All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
9.
Coral ages and island subsidence, Hilo drill hole
Journal of Geophysical Research: Solid Earth,
101
(5)
11599-11605
1996
ISSN: 21699313
Publisher: American Geophysical Union
Keywords:▾
age determination; coral; lava flow; radiocarbon dating; subsidence; thorium/uranium dating, USA, Hawaii, Hawaii
Abstract: ▾ A 25.8-m-thick sedimentary section containing coral fragments occurs directly below a surface lava flow (the ∼1340 year old Panaewa lava flow) at the Hilo drill hole. Ten coral samples from this section dated by accelerator mass spectrometry (AMS) radiocarbon and five by thermal infrared multispectral scanner (TIMS) 230Th/U methods show good agreement. The calcareous unit is 9790 years old at the bottom and 1690 years old at the top and was deposited in a shallow lagoon behind an actively growing reef. This sedimentary unit is underlain by a 34-m-thick lava flow which in turn overlies a thin volcaniclastic silt with coral fragments that yield a single 14C date of 10,340 years. The age-depth relations of the dated samples can be compared with proposed eustatic sea level curves after allowance for island subsidence is taken. Island subsidence averages 2.2 mm/yr for the last 47 years based on measurements from a tide gage near the drill hole or 2.5-2.6 mm/yr for the last 500,000 years based on the ages and depths of a series of drowned coral reefs offshore from west Hawaii. The age-depth measurements of coral fragments are more consistent with eustatic sea levels as determined by coral dating at Barbados and Albrolhos Islands than those based on oxygen isotopic data from deep sea cores. The Panaewa lava flow entered a lagoon underlain by coral debris and covered the drill site with 30.9 m of lava of which 11 m was above sea level. This surface has now subsided to 4.2 m above sea level, but it demonstrates how a modern lava flow entering Hilo Bay would not only change the coastline but could extensively modify the offshore shelf.
8.
Analysis of fractures intersecting Kahi Puka Well 1 and its relation to the growth of the island of Hawaii
Journal of Geophysical Research: Solid Earth,
101
(5)
11695-11699
1996
ISSN: 21699313
Publisher: American Geophysical Union
Keywords:▾
borehole logging; borehole televiewer; fracture geometry; tensile fracture; volcano growth, USA, Hawaii, Hawaii
Abstract: ▾ As part of the Hawaii Scientific Drilling Project, Kahi Puka Well 1 penetrated about 275 m of Mauna Loa basalts overlying a sequence of Mauna Kea flow units as it was drilled and cored to a total depth of 1053 m below land surface. A borehole televiewer (BHTV) was run in most of the well in successive stages prior to casing in order to obtain magnetically oriented acoustic images of the borehole wall. A total of 283 individual fractures were identified from this log and characterized in terms of strike and dip. These data are divided into three vertical sections based upon age and volcanic source, and lower hemisphere stereographic plots identify two predominant, subparallel fracture subsets common to each section. Assuming that most of the steeply dipping fractures observed in the BHTV log are tensile features generated within basalt flows during deposition and cooling, this fracture information can be combined with models of the evolution of the island of Hawaii to investigate the depositional history of these Mauna Loa and Mauna Kea basalts over the past 400 kyr. The directions of high-angle fractures appear to be generally parallel to topography or to the coastline at the time of deposition, as is supported by surface mapping of modern flows. Consequently, an overall counterclockwise rotation of about 75° in the strike of these fractures from the bottom to the top of the well represents a systematic change in depositional slope direction over time. We attribute the observed rotation in the orientations of the two predominant fracture subsets over the past 400 kyr to changes in the configurations of volcanic sources during shield building and to the structural interference of adjacent volcanoes that produces shifts in topographic patterns.
7.
