Upper quaternary vegetational and climatic sequence of the fuquene area (Eastern Cordillera, Colombia)

Phlaeogeography, Palaeoclimatology, Palaeoecology, 14(1973) 9 - 9 2 © Elsevier Scientific Publishing C o m p a n y , A m s t e r d a m - Printed in The Netherlands

UPPER QUATERNARY VEGETATIONAL AND CLIMATIC SEQUENCE OF THE FUQUENE AREA (EASTERN CORDILLERA, COLOMBIA)

B. VAN GEEL and T. VAN DER HAMMEN

Hugo de Vries-Laboratorium, Department of Palynology, University of Amsterdam, Amsterdam (The Netherlands} (Accepted for publication October 11, 1972)

ABSTRACT* Van Geel, B. and Van der H a m m e n , T., 1973. Upper Quaternary vegetational and climatic sequence of the F u q u e n e area (Eastern Cordillera, Colombia). Palaeogeogr., Palaeoclimatol., Palaeoecol., 14: 9 - 9 2 .

In this paper the results of a pollen-analytical study of three bore holes of lake deposits in the F u q u e n e Valle de Ubatd area, Colombian Cordillera Oriental (5 ° N; elev. 2,580 m) are given. By m e a n s of 14C dates and comparison with other pollen diagrams and dates from the Eastern Cordillera, it was possible to correlate the local pollen zones and chronostratigraphical units with the European chronostratigraphical sequence. The longest diagram (Fuquene II) represents some 30,000 years, including part of the Middle Pleniglacial, the Upper Pleniglacial, the Late Glacial and the Holocene. During the Middle Pleniglacial, Polylepis wood was an important constituent of the vegetation. During climatic extremes o f the Upper Pleniglacial an open pdramo ~egetation existed. During the main part of the Upper Pleniglacial (from ca. 21,000 to ca. 13,000 B.P.) the lake level was low and the climate dry. The lake level rose again in the beginning of the Late Glacial, and the area around the lake became forested. At the beginning of the El Abra Stadial (Late Dryas Stadial) there was a marked cooling and the lake became lower once more; this had a great impact on the vegetation which became partly open again. The beginning of the Holocene is marked by a gradual increase of forest elements, especially of Quercus (oak.) Oak forests dominated the area during the greater part of the Holocene. During the " h y p s i t h e r m a l " , elements growing today at a lower level, such as Cecropia, Aealypha (and possibly Alchornea), m u s t have been growing in the area, intermixed with the oak forest. At the same time there was a considerable increase of Urticaceae in the undergrowth of these forests. The vegetation zones were probably situated several h u n d r e d s of metres higher than they are at the present time. The influence of m a n on vegetation had started already before the beginning of our era, but there is a sudden increase of this influence (e.g., increase of Dodonaea, decrease of Quercus and Urticaceae) somewhere around 2,000 B.P. Later on, the diagram shows the rapid ultimate decline of the forest elements and an increase of Gramineae. Today nothing is left of the original oak forests and their place is taken by arable land or by secondary plant c o m m u n i t i e s with low brushwood. In the lake sediments, thin layers of volcanic ash were found dated approximately 9,000 B.P., 11,000 B.P., and 21,000 B.P., respectively; a series of three ash-layers was deposited between approximately 22,000 B.P. and 26,000 B.P. and one possibly at approximately 30,000 B.P. These layers have been found in several other sections in the Eastern Cordillera and are the basis for a tephrochronology. * For Spanish abstract see p.91.

16

B. VAN GEEL AND T. VAN DER HAMMEN

:UQUENE THE CURVES C,E

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Fig.4. Sections, Fuquene, with zonation, characteristic changes of some of the pollen curves, horizons with volcanic ash (mica), ~+C dates, and chronostratigraphy.

Subzone V-I Gramineae percentage relatively low. Polylepis dominant. Pollen of Alchornea, Acalypha, Daphnopsis and Dodonaea present. Polylepis may reach percentages of over 50 %, but between sample 90 and sample 83 the curve falls to less than 20 %. This fall coincides with the rise of the curves o f the plants of the hygrosere (Cyperaceae, Myriophyllum, Umbelliferae) and a rise of the Fungi curve. Maxhna o f these curves coincide with the deposition o f more humic clays. The samples 85 to 82 show a

VEGETATIONALAND CLIMATICSEQUENCEOF EASTERNCORDILLERA

11

INTRODUCTION The next highptain north of the "Sabana de Bogot~i" in the Colombian Cordillera Oriental is the "Valle de Ubat6-Chiquinquir~". Its elevation is approximately the same ca. 2,580 m above sea level. Like the "Sabana de Bogota", it must have been a very big lake in the Pleistocene. Today the main remnants of this lake are (Fig.l) the large Laguna de Fuquene and the smaller Lagunas de CucunuM and Palacio (the last one not to be confounded with the lakes in "P~ramo de Palacio", lying at a much greater elevation). At present the Laguna de Fuquene (location 5027 ' N and 73046 ' W) has a length of ca. 8 km and a breadth of ca. 4 km; the mean depth is 5 m. Recently the lake level was somewhat lowered by human intervention; that made it possible to collect, by means of a Dachnovsky sampler, the two sections rather far into the area originally occupied by the lake (Fig.l). The first section (Fuquene I), collected by the second author in the summer of 1966, was studied together with E. Gonzfilez. The second section (Fuquene II) and the section Laguna de Palacio were collected by F. Lucas (at that time assistant for the Colombia project) in the summer of 1967 and analysed by the first author. The present study is part of a project on the Quaternary geology and palynology of Colombia, carried out with financial support from the Netherlands Foundation for Tropical Research WOTRO.

PRESENT CLIMATEAND VEGETATION The present climate is best illustrated by the rainfall/temperature graphs of Fig.2, representing, from south to north, the conditions at Ubat6, Laguna de Fuquene and Chiquinquir~, respectively. The three sites are all at approximately the same elevation and show a similar relative distribution of rainfall throughout the year, the dry seasons being in December-January-February and July-August. The mean annual temperature is between 13.7 and 15.4°C. The lowest monthly temperatures occur in the dry seasons, the highest in the wet seasons. The maximum difference in monthly temperatures in all three curves is of the order of 1.5°C. Daily differences in temperature may be considerable and sometimes night frost occurs during the dry seasons. There is, however, a considerable difference in the total annual rainfall. It increases from south to north from 770 mm through 887 mm to 1076 mm. In terms of the system of formations of Holdridge, applied to Colombia (Espinal and Montenegro, 1963), this means that the first two sites are located in the area of the dry low montane forest and the last in the area of the wet low montane forest. The actual horizontal distribution of formations in the area is shown in Fig.3 (adapted from Inst. Geogr. Ag. Codazzi, 1965). Vertically, the wet and dry low montane forest extends from approximately 2,000 m to about 3,000 m and the mean annual temperature is between 12° and 18°C. The dry low montane forest receives an annual rainfall of 500-1,000 mm, the wet low montane forest one of 1,000-2,000 ram.

12

B. VAN GEEL AND T. VAN DER HAMMEN

CHIQUINQUIRA 200 180 160

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Fig.2. Rainfall and temperature graphs for Ubatd, Laguna de Fuquene and Chiquinquir~i (redrawn from Inst. Geogr. Ag. Codazzi, 1965).

