Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 www.elsevier.com/locate/palaeo

Late Miocene climate and life on land in Oregon within a context of Neogene global change

Gregory J. Retallack*

Department of Geological Sciences University of Oregon, Eugene, OR 97403-1272, United States Received 13 November 2003; received in revised form 2 July 2004; accepted 20 July 2004

Abstract

Clarendonian (12 Ma) fossil soils, plants, molluscs, fish, and mammals of eastern Oregon allow reconstruction of late Miocene paleogeography, paleoclimate, and paleoecology on land between the global thermal maximum of the middle Miocene (16 Ma) and global cooling and drying of the late Miocene (7 Ma). Six different pedotypes of paleosols recognized near Unity and Juntura allow reinterpretation of local mammalian paleoecology. Fossil beavers dominated gleyed Entisols of riparian forest. Abundant camels and common hipparionine horses dominated Alfisols of wooded grassland and grassy woodland. Diatomites overlying mammal-bearing beds have bullhead catfish [Ictalurus (Ameiurus) vespertinus], as well as fossil leaves dominated by live oak (Quercus pollardiana). Fossil plants and soils of Unity and Juntura are most like those of grassy live oak woodland and savanna on the western slopes of the Sierra Nevada in northern California today. Fossil plants and soils indicate mean annual temperature of 12.9 (7.7–17.7) 8C and mean annual precipitation of 879 (604–1098) mm. Miocene paleoclimatic changes in eastern Oregon show no relationship to changes in oxygen isotopic composition of marine foraminifera, usually taken as an index of global paleoclimatic change. Mismatch between land and sea paleoclimatic records is most likely an artefact of global ice volume perturbation of oxygen isotopic values. Instead, Miocene paleoclimatic change in eastern Oregon parallels changes in carbon isotopic composition of marine foraminifera, presumably through fluctuations in greenhouse gases. D 2004 Elsevier B.V. All rights reserved.

Keywords: Miocene; Paleosols; Plants; Mammals; Oregon

1. Introduction future global change. Evidence of global middle Miocene (16 Ma) warmth includes lateritic paleosols Because Miocene soils, plants, and animals were as far north and south as South Australia, Japan, close to our own time and modern in many respects, Oregon, and Germany (Schwarz, 1997). Middle the surprisingly large amplitude of Miocene paleo- Miocene thermophilic trees such as sweetgum climatic change is of interest for understanding (Liquidambar pachyphylla) grew as far north as Alaska (Wolfe and Tanai, 1980), and coconuts * Tel.: +1 541 3464558; fax: +1 541 3464692. (Cocos zeylanica) dispersed as far south as New E-mail address: [email protected]. Zealand (Fleming, 1975). Middle Miocene thermo-

0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2004.07.024 98 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 philic large foraminifera, corals, and molluscs These global trends also were felt in eastern extended as far north as Oregon, Alaska, Japan, Oregon, where fossil leaves indicate marked cooling and Kamchatkta (Moore, 1963; Itoigawa and Yama- and drying between about 16 and 15 Ma (Wolfe et al., noi, 1990; Oleinik and Marincovich, 2001), and as 1997; Graham, 1999), and a second cooling and far south as South Australia and New Zealand (Li drying to a modern flora by latest Miocene (7 Ma; and McGowran, 2000; Fleming, 1975). These Chaney, 1948). Paleosols of eastern Oregon show indicators of warmth disappeared from such high similar changes between middle Miocene mesic latitudes by later middle Miocene (15 Ma), when forests and late Miocene sagebrush steppe (Bestland cold water minerals (glendonite pseudomorphs of and Krull, 1997; Retallack et al., 2002a; Sheldon, ikaite) formed in marine rocks of Oregon (Boggs, 2003). Associated mammal faunas include a transition 1972). Benthic foraminiferal oxygen isotopic values from three-toed, mixed-feeding horses of the middle also indicate a global middle Miocene marine Miocene (15 Ma, Barstovian) to modern monodactyl thermal maximum, followed by late Miocene global grazing horses by late Miocene (7 Ma, Hemphillian; cooling (Zachos et al., 2001). Downs, 1956; Shotwell, 1970).

Fig. 1. Late Miocene fossil localities of Juntura, Ironside, and Unity, eastern Oregon, with detailed geological map and cross-section around Unity (Thayer, 1957; Thayer and Brown, 1973; Reef, 1983; Walker and MacLeod, 1991). Numbered fossil localities and fossils are listed in Tables 4–5; unnumbered localities have not yet yielded identifiable specimens. G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 99

This study examines paleoclimate and paleo- collections of fossil plants and fish are also ecology of the intervening part of the late reported, as well as new mapping of the area Miocene within the context of Miocene global around Unity (Fig. 1) and an assessment of the paleoclimatic extremes, using evidence from fossil paleoenvironmental significance of paleosols asso- soils, plants, molluscs, fish, and mammals in the ciated with these fossils (Figs. 2 and 3). The eastern Oregon. Previous study of mammalian record of Neogene paleoclimatic fluctuation from communities of this age from near Juntura these and other paleosols in eastern Oregon and (Shotwell, 1963; Shotwell and Russell, 1963), Washington (Retallack, 1997b) does not correlate Ironside (Merriam, 1916), and Baker City (Downs, with oxygen isotopic records from deep-sea 1952) are here supplemented with additional foraminifera but is in phase with foraminiferal collections from near Unity, including reappraisal variations in carbon isotopic composition (Zachos of a locality for a previously collected gompho- et al., 2001). This may indicate a closer relation- there skull and jaws (Orr and Orr, 1999). New ship with the carbon cycle and greenhouse gases,

Fig. 2. Measured section of the Ironside Formation in Windlass Gulch, 3 miles northeast of Unity, Baker County, Oregon, showing paleosols and their development, calcareousness, and hue (using conventions of Retallack, 1997a, 2001b). 100 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123

heur County, Oregon (Fig. 3) at fossil quarries of Shotwell (1963). Petrographic thin sections were cut of all the collected rocks in order to support field identifications of lithologies, and 36 thin sections were point-counted to determine paleosol textures and mineral composition (following the methods of Retallack, 1997a, 2001b). Clays and evaporite minerals were identified by X-ray diffraction using a Rigaku computer-automated goniometer. Six distinct kinds of paleosols, or pedotypes, were recognized (Table 1) throughout the mapped area (Figs. 1 and 2) and also near Juntura (Fig. 3) and Ironside. Each pedotype represents a distinct ancient environment (Table 2). The pedotype names are from the Sahaptin Native American language (Rigsby, 1965; Delancey et al., 1988) and are part of a wider classification of Oregon Cenozoic paleosols (Retal- lack et al., 2000). Descriptive and analytical data for these paleosols are presented in Fig. 5 and Table 1. Chemical analyses of 21 paleosol specimens by Bondar Clegg of Vancouver, Canada, used X-ray fluorescence of a borate-fused bead for major ele- ments, titration for ferrous iron, and gravimetry for loss on ignition. Bulk density for each specimen was determined using the clod method. Of 109 paleosols Fig. 3. Geological sections of fossil quarries excavated by Shotwell logged near Unity and 42 near Juntura, 45 had (1963) near Juntura, Oregon, showing paleosols and their develop- pedogenic carbonate, and 5 were chemically analyzed ment, calcareousness, and hue (using conventions of Retallack, for paleoclimatic interpretation. These data are added 1997a, 2001b). to 754 pedogenic carbonate measurements and 92 chemical analyses of other paleosols from Oregon and such as CO2 and CH4 (Retallack, 2002), than with Washington ranging back in age to 28.7 Ma (Gus- deep-sea temperature or polar ice volume tracked tafson, 1978; Bestland and Krull, 1997; Tate, 1998; by oxygen isotopic composition. Retallack, 2004), in order to assess local Neogene paleoclimate and its correspondence with global paleoclimatic change (Zachos et al., 2001). 2. Materials and methods

Mapping and measurement of two stratigraphic 3. Geological background sections near Unity, Baker County, Oregon (Figs. 2 and 4) involved collection of 95 rock specimens Only rocks of the Clarendonian North Ameri- and 62 fossils, which have been catalogued in can Land Mammal bAgeQ around Unity are collections of John Day Fossil Beds National described and mapped in detail here (Figs. 1 Monument, Kimberly, Oregon (Scott Foss curator: and 2). Few fossils have been recovered from catalog on line at http://www.museum.nps.gov/). poor exposures of the Ironside Formation near Paleocurrents were sighted along trough cross bed Ironside (Merriam, 1916) and Baker City, Oregon axes using a Brunton compass. Two stratigraphic (Downs, 1952). The Unity, Ironside, and Baker sections also were measured near Juntura, Mail- City sequences and local faunas are similar to G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 101

