An early Permian coastal flora dominated by Germaropteris martinsii from basinal sediments in the Midland Basin, West Texas

Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 409–422

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An early Permian coastal flora dominated by Germaropteris martinsii from basinal sediments in the Midland Basin, West Texas Robert W. Baumgardner Jr. a,⁎, William A. DiMichele b, Nathalia de Siqueira Vieira c a b c

Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78713, United States Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, United States Universidade Federal de Ouro Preto, Engenharia Geologica, Ouro Preto, Minas Gerais 35400000, Brazil

a r t i c l e

i n f o

Article history: Received 1 February 2016 Received in revised form 30 June 2016 Accepted 19 July 2016 Available online 21 July 2016 Keywords: Peltasperm Sphenopteris Supaia Wolfcamp

a b s t r a c t Fossils found in cores from wells in the Midland Basin of West Texas include several kinds of terrestrial plants and a variety of marine animal remains. Depositional settings ranged from basin slope to deep-water basin floor, hence the presence of land plants was unexpected. The fossil plant assemblage is depauperate, dominated by Germaropteris martinsii, a Permian-age peltasperm. Other specimens include the peltasperm Supaia, Sphenopteris germanica, axes of uncertain affinity, and incertae sedis remains presumed to be terrestrial plants. Fossil plants are found predominantly in fine-grained, siliceous mudrocks between coarser-grained calcareous floatstones and wackestones/packstones interpreted as debrites and turbidites, suggesting that the plants were carried from land by surface currents before sinking to the basin floor and being buried by slowly accumulating hemipelagic sediment. Specimens were examined from drillcores in 14 wells spanning an interval from the lower Wolfcamp through the lower Leonard. This record of G. martinsii in lower Permian Wolfcamp rocks is among the earliest occurrences of these plants, which have been found most abundantly in upper Permian strata of Western Europe. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Peltasperms are a group of seed plants originating in the late Paleozoic from seed-fern ancestors and characterized by specialized shieldlike reproductive organs (Kerp et al., 2001; Poort and Kerp, 1990). They were an important part of the vegetation in equatorial, seasonally dry habitats of Euramerica, during the Permian (e.g. DiMichele et al., 2005; Kustatscher et al., 2014; Schweitzer, 1986). Nearly all peltasperm occurrences are in inland, alluvial, coastal-plain settings, commonly in small lakes formed from abandoned channels or in channel deposits themselves. Germaropteris martinsii (Kustatscher et al., 2014) is a peltasperm that has been reported almost exclusively from the late Permian. In contrast to most other peltasperms, it is most commonly reported from nearshore marine environments. This study reports an occurrence of Germaropteris martinsii in rocks significantly older than previously known, in an environment not ordinarily associated with terrestrial plants: deep-basin marine sediments. The Midland Basin, a Permian-age intracratonic basin (Fig. 1), is bounded by uplifts (Ewing, 1993) and carbonate platforms. The basin began to form in the Early Pennsylvanian as the Central Basin Uplift formed and flanking basins subsided (Hills, 1985). The margins of the Midland Basin are marked by the Central Basin Platform on the west, the Northern and Eastern Shelves, and the Ozona Arch to the south ⁎ Corresponding author. E-mail address: [email protected] (R.W. Baumgardner).

http://dx.doi.org/10.1016/j.palaeo.2016.07.024 0031-0182/© 2016 Elsevier B.V. All rights reserved.

(Fig. 1). During early Permian time the basin filled with submarine fan deposits, fine-grained hemipelagic sediments, and detrital carbonate mass-flow deposits derived from surrounding shelves (Hamlin and Baumgardner, 2012). Near the basin center, in Reagan County, early Permian Wolfcampian (Asselian–Artinskian) sediments are about 480 m (1500 ft) thick and the overlying lower Leonardian (Artinskian– Kungurian) is about 100 m (350 ft) thick (Fig. 2). Within the basin boundaries, the Wolfcamp is underlain by Pennsylvanian-age rocks in conformable contact. In 1965–1966, four oil-and-gas wells were drilled into Permian strata in northern Reagan County (Fig. 1, inset). Ten-cm (4-inch) diameter cores were collected at various depths from the lower Leonard interval to the lower Wolfcamp (Fig. 2). Recently, these cores have been the subject of a study of basinal mudrocks (Baumgardner et al., 2016). In the course of that study, fossils of land plants were discovered in basinal mudrock facies. This discovery presented an opportunity to assess the presence of land plants in deep-water, basinal rocks, which commonly are not accessible in outcrop in West Texas. 2. Early Permian paleoclimate and sea level The early Permian has been characterized as an icehouse period, a time of high-amplitude and high-frequency eustatic fluctuations caused by repeated building and melting of continental glaciers in southern Gondwana (Rygel et al., 2008) (Fig. 2). The Pennsylvanian-Permian transition occurred during a time of massive expansion of glaciers, and

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103º W

105º W

N

NM TX

4 2 1

101º W

3

N

wes North lf She

33º N 1 O. L. Greer 1 2 O. L. Greer 2 3 Rupert P. Ricker 1 4 R. Ricker 1

or

th

n Sh e er

t

Gaines

33º N Midland Basin

Reagan Co., TX

sin Ba al ntr orm Ce Platf

Delaware Basin Di

ab

N

lo

Pl

at

fo

Texas

0

Glasscock Upton

Tom Green

Oz Crockett ona A r ch She Cha ffield nne l

rm

31º N

Val Verde Basin

Brewster thon Structu Mara ral B ita− elt h c a Ou = peltasperm in literature

100 mi

= peltasperm and related plants, this study

29º N 100 km

105º W

Mitchell Sterling

Reagan

y ve el Ho hann C

0

Eastern Shelf

Howard

Hudspeth

31º N

lf

103º W

101º W

29º N QAe4502(a)

Fig. 1. Early Permian paleogeography of western Texas, and locations of peltasperms and related terrestrial plants. Details of peltasperm occurrences shown are listed in Table 1. Locations of peltasperm occurrences from the literature (open stars) are based on sources listed in Table 1. Counties are labeled where terrestrial plants have been reported. Location in Reagan County represents four closely spaced wells (inset map) which comprise most of the data in this study. Reagan County wells are the only ones near basin center. Permian geologic features after Silver and Todd (1969), and Hamlin and Baumgardner (2012).

continental ice sheets are inferred to have been at maxima during Asselian and early Sakmarian (early Wolfcampian) time (Fielding et al., 2008). Sea-level lowstand during the early Wolfcampian was followed by progressively higher sea-level highstands through later Wolfcampian and early Leonardian time (Wahlman and Tasker, 2013). At the same time, there was a consistent, oscillating trend toward increased aridity in western Pangea as icehouse conditions waned (Fig. 2). Paleosols in New Mexico and western Texas indicate a significant transition from on-average subhumid climate during the latest Pennsylvanian to semiarid climate during the Wolfcampian to arid climate during the Leonardian (Tabor et al., 2008). Although these changes have been attributed to northward tectonic drift of about 8° from Virgilian to Leonardian time (Tabor et al., 2008) (Fig. 2), conflicting but unpublished paleomagnetic data suggest westward rather than northward drift. In addition, the warming and drying trend that characterizes western Pangea is characteristic of a broad expanse of the central portion of the continent (e.g., Opluštil et al., 2013) and is part of a longterm drying trend that began in the Middle Pennsylvanian. 3. Geology 3.1. Lithostratigraphy The Wolfcamp Formation was named by Udden (1917) based on outcrops he described in the Glass Mountains of Brewster County,

