Cyclicity, Dune Migration, and Wind Velocity in Lower Permian Eolian Strata, Manitou Springs, CO

Home , Entrada Sandstone, Fountain Formation, Late Paleozoic icehouse, Lyons Formation

James Daniel Pike, B.S.

A Thesis

Geology

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCES

Approved

Dustin E. Sweet Chair of Committee

Tom M. Lehman

Jeffery A. Lee

Mark Sheridan Dean of the Graduate School

August, 2017

ACKNOWLEDGMENTS I would like to extend my greatest thanks to my advisor Dr. Dustin Sweet, who was an excellent advisor during this research. Dr. Sweet was vital throughout the whole process, be it answering questions, giving feedback on figures, and imparting his extensive knowledge of the ancestral Rocky Mountains on me; for this I am extremely grateful. Dr. Sweet allowed me to conduct my own research without looking over my shoulder, but was always available when needed. When I needed a push, Dr. Sweet provided it.

I would like to thank my committee memebers, Dr. Lee and Dr. Lehman for providing feedback and for their unique perspectives. I would like to thank Jenna Hessert, Trent Jackson, and Khaled Chowdhury for acting as my field assistants. Their help in taking measurements, collecting samples, recording GPS coordinates, and providing unique perspectives was invaluable. Thank you to Melanie Barnes for allowing me to use her lab, and putting up with the mess I made.

This research was made possible by a grant provided by the Colorado Scientific Society, and a scholarship provided by East Texas Geological Society. I would like to extend my sincerest gratitude, as their support helped to offset expenses incurred during this research. I would like to thank the city of Colorado Springs for allowing me to work at Red Rock Canyon Open Space, and for giving me the permission to collect samples.

Lastly, I would like to thank friends and family for their support, and for making my years as a graduate student special. I would like to thank Eric Friedman, Alden Netto, Andy Corredor, and Jared Olafsson for being great friends.

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TABLE OF CONTENTS ACKNOWLEDGMENTS ...... ii

ABSTRACT ...... iv

LIST OF TABLES ...... v

LIST OF FIGURES ...... vi

1. INTRODUCTION ...... 1

2. TECTONIC SETTING AND STRATIGRAPHY...... 3

3. METHODS ...... 9

4. INGLESIDE FORMATION STRATIGRAPHY, SEDIMENTOLOGY AND TRANSPORT DIRECTION ...... 10

4.1 Sandstone Facies ...... 10 4.2 Sandstone Facies Interpretation ...... 17 4.3 Siltstone Facies ...... 17 4.4 Siltstone Facies Interpretation ...... 18 4.5 Hierarchical Surface Framework of Dune Stratigraphy ...... 18 4.6 Character of Super Bounding Zones ...... 20 4.7 Grain-size and Sediment Transport Data ...... 22 5. DISCUSSION ...... 25

5.1 Paleowind Speed ...... 25 5.2 Paleowind Directions ...... 25 5.3 Drivers of Cyclicity in the Rock Record...... 28 5.4 Effective Precipitation Variation ...... 30 5.5 Climate Change Drivers ...... 30 5.6 Reservoir Heterogeneity ...... 33 6. CONCLUSIONS ...... 36

7. REFERENCES ...... 37

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ABSTRACT The Permian of western North America is characterized by a long-term drying trend, due in part to supermonsoonal conditions related to the assembly on Pangea. This trend is reflected in the gradational contact of the Pennsylvanian alluvial-fluvial Fountain Formation and the early Permian eolian Ingleside Formation. The Ingleside Formation at Manitou Springs is characterized by two major eolian depositional intervals, punctuated by fluvial-alluvial facies. The shift from eolian to alluvial-fluvial depositional systems represents a major pulse of humidity during an otherwise arid period. Eolian facies are moderately-sorted, subrounded, fine-grained, sub-arkosic sandstone. Cross stratification is up to 9 meters, and strata exhibits internal ripple laminae. Eolian cross-strata are periodically truncated by parallel to sub-parallel zones consisting of laterally continuous massive to weakly planar stratified muddy sandstones. Rhizoliths are locally present within these zones, and zones demonstrate abundant clay and carbonate cementation in thin section. Zone thicknesses range from true surfaces with no thickness up to 1.7 meters. These zones are highest-order present in the stratigraphy, and are inferred to be Super Bounding Surfaces (SBS), which likely reflect deflation of the erg field to an elevated water table due to changes in sedimentary flux, aerodynamic and/or environmental conditions. Following erosion to an elevated water table, deposition occurred in a stabilized and/or wet sand flat system. Fourteen SBS zones were identified in the eolian strata at Red Rock Canyon Open Space. SBS zones separate distinct intervals of eolian migration and deposition.

Mean paleowind directions for the measured intervals range from 230 to 254 degrees, indicating northeasterly to easterly winds. Wind directions are consistent with an equatorial circulation pattern, and are likely influenced by the lack of highlands to the west (Woodland Park Trough). Paleowind threshold velocities range from 24.1 Km/hr to 32.4 Km/hr using D10 grain sizes and a height of 1.5 meters above bedding surfaces. As SBS are low porosity, low permeability zones, they likely act as fluid baffles and partition reservoir intervals from one another. Additionally, these zones can act as pathways along which fluids can flow.