Fig. 4. Badlands of the late Miocene Ironside Formation in central Windlass Gulch (95–135 m of measured section Fig. 2), northeast of Unity. A gray airfall tuff is visible to the lower right and two thin white tuffs in the middle of these badlands. better-known sequences and faunas of the Juntura ized palm wood (Palmoxylon sp. indet.). However, Formation near Juntura, Malheur County (Fig. 3; Walker (1990) reports K–Ar ages from hornblende and Bowen et al., 1963; Greene, 1973; Fiebelkorn et plagioclase of 19.6F0.8 and 19.5F0.6 Ma, respec- al., 1982; Johnson et al., 1996). tively (early Miocene), and regarded these rocks as outliers of the late Eocene to early Miocene John Day 3.1. John Day Formation (late Eocene–early Formation. The laharic tuff breccia is overlain by a 100- Miocene) m-thick rhyodacitic flow of similar petrographic and geochemical composition to the tuff breccia, additional The oldest rocks exposed near Unity are 300 m of tuff breccia, and local basalt flows (Reef, 1983; Walker, rhyodacitic tuff breccias, interpreted as lahars by Reef 1990). These volcanic rocks are overlain by about 20 m (1983). He considered them Eocene in age, based on of red claystone, including numerous paleosols of the fossil leaves (Rhamnidium chaneyi) and permineral- Luca pedotype, which are late middle Eocene to early

Table 1 Paleosols of the Ironside and Juntura Formations and their classification Pedotype Sahaptin Diagnosis Australian F.A.O. U.S. Soil meaning classification World Map Taxonomy (Stace et al., 1968) (F.A.O., 1974) (Soil Survey Staff, 1999) Abiaxi Bitterroot Near-mollic surface (A) horizon over Brown clay Eutric Cambisol Haplosalid weakly weathered subsurface (Bw) Cmti New Shale and siltstone with root traces Alluvial soil Eutric Fluvisol Fluvent Monana Underneath Thin impure lignite (O) on hale and Humic gley Eutric Histosol Fibrist siltstone (A) with shallow root traces Skaw Scare Thin dark gray to black spotted siltstone Wiesenboden Eutric Gleysol Mollic with root traces (A) over bedded siltstone Endoaquent Tutanik Hair Near-mollic brown thick surface (A) with Brown earth Chromic Luvisol Typic deep calcareous and siliceous Natrixeralf rhizoconcretions and nodules (Bk) Xaus Root Sandstone with root traces (A) often Alluvial soil Eutric Fluvisol Psamment ferruginized over bedded sandstone 102 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123

Table 2 Paleosols of the Ironside and Juntura Formations and their interpretation Pedotype Paleoclimate Past vegetation Past animal life Paleotopographic Parent Time of setting material formation Abiaxi No indication Early successional cf. Cormohipparion Riparian fringe Volcaniclastic 1000–2000 wooded grassland sphenodus, Prosthennops, and low terraces silt years Gomphotherium osborni of floodplain Cmti No indication Riparian early Proboscidea indet., Streamside levee Volcaniclastic 5–100 successional Merycodus deposits silt years woodland Monana No indication Swamp woodland None found Lake margin and Volcaniclastic 100–1000 floodplain swamp silt and years diatomite Skaw No indication Riparian floodway Meterix, Scapanus, Seasonally Volcaniclastic 50–1000 woodland: Hypolagus, Spermophilus waterlogged silt years Gramineae, junturensis, Diprionomys, streamside swale Equisetum, Eucastor malheurensis, Populus, Salix Peromyscus, Vulpes, Mammut furlongi, Prosthennops, Merychyus Tutanik Subhumid Grassy woodland Mylagaulus, Mammut Well-drained Volcaniclastic 2000–5000 (800–1000 mm furlongi, cf. floodplain silt years mean annual Cormohipparion precipitation), sphenodus, Aphelops, summer-dry Procamelus grandis, Megatylopus Xaus No indication Riparian early Merycodus Streamside sand Volcaniclastic 5–100 successional bars sand years woodland

Oligocene (Uintan to Orellan) in age near Clarno and (Walker, 1990) were far inland from subduction of the the Painted Hills, Oregon (Bestland et al., 1999; Farallon Plate during the middle Miocene (Orr et al., Retallack et al., 2000). Comparable red paleosols also 1992). Middle Miocene Strawberry stratovolcanoes are found in the upper John Day Formation east of rose at least 1000 m above valley floors of the Kimberly, Oregon, where they formed on well-drained Paleozoic and Mesozoic basement (Robyn, 1977). uplands (Retallack et al., 2000). Dooley Volcanics near Unity are 150 m thick and include three distinct units of rhyolitic, welded, ash 3.2. Strawberry and Dooley Volcanics (middle flow tuffs (Reef, 1983). The ash flow tuffs are light Miocene) gray with abundant pumice, rock fragments, and phenocrysts of plagioclase, biotite, and quartz. Platy, 2-pyroxene, basaltic andesites are character- Dooley Volcanics reach a thickness of 2400 m istic of middle Miocene (radiometric ages 15–10 Ma), around volcanic centers only a few kilometers to the Strawberry Volcanics, with smaller amounts of basalt, north and northwest of the mapped area. One of the rhyolite, rhyolitic tuff, vent breccia, and micronorite last eruptive events of the Dooley Volcanics was a (Robyn, 1977). The Strawberry Volcanics are calcalka- rhyolite dome dated by K–Ar at 14.7F0.4 Ma line and were not comagmatic with voluminous (Evans, 1992). tholeiitic basalts of the Columbia River Basalt Group, which also are middle Miocene (radiometric age 17–15 3.3. Ironside Formation (late Miocene) Ma; Sheldon, 2003). Calcalkaline volcanism is pro- duced by melting above subduction zones, but Straw- The Ironside Formation is at least 250 m of berry Volcanics and other coeval andesitic volcanoes conglomerates, siltstones, diatomites and lignites G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 103

Fig. 5. Petrographic and chemical data for newly described paleosols of Tutanik and Xaus paleosols from 4 to 6 m, Tutanik, Cmti, Xaus, Skaw, and Abiaxi paleosols from 41 to 46 m, and Abiaxi, Cmti and Skaw paleosols from 229 to 232 m in reference section of Ironside Formation in Windlass Gulch (Fig. 2). 104 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 named for the small village of Ironside, 15 km east 1998), although nomenclatural difficulties remain. on U.S. highway 26 from Unity (Thayer, 1957; For example, a fossil proboscidean skull from Unity Thayer and Brown, 1973). Sediments and paleosols on display at the Oregon Museum of Science and along the highway east of Ironside are identical with Industry in Portland (Fig. 6C–D) has remained those near Unity and particularly with the lower part undescribed beyond a photograph and account of of a measured section in Windlass Gulch (0–7 m in its collection (Baldwin, 1964; Orr and Orr, 1999). Fig. 2). Diatomites like those in the upper part of The excavation is still visible within an Abiaxi the Ironside Formation near Unity, also crop out in paleosol on a low knoll southeast of a prominent the hills north of Ironside. A fossil locality southeast bluff, east of Unity (locality 8 of Table 4; Walker, of Baker City also exposes tuffs and conglomerates 1990, figs. 5 and 9). George Gaylord Simpson like those of the lower Ironside Formation (95–100 examined the specimen in 1953 and suggested it was minFig. 2) in Windlass Gulch (Downs, 1952; bMiomastodon merriamiQ (Orr and Orr, 1999). A more Evans, 1992). appropriate name is bGomphotherium cingulatumQ These three areas are linked by late Miocene of Downs (1952), based on a lower jaw discovered fossil mammals of the Clarendonian North American by Albert Werner at a locality 15 km east of Baker Land Mammal "Age" (8.4–12.3 Ma of Prothero, City and about 80 km northeast of Unity. This and

Fig. 6. Late Miocene (Clarendonian) fossil mammals from Unity: (A)–(B) Hipparionini gen. indet., molar fragments (JODA specimens 9004 and 9017, respectively); (C)–(D) Gomphotherium osborni, skull and mandible (Oregon Museum of Science and Industry); (E) Prosthennops sp. indet., molar with chipped crown (JODA9000). Scale bars as indicated. G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 105 other validly established taxa were not recognized rium and two additional proboscidean species are by Lambert and Shoshani (1998), who considered recognized from the Clarendonian Juntura Formation the genus oversplit. Tobien (1972) went so far as to to the south in Malheur County (Shotwell and include all North American Gomphotherium in Russell, 1963): a two-tusker bMammut furlongiQ (a bGomphotherium productumQ. Here, I follow Mad- species not recognized by Lambert and Shoshani, den and Storer (1985) in using their broadly defined 1998), and a shovel-tusker similar to Platybelodon Gomphotherium osborni (Barbour) for the Unity barnumbrowni (but regarded as a new genus by skull. Another gomphothere tooth, probably con- Lambert and Shoshani, 1998). specific, was found by Elmer Molthan in the There are also nomenclatural problems with Ironside Formation 400 m south of Ironside Post Clarendonian horse teeth from Unity and Juntura, Office, which is only 15 km east of Unity because among the numerous teeth and jaws, there is (bTetrabelodonQ sp. of Merriam, 1916). Gomphothe- no skull with facial fossae or other diagnostic

