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Home , Cedar Mesa Sandstone, Cutler Formation, Group (stratigraphy), Kaibab Limestone, Mesa, Organ Rock Formation

FLORAS FROM THE - CUTLER OF SOUTHEASTERN by William A. DiMichele1*, C. Blaine Cecil2, Dan S. Chaney1, Scott D. Elrick3, and W. John Nelson3

ABSTRACT

Fossil plants have been collected and described from strata near the Pennsylvanian-Permian boundary in three areas of San Juan County, Utah. Collections made near Indian Creek east of Canyonlands National Park comprise mainly tree fern foliage and sphenopsids from one stratigraphic level, and large logs of conifers with rare conifer foliage from a higher level. A site on Lime west of Bluff, Utah, yielded abundant large branches of walchian conifers together with calamitaleans and cordaitalean foliage. Sites in Valley of the Gods State Park, west of Lime Ridge, produced mainly stems, with variable occurrences of foliage. Most of the stems are calamitalean or the large tree fern Caulopteris, but a single medullosan pteridosperm specimen also was found, as were several small fragments of the lycopsid Sigillaria. Tree fern foliage, Pecopteris, rare neuropterid foliage, and fragments of leaf- bearing conifer branches also were identified. Thus, our collections contain a mixture of plants adapted to season- ally dry conditions (conifers and possibly cordaitaleans) and those requiring wet substrates (calamitaleans, tree ferns, lycopsids and pteridosperms). , , loess, and gypsum indicate aridity, on average, but with intervals of more humid conditions. The combination implies an arid eolian depositional system traversed at times by streams sourced on the Uncompahgre highland.

INTRODUCTION in San Juan County, Utah, from approximately the Penn- sylvanian-Permian boundary. These floras are of inter- Floras of the Pennsylvanian-Permian transition are est for several reasons. Perhaps most importantly is their broadly represented across the equatorial regions of the paleogeographic position, in far western Pangea. Based on supercontinent of Pangea (e.g., Kerp and Fichter, 1985; sedimentary patterns and studies of paleosols, this area ex- Tidwell, 1988; Hunt and Lucas, 1992; Blake and others, perienced extreme aridity through most of the later Penn- 2002; Roscher and Schneider, 2006; Wagner and Álvarez- sylvanian, but apparently experienced a return of sufficient Vázquez, 2010; Blake and Gillespie, 2011; Lupia and Ar- moisture during latest Pennsylvanian and earliest Permian mitage, 2013; Opluštil and others, 2013; Tabor and others, to dramatically alter the regional environments before arid 2013; Wang and Pfefferkorn, 2013). The content of these conditions returned (Soreghan and others, 2002; Tabor and floras is similar, especially in the Euramerican areas, which Poulsen, 2008; Jordan and Mountney, 2012). The period stretch from the present-day western through of resurgent moisture was wet enough to support some Eastern (figure 1). Many taxa typical of Eurameri- species typically found in wetland floras of the same age, can floras also occur in Chinese/Cathaysian assemblages in the more central parts of the Pangean supercontinent. (Hilton and Cleal, 2007). On average, these floras reflect The floras found in San Juan County are mixed, including the long-term, multi-million-year trend of increasing arid- species typical of seasonally dry environments as well as ity that characterized much of the Pangean tropics begin- the wetland taxa. Mixed assemblages strongly suggest an ning in the late Middle Pennsylvanian (Cecil, 1990), par- overall landscape of seasonal moisture limitation, within ticularly in the central and western areas. However, the which the wetland taxa were confined to parts of the land- floras also reveal a considerable amount of spatio-temporal scape with high-water tables, such as the margins of rivers variability in expression of this trend. In western Pangea and streams or low-lying parts of floodplains. Such places in particular, especially in areas some distance north of the are also the most favorable for preservation, thus making equator, the long-term aridification trend may have been the wetland plants “more apparent” than might be expected reversed in the short term by a limited period of increased were the fossil flora drawn proportionally from all habitats moisture input around the Pennsylvanian-Permian bound- on the landscape of the time. It is difficult to account for ary (Tidwell, 1988; Soreghan and others, 2002). the presence of taxa adapted to periodically dry substrates This article describes fossil plants from three areas within overall wetland landscapes characterized by humid