Texas. The type section consists of about 180 m (600 ft) of limestone, limestone conglomerates, and shales (Adams et al., 1939). Ross (1963) revisited the type section and described the Wolfcamp as a complex set of facies deposited in near-shore environments. He divided the Wolfcamp Series into the Neal Ranch Formation and the Lenox Hills Formation, based on different fusulinid assemblages, later interpreted by Wilde (1990) as his PW-2 and PW-3 fusulinid zones, respectively (Fig. 2). Wilde (1976) observed that the lithology of the Wolfcamp is extremely variable in response to changes in depositional environment. Indeed, within the boundaries of the Midland Basin, lithology of the Wolfcamp ranges from massive allochthonous limestone slide blocks (Van Der Loop, 1990) to laminated mudrocks (Hamlin and Baumgardner, 2012). The overlying Leonard Formation (Fig. 2) was named by Udden et al. (1916) based on outcrops in the Glass Mountains. The type section consists of about 550 m (1800 ft) of limestones and dark siliceous shales. Within the boundaries of the subsurface Midland Basin, the lower Leonard interval studied in this paper refers to that part of the Leonard underlying the Dean Sand (Fig. 2), which is correlative with the Tubb sandstone member on the Central Basin Platform (Table 1). The Wolfcamp and lower Leonard lithostratigraphic intervals in the subsurface of the Midland Basin have been subdivided based on well-log signatures (Baumgardner et al., 2016; Hamlin and Baumgardner, 2012). The lower Leonard is characterized by high resistivity and thin bed spikiness. The base of the lower Leonard is marked by a widespread high gamma-ray log interval—the Wolfcamp shale marker

PL-1

lower Leonard

Core Fossil 20

1

Res

10000

2400 8000 9000

widespread ice sheets Maximum eustatic

D.

Strawn

Bursum Fm.

0

40

80

120

(m)

Cisco

Cisco Canyon Strawn

9800

Missour- Virgilian ian

Canyon

M.

PW-1

Bursum

3000

Kasimov- Gzhelian ian

9600

298.9 Ma

2900

9400

9200

sea-level change (m) lower Wolfcamp

2800

Nealian

lower Hueco

(m)

8800

(ft)

8600

tectonic drift

2700

PW-2

295.5 Ma

Asselian

2500

8200

upper Wolfcamp

8400

upper Hueco

2600

Lenoxian

PW-3

mWu Wolfcampian

Sakmarian

Lower Permian

150

Wolfcamp shale marker

290.1 Ma

Pennsylvanian

GR

Humid

Dean

Maximum global sealevel change

Subhumid Semiarid Arid

PL-2

SW U.S. Climate

O. L. Greer #2 API 42-383-10575 Depth

Formation Name

Composite Data (4 wells)

411

7800

Substage

NA Stage

Fusulinid Zones

Artinskian

279.3 Ma

Leonardian

Kungurian Global Stage

Series

R.W. Baumgardner Jr. et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 409–422

QAe4501(a)

Fig. 2. Stratigraphy, fusulinid zones, composite core and fossil data, wireline logs, and paleoclimate of the early Permian in Midland Basin area, Texas. Fusulinid zones from Wahlman and Tasker (2013); after Ross (1963) and Wilde (1990). Composite core and fossil flora data are shown for four Reagan County wells (Fig. 1, inset), plotted relative to the top of the Wolfcamp in each well. Composite fossil data are shown as occurrence in each 10-ft (3-m) depth interval. Wireline logs (GR = gamma ray and RES = resistivity) are for O. L. Greer #2 well, the deepest of the four wells in Reagan County, TX. Radiometric ages are from Henderson et al. (2012). Paleoclimatic interpretations after Rygel et al. (2008) and Tabor et al. (2008). NA Stage = North American Stage. D. = Desmoinesian. M. = Moscovian. mWu = mid-Wolfcampian unconformity.

(Fig. 2). The underlying upper Wolfcamp has lower resistivity and fewer thin bed spikes than the lower Leonard. The upper part of the lower Wolfcamp is similar to the upper Wolfcamp, but below that the lower Wolfcamp has relatively low resistivity, flat gamma ray response, and rare spikes. The boundary between the upper and lower Wolfcamp aligns approximately with the mid-Wolfcampian unconformity, which separates the Neal Ranch Formation from the Lenox Hills (Fig. 2). By comparing well-log signatures with core Hamlin and Baumgardner (2012) concluded that the lower Wolfcamp is more siliciclastic than the upper part. Sediments become more calcareous upward as carbonate-rich beds increase in thickness and become more common. The upper Wolfcamp contains more and thicker coarse-grained calcareous interbeds, including floatstones, wackestones, and packstones, as well as more-calcareous mudrock. The lower Leonard is composed of thinly bedded, mixed lithofacies dominated by calcareous mudrock.

Taken together, the Wolfcamp and lower Leonard intervals are about 580 m (1850 ft) thick in northern Reagan County (Fig. 2). 3.2. Chronostratigraphy Current understanding of the chronostratigraphy of the Wolfcampian and early Leonardian is shown in Fig. 2. Historically, boundaries of North American Wolfcampian and Leonardian stages were constrained by fusulinid biostratigraphy (Candelaria et al., 1992; Wilde, 1975, 1990). The Wolfcampian stage was divided into three fusulinid biostratigraphic zones (summarized in Wahlman and Tasker, 2013). In the subsurface Permian Basin, those three intervals were commonly referred to, in ascending order, as the Bursum, lower Hueco, and upper Hueco. Wilde (1990) referred to the three zones as PW-1, PW-2, and PW-3, respectively (Fig. 2). Wilde (1990) further referred to the lower Leonard as the PL-1

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Table 1 Stratigraphic position, depositional setting, rock type, and location of peltasperms and related terrestrial plants in western Texas reported in the literature. This study reports one of the oldest occurrences of peltasperms and the oldest Germaropteris martinsii in West Texas. No other peltasperms have been reported in deep-water marine sediments. Stratigraphy for Mitchell County location was not reported by DiMichele et al. (2000) but is inferred from well logs. Occurrences are listed (left to right) as seen on Fig. 1 (west to east). Data are from 1 = Adams (1933); 2 = Albritton and Smith (1965), modified after Cys (1976); 3 = DiMichele et al. (2000); 4 = Glasspool et al. (2013); 5 = King (1934); 6 = Mamay et al. (1988); 7 = Ross (1963); and 8 = this study.

Road

Glorieta Glorieta

Canyon [No outcrop Cathedral Mountain

Upper Choza

Leonard

above the Leonard

Clear Fork

Clear Fork

Clear Fork

Middle

Fm.]

Leonard

Wilkie

Vale Arroyo

Ranch Skinner

Tubb

Permian System

Ranch Leonard Fm.

Dean

Dean

Dean

Dean

Lower

Lower

Lower

Lower

Lower

Leonard

Leonard

Leonard

Leonard

Leonard

Wolfcamp

Wolfcamp

Wolfcamp

Wolfcamp

Wolfcamp

Lenox Hills Fm. Neal Ranch Hueco

Wolfcamp

Fm. Pro-delta,

Setting

Rock

Marginal Near-shore

Marlstone

Type

present

Location

shallow embayment

Lagoon,

Marginal to

Bay or

Not

Near-

beach, pond

deep marine

lagoon

reported

coastal

Mudstone,

siltstone,

Dolomite,

Siliceous

siltstone

shale

siltstone

mudrock

Dolomite

Not

Silty gray

reported

mudstone

Delnortea

Pecopteris,

Comia sp.,

Germaropteris

Delnortea

Indeter-

Delnortea

abbottiae,

peltasperms,

Taeniopteris,

martinsii,

abbottiae

minate

abbottiae,

Glenopteris?

Taeniopteris,

sphenopsid,

Delnortea

Supaia,

affinity

Taeniopteris,

Spheno-

conifer,

Supaia,

abbottiae,

Sphenopteris

phyllum?

sphenopterid,

Taeniopteris,

callipterid

pecopterid

conifer

Pecopteris, Plants

marine

Callipteris,

Outcrop,

Outcrop,

Finlay

Del Norte

Mtns.

Mtns.

Hudspeth

NW Brewster

County2

County6

Outcrop,

conifer, sphenopterid, pecopterid SE

Cored wells,

Outcrop

N Robertson

See

Currie #3

Westbrook

Unit wells

Table 3

well

Field

NE Brewster

Gaines

various, See

Glasscock

Mitchell

Tom Green

County4,5,7

County3

County1

County3

County3

Glass Mtns.

= occurrence of peltasperm

zone, based mainly on fusulinid faunas described from the lower Leonardian of the Glass Mountains stratotype. Wilde (1975, 1990) and others (Mazzullo and Reid, 1987; Reid and Reid, 1989) reported lower Leonardian fusulinids from the lower Leonard of the subsurface Midland Basin, and reported Wolfcampian fusulinids from the underlying upper and middle Wolfcamp. Furthermore, specimens of the Leonardian-age fusulinid Parafusulina were found in the O. L. Greer 1 core just below a depth of 7709.5 ft (2349.9 m—the cores are calibrated in feet) (Ritter and Baesemann, 1991) and at 8052 ft (2454.2 m), evidence of “unequivocal Leonardian” (Sanderson, 1968). Both occurrences are in the lower Leonard interval. The Pennsylvanian–Permian boundary horizon has changed since Wilde (1990) published his fusulinid-based zonation. Recently, the establishment of a new conodont-based global Pennsylvanian–Permian boundary in the Permian system stratotype of Eurasia, and the correlation of that horizon to North America, has resulted in an upward shift of the North American Pennsylvanian–Permian boundary from the base to the top of the Bursum interval (Fig. 2) (Wahlman and Tasker, 2013). Therefore, the so-called Bursum interval (Wilde's PW-1 zone) is now

Fig. 18

QAe4503(a)

considered to be latest Pennsylvanian (latest Virgilian) in age, and the early Permian Wolfcampian stage consists of two fusulinid zones: the lower Hueco and upper Hueco. In sum, based on scant biostratigraphic data from subsurface basinal facies, the lower Leonard referred to in this study is early Leonardian in age (Fig. 2). The Wolfcamp aligns approximately with the Wolfcampian stage, and the Bursum is Late Pennsylvanian in age. This matter remains in flux, however. Lucas (2013a, 2013b) has pointed out that Streptognathodus isolatus, the conodont on which the base of the Permian is defined, is both quite rare, and thus difficult to find in most geological sections, and time transgressive. Lucas (2013b) recommends returning to the traditional Permian base, as delimited by fusulinids, which place that boundary at the base of the Wolfcampian and approximately at the base of the Asselian, and thus at the base of the Bursum Formation. Furthermore, it should be noted that ongoing biostratigraphic studies on fusulinids and conodonts from Wolfcamp and lower Leonard basinal mudstone cores from the subsurface Midland Basin may alter these chronostratigraphic interpretations. Preliminary results from integrated conodont and fusulinid biostratigraphic studies

R.W. Baumgardner Jr. et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 409–422

on Midland Basin basinal facies cores demonstrate that (1) the Wolfcampian–Leonardian boundary appears to be lower in the section than previously thought, apparently in the upper part of the upper Wolfcamp interval (Fig. 2); (2) most of the upper and middle Wolfcamp intervals are Wolfcampian in age; and (3) the lower part of the lower Wolfcamp is probably Late Pennsylvanian (Missourian–Virgilian) in age (Greg Wahlman, pers. comm., 2016). 3.3. Depositional environments Wolfcamp and lower Leonard rocks in northern Reagan County accumulated in basinal, deep-water settings. Estimates of maximum water depth in the Midland Basin range from 300 m (1000 ft) at the beginning of Permian time (Hobson et al., 1985) to 600 m (2000 ft) during early Leonardian time (Montgomery, 1996). These depths are much greater than average depth to coarse-grained ripples (60 m [200 ft]) in coastal areas reported by Rygel et al. (2008) and interpreted by them as the depth to storm wave base. Four lithofacies—interpreted from core descriptions, mineralogical (XRD) data, and elemental geochemical (XRF) data—are present in the upper Wolfcamp and lower Leonard: siliceous mudrock, calcareous mudrock, muddy bioclast–lithoclast floatstone, and skeletal wackestone/packstone (Fig. 3) (Baumgardner et al., 2016). The first facies, dark gray to black siliceous mudrock, is the dominant facies and forms the thickest intervals (up to 4 m [13 ft] thick). These rocks commonly are massive or have faint, discontinuous, mm-scale

