ABSTRACT Hydrothermal experiments with primary detrital components of feldspathic sands (orthoclase, albite, quartz, and calcite) were conducted to simulate possible diagenetic changes in geosynclinal sedimentary accumulations and the geothermal reservoir of the Imperial Valley area, California. Phyllosilicate and zeolite mineralization was produced at 200°C and 1 Kb Ph 2 o and at 300°C and 1 and 3 Kb Ph 2 o. Scanning electron microscope examination of the detrital grains shows the development of authigenic minerals and solution features. Phyllosilicate development occurred as dense surface coatings on orthoclase crystals in concentrated brines and as scattered grain clusters in dilute brines. Cation concentration is considered to be a controlling factor in phyllosilicate formation and growth. During formation the phyllosilicate crystals appear to utilize the surficial feldspar lattice structure as a preferred growth site. Electron diffraction studies indicate the crystals are a 1 Md mica similar to illite. Initial phyllosilicate formation occurs principally on orthoclase in systems containing this mineral, but is disseminated on other mineral surfaces in systems without orthoclase. This experimental development of authigenetic illite via the destruction of potassium feldspar may offer a potential mechanism to help explain the resulting mineralogy of diagenetic processes occurring in natural sediments such as in feldspathic sands and argillaceous sediments.
A stable-isotope stratigraphy was established for planktonic and benthic foraminifers from upper Miocene-lower Pliocene pelagic sediments from the Mid-Atlantic Ridge.A correlation of stable-isotope and biostratigraphic data with magnetostratigraphic age revealed the following: (1) the late Miocene carbon-isotope shift in the South Atlantic bottom waters was minute compared with the shift reported for other deep-sea locations (Haq et al., 1980), (2) a significant cooling or continental ice-volume increase occurred between 5.7 and 5.2 Ma, and (3) a period of warming or ice-volume decrease followed, with the rate of warming increasing beginning at 4.5 Ma and reaching a climax at 4.3 Ma.The timing of these paleoceanographic events is correlated with the onset and termination of the Messinian salinity crisis in the Mediterranean Sea.
Research Article| July 01, 1984 Numerical ages of Cenozoic biostratigraphic datum levels: Results of South Atlantic Leg 73 drilling KENNETH J. HSÜ; KENNETH J. HSÜ 1Geological Institute, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar JOHN La BRECQUE; JOHN La BRECQUE 2Lamont-Doherty Geological Observatory, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar STEPHEN F. PERCIVAL; STEPHEN F. PERCIVAL 3Mobil Exploration and Production Services, Inc., Dallas, Texas 75221 Search for other works by this author on: GSW Google Scholar RAMIL C. WRIGHT; RAMIL C. WRIGHT 4Exxon Production Research Company, Houston, Texas 77001 Search for other works by this author on: GSW Google Scholar ANDREW M. GOMBOS; ANDREW M. GOMBOS 4Exxon Production Research Company, Houston, Texas 77001 Search for other works by this author on: GSW Google Scholar KENNETH PISCIOTTO; KENNETH PISCIOTTO 5Scripps Institution of Oceanography, La Jolla, California 92093 Search for other works by this author on: GSW Google Scholar PETER TUCKER; PETER TUCKER 6University of Edinburgh, Edinburgh, Scotland Search for other works by this author on: GSW Google Scholar NIKOLAI PETERSON; NIKOLAI PETERSON 7Munich University, Munich, Germany Search for other works by this author on: GSW Google Scholar JUDITH A. McKENZIE; JUDITH A. McKENZIE 8Geological Institute, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar HELMUT WEISSERT; HELMUT WEISSERT 8Geological Institute, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar ANNE MARIE KARPOFF; ANNE MARIE KARPOFF 9Geology Institute, Strasbourg, France Search for other works by this author on: GSW Google Scholar MAX F. CARMAN, Jr.; MAX F. CARMAN, Jr. 10University of Houston, Houston, Texas 77004 Search for other works by this author on: GSW Google Scholar EDWARD SCHREIBER EDWARD SCHREIBER 11City University of New York, Flushing, New York 10021 Search for other works