VEGETATIONAL AND CLIMATIC SEQUENCE OF EASTERN CORDILLERA

13

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The next higher formations, the wet and very wet montane forest, is found between approximately 3,000 m and 3,500 m. The mean annual temperature is between approximately 12 ° and 6°C. The wet montane forest receives an annual rainfall of 5 0 0 -

14

B. VAN GEEL AND T. VAN DER HAMMEN

1,000 ram, the very wet montane forest one of 1,000-2,000 mm. At still higher elevations (above approx. 3,500 m) the subalpine P~ramo formation is found. The formation that extends in a wide area around the lakes where our sections were taken is the dry low montane forest (Fig.3). The primary vegetation, however, has been destroyed and changed by human interference and there has been serious soil erosion on the slopes. Today a very poor secondary vegetation has taken its place with, e.g., Dodonaea viscosa, Baccharis sp. Barnadesia spinosa, Schinus molle, and Solanum sp. At one site there are a few trees of Quercus (oak) near a place called Puerto Roble. Other species found frequently in this formation are Phyllanthus salviaefolius, Croton sp., Montanoa sp., Durantha mutisii, Oreopanax sp., Tara spinosa, Prunus capuli, Escallonia sp. (Espinal and Montenegro, 1963). Most of the area of the dry low montane forest in the Eastern Cordillera has been seriously affected by human action, since the beginning of Indian agriculture. For that reason it is difficult to reconstruct the composition of the original forest. It may have been a dry type of Querceturn or I~einmannietum and/or a mixed forest with, amongst other species, Phyllanthus, Croton and Oreopanax. The wet low montane forest in the Chiquinquir~ area (Fig.3) is developed as oak forest (Quercetum). The wet and very wet montane forests are, in this area, represented by Weinmannia forest (Weinrnannietum). The subalpine Pframo is hardly represented in the area (Fig.3). Elsewhere dwarf forest of, e.g., the Compositae Baccharis and Eupatorium is frequent, while stands of Polylepis forest, already present in the upper part of the montane forest zone, may be locally common. Open P~ramo meadows dominate above ca. 3,800 m, but are already frequent above, 3,500 m (locally above 3,200 m); it is, however, difficult to know to what extent human interference (burning) has lowered the lower boundary of the open Pfirarno and extended its surface in the Subalpine Pdtrarno zone.

Indicator plants In the lower part of the low montane forest at elevations between 2,000 and 2,400 m, outside the highplain, several genera, such as Cecropia, Acalypha and Alchornea, attain the highest level of occurrence. In the area between Virolin and P~ramo de la Rusia (about 100 km NE of Fuquene) we found oak forests with Cecropia and/or Ceroxylon between 2,100 m and 2,300 malt. A few Cecropia trees were still seen as high as 2,600 malt., Ceroxylon as high as 2,750 malt. While oak forest is common in the western part of the Cordillera Oriental between 2,000 m and 3,000 malt., it is less common between 3,000 m and 3,500 m, and is lacking in the eastern part of the Cordillera Oriental. Although the ecology of the oak in Colombia is still insufficiently known, there are certain groups of plants in both the Quercus and the Weinmannia forests that proved to be good indicators. For our present study it is, for instance, important to know that, generally speaking, tree-ferns (Cyathea, Alsophila, Dicksonia) and Urticaceae are indicators for the wetter type of montane forests. Dodonaea is an indicator for the more xerophytic vegetation and for soil erosion in the area of the dry low montane forest. Polylepis occurs between approximately

VEGETATIONALAND CLIMATICSEQUENCE OF EASTERN CORDILLERA

15

3,200 m and 4,000 malt., but seems to be most abundant around 3,500 m alt. Podocarpus has become a rather rare tree in the Cordillera Oriental, because of its valuable wood. Its vertical range is rather wide, so that we not only repeatedly found it in wet oak forests between 2,600 and 3,000 malt., but also frequently in the belt of Weinmannia tomentosa forest above the oak forest belt in the area of P~iramo de la Rusia at an altitude between 3,250 and 3,500 m. Amongst the plants of the hygrosere, Myriophyllum seems to be an excellent indicator for cold conditions; all recent records of this genus are from lakes in the P~iramo. Most recent records of Iso~tes are equally from lakes above 3,000 m. Another excellent temperature indicator is the alga Coelastrum reticulatum (see the paragraph "some data on other microfossils"). POLLEN DIAGRAMSFUQUENE I AND II (Fig.5 and 6) Both sections were taken in the Laguna de Fuquene, one in the south, the other in the northeastern corner (Fig.l); section Fuquene I is 985 cm deep, Fuquene II 1200 cm. Both were collected with the Dachnovsky sampler. The sections, with a compilation of data, are shown in Fig.4, the pollen diagrams in Fig.5 and 6. The local pollen zones are indicated in Fig.4 as well as in the diagrams. The pollen diagrams are represented as lversen diagrams, the pollen total consisting of trees, shrubs (excluding Compositae), and Gramineae. The general diagram (left side in Fig.5 and second from left in Fig.6) represents at its left side the forest elements, at its right side the grasses and Polylepis-Acaena pollen. Of section Fuquene II a different general diagram is shown at the extreme left side of Fig.6. In this case the Compositae are included in the pollen total and the Urticaceae are excluded. The woody elements are at the left side of this diagram (with a separate curve for Polylepis-Acaena), followed at the right by Compositae and Gramineae. A zonation was applied that is intended for local use only. Zones have been indicated by letter symbols, subzones by roman cipher symbols. The pollen diagrams clearly show considerable variations in the relation of pollen from forest elements to pollen of elements of the open vegetation. There are also considerable fluctuations in the different forest elements. Important are the changes in the pollen percentages of plants of the hygrosere (Cyperaceae, Polygonum, Rumex, Typha, Umbelliferae such as Hydrocotyle, etc.). Maxima of these groups coincide with the presence of more plant remains in the sediments and there is no doubt that they represent periods of low lake levels when the hygrosere extended over large parts of the area at present covered by the lake water (for the same phenomenon in the Sabana de Bogotg, see, e.g., Van der Hammen and Gonzalez, 1965a). A short description of the zones and subzones is given below, including already some interpretation. Diagram Fuquene II gives upon the whole a more detailed and more complete picture than Fuquene I; however, subzone Y-I is better represented in Fuquene I.

16

B. VAN GEEL AND T. VAN DER HAMMEN

:UQUENE THE CURVES C,E

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Fig.4. Sections, Fuquene, with zonation, characteristic changes of some of the pollen curves, horizons with volcanic ash (mica), ~+C dates, and chronostratigraphy.

Subzone V-I Gramineae percentage relatively low. Polylepis dominant. Pollen of Alchornea, Acalypha, Daphnopsis and Dodonaea present. Polylepis may reach percentages of over 50 %, but between sample 90 and sample 83 the curve falls to less than 20 %. This fall coincides with the rise of the curves o f the plants of the hygrosere (Cyperaceae, Myriophyllum, Umbelliferae) and a rise of the Fungi curve. Maxhna o f these curves coincide with the deposition o f more humic clays. The samples 85 to 82 show a

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.

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7

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l l l l l l l [ l l m i l l l l l l l [

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INCLUDED IN THE SUM OF OTHER I~

PERCENTAGE CALCULATED AT THE SUM OF " PORCENTAJE CALCULADO A BASE DE LA St..

0

10

20

L

i

i

30 40 L

,

50

60

70

80

i

J

,

i

9 0 100 ,

PERCENTAGE CALCULATED AT THE NUMBER PORCENTAJE CALCULADO A ~ASE DEL NU~ 0

1000

2000

3000

4000

5000

z 0 t~ Ld

g~ W

40

50

2000

60

3000

70 8 0

90

10

20

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3O

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-40 ~ . . . . 4-

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o.

