|
| The Whitestone Limestone carbonate hardground is located in the Walnut Formation of Travis County, Texas. It is Lower Cretaceous, Middle Albian in age. The weathered surface of this rock is a very pale orange color while the fresh cut surface is a grayish orange. The carbonate hand sample shows visible grains of shell fragments. Biologic borings are also found throughout the hand sample. The hand sample shows a sparry calcite matrix. The thin section of the Whitestone Limestone also depicts a calcite spar and echinoderm fossil fragments surrounded by an oolitic coating made out of aragonite crystals. The grains, which are composed of all oolitic covered echinoderm fragments, all moderately well sorted and sub-angular to sub-rounded. The carbonate is grain supported. Under the Folk classification system, the Whitestone Limestone is an Oobiosparite and under the Dunham classification system it is a grainstone. The depositional enviornment is warm, agitated, shallow marine water above the wavebase. |
|
 |
|
Figure 1. This photograph of a thin section of the Whitestone Limestone shows the echinoderm fragments. The dark outline around each fragment is an oolitic coating made from aragonite crystals. Width of view= 3.0 mm (40x).
|
 |
|
Figure 2. The Whitestone Limestone has a crystalline calcite spar or "sparry matrix" which cements the echinoderm fragments together. Width of view= 1.2 mm (100x).
|
 |
|
Figure 3. In this picture, again, oolite covered echinoderm fragments are visible. The oolitic coating (dark outlines of fragments) forms in warm, agitated Calcium Carbonate rich water. Width of view= 1.2 mm (100x).
|
 |
|
Figure 4. This photograph shows the shape and sorting of the echinoderm grains. The carbonate is moderately well sorted and the grains vary between sub-angular and sub-rounded roundness. Width of view= 1.2 mm (100x). |