Nautiloids from the Red Chalk Formation of Hunstanton

S M Bowerman (UK)

Nautiloid specimens from the Red Chalk Formation of Hunstanton are rare but can occasionally be collected. Most specimens found are incomplete and are generally collected from beach level rather than in situ, so determining from which unit and zone (unit A, B and C depending on which author is referred to) within the formation a specimen originated from is problematical.

Comparison of the lithology of the matrix surrounding a specimen with samples from known levels within the horizon may be possible. For example, one may carry out a clast count or sediment colour comparison, although the latter is dependent on the degree of weathering the specimen has been subject to. It seems unlikely, based on the lithological evidence of the specimens I collected that any originate from the lowest unit, bed C, which is a soft, dark red marly unit. This suggests that a Middle Albian provenance for these specimens may be ruled out. Therefore, it is apparent that all of these are from Upper Albian Age and originate from either bed B or Bed A.

The specimen in Fig. 2 demonstrates complete whorls and is involuted with a small umbilicus and some suture lines are visible. Preserved shell material is also evident. Another specimen I have examined consists of approximately three-quarters of the original, although the specimen is extremely water worn. A third specimen was the least complete and the state of preservation is poor. The two latter specimens do not have any shell material preserved as a result of weathering and the action of water (as mentioned above), although septa are visible on the phragmacones of both specimens.

The specimen shown is the largest collected and was found at the base of the cliff in 2002. The photo shows partial preparation. Precise identification has proven difficult. The Sedgwick Museum, Cambridge has tentatively suggested that the specimen may be of Hunstantonensis sp.