Late Quaternary alluviation along intermittent streams in Kakadu National Park, Northern Territory

Sedimentation along small, intermittent streams on Kapalga Research Station in Kakadu National Park may have responded to increased base levels follow ing post-glacial flooding of the valleys of the Alligator Rivers. Alternati vely, regional climate changes may have controlled sedimentation. Using the rmoluminescence dating, we determined that sediments from two streams at Ka palga date from 21.5 +/- 4.0 ka. On a third stream sediments dated from 7.6 +/- 1.1 ha, with younger Sediments occurring downstream. We interpreted th e pre-Holocene dates and the lack of evidence of upstream progradation to i ndicate that climate variation was more important to sedimentation than bas e levels. Predicted increases in rainfall variability and in the frequency of high-intensity rainfall under enhanced greenhouse conditions may cause r enewed sediment mobilisation. At the outflow of one stream on to the South Alligator flood plain, we found 15 m of sandy alluvia underlying 3-5 m of e stuarine muds deposited as a result of sea-level rise. These sandy alluvia dated from about 77 ha at 4 nl to more than 300 ha at 19 m depth. These age s are consistent with those recorded on the Magela Creek system, 50 fim to the cast.