This is the basic chronology for the cave-fill in the east road cut of the predominately sandstone-filled cave. The original cave floor is not exposed in this outcrop. The following discussion involves only the exposed section; prior "phases" of cave deposition may have taken place. In a humid climate, the maximum lifespan for an epigenic (dissolution from meteoric water and organic acids) cave is around 10 m.y. After this time the cave is unroofed from denudation of the landscape.
The first phase of deposition fills in about 75% of the visible accommodation space. Upon inspection with a binocular scope, this rock appears to be a quartz arenite. The top of this section may have been a dry cave floor for some duration before and during the deposition of the second phase.
The second phase obviously represents some change in the environment. Base levels may have dropped, the sediment source changed, this cave passage filled and water flowed through an alternate passage, climate changed, etc. It does appear that erosion took place on the south side of the sand-fill before or during the deposition of this dark gray siltstone. The base of the limestone slump doesn't resemble typical Burlington-Keokuk Limestone. This may simply be from weathering of slumped beds, or it could be a portion of a preserved speleothem.
The third phase is similar to the first in lithology. The processes that took place during these two times were likely similar. The two sandstone bodies in this section parallel the cave roof, meaning the cave passage was likely filled at this point.
The fourth phase drapes over the third. This suggests that further dissolution occurred sometime after the third phase was deposited. Another possibility is that this layer is simply a crust which developed on the cave roof and only appears to be depositional. It does appear, however, to be similar in lithology to phase two deposition.
