Pass Area Research Articles

Pore‐water pressure measurements: Mississippi delta submarine sediments

Abstract A pore‐water pressure probe (piezometer) was implanted in Mississippi delta sediments at a preselected site (Block 28, South Pass area, 29°00´N, 89°15´W) 145 m from an offshore production platform (water depth approx. 19 m) in September 1975. Total pore‐water pressures (uw ) were monitored for extended periods of time at depths of approximately 15 and 8 m below the mudline concurrently with hydrostatic pressures (u8 ) measured at depths of 15 m and approximately 1 m below the mudline. Relatively high excess pore‐water pressures, ue = (uw ‐u8 ), were recorded at the time of probe insertion measuring 99 kPa (14.4 psi) at 15 m and 50 kPa (7.3 psi) at 8 m. Six hours after the probe was implanted, excess pore pressures were still high at 81 kPa (11.8 psi, 15 m) and 37 kPa (5.4 psi, 8 m). Pore pressures appeared to become relatively constant at the 8‐m depth after 7 h had elapsed, and at the 15 m depth after 10–12 h. Excess pore‐water pressures averaged 72 kPa (10.4 psi, 15 m) and 32 kPa (4.6 psi, 8 m)...

Petrology and origin of stratified scree in New Zealand

Stratified scree in the Porters Pass area of the South Island New Zealand consists of up to 30 m of alternating bands of angular gravel and gravelly silt. The gravel consists of frost-shattered bedrock, while the silt appears to have originated from weathered till that entered the area as loess. Every 10 m of stratified scree actually contains at least 5 m of loess. Glaciers left oversteepened slopes on which screes subsequently formed, probably during later nearby glacial advances. The more gently sloping land may have been covered in vegetation as dense as today, but every l0-118 yr, widespread destruction of the vegetation resulted in a marked period of loess deposition. Thus the stratified scree of Soons (1962) has a different origin to that postulated for the grezes litées of European workers.

Stratigraphic, structural, and metamorphic relationships in the Dansey Pass area, Otago, New Zealand

Abstract In the Dansey Pass area, greywacke, semischist, and schist on the north-eastern margin of the Otago schist arc show a progressive increase in metamorphic grade from prehnite-pumpellyite to greenschist facies, or in terms of textural development, from non-foliated greywacke of textural zone 1 to laminated schist of textural zone 3B. Locally a stratigraphic sequence some 15000 m thick can be recognised, in which the metamorphic grade increases towards the top. The rocks have been affected by four periods of folding. The earliest phase, probably initially penecontemporaneous with the later stages of sedimentation, resulted in steeply dipping strata, overturned throughout extensive areas. Phase II folding may have commenced as the early phase progressed, as early Phase II structures show evidence of soft sediment deformation, although other evidence indicates that Phase II continued until well into the metamorphic event. Isograds and isotects are not folded by Phase II structures, however, indicating...

Ice in Coulthard Cave, Alberta

Coulthard Cave is located in the Crowsnest Pass area of southwestern Alberta, at an elevation of 2650 m above mean sea level. The entrance of the cave faces north, and alt but one of the passages in the cave end in massive ice blockages. Oriented ice samples were removed and studied by crystallographic techniques in a cold laboratory which revealed a layering (not evident to the eye) similar to that formed by the freezing of a horizontal water surface, i.e. a 'pond.' Although present-day temperatures in the cave never exceed 0 °C, large scallop-like depressions in the ice suggest slow erosion by sublimation. An experiment indicated a sublimation rate of 3 mm/yr. Sublimation of the ice permits entrapped sediment to reach the ice surface. Continual downward lowering of the ice surface facilitates the movement by normal trajectory of sediment toward the scallop edges where it forms interstitial ridges. These ridges form on both vertical and overhanging ice surfaces. It is concluded that the ice probably did not form during the Pleistocene Period but rather after the late Hypsithermal warm period.

Development and Economic Implications of Paleokarst, Molas Pass Area, Southwestern Colorado: ABSTRACT