1Department of Paleobiology, National Museum of Natural History, Smithsonian DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelson, W.J., 2014, Institution, Washington, DC Fossil floras from the Pennsylvanian-Permian Cutler Group of southeastern 2U.S. Geological Survey National Center, 12201 Sunrise Valley Drive, Reston, VA Utah, in MacLean, J.S., Biek, R.F., and Huntoon, J.E., editors, of 3Illinois State Geological Survey, University of Illinois, IL Utah’s Far South: Utah Geological Association Publication 43, p. 491–504. *Corresponding author; [email protected] 492 FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. outstripped subsidence. During the Pennsylvanian-Permi the During subsidence. outstripped sedimentation and down winding was tectonism time, ian Pennsylvan- Late By basin. land-locked nearly the in lated accumu places, in thick kilometers 2 than more strata, tic Pennsylvanian, when cyclic carbonate, , and clas Middle the during commenced Development zone. fault major a by northeast the to Uplift Uncompahgre the from separated 2003) (Barbeau, basin flexural intraforeland a is Basin Paradox The 2). (figure Utah southeastern and rado Colo southwestern of much underlies that feature an-age the southwestern part of the , a Pennsylvani macroflora hasbeenidentified(orpreserved). no where areas in even vegetation, widespread for dence evi note we addition, In Creek. Indian of northeast area Moab the from (1988) Tidwell by described flora served better-pre and richer a complement ferns, tree rattialean predominantly of walchian conifers, calamitaleans and ma the of Valley composed 2).floras, (figure These Creek Indian and Gods, Ridge, Lime Utah: County, Juan San day corridors—as inthewesternUnitedStatestoday. permit wetland-plant survival in isolated patches or narrow wise seasonally dry backgrounds, are commonly found and other within areas, wetter localized contrast, in climates; sylvanian toPermian.Studyareamarkedbywhitecircle.MapcourtesyofRonBlakey 1. Figure The localities discussed in this paper are situated in situated are paper this in discussed localities The inpresent areas three from floras report we Herein Paleogeographic reconstruction of Pangea and major oceanic areas at the approximate time of the transition from the Penn the from transition the of time approximate the at areas oceanic major and Pangea of reconstruction Paleogeographic Tectonic Setting GEOLOGY ------Snake Canyon at Lime Ridge, southern San Juan County, Juan San southern Ridge, Lime at Canyon Snake Lime Ridgeand Valley oftheGods tally distinctstrata. environmen often various, the through drawn been have floras highlight some ambiguities in the way time horizons a on large intertongue scale (figure 2). As discussed briefly below, the fossil and transgressive time are boundaries have been assigned to the Cutler Group or Formation. Unit that beds red of entirely consists succession boundary,the systemic the to Proximal rocks. transitional the to mations for Canyon Elephant and Rico, Trail,Honaker names the Varioustime. applied through authors increasing latter the gray marine and red terrestrial siliciclastics, with of layers alternating to way gave gradually strata marine dominantly time Pennsylvanian Late the during speaking, and others (2002) and Huntoon and others (2002). Broadly position is beyond the scope of this paper, but see Soreghan complex, and some aspects remain controversial. A full ex is Basin Paradox the in rocks Permian earliest and vanian others, 2002). and Soreghan 1996; others, and Dubiel 1981; Stevenson, and (Baars subhumid to arid from fluctuated that regime climatic a under sedimentation marine restricted and lian, eo fluvial, of site the became area study the transition, an Our collections from Valleycollections of Our north and Gods the of Pennsyl latest to applied nomenclature Stratigraphic UGA Publication 43(2014) , ColoradoPlateauGeosystems,Inc. —Geology of Utah'sFar South ------FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH –

Figure 2. Stratigraphic terminology used and geographic location of samples discussed and in this paper. IC = Indian Creek, LR = Lime Ridge, SH = Setting Hen, SS = Seven Sailors. DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. are from the Halgaito Formation (figures 2 and 3). In Valley forming that is light colored, fine grained, and of the Gods, the Halgaito and overlying - exhibits giant-scale cross-bedding. Within a few kilometers stone have eroded to pinnacles and that have been eastward, the changes to interbed- given fanciful names such as Santa Claus and Rudolph, De ded sandstone, mudstone, siltstone, gypsum, and thin lay- Gaulle and His Troops, and Rooster . These natural ers of cherty limestone. A measured section through the sculptures are reminiscent of those in the better-known Cedar Mesa Sandstone at Lime Ridge is 257 to 278 meters to the south in , but there the pin- thick, depending on the choice of upper contact. nacles are carved from the younger Organ Formation The age of the Halgaito Formation is loosely con- and De Chelly Sandstone. strained. According to Vaughn (1962), its point Variously classified as a formation, member, or tongue to Wolfcampian (early Permian) age. of the Cutler Group or Formation (Baker and Reeside, from the uppermost Rico limestone beds favor a Late Penn- 1929; O’Sullivan, 1965; Dubiel and others, 1996), the Hal- sylvanian age, but an earliest Permian age cannot be ruled gaito is 70-120 meters thick and consists of predominantly out (O’Sullivan, 1965). red mudstone, siltstone, sandstone, and minor conglomer- A Halgaito section measured north of Snake Canyon ate (figure 3). Below the Halgaito is the Rico Formation, a at Lime Ridge (figures 3 and 4.1) is 76 meters thick and unit of terrestrial red beds alternating with thin but wide- contains about 50% sandstone that is light gray to medium spread layers of fossiliferous marine limestone. The Rico- reddish brown, very fine to fine grained, and calcareous. Halgaito contact is time transgressive. Above the Halgaito Low-angle cross-bedding and ripple marks are common, as is the Cedar Mesa Sandstone, which undergoes a marked are shallow channels. Other features include mud cracks, facies change between Valley of the Gods and Lime Ridge. indistinct burrows and root traces, and zones of carbon- In the type area north of Valley of the Gods, the Cedar ate nodules (pedogenic?). Most sandstone apparently rep- Mesa Sandstone is predominantly an eolian facies of cliff- resents deposits of small streams, which is where plant

MacLean, J.S., Biek, R.F., and Huntoon, J.E., editors 493 494 FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. above the base of the Halgaito, and thus are in the same the in are thus and Halgaito, the of base the above meters 25 and 20 between occur sites three all determine, can we best ValleyGods. in As the Butte of Sailors Seven near (3) Valleyin and Butte Gods, Hen the Setting of near (2) 163, Highway U.S. along Ridge Lime of flank east the are rareconstituents. intraformational of lenses and thick timeters cen 20 than less limestone micritic silty, of Beds (loess). deposits eolian as formed have may Halgaito, the of base the near bed orange prominent a especially siltstone, sive mas of Beds development. soil weak of bur suggestive rows, and roots indistinct and structure blocky have beds Some mottling. gray with brown to red largely siltstone, and mudstone of intervals are beds sandstone Separating silt. and sand wind-blown of accumulations represent may beds massive few a but 4.2), (figure preserved are fossils (Valley oftheGods)andCedarPoint.Scaleinmeters. Figure 3. We collected fossil plants from the Halgaito: (1) on (1) Halgaito: the from plants fossil collected We Measured lithological sections from the east flank of Lime Ridge (Highway 163, just north of Snake Canyon), Setting Hen Butte - - - ers, 2013). oth and (Chaney Ridge Lime at collected was myriapod, channel-lag deposits. in preservation their given established be cannot remains these of deposition of environment original the Butte; Sailors Seven near channel a of conglomerate basal the in occur fragments bone unidentified and teeth Shark 5.1-5.3). and 3, 2, (figures Butte Sailors Seven and Butte Hen Setting both at identified complex sandstone-filled channel or channel trending, southwest same the to belong Ridge Lime at deposits channel the that however, lished, estab be cannot It wide. meters 20 to 10 and deep so or meter a each channels, shallow crosscutting of a in arranged is It preservation. fossil bedding enhance which surfaces, along drapes clay having sometimes sandstone medium-bedded to thin- fine-grained, is cases all in rock plant-bearing interval of small channels (figure 3). The host UGA Publication 43(2014) Diplichnities —Geology of Utah'sFar South , the trackway of a giant - - FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J.

