Antarctic Glaciation during the Tertiary Recorded in Sub-Antarctic Deep-Sea Cores

Study of 18 Cenozoic South Pacific deep-sea cores indicates an association of glacially derived ice-rafted sands and relatively low planktonic foraminiferal diversity with cooling of the Southern Ocean during the Lower Eocene, upper Middle Eocene, and Oligocene. Increased species diversity and reduction or absence of ice-rafted sands in Lower and Middle Miocene cores indicate a warming trend that ended in the Upper Miocene. Antarctic continental glaciation appears to have prevailed throughout much of the Cenozoic.     

Gulf stream: velocity fluctuations during the late cenozoic

Biostratigraphic analysis of seven piston cores from the southeastern Blake Plateau suggests that the upper Miocene to Recent sedimentary section at this location represents a history of deposition of calcareous ooze alternating with current-induced nondeposition or erosion. This record is primarily a result of long-term fluctuations in the velocity of the western boundary current or Gulf Stream, which sweeps the plateau. High-velocity phases of this current system, as signaled by hiatuses in the section, lie within the time limits 4.8 to 6.1, 3.9 to 4.4, 2.3 to 2.9, and 0 to 1.5 million years before present (B.P.). These time intervals are coeval with dated episodes of climatic decline and glaciation. The most intense acceleration of the Gulf Stream, as indicated by deep erosion of the Blake Plateau, occurred in the latest Miocene to earliest Pliocene (4.8 to 6.1 million years B.P.) in conjunction with a major expansion of the Antarctic ice cap. Subsequent accelerations of the Gulf Stream coincide with early Pliocene cooling in the Southern Hemisphere, worldwide expansion of high-altitude-high-latitude glaciers in the late Pliocene, and the classical glaciations of the Pleistocene. An additional, protracted increase in the average velocity of the Gulf Stream, which began in the late Miocene and culminated in the mid-Pliocene (about 3.8 million years B.P.), can be attributed to the gradual emergence of the Central American isthmus.     

Amino Acid composition of planktonic foraminifera: a paleobiochemical approach to evolution

A unique, species-specific amino acid composition is identified with each of 16 species of planktonic Foraminifera isolated from the tops of deep-sea sediment cores. This amino acid pattern appears to directly reflect the genotype. The total amino acid content ranges from 2.0 to 4.2 micromoles per gram of calcified tissue or 0.02 to 0.04 percent by weight. Analyses of two Early Miocene species indicate that characteristic compositional differences are sufficiently well preserved over geologic time to determine phylogenetic affinities among extinct species living at least 18 million years ago.     

Antarctic Bottom Water: Major Change in Velocity during the Late Cenozoic between Australia and Antarctica

Paleomagnetic and micropaleontological studies of deep-sea sedimentary cores between Australia and Antarctica define an extensive area centered in the south Tasman Basin, where sediment as old as Early Pliocene has been systematically eroded by bottom currents. This major sedimentary disconformity has been produced by a substantial increase in velocity of Antarctic bottom water, possibly associated with late Cenozoic climatic cooling and corresponding increased glaciation of Antarctica.     

New evidence on the size and possible effects of a late pliocene oceanic asteroid impact

Debris from a late Pliocene asteroid impact is spread across at least 600 kilometers of the ocean floor in the southeast Pacific. On the basis of iridium concentrations in sediments from six deep-sea cores, the asteroid diameter was at least 0.5 kilometer; the impacting projectile may have been one of the largest in the last few million years. The stratigraphic age of this impact is the same as that inferred for the onset of Northern Hemisphere glaciation.     

The paleomagnetic field from equatorial deep-sea sediments: axial symmetry and polarity asymmetry

Paleomagnetic data from 89 equatorial deep-sea sediment cores indicate that the configuration of the time-averaged geomagnetic field depends strongly on polarity state but that it remains within 1 degree of axial symmery throughout the Pliocene and Pleistocene (last 5 million years). The relative magnitude of the nondipole field was greater by almost a factor of 2 during reverse than during normal polarity intervals. These results thus support earlier suggestions that there may be a standing (nonreversing) component of the geomagnetic dynamo.     

