Depositional environments and paleogeography of the Winnipeg Group (Ordovician), Williston Basin, North Dakota

The Winnipeg Group (Upper Ordovician) unconformably overlies the Deadwood Formation (Cambrian - Lower Ordovician) over most of North Dakota, except in the extreme eastern part, where it lies directly on Precambrian basement rocks. The Winnipeg is conformably overlain by the Red River Formation (Upper Ordovician). The Winnipeg reaches a maximum thickness of 448 feet (136.6 m) in the center of the basin, Williams County. The Winnipeg Group consists of three formations, in ascending order, the Black Island, Icebox, and Roughlock Formations. The Black Island Formation is, herein, formally divided into the Hawkeye Valley and the Garland Members. The Hawkeye Valley Member consists of two lithofacies: a red-bed lithofacies and a green quartz wacke lithofacies. The red-bed lithofacies consists of two lithotypes: a red quartz arenite and a red clayshale. The Hawkeye Valley Member reaches a maximum thickness of 128 feet (39 m) in Williams County and is restricted to the western half of North Dakota and the immediately surrounding areas. Abundant desiccation cracks and the distinctive red color strongly suggest that the red-bed lithofacies was deposited in a subareal environment. The red-bed lithofacies represents a fluvial/deltaic environment and the green quartz wacke lithofacies represents a.nearshore marine or lagoonal environment. The Garland Member consists of two lithofacies: a quartz arenite lithofacies and a green quartz wacke lithofacies. The green quartz wacke lithofacies is similar in character to the green quartz wacke lithofacies within the Hawkeye Valley, which represents the initial deposits of the Late Ordovician transgression. The quartz arenite lithofacies consists of three lithotypes: a bioturbated quartz arenite, a structured quartz arenite, and a structureless quartz arenite. The Garland Member reaches a maximum thickness of 169 feet (52 m) in McKenzie County. Prominent sedimentary structures and good sorting in the structured quartz arenite indicate that deposition occurred in an active foreshore or nearshore environment. The high degree of bioturbation and lack of sedimentary structures in the bioturbated quartz arenite lithotype indicate deposition in a relatively low-energy environment below normal wave base. The lithofacies found within the Garland Member thus represents a shallow marine environment. The Icebox Formation is a fossiliferous, bioturbated shale with occasional sandstones, and represents an offshore deposit. The Icebox Formation reaches a maximum thickness of 167 feet (51 m) in Grand Forks County; the maximum thickness in the center of the basin is 156 feet (48 m) in McKenzie County. The Roughlock Formation is a fossiliferous, calcareous shale deposited in a deeper marine environment. The Roughlock reaches a maximum thickness of 95 feet (29 m) in the extreme eastern part of North Dakota and grad1.µUly thins to the west. The contacts between all of the units within the Winnipeg are intertonguing and gradational. At the end of the Llanvirnian (Middle Ordovician) there was a major sea level drop, causing erosion of much of the Deadwood Formation. Sea level rose again during the Chazyan Stage (latest Middle Ordovician), and the Hawkeye Valley was deposited unconformably on the Deadwood. As sea level continued to rise, the Garland was deposited, followed by offshore marine Icebox shales. Local topographic highs probably had sufficient relief to cause the formation of sand bodies during Icebox deposition. Still farther offshore, where the influx of clays was minor, the calcareous shales of the Roughlock were deposited, and finally deposition of the Red River limestones occurred

Seasonal Variations in Water Quality Parameters of the Mississippi River near St. Cloud, MN

ABSTRACT - Water quality parameters were monitored in the Mississippi River and three tributaries (Harris Channel, Watab Creek, and Sauk River) from July 1980 to April 1981. Results were correlated with water temperature and discharge to assess seasonal changes. Effects of tributary inflow on the river were determined. Planktonic carbon was estimated with the firefly luciferin-luciferase system which measures adenosine triphosphate extracted from viable cells. Particulate organic matter, planktonic carbon, and percentage viable carbon were correlated with temperature (p ~ 0.6) while nitrate plus nitrite was inversely correlated with temperature and discharge. Only the Sauk River affected the water quality of the Mississippi River by adding elevated levels of dissolved electrolytes, total phosphorus, particulate organic matter, and planktonic carbon. Relatively low levels of planktonic carbon (155 μg/1) in the river indicated good water quality. Seasonal changes in water quality parameters of rivers must be considered in designing useful monitoring programs

Adaptive Filters Revisited - RFI Mitigation in pulsar observations

Pulsar detection and timing experiments are applications where adaptive filters seem eminently suitable tools for radio-frequency-interference (RFI) mitigation. We describe a novel variant which works well in field trials of pulsar observations centred on an observing frequency of 675 MHz, a bandwidth of 64 MHz and with 2-bit sampling. Adaptive filters have generally received bad press for RFI mitigation in radio astronomical observations with their most serious drawback being a spectral echo of the RFI embedded in the filtered signals. Pulsar observations are intrinsically less sensitive to this as they operate in the (pulsar period) time domain. The field trials have allowed us to identify those issues which limit the effectiveness of the adaptive filter. We conclude that adaptive filters can significantly improve pulsar observations in the presence of RFI.Comment: Accepted for publication in Radio Scienc