Figure 4. East flank of Lime Ridge. 1. General view of the fossil-bearing channel deposit, from which plant collections (USNM locality 43579) were made, forming the low ridge in the lower portion of the outcrop (white arrow). 2. Detail of fossiliferous channel sediments, comprising a trough-shaped sandstone-filled scour. 3. Cordaites sp. foliage. USNM559863. 4. Annularia sp. USNM559862. 5. Walchia sp. Mat of branches, including a branch base (center left). Pencil barrel for scale in upper right corner. USNM559864. 6. Walchia sp. Ultimate branchlet. Field photograph.

Indian Creek cross-bedded of possible eolian origin (figures 6.1-6.4). The plant-bearing deposits appear to constitute a Indian Creek is a northwest-flowing tributary of the floodplain sequence. River in northern San Juan County. Our collec- Based on mapped elevation change and structural dip tions were made near the stream approximately 19 kilom- of 2° to the northeast, the Cedar Mesa Sandstone is approx- eters northeast of the junction of the Green and Colorado Rivers (figure 2). imately 120 meters thick in the collecting area. This unit is Plant fossils occur in rocks that Huntoon and others composed of sandstone, siltstone, and mudstone in various (1982) mapped as “undivided Cutler-Cedar Mesa Sand- shades of red. The lower half of the formation is roughly stone transition.” For brevity, we refer to this unit as the 90% sandstone in beds as thick as 20 meters, which erode Cedar Mesa Sandstone. Most of our collections came to a series of joint-bounded buttes and monoliths. Most of from the basal 10 meters of the Cedar Mesa Sandstone, the sandstone is light colored, fine grained, well sorted, and but two collections of mineralized logs were made 20 to exhibits cross-bedding in sets many meters thick. Inter- 30 meters above the base. Plant compression fossils occur preted as eolian , these strata locally contain gypsum in thin-bedded siltstones, which fill scours and are inter- crystal casts, formed in interdune , and logs of calated with thin, trough-shaped beds of sandstone. These silicified wood. Other sandstone in the lower Cedar Mesa lie immediately above rooted, calcic Vertisols and below Sandstone is deeper reddish brown and displays low-angle

MacLean, J.S., Biek, R.F., and Huntoon, J.E., editors 495 496 FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. = 1centimeter. Fieldphotograph. 8. photograph. Field stem. the of part lower the in present 6. photograph. Field arrow.white by marked base Viewchannel, Butte. fossiliferous Hen of Setting 4. which from sandstone Tabular,planar-laminated Butte. Hen Setting 2. ledge. resistant as right the 5. Figure Valley of the Gods. 1. Seven Sailors Butte. Fossiliferous channel edge marked by white arrow. Channel deposits extend to extend deposits Channel arrow. white by marked edge channel Fossiliferous Butte. Sailors Seven 1. Gods. the of Valley Caulopteris sp. USNM559861. 7. Medullosan pteridosperm stem with reflexed leaf petiole; a less obvious petiole is petiole obvious less a petiole; leaf reflexed with stem pteridosperm Medullosan 7. USNM559861. sp. Sigillaria brardii Sigillaria . Scale = 1 centimeter.1 9. = photograph. Scale Field . Calamites gigas Calamites UGA Publication 43(2014) . Field photograph. 5. photograph. Field . Walchia —Geology of Utah'sFar South sp. (5.9) was collected. 3. collected. was (5.9) sp. Walchia Calamites gigas Calamites sp. Scale sp. . FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J.

