Pliocene impact crater discovered in Colombia: Geological evidences from tektites

Abstract

Introduction: The geological and paleontological record have revealed that impacts of large extraterrestrial bodies may cause ecosystem devastation at a global scale [1], whereas smaller impacts have more regional consequences depending on their size, impact angle and composition of the target rocks [2]. Approximately 200 impact structures are currently confirmed on Earth and each year a small number is added to this list but only nine verified impact craters have been detected on the South American continent despite its large area [3]. Here we provide evidence of a large, buried impact crater, the Cali Crater, located in western Colombia (Fig. 1) and dated to mid-Pliocene, i.e., 3.28 ± 0.07 million years.

Methodology: We studied tektites and other impactites from the newly discovered, Pliocene Cali Crater by optical microscopy, petrography, scanning electron microscopy, energy-dispersive X-ray analyses (EDS), major- and trace-element (including High Si-derophile Elements, HSE) analyses by ICP-AES and ICP-MS respectively, 40Ar/39Ar geochronology, and X-ray absorption spectroscopy [4]. We further investigated the crater by extensive geological field survey, labwork and geophysical methods including gravimetry and seismic profiling [4]. Herein we focus on the geo-chemical and geochronological results of our study.

The impact crater and the local geology: The Cali Crater is located in the Cauca Sub-Basin between the Western and Central Colombian Cordillera, SE of Cali, in a geologically complex and tectonically modify area Fig 2 [5]. Using seismic data we determine the outer ring of the buried Cali impact crater has major axis of 36 km and a minor axis of 26 km. The morphology, hydrology, and minerology of the region has been modified by the impact event. The Cauca river crosscuts the impact crater in a North-South direction. The target rock was composed of interbedded lithic sandstones and quartzites.

The Calitites: Tektites are abundant and around 550 individual tektites were collected for this work. They are associated with alluvial fan deposits along a 240 km stretch in the Cauca river valley, suggesting that they were carried down from the cordilleras [6]. The Cali crater is located in the middle of the area of tektite distribution. The tektites are ~1–15 cm, sub-angular with well-developed pits and some with striations and banding (Figure 1). They are composed of greenish to brownish translucent heterogeneous glass with bubbles and glassy inclusions and bubles (Figure 1), and in some cases iron particles are present [4]. The bulk composition of the tektites is 70–77 wt% SiO2 and 13–20 wt% Al2O3. These were already de-scribed as tektites by Barnes (1958)[7], but then grouped with Peruvian tektites/obsidian of different ages and collectively called “Americanites” [8]. Locally the tektites are presently called, “Colombianites” or “piedra de rayo” (lightning stones). The tektites have also in more recent scientific publications been called “Colombianites”, and interpreted as obsidian, volcanic glass, from the Paletará Caldera [9]. However, their age and Sr-Ca and Mn-Ti relations do not match locally formed obsidian. Due to these circumstances we avoid using these previous names and designate the tektites Calitites denoting their origin being tektites and their direct link to the Cali impact crater.

Dating of the Calitites: Fragments from three tektites were dated using 40Ar/39Ar geochronology (see material and methods in Supplementary Information). These measurements yield plateau ages at 3.22 ± 0.07, 3.23 ± 0.06 and 3.29 ±0.02 Ma with a weighted mean of 3.25 ±0.04 Ma (all errors at 2σ (see [4] for detailed information). The age of the Calitites correlates well to age of the core samples recuperated from the Cali crater site.

Acknowledgements: We acknowledge the support from NASA Planetary Science Division (AO). The research was jointly supported by the Swedish Re-search Council (VR grant 2015-04264 to VV; 2008–3447 to AS) and the Lund University Carbon Cycle Centre (LUCCI). Financial support was received through grants from the Swedish Research Council 2008–3447 (AS). We acknowledge the support of the Colombian Geological Survey (SGC) for financial support for fieldwork, especially Director Dr. Oscar Paredes).

