Paleogeography and Sedimentary Development of Two Deep-marine Foreland Basins

Book excerpt: This dissertation comprises three chapters focusing on the evolution of marine sedimentary successions that formed as the fill of large submarine channel belts and their tributary systems. These channel belts serve as conduits for gravel- and sand-laden sediment gravity flows along the axes of narrow, elongate foreland basins. In the past, axial channel belts have not been widely recognized in submarine foreland basins (Mutti et al., 2003). However, recent studies have demonstrated the presence of axial channels, 3-8 km in width and > 100 km in length, in a number of marine foredeeps including the Cretaceous Magallanes Basin, southern Chile, and the Tertiary Molasse Basin, northern Austria (De Ruig and Hubbard, 2006; Hubbard et al., 2008, 2009). Additional studies have shown that similar channels are common in submarine trough-shaped basins in other convergent margin settings such as the Peru-Chile trench (Thornburg et al. 1990, Völker et al., 2006), the Hikurangi trough, offshore New Zealand (Lewis and Pantin, 2002), and the Nankai trough, offshore Japan (Fig. 1 in Moore et al., 2007), as well as in modern oceanic rift basins, such as the Maury channel in the Northeast Atlantic Rockall Basin (Cherkis et al., 1973) and the Northwest Atlantic Mid-Ocean Channel (NAMOC) in the Labrador Sea (Hesse et al., 1987, 1990; Hesse, 1989, Klaucke et al., 1998). These occurrences suggest that axial channels may be common sediment transport fairways in elongate deep-water basins in a variety of tectonic settings. This thesis investigates the sedimentary evolution, stratigraphic architecture, and paleogeography of such channel systems in two distinct, yet analogous and complementary research areas: the Magallanes foreland basin in southern Chile, and the Molasse foreland basin in northern Austria. The main objectives of this study are: a)to characterize the processes of submarine sediment transport and deposition in the study areas, b)to explain the associated filling patterns of ancient submarine axial channels and their tributaries, and c)to reconstruct the paleogeography of an ancient seafloor in order to better understand deep-marine sediment dispersal patterns in narrow elongate basins. The Magallanes Basin is a retro-arc foreland basin characterized by a deep-marine filling history from the Cenomanian/ Turonian (Fildani et al., 2003; Fosdick et al., in press) to the Campanian (Chapter 3). The numerous coarse-grained submarine channel and lobe complexes of the Turonian to Campanian Cerro Toro Formation represent a large north-south oriented channel belt that funneled sediment gravity flows along the axis of the foreland basin parallel to the active thrust front (Hubbard et al., 2008). This main axial trunk channel belt was probably fed by at least one, and possibly numerous, tributary channel systems coming off the Andean mountain front to the west. Similarly, sedimentation within the Upper Austrian Molasse Basin during the late Oligocene to early Miocene was largely controlled by an axial trunk channel that was fed by a deltaic system to the west and a tributary system lying along the Inntal fault zone to the southwest (De Ruig and Hubbard, 2006). Three studies were undertaken in order to illuminate the processes and architecture of the fill of submarine foreland basin axial channels: the interaction of submarine debris flows and turbidity currents within the axial channel in the Molasse Basin (Chapter 1), the stratigraphic and architectural evolution of coarse-grained deep-water deposits in a tributary system setting in the Magallanes Basin (Chapter 2), and the paleogeography of the Magallanes Basin axial channel belt and its tributary system and the associated basin-filling pattern over time (Chapter 3). Multiple techniques were combined to achieve these goals, including field mapping, sedimentological analysis of outcrops and rock cores, interpretation of wireline logs and 3D seismic-reflection data, U/Pb dating of zircons, strontium isotope stratigraphy, and a novel approach to lithofacies proportion modeling (Stright et al., 2009).