925 research outputs found
Late Albian paleoceanography of the western subtropical North Atlantic
No full textA late Albian–early Cenomanian record (~103.3 to 99.0 Ma), including organic-rich deposits and a ?13C increase associated with oceanic anoxic event 1d (OAE 1d), is described from Ocean Drilling Program sites 1050 and 1052 in the subtropical Atlantic. Foraminifera are well preserved at these sites. Paleotemperatures estimated from benthic ?18O values average ~14°C for middle bathyal Site 1050 and ~17°C for upper bathyal Site 1052, whereas surface temperatures are estimated to have ranged from 26°C to 31°C at both sites. Among planktonic foraminifera, there is a steady balance of speciation and extinction with no discrete time of major faunal turnover. OAE 1d is recognized on the basis of a 1.2‰ ?13C increase (~100.0–99.6 Ma), which is similar in age and magnitude to ?13C excursions documented in the North Atlantic and western Tethys. Organic-rich “black shales” are present throughout the studied interval at both sites. However, deposition of individual black shale beds was not synchronous between sites, and most of the black shale was deposited before the OAE 1d ?13C increase. A similar pattern is observed at the other sites where OAE 1d has been recognized indicating that the site(s) of excess organic carbon burial that could have caused the ?13C increase has (have) yet to be found. Our findings add weight to the view that OAEs should be chemostratigraphically (?13C) rather than lithostratigraphically defined
Santonian–Campanian (Late Cretaceous) planktonic foraminiferal turnover, depth ecology and paleoceanographic implications
No full textThe Santonian–Campanian time interval is a transitional phase from the extreme greenhouse warmth during the Turonian to more temperate conditions and to a thermohaline circulation that was more like that of the modern day. These environmental changes led to a re-organization of marine ecosystems in deep-sea and superficial settings and to the formation of well-developed faunal bioprovinces that were analogous to the present. This environmental instability likely led to a major faunal turnover among planktonic foraminifera including extinction of the genera Marginotruncana and Dicarinella and diversification within the genera Globotruncana, Globotruncanita and Contusotruncana (Premoli Silva and Sliter, 1999).
Relatively few studies on the composition of Santonian-Campanian planktonic foraminiferal assemblages are available in the literature, and those have never been coupled with reliable species-specific stable isotope (δ13C and δ18O) analyses, mainly because: (1) DSDP (Deep See Drilling Project), ODP (Ocean Drilling Program) and IODP (Integrated Ocean Drilling Program) cruises recovered relatively few and discontinuous stratigraphic sequences belonging to this interval, and (2) planktonic foraminifera from deep-sea sites are often diagenetically altered and do not yield reliable isotopic records of paleoenvironmental condtions.
The unusual recovery of pristinely preserved planktonic foraminifera from Santonian–Campanian sequences in southeastern Tanzania (Tanzania Drilling Project, TDP Sites 28 and 32, see Jiménez Berrocoso et al., 2012), allowed examination of faunal changes and well resolved, species-specific stable isotope (δ13C and δ18O) data. These data are ideal for inferring paleoecological preferences of different species and for tracing major paleoceanographic changes. Results obtained from TDP material have been compared with δ13C and δ18O values inferred from specimens recovered at two low-to-mid latitude sites (1) Shatsky Rise (ODP Leg 198, Hole 1210B; northwestern Pacific Ocean) and (2) Exmouth Plateau (ODP Leg 122, Hole 762C; eastern Indian Ocean) to detect possible shifts in species habitat preferences in different paleoceanographic contexts.
At all the examined localities, we recognize consistent changes in the composition of planktonic foraminiferal assemblages that enable subdivision of the stratigraphic records into faunal intervals, each one characterized by a distinctive taxonomic composition. With the exception of the extinction of the typical Santonian fauna (marginotruncanids, dicarinellids), most of the observed compositional changes did not occur synchronously among sites, suggesting that changes were likely driven by local rather than global forces.
The stable isotopic results suggest consistent depth stratification and other paleoecological differences among species. In agreement with other recent studies, our results show that the depth-distribution models based on shell morphology and analogies with modern taxa are not applicable for Cretaceous planktonic foraminifera. Combined geochemical and paleontological observations suggest that during the late Campanian the water column in Tanzania was well stratified with a deep thermocline and a thick mixed layer whereas less stratified and/or mesotrophic conditions prevailed at least in some intervals at Shatsky Rise and Exmouth Plateau.
