Tempestite Deposits on a Storm‐influenced Carbonate Ramp: An Example From the Pabdeh Formation (Paleogene), Zagros Basin, Sw Iran

Abstract

The Pabdeh Formation is part of a thick carbonate-siliciclastic succession in the Zagros Basin of SW Iran which includes carbonate reservoirs of Cretaceous and Cenozoic ages. From field observations and petrographic and facies analysis of exposures in the type section of the Pabdeh Formation, four lithofacies were recognized. These are from oldest to youngest: (i) a mottled, bioturbated bioclastic wackestone/mudstone facies; (ii) a wackestone/packstone facies with horizontal burrows on bedding planes; (iii) a thin-bedded bioclastic wackestone/mudstone facies alternating with thin bioclastic-oolitic-intraclastic intervals; and (iv) a bioclastic foraminiferal / algal / peloidal packstone facies. These observations indicate that facies evolved upwards from deep outer-ramp deposits to inner-ramp deposits within a shoal complex, suggesting progradation of the ramp depositional system.Storm events significantly influenced the ramp system. Storm-generated surges transported sediments from nearshore to the deeper outer-ramp environment where they were deposited as shell-lags, composed mostly of bioclastic packstones, rich in pelagic microfauna with sharp, undulatory erosional basal contacts. The packstones rest on outer ramp mudstones deposited below storm base level. Sedimentary structures in the Pabdeh Formation are those typical of storm deposits, such as hummocky cross-stratification, ripple cross-lamination, ripple marks, escape burrows on the tops of the beds, couplets of fine-and coarse-grained laminae and mixed fauna, as well as intraclasts derived from underlying facies. These distinctive sequences are interpreted to have been generated by waning storm-generated currents. The dominance of fine-grained sediments (medium to fine sand); the lack of large-scale hummocky cross-stratification; the minor amounts of intraclasts derived from underlying facies; the paucity of amalgamated tempestite beds; and the finely-laminated (mm to cm scale) couplets of coarse and fine lamina all suggest a distal tempestite facies. Palaeogeographic reconstruction of the Zagros Basin during the Eocene indicates that the study area was situated in tropical, storm-dominated palaeolatitudes.

Sedimentology and sequence stratigraphy of a Tithonian–Valanginian carbonate ramp (Vaca Muerta Formation): A misunderstood exceptional source rock in the Southern Mendoza area of the Neuquén Basin, Argentina

“…These shallow areas of the carbonate ramp are represented by facies association 2. Similar examples in the sedimentary record are the Betic Middle Jurassic carbonate ramp deposits of Spain (Molina et al, 1997), the Umbria-Marche Middle Jurassic of Italy (Monaco, 1992), and some Paleogene deposits of southwestern Iran (Mohseni and Al-Aasm, 2004), among others.…”

Review of the enigmatic Eocene shark genus Xiphodolamia (Chondrichthyes, Lamniformes) and description of a new species recovered from Angola, Iran and Jordan

“…The shark tooth comes from the mid outcrop of the Pabdeh Formation, in a buff argillaceous limestone dated to the Late Eocene [biozone 52 in Wynd, 1965;biozone 8 in Hosseinzadeh, 2008;equivalent to biozone P18 (Berggren et al, 1995) and E15-E16 (Berggren and Pearson, 2005)]. Although the Pabdeh Formation is dominated by a pelagic microfauna, facies analyses indicate that it was deposited in an outer ramp setting which evolved toward to a shallower storm-influenced ramp (Mohseni and Al-Aasm, 2004;Hosseinzadeh, 2008). Palaeogeographic reconstructions of the Tethys during the Paleogene suggest that the Zagros Basin was situated at the leeward side of a platform edge during the Eocene (Ziegler, 2001), as observed in other Cenozoic ramps in the Middle East (Wilson, 1975;Murris, 1980;Baturin, 1982).…”

“…1). The Pabdeh formation (James and Wynd, 1965), occurring in the northwest-southeast trending Zagros Mountain range, is part of a thick carbonate-silicoclastic succession in the Zagros Basin of SW Iran (Mohseni and Al-Aasm, 2004). Different ages have been attributed to the Pabdeh formation, e.g.…”

Facies architecture of a Late Jurassic carbonate ramp: the Korallenoolith of the Lower Saxony Basin

“…The fauna and bioturbated texture indicate open-marine conditions (Brachert 1992;Mohseni and Al-Asam 2004;Collin et al 2005). Hummocky upper surfaces and normal grading point to storm deposition above storm wave-base (Duke 1985;Walker and Plint 1992).…”