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T. H. Nilsen

Publications and source records attributed to T. H. Nilsen.

At least 19 recordsLinked to original sources
USGS1991

Franciscan Complex, Coast Range ophiolite and Great Valley sequence: Pacheco Pass to Del Puerto Canyon, California

This field trip covers part of the Diablo Range and adjacent San Joaquin Valley of central California (Fig. 1 ). The core of the range is made up of rocks of the Franciscan Complex, flanked by Coast Range ophiolite (CRO) and Great Valley sequence (GVS). The Franciscan Complex in this area consists of deformed and metamorphosed sedimentary and volcanic rocks containing fossils of Late Jurassic to Late Cretaceous age. These rocks are believed to represent an accretionary wedge that was subducted to depths of 12-20 mi (20-30 km). The Middle to Late Jurassic CRO represents a slab of oceanic upper mantle and crust that was trapped between the Sierran magmatic arc and the Franciscan trench. The Upper Jurassic to Upper Cretaceous GVS is a thick accumulation of mudstone, sandstone, and con- glomerate that was deposited on the ophiolite in a forearc-basin setting. The objectives of this field trip are to examine good exposures of these three major units in order to better understand their sedimentary, igneous, and metamorphic histories, to examine some of the major faults bounding the units, and to gain an understanding of the tectonic history of this portion of the Coast Ranges.

Book chapter↗
USGS1984

Submarine-fan facies associations of the Eocene Butano Sandstone, Santa Cruz mountains, California

The Eocene Butano Sandstone was deposited as a submarine fan in a relatively small, partly restricted basin in a borderland setting. It is possibly as thick as 3000 m and was derived from erosion of nearly Mesozoic granitic and older metamorphic rocks located to the south. Deposition was at lower bathyal to abyssal water depths. The original fan may have been 120-to 160-km long and 80-km wide. Outcrops of submarine-canyon, innerfan, middle-fan, and outer-fan facies associations indicate that the depositional model of Mutti and Ricci Lucchi can be used to describe the Butano Sandstone. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Trench-fill submarine-fan facies associations of the Upper Cretaceous Chugach terrane, southern Alaska

Turbidites of the Upper Cretaceous Chugach terrane of southern Alaska were deposited in a trench during northward-directed subduction. The fault-bounded outcrop belt of the Chugach terrane is about 2000-km long and 100-km wide and was accreted to Alaska during the Cenozoic. Turbidites are at least 5000 m thick, are extensively deformed, have been regionally metamorphosed, and have been intruded by anatectic granites. Facies associations indicate an east-to-west progression from inner-fan to middle-fan, outer-fan, fan-fringe, and basin-plain deposits. To the north is a marginal trench-slope facies association and a basin. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Submarine-fan facies associations of the Upper Cretaceous and Paleocene Gottero Sandstone, Ligurian Apennines, Italy

The Upper Cretaceous and Paleocene Gottero Sandstone was deposited as a small deep-sea fan on ophiolitic crust in a trench-slope basin. It was thrust northeastward as an allochthonous sheet in Early and Middle Cenozoic time. The Gottero, as thick as 1500 m, was probably derived from erosion of Hercynian granites and associated metamorphic rocks in northern Corsica. Outcrops of inner-fan channel, middle-fan channel and interchannel, outer-fan lobe, fan-fringe, and basin-plain facies associations indicate that the depositional model of Mutti and Ricci Lucchi for mixed-sediment deep-sea fans can be used. The original fan had a radius of 30 to 50 km. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Regional variations in the fluvial Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate, Brooks Range, Alaska

