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Map showing the extent of the Cretaceous Western Interior Seaway of North America during the Bearpaw cyclothem at Baculites baculus time (after Williams and Stelck, 1975).
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δ18O and δ13C values of ammonites and inoceramids provide information on the paleoenvironmental conditions in the Western Interior Seaway (WIS) during the Campanian–Maastrichtian Bearpaw marine cycle, the last major Transgression–Regression (T–R) cycle to affect the seaway during the Cretaceous Period. Ammonites and inoceramids exhibit distinct sta...
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... the Cretaceous Period, the Western Interior of North America was the site of a vast foreland basin, extending from the Gulf of Mexico to the Arctic Ocean and from eastern British Columbia to western Ontario ( Fig. 1). Both Tethyan waters from the Gulf of Mexico and Boreal waters from the Arctic Ocean (after Williams and Stelck, 1975). invaded the basin. They became confluent in Late Albian time to form the Western Interior Seaway, which persisted, variably expanded and shrunken, until Maastrichtian times. Of Kauffman's (1977) ten eustatically ...
Context 2
... the Cretaceous Period, the Western Interior of North America was the site of a vast foreland basin, extending from the Gulf of Mexico to the Arctic Ocean and from eastern British Columbia to western Ontario ( Fig. 1). Both Tethyan waters from the Gulf of Mexico and Boreal waters from the Arctic Ocean (after Williams and Stelck, 1975). invaded the basin. They became confluent in Late Albian time to form the Western Interior Seaway, which persisted, variably expanded and shrunken, until Maastrichtian times. Of Kauffman's (1977) ten eustatically ...
Citations
... 100-66 Ma;Caldwell, 1974;Slattery et al., 2013), spanning 45° latitude, which experienced a wide range of environmental shifts. Fluctuating sea levels ( Fig. 1C), for example, modified basin geometry and water-mass distributions, impacting marine life (e.g., He et al., 2005;Kauffman, 1984;Lowery et al., 2018). A restricted connection between the WIS and the open ocean affected oceanic conditions relative to the GCP and may have influenced biotic provinces (Kauffman, 1984, and references therein;Lowery et al., 2018). ...
... The WIS and GCP provinces may have resulted from geochemical and bathymetric changes across the transcontinental arch (TA), which may have acted as a bathymetric high between the regions (He et al., 2005;Lowery et al., 2018, and references therein), rather than resulting from latitudinal factors (e.g., temperature). Geochemical studies have found evidence for nonnormal marine conditions in the WIS, including low salinity or brackish conditions (Cochran et al., 2003;Dennis et al., 2013;Fricke et al., 2010) and lower δ 18 O values of seawater than in the open ocean (Fricke et al., 2010;Petersen et al., 2016). ...
... Geochemical studies have found evidence for nonnormal marine conditions in the WIS, including low salinity or brackish conditions (Cochran et al., 2003;Dennis et al., 2013;Fricke et al., 2010) and lower δ 18 O values of seawater than in the open ocean (Fricke et al., 2010;Petersen et al., 2016). There is also evidence for stratification within the WIS during the Campanian and Maastrichtian, produced by mixing water masses (He et al., 2005;Lowery et al., 2018). These factors could have created a habitat barrier between the GCP and WIS, facilitating provincialism. ...
The Western Interior Seaway (WIS) was historically divided into latitudinal faunal provinces that were taxonomically distinct from the adjacent Gulf Coastal Plain (GCP) and that shifted in space due to sea-level changes. However, no rigorous quantitative analyses using recent taxonomic updates have reassessed these provinces and their associations. We used network modeling of macroinvertebrate WIS and GCP fauna to test whether biotic provinces existed and to examine their relationships with abiotic change. Results suggest a cohesive WIS unit existed across the Campanian, and distinct WIS and GCP provinces existed in the Maastrichtian. Sea-level changes coincided with changes in network metrics. These results indicate that, while the WIS did not contain subprovinces in the Late Cretaceous, environmental factors influenced faunal associations and their communication over time.