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LIST OF TABLES

4.1 Individual Dune Foreset Profiles...... 14 5.1 Entrainment and Saltation Velocities ...... 26

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LIST OF FIGURES 2.1 Ancestral Rocky Mountains Tectonic Elements...... 4 2.2 Red Rock Canyon Open Space Lithostratigraphy ...... 8 4.1 Red Rock Canyon Open Space Geologic Map ...... 11 4.2 Red Rock Canyon Open Space Stratigraphic Column...... 12 4.3 Ingleside Formation Ternary Plots...... 13 4.4 Red Rock Canyon Open Space Photographs ...... 15 4.5 Ingleside Formation Photomicrographs ...... 16 4.6 Eolian Grain Size Trends ...... 23 4.7 Down-Dip Rose Diagrams ...... 24 5.1 Early Permian Highstand-Lowstand Map...... 27 5.2 Hydrocarbon Permeability Framework...... 34

vii Texas Tech University, James Daniel Pike, August 2017

Chapter 1

Introduction

Eolian depositional systems are fairly well documented, and have been studied since at least the 1930’s (Shotton, 1937; Bagnold, 1941). Eolian systems record a variety of climate parameters, including wind and humidity variation, and are fairly sensitive to climatic changes (Lancaster, 1997; Forman et al., 2008). The relation of the water table and relative humidity with eolian systems has been studied for some time (Stokes, 1968;

Adams and Patton, 1979; Kocurek and Havolm, 1993; Blanchard et al., 2016). The sensitivity of eolian systems makes them well suited for relating the rock record to paleoclimate variability. For example, through-going surfaces, termed super bounding surfaces (SBS) have been attributed to significant paleoenvironmental events including an elevated water table (Stokes, 1968; Kocurek, 1988). Moreover, these surfaces are often cyclical and, if present, the eolian strata can provide an archive of relative humidity, from arid to semi-arid during dune mobilization to increased humidity during SBS formation.

The Ingleside Formation of the early Permian is exposed along the eastern flank of the modern Front Range of Colorado, and consists of mixed eolian and shallow marine facies (Maughan and Wilson, 1960; Sipe, 1984; Maughan et al., 1985). A great deal of paleoenvironemtal studies of Colorado Plateau eolian sandstone units have been undertaken (Kocurek, 1981a; Loope, 1984; Havolm et al., 1993; Lawton et al., 2015); however, eolian paleoenvironmental data along the modern Front Range is

1 Texas Tech University, James Daniel Pike, August 2017 underrepresented. The Ingleside Formation at Red Rock Canyon Open Space (RRCOS) is well exposed, and presents an excellent opportunity to study the paleoclimate record in eolian strata; specifically, assessing the stratigraphy for potential SBS and the associated relative humidity archive. In addition, SBS events provide a time significant framework with which to analyze the variation of wind speed and direction through time. The interplay of climate variation recorded in the Ingleside Formation provides a data point to further understanding of early Permian climate. The early Permian is an important period, reflecting a massive deglaciation and shift from icehouse to greenhouse conditions

(Montanez et al., 2007). Late Paleozoic deglaciation has been linked with carbon cycle perturbations (Montanez et al., 2007; Horton and Poulsen, 2009), and sea level varied by as much as 100-120 meters (Rygel et al. 2008). The durations and magnitudes of climate shifts could have implications in today’s shifting climate.

The purpose of this research is to build a paleoenvironmental framework using the rock record found at RRCOS in Manitou Springs, Colorado. This research involved a mix of field and lab work, and data collected includes grain size, foreset orientations, measured sections, petrographical, and photographs.

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Chapter 2

Tectonic Setting and Stratigraphy

The Ancestral Rocky Mountains (ARM) were a series of Precambrian-cored uplifts in the interior of western equatorial Pangaea during the late Paleozoic (Fig. 2.1);

(McKee, 1975). Evidence of significant erosion is recorded in coarse arkosic deposits adjacent to Precambrian basement, with structural offset between basins and uplifts up to

10 km (Kluth and Coney, 1981; Soreghan et al., 2012). The mechanism by which the

ARM formed is uncertain, due to an intraplate setting, as far as 1500 km from the nearest plate margin and an orthogonal trend to the best documented collisional margin (Kluth and Coney, 1981; Ye et al., 1996; Dickinson and Lawton, 2003). The most widely accepted theory invokes the sequential closure of Gondwana and Laurentia along the

Marathon-Ouachita belt as the principle tectonic driver (Kluth and Coney, 1981;

Dickinson and Lawton, 2003).

During the Early Pennsylvanian (Bashkirian), one of the core ARM uplifts, the ancestral Front Range, shed sediments eastward into the Denver Basin (Hubert, 1960;

Suttner et al., 1984; Sweet and Soreghan, 2010a). The ancestral Front Range was likely oriented northwest-southeast, and at least partially separated from the Ute Pass uplift to the south by the Woodland Park trough in the Manitou Springs region (Fig. 2.1) (Sweet and Soreghan, 2010a). The Pennsylvanian to lower Permian strata record fan-delta, braid plain and eolian depositional environments (Suttner et al. 1984; Sweet and Soreghan,

2010a; Sweet et al., 2015).

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Figure 2.1: Late Pennsylvanian to early Permian tectonic elements of the ancestral Rocky Mountains. After Sweet et al. (2015), with data compiled from Lindsey et al. (1986), Baltz and Myers (1999) Hoy and Ridgeway (2002), Sweet and Soreghan (2010a). Equator positions estimated from Peterson (1988). Abbreviation- WPT=Woodland Park Trough

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Globally, the early Permian is characterized by multiple second-order transgressive-regressive events which developed during a time of first-order sea level fall and emergence of continents (Golonka, 2000). A long-term drying trend persisted throughout the Permian (Parrish, 1993; Tabor and Montanez, 2004). At lower latitudes, high-frequency glacioeustatic cylces were significant in the early Permian, but became less significant towards the end of the early Permian (Veevers and Powell, 1987;

Golonka, 2000; Rygel et al., 2008). Commonly, a steep temperature gradient is inferred between the equator and the poles (e.g. Golonka, 2000); however, other studies suggest at least periodic equatorial cold conditions during the Pennsylvanian through the early

Permian (D’orsay and van de Poll, 1985; Dutta and Suttner, 1986; Soreghan et al., 2008;

Sweet and Soreghan, 2008, 2010b; Giles 2012; Keiser et al. 2014; Soreghan et al., 2015).

