Pliocene Impact Crater Discovered in Colombia: Geological, Geophysical and Seismic Evidences
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Lunar and Planetary Science XLVIII (2017) 2466.pdf PLIOCENE IMPACT CRATER DISCOVERED IN COLOMBIA: GEOLOGICAL, GEOPHYSICAL AND SEISMIC EVIDENCES. J. Gómez1, A. Ocampo2, V. Vajda3, J. A. García4, A. Lindh5, A. Scherstén5, A. Pitzsch6, L. Page5, A. Ishikawa7, K. Suzuki8, R. S. Hori9, M. Buitrago10, J. A. Flores10 and D. Barrero11; 1Colombian Geologi- cal Survey, Diagonal 53 #34–53 Bogotá, Colombia ([email protected]); 2NASA HQ, Science Mission Direc- torate, Washington DC 20546, US; 3Department of Palaeobiology, Swedish Museum of Natural History, SE–104 05 Stockholm, Sweden; 3Universidad Libre, Sociedad Astronómica ANTARES, Cali, Colombia; 5Department of Geol- ogy, Lund University, Sweden; 6MAX–lab, Lund University, Sweden/ Helmholtz Zentrum Berlin, Institute Methods and Instrumentation for Synchrotron Radiation Research, Berlin, Germany; 7Department of Earth Science & As- tronomy, Graduate School of Arts and Sciences, The University of Tokyo, Japan; 8IFREE/SRRP, Japan Agency for Marine–Earth Science and Technology, Natsushima, Yokosuka 237–0061, Japan; 9Department of Earth Science, Graduate School of Science and Engineering, Ehime University, 790–8577, Japan; and 10Department of Geology, University of Salamanca, Spain and 11Consultant geologist, Bogotá, Colombia. Introduction: The paleontological record clearly sedimentites; (8) Triassic intrusive; and (9) Permian to reveals that impacts of large extra–terrestrial bodies Cretaceous metamorphic rocks. may cause ecosystem devastation at a global scale [1], The impact crater and the local geology: The whereas smaller impacts have more local consequenc- Cali Crater is located in the Cauca Sub–Basin between es depending on their size, impact angle and composi- the Western and Central Colombian cordilleras, SE of tion of the target rocks [2]. Approximately 190 impact Cali, in a geologically complex area [5]. The outer ring structures are currently confirmed on Earth and each of the covered Cali impact crater has a major axis of year a small number is added to this list but only nine 36 km and a minor axis of 26 km (Fig. 1), and the cor- verified impact craters have been detected on the responding size of the inner ring is 12.7 km by 8.7 km, South American continent despite its large area [3]. respectively. The basement to the east consists of Per- Here we provide geological and geophysical evidences mian–Triassic and Lower Cretaceous metamorphic of a large, buried impact crater, the Cali Crater, located rocks. These are intruded by Meso–Cenozoic granit- in southwestern Colombia (Fig. 1) and dated as mid– oids (Fig. 1), separated from a sliver of the Upper Cre- Pliocene, i.e., 3.28 ± 0.07 million years [4]. taceous Caribbean–Colombian Oceanic Plateau (CCOP) [6]. These rocks were accreted to the active a b ea VC7910Patacore-1 75° W S n 70° W ea b ib r t a l Yumbo Palmira 10° N C u 76° 30' W 76° 15' W margin of South America pre–Eocene times [7], by the a F 3° 30' N Juga-1 a Salsa-1 River Cauca–Almaguer Fault. Over the CCOP basement, the m i l a C - 5° N a Bogotá u Cauca Sub–Basin contains an Eocene to lower Mio- g Cauca Cali a D Pacific Ocean Colombia VC7906 Pradera Candelaria cene sequence, unconformably overlain by a flat–lying t l Candelaria-1 u a B F e l r 0° l a e middle Miocene to Holocene cover (Fig. 1). v u i s g t Western Cordillera a a Florida Central Cordillera F t m l l a u A Eastern Cordillera u a IR - Seismic interpretation: Previous works in the l t D do F a a Tektites distribution esbarat riv er c ia Geological map area t u a Jamundí a P Miranda C 3° 15' N - Puerto Cauca Sub–Basin based on seismic data have shown a c Tejada u a VC7904 1a 1b 1c 2 Padilla C that the Cauca Sub–Basin is a basement involved fold Paila rive Villa Rica r 3a 3b 4 5 Corinto VC7902 T o m and thrust belt in a thick–skinned west vergent fore- in i t 6a 6b 6c 7 o l ri u ve r a F river o land style deformation, with stratigraphic evidence 8 9 Timba OR im Fault n o r Concealed fault e J Normal fault indicating that the Cauca Sub–Basin was deformed n a Thrust fault S Concealed boundary crater Caloto Santander VC7904 Seismic line Buenos during Oligocene and latest Miocene [8]. 