학술논문
New Bilbilian (early Cambrian) archaeocyath-rich thrombolitic microbialite from the Lancara Formation (Cantabrian Mts., northern Spain)/Nuevas microbialitas de arqueociatos y trombolitos del Bilbiliense (Cambrico inferior) de la Formacion Lancara (Cordillera Cantabrica, norte de España)
Document Type
Academic Journal
Source
Journal of Iberian Geology. July 1, 2012, Vol. 38 Issue 2, p313, 18 p.
Subject
Language
Spanish; Castilian
ISSN
1698-6180
Abstract
1. Introduction The lower-middle Cambrian Lancara Formation (Oele, 1964) is mainly composed of dolostone, limestone and occasional shale interbeds, ranging from 150 m up to 225 m in thickness (Aramburu [...]
Recent palaeontological and microfacies studies carried out on the Lancara Formation (early Cambrian) provide evidence for an interesting, previously undescribed association of archaeocyaths (Salce locality) and microbialites (Salce and Barrios de Luna localities). The archaeocyathan assemblage consists of Archaeocyathus laqueus (Vologdin, 1932) and Pycnoidocyathus erbiensis (ZHURAVLEVA, 1955), indicating an early Bilbilian age (Stage 4, Series 2, Cambrian) for these materials. The analysis of the upper part of the lower member has allowed differentiation of eleven carbonate facies that have been grouped into: i) non- skeletal grain packstone-grainstone, ii) fenestral mudstone-packstone, iii) heterolithic stylonodular facies, iv) microbialites, v) bioclast-intraclast packstone-grainstone. Archaeocyaths occur reworked in stylonodular facies as well as forming small archaeocyaths- thrombolitic patches (centimetre-scale). The archaeocyath-rich thrombolitic microbialites from Salce were developed in very shallow subtidal conditions surrounded by other microbialites and small lenticular intertidal bars in the inner ramp. Toyonian biostratigraphic and paleobiogeographic analyses have also been carried out. After the comparison with Toyonian archaeocyathan rich facies from Gondwana, it has become evident that the early Cambrian record from the Cantabrian Mountains provides the richest generic assemblage from Gondwana for Toyonian time. Keywords: Archaeocyaths, Microbialite, Lancara Formation, early Cambrian, Somiedo-Correcilla Subunit, Cantabrian Mountains Los recientes estudios paleontologicos y de analisis de microfacies de los materiales carbonatados de la Formacion Lancara (Cambrico inferior) han deparado el hallazgo de una inedita asociacion de arqueociatos (localidad de Salce) y microbialitas (localidades de Salce y Barrios de Luna). La asociacion de arqueociatos esta constituida por Archaeocyathus laqueus (Vologdin, 1932) y Pycnoidocyathus erbiensis (ZHURAVLEVA, 1955), lo que indica una edad Bilbiliense (Piso 4, Serie 2, Cambrico) para estos materiales. En el analisis de los niveles carbonatados, a techo del miembro inferior, se han distinguido once tipos de facies que han sido agrupadas en: i) packstone-grainstone de granos no esqueleticos, ii) mudstone-packstone con fabrica fenestral, iii) facies estilonodulares heteroliticas, iv) microbialitas, v) packstone-grainstone bioclasticos e intraclasticos. Los arqueociatos aparecen resedimentados en las facies estilonodulares y formando pequenos parches tromboliticos (escala centimetrica). Las microbialitas de arqueociatos y trombolitos de Salce se desarrollaron en condiciones submareales muy someras rodeadas de otras microbialitas y pequenas barras lenticulares en zonas intermareales de la rampa interna. Se han realizado analisis bioestratigraficos y paleobiogeograficos para el Toyoniense. Tras comparar las facies del Toyoniense ricas en arqueociatos de Gondwana, se manifiesta de manera evidente que el registro del Cambrico inferior de la Cordillera Cantabrica aporta la asociacion generica mas rica de Gondwana durante el Toyoniense. Palabras clave: Arqueociatos, Microbialitas, Formacion Lancara, Cambrico inferior, Subunidad Somiedo-Correcilla, Cordillera Cantabrica.
Recent palaeontological and microfacies studies carried out on the Lancara Formation (early Cambrian) provide evidence for an interesting, previously undescribed association of archaeocyaths (Salce locality) and microbialites (Salce and Barrios de Luna localities). The archaeocyathan assemblage consists of Archaeocyathus laqueus (Vologdin, 1932) and Pycnoidocyathus erbiensis (ZHURAVLEVA, 1955), indicating an early Bilbilian age (Stage 4, Series 2, Cambrian) for these materials. The analysis of the upper part of the lower member has allowed differentiation of eleven carbonate facies that have been grouped into: i) non- skeletal grain packstone-grainstone, ii) fenestral mudstone-packstone, iii) heterolithic stylonodular facies, iv) microbialites, v) bioclast-intraclast packstone-grainstone. Archaeocyaths occur reworked in stylonodular facies as well as forming small archaeocyaths- thrombolitic patches (centimetre-scale). The archaeocyath-rich thrombolitic microbialites from Salce were developed in very shallow subtidal conditions surrounded by other microbialites and small lenticular intertidal bars in the inner ramp. Toyonian biostratigraphic and paleobiogeographic analyses have also been carried out. After the comparison with Toyonian archaeocyathan rich facies from Gondwana, it has become evident that the early Cambrian record from the Cantabrian Mountains provides the richest generic assemblage from Gondwana for Toyonian time. Keywords: Archaeocyaths, Microbialite, Lancara Formation, early Cambrian, Somiedo-Correcilla Subunit, Cantabrian Mountains Los recientes estudios paleontologicos y de analisis de microfacies de los materiales carbonatados de la Formacion Lancara (Cambrico inferior) han deparado el hallazgo de una inedita asociacion de arqueociatos (localidad de Salce) y microbialitas (localidades de Salce y Barrios de Luna). La asociacion de arqueociatos esta constituida por Archaeocyathus laqueus (Vologdin, 1932) y Pycnoidocyathus erbiensis (ZHURAVLEVA, 1955), lo que indica una edad Bilbiliense (Piso 4, Serie 2, Cambrico) para estos materiales. En el analisis de los niveles carbonatados, a techo del miembro inferior, se han distinguido once tipos de facies que han sido agrupadas en: i) packstone-grainstone de granos no esqueleticos, ii) mudstone-packstone con fabrica fenestral, iii) facies estilonodulares heteroliticas, iv) microbialitas, v) packstone-grainstone bioclasticos e intraclasticos. Los arqueociatos aparecen resedimentados en las facies estilonodulares y formando pequenos parches tromboliticos (escala centimetrica). Las microbialitas de arqueociatos y trombolitos de Salce se desarrollaron en condiciones submareales muy someras rodeadas de otras microbialitas y pequenas barras lenticulares en zonas intermareales de la rampa interna. Se han realizado analisis bioestratigraficos y paleobiogeograficos para el Toyoniense. Tras comparar las facies del Toyoniense ricas en arqueociatos de Gondwana, se manifiesta de manera evidente que el registro del Cambrico inferior de la Cordillera Cantabrica aporta la asociacion generica mas rica de Gondwana durante el Toyoniense. Palabras clave: Arqueociatos, Microbialitas, Formacion Lancara, Cambrico inferior, Subunidad Somiedo-Correcilla, Cordillera Cantabrica.