The Ethno Geology of Shiprock, Navajo Volcano Fields, New Mexico
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The ethno geology of Shiprock, Navajo Volcano Fields, New Mexico A Senior Capstone Project Presented to the Faculty of the Southwest Studies Department The Colorado College By Fransiska Kate Dannemann May 2012 Introduction The Navajo Nation of the Four Corners Region, United States, is currently the largest Native American tribe. Their traditional lands are filled with astounding geologic phenomena, which are often considered sacred, and thus inaccessible to non-Natives. These sacred lands are marked by legends and myths describing their cultural significance. Within the Navajo culture, myths exist to develop and maintain a sense of place as a form of establishing personal and societal identity (Semken 2005). In general, myths focus on expressing the limits and workings of the world as well as a cultural group’s place in nature with strong religious and ritual overtones. Due to these religious and or ritual overtones, myths are often transmitted orally within a ceremonial setting. Geologic phenomena and events are likely central aspects of cultural myths and legends due to two factors: a culture’s need to process and warn future generations of natural disasters, as well as the compelling desire to establish a sense of place (Masse et. al 2007, Cajete 2000). Strong connections between ancient myths and geologic phenomena are seen across the globe. Examples include the Delphic Oracle in Greece, where myths suggest that priestesses inhaled vapors rising from a chasm in the earth beneath her. Recent geologic investigation has revealed fault traces beneath the oracle, from which gasses could leak during seismic rupture events. The myth of the destruction of Atlantis is supported by dating and imaging of the 1625 BC super volcano Thera. In the Pacific Islands, stories abound regarding battles between the fire diety Pele and other gods, the historical dating of these battles corresponds to radiocarbon dating of scorched vegetation beneath lava sheets (Krajick, 2005). Currently, attention is being drawn to the Pacific Northwest, where aboriginal stories relate seismic events to battles between a great whale and a thunderbird. 1 Despite both the involved geologic history of the American Southwest, and the presence of several distinct Native American tribes living in this area, little attention has been given to potential connections between Native folklore and geologic formations. One possible explanation for this lack of geomythological research focusing in the American Southwest is the overwhelming amount of legends and tales about the area. In the words of Peter Nabokov, “one strategy that the Navajo employed to claim the Southwest as their motherland was to smother it with stories.” Because the Navajo peoples allege that they “emerged from the bowels of the earth in the Four Corners area of the Southwest to find their sacred landscape ready and waiting and already protected by their four sacred mountains,” it became necessary to weave a complex fabric of cultural tales and legends to support this creation story. These stories are of great importance to the Navajo people, who place great value upon establishing and understanding a sense of place. Gregory Cajete describes the cultural importance of both myth and land as he states, “In the same fashion as myth, land becomes an extension of the Native mind, for it is the place that holds memory.” Examining aboriginal myths from an ethno geologic perspective places emphasis upon the sense of place and cultural value associated with creation stories while geomythological analysis places emphasis upon the validity of these myths. Within the context of the American Southwest, several questions arise regarding the purpose of cultural stories regarding sacred places: Do Navajo creation myths serve to accurately describe historical geologic phenomenal? Or are geologic features used as a backdrop for communicating overarching cultural themes and ideas? This paper focuses on the mythology and colloquial stories regarding Shiprock, a diatreme with radiating dikes located in the Four Corners region, to better understand the Navajo connections between geologic formations and cultural associations. 