Evaporites in pustular mat. The granular texture within broken pustule consists of small, authigenically formed, discoidal gypsum crystals. Crystal growth breaks up mat which is then eroded by wind. This is on the upper edge of the algal/cyanobacterial zone of the Abu Dhabi coastal zone. Coin for scale.
View of intertidal, leathery, pustular to knobby algal stromatolite with extensive associated halite and gypsum on the surface (white) and interstitially within the sediment. Abu Dhabi coastal zone.
Recent Abu Dhabi coastal zone. Seaward (lower intertidal) edge of algal/cyanobacterial mat zone. The transition from non-mat to stromatolitic sediments is controlled by the duration of wetting and the grazing by marine organisms, especially Cerithid gastropods. Boot for scale.
Shovel core of sediments from the Abu Dhabi coastal zone. Sediments range from pustular to blistered middle - to upper-intertidal mat zone. Note organic rich, finely laminated deposit with little introduced carbonate sediment. Coin for scale, diameter 2.5cm.
Cross-section of ponded algal stromatolitic sediment from Abu Dhabi coastal zone. Note interlayering of black, orgainc rich, blue-green algal/cyanobacterial mats with light-colored micritic carbonates derived from lagoonal areas during storms. Scale divisions in cm.
View looking down onto middle-intertidal, leathery, pustular to knobby algal and/or cyanobacterial stromatolite. Knobby or blistered textures help to retain water on the mat surface during low tides. Scale divisions in cm.
View looking down onto middle-intertidal, leathery, desiccation-cracked algal and/or cyanobacterial stromatolite. Desiccation polygons in various parts of the middle-upper intertidal zone range from 10cm to more than 2m across. Scale in cm.
Tough, leathery algal/cyanobacterial mats from ponded area near Abu Dhabi, where they have been partially torn up into large intracalsts by a strom. Scale 2m.