Paper No. 7
Presentation Time: 10:20 AM
POST-IMPACT DEPOSITION AT THE EDGE OF THE LATE DEVONIAN ALAMO BRECCIA, SE NEVADA
The shoreward thinning of the Alamo impact breccia, from the Ring to Runup impactogenic realms, is preserved in the Guilmette Formation of eastern Lincoln County. A series of high resolution stratigraphic sections along 15 km of the northern Hiko Hills and Six Mile Flat ranges provides both shore-parallel and onshore records of sedimentological and biological recovery of the inner shelf. Offshore, the top of the Alamo Breccia is well graded and penetrated by boxwork and spreite burrows, but onshore the breccia is reworked, eroded and highly dolomitized likely owing to subaerial exposure. Above the breccia, lithofacies cycle between peritidal and subtidal lagoon-dominated settings amid a general transgressive trend, but are bisected by multiple, asynchronous pulses of channelized quartz sandstone. Diversity of organisms generally increases up-section, with thick stromatoporoid wackestones and coral-bryozoan patch reefs. Continued refinement and correlation of the local facies architecture in the aftermath of the Alamo Event will combine with other studies in Lincoln County to create a basin-wide reconstruction of the impact basin and its post-impact recovery.