Figure 6. Indian Creek. 1. Collecting area USNM locality 43582. Collections made in left side of area. 2. Collecting site USNM locality 43582, closeup. 3. Collecting area USNM locality 43577. 4. Collecting site locality 43577, closeup. Plants come from clayey im- mediately below the sandstone ledge. 5. Pecopteris sp., showing three pinnae. USNM559865. 6. Pecopteris sp. Closeup of central pinna illustrated in 6.5. 7. Fertile pecopterid, Asterotheca sp., pinna fragment. USNM559866. Scale bars in 5-7 = 1 centimeter.

MacLean, J.S., Biek, R.F., and Huntoon, J.E., editors 497 498 FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. n a woe aea bac sses smtms densely sometimes systems, branch lateral whole as and branches of fragments as occur Walchianspecimens 4.6). 4.3- (figures foliage cordaitalean rare and foliage, cluding but in calamitaleans, of component significant a contains also conifers, walchian by dominated is site Ridge Lime cal Collections,underthefollowinglocalitynumbers: the U.S. National Museum of Natural History, Paleobotani rial Pangeaduringthistime. equato western of climate and landscape the into insights valuable yield they “trophies”, museum-quality are fossils these of none Although existed. it which in landscape the about implications and preservation, of type abundance, in varies floras our of component floral dry seasonally phic, 2012; Jordan and Mountney, 2012). others, The typically and xeromor Dubois 2010; others, and Sur 2008; Poulsen, others, 2008; and (e.g.,Langford Tabor and gea, exemplified by extensive deposits of loess, dune sands Pan western of areas large over early aridity climatic and Permian Pennsylvanian Late of evidence abundant the with contrasts finding This element. wetland distinct a ing and Valley oftheGods. Ridge Lime from those than younger are likely and mian, Per definitely are Sandstone Mesa Cedar basal the from plants fossil basis, this 1990; Verville,On and 1990). Sanderson others, and (Loope fusulinids Wolfcampian early Virgilianboth and yields and Formation Halgaito the with southward intertongues Canyon Elephant is the as evidently younger, but Formation, Rico the resembles Canyon Elephant The 1982). others, and (Huntoon limestone est per contact is drawn at the top of the stratigraphically high able beds of marine limestone (Baars, 1962, 1991). The up of terrestrial red beds alternating with thin but widely consists trace which Formation, Canyon Elephant the is Creek iage andstems. fol- fossil yielded have siltstone and shale to bedded thinly laminated of deposits Locally, non-fossiliferous. and non-fissile, brown, reddish dark also is siltstone and stone tic of fluvial channels. Less resistant to , most mud characteris features cut-and-fill with along cross-bedding 5. 4. 3. 2. 1. The flora from the shallow-channel complex atthe complex shallow-channel the from flora The in housed are paper this in described collections All Floras from all three sites are noteworthy for contain Indian at Sandstone Mesa Cedar the Underlying Indian Indian Creek upper level—41413, 41420, 43578 43577, 43582 Indian Creek lower level—41414-41419, 41652, Seven Sailors Butte—43583-43686 Hen Butte—43580-43581Setting Ridge—43579Lime FOSSIL FLORAS Lime Ridge ------Cordaitaleans, in contrast to both walchian conifers and ca of otherwisedrylandscapes (DiMichele and others,2006). tive rivers, and to have been able to grow in the wetter parts ly shifting substrates (Gastaldo, 1992), including within ac described here, appear to have been able to colonize rapid and many of the species, such as those however,found in complex, the deposits is group The moisture. soil high with habitats preferring as confidently regarded be can taleans calami years, 150 past the over Euramerica across observations from of thousands of basis the On level. species the to identified be cannot again, but, tips pointed bluntly age shows characteristic strap-shaped, elongate leaves with resemble leaves of specific for large number and whorls foliage ovoid their preserved identification, enough well not are Although fossils common. these are foliage, attached with branches large including fossils, Calamitalean 2003). Dulong, and Cecil (sensu climates semiarid to subhumid dry likely ly most 2014), others, and Bashforth 2005; Bashforth, and (Falcon-Lang aridity seasonal of indicators environmental physical with closely correlate Walchians surfaces. ding bed many on site the throughout present are matted. They from Valley of the