections on the shorter cell walls. Cell size is 9 5 - 8 0 x 12 10gm in the middle of seed, decreasing in size towards the apex and base o f the seed. Ecology and distribution: Juncus represents a cosmopolitan genus, and frequently occurs in swampy areas. Juncus occurs in all altitudinal vegetation belts of Colombia. Remark: Identification based on Wijninga and Kuhry (1993) and K6rber-Grohne (1964). T376 Compositae. Plate IV Achene fragment. Remark: For complete description and illustration of Compositae achenes see Wijninga and Kuhry (1990, 1993) and Wijninga (1996b). T377 Sacoglottis Martius (Humiriaceae). Plate IV Syncarpous endocarp, woody, sio=obovate, ts=elliptic, h,=obovate. Size ( n = 2 ) I x w x t = 3.8-3.3 x 2.8-2.4 x 1.7-1.2 mm. Carpels 5, radially arranged. Endocarp consists of valves and straight thin longitudinal septae. The septae are united around the axis to form a five-rayed central structure. The valves completely fill the space between the septae; they are mostly elliptic in shape. The resin cavities are 2-4 mm across and c. 2 3 mm deep, and occur only on the valves. Ecology and distribution: Sacoglottis is found at present throughout the neotropics below 1200 m altitude. Sacoglottis species are all trees, and occur in rain forest, savanna, marshy upland forest and on river banks (Cuatrecasas, 1961 ).

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Discussion: The general morphology of Sacoglottis T377 resembles that of other recorded fossil Sacoglottis endocarps. Compared with the similar types (T196, T296) from the high plain of Bogotfi, the size of the resin cavities is larger in the endocarps T377 (Wijninga and Kuhry, 1990; Wijninga, 1996a). Although fossil endocarps of Sacoglottis normally show large differences in size and shape, the size of the resin cavities in the endocarps of other Sacoglottis types was usually uniform. Remark: Identification based on Berry (1922), Cuatrecasas (1961), Wijninga and Kuhry (1990) and Wijninga (1996a).

Acknowledgements The comments on the manuscript by H. Hooghiemstra are much appreciated. K.F. Helmens (at present University of Lapland) is thanked for providing additional lithostratigraphical data. The comments by J. Jansonius, K. Graf, and an anomynous reviewer are much appreciated. The director and staff of the Instituto de Ciencias Naturales (Universidad Nacional, Bogota) are thanked for their hospitality and logistic and financial support during the fieldwork. Sincere thanks to E. Beglinger for the preparation of the pollen samples and to J. Dahmen for printing the photographs. WOTRO (Netherlands Foundation for the Advancement of Research in the Tropics and Developing Countries, grant W75-314) provided financial support.

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