Narjess Karoui-Yaakoub

Paleoecology of the Cretaceous–Tertiary mass extinction in planktonic foraminifera

Abstract Paleobiogeographic patterns of the Cretaceous–Tertiary (K–T) mass extinction in planktonic foraminifera in Tunisia, spanning environments from open marine upper bathyal, to shelf and shallow marginal settings, indicate a surprisingly selective and environmentally mediated mass extinction. This selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction, including species richness, ecological generalists, ecological specialists, surface and subsurface dwellers, whether based on the number of species or the relative percent abundances of species. The following conclusions can be reached for shallow to deep environments: about three quarters of the species disappeared at or near the K–T boundary and only ecological generalists able to tolerate wide variations in temperature, nutrients, salinity and oxygen survived. Among the ecological generalists (heterohelicids, guembelitrids, hedbergellids and globigerinellids), only surface dwellers survived. Ecological generalists which largely consisted of two morphogroups of opportunistic biserial and triserial species also suffered selectively. Biserials thrived during the latest Maastrichtian in well stratified open marine settings and dramatically declined in relative abundances in the early Danian. Triserials thrived only in shallow marginal marine environments, or similarly stressed ecosystems, during the latest Maastrichtian, but dominated both open marine and restricted marginal settings in the early Danian. This highly selective mass extinction pattern reflects dramatic changes in temperature, salinity, oxygen and nutrients across the K–T boundary in the low latitude Tethys ocean which appear to be the result of both long-term environmental changes (e.g., climate, sea level, volcanism) and short-term effects (bolide impact).

The Cretaceous^Tertiary (K^T) mass extinction in planktic foraminifera at Elles I and El Melah, Tunisia

Planktic foraminiferal faunas across the K–T transition at Elles and El Melah in northwestern and northeastern Tunisia, respectively, reveal patterns of species extinctions and species survivorship similar to those found at the El Kef stratotype and the Ain Settara sections. Slightly more than 2/3 of the species disappeared at or before the K–T boundary event and slightly less than 1/3 survived into the Danian where most disappeared sequentially within zone P1a (Parvularugoglobigerina eugubina). Relative species abundance patterns reveal that the 13–16 K–T survivors dominated (80%) the assemblages in the latest Maastrichtian, whereas the K–T extinct species were rare and totaled less than 20% of the total assemblages. The K–T survivors are generally small with little surface ornamentation and geographically widespread from low to high latitudes. In contrast, K–T extinct species are large, highly ornamented and geographically restricted to low latitudes. This indicates that the K–T mass extinction was selective, rather than random, and predominantly affected the less robust tropical species. With the exception of the opportunistic Guembelitria species which dominate the early Danian, most K–T survivor species suffered severely as is evident by the decreased species populations after the K–T event. Their eventual demise appears to have been related to post-K–T environmental changes and competition from evolving Tertiary species. These results reveal a complex mass extinction pattern that in addition to the K–T impact event is keyed to long-term environmental changes preceding and following this event.

Enregistrement des événements remarquables de la limite Crétacé-Tertiaire dans la coupe d'Ellès (Tunisie)

Abstract The review of the Cretaceous–Paleogene interval deposits of the Elles section based on a detailed sampling gives a good characterization of the K/T boundary and reconstitution of the geological events underlining this boundary. Thus, the discovery of a thin Ir-rich layer, with Ni and Cr-rich spinel and shocked quartz is a well preserved record of the known cosmic event that occurred at that time. This sudden event is also corroborated by the quantitative and qualitative organic components distribution along the K/T interval. Added to some other long-term events (e.g. climatic, eustatic), it generated a mass extinction, at the K/T boundary, of specialists among the Globotruncanids and Heterohelicids planktic foraminifera species. Following this biological crisis, the biotic turnover into the Danian is slow. The underlining of all the Cretaceous–Tertiary interval biozones attests that the Elles section is complete. If compared to the K/T stratotype and El Kef II sections, the Elles section is found to display a better exposure of the K/T interval and shows more expanded zones and subzones. Such characteristics promote the Elles section to be considered as a parastratotype.

Late Cretaceous and Palaeocene clays of the northern Tunisia: potential use for manufacturing clay products

Late Cretaceous and Palaeocene clay deposits of the northern Tunisia were studied for potential valorization in clay product manufacturing. To achieve this goal, physicochemical characterization based on multidisciplinary approaches including mineralogy, geochemistry and thermal analyses was carried out. Clay samples collected from the Bir M’Cherga and Tajerouine study sites have undergone chemical analysis by using atomic absorption spectroscopy. The obtained results showed that the studied samples were mainly composed of silica, alumina, calcium and iron oxide. Mineralogical analysis confirmed the results of chemical analysis; it showed the main peaks of quartz, calcite, kaolinite, smectite and illite. Those clay samples were used as natural resources for manufacturing earthenware tiles. Mixtures of clays and dolomites were prepared from the Late Cretaceous and Palaeocene clays and then heated to the desired temperature to obtain different earthenware products. Finally, the prepared clay products were tested via different geotechnical analyses. It was found that the clay percentage needed to be decreased in the starting mixture to enhance the properties of the final products. Those results also indicated that industrial application of both Late Cretaceous and Palaeocene clays of the northern Tunisia could be done, especially for manufacturing clay products.

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.

Middle-to-Late Pleistocene malacofauna from the archeopaleontological site of Oued Sarrat (Tajerouine area, NW Tunisia)

The malacofauna collected from the archeopaleontological site in Oued Sarrat (Tajerouine area, NW Tunisia) is the first reference from the Middle and Late Pleistocene stratigraphic series in Tunisia. These malacologic assemblages are abundant but little diversified; they are considered as continental, lakeside, and fluviatile ecosystem forms. They are associated with bones of small and large vertebrates and lithic artifacts. The dominant species of gastropods are Cernuella virgata (Da Costa, 1778), Xerosecta cespitum (Draparnaud, 1801), and Sphincterochila baetica (Rossmässler, 1854) which are typical of the Mediterranean regions. The abundance of these pulmonate terrestrial gastropods indicates a post-mortem transport of shells by floods and fluvial channels. The only bivalve, Unio ravoisieri (Deshayes, 1847), still common in the rivers of northern Tunisia, characterizes a typical lakeside environment, with relatively low energy. Considering the recently discovered associated vertebrate remains, their occurrence corroborates the onset of a paleoenvironment landscape with swamps, or even a shallow freshwater paleolake with close forests. Hence, this environment also inhabited by a diversity of large mammal species and other abundant microvertebrates and invertebrates was a support for human survival within these northern African latitudes.

Planktonic foraminiferal biostratigraphy and paleoenvironment of the Danian/Selandian in west-central Sinai (Egypt), implications from the Nukhul section

The foraminiferal analysis at the Danian/Selandian boundary of the Nukhul section (Egypt) enabled us to determine the biozones of Praemurica uncinata (P2); Morozovella angulata (P3a); Igorina albeari (P3b), and Acarinina soldadoensis/Globanomalina pseudomenardii (P4c). Thus, the base of Selandian is defined by the first occurrence of I. albeari and the P4c subzone covers unconformably the P3b subzone. The quantitative and qualitative analysis of the planktonic and benthic foraminifera assemblages and the isotopic analysis permitted characterization of the paleoclimate and paleoenvironment. Thus, at the middle to upper Danian, the environment was marine intertidal under a relatively cold climate. At the lower Selandian base of the Thanetian, a rise in the sea level was recorded and the warmer climatic conditions seem to be settling. In the upper Thanetian, we note the installation of colder weather conditions and a further sudden drop in sea level.