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Journal of Sedimentary Research, 2013, v. 83, 1147–1161
Research Article
DOI: 10.2110/jsr.2013.89
A LINKAGE AMONG PANGEAN TECTONISM, CYCLIC ALLUVIATION, CLIMATE CHANGE, AND BIOLOGIC
TURNOVER IN THE LATE TRIASSIC: THE RECORD FROM THE CHINLE FORMATION, SOUTHWESTERN
UNITED STATES
STACY C. ATCHLEY,1 LEE C. NORDT,1 STEPHEN I. DWORKIN,1 JAHANDAR RAMEZANI,2 WILLIAM G. PARKER,3
SIDNEY R. ASH,4 AND SAMUEL A. BOWRING2
1
Department of Geology, Baylor University, 101 Bagby Avenue, Waco, Texas 76706, U.S.A.
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, U.S.A.
3
Division of Resource Management, Petrified Forest National Park, Box 2217, Petrified Forest, Arizona 86028, U.S.A.
4
Department of Earth and Planetary Sciences, Northrop Hall, University of New Mexico, Albuquerque, New Mexico, 87131, U.S.A.
e-mail: stacy_atchley@baylor.edu
2
ABSTRACT: High-precision geochronology provides unprecedented insights into the depositional history of the Upper Triassic
Chinle Formation of the Colorado Plateau, as well as its paleoenvironmental and paleobiological records. The Chinle
succession exposed in the Petrified Forest National Park (PEFO) and vicinity, Arizona, includes two large-scale alluvial
composite sequences. Although each composite sequence fines upward, the upper composite sequence is more dominated by
coarser-grained deposits. Petrographic analysis of sandstone lithic content indicates an upward decrease in the proportion of
volcanic rock fragments in each composite sequence. Paleocurrent indicators in the lower composite sequence suggest a variable
paleoflow direction, whereas northward paleoflow dominated the upper composite sequence. The change in paleoflow appears to
coincide with a reorganization of alluvial depositional processes and associated source terranes, and precedes a rapid
acceleration in basin subsidence.
Climate proxy records from paleosol geochemistry indicate a gradual shift from humid to dry conditions across the transition
between the lower and upper composite sequences and the Adamanian–Revueltian biotic turnover. Composite-sequence
depositional reorganization, climatic shift and biologic turnover, in turn, appear to coincide with episodes of magmatism
recorded in Triassic granitoid plutons presently exposed in southern California. Taken collectively, these observations suggest
that the Late Triassic depositional, climatic, and ecologic history at PEFO may be related to emergence of the incipient
Cordilleran magmatic arc along the convergent western margin of Pangea. A new U-Pb date for the lower part of the Chinle
Formation suggests that most or all of the formation was deposited in the Norian Stage.
INTRODUCTION
The Upper Triassic Chinle Formation of the southwestern United
States archives a remarkable record of terrestrial ecosystems that existed
across the western portion of equatorial Pangea. Among the thickest and
most easily accessible outcrop exposures occur at Petrified Forest
National Park (PEFO) in northeastern Arizona. Although the Chinle
Formation at PEFO has been extensively studied (see summary in Parker
and Martz 2011), a reliable lithostratigraphic framework and highprecision geochronology have only recently become available (Martz and
Parker 2010; Ramezani et al. 2011; Martz et al. 2012). It has long been
recognized that two distinct vertebrate faunal assemblages occur in the
Chinle Formation of Arizona, the Adamanian and the Revueltian (e.g.,
Heckert and Lucas 2002); however, the exact stratigraphic position of the
turnover was ambiguous (Parker 2006). The recent lithostratigraphic
revisions of the Chinle Formation at PEFO by Martz and Parker (2010)
allow the precise placement of the Adamanian–Revueltian (A-R)
boundary in the lower portion of the Lots Wife beds of the Sonsela
Member (Parker and Martz 2011). Furthermore, a distinctive floral
change also occurs at the same stratigraphic position (Reichgelt et al.
2013). These new data, along with the newly established geochronologic
Published Online: January 2014
Copyright E 2013, SEPM (Society for Sedimentary Geology)
framework (Ramezani et al. 2011), allow the determination of possible
causal events related to this biotic turnover.
In this paper, we supplement the geochronologic framework of
Ramezani et al. (2011) with two new U-Pb zircon ages from key
stratigraphic intervals. The resulting age model and associated stratigraphic and paleoclimatic record is the most refined ever established for
the Chinle Formation. From this record, the history of cyclic
environmental change and corresponding biotic turnover is temporally
correlated to the Late Triassic tectonic history and physiographic
evolution of western Pangea. As such, this paper sheds light on the
previously undetected balance between life, paleogeography, and
tectonism in the Late Triassic of the southwestern United States.
PALEOGEOGRAPHIC SETTING
The Chinle Formation was deposited in fluvial and lacustrine
environments in a large backarc basin that extended across what is
presently the Colorado Plateau of the southwestern United States
(Stewart et al. 1972; Blakey and Gubitosa 1983, 1984; Dubiel et al.
1991; Dubiel 1994; Dubiel and Hasiotis 2011; Cleveland et al. 2007)
1527-1404/13/083-1147/$03.00
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S.C. ATCHLEY ET AL.
FIG. 1.—A) Late Triassic paleogeographic
reconstruction of the southwestern U.S.A. and
its location along the western margin of equatorial Pangea (modified from Cleveland et al.
2007 and Trendell et al. 2012). B) Location of
Petrified Forest National Park (PEFO) in
northeastern Arizona, and the position of
outcrop exposures used to construct the composite measured section provided in Appendix
A. Outcrop locations are denoted with stars and
annotated with geographic reference names.
(Fig. 1A). The basin was located near the western equatorial convergent
margin of the Pangean supercontinent approximately 5 to 15u north of
the paleo-equator (Scotese 1994; Molina-Garza et al. 1995), and was
bounded by various foreland uplifts to the east and north and by the
nascent Cordilleran magmatic arc complex to the south and west
(Harshbarger et al. 1957; Cooley and Davidson 1963; Dickinson 1981;
Lawton 1994; Scotese 1994; Molina-Garza et al. 1995) (Fig. 1A). The
associated Late Triassic paleoclimate was dominated by westerly
monsoonal flow (Parrish 1993). The Chinle Formation at PEFO is
located in the southern portion of the Chinle Basin near the axis of what
was a northwest-flowing fluvial drainage complex during the Late
Triassic (Riggs et al. 1996; Tanner and Lucas 2006; Dickinson and
Gehrels 2008). The main fluvial unit of the formation, known as the
Sonsela Member (see Fig. 2A for its position in the study interval), has a
predominately northeastward paleocurrent signature and contains a high
proportion of volcanic clasts suggesting that these sediments were relayed
to the trunk stream by a major tributary system originating from a rising
tectonic arc to the west (Riggs et al. 2012; Howell and Blakey 2013).
There is a distinct change in depositional style from an architecture
dominated by sheet sandstone and conglomerate in the lower Sonsela
Member to a finer-grained assemblage with ribbon sandstones in the
upper Sonsela possibly related to dynamic subsidence and aggradation in
the Chinle Basin (Howell and Blakey 2013).
METHODS
Outcrop and Petrographic Descriptions
A 390 m composite section of the Chinle Formation was compiled from
seven locations within and adjacent to PEFO (Fig. 1B; Appendix A). The
section encompasses, from bottom to top, the Mesa Redondo, Blue Mesa,
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
Sonsela, Petrified Forest, and lower Owl Rock members of the Chinle
Formation in northeastern Arizona (e.g., Ramezani et al. 2011)
(Appendix A, see Acknowledgments). The vertical succession of 104
‘‘fluvial aggradational cycles (FACs)’’ that constitute the Chinle
Formation at PEFO were measured and sedimentological data
collected following the guidelines of Atchley et al. (2004). Data
collected include stratal thickness, grain size, sedimentary structures,
lithostratigraphic boundaries, and the occurrence of paleosols (Appendix A). In addition, paleocurrent measurements were made on all
sandstones with unequivocal directional indicators, e.g., trough crossbeds, planar-tabular crossbeds, current ripples, and the orientation of
petrified logs. These directional data were collected and plotted as
summary rose diagrams for each sandstone from which measurements
were taken. The rose diagrams appear in their order of stratigraphic
occurrence in Appendix A, and each diagram is annotated with a listing
of the structure(s) upon which they are based. Thin sections from 37
sandstone specimens collected throughout the composite section were
point-count analyzed (300 counts/specimen) to determine the abundance of framework grains.
Paleosols
Field Description and Laboratory Analyses.—Paleosols were described
in the field for texture, ped structure, color, iron redoximorphic features,
iron reduction features after roots (drab root halos), slickensides, and
carbonate nodules (Soil Survey Staff 1999). Properties served as
guidelines to assign master and subordinate horizon symbols to unique
layers in each paleosol profile (Table 1). Horizon thickness measurements
were decompacted using coefficients for floodplain silt and clays (Sheldon
and Retallack 2001), because paleosols in the study area formed in similar
environments and because of insufficient data to confidently assign
taxonomically defined soil orders (Soil Survey Staff 1999) whereby orderspecific coefficients could be applied.
The first B horizon of each paleosol was sampled in bulk for
geochemical analysis to estimate mean annual precipitation (MAP).
Major-element concentrations were determined by a four-acid sample
digestion by ICP-MS and SiO2 by X-ray diffraction on pressed pellets
(ALS Chemex, http://www.alsglobal.com/). The elements are reported as
oxides in weight percent (Table 1). Pedogenic carbonate nodules were
sampled from B horizons for stable carbon isotopic analysis and
calculation of atmospheric pCO2 concentrations. A triplicate average
isotopic composition of micro-drilled powder from each paleosol is
reported, except in two paleosols where small carbonate amounts limited
sampling to single aliquots. Isotopic analysis of carbonates was
accomplished by evolving CO2 from calcite on a Thermo Scientific Gas
Bench II with subsequent isotope-ratio measurements performed on a
Delta-V Advantage mass spectrometer at Baylor University. Duplicate
analyses (n 5 10) of IAEA standard NBS-18 resulted in an average d13C
value of 25.01% with a standard deviation of 6 0.03.
Drainage Indexes.—We devised a simple threefold system to characterize paleosol drainage in the study area, similar to the one designed by
Atchley et al. (2004) where color and color patterns (Munsell Soil Color
Book 2009) relate to differences in the redox state of iron (Vepraskas
1992; Soil Survey Staff 1999; Nordt and Driese 2009; Vasilas et al. 2011).
Drainage categorization was performed independently of taxonomic
classification and depended principally on paleosol color with horizon
symbols used as guidance for drainage consideration. Emphasis was
placed on color and color patterns in the upper 1 m of each profile, where
plant roots tend to concentrate. We used the upper 1 m of each
decompacted profile even in cases where minor erosion may have
removed part of the A horizon. Kraus and Hasiotis (2006) and PiPujol
and Buurman (1994) have shown that many iron redoximorphic features
1149
are conservatively preserved in paleosols in the rock record, especially if
not having experienced deep burial conditions conducive to diagenetic
mineral transformations. To the contrary, post burial gley features after
roots are excluded from drainage interpretations because these iron
reduction zones are thought to have formed after burial in response to the
decomposition of root material from the last crop of plants growing on
the surface (Retallack 1991).
