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
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.
Click on the
thumbnail for an enlarged view
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
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.
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.
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
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.