Heard, T.G.; (2008) Ichnology and sedimentology of deep-marine clastic systems, Middle Eocene, Ainsa-Jaca basin, Spanish Pyrenees. Doctoral thesis , University of London.

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Abstract

Despite considerable research into the characterisation of the architectural elements of submarine fans, few studies have attempted the full integration of ichnology and sedimentology. In this thesis, a quantitative analysis of trace fossils from the Early-Middle Eocene deep-marine clastic systems, Ainsa-Jaca basin, Spanish Pyrenees, shows that trace fossils are powerful discriminators of deep-marine fan and related environments. Sixteen fan and related environments have been recognised in the Ainsa-Jaca basin, from upper-slope gully to distal basin-floor. In the more laterally confined and channel-dominated Ainsa basin, there is a trend of increasing bioturbation intensity and trace-fossil diversity away from channel-axis to off-axis environments. In the more unconfined and distal Jaca basin, there is a trend of increasing trace-fossil diversity and number of pre-depositional trace fossils including graphoglyptids from the channel-lobe transition to the fan-fringe. The trace-fossil assemblages of the Ainsa-Jaca basin are characteristic of a number of subichnofacies of the Nereites ichnofacies. In the distal Jaca basin, the Paleodictyon subichnofacies occurs in the lobe-fringe and fan-fringe, whereas the distal basin-floor has a trace-fossil assemblage typical of the Paleodictyon subichnofacies, but with a high proportion of post-depositional fodinichnia. Trace-fossil assemblages of proximal basin, axial, environments are characteristic of the Ophiomorpha rudis subichnofacies, whilst proximal off-axis environments, have a mixed Paleodictyon-Ophiomorpha rudis subichnofacies trace-fossil assemblage. In core, a detailed ichnofabric study of the proximal Ainsa channel system shows a clear trend of increasing bioturbation intensity and trace-fossil diversity from channel axis to levee-overbank. Spectral analysis of bioturbation intensity in thin-bedded turbidites deposited in overbank and interfan environments from one of the wells (A6), suggests, for the first time from a siliciclastic turbidite succession at a tectonically active plate margin, a strong cyclicity interpreted to reflect the -41 k.yr and -112 k.yr. Milankovitch frequencies. It is, therefore, proposed that global climate change acted as the principal environmental driver in controlling changes in bottom-water conditions within the deep-marine Ainsa basin.

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