Paleomagnetism of Eocene rocks of the Kelowna and Castlegar areas, British Columbia: studies in determining paleohorizontal

1989 ◽  
Vol 26 (4) ◽  
pp. 829-844 ◽  
Author(s):  
M. Bardoux ◽  
E. Irving
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Bedding Plane ◽  
Normal Extension ◽  
South Central ◽  
Normal Polarity ◽  
Coast Plutonic Complex ◽  
Partial Unfolding

The middle Eocene Marron volcanics (mean age 52 ± 2 Ma) of the Kelowna outlier form the upper part of the hanging wall of the westerly dipping Okanagan Valley fault (OVF) in south-central British Columbia. They overlie Quesnellia. The OVF is currently interpreted as the westernmost member of a network of low-angle extension faults in the southern Omenica belt. The OVF was active in the middle Eocene at much the same time that the Marron volcanics were cooling. Relative to present horizontal, the magnetizations are widely scattered (Fisher's precision parameter k = 8) and after correction for bedding attitudes, there is no significant improvement (k = 9). Evidently, some magnetizations were acquired before (referred to as category 1) and others after (category 2) tilting; that is, the horizontal plane at the time of magnetization sometimes did and sometimes did not coincide with the bedding plane. Partial unfolding experiments, carried out on the two categories separately, yield a precision comparable to that expected for paleosecular variation, and a mean direction (D, I) of 352°, 70° (24 sites spanning 2000 m, 275 specimens, k = 23, α95 = 6°, paleopole 86°N, 230°E, A95 = 10°). The Marron is predominantly normally magnetized. Rock units slightly older and others slightly younger are reversely magnetized. The transition from reversed to normal polarity occurs in basal beds of the Marron Formation. The overall mean direction of the Marron and stratigraphically adjacent units is 352°, 69 °(28 sites, 300 specimens, spaning 4000 m, k = 21, α95 = 6°), yielding a paleopole at 85°N, 197°E (A95 = 10°), which is in excellent agreement with that for middle Eocene rocks of cratonic North America. Hence this part of Quesnellia had reached its present position relative to North America by middle Eocene time, and there has been no significant rotation of it. In contrast, the mean direction (020°, 72°, k = 9, α95 = 11°) after correction for bedding (calculated assuming the magnetization to be entirely pretilting) implies a clockwise rotation of 28°. We believe that this is incorrect; the apparent rotation, we argue, is caused by wrongly assuming that the bedding plane always coincides with the paleohorizontal at the time magnetism is acquired.Further tests have been carried out on intrusive and metamorphic core-complex rocks in the region of Eocene crustal extension 100 km to the east of Kelowna. These rocks are coeval with the Marron, and are located in both the hanging walls and footwalls of the Slocan Lake normal extension fault, which dips 30° eastward. Paleodirections are very different from those at Kelowna (four bodies, mean direction (D, I) 60°, 52°, k = 66, α95 = 6°), and we argue that this divergence is caused by tilting 37 ± 10° to the west antithetical to the Slocan Lake fault. We suggest that paleomagnetism provides a means by which tilts in such plutonic and metamorphic terrains can be determined. We suggest further that such tilts may have been responsible for some of the aberrant magnetizations observed in plutonic rocks of the Coast Plutonic Complex being much more widespread in the cordillera than previously envisioned.

Middle Eocene sedimentary and volcanic infilling of an evolving supradetachment basin: White Lake Basin, south-central British Columbia

2005 ◽  
Vol 42 (1) ◽  
pp. 49-66 ◽  
Author(s):  
Jason D McClaughry ◽  
David R Gaylord
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Metamorphic Core Complex ◽  
Lake Basin ◽  
Alluvial Fans ◽  
Core Complex ◽  
South Central ◽  
Metamorphic Core ◽  
Okanagan Valley

