Ramsholt Fossil Hunting

1821 – James Sowerby recorded fossils from Ramsholt
One of the earliest published fossil records from Ramsholt came in 1821, when Sowerby noted fossils from a newly discovered bed of clay near Woodbridge. This is one of the first known scientific records of fossils from the Ramsholt area.

1835 – Edward Charlesworth distinguished the Coralline and Red Crags at Ramsholt
Ramsholt became historically important when Charlesworth showed that two distinct crag formations were present here. He named the upper deposit the Red Crag and the lower deposit the Coralline Crag, making Ramsholt one of the key localities in the early history of East Anglian Crag geology.

1850 – Culicia woodii figured from Ramsholt material
The coral Culicia woodii was figured in the classic British Tertiary coral monograph of Milne Edwards and Haime, and Ramsholt became especially well known for this species. The locality was long noted for fossils that are rare elsewhere in the Coralline Crag.

1871 – Joseph Prestwich published a detailed account of the Ramsholt section
Prestwich included Ramsholt in his major work on the East Anglian Crags, giving one of the classic detailed descriptions of the section and its fauna. His account became the standard reference for the site for many years.

Mid 19th century – the Ramsholt phosphatic bed became part of the Suffolk coprolite story
The basal phosphatic bed at Ramsholt was recognised as part of the wider Suffolk bone-bed and coprolite deposits. Although the Ramsholt bed itself was not worked on the same scale as some other Suffolk sites, nearby Rockhall Wood saw commercial phosphate extraction in the 1860s.

1982 – Multifascigera debenensis described from Ramsholt Cliff
The large cyclostome bryozoan Multifascigera debenensis was described in 1982, with Ramsholt Cliff as its type locality. This made Ramsholt the type site for one of its most distinctive Coralline Crag fossils.

1993 – Ramsholt designated the type locality of the Ramsholt Member
Modern stratigraphic work formally made Ramsholt the type locality for the Ramsholt Member of the Coralline Crag Formation. This confirmed the site’s importance not only for fossils, but also for the formal geology of the Suffolk Crags.

Ramsholt Cliff is really a densely wooded, much-slipped river-bank slope rather than a clean open cliff. Bedrock is seen intermittently in temporary toe exposures, small excavations and on the foreshore at low tide, so the breakdown below is a composite site log rather than a permanently open continuous face.

No formal published bed numbering is in current use for the exposed Ramsholt section. The RC beds below are therefore site-use divisions based on the main unconformities, lag gravels and lithological packages recognised in the Geological Conservation Review and BGS accounts.

THAMES GROUP

Harwich Formation (Lower Eocene)

Bed RC1 — Rare Harwich Formation Ash-Bands And Harwich Stone Band Remnants

Rare low-tide patches of greenish-grey argillized volcanic ash bands and hard carbonate-cemented Harwich Stone Band material occur on the foreshore below the main slipped bank. At Ramsholt these beds are more commonly encountered as reworked cobbles in the younger Crag basal lags than as a clear in situ section. They represent the upper part of the Harwich Formation, an ash-rich shallow-marine shelf deposit, and they are important here chiefly because their presence shows that erosion had already cut deeply into the upper Thames Group before the Pliocene Crag transgression.

London Clay Formation (Lower Eocene)

Bed RC2 — Eroded Top Of The London Clay Formation

Only the uppermost London Clay is normally available, forming the mudstone substrate below the Coralline Crag and locally visible low in the bank or on the foreshore. In regional facies it is a blue-grey to grey-brown silty clay and clayey silt with pyrite and carbonate concretions, but at Ramsholt the key feature is its irregular undulose erosional top surface. The Coralline Crag rests on this surface across a hiatus of roughly 50 million years. Phosphatic mudstone pebbles, reworked shark teeth and other derivative debris in the basal Crag lag show how strongly the London Clay was stripped and winnowed before Pliocene marine sedimentation began.

CRAG GROUP

Coralline Crag Formation (Pliocene)

Ramsholt Member

Only the Ramsholt Member is preserved at Ramsholt Cliff. The Coralline Crag here is an erosional remnant capped directly by Red Crag, unlike the main Coralline Crag outcrop where younger Coralline members overlie the Ramsholt Member.

Bed RC3 — Basal Coralline Crag Phosphorite Lag (“Coprolite Bed” / “Nodule Bed” / “Suffolk Bone-Bed”)

A thin but locally conspicuous conglomeratic lag rests directly on the London Clay unconformity at the base of the Coralline Crag. It contains abundant phosphatic nodules, scattered phosphatized bone fragments, irregular cobbles of phosphate-cemented sandstone or “boxstones”, and large angular to rounded fragments of calcareous mudstone; a few more exotic clasts, including Jurassic limestone and quartzite cobbles, are also recorded. Much of the material was reworked from the underlying Eocene, but some boxstones and phosphatized bones came from older Neogene sands once present in the district, traditionally referred to as the Trimley Sands. Winnowing concentrated the denser pebbles, bones and sandstone cobbles into a classic remanié transgressive lag on the Pliocene erosion surface.

Bed RC4 — Lower Ramsholt Member Transgressive Calcareous Sands (with Bed RC3, c. 0.6–1.8 m for the basal transgressive package)

Above the basal lag lie fine- to medium-grained shelly calcareous sands forming the lower transgressive part of the Ramsholt Member. These sediments are carbonate-rich, generally silty, and represent the first in-place marine deposition above the erosional phosphorite lag. Compared with the cross-bedded Sudbourne Member seen elsewhere, the Ramsholt Member facies here lacks strong primary cross-bedding and instead records relatively slow accumulation under weaker bottom currents in shallow marine conditions during the early phase of the Coralline transgression.

