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A Paleopedological and Ichnological Approach to Spatial and Temporal Variability in

Pennsylvanian-Permian Strata of the Lower Dunkard Group

A thesis presented to

the faculty of

the College of Arts and Sciences of Ohio University

In partial fulfillment

of the requirements for the degree

Master of Science

Michael G. Blair

August 2015

This thesis titled

A Paleopedological and Ichnological Approach to Spatial and Temporal Variability in

Pennsylvanian-Permian Strata of the Lower Dunkard Group

MICHAEL G. BLAIR

has been approved for

the Department of Geological Sciences

and the College of Arts and Sciences by

Daniel I. Hembree

Associate Professor of Geological Sciences

Robert Frank

Dean, College of Arts and Sciences 3

ABSTRACT

BLAIR, MICHAEL G., M.S., August 2015, Geological Sciences

A Paleopedological and Ichnological Approach to Spatial and Temporal Variability in

Pennsylvanian-Permian Strata of the Lower Dunkard Group

Director of Thesis: Daniel I. Hembree

Paleosols record a wealth of paleoenvironmental, paleoecological, and paleoclimatic information. Plants and soil-dwelling animals both affect and are affected by soil properties, and, therefore, their traces serve to further refine the interpretations of paleosols. These characteristics make paleosols and ichnofossils particularly valuable in understanding lateral variability in the complex fluvial system represented by the upper fluvial plain facies province of the Upper Pennsylvanian to Lower Permian Dunkard

Group. These deposits represent proximal to distal expressions of a migrating river and associated floodplain microenvironments. By understanding the degree to which soils and organism behaviors change over short distances at a given time, interpretations of regional change through vertical successions can be better calibrated. This study integrates physical properties of paleosols and ichnofossils at outcrop, hand sample, and thin section scales with chemical properties determined by X-ray fluorescence (XRF) and

X-ray diffraction (XRD). These analyses provide bulk geochemical and clay mineralogical information to derive estimates of mean annual precipitation and various chemical weathering processes. Consideration of these factors allows interpretation of small-scale spatial and temporal variability to be recognized and understood in terms of local versus regional changes in environmental and climatic conditions. 4

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Daniel Hembree for his support and patience, as well as my committee members, Dr. Craig Grimes and Dr. David Kidder. I would also like to thank Jeff Shaffer and Lauren Johnson for providing field assistance during the summer of 2014. I am extremely grateful for the support of my friends and family, especially my parents, Ron and Cathy Duchovic, and brother, Joel Blair.

This research would not have been possible without funding from the Geological

Society of America, the American Chemical Society Petroleum Research Fund (52708-

UR8), and the Ohio University Department of Geological Sciences Al umni Graduate

Research Grant.

TABLE OF CONTENTS

Page

Abstract………………………………………………………………………………… 3

Acknowledgments………………………………………………………………………4

List of Tables……..……………………………………………………………………. 9

List of Figures…...……………………………………………………………………..11

1 Introduction……………………………………………………………………....15

2 Geologic Setting………...………………………………………………………. 18

3 Methods…………………………………………………………………………. 24

3.1 Field……………………………………………………………………….. 24

3.2 Laboratory………………………………………………………………… 26

3.2.1 Thin Sections………………………………………………………... 26

3.2.2 Bulk Geochemistry………………………………………………….. 26

3.2.3 Clay Mineralogy…………………………………………………….. 27

4 Results…………………………………………………………………………... 32

4.1 Sedimentology and Stratigraphy………………………………………….. 32

4.2 Flora……………………………………………………………………….. 33

4.2.1 Plant Impressions…………………………………………………… 33

4.2.2 Rhizohaloes…………………………………………………………. 34

4.2.2.1 Reduced rhizohaloes…………………………………………. 34

4.2.2.2 Yellow rhizohaloes…………………………………………... 35

4.2.2.3 Diffuse purple rhizohaloes…………………………………… 35 6

4.2.3 Rhizoconcretions……………………………………………………. 35

4.2.4 Rhizotubules………………………………………………………… 36

4.2.5 Root Casts…………………………………………………………… 36

4.3 Fauna (Ichnofossils)………………………………………………………. 37

4.3.1 Scoyenia……………………………………………………………... 37

4.3.2 Arenicolites…………………………………………………...... 42

4.3.3 Skolithos…………………………………………………………….. 42

4.3.4 Cochlichnus…………………………………………………...... 43

4.3.5 Mermia……………………………………………………………… 43

4.3.6 Naktodemasis………………………………………………...... 44

4.3.7 Isopodichnus………………………………………………………… 44

4.3.8 Planolites……………………………………………………………. 45

4.3.9 Coprolites…………………………………………………………… 45

4.3.10 Pedotubules…………………………………………………………. 45

4.4 General Section Paleosols………………………………………………… 47

4.4.1 Paleosol 1 (P1)………………………………………………………. 47

4.4.2 Paleosol 2 (P2)………………………………………………………. 48

4.4.3 Paleosol 3 (P3)………………………………………………………. 54

4.4.4 Paleosol 4 (P4)………………………………………………………. 56

4.4.5 Paleosol 5 (P5)………………………………………………………. 57

4.4.6 Paleosol 6 (P6)………………………………………………………. 61

4.4.7 Paleosol 7 (P7)……………………………………………………….67 7

4.4.8 Paleosol 8 (P8)………………………………………………………. 69

4.4.9 Paleosol 9 (P9)………………………………………………………. 74

4.5 Coeval Profiles……………………………………………………………. 78

4.5.1 General Description…………………………………………………. 78

4.5.2 Northwest (NW-CP)………………………………………………… 85

4.5.3 Northwest Island (NWI-CP)………………………………………… 85

4.5.4 Northeast Island (NEI-CP)………………………………………….. 86

4.5.5 Northeast (NE-CP)………………………………………………….. 89

4.5.6 Southwest (SW-CP)………………………………………………… 90

4.5.7 Southwest Island (SWI-CP)………………………………………… 94

4.5.8 Southeast Island (SEI-CP)………………………………………….. 94

4.5.9 Southeast (SE-CP)………………………………………………….. 98

5 Discussion……………………………………………………………………… 104

5.1 Soil Forming Factors…………………………………………………….. 104

5.1.1 Parent Material……………………………………………………... 104

5.1.2 Climate……………………………………………………………... 106

5.1.3 Topography………………………………………………………… 114

5.1.4 Biota………………………………………………………………... 115

5.2 Vertical Variability………………...…………………………………….. 116

5.3 Lateral Variability………………………………...……………………… 122

5.4 Paleoclimate……………………………………………………………… 124

5.5 Soil Ecosystems………...………………………………………………... 127 8

5.5.1 Plants……………………………………………………………….. 127

5.5.2 Soil Animals………………………………………………………...133

6 Conclusion……………………………………………………………………....137

References……………………………………………………………………...... 141

Appendix 1: Bulk Geochemistry (General Section)…………………………………. 148

Appendix 2: Bulk Geochemistry (CP Profiles)……………………………………….149

Appendix 3: Weathering Indices through the General Section…………………..….. 150

LIST OF TABLES

Page

Table 3.1 Oxides and ranges reported by ALS Chemex following XRF analysis of bulk geochemistry…………………………………………………………………………… 28

Table 3.2 Molecular weathering ratios (From Retallack, 2001)……………..………... 29

Table 3.3 Paleoprecipitation proxies…………………………………………………... 29

Table 4.1 General section paleosol summary table, P1-P3. P1 and P2 are isolated from other units by buried upper and lower contacts. Stratigraphically higher paleosols (P3- P9) are separated by laterally continuous sandstone beds, which are used to dileneate paleosol-containing depositional cycles. Genetically distinct paleosols within a given cycle are highlighted, with colors corresponding to letters “a” (green, i.e. “3a”) through “c” (yellow, i.e. “3c”). Clay mineralogy is only reported in paleosols with a <4 m fraction greater than 10%. Only mineral species with >10% abundance are listed in parentheses following the total weight % of the clay size fraction for a given paleosol horizon.……………………………………………………………………………………… 50

Table 4.3 General section clay mineralogy from X-ray diffraction (XRD) of the <4 micron fraction of general section paleosols. R1 M-L I/S 30%S: ordered mixed-layer illite/smectite with 30% smectite. R1 M-L I/S 20%S: ordered mixed-layer illite/smectite with 20% smectite. Negative values in the location column and a single asterisk next to the paleosol number indicate paleosols sample from the northwest trench, which was measured in 20 cm intervals descending from -20 to -700 from the stratigraphically lowest laterally continuous sandstone exposed in the northeast general section trench. The double asterisk next to P6 samples indicates that these were taken from the same depositional cycle as those taken from the northeast trench, but were sampled on the northwest corner of the study area where the paleosol is better exposed. Triple asterisks indicate an approximate location (±20 cm). The sample highlighted in pink was lost in transport and not analyzed.……………………………………………………………. 53 10

Table 4.4 General section paleosol summary table, P5-P4. Same conventions used as the previous summary table, but a a light purple-blue shade was added to include paleosols a fourth paleosol (“d”) within a depositional cycle, in this case P5d, interpreted as an Inceptisol.……………………………………………………………………………..... 66

Table 4.5 General section paleosol summary table, P6-P7 (see Table 4.1 for more detail).………………………………………………………………………………….. 73

Table 4.6 General section paleosol summary table, P8-P9. Same convention as previous summary tables, with the exception of P9d, which is highlighted in pink and is the uppermost paleosol described in the general section (see Table 4.1 for more detail).………………………………………………………………………………………. 81

Table 4.7 Coeval paleosol weathering indices. Locations are measured in from the top of the highest pedogenically modified bed (“0”) downward in decreasing increments of 20 cm. Yellow shading indicates a parent material sample from the base of the profile, blue shading indicates samples taken from the red-brown mudstone portion of the main coeval paleosol profile (MPS), and green shading indicates samples taken from the weakly pedogenically modified burying sediments (BPS) over MPS……………….………..... 82

Table 4.8 Coeval paleosol clay mineralogy (see Table 4.3 for more detail)………...... 83

Table 4.9 Coeval paleosol summary table, NW-NWI. Follows same conventions used for general section summary tables and color schemes introduced in the weathering index summary table. ………………………………………………………………………… 88

Table 4.10 CP summary table NEI-NE (see previous summary tables for more information)……………………………………………………………………………. 93

Table 4.11 CP summary table SW (see previous summary tables for more information)……………………………………………………...... 96

Table 4.12 CP summary table SWI (see previous summary tables for more information)……………………………………………………………………………100

Table 4.13 CP summary table SEI-SE (see previous summary tables for more information)……………………………………………...... 103

LIST OF FIGURES

Page

Figure 2.1 Geographic setting of this study. A) Dunkard basin outlined. B) Global paleogeography during the early Permian. C) Regional paleogeography of the early Permian with political map overlain for context. Approximate study location is marked on each map. Dunkard basin map from Google Earth, paleogeographic maps from Ron Blakey, NAU Geology…………………………………………………………………. 21

Figure 2.2 Large scale stratigraphic column of Late Pennsylvanian (southeast Ohio; modified from Hembree and Nadon, 2011) through Permian (West Virginia and southwest Pennsylvania; modified from Fedorko and Skema, 2013) deposits of the Dunkard Group. Approximate stratigraphic position of the study area outlined in red...22

Figure 2.3 Generalized stratigraphic columns. Red color indicates pedogenically modified red mudstones. A) From exposures near Marietta, OH. Base of northwest general section trench in the study area roughly correlates with Creston Reds. Modified from Martin (1998). B) Idealized cycle in the upper fluvial plain facies province. Modified from Fedorko and Skema (2013)……………………………………………. 23

Figure 3.1 Field site overview. Location of time-equivalent sections indicated by red dots. The primary location for the general section is indicated by the green dot. The lowest exposures are located near the star and comprise the first 8 m of the general section. Text next to red dots indicates the names of individual coeval profiles.…..…………………………………………………………………………….. 30

Figure 3.2 A) Primary location used for construction of the general section. B) Upper 5 m of the northwest general section trench. C) Representative image of the 8 coeval sections (NW-CP). D) Excavation of a paleosol, part of the general section to the northeast (P3)…………………………………………………………………………... 31

Figure 4.1 Plant impressions. A) Pecopteris in grey siltstone. B) Large fronds in sandstone float C) Calamites in float from the uppermost sandstone of the general section. D) Nueropteris leaves in red shale over P7. E) Large fronds in sandstone float. F) damaged Neuropteris from red shale. G) Pecopteris in red shale……………………... 38

Bifurcating diffuse purple rhizohalo (SE-CP, A/B horizon, MPS). G) Reduced rhizohalo with organic core (SWI-CP, Bw horizon, MPS). H) Photomicrograph of horizontal red rhizohalo with organic core (P3c, NE exposure). ………...…………………………… 39

Figure 4.3 Rhizoconcretions. A) Downward branching calcareous rhizoconcretions from P5a (Bssk3). B) Calcareous rhizoconcretions and nodules weathering out of P5a (Bssk2). C) Downward tapering calcareous rhizoconcretion (P6a). D) Tapering calcareous rhizoconcretion (NE-CP, A/B horizon, MPS)…………………………………………. 40

Figure 4.4 Rhizotubules. A) Calcareous rhizotubule (SEI, Bssk, MPS). B) Vertically oriented ferruginous rhizotubule (NWI, A/B, MPS). C) Photomicrograph of sparry rhizotubule (P3c, Bw). D) Subhorizontal ferruginous rhizotubule (SEI, A/B, MPS). E) Horizontally branching calcareous rhizotubule (P3a, Cg).…………………………….. 41

Figure 4.5 Animal ichnofossils. A) Scoyenia in thinly bedded sandstone float (MS4?). B) Bedding plane exposure of vertical burrows (Skolithos or Arenicolites) in MS3. C) Cochlichnus in sandstone float (MS4?). Mermia was observed in float from the same sandstone bed. D) Photomicrograph of Naktodemasis from the Bss horizon of a calcic- Vertisol. E) Isopodichnus on sandstone bedding plane (MS8). F) Planolites in sandstone float. G) Photomicrograph of diagonal concentration of opaque grains along partially reduced path, interpreted as possible ferruginized pellets.…………………………….. 46

Figure 4.6 Pedotubules. A) S-shaped green pedotubule (P3b, A/B). B) Vertically oriented calcareous pedotubule (P5a, Bssk2; 1 m). C) Sub-vertically oriented green pedotubule (P5a, Bssk1)…………………………………………………………………………….47

Figure 4.7 P1-P2. A) P2 trench, showing gley colors and indurated root ball (by hammer). B) Photomicrograph of compressed ferruginous rhizotubule with thin grey halo (40x magnification). C) P1 trench.…………………………………………………….. 51

Figure 4.8 P3-P4. A) Overview of exposure. B) Argillan with metallic luster (P4a, Bw); note small slickensides. C) P3b-P3c; note large slickensides in P3b (left of pick). D) Yellow clastic dike cutting through the greenish grey sandy matrix of P3a (Cg)……... 59

Figure 4.9 P5 A) P5a (Bssk1) through P5b (C). B) Calcareous nodules and concretions around a downward branching green rhizohalo (Bssk2). C) Coarse, dark mottle (P5a, A/B2)…………………………………………………………………………………... 65

Figure 4.10 P6. A) Overview of NW trench. B) Matrix with yellow rhizohaloes (P6b, Bssk, NW trench. C) Mottling at the base of P6b (NW trench)……………………….. 70

Figure 4.11 P7 (NE-CP). A) Overview of trench. B) Photomicrograph of horizontal ferruginous pedotubule. C) Photomicrograph of ferrans, argillans, and blocky structure. …………………………………………………………………………………………. 72 13

Figure 4.12 P8-P9. A) Coarse, irregular mottles in P9d. B) Contact between P9c and P9d. Note platy structure in P9d and yellow color from ferrans and rhizohaloes in P9c. C) Contact between P9b (lower red-brown zone) and P9c (upper purple zone). D) Contact between P8a and P8b. Dark band is the A horizon of P8a…………………………….. 80

Figure 4.13 Coeval paleosol weathering indices. The last four columns (Na2O through MgO) are leaching values (base/TiO) rather than oxide wt. %.……………………….. 84

Figure 4.14 NW-CP. A) Mottled matrix and horizontally oriented ferruginous rhizotubules (BPS, Bw). B) Photomicrograph of pedogenic iron nodule (MPS, Bss1, 100x magnification). C) Network of fine yellow rhizoliths (MPS, Bss1). D) Photomicrograph of ferrans and surrounding peds depleted in iron…………………… 87

Figure 4.15 NWI-CP. A) Photomicrograph of coarse granotubule cutting through fine grained BPS matrix; interpreted to be a passively filled burrow or root channel (100x magnification). B) Photomicrograph showing cross section of a ferruginous rhizotubule with minor amounts of carbonate (MPS, Bss1). C) Photomicrograph of Bss1 matrix with iron nodules and exhibiting bimasepic microfabric. D) Photomicrograph of reduced peds and thick ferrans, typical of the thin sections from Bss horizons over Cg horizons. D) Yellow clastic dike (left of and parallel to shovel) extending from Cg horizon of MPS into MS5.……………………………………………………………………...……….. 91

Figure 4.16 NEI-CP. A) Mottles and ferruginous rhizotubules (MPS, A/B). B) Fine, calcareous rhizotubule (MPS, Bssk). C) Lower MPS boundary with redox depletions in Bss3 and redox concentrations in Cg…………………………………………………... 92

Figure 4.17 SW-CP. A) Photomicrograph of sand filled root cast (BPS, Bw). B) Slickenside in BPS. C) Boundary between MPS and BPS. D) A/B horizon of MPS (green pen is pointing to bottom of downward tapering diffuse purple rhizohalo with a discontinuous yellow outline).………………………………………………………….95

Figure 4.18 SWI-CP. A) Photomicrograph of teardrop-shaped coprolite (MPA, A/B). B- D) Photomicrographs of variations in size and distribution of iron nodules in the Cg horizon of the MPS interval. …………………………………………………………... 99

Figure 4.19 SEI-CP. A) Photomicrograph of non-calcareous nodule with oxidized core (40x magnification). B) Photomicrograph of pedogenic carbonate nodule with opaque core (200x magnification). C) Reduction halos surrounding small (~2 mm) rounded pebbles in the oxidized matrix of the weakly developed Bssk horizon. D) Wavy lower boundary between the Bss2 and Cg horizons. Red mottle by hammer.……………….101

Figure 4.20 SE-CP. A) Overview of trench from wavy Cg/Bss boundary (MPS) through BPS. B) Downward branching diffuse purple rhizohalo (MPS, A/B). C) Photomicrograph of carbonate nodule, from Bssk horizon (D).……….………………………………… 102

Figure 5.1 Mean annual precipitation (MAP), drainage, and seasonality estimates through the general section. MAP is reported in mm/year, and was calculated using the CALMAG weathering index for Vertisols and the CIA-K weathering index for all other paleosols. MAP estimates were only made using imperfect to well drained Inceptisols and Vertisols. Drainage was estimated for all paleosols. Highlighting indicates the estimated strength of seasonality based on available physical and chemical evidence, and ranges from weak (blue) to very strong (red)……………………………..…………...113

Figure 5.2 Interpreted topographic relationships of CP profiles. Red arrow points in the approximate direction of the paleochannel………………………………………….....124

1 INTRODUCTION

This study involved the investigation of Upper Pennsylvanian-Lower Permian

Dunkard Group continental sedimentary sequences located near Parkersburg, West

Virginia. These outcrops are representative of the Lower Dunkard Group upper fluvial plain facies province (Cecil, 2013; Fedorko and Skema, 2013). Vertical and lateral variation in sedimentology and pedogenic development was examined in order to gain insight into the evolution of the terrestrial landscape during this transitional period in

Earth’s history. Emphasis was placed on variation in paleosol properties within time- equivalent intervals and the correlation of pedotype-specific ichnofossil assemblages.

Soils form in response to a number of environmental factors including climate, parent material, biota, topography, and time (Retallack, 1997; Retallack, 2001; Brady and

Weil, 2010; Chapin III et al., 2011). Just as knowledge of these parameters can allow modern soil scientists to predict where certain soils will form, physical and chemical properties of paleosols allow the inference of environmental conditions in the past. A change in any of these factors can result in soil with dramatically different properties

(Hole, 1981; Retallack, 1997; Kraus, 1999; Brady and Weil, 2010; Chapin III et al.,

2011). Well-drained, upland, sandy soils can form within tens of meters from poorly drained, waterlogged, lowland, clayey soils. As a result, interpretations of factors such as climate are tenuous if paleosols are described from a single exposure. It is only through a better understanding of local heterogeneity that regional conditions can be confidently inferred. 16

Continental ichnofossils provide information about environmental and substrate conditions over and above that which is afforded by relatively rare body fossils. The utility of ichnofossils stems from the fact that they are produced in situ and, therefore, represent original plant and animal communities. The composition of these communities, their behaviors, and the resulting ichnofossil morphologies are influenced by environmental conditions such as substrate consistency, sediment moisture content, nutrient abundance, redox conditions, depth to water table, precipitation, seasonality, and frequency of disturbance events (Hole, 1981; Retallack, 1997; Hembree and Nadon,

2011). In polygenetic paleosols, where pedogenic overprinting complicates interpretations of original soil conditions, relative timing through cross-cutting relationships may prove useful (Buatois and Mangano, 2000).

Understanding the extent with which autogenic processes control lateral changes in paleoenvironment and paleoecology in a single time interval allows for better recognition of vertical variation as evidence of allogenic processes such as a changing climate at the Pennsylvanian-Permian transition. Since there have been few studies using

Dunkard Group paleosols and ichnofossils for the purpose of interpreting paleoenvironment, paleoecology, and paleoclimate, this research improves understanding of these conditions in the continental settings of the Dunkard basin. Correlation of suites of continental ichnofossils to specific environmental conditions may be applied more broadly to paleosols in general, especially those of the late Paleozoic.

Field and laboratory investigation was conducted to achieve three primary goals:

1) identify variations in physical and chemical properties of time-equivalent paleosols; 2) 17 determine whether different ichnofossil assemblages correlate to paleosols with specific properties with increasing distance from paleochannels; 3) determine whether variability in coeval paleosol properties can be used to distinguish allogenic change from autogenic variation in local architecture and environment.

2 GEOLOGIC SETTING

The Dunkard Group records terrestrial conditions during the Upper

Pennsylvanian-Lower Permian in the distal Dunkard foreland basin (Martin, 1998; Cecil,

2013; Fedorko and Skema, 2013; Schneider, 2013). Exposures of the Dunkard Group are present in southeastern Ohio, northwestern West Virginia, and southeastern

Pennsylvania. The basin (Fig. 2.1A) has an area of approximately 12,800 km2 and is roughly elliptical, with its long axis parallel to the Allegheny Mountains (Martin, 1998).

Paleogeographic studies place the basin within 5o of the equator at the time of deposition

(Fig. 2.1B, C) and soil development (Giles, 2013). Sediment was derived from the weathering of the Allegheny Mountains that were transported in a predominantly northward direction during the late Paleozoic (Martin, 1998). Late Paleozoic strata record relatively rapid fluctuations in eustasy and climate as a result of Gondwanan glaciation

(Olszewski and Patzkowsky, 2002; Raymond and Metz 2004).

Conodont and fusilinid biostratigraphy has placed the Ames Limestone of the

Conemaugh Group (Fig. 2.2) within the Pennsylvanian (Merrill, 1975; Saltsman, 1986).