413

bedding (Fig. 3A). They are fissile where clay minerals exceed 40%. Bioclasts (b5%) include thin-shelled mollusks; agglutinated foraminifera; and, rarely, crinoids, uniserial foraminifera, and ammonites. Finegrained (mostly b4 μm) pyrite framboids are common throughout. Phosphatic nodules (≤ 4.6 cm) are common locally and burrows are rare. Average total organic carbon (TOC) content (3.6%) is highest in this facies (Table 2, Supplemental Information). The second facies, calcareous mudrock, contains more carbonate (finely comminuted bioclasts and replacive calcite) than average siliceous mudrock. Structure is mostly massive, with mm-scale laminae present locally, composed of lime mud or silt-size clasts (Fig. 3B). Beds range from a few centimeters (inches) to 1.8 m (6 ft) thick. On average, clay minerals comprise 9% of calcareous mudrock, about one-fourth the amount in average siliceous mudrock (Table 2, Supplemental Information). Bioclasts, especially radiolarians and calcispheres, are much more common (up to 30% locally) than in siliceous mudrock. Pyrite framboids are common, as in siliceous mudrock, but phosphatic nodules and burrows are rare. The third facies, muddy bioclast–lithoclast floatstone, is an unsorted mixture of muddy matrix-supported carbonate bioclasts and lithoclasts in beds 0.6 to 2.7 m (2 to 9 ft) thick. Most clasts are 2–4 mm in diameter but range up to 55 mm (Fig. 3C). The most common bioclasts are echinoderms, followed by brachiopods and crinoids, then foraminifera, fusulinids, radiolarians, and sponge spicules. Rarest of all, represented by only a few specimens, are bivalves, bryozoans, dasycladacean green

Fig. 3. Photographs of core specimens showing four facies interpreted from Reagan County cores. A. Siliceous mudrock, showing discontinuous, mm-scale bedding. B. Calcareous mudrock, showing horizontal bedding (upper 2 cm) and massive texture. C. Muddy bioclast–lithoclast floatstone, an unsorted mixture of matrix-supported bioclasts and lithoclasts. D. Skeletal wackestone/packstone displays low-angle crossbeds demarcated by silt-size to very fine sand-size skeletal carbonate grains.

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algae, rugose corals, trilobites, and Tubiphytes. Many of these (bivalves, brachiopods, dasycladacean green algae, echinoids, fusulinids, and trilobites), while living, were denizens of shelf environments including shelf-margin reef builders (sponges, rugose corals, and Tubiphytes) (Scholle and Ulmer-Scholle, 2003). Average pyrite content (2%) is half that in siliceous mudrock. Most pyrite framboids are smaller than 6 μm and burrows are rare. Average TOC content in this facies (1.4%) is less than half that in siliceous mudrock (Table 2, Supplemental Information). The fourth facies, skeletal wackestone/packstone, is composed mostly of silt-size to very fine sand-size skeletal carbonate and quartz grains in beds 1–120 cm (0.5–48 in. thick (Fig. 3D). Locally, skeletal grains range up to 7 mm in diameter. Skeletal wackestones/packstones have the lowest average clay mineral content of the four facies (8%) (Table 2, Supplemental Information). Identifiable skeletal grains in wackestones/packstones include crinoids, echinoderms, fusulinids, brachiopods, foraminifera, sponge spicules, and, rarely, trilobites, Tubiphytes, dasycladacean green algae, and thin-shell mollusks. As with floatstones, most specimens are disarticulated and broken, and were inhabitants of shelf environments (Scholle and Ulmer-Scholle, 2003). Ripples and crossbeds in some wackestones/packstones are interpreted as evidence of deposition by turbidity flow. Pyrite framboids are rare because of the scarcity of mud matrix in which they form, and, likewise, burrows are rare. Average TOC content (1.6%) is low. These facies represent two primary modes of deposition: (1) hemipelagic settling from the water column (fine-grained mudrock facies are hemipelagic, accumulating slowly over long periods of time as sediments settled out of the water column to the basin floor); and (2) sediment density flow (allochthonous carbonate sediments— floatstones and wackestones/packstones—were deposited rapidly by sediment density flows moving across the basin floor from their sources along the basin margins). Several lines of evidence indicate that the depositional environment of these sediments was dysoxic to anoxic most of the time. High organic carbon contents (up to 6.8% locally) are characteristic of reducing conditions (Demaison and Moore, 1980). Rarity of burrows suggests a lowoxygen environment hostile to infauna. Widespread presence of small (b6 μm diameter) pyrite framboids is evidence of reducing conditions (Wilkin et al., 1996), as are phosphatic nodules (Ece, 1990), which are locally abundant. Finally, sedimentary molybdenum concentrations are higher than 25 ppm locally (Baumgardner et al., 2016), a level recognized as indicative of euxinia (Dahl et al., 2013). 4. Previous work Land plants, including peltasperms have been reported previously from Permian-age rocks in West Texas (DiMichele et al., 2005). Adams (1933) reported what he interpreted as a fossil “fern” (later identified as the probable gigantopterid seed-plant Delnortea abbottiae [DiMichele et al., 2000]) in limestone of the Clear Fork from a cored well in Glasscock County (Fig. 1; Table 1). He interpreted the depositional setting as lagoon or bay. King (1934) reported a fossil conifer (Walchia) from the Wolfcamp Formation in the Glass Mountains. Ross (1963) reported plant fragments (presumably land plants) in black shale and thin calcarenite beds of the Neal Ranch Formation (lower Wolfcamp), which were deposited in a ‘near-shore environment’. Albritton and Smith (1965) reported fragmentary but well-preserved “fronds and leaves of land plants” mingled with shells of benthonic marine organisms in Leonardian-age marlstones in the Finlay Mountains. The land plants included Callipteris sp. (since subdivided into a number of different genera—Kerp and Haubold, 1988—some of which are now called Germaropteris [Kustatscher et al., 2014]), Pecopteris sp., possible Glenopteris sp., and Sphenophyllum sp. Albritton and Smith (1965) interpreted the depositional setting as nearshore, where water was shallow enough for the seafloor to be swept by currents and to be populated by bryozoans and brachiopods. Mamay et al. (1988) found land

plants (mostly Delnortea abbottiae and Taeniopteris sp.) mingled with marine gastropod shells in laminated mudstones and calcareous siltstones of the Leonardian Road Canyon Formation, interpreting the depositional environment as marginally marine “with low-energy introduction of plant material into the finely laminated enclosing sediments.” DiMichele et al. (2000) found callipterids (1) in dolomites and wackestones of the Leonardian Clear Fork Group on the Central Basin Platform in deposits interpreted as lagoonal, beach, and ponded water, and (2) in near-coastal Clear Fork (Choza Formation) mudstones on the Eastern Shelf of the Midland Basin in Tom Green County. Most recently, Glasspool et al. (2013) described a diverse assemblage of plants at the type section of the Neal Ranch Formation (lower Wolfcamp). They documented 27 genera, including species such as Peltaspermum sp., Supaia sp., and Sphenopteridium manzanitanum in shallow marine, pro-delta deposits (Fig. 1; Table 1). Terrestrial plants have been observed in marine rocks in deposits interpreted as debrites (Spicer and Thomas, 1987) and turbidites (Saller et al., 2006). The inferred means of transport is either by debris flow or turbidity current from the shore to the basin floor. On the other hand, terrestrial plants can be transported long distances by surface currents. Land plants have been observed at sea floating miles from land at least since Christopher Columbus recorded on 11 October 1492 in the logbook of his first voyage that the crew of the Pinta saw land grasses (“yerva que nace en tierra”) and that men on the Nina saw a small branch covered with berries (“un palillo cargado d'escaramojos”), N150 km (90 mi) from landfall (Delgado, 1989). Gastaldo (1994) reported whole leaves of hardwood trees transported N50 km (30 mi) from upper delta or inland settings to seaward edges of tidal flats. A recent anecdotal report describes palm trees floating 16–24 km (10–15 mi) off the coast of West Africa near the mouth of the Congo River (Ron Shaw, pers. comm., May 2015). 5. Methods In this study, plant fossils were observed first on CT scans of the R. Ricker 1 core. The core was scanned using a multislice medical X-ray tomography (CT) device in dual-energy helical mode at a voxel resolution of 488 μm. Slices were spaced 670 μm apart (J. Walls, Ingrain Inc., pers. comm., 2014). Fossils typically appeared on one or two adjacent slices, thus most are less than about 1 mm thick. This serendipitous discovery prompted a thorough examination of all broken core ends (which expose bedding planes) on the R. Ricker 1 core and three other cores from northern Reagan County, Texas (Fig. 1, inset). Together the four cores cover parts of the stratigraphic interval from near the base of the Wolfcamp to the top of the lower Leonard interval (Fig. 2). Core ends were examined under bright, oblique incandescent light to enhance microrelief of fossil organic compressions and molds, as well as reflectivity of carbonaceous coatings. The most complete specimens from all cores were archived for further study. Because of the quantity of material present on broken core ends, further sampling by splitting core was deemed unnecessary for gathering a representative sample of the population of fossils present. N7000 core ends were examined. Of those, between 70 and 90% did not have a matching counterpart; therefore, between 4900 and 6300 unique surfaces were examined on these four cores. Most specimens examined in this study come from four cored wells in northern Reagan County (Fig. 1, inset). These cores represent the major focus of this study because of their proximity to one another and their relatively complete stratigraphic continuity through the upper Wolfcamp and lower Leonard intervals. Following study of the four Reagan County cores, 31 other cores in the Midland Basin were examined. Only 10 of those cores had identifiable remains of terrestrial plants (Fig. 1). None had flora as abundant as the Reagan County cores, nor were these cores as long as those from Reagan County (Fig. 4). These cores sampled environments closer to basin margins than those sampled from the Reagan County cores (Fig. 4, inset). Total

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approximately the same as the number of specimens observed. A total of 196 plant-bearing surfaces were counted on all 14 cores (Table 4, Supplemental Information). Of those, 121 were collected and archived.

length of these ten cores is about 400 m (1330 ft), and about 6000 broken core ends were examined. Specimens collected for preservation and additional study (Table 3, Supplemental Information) are archived at the NonVertebrate Paleontology Lab, The University of Texas at Austin. Each sample is registered with the System for Earth Sample Registration (SESAR) and assigned an International GeoSample Number (IGSN). Metadata profiles for samples can be accessed at www. geosamples.org. Digital photographs of each sample were deposited at the Non-Vertebrate Paleontology Lab and are accessible through the iDigBio portal online. The proportional abundance of each type of plant observed in the full sample was determined using the hand-sample/quadrat method of Pfefferkorn et al. (1975). Each unique surface was counted as a single sampling quadrat (quadrat = standard sampling unit), regardless of how many specimens were present on that surface. Opposite-face, part and counterpart surfaces were counted only once. Surfaces devoid of plant material were not included in the calculations. Estimates of abundance of taxa are reported, therefore, as the number of “quadrats” on which a fossil taxon was observed as a proportion of the total number of fossiliferous quadrats. This method provides an estimate of frequency, not a count of the actual number of unique specimens observed (which could be higher than the number of quadrat observations, but not lower). In addition, it is hypothetically possible for all taxa observed to be present on all quadrats. In practice, however, we generally observed single plant specimens on each quadrat surface; consequently, the frequency with which any taxon was observed is

6. Paleobotany 6.1. Floral composition The flora consists of three identifiable types of plants. Several additional specimens, either of problematic affinity or identifiable only as “axes” also are discussed and illustrated. References to fuller taxonomic treatments, where appropriate, are provided. Germaropteris martinsii (Germar in Kurtze 1839) Kustatscher, Kerp et Van Konijnenburg-van Cittert is a member of the Peltaspermales, an advanced group of seed ferns common and diverse in Permian sediments (DiMichele et al., 2005; Kustatscher et al., 2014) (Fig. 5). The plant had advanced reproductive morphology (Poort and Kerp, 1990); its taxonomic history is complex, and it was recently moved from Peltaspermum to the new genus Germaropteris Kustatscher, Kerp et Van Konijnenburg-van Cittert (see Kustatscher et al., 2014, for a summary of the nomenclatural history of the plant). The plants bore small fronds that, based on the preservation of leaves with intact bases in our sample (Fig. 5A), appear to have been deciduous. They were once to rarely three times pinnate (Fig. 5A–F). Pinnules were small, thick and ovoid to nearly round in shape, and can be characterized as “xeromorphic”; they often are preserved in our samples in a highly reflective, vitrinized state (Fig. 5D), indicating that they were thick and,

B. Robertson 1 All Day `N11` 2 E. L. Powell D1 Council `C` 108 Rupert P. Ricker 1 O. L. Greer 1 N. Eddleman 1 42-165-31398 42-227-35422 42-173-30258 42-431-32630 42-383-10519 42-383-10189 42-461-03777 T. S. Riley D9 Fryar 2037 Glass `G’ 1514L R. Ricker 1 O. L. Greer 2 R. D. Johnson 1 Baggett 29 1 42-165-10076 42-227-34057 42-431-32095 42-383-10611 42-383-10575 42-461-32848 42-105-10271 500 100

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Fig. 5. Core photographs of Germaropteris martinsii. A. Leaf fragment shows length of pinnules increases upward from base of petiole (lower right). B. Robertson 1 core. Depth 9683.3 ft (IGSN: IEWRB002U).B. Large penultimate pinna fragment. R. Ricker 1 core. Depth 7981.29 ft (IGSN: IERWB002I). C. Tip of leaf. Rupert P. Ricker 1 core. Depth 7917 ft (IGSN: IERWB002P). D. Penultimate pinna with laterals. R. Ricker 1 core. Depth 7995.5 ft (IGSN: IERWB002J). E. Germaropteris martinsii showing shrinkage, perhaps due to drying or to osmotic factors. Preservation is different from other specimens (e.g., panel A). O. L. Greer 1 core. Depth 7721.7 ft (IGSN: IERWB0002). F. Tip of leaf (bent to right). O. L. Greer 1 core. Depth 8021 ft (IGSN: IERWB0019). G. Closeup of pinnules. O. L. Greer 1 core. Depth 7944.9 ft (IGSN: IERWB000X).

