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An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ophis (snake) is found in the name of ophiolites, because of the superficial texture of some of them. Serpentinite especially evokes a snakeskin.
In this example, the study of layered rocks and the fossils they contain is called biostratigraphy and utilizes amassed geobiology and paleobiological knowledge. Fossils can be used to recognize rock layers of the same or different geologic ages, thereby coordinating locally occurring geologic stages to the overall geologic timeline.
In north central Illinois, the bottom half is dominantly a yellowish gray coarse crystalline dolomite (rock form of the mineral dolomite which is related to calcite). It does not contain many fossils, although large trilobites and large cephalopods are known from Elmer-Lason Quarry.
This rock was part of the Roman aqueduct of Mons/Montauroux–Fréjus and was most probably derived from the karst area in the vicinity. In geology, lamination (from Latin lāmina 'thin layer') is a small-scale sequence of fine layers (pl.: laminae; sg.: lamina) that occurs in sedimentary rocks.
The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures, fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen. The taxonomy of fossils is not a valid lithological basis for defining a formation. [2]
Sedimentary rocks are laid down in layers called beds or strata. A bed is defined as a layer of rock that has a uniform lithology and texture. Beds form by the deposition of layers of sediment on top of each other. The sequence of beds that characterizes sedimentary rocks is called bedding.
It is bounded on the west and south-west sides by a concave arc of Precambrian rocks called the Narcea window, and the Villabandin window in the Narcea antiform. The Herreria Formation from the Lower Cambrian consists of shale and feldspathic sandstone alternating, with some conglomerate. These have a thickness of 1 to 1.5 km.
Fossils of graptolites, radiolarians, conodonts, and occasionally brachiopods and sponges are found. The geological formation east of Queanbeyan used to be known as the Muriarra Formation. This alternates between sandstone with a high quartz content and mica, and phyllite. Radiolarian chert is found in the central section.