Bear Rock Formation Research Articles

A new Early Devonian (Emsian) arthrodire from the Northwest Territories, Canada, and its significance for paleogeographic reconstruction

An heterostiid arthrodire, Herasmius dayi sp. nov., is described from upper Lower Devonian marine deposits of the Bear Rock Formation along the Anderson River, Northwest Territories, Canada. New elements described for the genus for the first time include the suborbital, submarginal (also new for the family Heterostiidae), the lateral shoulder girdle with posterior lateral, anterior dorso-lateral, and posterior dorso-lateral plates and possible infragnathal plate. We present a new reconstruction of the cranial region of Herasmius, previously known only from supposedly freshwater – shallow marine deposits of roughly the same age in the Wood Bay Group of Spitsbergen. The late Early Devonian fishes that are common to the Arctic region of northwestern Canada and the island of Spitsbergen in the Svalbard archipelago of Norway, the porolepiform Heimenia and the arthrodire Herasmius described here, demonstrate the existence of a barrier-free paleogeographic connection between those continental blocks by the late Early Devonian. Comparison of the entire Anderson River vertebrate fauna with other boreal faunas of similar age indicates additional paleogeographic connections north of and around the Old Red Sandstone Continent to the Baltic region, central Europe, and even to the New Siberian Islands and South China, in contrast to most current published paleogeographical reconstructions.

Geochemical Modelling of Fluoride Concentration in Hard Rock Terrain of Madhya Pradesh, India

Abstract:The aim of the present study is to locate and decipher the groundwater quality, types, and hydrogeochemical reactions, which are responsible for elevated concentration of fluoride in the Chhindwara district in Madhya Pradesh, India. Groundwater samples, quality data and other ancillary information were collected for 26 villages in the Chhindwara District, M.P. India during May 2006. The saturation index was computed for the selected samples in the region, which suggest that generally most of the minerals are saturated with respect to water. The concentration of fluoride in the region varies from 0.6 to 4.74 mg/l, which is much higher as per the national and international water quality standards. The study also reveals that the fluoride bearing rock formations are the main source of the higher concentration of fluoride in groundwater along with the conjuncture of land use change. Moreover, the area is a hard rock terrain and consists of fractured granites and amygdaloidal and highly jointed compact basalt acting as good aquifer, which is probably enriching the high content of fluoride in groundwater. High concentration of fluoride is found in deeper level of groundwater and it is possible due to rock‐water interaction, which requires further detailed investigation. The highly alkaline conditions indicate fluorite dissolution, which works as a major process for higher concentration of fluoride in the study area. The results of this study will ultimately help in the identification of risk areas and taking measures to mitigate negative impacts related to fluoride pollution and toxicity.

Assessment of toxicity of two types of drill cuttings from a drilling rig on the Trinidad East coast using Metamysidopsis insularis

This study investigated the relative toxicity of water-based cuttings (WBC) and synthetic oil-based cuttings (SOBC) to the marine species, Metamysidopsis insularis. Results obtained indicate that SOBC (LC50 1.2 (0.85–1.6)%) was more toxic to M. insularis than WBC (LC50 9.9 (8.3–11.8)%), with similar metal contents in both types of cuttings. The elevated levels of metals found in the cuttings when compared to surficial sediments may be due to both drilling fluids, as well as the rock strata from which the cuttings were obtained. Furthermore, total petroleum hydrocarbon (TPH) analyses demonstrated significantly higher concentrations of TPH present in SOBC (14,680 ± 1250 mg kg−1) compared to WBC (860 ± 115 mg kg−1). This may also be due to the increased depth and hence oil bearing rock formations in the selected sampling area, along with the associated synthetic oil-based drilling fluid. These findings therefore supply evidence that drill cuttings after treatment prior to discharge are potentially toxic to marine organisms.

Towards direct detection of gold bearing rock formations from seismic data, St. Ives gold camp, Western Australia

In 2004, Gold Fields Limited and Curtin University of Technology undertook a project to assess the feasibility of the application of high resolution reflection seismic for gold exploration in Western Australia. A large scale regional survey several years before had indicated that deeper structures can be successfully imaged with course seismic acquisition techniques. These surveys provided images on a regional and camp-scale only while shallower structures of direct interest to exploration remained unresolved. The acquisition of high resolution seismic intended to detect economically viable targets for mineral exploration, turned out to be not a trivial endeavour. Seismic lines which traversed over and along busy mine site roads, around restricted areas, and through irregular, jagged terrain result in crooked-line geometry, often saturated with ambient noise, and running in an unfavourable direction with respect to the dominant trend of the major structures. This creates out-of-plane reflections and limits the effectiveness of pre-stack and post- stack imaging techniques and severely affects the calibration with sonic logs. While mine-sites generally have an abundance of borehole drilling data, sonic logs are in sparse supply and often restricted to shallow depths by hydrocarbon standards (200-900 meters), which presents a difficulty for seismic data inversion and subsequent lithological interpretation.

An Early Devonian (Emsian) acanthodian from the Bear Rock Formation, Anderson River, Northwest Territories, Canada

A new genus and species of an Early Devonian (Emsian) mesacanthid acanthodiform from outcrops of the Bear Rock Formation along the Anderson River, Northwest Territories, Canada, is described. The new taxon is distinct from other mesacanthid genera and (or) species in having mesiolaterally expanded skull roof plates and paired nasal bones. Mesacanthids have fin-spines that are similar in size, number, position, and proportions. This new genus is the fourth in the family Mesacanthidae. The wider distribution and apparent taxonomic diversity represented by the discovery of the new genus are indications that the latest-surviving and arguably most advanced acanthodian group, the Acanthodiformes, was already well established in the Early Devonian.