The wholly allochthonous Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate is one of the most extensive fluvial deposits in North America. It crops out for 950 km along the crest of the Brooks Range in a series of thrust plates and is as thick as 2615 m. The Kanayut forms the fluvial part of a large, coarse-grained delta. The lower part of the Kanayut (the Ear Peak Member) overlies marginal-marine and prodelta turbidite deposits and consists of fining-upward meandering-stream-channel cycles of conglomerate and sandstone within black to maroon floodplain shale deposits. The middle part of the Kanayut (the Shainin Lake Member) lacks shale and consists of fining-upward couplets of channelized conglomerate and parallel- to cross-stratified sandstone interpreted as braidplain deposits. These deposits contain the largest clasts (23 cm) and were deposited during maximum progradation of the fluvial sequence. The upper part of the Kanayut (the Stuver Member), which consists of fining-upward meandering stream cycles similar to those of the lower part, grades upward into overlying Lower Mississippian tidal and marginal-marine deposits. Paleocurrent data and distribution of largest clasts indicate that the Kanayut was deposited by southwest-flowing streams fed by at least two major trunk streams that drained a mountainous region to the north and east. Comparison of stratigraphic and sedimentologic data collected at three selected locations representative of proximal, intermediate and distal parts of the Kanayut basin reveal regional variations in its fluvial character. These include a decrease in total thickness of fluvial strata, an increase in total thickness of associated marine sandstone, the pinch-out of the coarse-grained middle part of the Kanayut and decreases in the conglomerate/sandstone and sandstone/shale ratios from proximal to distal areas of the basin. The coarse-grained parts of the fluvial cycles decrease in thickness and lateral extent from proximal to distal areas of the basin. In more distal areas of sedimentation, the middle parts of some fluvial cycles consist of calcareous and bioturbated marine sandstone. Although thinner than in more proximal areas, the associated fine-grained upper parts of some cycles also contain marine features and suggest that these strata represent the deposits of interdistributary bays. These features are interpreted to indicate that the proximal deposits of the Kanayut Conglomerate were deposited by large, stable fine-grained meandering rivers (the Ear Peak and Stuver Members) and gravelly braided rivers (Shainin Lake Member) on the upper delta plain of the Kanayut delta. Sedimentation in more distal locations, interpreted to represent lower delta plain deposits, was by smaller distributary rivers with characteristics of both braided and meandering streams. Near their interface with marginal marine deposits the fluvial deposits were locally strongly influenced by tidal or estuarine conditions. ?? 1984.

Sedimentary Geology↗
USGS1982

Sedimentology and stratigraphy of the Kanayut Conglomerate, central Brooks Range, Alaska: Report of 1980 field season

The Upper Devonian Kanayut Conglomerate crops out along the crest of the Brooks Range of northern Alaska for a distance of almost 1000 km. It ranges in thickness from 2600 m in the Atigun River area to 700 m south of Anaktuvuk Pass and has been subdivided into four regionally persistent members: (a) the basal sandstone member, consisting of marine sandstone and shale with some conglomerate; (b) the lower shale member, consisting of nonmarine quartzite, conglomerate and shale; (c) the middle conglomerate member, consisting of nonmarine pebble and cobble conglomerate and quartzite; and (d) the Stuver Member, consisting of nonmarine sandstone and shale. The Kanayut conformably overlies the Upper Devonian marine Hunt Fork Shale and is conformably overlain by the Mississippian marine Kayak Shale. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The basal sandstone member of the Kanayut Conglomerate, which overlies prodelta turbidites of the Hunt Fork Shale, contains marginal-marine coarsening-upward channel-mouth bar sequences. It is conformably overlain by the lower shale member. Measured sections of the nonmarine members of the Kanayut show that the lower shale member ranges in thickness from 120 m to 1115 m and consists of fining-upward cycles interpreted to have been deposited by meandering streams on a broad floodplain. These cycles contain, in ascending order, channelized basal conglomerate, trough cross-stratified sandstone, and ripple-marked siltstone. The cycles are interpreted to be channel and point-bar deposits. Individual cycles average about 10 m in thickness and are separated by intervals of black, brown or maroon floodplain shale deposits. These typically contain thin coarsening-upward units that probably represent prograding levee sequences and irregular and ungraded sandstone bodies interpreted to be crevasse-splay deposits. In the Okokmilaga River area, the lower shale member contains a distinctive coarse-grained unit which is burrowed and interpreted to represent a widespread marine incursion. The middle conglomerate member, which ranges in thickness from 155 m to 525 m, consists of braidplain deposits. It contains fining-upward couplets of conglomerate and parallel-stratified or cross-stratified sandstone that average 2-7 m in thickness. The couplets record deposition in channels and on bars of braided streams. The middle conglomerate member contains the largest clasts, little or no shale, and represents the maximum progradation of nonmarine sedimentation in the Kanayut depositional system. The Stuver Member consists of fining-upward cycles that resemble those of the lower shale member. It ranges in thickness from 160 m to 1400 m and grades upward into tidal and marginal-marine deposits of the Kayak Shale. Conglomerate in the Kanayut is compositionally very mature, averaging 82 percent white, gray, black or red chert clasts, 14 percent vein quartz clasts, 3 percent quartzite clasts, and less than I percent other lithologies, mainly argillite. Although red chert is locally abundant in the Shainin Lake-Galbraith Lake area, there is little variation in conglomerate composition in the Kanayut, suggesting derivation from a single major source terrane.

