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Lacustrine carbonates and pedogenesis: sedimentology and origin of palustrine deposits from the Early Cretaceous Rupelo Formation, W Cameros Basin, N Spain
Author(s) -
PLATT NIGEL H.
Publication year - 1989
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.1365-3091.1989.tb02092.x
Subject(s) - geology , pedogenesis , facies , subaerial , paleontology , evaporite , carbonate , diagenesis , sedimentology , chemostratigraphy , geochemistry , sedimentary rock , isotopes of carbon , structural basin , total organic carbon , ecology , materials science , biology , soil science , metallurgy , soil water
The Berriasian Rupelo Formation of the W Cameros Basin consists of a 2–200 m thickness of marginal and open lacustrine carbonate and associated deposits. Open lacustrine facies contain a non‐marine biota with abundant charophytes (both stems and gyrogonites), ostracods, gastropods and rare vertebrates. Carbonate production was mainly biogenic. The associated marginal lacustrine (‘palustrine’) facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics. Silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history. The succession was laid down in a low gradient, shallow lake complex characterized by wide fluctuations of the shoreline. Carbon and oxygen stable isotope analyses from the carbonates show non‐marine values with ranges of δ 13 from − 7 to − 11‰and δ 18 from − 3 to − 7.5‰. Differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake. Analyses from the entire sample suite plot on a linear trend; isotopic compositions become lighter with increasing evidence of pedogenic modification. This suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil‐derived CO 2 . The stable isotope data thus support evidence from petrography and facies relations that ‘palustrine’limestones form through pedogenic modification of lake carbonates.