GSA Connects 2021 in Portland, Oregon

Paper No. 139-11
Presentation Time: 10:50 AM


TASISTRO-HART, Adrian and MACDONALD, Francis, Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106

The Phanerozoic sedimentary sequences of North America have motivated a variety of hypotheses for flooding including extensional, flexural, thermal, and dynamic processes and their interplay with eustatic variability. Macrostrat, a spatially resolved database of geology on North America, provides a means of investigating these mechanisms and potentially extracting a eustatic signal. Although sediment unit thicknesses and volumes recorded within Macrostrat are not consistent with high resolution, independently generated isopachs, the presence or absence of sediments of a particular age in each column provides a measure of areal extent of sedimentation. Continental flooding computed from the area fraction of marine sediments on North America and extrapolated to global continental flooding produces a Phanerozoic eustatic M-curve with Paleozoic magnitudes comparable to eustasy inferred from the Arabian platform. This eustatic curve, however, deviates from late Mesozoic to Cenozoic sea level estimates, when the record of North American flooding is driven by the Western Interior Basin. We reproduce a previously reported ~56 My timescale of variability in continental flooding; notably, this cyclicity is strongest for interior sedimentary variability away from the margins. The peaks in continental flooding that compose this ~56 My signal correspond broadly to Sloss sequences, and the spatial resolution of sedimentation permits the evaluation of causal tectonic events and forcings. In particular, these flooding events are associated with tectonic activity on adjacent margins, including long wavelength dynamic subsidence resulting from slab drawdown during subduction. We explore how the ~56 My timescale might be related to a typical timescale of margin activation associated with plate motion rates and geometric constraints rather than a periodic geodynamic forcing. Finally, because downwards motion of the continent from slab drawdown may be partially compensated by upwards lithospheric motion in the oceans (to maintain Earth’s average radius), these tectonic events could be contributors to, not alternatives explanations for, a global eustatic signal.