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The Western Interior Seaway (WIS) was a shallow and expansive body of water that covered the central United States during the Late Cretaceous. Attempts to reconstruct temperatures in the seaway using the oxygen isotopic composition of biogenic carbonates have suffered from uncertainty in the oxygen isotopic composition of seawater (δ 18 O w ) in the semi-restricted basin. We present new reconstructed temperature and δ 18 O w data from marine and estuarine environments in the WIS and freshwater environments in WIS source rivers, derived from clumped isotope analyses of bivalve and gastropod shells. We find temperatures of 5–21 °C, δ 18 O w values below contemporaneous Gulf of Mexico marine sites, and a strong correlation between δ 18 O w and environmental setting. We propose that decreasing δ 18 O w values reflect decreasing salinity driven by an increasing contribution of continental runoff. Using a two-end-member salinity-δ 18 O w mixing model, we estimate salinities of 29–35 psu (practical salinity units) for the deep marine, 20–32 psu for the shallow marine, and 11–26 psu for the estuarine environments of the WIS. New climate model simulations agree with reconstructed temperatures and salinities and suggest the presence of salinity driven stratification within the seaway.

Carbonate clumped isotope paleothermometry is a promising method for paleoclimate reconstructions and understanding diagenetic processes, although clumped isotope compositions (measured as Δ47 values) can be altered by recrystallization and thermal resetting. Several studies have investigated the effects of deep burial and exhumation on Δ47 values; we present Δ47 values of samples from an ∼4500-m-long drill core from Andros Island, Bahamas, which represent the spectrum from shallow to deep burial conditions. These limestones and dolomites originally formed under near-surface temperature conditions, which are reflected by ∼27 °C Δ47 temperatures in samples buried to

The δ 18 O values of river waters in Late Cretaceous and Paleogene basins of Alberta, Montana, Wyoming, and Colorado are calculated from the isotopic composition of unaltered aragonite mollusk fossils. The isotopic composition of these river waters has significant implications for the uplift and climate history of the mountains surrounding the basins. Our data show that the δ 18 O values of river water varied dramatically, ranging from −23‰ to −5‰ relative to Vienna standard mean ocean water, with an uncertainty of ±2‰. Close stratigraphic association of river deposits with very different isotopic values indicates two different water sources: rainfall in the warm, low-elevation basins and snowfall in surrounding mountains. The δ 18 O difference between basinal and highland precipitation suggests that local relief was similar to today9s, on the order of 2.5–3 km. Seasonal variation in shell δ 18 O values also indicates that there are times when large snow fields in the Maastrichtian and Paleocene mountains of Montana and Wyoming survived summer melting and were multiannual features.

We report a large, positive, carbon isotope excursion in the Kinderhookian Stage of the Lower Mississippian in North America and propose that the excursion is linked to the Antler orogeny. The δ13C excursion reaches +7.1‰ in the upper part of the Joana Limestone in southeast Nevada and correlates with peaks recognized in Europe and elsewhere in North America. This isotopic shift, one of the largest known Phanerozoic δ13C events, is found within the upper part of the Siphonodella isosticha –Upper crenulata conodont Zone; its formation coincided with a time of rapid subsidence of the Joana platform within the Antler foreland basin. We interpret the large changes in δ13C values to reflect enhanced organic carbon burial rates in response to tectonic deepening followed by creation of a restricted water mass at depth in the Antler foredeep and other foredeeps of similar age. The presence of a large δ13C excursion in the upper part of the S. isosticha Zone is consistent with a late Kinderhookian (Tournaisian) glacial episode.

Isotope (δ 18 O) and minor element (Mg/Ca, Sr/Ca) analyses of a fossil shell of the marine mussel Mytilus trossulus (Gould) from the Whisky Run terrace at Coquille Point, Bandon, Oregon, enable reconstruction of a paleoclimatic profile for the temperate northeastern Pacific ca. 80–85 ka. The Whisky Run terrace is correlative with marine oxygen isotope (δ 18 O) substage 5a, the final sea-level highstand of the last interglacial complex. Herein we provide sea-surface temperature estimates and report on a new technique that allows estimates to be made of δ 18 O of seawater and riverine discharge from the skeletal chemistry of a single mussel shell. Estimates of mean annual temperature from Mg/Ca ratios are lower than those suggested by the accompanying fossil fauna, and significantly lower than present-day conditions. The data also suggest a decrease in the range of seasonal temperature extremes at 80 ka compared to today. Estimates of the fresh-water and seawater δ 18 O end members, −4.5‰ and +0.5‰, respectively, are slightly greater than modern values.

Paleotemperatures have been widely deduced from skeletal 18 O/ 16 O ratios, but these are also dependent on salinity. Without an independent measure of salinity, 18 O/ 16 O ratios cannot provide accurate data on past temperature and climate. We grew marine mollusks (bivalves) in the field while real-time data on local seawater temperature and chemistry (Mg, Ca, δ 18 O, and salinity) were gathered. Here we show that for Mytilus trossulus, skeletal Mg/Ca ratios provide an accurate measure of temperature and that weekly sea-surface temperatures may be estimated with an apparent accuracy of approximately ± 1.5 °C. Thus, with analyses of both Mg/Ca and δ 18 O from the same specimen, it is possible to determine seawater temperature and δ 18 O.

