Late Cenozoic Biostratigraphic and Paleoecologic Studies of Arctic Ocean Deep-Sea Cores: ABSTRACT
1970; American Association of Petroleum Geologists; Volume: 54; Linguagem: Inglês
10.1306/5d25cd15-16c1-11d7-8645000102c1865d
ISSN1558-9153
Autores Tópico(s)Geology and Paleoclimatology Research
ResumoDeep-sea cores from the central Arctic basin, collected by Lamont Doherty Geological Observatory and the U.S. Geological Survey, yield significant faunal and lithologic evidence of alternating cold and milder periods during late Pliocene and Pleistocene times. Biostratigraphic and lithologic correlations between cores, some with established paleomagnetic stratigraphy, supplemented by radiometric dating and O1816/ determinations, were used to estimate ages and sedimentation rates as well as to reconstruct the climatic and oceanographic history of the Arctic. The time interval represented by the longest core (T3-67-12) is thought to exceed 3 m.y. Ice-rafted debris throughout the cores indicates that End_Page 2485------------------------------ high-latitude glaciation commenced more than 3 m.y. ago. Three climatic units are distinguished. The oldest, Unit III, consists of Mn- and Fe-rich Foraminifera-poor sediments. Calcareous Foraminifera, in part corroded, are thick-shelled forms. Arenaceous Foraminifera (Glomospira gordialis, Cyclammina pusilla, and Alveolophragmium subglobosum) dominate the benthic assemblages. Lower than present sedimentation rates could account for the selective solution of the less resistant calcareous tests and the impoverished character of the fauna. Unit II, deposited between 3 and 0.7 m.y. ago, is poor in Fe and Mn oxides, and Foraminifera. It contains one Foraminifera-rich layer; the predominant foraminifer in this layer is temperate-subarctic, euryhaline Globigerina quinqueloba (O1816/ determinations). This species occurs with sinistral Globigerina pachyderma throughout Unit II. Fragile calcareous benthonic Foraminifera (Stetsonia horvathi, Sphaerodina bulloides and Bolivina sp. A n. sp.) periodically abound, constituting up to 88% of the fauna. Concentration of thin-walled benthonic Foraminifera suggests that the near absence of planktonic forms was due to adverse environmental conditions rather than to dissolution of the less resistant tests. It is assumed that the Arctic was free of permanent pack-ice during the deposition of Units II and III. Unit I was deposited within the last 0.1 m.y., a time of conspicuous climatic fluctuations as indicated by the temporal variations in fauna and in mineral/fauna ratio. Beds rich in Foraminifera and in Mn and Fe oxides alternate with layers poor in both Foraminifera and Mn and Fe oxides. The former represent conditions similar to present (permanent pack-ice cover) and contain sinistral G. pachyderma almost exclusively. G. quinqueloba attains high frequencies at the beginning and end of some of these cold periods. In the Foraminifera-poor beds, deposited during pack-ice-free intervals, sinistral G. pachyderma is accompanied by G. quinqueloba; other low-latitude Foraminifera are present in a few places. Pteropods (Limacina helicina) are preserved principally in core tops. End_of_Article - Last_Page 2486------------
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