Deep-sea Sections Research Articles

Stepwise mass extinctions and impact events: Late Eocene to early Oligocene

Species ranges and relative abundances of dominant planktonic foraminifers of eight late Eocene to early Oligocene deep-sea sections are discussed to determine the nature and magnitude of extinctions and to investigate a possible cause-effect relationship between impact events and mass extinctions. Late Eocene extinctions are neither catastrophic nor mass extinctions, but occur stepwise over a period of about 1–2 million years. Four stepwise extinctions are identified at the middle/late Eocene boundary, the upper Globigerapsis semiinvoluta zone, the G. semiinvoluta/Globorotalia cerroazulensis zone boundary and at the Eocene/Oligocene boundary. Each stepwise extinction event represents a time of accelerated faunal turnover characterized by generally less than 15% species extinct and in itself is not a significant extinction event. Relative species abundance changes at each stepwise extinction event, however, indicate a turnover involving > 60% of the population implying major environmental changes. There microtektite horizons are present in late Eocene sediments; one in the upper G. semiinvoluta zone (38.2 Ma) and two closely spaced layers only a few thousand years apart in the lower part of the Globorotalia cerroazulensis zone (37.2 Ma). Each of the three impact events appears to have had some effect on microplankton communities. However, the overriding factor that led to the stepwise mass extinctions may have been the result of multiple causes as there is no evidence of impacts associated with the step preceding, or the step following the deposition of the presently known microtektite horizons.

Correlation and geochronology of middle Eocene strata from the Western United States

In this study I integrate marine and continental biostratigraphy, magnetic polarity stratigraphy, and radioisotopic chronology in a synthetic correlation of middle Eocene strata from the western United States. More than 2000 m of section were sampled from volcaniclastic deposits, Aycross and Tepee Trail Formations (northwestern Wyoming); lacustrine and fluviatile deposits, Washakie Formation (southwestern Wyoming); and intertonguing marine and continental strata, La Jolla and Poway Groups (San Diego area, California). Detailed demagnetization studies on numerous pilot samples from all three field areas revealed moderately complex magnetizations. Most sample NRM's are dominated by a strong normal polarity magnetic component; alternating field demagnetization does not consistently isolate the primary magnetization. High blocking temperature hematite is frequently a significant carrier of remanence. Therefore, most samples were subjected to detailed, stepwise alternating field and thermal demagnetization to 600–650°C. The East Fork Basin area (northwestern Wyoming) magnetic polarity sequence consists of five major polarity intervals, A- to E-; the thick Washakie Formation sequence contains four, A+ to D-; and the San Diego area sequence has four polarity intervals, A- to D+. A new biochronologic interval, the Shoshonian Land Mammal Subage (Earliest Uintan), is defined and characterized. In all three field areas Shoshonian (Earliest Uintan) faunas and the Bridgerian/Uintan boundary occur within a single long reversed polarity interval. Correlation of marine biostratigraphy between the San Diego area section and deep sea sections allows precise identification of San Diego polarity interval B+ as Chron C21N. Therefore, the Bridgerian/Uintan boundary and earliest Uintan faunas occur within the reversed interval of Chron C20R. High-temperature, KAr dates bracketing this horizon in northwestern Wyoming provide an age estimate of approximately 49.5 Ma for the top of Chron C21N and 49 Ma for the Bridgerian/Uintan boundary. Berggren et al. (1985) use the age estimate of 49.5 Ma for the top of anomaly 21 (younger boundary of Chron C21N) as one calibration point for the generation of a Paleogene geochronology. The methodology and conclusions of this geochronology are compared to those of other recent geochronologies. Data from independent studies integrating high temperature radioisotopic dates, biochronology, and magnetochronology are used to test the validity of the Berggren et al. (1985) geochronology.