This unit is separated from the Dunkard Group by the Monongahela Group (Martin,

1998). Due to the lack of volcanic and marine deposits above the Conemaugh, radiometric dating and biostratigraphy are of limited use in determining a precise age for the Dunkard Group. Many previously used fossil groups such as the callipterids cross the

Pennsylvanian-Permian boundary, although recent work with spiloblattinid biostratigraphy suggests a Permian age for the Dunkard Group (DiMichelle, 2013;

Schneider, 2013). This interpretation is tenuous since palynological evidence has 19 historically favored a Pennsylvanian age (Martin, 1998). Recent work, however, has shown the lack of gymnosperm pollen to be the result of sampling bias rather than reflective of broader terrestrial ecology (DiMichelle et al., 2006; Eble et al., 2013). For these reasons, the Dunkard Group has been traditionally described as representing a transitional time between these two periods.

Traditionally, the transition from the Pennsylvanian to the Permian is interpreted as a transition from swampy, ever-wet conditions to a relatively more arid climate with a strong seasonal component (DiMichelle et al., 2006; DiMichele et al., 2013; Oplustil,

2013). Evidence for this environmental shift is commonly attributed to the ubiquity and lateral continuity of histic horizons during Pennsylvanian times followed by a sharp decline in continuous coal beds during the Permian (Martin, 1998; DiMichelle et al.,

2006). This climatic shift was happening at the same time that Pangaea was assembling, with increasing subaerial exposure within the Dunkard basin. By focusing on this time period, it is possible to learn more about how tropical to temperate terrestrial ecosystems respond to regional changes in temperature and precipitation.

Dunkard units (Fig. 2.3) consist of fissile red, black, green, or gray shale, gray and green siltstone, typically massive red and green claystone and mudstone, micaceous sandstone, limestone, and coal (Martin, 1998; Cecil, 2013; Fedorko and Skema, 2013).

Limestone becomes more common from the south to the north (Martin, 1998; Cecil,

2013; Fedorko and Skema, 2013). Coal beds follow the same trend, thickening and having less well-developed clastic interbeds to the north (Martin, 1998, Fedorko and

Skema 2013). Calcareous nodules and cement are common throughout the range of 20

lithologies (Martin, 1998; Fedorko and Skema, 2013). Dunkard Group strata have been

interpreted as representing three facies provinces from north to south, introduced by

Martin (1998) as the fluvial-lacustrine-deltaic plain, lower fluvial plain, and upper fluvial

plain. Subaerial exposure increases to the south, where pedogenically altered beds

thicken and become more common. The majority of the beds in the Dunkard Group are

discontinuous, with few persisting for more than a few square kilometers. Exceptions

include the Waynesburg Coal, which marks the Monongahela-Dunkard boundary, and the

Washington Coal, located 60–90 m above the Waynesburg Coal. The Dunkard Group is

subdivided into the Washington and Greene formations, the latter being the youngest

strata of the region (Martin, 1998; DiMichelle et al., 2013; Fedorko and Skema, 2013). B Recent work places the study area in the upper fluvial plain facies of the Lower

Dunkard Group (Cecil, 2013; Fedorko and Skema, 2013). This province is characterized

by variably colored fissile to massive mudstone through sandstone, with thin to absent

coal beds, and a lack of lacustrine limestone (Fig. 2.3B) (Martin, 1998; Fedorko and

Skema, 2013). Outcrops of the upper fluvial plain strata are cyclic in nature and have

been interpreted as being predominantly autogenically controlled, representing channel

migration in fluvial systems (Cecil, 2013). Fedorko and Skema (2013) described the

lowermost paleosol in the study area as being coeval with the Washington Limestone,

and have tentatively identified the Washington Coal to the south of the exposure at a

slightly lower stratigraphic position. The position relative to the Washington Coal and

Washington Limestone suggests the basal paleosol of the study area is correlative with

the Creston Reds near Marietta, Ohio (Martin, 1998). 21

24 3 METHODS

3.1 Field

The study area is located at the intersection of US Route 50 and Dupont Rd, approximately 1.2 km west of Blennerhassett, WV (Lat: 39°16’1.55”N, Long:

81°38’48.01”W) (Figure 3.1). A general stratigraphic section of a 46.5 m vertical exposure was made on the northeast edge of the outcrop, which possessed the highest quality exposures from bottom to top (Figs. 3.1 and 3.2A). Additionally, an 8 m section on the NW corner of the study area was trenched, sampled, and described due to the discovery of facies with significantly different environmental signatures from the rest of the study area. The resulting 54.5 m section was measured and described in 20 cm intervals. Samples were collected every 20 cm through the first 24 m of the section.

Interpreted B and C horizons of paleosols were sampled through the remainder of the general section.

Detailed 1.5–2.0 m stratigraphic sections of a single depositional cycle (Fig. 3.2C) were constructed at eight different locations in the study area. These were located at the northwest, northeast, southwest, and southeast corners of the field site, with paired trenches on the internal “islands” generated by construction of the cloverleaf interchange

(Fig. 3.1). Fresh exposures were produced by excavating trenches approximately 2 m wide and 50–100 cm deep. These sections were described and sampled every 20 cm.

General descriptions of lithologic units included bed thickness, the nature of contacts between beds, primary sedimentary structures, composition, fabric, texture, ichnofossils, body fossils, and color. Units interpreted as paleosols were described top-

25 down, with a focus on identification of horizons, genetic history (e.g. compound or composite), and parent material. This information aided in initial interpretations as to precipitation, soil moisture and consolidation, drainage, and seasonality. Paleosol descriptions included the nature of the upper contact (gradational, sharp, diffuse, wavy, smooth), color distribution and abundance, texture (clay:silt:sand), structure (shape, arrangement, size, distinctness of peds), horizon characteristics (degree of development, location, thickness, and boundaries), rhizolith and other ichnofossil properties

(architecture, dimensions, orientation, abundance, preservation), and other notable properties (cutans, slickensides, nodules, concretions, degree of cementation and composition of cement, organic matter, body and plant fossils, layers or lenses of differently textured sediment, fractures). Paleosol matrix and mottle colors were described using the Munsell color system (Munsell Color, 1975). Paleosols were assigned a classification using the model introduced by Mack et al. (1993) and the U.S. Soil

Taxonomy system (Soil Survey Staff, 1999).

When possible, plant and animal ichnofossils and body fossils were collected for identification and description in the laboratory. Detailed descriptions were made at the time specimens were collected including stratigraphic position, lithology of the host rock, orientation, and any other information that provided greater context for making interpretations in the lab (e.g. in situ versus detrital). Field descriptions of ichnofossils indicated the presence or absence of branching, chambers, and lining, general architecture, and contrast between burrow fill and matrix.

26 3.2 Laboratory

3.2.1 Thin Sections

Samples were collected from paleosols in the general (n=17) and coeval (n=31) sections. Thin sections were also prepared from samples taken from a calcareous rhizoconcretion, the B horizon of the paleosol in the cycle below the coeval sections

(exposed on the NW corner of the field site), and a strongly calcareous siliciclastic unit near the top of the general section. Thin sections were prepared by Texas Petrographics

(Houston, TX) and were mounted on 2.5 x 5 cm (n=34) and 5 x 7.5 cm (n=17) slides.

Thin sections were analyzed for grain size, small-scale structure (i.e. peds), ichnofossils (i.e. burrows, fecal pellets, rhizoliths), and microfabric using a Motic BA300 polarizing microscope. These details aid in interpretations as to time and intensity of soil formation as well as original soil structure. Digital photographs were taken using a

Moticam 10 microscope mounted camera.

3.2.2 Bulk Geochemistry

Samples were analyzed by ALS Chemex (Reno, NV) using X-ray fluorescence

(XRF) to determine bulk geochemistry (n=40). Samples underwent lithium borate fusion and were then analyzed using a XRF spectrometer, analytes and detection ranges are given in Table 3.1. Weight percents of oxides and loss on ignition data were included in the final report.

Reported weight percents of oxides were normalized to their molecular weights, allowing weight ratios of oxides to be compared within and between units. Proportions of

27 oxides of Fe, Mg, Al, Si, Ca, K, Na, and Ti were used to determine weathering magnitudes (Retallack, 2001; Sheldon and Tabor, 2009). The use of several weathering indices bolsters interpretations of dominant pedogenic processes (Table 3.2) Since soils of wetter climates generally have lower base saturation and pH due to elluviation of base cations (Retallack, 2001; Brady and Weil, 2010; Chapin III et al., 2011), a lower ratio of oxides of the base cations Ca2+, Mg2+, Na+, and K+ with respect to alumina suggests a greater mean annual precipitation (MAP). MAP was estimated (Table 3.3) using the chemical index of alteration without potash (CIA-K) (Sheldon et al., 2002) and

CALMAG weathering indices (Nordt and Driese, 2010). The latter was introduced in order to derive more accurate paleoprecipitation estimates from Vertisols.

3.2.3 Clay Mineralogy

Samples were analyzed by K/T Geoservices Inc. (Houston, TX) using X-ray diffraction (XRD) analysis to determine clay mineralogy. Preparation involved disaggregation and centrifuge segregation of the clay-size (<4 micron) fraction. The dried bulk (>4 micron) fraction was weighed in order to determine the weight percent of the clay-sized fraction. Oriented clay mounts were produced from clay suspensions following decantation via vacuum deposition on nylon membrane filters. In order to better identify expandable clays, mounts were placed on glass slides in the presence of ethylene glycol vapor. Clay mineralogy was determined using a Siemens D500 powder diffractometer.

This used a CuKa radiation source (40 Kv, 35 mA). Clay mounts were analyzed at a rate of 1o/min. over a range of 2-36o 2Ɵ. Diffraction data was analyzed using integrated peak areas and empirical reference intensity ratio factors. Comparison of experimental data

28 with simulated diffraction profiles allowed identification of mixed-layer clays and determination of expandable interlayer ordering and percentage.

XRD data are reported as weight percentages with a detection limit of 1–5% and a sum of 100%. This means estimates of any individual mineral will necessarily affect the reported percentage of other minerals. Furthermore, only crystalline material is able to be quantified using XRD. Variable crystallinities of minerals is a potential source of error.

Because of the assumptions being made and the potential problems in accurate determination of clay mineralogy, the method used is considered semi-quantitative.

Despite the methodological limitations, clay mineralogy is useful in the determination of chemical weathering and soil horizon properties (Retallack, 2001;

Sheldon et al 2002; Torres and Gaines 2013). The composition of clay minerals is related to degree of pedogenesis (Table 3.2), which is in turn strongly correlated with precipitation.

Table 3.1 Oxides and ranges reported by ALS Chemex following XRF analysis of bulk geochemistry.

Analytes and ranges (wt. %)

Al2O3 0.01-100 Fe2O3 0.01-100 Na2O 0.01-10 SrO 0.01-1.5

BaO 0.01-66 K2O 0.01-15 P2O5 0.01-46 TiO2 0.01-30

CaO 0.01-60 MgO 0.01-50 SO3 0.01-34 LOI 0.01-100

Cr2O3 0.01-10 MnO 0.01-39 SiO2 0.01-100 LOI at 1000 deg. C

Table 3.2 Weathering indices (From Retallack, 2001).

Process Ratio Formula

Base Loss alumina:bases Al2O3/(CaO+MgO+K2O+Na2O)

Hydrolysis alumina:silica Al2O3/SiO2

Calcification Ca-Mg:alumina (CaO+MgO)/ Al2O3

Salinization sodium:potassium Na2O/K2O

Leaching base:Ti (CaO, MgO, K2O, Na2O)/TiO2

Table 3.3 Paleoprecipitation proxies.

Weathering Index Formula Paleoprecipitation Eq.

(0.0197*CIA-K) CIA-K 100 x ( Al2O3/( Al2O3+CaO+NaO)) 221.1 (Sheldon et al., 2002) 221.1(0.0197*CALMAG) (Nordt and Driese, CALMAG 100 X (Al2O3/( Al2O3+CaO+MgO)) 2010)

32 4 RESULTS

4.1 Sedimentology and Stratigraphy

Seven complete depositional cycles were observed in the general section, ranging in thickness from approximately 2–12 m. Eight sandstone marker beds were used to delineate the cycles. The sandstone beds are greenish grey and micaceous, typically with tabular to ribbon architecture, and range in thickness from 1–5 m. These units contain small to relatively large (1–100 cm) plant impressions (Fig. 4.1), locally dense Scoyenia

(Fig. 4.5), and, less commonly, Cochlichnus (Fig. 4.5C) and Mermia. Arenicolites is locally abundant (Fig 4.5B). The thickest sandstone bodies are laterally and vertically heterogeneous and comprised of multiple distinct beds, sometimes with discontinuous intercalated shale. Sandstone architecture in the study area is consistent with previous work that interpreted Dunkard Group deposits of the upper fluvial plain facies province as resulting from a large anastomosing river system (e.g. Martin, 1998; Cecil, 2013).

Tabular sandstone beds tend to exhibit parallel lamination, although climbing ripples and cross lamination are locally present. These have been interpreted to represent crevasse splay and levee deposits in anastomosing river systems (Makaske, 2001). Ribbon sandstone beds are recognized by having sharp, concave bases and usually gradational, fining upwards tops. These are typically thicker than tabular bodies and exhibit cross lamination. These are generally interpreted to be channel fill structures (Miall, 1985;

Makaske, 2001). Lateral variations in sandstone architecture inform interpretations as to the location of paleochannels versus proximal floodplain. Tabular sandstone beds may exist as wing structures associated with ribbon sandstones, generally adjacent to one or

33 more ribbon sandstone body. These wings represent crevasse splays and channel mouth bars (Makaske, 2001). A clear transition from one dominant geometry to the other is usually apparent in the east-west direction, although channel fills of the ribbon sandstone beds are variably oriented. Although no deeply incised channel fill structures (i.e. greater than 5 m) are present in the immediate study area, a few were observed within 3 km to the south-southeast. These are all oriented in a predominantly north-south direction. A paleocurrent study identified this as the regional transport direction (Martin, 1998).

The upper portions of the sandstone marker beds often have clastic dikes and rarely show other signs of shallow pedogenic development (Figs. 4.8D, 4.15E). These fine upwards into generally red-brown, pedogenically altered mudstone units, with a small but variable sand-sized fraction. These units range from 2–8 m in thickness, but often show evidence of a polygenetic origin. Mudstones are overlain by approximately

0.5 m or less of shale or platy mudstone. The lower ~20 cm of the platy mudstone units often shows signs of pedogenesis and plant impressions (Fig. 4.1) are very common in shale. A sharp erosional contact with an overlying sandstone unit marks the beginning of the next cycle.

4.2 Flora

4.2.1 Plant Impressions

Plant impressions are common on bedding planes of shale and sandstone units.

These range from small, damaged leaves in shale (Fig. 4.1D, F) to more complete specimens in sandstone (Fig. 4.1B-C, E). Ferns dominate floral assemblages (Fig. 4.1 A,

34 B, E, G) and leaves and leaf fragments of Cordaites are also common, especially in fine- grained facies (Fig. 4.1D). One cordaitean trunk fragment was observed in a fissile mudstone near the top of the coeval interval examined on the northeast island (NEI-CP).

Stem fragments of Calamites are less common. One large, relatively intact calamaitean was observed, with intact branches and in association with disarticulated Annularia (Fig.

4.1C).

4.2.2 Rhizohaloes

Rhizohaloes (Fig. 4.2) result from differences in the physical and chemical properties within and around root channels (Kraus and Hasiotis, 2006). These are relatively common macro- and micromorphological features, and account for the majority of rhizoliths observed during the course of this study. Rhizohaloes in weakly developed paleosols (i.e. Entisols and Inceptisols) tended to be observable in thin section only.

Relatively large (> 2cm) diameter rhizohaloes are common in the upper portions of well- developed, better drained paleosols (e.g. P5a-P5c and P7). Fine, reduced rhizohaloes are found throughout most paleosols, but with widely varying density and expression.

4.2.2.1 Reduced rhizohaloes

Reduced rhizohaloes are common in red-brown mudstones. They typically appear as fine (<1 mm–1.0 cm), downward branching (Fig. 4.2C, E), green to grey mottles.

Depth is typically ~1–8 cm, but deeper (~0.5 m) reduced rhizohaloes were uncommonly observed. Red rims are often observed in thin sections (Fig. 4.2H), occasionally grading from grey to yellow to red (Fig. 4.2D). Occasionally these possess a discontinuous

35 organic core (Fig. 4.2A, E, G, H). Reduced rhizohaloes are rare in fissile units overlying red-brown mudstones, where they are almost exclusively fine (1-2 mm) and horizontally oriented.

4.2.2.2 Yellow rhizohaloes

Yellow rhizohaloes (Fig. 4.2B) are uncommon, but occur in high abundance at depths greater than 1 m where observed. They are fine (2–4 mm), downward branching mottles that form dense networks in a calcareous red-brown mudstone (Fig. 4.10) and a purple mudstone (Fig. 4.11).

4.2.2.3 Diffuse purple rhizohaloes

Diffuse purple rhizohaloes are 2–8 cm wide at the top, and generally taper and occasionally branch downward (Fig. 4.2F). They were primarily observed in the coeval paleosols, where they commonly project downward 15–30 cm into a blocky red-brown mudstone from the upper contact with a more fissile unit.

4.2.3 Rhizoconcretions

Rhizoconcretions (Fig. 4.3) form when minerals precipitate around a root or cluster of fine roots (Klappa, 1980; Retallack, 2001; Kraus and Hasiotis, 2006). They may be calcareous, ferruginous, or, more rarely, a combination of the two. Calcareous rhizoconcretions are the most common type of rhizolith in the study area. They are generally observed as a series of stacked, red-brown to grey concretions, often with a circular to elliptical cross section, and which taper or branch downward. Diameters range

36 1–5 cm. They are often at 10–30 cm deep and are found in high abundance in calcareous red-brown mudstones (4.3B).

4.2.4 Rhizotubules

Rhizotubules form when minerals cement a former root channel (Klappa, 1980;

Kraus and Hasiotis, 2006). Rhizotubules (Fig.4.4) are either calcareous or ferruginous and are differentiated from rhizoconcretions by a lack of concentric banding in cross section or stacking in profile. Ferruginous rhizotubules (Fig. 4.4B, D) are most commonly found within the upper portions of paleosol profiles where they occur in a variety of orientations. Rhizotubule diameter is generally constrained within 0.5 and 1 cm. Ferruginous rhizotubules are often the only macroscopic rhizoliths in weakly developed paleosols. Calcareous rhizotubules (Fig. 4.4A, C, E) are common as very fine

(≤ 1 mm), downward branching, white mottles in calcareous red-brown mudstones.

Larger scale (1–3 cm width, 20–60 cm exposed length), purple, calcareous rhizotubules were observed as horizontally oriented and branching features on the bedding plane of a greenish grey sandstone (Fig. 4.4E). Although uncommon in other units, this was the only macroscopic rhizolith preservational style observed in the lowest sandstone marker bed (MS1).

4.2.5 Root Casts

Root casts form when sediment is washed into former root channels (Klappa,

1980). Downward tapering and occasionally branching features were rarely observed as

37 zones of coarser sediment (Fig. 4.17A). This is the least common taphonomic mode of original root-path identification in the study area. Field investigation revealed two downward tapering and branching, coarse sand-filled granotubules that are likely root casts (Figs. 4.14, 4.15). Both are approximately 5 cm wide at the top and approximately

30 cm deep. One thin section from a poorly developed paleosol (4.17A) revealed a vertically oriented root cast (~0.1 mm x 1.0 cm) with horizontal reduced rhizohaloes with red rims projecting laterally.

4.3 Fauna (Ichnofossils)

Ichnofossils are most common on bedding planes of sandstones. These assemblages primarily consist of linear to sinuous structures, commonly with a horizontal component. Structures interpreted as animal traces are rare in shale, but include simple horizontal trails and vertical shafts where observed. Unambiguous ichnofossils are least common within mudstones.

4.3.1 Scoyenia

Description: Scoyenia (Fig. 4.5A) is defined as a horizontal to subhorizontal burrow with scratch marks that produce a ropey texture. Burrow diameters range 0.2 to

1.0 cm. This ichnofossil was only observed in sandstones.

Interpretation: The association with thinly bedded sandstones suggests that

Scoyenia was produced in proximal overbank crevasse splay deposits during periods of time when sediments were moist, but not necessarily subaqueous (Hasiotis, 2002; Buatois and Mangano, 2010). Buatois and Mangano (2011) correlate Scoyenia with desiccated

38 overbank deposits. Scoyenia has been attributed to the feeding and peristaltic locomotion of larval coleopterans (Hasiotis, 2002).

Figure 4.2 Rhizohaloes. A) Photomicrograph of red rhizohaloes with organic cores (P6b). B) Yellow rhizohaloes (P6b, Bssk). C) Photomicrograph of reduced rhizohalo (SEI-CP, A/B horizon, MPS). D) Photomicrograph of yellow rhizohalo with reduced core surrounded by discontinuous organic matter (P5a, Bssk1). E) Photomicrograph of bifurcating reduced rhizohalo with discontinuous organic core (NW-CP, BPS). F) Bifurcating diffuse purple rhizohalo (SE-CP, A/B horizon, MPS). G) Reduced rhizohalo with organic core (SWI-CP, Bw horizon, MPS). H) Photomicrograph of horizontal red rhizohalo with organic core (P3c, NE exposure).

42 4.3.2 Arenicolites

Description: Paired burrow openings on bedding plane surfaces are attributed to

Arenicolites, which are simple U-shaped burrows. Burrow diameters range 0.2–1.0 cm, with openings spaced 2–4 cm apart. Arenicolites are locally dense, making it difficult to distinguish from Skolithos when only visible in plan view (Fig. 4.5B). Arenicolites was only observed in sandstones.

Interpretation: Arenicolites is interpreted as representing dwelling behavior of larval insects in high moisture environments (Hasiotis, 2002). Burrows may have been made subaerially in saturated sediments or in low energy, subaqueous settings.

Arenicolites requires firm enough sediments for the U-shaped tube to maintain its form.

Arenicolites was likely produced in proximal overbank deposits while the sediment was firm but moist, suggesting that some time had passed between flooding and colonization

(Buatois and Mangano, 2011).

4.3.3 Skolithos

Description: Unpaired burrow openings on bedding plane surfaces are attributed to Skolithos (Fig. 4.5B), which is characterized by simple vertically oriented burrows.

Burrow diameters range 0.2–1.0 cm. Skolithos is locally dense on sandstone bedding planes.

Interpretation: Skolithos is commonly associated with high energy, sandy active channel and sandbar deposits, but the purpose of the structure and the identity of the tracemaker is poorly constrained (Buatois and Mangano, 2011).

43 4.3.4 Cochlichnus

Description: Cochlichnus (Fig. 4.5C) is characterized by simple, regular, sinusoidal trails of consistent width (~0.2-1.5 cm). It is relatively common on bedding planes of thinly bedded sandstone, although typically found in low abundance relative to other ichnogenera.

Interpretation: Cochlichnus has been attributed to the subaqueous locomotion of annelids along or shallowly beneath the sediment surface (Hasiotis, 2002). It is associated with quiet water fluvial and lacustrine settings, and indicates that the water table was above the sediment surface when the ichnofossil was produced (Hasiotis, 2002; Buatois and Mangano, 2011). The association with thinly bedded sands suggests that Cochlichnus was produced in proximal, overfilled-overbank, crevasse splay deposits (Buatois and

Mangano, 2011).

4.3.5 Mermia

Description: Mermia is characterized by looped horizontal trails and is very rarely found on the bedding planes of sandstones. Trails are typically ~0.5 cm in width and may cover an area of up to 20 cm2.

Interpretation: Mermia is considered to be a non-specialized, subaqueous feeding trace, and has been attributed to the behavior of larval insects in overfilled overbank deposits prior to floodplain desiccation (Buatois and Mangano, 2002, 2011).

44 4.3.6 Naktodemasis

Description: Naktodemasis was observed in a single thin section from the Bss horizon of P3b (Fig. 4.5D). It was recognized by the presence of dense, arcuate menisci in an unlined, subhorizontal burrow. The exposed length of the burrow is ~3mm and the width is <1 mm.

