Subsurface geology of Eniwetok Atoll, with sections on carbonate mineralogy, petrography of the basalt beneath the limestones, and dating of carbonate rocks by ionium-uranium ratios

Calcitization of aragonite in Pleistocene limestones of Enewetak Atoll, Bahamas, and Yucatan —An alternative to thin-film neomorphism

“…Those intensely altered intervals occur (1) in paleo-soil zones immediately below exposure surfaces and (2) in 2-5 m thick intervals interpreted as paleo-freshwater lenses between exposure surfaces (Saller and Moore, 1989). Petrographic, trace elemental, and stable isotopic data from the XRI-I, XEN-l, and XAR-I wells indicate that most LMC cements precipitated in meteoric vadose and phreatic environments (Goter and Friedman, 1988;Saller and Moore, 1991; similar to conclusions of Schlanger, 1963 andGross andTracey, 1966, from different Enewetak wells). Patterns of meteoric diagenesis in the Pleistocene of Enewetak are described in detail in Goter and Friedman (1988) and Saller and Moore (1989).…”

“…Chalkified aragonite is also very common in Pleistocene strata on Enewetak (Schlanger, 1963;Goter and Friedman, 1988) and apparently represents an intermediate state of alteration between unaltered aragonite and either completely dissolved aragonite or calcitized aragonite (Sallerand Moore, 1989).Chalkification (also described by Goter, 1979 andGoter andFriedman, 1988) involves the delicate, microscopic dissolution of a significant amount of a grain's original aragonite ultrastructure 3b,. In chalkified areas, dissolution is widely disseminated, resulting in a residual meshwork of aragonite and organic material, preserving some original fossil wall structure, but leaving 40-90% intrafabric porosity (Figs.…”

A geological perspective of the upland biota of Laysan atoll (Hawaiian Islands)

“…Between 1 5 and 9 to 10 million years RP the height of the island was drastically reduced due to subaerial erosion and tectonic subsidence. A glacio-eustatic drop in sea level that took place during this time interval caused the emergence of Eniwetok, Bikini, and Midway atolls (Schlanger, 1963;Ladd, Tracey & Gross, 1970;Schlanger & Douglas, 1974), converting them into high limestone islands; presumably proto-Laysan Island also underwent emergence. By 9 million years BP these high limestone islands had submerged and become atolls once again (Fig.…”

“…As long as the island remained in a tropical environment where reef growth could keep pace with subsidence, an atoll developed on the sinking volcanic foundation. His subsidence theory was upheld by results of drilling at Eniwetok (Schlanger, 1963). Recent studies on the eruption rate of Kilauea volcano on Hawaii and estimates of the volume of the volcanic edifice that forms the island show that the entire structure could have been built in a few hundreds of thousands of years; the calculated rate of eruption of Kilauea is 0.11 km3/year (Shaw, 1973) press) the dates at which major volcanism along the chain essentially ceased have been determined in some detail (Fig.…”

Some physical constants for the Marshall Islands area

“…As detailed descriptions of the lithology and petrography of the various cores are given in other chapters of Professional Paper 260 (Ladd and Schlanger, 1960;Schlanger, 1962;Macdonald, 1962) only the most generalized statement of rock type is given for the various specimens cited in the present discussion. The reader is referred to the more detailed descriptions for additional petrographic data.…”