Abstract
espanolEn este estudio, investigamos la bioestratigrafia y paleoecologia de la Formacion Asmari. El area de estudio se localiza en la zona de Izeh, Cuenca de Zagros. Cuatro secciones en afloramientos fueron muestreadas (Halayjan, Kuh Shur, Kuh-e Bad y Gharibi Ha). Con base en la distribucion de grandes foraminiferos bentonicos y planctonicos, cinco zonas de asociacion fueron reconocidas. Las asociaciones 1 y 2 indican una edad correspondiente al Chattiano; la asociacion 3 esta restringida al Aquitaniano, y las asociaciones 4 y 5 sugieren una edad correspondiente al Burdigaliano. Durante el Chattiano, los depositos de carbonato de la Formacion Asmari, fueron compuestos principalmente por algas coralinas y rojas, asi como por foraminiferos bentonicos grandes y aplanados. Los componentes comunes en el Aquitaniano son abundantes foraminiferos impreforados y Favreina asmaricus. El Burdigaliano se caracteriza por corales, algas coralinas y foraminiferos perforados e imperforados. Durante el Burdigaliano, hacia el SE del area de estudio (seccion Gharibi Ha), los depositos someros son sobreyacidos abruptamente por caliza pelagica. Lo anterior se interpreta como el resultado de una inclinacion regional, que inicio en la parte superior del Burdigaliano. Las asociaciones bioticas sugieren que la sedimentacion de carbonatos ocurrio en aguas tropicales a subtropicales, en condiciones oligotroficas a mesotroficas. Las asociaciones de granos de carbonato en la Formacion Asmari, sugieren una asociacion heterozoica. Con base en parametros paleoecologicos en el area de estudio (tales como: nutrientes, profundidad, iluminacion y salinidad), la Formacion Asmari corresponde a una asociacion de nanoplancton/foraminiferos – foraminiferos/algas, a foraminiferos/moluscos, depositadas en un ambiente con condiciones ligeramente hipersalinas a salinas normales. En la zona eufotica se presentan abundantes foraminiferos imperforados. Hacia la parte profunda de la Cuenca se desarrollaron rotalidos lenticulares, bajo condiciones mesofoticas, y grandes lepidociclinas-numulites, caracterizan a los sedimentos de la profunda zona oligofotica EnglishIn this study, biostratigraphy and paleoecology of the Asmari Formation have been investigated. The study area is located in the Izeh zone, Zagros Basin. Four outcrop sections (Halayjan, Kuh Shur, Kuh-e Bad and Gharibi Ha) have been sampled. Based on distribution of the larger benthic and planktonic foraminifera, five assemblage zones have been recognized. Assemblages 1 and 2 indicate Chattian; assemblage 3 is restricted to Aquitanian and assemblages 4 and 5 suggest Burdigalian. During the Chattian, the carbonate deposits of the Asmari Formation are mostly composed of coralline red algae and large and flat benthic foraminifera. The common components of the Aquitanian are abundant imperforate foraminifera and Favreina asmaricus. The Burdigalian is characterized by coral, coralline algae, and perforate and imperforate foraminifera. During the Burdigalian toward the SE of study area (Gharibi Ha section), the shallow water deposits are abruptly overlain by pelagic limestone. It is interpreted as the result of a regional tilting that started in the upper part of the Burdigalian. The biotic associations suggest that carbonate sedimentation occurred in tropical to subtropical waters under oligotrophic to mesotrophic conditions. The carbonate grain associations in the Asmari Formation suggest heterozoan association. According to paleoecological parameters (such as: nutrient, depth, light and salinity) in the study area, the Asmari Formation belongs to nannofor—foralgal to foramol association which were deposited in slightly hyper to normal saline environment. In the euphotic zone, abundant imperforate foraminifera are present. Basinward, lens shaped rotalids developed in mesophotic conditions, and large lepidocyclinid–nummulitids characterize the sediments of the deeper oligophotic zone.
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