Time-Averaging, Overcompleteness, and the Geological Record

Abstract

Time-averaging makes events that happened at different times appear to be synchronous in the geological record. It can generate overcompleteness by concentrating objects (e.g., fossils, clasts) from a longer time interval into a unit that formed during a shorter interval. Time-averaging results both from extrinsic agents (e.g., vertical mixing, condensation, analytical pooling of data) and the intrinsic properties of the fossilized objects (preservational potential and abundance). Variation in intrinsic and extrinsic factors results in disharmonious time-aver aging: different taxa preserved together may be time-averaged over different time-scales. Because extrinsic and intrinsic factors vary in time and space, the geological record is characterized by vertical and lateral variations in time-averaging. The importance of time-averaging depends on the time-aver aging threshold, which is determined by the time-scale of the process of interest. Significant time-aver aging occurs when the scale of temporal mixing exceeds the time-scale of the process. Insignificant time-averaging occurs under opposite conditions. Accordingly, the consequences of time-averaging can be viewed as a function of the time-averaging threshold. Insignificant time-averaging eliminates noise by erasing short-term fluctuations and enhancing persistent signals. Significant time-averaging reduces resolution by the cumulative averaging of short-term signals. It may also generate false patterns by making diachronous events appear to be synchronous.