MUDSTONE AGGREGATES OF THE SECOND WHITE SPECKS AND CARLILE FORMATIONS IN EASTERN ALBERTA, AGGREGATE ORIGINS AND PALEO-ENVIRONMENT

Mudstone aggregates form the main detrital component of mudstone dominated strata of the Upper Cretaceous Second White Specks and Carlile formations. However, although they form a conformable succession, the formations were deposited in very different settings within the Interior Cretaceous Seaway. The Second White Specks Formation is comprised of organic rich mudstones with a large content of calcareous macrofossils micro fossils, and at several levels calcareous sandstone beds. In contrast, the Carlile Formation is comprised of commonly intensely bioturbated non-calcareous mudstones with a variable content of silt and sand sized silica grains, with the strata forming relative large mudstone clinoforms in contrast to the tabular stratal architecture of the Second White Specks strata. The mudstone aggregates are well-preserved in the studied strata due to the relative shallow maximum burial of approximately 1500-2000m. The aggregates occur as silt to sand sized particles with different composition, with the oval shape indicating they are only slightly compacted and that they were semi-indurated at the time of deposition. Potential origin of the mudstone aggregates includes extrabasinal grains, and or intrabasinal rip-up clasts or Crustacean micro-coprolite fragments. However, the presence of Cretaceous microfossils within the aggregates clearly demonstrated that the majority of the mudstone aggregates are intraformational, however their often different composition from the surrounding matrix mud show they were transported a significant distance from their site of origin to the depositional locality. Further, significant abrupt vertical changes in the grain size of the mudstone aggregates and their chemical composition shows that the area of origin or changes between dominantly intra-formation rip-up clasts to micro-coprolite changed, related to relative sea level changes. However, as individual sequence stratigraphic units often have relative uniform composition of the mudstone aggregates, and composition of the mudstone aggregates don’t seem to be strongly related to water depth but rather changes in circulation within the Interior Seaway.