The Devonian Martin Formation outcrops in Northern Arizona, along the Mogollon Rim, and in South Eastern Arizona. 350 to 400 Million years in age, this formation has been renamed, reclassified and had its members by some elevated to formational status. For the most part, it is called the "Martin Formation" in northern and central Arizona, and in the southern parts of our state, the "Martin Limestone" Primarily a marine formation, the Martin has a single lower Beckers Butte member south of Globe and just north of Payson, which contains a primitive land plant locality, one of only a small handful of such occurrences in the entire world.
In Northern and Central Arizona, the Martin formation contains the Jerome member (or IS the Jerome Formation, depending on what you read!) which is divided into three basic members. The lower member, was described by Teichert as the Fetid Dolomite member, characterized by the strong petroliferous odor (strong propane like odor) when struck or freshly broken with a hammer. It consists of a dark dolomitic limestone with few if any fossils. The Middle Member is a light gray highly aphanitic (ultra fine grained) dolomite. Sedimentary structures such as mud cracks, load casts, and intraformational conglomerate are common in this member, however fossils are very scarce as well. The upper member, contains various dolomites including fetid types, sandstones, and conglomerates, and sandy dolomite units. The upper member is highly fossiliferous, and contains a rich variety of corals, stromatoporoids, brachiopods and gastropods. Most are silicified, and can be easily removed by immersing in dilute muriatic acid. The Beckers Butte member does not occur in abundance in Northern Arizona, only as a basal unit in the central part of the state.
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The Jerome member of the Martin Formation forms distinct ledges along Flowing Springs road just north of Payson. This is the upper member of the Jerome Formation, and alternates from cliff forming dolomites to less resistant slope forming shales.
This image demonstrates the large unconformities in the Paleozoic sedimentary rocks down Flowing Springs Road, just north of Payson. The base of this ridge is 1.2 By Precambrian granite, overlain by a distinct protruding ledge of Precambrian Tapeats sandstone. The overlying dolomitic limestone is the Jerome Formation, upper member, and contains arthrodire fish material.
Differential erosion accounts for this unique outcrops appearance down Houston Mesa road, just north of Payson.. Here, in the Jerome Formations upper member, this marker type lithology can be spotted over much of the Mogollon Rim. Just above this outcrop, we found a diversity of silicified corals, brachiopods and stromatoporoids.
The fabulously rich and scenic outcrops of the Jerome formations upper member can be found near Camp Verde, Here, standing on top of a steep and 900 foot tall ridge, I overlooked an adjacent ridge, with angled strata forming the Devonian outcrop found here. Massive amounts of silicified corals and brachiopods can be found in this area, including the huge beachball sized globes of the Hexagonaria corals.
This is an excellent image to demonstrate the common pinkish weathering found in the upper shales of the Jerome Formation. Note the sharp edges, and both thin and thick bedding. Shales of this type ring with a bell like tone when struck by a hammer. This locality, down Control Road 64, north of Payson had excellent Pachyphyllum Woodmani corals, which resemble the surface of the moon, with the coral calyces looking like lunar craters with raised rims! We also found many "brainstones", quartz geodes that have a pink outer color, and a lumpy brain like appearance. They are basically silicified evaporite nodules.
Another excellent view of the dolomite bedding and thicker horizons of limey shales found near Camp Verde. This "aerial view" was from a tall adjacent ridge.
Thamnopora tabulate corals are packed in at incredible densities . We found the preservation to be superb here, acid baths revealed perfectly articulated specimens of Aulopora, Hexagonaria, and large squat rugose corals in exquisite detail.
The Limestones and limey shales contained large numbers of predominantly a tabulate coral known as Thamnopora. (Earlier publications called them "Cladopora") This beautiful branching coral formed huge colonies and sub reefs on the open sea floor. While this locality is not technically a reef, it is a rich assembly of low diversity shallow water fauna. ("Thatcoensis")
My wife Dawn sits with a huge grin on a fabulously fossiliferous outcrop of the Jerome member. Thamnopora is common all the way from here through Jerome, to north of Payson. It is THE most common coral in the Martin formation in northern Arizona.