•  
  •  
 

Abstract

Billions of large orthocone nautiloids occur within an extremely persistent lime packstone bed of the Redwall Limestone through the Grand Canyon region, Arizona and Nevada. The platform facies of the packstone bed is 2 m thick at the top of the Whitmore Wash Member (Osagean Series of Mississippian System). Abundant nautiloids occur within the platform facies of the bed from Marble Canyon, Arizona westward 290 kilometers to Las Vegas, Nevada. The slope facies of the bed, where nautiloids are rare, is 3-to-14-m-thick, light-gray-weathering grainstone occurring northwest of the platform facies in southern Nevada, extreme northwestern Arizona, and southwestern Utah. Both platform and slope facies of the bed are named formally Whitmore Nautiloid Bed (WNB). Bed area exceeds 3 x 104 km2 and bed volume exceeds 100 km3.

Orthocone nautiloids assignable to the genus Rayonnoceras show evidence that bodies occupied the shells during mass kill and burial of an entire population. Shell orientation, inverse grading, outsized coral heads, and water-escape pipes indicate rapid deposition of the platform facies from a high-velocity, laminar, low-cohesion, fluidized dispersion of carbonate sand and silt. This moving dispersion can be called a hyperconcentrated flow (volume concentration sediment ≈ 35%, flow density ≈ 1.6 g/cm3). Nautiloids and large coral heads were separated within the dispersion being supported as a raft above the highest-density, strongly fluidized, laminar flow. The flow event resembles the process that suspends lithic fragments and pumice clasts within a pyroclastic density current. WNB has internal structure resembling ignimbrite. The hyperconcentrated flow was initiated as a liquefied flow slide, probably in southwest Colorado, and hydroplaned toward southern Nevada at velocity ≈ 5 m/s through the carbonate platform in northern Arizona. When the flow encountered the slope in southern Nevada and southwest Utah, it was transformed into a turbulent, concentrated flow (volume concentration sediment ≈ 25%) depositing most of its sediment mass. Further westward in Nevada the flow lost its hydroplane and became a tractive current. This is the first documentation in the geological literature of a regionally extensive hyperconcentrated sediment gravity flow upon a marine carbonate platform.

Keywords

Grand Canyon, Redwall Limestone, Anchor Limestone, Whitmore Nautiloid Bed, hyperconcentrated flow

Disclaimer

DigitalCommons@Cedarville provides a publication platform for fully open access journals, which means that all articles are available on the Internet to all users immediately upon publication. However, the opinions and sentiments expressed by the authors of articles published in our journals do not necessarily indicate the endorsement or reflect the views of DigitalCommons@Cedarville, the Centennial Library, or Cedarville University and its employees. The authors are solely responsible for the content of their work. Please address questions to dc@cedarville.edu.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.