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Sedimentitas marinas del Neógeno en la bahía de Tumaco, Nariño
Cenozoic Evolution of the Sierra Nevada de Santa Marta, Colombia
By Mauricio PARRA, Sebastián ECHEVERRI, Ana María PATIÑO, Juan Carlos RAMÍREZ, Andrés MORA, Edward R. SOBEL, Ariel ALMENDRAL and Andrés PARDO–TRUJILLO
The highest coastal relief on Earth occurs in the Sierra Nevada de Santa Marta in northern Colombia. With an average elevation of ca. 4 km and peaks up to ca. 5.8 km high, this small mountain range lie only 85 km to the south of an abyssal plain ca. 3.5 km deep in the Caribbean Sea. A compilation of sparse bedrock and detrital low‒temperature thermochronometric data, new detrital apatite fission‒track and apatite (U‒Th)/He data from modern river sediment, and stratigraphic patterns of adjacent Miocene ‒ Pliocene basins document an episodic tectonic development of the Sierra Nevada de Santa Marta. Paleocene initial collision of oceanic crust along western Colombia triggered initial exhumation and westward monoclinal tilting of the formerly contiguous Central Cordillera and the Santa Marta Massif. Subsequent late Eocene (ca. 35 Ma) dismembering of both ranges occurred in association with right lateral translation of the Caribbean Plate against the northwestern continental margin of Colombia. This episode marked the onset of contrasting exhumation histories, characterized by low denudation and pediment‒formation in the Central Cordillera, as opposed to rapid, episodic exhumation of the Santa Marta Massif, associated with normal faulting and opening of extensional basins along its southwestern margin. Multiple approaches to extracting exhumation rates from thermochronometry, including 1D and 3D reconstructions, reveal that following rapid late Eocene ‒ early Miocene rock uplift, asymmetric exhumation characterized the Sierra Nevada. On the souhwestern margin, moderate to rapid exhumation favored progradation of alluvial fan deposits on top of underlying shallow marine and fan delta facies. In contrast, diminished exhumation prompted a reciprocal stratigraphy in the northern margin, where facies retrograde, leading to accumulation of shallow marine facies onto fan delta and alluvial fan deposits. Thermochronometric ages of outcropping units, retrieved in modern river sand, imply a very recent (<2 Ma) pulse of exhumation, possibly triggered by removal of lower crust, whose precise magnitudes and time constraints remain unknown.
Keywords: Sierra Nevada de Santa Marta, Caribbean Plate, thermochronology, sediment provenance.