UNDERSTANDING HOW DELTA DYNAMICS INFLUENCE PALEOENVIRONMENTAL PROXY RECORDS (Invited Presentation)

Deltas are some of the most dynamic landscapes on Earth and they are a critical archive for reconstructing terrestrial and oceanographic conditions throughout Earth history, particularly how deltas have responded to past changes in climate. However, deltas also show a range of internally generated (autogenic) dynamics, such as channel avulsion, which cause their stratigraphic record to be incomplete, even for relatively long-period climatic forcing. Previous work has demonstrated that high-fidelity paleoenvironmental proxy records are likely to be preserved only in settings where the characteristic autogenic dynamics are small relative to the long-term sediment accumulation rate. Furthermore, the accuracy of paleoclimate proxy records can be improved by combining multiple partially preserved records into an ensemble. While it seems obvious that more records are needed to fully characterize a highly variable system, it is not clear how one might predict how many records would be necessary in any given deltaic system or how far apart those records need to be in order to build a complete ensemble paleoenvironmental proxy record. Here, we evaluate how many 1D observations are needed to fully characterize paleoenvironmental proxies from delta deposits with different scales of variability and long-term accumulation rates. We used DeltaRCM, a reduced complexity delta evolution model, to generate synthetic stratigraphy. We varied the scale of autogenic dynamics in each delta by changing the ratio of coarse and fine sediment supplied to each system, and we built deltas under different rates of sea-level rise. Our analysis shows that the number randomly located 1D cores needed to generate complete ensemble proxy record scales directly with the autogenic timescale relative to accumulation rate. Our results are important not only to better plan sampling strategies in deltas, but offer new ways to assess the likely completeness of existing records within dynamic landscapes.