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Oncolites from lacustrine sediments in the Cretaceous of north‐eastern Spain
Author(s) -
FREEMAN TOM,
ROSELL JUAN,
OBRADOR ANTONIO
Publication year - 1982
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1982.tb01806.x
Subject(s) - marl , geology , terrigenous sediment , petrography , cretaceous , sedimentary rock , paleontology , accretion (finance) , geochemistry , calcite , carbonate , structural basin , physics , materials science , astrophysics , metallurgy
ABSTRACT Compact micritic oncolites up to 8 cm in maximum diameter occur within Maestrichtian (Upper Cretaceous) Garumniense continental marls of Sierra del Montsec (Lerida Province) of north‐eastern Spain. Synsedimentary development is documented by patches of terrigenous quartz that occur among oncolitic protuberances. Soluble nuclei (limestone fragments and bivalves) further suggest an origin through accretion, rather than that of soil pisolite. Similarities between the petrography and isotopic compositions of the oncolites and those of interbedded Garumniense limestones suggest similar sedimentary origins. However, these lacustrine oncolites, like modern counterparts described by others, probably developed through in situ metabolic precipitation of calcium carbonate. Evidence of this origin is their high degree of concentricity, which is unlikely to have developed through sedimentary accretion, inasmuch as the oncolites ‘float’ in quiet‐water marls.