Barton on Sea Fossil Hunting

Early 19th century onwards – Barton Cliff became one of Britain’s classic Eocene fossil localities
Barton Cliff has been collected for more than two centuries and quickly became famous for its rich Eocene fossils. Its importance lies not only in the huge number of shells, but also in its vertebrates, including sharks, bony fish, turtles, birds and mammals.

1888 – Gardner, Keeping and Monckton documented the Barton Beds succession and faunal changes
The classic 1888 work by Gardner, Keeping and Monckton divided the Barton Beds into Lower, Middle and Upper parts using changes in the fossil fauna. This helped establish Barton as one of the key reference sections for British Eocene fossils.

1925–1926 – Marjorie Chandler described the flora of neighbouring Hordle Cliff
Chandler’s work documented fossil leaves, fruits and seeds from the younger Headon Hill Formation at Hordle Cliff, farther east along the coast. It belongs to the broader historical “Barton Cliffs” section, but is distinct from the marine Barton Group fossils described in this guide.

1972 – first land mammals recorded from the marine Barton Beds by J. J. Hooker
One of the most important scientific breakthroughs at Barton came in 1972, when J. J. Hooker published the first land mammals from the marine Barton Beds of Hampshire. This was especially significant because mammals in clearly marine Eocene strata are unusual and helped improve correlation with continental faunas.

1979 – Notorhynchus kempi described from Barton Cliff material
Barton Cliff produced material later named Notorhynchus kempi by Ward in 1979. This added to the site’s importance for fossil sharks and showed how significant Barton is for Eocene vertebrate faunas as well as shells.

1986 – Hooker’s major mammal study established Barton as a key Eocene mammal site
Hooker’s 1986 monograph on mammals from the Bartonian of the Hampshire Basin made clear just how important Barton is for Eocene mammals. Barton Cliff became one of the key British reference sites for understanding mammal faunas of this age.

Late 20th century – Barton recognised as Britain’s most productive Mid Eocene reptile site
Later reviews showed that Barton Cliff is the most productive British Mid Eocene site for reptiles, with turtles, lizards and snakes all recorded. It also remained one of the richest British Eocene fish localities, with at least 30 chondrichthyan taxa recognised from the section.

Modern work – Barton continues to be a key reference site for Eocene marine fossils
Barton-on-Sea remains one of the most important British Eocene fossil sites, with ongoing study of museum collections and continued collecting from the cliffs and foreshore. Its importance now lies in the combination of abundant molluscs, major vertebrate faunas and the classic plant assemblages from the wider Barton Cliffs succession.

BARTON GROUP

Barton Clay Formation

The modern lithostratigraphy used here follows the British Geological Survey and Edwards & Freshney scheme, in which the classic marine Barton succession at Barton-on-Sea is divided into the Barton Clay Formation, the Chama Sand Formation and the Becton Sand Formation. For bed-scale detail, the published Burton bed lettering is retained because it remains the standard practical horizon scheme at the type locality: the Barton Clay extends up to and including Bed G, Bed H is the Chama Sand, and Beds I–K belong to the Becton Sand.

Bed A0 — Basal Pebble Bed / Transgressive Lag

At the accepted lithostratigraphic base of the Barton Clay, a rounded flint pebble lag rests sharply on the underlying Boscombe Sand. This bed is the natural transgressive break at the base of the marine Barton sequence and records erosion and ravinement at the start of a new Eocene marine incursion. In Hooker’s cyclic notation the basal interval is A0, below Burton’s A1. The pebble lag is followed by a clay interval about 3 m thick before the incoming Nummulites prestwichianus datum used in older boundary definitions.

Bed A1 — Nummulites prestwichianus Bed

This green glauconitic sandy clay is the classic Nummulites prestwichianus horizon near the base of the Barton Clay. Historically, the base of the Bartonian was long taken at the bottom of this bed, even though the modern lithostratigraphic base of the formation is placed lower, at the basal pebble bed. It belongs to the shell-rich lower Barton interval and marks the onset of fully marine Barton Clay deposition. Beds A1–A3 together have yielded a notable vertebrate fauna including sharks, rays, bony fishes and the rare frog record from the Barton succession, though A1 itself is now commonly poorly exposed because of sea-defence works and weathering.

