A probable cave breccia in Middle Cambrian limestone, southern Nevada; petrography and paleomagnetic constraints on the time of formation

Abstract

ABSTRACT A spectacular limestone breccia, which occurs at or near the contact between the Carrara Formation (Early-Middle Cambrian) and Bonanza King Formation (Middle Cambrian) in the Desert Range, southern Nevada, probably reflects a cave that has subsequently collapsed and healed. The breccia blocks are angular; represent a diverse suite of shallow-water limestones that can be recognized laterally in undisputed strata; and exhibit clean truncation of late diagenetic fabrics, such as stylolites and blocky spar cements, at clast edges. In the blocks, the in situ directions of a secondary magnetization have been scattered. The age of this magnetization probably lies in the range Late Cretaceous to mid-Cenozoic, which suggests that the time of brecciation is no older than Late Cretaceous. The reccia must be older than late Tertiary, however, because it is truncated by Basin-and-Range normal faulting.