THE INFLUENCE OF FIELD SAMPLING AREA ON ESTIMATES OF STRATIGRAPHIC COMPLETENESS

The estimation of stratigraphic completeness is an essential step in s tratigraphic analysis. Stratigraphic successions should therefore alwa ys be sampled in the field in ways that make completeness estimation f easible. The use of conventional measured sections is liable to lead t o estimation problems, because data from measured sections are prone t o distortion by what is here termed ''spatio-temporal masking'': an ef fect by which variation that is primarily spatial in its nature masks variation that is primarily temporal. This paper describes the origin and significance of spatio-temporal masking and then uses a simulation of stratigraphic space-time diagrams to investigate the degree to whi ch spatio-temporal masking distorts completeness estimates. The simula tion shows that a succession's completeness can only be estimated succ essfully from measured sections that have appropriately sized field sa mpling areas; the simulation also shows how to determine the appropria te sizes of sampling area for different types of successions. This pap er uses a more general definition of completeness than is customary: t he completeness of a succession is defined as the proportion of that s uccession's space-time diagram that is not made up of erosion. This de finition lets completeness estimation be treated as a standard problem in stereology and lets existing completeness estimation techniques be modified to give practical solutions to this problem.