Dry continental interiors and high-latitude wet belts existed (Golonka, 2000), and the

Central Pangaean mountain belt may have created a significant rain shadow at low to mid-latitudes (Golonka, 2000). Significant volumes of Pennsylvanian-Permian loess is preserved in equatorial basins (Soreghan et al., 2008) that was largely derived from ARM uplifts and the Central Pangaean mountain belt (Dubois et al., 2012; Sweet et al., 2013;

Giles et al., 2013; Foster et al., 2014).

In the early Permian of equatorial Pangaea, there are two likely atmospheric circulation patterns. West-northwesterly winds are indicative of monsoonal circulation and cross equatorial flow (Parrish and Peterson, 1988). Easterly winds on the other hand are indicative of normal equatorial and subtropical zonal circulation, which may have been favored by a central epeiric sea (Parrish and Peterson, 1988). During the northern hemisphere summer, the continental interior of Pangaea was heated, resulting in the

5 Texas Tech University, James Daniel Pike, August 2017 formation of strong low-pressure cell systems (Patzkowsky et al., 1991). Coincidentally, the southern hemisphere formed a high-pressure cell over the continental landmass

(Patzkowsky et al., 1991). The location of high-pressure and low-pressure systems alternated with the reversal of seasons (Patzkowsky et al., 1991). The pressure difference between cells resulted in cross-equatorial flow and a monsoonal effect similar to the one seen in southern Asia today, though larger in magnitude due to greater interior heating of the supercontinent, giving rise to the term supermonsoon (Parrish and Peterson, 1988).

Earliest evidence of supermonsoonal conditions can be found in the Pennsylvanian

(Robinson, 1973; Patzkowsky et al., 1991; Soreghan et al., 2002; Soreghan and Soreghan,

2007; Soreghan et al., 2008; Soreghan et al., 2014). Monsoonal conditions ceased in the

Jurassic, coinciding with the breakup of Pangaea (Parrish and Peterson, 1988).

Supermonsoonal conditions were most pronounced in western equatorial Pangaea, as the

Central Pangaean mountain belt diminished the effect to the east (Parrish and Peterson,

1988).

The Ingleside Formation is exposed along the eastern flank of the modern Front

Range, and consists of eolian and shallow marine sandstone and carbonate strata (Sipe,

1984). The Ingleside Formation is likely correlative with the upper Casper Formation found in Wyoming (Miller and Thomas, 1936). Because the Ingleside Formation interfingers with marine deposits to the north, the strata is inferred to be proximal to an epeiric sea (Sipe, 1984). Early Permian strata along the front range of Colorado and

Wyoming records an eroding highland, alluvial fans, and a coastal plain (Blakey et al.,

1988). In RRCOS, the Ingleside Formation is 215 meters thick, and was previously mapped as the Lyons Formation (Trimble and Machette, 1979); however, the contact

6 Texas Tech University, James Daniel Pike, August 2017 between the Fountain Formation and the overlying Permian strata is conformable. Sweet et al. (2015) coupled these observations with sedimentologic data to suggest a new lithostratigraphic correlation that places the Ingleside Formation conformably atop the

Fountain Formation at RRCOS (Fig. 2.2) (Sweet et al. 2015).

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Figure 2.2: RRCOS, Manitou Springs, Colorado lithostratigraphic relationships. The primarily eolian Ingleside Formation overlies the predominantly alluvial-fluvial Fountain Formation, with the gradational contact roughly coinciding with the Virgilian-Wolfcampian transition. Glacial periods from Frank et al. (2015).

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Chapter 3 Methods Field data collected at RRCOS includes measured stratigraphic section, bedding and foreset attitudes, lithologic samples, and panoramic photos. The stratigraphic section was measured 1:40 scale using a Jacob staff and Brunton compass. Samples were collected for grain size and petrographic analysis. Foreset attitudes were collected for sediment transport direction.

A high-resolution panoramic photograph was taken of the topographic sandstone ridges found in RRCOS. From this photograph, a hierarchical framework of cross-cutting relationships was developed for the eolian strata based on previous research of eolian surfaces (Brookfield, 1977). Eolian foresets were measured at various stratigraphic intervals. The strata at RRCOS is steeply dipping and removal of that tilt was accomplished by restoring surfaces that were likely near horizontal at time of deposition with an equal area stereonet. Rotation of the North American continent since the early

Permian (Domeier et al., 2012) was also removed. Stereonet 9.5© developed by Richard

Allmendinger was used to unfold the data. Down-dip azimuths were plotted on an equal- area rose diagram using GeoRose 5.1© from Yong Technology Inc.

Lithology samples collected from RRCOS were disaggregated for grain-size analysis using the citrate-bicarbonate-dithionite (CBD) method (Mehra and Jackson,

1960; Janitzky, 1986). Samples were run through a series of sieves to remove the silt fraction, as silt would have been transported primarily in suspension. Grain-size distributions were analyzed with a Beckman-Coulter LS-13230 laser particle-size analyzer.

