Blackberry Hill
| Blackberry Hill Stratigraphic range: Cambrian |
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|---|---|
| Location | |
| Region | Wisconsin |
| Country | United States |
| Type section | |
| Named for | Topographic feature (a summit) in Marathon County |
Blackberry Hill is a series of quarries and outcrops in Central Wisconsin that is notable for its large concentration of trace fossils in Cambrian rocks. One quarry in particular, located in Marathon County, also has the distinction of preserving some of the first land animals. The site is a prolific Cambrian Konservat-Lagerstätte. It includes three-dimensional casts of soft bodied and lightly scleritized invertebrates and a variety of exceptionally preserved types of trace fossils.
The strata at Blackberry Hill are known to belong to the Elk Mound Group; however, the lack of good stratigraphic markers (i.e., index fossils) in some Blackberry Hill localities, coupled with uncertainties about the age range of the Elk Mound Group itself, make it difficult to assign a precise age to these strata. Many researchers consider these rocks to be Late Cambrian, which is the age to which the Elk Mound Group was originally assigned; however, some recent authors now believe the Elk Mound Group and the fossils of Blackberry Hill could date back to the Middle Cambrian, based on certain fossils obtained from other areas.
Most of the strata are composed of well bedded quartz sandstone and orthoquartzite. They were deposited mainly on intertidal and supratidal sand flats along the southern shoreline of the supercontinent Laurentia.Ripple marks and numerous other sedimentary structures identical to those found on modern beaches abound on the strata surfaces. One of the most conspicuous features is extensive areas of specific structures not unlike those associated with modern biofilms and microbial mats. There is mounting evidence suggesting that the feeding potential of this presumed microbial material was one of the forces that lured the first animals out of the sea. It is also believed that the same material aided in the exceptional preservation of many of Blackberry Hill’s trace fossils.
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