Subaqueous Springs Research Articles

QUANTIFYING RIVER ACCRETION IN THE UPPER RIO GRANDE GORGE, NEW MEXICO, BY USING AN ACOUSTIC DOPPLER CURRENT PROFILER

ABSTRACTThe section of the upper Rio Grande in New Mexico is important to downstream water management and the administration of water rights. It has long been believed that this remote reach of the Rio Grande is characterized by significant groundwater accretions, which contribute to water available for downstream uses. This study focused on the uppermost 30 miles of the Rio Grande in New Mexico seeking to establish locations of groundwater accretions in the reach and document magnitude of gain. In order to quantify the accretion of the upper Rio Grande, an expedition using inflatable kayaks, an acoustic Doppler current profiler (ADCP) and an electromagnetic meter was carried out in the fall of 2008 when natural surface flow was low. The study area covered a stretch of 31 miles. The expedition was able to determine that the total accretion of this stretch of the Rio Grande was 22 ft3s−1 with an average accretion rate of 0.73 ft3s−1 mile−1. Most of the reach exhibited minimal gain or loss, and most of the accretion was centred in Sunshine Valley. One of the most significant results was encountering a large artesian, subaqueous spring, which might be the largest documented spring in New Mexico and contributes nearly 50% of the accretion in the reach. The study was also able to characterize the exact locations of other significant groundwater inputs. In addition to quantifying the accretion of part of the upper Rio Grande, the study provides the framework for using advanced technology in the form of an ADCP to determine river accretions in remote locations. ADCPs offer the benefit of reducing measurement time and measurement error, collect high‐resolution data and are non‐intrusive. Overall, the use of ADCP technology to determine river accretion offers an improvement over traditional methods, and it is the hope of the authors that this technology is utilized for river accretion studies in the future. Copyright © 2011 John Wiley & Sons, Ltd.

Distribution of subfossil ostracod assemblages in lacustrine profundal sediments of north-eastern Poland

The distribution of ostracod valves was studied in seven short (< 50 cm) sediment cores collected from the sublittoral-profundal zones (depth > 12 m) of four lowland, dimictic lakes (Kameduł, Szelment Mały, Szelment Wielki and Szurpiły) situated in the Eastern Suwałki Lakeland of NE Poland. These postglacial channel lakes are still moderate in trophy level, but to some extent, they differ from each other in the increase of anthropogenic alterations, especially in their hypolimnion. The studied sediment sequences, corresponding roughly to the period of the last ca. 300 years, yielded ca. 5500 valves of 20 ostracod species, out of which only seven are here considered as the autochthonous profundal component of the fossil assemblages: Candona candida, C. neglecta, Fabaeformiscandona protzi, F. tricicatricosa, Bentocypria curvifurcata, Cytherissa lacustris and Limnocytherina sanctipatricii. Valves of the remaining species were most probably subjected to postmortem transport from shallow water deposits or from lakeside and/or subaqueous springs, and thus were not deposited in situ at the deep bottom. By clustering classification and multi-dimensional scaling ordination, three major assemblage types were recognised in the moderately eutrophicated parts of the studied lakes: (a) assemblage dominated by C. candida, (b) assemblage dominated by C. lacustris and (c) the most diverse assemblage, in which four species (C. lacustris, C. candida, F. protzi and C. neglecta) occur in more or less equal percentages. On the other hand, sediments of the most eutrophic basins of the lakes (especially in Kameduł and Szelment Mały) are characterised by the decline of total valve abundances and complete extinction of C. lacustris, a species indicative of low trophy, so that, in extreme cases, a few valves (if any) of more eurytopic or only allochthonous species could be found in some of the uppermost layers. Successional transitions of the recognised assemblage types are discussed according to the generalised model of the deep lacustrine ostracod succession previously established for the Polish lakes on the country scale. The recorded assemblages correspond well with the trophic diversity of the studied lakes, confirming inferences based on previously published data on other trophy indices from this area. Finally, additional data on modern profundal ostracod fauna from dredge samples of the studied lakes are also provided.

