Geology topics
Research about Enewetak Atoll
Source-linked reports with geographic coverage including Enewetak Atoll.
Strontium-isotope stratigraphy of Enewetak Atoll
87 Sr/ 86 Sr ratios determined for samples from a 350 m core of Neogene lagoonal, shallow-water limestones from Enewetak Atoll display a remarkably informative trend. Like the recently published data for Deep Sea Drilling Project (DSDP) carbonates, 87 Sr/ 86 Sr at Enewetak increases monotonically but not smoothly from the early Miocene to the Pleistocene. The data show intervals of little or no change in 87 Sr/ 86 Sr, punctuated by sharp transitions to lower values toward greater core depths. The sharp transitions correlate with observed solution disconformities caused by periods of subaerial erosion, whereas the intervals of little or no change in 87 Sr/ 86 Sr correspond to intervals of rapid accumulation of shallow-water carbonate sediments. When converted to numerical ages using the published DSDP 590B trend, the best-resolved time breaks are at 282 m (12.3 to 18.2 Ma missing) and 121.6 m (3.0 to 5.3 Ma missing) below the lagoon floor. At Enewetak, Sr isotopes offer a stratigraphic resolution for these shallow-marine Neogene carbonates comparable to that of nannofossil zonation in deep-sea carbonates (0.3-3 m.y.). In addition, the correlation of times of Sr-isotope breaks at Enewetak with times of rapid Sr-isotope change in the DSDP 590B samples confirms the importance off sea-level changes in the evolution of global-marine Sr isotopes and shows that the Sr-isotope response to sea-level falls is rapid.
Pacific Enewetak Atoll Crater Exploration (PEACE) program, Enewetak Atoll, Republic of the Marshall Islands. Part 1: Drilling operations and descriptions of boreholes in vicinity of KOA and OAK craters
From mid-1984 through mid-1985, the United States Geological Survey (USGS) engaged in an investigation of two craters formed from high-yield, near-surface nuclear bursts in the Marshall Islands at Enewetak Atoll (figures 1 and 2). Supported by the Defense Nuclear Agency (DNA), this cooperative venture is referred to by the acronym PEACE, derived from its official name, Pacific Enewetak Atoll Crater Exploration Program. The craters studied, KOA and OAK, resulted from 1.4- and 8.9-megaton, near-surface bursts detonated near the northern perimeter of the Enewetak lagoon on May 12 and June 28, 1958, respectively. At that time, Enewetak was administered by the United States Government under the auspices of the Trust Territories of the Pacific Islands (TTPI) and formed a part of the Pacific Proving Grounds (PPG). OAK and KOA are among the only high-yield nuclear craters available for studies of cratering processes and crater-related effects.