PRELIMINARY PALEOMAGNETIC RESULTS FROM THE DEFORMED AND DOLOMITIZED LATE DEVONIAN ALAMO BRECCIA, DELAMAR RANGE, CENTRAL NEVADA

Preliminary paleomagnetic results are presented from the Late Devonian Guilmette Formation and the Alamo Breccia member exposed in the Delamar Range of Lincoln County, Nevada. Samples were collected from dolomitized, tilted carbonates in the Guilmette Formation, as well as from small folded beds interpreted as megaclasts in the Alamo Breccia. Previous workers have suggested that the folds and megaclasts formed as a result of the Devonian Alamo bolide impact event.

AF demagnetization from the Guilmette Formation indicates a characteristic remanent magnetization (ChRM) with south-southeasterly declinations and shallow-to-moderate negative inclinations in geographic coordinates, interpreted as Triassic in age. The deformed beds contain a ChRM with northerly declinations and positive inclinations in geographic coordinates. A tilt test on this ChRM is inconclusive. Depending on the results of the tilt test, the ChRM could be a post-tilting Tertiary or pre-tilting Triassic remagnetization. The ChRMs are tentatively interpreted as CRMs that reside in magnetite. These results suggest at least one post-impact CRM in contrast with other results from the Alamo Breccia closer to the impact site which suggest a Devonian magnetization.

The extensive dolomitization and presence of “zebra dolomites” in the Delamar Range, vs. the non-dolomitized limestones at the Alamo breccia type section may yield clues to the origin of the CRM(s). Thermal demagnetization, rock magnetic, and petrographic studies are underway to better constrain the timing and origin of the remagnetization event(s).