Discussion and Conclusions

The presence of significant numbers of sites and samples carrying a reversed polarity magnetization indicates that these units are older than the Brunhes polarity interval. Given the external constraints on the age of the cave, it is most likely that the long reversed interval sampled in the section is the Matuyama polarity interval (0.781-1.757 Ma; Cande and Kent, 1995). This interpretation suggests the strata represent a duration of no more than a million years and probably less. This estimate results in a minimum average sediment accumulation rate of 0.9 mm per thousand years. If site 1 lies within the Brunhes, then that further delineates the age of the strata.

Sites 4-7 show strong normal overprinting, poor remanence, and high standard deviation, making them difficult to interpret. It is possible that this interval is normally magnetized. Given that the data suggest that sites 2 and 3 are reversed polarity, sites 4-7 could represent Chron 1r.1n from 0.984 to 1.049 Ma ago (Cande and Kent, 1995), commonly called the Jaramillo Event. This conclusion would be consistent with the other paleomagnetic and stratigraphic data and may place further constraints on the age of individual units. This interpretation dates most of the strata above 50 cm to less than 1 Ma ago. Care must be exercised in using this interpretation, owing to the ambiguity of the magnetic signature.

From these observations, we conclude the following:

1. The evidence for reversed polarity for three positions in the sample section is very strong: approximately 30 cm depth in horizon D, approximately 90 cm depth in horizon H, and approximately 110 cm depth in horizon I. This places the sampled interval within the Matuyama reversed polarity interval. It is also possible that a brief normal interval (Chron 1r.1n) occurs within the sampled section.

2. The section sampled between horizons C and I probably represents less than a million years of time.

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