The Paja Formation was first described by O.C. Wheeler, according to Morales (1958),[2] and named after
Quebrada La Paja, a tributary of the
Sogamoso River. The
type section is exposed on the northern banks of the quebrada at the confluence of the Sogamoso River in
Betulia,
Santander.[3][4]
The formation is divided into the Lutitas Negras Inferiores, Arcillolitas Abigarradas and Arcillolitas con Nódulos Huecos Members, and stretches across 450 kilometres (280 mi) from northeast to southwest. The Paja Formation overlies the
Ritoque and
Rosablanca Formations and is overlain by the
Simití and
Tablazo Formations and dates from the
Hauterivian to
Late Aptian.
The type section of the Paja Formation is found at the banks of Quebrada La Paja in Betulia, Santander, where the formation has a thickness of 625 metres (2,051 ft).[5] Outcrops of the formation extend from
Simití in the north, close to the border of Santander and
Bolívar, where the formation is offset by the
Simití Fault,[6] to the Pauna Anticlinal in
San Pablo de Borbur, where the formation is
thrusted over the
Ritoque Formation in the south.[7] In the southern extension of the exposures, the formation crops out in the north of
Tununguá, near the
Ibacapí Fault.[8]
Fossiliferous outcrops near Villa de Leyva on the Altiplano Cundiboyacense
In northeastern Boyacá, the formation underlies the urban center of
Moniquirá (not to be confused with Monquirá, a vereda of nearby
Villa de Leyva) and is crossed by the
Moniquirá River.[18] West of
Arcabuco in the Villa de Leyva Synclinal, the formation is cut by the
Arcabuco River.[19] In the vicinity of
Pauna and San Pablo de Borbur, the formation crops out in an extensive area. Here, the Paja Formation is offset by the
Río Minero and
Pedro Gómez Faults and occurs in the
footwall of the
La Venta Fault.[20] North of
Lake Fúquene, the town centers of
Tinjacá and
Sutamarchán are built on top of the Paja Formation. In this area, the formation extends into the northern part of Cundinamarca,[7] where the urban centers of
Yacopí and
La Palma rest on the formation.[21]
Villa de Leyva
Surrounding the touristic town of
Villa de Leyva, the formation crops out in the hills in a
microclimatic location, known as the La Candelaria Desert (
Spanish: Desierto de La Candelaria), stretching across Villa de Leyva,
Santa Sofía and
Sáchica.[7][22] Along the highway
Tunja-Villa de Leyva, the formation is heavily
folded and
faulted along a stretch of 500 metres (1,600 ft).[23] In the vicinity of Villa de Leyva, the formation has provided many fossils of marine reptiles, as well as the dinosaur Padillasaurus.
Stratigraphy
The Paja Formation overlies the
Ritoque and
Rosablanca Formations and is concordantly overlain by the
San Gil Group and
Tablazo Formations in the eastern extent,[24][25] and the
Simití Formation in the northwestern Middle Magdalena Valley.[11] In the Western emerald belt, the contact with the Rosablanca Formation is concordant and abrupt.[26] The total thickness of the formation varies across its extent, but can reach up to 940 metres (3,080 ft).[27]
Members
The Paja Formation is subdivided into three members, from oldest to youngest:
Lutitas Negras Inferiores (Lower Black Shales) – a sequence of 340 metres (1,120 ft) of
black shales and sandy shales with a segment containing
calcareous nodules. The age of this member is estimated at
late Hauterivian, based on
ammonites analyzed by
Fernando Etayo.[28]
Arcillolitas Abigarradas (Mottled Claystones) – a series of multicolored
claystones with abundant calcareous fossiliferous nodules, reaching a thickness of 480 metres (1,570 ft). In the upper 235 metres (771 ft) of this member, intercalations of
gypsum occur. The age of the middle member of the Paja Formation is estimated at
early Barremian to
late Aptian on the basis of ammonites described by Fernando Etayo.[28]
Arcillolitas con Nódulos Huecos (Claystones with Hollow Nodules) – the upper member of the formation of approximately 174 metres (571 ft) thick consists of yellowish and grey claystones containing hollow nodules. Ammonite analysis has led to an estimated late Aptian age for the member.[27]
In the northern part of the Middle Magdalena Valley, the Paja Formation comprises dark grey to blueish shales, intercalated with grey to yellowish fine-grained
sandstones and
fossiliferous limestones, locally with a sandy component.[29] Bürgl in 1954 reported beds of
tuff in the Paja Formation near Villa de Leyva.[30]Thin section analysis of samples of the Paja Formation has provided insight in the
micritic components of the sediments, where three microfacies were recognized; biomicritic
wackestones, foraminiferous
packstones and sandy biomicritic
floatstones containing fragments of
echinoderms,
bivalves,
crinoids and
gastropods cemented by
hematite.[31]
The Paja Formation correlates with the
Tibasosa Formation to the east on the northern Altiplano Cundiboyacense in Boyacá and with the
El Peñón Formation pertaining to the
Villeta Group to the south in the Eastern Ranges. The formation is laterally equivalent with the black shales of the
Fómeque Formation in the eastern part of the Eastern Ranges and the
