Abstract
Abstract. Shore platform stromatolites (SPS) were first noted at Cape Morgan on the south-east African seaboard. Since then they have been found growing discontinuously in rocky peritidal zones along the entire southern African seaboard. They have also been found on the southwest Australian coast, at Giant's Causeway in Northern Ireland, and more recently at Harris on the Scottish Hebridean Atlantic coast. In this paper SPS occurrence and SPS potential as analogues for Precambrian fossil stromatolites, as well as potential stromatolite occurrences in shore platform regions on Mars, are assessed. Sub-horizontal surfaces promote stromatolite development, while tufa develops on cliffs and steep rocky surfaces. Tufa and stromatolites are end members of a spectrum dictated by coastal topography. Extant SPS occur on well indurated shore platforms in high wave energy settings, often around or near headlands. They can be associated with boulder beaches, boulder ridges, storm swash terraces, coastal dunes, and peat bogs. In contrast to other extant stromatolites, SPS are produced primarily by mineral precipitation, although minor trapping and binding stromatolites do occur. From a geological perspective, SPS develop in mildly transgressive siliciclastic settings in various climatic and tidal regimes. We suggest that SPS could be preserved in the geological record as micritic lenses on palaeo-shore platform surfaces. SPS share many features with Precambrian stromatolites and are a valid modern analogue despite the widely different atmospheric and oceanic conditions of the Archean. We suggest that terraces associated with former oceanic or lacustrine flooding surfaces on Mars are potential targets in the search for palaeo-SPS on Mars.
Highlights
The oldest known stromatolites include those of the Isua Group (3.7 Ga), Greenland (Nutman et al, 2016); the Strelley Pool occurrence (3.43 Ga), Australia (Allwood et al, 2006); the Barberton Mountain Land (3.22 Ga), South Africa (Gamper et al, 2011); and the Pongola Group (2.9 Ga), South Africa (Mason and von Bruun, 1977; Bolhar et al, 2015)
Shore platform stromatolites (SPS) often occur in association with tufa but the proportions vary with the coastal geomorphology
If the coastline is cliffed or dominated by high-angle surfaces, tufa dominates (Fig. 2a, b), whereas SPS typically occur within rock pools on competent sub-horizontal shore platforms (Fig. 2a)
Summary
The oldest known stromatolites include those of the Isua Group (3.7 Ga), Greenland (Nutman et al, 2016); the Strelley Pool occurrence (3.43 Ga), Australia (Allwood et al, 2006); the Barberton Mountain Land (3.22 Ga), South Africa (Gamper et al, 2011); and the Pongola Group (2.9 Ga), South Africa (Mason and von Bruun, 1977; Bolhar et al, 2015). Stromatolite-building organisms probably dominated the Earth during the Archean and Proterozoic eons, but under contemporary conditions only thrive in extreme environments that limit metazoan competition. Such environments include geothermal springs (Jones et al, 2000; Berelson et al, 2011), peritidal marine environments (Logan et al, 1964; Reid et al, 2000; Smith and Uken, 2003; Smith et al, 2005, 2011; Perissinotto et al, 2014; Rishworth et al 2016; Edwards et al, 2017), and salt lakes (Martin and Wilczewski, 1972). Smith et al.: The extant SPS facies association crust to depths of (at least) 7 km (Sankaran, 1997) and within the troposphere (DeLeon-Rodriguez et al, 2012)
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