... These studies reveal that the δ 18 O and δ 13 C composition of scaphitids, baculitids, and nostoceratids more closely match the isotopic composition of associated benthic faunas than known planktic organisms. This has been interpreted as an indication that they were living near where they were collected (Tsujita & Westermann, 1998;He, Kyser & Caldwell, 2005;Landman & Klofak, 2012;Landman et al., 2012b;Sessa et al., 2015). Berry (2018a,b) and Landman et al. (2019) are among the few studies to suggest that some heteromorph conchs could undergo long-term and/or long-distance post-mortem drift. ...
... 10). Most analyses to date have been focused on baculitids and scaphitids from the Late Cretaceous (He et al., 2005; 2012b). Variation in the oxygen isotope ratio (δ 18 O) reflects changes in temperature or the oxygen isotope ratio of sea water, which often covaries with salinity (Mátyás et al., 1996). ...
... These data may also suggest seasonally protracted spawning like some modern cephalopods (Rocha, Guerra & González, 2001). Other work spanning multiple Campanian ammonoid zones from the Western Interior Seaway suggests Didymoceras was living in warmer or more brackish water than co-ocurring Scaphites and Baculites (He et al., 2005). ...
Heteromorphs are ammonoids forming a conch with detached whorls (open coiling) or non-planispiral coiling. Such aberrant forms appeared convergently four times within this extinct group of cephalopods. Since Wiedmann's seminal paper in this journal, the palaeobiology of heteromorphs has advanced substantially. Combining direct evidence from their fossil record, indirect insights from phylogenetic bracketing, and physical as well as virtual models, we reach an improved understanding of heteromorph ammonoid palaeobiology. Their anatomy, buoyancy, locomotion, predators, diet, palaeoecology, and extinction are discussed. Based on phylogenetic bracketing with nautiloids and coleoids, hetero-morphs like other ammonoids had 10 arms, a well-developed brain, lens eyes, a buccal mass with a radula and a smaller upper as well as a larger lower jaw, and ammonia in their soft tissue. Heteromorphs likely lacked arm suckers, hooks, tentacles , a hood, and an ink sac. All Cretaceous heteromorphs share an aptychus-type lower jaw with a lamellar calcitic covering. Differences in radular tooth morphology and size in heteromorphs suggest a microphagous diet. Stomach contents of heteromorphs comprise planktic crustaceans, gastropods, and crinoids, suggesting a zooplanktic diet. Forms with a U-shaped body chamber (ancylocone) are regarded as suspension feeders, whereas orthoconic forms additionally might have consumed benthic prey. Heteromorphs could achieve near-neutral buoyancy regardless of conch shape or ontog-eny. Orthoconic heteromorphs likely had a vertical orientation, whereas ancylocone heteromorphs had a near-horizontal aperture pointing upwards. Heteromorphs with a U-shaped body chamber are more stable hydrodynamically than modern Nautilus and were unable substantially to modify their orientation by active locomotion, i.e. they had no or limited access to benthic prey at adulthood. Pathologies reported for heteromorphs were likely inflicted by crustaceans, fish, marine reptiles, and other cephalopods. Pathologies on Ptychoceras corroborates an external shell and rejects the endocochleate hypothesis. Devonian, Triassic, and Jurassic heteromorphs had a preference for deep-subtidal to offshore facies but are rare in shallow-subtidal, slope, and bathyal facies. Early Cretaceous heteromorphs preferred deep-subtidal to bathyal facies. Late Cretaceous heteromorphs are common in shallow-subtidal to offshore facies. Oxygen isotope data suggest rapid growth and a demersal habitat for adult Discoscaphites and Baculites. A benthic embryonic stage, planktic hatchlings, and a habitat change after one whorl is proposed for Hoploscaphites. Carbon isotope data indicate that some Baculites lived throughout their lives at cold seeps. Adaptation to a planktic life habit potentially drove selection towards smaller hatchlings, implying high fecundity and an ecological role of the hatchlings as micro-and mesoplankton. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary 66 million years ago is the likely trigger for the extinction of ammonoids. Ammonoids likely persisted after this event for 40-500 thousand years and are exclusively represented by heteromorphs. The ammonoid extinction is linked to their small hatchling sizes, planktotrophic diets, and higher metabolic rates than in nautilids, which survived the K/Pg mass extinction event.