Historical local thickness: about 6 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed A2 — Lower Barton Sandy Clay Interval

In the historical BGS tabulation, A2 is about 4 m of glauconitic clay between A1 and the heterolithic A3 interval. Recorded fossils include Turricula lanceolata, Athleta athleta, Nummulites rectus, fish otoliths and shark teeth. The nummulitid occurrence lies about 6 m above the N. prestwichianus horizon. Exposure has been affected by protection and concealment, but that does not erase the published bed description.

Bed A3 — Upper Lower Barton Sands / Reworked Lower Barton Horizon

A3 forms the top of the first Barton cycle and is sandier, more reworked and more regressive in character than the beds below. The BGS historical table describes stiff grey clay with thin grey sand beds here, and Hooker noted abraded fossils here, showing considerable reworking during shallowing. Volutospina ambigua is especially characteristic. The lower Barton interval as a whole can also yield small corals, echinoderm remains, crab material, fish teeth, turtle fragments, worn freshwater shells and driftwood, showing both rich marine life and the proximity of land.

Historical local thickness: about 3 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed B — Basal Transgressive Bed Of The Second Barton Cycle

Bed B begins above a sharp burrowed junction and records renewed marine flooding after the regressive top of A3. Glauconitic silty clays and sandy muds are characteristic, and the bed marks the return to deeper, more argillaceous shelf conditions at the start of the second major Barton cycle. The historical BGS table describes grey clay with Pholadomya. West’s annotated local Burton list also records Volutospina athleta as common in B, while the BGS table lists Athleta athleta in A2; these occurrence records are not mutually exclusive.

Historical local thickness: about 1.2 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed C — Voluta suspensa Bed

Bed C is one of the most recognisable beds in the modern Barton cliff, especially between Naish Farm and the first Barton sea defences. It is a more truly argillaceous marine clay than the lower Barton sands and is easily identified because it lies between septarian nodule bands and includes a conspicuous pale, burrowed marl or “white band” in its central part. The bed is named from the classic large gastropod horizon traditionally called the Voluta suspensa Bed and forms one of the best field marker levels in the middle part of the Barton Clay.

Historical local thickness: about 1.8 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed D — Middle Barton Clay And Nodule Interval

Bed D is generally seen now in slumped scarps and disturbed cliff rather than as a clean, continuous in situ face. It consists of shelly clay and sandy clay with nodule horizons and belongs to the same septarian-bearing middle Barton interval as Beds C and E. Sycostoma pyrus is especially characteristic. In the present cliff it is important not only stratigraphically but also geomorphologically, because this middle Barton clay package commonly coincides with zones of slipping and bench development.

Historical local thickness: about 6 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed E — Earthy Bed

This earthy, shell-rich clay and silt horizon is one of the great fossil beds of Barton-on-Sea. The bed is famous for well-preserved aragonitic molluscs. The checked BGS account lists Cornulina minax, Clavilithes macrospira, Sycostoma pyrus, Crassatella sulcata and Cardiocardia sulcata specifically from E. Turritella imbricateria, Volutospina ambigua, the large Volutospina luctator, and Xenophora agglutinans are particularly characteristic. In collector terms it is one of the richest horizons in the entire Barton Clay succession.

Historical local thickness: about 1.5 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed F — Upper Barton Clay Above The Earthy Bed

Above the Earthy Bed, Burton’s Bed F comprises upper Barton clays and sandy clays that are now commonly obscured by slumping, vegetation and coastal engineering works. The interval continues the upward-shallowing trend of the second Barton cycle and includes nodule-bearing weak horizons with increasing sandy content. Modern cliff and ground-model studies distinguish F1 and F2 levels within this upper Barton clay package, with a documented shear surface at the F1/F2 contact at Marine Drive West. These engineering subdivisions should not be treated as two extra beds added to Burton’s F.

