Monbusho International Scientific Research Program Reports by 1990 and 1991 Grants for Field ResearchProject Number: 02041050 (1990 to 1991)Phylogenetic Studies of South American MonkeysHead Investigator: Yasuo NOGAMI, Professor, Primate Research Institute, Kyoto Universit

Danhara, Tohru

Setoguchi, Takeshi

Takai, Masanaru

Takemura, Atsushi

Kyoto University Research Information Repository

Title Fission-Track Ages of the Villavieja Formation of the MioceneHonda Group in La Venta, Department of Huila, ColombiaAuthor(s)Takemura, Atsushi; Takai, Masanaru; Danhara, Tohru;Setoguchi, TakeshiCitationKyoto University overseas research reports of new worldmonkeys (1992), 8: 19-27Issue Date1992URL http://hdl.handle.net/2433/199688RightType ArticleTextversionpublisherKyoto UniversityKyoto University Overseas Research Reports of New World Monkeys (1992) 8: 19-27 Kyoto University Primate Research Institute 19 Fission-Track Ages of the Villavieja Formation of the Miocene Honda Group in La Venta, Department of Huila, Colombia Atsushi TAKE MURA Hyogo UnルersiかofTeacher Education, 942-1 Shimokume，】＇ashiro,Hyogo 673-14, Japan Masanaru T AKAi Primate Research Institute, Kyoto UniνersiりらInuyama, Aichi 484, Japan Tohru DANHARA Kyoto Fission-Track Ltd., 33 Umezukita-cho, U1わ10-ku,Kyoto 606, Japan and Takeshi SETOGUCHI Primate Research Institute, Kyoto University, Inuyama, Aichi 484, Japan INTRODUCTION Tertiary continental sediments are widely exposed along the valley of Magdalena River between the Central and Eastern Cordillera, in Colombia, South America. Many fossil vertebrates including fossil monkeys occur in the Miocene Honda Group, and these fossils紅Cknown as the La Venta fauna (Stirton, 1951). Takemura and Danh訂a(1985) presented fission-track ages of the Honda Group, which ranged about 16 to 15 Ma in age. A cooperating paleontological survey organized by Primate Research Institute of Kyoto University and INGEOMINAS was carried out in 1990. More than 200 fossils of monkey teeth were excavated through this survey仕omthe Tatacoa Red Member [the Upper Red Bed of Fields (1959)] of the Villavieja Formation in the Honda Group. However, the Tatacoa Red Member overlies other members of the Villavieja Formation dated by the fission-track method. Although Takemura and Danhara (1985) correlated the La Venta Fauna to the Friasian Stage of South American Land Mammal Ages (Marshall et al., 1977), the fossil monkeys obtained by this survey shall be somewhat younger. In this paper, we made detailed stratigraphic work on the Tatacoa Red Member and fission-track dating of three samples from this unit. Because the obtained ages range from 12.6 to 13.6 Ma, it is concluded that the upper p訂tof the Honda Group in the La Venta badlands was deposited during Middle Miocene. GEOLOGICAL SETTING AND MATERIAL The studied area in this paper is situated in the La Venta badlands, which are located along the valley of Magdalena River between the Central and the Eastern Cordillera, Colombian 20 久（-PANAMA 。500 』kmPERU Figure 1. Locality of La Venta in Colombia, South Americc Andes (Fig. 1）.百1esampling point for fission-track dating is about 5 km east of Villavieja, Department of Huila (Fig. 2). Several lithos佐atigraphicstudies had been repo口edon the Honda Group in出isarea. Fields (1959) proposed stratigraphic framework of the Honda Group exposed in the La Venta badlands. Van Houten and Travis (1968) and Wellman (1970) studied stratigraphy and sedimentology of the whole Honda Group extending from Gigante to La Dorada, along the Magdalena Valley. However, the stratigraphy of these two studies is too rough to determine the horizons of fossil localities and dating samples. Takemura (1983) had studied detailed S住atigraphyaround the Kioto Site in Llanos de Molina (Fig. 2). Takai and Setoguchi (1990) carried out detailed stratigraphic work on the upper part of the Honda Group exposed in the La Venta badlands. They had modified the stratigraphy made by Fields (1959). Takai et al. (1992) renamed the stratigraphic units of Fields (1959) to formations and members, because the unit names described by Fields (1959) were informal. We use the stratigraphic framework proposed by Takai et al. (1992). ぐ久〈???????