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The Devonian is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at 419.2 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.9 Ma. It is named after Devon, South West England, where rocks from this period were first studied.
The PaleozoicEra is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods :
A trace fossil, also known as an ichnofossil, is a fossil record of biological activity by lifeforms but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization. The study of such trace fossils is ichnology and is the work of ichnologists.
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a primary driver of biodiversity. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.
Trace fossils are classified in various ways for different purposes. Traces can be classified taxonomically, ethologically, and toponomically, that is, according to their relationship to the surrounding sedimentary layers. Except in the rare cases where the original maker of a trace fossil can be identified with confidence, phylogenetic classification of trace fossils is an unreasonable proposition.
The geology of Antarctica covers the geological development of the continent through the Archean, Proterozoic and Phanerozoic eons.
The history of paleontology traces the history of the effort to understand the history of life on Earth by studying the fossil record left behind by living organisms. Since it is concerned with understanding living organisms of the past, paleontology can be considered to be a field of biology, but its historical development has been closely tied to geology and the effort to understand the history of Earth itself.
Zoophycos is a somewhat cosmopolitan ichnogenus thought to be produced by moving and feeding polychaete worms.
Cruziana is a trace fossil consisting of elongate, bilobed, approximately bilaterally symmetrical burrows, usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension. It is found in marine and freshwater sediments. It first appears in upper Fortunian rocks of northern Iran and northern Norway. Cruziana has been extensively studied because it has uses in biostratigraphy, and because the traces can reveal many aspects of their makers' behavior.
The Tumblagooda Sandstone is a geological formation deposited during the Silurian or Ordovician periods, between four and five hundred million years ago, and is now exposed on the west coast of Australia in river and coastal gorges near the tourist town of Kalbarri, Kalbarri National Park and the Murchison River gorge, straddling the boundary of the Carnarvon and Perth basins. Visible trackways are interpreted by some to be the earliest evidence of fully terrestrial animals.
Skolithos is a common trace fossil ichnogenus that is, or was originally, an approximately vertical cylindrical burrow with a distinct lining. It was produced globally by a variety of organisms, mostly in shallow marine environments, and appears as linear features in sedimentary rocks.
An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited.
Arenicolites is a U-shaped ichnotaxon dating from Ediacaran times onwards in South Australia. The trace shown by this fossil, is a pair of closely spaced circles on a bedding plane. In vertical section the traces are U- or J-shaped. They appear to be burrows made by a kind of worm.
Gangamopteris is a genus of Carboniferous-Permian plants, very similar to Glossopteris. Previously, it was classified as fern with reproduction by seed. The genus is usually only applied to leaves, making it a form taxon. Gangamopteris dominates some coal deposits, such as those of the Beacon Supergroup.
Heimdallia is an ichnogenus comprising a strange planar trace that does not have a circular cross-section; its maker may have been fed upon by Beaconella.
The Beacon Supergroup is a geological formation exposed in Antarctica and deposited from the Devonian to the Triassic. The unit was originally described as either a formation or sandstone, and upgraded to group and supergroup as time passed. It contains a sandy member known as the Beacon Heights Orthoquartzite.
Fault Bluff is a 2,320 metres (7,600 ft) high rock bluff located about 9 nautical miles (17 km) northeast of Mount Longhurst in the Cook Mountains of Antarctica. The rock bluff was visited in the 1957–58 season by the Darwin Glacier Party of the Commonwealth Trans-Antarctic Expedition, 1956–58. They originated the name which presumably refers to a geological fault at the bluff.
Mount Ritchie is a mountain rising over 1600 m in the southeast part of Warren Range, Antarctica. The feature is 5.6 km (3 nmi) northeast of Wise Peak on the west side of Deception Glacier. Named by the Victoria University of Wellington Antarctic Expedition (VUWAE), 1970–71, after Alex Ritchie, curator of fossils at the Australian Museum, Sydney, a member of the VUWAE party that discovered important sites of fossil fish in this Skelton Neve area.
The Bokkeveld Group is the second of the three main subdivisions of the Cape Supergroup in South Africa. It overlies the Table Mountain Group and underlies the Witteberg Group. The Bokkeveld Group rocks are considered to range between Lower Devonian (Lochkovian) to Middle Devonian (Givetian) in age.
References
- 1 2 Gevers, T.W.; Frakes, L.A.; Edwards, L.N.; Marzolf, J.E. (1971). "Trace Fossils in the Lower Beacon Sediments (Devonian), Darwin Mountains, Southern Victoria Land, Antarctica". Journal of Paleontology . 45 (1): 81–94. JSTOR 1302754.
- ↑ Woolfe, K.J. (1993). "Devonian depositional environments in the Darwin Mountains: Marine or non-marine?". Antarctic Science . 5 (2): 211–220. Bibcode:1993AntSc...5..211W. doi:10.1017/S0954102093000276. S2CID 129509428.
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