Bed RC5 — Upper Ramsholt Member Shelly Bioturbated Calcareous Sands

The rest of the Coralline Crag at Ramsholt comprises strongly bioturbated, shelly, mud-rich calcareous sands, bringing the total Coralline thickness here up to a maximum of about 2.9 m. These beds are exceptionally important because the deposit has escaped the widespread aragonite dissolution seen at many other Coralline Crag localities. The fauna is rich and distinctive: the large cyclostome bryozoan Multifascigera debenensis has its type locality here; large irregular colonies of Turbicellepora coronopus are abundant; the barnacle Balanus concavus is classically characteristic; the coral Culicia woodii is preserved in situ within bryozoan colonies and may be accompanied by the commensal barnacle Pyrgomina anglicum; and the molluscan fauna includes Glycymeris glycymeris, Dosina casina, Arctica islandica, Venericardia aculeata scaldensis and Astarte omalii, with occasional articulated large bivalves. These beds represent a shallow-marine bioclastic sand and silty sand environment with moderate to strong bioturbation, relatively slow net sedimentation and a rich bryozoan–mollusc–barnacle–coral community.

Total Thickness Of Coralline Crag At Ramsholt Cliff: Up To About 2.9 Metres, Varying Laterally Between The Lower And Upper Unconformities

The later Red Crag transgression removed or reworked much of the older Coralline outlier. Ramsholt is therefore especially valuable because it is the one locality where the Ramsholt Member can be seen lying directly beneath the Red Crag rather than beneath younger Coralline Crag members.

Red Crag Formation (Upper Pliocene To Earliest Pleistocene)

Bed RC6 — Red Crag Basal Lag / Basement Bed

At the base of the Red Crag there is a thin but very important ferruginous basal lag or basement bed, here rich in phosphatic pebbles and boxstones and locally banked directly onto London Clay where the Coralline Crag has been stripped away. At Ramsholt this lag is a second major remanié horizon and records the erosive base of the later Red Crag transgression. Reworked phosphatic debris is abundant, and the bed explains why the locality yields a mixed derivative assemblage containing material from several different ages.

Bed RC7 — Red Crag Shell-Rich Ferruginous Sands (probably more than 2 m in places)

Above the basal lag are reddish-brown, shell-rich ferruginous sands of the Red Crag, laterally variable in thickness and exposure. Structures are rarely seen cleanly in the overgrown river-bank section, but the unit belongs to the characteristically coarse, poorly sorted, abundantly shelly and generally cross-bedded Red Crag facies, here overlying either the Coralline Crag or directly the London Clay. The fauna recorded from the site includes Aequipecten opercularis, Mytilus, Glycymeris, Cerastoderma, Astarte and Neptunea contraria. These sands represent a younger shallow-marine shell-sand deposit, probably tidally worked, laid down after significant erosion of the earlier Coralline outlier.

Total Thickness Of Red Crag At Ramsholt Cliff: Laterally Variable And Probably More Than 2 Metres In Places

Historical And Stratigraphic Significance

Ramsholt Cliff is one of the classic East Anglian Crag localities described by the early workers on the Suffolk Pliocene. It was central to Charlesworth’s recognition that the ferruginous Red Crag was distinct from the underlying Coralline Crag, and it remains critical because it shows the lower and upper Crag unconformities in one small outlier, preserves the unusual undissolved aragonitic fauna of the Ramsholt Member, and demonstrates that the later Red Crag transgression cut down variably through Coralline Crag into London Clay.

Depositional Environment

The upper Thames Group at Ramsholt records early Eocene shallow-marine shelf sedimentation, including ash-rich Harwich beds and quieter muddy London Clay deposition. After a hiatus of about 50 million years, the basal Coralline lag marks a Pliocene marine transgression that reworked Eocene mudstones and remnants of otherwise missing Neogene deposits; the overlying Ramsholt Member accumulated as shelly, bryozoan-rich, bioturbated calcareous sands and silty sands in a shallow-marine setting with relatively weak bottom currents. The younger Red Crag represents a later, more strongly reworked shallow-marine shell-sand deposit with its own erosive basal lag and further truncation of the older Coralline outlier.

Total Thickness Covered Here

Only the uppermost Thames Group surface plus up to about 2.9 m of Coralline Crag and more than 2 m of Red Crag are normally accessible in the cliff and foreshore. Much of the locality’s stratigraphic importance lies not in a thick continuous cliff but in the two major unconformities and the derivative phosphatic lag beds that record otherwise missing intervals of East Anglian Cenozoic history.

References

Charlesworth, E. (1835) on the distinction between Coralline Crag and Red Crag at Ramsholt.
Prestwich, J. (1871a) on the East Anglian Crags and the Ramsholt section.
Balson, P.S. (1980, 1989, 1990a) on Suffolk phosphorites, “boxstones” and the Neogene history of East Anglia.
Balson, P.S., Mathers, S.J. & Zalasiewicz, J.A. (1993). The lithostratigraphy of the Coralline Crag (Pliocene) of Suffolk.
Daley, B. & Balson, P. (1999). British Tertiary Stratigraphy, Geological Conservation Review Series 15, especially the Ramsholt Cliff chapter.
Holcombe (1966) on the Red Crag fauna of Ramsholt.
Balson, P. & Taylor, P. (1982) on Multifascigera debenensis; Cadée & McKinney (1994) and Tilbrook (1997) on coral–bryozoan–barnacle associations in the Coralline Crag.
British Geological Survey Lexicon entries: Thames Group, Harwich Formation, London Clay Formation, Coralline Crag Formation, Ramsholt Member and Red Crag Formation.
British Geological Survey: Woodbridge and Felixstowe district, Sheet 208 and 225, brief explanation.