High Carbon Isotope Values Research Articles

Palaeoecology of late Early Miocene fauna in the Namib based on 13C/ 12C and 18O/ 16O ratios of tooth enamel and ratite eggshell carbonate

We explored the stable light isotope ecology of a sample of extinct Namibian mammals from the early Miocene, a period when conditions are believed to have been relatively warm and moist. Where possible we compared isotope values of mammalian tooth enamel (Rhinocerotidae, Suidae, Climacoceratidae, Pliohyracidae, Gomphotheriidae and Deinotheriidae) with those of eggshells of a co-existing Aepyornithoid (19–20 Ma). In general, the isotopic values of tooth enamel in all mammalian fauna, including likely mixed feeders/grazers, are consistent with C 3 diets as expected for this period, and the ratite eggshells are consistently enriched in both 13C and 18O compared to the mammals. High eggshell carbon and oxygen isotope values at the sites of Grillental and Elisabethfeld suggest that ratite birds occupied a dry niche that possibly included CAM plants, while results for Langental suggest moister, cooler conditions. Arrisdrift (ca. 17–17.5 Ma) mammalian tooth enamel values overlap those of the 19–20 Ma sites. The dataset for Arrisdrift reveals distinctive patterning between species. In particular the two suid species differ significantly in δ 18O and δ 13C, suggesting distinct ecological niches consistent with predictions from their dental morphology. On the other hand, two distinct data populations for one species of Prohyrax may suggest different environmental conditions during the period in which the site formed.

Magnetic susceptibility and selected geochemical–mineralogical data as proxies for Early to Middle Frasnian (Late Devonian) carbonate depositional settings in the Holy Cross Mountains, southern Poland

The magnetic susceptibility (MS) and other petromagnetic features of Early to Middle Frasnian carbonates from the Holy Cross Mountains (southern Poland) were studied. They were correlated with the Eovariscan tectonic activity and palaeoenvironmental changes. The MS logs were compared with the available geochemical and mineralogical data. A substantial paramagnetic contribution to the MS of the Frasnian carbonates is evidenced by a poor correlation of this parameter with the isothermal remanent magnetization values, and by a decrease of MS values at low temperatures. An estimation of paramagnetic input indicates the dominance of this contribution to the magnetic susceptibility in 60% of studied samples. The MS low widely documented in samples through the Palmatolepis punctata Zone is particularly due to limited input of paramagnetic mineral particles into the basin where also amounts of larger detrital grains of quartz, hematite and goethite were significantly reduced. This depression corresponds well to anomalously high carbon isotope ( δ 13C) values for carbonates. Nevertheless, a transient MS rise across the E-MF boundary, linked with an increase in detrital quartz content, suggests together that both the initiation and termination phases of the punctata Event indeed coincided with increased terrigenous (?eolian) input from uplifted lands. The MS high identified in the lower part of the Palmatolepis hassi Zone coincides with higher content of detrital quartz, hematite and goethite, being accompanied by low δ 13C values. In spite of similar MS stratigraphic signatures in other basins, the increased detrital input of proximal provenance is likely connected with the first Variscan tectonic events that spread over the region and subsequently led to gradual closing of the Saxothuringian ocean segments with basement uplift in the area of the Mid-German Crystalline High.

Environmental change during the Late Famennian and Early Tournaisian (Late Devonian–Early Carboniferous): implications from stable isotopes and conodont biofacies in southern Europe

AbstractA biostratigraphic correlation of the Devonian/Carboniferous (D/C) boundary sections from the Carnic Alps, the Graz Palaeozoic, the Montagne Noire and the Pyrenees resulted in a high‐resolution record of the carbon isotopic composition of micrites (δ13Ccarb), of sedimentary organic matter (δ13Corg) and of oxygen isotope ratios of conodont apatite (δ18Ophosph). The studies focused on the interval between the Upper postera Zone (Late Famennian) and the sandbergi Zone (Lower Tournaisian). For the first time, weak but significant positive carbon isotope excursions in micrites and in the sedimentary organic matter is reported from the Middle and Upper expansa zones of the Carnic Alps. They coincide with a decrease in the oxygen isotope values of conodont apatite. The excursions indicate changes in the global carbon cycle during an episode of high seawater temperatures, and correlate with sedimentary change and a stepwise eustatic rise in the Rhenish Massif. High carbon isotope values were also measured in limestones from the Graz Palaeozoic in the Upper praesulcata Zone, which were previously reported from the Rhenish Massif, Carnic Alps, Montagne Noire and the North America continent. The change from a palmatolepid–polygnathid conodont biofacies to a palmatolepid–bispathodid–branmehlid biofacies in the expansa Zone in the Carnic Alps is obviously influenced by anoxic conditions and repeated transgressive phases. The protognathodids and the polygnathids start to radiate in the Upper praesulcata Zone, after the main end‐Famennian extinction episode. This is connected with the disappearance of the palmatolepids, and environmental stress created by worldwide anoxic conditions, climate change and sea‐level changes, stimulated the radiation of both protognathodids and the polygnathids. The regional correlation of the geochemical records as well as interpretations of these records on a global scale indicate that changes in conodont biofacies of Late Famennian–Early Tournaisian limestones were caused by a complex pattern of environmental changes. Copyright © 2008 John Wiley & Sons, Ltd.