Paleosols classified as Drainage Index 1 are dominated (. 50% of
excavated outcrop surface area) by gley (gley hue Munsell pages 10Y,
5GY, 10GY, 5PG, N) matrix colors interpreted to have formed under the
influence of a persistently high water table, with or without iron
concentrations in the form of soft masses or concretions (Fig. 3A, B;
Table 1). All poorly drained paleosols were described with the symbol
‘‘g’’ somewhere in the critical depth interval (i.e., Bg, Bssg, Bkg). Here,
most iron is assumed to have been reduced and leached from the paleosol
under anaerobic conditions. Many of the paleosols in this drainage
category are Vertisol-like and undoubtedly experienced periodic desiccation because of the shrink–swell features. However, modern Vertisols can
be poorly drained and have hydric indicators (Vasilas et al. 2011) or aquic
soil moisture regimes (Soil Survey Staff 1999) that formed shrink–swell
features during brief episodes of drying (Nordt and Driese 2009; Jacob et
al. 1997).
Paleosols classified as Drainage Index 2 have gley colors comprising
between . 2% and 50% of the matrix observed on excavated outcrop, or
gray colors (1 or 2 chroma of 5R-7.5YR hue Munsell pages) constituting
between . 2% and 100% of the matrix surface area observed on
excavated outcrop, and are interpreted as having intermediate drainage
conditions (Fig. 3C, D, E; Table 1). These paleosols may or may not be
accompanied by iron concentrations in the form of soft masses or
concretions. If the profile is a comingling of gley (or gray) colors and high
chroma colors, or if the profile is dominated by gray colors, then the
paleosol water table is interpreted to have been fluctuating. The rationale
for treating low-chroma gray colors in this way is that some pigmentation
still remains and indicates incomplete reduction and leaching of iron
(Vasilas et al. 2011). Drainage Index 2 paleosols are identified with any
horizon symbol except ‘‘g,’’ although to distinguish these paleosols from
other drainage categories we place the symbol ‘‘g’’ in parentheses as part
of the horizon sequence (i.e., Bss(g) or Bw(g)). Most pedologists do not
use the gley symbol unless the soil is poorly drained or dominated by
properties indicating poor or very poor drainage (Soil Survey Staff 1999).
Paleosols classified as Drainage Index 3 have high chroma matrix
colors and , 2% iron depletions, whether gley or gray, and are
interpreted as well drained (Fig. 3F, G; Table 1). This drainage index
indicates that saturation and reduction did not occur for sufficient time to
significantly mobilize iron. These paleosols are described with any
horizon symbol except ‘‘g’’ or the use of ‘‘g’’ in parentheses as in Drainage
Index 2 paleosols.
Mean Annual Precipitation (MAP).—Mean annual precipitation
(MAP) was estimated using the CALMAG geochemical weathering
index of Nordt and Driese (2010) and the CIA-K geochemical weathering
index of Sheldon et al. (2002) (Table 1). CIA-K is defined as [Al2O3/
(Al2O2 + CaO + Na2O)]*100, where bulk paleosol oxides are determined on the first B horizon and are expressed as molar weight
percentages. CALMAG is identical except that it substitutes MgO for
Na2O. In the plot of MAP provided in Figure 2I, CALMAG rainfall
estimates were applied only to paleosols with ‘‘ss’’ horizon symbols
because they are similar to modern Vertisols, from which the CALMAG
proxy is based. The CIA-K proxy is applied to all of the other soil orders
in the study area, which is consistent with those included in the CIA-K
database (i.e., Inceptisols, Aridisols, Alfisols, Mollisols, Ultisols). We
included all paleosols in the study area in the MAP calculations regardless
of drainage index because poorly drained soils are included in the original
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S.C. ATCHLEY ET AL.
FIG. 2.—A time-calibrated depiction of Chinle Formation stratigraphy and related attributes derived from the outcrop composite section (Appendix A). Also shown is
the position of the Adamanian–Revueltian (A-R) faunal turnover at Petrified Forest National Park (PEFO). A) Lithostratigraphic (after Martz and Parker 2010),
geochronologic (in part after Ramezani et al. 2011), and sequence stratigraphic framework. B) Stacked bar chart of lithologic proportions within fluvial aggradational
cycles (FACs). The lithologic composition of each FAC is depicted by a stacked bar chart with the midpoint of each FAC bar placed at its interpolated age between dated
tuffaceous sandstones. C) Cumulative deviation from mean grain size for the coarsest size fraction observed in FACs. D) Estimate of sedimentation rate for individual
FACs (raw data) and as a three-point average. The three-point average presented here and for paleosol drainage, Part H, below, are calculated as the average of a given
data point in time and the preceding and following data point. FAC accumulation rate is calculated by dividing decompacted FAC thickness by the amount of time
bracketed between FACs from linear interpolation between dated tuffaceous sandstones. FAC decompaction is based on the algorithms of Sheldon and Retallack (2001).
Because of similarity in the composition of parent material and uncertainty in the assignment of equivalent Modern soil orders to Chinle paleosols, compaction constants
for floodplain mud and sand reported in Sheldon and Retallack (2001) were used in FAC decompaction calculations. E) Subsidence plot from cumulative FAC
decompacted thickness. See comments regarding FAC decompaction in the caption for Part D, above. F) Fraction of potassium feldspar, plagioclase, and volcanic rock
fragment framework grain abundance in sandstones. G) Dominant paleoflow directional tendency (see Appendix A for the location of corresponding rose diagrams and
listing of features used in paleocurrent measurement). H) Paleosol drainage as three-point average. I) Estimates of mean annual precipitation (MAP) derived from
paleosols and the occurrence of common pedogenic carbonate. J) Estimates of atmospheric pCO2 estimates derived from paleosols. K) The biostratigraphic range of
terrestrial fauna (modified from Parker and Martz 2011) and pollen biozones (Reichgelt et al. 2013) along with the trend of plant-leaf preservation as either megafossils or
mesofossils (Ash 2010a, 2010b). L) The timing of pluton emplacement within the Cordilleran magmatic arc (Barth and Wooden 2006; Barth et al. 2011).
Marbut (1935) database for CIA-K and because Vertisols upon which
CALMAG was developed also included poorly and somewhat poorly
drained soils. Inclusion or exclusion of poorly drained paleosols produces
no discernible difference in the rainfall curve.
Atmospheric pCO2.—Atmospheric CO2 concentrations (ppmV) are
estimated from paleosols with carbonate nodules using the paleobarometer of Cerling (1999) modified to Late Triassic conditions at PEFO
using the procedures of Nordt et al. (2003) (Table 2). The paleobarometer equation is atm CO2 (ppmV) 5 Sz [(d 13Cs * 1.044 d13Cr 2 4.4)/
(d13Catm 2 d 13Csoil)]. Sz is soil CO2 concentration taken as
1500 ppmV following Breecker et al. (2010) under the assumption that
pedogenic carbonate nodules form during the driest season of the year,
when soil CO2 concentrations are lowest. d13Cs is soil CO2 estimated
from temperature-dependent carbonate equilibria reactions from the
d13C of pedogenic carbonate nodules (Romanek et al. 1992). The
average value of three micro-drilled powder samples from pedogenic
carbonate nodules collected from each paleosol is reported in Table 2
and plotted in Figure 2J. For the carbonate equilibria reactions, we
assume soil temperatures of 25uC because of the tropical paleogeographical
location of the study area. The d13C of atmospheric CO2 is determined by
taking average marine limestone d13C values for the time interval from 222
to 207 Ma from Korte et al. (2005) and adding 8.5 per mil as an equilibrium
fractionation factor between marine carbonate and atmospheric CO2 (LynchStieglitz et al. 1995). Because the abundance of paleosol organic carbon is so
low in the study area, we estimated the respired d13Cr by rearranging the
empirically derived equation of Arens et al. (2000) once the d13C of atmospheric CO2 was known. This relationship is expressed as d13Catm 5 (d13Corganic + 18.67)/1.10. The derived d13Cr values (or d13Corganic) are similar to
two measured d13C values of leaf remains from mudstones in the upper portion
of the Sonsela Member (224.16%, 226.28%).
U-Pb Geochronology
Two fist-sized specimens of tuffaceous sandstone were collected from
key stratigraphic intervals of the lower Chinle Formation in and outside
of PEFO and dated by the U-Pb isotope-dilution thermal-ionization mass
spectrometry (ID-TIMS) method in order to further refine the existing
geochronologic framework of the formation. Fourteen hand-selected
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
1151
FIG. 2.—Continued.
single zircon grains pre-treated by the CA-TIMS technique of Mattinson
(2005) were analyzed following the analytical procedures described in
Ramezani et al. (2011).
Data reduction, error propagation, and date calculation was carried out
using EARTHTIME algorithms and software applications (Bowring et al.
2011; McLean et al. 2011). Our calculated dates are based on weighted mean
206
Pb/238U dates derived from a coherent cluster of the youngest zircon analyses
in each sample that are reported at 95% confidence level (Table 3, Fig. 4) and
are interpreted as the maximum depositional age of the sample. Uncertainties in
U-Pb dates are reported as 6 X/Y/Z Ma, where X is the internal (analytical)
uncertainty in the absence of all external errors, Y incorporates the U-Pb tracer
calibration error, and Z includes the latter as well as the decay constant errors of
Jaffey et al. (1971). In order to establish a high-resolution chronology based on
the results produced by the same isotopic technique and using the same tracer,
only the analytical uncertainties (X) need to be considered.
Biostratigraphy
Occurrences of fossil index taxa for the Adamanian and Revueltian
faunal assemblages were plotted following Parker and Martz (2011) and
are based on their presentation of the precise placement of fossil localities
into the local stratigraphy. Fossil identifications follow the apormorphybased procedure outline by Nesbitt and Stocker (2008). The data for the
early dinosaur Chindesaurus bryansmalli and the pseudosuchian Revueltosaurus callenderi are modified based on recent discovery of new material
from PEFO. The new data also reflect the updated taxonomy for the
phytosaur Pseudopalatus (now Machaeroprosopus) following Parker et al.
(2013). Voucher specimens for all of the vertebrate biostratigraphic data
are provided in Table 4.
RESULTS
U-Pb Geochronology
The U-Pb age results presented here are consistent with, and further
enhance, the detailed geochronologic framework established by Ramezani et al. (2011) for the Chinle succession at PEFO and vicinity. The
closely spaced and dated tuffaceous beds that now encompass the entire
succession have mutually resolvable ages that conform to the stratigraphic order, substantiating their interpretation as reliable indicators of
depositional age. The two additional dates provided in this study are
derived from samples SS-7 and SS-24 (see stratigraphic location in
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S.C. ATCHLEY ET AL.
TABLE 1.—Paleosol horizons, drainage indexes, and bulk oxides for geochemical calculation of mean annual precipitation (MAP). The gray shaded rows
highlight paleosols that bracket the Adamanian–Revueltian (A-R) faunal transition. See Appendix A for the stratigraphic location of paleosols in the Chinle
Formation composite measured section.
