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D. J. Nichols

Publications and source records attributed to D. J. Nichols.

At least 37 records · Page 2Linked to original sources
USGS1997

Correlation of Upper Cretaceous strata from Lima Peaks area to Madison Range, southwestern Montana and southeastern Idaho, USA

An 40 Ar/ 39 Ar age of 85.81 Ma±0.22 my was obtained on sanidine from a volcanic procellanite bed near the top of the 2135+m-thick Upper Cretaceous Frontier Formation in the Lima Peaks area of southwestern Montana. This early Santonian age, combined with previously determined age data including a palynological age of Cenomanian for the lower Frontier at Lima Peaks, and a U-Pb isotopic date of about 95 Ma for the base of the Frontier Formation in the eastern Pioneer Mountains north of the Lima Peaks area, provides an age range for the nonmarine formation. In the Madison Range, farther east in southweastern Montana, this age range corresponds to marine strata of not only the Frontier Formation, but also the overlying Cody Shale and Telegraph Creek Formation, a sequence that totals less than 760 m thick. The Upper Cretaceous marine formations of the Madison Range are closely zoned by molluscan faunas that are well constrained with radiometric dates. The 40 Ar/ 39 Ar age of 85.81 Ma±0.22 my at Lima Peaks is bracketed by radiometric dates for the Scaphites depressus—Protexanites bourgeoisianus biozone and the overlying Clioscaphites saxitonianus—Inoceramus undulatopilcatus biozone of the Western Interior. Fossils of both of these biozones are present in the Cody Shale and the Telegraph Creek Formation in the Madison Range. The Telegraph Creek contains two units of volcanic ash that are approximate time equivalents of the volcanic procellanite of the Lima Peaks area. Clasts in the conglomerate of the upper part of the Frontier in the Lima Peaks area were shed during the initial stages of uplift of the Blacktail-Snowcrest Highlands which rose to the north. The dated porcellanite lies above the conglomerates and indicates that the uplift was initiated by middle or late Coniacian, 87–88 Ma.

Idaho, Montana↗
USGS1995

The role of palynology in paleoecological analyses of Tertiary coals

Pollen, spores, and other plant microfossils are important constituents of Tertiary coals, both as petrographic components (the maceral sporinite) and as distinctive indicators of the nature of the depositional environment in which the coal-forming peat accumulated. Palynological analyses, which have been conducted on Tertiary coals since the 1930's, play an increasingly important role in modern paleoecological analyses of coals. Among the most important factors controlling the petrographic composition and facies characteristics of coal deposits are the types and relative abundances of plants that composed the peat. At present, wetland environments in which peat accumulates (mires) range from marshes and bogs to forested swamps; each is inhabited by distinctive plant communities. These plant communities are associated with varied conditions of climate, water depth, chemistry, and nutrient supply, and the floras can be indicative of these conditions. In the Tertiary Period, plant communities of mires were also highly diverse and specialized (especially as compared with those of the Carboniferous). The dominant species in some Paleocene mire floras were gymnosperms, but continuing a trend begun in Late Cretaceous time, angiosperms became increasingly prominent through the Tertiary. The diverse: angiosperm-dominated mire floras produced coals that vary significantly in facies and hence in quality. Such contrasts are evident in contemporaneous coals from different paleolatitudes, as well as among, coals of different ages within the Tertiary, as exemplified by selected deposits in the western United. States. The palynofloras of these coals reflect the floristic composition of the plant communities of the ancient mires.

