Ashton F. Embry

Bio: Ashton F. Embry is an academic researcher from Geological Survey of Canada. The author has contributed to research in topics: Arctic & Devonian. The author has an hindex of 33, co-authored 77 publications receiving 4729 citations. Previous affiliations of Ashton F. Embry include Natural Resources Canada & BP Canada.

A Late Devonian Reef Tract on Northeastern Banks Island, N.W.T.

Abstract: The Upper Devonian Weatherall Formation, outcropping on northeastern Banks Island, N.W.T., contains a 200-ft-thick limestone unit here termed the Mercy Bay Member. The member is Middle to Late Frasnian in age. Gyrfalcon Bluff has been chosen as the type section. Mercy Bay Member outcrops on the extreme northeastern portion of Banks Island, and many excellent exposures permit detailed paleogeographical and paleoecological studies. The member contains numerous organic build-ups and represents a Late Devonian reef tract located in the marine-shelf environment of an exogeosyncline situated between a tectonic highland to the northwest and a stable craton to the southeast. The main facies changes in the Mercy Bay Member occur in an east-west direction. The organic build-ups in the eastern part of the study area are narrow, linear bioherms trending north-south. They are encased in younger terrigenous clastic rocks. To the west the organic build-ups, which are biohermal in the lower part and biostromal in the upper, are more numerous. The lower bioherms trend east-west. Penecontemporaneous interbiohermal strata consist of dark, fine-grained argillaceous limestone. Organic build-ups on the western edge of the outcrop area are bioherms which trend north-south. The lower portion in all organic build-ups consists of corals and tabular stromatoporoids. These are interpreted as biogenetic banks constructed in the quiet and intermediate-energy zones (water depths more than 30 ft). The upper portion is composed of massive stromatoporoids. This facies represents rigid reefs constructed in the high-energy zone (above 30 feet). Successive sea-level rises allowed the reefs to grow upward. Cessation of reef growth was caused by an influx of terrigenous sediment related to the seaward migration of the northern and western shorelines. The outcropping organic build-ups of the Mercy Bay Member are tightly cemented, but frequent bitumen occurrences indicate that they were once oilbearing. Organic build-ups of the Mercy Bay Member probably occur in the subsurface to the west. End_Page 730------------------------

Absolute water depth limits of late devonian paleoecological zones

Abstract: A refined scheme of reefal limestone classification, which places more emphasis on the > 2 mm components (conglomeratic fraction) and on the mode of organic binding, allows for a more detailed facies description of organic buildups. The classification has been applied to Late Devonian organic buildups which outcrop on northeastern Banks Island, Canadian Arctic Archipelago. The distribution and sequences of facies in one organic buildup has led to the determination of absolute water depth limits of three major Late Devonian paleoecological zones. Corals were the dominant fauna below 70 feet (21 m.); tabular stromatoporoids flourished between 70 feet (21 m.) and 30 feet (9 m.) of water depth; massive stromatoporoids were the dominant fauna between 30 feet (9 m.) and sea level. The main controlling factor on the depth limits of the zones was wave energy (normal wave base, 30 feet [9 m.]; storm wave base, 70 feet [21 m.]).

T–R sequence stratigraphy, facies analysis and reservoir distribution in the uppermost Triassic–Lower Jurassic succession, western Sverdrup Basin, Arctic Canada

Abstract: Widespread porous and permeable sandstones of the Heiberg Formation/Group (uppermost Triassic-Lower Jurassic) are host to oil and/or gas in sixteen fields in the western Sverdrup Basin of the Canadian Arctic Islands. The sandstones are part of three, third-order, T–R (transgressive–regressive) sequences which are of Rhaetian–Hettangian, Sinemurian and Pliensbachian–Toarcian age. The general depositional/tectonic setting for the three T–R sequences was a marine shelf undergoing relatively low subsidence. Sediment influx to the shelf was generally low and increased eastward toward a deltaic input centre located in the south-central portion of the basin. Each T–R sequence is bounded by subaerial unconformities (usually modified by shoreface erosion) on the basin margin and by correlative transgressive surfaces farther seaward. A maximum flooding surface within each sequence separates a lower transgressive systems tract from an overlying regressive systems tract. The transgressive systems tract thickens eastward in each sequence and consists of a variety of facies including massive to cross-bedded sandstone (inner shelf), rippled to burrowed sandstone (mid-shelf), glauconitic sandstone, siltstone and shale (outer shelf) and oolitic ironstone (starved inner shelf). The predominant facies recognized in the regressive systems tracts are burrowed, grey shale and siltstone (offshore shelf), rippled to burrowed siltstone and sandstone (lower shoreface-mid shelf), cross-bedded to massive sandstone (upper shore face-inner shelf) and carbonaceous shale and siltstone with a highly variable sandstone content (lagoon, coastal plain). In the Rhaetian–Hettangian sequence a distinctive restricted marine facies association (foreshore-offshore shelf) is widespread and is characterized by an almost total lack of burrowing and by red and green coloration of shale–siltstone units. Oil and gas are structurally trapped almost exclusively in the uppermost porous sandstones of the succession beneath thick argillaceous deposits of the Jameson Bay Formation. The stratigraphic position of such sandstones varies across the study area. Regressive shoreface–foreshore sandstones of the Rhaetian–Hettangian sequence form the main reservoirs along the southwest basin margin. Farther northeast the regressive inner shelf to coastal plain sandstones of the Sinemurian sequence and the transgressive inner shelf sandstones of the Pliensbachian–Toarcian sequence are the main reservoirs. Comparison of the sequence bounding events with the Haq et al. (1988) curve reveals both matches and mismatches. This result, plus the occurrence of major changes in the amount and location of sediment input and in subsidence pattern from one sequence to the next, suggest that regional tectonics was the main factor controlling sequence development.

Transgressive–regressive (T–R) sequence analysis of the Jurassic succession of the Sverdrup Basin, Canadian Arctic Archipelago

Abstract: Transgressive–regressive (T–R) sequence analysis has been applied to the Jurassic succession of the Sverdrup Basin with sequence boundaries drawn at subaerial unconformities or the correlative tran...

High prevalence of vitamin D inadequacy and implications for health.

Abstract: During the past decade, major advances have been made in vitamin D research that transcend the simple concept that vitamin D is Important for the prevention of rickets in children and has little physiologic relevance for adults. Inadequate vitamin D, in addition to causing rickets, prevents children from attaining their genetically programmed peak bone mass, contributes to and exacerbates osteoporosis in adults, and causes the often painful bone disease osteomalacia. Adequate vitamin D is also important for proper muscle functioning, and controversial evidence suggests it may help prevent type 1 diabetes mellitus, hypertension, and many common cancers. Vitamin D inadequacy has been reported in approximately 36% of otherwise healthy young adults and up to 57% of general medicine inpatients in the United States and in even higher percentages in Europe. Recent epidemiological data document the high prevalence of vitamin D inadequacy among elderly patients and especially among patients with osteoporosis. Factors such as low sunlight exposure, age-related decreases in cutaneous synthesis, and diets low in vitamin D contribute to the high prevalence of vitamin D inadequacy. Vitamin D production from cutaneous synthesis or intake from the few vitamin D-rich or enriched foods typically occurs only intermittently. Supplemental doses of vitamin D and sensible sun exposure could prevent deficiency in most of the general population. The purposes of this article are to examine the prevalence of vitamin D inadequacy and to review the potential implications for skeletal and extraskeletal health.