Reef‐capping laminites in the Upper Silurian carbonate‐ to‐evaporite transition, Michigan Basin, south‐western Ontario

Abstract

Silurian pinnacle reefs in the subsurface of the south‐western Ontario portion of the Michigan Basin display a variety of laminated carbonates (laminites) within predominantly muddy reef‐capping facies in the upper part of the Guelph Formation and the overlying A‐1 Carbonate of the Salina Group. Laminites, which are limestone, dolomite or partially dolomitized limestones, have a range of morphologies, from simple planar to a variety of wavy and serrated forms. Individual laminae are composed mainly of micrite, microspar or replacive dolomite, and vary internally from isopachous and continuous over the diameter of the core to non‐isopachous and often discontinuous. Clotted and peloidal micrite, sometimes defining small knobs and chambers, is interpreted as being microbial in origin and occurs within all types of laminites. Fibrous cement locally comprises laminite clasts in breccias or coats clasts in breccias, and also occurs as spherulites in the interparticle spaces in breccias. Although similar laminites have been described from elsewhere in the Michigan Basin and interpreted as caliche, travertine and abiotic subtidal stromatolites, the laminites in south‐western Ontario are most realistically regarded as microbial. The causes for the variations in morphology and characteristics of the constituent laminae are uncertain, although fluctuations in local microenvironmental conditions would have been important, set against a backdrop of an increasingly restricted overall setting. Caliche or travertine origins for these laminites are unlikely in general, except perhaps locally at the subaerial exposure surface at the tops of pinnacle reefs.

Identification of the late Homerian Mulde Excursion at the base of the Salina Group (Michigan Basin, USA)

“…; Coniglio et al . ). Along the western margin of the Michigan Basin in Wisconsin, this transition occurs near the Racine‐Waubakee formation boundary (Figs , ; Mikulic ; Mikulic & Kluessendorf , ; McLaughlin et al .…”

Diagenesis or dire genesis? The origin of columnar spar in tufa stromatolites of central Greece and the role of chironomid larvae

“…Failure to adequately answer such questions on young and active deposits has influenced discussions of the abiotic evaporitic (Pope et al, 2000) versus microbial (Coniglio et al, 2004) origin of fibrous calcite laminites capping Silurian reefs, as well as attempts to distinguish between Proterozoic stromatolites of biological origin (seen as evidence for photosynthetic oxygen-producing cyanobacteria, which are some of the most important organisms to have evolved) versus pseudostromatolites of purely physico-chemical origin. For example, Riding (2008) wrote: ''Firstly, Precambrian stromatolites basically consist of one or both of two components: fine-grained carbonate and sparry carbonate.…”

Statistical based hydromechanical models to estimate poroelastic effects of CO2 injection into a closed reservoir

“…Such reefs have typically undergone primary production and, in some cases, secondary recovery . CO 2 has been injected into a small number of reefs that have the potential capacity for supporting CO 2 sequestration . Reefs along the Northern Pinnacle Reef Trend developed in a shallow shelf carbonate depositional system Figure 1(a).…”

“…CO 2 has been injected into a small number of reefs that have the potential capacity for supporting CO 2 sequestration . Reefs along the Northern Pinnacle Reef Trend developed in a shallow shelf carbonate depositional system Figure 1(a). shows the generalized lithostratigraphic column presenting the vertical and lateral succession of Silurian formations in the Michigan basin.…”