Interpretation: This ichnogenus is synonymous with adhesive meniscate burrows

(AMB’s) described by Hasiotis (2002), and it has been suggested that both Naktodemasis and AMB’s are better identified as the ichnogenus Taenidium (Buatois and Mangano,

2011). Naktodemasis was likely produced by a small hygrophilic to terraphilic soil animal, such as larval coleopterans and hemipterans (Hasiotis, 2002; Smith et al.,

2008c;). The active backfill suggests the tracemaker digested and excreted sediment as it moved through the soil (Buatois and Mangano, 2011).

4.3.7 Isopodichnus

Description: Isopodichnus, a somewhat contentious terrestrial ichnogenus that is essentially identical to the marine ichnogenus Cruziana (Buatois and Mangano, 2011), was very rarely found in sandstone (Fig. 4.5E) and shale. It is a sinuous horizontal trail with raised edges. Examples in the study area were 2–4 mm wide and up to 7 cm long.

Interpretation: Isopodichnus is interpreted as the grazing trace of bilobate arthropods (Buatois and Mangano, 2011) or snails (Hasiotis, 2002) in soft, saturated substrates (Hasiotis, 2002) in proximal to distal floodplain deposits. The lack of scratch marks suggests the tracemaker lacked appendages or the substrate was too soft to allow their preservation (Buatois and Mangano, 2011).

45 4.3.8 Planolites

Description: Planolites (Fig. 4.5F) are simple horizontal to subhorizontal, nearly straight passively filled burrows with elliptical cross sections. Widths and lengths range from 0.3–2 cm, and 2–6 cm, respectively.

Interpretation: The simple morphology and lack of distinctive features such as scratch marks means a wide variety of tracemakers and environments could have been responsible for producing Planolites (Smith et al., 2008c; Buatois and Mangano, 2011).

4.3.9 Coprolites

Few coprolites were confidently identified in the study area, although one clear example was identified in thin section (Fig. 4.18A). Linear concentrations of sand-sized, circular, opaque glaebules visible in thin sections (Fig. 4.5G) are similar to glaebules interpreted as fecal pellets in other studies (Retallack, 2000) and likely represent fecal pellets within burrows. An alternative interpretation of similar features is provided by

Rosenau et al. (2013a) who identified opaque glaebules as pyritized root fragments.

4.3.10 Pedotubules

Many macro- and micromorphological features of paleosols can be interpreted as having been formed by biological activity, but cannot be confidently identified as either plant or animal traces; these features are referred to as pedotubules (Brewer, 1976).

Pedotubules (Fig. 4.6) in the study area are typically vertically to horizontally oriented linear features, recognized by variations in color, composition, or induration relative to

46 the surrounding matrix. Diagnostic features such as linings, scratch marks, coprolites, and downward tapering or branching are either lacking or ambiguous.

Figure 4.6 Pedotubules, locations highlighted by adjacent black lines. A) S-shaped green pedotubule (P3b, A/B). B) Vertically oriented calcareous pedotubule (P5a, Bssk2; 1 m). C) Sub-vertically oriented green pedotubule (P5a, Bssk1).

4.4 General Section Paleosols

4.4.1 Paleosol 1 (P1)

Description: P1 (Fig. 4.7C; Table 4.1) is a coal with a platy structure. Sand-sized pyrite crystals are dispersed through the unit. The lower contact is buried, with an exposed thickness of approximately 20 cm. A clear boundary separates P1 from an organic-rich shale with red and orange mottles in the lower 30 cm, grading into a uniformly dark matrix in the upper 20 cm. Both P1 and the overlying shale contain abundant plant impressions.

Interpretation: Histosols are strong indicators of waterlogged and reducing conditions (e.g. Retallack, 2001; Brady and Weil 2010; Chapin III et al., 2011).

Appropriate conditions for peat accumulation are most likely to be found in the distal portion of floodplains, where the water table may be at or above the surface (Kraus,

48 1999). P1 may have developed in a backswamp under similar regional conditions as other paleosols in the study area. Alternatively, the absence of Histosols in any stratigraphically higher position over an area of at least one square kilometer is suggestive of an allogenic explanation. A tropical climate, for example, with greater amounts of precipitation evenly distributed throughout the year may have promoted the development of histic epipedons on a large scale. This interpretation is supported by many previous studies that reference regional coals in lower stratigraphic intervals (e.g. Martin, 1998; DiMichelle et al., 2001;

Cecil, 2013; Eble et al., 2013). Recent work by Fedorko and Skema (2013) tentatively identified the Washington Coal at a stratigraphic position somewhere beneath P3 to the south of the study area. If this interpretation is correct, it is likely that P1 is the same unit.

Classification: P1 is classified as a Histosol using the classification scheme proposed by Mack et al. (1993) and that of the Soil Survey Staff (1996).

4.4.2 Paleosol 2 (P2)

Description: P2 (Fig. 4.7A, B; Table 4.1) is a 60 m thick, purple mudstone with platy structure and a gradational lower boundary with a red shale. P2 is characterized by a nearly 50 cm thick Bw horizon with a drab purple matrix and green, yellow, and orange mottles. Clay skins, ferruginous rhizotubules (4.7B), small iron nodules, and fine green rhizohaloes are the dominant features. The matrix is very fine grained and has an omnisepic microfabric. Matrix sediments commonly appear disrupted in thin section.

Sand-sized opaque spheres, likely iron nodules, are concentrated in some of these disrupted zones. A CIA-K value of 97.29 was calculated from samples of the Bw horizon

(Table 4.2). P2 has a moderate clay sized fraction (18%), and is dominated by illite and

49 mica (25%) and chlorite (21%), the latter having one of the highest values in the study area (Table 4.3).

Interpretation: P2 formed under variable hydrologic conditions. The presence of iron nodules, ferruginous rhizotubules, and mottles suggests a widely fluctuating water table (Kraus, 1999; Retallack, 2001). The drab purple matrix is indicative of dispersed hematite and develops in imperfectly drained, organic-rich soils are water saturated much of the year (Wright et al., 2000). These conditions result in the mobilization of iron oxides (Bigham et al., 1978; Torrent et al., 1980). The relatively deep rooting indicated by rhizoliths and a vertically oriented, 12 cm wide, 44 cm deep, lens-shaped feature with an indurated outline interpreted to be a large root ball (Fig. 4.7A), suggests that drainage was not always poor. This is further supported by the disrupted sedimentary fabric and aligned opaque spheres, interpreted to be the result of air-breathing, soil animals moving through and defecating in the soil. These features suggest that at least portions of the profile were periodically above the water table.

An especially low salinization value for P2 (Table 4.2) is likely the result of greater precipitation amounts, possibly without pronounced wet and dry seasons. A MAP estimate of 1503 mm was obtained using the CIA-K weathering index and is the highest value determined through the use of paleoprecipitation proxies in the study area (Table

4.2).

Classification: P2 is classified as a Protosol (Mack et al., 1993) and interpreted as an Inceptisol (Soil Survey Staff, 1996).

Table 4.1 General section paleosol summary table, P1-P3. P1 and P2 are isolated from other units by buried upper and lower contacts. Stratigraphically higher paleosols (P3-P9) are separated by laterally continuous sandstone beds, which are used to dileneate paleosol-containing depositional cycles. Genetically distinct paleosols within a given cycle are highlighted, with colors corresponding to letters “a” (green, i.e. “3a”) through “c” (yellow, i.e. “3c”). Clay mineralogy is only reported in paleosols with a <4 m fraction greater than 10%. Only mineral species with >10% abundance are listed in parentheses following the total weight % of the clay size fraction for a given paleosol horizon.

Paleosol Horizon Macromorphology Micromorphology Upper Boundary-Position Clay Mineralogy (<4 mm) Classification (Mack) Classification (Soil Survey Staff) Drainage platy structure, argillans (metallic 16.10 % (19.2% Kaolinite, 12.10 3 Bw wavy, clear Protosol Inceptisol good luster), small slickensides % Chlorite) fine green vertically oriented A/B Smooth, clear calcic-Vertisol Vertisol good rhizoliths, dark faintly mottled matrix

red-brown (10R 3/4) fining upwards subangular blocky structure, backfilled burrow, Bss silts and clays, slickensides, blocky diffuse 18.6% (26.7% Kaolinite) mosepic fabric structure, green mottles

micaceous sands with clear relict bedding, abundant purple carbonate nodules, Scoyenia & Arenicolites , 14.5% (25% Kaolinite, 11.5 % Cgk calcareous rhizotubules, Fe nodules wavy, clear gleyed-Protosol Entisol poor calcareous rhizotubules, relict Chlorite) bedding, little pedogenic modification, oxidized clastic dikes

coalescing Fe-Mn nodules, very fine grained, platy structure, large root ball where omnisepic, dark-cored fine roots, pellet-filled 18% (17.1% Kaolinite, 20.70% 2 Bw trenched, Fe rhizotubules, clay skins, Smooth, clear Protosol Inceptisol imperfect burrow, small carbonate nodules, disrupted Chlorite) fine green rhizoliths matrix (biological) gradation from red shale to Bw, C N/A diffuse platy structure 1 O coal N/A Smooth, clear N/A Histosol Histosol poor

Table 4.2 General section molecular weathering ratios, chemical index of alteration (CIA-K), CALMAG, estimated mean annual precipitation (MAP). Calculated using bulk geochemistry data derived from whole-rock X-ray fluorescence (XRF) of samples from general section paleosols. Negative values in the location column and a single asterisk next to the paleosol number indicate paleosols sample from the northwest trench, which was measured in 20 cm intervals descending from -20 to -700 from the stratigraphically lowest laterally continuous sandstone exposed in the northeast general section trench. The double asterisk next to P6 samples indicates that these were taken from the same depositional cycle as those taken from the northeast trench, but were sampled on the northwest corner of the study area where the paleosol is better exposed. Leaching Paleoprecipitation Paleosol Location Sample Horizon Base Loss Hydrolysis Salinization Calcification CaO MgO Na2O K2O CIA-K MAP CALMAG MAP 9 4160 40 Bw 3.28 0.41 0.15 0.12 0.60 2.32 0.59 3.82 95.32 1445.76 89.19 1281.26 9 4000 39 Bss 3.69 0.35 0.24 0.12 0.62 1.98 0.63 2.62 94.55 1424.01 89.25 1282.93 9 3900 38 Bk 1.33 0.32 0.21 0.55 8.45 2.95 0.71 3.40 9 3440 37 Bw 3.51 0.42 0.19 0.11 0.26 2.31 0.64 3.45 96.27 1473.13 90.10 1304.45 8 2900 36 Bt 3.61 0.37 0.23 0.11 0.35 1.92 0.68 2.99 95.41 1448.50 90.43 1313.03 8 2780 35 Bw 2.54 0.35 0.31 0.24 3.02 1.81 0.74 2.41 84.36 1165.13 80.80 1086.03 8 2720 34 Cg 2.57 0.33 0.31 0.22 2.38 1.94 0.82 2.67 7 2470*** 7 Bw 3.74 0.44 0.15 0.10 0.27 2.34 0.58 3.84 97.04 1495.76 90.91 1325.47 7 2400*** 8 Bss 4.69 0.38 0.24 0.07 0.29 1.21 0.56 2.40 95.92 1463.02 92.36 1363.93 7 2280*** 9 Cg/R 2.18 0.21 0.85 0.26 1.71 1.88 1.30 1.54 6** 1900*** 24 Bk 1.72 0.30 0.15 0.38 4.81 2.65 0.52 3.41 78.61 1040.31 72.42 920.89 6** 1860*** 25 Cg 2.35 0.25 0.42 0.23 1.96 1.93 0.99 2.37 6 1820 33 Cg 3.10 0.41 0.14 0.15 0.63 2.82 0.50 3.60 6 1740 32 R 3.03 0.38 0.20 0.15 0.58 2.52 0.64 3.22 5 1100 31 Bssk 1.36 0.33 0.17 0.47 7.89 2.53 0.86 5.14 71.88 911.13 68.22 847.69 5 980 30 A/B 1.50 0.35 0.15 0.40 7.14 2.26 0.79 5.33 74.59 961.04 71.23 899.46 5 900 29 Bssk 1.45 0.36 0.14 0.43 7.92 2.14 0.74 5.21 72.84 928.56 69.76 873.88 5 360 28 C 2.92 0.47 0.14 0.16 1.98 2.75 0.61 4.50 4* -80 20 Bw 3.60 0.45 0.08 0.11 0.67 2.34 0.32 4.23 96.50 1479.76 90.05 1303.12 3 40 26 Bw 3.34 0.46 0.11 0.13 1.39 2.74 0.54 5.06 94.39 1419.64 88.74 1269.96 3* -340 21 Bss 3.14 0.28 0.23 0.13 0.80 1.49 0.65 2.86 92.63 1371.24 88.84 1272.47 3* -460 22 Cg 3.22 0.28 0.34 0.12 0.30 1.88 0.87 2.58 2* -560 23 Bw 3.76 0.45 0.08 0.10 0.41 2.23 0.30 3.86 97.29 1503.10 90.62 1318.01 *low NW trench **high NW trench ***approximate 53

Table 4.3 General section clay mineralogy from X-ray diffraction (XRD) of the <4 micron fraction of general section paleosols. R1 M- L I/S 30%S: ordered mixed-layer illite/smectite with 30% smectite. R1 M-L I/S 20%S: ordered mixed-layer illite/smectite with 20% smectite. Negative values in the location column and a single asterisk next to the paleosol number indicate paleosols sample from the northwest trench, which was measured in 20 cm intervals descending from -20 to -700 from the stratigraphically lowest laterally continuous sandstone exposed in the northeast general section trench. The double asterisk next to P6 samples indicates that these were taken from the same depositional cycle as those taken from the northeast trench, but were sampled on the northwest corner of the study area where the paleosol is better exposed. Triple asterisks indicate an approximate location (±20 cm). The sample highlighted in pink was lost in transport and not analyzed.

Paleosol Location Sample Horizon R0 90S*M-L I/S R1 30S**M-L I/S R1 20S***M-L I/S Illite & Mica Kaolinite Chlorite Quartz K-Feldspar Plagioclase Calcite Siderite Hematite <4 micron wt% 9 4160 40 Bw 0.00 4.70 0.00 27.90 30.10 16.00 7.40 0.00 1.90 0.00 1.70 10.30 31.20 9 4000 39 Bss 29.30 0.00 4.60 8.30 26.30 3.20 19.20 0.00 1.20 0.00 1.60 6.30 34.30 9 3900 38 Bk 7.40 0.00 3.50 9.40 11.20 3.50 25.10 0.00 1.80 24.50 1.70 11.90 25.90 9 3440 37 Bw 0.00 4.40 0.00 29.80 30.70 12.60 5.20 0.00 1.10 0.00 1.10 15.10 19.30 8 2900 36 Bt 0.00 5.00 0.00 26.70 42.00 9.20 5.30 0.00 1.10 0.00 0.70 10.00 35.20 8 2780 35 Bw 0.00 6.40 0.00 19.50 41.10 6.70 10.00 0.00 1.20 0.00 1.70 13.40 28.70 8 2720 34 Cg 0.00 3.50 0.00 26.20 46.70 14.50 4.30 0.50 1.00 0.00 1.30 2.00 26.90 7 2470*** 7 Bw 0.00 0.00 5.60 26.50 30.30 24.90 6.90 0.90 3.50 0.40 1.00 0.00 9.20 7 2400*** 8 Bss 7 2280*** 9 Cg/R 0.00 0.00 6.20 25.10 24.90 14.50 8.40 0.00 1.00 0.00 0.00 19.90 21.10 6** 1900*** 24 Bssk 0.00 9.00 0.00 19.30 20.60 12.10 11.30 0.00 2.20 6.20 0.00 19.30 16.10 6** 1860*** 25 Cg 0.00 5.10 0.00 24.20 36.30 16.00 10.30 0.00 3.20 1.50 3.40 0.00 13.00 6 1820 33 Cg 0.00 3.70 0.00 20.80 19.90 22.60 6.50 0.70 2.80 0.00 2.00 21.00 14.70 6 1740 32 R 0.00 3.80 0.00 32.00 22.10 17.20 13.20 0.70 5.90 0.00 5.10 0.00 14.90 5 1100 31 Bssk2 0.00 6.00 0.00 22.50 4.10 5.10 15.40 0.00 1.30 30.10 3.10 12.40 20.10 5 980 30 A/B2 0.00 9.00 0.00 25.60 4.40 3.80 20.30 0.00 2.60 13.30 4.80 16.20 20.40 5 900 29 Bssk3 0.00 10.40 0.00 33.60 5.30 4.20 17.00 0.00 2.10 9.10 3.20 15.10 14.10 5 360 28 C 0.00 0.00 3.70 25.30 24.90 19.80 10.30 0.50 2.10 1.60 0.00 11.80 15.10 4 120 27 Bw 0.00 2.50 0.00 12.50 14.90 7.20 3.70 0.50 0.80 41.00 1.10 15.80 11.20 4* -80 20 Bw 0.00 0.00 4.30 24.70 21.40 13.70 17.60 0.60 4.20 0.00 2.80 10.70 25.70 3 40 26 Bw 0.00 6.40 0.00 18.80 19.20 12.10 14.30 0.80 2.90 0.70 3.90 20.90 16.10 3* -340 21 Bss 0.00 4.90 0.00 27.00 26.70 2.50 8.80 0.00 0.90 0.00 4.20 25.00 18.60 3* -460 22 Cgk 0.00 4.60 0.00 27.10 25.00 11.50 11.40 0.00 2.50 11.90 3.10 2.90 14.50 2* -560 23 Bw 0.00 0.00 7.40 24.90 17.10 20.70 9.40 0.00 2.70 0.00 3.20 14.60 18.00 *low NW trench **high NW trench

4.4.3 Paleosol 3 (P3)

Description: P3 (Fig. 4.8; Table 4.1) is comprised of three distinct units: 1) micaceous sandstone (P3a), 2) blocky, red-brown mudstone (P3b), and 3) platy, red- brown mudstone (P3c). The sandstone is pale green, with relict bedding and clastic dikes

(Fig. 4.8D) as well as tabular, horizontally branching, purple, calcareous rhizotubules

(Fig. 4.4E) and carbonate nodules. Scoyenia and Arenicolites are locally dense on exposed bedding planes. Fine, sparry, calcareous rhizotubules and iron nodules are common in thin section. The upper boundary with the overlying mudstone is wavy, with carbonate nodules present in both units.

P3b (Fig. 4.8C) contains abundant, large slickensides, green mottles, and exhibits subangular blocky structure. A meniscate, actively backfilled burrow was observed in thin section (Fig. 4.5D). Vertically oriented green rhizohaloes extend downward from the sharp upper contact with P3c. A CALMAG weathering index value of 90 was calculated for this unit (Table 4.1).

P3c exhibits a platy structure and argillans with a metallic luster (Fig. 4.8B), calcareous rhizotubules, small slickensides, sand-sized iron nodules with yellow rims, and rare pedogenic carbonate.

Interpretation: P3 is a compound profile comprising three genetically distinct paleosols. Pedogenic development of P3 began in a high energy, proximal setting with a high water table. This could have occurred within the channel margins, such as on a point bar or channel island, or in a proximal overbank setting on crevasse splay sands.

The relatively sudden shift towards finer sediment deposition and more oxidizing conditions may have occurred following avulsion, which would have moved the active channel to a more distal location (Kraus, 1999; Boggs Jr., 2012). A MAP estimate of

1272 mm was obtained for the first mudstone using the CALMAG weathering index

(Table 4.2). Due to the presence of vertic features like large, intersecting slickensides, precipitation is interpreted as having been strongly seasonal with pronounced wet and dry seasons (Retallack, 2001; Smith et al., 2008c; Hembree and Nadon, 2011). The oxidized matrix, vertically oriented roots, and calcite suggest that this soil was well-drained, having formed well above the normal water table (Retallack, 2001; Sheldon, 2005).

Green rhizohaloes and mottles concentrated around the top of the profile are interpreted to reflect localized reduction due to the decay of organic matter (Kraus and Hasiotis,

2006).

Later migration of the river to a more proximal position resulted in greater susceptibility to floods (Kraus, 1999; Smith et al., 2008c; Boggs, Jr., 2012; Trendell,

2013). This is indicated by the scouring of the upper part of the profile represented by

P3b resulting in the absence of an A horizon and the truncation of the upper rhizohaloes

(Kraus, 1999). The coarser matrix, argillasepic microfabric, and milder pedogenic development of P3c relative to P3b suggest less time for soil formation due to a more proximal position and reduced landscape stability (Mack and James, 1992; Kraus, 1999;

Retallack, 2001); however, sedimentation was still slow enough to allow the formation of illuviation features such as argillans and pedogenic carbonate.

Classifications: P3a is classified as a gleyed-Protosol (Mack et al., 1993) and interpreted as an Entisol (Soil Survey Staff, 1996). P3b is classified as a calcic-Vertisol

(Mack et al., 1993) and interpreted as a Vertisol (Soil Survey Staff, 1996). P3a is classified as a Protosol (Mack et al., 1993) and interpreted as an Inceptisol (Soil Survey

Staff, 1996).

4.4.4 Paleosol 4 (P4)

Description: P4 (Fig 4.8; Table 4.4) is an approximately 1.8 m thick, red-brown mudstone with a wavy, gradational lower contact with the underlying sandstone. P4 is subdivided into two distinct units, P4a and P4b. P4a is 85 cm thick and characterized by coarse green mottles, fine-grained fragments of organic matter, argillans with a metallic luster (Fig. 4.8B), and sparry rhizotubules and void infillings. This interval has a relatively large clay size (<4 micron) fraction, at 25.70%, a quarter of which is kaolinite

(Table 4.3). The CIA-K value is 97 (Table 4.10). The upper boundary with P4b is abrupt.

The lower 105 cm of P4b is platy, and contains iron-cored carbonate nodules, leaf impressions, fine green rhizohaloes, and green mottles. The upper 30 cm of P4b is characterized by a platy structure, carbonate nodules and concretions, vertically oriented, fine green rhizohaloes, and calcareous rhizoconcretions.

Interpretation: P4 is a compound paleosol profile composed of two distinct paleosol profiles. P4a was well drained, which helped to facilitate ped development

(Brady and Weil, 2010). However, slickensides, mottles, and iron nodules indicate periodic water saturation (Vepraskas, 2001; Trendell et al., 2013). Carbonate in this

57 interval is present as sparry rhizotubules and microscopic pedogenic carbonate nodules.

MAP is estimated to be 1480 for P4a based on the CIA-K value (Table 4.2).

P4b is characterized by the calcareous upper portion of the profile, which represents the part of the soil that regularly remained above the water table. The abundant carbonate is suggestive of good drainage and seasonally dry conditions (Retallack, 2001).

The mottled, platy zone below was frequently water saturated, resulting in the mobilization of iron and preservation of organic matter (Retallack, 2001; Brady and Weil,

2010).

Classifications: P4a is classified as a Protosol (Mack et al., 1993) and interpreted as an Inceptisol (Soil Survey Staff, 1996). P4b is classified as a Calcisol (Mack et al.,

1993) and interpreted as an Inceptisol (Soil Survey Staff, 1996). Although pronounced horizonation is lacking, these profiles exhibit more pronounced pedogenic development than other similarly classified profiles in the study area.

