As a prominent isolated oceanic atoll-like reef within the Oceanic Shoals Biozone to the west of the Kimberley coast, Scott Reef is a small carbonate platform located in a distal ramp setting on Australia's Northwest Shelf. Rising from depths of 400-700 m it is a complex of two large isolated coral reefs separated by a deep channel; the pear-shaped North Reef and the crescent-shaped South Reef. Small differences in subsidence rates indicate differential subsidence between the paired platforms. Holocene (MIS 1, last 10 ka) reef initiation was at 11.3 ka, soon after Meltwater Pulse 1B thereby bracketing the Holocene growth phase to the subsequent deglaciation sea-level rise. The crest of southeast North Reef (and the rising sea-level) reached close to present sea level (-1.5m LAT) by 2.7 ka ago. There is no record of the southwest Australian sea level high stand of about +2m some 7 ka BP. The Holocene reef growth history record obtained for this long lived and resilient reef system is one of the most detailed yet for the western margin of Australia.

The Kimberley region in remote northwest Australia has poorly known reef systems of two types; coastal fringing reefs and atoll-like shelf-edge reefs. As a major geomorphic feature (from 12ºS to 18ºS) situated along a subsiding continental margin, the shelf edge reefs are in a tropical realm with warm temperatures, relatively low salinity, clear low nutrient waters lacking sediment input, and Indo-West Pacific corals of moderate diversity. Seismic architecture of the Rowley Shoals reveals that differential pre-Holocene subsidence and relative elevation of the pre-Holocene substrate have controlled lagoon sediment infill and reef morphology, forming an evolutionary series reflecting differential accommodation in three otherwise similar reef systems. The Holocene core described for North Scott Reef confirms previous seismic interpretations, and provides a rare ocean-facing reef record. It demonstrates that the Indo-Pacific reef growth phase (RG111) developed during moderate rates of sea level rise of 10 mm/year from 11 to about 7-6.5 ka BP until sea level stabilization, filling the available 27 m of pre-Holocene accommodation. Despite the medium to high hydrodynamic energy imposed by the 4m tides, swell waves and cyclones the reef-building communities represent relatively low-wave energy settings due to their southeast facing and protection afforded by the proximity of the South Reef platform. This study demonstrates the resilience of reefs on the subsiding margin whilst linking Holocene reef morphology to the relative amount of pre-Holocene subsidence.

Scott Reef is located on the northwest margin of Australia at 14 degrees 03'S and 121 degrees 17'E. It consists of a bifucated topographic high, at the edge of a carbonate platform established in the Late Eocene. The modem reef system is partially emergent during low tide (4m range). it is exposed to strong swell and Indian Ocean tropical cyclones and located on. Mail passage of the Indonesian Throughflow (ITT) Nutrient levels are low; temperature ranges between 25-30 degrees C and salinity 34.5 and 34.7. The Holocene reefs show resilience to bleaching other oceanographic even North and South Holocene reefs show similar average accretion rates of similar to 3.2mm/yr, however they may have developed morphologically distinctly due to differential accommodation and associated. lateral accretion. Reef initiation was established as early as 11.5 ka BP with dominant slow growing domal and tabular branching coral facies in semi-protected sites and coralline algal crusts in more exposed sites. Porites geochemical analysis points to a cooler SST window around 8.3 ka, and a higher SSS window at 5.8 ka (not yet calibrated). These findings extend our knowledge regional and climatic clients through Holocene time.

O recife parcialmente exposto da Praia de Jacaraípe é formado por algas calcárias vermelhas incrustantes com até 40 cm em espessura sobre uma comunidade recifal holocênica. Este trabalho visa descrever a composição da flora atual e estrutura do fitobentos desta comunidade, todavia não estudada. O levantamento ocorreu no verão e inverno, no platô e borda recifal. Foram amostrados 10 quadrados aleatórios ao longo de transectos de 20 m em cada habitat. Os resultados apontam para a presença de doze clorofíceas, quatro feofíceas, 34 rodofíceas e uma fanerógama marinha, totalizando 35 gêneros e 51 táxons. Foi identificada uma variação sazonal na riqueza específica somente na borda recifal, a qual apresentou uma flora menos rica no inverno. As algas calcárias articuladas tiveram maior biomassa e cobertura nas duas épocas estudadas. A distribuição espacial e temporal da flora está em acordo com padrões de tipo de substrato, hidrodinâmica e turbidez da água do mar encontrados em áreas recifais de todo o Brasil.