CALMAG3
Bulk Oxides (wt. %)
CIA-K3
Paleosol
Horizon Sequence1
Drainage2
Al2O3
CaO
MgO
Na2O
Index
MAP (mm)
Index
MAP (mm)
MR43
MR44
MR45
MR46
MR47
MR48
MR49
MR49.5
MR50
MR51
T1
T2
T3
T4
T4.5
T5
T6
T7
T8
T9
T10
T11
GT12/13
GT14
GT15
GT16
GT17
GT17.25
GT17.50
GT18
GT19
GT20
GT21
GT22
BM23
BM24
BM25
BM26
BM27
BM27.5
BM28
BM29
BM29.5
BM30
ML52
ML53
ML54
ML55
ML56
ML57
ML58
ML59
ML60
ML60.5
ML61
ML62
ML63
ML64
ML65
ML66
ML67
ML68
C32
C33
C34
Bw(g)
Bw/C (g)
A/C-Bw(g)-C
A-Bssg1-Bssg2-C
A-Bw(g)/C
A/C(g)-C
A-Bw1(g)/C-Bw2(g)/C
A-Bw(g)-C
Bw(g)-C
Bt1(g)-Bt2(g)
A-Bw/C
A-Bw/C
Bssg1-Bssg2-BCg
A1-A2-Bssg1-Bssg2-C
Bss(g)-C
A-Bssg-BCg
A-Bss(g)-C
A(g)-C
Bssg1-Bssg2-C
A-Bssg
A-Bssg
A-Bssg-BCssg
A-Bss1-Bss2-C
A-C(g)
A-Bg1/C-Bg2/C-C
A-Bw1(g)-Bw2(g)-C
A-Bw(g)-BC(g)-C
Bg/C
Bkg
A-Bss1(g)-Bss2(g)-BCss-C
Bss1(g)-Bss2(g)-Bss3(g)-C
A-Bss1(g)-Bss2(g)-BC(g)
Bss1(g)-Bss2(g)
A-Bssg-C
A1-A2-Bss1(g)-Bss2(g)-BC
A-Bss(g)-C
A-Bss(g)
A-Bss1(g)-Bss2(g)-BC
A/C-Bw(g)-B(g)/C-C
A-Bw(g)/C-C/B
A-Bw1(g)-Bw2(g)-BC-C
A/C(g)-C(g)
A-Bw(g)
Bssg1-Bssg2-Bssg3-BC
A-Bss1(g)-Bss2(g)-BC-C
A/C-Bw(g)/C-CB(g)
A-Bw(g)-BC(g)-C
A/C(g)-Bw(g)/C
Bssk(g)-C(g)
A/C(g)-C/A(g)
A-Bk(g)
A-Bkg1-Bkg2-C
Akg-Bkg1-Bkg2-Bkg3
Bsskg1-Bsskg2
Bk1(g)-Bk2(g)
Bk(g)-CB(g)-C
Ak-Bk(g)-C
A/C-Bw(g)/C
A-Bk(g)-C/B(g)-C
A/C-Bk1-Bk2
Bssk1(g)-Bssk2(g)-Bk(g) -C
Ak-Bssk(g)
A-C(g)
A-Bssk1-Bssk2-Bssk2-CB
A-Bssk(g)-BC(g)
2
2
2
1
2
2
2
2
2
2
2
2
1
1
2
1
2
2
1
1
1
1
3
2
1
2
2
1
1
2
2
2
2
1
2
2
2
2
2
2
2
2
2
1
2
2
2
2
2
2
2
2
1
1
2
2
2
2
2
2
2
2
2
2
2
n/d
17.15
16.51
16.45
12.50
n/a
16.23
13.52
15.58
16.79
15.79
n/d
19.74
17.30
16.77
19.74
17.59
n/a
16.72
19.36
18.59
17.81
14.32
n/a
14.28
17.34
10.96
n/d
n/d
15.55
17.34
16.77
14.24
16.36
15.36
17.15
16.91
16.06
15.19
14.36
15.53
n/a
14.56
16.34
14.28
14.36
12.64
12.33
14.00
n/a
13.05
13.01
11.90
12.71
14.19
12.92
12.94
13.45
12.77
13.86
14.64
14.70
n/a
13.28
14.00
n/d
0.80
0.87
0.67
0.62
n/a
0.80
0.76
0.84
0.42
0.67
n/d
0.83
0.91
0.70
0.83
0.63
n/a
0.85
0.83
0.88
0.57
0.36
n/a
0.46
0.69
0.34
n/d
n/d
0.71
0.69
0.70
0.70
0.74
0.63
0.53
0.59
0.55
0.52
0.41
0.48
n/a
0.57
0.60
1.08
0.81
1.05
1.06
2.13
n/a
4.13
3.79
10.11
7.84
1.65
2.41
0.98
4.12
5.00
1.90
2.66
1.69
n/a
5.03
7.67
n/d
1.85
1.73
1.58
1.75
n/a
1.55
1.30
1.10
0.83
1.13
n/d
1.48
1.48
1.37
1.48
1.35
n/a
1.25
1.35
1.22
1.42
1.28
n/a
1.12
1.32
0.98
n/d
n/d
1.83
1.50
1.47
1.57
1.85
1.78
1.55
1.45
1.43
1.42
1.38
1.40
n/a
1.30
1.40
1.63
1.63
1.57
1.57
2.22
n/a
1.29
1.50
1.24
1.33
1.36
1.15
1.18
2.04
1.57
1.58
1.65
1.61
n/a
2.43
2.48
n/d
0.36
0.36
0.35
0.30
n/a
0.30
0.16
0.12
0.73
0.67
n/d
1.12
1.13
0.89
1.12
0.89
n/a
1.15
1.16
1.37
1.28
0.78
n/a
0.89
1.19
0.69
n/d
n/d
1.28
1.25
1.31
1.43
1.55
1.47
1.37
1.39
1.60
1.55
1.16
1.43
n/a
1.48
1.48
1.27
0.90
1.29
1.36
1.35
n/a
1.12
0.90
0.88
0.84
0.89
1.15
1.08
1.29
1.02
0.96
0.74
0.82
n/a
1.87
1.85
n/d
n/a
n/a
75.8
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/d
79.7
76.1
77.9
79.7
79.3
n/a
77.9
79.7
79.8
79.3
78.4
n/a
n/a
n/a
77.8
n/d
n/d
72.2
77.3
77.0
73.0
73.1
73.0
77.7
78.0
77.5
n/a
n/a
n/a
n/a
n/a
77.8
70.0
n/a
n/a
n/a
59.5
n/a
n/a
n/a
n/a
38.9
n/a
n/a
n/a
n/a
n/a
n/a
55.2
59.7
n/a
46.4
40.8
n/d
n/a
n/a
1280
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/d
1369
1290
1328
1369
1360
n/a
1328
1370
1371
1364
1343
n/a
n/a
n/a
1327
n/d
n/d
1313
1316
1308
1217
1219
1221
1324
1331
1320
n/a
n/a
n/a
n/a
n/a
1326
1153
n/a
n/a
n/a
914
n/a
n/a
n/a
n/a
446
n/a
n/a
n/a
n/a
n/a
n/a
817
916
n/a
617
488
n/d
89.3
88.3
n/a
88.6
n/a
89.3
89.5
90.0
85.2
89.5
n/d
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
86.1
84.4
n/a
n/d
n/d
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
81.3
84.6
82.8
n/a
80.7
n/a
n/a
82.9
75.8
74.7
n/a
n/a
58.2
60.8
53.9
n/a
76.0
67.3
78.4
58.3
54.2
73.3
n/a
n/a
n/a
n/a
n/a
n/d
1284
1260
n/a
1266
n/a
1284
1280
1302
1289
1289
n/d
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1205
1166
n/a
n/d
n/d
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1097
1170
1130
n/a
1084
n/a
n/a
1132
934
963
n/a
n/a
696
733
634
n/a
988
833
1036
697
643
937
n/a
n/a
n/a
n/a
n/a
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
1153
TABLE 1.— Continued.
CALMAG3
Bulk Oxides (wt. %)
CIA-K3
Paleosol
Horizon Sequence1
Drainage2
Al2O3
CaO
MgO
Na2O
Index
MAP (mm)
Index
MAP (mm)
C35
C36
C37
C38
C39
GS1
GS2
GS4
GS5
LP40
L41
L42
CH68.25
CH 68.5
CH 68.75
CH 69
CH 70A
CH 70B
CH 71
CH 71.5
CH 72
CH 74
CH 75
CH 76.1
CH 76.2
CH 76.5
CH 77
Bk1(g)-Bk2(g)-BC(g)-C
Bk1(g)-Bk2(g)-Bk3(g)-BC
AB-Bw1-Bw2-BC-C
AB-Bw1/C-Bw2/C
AB1-AB2-Bk-B/C
A/Cg1-A/Cg2-B/Cg1-B/Cg2
A-Bss1(g)-Bss2(g)-C
A-Bss1(g)-Bss2(g)-BC-C
Bss(g)-Bw1-Bw2-BC
A-Bw/C
A-Bss1-Bss2-C
Bss(g)-C(g)
A-Bw-C
A-Bw/C
Bk1-Bk2
Bkm(g)-Bk1(g)-Bk2-Ck
A(g)/C1-A(g)/C2-BC/C
Bw-BC
A-Bss-C
Bssk
A-Bssk(g)-BC(g)
A-Bss-BC
A-Bkm1(g)-Bkm2(g)-C
BkC1(g)-BkC2(g)-C
A1-A2-Bkm(g)
A-C(g)
A-Bw/C
2
2
3
3
3
1
2
2
2
3
3
2
3
3
3
2
2
3
3
3
2
3
2
2
2
2
3
14.05
13.39
15.05
14.70
13.45
n/a
16.00
16.36
14.81
14.36
15.81
14.49
11.03
8.71
14.58
7.73
n/a
5.84
8.01
12.83
14.22
13.73
3.42
3.87
3.02
n/a
3.49
1.44
4.84
2.11
2.04
4.76
n/a
1.15
0.85
1.46
0.92
1.55
2.02
7.95
17.43
29.40*
21.00*
n/a
24.22*
17.50*
6.27
1.44
0.63
38.22*
21.07*
30.52*
n/a
17.43
2.42
2.32
2.45
2.53
3.30
n/a
2.25
2.27
2.47
2.22
2.33
2.33
2.62
3.02
4.65
2.78
n/a
3.13
2.92
1.92
2.92
2.50
1.68
1.35
1.67
n/a
1.92
1.85
1.54
0.98
1.02
0.88
n/a
1.62
1.60
1.75
1.75
1.32
1.47
1.62
0.90
0.98
0.73
n/a
0.51
1.24
1.59
1.70
1.97
0.19
0.39
0.12
n/a
0.43
n/a
n/a
n/a
n/a
n/a
n/a
67.14
69.04
62.35
n/a
64.3
60.1
n/a
n/a
n/a
n/a
n/a
n/a
16.9
42.2
58.5
64.6
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
1088
1131
979
n/a
1020
925
n/a
n/a
n/a
n/a
n/a
n/a
-26
519
892
1027
n/a
n/a
n/a
n/a
n/a
71.3
54.1
73.3
73.1
57.1
n/a
n/a
n/a
n/a
78.8
n/a
n/a
39.1
20.8
16.37
16.4
n/a
11.4
n/a
n/a
n/a
n/a
4.66
9.03
5.14
n/a
9.7
900
642
937
933
499
n/a
n/a
n/a
n/a
1044
n/a
n/a
478
333
305
305
n/a
277
n/a
n/a
n/a
n/a
242
264
245
n/a
268
n/d, No data available because of insufficient paleosol sampling.
n/a, Not applicable for MAP estimates either because the paleosol did not contain a B horizon or because CALMAG was used on Vertisol-like paleosols for MAP
(horizons with the ‘‘ss’’ symbol) and CIA-K for MAP on all other paleosols.
* Paleosol CaO concentrations exceeding the upper limit of the modern CALMAG and CIA-K data sets, possibly underestimating MAP.
1
Horizon symbols following the Soil Survey Staff (1999). Profiles that do not begin with an A horizon are truncated. Horizons in italics were analyzed for bulk oxides
for MAP calculations. See text for further explanation.
2
Drainage Indexes: 1, paleosols dominated by gley colors formed in association with a persistently high water table, designated by the horizon symbol ‘‘g’’ (i.e. Bssg);
2, paleosols with comingling of high chroma and gley or gray matrix colors, or dominated by gray colors, indicating periodic saturation and designated with the symbol
‘‘g’’ in parenthesis (i.e., Bss(g); 3, paleosols dominated by high chroma matrix colors with few to no iron reduction features (i.e., Bss).
3
MAP estimates based on CALMAG for Vertisol-like paleosols (‘‘ss’’) and CIA-K for all other paleosols with B horizons. Error for CALMAG is 6 108 mm and for
CIA-K 6 172 mm. See text for further explanation.