... The use of inoceramid δ 18 O values in paleoclimate reconstructions, however, has been limited in the past. This is because well-preserved shells of these bivalves often display δ 13 C and δ 18 O signatures that diverge from those expected by equilibrium precipitation with the ambient water (Tourtelot and Rye, 1969;Pirrie and Marshall, 1990;Ludvigson et al., 1994;Elorza and Garcia-Garmilla, 1996;Fisher and Arthur, 2002;He et al., 2005;Henderson and Price, 2012;Zakharov et al., 2012;Walliser et al., 2019). Disequilibrium fractionation of carbon isotopes have been reported as a positive shift of the shell δ 13 C values, which was interpreted to be indicative for chemosymbiosis-related vital effects (MacLeod and Hoppe, 1992;Walliser et al., 2018Walliser et al., , 2019, whereas negative offsets of inoceramid δ 18 O values have been attributed to exposure of the organisms to 16 O-loaded pore fluids (Pirrie and Marshall, 1990;Walliser et al., 2019). ...
... Whether or not inoceramid shells can be considered faithful geochemical proxy archives for Late Cretaceous paleoclimate studies is still a matter of debate. This is mainly because inoceramid remains often display δ 13 C values that are more positive than those measured in coeval organisms, whereas their δ 18 O values can be either more negative than expected for equilibrium isotope fractionation (Tourtelot and Rye, 1969;Pirrie and Marshall, 1990;Ludvigson et al., 1994;Elorza and Garcia-Garmilla, 1996;Fisher and Arthur, 2002;He et al., 2005;Henderson and Price, 2012;Zakharov et al., 2012;Walliser et al., 2019). However, inoceramid shells can also exhibit stable isotope values comparable to those of coeval organisms for which equilibrium isotope fractionation has been assumed (MacLeod and Hoppe, 1992; Jiménez Berrocoso et al., 2008;Walliser et al., 2018). ...
... 0.3‰ higher than the δ 18 O minima measured in I. hercules. As mentioned before, inoceramid-derived δ 18 O shell values have been found to be lower (e.g., Tourtelot and Rye, 1969;Pirrie and Marshall, 1990;Fisher and Arthur, 2002;He et al., 2005;Henderson and Price, 2012;Zakharov et al., 2012) to those expected from equilibrium fractionation. Previous authors justified the lower-than-expected shell δ 18 O values assuming vertical stratification of the water body (Tourtelot and Rye, 1969;Morrison and Brand, 1988), local freshwater input (Zakharov et al., 2012), or exposure of the organisms to pore waters (Pirrie and Marshall, 1990;Walliser et al., 2019). ...
The δ¹⁸O record of well-preserved shells of the inoceramid Inoceramus hercules from the Úpohlavy working quarry (Czech Republic) provides an insight into the climate variability in the late Turonian benthic environment of the Bohemian Cretaceous Basin. Similar to modern bivalves, this inoceramid species built its shell near equilibrium with the oxygen isotope value of the ambient water. Due to the nearly year-round shell growth, sequentially sampled δ¹⁸O values allowed to estimate the narrowest sub-annual temperatures fluctuations that prevailed during lifetime of the organisms. In accordance with previous studies, reconstructed temperatures suggest colder water conditions (19.0 ± 0.9 °C) during the earliest late Turonian (coinciding with the Hyphantoceras Event; also known as Hitch Wood Event) than during the later part of the substage (20.9 ± 1.1 °C). Climate warming, however, did not affect the sub-annual temperature fluctuations evenly, but predominantly affected the warmest part of the year (at least +4.0 °C). On the contrary, the coldest recorded temperatures remained more or less invariant, varying not (much) more than +1.0 °C across the studied time interval. The observed changes in the benthic temperature estimates likely reflect shifts in seasonal sea surface temperature amplitudes in response to climate forcing. Given the widespread distribution of I. hercules in the upper Turonian–lower Coniacian hemipelagic strata of Europe, the present study sets the basis for future continent-wide sub-annually-resolved climate reconstructions.
