STRATIGRAPHIC COMPLETENESS AND THE SADLER EFFECT IN MULTI-DIMENSIONS: EXPERIMENTAL OBSERVATIONS & THEORY

Stratigraphy contains the most complete record of information necessary to quantitatively reconstruct paleolandscape dynamics, but this record contains significant gaps over a range of time and space scales. These gaps result from stasis on geomorphic surfaces, and from erosional events. Stratigraphic gaps also influence apparent sediment accumulation rates: commonly referred to as “The Sadler Effect”, where accumulation rates vary as a function of the time window they are measured over. We examine stratigraphic completeness and the Sadler Effect in a suite of 11 physical experiments where the topography of aggrading deltas was monitored at high temporal and spatial scales. These experiments cover a range of boundary conditions, either with constant or dynamic forcings. Our analysis centers on two time scales: (1) the time at which a record is discretized (t) and (2) the time necessary to build a deposit with mean thickness equivalent to the maximum topographic roughness (T_c). Here we are particularly interested in examining how stratigraphic completeness and the Sadler Effect vary as one moves from 1D observations to 2&3D. In constant boundary condition experiments and in 1D, we find that stratigraphic completeness increases as a power law function of t/T_c until reaching 100% completeness at time scales equal to T_c. As the width of an observation window increases in 2 or 3D the completeness of a record also increases following a power-law trend. Similar to recently published observations from global compilations, we find that average accumulation rates compiled from multiple 2D transects removes the Sadler Effect. However, we note that individual 2D transects can strongly vary from the mean trend due to variability of the transport direction in 3D. Due to mass conservation, the Sadler Effect is completely removed from estimates of accumulation rates when working in 3D. These results place quantitative limits on the fidelity of the stratigraphic record, and thus aid prediction of a depositional environment’s capacity to store environmental signals.