The analysis and prediction of lateral instability in highly stressed, near-surface rock strata

1982 ◽  
Vol 19 (4) ◽  
pp. 451-462 ◽  
Author(s):  
J. Roorda ◽  
J. C. Thompson ◽  
O. L. White
Keyword(s):  
New York ◽  
New York State ◽  
In Situ Stress ◽  
Short Term ◽  
Lateral Instability ◽  
Near Surface ◽  
Southern Ontario ◽  
Pressure Ridge ◽  
Rock Strata

The potential for lateral instability of highly stressed, near-surface sedimentary rocks such as the Paleozoic deposits of southern Ontario and western New York State is investigated analytically. The minimum magnitude of the in-situ stress required for a pressure ridge to form is easily computed once values are obtained for the stratum thickness and short-term Young's Modulus, the weight of overburden, and the residual friction with the over- and underlying material. Consideration is also given to the increased likelihood of instability associated with excavations of different widths and depths. Keywords: rock, excavations, quarries, instability, pressure ridges, mechanisms.

scholarly journals Thermally-controlled color gradient for fossils and associated sediments: implications for paleoecology

1992 ◽  
Vol 6 ◽  
pp. 14-14
Author(s):  
Gordon C. Baird ◽  
Timothy W. Lyons ◽  
Carlton E. Brett
Keyword(s):  
New York ◽  
New York State ◽  
Foreland Basin ◽  
Field Work ◽  
Black Shales ◽  
Foreland Basins ◽  
Regional Study ◽  
Southern Ontario ◽  
Color Gradient ◽  
Appalachian Foreland

Regional study of Middle-Late Ordovician and Middle-Late Devonian carbonate and siliciclastic deposits in the northern Appalachian foreland basin reveals a prominent pattern of eastward-darkening of marine mudrocks and associated fossils. Exoskeletons of certain trilobite genera transform from a saddle brown coloration in southern Ontario exposures to black and near-black in central and eastern New York. Similar eastward darkening of mudstones and argillaceous carbonate units is observed to be covariant with conodont color alteration (C.A.I.) values across this same region. This pattern is coupled with other lines of evidence for eastward increases in heat-of-burial for strata across New York State, indicating that the darkening is linked to this control. Laboratory heating of thermally “cold”, light-colored samples shows that this process can be simulated under controlled conditions. The darkening of fossils and mudrocks probably occurs due to thermal maturation of organic matter within these materials.Darkening of certain fossiliferous mudrock facies from color values as high as N 7.5 at a C.A.I. of 1.0 to those of N 2.5 at C.A.I. of 3.5 has important implications for paleoecological interpretations. Where obvious fossil-rich beds are absent and field work cursory, it might be tempting to infer a shelf-to-basin transition in the uprank direction where none exists. Where skeletal packstone and grainstone beds are common in thermally mature deposits it is possible that intervening dark-colored shales may be erroneously interpreted as basinal, organicrich (black) shales and the grain-supported beds as turbidites, when, in fact, such beds are shallow-shelf tempestites. We believe that similar value gradients should be present wherever local or regional heat-flow anomalies or differential burial patterns are developed. Foreland basins bordering orogens should contain such gradients and workers must be alert to this illusory color effect when working on complex facies in such settings. It is probable that many paleoenvironmental judgments may have been colored by misinterpretations of this type.

scholarly journals Diagenetic apatite character and in situ ion microprobe U–Pb age, Keeseville Formation, Potsdam Group, New York State

2017 ◽  
Vol 54 (7) ◽  
pp. 785-797 ◽  
Author(s):  
Quentin Gall ◽  
William J. Davis ◽  
David G. Lowe ◽  
Quinn Dabros
Keyword(s):  
New York ◽  
Fluid Flow ◽  
New York State ◽  
Ion Microprobe ◽  
Crystal Length ◽  
Aeolian Processes ◽  
York State ◽  
Orogenic Events ◽  
Obvious Source

