Sedimentology and Carbonatogenesis of the Upper Campanian Limestones in Jebel Berda (South Central Tunisia)

The Upper Cretaceous (Campanian) Lea Park Formation of south-central Saskatchewan, a product of continuous deposition in the Claggett sea of the Western Interior basin, contains unusually well-preserved fossil shells ideally suited for analysis of their chemical and isotopic compositions.Although both ammonites and bivalves secreted shells in isotopic equilibrium with the waters in which they lived, ammonites usually have higher δ18O and lower δ13C values than coexisting bivalves. These values point to the ammonites and bivalves having inhabited isotopically distinct waters within the Claggett sea. The benthonic bivalve Inoceramus is inferred to have lived in a thin bottom layer, the isotopic composition of which was modified by that of pore waters expelled at the sediment–water interface following compaction of sediments. The nekto-benthonic ammonites Scaphites and Baculites are inferred to have lived mostly at successively higher levels in the water column, the isotopic composition of which was modified by an influx of meteoric waters.Variations in trace-element/Ca ratios in molluscan shells are attributed to changes in the chemical composition of the Claggett sea, with essentially constant 87Sr/86Sr ratios suggesting that most chemical variations resulted from processes operating within the basin rather than at mid-ocean ridges. Sr concentrations in the sea decreased during Lea Park deposition, presumably as a result of weathering of increased proportions of igneous rocks relative to carbonate rocks in the western sourcelands. Anomalous Mg/Ca ratios are present in molluscan shells at a biostratigraphically correlative level. These ratios are primary and attributed to weathering of Mg-rich igneous rocks on the western flank of the basin. Probably produced in less than 40 000 years, the anomalous Mg/Ca ratios may form a chemostratigraphic and chronostratigraphic marker for the correlation of upper Campanian rocks.

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Palygorskite genesis through silicate transformation in Tunisian continental Eocene deposits

Clay Minerals ◽

10.1180/0009855033820088 ◽

2003 ◽

Vol 38 (2) ◽

pp. 187-199 ◽

Cited By ~ 11

Author(s):

F. Jamoussi ◽

A. Ben Aboud ◽

A. López-Galindo

Keyword(s):

Rare Earth ◽

Chemical Composition ◽

Rare Earth Elements ◽

Clay Fraction ◽

Geochemical Characteristics ◽

North Central ◽

Textural Characteristics ◽

Central Tunisia ◽

South Central

AbstractThe mineralogical and geochemical characteristics of Eocene continental sediments in south central Tunisia (Chebket Bouloufa and Jebel Hamri) and in north central Tunisia (Jebel Lessouda and Jebel Rhéouis), which contain considerable amounts of palygorskite, were studied. The clay fraction of the sediments also comprises illite, kaolinite, Mg smectite and Al smectite, together with carbonates (calcite and/or dolomite), quartz, gypsum and feldspars, all of which are present in extremely variable proportions.The textural characteristics of the samples containing most palygorskite, as well as the chemical composition of the fibres and the contents of certain trace and rare earth elements suggest that the genesis of this fibrous clay is intimately linked to the diagenetic transformation of illite, mixedlayered minerals and/or Al smectite, as has also been observed in contemporaneous deposits in Morocco.

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