Fig. 7. Fossil plants and fish from the Ironside Formation near Unity, Oregon: (A) sycamore, Platanus dissecta, leaf (specimen JODA9408); (B) box elder, Acer negundoides, winged seed (JODA9409); (C) white oak, Quercus prelobata leaf (JODA9053); (D) live oak, Quercus pollardiana leaf (JODA9058a); (E) shagbark hickory, Carya bendirei, leaf (JODA9055); (F) swamp ash, Fraxinus dayana, winged seed (JODA9050a); (G) bullhead catfish, Ictalurus (Ameiurus) vespertinus, skull and partial skeleton (JODA9043a). Scale bars all 1 cm. 106 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 features. The names given to these teeth (bHipparion diatomites of the Coal Valley Formation of Nevada anthonyiQ of Merriam, 1916 and bHipparion con- dated by the K–Ar technique at 11.4–9.4 Ma (Golia doniQ of Shotwell and Russell, 1963) are considered and Stewart, 1984). by MacFadden (1984) likely junior synonyms of Cormohipparion occidentale or Cormohipparion sphenodus, the latter most likely on the basis of 4. Late Miocene paleogeography of eastern Oregon size. Shotwell and Russell (1963) considered that the large collection of teeth and jaws from 4.1. Sedimentological evidence Juntura represented only one species. Late Miocene geological age is also indicated by The depositional basin of the Ironside Forma- fossil plants from near Unity and Juntura. A new tion was bounded by volcanic terranes in the fossil plant assemblage in Juniper Gulch near Unity Strawberry and Dooley Volcanics to the north and (Fig. 7; locality 6 of Table 4, at 160 m in Fig. 2)is west, and fault blocks of Paleozoic and Mesozoic here designated the Unity flora. Entire to weakly basement to the north and southwest. There was dentate oak leaves like those dominating this erosional paleorelief on the underlying Dooley assemblage have been identified as bQuercus Volcanics and Clarno Formation, as indicated by hannibaliQ, but this name has been included within several inliers cropping out south of Juniper Quercus pollardiana (Knowlton) by Axelrod (1995) Gulch. The stepped system of northeast-extensional or identified with the similar, but more dentate, faults (Fig. 1) did not exist during deposition, living Quercus chrysolepis (Wolfe for Leopold and when this broad alluvial and lacustrine basin Wright, 1985). The Unity flora is taxonomically extended southeast from highlands to the north most like the late Miocene Stinkingwater flora in the and west (Fig. 8). Juntura Formation near Juntura (Chaney and Axel- Basin-marginal boulder breccias and conglomer- rod, 1959) and the Weiser flora from the Poison ates interfinger with diatomites and tuffaceous Creek Formation of Idaho (Dorf, 1936; Leopold and siltstones of the Ironside Formation in road cuts Wright, 1985). over Dooley Mountain and north of Whited The thick gray volcanic ash of the Ironside Reservoir (Fig. 1). Paleocurrent directions measured Formation at 171 m in Windlass Gulch is minera- from trough cross bedding in conglomeratic paleo- logically most similar to the 11.31 Ma CPTXI Ash of channels in the Windlass Gulch section (Fig. 9) the Great Basin (Perkins et al., 1998), and another indicate that streams flowed southeast. This early gray tuff at 101 m is most like the 11.59 Ma CPTIX phase of river channels and floodplains was Ash (Figs. 2 and 3). A geological age of 11–12 Ma is followed by extensive oligotrophic lakes, which similar to the age of the Juntura Formation, 78 km to eventually accumulated diatomites out to the hilly the south in Malheur County. A whole-rock K–Ar margins of the depositional basin. A final deposi- date for 12-m-thick basalt 152 m stratigraphically tional phase of diminished lake area is recorded by below a fossil mammal quarry (OU locality 2337 of fluvial gravels and lignites at the top of the exposed Fig. 3) and 85 m above the Stinkingwater flora sequence near Unity (Fig. 2). (Chaney and Axelrod, 1959) near Juntura is 12.4 Ma (Evernden and James, 1964; corrected using Dal- 4.2. Paleosol evidence rymple, 1979). A tuff 76 m stratigraphically above the mammal quarry has been dated by K–Ar on Various paleosols represent different sedimentary shards at 11.5F0.6 Ma (Fiebelkorn et al., 1982), and environments and communities within these river the Devine Canyon ashflow tuff at the base of the valleys and lake shores. Weakly developed paleosols Drewsey Formation, 107 m above the quarry, has (Abiaxi, Cmti, Xaus) represent ephemeral commun- been dated by 39Ar/40Ar of sanidine as 9.7 Ma ities on the landscape, such as vegetation colonizing (Johnson et al., 1996; five similar K–Ar dates are stream and lake margins after flooding. Weakly tabulated by Greene, 1973). Also comparable in age developed carbonaceous paleosols (Skaw) represent and lithology are volcanic ashes, conglomerates, and riparian or lake-margin marsh, and moderately G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 107

Fig. 8. Reconstructed late Miocene (Clarendonian) landscape ecology of the area near Unity, eastern Oregon.

developed peaty paleosols (Monana) represent swamp woodlands, where decay of organic debris was suppressed by seasonally high water table. In contrast, Tutanik paleosols represent stable floodplains and alluvial terraces. Tutanik paleosols are thick, brown, and have little relict bedding due to bioturbation (including siliceous rhizoconcretions; Fig. 10A–B) and to development of soil structure Fig. 9. Paleocurrents measured from trough cross bedding in (fine subangular blocky peds) and microfabric (skel- conglomerates at 123–131 m (left) and 33–39 m (right) in the masepic porphyroskelic plasmic fabric of Brewer, measured section in Windlass Gulch (Fig. 2). 1976). They are also more aluminous and less rich in 108 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123

Fig. 10. Chalcedony nodules and rhizoconcretions from Tutanik paleosols of the Ironside Formation near Unity, Oregon: (A) petrographic thin section under crossed nicols of three rhizoconcretions (black holes with bright banded haloes) in oblique (lower left) and cross-sections (specimen JODA9225); (B) rhizoconcretion (JODA9311); (C) near-spherical nodule (JODA9310a); (D) lobed nodule (JODA9310b); (E) cigar- shaped nodule (JODA9309a); (F) tear-shaped nodule (JODA9310c); (G) cross-section of septarian nodule (JODA9310d); (H)–(I) petrographic thin sections under crossed nicols of dendritic chalcedony and void-filling dolomite (JODA9310d). Scale bars as indicated. alkalis and alkaline earths than associated paleosols (Bradbury et al., 1985). Significant (8%) amounts of (Fig. 5). Although volcanic ash was an important part C. subtilis in one sample (Van Landingham, 1967) of Tutanik paleosol parent material, few recognizable may indicate connection to the sea by way of low- shards have escaped weathering. This degree of gradient streams (Bradbury et al., 1985). Fossil weathering is found after 8–27 ka in tropical highland aquatic molluscs from Juntura and Unity (Tables 4– soils of New Guinea (Ruxton, 1968). Tutanik 5; Taylor, 1985) are evidence for a Miocene course of paleosols have common clay skins in thin section the Snake River southwest into the Pit River of and a higher proportion of fine pedogenic clay than northern California, before Basin and Range faulting associated paleosols (Fig. 5). The degree of enrich- and northward capture by the Columbia River (Van ment of clay is intermediate between that seen in TassellL et al., 2001). Lakes were also needed by upper Modesto soils dated at 10 Ka and lower many of the fossil birds (Brodkorb, 1961): cormor- Modesto soils dated at 40 Ka in alluvium of the ants, coots, mergansers, teals, and extinct straight- Merced River, San Joaquin Valley, California billed flamingos (Table 5). (Harden, 1982, 1990).

