Skeletal - Calcareous Algae - Cyanobacteria (Al/5/Jur/Eng)

2.5x cross nicols
2.5x wave plate
5x wave plate
Outstanding feature Algal laminae with pseudomorphs of gypsum filled by calcite spar
Folk Classification Micrite layer interbedded with pelsparite. The spar pseudomorphs gypsum blades
Dunham Classification Mudstone layer interbedded with pellet packstone. Calcite cement pseudomorphs gypsum blades
Common Grains Pellets and calcite blades pseudomorph gypsum
Sorting Poor
Rounding Poor
Micritization & envelopes Micritic intraclasts and pellets
Cement & diagenetic fabric Calcite blades pseudomorph gypsum rossettes
Porosity None
Depositional Setting Upper tidal flat to upratidal tidal flat with algal mats overlieing a gypsum mush
Diagenetic history Replacement of gypsum by calcite

Fossil Forest, Jurassic age sediments from Lullworth Cove, Dorset in the U.K. Fabric replacement by micrite and spar; gypsum blades replaced by calcite spar. This thin section that cuts across both the fabric of algal stromatolites and their associated diagenetic fabric from an intertidal to supratidal setting.

Thursday, November 11, 2021
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