Carbonate rock deposits found within the mountain ranges of south-central Nevada, USA, record evidence of a catastrophic impact event known as the Alamo impact. This event occurred roughly 382 million years ago when the ancient seafloor was struck and a submarine crater was formed. The crater was filled-in with fragmented rock, and later with more typical ocean deposits, as the energy from the impact lessened and the environment returned to normal.
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| The Alamo impact crater [Credit: Google Earth] |
By studying the distribution and features of the post-impact ocean deposits and fragmented rock that filled the crater, Andrew J. Retzler of Idaho State University and colleagues present a new map characterizing the size and shape of the Alamo crater.
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This is a map view of the impact region outlining the Alamo impact crater and
the possible location (dotted lines and question marks) of its complex crater features
[Credit: Retzler et al. and Geosphere] |
Their results,
published in the journal Geosphere, indicate that only about half of the Alamo impact crater and its related deposits are now exposed within the region, and they estimate its total diameter to be between 111 and 150 km. This is more than double previous estimates and, if correct, places the Alamo crater as one of the largest marine impacts in the last 550 million years, conservatively larger than the well-studied Chesapeake Bay impact crater (about 35 million years old) on the eastern shore of North America.
Source: Geological Society of America [January 23, 2015]
