![]() ![]() ![]() Sadler and Strauss (1990) showed that as time increases, the likelihood for preservation of a sedimentary package decreases ( Fig. It is the removal of those deposits during time scales longer than that of the original t that is captured by lower net sediment accumulation rates over longer time intervals. However, those sedimentary bodies are often scaled to that given time scale t ( Sadler, 1981 Sadler and Strauss, 1990 Schumer and Jerolmack, 2009 Miall, 2014a). Theoretical models of the unsteadiness of sedimentation over time, generated from calculated average sedimentation rates for t, inherently capture erosion of sedimentary bodies through the use of average sedimentation rates as the dependent variable ( Sadler, 1981 Strauss and Sadler, 1989 Sadler and Strauss, 1990 Miall, 2014a). The frequency and magnitude of deposit erosion (or preservation) at the scale of a sedimentary body have received relatively little attention in the context of stratigraphic completeness (e.g., Trabucho-Alexandre, 2014 Mahon et al., 2015). preservation) a record consists of sediment deposited over t that is not subsequently eroded ( Sadler and Strauss, 1990 Fig. The most important factor for completeness, however, is leaving a record (i.e. Sadler’s (1981) initial investigation used net sediment accumulation as the dependent variable, which captures the three factors that control completeness: deposition, stasis, and erosion. The completeness of a stratigraphic section is defined as “the fraction of time intervals of some specified length ( t) that have left a record” ( Sadler and Strauss, 1990, p. Following this, Sadler and Strauss (1990) defined the concept of stratigraphic completeness in order to evaluate the amount of time that has been recorded in a stratigraphic section. This concept is commonly referred to as the “Sadler effect.” The results of Sadler’s synthesis reveal the impact of increasing the number and duration of intervals of stasis or erosion as the window of observation increases ( Miall, 2014a), resulting in an apparent decrease in sediment accumulation rates with time. ![]() Sadler (1981) showed that rates of sediment accumulation are inversely related to the time scale over which they are measured. A comparison between data sets allows for an estimation of the time span represented by meander-belt deposits in the deep time record. The results presented here document a systematic, monotonic decrease in preservation over time, which is consistent regardless of the spatial or temporal scale and agrees with probabilities of preservation at long time scales proposed by previous workers. The results of this study document a decrease in preservation over time that follows a natural logarithmic function of decay we have termed this the “survivability” curve. The processes that lead to a decrease in preservation include intra-meander-bend erosion (due to downstream translation or bar rotation), and increasing meander-bend sinuosity and eventual cutoff (neck and chute), as well as inter-meander-bend erosion due to avulsion and subsequent migration of the meandering channel. Results of our analysis show that the average preservation percent ranges from 27.3% to 67.8% for an accretion package, 35.0% to 85.1% for a bar, and 38.2% to 67.6% for a meander belt. Migrated area between successive reconstructed paleochannel positions was measured, representing: total area of net bar migration (MA), the area of bar preserved (PA), and percent of bar preserved (PA/MA), at the accretion package, bar, and meander-belt scale. In each data set, the evolutionary history of a series of meander-belt elements was discerned. Data sets were evaluated for a numerical model, the modern Mississippi River valley, and the Cretaceous McMurray Formation. We quantified stratigraphic completeness in meander-belt deposits through deducing the total area of bar sedimentation versus what is ultimately preserved in the depositional record, using area as a surrogate metric for sediment volume. The fragmentary nature of the stratigraphic record is particularly evident with respect to fluvial deposits, which are characterized by a hierarchy of depositional units deposited over a wide range of time scales and sedimentation rates. ![]()
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