TWO-STAGE TSUNAMI RESURGE DEPOSITION IN THE WAKE OF THE ALAMO IMPACT, LINCOLN COUNTY, NEVADA
At the onshore Runup realm localities, clasts align roughly E-W (256.5°, sd=22.0°). The Ring realm localities, by contrast, exhibit two separate modes of flow axis, either N-S (341.9°, sd=18.0°) or E-W (260.9°, sd=19.8°). Mixing of the two modes at one locality has not been observed, which suggests that the clasts record paleoflows that are distinct in their process and timing.
We propose a two-stage depositional model for the resurge of water and sediment in the waning tsunami. In this model, the E-W axis represents a high energy, westward (offshore) sheet-like flow that deposited clasts early in the tsunami resurge, whereas N-S oriented clasts represent later stage, channelized flow. E-W orientations in the Runup realm may represent either shoreward uprush or early resurge. Later-stage resurge likely recycled some earlier deposited E-W oriented tsunami breccias. Preservation of the earlier E-W directed clasts is greatest on seafloor that rose topographically higher, or was spared from excavation and reworking by later-stage channelized flow. The N-S orientation of the proposed late-stage tsunami breccia may follow a shore-parallel basin hypothesized for the Ring realm.