Santonian Working Group

To all members

During the last two year I have looked after the Santonian and Campanian WGs. Now, works are on "a good way" and I prefer to continue with one WG. Colleagues were sensible to my wish, and Prof. Jake Hancock agreed to chair the Campanian WG, during our meeting at Brussels. I am indebted all of you for your kind collaboration.

   Therewith you can find a copy of my short report on the Santonian WG conclusions. It is the base for a contribution, which will consist on the current position, including the evidence, about the Santonian Stage, Coniacian-Santonian boundary marker and its stratotype, substages, etc.

   I would appreciate your comments. I should expande four fold the report, explaining why and how we have chosen the marker, rejected other possibilities, etc.

   I am sure, I have lost part of your arguments, and I think your comments are the best way to complete my own notes.

   I am expecting for your news at your earliest convenience (*)

(*) I must send the MS by November 15th. So, please send me your comments no later than October 25th, if possible.

The Santonian WG currently consists of 39 members from 14 countries. The meeting was attended by 34 members.

Historical
   The Santonian Stage was proposed by Coquand (1857)) at Javrezac and Saintes (SW France). Its boundary is drawn at a hardground between glauconitic limestone of the Coniacian below and marls of the Santonian above.
   In 1983 (Birkelund et al. - I Symposium on Cretaceous Stage Boundaries) the concensus was that the first appearance of Texanites (Texanites) and of Inoceramus (Cladoceramus) undulatoplicatus are the two best boundary criteria. Texanites (Texanites) has been used over a wide area, although in classic regions of north-west Europe this subgenus is far too rare to be a practical marker (Hancock, 1991). Inoceramus (C.) undulatoplicatus is widespread, and owing to its characteristic form and sculture is easy to determine. The appearance of Inoceramus siccensis, is well known in N. Africa associated with Texanites, and it could be another possible marker for the base of the Santonian.

Criteria proposed for the Coniacian-Santonian boundary
1) FAD's Texanites (Texanites)
2) FAD's Sigalia carpatica
3) FAD's Dicarinella asymetrica
4) FAD's Inoceramus siccensis
5) FAD's Inoceramus (Cladoceramus) undulatoplicatus
6) FAD's Inoceramus (Sphenoceramus) pachti

No nannofossil event is suitable for the Coniacian-Santonian boundary

Selected marker for the Coniacian-Santonian boundary

FAD's Inoceramus (Cladoceramus) undulatoplicatus

   It is a taxon easely recognisable and widespread. It is known from N. America, Europe, N. Africa, Far East Russia.
This proposal has been approved by majority. Yes=23; No=1; Abstentions=2
Secondary marker: Sigalia carpatica. This planktonic foraminifera is widespread in the Mediterranean Region and N. America. It is associate with Inoceramus siccensis and Texanites in Tunisia. In N. Spain (Navarra) it is very close to the LAD's of Inoceramus (C.) undulatoplicatus.

Rejected
Texanites (Texanites). Its first occurrence is below the FAD's Inoceramus (C.) undulatoplicatus. It has been cited in assemblage with Coniacian inoceramids.
Dicarinella asymetrica. Its first appearance is above the FAD's Sigalia carpatica not suitable to characterize the Coniacian-Santonian boundary. It is restricted to basinal facies.
Inoceramus siccensis. Only known from N. Africa, although it may be correlated with other areas through the FAD's S. carpatica.
Inoceramus (Sphenoceramus) pachti. It is a boreal species rare at middle latitudes and in paleotropics (Tethys) unknown.

Boundary Stratotype Section
Up till now, we can not made a formal proposal, because we need to know and integrate biostratigraphy.
We have selected three candidates:
1) Olazagutía Quarry (Navarra, Spain). Prof. Lamolda would collate data and report to the Chairman.
2) Seaford Head (Sussex, England). Dr. Mortimore and Mr. Wood would collate data and report to the Chairman.
3) Ten Mile Creek (Dallas, Texas). Prof. Kauffman and Dr. Gale would collate data and report to the Chairman.
Data and reports have to be sent by february 1996.
This proposal was approbed UNANIMOUSLY (Yes=34; No=0; Abstentions=0)

Substages of the Santonian Stage
After discussion was made this motion;
1) The WG favoured a 3 fold division of the Santonian
2) Formal proposals are premature at present
3) A possible datum for the base of the Middle Santonian is the extinction point of Inoceramus (C.) undulatoplicatus.
4) A possible datum for the base of the Upper Santonian is the first occurrence of Uintacrinus socialis.
The WG agreed with it: Yes=15; No=0; Abstentions=6.

Substage boundary stratotypes: Up till now, the WG has no proposal for the substage boundary stratopypes. Possible boundary sections in Texas, along the Channel Coast, in Germany and Mangyschlak were discussed. Integration of macro-, micro-, nannofossil datums, stable isotopes and paleomagnetism, is necessary before further progress is possible.

Conclusions: The WG proposes as boundary marker the FAD's Inoceramus (Cladoderamus) undulatoplicatus and as secondary marker the FAD's Sigalia carpathica. There is no formal proposal as boundary stratotype. The WG should decide on three candidates: Olazagutía Quarry; Seaford Head and Ten Mile Creek. There are no formal proposals for substage markers, although it is favoured a 3 fold division, whose possible indices are: LAD's Inoceramus (C.) undulatoplicatus for the base of the Middle Santonian, and the FAD's Uintacrinus socialis for the base of the Upper Santonian. Several sections in Texas, Channer Coast, Germany, Mangyschlak were discussed, but no formal proposal is possible.