... Rudists and, to a lesser extent, inoceramids have been in the focus of many paleoclimate studies. However, because these taxa lack modern representatives, the validity of their stable isotope values for paleotemperature reconstructions has been questioned in the past [32], in particular for the inoceramids [35][36][37][38][39][40][41][42][43]. Rudist shells often display a positive correlation between δ 13 C and δ 18 O values. ...
... Following the Aptian-early Turonian 'supergreenhouse' event (90)(91)(92)(93)(94)(95) [1,2], the Late Cretaceous world experienced a time interval of significant global cooling [3][4][5] previous studies have also hypothesized disequilibrium fractionation related to species-specific vital effects [36,43]. This is because inoceramids often display higher δ 13 C values and (sometimes) lower δ 18 O values than those of coeval organisms [35][36][37][38][39][40][41][42][43]. Such isotopic signatures are observed in those inoceramids that colonized dysoxic and H 2 S-rich environments (stagnant bottom waters or cold seeps) [43,52,54,56,57], and mimic the δ 13 C and δ 18 O signals of modern thioautotrophic bivalves [58][59][60][61]. ...
In this study we attempted to assess whether seasonal upwelling or a steady thermocline persisted at the western margin of the Tethys Ocean during the late Turonian–early Coniacian interval. For this scope, we employed novel and published stable oxygen isotope (δ¹⁸O) data of various organisms (bivalves, bivalves, brachiopods, fish and belemnites). New seasonally resolved temperature estimates were based on the δ¹⁸O record of sequentially sampled inoceramid (Inoceramus sp.) and rudist (Hippurites resectus) shells from the Scaglia Rossa and Gosau deposits of northern Italy and western Austria, respectively. Diagenetic screening was performed using reflected light, cathodoluminescence (CL), scanning electron microscopy (SEM) and stable isotope analysis. Originally preserved δ¹³C and δ¹⁸O values were used to characterize the lifestyle of the bivalves and detect vital effects that could have biased oxygen isotope-based temperature reconstructions. Inoceramid δ¹⁸O values provide–for the first time–information on temperatures of Tethyan benthic waters, which were, on average, 14.4 ± 0.6 °C and fluctuated seasonally within a range of less than 2 °C. Such a thermal regime is in line with the temperatures postulated for late Turonian boreal water masses and support the existence of a cold water supply from the North Atlantic to the Tethyan bottom. Bottom cooling, however, did not affect the shallow water environment. In fact, the rudist-based temperature estimates for shallow water environment revealed a mean annual range of 11 °C, between 24 and 35 °C (assuming a seasonally constant δ18Ow = 1.0 ‰), which are among the warmest temperatures recorded over the entire Late Cretaceous. Our findings, thus, suggest a strong thermal and food web decoupling between the two environments. The absence of a seasonal vertical homogenization of different water bodies suggests the existence of a steady thermocline and, therefore, contrasts with the presence of an active coastal upwelling in the region as hypothesized by previous authors.
... The water temperatures computed from stable oxygen isotopic analyses of shells indicate that both heteromorph and planispiral ammonoids from the Lower Aptian of the Ulyanovsk region are more similar to the benthos than contemporaneous planktic foraminifera (Zakharov et al., 2013). This general relationship is comparable to isotopic studies of Cretaceous molluscs from elsewhere (Smyshlyaeva et al., 2002;Moriya et al., 2003;Zakharov et al., 2003Zakharov et al., , 2004He et al., 2005;Cochran et al., 2010;Landman, Cobban & Larson, 2012;Sessa et al., 2015). Therefore, Audouliceras probably lived in relatively shallow water (<50 m; Zakharov et al., 2013), near the seafloor, and had a somewhat demersal lifestyle. ...
