Shell chemistry of the boreal Campanian bivalve &amp;lt;i&amp;gt;Rastellum diluvianum&amp;lt;/i&amp;gt; (Linnaeus, 1767) reveals temperature seasonality, growth rates and life cycle of an extinct Cretaceous oyster

Niels J De Winter,Stijn J M Van Malderen,Clemens V Ullmann,Steven Goderis,Anne M Sørensen,Frank Vanhaecke,Christophe Snoeck,Nicolas Thibault,Stijn Goolaerts,Philippe Claeys

doi:10.5194/bg-17-2897-2020

Abstract

Abstract. The Campanian age (Late Cretaceous) is characterized by a warm greenhouse climate with limited land-ice volume. This makes this period an ideal target for studying climate dynamics during greenhouse periods, which are essential for predictions of future climate change due to anthropogenic greenhouse gas emissions. Well-preserved fossil shells from the Campanian (±78 Ma) high mid-latitude (50∘ N) coastal faunas of the Kristianstad Basin (southern Sweden) offer a unique snapshot of short-term climate and environmental variability, which complements existing long-term climate reconstructions. In this study, we apply a combination of high-resolution spatially resolved trace element analyses (micro-X-ray fluorescence – µXRF – and laser ablation inductively coupled plasma mass spectrometry – LA-ICP-MS), stable isotope analyses (IRMS) and growth modeling to study short-term (seasonal) variations recorded in the oyster species Rastellum diluvianum from the Ivö Klack locality. Geochemical records through 12 specimens shed light on the influence of specimen-specific and ontogenetic effects on the expression of seasonal variations in shell chemistry and allow disentangling vital effects from environmental influences in an effort to refine paleoseasonality reconstructions of Late Cretaceous greenhouse climates. Growth models based on stable oxygen isotope records yield information on the mode of life, circadian rhythm and reproductive cycle of these extinct oysters. This multi-proxy study reveals that mean annual temperatures in the Campanian higher mid-latitudes were 17 to 19 ∘C, with winter minima of ∼13 ∘C and summer maxima of 26 ∘C, assuming a Late Cretaceous seawater oxygen isotope composition of −1 ‰ VSMOW (Vienna standard mean ocean water). These results yield smaller latitudinal differences in temperature seasonality in the Campanian compared to today. Latitudinal temperature gradients were similar to the present, contrasting with previous notions of “equable climate” during the Late Cretaceous. Our results also demonstrate that species-specific differences and uncertainties in the composition of Late Cretaceous seawater prevent trace element proxies (Mg∕Ca, Sr∕Ca, Mg∕Li and Sr∕Li) from being used as reliable temperature proxies for fossil oyster shells. However, trace element profiles can serve as a quick tool for diagenesis screening and investigating seasonal growth patterns in ancient shells.

Highlights

The Late Cretaceous was marked by a long cooling trend that brought global mean annual temperatures (MATs) down from the mid-Cretaceous climate maximum (±28 ◦C surface ocean temperatures) in the Cenomanian and Turonian (±95 Ma) to slightly cooler temperatures (±22 ◦C surface ocean temperatures) around the Campanian–Maastrichtian boundary (±72.1 Ma; Clarke and Jenkyns, 1999; Pearson et al, 2001; Huber et al, 2002; Friedrich et al, 2012; Scotese, 2016)
We apply a combination of high-resolution spatially resolved trace element analyses, stable isotope analyses (IRMS) and growth modeling to study short-term variations recorded in the oyster species Rastellum diluvianum from the Ivö Klack locality
The lack of burial and tectonic activity in the region favored Rastellum diluvianum fossil shells from Ivö Klack that were well preserved, as is evident from the excellent preservation of growth structures typical for ostreid shells as well as from the limited evidence for geochemical changes associated with diagenetic alteration

Summary

Introduction

The Late Cretaceous was marked by a long cooling trend that brought global mean annual temperatures (MATs) down from the mid-Cretaceous climate maximum (±28 ◦C surface ocean temperatures) in the Cenomanian and Turonian (±95 Ma) to slightly cooler temperatures (±22 ◦C surface ocean temperatures) around the Campanian–Maastrichtian boundary (±72.1 Ma; Clarke and Jenkyns, 1999; Pearson et al, 2001; Huber et al, 2002; Friedrich et al, 2012; Scotese, 2016). The rocky-shore deposits of Ivö Klack are characterized by a diverse shelly fauna, consisting of well-preserved fossils and fragments of brachiopods, belemnites, echinoids and asteroids, polychaete worms, gastropods, corals, ammonites, and thick-shelled oysters, with a total of almost 200 different recognized species (Surlyk and Sørensen, 2010) In this diverse rocky-shore ecosystem, various habitat zones can be distinguished, each with their distinct suite of organisms adapted to local conditions of varying amounts of sunlight, sedimentation and turbulence (Surlyk and Christensen, 1974; Sørensen et al, 2012). This unique combination of marine biodiversity and preservation of original calcite shell material makes the localities in the Kristianstad Basin ideal for studying sub-annual variability in shell chemistry and reconstructing paleoseasonality and environmental change in the Campanian (Sørensen et al, 2015)

Methods

Discussion

Conclusion