Chemical diagenetic constraints on the timing of cataclasis in deformed sandstone along the Pine Mountain overthrust, eastern Kentucky

Abstract

Cathodoluminescence imaging reveals that sandstones of the middle Pennsylvanian Lee Formation and Breathitt Group along the Pine Mountain Overthrust (PMO) contain inter- and intra-granular authigenic quartz in proportions that differ markedly between samples of contrasting deformational state. Fracture surfaces generated during fault movement provided nucleation substrates favorable for the emplacement of substantial amounts of intragranular quartz (up to 11 volume percent in the Lee Formation). Relatively undeformed sandstones contain cement that is dominantly intergranular whereas sandstones from highly deformed cataclasites along the trace of the PMO contain cement that is dominantly localized within intragranular fractures. Therefore, the chemical diagenetic histories of different samples of Breathitt and Lee sandstones diverged markedly as a consequence of differing deformational histories and the cementation history thus constitutes a record that is relevant to deciphering the timing of deformation.The small quantities of early-formed, intergranular cement within the cataclasites (average 3.7 volume percent), show evidence of breakage and accordingly, must have largely pre-dated the deformation. Quartz cementation modeling (Touchstone™) suggests that emplacement of this pre-deformational intergranular cement within these deformed rocks can be bracketed within a period from approximately 280 to 260 Ma. An interpretation of fault movement that shortly post-dates this initial period of quartz cementation is consistent with other estimates for the timing of the Alleghanian orogeny. Because of their protracted period of burial, rocks in the vicinity of the PMO remained at temperatures amenable to continued quartz cementation until the middle Cenozoic, and thus, most of the quartz cementation in the cataclasites and also in the surrounding undeformed sandstones post-dates movement on the fault.