Late Pleistocene interglacial deposits at Pennington Marshes, Lymington, Hampshire, southern England

Fossiliferous organic sediments interstratified within fluvial gravels at Pennington Marshes, Lymington, have been recovered in boreholes and investigated. The organic deposit, here defined as the Pennington Organic Bed, occurs between -3.9 to -5.3 m OD and has been traced 200 m across the immediate area. Pollen analyses indicate a temperate flora of interglacial character. Molluscan and ostracod assemblages contain no brackish elements and are typical of a shallow, freshwater stream or abandoned channel. A change from an aquatic to a terrestrial molluscan fauna indicates progressive drying out of the water body. The Pennington Organic Bed cannot be confidently attributed to any particular stage, but since it occurs within a lower terrace than that at Stone Point, 15 km to the NE, it is probably younger and an early Ipswichian age (Ip IIa?) is suggested. The Pennington Lower Gravel, below the organic deposit, is therefore probably Wolstonian and the Pennington Upper Gravel, above them, Devensian in age. The estuarine interglacial deposits at Stone Point, previously believed to have been Ipswichian, are likely to belong to an earlier stage. It is possible, although less likely, that they accumulated during a later part of the Ipswichian as the transgression aggraded to the level of the higher terrace surface. Similarly, if the gravels at Stone Point resulted from a tributary river, rather than the Solent River itself, this could also explain the altimetric differences and allow the organic deposits to be attributed to different parts of the same stage. However, there is no evidence to support either of these alternative possibilities.