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Chapter 4

Ingleside Formation Stratigraphy, Sedimentology and Transport Direction 4.1 Sandstone Facies

The best exposed and most voluminous facies of the Ingleside Formation at

RRCOS crops out as two large sandstone ridges along the Red Rock Canyon Trail and

Quarry Pass Trail (Fig. 4.1). The facies is a well to moderately sorted, subrounded, cross- bedded sandstone (Fig. 4.2). This facies is classified as a quartzarenite to subarkose, and shows decreasing pore cement through time (Fig. 4.3). After removal of steeply dipping eastward tilt, cross beds can be divided into low angle (<10 degrees) and high angle (up to 30 degrees) dipping sets. Individual cross beds of the high-angle sets are up to 20m in length and up to 10.5m high. Cross beds are both normal and reverse graded, with locally present wind ripples, especially on the low-angle sets. Commonly, dip angles of the high- angle cross beds shallow to a few degrees in the down-dip direction (Table 4.1). Packages of eolian strata are separated from one another by zones of planar laminated and massive sandstone, which range in thickness from 1.7 meters to true surfaces with zero thickness

(Fig. 4.4). These zones are typically more poorly sorted and finer grained than foreset strata. Zones are heavily cemented, both by carbonate and clay cements (Fig. 4.5), and commonly exhibit rhizoliths, bleaching, and mottling (Fig. 4.4).

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Figure 4.1: Geologic map of RRCOS. Note the two large sandstone fins, the western ‘quarried fin’, and the eastern ‘panorama fin’, separated by recessive facies. Localities where section was measured is shown in red.

Texas Tech University, James Daniel Pike, August 2017

Table 4.1: Profiles of two individual dune foresets, measured at half meter and meter intervals respectively. Both profiles show a down-dip shallowing of dip angles, as well as a coarse toe, often found in grainflow deposits (Kocurek 1991). These coarser deposits represent runout of coarser grains, which outpace finer grains downslope.

Figure 4.2: Stratigraphic section of the 210 meters of the Ingleside Formation at RRCOS.

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Figure 4.3: Ternary plots of framework grains and matrix space from the base and top of each sandstone fin. Matrix space includes porosity, cement and grains <62μm. Qt=Quartz, Ft=Feldspar, L=Lithics, Mx=Unoccupied pore space+cement

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Table 4.1: Individual dune foreset profiles

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Figure 4.4: Photographs of the Ingleside Formation at RRCOS. A.) Complex cross-bedding with multiple foreset orientations. Pencils shown for scale and to highlight orientations. Despite this complexity, most foresets are simple grainflow deposits. B.) Calcified rhizoliths in SBS 3 of the western fin. C.) SBS B and C of the eastern fin truncating grainflow foresets. D.) Recessive nature of SBS zone 3. SBS zone is recessing into quarried cliff face. E.) Cross bedded very coarse sandstone of the alluvial-fluvial facies. F.) Eastern sandstone fin of RRCOS. Large scale grainflow foresets are easily visible. Recessive alluvial-fluvial facies are present in the vegetated foreground of the image.

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Figure 4.5: Photomicrographs of the Ingleside Formation of RRCOS. A). and B). Sample from meter 177.8 of the measured section, SBS C. Quartz grains are finer than eolian strata, and nearly all pore space is occupied by clay cements. C). and D). Sample from meter 174.8 of the measured section, from an eolian foreset. Quartz grains are subangular to subrounded, and very little clay cement is present. E). and F). Sample from meter 40.8 of the measured section, SBS 3. Sample is almost entirely carbonate, with few quartz grains present.

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Individual zones or surfaces are laterally continuous through RRCOS, approximately 0.8 miles.

4.2 Sandstone Facies Interpretation

The cross-bedded sandstone facies is inferred to represent an ancient eolian dune field. The high-angle cross beds are inferred to represent the lee sides of dunes, or foresets, as indicated by internal laminae reflecting grading attributed to grain-flow and the down-dip shallowing of the foreset (Table 4.1); (Kocurek, 1991). Alternatively, the low-angle cross beds commonly contain wind-ripple laminations, and are inferred as preserved stoss strata (Kocurek, 1991). Based on stratification style of foresets and predimonintally uniform orientations, individual dunes are interpreted as being transverse/crescentic dunes, where the orientation of the dune crestiline is within 15 degrees of the orientation of dominant wind directions (Kocurek, 1991). 2nd order surfaces were identified in most of the eolian intervals of both fins (Plate 1); as these surfaces are present, eolian intervals reflect crescentic draas migrating through space

(Brookfield, 1977; Kocurek, 1991). The western fin could reflect a simpler dune field, as fewer 2nd order surfaces were identified. Additionally, the grainsizes of the western fin suggest a more proximal setting. The separating zones or surfaces are interpreted as super bounding surfaces (SBS), which represent intervals of dune field deflation and non- deposition (Stokes, 1968; Loope, 1984; Kocurek, 1988). Rejection of alternative interpretations for the SBS is discussed below.

4.3 Siltstone Facies

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The two sandstone ridges are punctuated by poorly outcropping strata. These strata are 64 meters thick, and of varying character, but predominantly siltstone and fine- grained massive sandstone. Sedimentary structures include crude stratification, planar stratification, platy laminations, cross stratification, trough cross stratification, or internally massive (Fig. 4.2). Grain sizes range from very fine sand/silt to granules.

Strong paleosol horizons are present, as are lithic grains, caliche nodules, and rip-up clasts associated with scouring.

4.4 Siltstone Facies Interpretation

The lack of outcrop does not enable a better interpretation of the recessive facies other than alluvial. Planar and trough cross-stratification are typically strong indicators of fluvial systems, particularly when found in conjunction with basal coarse lags and scouring (e.g., Miall, 1978). Paleosol horizons and caliche nodules likely formed in interfluves. Crude stratification and granule deposits can often be found in alluvial systems (e.g., Soreghan et al., 2009; Sweet and Soreghan, 2010a).

4.5 Hierarchical Surface Framework of Dune Stratigraphy

A high-resolution panoramic photograph of the eastern sandstone ridge at RRCOS was digitally mapped in order to build a hierarchical framework of eolian strata (Plate 1).