The middle Eocene White Lake and Skaha formations in the White Lake Basin, British Columbia record the sedimentary and volcanic infilling of a supradetachment basin that developed during the latter stages of Shuswap metamorphic core complex exhumation. The 1.1-km-thick White Lake Formation is characterized by volcanogenic sediment gravity flow, fluvial, and sheetflood facies interbedded with volcanic deposits. Facies relations suggest White Lake strata accumulated on coalesced, west-sloping alluvial fans that drained an active volcanic center. The overlying 0.3-km-thick Skaha Formation records increased tectonism and mass-wasting. Pervasively shattered Skaha avalanche, slide, and sheetflood deposits accumulated on alluvial fans, shed from hanging-wall and footwall sources exposed along the Okanagan Valley fault. Clast compositions of the White Lake and Skaha formations record alluvial and tectonic stripping that locally eliminated hanging-wall blocks. Mylonite clasts in upper Skaha beds imply significant Okanagan Valley fault footwall uplift during the middle Eocene and syntectonic erosion of the Shuswap metamorphic core complex. The syntectonic sedimentary record preserved within the White Lake Basin elucidates the relations and timing between core complex exhumation and extensional tectonism in this region. The White Lake and Skaha formations are the apparent age equivalent of the Klondike Mountain Formation of northern Washington (USA.). White Lake Basin strata, however, are more complexly interstratified, post-depositionally disrupted, and contain a more complete record of core complex unroofing. Variations in the spatial distributions and textural and compositional character of middle Eocene strata in this area underscore the need to exercise care when developing regional-scale sedimentary–tectonic–volcanic models.

Systematics and phytogeography of selected Eocene Okanagan Highlands plants

2005 ◽  
Vol 42 (2) ◽  
pp. 205-214 ◽  
Author(s):  
Melanie L DeVore ◽  
Kathleen B Pigg ◽  
Wesley C Wehr
Keyword(s):  
British Columbia ◽  
North America ◽  
North American ◽  
Middle Eocene ◽  
Rapid Evolution ◽  
Witch Hazel ◽  
South Central ◽  
The Republic ◽  
Okanagan Highlands ◽  
Early Radiation

The diverse Early to Middle Eocene Okanagan Highlands floras of south central British Columbia and northeastern Washington reflect a time of rapid evolution and the early radiation of many dicot families that are currently significant elements of temperate floras. Recent studies of the Republic, Washington flora (Klondike Mountain Formation) and related Okanagan floras in British Columbia have documented both the earliest, and sometimes the only, known fossil occurrences of genera. Today many once more widespread taxa are restricted, particularly to Asian and (or) eastern North American refugia. Examples include members of the families Betulaceae (birch, hazelnut), Rosaceae (rose), Hamamelidaceae (witch hazel), and the endemic Asian family Trochodendraceae. Earliest occurrences are noted for Neviusia (Rosaceae), Trochodendron (Trochodendraceae), Corylus and Carpinus (both Betulaceae). The first unequivocal leaf records of Corylopsis and Fothergilla (both Hamamelidaceae), and two new Eocene species of the extinct fruit Palaeocarpinus (Betulaceae) are also recognized. Today, Trochodendron and Corylopsis are restricted to Asia, whereas Neviusia and Fothergilla, genera with close Asian relatives, occur only in North America. Corylus johnsonii from Republic is most similar to the extant Asian species C. heterophylla, C. wangii, and C. ferox. Neviusia leaves from One Mile Creek near Princeton, British Columbia are more similar to N. cliftonii, an endemic from Mount Shasta, California, than to N. alabamensis of southeastern North America. A better documentation of the Okanagan Highlands floras is essential to our understanding of the evolution of North American temperate floras and the nature of Asian – North American disjunct taxa.

Upper limit of docking time for Stikinia and Terrane I: paleomagnetic evidence from the Eocene Ootsa Lake Group, British Columbia

1990 ◽  
Vol 27 (2) ◽  
pp. 212-218 ◽  
Author(s):  
T. A. Vandall ◽  
H. C. Palmer
Keyword(s):  
British Columbia ◽  
North America ◽  
Large Scale ◽  
Middle Eocene ◽  
Pole Position ◽  
Upper Limit ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
The Mean ◽  
Reversed Polarity

The Middle Eocene Ootsa Lake Group is exposed in the central portion of the Stikine Terrane, where it was sampled along the shoreline of Tahtsa Reach and Whitesail Reach. The group consists of dominantly subaerial flows, which range in composition from basalt to rhyolite, that unconformably overly the Jurassic Hazelton Group. Detailed alternating-field and thermal stepwise demagnetizations were done on all specimens from the 21 sites collected. The presence of a normal- and reversed-polarity remanence, a positive fold test, and high coercivities and unblocking temperatures indicate that a prefolding primary remanence has been isolated. The mean tilt-corrected direction of D = 002.2°, I = 69.2 °(α95 = 7.4°) from 13 sites for which paleohorizontal is well known yields a pole position at 354.6°E, 88.0°N (A95 = 11.5°), which is statistically indistinguishable from published 50 Ma reference poles for cratonic North America. This evidence demonstrates that the proposed large-scale northward displacement of Stikinia since mid-Cretaceous was completed by at least Middle Eocene time. This result is consistent with other paleomagnetic results from Stikinia, Quesnellia, and the Coast Plutonic Complex indicating that much of the allochthonous Cordillera had assembled and docked with cratonic North America by the Middle Eocene.

