Paleohydrologic and stratigraphic implications of early diagenetic carbonate cements: Examples from marginal marine deposits of the Cretaceous Western Interior Seaway

Stratigraphically constrained assessment of paleogroundwater systems bordering the mid-Cretaceous Western Interior Seaway was facilitated by delta 18O and delta13C analyses of early diagenetic carbonate cements from fluvial/estuarine deposits and paleosols. Objectives of this investigation were to: (1) establish the potential of using early diagenetic carbonate cements to serve as proxies for paleoclimatic variability in time and space where cements precipitate from meteoric waters that were recharged in large catchment basins; (2) evaluate the effect of relative sea level rise on the precipitation of early diagenetic carbonate cements; and (3) further assess the utility of early diagenetic carbonate cements within nonmarine strata for sequence stratigraphic interpretations.; delta18O values of early diagenetic carbonate cements have been compared to delta18O compositions of approximately coeval paleosol sphaerosiderite nodules from the Dakota, Swan River, Ashville, and Boulder Creek formations. In each region the sphaerosiderite delta 18O values are less depleted than those from coeval sandstones and mudstones, establishing the basis for a proxy measure of locally versus regionally recharged groundwater systems.; Dinosaur tracks preserved in the Dakota Formation, Jefferson County, Nebraska are interpreted to mark a parasequence boundary within the Muddy Cycle. Cement delta18O values of the track-bearing interval exhibit a complex history of groundwater flow through the region; but indicate initiation of cementation was in part controlled by a relative marine onlap. Early lithification of the horizon facilitated the preservation of the dinosaur tracks. Temporal evaluation of phreatic carbonate cements within marginal to shallow marine deposits of the Swan River and Ashville formations in Manitoba and Saskatchewan reveal delta18O values indicative of submarine discharge of meteoric groundwaters. Variability of delta18O compositions through the depositional cycle is marked by a gradual depletion following the maximum flooding surface, with a relatively sharp enrichment (∼2‰) within the upper regressive systems tract.; Chemical evaluations of phreatic siderite cements within fluvial deposits of the Boulder Creek Formation in British Columbia indicate delta 18O values are ∼4‰ lighter than adjacent paleosol sphaerosiderite. delta 18O compositions and cation ratios are used to interpret marine influences on paleogroundwater systems in coastal plain settings and, therefore, relative changes in sea level.