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Keywords:

  • Carbonate platform;
  • Cretaceous;
  • discontinuity surface;
  • Oman;
  • subaerial exposure

Abstract

Hiati of various duration in carbonates are commonly expressed as discontinuity surfaces. The understanding of processes that form and affect these surfaces leads to an improved sequence-stratigraphic interpretation, a reliable outcrop correlation, and better models for reservoir compartmentalization. Various intraformational discontinuities were analysed and interpreted in a well-exposed study window, 2·5 km in lateral length and 60 m in height comprising the Barremian-Aptian Qishn Formation (Haushi-Huqf area, central Oman). This study focuses on the lateral extent and morphology of the surfaces, the petrography of the underlying rocks, and the facies changes and geochemical trends across these discontinuities. Furthermore, the lateral variability of discontinuity surfaces was documented. Three genetic types of discontinuities are differentiated: (i) erosion surfaces; (ii) omission surfaces (hard- and firmgrounds); and (iii) composite surfaces with evidence for both subaerial exposure and submarine boring. Field observations, combined with petrographic and geochemical data, suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea-level fluctuations of regional scale. In contrast, a large number of laterally limited surfaces (<1 km) are related to locally active processes such as waves and current erosion. The lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity, the sea-floor topography, waves and currents and differential erosion. The most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment. This variability is caused by spatial variability in the tidal flat environment, meteoric alteration and differential erosion. This study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces. This variability must be kept in mind when interpretations and correlations are based on one-dimensional sections or cores.