Appendix A). Six out of eight zircon analyses from sample SS-7 form a
coherent cluster with a weighted mean 206Pb/238U age of 220.124 6 0.068/
0.12/0.26 Ma and a mean square of weighted deviates (MSWD) of 0.64.
Another two analyses with 206Pb/238U dates of 221.45 Ma and 221.58 Ma
represent an older (detrital) zircon population (Fig. 4). Sample SS-24 occurs
in strata that constitute the lowermost Chinle deposits, located at Hunt Valley
21 km southeast of PEFO (Fig. 1B) and is correlated to the stratigraphically
lowest strata exposed in the westernmost portion of the Tepees area of PEFO
(Ramezani et al. 2011). Of six zircon grains analyzed from this sample, five
form a coherent cluster with a weighted mean 206Pb/238U age of
227.604 6 0.082/0.13/0.28 Ma (MSWD 5 1.5, Fig. 4). One older analysis
at 229.93 Ma is considered detrital. Recent revisions to the Triassic timescale
(the ‘‘Long Norian’’ option) place the Carnian–Norian stage boundary at
approximately 228.4 Ma (e.g., Furin et al. 2006; Ogg 2012); therefore, the age
of sample SS-24 suggests that most of the Chinle Formation is Norian in age.
Age estimates for fluvial aggradational cycles (FACs) are based on
linear interpolation between each of the nine dated tuffaceous beds and
sandstones (Fig. 2A, B), and assume that each FAC is likely the product
of a geologically instantaneous depositional event, such as avulsion (e.g.,
Kraus and Wells 1999; Atchley et al. 2004).
Paleosols
Ninety-two paleosols were identified in the study interval (Table 1).
Horizon symbols indicate that 23% of the paleosols ended in the early stages
of pedogenesis (A–C, A/C, Bw/C, Bg/C, Bw, Bg) by burial from rapid
aggradation. These paleosols have properties similar to modern Entisols
and Inceptisols with relict bedding and weak ped structure (Soil Survey
Staff 1999) and decompacted thicknesses ranging from ca. 50 cm to as much
as 2 m. Advanced stages of pedogenesis follow various pathways in relation
to differences in parent material and climate. These include the formation of
shrink–swell processes (Bss, Bssk, Bssg, Bsskg) responding to high clay
content and smectite-rich parent materials similar to Modern Vertisols
(41%), the accumulation of pedogenic carbonate (Bk, Bkm) similar to
modern Aridisols (14%) during periods when MAP dropped below ca.
400 mm, the formation of peds (Bw, Bg) or minor accumulations of
carbonate (Bk) similar to modern Inceptisols (36%), and the accumulation
of clay skins (Bt) in paleosols with Alfisol-like features (1%) that formed
under high rainfall in silty parent materials (Soil Survey Staff 1999). Most of
these more advanced states have paleosol profiles between 1 and 3 m thick.
Paleosols not having A horizons (28%) are assumed to have been eroded
prior to burial, complicating taxonomic comparison.
1154
S.C. ATCHLEY ET AL.
JSR
FIG. 3.—Selected outcrop photographs of representative paleosols and outcrop stratal successions. The rock hammer in Parts A–G is approximately 28 cm long. A, B)
Drainage Index 1 poorly drained paleosols: A) MR46 (FAC 3) of the Mesa Redondo Member with gley matrix colors (10Y) and slickensides, and B) ML 60 (FAC 58) of
the Petrified Forest Member with gley matrix colors (5PB), soft iron masses (7.5YR) in the Bkg2, carbonate rhizocretions after roots in both the Bkg1 and Bkg2 (white
masses), and post burial gley in A horizon. C, D, E) Drainage Index 2 intermediate drained paleosols: C) GT17 (FAC 28) of the Blue Mesa Member with gray matrix
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
1155
TABLE 2.— Data for estimating atmospheric pCO2 concentrations using the paleosol barometer for paleosols containing carbonate segregations (Cerling
1999). See text for explanation of variables. All d13C values are presented as %.
Paleosol
d 13Csoilcarb
d 13CsoilCO2
d 13Cmarine
d 13CatmCO2
d 13CrCO2
Soil TuC
AtmCO2 ppmV
GT17.5
GT21
ML56
ML58
ML59
ML60
ML60.5
ML61
ML62
ML63
ML65
ML66
ML67
ML68
C33
C34
C35
C38
CH68.75
CH69
CH71
CH72
CH74
CH75
CH76.1
CH76.2
28.8260.82
28.32
28.3660.80
28.3860.10
28.9660.17
28.3060.04
27.7960.04
28.2360.15
27.9760.88
27.7260.17
28.8060.02
28.0760.39
29.1060.25
210.7660.36
28.1560.84
28.5761.43
28.0060.22
27.8560.09
26.8060.61
26.9760.28
27.9260.70
27.0560.15
27.58
26.3460.14
25.23
25.7560.73
217.80
217.30
217.34
217.35
217.74
217.28
216.77
217.21
216.95
216.70
217.78
217.05
218.08
219.74
217.13
217.55
216.98
216.83
215.78
215.94
216.90
216.03
216.56
215.32
214.21
214.73
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
2.63
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
25.87
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
225.13
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
382
465
457
455
360
467
560
480
526
573
385
508
340
119
494
422
521
548
766
729
536
710
601
875
1193
1035
Sixteen of the paleosols (17%) formed under poorly drained
conditions and thus were categorized as Drainage Index 1 (Table 1).
All but three of these paleosols formed prior to the faunal turnover and
include the poorly drained ‘‘blue’’ paleosols of Therrien and Fastovsky
(2000) and Loughney et al. (2011) that predominantly preserve the
remains of rare vertebrate taxa such as theropod dinosaurs, gleysols of
Dubiel and Hasiotis (2011), and paleosols with aquic soil moisture
regimes in the Blue Mesa and Sonsela members from Trendell et al.
(2012). Fourteen of the paleosols (15%) classify as Drainage Index 3
(well drained), and all but one occurs after the faunal turnover. The
remainder of the paleosols indicate periodic wetness (Drainage Index 2)
and represent 70% of the total observed paleosols before the faunal
turnover and 65% of the paleosols after. The overall improvement in
paleosol drainage is consistent with Therrien and Fastovsky (2000)
reporting a decline in water-logged paleosols after what we define as the
A-R turnover.
Rainfall estimates prior to the faunal turnover range from ca. 1000 to
1400 mm annually, and are consistent with both geochemically derived
calculations for the Blue Mesa and Sonsela members (Trendell et al. in
press), and trends of paleosol drainage discussed in the preceding
section showing a preponderance of more poorly drained paleosols in
the lower part of the stratigraphic interval. The onset of a protracted
decline in MAP approximately coincided with the faunal turnover and
remained below 1000 mm annually once pedogenic carbonate began
accumulating in the paleosols. The occurrence of pedogenic carbonate is
denoted by the preponderance of horizons described with the Bk
symbol (Table 1, Fig. 2I). As a consequence of the appearance of
pedogenic carbonate, others have proposed the emergence of a semiarid
climate, but never quantitatively so in the Petrified Forest and Owl
Rock members (e.g., Therrien and Fastovsky 2000; Dubiel and Hasiotis
2011).
Estimates of atmospheric pCO2 using the paleosol carbonate barometer are more limited because only two paleosols prior to the faunal
turnover contain pedogenic carbonate. It appears, however, that
atmospheric pCO2 increased through Chinle deposition. Prior to the
faunal turnover, two data points for pCO2 average 423 ppmV (Table 2).
The interval following the faunal turnover from ML56 (FAC 54) to C38
(FAC 77) has pCO2 values that vary but generally increase from
approximately 400 to 550 ppmV (Table 2). Following this interval, an
increase in pCO2 is recorded in the Owl Rock Member beginning with
CH68.75 (FAC 87). Values in this interval average 806 ppmV (n 5 8),
and are as high as 1193 in CH76.1 (FAC 98) and they represent a
doubling of average atmospheric pCO2 concentrations from pre-turnover
conditions.
r
colors (10R) and soft iron masses (7.5YR) in the Bw(g), D) ML53 (FAC 51) of the Sonsela Member with gray matrix colors (5R) and post burial gley after roots in all
horizons, and E) CH75 (FAC 97) of the Owl Rock Member with gray matrix colors (7.5R) and indurated carbonate reflecting a complex drainage history. F, G) Drainage
Index 3 well drained paleosols: F) C39 (FAC 78) of the Petrified Forest Member with high-chroma matrix colors (7.5R) and post-burial gley after roots in all horizons,
and white carbonate nodules in the Bk horizon, and G) CH68.5 (FAC 87) of the Owl Rock Member with high chroma matrix colors (10R) and strong ped structure. H, I,
J) Outcrop photopanoramas annotated with the distribution of fluvial aggradational cycles (FACs): H) FAC 97 to 99 in the Owl Rock Member at the Chinde Mesa
locality. The total thickness of the photographed section is approximately 40 m; I) FAC 51 to 62 in the Sonsela Member at the Mountain Lion Mesa locality. Also shown
is the location of the Adamanian–Revueltian (A-R) faunal turnover. The total thickness of the photographed section is approximately 30 m; J) FAC 36 to 49 in the
uppermost Blue Mesa and lower Sonsela members at the Blue Mesa locality. The total thickness of the photographed section is approximately 50 m.
1156
JSR
S.C. ATCHLEY ET AL.
TABLE 3.—U-Pb data for the analyzed zircon from the tuffaceous sandstones of the Chinle Formation. See Appendix A for the location of samples in the
Chinle Formation composite measured section.
Composition
{
Sample
Fractions{
Pbc{
SS-7 Tuffaceous
z1
z2
z3
z4
z5
z6
z7
z8
sandstone from
0.8
20.9
0.3
86.7
0.4
59.3
0.5
54.4
0.4
22.9
0.9
10.0
0.3
84.0
0.6
10.9
pg
Pb*
Pbc
Th
U
Ratios
206
1
Pb
Pb
204
208
#
Pb
Pb
206
206
{{
Pb
U
238
err
2s%
72 meters above the base (Blue Mesa Member)
2.35
861.7
0.745 0.034950 (.10)
0.80
4832.4
0.255 0.034970 (.05)
0.98
3180.6
0.309 0.034738 (.07)
0.99
2910.5
0.313 0.034743 (.06)
0.87
1272.8
0.275 0.034733 (.09)
1.01
544.8
0.321 0.034702 (.16)
0.78
4710.5
0.248 0.034739 (.06)
1.00
594.0
0.316 0.034707 (.16)
SS-24 Tuffaceous sandstone from
z1
0.2
38.4
z4
0.3
31.7
z5
0.2
34.5
z6
0.6
35.7
z7
0.3
94.7
z8
0.5
49.9
{{
207
Pb
U
235
Age (Ma)
err
2s%
207
{{
Pb
Pb
206
0.24388 (1.10) 0.05063
0.24424 (.25) 0.05068
0.24243 (.33) 0.05064
0.24269 (.43) 0.05068
0.24264 (.85) 0.05069
0.24340 (1.87) 0.05089
0.24213 (.27) 0.05057
0.24297 (1.70) 0.05079
2 meters above the base (Mesa Redondo Member)
1.39
1883.1
0.439 0.036311 (.09)
0.25433
1.07
1671.7
0.338 0.035906 (.11)
0.25116
1.46
1670.3
0.462 0.035967 (.09)
0.25256
1.24
1812.2
0.391 0.035931 (.08)
0.25167
1.21
4809.4
0.382 0.035938 (.06)
0.25151
1.24
2520.3
0.394 0.035939 (.08)
0.25174
(.69)
(.72)
(.68)
(.59)
(.26)
(.46)
0.05082
0.05076
0.05095
0.05082
0.05078
0.05083
err
2s%
206
Pb
U
err
2s
(1.07)
(.23)
(.30)
(.42)
(.83)
(1.83)
(.25)
(1.65)
221.45
221.58
220.13
220.17
220.10
219.91
220.14
219.94
0.22
0.12
0.14
0.13
0.19
0.34
0.12
0.35
(.66)
(.69)
(.64)
(.57)
(.23)
(.43)
229.93
227.41
227.79
227.56
227.61
227.61
0.21
0.24
0.20
0.18
0.14
0.19
238
207
207
235
206
Pb
Pb
corr.
coef.
