For this weeks WordPress Photographic Challenge, I’m taking the word ‘Delta’ literally. My six photos show just a wee bit of a massive deltaic sequence, bigger than the Mississippi delta in the southern US, and also a fair bit older too. I took these photos on the southern coastline of Fife (you can just see Kirkcaldy in the background of the first two).
This series of beds (Carboniferous in age 360 to 299 million years ago), not only covered a fair chunk of Scotland and Northern England, but they also stetched from North America, through to Germany and beyond (what must be remembered, however, is that the Atlantic Ocean didn’t exist back then, and all the continents were much closer together – this was used as evidence for plate tectonics and continental drift).
The first photo shows a small channel deposit, of relatively coarse sandstone, cutting through the finer silts and muds that make up previous overbank deposits. You can actually see the shape of the channel in this and the featured image photo!
These deposits make up part of the Lower Limestone Formation – which consist of sedimentary rock cycles, which formed local environments dominated by swamps, estuaries and deltas.
The third photo (unfortunately not a very good photo – I took these on a small compact camera 6 years ago), shows some cross bedding (evidence of a river deposit) which can be seen in the side of the channel deposit.
The fourth and fifth photos show the underlying finer silts and muds of the previously deposited overbank deposits, you can see evidence of wood fragments and rootlets.
The final image shows scour marks (caused by pebbles being pushed along the base of the river channel, and leaving scour marks).
The bulk of a deltaic deposit consists of the much finer grained material of the overbank deposits, but every once in a while, a river channel cuts through, representing a complete ‘change’ in the type of material deposited, ie coarser sandstones. It’s these sandstones, that act as reservoirs for any oil and gas that may have been produced in the organic rich surrounding muds.