Evidence for bolide impact?

Blobrana

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Posts: 131433

Date: Dec 30 19:58 2011

Triassic-Jurassic extinction event	Permalink

A recent news article in the journal Nature features Professor Paul Olsen and Lamont colleague Dennis Kent's fieldwork on the coast of Wales - one location where they are looking for evidence that a giant impact 200 million years ago may have triggered a mass extinction and paved the way for the rise of the dinosaurs. The recently revised age of a structure remaining from a massive impact near Rochechouart, in western France overlaps with the late Triassic mass-extinction event. This development has sent Olsen and Kent on a global quest to gather rock samples that might help them develop a timeline of events leading up to the newly dated impact. Sorting out the relative timing of events around the world will help create a fuller picture of what exactly happened and how life responded, a puzzle that has been on Olsen's mind for more than 20 years. Source __________________

Blobrana

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Posts: 131433

Date: May 14 20:11 2011

Lavernock beach	Permalink

Welsh beach could reveal why dinosaur mass extinction happened 200m years ago The secrets behind a dinosaur mass extinction 200 million years ago may lie on a beach near Barry Island. An international team have descended on Lavernock beach, near the famous area of south Wales, to analyse segments of rock will may hold the clue to the early days of the species. The mass extinction led to the emergence giant herbivores, velociraptors and tyrannosaurs. Read more __________________

Blobrana

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Posts: 131433

Date: May 12 23:53 2011

Saint George's Channel crater	Permalink

Giant dinosaurs like the Tyrannosaurus Rex were able to evolve after a huge meteorite blasted into the Irish Sea, scientists claimed yesterday. The colossal impact 200 million years ago left a crater the size of Kildare (~50km wide) in St George's Channel. The 29,000kph strike created a tsunami that swamped huge parts of Europe and triggered a wave of climate change, allowing formerly puny dinosaurs to grow into massive monsters. Read more __________________

Blobrana

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Posts: 131433

Date: May 12 22:28 2011

RE: Evidence for bolide impact?	Permalink

Somerset geology At the end of the Permian (290-248 million years ago) and Triassic periods, the Variscan orogeny resulted in the formation of several mountainous areas including Dartmoor in the south, Exmoor and the Quantocks, and the Mendips. In the Taunton area Permian (295-250 million years ago) red sandstones and breccia outcrop, although rocks of Triassic age (248-204 million years ago) underlie much of Somerset and form the solid geology of the Somerset Moors and Levels. There are no glacial deposits. The Triassic rocks consist of red marls, sandstones, breccias and conglomerates which spread over the older rocks. The Dolometic Conglomerate is an old shingle beach of Keuper Marl age. The Rhaetic Beds are full of fossils due to invasion of the Jurassic Sea. The Lias consists of clays and limestones, the latter being quarried and are famous for their fossils. Blue Lias was used locally both as a building stone and as a source of lime for making Lime mortar Read more __________________

Blobrana

L

Posts: 131433

Date: May 12 22:11 2011

latest Triassic impact	Permalink

Title: Uniquely extensive soft-sediment deformation in the Rhaetian of the UK: Evidence for earthquake or impact? Authors: Michael J. Simms The lower part of the Cotham Member in the Penarth Group (latest Triassic, Rhaetian) of the UK incorporates a uniquely extensive metre-scale horizon of soft-sediment deformation. Interpreted as a seismite, it shows evidence for only a single seismic event even at its thickest development. It is recorded from more than forty sites across at least eight discrete sedimentary basins covering N250,000 km², and originally must have covered a still larger area. Such a widespread horizon of soft-sediment deformation, unique for the UK Phanerozoic and implying a seismic event of exceptional magnitude, is difficult to account for by conventional terrestrial mechanisms. Contemporaneous volcanism in the Central Atlantic Magmatic Province (CAMP) was too far distant to cause the deformation, and the tectonic setting of the region was not conducive to earthquakes on this scale. Slump fold long axes suggest an epicentre broadly in the southern Irish Sea or St. George's Channel. Impact of a km-scale asteroid here potentially could produce the observed sedimentological effects across the UK, but any late Triassic impact structure would now be concealed by a km or more of younger strata. At its thickest development, in Northern Ireland, the seismite is succeeded by a rip-up breccia and hummocky- and wave-rippled cross stratification. These facies, and their position immediately above the seismite, are consistent with the effects of a tsunami arising directly from the seismic event. Tentative evidence for a tsunamite of this age has also been reported from southern France. The putative tsunamite in Northern Ireland is succeeded by a desiccation-cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern England. Read more (1.58mb, PDF) 34. ST AUDRIES BAY ST 1043 3.6 km E of Watchet Mercia Mudstone-Grey Marl-Westbury Beds-Lilstock Formation-Blue Lias Quite an attractive bay with good accessible exposures of red Mercia Mudstone group mudstones and siltstones, Tea Green Marl, Grey Marl, Westbury Beds (dark shales with thin limestones), Lilstock Formation (limestones and marls). The latter contains a bed with slump structures possibly the result of an earthquake or asteroid!). There are ammonites on the foreshore to the west of the Bay. The succession records the transition from a desert plain environment to fully marine conditions. Read more (554kb, Doc) __________________