~,~o ~o÷o . ~o~-+30;0

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2-

p

30

-

~oT

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1,o 2o I

1ooo

RELATION BETW POLLEN OF FOR ELEMENTS AND 0 M ICRO- FOSSILS. RELACION ENTRE; DE E L E M E N T O S [ B,O S Q U E Y OTR~ M I CROFOSILES.. I 10 20 30 4 0

-50

llnntul~i

- 6 0 j,

~ l I I I I I r I I I ', ',',' ~

41CR0 -FOSSiI-S - ELEM-ENTOS INCLUIDOS EN LA SUMA DE OTRO-S MICRO~FOSILES FHE OTHER MICRO-FOSSILS bM~ DE LOS OTROS MICROFOSILES-(FUNGI, BOTRYOCOCCUS, COELASTRUM RETICULATUM, PEDLASTRUM, TETRAEDRON)

OF ~ ' - P O L L E N , I N D I C A T E D IN THE LAST COLUMN 4ERO DE ~E - POLEN. I N D I C A D O EN LA ULTIMA C O L U M N A

EEN EST

THER -I ;:'OLEN 0 CrTI,

-- - -

-- -

O¸

r--~

5 3 9 8 15 -15

BORRERIA 0 , 3 % BORRERLA 0 , 3 % BORRERIA O,3%;GAIADENDRON 0,3%;HEMITELIA .BORRERIA 0,6 % ; A S T R O N I U M - T Y P E 0 , 3 °1o ANACARDIACEAE 0,3% ,

0,3%

100

--20 /

- 15 t V I S M I A 0 , 2 % ---10 --21 GAIADENDRON 0,3% -9 ~PHYLLANTHU$ O,3 % - - - 6~- - 13 PHYLLANTHUS 0 , 3 % VIBURNUM 0 , 3 % BORRERIA 0 , 8 % VIBURNUM 0,3%

I

CORIARIA CORIARIA

2OO

i

0,6 °1o 1,5 % 300

CORIARIA 0 , 5 C0RIARIA 0,3 PHYLLANTHUS CORIARIA 0,9 CORIARIA 0,4

eli % O,3 % % %; PHYLLANTHUS

0,4 % ,400

V I B U R N U M O,3 % PROTEACEAE O.3% ANACARDIACEAE O,5 %

500 CORIA RIA

O,6 %

DRYMI$ 0,3 % BORRERIA 0,3 %

6CC

C P PERI TYPE 1 C P PERI TYPE 1

0,4 "1. 0,4 %

,

CORIARIA

0 , 4 °1o 7OO

CORIA RIA

O,6 %

DRYMIS 0,3 % BORRERIA 0,3 %

C P PERI TYPE 1 C P P E R I TYPE 1

0,4% 0,4%,

CORIARIA

0,4%

PANOP$1$ 0 , 4 % AETHANTUS 0 , 4 % PHYLLANTHUS 0,4 % HELIOCARPUS

0,7%

SYMPLOCOS

O,3 %

MELIACEAE

0.3 %

p.,.

ANACARDIACEAE 0 , 3 % ; SYMPLOCO$ 0 , 3 % CORIARIA O,3 %

- -

HELIOCARPUS

0.3%

POLYGALACEAE

0,3% ; GUNNERA 0 , 3 % ;

58

--65

PROTEACEAE :CORIARIA •

54 55 r z w ..J

i

CROTON O,3 %

O,3 % ; SYMPLOCOS 0.3 %

0,3% F

Botryococcus Fungi

Coelast.rum ret.. Tetraedron

:E

U El>,.

uo

7,

0 z U'~

El a.

z 0 n~ 0 El ,¢ DE I-El I--

INSERT SED. 2: 0 , 9 % cf VIBURNUM: 2x CACTACEAE : lx ; GERAN IUM : lx GUNNERA: 0,5% ; LAP, IATAE: 0,5% ILEX: 0,6=/o; BOCCONIA: 096% ANACARDIACEAE : Or7 olo

r

P

b

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.9

-D

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no

o

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b 4-

t ÷

t"

JUGLANS: l x

BOCCON IA: O,B% ANACARDfACEAE : 0,4 o~ RANUNCULACEAE: 0 . 3 % ; C 3 P 3 PSILATE 1: O,3"1.

RANUNCULACEAE : 0,4% i STYLOCERAS: 0~7 °/o

STYLOCERAS : 0 , 5 % ; I L S -- ELEMENTOS

INCLUIDOS EN LA SUMA

DE OTROS MICROFOSILI~S

fO 0 L~ LO

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2

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, I'~NCLUDED

TREES AND SHRUBS ......... IPOLYLEPIS/ ARBOLES Y ARBUSTOSI L~MAMimr-A~ : ACAENA • LAKE CLAY-ARCILLA

DE L A G U N A

'ollen diagram L a g u n a de F u q u e n a III.

ARCILLOSA

QUERCUS

-- , N C L U I D O S

EN I f

0 10 2 0 3 0 4 0 5 0 6 0 __ SCALE FOR ALL CURVES ESCALA PARA LAS CURVAS

D ALNUS •

CLAYEY PEAT - TURBA

IN T H E P O L L E N S U M

P O D O C A R PUS OTHER

FOREST ELEMENTS

- OTROS

ELEMENTI

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k

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p

_

VEGETATIONAL AND CLIMATIC SEQUENCE OF EASTERN CORDILLERA

73

maximum for Pediastrum. Zone V-I seems to be a period with a relatively high lake level, ending with drier conditions. If we take the whole succession of the diagrams into consideration, temperature conditions may be called "interstadial" (see following).

Subzone V-H The Gramineae curve rises. The curves of the hygrosere show maxima. During this zone the lake level was low and the temperature became increasingly colder.

Zone W During this zone the Gramineae are dominant.

Subzone W-I Gramineae percentages very high. The climate must have been very cold, the curves of the plants of the hygrosere and the sedimentation indicating a low lake level.

Subzone W-H In this subzone the Gramineae curve and the curves of the plants of the hygrosere show a relative minimum. Polylepis and Alnus show a relative maximum. During this subzone there must have been a slight amelioration of the climate.

Subzone W-11I Gramineae percentage high.

Subzone W-IV The Gramineae curve shows a slight fall and there is a minor rise of the forest elements, especially of Weinmannia.

Subzone W-V The Gramineae curve shows an absolute maximum. The vegetation must have been completely open, without forest elements. The climate must have been very cold (maxima of Cruciferae !). The maxima of the Cyperaceae, Umbelliferae, Myriophyllum and Fungi, coinciding with the deposition of dark, humic clay, indicate a lower lake level. The Pediastrum curve shows a marked rise at the transition of zone W-V to zone Y-I.

74

B. VAN GEEL AND T. VAN DER HAMMEN

Subzone Y-I At the beginning of this zone there is a steep fall of the Gramineae and a sudden increase of tree pollen. The curves of the plants of the hygrosere and the Fungi curve show a decline. Dodonaea shows a maximum. There can be no doubt that a forest with Quercus and Myrica established itself on the hills around the lake, whereas Alnus extended on the flat valley bottom. The curves of Acalypha and Cecropia start in this zone and the alga Coelastrum reticulatum is present. They all indicate a warmer climate than before. The lake level must have been higher than .before. A subdivision of zone Y-I in the Fuquene I section could be made, because the rate of sedimentation during this zone was faster than in the Fuquene II section (Y-Ia: minimum of Gramineae; Y-Ib: minor rise of Gramineae; Y-Ic: minimum of Gramineae).

SubzoneY-H During zone Y-II the Gramineae curve rises again. The Compositae curve shows a maximum. The Cyperaceae show a marked rise, indicating a low lake level. Myriophyllum does not reach 5 % and falls off to zero in sample 32 (apparently Myriophyllum was present in the lake only during the colder climatic phases; this is in agreement with its recent occurrence, all records being from lakes in the Pfiramo). The Potamogeton curve shows its first clear maximum (flowering Potamogeton seems to be more frequent in the warmer Holocene). There is also a considerable maximum of Pediastrum, and Lemna shows a continuous curve; Coelastrum reticulatum disappears. These facts point to a cooler climate and a lower lake level.

Subzone Z-I Zone Z-I shows a gradual fall of the Gramineae curve and a rise of the curves for trees and shrubs. From sample 32 onward, Coelastrum reticulatum is present.

SubzoneZ-H During zone Z-II the forest elements dominate, especially Quercus. The high percentage ofAcalypha, Alchornea and Cecropia indicate that these trees were growing at a higher level than they are growing in the same area today. This subzone can be divided into two parts, a and b. In Z-IIa Quercus dominates; in Z-lib other forest elements; this can be clearly seen in Fuquene I and less so in Fuquene II.

