Compaction Properties of Fine-Grained Carbonate Sediments and Implications for the Bone Spring and Cutoff Formations

Hurd, Gregory S.; Kerans, Charles; Flemings, Peter; Schneider Reece, Julia; Janson, Xavier

Compaction of carbonate mud (clay- and silt-sized particles) has been cited by a number of workers as a primary cause of rotational subsidence, synsedimentary fractures, and unconformities created by differential compaction. These interpretations are based primarily upon studies that analyze sediments with unknown stress histories. Consequently, many fundamental questions remain unanswered. How much can carbonate mud compact? How does compaction affect the mechanical properties of carbonate mud? What visual observations can be related to changes in overburden stress? What is the relationship between porosity, permeability, and overburden stress? This study aims to answer these questions by producing reconstituted samples of modern carbonate mud and loading them in a laboratory setting. Using resedimentation techniques, we produced homogenous samples with known stress histories. We have compacted these samples using methods of incremental loading and constant rate of strain as outlined by the American Society for Testing and Materials. Our study demonstrates that reconstituted samples of carbonate mud may compact up to ~60% of their initial volume during the first few meters of burial, and compact to ~81% of their initial volume within the first few thousand meters of burial. We explore the relationships between porosity, permeability, unconfined compressive strength, and overburden stress in our experiments. We also use scanning electron and thin section microscopy techniques in order to investigate how compaction affects the fabric of carbonate sediments. Comparing these results to experiments performed on siliciclastic sediment with a comparable grain size distribution allows important results. I hypothesize that carbonate mud compacts differently than siliciclastic mud due to differences in grain shape. We hypothesize that a lower surface area per mass ratio allows carbonate mud to retain a higher initial porosity relative to siliciclastic mud in an uncompacted state. As a result, the loss of initial volume during compaction may be more substantial in carbonate mud compared to siliciclastic mud. We also present observations from our outcrop studies of the Permian-Age Bone Spring and Cutoff Formations. We will demonstrate how data from our compaction experiments can be used in order to improve our interpretation of these formations.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013