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The Hauteri vian to upper Albian carbonate sediments drilled on Resolution Guyot are all of shallow-water origin. The volcanic basement is covered by dolomitized oolitic and oncolitic grainstones of an inner-ramp setting. At 1400 m below seafloor (mbsf), they pass into peritidal facies punctuated by small coral and mdist bioherms and by beach sediments. Oolites dominate between 790 and 680 mbsf. The upper part of the guyot (from 680 mbsf up to the phosphate-iron-manganese crust capping the Cretaceous platform) is composed of lagoonal carbonates exhibiting some calcrete horizons. The material collected from Holes 867B and 868A implies that the platform was rimmed by barrier islands and storm beaches, and that reefs (rudists and sponges) were of minor importance. This is in contrast to modern atolls, where reefs are the major rim builders. In the late Albian, the platform was subaerially exposed and karstified, then drowned. Although average recovery was low (15.4% for Hole 866A, 29.2% for 867B, 46.3% for 868A), the cored material clearly shows that the sedimentary record is composed of small, meter-scale sequences. They are especially well developed in platforminterior, lagoonal-peritidal settings, where facies evolution indicates cyclic deepening and shallowing of the depositional environment. Boundaries of small-scale sequences are commonly accentuated by calcified algal-microbial mats, bird's eyes, desiccation fissures, or calcretes. Karstified surfaces and limonitic crusts appear locally. Early transgressive facies include organic-rich clays, algal-microbial mats, and reworked pebbles. Maximum flooding is suggested by more marine fauna and, in many places, by intensified bioturbation. Early dolomitization is stratabound, which may result from confinement of dolomitizing fluids by clay layers. The lagoonal-peritidal sequences are probably related to climatic and/or eustatic fluctuations in the Milankovitch frequency band. This hypothesis is supported by the cyclical pattern of the downhole logs. Meter-scale oolite sequences commonly exhibit keystone vugs at their tops, indicating the upper swash zone in a beach environment. Deeper water is suggested by bioturbation. Such sequences can have an autocyclic (dune migration) or allocyclic (sea-level fluctuations) origin. Small-scale shallowing-upward sequences in Hole 867B illustrate the facies evolution from shoreface to foreshore and to shallow lagoon behind a barrier beach, including washover deposits. The sponge bioherms observed in an offshore setting in Hole 868A grew on erosion surfaces and hardgrounds and were commonly buried or truncated by tempestites. The depositional sequences in these high-energy environments were therefore mostly controlled by storm activity. The lowermost part of Hole 866A probably was deposited on a shallow ramp, whereas the bulk of the facies represents a generally protected, lagoonal, inner-platform environment. Holes 867B and 868A and the uppermost part of Hole 866A suggest that the platform rim was composed of storm-dominated beach ridges, which protected the lagoon behind them. The sponge-rudist bioherms lived in front of the beach rim and produced carbonate elements that were washed onto the beaches and farther into the lagoon. Abundant carbonate production in the lagoon always maintained shallow water depths. This general facies distribution was modulated by low-amplitude, high-frequency sea-level fluctuations that created the small-scale sequences.

Small-Scale Shallow-Water Carbonate Sequences of Resolution Guyot (Sites 866, 867, and 868)