Paper No. 87-4
Presentation Time: 9:00 AM-1:00 PM
PETROLOGY AND PETROGRAPHY OF EDIACARAN NOONDAY DOLOSTONE TUBESTONE STROMATOLITE CLASTS WITHIN IBEX FORMATION SLOPE APRON POLYMICT CONGLOMERATE BEDS, DEATH VALLEY REGION, CALIFORNIA
Classical Cryogenian (Marinoan) deglacial successions comprise a standard, three-tract sequence stratigraphic framework, from glacial lowstand to transgressive and highstand systems tracts caused by the flooding of coastal margins resultant from Snowball Earth melting (Hoffman 2011). The Noonday Dolomite may defy this framework (Creveling et al., 2016). Here I present field observations of stromatolite bioherm morphology, including measurement of tube structures, at the plaformal Winters Pass (WP) field location, and complementary petrology on bioherm clasts from a downdip Saddle Peak Hills (SPH) debris apron locality, to provide evidence for a more complex post-glacial history. Winters Pass bioherm tube structures (Corsetti et al 2005) decrease in length and display less vertical inheritance with increasing height within each mound. Tubestone stromatolite clasts within the SPH polymict conglomerate display more irregular and stunted structures and, only rarely, “traditional” vertically accreting tubes. Less diagenetically altered clasts within the SPH preserve textures indicating “tube structures” that have been filled at an angle oblique to stromatolite growth. We interpret more angular tubes with non-normal to bedding orientations as affected by karst dissolution, as with cracks and fractures that appear to have been widened or created by dissolution and filled after transport to the slope apron. The irregular tube structures in slope apron clasts are unique to the topmost portions of in situ WP bioherms and their presence indicates that this unit preserves only the uppermost, subaerially exposed sections of the ‘lower Noonday’ mounds. These features indicate that the bioherms developed in warm, shallow seas during transgression, were subaerially exposed and subject to karst dissolution during a second lowstand, perhaps resulting from a period of post glacial isostatic adjustment, before being eroded and deposited into the basin. This study elucidates the complexity inherent in melting glaciers and ice sheets and their expression in the geologic record.