Reef Base Research Articles

Modern middens: Shell recycling for restoring an endangered marine ecosystem in Victoria, Australia

SummaryShellfish reefs are one of the most depleted marine ecosystems in the world, and there is considerable interest and efforts to restore the ecosystems. When degraded reefs require the addition of new substrate to support oyster re‐establishment, recycled shells can be used to rebuild new reef bases. Shell recycling as a means of procuring shells was first introduced in Australia by The Nature Conservancy in 2015, through the establishment of the ‘Shuck Don’t Chuck’ Shell Recycling Project in Victoria. The recycling project was first piloted in the regional city of Geelong with the aim of providing sufficient quantity of clean, recycled shell to support reef base construction for shellfish reef restoration in Port Phillip Bay. The project has subsequently expanded into markets and restaurants in Melbourne. Community involvement and restoration promotion are important secondary outcomes of the programme. We provide lessons from our experience to date and a step‐by‐step guide of how to establish a shell recycling project from initial pilot and trial stages to a full programme. These steps include the following: (i) recruitment of shell recycling partners, (ii) transport and logistics, (iii) shell storage sites, (iv) biosecurity and curing protocols, (v) hatchery use, (vi) reef deployment, and (vii) community engagement. Shell recycling is an effective way to not only source substrate for restoring shellfish reefs, but also to reduce the amount of waste going to landfill and should be considered as part of any shellfish reef restoration project which utilises shell products.

Study on variously dolomitized reservoir reef at platform margin of Changxing Formation in northeastern Sichuan Basin, southwestern China

Dolomitization of reservoir reefs is common at platform margins of the Changxing Formation in northeastern Sichuan Basin, southwestern China. We carried out a research on these variously dolomitized reef microfacies based on sedimentology and petrology theories and geochemical technologies. The results show that the reservoir reefs at the platform margins of the formation can be divided into several microfacies: reef flats/caps, reef cores, reef bases, etc. The reef flats contain mostly crystal grain dolomites, the reef cores are made up of largely (calcite) reef dolomites, and the reef bases are generally dolomite limestone/calcite dolomites. Samples taken from different microfacies of the reefs were measured and showed a relatively high content of Fe and Sr and low content of Mn, with Mn/Sr ranging between 0.057 and 2. Samples from the east flank of the Kaijiang–Liangping trough and the Exi–Chengkou trough have higher Fe and Mn contents and Mn/Sr ratios than those from the west flank of the Kaijiang–Liangping trough. Dolomites in reef flats have the highest Fe and Mn contents and Mn/Sr ratios, followed by dolomites from reef cores, and those from reef bases are found to have the lowest Fe and Mn contents. Isotopic analyses of the samples from different microfacies of the reefs indicate more negative δ13C and δ18O values than that of limestone in seawater during the Changxing deposition period. The δ18O values were increasingly more negative in the order of reef flat–reef core–reef base. Based on the study, we propose that the dolomitization processes the reefs at different platform margins experienced have the following features: (1) Meteoric water affected dolomites at the eastern flank of the Kaijiang–Liangping and Exi–Chengkou troughs more than those of the west flank of the Kaijiang–liangping trough. From the microfacies perspective, the influence of meteoric water decreases from reef flats to cores and then to bases. Apart from meteoric water, the dolomitization was also under control of seawater at the same period. (2) Meteoric water dolomitization is closely linked to sedimentary microfacies. Reef flats and cores with better porosity and permeability are more dolomitized than reef bases containing mostly micrite with bioclastics. (3) Dolomitization processes driven both by early mixing of water and “juiced” marine fluids during the shallow burial and compaction stage were all completed before the first stage of hydrocarbon emplacement. Hydrothermal dolomitization occurred locally and its contribution to the whole reef dolomitization of the formation may be negligible.

Relationship between depositional textures and seismic velocities of the Yijianfang Ordovician reef complexes in the Bachu area, west Tarim Basin, China

Abstract The Yijianfang Ordovician reef complexes in the Bachu area, western Tarim Basin contain eight facies elements: reef cores, fore-reef breccias, reef bases, tidal channels, fore-reef inner shoals, fore-reef outer shoals, back-reef inner shoals, and back-reef outer shoals. The reef cores and fore-reef breccias are characterized by Calathium bafflestones and rudstones, respectively. The reef bases are composed of skeletal packstones with moderately sorted grains of 0.1–2.5 mm diameter, whereas the tidal channels are dominated by cross-bedded packstones in which the grains are moderately to poorly sorted with a diameter of 0.3–6 mm. The fore-reef and back-reef inner shoals are composed of grainstones, while the fore-reef and back-reef outer shoals are dominated by packstones. From inner to outer part of the shoals, the grain content becomes gradually less, the size of grains becomes gradually finer, and the grains become worse sorted. The fore-reef and back-reef inner shoals tend to be potential reservoirs for hydrocarbon. Studies on predictive relationship between depositional textures and seismic velocities show that the seismic velocities decrease with an increase of grain content or median grain diameter, and a decrease of standard deviation. With these correlations, acoustic data could provide useful information about recognizing the depositional textures of reef complexes, which is crucial to predict facies of the reef complexes based on seismic data. Seismic simulated experiment reveals that the mound seismic reflection configurations of the reef cores are pronounced, surrounding which the potential reservoirs can be recognized in the synthetic seismic profiles.