Resumen de Relaciones entre los cambios secuenciales y la evolución biológica en los Nummulites del Eoceno y las carófitas del Cretácico

Josep Serra i Kiel, Carles Martín-Closas

• español

  Las Secuencias Deposicionales y la evolución de los ecosistemas presentan un desarrollo semejante. Los episodios iniciales se caracterizan por una entrada brusca de energía externa; posteriormente, la energía acumulada se degrada en un proceso lento. Las modificaciones de los ecosistemas quedan reflejados en diferentes comportamientos evolutivos de los organismos.

  El estudio de las relaciones entre el desarrollo de una Secuencia Deposicional, los cambios de los ecosistemas y el comportamiento evolutivo de dos taxa diferentes (Nummulites del Eoceno y carófitas del Cretácico) ha permitido establecer en que momento del desarrollo de una Secuencia Deposicional se sitúan los procesos de especiación, extinción, transformación anagenética y stasis.

  Los intervalos transgresivos que implicaron una ampliación del hábitat, favorecieron en ambos casos los procesos de especiación. Los procesos de extinción en Nummulites estuvieron relacionados con cambios en la circulación de aguas marinas durante el desarrollo de prismas progradantes. En las carófitas estos procesos tuvieron lugar por inundación de los ambientes lacustres-palustres carbonatados y cuando estos ambientes fueron sustituidos por marismas siliciclásticas con las primeras angiospermas acuáticas. Las transformaciones anagenéticas y las etapas de stasis reflejan momentos de estabilidad ambiental (estabilización de altos o bajos niveles del mar en el caso de las carófitas).

• English

  Speciation, extinction, anagenetic transformation and stasis of both Eocene Nummulites of the South-Pyrenean Basin and Cretaceous Charophyta from the Mesogea ocurred at particular moments during the development of a Depositional Sequence, as it has been observed in a comparison between the evolution of this taxa, the changes in their respective ecosystems and the development of the related Depositional Sequences.

  Larger foraminifera and charophyte speciation took place during sea level rises that widened and diversified the habitats of these organisms.

  Species extinctions occurred in different paleoenvironmental settings. Nevertheless, all these situations result from physical or ecological changes, that made the development of large foraminifera or charophytes difficult. Thus, the extinction of Nummulites is often associated with reductions in the' surface of the carbonatic platforms. At the end of Bartonian, the extinction of large Nummulites can be correlated with a change in the form of the basin margin, that passed from being homoclinal to present an accentuated slope. This slope was created by a progradating highstand system tract that probably produced important changes in the submarine currents. The new basin margin form favoured the development of submarine convective currents and the eutrofisation of waters, which determined the substitution of Nummulites by other, more competitive organisms like corals. In an other example we conclude that Assilina became prematurely extinct in the Upper Lutetian of the South-Pyrenean Basin as a result of the substitution of the carbonatic sedimentation in the plataform by a siliciclastic, muddy, prodeltaic sedimentation. In that case, the Iast cause of the extinction was a tectonic reactivation of the detritic supplies.

  In the Mesogean Charophyta, the extintion of species is related to the flooding of the oligotrophic, stable and wide carbonatic swamps ("Purbeck-Weald" facies) in the Aptian. These environments were substituted by paralic siliciclastic swamps, inadequate for the development of charophytes. At the same time, subaquatic angiosperms became dominant in the marshy environments and displaced charophytes.

  The anagenetic transformation of species has only been studied in the Clavatoraceae, a charophyte family with a large number of gradually changing species.