Despite the large number of studies on the Paleocene–Eocene thermal maximum (PETM), the knowledge of environmental and biotic responses in shallow marine environments remains quite poor. Benthic foraminiferal assemblages of the Sidi Nasseur and Wadi Mezaz sections in Tunisia were studied quantitatively and the paleoecologic interpretations provide new insights into the complex relationship between PETM global warming and perturbations of shallow marine settings. These sections expose upper Paleocene to lower Eocene shales and marls of the El Haria Formation up to the phosphate layers of the Chouabine Formation underlying the El Garia limestones. The Sidi Nasseur section contains a more complete and expanded Paleocene–Eocene boundary interval compared to Wadi Mezaz, although being truncated at the top. The Wadi Mezaz section contains a more complete post-PETM interval. The studied interval can be subdivided into a sequence of 4 biofacies, representing respectively a latest Paleocene biofacies, two PETM biofacies and one post-PETM Eocene biofacies. The latest Paleocene biofacies 1 consists of numerous calcareous benthic foraminifera (e.g. Anomalinoides midwayensis, Frondicularia aff. phosphatica and various Bulimina and Lenticulina species), abundant noncalcareous taxa (Haplophragmoides) and rare planktic foraminifera, indicating a slightly hypersaline eutrophic inner neritic to coastal environment, regularly interrupted by oxygen deficiency (moderate dysoxia). During the latest Paleocene, this highly productive environment shallowed as indicated by the increasing abundances of A. midwayensis. The variable dominance of non-calcareous agglutinated taxa in biofacies 1 indicates post-mortem dissolution effects. The TOC δ13Corg record reveals a sharp negative excursion, marking the base of the Eocene. In general, the absence of lithologic changes, an increasing sedimentation rate and absence of reworking indicate that the initial part of the PETM is complete and expanded in the Sidi Nasseur section. A sharp faunal turnover coincides with this negative δ13Corg excursion and is characterized by the disappearance or diminution of common Paleocene taxa in this area. During the PETM, benthic foraminifera are less abundant and consist of opportunistic non-calcareous taxa together with deeper dwelling (middle neritic) lagenids and buliminids (biofacies 2 and 3). Planktic foraminifera, dominated by flat-spired Acarinina (mainly A. multicamerata), become more abundant, as observed in many open marine sequences worldwide. All these faunal parameters suggest more stressed probably severe dysoxic sea floor conditions within a transgressive phase during the onset of the PETM. An estimation of the total duration of the Sidi Nasseur PETM interval is difficult to establish, yet the lack of recovery carbon isotope values suggests that the preserved PETM interval reflects only a part of the CIE “core”. The top of the PETM interval is truncated due to local (?) erosion during the early Eocene. The Eocene recovery fauna is mainly composed of Lenticulina and Stainforthia species (biofacies 4), indicating restricted coastal to hyposaline lagoonal eutrophic conditions, distinctly different from earlier environmental conditions.
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The Palaeogene Diomedeoididae are amongst the earliest representatives of procellariiform birds (albatrosses, tubenoses, and allies). Although several fossils of these birds have been reported in the past, many details of their osteology remained unknown. Here we describe a comprehensive collection of diomedeoidid fossils from the Rupelian stratotype in Belgium, which was found more than 100 years ago. The material includes all major limb elements as well as other cranial and postcranial bones, and allows the recognition of previously unknown features of phylogenetic significance. Based on these new osteological data, diomedeoidids were for the first time subjected to a phylogenetic analysis, which resulted in a position outside a clade including Hydrobatidae (northern storm-petrels), Pelecanoididae (diving-petrels), and Procellariidae (fulmars, petrels, shearwaters, and allies), either as the sister taxon of Diomedeidae (albatrosses) or as that of all crown group Procellariiformes. The latter placement is better supported by the osteological evidence, and diomedeoidids lack several apomorphies of crown group Procellariiformes. Previously unrecognized derived features are reported that support a monophyletic Hydrobatidae, thus contradicting recent proposals that Oceanitinae (southern storm-petrels) are the earliest diverging crown group Procellariiformes. The new fossils also have a bearing on the convoluted taxonomy of diomedeoidids, and Diomedeoides Fischer, 1985 is synonymized with Rupelornis van Beneden, 1871. Diomedeoides lipsiensis (Fischer, 1983) is synonymous with Rupelornis definitus (van Beneden, 1871), a species that exhibits a large size range.
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