221.59
221.89
220.41
220.62
220.58
221.20
220.16
220.85
223.1
225.2
223.4
225.5
225.6
235.0
220.4
230.5
0.27
0.46
0.48
0.29
0.27
0.31
0.39
0.34
230.09
227.52
228.66
227.93
227.80
227.99
231.7
228.7
237.6
231.7
229.8
231.9
0.43
0.32
0.46
0.32
0.51
0.38
Pb
U
Corr. coef. 5 correlation coefficient. Age calculations are based on the decay constants of Jaffey et al. (1971).
{
All analyses are single zircon grains and pre-treated by the thermal annealing and acid leaching (CA-TIMS) technique. Data used in age calculations are in bold.
{
Pbc is total common Pb in analysis. Pb* is radiogenic Pb concentration.
1
Measured ratio corrected for spike and fractionation only.
#
Radiogenic Pb ratio.
{{
Corrected for fractionation, spike, blank, and initial Th/U disequilibrium in magma. Mass fractionation correction of 0.25%/amu 6 0.04%/amu (atomic mass unit)
was applied to single-collector Daly analyses. All common Pb is assumed to be blank. Total procedural blank was less than 0.1pg for U. Blank isotopic composition:
206
Pb/204Pb 5 18.42 6 0.35, 207Pb/204Pb 515.36 6 0.23, 208Pb/204Pb 5 37.46 6 0.74.
Cyclic Stratal Hierarchy and Associated Trends
FACs are the smallest-scale recurring stratal feature recognized in the
Chinle Formation, typically ranging from one to several meters in
thickness, and they either occur as a succession of generally finingupward deposits that have a paleosol weathered into their upper
boundary or have an upper boundary that lacks a paleosol and is
abruptly overlain by the oftentimes coarser deposits of the overlying FAC
(Appendix A; Fig. 3H, I, J). A plot of the estimated age for each of the
104 FACs observed in the study interval indicate that Chinle deposition
was periodically interrupted by prolonged (ca. 2–5 Myr) episodes of low
accommodation that are conspicuous on Figure 2B, i.e., as intervals
where few FACs were deposited between dated sandstones. The lithologic
composition of each FAC is depicted on Figure 2B by a stacked bar chart
with the midpoint of each FAC bar placed at its interpolated age between
dated sandstones. FAC bar width in Figure 2B, and therefore duration, is
plotted as a uniform thickness throughout the FAC succession.
Accordingly, low-accommodation intervals are recognized as consecutive
FAC bars that have wide gaps between them, i.e., few FACs deposited
over time, whereas intervals of high accommodation are characterized by
FIG. 4.—Date distribution plots for the analyzed zircon samples of this study. Vertical axis is
the measured 206Pb/235U age (see Table 3 for
complete analytical data). Bar heights represent
2s analytical uncertainty of individual analyses;
bars highlighted red are older (detrital) analyses
excluded from age calculation. Shaded horizontal band and its width represent the calculated
weighted mean age and its 2s internal error,
respectively. MSWD, mean square of weighted
deviates; n, number of analyses included in the
calculated date.
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
1157
TABLE 4.—Voucher specimens used to construct stratigraphic range charts for fossil vertebrates in Figure 2K (See Martz and Parker 2010 for a description
and correlation of lithostratigraphic units).
Taxon A
Smilosuchus
Pravusuchus
Calyptosuchus
Desmatosuchus
Paratypothoracisini
Poposaurus
Dicynodontia
Large metoposaurs
Machaeroprosopus
(5 Pseudopalatus)
Typothorax
Revueltosaurus
Shuvosauridae
Chindesaurus
Taxon B
Occurrence
Locality #
Phytosauria
Stratigraphic Unit
Highest
PFV178
Rainbow Forest Bed
Lowest
PFV142
upper Blue Mesa Member
Phytosauria
Highest
PFV053
Jim Camp Wash beds
Lowest
PFV099
Kellogg Butte (Jasper Forest) bed
Aetosauria
Highest
PFV304
Jim Camp Wash beds
Lowest
PFV212
upper Blue Mesa Member
Aetosauria
Highest
PFV212
upper Blue Mesa
Lowest
PFV198
upper Blue Mesa
Aetosauria
Highest
PFV092
Martha’s Butte beds
Lowest
PFV161
Camp Butte beds
Poposauroidea
Highest
PFV161
Camp Butte beds
Lowest
PFV336
lower Blue Mesa Member
Synapsida
Highest
PFV 098
Lot’s Wife beds
Lowest
PFV124
upper Blue Mesa Member
Temnospondyli
Highest
PFV100
Kellogg Butte (Jasper Forest) bed
Lowest
PFV199
upper Blue Mesa Member
Phytosauria
Highest
PFV002
Black Forest Bed
Lowest
PFV037
Jim Camp Wash beds
Aetosauria
Highest
PFV302
Petrified Forest Member (upper part)
Lowest
PFV367
Kellogg Butte (Jasper Forest) bed
Pseudosuchia
Highest
PFV297
Petrified Forest Member (lower part)
Lowest
PFV089
Jim Camp Wash beds
Poposauroidea
Highest
PFV302
Petrified Forest Member (upper part)
Lowest
PFV055
Martha’s Butte beds
Dinosauria
Highest
PFV018
Petrified Forest Member (lower part)
Lowest
PFV089
Jim Camp Wash beds
1
PEFO, Petrified Forest National Park; UCMP, University of California Museum of Paleontology; AMNH, American
Museum of Natural History.
FAC bars that are tightly fit, i.e., many FACs deposited over time. A
total of four low-accommodation intervals are observed in the Chinle
Formation at PEFO, and the interval having the longest duration extends
from ca. 218 to 213 Ma and coincides with the contact between two
hectometer-scale ‘‘composite sequences’’ (Fig. 2A, Appendix A; sensu
Atchley et al. 2004 and Atchley et al. 2013). Similar large-scale alluvial
depositional cycles have been previously documented in the region (e.g.,
Lucas 1993; Marzolf 1993; Tanner and Lucas 2006). Each composite
sequence at PEFO fines upward and has the highest proportion of
bedload channel deposits within its lower portion. Composite-sequence
deposition was interrupted by the three shorter-duration low-accommodation intervals, and suggests a hierarchical accommodation history, i.e.,
higher-frequency accommodation cycles superimposed on lower-frequency ‘‘composite sequence’’ accommodation cycles. The uppermost lowaccommodation interval (ca. 210 to 208 Ma) is inconspicuous and weakly
developed, and suggests high-frequency accommodation loss subdued by
the influence of contemporaneous lower-frequency and more pronounced
accommodation gain. Rather than a single conspicuous surface of
erosional truncation, the composite sequence boundary, and shorterduration low accommodation intervals as well, occur as relatively
condensed intervals of slow deposition that likely include multiple
obscure depositional breaks, i.e., paraconformity(ies), of unknown
duration. With the exception of the abrupt increase in grain size across
the low-accommodation transition between the lower and upper
composite sequence, conspicuous sedimentologic and/or pedologic
indicators of long-term weathering and/or erosion were not observed in
association with low-accommodation intervals, e.g., pronounced local or
regional incision, particularly well developed and well drained paleosols,
increased proportion of bedload channel deposits, etc.
Multiple observations suggest the transition between the lower and
upper composite sequence is gradual and of noteworthy stratigraphic
1
Voucher #
PEFO 34866
PEFO 31156
AMNH 7222
PEFO 31218
PEFO 34045
PEFO 26667
PEFO 26668
PEFO 31177
PEFO 34887
PEFO 34632
PEFO 34865
TMM 43683-1
UCMP 26682
UCMP 27095
PEFO 4843
PEFO 34287
UCMP 126750
PEFO 5034
PEFO 34929
PEFO 34918
PEFO 33787
PEFO 36759
PEFO 34924
PEFO 4859
PEFO 4849
PEFO 34875
and ecologic significance. First, bedload channel sandstone bodies are
generally coarser-grained in the ‘‘upper’’ composite sequence and remain
coarser-grained through FAC 69 (Flattops #2 Sandstone) at ca.
212.1 Ma (Appendix A; Fig. 2C). The onset of the grain-size increase
occurs in the Sonsela Member (FAC 37 at ca. 219.7 Ma) and reaches
maximum grain size in younger Sonsela channel sandstones from FAC
47 (unnamed sandstone at ca. 218.4 Ma) to FAC 62 (Flattops #1
Sandstone at ca. 212.9 Ma) (Fig. 2C). Above FAC 69 (ca. 212.1 Ma) to
the top of the study interval in the Owl Rock Member, channel
sandstone bodies become finer-grained (Appendix A; Fig. 2C). Second,
sedimentation rates markedly increase in the ‘‘upper’’ composite
sequence above FAC 62 (Flattops #1 Sandstone) at ca. 212.9 Ma,
and though of comparable total range in values, are biased towards a
higher overall range (and higher average) than observed in the ‘‘lower’’
composite sequence (Fig. 2D). Correspondingly, subsidence rapidly
accelerates in the ‘‘upper’’ composite sequence beginning at ca.
212.9 Ma (Fig. 2E). Third, from base to top in each composite sequence
the proportion of labile (particularly volcanic) grains in channel
sandstones generally decreases (Fig. 2F). Fourth, paleocurrent indicators collected from channel sandstones in the lower composite sequence
suggest a tendency towards variable paleoflow direction, whereas in the
upper composite sequence a tendency towards northward paleoflow
(Fig. 2G). Noteworthy in regards to paleoflow estimates, however, is
that with the exception of data on fossil log orientation in both the Black
Forest Bed (derived from Ash 1992) (FAC 87) and the Jasper Forest Bed
(FAC 49), all paleocurrent measurements were collected from unidirectional channel bedforms (Appendix A). As such, although it is possible
that some directional tendencies depicted in Figure 2G may record
meandering channel and intrachannel flow trajectories contrary to
regional depositional dip, the transition from variable to fairly consistent
northward paleoflow is arguably due to a change in regional dip. Fifth,
1158
JSR
S.C. ATCHLEY ET AL.
climate proxies derived from the chemical analysis of paleosol horizons
and associated carbonate nodules indicate a decrease in MAP and an
increase in atmospheric pCO2 in the upper composite sequence
(Fig. 2I, J). Although the increasing pCO2 trend is in part based upon
only two measurements in the ‘‘lower’’ composite sequence, previous
reconstructions of atmospheric pCO2 from Chinle Formation pedogenic carbonate in southeastern Utah (Prochnow et al. 2006) and
north-central New Mexico (Cleveland et al. 2008) have similarly
documented an increasing pCO2 trend within the Upper Triassic
section. These works possibly corroborate the pCO2 trend at PEFO;
however, the lack of a rigorous geochronology in these earlier studies
does not allow precise correlation with the results presented in this
paper. Sixth, paleosol attributes suggest a transition from more poorly
drained conditions in the lower composite sequence to well drained
conditions in the upper composite sequence (Fig. 2H). The overall
improvement in soil drainage is similar to the decreasing trend in MAP.