4.3. Paleontological evidence 5. Late Miocene paleoclimate of eastern Oregon

Diatomites near Unity have not been studied in 5.1. Evidence from paleosols detail, but of 108 diatom taxa described from coeval diatomites of Juntura, only two are found in estuaries Only Tutanik paleosols are useful paleoclimatic and the sea: bCoscinodiscus miocenicusQ and proxies, because other pedotypes were too weakly bCoscinodiscus subtilisQ of Van Landingham (1967; developed to show a paleoclimatic signature. Differ- perhaps better referred to Actinocyclus according to ences between Tutanik and other comparably devel- Bradbury et al., 1985). Melosira granulata, Melosira oped Cenozoic paleosols from Oregon may reflect distans, and Fragilaria construens dominate individ- changing Neogene paleoclimate. Tutanik paleosols ual collections (58–88%) and indicate fresh water of are generally similar in their brown color and clayey low alkalinity, low in dissolved solids, neutral to subsurface (argillic horizons) to Skwiskwi paleosols slightly acidic in pH, and low in nutrient levels of the Oligocene John Day and latest Miocene G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 109

Rattlesnake Formations (Retallack et al., 2000, times 100 (following Sheldon et al., 2002), as 2002a), and to early Miocene Tima paleosols of follows: the John Day Formation (Retallack, 2004). Tutanik paleosols lack thick silcretes of Tima paleosols and P ¼ 139:6 þ 6:388D 0:01303D2 have silica–micrite rhizoconcretions (Fig. 8A–B) and chalcedony septarian nodules (Fig. 8C–I) unknown P ¼ 221e0:02C in Skwiskwi paleosols. The large amount of silt (never less than 27% by volume) and sodium (soda/ T ¼18:516ðÞþS 17:298: potash ratiosN1) also ally Tutanik paleosols with Tima rather than Skwiskwi paleosols. Tutanik Paleoclimatic results of these calculations (Table 3) paleosols also differ from paleosols of the late are 450–800 mm mean annual precipitation from Miocene (7 Ma) Rattlesnake Formation, such as depth to carbonate and 600–1100 mm from chemical the Tatas pedotype, which was crumb-structured, composition of clayey horizons. Because the carbo- moderately leached, and calcareous (Retallack et al., nate-depth transfer-function was designed for use with 2002a). Tutanik paleosols thus show greater affin- nodules (Retallack, 1994, 2000), rather than rhizo- ities with interpreted summer-dry (xeric) paleosols, concretions, these estimates are less likely to be such as Tima, than summer-wet (ustic) paleosols, reliable than the subhumid regime estimated from such as Swkiskwi and Tatas. chemical composition of B horizons. Geochemical Modern soils like Tutanik paleosols are found composition of paleosol parent rhyodacitic and near Redding, northern California (map unit Lc3-2a andesitic airfall ash shows insignificant change with duric phase of F.A.O., 1975), where mean through time compared with paleosol modification annual temperature is 17.7 8C, and mean annual (Perkins et al., 1998; Retallack et al., 2000). precipitation is 1040 mm, January and July temper- A highly seasonal climate is indicated by concen- atures are 8 and 29 8C, respectively, and precip- trically banded rhizoconcretions with silica and itation is 216 mm in January, but only 5 mm in July micrite in Tutanik paleosols (Fig. 10A–B). Season- (Ruffner, 1985). In contrast, for Baker City near ality is also indicated by the unusually abundant silt Unity, mean annual temperature is 7.6 8C, mean and soda in Tutanik paleosols, especially considering annual rainfall is 270 mm, temperature is more their likely mean annual precipitation (Table 3). In seasonal (4 8C in January, 19 8C in July), but such rainy climates, there would not be so much salt precipitation is less seasonal (35 mm in January, 12 or dust unless summers were very dry, and most rain mm in July; Ruffner, 1985). and snow were during winter and spring. Furthermore, Independent estimates of former precipitation can the scarce carbonate and distinctive silica–micritic be gained from chemical composition of clayey rhizoconcretions (Fig. 10A–B) are like those found in horizons and from carbonate in rhizoconcretions of modern soils of Mediterranean (summer-dry) climates Tutanik paleosols at depths of 79–91 cm. This (Chadwick et al., 1987, 1995). Siliceous rhizoconcre- depth (D in cm) can be used to estimate mean tions from a few Tutanik paleosols (45, 59, and 69 m annual rainfall ( P in mmF156) using a transfer in Fig. 2) grade insensibly through cigar- and tear- function derived from study of modern soils shaped forms into ellipsoidal septarian nodules of a (Retallack, 1994), once allowance is made for burial form not previously reported from paleosols (Fig. compaction (Sheldon and Retallack, 2001) due to at 10C–F). Some of these contain fossil wood or lumpy least 60 m of overlying Pleistocene fanglomerate root traces morphologically comparable to rhizobially (Evans, 1992). A large database of chemical nodulated roots. Others are hollow and cracked, with analyses of North American soil B horizons has void-filling dolomite rhombs (Fig. 10G,I). Micro- been used to derive yet other transfer functions for fabric of the nodules is radially oriented, dendritic mean annual precipitation ( P in mmF182) and chalcedony, creating an external fabric reminiscent of mean annual temperature (T in 8CF4.4) from two cone-in-cone structure. The ellipsoidal nodules are chemical measures: S, the molar ratio Na2O+K2O/ superficially similar to chalcedony nodules of the Al2O3;andC, molar Al2O3/(Al2O3+CaO+Na2O) bbutton bedsQ, a lacustrine facies of the middle 110 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123

Table 3 Mean annual temperature and precipitation for Tutanik paleosols of the Ironside Formation Estimated geological Stratigraphic level Mean annual precipitation Mean annual precipitation Mean annual temperature age (Ma in Fig. 5) (m in Fig. 3) (mm) from Bk (mm) from chemical (8C) from chemical composition composition 11.59 100.5 644F156 (503–785) 11.60 Unity Reservoir 657F156 (516–798) 11.69 83 588F156 (447–729) 916F182 (734–1098) 13.3F4.4 (8.9–17.7) 11.83 45.1 601F156 (460–742) 934F182 (752–1116) 13.2F4.4 (8.8–17.6) 11.95 16.6 643F156 (502–784) 11.96 14 617F156 (476–758) 11.97 12.5 626F156 (485–767) 11.00 Ironside 640F156 (499–781) 12.00 5.2 627F156 (486–768) 786F182 (604–968) 12.1F4.4 (7.7–16.5) 12.01 3.3 636F156 (495–777) 12.02 1.7 649F156 (508–790) 12.10 Denny Flat 571F156 (430–712) 12.11 Denny Flat 594F156 (453–735) Means All listed 623F156 879F182 12.9F4.4

Miocene Barstow Formation of California (Palmer, summer-dry paleoclimatic regime for the Unity flora 1957). My own examination of the Barstow nodules is also compatible with frequent wildfires indicated found conspicuous relict bedding and microcrystalline by charcoal associated with middle to late Miocene textures, unlike the septarian and radial-dendritic fossil floras of southeastern Oregon (Taggart et al., crystal form of the Unity nodules. Nevertheless, 1982; Taggart and Cross, 1990). highly alkaline late-summer aridity could have played a role in the formation of both kinds of siliceous 5.3. Evidence from fossil animals nodules. Abundance of bullhead catfish in siltstones with 5.2. Evidence from fossil plants the Unity flora (Fig. 7; Table 4) can be contrasted with the overlying diatomites, which have a sparse Close floristic composition of Unity (Table 5) fish fauna of other kinds of fish. The leaves and and Stinkingwater floras (Chaney and Axelrod, catfish probably represent a nearshore lacustrine 1959) with the modern flora of California supports habitat distinct from that of the open lake. Bullhead evidence from associated paleosols for extension of catfish lived in western North America from the Mediterranean climate into eastern Oregon during Eocene to Pliocene, but after that time became the late Miocene. The paleoclimatic affinities of restricted to eastern North America. They have been these floras are quite distinct from more humid and artificially reintroduced to Oregon and Idaho within warm climates evident during the middle Miocene the last 120 years. Today, they live in low-gradient thermal maximum, represented locally by the streams and lakes at elevations less than 1000 m in Austin, Tipton, Baker, and Mascall floras (Oliver, warm temperate climates with at least 230 frost-free 1934;BrownforGilluly, 1937; Chaney and days and at least 400 mm mean annual precipitation Axelrod, 1959), and before the advent of modern (Van Tassell et al., 2001). sagebrush and riparian communities during the Brodkorb (1961) invokes Bergmann’s rule (Brown Pliocene (Chaney, 1948; Ashwill, 1983, Retallack and Lomolino, 1998) to argue for a warmer than et al., 2002a). Mean annual precipitation of around present climate from the small size of Juntura 900–1000 mm and mean annual temperature of 13 cormorants, coots, and teals compared with living (8–18) 8C have been estimated from other late relatives. Oxygen isotopic studies of fossil mammal Miocene fossil floras of the Great Basin (Wolfe, teeth from Juntura, Oregon, indicate mean annual 1994; Wolfe et al., 1997; Graham, 1999). A temperatures of about 18 8C, and a mean annual range G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 111

