Online Journal for E&P Geoscientists

Maurer, Florian ^*1; Krystyn, Leopold ²; Martini, Rossana ⁴; Rettori, Roberto ³
(1) Maersk Olie og Gas, Copenhagen, Denmark. (2) Institut fuer Palaeontologie, Universitaet Wien, Vienna, Austria. (3) Dipartimento Scienze della Terra, Universita degli Studi di Perugia, Perugia, Italy. (4) Universite de Geneve, Geneva, Switzerland.

Sequence-stratigraphic reference models for the Arabian Plate suggest a widespread hiatus of some 20 myr spanning from the Late Triassic (Norian) to Early Jurassic (Sharland et al. 2001; Haq and Al-Qathani, 2005). We challenge this interpretation with biostratigraphic and sedimentological data from a 400 m thick succession of carbonates and siliciclastics in the Musandam Peninsula (UAE and Oman) straddling this stratigraphic interval.

The succession starts with tidal-dominated carbonates in the Late Norian (Triasina hantkeni foraminifera zone). This unit comprises subtidal mudstones and intra-supratidal algal boundstones and includes a level of source rocks, as seen in U/Th ratios of outcrop gamma ray data. Still in the Late Norian a tectonic reorganisation is observed, evidenced by local subaerial exposure, widespread occurrence of conglomerates and a change from purely carbonate to mixed carbonate/siliciclastic sedimentation. The following latest Norian to Rhaetian strata are distinctly cyclic in nature. Shallowing upward cycles typically show transgressive claystones and sandstones at the base and carbonates with abundant shallow-water biota towards the top, while carbonate tempestites occur throughout. These cycles resemble the Upper Triassic Lofer cycles as expressed in the Koessen Basin of the Northern Calcareous Alps. The Rhaetian, identified by the occurrence of the conodont Misikella posthernsteini, terminates with rudstones and boundstones rich in Retiophyllia-type corals and hypercalcified sponges. These are overlain by azoic oolithic grainstones and mudstones, followed again by mixed carbonate/siliciclastic facies with the Sinemurian (Lower Jurassic) foraminifer Orbitopsella.

A break in sedimentation across the Triassic/Jurassic boundary is evident from the abrupt facies change and from reworked intraclasts in the basal oolites. Based on our data we estimate a duration of less than 10 myr for the hiatus, and thus a much shorter time span than hitherto proposed.