Long-term tidal cycle influences on a Late-Holocene clay mineralogy record from the Cariaco Basin

Recent analyses of coastal mudbank dynamics along northeastern South America indicate significant sediment remobilization associated with the 18.6 y lunar nodal tide over the last 20 y. We present a near annually-resolved record of quartz and illite/illite–smectite abundances spanning the last 800 y from the Cariaco Basin (Venezuela) that suggests effects of the lunar nodal tide have played an important role in coastal processes over the last 8 centuries. Spectral analysis results of the clay and fine silt data include a statistically significant peak at 18.3 y in both the quartz and illite/illite–smectite records that is identified with the 18.6 y lunar nodal tide. Remobilization of shelf sediments by mean high water line variations driven by the lunar nodal tide is presented as the probable explanation of this signal in the Cariaco Basin mineral content. Since the period of this astronomically determined signal is constant with time it can be used to calibrate high-resolution age models. We modify our existing age model by tuning the 18.3 y component of the illite data to the 18.6 y period, and explore its impact on the age/depth relationship. We suggest that the 18.6 y signal can be used to refine existing chronologies where detected.