〜?N ドーーo 1 ・ 2 km Figure 2. Topographic map around the Tatacoa Desert showing the localities of sampling sites for fission-track dating (Ff-site) and occ町encesof fossil monkeys (x). Filled circles indicate the localities of the geological columns shown in Fig. 3. Las Mesitas Formation 22 TATACOA RED MEMBER ???↑〈???FT site 鶴蕗red,dark red E認brown,light red EB ocher, yellow Eコgrey,light grey Eコwhite〈「，??〉〈」」?〉? ???A ????????????Masato Site Clay Sand "' Figure 3. Columnar sections of the Tatacoa Red Member in the Tatacoa Desert. The width of each layer in these columns indicates the grain size. The locality of each column is shown in Fig.2. The Honda Group in the La Venta badlands is divided into three formations, the Cervetana Formation, the Villavieja Formation and批LasMesitas Formation, in ascending order. The Las Mesitas Formation corresponds to the ”Las Mesitas Sands and Clays" of Fields (1959) and Takai and Setoguchi (1990), and the Cervetana Formation corresponds to the "Cerbatana Gravels and Clays" of Takai and Setoguchi (1990) and the”El Libano Sands and Clays" of Fields (1959）.百1eVillavieja Formation is divided into four members, the Molina Member, the Los Mangos Red Member, the Las Lajas Member and the Tatacoa Red Member, in ascending order. 百1eTatacoa Red Member, which co汀espondsto the "Upper Red Bed" of Fields (1959), is exposed at the southmost part of the studied訂eaof Takai et al. (1992). This area is a fairly scenic place and is known as the Tatacoa Desert (Desierto de La Tatacoa, Fig. 2). The samples for fission-track dating were obtained from one outcrop in the Tatacoa Desert (Fig. 2, Ff Site). The Tatacoa Red Member strikes about N80°W to EW and dips 3° to 5°S. This member crops out extending in E-W direction. The Tatacoa Red Member is composed of red claystone with intercalated siltstone and sandstone (Fig. 3). The claystones訂eusually red, dull-red or brown and sometimes grey in color. The siltstones and the sandstones紅edull-red, brown, yellow or grey, and紅esometimes Clay Sand 111 ー窟輯欄reddark red 川トー002輔踊闇j←ω悶br側n’lightr 工；；i悶。cher, e d 巳ヨgrey,light grey ）~010 ‘－ 011 亡コwh胎Sm ＝·•ー001003 -o t::-012 013 Figure 4. Columnar section of the Ff Site and sampling horizons for fission－住ackdating. The width of each layer in this column indicates the gr 出nsize. 23 tuffaceous. The outcrops of this member are usually red cliffs with many light color bands. These bands have various thicknesses and yellow, grey or white color. We can trace these bands at many outcrops and can use these bands as key beds to aid correlation within this member (Fig. 3). At the western part of the Tatacoa Desert around the Masato Si臼（Fig.2, 3), a thick sandstone layer with cross lamination is intercalated in the lowermost p訂tof this member. However, this remarkable sandstone is never observed at the eastern p紅t.The upper and the lower limits of this unit訂eeasily recognized (Fig. 3). At many points in the Tatacoa Desert, the boundary between this member and the underlying Las Lajas Member can be observed. The colors of beds vary from red to yellow or yellowish brown at the lowermost part of this unit, which is underlain by grey siltstone of the Las Lajas Member with a distinct boundary.