T313 New Developments in Microbialites (Posters)

Wednesday, 22 October 2014
9:00 AM - 6:30 PM
Exhibition Hall C

BIZARRE PATTERNS FOUND IN UPPER CAMBRIAN STROMATOLITES

Paper number: T313-10
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Upper Cambrian stromatolites of the Notch Peak Formation in southwestern Utah are often furnished with bizarre patterns in their inner core as seen in plan-view. Patterns can be round, sub-round or elongate, and either standalone within the larger stromatolite structure, or connect with the laminated outer portion of the stromatolite. Slabbing of the stromatolites, as well as thin-section work, reveals a composite structure consisting of three main parts: 1. A round to sub-round inner core composed of small, mound-like masses separated by cm-scale channels filled with coarser-grained, bio-clastic material. 2. An outer, finely laminated micritic zone enclosing the inner core. 3. An interspatial zone separating the stromatolites that consists of coarse-grained, bioclastic material. Cross-cutting and growth related relationships seem to suggest four phases of deposition: 1. An initiation phase whereby small, concave-up mounds randomly grow at the sediment-water interface and are separated from each other by cm-scale channels. 2. A consolidation phase whereby a small group of mounds, complete with channels, coalesce into a single round to sub-round core. 3. A distinctly stromatolitic phase whereby the consolidated core becomes encased in fine micritic laminations. 4. A burial stage whereby the stromatolite is completely buried in coarser-grained interspatial material. Stage 4 represents a simple depositional process. The processes responsible for growth in stages 1 – 3, however, are as yet unknown.