Eocene age for Ag–Pb–Zn–Au vein and replacement deposits of the Kokanee Range, southeastern British Columbia

1992 ◽  
Vol 29 (1) ◽  
pp. 3-14 ◽  
Author(s):  
G. Beaudoin ◽  
J. C. Roddick ◽  
D. F. Sangster
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Spatial Association ◽  
High Heat ◽  
Time Interval ◽  
Genetic Link ◽  
Metasedimentary Rocks ◽  
Magmatic Event

The Ag–Pb–Zn–Au vein and replacement deposits of the Kokanee Range, southeastern British Columbia, are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks in the hanging wall of the transcrustal Slocan Lake Fault, Field relations indicate that mineralization is younger than the Nelson batholith and a Middle Jurassic foliation in the Ainsworth area but coeval or older than Eocene unroofing of the Valhalla metamorphic core complex in the footwall of the Slocan Lake Fault. Lamprophyre and gabbro dykes are broadly coeval with mineralization and have biotite and hornblende K–Ar ages defining a short-lived Middle Eocene alkaline magmatic event between 52 and 40 Ma. An older, Early Cretaceous alkaline magmatic event (141 – 129 Ma) is possible but incompletely documented.K–Ar and step-heating 40Ar/39Ar analyses on hydrothermal vein and alteration muscovite indicate that hydrothermal fluids were precipitating vein and replacement deposits 58–59 Ma ago. Crosscutting relationships with lamprophyre dykes indicate the Kokanee Range hydrothermal system lasted for more than 15 Ma. Eocene crustal extension resulted in a high heat flow and structures which were probably responsible for hydrothermal fluid movement and flow paths.A 100 Ma time interval is documented between batholith emplacement and spatially associated mineralization, ruling out any genetic link between the two. Similar large age differences between granite intrusion and peripheral mineralization have recently been documented for two world-sea le Ag–Pb–Zn vein districts, which suggest that spatial association between granite and Ag–Pb–Zn mineralization is not sufficient to infer a genetic link.

Paleomagnetism of the Triassic Nikolai Greenstone, McCarthy Quadrangle, Alaska

1977 ◽  
Vol 14 (11) ◽  
pp. 2578-2592 ◽  
Author(s):  
J. W. Hillhouse
Keyword(s):  
British Columbia ◽  
High Temperature ◽  
North America ◽  
Vertical Axis ◽  
Upper Triassic ◽  
Present Position ◽  
Stable Component ◽  
South Central ◽  
Early Mesozoic ◽  
Lamellar Texture

Paleomagnetic evidence indicates that the extensive early Mesozoic basalt field near McCarthy, south-central Alaska, originated far south of its present position relative to North America. Results obtained from the Middle and (or) Upper Triassic Nikolai Greenstone suggest that those basalts originated within 15° of the paleoequator. This position is at least 27° (3000 km) south of the Upper Triassic latitude predicted for McCarthy on the basis of paleomagnetic data from continental North America. The Nikolai pole, as determined from 50 flows sampled at 5 sites, is at 2.2° N, 146.1° E (α95 = 4.8°). The polarity of the pole is ambiguous, because the corresponding magnetic direction has a low inclination and a westerly declination. Therefore, the Nikolai may have originated near 15° N latitude or, alternatively, as far south as 15° S latitude. In addition to being displaced northward, the Nikolai block has been rotated roughly 90° about the vertical axis. A measure of the reliability of this pole is provided by favorable results from the following tests: (1) Within one stratigraphic section, normal and reversed directions from consecutive flows are antipolar. (2) Consistent directions were obtained from sites 30 km apart. (3) Application of the fold test indicated the magnetization was acquired before the rocks were folded. (4) The magnetizations of several pilot specimens are thermally stable up to 550 °C. The stable component is probably carried by magnetite with lamellar texture, a primary feature commonly acquired by a basalt at high temperature during initial cooling of the magma. Geologic and paleomagnetic evidence indicates that the Nikolai is allochthonous to Alaska and that, together with associated formations in southern Alaska and British Columbia, it is part of a now disrupted equatorial terrane.

