Abstract

Modern sedimentologists often study the relationships between hydrological parameters and bedforms, a forward problem. This investigation attempts to perform a solution of the inverse problem based upon observations from the Permian. The Bell Canyon Rader debrite which crops out in Guadalupe Mountains National Park (Rader Ridge, along Highway 62, McKittrick Canyon and vicinity) reveals a Late Guadalupian catastrophic submarine event. LiDar, XRF, and photogrammetric grain-size analyses were applied to the up to ~5m sized megabreccia reefal boundstone-wackestone clast dimictite and the two distinct hummocky cross stratification (HCS) cosets that overlie. Within the sandy matrix, the smaller megabreccia clasts indicate limited rounding and short distance transport while the larger clasts exhibit surrounding furrows from sliding and plowing along the base. The overlying 0.3 to 0.5 m amplitude, 2m strike wavelength HCS structures exhibit internally oriented graded gravel to silt-sized intraclasts and fossils within a mud matrix. The inferred water depths (>200m) from paleobathymetric geometric restorations, anoxic XRF proxies and the absence of postdepositional burrowing argue against the more common shallow to shelf storm wave origins for the HCS. Therefore, a deep water, upper flow regime antidune interpretation for these bedforms appears more likely.

To model these antidunes, dimensions of the slide were estimated from the decompaction of regional isopachs of two Rader massive subsurface deposits which thin basinward: one from the North of the Delaware Basin and the second from the East. Each of these slides contain an approximant minimum of 55 cubic kilometers of sediment. High Performance Computing (HPC) was conducted using NHWave for the submarine slide and a fully nonlinear Bousinesq FUNWAVE-TVD program for the wave generation reveal these slides would have created within 200 sec megaTsunami waves more than 50m in height, speeds of 50 m/sec and with multiple generated bottom currents with Froude numbers exceeding 0.84. Such hydrologic conditions are consistent with the formation of the observed deepwater antidune HCS.

Integrating the event stratigraphy of these results suggest that portions of the pre-fractured Capitan reef became partially exposed and unstable during a global and Delaware Basin sea level lowstand. With earthquake triggers likely originating from the South America-North America collision to the South (e.g. “jello” tectonics observed in outcrop), on at least two occasions portions of the shelf edge collapsed and slid basinward depositing mega breccia debrites. These episodic slides generated megatsunami waves and deep water antidune HCS on the sea floor bottom. Deep water HCS-Megatsunamiites should not be limited to the Rader slide, but through their recognition and modeling such occurrences may provide depositional process insight into discovered and undiscovered slides elsewhere, some of which have made attractive petroleum exploration targets, e.g. the Bone Spring Mescalero Escarpe Field and Poza Rica of Mexico.