Determination of the burrial temperature in the Ordovician of Thuringia and Scandinavia by means of conodont colour

Fuchs, Arnold

doi:10.1127/njgpm/1989/1989/390

Cited by 3 publications

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“…The Ponga-Cuera unit has a low-thermal history and widespread development of dissolution and neocrystallization conodont microtextures. In other areas these alterations have usually been related to dolomitization, deformation and/or hydrothermal fluids, with CAI ≥3 for the two latter processes (Rejebian, Harris & Huebner, 1987; Fuchs, 1989; Helsen, 1995, 1997; Janssen, Friedel & Paech, 1988; Königshof, 1992, 2003; Nöth, 1998; Königshof & Boncheva, 2005). In the present case, dolomitization and deformation can be rejected because the host rocks of all the conodont samples have always been unstrained limestones with low CAI values.…”

Section: Discussionmentioning

confidence: 99%

Conodont alteration and tectonothermal evolution of a diagenetic unit in the Iberian Variscan belt (Ponga-Cuera unit, NW Spain)

et al. 2010

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-Tectonothermal analysis of a mainly carbonate unit located in the external part of the Variscan orogen in NW Spain is dealt with using the conodont colour alteration index (CAI) and the study of textures of these microfossils. The Kübler index of the illite (KI) is used as a complementary method. The area is characterized by a great uniformity in the CAI values, which in most cases are < 2, indicating diagenetic conditions. In spite of the low CAI values, textures show great variety and were mainly originated by diagenetic processes of apatite dissolution and precipitation. The conodonts underwent a long period of heating (probably from the Pennsylvanian to the Cenozoic) to low temperatures (< 100• C) to reach the low CAI values measured. Assuming a normal geothermal gradient, these temperatures required an overburden < 3 km that in part was due to burial and in part to tectonic superimposition. Minor local anomalies in the CAI values and some textural alterations, related to dissolution and precipitation of authigenic minerals, could be due to epithermal activity that gave rise to various ore deposits in the studied area mainly during Permian times.

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