Cyclic Flow of Salt Water in the Biscayne Aquifer of Southeastern Florida

Abstract. Observations over a period of nearly 20 years confirm the fact that the salt-water front in the Biscayne aquifer along the coast of the Miami area, Florida, is dynamically stable at a position seaward of that computed according to the Ghyben-Herzberg principle. During periods of heavy recharge the fresh-water head is high enough to cause the fresh water, the salt water, and the zone of diffusion between them to move seaward. In addition to this bodily movement of the system, there is a seaward flow of diluted salt water in the zone of diffusion. When the fresh-water head is low, salt water in the lower part of the aquifer intrudes inland, but some of the diluted sea water in the zone of diffusion continues to flow seaward. Cross sections showing equipotential lines in terms of equivalent fresh-water head show that the sea water flows inland, becoming progressively diluted with fresh water, to a line along which there is no horizontal component of flow, after which it moves upward and returns to the sea. The cyclic flow acts as a deterrent to the encroachment of sea water because of return to the sea of a part of the inland flow. I Introduction. The basic premise of the Cl~yben-Herzberg principle is that the position oi the interface between fresh water and salt ~ater in a coastal aquifer will be governed by a hydrostatic equilibrium between fresh water and the more dense sea water. Hubbert [1940, pp. 921-9261 showed, however, that because fresh water was known to flow seaward, the position of the interface would be governed by a dynamic tween the densities of sea water (p,) and fresh water. Observations over a period of nearly 20 years indicate that the salt front in the Biscayne aquifer of the Miami, Florida, area is dynamically stabilized seaward of the theoretical position given by either concept (h) with reference to sea level a t the point on It is the intent of this paper to illustrate by the interface multiplied by the ratio of the field observations that the salt water is no

MAPS, SECTIONS, AND STRUCTURE-CONTOUR DIAGRAMS SHOWING THE GEOLOGY AND GEOCHEMISTRY OF THE MOUAT NICKEL-COFFER PROSPECT, STILLWATER COMPLEX, STILLWATER COUNTY, MONTANA

ABSTRACT Deposits of magmatic nickel-copper (Ni-Cu) sulfides are concentrated near the base of the Stillwater Complex, a Late Archean mafic to ultramafic layered intrusion exposed on the north edge of the Beartooth Mountains, Montana. Extensive drilling and limited underground development work by the Anaconda Minerals Company has delineated the sub-surface extent of one of these deposits, the Mouat Ni-Cu prospect or deposit. Structural interpretation shows that rocks of the Mountain View area of the Stillwater Complex are folded into a broad syncline which is inclined and cut by several generations of faults. The oldest faults strike northeast and have near vertical dips. These faults are cut by northweststriking, near vertical faults showing left-lateral separation. Apparent separation on these faults are less than 500 ft. Two high-angle reverse faults, the Lake fault and the Bluebird thrust, truncate the Mouat deposit on the northeast and the southwest, respectively. Sulfide minerals that constitute this deposit are concentrated at the lower contact of the Stillwater Complex within the Basal series and within and adjacent to very discontinuous, irregularly shaped Stillwater-associated sills and dikes that intrude the metasedimentary rocks underlying the complex. The base of the Stillwater Complex shows considerable relief over short distances; as a result, the thickness of the Basal series ranges from 0 to 450 ft. However, there is no clear evidence that sulfides at the base of the complex pooled in depressions on the floor of the complex. Intensity of faulting and the discontinuous nature of the matrix-to-massive sulfide mineralization do not allow probabilistic tonnage and grade estimates to be made despite the density of drilling

Morphology of the petrosal and stapes of Borealestes (Mammaliaformes, Docodonta) from the Middle Jurassic of Skye, Scotland

