STRATIGRAPHIC ARCHITECTURE AND AVULSION DEPOSITS OF A LOW NET- SAND CONTENT FLUVIAL SUCCESSION: LOWER WASATCH FORMATION, UINTA BASIN by Kassandra L. Sendziak A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology). Golden, Colorado Date _____________ Signed: ____________________________ Kassandra L. Sendziak Signed: ____________________________ Dr. David R. Pyles Thesis Advisor Golden, Colorado Date _____________ Signed: ____________________________ Dr. John D. Humphrey Professor and Head Department of Geology and Geological Engineering ii ABSTRACT This study documents the stratigraphic architecture of channel and floodplain strata of low net-sand content fluvial deposits in outcrops of the lower Wasatch Formation, Desolation Canyon, Uinta Basin, Utah. The lower Wasatch Formation has a net sand-content of 0.27 and contains predominantly floodplain strata (79% in the field area). Three types of crevasse splays are recognized in this field area based on their physical relationship to adjacent channel-belt strata. Associated coeval splays are laterally adjacent and are physically connected to a channel-belt element, indicating that the crevasse splay was deposited coeval with the channel fill. Unassociated splays are spatially isolated from channel-belt elements and are interpreted to represent a failed avulsion. Associated non-coeval splays underlie the channel-belt element and are interpreted to be genetically related to the overlying channel-belt element, and therefore are a record of a successful avulsion. Three distinct types of associated non-coeval splays are identified in this study area based on physical, observable characteristics: type I, type II, and type III. A conceptual model is proposed that describes longitudinal changes in associated non-coeval splay deposits where type I, type II, and type III splay units represent proximal, medial, and distal positions in splay deposits relative to the source channel, respectively. Decreases in the following characteristics of splays occur with increased distance from the source channel: (1) thickness of splay unit, (2) thickness and abundance of splay beds, (3) net-sand content, (4) grain size, and (5) erosion. The occurrence of floodplain and channel-belt strata in a vertical transect through the outcrop are evaluated to: (1) determine whether the dominant avulsion style is aggradational or incisional, and (2) relate channel story type (i.e. downstream versus lateral accreting) to avulsion style. The correlation between the abundance of splay beds and the abundance of overlying channel-belt elements is interpreted to indicate that the succession resulted from predominantly aggradational avulsion processes. The occurrence of splay beds below channel- iii belts containing predominantly downstream-accreting stories is interpreted to indicate that these channels resulted from predominantly aggradational avulsion processes. The lack of splay beds below channel-belts containing predominantly lateral-accreting stories is interpreted to indicate that these channels resulted from predominantly incisional avulsion processes. iv TABLE OF CONTENTS ABSTRACT ................................................................................................................................III LIST OF FIGURES ................................................................................................................... VI LIST OF TABLES ..................................................................................................................... VII ACKNOWLEDGEMENTS ....................................................................................................... VIII CHAPTER 1 INTRODUCTION ................................................................................................ 1 3.1 Lithofacies........................................................................................................... 9 3.2 Architectural and Hierarchical Fluvial Classification ............................................ 9 CHAPTER 4 ARCHITECTURE OF THE LOWER WASATCH FORMATION ..........................17 4.1 Channel-Belt Architecture ................................................................................. 17 4.1.1 Channel-Belt Elements ..................................................................................... 17 4.1.2 Channel-Belt Stories ......................................................................................... 18 4.2 Floodplain-Belt Architecture .............................................................................. 20 4.2.1 Floodplain-Belt Elements ...................................................................................20 4.2.2 Floodplain-Belt Stories .......................................................................................20 CHAPTER 5 CREVASSE SPLAY TYPES ..............................................................................26 CHAPTER 6 DISCUSSION ....................................................................................................31 6.1 Spatially Varying Characteristics of Associated Non-Coeval Splays (i.e. Avulsion Complexes) ....................................................................................................... 31 6.2 Upward Trends: Relationship between Floodplain and Channel-Belt Elements 33 CHAPTER 7 APPLICATIONS .................................................................................................40 CHAPTER 8 FUTURE WORK ................................................................................................43 CHAPTER 9 CONCLUSIONS.................................................................................................44 REFERENCES CITED ..............................................................................................................46 SUPPLEMENTAL FILES ..........................................................................................................52 v LIST OF FIGURES Figure 2.1 Location map of the Uinta Basin and chronostratigraphic chart of basin fill ......... 6 Figure 2.2 Topographic map of the study area ..................................................................... 7 Figure 2.3 Photographs of the study area ............................................................................ 8 Figure 3.1 Quantitative data of the lower Wasatch Formation in the field area ....................13 Figure 3.2 Lithofacies photographs .....................................................................................14 Figure 3.3 Three-level hierarchical classification scheme ...................................................15 Figure 4.1 Examples of downstream accreting channel-belt stories and elements ..............22 Figure 4.2 Examples of laterally accreting channel-belt stories and elements .....................23 Figure 4.3 Example of crevasse channel story ....................................................................24 Figure 4.4 Examples of crevasse-splays and floodplain-fine deposits .................................25 Figure 5.1 Field example and schematic diagram of an associated coeval splay ................28 Figure 5.2 Field examples and schematic diagram of associated non-coeval splays. .........29 Figure 5.3 Field examples and schematic diagram of unassociated splays. ........................30 Figure 6.1 Field example and schematic diagram of type I splays ......................................35 Figure 6.2 Field example and schematic diagram of type II splays......................................36 Figure 6.3 Field example and schematic diagram of type III splay s ....................................37 Figure 6.4 Schematic of spatially varying characteristics of associated non-coeval splays .38 Figure 6.5 Upward trends of the lower Wasatch Formation .................................................39 Figure 7.1 Gamma Ray signatures of associated non-coeval spaly types ...........................42 vi LIST OF TABLES Table 3.1 Lithofacies descriptions ......................................................................................14 vii ACKNOWLEDGEMENTS There are many people with whom this project would not have been possible. I am particularly grateful for the guidance of my advisor Dr. David Pyles. The knowledge and enthusiasm he shares for the scientific method have made me a better scientist, geologist, and critical thinker. I would also like to thank other members of my committee: Dr. Rick Sarg, committee-chair, for his support and guidance regarding coursework, research, and my future as a geologist; Dr. Bryan Bracken, for his time in and out of the field, mentoring, and support throughout this project; and Dr. Matthew Pranter, for his guidance and encouragement. I would like to express my greatest gratitude to Grace Ford. This project would not have started nor been completed without her encouragement and extraordinary mentoring in and out of the field. I wish to acknowledge Chelsea Philippe for her assistance in getting us safely down the river and through many days in the field, I might not have survived without her. Additional field assistance from Neil Sharp is also greatly appreciated. I would like to thank other members of the CoRE team for their support throughout this project: Jane Stammer, Jeremiah Moody; Greg Gordon; Charlie Rourke, Linda Martin, and Cathy Van Tassel. Finally, I would like to thank my parents, Linda and Walter Sendziak, most of all.