During mapping, surfaces were defined SBS, first-order, second-order, third-order, or cross bedding foresets after the work of Stokes (1968), Brookfield (1977), and Kocurek

(1988). First-order surfaces represent the movement of individual dunes or draas across an area, and are locally overlain by interdune/interdraa deposits (Brookfield, 1977).

Second-order surfaces are moderately dipping surfaces which represent the passage of

18 Texas Tech University, James Daniel Pike, August 2017 dunes across draas (Brookfield, 1977). Third-order surfaces bound bundles of laminae within sets of cross laminae, and represent reactivation of the lee slope due to wind fluctuations (Brookfield, 1977). SBS always cut across all other surfaces and are through- going along the entire exposed outcrop. With the exception of first-order surfaces, all surface hierarchies identified by Brookfield (1977) were identified and mapped in the eastern ridge of RRCOS.

Zones up to a few meters thick, as well as true surfaces with no thickness could be traced across the entire exposed outcrop along both ridges (Plate 1). These are interpreted as SBS, and their importance and character are discussed in the subsequent section.

Alternatively, the through-going zones could reflect interdune/interdraa deposits atop first-order surfaces, which are commonly characterized by irregular basal surfaces that result in microtopography due to water or wind scouring (Kocurek, 1981b). Associated interdune deposits in wetter conditions commonly exhibit root structures, adhesion features, brecciated laminae, evaporative structures, contorted structures, wavy laminae, water ripples, and subaqueous cross strata (Kocurek, 1981b). Interdune deposits are laterally variable, both parallel and perpendicular to wind direction, and often grade from wet to dry interdune deposits (Kocurek, 1981b; Hummel and Kocurek, 1984). Interdune deposits commonly pinch out as lenticular bodies when viewed perpendicular to paleowind direction, and rise irregularly relative to paleohorizontal when viewed parallel to paleowind direction (Kocurek, 1981b). Spacing of interdune strata varies across a dune field (Kocurek, 1981b). While the zones of RRCOS show some sedimentary features commonly associated with interdune deposits (rhizoliths, wavy laminae), they are continuous over the entirety of the outcrop, and maintain constant stratification style

19 Texas Tech University, James Daniel Pike, August 2017 laterally. Thicknesses of zones are relatively constant, as is the spacing between them.

The basal portion of these zones does not demonstrate microtopography commonly associated with first-order surfaces. Additionally, these zones do not show a bimodal grain size distribution as is typically seen in interdraa deposits (Clemmensen 1989;

Langford et al. 2008). These observations bolster the interpretation that the zones found in RRCOS are SBS.

The reason for the lack of first-order surfaces and interdune deposits is uncertain.

Based on the style of stratification, eolian strata of RRCOS could represent a dry dune field (Kocurek and Havolm, 1993). Dry eolian systems range from those where dunes migrate across a barren substrate (Finkel, 1959), to those where interdune flats are absent, and replaced by depressions between dunes (Sweet et al., 1988). Dunes are often built in dry systems at the expense of interdune deposits (Kocurek et al., 1992), and in many cases accumulation in dry systems does not occur until bed-form growth has progressed to the point where interdune flats have been eliminated (Wilson, 1971). Maybe most importantly, interdune deposits within dry eolian systems are rarely preserved in the rock record (Hummel and Kocurek, 1984).

4.6 Character of Super Bounding Zones

Six SBS can be found in the strata of the western sandstone ridge, and are defined by numbers 1-6. These range in thickness from 0.4 to 1.7 meters. Dune strata bounded by

SBS ranges from 1.5 to 15 meters in thickness. Zones 2, 3, 4, and 6 are mottled, recessive, finer grained than eolian strata, and exhibit rhizoliths up to 60 cm in length.

Rhizoliths in these zones are calcified; calcite cement fills almost all pore space in these

20 Texas Tech University, James Daniel Pike, August 2017 zones (Fig. 4.4). Zone 1 demonstrates a fining-upward trend through the interval, a scoured granule lag, granule lenses, and is capped by a well-sorted, fine-grained, planar- stratified sandstone. Zone 5 is coarser than surrounding eolian strata, and shows rhizoliths and stabilization toward the top of the zone. SBS zones 2-5 are inferred as representing calcic paleosol formation and stabilization of the dune field. Zone 1 shows signs of water reworking, and is inferred to represent a subaqueous depositional system.

In the eastern sandstone ridge, eight surfaces or zones are present, defined by the letters A-H, and ranging in thickness from 0 to 1.2 meters thick. Intervals of eolian strata bounded by SBS zones range in thickness from 1.6 to 14.5 meters. Surfaces A and H are true surfaces with no thickness. Zones B, C, D, E, and G are recessive in nature, truncate eolian strata, and show weak parallel laminations, mottled wavy laminations, and scouring. Zone C truncates eolian strata, but does not show a lithological change like other surface zones. Here, zones are finer grained than surrounding eolian strata, and pore space is almost entirely filled with clay cements (Fig. 4.5 A,B).

