Journal of Sedimentary Research, 2010, v. 80, 666–677
Research Article
DOI: 10.2110/jsr.2010.061
APPLICATION OF QUARTZ SAND MICROTEXTURAL ANALYSIS TO INFER COLD-CLIMATE
WEATHERING FOR THE EQUATORIAL FOUNTAIN FORMATION (PENNSYLVANIAN–PERMIAN,
COLORADO, U.S.A.)
DUSTIN E. SWEET* AND GERILYN S. SOREGHAN
Conoco-Phillips School of Geology and Geophysics, University of Oklahoma, 100 East Boyd Street, Norman, Oklahoma 73019, U.S.A.
e-mail: [email protected]
ABSTRACT: Climatic interpretations of the upper Paleozoic (Permo-Pennsylvanian) Fountain Formation, a coarse-grained
fan-delta system that formed in western equatorial Pangea, are difficult to constrain owing to a general lack of climatic
indicators so typical of coarse clastic systems. We applied scanning electron microscopy (SEM) to analyze quartz grains in this
system in an attempt to test the hypothesis of a glacial influence on these strata. SEM observations of first-cycle quartz grains
from these strata reveal microtextures formed from fracturing during grain transport, even after diagenetic overprinting
occurred under moderate burial conditions (up to 3.5 km depth and 100uC). Transport-induced microtextures can be grouped
based on inferred fracture process into: (1) high-stress fractures, consisting of fractures created through sustained high shear
stress, such as grooves, deep troughs, and gouges, and are inferred to occur predominantly during glacial transport; (2)
percussion fractures, consisting of fractures created by grain-to-grain contact during saltation or traction flow, such as
randomly oriented v-shaped cracks and edge rounding; and (3) polygenetic fractures, such as conchoidal fractures, arc-shaped
steps, linear steps, and linear fractures, that occur under a wide range of transport processes and thus possess no environmental
significance. Delineation of high stress, percussion, and polygenetic fracture types demonstrate that the Fountain Formation
quartz grains exhibit microtextures similar to both till and glaciofluvial deposits, suggesting that periods of upland glaciation
occurred in the source region of the Fountain Formation (Ute Pass uplift).
The abundance of high-stress fractures peaks at two stratigraphic intervals. These intervals are inferred to record the
presence of ice in the Ute Pass uplift and are correlative with polygonally fractured paleosurfaces in the Fountain Formation
that are interpreted to reflect cold-temperature weathering. Moreover, the peak intervals are approximately coeval with
inferred episodes of ice maxima from high-latitude localities, as well as other low-latitude localities. Geologically reasonable
stream gradients and estimated transport distance suggest a best-estimate elevation of the ice terminus of , 1500 m, but
possibly ranging to 3000 m. These data suggest that upland glaciers episodically existed within this equatorial setting and that
further use of this technique may reveal more evidence of ice in other proximal deposits of the ancestral Rocky Mountains, as
well as other systems of various geologic ages.
INTRODUCTION
Scanning electron microscopy (SEM) analysis of microtextures on
quartz grains has long been used to attempt interpretation of depositional
environments within Neogene deposits (e.g., Krinsley and Takahashi
1962; Krinsley and Donahue 1968; Krinsley and Doornkamp 1973).
Nonetheless, a variety of processes in a wide range of depositional
environments can produce similar types of microtextures—a concept
known as equifinality. Recent work, however, indicates that wet-based
glacial environments tend to produce a unique suite of microtextures, as a
result of the extraordinary stress imparted to grains in a subglacial
environment (e.g., Mahaney 2002; Mahaney and Kalm 2000). Despite
advances in SEM microtextural characterization of sediments from
glacial environments, such analysis has not been applied widely to preNeogene strata presumably owing in part to the overprinting effects of
diagenesis and sediment recycling.
* Present Address: Chevron Energy Technology Company, 1400 Smith #38079,
Houston, Texas 77002, U.S.A.
Copyright E 2010, SEPM (Society for Sedimentary Geology)
Recently, Soreghan et al. (2008a) proposed episodic and widespread
cold conditions, including glaciation, within the Ancestral Rocky
Mountains (ARM) of Pennsylvanian–Permian tropical Pangea. Additionally, Sweet and Soreghan (2008) have suggested a cold-weathering
origin for paleosurfaces exhibiting polygonal fractures within the
Fountain Formation of the ARM. Here, we present SEM microtextural
analysis of quartz grains recovered from the Pennsylvanian–Lower
Permian(?) Fountain Formation deposited on the northern flank of the
ancestral Ute Pass uplift of the ARM to assess: (1) the application of
SEM microtextural analysis to climate interpretation in ancient strata and
(2) the hypothesis of low-latitude glaciation within western equatorial
Pangea. The results of this study are consistent with the hypothesis of
episodic influxes of grains exhibiting glacially induced microtextures in
this equatorial setting.
GEOLOGIC BACKGROUND
The ARM form an intraplate collage of basement-cored uplifts and
intervening sedimentary basins (Fig. 1; Kluth and Coney 1981) that
1527-1404/10/080-666/$03.00
JSR
COLD-CLIMATE WEATHERING IN EQUATORIAL PANGEA
667
FIG. 1.—Late Pennsylvanian paleogeography
of the southern ancestral Front Range and Ute
Pass uplifts. Manitou Springs study area shown
as outlined area on northeastern margin Ute
Pass uplift. Latitudinal position is estimated
from Scotese (1997). Inset: Displays outline of
Colorado in the United States interior and
location of ARM uplifts (in gray; modified from
Kluth and Coney 1981). The black box is the
approximate area of the enlarged view.
developed within western equatorial Pangea in late Paleozoic time.
Mantling the basement-cored uplifts are coarse-grained wedges of firstcycle arkosic sediments. In the study area, the coarse clastic wedge shed
eastward from the ancestral Front Range uplift is represented by the
Fountain Formation (Fig. 1; e.g., Hubert 1960; Mallory 1972, 1975). The
Fountain Formation records coarse-grained fan-delta and braided-river
deposition (Suttner et al. 1984; Maples and Suttner 1990; Sweet and
Soreghan 2010).
Despite numerous studies of the Fountain Formation, interpretations
of the climate that prevailed during deposition are conflicting. Early
workers interpreted a warm-humid climate on the basis of an inferred
lateritic paleosol, local coaly layers, and scattered plant fragments
(Wahlstrom 1948; Hubert 1960), all restricted to the lower 150 m of the
900-m-thick formation. Mack and Suttner (1977) demonstrated that the
compositional maturity of the first-cycle sediments composing the lower
Fountain Formation exceeds that of first-cycle sediments from modern
drainages in the region, and used these results to advocate warm-humid
(tropical) conditions for the lower part of the Fountain Formation.
Conversely, Raup (1966) and Walker (1967) cited the interstitial clay
composition and hematite content of the Fountain Formation as evidence
for a warm-arid climate. More recently, Suttner and Dutta (1986) and
Dutta and Suttner (1986) suggested that an upward increase in
mineralogical immaturity, together with the decrease in inferred
neoformed kaolinite upward in the Fountain Formation reflect a change
from warm-humid to warm-semiarid conditions.
All previous researchers favor a warm climate; yet none of the
indicators used bear solely on temperature. For instance, coal reflects
high effective moisture under a wide range of temperatures (Parrish 1998;
Begossi and Della Fávera 2002; Barber et al. 2003). Additionally, Suttner
and Dutta (1986) noted that compositional immaturity characterizes both
cool and warm-arid climates. Sweet and Soreghan (2008) documented
polygonally fractured bedding surfaces in the Fountain Formation
inferred to record repeated thermal contraction of frozen ground. The
only proxies that bear exclusively on temperature conditions during
deposition of the Fountain Formation are those of Dutta and Suttner
(1986) (d18Ovalues of neoformed clays) and Sweet and Soreghan (2008),
both of which indicate anomalously cool equatorial temperatures.