The biomechanics of uncoiled heteromorph ammonoids with body chambers that terminate in U-shaped hooks (ancylocones) were investigated with virtual and physical models of Audouliceras renauxianum. Virtual models were used to compute the hydrostatic properties of this morphotype. Audouliceras has the capacity for neutral buoyancy and this suggests that other taxa with similar proportions had this ability as well. Hydrostatic stability gradually increases during ontogeny, coincident with the larger degree of uncoiling. The juvenile planispiral stage has a similar stability and apertural orientation to the extant Nautilus. The adult stage, however, undergoes an increase in stability by a factor of over 3, while assuming an upwardfacing posture. Counterintuitively, the stage during the formation of the shaft (before the growth of the U-shaped hook) is oriented horizontally. This intermediate stage would have had poor horizontal mobility due to the positioning of the hyponome below the centre of mass. The juvenile planispiral stage and mature stage, however, would have been well suited to horizontal backward movement with minimal rocking. Ancylocones are generally thought of as quasiplanktic vertical migrants. Thus, their relative horizontal swimming ability has been largely disregarded. Experiments on 3D printed, neutrally buoyant physical models reveal that hydrodynamic drag is indeed larger compared to Nautilus. However, Audouliceras could reach similar maximum horizontal velocities depending on the available thrust. Sepia-like thrusts yield velocities similar to equivalently sized Nautilus (c. 15 cm/s), while Nautilus-like thrusts yield velocities not much lower (c. 11 cm/s). Due to the hydrostatic properties of the ancylocone, the
adult model undergoes less rocking (±4.5°) during movement than Nautilus (±10°). The minimal hydrodynamic consequences for ancylocones suggest that stability, orientation and directional efficiency are key selective pressures for some heteromorph shells, which may have primarily served as hydrostatic devices.
... This shape would have caused considerable hydrodynamic drag, and the cumbersome orientation of the aperture may have further hindered rapid movement and migration over long distances ). Fossils of this genus from the Western Interior Seaway of the United States yield isotopic compositions similar to those of benthic inoceramids, suggesting they lived very close to the seafloor (He et al. 2005;Slattery et al. 2007). Didymoceras is known from methane seeps in the Western Interior Seaway, which may have served as oases in terms of food supply and oxygenation on a seafloor that was otherwise rather poor in prey (Kauffman et al. 1996;Landman et al. 2012Landman et al. , 2018. ...
... All virtual models of Didymoceras have the capacity for neutral buoyancy throughout each ontogenetic stage and must leave some amount of cameral liquid in the phragmocone to maintain this condition. Therefore, while isotopic studies suggest this genus was demersal and lived very close to the benthos (He et al. 2005(He et al. , 2016, it still retained the ability to hover around, close to the seafloor. This life mode would enable the ammonoid to push up off the seafloor with minimal effort to evade predators or pounce on prey items. ...
The seemingly aberrant coiling of heteromorphic ammonoids suggests that they underwent more significant changes in hydrostatic properties throughout ontogeny than their planispiral counterparts. Such changes may have been responses to different selective pressures at different life stages. The hydrostatic properties of three species of Didymoceras ( D. stevensoni , D. nebrascense , and D. cheyennense ) were investigated by creating virtual 3D models at several stages during growth. These models were used to compute the conditions for neutral buoyancy, hydrostatic stability, orientation during life, and thrust angles (efficiency of directional movement). These properties suggest that Didymoceras and similar heteromorphs lived low-energy lifestyles with the ability to hover above the seafloor. The resultant static orientations yielded a downward-facing aperture in the hatchling and a horizontally facing aperture throughout most of the juvenile stage, before terminating in an upward direction at maturity. Relatively high hydrostatic stabilities would not have permitted the orientation of Didymoceras to be considerably modified with active locomotion. During the helical phase, Didymoceras would have been poorly suited for horizontal movement, yet equipped to pirouette about the vertical axis. Two stages throughout growth, however, would have enhanced lateral mobility: a juvenile stage just after the formation of the first bend in the shell and the terminal stage after completion of the U-shaped hook. These two more mobile phases in ontogeny may have improved juvenile dispersal potential and mate acquisition during adulthood, respectively. In general, life orientation and hydrostatic stability change more wildly for these aberrantly coiled ammonoids than their planispiral counterparts.
