Siliciclastic Sandstone Diagenesis: Are Existing Models Correct?

Dear Colleagues,

Geology is an exact science that is dependent on past and present observations. These observations, however, provide subjective results and interpretations that are biased by the observer. This has changed in recent decades because of the increasing number of analytical techniques and digital measuring methods for laboratory and field applications. Since the beginning of this century, overwhelming amounts of quantitative and semi-quantitative data have become available for geological interpretation. In particular, for sedimentary petrography and diagenetic studies of sandstone shales, this should have consequences. In reality, many of the models dating from the 1950s or 1960s are still followed. Thus, it seems that geological science is quite conservative and lethargic. Models and paradigms, and even the routines for deriving models, have remained largely the same.

Science should not only be innovative and embrace new types of data for better interpretations but must also include the scrutiny of existing models. The latter should be questioned, tested and, if necessary, improved or replaced by models that better explain the observations and analytical data. The existing diagenetic models are still not capable of predicting the behavior of sediments and sedimentary rocks and their properties for hydrocarbon and geothermal applications, as well as for heat, CO₂, and H₂ storage. Therefore, it is time for retrospection. The wealth of new analytical data, not only in terms of quantity but also increased quality, allows retrospection and the questioning and testing of the existing models.

The new models, analytical techniques, and their results need to be critically approached. All too often, new techniques are applied on a large scale, but the proper deliberation of their use is often neglected. Technically, the methods will be correct, but what does the resulting data actually mean? During burial, the physical and chemical conditions are constantly changing, resulting in mechanical and chemical reactions between the sediment and sedimentary rock. The latter changes are caused by the interaction between susceptible sedimentary and diagenetic components with the interstitial fluids. These changes make interpretations of mineralogical assemblages and the chemical and isotopic compositions of mineral components difficult, if not impossible. Even if they are correct, does this lead to improvement in the predictive power of diagenetic models?

Until now, sandstone diagenesis has been case-specific, with an explanatory model, paragenesis, and a set of underlying factors for each case. If this is correct, any predictive power of the models, including the lateral and vertical extrapolation of measured properties within single sediment bodies and basin fills, will remain elusive. On the other hand, maybe the current approach is, at least partly, wrong.

Amongst the topics to deal with are the following:

• Diagenetic paragenesis or timing of diagenetic processes (e.g., the dissolution of detrital components or methods).
• Changes in mineral assemblages (e.g., the pelletization or chlorination of smectites or kaolinite).
• Minerals assemblages, diagenetic effects, and provenance.
• Microquartz
• Geochemical data (SEM-EDS, Microprobe, ICP-MS, etc.).
• Stable isotope data.
• Fluid inclusion data.

Dr. Nicolaas Molenaar
Prof. Dr. Georgia Pe-Piper
Guest Editors

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• sandstone diagenesis
• controversies
• scrutiny of models
• alternatives