Report of the Committee on Paleoecology, 1936-1937; Presented at the Annual Meeting of the Division of Geology and Geography, National Research Council, May 1, 1937 (1937)

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-7 - PALEOECOfcCGY OF THE FCHAMDCEFERA ; . ', ••'.'.J. A. Cushman ». •• ... . •. . : . • •'- • ;' ••' /• Althcjugh foraminifera are now known throughout the fossil series from the Cambrian to the Recent oceans, very little has been written in regard to their ecology or about the controls of their distributions. Our growing knowledge as to the ecology of this group must be based largely, as in other groups, on the living species, their associations and'environmental conditions of life. For convenience in .discussion, the foraminifera may be divided into bottom-livJj^g and pelagic groups. The latter group is the more specialized and later in .its development and will be considered first* . ,.'';.-••' -,••••". -..; .... . i - .. -! s. -, ^ Pelagic F oraminifera ' ,'.,. Peculiar characters have developed in, the f oraminifera .to adapt them to pelagic existence. They occur only in comparatively warm waters , so far as is known. Owing to their floating life in which there is littla. need of the development of dorsal and ventral sides for attachment or pro- tection of the aperture and the extended protoplasm, a generally rounded form is developed, This is carried to its perfection in Qrbuljria which in the adult consists of a test in the shape of a perfect sphere-. In order to float in the water the protoplasm is-extended from the test and becomes filled with gas so that the whole mass .is many times the size .of the orig- inar.test. In order £o support this greatly enlarged protoplasmic mass . spine's are developed, .on the exterior of the test., in some species longer than the diameter of the test itself. These make useful supports for the protoplasmic mass and may provide a certain amount of protection for the. . ; anirial itself against enemies.., j£n other groups.'such as-globigerina,. ' ",.",:f? Globifferinoides and. Globigerinella the .phambers. are themselves subspheri- ckl ahd the whole mass of the" test is' more, or.,less globularv Other genera, of the" gLoborotaljiidae, for example „ have d.ejreioped a more flattened form and much shorter spines but yet meet the conditions of a pelagic environ- ment so that, they appear in enqrmous numbers but with only a few species.. As a rule- the pelagic foraminifera exist in the, warm .surface waters, of the Gulf Stream-and the similar warm currents of the other oceans. -.; They exist until they meet cold currents and then 'apparently die quickly, ancf. their tests'.form the Globigerina-ooze of the ocean bottom. Their , . empty tests are' also rained down upon the ocean bottom beneath these . . warmer currents of all the oceans. In such areas the tests of pelagic ', "^ forms make up a very.large percent of the entire ocean "bottom.,,. .. * ' 'i * r ''i*' In certain other very specialized genera such as Tretomphalus a pelagic existence .may develop during the adult stage only., The test in this genus is a bottom living form of. coral-reefs but at the:final stage in its development, produces a large globular chamber which is gas-filled and'sends the test to the! surface where .it apparently reproduces by

zoospores. This is a very specialized development and has apparently occurred only in late Tertiary time. At certain seasons or under certain conditions which we do not understand there must be an enormous develop- ment of these forms, as they have been reported as forming definite "windrows" along the beach in the Australian regions so numerous are the tests at certain times. The more normal pelagic forms are know to occur as early as the Lower Cretaceous and in the Upper Cretaceous form a large portion of the fauna in some formations. Many of the same pelagic genera developed in the Cretaceous exist in the present oceans, and it seems rather warranted to infer that conditions at the two periods were more or less similar as to the temperature of the ocean surface. That warm ocean currents existed at those and later periods seems safe to infer as in the depositional se- ries pelagic forms may dominate in some layers and then for a time give way to those of more shallow or colder waters just as they do in cores recently taken from the present ocean floor. During Tertiary times masses of pelagic foraminifera were deposited in "Globigerina-oozes" com- parable in most features with those which are developed today. The dis- tribution of such deposits should indicate rather closely the areal ex- tent of the warm ocean currents of those periods, and when more is known of the distribution perhaps even the directions of the currents may be determined. Bottom-living Foranrlnifera i The foraminifera which now live on the ocean bottom may first of all be divided into brackish water and truly marine forms. The former which compose a specialized group will be discussed first. Brackish-water Foraminifera—In certain regions such as Lake Maracaibo, Venezuela, the southern extension of San Francisco Bay and other regions, are developed faunas which are restricted in number of species and genera. Moreover, the same sort of grouping exists in widely separated brackish- water area. As might be supposed, these consist partly of arenaceous foraminifera which are especially fitted to withstand acidic conditions but strangely enough some of the highly calcareous forms also appear. The Miliolidae are represented by a few species of Quinqueloculina and Triloculina and the Nonionidae by certain species of Elphidium. Very similar restricted faunas consisting of the same genera are known in the latter part of the Tertiary and undoubtedly also represent brackish-water conditions. It should be possible in the future when the distribution of these faunas is better known to predict the position of the shore line and that of the open ocean from the restriction or addition to the faunas in one direction and the other. It should also indicate something of the relative salinity of the water at the time these faunas were deposited. Marine Foraminifera—Of the foraminifera living in the present oceans un- der marine and non-brackish conditions it is convenient to divide the faunas into three groups just as is done with other animals, making three groups; (1) those of littoral or comparatively shallow waters, (2) those of the

