Tor H. Nilsen

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.

Preparation and Use of Isopleth Maps of Landslide Deposits

Isopleth maps derived from landslide inventory maps generalize and quantify the areal distribution of landslide deposits in contour form and may be uniquely useful for some types of regional planning. The isopleth format permits incorporation of landslide information with other quantified map data in the preparation of slope stability maps. The isopleth map of landslide deposits in San Mateo County, California (scale 1:300,000), serves as an example of this technique.

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

Abstract 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.

Old red sedimentation in the buelandet-vaerlandet devonian district, western norway

Abstract A preserved maximum thickness of 3,400 m of Devonian breccia, conglomerate, and sandstone of the Buelandet-Vaerlandet Formation crop out in the Buelandet-Vaerlandet district. The sedimentary rocks rest unconformably on Cambro-Silurian greenschist. Fragments of Psilophyton sp. found in the upper part of the stratigraphic sequence suggest an Early Devonian or early Middle Devonian age. The strictly continental sediments were deposited in a structurally formed half-graben by streams draining a complex crystalline source area to the north. This depositional basin was one of six separate Devonian basins located in the area of the former eugeosynclinal portion of the Caledonian geosyncline. The initial tectonism, resulting in the formation of Devonian grabens, was later followed by folding and faulting of the sedimentary basins during the Svalbardian disturbance. The tectono-sedimentologic environment of the Buelandet-Vaerlandet district is thought to have been similar to that of the Triassic Newark basins of the North American Appalachian Mountains. The oldest member of the here-named Buelandet-Vaerlandet Formation, the Melvaer Breccia, consists of angular, chaotically arranged greenschist fragments deposited as mudflows, sheetfloods and talus accumulations on the surfaces of alluvial fans. The intermediate Vaeroy Conglomerate consists of polymict alluvial fanglomerates deposited by braided distributaries of major streams that cut deep canyons into the northerly provenance area. The youngest unit is the Sorlandet Sandstone Member, a green arkosic deposit of larger braided streams, with local gravel bars preserved. Textural, fabric and paleocurrent data indicate a facies gradation southward along the paleoslope from breccia to sandstone. Tectonic uplift of the source area contemporaneous with fan sedimentation is suggested by the thickness and coarseness of fanglomerates. Rapid deposition in upperflow regime conditions, and a temperate or humid climate are indicated.

Oligocene tectonics and sedimentation, California

Abstract During the Oligocene epoch, California was marked by extensive nonmarine sedimentation, in contrast to its pre-Oligocene and post-Oligocene depositional history. The Oligocene continental deposits are especially widespread in southern California and fill a number of small and generally partly restricted basins. Fluvial facies in many basins prograded over previously deposited lower Tertiary turbidites. Volcanism, from widespread centers, was associated with the nonmarine sedimentation. However, some basins remained marine and a few contain Oligocene turbidites and pelagic sediments deposited at bathyal depths. The Oligocene redbeds of California do not form a post-orogenic molasse sequence comparable to the Old Red Sandstone or Alpine molasse. They are synorogenic and record local uplift of basins and surrounding source areas. Late Cretaceous to contemporary orogenesis in California has been generally characterized by the formation of small restricted basins of variable depth adjacent to small upland areas in response to strike-slip faulting. Deposition of Oligocene redbeds was associated with climatic change from warm and humid to cold and semiarid, and a global lowering of sea level. Oligocene tectonism occurred during the transition from subduction of the Farallon Plate to initiation of the modern San Andreas transform system. However, the major influence that caused uplift, formation of fault-bounded basins, and extensive redbed deposition, especially in southern California, was the approach of the Pacific—Farallon spreading ridge to the western margin of California.

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.

Offset along the San Andreas fault of Eocene strata from the San Juan Bautista area and western San Emigdio Mountains, California

Analyses of Eocene strata that rest on gabbroic basement rocks in the western San Emigdio Mountains and northernmost Gabilan Range indicate that the 2 sequences have been offset right-laterally 305–320 km along the San Andreas fault. In both areas, basal shallow-marine conglomerate of Penutian age grades upward into shale of Ulatisian and Narizian age that was deposited at bathyal water depths in a basin with access to open ocean. Additional similarities in the upper Eocene and Oligocene stratigraphic units suggest original contiguity of the depositional basins. The inferred offset indicates that the Salinian block was attached to western California by at least early Eocene time. The longer distances of northward transport of the Salinian block that are suggested by preliminary paleomagnetic data from upper Mesozoic granitic rocks and Upper Cretaceous and Paleocene strata must have occurred during Paleocene or earlier time.

Influence of the Greenland-Scotland Ridge on the Geological History of the North Atlantic and Norwegian-Greenland Sea Areas

The Greenland-Scotland Ridge was a controlling factor in the development of many aspects of the geologic history of the North Atlantic and Norwegian-Greenland Sea areas. It grew and evolved as a transverse ridge during the separation of the North-American-Greenland and North European plates by seafloor spreading processes. The ridge consists from northwest to southeast of the Denmark Strait, the volcanically active Icelandic Plateau, the volcanically inactive and aseismic Iceland-Faeroe Ridge, the Faeroe Islands block, a series of smaller banks and ridges that include Faeroe Bank, Bill Bailey Bank, Lousy Bank, and the Wyville-Thomson and Ymir Ridges, and the Faeroe-Scotland and Faeroe Bank Channels. The Greenland-Scotland Ridge is thus formed of an interconnected assemblage of subaerial and submarine volcanic plateaus, uplifted fragments of oceanic crust, rifted microcontinental blocks, narrow subsided channels, and sediment drifts.

Deep-Sea-Fan Channel-Levee Complexes, Arbuckle Field, Sacramento Basin, California

Mud-rich deep-sea-fan systems throughout the world yield significant accumulations of hydrocarbons. However, these distinctive turbidite deposits remain as yet poorly understood. Although several modern mud-rich deep-sea fans such as Mississippi fan (Kastens and Shor, 1985; Stelting et al., 1985; Bouma et al., 1986), Amazon fan (Damuth et al., 1983; Flood and Damuth, 1987; Damuth et al., 1988; Manley and Flood, 1988), Bengal fan (Emmel and Curray, 1985), and Rhone fan (Droz and Bellaiche, 1985) have been extensively studied, relatively few ancient mud-rich deep-sea fans have been described in detail. McCabe (1978) and Melvin (1986) provided useful descriptions of two Carboniferous delta-fed mud-rich fan sequences, although no ancient fans of this type have been directly related to hydrocarbon accumulations.

Gottero Turbidite System, Italy

The 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.