With the emergence of the Mississippian Leadville Limestone, a climatically specific subaerial tower-karst surface developed in the Molas Pass area, with 80 ft of local relief. Much of this surface is buried under different thicknesses of the Early Pennsylvanian Molas Formation, in part a regolith of siltstone and residual clays from the limestone solution. Rising like small peaked knobs from a plain are three examples of the tower karst found near Molas Pass, the Molas Lake tower, Waterfall tower, and Sultan Creek tower. These illustrate the relatively low limestone solubility, strong fracturing, both joint and fault, and high water-table variations conducive to both tower and the related Kegelkarst formation. Folding may produce adverse conditions for the karst tending to hasten cavern integration and limestone removal. Tower karst and the predominance of kaolinite in the lower Molas, together with silica and hematite produced from soil ferralitization, suggest a subtropical to tropical climate with heavy rainfalls followed by rapid evaporation. The modern localization of this type of karst to areas below 30° of latitude implies a northward migration of the Molas Pass area since the Early Pennsylvanian. The complex stratigraphic relations between the fine-grained Leadville Limestone and the underlying Ouray dolomitic grainstone have made their field separation difficult and may indicate which areas were above and below sea level during the karst formation. This suggests a relative elevation of 100-200 ft for the Leadville at the time of the maximum tower-karst formation. The geologic controls on tower-karst development as observed in the Molas Pass area correlate well with the climate and geologic controls in a modern tower-karst analogue, central Jamaica. An understanding of the mechanisms of tower-karst formation and burial is directly applicable to petroleum stratigraphic trap location as in the Elk Basin field of northern Wyoming-southern Montana, and the localization of base metal sulfide ore deposits as at Gilman, Colorado. End_of_Article - Last_Page 915------------

A Reexamination of the Geology of the Frank Slide

The landslide from the east face of Turtle Mountain that destroyed the southern end of the town of Frank in the Crowsnest Pass area of southwestern Alberta has become a classic example because it is one of the largest for which eye witness accounts and a contemporary scientific examination exist. Textbook accounts rely on the reports published shortly after the slide's occurrence in 1903.The slide was thought to have moved down the dip of a steeply inclined set of joints and has therefore been classified variously as a rockfall or block flow. Later regional and geological mapping has shown that the crest of Turtle Mountain lay close to the axis of the Turtle Mountain Anticline. A new detailed map shows that the slide mass lay on the steeply eastward dipping limb of the anticline and the crest of the fold lay very close to the crown of the slide. The slide probably took place on bedding surfaces with the orientation of the scarp and lateral margins of the slide controlled by joint sets. The surface of rupture close to the toe of the slide followed a minor thrust above the Turtle Mountain Fault. The slide is better classified as a rock slide.

Tetroon studies of diffusion potential in the Airshed surrounding the Crowsnest pass area

Abstract A series of constant‐level balloon flights was made in the Crowsnest Pass area under westerly wind conditions, for the purpose of investigating the diffusion properties of the surrounding airshed. The balloon trajectories showed the existence of large sustained velocities over the mountainous region. The magnitudes of the vertical motions were found to be dependent on wind direction. Under moderately strong wind speeds, they appear to have been insensitive to the vertical temperature gradients which were measured within the first 31 m of the ground. Diffusion coefficients were calculated from the tetroon data. They were usually found to be about twice as large as the comparable data presented by Pasquill.

OBSERVATIONS ON SNOW ALGAE IN CALIFORNIA1,2

SUMMARYAlgae that impart a red color to snowfields are rather common in California. Red snow occurs mainly in the Sierra Nevada at altitudes of 10,000–12,000 ft (3050–3600 in) and can occur at high altitudes where snow persists in other parts of the state. The distribution in the Sierra was similar in 1969 and 1970, contrasting snowfall years. Colored snow was found from May to October in old, wet snow‐fields. The predominant color was red and occurred as surface patches in depressions in the snow. The color could extend as deep as 30 cm below the snow surface.Algae in the snowfields of the Tioga Pass area (Sierra Nevada) were large, red, spherical cells of Chlamydomonas nivalis. No other algae were seen. Their distribution, as measured by cell numbers and chlorophyll a, was patchy. Algal cells and chlorophyll a were mainly distributed at or near the snow surface but extended down to a depth of 10 cm. Light intensity was greatly attenuated by snow, but enough light for photosynthesis was found at 50 cm below the surface. Nutrient content of one snow sample was very low. The populations were very actively photosynthetic and took up as much as 65% of added 14CO2 in only 3 hr. It was tentatively concluded that CO2 limits in situ photosynthesis. Photosynthesis was inhibited by melting snow samples. Rough calculations of the growth rate suggested in situ generation times of only a few days for these algae.

Progressive Metamorphism from Prehnite-Pumpellyite to Greenschist Facies in the Dansey Pass Area, Otago, New Zealand

Mesozoic graywackes on the northern margin of the Otago schist belt show a progressive metamorphic increase from prehnite-pumpellyite facies, through pumpellyite-actinolite to greenschist facies. Corresponding, but only crudely coincident, progressive textural modification ranges from massive, nonfoliated graywacke, through schistose graywacke, semischist, to thorough-going laminated quartzo feldspathic schist. Isograds marking the disappearance of prehnite and clastic potash feldspar, and the replacement of pumpellyite by clino-zoisitic epidote have been mapped, and probable reactions occurring at them are explored by modal analyses of chemically similar rocks. The thickness of the pumpellyite-actinolite facies is about 9 km. The great width of this and adjacent facies zones are not readily reconcilable with conventional concepts of geothermal gradients and PT fields of individual metamorphic facies. Tectonic disturbance of geothermal gradients during synmetamorphic deformation appears to be a possible explanation.

