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Steven A. Austin, 465 Scaife Road, Sewickley, PA 15143

Author's Biography

Steven A. Austin is adjunct professor at Cedarville University. He is senior research associate at Logos Research Associates. He is owner of Austin Research Consulting Inc., a California corporation.

Presentation Type

Full Paper Presentation


Bidahochi Basin is an elongate, 300-kilometer-long structural depression in the Painted Desert region of northeastern Arizona. Today, that basin is occupied by the Little Colorado River directly east of Grand Canyon. For more than 150 years geologists have been pondering the notion that a lake once occupied a large part of Bidahochi Basin. In 1936 Howel Williams named it Hopi Lake. Are strandlines from a Pliocene lake imprinted on limestone slopes of Kaibab Formation in western Bidahochi Basin? Our inquiry led us to study Google imagery from Coconino County just east of Flagstaff, Arizona. There the Kaibab Formation is a ramp dipping northeastward. We surveyed a 25-square-kilometer tract, assembled a composite image, and overlayed a digital elevation model. The compiled image file has 0.5-meter resolution with 2-meter contour overlay. We discovered several fields of linear, nearly horizontal, ridgelike landforms on Kaibab Formation slopes at elevation of ~1750 m (5740 ft). We selected several landforms for on-the-ground study. Adjacent to Buffalo Range Road on the north side of Wagon Box Draw we surveyed the limestone dip slope of a gently plunging syncline south of an anticline. “Nate’s Hill” (lat/long: 35.099, -111.181) is our name for the largest landform field. Landforms are expressed upon gentle slopes as much as 0.08 (rise over run). Landforms are ridgelike and linear being composed of three elements: berm, face and flat. The berm contains the crest line of exposed limestone that is the high point of the structure with the line of the berm crest expressing nearly horizontal orientation. The face is the dipping plucked limestone surface just downslope of the berm. The flat is the nearly horizontal soil surface just downslope of the face. The berm and face expose light-beige-colored limestone, whereas the flat is covered by darker brownish aeolian soil with short xerophytic shrubs. Landform lineation is impressive on high-resolution satellite photos and low-altitude drone photos because of the color and texture contrast between the rocky ridgelike berm and adjacent soil-covered flat. Typical spacing between berms is 20 m (+/- 5) over the ground. Height of the landform between adjacent berms is up to 1 meter with landforms occurring in steplike terraces ascending the limestone slope. These three landform elements are deflected by topographic irregularities as if a shoreline of a lake rose over the curved surface of limestone forming coves and points. Sometimes a very thin calcite crust (“tufa”) remains accreted to the face element of the landform.

Within the 25-square-kilometer tract around Wagon Box Draw, we identified the durable and persistent “limestone platform unit” that is less than 3 meters thick. This distinctive stratum occurs within the upper Harrisburg Member of the Kaibab Formation observed at a few places about 3 meters beneath the Moenkopi Formation. Outcrop strike and dip measurements at Nate’s Hill clearly demonstrate that the dip angle of limestone bedding is concordant with the step exposure of the landform. That means that numerous outcrop ledges express the strike line exposure of a single stratum, and disproves the notion that outcrop ledges are caused by a succession of outcropping strata. Nate’s Hill must be the syncline’s dip slope dominated by the limestone platform marker unit from the uppermost Harrisburg Member.

Landforms on the dip slope are not controlled by vertical limestone joints, because landform alignments deviate greatly from steady joint orientation. Could hummocky, dunelike or boudinage bedding structure within the limestone cause ridges to be expressed on the dip slope? We have not found hummocks in the uppermost Harrisburg Member with 20-meter spacing. Reflect upon the improbability that crests of ancient limestone hummocks, dunes or boudins would follow present topographic contour. Remarkably, linear landforms strongly parallel the 2-meter topographic contour overlay except where the limestone is deformed adjacent to faults. We observed a berm structure that could be traced 1 kilometer along the limestone dip slope yet its elevation appears to vary by less than a meter. The limestone dip slope at Nate’s Hill is terminated on its northeastern edge by the graben structure hosting Buffalo Range Road, with the associated landforms northeast of the graben having 15-meter lower elevation compared to the southwestern side. We interpret these Wagon Box Draw landforms to be old strandlines carved within the limestone slope as Hopi Lake rose to fill Bidahochi Basin. Could Bidahochi Basin have held a large post-Flood lake? Could complete filling of Hopi Lake have initiated spillover erosion of Grand Canyon? Our ongoing project seeks to answer some of these important and persistent questions.

Landform overflight video posted at: https://www.youtube.com/watch?v=wbKdxMW9NgY




Shoreline landforms, erosional terrace, depositional terrace, transgression, tufa, Hopi Lake, Bidahochi Basin, Lake Bonneville, Grand Canyon




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