by this author on: GSW Google Scholar Author and Article Information KENNETH J. HSÜ 1Geological Institute, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland JOHN La BRECQUE 2Lamont-Doherty Geological Observatory, Palisades, New York 10964 STEPHEN F. PERCIVAL 3Mobil Exploration and Production Services, Inc., Dallas, Texas 75221 RAMIL C. WRIGHT 4Exxon Production Research Company, Houston, Texas 77001 ANDREW M. GOMBOS 4Exxon Production Research Company, Houston, Texas 77001 KENNETH PISCIOTTO 5Scripps Institution of Oceanography, La Jolla, California 92093 PETER TUCKER 6University of Edinburgh, Edinburgh, Scotland NIKOLAI PETERSON 7Munich University, Munich, Germany JUDITH A. McKENZIE 8Geological Institute, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland HELMUT WEISSERT 8Geological Institute, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland ANNE MARIE KARPOFF 9Geology Institute, Strasbourg, France MAX F. CARMAN, Jr. 10University of Houston, Houston, Texas 77004 EDWARD SCHREIBER 11City University of New York, Flushing, New York 10021 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1984) 95 (7): 863–876. https://doi.org/10.1130/0016-7606(1984)95<863:NAOCBD>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation KENNETH J. HSÜ, JOHN La BRECQUE, STEPHEN F. PERCIVAL, RAMIL C. WRIGHT, ANDREW M. GOMBOS, KENNETH PISCIOTTO, PETER TUCKER, NIKOLAI PETERSON, JUDITH A. McKENZIE, HELMUT WEISSERT, ANNE MARIE KARPOFF, MAX F. CARMAN, EDWARD SCHREIBER; Numerical ages of Cenozoic biostratigraphic datum levels: Results of South Atlantic Leg 73 drilling. GSA Bulletin 1984;; 95 (7): 863–876. doi: https://doi.org/10.1130/0016-7606(1984)95<863:NAOCBD>2.0.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract Six sites were drilled in the South Atlantic during the Leg 73 cruise of the Deep Sea Drilling Project (DSDP). Hydraulic piston coring at five of the six sites obtained a nearly complete sequence of undisturbed Cenozoic samples. The magnetostratigraphy at those sites was investigated by close sampling representing time intervals of about 104 yr.Most of the Cenozoic nannofossil and many of the foraminiferal zonal boundaries were accurately determined and magnetostratigraphically calibrated at those five Leg 73 boreholes. Their numerical ages have been computed assuming a linear spreading rate and a radiometric age of 66.5 m.y. for the Cretaceous-Tertiary boundary. Alternative magnetostratigraphic ages were obtained with the adoption of a 63.5-m.y. age for the Cenozoic. Our data confirm previous determinations of the Pleistocene-Pliocene boundary at 1.8 (1.7) m.y. B.P. and of the Pliocene-Miocene boundary at 5.1 (5.0) m.y. B.P. The Miocene-Oligocene boundary is placed within chron C-6 C, with a magnetostratigraphic age of 23.8–24.0 (22.7–22.9) m.y. The Oligocene-Eocene age is also very precisely located within chron C-13 R, with a magnetostratigraphic age of 37.1–37.2 (35.5–35.6) m.y. The Eocene-Paleocene boundary should be located within an uncored interval of chron C-24, with a magnetostratigraphic age of 59.0 (55.4) ± 0.2 m.y.A general accord of the magnetostratigraphic ages from Leg 73 sites and the radiometric ages published in the literature for the various zonal boundaries validates the assumption of a linear sea-floor–spreading rate during the Cenozoic. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The strontium-isotope dating method, based on the strontium-isotope seawater curve, was used to date stratigraphic events recognized in carbonate sediments drilled during Leg 133 on the Queensland and Marion plateaus.The strontium isotope ages of these events are used to correlate paleoceanographic changes, delineated from oxygen isotope signals, and paleoenvironmental or facies changes recorded in the lithostratigraphy.Results indicate that a strong connection exists between prevailing paleoenvironmental conditions and the developmental style of a carbonate platform.Also, the strontium-isotope ages of discrete dolomite intervals within the sequences were determined, indicating that multiple dolomitization events took place and that a hydrodynamically driven process may be currently active within the modern carbonate platform.