Geological setting, paragenesis and fluid history of the Walford Creek Zn‐Pb‐Cu‐Ag prospect, Mt Isa Basin, Australia*

The low‐grade Walford Creek Zn‐Pb‐Cu‐Ag deposit is located on the faulted northern margin of the Proterozoic Mt Isa Basin. Mineralisation is localised by the Fish River growth fault and its intersection with reduced organic‐rich shale units within the Mt Les Siltstone. The Mt Les Siltstone (1640 ± 7 Ma) is a fine‐grained, mixed clastic‐carbonate sequence deposited predominantly below storm wave‐base in a basin controlled by synsedimentary faulting. Four sulfide generations are recognised. Stage I consists of synsedimentary pyrite and marcasite deposited within three lenses as microbially precipitated mounds from subaqueous springs that vented from the Fish River Fault, with evidence for extensive detrital reworking. Early diagenetic stratiform and stratabound, primary porosity cavity‐fill sphalerite, galena with or without pyrite and quartz mineralisation (Stage II) has overprinted Stage I sulfides. Fluid‐inclusion data are consistent with metal transport by >180°C NaCI‐rich fluids (6–7 wt% eq. NaCI), and with precipitation by mixing with cool, low‐salinity (1 wt%), dilute fluids (<50°C). Mineralisation formed shortly after sediment deposition from connate lacustrine water, or during uplift and erosion of the succession prior to deposition of the overlying Doomadgee Formation. In the second case, the low‐salinity fluids are meteoric groundwater. Stage III sulfides consist of cavity‐filling and vein sphalerite, galena and chalcopyrite. Stage III was deposited by cooling and mixing of hypersaline (150–170°C) MgCI2 brines (∼25 wt% eq.) with ambient (<70°C) CaCI2‐MgCI2 brines. Salinities for all Stage III fluids range between 18 to 25 wt%. Mineralisation post‐dates stylolitisation and probably formed at a depth of 1–2 km. Stage IV mineralisation comprises vein chalcopyrite, sphalerite and galena, which were deposited by conductive cooling in association with reduction of hypersaline (125°C) CaCI2 brines (∼30 wt% eq.). Stages III and IV formed after deposition of the Doomadgee Formation, but prior to maximum burial. The Walford Creek mineralisation shows affinities with both early sediment‐hosted stratiform and late Mississippi Valley‐type styles of mineralisation. The diversity of mineralisation styles are a product of multiple mineralisation events that extended from sedimentation through to deep burial. The prolonged mineralisation history has resulted from the Fish River Fault episodically tapping deep‐seated hydrothermal fluids of varying compositions. The local sedimentary fades have been an efficient base‐metal trap from the time of sedimentation to late diagenesis or later.

Lithofacies and Biofacies of Mid-Paleozoic Thermal Spring Deposits in the Drummond Basin, Queensland, Australia

The Devonian to Carboniferous sinters of the Drummond Basin, Australia, are among the oldest well established examples of fossil subaerial hot springs. Numerous subaerial and subaqueous spring deposits are known from the geological record as a result of the occurrence of economic mineral deposits in many of them. Some are reported to contain fossils, but very few have been studied by paleobiologists; they represent an untapped source of paleobiological information on the history of hydrothermal ecosystems. Such systems are of special interest, given the molecular biological evidence that thermophilic bacteria lie near the root of the tree of extant life. The Drummond Basin sinters are very closely comparable with modern examples in Yellowstone National Park and elsewhere. Thirteen microfacies are recognisable in the field, ranging from high temperature apparently abiotic geyserite through various forms of stromatolitic sinter probably of cyanobacterial origin to ambient temperature marsh deposits. Microfossils in the stromatolites are interpreted as cyanobacterial sheaths. Herbaceous lycopsids occur in the lower temperature deposits.