Late Pleistocene stratigraphy of south-central British Columbia

1978 ◽  
Vol 15 (6) ◽  
pp. 971-980 ◽  
Author(s):  
Robert J. Fulton ◽  
Geoffrey W. Smith
Keyword(s):  
British Columbia ◽  
North America ◽  
Great Lakes ◽  
Late Pleistocene ◽  
Pacific Coast ◽  
Coastal Regions ◽  
South Central ◽  
The Pacific ◽  
Valley Area ◽  
Coast Region

The late Pleistocene deposits of south-central British Columbia record two major glacial and two major nonglacial periods of deposition. The oldest recognized Pleistocene deposits, called Westwold Sediments, were deposited during a nonglacial interval more than 60 000 years ago. Little information is available on the climate of this period, but permafrost may have been present at one time during final stages of deposition of Westwold Sediments. The latter part of this nonglacial period is probably correlative with the early Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. However, deposition of the Westwold Sediments may have begun during the Sangamon Interglacial.Okanagan Centre Drift is the name applied to sediments deposited during the glaciation that followed deposition of Westwold Sediments. Okanagan Centre Drift is known to be older than 43 800 years BP and probably is older than 51 000. It is considered to correlate with an early Wisconsin glacial period.Bessette Sediments were deposited during the last major nonglacial period, which in south-central British Columbia persisted from at least 43 800 years BP (possibly more than 51 000) to about 19 000 years BP. This episode corresponds to Olympia Interglaciation of the Pacific Coast region and the mid-Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. During parts of Olympia Interglaciation the climate was probably as warm as the present-day climate in the interior of British Columbia. Information from coastal regions indicates that there may have been periods of cooler and moister climate.Kamloops Lake Drift was deposited during the last major glaciation of south-central British Columbia. Ice occupied lowland areas from approximately 19 000 to 10 000 years BP. This period corresponds approximately to the Fraser Glaciation of the Pacific Coast region and the late Wisconsin Substage of central and eastern parts of North America.

Petrology and geochemistry of the Kamloops Group volcanics, British Columbia

1981 ◽  
Vol 18 (9) ◽  
pp. 1478-1491 ◽  
Author(s):  
Thomas E. Ewing
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Primary Source ◽  
Low Pressure ◽  
Rock Types ◽  
South Central ◽  
High K ◽  
Petrology And Geochemistry

The Kamloops Group is an alkali-rich calc-alkaline volcanic suite of Early to Middle Eocene age, widespread in south-central British Columbia. Rock types in the suite range from high-K basalt through andesite to rhyolite. The suite is characterized by relatively high K2O, Sr, and Ba, but low Zr, Ti, and Ni concentrations, only moderate Ce enrichment, and little or no Fe enrichment. Initial ratios 87Sr/86Sr are about 0.7040 in the western half, and about 0.7060 in the eastern half of the study area. No difference in chemistry or mineralogy marks this sharp transition. Chemically similar suites include the Absaroka–Gallatin suite in Wyoming and the lower San Juan (Summer Coon) suite in Colorado. The content of K2O at 60% SiO2 increases regularly eastward across southern British Columbia. The chemical data support the subduction-related continental arc origin of the Kamloops Group volcanics.The volcanic rocks consist in the main of augite–pigeonite andesites ranging from 52 to 62% silica, with subordinate quantities of olivine–augite–pigeonite basalt and biotite rhyodacite and rhyolite. The andesites and basalts were derived by a combination of low-pressure fractional crystallization, higher pressure fractional crystallization, and variable parental magmas, whereas low-pressure fractional crystallization of plagioclase, biotite, and apatite from parental basalt and andesite produced the rhyolites. The parental magmas were basalts and basaltic andesites with high K, Sr, and Ba. The primary source of these magmas is inferred to have been an alkali-enriched hydrous peridotite with neither plagioclase nor garnet present in the residuum.

Fagus (Fagaceae) fruits, foliage, and pollen from the Middle Eocene of Pacific Northwestern North America

2004 ◽  
Vol 82 (10) ◽  
pp. 1509-1517 ◽  
Author(s):  
Steven R Manchester ◽  
Richard M Dillhoff
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Eocene ◽  
Molecular Evidence ◽  
Secondary Vein ◽  
Early Oligocene ◽  
Fossil Evidence ◽  
Ca 50 ◽  
Northwestern North America

Fruits and leaves from the Middle Eocene of McAbee, British Columbia, and Republic, Washington, provide an earlier record for the genus Fagus than previously accepted for this member of the Fagaceae. The fruits are trigonal nuts borne within spiny four-valved cupules on long peduncles. The leaves are borne alternately on the twigs and are ovate to elliptic with craspedodromous secondary veins and simple teeth distributed one per secondary vein. The shale preserving these megafossils also contains dispersed pollen with morphology and ornamentation diagnostic of Fagus. Previously, the oldest Fagus occurrences confirmed by fruits were early Oligocene (ca. 32 Ma). The recognition of Middle Eocene (ca. 50 Ma) representatives helps to reduce the disparity between molecular evidence favoring Fagus as a primitive genus within Fagaceae, and fossil evidence, which had indicated older occurrences of Castanea and Quercus than Fagus.Key words: Eocene, Fagus, fossil, foliage, fruits, British Columbia.