Table 4 Late Miocene (Clarendonian) megafossils of the Ironside Formation, near Unity, Oregon Fossil taxon Similar living taxon Common name Loc. Equisetum sp. indet. Equisetum arvense Common horsetail 1–2 Gramineae sp. indet. Gramineae Grass 1–2 Sagittaria sp. indet. Sagittaria cuneata Arum-leaved arrowhead 3 Salix sp. indet. Salix scouleriana Scouler’s willow 3 Populus sp. indet. Populus balsamifera Black cottonwood 3 Trapa americana Knowlton (1898) Trapa natans Water chestnut 3–5 Platanus dissecta Lesquereux (1878) Platanus occidentalis Sycamore 6 Quercus pollardiana (Knowlton) Axelrod (1995) Quercus chrysolepis Maul oak 6 Quercus prelobata Condit (1944) Quercus garryana Oregon white oak 6 Quercus simulata Knowlton (1898) Quercus myrsinaefolia Chinese oak 6 Cercocarpus ovatifolius Axelrod (1985) Cercocarpus betuloides Birchleaf mountain 6 var. blancheae mahogany Acer negundoides MacGinitie (1934) Acer negundo Box elder 6 Fraxinus dayana Chaney and Axelrod (1959) Fraxinus caroliniana Swamp ash 6 Carya bendirei (Lesquereux) Chaney and Axelrod (1959) Carya ovata Shagbark hickory 6 Ptelea miocenica Berry (1931) Ptelea trifoliata Carolina hop tree 7 Radix junturae Taylor (1963) Radix auriculata Aquatic big-ear snail 7 Ictalurus (Ameiurus) vespertinus Miller and Smith (1967) Ictalurus melas Black bullhead catfish 6 Gomphotherium osborni (Barbour) Madden and Storer (1985) None Extinct four-tusker 8 Prosthennops sp. indet. None Extinct large peccary 8 Rhinocerotidae sp. indet. None Large extinct rhino 9 cf. Cormohipparion sphenodus (Cope) None Extinct cursorial 10 MacFadden and Skinner (1977) three-toed horse cf. Megatylopus gigas Matthew and Cook (1909) None Extinct large camel 11 cf. Merycodus sp. Antilocapra americana Pronghorn 11–12 Note: these are identifcations of newly collected material in collections of John Day Fossil Beds National Monument. Legal and NAD27 UTM coordinates to localities are 1—Windlass Gulch section 60 m NWH NEH SEH SEH S33 T12S R38E 11T 0416253 4925216; 2—Windlass Gulch section 44 m NWH NEH SEH SEH S33 T12S R38E 11T 0416262 4925216; 3—Windlass Gulch section 61 m NWH NEH SEH SEH S33 T12S R38E 11T 0416262 4925216; 4—Denny Flat southeast SEH SEH SEH SWH S2 T13S R37E 11T 0409723 492339; 5—Denny flat southeast NEH NEH NEH NEH S2 T13S R37E 11T 0409761 492353; 6—Windlass Gulch section 158 m NWH NWH SWH SWH S34 T12S R38E 11T 0416526 495228; 7—Windlass Gulch section 225 m NEH NWH SWH S34 T12S R38E 11T 0416665 4925404; 8—east of Unity SEH NEH SEH NWH S11 T13S R37E 11T 0408804 4922516; 9—Windlass Gulch section 100 m NEH SWH SWH SWH S34 T12S R38E 11T 0416596 4925185; 10—Windlass Gulch section 5 m SEH NWH SEH SEH S33 T12S R38E 11T 0416227 4925153; 11—Denny Flat northwest NWH SWH SWH SWH S35 T12S R37E 11T 0408416 4925224; 12—Windlass Gulch section 89 m NEH NEH SEH SEH S33 T12S R38M 11T 0416315 4925249. of temperature of some 25 8C(Kohn et al., 2002), 6. Late Miocene palaeoecology of eastern Oregon compared with 7.6 and 23 8C, respectively, for Baker City today (Ruffner, 1985). 6.1. Evidence from paleosols Indications of a late Miocene climate at Juntura, wetter than at present, come from the sewellel A detailed local mosaic of vegetation (Fig. 8) (Tardontia in Table 5). Similar aplodontids are can be inferred from the relationship of paleosols to now restricted to Oregon and Washington, west of local sedimentary facies and from plant-induced the Cascades (Shotwell, 1958). The western Amer- features of the paleosols (Figs. 2 and 3; Table 3). ican mole (Scapanus) is also now found well west Tutanik paleosols are finely structured (granular of Juntura and Unity (Hutchison, 1968). On the peds about 1 cm across) with abundant fine root other hand, subhumid to semiarid rangeland con- traces as well as scattered rhizoconcretions, as in ditions are indicated by ground squirrels, pocket soils supporting grass with scattered woody shrubs gophers, and extinct mylagaulines (Shotwell, 1958, or trees (Retallack, 1997b, 2001b). The paleosols 1970). lack fine crumb peds found in sod-forming grass- 112 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123

Table 5 Table 5 (continued) Late Miocene (Clarendonian) megafossils of the Juntura Formation Fossil taxon Common name near Juntura Ammospermophilus junturensis Ground squirrel Fossil taxon Common name (Shotwell & Russell) Korth, 1994 Sphaerium sp. cf. S. lavernense Aquatic lake orb Ammospermophilus sp. indet. Ground squirrel Herrington (Herrington and mussel Eutamias sp. indet. Extinct chipmunk Taylor, 1958) Hystricops sp. indet. Extinct large beaver Pisidium sp. cf. P. clessini Aquatic pea clam Eucastor malheurensis Shotwell Extinct beaver Neumayr and Paul (1875) and Russell (1963) Pisidium sp. indet. Aquatic pea clam Microtoscoptes sp indet. Extinct vole Fluminicola junturae Taylor, 1963 Aquatic pebble snail Copemys dentalis (Hall) Extinct small field Hydrobiidae indet. Small aquatic snail Lindsay, 1972 mouse Viviparus turneri Hannibal, 1912 River snail Copemys sp. cf. C. esmeraldensis Extinct large field Radix junturae Taylor, 1963 Aquatic big-ear snail (Wood) Lindsay, 1972 mouse Carinifex shotwelli Taylor, 1963 Keeled ramshorn snail Copemys sp indet. Extinct large field Promenetus sp. indet. Aquatic ramshorn snail mouse Ictalurus peregrinus Lundberg, 1975 Catfish Leptodontomys sp. indet. Extinct pocket mouse Cyprinidae gen. indet. Squawfish Perognathus sp. indet. Pocket mouse Catastomidae gen. indet. Sucker Diprionomys sp. indet. Extinct pocket mouse Phalacrocorax leptopus Small cormorant Pliosaccomys sp. indet. Extinct pocket gopher Brodkorb, 1961 Macrognathomys nanus Hall, 1930 Extinct birch mouse Ciconiidae gen. indet. Extinct stork Borophagus sp. indet. Short-face bone- Megapaloelodus opsigonus Straight-billed crushing dog Brodkorb, 1961 early flamingo Aelurodon sp. indet. Long-face bone- Eremochen russelli Small goose crushing dog Brodkorb, 1961 Vulpes sp. indet. Fox Querquedula pullulans Small teal Leptarctus sp. indet. Extinct badgerlike Brodkorb, 1961 mustelid Ocyplonessa shotwelli Extinct merganser Hoplictis sp. indet. Extinct like honey Brodkorb, 1961 badger Neophrontops dakotensis Extinct Old Sthenictis junturensis Shotwell and Extinct otterlike Compton, 1935 World vulture Russell (1963) musteline Fulica infelix Brodkorb, 1961 Small coot Pseudailurus sp. indet. Extinct small cat Meterix sp. indet. Extinct large shrew Gomphotherium sp. indet. Extinct four-tusk Anouroneomys minimus Hutchison Extinct small shrew proboscidean & Bown (Bown, 1980) Mammut furlongi Shotwell and Extinct two-tusk Mystipterus sp indet. Extinct nonburrowing Russell (1963) mastodon mole cf. Platybelodon barnumbrowni Extinct shovel-tusker Scalopoides sp. indet. A Extinct weakly (Barbour) Barbour, 1932 burrowing mole cf. Cormohipparion sphenodus (Cope) Extinct three-toed Scalopoides sp. indet. A Extinct weakly MacFadden and Skinner (1977) horse burrowing mole Tapiridae gen. indet. Tapir Scapanus sp. cf. S. shultzi Western American Aphelops sp. indet. Extinct hornless Tedford, 1961 mole rhinoceros Chiroptera gen et sp. indet. Extinct bat, like big Prosthennops sp. indet. Extinct large peccary brown bat Merychyus major Leidy, 1858 Extinct piglike oreodon Hesperolagomys sp. cf. H. galbreathi Extinct pika Procamelus grandis Gregory, 1942 Extinct camel Dawson (Clark et al., 1964) Megatylopus sp. indet. Extinct large camel Hypolagus sp. cf. H. fontinalis Extinct rabbit Note: this is a compilation of the Black Butte local fauna of Dawson, 1958 Shotwell (1963, 1967, 1970), Hutchison (1968), and Taylor (1963) Tardontia sp. cf. T occidentale Extinct sewellel as revised by Honey et al. (1998), Lambert and Shoshani (1998), (Macdonald) Shotwell, 1958 Baskin (1998), Martin (1998), Lander (1998), and Wright (1998). Mylagaulus sp. indet. Extinct horned rodent Epigaulus minor Hibbard and Extinct horned rodent land soils (Mollisols, Phaeozems, Chernozems; Phillis (1945) Retallack et al., 2002a), so that grasses were most likely bunch grasses. G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 113

