Thomas H. Morris

Sediments of the Lomonosov Ridge and Makarov Basin: A Pleistocene stratigraphy for the North Pole

Sediments of 16 short cores taken as part of the Lomonosov Ridge Experiment (LOREX) can be organized into the first Pleistocene stratigraphy for the North Polar region. This stratigraphy can be correlated with stratigraphic units described from the Alpha-Chukchi areas, ∼300 km distant. The LOREX cores include at least 12 sedimentary subunits differentiated by texture, color, and carbonate content. The units are silty and arenaceous lutites and are principally glacial-marine. Benthic and planktonic foraminifera, degree of bioturbation, and Fe-Mn micro-nodule abundance generally are positively correlated. Foraminifera in core B-8, from 3,956 m in the Makarov Basin, may have been affected by CCD fluctuations that did not affect fossils in core B-24, from 1,600 m on the crest of the Lomonosov Ridge. The 12 stratigraphic units were deposited during the late Pleistocene and represent the same major sedimentary events as those of stratigraphic units K, L, and M of the Amerasian Basin. This correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial-marine sediment. Times of major glacial ice transport reflect deglaciation events in the central Arctic Ocean. Surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50% of the Arctic Ocean. Even thin sedimentary units deposited during relatively long time intervals are correlated over >500,000 km 2 .

Active and inactive groundwater flow systems: Evidence from a stratified, mountainous terrain

We present a new conceptual model of groundwater flow that describes active and inactive groundwater flow regimes. The model is based on an analysis of interactions between surface water and shallow and deep groundwater in the 240-km-long Wasatch Range and Book Cliffs, Utah, USA. Active zone groundwater flow paths are continuous, responsive to annual recharge and climatic variability, and have groundwater resident times “ages” that become progressively older from recharge to discharge area. Active zone groundwater systems discharge at thousands of springs that issue from the 700+-m-thick, gently dipping, clastic bedrock formations. Springs waters contain appreciable 3 H and anthropogenic 14 C. In contrast, inactive zone groundwater has extremely limited or no communication with annual recharge and has groundwater mean residence times that do not progressively lengthen along the flow path. Groundwater in the inactive zone may be partitioned, occur as discrete bodies, and may occur in hydraulically isolated regions that do not have hydraulic communication with each other. Inactive zone groundwater is encountered in-mines (coal-mines 300–700 m below ground surface) where groundwater discharge rates decline rapidly and the waters have δ 2 H and δ 18 O compositions that are distinguishable from near surface groundwater. In general, deep waters have no 3 H and have mean 14 C residence times of 500 to 20,000 yr (45.9 to 4.9 pmc). Chemical evolution modeling, porosity-permeability core plug analysis, and in-mine hydrographs also indicate hydraulic partitioning.

Large-Rock Avalanche Deposits, Eastern Basin and Range, Utah: Emplacement, Diagenesis, and Economic Potential

Large-rock avalanche deposits are a common component of the basin fill within the extensional tectonic terrain of the Basin and Range; these deposits recently have been interpreted to host oil and gas within the Railroad Valley area of eastern Nevada. Large blocks of brecciated bed rock are a primary component of these avalanche deposits and are potentially excellent oil and gas reservoirs. Our work provides further insight into the emplacement and economic potential of these deposits. Exposed large-rock avalanche deposits of the Miocene Oak City Formation on the western margin of the Canyon Range, Utah, contain coherent breccia blocks up to 3.5 km long, 1 km wide, and 200 m thick. These deposits were derived from the near-vertical dipping bed rock of the adjacent Canyon Range and now are exposed as much as 5.5 km from the range front within the Sevier Desert basin. Emplacement was relatively rapid, as indicated by three well-developed breccia facies within the carbonate breccia blocks. Stratigraphically, from the base the facies include (1) matrix-rich breccia, (2) jigsaw breccia, and (3) crackle breccia. The deposits were cut and segmented by a series of syndepositional normal faults that developed during late Miocene and post-Miocene extension. Primary porosity w s reduced by cement soon after burial. Cathodoluminescence cement patterns indicate that initially the basinward breccia blocks were more deeply buried relative to the water table than the breccia blocks proximal to the Canyon Range. After initial cementation, the basinward blocks were uplifted relative to the water table. Secondary porosity approaches 8% in the carbonate blocks and is greater than 14% within the jigsaw breccia. The size and porosity of these breccia blocks indicate their potential as reservoir targets.

Oldest and lowest latitudinal occurrence of Palaeoaplysina; Middle Pennsylvanian Ely Limestone, Burbank Hills, Utah

A primitive variety of Palaeoaplysina laminaeformis Krotov is the primary biotic constituent of a two-meter-thick biostrome in the upper Ely Limestone of western Utah. Associated fusulinaceans and stromatoporoids indicate an early Desmoinesian (Middle Pennsylvanian) age, making it the oldest documented occurrence of non-ancestral Palaeoaplysina in the world. Plate-supported packstone with 40-60% interstitial peloidal mud and silt-size fossil debris constitutes the dominant biostrome rock fabric. During the Late Carboniferous, non-ancestral palaeoaplysinids were restricted to the Ely and Sublett basins of Utah and Idaho, respectively. By Early Permian time, however, they played a significant role in the construction of reefs and biostromes across the entire northern margin of Laurussia.

A predictive model of reservoir continuity in fluvial sand bodies of a lacustrine deltaic system, Colton Formation, Utah

Abstract The Paleocene/Eocene Colton Formation of east-central Utah is interpreted to be a fluvial-dominated lacustrine deltaic sequence that prograded from the southeast into ancient Lake Uinta. Predictability of reservoir continuity is based largely on understanding the nature of impermeable mudstone drapes within multilateral and multistory sandstone bodies. Fluvial sandstones are categorized into three systems according to associated facies, channel morphologies, and percent sandstone found within the section. Suspended-load systems dominate the western distal end of Colton exposures and are characterized as follows: meandering to sinusoidal fluvial systems, abundant multilateral accretion sets, and low sandstone percent (< 30%). Reservoir characteristics include poor porosity (< 9%) and permeability (< 0.6 md), poor reservoir continuity, small reservoir size, and good potential for development of numerous hydrocarbon traps. Mixed-load systems are typified by sinusoidal fluvial channels, large multilateral accretion sets, and intermediate sandstone percent (25-45%). Reservoirs display good porosity (approx. 18.5%) and permeability (< 50 md), intermediate reservoir continuity, intermediate to large reservoir size, and good potential to develop numerous hydrocarbon traps. Bed-load systems are characterized by relatively straight channels, very few point bar sequences, and high sandstone percent (< 45%). Reservoir characteristics display very good porosity (19.6-22.6%) and permeability (0.133-2.657 darcies), good reservoir continuity, large reservoir size, and less potential for hydrocarbon trap development. Distributary mouth bar sandstones display excellent reservoir characteristics including good porosity (20%) and the most homogeneous permeability (< 200 md) of the four volumetrically important sandstone facies. Recognition criteria of the four reservoir sandstone facies include sandstone percent in the section, grain size, thickness of the sandstone body, thickness of the sandstone interval, porosity and permeability of sandstones, and the nature of mudstone drapes between multilateral and multistory sandstone bodies. Improved technology in horizontal drilling may be used to link large noncommunicating multilateral accretion sets.