THE K T BOUNDARY AT BELOC (HAITI) - COMPARED STRATIGRAPHIC DISTRIBUTIONS OF THE BOUNDARY MARKERS/

At Beloc, Haiti the Cretaceous-Tertiary boundary (KTB) is characterize d by a spherule bed containing glass particles. These particles are co nsidered by some authors as remains of tektites resulting from a nearb y impact. However, because of the stratigraphic complexity of the Belo c sections the genetic link between the KTB cosmic event and the spher ule bed is not obvious. In this paper, we report new data on shocked q uartz and Ni-rich spinels at Haitian KTB sites. The detailed stratigra phy of these minerals shows that there is no empty gap in the sediment ary sequence. The first and largest shocked quartz is found in the upp er part of the spherule layer. They are abundant and size graded over the 25-30 cm of carbonate-rich sediments overlying this layer. The fir st Ni-rich spinels, which are also rich in Cr, appear in the carbonate sediments. The size grading of the spherules and shocked quartz and t he stratigraphical overlapping of their distributions suggests that th ese two components were derived from the same event. Although differen t from typical impact glasses (tektites), Beloc glass particles must b e considered as impact-derived products. The enormous fluence of shock ed quartz (approximate to 10(4) grains/cm(2)) is consistent with a pro ximal event. The upper part of the sequence is more complex. A second distribution of shocked quartz associated with Ni-rich spinels of diff erent compositions appears in the layer containing the maximum Ir conc entration. We propose that these features, which are not easily explai ned by a sedimentary artifact, result from a second collisional event.