Sedimentary environments and Holocene evolution of the Suffolk estuaries.
A stratigraphic investigation of the marshland adjacent
to the five main estuaries in Suffolk and offshore of the
Alde estuary has been made. The results are used to
establish a Holocene evolution for the Suffolk coast and are
compared with coastal sequences elsewhere in East Anglia.
The stratigraphy of the Blyth estuary in north Suffolk
comprises four lithostratigraphic units; a basal freshwater
peat overlain by estuarine Lower Clay, Middle Peat and Upper
Clay representing two phases of transgressive overlap
sandwiching a phase of regressive overlap. Peat formation
began about 6750 yrs BP and continued until 6500 yrs BP when
the sequence was inundated and eroded by marine waters during
the initial phases of transgressive overlap. Estuarine
silt/clay deposition (both low and high intertidal flat)
persisted until about 4500 yrs, BP when a transition to
further peat growth occurred. The second phase of estuarine
sedimentation (predominantly high intertidal flat) began at
about 4300 yrs BP. These dates correlate well with dates for
similar tendencies of sea-level movement in the Fens, north
Norfolk and Broadland.
The Blyth sequence contrasts with the Holocene sequence
in the Deben, Orwell and Stour estuaries in south Suffolk
which comprises a continuous estuarine clastic sequence
without an intermediate peat. Estuarine conditions are
believed to have begun about 8000 yrs BP and a high
subsidence rate combined with low'sediment accumulation rates
caused the estuaries to remain flooded throughout the
The onshore data, plus data offshore from the Alde
estuary has been used to evaluate the position of the coast
after 8700 yrs BP. The coastal evolution is interpreted to
have been controlled by the movement of coastal barrier or
spit systems. A significant barrier breaching episode is
believed to have occurred post-7000 yrs BP causing erosional
contacts and development of higher energy-estuarine
environments. After, this time, the, Blyth estuary was
significantly affected by further spit or barrier growth.
The Alde, Deben, Orwell and Stour estuaries, however, were
essentially barrier (spit) free during the Holocene and
protected from southerly longshore drift by a land barrier
north of the Alde estuary. The land barrier was eventually
breached and subsequent formation of Orford Ness and
Landguard Spit began.
The present-day inland saline penetration up the river
Blyth is the maximum achieved at any time during the
Holocene. This contrasts with Broadland and Fenland where
the maximum penetration occurred about 2000 years earlier.
The main reason for the differences appears to be a higher
coastal erosion rate in Suffolk compared to Norfolk (Fenland
is actively prograding).