Calcifying tufa stromatolites are forming on a high energy coast of the South African Indian Ocean. The tufa stromatolites form in upper intertidal to supra tidal rock pools, encrust bedrock and are linked both laterally and vertically to physico-chemical properties of their pool water. Calcification only occurs in pools where dissolved carbonate-rich, spring-fed groundwater is routed, and d18O values are consistent with calcification in a mixture of freshwater and seawater. Increasing pH and less negative isotope values away from the spring are consistent with CO2 degassing and in-stream calcification, albeit with some in-mixing of seawater. The rocky shore setting of these active tufa stromatolites is new and invites serious comparison with some Archaean rocky substrate peritidal stromatolites (e.g. the c. 3.45 Ga Strelley Pool sequences, Pilbara Craton). This new association shows that initial encrustation of rocky intertidal substrates can begin with freshwater influence in the intertidal zone, a facies detail that should be sought in ancient peritidal stromatolites

The duration of shoreline occupation at a given sea-level, coastal response to sea-level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf. Using bathymetric and seismic observations, this article documents the evolution and preservation of an incised valley and lithified barrier complex between À65 m and À50 m mean sea-level on a wave-dominated continental shelf. The barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive backbarrier sediments. The ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons. The incised valley trends shore-parallel behind the barrier complex and records an early phase of valley filling, followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley. Sea-level stability at the outer barrier position (ca À65 m) enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sealevel rise to À58 m when the lagoon formed. These lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features. An abrupt rise in sea-level to À40 m, correlated with melt-water pulse 1B, enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers. This situation is unique to subtropical coastlines where early diagenesis is possible. The overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement, partly burying the ridges and protecting the underlying sediments. The high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline, early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping.

The study provides a 9-month record of Malilangwe Reservoir water chemistry periodicity, for the period between February and October 2011. Malilangwe Reservoir is a small (211 ha), shallow (mean depth 4.54 m) reservoir situated in the southeastern lowveld of Zimbabwe. The reservoir has not spilled in nearly 11 years, which makes it a unique system as most reservoirs of comparable size spill annually. This is the first bathymetric and limnological study of the reservoir where the morphology and physicochemical quality of the water body were examined. The reservoir was not strongly stratified during the hot-wet and hot-dry season with oxygen depletion of < 2 mg·ℓ -1 DO being observed in the bottom layers (<6 m depth). Nutrient concentrations varied throughout the seasons. The reservoir exhibited marked seasonal fluctuations in water level, which decreased by over 149 cm between February and October. The N:P ratio rose to as high as 10.9 and generally reflected high levels of phosphorus in the reservoir. There were significant differences (p<0.05) in Secchi depth transparency between the study sites. Differences observed in water quality were due to water level fluctuations, with poor water quality conditions being experienced during the hot-dry season and the cool-dry season when water levels were low. The reservoir was classified as being mesotrophic. Therefore, there is a risk of eutrophication, especially since the reservoir is currently merely a sink for nutrients.

This study of the bathymetry of the mid-shelf of the Durban Bight, KwaZulu-Natal revealed a series of previously undocumented seafloor features. These features were mapped using a high-resolution multibeam bathymetric echosounder and a detailed map of the seafloor topography was produced. We recognised several features that closely resemble features of contemporary segmented lagoon and lake systems: semicircular seafloor depressions, arcuate ridges, cuspate spits and prograding submerged barriers. Based on the striking similarity in morphology to Kosi Bay -a segmented lagoon system from the sandy northern KwaZulu-Natal coastal plain -a similar evolutionary model is proposed. This model is of an incised valley formed following a sea level lowering to the Last Glacial Maximum at about 18 000 BP. Thereafter, continued transgressive infilling occurred to a point where an extensive lagoon and back-barrier system was established. At this point, sea levels remained static, causing the net segmentation of the system and the slow closure of the tidal basins or circular depressions. This type of seafloor topography is rarely preserved and is the result of fortuitous cementation after deposition and the later removal of sediment that would ordinarily bury such features.

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