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The current study presents new bed‐by‐bed brachiopod δ13C and δ18O records from Öland, Sweden, which together with previously published data from the East Baltic region, constitutes a high‐resolution paired brachiopod and bulk rock carbon and oxygen isotope archive through the Lower to Upper Ordovician successions of Baltoscandia. This new data set refines the temporal control on the global Ordovician δ18O‐trend considerably, improving paleoenvironmental reconstructions through the main phase of the Great Ordovician Biodiversification Event (GOBE). The new brachiopod carbon and oxygen isotope records from Öland display strong similarity with the East Baltic records, elucidating the regional consistency as well as global correlation utility of the ensuing composite Baltoscandian Lower to Middle Ordovician carbon and oxygen isotope record. The carbon isotope record from Öland indicates that the widely reported Middle Ordovician carbon cycle perturbation—MDICE (Mid‐Darriwilian Carbon Isotope Excursion)—is recorded in both brachiopods and bulk carbonates. The oxygen isotope record reveals a long‐term Lower to Upper Ordovician trend of increasingly heavier brachiopod δ18O values, with a pronounced increase during the Middle Ordovician Darriwilian Stage. We interpret this trend as dominantly reflecting a paleotemperature signal indicating progressively cooler Early to Middle Ordovician climate with glacio‐eustasy. Our Baltic δ18O values are therefore consistent with postulations that the biotic radiations during the GOBE and climatic cooling during the Darriwilian were strongly linked. Plain Language Summary: Oxygen isotope values obtained from fossil brachiopod shells have traditionally been used as a faithful paleoclimatic proxy to shed light on temperature trends in ancient oceans. However, because brachiopod shells are susceptible to diagenetic overprint after burial, secular oxygen isotope trends derived from these fossils are often questioned—notably the farther one goes back in geological time. This study presents temporally well‐resolved oxygen isotope data from Lower–lower Upper Ordovician sedimentary rocks of Öland, Sweden, tied precisely to conodont biostratigraphy on the bed‐by‐bed scale. This interval is important in Earth history as it brackets the greatest marine biodiversification event known in the fossil record and coincides with a global climatic cooling phase (determined based on proxies other than oxygen isotopes). The current study therefore provides an excellent test of the spatial and temporal consistency of the secular Ordovician oxygen isotope trend. We find that although our data is probably affected by diagenetic modification, primary paleoclimatic signals are preserved. Furthermore, as current global Ordovician oxygen isotope records lack sufficient resolution because they comprise data from geographically widely distributed low‐paleolatitude localities, our new high‐resolution data set from one mid‐paleolatitude region, provides significant temporal insights that considerably improves our understanding of the Ordovician climate. Key Points: New paired Baltic carbonate data set improves Ordovician 18O‐ and 13C‐recordThe new data supports a Middle Ordovician sea surface temperature coolingRegional/intra‐basinal consistency of oxygen isotope trends indicate primary nature of paleoenvironmental changes [ABSTRACT FROM AUTHOR]

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 – µ XRF – 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. [ABSTRACT FROM AUTHOR]

Macrofossil calcite plays a central role for palaeoenvironmental reconstructions because its preservation state and geochemical signatures can be checked using a variety of screening techniques. Reconstructions of the ecology and seawater composition from such data require knowledge about species-specific compositions of well-preserved calcitic fossils. Comprehensive datasets, recording averages, intraspecimen and intraspecific variability of geochemical proxies in fossil calcite, however, are still largely lacking. Here we report δ 13 C and δ 18 O values, as well as Mg/Ca, Sr/Ca and Mn/Ca ratios of 204 aliquots sampled along transects through three rostra of the late early Campanian belemnite species Belemnellocamax mammillatus . Geochemical signatures of partially altered samples are consistent to those reported for early marine calcite cementation and show trends towards moderately higher Mn/Ca, heavier δ 13 C and lower Sr/Ca. In contrast, Mg/Ca ratios and δ 18 O values remain similar to projected original values. Median δ 18 O values of − 0.3 to 0.0‰ are comparable to the heaviest values of coeval oysters from the same localities, and internal variability of the well-preserved parts of the rostra is low. These findings suggest that B . mammillatus lived mostly in the deep part of the basin where seasonal changes were low and water temperatures cool. The δ 13 C is offset from oysters and most coeval belemnite species from the same region, and from bulk rock values of other European localities by several permil towards lighter values. This offset suggests that a strong vital effect impacted the carbon isotopes of the investigated species during calcification. Average Mg/Ca ratios of 11.5 mmol/mol and Sr/Ca ratios of 2.13 mmol/mol (n = 155) are found for the well-preserved parts of the belemnite rostra. The intraspecimen variability of Mg/Ca and Sr/Ca ratios between 7 and 20% (2 relative standard deviations) is similar amongst the specimens, but intraspecific variability of Mg/Ca is significantly higher than for Sr/Ca. Average Sr/Ca ratios of 2.1 ± 0.2 mmol/mol and Mg/Ca of 11 ± 3 mmol/mol are proposed for the late early Campanian B . mammillatus of the Kristianstad Basin. [ABSTRACT FROM AUTHOR]

The Middle Ordovician (~460-470 Ma) in Baltoscandia is mainly represented by the so called 'orthoceratite limestone'. This is a geographically wide-spread condensed sedimentary succession of a few tens of meters thickness consisting of fine-grained limestones deposited at middle paleolatitudes. These successions have a long history of detailed litho- and biostratigraphical research, which in recent years is complemented with chemostratigraphical investigations (mainly stable carbon isotopes). New mm-resolution XRF elemental core scanning data from the Tingskullen-1 and Kårehamn P4 cores from the island of Öland, Sweden, reveal the potential to further test the hypothesis of the presence of Milankovitch scale cyclicity in these records. This new high-resolution data also resolves the regular occurrence of hardgrounds in this 'orthoceratite limestone', as for example expressed in minima in carbonate content and peaks in detrital elements. These dissolution surfaces have been suggested to be related to carbonate production-dissolution alternations. It is interesting that many of the relative changes in the elemental profiles seem to be related to these dissolution horizons and show a certain regularity in occurrence on different spatial levels. The ratio between the different periods, in combination with specific patterns of amplitude modulation - both visually and statistically inspected - suggests the presence of a precessional scale variability, bundled in eccentricity cycles. Besides the existing integrated stratigraphical framework, these interpretations can be tested by ongoing geochronological work (CA-TIMS U-Pb dating of zircons from volcanic ash layers present in these successions). The prospective of building an astronomical timescale for the Middle Ordovician can shed new light on its climate dynamics and associated tempo and duration of important events such as the Great Ordovician Biodiversification Event (GOBE) and the middle Darriwilian carbon isotope excursion (MDICE). [ABSTRACT FROM AUTHOR]