A NEW ANALYTICAL PROCEDURE TO GRAPHICALLY CHARACTERIZE THE TAPHONOMIC PROPERTIES OF SKELETAL CARBONATES. AN EXAMPLE FROM MIOCENE LIMESTONES OF NEW ZEALAND

Abstract

ABSTRACT A new graphical representation of the taphonomy of skeletal carbonates observed at the thin-section scale is proposed, demonstrating their utility in drawing information about the effects of early sea-floor processes on the post-mortem fate of fossil hard parts. The graphical representations consist of two-axis diagrams, which integrate the degree of fragmentation, abrasion, bioerosion, and encrustation as primary descriptors of the average state of fossil remains in a Miocene limestone section from southeastern North Island of New Zealand. Numerical values are expressed as percentages that represent the contribution of each factor to alteration (i.e., the four factors represent up to 25% each of the total alteration), the sum of values quantifying the amount of departure from pristine condition. Data are plotted in a cumulative form that reflects synergistic action of sea-floor processes towards hard parts destruction. One important virtue of this graphical representation is that the nature, degree, and variability of taphonomic alteration can be visualized and compared in a single diagram for several grain categories within a sample, and between samples. The proposed scheme is particularly flexible because more than four taphonomic categories can be integrated, independently from the number of alteration classes specific to each category, provided conversion of scores obtained in each taphonomic categories into percentages. Compiled results of such taphonomic analyses could be used in the future to identify specific depositional conditions, such as hydraulic regime, transportation, and residence time on the sea floor (a potential proxy to net accumulation rates).