Finally, the transition between the lower and upper composite sequences
includes a reorganization in fauna (Parker and Martz 2011), i.e., the AR turnover, and flora (Litwin et al. 1991; Reichgelt et al. 2013)
(Fig. 2K). The turnover coincides with a red, silicified plant-rich
horizon first recognized and studied by Creber and Ash (1990), i.e.,
the persistent red ‘‘silcrete’’ of Parker and Martz (2011), observed in
FAC 52 and estimated to have occurred at ca. 216.7 Ma (Fig. 2K;
Appendix A). Several groups of vertebrates were significantly impacted
at the A-R turnover, including phytosaurs, aetosaurs, poposauroids,
and dicynodonts, with the latter disappearing completely and the others
undergoing significant reorganization (Parker and Martz 2011). This
includes the complete disappearance of non-pseudopalatine leptosuchomorph phytosaurs (sensu Stocker 2010), trilophosaurs, desmatosuchine
aetosaurs, the aetosaur Calyptosuchus wellesi, and the poposauroid
Poposaurus gracilis (Parker and Martz 2011). Although representatives
of all these taxa have not been found all the way up to the A-R
boundary within PEFO, this is probably the result of preservation and
sampling biases. Because the identical extinction pattern occurs
elsewhere in the southwestern U.S. (e.g., Martz et al. 2013), it is likely
that all were affected by the same event at the A-R boundary. It is
predicted that further discoveries will extend the ranges of these taxa
closer to the turnover horizon, similarly to how recent finds have
extended the ranges of the Revueltian index taxa Chindesaurus
bryansmalli and Revueltosaurus callenderi (compare Fig. 2K to fig. 5
in Parker and Martz 2011).
In general, surviving fauna and flora across the A-R boundary have a
greater tolerance for drier or more alkaline conditions (Parker and
Martz 2011). Particularly, large metoposaurid amphibians and the
semiaquatic dicynodont Placerias significantly decline in numbers or
disappear, and unionid bivalves, which favor alkaline conditions (Smith
2001), dramatically increase in abundance (Martz and Parker 2010;
Parker and Martz 2011) (Fig. 2K). Similarly, palynomorphs suggest
that ferns and horsetails (humid climate) were more common before the
turnover, and voltzialean and araucariacean gymnosperms (semiarid
climate) were more common afterwards (Reichgelt et al. 2013)
(Fig. 2K). In addition, plant-leaf preservation changes from large,
well-preserved and undamaged (megafossils) before the turnover, to
small, poorly preserved, and fragmented (mesofossils) after the turnover
(Ash 2010a, 2010b) (Fig. 2K). Leaf preservation may also be related to
climate, inasmuch as fragmented preservation is favored in bedload
fluvial systems (e.g., Greenwood 1991) that are characteristic of drier
climates, and that are more common in the upper composite sequence
(Fig. 2B, D). This possibility is controversial, however, due to the
potential for plant preservational bias in riparian zones that are
geomorphically rather than climatically controlled (e.g., Demko et al.
1998).
DISCUSSION
Tectonism and eustasy have been proposed to account for similar
large-scale depositional cycles observed in the Chinle succession of the
southwestern United States (e.g., Marzolf 1993; Lucas et al. 1997; Tanner
2003). The lack of necessary age control to correlate these cycles with
contemporaneous mechanisms, however, has rendered past interpretations speculative. Recently, the geochronology of Ramezani et al. (2011)
at PEFO has been integrated by Howell and Blakey (2013) with
sedimentologic and stratigraphic observations of the Sonsela Member.
These combined results suggest that a relationship may exist between the
onset of Sonsela Member deposition and tectonism across the Cordilleran
magmatic arc and neighboring backarc basin. Enhancements to the U-Pb
geochronology of Ramezani et al. (2011) provided in this paper and their
incorporation with sedimentologic, stratigraphic and pedologic observations for the entire Chinle Formation at PEFO provide results that
further advance our understanding of the Late Triassic of western Pangea
by detecting a potential linkage between not only regional tectonic and
depositional trends but also climatic and ecologic trends.
Although the earliest record of Cordilleran arc magmatism has been
obscured by subsequent episodes of Mesozoic orogeny and deformation,
Chinle ages provided in this study are generally consistent with those of
several granitoid plutons exposed along the Sierra Nevada and Mojave
arc segments of southern California, as determined by in situ U-Pb zircon
geochronology (e.g., Barth and Wooden 2006; Barth et al. 2011).
Accordingly, the deposition of the lower composite sequence was
concomitant with emplacement of the Scheelite plutonic suite (ca. 226
to 218 Ma) and its associated ignimbrites (as old as 232 Ma; Barth et al.
2011), whereas the upper composite sequence overlaps in age with the San
Gabriel plutonic complex of the eastern Mojave Desert (ca. 218 to
207 Ma, Barth and Wooden 2006) (Figs. 1A, 2L). Plutonic clasts,
however, are notably rare compared to the abundant volcanic clasts in
Chinle sandstones (Riggs et al. 2012), suggesting sediment derivation
from the early-stage arc volcanic edifices without appreciable input from
plutonic or shallow subvolcanic elements. These indicate that uplift of the
incipient arc provided a southwestward highland source terrain from
which sediment was shed as a northeastward-prograding wedge towards
the axial drainage of the Chinle backarc basin (e.g., Reynolds et al. 1989;
Dickinson and Gehrels 2008; Howell and Blakey 2013) (Fig. 1A).
Observations in the Chinle at PEFO support (and further refine) this
interpretation. The initial increase and subsequent decrease in grain size
across and above the composite sequence boundary interval, and increase
in both sedimentation and associated subsidence rates above the
boundary interval, may document a burgeoning phase of convergentmargin uplift and backarc-basin subsidence (Fig. 2C, D, E). The
transition from variable to northward paleoflow at ca. 216 to 217 Ma
is interpreted to record the arrival of the arc-derived progradational
alluvial wedge across what is now PEFO (Fig. 2G). The partitioning of
the Chinle into two composite sequences indicates that sediment dispersal
and accumulation may have been related to pulses of, rather than
continuous, uplift and subsidence. This may also be true for the stratal
successions in the composite sequences that are bounded by the
intercalated shorter-duration low-accommodation intervals, inasmuch
as alluvial depositional cycles at this (ca. 5 Myr) or higher frequency have
been previously correlated to foreland tectonic processes in similar
settings (e.g., Catuneanu and Elango 2001). Although climate shift may
also produce similar higher-frequency depositional cycles, climatically
induced cyclic successions are primarily controlled by processes (e.g.,
astronomical forcing) that operate on shorter (104 to 105 year) time scales
(sensu Catuneanu 2006; e.g., Retallack 1986). More significantly at
PEFO, there is no observed correspondence between higher-frequency
alluvial cycles and paleosol-derived climate indicators (i.e., MAP, pCO2,
and paleosol drainage) (Fig. 2).
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
Past studies of the Chinle Formation have placed the A-R turnover
between two large-scale alluvial cycles similar, but not identical, to the
composite sequences documented in this paper (Lucas 1991, 1993;
Heckert and Lucas 1996; Howell and Blakey 2013). The causal
mechanism(s) for the A-R biological turnover, however, have been
poorly understood. The coincidence of the A-R turnover with the
transition between the lower and upper composite sequences at PEFO
may indicate an ecologic disruption related to a change in regional
physiography and climate as controlled by convergent tectonism. The
biotic turnover correlates closely with the onset of reduced MAP and
transition from lower-competence fluvial systems with variable paleoflow
direction (putative axial flow) to higher-competence fluvial systems with a
northward paleoflow direction (putative arc-derived progradational
alluvial wedge), and to a lesser degree increasing pCO2 (Fig. 2B, C, G,
I, J, K). The long-term increase in atmospheric pCO2 (equilibrated
globally) follows an increasing trend that lags, but is otherwise similar to,
the reduction in MAP (Fig. 2I, J). The increase in pCO2 may reflect
accelerated spreading center and arc volcanism during the rifting of
Pangea, whereas the decrease in MAP may be the result of a regional rain
shadow to westerly monsoonal flow related to the emerging Cordilleran
arc complex, and(or) as previously suggested, concurrent continental drift
from humid equatorial to drier subtropical paleolatitudes (Dubiel et al.
1991; Tanner and Lucas 2006).
CONCLUSIONS
Lower and upper composite sequences are recognized in the Chinle
Formation, and each coincides with episodes of Cordilleran arc plutonism.
Paleosol analyses document climate aridification across the transition
between the lower and upper composite sequences. This transition, in turn,
coincides with a biological turnover characterized by life predisposed to
humid conditions, prior to the turnover, and semi-arid conditions, after the
turnover. Collectively, these findings support the possibility that the Late
Triassic depositional, climatic, and ecologic histories are intertwined, and
progressed in response to emergence of the incipient Cordilleran magmatic
arc along the convergent western margin of Pangea.
ACKNOWLEDGMENTS
This study was funded in part by the Petroleum Research Fund via grant
PRF#45548-AC8 awarded to S. Atchley and L. Nordt. Financial support for
geochronologic work was received from National Science Foundation grant
EAR-1024196/1023788 to S. Bowering and D. Fastovsky. Additional funding
was provided through a faculty research and travel endowment administered
by the Baylor University Department of Geology. The age model, results, and
interpretations presented in the manuscript benefitted from numerous
discussions with David Fastovsky. The initial concept for the project is
based upon regional field reconnaissance by former Baylor University Ph.D.
student David M. Cleveland. Jeffrey Martz provided a field introduction to
the lithostratigraphic framework at PEFO. The manuscript quality was
improved as a result of thorough reviews provided by R.F. Dubiel and an
anonymous reviewer, associate editor J.E. Huntoon, and corresponding
editor J.B. Southard. Appendix A is available from JSR’s Data Archive:
http://sepm.org/pages.aspx?pageid 5 229.
REFERENCES
ARENS, N., JAHREN, A., AND AMUNDSON, R., 2000, Can C3 plants faithfully record the
carbon isotopic composition of atmospheric carbon dioxide?: Paleobiology, v. 26,
p. 137–164.
ASH, S., 1992, The Black Forest Bed, a distinctive unit in the Upper Triassic Chinle
Formation, northeastern Arizona: Arizona–Nevada Academy of Science, Journal,
v. 24–25, p. 59–73.
ASH, S.R., 2010a, Summary of the Upper Triassic flora of the Newspaper Rock Bed and
its paleoclimatic implications, in Trendell, A., ed., Paleosols and Soil Surface System
Analogs: Workshop Field Guide, SEPM–NSF Research Conference, Baylor
University Department of Geology and hosted by Petrified Forest National Park,
Arizona, USA, p. 59–71.
1159
ASH, S.R., 2010b, Preliminary observations on the Upper Triassic plant debris beds
exposed in the road cuts along old US 180, Petrified Forest National Park, Arizona, in
Trendell, A., ed., Paleosols and Soil Surface System Analogs: Workshop Field Guide,
SEPM–NSF Research Conference, Baylor University Department of Geology and
hosted by Petrified Forest National Park, Arizona, USA, p. 131–134.
ATCHLEY, S.C., NORDT, L.C., AND DWORKIN, S.I., 2004, Eustatic control on alluvial
sequence stratigraphy: a possible example from the K/T transition of the Tornillo
Basin, Big Bend National Park, West Texas: Journal of Sedimentary Research, v. 74,
p. 391–404.
ATCHLEY, S.C., NORDT, L.C., DWORKIN, S.I., CLEVELAND, D.M., MINTZ, J.S., AND
HARLOW, H., 2013, Alluvial stacking pattern analysis and sequence stratigraphy:
concepts and case studies, in, Driese, S.G., and Nordt, L.I., eds., New Frontiers in
Paleopedology and Terrestrial Paleoclimatology: SEPM, Special Publication 104,
p. 109–130.
