Luc G. Bulot

Paleobiogeography of Early Cretaceous Ammonoids

Ammonoids were dominant elements of marine Cretaceous faunas. Their fossils are important biostratigraphic indicators, in some cases with worldwide distribution. Their paleobiogeographic distributions were influenced by changing continental positions, currents, sea level change, and perhaps by their mode of life as reflected in the evolution of many diverse lineages of heteromorphic, possibly rather vertically migrating than horizontally swimming taxa through the Cretaceous. Here, we review the current paleobiogeographic understanding of Late Cretaceous ammonoid distribution in an effort to complement and add to previous work in this field. Four principal paleobiogeographic areas can be distinguished in the Cretaceous: The Boreal Realm, the Tethyan Realm, the Pacific Realm, and the Austral Realm. A Tethyan Superrealm is repeatedly recognized throughout the Late Cretaceous, although represented by varying taxa. Migration between the realms and provinces appears to be linked to changes of migration routes, triggered by sea level changes. At the end of the Cretaceous, provincialism disappears, preceding the extinction of the Ammonoids.

Sequence Stratigraphy of the Albian – Turonian Interval of Southwest Iran based on Outcrop and Subsurface Data

The Albian-Turonian of SW Iran is characterized by two types of carbonate depositional systems: an Albian muddy, benthic foraminifera-dominated, ramp type system, and a Cenomanian-Turonian rudist-rimmed platform to intrashelf basin type system. Third order depositional sequences have been defined in these, constrained by new biostratigraphic and outcrop information, which allowed to evaluate the relative influence of tectonics and eustatism on the sedimentation patterns.

Revised Biostratigraphy and Sequence Stratigraphy of the Gadvan, Dariyan and Kazhdumi Formations, SW Iran

A regional sequence stratigraphic model is presented for the Barremian to Lower Albian sedimentary systems of southwest Iran. Illustrated with nine seismic scale outcrop sections, and constrained by new biostratigraphic and chemostratigraphic age dating (ammonites, pelagic forams, orbitolinids and carbon and oxygen isotope curves), it proposes a fundamental revision of the geometrical relationships between classically used lithostratigraphic units. The relative influence of both eustatic sea-level fluctuations and regional tectonic control are demonstrated. These new insights have significant implications for both the understanding of the factors controlling sedimentation, as well as the architecture of the mid-Cretaceous petroleum systems in the studied region.