The Brazilian coral reefs form structures significantly different from the well known coral reef models, because (i) they have a characteristic initial growth form of mushroom-shaped coral pinnacles called chapeiroes, (ii) they are build by a very low diversity coral fauna, rich in endemic species, which are relic forms, remnant of an ancient coral fauna dating back in the Tertiary, (iii) incrusting coralline algae have an important role in the construction of the reef structure, and (iv) the nearshore bank reefs are surrounded and even filled with muddy siliciclastic sediments. The isolated reefs columns, the chapeiroes, fuse together at their tops, forming large compound reef structures of varied sizes, with horizontal tops, and somewhat irregular shape. They can be completely exposed during low tides. These reef structures are distributed into three major sectors along the tropical coast of Brazil: the northern, the northeastern and the eastern coasts. There are different types of bank reefs, fringing reefs and an atoll. Corals, milleporids and coralline algae build the rigid frame of the reefs. The coral fauna, so far identified, comprises less than eighteen species, being some of them endemic to the Brazilian waters. Quaternary sea-level fluctuations affected the growth of the reefs in Brazil; transgressive and regressive seas marked different stages of reef development. The areas where the major coral reefs occur correspond to regions where nearby urban centres are experiencing accelerated growth and tourist development is increasing very fast. The major human impacts to the reef ecosystem are mostly associated with agricultural activities (sugarcane and timber), mineral and chemical industries and oil exploration. Increased sedimentation due to removal of the Atlantic rainforest and the disposal of industrial and urban effluents, are additional stresses to the coastal marine environment in Brazil. There are not many institutions concerned with preservation of the Brazilian coral reefs, and they are also fairly new.

The continental shelf of the State of Rio Grande do Norte, Brazil, is an open shelf area located 5°S and 35°W. It is influenced by strong oceanic and wind‐driven currents, fair weather, 1·5‐m‐high waves and a mesotidal regime. This work focuses on the character and the controls on the development of suites of carbonate and siliciclastic bedforms, based on Landsat TM image analysis and extensive ground‐truth (diving) investigations. Large‐scale bedforms consist of: (i) bioclastic (mainly coralline algae and Halimeda) sand ribbons (5–10 km long, 50–600 m wide) parallel to the shoreline; and (ii) very large transverse siliciclastic dunes (3·4 km long on average, 840 m spacing and 3–8 m high), with troughs that grade rapidly into carbonate sands and gravels. Wave ripples are superposed on all large‐scale bedforms, and indicate an onshore shelf sediment transport normal to the main sediment transport direction. The occurrence of these large‐scale bedforms is primarily determined by the north‐westerly flowing residual oceanic and tidal currents, resulting mainly in coast‐parallel transport. Models of shelf bedform formation predict sand ribbons to occur in higher energy settings rather than in large dunes. However, in the study area, sand ribbons occur in an area of coarse, low‐density and easily transportable bioclastic sands and gravels compared with the very large transverse dunes in an offshore area that is composed of denser medium‐grained siliciclastic sands. It suggests that the availability of different sediment types is likely to exert an influence on the nature of the bedforms generated. The offshore sand supply is time limited and originates from sea floor erosion of sandstones of former sea‐level lowstands. The trough areas of both sand ribbons and very large transverse dunes comprise coarse calcareous algal gravels that support benthic communities of variable maturity. Diverse mature communities result in sediment stabilization through branching algal growth and binding that is thought to modify the morphology of dunes and sand ribbons. The occurrence and the nature of the bedforms is controlled by their hydrodynamic setting, by grain composition that reflects the geological history of the area and by the carbonate‐producing benthic marine communities that inhabit the trough areas.

