K/T BOUNDARY SEQUENCE OF THE PEÑALVER FORMATION: THE DEEP-SEA TSUNAMI DEPOSIT IN NORTHWESTERN CUBA

The Peñalver Formation in northwestern Cuba is one of the thickest (>180 m) K/T boundary deposits in the world. It is composed of a lower gravity flow unit and an upper homogenite unit, the latter being interpreted as a deep-sea tsunami deposit (Kastens and Cita, 1981; Takayama et al., 2000). According to our previous study at the type locality, the upper homogenite unit has homogeneous appearance, and neither erosional nor current structures are observed (Takayama et al., 2000). However, our recent study revealed slight compositional oscillations characterized by variation in serpentine lithic content within the upper homogenite unit, which is repeated >6 times. These oscillations are associated with variation in coarse fraction content within insoluble residues and are interpreted as reflecting the repeating vertical remixing and/or lateral supply of the clastic particles caused not by gravity flow but by tsunami repetitions, because there is no erosional and current structure. We have also found that the Peñalver Formation shows lateral lithological variations, over >150 km. At Santa Isabel (60 km to the west of Havana) and Matanzas (90 km to the east of Havana), the upper homogenite unit is much thinner compared with that of the type locality in Havana, and has erosional surface at its base. These differences may reflect difference in the influence of tsunamis reflecting the difference in the depositional depth at each locality. In spite of these lithological variations, grain composition and grain size in the upper homogenite unit are very similar throughout the studied localities. Thus, the upper unit of the Peñalver Formation was probably formed by rapid sedimentation from widely expanded sediment suspended cloud caused by energetic impact-induced tsunamis in the Caribbean basin.