Subzone Z-III This zone is characterised by the rise of Dodonaea, Compositae, Cyperaceae,

VEGETATIONALAND CLIMATICSEQUENCE OF EASTERN CORDILLERA

75

Polygonum and Chenopodiaceae. Towards the end of the zone there is a rise of the Gramineae and a fall of the pollen percentages of trees and shrubs. The lake level must have been lower again and the final disappearance of the forest elements must have been caused by deforestation by man. The rise of Dodonaea must be indicative of soil erosion. The pollen diagrams and ~4C dates (see the corresponding paragraph), and a comparison with the dated sequence elsewhere in the Cordillera Oriental (van der Hammen and Gonzilez, 1960a,b, 1965a,b; Van der Hammen, 1968, etc.) leave no doubt about the chronostratigraphical interpretation of the sections. Zones V and W must correspond with the Pleniglacial of the last Glacial period, zone Y with the Late Glacial and zone Z with the Holocene. Zone V must correspond with the Middle Pleniglacial, zone W with the Upper Pleniglacial. Subzone Y-I must correspond with the sequence of Late Glacial interstadials (at least with the B~blling and Aller~bd), subzone Y-II with the Younger Dryas time. The dating of the zones will be more amply discussed in the next paragraphs. The pollen diagrams from Fuquene represent the best continuous record in Colombia of the last 30,000 years. It permits a detailed reconstruction of the history of vegetation and of several climatic factors, including both temperature and humidity. For this reconstruction we refer to the last paragraph of this paper.

THE POLLEN DIAGRAM LAGUNADE PALACIO (Fig.7) The lake (location 5°15 ' N 73o48 ' W) lies at 5 km south of Ubat~ (Fig.l). A 1,025-cmlong section sample was collected by F. Lucas in 1968. From 1,025 cm to 770 cm lake clay was deposited, from 770 cm to 120 cm clayey peat, and from 120 cm to 0 cm lake clay. In the whole section pollen grains are not corroded, but from the diagram (Fig.7) it will be clear that only very small quantifies of pollen were deposited in the peaty layer from 770 cm to 120 cm. This fact has also been noted in similar sediments in other lakes in the Cordillera Oriental. Conceivably, special air conditions in certain types of vegetation of the hygrosere (e.g., those dominated by large species of Scirpus) do not permit the deposition of pollen from the atmosphere directly above this vegetation. A sufficiently large pollen total could not be reached. The figures indicated in the diagram are the numbers of grains, recorded in the slides. The diagram apparently reflects the principal changes in the local vegetation (dominance of Alnus). At about 920 cm several curves begin or show a rise at this level, and when we compare this with the Fuquene diagrams it seems that this might correspond with the beginning of zone Y. However, the complete local dominance of alder in the lower part probably caused the absence of these elements in this part of the diagram.

76

B. VAN GEEL AND T. VAN DER HAMMEN Important changes in the diagram are: sample 76: appearance ofDodonaea, Urticaceae, Miconia, Insert. sed. I and Coelastrum

reticulatum sample 75: appearance of Acalypha sample 74: decline of Geranium sample 70: appearance of Tetraedron sample 69: appearance of Alchornea samples 70-68: decline of Myriophyllum and rise of Potamogeton. The interval lying roughly between samples 78 and 65 shows a number of characteristics similar to those of zone Y-II, such as higher percentages of Compositae and Gramineae, and a lower lake level (rise of Cyperaceae pollen and fungal spores, decline of Botryocoecus). The 14C date of 10,550 -+ 60 B.P. (Col.117; GrN 6100) at the depth of sample 69 confirms this interpretation. The lower part of the section (sample 78 to 84), then, could represent zone Y-I. The slightly higher percentages of Polylepis in some samples and the higher lake level plead in favour of this interpretation. The dominating percentages of Alnus pollen must hail from extensive local alder forest surrounding the lake, and the higher percentages of Valeriana, Geranium, Jamesonia, etc., must likewise be of in-situ vegetation. The succession does not resemble that in the Fuquene diagrams very much, but is very similar to the contemporaneous sequence in the "Sabana de Bogot~" (see the diagram CUX upper part, Fig.7 in Van der Hammen and Gonzalez, 1960a). At about 770 cm the formation of peat begins, and it seems as if this level corresponds roughly with the beginning of zone Z (Holocene). At the level of sample 70 the Typha curve starts and in the first 75 cm of the peaty layer the relatively abundant pollen grains of Typha may indicate that this plant was one of the peat-forming elements. For the same reason we think that Cyperaceae were amongst the peat formers. From 475 cm to 400 cm Begonia pollen occurs; indicating that Begonia was growing very near to the site of the section. Fungal spores (probably of local origin) are very abundant in the peat. From sample 9 onward, several samples contained sufficient pollen grains to reach a reasonable pollen total. Samples 7 to 9 show higher Botryococcus and lower Fungi percentages, while clay was deposited. Apparently the lake level was somewhat higher for a short while. The rise of Dodonaea and Compositae indicates that this upper part of the diagram corresponds with zone Z-Ill.

NEWLY RECOGNISEDOR UNKNOWNSPOROMORPHS

Acalypha In the Fuquene I section the pollen grains ofAcalypha (Euphorbiaceae) were included in the curve of the Urticaceae, as this type of grains was thought to belong to one of the

VEGETATIONALAND CLIMATICSEQUENCE OF EASTERN CORDILLERA

77

pollen types of this family, when this material was counted years ago. In the sections Fuquene II and Laguna de Palacio this pollen type was recognised and separately recorded as Acalypha.

Polylepis Polylepis pollen cannot easily be separated from Acaena pollen. Since a differentiation of these two would be of considerable importance (Polylepis is a tree, Aeaena herbaceous or a dwarf shrub), Dr. A. Smit of our laboratory started a scanning electron microscope study of their pollen morphology in detail. Although these studies have not yet been completed, it has already appeared that most of the grains found are of Polylepis. Palmae-type (P1 .I,1) Monocolpate, irregularly scabrate. Grains of this type were found in section Fuquene II in the upper part of zone Z-II and in zone Z-III.

Lemna-type (P! .I,2) Monoporate, echinate.

Ambrosia-type (P1 .I,3) Tricolporate, echinate (Compositae-Tubuliflorae). Spines short.

Begonia-type (P1 .I,4) Tricolpate, striate; striation fine and meridional. Grains of this type were found in many samples of the zones Z-I and Z-II of the Fuquene II section. The samples 23 to 20 show a maximum for the Begonia-type.

C3P3 echinate 1 (Pl.I,5) Tricolporate, echinate. Grains of this type were found in almost all slides of zone Z of the Fuquene II section. Relationship unknown, possibly Loranthaceae.

Cperi 1 (Pl.I,6) Pericolpate, reticulate. Grains of this type were found in the zones, V-I, V-II, Y-II, Z-I and the lower part of zone Z-II of the Fuquene II section. The spectra of the samples 18 to 12 show higher percentages of this pollen type.

PLATE 1

~ i~i~!% ~ i~ i~ 3.

5.

4.

ii!~!!! 6

10.

9

8. 0

10

20

30

40

5 0 .~

Newly recognised or u n k n o w n pollen types from the sections in the F u q u e n e area. 1. 2. 3. 4. 5.

Palmae-type. Lemna-type. Abrosia type. Begonia-type. C3P 3 echinate 1.

6. 7. 8. 9. 10.

C peri 1. C3P3 psilate 1. Phyllanthus. CP peri type 1. Coriaria.

~ ~~

/ i l i !?~¸¸¸ ~ ~i~ i~~

VEGETATIONALAND CLIMATICSEQUENCEOF EASTERNCORDILLERA

79

C3P3 psilate 1 (P11,7) Tricolporate, psilate. Grain thick-walled, with coarse columellae. Grains of this type were found in many samples of the upper part of zone V-I, zone V-II, zone W-I and the upper part of zone Z-III of the Fuquene II section.

Phyllanthus (P1 .I,8) Syncolporate, "reticulate". Five grains in the Fuquene II section.

CPperi 1 (Pl.I,9) Colpus with pore on the six edges of the pyramid-shaped grain. Two grains in section Fuquene II (samples 56 and 57).