The Fountain Formation consists of three tectonostratigraphic units
(lower, middle, and upper) separated by unconformities of varied
duration (Fig. 2; Sweet and Soreghan 2010). These tectonostratigraphic
units are defined by a combination of variations in facies, sedimentology,
structure, paleocurrents, and paleohydraulics and provide a framework
that enables relative dating in the poorly dated Fountain Formation
(Sweet and Soreghan 2010). Morrowan–Atokan (Bashkirian) marine
invertebrate and plant fossils occur in the basal Glen Eyrie Member of the
lower Fountain Formation (Chronic and Williams 1978; Suttner et al.
1984). The middle Fountain Formation bears no age-diagnostic fossils,
but records the same depositional system (i.e., fan delta) as the lower unit
and thus is considered only slightly younger than the lower unit. The
upper Fountain Formation has no age control in the study area except
through relative stratigraphic position. In northern Colorado, the
uppermost Fountain Formation is tightly constrained by Virgilian
fusulinids recovered 4 m below the contact with the overlying Ingleside
Formation which includes Wolfcampian fusulinids (Maughan and
Ahlbrandt 1985). Sweet and Soreghan (2010) provide an overview of
the age of the upper part of the Fountain Formation and propose that it
is latest Pennsylvanian to possibly earliest Permian in age; thus the
unconformity separating the upper and middle units ranges from
Desmoinesian to latest Pennsylvanian (Fig. 2).
METHODS
Samples were collected from strata that represent three depositional
environments or processes (fluvial, debris flow, and marine shoreface).
For each of the 15 samples, 10–55 individual quartz grains were analyzed
using the SEM; however, only those grains that exhibited microtextures
considered mechanical, rather than diagenetic, were used in analyses
presented herein.
Samples were disaggregated for microtextural analyses by removing
iron oxide cement with the citrate–bicarbonate–dithionite (CBD) method
668
JSR
D.E. SWEET AND G.S. SOREGHAN
to estimate percentage of grain covered or relative importance of
particular microtextures. Quantitative summary analyses were plotted
following methods outlined in Mahaney and Kalm (2000) and Mahaney
et al. (2001).
DIAGENESIS AND ANTIQUITY OF MICROTEXTURES
The Fountain Formation is a first-cycle arkose, as evinced by its
textural and compositional immaturity and its paleogeographic context
adjacent to the Precambrian basement (granitoid) source (Suttner et al.
1984; Kairo et al. 1993). Burial depth is constrained to , 3.5 km based
on vitrinite reflectance (Ro 5 0.61%, hvBb 5 100uC) analysis on coal
recovered from the lower Fountain Formation and employing a modern
geothermal gradient of 30uC/ km for the Denver Basin (Raynolds et al.
2001). The Fountain Formation was exhumed at Manitou Springs during
Laramide-age shortening, thus maximum burial and temperature
conditions most likely occurred in the latest Cretaceous to early
Paleogene. The grains of the Fountain Formation are composed
predominantly of quartz and feldspar with varying amounts of muscovite
and biotite. Primary diagenetic products formed during burial consist of
authigenic clay, quartz overgrowths and ‘‘turtle-skin’’ quartz as described
by Folk (1978) (Fig. 3). At least one of these precipitation features are
found on each quartz grain analyzed, and commonly precipitation
completely obscures the grain surface. However, of the 542 quartz grains
analyzed, 330 (61%) exhibit fracture surfaces that pre-date diagenesis, as
indicated by: (1) precipitation of ‘‘turtle-skin’’ quartz on the fracture
surface, (2) partial encroachment of quartz overgrowths onto fracture
surfaces, or (3) presence of dissolution pits on fracture surfaces. Thus, the
pre-diagenetic fractures must have formed during the late Paleozoic
because the Fountain Formation consists of first-cycle sediments derived
directly from the adjacent Precambrian basement (Hubert 1960) and reexposed as a result of Laramide orogenesis. On a few grains, pristine
fracture surfaces cut across precipitation features, indicating new
fracturing induced during disaggregation, the sampling process, or
regional stress in situ. Such fractures were ignored during analyses.
FIG. 2.—Fountain Formation stratigraphy of the Manitou Springs region, after
Sweet and Soreghan (2010). The upper Fountain Formation is gradational with
either the Lyons or Ingleside formations, such that A) indicates the stratigraphic
relationships of the upper Fountain Formation if the overlying unit is Ingleside
and B) indicates stratigraphic relationships of the upper Fountain Formation if the
overlying unit is Lyons. Note that only one of the overlying eolian units is present
in any given region; see Sweet and Soreghan (2010) for further discussion. Vertical
black lines represent inferred time missing at unconformities; however, the
duration of individual unconformities is weakly constrained. Time scale is from
Gradstein et al. (2004). IPlf 5 lower Fountain Formation; IPmf 5 middle
Fountain Formation; IPuf 5 upper Fountain Formation.
(Mehra and Jackson 1960; Janitzky 1986). The sand + gravel fraction
was wet-sieved and the 3–1.5 mm, 1.5–0.7 mm, and 0.7–0.3 mm fractions
were analyzed. To avoid introduction of laboratory-induced fracturing,
samples were not sonicated. Quartz grains were randomly selected with a
binocular microscope for SEM analysis as outlined by Mahaney et al.
(1988).
Individual grains were placed on an aluminum SEM stub and sputter
coated with a gold–palladium mixture. Grains were examined with a Zeiss
960 SEM, tungsten filament and 15 kV accelerating potential. All grains
were individually verified as quartz by energy-dispersive spectrum (EDS)
analysis.
The atlases of Krinsley and Doornkamp (1973) and Mahaney (2002)
were used to identify microtextures, following the characteristics listed in
Table 1 (see also Acknowledgments section for URL of supplemental
Table). Each microtexture evaluated was recorded as either present or not
present following the methods of Mahaney (2002); no attempt was made
CHARACTERISTICS OF MICROTEXTURES
Quartz grains display a wide variety of textural characteristics. Grain
rounding ranges widely from angular to well rounded, and sorting is
typically poor to very poor. Overall, the most abundant microtextures are
conchoidal fractures, subparallel linear fractures, and edge-rounding
fractures (Figs. 4, 5). Microtextural variance based on grain size was not
observed. Because the samples represent various facies, it is useful to
examine and compare data both from similar facies and similar
stratigraphic levels.
Facies Trends
Marine shoreface facies occur in the lower and middle Fountain
Formation and typically exhibit more mineralogical and textural maturity
than the other facies. SEM analysis indicates that nearly 60% of the grains
contain edge rounding and low relief (Fig. 5A). Breakage blocks,
randomly oriented v-shaped cracks, arc-shaped steps, conchoidal
fractures, and subparallel linear fractures occur on 20–30% of the grains
(Figs. 4, 5A). Grooves, gouges, and troughs are relatively rare.
Only debris flows in the middle Fountain Formation were sampled for
this study. Quartz grains from the debris flow facies exhibit a relatively
high percentage (30–50%) of breakage blocks, conchoidal fractures, and
edge rounding (Fig. 5B), whereas 15–25% of the grains show subparallel
linear fractures, arc-shaped steps, and linear steps (Fig. 4). Grains are
characterized predominantly as having medium relief, commonly
associated with sharp angular features. Gouges, grooves, and troughs
are least abundant in this facies.
JSR
COLD-CLIMATE WEATHERING IN EQUATORIAL PANGEA
669
TABLE 1.— SEM microtexture nomenclature and characteristics.
