Wavelet analysis of variations in geochemical and microfossil data across the Cretaceous/Tertiary boundary at Flaxbourne River, New Zealand

Abstract

Wavelet analysis of 58 elemental, mineralogical, and bioclastic variables, taken from 33 samples collected at -2 to +5 m across the Cretaceous/Tertiary (K/T) boundary at Flaxbourne River, eastern Marlborough, identified 9 classes of variables exhibiting 3 main styles of behaviour: (1) classes 1, 3, and 5 exhibit abrupt enrichment at the boundary with either sudden, rapid, or gradual decline in the Paleocene (e.g., Zn, Cr, Pb, Ni, Al, Fe, Rb, Th, Ga, quartz); (2) classes 2 and 4 exhibit an abrupt decrease at the K/T boundary followed by progressive decline in the Paleocene (e.g., Ca, Mn, Sr, La, Sc, calcite), and (3) classes 6, 7, and 9 exhibit a minor change at the boundary followed by progressive increase in the Paleocene (e.g., Ba, Si, Ba/Ti, radiolarian diversity, radiolarian abundance, diatom/ radiolarian ratio). In class 8 (δ13C, δ18O) there is little change other than a gradual increase or gradual decrease across the boundary. Classes 1–6 include 37 of the 59 variables analysed and the first principal component accounts for ≥75% of variation, indicating a significant level of congruity through time that is lacking among the trajectories of the wavelet trends of the members of classes 7–9. Nine parameters display unclassifiable trends, due either to truly unique trends or anomalous values. The analysis was undertaken with no prior geological-based grouping of any of the variables. Nonetheless, the resulting classification groups well-established K/T boundary markers as well as paleoenvironmental indicators. However, where postdepositional processes have affected the values of parameters (e.g., opal-CT, stable isotopes), wavelet trends either display a low level of coherency and/or fail to follow simple geological trends. © 2003 Taylor & Francis Group, LLC.