ALBERT

Description: Petrological and 13 C analyses were undertaken on contiguous specimens of coal and intercalated minor organic-rich clastic sediments collected from coal seams spanning the Cretaceous-Paleogene boundary in the Alberta and Saskatchewan portions of the Western Interior Basin. The generally high smectite content of the coal suggests that the original mires were largely small, disconnected, and rheotrophic, readily receiving abundant waterborne detrital clastic material of largely volcanic origin. Nevertheless, using the distinctive claystone that marks the Cretaceous-Paleogene boundary as a regional datum, it is possible to correlate cycles in the vitrinite and inertinite composition of the coals over 〉500 km. Estimates of peat accumulation rates suggest that the cycles in vitrinite and inertinite composition represent regional, cyclic fluctuations in wildfire and oxidation of the peatlands and overlying canopy at a frequency of hundreds to thousands of years. The likely causes of these fluctuations were cyclic, regional-scale changes in temperature. The Cretaceous-Paleogene boundary event occurred early during a phase of gradually increasing temperature and/or decreasing rainfall, but peak wildfire and desiccation of peat occurred up to 14,000 yr later than the Cretaceous-Paleogene boundary, and the mires did not experience significant water stress in the immediate aftermath of the extinction event. A persistent, 1.5–3.0 negative 13 C excursion occurs across the Cretaceous-Paleogene boundary, but it cannot be readily separated from four, further negative excursions later in the earliest Danian. The negative carbon isotope excursion linked to the Cretaceous-Paleogene boundary began a few hundred years before the event itself, and recovery occurred within 21 k.y., and possibly in as little as just a few thousand years, consistent with recently calibrated shallow-marine 13 C records. Hence, the atmospheric and surface ocean carbon pools were coupled at this time. The absence of evidence for catastrophic change in the climatic regime at the time of the Cretaceous-Paleogene extinction in these mires supports the notion that the negative shift in atmospheric 13 C was brought about by changes in the 13 C composition of the surface ocean. This is consistent with the greater magnitude of extinction experienced by marine fauna relative to the terrestrial realm.

Description: While marine records of the Eocene-Oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on Antarctica, continental records indicate substantial spatial variability. Marine Eocene-Oligocene transition records are marked by an ~+1.1 foraminiferal 18 O shift, but continental records rarely record the same geochemical signature, making both correlation and linking of causal mechanisms between marine and continental records challenging. Here, a new high-resolution continental 18 O record, derived from the freshwater gill-breathing gastropod Viviparus lentus , is presented from the Hampshire Basin, UK. The Solent Group records marine incursions and has an established magnetostratigraphy, making it possible to correlate the succession directly with marine records. The V. lentus 18 O record indicates a penecontemporaneous, higher-magnitude shift (〉+1.4) than marine records, which reflects both cooling and a source moisture compositional shift consistent with the growth of Antarctic ice. When combined with "clumped" isotope measurements from the same succession, about half of the isotopic shift can be attributed to cooling and about half to source moisture change, proportions similar to marine foraminiferal records. Thus, the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the Eocene-Oligocene transition not observed in continental interior records.

Description: Sub-arctic Cretaceous (Berriasian–late Valanginian, ca. 145–134 Ma) marine temperatures obtained from fossil mollusks (belemnites) are determined using carbonate clumped isotope thermometry, an approach based on the "clumping" of 13 C and 18 O in the carbonate mineral lattice into bonds with each other. From our analyses we infer sub-arctic Early Cretaceous marine temperatures ranging from 10 °C to 20 °C. These possibly seasonally biased, warm sub-arctic temperatures are warmer than present mean summer water temperatures at 60–65°N and are therefore consistent with a warmer "greenhouse" world featuring a shallow (equable) latitudinal temperature gradient. Our combined temperature and 18 O belemnite data imply seawater 18 O values that have a remarkably modern character in that they are similar to modern high-latitude seawater but more positive than modeled Cretaceous seawater. We identify a cooler late Valanginian interval (ca. 134 Ma) with temperatures consistent with polar regions a few degrees above freezing and also coincident with increased 18 O seawater values. Thus we find evidence of intervals when polar ice was unlikely, and also when polar ice was plausible. Both scenarios support the view of generally warm but dynamic polar climates during greenhouse intervals that were punctuated by periods of ice growth.

Description: Significant changes in global climate and carbon cycling occurred during the Early Cretaceous. This study examines the expression of such climatic events in high-latitude Svalbard together with the stratigraphic utility of carbon-isotope stratigraphies. Isotopic analysis of fossil wood fragments (from the Rurikfjellet, Helvetiafjellet, and Carolinefjellet formations, Festningen, Spitsbergen) record a distinctive pattern including a negative isotope excursion preceding a positive event, correlatable with the global early Aptian isotope event. Our carbon-isotope profile improves the stratigraphic correlation and relative dating of the succession. We show that the upper part of the Helvetiafjellet Formation was deposited during the early Aptian, and not the late Barremian, as previously thought. Furthermore, we estimate an age for the abrupt contact of the Rurikfjellet Formation with the overlying Helvetiafjellet Formation (associated with a pulse of igneous activity) to be ca. 129 Ma or ca. 124 Ma, depending on which age model for the Early Cretaceous is used. The well-known dinosaur footprints of the Helvetiafjellet Formation at Festningen are constrained to the middle Barremian and, coupled with floral data, support a warm late Barremian prior to the Aptian carbon-isotope event. The appearance of glendonites at 655 m in the Carolinefjellet Formation is consistent with global cooling in the late Aptian–early Albian.