R. M. Stainforth
The Micropaleontologist 1949 - 3:3:12
P. Brönnimann has an article in the previous number of this Quarterly entitled “Notes on the ecologic interpretation of fossil Globigerina oozes from the West Indies.” As author of one of the two papers he discusses, I naturally noticed the opposed views expressed by Senn and myself and I wrote to Dr. Senn on the matter. Soon after receiving his reply, written from the hospital in Switzerland, I received the sad news of his unexpected and widely regretted death. I believe it would not come amiss to quote the relevant portions of the two letters which passed. Omitting extraneous matter and the personal courtesies, they run as follows:
Stainforth to Senn: November 1, 1948
“...It seems that we have both been considering the paleogeographic aspect of the Tertiary Globigerina marls, and have come to markedly different conclusions concerning their depths of deposition. For the reasons set out in my paper I can not visualize a greater depth than 500 meters for the Cipero, despite its similarity to modern Globigerina oozes. Some of these reasons are not applicable to the Eocene Navet marls—they do not seem to grade into a shallower facies along the Southern Range trend, and I know of no equivalents to the Oligocene Ste. Croix beds—hence these Eocene marls in Trinidad may have been deposited at a greater depth than their Oligocene analogue, the Cipero.
“In so far as my arguments for a relatively shallow depth for the Cipero are based on local factors not present in Barbados, I can not criticize your conclusions, but I shall never whole-heartedly believe in the profound depths you postulate.”
Senn to Stainforth: January 14, 1949
“...Concerning your remarks about my paper, you are not correct to say ‘that we have both been considering the paleogeographic aspect of the Tertiary Globigerina marls, and have come to markedly different conclusions concerning their depths of deposition.’ I have considered only the Globigerina marls of Barbados and have postulated a great depth only for the Codrington College marl as it is in downwards transition with sediments in which the CaCO3 dissolution becomes apparent. On page 314 [Senn, A., Die Geo!ogie der Insel Barbados, B.W.I. (Kleine Antillen) und die Morphogenese der umliegenden marinen Grossformen (The geology of Barbados, B.W.I., and the genesis of associated primary geomorphologic features). Eclogae Geol. Helv., 1948, vol. 40 (1947), no. 2] I clearly stated that ‘the Upper Oligocene Globigerina marls have been deposited in considerably less depths than the Globigerina marls of the Oceanic formation.’ For the Globigerina marls of the Bissex Hill formation it is obvious that their lower part, including algal limestones, has been deposited in less than 100 meters, the upper part at somewhat more than 100 meters. I certainly agree with your depth attribution of the Globigerina marls of the Cipero formation, …but one should never generalize! Moreover one never has to forget that Globigerina oozes are formed in the present seas at depths varying between 4500 meters and 100 meters or even less and one does not have positive criteria yet to characterize the various depth zones. I am myself still uncertain concerning the depths at which the Globigerina marls of the Oceanic formation were deposited and have therefore proposed to Professor Reichel of Basle University to have a doctorate thesis made on this subject...”
Little additional comment is necessary. Senn was quite right to claim that our conclusions were not mutually contradictory. The special features which indicate a relatively shallow depth for the Oligocene Cipero are not present in the superficially similar Eocene Navet of Trinidad nor Oceanic of Barbados. The main point is that Globigerina ooze conditions can and doubtless could in past time exist at all depths down from a certain minimum. The Cipero appears to have been deposited near this minimum but the Eocene marls may represent greater depth.
It is to be hoped that the suggestion of further study of the Oceanic marls will be followed up. For a long time the belief in abyssal deposition was widely held but more recently the age-assignments of the Barbados deposits have been drastically revised (compare Senn 1948 with Schuchert 1935 - Antillean-Caribbean Region), the validity of radiolarian deposits challenged as indicators of great depth, and likewise the significance of the echinoid Cystechinus as an abyssal form.