Tertiary sediment from the East pacific rise

More than 50 cores ranging in age from Pliocene to Lower Miocene have been recovered from the East Pacific Rise. Near the crestal regions the sediment cover is thin or lacking, and only Pleistocene sediments were recovered. On the flanks, the sediment thickness increases and pre-Pleistocene sediments are encountered. This pattern of increasing age and increasing sediment thickness away from the axis of the rise is in agreement with that predicted for spreading of the ocean floor.     

Seven million years of glaciation in greenland

Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region.     

Absolute dating of Caribbean cores p6304-8 and p6304-9

Two deep-sea cores from the central Caribbean have been dated by the thorium-230/ protactinium-231 method. The ages obtained are in agreement with the ages previously obtained from other deep-sea cores from the same area. Because of their greater precision, the new dates provide a more accurate time scale for the past 170,000 years.     

Geologic evolution of northern tibet: results of an expedition to ulugh muztagh

A reconnaissance expedition across the northern margin of the Tibetan plateau revealed evidence of a late Cenozoic northward progression of the locus of crustal shortening and, therefore, of a northward growth of the area encompassed by the plateau. Active reverse faults crop out at the foot of the Altyn Tagh, on the northern edge of the plateau, and at the bases of several ranges within the Altyn Tagh and Kunlun, where the elevations of the neighboring basins are less than 4000 meters. Farther south, where elevations are higher, there was no evidence of recent faulting, but late Cenozoic rock in the Ayak Kum K?l basin has been strongly folded. South of this basin, Ulugh Muztagh, apparently the highest mountain in the eastern Kunlun, is underlain by late Miocene, tourmaline-bearing and two-mica granite. These rocks suggest that thickening of continental crust had begun in this area by late Miocene time. Overlying quartz-sanidine welded tuffs of Pliocene age imply that uplift and erosion occurred between Miocene and Pliocene time, but with little subsequent erosion. In addition, we found an east-west trending belt of mafic and ultramafic rock that probably marks a suture of a crustal fragment with southern Asia in Triassic or more recent time.     

Climate response to orbital forcing across the Oligocene-Miocene boundary

Spectral analyses of an uninterrupted 5.5-million-year (My)-long chronology of late Oligocene-early Miocene climate and ocean carbon chemistry from two deep-sea cores recovered in the western equatorial Atlantic reveal variance concentrated at all Milankovitch frequencies. Exceptional spectral power in climate is recorded at the 406-thousand-year (ky) period eccentricity band over a 3.4-million-year period [20 to 23.4 My ago (Ma)] as well as in the 125- and 95-ky bands over a 1.3-million-year period (21.7 to 23.0 Ma) of suspected low greenhouse gas levels. Moreover, a major transient glaciation at the epoch boundary ( approximately 23 Ma), Mi-1, corresponds with a rare orbital congruence involving obliquity and eccentricity. The anomaly, which consists of low-amplitude variance in obliquity (a node) and a minimum in eccentricity, results in an extended period ( approximately 200 ky) of low seasonality orbits favorable to ice-sheet expansion on Antarctica.     

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.     

Manganese and related elements in the interstitial water of marine sediments

Analyses for manganese, nickel, iron, cobalt, sodium, and lithium in the interstitial water of cores from the southern California borderland and six deep-sea cores in the area of the East Pacific Rise show great variation in concentration of trace elements. Oxidizing near-shore sediments showed a 50-fold enrichment in manganese in contrast to sulfide-rich reducing sediments, which showed no enrichment. Deep-sea sediments were variable in their concentration of the trace metals. All but one core showed a high enrichment in dissolved manganese, with a maximum of 6.6 parts per million. Two cores showed a 100-fold enrichment in nickel and cobalt. The manganese appears to be in solution either as Mn(2+) or as a complex. The results appear to support manganese nodule formation in deep-sea sediments through a diffusion of manganese from depth to the surface.     

Tertiary sediment from the mid-atlantic ridge

Lower Miocene microfossils occur in basaltic glass in two dredge hauls from the crestal area of the Mid-Atlantic Ridge near 30 degrees N. From the ridge and adjoining abyssal hills 43 pre-Pleistocene cores were identified, including one Cretaceous and four Eocene. Dredgings and cores now available suggest that the upper layer of the crust of the ridge is constructed of layers of interbedded sediments and basalt flows. The data rule out the possibility of large-scale continental drifting or spreading of the ocean floor since the Lower Miocene.     

