Greenhouse World Research Articles

Eustatic, tectonic, and climatic signatures in the Lower Cretaceous siliciclastic succession on the Eastern Russian Platform

A methodical approach to identifying major abiotic events in the siliciclastic succession accumulated in the shallow epicontinental basin on the Eastern Russian Platform during the Early Cretaceous is presented. On the basis of a reliable chronostratigraphic framework a comparison between global and regional sea level curves was undertaken. The intervals during which the global and regional sea level curve trends are similar correspond to a predominance of eustasy in the particular basin. Alternatively, tectonic activity dominates during intervals when there is no similarity between the trends of the global and regional sea level curves. Three intervals of noncoincidences of trends of these two curves matched with major tectonic events that took place within the Eastern Russian Platform in the Early Cretaceous: the Early Hauterivian tectonic uplift, subsequent Late Hauterivian subsidence and the Late Albian uplift. The main consequences of the tectonic activity were two large regional unconformities and hiati. The comparison of main global and regional sea level trends also reveals major climatic events. “The cold snaps” that occurred during the Early Cretaceous greenhouse world (Hu et al., 2012) coincided with simultaneous global and regional sea level lowstands, peak shallowing of the basin and the almost complete absence of sediments. “The cold snap” is identified in the Late Aptian sedimentary sequences on the Eastern Russian Platform.

Herd structure in Late Cretaceous polar dinosaurs: A remarkable new dinosaur tracksite, Denali National Park, Alaska, USA

The discovery of a new tracksite of mostly hadrosaurid dinosaur footprints, made by a herd living in an ancient high-latitude continental ecosystem, provides insight into the herd structure and behavior of northern polar dinosaurs and perspective on populations of large-bodied herbivores in an Arctic greenhouse world. This tracksite occurs in the Upper Cretaceous Cantwell Formation in the Alaska Range (Denali National Park, Alaska, United States), and it is the largest tracksite known from this far north. Preservation of the tracksite is exceptional: most tracks, regardless of size, contain skin impressions and they co-occur with well-preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects. Statistical analyses of the tracks show that individuals of four different age classes of hadrosaurids lived together in a large social group. Our research results independently corroborate the growth curve for hadrosaurids proposed by paleohistologists that suggests that these dinosaurs experienced a period of rapid growth early in their life history.

Three dimensional coupled model approaches to terrestrial methane cycling during Paleogene greenhouse climates

The biogeochemical cycling of methane presents a major challenge for paleoclimate scientists, as although this critical greenhouse gas (GHG) has the forcing potential to drive significant changes in the Earth System, there are no proxy methods for reconstructing it’s ancient atmospheric concentration. This is especially important as biogenic methane emissions are controlled by environmental conditions such as temperature and precipitation, and so methane has significant power as a positive or negative feedback on global climate change. Understanding how methane emissions and cycling acted in the high pCO2 greenhouse worlds of the Paleogene potentially bridges the gap between our understanding of other, better (although arguably still poorly-) constrained GHGs and global temperature. The recent application of advanced three dimensional global modelling strategies to the problem of Eocene trace GHG concentrations has begun to show how important these may be in high-CO2 worlds (Valdes et al, 2005; Singarayer et al, 2011; Beerling et al, 2011), suggesting that as much as 2.7 °C of global warming may be contributed. This approach couples the unified Hadley Centre climate model (HadCM3L) with Sheffield Dynamic Global Vegetation Model (SDGVM; Beerling et al, 1997) to simulate trace gas emissions, and the atmospheric chemistry model STOCHEM to simulate the concentration of methane and ozone in the troposphere Here we present early results of a project to extend and develop the results of these earlier works, with revised and improved biogeochemistry and vegetation models, and broader consideration of boundary and initial conditions. These new results will be compared to indirect proxy methods to determine Paleogene methane emissions using lipid biomarker carbon isotopes in Eocene wetland settings (preserved as lignites) to probe past methanogenic and methanotrophic populations and constrain ancient methane emissions in high-CO2 worlds.