Pacific Miocene carbon isotope stratigraphy using benthic foraminifera

Seven Miocene Pacific Ocean Deep Sea Drilling Project sites from four different water masses (planktonic foraminiferal biogeographic regions) have been correlated using 18 prominent carbon isotopic events defined in the benthic foraminiferal δ 13C records in DSDP Site 289. The correlations are based on the assumption that there are global or at least Pacific-wide controls on the δ 13C of deep-water HCO 3 −. Each of the individual δ 13C records is correlated to Site 289 based on the shape of the curves in a manner analogous to that used to correlate sea-floor magnetic anomaly patterns. The results of this correlation experiment confirm that planktonic foraminiferal biostratigraphy and carbon isotopic stratigraphy are consistent within the tropical surface water mass and precise to ±100,000 years. Correlations between surface water masses suggest that the precision of foraminiferal biostratigraphy is on the average less than ±200,000 years due to the lack of cosmopolitan marker species and diachronism of species occurrences. Carbon isotope stratigraphy used in conjunction with biostratigraphy has the potential to provide an easily utilized, globally applicable, correlation tool (with an interregional precision of ±100,000 years or better) as more continuous and undisturbed deep-sea sections become available as a result of the Hydraulic Piston Coring Program.

Quantitative nannofossil correlation to open ocean deep-sea sections from Plio-Pleistocene boundary at Vrica, Italy

Although numerous studies have been performed on material from the Vrica section, southern Italy1–3 with a view to establishing its suitability as a type section for the Plio-Pleistocene boundary, these studies have failed either to establish the age of the boundary, or to achieve accurate correlation to other regions. We report here quantitative studies of selected nannofossil species in this section which unambiguously correlate it with open ocean piston cores in which an accurate chronology has been established. The age of the Plio-Pleistocene boundary as proposed by Colalongo et al.4 is estimated to be ∼1.6 Myr.

Diagenesis of Carbonates in Deep-Sea Sediments--Evidence From SR/CA Ratios and Interstitial Dissolved SR2+ Data

ABSTRACT Laboratory determinations of the distribution coefficient of strontium in calcite (kSr) have confirmed the earlier results of Katz et al. (1972). In addition, we observed that at higher concentrations of strontium, values of kSr were somewhat lowered. Chemical analyses of several deep-sea carbonate sediment sections and their associated porewaters (DSDP Sites 288, 289, 315, 317, and 357) as well as previously published data of other workers (DSDP Sites 116 and 305) have been used to demonstrate that these kSr values are appropriate for use in diagenetic studies. We have successfully modeled the distribution of strontium in the pore waters and sediments. As a result, we conclude that recrystallization of these carbonates (and many other limestones as well) is essentially isochemical, the cement being derived from within the formation. Advective fluid flow through the rock is unnecessary to explain its lithification. Recrystallization of the bulk of the calcite in deep-sea sections is largely complete within the upper few undred meters, but cementation is generally a later process. These results have important implications for the study of oxygen isotopic compositions of foraminifers and coccoliths in many sediments older than about 20 m.y. B.P. From correlations between changes in Sr/Ca and Mg/Ca ratios of recrystallized carbonates of DSDP Site 305 a distribution coefficient of magnesium in calcite sediments of 8.1 10-4 (5° C) has been estimated. This value is many times smaller than previously published values.

New Zealand and Australian Cenozoic Sedimentary Cycles and Global Sea-Level Changes