Microtexture
Characteristics(1)
A. Grain fracturing microtextures
Edge rounding
Rounded edges on grains
V-shaped cracks
Abrasion features
Arc-shaped steps
Breakage blocks
Conchoidal
fractures
Fracture faces
Linear steps
Sharp angular features
Subparallel linear
fractures
Crescentic gouges
V-shaped fractures of variable size and depth
on grain surfaces
Rubbed or worn down grain surfaces
Arcuate fractures on grain surfaces, typically
depths greater than micrometers
Space represented by removal of block of
variable size on grain, typically on grain edge
Smooth curved fractures with ribbed
appearance
Large, smooth, and clean fractures of at least
25% of grain surface
Widely spaced (. 5 mm) linear fractures on
grain surface
Distinct sharp edges on grain surface
Deep troughs
Mechanically upturned
plates
Straight grooves
Linear fractures on grain surface, typically less
than , 5 mm spacing
Crescent-shaped gouges on grain surface,
typically . 5 mm deep
Grooves . 10 mm
Partially torn loose plates from the mineral
surface
Linear grooves on mineral surface , 10 mm
Curved grooves
Curved grooves on mineral surface , 10 mm
B. Diagenetic microtextures
Dissolution etching
Grain surface with a net of pits or cavities
Weathered surface
Mechanically and/or chemically altered surface
containing preexisting microtextures
Precipitation features
Coatings or euhedral growth of SiO2 or Fe2O3
on grain surface
C. Grain relief(2)
Low relief
Nearly smooth surface without topographic
irregularities
Medium relief
Semi-smooth surface with topographic
irregularities
High relief
Topographically irregular surface with
pronounced swells and swales
(1)
(2)
Process of microtexture formation
Percussion (fracturing)
Percussion (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Polygenetic (fracturing)
Sustained high-stress (fracturing)
Sustained high-stress (fracturing)
Sustained high-stress (fracturing)
Sustained high-stress (fracturing)
Sustained high-stress (fracturing)
Chemical dissolution (diagenesis)
Weathering (diagenesis)
Mineral growth (diagenesis)
Entire history of grain
Entire history of grain
Entire history of grain
Selected reference(s)
Campbell and Thompson 1991; Mahaney and
Kalm 1995, 2000; Mahaney 2002
Campbell and Thompson 1991; Mahaney and
Kalm 1995, 2000; Mahaney 2002
Mahaney and Kalm 1995, 2000; Mahaney 2002;
Mazzullo and Ritter 1991
Campbell and Thompson 1991; Mahaney and
Kalm 1995, 2000; Mahaney 2002
Campbell and Thompson 1991; Helland and
Diffendal 1993
Campbell and Thompson 1991; Mahaney and
Kalm 1995; Mahaney 2002
Mahaney 2002
Campbell and Thompson 1991; Mahaney and
Kalm 1995; Mahaney 2002
Campbell and Thompson 1991; Mahaney and
Kalm 1995; Mahaney 2002
Helland and Diffendal 1993; Mahaney and Kalm
1995, 2000; Mahaney 2002
Campbell and Thompson 1991; Mahaney et al.
1988; Mahaney 2002
Mahaney and Kalm 1995, 2000; Mahaney 2002
Mahaney and Kalm 2000; Mahaney 2002
Helland and Diffendal 1993; Mahaney and Kalm
1995, 2000; Mahaney 2002
Helland and Diffendal 1993; Mahaney and Kalm
1995, 2000; Mahaney 2002
Mahaney and Kalm 1995; Mahaney 2002
Helland and Diffendal 1993; Mahaney and Kalm
1995; Mahaney 2002; Mazzullo and Ritter 1991
Folk 1978; Helland and Diffendal 1993; Mahaney
2002; Mazzullo and Ritter 1991
Campbell and Thompson 1991; Mahaney and
Kalm 1995; Mahaney 2002
Campbell and Thompson 1991; Mahaney and
Kalm 1995; Mahaney 2002
Campbell and Thompson 1991; Mahaney et al.
1988; Mahaney and Kalm 1995; Mahaney 2002
Descriptions predominantly synthesized from Mahaney (2002)
Relief is defined as the difference between high and low points on grain surface
The fluvial facies are ubiquitous throughout the lower, middle, and
upper Fountain Formation (Sweet and Soreghan 2010). Quartz grains
from the fluvial facies display the widest variation in microtextures. Edgerounding fractures are the most common, found on nearly 60% of the
examined grains (Fig. 5C). Other prominent microtextures are conchoidal
and subparallel linear fractures, arc-shaped and linear steps, randomly
oriented v-shaped cracks, and breakage blocks. Relative to the debrisflow and shoreface facies, grooves, troughs, and gouges occur in highest
abundance in the fluvial facies. Mechanically upturned plates occur
uniquely in this facies (Fig. 4H). Similar to the debris-flow facies, grains
typically exhibit medium relief, although many display high relief.
Interpretation.—The textural and mineralogical maturity enhancement
of marine facies relative to other facies has been interpreted as an
environmental effect attributable to wave action in the shoreface (Kairo
et al. 1993). The high percentage of edge rounding and low relief probably
record this shoreface environmental effect; however, nearshore eolian
processes may also account for some these microtextures. The presence of
grooves, troughs, and gouges in the marine facies are inferred to reflect
nonmarine transport because these microtextures require considerable
and sustained pressure (e.g., Mahaney and Kalm 2000; Mahaney 2002),
conditions atypical of the marine realm.
Quartz grains from debris-flow facies are commonly partially encased
by clay minerals that were not completely removed by the CBD process,
and also exhibit the precipitated quartz common to other facies. These
two factors resulted in a relatively low population (14 of 22) of grains
with observable ancient microtextures. The debris-flow grains preserve a
higher proportion of angular grains than the other facies, presumably
because the laminar flow typical of debris flows inhibits the mechanical
interaction of grains necessary to abrade edges.
Overall, variation in microtextural attributes of grains amongst the
studied facies is subtle, suggesting that environment of deposition did not
impart a dramatic signal in overall microtextural character. However, the
lack of v-shaped cracks on grains in the debris-flow facies and the wide
diversity of fractures observed in grains from fluvial facies probably
reflect processes intrinsic to these environments that partially controlled
670
JSR
D.E. SWEET AND G.S. SOREGHAN
grooves, troughs, and gouges, all reflecting considerable and sustained
pressure (Mahaney and Kalm 2000), are unlikely to be a result of fluvial
processes. Instead, they suggest the influence of process(es) within a
different environment that affected grain microtextures previous to fluvial
entrainment, as discussed below.
DISCUSSION
FIG. 3.—SEM image showing common diagenetic features exhibited on
Fountain Formation quartz grains. Qog 5 quartz overgrowth; Cc 5 clay
coating; Ts 5 turtle-skin silica coating.
for those microtextures. For example, randomly oriented, v-shaped
cracks are thought to record percussion (Campbell and Thompson 1991;
Jackson 1996; Mahaney and Kalm 2000; Mahaney 2002), a process that is
rare in debris flows owing to minimal intergranular collisions (e.g., Costa
1988), as noted above. In contrast, percussion is an important process in
the saltation transport common to both fluvial and shoreface environments, and the relative abundance of v-shaped cracks in these facies
probably reflects that difference.
Stratigraphic Trends
Samples from different stratigraphic horizons reflect different time
horizons, such that grouping facies results in time averaging of the
textural data. The Fountain Formation has poor age control, but the
tectonostratigraphic units proposed by Sweet and Soreghan (2010;
defined earlier) provide a relative chronostratigraphic framework for
samples (Fig. 2). Of the three facies, only fluvial facies occur in all three
tectonostratigraphic units; hence, samples from this facies were compared
with one another to address stratigraphic variation of microtextures.
Microtextural frequency plots from fluvial facies of the lower, middle
and upper Fountain Formation (Fig. 5D, E, F) all show a predominance
of medium-relief grains, edge-rounding fracturing (50–70%), and
randomly oriented, v-shaped cracks (20–30%). Conchoidal and subparallel linear fractures are also relatively prominent features, present on 20–
40% of the grains. A notable intersample difference is the higher
percentage of gouges, grooves, and troughs observed on grains of the
middle Fountain tectonostratigraphic unit relative to those of the other
units (Fig. 5D, E, F).