Calcareous nannoplankton response at the culmination of the Paleogene greenhouse world

Calcareous nannoplankton response at the culmination of the Paleogene greenhouse world

Low-latitude climate variability in the Heinrich frequency band of the Late Cretaceous greenhouse world

Abstract. Deep marine successions of early Campanian age from DSDP (Deep Sea Drilling Project) site 516F drilled at low paleolatitudes in the South Atlantic reveal distinct sub-Milankovitch variability in addition to precession, obliquity and eccentricity-related variations. Elemental abundance ratios point to a similar climatic origin for these variations and exclude a quadripartite structure as an explanation for the inferred semi-precession cyclicity in the magnetic susceptibility (MS) signal as observed in the Mediterranean Neogene for precession-related cycles. However, semi-precession cycles as suggested by previous work are likely an artifact reflecting the first harmonic of the precession signal. The sub-Milankovitch variability, especially in MS, is best approximated by a ~7 kyr cycle as shown by spectral analysis and bandpass filtering. The presence of sub-Milankovitch cycles with a period similar to that of Heinrich events of the last glacial cycle is consistent with linking the latter to low-latitude climate change caused by a non-linear response to precession-induced variations in insolation between the tropics.

Nd isotopic structure of the Pacific Ocean 70–30 Ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world

AbstractThe oceanic meridional overturning circulation (MOC) is a crucial component of the climate system, impacting heat and nutrient transport, and global carbon cycling. Past greenhouse climate intervals present a paradox because their weak equator‐to‐pole temperature gradients imply a weaker MOC, yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients. To investigate the mode of MOC that operated during the early Cenozoic, we compare new Nd isotope data with Nd tracer‐enabled numerical ocean circulation and coupled climate model simulations. Assimilation of new Nd isotope data from South Pacific Deep Sea Drilling Project and Ocean Drilling Program Sites 323, 463, 596, 865, and 869 with previously published data confirm the hypothesized MOC characterized by vigorous sinking in the South and North Pacific ~70 to 30 Ma. Compilation of all Pacific Nd isotope data indicates vigorous, distinct, and separate overturning circulations in each basin until ~40 Ma. Simulations consistently reproduce South Pacific and North Pacific deep convection over a broad range of conditions, but cases using strong deep ocean vertical mixing produced the best data‐model match. Strong mixing, potentially resulting from enhanced abyssal tidal dissipation, greater interaction of wind‐driven internal wave activity with submarine plateaus, or higher than modern values of the geothermal heat flux enable models to achieve enhanced MOC circulation rates with resulting Nd isotope distributions consistent with the proxy data. The consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients.

Marine Ecosystem Responses to Cenozoic Global Change

The future impacts of anthropogenic global change on marine ecosystems are highly uncertain, but insights can be gained from past intervals of high atmospheric carbon dioxide partial pressure. The long-term geological record reveals an early Cenozoic warm climate that supported smaller polar ecosystems, few coral-algal reefs, expanded shallow-water platforms, longer food chains with less energy for top predators, and a less oxygenated ocean than today. The closest analogs for our likely future are climate transients, 10,000 to 200,000 years in duration, that occurred during the long early Cenozoic interval of elevated warmth. Although the future ocean will begin to resemble the past greenhouse world, it will retain elements of the present "icehouse" world long into the future. Changing temperatures and ocean acidification, together with rising sea level and shifts in ocean productivity, will keep marine ecosystems in a state of continuous change for 100,000 years.

Dynamic polar climates in a greenhouse world: Evidence from clumped isotope thermometry of Early Cretaceous belemnites

Research Article| August 01, 2013 Dynamic polar climates in a greenhouse world: Evidence from clumped isotope thermometry of Early Cretaceous belemnites Gregory D. Price; Gregory D. Price 1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth PL4 8AA, UK Search for other works by this author on: GSW Google Scholar Benjamin H. Passey Benjamin H. Passey 2Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA Search for other works by this author on: GSW Google Scholar Geology (2013) 41 (8): 923–926. https://doi.org/10.1130/G34484.1 Article history received: 13 Feb 2013 rev-recd: 15 Apr 2013 accepted: 18 Apr 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gregory D. Price, Benjamin H. Passey; Dynamic polar climates in a greenhouse world: Evidence from clumped isotope thermometry of Early Cretaceous belemnites. Geology 2013;; 41 (8): 923–926. doi: https://doi.org/10.1130/G34484.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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 13C and 18O 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 δ18Obelemnite data imply seawater δ18O 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 δ18O 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. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Does Antarctic glaciation cool the world?

