Integrated stratigraphy of the Ypresian–Lutetian transition in northern Tunisia: Correlation and paleoenvironmental reconstruction

• We correlate the Sejnen section in Tunisia with the Y/L stratotype defined at Gorrondatxe in Spain.
• Micropaleontological, mineralogical and geochemical data enable us to place the Y/L at the Sejnen section.
• Planktic foraminifera E6, E7a, E7b, E8 and E9 Zones were identified with a hiatus across the E8/E9 limit.
• Benthic foraminifera and clay minerals indicate a warm bathyal paleoenvironment.
• The Sejnen section is a suitable potential auxiliary section or hypostratotype for the Y/L boundary.

Micropaleontological, mineralogical and geochemical data of the Ypresian–Lutetian transition at the Sejnen section, Tunisia, allowed us to trace a precise correlation with the Global Stratotype Section and Point for the Ypresian/Lutetian boundary recently defined at Gorrondatxe, Spain. The planktic foraminifera assemblages are diversified and enable the biozones of Acarinina pentacamerata (E6), Acarinina cuneicamerata (E7a), Turborotalia frontosa (E7b), Guembelitrioides nuttalli (E8) and Globigerinatheka kugleri/Morozovella aragonensis (E9) to be identified, revealing a hiatus across the E8/E9 boundary. Comparison with the boundary stratotype indicates that the Ypresian/Lutetian boundary in the Sejnen section is located near the base of the E7b zone, just above the first appearance of the species T. frontosa. In the Sejnen section, there are several events identical to those recorded in the boundary stratotype at the Gorrondatxe section. In the middle of this interval, the species diversity of planktic foraminifera is the first to decline, followed by that of the benthic foraminifera in the two sections. Furthermore, taxa with calcareous test peter out while those with agglutinated test reach their peak. There is a marked fall in carbonates in the two sections; while also variations in clay minerals, smectite and kaolinite are very abundant. In the Sejnen section, smectite is the dominant mineral and silica reached its peak. All these data indicate that in northern Tunisia at the Ypresian–Lutetian transition, the marine environment was deep and bathyal, with low energy, oxygenated and characterized by a warm tropical to subtropical climate. Consequently, the Sejnen section may be a suitable section to be defined as auxiliary section (=hypostratotype).