Hunstanton Fossil Hunting

The units below are described from youngest to oldest. They represent the cliff and shore between North Promenade and St Edmund’s Point, not a complete regional Chalk column. Bed boundaries include non-sequences, and exposures change as the beach and cliff retreat.

Quaternary superficial cover

Glacial and other superficial material locally overlies the Cretaceous rocks across a very large time gap. It is not a member of the Chalk. This cap is omitted from any scaled bedrock measurement because its thickness and exposure vary along the cliff.

CHALK GROUP

GREY CHALK SUBGROUP

Ferriby Chalk Formation

The Cenomanian succession is predominantly flint-free marly chalk with harder, shelly intervals. The cliffs expose only part of the formation; thicknesses quoted for the full formation elsewhere should not be applied to this exposure. From higher to lower in the accessible published succession, important markers are the Ammonite Bed, Totternhoe Stone, intervening marly and nodular chalk, Upper and Lower Inoceramus beds, and basal Paradoxica Bed.

Local measured sections and thicknesses. The following descriptions use the lighthouse composite section in Gallois (1994), supplemented by the later Geological Conservation Review account. These are published measurements of particular beds, not measurements of the present cliff or a complete Ferriby Chalk thickness. The memoir’s overview and its detailed lighthouse log give different thicknesses for some named beds; those differences are retained rather than silently selecting a universal value.

Chalk above the Ammonite Bed

The lighthouse log records, from top down, about 1.50 m of weathered, frost-disturbed chalk; 1.02 m of thin-bedded chalk with a concentration of marl wisps; 0.18 m of clay-rich chalk with closely spaced marl laminae; 0.41 m of softer thin-bedded chalk; a 0.10 m chalk–marl alternation; and 0.46 m of harder chalk with sparse marl streaks. These distinguishable lithological intervals are left unnamed: no regional marl name is imposed without a demonstrated correlation. The uppermost part is modified by weathering and cryoturbation. Higher markers such as the Nettleton Stone and Plenus Marls occur in the wider district and borehole record, but are not added as visible beds in this cliff guide.

Ammonite Bed and Upper Orbirhynchia Band

Immediately above the Totternhoe Stone lies a hard white chalkstone, represented by a 0.30 m very hard grey-white interval in the lighthouse log. Large, relatively uncrushed ammonites include Parapuzosia (Austiniceras) austeni. Its Orbirhynchia mantelliana fauna links it with the Upper Orbirhynchia Band, rather than with the lower brachiopod-rich level beneath the Totternhoe Stone. The GCR interpretation places this interval towards the top of the Turrilites costatus Subzone. Fossil-bed correlation does not imply that every ammonite-bearing loose block can be assigned to it.

Totternhoe Stone

A grey, gritty and strongly burrowed chalk rests on an erosional surface. Its lower part contains glauconitised and phosphatised chalk pebbles, some bored, and a concentration of shell debris. The detailed lighthouse log measures 0.48 m, whereas the memoir’s general account gives about 0.7 m at Hunstanton. Burrows filled with the darker gritty sediment descend into the underlying paler chalk, reaching 0.6 m in the measured lighthouse section. Fossils documented by the GCR include abundant Entolium orbiculare and Oxytoma seminudum, the serpulid Glandifera rustica, brachiopods including Grasirhynchia martini and Modestella geinitizi, and the belemnites Praeactinocamax primus and Belemnocamax boweri. Ammonites are commonly flattened or imperfect moulds. The bed is Middle Cenomanian; the basal erosion surface omits part of the Lower–Middle Cenomanian transition, including evidence of the basal Middle Cenomanian Cunningtoniceras inerme Zone.

Lower Orbirhynchia Band and underlying marly chalk

Below the Totternhoe Stone, brachiopod-rich marly chalk contains Orbirhynchia mantelliana, distinguishing the Lower Orbirhynchia Band. Beneath it are nodular and marly chalks with Inoceramus of the virgatus group. These faunal levels constrain correlation within the Mantelliceras dixoni Zone. The lighthouse log subdivides the interval below the Totternhoe Stone, downward, into 0.59 m of soft chalk penetrated by burrows from above, 0.13 m of chalk and marl, 0.61 m of chalk with few marl wisps, a 0.05 m marl-wispy interval, 1.07 m of chalk with scattered marl, and a further 0.15–0.23 m marl-wispy interval above the Upper Inoceramus Bed. These are measured lithological subdivisions, not six newly named formal beds.

Upper Inoceramus Bed and Turrilitoid Plane

This is the upper of two shell-debris-rich chalk intervals. The lighthouse log gives 1.12–1.14 m; the memoir’s general description gives 1.07 m. A conspicuous internal bedding plane occurs roughly half a metre above its base. The lower part contains a glauconitised surface, called the Turrilitoid Plane, associated with large poorly preserved heteromorph ammonites assigned to Hypoturrilites and/or Mariella. Thin-shelled inoceramids are prominent. The GCR places the renewed coarse shelly sedimentation near the base of the Mantelliceras dixoni Zone, revising the older memoir’s tentative correlation with the saxbii Subzone. The discrepancy concerns interpretation, not a second bed.

