Regional depositional setting and pore network systems of the El Garia Formation (Metlaoui Group, Lower Eocene), offshore Tunisia

Abstract

The Metlaoui Group was deposited on a broad ramp that deepened to the northeast into the Tethyan Sea. The ramp contains a series of broad facies belts. The inner-ramp facies belt is composed of three facies tracts: (1) Faid sabkha (most landward) characterised by skeletal-poor dolomudstones and wackestones and interbedded evaporites, (2) Ain Merhotta restricted shallow-lagoon facies composed of sparse skeletal wackestones, packstones, and cross-bedded gastropod grainstones; (3) updip El Garia high-energy shoal complex (most seaward) composed of red algal-discocyclinid grainstones and packstones which are locally cross-bedded. The El Garia carbonates in the mid-ramp setting are predominantly composed of large, flat nummulites. Dominant textures are burrowed, mud-poor packstones and poorly sorted or bimodal grainstones. The accumulation was located below fair-weather wave base and above storm wave base, at a water depth estimated to have ranged from 30 to 60 m (middle neritic). The deep-water (deep neritic), outer-ramp Ousselat Member consists of coarse silt- to medium sand-sized nummulithoclastic debris that grades from coarser to finer debris down the ramp. The Bou Dabbous Formation is composed of basinal foraminiferal mudstones, wackestone and packstones deposited by suspension and less commonly by gravity-flow deposition in upper bathyal water depths. Reservoir quality is variable, with most lime packstones and grainstones having moderate to high porosity (related to intraparticle and microporosity), but only poor to fair permeability (generally less than 10 mD). The higher-quality reservoirs have preserved interparticle porosity with permeabilities ranging from tens of millidarcys to several darcys. Permeable nummulitic packstones and grainstones are favoured by the following factors: (1) low abundance of lime mud, (2) low abundance of nummulithoclastic debris, (3) low abundance of echinoderm fragments, (4) moderate sorting, (5) minor precipitation of late burial cements, (6) dolomitization.

Depositional architecture and sequence stratigraphy of the Oligo–Miocene Asmari platform; Southeastern Izeh Zone, Zagros Basin, Iran

“…There is a general consensus (Loucks et al 1998;Pomar 2001;Barattolo et al 2007) that Nummulites accumulations commonly reflect high production rates in mid-ramp settings. On the landward side of this facies belt, subfacies II-3 contains highly-robust forms of nummulitids, commonly associated with porcellaneous foraminifera (II-3); this subfacies represents the innermost middle-ramp facies.…”

Late Paleocene–early Eocene Tethyan carbonate platform evolution — A response to long- and short-term paleoclimatic change

“…From literature data it is not possible to draw a coherent picture on the dominant organism distribution in the (Bolle et al, 1999). In the El Garia Formation and the Ousselat Member of the Metlaoui Group in the Ypresian, nummulitic banks accumulated on the middle to outer shelf across central and northwestern Tunisia (Moody, 1987;Zaier et al, 1998;Loucks et al, 1998). The Ypresian carbonate ramp consists of elongate nummulitic banks, running parallel to the paleoshoreline and shows no patch reef-like bodies (Moody, 1987 (Herbig, 1986;Trappe, 1991Trappe, , 1992.…”

Tectonically driven carbonate ramp evolution at the southern Tethyan shelf: the Lower Eocene succession of the Galala Mountains, Egypt

“…Schaub 1992;Serra-Kiel et al 1998;Scheibner and Speijer 2009), oil potential (e.g. Loucks et al 1998;Ahlbrandt 2001;Baaske et al 2008) and the response to long-and short-term palaeoclimatic change (e.g. Scheibner et al 2005Scheibner et al , 2007Pujalte et al 2009; summary by Scheibner and Speijer 2008, and references therein).…”