High and dry in central Tibet during the Late Oligocene

The time at which the Tibetan Plateau rose to its present high elevation remains controversial, with estimates ranging from 40 Ma to more recent than 7 Ma. New stable isotope analyses of modern and accurately dated ancient paleosol carbonate in the Nima basin of central Tibet point to an arid climate and high paleoelevation (4.5–5 km, comparable to today's setting) by 26 Ma. Oxygen isotope values of ancient (26 Ma) soil carbonate are both very negative and indistinguishable–after modest corrections for changes in global climate–from the lowest (least evaporated) oxygen isotope values of modern soil carbonates in the area. Substantial enrichments in oxygen-18 in paleolacustrine carbonates, as well as high carbon isotope values from paleosol carbonates, indicate considerable lake evaporation and low soil respiration rates, respectively, and both are consistent with the present arid climate of the Nima area. Blockage of tropical moisture by the Himalaya and perhaps the Gangdese Shan probably has contributed strongly to the aridity and very negative oxygen isotope values of soil carbonate and surface water in the Nima area since at least the Late Oligocene. The maintenance of high elevation since at least 26 Ma suggests that any flow of lower crust from beneath central Tibet must have been balanced by coeval northward insertion of Indian crust beneath the Plateau.

Fluctuations in epeiric sea carbonate production during Silurian positive carbon isotope excursions: A review of proposed paleoceanographic models

Positive excursions in the carbon isotopic ratio of marine carbonates ( δ 13C carb) are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans. Regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced, the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains. The notion that high δ 13C carb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings. What is surprising is that major positive carbon isotope excursions during the Silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas. In fact, Silurian δ 13C carb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally. This discrepancy has sparked considerable debate among Silurian carbon isotope specialists but has offered a valuable opportunity to re-examine the intricate connections among nutrients, primary productivity, carbonate sedimentology, and the global carbon cycle in the lower Paleozoic. Here, we consider several sedimentological and geochemical features of one of these Silurian positive carbon isotope ( δ 13C carb) excursions and discuss the broader implications of current Silurian δ 13C carb models to the interpretation of lower Paleozoic carbonate sequences.

Global dominance of coralline red-algal facies: A response to Miocene oceanographic events

Research Article| June 01, 2005 Global dominance of coralline red-algal facies: A response to Miocene oceanographic events Jochen Halfar; Jochen Halfar 1Institut für Geologie und Paläontologie, Universität Stuttgart, Herdweg 51, 70174 Stuttgart, Germany Search for other works by this author on: GSW Google Scholar Maria Mutti Maria Mutti 2Institut für Geowissenschaften, Universität Potsdam, Postfach 60 15 53, 14415 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Geology (2005) 33 (6): 481–484. https://doi.org/10.1130/G21462.1 Article history received: 13 Dec 2004 rev-recd: 31 Jan 2005 accepted: 04 Feb 2005 first online: 03 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 Jochen Halfar, Maria Mutti; Global dominance of coralline red-algal facies: A response to Miocene oceanographic events. Geology 2005;; 33 (6): 481–484. doi: https://doi.org/10.1130/G21462.1 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 Rhodoliths (free-living coralline red algae) can thrive under a wide range of temperatures, reduced light, and increased nutrient levels, and often form a distinct so-called rhodalgal lithofacies that is an important component of Cenozoic shallow-water carbonates. Global distributions illustrate that from the late-early to early-late Miocene (Burdigalian–early Tortonian), rhodalgal facies reached peak abundances and commonly replaced coral-reef environments, accompanied by a decline in other carbonate-producing phototrophs. We argue that the dominance of red algae over coral reefs was triggered in the Burdigalian by enhanced trophic resources associated with a global increase in productivity, as evidenced by a long-term shift toward higher carbon isotope values. Rhodalgal lithofacies expanded further in the middle Miocene when strengthened thermal gradients associated with the establishment of the East Antarctic Ice Sheet led to enhanced upwelling while climate change generated increased weathering rates, introducing land-derived nutrients into the oceans. Globally cooler temperatures following a climatic optimum in the early-middle Miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs. The global shift in nearshore shallow-water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow-water carbonate facies as indicators of past oceanographic conditions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Palaeoclimatic implications of the growth history and stable isotope (δ 18O and δ 13C) geochemistry of a Middle to Late Pleistocene stalagmite from central-western Italy