Other paleosols with prominent relict bedding summer. Mesic elements in the Unity flora (Carya, and large woody root traces supported plant Ptelea) are not found in modern Californian live oak formations early in ecological succession after woodlands. These middle Miocene holdover taxa are disturbance. For example, Xaus paleosols of in- evidence that late Miocene dry woodlands of Unity channel sandy bars probably supported riparian were not exactly like Californian vegetation today. woodland, and Cmti and Abiaxi paleosols of levee No taxodiaceous conifers were found near Unity, siltstones probably supported riparian gallery wood- where they would be expected considering charcoal land. Cmti paleosols are thinner, less sodic, and and woody root traces in Monana paleosols. These have more relict bedding than Abiaxi paleosols (Fig. swamp conifers are common in the coeval Stinking- 7), indicating a shorter period of vegetation growth water flora of Juntura (Chaney and Axelrod, 1959) and successional development. Early successional and the Weiser flora of Idaho (Dorf, 1936). marsh ecosystems are represented by carbonaceous Fossil grasses are represented by sheathing leaves clayey paleosols with small root traces and relict near Unity (Table 4) and by abundant pollen in coeval bedding (Skaw pedotype). Swamp ecosystems are rocks of Idaho (Leopold and Wright, 1985). Miocene represented by lignitic paleosols with large woody grasses of the Great Plains and Oregon are unlikely to root traces (Monana pedotype). The swamp paleo- have been floristically similar, given differences sols have impure coals and charcoal and were between fossil dicot floras of Oregon and the Great probably seasonally dry, but there is no comparable Plains (Thomasson, 1979; Graham, 1999; Strfmberg, evidence of seasonal exposure of marsh paleosols, 2002) and differences between sodic–silicic Miocene which may have been associated with perennial paleosols of Oregon (Retallack, 2004) and calcareous watercourses. Miocene paleosols of the Great Plains (Retallack, 1997b, 2001b). A comparable modern vegetation 6.2. Evidence from fossil plants distinction is the western wheat grass (Agropyron spicatum) rangeland province of northern California Only one kind of paleosol contained preserved and the Great Basin, and blue grama (Bouteloua fossil plants: weakly developed paleosols of the gracilis) grasslands of the western Great Plains Skaw pedotype (localities 1–3 of Table 4). The best (Leopold and Denton, 1987). preserved fossil plants were found within laminated diatomites and siltstones (localities 4–7 of Table 4). 6.3. Evidence from fossil animals These are interpreted as leaf litter of marsh soils (Skaw pedotype) and leaves blown into an oligo- Quarry collections from Juntura formed the basis trophic lake, respectively. In all cases, there is a bias for Shotwell’s (1963) pioneering study of Clarendo- toward aquatic plants, such as water chestnut, nian mammalian paleocommunities (Fig. 11), and arrowhead, and horsetail. these quarries were revisited in order to examine Despite these taphonomic limitations, the Stin- their paleosols (Fig. 3). Shotwell’s (1963) bpond kingwater, Weiser, and Unity floras include locally bank communityQ came from Skaw paleosols (the abundant fossil grasses and live oak comparable to only pedotype found), whereas his bsavanna those of summer-dry parts of California today. The communityQ came largely from sandstones immedi- Unity flora is most similar to interior live oak ately overlying a Tutanik paleosol. His bsavanna woodland of Barbour and Major (1988) and canyon communityQ was mainly camels, hipparionine live oak woodland of Sawyer and Keeler-Wolf horses, two-tusker mastodon, and rhinoceros. The (1995). These oak woodlands are at moderate bpond bank communityQ, which from paleosol and elevation below the zone of abundant conifers on sedimentological evidence appears more likely to the southwestern slopes of the Sierra Nevada have been riparian woodland, was mainly fish and flanking the northern California Great Valley. The turtles, but also had many beavers, as well as rabbits oak trees are largely evergreen and up to 15 m high and a variety of rodents and insectivores (Table 5). in both closed and open formation. Their grassy The weak development and carbonaceous and understorey is brown and dry for most of the manganiferous composition of Skaw paleosols are 114 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123

bles, or other hard debris (Lambert, 1992). Four- tuskers (Gomphotherium) also show tusk wear from bark stripping and digging, and two-tusk mastodons (Mammut) are known from Pleistocene stomach contents to have eaten conifer needles, cones, and grass (Lambert and Shoshani, 1998). Associated paleosols are Abiaxi for Gomphotherium, Tutanik for Mammut, and probably Skaw for cf. Platybelo- don (uncertainty comes from poor exposure and inexact location). The inferred paleoenvironments of these paleosols (Table 3) cannot be claimed to represent habitat preferences based on only one or two specimens of each species. Paleosols also support the idea that late Miocene rangelands of the Pacific Northwest were distinct from those of the Great Plains (Leopold and Denton, 1987). Late Miocene summer-dry siliceous alfisol and aridisol Fig. 11. Specimen numbers of fossil mammals of Clarendonian bsavannaQ and bpond bankQ communities by Shotwell (1963), from paleosols of Oregon (Retallack et al., 2002a) can be quarries of Fig. 3. Numerous fish and turtle bones from locality contrasted with summer-wet Mollisols of Nebraska 2337 are not included in these figures. and Montana (Retallack, 1997b, 2001b). The hippar- ionine province of the Pacific Northwest was distinct evidence of seasonally inundated streamside swales from a Pliohippus province of southern California and (Table 2), where fish were trapped and devoured by the Great Plains during the Clarendonian (Shotwell, predators. 1963). Late Miocene (7 Ma) grazing Pliohippus in Contrary to Shotwell (1963), Bernor et al. (1988) Oregon appeared in calcareous Mollisol paleosols concluded that coeval late Miocene (11 Ma) reflecting an incursion of summer-wet Gulf Coast air hipparionine horses of Austria were forest browsers, masses into eastern Oregon at that time (7.3 Ma; because forest leaves were found in associated lake Retallack et al., 2002a). The tridactyl mixed-feeding beds. This view is not supported by the abundance hipparionines may reflect rigors of summer-dry range- of hipparionines in Tutanik paleosols and rarity in land vegetation botanically and structurally distinct Skaw paleosols of Juntura and Unity (Fig. 11). from summer-wet rangeland of monodactyl grazing Later studies of hipparionine tooth wear (Hayek et Pliohippus. Comparable differences in vegetation and al., 1992) and associated mammalian fauna (Webb, seasonality may also explain the numerical dominance 1983) also support Shotwell’s (1963) conclusion that of foregut-fermenting ruminant camels over hindgut- hipparionines were grassland and grassy woodland fermenting horses at Juntura (Fig. 11) and other mixed feeders. Open grassy terrane was also western Clarendonian faunas (Tedford and Barghoorn, required by an extinct species of Old World vulture 1993), whereas horses dominated Clarendonian from Juntura (Table 5). assemblages of Nebraska and Texas (Webb, 1983). Proboscideans are now associated with mosaics of Muzzle morphology of the camels Procamelus and grassy and woody vegetation, which they maintain Megatylopus has been taken to indicate that they were by destructive feeding (Owen-Smith, 1988). A browsers, perhaps mixed feeders, but not grazers diversity of proboscidean habitats may be expected (Dompierre and Churcher, 1996). Similar dominance from the high diversity of Clarendonian probosci- of ruminants over perissodactyls is found in Kenyan deans, including eight genera in North America and (Retallack et al., 2002b) and Greek (Solounias, 1981) three in the Unity and Juntura faunas (Tables 4–5). Miocene faunas. By reprocessing their cud, ruminants Shovel-tuskers (Platybelodon) are commonly por- are sustained by less-nutritious forage than perisso- trayed as aquatic shovelers, although tusk wear dactyls of comparable body sizes (Janis et al., 1994). patterns indicate scraping against bark, twigs, peb- Summer-dry seasons in Kenya, Greece, and western G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 115