Gods. Most significant are a few speci few a are significant Most Valleyfrom Gods. the of possible pteridosperm affinitywerefound. of specimens preserved poorly some though Gods, the of at Valley identified was foliage pteridosperm unequivocal No stems. these of typical be can as marked, weakly are bases leaf attached possibly other of locations the stem); the on lower at hinted is which of one and clearly can seen be which of (one fronds of portions basal attached ent, > 7 centimeters in diameter and is characterized by persist is stem Butte. This Sailors Seven at found was 5.7) (figure pteridosperm medullosan a to attributable stem single A teris would be attributable to stems the rows opposite two in arranged (if the stem around helically arranged 5.6) figure in arrow white of tree marattialean the of ferns, of stems diameter large are Buttes ors 2005). nykh, Sail Seven and Hen Setting at common Also Naugol 1996; Rößler, and Barthel (see stress moisture of conditions under lived have to thought calamitalean eter to belong stems abundant most The foliage. of fragments rare with along sandstone, in casts as preserved (stems) axes large of mostly consist others, 2009;Raymondand2010). and Opluštil 2005; Bashforth, and Falcon-Lang (e.g., eas ar upland to settings peat-forming and wetlands swampy their environmental preferences, growing everywhere from in widespread exceptionally group, a as are, lamitaleans, Caulopteris , tree-fern foliage occur in association with the stems. the with association in occur foliage tree-fern , ml bt o ohr eln pat wr identified were plants wetland other of bits Small 5.4-5.9) (figure Gods the Valleyof from Collections UGA Publication 43(2014) Caulopteris is leaf scars (one of which is marked by a by marked is which of (one scars leaf is Megaphyton Valley oftheGods Annularia carinata Annularia type. The most diagnostic feature diagnostic most type. The Calamites gigas Calamites ). A few fragments of —Geology of Utah'sFar South . Cordaitalean foli Cordaitalean . , a large diam large a , Pecop ------mens of the wetland lycopsid Sigillaria (figure 5.8). These DISCUSSION are most likely S. brardii, effectively the only species of Sigillaria in the Late Pennsylvanian and Permian. Pfeffer- Pennsylvanian-Permian boundary floras from the San korn and Wang (2009) demonstrated that the deeper roots Juan County, Utah region are few in number but signifi- of S. brardii allowed this species to tolerate drought better cant indicators of vegetation in western equatorial Pangea. than the other giant lycopsids. The region was strongly influenced by winds off the Pan- Also identified from Valley of the Gods are afew thalassa to the west, as well as by periodic climatic FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – specimens of walchian conifers (figure 5.9). All poorly pre- and sea-level changes induced by Southern Hemisphere, served, these specimens came from fissile, planar-laminat- high latitude glaciation (reviewed in Tabor and Poulsen, ed sandstone that occupied broad, shallow troughs within a 2008; see also Soreghan and others, 2002; Montañez and channel (figure 5.2). Such occurrences indicate that walchi- others, 2007). In general, floras discussed herein are con- ans were present on the landscape, probably in interfluves sistent with a long-recognized trend toward increasing where moisture deficits would be most strongly amplified tropical aridity throughout the entire Euramerican region, under a prevailing, background seasonally dry climate re- within which there were shorter episodes of wetter climate, gime. perhaps less than 1-3 million years in duration (Tabor and In addition to actual fossils, sedimentary features Poulsen, 2008). at Valley of the Gods suggest widespread plant coloniza- A wetter episode (at least dry sub-humid) proposed tion of the landscape. For example, a flaggy siltstone bed to occur near the Pennsylvanian-Permian boundary in the near Setting Hen Butte contains more than 100 vertical, Colorado (Soreghan and others, 2002) is consistent cylindrical features that penetrate the entire 15 centimeter with the floras we describe in this paper. This period of in- thickness of the bed. Consistently about 4 centimeters in creased moisture may be associated with cycles of glacia- diameter, these cylinders have haloes of gray against the tion at high elevations within the Ancestral Rocky Moun- red background, suggesting chemical reduction caused by tains, in the Uncompahgre highlands (Soreghan and others, organic matter (figure7). Although these might be roots, 2008), fueled by a combination of cold temperatures and their random spacing and lack of dense clumps (as might periodic increases in moisture delivery to the area. If cy- be expected from roots emanating from a stem base), to- cles of glaciation occurred across the Pennsylva- gether with occurrence of a paleosol directly below, sug- nian-Permian boundary in the Ancestral Rockies, and we gests that the cylinders represent small, upright stems that acknowledge that such proposals are controversial, they were partially buried in sediment. DiMichele and others could account for the periodic occurrence of wetland flo- (2012) described similar features (attributed to the prob- ras—or of any kind of floras—intercalated with intervals able peltasperm, Supaia) from the lower Permian Abo For- of extreme aridity. The close spatial physical proximity mation of . of sand dunes and flood- soils and channels, such as at Indian Creek (Stanesco and Campbell, 1989), may not DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. Indian Creek necessarily be indicative of contemporaneity. Rather, the The twelve small collections made along Indian paleosols and channels preserving wetland plants might Creek consist of two principal components, marattialean more likely represent periods of perennial to intermittent tree-fern foliage and stems of sphenophyllalean sphenop- stream flow, accompanied by channel incision into, and sids. The tree-fern foliage (figs. 6.5-6.7) is both vegetative floodplain development on, landscapes of stabilized dune (Pecopteris) and fertile (Asterotheca). No species deter- fields during wet, cold, glacial intervals. The dunes may minations could be made with confidence, on the basis of have become active again during warmer, arid interglacial the specimens preserved. Tree ferns are common elements intervals. Under such depositional conditions, bounding of wetland floras from both peat and mineral substrates. surfaces within the eolian deposits would mark periods They produced large numbers of small, highly dispers- of stabilization, caused either by rising water tables or in- ible spores, giving them prodigious colonization abilities. creased precipitation. As a consequence, they were elements of many different Pennsylvanian-Permian boundary floras from New kinds of landscapes, as long as there were wet substrate Mexico (Tidwell and others 1999; DiMichele and others, areas present that could be reached by their wind-dispersed 2004; DiMichele and Chaney, 2005; DiMichele and others, spores. 2010) and Utah (Mamay and Breed, 1970; Tidwell, 1988) One of the channel scours also contains abundant, are similar to those reported here, and reveal a mix of plants silicified coniferophyte logs (Stanesco and others, 2002). typical of both wetlands and dry substrates. Such floras do These logs appear to have been transported and may rep- not require widespread wet climates. Rather, they suggest resent a “log jam”, such as those reported from older rocks that the prevailing climate was one of seasonal, locally se- in the eastern U.S. and Canada (e.g. Gastaldo and Degges, vere, drought, within which there were wet areas capable 2007; Gibling and others, 2010). The conifer Walchia also of supporting certain kinds of wetland plants, particularly was found in sandstone from beds at this stratigraphic level. those with high dispersal capabilities and capacities to tol-

MacLean, J.S., Biek, R.F., and Huntoon, J.E., editors 499 500 FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. ity ofbasicstructure. Scale=10centimeters. 4.Paleosolbelowthesiltstone bedillustratedin(7.1). illustrating central core and root-like features surrounding the core area. Scale = 10 centimeters. 3. Pair of reduced areas showing similar Figure 7. Valley of the Gods, near Setting Hen Butte. 1. Siltstone surface covered with areas of iron reduction. 