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Origin and migration of palaeofluids in the Upper Visean of the Campine Basin, northern Belgium
Author(s) -
MUCHEZ PHILIPPE,
MARSHALL JIM D.,
TOURET JACQUES L. R.,
VIAENE WILLY A.
Publication year - 1994
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.1365-3091.1994.tb01395.x
Subject(s) - geology , meteoric water , calcite , fluid inclusions , recrystallization (geology) , mineralogy , geochemistry , carboniferous , pseudomorph , petrography , structural basin , geomorphology , paleontology , quartz , hydrothermal circulation
Upper Visean limestones in the Campine Basin of northern Belgium are intensively fractured. The largest and most common fractures are cemented by non‐ferroan, dull brown‐orange luminescent blocky calcite. First melting temperatures of fluid inclusions in these calcites are around ‐57°C, suggesting that precipitation of the cements occurred from NaCl‐CaCl 2 ‐MgCl 2 fluids. The final melting temperatures ( T m ice ) are between ‐5 and ‐33°C. The broad range in the T m ice data can be explained by the mixing of high salinity fluids with meteoric waters, but other hypotheses may also be valid. Homogenization temperatures from blocky calcite cements in the shelf limestones are interpreted to have formed between 45 and 75°C. In carbonates which were deposited close to and at the shelf margin, precipitation temperatures were possibly in the range 70‐85°C and 72‐93°C, respectively. On the shelf, the calcites have a δ 18 O around ‐9.3‰ PDB and they are interpreted to have grown in a fluid with a δ 18 O between −3.5 and +1.0‰ SMOW. At the shelf margin, blocky calcites (δ 18 O∼ ‐ 13.5‰ PDB) could have precipitated from a fluid with a δ 18 O betweenn ‐4.0 and ‐1.1‰ SMOW. The highest oxygen isotopic compositions are comparable to those of Late Carboniferous marine fluids (δ 18 O= ‐ 1‰ SMOW). The lowest values are more positive than a previously reported composition for Carboniferous meteoric waters (δ 18 O= ‐7‰ SMOW). Precipitation is likely to have occurred in marine‐derived fluids, which mixed with meteoric waters sourced from near the Brabant Massif. Fluids with a similar negative oxygen isotopic composition and high salinity are actually present in Palaeozoic formations. The higher temperature range in the limestones near the shelf margin is explained by the upward migration of fluids from the ‘basinal’ area along fractures and faults into the shelf.