CHRONOSTRATIGRAPHY AND CORRELATION OF THE PLIOCENE AND.pdf

.Pergamon Quaternary International, Vol. 40, pp. 81-91, 1997.

PO: Sl~l82(96)00064-X

C 1997 INQUA/ Elsevier Science Ltd All rights reserved. Printed in Great Britain.

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CHRONOSTRATIGRAPHY AND CORRELATION OF THE PLIOCENE AND QUATERNARY OF COLOMBIA

Thomas van der Hammen*t and Henry Hooghiemstra* *Hugo de Vries lAboratory, Department of Palynology and Paleo/Actuo-ecology, University of Amsterdam,

Kruislaan 318, 1098 SM Amsterdam, The Netherlands1 tTropenbos-Colombia, Bogota, Colombia

Names for the chronostratigraphic units of the Pliocene and Quaternary of Colombia are defined and formalized based on studies of outcrops and deep bore holes in the area of the high plain of Bogota. Chronostratigraphic, biostratigraphic and lithostratigraphic sequences have been correlated as far as possible. A tentative correlation with the marine oxygen isotope stratigraphy is indicated.

Pliocene chronostratigraphic units are provisionally characterized by abundance/first appearance in the pollen record of specific floral elements: Mauritia zone (Tequendamian: ca. 5.~.2 Ma), Hedyosmum zone (Facatativanian: ca. 4.2-3.5 Ma), Myrica zone (Sisganian: ca. 3.5-3.1 Ma), Borreria zone (Chocontanian: ca. 3.1-2.7 Ma and Engativanian: ca. 2.7-2.4!2.2 Ma), although precise boundaries cannot yet be established. The Engativanian is a transitional phase, characterized by a continuous temperature decrease in successive cold episodes, and may include the latest part of the Pliocene and the earliest part of the Quaternary.

Quaternary chronostratigraphic units are precisely limited by levels of pronounced climatic change; these boundaries are near to the first appearance/abundance of Juglan.s-Plantago (Funzanian: ca. 2.4!2.2-1.0 Ma), Alnus (Fuchanian: ca. 1000-660 ka and Cotanian: ca. 660-335 ka), and Quercus (Subanian: ca. 335-128 ka, Bacatanian: ca. 128-73 ka, Fuquenian: ca. 73-10 ka, and the Holocene). The relationship with the officially defined position of the base of the Quaternary, at ca. 1.80 Ma, is shown. The last glaciation in Colombia is named the Cocuy glaciation. @ 1997 INQUA/ Elsevier Science Ltd. All rights reserved.

INTRODUCTION

In recent decades, we have learned increasingly about the Quaternary and Pliocene stratigraphy of the high plain of Bogota and its surrounding areas (Van der Hammen and GonzaJ.ez, 1960a, 1963, 1964; Van der Hammen et al., 1973, 1980; Vander Hammen, 1974, 1978, 1981a, b, 1992; Andriessen et al., 1993; Helmens, 1990; Helmens and Van der Hammen, 1994). Important findings also have come to light in other areas such as the Colombian Central Cordillera (Thouret and Van der Hammen, 1981, 1983; Thouret, 1988; Thouret et al., 1995), and the Amazon basin (Van der Hammen et al., 1991a, b). Of prime importance for subdividing the Quaternary of Colombia are pollen records of lacustrine deposits on the high plain of Bogota (Fig. 1 ), which represent the last 3 million years (=3 Ma) (Vander Hammen and GonzaJ.ez, 1960a, 1964; Van der Hammen et al., 1973; Hooghiem-stra, 1984, 1989, 1995; Hooghiemstra and Sarmiento, 1991; Hooghiemstra and Cleef, 1995, in preparation; Hooghiemstra and Ran, 1994a, b). This pollen sequence can be correlated with the marine oxygen isotope stratigraphy (Hooghiemstra et al., 1993) and with the stratigraphic sequence of the borders of the high plain of Bogota (Helmens, 1990), its adjacent valleys and with other zones studied in Colombia. We now have a more detailed understanding of the last interglacial and glacial (especially the late Glacial) and Holocene, thanks to

1The Netherlands Centre for Geo-ecological Research, ICG.

81

palynological data from numerous lakes in different parts of Colombia (Van Geel and Van der Hammen, 1973; Melief, 1985).

The objective of this paper is to define and formalize the chronostratigraphy of the Pliocene and Quaternary of Colombia and its nomenclature. Another aim is to correlate the chronostratigraphic, biostratigraphic and lithostratigraphic sequence and nomenclature to the greatest extent possible.

