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Prior to Ocean Drilling Program Leg 155, the architecture of the Amazon Fan, as well as those of other modern submarine fans, had been investigated primarily by seismic reflection profiles. The acoustic facies and stratal patterns observed on these profiles provided a wealth of information that allowed deciphering fan growth patterns and the geometry of fan deposits. However, lithofacies could only be inferred from the seismic reflection data. Here we analyze grain-size data from 13 sites drilled during Leg 155, and place the results in the context of the stratigraphic units interpreted from seismic reflection data. Clay, silt, and fine sand are the dominant grain sizes of all cores retrieved from the Amazon Fan. In this mud-rich fan, sand is concentrated within the channel thalweg, at the base of channel-levee systems within the middle fan, and forms a significant fraction of the lower fan deposits drilled. All channel-levee deposits drilled are characterized by a fining-upward trend and by an overall coarsening in the downfan direction. Downfan coarsening of the levee deposits probably results from very efficient sorting associated with the channelized flow of turbidity currents together with the overall decrease in channel relief downfan. Finingupward cycles within a channel-levee system are observed in the middle fan where multiple phases of levee development are stacked upon each other. Each growth phase is marked by an abrupt coarsening that marks a channel bifurcation occurring downslope, followed by a fining-upward sequence of levee aggradation. Channel bifurcation results in the reworking of older channel deposits, and the formation of laterally widespread units. High-amplitude reflections (HARs) beneath the channel axis and high-amplitude reflection packet (HARPs) units are composed of two distinct grain-size populations. HARs and HARPs are the coarsest units that form the fan, with sizes up to 0 ø. Both units display an overall coarsening downfan. These characteristics are likely the result of multistep transport of sand downfan. Thick acoustically transparent units on seismic profiles are correlated to large mass-transport deposits, displaying grain-size characteristics similar to levee deposits with an overall finingupward and downfan-coarsening trend.

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The stability of a mudflat in the Humber estuary, South Yorkshire, was investigated at seven sites along a shore-normal transect during early spring. This was carried out using the benthic flume Sea Carousel, and from the investigation of surface samples in a laboratory equivalent to the Sea Carousel, the Lab Carousel. A clear trend in erosion threshold [%(0)] was evident, showing two maxima: the greatest on the inner mudflat (0.78 Pa); and a second on the central mudflat (0.75Pa). We ascribe these maxima to two causes: (1) desiccation of the inner mudflats; and (2) biostabilization by algae of the central flats. Our results suggest that of these factors biostabilization was the dominant one at the time of the study. Most of the variation in erosion rate is explained through the sediment bulk density (Pb) and colloidal carbohydrate (DCHO): [To(0)] = 0.511.931og10(DCHO + 2.5 × 10-4pb] q-1.7; r 2 = 0.63. Thus variations in DCHO had O(104) greater impact on erosion threshold than equivalent variations Pb. The relationship between mean erosion rate (Era) and current speed (Uy) was similar for all sites and is defined by the exponential function: Em = 2.47 × 10 -6 • 10(3-749uy) kgm -2 s -1 . In situ mean still-water settling rates (Ws) were up to 2.46 × 10-3m s -l, which is up to an order of magnitude faster than was measured in other estuaries at similar suspended sediment concentrations, S. The decay constant, k, for still-water settling appeared to be a linear function of S, and compared favourably with values derived from five Canadian coastal mudflats. Results from Lab Carousel showed that the erosion thresholds were the same as those measured in situ, using Sea Carousel. Furthermore the spatial trends in erosion were at University of Chicago on July 24, 2015 http://sp.lyellcollection.org/ Downloaded from 26 C. L. AMOS ET AL.