Petrography and environmental controls on the formation of Phanerozoic marine carbonate hardgrounds

Process‐based Modelling of Syn‐depositional Diagenesis

“…In environments where little to no sediment deposition occurs over long timescales, hardground formation is the primary process underway. Rates of marine cementation within near--surface sediments are often reported as a time to achieve lithification due to cement precipitation and range from a year, to many thousands of years (Christ et al, 2015). These time scale estimates, along with the dependence of marine cementation upon water temperature and hydrodynamic energy suggests that this process is sensitive to fluctuations in climatic and oceanographic boundary conditions on an annual to millennial time scale.…”

“…However, within cm of the sediment surface organically--matter oxidation can significantly modify the carbonate chemistry of the porewaters, leading to dissolution or precipitation depending on the reactivity of the organics and availability of sulfate and iron (Mackenzie, 2005). Marine hardgrounds have been widely recognized as an important control on later fluid flow (Read & Horbury, 1993;Christ et al, 2012;Shekdar et al, 2014), but the impact of early marine dissolution or stabilization of aragonite has received less attention in the geological literature (Christ et al, 2015).…”

“…At this earliest stage, cementation and micritization are generally recognised as the dominant rock--altering processes in effect. The recent review of marine cementation by Christ et al (2015) highlights a broad relationship between water depth and rates of marine cementation based upon several coincident factors. Specifically, near--surface waters with their higher energy and warmer waters are likely to be more favourable to marine cementation.…”

Internal fabric of giant domes in the Mesoarchean Steep Rock carbonate platform, Superior Province, Canada

“…Unfortunately, there is no documentation of hardgrounds found in 471 carbonate sequences prior to the Proterozoic, making comparisons of the alteration surfaces in 472 the giant domes to similar features impossible (Christ et al, 2015). 473…”

“…Precipitation from offshore derived waters would be capable of driving the replacement 454 reactions, and possibly open space filling cements producing the ferroan dolomite and silica 455 present in the upright structures. This does not necessarily negate a biological origin for the 456 supports as possibly they arrange in hexagonal patterns and would probably provide permeability 457 conduits.D r a f t 22 marine cementation and are thought to be associated with periods of reduced sedimentation 463 (Shinn, 1969;Purser, 1969;Kennedy and Garrison, 1975;Schlager and James, 1978;Bromley 464 and Allouc, 1992;Savrda, 1995;Obrochta et al, 2003;Roberts and Boyd, 2004;McLaughlin et 465 al., 2008;Christ et al, 2015). In particular, regressive-marine hardgrounds can develop as a 466 result of sediment entrainment and non-deposition due to wave activity (Christ et al, 2012).…”