Chalk separating the two Inoceramus beds

The named shell-rich intervals are separated by 0.37–0.46 m of hard off-white chalk in the lighthouse log. Marl wisps form weak partings. Keeping this intervening chalk separate matters: the Upper and Lower Inoceramus beds are not a single uninterrupted shell bank.

Lower Inoceramus Bed

Grey gritty chalk with abundant complete and broken inoceramid shells overlies a hard irregular surface. A basal concentration of glauconitised and phosphatised chalk pebbles records erosion and reworking. The detailed lighthouse composite gives 0.92–0.95 m, while the memoir’s general text quotes 0.46 m; these cannot be treated as an unqualified single locality thickness. The GCR documents Inoceramus crippsi, Rastellum colubrinum, small Holaster bischoffi, rare Neohibolites ultimus and ammonites including Schloenbachia. Its later biostratigraphical interpretation assigns the bed to the Sharpeiceras schlueteri Subzone of the Mantelliceras mantelli Zone.

Paradoxica Bed: upper and lower divisions

The lowest Ferriby Chalk is exceptionally hard, burrowed chalkstone, 0.43 m thick in the lighthouse log. Its branching Thalassinoides paradoxicus network was historically mistaken for a sponge. Several closely spaced hardgrounds and green-stained surfaces record interrupted deposition and early seabed cementation. A prominent internal erosion surface separates lower and upper divisions. The upper division is retained in much of the southern and central section but dwindles to patches or disappears near St Edmund’s Point. The lower division contains Aucellina bivalves and Neohibolites ultimus; larger terebratulid brachiopods and inoceramids occur above. The GCR correlates the lower fauna with the ultimus/Aucellina event and the Neostlingoceras carcitanense Subzone, while noting that the index ammonite itself has not been recorded here.

Red boundary marl and the Albian–Cenomanian hiatus

A thin, laterally variable, dark-red marl occupies hollows above the eroded Red Chalk and below the Paradoxica Bed. Historical authors assigned it differently: it has been included at the top of the Red Chalk or treated separately at the base of the younger succession. Fossils include small terebratulids and Neohibolites ultimus. Comparison with more complete sections shows missing time beneath the Cenomanian chalk. The red colour therefore does not establish an Albian age by itself. Andrews and colleagues distinguish a possible Frutexites crust from projecting iron-stained nodules, rejecting those nodules as proof of an intertidal stromatolite environment.

Totternhoe Stone and adjacent chalk. The gritty Totternhoe Stone rests on an eroded and burrowed surface. Its fossils include Entolium orbiculare, Oxytoma seminudum and serpulid tubes. The overlying Ammonite Bed contains large ammonites assigned to Parapuzosia (Austiniceras) austeni. These are stratigraphical records, not a promise of readily accessible specimens.

Inoceramus beds and Paradoxica Bed. Shell-rich chalk records concentrated inoceramid debris and complete valves. At the base, welded hardgrounds and branching burrows give the Paradoxica Bed its distinctive appearance. The sedimentary record is interrupted both within this lower chalk and at its junction with the red beds.

Separate underlying formation: not part of the Chalk Group.

Hunstanton Formation: the Red Chalk

This is a separate formation rather than the lower member of the Ferriby Chalk in the current BGS Lexicon. At Hunstanton it comprises approximately 1–1.1 m of red to pink, partly sandy limestone and marly seams. Three main limestones with two separating marls form the traditional local subdivision. The five named members defined at Speeton belong to that Yorkshire succession and are not imported into this guide.

The main limestone sequence is Middle to Late Albian. Fossils and erosion surfaces show that it is strongly condensed, with intervals missing inside it as well as at its upper boundary. A thin, locally variable red marl at the top has been treated differently in historical accounts; the boundary should not be placed from colour alone. Research on the iron-stained structures distinguishes a possible microbial crust from non-microbial nodules, so an intertidal origin is not assumed.

Local subdivision. The five numbered units below are the lighthouse-section beds of Gallois (1994), listed from top down. Beds 5, 3 and 1 are the three principal limestones traditionally lettered A, B and C; beds 4 and 2 are their intervening marly seams. Those letters and numbers belong to this local scheme and must not be confused with the later HC numbering used for other Red Chalk sections.

Bed 5: upper limestone, divisions 5b and 5a

This 0.38–0.43 m bed is hard pink-to-red, fine-grained limestone, strongly mottled by burrows and nodular when weathered. An irregular purple-red surface in its upper part separates 5b from 5a. Sand and small angular pebbles increase downwards. Fossils recorded from 5b include Aucellina and Neohibolites praeultimus; 5a contains brachiopods, belemnites and inoceramids, including Inoceramus lissa in its upper part. Modern regional synthesis recognises successive Late Albian intervals and breaks within this condensed limestone; it should not be drawn as an uninterrupted record of every intervening ammonite zone.