The Pliocene-Quaternary boundary has been debated widely. According to its definition by the lUGS Stratigraphical Commission, the boundary corresponds to the top of the Olduvai paleomagnetic epoch (ca. 1.65 Ma). This criterion is difficult to apply in most continental pollen records and climatic change is the most appropriate basis for correlation on a global scale. Therefore, in terrestrial records the first pronounced cold period was used as a criterion (Zagwijn, 1960, 1975; see also the important discussion in Zagwijn, 1992) and places the Pliocene-Quaternary boundary at ca. 2.5-2.3 Ma.

The Quaternary poses a special problem of chronos-tratigraphic subdivision. There is biostratigraphic evi-dence with data on the appearance and disappearance of taxa and associations. There is also the sequence of significant climatic changes, which are mirrored in major changes in the vegetation. Most of these climatic changes are global in nature and offer an excellent basis for chronostratigraphy, by providing means to differentiate between stages (Zagwijn, 1992). Given these considera-

82 T. Van der Hammen and H. Hooghiemstra

/

/. / \

/

0 5 10

*

/

\ \ /

...... /

... \. N"'

Cboconta ~ ChocontAl Choconta-4 /

\ /c; .\ ./

/ /\

\~ .;;>. \rr.

\

FIG. 1. Map of the Eastern Cordillera of Colombia, indicating the location of the basin of Bogota at 2550 m altitude. Locations of main

pollen records discussed in the text are shown by a star.

tions, we propose in this paper a formal chronostrati-graphy (chronostratigraphic nomenclature) for the Qua-ternary of Colombia as a general framework for correlating in time the biostratigraphie& and lithostrati-graphies of the different geographic regions having different geographic, climatic and environmental condi-tions. The chronostratigraphic nomenclature suggested for the Pliocene is more provisional, since precise boundaries are still impossible to determine.

BIOSTRATIGRAPHY AND IUSTORIC PHYTOGEOGRAPIDC ASPECTS OF THE IDGH PLAIN OF BOGOTA-EASTERN CORDILLERA

A biostratigraphic zonation of the Pliocene and Quaternary of Colombia was proposed by Van der Hammen et al. (1973). Seven biozones were identified and are distinguished mainly by successive immigrations of taxa (Fig. 2). Biozones I through IV were based on a palynological analysis of intervals of organic sediments separated by intervals of white sand and clay, without pollen. For this reason, the precise boundaries between these biozones are unknown. Biozones V through VII were based on the continuous sequence of lake sediments in the 195 m deep bore hole Ciudad Universitaria (CUX-CUY) from the high plain of Bogota (Van der Hammen and Gonza.J.ez, 1964; Van der Hammen et al., 1973).

0.2-

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0.8-

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~ "'(

VI

Tnxa wilh 'first nppcolnmL'C dale' in lhc Hogo1D urcn (b:s..cd nn l'tlknt~~~"d!l m~ntiutk.'ll inlhc h'ltl)

"TT c :I N Ill

NNNNNNNN~ c c

N

111!1!111 tropical forest elements stilandellll fot?st e/ exrl LC.::I ~fld SWancfellll ! I lsub/piramo e/HJenls r'.' I savanna elements

N s

N

N

FIG. 2. Composite pollen record from the lower Pliocene to latest Pleistocene of the sediments of the basin of Bogota (after Van der Hammen et al., 1973; Hooghiemstra, 1984Hooghiemstra, 1989). Successive altitudinal positions during upheaval of the Eastern Cordillera are represented by biozones I to IV. The basin reached modem elevations (ca~ 2550 m) around 3.5 Ma. A successive immigra-tion of flora elements which originated from temperate and cool zones of the northern and southern hemisphere is demonstrated. n = northern hemisphere element (holarctic affinity); s = flora element of southern South America (austral-antarctic affmity); s, n =origin may be from both geographical areas; c = cosmopolitan element; * = relation with southeast Asia (laurasiatic element; Vander Hammen and Cleef, 1983).

Adapted after Hooghiemstra-and Cleef (in preparation).

Chronostratigraphy and Correlation of the Pliocene and Quaternary of Colombia 83

Biozone IV is also represented in bore hole Funza-11, allowing us to distinguish more precisely the boundary between biozones IV and V. The IV-V boundary could be identified at a depth of 405 min Funza-IT (Fig. 3), based on the depth where Juglans and Plantago are first observed (although a few grains can be found occasion-ally at lower levels). Daphnopsis is more frequent below this boundary; Hypericum is more frequent above. High percentages of Borreria are characteristic of biozone IV. The lower portion of biozone V is transitional in appearance, while the upper part has Borreria values that are already quite low. In biozone V, Polylepis replaces Hypericum as the most important element in the high-Andean (=upper montane) dwarf forest belt. Other characteristics of this boundary can be seen in the complete diagram of Funza-II and to some extent in Fig. 3. The boundary between biozones IV and V is estimated at 2.2 to 2.4 Ma, while the base of biozone IV could be dated at least 3.2 Ma.

