Thick bay-fill sequences that often culminate in strandplain development serve as important sedimentary archives of land-ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground-penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes -notably a reduction in wave energy in response to coastal embayment infilling -in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4 m highstand at ca 5Á8 ka, the 75 km 2 Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi-enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressiveregressive sequence, and backed by a highstand barrier-island. The strandplain is immediately underlain by 5 to 16 m of seaward-thickening, fluvially derived, Holocene-age, basin-fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand-dominated to mud-dominated; (ii) beachface slopes decrease from >11°t o ca 7°; and (iii) progradation rates increase from 0Á4 to 1Á8 m yr À1 . Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea-level fall and sediment infilling and a decrease in onshore wave-energy transport from 18 to 4 kW m À1 . The combination of allogenic (sediment supply, falling relative sea-level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records.
Coastal sedimentation is driven by a combination of wave and tidal energy, sediment supply, and relative sea-level change. During the Holocene, these factors have combined to fill coastal embayments along the headland-dominated coast of Santa Catarina, Brazil. Here, three partially filled basins exhibit marked variability in their sediment sources, wave exposure and resulting stratigraphy and beach morphology. Hydrodynamic modeling highlights the primary roles of sediment supply and wave energy in producing three vastly different basin-fill sequences. The lack of a river source to the Pinheira Strandplain results in a bayfill sequence dominated by shelf-derived sand. Along the open coast of Navegantes, high wave energy removes fine sediments derived from the Itajaí-Açu rivers, producing a sand-dominated sequence. At Tijucas, fed by the much smaller Tijucas River, fronting headlands minimize wave energy, allowing for the accumulation of fluid mud in the shoreface. The result is a basin-fill sequence larger than that at Navegantes, but dominated entirely by mud.
The São Paulo Ridge (SPR) is a 350 km-long linear geological feature located in the Continental Margin off Brazil (Latitude 28-29 • S, Longitude 40-45 • W). In 2013, the region was mapped during the SW Atlantic "Iata-Piuná" expedition and explored by a series of deep-sea dives of the manned submersible Shinkai 6500. A digital bathymetric model analyzed for seafloor morphology, delimited four major bathymetric sectors namely plateau, ridge crest, ridge escarpment and ridge foot. These sectors further enclosed 12 morphological features at smaller spatial scales (structural classes) including plains, valleys, peaks, terraces, and troughs. Video profiles across the depth gradient (4,219-2,644 m depths) revealed that the slopes of the SPR southern flank were gentle and terraced, mostly covered by biogenic sediments and interrupted by rocky cliffs/crests, dispersed outcrops and loose particles. The North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) overlaid at the escarpment along which they established colder (0.4-1.0 • C; 4,200-3,400 m) and warmer (2.0-3.0 • C; 3,400-2,600 m) habitats, respectively. Physical components were used to define seven seascape units in the ridge foot (2), escarpment (3), and plateau-ridge crest (2), where a total of 914 organisms of the epibenthic and benthopelagic megafauna were recorded. Over 70% of these records were sessile suspension feeders, including sponges (61.5%) and anthozoans (11.4%). Most taxonomic groups concentrated above 3,800 m, under the influence of NADW, where densities reached maximum values (mean 0.26 organisms.m −2 ; 0.024-0.027 organisms.m 2 95% CI). Also, nearly half of megafauna records concentrated in patches delimited by the 3,800-3,300 m and 2,900-2,700 m isobaths. The deepest patch (3800-3300 m) coincided with the interface zone between AABW and NADW, where mixing processes create a density gradient. Evidences suggested that topography-related deep-water flow dynamics, and not substrate availability, drives benthic megafauna distribution at meso-habitat scale.
Shallow geophysical investigations in the upper reaches of North Bay, Florianópolis reveal four seismic facies. These are interpreted as crystalline basement, Quaternary sediments, a bayhead delta and Holocene lagoon/embayment sediments, respectively. The 15 mthick Bayhead delta unit was deposited on top of a flooded, undulating land surface, suggesting rapid flooding during sea level rise. This created accommodation space for accumulation of bayhead delta sediments. The Bayhead delta unit contains abundant seaward-dipping foresets and small delta-to, channel-fill sequences. The upper surface is planar suggesting tidal ravinement during subsequent sea level rise to the late Holocene highstand. The upper surface is overlain by up to 10 m of fine-grained sediments typical of tranquil water deposition, but close to river mouths, a more proximal unit contains bedded gravel and sand, representing contemporary fluvial deposition. The present absence of bayhead delta sediments is attributed to lack of accommodation space.
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