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Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
‘Microfossils’ are found in the deep ocean bottom. The fossils contain siliceous matter. The microfossils were produced from the remains of algae bacteria microorganisms. The remains of the microorganism, on being compressed and cemented, become constituents of the rock. Chemically the microorganisms composed of siliceous compounds (SiO2 units) form “siliceous rock” or “siliceous ooze”. Siliceous ooze is a soft deposit of fine-grained siliceous remains along with some clay. Various types of microfossil exist.
Processes of Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
In the deeper parts of the ocean, where the temperature is low, pressure is high and the water is acidic due to dissolved gases, the carbonate is dissolved. This condition is likewise suitable for precipitation of dissolved silica, which has an extremely small residence time. Silica precipitation in deep ocean-waters in the form of chert is aided by microscopic marine organisms such as radiolaria and diatoms. Much of the deep ocean bottom is covered by siliceous ooze and also by extremely fine-grained, muddy sediments derived from land. It must be remembered that chemical precipitation is not confined to oceanic areas only. Natural springs, playas and caverns are some areas on land where chemical precipitation takes place.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
In summary, these three pioneering expeditions (DSDP 21, 29 and 30) provided the first information about the basaltic basement age and the sediment fill of a number of deep Southwest Pacific basins on the Australian Plate, which had very varied histories; some are as old as Cretaceous and some as young as Pliocene. The expeditions spot-cored the overlying sequences, which frequently contained ash. Depending on the paleo-water depth and the tectonic setting, the infills comprise layers of tuff, abyssal clay, siliceous ooze, calcareous ooze and calcareous turbidites derived from shallow water. The basins formed during early rifting of continental ribbons from Australia and parts of Antarctica associated with backarc spreading, later spreading caused by roll-back related to a westerly dipping subduction zone between the Australian and Pacific plates, and various adjustments to the dip direction of subduction caused by the reorganisation of plate boundaries about 50 million years ago (e.g. Arculus et al., 2019).