Channelized systems in an inner carbonate platform setting: differentiation between incisions and tidal channels (Natih Formation, Late Cretaceous, Oman)

Abstract

The Natih Formation (late Albian-early Turonian, Oman) corresponds to a very broad inner carbonate platform extending over more than 800 km between the Arabian Shield to the south and the Tethys continental margin to the north. Two types of channelized systems have developed recurrently on this inner carbonate platform: † incisions corresponding to strictly erosive drainage systems which formed at the top of the subaerially-exposed platform during significant drops of relative sea level; † tidal channels corresponding to partly erosive but mainly constructive/depositional systems which formed during phases of flooding of the inner platform.The comparative analysis of the basal surface and fill of incisions and tidal channels, based on the study of several outcrops in the Oman Mountains allows the recognition of the similarities and the main differences between these two types of channelized systems which both develop in an inner carbonate platform setting. One of the main criteria of differentiation is the stratigraphic context in which incisions and channels develop. Incisions develop at the top of regressive sequences, whereas the channels analysed here developed during phases of flooding or maximum flooding, during which higher energy processes such as tidal currents developed on the platform.The incision surface is clearly defined, with diagenetic effects such as silicification and dolomitization below, and with the systematic fill of subjacent burrows and cracks by sparitic calcite crystals. The basal erosion surface of channels is often multiple and composite, systematically burrowed, and associated with no significant diagenetic effect.Channels are generally less deep than incisions but their width is very similar. Incisions are longer than channels and present a section that is, on the whole, symmetrical and regular, whereas channels locally have one margin that is steeper and more erosive than the other.Finally, the less diagnostic parameter of differentiation is their fill. Indeed, incisions and channels are similarly filled during phases of flooding of the inner platform. Incisions and channels form significant heterogeneities at the reservoir scale. It is therefore necessary to be able to recognize these two types of channelized systems, in order to predict their geometry, extent and fill type, and the eventual occurrence of associated reservoir bodies in the more distal direction (forced regressive wedges/bioclastic shoals).The inner part of carbonate platform systems is generally a very flat, shallow-water area which is more or less extensive behind the platform margin. The depositional system in this kind of environment is overall an aggradation of very continuous and low-energy muddy lagoonal facies.At the scale of third-order sequences, the stratigraphic record of this depositional system appears therefore very tabular, suggesting 'layer-cake' horizontal correlations of time lines. However, within these third-order sequences, a high level of sedimentary and stratigraphic heterogeneity may occur, ...

New Alveolinoidea (Foraminifera) from the Cenomanian of Oman

“…The upper Albian/Turonian Natih Formation consists of mainly mud-supported and some grain-supported limestone (with local rudist development) alternating with intraplatform basin organic rich calcareous shales. Deposition was interrupted several times by subaerial exposure with emersion and incision (Immenhauser et al, 2000;Droste and Van Steenwinkel, 2004;Gr elaud et al, 2006Gr elaud et al, , 2010Homewood et al, 2008). Outcrop sedimentology of the Natih Fm.…”

Diagenetic controls on reservoir properties of carbonate successions within the Albian–Turonian of the Arabian Plate

“…Exposure features vary from incipient microkarst to epikarst and deep channel incision (e.g. Droste 2010; Grelaud et al 2006Grelaud et al , 2010. Within transgressive sequences, there is a back-stepping of the clastic delta and shoreface complex as carbonate sedimentation was re-established under conditions of higher relative sea level (Fig.…”

“…Coupled with the increasing effects of compression associated with the first Alpine event, this led to fault reactivation and halokinesis. Within Oman, incisions of tens of kilometres width with a mixed carbonate-clastic fill attest to sedimentation within eastward-migrating channelized systems (Grelaud et al 2010). Line A-B shows the orientation of the cross section in Figure 11.…”

“…These fabrics formed within both deeper water packstone/wackestone facies and lagoonal packstone/wackestone facies (Burchette & Britton 1993;Taghavi et al 2006;Cross et al 2010;Hollis et al 2010), they are commonly associated with third-order transgressive systems tracts (e.g. USF1 of Taghavi et al 2006;MaJ-MaE of Cross et al 2010; Sequence II (Natih C/D) of Grelaud et al 2010 andHollis et al 2010). At its most extreme, ongoing cementation during the period of slowed sedimentation around maximum flooding surfaces resulted in pervasive cementation and the creation of thick (decimetre scale), laterally continuous flow barriers (Cross et al 2010).…”

Siliciclastics in the Upper Triassic dolomite formations of the Krížna Unit (Malá Fatra Mountains, Western Carpathians): constraints for the Carnian Pluvial Event in the Fatric Basin

“…Because of imperfect size-sorting, mixing of lithoclasts of various origin and erosional contact with the underlying bed the described rudites seem to represent the storm lags (see Demicco & Hardie 1994 for comparison). In the second explanation, the breccias could represent the basal high-energy infill of channel incision, formed in an erosive drainage system at the top of a subaerially exposed platform during drops of relative sea level (see Grélaud et al 2010 for comparison).…”