An occurrence of diagenetic fluorapatite cement is documented within the Cambro-Ordovician Keeseville Formation, Potsdam Group, near Chateaugay in New York State. The fluorapatite cement occurs as stratiform layers within ephemeral fluvial quartz arenites, which have been reworked by aeolian processes prior to burial. The paragenetic sequence includes the following: compaction of dust-rimmed grains → quartz cementation → minor kaolinite → fluorapatite cementation followed by secondary dissolution porosity and telogenetic hematite cementation. Mesogenetic illitization of kaolinite may have taken place prior to or following fluorapatite cementation. The fluorapatite occurs as elongated bladed crystals that characteristically contain ladder-like, inclusion-rich cores running parallel to crystal length, surrounded by clearer rims, and larger blocky crystals towards the middle of interstices. In situ SHRIMP analyses of blocky fluorapatite crystals yield a U–Pb age of 486 ± 29 Ma, indicating that the cement formed during mesogenetic burial processes and (or) during fluid flow driven by Taconic orogenic events. There is no obvious source of phosphorous for the fluorapatite cement within the Potsdam Group, but phosphorous-rich lithologies are known from the adjacent basement of the Adirondack Dome. Phosphorous-rich fluids may have been derived from these basement lithologies. The occurrence of the rare fluorapatite cement in the Keeseville Formation adjacent to the Chateaugay Lake Fault raises the possibility that alkaline phosphatic fluids were focused within the fault and migrated laterally away from the fault into the host Keeseville Formation to form stratiform fluorapatite cement in the sandstone.

The salivary gland chromosomes of Prosimulium multidentatum Twinn and three forms included in Prosimulium magnum (Dyar and Shannon) (Diptera:Simuliidae)

1969 ◽  
Vol 47 (5) ◽  
pp. 943-949 ◽  
Author(s):  
P. O. Ottonen ◽  
Ramachandran Nambiar
Keyword(s):  
New York ◽  
Salivary Gland ◽  
Great Lakes ◽  
Sex Chromosomes ◽  
Species Complex ◽  
New York State ◽  
Great Lakes Region ◽  
Southern Ontario ◽  
York State ◽  
The Third

Further study of the morphology of salivary gland chromosome complements within the range described for Prosimulium magnum showed the species to consist of three cytologically distinct populations. The first two forms are without sex chromosomes, (1) a form analogous to the species chromosomal standard, P. magnum, (2) a form which is differentiated by the fixed inversion IIS-25, but (3) the third form has cytological XcYc sex determination. In the Great Lakes region these three forms of the P. magnum complex and P. multidentatum are sympatric in three separate areas, Michigan, Southern Ontario, and Western New York State. Natural hybrids between the forms have so far been obtained only infrequently, and the known hybrids are described. Some chromosomal aspects of speciation are discussed in relation to the present observations on the species complex.

Supernormal fluid pressures in sedimentary rocks of southern Ontario – western New York State

1992 ◽  
Vol 29 (1) ◽  
pp. 80-93 ◽  
Author(s):  
K. G. Raven ◽  
K. S. Novakowski ◽  
R. M. Yager ◽  
R. J. Heystee
Keyword(s):  
New York ◽  
Sedimentary Rock ◽  
New York State ◽  
Sedimentary Rocks ◽  
Fluid Pressure ◽  
Gas Migration ◽  
Southern Ontario ◽  
York State ◽  
Monitoring Wells ◽  
Pressure Transducers

Fluid pressures up to 1.7 times greater than hydrostatic have been measured in argillaceous Paleozoic rocks of low permeability in southern Ontario and western New York State. These supernormal formation fluid pressures were measured at depths of 50–310 m using submersible pressure transducers with straddle packers and multiple-packer casings isolating the test intervals. Measurements were obtained over periods of 7–46 months following casing installations. The pressure measurements from 11 monitoring wells are compiled and supporting hydrogeologic data for 5 selected wells are used as examples to illustrate the occurrence of supernormal fluid pressures in the Ordovician, Silurian, and Devonian sedimentary sequence of southern Ontario and western New York State. Possible explanations for the occurrence of supernormal fluid pressures in sedimentary rock are evaluated considering the available geologic and hydrogeologic information obtained from the monitoring wells. Based on this review, it is hypothesized that gas migration and accumulation from deeper distant sources via permeable vertical pathways is the most plausible explanation for the observed fluid pressures, although secondary contributions from local neotectonic activity are also possible. The implications of such supernormal fluid pressures on regional groundwater flow in sedimentary rocks and related activities such as waste disposal in sedimentary rock are briefly discussed. Key words : supernormal fluid pressure, sedimentary rocks, gas migration.

Near-surface in situ stress: Introduction

1984 ◽  
Vol 89 (B11) ◽  
pp. 9321 ◽  
Author(s):  
Terry Engelder ◽  
Marc L. Sbar
Keyword(s):  
In Situ Stress ◽  
Near Surface
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