Sabkha

Photo looking straight down at brown sabkha surface. Polygonal pattern poorly defined by irregular polygon margins. Foot for scale. Polygons approximately 70cm wide.

The surface of the sabkha supratidal zone is covered in halite polygons. Infrequent rainfall, sometimes less than once per year, pools in the polygon centre where the water dissolves the halite to leave corroded polygon rims. #SabkhaSaturday

A flat featureless sandy surface at the shoreline. A water filled channel meanders seaward. A few isolated mangrove trees are at the channel margin.

For today’s #SabkhaSaturday offering, we present…

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…. an intertidal creek in the Abu Dhabi Sabkha. These meandering channels are the focal points of flow during the later stages of ebb tides. Thus, transporting significant amounts of sediment seawards.

Picture from the Abu Dhabi sabkha showing a flat surface with a poorly developed polygonal pattern. The edges of polygons are curled upward and inward.

Desiccation polygons in thin microbial mats. As mats dehydrate and contract, the edges of polygons roll inwards to produce characteristic open dishes. These edges are particularly susceptible to erosion and transport - acting to ‘seed’ new mats if deposited in a suitable environment. #SabkhaSaturday

Photo looking down onto the sandy surface in the sabkha. The image shows pustules up to 5 cm in diameter. Gastropod shells are abundant.

Back on the surface of the sabkha this #SabkhaSaturday. The pustular surface seen in this image is caused by the displacive growth of a halite cement between the bioclastic sand grains. This ephemeral cement will be dissolved by rain fall, storm surges or, even, humidity.

Dig just below the surface of the supratidal zone of the sabkha and you may be lucky enough to find anhydrite. At Earth’s surface, the high temperatures and salinities required to produce this anhydrous form of calcium sulphate are relatively rare,

#SabkhaSaturday
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This #SabkhaSaturday it’s time to ‘dig deeper’ into the Abu Dhabi Sabkha. This 60cm deep hole reveals a 25cm thick laminated microbial material buried just 5cm below the surface. The lighter coloured zone in the mats is recording multiple events where lagoons sands were washed onto them.
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This #SabkhaSaturday finds a mangrove tree (Avicennia marina) growing in the fine sand grade sediments of the intertidal zone of the Abu Dhabi sabkha. Note the aerial roots (pneumatophores) showing the extent of the root network. These facilitate the aeration necessary for root respiration.

For today’s #SabkhaSaturday, we offer an accumulation of gastropods. Gastropods are abundant in lagoons adjacent to the Abu Dhabi sabkha. Postmortem transport concentrates them into beach ridges and spits. If preserved, these ‘gastropod rudstones’ would confuse palaeoenvironmental interpretation.
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For the final #SabkhaSaturday of 2023 we are in the polygonal microbial mats zone of the Abu Dhabi sabkha. The mats develop in the ‘Goldilocks Zone’ at the uppermost intertidal where they are ‘not so wet’ that they can be grazed or ‘so dry’ as they desiccate. ⚒️🧪

Today’s #SabkaSaturday offering is this distinctive feeding bioturbation trace in the middle intertidal zone of the Abu Dhabi sabkha. This is formed by a Greater Flamingo standing at the centre and rotating on the spot as it feeds🦩⚒️

Two people standing in a flat landscape with metre scale halite polygons.

For this week’s #SabkhaSaturday, our offering is a rather nice example of metre-scale halite polygons in the supratidal zone of the Abu Dhabi sabkha.

These features form through lateral displacement during halite precipitation.

A photo of a very flat landscape with footprints leading off into the distance.

The Abu Dhabi sabkha is flat. Very flat. The average angle of slope seaward is 0.07 degrees. Here, we are in the uppermost intertidal zone looking landward. Note the footprints in the microbial mats at the surface. Two people are in this image for scale (you may need to zoom!).
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Of course you do, it’s only natural!

Mud?

Nope!

Our second #SabkhaSaturday sees us wading through the dominantly very-fine to fine grained #carbonate sediments of the intertidal zone in the Abu Dhabi #sabkha. These sediments are anoxic only a few cm below the surface yet are surprisingly heavily bioturbated (not just by us!). 🧪⚒️

Polygonal growth pattern in microbial mats in the Abu Dhabi Sabkha

Let’s kick off our 1st #SabkhaSaturday with some microbial mats in Abu Dhabi. Microbial mats can develop with a range of morphologies. This polygonal growth pattern, with uplifted margins, is typical of rapid healthy growth in the uppermost intertidal zone.
Explained here: dx.doi.org/10.1002/dep2...