BARTH, A.P., AND WOODEN, J.L., 2006, Timing of magmatism following initial
convergence at a passive margin, southwestern U.S. Cordillera, and ages of Lower
Crustal magma sources: The Journal of Geology, v. 114, p. 231–245.
BARTH, A.P., WALKER, J.D., WOODEN, J.L., RIGGS, N.R., AND SCHWEICKERT, R.A., 2011,
Birth of the Sierra Nevada magmatic arc: early Mesozoic plutonism and volcanism in
the east-central Sierra Nevada of California: Geosphere, v. 7, p. 877–897.
BLAKEY, R.C., AND GUBITOSA, R., 1983, Late Triassic paleogeography and depositional
history of the Chinle Formation, southern Utah and northern Arizona, in Reynolds,
M.W., and Dolly, E.D., eds., Mesozoic Paleogeography of the West-Central United
States: SEPM, Rocky Mountain Section, p. 57–76.
BLAKEY, R.C., AND GUBITOSA, R., 1984, Controls of sandstone body geometry and
architecture in the Chinle Formation (Upper Triassic), Colorado Plateau: Sedimentary Geology, v. 38, p. 51–86.
BOWRING, J.F., MCLEAN, N.M., AND BOWRING, S.A., 2011, Engineering cyber
infrastructure for U-Pb geochronology: Tripoli and U-Pb Redux: Geochemistry,
Geophysics, Geosystems, v. 12, Q0AA19.
BREECKER, D.O., SHARP, Z.D., AND MCFADDEN, L.D., 2010, Atmospheric CO2
concentrations during ancient greenhouse climates were similar to those predicted
for the A.D. 2100: Proceedings of the National Academy of Sciences, v. 107, p. 576–
580.
CATUNEANU, O., AND ELANGO, D., 2001, Tectonic control on fluvial styles: the Balfour
Formation of the Karoo Basin, South Africa: Sedimentary Geology, v. 140, p. 291–
313.
CATUNEANU, O., 2006, Principles of Sequence Stratigraphy: Amsterdam, Elsevier, 375 p.
CERLING, T., 1999, Stable carbon isotopes in paleosol carbonates, in Thiry, M., and
Simon-Coincon, R., eds., Palaeoweathering, Palaeosurfaces and Related Continental
Deposits: International Association of Sedimentologists, Special Publication, v. 27,
p. 43–60.
CLEVELAND, D.M., ATCHLEY, S.C., AND NORDT, L.C., 2007, Continental sequence
stratigraphy of the Upper Triassic (Norian–Rhaetian) Chinle strata, northern New
Mexico, U.S.A.: allocyclic and autocyclic origins of paleosol-bearing alluvial
successions: Journal of Sedimentary Research, v. 77, p. 909–924.
CLEVELAND, D.M., NORDT, L.C., DWORKIN, S.I., AND ATCHLEY, S.C., 2008, Pedogenic
carbonate isotopes as evidence for extreme climatic events preceding the Triassic–
Jurassic boundary: implications for the biotic crisis?: Geological Society of America,
Bulletin, v. 120, p. 1408–1415.
COOLEY, M.E., AND DAVIDSON, E.S., 1963, The Mogollon Highlands—their influence on
Mesozoic and Cenozoic erosion and sedimentation: Arizona Geological Society,
Digest, v. 6, p. 7–35.
CREBER, G., AND ASH, S.R., 1990, A widespread fungal epidemic on Upper Triassic trees
in the southwestern United States: Review of Palaeobotany and Palynology, v. 63,
p. 189–195.
DEMKO, T.M., DUBIEL, R.F., AND PARRISH, J.T., 1998, Plant taphonomy in incised
valleys: implications for interpreting paleoclimate from fossil plants: Geology, v. 26,
p. 1119–1122.
DICKINSON, W.R., 1981, Plate tectonic evolution of the southern Cordillera: Arizona
Geological Society, Digest, v. 14, p. 113–135.
DICKINSON, W.R., AND GEHRELS, G.E., 2008, U-Pb ages of detrital zircons in relation to
paleogeography: Triassic paleodrainage networks and sediment dispersal across
southwest Laurentia: Journal of Sedimentary Research, v. 78, p. 745–764.
DUBIEL, R.F., 1994, Triassic deposystems, paleogeography, and paleoclimate of the
Western Interior, in Caputo, M.V., Peterson, J.A., and Franczyk, K.L., eds.,
Mesozoic System of the Rocky Mountain Region: SEPM, Rocky Mountain Section,
p. 133–155.
DUBIEL, R.F., AND HASIOTIS, S.T., 2011, Deposystems, paleosols, and climatic variability
in a continental system: the Upper Triassic Chinle Formation, Colorado Plateau,
U.S.A., in Davidson, S.K., Leleu, S., and North, C.P., eds., From River to Rock
Record: The Preservation of Fluvial Sediments and their Subsequent Interpretation,
SEPM, Special Publication 97, p. 393–421.
DUBIEL, R.F., PARRISH, J.T., PARRISH, J.M., AND GOOD, S.C., 1991, The Pangaean
megamonsoon: evidence from the Upper Triassic Chinle Formation, Colorado
Plateau: Palaios, v. 6, p. 347–370.
FURIN, S., PRETO, N., RIGO, M., ROGHI, G., GIANOLLA, P., CROWLEY, J.L., AND BOWRING,
S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: implications for
the Triassic time scale and the Carnian origin of calcareous nannoplankton and
dinosaurs: Geology, v. 34, p. 1009–1012.
GREENWOOD, D.R., 1991, Chapter 7: The taphonomy of plant macrofossils, in Donovan,
S.K., ed., The Processes of Fossilization: London, Belhaven Press, p. 141–169.
1160
S.C. ATCHLEY ET AL.
HARSHBARGER, J.W., REPENNING, C.A., AND IRWIN, J.H., 1957, Stratigraphy of the
Uppermost Triassic and the Jurassic Rocks of the Navajo Country: U.S. Geological
Survey, Professional Paper 291, 74 p.
HECKERT, A.B., AND LUCAS, S.G., 1996, Stratigraphic description of the Tr-4
unconformity in west-central New Mexico and eastern Arizona: New Mexico
Geology, v. 18, p. 61–70.
HECKERT, A.B., AND LUCAS, S.G., 2002, Revised Upper Triassic stratigraphy of the
Petrified Forest National Park, Arizona, USA, in Heckert, A.B., and Lucas, S.G.,
eds., Upper Triassic stratigraphy and paleontology: New Mexico Museum of Natural
History and Science, Bulletin, v. 21, p. 1–36.
HOWELL, E.R., AND BLAKEY, R.C., 2013, Sedimentological constraints on the evolution
of the Cordilleran arc: new insights from the Sonsela Member, Upper Triassic Chinle
Formation, Petrified Forest National Park (Arizona, USA): Geological Society of
America, Bulletin, published online, doi:10.1130/B30714.1.
JACOB, J.S., GRIFFIN, R.W., MILLER, W.L., AND WILDING, L.P., 1997, Aquerts and
aquertic soils: a querulous proposition, in Vepraskas, M.J., and Sprecher, S.W., eds.,
Aquic Conditions and Hydric Soils: The Problem Soils: Soil Science Society of
America, Special Publication 50, p. 61–78.
JAFFEY, A.H., FLYNN, K.F., GLENDENIN, L.E., BENTLEY, W.C., AND ESSLING, A.M., 1971,
Precision measurement of half-lives and specific activities of 235U and 238U: Physical
Review, C4, p. 1889–1906.
KORTE, C., HEINZ, K.W., AND VEIZER, J., 2005, d13C and d18O values of Triassic
brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 226, p. 287–306.
KRAUS, M.J., AND HASIOTIS, S.T., 2006, Significance of different modes of rhizolith
preservation to interpreting paleoenvironmental and paleohydrologic settings;
examples from Paleogene paleosols, Bighorn Basin, Wyoming, U.S.A.: Journal of
Sedimentary Research, v. 76, p. 633–646.
KRAUS, M.J., AND WELLS, T.M., 1999, Recognizing avulsion deposits in the ancient
stratigraphical record, in Smith, N.D., and Rogers, J., eds., Fluvial Sedimentology VI:
International Association of Sedimentologists, Special Publication 28, p. 251–268.
LAWTON, T.F., 1994, Tectonic setting of Mesozoic sedimentary basins, in Caputo, M.V.,
Peterson, J.A., and Franczyk, K.J., eds., Mesozoic Systems of the Rocky Mountain
Region, USA: SEPM, Rocky Mountain Section, p. 1–25.
LITWIN, R.J., TRAVERSE, A., AND ASH, S.R., 1991, Preliminary palynological zonation of
the Chinle Formation, southwestern U.S.A., and its correlation to the Newark
Supergroup (eastern U.S.A.): Review of Palaeobotany and Palynology, v. 68, p. 269–
287.
LOUGHNEY, K.M., FASTOVSKY, D.E., AND PARKER, W.G., 2011, Vertebrate fossil
preservation in blue paleosols from the Petrified Forest National Park, Arizona,
with implications for vertebrate biostratigraphy in the Chinle Formation: Palaios,
v. 26, p. 700–719.
LUCAS, S.G., 1991, Sequence stratigraphic correlation of nonmarine and marine Late
Triassic biochronologies, western United States: Albertiana, v. 4, p. 11–18.
LUCAS, S.G., 1993, The Chinle Group: revised stratigraphy and chronology of Upper
Triassic nonmarine strata in the western United States: Museum of Northern Arizona,
Bulletin 59, p. 27–50.
LUCAS, S.G., HECKERT, A.B., ESTEP, J.W., AND ANDERSON, O.J., 1997, Stratigraphy of
the Upper Triassic Chinle Group, Four Corners region, in Anderson, O.J., Kues, B.S.,
and Lucas, S.G., eds., Mesozoic Geology and Paleontology of the Four Corners
Region: New Mexico Geological Society, Guidebook 48, p. 81–108.
LYNCH-STIEGLITZ, J., STOCKER, T., BROECKER, W., AND FAIRBANKS, R., 1995, The
influence of air–sea exchange on isotopic composition of oceanic carbon: observations
and modeling: Global Biogeochemical Cycles, v. 9, p. 653–665.
MARBUT, C.F., 1935, Soils of the United States, in Baker, O.E., ed., Atlas of American
Agriculture, Part III: U.S. Department of Agriculture, U.S. Government Printing
Office, Advance Sheets, no. 8, 98 p.
MARTZ, J.W., AND PARKER, W.G., 2010, Revised lithostratigraphy of the Sonsela
Member (Chinle Formation, Upper Triassic) in the southern part of Petrified Forest
National Park, Arizona.: PLoS ONE, February 2010, v. 5, Issue 2, 26 p.
MARTZ, J.W., PARKER, W.G., SKINNER, L., RAUCCI, J.J., UMHOEFER, P., AND BLAKEY, R.,
2012, Geologic map of Petrified Forest National Park, Arizona: Arizona Geological
Survey, Contributed Map CR-12-A, 1 map sheet, 1:50,000 map scale, 18 p.
MARTZ, J.W., MUELLER, B., NESBITT, S.J., STOCKER, M.R., PARKER, W.G., ATANASSOV,
M., FRASER, N.C., WEINBAUM, J.C., AND LEHANE, J., 2013, A taxonomic and
biostratigraphic re-evaluation of the Post Quarry vertebrate assemblage from the
Cooper Canyon Formation (Dockum Group, Upper Triassic) of southern Garza
County, western Texas: Royal Society of Edinburgh, Earth and Environmental
Transactions, v. 103, p. 313–338.