X-ray Emission from the Host Clusters of Powerful AGN

(Abridged) We report the detection of X-ray emission from the host cluster of the radio-quiet quasar H1821+643 with the ROSAT HRI, and the non-detection of the host cluster of the radio-loud quasar 3C206 using the EINSTEIN HRI. CL1821+643 has a rest-frame 0.1-2.4 keV luminosity of 3.74$\pm$0.57 h$_{50}^{-2}$ 10^45 ergs/sec, 38% from a barely resolved cooling flow component, which places it among the most X-ray luminous clusters known. The cluster emission complicates interpretation of previous X-ray spectra of this field; in particular, the observed FeK$\alpha$ emission can probably be attributed entirely to the cluster, and either the quasar is relatively X-ray quiet for its optical luminosity or the cluster has a relatively low temperature for its luminosity. We combine these data with the recent detection of X-ray emission from the host cluster of the `buried' radio-quiet quasar IRAS 09104+4109, our previous upper limits for the host clusters of two z$\sim$0.7 RLQs, and literature data on FR II radio galaxies and compare to the predictions of three models for the presence and evolution of powerful AGN in clusters: the low-velocity-dispersion model, the low-ICM-density model, and the cooling flow model. Neither of the latter two models can explain all the observations. We suggest that strong interactions with gas-containing galaxies may be the only mechanism needed to explain the presence and evolution of powerful AGN in clusters, consistent with the far-IR and optical properties of the host galaxies studied here. However, the cooling flow model cannot be ruled out for at least some objects, and it is likely that both processes are at work. Each scenario makes predictions for future X-ray and optical observations which can test their relative importance.Comment: Scheduled for the April 1997 Astronomical Journal; 35 pages including 5 figures; also available from http://ethel.as.arizona.edu/~pathall/astro.htm

RCS043938-2904.9: A New Rich Cluster of Galaxies at z=0.951

We present deep I, J_s, K_s imaging and optical spectroscopy of the newly discovered Red-Sequence Cluster Survey cluster RCS043938-2904.9. This cluster, drawn from an extensive preliminary list, was selected for detailed study on the basis of its apparent optical richness. Spectroscopy of 11 members places the cluster at z=0.951 +- 0.006, and confirms the photometric redshift estimate from the (R-z) color-magnitude diagram. Analysis of the infrared imaging data demonstrates that the cluster is extremely rich, with excess counts in the Ks-band exceeding the expected background counts by 9 sigma. The properties of the galaxies in RCS043938-2904.9 are consistent with those seen in other clusters at similar redshifts. Specifically, the red-sequence color, slope and scatter, and the size-magnitude relation of these galaxies are all consistent with that seen in the few other high redshift clusters known, and indeed are consistent with appropriately evolved properties of local cluster galaxies. The apparent consistency of these systems implies that the rich, high-redshift RCS clusters are directly comparable to the few other systems known at z ~ 1, most of which have been selected on the basis of X-ray emission.Comment: 12 pages, 1 color figure. Accepted for publication on The ApJ Letter

A z=0.9 supercluster of X-ray luminous, optically-selected, massive galaxy clusters

We report the discovery of a compact supercluster structure at z=0.9. The structure comprises three optically-selected clusters, all of which are detected in X-rays and spectroscopically confirmed to lie at the same redshift. The Chandra X-ray temperatures imply individual masses of ~5x10^14 Msun. The X-ray masses are consistent with those inferred from optical--X-ray scaling relations established at lower redshift. A strongly-lensed z~4 Lyman break galaxy behind one of the clusters allows a strong-lensing mass to be estimated for this cluster, which is in good agreement with the X-ray measurement. Optical spectroscopy of this cluster gives a dynamical mass in good agreement with the other independent mass estimates. The three components of the RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3 Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we interpret this structure as the high-redshift antecedent of massive (~10^15 Msun) z~0.5 clusters such as MS0451.5-0305.Comment: ApJ Letters accepted. 5 pages in emulateapj, 3 figure

A ROSAT Search for X-ray Emission from Quasar Host Clusters

We report the results of a search for X-ray emission from quasar host clusters at moderate redshift using the {\sl ROSAT} HRI. We detect no emission from the host clusters of 3C~263 (z=0.646) and PKS~2352-34 (z=0.706) to 3$\sigma$\ limits of 3.26 and 2.86 $\times$10$^{44}$\ ergs~s$^{-1}$ respectively (H$_o$=50, q$_o$=1/2) for clusters with r$_{core}$=125~kpc and T=5~keV. These limits show that these quasar host clusters are not substantially more X-ray luminous than optically or X-ray selected clusters of similar richnesses at z$\gtrsim$0.5. We also report the possible detection of a clump of X-ray emitting gas coincident with the brightest radio lobe of 3C~263. This may be evidence for the existence of a clumpy ICM in the host cluster of 3C~263.Comment: Scheduled for the August 1995 Astronomical Journal; 21 pages including figures in uuencoded compressed PostScript format; also available from http://astro.as.arizona.edu/~pathall/preprints.htm

Insects of Western North America. 2. The cicadas of Colorado (Homoptera: Cicadidae, Tibicinidae)

May 15, 2002