• Wind Cave National Park - Two Worlds

    Wind Cave

    National Park South Dakota

1959 NSS Expedition to Wind Cave Sediments and Breakdown

The fills of Wind Cave are quite varied. Detrital fill varies in size from clays to breakdown blocks tens of feet across. Chemical sediments appear frequently as a cementing agent for the detrital material. The types of sediments may be classified as follows:

  • Crystallized fills
  • Cemented fill breccias
  • Filled sink structures
  • Loose fill breccias
  • Clay fills
  • Breakdown

Crystallized fills

The crystallized fills are apparently related to the layers of silty cemented sediment that appear interlayered in the crystallization sequence of the boxwork, but it is not clear which sedimentation epoch they correlate to.

Cemented fill breccias

In the room, "The Bachelor's Quarters", the cave walls are composed of a cemented breccia. The breccia is composed of angular limestone blocks up to 5 inches across with some sandstone and chert fragments. The matrix in red silt cemented with a fine-grained calcite. The breccia occurs in the J and K Stratigraphic Horizon. (See section on stratigraphic relationships.) The cave passage cuts the breccia and extends into solid bedrock above and below. The possibility exists that this breccia is related to the Pennsylvanian age karst surface known to exist at the Pahasapa-Minnelusa contact. Weathering of the walls contributes irregular blocks of breccia, weathered out angular fragments, and silt to the detritus on the floor. A similar area occurs in parts of the Attic.

Loose fill breccias

Commonly displayed in much of the upper levels of the cave but particularly well developed in Plummer's Pit are thick sections of loose fill breccia. They commonly consist of angular limestone fragments, sharp angular fragments of gray chert up to 5 inches across, and some partly rounded red to purple sandstone pebbles. The matrix is a fine grained deep red silt. The material is not cemented and will easily fall apart and yet is consistent enough to support vertical walls 30 to 50 feet high in the pit. On casual inspection the loose fill breccia appears to be very similar to the cemented fill breccia. However, a detailed microscopic study of the matrix will be necessary to prove this.

Filled Sink Structures

Filled sink structures are masses of sandstone intersected by the cave within the limestone. One example exists at the northwestern end of the upper level passage above the Pearly Gates By-Pass. A second and more spectacular filled sink occurs on the Fairy Palace Loop. Both of these occur at the ends of passageways and only one side is accessible. The filled sink on the Fairy Palace Loop consists of an irregular shaped body of red-brown medium grained sandstone completely filling the passage. The body lies unconformably against the limestone. The sandstone shows bedding of various shades of brown and varies in thickness from fractions of an inch to more than a foot. While the limestone is nearly horizontal here, the sandstone dips 42°. Some cross-bedding is present. A sketch is shown in Figure 9.

 
Sketch of filled sink structure on Fairy Palace Loop. Note variation in bedding and crossbedding.

Figure 9. Sketch of filled sink structure on Fairy Palace Loop. Note variation in bedding and crossbedding.

The hypothesis is advanced that these sandstone bodies represent the filled remnants of Pennsylvania age sinkholes that were formed on the karst uncomformity between the Pahasapa limestone and the Minnelusa sandstone. The testing of this hypothesis must await a detailed comparison between the lithologies of the filled-sink sandstone and the lower beds of the Minnelusa sandstone.

Clay Fills

Unconsolidated clays such as make up most of the fill of many limestone caves are rare in Wind Cave. The passage near the "Bleeding Heart" in the Garden of Eden section of the cave show damp brown fine grained fills that seem to be principally clay and silt.

Breakdown

Breakdown occurs in large blocks and in smaller chips. The block breakdown ranges in size from a few feet to more than 20 feet in length. The blocks are commonly several feet thick and would appear to extend over several beds. The tops and bottoms of blocks are flat and are probably bedding planes. Some sides are planar and may represent joint faces; others are irregular. Regular (nearly rectangular) block breakdown occurs near the entrance to Brown Canyon. Large and very irregular blocks occur on the floor of the Attic. The chip breakdown is scatted over many parts of the cave. It consists of irregular limestone fragments ranging in size from a few inches to several feet.

Did You Know?

Natural Entrance of Wind Cave

Winds caused by changes in barometric pressure are what give Wind Cave its name. These winds have been measured at the cave's walk-in entrance at over 70 mph. The winds at the natural entrance of the cave attracted the attention of Native Americans and early settlers.