Several suites of undisturbed cores obtained by continuous hydraulic piston coring provided material for the investigation of Cenozoic paleoceanography.The faunal record is complete, except for the early Eocene.The isotope records have gaps in the early Eocene and in the early and middle Miocene.Hundreds of samples were studied and thousands of analyses were carried out.Detailed results and conclusions are presented in several separate chapters of this volume.This report is a synthesis.Studies of calcite dissolution in pelagic sediments indicate that calcite compensation depth (CCD) and lysocline underwent two types of changes during the Cenozoic.The first-order changes, which have a periodicity of some I0 7 yr., have amplitudes (depth difference from the medium) of more than 1,000 m.The Eocene and Miocene were epochs of high CCD.The deepening of the CCD in the late Eocene and early Oligocene was stepwise, but it was more abrupt in the early Pliocene.We attribute the higher CCD in the Eocene and Miocene to a relatively low production rate of calcareous plankton in the open oceans; during those epochs many of the nutrients had been consumed by phosphate deposition and by siliceous plankton.The second-order changes, which have a periodicity of I0 4 or I0 5 yr., represent CCD variations in response to changes from interglacial to glacial paleoenvironments during the Pliocene and Quaternary; the amplitude was a few hundred meters only.Evidence suggests that increased dissolution due to the more active bottom waters during the glacial stages in the Atlantic far overshadowed the effect of possible increases in fertility.The oxygen-isotope record shows an overall increase of δ 18 θ values since the middle Eocene, with a moderate reversal of the general trend during the late Oligocene and early Miocene.Whereas the early Paleogene trend of the Atlantic middle-latitude sites closely simulated that of the southern oceans, vertical and latitudinal gradients began to develop in the Oligocene and continued to steepen with time, so that the present thermal structure of the ocean waters above our sites is similar to that of the equatorial Pacific.The cause of the increased δ 18 θ values should have been related to increased ice volume on Earth and to temperature declines.However, the relative importance of the two different factors at any given time cannot be ascertained.We favor the hypothesis that the Antarctic Ice Cap started to form in the late Eocene and suggest that the early Oligocene ice volume was larger than it is today.The middle Miocene oxygen shift has also been registered at one of our sites, but its magnitude is smaller, and the corresponding environmental changes should have been less impressive, than those in the late Eocene and early Oligocene.The carbon-isotope record shows a parallel trend between the planktonic and benthic foraminifers since the beginning of the Oligocene and a divergent trend as well as a steeper gradient during the middle Eocene.Peak values of δ 13 C are found in the benthic foraminifers of Eocene and Miocene age.The Eocene peak may have resulted from decreases in terrestrial biomass due to the destruction of forests by advancing glaciers.However, the Miocene peak was probably a consequence of preferential sedimentation and the burial of organic carbon relative to carbonate carbon.Abrupt changes in carbon-isotope values have also been noted: the Oligocene carbon shift is parallel to the oxygen shift, whereas the Pliocene-Quaternary short-term carbon trends are opposite to the oxygen trends, with lighter carbon becoming enriched during glacial stages.We interpret those changes as manifestations of different responses of the terrestrial biomass to changes in climate and sea level.A minute late Miocene carbon shift has been found in our record; the Atlantic was apparently less affected by the reorganization of bottom-water circulation 6 Ma than the Pacific and Indian oceans, which display more significant changes in the isotope compositions of dissolved carbonates.Studies of fauna from sediments dated by precision stratigraphy indicate that the psychrosphere and the thermohaline circulation of the Atlantic started in the late Eocene, with precursor events in the middle Eocene.Faunal evidence suggests a northern source for the cold bottom water in regions east of the Mid-Atlantic Ridge.
