INTRODUCTION Bidahochi Basin is an elongate, 300-kilometer-long structural depression in the Painted Desert region of northeastern Arizona (Figure 1). Today, that basin is occupied by the Little Colorado River directly east of Grand Canyon. For more than 160 years geologists have been pondering the notion that a lake once occupied a large part of Bidahochi Basin. During an expedition to the Southwest in 1858, John Newberry, the first geologist to explore Grand Canyon, proposed that an enormous lake was responsible for spillover erosion along the course of the modern Colorado River (Newberry 1861). The noteworthy and enduring legacy of Newberry’s original hypothesis among both creationist and evolutionist geologists has recently been recounted (Austin et al. 2020). Newberry’s hypothesis is tectonic process created a 300-kilometer elongate depression in Northeastern Arizona that was older than the Colorado River. That depression was recognized as the “synclinal trough or basin” during Newberry’s 1858 explorations where at Hopi Buttes he measured the thickness of fine carbonate cemented sandstone, siltstone and claystone that he believed to be Miocene lake deposits. Newberry (1861, pp. 19, 20) described his lake spillover hypothesis: Doubtless in earlier times it [Colorado River] filled these basins to the brim . . . its accumulated waters, pouring over the lowest points in the barriers which opposed their progress towards the sea, have cut them down from summit to base, forming that remarkable series of deep and narrow canyons . . . leaving open areas . . . which were once lakes and afterwards fertile valleys – arid and sterile wastes.” Later generations of geologists took up the task of defining and naming features that John Newberry first recognized. That 300-kilometerlong tectonic depression has recently been named “Bidahochi Basin” (Dallegge et al. 2003; He and Kapp 2021). Newberry’s fine-grained clastic deposits in the Hopi Buttes were assigned to the Mio-Pliocene Bidahochi Formation (Reagan 1924). The putative Pliocene paleolake that filled the topographic depression was named “Hopi Lake” by Howel Williams as he was describing the volcanic strata of Hopi Buttes (Williams 1936). Some geologists started calling that paleolake “Lake Bidahochi” (Meek and Douglass 2001), but Williams’ name “Hopi Lake” has priority. Creationist geologists Steven A. Austin, Cedarville University, 251 N. Main St., Cedarville, Ohio 45314, mudflowman@comcast.net Edmond W. Holroyd III, Carmel Consulting, Arvada, Colorado, eholroyd@juno.com Thomas F. Folks, St. George, Utah, nigelt1@msn.com Nate Loper, Canyon Ministries, 2727 W Rte 66, Flagstaff, Arizona 86001, nate@canyonministries.org © Cedarville University International Conference on Creationism. The views expressed in this publication are those of the author(s) and do not necessarily represent those of Cedarville University. 9th 2023 Austin S.A., E.W. Holroyd III, T.F. Folks, and N. Loper. 2023. Shoreline transgressive terraces: Tufa-encrusted landforms indicate rapid filling and failure of Hopi Lake, western Bidahochi Basin, northeastern Arizona. In J.H. Whitmore (editor), Proceedings of the Ninth International Conference on Creationism, pp. 346-362. Cedarville, Ohio: Cedarville University International Conference on Creationism. SHORELINE TRANSGRESSIVE TERRACES: TUFA-ENCRUSTED LANDFORMS INDICATE RAPID FILLING AND FAILURE OF HOPI LAKE, WESTERN BIDAHOCHI BASIN, NORTHEASTERN ARIZONA For more than 160 years geologists have been pondering the notion that a lake once occupied a large part of Bidahochi Basin in the Painted Desert of northeastern Arizona and western New Mexico. Could the 300-kilometer-long Hopi Lake have spilled over the Kaibab Upwarp to erode Grand Canyon? A composite satellite image of a 25-square-kilometer tract from Coconino County adjacent to Buffalo Range Road in Wagon Box Draw displays terracelike landforms within the structural ramp of Kaibab Formation. Landforms are terraces expressed upon gentle slopes as low as 0.02 (rise over run 1:50) within the uppermost limestone beds of the Harrisburg Member of the Kaibab Formation at elevation of ~1750 m (5740 ft). A typical 20-meter-wide, steplike terrace has a thin, centimeter-thick, light yellow-brown, porous carbonate encrustation we term “tufa.” The transgressive Lake Bonneville depositional terrace model of Chen and Maloof (2017) is applied to the limestone dip slope at Wagon Box Draw. As the wave-dominant shoreline rises over the dip slope, our model specifies how the terrace is first eroded into thin-bedded limestone and, later, is deposited with residual gravel. Lastly, because of continued quick transgression, the shoreline depositional terrace is accreted with a thin crust of tufa. We consider and dispute four alternates to our shoreline transgressive terrace model (landform outcrop pattern caused by level strata, spacing caused by bedrock joints, dunelike or boudinage structural expression in limestone bed, and soil solifluction with gravity compaction). We interpret these Wagon Box Draw shoreline terraces to have been carved within the limestone slope as Hopi Lake rose to fill Bidahochi Basin. We believe that filling of Bidahochi Basin was accelerated by breaching of another big lake upstream in Utah. Top-down overflow of higher basins promoted quick filling of Bidahochi Basin, initiated catastrophic spillover of Kaibab Upwarp, began rapid drainage of Hopi Lake, and resulted in catastrophic erosion of Grand Canyon. ABSTRACT KEYWORDS Shoreline landforms, erosional terrace, depositional terrace, transgression, tufa, Hopi Lake, Bidahochi Basin, Lake Bonneville, Grand Canyon.
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