Abstract
Apatite fission track (AFT) central ages from Carboniferous (Stephanian) tonsteins of the Sabero Coalfield, NW Spain, range from 140.8 ± 7.5 to 65.8 ± 8.1 Ma (Cretaceous), with mean c-axis projected track length values ranging from 12.5 to 13.4 μm. Mean random vitrinite reflectance (R r) of these samples ranges from 0.91 to 1.20 %, which can be translated into maximum palaeotemperatures of ca. 130 to 180 °C. All analysed samples experienced substantial post-depositional annealing. The considerably younger AFT ages compared to the depositional ages of the samples and R r data indicate the certainty of the occurrence of at least one heating event after the deposition of strata. The unimodal track length distributions, the relatively short mean track length, and the rather low standard deviation (SD) (1.0–1.6 μm) indicate a relatively simple thermal history that could be related to the post-Late Variscan heating event followed by prolonged residence in the apatite partial annealing zone (APAZ). Geological data combined with thermal models of AFT data indicate that Stephanian strata reached the maximum palaeotemperatures in the Permian period, which was therefore the major time of the coalification processes. The Permian magmatic activity was responsible for a high heat flow, which, with the added effect of sedimentary burial, could account for the resetting of the AFT system. It appears that the fault-related hydrothermal activity could have redistributed heat in areas of significant subsidence. Cooling occurred in the Triassic–Cretaceous times after a high heat flow Permian regime. A post-Permian maturation of the Stephanian organic matter is not very likely, since there is no evidence of a high Mesozoic burial that was sufficient to cause a significant increase in the palaeotemperatures. Finally, exhumation and associated erosion rates may possibly have been faster in the Tertiary, causing the present exposure of the studied rocks.
Highlights
At the end of the Variscan orogeny, several small coal basins developed along major structural lines (Colmenero and Prado 1993; Colmenero et al 2008) in what is the Cantabrian Mountain region of Northern Spain
This study examines the thermal history of one of these small basins (~12–15 km long and 3–4 km wide) located along the eastern end of the Sabero–Gordon fault line (Fig. 1) that contains the Sabero Coalfield (Heward and Reading 1980; Knight 1983; Knight et al 2000)
As little is known about the post-Variscan cooling history of this region (Carrière 2006; Grobe et al 2010), we conducted an apatite fission track (AFT) thermochronometry study to define the thermal history of the Late Carboniferous (Stephanian) sediments of the Sabero Coalfield
Summary
At the end of the Variscan orogeny, several small coal basins developed along major structural lines (Colmenero and Prado 1993; Colmenero et al 2008) in what is the Cantabrian Mountain region of Northern Spain These basins are considered to have initially formed as small pullapart basins along strike-slip fault systems under a Late Carboniferous syn-orogenic transtensional regime (Julivert 1971; Reading 1975; Heward and Reading 1980; Wagner and Winkler-Prins 1985; Alonso et al 1995; García-López et al 1997, 2007; Bastida et al 1999). The Sabero sedimentary sequence includes volcanic ash layers (tonsteins; Knight et al 2000; Botor 2005) that provide precise time–temperature reference points in the stratigraphy, essential for accurate thermal history reconstruction
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