References: [1] Vajda, V. et al. (2015) Gondwana Research, 27, 1079–1088. [2] Morgan, J. et al. (1997) Nature 390, 472–476. [3] The Earth Impact Database http://www.passc.net/EarthImpactDatabase/index.html [4] Vajda et al. (2017) Gondwana Research in press. [5] Gómez, J. et al. (2013) Colombian Geological Survey. Bogotá. [6] Stutzer, O. (1926) Compilación de los estudiosgeológicos oficiales en Colombia 1917–1933 2, 245–255. [7] Barnes, V. E. et al. (1958) Nature 181, 1457–1458. [8] Friedman, I. et al. (1958) Science 127, 91. [9] Bellot-Gurlet, L. et al. (2008) J. Archaeolog. Sci. 35, 272–289. [10] Osinski, G. R. et al. (2008) Me-teorit. Planet. Sci. 43, 1939–1954 [11] Dressler, B.O. Reimold, W.U. (2001) Earth Sci. Rev. 56, 205–284.

Full text

PLIOCENE IMPACT CRATER DISCOVERED IN COLOMBIA: GEOLOGICAL EVIDENCES FROM
TEKTITES. A. Ocampo1, J. Gómez2, J. A. García3, A. Lindh4, A. Scherstén4, A. Pitzsch5, L. Page4, A. Ishikawa6,
K. Suzuki7, R. S. Hori8, Margarita Buitrago9 and José Abel Flores9, D. Barrero10
, V. Vajda11; 1NASA HQ, Science
Mission Directorate, US (aco@nasa.gov), 2Colombian Geological Survey, Bogotá, Colombia; 3Universidad Libre,
Sociedad astronomica ANTARES, Cali, Colombia; 4Department of Geology, Lund University, Sweden; 5MAX–lab,
Lund University, Sweden/ Helmholtz Zentrum Berlin, Institute Methods and Instrumentation for Synchrotron Radia-
tion Research, Berlin, Germany; 6Department of Earth Science & Astronomy, The University of Tokyo, Japan;
7IFREE/SRRP, Japan Agency for Marine–Earth Science and Technology, Yokosuka, Japan; 8Department of Earth
Science, Ehime University, Japan; 9Department of Geology, University of Salamanca, Spain. 10Consultant geologist,
Bogotá, Colombia; 11Department of Palaeobiology, Swedish Museum of Natural History, Sweden
Introduction: The geological and paleontologi-
cal record have revealed that impacts of large extra-
terrestrial bodies may cause ecosystem devastation at a
global scale [1], whereas smaller impacts have more
regional consequences depending on their size, impact
angle and composition of the target rocks [2]. Approx-
imately 200 impact structures are currently confirmed
on Earth and each year a small number is added to this
list but only nine verified impact craters have been
detected on the South American continent despite its
large area [3]. Here we provide evidence of a large,
buried impact crater, the Cali Crater, located in western
Colombia (Fig. 1) and dated to mid-Pliocene, i.e., 3.28
± 0.07 million years.
Methodology: We studied tektites and other im-
pactites from the newly discovered, Pliocene Cali
Crater by optical microscopy, petrography, scanning
electron microscopy, energy-dispersive X-ray analyses
(EDS), major- and trace-element (including High Si-
derophile Elements, HSE) analyses by ICP-AES and
ICP-MS respectively, 40Ar/39Ar geochronology, and X-
ray absorption spectroscopy [4]. We further investi-
gated the crater by extensive geological field survey,
labwork and geophysical methods including gravimetry
and seismic profiling [4]. Herein we focus on the geo-
chemical and geochronological results of our study.
The impact crater and the local geology: The
Cali Crater is located in the Cauca Sub-Basin between
the Western and Central Colombian Cordillera, SE of
Cali, in a geologically complex and tectonically modify
area Fig 2 [5]. Using seismic data we determine the
outer ring of the buried Cali impact crater has major
axis of 36 km and a minor axis of 26 km. The mor-
phology, hydrology, and minerology of the region has
been modified by the impact event. The Cauca river
crosscuts the impact crater in a North-South direction.
The target rock was composed of interbedded lithic
sandstones and quartzites.
The Calitites: Tektites are abundant and around
550 individual tektites were collected for this work.
They are associated with alluvial fan deposits along a
240 km stretch in the Cauca river valley, suggesting
that they were carried down from the cordilleras [6].
The Cali crater is located in the middle of the area of
tektite distribution. The tektites are ~1–15 cm, sub-
angular with well-developed pits and some with stria-
tions and banding (Figure 1). They are composed of
greenish to brownish translucent heterogeneous glass
with bubbles and glassy inclusions and bubles (Figure
1), and in some cases iron particles are present [4].
The bulk composition of the tektites is 70–77 wt%
SiO2 and 13–20 wt% Al2O3. These were already de-
scribed as tektites by Barnes (1958)[7], but then
grouped with Peruvian tektites/obsidian of different
ages and collectively called “Americanites” [8]. Local-
ly the tektites are presently called, “Colombianites” or
“piedra de rayo” (lightning stones). The tektites have
also in more recent scientific publications been called
“Colombianites”, and interpreted as obsidian, volcanic
Figure 1. Variety of Calitites
A. Tektite 1 in plain light, note pitted surface;
B. Tektite 2 in transmitted light; C. Tektite 3 in plain
light note heavy striation formed during impact process.
This striation is persistent through the interior of the
tektite. D. Tektite 3, striated area as in C now seen in
thin section containing particles – mainly Fe.
2832.pdfLunar and Planetary Science XLVIII (2017)

