Formation of Palimpsest Sediments, Conception Bay, Southeastern Newfoundland

Abstract

Grain-size analysis of 74 samples shows that gravel, very fine sand, and mud populations compose the principal bottom sediments in Conception Bay, southeastern Newfoundland. These individual populations, plus mixtures of the populations, gives rise to 11 textural types. The sediments were deposited as glacial drift during periods of lower sea level and then reworked into discrete particle-size populations during postglacial marine transgression. Subsequent deposition of the winnowed finer grained populations as distinct sedimentary units in deep water and upon coarser lag deposits in shallower water resulted in the variety of textural types. These are defined by Swift and others (1971) as palimpsest sediments. A model proposed for formation of the 11 textural types in Conception Bay is probably applicable to other formerly glaciated inlets. The relation between mean size and sorting (standard deviation) of the trimodal sediments is complex because there are several possible combinations of mixing of particle-size populations. Analysis of this relation is useful for identifying sediments composed of mixtures of particle-size populations.