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Capitan backreef strata of the upper Yates and lowermost Tansill formations are characterized by three cycles composed of a lower siliciclastic unit and an upper carbonate unit. The cycles are bounded by sharp and erosive surfaces on the shelf that become concordant and disappear within concordant outer-shelf margin strata. Breccias are occasionally associated with cycle boundaries. Composite eustatic variations (100-k.y. cycles superimposed on 400-k.y. c

ycles) control both the deposition and the internal organization of these siliciclastic/carbonate units. The sandstones were transported onto the shelf by eolian processes during sea-level lowstands and then reworked in the outer shelf by marine processes by the following transgression. The upper carbonates, transitional down into sandstones, are interpreted as subtidal to supratidal deposits. Relative sea-level drops sub-aerially exposed cycle tops, but marine reworking after exposure modified the cycle boundaries. Dolomitized and undolomitized clasts of the underlying rock are reworked locally at the base of cycles.

Syndepositional diagenetic events record several phases of marine cementation, neomorphism and dissolution, replacive dolomitization, and primary dolomite precipitation. The paragenetic constraints on the timing of syndepositional diagenetic events allow for the establishment of a relationship between the stratigraphic cyclic patterns and the early diagenetic features. Most of the marine cementation (Mg-calcite and aragonite) occurs during transgressive phases, as well as replacive dolomitization of the inner-shelf restricted facies. During relative sea-level falls, metastable phases are dissolved and sediments and early marine cements are replaced by dolomite in the shelf-crest and outer-shelf facies, and dolomite cement precipitates in inner-shelf and shelf-crest fenestral pores. Integration of sedimentologic observations and timing of diagenetic events documents three relative sea-level falls. The association of dolomites with evaporite nodules and their enrichment in δ18O (up to 4.1‰) with respect to normal marine values, suggest that precipitation occurred from evaporation-concentrated seawater.

Integration of sedimentologic and diagenetic studies of Guadalupe Mountains outcrops suggests that composite sea-level variations controlled the deposition of cyclic strata and distribution of syndepositional diagenetic features. Because syndepositional diagenesis records the effects of relative eustatic variations, its distribution can be predicted.

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