Abstract. In this study, we compare the simulated climatic impact of adding an Antarctic ice sheet (AIS) to the "greenhouse world" of the Eocene and removing the AIS from the modern world. The modern global mean surface temperature anomaly (ΔT) induced by Antarctic Glaciation depends on the background CO2 levels and ranges from −1.22 to −0.18 K. The Eocene ΔT is nearly constant at ~−0.25 K. We calculate an climate sensitivity parameter S[Antarctica] which we define as ΔT divided by the change in effective radiative forcing (ΔQAntarctica) which includes some fast feedbacks imposed by prescribing the glacial properties of Antarctica. The main difference between the modern and Eocene responses is that a negative cloud feedback warms much of the Earth's surface as a large AIS is introduced in the Eocene, whereas this cloud feedback is weakly positive and acts in combination with positive sea-ice feedbacks to enhance cooling introduced by adding an ice sheet in the modern. Because of the importance of cloud feedbacks in determining the final temperature sensitivity of the AIS, our results are likely to be model dependent. Nevertheless, these model results suggest that the effective radiative forcing and feedbacks induced by the AIS did not significantly decrease global mean surface temperature across the Eocene–Oligocene transition (EOT −34.1 to 33.6 Ma) and that other factors like declining atmospheric CO2 are more important for cooling across the EOT. The results illustrate that the efficacy of AIS forcing in the Eocene is not necessarily close to one and is likely to be model and state dependent. This implies that using EOT paleoclimate proxy data by itself to estimate climate sensitivity for future climate prediction requires climate models and consequently these estimates will have large uncertainty, largely due to uncertainties in modelling low clouds.

Early Cenozoic Differentiation of Polar Marine Faunas

The widespread assumption that the origin of polar marine faunas is linked to the onset of major global cooling in the Late Eocene – Early Oligocene is being increasingly challenged. The Antarctic fossil record in particular is suggesting that some modern Southern Ocean taxa may have Early Eocene or even Paleocene origins, i.e. well within the Early Cenozoic greenhouse world. A global analysis of one of the largest marine clades at the present day, the Neogastropoda, indicates that not only is there a decrease in the number of species from the tropics to the poles but also a decrease in the evenness of their distribution. A small number of neogastropod families with predominantly generalist trophic strategies at both poles points to the key role of seasonality in structuring the highest latitude marine assemblages. A distinct latitudinal gradient in seasonality is temperature-invariant and would have operated through periods of global warmth such as the Early Cenozoic. To test this concept a second global analysis was undertaken of earliest Cenozoic (Paleocene) neogastropods and this does indeed show a certain degree of faunal differentiation at both poles. The Buccinidae, s.l. is especially well developed at this time, and this is a major generalist taxon at the present day. There is an element of asymmetry associated with this development of Paleocene polar faunas in that those in the south are more strongly differentiated than their northern counterparts; this can in turn be linked to the already substantial isolation of the southern high latitudes. The key role of seasonality in the formation of polar marine faunas has implications for contemporary ecosystem structure and stability.

Reconstructing Late Ordovician carbon cycle variations

The role of carbon dioxide in regulating climate during the early Paleozoic, when severe glaciations occurred during a putative greenhouse world, remains unclear. Here, we present the first molecular carbon isotope proxy-based estimates for Late Ordovician (early Katian) pCO2 levels, and explore the limitations of applying this approach to the reconstruction of Paleozoic pCO2. Carbon isotope profiles from three sites in Laurentia (Iowa, Ontario and Pennsylvania) and one site in Baltica (Estonia) exhibit overall low isotope fractionation between organic and inorganic carbon during photosynthesis (εp) and these values declined during the early Katian carbonate carbon isotope excursion (or Guttenberg Carbon Isotope Excursion, GICE). Algal εp values are sensitive to changes in CO2 concentrations, algae cell morphologies, and cell growth rates. To constrain these factors, we present molecular evidence that a decrease in the relative abundance of cyanobacteria and a change in the eukaryotic algae community co-occurred with the GICE. Regardless of local biotic or oceanographic influences, a decline in εp values indicates photosynthesis was sensitive to carbon concentrations, and via analogy with modern taxa, constrains pCO2 to below ∼8× pre-industrial levels (PIL), or about half of previous estimates. In addition, the global, positive carbon isotope excursions expressed in a wide variety of sedimentary materials (carbonate, bulk organic matter, n-alkanes, acyclic and cyclic isoprenoid hydrocarbons), provide compelling evidence for perturbation of the global carbon cycle, and this was likely associated with a decrease in pCO2 approximately 10 million years prior to the Hirnantian glaciations. Isotopic records from deeper water settings suggest a complex interplay of carbon sources and sinks, with pCO2 increasing prior to and during the early stages of the GICE and then decreasing when organic carbon burial outpaced increased volcanic inputs.