-9 - .Continental Shelf, and, (3) those of abyssal depths. While there are genera which 'are found under all three of these different conditions .'wary few species, if any, occur in all three, , Littoral Foraminifera, The faunas of shallow waters, under 50 fathoms vary'greatly according to temperature and bottom conditions. For example, there are probably no species existing in 5rlO fathoms on the coral reefs of Jamaica or Cuba that exist at the same depths off the Coast of New England, The clearness of the water is a decided factor in the tropics, and where muddy water is brought in (or perhaps the lowered salin- ity 'may also be a factor) the fauna is rapidly changed™ Off the coast of Jamaica it was found that various species lived on the short .eei-grass (Posidonia) and were very abundant where that plant flourished. Some of the larger"foraminifera of ccral reef regions such as MarginopOTa, etc., have associated with them certain algae in a commensal relation. As these algae are limited in their-'vertical range by the depth of penetration of sunlight' necessary to photosynthesis they also limit the distribution of the foraminifera in the association. There is a considerable fauna in the tropics limited in this way, and it may be rather safely inferred that some of .the. later Tertiary faunas of similar association indicate like environ- mental conditions. One 'thing at least to be watched for is that such forms may be carried out into deeper water by ,wave and current action and occur with other than their normal association^ Such specimens are, how- ever, usually rather obviously worn and their association through mechani- •cal means can usually be dscertalned.: . - ,. • . . In temperate and arctic regions the bottom conditions, .whether . .sandy or muddy may change very suddenly, as in Vineyard Sound arid Buzzards Bay,"and it has been found that many constituents of the foraminiferal fauna change likewise. These associations have not yet been worked out in detail as they should be and until this is carefully done it will be impossible' to apply this data in the study of fossil faunas which probably lived under similar conditions. In general there'are certain genera and species which are characteristic of comparatively shallow waters and those which should be much more definitely knowft than at present, '"•'. Foraminifera'of the Continental Shelf, From 50-500-fathoms off the continental shelves there is developed.a very rich fauna in.which the Lagenidae, Polymorphinidae, Buliminidae, Rotaliidae and some of the arena- ceous foraminifera are very characteristic and abundant* The"range in depth, is less restricted as temperature seems to be the most., definite con- trol^-.' As temperatures at these depths are less variable and have less seasonal range the environmental conditions are more uniform, and as a re- sult the species are widely distributed. That such conditions have pre- vailed during the Tertiary;,' at least, is shown by the Eocene, Oligocene and Miocene deposits of the Gulf and Atlantic Coastal Plain regions of the Southeastern United States where the faunas of apparently the same ages change as one goes toward the present shore line just as the faunas of the present ocean change in passing-outvfrom- shore line,, .„

- 10 - Abyssal Foraminifera.. Due to the solvent action of water under pressure most of the calcareous foraminifera disappear at about 2000 fath- oms and the resulting fauna is largely composed of arenaceous foraminifera which are not greatly affected by these conditions. The statement some- times made that arenaceous foraminifera live best under abyssal conditions is probably not true as they are often much more abundant in littoral dredgings and the fact of their apparent abundance in abyssal dredgings is due solely to the absence of the calcareous forms. ... The occurrence of typical abyssal deposits is not, so far as I am aware, known at all in the fossil series. Factors to be Eliminated in Correlation • -i Two faunas with much the same elements would naturally be consid- ered of the same age. One must take under consideration, however, that faunas migrate or live on in one region when from ecologic changes they disappear in others. As an example, a number of species of the lower Oligocene of Mississippi now exist, or at least very closely allied ones, in the Indo-Pacific region. Miocene species of the area about the Eastern Mediterranean are found living today about Australia and adjacent areas while they are apparently extinct in the Mediterranean itself. Re-working of faunas is evident in the case of the foraminifera and should arrays be held as a possibility. Where highly fossiliferous sedi- ments are borne away by rivers or by wave action, the contained foraminif- era may be carried some distances and redeposited with living faunas. There are numerous known instances of this and many more will undoubtedly be discovered. Criteria for the Study of Ecology of the Foraminifera One of the most certain methods of getting basic data for a study of the distribution of living foraminifera and the part that ecologic fac- tors play in that distribution is an intensive study of the occurrence of species in definite regions. At present a study of the foraminifera of Monterey Bay, California, has been carefully made. Studies are under way on a number of lines of samples taken along our Atlantic Coast from Florida to the Gulf of Maine. These lines were taken from shallow water well out onto the slope of the Continental Shelf and have been carefully taken with bottom temperatures and depths. A qualitative and quantitative study of those samples is under way, and it is hoped the results will give basic data for the study of at least late Tertiary sediments with considerable accuracy as to the ecologic conditions under which they were deposited. Cushman Laboratory for Foraminiferal Research, Sharon, Massachusetts.