Morphology and origin of erosion surfaces in the Cardium Formation (Upper Cretaceous, Western Interior Seaway, Alberta) and their implications for rapid sea level fluctuations

Abstract

The morphology of three basin-wide erosion surfaces has been defined using 7869 resistivity well logs, over an area of about 50 000 km2. The lowest of these, designated E6, is topographically smooth, and has no incised steps or low areas. It cuts into marine mudstones, and indicates either an uninterrupted erosive transgression following a major lowering of relative sea level, or wave scouring of the substrate following a very minor lowering of sea level. Erosion surface E6.5 also cuts into marine mudstones, but its overall morphology is less well understood owing to subsequent dissection by surface E7. This surface (E7) is characterized by three strike-parallel linear low areas that die out northwestward. These linear lows are up to 40 km wide, 36 m deep, and have irregular to symmetrical cross-sectional profiles. They cut into, and are filled with, marine mudstones, and their origin is enigmatic. The differences in the morphologies of the surfaces suggest the interplay of several controlling parameters: (i) steady transgression versus transgression interrupted by stillstands; (ii) absolute depth of erosion during transgression, which in turn controls the preservation or erosion of incised river valleys; (iii) wave scouring of substrate in response to minor lowerings of sea level; and (iv) availability of coarse sediment and river gradients steep enough for its transport to the shoreline. The average time span between erosion surfaces is 300 000 – 350 000 years. This timing is hard to explain tectonically, or in terms of global eustacy, suggesting the possibility of glacio-eustatic control of fluctuations in relative sea level.

Sequence stacking patterns in the Western Canada foredeep: influence of tectonics, sediment loading and eustasy on deposition of the Upper Cretaceous Kaskapau and Cardium Formations

“…4), and also the nine allomembers in the overlying Cardium Formation (summarized from Plint et al. , 1986, 1988; Hart, 1990; Wadsworth & Walker, 1991; Hart & Plint, 1993b, 2003). Figure 5 is divided by a vertical line that separates observed spatial relationships, to the right, from interpolated relationships to the left.…”

“…, 1986). A subsequent study by Hart (1990) showed that below the ‘E1’ surface, the ‘E0’ and ‘GS’ surfaces could also be mapped, and Wadsworth & Walker (1991) showed that surface ‘E6·5’ was locally preserved. In the present paper, the nine Cardium allomembers bounded between the ‘GS’ and ‘E7’ surfaces are designated ‘C1’ to ‘C9’ to differentiate them from the 28 allomembers of the underlying Kaskapau Formation (Fig.…”

Chapter 1: Integrated, High-Resolution Allostratigraphic, Biostratigraphic and Carbon-Isotope Correlation of Coniacian Strata (Upper Cretaceous), Western Alberta and Northern Montana

“…The E7 surface separates the Cardium Formation from the overlying Muskiki Member, and constitutes a prominent and robust stratigraphic marker across the basin. In the vicinity of the foothills and in the adjacent subsurface, E7 has up to several tens of meters of erosional relief in the form of NW-SE elongate, NE-facing "steps" (e.g., Wadsworth and Walker, 1991). In consequence, the thickness of rock between E7 and overlying surfaces CS1 and CS2 can vary dramatically, reflecting the progressive onlap and burial of preexisting topography by lower Muskiki sediments.…”

Interactions climat-eustatisme-tectonique. Les enseignements et perspectives du Crétacé supérieur (Cénomanien-Coniacien)

“…Neanmoins, I'intervalle de temps moyen ecoule entre les surfaces d'erosion est compris entre 300 000 et 350000 ans. Cette chronologie est difficile a expliquer tectoniquement ; les variations du niveau marin a haute frequence seraient ici controlees par glacio-eustatisme [23]. Dans cet exemple est mis en evidence Ie role d'oscillations du niveau marin ahaute frequence sur une composante basse frequence transgressive, accompagnee d'une activite tectonique.…”

“…Le developpement de episodes de regression forcee que I'on enregistre a la limite Cenomanien-Turonien, ainsi que les creu ements et remplissages de vallees de la limite Turonien-Coniacien pourraient trouver leur explication dans des variations rapides du niveau marin sous la dependance d'un mecanisme glacio-eustatique. Ce type de controle a deja ete suggere pour ces exemples [2,23,135] com me pour d'autres [22,26,109,136,137]. Meme si les evidences directes de glaciations manquent pour Ie Cretace superieur, il semble que cette hypothese ne doive pas etre totalement eJiminee ; il faut en effet reconnaltre que nous sommes la dans un champ de recherches relativement vierge.…”