We describe, in unprecedented detail, the petros-als and stapes of the docodont Borealestes from the Middle Jurassic of Scotland, using high resolution lCT and phase- contrast synchrotron imaging. We describe the inner ear endocast and the vascularized interior structure of the pet-rosal, and provide the first endocranial view of a docodontan petrosal. Our study confirms some similarities in petrosal and stapedial morphology with the better known Haldan-odon of the Late Jurassic of Portugal, including: (1) the degree of curvature of the cochlea; (2) multiple features related to the highly pneumatized paroccipital region; (3) the shape of lateral trough, the fossa of the M. tensor tym-pani, and the ridge on the promontorium; (4) the round shape of the fenestra vestibuli; and (5) overall morphology of the stapes. But Borealestes differs from Haldanodon in having a bony ridge that separates the tympanic opening of the prootic canal, the secondary facial foramen and the hia-tus Fallopii, from the fenestra vestibuli. We identify two new vascular structures: the anterior and posterior trans-cochlear sinuses, which traverse the pars cochlearis around the cochlear nerve (VIII). These trans-cochlear sinuses have not been observed in previous docodont specimens, and could be an autapomorphy of Borealestes, or apomorphic for this clade. We also establish the anatomical relationship of the circum-promontorium plexus to the inner endocast. The high quality of our scans has made these structures visible for the first time

Sediment geochemistry of streams draining abandoned lead / zinc mines in central Wales: the Afon Twymyn

Purpose Despite the decline of metal mining in the UK during the early 20th century, a substantial legacy of heavy metal contamination persists in river channel and floodplain sediments. Poor sediment quality is likely to impede the achievement of ’good’ chemical and ecological status for surface waters under the European Union Water Framework Directive. This paper examines the environmental legacy of the Dylife lead/zinc mine in the central Wales mining district. Leachable heavy metal concentrations in the bed sediments of the Afon Twymyn are established and the geochemical partitioning, potential mobility and bioavailability of sediment-associated heavy metals are established. Materials and methods Sediment samples were collected from the river bed and dry-sieved into two size fractions (<63 μm and 64–2,000 μm). The fractionated samples were then subjected to a sequential extraction procedure to isolate heavy metals (Pb, Zn, Cu, Cd, Fe, Mn) in three different geochemical phases. Sediment samples were then analysed for heavy metals using ICP-AES. Results and discussion The bed sediment of the Afon Twymyn is grossly polluted with heavy metals. Within the vicinity of the former mine, Pb concentrations are up to 100 times greater than levels reported to have deleterious impacts on aquatic ecology. Most heavy metals exist in the most mobile easily exchangeable and carbonate-bound geochemical phases, potentially posing serious threats to ecological integrity and constituting a significant, secondary, diffuse source of pollution. Metal concentrations decrease sharply downstream of the former mine, although there is a gradual increase in the proportion of readily extractable Zn and Cd. Conclusions Implementation of sediment quality guidelines is important in order to achieve the aims of the Water Framework Directive. Assessments of sediment quality should include measurements of background metal concentrations, river water physico-chemistry and, most importantly, metal mobility and potential bioavailability. Uniformity of sediment guidelines throughout Europe and flexibility of targets with regard to the most heavily contaminated mine sites are recommended

Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK

Fluvial sedimentary successions represent porous media that host groundwater and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. The permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation in England (UK), are described, from core-plug to well-test scale up to ~1 km depth. Within such lithified successions, dissolution associated with the circulation of meteoric water results in increased permeability (K~10−1–100 m/day) to depths of at least 150 m below ground level (BGL) in aquifer systems that are subject to rapid groundwater circulation. Thus, contaminant transport is likely to occur at relatively high rates. In a deeper investigation (> 150 m depth), where the aquifer has not been subjected to rapid groundwater circulation, well-test-scale hydraulic conductivity is lower, decreasing from K~10−2 m/day at 150–400 m BGL to 10−3 m/day down-dip at ~1 km BGL, where the pore fluid is hypersaline. Here, pore-scale permeability becomes progressively dominant with increasing lithostatic load. Notably, this work investigates a sandstone aquifer of fluvial origin at investigation depths consistent with highly enthalpy geothermal reservoirs (~0.7–1.1 km). At such depths, intergranular flow dominates in unfaulted areas with only minor contribution by bedding plane fractures. However, extensional faults represent preferential flow pathways, due to presence of high connective open fractures. Therefore, such faults may (1) drive nuclear waste contaminants towards the highly permeable shallow (< 150 m BGL) zone of the aquifer, and (2) influence fluid recovery in geothermal fields