4.4.5 Paleosol 5 (P5)

Description: P5 (Fig. 4.9; Table 4.4) is a thick (12 m), predominantly red-brown mudstone interval subdivided into P5a and P5b. P5a includes the third sandstone marker bed (MS3), which is greenish grey with yellow clastic dikes and fines upwards to a red- brown shale, and approximately 10 m of massive mudstone. The sandstone contains many structures interpreted to be burrows, primarily Scoyenia. Carbonate nodules and slickensides cross into the overlying red-brown shale, which has less distinct bedding than the sandstone. The shale is approximately 80 cm thick, and has a gradational contact

58 with the red-brown mudstone above (Fig. 4.9A). The mudstone exhibits blocky structure and large (0.5–1.0 m), intersecting slickensides, usually with indurated carbonate accumulated along these fracture planes. Carbonate nodules and concretions, some with alternating bands of hematite, are abundant (Figs. 4.3B, 4.9B), as well as calcareous rhizoconcretions and deeply penetrating (0.5–1.0 m), vertically oriented, green rhizohaloes (Fig. 4.6C). Some green rhizohaloes, especially the finer ones (< 1 cm width), were observed to branch downward (Fig. 4.9B). Thin sections throughout the calcareous red-brown mudstone interval (n=4) exhibit porphyroskelic mosepic microfabric. Iron is common in the matrix and as ferrans.

Coarse (5-15 cm) green, yellow, and diffuse purple rhizohaloes were dispersed throughout the profile, but mottling was concentrated in two zones around meters 8.0 and

10.0. Coarse (5-20 cm), dark grey mottles (Fig. 4.9C) with yellow haloes are found exclusively in the two zones where rhizohaloes are concentrated (Fig. 4.9C). Peds observed in thin section are smaller in the two mottled zones than elsewhere in the profile.

There is a much lower percentage of kaolinite and a larger percentage of mixed layer illite-smectite in P5a than found in most other profiles (Table 4.3). CALMAG values calculated from the matrix of the non-mottled zone range from 68 to 71 (Table

4.2).

The contact between P5a and P5b is uneven due to the presence of clastic dikes.

P5b is a platy mudstone and has a variegated red and green matrix, clastic dikes, clay skins, and relict bedding.

Interpretation: P5 is a compound truncated set, subdivided into seven horizons representative of four individual paleosol profiles. P5a is a composite paleosol, comprised of three genetically distinct and overlapping cumulative profiles that show nearly identical pedogenic development. Delineation of the genetically distinct profiles was based on the identification of zones with coarse, dark mottles as former A horizons.

This is due to the interpretation that these mottles represent concentrations of relatively large amounts of organic matter, a defining characteristic of A horizons (e.g. Retallack,

2001; Brady and Weil 2010; Chapin III et al., 2011), that created locally reducing and anoxic conditions, allowing some of that organic carbon to be preserved and mobilizing iron, resulting in yellow haloes (Torres and Gaines, 2013; Trendell et al., 2013). The preservation of organic matter in the usually well drained P5a profiles suggests rapid burial of individual soils (Smith et al., 2008c). Additionally, deep (>1 m) green rhizohaloes and pedotubules have their upper exposures concentrated at approximately this level. The depth of rhizohaloes and pedotubules, the presence of calcite nodules and calcareous rhizoconcretions, and red oxidized matrix suggest the profiles were well- drained (Retallack, 2001; Sheldon, 2005 Smith et al., 2008c; Brady and Weil, 2010;

Torres and Gaines, 2013). Each of the three strongly calcareous profiles was likely well above (~2 m non-decompacted thickness) the normal water table. Large, intersecting slickensides provide evidence that precipitation was seasonally distributed (Retallack,

2001; Driese, 2005; Brady and Weil, 2010). MAP estimates based on CALMAG values range from 848 to 874 mm/year (Table 4.2). These are the lowest paleoprecipitation values estimated in the general section. Despite these low estimates, iron nodules and

61 ferrans indicate periodically wet conditions (e.g. Retallack, 2001; Smith et al., 2008c;

Brady and Weil, 2010; Chapin III et al., 2011). Although MAP estimates are lower than for other units, the strong indicators of seasonality suggest that this precipitation fell over a short period of time during the rainy season over an otherwise dry subhumid to semiarid to arid landscape (Retallack, 2001; Cecil, 2013). The wavy upper contact and clastic dikes associated with the youngest of the three profiles (P5b) is interpreted as mukkarastructure, the subsurface expression of gilgai micro-relief (Retallack, 2001;

Driese and Ober, 2005; Brady and Weil, 2010).

P5b is weakly developed. Weakly developed profiles result when sedimentation outpaces pedogenic processes. The presence of relict sedimentary structure suggests there was insufficient time or drainage for ped development and horizonation (Kraus, 1999;

Retallack, 2001; Brady and Weil, 2010). Mottling and clastic dikes suggests that the profile alternated between periods of saturation and desiccation (Retallack, 2001; Brady and Weil, 2010).

Classifications: The three overlapping profiles comprising the composite paleosol profile of P5a are classified as calcic-Vertisols (Mack et al., 1993) and are interpreted as

Vertisols (Soil Survey Staff, 1996). P5b is classified as a Protosol (Mack et al., 1993), and is interpreted as an Entisol (Soil Survey Staff, 1996).

4.4.6 Paleosol 6 (P6)

Description: The majority of P6 (Fig. 4.10; Table 4.5) was inaccessible in the NE corner of the study area so a separate profile was excavated on the NW corner (Fig.

4.10A). The macromorphological features of the NW P6 profile were compared to exposures of the same interval (MS4 to MS5) at other locations in the study area; general trends in these features remained consistent where investigated.

The base of P6 is comprised of laminated, greenish grey, fining upward, micaceous sandstone (P6a). Coarse red mottles are common near the wavy contact with the overlying red-brown mudstone (Fig. 4.10C). Stacked, downward-tapering calcareous rhizoconcretions are rare and project downward from the contact for 10–20 cm (Fig.

4.3C). Clastic dikes, carbonate nodules, slickensides, and yellow mottles are also present near the contact. The clay-sized fraction is ~25% chlorite, a much higher concentration than observed in other profiles with the exception of P2 (Table 4.3).

The overlying dark reddish brown, calcareous mudstone (P6b) fines upwards, with up to 3% coarse sand in the lower 30 cm. The mudstone exhibits blocky structure and possesses large, intersecting slickensides that become better defined with increasing depth. Iron and calcite cement the matrix. Carbonate nodules and Fe-CaCO3 concretions are common and dispersed throughout the profile. Dark-cored, downward branching rhizohaloes were observed in thin section (Fig. 4.2A). The upper 1 m of the mudstone contains abundant, fine (~2 mm width), downward branching, yellow rhizohaloes (Fig.

4.10B). A dark grey mudstone band, roughly 10 cm thick, overlies the red mudstone and separates it from a red shale unit. The latter unit lacks evidence of pedogenic alteration.

The CALMAG value obtained for the matrix of the red mudstone is 72 (Table 4.10).

Interpretation: P6 is a compound truncated set, and represents a typical cycle for the field site. The occurrence of truncated rhizoliths at the top of the sandstone suggests that it was

63 exposed to pedogenic processes prior to erosion and burial (Kraus, 1999). The coarse matrix and retention of primary sedimentary structures suggests a proximal position on the floodplain and high rates of sedimentation (Mack and James, 1992; Kraus, 1999,

Smith et al., 2008c; Trendell et al., 2013). The gley colors indicate frequent water saturation, although dry periods are indicated by the presence of carbonate nodules and slickensides (Retallack, 2001; Smith et al., 2008c; Breecker, 2010). The thick, well- developed profile and fine-grained matrix of P6b suggests development on a more distal portion of the paleolandscape, as these sedimentological characteristics are associated with lower sedimentation rates and greater landscape stability (Krause, 1999; Trendell et al., 2011). The profile was usually well-drained, indicated by the relatively deep and abundant rhizohaloes and red matrix (Sheldon, 2005; Kraus and Hasiotis, 2006; Smith et al., 2008c). Iron and calcite mobilization indicates wet periods for part of the year, while slickensides and calcite retention suggest extended dry periods (Retallack, 2001; Smith et al., 2008c; Torres and Gaines, 2013). Interpretations as to floodplain position and changes associated with this through time are similar to other profiles; however, this profile exhibits transitional characteristics between the underlying thick, polygenetic paleosol sequence (P5) and those of the next cycle. This is reflected most clearly in the amount, style, and distribution of carbonate. Furthermore, the MAP value of 921 mm is intermediate between the under- and overlying cycles (Table 4.2). Well-drained soils are considered to be fairly reliable indicators of paleoclimate (Retallack, 2001), so the combination of physical and chemical properties suggests an allogenic influence in

64 pedogenic development, with a transition to a more humid climate occurring over this interval (Retallack, 2001; Smith et al., 2008c).

Deep rhizohaloes are suggestive of a low water table and moderate to good drainage (Retallack, 2001; Hasiotis, 2002; Kraus and Hasiotis, 2006), but their yellow color indicates relatively high soil moisture or organic matter content (Kraus and

Hasiotis, 2006; Hembree and Nadon, 2011). Vertic features and the composition of concretions suggest a seasonal distribution to precipitation (Retallack, 2001; Driese and

Ober, 2005; Brady and Weil, 2010). The abundance of rhizohaloes and the dark band interpreted to be the A horizon of the profile, suggest that conditions were favorable for plant growth and that the soil was able to support relatively dense plant communities

(Trendell et al., 2013). Preservation of the A horizon likely required burial during the wet season, when plants would have been more active and a short-term shift to more reducing conditions would have allowed organic matter accumulation and preservation (Cecil et al., 1985).

Classifications: P6a is classified as a gleyed-Protosol (Mack et al., 1993) and interpreted as an Entisol (Soil Survey Staff, 1996). P6b is classified as a calcic-Vertisol

(Mack et al., 1993) and is interpreted as a Vertisol (Soil Survey Staff, 1996).

Figure 4.9 P5. A) P5a (Bssk1) through P5b (C). B) Calcareous nodules and concretions around a downward branching green rhizohalo (Bssk2). C) Coarse, dark mottle (P5a, A/B2).

abundant carbonate nodules, fine Bssk1 green rhizoliths, mukkara structure uneven, clear calcic-Vertisol Vertisol good and clastic dikes at upper boundary

Large dark mottles with yellow A/B1 diffuse calcic-Vertisol Vertisol good haloes stage II, abundant carbonate nodules (5-10 cm diameter) and rhizoconcretions, deep (~1 m) green porphyroskelic, pedogenic carbonate filaments Bssk2 rhizoliths and pedotubules, blocky and nodules, abundant Fe in matrix, very fine diffuse 20.10% structure, slickensides, dispersed grained, ferrans coarse yellow, green, and diffuse purple mottles granular to subangular blocky structure, pedogenic carbonate, mosepic microfabric, densely rooted, fine grained with coarse A/B2 see A/B1 diffuse 20.40% calcic-Vertisol Vertisol good glaebules, ferrans, calcareous rhizoconcretions, rare Fe alternating with carbonate in nodules and rhizoliths 14.1 % (10.40% mixed-layer Bssk3 see Bk2 diffuse Illite/Smectite with 30% Smectite) silt and clay, platy structure, grey 15.10% (24.90% Kaolinite, Cg diffuse mottles 19.80% Chlorite) stage II, abundant carbonate 4 Bk nodules and rhizoconcretions, fine wavy, clear Calcisol Inceptisol good green rhizoliths platy structure, green mottles, Fe- C cored carbonate nodules, leaf diffuse impressions, fine green rhizoliths

angular blocky structure, green calcareous rhizotubules, small Fe nodules with mottles, dispersed powdery yellow rims, argillasepic (locally mosepic), spar- 25.70% (21.4% Kaolinite, 13.70% Bw erosional Protosol Inceptisol good carbonate, shiny clay skins, filled void, redox streaks and spots, pedogenic Chlorite) slickensides carbonate streaks grey-green fining upward sand to Cg wavy, clear silt, platy structure

4.4.7 Paleosol 7 (P7)

Description: P7 (Fig. 4.11; Tables 4.5 and 4.10) is similar to P6 in macromorphological characteristics, but lacks the abundant carbonate that defines the older mudstone. The cycle that contains P7 was investigated in seven other locations to examine lateral variability in time equivalent intervals within the study area (Figs. 4.13-

4.20; Tables 4.7-4.13)

P7 is divided into two parts. The first is an interval which is comprised of the fifth sandstone marker bed (MS5), which is blueish grey and fines upward, and just over a meter of overlying reddish brown mudstone (MPS). The second is a 20 cm thick, platy mudstone that overlies MPS, with which it shares a clear, wavy boundary (BPS). Near the wavy boundary of the sandstone with the overlying mudstone, there is a transition from platy to blocky structure and a significant increase in clay content. In this zone the mudstone is greyish green, with large slickensides and red, orange, and yellow mottles. A wavy boundary separates this green mudstone from the overlying dark reddish brown mudstone (Fig. 4.11A).

The lower portion of the reddish brown mudstone of MPS is also clay enriched, mottles are common here. Ferrans and argillans were observed in thin section (Fig.

4.11D). Light grey, downward branching rhizohaloes with dark cores are observable in thin sections. The CALMAG value for this portion of the profile is 92 (Table 4.2). A gradation to a more calcareous zone separates the lower and upper portions of the MPS.

Thick (2–4 cm width), downward tapering and occasionally branching rhizohaloes extend

20 cm into the upper, dark mottled portion of the profile.

BPS is a dusky brown mudstone with relict bedding and rare, small iron nodules.

BPS thin sections reveal an argillasepic microfabric and horizontally oriented iron tendrils (Fig. 4.11B). Fine, horizontally branching, red and green rhizohaloes are uncommon but present, as are various plant impressions. Small slickensides and argillans are rare. The CIA-K value for BPS is 97 (Table 4.10).

Interpretation: P7 is a compound paleosol. MPS shows a much greater degree of pedogenic development, suggesting a long period (~103–104) of landscape stability, followed by burial of the profile and a brief period (~102) of renewed pedogenic development (Kraus, 1999; Retallack, 2001; Sheldon, 2005; Smith et al., 2008; Torres and Gaines, 2013). The upper 30 cm show no clear signs of pedogenic development, suggesting that sedimentation outpaced pedogenesis over this interval (Kraus, 1999).

Reduced carbonate abundance and a greater base loss value (Table 4.2) suggests wetter conditions than those indicated by the better developed portions of P5 and P6 (i.e. P5a and P6b). The presence of slickensides and pedogenic carbonate, however, indicate that precipitation was still seasonally distributed and moderate enough to allow carbonate to persist in the profile (Brady and Weil, 2010; Cecil, 2013). The reduced lower portion of the profile provides an estimate for the location of the paleo-water table. Mottling and iron mobilization in the red mudstone, combined with clay accumulations and high chroma mottles in the green mudstone, suggest that the water table did fluctuate above and below this boundary (Retallack, 2001; Vepraskas, 2001; Brady and Weil, 2010).

MAP estimates are 1364 and 1496 mm/yr based on the CALMAG and CIA-K weathering indices of the mudstone and shale, respectively (Table 4.2). Estimates are much closer

69 when the same weathering index is used for each; however, vertic features in the mudstone make the CALMAG index the preferred method for MAP estimation (Nordt and Driese, 2010b).

Classifications: MPS is classified as a calcic-Vertisol (Mack et al., 1993) and interpreted as a Vertisol (Soil Survey Staff, 1996). BPS is classified as a Protosol (Mack et al., 1993) and interpreted as an Entisol (Soil Survey Staff, 1996).

4.4.8 Paleosol 8 (P8)

Description: P8 is divided into two intervals, P8a and P8b (Fig. 4.12; Table 4.6).

P8a is comprised of laminated micaceous sandstone (MS6) that grades into grey-green shale. This fissile unit contains calcareous mottles and possesses a strongly calcareous matrix immediately above and below a wavy contact with a red-brown mudstone. The mudstone has blocky structure with argillans and iron nodules concentrated near the top.

The CIA-K value for P8a is 84 (Table 4.2).

P8b is characterized by coarse (4–10 cm) green mottles and platy structure, and is separated from P8a by a 4 cm thick, dark band (Fig. 4.12D). The upper 70 cm contains slickensides and red, orange, yellow, and grey mottles. A CIA-K value of 95 was calculated for P8b (Table 4.2). The upper contact with a thin (<10 cm) grey mudstone is abrupt and smooth.

Figure 4.10 P6. A) Overview of NW trench. B) Matrix with yellow rhizohaloes (P6b, Bssk, NW trench. C) Mottling at the base of P6b (NW trench).

Both P8a and P8b contain a relatively large clay-sized fraction, 28.7 and 35.2%, respectively (Table 4.3). Clay minerals are dominated by kaolinite, but is also notable for the presence of mixed layer illite-smectite, although values only range from 5.0 to 6.4%

(Table 4.3).

Interpretation: P8 is a compound profile that represents two distinct episodes of pedogenesis. The well-developed blocky peds, clay skins, carbonate nodules, and the fine-grained red calcareous matrix of P8a suggest that conditions were relatively dry and stable during its development (Kraus, 1999; Retallack, 2001; Brady and Weil, 2010). The presence of iron and carbonate nodules within the same profile implies alternating wet and dry periods, as in a monsoonal climate (Retallack, 2001; Retallack, 2005; Kraus and

Hasiotis, 2006; Sheldon and Tabor, 2009). Profiles like P2b show similar types of pedogenic development, but with more pronounced slickensides. Since these can develop quickly under favorable conditions, precipitation during active P8a pedogenesis may have been distributed throughout the year rather than in distinct rainy seasons (Sheldon,

2005; Trendell et al., 2013). Other than carbonate content, P8a and P8b are chemically similar (Table 4.2).

The greyish brown matrix, conspicuous mottles, and abundant pedogenic iron nodules in P8b suggest more prolonged wet periods than were present during the development of the P8a profile (Driese and Ober, 2005; Sheldon and Tabor, 2009). MAP estimates of 1165 mm/yr and 1449 mm/yr were determined for P8a and P8b, respectively

(Table 4.2).

Figure 4.11 P7 (NE-CP). A) Overview of trench. B) Photomicrograph of horizontal ferruginous pedotubule. C) Photomicrograph of ferrans, argillans, and blocky structure.

Table 4.5 General section paleosol summary table, P6-P7 (see Table 4.1 for description).

Paleosol Horizon Macromorphology Micromorphology Upper Boundary-Position Clay Mineralogy (<4 mm) Classification (Mack) Classification (Soil Survey Staff) Drainage Dusky brown (5YR 2/2) siltstone, weak pedogenic development, fine 7 C laminated, argillasepic, horizontal fine roots smooth, clear Protosol Entisol imperfect green rhizoliths and rare horizontal trails Thin dark mottled zone (N4) over porphyroskelic mosepic microfabric, reduction 20 cm of thick and sometimes spots, rhizoconcretions, granotubule, reduced A/B branching downward tapering smooth, clear calcic-Vertisol Vertisol good clayey isotubule with possible pellets, rare rhizohaloes in a red-brown (10R calcareous glaebules, rare small Fe nodules 3/4) matrix Stage 1 calcic horizon, red-brown (10R 3/4) matrix, calcareous Bk diffuse rhizoconcretions and glaebules, slickensides, small green mottles Red, yellow, orange, and green porphroskelic mosepic microfabric, subangular mottles, red-brown (10R 3/4) blocky structure, ferrans, abundant clay, Bss diffuse matrix, blocky structure, large reduced rhizohaloes with some organic matter intersecting slickensides in core greyish green (10G 4/2), clayey, Btg blocky structure, large slickensides, wavy, clear red, orange, and yellow mottles Blueish grey (5B 5/1), platy 21.10% (24.90% Kaolinite, Cg diffuse structure, sandy 14.50% Chlorite) 6 A Dark (N4), platy, carbonate nodules smooth, clear calcic-Vertisol Vertisol good

fine grained, red (10R 3/4) calcareous matrix, abundant deep 16.10% (20.60% Kaolinite, 12.10 Bssk diffuse yellow rhizohaloes, calcareous % Chlorite) glaebules (5Y 8/1), blocky structure Fine grained with few small pebbles porphyroskelic insepic microfabric, carbonate (1-3%), red (10R 3/4) calcareous nodules, abundant Fe in matrix and small Bss diffuse matrix with large intersecting dispersed nodules, organic-cored rhizohaloes, slickensides Fe-CaCO3 concretions Sandy, grey-green (5G 6/1) with red mottles, clastic dikes, calcareous 14.7% (19.90% Kaolinite, 22.6% Cg rhizoconcretions, relict bedding, rare wavy, clear gleyed-Protosol Entisol poor Chlorite) carbonate nodules, ferrans, olive- yellow mottles (10Y 5/4)

Classifications: P8a is classified as a Calcisol (Mack et al., 1993) and interpreted as an Inceptisol (Soil Survey Staff, 1996). P8b is classified as an Argillisol (Mack et al.,

1993) and interpreted as an Inceptisol (Soil Survey Staff, 1996).

4.4.9 Paleosol 9 (P9)

Description: P9 (Fig. 4.12; Table 4.6) consists of a fining upward, dark reddish brown, sandy siltstone (P9a), a thick (~4 m), blocky, dark reddish brown to blackish red mudstone (P9b), a thinner (1.8 m) purple mudstone (P9c) with yellow mottles, and a variegated and highly mottled fissile mudstone that coarsens upwards (P9d). The overlying sandstone marker bed (MS8) contains leaf impressions, clastic dikes, and carbonate nodules.

The silty portion of P9a contains light greenish grey mottles and dispersed powdery carbonate that defines the fine-grained upper portion of this unit. A thin (10–20 cm) laminated sandstone unit with many plant impressions separates P9a from P9b. A

CIA-K value of 96 was obtained for P9a (Table 4.2).

The lower 20 cm of P9b contains numerous coalescing carbonate nodules. These become smaller and more dispersed up the profile. Intersecting slickensides define the upper 3 m of P9b. A granular mix of carbonate and iron nodules fills slickenside planes, unlike the iron or carbonate cement that lines slickensides in other red mudstones.

Slickenside infilling becomes more calcareous with depth. Toward the top of P9b, there are coarse (4–8 cm), greenish grey mottles, fine (0.4–1.5 cm), yellow and green mottles, faint dark red mottles, and downward branching red rhizohaloes with yellow cores. Thin

75 section analysis revealed a porphyroskelic insepic microfabric, calcareous pedotubules, dispersed sand-sized iron nodules, small carbonate nodules, and concretions with alternating bands of Fe and CaCO3. The contact between P9b with P9c is clear and nearly smooth (Fig. 4.12C)

P9c contains large, intersecting slickensides with glassy surfaces. The matrix contains pervasive fine (1–3 mm) yellow rhizoliths and coarse (2–12 cm) yellow mottles

(Fig. 4.12B). Cutans identified in thin sections include ferrans and, to a lesser degree, argillans. Opaque streaks of Fe and reduced zones were also observed in thin section.

Analysis of clay mineralogy revealed a large clay sized fraction (34.3%), with a much greater proportion of smectite (29.3% mixed-layer clay minerals with 90% smectite) than found in any other profile (Table 4.3). A CALMAG value of 89 was calculated for P9c

(Table 4.2).

P9d contains large (up to 5 cm) carbonate nodules, mottles, and a platy structure

(Fig. 4.12A). Slickensides, some large, are present, but are generally found in isolation.

Clastic dikes are common. The matrix contains a relatively large clay sized fraction

(31.2%), which is dominated by illite, mica, and kaolinite (Table 4.3). A CIA-K value of

95 was calculated for P9d (Table 4.2).

Interpretation: P9 is a compound profile subdivided into four genetically distinct paleosols. P9a is thin, weakly developed, relatively coarse, and contains redox depletions

(low chroma mottles), suggesting that it formed on a proximal setting with imperfect drainage (Vepraskas, 2001; Driese and Ober, 2005; Smith et al., 2008c). The relatively weak development and the thin sandstone that separates P9a from P9b suggest that the

76 time P9a was subject to pedogenic processes was limited (Kraus, 1999; Trendell et al.,

2013). MAP for P9a, calculated using the CIA-K weathering index, is estimated to be

1473 mm/yr (Table 4.2).

