Paper No. 10
Presentation Time: 1:30 PM-5:30 PM
CONSTRAINT ON THE DEPOSITIONAL PROCESS OF THE K/T BOUNDARY PROXIMAL DEEP-SEA DEPOSIT IN NORTHWESTERN CUBA BASED ON SHOCKED QUARTZ DISTRIBUTION AND ITS GRAIN SIZE
The Penalver Formation and its equivalents in northwestern Cuba is the thickest (> 180 m) deep-sea proximal K/T boundary deposit in the world. Because of this, it is suitable for studying the disturbance and recovery process in the proximal deep-sea area caused by K/T impact. It is continuously exposed on land and its depositional age is biostratigraphically well constrained between the latest Maastrichtian and the lower Danian. It is composed of a lower gravity flow unit and an upper "homogenite" unit. The upper "homogenite" unit is interpreted as a deep-sea tsunami deposit (Takayama et al., 2000). Compositional oscillations are recognized in this unit, which is probably reflecting repeated tsunamis after the impact (Goto et al., 2002). In this study, we examined shocked quartz distribution, grain size, and orientation of PDFs of the Penalver Formation at the type locality, Matanzas and Santa Isabel to constrain the depositional process of the Penalver Formation. The lower gravity flow unit is characterized by a normally graded bed at the type locality, and amalgamation of 2 and 5 normally graded beds at Matanzas and Santa Isabel, respectively. There is no shocked quartz in the first (lowermost) gravity flow bed in Matanzas and the first to third gravity flow beds in Santa Isabel, which indicates that these beds must have deposited before the arrival of shocked quartz. Overlying gravity flow beds contain shocked quartz of less than 1 % (shocked quartz/ quartz) and their grain size distribution shows bi-modal distribution. The upper "homogenite" unit contains shocked quartz of approximately 1.5 to 3 % and its grain size distribution shows uni-modal distribution. Grain size distribution and maximum grain size are almost the same between shocked quartz grains and other quartz grains, suggesting that shocked quartz grains in the upper "homogenite" unit deposited together with other sedimentary particles after the agitation by repeated tsunamis.