Interpretation.—The high frequency of edge-rounding fracturing and vshaped cracks, both thought to record percussion (Mahaney and Kalm
2000; Mahaney 2002), presumably reflect intergranular collision during
fluvial transport. However, the stratigraphic variation in frequency of
Historically, data on microtextural frequency have been displayed in
histogram-type plots (Fig. 5) (Campbell and Thompson 1991; Mahaney
et al. 1991; Mahaney 1995; Mahaney and Kalm 1995, 2000; Mahaney
2002). The large number of variables (grain characteristics) in these plots,
however, makes it difficult to compare data sets, unless there are very
large contrasts in frequency data, such as in Mahaney and Kalm (2000).
Therefore comparison of data to assess transport process(es) is facilitated
by grouping microtextures created by similar fracturing processes.
Whereas many microtextures can be created in various environments
through various processes, some are thought to record specific transport
processes. Notably, randomly oriented, v-shaped cracks and edgerounding fracturing are commonly interpreted to reflect percussion
(saltation) transport (e.g., Campbell and Thompson 1991; Mahaney and
Kalm 2000; Mahaney 2002). In contrast, straight and curved grooves,
deep troughs, and crescentic gouges are thought to reflect sustained high
shear stress (e.g., Mahaney and Kalm 2000; Mahaney 2002). Accordingly,
a potentially useful approach involves classifying mechanically induced
microfractures into one of three genetic groupings: (1) high-stress
fractures, (2) percussion fractures, and (3) polygenetic fractures, or those
created through a variety of processes. These groups can then be plotted
on a ternary diagram for semiquantitative intersample comparison
(Fig. 6).
Plotting all of the fluvial samples on a high stress–percussion–
polygenetic fracture ternary diagram reveals a first-order trend that is
subparallel to the polygenetic–percussion join (Fig. 6), suggesting that
grains experienced varying amounts of intergranular collision that
resulted in the v-shaped cracks and edge rounding defining the percussion
apex. However, all grains except one are shifted from the polygenetic–
percussion join, indicating that they experienced sustained high stress at
some point during transport, in order to form the textures defining the
high-stress apex.
High-stress microtextures require grain-to-grain contact under high
shear stress and have been reported from grains entrained in highly
viscous debris flows, structural shear zones, and glacial environments
(Mahaney 2002). Debris flows are an unlikely cause for the high-stress
textures present on the grains in the high stress–percussion–polygenetic
ternary diagram because only samples from the fluvial facies were used in
the analysis and debris flows are an overall minor part of the depositional
system (Suttner et al. 1984; Sweet and Soreghan 2010). The major late
Paleozoic structures in the study area are the Ute Pass fault and
associated folding (Kluth 1997; Suttner et al. 1984; Sweet and Soreghan
2010). Flexural slip along bedding planes associated with these structures
could conceivably have produced high-stress textures on syntectonic
grains; however, no slip indicators (e.g., slickensides) have been
recognized on bedding surfaces in the study area. Late Paleozoic
movement on the Ute Pass fault might also have produced high-stress
textures on grains in the fault zone, which could have then been
incorporated into the depositional system wherever the Ute Pass fault
plane breached the surface. However, such grains eroding from the fault
zone represent a very small volume relative to the entire system, such that
production of high-stress features in this manner should be quite rare
overall. More importantly, Sweet and Soreghan (2010) demonstrated that
the Ute Pass fault was inactive and thus buried by the time of deposition
of the upper Fountain Formation, yet this upper unit contains grains
exhibiting high-stress microtextures. Therefore, a structural genesis for
JSR
COLD-CLIMATE WEATHERING IN EQUATORIAL PANGEA
671
FIG. 4.—SEM images of a variety of microtextures from quartz sand grains from the Fountain Formation. A) Well-rounded quartz grain recovered from marine
shoreface facies. This grain displays numerous randomly oriented v-shaped cracks (vc; only a few highlighted for clarity) and is coated with turtle-skin silica and local
authigenic clay minerals. B) Angular quartz grain displaying high-relief, subparallel linear fractures (lf) and a deep trough (dt). C) Straight grooves (sg) on a fracture face.
D) Straight grooves (sg) and linear steps (ls). A euhedral quartz overgrowth (ov) has formed at the terminus of the grooves. E) Irregularly shaped grain displaying highrelief and arc-shaped steps (as). Grain surface is coated with turtle-skin silica, local clay minerals, and mica grain. F) Fractured grain surface covered with turtle-skin silica
displaying remnant crescentic gouges (cg). G) Fracture face (ff) on grain surface shows evidence for edge rounding (er) fracturing including v-shaped cracks (vc). H)
Mechanically upturned plate (mup) on grain surface with local pockets of quartz precipitation (qp) on upturned plate. I) Well-rounded grain recovered from marine
shoreface facies showing randomly oriented v-shaped cracks (vc).
high-stress microtextures recorded in the Fountain Formation is
untenable as an explanation for the majority of the grains affected.
Most of the Fountain Formation data plot between published data
from glacially influenced Quaternary sediments (i.e., till and glaciofluvial)
and Devonian fluvial sandstone (Mahaney and Kalm 2000). This
observation suggests that the majority of the Fountain Formation
samples exhibit a high-stress microtexture occurrence suggestive of
glacially influenced sediments (Fig. 6). Accordingly, these high-stress
fractures are inferred to be the result of glacial transport, most likely from
upland glaciation in the ancestral Ute Pass uplift. However, the samples
672
D.E. SWEET AND G.S. SOREGHAN
JSR
FIG. 5.—Comparison of SEM microtexture frequency of: A) quartz grains from marine facies; B) quartz grains from debris-flow facies; C) quartz grains from fluvial
facies; D) quartz grains from the lower Fountain Formation; E) quartz grains from the middle Fountain Formation; F) quartz grains from the upper Fountain
Formation. Quartz grains that exhibited complete diagenetic overprint were not used in the analysis. Percentage values represent the total number of grains in each
sample that exhibited the particular microtexture relative to the total grains in the sample.
also exhibit percussion fracturing suggesting that grains were entrained
fluvially, and in some cases transported to the marine environment, after
initial glacial transport. Because the majority of samples exhibit a higher
frequency of high-stress fractures than glaciofluvial sediments, it is possible
that the Fountain Formation grains were transported a relatively short
distance such that high-stress fractures survived complete overprinting in
the fluvial environment. In summary, the overall suite of fractures exhibited
on grain surfaces is best characterized by a glacially produced high-stress
component and a glaciofluvially produced percussion component. In the
most distal reaches of the depositional system, marine and nearshore eolian
process probably account for some of the percussion fracturing.
A plot of relative abundance of high-stress fractures versus stratigraphic level shows two peaks of 22 and 31% with intervening minima of
0% and 4% (Fig. 7). These peaks deviate from the average of 14% with a
standard deviation of 8.3, thus these peaks are larger than or equal to 1s.
The stratigraphic extent of these peaks is not well constrained due to
sample spacing, thus true maximums are unconstrained. Furthermore,
timing and duration of the peaks are limited. Nevertheless, the existence
of these peaks indicates stratigraphic levels marked by a significant
occurrence of high-stress microtextures. Because the microtextures are
inferred as glacial in origin, we suggest that the peaks record periods of
upland glaciation or perhaps immediate postglacial times, depending on
the lag time until final deposition. The majority of samples exhibit highstress microtextures, which could be interpreted to reflect nearly constant
presence of ice atop the Ute Pass uplift during deposition of the Fountain
Formation. However, given the episodic nature of glaciation, the peaks
could approximate presence of ice and the intervening low high-stress
intervals could reflect recycling of grains, as discussed below.
JSR
COLD-CLIMATE WEATHERING IN EQUATORIAL PANGEA
673
FIG. 6.—Ternary diagram illustrating the relative abundances of polygenetic, high-stress, and
percussion fractures. Percentages represent the
summation of times that microtextures in their
respective group (polygenetic, high stress, and
percussion) were counted relative to the total
counts of mechanical microtextures for the entire
sample. Solid black dots are samples used in this
study. Each sample consists of 10–32 quartz
grains, and the percentage of microtextural
occurrence is read from the corresponding axis.