less commonly, wrinkled (Fig. 5E), suggesting that such specimens had dried out and originally were quite succulent. Terminal pinnules are small and of the same form as pinnules borne on lateral pinnae (Fig. 5C, F). Pinnae can be widely spaced to quite crowded, appearing in the latter instance as a sheet of rounded pinnules (Fig. 5G). The pinnules also are borne directly and densely on the frond rachis (so-called rachial pinnules), characteristic of peltasperms. Germaropteris martinsii is widespread in Lopingian sediments, early late Permian, throughout the central Pangean equatorial region. There are reports of the plant, however, from older, early Permian strata (e.g., DiMichele et al., 2000; Galtier and Broutin, 2008), generally as fragmentary remains and thus needing to be identified with caution. The occurrences reported here

confirm the presence of this plant in early Permian strata, pushing that occurrence well back into the Wolfcampian–Cisuralian. Three specimens were found that we attribute to the peltasperm Supaia White (White, 1929) (Fig. 6A–D). The leaves are small and forked (Fig. 6A; possibly also Fig. 6B, a frond fragment) and once pinnate, with pinnules extending down the petiole below the fork. Pinnules are large, slightly exceeding 2 cm in length and 1 cm in width, and alethopteroid (decurrent bases; strong, persistent midveins; subparallel lateral margins) but not confluent. They are of flat aspect, and the midvein is not sunken, suggesting that the lamina was not arched enough to produce a sunken midvein. However, the midvein is wide, up to 1 mm at the base, and quite prominent, extending two-thirds of

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Fig. 6. A.–D. Core photographs of Supaia White. A. Pinnate, forked leaf. R. Ricker 1 core. Depth 7907.42 ft (IGSN: IERWB002F). B. Possible leaf fragment with overlapping pinnules. O. L. Greer 1 core. Depth 7937.7 ft (IGSN: IERWB000U). C. Pinnate leaf with longitudinal wrinkles. Black rectangle shows position of panel D. Thomas S. Riley D-9 core. Depth 9146.9 ft (IGSN: IERWB002T). D. Inset of panel C showing detail of longitudinal wrinkles. E. Terminus of a pinna of Sphenopteris germanica Weiss. All Day N-11 #2 core. Depth 7547.2 ft (IGSN: IERWB0038). F. Seedling leaf or bract of unidentified plant, unattributed here as incertae sedis. Nellie Eddleman #1 core. Depth 9081 ft (IGSN: IERWB003A).

the way to the pinnule tip. Secondary veins are nearly invisible. It is unclear if they angle upward steeply from the midvein or if they are parallel. Some of what appears to be veins may, in fact, be longitudinal wrinkles (see especially Fig. 6C, D) indicative of thick, stiff, coriaceous

lamina texture (as in the Supaia specimen illustrated by DiMichele et al., 2015; their Fig.8.1). The petiole and rachises are marked by well-developed sclerenchymatous plates or clusters of sclerenchymatous cells oriented transversely. Supaia is a common component of

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early Permian floras from the western United States and has been identified in abundance in the Wolfcamp and early Leonard of New Mexico (DiMichele et al., 2007) and Arizona (White, 1929), as well as in early Permian deposits from other parts of equatorial Pangea, including Western Europe and China (Galtier and Broutin, 2008; Gand et al., 1997; Wang, 1997). The third kind of foliar plant remains found in the core material is attributable to Sphenopteris germanica Weiss (Barthel, 2006), a plant of uncertain taxonomic affinities. The fossil is a single small fragment of the terminus of a pinna, but it shows the distinctive shape and deeply incised laminae that can either be interpreted as (1) pinnules, or (2) as a lobate pinnule with fan-shaped, open dichotomous venation and a terminal pinnule that is elongate, basally lobed via adherence to the subjacent lamina, and blunt tipped (Fig. 6E). Sphenopteris germanica had been considered a marker plant for the Permian (see discussion in Pfefferkorn and Resnik, 1980); the genus, but possibly one or more different species, has now been found well back into strata of Middle and Late Pennsylvanian age in western Pangea (e.g., DiMichele et al., 2013; Dimitrova et al., 2011; Lucas et al., 2013; Tabor et al., 2013). Sphenopteris germanica compares very closely with what Mamay (1992) described as Sphenopteridium manzanitanum Mamay from Late Pennsylvanian strata in New Mexico (DiMichele et al., 2013). Prior to Mamay's description, Sphenopteridium had been considered to be restricted to the Mississippian; Mamay (1992) found a distinctive structure similar in some respects to the reproductive organs known from Sphenopteridium in association with, but not in attachment to, S. germanica–type foliage and thereby made his generic determination. The reproductive organs of Sphenopteris germanica have been suggested to be different from those attributed to Sphenopteridium manzanitanum (Barthel, 2006; Remy, 1978), though in neither case are these structures known in attachment. This group is in need of revision; although the names Sphenopteris germanica and Sphenopteridium manzanitanum are used somewhat interchangeably among some of the above-cited papers, Sphenopteris germanica is preferred in the absence of clear association between reproductive and vegetative remains. One of the most perplexing plants in the assemblage is a small object of indeterminate organ affinity and taxonomic assignment (Fig. 6F). It consists of a short petiole approximately 1 mm long with a bifid lamina, about 8.5 mm maximum width, just below the fork. The fork in the

lamina is approximately 1.5 cm above the base of the petiole. The total length of the object is approximately 2.1 cm. A compression border rims the edges of the laminae, suggesting that it might have been slightly inrolled. The object appears to have internal venation in the lamina, suggesting affinities with vascular plants. A midvein b 1 mm wide extends from the petiole base, forks well below the lamina bifurcation, and extends into each of the lobes, where it becomes difficult to differentiate above the point of lamina bifurcation but may extend to the tip of each lobe. Secondary veins are not apparent. The surface of the lamina is covered by fine, elongate, longitudinal striations that cross over the midvein and thus are not lateral veins. Perhaps this small object is a seedling leaf or associated with a reproductive structure such as a bract. It is unlike anything we know and so remains unattributed here as incertae sedis. A number of plant remains were identified only as axes. Among these was a single specimen possibly of calamitalean affinity based on its ribbed surface (Fig. 7A). However, the specimen is limited in longitudinal extent and so the identification must remain uncertain. Most of the axes found are not attributable to particular plant taxa, and as material was transported a long distance, cannot be assumed with confidence to have been derived from the most common foliar element, Germaropteris. Some of these axes have unusual morphologies that do not permit us to distinguish between taphonomic/preservational happenstance and original morphological characteristics of the living plant (e.g., Fig. 7A, which seems to have nodes but lacks ribbing typical of calamitaleans or any indications of leaf or branch scars at these “nodes”). Other axes clearly were woody and are preserved totally or partially as vitrain (Fig. 7B). 6.2. Abundance and distribution of plant remains The quantification of taxonomic abundance is based on the total number of fossiliferous quadrats observed in the 14 cores listed in Table 3 (Supplemental Information). The most abundant plant in the collection is Germaropteris martinsii, which appears on 45 out of 196 total fossiliferous quadrats examined (Table 4, Supplemental Information). Another 136 specimens were identified as peltasperms but not positively as G. martinsii, although that is the most likely identification for most of these specimens. These are followed by woody axes on

Fig. 7. Core photographs of unidentified axes of terrestrial plants. A. Axis with possible nodes. O. L. Greer 1 well. Depth 8012 ft (IGSN: IERWB0015). B. Vitrinized woody stem. O. L. Greer 2 well. Depth 9504.9 ft (IGSN: IERWB002N).