The age structure and stable isotope composition of a stalagmite (CC1) from an upland cave in central-western Italy were studied to investigate regional response to global climatic changes. Four growth phases are constrained by 28 thermal ionization and multi-collector inductively coupled plasma mass spectrometry Th–U ages and reveal intermittent deposition through the period between Marine Isotope Stage (MIS) 11 and 3 (∼380 and ∼43 kyr). Most of the growth took place between ∼380 and ∼280 kyr, a period punctuated briefly by a hiatus in deposition through the glacial maximum of MIS 10. Growth was terminated abruptly at 280 kyr just prior to the MIS 8 glacial maximum. With a present-day chamber temperature of 7.5 °C, the timing of hiatuses close to these glacial maxima point to freezing conditions at the time. No deposition was recorded through the entirety of MIS 7 and most of MIS 6, whilst two minor growth phases occurred at ∼141–125 and ∼43 kyr. Growth at 141 kyr indicates temperatures >0 °C at a time when MIS 6 ice volumes were close to their maximum. High stable carbon isotope (δ 13C) values (−2.8‰ to +3.1‰) throughout the stalagmite's growth reflect a persistently low input of biogenic CO 2, indicating that the steep, barren and alpine-like recharge area of today has been in existence for at least the last ∼380 kyr. During MIS 9, the lowest δ 13C values occur well after maximum interglacial conditions, suggesting a lag in the development of post-glacial soils in this high-altitude karst. The stable oxygen isotope (δ 18O) trends match the main structural features of the major climate proxy records (SPECMAP, Vostok and Devils Hole), suggesting that the δ 18O of CC1 has responded to global-scale climate changes, whilst remarkable similarity exists between CC1 δ 18O and regional sea-surface temperature reconstructions from North Atlantic core ODP980 and southwest Pacific marine core MD97-2120 through the most detailed part of the CC1 record, MIS 9–8. The results suggest that CC1 and other stalagmites from the cave have the potential to capture a long record of regional temperature trends, particularly in regards to the relative severity of Pleistocene glacial stages.

Chemostratigraphy of Paleoproterozoic carbonate successions of the Wyoming Craton: tectonic forcing of biogeochemical change?

The Archean Wyoming Craton is flanked on the south and east by belts of Paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop. However, carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy. The ∼10 km thick Paleoproterozoic Snowy Pass Supergroup in the Medicine Bow Mountains was deposited on the present-day southern flank of the Wyoming Craton; it contains three discrete levels of glacial diamictite correlative with those in the Huronian Supergroup, on the southern margin of the Superior Craton. The Nash Fork Formation of the upper Snowy Pass Supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the Paleoproterozoic glacial epoch. Carbonates at the base of the Nash Fork Formation record remarkable 13C-enrichment, up to +28‰ (V-PDB), whereas those from overlying members of the lower Nash Fork Formation have δ13C values between +6 and +8‰. Carbonates from the upper Nash Fork Formation above the carbonaceous shale have carbon isotope values ranging between 0 and +2.5‰. The transition from high carbon isotope values to those near 0‰ in the Nash Fork Formation is similar to that at the end of the ca. 2.2–2.1 Ga carbon isotope excursion in Fennoscandia. This chemostratigraphic trend and deposition of BIFs, Mn-rich lithologies, carbonaceous shales and phosphorites at the end of the global ca. 2.2–2.1 Ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the Kenorland supercontinent. Correlative carbonates from the Slaughterhouse Formation in the Sierra Madre, WY, and from the Whalen Group in the Rawhide Creek area in the Hartville Uplift, WY, have highly positive carbon isotope values. In contrast, carbonates from other exposures of the Whalen Group in the Hartville Uplift and all carbonate units in the Black Hills, SD, have carbon isotope values close to 0‰. Combined with existing geochronologic and stratigraphic constraints, these data suggest that the Slaughterhouse Formation and the succession exposed in the Rawhide Creek area of the Hartville Uplift are correlative with the lower and middle Nash Fork Formation and were deposited during the ca. 2.2–2.1 Ga carbon isotope excursion. The Estes and Roberts Draw formations in the Black Hills and carbonates from other exposures in the Hartville Uplift postdate the ca. 2.2–2.1 Ga positive carbon isotope excursion and are most likely correlative with the upper Nash Fork Formation. The passive margin, on which the carbonates with highly positive carbon isotope values were deposited, extended around the southern flank of the Wyoming Craton through the Sierra Madre, Medicine Bow Mountains and Hartville Uplift. The presence of carbonates with carbon isotope values close to 0‰ in the upper Nash Fork Formation and the Whalen Group indicates that the passive margin persisted on the southern flank of the Wyoming Craton after the carbon isotope excursion. Rifting in the Black Hills, likely related to the final breakup of the Kenorland, succeeded the carbon isotope excursion, since the Estes and Roberts Draw formations, deposited during rifting and ocean opening on the eastern flank of the Wyoming Craton, postdate the carbon isotope excursion.