百1eupper limit of this member is observed in the outcrop just south of FT Site (Locality C of Fig. 2). Grey, fine to medium sandstone of the Las Mesitas Formation overlies red claystone of the Tatacoa Red Member with a distinct boundary. Three samples from FT Site were dated by the fission-track method. Fig. 4 shows the horizons of these samples in the outcrop of FT Site. The lithology of Sample 002 is a grey and reddish brown tuffaceous siltstone. These two colors are mixed together irregularly within出issiltstone layer of 75 cm thick. Sample 003 is a bluish grey tuffaceous claystone with irregular red patches. The thickness of this layer is 35 cm and this layer is one of the distinct white bands in this outcrop. We can trace this layer in the eastern part of出eTatacoa Desert and used 50m Eヨgreysand & mud Eヨredmud 10 。~7.8士0.5Ma (Gigante Formation) LAS MESITAS FORMATION 〈???〉〈」」?〉CERVETANA FORMATION ??? ????????????????????Molina Member Tatacoa Red Member Las Lajas Member 文H_o~巾o~sof the localities OT TOSSll monKeys 匿lg即吋。me峨sand & mud ??↑〈??24 Figure 5. Summarized s 廿atigraphyof the Honda Group in the La Venta Badlands with the fission－汀ackages. The stratigraphy is after Takai et al. (1992), and出efission－住ackages訂eafter Takemura & Danhara (1983) (the Gigante Formation) and Takemura & Danhara (1985) (the Molina and the Los Mangos Red Members). this layer for the correlation among many outcrops (Fig. 3). Sample 004 was taken仕oma thin (less than 5 cm thick) layer of white fine tuffaceous sandstone. This layer is intercalated within a distinct grey band observed in the uppermost pa 口ofthis outcrop. We used these samples of tuffaceous sandstone or mudstone, because no pure tuff layer is intercalated within the Tatacoa Red Member in this area. We had sampled materials in 12 horizons in this locality (Fig. 4), washed these S白nplesby water and concentrated heavy minerals by panning in Villavieja. Both the heavy mineral fraction and the rock samples of each material were brought to Japan and three samples mentioned above, which contain good zircon gra 加s,were dated at Kyoto Fission-Track Ltd .. FISSION-TRACK DATING The three samples collected from the Tatacoa Red Member were dated by the fission－佐ackmethod. The results of this dating are shown in Table 1. Zircon grains of each sample mounted in PFA (copolymer of te町afluoroehy lene-perfl uoro-alkoxyethylene) sheets were etched by a melt of KOH and NaOH at 225°C for 34 hours. After this etching, spontaneous fission-tracks on both external and internal surfaces of the zircon grains were counted. PFA sheets were covered with external fission-track detectors of muscovite and irradiated in the TRIGA Mark II nuclear reactor of St. Paul’s University (Rikkyo 25 Daigaku), Japan. Induced fission-tracks were counted on the muscovite detectors, which were etched wi 出hydrofluoricacid. The thermal neutron fluence was monitored with an uranium dosimeter glass, NBS-SRM612. Recently, I.U.G.S. Subcommission on Geochronology recommended the standardization of fission-track calibration (H町ford,1990a; 1990b). We used here calibration factors (z-values) of 370±4 for EDI method and 372±5 for ED2, reported by Danhara et al. (1991) for the Rot紅ySpecimen Rack of the reactor of St. Paul’s University. All the samples treated here contain a significant fraction of zircon grains with ex甘emelyhigh density of spontaneous fission住民ks.These grains can easily be distinguished仕omthe other zircon grains with low density of spontaneous tracks. In this paper, we regarded these low-density grains as essential ones and used them for dating. We calculated the fission－官邸kages of both ED 1 (using internal surf aces of zircon grains and external surfaces of external detectors) and ED2 (using external surfaces of