Deep marine environments The specification says that you need to be able to: describe the characteristic products of sedimentation in deep marine basin environments: formation of turbidites of greywackes and shales, and calcareous and siliceous oozes from microfossils and explain the processes which formed them. Sandstones: Greywacke Greywackes are texturally immature with > 15% matrix. They are also compositionally immature. Greywackes have a diverse mineralogy; they may contain quartz, feldspar, mica, clay minerals, mafic minerals, rock fragments (volcanic, metamorphic), with a matrix of carbonates, clay, pyrite, and organics. Greywacke Formation: The poor sorting suggests rapidly changing energy conditions and rapid deposition. The classic mechanisms are turbidity flows. These are rapid debris flows down the continental slope onto the abyssal plain. As the flow slows down sediment is deposited, coarse first and then fine last. This produces graded bedding. Shale Definition: A fine grained sedimentary rock that is fissile (can be split easily). A bit like slate but much softer. The clay particles have been aligned by compaction. Deep Ocean Shales These need low energy conditions like those found in deep oceans away from any currents. Calcareous and silicious oozes An ooze is a very fine grained sediment usually made of microfssils. These can be: 1. Calcareous: coccoliths, foraminifera. 2. Silicious: diatoms Carbonaceous oozes Such oozes can form in deep water but no deeper than 5 km above the carbonate compensation depth. Chalk: This is a very fine grained limestone with a micrite texture. No grains can be seen and it is even difficult with a hand lens. They are rich in calcite usually > 90% and sometimes as high as 99%. As a sediment it was a calcareous ooze consisting of the skeletons of planktonic organisms: Chalk Coccoliths calcareous algae Foraminifera micro-organisms As they died they settled out from the water and as they were pelagic (free swimming or floating) creatures. They settle out in a quiet water environment and over time large accumulations of these skeletons can accumulate. It is thought that chalk formed in a shelf environment well away from land where there were no currents to disturb the ooze/mud. Silicious Oozes Silicious microfossils like diatoms sink gently to the seabed to produce an ooze. When solidified these form chert. These will form particularly below the carbonate compensation depth.