An 84-kyr paleomagnetic record from the sediments of Lake Baikal, Siberia
Journal of Geophysical Research: Solid Earth,
101
(5)
11365 – 11385
1996
ISSN: 21699313
Publisher: American Geophysical Union
Keywords:▾
Russian Federation, Lake Baikal; geomagnetic field; palaeointensity; palaeomagnetism; Quaternary; secular variation
Abstract: ▾ We have conducted a paleomagnetic study of sediment cores obtained from the Selenga prodelta region of Lake Baikal, Russia. This record, which spans approximately the last 84 kyr, contributes to a better understanding of the nature of geomagnetic field behavior in Siberia and is a useful correlation and dating tool. We demonstrate that the Lake Baikal sediments are recording variations in the geomagnetic field. The directional record displays secular variation behavior with a geomagnetic excursion at 20 ka and additional excursions appearing as large-amplitude secular variation at 41, 61, and 67 ka. Smoothing of the geomagnetic excursion behavior occurs in Lake Baikal sediments owing to the intermediate sedimentation rate (13 cm kyr-1). The Lake Baikal relative paleointensity record correlates to absolute paleointensity data for the last 10 kyr and to relative paleointensity records from the Mediterranean Sea and Indian Ocean for the last 84 kyr. This correlation suggests a strong global (i.e., dipole) component to these records and further supports the reliability of sediments as recorders of relative geomagnetic paleointensity. We show that a relative geomagnetic intensity stratigraphy has a potential resolution of 7 kyr by correlating continental and marine records. The geomagnetic intensity stratigraphy helps constrain the age of the difficult to date Lake Baikal sediments.
6.
Continental climate response to orbital forcing from biogenic silica records in lake baikal
Nature,
378
(6559)
769 – 771
1995
ISSN: 00280836DOI:10.1038/378769a0
Keywords:▾
Russian Federation, Lake Baikal; silicon dioxide; biogenic silica; climate response; continental climate; ice sheet dynamics; ocean dynamics; orbital forcing; climate; climate change; custody; dynamics; heat stroke; lake; orbit; rhythm; Russian Federation; sea
Abstract: ▾ CHANGES in insolation caused by periodic changes in the Earth's orbital parameters provide the primary forcing for global ice ages1–6. But it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets. Here we investigate this question using the record of biogenic silica in Lake Baikal as a proxy for climate change in this high-latitude mid-continental region. We find a good correlation between this record and that of marine oxygen isotopes4. Over the past 250 kyr the Baikal record exhibits both a strongly nonlinear component (manifested in a 100-kyr periodicity) and weaker direct-insolation components (manifested in the 41-kyr (obliquity) and 23- and 19-kyr (precession) orbital cycles). These results show that even though extreme continental climates such as this are influenced directly by insolation variations, they are dominated by the nonlinear rhythm of the oceans and ice sheets. © 1995 Nature Publishing Group.
5.
What brought them up? Exhumation of the Dabie Shan ultrahigh- pressure rocks
Geology,
23
(8)
743 – 746
1995
ISSN: 00917613Keywords:▾
China; Dabie Mountains; Geology; Continental crusts; Eastern China; Identation; Magmatic complexes; Stretching lineations; Transtension; Triassic; Ultrahigh pressure rocks; Cretaceous; exhumation; tectonics; transtension; Triassic; ultra high pressure metamorphism; Silica
Abstract: ▾ Metamorphic coesite and diamond in the Dabie Shan, eastern China, testify to subduction of continental crust to >100 km depth. Exhumation of these ultrahigh-pressure rocks through the crust encompassed two stages. 1) South-dipping foliation, southeast-plunging stretching lineation, lineation-parallel isoclinal folds, and boudins indicate extreme subhorizontal shortening and subvertical extension during top-to-northwest shearing at 200-180 Ma. 2) Northwest-southeast sub-horizontal extension from 133 to 122 Ma was concentrated within an asymmetric structural dome in a magmatic complex that forms the northern half of the Dabie Shan. The preferred exhumation model involves two stages: Triassic identation - vertical extrusion and erosion - followed by Cretaceous plate margin transtension. -from Authors
4.
A rock-magnetic record from Lake Baikal, Siberia: Evidence for Late Quaternary climate change
Earth and Planetary Science Letters,
122
(1-2)
221 – 238
1994
ISSN: 0012821XKeywords:▾
Russian Federation, Lake Baikal; Russian Federation, Siberia, Lake Baikal; aeolian transport; climate change; marine oxygen isotope record; oxygen isotope; Quaternary; rock magnetic record
Abstract: ▾ Rock-magnetic measurements of sediment cores from the Academician Ridge region of Lake Baikal, Siberia show variations related to Late Quaternary climate change. Based upon the well-dated last glacial-interglacial transition, variations in magnetic concentration and mineralogy are related to glacial-interglacial cycles using a conceptual model. Interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals. Glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals. The variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods. We also infer an increased contribution of eolian sediment during the colder, windier, and more arid glacial conditions when extensive loess deposits were formed throughout Europe and Asia. Eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals. Variations in magnetic concentration and mineralogy of Lake Baikal sediment correlate to the SPECMAP marine oxygen-isotope record. The high degree of correlation between Baikal magnetic concentration/mineralogy and the SPECMAP oxygen-isotope record indicates that Lake Baikal sediment preserves a history of climate change in central Asia for the last 250 ka. This correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method. Future work must include providing better age control and additional climate proxy data, thereby strengthening the correlation of continental and marine climate records. © 1994.
