Publication: Tipología y significado de bioturbaciones en facies evaporíticas continentales: Mioceno de la Cuenca de Madrid
Loading...
Files
Full text at PDC
Publication Date
1997
Authors
Advisors (or tutors)
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
Sociedad Geológica de España
Citations
Exportar
Abstract
Los complejos lacustres desarrollados durante el Mioceno en la Cuenca de Madrid están en buena parte constituidos por depósitos evaporíticos dentro de los cuales se reconocen diversos tipos de icnitas. En función del grado de bioturbación del sedimento, de la geometría y morfología de las trazas, sus dimensiones, estructuración interna y tipo de relleno, así como de las facies en que se presentan, se han distinguido seis tipos de icnitas: 1) Sistemas de chimeneas y túneles con relleno pasivo y diámetro de orden
rnilimétrico, 2) Sistemas de chimeneas y túneles con relleno pasivo y diámetro de orden centimétrico, 3) Chimeneas y túneles con relleno en menisco y diámetro subrnilimétrico-rnilimétrico, 4) Chimeneas y túneles con relleno en menisco y diámetro de orden centimétrico, 5) Tubos con ramas verticales y horizontales, relleno masivo y diámetro de orden centimétrico, y 6) Pisadas de vertebrados. Los organismos causantes de estas bioturbaciones son, en el caso de las icnitas de tipo 1 y 2, raices de plantas, herbáceas en el primer caso y arbustos en el segundo. Las icnitas de tipo 3, 4 Y 5 son debidas a la acción de insectos (larvas de
Chironomidae?, etc ... ) y anélidos. Tanto los insectos como los anélidos pueden haber tenido un cierto papel en la formación de algunas icnitas de tipo 1. Por su parte, las pisadas de vertebrados, atribuidas en algunas ocasiones a Hiénidos de pequeño tamaño y en otras a animales de mayor envergadura, forman un grupo aparte por sus características morfológicas. Los diferentes tipos de icnitas reconocidos se presentan por lo general asociados a una o más facies sedimentarias evaporíticas. Se han distinguido un total de 6 asociaciones de facies que comprenden ambientes y/o subambientes de llanura lutítica, margen lacustre y zonas lacustres más abiertas, apreciándose diferencias en cuanto al carácter efímero o perenne de estos lagos salinos. Las
bioturbaciones presentes en los sedimentos evaporíticos estudiados permiten avanzar en la casuística de la
interrelación bioturbación-alteración del sedimento y control de éstas sobre procesos diagenéticos, tanto tempranos como más tardíos, en depósitos evaporíticos. Los efectos de la bioturbación se centran en aspectos tales como distribución de carbonato y zonas de oxidación/reducción en el sedimento, reemplazarnientos (p. ej. silicificaciones) y cementaciones, entre otros
Lake complexes developed in the Madrid Basin through Miocene are largely formed of evaporite deposits (Calvo et al., 1989 a; Ordóñez et al., 1991). Several types of ichnites can be recognized within these sediments. On the basis of bioturbation degree, trace geometries and magnitudes, intemal filling, and lithofacies in which the traces occur, six types of ichnites have been distinguished: 1) shaft and tunnel network formed of millimetric, passive filled tubes, 2) shaft and tunnel network forrned of centimetric, passive filled tubes, 3) shafts and tunnels (burrows) showing back-filling, submillimetric to millimetric in diameter, 4) shafts and tunnels (burrows) with back-filling, centimetric in diameter, 5) traces with vertical and horizontal branches showing massive :filling-centimetric in diameter, and 6) vertebrate tracks. The bioturbation of the evaporite sediments was caused either by plant roots, which is the case for type-1 (grass roots) and type-2 (bushes), or anirnals. Types-3, 4 and 5 are thought to be due to insects (larvae of Chironomidae?, etc ... ) and annelids. Insects and annelids also could play sorne role on the formation of sorne type-1 ichnites. On the other hand, vertebrate tracks, which may be attributed to small Hyenids or other bigger marnmals, form a separate group of ichnites. Each ichnite type occurs cornmon1y associated with one or more sedimentary facies. Six different facies associations that inelude the described ichnites have been distinguished: A) Mudflat -saline lake facies association, the flats being related to small alluvial fans; B) Mudflat-saline lake complex related to widely developed alluvial systems, C) Mudflat-ephemeral carbonate pond subenvironrnent; D) Mudflat-lake margin facies association; E) Ephemeral saline lake; and F) Lake margin-open saline 1ake association. An idealized model of distribution of the ichnites in these depositional systems is proposed. Bioturbation of the primary evaporite deposits leads to modification ofboth texti,rre and fabric thus conditionating early and later diagenetic processes within the sedimento In this paper sorne of these aspects are considered and we make sorne emphasis on the role of bioturbation in diagenetic processes such as replacement and cementation of the evaporite deposits
Lake complexes developed in the Madrid Basin through Miocene are largely formed of evaporite deposits (Calvo et al., 1989 a; Ordóñez et al., 1991). Several types of ichnites can be recognized within these sediments. On the basis of bioturbation degree, trace geometries and magnitudes, intemal filling, and lithofacies in which the traces occur, six types of ichnites have been distinguished: 1) shaft and tunnel network formed of millimetric, passive filled tubes, 2) shaft and tunnel network forrned of centimetric, passive filled tubes, 3) shafts and tunnels (burrows) showing back-filling, submillimetric to millimetric in diameter, 4) shafts and tunnels (burrows) with back-filling, centimetric in diameter, 5) traces with vertical and horizontal branches showing massive :filling-centimetric in diameter, and 6) vertebrate tracks. The bioturbation of the evaporite sediments was caused either by plant roots, which is the case for type-1 (grass roots) and type-2 (bushes), or anirnals. Types-3, 4 and 5 are thought to be due to insects (larvae of Chironomidae?, etc ... ) and annelids. Insects and annelids also could play sorne role on the formation of sorne type-1 ichnites. On the other hand, vertebrate tracks, which may be attributed to small Hyenids or other bigger marnmals, form a separate group of ichnites. Each ichnite type occurs cornmon1y associated with one or more sedimentary facies. Six different facies associations that inelude the described ichnites have been distinguished: A) Mudflat -saline lake facies association, the flats being related to small alluvial fans; B) Mudflat-saline lake complex related to widely developed alluvial systems, C) Mudflat-ephemeral carbonate pond subenvironrnent; D) Mudflat-lake margin facies association; E) Ephemeral saline lake; and F) Lake margin-open saline 1ake association. An idealized model of distribution of the ichnites in these depositional systems is proposed. Bioturbation of the primary evaporite deposits leads to modification ofboth texti,rre and fabric thus conditionating early and later diagenetic processes within the sedimento In this paper sorne of these aspects are considered and we make sorne emphasis on the role of bioturbation in diagenetic processes such as replacement and cementation of the evaporite deposits