Synthesis of stratigraphic correlations of the Amazon Fan

Abstract

The older part of the Amazon Fan sequence penetrated on Leg 155 predates the last interglacial but is probably no older than oxygen isotopic Stage 8. The presence or absence of the zonal fossil E. huxleyi in sediments interpreted as isotopic Stage 7 appears variable, as the result of ecologic changes, dissolution, or reworking. Last interglacial highstand deposits are identified at Sites 942 and 946 from a microfossil assemblage, isotopic character, and the paleomagnetic Blake Event. They may have been removed by erosion by mass-transport deposits at other deep sites. The available data do not allow a consistent stratigraphy to be developed for the late Pleistocene (Stages 4 and 3) prior to the paleomagnetic Lake Mungo Excursion (32 ka).A consistent correlation is developed for sequences younger than the Lake Mungo Excursion using oxygen isotopes of planktonic foraminifers, magnetic susceptibility, and paleomagnetic intensity and inclination. This correlation confirms that there is considerable variability in oxygen isotopic variations across the fan. The last glacial maximum is represented by the middle part of the Brown Channel-levee System. Shipboard seismic correlations are shown to be generally correct and confirm that major channel-levee systems formed sequentially. Several levees continued to accumulate mud with silt laminae, derived from flow-stripping of turbidity currents, after shifting of the active channel. A tentative age model is based on sparse 14 C dates and the correlation of paleomagnetic intensity events with the global stack.

Channel-mouth lobe complex of the recent Amazon Fan: The missing piece

“…The deposition of these channels corresponds to the Late Quaternary turbidite activity in the period from the Last Glacial Maximum to the following rise of sea-level, ie. ∼20 ka cal BP to ∼10 ka cal BP (Showers and Bevis, 1988;Piper et al, 1997b).…”

“…the littoral drift, exports fine-grained sediments to the French Guiana shelf and upper slope. The end of the turbidite activity on the Amazon Fan has been dated at 10,1 cal ka BP (Showers and Bevis, 1988;Piper et al, 1997b).…”

“…The objectives of this paper are to investigate the channel-mouth lobe complex of the recent Amazon Fan in order to: (1) characterise the morphology and acoustic facies of the distal Amazon channel termination area, and (2) propose a model for the stratigraphic construction of the Amazon channel-mouth lobe systems for the period after the Last Glacial Maximum, between ∼ 20 cal ka BP and ∼ 10 cal ka BP (10,1 cal ka BP) (Showers and Bevis, 1988;Piper et al, 1997b). This study points out new insights for the understanding of the architecture of channel-mouth lobe systems and raises questions concerning the processes that control the shape and location of channelmouth lobe systems, the timing of construction and the relationship between changes in relative sea-level and sediment supply.…”

Late Weichselian fluvial evolution on the southern Kara Sea Shelf, North Siberia

“…For the Kara Sea, these values are found at the shelf/slope break where all of the identified channel-levee systems are located. Average sediment thickness at thalweg is 15 m, which is in good agreement to the average life span of 2 kyrs (Piper et al, 1997). Documented channel-levee complexes are not likely to have been connected or formed at the same time, although channel thalweg depths could indicate a progressive northward deepening (Fig.…”

“…Maslin and Mikkelsen (1997) report sedimentation differing in three orders of magnitude rates of 5 cm/kyr during interglacial times with only pelagic background sedimentation and 5000 cm/kyr during glacial times when sediments are channelled to the deep sea. Typical "life spans" of individual channellevee systems vary between 1 and 3 kyrs (Piper et al, 1997). Once a submarine levee route has been established it is relatively stable, and major adjustments in the selfstabilizing channels pathway are unlikely, ignoring the surrounding morphology.…”