A Gap in the Geologic Record

A Gap in the Geologic Record (HM1AZN)

Location: Petrified Forest National Park, AZ 86028 Apache County
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Country: United States of America
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N 35° 4.14', W 109° 47.677'

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Inscription
The black basalt that caps the cliffs before you stands in stark contrast to the colorful Chinle Formation visible throughout the Painted Desert.

Below this layer of basalt, a horizontal line cuts across the face of the mesa and separates rocks of two different geologic periods. The pink mudstone below this line belongs to the Chinle Formation deposited about 225 million years ago. The brown mudstone and basalt layers above the line represent the Bidahochi Formation deposited only 5 to 8 million years ago.

How is it that only this thin line represents more than 200 million years of geologic history? This gap is known as an "unconformity." Geologists believe the missing layers were more than 1,000 feet (305 m) thick and that they were eroded over the years by running water and wind - forces that continue to shap this landscape. The emplacement of the basalt has temporarily stopped erosion on the Painted Desert rim, while it has continued in the valley below.
Details
HM NumberHM1AZN
Tags
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Placed ByNational Park Service, U.S. Department of the Interior
Marker ConditionNo reports yet
Date Added Friday, September 19th, 2014 at 11:14am PDT -07:00
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Locationbig map
UTM (WGS84 Datum)12S E 609903 N 3881359
Decimal Degrees35.06900000, -109.79461667
Degrees and Decimal MinutesN 35° 4.14', W 109° 47.677'
Degrees, Minutes and Seconds35° 4' 8.40" N, 109° 47' 40.62" W
Driving DirectionsGoogle Maps
Area Code(s)928
Closest Postal AddressAt or near 301-399 Unnamed Road, Petrified Forest National Park AZ 86028, US
Alternative Maps Google Maps, MapQuest, Bing Maps, Yahoo Maps, MSR Maps, OpenCycleMap, MyTopo Maps, OpenStreetMap

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