Alaska↗
USGS1982

Sedimentology and stratigraphy of the Kanayut Conglomerate, central and western Brooks Range, Alaska: Report of 1981 field season

The Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate forms a major stratigraphic unit along the crest of the Brooks Range of northern Alaska. It crops out for an east-west distance of about 900 km and a north-south distance of about 65 km. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The Kanayut is as thick as 2,600 m in the east-central Brooks Range. It thins and fines to the south and west. The Kanayut forms the middle part of the allochthonous sequence of the Endicott Group, an Upper Devonian and Mississippian clastic sequence underlain by platform limestones of the Baird Group and overlain by platform limestone, carbonaceous shale, and black chert of the Lisburne Group. The Kanayut overlies the marine Upper Devonian Noatak Sandstone or, where it is missing, the marine Upper Devonian Hunt Fork Shale. It is overlain by the marine Mississippian Kayak Shale. The Kanayut Conglomerate forms the fluvial part of a large, coarse-grained delta that prograded to the southwest in Late Devonian time and retreated in Early Mississippian time. Four sections of the Kanayut Conglomerate in the central Brooks Range and five in the western Brooks Range were measured in 1981. The sections from the western Brooks Range document the presence of fluvial cycles in the Kanayut as far west as the shores of the Chukchi Sea. The Kanayut in this area is generally finer grained than it is in the central and eastern Brooks Range, having a maximum clast size of 3 cm. It is probably about 300 m thick. The upper and lower contacts of the Kanayut are gradational. The lower Kanayut contains calcareous, marine-influenced sandstone within channel deposits, and the upper Kanayut contains probable marine interdistributary-bay shale sequences. The members of the Kanayut Conglomerate cannot be differentiated in this region. In the central Brooks Range, sections of the Kanayut Conglomerate at Siavlat Mountain and Kakivilak Creek are typically organized into fining-upward fluvial cycles. The maximum clast size is about 3 cm in this area. The Kanayut in this region is 200-500 m thick and can be divided into the Ear Peak, Shainin Lake, and Stuver Members. The upper contact of the Kanayut with the Kayak Shale is very gradational at Kakivilak Creek and very abrupt at Siavlat Mountain. Paleocurrents from fluvial strata of the Kanayut indicate sediment transport toward the west and south in both the western and central Brooks Range. The maximum clast size distribution generally indicates westward fining from the Shainin Lake region.