... The values of d 18 O correspond to temperatures of 20-308C and are consistent with ambient temperatures of the WIS during the deposition of the Baculites compressus-B. cuneatus Zones (Tourtelot and Rye 1969;He et al. 2005;Cochran et al. 2010). They are also consistent with temperatures calculated for adult specimens of B. compressus from the same site . ...
Cold methane seeps were common in the Late Cretaceous Western Interior Seaway of North America. They provided a habitat for a diverse array of fauna including ammonites. Recent research has demonstrated that ammonites lived at these sites. However, it is still unknown if they hatched at the seeps or only arrived there later in ontogeny. To answer this question, we documented the abundance and size distribution of small specimens of Baculites and Hoploscaphites at eight seep sites in the Pierre Shale of South Dakota. The specimens of Hoploscaphites range from 0.8 to 8.1 mm in shell diameter, with most of them falling between 1 and 1.5 mm. The specimens of Baculites range from 0.7 to 19.2 mm in length, with most specimens falling between 6 and 8 mm. The small size and morphology of these specimens indicate that they are neanoconchs, that is, newly hatched individuals that lived for a short time after hatching. We also analyzed the isotope composition (δ13C and δ18O) of 12 small specimens of Baculites and one specimen of Hoploscaphites with excellent shell preservation from one seep deposit. The values of δ13C and δ18O range from -16.3 to -2.5‰ and -3.0 to -0.9‰, respectively. The values of δ18O translate into temperatures of 19–28°C, which are comparable to previous estimates of the temperatures of the Western Interior Seaway. The low values of δ13C suggest that the tiny animals incorporated carbon derived from anaerobic oxidation of 12C-enriched methane into their shells. Evidently, they must have lived in close proximity to seep fluids emerging at the sediment-water interface and the associated microbial food web. However, this may have contributed to their demise if they were exposed to elevated concentrations of H2S derived from the anaerobic oxidation of methane.
... Numerous studies have analyzed fossils from the Cretaceous Western Interior Seaway of North America. However, the results have yielded enigmatic patterns, including anomalously low δ 18 O values in shallowdwelling taxa such as nektonic mollusks and higher δ 18 O values in infaunal mollusks versus epifaunal ones (e.g., Wright, 1987;He et al., 2005). Researchers suggest that these patterns reflect a complex, salinity-stratified water column (e.g., Wright, 1987;Hudson and Anderson, 1989;FIGURE 10.3 Oxygen isotope records of tropical/subtropical and temperate fossils and planktonic foraminifera for the Mesozoic. ...
... TWE 5 Toarcian Warm Event, TACE 5 ToarcianÀAalenian Cool Event, and OAE 5 oceanic anoxic event (e.g., Jenkyns et al., 2002). He et al., 2005;Petersen et al., 2016). Because of this complexity, these data are not included in the Mesozoic compilation. ...
Variations in the ¹⁸O/¹⁶O ratio of marine fossils and microfossils record changes in seawater ¹⁸O/¹⁶O and temperature and provide the basis for global correlation. Based on more than 64,000 measurements, this chapter presents oxygen isotope curves for Phanerozoic foraminifera, mollusks, brachiopods, and conodonts, as well as for Precambrian limestones, dolostones, and cherts. Periodic oxygen isotopic variations in deep-sea foraminifera define marine isotope stages that, when combined with biostratigraphy and astronomical tuning, provide a late Cenozoic chronostratigraphy with a resolution of several thousand years. Oxygen isotope events of late Cenozoic, Mesozoic, and Paleozoic age mark local and global climate change and serve as chemostratigraphic markers for regional and global correlation. Precambrian oxygen isotope stratigraphy is hampered by the lack of unaltered authigenic marine carbonate and phosphate.