The fine-grained matrix and degree of pedogenic development of P9b is interpreted to reflect low sedimentation rates associated with a stable, distal position on the landscape (Kraus, 1999; Smith et al., 2008; Trendell et al., 2013). Slickensides and carbonate nodules in P9b indicate that the profile experienced periods of good drainage and desiccation, although the mobilization of carbonate and mottling would require wetter periods with reduced drainage (Sheldon et al., 2008).

P9b is similar to P5a in many regards (e.g. red-brown matrix, calcareous elements, argillans, blocky structure), but lacks the conspicuous calcite-cemented slickensides that define the latter. Slickensides in P9b are smaller scale (50–75 cm), but still intersect throughout the profile above the Bk horizon. The highly calcareous nature of the profile, in combination with reduced rhizohaloes and calcareous rhizoconcretions, suggests good drainage following periods of saturation and low enough precipitation to allow the persistence of carbonate in P9b (Retallack, 2001; Smith et al., 2008c; Brady and Weil, 2010; Torres and Gaines, 2013). The mottled and densely rooted upper portion of P9b is interpreted to be an A/B horizon. Fine green rhizohaloes are the result of complete reduction, whereas red rhizohaloes with yellow cores represent movement and re-precipitation of oxidized iron outward from the root shaft (Kraus and Hasiotis, 2006;

Trendell et al., 2013). Remaining iron minerals in the center of these rhizohaloes were hydrated, with the yellow color likely the result of goethite formation (Kraus and

Hasiotis, 2006). The coarse, low chroma mottles at the upper boundary likely formed in much the same way as the green rhizohaloes, with redox depletions forming around decaying organic fragments rather than following root paths (Vepraskas, 2001). The iron nodules and powdery carbonate that have concentrated along slickensides appear to have been flushed down from P9c. P9b is partially overprinted at its upper boundary with P9c, making P9b and P9c a composite profile. A MAP estimate of 786 was obtained using the

CALMAG weathering index, but this is likely a low estimate due to the high concentration of carbonate in the profile.

The purple color of P9c’s matrix is interpreted as resulting from similar processes that produced the drab, purple matrix of P2 including the presence of dispersed hematite and organic matter, suggesting frequently saturated conditions, with significantly reduced drainage and a higher water table (Kraus and Hasiotis, 2006; Smith et al., 2008c; Trendell et al., 2013). The prominent slickensides and ubiquitous fine, yellow rhizohaloes indicate that pronounced wet periods alternated with dry periods (Kraus and Hasiotis, 2006; Smith et al., 2008c; Trendell et al., 2013). MAP values obtained for P9b, 1283 mm/yr, were calculated using the CALMAG weathering index (Table 4.2).

The truncated upper boundary of P9c indicates an erosive event, while poor pedogenic development and relict sedimentary structures suggest higher sedimentation rates during exposure of P9d to pedogenic processes (Kraus, 1999; Smith et al., 2008c;

Trendell et al., 2013). P9d developed under fluctuating hydrologic conditions, indicated by the presence of mottles, carbonate nodules, and slickensides (Vepraskas, 2001;

Trendell et al, 2013). A MAP estimate of 1446 mm/yr was estimated using the CIA-K weathering index.

Classifications: P9a is classified as a Protosol (Mack et al., 1993), and interpreted as an Inceptisol. P9b is classified as a vertic-Calcisol (Mack et al., 1993) and interpreted as a Vertisol (Soil Survey Staff, 1996). P9c is classified as a Vertisol (Mack et al., 1993) and interpreted as a Vertisol (Soil Survey Staff, 1996). P9d is classified as a calcic-

Protosol (Mack et al., 1993) and interpreted as an Inceptisol (Soil Survey Staff, 1996).

4.5 Coeval Profiles

4.5.1 General Description

Coeval profiles comprise the mudstone interval (P7) between the 5th and 6th sandstone marker beds (MS5-MS6) (Fig. 4.11, 4.14-4.20; Tables 4.9-4.13). MS5 is approximately 1.5–2.0 m thick, fines upward, and possesses a 0.5 m gradational upper contact with clastic dikes, slickensides, ferrans, argillans, and high chroma mottles. The fining upward sandstone of MS5 and the overlying red-brown mudstone comprise the

MPS portion of CP profiles. The contact between the sandstone and mudstone is wavy.

The mudstone has blocky structure and generally exhibits slickensides throughout, but these are best developed in the lower portions of the unit. The middle of the unit typically has fine, downward branching rhizohaloes and some combination of iron and carbonate nodules that define a portion of the profile. The upper 20–30 cm is commonly mottled, often with thick (2–5 cm) downward tapering and occasionally branching, diffuse

79 rhizohaloes. A wavy, abrupt boundary separates MPS from a fine-grained and typically platy mudstone unit (BPS) that possesses some indicators of weak pedogenic development. Leaf impressions are common on relict bedding planes in the BPS interval.

Approximately 40 cm above the platy mudstone is a well-sorted, fine-grained shale that lacks evidence of pedogenesis. An erosional upper contact with MS6 marks the upper boundary of the coeval profiles. Properties of individual MPS profiles vary only slightly from that of P7 and classifications are identical to P7a. Modern soil taxonomic interpretations of BPS intervals vary only slightly and are dependent upon the degree of pedogenic development.

All MAP estimates using the CALMAG weathering index range from 1290–1390 mm/yr (Table 4.7). Base loss is relatively high, with values ranging from 3.86 to 4.71 in

Bss horizons, indicating relatively high amounts of chemical weathering (Table 4.7).

Figure 4.21 summarizes changes in weathering indices through the eight CP profiles.

Clay mineralogy (Table 4.8) is variable within and between profiles, however, samples taken from Bss horizons of all MPS paleosols have a greater clay sized fraction and significantly more kaolinite and less illite and mica than the MPS C horizons or the weakly developed BPS profiles.

Paleosol Horizon Macromorphology Micromorphology Upper Boundary-Position Clay Mineralogy (<4 mm) Classification (Mack) Classification (Soil Survey Staff) Drainage Mottled, large isolated slickensides, 31.20 % (30.10% Kaolinite, 9 Bw wavy, clear calcic-Protosol Inceptisol imperfect carbonate nodules, clastic dikes 16.00% Chlorite)

Purple (5RP 2/2) matrix with ferrans, few argillans, porphyroskelic mosepic 34.3 % (29.30% mixed layer common, coarse yellow (5Y 5/6) Bss to skelsepic, Fe-rich opaque streaks and diffuse Illite/Smectite with 90% smectite, Vertisol Vertisol imperfect mottles, conspicuous large reduced zones 26.30% Kaolinite) intersecting slickensides

Coarse (5-10 cm) greenish grey A/B smooth, clear vertic-Calcisol Vertisol good mottles, slickensides

Fine yellow mottles, clay skins, porphyroskelic insepic microfabric, rhizohaloes green rhizoliths, darker zones (5R and calcareous rhizotubules, well sorted fine Bss 2/2), slickensides with powdery clay and silt, dispersed small Fe nodules, Fe- smooth, diffuse

CaCO3 and Fe nodules, red CaCO3 rhizoconcretion, rare small micritic to rhizohaloes with yellow cores sparry carbonate nodules; slickensides filled

Blocky structure, calcareous rhizoconcretions, shiny clay skins, Bk dispersed carbonate nodules begin diffuse 25.90% (11.2% Kaolinite) to coalesce in a nearly indurated zone above a 15 cm sand lense Lite grey-green mottles in red 19.30% (30.70% Kaolinite, Bw matrix (10R 3/4), some dispersed smooth, abrupt Protosol Inceptisol imperfect 12.60% Chlorite) powdery carbonate

Increasing evidence of pedogenic development up section in laminated C gradational to platy sandy silt, contains vertical burrows

greyish brown (5YR 3/2), fining upward, abundant small porphyroskelic mosepic microfabric, abundant 8 Bt smooth, abrupt 35.20% (42.00% Kaolinite) Argillisol Inceptisol imperfect slickensides, clay skins, grey, Fe in matrix orange, red, yellow mottles

Dark reddish brown (10R 3/4), platy C diffuse structure, coarse green mottles

Organic-rich, platy structure, hematite cement A Dark (N4) horizon smooth, abrupt Calcisol Inceptisol good and small Fe nodules, clay-filled tubule Red-brown matrix, Fe nodules, Bw smooth, clear 28.70% (41.10% Kaolinite) blocky structure, clay skins

Red-brown calcareous matrix with Bk diffuse grey calcareous mottles and nodules

Fining upward sand to silty clay, 26.90% (46.70% Kaolinite, Cg greyish green (10G 4/2), relict wavy, clear 14.50% Chlorite) bedding

Leaching Paleoprecipitation Paleosol Location Sample Horizon Base Loss Hydrolysis Salinization Calcification CaO MgO Na2O K2O CIA-K MAP CALMAG MAP NW -20 1 Bw 3.86 0.47 0.18 0.09 0.26 2.28 0.72 3.91 96.59 1482.46 91.61 1343.87 -100 2 Bss 3.86 0.40 0.27 0.12 1.09 1.43 0.66 2.41 92.52 1368.23 89.54 1290.19 -200 3 C/R 2.15 0.20 0.85 0.26 2.35 1.73 1.49 1.74 NWI -100 4 Bss 4.56 0.40 0.20 0.11 0.94 1.34 0.40 2.00 94.07 1410.57 90.35 1311.06 -200 5 C/R 2.81 0.33 0.31 0.20 1.31 2.55 0.75 2.38 NEI -80 6 Bss 4.71 0.38 0.11 0.10 0.64 1.40 0.23 2.09 95.96 1464.13 90.95 1326.51 NE -40 7 Bw 3.74 0.43 0.14 0.10 0.26 2.21 0.49 3.65 97.04 1495.76 90.91 1325.47 -120 8 Bss 4.59 0.38 0.20 0.08 0.42 1.30 0.47 2.34 95.92 1463.02 92.36 1363.93 -200 9 C/R 3.08 0.24 0.55 0.13 0.41 1.84 1.14 2.06 SW -60 10 Bw 3.56 0.42 0.16 0.10 0.20 2.15 0.58 3.66 96.79 1488.21 90.87 1324.54 -160 11 Bss 4.12 0.40 0.23 0.10 0.63 1.47 0.59 2.62 94.69 1427.89 91.25 1334.32 -260 12 C/R 2.86 0.27 0.47 0.15 0.22 2.46 1.13 2.39 SWI -120 13 Bss 4.69 0.38 0.24 0.09 0.41 1.38 0.50 2.07 95.73 1457.40 91.96 1353.17 -180 14 C/R 3.49 0.33 0.35 0.12 0.27 2.02 0.85 2.45 SEI -120 15 Bss 4.37 0.37 0.10 0.10 0.61 1.44 0.25 2.41 95.99 1465.10 90.91 1325.47 -180 16 C 3.80 0.28 0.28 0.08 0.24 1.18 0.68 2.42 SE -20 17 Bw 3.74 0.44 0.15 0.10 0.27 2.34 0.58 3.84 96.87 1490.66 90.98 1327.39 -120 18 Bss 4.69 0.38 0.24 0.07 0.29 1.21 0.56 2.40 96.08 1467.72 93.32 1389.99 -200 19 C/R 2.18 0.21 0.85 0.26 1.71 1.88 1.30 1.54

Table 4.8 Coeval paleosol clay mineralogy (see Table 4.3 for more detail). Paleosol Location Sample Horizon R1 30S**M-L I/S R1 20S***M-L I/S Illite & Mica Kaolinite Chlorite Quartz K-Feldspar Plagioclase Calcite Siderite Hematite <4 micron wt% NW 1 Bw 25.4 0 27.5 25.5 11.4 5.6 0 0.6 0 0 4 18.70 2 Bss 8.4 0 15.1 46.4 6.2 8.8 0 0 0 0 15.1 25.20 3 C/R 0 6.4 21.2 34.2 26.1 5.4 0 3 0.9 2.8 0 7.90 NWI 4 Bss 8.9 0 17 48.1 14.4 6.1 0 0 0 0 5.5 18.90 5 C/R 0 6.4 16.5 23.8 26 12.8 0.7 3.2 0 10.6 0 17.50 NEI 6 Bss 0 9.4 15.4 47.9 6.9 10.4 0 1.4 0 0 8.6 31.20 NE 7 Bw 0 6.2 25.1 24.9 14.5 8.4 0 1 0 0 19.9 21.10 8 Bss 9 C/R 0 5.6 26.5 30.3 24.9 6.9 0.9 3.5 0.4 1 0 9.20 SW 10 Bw 0 5 29.5 28.9 19.6 7.8 0.7 1 0.4 0.8 6.3 24.70 11 Bss 0 5.3 24.8 41.7 5.3 10.7 0.7 1.1 0 0 10.4 30.90 12 C/R 0 3 33.6 24.6 30.1 5.6 0.4 1.7 0 1 0 11.00 SWI 13 Bss 0 4.3 18.5 49.3 11 5.1 0 1.7 0 0 10.1 33.60 14 C/R 0 4.2 24.8 43.6 14.2 10.1 0.6 1.8 0 0.7 0 19.10 SEI 15 Bss 0 4.1 20.1 44.1 10 11 0.9 1.4 0 0.9 7.5 24.40 16 C 5.4 0 27.5 44.3 10 9.8 0.7 2.3 0 0 0 18.10 SE 17 Bw 3 0 29 30.5 17.2 7 0.4 1.3 0 0.4 11.2 25.80 18 Bss 0 5.2 16.9 41.7 6 13.6 0.4 0.9 0 0.2 15.1 29.40 19 C/R 0 3.4 22.4 25.7 32.6 7.4 0.4 3.6 0 4.5 0 8.60

Figure 4.13 Coeval paleosol weathering indices. The last four columns (Na2O through MgO) are leaching values (base/TiO) rather than oxide wt. %.

4.5.2 Northwest (NW-CP)

Description: NW-CP (Fig. 4.14, Table 4.9) is considerably more enriched in iron than other CP profiles; Fe cements the MPS matrix, resulting in a more indurated mudstone. Nodules (Fig. 4.14B) and ferruginous rhizotubules are common in both the

MPS and BPS portions of the profile. Sand-sized Fe nodules were observed in association with nearly linear reduced features. Reduced rhizohaloes with organic cores were observed in thin section (Fig. 4.2E). Fine (1–3 mm), yellow and green, downward branching rhizohaloes (Fig. 4.14C) are common throughout the middle of MPS.

Carbonate is rare and limited to powdery grey mottles and as bands in concretions that alternate between Fe and CaCO3. A 60 cm, inverted Y-shaped, sandy zone is located in the grey shale over BPS.

BPS displays the greatest degree of pedogenic development in the NW-CP trench

(Fig. 4.14A), with angular blocky peds and ferrans indicating the development of soil structure. Because of these pedogenic features, BPS is interpreted as an Inceptisol in the northwest exposure.

4.5.3 Northwest Island (NWI-CP)

Description: NWI-CP (Fig. 4.15, Table 4.9) contains a high concentration of iron, but nodules and rhizotubules (Fig. 4.15B) are concentrated in the upper 40 cm of MPS.

Below this horizon, there is a 40 cm interval that is defined by calcareous mottles, nodules, and rhizotubules. Rhizotubules were observed in cross section in thin sections,and contain both iron and carbonate (Figs. 4.15B). Although the upper boundary is mottled, no diffuse purple mottles were observed in this section. A sandy, J-shaped feature extends from BPS to a depth of about 35 cm into MPS (Fig. 4.15A). The upper 75 cm contains fine, downward branching rhizohaloes. These are green in the Fe-rich zone and grey and calcareous below. Thin sections reveal blocky structure and ferrans near the base of MPS (Fig. 4.15D). The sandy base of MPS contains coarse (5–20 cm), red mottles, slickensides, and clastic dikes (Fig. 4.15E) that extend into MS5.

Small red and green mottles are abundant in the BPS matrix, which rarely exhibits small-scale slickensides. BPS thin sections reveal the development of soil structure in the form of blocky peds, ferrans, slickensides, and clay skins. BPS is interpreted as an

Inceptisol in this trench. The base of MS6 displays abundant bioturbation, a common feature in CP profiles.

4.5.4 Northeast Island (NEI-CP)

Description: NEI-CP (Fig. 4.16; Table 4.10) has a 15-cm-thick zone below BPS containing numerous coarse (2–8 cm) mottles. The mottles are primarily drab grey and green (Fig. 4.16A). A few smaller red mottles, some with yellow haloes, are also present.

Iron nodules and ferruginous rhizotubules (Fig. 4.16A) are dispersed through a 30 cm

Table 4.9 Coeval paleosol summary table, NW-NWI. Follows same conventions used for general section summary tables and color schemes introduced in the weathering index summary table.

Section Horizon Upper Boundary Macromorphology Micromorphology Ichnofossils Clay Mineralogy (<4mm) Classification (Mack) Classification (USDA) subangular blocky peds, 18.7% (25.5% Kaolinite, insepic porphyroskelic fabric, platy structure, slickensides, Fe 11.4% Chlorite, 25.4% mixed- NW Bw smooth, clear organic cored rhizohaloes, Fe rhizotubules (rare) Protosol Inceptisol nodules and rare rhizotubules layer Illite/Smectite with 30% ferrans, Fe in matrix and Smectite) concentrated in small nodules

large diameter downward blocky structure, Fe nodules and tapering and rarely A/B smooth, abrupt Vertisol Vertisol rhizotubules branching rhizohaloes, Fe rhizotubules subangular blocky peds, blocky structure, Fe nodules and Fe rhizotubules, fine yellow mosepic plasmic fabric, Fe in rhizotubules, large slickensides and green downward Bss1 diffuse matrix and forming small and wedge shaped peds, dense branching rhizohaloes nodules and rare concretions fine roots (dense) (some with carbonate) downward tapering fine rhizohaloes with organic dense and indurated, small matter in reduced cores, reduciton spots, large intersecting blocky structure, weakly buff cored circular cross Bss2 diffuse slickensides, rare vertically developed sepic fabric, 25.2% ( 46.4% Kaolinite) section with thick, oriented wispy grey carbonate ferrans gradational black to gleyed mottles halo, yellow rhizohaloes with hematite core sepic plasmic fabric (more developed toward upper few faint rhizohaloes with Cg wavy, clear fining upward sand boundary), fragmented reduced core and light organic matter, abundant Fe brown halo nodules silty, red-brown matrix, platy Sandy, passively filled structure, small slickensides, clay angular blocky peds, Fe in NWI Bw smooth, clear burrow; rare Fe Protosol Inceptisol skins, small red and green matrix an small nodules rhizotubules mottles A/B smooth, clear Vertisol Vertisol wedge peds, porphyroskelic fine green rhizohaloes, Fe insepic microfabric, Fe in coarse red and yellow mottles, rhizotubules, passively filled Bss1 diffuse matrix and nodules, Fe- Fe nodules, blocky structure burrow originating in CaCO3 concretions, small burying sediments micritic nodules Stage I calcic horizon, grey porphyroskelic insepic rare calcareous powdery carbonate mottles, Bssk diffuse microfabric, carbonate rhizoconcretions, fine light- slickensides, rare orange and glaebules, small Fe nodules grey rhizohaloes yellow mottles angular blocky peds, thick large slickensides, grey-green ferrans, porphyroskelic probable dense roots 18.9% (48.1% Kaolinite, 14.4 Bss2 diffuse reduction spots, rare coarse grey- mosepic microfabric, Fe obscured by overprinting % Chlorite) green mottles nodules and cement Fining upwards, platy to blocky 17.5% (23.8% Kaolinite, Cg wavy, clear structure, clastic dikes, coarse 26.0% Chlorite) red mottles, ferrans

89 interval between the mottles and a carbonate-rich zone below. Fine (1–2 mm), downward branching, grey calcareous rhizotubules extend to a depth of 90 cm into MPS (Fig.

4.16B). The matrix is moderate brown to this depth; the matrix becomes redder below and contains small, rounded pebbles. Coarse (4–20 cm), red mottles are common below the wavy boundary between the red mudstone and greenish grey sandy bottom of the

MPS interval (Fig. 4.16C).

The BPS interval contains horizontally oriented, branching, fine (≤ 3 mm), green rhizohaloes. Small slickensides and plant impressions are also abundant. Due to the lack of prominent pedogenic features other than rhizoliths, BPS is interpreted here as an

Entisol.

4.5.5 Northeast (NE-CP)

Description: NE-CP (Fig. 4.11, Table 4.10) contains similar mottling near the top of MPS as does NEI-CPS. Carbonate accumulations including nodules and grey mottles span a depth of 25–55 cm in MPS. Rhizoconcretions consist of alternating calcareous and ferruginous bands. The lower boundary between the red-brown mudstone and greenish grey mudstone is wavy (Fig. 4.11A), and enriched in clay (Fig. 4.11C).

The BPS interval shows little evidence of pedogenic modification. Small scale slickensides and argillans were observed. Rare horizontal trails were observed on bedding planes, in association with common plant impressions. Thin sections reveal an argillasepic microfabric with rare, horizontally oriented ferruginous pedotubules (Fig.

4.11B). Due to the lack of prominent pedogenic features other than rhizoliths, BPS is interpreted here as an Entisol.

4.5.6 Southwest (SW-CP)

Description: SW-CP (Fig. 4.17; Table 4.11) contains numerous, downward tapering, diffuse purple rhizohaloes (Fig. 4.17D), some with discontinuous yellow haloes, especially near the top of MPS. Powdery carbonate is present in grey mottles in the upper

30 cm of MPS. Vertically oriented, fine (2–5 mm), greenish grey mottles are dispersed throughout the profile. Iron nodules are widely dispersed. Thin sections reveal numerous coalescing sand-sized iron nodules and small carbonate glaebules. The MPS profile fines upward, with a notable increase in the sand-sized fraction near the base. Microfabric ranges from porphyroskelic insepic near the top to agglomeroplasmic mosepic near the bottom. Red, yellow, purple, and greenish grey mottles are common near the boundary between the red and green mudstones of MPS. Thick ferrans and blocky peds are visible in a thin section taken from the base of the red-brown mudstone.

Slickensides (Fig. 4.17B), small yellow mottles, and a heterogeneous, variegated matrix characterize the BPS interval, which has a clear, slightly wavy lower boundary with MPS (Fig. 4.17C) A vertically oriented root cast with reduced horizontal rhizohaloes was observed in thin section (Fig. 4.17A). Due to the lack of prominent pedogenic features other than rhizoliths, BPS is interpreted here as an Entisol.

Table 4.10 CP paleosol summary table, NEI-NE (see previous summary tables for more information).

