Larger Foraminifera from Eniwetok Atoll drill holes

Sixty-two species and one variety of larger Foraminifera from the Eniwetok Atoll drill holes K-1B, E-1, and F-1 were identified and many of these are described, discussed, and illustrated. Five species are listed from the Recent, Pleistocene, and Pliocene. There are 35 species, 3 new, and 1 variety reported from the Miocene. They are divided according to the Indo-Pacific time scale as follows: 5 species from Tertiary g, 4 species and 1 variety from Tertiary f, and 26 species from Tertiary e. Of the 23 species found in the upper Eocene, Tertiary 5, 8 are new. One of these Eocene species is still living. No species were found which could be considered diagnostic of the Oligocene, Tertiary o and d. The stratigraphic section is as follows: 0-615 feet, Recent, Pleistocene, and Pliocene; 615-860 feet, Tertiary g, Miocene; 860-1,080 feet, Tertiary /, Miocene; 1,080-2,687 feet, Tertiary e, Miocene; 2,687-2,780 feet, without diagnostic fossils; 2,7804,553 feet, Tertiary 5, upper Eocene. The Eniwetok Atoll drill holes are correlated with those at Bikini island using as points of reference the first appearance of diagnostic species. In the Eniwetok Atoll holes these points of reference, with one exception, are higher than those at Bikini. The top of the Lepidocyclina (Eulepidina) abdopustula zone (lowermost Tertiary e, Miocene) in all the drill holes occurs at nearly the same depth. It is possible to correlate the major part of the section in these drill holes with surface outcrops of Saipan, the Malay Archipelago and other Pacific localities. However, the lower section of Tertiary e between 1,925 and 2,687 feet in the drill holes does not appear to have a stratigraphic equivalent so far reported from outcrops in the Pacific area. Most of the sediments s^m to have accumulated at depths somewhere between 20 and 70 fathoms, and the sediments containing larger Foraminifera probably accumulated in quiet water at a depth between 20 and 40 fathoms. These shallowwater conditions are indicated by the extreme scarcity of Cyclocfyp&us, a deep-water genus. INTRODUCTION During the years 1951 and 1952, three holes were drilled on Eniwetok Atoll as a part of a test program of the Atomic Energy Commission and the Los Alamos Scientific Laboratory. In 1951 the first of these, designated K-1B, was drilled on Engebi Island to a depth of 1,285 feet. During the summer of 1952, hole F-1 was drilled on Elugelab Island to a depth of 4,630 feet, and hole E-1 on Parry Island was completed at a depth of 4,222 feet. A preliminary report on the drilling operations, sample recovery, and geology has been published (Ladd and others, 1953). The index map (fig. 254) shows the location of the drill holes. The writer examined all the samples from hole K-1B and the cores from the two other holes. In the time available, however, he was not able to examine all jthe samples of cuttings; larger Foraminifera from these samples were obtained for detailed study by Mrs. Evelyn Bourne under the supervision of H. S. Ladd, who says (written communication)— Depth figures for cuttings from the drill holes on Bikini island and Eniwetok Atoll have not been corrected for lag. During the drilling of F-1 and E-1 on Eniwetok Atoll, a series of dye tests was made, and the amount of lag at different depths calculated. A full report on the tests and a tabular listing of the corrections will appear in later chapter describing drilling procedure. It must be remembered, however, that the calculated corrections are interpretations based upon somewhat inadequate data. For this reason, in the present report and in others that will follow the depth figures used record the depth of the bit at the time the samples were collected. Matrix-free specimens were obtained in abundance from many of the cuttings and from certain of the cores that could be disintegrated readily. Some 700 oriented thin sections of the larger Foraminifera recovered from these samples were made by the writer. In addition, several hundred thin sections of the cores were studied in detail as a check against the results of the study of matrix-free specimens. From hole K-1B there are samples of cuttings from 337 feet to 1,238 feet with a core at 1,038-1,040 feet. From hole E-1 there are samples of cuttings from 600 feet to 3,130 feet with cores at 2,003-2,028 feet (core 1), 2,802-2,808 feet (core 2), and 4,078-4,100 feet (core 3). From hole F-1 there are samples of cuttings from 20970 feet, 1,040-1,240 feet and 2,000-2,130 feet with cores at 170-190 feet (core 1), 600-625 feet (core 2), 1,2301,248 feet (core 3), 1,718-1,740 feet (core 4), 1,978-2,003 feet (core 5), 2,662-2,687 feet (core 6), 3,052-3,055 feet 745 744 BIKINI AND NEARBY ATOLLS, MARSHALL ISLANDS 162°00' Iff 2ff 162«3<y