both zircon gr 出nsand external detectors). The fission位ackdata of zircon are sometimes influenced by uneven dis甘ibutionof uranium within each zircon crystal (Danhara et al., 1991). However, our age data show that the age values calculated from EDI and ED2 methods are nearly equal in all samples. Therefore, we use the mean value of both ED 1 and ED2 methods in each sample as a geological age estimate in this paper. The results訂eas follows in descending order: Sample 004 13.6 ± 0.5 Ma Sample 002 13.6 ± 0.7 Ma Sample 003 12.6 ± 0.7 Ma Table 1. Results of fission-track dating in the Tatacoa Red Member. Mineral and Spontaneous Induced Dosimeter Sample number of Ps (Ns) Pi (Ni) P（χ2) Pd (Nd) r u Age±lσ（Ma) method No. crystals ~cm勺~cm-22 ｛%｝ pa4/cm22 002 zircon 28 2.74xla6 666 3.02xla6 734 46 8.34 1241 0.616 288 14.1±0.9 EDI 002 zircon 30 8.44xHP 252 2.08xla6 252 >99 8.58 1270 0.824 162 12.9土1.0ED2 Mean 13.6土0.7003 zircon 30 2.36xla6 1598 2.93xla61981 9 8.41 1244 0.670 280 12.5±0.6 EDI 003 zircon 30 7.70xHP 383 l.91xla6 950 38 8.59 1270 0.238 178 12.9±0.9 ED2 Mean 12.6±0.5 004 zircon 30 2.49xla6 2403 2.79xla6 2698 <1 8.43 1247 0.819 266 13.9士0.6EDl 004 zircon 30 8.41xHP 459 2.06xla6 1126 76 8.59 1270 0.749 193 13.佐0.8ED2 Mean 13.6±0.5 (1) p and N are the density and the to凶numberof fission tracks counted，陀spectively.(2) Analyses were made by the external method using geome町factorsof 0.5 and 1 for 2n/47t (EDl）加d2π／2π匹D2),respectively. (3) Ages we問calculatedusing a dosimeter glass SRM612 and age calibration factors ~(EDl) = 370土4andC(ED2) = 372±5. (4) P（χ2) is由eprobability of Obtaining the X2-value for V degrees of freedom (where V=number Of crystals・1).(5) r is血ecorrelation coefficient between Ps and Pi. (6) U is町aniumcontent. (7) Samples were irradiated using TRIG A MARK II nuclear reactor of St. Paul’s University (Rikkyo Daigaku), Jap加．26 DISCUSSION The resulting three ages, indicating Middle Miocene age by the fission－佐ackmethod，紅Cnearly identical. Takemura and Danhara (1985) reported fission-track ages from three horizons in the Villavieja Formation. Sample LV 13 with an age of 15.7±1.1 Ma was taken from the Los Mangos Red Member and Samples KS 4 and LV8 with respective ages of 14.6±1.1 Ma and 16.1±0.9 Ma were from the Molina Member of Takai et al. (1992). Although these age values seem to be somewhat older than the ages obtained in this paper, all the ages紅esimilar considering their eπors. 百1efission track ages in this paper were obtained from samples of tuffaceous sandstone or mudstone. The zircon grains within these samples had been more or less住ansported仕omtheir origins and sedimented in the La Venta badlands. Therefore, the geological age of the sedimentation of the Tatacoa Red Member should be somewhat younger than the fission町ackages. Takemura and Danhara (1983) dated pumices in volcanic sediments from the Gigante Formation and reported fission track ages of 7 .1士0.7Ma and 7.8±0.5 Ma. The difference of these two values corresponds to two possible ways of grouping the grain-by-grain ages within the sample. These two values are nearly equal and紅econcordant with the age of the Gigante Formation (8.5±0.4 Ma) repo口edby Van Houten (1976) using the K-Ar method. Because the Gigante Formation unconformably overlies the Honda Group (Takemura, 1983), the geological age of the Honda Group is older than the ages obtained from the Gigante Formation of Late Miocene age. Several stratigraphic studies were made on the Honda Group in the La Venta badlands (Fields, 1959; Van Houten and Travis,1968; Wellman, 1970; Tak 泊andSetoguchi, 1990; Tak出et al., 1992). According to these studies, neither unconformities nor distinct facies changes occur within the Honda Group in this area. Therefore, no