Open circle is the average of all samples, consisting
of 234 quartz grains. Quartz grains that exhibited
complete diagenetic overprint were not used.
Polygenetic fracture apex includes fracture faces,
subparallel linear fractures, conchoidal fractures,
arc-shaped steps, linear steps, and breakage
blocks. High-stress fracture apex includes curved
grooves, straight grooves, deep troughs, and
mechanically upturned plates. Percussion fracture
apex includes randomly oriented v-shaped cracks
and edge rounding. Note that the data from this
study (black circles) are displaced from the
polygenetic–percussion join towards the highstress apex. Mahaney and Kalm (2000) and
Mahaney et al. (1996) points are a summation of
all samples within respective studies: open
triangle 5 , 575 quartz grains; black
triangle 5 , 350 quartz grains, black
cross 5 , 75 quartz grains, , 450 quartz grains.
ADDITIONAL EVIDENCE FOR LATE PALEOZOIC EQUATORIAL GLACIATION
If SEM microtextural data in the Fountain Formation suggests
glacially influenced sediments, then additional evidence consistent with
glacial outwash and periodic cool climate should also occur. Indeed,
areally extensive, polygonally fractured bedding surfaces occur in at least
two discrete stratigraphic intervals of the Fountain Formation (Sweet and
Soreghan 2008). These surfaces are inferred to represent thermal
contraction of frozen ground and indicate anomalously cool conditions
for those times. In addition, one of the most volumetrically significant
facies in the entire succession is hyperconcentrated-flood-flow deposits
(Sweet and Soreghan 2010). These flood deposits indicate that the system
contained abundant water and loose sediment, conditions consistent with
proglacial deposition (e.g., Maizels 1993, 1997; Marren 2002). Furthermore, the cobbles of the Fountain Formation are overwhelmingly
faceted, a shape more typical of glacial processes, albeit nondiagnostic
in isolation.
Glacial striae on bedrock or cobbles are often associated with late
Paleozoic Gondwanan glacial deposits and commonly considered the
‘‘gold standard’’ in demonstrating the presence of glaciation. Yet,
Dowdeswell et al. (1985) demonstrated that the presence of striae in
(modern) glacial till varies greatly (, 3% to 65% of clasts), dependent
upon lithology. No striae, other than those observed through SEM on
grain surfaces, have been observed on Fountain Formation cobbles or
subjacent granitic bedrock. However, such macrostriae would be unlikely
to be preserved in the Ute Pass uplift bedrock owing to overprinting by
Laramide uplift and modern erosion. Furthermore, Fountain Formation
cobbles are predominantly coarse-grained granite of the Ute Pass uplift
(Trimble and Machette 1979), lithologic types that typically do not yield
striae (Dowdeswell et al. 1985). Hence, in such cases, where lithologic
control may negatively affect preservation of macrostriae, the use of
SEM-based microtextural analyses may be particularly useful in
attempting to discern a possible glacial influence on sedimentation.
Regionally, evidence for Permo-Pennsylvanian glaciation within
equatorial Pangea has been suggested. Soreghan et al. (2009) reinterpreted the Permo-Pennsylvanian Cutler Formation—coarse clastic strata
shed from the Uncompahgre uplift—as a product of proglacial
deposition, evinced by the presence of features such as dropstones,
faceted clasts, and abundant deposits of hyperconcentrated flood flows
and large-magnitude floods. Furthermore, Soreghan et al. (2008a, b)
inferred late Paleozoic glaciation in western equatorial Pangea on the
basis of evidence for a Paleozoic, glacially carved landscape (Unaweep
Canyon) and widespread loess deposits of this age. D’Orsay and van de
Poll (1985) documented microtextures on quartz grains that they
suggested are indicative of glacial transport in the Pennsylvanian
Parrsboro Formation of Nova Scotia. All of these studies provide
corroborative evidence for the existence of upland glaciation in the late
Paleozoic highlands of equatorial Pangea.
TRANSPORT DISTANCE AND CONSTRAINTS ON ICE-TERMINUS ELEVATION
Glacial meltwater streams should contain a component of grains with
high-stress fractures imparted during previous glacial transport. Indeed,
Jackson (1996) recognized that, under conditions of low discharge, low
velocity, and short transport distances (, 1 km) v-shaped cracks
developed atop high-stress microtextures that formed during earlier
glacial transport. Thus, fluvial transport will overprint high-stress glacial
fractures, but no systematic studies have assessed the fluvial transport
distance or other variables necessary to completely obliterate the glacial
signal. The Ute Pass uplift was , 70 km wide, which constrains the
maximum transport distance for the sediments in the Fountain
depositional system. However, because the Ute Pass uplift was
structurally bounded on only its northeast margin (Kluth and McCreary
2006; Sweet and Soreghan 2010), the uplift was likely asymmetric, with
the topographic crest closer to the faulted margin; hence, transport
distances were likely , 35 km (Figs. 1, 8).
Stream gradients in glacial systems are quite variable. Exceptionally
high gradients commonly prevail proximal to ice hosted on crystalline
bedrock, but decrease to gradients of 0.1–0.01 within a few kilometers of
the ice terminus, such that most upland systems typically approach 0.05
within 20 km (Table 2). These admittedly broad constraints on stream
gradients and transport distances provide a means to estimate the
674
D.E. SWEET AND G.S. SOREGHAN
JSR
elevation of the ice terminus (Fig. 8). Using a stream gradient of 0.05 and
maximum transport distance of 30 km, the estimated ice elevation was
1500 m (Fig. 8) above sea level because the lower and middle Fountain
Formation were deposited essentially at sea level, as evidenced by
intercalated marine strata (Suttner et al. 1984; Maples and Suttner 1990).
However, as Figure 8 shows, selection of a different gradient or transport
distance results in quite variable estimates of ice elevation; even given
such variation, however, it is unlikely that the elevation of the ice
terminus exceeded 3000 m. The upper Fountain Formation, however,
lacks intercalated marine strata proximal to the Ute Pass uplift such that
arguments relying on stream gradient and transport distance constrain
relief only above the elevation of the Fountain depositional slope.
Theoretically, glacial ice can occur at any elevation on Earth given a
high enough accumulation-to-ablation ratio. During the last glacial
maximum (LGM), terminal moraines in equatorial settings reached
elevations of 2300–3400 m in Africa (Hastenrath 2009), and the
equilibrium line altitude is estimated at 3400 m in the Andes (Lachniet
and Vazquez-Selem 2005). Elevation differences reflect local ablation and
accumulation conditions. The proposed maximum elevation of 3000 m
for the ice terminus of the ancestral Ute Pass uplift (Fig. 8) is within the
upper extent of these ranges, but 3000 m is a probable maximum, and
elevations may have been significantly lower. Thus, the climatic
conditions producing ice in the ancestral Ute Pass uplift were either
much colder, or wetter, or both relative to LGM equatorial conditions.
Soreghan et al. (2008a) have suggested that ice reached elevations of
1000–1500 m in the Uncompahgre uplift of the ancestral Rocky
Mountains, a finding consistent with these results.
STRATIGRAPHIC DISTRIBUTION OF INFERRED COLD-WEATHERING PULSES
FIG. 7.—Plot of relative abundance of high-stress fractures with stratigraphic
position. Quartz grains that exhibited complete diagenetic overprint were not used
in the analysis. Relative abundances were estimated by summing all grains that
exhibited high-stress fractures within the sample versus the total number of grains
that exhibited any mechanical microtextures within the same sample (shown as
percentages). Lower (LFF), middle (MFF), and upper (UFF) part of the Fountain
Formation are tectonostratigraphic units separated by intraformational unconformities (wavy lines) as defined by Sweet and Soreghan (2010). The labels I and II
indicate maxima in frequency of occurrence in high-stress fractures.
