Lacustrine stromatolites: Useful structures for environmental interpretation – an example from the Miocene Ebro Basin

Abstract

The significance of stromatolites as depositional environmental indicators and the underlying causes of lamination in the lacustrine realm are poorly understood. Stromatolites in a ca 600 m thick Miocene succession in the Ebro Basin are good candidates to shed light on these issues because they are intimately related to other lacustrine carbonate and sulphate facies, grew under variable environmental conditions and show distinct lamination patterns. These stromatolites are associated with wave‐related, clastic‐carbonate laminated limestones. Both facies consist of calcite and variable amounts of dolomite. Thin planar stromatolites (up to 10 cm thick and less than 6 m long) occurred in very shallow water. These stromatolites represented first biological colonization after: (i) subaerial exposure in the palustrine environment (i.e. at the beginning of deepening cycles); or (ii) erosion due to surge action, then coating very irregular surfaces on laminated limestones (i.e. through shallowing or deepening cycles). Sometimes they are associated with evaporative pumping. Stratiform stromatolites (10 to 30 cm high and tens of metres long) and domed stromatolites (10 to 30 cm high and long) developed in deeper settings, between the surge periods that produced hummocky cross‐stratification and horizontal lamination offshore. Changes in stromatolite lamina shape, and thus in the growth forms through time, can be attributed to changes in water depth, whereas variations in lamina continuity are linked to water energy and sediment supply. Growth of the stromatolites resulted from in situ calcite precipitation and capture of minor amounts of fine‐grained carbonate particles. Based on texture, four types of simple laminae are distinguished. The simple micrite and microsparite laminae can be grouped into light and dark composite laminae, which represent, respectively, high and low Precipitation/Evaporation ratio periods. Different lamination patterns provide new ideas for the interpretation of microbial laminations as a function of variations in climate‐dependent parameters (primarily the Precipitation/Evaporation ratio) over variable timescales.

Columnar microbialites of the upper Miocene of Mallorca (Spain): A new morphogenetic model based on concurrent accretion and bioturbation – uncommon or overlooked?

“…The resulting laminae in the columns had low synoptic relief due to continuous current scouring and interaction with the interstitial sediment (e.g. Grotzinger & Knoll, 1999; Dupraz et al., 2006; Bosak et al., 2013; Tosti & Riding, 2017; Martin‐Bello et al., 2019). The columns of the studied Miocene biostrome are macroscopically very similar to some Proterozoic examples, with some characteristics suggesting that columns were accretionary structures: (i) the presence of microbialite bridges repeatedly joining adjacent columns (Figs 7F, 10A and 10C); (ii) the occurrence within the columns of scarce and scattered grains equivalent to those in the intercolumn space (Figs 12 and 13); and (iii) the presence of scarce and faint convex laminae in the columns (Figs 12 and 13).…”

“…Grotzinger & Knoll, 1999; Batchelor et al., 2003; Dupraz et al., 2006; Bosak et al., 2013, and references therein), or through the comparative analyses of modern and fossil examples (e.g. Semikhatov et al., 1979; Grotzinger & Knoll, 1999; Andres & Reid, 2006; Bosak et al., 2013; Hickman‐Lewis et al., 2019; Martin‐Bello et al., 2019). Virtually all of these examples and models emphasise the origin of microbialite columns as accretionary products of benthic microbial communities interacting with the environment, but only very few examples have highlighted syn‐depositional or post‐depositional metazoan disruption (i.e.…”

A multi‐scale approach to laminated microbial deposits in non‐marine carbonate environments through examples of the Cenozoic, north‐east Iberian Peninsula, Spain

“…The geometry and extent of these units are controlled by the small slope of the lake floor's surface and the shallow water depth, which, based on changes in the FA, varies by up to 4 m. Within these units, the stromatolites constitute extensive tabular bodies, small bioherms and very abundant thin bodies that are associated with grainy‐muddy laminated facies (Figure 20). The geometry of these microbial structures seems to be related to the water level and hydrodynamic conditions in this part of the basin (Casanova, 1994; Martin‐Bello et al, 2019a), rather than to tectonics or subsidence. Lacustrine stromatolites associated with surge activity as seen in the Ebro Basin have not been extensively reported in other basins, except for a few reports from the late Archean in Western Australia (Awramik & Buchheim, 2009), in the Eocene of Green River Formation (Graf et al, 2015), and in the Oligocene–Miocene lacustrine microbial and metazoan buildups in the Limagne Basin, French Central Massif (Roche et al, 2018).…”

“…Several authors, including Monty (1976), Hofmann (1973) and Nehza et al (2009), among others, have noticed the difficulty in interpreting the temporal significance of stromatolitic lamination, mainly because of its fractal nature, which produces multiple ranks of laminae and of lamina arrangement (Martín‐Bello et al, 2019a, 2019b).…”

Stromatolites and calcitized evaporite in a hypersaline playa lake: Rossport Formation (Mesoproterozoic, Ontario)

“…Proterozoic lacustrine stromatolites have been associated with restricted alkaline or hypersaline conditions (Cheadle, 1986a; Fedorchuk et al, 2016; Rogala et al, 2005, 2007); similar conditions of hypersalinity in Phanerozoic lacustrine (Awramik & Buchheim, 2015; Gallois et al, 2018; Martin‐Bello et al, 2019), marine (Mercedes‐Martín et al, 2014; Oliveri et al, 2010), and Recent (Gomez et al, 2014; Keim et al, 2020) lacustrine settings are associated with intervals of stromatolite growth and with bedded sulphate deposition (Gomez et al, 2014; Mlewski et al, 2018). The Mesoproterozoic Sibley Group, although dominantly clastic (Franklin et al, 1980) contains a thin horizon of stromatolites and microbial laminites interpreted as occurring under restricted, hypersaline lake conditions (Cheadle, 1986a; Rogala et al, 2005).…”