glass, from the Paletará Caldera [9]. However, their
age and Sr-Ca and Mn-Ti relations do not match local-
ly formed obsidian. Due to these circumstances we
avoid using these previous names and designate the
tektites Calitites denoting their origin being tektites and
their direct link to the Cali impact crater.
As noted elsewhere [10–11], the chemical composi-
tion of tektites is strongly controlled by the composi-
tion of the target rocks. Further, the internal structure
and surface, and internal texture of the Calitites support
an impact origin. Thus, we strongly propose that the
origin of the tektite-strewn field is related to the Cali
impact.
Dating of the Calitites: Fragments from three tek-
tites were dated using 40Ar/39Ar geochronology (see
material and methods in Supplementary Information).
These measurements yield plateau ages at 3.22 ± 0.07,
3.23 ± 0.06 and 3.29 ±0.02 Ma with a weighted mean
of 3.25 ±0.04 Ma (all errors at 2 (see [4] for detailed
information). The age of the Calitites correlates well to
age of the core samples recuperated from the Cali
crater site.
Fig. 2. Geological map of the Cali Crater [5]. (a) Location of
the geological map area. (1) Quaternary, (1a) Alluvial depos-
its; (1b) Volcanoclastic deposits; (1c) Alluvial fans; (2) Up-
per Pliocene volcanites; (3) Miocene, (3a) Claystones, silt-
stones, coarse grained sandstones, conglomerates and dacitic
tuffs and (3b) Intrusives; (4) Eocene–Oligocene sediment-
ites; (5) Paleocene intrusive; (6) Upper Cretaceous, (6a)
Marine sedimentites, tuffs and agglomerate; (6b) Basalts and
(6c) Gabbros and tonalites; (7) Lower Cretaceous marine
sedimentitas; (8) Triassic intrusive; and (9) Permian to Cre-
taceous Metamorphic rocks.
Acknowledgements: We acknowledge the support
from NASA Planetary Science Division (AO). The
research was jointly supported by the Swedish Re-
search Council (VR grant 2015-04264 to VV; 2008–
3447 to AS) and the Lund University Carbon Cycle
Centre (LUCCI). Financial support was received
through grants from the Swedish Research Council
2008–3447 (AS). We acknowledge the support of the
Colombian Geological Survey (SGC) for financial
support for fieldwork, especially Director Dr. Oscar
Paredes).
References: [1] Vajda, V. et al. (2015) Gondwana
Research, 27, 1079–1088. [2] Morgan, J. et al. (1997)
Nature 390, 472–476. [3] The Earth Impact Database
http://www.passc.net/EarthImpactDatabase/index.html
[4] Vajda et al. (2017) Gondwana Research in press.
[5] Gómez, J. et al. (2013) Colombian Geological Sur-
vey. Bogotá. [6] Stutzer, O. (1926) Compilación de los
estudiosgeológicos oficiales en Colombia 1917–1933
2, 245–255. [7] Barnes, V. E. et al. (1958) Nature 181,
1457–1458. [8] Friedman, I. et al. (1958) Science 127,
91. [9] Bellot-Gurlet, L. et al. (2008) J. Archaeolog.
Sci. 35, 272–289. [10] Osinski, G. R. et al. (2008) Me-
teorit. Planet. Sci. 43, 1939–1954 [11] Dressler, B.O.
Reimold, W.U. (2001) Earth Sci. Rev. 56, 205–284.
2832.pdfLunar and Planetary Science XLVIII (2017)