Sedimentación y paleogeografía del Cretacico y Cenozoico del Litoral Pacifico de Costa Rica

Autor: Jacques Bourgois, G. Glacon, Jacques Azema, Peter Baumgartneri, Claudia Mora, J. Sigal, Jacques Butterlin
Rok vydání: 2011
Předmět:
Zdroj: Central American Journal of Geology; Revista Geológica de América Central: Número 01
Revista Geológica de América Central; Revista Geológica de América Central: Número 01
Portal de Revistas UCR
Universidad de Costa Rica
instacron:UCR
ISSN: 2215-261X
0256-7024
DOI: 10.15517/rgac.v0i01.10469
Popis: The systematic strátigraphy of the Pacific littoral of Costa Rica has been reorganized in three supergroups: 1. Papagayo: mafíc and ultramafic oceanic basements and volcanicaIly or tectonically associated sediments. 2. Garza: oceanic sedimentary cover including pelagics (Sabana Grande Group) and slope deposits (Sámara Group). 3. Mal País: neritic sedimentary cover, subdivided into 5 epochs. A major, upper Santonian tectonic event divides the geologic history into two phases: 1. The Nicoya Complex with its Bathonian/Callovian Santonian (BAUMGARTNER 1984) oceanic sedimentary cover and the Santa Elena Peridotite form together a nappe edifíce with a southern vergence (BOURa15— et al. in press). 2. Since the Campanian, this structure is part of the stable isthmic crust, the substrate of the studied upper Senonian-Cenozoic sedimentary sequen ces, affected by open folding and normal faulting only. No accretionary struc-tures related to subduction along the Middle-American Trench, effective since ttat latest Senonian, have been observed. Ocean floor contínued te form during the latest Senonian-early Paleocene in a primitive island arc environment (Que-pos, Osa). Campanían-middle Eocene pelagic (and background) sedimentation followed the paleooceanographic trends observed in the Pacific, amplified by local (equatorial, eastern ocean margin) hígh fertility. A shallow CCD is reflected by Santonían-lower Campanían and upper Paleocen-middle Eocene radiolarían-rich siliceous deposits. In the late Campanian-Maestrichtian a drastic drop of the CCD overruled subsidence and resulted in deposition of foramínifer-rich pelagic limestones. Thick Maestrichtian-Paleocene turbidite and mass flow sequences were deposíted in YW-SE trending elongate basins and document the erosion of an emerged andesitic volcanic are, che product of active subduction, surrounded by narrow carbonate and silicic/astio shelves, set aboye steep, unstable slopes. A tectonic event at the middleilate ocene boundary caused mayor gravitative s/iding and slumping of the upper part of the oceanic sequence, subsequent uplift and a regional, unconformable onset of shallow carbonate deposition, while turbiditc sedimentation persisted in some arcas (Santa Elena, Quepos). An inferred thickened oceanic crust in ísostatic equilibrium should form a sea floor at subphotie depths. However, tectonie uplift has repeatdly brought the substrate te shallow depth and allowed the deposítion of unconformable, thin, shortlived, neritic sequences, forffied during five succesive epochs: Epoch 1. Campanian-Maestriehtian: The structurally highest parts of the upper Santonian orogen were uplifted te subaerial and shallow photic depths where rudis-tid limestones developed. Epoch 2. Paleocene-early Encone: Voleanic activity related tu subduction gave rise tu an island are surrounded by shallow platforms NE of the study area, only known from reworked carbonate elasts in slope deposits (Sámara, Quepos). Epoch 3. Middle-late Eoeene: Tectonic uplift brought most of the area tu shallow photic depth which led tu the formation uf the widespread largor foramini-fer - red algal limestones. Epoch 4. Olígocene-early Miocene: Most of the central area was emerged and only near the trench (Nosara-Mal País) thin shallow clastic sequences developed, while turbidíte basins persisted in the NW and SE (Dept. Rivas, Nicaragua, Fila Costeña). Epoch 5. Late Miocene-Pleistocene: Littoral deposíts are concentrated around the south of Nieoya, in areas of recent uplift (FISCHER 1980). En base a criterios genéticos se reorganiza la estratigrafía sistemática del litoral pacifico en tres supergrupos: 1. Papagayo: basamentos básicos y ultrabá-sicos oceánicos. 2. Garza: cobertura sedimentaria oceánica. 3. Mal País: eober-tlira sedimentaria nerítica, subdividida en 5 épocas. Se describen 6 nuevas forma cienes. La historia geol6gica queda subdividida en dos fases: 1. El Complejo de Ni-coya (Batoniano/Calloviana-Santoniano) y la Perídotita de Santa Elena constituyen un edificio de mantos de corrimiento del Santoniano superior con vergencia de nor te a sur. 2. Desde el Campaniano esta estructura forma parte de la corteza esta-ble istmica, afectada únicamente por plegamiento abierto y fallamiento normal. No se han observado estructuras de acreción relacionadas con la fosa mesoamericana, establecida desde el Senoniano terminal. Aparte de las calizas con rudístides del Senoniana superior (Epoca 1), la se dimentaci6n pelágica desde el Campaniano al Eoceno medio obedeció' a cambios paleo ceanográficos conocidos del Pacifico, ocasionando los depasitas silíceos del Santo niana-Campaniano y del Paleoceno superior-Eoceno medio. Las potentes' secuencias turbidíticas del Maestrichtiano-Paleaceno documentan la erosiOn de un arco volcá-nico andesitico emergido, producto de la subducciOn activa, rodeado de platafor-mas someras silicoclásticas y carbonatadas (Epoca 2). Un evento tectónico en e1 límite Eoceno medio/superior causa desprendimien-tos y deformaciSn por gravedad en el techo de la secuencia oceánica, levantamien to drástico y un nuevo establecimiento en grandes áreas de depositaci6n neríticí carbonatada (Epoca 3) discordante, mientras que la sedimentaciGn turbidítica per sistió (Santa Elena, Quepos). Sediwentos neríticos someros se depositaron discordantemente en el sector central durante el Oligoceno-Mioceno inferior (Epoca 4) y durante el Mioceno su-perior-Pleistoceno (Epoca 5), mientras que secuencias turbidíticas potentes se acumularon en el sur (Oligoceno-Míoceno: Fila Costeña, Plioceno: Osa, Burica).
Databáze: OpenAIRE
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