Cortoids and Micrite Coated Grains

1. Micrite coated grains

Grainstone with micrite coated (constructive envelopes) peloids and bioclasts. Some coated grains might represent incipient superficial ooids.

Mississippian, South Wales, UK

2. Micrite coated grains

Ooidal grainstone with one crinoid fragment (on the right) with an irregular micrite coating due to micritisation by endolithic micro-organisms (destructive envelope).

Pennsylvanian, Asturias, N Spain, cf. Bahamonde et al. (2015, 2017)

3. Micrite coated grains

Grainstone with micritized grains, bioclasts (mostly brachiopods) with destructive micrite envelopes and intraclasts with thin micrite coating.

4. Micrite coated grains

Grain- to packstone with mollusc biomoulds of which only the micritized outer rim is preserved. The original aragonite mineralogy of bivalve and gastropod shells has been neomorphosed into calcite spar (field of view 3 mm).

5. Micrite coated grains

Grainstone with quartz grains, bioclasts and peloids with a destructive and constructive micrite envelope. In the upper right corner the detrital quartz grain has a superficial ooid coating.

Thin section kindly provided by T. Geel, Vrije Universiteit, Amsterdam

6. Micrite coated grains

Previous image in crossed polarizers of a grainstone to packstone consisting of ooids (thin coatings, superficial, developed around quartz grains) and micrite coated bioclasts with a destructive (bioerosion) and constructive micrite envelope.

Thin section kindly provided by T. Geel, Vrije Universiteit, Amsterdam

7. Micrite coated grains

Grainstone with skeletal fragments affected by boring activity of endolithic micro-organisms: in the bottom right an alveolinid foraminifer with large borings, on the centre left a Nummulites foraminifer with a destructive micrite envelope.

Thin section kindly provided by T. Geel, Vrije Universiteit, Amsterdam

8. Micrite coated grains

Packstone with micrite coated echinoid spines (lower left corner) and foraminifera (Lenticulina) from Lower Jurassic middle ramp facies.

Lower Jurassic, High Atlas, Morocco, cf. Merino-Tome' et al. (2012), Della Porta et al. (2013)

9. Micrite coated grains

In the centre an aggregate grain including a bivalve shell and other bioclasts; other bioclasts (forams, gastropods) are coated by a homogeneous micrite envelope.

Lower Jurassic, High Atlas, Morocco, cf. Merino-Tome' et al. (2012)

10. Micrite coated grains

Packstone with micrite coated siliceous sponge fragments, foraminifera (Involutina liassica) and echinoderm fragments from Lower Jurassic middle ramp.

Lower Jurassic, High Atlas, Morocco, cf. Merino-Tome' et al. (2012)