2 Geology of the Shiprock Region Location The Navajo Volcanic Field of the Four Corners Region contains 50 to 80 volcanic necks, plugs and associated dikes (Semken, 2003). The field extends north to south from Gallup, NM to Mesa Verde, CO and east to west from the Monument upwarp to the San Juan Basin (Figure 1). These igneous features were emplaced within the 40-45 km thick crust of the Colorado Plateau, where sedimentary strata are underlain by Precambrian crystalline basement rock. Figure 1: Location of Navajo Volcanic Field (Williams, 1936) 3 Sedimentary Environment Six craton-wide unconformities mark the post-Precambrian stratigraphic record of North America (Sloss et. al, 1963). Each unconformity represents a stratigraphic sequence of a major seaway transgression and regression within the North American interior. The first of these sequences is the Sauk Sequence, which ranges in age from latest Precambrian to Early Ordovician. Sauk seas across the continental platform of western Laurentia deposited limestone and dolostones; however, erosion associated with seaway regression, removed most depositional evidence. This Precambrian to Early Ordovician unconformity is clearly seen in the Four Corners Region Stratigraphic Column (Figure Two). The Tippecanoe Sequence ranges in age from Middle Ordovician to Early Devonian, representing a shallow sea environment covering present-day Arizona, New Mexico, West Texas and northern Mexico. The Kaslaskia Sequence ranges in age from Early Devonian to Mississippian, representing a major marine transgression. Deposition throughout this sequence includes limestone and dolostone deposits (Leadville Limestone, Ouray Limestone). The interfingered calcareous shale and earthy limestone deposits of the Elbert Formation, and the glauconitic shales, dolomites, coals, evaporates and limestone of the Aneth formation, indicate several marine transgressions and regressions throughout the Kaskaskia (Turner, 1958; Baldridge, 2004). The Absaroka Sequence, ranging in age from Mississippian to Early Jurassic, deposited the first significant sandstones and shales in the Four Corners. This transgression, occurring simultaneously with Laurentian-Gondwana collision driven uplift, produced a diverse range in depositional environments. Red soil beds, created through iron oxidation, characterize the lithology of the Southwest during the Absaroka Sequence. Sandstones dominate formations throughout the Permian, represented in the Halgaito (red siltstone and mudstones), Cedar Mesa 4 Sandstone, Organ Rock (red mudstones), and the DeChelly Sandstone. These formations suggest paleoenvironments marked by an arid seacoast with mud and sand dune deserts, and Ancestral Rocky Mountain alluvial plains. Three Triassic formations: Moenkopi red mud and sandstones, Chinle mudstones, sandstones and limestones with petrified wood deposits and Wingate eolian erg sandstones, represent Absaroka sea regression and the development of alluvial plains and a transcontinental river drainage system. Wingate eolian sandstones represent the movement of the North American section of Pangea into the tradewind belt of the northern hemisphere, forming dune sands. The Zuni Sequence ranges in age from Middle Jurassic to middle Paleocene. A change in the Farallon Plate subduction angle produced an inland foreland basin, which flooded throughout the Cretaceous. The Western Interior Seaway extended from Utah and Arizona to Iowa and Missouri. The first major formation associated with the Western Interior Seaway is the Dakota Sandstone, which reflects a fluvial or deltaic depositional environment and associated tidal flats. Deposition of Mancos Shale implies a deepening of seawaters. The Point Lookout Sandstone, representing a deltaic depositional environment, reflects the recession of this seaway. A second transgression of the Western Interior Seaway, creating the Lewis Sea, is marked in the Cliff House Sandstone, Lewis Shale, and Pictured Cliffs Sandstone Formations, implying a similar deepening of seawaters over time. The Fruitland and Kirtland Formations, composed of mudstones, sandstones and coal, represent alluvial plain and coastal marsh depositional environments (Baldridge, 2004). The recession of the Lewis Sea marks the final time oceans covered the North American continent. Post-regression, sandstone, conglomerate and mudstone sediment (San Jose Formation, Nacimiento Formation, Ojo Alamo Sandstone) represent continental alluvial fans, plains, streams and swamps. 5 Figure 2: Stratigraphic column for Four Corners Area (Anderson & Lucas, 1997) Structural Setting The Colorado Plateau is bordered on the west by the Basin and Range province and on the east by the Rocky Mountains. Despite the active tectonic development of these two areas throughout the Cretaceous and Tertiary periods, the Plateau was not subjected to significant tectonic activity. Subduction of the Kula and Farallon plates beneath the western margin of the 6 North American plate drove most, if not all, tectonic activity throughout the Jurassic and Cenozoic Eras in the American Southwest (Figure Three). Two main orogenies, the Jurassic to 50 Ma Sevier Orogeny and the 80-50 Ma Laramide orogeny, are responsible for most deformation across the region. Compressional deformation associated with the Sevier Orogeny affected sedimentary units across the Four Corners