Constraining the temporal context of these data precisely is difficult
owing to lack of absolute dates and the generally barren character of the
strata. Age constraints consist of numerous conodonts recovered from
marine beds housed in the lower Fountain Formation including
Idiognathoides sinuatus (Suttner et al. 1984), which indicates an early
Pennsylvanian conodont zone ranging from , 315–317 Ma (Davydov et
al. 2004). These conodont-bearing strata occur approximately 75–
100 meters above base and were correlated using a series of unpublished
measured sections (Fig. 7; Suttner, unpublished data). The lowest peak (I)
in high-stress fractures resides in the middle Fountain Formation.
However, the middle Fountain Formation is separated from the lower
Fountain Formation by an intraformational unconformity of likely
minimal duration (Fig. 9; Sweet and Soreghan 2010); nevertheless the
biostratigraphic age control for the lower Fountain Formation yields an
approximate age for the middle Fountain Formation. The estimated age
for this interval is middle to late Atokan. Peak (I) is roughly coeval with
bedding planes that contain polygonal fractures attributed to repeated
cooling of frozen ground (Fig. 9; Sweet and Soreghan 2008). The upper
Fountain Formation is late Virgilian to early Wolfcampian(?) in age
FIG. 8.—Diagram showing the interpreted
general structural relationship of the Ute Pass
uplift and fan-delta depositional wedge during
deposition of the lower and middle parts of the
Fountain Formation. Location of cross section
(A–A9) is shown in Figure 1. Variable x defines
the distance from the Ute Pass crest to the
northeastern structural margin and essentially
estimates proglacial transport distance. Variable
z is the elevation of ice as a function of x and
stream gradient. Note that the Ute Pass uplift is
, 70 km wide (Kluth and McCreary 2006;
Sweet and Soreghan 2010). Inset: Estimates of
ice elevation (z) as a function of a variety of x
values and stream gradients.
JSR
COLD-CLIMATE WEATHERING IN EQUATORIAL PANGEA
675
TABLE 2.— Proglacial stream gradients of various upland glaciers.
Glacier Name
Bedrock type
Location
Average stream gradient
from ice terminus to
10 km
Nisqually
Soule’
Franz Josef
Agassiz
Scott
Herron
Unnamed
volcanic
granite
schist, gneiss and volcanics
carbonate
granite, volcanic and sedimentary
granite and sedimentary
volcanic
Washington, USA
Alaska, USA
New Zealand
Montana, USA
Alaska, USA
Alaska, USA
Peru
0.1
0.06
0.12
0.09
0.02
0.02
0.08
0.03
n/a
0.08
0.05
0.01
0.01
0.06
0.02
n/a
n/a
n/a
n/a
0.01
0.05
0.07
0.04
0.03
Average
(Sweet and Soreghan 2010) and houses the upper (II) peak in high-stress
fractures. This peak is also approximately coeval with the coldweathering polygonal fractures reported by Sweet and Soreghan
(2008)(Fig. 9).
The correspondence of peaks in high-stress fractures with other
indicators of cold temperatures in the Fountain depositional system
(Fig. 9) reinforces the interpretation of possible upland glaciation. Owing
to the low-latitude paleoposition of the Fountain system, episodes of
upland glaciation likely correlate to globally cold intervals. Recent work
in late Paleozoic strata of the Gondwanan region has demonstrated pulses
of glacially influenced sediments separated by inferred nonglacial
sediments (Isbell et al. 2003; Fielding et al. 2008). The high-stress peaks
(I and II) are broadly coeval with individual glacial episodes from high-
Average stream gradient
from ice terminus to
20 km
Average stream gradient
from ice terminus to
20 km
latitude Pangea (Fig. 9), suggesting that anomalously cool episodes in
equatorial Pangea may correspond with Gondwanan ice maxima.
CONCLUSIONS
SEM analysis of quartz grains from the Pennsylvanian–Early
Permian(?) Fountain Formation demonstrates that glacial-transportrelated fracturing is preserved even through the mask of diagenetic
overprinting. Transport-induced microtextures can be grouped into three
categories based upon fracture mechanism: (1) high-stress fractures, such
as troughs, grooves, and gouges obtained through sustained high shear
stress; (2) percussion fractures, such as randomly oriented v-shaped
cracks and edge rounding fracturing obtained through saltation and/or
FIG. 9.—Chart of Fountain Formation climatic indicators compared to late Paleozoic
glacial episodes. SEM microtextural data and
polygonal fractures are placed within the respective tectonostratigraphic unit, but age control within the tectonostratigraphic units is
crude. See Figure 7 caption for explanation of
the calculation of high-stress microtextures
percentages and definition of labels (I) and (II).
Glacial episodes of: eastern Australia from
Fielding et al. (2008), Gondwana from Isbell et
al. (2003), and Siberia from Epshtyn (1981a,
1981b) and Chumakov (1994). Vertical lines
denote time represented by intraformational
unconformities. Time scale is from Gradstein et
al. (2004) Ma 5 million years (megaannum).
676
D.E. SWEET AND G.S. SOREGHAN
traction flow; and (3) polygenetic fractures, such as steps, conchoidal
surfaces, and lineaments obtained in a variety of depositional environments and fracture processes.
The nature and abundance of microtextures in the Fountain Formation
show similarities to microtextures from Quaternary till and glaciofluvial
sediments, suggesting genetic similarities, including an origin from sustained
grain-to-grain shear stress in a glacial environment. The glacially imprinted
quartz grains subsequently entered the proglacial environment and were
subjected to predominantly percussion-related fracturing.
The stratigraphic occurrence of high-stress (inferred glacial) fractures
exhibit two peaks. Each peak is interpreted to record an interval of
upland glaciation in the Ute Pass uplift. Residence time in the drainage
basin may effectively time average the high-stress data such that quartz
grains exhibiting high-stress fractures were delivered even during times of
no upland ice. The complicating effects of crude age constraints in the
Fountain Formation and the residence time of the sediments in the
drainage basin preclude estimates of durations for the existence of upland
glaciers. General constraints on transport distance and possible proglacial
stream gradients suggest that the elevation of ice was most likely
, 1500 m, although elevations up to 3000 m are possible given
exceptionally steep stream gradients.
Peak occurrences of high-stress fractures correlate with the presence of
polygonally fractured paleosurfaces in the Fountain Formation that are
inferred to reflect cold-temperature weathering. Age models for the
Fountain Formation are crude, but geologic arguments allow the
possibility that the peaks in high-stress fractures correlate with peak
Gondwanan glaciations. Hence, these data support the hypothesis that
equatorial Pangea was punctuated by anomalously cool conditions, as
suggested by Soreghan et al. (2008a), Soreghan et al. (2008b), Soreghan et
al. (2009), and Sweet and Soreghan (2008).
SEM microtextural analysis may be useful to assess a glacial influence
where ice-contact facies are lacking, even in strata that have undergone
moderate burial. Furthermore, the use of the classification scheme and
associated ternary plot developed here provides a means to assess such
data in a semiquantitative manner.
ACKNOWLEDGEMENTS
This work formed part of D. Sweet’s PhD research and was funded in part
by GSA graduate student research grants, Sigma Xi Grants-in-Aid of
Research, Colorado Scientific Society Research Grant, J.D. Love Field
Geology Fellowship, SEPM Presidential Fund student grant, and NSF grant
# EAR-0230332 awarded to Soreghan. Constructive and helpful reviews by
John Isbell, Martin Gibling, Eugene Rankey, and an anonymous reviewer
greatly improved the manuscript. We thank P. Larson of the Sam Noble
Electron Laboratory for Scanning Electron Microscopy technologic training,
Z. Reches and M. Soreghan of the University of Oklahoma for numerous
discussions, and B. Cardott of the Oklahoma Geological Survey for vitrinite
reflectance. Lastly, We thank K. Schroeder of the Colorado Springs Parks
Department for access and sampling permission of the study area. A
Supplemental Table is available from JSR’s Data Archive, http://www.sepm.
org/jsr/jsr_data_archive.asp.
