Localities and Geology

The Cambrian Lagerstätten of Utah were laid down in an ancient environment very different from that of Utah today.  During the Cambrian period, present-day Utah was positioned nearly at the equator and much of it was covered by an ancient ocean.

Rock units bearing exceptional preservation of soft-parts were deposited under very low to completely oxygen-free conditions. This prevented the soft-parts from being quickly decomposed by microbes and scavengers.

 An illustration of the ancient "paleogeography" of North America (known to geologists as “Laurentia”) is provided below.  This map shows the approximate position of Utah (red star) during the Cambrian, as well as the position of the famous Burgess Shale of British Columbia.

"Brown and tan island that represents the position of Utah during Cambrian with two stars highlighting Utah fossils and Burgess Shale"
(Image produced using PaleoGIS)

While the overall fossil record of Utah is great, Burgess Shale type preservation of soft-parts mostly occurs in just four Cambrian deposits:

  • Spence Shale Member of the Langston Formation
  • Marjum Formation
  • Wheeler Formation
  • Weeks Formation

In turn, individual sites of Burgess Shale type preservation within these four rock units are restricted to three mountain ranges:

  • Wellsville Mountains (Box Elder County)
  • House Range (Millard)
  • Drum Mountains (Millard County)
"Utah with marks showing the sites of Burgess Shale preservation"

Wellsville Mountains, Box Elder County

"Two towns connected by a highway on the left and on the middle right past the two towns there is the Wellsville mountains"

The Wellsville Mountains are located just east of Brigham City, Utah in Box Elder County. Burgess Shale type preservation occurs in one rock unit, the Spence Shale Member of the Langston Formation. The position of the Langston Formation relative to other Cambrian strata exposed in the Wellsville Mountains is shown below.

"Highlights the Langston Formation relative to other positions within the mountain "

House Range, Millard County

"A mountain range across a barren and hilly land"

The House Range is located in Millard County, Utah. Within the House Range, Burgess Shale type preservation occurs within three rock units: the Wheeler Formation, the Marjum Formation, and the Weeks Formation. The stratigraphic positions of these three rock units are shown below.

"The rock formations within Millard Mountain and highlights three in the middle that contain Burgess Shale"

Drum Mountains, Millard County

"A barren land with mountain ranges in the middle"

The Drum Mountains are also located in Millard County, Utah. Within the Drum Mountains, Burgess Shale type preservation occurs within the Wheeler Formation. A stratigraphic section showing the position of the Wheeler Formation relative to other rock units in the Drum Mountains is shown below.

"Formations of rock in Drum Mountains with the highlight of wheeler formation which is second to last"

To learn more about the geology of Utah, visit the Utah Geological Survery homepage.