Abstract The inner portion of the continental shelf of Rio Grande do Norte State, Brazil has been investigated by Landsat-TM imagery and by scuba diving. The area experiences high-energy, shoreline and shelf-margin parallel currents driven by a combination of oceanic, tidal and wave processes. The high meso-tidal range (<4 m) further distributes the high-energy waters over the entire inner shelf region (0–25 m). This shelf is a high-energy, distally steepened ramp in which the distribution of carbonate and siliciclastic facies belts is controlled by the energy of the environment, the sources of siliciclastic sediment and the Quaternary history of the area. Carbonate sediments are generated throughout the sublittoral zone and are dominated by calcareous red and green algae. Small, low-diversity coral patch reefs occur in shallow areas. Quartz-rich sands form beaches and subaerial longitudinal dunes, and an offshore, submarine, sandstone outcrop interpreted as a former Quaternary shoreline. This sandstone has been eroded during the Holocene transgression to generate quartz sands deposited in a train of transverse dunes migrating parallel to the coast. Longitudinal sand ribbons comprising bioclastic gravelly sands attest to high-energy, shore-parallel currents in the inner shelf. Branching coralline algae (maërl) form stabilized sea-floor areas. Preliminary 14C dating indicates a Pleistocene highstand period when coarse algal sands accumulated. Holocene lowstand conditions spread quartz-rich sands over the inner ramp area, which were reworked during the Holocene transgression. Present-day erosion, transport and in situ carbonate production results in mixing of these earlier carbonate and siliciclastic units. The Brazilian ramp has similar, but narrower morphology, when compared with the distally steepened ramps of the Yucatan and west Florida. All three ramps are swept by coastline-parallel currents. In Brazil, the higher-energy, windward-facing, inner ramp has calcareous algal sands and patch reefs compared with the inner ramps of the leeward-facing Gulf of Mexico examples that accumulate molluscan sands. Outer ramp facies in each example are planktonic foraminiferal oozes.

A preliminary characterization of seabed morphology and mapping of algal patches within a sandstream on the northeast Brazilian continental shelf off Cape Calcanhar (where the South American coast turns sharply to the west) is presented. The study area (30 km x 30 km) is swept by unidirectional, wind-driven, tidally rectified currents, under the influence of the North Brazil Current. The study was made by use of Landsat Thematic Mapper (TM) data of the seafloor down to 40 m depth, digital bathymetric data from smooth sheets furnished by the Brazilian Navy, echo-sounder profiling and underwater surveying by SCUBA diving. A mesoscale shore-parallel natural zonation of the sandstream was observable on the TM-images: (a) an inner zone dominated by sediment resuspension caused by wave-driven turbulence and tidal currents; (b) an intermediate zone dominated by sand ribbons and other longitudinal bedforms; (c) an outer zone dominated by large-scale sand waves (underwater sand dunes) limited offshore by shore-parallel sandbanks.Image-assisted in situ work, carried out on the latter zone, gave the following results:(1) Morphology and sand composition-the asymmetric sand waves are made of medium quartz sand, with almost straight crests of lengths up to 4 km, heights between 3 and 7 m, and avalanche lee slopes of 30-degrees; on the stoss sides we recorded the presence of ripples and absence of megaripples and benthic ecosystems; on interdune areas, benthic ecosystem patches dominated by foliaceous and calcareous algae were found.(2) Sediment transport-active bedload transport was observable only during the winter season, when the strongest wind-forced currents induce flow separation at the crests and avalanche streams on the lee slope. Within the interdune areas, under the influence of the lee vortices, benthic community data confirms no appreciable abrasion due to sand transport.(3) Biology-species composition and biomass estimates from the algal patches in the first upstream trough are presented, and species composition of bryozoa observed as epibionts on live gastropod shells are analysed.This sandstream shows some similarities to one described from the southeast African continental shelf, which is also under the influence of unidirectional currents.