Section Horizon Upper Boundary Macromorphology Micromorphology Ichnofossils Clay Mineralogy (<4mm) Classification (Mack) Classification (USDA) shaly, red-brown (10R 2/2) matrix rare small slickensides, rare, horizontally branching NEI C erosional Protosol Entisol relict bedding with plant green rhizohaloes impressions Common coarse grey mottles, A/B smooth, clear rare green and red mottles (some Vertisol Vertisol with yellow haloes) fine brown (5YR 3/4), Fe reduced rhizohaloes with Bss1 diffuse nodules, blocky structure, discontinuous organic cores slickensides porphyroskelic insepic fine green downward Stage I calcic horizon, grey microfabric, carbonate branching rhizoliths, fine Bssk diffuse powdery carbonate mottles, glaebules, rare small Fe calcareous rhizotubules, slickensides, rare red mottles nodules organic-cored rhizohaloes brown matrix (5YR 3/4), blocky deep downward branching Bss2 diffuse 31.2% (47.9% Kaolinite) structure, slickensides fine green rhizohaloes dark reddish brown matrix (10R blocky peds, thick ferrans, 3/4) sandier with small rounded some sepic plasmic fabric Bss3 diffuse pebbles, fining upward, blocky development, rare small structure, slickensides carbonate nodules sandy greenish grey matrix (5G Cg wavy, clear 6/1), fining upwards, relict bedding horizontally oriented dark brown (5YR 2/2) matrix, relict argillasepic microfabric, relict 21.1% (24.9% Kaolinite, NE C smooth, clear streaks (indistinct roots or Protosol Entisol bedding, plant impressions bedding 14.5% Chlorite) burrows) dark band (N4) at top, red reduced clayey zones with horizontal Fe mottles (occasionally with yellow porphyroskelic mosepic rhizoconcretions, deep (25 A/B smooth, abrupt haloes), grey mottles, diffuse Vertisol Vertisol microfabric in nearly opaque cm) downward tapering downward tapering mottle, small matrix rhizohalo reduction spots coarse grey calcareous mottles, Bssk diffuse calcareous rhizoconcretions slickensides, reduction spots Bss diffuse slickensides, blocky structure grayish green (10G 4/2) argillans and ferrans, coarse red mottles subangular blocky structure, Bgt wavy, clear with yellow haloes, blocky ferrans and argillans structure fining upwards micaceous sand, Cg diffuse granular structure laminated to platy structure

4.5.7 Southwest Island (SWI-CP)

Description: SWI-CP (Fig. 4.18; Table 4.12) contains non-branching, downward tapering, diffuse purple rhizohaloes that extend 15 cm down into MPS from its upper boundary. Iron nodules and ferruginous rhizotubules are common in the upper 30 cm of

MPS. A teardrop-shaped coprolite (5.18A) was observed in a thin section taken from the same interval as the mottles and ferruginous rhizotubules. A 10 cm interval defined by coarse (3–8 cm) yellow mottles, reduction spots, and fine (1–2 mm), downward branching, reduced rhizohaloes directly overlies a grey zone of powdery carbonate with a maximum thickness of 15 cm. The zone of carbonate accumulation is separated from the fining upward sandstone of MS5 by 60 cm of slickensides, dispersed carbonate nodules, and very rare calcareous rhizoconcretions, and a 30-cm-interval with many coarse (2–15 cm), red, yellow, and dark green mottles. Sand-sized iron nodules are common in thin sections of the greenish grey sandstone that forms the base of MPS (Fig. 4.18 B-D)

BPS is characterized by 80 cm of red-brown mudstone and green-grey siltstone.

These contain small slickensides, argillans, plant impressions, and yellow mottles. Due to the lack of prominent pedogenic features other than rhizoliths, BPS is interpreted here as an Entisol.

4.5.8 Southeast Island (SEI-CP)

Description: SEI-CP (Fig. 4.19; Table 4.13) contains downward tapering, diffuse, purple rhizohaloes in the upper 20 cm of MPS. Redox concentrations, in the form of coarse (4–10 cm) red mottles, some with yellow haloes, are clustered immediately below

Table 4.11 CP paleosol summary table, SW (see previous summary tables for more information).

Section Horizon Upper Boundary Macromorphology Micromorphology Ichnofossils Clay Mineralogy (<4mm) Classification (Mack) Classification (USDA) argillasepic to insepic microfabric, relict bedding, sand filled root channel with small yellow mottles, grayish 24.7% (28.9% Kaolinite, SW C smooth, clear granotubule, red and green laterally branching red Protosol Entisol green (10G 4/2) matrix 19.6% Chlorite) mottled matrix, rare small Fe rhizohaloes nodules small red mottles, red-brown matrix, vertically oriented fine downward tapering diffuse A/B smooth, abrupt green mottles, few coarse yellow rhizohaloes with Vertisol Vertisol calcareous mottles near transition purple cores to Bss1 porphyroskelic insepic microfabric, small coalescing reduced rhizohaloes with coarse red mottles, few Fe nodules, carbonate organic cores in association dispersed Fe nodules, vertically Bss1 diffuse glaebules, locally sandy, with granotubules, 30.9% (41.7% Kaolinite) oriented fine green mottles, granotubules, dispersed downward tapering diffuse slickensides, reduction spots organic fragments, actively purple mottles filled burrow vertically oriented green mottles, Bss2 diffuse slickensides, common reduction spots agglomeroplasmic mosepic microfabric, relatively sandy red, yellow, purple, and greenish Bss3 diffuse matrix, rare small carbonate gray mottles, slickensides nodules, thick ferrans, blocky peds red and yellow mottles, Btg wavy, clear slickensides, clay skins intertextic mosepic fining upward micaceous 11.0% (24.6% Kaolinite, Cg diffuse microfabric, dispersed small sandstone 30.1% Chlorite) Fe nodules

97 the upper boundary with BPS. Below the mottles, there is a 40 cm interval that is strongly enriched in iron in the form of nodules and rhizotubules, the latter occasionally intercalated with CaCO3. Downward branching, reduced rhizohaloes were observed in thin sections from this interval. Carbonate becomes common in the 15 cm below the ferruginous zone, primarily in the form of coarse, powdery carbonate glaebules. Sand- sized carbonate nodules are dispersed through this interval (Fig. 4.19B). From this point down, small (~2mm) rounded pebbles are commonly dispersed throughout the matrix, often with greenish grey reduction haloes surrounding them (Fig. 4.19C). Fine (1–2 mm), downward branching, reduced rhizohaloes are common in the 30 cm separating the carbonate enriched zone from a mottled zone in the lower 30 cm of the red-brown mudstone portion of the MPS profile. Coarse (8–15 cm), yellow mottles and green reduction spots are common in the mottled zone. Just below the wavy boundary with the greenish grey sandstone, there are coarse (8–15 cm) red mottles, sometimes with yellow haloes (Fig. 4.19D).

BPS contains small slickensides (≤10 cm) and rare argillans. Due to the lack of other prominent macroscopic pedogenic features, BPS is tentatively interpreted here as an

Entisol. This interpretation would be better supported if rhizoliths could be identified in thin section, but none were produced for the BPS intervals of the four island profiles.

4.5.9 Southeast (SE-CP)

Description: SE-CP (Fig. 4.20, Table 4.13) fines upward from MS5 and contains slickensides and red and yellow mottles near the wavy boundary with the red-brown mudstone (Fig. 4.20A). Red, yellow, and green mottles are common over the lowermost

60 cm of MPS. A 15–20 cm interval characterized by fine, downward branching rhizohaloes marks a transition from the lower mottled zone to a 25 cm interval defined by powdery calcareous glaebules (Fig. 4.20C, D). The upper 30–35 cm of MPS contains small to large (0.5–2.0 cm), downward tapering and branching, diffuse, purple rhizohaloes (Fig 4.20B). Small (4–10 cm) slickensides are common over this interval. Fe-

CaCO3 concretions are rarely observed in the lower 5–10 cm. Small (1–2 cm) yellow, red, and green mottles are replaced by coarse (3–15 cm) grey, purple, yellow, and red mottles, the latter typically with yellow haloes.

BPS is relatively thick (80 cm), but only show weak evidence of pedogenic development in the form of small-scale (4–8 cm) slickensides and argillans. These were only observed in the 30 cm over MPS, with the upper 50 cm being considerably more massive and homogeneous in appearance than in other coeval profiles. A low angle clastic dike occurs at the boundary between BPS and the overlying sedimentary unit. BPS is interpreted as an Entisol.

Figure 4.18 SWI-CP. A) Photomicrograph of teardrop-shaped coprolite (MPA, A/B). B- D) Photomicrographs of variations in size and distribution of iron nodules in the Cg horizon of the MPS interval.

100

Table 4.12 CP paleosol summary table, SWI (see previous summary tables for more information).

SWI C Smooth, clear small clay skins and slickensides rare calcareous rhizotubules Protosol Entisol

Red-brown matrix, downward tapering diffuse purple mottles, yellow and red mottles, reduction Large purple rhizohaloes, A/B wavy, abrupt Vertisol Vertisol spots, Fe nodules, slickensides, Fe rhizotubules blocky structure, rare calcareous glaebules Red-brown matrix, slickensides, Bw diffuse blocky structure, yellow mottles fine white rhizohaloes and reduction spots Coalescing powdery carbonate glaebules, slickensides, reduction Bk diffuse spots, blocky structure, red- brown matrix porphyroskelic mosepic microfabric, teardrop-shaped rare carbonate nodules, large coprolite, organic fragments, 33.6% (49.3% Kaolinite, Bss1 diffuse greyish mottle, blocky structure, sand sized carbonate nodules, 11.0% Chlorite) slickensides, red-brown matrix abundant Fe in matrix and nodules yellow, red, and deep green rare calcareous Bss2 diffuse mottles, slickensides, blocky rhizoconcretions structure, red-brown matrix weak blocky structure, fining upward micaceous 19.1% (43.6% Kaolinite, Cg wavy, clear ferrans, granular to sandstone 14.2% Chlorite) intertextic, mosepic

101

102

103

Table 4.13 CP paleosol summary table, SEI-SE (see previous summary tables for more information).

Section Horizon Upper Boundary Macromorphology Micromorphology Ichnofossils Clay Mineralogy (<4mm) Classification (Mack) Classification (USDA) small slickensides and rare clay SEI C smooth, clear Protosol Entisol skins horizontal Fe-rimmed slickensides, blocky structure, red-porphyroskelic mosepic to calcareous rhizotubules, A/B wavy, abrupt brown matrix, coarse red and skelsepic, organic fragments, Vertisol Vertisol downward tapering diffuse yellow mottles abundant Fe nodules purple mottles blocky peds, Fe cored carbonate nodule, abundant Powdery calcareous mottles and small to large carbonate Bssk diffuse filaments, slickensides, blocky nodules and accumulations, structure Fe-rich matrix, few Fe nodules vertically oriented reduced slickensides, red-brown matrix, 24.4% (44.1% Kaolinite, 10% Bss1 diffuse rhizohaloes with organic blocky structure Chlorite) cores,

agglomeroplasmic to porphyroskelic insepic slickensides, red-brown matrix, microfabric, blocky structure, Bss2 diffuse blocky structure, yellow mottles, ferrans, significant sand-sized reduction spots fractions, small carbonate nodules, reduced zones

fining upward sand, clastic dikes, intertextic to Cg wavy, clear coarse red mottles occasionally agglomeroplasmic insepic Fe rhizotubules 18.1% (44.3% Kaolinite) with yellow haloes microfabric, small Fe nodules

platy structure, clay skins, few 25.8% (30.5% Kaolinite, SE C smooth, clear small slickensides, coarse green Protosol Entisol 17.2% Chlorite) mottles

porphyoskelic mosepic thick, downward tapering blocky structure, large microfabric, rare clay purple rhizohaloes, abundant A/B diffuse Vertisol Vertisol intersecting slickensides infillings, rare small carbonate small organic cored nodules, redox mottling rhizohaloes

porphyroskelic insepic Stage I calcic horizon, powdery Fe rhizotubule, yellow microfabric, common circular Bssk diffuse calcareous grey mottles (coarse, rhizohaloes with red cores, carbonate nodules, variably vertically oriented) reduced rhizohaloes sized Fe nodules porphyroskelic mosepic microfabric, blocky peds, blocky structure, large Bss diffuse thick ferrans, Fe nodules, 29.4% (41.7% Kaolinite) intersecting slickensides reduction spots, rare small carbonate nodules blueish grey (5B 5/1) sand, fining Cg wavy, clear upward, slickensides, coarse red mottles

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5 DISCUSSION

5.1 Soil-Forming Factors

The physical and chemical properties of paleosols and bounding sedimentary units provide a record of landscape evolution in the study area. Paleosols vary in degree and dominance of pedogenic development and processes. Paleosol B horizons are particularly useful for interpreting soil-forming conditions due to the fact that they reflect significant alteration of the parent material over extended periods of time, including accumulations of clays and iron oxides and the development of soil structure. Soil B horizons are the most important part of a soil profile for recognizing pedological features required for soil classification (Brady and Weil, 2010). Furthermore, B horizons have a relatively high preservation potential, unlike overlying organic-rich A horizons, which may be lost to erosion (Kraus, 1999). These variations suggest hydrological differences related to topography and channel position as well as broader changes in climate.

5.1.1 Parent Material

The specific clay minerals present in B horizons are partially controlled by precipitation, with greater precipitation correlating to mineral species of lesser silica content (Retallack, 1997; Brady and Weil, 2010; Chapin III et al., 2011). Since clay mineralogy is mostly stable once a soil is buried, the relative abundance of mineral species reflects conditions during soil formation where paleosols are unaffected by

105 metamorphism (Trendell, 2013). Clay mineralogy is also controlled by parent material composition, so an understanding of the geologic setting and samples taken from C or R horizons are necessary to put mineralogical analysis in context. The clay mineral weathering pattern of kaolinite  smectite  vermiculite  chlorite and mixed-layer phyllosilicate  illite and mica is generally suggestive of climatic conditions grading from hot and humid to cool and dry (Sheldon and Tabor, 2009). While many of the paleosol B horizons in the study area show a relatively high abundance of kaolinite with illite and mica, these values are also generally elevated in samples of the parent material

(Table 4.2). Both mica and kaolinite are also abundant in non-pedogenically altered

Dunkard deposits (Martin, 1998). Smectite is found in significantly greater abundance in

B horizons relative to C horizons (Table 4.3). This suggests a pedogenic origin for smectite, unlike kaolinite, illite, and mica, which were at least partially inherited from the parent material.

Soils formed on alluvium, which includes the paleosols in the study area, usually have inherited some secondary minerals from the parent material (Brady and Weil, 2010).

Paleosol interpretations based on clay mineralolgy, therefore, need to take parent material into account and recognize that the some of the original heterogeneity in alluvial parent materials may be obscured as a soil matures (Retallack, 2001). The well-developed paleosol profiles in the study area fine upwards from sandstone to mudstone. This would have originally been a parent material of unconsoloidated and poorly sorted micaceous sandy alluvium deposited on the proximal floodplain. If soil development occurred during migration of the river away from the profile or following avulsion, intermittent

106 additions of progressively finer grained materials would be expected, although no relict sedimentary structures survived, suggesting sedimentation was outpaced by pedogenesis

(Kraus, 1999; Hasiotis, 2002).

5.1.2 Climate

Paleosols in the study area reflect changes in the amount and distribution of precipitation. Mean annual precipitation (MAP), drainage, and seasonality are interpreted

(Fig 5.1) through qualitative and semi-quantitative characteristics such as the presence of pedogenic carbonate (Mack and James, 1992; Retallack, 2000; Sheldon and Tabor, 2009;

Brady and Weil, 2010), iron mobilization features (Brady and Weil, 2010), and the degree of chemical weathering (Sheldon et al., 2002; Nordt and Driese, 2010).

Pedogenic carbonate accumulates over wide ranges of MAP, but will not form in extremely arid or humid climates (Retallack, 2000; Royer, 2000; Cecil and Dulong, 2003;

Brady and Weil, 2010; Torres and Gaines, 2013). Furthermore, its presence implies seasonal precipitation and some degree of aridity (Sheldon and Tabor, 2009; Breecker,

2010; Torres and Gaines, 2013). Pedogenic carbonate has been observed in soils with

MAP ranging a few hundred millimeters to nearly 1000 mm (Kraus and Hasiotis, 2006), with the greatest concentrations of solute found in soils of semiarid to subhumid climates

(Cecil and Dulong, 2003). Soil Bk horizons are conspicuous illuvial carbonate accumulations that develop in response to alternating wet and dry periods in a manner which is controlled by temperature and precipitation (Retallack, 2001; Hembree and

Nadon, 2011). Calcium carbonate is mobilized during wet periods, when it enters into

107 soil solution and is transported downward through the profile (Brady and Weil, 2010;

Chapin III et al., 2011). As conditions become drier, carbonates precipitate at a depth which generally correlates to MAP (Mack and James, 1992; Retallack, 2001). Soil Bk horizons in the study area vary widely in degree of development, but carbonate is present in nearly every paleosol studied.

Ground water carbonate, which is often difficult to differentiate from soil carbonate accumulations resulting from the downward movement of rainwater (Kraus,

1999), has been observed in modern Vertisols on the Mississippi River floodplain with

MAP in excess of 1500 mm/yr (Aslan and Autin, 1998). Carbonate-rich water rises through soil pores by capillary action, precipitating carbonate at and above the seasonal high water table. The possible influence of a fluctuating water table needs to be considered when attempting to understand the climatic implications of carbonate in the study area, especially in the case of MPS profiles, since these have relatively high MAP estimates (Table 4.7) and are well developed enough to have had the opportunity for significant leaching.

Pedogenic carbonates tend to be micritic, while groundwater carbonate is more often sparry or bladed (Retallack, 2001). Bk horizons of MPS paleosols are micritic.

However, pedogenic carbonates are precipitated at greater depth and are less developed with greater precipitation (Brady and Weil, 2010). The high MAP estimates for MPS profiles suggest that carbonate should be deep and poorly developed within these soils, if present at all (Aslan and Autin, 1998; Retallack, 2001). Ground water carbonate is often either symmetrically distributed or forms a flat base with an upward increase in carbonate

108 content (Tanner, 2010). This does not seem to describe Bk horizons in MPS profiles.

Ground water carbonate also tends to fill voids and cavities, such as root channels, as groundwater is pulled upward by capillary draw (Alonso-Zarsa, 2003). The vertical orientation of many calcareous mottles in MPS profiles suggests that this type of process may have produced Bk horizons in MPS paleosols; however, the absence of clear redoximorphic features at and below the Bk horizons in all MPS profiles makes a pedogenic origin possible, since more conspicuous gley features would be expected if the water table was raised to the level of the Bk horizons for an extended period (Alonso-

Zarsa, 2003). While SE-CP and NWI-CP exhibit mottling that might be attributed to water table fluctuations up to the base of Bk horizons, this is not observed in other MPS profiles with Bk horizons.

Although the Bk horizon development in MPS profile never exceeds Stage I of

Machete (1985), it occupies a shallow position (~60 cm) in the profile compared to the well-developed and deep (~3 m) Bk horizon of P9b. The latter profile was better drained and interpreted to reflect drier climatic conditions than MPS profiles do, so it is worth considering the significant differences in depth and development. Drier conditions would also have meant a greater input of carbonate, since soil carbonate is largely windblown in origin (Mack and James, 1992). While this does not reconcile differences in Bk horizon depth between MPS profiles and P9b, it does help to account for differences in carbonate content, especially considering the high MAP estimates for MPS profiles. In fact, some work has suggested that precipitation estimates for MPS profiles exceeds upper limits for

109 the pedogenic carbonate (Aslan and Autin, 1998; Retallack, 2000; Kraus and Hasiotis,

2006).

Considering all the evidence for both pedogenic and ground water origins of carbonate in MPS profiles, neither explanation seems entirely satisfactory. Soils may exhibit a mix of pedogenic carbonate (i.e. alluvial) and ground water carbonate, especially in seasonally dry floodplain soils (Retallack, 2001; Alonso-Zarsa, 2003).

Furthermore, pedogenic carbonate and may reflect a polygenetic history to MPS profiles, with Bk horizons developing during a drier period followed by a transition to more humid conditions that resulted in leaching of these relict features (Tanner, 2010). Unfortunately, there is insufficient evidence to support a polygenetic origin for MPS carbonate and the presence of weakly developed Bk horizons in MPS profiles remains problematic.

The distribution and redox state of iron throughout the matrix of a paleosol can be recognized by the profile’s color, and is related to former drainage conditions (Kraus,

1999; Retallack, 2001; Vepraskas, 2001; Kraus and Hasiotis, 2006) and MAP, although a robust model for quantitative MAP estimation based solely on iron content does not currently exist (Sheldon and Tabor, 2009). Abundant oxidized iron (i.e. hematite) results in a red matrix (e.g. P5a and P9b), whereas increasing amounts of goethite result in brown (P8b) to yellow (mottling in P9c) colors (Kraus and Hasiotis, 2006). If hematite is widely dispersed and goethite is absent, the result is a purple matrix (i.e. P2 and P9c)

(Wright et al., 2000; Kraus 2001). Paleosols developed under reducing conditions are commonly green or grey (P3a), resulting from the mobilization and removal of Fe from the profile (Retallack, 2001; Brady and Weil, 2010; Trendell et al., 2013). Iron and

110 manganese nodules and rhizotubules reflect fluctuating hydrological conditions, forming as a result of the mobilization of Fe and Mn during water saturated periods and precipitation of oxides during dry periods (Vepraskas, 2001). This same process results in the formation of Fe and Mn rims around reduced rhizohaloes and reduction mottles in the paleosol matrix (Torres and Gaines, 2013; Trendell et al., 2013). Often, Fe concentrations in the form of high chroma mottles and rhizohaloes, Fe rhizotubules, and dark to greenish grey mottles with red, yellow, or orange rims will form near organic-rich A horizons

(Vepraskas, 2001). In contrast, low chroma mottling is associated with water table fluctuations, and may be found with or beneath groundwater carbonate accumulations

(Mack and James, 1992; Vepraskas, 2001).

MAP can be semi-quantitatively estimated using the CIA-K and CALMAG weathering indices (Tables 4.2, 4.7) (Sheldon et al., 2002; Nordt and Driese, 2010b).

Sheldon et al. (2002) introduced an empirical study of a modern climosequence, where

MAP was compared to bulk geochemistry of 126 soils. Their findings revealed a robust relationship (R2=0.72) between CIA-K (Table 3.2) and MAP. Nordt and Driese (2010b) conducted a similar study, but focused exclusively on Vertisols. They found that a new weathering index, CALMAG (Table 3.2), provided an even more robust (R2=0.90) relationship with MAP. Topographic lows were used exclusively for the study, since these best reflect climate-sensitive chemical properties (Driese et al., 2005). Although

MAP was calculated for all Vertisols in the study area regardless of inferred topographic relief (Tables 4.2, 4.7), the tightly constrained estimates for CP profiles suggest that this is not a significant methodological concern. Due to the more robust relationship with

111

MAP provided by the CALMAG index, this proxy was used to report MAP for all paleosols interpreted as Vertisols in the study area. The CIA-K paleoprecipitation proxy was used to report MAP in other soil orders, but both CALMAG and CIA-K were calculated for each paleosol. Because differences in MAP are more tightly constrained between profiles interpreted to differ predominantly for autogenic reasons (i.e. MPS vs.

BPS), a single proxy may produce more reliable results when provenance has not changed changed. Nordt and Driese (2010b) explained that CALMAG values are largely inherited from parent materials, so it is likely that this single weathering index could be appropriately used to report MAP for all paleosols in the study area.

Developing an understanding of the annual distribution of precipitation during pedogenesis is just as important as MAP is to interpretations of local environmental conditions and paleoclimate. Strong seasonal differences in precipitation can result in drastically different paleosol properties than would be expected if the same MAP was evenly distributed throughout the year (Retallack, 2001; Driese and Ober, 2005; Sheldon and Tabor, 2009; Cecil, 2013; Trendell et al., 2013). Soils enriched in soluble cations and exhibiting Fe and Mn mobilization are suggestive of a strongly seasonal climate

(Retallack, 2001; Torres and Gaines, 2013). In less mature soils with high concentrations of smectite, slickensides and other vertic features will develop if there is an extended dry season (Torres and Gaines, 2013; Trendell et al., 2013). Modern smectite-rich soils are additionally characterized by a high pH and base cation activity, and develop in intermittently poorly drained environments (e.g. monsoonal), often in association with hematite and calcite (Sheldon and Tabor, 2009; Brady and Weil, 2010; Torres and

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Gaines, 2013). In general, soils developed under a monsoonal climate contain small, dispersed carbonate nodules as well as ferruginous and calcareous concretions, sometimes interlayered (Retallack, 2001; Vepraskas, 2001; Sheldon, 2005; Sheldon and

Tabor, 2009).