The boundary between biozones V and VI corresponds to the beginning of the Alnus (alder) record and its age is estimated at 1.0 Ma (Hooghiemstra and Sarmiento, 1991; Andriessen et al., 1993). The boundary between biozones VI and VII corresponds to the start of the Quercus (oak) pollen record, and its age is estimated at ca. 330 ka (Hooghiemstra and Sarmiento, 1991; Hooghiemstra and Ran, 1994a). The percentages of Quercus increase distinctly after ca. 200 ka, indicating that Quercus forest is a prominent type of zonal vegetation from that time onward.

Figure 3 shows the downcore distribution of some 20 taxa based on the pollen records of bore holes Funza-I and Funza-11. Most are immigrants from the northern hemi-sphere (or could have come from either the southern or northern hemispheres); Rhus, Clethra, Symplocos and Hedyosmum have amphipacific phytogeographic relations (Laurasiatic Tertiary) (Van der Hammen and Cleef, 1983). However, a detailed analysis of Funza II has yet to be completed and the first appearance dates of elements less pronounced than Alnus and Quercus could change somewhat.

Several observations are in order with respect to initial appearances. Based on what we now know, the Caryophyllaceae family appears for the first time in the upper part of biozone IV. A comparison between the pollen assemblages of sediments in biozones III and IV shows the latter also contains (at least locally) the first appearance of Umbelliferae, Geranium, Aragoa, Poly-lepis and Myriophyllum. There is a clear increase in abundance of Plantago pollen grains in biozone V, but minor percentages indicating local presence only, occur in biozone IV. In recent studies, small percentages of Hedyosmum were found locally in the sediments of biozone I (Wijninga, pers. commun. 1994) and also seem to be present locally in Miocene sediments of the Amazon (Hoorn, pers. commun. 1994). This could mean that biozone II is characterized by the continuous and relatively abundant presence of Hedyosmum, while biozone I apparently may have low percentages and very local representation of Hedyosmum. Finally, we have no

knowledge as yet of a series of continuous sediments that could include the boundary between biozones lli and IV. Figure 3 also shows intervals with characteristic vegeta-tional-environmental conditions (high or low frequency of certain taxa), indicated by the letters 'a' through 'h'.

In the following paragraphs we will first discuss the Pliocene, followed by the time interval represented by the 540 m of lacustrine sediments from the high plain of Bogota (represented especially in the bore holes Funza-1 and Funza-11). These sediments correspond to the period of biozone IV, of upper Pliocene age, through biozone VII, of late Pleistocene age.

CHRONOSTRATIGRAPHY AND CHRONOSTRATIGRAPHIC NOMENCLATURE

Van der Hammen and Gonzalez (1964) and Van der Hammen et al. (1973) placed the basis of the Quaternary, in accordance with the criterion Zagwijn (1960) used for European pollen stratigraphy, at the first major cooling around 2.5 Ma. They divided the Quaternary of Colombia into three major parts: the 'Lower', 'Middle' and 'Upper' Quaternary. The beginning of these subdivisions could be determined by the first appearance of Alnus (base of the 'Middle' Quaternary) and Quercus (base of the 'Upper' Quaternary). The respective ages of these boundaries are ca. 1 Ma and ca. 330 ka (Hooghiemstra and Sarmiento, 1991; Andriessen et al., 1993). Dividing the Quaternary into the Juglans!Plantago zone (biozone V), the Alnus zone (biozone VI), and the Quercus zone (biozone VII) (see Fig. 5) seems a highly practical proposal for Colombia. Although the first appearance of Alnus and Quercus in the north and south of Colombia might not be exactly synchronic, both trees are anemophilous and produce large quantities of pollen, which is spread by eolian transport easily over great distances; rivers also carry (and deposit) pollen of Alnus and Quercus. For this reason, their first appearance in sediments should be quite close to synchronic. Nevertheless, chronostratigraphic boundaries should be established on the basis of the most significant change in climate nearest to the initial appearances mentioned (or, in general and to the extent possible, those nearest the biostratigraphic boundaries).

