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 Volume 2 Chapter 13

Chapter  13

Plesiosaurs, Palaeoenvironments, and the Paja Formation Lagerstätte of Central Colombia: An Overview   

Leslie F. NOÈ  and Marcela GÓMEZ–PÉREZ

https://doi.org/10.32685/pub.esp.36.2019.13


Citation is suggested as: 

Noè, L.F. & Gómez–Pérez, M. 2020. Plesiosaurs, palaeoenvironments, and the Paja Formation Lagerstätte of central Colombia: An overview. In: Gómez, J. & Pinilla–Pachon, A.O. (editors), The Geology of Colombia, Volume 2 Mesozoic. Servicio Geológico Colombiano, Publicaciones Geológicas Especiales 36, p. 441–483. Bogotá. https://doi.org/10.32685/pub.esp.36.2019.13​


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Abstract 


The Cretaceous Paja Formation of the alto Ricaurte of the Eastern Cordillera of central Colombia was laid down under an epicontinental sea during Hauterivian – Aptian times. The Paja Formation epicontinental sea was home to a diverse, and now well–preserved, pelagic marine fauna that includes members of Plesiosauria, other marine reptiles, fish, and ammonites. However, the benthic fauna is depauperate, preserving just a few thin–shelled bivalves and evidence of microbial mats. This suggests dysoxic–anoxic bottom waters, separated from oxic surface waters by a chemocline–pycnocline. The exceptional preservation of the Paja Formation fauna makes the alto Ricaurte a unique Lower Cretaceous marine vertebrae Lagerstätte. Previous palaeoenvironmental interpretations of the Paja Formation, based on observations of the gypsiferous, dark mudrock sequence, suggested an intertidal evaporitic (sabkha) environment. However, integration of sedimentological, palaeobiological, taphonomic, and diagenetic data provides evidence for deeper water conditions. The exquisite preservation and articulation of the skeletons of large marine reptiles, three–dimensionally preserved fish, beautifully ornamented ammonites, and delicate plants, do not accord with a sabkha environment. Sabkha is typical of mid–latitude, dryer climates under the descended limb of the Hadley atmospheric cell, rather than a wet tropical equatorial location of the Paja Formation. Mineralogical arguments used to infer the presence of sabkha are not primary depositional features, but due to secondary migration of mineral–rich fluids. These fluids probably had their source in the earliest Cretaceous topographic high now beneath the Sabana de Bogotá, and were driven by hydraulic pressure generated by volumetric changes due to hydration of anhydrite into gypsum due to the post–Cretaceous rise of the northern Andes mountain chain. The separation of primary and secondary diagenetic features is thereby critical for understanding the evolution of the Paja Formation sedimentary basin in the alto Ricaurte.​


Keywords:   Lagerstätte, Lower Cretaceous, Paja Formation, palaeoenvironments, Plesiosauria.


Resumen 

La Formación Paja de la región del alto Ricaurte en la cordillera Oriental de Colombia se depositó en un mar epicontinental durante el Hauteriviano–Aptiano. Este mar tenía una fauna marina pelágica diversa que se encuentra hoy en día muy bien preservada e incluye miembros del orden Plesiosauria, otros reptiles marinos, peces y amonitas. Sin embargo, la fauna bentónica está empobrecida, se conservan solo algunos bivalvos de conchilla delgada y evidencia de tapetes microbiales. Esto sugiere que las aguas profundas eran de carácter disóxico–anóxico, separadas de las aguas superficiales oxigenadas por la quimoclina–picnoclina. La preservación excepcional de la fauna de la Formación Paja hace que el alto Ricaurte sea un Lagerstätte de vertebrados marinos del Cretácico Inferior único a nivel mundial. Interpretaciones previas del paleoambiente de la Formación Paja, basadas en observaciones de la secuencia de lodolitas oscuras yesosas, sugirieron un ambiente evaporítico intermareal (sabkha). Sin embargo, la integración de datos sedimentológicos, paleobiológicos, tafonómicos y diagenéticos proporciona evidencia de condiciones de aguas más profundas. La exquisita preservación y la articulación de los esqueletos de grandes reptiles marinos, peces, amonitas bellamente ornamentadas y plantas delicadas no concuerdan con un ambiente de sabkha. Los sabkhas son característicos de latitudes medias y climas más secos, localizados bajo la rama descendente de la celda atmosférica de Hadley, antes que típicos de la localización más ecuatorial tropical húmeda de la Formación Paja. Los argumentos mineralógicos utilizados para inferir la presencia del sabkha no son característicos de deposición primaria, sino debido a la migración secundaria de fluidos ricos en minerales. Estos fluidos probablemente tenían su origen en la topografía alta del Cretácico más temprano, ahora debajo de la Sabana de Bogotá, y fueron impulsados por la presión hidráulica generada por los cambios volumétricos debidos a la hidratación de la anhidrita en yeso como un resultado del levantamiento pos–Cretácico de la cadena montañosa norte de los Andes. Por lo tanto, la separación entre características diagenéticas primarias y secundarias es crítica para comprender la evolución de la cuenca sedimentaria de la Formación Paja en el alto Ricaurte.

Palabras clave: Lagerstätte, Cretácico Inferior, Formación Paja, paleoambientes, Plesiosauria.


Ab​breviations 

AA                                       Arcillolitas Abigarradas

AcNH                             Arcillolitas con Nódulos Huecos

CIP                                    Centro de Investigaciones Paleontológicas km 4, vía Santa Sofía, Villa de Leyva, Boyacá, Colombia

ECC                                   Eastern Cordillera of Colombia

LNI                                    Lutitas Negras Inferiores

JAVCM                       Junta de Acción Comunal, vereda Monquirá (now MJACM)

LFN                                   Leslie Francis NOÈ

MG–P                           Marcela GÓMEZ–PÉREZ

MJACM                     Museo El Fósil, vereda Monquirá, Boyacá, Colombia

OAEs                              Oceanic anoxic events

SGC                                  Servicio Geológico Colombiano Dirección de Geociencias Básicas Museo Geológico José Royo y Gómez                                                                             Diagonal 53 n.° 34–53, Bogotá D. C., Colombia

TOC                                  Total organic carbon

UCMP                            University of California Museum of Palaeontology

                                                  1101 Valley Life Sciences Building, Berkeley

                                                 California 94720, USA

UN                                     Universidad Nacional de Colombia Departamento de Geociencias 

                                                 Carrera 45 n.° 26–85, Bogotá D. C., Colombia​



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