Factors controlling the genesis of FeMn crusts in stratigraphic breaks of the eastern Betic Cordillera (SE Spain) deduced from numerical analysis of geological data
✍ Scribed by R. Jiménez-Espinosa; J. Jiménez-Milĺan; L. Nieto
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 759 KB
- Volume
- 114
- Category
- Article
- ISSN
- 0037-0738
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✦ Synopsis
Fe-Mn crusts occur in four stratigraphic breaks of Jurassic pelagic swell sequences in the eastern Betic Cordillera. Crusts were characterized by quantitative and qualitative variables deduced from their stratigraphic position (under-and overlying lithologies), texture (thin or banded), mineralogical and chemical composition. Quantitative chemical variables were summarized in two new variables using principal component analysis. Component A groups detrital elements, and Fe with chalcophile elements, which suggests a seawater enrichment by detrital and hydrothermal contributions. Component B associates elements of hydrogenous precipitation and adsorption during exposure of Fe-oxide to the seawater. Relations between quantitative and qualitative variables were established by the use of correspondence analysis. Variables form two groups: TX1 (variables representing thin crusts, type I) and TX2 (banded crusts, type II). Thin crusts are related with chemical variables denoting high detrital element contents (A1), low Mn, REE, and transition metal element contents (B3), presence of detrital minerals (DET) and Mn-Co-poor goethite (GT). Banded crusts are associated with variables representing low detrital element contents (A2, A3), high Mn, REE, and transition metal element contents (BI, B2), presence of Mn-Co-rich goethite (MNG), Mn-oxyhydroxides (MNO), and REE-phosphates (PH). These associations indicate that, in the type II crusts, adsorption processes have a greater importance than in the type I crusts. Correspondence analysis helps to clarify the geological variables determining the extent of the adsorption processes, since variables related with textural type I are associated to lithological variables (OCL: overlying cherty limestones; UML3: underlying thick rhythmite of marls and limestones) indicating a geological context of pelagic swell slightly deeper than those associated with the textural type II (UCC: underlying crinoidal calcarenite; UMLI: thin underlying marl-limestone rhythmite).