The influence of paleogeography in epicontinental seas: A case study based on Middle Devonian strata from the MacKenzie Basin, Northwest Territories, Canada

摘要

The history of Middle Devonian sea level changes are recorded in the Chinchaga Formation, Lonely Bay Formation, Horn Plateau Formation, and the Horn River Formations that originated in the MacKenzie Basin, which is located in the southern Northwest Territories, Canada. These strata record an almost consistent sea-level rise throughout the Middle Devonian with punctuated deepenings. Deposition began in the MacKenzie Basin in the Eifelian with restricted shallow water evaporites and dolomites of the Chinchaga Formation. Overlying the Chinchaga Formation are the open-marine carbonates belonging to the Lonely Bay Formation, which were overlain by the Horn Plateau Formation buildups. Pelagic shales of the Horn River Formation in the Late Givetian/Early Frasnian later covered these buildups. During the Early and Middle Devonian many continental basins in North America had limited interactions with open ocean waters. These restricted shallow-water basins were vulnerable to the effects of clastic shedding and evaporitic drawdown that commonly caused local lowstands. Several of these shallow basins, including the MacKenzie Basin, have been used to construct Devonian sea-level curves. Comparison of the Middle Devonian strata that formed in the MacKenzie Basin with well-established sea level curves shows that the Late-Givetian regression interpreted from some of those successions is not evident in the succession found in the MacKenzie Basin. This probably reflects the fact that the Mackenzie Basin was directly linked to the open ocean and was not influenced by the changes in sea level that affected many of the enclosed basins.