Abstract
Tectonic stylolites are indicators of compressive deformation episodes in rocks and are commonly studied in terms of their geometrical attributes’ length (L), and maximum (D max ) and average (D avg ) amplitudes. These parameters were analyzed for vertical stylolites from a sinistral strike-slip fault zone in limestones from the Guia Formation, Paraguay Belt, and compared mathematically to scarce vertical stylolites away from the fault zone. The study aimed to understand the role of strain-induced stylolites on the thinning of faulted limestone layers. Stylolites range from 2.66 up to 28.15 mm in length and from 0.143 up to 1.378 mm in amplitude. The total contractional strain (ϵ) was calculated for 49 stylolites with maximum amplitude peaks of 0.762 mm, using the Kostrov formula. The strain produced layer thinning and growth of the stylolite population. Regions of high stylolite concentration accommodated 16.92% contractional strain, whereas strain values of 3.29% are present in portions with low stylolite density. Layer thinning is directly proportional to contractional strain (ϵ) values spatially induced by faulting. The stylolite morphology plays an essential role in the permeability structure at the reservoir scale, where it can act as a barrier or a channel for fluid flux.
Highlights
Deformation structures in rocks are an essential source of information to understand the tectonic history of a region
A quantitative analysis of stylolites, investigating the displacement-length relationship according to morphological measurements, improved the comprehension of stylolites development and the amount of contractional strain in carbonates in the wallrock of a sinistral strike-slip fault
Our findings agree with previous work on stylolite-related contractional strain (Benedicto and Schultz 2010), statistical analyses of stylolite morphology (Karcz and Scholz 2003, Peacock and Azzam 2006), and numerical simulations of stylolite growth (Koehn et al 2007)
Summary
Deformation structures in rocks are an essential source of information to understand the tectonic history of a region. The study of microstructures helps to comprehend the deformation processes that affect rocks in two ways: to understand the mechanism(s) of deformation and to reconstruct the deformational framework (Passchier and Trouw 2004). Stylolites are structures present in fine-grained rocks, in calcareous rocks (Dunnington 1954, Park and Schot 1968, Railsback 1993, André 2010, Rolland et al 2012, 2014, Koehn et al 2016). Stylolites exhibit teeth-like structures along their length, whose peaks relate to the magnitude of the stress they have undergone (Koehn et al 2012, Ebner et al 2009). The history of deformation is interpreted as the result of progressive deformation during a transpressional-transtensional episode from the Neoproterozoic up to the Cambrian (Santos et al 2020)
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