3° 00' N de Quilichao River Aires Tektites localities Dry well City Town Scale 5 0 5 10 km The Cali impact crater shows a relative small nega- Highway Major road tive anomaly caused by the low–density sedimentary Fig. 1. Geological map of the Cali Crater [5]. (a) Loca- cover. In order to precise the nature of this negative tion of the geological map area. (1) Quaternary, (1a) anomaly, uninterpreted seismic lines to the E and SE alluvial deposits; (1b) volcanoclastic deposits; (1c) of Cali were obtained from the Colombian Agencia vlluvial fans; (2) upper Pliocene volcanites; (3) Mio- Nacional de Hydrocarburos (ANH). cene, (3a) claystones, siltstones, coarse grained sand- The Cauca Sub–Basin was divided in seven uncon- stones, conglomerates and dacitic tuffs and (3b) intru- formity stratigraphic sequences [8] for the seismic line sives; (4) Eocene–Oligocene sedimentites; (5) Paleo- VC7910 and Candelaria–1 well drilled in 1965. This cene intrusive; (6) Upper Cretaceous, (6a) marine sed- provides a unique stratigraphic control for the 106 km imentites, tuffs and agglomerate; (6b) Basalts and (6c) through the crater, providing a new 2D seismic inter- gabbros and tonalites; (7) Lower Cretaceous marine Lunar and Planetary Science XLVIII (2017) 2466.pdf pretation of the lines VC7906, VC7904 and VC7902 youngest sedimentary sequence that unconformably (Fig. 2). overlies and conceals the older sequences of the Cauca Sub–Basin. 0 It is worth to note that in the seismic lines VC7906, U4 U3 1 U2 VC7904 and VC7902, the basement–involved fold and U1 IR thrust belt seen in the seismic lines VC7908 and 2 VC7910 is lacking. By contrast, a symmetrical pattern 5 km 3 of normal faults with downward and inward displace- ments is observed along the edges of these seismic S1 S2 S3 S4 S5 S6 S7 WSR lines (Fig. 2), characteristic of large basin structures. Old thrust Truncation Furthermore, other two distinctive features of large impact structures are the structural disruptions, with no Fig. 2. Interpreted seismic line VC7904 from Cauca coherent seismic reflector in the central zone, the Inner Sub–Basin showing structural style, regional uncon- Ring (Fig. 2). In addition, continuous reflectors, not formities, seismic sequences and geometry of the Cali affected by the impact (pre–existing old thrust), are Crater. Vertical scale is two–way travel time in sec- present beneath the disrupted zone (Fig. 2). onds. (U1) Sub–Eocene unconformity; (U2) Sub– Substantiating our discovery of the Cali impact Oligocene unconformity; (U3) Sub–Miocene uncon- crater, stereomicroscope analysis of the cuttings of the formity; (U4) Sub–upper Pliocene unconformity; (IR) Candelaria–1 well showed the occurrence of micro- Inner ring and (WSR) Without Seismic Resolution. spherules in the layer at a depth of 1,500–1,750 feet Sequence S1 shows Upper Cretaceous rocks of (~457–533 m). The microspherules occur within se- oceanic affinity including ultramafic complexes, gab- quence S5, which is interpreted as the crater fill depos- bros associated with tonalites, basalts, dacites and rhy- its. The seismic lines VC7906, VC7904 and VC7902 olites associated with sedimentary rocks of marine reveal another important structural feature. Based on origin. Sequence S2 corresponds to the lower Eocene morphotectonic and paleoseismic evidence, the present Chimborazo Formation composed of by coarse con- elliptical shape of the Cali impact crater could be ex- glomerates interbedded with reddish muddy sand- plained by Holocene tectonic activity [9]. Consequent- stones and siltstones overlain by cyclothems of quartz ly, the present elliptical shape of the Cali impact crater sandstones, siltstones, mudstones, shales and coal of could be explained by this horizontal movement still the basal Oligocene Guachinte Formation. Sequence being active during the Holocene [9]. S3 is the Ferreira Formation, which consists of upward As a final geological consideration, the Dagua– thinning units of quartz conglomeratic sandstones, Calima Fault is a normal fault (huge land–slide) that quartz sandstones, fossiliferous sandstones, coal seams could have been formed by the Cali asteroid impact at and shales. Sequence S4 comprises the Miocene La 3.3 Ma. Its current position north of Cali impact crater Paila Formation predominantly composed of lithic could be explained by the displacement of the Western sandstones and polymictic conglomerates interbedding Cordillera along of the Cauca–Patia Fault with strike– with dacitic tuffs. This is in the southern part repre- slip fault, right–lateral offset. The Dagua–Calima Fault sented by the coeval Esmita Formation composed of is the only normal fault in Colombian Andes that is black siltstones, dark clays, gray to green sandstones, characterized by strike–slip faults and thrust faults [5]. carbonaceous shales and quartz conglomerates. References: [1] Vajda, V. et al. (2015) Gondwana Re- Within the impact basin a new seismic sequence search, 27(3): 1079–1088. [2] Morgan, J. et al. (1997) Size (S5) was identified, which is consistent with the age of and morphology of the Chicxulub impact crater. Nature 390, 3.3–3.25 Ma for the tektites [4] (Fig. 2). Importantly, 472–476. [3] The Earth Impact Database sequence S5 was not found in any seismic line to the http://www.passc.net/EarthImpactDatabase/index.html (im- north or south of the Cauca–Patía Basin, supporting pact database). [4] Vajda et al., (2016) Impact crater discov- the impact origin for S5.