Long‐term evolutionary and ecological responses of calcifying phytoplankton to changes in atmospheric CO2

AbstractCalcifying phytoplankton play an important role in marine ecosystems and global biogeochemical cycles, affecting the transfer of both organic and inorganic carbon from the surface to the deep ocean. Coccolithophores are the most prominent members of this group, being well adapted to low‐nutrients environments (e.g., subtropical gyres). Despite urgent concerns, their response to rising atmospheric carbon dioxide levels (pCO2) and ocean acidification is still poorly understood, and short‐term experiments may not extrapolate into longer‐term climatic adaptation. Current atmospheric pCO2 (~390 ppmv) is unprecedented since at least 3 million years ago (Ma), and levels projected for the next century were last seen more than 34 Ma. Hence, a deep‐time perspective is needed to understand the long‐term effects of high pCO2 on the biosphere. Here we combine a comprehensive fossil data set on coccolithophore cell size with a novel measure of ecological prominence: Summed Common Species Occurrence Rate (SCOR). The SCOR is decoupled from species richness, and captures changes in the extent to which coccolithophores were common and widespread, based on global occurrences in deep‐sea sediments. The size and SCOR records are compared to state‐of‐the‐art data on climatic and environmental changes from 50 to 5 Ma. We advance beyond simple correlations and trends to quantify the relative strength and directionality of information transfer among these records. Coccolithophores were globally more common and widespread, larger, and more heavily calcified in the pre‐34 Ma greenhouse world, and declined along with pCO2 during the Oligocene (34–23 Ma). Our results suggest that atmospheric pCO2 has exerted an important long‐term control on coccolithophores, directly through its availability for photosynthesis or indirectly via weathering supply of resources for growth and calcification.

Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch

The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth's climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future as a consequence of unabated anthropogenic carbon emissions. Climatic conditions of the early Eocene 'greenhouse world', however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 °C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing.

Marine rapid environmental/climatic change in the Cretaceous greenhouse world

The Cretaceous Period serves as a relevant model to understand greenhouse climate evolution. As atmospheric CO2 concentrations continue to rise in the twenty-first century, critical questions put forward are 1) how the Cretaceous Earth System could have been maintained in the “greenhouse” state, if there are some variations, 2) why and how fast did climatic and palaeoenvironmental changes happened during the Cretaceous, and 3) what records were preserved in the Earth's archives that enable the comparison of Cretaceous rates of paleoenvironmental changes with today's global changes. In fact, rapid and severe global environmental and climatic changes happened in the Cretaceous greenhouse world including oceanic anoxic events, oceanic red beds, “cold snaps” or glaciations and carbonate platform drowning events. This special issue originated from the final workshop of UNESCO International Geoscience Program IGCP 555 and the Pardee session of the Geological Society of America 2010 annual meeting. Participants and contributors mainly focused on the causes, processes, and consequences of rapid environmental/climatic changes that happened in the Cretaceous greenhouse world.

Early Cretaceous palaeoceanography of the Greenland–Norwegian Seaway evidenced by calcareous nannofossils

Abstract Reconstructions of the palaeoclimate of the Early Cretaceous are controversial, varying from a warm-temperate greenhouse world to icehouse conditions. We studied calcareous nannofossil assemblages of sediments from North-East Greenland (Wollaston Forland and Kuhn O) of Late Ryazanian–Barremian age in order to better understand the palaeoclimate and palaeoceanography of the high latitudes. The calcareous nannofossil assemblages are characterized by abundant Crucibiscutum spp. and Watznaueria spp., Biscutum constans and other Boreal taxa. They show also influxes of Tethyan and low to mid latitudinal taxa like nannoconids (e.g. Nannoconus bermudezii , Nannoconus dolomiticus , Nannoconus steinmannii ), pentaliths ( Micrantholithus hoschulzii , Micrantholithus obtusus ), conuspheres, Speetonia colligata and Cruciellipsis cuvillieri in the Upper Ryazanian and Lower Hauterivian. Reconstructed surface water conditions, indicated by fluctuations in the assemblage compositions, suggest cool conditions for the Late Ryazanian, a cold climate for the Valanginian, and warm climatic conditions for the Hauterivian–Barremian. High meridonial temperature gradients and cool–cold climatic conditions in the high latitudes caused supposedly the formation of deep water in the South Anyui Gulf in the Late Ryazanian–Valanginian. Palaeoceanographic changes, reflected in a counter-balanced ocean current system in the Greenland–Norwegian Seaway, allowed Tethyan biota to spread as far north as North-East Greenland during the Late Ryazanian.