International Journal of Coal Geology↗
USGS1994

Cretaceous rocks from southwestern Montana to southwestern Minnesota, northern Rocky Mountains, and Great Plains

In Montana, Wyoming, North and South Dakota, and Minnesota, Cretaceous strata are preserved in the asymmetric Western Interior foreland basin. More than 5,200 m (17,000 ft) of Cretaceous strata are present in southwestern Montana, less than 300 m (1,000 ft) in eastern South Dakota. The asymmetry resulted from varying rates of subsidence due to tectonic and sediment loading. The strata consist primarily of sandstone, siltstone, mudstone, and shale. Conglomerate is locally abundant along the western margin, whereas carbonate is present in most areas of the eastern shelf. Sediment was deposited in both marine and nonmarine environments as the shoreline fluctuated during major tectonic and eustatic cycles. A discussion of Cretaceous strata from southwestern to east-central Montana, the Black Hills, eastern South Dakota, and southwestern Minnesota shows regional stratigraphy and facies relations, sequence, boundaries, and biostratigraphic and radiometric correlations. The thick Cretaceous strata in southwestern Montana typify nonmarine facies of the rapidly subsiding westernmost part of the basin. These strata include more than 3,000 m (10,000 ft) of synorogenic conglomerate of the Upper Cretaceous part of the Beaverhead Group. West of the Madison Range, sequence boundaries bracket the Kootenai (Aptian and Albian), the Blackleaf (Albian and Cenomanian), and the Frontier Formations (Cenomanian and Turonian); sequence boundaries are difficult to recognize because the rocks are dominantly non-marine. Cretaceous strata in east-central Montana (about 1,371 m; 4,500 ft thick) lie at the approximate depositional axis of the basin and are mostly marine terrigenous rocks. Chert-pebble zones in these rocks reflect stratigraphic breaks that may correlate with sequence boundaries to the east and west. Cretaceous rocks of the Black Hills region consist of a predominantly marine clastic sequence averaging approximately 1,524 m (5,000 ft) thick. The Cretaceous System in eastern South Dakota (457 to 610 m; 1,500 to 2,000 ft thick) consists of a marine shelf sequence dominated by shale and limestone. Major sequence boundaries in South Dakota are at the base of the Lower Cretaceous Lakota Formation, Fall River Sandstone, and Muddy Sandstone, and bracket the Upper Cretaceous Niobrara Formation.

Book chapter↗
USGS1993

Palynostratigraphic correlation of the Fort Union formation (Paleocene) in the Wind River Reservation and Waltman Area, Wind River Basin, Wyoming

Palynologic samples of the Fort Union Formation (Paleocene) were collected from selected composite measured sections and a drill hole in the Wind River Basin. Intervals studied are in outcrop in the Wind River Reservation in the Shotgun Butte area and near Hudson, Wyoming, and in the subsurface in the Muddy Ridge field. Age determinations were made using the palynostratigraphic zonation originally developed near Waltman, Wyoming, in the northeastern part of the basin. Although parts of the zonation have been called into question by other recent work in the basin, only the basal Paleocene biozone (P1) is in need of modification, and the zonation remains an effective tool for age determination and correlation in these rocks. Age control is sparse in parts of some sections studied, mostly because of a dominance of sandstone and conglomerate facies, but palynostratigraphy permits correlation of the study areas with each other and with the Waltman reference section. Palynology supports the following correlations: The lower unnamed member of the Fort Union Formation in the Shotgun Butte area correlates stratigraphically and chronologically with the lower part of the formation in the subsurface at Muddy Ridge field, with a short interval in the Hudson area, and with the lower and middle parts of the unnamed member in the Waltman area. The Shotgun Member correlates chronologically with the coal-bearing upper part of the Fort Union Formation in the subsurface at Muddy Ridge field and with the upper part of the unnamed member and Waltman Shale Member in the Waltman area. These correlations show that significant coal deposits in the subsurface have little or no expression in outcrop because of changes in facies.

Conference Paper↗
USGS1992

A new Cretaceous-Tertiary boundary locality in the western Powder River basin, Wyoming: Biological and geological implications

A newly discovered Cretaceous-Tertiary (K-T) boundary locality in the western Powder River basin, Wyoming, is characterized by a palynologically defined extinction horizon, a fern-spore abundance anomaly, a strong iridium anomaly, and shock-metamorphosed quartz grains. Detailed microstratigraphic analyses show that about one third of the palynoflora (mostly angiosperm pollen) disappeared abruptly, placing the K-T boundary within a distinctive, 1- to 2-cm-thick claystone layer. Shocked quartz grains are concentrated at the top of this layer, and although fern-spore and iridium concentrations are high in this layer, they reach their maximum concentrations in a 2-cm-thick carbonaceous claystone that overlies the boundary claystone layer. The evidence supports the theory that the K-T boundary event was associated with the impact of an extraterrestrial body or bodies. Palynological analyses of samples from the K-T boundary interval document extensive changes in the flora that resulted from the boundary event. The palynologically and geochemically defined K-T boundary provides a unique time-line of use in regional basin analysis.