large time-gap should exist within the Honda Group, and the geological age of the Villavieja Formation can be regarded as Middle Miocene (Berrgren etαl., 1985; Harland et al., 1990). ACKNOWLEDG 九'IENTSWe thank Mr. Hiroyuki Maeda of Department of Geology and Mineralogy, Faculty of Science, Kyoto University for his help in sampling and panning in Villavi司a.We also thank Dr. Masao Kasuya of Kyoto Fission-Track Ltd. for critically reading the manuscript and Dr. Keiji Takemura for valuable discussion and comments. The first author especially thanks Prof. Akira Tokuyama, Associate Prof. Toshiharu Nishimura and Dr. Yasuhiro Shibue for their assistance to carry out this study. REFERENCES Beπgren, W. A., Kent, D. V. and Van Couvering, J. A. (1985): The Neogene: Part 2. Neogene geochronology and chronostratigraphy. In (Snelling, N. J., ed.) Geochronology and the geological record, Geo!. Soc. London, Spec. Paper, pp. 211-260. Danhara, T., Kasuya, M., Iwano, H. and Yamashita, T. (1991): Fission－甘ackage calibration using internal and external surfaces of zircon. lour. Geo!. Soc. Japan, 91, 977-985. Fields, F. W. (1959): Geology of the La Venta Badlands, Colombia, South America. Univ. Calif. Pub!. Geo!. Sci., 32, 405-444. H訂land,W. B., Armstrong, R. L., Cox, A. V., Cr出g,L. E., Smith, A. G. and Smith, D. G. (1990): A geologic time scale 1989. Cambridge Univ. Press, pp263. 27 Hurford, A. J. (1990a): Standardization of fission位ackdating calibration: Recommendation by the Fission Track Working Group of the I.U.G.S. Subcommision on Geochronology. Chem. Geo!., 80, 171-178. Hurford, A. J. (1990b): International Union of Geological Sciences Subcommision on Geochronology recommendation for the standardization of fission track dating calibration and data reporting. Nucl. Tracks Radiat. Meas., 17, 233・236.Marshall, L. G., Pascual, R., Curtis, G. H. and Drake, R. E. (1977): South American geochronology: Radiometric time scale for Middle to Late Tertiary mammal-bearing horizons in Patagonia. Science, 195, 1325-1328. Stirton, R. A. (1951): Ceboid monkeys from the Miocene of Colombia. Univ. Calif. Pub!. Geo!. Sci., 28, 315-356. Tak 出，M.and Setoguchi, T. (1990): Geology and localities of monkey fossils in the La Venta Badlands, Colombia, South America. Kyoto Univ. Overseas Res. Rep. New World Monkeys, Kyoto Univ. Primate Res. Inst., 7, 1-7. Tak 出，M.,Takemura, K., Takemura, A., Villarroel, C., Hayashida, A., Danhara, T., Ohno, T., Franco, R., Setoguchi, T. and Nogami, Y. (1992): Geology of La Venta, Colombia, South America. ibid., 8, 1-17. Takemura, K. (1983): Geology of the east side hills of the Rio Magdalena from Neiva to Villavieja, Colombia. ibid., 3, 19-28. Takemura, K. and Danhara, T. (1983): Fission-track age of pumices included in the Gigante Formation, North of Neiva, Colombia. ibid., 3, 13-15. Takemura, K. and Danhara, T. (1985): Fission-track dating of the upper part of Miocene Honda Group in La Venta Badlands, Colombia. ibid., 5, 31-38. Van Houten, F. B. (1976): Late Cenozoic volcaniclastic deposits, Andean foredeep, Colombia. Geo!. Soc. Am. Bull, pp481-495. Van Houten, F. B. and Travis, R. B. (1968): Cenozoic deposits, Upper Magdalena Valley, Colombia. Am. Assoc. Petr. Geol. Bull., 52, 675-702. Wellman, S. S. (1970): Stratigraphy and pe住ologyof the nonmarine Honda Group (Miocene), Upper Magdalena Valley, Colombia. Geo!. Soc. Am. Bull., 81, 2353-2374. 

Fission-Track Ages of the Villavieja Formation of the Miocene Honda Group in La Venta, Department of Huila, Colombia

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Fission-Track Ages of the Villavieja Formation of the Miocene Honda Group in La Venta, Department of Huila, Colombia

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