John Day Fossil Beds -National Monument

Filed under: regular postings — Gary January 27, 2007 @ 1:34 pm

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John Day Fossil Beds National Monument is a 14,000 acre (57 km²) park near Kimberly, Oregon. Located within the John Day River Basin, this U.S. National Monument is world-renowned for its well-preserved, remarkably complete record of fossil plants and animals, a record that spans more than 40 of the 65 million years of the Cenozoic Era (also known as the Age of Mammals and Flowering Plants). The monument is divided into three units: Painted Hills (named for the delicately colored stratifications) northwest of Mitchell, Sheep Rock which is northwest of Dayville, and Clarno which is 20 miles west of Fossil. Blue Basin is a volcanic ash bowl transformed into claystone by eons of erosion, colored pastel blue by minerals.

Visitors can follow trails into the badlands and examine fossils displayed at the visitor center while scientists continue field investigations and the painstaking analysis of the monument’s vast fossil record.

The fossil beds contain vestiges of the actual soils, rivers, ponds, watering holes, mudslides, ashfalls, floodplains, middens, trackways, prairies, and forests, in an unbroken sequence that is one of the longest continuous geological records. The rocks are rich with the evidence of ancient habitats and the dynamic processes that shaped them; they tell of sweeping changes in the John Day Basin. Great changes, too, have taken place in this area’s landscape, climate, and in the kinds of plants and animals that have inhabited it.

The strata represented at John Day Fossil Beds consist of four geologic formations, presented here from top (most recent) to bottom (oldest):

  • Rattlesnake Formation (8 – 6 mya)

These most recent strata, named for typical exposures along Rattlesnake Creek, are less fossiliferous than the older formations but contain fragmentary fossils of horses, sloths, rhinos, camels, peccaries, pronghorns, dogs, bears and others, with a preponderance of grazing animals over browsers, betokening a dry, cool climate that was dominated by grasslands.

  • Mascall Formation (15 – 12 mya)

This is a warmer, wetter period. At its base, a roughly five-million-year interval between deposition of the Mascall Formation and the John Day Formation that underlies it is marked by intermittent flows of basaltic lava that repeatedly leveled and denuded the region. A period of moderate climate ensued, with more precipitation than today’s, building up some 200 m of fluvial-lacustrine siltstones and sandstones that are the remains of highly fertile volcanic soil which supported a lush mixture of hardwood forest and open savanna grassland, already home to a great variety of recognizable horses, camels, and deer, as well as bears, weasels, dogs, and cats. At the same time large mammals made a resurgence: among them were the gomphotheres rhinos and bear-dogs.

  • John Day Formation (37 – 20 mya)

Deciduous forests in a wide range of systems characterize this early Miocene sequence. More than 100 groups of mammals have been found in this formation as well, including representatives of dogs, cats, swine, oreodonts, horses, camels, rhinos, and rodents. During this time, repeated volcanic events each left their unique “fingerprint” in thin layers of volcanic ash that have hardened to tuff. Securely dated by direct radiometric means and by comparison with the same ash layers at other locations the ash layers, like chapter headings, provide dated markers for the formation.

  • Clarno Formation (50 – 35 mya)

The mantle of evergreen tropical to subtropical forests are revealed by a splendid sample of fossil seeds, nuts and fruits, leaves and woody structures, including fossilized remains of a member of the banana genus. Hundreds of species have been identified in this richly diverse ecosystem. Among the notable mammals were the giant browsers, the brontotheres and amynodonts, strong-jawed scavengers, hyaenadonts, and ruggedly framed predators such as Patriofelis. None of these left modern descendants.

The Clarno Unit is 1,969 acres in size and is located 18 miles west of the town of Fossil. It features hiking trails, exhibits, and a picnic area; The modern vegetation here is typical of Central Oregon’s near-desert environment with a variety of grasses, sagebrush and juniper.

The cliffs of the Palisades are the most prominent landform in the Clarno Unit. The Palisades were formed 44 million years ago by a series of volcanic mudflows called lahars . The Palisades, preserved a great diversity of fossils in an environment very different from that of today. At that time, volcanoes towered over a landscape covered by near-tropical forest fed by approximately 100 inches of rain per year. Tiny four-toed horses, huge rhino-like brontotheres, crocodilians, and meat-eating creodonts roamed the ancient jungles.
Exploration and study of the John Day fossil beds continues today. In many of the beds, the fossils are widely scattered, and their occurrence cannot be predicted. Many types of fossils deteriorate rapidly once erosion exposes them to the elements. Thus the fossil beds are continually canvassed by paleontologists.

The area’s National Monument status was authorized October 26, 1974 and established in 1975.

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