Alaska↗
USGS1981

Paleogeography and sedimentology of Upper Cretaceous turbidites, San Diego, California

Upper Cretaceous (Campanian and Maestrichtian) marine strata of the Rosario Group in the San Diego area include the Point Loma Formation and overlying Cabrillo Formation. These units contain six facies associations: (1) shelf and lagoonal sandstone, (2) slope and basin-plain(?) mudstone, (3) outer-fan lobe sandstone, (4) middle-fan channel-fill sandstone, (5) middle-and inner-fan interchannel and channel-margin thin-bedded turbidites and mudstone, and (6) inner-fan channel-fill conglomerate and sandstone. The facies associations define a deep-sea fan deposited by westward-flowing sediment gravity flows that transported sediments derived chiefly from batholithic and prebatholithic metamorphic rocks of the Peninsular Ranges. The sedimentary basin initially deepened abruptly, partly aided by eustatic sea-level rise. The fan then prograded westward into the basin, with a retrogradational phase recorded in the uppermost part of the sequence, which is erosionally truncated by transgressive lower Eocene conglomerate. The fan was deposited along the eastern edge of a forearc basin similar to that of the Great Valley sequence in northern California. The western part of the fan, which probably contained mostly outer-fan lobe and associated basin-plain deposits, appears to have been truncated by late Cenozoic strike-slip faulting associated with the San Andreas fault system. The fan and remnants of the western part of the basin and associated subduction complex may be present on the northwest in the Channel Islands region or still farther north.

California↗
USGS1978

Lower Tertiary laterite on the Iceland-Faeroe Ridge and the Thulean land bridge

CORES of a lower Tertiary lateritic palaeosol resting on basalt were recovered1 from Deep Sea Drilling Project Site 336 (Leg 38) on the north-east flank of the Iceland-Faeroe Ridge (Fig. 1), a major aseismic oceanic ridge that, together with Iceland, forms the Icelandic transverse ridge 2. The transverse ridge extends from the West European continental margin to the East Greenland continental margin, forming the geographic boundary and a partial barrier to flow of water between the Norwegian-Greenland Sea to the north and the northern North Atlantic Ocean to the south. The palaeosol indicates that at least part of the Iceland-Faeroe Ridge was above sea level during early Tertiary time3. Palaeogeographic and palaeooceanographic reconstructions suggest that it formed the main part of the Thulean land bridge that connected South-east Greenland and the Faeroe islands during the early Tertiary4. This report summarises the subsidence history of the Iceland-Faeroe Ridge relative to early Tertiary seafloor spreading, basaltic volcanism, and the development of the proposed Thulean land bridge. ?? 1978 Nature Publishing Group.

Nature↗
USGS1977

Landslides

Landslides are frequent in areas where there is high seismicity and steep slopes. Landslides associated with earthquakes may cause as much damage as the initial ground shaking. They may also occur long after the earthquake. Some of the major earthquakes that have occurred during the past 15 years demonstrate the hazards of seismically triggered landslides. THe Hebgen Lake, Mont., earthquake of 1959 triggered a very large landslide (fig. 1) that killed and injured many people, formed a temporary lake, and blocked travel in the area. The Anchorage, Alaska, earthquake of 1964 triggered extensive subaerial (fig 2.) and submarine landslides; tsunamis (seismic sea waves) generated by the submarine landslides caused extensive damage and many fatalities in coastal areas. The earthquake in western Peru in 1970 triggered a massive debris avalanche (fig. 3) that destroyed the cities of Yungay and Ranrahirca; it probably caused about one-half of the 38,000 fatalities attributed to the earthquake. The San Fernando, Calif., earthquake of February 9, 1971, triggered more than 6000 individual landslides, most of which were small (fig. 4), in the surrounding upland areas. Fortunately, only a few of them damaged manmade structures because residential and industrial development had been restricted almost wholly to the relatively flat floor of the San Fernando Valley. Each of the major earthquakes described above had magnitudes greater than 6.5. Although smaller earthquakes may cause less damage to manmade structures by ground shaking, they are capable of triggering slope failures, especially renewed movements of old, marginally stable landslide deposits (fig. 5), in hillside areas.

Earthquake Information Bulletin (USGS)↗