Gold Mining and Estuarine Evolution: A Study of the Accelerated Sedimentation of Parapara Inlet, Golden Bay, New Zealand

<p>Estuaries are depositional environments formed within drowned river embayments which receive sediment from both marine and terrestrial sources. In many cases a beach-barrier sequence forms subaerially at the mouth of the flooded embayment and the area behind it is termed a barrier estuary. Such estuary types are found around the New Zealand coast especially in areas of relative tectonic stability and their sediments are often used to reconstruct Holocene sea level. Infill of these estuaries is initially dominated by marine flood tide delta sediments, with later infill occurring through fluvial processes. The final stages of infill within these estuaries is poorly understood. Parapara Inlet in Golden Bay, New Zealand, is a Holocene barrier estuary influenced by hydraulic sluice mining within its river catchment. A study of Parapara Inlet was undertaken to discover how human disturbance within a river catchment can affect the evolution of a barrier estuary, by comparing previous models of barrier estuary evolution to the stratigraphy record within Parapara Inlet. 18 vibracores were sampled from Parapara Inlet in November 2009. Radiocarbon dating (AMS) within these cores provided a maximum age of 7090-6910 Cal BP. Deposition within the estuary has occurred in three stages; the first in Pre-Holocene marsh or lake environments; the second after inundation 6500-7500 years Cal BP, as fluvial sediments dominate the centre of the estuary; and thirdly in a series of quartz dominated gravels and sands within 1m of the surface. These units vary from the traditional models of evolution as the topography of the estuary has influenced the extent of deposition within the central mud basin. Mining sediment forced Parapara Inlet into a late stage of evolution, however the amount of sediment provided through sluice mining was not large enough to force the estuary into a supratidal stage.</p>

Gold Mining and Estuarine Evolution: A Study of the Accelerated Sedimentation of Parapara Inlet, Golden Bay, New Zealand

<p>Estuaries are depositional environments formed within drowned river embayments which receive sediment from both marine and terrestrial sources. In many cases a beach-barrier sequence forms subaerially at the mouth of the flooded embayment and the area behind it is termed a barrier estuary. Such estuary types are found around the New Zealand coast especially in areas of relative tectonic stability and their sediments are often used to reconstruct Holocene sea level. Infill of these estuaries is initially dominated by marine flood tide delta sediments, with later infill occurring through fluvial processes. The final stages of infill within these estuaries is poorly understood. Parapara Inlet in Golden Bay, New Zealand, is a Holocene barrier estuary influenced by hydraulic sluice mining within its river catchment. A study of Parapara Inlet was undertaken to discover how human disturbance within a river catchment can affect the evolution of a barrier estuary, by comparing previous models of barrier estuary evolution to the stratigraphy record within Parapara Inlet. 18 vibracores were sampled from Parapara Inlet in November 2009. Radiocarbon dating (AMS) within these cores provided a maximum age of 7090-6910 Cal BP. Deposition within the estuary has occurred in three stages; the first in Pre-Holocene marsh or lake environments; the second after inundation 6500-7500 years Cal BP, as fluvial sediments dominate the centre of the estuary; and thirdly in a series of quartz dominated gravels and sands within 1m of the surface. These units vary from the traditional models of evolution as the topography of the estuary has influenced the extent of deposition within the central mud basin. Mining sediment forced Parapara Inlet into a late stage of evolution, however the amount of sediment provided through sluice mining was not large enough to force the estuary into a supratidal stage.</p>

