A Carbonate Hardground from the Snowy Range Formation (Upper Cambrian) of Park County, Wyoming (section authored by Jared Rhode)

The carbonate rock pictured exists in the Snowy Range formation and is Upper Cambrian in age. The fresh surfaces of the hand specimen are olive grey in color, while the weathered surfaces appear a light olive grey or yellowish grey. When looking at the hand specimen, there are many intraclasts present that vary in size. Some of these intraclasts are very large in size. The matrix of this rock is a sparry calcite matrix and can be seen in the hand specimen, as well as in thin section. In thin section, the grains appear to be very angular and poorly sorted. When looking at the grains in particular, one can see that about ninety five percent of the grains present are intraclasts, while the other five percent consist of echinoderms. When giving the hardground a Folk classification name it is a biointrasparite and when using the Dunham classification system it is considered a grainstone.

Jared Rhode, First-Year student at The College of Wooster. Jared is from Port Clinton, Ohio.

Figure 1. This photograph of a thin section of my carbonate hardground shows an echinoderm grain (center). The echinoderm is surrounded by a sparry calcite matrix which is also evident. A small amount of the echinoderm has been replaced by sparry calcite cement. Two large intraclasts can also be seen to the left and the right of the photograph. Width of view = 3.0 mm (40x).

Figure 2. This thin section photograph shows a very unique shaped intraclast (center). The intraclast is surrounded by sparry calcite once again, but also has a coating of sparry calcite. A smaller intraclast is also visible below the larger one. Width of view = 3.0 mm (40x).

Figure 3. The thin section shown here shows another echinoderm grain (center). You can once again see a few small intraclasts throughout the photograph, as well as the sparry calcite matrix. Width of view = 3.0 mm (40x).

Figure 4. This photograph show a large intraclast in the center of the thin section that is once again surrounded by sparry calcite cement. When looking at the bottom of the thin section, one clearly see the structure of the calcite crystals. Width of view = 3.0 mm (40x).