Rudists

Abstract: The stratigraphy of the uppermost levels of the Menderes Massif is controversial and within its details lie vital constraints to the tectonic evolution of south-western Turkey. Our primary study was carried out in four reference areas along the southern and eastern Menderes Massif. These areas lie in the upper part of the Menderes metamorphic cover and have a clear stratigraphic relationship and contain datable fossils. The first one, in the Akbuk–Milas area, is located south-east of Bafa Lake where the Milas, then Kizilagac and Kazikli formations are well exposed. There, the Milas formation grades upwards into the Kizilagac formation. The contact between the Kizilagac and the overlying Kazikli formation is not clearly seen but is interpreted as an unconformity. The Milas and Kizilagac formations are also found north of Mugla, in the region of Yatagan and Kavaklidere. In these areas, the Milas formation consists of schists and conformably overlying platform-type, emery and rudist-bearing marbles. Rudists form the main palaeontological data from which a Santonian–Campanian age is indicated. The Kizilagac formation is characterized by reddish–greyish pelagic marbles with marly-pelitic interlayers and coarsening up debris flow deposits. Pelagic marbles within the formation contain planktonic foraminifera and nanoplankton of late Campanian to late Maastrichtian age. The Kazikli formation is of flysch type and includes carbonate blocks. Planktonic foraminifera of Middle Palaeocene age are present in carbonate lenses within the formation. In the Serinhisar–Tavas area, Mesozoic platform-type marbles (Yilanli formation) belonging to the cover series of the Menderes Massif exhibit an imbricated internal structure. Two rudist levels can be distinguished in the uppermost part of the formation: the first indicates a middle-late Cenomanian age and the upper one is Santonian to Campanian in age. These marbles are unconformably covered by the Palaeocene–Early Eocene Zeybekolentepe formation with polygenetic breccias. In the Cal–Denizli area, the Menderes massif succession consists of cherty marbles and clastic rocks with metavolcanic lenses. The Lower–Middle Eocene Salvan formation lies unconformably on this sequence and is interpreted as equivalent to the marble horizons at Serinhisar but with pelagic facies. The Salvan formation consists of shale, mafic volcanic rock, lenses of limestone and blocks of recrystallized limestone. The Salvan formation is dated here for the first time by Early–Middle Eocene foraminifera and nanoplankton from the matrix of the formation. An angular unconformity exists between the Upper Cretaceous and Lower Tertiary sequences, suggesting that a phase of deformation affected the southern and eastern part of the Menderes Massif at this time. This deformation may be caused by initial obduction of the Lycian ophiolite onto the passive margin to the north of the Menderes carbonate platform during the latest Cretaceous. Drowning of the platform led to termination of carbonate deposition and deposition of deep water flysch-like clastic sediments.

Abstract: The tectonic features of Tunisia are complex and include folds, all types of faults, evaporite diapirs, and the Saharan flexure, which separates a stable Paleozoic province on the south from a subsidence zone of Mesozoic and Cenozoic strata of the offshore Ashtart and Tripolitania basins. The remainder of the offshore region is mostly stable shelf of the Pelagian craton, which also extends onshore. The present study focused on this shelf, where two carbonate intervals contain proven hydrocarbon reservoirs: the Metlaoui Formation of earliest Eocene (Ypresian) age and the Zebbag Formation of Late Cretaceous (Turonian) age. Regionally, well-defined belts of Metlaoui carbonates trend northwest. On the northeast are open-marine deep-water micrites and marls with abundant planktonic foraminifers. Thick bars of nummulitid packstone/grainstone were deposited in shallow water at an angle to the paleoshelf. The reservoir is confined largely to the bars, and visible effective porosity is best developed in those areas among the foraminifers filled with sand-size nummulitid debris, where secondary solution enlargement has occurred. This lithology tested oil in two recent wildcat wells and is a commercial reservoir at Sidi El Itayem and Ashtart fields. Distribution of Zebbag carbonates is more complex. A northwest-trending platform was bounded on three sides by deep water, where shale and micrite with planktonic foraminifers were deposited. Predominately back-reef and lagoonal foraminifer/rudist wackestones and packstones occur in narrow belts, apparently controlled at least locally by block faulting. They tested oil in two recent discoveries. The most significant porosity is interparticle, generally enlarged by solution, in foraminifer packstones, but intraparticle voids in foraminifers and rudists commonly contribute to the porosity. Analyses of surface and subsurface samples identified the Bahloul (basal Turonian) and Bou Dabbous (Ypresian) formations as source rocks. Fluorescence spectra of several oils were compared with extracts from these samples and indicate the Bahloul to be the source of oils in recent Metlaoui and Zebbag discoveries.