References
Jiménez Berrocoso A., Huber B.T., MacLeod K.G., Petrizzo M.R., Jacqueline A. Lees J.A., Ines Wendler I., Helen Coxall H., Mweneinda A. K., Falzoni F., Birch H., Singano J.M., Haynes S., Cotton L., Wendler J., Bown P.R., Robinson S.A., Gould J. (2012). Lithostratigraphy, biostratigraphy and chemostratigraphy of Upper Cretaceous and Paleogene sediments from southern Tanzania: Tanzania Drilling Project Sites 27 to 35. Journal of African Earth Sciences, v. 70, p. 36-57
Premoli Silva and Sliter, 1999. Cretaceous paleoceanography: evidence from planktonic foraminiferal evolution. In E. Barrera, and C. C. Johnson, eds. The Evolution of the Cretaceous Ocean-Climate System. Special Paper of the Geological Society of America 332:301–328
A new Late Cretaceous record of oxygen and carbon trends from the southern mid latitudes (ODP Leg 122) and insights on planktonic foraminiferal evolution
No full textLate Cretaceous cooling trend and planktonic foraminiferal turnover: a new species-specific delta18O record from the southern mid latitudes
No full textPlanktonic foraminiferal endemism at southern high latitudes following the terminal Cretaceous extinction
No full textAustral planktonic foraminiferal assemblages from immediately above the Cretaceous/Paleogene (K/Pg) boundary at Ocean Drilling Program Hole 690C (Maud Rise, Weddell Sea) and International Ocean Drilling Program Hole U1514C (southeast Indian Ocean) show a much different record of post-extinction recovery than anywhere outside the circum-Antarctic region. Species of Woodringina and Parvularugoglobigerina, genera with well-documented evolutionary successions within the early Danian P0 and Pα biozones at tropical/subtropical and mid-latitude localities, are absent from southern high latitude sequences. This study proposes new criteria for biostratigraphic correlation of the lowermost Danian Antarctic Paleocene AP0 and AP1 Zones using stratophenetic observations from Scanning Electron Microscope images of lower Danian planktonic foraminifera at deep-sea sites in the southern South Atlantic and southern Indian Ocean. The small but distinctive species Turborotalita nikolasi (Koutsoukos) is a highly reliable index species for the lowermost Danian as it consistently occurs immediately above the K/Pg boundary at multiple southern high latitude sites, which is consistent with its distribution at middle and low latitudes. Also useful for cross-latitude correlation is Parasubbotina neanika n. sp., which first appears within the lowermost Danian worldwide. The geographic distribution of the New Zealand species Antarcticella pauciloculata (Jenkins) and Zeauvigerina waiparaensis (Jenkins), as well as Eoglobigerina maudrisensis n. sp. from just above the K/Pg in the southern South Atlantic and southern Indian Ocean, helps define the extent of the Austral Biogeographic Province and provides evidence for marine communication via marine seaways across Antarctica. While An. pauciloculata was previously considered a benthic species, new stable isotope evidence demonstrates that it lived a planktonic mode of life. It is possible this species evolved from a benthic ancestor and that the benthic to planktonic transition occurred through an intermediate tychopelagic lifestyle at a time when calcareous plankton were less abundant as a result of the terminal Cretaceous mass extinction
Insights into the meridional ornamentation of the planktonic foraminiferal genus Rugoglobigerina (Late Cretaceous) and implications for taxonomy
No full textWall texture and ornamentation in Cretaceous planktonic foraminifera, as with modern and Cenozoic taxa, are generally considered to be genetically controlled and thus taxonomically significant. For instance, the iterative development of meridional ornamentation is a diagnostic criterion used to discriminate between the Santonian-early Campanian genus Costellagerina, and the Campanian-Maastrichtian genus Rugoglobigerina. An alternative ecophenotypic explanation for differences based on observed poleward decreases in meridional ornamentation has not been widely accepted largely due to absence of evidence.Our study of Rugoglobigerina specimens recovered at three mid-low latitude localities (Exmouth Plateau, eastern Indian Ocean; Shatsky Rise, northwestern Pacific Ocean; Eratosthenes Seamount, eastern Mediterranean) confirms that meridional ornamentation is a primary character of their tests, but development of this feature is highly variable throughout the geographic and stratigraphic distribution of the genus. Within assemblages of Rugoglobigerina, there is a continuous morphological range from specimens with well-developed costellae arranged in a meridional pattern to specimens with relatively short ridges that are randomly oriented to meridionally aligned. Stable isotope (δ13C and δ18O) analyses indicate that specimens showing a more strongly developed meridional ornamentation consistently yield higher δ13C values than co-occurring less ornamented morphotypes at each examined locality, whereas patterns in the δ18O values are site-dependent. Interpretation of these patterns is not simple and might be related to different controlling factors acting together or separately. Potential explanations for the differential development of the ornamentation