the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Silica diagenesis-driven fracturing in limestone: an example from the Ordovician of Central Pennsylvania
Emily M. Hoyt
John N. Hooker
Abstract. Fracture patterns, interactions, and crosscutting relationships are tools for interpretation of fractures as paleostress indicators for past tectonic events and as past or present-day fluid-flow networks. In the Appalachian Basin in Central Pennsylvania along Mount Nittany Expressway Route 322 lies a significantly stratified fracture set hosted in Ordovician age limestone. Tectonic strain is a problematic mechanism for these fractures because they are hosted in individual beds lacking apparent mechanical significance relative to other limestone beds in the outcrop. Many of the fractures are layer-parallel, a characteristic commonly observed in shales, due to shales' mechanical anisotropy and tendency to develop fluid overpressures; however, these fracture-hosting limestones lack obvious mechanical anisotropy. Fracture orientations vary, but desiccation, bentonite swelling, and dolomitization are eliminated by an interpreted transgressional paleoenvironment and a deficiency of the hypothesized minerals.
X-ray diffraction determined the composition of samples collected, point-count quantification determined fracture intensity, and optical petrography recorded scaled petrographic photographs. Comparison between fracture intensity and host-rock minerals reveal that silica content is consistently depleted in fractured layers relative to unfractured layers. The diagenetic transition of biogenic silica to quartz is suggested to be the driving mechanism based on silica being present as biogenic grains, as well as cement and detrital grains, and fractures being filled with calcite cement. Silica migration explains the volume lost from fractured layers in a proposed horizontal fracturing mechanism whereby the host rock shrinks but is excluded from vertical contraction.
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Emily M. Hoyt and John N. Hooker


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RC1: 'review of silica-diagenesis driven fracturing', Anonymous Referee #1, 20 May 2020
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SC1: 'Referee 1 preliminary response', John Hooker, 22 Jun 2020
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AC2: 'Short comment is from the authors', John Hooker, 03 Jul 2020
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SC1: 'Referee 1 preliminary response', John Hooker, 22 Jun 2020
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RC2: 'Minor revision', Vincenzo Guerriero, 19 Jun 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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RC3: 'Point Quantification', Vincenzo Guerriero, 19 Jun 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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RC4: 'Vertically pinned rock layer', Vincenzo Guerriero, 19 Jun 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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RC5: 'Point Quantification', Vincenzo Guerriero, 20 Jun 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
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AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020


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RC1: 'review of silica-diagenesis driven fracturing', Anonymous Referee #1, 20 May 2020
-
SC1: 'Referee 1 preliminary response', John Hooker, 22 Jun 2020
-
AC2: 'Short comment is from the authors', John Hooker, 03 Jul 2020
-
SC1: 'Referee 1 preliminary response', John Hooker, 22 Jun 2020
-
RC2: 'Minor revision', Vincenzo Guerriero, 19 Jun 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
RC3: 'Point Quantification', Vincenzo Guerriero, 19 Jun 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
RC4: 'Vertically pinned rock layer', Vincenzo Guerriero, 19 Jun 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
RC5: 'Point Quantification', Vincenzo Guerriero, 20 Jun 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
-
AC1: 'Preliminary response to Dr. Guerriero', John Hooker, 03 Jul 2020
Emily M. Hoyt and John N. Hooker
Emily M. Hoyt and John N. Hooker
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