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R. J. McLaughlin

Publications and source records attributed to R. J. McLaughlin.

31 records · Page 2Linked to original sources
USGS1983

Tectonic uplift of a middle Wisconsin marine platform near the Mendocino triple junction California

An uplifted wave-cut marine platform eroded across bedrock of the Franciscan Complex at Point Delgada, northern California, is overlain by 0.5 to 5 m of wave-worked pea gravel, which is in turn directly overlain by fluvial gravel and silt deposited as alluvial fans. Woody plant debris at the base of the fluvial deposits includes cones of Brewer spruce ( Picea breweriana ), which today are found only at higher elevations and latitudes. Fossil wood debris from this horizon yields a 14 C date of 44,800 ± 1,300 yr. The 44,800 yr radiocarbon age for the base of the fluvial deposits establishes an approximate age for the immediately underlying marine gravels and wave-cut platform. We tentatively correlate this terrace with the middle Wisconsin high sea-level stand at −37 m, dated at about 45,000 yr B.P. If this age is correct, the tectonic uplift since middle Wisconsin time has been 44 m, and the average rate of uplift has been at least 1.0 m/1,000 yr. This relatively high rate is probably related to interaction among the Pacific, Gorda, and North American plates at the Mendocino triple junction.

Geology↗
USGS1982

Post-middle Miocene accretion of Franciscan rocks, northwestern California.

Deformed sedimentary rocks assigned to the Franciscan assemblage in the King Range S of Cape Mendocino, N California, are dominantly deep-water argillite and sandstone occurring as thick- to thin-bedded, locally channelized marine turbidities of arkosic to andesitic volcaniclastic composition. The King Range appears to be a displaced terrane of oceanic basement overlain by Palaeogene(?) and Neogene sedimentary and igneous rocks of continental and oceanic derivation.-Authors

Geological Society of America Bulletin↗
USGS1981

Map showing mineral-resource potential of the King Range and Chemise Mountain Instant Study Areas, Humboldt and Mendocino counties, California

The potential for economic development of energy-related or metallic mineral resources in the King Range and Chemise Mountain Instant Study Areas is low to moderate as indicated by geologic, geophysical, and geochemical investigations. No oil or gas seeps or coal seams were detected within the King Range or Chemise Mountain Study Area. The low porosity and permeability of the Franciscan sandstones that underlie these areas indicate a very low potential for oil or gas. The geothermal resource potential of these areas also is low. Minor manganese resources occur adjacent to the southeast corner of the King Range Instant Study Area near Queen Peak. The manganese forms small stratabound deposits associated with radiolarian chert and pillow basalt. The known deposits are too small and the manganese too low in concentration for further economic exploitation. Similar manganese mineralization may be within the belt of melange in the southeast corner of the King Range area and within the Chemise Mountain Instant Study Area, but economic deposits are unlikely. Although there has been historical base- and precious-metal exploration activity north of the King Range in the Mattole River drainage, our geologic and geochemical field data indicate almost no gold potential and low potentials for lead, zinc, copper, and silver. During this investigation, one high-grade vein and several minor veins containing lead, zinc, copper, and silver were discovered at Point Delgada immediately south of the King Range Instant Study Area. The vein mineralization is Miocene and cuts Cretaceous basalt flows, dikes, flow breccia, and younger overlying sedimentary rocks of the King Range. The vein mineralization at Point Delgada could be remobilized from more extensive unexposed stratabound base-metal mineralization at depth. Traces of lead and zinc detected within the King Range Instant Study Area may have similar stratabound or vein origins, but no resource potential is indicated. Minor copper mineralization with associated lead, zinc, and manganese anomalies within the Chemise Mountain Instant Study Area is of low economic potential because of the shearing, isolation, and lenticularity of the basaltic and cherty rocks within the melange mineralization.

California↗
USGS1978

Distribution and character of upper Mesozoic subduction complexes along the west coast of North America

Structurally complex sequences of sedimentary, volcanic, and intrusive igneous rocks characterize a nearly continuous narrow band along the Pacific coast of North America from Baja California, Mexico to southern Alaska. They occur in two modes: (1) as complexly folded but coherent sequences of graywacke and argillite that locally exhibit blueschist-grade metamorphism, and (2) as melanges containing large blocks of graywacke, chert, volcanic and plutonic rocks, high-grade schist, and limestone in a highly sheared pelitic, cherty, or sandstone matrix. Fossils from the coherent graywacke sequences range in age from late Jurassic to Eocene; fossils from limestone blocks in the melanges range in age from mid-Paleozoic to middle Cretaceous. Fossils from the matrix surrounding the blocks, however, are of Jurassic, Cretaceous, and rarely, Tertiary age, indicating that fossils from the blocks cannot be used to date the time of formation of the melanges. Both the deformation of the graywacke, with accompanying blueschist metamorphism, as well as the formation of the melanges, are believed to be the result of late Mesozoic and early Tertiary subduction. The origin of the melanges, particularly the emplacement of exotic tectonic blocks, is not understood.

Alaska, California, Oregon, Washington↗
USGS1978

Significance of age relations above and below upper jurassic ophiolite in the Geysers-Clear Lake region, California

In The Geysers-Clear Lake area of northern California, a fragmented Upper Jurassic ophiolite overlain depositionally by the Great Valley sequence is juxtaposed over deformed and metomorphosed rocks of the Franciscan assemblage along the Coast Range thrust. The basal strata of the Great Valley sequence consist of thick breccias of mafic clasts, identical in composition to the upper part of the ophiolite. These breccias and their contact relations suggest that more than 1 km of the upper part of the ophiolite was locally eroded in early Tithonian time. On the basis of their radiolarian faunas, cherts in the Franciscan assemblage below the ophiolite range in age from Late Jurassic (early Tithonian) to Late Cretaceous (early Cenomanian). Of particular significance is an individual chert body (= The Geysers chert) of this age range. The early Cenomanian radiolarians, except for two occurrences associated with pelagic limestone, are significantly younger than those previously reported from the Franciscan assemblage. The existence of a sequence of Late Jurassic to Late Cretaceous radiolarian chert places critical constraints on subduction models for emplacement of the Franciscan assemblage beneath the Coast Range ophiolite and Great Valley sequence in The Geysers-Clear Lake area. From early Tithonian to post-early Cenomanian time, the Franciscan assemblage received pelagic sedimentation far from any site of subduction. By other data, blueschist metamorphism of subducted Franciscan strata also occurred during this time. The radiolarian data from The Geysers area permit a correlation with Upper Cretaceous pelagic limestones in the Laytonville area northwest of The Geysers and also imply that the Great Valley sequence was never depositionally in contact with the Franciscan assemblage.

California↗