sandstones of
Las Juntas Formation in the
Sierra Nevada del Cocuy.[24] In the Middle Magdalena Valley to the west, the formation partly overlies and partly is laterally equivalent to the
limestones of the Rosablanca Formation. The Paja Formation is diachronous with the Ritoque and Rosablanca Formations.[27] To the northeast of the extent of the formation, it correlates with the upper part of the
Río Negro Formation,[32] and the lowermost
Tibú-Mercedes Formation of the
Catatumbo Basin.[33]
The thin section analysis led to the interpretation of a shoreface to lower shoreface environment,[36] in the internal parts of a carbonate platform,[37][38] where
transgressions and
regressions caused the variations in grain sizes and lithologies.[39] The Barremian to Aptian sequence shows evidence of an overall relative sea level fall with open marine sedimentation in the lowest member and
tidal deposits in the upper part of the formation.[40]
One of the longest anoxic intervals of geologic history occurred during the Cretaceous, from about 125 to 80 Ma (early Aptian to
early Campanian). During this
Oceanic Anoxic Event, there were two spikes, the
Selli event, dating to the early Aptian (approximately 120 Ma) was active during deposition of the black shales of the Paja Formation.[41] The formation contains three spikes of δ13C, with values above 1.5‰, in the lower, middle to upper and upper Paja Formation.[42] These spikes indicate a global change in the carbon cycle and the preservation of organic matter due to poor oxygenation of sea waters. The cause of these elevated δ13C levels may have been a global increase in volcanic activity.[43]
The Paja Formation is one of the stratigraphic units cropping out in the
Western emerald belt.[44] Mineralization in the formation has been dated on the basis of 40Ar/39Ar analysis of
muscovite minerals. In western
San Pablo de Borbur, Boyacá, the mineralization dates to the
Late Eocene at 36.4 ± 0.1 and 37.3 ± 0.1 Ma.[45] In the northwestern part of
Muzo, Boyacá, mineralization happened during the
Early Oligocene, at 31.4 ± 0.3 Ma.[46] Previous geologic researchers considered the Paja Formation hosted emeralds,[47] and later definition of the stratigraphy of Colombia separated one of the main emerald formations of Colombia as the contemporaneous Barremian
Muzo Formation, providing emeralds in the
La Pita mine and important
Coscuéz mine.[48]
Within the Arcillolitas Abigarradas Member of the Paja Formation, some horizons preserve abundant wood, which is frequently bored by pseudoplanktonic pholadoid bivalves, commonly referred to as "
shipworms" or "piddocks". The presence of wood boring bivalves in Paja Formation seas indicates the continued presence of xylic substrates, and long residence time of floating wood.[1]
In respect of the 'world's most complete record of Lower Cretaceous marine reptiles and associated fauna', the
International Union of Geological Sciences (IUGS) included the 'Marine Reptile Lagerstätte from the Lower Cretaceous of the Ricaurte Alto' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an IUGS Geological Heritage Site as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.'[61]
A species of the genus Desmatochelys, sea turtles that belongs to the extinct family
Protostegidae. Is the oldest known sea turtle, and a specimen was found with eggs still inside her.
A
durophagous turtle member of the Sandownidae; is the first record for this group in South America. This species occurs too in the
Glen Rose Formation in USA
A
brachiosaurid dinosaur, that makes the first record of a terrestrial animal in the area, and the first Cretaceous brachiosaurid known outside from North America
Fossils of a member of Teleosauroidea with an estimated body length of 9.6 m, representing the most recent definitive record of Teleosauroidea reported
Villamil, Tomas. 2012. Chronology Relative Sea Level History and a New Sequence Stratigraphic Model for Basinal Cretaceous Facies of Colombia, 161–216.
Society for Sedimentary Geology (SEPM).
Cortes, Dirley; Hans C.E. Larsson; Erin E. Maxwell; Mary L. Parra Ruge; Pedro Patarroyo, and Jeffrey A. Wilson. 2019. An Early Cretaceous teleosauroid (Crocodylomorpha: Thalattosuchia) from Colombia. Ameghiniana in press(). .. .
doi:
10.5710/AMGH.26.09.2019.3269
Hampe, O. 1992. Ein großwüchsiger Pliosauride (Reptilia:Plesiosauria) aus der Unterkreide (oberes Aptium) von Kolumbien. Courier Forschungsinstitut Senckenberg 145. 1–32. .
Acosta, C.E.; G. Huertas, and P.M. Ruiz. 1979. Noticia preliminar sobre el hallazgo de un presunto Kronosaurus (Reptilia: Dolichorhynchopidae) en el Aptiano superior de Villa de Leiva, Colombia. Lozania (
Acta Zoologica Colombiana) 28. 1–7. .
Welles, S.P. 1962. A new species of elasmosaur from the Aptian of Colombia and a review of the Cretaceous plesiosaurs. University of California Publications in Geological Sciences 44(1). 1–96. .
Beltrán, Alejandro; José Alfredo Lancheros; Carolina López; Claudia Chaquea; Alejandro Patiño; Angela Guerra; Julio C. Cabrera; Claudia I. Quintero, and Simón Emilio Molano. 2008. Plancha 134 – Puerto Parra – 1:100,000, 1.
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