Continental Scientific Drilling Project of Cretaceous Songliao Basin: Scientific objectives and drilling technology

The Continental Scientific Drilling Project at the Cretaceous-age Songliao Basin is a drilling initiative under the framework of the International Continental Scientific Drilling Program, to recover a nearly complete Cretaceous terrestrial sedimentary record in the Songliao Basin, northeastern China. The recovered cores will provide unique opportunities for the geosciences community to advance the understanding of climate change in the Cretaceous greenhouse world, and provide a documentation of geological events relevant to the carbon cycle during this time period.This drilling project will address significant geological questions, such as the identification of important stratigraphic boundaries and the marine-terrestrial correlations of stratigraphy, the reasons for the biotic response to the terrestrial environmental changes, the terrestrial response to the Cretaceous oceanic anoxic events, the formation of terrestrial petroleum source rocks, and the mechanisms for the Cretaceous magnetic Normal Superchron (CNS).In the first stage of this drilling project, the SKI drilling, rock cores of 2485.89m in total length were recovered and the recovery ratio reached 96.46%. A series of drilling and coring technologies including regular, confined, directional, and sealed coring, were utilized to ensure a higher recovery ratio for the core, and will be described at the end of this paper. Well loggings were conducted right after coring. Core handling and storage were arranged in such a way that the scientific research was conducted on half of each core, whereas the other half of each core was preserved for long-term storage. The upcoming second stage, the SKII drilling, will combine with data from the existing SKI to provide complete high-resolution climate records of the terrestrial environment for the whole Cretaceous time period.

Evolution of middle to Late Cretaceous oceans—A 55 m.y. record of Earth's temperature and carbon cycle

Research Article| February 01, 2012 Evolution of middle to Late Cretaceous oceans—A 55 m.y. record of Earth's temperature and carbon cycle Oliver Friedrich; Oliver Friedrich * 1Scripps Institution of Oceanography, University of California−San Diego, 9500 Gilman Drive, La Jolla, California 92093-0244, USA *Current address: Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany. Search for other works by this author on: GSW Google Scholar Richard D. Norris; Richard D. Norris 1Scripps Institution of Oceanography, University of California−San Diego, 9500 Gilman Drive, La Jolla, California 92093-0244, USA Search for other works by this author on: GSW Google Scholar Jochen Erbacher Jochen Erbacher 2Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Oliver Friedrich * 1Scripps Institution of Oceanography, University of California−San Diego, 9500 Gilman Drive, La Jolla, California 92093-0244, USA Richard D. Norris 1Scripps Institution of Oceanography, University of California−San Diego, 9500 Gilman Drive, La Jolla, California 92093-0244, USA Jochen Erbacher 2Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany *Current address: Institut für Geowissenschaften, Goethe-Universität Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany. Publisher: Geological Society of America Received: 01 Aug 2011 Revision Received: 07 Sep 2011 Accepted: 08 Sep 2011 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (2): 107–110. https://doi.org/10.1130/G32701.1 Article history Received: 01 Aug 2011 Revision Received: 07 Sep 2011 Accepted: 08 Sep 2011 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Oliver Friedrich, Richard D. Norris, Jochen Erbacher; Evolution of middle to Late Cretaceous oceans—A 55 m.y. record of Earth's temperature and carbon cycle. Geology 2012;; 40 (2): 107–110. doi: https://doi.org/10.1130/G32701.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A new 55 m.y. global compilation of benthic foraminifera δ13C and δ18O for the middle to Late Cretaceous shows that there was widespread formation of bottom waters with temperatures >20 °C during the Cretaceous greenhouse world. These bottom waters filled the silled North Atlantic and probably originated as thermocline or intermediate waters in the tropical oceans. Carbon burial during the Cretaceous oceanic anoxic events produced a positive δ13C shift in global carbon reservoirs, but this is not particularly large, especially by comparison with the remarkable Late Paleocene carbon maximum. The interbasin δ13C gradient was unusually large during the Cretaceous hot greenhouse, probably because the North Atlantic sills prevented the free exchange of waters in the deep basin. The hot greenhouse ended when the Equatorial Atlantic Gateway opened sufficiently to flood the deep North Atlantic with relatively cool polar waters formed in the Southern Ocean. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Systems tract successions under variable climatic and tectonic regimes: A quantitative approach

