Reinterpretation of the depositional environment of the Yellowstone “fossil forests”

Fritz, William J.

doi:10.1130/0091-7613(1980)8<309:rotdeo>2.0.co;2

Cited by 33 publications

(12 citation statements)

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“…It is therefore surprising to find large permineralized stumps rooted in Patat paleosols. Comparable large permineralized stumps also are found in modestly developed paleosols within Eocene volcanic mudflows in northern Yellowstone National Park, Wyoming (Fritz, 1980;Retallack, 1981bRetallack, , 1997a. A large stump in the type Patat clay is 39 cm in diameter and 60 cm high.…”

Section: Former Vegetationmentioning

confidence: 97%

Eocene and Oligocene Paleosols of Central Oregon

Retallack¹,

Bestland²,

Fremd³

1999

Eocene and Oligocene Paleosols of Central Oregon

141

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Scenic red color-banded claystones of the Clarno and Painted Hills areas of central Oregon are successions of fossil soils that preserve a record of Eocene-Oligocene paleoclimatic change. Conglomerates of the middle Eocene Clarno Formation near Clarno contain largely weakly developed paleosols compatible with an environment of volcanic lahars around a large stratovolcano. Deeply weathered paleosols (Ultisols) around a volcanic dome and overlying these conglomerates indicate a climate that was subtropical (mean annual temperature or MAT 23-25°C) and humid (mean annual precipitation or MAP of 900-2,000 mm). Comparable paleoclimates are indicated by fossil floras from the conglomerates, which show diversity and adaptive features similar to modern vegetation of Volcan San Martin, Mexico. An erosional disconformity in the Clarno area separates these older beds from less deeply weathered red paleosols (Alfisols) in the middle Eocene upper Clarno Formation. The change in paleosols may represent a decline in both temperature (MAT 19-23°C) and rainfall (MAP 900-1,350 mm), with dry seasons. Strongly developed lateritic paleosols (Oxisols and Ultisols) in the uppermost Clarno and lowermost John Day Formations in the Painted Hills record return to more humid conditions during the late Eocene. These paleosols are similar to soils of southern Mexico and Central America in climates that are subtropical (MAT 23-25° C) and humid (MAP 900-2,000 mm). Kaolinitic and iron-rich, red paleosols (Ultisols) of the lower Big Basin Member of the John Day Formation near Clarno and the Painted Hills are erosionally truncated and abruptly overlain by smectitic and tuffaceous paleosols (Inceptisols and Alfisols) of the middle Big Basin Member. This truncation surface can be correlated with the local Eocene-Oligocene boundary. Paleosols of the middle Big Basin Member are most like those of the Central Transmexican Volcanic Belt and indicate an early Oligocene paleoclimate appreciably cooler (MAT 16-18° C) and drier (MAP 600-1,200 mm) than during the late Eocene. Root traces and clay accumulations in the paleosols indicate forest vegetation, also evident from fossil leaves of the lake-margin Bridge Creek flora.The mid-Oligocene upper Big Basin Member of the John Day Formation includes distinctive brown as well as red paleosols (Alfisols). Its paleosols indicate a paleoclimate drier (MAP 500-700 mm) than before, and more grasses in the forest understory.Another erosional truncation marks the base of the late Oligocene (early Arikareean), olive-brown lower Turtle Cove Member of the John Day Formation. Calcareous paleosols with near-granular soil structure (Inceptisols and Aridisols) indicate an even

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Section: Former Vegetationmentioning

confidence: 97%

Eocene and Oligocene Paleosols of Central Oregon

Retallack¹,

Bestland²,

Fremd³

1999

Eocene and Oligocene Paleosols of Central Oregon

141

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“…Lahars involve loose pyroclastic ash and flow due to a high water content, derived either from precipitation or from the bursting of a crater lake. Particularly good examples of lahars recently occurred during and subsequent to the 1980 Mount St Helens eruption in Washington State, USA (Fritz, 1980;Fink et al, 1981;Harrison and Frits, 1982). …”

mentioning

confidence: 96%

Debris flows

Innes

1983

Progress in Physical Geography: Earth and Environment

270

127

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“…Transport of tree stumps in an upright position has been reported in volcanic mud flows (Fritz, 1980) and in lakes associated with mud flows (Coffin, 1983). However, in such cases the nature of the enclosing sediment, associated non-upright stumps, and the physical wear of stumps and other plant debris within the deposits are clear evidence of transport.…”

Section: Discussionmentioning

confidence: 99%