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7 quadrats, Supaia sp. on 3, leaves of unidentified affinity on 3, Sphenopteris germanica on 1, and the small bifid leaf of uncertain affinity on 1. There were a number of specimens that we initially believed might have affinities with calamitaleans, conifers, or gigantopterid seed plants but that upon closer examination should be considered to be plant material of suggestive but uncertain affinity. The Reagan County specimens, which compose most of the assemblage (154 of 196 quadrats), were transported some distance from shoreline into the deep basin. It is possible that there was a considerable effect of sorting on the macrofloral composition. The overwhelming abundance of Germaropteris martinsii must be considered, therefore, in light of the presence of rare but distinctive elements such as Supaia sp. and Sphenopteris germanica. These rare elements add weight to the likelihood that the quantitative composition of the flora is not reflective of the makeup of the parent vegetation, at least not on a regional scale. These elements may reflect sampling of river or estuary margins and shoreline settings, however, where high dominance of single plant species might be expected to occur over large areas because of the stressfulness of the physical environment, and from which a transported flora is likely to have been derived. More terrestrial plant specimens are present in the lower Leonard than in the upper Wolfcamp (Fig. 8), based on measurements on the O. L. Greer 1 core, the only core that spans both intervals. On average, the lower Leonard has twice as many fossils per 10-ft interval of core (2.3 compared to 1.1). Sampling bias was assessed by counting the number of unique core ends for two 100-ft intervals in the same core, one in the lower Leonard and one in the Wolfcamp (Table 5, Supplemental Information). Over a 100-ft interval in the Wolfcamp in the O. L. Greer 1 core, 524 unique surfaces were present. Over a 100-ft interval in the lower Leonard, slightly fewer (505) unique surfaces were present, a difference of only 4%, which supports the interpretation of a lessfossiliferous Wolfcamp interval and indicates that the abundance of fossils found is not a function of the number of surfaces examined. In addition, unique core ends were counted in the 10-ft (3-m) interval with most abundant plant fossils (8020–29 ft) and in one with no plant fossils (8100–09 ft). The interval from 8020 to 8029 ft had 64 unique core ends. The interval with no plant fossils had 66 unique core ends, but lithology in that interval was coarser-grained. This difference in lithology accounts for about half of the difference between plant abundance in the Wolfcamp and Leonard intervals. Nearly nonfossiliferous, coarse-grained floatstones, interpreted as debrites, account for about one-quarter of Wolfcamp thickness present in the O. L. Greer 1 core, but they are absent in the lower Leonard (Fig. 8). In this study, peltasperms are most common in siliceous mudrocks. Unlike a previously published account (Spicer and Thomas, 1987), few terrestrial plant fossils were found in facies interpreted as debrites (muddy bioclast-lithoclast floatstones) or turbidites (skeletal wackestones/packstones). On the contrary, N 90% of 142 peltasperm specimens in Reagan County cores were found in finer-grained, hemipelagic deposits, between coarser-grained floatstones and wackestones/packstones. A similar pattern was observed in cores from the basin margins (Fig. 4). Woodlike, parallel-veined plant debris, mostly fragments b1 cm (0.4 in) in diameter, occurs in coarse-grained, carbonate-clast-rich sediments and indicates that terrestrial plants are transported in debrites and turbidites but do not remain intact. Peltasperms and marine benthic fossils were found in close vertical proximity to one another in a few cores and, rarely, on the same bedding plane. No evidence of subaerial exposure of bedding planes, such as roots or soils, was found. The oldest occurrence of Germaropteris in the Midland Basin, based on depth in core, is that from the O. L. Greer #1 well (Fig. 4). A deeper occurrence of Sphenopteris germanica was identified in the All Day N11 #2 core, but that was not associated with peltasperm remains. A peltasperm not identifiable as Germaropteris was found in the Baggett 29 #1 well. The occurrences in these wells appear to represent some

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of the oldest reported occurrences of Germaropteris martinsii in North America.

7. Discussion Terrestrial plant fossils were found primarily in laterally persistent basinal siliceous mudrocks in lower Leonard and Wolfcamp intervals. The depositional setting in Reagan County was near the paleogeographic center of the Midland Basin (Fig. 1), about 64 km (40 mi) from the Central Basin Platform and 32 km (20 mi) from the Eastern Shelf. Lack of current-derived sedimentary structures, except in coarse-grained wackestones/packstones, indicates that these sediments were deposited below storm wave base. Common occurrence of laminae indicates that fine-grained sediments are largely hemipelagic in origin, settling out of the water column to the sediment/water interface on the floor of the basin. The remaining wells, outside of Reagan County, are closer to basin margins. Plant-hosting sediments in those wells are mostly fine-grained mudrocks, interpreted as hemipelagic deposits. These deposits are interbedded with coarse-grained, sometimes conglomeratic, carbonate beds, reflecting proximity to their source. Terrestrial plants in a marine setting are not commonly reported. These plants arrived in the Midland Basin probably after rafting from the basin margins and sinking to the basin floor (Fig. 9). Anoxia protected the plant remains from destruction and consumption by bacteria and burrowing infauna. The presence of plant material in 14 cores scattered across the basin suggests that these fossils may be common in brackish-to-marine Permian-age siliceous mudrocks throughout the Midland Basin, especially in the lower Leonard interval. The present study is one of the first reported occurrences, as far as we know, of peltasperm leaves in deep-water (epicontinental), basinal sediments in the early Permian. The preservation of Germaropteris martinsii in particular may reflect its notably thick leaves and heavy, waxy cuticle (Kustatscher et al., 2014), traits that contribute to preservation and may explain how leaves remained largely intact after transport from the coastal zone to the deep basin. The plant group to which Germaropteris martinsii belongs, the peltasperms, underwent a major evolutionary radiation in the Permian and, based on associations of reproductive and vegetative organs, may include such groups as callipterids, supaioids, comioids, and gigantopterids, among others (DiMichele et al., 2005; Kerp et al., 2001; Kerp and Haubold, 1988; Poort and Kerp, 1990; Wang, 1997). Germaropteris martinsii, whose closest affinities are with the callipterids, had earlier been classified as a member of the genus Callipteris, now considered to be an invalid name (Kerp and Haubold, 1988).