The SBS of the eastern ridge are interpreted as forming in a sand flat depositional system, under heavy influence of a very near water table, similar to other interpretations of eolian strata (Stokes, 1968; Loope, 1981; Havolm and Kocurek, 1994). Differences in cementation and stabilization between the SBS of the two ridges are interpreted to result from effective precipitation differences during stabilization events. The events found in the western sandstone ridge exhibit calcite cements and calcified rhizoliths, indicating at least semi-arid conditions (Mack et al., 1994), whereas the SBS of the younger ridge exhibit more clay content and localized lenticular bodies of coarse sand and granules, indicating water reworking. 21 Texas Tech University, James Daniel Pike, August 2017

4.7 Grain-size and Sediment Transport Data

For the two ridges, samples were collected for grain-size analyses from each interval bounded by a SBS. One to two samples were collected from each interval of the western ridge, as the eolian strata of this ridge is not as well exposed. Three samples were collected for each interval of the eastern ridge. The mean grain size for all intervals is between 2 and 3φ (Fig. 4.6), indicating fine sand. The coarsest interval of the western ridge is interval 2 with a mean grain size of 2.32φ, while the finest is interval 3 with a mean of 2.83φ. For the eastern ridge, the coarsest interval is C with a mean grain size of

2.038φ, while the finest interval is D with a mean of 2.74φ. The western ridge is moderately sorted on average, while the eastern ridge is well to very well sorted. For the western ridge, two fining trends are observed, one from surfaces 1 to 3 and the other from surfaces 4 to 6 (Fig. 4.6). For the eastern ridge, grain size is fairly constant, though there seems to be a small fining trend from interval E through interval H.

Foreset attitudes (n=760) were measured for the two ridges. In addition, SBS attitude measurements (n=153) were made to estimate a paleohorizontal surface and to restore the steeply dipping (up to 70 degrees) strata of the Ingleside Formation. Down-dip direction of lee side foresets was used as a proxy for wind direction. Based on 222 measurements, the mean down-dip direction of the western ridge is 214 degrees, with a standard deviation of 83 degrees. However, many of these measurements had low dip angles, likely meaning they are preserved stoss slopes. After removal of measurements with dip angles less than 15 degrees, the mean is 230 degrees with a standard deviation of

50 degrees (Fig. 4.7). Based on 538 measurements, the mean down dip direction of the eastern ridge is 254 degrees, with a standard deviation of 33 degrees (Fig. 4.7). 22 Texas Tech University, James Daniel Pike, August 2017

Figure 4.6: Grain size distribution of each interval bounded by a SBS. Grain sizes of the eastern fin remain fairly constant through time, while more variation is present in the western fin. Eolian intervals of the western fin are more poorly sorted. 23 Texas Tech University, James Daniel Pike, August 2017

Figure 4.7: Area-weighted rose diagrams demonstrating orientations of unfolded, down-dip azimuths of eolian foresets of the western (A and C) and eastern (B) fins. Fig. 4.7A represents down dip orientations before low dip-angle (<15 degrees) measurements were removed. Approximately 100 low dip-angle measurements were removed from the western fin, as these are believed to be stoss slopes (4.7C). 4.7D represents a sum of downdip directions from both ridges.

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Chapter 5

Discussion

5.1 Paleowind Speed

Paleowind speed thresholds for entrainment and saltation were calculated using equations from R.A. Bagnold (1941). At a height of 1.5 meters, and using the D10 grain size for each dune interval bounded by a SBS, the following velocities were generated

(Table 5.1). For the western ridge, estimated entrainment velocities range from 24.1 km/hr for interval 6, to 32.4 km/hr for interval 1. After saltation was initiated, estimated velocities ranged from 20.05 to 27.2 km/hr for intervals 6 and 1, respectively. For the eastern ridge, entrainment velocities range from 25.4 km/hr for interval D to 28.29 km/hr for interval C. Velocities under saltation range from 21.16 to 23.58 km/hr for intervals D and C, respectively. Paleowind speeds are on the same order as those reported for other dune fields, both coastal and inland (Fryberger and Dean, 1979; Sauermann et al., 2003).

5.2 Paleowind Directions

The predominantly southwestern downdip directions are indicative of normal equatorial and subtropical zonal circulation (Parrish and Peterson, 1988; Peterson, 1988).

The minor northeastern compinent of downdip directions of the western ridge could be indicative of monsoonal circulation (Parrish and Peterson, 1988); however, there is too little data to state this with certainty. The inland epeiric sea found to the east of the ARM

(Fig. 5.1) likely favored a normal zonal circulation, and it seems possible that winds blew in from the epeiric sea (Parrish and Peterson, 1988). Additionally, topography is often an aerodynamic and accumulation control (Mainguet, 1978; Fryberger and Ahlbrandt, 25 Texas Tech University, James Daniel Pike, August 2017

Table 5.1: Paleowind speed thresholds for entrainment and saltation at a hieight of 1.5 meters, using the D10 grain size.

26 Texas Tech University, James Daniel Pike, August 2017

Figure 5.1: Highstand and lowstand shoreline positions of the early Permian, Colorado. Highstand and lowstand positions were taken from Rascoe and Baars (1972) and Blakey (2009). Abbreviations- LFS=Loveland Filtration Site, wind directions from Sweet et al. 2015, WPT=Woodland Park Trough, RRCOS=Red Rock Canyon Open Space, UPU= Ute Pass Uplift

27 Texas Tech University, James Daniel Pike, August 2017

1979). It seems reasonable that ARM topography placed some control on local aerodynamic conditions and accumulation of the dune field. To the north, wind directional data from coeval deposits demonstrate a more southerly wind direction than those of RRCOS (Sweet et al., 2015). This difference in orientations is inferred as being due to the topographic control of the ancestral Front Range to the west and the epeiric sea to the east (Parrish and Peterson, 1988; Sweet et al., 2015). The lack of a southerly component at RRCOS could reflect a lack of topography to the east, as indicated by the proposed Woodland Park trough that at least partially segmented the ancestral Front

Range from the Ute Pass block (Fig. 2.1) (Kluth and McCreary, 2006; Sweet and

Soreghan, 2010a).

The orientation of foresets is not always an accurate indicator of primary wind direction. Dune fields with multiple superimposed bedforms, and abundant third-order bounding surfaces are indicative of dune fields with multiple wind directions and non- parallel migration directions (Kocurek, 1991). Large, simple sets of grain flow cross- strata, as seen in RRCOS, are more likely to reflect regional paleowinds (Kocurek, 1991).