Differences in quantity and distribution of precipitation are also partly responsible for changes in sedimentation that may be reflected in the expression of polygenetic paleosols (Kraus, 1999; Torres and Gaines, 2013). Thick, cumulative profiles (i.e. P5) may develop during periods where slow, steady sedimentation is outpaced by pedogenesis (Kraus, 1999). Low sedimentation rates may be the result of reduced precipitation (Torres and Gaines, 2013); although Cecil and Dulong (2003) report the highest solid sediment discharge in dry, subhumid climates with pronounced seasonality.

Highly seasonal subhumid climates are interpreted to have prevailed during active pedogenic development of calcic-Vertisols in the study area. Frequent intense flooding may result in thinner compound and composite paleosols (Kraus, 1999; Torres and

Gaines, 2013). Interpretations based on the preservational style of alluvial paleosols must also take into account topography and floodplain position, however, since these factors will strongly influence the development of polygenetic paleosols (Aslan and Autin, 1998;

Kraus, 1999; Smith et al., 2008).

113

114 paleosols. MAP estimates were only made using imperfect to well drained Inceptisols and Vertisols. Drainage was estimated for all paleosols. Highlighting indicates the estimated strength of seasonality based on available physical and chemical evidence, and ranges from weak (blue) to very strong (red).

5.1.3 Topography

Since soils on the distal floodplain have more opportunity to develop, their properties will reflect a larger number of factors than soils on the more frequently disturbed proximal floodplain (Mack and James, 1992; Kraus, 1999; Sheldon and Tabor,

2009). Additionally, drainage tends to decline moving from the proximal floodplain to the distal floodplain resulting from the presence of finer sediments and a higher water table (Mack and James, 1992; Kraus, 1999; Smith et al., 2010). Poorly drained soils are commonly gleyed, showing evidence of reducing and anoxic conditions (e.g. Retallack,

2001; Sheldon and Tabor, 2009; Brady and Weil, 2010). Reducing and anoxic conditions mobilize ferrous iron, causing its depletion in waterlogged settings, provided the soil contains reducible iron, a microbial population capable of organic matter decomposition, and abundant organic carbon (Vepraskas, 2001; Driese and Ober, 2005; Kraus and

Hasiotis, 2006; Sheldon and Tabor, 2009; Brady and Weil, 2010; Atchley, 2013). Anoxia inhibits colonization by plants and animals, so bioturbation is limited in poorly drained lowlands like swamps or bogs (Retallack, 2001; Hasiotis, 2002). Intermittent waterlogging gives soil a mottled appearance and is ideal for the creation of subsurface carbonate accumulations (Retallack, 2001; Hembree and Nadon, 2011). Soils with well- developed horizons with features reflecting oxidizing conditions such as the presence of hematite form in well-drained settings (Kraus, 1999; Vepraskas, 2001; Sheldon and

115

Tabor, 2009). Deep roots and abundant bioturbation are also expected in well-drained soil

(Retallack, 1988; Kraus, 1999; Sheldon and Tabor, 2009). Soils exhibiting features consistent with good drainage form on topographic highs (Kraus, 1999), especially when underlain by sandy sediment (Brady and Weil 2010; Chapin III et al., 2011).

5.1.4 Biota

Rhizoliths are abundant in many Dunkard Group paleosols and provide specific environmental information depending on preservational style. While specific interpretations of floral assemblages are not possible based solely on rhizolith morphology, arborescent plants and groundcover are more likely to be responsible for larger rhizoliths and networks of fine rhizoliths, respectively (Hembree and Nadon,

2011). Rhizoliths are also useful in determining the position of the paleo-water table, revising MAP estimates, and as important clues as to former soil moisture and drainage conditions (Klappa, 1980; Kraus and Hasiotis, 2006; Smith et al., 2008; Trendell et al.,

2013).

Rhizohaloes are reflective of specific drainage conditions when diagenesis can be ruled out as the cause of mottling (Kraus and Hasiotis, 2006). Red mottles indicate moderate to well-drained soil due to the oxidizing conditions surrounding roots suggested by the presence of hematite (Smith et al., 2008; Trendell et al., 2013). Yellow mottles are indicative of the presence of the hydrated iron-oxide goethite, which is interpreted as representing imperfectly drained, frequently wet soil conditions (Kraus and Hasiotis,

2006; Hembree and Nadon, 2011). Green rhizohalo cores are created under reducing

116 conditions, with microbially mediated iron depletion around roots (Retallack, 2001;

Kraus and Hasiotis, 2006). Reduced rhizohaloes with iron enriched cores form in anoxic, gleyed soils that concentrate iron in oxygen-rich former root channels (Kraus and

Hasiotis, 2006). The presence of dark gray cores within green mottles suggests waterlogged, anoxic conditions favorable to the preservation of organic matter (Kraus and Hasiotis, 2006). Rhizoconcretions and rhizotubules provide evidence for periodic wetting and drying, forming in much the same manner as Bk horizons, with carbonates and iron oxides precipitating within root channels or around living roots (Smith et al.,

2008; Hembree and Nadon, 2011). Other morphological characteristics such as depth, branching, general architecture (i.e. predominantly vertical or horizontal growth), and size provide information about soil properties and paleoecology (Retallack, 2001;

Hasiotis, 2002). For example, tabular root systems are characteristic of poorly drained soils with a high water table, whereas deep roots suggest good drainage (Retallack,

1988).

5.2 Vertical Variability

The general section records the evolution of a terrestrial landscape under different climate and landscape stability regimes. Sandstone units in the study area typically exhibit ribbon or sheet architecture over large (km-scale) distances. This is consistent with previous interpretations that cycles of the upper fluvial plain facies province were deposited by a large, low-gradient anastomosing river (Martin, 1998).

117

The oldest strata, coal and organic-rich shale, reflect formation in well-vegetated distal lowlands with a high water table. The water table was at or above the surface of the landscape during development of P1, a Histosol, and conditions were at least locally reducing and anoxic, resulting in a relatively thick accumulation of organic matter

(Retallack, 2001; Brady and Weil, 2010). Acidic and reducing environmental conditions gave way to better drainage and predominantly alkaline soils, facilitated by both climatic drying and a transition to a more channel-proximal position on the paleolandscape.

Although drainage and redox state fluctuated during deposition and pedogenesis of the remaining general section units, no other paleosols are suggestive of the kind of waterlogged conditions implied by P1.

P2 has relatively high base loss values (Table 4.10), suggesting relatively high levels of leaching (Retallack, 2001; Sheldon and Tabor, 2009). Leaching requires the movement of water through the profile (Brady and Weil, 2010), so although Fe depletions and nodules suggest that the profile was frequently saturated, it was not always waterlogged. Iron depletions throughout the exposed profile suggest that the water table was at or above the top of P2 for an extended period of time (Vepraskas, 2001; Smith et al., 2008); however, the exact time required for iron reduction to commence is highly variable and depends on factors such as temperature and soil organic matter content

(Vepraskas, 2001). The depth of rhizoliths suggests that the upper 45 cm of the profile was at least moderately well drained during dry periods, since roots typically do not grow into permanently saturated soils (Retallack, 2001). The lack of abundant organic matter suggests that, although conditions were wet, they were not typically anoxic since

118 organic matter degrades rapidly in oxygenated soils (Retallack, 2001; Sheldon, 2005).

The purple matrix color is also usually attributed to imperfect drainage, dispersed hematite, and abundant organic matter (Kraus and Hasiotis, 2006; Trendell et al., 2013).

This suggests that the soil was organic-rich, although any organic carbon remaining after burial has been lost to early diagenesis (Retallack, 2001; Sheldon, 2005). Despite evidence for fluctuating drainage conditions, there are no features suggestive of regular desiccation, and an udic soil moisture regime is interpreted (Brady and Weil, 2010; Cecil,

2013). This is associated with moist subhumid climates with a significant wet season

(Cecil, 2013). In either case, the combined amount of precipitation and stored soil moisture is at least as great as the amount of water lost to evapotranspiration (Brady and

Weil, 2010; Cecil, 2013).

Caution is warranted in making paleoclimate interpretations based on poorly drained soils (Retallack, 2001). Although the profile was not always waterlogged or entirely gleyed, the evidence for imperfect drainage makes P2 of limited use in making large scale environmental interpretations. A possible autogenic explanation for the differences between P1 and P2 involves the lateral migration of a main river channel towards the profiles, resulting in a more proximal position on the floodplain, where a lower water table, higher sedimentation rates, and coarser grain size would allow drainage to be improved relative to P1 (Kraus, 1999; Hasiotis, 2002; Trendell et al.,

2013). Regardless of whether differences between P1 and P2 are due to climatic or fluvial processes, P2 does appear to follow a trend towards better drainage, increasing seasonality, and increasing aridity.

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Above P2, fluvial cycles become well-defined and repetitive. P3a is weakly developed, with large clastic dikes, burrows, and tabular calcareous rhizotubules, indicating high rates of sedimentation in a proximal setting with a typically high water table (Kraus, 1999; Retallack, 2001; Hasiotis, 2002; Smith et al., 2008). These characteristics are consistent with channel islands or bars between or adjacent to active river channels (Tooth et al., 2013). Sandstone beds up-section are locally densely bioturbated with or without accompanying tracks and trails, but do not necessarily show any clear pedogenic development.

Frequent flooding events in aggradational systems preclude pedogenesis due to high rates of sedimentation (Kraus, 1999). The abundance and morphology of burrows in many sandstone beds is consistent with bioturbation commonly associated with crevasse splay (Buatois and Mangano, 2001; Buatois and Mangano 2011). Although burrows are locally dense, the general lack of hydrophilic ichnofossils suggests a short window for colonization (Buatois and Mangano, 2011), which would be expected in a frequently disturbed setting prone to flooding (Smith et al., 2008). Where crosscutting does occur,

Scoyenia, which is well defined and striated, crosscuts Mermia and Cochlichnus, which are sinuous and poorly defined bedding plane traces. This transition suggests relatively rapid drying and burial. The relatively coarse grain size and stacked thin beds suggests a proximal location on the floodplain (Kraus, 1999; Smith et al., 2008).

Taking ichnological and sedimentological information into account, it appears that bioturbated sandstone beds represent discrete flooding events (Smith et al., 2008).

Flooding of the proximal floodplain resulted in the rapid deposition of organic rich

120 sediments that were exploited early on by hydrophilic organisms while the floodplain remained subaqueous (Hasiotis, 2002; Buatois and Mangano, 2011). As the floodplain dried, hygrophilic, and potentially terraphilic, organisms would exploit remaining food resources in an increasingly firm substrate (Hasiotis, 2002). Dewatering of sediments allowed details like scratch marks to be preserved, while oxygenation promoted deeper burrowing suggested by the vertical components of Scoyenia, Arenicolites, and Skolithos commonly found in the same firmground assemblages (Buatois and Mangano, 2001).

This further supports the interpretation that these units resulted from large crevasse splays, which are common in anastomosing river systems (Miall, 1985; Makaske, 2001).

A degree of landscape instability is indicated over the interval comprising P3 and

P4, where thin (~1 m) and truncated calcic-Vertisols are separated by outcrop-scale (≥ 0.5 km2) shale and sandstone bodies. The Vertisols are the first pedogenically altered beds to exhibit a strong seasonal signal.

Cycles through the remainder of the general section follow the same pattern.

Bioturbated micaceous sandstone fines upwards to a Cg-horizon. Fine-grained, overlapping B-horizons grade into a more densely rooted and mottled A/B horizon boundary. A smooth, clear upper boundary separates the thick, relatively well-developed profile from a weakly developed and genetically distinct C or Bw horizon. Above this, variegated red-brown and grey-green shale is truncated by the base of the next sandstone body. This cyclic pattern is interpreted as a result of the following sequence of events:

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A. Large-scale floods deposited coarse sediment on the proximal floodplain. These

deposits were quickly colonized by biota responsible for observed ichnofossils

(e.g. Scoyenia, Cochlichnus, Planolites, Arenicolites, Skolithos). Subaerial

exposure was generally brief until the gradational upper boundary. Evidence for

this includes the distinctness of ichnofossils and a general lack of pedogenic

development and rhizoliths.

B. Lateral channel migration resulted in the fining-upward trend and movement to a

distal floodplain setting leading to sufficient landscape stability for the formation

of relatively thick paleosol profiles.

C. Overlapping B horizons reflect dynamic environmental conditions specific to

each individual profile, but almost all exhibit evidence for seasonally distributed

precipitation

D. Avulsion shifted the channel and returned the profiles location to a more proximal

setting. This resulted in the truncation of A horizons and deposition of fine-

grained sediments. These sediments were weakly modified by pedogenic

processes.

E. Increased sedimentation outpaced pedogenesis, with generally unmodified shale

deposited on top of individual cycles.

F. A return to high energy conditions resulted in the erosion of the upper boundary

of the shale and deposition of coarse, clastic sediments.

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5.3 Lateral Variability

Coeval paleosol profiles are significantly more similar to each other than to other paleosols encountered through the vertical section. All coeval paleosols contain evidence of iron and carbonate mobilization and precipitation, rhizoliths, slickensides, and a reddish brown mottled matrix. In addition, burying sediments all show some degree of pedogenesis. Differences in the amount and distribution of pedogenic carbonate, iron, and rhizolith preservation, however, provide a higher resolution view of lateral changes in pedogenesis related primarily to different hydrological conditions. Those profiles containing abundant iron, especially NW-CP, formed under conditions of relatively poor drainage and frequent saturation. Profiles with more pronounced carbonate accumulations formed under conditions of better drainage (e.g. SWI-CP).

Since all eight profiles are Vertisols, significant variations in topography are expected (Fig 5.2), and not necessarily related to distance from an active channel

(Retallack, 2001; Nordt and Driese, 2010b). While the regional gradient during Dunkard deposition was estimated as having been 20 cm/km (Cecil, 2013), small-scale topographic differences almost certainly resulted from the characteristic gilgai topography associated with Vertisols. Retallack (2001) described the formation of nuram gilgai, characterized by equant mounds and depressions (up to 3 m deep), in low gradient settings. Gilgai are complex, and often contain features such as shelves and inner depressions (Retallack, 2001). This type of landscape exhibits differential pedogenic development between mounds and depressions (Nordt and Driese, 2010b).

Microtopographic highs are better drained by virtue of their higher position above the

123 water table, so deeper roots, more carbonate, less iron, and less mottling would be expected relative to profiles developed in depressions (Retallack, 2001; Driese and Ober,

2005). This heterogeneity in the landscape was likely responsible for a patchy distribution of vegetation, and likely accounts for some of the differences in rhizolith preservation (Retallack, 2001), although hydrology also played a key taphonomic role.

Since organic matter is concentrated in A horizons, roots near the tops of profiles have a better chance of being preserved as Fe rhizotubules or red rhizohaloes with reduced cores. This is due to reduced pH and Eh values in root channels, associated with surface water saturating the upper portion of profiles during wet seasons and the microbially mediated decomposition of organic matter (Kraus and Hasiotis, 2006). This process is responsible for iron mobilization in A/B horizons of CP profiles, which contain red rhizohaloes and more amorphous reduced mottles, which have been attributed to zones enriched in organic detritus (Vepraskas, 2001). Variations in pedogenic development of

BPS sediments is likely related to their spatial relationship to the active channel as well.

More distal profiles typically exhibit greater development than proximal profiles (Mack and James, 1992; Kraus, 1999; Smith et al., 2008), although this relationship is complicated by the topographic heterogeneity of the Vertisol-dominated paleolandscape.

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Figure 5.2 Interpreted topographic relationships of CP profiles. Red arrow points in the approximate direction of the paleochannel.

5.4 Paleoclimate

P1 and P2 lack strong evidence of a seasonal distribution of precipitation, although P2 does display features consistent with variable hydrologic conditions including redoximorphic features such as mottles and pedogenic iron nodules (Vepraskas,

2001; Brady and Weil, 2010). While climate interpretations would be more robust if the lateral extent of both were better constrained, conditions were at least locally humid, with soil moisture regimes ranging from aquic (P1) to udic (P2), probably having formed under a humid to moist subhumid precipitation regime (Cecil, 2013). Above this, most paleosols display clear evidence for strongly seasonal patterns of precipitation. P3 and P4 were likely developed under dry subhumid precipitation, with soil moisture in the better developed, distal expressions interpreted as ustic during pedogenesis (Cecil, 2013).

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The thick, cumulative profile, low CALMAG values and associated MAP estimates, abundant pedogenic carbonate, and deep rooting suggest P5a soils were well drained, with reduced precipitation and a more pronounced dry season during active pedogenesis (Retallack, 2001; Smith et al., 2008; Sheldon and Tabor, 2009; Breecker,

2010; Nordt and Driese, 2010b; Torres and Gaines, 2013). Although Fe in the profile suggests conditions were periodically saturated, this likely occurred over brief periods of heavy rainfall (Vepraskas, 2001). During this time period, monsoonal and strongly seasonal precipitation likely correlated with an ustic soil moisture regime (Sheldon and

Tabor, 2009; Cecil, 2013). The thickened profile and low MAP estimate relative to paleosols bounding P5 is similar to changes described in paleosols in and around the

PETM interval (Smith et al., 2008).

Conditions became progressively wetter through P7, a change which is supported by qualitative and quantitative differences up section. When comparing P5a, P6 and P7, there is less carbonate, more redoximorphic features such as mottling, more iron, shallower rhizoliths, more kaolinite (Table 4.3), and less smectite (Table 4.3) in each successively higher well-developed profile. P5b is excluded because poorly developed soils, like Entisols and Inceptisols, are mainly limited by time and their features are less representative of other soil-forming factors (Retallack, 2001; Brady and Weil, 2010).

Increasing humidity is further supported by a general trend of increased chemical weathering in Bss horizons from the three well-developed profiles (Table 4.2).

P8a and P8b contain elevated concentrations of kaolinite and mobilized iron relative to the underlying paleosols (Table 4.3). There is a significant clay size fraction to

126 both genetically distinct parts of the compound profile (Table 4.3), but P8b contains very little pedogenic carbonate and a greater number of hydromorphic features. MAP estimates are similar to P7 and P9 (Table 4.2), but the profile lacks indicators of strong seasonality (Retallack, 2001; Sheldon, 2005). Since vertic features are developed on the scale of decades to centuries (Trendell et al., 2013), and the profile contains a sufficient clay sized fraction including smectite (Table 4.2), the absence of these features in this profile suggests a more uniform distribution of annual precipitation. This trend continue through P9a and P9b, although the abundant carbonate, more homogeneously red matrix, low weathering values, and small amount of kaolinite suggest precipitation was reduced over the interval comprising P9b relative to P9a.

Above P9b, there is a pronounced return to evidence suggesting strongly seasonal conditions including large, intersecting slickensides in P9c. P9d also contains indicators of seasonality in the form of slickensides, pedogenic carbonate nodules, and clastic dikes.

MAP estimates and weathering indices are generally consistent with all but P5.

While cyclicity in the Dunkard basin is generally thought to reflect aperiodic and idiosyncratic autogenic fluvial processes, allogenic changes related to Milankovitch cycles have been invoked to explain cyclothems, especially those of the Pennsylvanian

(Cecil, 2013). During the Late Paleozoic Ice Age, cooler periods with the highest ice volumes and lowest sea level are correlated with highest precipitation. Although most evidence for drier conditions only loosely implies a connection to eustasy, intervals that seem to have been influenced by a changing climate (e.g. P5) do suggest that such a connection is plausible.

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5.5 Soil Ecosystems

Ichnofossil characteristics of both plant and animal trace makers, provide insight into the physical and biological properties of ecosystems (Hasiotis, 2002; Smith et al.,

2008; Buatois and Mangano, 2011). The diversity, abundance, and complexity of ichnofossils can provide insight into local physical environmental parameters such as drainage and substrate consistency as well as the state of ecological succession, soil pH, presence of environmental stresses, and temperature (Bardgett et al., 1998; Buatois and

Mangano, 2002; Smith et al 2008; Buatois and Mangano, 2011; Hembree and Nadon,

2011).

5.5.1 Plants

Primary producers form the base of terrestrial ecosystems, making them fundamental in understanding bottom up controls on ecosystem structure (Brady and

Weil, 2010). Plant communities are both reflective of and responsible for various environmental conditions (Retallack, 2001; Brady and Weil, 2010; Trendell et al., 2013).

Climate, time, frequency and magnitude of disturbance, local hydrological and sedimentological conditions, and nutrient availability are examples of external factors that, in part, determine what plants will live in a given location (Brady and Weil, 2010).

Once established, plant communities affect nutrient cycling, soil structure, chemistry, and local microclimate (Retallack, 2001; Brady and Weil, 2010). The same factors associated with certain plant communities are also strongly correlated with soil properties

(Retallack, 2001; Brady and Weil, 2010). Certain plants will preferentially grow in

128 settings associated with specific soil types, and exert a strong influence on pedogenesis in the soils in which they are rooted (Retallack, 2001; Brady and Weil, 2010). As a result, important environmental information is provided by the recognition of trends in ancient plant communities. Data obtained directly from fossil evidence and inferred from root traces and paleosol properties are critical to developing an understanding of changes in

Late Paleozoic terrestrial ecosystems (Retallack, 2001).

While the presence of certain types of plants may strongly indicate preexisting environmental conditions, it is important to understand how plants function as ecosystem engineers. Plants alter porosity and permeability through root pedoturbation (Retallack,

2001; Vepraskas, 2001). This alteration results in the formation of soil structure on a larger scale, and on a finer scale individual voids created by root paths allow infiltration of oxidizing waters to greater depth and provide a habitat for soil fauna (Retallack, 2001).

Water holding capacity is increased as plant-derived detritus decomposes and byproducts are incorporated into the substrate as soil organic matter (Brady and Weil, 2010). Plants also help to bind the sediment with their roots and associated mycorrhizal hyphae, resulting in greater landscape stability in well-rooted soils verse loose sediment (Bearden and Peterson, 2000).

The uptake of cations requires a trade to maintain equilibrium, generally by releasing hydrogen ions into soil solution, resulting in a lower pH (Retallack, 2001;

Brady and Weil, 2010). This is compounded by the litter plants produce. Conifer leaves tend to be nutrient poor and, since they are almost exclusively evergreen, cycle slowly since more leaves are retained from year to year (Brady and Weil, 2010; Chapin III et al.,

129

2011). The litter that is produced results in acidification as decomposition releases organic acids that are leached through the soil profile (Retallack, 2001; Brady and Weil,

2010). The high nutrient content and pH indicated by the physical and chemical features of the paleosols in the study area is suggestive of rapid nutrient cycling due to the quick turnover of less recalcitrant plant detritus. This rapid cycling occurs in modern grasslands, which are associated with Mollisols and Vertisols (Retallack, 2001; Brady and Weil, 2011). Vertisols have a high cation exchange capacity and base saturation by virtue of their parent materials, but over time, these characteristics may be lost to chemical weathering from precipitation and uptake by plants (Retallack, 2001). Plants that are characterized by rapid cycles of growth, death, and decay help to maintain high nutrient levels and a circumneutral pH (Brady and Weil, 2010; Chapin III et al., 2011).

While grasses did not yet exist in the Paleozoic, other plants may have performed a similar function. Sphenopsids, which included weedy taxa like Calamites, are a potential candidate for this, as they possessed subsurface rhizomes capable of regeneration after breakage of the exposed part of the plant. (Phillips, 1984; DiMichelle et al., 2006; Benton and Harper, 2009).