Bed 4: upper red marly seam

A dark-red to reddish-brown, earthy, highly calcareous muddy seam is locally up to 30 mm thick. Sand grains, tiny quartz and ironstone pebbles and worn belemnites are conspicuous. Its irregular basal contact has been affected by local shearing, so the seam may be reduced or missing. The published fauna includes Moutonithyris dutempleana, Kingena spinulosa and several Neohibolites forms.

Bed 3: middle nodular limestone

The middle limestone is 0.41–0.43 m thick in the lighthouse section. Sandy, burrow-mottled pink and red chalky limestone contains clay-rich linings and pressure-solution seams and weathers into a rubbly nodular layer. Belemnites and brachiopods occur through it. The modern Albian interpretation recognises a major interruption within the middle limestone: an older basal component and younger Late Albian material cannot be treated as a single smoothly accumulated interval. The strongly ribbed inoceramid Actinoceramus sulcatus is associated with the condensed nodular succession in the regional synthesis.

Bed 2: lower red marly seam

The lower separating seam is dark-red, sandy calcareous clay, locally up to 20 mm thick. In places shearing has removed the clay, leaving an irregular iron-stained surface. It is a real local lithological marker, but its absence in one exposure does not demonstrate that the limestones on either side are the same bed.

Bed 1: basal sandy limestone

The basal 0.23–0.28 m is softer and much sandier than the higher Red Chalk. Downwards it changes, through strong burrowing, into pink and brown calcareous sand. Its lower contact is a sharp, approximately planar but burrowed surface on the Carstone. Recorded fossils include Moutonithyris dutempleana, inoceramid bivalves and Neohibolites minimus. Ammonites in the traditional lower limestone include Hoplites and support a Middle Albian age.

Separate underlying formation: not part of the Chalk Group.

Carstone Formation

The underlying marine sandstone contains iron-rich grains, quartz and pebbles. Its upper beds pass towards the more calcareous red succession, with burrowing across the transition. Older ammonites incorporated into basal phosphatic material are reworked fossils. The nearby Hunstanton Borehole proves 18.9 m of Carstone, but that is a borehole thickness, not the visible height of sandstone in the cliffs.

Detailed coastal subdivision. The BGS Albian compilation numbers five Carstone units C-HC1 to C-HC5 for Hunstanton Cliff and foreshore. The following top-down account retains those published identifiers. It is a composite coastal succession, not a claim that the whole thickness is visible above the beach at any one place or tide.

C-HC5: upper bioturbated sand, 0.13–0.42 m

Fine orange-brown ferruginous sand is soft and earthy, with sparse phosphatic nodules below and burrow fillings of red or pink mud brought down from the overlying beds. Its base is transitional. This interval combines Owen’s uppermost subdivisions 2ii–2iv of his Upper Carstone Member: a lower red sand with a nodule seam, an overlying olive-brown loamy sand and a thin clayey yellow-red sand at the top.

C-HC4: pebbly upper sandstone, about 0.80 m

Fine- to medium-grained orange-brown sandstone contains small phosphate nodules and pebbles. Burrowing is shown by partly phosphatised sandy fillings. It corresponds to Owen’s Upper Carstone bed 2i; the combination with C-HC5 should not erase the lithological contrast between the firmer lower sandstone and softer upper sands.

C-HC3: ferruginous sand above an erosion surface, 2.00–2.50 m

Brown to yellow pebbly sand contains mud drapes and occasional phosphate nodules towards its top. It passes down into a basal pebble concentration on an uneven eroded surface. Owen treated this as bed 1 of the Upper Carstone Member.

C-HC2: massive lower sandstone and basal phosphate bed, about 13.90 m

This thicker interval is dark-brown, massive, pebbly and locally gritty, with iron-rich ooids. At its base is a phosphate-pebble bed containing reworked Aptian ammonites, including Cheloniceras, Dufrenoyia, Prodeshayesites and Tropaeum. These older fossils date their source rocks rather than the enclosing Albian sandstone.

C-HC1: basal sandy clay, about 1.30 m

The lowest coastal Carstone unit is pebbly, ooidal clay with sandy parts and sparse large rounded nodules of fossiliferous phosphatic ironstone near its top. Its base is sharply irregular and burrowed against the older Roach. The Roach contact belongs to the lowest part of the composite coastal record and should not be represented as a normally conspicuous bed in the three-coloured cliff face.

References

BGS, The holostratigraphy of the Albian Stage, section 6.2.5: Hunstanton Cliff Carstone log

BGS, East Anglia regional geology: revised Red Chalk biostratigraphy

BGS Lexicon: Hunstanton Formation

BGS Lexicon: Ferriby Chalk Formation

BGS Lexicon: Carstone Formation

Mortimore, Wood and Gallois, British Upper Cretaceous Stratigraphy: Hunstanton Cliffs

Gallois (1994), Geology of King’s Lynn and The Wash

Andrews, Kendall and Hall (2015; online 2014), Microbial crust with Frutexites(?) and iron staining in chalks