REFERENCES
BARBER, K.E., CHAMBERS, F.M., AND MADDY, D., 2003, Holocene paleoclimates from
peat stratigraphy: macrofossil proxy climate records from three oceanic raised bogs in
England and Ireland: Quaternary Science Reviews, v. 22, p. 521–539.
BEGOSSI, R., AND DELLA FÁVERA, J.C., 2002, Catastrophic floods as a possible cause for
organic matter accumulation giving rise to coal, Parana Basin, Brazil: International
Journal of Coal Geology, v. 52, p. 83–89.
CAMPBELL, S., AND THOMPSON, I.C., 1991, The palaeoenvironmental history of late
Pleistocene deposits at Moel Tryfan, North Wales: evidence from Scanning Electron
Microscopy (SEM): Proceedings of the Geologists’ Association, v. 102, no. 2, p. 123–134.
CHRONIC, B.J., AND WILLIAMS, C.A., 1978, The Glen Eyrie Formation (Carboniferous)
near Colorado Springs, in Pruitt, J.D., and Coffin, P.E., eds., Energy Resources of the
Denver Basin: Rocky Mountain Association of Geologists, field conference
guidebook, p. 199–206.
JSR
CHUMAKOV, N.M., 1994, Evidence of Late Permian glaciation in the Kolyma River
basin: a repercussion of the Gondwana glaciations in northeast Asia?: Stratigraphy
and Geological Correlation, v. 2, p. 426–444.
COSTA, J.E., 1988, Rheologic, geomorphic, and sedimentologic differentiation of water
floods, hyperconcentrated flows, and debris flows, in Baker, V.R., Kochel, C.R., and
Patton, P.C., eds., Flood Geomorphology: New York, John Wiley & Sons, p.
113–122.
DAVYDOV, V., WARDLAW, B.R., AND GRADSTEIN, F.M., 2004, The Carboniferous Period,
in Gradstein, F.M., Ogg, J.G., and Smith, A.G., eds., A Geologic Time Scale 2004:
New York, Cambridge University Press, p. 222–248.
D’ORSAY, A.M., AND VAN DE POLL, H.W., 1985, Quartz grains surface textures: Evidence
for middle Carboniferous glacial sediment input to the Parrsboro Formation of Nova
Scotia: Geology, v. 13, p. 285–287.
DOWDESWELL, J.A., HAMBREY, M.J., AND RUITANG, W., 1985, A comparison of clast
fabric and shape in late Precambrian and modern glacigenic sediments: Journal of
Sedimentary Petrology, v. 55, p. 691–704.
DUTTA, P.K., AND SUTTNER, L.J., 1986, Alluvial sandstone composition and
paleoclimate, II. Authigenic mineralogy: Journal of Sedimentary Petrology, v. 56, p.
346–358.
EPSHTEYN, O.G., 1981a, Middle Carboniferous ice-marine deposits of northeastern
U.S.S.R., in Hambrey, M.J., and Harland, W.B., eds., Earth’s Pre-Pleistocene Glacial
Record: Cambridge, U.K., Cambridge University Press, p. 268–269.
EPSHTEYN, O.G., 1981b, Late Permian ice-marine deposits of the Atkan Formation in
the Kolyma river headwaters region, U.S.S.R., in Hambrey, M.J., and Harland, W.B.,
eds., Earth’s Pre-Pleistocene Glacial Record: Cambridge, U.K., Cambridge University
Press, p. 270–273.
FIELDING, C.R., FRANK, T.D., BIRGENHEIER, L.P., RYGEL, M.C., JONES, A.T., AND
ROBERTS, J., 2008, Stratigraphic imprint of the late Paleozoic Ice Age in eastern
Australia: a record of alternating glacial and non-glacial climate regime: Geological
Society of London, Journal, v. 165, p. 129–140.
FOLK, R.L., 1978, Angularity and silica coatings of Simpson Desert sand grains,
Northern Territory, Australia: Journal of Sedimentary Petrology, v. 48, p. 611–624.
GRADSTEIN, F.M., OGG, J.G., SMITH, A.G., BLEEKER, W., AND LOURENS, L.J., 2004, A
new geologic time scale, with special reference to Precambrian and Neogene:
Episodes, v. 27, p. 83–100.
HASTENRATH, W., 2009, Past glaciation in the tropics: Quaternary Science Reviews, v. 28,
p. 790–798.
HELLAND, P.E., AND DIFFENDAL, R.F., JR., 1993, Probable glacial climatic conditions in
source areas during deposition of the Ash Hollow Formation, Ogallala Group (late
Tertiary), of western Nebraska: American Journal of Science, v. 293, p. 744–757.
HUBERT, J.F., 1960, Petrology of the Fountain and Lyons formations, Front Range,
Colorado: Colorado School of Mines Quarterly, v. 55, p. 1–242.
ISBELL, J.L., MILLER, M.F., WOLFE, K.L., AND LENAKER, P.A., 2003, Timing of late
Paleozoic glaciation in Gondwana: was glaciation responsible for the development of
northern hemisphere cyclothems?, in Chan, M.A., and Archer, A.W., eds., Extreme
Depositional Environments: Mega End Members in Geologic Time: Geological
Society of America, Special Paper 370, p. 5–24.
JACKSON, G., 1996, Stratigraphy and paleohydraulic analysis of glacial and meltwater
sediments in the Mesa del Caballo area, Sierra de Santo Domingo, Venezuelan Andes,
in Mahaney, W.C., and Kalm, V., eds., Field Guide for the International Conference
on Quaternary Glaciation and Paleoclimate in the Andes Mountains, Quaternary
Surveys, Toronto, Ontario.
JANITSKY, P., 1986, Laboratory methods: citrate–bicarbonate–dithionite (CBD) extractable iron and aluminum, in Singer, M.J., and Janitzky, P., eds., Field and laboratory
procedures used in a Soil Chronosequence study: U.S. Geological Survey, Bulletin, B
1648, p. 38–41.
KAIRO, S., SUTTNER, L.J., AND DUTTA, P.K., 1993, Variability in sandstone composition
as a function of depositional environment in coarse-grained delta systems, in
Johnsson, M.J., and Basu, A., eds., Processes Controlling the Composition of Clastic
Sediments: Geological Society of America, Special Paper 284, p. 263–283.
KLUTH, C.F., 1997, Comparison of the location and structure of the late Paleozoic and
Late Cretaceous–early Tertiary Front Range uplift, in Bolyard, D.W., and
Sonnenberg, S.A., eds., Geologic History of the Front Range: Denver, Colorado,
Rocky Mountain Association of Geologists, p. 31–42.
KLUTH, C.F., AND CONEY, P.J., 1981, Plate tectonics of the Ancestral Rocky Mountains:
Geology, v. 9, p. 10–15.
KLUTH, C.F., AND MCCREARY, J.A., 2006, Reinterpretation of the geometry and
orientation of the late Paleozoic Front Range Uplift (abstract): Geological Society of
America, Abstracts with Programs, v. 38, no. 6, p. 29.
KRINSLEY, D.H., AND DONAHUE, J., 1968, Environmental interpretation of sand grain
surface textures by electron microscopy: Geological Society of America, Bulletin, v. 79,
p. 743–748.
KRINSLEY, D.H., AND DOORNKAMP, J.C., 1973. Atlas of Sand Grain Surface Textures:
Cambridge, U.K., Cambridge University Press, 91 p.
KRINSLEY, D., AND TAKAHASHI, T., 1962, Applications of electron microscopy to
geology: New York Academy of Science, Transactions, v. 25, p. 3–22.
LACHNIET, M.S., AND VAZQUEZ-SELEM, L., 2005, Last glacial maximum equilibrium line
altitudes in the circum-Caribbean (Mexico, Guatemala, Costa Rica, Colombia and
Venezuela): Quaternary International, v. 138–139, p. 129–144.
