Characterization, lateral variability and lateral extent of discontinuity surfaces on a Carbonate Platform (Barremian to Lower Aptian, Oman)

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 wellexposed study window, 2AE5 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.

C and O isotope stratigraphy in shallow-marine carbonate: a tool for sequence stratigraphy (example from the Lodève region, peritethian domain)

“…The low δ 13 C values could be related to the influence 13 C-depleted soil-zone CO2 that affected the bulk isotopic composition of supratidal facies (Allan & Matthews 1977;Allan & Matthews 1982;Immenhauser et al 2003). Indeed, negative carbon isotope trends are commonly believed to result from the uptake of light carbon derived from the deterioration of organic material in soils during subaerial exposure (Allan & Matthews 1982;Lohman 1988;Sattler et al 2005). The depleted composition of δ 18 O could be explained by the influence of 18 O-depleted early meteoric fluids linked to meteoric diagenesis of marine carbonates above the water table.…”

Bioerosional structures and pseudoborings from Late Jurassic and Late Cretaceous-Paleocene shallow-water carbonates (Northern Calcareous Alps, Austria and SE France) with special reference to cryptobiotic foraminifera

“…In addition, Gastrochaenolites and Trypanites have been reported repeatedly from discontinuity surfaces and hardgrounds (e.g. Bromley 1975;Kobluk et al 1977;Helm 1998;Wilson and Taylor 2001;Mikulas et al 2003;Benner et al 2004;Sattler et al 2005). Within ancient rocky shore complexes of transgressive sequences, Gastrochaenolites is often found in mobile pebble substrates that can be reworked within shallow-water transgressive sequences (e.g.…”

Allogenic and autogenic processes combined in the formation of shallow-water carbonate sequences (Middle Berriasian, Swiss and French Jura Mountains)

“…It is therefore the combination of autogenic/autocyclic and allogenic/allocyclic processes that is responsible for sediment deposition and the formation of the final sedimentary record. Many case studies have already shown and discussed the coexistence of autocyclic and allocyclic processes, for example: Sami and James (1994) in the Proterozoic of northwest Canada; Jiang et al (2003) in the Proterozoic of the Lesser Himalaya; Adams and Grotzinger (1996) in the Middle Cambrian of California; Cowan and James (1993) in the Late Cambrian of Newfoundland; Smith and Read (2001) in the Mississippian of Illinois; Yang et al (1998) in the Late Pennsylvanian and Early Permian of Texas; Bádenas et al (2010) in the Sinemurian of Spain; Carpentier et al (2010) in the Oxfordian of France; Sattler et al (2005) in the Barremian and Aptian of Oman; Lehmann et al (1998) in the Barremian to Albian of northeastern Mexico; Rankey (2002) in the Holocene of the Bahamas.…”