About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
CSPG Bulletin
Abstract
Marginal Marine Sedimentology and High Resolution Sequence Analysis; Bearpaw - Horseshoe Canyon Transition, Drumheller, Alberta
ABSTRACT
The 60m thick, Upper Cretaceous (Campanian - Maastrichtian) Bearpaw - Horseshoe Canyon transition zone is exposed in three-dimensions along the Red Deer Valley and its tributary Willow Creek, near Drumheller, Alberta. These clastic marine to marginal marine deposits represent shoreface, fluvio-estuarine, lagoonal and coastal plain environments. These deposits are divided into seven, informal allomembers (A to G), each of which contains a transgressive and regressive phase. Allomembers are defined by marine and brackish flooding surfaces which commonly occur above thin (0.3 to 2 m) coal seams. Erosional relief along these surfaces is minimal.
During regressive phases prograding sharp-based shorefaces (sometimes indicative of forced regressions) are deposited in the marine realm while nonmarine settings are characterized by non-deposition. Fluvial incision is associated with shoreline regression in allomembers A, C and D. Depositional records of transgressions in the marine realm are thin or absent. In nonmarine settings, however, transgressive deposits may attain substantial thicknesses where marine-influenced deposits infill some incisions and initially coals and then back-barrier/lagoonal deposits accumulate behind retreating barrier systems. The sharp, basal contacts of the coals with the underlying shoreface or back-barrier deposits represent the turnaround points from regressive to transgressive conditions. The overall succession represents a seaward-stepping or regressive system.
Estimated amounts of sea level change within each allomember range from approximately 4 to 12 m. Transgressive/regressive units have an estimated fourth order periodicity of 140,000 years.
Sequence analysis of the succession suggests that in terms of Exxon sequence stratigraphy, it may be subdivided in two ways depending upon the degree of resolvable detail applied. Application of high resolution sequence stratigraphic techniques suggest that the succession can be divided into three discrete, high frequency (4th order) sequences which constitute part of a third order composite sequence. Within these high frequency sequences, transgressive, highstand and a newly-proposed 'Falling-stage Systems Tract' (FST) are recognised. Alternatively, if high resolution details are ignored (e.g., in a seismic study), the succession may be regarded as part of one, third order sequence exhibiting transgressive and highstand systems tracts. However, because of the problems involved with applying Exxon sequence stratigraphy, Genetic sequence stratigraphy and T-R sequence stratigraphy on such a high resolution scale, allostratigraphic subdivision of the strata is preferred due to its simple application and flexibility.
RESUME
La zone de transition Bearpaw-Horseshoe Canyon du Cretace superieur (Campanien-Maastrichtien), d'une epaisseur de 60m, est exposee dans en trois dimensions le long de la vallee de la Red Deer et de son tributaire Willow Creek, pres de Drumheller, Alberta. Ces depots clastiques, marins a marins cotiers, representent les milieux suivants : zone infratidale ("shoreface"), fluvio-estuarien, lagunaire et plaine cotiere. Ces depots sont divises en sept allomembres officieux (A a G), chacun comprenant une phase transgressive et une phase regressive. Les allomembres sont definis par des surfaces d'inondation marines et saumatres qui se retrouvent habituellement au-dessus de minces (0,3 a 2m) filons houillers. Le relief d'erosion le long de ces surfaces est minimal.
Durant les phases regressives des depots a base nette de la zone infratidale, en progression vers la mer (indicatifs quelques fois de regressions forcees), sont formes dans le domaine marin alors que les milieux non-marins sont caracterises par l'absence de sedimentation. Le ravinement fluviatile est associe a la regression de la ligne de rivage dans les allomembres A, C et D. Les depots de transgression dans le domaine marin sont minces ou absents. Par contre, dans les contextes non-marins, les depots de transgression peuvent atteindre des epaisseurs importantes ou les depots a influence marine remblaient certains ravins, et d'abord des filons houillers puis des depots d'arriere-crete d'avantplage immergee/de lagune s'accumulent derrieres des systemes de barriere en retrait. Le contact net de la base des
End_Page 26-------------------------
filons houillers avec les depots de zone infratidale ou d'arriere barriere sous-jacents represente le point tournant entre conditions regressives et transgressives. La succession dans son ensemble represente un systeme en migration vers la mer ou regressif.
Une estimation de la quantite de changement du niveau de la mer a l'interieur de chaque allomembre varie entre a peu pres 4m et 12m. Les unites transgressives/regressives ont une periodicite de quatrieme ordre evaluee a 140,000 annees.
L'analyse sequentielle de la succession suggere qu'en termes de stratigraphie sequentielle au sens d'Exxon, elle peut etre divisee de deux manieres, dependant du degre de detail resoluble applique. L'application de techniques de stratigraphie sequentielle a haute resolution suggere que la succession peut etre divisee en trois sequences a haute frequence (4ieme ordre) distinctes qui constituent une partie d'une sequence de troisieme ordre composee. A l'interieur de ces sequences a haute frequence, des sequences transgressives, de haut niveau ("highstand") et le nouvellement-propose "Cortege de depot relies a la phase d'abaissement du niveau marin" ("Falling-stage System Tract (FST)") sont reconnus. Comme alternative, si les details a haute resolution sont ignores (par exemple, dans une etude sismique), la succession peut etre consideree comme faisant partie d'une sequence de troisieme ordre montrant des corteges de depot de transgression et de haut niveau ("transgressive and highstand systems tracts"). Par contre, a cause des problemes avec l'application de la stratigraphie sequentielle d'Exxon, la stratigraphie sequentielle genetique et la stratigraphie sequentielle T-R sur une telle echelle a haute resolution, la subdivision allostratigraphique des strates est preferable a cause de son application simple et de sa flexibilite.
Traduit par Marc Charest.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
Watermarked PDF Document: $14 | |
Open PDF Document: $24 |