| Full text | |
| Author(s): |
Total Authors: 4
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| Affiliation: | [1] Univ Sao Paulo, Inst Oceanog, Sao Paulo - Brazil
[2] US Geol Survey, PCMSC, Santa Cruz, CA - USA
Total Affiliations: 2
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| Document type: | Journal article |
| Source: | PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY; v. 36, n. 9 SEP 2021. |
| Web of Science Citations: | 0 |
| Abstract | |
Marine phosphorites are an important part of the oceanic phosphorus cycle and are related to the effects of long-term global climate changes. We use petrography, mineralogy, rare earth elements contents, and Sr-87/Sr-86-determined carbonate fluorapatite (CFA) and calcite ages to investigate the paragenesis and history of phosphatization of carbonate sediments, limestones, ferromanganese crusts, and ironstones from the summit of Rio Grande Rise (RGR), Southwest Atlantic Ocean. Phosphatization of all the rock types occurred throughout the Miocene from 20.2 to 6.8 million years ago (Ma), and occasionally during the Quaternary, mainly through the cementation of carbonate sediments by cryptocrystalline CFA, likely involving the dissolution of the smaller size fraction of foraminifera-nannofossil ooze. Porosity/permeability and abundance of fine calcite material were important factors determining the intensity of phosphatization of the various rock types. Phosphatization was initiated during a transition to a more dynamic circulation system in the South Atlantic Ocean, which remobilized phosphorus from deeper waters and increased primary productivity that culminated with the middle-Miocene Climatic Optimum between similar to 17 and 14.8 Ma. The relatively shallow-water depth of RGR summit during the Miocene provided proximity to the oxygen minimum zone, a reservoir for reactive phosphorus, especially during periods of enhanced phosphorus cycling spurred by surface primary productivity. The cessation of phosphatization at RGR resulted from a rapidly cooling and dry climate that characterized the Miocene-Pliocene transition. Our results support previous observations that periods of broadly intensified ocean circulation and local hydrodynamic changes were the key paleoceanographic links to phosphorite formation. (AU) | |
| FAPESP's process: | 16/24946-9 - Sea-level changes and Global Monsoon System: clues from marine cores in Brazil |
| Grantee: | Luigi Jovane |
| Support Opportunities: | Research Program on Global Climate Change - Thematic Grants |