Coriaria (PI.I,10) Tricolporate, scabrate. Fifteen grains in the Fuquene II section. SOME DATA ON OTHER MICROFOSSILS(Algae, Fungi and grana insert, sed.)

Gr.Insert.sed.1 (PI.II, 15) This fossil is present in almost all the slides of the Fuquene II section, but attains higher percentages in the Glacial and Late Glacial part of the diagram. Present in the sample 76-65 of the section Laguna de Palacio.

Gr.Insert.sed.2 (Pl.II,14) This fossil is present in the Glacial and Late Glacial part of the Fuquene II section, and in sample 2 of the section Laguna de Palacio.

Gr.Insert.sed.3 (PI.II,16) Present in the samples 70-65 of the section Palacio.

Tetraploa (PI.II, 17) The saprophytic fungus Tetraploa is rare in the Glacial and Late Glacial part of the Fuquene II section (sample 83:1 x: sample 4 7 : 2 x; sample 39:2 x). In the Holocene part of the diagram Tetraploa is'present in low percentages in almost every slide. In sample 1 this fungus shows a maximum of 39 %. In the section Laguna de Palacio Tetraploa is present in the samples 74, 73, 9, 8, 7 and 1.

80

B. VAN GEEL AND T. VAN DER HAMMEN

P L A T E II

J 12.

11.

13.

14.

0I

10i

20 i

30

40

/ii

15.

16.

?

25

5o

17.

,~ ~o,o 12,5,,4

Algae, Fungi and Gr. Insert. sed. from the sections in the Fuquene area. 11. 12. 13. 14.

Coelastrum reticulatum. Tetraedron. Hystr.-type 2. Gr. Insert. sed. 2.

15. Gr. Insert. sed. 1. 16. Gr. Insert. sed. 3. 17. Tetraploa-type.

VEGETATIONALAND CLIMATICSEQUENCEOF EASTERNCORDILLERA

81

Fungi, Botryococcus, Coelastrum reticulatum, Pediastrum and Tetraedron In all the sections the percentages of each of these (parts of) organisms are calculated of a total of about 150 of all these organisms. The curves (or a composite diagram) can be found in the second (right-hand) part of the diagrams. In the Fuquene II section there have also been made calculations of the percentages of these organisms calculated at an often rather low Z-pollen, indicated in the last column of the diagram.

Fungi in the section Fuquene H The curve of the fungi, calculated as a percentage of the total of the other microfossils, shows a striking conformity with the curves of the higher plants of the hygrosere. The fungi curve, calculated at a Z-pollen, seems to confirm that the maxima of the first curve are not only relative, but at the same time caused by an increase in absolute numbers. Stands of plants usually have their quotum of saprophytic and parasitic fungi, and the hygrosere around the lake has not been an exception as far as we can ascertain. This is presumably the cause of the conformity of the fungi curve with the curve of the plants of the hygrosere. No attempts were made to separate and to identify the fungal spores, with the exception of the characteristic Tetraploa-type (Pl.II,17).

Bo tryococcus Very abundant in all the sections. We have as yet no explanation for several intervals with a considerably higher absolute abundance of this organism.

Coelastrum reticulatum (PI.II,11) In the diagram Fuquene lI this alga, belonging to the Chlorococcales, is present during the warmer phase in the Late Glacial and during the Holocene. In the section Laguna de Palacio this fossil is present in some intervals between the samples 77 and 67. The vertical distribution and abundance of this alga strongly suggests a dependence on the average temperature. This is confirmed by Rodhe (1948), who mentions that Coelastrum grows best at 20°-25°C and is found in abundance in summer; for more details, see Round (1967) and Bourrelly (1966).

Hystrichosphaeridae-type 2 !PHI, 13) This fossil is present in some intervals between the samples 63 and 2 of the section Laguna de Palacio.

82

B. VAN GEEL AND T. VAN DER HAMMEN

Pediastrum There are several maxima in the Pediastrum curve. In section Fuquene II the first important maximum starts between samples 85 and 84. There were so many specimens of Pediastrum in the slide, that no sufficient pollen total could be reached. The next important maximum starts with sample 49. Pediastrum shows lower percentages during the warmer phase of the Late Glacial (subzone Y-I). The cooler subzone Y-II (El Abra Stadial) starts with a Pediastrum rise. The curve falls off gradually by the beginning of the Holocene. One of the possibilities of interpretation of these maxima is the following. Sudden climatic changes cause destruction of the in-situ vegetation. A possible consequence is an increase of nutrients for aquatic organisms like Pediastrum. The first maximum coincides with a steep decline of Polylepis. The second maximum is concomitant with the change from Upper Pleniglacial to the warmer phase of the Late Glacial. The third maximum starts with the beginning of the colder subzone Y-II, which must have been the cause of the dying-off of the forests, that must certainly have been present around the lake. The last two maxima of Pediastrum are also manifest in Fuquene I. An interesting fact is that the small Lemna maximum coincides with the maximum of Pediastrum of the Younger Dryas time. Maybe this is an indication for a shallow lake, rich in nutrients. The maximum of Pediastrum in zone Y-II also seems to be present in the lower part of section Laguna de Palacio. Tetraedron (cf. Tetraedron minimum) (PI.II, 12) Tetraedron is present in zone Z of the Fuquene II section and in the samples 7 0 - 6 3 of the section Palacio. These organisms are rather small and they probably disappear in slightly corroded layers. That is the reason why we do not venture to interpret the Tetraedron curve. Conclusions Algae and fungal remains present in our sections seem to yield most valuable information. Coelastrum reticulatum indicates temperature ranges, Pediastrum probably eutrophiation of the (shallow) water by decaying remnants of dead vegetation and the total curve of fungal spores, the local extension (or presence) of the hygrosere during a relatively low lake level. ABSOLUTE DATING In the section Laguna de Fuquene II there are several darker layers intercalated in the grey lake clay. They are richer in organic material. When the pollen diagram was completed, two samples from this darker material were selected from the available

VEGETATI ONAL AND CLIMATIC SEQUENCE OF EASTERN CORDILLERA

83

parallel cores, taken at a horizontal distance of not more than 40 cm from the main section. The outer part of these samples was peeled off, to avoid any possible contamination with younger material. Another sample was selected and taken in the same way from the section Laguna de Palacio. The 14C analysis of the three samples was carried out under the supervision of Dr. W. G. Mook at the Groningen Laboratory. The results are shown in Table I. The exact position o f every core used for ~4C dating in the analysed section was established by pollen analysis of several samples taken from that core. For that reason there may be a slight difference between the depth indicated below and the position indicated in the pollen diagram. The significance of the dates is discussed later and in the following paragraphs. TABLE I Analyses of three samples Laboratory number

Sample number

Section and depth

Material

Age

GrN 5839

Col.115

Fuquene II 478--497 cm

peaty clay

10,820 -+60 B.P.

GrN 5480

Col. 116A

Fuquene II 678-688 cm

peaty clay

20,575 4- 190 B.P.

GrN 6100

Col.117

Lag. de Palacio 827-848 cm

peaty clay

10,550 +-60 B.P.

With the aid of the two ~4C dates from Fuquene II an attempt was made to determine the approximate absolute age of the zone borders, taking into account that during zone W-V the sedimentation rate slowed down considerably because of a very low lake level. If we accept an equal rate of sedimentation for the rest of the section, we can calculate it between the date of ca. 10,800 B.P. at 500 cm and 0 B.P. at the top of the section. We then find the following interpolated dates: Base zone Z-III Base zone Z-IIb Base zone Z-IIa Base zone Z-I (Base zone Y-II 10,800

3,000 B.P. 5,000 B.P. 7,500 B.P. 9 , 0 0 0 - 9 , 5 0 0 B.P. B.P.)

