BIOSTRATIGRAPHY OF CRETACEOUS- TERTIARY BOUNDARY IN SOUTHWESTERN OF TRIPOLI/SABRATH BASIN OFFSHORE LIBYA (CONCESSION NC41)

The present study deals with Cretaceous- Tertiary unconformity in the southwestern part of the Tripoli- Sabratha Basin Off-Shore Libya (Concession 41). A detailed biostratigraphic study has mainly carried out by means of ditch cutting samples analysis from five wells: F1, N1, G1, P11and K1 NC41. Successive sediments above and below the Cretaceous / Tertiary boundary are related to the following formation: Metlaoui Formation, El Haria Formation (A&B Members), Abiod Formation, Aleg Formation, Doulelb Equivelant Formation and Zebbag or Zebbag Eq. Formation, that have a wide distribution in both Off-Shore Libya and Tunisia Biostratigraphic analysis led to the identification of Upper and Lower Paleocene Bio-Zones, according to the biostratigraphic scheme proposed by Agip (1985) for the Mediterranean area. In the study area the duration of the Cretaceous / Tertiary hiatus increases from east to west. The South- eastern side of NC41 (well F1) has a minimum hiatus of the Cretaceous/Tertiary unconformity. In the South-western side (Wells N1, G1, P1, &K1) the Cretaceous/Tertiary unconformity increases to reach the maximum hiatus in Well P1 where the Conacian/Santonian sediments (Douleb Eq) are overlain by the Lower Eocene sediment (Metlaoui Formation). Absolute value of the Cretaceous / Tertiary hiatus can be estimated by absence of successive bio-zones. Consequently, minimum approximates to 2 MY marked in Well F1, and maximum hiatus approximates to 30 MY marked in Well P1. The occurrence and relative abundance of planktonic and several benthic foraminiferal taxa can be used to recognize the depositional environments. During most of the Upper Cretaceous and Lower Paleocene deep marine conditions prevailed. Conversely, the Lower Eocene was mainly characterized by shallow marine conditions.

The Registration of the Mid-Paleocene Biotic Event (MPBE) in Tunisia

In Tunisia, the Paleocene biomarkers are identified within the El Haria Formation shales. The Selandian is absent in most of the Paleocene outcrops and the Thanetian is unconformable to different stages of the Cretaceous. In the middle of Selandian, with the beginning of the Globanomalina pseudomenardii (P4) zone, we note that the assemblage of planktonic foraminifera becomes very poorly preserved and much less abundant than at the base. It is represented by rare species and there has been a start of the microfauna dissolution tests and an enrichment in iron oxides, silica, and gypsum crystals. The dissolution process is increasing more and more and a drop in the content of carbonates is clearly recorded at the top of Selandian. However, we note that some small benthic foraminifera belonging to the genera Lenticulina and Anomalina escape the dissolution and very few planktonic foraminifera belonging to the genera Subbotina are preserved. This dramatic and abnormal dissolution extends over a considerable thickness. These features could be an expression of the mid-Paleocene biotic event (MPBE), registered for the first time in Tunisia. This intense dissolution is caused probably by the change in the solubility of carbonates, which may be related to the changes in the deep-water circulation or to the change in the productivity of the surface waters.

Verruca punica, a new species of verrucomorph barnacle (Crustacea, Cirripedia, Thoracica) from the Lower Danian (Palaeocene) of Tunisia

The discovery of a near-complete shell wall of a small verrucid barnacle from the Lower Danian (Palaeocene) portion of the El Haria Formation as exposed in the El Kef area (northwest Tunisia), permits its description as a new species with characters that, although conforming primarily to Verruca sensu stricto, show some similarities to Altiverruca Pilsbry, 1916, a genus that is not yet known from the fossil record. The present material extends the known geographic distribution of fossil verrucids, and constitutes one of the earliest species of Verruca to be documented subsequent to the Cretaceous/Palaeogene (K/Pg) boundary mass extinction event.

Etude preliminaire des argiles eocenes, mio-pliocenes et actuelles de la region de Metlaoui-M'Dilla et du cap Bon (Tunisie)

Eocene and Mio-Pliocene formations of the Gafsa region are differentiated by their clay minerals. The clays of the El-Haria formation are composed of equal amounts of montmorillonite and kaolinite. The overlying Eocene marine clays of Djebel M'Dilla are composed of montmorillonite, illite and traces of kaolinite, and include a bed of clay containing montmorillonite and sepiolite-attapulgite. The continental Mio-Pliocene deposits around Djebel M'Dilla contain a suite of minerals including kaolinite, attapulgite, illite, montmorillonite and chlorite. These minerals apparently do not have authigenic characteristics. Diffractograms obtained from these deposits indicate pronounced crystallinity of the minerals. Mineralogic variation in the clay lenses shows that, from the base to the top, illite and, to a lesser degree, kaolinite, gain importance at the expense of the montmorillonite. At Cape Bon, the Oligocene is rich in kaolinite with subordinate amounts of illite and montmorillonite. Vindobonian, Pliocene and Recent deposits contain the same phyllites but with kaolinite and montmorillonite in equal proportions and a lesser percentage of illite. The uniformity exhibited by the Miocene clays--suggesting monotonous accumulation from a single source of supply--reaffirms the fact that the composition of clays depends more on the nature of the source of supply than on the diagenetic modification produced in the course of sedimentation. The montmorillonitic mineral of these deposits is an unstable phyllite intermediate between a classic montmorillonite in the Eocene and an ammersoite in the post-Eocene.