The peltasperms, which appear to have originated as an evolutionary lineage in the Pennsylvanian, both diversified and expanded their geographic range in the Permian as subhumid to semiarid climates expanded in the tropical realms of Euramerica (Tabor et al., 2013; Tabor and Poulsen, 2008). During the middle and late Permian, they became important in the higher northern latitudes of Angara (modern Siberia) and in eastern equatorial regions of Cathaysian Pangea (modern China and Southeast Asia) that remained humid to subhumid because of a paleogeographic position along the juncture between Tethys and Panthalassa (Boucot et al., 2013). In most reported occurrences, the peltasperms appear to have been confined to subhumid conditions, where there was a definite dry season, inferred in part from their occurrences in deposits associated with calcic, vertic paleosols—strong indicators of seasonal climatic regimes. This habitat preference also has been inferred from peltasperm occurrence with other kinds of plants having xeromorphic morphologies. This includes, in particular, conifers and taeniopterids, but also wetland species such as the marattialean tree ferns and calamitalean sphenopsids that, based on their wide distributions, were able to disperse and locate wet areas of the landscape, even if small and remote (e.g., DiMichele et al., 2007; DiMichele et al., 2014). Some forms, notably Autunia conferta, are known from organic shales, suggesting that some ecotypes could tolerate swampy substrates (Kerp, 1988). Nearly all peltasperm occurrences are in inland, alluvial, coastal-plain settings, very commonly in small lakes formed from abandoned channels or in channel deposits themselves. Germaropteris is an exception to this eastward and northward late Permian shift. It has been reported almost exclusively from the Late Permian at several places in Europe and Great Britain (Kustatscher et al., 2014; Schweitzer, 1986), where it often occurs as a dominant element. The few previous reports of Germaropteris from the early Permian are all tentative, in part because they are so much older than the known range and thus unanticipated. One of these reports is from the Lodève Basin of southern France (Galtier and Broutin, 2008). Another is from the Central Basin Platform in Gaines County, Texas (DiMichele et al., 2000). In both instances, suspect Germaropteris (reported as Peltaspermum) is a rare element of the flora. There are reports also of reproductive organs attributable to the “true” peltasperms, a group to which Germaropteris belongs, at the Carboniferous–Permian transition (Kerp et al., 2001), suggesting that these lineages may go much further back in time than previously imagined. Groups showing such occurrences have been described recently as “Methuselah taxa” (Looy et al., 2014). Germaropteris martinsii also is an exception to the general habitat patterns of other peltasperms and suspected peltasperms. It is best preserved in marine environments where it is unlikely to have lived, yet

Fig. 9. Diagram of model for processes delivering macroscopic fragments of land plants to deep-water basinal settings. Fragments of land plants are carried off-shore by currents, lose buoyancy, and sink into oxygen-poor, deep-basin waters where they are buried by slowly accumulating hemipelagic sediment. After Baumgardner et al., 2016.

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where it is the most common, and sometimes the only, fossil plant species represented. From this pattern of occurrence, it can be concluded that G. martinsii may have grown in monotypic, or nearly monotypic, stands in areas along coastal strands or fringing estuaries and rivers draining the landscape, where remains of these plants could be entrained and carried out to sea. Occurrences in the study cores reflect this most common of the Late Permian Germaropteris occurrences. It might be concluded that the plant was tolerant of high-stress habitats with elevated salt content, indicative of a mangrove-type habitat affinity. Morphologically, Germaropteris martinsii is noteworthy for the great thickness of its leaf laminae, which nearly obscures venation. In compression, it often is preserved as vitrinized remains, suggesting very thick leaves, possibly of succulent habit. These features would conform with growth in salt-rich waters. The leaves were compound (composed of many small pinnules attached to rachises, like small fern leaves—though Germaropteris was a seed plant), a trait inherited from peltaspermous ancestors, many of which had compound leaves. Where preservation occurred under favorable conditions, Germaropteris also has been found to have a thick cuticle, the waxy material that covers plant external surfaces (Kustatscher et al., 2014). The increase in recognizable plant remains from late Wolfcampian to early Leonardian time, as observed in the O. L. Greer 1 core (Fig. 8), coincides with a relative rise in sea level and a shift to a warmer and drier climate (Fig. 2). Rising sea level during the late Wolfcampian and early Leonardian may have increased suitable habitat for peltasperms around the margins of the Midland Basin. A drier climate may have favored proliferation of these xeromorphic plants. Both trends could have increased the number of peltasperms and related plants available to be uprooted by storms or floods and transported to the deep basin (Fig. 9). 8. Conclusions Presence of Germaropteris martinsii in the lower Leonard–Wolfcamp interval is consistent with published reports of occurrences in the Midland Basin area, but the deepest occurrences shown here are older and much more abundant than those previously reported, and can be identified to species level with greater confidence. Dominance of Germaropteris martinsii in the flora recovered suggests that a warm, seasonally dry climate prevailed in the area during Leonardian– Wolfcampian time. An increase in the number of peltasperms observed from late Wolfcampian to early Leonardian time suggests that a larger area of the basin margin was populated by peltasperms during early Leonardian time, which may have resulted from sea-level rise, flooding of wide basin-margin shelves, and an increase in suitable habitat. Absence of peltasperms in cores of early Wolfcampian age suggests that the advent/spread of these plants into the Permian Basin area may have occurred during middle/late Wolfcampian time as sea level rose and climate became increasingly warmer and drier. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.palaeo.2016.07.024. Acknowledgments This work was supported by funding from the Mudrock Systems Research Lab consortium at the Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin (OSP 200803001). Members included Anadarko, Apache, BHP, BP, Cenovus, Centrica, Chesapeake, Chevron, Cima, Cimarex, Concho, ConocoPhillips, Cypress, Devon, Encana, ENI, EOG, EXCO, ExxonMobil, FEI, Hess, Husky, IMP, Kerogen, Marathon, Murphy, Newfield, Oxy, Penn Virginia, Penn West, Pioneer, QEP, Samson, Shell, StatOil, Talisman, Texas American Resources, The Unconventionals, US Enercorp, Valence, and YPF. Cores were donated to the CRC by Shell and BP Amoco/Altura. CT scan of the R. Ricker 1 core was provided by Ingrain, Inc., Houston, TX. Core access

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and sampling were provided by CRC personnel: James Donnelly, Andrew Faigle, Nathan Ivicic, Randy McDonald, Bill Molthen, and Brandon Williamson. The authors thank Robert Hook for his assistance with this project, including identification and selection of fossil specimens, and we thank Greg Wahlman for his guidance in sorting out the chronostratigraphy of the study interval. Ann Molineux, Director, and Angella Thompson of the Non-Vertebrate Paleontology Laboratory at The University of Texas at Austin were instrumental in archiving samples collected during this study. Megan Carter of the Interdisciplinary Earth Data Alliance (IEDA) facilitated registration of the sample metadata in the SESAR database. Text was edited by Stephanie Jones. Core photographs were prepared for publication by David Stephens. Illustrations were edited by Cathy Brown. Reviews by Thomas Algeo and two anonymous reviewers materially improved the manuscript. Publication authorized by the Director, Bureau of Economic Geology.

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