Application of the Controlled Source Radiomagnetotellurics (CSRMT) in the Study of Rocks Overlying Kimberlite Pipes in Yakutia/Siberia

Тhe task of searching for kimberlite pipes in covered areas of the Yakutia kimberlite province is very difficult due to the significant heterogeneity of the rocks overlying kimberlite pipes. The overlying strata of terrigenous sediments contain rocks of the trap complex (dolerite sills, tuff bodies). We consider the results of the controlled source radiomagnetotelluric (CSRMT) soundings in Yakutia/Siberia. Due to the great thickness of the overlying rocks (near 100 m) and the relatively small horizontal sizes of kimberlite pipes (80–200 m), they cannot confidently be detected directly. An additional difficulty in identifying pipe anomalies is the presence of a layer of conductive carbonaceous siltstones in the overlying strata. Therefore, the main aim of the CSRMT surveys was the study of overlying rocks and the search for indirect indications of the presence of pipes. Possibilities to study the structure of dolerite sills located within overlying sediments and to map the top edge of hosting carbonate rocks are demonstrated using the CSRMT data. The pinching out of dolerite sills above pipes («windows in traps») and the lowering of the top edge of hosting rocks at pipes can be considered as indirect indications of the presence of pipes.

Effect of terrigenous sediments on macroalgae functional-form groups of coral reefs in Capurganá, Colombian Caribbean

Increased sedimentation in the marine environment has been described as a key factor in the degradation of coral reefs. One of the most important biological components of coral reefs is macroalgae. The objective of this study was to determine whether the effects of terrigenous sediments on macroalgae affect the current state of the coral reef ecosystem. In an in situ experiment in Capurganá Bay, terrigenous sediments were added to artificial plates and the impact on the recruitment and growth of the macroalgae was examined. In this experiment, three treatments were used: sediment addition and two natural conditions, one up to 10 m distance from the sediment addition (control 1) and one between 15 and 20 m distance from the sediment addition (control 2). The results indicated a high complexity and variability in the response of reef algae to the effects of sedimentation depending on the sediment grade size deposited. The addition had a positive effect on the recruitment and growth of filamentous algae, primarily red algae, whereas it had a negative effect on coralline algae. The sediments found on the plates did not significantly change the macroalgal structure (P>0.05). However, a trend was observed in the change of the algal cover in each treatment. These results indicate that there is a wide range of response of the algae depending on the functional groups and the nature of the sediment.

BIOAVAILABLE AND TOTAL COPPER AND LEAD IN TERRIGENOUS SEDIMENTS IN THE INNER CONTINENTAL SHELF OFF VERACRUZ, SOUTHERN GULF OF MEXICO

The inner continental shelf adjacent to the city and port of Veracruz (ICSV) in the southern Gulf of Mexico, which is influenced by the Jamapa River, has been considered to be polluted. Moderate to high Cu and Pb concentrations have previously been reported in the shelf’s terrigenous sediments. These elements are derived from deposition of materials from mainland sources via river transport and may threaten marine life in the coastal area. Because Cu and Pb bioavailability has not been previously assessed in the region, the aim of this study was to determine (i) bioavailability and total concentrations of these elements in the terrigenous sediments of the ICSV, (ii) if concentrations of these elements in sediments are associated with distances from primary sources, and (iii) if concentrations differ during dry and rainy seasons. Bioavailable general average concentrations were 0.21 µg/g for Cu, and 0.24 µg/g for Pb, which accounted for 4.4-4.9 % of the total content. The bioavailable concentrations were higher during the rainy season, and in the fluvial plume of the Jamapa River. The total content of Cu and Pb was significantly associated with fine sediments and exhibited high concentrations in the new port facilities area. Hence, it is concluded that the Jamapa River is a primary source of trace metals to the ICSV. Finally, as concentrations of trace metals are lower than previous records for sediments in the southern Gulf of Mexico and lower than background levels and maximum permissible limits, the ICSV is presently not contaminated by Cu or Pb.

SCALE VALUE IN STUDYING THE SIZE OF PLACER GOLD

Placer gold particles are an integral part of terrigenous sediments. When studying the size of placer gold, it is advisable to use a logarithmic scale to explain the processes of gold accumulation and solve applied problems.