Engineering subdivisions F1 and F2

These distinguish lower and upper parts of the F clay interval in engineering models. The F1/F2 contact at Marine Drive West is a documented translational failure surface. The evidence used here does not give defensible separate bed thicknesses or bed-specific fossil lists for F1 and F2.

Historical local thickness: about 6 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Bed G — Stone Band / Shell Band

Bed G is the classic top of the Barton Clay and one of the most distinctive marker beds in the whole section. It is a highly winnowed, brown to reddish, sideritic shell lag rich in Turritella and bivalves, commonly forming hard slabs on the beach. Sycostoma pyrus is also characteristic. Sedimentologically it represents the most strongly reworked and shell-concentrated horizon of the second cycle, probably a storm-accumulated and/or wave-winnowed shell concentration laid down in very shallow marine conditions immediately before the Chama Sand.

Historical local thickness: about 0.3 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Total Thickness Of Barton Clay Formation In The Classic Barton Cliffs Type Section: Somewhat Over 30 Metres

Chama Sand Formation

Bed H — Chama Bed / Chama Sand Formation (c. 5.5 m)

Bed H, the old Chama Bed and the modern Chama Sand Formation, is about 5.5 m thick at Barton. The lower c. 3 m consists of bluish-grey sandy clay with numerous fossils; the upper c. 2.4 m is greenish-grey to bluish-grey clayey sand with fewer fossils, chiefly bivalves. The blue-green colour reflects abundant glauconite. The conspicuous white, thick-shelled bivalve Chama squamosa is the best field fossil, especially in the lower part with Lyria decora; the upper part is characterised by “Meretrix” incurvata and Volutilithes pertusus. Unlike many lower Barton shell seams, fossils are scattered through the bed rather than concentrated in thin shell layers. The formation marks a major shoaling event and heralds the more restricted conditions that follow upward.

Lower Chama sandy clay (about 3 m)

The lower bluish-grey sandy-clay interval is the more fossil-rich subdivision, with Chama squamosa and Lyria decora.

Upper Chama clayey sand (about 2.4 m)

The upper blue-green to greenish-grey clayey sand has fewer fossils, mainly bivalves. Shell loss through decalcification can leave moulds. These rounded subdivision measurements belong to the historical Barton section described by Burton and discussed by West.

Total Thickness Of Chama Sand Formation At Barton-on-Sea: Approximately 5.5 Metres

Becton Sand Formation

Bed I — Lower Becton Sand (c. 7.9 m)

Bed I forms the lower part of the Becton Sand Formation and consists of pale grey, yellow and white fine micaceous sands, clayey and silty at the base and only weakly coherent in many exposures. Fossils are generally sparse, though shell moulds occur in the upper part. The trace fossil Ophiomorpha is especially important here, indicating sandy middle- to upper-shoreface conditions without evidence of subaerial exposure. This bed represents the clean-sand, relatively high-energy phase above the Chama shoal.

Historical local thickness: about 8 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Becton Bunny Member

Bed J — Becton Bunny Bed / Olivella branderi Bed (c. 7.9 m)

Bed J is the muddy middle division of the Becton Sand and corresponds to the Becton Bunny Member. The historical BGS tabulation gives about 8 m of grey-brown clay with marine and estuarine shells, and records callianassid remains in soft concretions. West’s local account after Burton gives about 7.9 m, divided into lower and upper sandy-clay intervals described below. A marked break at its base separates it from the cleaner sands below. Fossils are numerous but usually fragile and include abundant Olivella branderi, together with Pollia, Nucula, Pitar, Potamides, Corbicula, Bayania and callianassid crustacean remains; West also records Nautilus from the Becton Bunny Bed. The mixed fauna shows a shift from marine into appreciably brackish conditions in a more sheltered sandy-muddy setting.

Lower Becton Bunny sandy clay (about 1.8 m)

The lower subdivision is drab-grey sandy clay in Burton’s section as reproduced and discussed by West.

Upper Becton Bunny sandy clay (about 6 m)

Greenish-grey sandy clay weathers pinkish where iron compounds oxidise. Small rounded iron-rich concretions occur about 3 m above the base of J and average around 10 cm across. These are rounded historical measurements: the stated 7.9 m total and rounded subdivisions should not be treated as mathematically exact equivalents.