Coeval crystallographic growth sectors were microsampled from a fracture-filling calcite cement crystal with well-developed crystal faces and concentric zoning to test empirically for isotopic sector zoning. Isotopic and minor element homogeneity among coeval parts of the {0112} and {2131} sectors suggests that isotopic sector zoning does not occur in calcite. Empirical results are compatible with theoretical considerations based on crystal surface geometry, growth mechanisms, and a thermodynamic growth model.

Paleomagnetic data from the interglacial Nyborg Formation (653 ± 7 Ma), northern Norway, compare with data from the Egersund dikes (ca. 650 Ma), southwest Norway, and demonstrate that tillite formations associated with the Varanger Ice Age in Baltica accumulated at latitudes greater than 30° S. Vendian glaciations are associated with reorganization of the Rodinia supercontinent, but they are controlled by latitude. The breakup of Rodinia and opening of the proto-Pacific imposed clockwise rotation and southward movement of Laurentia-Baltica. On their combined approach toward the south pole, Baltica and northeast Laurentia were first glaciated during the Varanger Ice Age (ca. 650 Ma) and then by the Ice Brook glacial events (625–580 Ma) when Laurentia had reached intermediate southern latitudes. During the 625–580 Ma period Laurentia and Baltica drifted apart, resulting in the opening of the Iapetus ocean, but both continents remained in high southern latitudes during most of the Vendian.

A combined stratigraphic and isotopic study across a Late Cambrian mass-extinction horizon (Pterocephaliid-Ptychaspid biomere boundary) in cratonal and miogeoclinal sections of the western United States reveals evidence for a pattern of sea-level rise, decreasing 87 /Sr 86 Sr ratios, and increasing δ 13 C. The positive shift in δ 13 C, reaching maximum values a few metres above the extinction interval, is interpreted to reflect elevated primary productivity and an increase in the rate of burial of organic matter during expansion of the oxygen-minimum zone. The 87 /Sr 86 Sr decrease is interpreted to reflect some combination of increased sea-floor spreading rates and decreased continental weathering rates. The δ 13 C and 87 /Sr 86 Sr trends independently support the field-based hypothesis that a sea-level rise led to catastrophic oceanic overturn, possibly culminating in anoxic conditions, that ultimately proved lethal to a large fraction of the existing shelf fauna.

Stable oxygen isotopic compositions of deep-marine calcite spars contained in Early and middle Cretaceous, bank-interior limestones exposed erosionally on the Bahama escarpment suggest that these spars are Late Cretaceous to Miocene in age, two-thirds of the spars being middle Eocene or older in age. The Eocene and older spars are identical to pelagic and fore-reef strata unconformably overlying truncated bank-interior carbonates exposed on the Bahama escarpment. Spars contained in limestones taken from the northwest Bahama escarpment are nearly all (20 of 22 analyses) Late Cretaceous (Campanian and Maastrichtian) to middle Eocene in age. Most (12 of 20 analyses) spars from southeast Bahama escarpment limestones are late Eocene or younger in age. Thus, isotopic data are consistent with the initiation of erosion of the Bahama escarpment in the Late Cretaceous and its continuation until the middle of the Eocene. In addition, these data suggest that erosion of the southeast Bahama escarpment continued into, or was renewed during, the late Eocene and possibly the Oligocene-Miocene. Continued, or renewed, erosion of the southeast Bahama escarpment probably reflects tectonic interaction with the Caribbean-North American plate boundary along the Puerto Rico trench, or the flow of Antarctic Bottom Water only at the base of the southeast escarpment.

Carbon and oxygen isotopic compositions have been determined for Holocene reefal carbonate grains and cements in samples from Enewetak, Bikini, Bermuda, and Belize to identify components that exhibit systematic isotopic fractionation relationships. These findings are compared with fractionation relationships determined from experimentally precipitated low-magnesium calcite (LMC), aragonite, and high-magnesium calcite (HMC) to determine if these relationships are observed in naturally precipitated carbonates. Compositional variation within individual samples is extreme (up to 6‰ in δ 13 C PDB and 3‰ in δ 18 O PDB). Experimental fractionation relationships fail to predict the range of observed compositions. Aragonite cements are enriched 1.0‰ to 1.4‰ in 13 C and 1.5‰ to 2.0‰ in 18 O relative to calcite equilibrium compositions; HMC cements are enriched by 0.3‰ to 0.4‰ in 13 C and by 1.8‰ to 1.9‰ to 18 O. For carbon, these results are in agreement with the experimental work of Rubinson and Clayton. For oxygen, our results suggest that fractionation factors of both aragonite and HMC may have been underestimated. Skeletal components exhibit inconsistent fractionation relative to inorganically precipitated marine cements, suggesting that marine cement compositions are more reliable indicators of the physicochemical conditions of precipitation than co-occurring skeletal carbonates.