A càrrec de Jean Gerard, Clastics Advisor, Repsol Exploración SA, Madrid
SEMINARIS DE LA FACULTAT DE GEOLOGIA I L'INSTITUT DE CIÈNCIES DE LA TERRA JAUME ALMERA

Universitat de Barcelona (UB)
Consell Superior d'Investigacions Científiques (CSIC)

Dia: dimarts 9 de desembre
Hora: 12.30 h
Lloc: sala d'actes de l'Institut Jaume Almera

Resum: Ichnology provides useful information on the environmental conditions
that prevailed during or shortly after sediment deposition. As such,
recognition and interpretation of trace fossils are now integrated in
advanced sedimentological core studies. Ichnofabric information is best
used in the full context of the sedimentary framework. Only then can
ichnology provide detailed environmental information that can be related
to depositional processes, relative palaeobathymetry and sequence
stratigraphy. The early successful use of trace fossils was greatly
advanced by Adolf Seilacher in the 1960's, who introduced the concept of
“ichnofacies” that split the marine realm into four main zones covering
nearshore environments to the deep basin. More recently, the use of
“ichnofabrics” has increased steadily since the ichnofabric concept was
first developed by Bromley and Ekdale in 1984. Later, sequence
stratigraphy concepts, which were first developed on seismic data
calibrated by biostratigraphy and core facies analysis, were spread in
both Industry and Academia. These concepts subsequently promoted
integration of data arising from all techniques including trace fossil
analysis. For example, combination of the broader ichnofacies system and
the detailed ichnofabric analysis can yield a better product than using
the systems separately. Ichnofabrics provide a finer resolution than
ichnofacies but neglect the broader picture. Ichnofabrics allow not only
large third-order cycle recognition, but can also identify and correlate
higher-frequency cycles by comparing the ichnofabric cycles and their
vertical stacking. This supports a clearer identification of significant
geological surfaces when correlating wells. The level of resolution
supplied by ichnofabrics thereby becomes more compatible and comparable
to reservoir characterization level. Sequence stratigraphers can extract
shallowing-upward and deepening-upward trends from the recurring
ichnofabric patterns, which supply reliable constraints for interpreting
and correlating all the bounding surfaces and patterns between wells.
From a reservoir viewpoint, the impact of bioturbation on early
diagenetic fluid flow is becoming increasingly highlighted, as it may
ultimately control micro-scale heterogeneity by enhancing (leaching) or
deteriorating (mixing mud and sand or cementing) the reservoir quality
of the sediment during burial history.

Jean is the editor and publisher of a photographic atlas prepared with
Richard Bromley. The atlas includes 437 photos and 31 illustrations
printed on a glossy paper (40.2x28.4cm), hardbound. Available early
December 2008.