Becton Sand Formation (above the Becton Bunny Member)

Bed K — Upper Becton Sand / Long Mead End Sands

Bed K forms the upper part of the Becton Sand above the Becton Bunny Member and includes the cleaner Long Mead End sands. It is mainly composed of white and yellow fine sands with some sandy loams, less muddy than Bed J and locally more beach- or barrier-like in aspect. Brackish shells occur in the loamier parts, including Cyrena, Dreissensia and Erodona, while the higher white and yellow sands have yielded Lucina gibbosula and Batillaria pleurotomoides. A thin greenish clay marks the approach to the overlying Headon Hill Formation farther east. This bed completes the marine Barton succession at Barton-on-Sea and records the final shoaling into restricted lagoonal and, beyond the section, freshwater conditions.

Historical local thickness: about 6 m in the BGS 1982 type-section tabulation. This is a source-specific bed estimate, not a measurement of present exposure.

Total Thickness Of Becton Sand Formation In The Barton Cliffs Type Area: About 22 Metres

Stratigraphic Significance

The Barton coastal section between Friar’s Cliff and Beacon Cliff is internationally important because it is the type section for the Bartonian Stage and includes the type sections of the Barton Clay, Chama Sand and Becton Sand formations. Historically the Bartonian was recognised from the Nummulites prestwichianus horizon near the base of Bed A1, although modern lithostratigraphy places the base of the Barton Clay at the basal pebble bed below. The section is also a key calcareous nannoplankton reference and the NP17 type area. The older GCR account, following Aubry (1986), placed the approximate NP16–NP17 boundary around Bed E. The later BGS regional framework instead places it low in the Barton Clay near the Nummulites prestwichianus horizon. These published placements differ; Bed E should therefore not be presented as an uncontested modern nannoplankton datum.

Depositional Environment

The Barton-on-Sea succession records three linked marine regressive–transgressive cycles. The basal pebble bed and lower Barton beds mark marine transgression over older sandy strata; A3 shows shallowing and reworking at the top of the first cycle; Bed B deepens again into a more argillaceous shelf-mud phase; Beds G, H and I record progressive shoaling from shell lag to glauconitic sandy shoal and then shoreface sand; and Beds J and K show increasing restriction, brackish influence and barrier or nearshore sand accumulation before the succeeding Headon lagoons. The Barton Clay fauna indicates a low-energy warm marine shelf with nearby land, and estimated water depths in the broader Barton sequence were variable, from relatively shallow inner-shelf settings to rather deeper shelf waters at some horizons.

Structural Style And Exposure

Barton-on-Sea must be treated as a composite landslipped coastal section, not as one neat continuously exposed cliff face. Sea-defence works and cliff instability have hidden much of the lower Barton at the central frontage, so Beds A1 and A2 are now rarely seen well; A3 may appear near the west end of the Naish Farm section depending on erosion; Bed C is the clearest middle Barton field marker; Beds D–F are commonly visible only in limited slumped scarps; Bed G is now uncommon but may appear in landslide debris; the Chama Sand is often best seen at the eastern end of the sea defences; and Beds I–K of the Becton Sand are best examined eastward near Becton Bunny and toward Long Mead End. The geology and the modern geomorphology are closely linked, with the upper Barton clay horizons, especially within Bed F, forming important slip surfaces.

Total Thickness Covered Here

The classic marine Barton-on-Sea succession described here totals roughly 58 metres in the Barton Cliffs type area: somewhat over 30 m of Barton Clay Formation, about 5.5 m of Chama Sand Formation, and about 22 m of Becton Sand Formation, before passage upward and eastward into the lower Headon Hill Formation. These are the rounded GCR type-area estimates. Other local logs differ: BGS records about 24 m for the Becton Sand at Barton, while engineering work uses a thicker Barton Clay succession and revised subdivisions. These figures are not interchangeable measurements of one presently exposed face.

