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Septarian concretions (or septarian nodules) are carbonate-rich concretions containing angular cavities or cracks (septaria; sg. septarium, from the Latin septum "partition, separating element", referring to the cracks or cavities separating polygonal blocks of hardened material).
Nodule is also used for widely scattered concretionary lumps of manganese, cobalt, iron, and nickel found on the floors of the world's oceans. This is especially true of manganese nodules. Manganese and phosphorite nodules form on the seafloor and are syndepositional in origin. Thus, technically speaking, they are concretions instead of nodules ...
The geologic column in Virginia begins at the Cambrian and spans to the Quaternary. [2] Although present, the state's Cambrian rocks preserve very few fossils and no documented individual deposit has proven a fertile collecting ground. [3] The state was covered by a warm shallow sea at the time. [1]
Pit 11 is now Braidwood State Fish and Wildlife Area, an Illinois state park. Fossil collecting is allowed at the park with a permit. [10] The site's importance was realized in the mid-nineteenth century: "the nodules of Mazon Creek, where fragments of plants, even of the softest texture, have been preserved in their integrity". [11]
The geology of Virginia began to form at least 1.8 billion years ago. The oldest rocks in the state were metamorphosed during the Grenville orogeny , a mountain-building event beginning 1.2 billion years ago in the Proterozoic , which obscured older rocks.
Natural Tunnel State Park is a Virginia state park, centered on the Natural Tunnel, a massive naturally formed cave that is so large it is used as a railroad tunnel. It is located in the Appalachian Mountains near Duffield in Scott County , Virginia .
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different particle sizes are deposited on top of each other. [1]
Geodes can form in any cavity, but the term is usually reserved for more or less rounded formations in igneous and sedimentary rocks. They can form in gas bubbles in igneous rocks , such as vesicles in basaltic lava ; or, as in the American Midwest , in rounded cavities in sedimentary formations.