Print this pageSequence Stratigraphy and Facies Architecture of Large Tidal-Fluvial Systems—Impact of Coastal Process Changes on the Coeval Nonmarine Strata
Shuji Yoshida1, Robert Dalrymple2, James
MacEachern3, Andrew D. Miall4, Andrew Willis5,
Ron Steel1, Allard W. Martinius6, Riyadh
Rahmani7, and Kerrie Bann8
1 The University of Texas at Austin, Austin, TX
2 Queen's University, Kingston, ON
3 Simon Fraser University, Burnaby, BC
4 University of Toronto, Toronto, ON
5 Petro-Canada, Calgary, AB
6 Statoil R&D, Trondheim, Norway
7 Saudi Aramco, Dhahran, Saudi Arabia
8 University of Alberta, Edmonton, AB
The sequence-stratigraphic interpretation of non-marine strata and their correlation with marine deposits are not easy. Therefore, considerable attention has been paid to the presence of tidal influence and brackish-water trace fossils within fluvial successions. Although such features have obvious significance as indicators of marine influence, their application is difficult because: (1) tidal-fluvial and brackish-water deposits are commonly difficult to identify, (2) they are controlled by multiple forcing factors which change temporally and spatially over a relative sea-level cycle, and (3) there are few studies which have investigated modern tidal-fluvial environments systematically.
In published non-marine sequence-stratigraphic models, tidal and brackish-water incursion into fluvial environments is generally used as an indicator of marine transgression, and the maximum flooding surface is placed at the level where tidal and brackish-water indicators are most prominent. We find, however, that these models, which are based on the unstated assumption of an invariant tidal range, are not readily applicable to some fluvial successions in the Cretaceous Western Interior Basin (e.g., the Castlegate Formation). In these examples, tidal and brackish-water influence appears to have penetrated long distances inland from the coeval shoreline during LST time (as indicated by channel amalgamation and grain-size trends), whereas their penetration at the time of ‘maximum transgression' appears to have been less. This implies that tidal range was greatest at LST time, allowing the development of lengthy tidal-fluvial transitions, whereas lower tidal ranges characterized late TST to HST shorelines. This raises the question of the meaning of ‘maximum flooding' in sequence-stratigraphic models.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005