The Beckers Butte Member

of the

Devonian Martin Formation

(Uploaded 12/27/08)

Lower to mid Devonian in age, the Beckers Butte member of the Martin Formation represent the oldest Devonian rocks in Central Arizona. The type locality is at Beckers Butte along U.S. Highway 60 in the Salt River Canyon, a prominent peak about 4,800 feet high that is capped by Redwall Limestone. The formation represents a fluvial environment of deposition, either in the form of sand filled channels or sheets of sand deposited by flowing rivers onto the Precambrian crystalline rocks, or the Cambrian sediments. Exposures are very scattered in extent, covering an area from the Salt River Canyon to Roosevelt Dam, with a few isolated outcrops up in the Pine/Verde River area.

The lowermost units in the formation consist of a basal conglomerate followed by finer grades of yellowish gray sandstones forming additional subunits. It thickness ranges up to 150 feet at Beckers Butte down to less than ten feet in other areas. The Beckers Butte member is overlain in most areas by the fetid dolomitic limestone of the Jerome member of the Martin Formation. Extreme care must be exercised not to confuse it with the underlying Cambrian Tapeats sandstone or Precambrian Troy Quartzite. There are also basal sandstone beds in the Jerome member above it that are usually confused with it.

At Beckers Butte on the White Mountain Indian Reservation, a poorly preserved psilophyte flora can be found in a bed of carbonaceous shales, and these are the rarest and earliest land plant fossils to be found anywhere in the world. No other fossils are reported from this formation at any other localities.

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Beckers Butte, the type locality of the Beckers Butte Member of the Martin formation. The butte is seen here, partially in the sun with the very bottom of the butte marking the transition into the Beckers Butte member. Most of the ridge in the foreground, is composed of Precambrian Mescal limestone.

Beckers Butte - This is the carbonaceous shale unit which makes Beckers Butte famous for its psilophyte Flora, which can be found in these shales which are very dark in color that occupy the lower portion of the picture. This is one of the rarest outcrops of its type in the world, and is strictly off-limits for collectors.

Close-up, only a few feet away from the dark carbonaceous shales. The very small plant fossils appear as very fine dark strands against the dark gray background. Preservation is generally very poor, however this formation preserves the first steps of land plants in the sequence of evolution.

Psilophyte Flora, an illustration from The Fossil Book by Fenton and Fenton. This reconstruction represents the plant fossils that can be found in the Beckers Butte member of the Martin formation.

Just north of the East Fork of the Verde north of Payson, the Beckers Butte member also outcrops. The limestone ledge seen here, represents the basal Devonian strata in this area.

Road cut along Highway 87 just north of Payson. The lower right corner of this outcrop is Beckers Butte member, and is very distinct because of its laminations from the upper Jerome member of the Martin formation.

Paleosol in the Beckers Butte member of the Martin formation north of Payson along Highway 87. Paleosols represent fossilized soil horizons in a terrestrial environment. There are no fossils in this layer, however the composition is unique, and is one of the few outcrops of its type in the state of Arizona. Notice the distinct bedding which gives the very different appearance than the marine Jerome formation which lies just above it.

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