Hydrothermally influenced cementation of sandstone — An example from deeply buried Cambrian sandstones from Bornholm, Denmark Henrik Friis a, ⁎, René Lyng Sylvestersen b , Lars Nicolai Nebel c , Mette Lise Kjær Poulsen d , Johan Byskov Svendsen d a Department of Earth Sciences, Aarhus University, C.F. Møllers Allé 120, DK-8000 Aarhus C, Denmark b Fur Museum, Department of Natural History, Museum Salling, Nederby 28, DK-7884 Fur, Denmark c LN Informatik, Elmevej 6, DK-8300 Odder, Denmark d DONG Energy, Exploration and Production, Agern Allé 24-26, DK-2970 Hørsholm, Denmark abstract article info Article history: Received 5 September 2009 Received in revised form 6 January 2010 Accepted 5 March 2010 Available online 15 March 2010 Communicated by G.J. Weltje Keywords: Quartz cement CL-zonation in quartz Hydrothermal cementation Cambrian sandstones on Bornholm (Denmark) are tightly cemented by quartz. Cementation occurred after deep burial as evidenced by a very strong compaction, partly mediated by intensive grain fracturing. The quartz cement has a complex cathodoluminescence (SEM-CL)-zonation which is related to variable substitution of Al in the quartz lattice. Based on the substitution pattern and SEM-CL-zonation, three phases of quartz growth can be identified. Phase 1 cement has a low SEM-CL-level and its volume corresponds approximately to the estimated volume of press-solved detrital quartz. It is related to the late compaction. Phase-2 cement is the volumetrically most important. It has an intricate SEM-CL-zonation and associated Al- substitution. It is referred to hydrothermal activity related to the Permo–Carboniferous magmatic and tectonic event. The cementation gradually reduced the influence of hydrothermal flow, and late Phase-3 cement has a low-intensity and more simple SEM-CL-pattern. The almost fully cemented sandstone was fractured and the fractures were filled by hydrothermal chlorite, sulphides and quartz. These minerals are also found sporadically as cement in the sandstones. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Quartz cement is an almost universal component in quartz rich sandstones, but the sources of silica and the timing of cementation may vary much from sandstone to sandstone. Many studies have identified internal sources like heterogeneously distributed pressure dissolution of detrital quartz (for example Molenaar et al., 2008), or reorganization of biogenic silica (Hendry and Trewin, 1995). Semi- internal silica sources (such as migration from interbedded shale) have also been introduced (Thyne, 2001; Molenaar et al., 2007; Stokkendal et al., 2009). Large scale import from external sources is advocated in many studies because of an apparent lack of reliable internal sources (Sullivan et al., 1997; Warren and Pulham, 2001). Although large scale mobility during burial diagenesis is supported by chemical data (Milliken et al., 1994) mechanisms for large scale import of silica has been strongly questioned (Bjørlykke, 1994; Ramseyer et al., 1999). Archer et al. (2004) argue for focused flow in fault systems as a mechanism for basin scale diagenetic transfer. A comprehensive review of the controversial points is given by Worden and Morad (2000). The Cambrian sandstones on Bornholm (Nexø Sandstone and Hardeberga Sandstone) are known to be strongly cemented by quartz (Hansen, 1936) resulting in very low porosity at present, although the timing of quartz cementation is somewhat debated. Buchardt et al. (1997) suggest that the quartz cementation preceded the oil generation of the overlying Alum Shale Formation, and therefore outdates the deepest burial of the sandstones, whereas Møller and Friis (1999) suggest that the Lower Cambrian sandstones were oil reservoirs before the final quartz cementation and that open porosity was still present at the time of deepest burial of the sandstones. The diagenetic history has partly been described by Møller and Friis (1999). We interpret the deep burial quartz cement in these Cambrian sandstones as caused by invasion of hydrothermal fluids from major fault systems. As a result, the major quartz cement phase is characterised by a complex SEM-CL-pattern (Scanning Electron Microscope Cathodoluminescence) and abnormal Al-substitution. We hope that this study may contribute to the identification of hydrothermal influence on diagenesis. Sedimentary Geology 227 (2010) 11–19 ⁎ Corresponding author. E-mail addresses: henrik.friis@geo.au.dk (H. Friis), rlsy@museumsalling.dk (R.L. Sylvestersen), lnn@lninformatik.dk (L.N. Nebel), mkpou@dongenergy.dk (M.L.K. Poulsen), jbs@dongenergy.dk (J.B. Svendsen). 0037-0738/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2010.03.002 Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo