Considerations about the current state of Tertiary stratigraphy in Colombia
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Universidad Industrial de Santander
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La estratigrafía del terciario marino y continental se ha establecido con base en unas secciones aisladas, poco numerosas e introduciendo las unidades cronoestratigráficas empleadas en Europa. La generalización de las correlaciones ha conducido a conclusiones in sostenible s no solo en relación con los resultados de las áreas vecinas sino también dentro del país. Una revisión de los principales puntos de la estratigrafía pone en evidencia una falta de correlación con los datos estratigráficos publicados en los últimos años en el Caribe y en Europa. Causa de esta discrepancia procede en parte de la insistencia en continuar empleando la llamada clasificación "conservativa". Sin embargo el problema no es tan simple como para indicar tan solo un desplazamiento del límite oligoceno-mioceno como consecuencia de colocar el aquitaniense en el mioceno (en la clasificación "conservativa" se coloca el aquitaniense en el oligoceno superior). Así pues aplicando los datos del área del Caribe, en la sección de Carmen.Zambrano (Departamento de Bolívar) el límite oligoceno-mioceno debe situarse dentro de la zona de Globigerina dissimilis de Petters y Sarmiento o bien en la base de la misma. Si bien el limite oligoceno-mioceno sufre un descenso en la sección de Carmen-Zambrano, el mioceno de la sección de Arroyo Saco (Departamento del Atlántico) se modifica en sentido contrario, de tal manera que el límite aquitaniense-burdigaliense corresponde al punto donde se colocaba el límite burdigaliense-helveciense. Por su parte el terciario continental presenta cambios aún más importantes. Sin duda el descenso del límite oligoceno-mioceno en la región del Caribe, hoy día completamente aceptado, conduce a una importante reducción del oligoceno, aún sin llegar a la posición extrema de aceptar su ausencia total. Las edades y las correlaciones deducidas de los análisis palinológicos tienen como fundamento los resultados obtenidos en las series marinas. Si los sedimentos marinos que correspondían al oligoceno medio y superior pertenecen ya al mioceno, indudablemente desaparecen todos los sedimentos de carácter continental atribuidos al oligoceno medio y superior; hecho que no es posible admitir y que está en contradicción con la existencia de una fauna de mamíferos precisamente del oligoceno superior. Estos resultados plantean el problema de poder establecer, con base en el diagrama polínico general de Colombia, que parte del antiguo oligoceno debe considerarse como mioceno y que otra parte debe corresponder al oligoceno medio y oligoceno superior. En las correlaciones que hemos establecido dentro del terciario marino se han adaptado las zonas de foraminíferos planctónicos utilizadas por Stainforth en lugar de las de BoIli, precisamente porque aquellas tienen un carácter más amplio y la lista de foraminíferos planctónicos publicada en Colombia no permite establecer una zonación tan detallada y en consecuencia es imposible buscar correlación con ellas. Dadas las condiciones actuales se impone no solo una revisión a fondo de la estratigrafía del terciario marino y continental sino también de las transgresiones, ciclos sedimentarios y fases tectónicas que caen por completo fuera de lugar.
The stratigraphy of the Marine and Continental Tertiary in Colombia have been established on account of a few and isolated sections and presenting the chronoestratigraphic units, used in Europe. Generalization of such correlations is questionable in relation with neighbor areas and even in the country itself. A review of the main points of the stratigraphy shows inconsistence and lack of correlation with the stratigraphic data published during the last years in the Caribbean region and in Europe. This is mainly due to the obstinacy in the use of the so called "conservative" classification. Nevertheless the problem is not solved with the displacement of the Oligocene-Miocene boundaries locating the Aquitanian in the Miocene instead of the Oligocene like in the "conservative" classification. In the section of Carmen-Zambrano (Department of Bolívar) the limit Oligocene-Miocene must be located into the Petters and Sarmiento's zone of Globigerina dissimilis or in the basis of this zone. In spite that the Oligocene-Miocene boundary has a general lowering in Colombia, the Miocene of the Arroyo Saco's section (Department of Atlántico) appears modified in the other direction, in such a manner that the Aquitanian-Burdigalian boundary corresponds to the point occupied before by the Burdigalian-Helvecian boundary. Besides the Continental Tertiary shows more outstanding changes. The lowering of the Oligocene-Miocene boundary in the Caribbean Region, generally accepted, means a reduction of the Oligocene. Ages and correlations deducted from palynological analysis have their foundation on the marine series. If the marine sediments which used to belong to the Middle and Upper Oligocene belong now to the Miocene, without doubt the same would happen with the respective continental sediments; but such fact is impossible to admit and it is contradictory with the existence of a faune of mammals precisely from the Upper Oligocene. Taking in account the previous results it is quite diffjcult to establish, in accordance with the composite palynological diagram of Colombia, what part of the old Oligocene it is possible to accept as Miocene, and as Middle and Upper Oligocene. In the Marine Tertiary we establish correlations adopting the zones of planktonic foraminifera presented by Stainforth instead of Bolli's because Stainforth's have a wider character and the list of planktonic foraminifera published in Colombia do not allow to establish a detailed zonation. With the present conditions it is necessary a complete review of the stratigraphy of the Marine and Continental Tertiary and also of transgressions, regressions, sedimentary cycles, and tectonic phases.
The stratigraphy of the Marine and Continental Tertiary in Colombia have been established on account of a few and isolated sections and presenting the chronoestratigraphic units, used in Europe. Generalization of such correlations is questionable in relation with neighbor areas and even in the country itself. A review of the main points of the stratigraphy shows inconsistence and lack of correlation with the stratigraphic data published during the last years in the Caribbean region and in Europe. This is mainly due to the obstinacy in the use of the so called "conservative" classification. Nevertheless the problem is not solved with the displacement of the Oligocene-Miocene boundaries locating the Aquitanian in the Miocene instead of the Oligocene like in the "conservative" classification. In the section of Carmen-Zambrano (Department of Bolívar) the limit Oligocene-Miocene must be located into the Petters and Sarmiento's zone of Globigerina dissimilis or in the basis of this zone. In spite that the Oligocene-Miocene boundary has a general lowering in Colombia, the Miocene of the Arroyo Saco's section (Department of Atlántico) appears modified in the other direction, in such a manner that the Aquitanian-Burdigalian boundary corresponds to the point occupied before by the Burdigalian-Helvecian boundary. Besides the Continental Tertiary shows more outstanding changes. The lowering of the Oligocene-Miocene boundary in the Caribbean Region, generally accepted, means a reduction of the Oligocene. Ages and correlations deducted from palynological analysis have their foundation on the marine series. If the marine sediments which used to belong to the Middle and Upper Oligocene belong now to the Miocene, without doubt the same would happen with the respective continental sediments; but such fact is impossible to admit and it is contradictory with the existence of a faune of mammals precisely from the Upper Oligocene. Taking in account the previous results it is quite diffjcult to establish, in accordance with the composite palynological diagram of Colombia, what part of the old Oligocene it is possible to accept as Miocene, and as Middle and Upper Oligocene. In the Marine Tertiary we establish correlations adopting the zones of planktonic foraminifera presented by Stainforth instead of Bolli's because Stainforth's have a wider character and the list of planktonic foraminifera published in Colombia do not allow to establish a detailed zonation. With the present conditions it is necessary a complete review of the stratigraphy of the Marine and Continental Tertiary and also of transgressions, regressions, sedimentary cycles, and tectonic phases.