AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
An Integrated System for Macro-Scale Anhydrite
Classification
(1) Carbonate Research, Shell International Exploration and Production, Rijswijk, Netherlands.
Most anhydrite
classification systems to date have focused primarily on the naming of
anhydrite
bodies, masses, or crystals themselves rather than focusing on both the mineral morphology and links to the sedimentary succession in which it occurs. Much of the reasoning for the lack of development of an integrated classification system for
anhydrite
may come from the inherent instability of the mineral, and therefore the difficulty making a link between any particular morphology and a specific formative process or environment. This sets
anhydrite
classification apart from other sedimentary classification schemes, as most of them (e.g., Dunham, McBride, etc.) naturally break into groups that can be related to sorting, textural maturity, mode of deposition, or other genetic process. A classification system for
anhydrite
has been developed that allows for information about the gross
anhydrite
volume and morphology, as well as host sediment type to be transmitted using a single type-name.
This new integrated anhydrite
classification scheme was developed using input from both previously developed schemes and field studies with a view to link
anhydrite
morphology and volume to precursor depositional process. These relationships have been shown to hold true in certain circumstances, with both gross
anhydrite
volume and morphology many times being characteristics that are particular to former depositional setting (bedded, laminated salinic
anhydrite
versus nodular sabkha
anhydrite
, as an example). By adding a host rock descriptor to the scheme, quite a bit of empirical information about the
anhydrite
is made available in a single name, which can then be more easily linked to genetic process. Such a scheme may have wide application in industry, where careful description and classification of
anhydrite
is a key component to understanding the distribution of reservoir rock types in the subsurface.