Alternative historical frameworks: comparison only

The detailed succession above follows the three-formation framework used by the GCR for the Barton type area: Barton Clay through G, Chama Sand H, and Becton Sand I–K. The following older member names divide the same beds differently. They are alternative classifications, not additional strata or thickness.

Barton Formation (historical BGS 1982 scheme)

Highcliff Member (historical scheme)

The lower historical division spans the basal clay interval and Beds A1–B in BGS Table 12. Bed B therefore remains in Highcliff in this classification, despite beginning a separate depositional cycle.

Naish Member (historical scheme)

The middle historical division comprises Beds C–G, including the nodule-bearing clays, Earthy Bed and Stone Band.

Becton Member (historical scheme)

The upper historical division comprises H–K. It includes the Chama Bed as well as the I–K succession, so it must not be equated to the narrower Becton Sand Formation used above.

King’s later framework

The BGS 2015 account describes King’s later subdivision of the Barton Clay into Elmore, Highcliff and Naish members and his Becton Formation, with the Chama interval treated as an informal bed. This is another distinct scheme. The Elmore Member is not inserted as a proven extra unit in the Barton cliff log here: the cited account establishes its island sections but does not supply an exact local Elmore bed log for this frontage.

Quaternary superficial cover above the Eocene succession

A major erosional interval separates the Eocene rocks from the much younger cliff-top deposits. The following observations come from the exact Highcliffe–Naish coastal sections in the BGS Bournemouth memoir; the individual examples are lateral comparisons, not one stacked measured log.

Naish cliff-top terrace gravel (about 2–4 m)

The memoir records freeze–thaw-disturbed river-terrace gravel from Naish Farm at SZ 2250 9315 eastwards to its mapped district edge, in its Tenth River Terrace account. The distorted base and pockets record cryoturbation rather than extra Eocene beds.

Brickearth above the Naish gravel (local thickness not specified)

The gravel is capped by brickearth, a fine-grained superficial cover. The cited coastal observation gives no separate brickearth thickness, so measurements from unrelated inland boreholes are not transferred here.

Separate Naish exposure at SZ 2243 9317

BGS recorded 1.5 m of gravel over 1 m of orange-buff, very fine silty Becton Sand, grading below into very clayey fine sand. This is an independent local exposure and does not replace the 2–4 m cliff-top gravel estimate farther east.

Highcliffe Ninth Terrace comparison at SZ 2134 9317

A separate western section comprised 0.5 m of topsoil over 2 m of poorly sorted, weakly bedded sand and gravel. Its upper 0.3 m was cryoturbated, with upright pebbles; that disturbed part is included within the 2 m gravel measurement.

Cryoturbated gravel margins near Highcliffe and Chewton

At SZ 2066 9312 and SZ 2234 9320 the memoir describes gravel pockets extending 2–3 m downward between tongues of Barton Clay. These are periglacial deformation structures at the contact, not separately deposited alternating clay and gravel beds.

References

Gardner, Keeping & Monckton (1888) on the classic Lower, Middle and Upper Barton divisions.
White (1917, 1921) on the Barton and allied Hampshire Basin shell beds.
Burton, E.St.J. (1929, 1933) on the faunal horizons and lettered bed scheme of the Barton succession.
Curry & Wisden (1958). Geologists’ Association guide to the Hampshire Basin.
Hooker, J.J. (1976, 1986) on cyclicity, mammalian biostratigraphy and the formal Barton Clay–Becton Sand lithostratigraphy.
Edwards, N. & Freshney, E.C. (1987a, 1987b) on the Barton Group stratigraphy and the Barton Clay, Chama Sand and Becton Sand formations.
Bristow, Freshney & Penn (1991). British Geological Survey memoir for the Bournemouth district.
British Geological Survey memoir for the Southampton district.
British Geological Survey Lexicon: Barton Group, Barton Clay Formation, Chama Sand Formation, Becton Sand Formation, Becton Bunny Member and Headon Hill Formation.
Geological Conservation Review / JNCC accounts for Barton Cliffs and Barton Cliff.
Aubry and co-authors on calcareous nannoplankton zonation of the Bartonian type section.