ABSTRACT:We present new sedimentologic and biostratigraphic data on the shallow-water limestone sequence of the quebrada Concha, the type locality of the Eocene Parritilla Formation in central Costa Rica. This unit appears at the base of the about 4.500 m thick sedimentary sequence of the Cenozoic Valle Central basin, unconformably overlying the Nicoya ophiolite complex. The Parritilla limestone contain a rich larger foraminiferal fauna from the early Middle Eocene (Lutetian) represented by well-preserved and diverse specimens of the Amphistegina-Helicostegina-Lepidocyclina(Polylepidina) phylogenetic line. On the basis of the high biostratigraphic resolution of the analyzed foraminiferal assemblage, we define the quebrada Concha sequence as a Lutetian type locality of Costa Rica and erect a new Eocene chronostratigraphic unit: the Parritillian. From a sedimentologic perspective, the Parritilla limestones represent a bioclastic carbonate sequence deposited on the southern border of the inner-arc basin in an open shallow-marine environment with locally restricted water circulation. In the study area, the uplifted ophiolite complex probably formed part of a neritic arc platform surrounding the volcanic edifices. Although Lutetian carbonate sedimentation began in response to a rapid marine transgression at ~49 Ma over the exposed basement, the carbonate development itself terminated abruptly with the deposition of the volcaniclastic sequence of the Caraigres Formation, resulting from the Eocene volcanic activity in adjoining areas. As suggested by these voluminous volcaniclastic deposits conformably overlying the Parritilla limestone sequence, the strong subsidence of the Lutetian arc platform was probably related to emergent andesitic edifices in the inner arc region of central Costa Rica. RESUMEN:Presentamos un estudio sedimentológico y bioestratigráfico de las calizas eocenas de la quebrada Concha, localidad tipo de la Formación Parritilla, ubicada en el sur del Valle Central de Costa Rica. Es una secuencia bioclástica de plataforma carbonatada de 150 m de espesor, depositada discordantemente sobre rocas cretácicas del Complejo de Nicoya, formando la base de la secuencia sedimentaria cenozoica de la cuenca intra-arco del Valle Central. Las asociaciones de macroforaminíferos de las calizas analizadas se caracterizan por especies de la línea filogenética Amphistegina-Helicostegina-Lepidocyclina (Polylepidina), típicas del Eoceno Medio, especialmente de la parte basal e inferior (Lutetiano). Con base en la alta resolución bioestratigráfica de esta asociación de foraminíferos, consideramos la quebrada Concha como localidad tipo del Lutetiano e introducimos una unidad cronoestratigráfica para el Eoceno Medio, la cual denominamos Parritillano, sinónimo del Lutetiano en Costa Rica. Sedimentológicamente las calizas de Parritilla representan acumulaciones bioclásticas de organismos bentónicos, depositadas sobre el basamento ofiolítico levantado en un ambiente marino somero y abierto, localmente bajo condiciones restringui...
This paper reports the discovery of six species of Late Cretaceous planktic foraminifera in early Paleocene hemipelagic limestones and tuffites from the Quepos promontory of Costa Rica as well as new Paleocene basement exposures in fila Chonta and Parrita indicating the extension of the basaltic basement complex to the northern hinterland area. The foraminiferal assemblage identified is composed of reworked keeled individuals of the species Rosita sp., Globotruncana f. arca (Cushman), Globotruncana cf. ventricosa (White), Globotruncana cf. linneiana (d'Orbigny), Globotruncanella sp., and Gansserina gansseri (Bolli). Of particular biostratigraphic significance is the presence of G. gansseri, a key species from the late Maastrichtian, in three localities studied, because it records in fact older hemipelagic strata within the Quepos Complex, suggesting that the exposed early Paleocene basement rocks probably represent its youngest suite. In the study area, the basement rock assemblage records an emergent edifice -a basaltic island-derived from submarine volcanic activity during the early Paleocene and probably Maastrichtian time. In the absence of evidence for accretion processes related to basement emplacement in this area, both the Cretaceous foraminiferal assemblage and the new Paleocene basement exposures suggest an in-situ origin of the Quepos Basic Complex in the Costa Rican forearc. RESUMEN:Se presenta el hallazgo de seis especies de foraminíferos planctónicos del Cretácico Tardío en calizas y tobitas hemipelágicas danianas del Complejo Básico de Quepos así como nuevos afloramientos del basamento del Paleoceno temprano al norte y noroeste de Quepos, en fila Chonta y Parrita. La asociación de foraminíferos está compuesta de formas cretácicas resedimentadas con quilla de las especies Rosita sp., Globotruncana f. arca (Cushman), Globotruncana cf. ventricosa (White), Globotruncana cf. linneiana (d'Orbigny), Globotruncanella sp. y Gansserina gansseri (Bolli). La presencia de G. gansseri, una especie guía del Maastrichtiano tardío, en tres localidades es de particular importancia bioestratigráfica, ya que señala la probable existencia de rocas cretácicas en los niveles inferiores inmediatos del Complejo de Quepos, sugieriendo que las rocas danianas expuestas representan la unidad más joven del basamento. En conjunto, las secuencias del basamento de Quepos, fila Chonta y Parrita forman parte del flanco de un aparato volcánico emergente -una isla volcánica-, producto de actividad basáltica en la región antearco de Costa Rica durante el Paleoceno temprano y probablemente Maastrichtiano. Considerando la ausencia de estructuras de acreción en el basamento, tanto la asociación de foraminíferos cretácicos como los nuevos afloramientos paleocenos del basamento sugieren una formación in situ del Complejo de Quepos en la región antearco de Costa Rica.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.