Wyoming↗
USGS1991

Chart showing correlations of upper Cretaceous Fox Hills Sandstone and Lance Formation, and lower Tertiary Fort Union, Wasatch, and Green River formations, from the eastern flank of the Washakie Basin to the southeastern part of the Great Divide Basin, Wyoming

The stratigraphic sections show surface and subsurface correlations of some Upper Cretaceous and lower Tertiary rocks along the eastern flank of the Washakie basin and southeastern part of the Great Divide basin, Wyoming. These rock crop out from near Baggs, Wyoming, to near Creston Junction, Wyoming, 50 mi (80km) to the north. This report is a continuation of our stratigraphic investigations from south of Baggs, Wyoming to Craig, Colorado.

Wyoming↗
USGS1990

Geologic and biostratigraphic framework of the non-marine Cretaceous-Tertiary boundary interval in western North America

Palynologically defined Cretaceous-Tertiary boundary sites in nonmarine rocks in western North America exhibit similar characteristics. All are marked by abrupt disappearance of the regional uppermost Cretaceous palynoflora at the level of an iridium anomaly; most also yeild shock-metamorphosed minerals. All are in coal-bearing, fluvial or paludal depositional settings, although the boundary horizon may be below, within, above, or at some stratigraphic distance from coal seams. At many sites the lowermost Tertiary beds contain assemblages overwhelmed by fern spores that, together with extinctions of some groups of angiosperms, are taken as evidence of regional devastation of terrestrial plant communities and subsequent recolonization by pioneer species. ?? 1990.

Review of Palaeobotany and Palynology↗
USGS1989

High-resolution leaf-fossil record spanning the Cretaceous/ Tertiary boundary

Theories t hat explain the extinctions characterizing the Cretaceous/Tertiary (K/T) boundary 1-3 need to be tested by analyses of thoroughly sampled biotas. Palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction 4-12 , but have not been combined with quantitative analyses of fossil leaves (megaflora). Megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution 13 , but have previously lacked the sample size and stratigraphic spacing needed to resolve latest Cretaceous floral history 5,14-18 . We have now combined megafloral data from a 100-m-thick composite K/T boundary section in North Dakota with detailed palynological analysis. Here the boundary is marked by a 30% palynofloral extinction coincident with iridium and shocked-mineral anomalies and lies ∼ 2 m above the highest dinosaur remains. The megaflora undergoes a 79% turnover across the boundary, and smaller changes 17- and 25-m below it. This pattern is consistent with latest Cretaceous climatic warming preceding a bolide impact.

Nature↗
USGS1989

Lower Cretaceous bentonitic strata in southwestern Montana assigned to Vaughn Member of Mowry Shale (East) and of Blackleaf Formation (West)

The Vaughn Member, newly assigned to the Mowry Shale in this report, comprises strata that crop out in the Greenhorn, Gravelly, Madison, and Gallatin ranges, and the Centennial and Beartooth mountains of southwestern Montana. Herein the member is correlated with the Vaughn Member of the Blackleaf Formation, which crops out to the west in the Lima Peaks area, Snowcrest Range, and Pioneer Mountains. Strata assigned to the Vaughn Member of the Blackleaf Formation in southwestern Montana exhibit the same contrasting relationships that exist in northwestern Montana. The Vaughn Member of the Mowry is late Albian in age, determined by bracketing with shallow water marine bivalves in the Muddy Sandstone below and palynomorphs in Mowry strata above. Palynomorphs from the Vaughn Member itself are typically mid-Cretaceous, but do not permit a more exact determination of age. -from Authors

Mountain Geologist↗