The John Day Formation is a series of rock strata exposed in the Picture Gorge district of the
John Day River basin and elsewhere in north-central
Oregon in the United States. The Picture Gorge exposure lies east of the
Blue Mountain uplift, which cuts southwest–northeast through the
Horse Heaven mining district northeast of
Madras. Aside from the Picture Gorge district, which
defines the type, the formation is visible on the surface in two other areas: another exposure is in the Warm Springs district west of the uplift, between it and the
Cascade Range, and the third is along the south side of the
Ochoco Mountains. All three exposures, consisting mainly of
tuffaceous sediments and
pyroclastic rock rich in
silica, lie
unconformably between the older rocks of the
Clarno Formation below and
Columbia River basalts above.[1]
Stratigraphy
The strata, which vary in age from 39 million years to 18 million years, were formed mainly from ashfalls from volcanoes due to a series of calderas now linked to the Yellowstone hotspot. Some of the major layers within the group exposed in the Picture Gorge district are the
Big Basin Formation and Bridge Creek Beds (35 to 32 million years), the
Turtle Cove Formation (30 to 28 million years), the
Picture Gorge Ignimbrite (28.7 million years), the
Kimberly Formation (28 to 25 million years), and the
Haystack Formation (25 to 18 million years).[2]
Located in the general vicinity of what became the Cascade Range, the John Day volcanoes emitted large volumes of ash and dust, much of which settled in the John Day basin. The rapid deposition of the ash preserved the remains of plants and animals living in the region. Some of the solidified ash and the fossils they contain are found in the
John Day Fossil Beds National Monument. Because ash and other debris fell during varied climatic and volcanic conditions and accumulated from many eruptions extending into the early
Miocene (about 20 million years ago), the sediment layers in the fossil beds vary in their chemical composition and color.[3] The lowermost layer contains red ash, such as that exposed in the Painted Hills Unit of the national monument.[4] The layer above it is mainly pea-green clay. On top of the pea-green layer are buff-colored layers.[3]
Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Fossils found in the John Day Formation include a wide variety of plants and more than 100 species of mammals, including dogs, cats,
oreodonts, horses, camels, and rodents.[5] Among the notable plant fossils are Metasequoia (Dawn Redwood), a
genus thought to have gone extinct worldwide until it was discovered alive in China in the early twentieth century.[6]
Among the paleobiota found in the formation is the Daeodon, whose type species, Daeodon shoshonensis, has been found in the formation.[7]
Panorama of some of the John Day Formation strata exposed in the Painted Hills Unit of the John Day Fossil Beds National Monument
^Woodburne, M.O.; Robinson, P.T. (July 1977). "A New Late Hemingfordian Mammal Fauna from the John Day Formation, Oregon, and its Stratigraphic Implications". Journal of Paleontology. 51 (4). The Society of Economic Paleontologists and Mineralogists: 750–57.
JSTOR1303741.
^
abcPeterson, Ryan; Samuels, Joshua; Rybcznskyi, Natalia; Ryan, Michael J; Maddin, Hillary C (April 2020).
"The earliest mustelid in North America". Zoological Journal of the Linnean Society. 188 (4): 1318–1339.
^
abProthero, D. (2016). "A new genus of hesperhyine peccary (Artiodactyla: Tayassuidae) from the late Oligocene of Oregon". New Mexico Museum of Natural History and Science Bulletin. 74: 205–211.
S2CID6287992.
The John Day Formation is a series of rock strata exposed in the Picture Gorge district of the
John Day River basin and elsewhere in north-central
Oregon in the United States. The Picture Gorge exposure lies east of the
Blue Mountain uplift, which cuts southwest–northeast through the
Horse Heaven mining district northeast of
Madras. Aside from the Picture Gorge district, which
defines the type, the formation is visible on the surface in two other areas: another exposure is in the Warm Springs district west of the uplift, between it and the
Cascade Range, and the third is along the south side of the
Ochoco Mountains. All three exposures, consisting mainly of
tuffaceous sediments and
pyroclastic rock rich in
silica, lie
unconformably between the older rocks of the
Clarno Formation below and
Columbia River basalts above.[1]
Stratigraphy
The strata, which vary in age from 39 million years to 18 million years, were formed mainly from ashfalls from volcanoes due to a series of calderas now linked to the Yellowstone hotspot. Some of the major layers within the group exposed in the Picture Gorge district are the
Big Basin Formation and Bridge Creek Beds (35 to 32 million years), the
Turtle Cove Formation (30 to 28 million years), the
Picture Gorge Ignimbrite (28.7 million years), the
Kimberly Formation (28 to 25 million years), and the
Haystack Formation (25 to 18 million years).[2]
Located in the general vicinity of what became the Cascade Range, the John Day volcanoes emitted large volumes of ash and dust, much of which settled in the John Day basin. The rapid deposition of the ash preserved the remains of plants and animals living in the region. Some of the solidified ash and the fossils they contain are found in the
John Day Fossil Beds National Monument. Because ash and other debris fell during varied climatic and volcanic conditions and accumulated from many eruptions extending into the early
Miocene (about 20 million years ago), the sediment layers in the fossil beds vary in their chemical composition and color.[3] The lowermost layer contains red ash, such as that exposed in the Painted Hills Unit of the national monument.[4] The layer above it is mainly pea-green clay. On top of the pea-green layer are buff-colored layers.[3]
Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Fossils found in the John Day Formation include a wide variety of plants and more than 100 species of mammals, including dogs, cats,
oreodonts, horses, camels, and rodents.[5] Among the notable plant fossils are Metasequoia (Dawn Redwood), a
genus thought to have gone extinct worldwide until it was discovered alive in China in the early twentieth century.[6]
Among the paleobiota found in the formation is the Daeodon, whose type species, Daeodon shoshonensis, has been found in the formation.[7]
Panorama of some of the John Day Formation strata exposed in the Painted Hills Unit of the John Day Fossil Beds National Monument
^Woodburne, M.O.; Robinson, P.T. (July 1977). "A New Late Hemingfordian Mammal Fauna from the John Day Formation, Oregon, and its Stratigraphic Implications". Journal of Paleontology. 51 (4). The Society of Economic Paleontologists and Mineralogists: 750–57.
JSTOR1303741.
^
abcPeterson, Ryan; Samuels, Joshua; Rybcznskyi, Natalia; Ryan, Michael J; Maddin, Hillary C (April 2020).
"The earliest mustelid in North America". Zoological Journal of the Linnean Society. 188 (4): 1318–1339.
^
abProthero, D. (2016). "A new genus of hesperhyine peccary (Artiodactyla: Tayassuidae) from the late Oligocene of Oregon". New Mexico Museum of Natural History and Science Bulletin. 74: 205–211.
S2CID6287992.