Controls on paleokarst heterogeneity. Integrated study of the Upper Permian syngenetic karst in Rattlesnake Canyon, Guadalupe Mountains, USA

Abstract

The present study contributes to a better understanding of early dissolution mechanisms for syngenetic karst development and provides constraints on the timing of formation of the Rattlesnake Canyon paleokarst system in the Guadalupe Mountains, New Mexico, U.S.A. Paleozoic paleokarsts commonly undergo burial and collapse, which reduces significantly the preservation of early fracture networks and geometries of dissolution. Rattlesnake Canyon constitutes a magnificent scenario for the study of global controls on Upper Permian karsting since early fracture networks and dissolution geometries are extremely well preserved and lack major tectonic deformation.

This thesis sheds light on the scientific knowledge of paleokarsts and can be of interest to the oil industry since paleokarsts are common targets of exploration. As the evolution of the reservoir properties is often diagenetically controlled, the diagenetic study was particularly useful in determining the degree of sealing following hydrocarbon charge.

1) Aims

This thesis seeks to improve our understanding of the relationship between early syndepositional fracture networks that are typically found in platform margins and syngenetic karst development.

The thesis includes multidisciplinary carbonate studies aimed at understanding the multiscale paleokarst heterogeneity by means of (i) the development of a conceptual model for the karst evolution, (ii) the construction of a 3D paleokarst model, (iii) the determination of the diagenetic history of the paleokarst system and (iv) the paleokarst reservoir characterization.

2) Thesis Structure

The thesis consists of 9 chapters and 2 appendices. Chapter 1 sets out the rationale for this thesis. Chapter 2 provides an introduction to the most basic aspects of karst science and to the hydrogeological model of Carbonate Island as well as an overview of the state-of-the-art paleokarst studies. The geological setting and the study area is detailed in Chapter 3.

The results of the thesis are contained in Chapters 4 to 7. Because of the multidisciplinary nature of this thesis, each of these chapters is dedicated to one discipline. Chapter 4 focuses on the analysis of field data to obtain a conceptual model for the evolution of the paleokarst system. Chapter 5 discusses the methodology to implement the 3D paleokarst model and provides data to assess the dimensions of the system in subsurface. Chapter 6 focuses on the diagenetic stages that affected and controlled the karst development. Finally, Chapter 6 offers a paleokarst reservoir characterization. A comprehensive approach and discussion of the results obtained in each of these chapters are included in Chapter 8. General and specific conclusions are presented in Chapter 9. Appendix One contains a representative image compendium of the petrographic features observed in the paleokarst filling sequence of Fault N. Appendix Two sets out the raw data from the geochemical analysis.

The paleokarst analysis using different disciplines provides a complete characterization of paleokarst heterogeneity and enables us to elucidate the controls of the system.

Aquesta tesi contribueix al coneixement dels mecanismes de dissolució que controlen el desenvolupament dels karsts singenètics i proporciona les claus per establir la seqüència de formació del sistema paleokàrstic de Rattlesnake Canyon, Guadalupe Mountains, New Mexico, EEUU. Degut al potencial com a reservori que tenen aquest tipus de sistemes, aquesta tesi no solament concorre al coneixement científic en relació als paleokarsts sinó que també pot ésser d’interès per la indústria del petroli.

a) Objectius

Aquest estudi cerca contribuir en el coneixement de les relacions entre les falles i fractures sindeposicionals i les estructures de dissolució a Rattlesnake Canyon, així com en el coneixement dels controls globals per la formació de karsts singenètics costaners.

La tesi inclou estudis multidisciplinaris dirigits a la determinació de la heterogeneïtat multi-escala del paleokarst de Rattlesnake Canyon mitjançant els següents objectius concrets: a) l’acompliment d’un model conceptual d’evolució del sistema kàrstic, b) la construcció d’un model 3D del sistema kàrstic, c) la determinació de la història diagenètica del paleokarst i d) la caracterització de les propietats de reservori del sistema.