Although there is no precise international definition (besides the Pliocene-Pleistocene boundary), it is com-mon usage that the early Quaternary starts at the first clear glacial period (ca. 2.4 Ma*), or at the top of the Olduvai magnetic epoch (ca. 1.65 Ma*), the middle Quaternary at Oxygen Isotope Stage 22 (ca. 0.9 Ma), and the late Quaternary at the beginning of the Eemian (corresponding to Oxygen Isotope Stage 5e; ca. 128 ka)(* recent recalibration of the paleomagnetic scale has resulted in the lowering of these dates to 2.6 Ma and 1.8 Ma, respectively). Figure 5 shows the relationship between the climatic sequence, the biozones, and the two possible major subdivisions of the Quaternary. Establish-ment of the precise position of what is considered as the first clear glacial period in Colombia will be possible when the lower part of the Funza-11 pollen record has

84

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T. Van der Hammen and H. Hooghiemstra

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Onwncnrc di~trihution and JlC."riod~ nf main ahuodatwc of taxa

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FIG. 3. Summary pollen diagram of core Funza-IT, pollen zones, estimated ages (provisionally; after Hooghiemstra and Ran (1994a) and Hooghiemstra and Cleef (submitted)), and biozones (after Vander Hammen et al., 1973). Changes of the contribution of 21 selected taxa to the zonal (regional) and azonal (local) montane vegetation throughout the Late Pliocene-Pleistocene is indicated. (Figure adapted from Hooghiemstra and Cleef, in preparation.) Solid lines: presence with relatively high percentages in the vegetation (note the first appearance dates of Alnus and Quercus). Densely dotted lines: continuous presence with low percentages in the vegetation. Widely dotted lines:

discontinuous presence with low percentages in the vegetation.

Chronostratigraphy and Correlation of the Pliocene and Quaternary of Colombia 85 Age

(Ma BP) 2.212.4

3 -

Chronostratigraphy

Engativanian

Chocontanian

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= ~ CJ e Facatativanian --4 -~

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FIG. 4. Chronostratigraphic units of the Pliocene of Colombia. Correlation with biostratigraphic zones and the lithostratigraphy of the sediments of the high plain of Bogota and surroundings is indicated.

been analyzed in detail (Hooghiemstra, in preparation); it is anticipated that this period is in the Engativanian. The chronostratigraphic units are described formally in the following section.

PLIOCENE CHRONOSTRA TIGRAPIDC UNITS

A continuous pollen sequence for the continental Pliocene in our area is not available. There are limited intervals of organic sediments, which provided the data for biostratigraphic zonation: biozones I, II, ill and IV (Van der Hammen et al., 1973). Consequently, as it is impossible to establish the base of chronostratigraphic units on the basis of any characteristic climatic event (or other event of chronological importance), most of the units cannot be described formally, with the exception of the latest, the Engativanian. Until we have sufficient data to establish these boundaries precisely, it is suggested the names Tequendamian, Facatativanian, Sisganian and Chocontanian be used provisionally, in a chronostrati-graphic sense (provisional chronostratigraphic units at stage level) (Fig. 4).

Tequendamian (prov.) For now, this chronostratigraphic unit will include the

time sequence of biozone I. The name is derived from Saito Tequendama (Tequendama Falls), near where sediments of that age are found (Van der Hammen et al., 1973; Wijninga, 1996a. b). Spanish name: Tequenda-mense.

Facatativanian (prov.) For now, this chronostratigraphic unit will include the

time sequence of biozone n. The name is derived from the city of Facatativa, where sediments of that age are found (Vander Hammen et al., 1973; Wijninga, 1996b). Spanish name: Facatativense.

Sisganian (prov.) For now, this chronostratigraphic unit will include the

time sequence of biozone m. The name is derived from Embalse de Sisga (Sisga Reservoir), where sediments of that age are found (Van der Hammen et al., 1973). Spanish name: Sisgense.


Chocontanian (prov.) This chronostratigraphic unit includes the 540 to 465 m

interval in bore hole Funza-ll (Figs 3 and 4 ), as the upper portion, and corresponds approximately to the lower part of biozone IV (interval 'a' in Fig. 3). However, the stratigraphic position of the base remains unknown. The name comes from the town of Choconta, where sediments of that age are found (Van der Hammen et al., 1973). Spanish name: Chocontense.

Engativanian

Characterized by the interval of 465 m (base) to 405 m (top) in bore hole Funza-ll, this chronostratigraphic unit corresponds to Funza-II pollen zones F2-X9, F2-X10 and F2-X11. The base coincides with a sharp drop in temperature and the temperature decrease continued, with minor fluctuations, until the onset of a new and drastic decline after 405 m core depth (Hooghiemstra, 1993; Hooghiemstra and Ran, 1994b). Using this period of temperature decrease, dated about 2.5 Ma, as the basis of the Quaternary (corresponding to the Praetiglian period in the European climatic subdivision as shown by Zagwijn, 1960, 1992), the Engativanian is a transitional phase and could correspond to the latest part of the Pliocene and the earliest part of the Quaternary. It represents the period of global cooling that led to the start of the ftrst pronounced series of cold episodes ('glacial' intervals) of the Quaternary. The age of the Engativanian is estimated from 2.8-2.7 Ma to 2.4-2.2 Ma. The Engativanian corresponds approximately to the upper part of biozone IV (subzone IVb) and to interval 'b' in Fig. 3. The name is derived from the town of Engativa on the high plain of Bogota. Spanish name: Engativense

