The K/T boundary at Beloc (Haiti): Compared stratigraphic distributions of the boundary markers

At Beloc, Haiti the Cretaceous-Tertiary boundary (KTB) is characterized by a spherule bed containing glass particles. These particles are considered by some authors as remains of tektites resulting from a nearby impact. However, because of the stratigraphic complexity of the Beloc sections the genetic link between the KTB cosmic event and the spherule bed is not obvious. In this paper, we report new data on shocked quartz and Ni-rich spinels at Haitian KTB sites. The detailed stratigraphy of these minerals shows that there is no empty gap in the sedimentary sequence. The first and largest shocked quartz is found in the upper part of the spherule layer. They are abundant and size graded over the 25–30 cm of carbonate-rich sediments overlying this layer. The first Ni-rich spinels, which are also rich in Cr, appear in the carbonate sediments. The size grading of the spherules and shocked quartz and the stratigraphical overlapping of their distributions suggests that these two components were derived from the same event. Although different from typical impact glasses (tektites), Beloc glass particles must be considered as impact-derived products. The enormous fluence of shocked quartz (≈104 grains/cm2) is consistent with a proximal event. The upper part of the sequence is more complex. A second distribution of shocked quartz associated with Ni-rich spinels of different compositions appears in the layer containing the maximum Ir concentration. We propose that these features, which are not easily explained by a sedimentary artifact, result from a second collisional event.