North America selected for ruminant-dominated fau- The resulting curve shows great variation in both nas able to cope with seasonal shortages of forage, precipitation (Fig. 12A–B) and temperature (Fig. 12C) whereas equid-dominated faunas of the Great Plains through time and is comparable with variation in and Gulf Coast were supported by year-round forage. carbon isotopic composition of benthic marine fora- minifera (Fig. 12F). Also comparable are time series of North American mammalian diversity, which was 7. Implications for global change

7.1. Neogene paleoclimate in eastern Oregon

A detailed Neogene paleoclimatic time series (Fig. 12A–C) can be constructed by extending the results from paleosols presented here to other paleosols, including paleosols from the early Miocene upper John Day Formation near Kimberly, Oregon (Retal- lack, 2004) dated by extrapolation from 40Ar/39Ar radiometry (Fremd et al., 1994), the middle Miocene Mascall Formation and Columbia River Basalts near Dayville, Oregon (Bestland and Krull, 1997; Sheldon, 2003) dated by magnetostratigraphy and radiometry (Draus and Prothero, 2002), the latest Miocene Rattlesnake Formation near Dayville, Oregon (Retal- lack et al., 2002a) dated by magnetostratigraphy (Hoffman and Prothero, 2002), the Mio–Pliocene Ringold Formation near Pasco and Taunton, Wash- ington (Gustafson, 1978; Smith et al., 2000) dated by magnetostratigraphy (Gustafson, 1985; Morgan and Morgan, 1995), and the Palouse Loess near Helix, Oregon, and Washtucna, Washington dated by mag- netostratigraphy, tephrochronology, and thermolumi- nescence dating (Busacca, 1989, 1991; Tate, 1998; Blinnikov et al., 2002).

