The formation was deposited in a tidal-dominated deltaic environment at high southern paleolatitudes at the edge of the
PaleozoicPaleo-Tethys Ocean. The Cuche Formation is highly
fossiliferous; many
Placoderm fish fossils, flora, bivalves, arthropods, crustaceans and ostracods have been discovered in the youngest Paleozoic strate of the Floresta Massif, while the underlying
Floresta Formation is richer in
trilobitebiodiversity.[1]
Etymology
The formation was first described as part of the Floresta Series by Olsson and Carter in 1939. The current definition was given by Botero in 1950.[2] The formation is named after the vereda Cuche of
Floresta,
Boyacá, where the formation
outcrops.[3] The word Cuche is taken from
Muysccubun, the language of the indigenous
Muisca, who inhabited the Altiplano Cundiboyacense before the
Spanish conquest.[4]
Regional setting
The Floresta Massif is a block in the northern part of the Altiplano Cundiboyacense, marked by a
metamorphic crystalline core overlain by Devonian to Carboniferous sedimentary sequences; from old to young, the
El Tíbet,
Floresta and Cuche Formations. The Paleozoic succession is overlain by sediments of much younger date; the
Late JurassicGirón and
Early CretaceousTibasosa Formations. The massif is bound to the east by the
Soapaga Fault and to the west by the
Boyacá Fault.[5]
At time of deposition of the Devonian formations, present-day northern South America was located at the edge of the
Paleo-Tethys Ocean on the southern hemisphere. The Paleozoic occurrence on the Altiplano is localized in outcrop; the majority of surface sediments are Cretaceous to Paleogene in age. Neogene uplift of the Eastern Ranges, with its main phase in the
Plio-
Pleistocene, caused the exhumation of older units at surface along major thrust faults in the Eastern Andes. In two phases during the Paleozoic, intrusions occurred into the sedimentary sequence, causing local metamorphism. The first phase is considered pre-Devonian and the latter phase post-Devonian. The remaining stratigraphy of the Cuche Formation appears little affected by this intrusive phase,[6] although slight metamorphism has been identified in later research.[7]
Description
Lithologies
The Cuche Formation is characterised by mostly cream and purple coloured
shales, with a basal unit of
micaceoussiltstones with intercalated yellowish-grey shales and 30 metres (98 ft) thick quartzitic and feldspar-rich
sandstone beds that colour red caused by
meteoric waters. The sandstones have an iron-rich cementation.[3] A middle unit of fine-grained sandstones with thin banks of siltstones follows the lower part and an upper sequence of shales with interbedded
ferruginousred beds.[2] The lower sequence contains
runzelmark syn-sedimentary structures.[3]
The age of the Cuche Formation has been estimated to be
Late Devonian to
Early Carboniferous,[2][13] after an original designation as
Permian-
Carboniferous by Botero in 1950, further restricted to the Carboniferous by Julivert in 1968.[14] The formation covers an area of approximately 36 square kilometres (14 sq mi) and ranges in thickness between 300 and 900 metres (980 and 2,950 ft).[2] Stratigraphically, the Cuche Formation is time equivalent with the
Diamante Formation of the Santander Massif to the north of the Altiplano Cundiboyacense.[15] To the west of
Paz de Río, the Cuche Formation is thrusted upon the
NeogeneConcentración Formation by the Soapaga Fault.[16] In the northern part of the Floresta Massif, the contact between the metamorphic
Otengá Stock and the Cuche Formation is formed by the Duga Fault.[17]
Based on the preservation of fossils, the lithologies, syn-sedimentary structures and stratigraphic position, a depositional environment of shallow low energy waters has been proposed, possibly in a
lagoonal setting at the edge of a regressional
Paleo-Tethys Ocean.[1][18] Other parts of the Cuche Formation were deposited in a continental environment, evidenced by the red beds and absence of marine fossils and abundant root imprints.[19] Overall, the sequence represents a coastal deltaic environment with frequent marine incursions, a tidal deltaic setting.[20][21]
Fossil content
The first identification of fossil content of the Cuche Formation was done by Botero, who studied the formation in 1950. Research in the early 1980s revealed the presence of many more fossils in the formation and among the first fossil flora found were species then identified as the genera Ginkgo and Baiera.[14] The lower units show poorly preserved plant remains and the overlying shales provided
arthropods and
crustaceans. In the middle units of the formation, more and better preserved plant fossils were found alongside bivalves,
ostracods (of the genus Welleria) and arthropods.[22]
The Cuche Formation contains unique
Placoderm fish fossils, first noted by Mojica and Villarroel in 1984.[23] Across the section, also plant fossils and bivalves are found. In this part of the sequence the first fish fossils were discovered. The top section provided
brachiopods (genus Lingula) and other at that moment undetermined fossil fragments.[24]
The fossil fish assemblage of the Cuche Formation presents a curious mixture of Euramerican "
Old Red Sandstone" (
Catskills,
Greenland,
Scotland and the
Baltic states)[20] species (Asterolepis and Holoptychius), and
Gondwanan taxa (Antarctilamna), suggesting the interchange of species between the paleogeographical regions, possibly at closer distance than is presented in most paleogeographical models.[33][34] This hypothesis is further strengthened by the discovery of typical Euramerican flora, as Archaeopteris.[26]
Asterolepis has been known only from Euramerican fossils, except for a specimen found in
Iran.[20] The fish of the Cuche Formation are quite different from Bolivian Devonian fossils, with the exception of Antarctilamna. The similar sediments of the
Colpacucho Formation in Bolivia have not provided the species discovered in the Cuche Formation, probably because of the cooler climate of the Devonian Bolivian seas more to the south than the paleogeographical position of northern Colombia (already around 51°S) at that time.[34]
In
2019, fragments of the
eurypteridPterygotus were retrieved from the formation. The find represents the first
sea scorpion from Colombia and the fourth from
South America.[38] The specimen (SGC-MGJRG.2018.I.5), assigned with uncertainty to P. bolivianus due to similarities with its holotype, represents the first eurypterid of Colombia and the fourth of South America. The fossil was dated as
Frasnian (Late Devonian), showing that Pterygotus did not become extinct during the
Middle Devonian as previously thought.[39]
Pardo Díaz, Marta Yolima; Marta Liliana Gil Padilla; Laura Natalia Garavito Rincón; Pedro Corredor Vargas; Carolina Gutiérrez Barrios; Wilson Parra, and Nancy Amaya Pedraza. 2014. Estudios técnicos, económicos, sociales y ambientales Complejo de Páramos Altiplano Cundiboyacense, 1–546.
Instituto de Investigación de Recursos Biológicos Alexander von Humboldt & CORPOBOYACÁ.
Rodríguez Parra, Antonio José, and Orlando Solano Silva. 2000. Mapa Geológico del Departamento de Boyacá - 1:250,000 - Memoria explicativa, 1–120.
INGEOMINAS.
Villafañez Cardona, Yohana. 2012. Análisis de procedencia de areniscas cuarzosas del Devónico-Carbonífero de la Formación Floresta (Norte de Santander): Consideraciones paleogeográficas regionales, 1–89.
EAFIT.
Gómez Cruz, Arley de Jesús; Mario Moreno Sánchez, and Alexander Lemus Restrepo. 2015. Diplicnites isp. del Devónico y Carbonífero de Colombia, _. Tercer Simposio Latinoamericano de Icnología, Colonia de Sacramento, Uruguay. Accessed 2017-05-05.