LOWER LIAS OF ROBIN HOOD'S BAY 



147 



Cymbites laevigatus and Angulaticeras sp. indet. occur in the lower 

 half of the subzone. 



Oxynotum Subzone, beds 472.1-486.2. More involute and com- 

 pressed Oxynoticeras like O. oxynotum rather than O. simpsoni first 

 occur in bed 472. 1 , so the base of the subzone is placed at that level. 

 Better specimens occur higher in the subzone, as well as fragments 

 of large specimens. Other oxynoticeratids present are two possible 

 specimens of Paroxy notice ras salisburgense in the lower half, and 

 Gleviceras doris and G. guibalianum in the upper half of the subzone. 

 Angulaticeras sp. indet., Bifericeras bifer and B. cf. vitreum, also 

 occur in the upper half of the subzone. 



RARICOSTATUM ZONE, Densinodulum Subzone, beds 486.3 

 and 487. The base of the subzone is placed at the first appearance of 

 Crucilobiceras in bed 486.3 and the top is limited by the first 

 occurrence of Echioceras in bed 488 marking the base of the 

 Raricostatoides Subzone. So the Densinodulum Subzone consists 

 only of the 1.0 m thick beds 486.3 and 487. C. densinodulum is 

 abundant in bed 486.3, but there are no other ammonites in the 

 subzone. 



Raricostatoides Subzone, beds 488^493.5. The base of the subzone 

 is placed at the first appearance of Echioceras: E. raricostatoides in 

 the basal one-third of the subzone is followed by E. intermedium in 

 the middle part, then by Paltechioceras planum in the upper one- 

 third of the subzone. Crucilobiceras densinodulum persists from the 

 subzone below into the basal bed, and the only other ammonite in the 

 subzone is Eoderoceras hastatum in the upper part. 



Macdonnelli Subzone, beds 494-495.7. This subzone is based on 

 the range of the index species Leptechioceras macdonnelli, which 

 occurs in the top and bottom beds and does not range higher. The 

 earliest Eoderoceras armatum occurs in the bottom bed, and the first 

 Polymorphitid, Gemmellaroceras tubellum, occurs in the top bed. 

 The only other ammonites present are the Oxynoticeratids Gleviceras 

 guibalianum near the top of the subzone and Radstockiceras 

 buvignieri in the bottom bed. The latter record seems to be the first 

 provable occurrence of Radstockiceras in the Raricostatum Zone. 



Aplanatum Subzone, beds 496-500. The base of the subzone is 

 placed at the first occurrence of Paltechioceras regustatum, and P. 

 tardecrescens (of which P. aplanatum is a synonym) becomes abun- 

 dant in the middle and upper parts of the subzone. Paltechioceras 

 first occurs in the top part of the Raricostatoides Subzone, but the 

 genus is much more common in the Aplanatum Subzone and does 

 not range higher. Another ammonite that is characteristic of the 

 Aplanatum Subzone is Eoderoceras armatum, which first appears as 

 rare examples in the Macdonnelli Subzone, but becomes much more 

 common in the Aplanatum Subzone; it ranges up to 0. 15 m below the 

 top of bed 499. but it does not occur higher and does not overlap with 

 Apoderoceras in the Taylori Subzone. Gemmellaroceras tubellum is 

 common in the middle part, and Gleviceras guibalianum occurs in 

 the lower part of the subzone. 



LOWER PLIENSBACHIAN 



The exposures at the base of the cliff in Wine Haven, Robin Hood's 

 Bay. have recently been proposed as the Global Stratotype Section 

 and Point (GSSP) for the base of the Pliensbachian Stage (Hesselbo 

 et al, 2000). The sequence across the Sinemurian/Pliensbachian 

 boundary is sufficiently expanded and rich in ammonites here to be 

 suitable for such an important global reference section. Hesselbo et 

 al.'s (2000: 604, fig. 4) stratigraphical sequence is closely similar to 

 the sequence described here, as are their ammonite records and 

 identifications. Their bed 73 at the base of the Pliensbachian is the 



Z 



< 

 X 



u 



< 



CO 



Z 



UJ 



O- 

 04 



UJ 



% 



O 



502 



501.3 



501.2 



501.1 



OS 



500 



499 



498 



znznjz 



t 3 Phricodoceras taylori 



6 Apoderoceras subtriangulare 



■ 1 Phricodoceras taylori 



h 



2 Apoderoceras sp. indet. 



1 Phricodoceras (avion 



1 Gemmellaroceras sp. indet. 



3 Apoderoceras subtriangulare 



63 Gemmellaroceras tubellum 



1 Apoderoceras subtrtangulare 



2 Bifericeras donovani 



_ 2 Apoderoceras subtrtangulare 



16 Bifericeras donovani 



• 1 Eoderoceras armatum 

 - 1 Gleviceras guibalianum 



h 



497 



6 Eoderoceras armatum 

 2 Paltechioceras tardecrescens 

 3CZp] 72 Paltechioceras tardecrescens 

 ^T~~_J j 8 Eoderoceras armatum 

 — P 1 5 Gemmellaroceras tubellum 



64 Paltechioceras tardecrescens 



_30 Eoderoceras armatum 



3 Gleviceras guibalianum 



1 2 Gemmellaroceras tubellum 



2 Eoderoceras armatum 

 - 2 Gleviceras guibalianum 

 2 Gemmellaroceras tubellum 



Fig. 23 The distribution of ammonites close to the Sinemurian/ 

 Pliensbachian boundary in Robin Hood's Bay. The ammonites listed 

 include those collected from the exposures across the boundary at both 

 Wine Haven and the foreshore immediately east of Robin Hood's Bay 

 town; there are no significant differences in the distribution of 

 ammonites at the two exposures. 



same as bed 501 here (see the correlation table of Fig. 19), and their 

 photograph (Hesselbo et al. 2000: fig. 3) shows the nodules of their 

 bed 72 (=bed 500 here) and the basal reference point of the 

 Pliensbachian low in the cliff at Wine Haven. 



Fig. 23 shows details of the stratigraphical distribution of 

 Bairstow's ammonites at the Sinemurian/Pliensbachian boundary. 

 The first ammonites to occur above the boundary are 16 Bifericeras 

 donovani Dommergues & Meister (one is figured in PI. 8. fig. 3) and 