An almandine garnet isograd in the Rogers Pass area, British Columbia: The nature of the reaction and an estimation of the physical conditions during its formation

In the Rogers Pass area of British Columbia the almandine garnet isograd results from a reaction of the form: 5.31 ferroan-dolomite+8.75 paragonite+4.80 pyrrhotite+3.57 albite+16.83 quartz+1.97 O2=1.00 garnet+16.44 andesine+1.53 chlorite+2.40 S2+1.90 H2O+10.62 CO2. The coefficients of this reaction are quite sensitive to the Mn content of ferroan-dolomite.

Observations on Some Valley Forms and Deposits in the Sani Pass Area, Lesotho

Abstract Deposits located in hollows, reminiscent of nivation cirques and restricted to altitudes over 2 900 m, are described form an area south of Sani Pass. The deposits consist of layers of gravel with and without boulders, alternating with organic clays. It is postulated that these deposits provide evidence of former climatic fluctuations.

The analcite-bearing volcanic rocks of the Crowsnest Formation, Alberta

The lower Cretaceous Crowsnest Formation of the Crowsnest Pass area, Alberta, is predominantly trachytic, but some sodic, analcite-rich, rocks occur. It consists of bedded pyroclastic and epiclastic material with minor flows and dikes. Most of the volcanism appears to have been explosive in nature. Almost all the igneous material is porphyry tic; nearly all the phenocrysts are zoned, and evidence of resorption is common. Sanidine phenocrysts show evidence of repeated growth and solution with as many as 60 cycles per crystal. The primary, igneous, analcite phenocrysts of the analcite phonolites and blairmorites crystallized at depth, and were preserved by rapid vertical transport and quenching at the surface. In many cases, however, partial or complete decomposition of the crystals occurred, and thermal discoloration of the analcite can be reproduced in the laboratory.

Present Fisheries Status of Sariakandi Fish Pass, Sariakandi, Bogra

J. bio-sci. 14: 133, 2006

Developments in Louisiana Gulf Coast in 1969

The Louisiana Gulf Coast includes the 38 southern parishes of Louisiana and 16 continental shelf areas offshore. Oil and gas are produced from strata ranging in age from Cretaceous to Pleistocene. There were 2,283 exploratory and development wells drilled in 1969, a decrease of 9% from the previous year. Of the exploratory wells, 20% were successful. Discovery of 21 new fields (17 onshore and 4 offshore) was made in 1969. The most important are Lake Verret, Assumption Parish; Wyandotte, St. Mary Parish; North Coulee Hippolyte, Calcasieu Parish; and Block 65 and Block 54, South Pass area. The most significant of the new pools and extensions were at Woodlawn, Jefferson Davis Parish; South Black Bayou, Cameron Parish; Grand Bayou, Assumption Parish; Block 71, West Cameron area; and Block 276 and Block 175, Eugene Island area. Geophysical activity declined offshore from the previous year, but was approximately the same as the previous year onshore. In 1969, 10 state lease sales and 2 federal offshore drainage sales were held.

Gravity measurements in Wyoming and central Colorado

Gravity surveys made by personnel from the University of Wyoming include the Laramie Mountains, the Medicine Bow Mountains, the Hanna Basin, and the South Pass area in Wyoming and the mountainous area west of Aspen in Colorado. These surveys are made with a Worden Master model gravimeter and are tied into gravity base stations established by the U.S. Air Force; almost all the stations are established on surveyed elevations. The purpose of these surveys is largely to study relationships in crystalline rocks.Detailed gravity surveys on spacing as close as ½ to 1 km have been conducted in the Precambrian core of the Laramie Mountains between 41°00′ to 42°00′N and 105°00′ to 105°4O′W. Rock types covered include Sherman granite, Laramie anorthosite, and related rocks and gneisses. Bouguer anomalies within Precambrian rocks range from −110 mgal over mafic gneisses in the north to −185 mgal over Sherman granite in the south [Hodge, 1966; Woodfill and Smithson, 1968]. Interpretation of these anomalies is being used to study petrogenesis of the anorthosite and structure of the geneisses. Gravity measurements extend out from the Laramie Mountains across a flanking fault into the Denver‐Julesberg Basin on the east and west into the Laramie Basin.