CHRONOSTRATIGRAPWC UNITS OF THE QUATERNARY

Although not corresponding to the officially accepted lower boundary of the Quaternary, we use here the ca. 2.5 Ma age as the basis of the Quaternary (see the discussion in Zagwijn, 1992). Figure 5 shows the relationship between our subdivision and terminology, and the JUGS-accepted base and subdivision of the Quaternary. The chronostratigraphic units of the Qua-ternary of Colombia are formally described here at the level of stages, based on deep bore holes drilled on and near the high plain of Bogota (Funza-! and Funza-ll, Ciudad Universitaria CUX-CUY, Laguna de Fuquene-ll and Laguna de Fuquene-ill).

Funzanian

Characteristic interval from 405 m (base) to 255m (top) in bore hole Funza-ll. In Funza-1, the top is located at approximately 257 m. This unit corresponds to Funza-11 pollen zones F2-X1 through F2-X8. The base corresponds to a sharp drop in temperature, which

represents the start of a glacial, in our view the fust of the Quaternary. It is a long stage, characterized by cold climatic conditions interrupted by relatively short inter-vals of an interglacial nature. The Funzanian corresponds to the early Quaternary. Its age is estimated from 2.4-2.2 Ma to 1.0 Ma. This chronostratigraphic unit corre-sponds approximately to biozone V and to intervals 'c' and 'd' in Fig. 3. The name is derived from the village of Funza on the high plain of Bogota.

The Funzanian can be subdivided into early, middle and late Funzanian; the early Funzanian from 405 to 380m in bore hole Funza-II (cold climate with relatively short interglacials), the middle Funzanian from 380 to 297 m in bore hole Funza-II (cold glacials and not very warm interglacials), and the late Funzanian from 297 to 257m in bore hole Funza-11 (cold glacials and relatively warm interglacials).

The cold stage at the start of the Funzanian probably corresponds to one of the last cold periods in the series of cold episodes with the stage numbers G6 (Stage 110 in the old numbering) to 96 (Tiedemann et al., 1994) of marine oxygen isotope stratigraphy. The cold stage at the start of the Funzanian probably also corresponds in time to the pollen-based cold Praetiglian interval of European chronostratigraphy (e.g. Zagwijn, 1960, 1992). Spanish name: Funzense.

Fuchanian

Characteristic interval from 257m (base) to 143m (top) of bore hole Funza-! (255m and 147m respectively in bore hole Funza-ll). This chronostratigraphic unit corresponds to Funza-! and Funza-11 pollen zones 21 to 29, and most of 30. The base corresponds to a significant rise in temperature, which coincides with the beginning of the ftrst major interglacial (number 10, counting from top downward; see Fig. 5). It includes interglacials 10, 9 and 8 'a' and 'b', the glacials separating these intervals, and ends with a sharp cooling at the start of the glacial between interglacials 8 and 7. The Fuchanian corresponds approximately to the lower part of biozone VI and to much of interval 'c' in Fig. 3. With the Fuchanian begins the middle Quaternary, characterized by a predominant periodicity in climatic change of ca. 100 ka which leads to the sequence of pronounced interglacials and glacials (Hooghiemstra et al., 1993). Its age is estimated from 1.0 to 0.66 Ma. This chronostratigraphic unit probably corresponds to Stages 17 through 25 of the marine oxygen isotope stratigraphic record. The name is derived from the Fucha River on the high plain of Bogota. Spanish name: Fuchense.

Cotanian

Characteristic interval from 147m (base) to 94 m (top) in bore hole Funza-11 (143 m and 94 m respectively in bore hole Funza-1). This unit corresponds to the pollen zones F2-14 through F2-20 in bore hole Funza-11. The base corresponds to a pronounced cooling and the top to a

Chronostratigraphy and Correlation of the Pliocene and Quaternary of Colombia

Estimated displacement CHRONOSTRATIGRAPHY BIOZONES LITHOSTRA Tentative of the upper forest line TIGRAPHY correlation based on pollen records Main (high plain of 180/16Q Funza-1 and Funza-ll Hl

1nterglacials Depth Funza Bogol:i) stages

-

-:: Ia Fuqueman u C)lip_F. g = F-11 = 0 ---

-

~ 2

'"""' Hncntnman F-1 s - - 5 2

--5lm 43m I'll I'll VII "' e e ""}. 3L,.,._....,, ::I 1....:. Subanian ~ && 7 c:::: .~.;.;.:.:.: ::I -.-:::: F-11 F-1 Cl C'll 0 9 c c u "0 0 s::::::