2. Detail of reduced area UGA Publication 43(2014) —Geology of Utah'sFar South - erate short moisture deficits. The most likely scenario is equatorial region. This is true both of the wetland and sea- that a number of perennial streams, sourced in the Uncom- sonally dry taxa. Although the number of dominant class- pahgre highlands, coursed across the coastal plain of the level groups, represented by distinct architectures, was former Paradox Basin en route to the western ocean. At more numerous than is typical of modern vegetation, the some intervals, perhaps during periods of mountain glacia- late Paleozoic tropics nonetheless hosted significantly few- tion as discussed above, these riverine corridors sustained er species, genera, and families than do the modern trop- large populations of plants adapted to wetter environments. ics. In a late Paleozoic world with far lower diversity than FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – Thus, at Valley of the Gods and Lime Ridge, we find today, many individual species, therefore, may have had fossils of large plants that represent all the major groups greater niche breadth than is typical among modern plants. of Pennsylvanian wetland plants: tree ferns, calamitaleans, Such resource breadth may have, perhaps to a consider- pteridosperms and lycopsids. The lycopsids and pteri- able extent, buffered their populations from environmen- dosperms are of particular note because they had large dis- tal changes. Most species had either wind dispersed pollen persal organs (megaspores for Sigillaria and large seeds in or spores, which would have contributed to high levels of the case of the pteridosperms) that could not be broadcast gene flow and made possible large effective population siz- widely. This observation implies either permanent western es—these factors may have been among the most important refugial areas for these plants during drought, or rapid ex- responsible for the lower numbers of species. There are few pansion of their populations along continuously developed tests of such hypotheses (but see Raymond and Costanza, wetland corridors during short intervals of widespread wet- 2007), and clearly the late Paleozoic, and the western areas ness. Tree ferns and calamitaleans could grow in margin- of Pangea, promise to be fertile areas for study of plant evo- ally wet areas, giving them the capacity to reach remote or lutionary and ecological dynamics. isolated sites with wet soils. The former produced billions of small, highly dispersible spores, which could reach re- ACKNOWLEDGMENTS mote wet areas. The latter included many streamside and lake margin specialists, which could recover from repeated We thank Jack Stanesco and Jackie Huntoon for in- disturbances (e.g., Gastaldo, 1992), and thus occupy small, troducing us to many of the fossil deposits reported here. but interconnected corridors with intermittent wetness. As Gary Gianniny, Dave Berman, and Amy Henrici contrib- noted above, perennial stream flow in fluvial systems may uted materially to our understanding of the geology. Arden have, at times, been maintained by ice melting in the An- Bashforth and Stan Opluštil provided helpful, constructive cestral Rocky , which provided wetland condi- reviews of an earlier version of this paper. The assistance tions in an otherwise dry, perhaps arid climate. of the Bureau of Land Management is gratefully acknowl- Plants reflecting seasonally dry conditions have been edged. The Small Grants Program of the National Museum reported in floras from the from strata as of Natural History supported this research. DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. old as Early Pennsylvanian (Tidwell, 1967). Such plants also occur in Pennsylvanian collections from the Midwest- REFERENCES ern coal fields (Feldman and others, 2005; Falcon-Lang and others, 2009) but only in small channels that show evidence Baars, D.L., 1962, Permian System of Colorado Plateau: Ameri- of seasonally dry conditions, developed between periods can Association of Petroleum Geologists Bulletin, v. 46, p. 149-218. of coal formation. Their presence in our Utah collections thus is hardly surprising. 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MacLean, J.S., Biek, R.F., and Huntoon, J.E., editors 503 504 FOSSIL FLORAS FROM THE PENNSYLVANIAN-PERMIAN CUTLER GROUP OF SOUTHEASTERN UTAH – DiMichele, W.A., Cecil, C.B., Chaney, D.S., Elrick, S.D., and Nelsom, W.J. Wagner, R.H., and Álvarez-Vázquez, C., 2010, The Carbonifer 2010,C.,Álvarez-Vázquez, The and R.H.,Wagner, ogy, v. 162, p. 239-324. Review of logical and Palynol connotations: Palaeobotany geo with synthesis A Peninsula: Iberian the of floras ous - - - Wang, J., and Pfefferkorn, H.W.,Carboniferous-Per Pfefferkorn, 2013, The and J.,Wang, anic climate in the tropics: International Journal of Coal Coal Geology,of v. 119, Journal p. 106-113. International tropics: the in climate anic microcontinent—Oce China North the on transition mian UGA Publication 43(2014) —Geology of Utah'sFar South - -