L'étude de la stratigraphie combinée à celle de la faune d'un puits d'extraction de silex, fouillé entre 1997 et 1999 à Petit-Spiennes, tente de retracer l'histoire détaillée du comblement d'un puits afin d'y rechercher des indices relatifs au travail minier. Elle montre que le comblement ne doit pas être conçu comme un événement synchrone mais doit se mesurer, au minimum, en terme de mois dans un environnement qui, lui, reste stable. La faune - et parmi celle-ci, surtout, les petits vertébrés intrusifs recueillis sur toute la hauteur du puits d'accès ainsi que les gastéropodes, - indiquent un milieu semi-forestier marqué par la présence de la Trouille. La découverte d'éléments fcetaux d'animaux domestiques suggère la pratique de lélevage dans un périmètre relativement proche de la mine e! par là même, celle d'un habitat aux alentours de 4500 8.P., époque du comblement de la structure. La stratigraphie offre, enfin, une illustration de phénomènes de tassement, décrits précédemment dans la littérature, ainsi que dévénements post-dépositionnels particuliers qui posent le problème du déplacement de certains restes dans un espace en théorie colmaté.
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RBINS Staff Publications
Marine sedimentary rocks of the late Eocene Pagat Member of the Tanjung Formation in the Asem Asem Basin near Satui, Kalimantan, provide an important geological archive for understanding the paleontological evolution of southern Kalimantan (Indonesian Borneo) in the interval leading up the development of the Central Indo-Pacific marine biodiversity hotspot. In this paper, we describe amoderately diverse assemblage of marine invertebrates within a sedimentological and stratigraphical context. In the studied section, the Pagat Member of the Tanjung Formation records an interval of overall marine transgression and chronicles a transition from the marginal marine and continental siliciclastic succession in the underlying Tambak Member to the carbonate platform succession in the overlying Berai Formation. The lower part of the Pagat Member contains heterolithic interbedded siliciclastic sandstone and glauconitic shale, with thin bioclastic floatstone and bioclastic rudstone beds. This segues into a calcareous shale succession with common foraminiferal packstone/rudstone lenses interpreted as low-relief biostromes. A diverse trace fossil assemblage occurs primarily in a muddy/glauconitic sandstone, sandy mudstone, and bioclastic packstone/rudstone succession, constraining the depositional setting to a mid-ramp/mid to distal continental shelf setting below fair-weather wave base but above stormwave base. Each biostrome rests upon a storm-generated ravinement surface characterized by a low-diversity Glossifungites or Trypanites trace fossil assemblage. The erosional surfaces were colonized by organisms that preferred stable substrates, including larger benthic foraminifera, solitary corals, oysters, and serpulid annelid worms. The biostromes comprised islands of highmarine biodiversity on the mud-dominated Pagat coastline. Together, the biostromes analyzed in this study contained 13 genera of symbiont-bearing larger benthic foraminifera, ∼40 mollusk taxa, at least 5 brachyuran decapod genera, and 6 coral genera (Anthemiphyllia, Balanophyllia, Caryophyllia, Cycloseris, Trachyphyllia, and Trochocyathus), as well as a variety of bryozoans, serpulids, echinoids, and asterozoans. High foraminiferal and molluscan diversity, coupled with modest coral diversity, supports the hypothesis that the origin of the diverse tropical invertebrate faunas that characterize the modern Indo-Australian region may have occurred in the latest Eocene/earliest Oligocene.
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RBINS Staff Publications 2025 OA