MACk, G.H., AND SUTTNER, L.J., 1977, Paleoclimate interpretation from petrographic
comparison of Holocene sands and the Fountain Formation (Pennsylvanian) in the
Colorado Front Range: Journal of Sedimentary Petrology, v. 47, p. 89–100.
JSR
COLD-CLIMATE WEATHERING IN EQUATORIAL PANGEA
MAHANEY, W.C., 1995, Pleistocene and Holocene glacier thickness, transport histories
and dynamics inferred from SEM microtextures on quartz particles: Boreas, v. 24, p.
293–304.
MAHANEY, W.C., 2002. Atlas of Sand Grain Surface Textures and Applications: Oxford,
U.K., Oxford University Press, 256 p.
MAHANEY, W.C., AND KALM, V., 1995, Scanning electron microscopy of Pleistocene tills
in Estonia: Boreas, v. 24, p. 13–29.
MAHANEY, W.C., AND KALM, V., 2000, Comparative SEM study of oriented till blocks,
glacial grains and Devonian sands in Estonia and Latvia: Boreas, v. 29, p. 35–51.
MAHANEY, W.C., VORTSICH, W., AND JULIG, P.J., 1988, Relative differences between
glacially crushed quartz transported by mountain and continental ice, some examples
from North America and East Africa: American Journal of Science, v. 288, p.
810–826.
MAHANEY, W.C., VAIKMAE, R., AND VARES, K., 1991, Scanning electron microscopy of
quartz grains in supraglacial debris, Adishy Glacier, Caucasus Mountains, USSR:
Boreas, v. 20, p. 395–404.
MAHANEY, W.C., CLARIDGE, G., AND CAMPBELL, I., 1996, microtextures on quartz grains
in tills from Antarctica: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 121,
p. 98–103.
MAHANEY, W.C., STEWART, A., AND KALM, V., 2001, Quantification of SEM
microtextures useful in sedimentary environmental discrimination: Boreas, v. 30, p.
165–171.
MAIZELS, J., 1993, Lithofacies variations within sandur deposits: the role of runoff
regime, flow dynamics and sediment supply characteristics: Sedimentary Geology,
v. 85, p. 299–325.
MAIZELS, J., 1997, Jökulhlaup deposits in proglacial areas: Quaternary Science Reviews,
v. 16, p. 793–819.
MALLORY, W.W., 1972, Pennsylvanian System, in Mallory, W.W., ed., Geologic Atlas
of the Rocky Mountain Region: Rocky Mountain Association of Geologists,
p. 131–132.
MALLORY, W.W., 1975, Middle and southern Rocky Mountains, northern Colorado
Plateau, and eastern Great Basin region, in McKee, E.D., and Crosby, E.J., eds.,
Paleotectonic Investigations of the Pennsylvanian System in the United States: U.S.
Geological Survey, Professional Paper 853-N, p. 265–278.
MAPLES, C.G., AND SUTTNER, L.J., 1990, Trace fossils and marine–nonmarine cyclicity in
the Fountain Formation (Pennsylvanian; Morrowan/Atokan) near Manitou Springs,
Colorado: Journal of Paleontology, v. 64, p. 859–880.
MARREN, P.M., 2002, Criteria for distinguishing high magnitude flood events in the
proglacial fluvial sedimentary record: the extremes of the extremes: extraordinary
floods: International Association of Hydrological Sciences, Publication, v. 271, p.
237–241.
MAUGHAN, E.K., AND AHLBRANDT, T.S., 1985, Pennsylvanian and Permian eolian
sandstone facies, northern Colorado and southeastern Wyoming, in Macke, D.L., and
Maughan, E.K., eds., Field Trip Guide Book: American Association of Petroleum
Geologists, SEPM, Rocky Mountain Section, National Energy Minerals Division,
and Rocky Mountain Association of Geologists, p. 99–113.
MAZZULLO, J., AND RITTER, C., 1991, Influence of sediment source on the shapes and
surface textures of glacial quartz sand grains: Geology, v. 19, p. 384–388.
677
MEHRA, O.P., AND JACKSON, M.L., 1960, Iron oxide removal from soils and clays by a
citrate–dithionite system buffered by sodium carbonate: Clays and Clay Mineralogy,
v. 7, p. 317–327.
PARRISH, J.T., 1998. Interpreting the Pre-Quaternary Climate from the Geologic Record:
New York, Columbia University Press, 338 p.
RAUP, O.B., 1966, Clay mineralogy of Pennsylvanian redbeds and associated rocks
flanking ancestral Front Range of central Colorado: American Association of
Petroleum Geologists, Bulletin, v. 50, p. 251–268.
RAYNOLDS, R.G.H., JOHNSON, K.R., ARNOLD, L.R., FARNHAM, T.M., FLEMING, F.,
HICKS, J.F., KELLEY, S.A., LAPEY, L.A., NICHOLS, D.J., OBRADOVICH, J.D., AND
WILSON, M.D., 2001, The Kiowa Core, a Continuous Drill Core Through the Denver
Basin Bedrock Aquifers at Kiowa, Elbert County, Colorado: U.S. Geological Survey,
Open-File Report 01-0185, 26 p.
SCOTESE, C.R., 1997. Paleogeographic Atlas, PALEOMAP Progress Report 90-0497,
Department of Geology, University of Texas at Arlington, Arlington, Texas, 45 p.
SOREGHAN, G.S., SOREGHAN, M.J., POULSEN, C.J., YOUNG, R.A., SWEET, D.E., AND
DAVOGUSTTO, O.C., 2008a, Anomalous cold in Pangean tropics: Geology, v. 36, p. 659–662.
SOREGHAN, G.S., SOREGHAN, M.J., AND HAMILTON, M.A., 2008b, Origin and significance
of loess in late Paleozoic western Pangea: a record of tropical cold?: Palaeogeography,
Palaeoclimatology, Palaeoecology, v. 268, p. 234–259.
SOREGHAN, G.S., SOREGHAN, M.J., SWEET, D.E., AND MOORE, K.D., 2009, Hot fan or
cold outwash? Hypothesized proglacial deposition in the upper Paleozoic Cutler
Formation, western tropical Pangea: Journal of Sedimentary Research, v. 79, p.
495–522.
SUTTNER, L.J., LANGFORD, R.P., AND O’CONNELL, A.F., 1984, New interpretation of the
stratigraphic relationship between the Fountain Formation and its Glen Eyrie Member,
in Suttner, L.J., ed., Sedimentology of the Fountain Fan-Delta Complex near Manitou
Springs and Canon City, Colorado: SEPM, Field Trip Guidebook, p. 31–61.
SUTTNER, L.J., AND DUTTA, P.K., 1986, Alluvial sandstone composition and
paleoclimate, I. Framework mineralogy: Journal of Sedimentary Petrology, v. 56, p.
329–345.
SWEET, D.E., AND SOREGHAN, G.S., 2008, Polygonal cracking in coarse clastics records
cold temperatures in the equatorial Fountain Formation (Pennsylvanian–Permian,
Colorado): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 268, no. 3–4, p.
193–204.
SWEET, D.E., AND SOREGHAN, G.S., 2010, Late Paleozoic tectonics and paleogeography
of the Ancestral Front Range: structural, stratigraphic and sedimentological evidence
from the Fountain Formation (Manitou Springs, Colorado): Geological Society of
America, Bulletin, v. 122, p. 575–594.
TRIMBLE, D.E., AND MACHETTE, M.N., 1979, Geologic map of the Colorado Springs–
Castle Rock area, Front Range urban corridor, Colorado: U.S. Geological Survey,
Map I-857-F, 1:100,000.
WAHLSTROM, E.E., 1948, Pre-Fountain and recent weathering on Flagstaff Mountain
near Boulder, Colorado: Geological Society of America, Bulletin, v. 59, p. 1173–1190.
WALKER, T.R., 1967, Formation of red beds in modern and ancient deserts: Geological
Society of America, Bulletin, v. 78, p. 353–368.
Received 18 November 2008; accepted 22 February 2010.