MARZOLF, J.E., 1993, Sequence-stratigraphic relationships across the palinspastically
reconstructed cordilleran Triassic cratonal margin, in Lucas, S.G., and Morales, M.,
eds., The nonmarine Triassic: New Mexico Museum of Natural History and Science,
Bulletin 3, p. 331–343.
MATTINSON, J.M., 2005, Zircon U/Pb chemical abrasion (CA-TIMS) method: combined
annealing and multi-step partial dissolution analysis for improved precision and
accuracy of zircon ages: Chemical Geology, v. 220, p. 47–66.
MCLEAN, N.M., BOWRING, J.F., AND BOWRING, S.A., 2011, An algorithm for U-Pb
isotope dilution data reduction and uncertainty propagation: Geochemistry,
Geophysics, Geosystems, v. 12, Q0AA18, doi:10.1029/2011GC003529.
MOLINA-GARZA, R.S., GEISSMAN, J.W., AND VAN DER VOO, R., 1995, Paleomagnetism of
the Dockum Group (Upper Triassic), northwest Texas: Further evidence for the J-1
cusp in the North American apparent polar wander path and implications for the
apparent polar wander and Colorado Plateau migration: Tectonics, v. 14, p. 979–993.
JSR
MUNSELLH, 2009, Soil Color Book, Revised Edition.
NESBITT, S.J., AND STOCKER, M.R., 2008, The vertebrate assemblage of the Late Triassic
Canjillon Quarry (Northern New Mexico, USA), and the importance of apomorphybased assemblage comparisons: Journal of Vertebrate Paleontology, v. 28, p. 1063–
1072.
NORDT, L.C., AND DRIESE, S.G., 2009, Hydropedological model of Vertisol formation
along the Gulf Coast Prairie Land Resource Area of Texas: Hydrological Earth
System Science, v. 13, p. 2039–2053.
NORDT, L., AND DRIESE, S., 2010, New weathering index improves rainfall estimates for
paleo-Vertisols: Geology, v. 38, p. 407–410.
NORDT, L., ATCHLEY, S., AND DWORKIN, S., 2003, Terrestrial evidence for two intense
greenhouse events in the latest Cretaceous: GSA Today, v. 13, p. 4–9.
OGG, J.G., 2012, Triassic, in Gradstein, F.M., Ogg, J.G., Schmitz, M., and Ogg, G., eds.,
The Geological Timescale 2012: Amsterdam, Elsevier, p. 681–730.
PARKER, W.G., 2006, The stratigraphic distribution of major fossil localities in Petrified
Forest National Park, Arizona: Museum of Northern Arizona, Bulletin 62, p. 46–61.
PARKER, W.G., AND MARTZ, J.W., 2011, The Late Triassic (Norian) Adamanian–
Revueltian tetrapod faunal transition in the Chinle Formation of the Petrified Forest
National Park, Arizona: Royal Society of Edinburgh, Earth and Environmental
Transactions, v. 101, p. 231–260.
PARKER, W.G., HUNGERBÜHLER, A., AND MARTZ, J.W., 2013, The taxonomic status of
the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the
Late Triassic of the western United States: Transactions Royal Society of Edinburgh,
Earth and Environmental Science, v. 103, p. 265–268.
PARRISH, J.T., 1993, Climate of the supercontinent Pangea: The Journal of Geology,
v. 101, p. 215–233.
PIPUJOL, M.D., AND BUURMAN, P., 1994, The distinction between ground-water gley and
surface-water gley phenomena in Tertiary paleosols of the Ebro basin, NE Spain:
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 110, p. 103–113.
PROCHNOW, S.J., NORDT, L.C., ATCHLEY, S.C., AND HUDEC, M.R., 2006, Multi-proxy
paleosol evidence for middle and late Triassic climate trends in eastern Utah:
Palaeogeography, Paleoclimatology, Palaeoecology, v. 232, p. 53–72.
RAMEZANI, J., HOKE, G.D., FASTOVSKY, D.E., BOWRING, S.A., THERRIEN, F., DWORKIN,
S.I., ATCHLEY, S.C., AND NORDT, L.C., 2011, High-precision U-Pb zircon geochronology of the Late Triassic Chinle Formation, Petrified Forest National Park
(Arizona, USA): temporal constraints on the early evolution of dinosaurs: Geological
Society of America, Bulletin, v. 123, p. 2142–2159.
REICHGELT, T., PARKER, W.G., MARTZ, J.W., CONRAN, J.G., vAN KONIJNENBURG-vAN
CITTERT, J.H.A., AND KURSCHNER, W.M., 2013, The palynology of the Sonsela
Member (Late Triassic, Norian) at Petrified Forest National Park, Arizona, USA:
Review of Palaeobotany and Palynology, v. 189, p. 18–28.
RETALLACK, G.J., 1986, Fossil soils as grounds for interpreting long term controls on
ancient rivers: Journal of Sedimentary Petrology, v. 56, p. 1–18.
RETALLACK, G.J., 1991, Untangling the effects of burial alteration and ancient soil
formation: Annual Review of Earth and Planetary Sciences, v. 19, p. 183–206.
REYNOLDS, S.J., SPENCER, J.E., ASMEROM, Y., DEWITT, E., AND LAUBACH, S.E., 1989,
Early Mesozoic uplift in west-central Arizona and southeastern California: Geology,
v. 17, p. 207–211.
RIGGS, N.R., LEHMAN, T.M., GEHRELS, G.E., AND DICKINSON, W.R., 1996, Detrital
zircon link between headwaters and terminus of the upper Triassic Chinle–Dockum
paleoriver system: Science, v. 273, p. 97–100.
RIGGS, N.R., BARTH, A.P., GONZÁLEZ-LEÓN, C.M., JACOBSEN, C.E., WOODEN, J.L.,
HOWELL, E.R., AND WALKER, J.D., 2012, Provenance of Upper Triassic strata in
southwestern North America as suggested by isotopic analysis and chemistry of zircon
crystals, in Rasbury, E.T., Hemming, S.R., and Riggs, N.R., eds., Mineralogical and
Geochemical Approaches to Provenance: Geological Society of America, Special
Publication 487, p. 13–36.
ROMANEK, C., GROSSMAN, E., AND MORSE, J., 1992, Carbon isotopic fractionation in
synthetic aragonite and calcite: effects of temperature and precipitation rate:
Geochimica et Cosmochimica Acta, v. 56 p. 419–430.
SCOTESE, C.R., 1994, Late Triassic paleogeographic map, in Klein, G.D., ed., Pangea
Paleoclimate, Tectonics, and Sedimentation during Accretion, Zenith, and Breakup
of a Supercontinent: Geological Society of America, Special Paper 288, p. 7.
SHELDON, N.D., AND RETALLACK, G.J., 2001, Equation for compaction of paleosols due
to burial: Geology, v. 29, p. 247–250.
SHELDON, N., RETALLACK, G., AND TANAKA, S., 2002, Geochemical climofunctions from
North American soils and application to paleosols across the Eocene–Oligocene
boundary in Oregon: Journal of Geology, v. 110, p. 687–696.
SMITH, D.G., 2001, Pennak’s freshwater invertebrates of the United States: Porifera to
Crustacea, 4th Edition: New York, John Wiley and Sons, 648 p.
SOIL SURVEY STAFF, 1999, Soil taxonomy: A basic system of soil classification for making
and interpreting soil surveys: U.S. Department of Agriculture–NRCS Agriculture
Handbook 436, Second Edition: Washington, U.S. Government Printing Office,
869 p.
STEWART, J.H., POOLE, F.G., AND WILSON, R.F., 1972, Stratigraphy and Origin of the
Chinle Formation and Related Upper Triassic Strata in the Colorado Plateau Region:
U.S. Geological Survey, Professional Paper 690, 336 p.
STOCKER, M.R., 2010, A new taxon of phytosaur (Archosauria: Pseudosuchia) from the
Late Triassic (Norian) Sonsela Member (Chinle Formation) in Arizona, and a critical
reevaluation of Leptosuchus Case 1922: Palaeontology, v. 53, p. 997–1022.
TANNER, L.H., 2003, Possible tectonic controls on Late Triassic sedimentation in the
Chinle Basin, Colorado Plateau: New Mexico Geological Society, Guidebook, 54th
Field Conference, Geology of the Zuni Plateau, p. 263–267.
JSR
PANGEAN TECTONISM AND ECOLOGIC CHANGE DURING THE LATE TRIASSIC OF THE SOUTHWESTERN U.S.A.
TANNER, L.H., AND LUCAS, S.G., 2006, Calcareous paleosols of the Upper Triassic
Chinle Group, Four Corners region, southwestern United States: climatic implications, in Alonso-Zarza, A.M., and Tanner, L.H., eds., Paleoenvironmental Record
and Applications of Calcretes and Palustrine Carbonates: Geological Society of
America, Special Paper 416, p. 53–74.
THERRIEN, F., AND FASTOVSKY, D.E., 2000, Paleoenvironments of Early Theropods, Chinle
Formation (Late Triassic), Petrified Forest National Park, Arizona: Palaios, v. 15, p. 194–
211.
TRENDELL, A.M., ATCHLEY, S.C., AND NORDT, L.C., 2012, Depositional and diagenetic
controls on reservoir attributes within a fluvial outcrop analog: Upper Triassic
Sonsela Member of the Chinle Formation, Petrified Forest National Park, Arizona:
American Association of Petroleum Geologists, Bulletin, v. 96, p. 679–707.
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TRENDELL, A.M., ATCHLEY, S.C., AND NORDT, L.C., 2013, Facies analysis of probable largefluvial-fan depositional system: the Upper Triassic Chinle Formation at Petrified Forest
National Park, Arizona, U.S.A.: Journal of Sedimentary Research, v. 83, p 873–895.
VASILAS, L.M., HURT, G.W., AND NOBLE, C.V., eds., 2011, Field Indicators of Hydric
Soils in the United States, Version 7.0: U.S. Department of Agriculture, Natural
Resources Conservation Service.
VEPRASKAS, M.J., 1992, Redoximorphic features for identifying aquic conditions: North
Carolina Agricultural Research Service, Technical Bulletin, v. 301, p. 33.
Received 29 January 2013; accepted 3 October 2013.
PAPER REVIEW:
Atchley et al., 2016. A LINKAGE AMONG PANGEAN TECTONISM, CYCLIC
ALLUVIATION, CLIMATE CHANGE, AND BIOLOGIC TURNOVER IN THE
LATE TRIASSIC: THE RECORD FROM THE CHINLE FORMATION,
SOUTHWESTERN UNITED STATES.
This is a pretty neat paper tying together a lot of the subjects that we’ve covered in class:
lithostratigraphy, biostratigraphy, chronostratigraphy, depositional systems, sequence
stratigraphy, paleosols, and paleoclimatology. Better yet it combines all of this
information to present a complete model of tectonic, environmental, and ecological
change. Quite a bit of the paper may be hard to understand, but you should be able to
mostly puzzle out what the paper is about.
I want 2 pages, single spaced, 12 point font, answering the following questions:
1. What is the basic question that the authors are trying to answer.
2. Give me a summary and brief explanation of all the tools the authors use to
create this model of tectonic, sedimentological, and biotic change. In other
words, list all the methods (MAP, radioisotopic dating, etc.) and provide a
brief (at least one full sentence) explanation of what information we get from
each method.
3. What is meant by “low accommodation” and “high accommodation?” What
impact does this have on the thickness of the sediment?
4. What are possible explanations for changes in accommodation?
5. What is the possible relation ship between climate and changes in plant and
animal communities? What is the evidence for it? You’ve already seen this
discussed in lab.
6. What relationship do the authors propose between tectonics and climate
change?
7. How might tectonics have therefore influenced changes in the plant and
animal communities?
DUE DECEMBER 6th; EMAIL TO ME.

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