Blobrana

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Posts: 131433

Date: Aug 24 16:34 2008

RE: Evidence for bolide impact?	Permalink

The stratigraphy of the Penarth Group (Late Triassic) of the East Devon coast The cliff and foreshore exposures in the Devon part of the Dorset and East Devon Coast World Heritage Site expose an unbroken late Triassic to early Jurassic succession. The change from the terrestrial, red-bed facies of the Triassic Mercia Mudstone Group to the fully marine conditions of the Jurassic Lias Group takes place via the Penarth Group, a succession of mudstones, siltstones and limestones deposited in lagoonal and sheltered shallow-marine environments of varying salinities. The Penarth Group as currently defined is divided into the Westbury Formation overlain by the Lilstock Formation, based on type sections in the Severn Estuary area. The lithology and sedimentology of the Westbury Formation strata exposed on the east Devon coast are closely comparable with those of the type area, but those of the Lilstock Formation are not. It is therefore proposed on lithological and historical grounds that this formation should be replaced by a Cotham Formation overlain by a White Lias Formation. This would reinstate, without any change in their original definitions, two of the oldest formally defined stratigraphical names in the British Phanerozoic. All three formations are lithologically distinctive, and are separated from their neighbours by erosion surfaces that represent non-sequences. Those at the bases of the Westbury and Cotham formations are overlain by pebble beds rich in vertebrate remains (bone beds). The Cotham Formation is a highly condensed succession comprised of thinly interbedded mudstones and limestones with ripple trains, stromatolites, desiccated surfaces and slumped beds, the last of which have been attributed to earthquakes or a bolide impact. The limestones of the White Lias Formation exposed on the east Devon coast are sedimentologically complex with channels, slumps and desiccated surfaces. The position of the Triassic-Jurassic boundary is currently under review. Possible positions include the base of the Cotham Formation, a horizon within the formation, the base of the White Lias, the base of the overlying Blue Lias Formation or a horizon within the Blue Lias Formation. Read more (718kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Jul 6 19:26 2007

Jurassic Coast project	Permalink

Jurassic Coast project to monitor fossil hunting damage The summer is upon us and along the 95 mile stretch of Jurassic Coast in Dorset and Devon on England's south coast will come thousands of fossil hunters from around the world hopeful of taking home a treasure or two. Many visitors clamber along with hammers in hand determined to chip their souvenirs out of the cliff face but they potentially do untold damage to the World Heritage Site. Over the coming months, experts from Bournemouth Universitys Environmental and Geographical Sciences Group will use a sophisticated laser scanning technique to monitor this form of erosion to see just how much damage if any is caused by the human fossil hunters. Funded by the Jurassic Coast Team and Natural England, the BU project is led by Andy Ford, a lecturer in Geoinformatics in the Universitys School of Conservation Sciences. Ford and his colleagues have already taken baseline scans at incredibly high resolution of the cliffs along the coast near Charmouth in Dorset prior to the influx of summer visitors. The process will be repeated at the end of the summer and again next spring to compare any changes in the terrain to help determine whether people or nature may be causing the most damage. "Using our new state-of-the-art laser we're able to automatically scan the entire cliff face at a resolution of centimetres over hundreds of square metres. What's more, once we tell the scanner where it is and what we want it to do it takes over and scans a section of the cliff, robot fashion, in comfortably under an hour. Back in the office, we stitch the sections together to make a very detailed virtual model of the entire cliff. It even takes its own pictures and pastes them over the model. The results are something to behold" - Andy Ford. Potential fossil hunters to the Jurassic Coast this summer should also be on the look-out for a new fossil warden who will patrol the beaches at Charmouth to deter people from chipping away at the cliffs. Stuart Godman is part of the Dorset County Councils Countryside Service. His role is to steer people away from the cliffs and back onto the beach where a number of fossils can be found in the soft mud. Source Read more at the Jurassic Coast website __________________

Blobrana

L

Posts: 131433

Date: Jul 5 15:59 2007

Dorset's Jurassic Coast	Permalink

A new warden is patrolling Dorset's Jurassic Coast to prevent intrusive fossil hunters hacking into the cliffs. Stuart Godman will be guarding the beaches at Charmouth until September to deter people from climbing up and chipping away at the cliffs. The county council has introduced the fossil warden amid increasing concern about safety and damage to the cliffs. It hopes Mr Godman will encourage fossil hunters to avoid the cliffs and instead look on the beach for fossils. Read more __________________

Blobrana

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Posts: 131433

Date: Jan 23 19:42 2007

RE: The Triassic-Jurassic extinction event	Permalink

Title: Triassic–Jurassic boundary events: Problems, progress, possibilities. Authors: Stephen P. Hesselbo, Christopher A. McRoberts, József Pálfy "The debate about extraterrestrial versus volcanic drivers for environmental change has not yet been concluded, and it is noteworthy that all of the candidate indicators of extraterrestrial impact - reports of PGE's and soft sediment deformation - occur shortly prior to CAMP volcanic activity. Pure coincidence aside, this observation keeps alive the idea that there is an 'impact signal'-LIP connection, even if the mechanisms remain highly controversial; for example, impact decompression melting, as recently articulated by Elkins-Tanton and Hager (2005), or lithospheric gas explosion (Phipps Morgan et al., 2005)." PDF (416 K) Read more __________________

Blobrana

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Posts: 131433

Date: Oct 9 17:28 2006

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