A global sea-level history determined by Vail et al consists of 23 sea-level cycles between the base of the Cenozoic and the Pliocene-Pleistocene boundary (65 to 1.8 Ma). We have examined the relation between this global sea-level history and the New Zealand and Australian continental margin shallow-marine sedimentary record. Sedimentary cycles in the Australian Cenozoic marginal-marine sequences are bounded by unconformities of various durations. The tectonic stability and aridity of the western and southwestern margin of Australia during the Cenozoic produced a sedimentary record dominated by hiatuses. This contrasts with the relatively complete sequences of the tectonically more active southeastern marginal basins. The four major sedimentary cycles in the Australian Cenozoic (Paleocene to early Eocene; middle to late Eocene; latest Oligocene to late middle Miocene; and latest Miocene to Quaternary) correlate with the supercycles Ta, Tb, Tc, Td, and Te of Vail et al. In New Zealand, most of the Cenozoic stages represent classic sedimentary cycles bounded by unconformities or correlative conformities formed as a result of large, rapid eustatic sea-level changes. The marine Tertiary sequence in New Zealand consists of 23 stages. Of the 18 stage boundaries between the end of the Paleocene (53 Ma) and the end of the Miocene (5 Ma), 16 appear to correlate with the boundaries of eustatic sea-level cycles. Eustatic sea-level lowstands are well recorded (as unconformities) in New Zealand as a result of its unique tectonic setting during the Cenozoic. For most of the early Cenozoic until the middle Oligocene (~ 30 Ma) New Zealand was generally subsiding. After the middle Oligocene this region began to be uplifted as the Pacific-Australian plate boundary migrated onto New Zealand, climaxing in the latest Cenozoic (late Pliocene-Quaternary), thus exposing a nearly complete sequence of marine Cenozoic strata well suited for the study of sedimentary cycles. Unconformities, which form as a result of eustatic sea-level changes, represent a very useful correlation tool, especially on continental margins with a sufficiently high terrigenous sediment supply, and can be used to supplement paleontologic correlations. Their ultimate usefulness for correlation depends on the rapidity of the sea-level changes or the speed at which sedimentary facies change in response to sea-level changes. If sea level changes rapidly (10 m/1,000 years), stratigraphic resolution will be high (±105 years) but resolution decreases as the speed of sea-level change decreases. Unconformities may well prove to be a vital tool linking the classic land-based sections around the world with deep-sea sections.

Early to Middle Miocene Planktonic Foraminiferal Datum Levels of the Equatorial and Subtropical Pacific

Early to Middle Miocene Planktonic Foraminiferal Datum Levels of the Equatorial and Subtropical Pacific

Global Increase in Quaternary Explosive Volcanism

The worldwide distribution of volcanic ash has been determinmined from 320 deep-sea sections drilled during the Deep Sea Drilling Project. The ash distribution in the deep-sea sections, which span the last 20 million years, indicates that there has been a much higher rate of explosive volcanism from both island arc and hot spot volcanoes during the last 2 million years. This episode, and perhaps another in the Middle Miocene cprrelates with previously reported widespread synchronism in increased volcanicity in certain oceanic islands. Increased Quaternary volcanism coincides approximately with that episode of the Cenozoic marked by major and rapidly fluctuating climatic change.

Sedimentation and Sediment-Mass Balance in Eastern Mediterranean Sea: ABSTRACT

Detailed studies of cores taken in the eastern Mediterranean Sea by the Woods Hole Oceanographic Institution and other institutions have enabled lithologic and time-stratigraphic correlations to be made between these cores, thereby contributing to an understanding of the sedimentation history of this basin during the Quaternary. The deep-sea stratigraphic section is a complex sequence of sapropels, turbidites, oozes, volcanic ashes, detrital and biogenic sands, and detrital silt beds. Integrated sedimentation rates since the Pliocene have averaged 10-20 cm/103 years and ranged from less than 1 to more than 100 cm/103 years. Rates during the Quaternary are slightly less, although variations do occur, primarily as a result of glacial/nonglacial climati controls. Patterns of sedimentation also have been affected by these climatic changes, with only relatively minor variations reflecting tectonism and changes in provenance. Volumetrically, the Nile River system is and has been the largest contributor of detrital material. Additional detritus is derived from Anatolia and from the Aegean Sea, the latter contributing predominantly finer material. The other borderlands do not supply large amounts; eolian material from north Africa is noticeable, however. Variations of this detrital input and in carbonate deposition have occurred primarily in response to climatic changes during the Quaternary. End_of_Article - Last_Page 793------------

The Pleistocene Epoch and the Evolution of Man [and Comments and Reply

Previous articleNext article No AccessThe Pleistocene Epoch and the Evolution of Man [and Comments and Reply]Cesare Emiliani, H. B. S. Cooke, C. S. Coon, Malcolm F. Farmer, John E. Frisch, Alexander Gallus, M. Gigout, R. Dale Givens, Roger T. Grange Jr., James J. Hester, Ralph L. Holloway Jr., W. W. Howells, Kenneth A. R. Kennedy, J. Kukla, G. Kurth, Gabriel W. Lasker, John M. Longyear III, M. A. MacConaill, Charles A. Reed, Karl H. Schwerin, Gunter Smolla, and L. Van ValenCesare Emiliani Search for more articles by this author , H. B. S. Cooke Search for more articles by this author , C. S. Coon Search for more articles by this author , Malcolm F. Farmer Search for more articles by this author , John E. Frisch Search for more articles by this author , Alexander Gallus Search for more articles by this author , M. Gigout Search for more articles by this author , R. Dale Givens Search for more articles by this author , Roger T. Grange Jr. Search for more articles by this author , James J. Hester Search for more articles by this author , Ralph L. Holloway Jr. Search for more articles by this author , W. W. Howells Search for more articles by this author , Kenneth A. R. Kennedy Search for more articles by this author , J. Kukla Search for more articles by this author , G. Kurth Search for more articles by this author , Gabriel W. Lasker Search for more articles by this author , John M. Longyear III Search for more articles by this author , M. A. MacConaill Search for more articles by this author , Charles A. Reed Search for more articles by this author , Karl H. Schwerin Search for more articles by this author , Gunter Smolla Search for more articles by this author , and L. Van Valen Search for more articles by this author Corrections to this articleErrataPDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Current Anthropology Volume 9, Number 1Feb., 1968 Sponsored by the Wenner-Gren Foundation for Anthropological Research Article DOIhttps://doi.org/10.1086/200876 Views: 8Total views on this site Citations: 8Citations are reported from Crossref Copyright 1968 The Wenner-Gren Foundation for Anthropological ResearchPDF download Crossref reports the following articles citing this article:Lenka Lisá, Petr Neruda, Zdeňka Nerudová, Ladislav Nejman Podhradem Interstadial; A critical review of the middle and late MIS 3 (Denekamp, Hengelo) in Moravia, Czech Republic, Quaternary Science Reviews 182 (Feb 2018): 191–201.https://doi.org/10.1016/j.quascirev.2017.12.024V. A. Bol’shakov On the mechanism of the Middle Pleistocene Transition, Stratigraphy and Geological Correlation 23, no.55 (Sep 2015): 536–550.https://doi.org/10.1134/S0869593815050019Maureen E. Raymo, Kerim H. Nisancioglu The 41 kyr world: Milankovitch's other unsolved mystery, Paleoceanography 18, no.11 (Mar 2003): n/a–n/a.https://doi.org/10.1029/2002PA000791J. Backman, N. J. Shackleton, Lisa Tauxe Quantitative nannofossil correlation to open ocean deep-sea sections from Plio-Pleistocene boundary at Vrica, Italy, Nature 304, no.59225922 (Jul 1983): 156–158.https://doi.org/10.1038/304156a0Hervé Le Treut, Michael Ghil Orbital forcing, climatic interactions, and glaciation cycles, Journal of Geophysical Research: Oceans 88, no.C9C9 (Sep 2012): 5167–5190.https://doi.org/10.1029/JC088iC09p05167J.J. Wymer Clactonian and Acheulian Industries in Britain—their chronology and significance, Proceedings of the Geologists' Association 85, no.33 (Jan 1974): 391–421.https://doi.org/10.1016/S0016-7878(74)80006-4V.P. Yakimov Hominoids, hominids and the problem of the lower boundary of the Anthropogene, Journal of Human Evolution 2, no.66 (Nov 1973): 567–577.https://doi.org/10.1016/0047-2484(73)90135-8 Desmond Collins Culture Traditions and Environment of Early Man, Current Anthropology 10, no.4, Part 14, Part 1 (Oct 2015): 267–316.https://doi.org/10.1086/201019Related articlesErrata19 Oct 2015Current Anthropology