Carbon and oxygen isotope profiles across Meso-Neoproterozoic limestones from central Brazil: Bambuı́ and Paranoá groups

We present carbon and oxygen isotopic data on carbonates along three profiles of the Neoproterozoic Bambuı́ group in central Brazil. This unit covers an area of more than 300 000 km 2 and comprises carbonate–silicliclastic sediments at the base that grade into siliciclastic sediments towards the top. The Bambuı́ group overlies by unconformity the Paranoá group, which consists mostly of siltstone, quartzite and minor limestone. The data presented here improve the stratigraphic correlation within the Bambuı́ basin and show that it evolved in an environment significantly different from that of the Paranoá basin. Our data show large fluctuations of δ 13C PDB in limestones from the Bambuı́ Group (from +0.8 to +13.5‰) in all the three studied areas. Some of these fluctuations represent stratigraphic markers that can be used as a chronostratigraphic tool within a basin scale. This observation is relevant considering the lack of fossil record and other stratigraphic markers in Neoproterozoic sequences. We also present the first isotopic profiles along the Paranoá–Bambuı́ transition, which shows that the δ 13C PDB values grade from +1.0‰ in the Paranoá group, to +2.6‰ in the lower portion of the Bambuı́ group, increasing up to +12‰ in the upper part of this unit. Based on our carbon isotope data, as well as other geological, mineralogical and Nd isotope studies, we argue that the sediments of the Paranoá group were deposited on an open platform that was fully connected to the ocean. On the other hand, the sediments of the Bambuı́ group were deposited in an epicontinental sea and during a tectonic inversion in a foreland basin at about 790–600 Ma. This unit displays an increased amount of clastic sediments upwards. We argue that the high carbon isotope values observed in limestones and marlstones from the Bambuı́ group are correlated to worldwide high carbon isotope values reported for the Neoproterozoic. However, we also point out that novel marine conditions induced by the tectonic inversion of the basin may also have contributed to increase the carbon isotopic composition of the Bambuı́ carbonates.

Mid-Depth Circulation of the Subpolar North Atlantic During the Last Glacial Maximum

Holocene and glacial carbon isotope data of benthic foraminifera from shallow to mid-depth cores from the northeastern subpolar Atlantic show that this region was strongly stratified, with carbon-13-enriched glacial North Atlantic intermediate water (GNAIW) overlying carbon-13-depleted Southern Ocean water (SOW). The data suggest that GNAIW originated north of the polar front and define GNAIW end-member carbon isotope values for studies of water-mass mixing in the open Atlantic. Identical carbon isotope values in the core of GNAIW and below the subtropical thermocline are consistent with rapid cycling of GNAIW through the northern Atlantic. The high carbon isotope values below the thermocline indicate that enhanced nutrient leakage in response to increased ventilation may have extended into intermediate waters. Geochemical box models show that the atmospheric carbon dioxide response to nutrient leakage that results from an increase in ventilation rate may be greater than the response to nutrient redistribution by conversion of North Atlantic deep water into GNAIW. These results underscore the potential rule of Atlantic Ocean circulation changes in influencing past atmospheric carbon dioxide values.