Systems tracts are linkages of contemporaneous depositional systems that accumulate under specific conditions of accommodation and sediment supply. They are identified by their stratal stacking pattern and position within the sequence. In practice, it is often difficult to assign accurately relative sea-level position to stacking patterns. Observations also show that systems tracts may succeed each other in different orders, not necessarily according to the prediction of an ideal model. The purpose of this study is to analyze the quantitative conditions for different possible combinations of systems tractswithin a cycle of relative sea-level change. Icehouse and greenhouse eustatic trends, active and passive tectonics, and varying depositional rates are considered as conditions. The systems tracts were defined based on the rate of accommodation change and depositional rate.Our quantitative calculations revealed that if the tectonics is active and the basement motion-time curve is segmented with sharp turning points between segments, eight possible successions of systems tracts may occur. If the basement motion is transitional between segments of subsidence and uplift, six scenarios are possible. Only three possible combinations of systems tracts can form in a sea-level cycle if the basement tectonics is passive. Variable depositional rate alone can be responsible for four different combinations of systems tracts under similar accommodation conditions. These combinations of systems tracts may occur primarily in greenhouse world. Eustasy under icehouse climatic conditions has rapid rates of change (up to 4000 m/myr), which are likelymany times faster thanwhat subsidence/uplift rates realistically can reach.As a consequence, only the full series of systems tract in the order of forced regression-lowstand normal regression-transgression-highstand normal regression can be predicted in icehouse, although the thickness of systems tracts in the real rock record may be rather small because of the fast rate of sea-level change.

Conodont apatite δ 18O values from a platform margin setting, Oklahoma, USA: Implications for initiation of Late Ordovician icehouse conditions

The uppermost Sandbian–lower Katian stratigraphic record documents a critical time period in Earth history. Lithological evidence and geochemical proxy records suggest that the uppermost Sandbian–lower Katian interval could represent a transitional phase from a long Cambrian–Ordovician greenhouse world to the Late Ordovician icehouse world. To examine this interval of Earth's history, oxygen isotopes of conodont apatite from the Bromide and Viola Springs Formations in southern Oklahoma were analyzed in order to provide sea-surface temperature estimates at a location that had little influence by terrigenous sedimentation. Our results are inconsistent with 1) previous suggestions that global cooling occurred across a prominent sequence boundary close to the Sandbian–Katian boundary across North America and 2) the hypothesis that there is a direct connection between volcanic mega eruption(s) and a significant long term impact on climate during the Sandbian–Katian of Laurentia. Furthermore, δ 18O values spanning the Guttenberg Carbon Isotope Excursion (GICE), an interval that has been interpreted as evidence for an early onset of the Late Ordovician glaciation, are variable. A + 1.5‰ δ 18O shift is observed in the lower GICE that is followed by a return to δ 18O values that fluctuate around a mean of 19.0‰ in the upper GICE. Together, these observations suggest a short-lived cooling event within the lower GICE. This cooling event may represent enhanced carbon burial and drawdown of atmospheric pCO 2 followed by a return to more stable low-latitude temperatures in the upper GICE.

Life at the top of the greenhouse Eocene world--A review of the Eocene flora and vertebrate fauna from Canada's High Arctic

Early–middle Eocene (ca. 53–38 Ma) sediments of the Eureka Sound Group in Canada’s Arctic Archipelago preserve evidence of lush mixed conifer-broadleaf rain forests, inhabited at times by alligators, turtles, and diverse mammals, including primates, tapirs, brontotheres, and hippo-like Coryphodon. This biota reflects a greenhouse world, offering a climatic and ecologic deep time analog of a mild ice-free Arctic that may be our best means to predict what is in store for the future Arctic if current climate change goes unchecked. In our review of the early–middle Eocene Arctic flora and vertebrate fauna, we place the Arctic fossil localities in historic, geographic, and stratigraphic context, and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these Eocene Arctic forests and their vertebrate inhabitants. The abundance and diversity of tapirs and plagiomenids (both rare elements in midlatitude faunas), and the absence of artiodactyls, early horses, and the hyopsodontid “condylarth” Hyopsodus (well represented at midlatitude localities) are peculiar to the Eocene Arctic. The Eocene Arctic macrofloras reveal a forested landscape analogous to the swamp-cypress and broadleaf floodplain forests of the modern southeastern United States. Multiple climate proxies indicate a mild temperate early–middle Eocene Arctic with winter temperatures at or just above freezing and summer temperatures of 20 °C (or higher), and high precipitation. At times, this high precipitation resulted in freshwater discharge into a nearly enclosed Arctic Ocean basin, sufficient to cause surface freshening of the Arctic Ocean, supporting mats of the floating fern Azolla . Fluctuating Arctic Ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges, allowing land plants and animals to disperse between North America and both Europe and Asia.