Abstract

Distinguishing an allogenic signal from trends and patterns produced by autogenic processes is a critical element in interpreting, understanding, and predicting strata. Lobyte3D is a new reduced-complexity model of dispersive flow over an evolving topography on fan systems that produces surprisingly complex potentially hierarchical strata despite a simple formulation. Two submarine-fan model scenarios are run, one with constant sediment input, and one with a sinusoidal variation in sediment input with an oscillation period of 25 ky and a peak-to-trough 80% volume change. Both model scenarios show that flows cluster to produce lobes which migrate and can rapidly switch location. Runs tests that can detect thickening and thinning bed trends and spectral analysis that detects the frequency of any signal present suggest that strata can be ordered even in the absence of any allogenic signal, with cycles and trends in bed thickness, but no single characteristic frequency. In the oscillating-supply scenario, an allogenic signal is present in places, particularly in the axial mid fan, but may be difficult to distinguish from the autogenic signal with only limited outcrop data, and without knowing a priori how the allogenic signal is likely to be preserved in complex and incomplete strata. Based on these limited model results we hypothesize that analysis of mid-fan vertical sections, using simple power-spectrum analysis and counting of the significant peaks present across a range of frequencies, may allow identification of a “signal bump” that could be evidence of the presence and nature of allocyclic forcing. Further Lobyte3D modeling work will explore if and how the “signal bump” is preserved with input signals across a range of frequencies and amplitudes, to guide further data collection and interpretation in outcrop and subsurface strata.

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