Thermal structure of the deep pacific ocean in the early pliocene

The thermal structure of the Pacific Ocean between water depths of about 1 and 4.5 kilometers is estimated from the oxygen isotopic ratio of benthonic foraminifera from deep-drilled and piston cores of early Pliocene age (about 3 to 5 million years ago). The ratio of oxygen-18 to oxygen-16 in the early Pliocene at each site varies by an average of only +/- 0.12 per mil (1 standard deviation). A plot of the oxygen isotopic ratio against modern bottom-water temperature is adequately fit by a line having a slope of - 0.26 per mil per degree Celsius (the equilibrium temperature dependence of calcite-water fractionation), suggesting that the temperature gradient of the Pacific Ocean during the early Pliocene was similar to that of today.     

Ventilation of the glacial deep Pacific Ocean

Measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial Pacific deep-sea cores suggest that during peak glacial time the radiocarbon age of water at 2-kilometers depth was no greater than that of today. These results make unlikely suggestions that a slowdown in deep-ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon-14 (14C) to carbon in the atmosphere and surface ocean during glacial time. Comparison of 14C ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14C to C ratio difference was not substantially different from today's.     

Geomagnetic reversal in brunhes normal polarity epoch

The magnetic stratigraphly of seven cores of deep-sea sediment established the existence of a short interval of reversed polarity in the upper part of the Brunches epoch of normal polarity. The reversed zone in the cores correlates well with paleontological boundaries and is named the Blake event. Its boundaries are estimated to be 108,000 and 114,000 years ago +/- 10 percent.     

A new greenland deep ice core

The polar ice sheets are rich sources of information on past atmospheric conditions, including paleoclimates. A new deep ice core has been drilled in south Greenland. Comparison of the oxygen isotopic profile with that from camp Century and with a deep-sea foraminifera record indicates that the new core reaches back to about 90,000 years before present in a continuous sequence. The details in the Wisconsin part of the ice core records seem to be climatically, significant, and the general trends reveal all of the relevant Emiliani stages recorded in deep-sea cores. The redated Camp Century record suggests a dramatic termination of the Eem/Sangamon interglacial.     

Iridium anomaly approximately synchronous with terminal eocene extinctions

An iridium anomaly has been found in coincidence with the known microtektite level in cores from Deep Sea Drilling Project site 149 in the Caribbean Sea. The iridium was probably not in the microtektites but deposited simultaneously with them; this could occur if the iridium was deposited from a dust cloud resulting from a bolide impact, as suggested for the anomaly associated with the Cretaceous-Tertiary boundary. Other workers have deduced that the microtektites are part of the North American strewn tektite field, which is dated at about 34 million years before present, and that the microtektite horizon in deep-sea cores is synchronous with the extinction of five radiolarian species. Mass extinctions also occur in terrestrial mammals within 4 million years of this time. The iridium anomaly and the tektites and microtektites are supportive of a major bolide impact about 34 million years ago.     

Episodes of aleutian ridge explosive volcanism

Earlier workers have overlooked deep-sea bentonite beds when unraveling the Cenozoic volcanic history of an area. In the North Pacific, identification of Miocene and older volcanic episodes is possible only if both altered (bentonite) and unaltered ash beds are recognized. Our study, which includes bentonite beds, shows that volcanism on the Aleutian Ridge and Kamchatka Peninsula has been cyclic. Volcanic activity seems to have increased every 2.5 x 10(6) years for the past 10 x 10(6) years and every 5.0 x 10(6) years for the time span from 10 to 20 x 10(6) years ago. The middle and late Miocene and the Quaternary were times of greatly increased volcanic activity in the North Pacific and elsewhere around the Pacific Basin. The apparent absence of a volcanic record before the late Miocene at Deep Sea Drilling Project site 192 is the result not of plate motion, as suggested by Stewart and by Ninkovich and Donn, but rather of the diagenesis of ash layers. Major, apparently global volcanic episodes occurred at least twice in the last 20 x 10(6) years. Yet, only one major glacial epoch (the Pleistocene) has occurred. Therefore, even though glaciation coincided with an increase in Quaternary volcanism, the increased volcanism itself may not have been the primary cause of global cooling.