New Developments Regarding the K‐T Event and Other Catastrophes in Earth History

c/_,f MINERALOGICAL CORRELATIONS OF NEAR-KTBOUNDARY DEPOSITS IN NORTHEASTERN MEXICO: EVIDENCE FOR LONG-TERM DEPOSITION AND VOLCANOCLASTIC INFLUENCE. T. Adatte l, W. Stinnesbeck 2, and G. Keller 3, qnstitut de G_ologie, I I rue Emile Argand, 2007 Neuchfitel, Switzerland, 2Facultad de Ciencias de la Tierra, Universidad Aut6noma de Nuevo Le6n, Ap. Postal 104, 67700 Linares, N.L. Mexico, 3Department of Geological and Geophysical Sciences, Princeton University, Princeton NJ 08544, USA. Whole-rock and clay-mineral analyses of five near-KT-boundary elastic deposits in NE Mexico indicate three lithologically and mineralogically distinct and correlatable units similar to those outlined based on lithological correlations [1,2]. The examined sections span a noah-northwest to south-southeast transect and include: La Sierrita, El Pe_on, E1Mulato, La Lajilla, and El Mimbral (Fig. 1). Two sections have been analyzed at Mimbral: in the channel center and at its edge. Whole-rock and clay-mineral compositions have been determined by XRD, using the methods of Kubler [3]. Unit I, which disconformably overlies the Mendez Formation is lithologically defined as a poorly cemented, spherule-rich layer characterized by high calcite (50-70%, Fig. 2) and low phyllosilicate contents (<20%), quartz, and plagioclase (albite, 5%). However, the composition of the sandy limestone layer (SLL) of unit 1 is significantly different with lower calcite, higher quartz, and plagioclase. This change in whole-rock content indicates a different detrital influx during deposition of these spherule-rich sediments [I,2]. The massive laminated sandstone of unit 2 is characterized by low calcite (20-40%) and phyllosilicate contents and a significant increase in quartz (up to 40%) and plagioclase (albite, 15-25%). Whole-rock composition of unit 3 reflects the lithological variations within this unit (including sandstone, sandy limestone, silts, and LOS RAMONES