Some observations on the nature of depositional and erosional surfaces

摘要

The stratal architecture of the Gulf os Suez can be discriminated on several different orders. There are the sequences that can be defined plaeontologically: however, since biostratigraphically detectable alcunae can be caused by several different processes, grahpic correlation time gaps do not always correlate to true depositional sequence bound-aries. Lacunae can occur at regressive surfaces of erosion, where part of the sedimentary record is removed during sea level faill, at ravinements and related transgressive surfaces of erosion, and at condensed intervals where sedimentation rates are so slow that several fossil zones are compressed. Depisitional sequences are bounded by regional erosional unconformities generated by a relative sea level fall. The bounding surfaces are reressive surfaces of subaerial or submarine erosion, Therefore, of the three catagires of lacunae listed above, only one, the first, consituttes a depositional sequence boundary. The number of depositional sequences related to long term relative sea level changes in the Suez Rift shuld, therefore, be expected to be smaller than the number of biostratigraphically defined sequences.