3.
Radiocarbon dating of Lake Baikal sediments--A progress report
Russian Geology and Geophysics,
3455-63
1993
2.
Initial results of U.S.‐Soviet paleoclimate study of Lake Baikal
Eos, Transactions American Geophysical Union,
73
(43)
457 – 462
1992
ISSN: 00963941Keywords:▾
Russian Federation, Lake Baikal; age determination; dating; palaeoclimate; Pleistocene/Holocene boundary; sediment core; seismic reflection profile
Abstract: ▾ Lake Baikal, a Miocene‐age rift lake in southeastern Siberia, is an especially promising site for paleoclimate studies. Its high‐latitude location (52°–56°N) makes it particularly sensitive to changes in solar insolation due to long‐period variations in the Earth's orbital parameters. These variations are widely believed to be the main forcing functions of climate change in the Quaternary [Hays et al., 1976; Imbrie et al., 1984. The extreme continentality of the climate in southeastern Siberia makes Baikal an ideal location to study temporal changes in seasonality. Baikal is also one of the few high‐latitude lakes that has not been glaciated during the last 1–2 million years [Grosswald, 1980], although a record of glaciation in its drainage basin is preserved in the lake sediments. Finally, Lake Baikal is the largest (23,000 km3), the deepest (1640 m), and one of the oldest extant lake systems in the world. The sedimentary section in the Baikal depression is more than 7 km thick and probably spans more than 15 million years [Hutchinson et al., 1992]. Accordingly, Lake Baikal sediments represent one of the longest and most complete continental climate records available anywhere in the world. ©1992. American Geophysical Union. All Rights Reserved.
1.
Sedimentation in Lake Malawi (East Africa) during the past 10,000 years: a continuous paleoclimatic record from the southern tropics
Palaeogeography, Palaeoclimatology, Palaeoecology,
85
(3-4)
351-366
1991
ISSN: 00310182Keywords:▾
carbonate precipitation; chemocline depth; climate; climate trend; diatom; Holocene; lake level; micrite; palaeoclimate; palaeoclimate record; salinity; sedimentation, Malawi, Lake Malawi
Abstract: ▾ A suite of piston cores recovered from Lake Malawi (9-14°S, 34-35°E), east Africa in 1986 has been analyzed for major and minor elements, organic C and N, calcium carbonate and diatoms. An internally consistent stratigraphy was constructed from calcium carbonate abundance and variations in the two most abundant diatom genera, Stephanodiscus and Melosira, with age control obtained primarily from 14C dating of the carbonate. Differences with time in Fe abundance in a transect of cores from different water depths have been interpreted to reflect changes in chemocline depth. The depth to the chemocline was on the order of 100 m shallower than present prior to 3500 yr B.P., indicating less seasonality. Carbonate production and preservation appears to be related to climatically induced changes in both salinity and chemical distributions in the water column. The carbonate, which precipitates from surface waters, is most abundant during the interval from about 10,000 to 6000 yr B.P. This micrite most likely represents periods of low lake level when salinity increased and carbonate precipitation was enhanced. Sedimentary evidence suggests that lake levels were 100-150 m lower than present during this period. This record is different from climatic trends in northern intertropical Africa, but appears to also be related to changes in insolation and monsoon circulation. This is the northernmost basin in Africa reported to exhibit a "southern hemisphere" response to the early Holocene northern hemisphere summer insolation maximum. The climatic hingeline north of Lake Malawi (∼ 9°S) implied by our results is significantly south of that indicated by general-circulation model simulations, however. The cores show evidence for periods of abrupt climate change during the interval of generally arid climate. © 1991.