Abstract: Albian Sea-Level Signals Constrained by Stable Isotopes - Nahr Umr Formation, Oman
IMMENHAUSER, A., W. Schlager, Free University, Amsterdam, The Nederlands ([email protected]) S.J. BURNS, Geologisch-Mineralogisches Institut, University of Bern, Switzerland
During the last decades, considerable work and discussion has focused on the causing mechanisms, amplitude and frequency of eustatic sea-level oscillations in the Cretaceous greenhouse world. Carbonate shelves and platforms are considered accurate gauges of changes in relative sea-level but only a very restricted number of geologic settings can be used pinpointing absolute water depths.
We have studied - within the framework of our Mid-Cretaceous
Sea-Level Project - the Albian interval of the Arabian Platform in
Northern Oman for its paleoceanographic and sea-level record. Five
sections were measured and sampled on an approximately 100 km long
transsect from paleo-marginal to paleo-basinal domains of an
intracratonic basin. In all sections ferruginous hardground
surfaces were recognised. Despite the lack of any diagnostic
features such as karstification or spar-filled burrows, these
hardgrounds were interpreted as subaerial exposure surfaces. This
interpretation was mainly based on evidence from densely sampled
carbon and oxygen isotope curves across these hardgrounds.
Pronounced drops in carbon isotope ratios in the magnitude
of 2.5
to 40
to values between +0.9 to -1.2
PDB were found in
sediments underneath these hardgrounds. In sediments overlying the
hardground surfaces values between +3 to 4
were obtained.
Based on these exposure surfaces an interpretation of the
paleobathymetry and sequence stratigraphy has been undertaken
suggesting that the Albian of Oman recorded seven
transgressive-regressive cycles of third-order magnitude
. Close
correlation of these events with depositional cycles recorded in
Albian sediments e.g. along the Texas Gulf Coast may suggest an
eustatic nature of these signals.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah