The Grand Canyon in Northern Arizona displays the most clearly visible sequence of sedimentary rocks in the state. The most prominent stratigraphic sequence forming the walls of this great geologic structure is the Mississippian Redwall Limestone. Located about midway in the Canyon walls, this sedimentary unit ranges in thickness from 500 to 700 feet in the Grand Canyon, and represents a series of periods two marine transgressions and two regressions of the Western and Southern Seaways. South of the Grand Canyon the Redwall is also represented in exposures along the Mogollon Rim sitting unconformably on the Devonian Martin formation. The fossil fauna of the Redwall is abundant and varied, and is most commonly preserved in inter bedded nodular cherts and cherty limestones. The most common fossils are Crinoids, corals, brachiopods, and foraminifers. Also found locally abundant are blastoids, gastropods, trilobites, ostracods, holothurians, calcareous algae and cephalopods.
The Redwall limestone
is widely exposed throughout Northern Arizona. These rocks are
of marine origin and include various types of clastic sediments.
The Redwall can be divided into four stratigraphic units, the
Whitmore Wash, Thunder Springs, Mooney Falls, and Horseshoe Mesa
Members. The two middle members are the primary lithologic units
found on the Mogollon Rim, which fortunately also happen to be
the most fossiliferous as well. It is also the source of many
locally well preserved fossil fauna such as solitary and colonial
rugose and tabulate corals, proetid trilobites, five genera of
blastoids, half a dozen crinoid families, numerous foraminifera
dominated by the family Endothyridae, fine to coarse mesh fenestrate
bryozoans, and an extremely large species of Straparollus gastropods,
and large selection of brachiopods dominated by the genus Spirifer.
Hosts of other marine invertebrates are also found here as well.
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Jerome Quarry, located along the Jerome Perkinsville road. Here the Mooney Falls member of the Redwall outcrops in profusion, filled with the fossils of crinoids and gastropods. The top of the quarry is primarily a massive encrinite. filled with stems, calyxes, and brachiopod hash. We also found in many of the fine cherts large numbers of gastropods and beautifully preserved crinoid parts.
More Jerome Quarry. Here, seen inside the fair sized quarry, the massive encrinites dominate, capped by a thinner bedded and much more fossiliferous limestone. The limestone here is very pure, and lacks any terrigenous components.
North of Payson on Highway 87 near the landfill we find large amounts of Mooney Falls member Redwall. Here, my wife Dawn is collecting in the oolitic member present here, which was jam packed full of huge straparollus gastropods. A very important key to realize about the oolitic facies, is that nearly always in our experience they are prime sources for large and varied gastropods. We feel that the possibility exists that the oolites formed around gastropod excrement, at least in areas on the Mogollon Rim.
Near the same locality as above, I am examining a brown chunk of oolitic limestone. We found Straparollus gastropods the size of dinner plates at this site! The oolitic limestones are usually thin bedded, and cover small areas.
Pulled over on Highway 260 east of Payson at a Redwall "paleokarst" locality. Here, we examine the unique deposit. What we find here is a deep red shaley in filling of the karsty Redwall surface. Although no fossils were found in the red shale which could be any age from late Mississippian onwards, we did find some fine trilobite pygidiums and crinoid calyxes in the brownish cherts on the hill top.
Found at the above site in the cherty limestones, was this stromatoporoid, with clearly visible layering. These invertebrates are found locally abundant in the Redwall, more often preserved in the cherts of the Mooney Falls member.
Parked at Jerome Quarry on another expedition, we gear up for searching for gastropods and hopefully nautiloids in the limestones and cherts. The hill in the background is Jerome Hill, with a base of the Devonian Martin formation capped by Mooney Falls Redwall Limestone, and finally at the very top a very peculiar red sandstone with vesicular cavities in it from the Permian Supai Group.
Down the Jerome Perkinsville road further, is the site along the old narrow gauge railroad track near the ghost town of Bodkin and Russel. This is McKee's site "Narrow Gauge in Bodkin" Mooney Falls Redwall site. Here we found no cherts at all, but a well preserved assemblage of brachiopods, and crinoid material.
Another view of the Mooney Falls member of the Redwall along the Mogollon Rim off of Tonto Creek Road along Highway 260. My wife is examining many of the highly fossiliferous cherts found in the roadway here. We found blastoids, and brachiopods at this site. Important to note that much of the fossiliferous cherts are concentrated by solution, and huge assemblages can be found on hill tops and ridges in the Redwall.
A group of us collection and surveying the Mooney Falls member of the Redwall along the Control Road 64 along the Mogollon Rim. In this expedition which I led, we found Cryptoblastus blastoid calyxes, something we had found no where else. See picture below.
My wife Dawn examines the brownish cherts on the hillside of the quarry in the above photo, on Control road 64. The highly fossiliferous limestones erode out to concentrate the cherts. The brownish cherts found here contain the most fossils. The brown coloration is often found in Redwall cherts, and is caused mostly by what appears as some sort of desert varnish like coating.
Along the road to Young, the Redwall Thunder Springs member outcrops along with the Mooney Falls member. In the Thunder springs we found limestones and cherts with numerous impressions of crinoid calyxes as seen here. These Abatocrinus basal cups had apparently settled in the limey bottom mud, and either preferential sorting by currents (winnowing) or other factors made them come to rest all with the stem downward.
Down the Young road, the cherts in the Thunder Springs member of the Redwall Limestone contain beautifully preserved fossils. This trilobite pygidium, Phillipsia Tuberculatus was fairly common locally in the brownish cherts. Photographed in situ, as it was found on the ground.
Karsty topography is the rule with the Mooney Falls member of the Redwall. Here, I am looking down a cavern, 12 feet deep or so in the Redwall, formed by solution. This cavity, near Young was typical of such occurrences in the area.