Using the same rate of sedimentation for zone Y-I, we find: Base zone Y-I in Fuquene II ca. 12,000 B.P. in Fuquene I ca. 14,000 B.P. The base of zone W-V is dated directly as 20,500 B.P. The lower zones consist again of normal lake sediments and if we accept the same rate of sedimentation as in the Late Glacial and Holocene, we find the following figures:

84

B. VAN GEEL AND T. VAN DER HAMMEN Base zone W-IV 22,000 B.P. Base zone W-III 23,500 B.P. Base zone W-II 24,500 B.P. Base zone W-I 25,000 B.P. Base zone V-II 27,500 B.P. Base of section Fuquene II (in zone V-I) 32,000 B.P.

These calculated "dates" cannot be confirmed as no ~4C dates are available from this lower part of the section. However, tephrochronology seems to confirm at least the order of magnitude of these values (see the next paragraph). VOLCANICASH IN THE SEDIMENTS(data for a tephro-chronology) Thin layers of volcanic ash were found in sections Fuquene I and II. They may be present as thin bands of pure white volcanic ash with mica, but also mixed with the lake clay~ In this last case the horizons with ash are easily recognisable from the concentration of platelets of mica in the lake clay. Although the two sections are some 6 km apart, the principal ash layers are clearly recognisable in both and occur in the same pollen zones (Fig.4). The youngest "tephra" occurs in subzone Z-I and must have an approximate age of 9,000 B.P. There is an indication of a thin ash layer near the limit of subzones Y-I and Y-II in Fuquene I with an approximate age of 11,000 B.P. It is interesting to compare these first two tephras with tephras I and 04 from Fuego Patagonia (Auer, 1965) that have approximately the same age. The next older tephra is found in the top of subzone W-IV, near the limit W-IV-V. Its age is about 21,000 B.P. A series of three ash layers is found in the interval from the top of V-II to the top of W-Ill. Their age could be between approximately 23,000 B.P. and 26,000 B.P. The deepest tephra is from zone V-I and could have an age of about 30,000 B.P. It is important to note here that we have found the tephras mentioned above in several places in the Cordillera Oriental in lake sediments and in soil sequences in which several intervals have been ~4C-dated. They provide guide horizons that are of considerable importance for correlation purposes. The mineralogical characteristics of the tephras are being studied in all the available sections and the entire question of the tephro-chronology of the area will be treated in a forthcoming publication. There is no young volcanism in this part of the Eastern Cordillera; the ash is certainly from the volcanoes in the Central Cordillera.

THE HISTORYOF THE AREASINCEMIDDLEPLENIGLACIALTIME (Fig.4-8)

Middle Pleniglacial During subzone V-I Polylepis woods dominated on the slopes surrounding the Laguna de Fuquene. There was little open vegetation and Quercus forest probably dominated in

VEGETATIONALAND CLIMATICSEQUENCE OF EASTERN CORDILLERA

85

the Andean forest belt below the Polylepis zone. This oak forest cannot have descended far down and conceivably might even have occupied a few protected places in valleys on the lowermost part of the slopes surrounding the highplain. Some Rapanea, Miconia, tree ferns (Cyatheaceae) and possibly some Weinmannia were probably elements occurring in the lower part of the Polylepis zone. The lake level was high and the climate wet. By the middle of this period there was a volcanic eruption in the Central Cordillera and a conspicuous ash layer was deposited in the lake. During subzone V-II there was a considerable increase of open vegetation (Gramineae). The Polylepis woods disappeared from the main part of the slopes, but were still present locally, probably on the lowermost part of the slopes. In the upper part of the Andean forest, Quercus seems to have declined and at the same time there was a temporary increase of, successively: (1) Rapanea; (2) Myrica and Miconia; and (3) Podoearpus. The lake level was lowered considerably, the hygrosere extended over a broad area around the lake (Myriophyllum, Cyperaceae, Umbelliferae, Polygonum, Rumex). At the very beginning of this zone there was a considerable temporary increase of the alga Pediastrum, possibly indicating eutrophiation of the water by decaying vegetable debris from the dying Polylepis woods and/or the beginning of the lowering of the lake level. During this subzone the forest cannot have descended far down from the highplain and it is possible that, just as during V-l, some forest was present in protected sites (small valleys) on the lowermost part of the slopes surrounding the lake. In the uppermost part of this subzone another thin layer of volcanic ash was deposited in the lake. The forest limit during zone V may have been approximately between 800 m and 1,000 m lower than it is today.

Upper Pleniglacial It is estimated that the zone border V-W may have an age of approximately 25,000 years and corresponds approximately with the limit Middle-Upper Pleniglacial. During subzone W-I the open vegetation (Gramineae) increased considerably and the forest limit must have been far below the level of the highplain; open pdramo prevailed, whilst the climate continued to be dry. A thin layer of volcanic ash was deposited in the lake. During subzone W-II, there was a minor decrease of Gramineae and a minor increase of Polylepis and of alder (Alnus) pollen. At the same time the level of the lake rose and the climate must have been temporally wetter. It is difficult to decide if the slight increase of the pollen of the above-mentioned trees is due to a slight rise in the temperature or to the wetter climate only. A thin layer of volcanic ash was deposited in the lake. During subzone W-Ill there is an increase of Gramineae and the lake level is lower again, indicating that the climate had become drier once more. Soon afterwards there is an increase of Miconia and Weinmannia, while Quercus is disappearing progressively. This seems to indicate that the upper zones of the Andean forest (at this time still

86

K VAN GEEL AND T. VAN DER HAMMEN

below the level of the highplain), consisted of Weinmannia forest and not of a Quercetum type of forest. During subzone W-IV the drier conditions were again interrupted by a short period of a slightly wetter climate, since there was a rise of the lake level. The Gramineae decreased slightly and, while the Weinmannia and Miconia curves retained their relative maximum, there was an increase of Podocarpus. This seems to indicate that this tree became more abundant in the upper zone of the Andean forest. In the uppermost part of this subzone a thin layer of volcanic ash was deposited. Subzone W-V begins some 20,500 years ago and ends probably 13,000 ( - 14,000) years ago. The open vegetation dominated completely and the forest limit must have been far below the level of the highplain. The lake level became extremely low, so that the hygrosere covered the site where the bore holes were drilled (Myriophyllum, Cyperaceae, Umbelliferae) and the sedimentation rate slowed down considerably (locally even down to zero). In the lower middle part there is an increase of Compositae and there are two marked peaks of Crucifereae that probably represent Draba, a common genus in the higher open p&amo and the super-pdramo zone. Everything seems to indicate that the climate was extremely cold and dry. The lowering of the forest limit during this zone must have been of the order of 1,500 m. If only a fall in temperature was responsible for this lowering, this would mean a decrease of 10°C of the mean annual temperature. During subzone W-V the mean annual temperature was probably about 6°(to 5°)C. Taking into account a considerable desiccation of the lake, it seems as if the annual rainfall must have been something between 100 and 400 ram, comparable to that of the dry puna of Peru.

The Late Glacial During subzone Y-I, that lasted until ca. 10,800 years ago, forest again invaded the highplain and the slopes of the mountains surrounding it. On the slopes, the forest consisted mainly of Quercus, but there was also an important increase in Myrica and Dodonaea. The abundance of the last-mentioned shrub is most interesting. To-day it is found on bare soils (eroded soil, xerophytic vegetation) below ca. 3,000 m. Dodonaea (like Myrica) has pioneer qualities and apparently could thrive on the bare soils left after the extreme cold and dry phase of subzone W-V, once the temperature had risen above an annual average of ca. 10°C. During the warmest part of the Late-Glacial "interstadial complex" (Guantiva Interstadial), the forest limit was probably more or less in the same position as it is today and the temperature only slightly (probably no more than by ca. 2°C) lower. The temperature was high enough to enable the alga Coelastrum reticulatum to live in the lake. The level of the lake underwent an important rise, inundating gradually most of the area that had fallen dry during the preceding interval; this, especially in conjunction with the rise of temperature, indicates a

VEGETATIONALAND CLIMATICSEQUENCE OF EASTERN CORDILLERA

87

considerable increase in the annual rainfall. The flat part of the plain not occupied by the lake was invaded by alder brook forest. In the lake, the alga Pediastrum, abundant near the zone border W-Y, rapidl3) became dominated by Botryococcus. Inundation possibly started earlier at the site of Fuquene I (where the top of the W-V sediments lies ca. 100 cm lower), so that in this place the sequence is thicker and more complete, and may be subdiv~.ded into two parts, separated by a minor rise of the Gramineae. At least in this place, zone Y-I must correspond approximately with the European B~lling and Aller¢d Interstadials (and possibly also the Susacfi Interstadial). There are indications of the deposition of a very thin layer of volcanic ash (in Fuquene I), near the limit of subzones Y-I and Y-II. During the deposition of zone Y-II, that started around 10,800 and ended ca. 9,500 years ago (El Abra stadial), the forest limit was pressed down again, probably to the order of some 800 m. Probably the proper forest limit lay somewhat below the highplain, but some forest was probably present in protected valleys on the lower part of the slopes, and Compositae dwarf forest probably was abundant. The lake level went down again, so that the hygrosere (Cyperaceae, Rumex, Polygonum) could extend over considerable parts of the former lake bottom; the climate became considerably drier. In the lake itself, Pediastrum increased again and Coelastrum reticulatum disappeared completely (because of the lowering of the temperature).

