Strontium isotope stratigraphy and geochemistry of the late Neogene ocean

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doi: 10.1016/0012-821X(89)90044-7
Author(s): Hodell, David A.; Mueller, Paul A.; McKenzie, Judith A.; Mead, Gregory A.
Author Affiliation(s): Primary:
Univ. Fla., Dep. Geol., Gainesville, FL, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 92(2), p.165-178. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 44 refs.; illus. incl. 3 tables
Summary: A curve describing the variation of the Sr isotopic composition of sea-water for the late Neogene (9-2 m.y. B.P.) was constructed from 87Sr/86Sr analyses of marine carbonate in the five Deep Sea Drilling Project sites 502, 519, 588, 590 and 593. The Sr isotopic composition of the oceans increased between 9 and 2 m.y. with several changes in slope. From 9 to 5.5 m.y. 87Sr/86Sr values were nearly constant at approx 0.708925. Between 5.5 and 4.5 m.y., Sr isotopic ratios increased monotonically at a rate of 1 times 10-4 per m.y. The steep slope during this interval provides the potential for high- resolution Sr isotope stratigraphy across the Miocene/Pliocene boundary. The rate of change decreases to near zero again during the interval 4.5-2.5 m.y., and ratios average 0.709025. The relatively rapid increase of 87Sr/86Sr between 5.5 and 4.5 m.y. must be related to changes in the flux or average Sr ratios of the major inputs of Sr to the oceans. Quantitative modelling suggests that the increase was probably caused by an increase in the dissolved riverine flux of Sr to the oceans, an increase in the average 87Sr/86Sr composition of river water, or some combination of these parameters. During the time interval of steep 87Sr/86Sr increase, other geochemical and sedimentological changes also occur. The simplest mechanism to explain Sr isotopic variation and other changes is an increase in the dissolved chemical fluxes carried by rivers to the ocean. This, in turn, implies increased chemical denudation rates of the continents and shelves during the late Neogene. The increased weathering rates are attributed to increased exposure of the continents by eustatic regression, intensified glacial/interglacial cycles, and accelerated rates of global tectonism beginning at 5.5 m.y. during the latest Miocene.
Year of Publication: 1989
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Atlantic Ocean; Carbonate sediments; Caribbean Sea; Cenozoic; Chemostratigraphy; DSDP Site 502; DSDP Site 519; DSDP Site 588; DSDP Site 590; DSDP Site 593; Deep Sea Drilling Project; Geochemistry; IPOD; Isotopes; Leg 68; Leg 73; Leg 90; Marine sedimentation; Marine sediments; Metals; Miocene; Neogene; North Atlantic; Pacific Ocean; Paleo-oceanography; Pliocene; Sedimentation; Sedimentation rates; Sediments; South Atlantic; South Pacific; Southwest Pacific; Sr-87/Sr-86; Stable isotopes; Stratigraphy; Strontium; Tertiary; Upper Miocene; West Pacific
Coordinates: N112925 N112925 W0792247 W0792247
S260813 S260811 W0113958 W0113959
S260642 S260642 E1611336 E1611336
S311002 S311001 E1632131 E1632130
S403029 S403028 E1674029 E1674028
Record ID: 1989031633
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom