Forearc Basin Evolution Along Accretionary Convergent Margins, Wrangell Mountains, Alaska

The Wrangell Mountains basin is a Mesozoic forearc basin that developed during a period of accretionary tectonics in the northwestern Cordillera. The basin contains ~ 4 km of Middle Jurassic to Late Cretaceous sedimentary strata, and is part of a series of subbasins that define the southern Alaska forearc basin. The Wrangell Mountains are an excellent place to study forearc basin development because the thick section of Mesozoic strata has been uplifted and is well exposed, structural and metamorphic deformation has been minimal, and a chronostratigraphic framework exists for most of the basin deposits. The general questions to be addressed by this research include: (1) How do depositional systems evolve through time in forearc basins? Can a sequence stratigraphic framework be established for the Wrangell Mountains basin that would be applicable to other forearc basins, especially those of the northern Pacific region? (2) What are the relationships between individual tectonic events along an accretionary convergent margin and corresponding depositional events in the forearc basin? Does the composition of sandstones and conglomerates in the Wrangell Mountains basin record growth and erosion of volcanic arcs, uplift of subduction complexes, and accretion of allochthonous terranes? (3) Can the subsidence history of a forearc basin be linked directly to tectonic processes that occur along an accretionary convergent margin? How does the subsidence history of the Wrangell Mountains basin compare with other parts of the southern Alaska forearc basin, and can differences in subsidence histories explain the distribution of petroleum and coal in various parts of the basin system?

Ryan Nichols at base camp in Wrangell Mtns. Note fold in background. Jeff Trop on Root Glacier Fm., Wrangell Mountains. Cross section of the Wrangell Mtns. basin. Incredible exposure of proximal submarine fan deposits of MacColl Ridge Fm. Wrangell Mountains. Base camp in Wrangell Mtns. Base camp in Wrangell Mountains. Measured sections from the Wrangell Mtns. Stratigraphic cross section of Wrangell Mountains basin.