The Holocene Subzone Z-I (ca. 9,500 to ca. 7,500 years B.P.) shows a rapidly rising forest limit resulting in the invasion of the area by oak forest. The lake level rose again. The climate became wetter and warmer. In the beginning of this subzone a thin layer of volcanic ash was deposited in the lake. During subzone Z-II (ca. 7,500 - ca. 3,000 B.P.) the climate became still warmer. During the first part, oak was the dominating ,tree. This is especially manifest in the southern part of the area (Fuquene I) where this forest was also poor in Urticaceae. Farther to the north, other trees were more common in this oak forest, and Urticaceae (and Cecropia) were also more abundant. This may be an indication that the southern part was somewhat drier and the accumulation of a more or less substantial humus layer was somewhat delayed there. In the middle part of Z-II there was a sudden or gradual decline of oak and Podocarpus, accompanied by a minor temporary increase ofMyrica, Miconia and Compositae. In the southern part there was a rise of Urticaceae. In the entire area, somewhat earlier, a pronounced rise of Cecropia was noticeable, but this was especially manifest in the northern part; later there was a marked increase of Acalypha. After the decline of Quercus, Weinmannia became considerably more important) taking into account that Weinmannia produces considerably less pollen than Quercus). The presence of abundant

88

B. VAN GEEL AND T. VAN DER HAMMEN

Cecropia and Acalypha on the slopes surrounding the highplain, required a somewhat warmer and wetter climate. It seems evident, therefore, that subzone Z-II represents the Holocene "'hypsithermal" in this area. The temperature may have been ca. 2°C higher than it is today. The lake level remained relatively high, with some minor lowerings in the middle of the subzone. At the beginning of zone Z-Ill (ca. 3,000 B.P.) there is a sudden decline of Cecropia and a minor fall of Acalypha. The climate apparently became cooler. Shortly thereafter the curves show a decline of Urticaceae, a minor maximum of Quercus and a marked rise of Dodonaea, and finally a marked increase of Gramineae and a decline of all forest elements. There is no doubt that these phenomena are related to the beginning (and finally total) destruction of the montane forest by man. The rise of the Dodonaea curve (indicating soil erosion) is found in many of the pollen diagrams in the Cordillera Oriental and seems to be an excellent indicator for the beginning of intensive Indian agriculture in the area. Striking is the occurrence of Dodonaea both in Late Glacial times and in the land-occupation phase. This is a striking parallel with such plants as Artemisia and Chenopodiaceae in NW Europe. In both cases they represent plants with pioneer qualities with similar requirements as to light, soil conditions, and temperature. In the Laguna de Palacio area there was a sudden rise of the lake level at the beginning of Z-Ill, indicating that the climate became wetter. However, later the lake level fell gradually. A comprehensive evaluation of the entire zone Z yields the following general conclusions. At first (Z-I), the climate became warmer and more humid, the forest limit rising, so that at the end of this subzone the slopes surrounding the lake were entirely covered by forest. During the first part of the next subzone (Z-II), this forest, in the southern part of the area, was predominantly composed of oak, with some Podocarpus and Juglans. Oak was somewhat less predominant and Urticaceae more numerous in the northern part, possibly indicating that the rainfall increased from south to north, as it does to-day. Soon the oak and Podocarpus started to decline, Cecropia becoming rather abundant in the north, less so in the south. In the south there was a marked rise of Urticaceae. In the middle of the subzone there a temporary decline of Cecropia occurred, some minor lowerings of the lake level took place, and Alnus had a relative minimum. These phenomena seem to indicate a somewhat drier climate. Weinmannia became more abundant and in the upper part of Z-II there was a noticeable increase of Acalypha. At the beginning of Z-Ill Cecropia suddenly disappeared from the area. The climate became cooler and in the beginning also wetter. Soon, however, human land occupation caused an increasing forest destruction, soil erosion and the extension of Dodonaea. Local subzone Z-I corresponds apparently with Andean pollen zones IV and V and with the European Preboreal p.p. and Boreal; local subzone Z-1I corresponds apparently with Andean pollen zones VI and VII and with the European Atlantic and Subboreal; subzone Z-Ill corresponds probably with Andean pollen zone VIII and the European Subatlantic.

!,

I

~C

r~jc

•

| <--k~w--high

. Jill!

izo

1

Cordillera Oriental

E u rope

.

i

Subatlantic

(v,o

i

2

3

Ld

L.

''

Z Ld Subboreal

(VII)

(1

U

I z~l

0

(Vt)

7

/

8

10

'

I

ZI

>

Y1

)

,°°°°

11 -,...._

12 13

0 (v)

T

m

9

Atlantic

d

Yi

I';'; i~

Boreal Late

=:~ ~oaot,v. lZ~q ,~ /

Fri¢}l~nd phise Dfyas Stadial

Allerll
f

14

15 16

Fuquene W

17

--

i

~1<

Stadial 18

19

U

20 m

Wl

m

?25

d el

w: w

m

Saravita Interval Suta Interval

w

iiiim

Late

v Santuario

!

!

U3 <~ . . . . . . . . . . . .

d

b ?30

Vertical movements of vegetation belts (and appE changes of average annual temp )

m

V

Interval

Early

Denekamp Interstadial

Chronostratigraphy and Correlation

Fig. 8. Curves for displacement of the vegetation zones and changes of lake level in the F u q u e n e area during the last 30,000 years, chronostratigraphy and correlations.

90

B. VAN GEEL AND T. VAN DER HAMMEN

CONCLUSIONS, CORRELATIONS AND CHRONOSTRATIGRAPHY

In Fig.8 we have tried to compile the principal data obtained from the Fuquene diagrams in two curves. The first indicates vertical movements of the vegetation zones (and approximate changes of the annual temperature), the other one the relative changes of the lake level (attributable to precipitation/evaporation). At the right side of Fig.8 are the local zones, the chronostratigraphical units for the Eastern Cordillera, and their correlation with European intervals. Although the general correlation of the principal units with the European ones is confirmed by 14C dating, here or in other Cordilleran diagrams, there are several reasons for using local nalnes for these zones. Sometimes (as in the case of the Denekamp Interstadial), the exact correlation of the boundaries is not yet known. In the case of the Saravita and Suta hltervals, a correlation may be highly probable (with, e.g., the Tursac hlterstadial), but it is not yet directly confirmed. In the case of the Guantiva lnterstadial, the differentiation between "Early" and "'Late" (corresponding with B~blling and Aller~d Interstadials, respectively) is often not clear. The Early El Abra Stadial corresponds exactly with the Younger Dryas Stadial, but in many diagrams it is not distinguishable from the Late Part comprising a major part of the Preboreal. The term "interval" was used in those cases where it was not yet clear if the use of the term interstadial was fully justified. The new names are here used for the first time, but will be fully defined and described in a later publication. In the middle column the stratigraphic position of the tephras (thin layers of volcanic ash) is indicated. They have not yet been numbered as it seelns advisable to wait for additional data from other areas in the Cordillera and for more exact datings. The most important result of the present study, corroborated by studies in the Sabana de Bogot~ (Schreve-Brinkman and Van der Halnmen, m preparation), is that after the humid Lower and Middle Pleniglacial, the following main part of the Upper Pleniglacial, between ca. 20,000 and 13,000 years ago, was extremely dry. This was again followed by a wet phase (ca. 13,000-11,000 B.P.), a short dry phase (ca. 11,000-9,500 B.P.) and (at least in the Fuquene area) a relatively humid Holocene. It is most interesting to compare these data from equatorial kanerica with those published by Kendall (1969) from equatorial Africa, which show a very similar succession. It seems, therefore, as if the actual data available are suggestive of the prevalence of a dry equatorial climate during the last principal phase of the last Glacial.