Karst geomorphology and hydrogeology of the bear rock formation — a remarkable dolostone and gypsum megabreccia in the continuous permafrost zone of northwest Territories, Canada

Karst geomorphology and hydrogeology of the bear rock formation — a remarkable dolostone and gypsum megabreccia in the continuous permafrost zone of northwest Territories, Canada

Early Devonian eurypterids from the Northwest Territories of Arctic Canada

A new eurypterid fauna from the Lower Bear Rock Formation (Early Devonian, Emsian) of Anderson River, in the Northwest Territories of the Canadian Arctic, is described. The material comprises an almost complete specimen and five isolated carapaces of Erieopterus microphthalmus; an incomplete carapace and telson referred to Drepanopterus sp.; and an isolated prosomal appendage of Carcinosoma sp. Associations include actinopterygian, sarcopterygian, and acanthodian fish, as well as lingulids, conchostracans, ostracodes, coprolites, and plant material. A nearshore marine environment is inferred. This assemblage provides the first Canadian record of Drepanopterus and the youngest Canadian occurrences of erieopterid and carcinosomatid eurypterids.

Hydrogeology of the central Mackenzie Valley

More than 100 springs, seeps and mineralized ponds in the central Mackenzie Valley have been investigated using chemistry, field observations and a general knowledge of the geology in conjunction with environmental isotopes. δ 2H and δ 18O values indicate precipitation (primarily snowmelt) as the source for all groundwaters sampled. Chemical analyses of the waters indicate that there are three major components: Ca 2+SO 4 2− dominates, followed by Na +Cl − and Ca 2+Mg 2+HCO − 3. The chemical data in combination with 34S data indicate that the Devonian Bear Rock Formation is the major aquifer throughout the valley. Other important bedrock aquifers include the Mt. Kindle, Franklin Mountain and Saline River Formations. Recharge is directly into bedrock through solution channels or karst systems within the Franklin Mountains. Discharge from the bedrock units is controlled by fold and fault structures. Permafrost is a major factor controlling groundwater recharge but does not significantly affect the location of groundwater discharge.

Isotope geochemistry of dissolved, precipitated, airborne, and fallout sulfur species associated with springs near Paige Mountain, Norman Range, N.W.T.

δ34S values determined for dissolved sulfate in water discharged by sulfurous springs near Paige Mountain identify gypsum beds in the Lower Devonian Bear Rock Formation as the sulfate source, whereas relatively low δ18O values show that as much as 30% of the sulfate may have gone through a reduction–re-oxidation cycle. Reduced sulfur species in the spring water have negative δ34S values as a result of microbiological isotope fractionation during sulfate reduction; airborne sulfur species (H2S, SO2, H2SO4) and gypsum formed through reaction of H2SO4 fallout with exposed carbonate rocks show similar negative δ34S values. Negative δ18O values for the sulfate radical in H2SO4 fallout and in the alteration product indicate that more than half of the oxygen reacting with airborne H2S is derived from water vapour.

34S and 18O abundances differentiate Upper Cambrian and Lower Devonian gypsum-bearing units, District of Mackenzie, N.W.T.—an update

Previous sulfur isotope data for the Lower Devonian Bear Rock Formation and the Upper Cambrian Saline River Formation in the District of Mackenzie, N.W.T. have been supplemented by additional sulfur isotope analyses as well as δ18O determinations on sulfates from outcrops, drill cuttings, and cores. Whereas the mean δ34S value for the Bear Rock Formation is lower than that of the Saline River Formation (+17.8 ± 1.8‰ versus +29.7 ± 2.2‰), the opposite trend was found for the mean δ18O values (+15.6 ± 1.0‰ versus +13.0 ± 1.5‰). The new data confirm that, for all samples analysed, there is no overlap between δ34S values for the two formations, while the δ18O data display some overlap. The earlier δ34S data for samples from an evaporitic section on the northeast side of the Norman Range (originally mapped as consisting entirely of Saline River Formation) indicated the presence of a thrust fault in the section, with Saline River strata overlying Bear Rock strata. The δ18O data for those samples, which fortuitously fall into two non-overlapping groups, confirm the earlier conclusions based on the δ34S data and allow us to define the position of the thrust-fault contact somewhat more closely.

Stratigraphic differentiation by sulfur isotopes between Upper Cambrian and Lower Devonian gypsum-bearing units, District of Mackenzie, N.W.T.

Sulfur isotope analyses of gypsum in outcrop and subsurface samples from the Lower Devonian Bear Rock Formation gave δ34S values ranging from + 10.3 to + 21.8‰ (mean + 16.1‰, standard deviation 2.85‰); samples from the Upper Cambrian Saline River Formation gave δ34S values ranging from + 24.7 to + 40.2‰ (mean + 30.3‰, standard deviation 3.65‰). The lower portion of one outcrop section of 532 ft (162.2 m) on the northeast side of the Norman Range (Franklin Mountains), mapped as Saline River Formation, showed anomalous δ34S values (+ 10.3–+ 18.7‰), suggesting correlation with the Bear Rock Formation. It is likely that at least 97 ft (29.6 m) of Bear Rock strata are present in this section, overlain by a maximum of 435 ft (132.6 m) of gypsiferous Saline River strata that form the base of the main thrust plate of the Norman Range in this locality.