94m (94m) .g C'll ;g c.;. "' ~ :s 0 II "' I'll e

= u "0 c u F-1 N I'll :.c 8& ~ 147m (143m) VI "' .J:j Q.. ==

,. ::I C'll I'll c Cf.) 19 .. < :.1> ~ 9~ Fuchanian -21 I'll

,;.:.:,;,:,: .... ~;) I v:

0.2

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>- Cf.) 1.0 -= ~ LIJ ~.;.;.;.;.: I 0:: 10 F-11 F-1 25 >-g .......__ < ~ 255m (257m) I ) z o::-u I < 0 ( 0:: ~ !! I z;, ~ ..!!! J O::c Cf.) ~--iil t--- F-11297 m -o ::l !'""I. ~ 0 ...l :,) u o.::: c >

0 N

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~ r--- F-ll 380m c

~ 1.1. 0 -~ .... u v. >.

--= .!:I uc.. Cf.) c 0 ell ~ LIJ u s~ z c 0 0 -u ;:J LIJ N g I'll "' '-' 1-J F-11465 m IV ;:: UJ.9 ( ~ :J ~ c Z:.~> ... .. LIJ = Q.. 0 g D ~ I'll u U'E .J:. :> ~ E oo -v t::: 0 - u 0 ...JU

1.4

1.8

2.2

2.6

IChocomanian I~ c 0 :.::! c...:; 0 ~ N 3.0 8 8 00

88 T. Vander Hammen and H. Hooghiemstra

rise in temperature. It includes the large interglacials 7, 6 and 5 (Fig. 5), and the intermediate glacials, beginning and ending with a glacial. The Cotanian corresponds approximately to the upper part of biozone VI and the upper part of interval 'e' and interval 'f' in Fig. 3. Its age is estimated between 660 ka and 335 ka. This chronos-tratigraphic unit probably corresponds to Stages 10 through 16 in marine oxygen isotope stratigraphy. The name is derived from the village of Cota on the high plain of Bogota. Spanish name: Cotense.

Subanian

Characteristic interval from 94 m (base) in the bore holes Funza-1 and Funza-IT to 43 m (top) in Funza-1 (and approximately 51 min Funza-IT). It corresponds to pollen zones 8 to 13 in bore holes Funza-1 and Funza-IT. The base reflects a distinct rise in temperature towards interglacial 4 (Fig. 5). The top also corresponds to a sharp increase in temperature, towards interglacial 2. Therefore, the Subanian includes interglacials 4 and 3, the glacial separating them, and the glacial after the third (between interglacials 3 and 2). This unit corresponds approximately to the lower part of biozone VIT and roughly to interval 'g' in Fig. 3. Its age is estimated from 335 to 128 ka. The Subanian probably corresponds to Stages 6 through 9 in marine oxygen isotope stratigraphy. The name comes from the village of Suba on the high plain of Bogota. Spanish name: Subense.

Bacatanian

Characteristic interval from 43 min Funza-1 (ca. 51 m in Funza-IT) and 31m in bore hole Ciudad Universitaria-X (Bogota; Van der Hammen and Gonzalez, 1960a, 1963)(base) to provisionally 30m in Funza-IT and 22.2 m in bore hole Ciudad Universitaria-X (top). This would correspond to pollen zones 5, 6 and 7 of the bore holes Funza-1 and Funza-IT, and to the complex of the last interglacial (number 2 in Fig. 5). The base corresponds to a pronounced rise in temperature and the top to a decline in temperature; interglacial conditions are interrupted by one or two extremely cold stages. The Bacatanian is also represented in the section of Paramo de Agua Blanca (pollen zone IV, Helmens and Kuhry, 1986) and the 43-27.5 m interval of bore hole Fuquene-m (Van der Hammen and Hooghiemstra, in preparation a). It corresponds to part of biozone VII and part of interval 'h' in Fig. 3. Its age is estimated from 128 to 73 ka. The Bacatanian chronostratigraphic unit corresponds to Stage 5 in marine oxygen isotope stratigraphy and to the Eemian and early Glacial (including the Brorup and Odderade interstadials) in Europe.

The name is derived from Bacata, an Indian place-name also constituting the basis for the name of the city of Santa Fe de Bogota. This interval was ftrst observed in Santa Fe de Bogota on the high plain of Bogota (bore hole Ciudad Universitaria). Spanish name: Bacatense.