ACKNOW LEDG EMENTS

The authors thank the Netherlands Foundation for Tropical Research WOTRO who sponsored the research, Dr. W. G. Mook (~4C dating) and Prof. A. D. J. Meeuse (revision of English text}.

~EGETATIONAL AND CLIMATIC SEQUENCE OF EASTERN CORDILLERA

91

NOTE ADDED IN PROOF Recently we came across a paper by Ekman and Fries (1970) with a description of Stauroph~a elegans, that corresponds closely to our Gr.Insert.sed.2. This microfossil represents a resting stage of a Suctorian among the Infusoria group of Protozoa. Ekman and Fries mention that the species occurs in fresh-water lakes, rivers and co~ stal waters of temperate and arctic Eurasia and Greenland - of Staurophrya is present ia the Glacial and Late-Glacial part of the Fuquene II section and is absent in the (warmer) Holocene part. RESUMEN

La secuencia de vegetaci6n y clima durante el Cuaternario Superior en el area de Fhquene {Cordillera Oriental, Colombia) En este trabajo se dan los resultados de un estudio palinol6gico de tres sondeos de sedimentos de laguna en el area Fflquene Valle de Ubat6, Cordillera Oriental de Colombia (5 ° L.N., altura 2.580 m.). Por medio de fechas de radiocarbono y comparaci6n con otros diagramas de polen y fechas de la Cordillera Oriental, fu~ posible correlacionar las zonas locales de polen y unidades cronostratigrificas con la secuencia cronostratigrifica europea. E1 diagrama mils largo (Fuquene ll) representa mils de 30.000 afios, hMuyendo parte del Pleniglacial Medio, el Pleniglacial Superior, el Tardiglacial y el Holoceno. Durante el Pleniglacial Medio el bosque de Polylepis era un elemento importante de la vegetaci6n. Bajo las condiciones climiticas extremas del Pleniglacial Superior existia una vegetaci6n de p~iramo abierto. Durante la parte principal del Pleniglacial Superior (desde cerca 21.000 hasta cerca 13.000 A.P.) el nivel de la laguna era bajo y el clima seco. El nivel de la laguna subi6 neuvamente en el principio del Tardiglacial y el area alrededor de la laguna se cubrio de bosque. En el principio del stadial de El Abra (of., Stadial Dryas Tardio) se present6 un notable enfriamento y el nivel de la laguna descendi6 neuvamente; lo cual tenfa un gran impacto sobre la vegetaci6n que en parte de nuevo se convirti6 en vegetaci6n abierta. E1 principio del Holoceno esti marcado pot un incremento gradual de elementos de bosque, especialmente de Quercus (roble). Bosques de roble dominaron el area durante la mayor parte del Holoceno. Durante el "Hypsithermal", elementos hoy dia creciendo a niveles m~s bajos, como Cecropia, Acalypha (y posiblemente Alchornea), deben haber crecido en el area, entremezclados en el bosque de roble. AI mismo tiempo habfa un incremento considerable de Urticaceae en el sotobosque. Las zonas de vegetaci6n probablemente estaban situadas varios centenares de metros mis altas que hoy d/a. La influencia del hombre sobre la vegetaci6n ya comenz6 antes del principio de nuestra era, pero hay un sflbito incremento de esta influencia (pot ejemplo incremento de Dodonaea, disminucion de Quereus y Urticaceae) alrededor de 2.000 A.P. Despues, el diagrama muestra la flltima r@ida declinaci6n de los elementos de bosque y un incremento

92

B. VAN GEEL AND T. VAN DER HAMMEN

de Gramineae. H o y dia nada se ha quedado de los bosques originales de roble y son reemplazados por areas de cultivo o por comunidades secundarias de plantas con pequefios arbustos. En los sedimentos de laguna se e n c o n t r a r o n capitas delgadas de ceniza volcanica (tephra), que se pueden fechar a p r o x i m a d a m e n t e c o m o 9.000 A.P., 11.000 A.P. y 21.000 A.P. respectivamente; una serie de tres " t e p h r a s " fue depositada entre a p r o x i m a d a m e n t e 22.000 A.P. y 26.000 A.P. y una a p r o x i m a d a m e n t e a 30.000 A.P. Estas " t e p h r a s " han sido encontradas en varios otras secciones de la Cordillera Oriental y forman la base para una T e p h r o c r o n o l g / a

REFERENCES Auer, V., 1965. The Pleistocene of Fuego-Patagonia. 4. Bog profiles. Ann. Acad. Sci. Fennicae, Set A[II, 80: 1-160. Barnett, H. L., 1960. Illustrated Genera of Imperfect Fungi. Burgess, Minneapolis, Minn., 228 pp. Bourrelly, P., 1966. LesAlguesd'Eau Douce. 1. LesAlgues Vertes. Boub~e, Paris, 511 pp. Ekman, P. and Fries, M., 1970. Studies of sediments from Lake Erken, eastern Central Sweden. Geol. FOren, Stockh. F6rh., 92(2): 214-224. Espinal, L. S. and Montenegro, E., 1963. Formaciones Vegetales de Colombia. Inst. Geogr. "Agustin Codazzi", Bogota, 201pp. Graham, A., 1962. The role of fungal spores in palynology. Z Palaeontol., 36(1): 60-68. Instituto Geografico "Agustin Codazzi", 1965. Suelos de Ubate-Chiquinquird. Bogota, 187 pp. Kendall, R. L., 1969. An ecological history of Lake Victoria Basin, Ecol. Monogr., 39:121 176. Rodhe, W., 1948. Environmental requirements of fresh-water plankton Algae. Symb. Bot. Upsaliens., 10:149 pp. Round, F. E., 1967. Light and temperature: Some aspects of their influence on Algae. In: D. F. Jackson (Editor), Algae, Man and the Environment. Syracuse University Press, Syracuse, N.Y., 554 pp. Schreve-Brinkman, E. J. and Van der Hammen, T. Palynology, stratigraphy and paleoecology of the E1 Abra Valley (in preparation). Van der Hammen, T., 1968. Climatic and vegetational succession in the Equatorial Andes of Colombia. Colloquium Geograficum, 9, (Geo-Ecology of the Mountainous Regions of the Tropical Americas), Bonn, pp.187-194. Van der Hammen, T. and Gonzalez, E., 1960a. Upper Pleistocene and Holocene climate and vegetation of the Sabana de Bogot~ (Colombia, South America). Leidse Geol. Meded, 25: 261-315. Van der Hammen, T. and Gonzalez, E., 1960b. Holocene and Late-Glacial climate and vegetation of Paramo de Palacio (Eastern Cordillera, Colombia, South America). Geol. Mijnbouw, 39(12): 737-746. Van der Hammen, T. and Gonzalez, E., 1965a. A pollen diagram for Laguna de la Iterrera (Sabana de Bogotd). Leidse Geol. Meded., 32: 183-191. Van der Hammen, T. and Gonzalez, E., 1965b. A Late-Glacial and Holocene pollen diagram from Cienaga del Visitador (Dept. Boyaca, Colombia). Leidse Geol. Meded., 32:193 201.