Pennsylvanian plant communities in the Tropical Euramerican province, which includes the study area, are subdivided into at least two major biomes (Phillips, 1984;

DiMichele, 2006). Wetlands are the best known and consist of coal swamp (i.e. P1) and floodplain wetland flora (i.e. P2), which grew in organic and mineral clastic substrates, respectively. Intermediate environments, such as clastic swamps, also existed. Floral assemblages in coal swamps were dominated by medullosean pteridosperms, and were

130 rounded out by locally common to abundant small arborescent lycopsids, or club-mosses

(DiMichelle et al., 2006). Calamites, which were arborescent horsetails, were present but not abundant (DiMichelle et al., 2006). Each group is represented by a low diversity of species in coal swamp settings (Phillips, 1984; DiMichele, 2006). Floodplain mudstone floral assemblages were mostly poorly rooted groundcover, including small sphenopsids, or horsetails, and ferns like Sphenopteris (Benton and Harper, 2009). These plants grew in weakly developed soils below arborescent taxa that include calamites, pteridosperms, and marattialian tree ferns (DiMichele et al., 2006). Calamites was particularly well adapted to frequently disturbed proximal floodplain settings, possessing a subsurface rhizome capable of regrowth after subaerial breakage and shallow burial post-flood (e.g.

Benton and Harper, 2009; Trendell et al., 2013). By the early to middle Permian, however, wetland assemblages had become depauperate, often represented by monospecific assemblages of tree ferns (DiMichelle, 2006; Benton and Harper, 2009).

These benefited from widespread spore dispersal, allowing them to jump between wetter areas over the increasingly dry landscape (Phillips, 1984; DiMichele et al., 2006).

Seasonally dry environments were taxonomically distinct from wetland settings with very little overlap in community composition (Bashforth et al., 2014; DiMichele et al., 2006). Early seed plants with more substantial roots define this biome. Specifically, seed ferns, ferns, and conifers were most abundant (DiMichelle et al., 2006; Benton and

Harper, 2009). Dryland ferns and seed ferns replaced lycopsids in floodplain wetland biomes by the end of the Pennsylvanian (Benton and Harper, 2009). Conifer derived

131 charcoal suggests wildfires were relatively common in dry uplands and seasonally dry lowlands, potentially related to atmospheric O2 levels (Rothwell et al., 1997).

Floral communities experienced an important turnover after the Pennsylvanian

(DiMichelle, 2006). Early conifers inhabited well-drained uplands such as valley sides

(Rothwell et al., 1997), but moved into floodplains during periods of decreased MAP and increased seasonality of precipitation (Bashforth et al., 2014). Increasingly strong indicators of seasonality are observed in Late Pennsylvanian and early Permian strata

(Cecil, 2013; Fedorko and Skema, 2013). A drying trend is indicated by paleopedological, geochemical, and paleontological data, with relatively widespread aridity by the Late Permian (Benton and Harper, 2009; Cecil, 2013; Fedorko and Skema,

2013). In general, this transition first occurred at high latitudes during the Carboniferous, with change reaching the tropics at the Penn-Perm transition (Rothwell et al., 1997;

DiMichele et al., 2006). Environmental changes, including a turnover in vegetation, appear to have been rapid (Retallack, 2006).

Studies have indicated that while both warming and drying occurred, the increase in aridity was more important to driving changes in vegetation (DiMichelle, 2006;

Benton and Harper, 2009). Precipitation patterns related to glacially controlled atmospheric and oceanic circulation were important throughout the Pennsylvanian, but large-scale drying during the Permian, especially within the interior of Pangaea, seems to have been compounded by tectonism (Phillips, 1984). Most significantly, drying correlates with a reduction in primary productivity (Cecil, 2013), although the abundant

132 rhizoliths observed in P5, the “driest” profile, do not necessarily suggest any obvious reduction in biomass.

During the Permian, contraction of wetlands allowed dryland flora from uplands and higher latitudes to track into floodplains (DiMichele et al., 2006). Early Permian plants were tolerant of seasonal drought and a low water table (Benton and Harper,

2009). Plant communities along permanent streams decreased in species richness, with weedy forms and riparian specialists defining these settings (DiMichele et al., 2006,

Trendell et al., 2013). Because of their proximal location, these plants needed to be tolerant to both flooding and burial. Fragmentation of wetlands resulted in the trend towards tree fern dominance (DiMichelle, 2006; Benton and Harper, 2009). These plants grew rapidly, requiring a minimal resource allocation to height ratio and had large fronds with many tiny spores ideal for widespread dispersal (DiMichele et al. 2006).

Sphenopsids continued to exploit frequently disturbed streamside habitats (Benton and

Harper, 2009; Trendell et al., 2013).

This differentiation of wet and dry flora is an important consideration when interpreting root traces and plant body fossils, since these likely did not belong to the same plant assemblages. Thick paleosols developed on distal floodplains with a seasonally dry climate likely hosted more drought- tolerant flora that was more limited by moisture than the ability to survive frequent disturbance due to floods (Benton and

Harper, 2009).

Plant impressions from the study area, which are common in red shale, grey-green siltstone, and micaceous sandstone, represent classic Pennsylvanian-Permian floral

133 assemblages including tree ferns ( Pecopteris), seed ferns (Neuropteris), conifers

(Cordaites), and horsetails ( Calamites), but are likely most representative of proximal vegetation along a riparian corridor (Benton and Harper, 2009; Trendell et al., 2013).

Individual leaves are most common in fine-grained facies, but more complete trees are preserved in the higher energy sandstones. Neuropteris is restricted to fine-grained overbank deposits such as the shale underlying marker sandstone beds and overlying paleosols. Calamites was only observed on the bedding planes of coarse sandstone, although small stem fragments of the sphenopsid could potentially be confused with those of Cordaites leaves. The bedding plane exposures in which plant impressions are found, however, are virtually always restricted to float limiting the ability to identify stratigraphic changes in plant communities through the general section.

5.5.2 Soil Animals

Soil animals are an integral part of soil systems, responding to and creating physical and chemical changes in soils in many ways (Retallack, 2001; Buatois and

Mangano, 2011). Hole (1981) identified twelve animal behaviors which most strongly affect soil properties. These include mounding, homogenization, open and backfilled burrow formation, ped creation and destruction, regulation of soil erosion, increasing decomposition rates, altering air and water conductivity, and the addition of biological material. These activities strongly affect and are strongly affected by faunal and floral community composition, with primary productivity directly correlating with arthropod diversity (Sheldon and Tabor, 2009). Paleosol animal ichnofossils are commonly

134 attributed to the feeding and dwelling of invertebrates (Hasiotis, 2002; Buatois and

Mangano, 2010; Buatois and Mangano, 2011); however, vertebrate aestivation and dwelling structures have also been described from Late Pennsylvanian and Permian paleosols (Hembree et al., 2004; Hembree and Nadon, 2011).

The nutrient-rich and vegetated terrestrial environments represented by the paleosols of the study area should have been able to host a diverse soil fauna, but little concrete evidence of their presence has been preserved. Changes in hydrological conditions play a significant role in ichnofossil preservation in paleosols (Sheldon and

Tabor, 2009). Such processes likely account for the rarity of ichnofossils in the paleosols of the study area. The only clear ichnofossils that can confidently be attributed to animals in a lithology other than sandstone are Isopodichnus, which was identified in both sandstone and red shale, and Naktodemasis which was identified in the Bss1 horizon of

P3b. Isopodichnus is interpreted as the grazing trace of a bilobate arthropod (Hasiotis,

2002; Buatois and Mangano, 2011) or gastropod (Hasiotis, 2002) whereas Naktodemasis is interpreted as an actively filled burrow of a larval arthropod (Smith et al, 2008).

Neoichnological studies identified a similar morphology (e.g. dense, thin arcuate menisci) in the burrows of hemipteran and coleopteran larvae (Hasiotis, 2002; Smith et al., 2008). In addition, concentrations of sand-sized iron nodules within linear features in paleosol thin sections are interpreted as potential evidence of soil animal burrowing and defecation, with iron nodules forming around a coprolite nucleus during early diagenesis

(e.g. Retallack, 2001).

135

Roots and burrows often display similar morphologies, and there may be no characteristics with which to distinguish the two (Retallack, 2001). In addition, pedoturbation due to wetting and drying of soils rich in expandable clays can create features that are morphologically similar to those produced by biota. Although the origin of such features may be uncertain, they can provide insight into environmental conditions. This is evident in the simple, vertically oriented reduced pedotubules of P5.

Although they neither taper or branch downward, the deep penetration and reduction in an otherwise oxidized matrix is strongly suggestive of a hygrophilic organism as the tracemaker (Smith et al., 2008). Reduction was likely caused by the decay of organic matter, likely either a root or burrow lining (Vepraskas, 2001; Kraus and Hasiotis, 2006).

Deep pedotubules suggest oxidizing conditions and a low water table (Retallack, 2001;

Hasiotis, 2002).

Although animal ichnofossils are rare in the paleosols, tracks, trails, and burrows are common in crevasse splay deposits. Typically these are most easily explained as arthropod locomotion, feeding, and dwelling. Sandstones are dominated by horizontal and vertical expressions of Scoyenia and Arenicolites. Trails are less common but are locally abundant. Larger Cochlichnus and Mermia are occasionally preserved with other tracks and trails. This is interpreted as a transition from a flooded softground, characterized by the Mermia ichnofacies, to a desiccated overbank firmground, characterized by the Scoyenia ichnofacies (Buatois and Mangano, 2001; Buatois and

Mangano, 2011). The traces are distinct and do not generally overlap, suggesting that most of the individual sandstone beds represent distinct flooding events and a relatively

136 short amount of time in which they were subaerially exposed (Hasiotis, 2002; Buatois and Mangano, 2011).

Considering abundance of arthropods in adjacent environments inferred from the sandstone beds, it is likely that these and other soil organism played an important role in soil formation. For most of the time the study area would have been a fertile, well- vegetated floodplain, capable of supporting a diverse community of plants and animals both above- and below-ground.

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6 CONCLUSION

Lateral differences in the properties of coeval paleosols were slight relative to the diversity of paleosols encountered through the entire vertical exposure. MPS paleosols are seasonally well-drained Vertisols with evidence of relatively high soil moisture content (Nordt and Driese, 2010b; Cecil, 2013). Iron nodules and rhizotubules, redox concentrations, and reduced rhizohaloes are evidence of periodic saturation and surface water gley (Kraus and Hasiotis, 2006; Vepraskas, 2013). Differences in the properties of the coeval paleosols are interpreted to primarily reflect differences in drainage. This is most easily recognized by the ratio of carbonate to iron and in rhizohalo preservational style. Through consideration of these features, differences in topography related to gilgai microrelief can be inferred. Iron-enriched profiles like NW-CP formed in poorly drained topographic lows, while profiles like SWI-CP that are enriched in carbonate formed on topographic highs. Differences in pedogenic development of BPS profile are suggestive of paleocatena-like relationships, with poorly-developed profiles, such as SE-CP, forming in proximal locations, and better-developed profiles, like NW-CP, forming in more distal locations (Kraus, 1999; Trendell et al., 2013). This is potentially complicated by the presence of gilgai, but there is a trend of greater BPS development to the northwest, regardless of interpreted MPS drainage condtions.

In contrast to the coeval paleosols, a great deal of variation exists in general section paleosols. While proximal, poorly developed (e.g. P3a, P5a, P6a, P9a) and poorly drained (e.g. P1) paleosols are probably more reflective of local floodplain conditions

(Aslan and Autin, 1998; Retallack, 2001), thick, better drained profiles (e.g. P5a, P6, P7,

138

P9b) may provide insight into climatic conditions during active pedogenesis (Retallack,

2001). Physical properties such as pedogenic carbonate and slickensides and chemical properties including clay mineralogy (Table 4.3 and 4.8) and chemical weathering indices

(Tables 4.2 and 4.7), of general section paleosols suggest that variable drainage due to position on the floodplain may not be enough to fully explain differences encountered through the entire vertical exposure. Cyclicity appears to have been predominantly controlled by avulsion, the primary fluvial process by which anastomosing rivers change through time (Makaske, 2001), but overprinted by climate. While climatic drying from the Pennsylvanian to the Permian as a general trend is well established (e.g. Martin,

1998; DiMichelle, 2006), smaller scale fluctuations appear to have contributed to paleosol properties.

Ichnofossil assemblages in paleosols were essentially restricted to various modes of rhizolith preservation. Fine, often microscopic, red rhizohaloes with reduced cores and horizontally branching green rhizohaloes were often the only ichnofossils in the poorly developed paleosols. Gleyed, sandy paleosols contain larger, horizontally branching calcareous rhizotubules and shallow, downward tapering rhizoconcretions. Better developed and better drained paleosols were more likely to have larger, vertically oriented rhizohaloes, especially in A/B horizons.

While rhizoliths are of limited use in paleoecological reconstruction, they are extremely valuable in estimates of paleodrainage. Where one form is truncated at a horizon boundary characterized by another dominant preservational style, changes in drainage through time can be recognized. This is the case in the transition from P3a to

139

P3b, where tabular rhizoliths suggestive of a high water table (Retallack, 2001; Hasiotis,

2002) are truncated at the upper boundary with a red-brown mudstone. The mudstone contains reduced rhizohaloes, which suggests seasonal saturation and surface water gley followed by drier periods with improved drainage. Considering sedimentology, pedogenic features like carbonate nodules and clastic dikes, weathering indices, and clay mineralogy, an autogenic origin for differences between P3a and P3b can be inferred.

Excluding chemical differences produced by gley processes, the weathering indices and mineralogical properties are very similar and both P3a and P3b show evidence of a strongly seasonal climate. Avulsion is the most likely cause of this change, with better developed, fine grained soils forming after channel switching moved the profile into a more distal position on the floodplain (Kraus, 1999).

The dominance of calcareous Vertisols in the upper fluvial plain facies province, and the interpretation that these paleosols represent strongly seasonal conditions, is consistent with previous research (Cecil, 2013; Fedorko and Skema, 2013). Thorough investigation suggests, however, significantly more humid conditions than the arid to semiarid conditions suggested by previous researchers (e.g. Martin, 1998; Cecil, 2013).

Sheldon (2005) cautioned against wholesale interpretations of red beds as indicators of aridity. Although strong indications of seasonal drying such as slickensides and pedogenic carbonate were found throughout well-drained profiles, the combined physical and chemical properties suggest rainy seasons were more pronounced than expected.

Even when the CALMAG weathering index is used, MAP values (Table 4.2) never fall below 800 mm/yr (P5a). This MAP value is associated with a subhumid climate, in which

140 rainfall exceeds evapotranspiration 4–6 months out of the year (Chapin III et al., 2011).

CALMAG values for Vertisols range from 68 to 89 indicating udic to perudic soil moisture regimes (Nordt and Driese, 2010b).

Cecil (2013) suggested that autogenic fluvial processes dominated sedimentation in the upper fluvial plain facies province. While this generally seems to be true, it ignores the utility of paleopedology in recognizing climate fluctuations in these deposits. Some attempt has been made to correlate major units between the upper and lower fluvial plain facies province (Fedorko and Skema, 2013). If fluctuations in seasonality and precipitation inferred from paleosols in the study area could be compared to allogenic glacio-eustatic fluctuations, it is possible that Late Pennsylvanian-Early Permian paleoclimate models could be made more robust.

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APPENDIX 1: BULK GEOCHEMISTRY (GENERAL SECTION)

Oxides repoted as wt. %.

Paleosol Location Sample Horizon MnO Cr2O3 P2O5 TiO2 SO3 SrO BaO SiO2 TiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O Provenance LOI 2* -560 23 Bw 0.04 0.02 0.09 0.90 <0.01 0.02 0.08 51.60 0.90 23.00 11.18 0.37 2.01 0.27 3.47 0.04 7.09 3* -460 22 Cg 0.08 0.02 0.06 0.99 <0.01 0.01 0.06 63.90 0.99 17.95 6.17 0.30 1.86 0.86 2.55 0.06 5.48 3* -340 21 Bss 0.06 0.02 0.37 0.95 0.01 0.02 0.07 60.90 0.95 17.35 9.45 0.76 1.42 0.62 2.72 0.05 5.57 3 40 26 Bw 0.03 0.02 0.53 0.72 0.01 0.04 0.08 50.40 0.72 23.40 10.28 1.00 1.97 0.39 3.64 0.03 7.23 4* -80 20 Bw 0.03 0.02 0.13 0.87 0.01 0.02 0.08 52.60 0.87 23.70 8.08 0.58 2.04 0.28 3.68 0.04 7.24 4 120 27 Bw 0.28 0.01 0.11 0.51 0.02 0.02 0.04 31.20 0.51 11.00 7.02 23.60 1.20 0.27 1.80 0.05 22.57 5 360 28 C 0.04 0.02 0.07 0.80 <0.01 0.02 0.08 49.40 0.80 23.00 10.67 1.58 2.20 0.49 3.60 0.03 7.69 5 900 29 Bssk 0.08 0.02 0.76 0.76 0.02 0.04 0.09 49.40 0.76 17.65 8.82 6.02 1.63 0.56 3.96 0.04 9.28 5 980 30 A/B 0.09 0.02 0.86 0.76 0.03 0.04 0.08 50.10 0.76 17.70 9.65 5.43 1.72 0.60 4.05 0.04 8.63 5 1100 31 Bssk 0.08 0.02 0.57 0.76 0.02 0.04 0.08 51.40 0.76 17.00 8.08 6.00 1.92 0.65 3.91 0.04 9.05 6 1740 32 R 0.05 0.02 0.15 1.00 <0.01 0.02 0.08 55.50 1.00 21.10 8.98 0.58 2.52 0.64 3.22 0.05 6.63 6 1820 33 Cg 0.05 0.02 0.18 0.88 <0.01 0.03 0.07 49.90 0.88 20.60 14.74 0.55 2.48 0.44 3.17 0.04 6.7 6** 1860*** 25 Cg 0.06 0.01 0.06 0.95 <0.01 0.02 0.05 64.90 0.95 16.15 4.08 1.86 1.83 0.94 2.25 0.06 6.09 6** 1900*** 24 Bss 0.08 0.02 0.27 0.85 0.01 0.04 0.06 54.60 0.85 16.65 8.89 4.09 2.25 0.44 2.90 0.05 8.32 7 2280*** 9 Cg/R 0.12 0.01 0.18 0.97 <0.01 0.01 0.04 66.30 0.97 13.60 6.61 1.66 1.82 1.26 1.49 0.07 4.82 7 2400*** 8 Bss 0.02 0.02 0.12 1.01 0.02 0.03 0.06 55.50 1.01 21.10 9.88 0.29 1.22 0.57 2.42 0.05 6.77 7 2470*** 7 Bw 0.04 0.02 0.08 0.86 0.01 0.03 0.08 51.00 0.86 22.60 12.02 0.23 2.01 0.50 3.30 0.04 6.47 8 2720 34 Cg 0.06 0.02 0.15 0.97 0.16 0.02 0.06 59.40 0.97 19.45 4.86 2.31 1.88 0.80 2.59 0.05 7.2 8 2780 35 Bw 0.04 0.02 0.11 0.94 0.01 0.03 0.06 55.30 0.94 19.10 7.71 2.84 1.70 0.70 2.27 0.05 8.15 8 2900 36 Bt 0.03 0.02 0.13 0.96 0.02 0.03 0.07 55.90 0.96 20.60 9.15 0.34 1.84 0.65 2.87 0.05 6.39 9 3440 37 Bw 0.04 0.02 0.06 0.95 0.01 0.03 0.08 53.40 0.95 22.20 11.10 0.25 2.19 0.61 3.28 0.04 5.63 9 3900 38 Bk 0.13 0.02 0.21 0.80 0.04 0.05 0.06 51.20 0.80 16.50 8.23 6.76 2.36 0.57 2.72 0.05 9.68 9 4000 39 Bss 0.04 0.02 0.06 0.91 0.01 0.04 0.06 55.60 0.91 19.60 11.48 0.56 1.80 0.57 2.38 0.05 6.05 9 4160 40 Bw 0.03 0.02 0.28 0.94 0.02 0.02 0.08 55.00 0.94 22.60 7.50 0.56 2.18 0.55 3.59 0.04 5.93 *low NW trench **high NW trench ***approximate location

149

APPENDIX 2: BULK GEOCHEMISTRY (CP PROFILES)

Oxides repoted as wt. %.

Paleosol Location Sample Horizon MnO Cr2O3 P2O5 TiO2 SO3 SrO BaO SiO2 TiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O Provenance LOI NW -20 1 Bw 0.04 0.02 0.11 0.86 0.02 0.03 0.07 50.7 0.86 23.8 10.36 0.22 1.96 0.62 3.36 0.04 7.10 -100 2 Bss 0.02 0.02 0.7 0.99 0.03 0.05 0.07 54.1 0.99 21.4 9.89 1.08 1.42 0.65 2.39 0.05 6.78 -200 3 C/R 0.13 0.01 0.03 0.86 0.01 0.01 0.04 67.9 0.86 13.55 5.37 2.02 1.49 1.28 1.5 0.06 5.4 NWI -100 4 Bss 0.03 0.02 0.14 1.04 0.03 0.03 0.06 55.3 1.04 22.2 7.49 0.98 1.39 0.42 2.08 0.05 7.99 -200 5 C/R 0.06 0.02 0.73 0.95 0.03 0.02 0.06 57.1 0.95 18.6 9.76 1.24 2.42 0.71 2.26 0.05 5.68 NEI -80 6 Bss 0.04 0.02 0.21 1.02 <0.01 0.03 0.05 54.8 1.02 20.9 10.62 0.65 1.43 0.23 2.13 0.05 7.42 NE -40 7 Bw 0.03 0.02 0.07 0.89 <0.01 0.03 0.07 51.5 0.89 22 12.49 0.23 1.97 0.44 3.25 0.04 6.47 -120 8 Bss 0.02 0.02 0.17 1.03 0.01 0.03 0.06 56.1 1.03 21.4 8.71 0.43 1.34 0.48 2.41 0.05 6.77 -200 9 C/R 0.04 0.01 0.02 0.93 0.01 0.01 0.04 66.1 0.93 15.6 6.52 0.38 1.71 1.06 1.92 0.06 4.82 SW -60 10 Bw 0.04 0.02 0.05 0.99 0.01 0.03 0.08 54.8 0.99 23.2 7.71 0.2 2.13 0.57 3.62 0.04 6.6 -160 11 Bss 0.02 0.02 0.35 1.01 0.02 0.04 0.07 55.9 1.01 22.1 7.73 0.64 1.48 0.6 2.65 0.05 6.95 -260 12 C/R 0.06 0.01 0.04 0.96 <0.01 0.01 0.06 62.6 0.96 17 7.9 0.21 2.36 1.08 2.29 0.06 4.92 SWI -120 13 Bss 0.02 0.02 0.17 1.05 0.01 0.03 0.06 56 1.05 21.5 8.47 0.43 1.45 0.53 2.17 0.05 7.26 -180 14 C/R 0.03 0.01 0.1 1.03 0.01 0.02 0.06 60.8 1.03 20.1 5.47 0.28 2.08 0.88 2.52 0.05 5.95 SEI -120 15 Bss 0.02 0.02 0.16 1.06 0.01 0.03 0.06 58.8 1.06 21.8 5.53 0.65 1.53 0.26 2.55 0.05 7.4 -180 16 C 0.02 0.02 0.02 1.07 0.2 0.02 0.05 66 1.07 18.4 3.49 0.26 1.26 0.73 2.59 0.06 5.33 SE -20 17 Bw 0.04 0.02 0.08 0.86 0.01 0.03 0.08 51 0.86 22.6 12.02 0.23 2.01 0.5 3.3 0.04 6.87 -120 18 Bss 0.02 0.02 0.12 1.01 0.02 0.03 0.06 55.5 1.01 21.1 9.88 0.29 1.22 0.57 2.42 0.05 6.72 -200 19 C/R 0.12 0.01 0.18 0.97 <0.01 0.01 0.04 66.3 0.97 13.6 6.61 1.66 1.82 1.26 1.49 0.07 4.86

150

APPENDIX 3: WEATHERING INDICES THROUGH THE GENERAL SECTION

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Thesis and Dissertation Services ! !