Parrish and Peterson (1988) compared measurements of Pennsylvanian through Jurassic eolian strata of the western US with predicted directions from a global climate model, and found a good correspondence for at least 75 percent of the data. Thus, it seems likely downdip foreset orientations at RRCOS serve as at least a first-order approximation of paleowind directions.

5.3 Drivers of Cyclicity in the Rock Record

28 Texas Tech University, James Daniel Pike, August 2017

There are several potential drivers of cyclicity in the rock record, including tectonism, eustasy, and paleoenvironmental fluctuations. The relationship of these drivers with the early Permian strata of RRCOS is discussed in the following section.

Tectonism has been recognized as a driver of cyclicity in the rock record for some time (i.e. Ettensohn 1994). In the Manitou Springs area, the Ute Pass Fault allowed for movement and uplift of pre-Cambrian basement (Sweet and Soreghan 2010). Work by

Sweet and Soreghan (2010) divided the Fountain Formation in Manitou Springs into three members, based on sedimentologic, stratigraphic and structural data. The lower and middle members were interpreted as being deposited syntectonically, while the upper member postdates tectonism (Sweet and Soreghan 2010). As the Fountain Formation ranges into latest Pennsylvanian and is gradational with the overlying Ingleside

Formation, Ute Pass Fault tectonism is believed to have terminated in the middle to late

Pennsylvanian (Sweet and Soreghan 2010). Elsewhere across the Ancestral Rocky

Mountains, similar cessations have been documented. Both the Wichita and

Uncompahgre uplifts were onlapped onto by early Permian strata (Soreghan et al. 2012).

Subsidence of the Ancestral Rocky Mountains during the early Permian was characterized by a fairly slow, broad, regional subsidence pattern (Soreghan et al. 2012).

Based on this data, tectonism can likely be discounted as a driver of cyclicity at RRCOS.

Based on inferred highstand and lowstand shoreline positions of the early Permian

(Fig. 5.1); ( Rascoe and Baars, 1972; Blakey, 2009), strata of RRCOS is interpreted as an inland dune field at least 70 km from the highstand shoreline as indicated by the nearest marine deposits, with a low relief floodplain separating the dune field from the shoreline

(Rascoe and Baars, 1972; Blakey, 2009). Based on the inland nature of the dune filed, it 29 Texas Tech University, James Daniel Pike, August 2017 seems unlikely that eustasy controlled water table levels. However, recent work has placed eolian systems into a sequence stratigraphic framework (Blanchard et al., 2016).

That work theorizes that eolian systems are deposited during lowstand periods, when shoreface sands are exposed for movement (Blanchard et al., 2016). Despite the inland nature of this dune field, sands were likely able to be mobilized during lowstands. With tectonism and eustasy likely ruled out as drivers of cyclicity in the early Permian strata of

RRCOS, climate has been isolated as a driver.

5.4 Effective Precipitation Variation

Variations in precipitation recorded in the early Permian strata at RRCOS are defined on three time scales. The transition from the fluvial strata of the Fountain

Formation to the predominantly eolian strata of the Ingleside Formation reflects a long- term drying trend, on the order of 10 Ma, and is consistent with other studies of the early

Permian (Parrish, 1993; Tabor and Montanez, 2004). Secondly, eolian strata of the

Ingleside Formation is punctuated by alluvial-fluvial facies, which are interpreted as a wet period between two drier periods represented by the two eolian ridges. Lastly, SBS- eolian cycles represent the highest frequency climate change archived in the stratigraphy and may correlate with glacioeustatic cycles, potentially on the order of 400k years per cycle (Heckel, 1986; Sur et al., 2010).

5.5 Climate Change Drivers

The long-term drying trend of the Permian is largely considered as driven by the slow amalgamation and northward drift of Pangaea (Parrish, 1993; Tabor and Montanez,

2004). The northward drift of western Pangaea resulted in progressive removal from

30 Texas Tech University, James Daniel Pike, August 2017 tropical latitudes to mid-latitudes (Loope et al., 2004). The assembly of Pangaea coincided with a long-term sea level fall that for central Pangaea resulted in a large land mass that was progressively isolated from marine influence.

The SBS-eolian cycles observed in the sandstone ridges reflect the highest frequency climate change recorded, and as such, the climate driver needed to act on that scale. Across western Pangaea, the late Paleozoic is characterized by more arid lowstands and more humid highstands (Soreghan, 1997; Soreghan, et al. 2002; Cecil et al., 2003).

Therefore, eolian strata of RRCOS is tentatively interpreted as being correlative with lowstand periods, while the SBS zones created under more humid conditions are interpreted as coeval to relative sea level highstands. Potentially, each SBS-eolian cycle represents a similar magnitude of time as glacioeustatic cycles observed elsewhere in equatorial Pangaea. If the SBS-eolian cycles are correlative with glacioeustatic cycles, then they could be driven by relative humidity differences that result from tropical weathering patterns tied to waxing and waining of glaciers at high lattitudes (i.e. icehouse conditions) (Heavens et al., 2012, 2015). Periodic equatorial glaciation of the central

Pangaean Mountains coincidental to Gondwana glacial maxima has been proposed

(Becq-Giraudon et al., 1996; Soreghan et al., 2007, 2008, 2009, 2014; Sweet and

Soreghan, 2008, 2010b; Keiser et al., 2015). If equatorial glaciers were present, then climate models predict that precipitation would be suppressed to lower than 200mm in the equatorial region, especially west of the Central Pangaean Mountains (Heavens et al.,

2015). This effect could explain loess mobilization and deposition in equatorial Pangaea

(Soreghan, 2008), and potentially eolian sand mobilization as well. In this scenario, the

SBS would still record an icehouse state but under periods of Gondwana glacial minima.

