Bulk calcite size fraction distribution and Sr/Ca composition for deep-sea sediments at selected age horizons

Author(s): Hampt Andreasen, Gretchen; Delaney, M. L.
Author Affiliation(s): Primary:
University of California at Santa Cruz, Earth Sciences Department, Santa Cruz, CA, United States
Volume Title: Marine Geology
Source: Marine Geology, 169(1-2), p.185-205. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0025-3227 CODEN: MAGEA6
Note: In English. 37 refs.; illus., incl. 7 tables
Summary: Strontium/calcium (Sr/Ca) ratios in bulk and foraminiferal calcite have been used to constrain the history of Sr/Ca in the oceans and to evaluate calcite diagenetic alteration. However bulk Sr/Ca records also may be influenced by differences in Sr uptake and/or in the diagenetic susceptibility of different calcium carbonate sedimentary components. We present data on the sediment size fraction and calcium carbonate distribution in bulk samples, Sr/Ca in a range of sedimentary size components, and Sr/Ca in bulk sediments. Ocean Drilling Program samples from sites on Ontong Java Plateau and Ceara Rise (in the western equatorial Pacific and Atlantic, respectively) and from sites in the eastern equatorial Pacific were selected to represent progressive stages in the diagenetic pathway from the sea floor through a range of burial depths equivalent to sediment ages of ∼5.6, ∼9.4, and ∼37.1Ma. Samples were subdivided by size to produce a unique data set of size-specific Sr/Ca ratios. Fine fraction (<45µm) Sr/Ca ratios are higher than those of all corresponding coarse fractions, indicating that fine nannofossil-dominated calcite has a Sr partition coefficient 1.3-1.5 times greater than that of coarse foraminifera-dominated calcite. Thus, absolute values of bulk Sr/Ca in contemporaneous samples reflect, in part, the ratio of fine to coarse calcite sedimentary components. Sr/Ca values in fine and coarse components also behave differently in their response to pre-burial dissolution and to recrystallization at depth. Coarse size components are sensitive to bottom water carbonate ion undersaturation, and they lose original Sr/Ca differences among contemporary samples over ∼10my. In contrast, fine components recrystallize faster in more deeply buried samples. Interpretation of the historical Sr/Ca record is complicated by post-depositional diagenetic artifacts, and thus our data do not provide clear evidence of specific temporal changes in oceanic Sr/Ca ratios over the past 10 million years. This paper represents the first systematic attempt to examine trends in calcite Sr/Ca as a function of sediment size fraction and age. Abstract Copyright (2000) Elsevier, B.V.
Year of Publication: 2000
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Alkaline earth metals; Atlantic Ocean; Calcite; Calcium; Carbonates; Ceara Rise; Chemical ratios; Deep-sea environment; Deep-sea sedimentation; Distribution; Equatorial Atlantic; Equatorial Pacific; Leg 130; Leg 138; Leg 154; Marine environment; Marine sedimentation; Marine sediments; Metals; North Atlantic; Ocean Drilling Program; Ontong Java Plateau; Pacific Ocean; Processes; SEM data; Sampling; Sedimentation; Sediments; Size distribution; Spatial distribution; Sr/Ca; Strontium; West Pacific
Coordinates: N001906 N033626 E1613538 E1563728
S030548 N111326 W0902851 W1103419
N034308 N092719 W0425429 W0442852
Record ID: 2000077989
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands