The Port Morant Formation (Upper Pleistocene, Jamaica): high resolution sedimentology and paleoenvironmental analysis of a mixed carbonate clastic lagoonal succession

The Port Morant Formation consists of a mixed clastic-carbonate sedimentary sequence that was deposited as a lagoon fill during the Sangamonian interglacial. Ten sedimentary facies are recognised and sequence stratigraphic analysis indicates the presence of transgressive and highstand systems tracts. The transgressive systems tract consists of a basal transgressive conglomerate (facies I), crustose coralline algal bindstones-boundstones (H) and 2 in high Solenastrea coral heads (HI). The highstand systems tract is represented by sediments of a braid delta/fan-delta prograding into the lagoon (IV and V), marine pebbly sandstones deposited adjacent to mangrove swamps (VU), more distal algal mudstones (VIII), and sheet-like (VI) and channelized (IX) conglomerates filling delta-top distributary channels. A barrier and/or fringing reef is present (X), but its relationship with the lagoon-fill sediments is obscure due to poor exposure. Carbonates are restricted to the transgressive systems tract and the barrier/fringing reef (transgressive and/or highstand systems tract). Two transgressive events are recognized, the transgressive systems tract (facies I to III) and facies VH, the latter either a second sea-level rise or due to delta abandonment. A single coral date from facies VH gave an age of 132 +/- 7 kyr. This indicates that the upper transgressive event (facies VU) belongs to the early highstand that has been recognized in isotope substage 5e, The lower transgressive event (facies I to III) in the Port Morant Formation is therefore either also of this age, or older. (C) 2001 Elsevier Science BN. All rights reserved.