Fuquenian

Characteristic interval from 27.5 m in bore hole Fuquene-m (Van der Hammen and Hooghiemstra, in preparation a), 28.5 m in Funza-IT and 22.2 m in Ciudad Universitaria-X (base) to the top at 4.1 m in bore hole Laguna de Fuquene-IT (Van Geel and Vander Hammen, 1973). This chronostratigraphic unit corresponds to pollen zones 2, 3 and 4 in bore holes Funza-1 and Funza-IT, to pollen zones 4 to 8 in bore hole Fuquene-m, and the pollen zones V, W andY in bore hole Fuquene-IT. The base of the Fuquenian corresponds to a drop in temperature. The Fuquenian corresponds to part of biozone Vll and a part of interval 'h' in Fig. 3. Its age is estimated from 73,000 to 10,150 BP. This chronostrati-graphic unit corresponds to Stages 2, 3 and 4 of the marine oxygen isotope stratigraphy. Its name is derived from the village of Fuquene and the lake at short distance, which bears the same name. The Fuquenian and its subdivision are discussed later in more detail (Van der Hammen, 1995; Vander Hammen and Hooghiemstra, in preparation a, b). This unit corresponds to what is known worldwide as the last glacial, particularly for different regions: i.e. the Wiirm glaciation, Weichsel glaciation, Wisconsin glaciation and the Merida glaciation. We hereby formally propose that this last glaciation in Colombia be named the Cocuy glaciation, since the sequence of moraines in the Sierra Nevada del Cocuy, described 20 years ago, is fairly complete and its absolute and relative dating permits an initial time profile of morainic stages (Vander Hammen et al., 1980/81). Also to be considered is the fact that maximum glacial extension was during the middle Pleniglacial and not during the late Pleniglacial. In other words, it was well in advance of the maximum extension of ice in the northern hemisphere. Spanish name: Fuquense.

Holocene

The Holocene, which corresponds to the last ca. 10,150 years, is clearly recognized in many parts of the world and is a chronostratigraphic unit precisely defined in time. It is registered in bore hole Fuquene-IT, represented adequately in the interval from 4.1 m to the surface (Van Geel and Van der Hammen, 1973), and in many other sections of Colombian lakes. The Holocene shows small fluctuations in temperature and considerable changes in precipitation (Vander Hammen and Gonzalez, 1960a, b, 1963, 1965; Wijmstra and Van der Hammen, 1966; Van der Hammen, 1962, 1974, 1986, 1992; Vander Hammen and Cleef, 1992; Melief, 1985; Salomons, 1986; Kuhry, 1988; Plazas et al., 1988).

CHRONOSTRATIGRAPHY, BIOSTRATIGRAPHY AND CORRELATION WITH

LimOSTRATIGRAPHY

Correlation within Colombia in general

A clear and important relationship between chronos-

Chronostratigraphy and Correlation of the Pliocene and Quaternary of Colombia 89

tratigraphy and biozones exists on and near the high plain of Bogota. Whereas biozone boundaries are based largely on the first appearance of pollen from immigrant anemophilous species (i.e. pollen that is produced in large quantities and transported by wind and frequently by rivers), they are probably more or less synchronic throughout Colombia. This is particularly plausible for boundaries established on the first continuous appearance, with significant percentages of pollen of Hedyosmum, Myrica, Alnus and Quercus. Based on recent sediments from the lower Magdalena River region, we know that pollen from Andean taxa (such as Alnus) can reach the tropical lowlands (Wijmstra, 1967). A very interesting sequence in this respect was found in bore hole Barranquilla-1, drilled in 1983 by Koch Colombia Inc. on the Caribbean continental shelf off Barranquilla and the mouth of the Magdalena River. Samples from the interval between a depth of 279m (915ft) and 690 m (2265 ft) were studied palynologically (VanderMeulen, 1987) and micropaleontologically (nannofossils; Ming Jung Jiang, mentioned in Van der Meulen, 1987). Hedyosmum and Myrica are found from the base of this interval upward, but Alnus makes its first appearance at 389m (1275 ft) and, from this depth upward, is relatively abundant in all samples. According to the nannofossil study, the Pliocene-Pleistocene boundary could be between 526 m (1725 ft) and 553 m (1815 ft) (boundary of Martini's zones NN 18 and 19, 1971, mentioned in Van der Meulen, 1987). These data appear to agree with the first immigration of Alnus into the South American continent, at approximately 1 Ma. The base of biozone VI is probably at 389m (1275 ft), which corresponds roughly to the base of the Fuchanian. Alnus also appears for the first time in the formations of Cerro de la Popa (Popa Hill) in Cartagena (Sole de Porta, 1960), in the middle of the bluish marl, which would indicate a Quaternary age for this marl and the coral limestone on the upper part of the hill.

