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 (?13C, ?18O) 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.