... A Campanian filter was applied to each search to constrain the age of fossil localities reported. a (Jenkyns et al. 2004), b(Hay et al. 1993), c (Otto-Bliesner et al. 2002, d(He et al. 2005), e(Liu 2009), f(Dennis et al. 2013). Map © Colorado Plateau Geosystems 2013. ...
... Such an investigative approach was employed by Pirrie & Marshall (1990), who concluded that lower δ 18 O values in inoceramids resulted from exposure to 18 O-depleted interstitial fluids. Excluding diagenetic overprinting (Carpenter et al. 1988;Elorza & García-Garmilla 1996), several other interpretations have been proposed, including vertical stratification (Whittaker et al. 1987;He et al. 2005;Zakharov et al. 2005) and local freshening (Zakharov et al. 2012) as well as vital effects (Tourtelot & Rye 1969;Morrison & Brand 1988) related to a planktonic lifestyle (see Discussion;MacLeod & Hoppe 1992), kinetic disequilibrium effects (Henderson & Price 2012) and preferential shell growth during summer months (Henderson & Price 2012). These studies, however, were based on δ 13 C and δ 18 O data from bulk shell analyses, which cannot be used to reconstruct environmental processes on short time-scales (seasonal to interannual). ...
... Ammonites and the inoceramid material presented features common to nacre in modern mollusc shells, for example macroscopic iridescent lustres and microscopically sharply defined layers of distinct aragonite tablets (Fig. 4C, D). Such features are often regarded as an indicator for good preservation and considered suitable for palaeoenvironmental studies (He et al. 2005;Petersen et al. 2016). However, the SEM observations sometimes revealed very thin (less than 10 μm thick) veins of early diagenetic DP1 cement within the nacreous layers of the inoceramid ISL (Fig. 4E). ...
... As a result of their vagile lifestyle, ammonites often show lower δ 13 C and higher δ 18 O values than other benthic organisms (He et al. 2005;Henderson & Price 2012;Tobin & Ward 2015). Low δ 13 C values reflect the increased contribution of 13 C-depleted metabolic carbon to the shell carbonate of the cephalopods as a response to the high energetic demands related to swimming (Tobin & Ward 2015). ...
Here, we present the first sclerochronological investigation of shells of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from the middle Campanian cold seep carbonate‐bearing strata of the Yezo Basin in Hokkaido (northern Japan). Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope values were measured in the aragonitic and calcitic shell layers of both species and compared to those of other co‐occurring benthic (mainly bivalves and gastropods) and demersal molluscs (ammonites). Sedimentological and stable isotope data suggest that these bivalves lived near cold seeps and were exposed to high H2S level in the seawater. The inoceramid shells exhibited higher δ¹³C and lower δ¹⁸O values than the coeval non‐cold seep molluscs. We ascribed the anomalous isotopic pattern to a combination of vital and environmental effects determined by the hosting of chemosymbionts and the exposure to warm interstitial waters. Inoceramid δ¹³C minima coincided with growth lines and likely reflect changes in nutrient supply by the chemosymbionts. Absolute temperatures estimated from δ¹⁸O values of Sphenoceramus schmidti and S. sachalinensis were, on average, ca. 4–5°C warmer than those reconstructed for the non‐seepage environment (19.3 ± 0.7°C). Short‐term δ¹⁸O fluctuations of the inoceramid material indicate local temperature ranges of up to 5.2°C, that is four times larger than those reconstructed from the benthic and demersal fauna (1.3°C). In general, our data suggest that the stable carbon and oxygen isotope values of the studied Sphenoceramus spp. were strongly affected by short‐term fluctuations in seepage activity and do not reflect seasonal fluctuations.