Duenas and Castro (1981) studied samples from the Las Palmas Member of the Mesa Formation in the Falan region. As these samples were found to contain neither Hedyosmum, Myrica nor Alnus, this member seems to belong to the Lower Pliocene and should therefore correspond to the Tequendamian.

There appears to be a clear biostratigraphic and chronostratigraphic correlation between sediments of the Tilata and Tunja formations on the high plains of Cundinamarca and Boyaca (Van der Hammen et al., 1973).

Correlation on and near the high plain of Bogota Chronostratigraphic, biostratigraphic and lithostrati-

graphic correlation on and near the high plain of Bogota seems possible, although certain problems remain to be solved. The boundary between the Sabana and Subacho-que formations in bore hole Funza-II may be placed at 320m (where layers of sand first appear) and the boundary between the Subachoque and Tilata formations

at 468 m. The upper 'unnamed member' (Helmens, 1990; Helmens and Van der Hammen, 1995) of the Tilata Formation, therefore, corresponds to the 468 to 585 m interval of bore hole Funza-IT, and is formally described here as the Guali Member.

The Guali Member of the upper Tilata Formation. Characteristic interval from 468 to 585 m in bore hole Funza-II. The base should be younger than the upper portion of the Guasca Member and rests on older rocks. The upper limit of the Gualf Member corresponds to the base of the interval correlated lithologically (and biostratigraphically) with the Subachoque Formation. This member consists of compacted grey and olive-green clay, clayey silt and several layers of lignite and sand. The sand is fine and exhibits biogenetic structures, undulating fragments of organic matter and occasionally gravel up to 5 mm in diameter. Some of these materials show signs of being colluvial. The Gualf Member, as described here, corresponds approximately to biozone IV a and to the Chocontanian chronostratigraphic stage. Its name is derived from Pantano de Gualf (Gualf Marsh); bore hole Funza-11 was drilled close to this marsh.

The correlation between chronostratigraphy, biostrati-graphy and lithostratigraphy on and near the high plain of Bogota is shown in Figs 4 and 5. The original descriptions of the lithostratigraphical units were given in Van der Hammen et al. (1973), Helmens (1990) and Helmens and Van der Hammen (1995).

The chronostratigraphic position of the Marichuela Formation is not known precisely; it may be of late Miocene or early Pliocene age. The Tllata Formation is of Pliocene age. The Tequendama Member is Tequen-damian (prov.) in age (early Pliocene; the possibility that it includes some of the late Miocene should not be excluded). The Tibagota Member is Facatativanian (prov.) in age, the Guasca Member is Sisganian and the Guali Member Chocontanian in age, but exact boundaries and precise correlations have yet to be determined.

The Subachoque Formation is basically Lower Quaternary (Pleistocene) and corresponds to the Funza-nian and the Engativanian (which would still be Late Pliocene and correspond, climatically speaking, to the transition from the Pliocene to the Quaternary). The upper boundary possibly transgresses the time line. Accord-ingly, the boundary in lateral areas of the high plain might be somewhat younger, and somewhat older in the central part.

The Sabana Formation is Fuchanian, Cotanian, Subanian, Bacatanian, Fuquenian and, in part, Holocene in age. The lower boundary may predate the chronostrati-graphic boundary to some degree, including for example part of the late Funzanian in the center of the high plain, according to the upper boundary of the Subachoque Formation.

The Cbia Formation corresponds to the Holocene and probably includes part of the late Fuquenian as well.

These definitions and correlations allow for a better definition of the position of sediments in the Choconta zone, shown on map sheet 3 (in preparation) in the


northern section of the Neogene and Quaternary map of the high plain of Bogota, located in the upper Bogota River Basin.

In the Choconta zone, the Tilata Formation has intervals corresponding respectively to the Tequendamian and Sisganian. The Facatativanian is probably represented as well. The highest part corresponds mainly to fluviatile sediments (the remains of a kind of giant fan east of Choconta) and is probably Chocontanian (corresponding to biozone IVa) in age. Therefore, it could correspond in time approximately to the Guali Member (Upper Tilata Formation). On the other hand, sediments with a strong colluvial influence, found throughout this zone, seem to be more recent, mainly biozone V and Funzanian in age. These sediments might correspond to colluvial facies or marginal solifluction of the Subachoque Formation, such as those found in Sesquile and Guasca (Van der Hammen et al., 1973; Bakker and Vander Wiel, 1984).

ACKNOWLEDGEMrnNTS We thank T.C. Partridge for organizing the stimulating session 'The

Pliocene/Pleistocene boundary' and discussions during the XIV INQUA congress in Berlin, August 1995. He is also thanked for constructive comment on an earlier version of this paper.

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