Diagenesis of Upper Jurassic concretions from the Antarctic Peninsula

Citation
Ra. Scasso et W. Kiessling, Diagenesis of Upper Jurassic concretions from the Antarctic Peninsula, J SED RES, 71(1), 2001, pp. 88-100
Citations number
79
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
JOURNAL OF SEDIMENTARY RESEARCH
ISSN journal
1527-1404 → ACNP
Volume
71
Issue
1
Year of publication
2001
Part
A
Pages
88 - 100
Database
ISI
SICI code
1527-1404(200101)71:1<88:DOUJCF>2.0.ZU;2-F
Abstract
Early-diagenetic calcite concretions are widespread in mudstone-tuff sequen ces deposited in Late Jurassic oxygen-deficient basins of the Antarctic Pen insula. Although obscured or destroyed in host rocks, original components a nd sedimentary structures are well preserved in concretions, in spite of si gnificant mineralogical and geochemical change during growth. Early diagene sis led to a rapid and almost total variation in the mineralogy within the concretions, independently of the original host lithologies. Siliceous part icles were replaced by chlorite and zeolites in suboxic, alkaline, and mode rately reducing renditions on the sea floor and in the first centimeters of burial. These conditions also led to localized early formation of phosphat e concretions. Pyrite developed subsequently because of high sulfide abunda nce in the sulfate reduction zone. Most calcite precipitation took place in the lower part of the sulfate reduction zone in a strongly alkaline enviro nment where sulfide content had been lowered by pyrite precipitation. In th is stage, the remaining siliceous elements were dissolved or replaced by ca lcite, Later diagenetic changes include enlargement of zeolites, minor chan ges in clay minerals, and the formation of calcite veins. The wide range of delta C-13 values in cement and vein calcite (-1,47 parts per thousand and -20.23 parts per thousand PDB) is explained by mixed carbon sources from o rganic matter oxidation and dissolution of calcareous shells. The low delta O-18 of calcite (-2,34 parts per thousand to -19.72 parts per thousand PDB ) is the result of recrystallization in contact with high-temperature diage netic or hydrothermal fluids flushed through micro-fractures in the concret ions, which also produced extensive vein formation.