The biostratigraphy of Cretaceous/Tertiary boundary sections from eight localities is summarized and compared in order to define a continuous or complete section. The El Kef, Tunisia, section is apparently the thickest C/T boundary section as yet discribed and contains all the biostratigraphical criteria required to define a complete section; that is, the uppermost Cretaceous Micula prinsii Zone, the "boundary clay" within the lowermost Tertiary Globigerina fringa Zine, followed by the Globigerina eugubina and pseudobulloides Zones. Using these zonations, a correlation of the stable-isotope stratigraphy from the various sections was made. The latest Cretaceous oceans and the earliest Tertiary oceans contained...
The boundary stratotype for the Miocene/Pliocene boundary, located at Capo Rosello, Sicily, occurs at a distinct lithostratigraphic change from Messinian evaporites to Zanclean open-marine sediments. Because bio- and magnetostratographic correlations of the stratotype with deep-sea sections have proven difficult, the authors propose to use strontium- and oxygen-isotope stratigraphies to correlate the earliest Pliocene at Capo Rosello with a marine sequence from the South Atlantic, DSDP Site 519. The Sr-isotope value of the sediments increases progressively between 6 and 4 Ma from approximately 0.708895 to 0.709026 with the M/P boundary at about 0.708948. Three cycles of rapid O-isotope fluctuations of 1.2 per thousand were recorded in the planktic forams between 5.10 and 4.96 Ma, which have been interpreted as an indication of unstable surface-current patterns related to a destabilization of the Antarctic ice sheet. The lowermost 11 m of the earliest Pliocene Trubi Fm. at Capo Rosello contains the MP1-1 and lowermost part of the MP1-2 zones and have an average Sr-isotope value of 0.708968, correlating them with the earliest Pliocene of Site 519. The sequence also contains 3 planktic cycles of O-isotope fluctuations of about 1.0 per thousands, which the authors correlate with the Site 519 cycles and interpret asmore » global warmings and coolings related to climatic instability. They conclude that the terminal flooding of the Mediterranean at the M/P boundary resulted in global climatic disturbances possibly associated with a reorganization of oceanic circulation due to the renewed injection of Mediterranean bottom waters into the Atlantic Ocean.« less
We established a composite oxygen-and carbon-isotope stratigraphy for the Pliocene in the central South Atlantic.Monospecific samples of benthic and planktonic foraminifers from pelagic sediments from DSDP Sites 519, 521, 522, and 523 were analyzed isotopically.The resulting benthic oxygen-isotope stratigraphy allowed three paleoclimatic periods in the Pliocene to be distinguished.During the early Pliocene (5.2-3.3Ma), low-amplitude climatic changes prevailed in a world that was less glaciated than during the Pleistocene.A net increase in global ice volume is documented in a 0.5% 0 positive shift in the average 18 O composition of the benthic foraminifers at 3.2 Ma.The middle Pliocene (3.3-2.5 Ma) is not only characterized by a more widespread glaciation of the Southern and Northern hemispheres but also by more drastic isotopic differences between glacial and interglacial times.A minor shift in the average 18 O composition of the benthic foraminifers marks the beginning of the late Pliocene-early Pleistocene climatic period (2.5-1.1 Ma).Alternating cold and warm climate is documented in both the oxygen-isotope record and in the pelagic sediments.During cold periods, sediments with a lower CaCO 3 content indicate more corrosive bottom-water conditions.More negative 13 C signals in the benthic foraminifers from these sediments suggest that the Antarctic Bottom Water current was intensified in glacial times.The oxygen-isotope composition of the measured planktonic foraminifers suggests that the surface water in this part of the South Atlantic remained relatively warm during the growth of the Pliocene glaciers.
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