Title

Preliminary analysis of grain-scale rock fabrics within the Carboniferous Namurian Basin; County Claire, western Ireland.

Poster Number

16B

Lead Author Major

Geology

Lead Author Status

5th year Senior

Second Author Major

Geology

Format

Poster Presentation

Faculty Mentor Name

Kurtis Burmeister

Faculty Mentor Email

kburmeister@pacific.edu

Faculty Mentor Department

Geological and Enviromental Sciences

Abstract/Artist Statement

A preliminary analysis of penetrative grain-based and magnetic fabrics in samples collected within the Namurian Basin suggests that the rocks were deformed by tectonic convergence associated with the Variscan orogeny in all but one location. Five samples were collected along a south (nearest to a collisional mountain belt) to north (towards the undeformed continental interior) transect across the Loop Head Peninsula. Analysis of fabrics defined by the shape and alignment of grains within these samples was conducted using petrographic microscopes and the EllipseFit computer program. The results of this analysis suggests the rocks accumulated very low amounts of penetrative strain (εs values of less than 0.2). The southernmost sample (1) is from the Ross Formation at Killbaha Bay, and is the only sample that contains a weak prolate fabric likely associated with tectonic convergence. Remaining samples were collected from the Ross Formation (at Ross Bay and Bridge of Ross) the Tullig (at Killard Bay), and Killkee Formations (at Quilty) and all have well developed flattening fabrics that are likely associated with deposition and compaction. To better understand these grain-based fabrics, we also used the anisotropy of magnetic susceptibility to analyze the alignment of magnetic minerals within the samples. The results of our AMS analysis seem to contradict our measured grain-based fabrics in that Samples 1 and 2 (both from the Ross Formation), 4 (from the Tullig Formation), and 5 (from the Kilkee Formation), have magnetic minerals that are prolate and indicative of elongation during the Variscan orogeny. While sample 3 (from the Ross Formation) contains a flattening fabric, and does not appear to have accumulated any tectonic strain. These observed differences between the grain-based and magnetic fabrics could be associated with several factors, including the ability to define grain boundaries when conducting the grain-based analysis and our interpretation of the magnetic mineralogy responsible for carrying the measured AMS fabrics.

Location

DeRosa University Center, Ballroom

Start Date

29-4-2017 1:00 PM

End Date

29-4-2017 3:00 PM

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Apr 29th, 1:00 PM Apr 29th, 3:00 PM

Preliminary analysis of grain-scale rock fabrics within the Carboniferous Namurian Basin; County Claire, western Ireland.

DeRosa University Center, Ballroom

A preliminary analysis of penetrative grain-based and magnetic fabrics in samples collected within the Namurian Basin suggests that the rocks were deformed by tectonic convergence associated with the Variscan orogeny in all but one location. Five samples were collected along a south (nearest to a collisional mountain belt) to north (towards the undeformed continental interior) transect across the Loop Head Peninsula. Analysis of fabrics defined by the shape and alignment of grains within these samples was conducted using petrographic microscopes and the EllipseFit computer program. The results of this analysis suggests the rocks accumulated very low amounts of penetrative strain (εs values of less than 0.2). The southernmost sample (1) is from the Ross Formation at Killbaha Bay, and is the only sample that contains a weak prolate fabric likely associated with tectonic convergence. Remaining samples were collected from the Ross Formation (at Ross Bay and Bridge of Ross) the Tullig (at Killard Bay), and Killkee Formations (at Quilty) and all have well developed flattening fabrics that are likely associated with deposition and compaction. To better understand these grain-based fabrics, we also used the anisotropy of magnetic susceptibility to analyze the alignment of magnetic minerals within the samples. The results of our AMS analysis seem to contradict our measured grain-based fabrics in that Samples 1 and 2 (both from the Ross Formation), 4 (from the Tullig Formation), and 5 (from the Kilkee Formation), have magnetic minerals that are prolate and indicative of elongation during the Variscan orogeny. While sample 3 (from the Ross Formation) contains a flattening fabric, and does not appear to have accumulated any tectonic strain. These observed differences between the grain-based and magnetic fabrics could be associated with several factors, including the ability to define grain boundaries when conducting the grain-based analysis and our interpretation of the magnetic mineralogy responsible for carrying the measured AMS fabrics.