Timing of the late Quaternary Amazon Fan Complex masstransport deposits

Abstract

The Amazon Fan at the mouth of the Amazon River is a large, highly structured muddy deep-sea fan. Sediment recovered by Ocean Drilling Program Leg 155 has allowed us to reconstruct the structure of the late Quaternary Amazon Fan Complex. A significant sedimentary component of the complex are the mass-transport deposits (MTDs) formed by catastrophic failure of the continental slope. There are two sets of MTDs: the near-surface MTDs and the deep MTDs. The near-surface MTDs are divided into the Eastern and Western Debris Flows which are capped by Holocene sediments. The deep debris flows are divided into the Unit R MTD in the western Amazon Fan complex, and the Deep Eastern MTD in the eastern Amazon Fan Complex. The MTDs each cover an area of up to 25 000 km 2, reach a maximum thickness of 200 m, and consist of approximately 50 000 gigatonnes of sediment. A characteristic of the MTDs is the inclusion of reworked glacial and interglacial material from both the continental slope and the surrounding fan. The relatively thin interglacial deposits below the MTDs are from the nanofossil zones CN14b and CN15a and thus younger than 460 ka. Bio-, seismic-and magnetostratigraphy and sedimentation rate constraints have been used to date the top of both the near-surface and the deep MTDs. It seems that the near-surface Western and Eastern Debris Flows were last active during Termination I. The Deep Eastern MTD was last active at about 33 ka, while the Unit R MTD was last active at about 45 ka. It is inferred that the interglacial deposits beneath these MTDs were formed during Oxygen Isotope Stages 7, 9 and 11. We speculate that the MTDs were triggered by climatically induced changes in sea level, and that the interglacial deposits may have acted as slip planes for the MTDs.

Biogeography of tropical reef fishes: the South Atlantic puzzle

“…Another non‐excluding possibility is that genetic flow would be completely severed during low sea‐level periods (cf. Maslin & Mikkelsen, 1998; Arz et al. , 1999; Knoppers et al.…”

“…Another non-excluding possibility is that genetic ow would be completely severed during low sea-level periods (cf. Maslin & Mikkelsen, 1998;Arz et al, 1999;Knoppers et al, 1999). During one of the recent lowest stands ()50/70 m at 12.7±11.2 ka BP BP ) (Arz et al, 1999), the Amazon freshwater and material was directly exported to the upper shelf slope (present day shelf break is at 75±80 m).…”

Sediment partitioning, continental slopes and base‐of‐slope systems

“…MTCs form a large stratigraphic component of many ancient and modern deep-water margins around the world (Martinsen, 1989;Maslin & Mikkelsen, 1998;Martinsen et al, 2003;Newton et al, 2004;Moscardelli & Wood, 2015). In some settings, up to 70% of the entire slope and deep-water stratigraphic column is composed of MTCs and associated deposits (Fig.…”

Sinuous deep-water channels: Genesis, geometry and architecture

“…3) and each cover an area of 415,000 km 2 ; in places they destroy and/or bury channel-levee systems (Damuth and Embley, 1981;Maslin and Mikkelsen, 1998;Maslin et al, 2005). Two older buried MTDs are also visible on seismic profiles (Flood et al, , 1997Maslin and Mikkelsen, 1998;Maslin et al, 2005). The upper parts of MTDs consists of hummocky slump or slide deposits while, further downslope, thin debris-flow deposits extend for up to 300 km.…”

“…Details of Amazon Fan evolution and stratigraphy are outlined in numerous studies (Damuth and Kumar, 1975;Damuth et al, 1983bDamuth et al, , 1988Damuth et al, , 1995Damuth and Flood, 1984;Manley and Flood, 1988;Flood et al, 1991;Lopez, 2001;, including results of ODP Leg 155 (Flood et al, , 1997Maslin and Mikkelsen, 1998;Rimington et al, 2000). Amazon Fan has been largely inactive throughout the Holocene sea-level highstand, but was previously active during times of lowered sea level when the Amazon River was directly connected to Amazon Canyon.…”