include: (1) adaptation to different ecological niches within a population, (2) species-level genetic differences, (3) variation in metabolic rate or activity within individuals, and (4) changes in the seawater carbonate ion saturation through space and time, including seasonality. In addition, we highlight the difficulty of discriminating between Rugoglobigerina and Costellagerina when they co-occur in lower Campanian deposits and among Rugoglobigerina, Costellagerina and Archaeoglobigerina at high latitude localities where species placed in all three genera show very similar shell morphology and ornamentation. Finally, our study challenges the general assumption that some external features of the wall are sufficiently reliable for taxonomic discrimination of Cretaceous planktonic foraminifera. This latter conclusion suggests that environmental conditions such as water temperature, water column stratification, nutrient concentration and carbonate ion saturation may have played a key role in triggering the external expression of genetically controlled wall ornamentation in the planktonic foraminifera
Santonian-Campanian planktonic foraminifera from Tanzania, Shatsky Rise and Exmouth Plateau : species depth ecology and paleoceanographic inferences
No full textThe Santonian-Campanian interval is of particular interest as it encompasses a cooling trend after the Late Cretaceous greenhouse maximum warmth of the Turonian as well as a possibly related major faunal turnover among planktonic foraminifera. The recovery of pristinely preserved planktonic foraminifera from Santonian-Campanian sequences in southeastern Tanzania allows examination of faunal changes and documentation of species-specific stable isotope (δ13C and δ18O) signatures. These isotopic data are ideal for inferring species paleoecological preferences and for tracing major paleoceanographic changes. This study reports the first δ18O and δ13C data generated on "glassy" specimens of Marginotruncana coronata, M. undulata, M. marginata, and M. pseudolinneiana and Sigalia carpatica. Additional results from Shatsky Rise (Ocean Drilling Program Leg 198, Hole 1210B) and Exmouth Plateau (ODP Leg 122, Hole 762C) provide geographic control on species habitat preferences and paleoceanographic context. Isotopic analyses suggest that double-keeled species, including Globotruncana bulloides, Contusotruncana fornicata, C. plummerae and probably marginotruncanids, inhabited the surface mixed layer, whereas the biserial Gublerina rajagopalani was a permanent thermocline dweller. Thus, our study confirms recent suggestions that the depth-distribution models based on shell morphology and analogies with modern taxa are not applicable. At all the examined localities, changes in planktonic foraminiferal assemblages are used to define several ecological intervals, each one characterized by a distinctive taxonomic composition and/or increasing/decreasing species diversity. Combined geochemical and paleontological observations suggest that, by the middle-late Campanian, a stratified upper water column developed in Tanzania while less stratified and/or mesotrophic conditions prevailed at Shatsky Rise and Exmouth Plateau
Coniacian–Santonian planktonic foraminifera and stable isotope records from Tanzania and identification of the base of the Santonian Stage
No full textProgress in late Cretaceous planktonic foraminiferal stable isotope paleoecology and implications for paleoceanographic reconstructions
No full textEcologic control on the development of meridional ornamentation in the planktonic foraminiferal genus Rugoglobigerina (Late Cretaceous) and implications for taxonomy
No full textThe wall ornamentation in Cretaceous planktonic foraminifera has been considered genetically controlled and taxonomically significant in analogy with Cenozoic taxa. For instance, the development of the meridional ornamentation is a diagnostic criterion used to discriminate the Late Cretaceous genera Costellagerina and Rugoglobigerina. Although some authors noted that the development of meridional ornamentation decreases poleward and could be ecologically controlled, this hypothesis was rejected for absence of evidence.
Our study based on Rugoglobigerina specimens recovered at three mid-low latitude localities (Exmouth Plateau, Indian Ocean; Shatsky Rise, Pacific Ocean; Eratosthenes Seamount, Mediterranean Sea) confirms that the development of the meridional ornamentation is variable throughout the geographic and stratigraphic distribution of the genus. Stable isotope (δ13C and δ18O) analyses indicate that specimens showing a more developed meridional ornamentation always yield higher δ13C values than co-occurring less ornamented morphotypes and we interpret these data to indicate an ecologic/metabolic control regulating the development of the meridional ornamentation. Moreover, we highlight the difficulty in discriminating between Rugoglobigerina, Costellagerina and Archaeoglobigerina at mid-high latitudes, where species show identical shell morphology and ornamentation. Our study challenges the assumption that the external features of the wall represent reliable criteria for the taxonomic discrimination of Cretaceous planktonic foraminifera
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