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RE: Santa Fe impact structure
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Scientists are currently studying the Santa Fe impact structure to determine when this event took place. Right now they can only say the meteorite struck sometime between 1.2 billion and 330 million years ago. Certainly it happened far enough in the past for the impact crater to be completely altered or eroded.
Complicating the question is the "Great Unconformity", an event that wiped about a billion years of history out of the geologic record of this region. The disappearance of these tons of rocks was due to erosion -- seas receded, and the newly exposed rocks wore away through wind, rain and other weathering processes. Then the seas flooded in again and sediments began forming new layers. The result is that a 330-million-year-old rock layer now lies directly on top of rocks that vary between 1.2 and 1.6 billion years old, depending on the location.

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HPark crater
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Latitude: 35.73, Longitude: 105.86

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How could evidence of a major asteroid impact have been missed when it was in plain sight all along? The telltale signs of a huge impact site were sitting alongside a busy road 8 kilometres north-east of Santa Fe, New Mexico.
Unusual cracks radiating from the tips of cone-shaped structures in rocks along the Santa Fe National Forest Scenic Byway were first spotted by independent geologist Tim McElvain. He called in experts, who identified the projections as shatter cones, distinctive structures that form when shock waves from a high-speed impact fracture the underlying rock.

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Title: Shatter Cone Exposures Indicate a New Bolide Impact Structure near Santa Fe, New Mexico
Authors: Fackelman, S. P.; McElvain, T. H.; Morrow, J. R.; Koeberl, C.

The discovery of bona fide shatter cones in an area at least 3 km2 in extent near Santa Fe, New Mexico, USA, indicates the presence of a so-far unknown, deeply eroded impact structure that is between ~320 Ma and ~1 Ga in age.

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Title: EVIDENCE FOR AN IMPACT STRUCTURE IN THE SANGRE DE CRISTO MOUNTAINS NEAR SANTA FE, NEW MEXICO.
Authors: H. E. Newsom, W. E. Elston, B. A. Cohen, E. L. Tegtmeier, M. T.Petersen, A. S. Read, and T. H. McElvain

Shatter cones discovered in 2005 in road cuts on NM 475 in the Sangre de Cristo Mountains equal those of Sudbury and Vredefort in cm-to-m size. Breccias in Proterozoic crystalline basement and fault blocks of Mississippian-Pennsylvanian carbonates are now being examined to determine whether their distribution is compatible with development stages observed in other large impact structures including:
1) Excavation stage - Ejecta blanket, fall-back breccia, in situ breccias of crater wall and floor.
2) Breccia dikes and pseudotachylites injected into the crater wall and floor, subsequent to the shock wave responsible for shatter cones.
3) Landslide blocks and megabreccias (clasts >1 m) from collapse of the crater wall during the enlargement stage.

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Title: Shatter cone and microscopic shock-alteration evidence for a post-Paleoproterozoic terrestrial impact structure near Santa Fe, New Mexico, USA
Authors: Siobhan P. Fackelmana, Jared R. Morrowb,

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sft
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Latitude: 3544'42.56"N, Longitude: 10552'43.24"W

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