PREFERENTIAL RECRYSTALIZATION AS THE ORIGIN OF LAMINATION IN THE NEOPROTEROZOIC BECK SPRING DOLOMITE, DEATH VALLEY, CALIFORNIA

The lower part of the Beck Spring Dolomite was examined at macro- and microscopic levels to determine the nature of the prominent mm-scale laminations exhibited by the unit. At hand sample scale, the laminations consist of alternating dark and light gray bands, attributed by previous workers as microbial in origin. However, microscopic investigation revealed that the mm-scale laminations are composed of zones of varying levels of recrystalization. Light gray portions are completely neomorphosed to spar, are noted to crosscut the dark lamination, and commonly contain finely disseminated micron-scale opaque mineral inclusions. Any original fabrics are obscured by the neomorphism. The dark gray laminations appear better preserved and retain remnants of an even finer, micritic, wavy, micron-scale lamination. The wavy micron-scale lamination may indeed indicate some microbial control, but the prominent mm-scale lamination so obvious in hand sample is in fact a secondary feature. The micron-scale laminations are predominantly parallel to mm-scale laminations, perhaps suggesting some primary control on secondary recrystalization and mm-scale textures in the Beck Spring Dolomite.