Strain adjustments associated with earthquakes in southern California

Abstract A technique for the calculation of strain changes in a two-dimensional elastic body with arbitrary internal dislocations is presented. This technique is applied to the southern California region by assigning a specific fault and fault slip function for each major earthquake that has occurred since 1812. Although the model used has serious shortcomings when applied to the real Earth, certain important features concerning strain energy changes associated with earthquakes are brought out. The occurrence of earthquakes over the past 150 years has resulted in net increases in stored strain energy in a number of regions including the northern end of the Gulf of California, the Cajon Pass area, and the northern part of the Carizzo Plain. Large regions of strain energy decrease can also be seen, the most important of which is in the vicinity of Fort Tejon.

Developments in Louisiana Gulf Coast in 1968

The Louisiana Gulf Coast includes the 38 southern parishes of Louisiana and 16 continental shelf areas offshore. Oil and gas are produced from strata ranging in age from Cretaceous to Pleistocene. There were 2,505 exploratory and development wells drilled in 1968, an increase of 394 from the previous year. Of the 801 exploratory wells, 21% were successful. Discovery of 26 new fields (17 onshore and 9 offshore) was made in 1968. The most important are West Manchester, Calcasieu Parish; Block 14, East Cameron Area; Block 61, South Pass Area; and Block 290 and Block 305, Main Pass Area. The most significant of the 139 new pools and extensions were at Bayou Bouillon, St. Martin Parish; Bayou Carlin, St. Mary Parish; Tigre Lagoon, Vermilion Parish; Block 204 and Block 239 Ship Shoal Area; and Block 56, West Cameron Area. Geophysical activity decreased from the previous year, mainly onshore. In 1968, 6 state lease sales and 1 federal offshore drainage sale were held. A record bid of $27,401 per acre was made on a West Delta offshore tract.

Developments in Louisiana Gulf Coast in 1967

The Louisiana Gulf Coast includes the 38 southern parishes of Louisiana and 16 continental-shelf areas offshore. Oil and gas are produced from strata ranging in age from Cretaceous to Pleistocene. There were 2,111 development and exploratory wells drilled in 1967, 18% fewer than in 1966. Of the 775 exploratory wells, 22% were successful. Of the 17 new-field discoveries (7 onshore and 10 offshore), the most important are: South Judice field, Lafayette Parish; Manchac Point field, West Baton Rouge Parish; Block 207 field, Ship Shoal Area; and Block 144 field, Main Pass Area. The most significant of the new pools and extensions are in Clear Creek field, Allen Parish; West Lake Arthur field, Jefferson Davis Parish; Block 43 field, Grand Isle Area; Block 30 field, West Delta Area; and Block 133 field, West Delta Area. Geophysical activity declined significantly from the previous year. The federal offshore lease sale in June, in which 744,000 acres were sold for $510,079,177, was the largest ever in the Louisiana offshore.

Stratigraphy and Correlation of the Precambrian Belt Supergroup of the Southern Lewis and Clark Range, Montana

Several well-exposed and little-deformed Belt Supergroup sections have been studied in the southern Lewis and Clark Range. In the area studied, the Belt thins eastward or northeastward due both to primary sedimentation and to pre-Middle Cambrian erosion. These rocks can now be more precisely correlated with the well-known sections near Bonner, Helena, and Glacier National Park. In the western part of the area, the Missoula Group is thickest and lithologically intermediate between the sections at Bonner and Marias Pass. Formation names from these two sections are applied in the southern Lewis and Clark Range. The thin Belt sequence in the eastern part of the area includes the lower part of the Missoula Group and older formations that may be traced southward into the Helena, Empire, and Spokane Formations of the Helena area. Consequently, the Helena Dolomite of the Helena area, the Siyeh Formation of the Marias Pass area, and the “Newland Limestone” of the Bonner area are probably lateral equivalents.

Developments in Louisiana Gulf Coast in 1966

The Louisiana Gulf Coast includes the 38 southern parishes of Louisiana and the 16 continental-shelf areas offshore. Oil and gas are produced from sediments ranging in age from Cretaceous to Pleistocene. There were 2,570 development and exploratory wells drilled in 1966, 12% fewer than in 1965. Of the 875 exploratory wells, 23% were successful. Of the 44 new-field discoveries (21 onshore and 23 offshore), the most important are: Block 133 field, West Delta Area; Coon Point field, Ship Shoal Area; and St. Amelia field, St. James Parish. The most significant of the 185 new pools and extensions include Block 6 field, Main Pass Area; Block 16 field, Grand Isle Area; Block 58 field, West Delta Area; Fordoche field, Pointe Coupee Parish; Bayou Hebert field, Vermilion Parish; and Garden City field, St. Mary Parish. Geophysical and drilling activity declined slightly from the previous year. Lease activity for the total area compared favorably with 1965.