31 Texas Tech University, James Daniel Pike, August 2017

Climate models suggest that icehouse interglacials would result in slightly wetter equatorial regions (Heavens et al., 2015).

Climate drivers from eolian to fluvial/alluvial deposition are more difficult to assess. Based on recent global circulation climate modelling of the early Permian, it seems icehouse periods were much more arid than their greenhouse counterparts

(Heavens et al., 2015). Atmospheric greenhouse gases and sea level decreased during icehouse periods, resulting in more aridity in western equatorial Pangaea (Heavens et al.,

2015). The late Paleozoic icehouse has recently been characterized as localized dynamic ice sheets in Gondwana that came and went (Isbell et al., 2003; Fielding et al., 2008), rather than protracted long-lived ice sheets (e.g., Crowell, 1999). Thus, the late Paleozoic

“icehouse” time period is really a series of icehouse-to-greenhouse transitions where each interval of ice buildup in Gondwana represents an icehouse climate state. Based on climate modelling, greenhouse conditions were likely too humid for eolian mobilization and deposition (Heavens et al., 2015). Thus, it seems reasonable that the strata represented by the eolian ridges could reflect buildup of Gondwana ice, where waxing and waning of that ice was previously inferred to coincide with eolian-SBS cycles.

Conversely, the intervening wetter alluvial-fluvial facies may record the loss of

Gondwanan ice. Based on this, the eolian strata at RRCOS could correlate to the P1 and

P2 glacial cycles of Frank et al. (2015); (Fig. 2.2). When using a 400k time duration for each SBS interval, the western ridge represents 2.4 m.y., while the eastern ridge represents 3.2 m.y. The P1 and P2 glacial cycles are approximately 8 and 7 m.y. respectively (Frank et al. 2015). These calculations assume no error in the Frank et al.

(2015) age model, meaning durations could resolve better if error is present.

32 Texas Tech University, James Daniel Pike, August 2017

Alternatively, it is possible that only the end of the P1 and beginning of the P2 are captured in the RRCOS stratigraphy. It is also likely that some record is missing from

RRCOS. If the alluvial-fluvial facies represent an interglacial period, then the interval spans 4 to 5 million years based on the age model of Frank et al. (2015).

5.6 Reservoir Heterogeneity

Late Paleozoic eolian strata is a hydrocarbon reservoir interval in the Denver

Basin (Higley and Cox, 2007). 187 wells in the Denver Basin have recorded production from Paleozoic age rocks (Higley and Cox, 2007). Production from these 187 wells is on the order of 26.3 MMBO and 0.6 BCF of gas, though some of this production is likely intermingled with production from Mesozoic reservoirs (Higley and Cox, 2007).

Eolian reservoir heterogeneity is an important factor in regards to hydrocarbon exploration. With the exception of some dry eolian systems, interdune or non-eolian deposits will be present to some degree. Deposits associated with first-order surfaces and

SBS are typically finer grained, heavily cemented, and thus much lower porosity and permeability values. These zones therefore act as fluid baffles, and both compartmentalize reservoir intervals and act as pathways along which fluid can flow

(Fig. 5.2); (Chandler et al., 1989; Fryberger et al., 1990; Carr-Crabaugh and Dunn,

1996). Stratification type is also an important factor for permeability. A study of the Page

Sandstone examined how permeability varied in eolian deposits (Chandler et al., 1989).

That study found that extra-erg and interdune depoits were least permeable (0.67-

1,800md), followed by wind-ripple (900-5,200md) and grain-flow (3,700-12,000md) strata (Chandler et al., 1989). This study presents an outcrop analogue for the potential

33 Texas Tech University, James Daniel Pike, August 2017

Figure 5.2: Conceptual permeability framework for dune/interdune and dune/extradune deposits. In an eolian system, Interdune and extradune deposits are the lowest permeability deposits. These zones act as fluid baffles and partition reservoir intervals from one another. As SBS are laterally extensive, hydrocarbons would flow until a trap is encountered.

34 Texas Tech University, James Daniel Pike, August 2017 variability of subsurface reservoirs in the Denver Basin, such that the surface hierarchical model could be adapted into permeability flow models for secondary and tertiary hydrocarbon recovery.

35 Texas Tech University, James Daniel Pike, August 2017

Chapter 6

Conclusions

1. 14 SBS zones were identified in the eolian strata of RRCOS. These zones are

laterally continuous, exhibit a consistent stratification type throughout the study

area, have planar basal surfaces, and spacing between surfaces is constant.

Intervals between the SBS represent distinct intervals of eolian depositon, and

thus arid to semi-arid periods; whereas the SBS indicate dune field stabilization

during wetter periods.

2. Easterly winds were identified as dominant, indicated by mean down-dip

directions of 230 and 254 for the western and eastern ridges, respectively.

Entrainment velocities for the D10 range from 24.1 to 32.4 km/hr at a height of 1.5

meters. Wind directions are consistent with a zonal equatorial circulation, which

may also be influenced by a paleotopographic region to the east of the study area.

3. Relative humidity varies on three time scales in the Ingleside Formation at

RRCOS. The early Permian drying trend, on the order of ~10 ma, is reflected in

the transition from the Fountain Formation to Ingleside Formation. The alluvial-

fluvial facies punctuate two periods of eolian deposition, and represent an

increase in humidity between drier periods. Eolian-SBS cyclicity is the highest

frequency climate change recorded and may have been linked with glacioeustasy.

4. SBS represent low porosity, low permeability zones which separate eolian

interval reservoirs from one another. These zones act as fluid baffles, and

pathways along which hydrocarbons can flow.

36 Texas Tech University, James Daniel Pike, August 2017

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