Fig. 12. Miocene paleoclimate of eastern Oregon follows the oceanic foraminiferal carbon isotopic record but not the oceanic oxygen isotopic record nor the record of volcanism in Oregon: (A) mean annual precipitation from depth to Bk horizon of 799 paleosols (heavy line and 1r error envelope): (B) mean annual precipitation from chemical composition of 97 paleosol Bt horizons (heavy line and 1r error envelope); (C) mean annual temperature from chemical composition of paleosols (heavy line and 1j error envelope): (D) frequency of lavas erupted from Cascades volcanoes 18 (from McBirney et al., 1974); (E) oxygen isotopic data (y Oapatite) from fossil horse teeth in Oregon and Nebraska (Kohn et al., 2002; 18 Passy et al., 2002); (F) oxygen isotopic (y Ocarb) and carbon 13 isotopic values (y Ccarb) of 8959 samples of marine foraminifera from deep-sea cores (from Zachos et al., 2001). Abbreviations are Geringian (G.), Monroecreekian (MO.), Harrisonian (HA.), Hemi- ngfordian (HEMI.), Barstovian (BAR.), Clarendonian (CLAR.), Hemphillian (HEM.), and Blancan (BLA.). Most recent Irvingto- nian and Rancholabrean are unlabelled. 116 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 higher during warmer and wetter times than during A possible reason for mismatch of marine oxygen cooler and drier times (Alroy et al., 2000; Janis, 2002). and continental paleoclimatic records is the Cenozoic evolution of C4 photosynthetic pathways in land 7.2. Mismatch of Neogene terrestrial and marine plants. The C4 (Hatch–Slack) pathways of tropical oxygen isotopic records grasses result in isotopically heavier plant carbon than C3 (Calvin–Benson) pathways (Cerling et al., 1997), Neither paleoclimatic fluctuations from paleosols and this pathway increases oxygen isotopic values of (Fig. 12A–C) nor oxygen isotopic fluctuations from plant as well because operating on CO2 (Farquhar et mammal teeth (Fig. 12E) correspond with fluctua- al., 1993). The antiquity of the C4 pathway has been tions in oxygen isotopic composition of benthic estimated from phylogenetic analyses at 25 Ma marine foraminifera (Fig. 12F). Marine and terrestrial (Kellogg, 1999), from isotopic analyses of paleosols carbonate oxygen isotopic records do not correspond at 15 Ma (Kingston et al., 1994; Morgan et al., 1994), during the late Paleocene (Koch et al., 2003) or late and from isotopic and anatomical studies of permin- Permian (MacLeod et al., 2000) either. Although eralized fossil grasses at 12.5 Ma (Nambudiri et al., marine oxygen isotopic records have been regarded 1978; age revised by Whistler and Burbank, 1992). as a global paleoclimatic standard (Zachos et al., Isotopic studies of paleosol carbonate and mammalian 2001), their mismatch with continental records is a teeth show that C4 grasses became widespread in the fundamental problem for global change studies. southern Great Plains after 6.6 Ma but were never The mismatch between North American mamma- common in Oregon or the northern Great Plains lian evolutionary dynamics and marine oxygen iso- (Cerling et al., 1997; Passy et al., 2002; Fox and topic records has been discussed at length by Alroy et Koch, 2003). C4 grasses avoid cool and summer-dry al. (2000), who attribute the mismatch to biotic climates today (Sage et al., 1999). The spread of C4 insensitivity to climatic forcing. This is contrary to grasses after 6.6 Ma is too late to explain the earlier the observation of iterative evolution of mammal divergences of marine carbon and oxygen isotopic ecomorphs within North American land mammal records (Fig. 12F), mismatch of marine and terrestrial bagesQ which average 2.3 Myr in duration (Martin, oxygen isotopic records (Fig. 12A–C,F), and the 1994; Meehan and Martin, 1994; Meehan, 1996, generally upward trend of marine oxygen isotopic 1999). The sediments of each mammal age in the values (Fig. 12F). Great Plains are bounded at the base by erosional A more likely explanation for mismatch of the downcutting, interpreted as evidence of a wet climatic oceanic oxygen isotopic and continental paleocli- phase, and terminated by shallow calcic paleosols or a matic proxies is isotopic depletion as rain shadows caprock caliche, interpreted as evidence of a dry spread and intensified with uplift of the Cascade climatic phase (Schultz and Stout, 1980). I have made volcanic and other western mountain ranges (Kohn comparable observations in Montana and Oregon et al., 2002). The idea of Cenozoic drying by means (Retallack, 1997b, 2001a; Retallack et al., 2002a). of an orographic rain shadow has been a traditional Late Oligocene mammalian communities of Oregon explanation for pronounced Neogene aridity evident also show alternation between sagebrush steppe with from fossil plants (Chaney, 1948; Ashwill, 1983). Hypertragulus and wooded grassland communities The growth of the Oregon Cascades can be inferred with Nanotragulus on Milankovitch time scales (41– from numerous radiometrically dated eruptions (Fig. 100 ka) within paleosols with differing depth to calcic 12D; McBirney et al., 1974; Priest, 1990), but this horizons reflecting alternating semiarid and subhumid does not match either marine or continental records paleoclimates (Retallack, 2004; Retallack et al., 2004). (Fig. 12A–F). The Cascade and Klamath Mountain Finally, there is annual variation in oxygen isotopic rain shadow has been important in creating generally composition of growth bands within Miocene mam- dry long-term climate in eastern Oregon since the malian tooth enamel (Fox, 2001; Kohn et al., 2002). late Oligocene (30 Ma; Retallack et al., 2000). North American mammals show clear sensitivity to Rocky Mountain barriers isolated eastern Oregon climate on time scales ranging from evolutionary to from Gulf Coast cyclonic circulation since at least ecological contrary to Alroy et al. (2000). early Miocene (19 Ma), as indicated by the G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 117 appearance of sodic–silicic rather than calcic paleo- of biomass. A middle Miocene high in atmospheric sols (Retallack, 2004) and very different oxygen CO2 has been confirmed by stomatal index estimates isotopic composition of fossil horse teeth in Oregon of atmospheric CO2 (Ku¨rschner et al., 1996; Retallack, and Nebraska (Fig. 12E). Fossil floras from the 2001c, 2002). Oceanic proxies of atmospheric CO2 do northern Great Basin indicate high altitudes since at not show such variation (Pagani et al., 1999; Pearson least the early Miocene, for example, 2100 m for the and Palmer, 2000) but may be compromised by middle Miocene 49 Camp flora of northwestern volatility of isotopic composition and runoff (Retal- Nevada (Wolfe et al., 1997). Eastern Oregon was lack, 2002). Despite these problems, a useful working elevated during Miocene initial eruptions of the hypothesis is control of paleoclimate by a varying Yellowstone hot spot (Humphreys et al., 2000). greenhouse effect from changing atmospheric con- The most important reason for a mismatch of centrations of CO2. oceanic and continental records is isotopic enrichment Plausible mechanisms for transient climatic warm- of oceanic oxygen by growth of isotopically depleted ing include impact, volcanism (Coutillot, 2002) and polar ice caps, which has long been recognized to methane clathrate release (Kennett et al., 2002). There compromise direct paleotemperature interpretation of are numerous large (N10 km diameter) Neogene marine oxygen isotopic values (Zachos et al., 2001). craters: Haughton, Canada (24 km, 23F1 Ma), Ries, This factor is not unrelated to the growth of mountains Germany (24 km, 15F0.1 Ma), Karla, Russia (10 km, with their expanding rain shadows, because montane 5F1 Ma), ElTgygytygn, Russia (18 km, 3.5F0.5 Ma), ice caps enrich the isotopic composition of atmos- Bosumtwi, Ghana (10.5 km, 1.03F0.02 Ma), and pheric oxygen as well. Ice cap fluctuation in volume Zhamanshin, Kazachstan (14 km, 0.9F0.1 Ma; introduces a highly variable bias into paleotemper- Dressler and Reimold, 2001; website http:// ature interpreted from the oxygen isotopic record of www.unb.ca/passc/impactdatabase accessed Jan. 10, marine benthic foraminifera. This bias can be cor- 2003). Time series of volcanic eruptions are also rected using independent estimates of paleotemper- strongly episodic (McBirney et al., 1974), with some ature from Mg/Ca ratios of foraminifera (Lear et al., exceptionally large eruptions, such as the middle 2000), but this is compromised by dissolution and Miocene Columbia River flood basalts of Oregon other forms of diagenesis (de Villiers, 2003), and by (Wignall, 2001). Columbia River Basalts and Ries crustal recycling and other long-term influences on Crater impact may have been involved in the middle ocean chemistry (Veizer et al., 2000). Miocene peak of global warmth, but why was there not a comparable warm spike after the 23-Ma 7.3. Neogene greenhouse–icehouse fluctuation and its Haughton Crater or a better correlation between causes North American paleoclimate and Cordilleran volcan- ism (Fig. 12D). Because of methane’s distinctively Greenhouse mechanisms for Neogene paleocli- low carbon isotopic values, such methane outbursts matic variation are suggested by correspondence of are suspected when carbon isotopic compositions fall the Oregon paleosol sequence (Fig. 12A–C) with the by more than 4x (Jahren et al., 2001). There are no marine signal of carbon sequestration inferred from negative excursions of this magnitude in Neogene benthic foraminiferal y13C decrease and carbon oxi- carbon isotopic records (Fig. 12F), thus methane is dation inferred from benthic foraminiferal y13C unlikely to be the whole explanation either. increase (Fig. 12F). High carbon isotopic values in A counterpoint to transient carbon-oxidizing events the middle Miocene ocean correspond to warm-wet was progressive long-term Neogene global cooling, conditions in Oregon, whereas low carbon isotopic perhaps related to changing oceanic current config- values in the Plio–Pleistocene ocean corresponded to uration (Broecker, 1997), mountain uplift (Raymo and cool-dry conditions in Oregon. High carbon isotopic Ruddiman, 1992), or biotic intensification of weath- values in marine foraminifera reflect diminished burial ering with sod–grassland coevolution (Retallack, of chemically reduced carbon and higher atmospheric 2001a). Both mountain uplift and increased oceanic CO2 levels due to some combination of oceanic thermohaline circulation create oligotrophic alpine and respiration, volcanic emission, or impact destruction polar marine communities, with less carbon sequestra- 118 G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 tion potential, but grasslands provided more organic by plants and animals. Such reciprocating coevolution and nutrient-rich runoff to oceanic phytoplankton is apparent from current estimates of the times for (Retallack, 2001b). Grasslands in addition had greater evolution of bunch grassland paleosols (33 Ma), short- amounts of soil carbon, higher albedo, and lower rates sod grassland paleosols (19 Ma), and tall-sod grass- of transpiration than the woodlands and shrublands land paleosols (7.3 Ma; Retallack, 1997b, 2001b, they replaced in subhumid to semiarid regions of the 2004; Retallack et al., 2002a), which alternate with world (Nepstad et al., 1994; Jackson et al., 2002), and evolution of horse tridactly (36 Ma), cursoriality (25 this also could have contributed to global drying and Ma), hypsodonty and springing gait (17 Ma), mono- cooling (Retallack, 2001b). This mechanism of global dactyly, wide muzzles, and knee-locking (12 Ma), and change is biological, because it is driven by coevolu- large size and passive-stay shoulder (5 Ma; MacFad- tion of grasses and grazers, with crumb-textured, den, 1992; Janis and Wilheim, 1993; Hermanson and organic, fertile soils nourishing hypsodont ungulates MacFadden, 1992, 1996). This schedule is compatible capable of withstanding abrasion from dusty, siliceous with a coevolutionary process long envisioned for grasses (Retallack, 2001a). The progressive evolution grassland ecosystems (Jacobs et al., 1999). Global and spread of crumb-textured soils, siliceous grasses, change involves more than just impact or volcanic and hypsodont ungulates proceeded against a backdrop forcing, but a complex interplay of factors for which of volatile climatic change, and both short-sod and tall- detailed proxies are now becoming available (Fig. 12). sod grassland paleosols appearing at times of relatively These various records will have to become even more high temperature and humidity (Fig. 12A). Grasslands detailed before answers become clear. did not merely fill in dry times and places (Kohn et al., 2002) but were a biological force for climatic cooling and drying in their own right (Retallack, 2001b). Acknowledgements Paleoclimatic warm spikes due to volcanism, bolide impact, and methane clathrate release may also have For introduction to the fossils of this area, I been exacerbated by newly coevolved Cenozoic thank Ted Fremd and his collecting crew, Scott grasslands, because ruminants liberate CO2 and CH4. Foss, Lia Vella, Delda Findieson, Alois Pajak, The middle Miocene thermal optimum was a time of Daniella Gould, Matthew, and La Rue Rogers. Kent unusually high diversity of North American plants and Nelson allowed access to his land near Hereford. mammals, in part due to evolution within high- Mary Oman of the Baker City Bureau of Land productivity grassland–woodland mosaics in a warm- Management helped with geological reconnaissance, wet CO2 greenhouse (Janis, 2002), and in part due to funding, and research clearance. Megan Smith, Ben immigration from Asia through high-latitude land Cook, and Russell Hunt helped with fieldwork and bridges (Wolfe and Tanai, 1980; Kohno, 1997; fossil collection. Alicia Duncan prepared numerous Lambert and Shoshani, 1998; Webb, 1998). There difficult petrographic thin sections, and Nathan were more grazing mammal species then ever before, Sheldon provided bulk density measurements. and also more browsers than before or after (Janis et al., 2000). The middle Miocene greenhouse peak was preceded and followed by several other episodes of References greenhouse paleoclimate of lesser magnitude, includ- ing early Clarendonian communities described here. Alroy, J., Koch, P.L., Zachos, J.C., 2000. Global climate change and North American mammalian evolution. Paleobiol. Suppl. 26, Warm-wet conditions of greenhouse transients, even if 259–288. initiated by tectonic or impact forcing, would be Ashwill, M., 1983. Seven fossil floras in the rain shadow of the enhanced by increased mammalian diversity and Cascades Mountains. Or. Geol. 45, 107–117. cropping of vegetation. Cold-dry conditions follow Axelrod, D.I., 1985. Miocene floras from the Middlegate Basin, carbon and water sequestration by grassland soils, their west-central Nevada. Univ. Calif. Publ. Geol. Sci. 129 (279 pp.). Axelrod, D.I., 1995. The Miocene Purple Mountain Flora of high albedo and burial of carbon-rich grassland soil western Nevada. Univ. Calif. Publ. Geol. Sci. 139 (62 pp.). crumbs. Paleoclimatic cycles on million-year time Baldwin, E.M., 1964. Geology of Oregon. Cooperative Book Store, scales could reflect alternating evolutionary advances Eugene. 165 pp. G.J. Retallack / Palaeogeography, Palaeoclimatology, Palaeoecology 214 (2004) 97–123 119

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