Study of Heavy Minerals from the Vjosa and Mati river delta sediments in Albania

This research is focused on the determination of the heavy minerals (HM) load of the Vjosa and Mati river delta deposits along the Albanian coastline and it is based on X-ray Diffractometry. The Albanian coastline consists of sandy beaches at the north (Adriatic coastline) and rocky escarpments at the south (Ionian coastline). Several layers of heavy mineral deposits, up to 50 cm thick, with heavy mineral fraction up to 95% and 88% of total sample for Vjosa and Mati sediments respectively, are identified. The layers enriched in heavy minerals from Vjosa delta deposits are almost black in colour, while at Mati delta these layers are dark green coloured. Separation of the heavy from the light fraction was performed, in order to compare the different fractions between the two studied delta areas. The accumulation of HM occurs mainly in the fraction of 125-250 µm in the sediments of both deltas. The HM dominate in the magnetic field of 0.4-0.8 A/m. XRD analysis results show a great variety of minerals present in the delta samples which can be attributed to the wide variety of geological zones and lithologies that are intersected by the Vjosa and Mati rivers, respectively. In the 63-425 μm fraction rich in heavy minerals of both delta systems considerable amounts of magnetite (up to 39.4% in Vjosa samples), chromite (up to 20.2% in Vjosa samples), garnet (up to 13.6% in Vjosa samples), ilmenite (up to 8.3% in Mati samples), rutile (up to 4.7% in Mati samples), hematite (up to 2.2% in Mati samples), and zircon (up to 2.1% in Vjosa samples) are observed. Rock forming minerals such as pyroxene, amphibole, and epidote compose significant percentages of this fraction. In addition, the presence of gold grains in Vjosa delta sediments is remarkable. Both catchment areas consist to a great extent of similar formations such as the Mirdita Ophiolite Zone and the Pindos Ophiolite complex, providing thus a similar HM fingerprint at both delta areas. Minerals that occur in higher abundances reflect the extensive presence in the drained areas of related parent rocks which are rich in these minerals and which are often more vulnerable to weathering. The samples of Vjosa river delta show high percentage of carbonate constituents, which is related to the presence of carbonate rocks of the Ionian and Kruja tectonic zones within which the hydrographic network of the Vjosa River has been developed. The samples of Mati river delta show lower abundance of carbonate minerals, reflecting the limited presence of carbonate rocks at the Kruja Zone, which occur in the catchment area of the river near its mouth.

A shallow compaction model for Holocene Mississippi Delta sediments

The extensive loss of land elevation and the consequent exposure to flood hazards are seriously threatening the long-term survival of the Mississippi Delta. Shallow compaction of the top soil is one of the major components contributing to the relative sea level rise. In the last decades, more subsidence measurements have become available and recent studies demonstrate that compaction of Holocene strata is dominant. Here we propose a novel application aimed at modeling the present-day shallow compaction due to consolidation processes in the top soil. Soil compaction is properly computed and accounts for the large soil grain motion and the delayed dissipation of pore-water overpressure. The grain motion is described by means of a Lagrangian approach with an adaptive mesh where the grid nodes follows the accretion/compaction processes. Model calibration is obtained from stratigraphic and geochrology information collected at the Myrtle Grove Subsidence Superstation, where a nearly 40 m-deep sediment core that penetrates the entire Holocene succession allows testing model results over long (millennial) timescales. Model validation with available observations from rod surface-elevation table – marker horizon (RSET-MH) data enables the model to predict future scenarios.

Sediment discharge from alpine glaciers in times of increased melt – an example from the Austrian Alps

&lt;p&gt;Glaciated mountains are zones of high sediment dynamics and at the same time very sensitive to climate change. In times of increased summer temperatures and high melt rates have been related to observed increase in sediment dynamics at various locations. However, this response seems to be highly variable also on regional scales indicating that controlling factors have yet not been fully identified and understood. Sediment output from glaciated catchments affects sediment budgets, streamflow ecology and hydropower generation. Data on sediment discharge from proglacial areas in the Alps is scarce. Knowledge on sediment responses to increasing temperatures and changing climates is crucial for river and reservoir management and climate change adaptation.&lt;/p&gt;&lt;p&gt;We contribute to this debate by quantifying sediment discharge from the Obersulzbachkees glacier, Hohe Tauern, Austria based on recent lake deposition volume. Located at the valley head of the Obersulzbach valley, the glacier experienced rapid degradation within the last 20 years and also showed high rates of sediment discharge. The formerly large single glacier disintegrated into five remaining parts and a large proglacial lake formed. Sediment discharge from these smaller glaciers is captured by the lakes and a huge delta has developed after retreat of ice from the lake. We quantified the lake and delta sediments using ground penetrating radar and sub-bottom profiling and revised our previous estimations by including new data increasing the accuracy of our finding. The Obersulzbachkees retreated by 400-800 m in distance between 1999 and 2019 and lost more than 3 km&amp;#178; of glacier area. Between 2007 and 2019 more than 600,000 m&amp;#179; of sediments have been deposited within the lake delta only. We discuss sediment discharge from glacier to lake in relation to glacier retreat and climate conditions since lake formation and relate our findings to both changes in the catchment and runoff and sediment output dynamics from the lake.&lt;/p&gt;