Stratigraphy and paleomagnetism of Brunhes and Matuyama (>790 ka) Quaternary deposits at Merritt, British Columbia

1992 ◽  
Vol 29 (1) ◽  
pp. 76-92 ◽  
Author(s):  
R. J. Fulton ◽  
E. Irving ◽  
P. M. Wheadon
Keyword(s):  
British Columbia ◽  
Quaternary Deposits ◽  
Lacustrine Deposits ◽  
South Central ◽  
Last Glaciation ◽  
Normal Polarity ◽  
Reversed Polarity

A succession of Quaternary deposits in the Merritt basin of south-central British Columbia contains evidence for four glaciations and two interglaciations. Paleomagnetic signatures in these sediments are of three types: normal polarity, proposed to have been acquired during the Brunhes Normal Polarity Chron; reversed polarity, proposed to have been acquired during the Matuyama Reversed Polarity Chron; and reversed polarity (Matuyama age) all but obscured by a normally magnetized overprint (Brunhes age).Reversely magnetized deposits at the base of the succession include glacial lacustrine deposits, interpreted as representing two different glaciations, and a paleosol and a succession of nonglacial sediments, which are evidence of two interglaciations. As the reversed polarity of these deposits is proposed to have been acquired during the Matuyama Reversed Polarity Chron, they are older than 790 ka.Normally magnetized deposits, which make up the rest of the succession, contain evidence for only two glaciations, but traces of other glaciations may have been removed during the erosion interval encompassed by a major unconformity that underlies deposits of the last glaciation. All are referred to the Brunhes Normal Polarity Zone. In addition to these glacial and interglacial deposits, a series of normally magnetized Quaternary basalt flows forms a bench 90 m above the floor of the basin. These basalts were extruded after 790 ka but before the penultimate glaciation.

Ulmus leaves and fruits from the Early–Middle Eocene of northwestern North America: systematics and implications for character evolution within Ulmaceae

2005 ◽  
Vol 83 (12) ◽  
pp. 1663-1681 ◽  
Author(s):  
Thomas Denk ◽  
Richard M. Dillhoff
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Eocene ◽  
Cladistic Analysis ◽  
Character Evolution ◽  
Modern Species ◽  
Perianth Tube ◽  
Fossil Flowers ◽  
Northwestern North America

Leaves and fruits of Ulmus from the Early–Middle Eocene of British Columbia and Washington are assigned to two species. Ulmus okanaganensis sp.nov. is based on leaves attached to flowering and fruiting twigs and isolated leaves and fruits. Leaves display a polymorphism ranging from large leaves with compound teeth with a blunt apex to small ones with simple teeth resembling those of Zelkova. In extant Ulmus, sucker-shoot leaves, elongation-shoot leaves, and leaves on short annual branches often display a very similar polymorphism. In the fossil, flowers are arranged in fascicles having short pedicels. Fascicles are formed in the axils of leaves of current-year shoots and appear together with the leaves. This is uncommon in modern species of Ulmus, where leaves appear either in spring on previous-year shoots or in autumn in the axils of leaves of current-year shoots. Fruits of U. okanaganensis are samaras with extremely reduced or absent wings. Unwinged fruits of modern Ulmus are typically ciliate along the margin of the endocarp and the persistent styles but only a single fruit of U. okanaganensis has been found preserving hairs. The small, shallowly lobed perianth is situated below the endocarp. A second type of foliage is assigned to Ulmus chuchuanus (Berry) LaMotte. This foliage is wider than that of U. okanaganensis and has more densely spaced secondary veins. It also has characteristic compound teeth with primary and subsidiary teeth displaying conspicuously different orientations. Leaves of U. chuchuanus co-occur with a second type of fruit but have not been found in attachment. These fruits are larger than in U. okanaganensis, with a narrow wing, persistent styles, and a large and wide persistent perianth that tapers abruptly into the perianth tube. A cladistic analysis suggests that U. okanaganensis is nested within the subgenus Ulmus, which is a paraphyletic grade basal to the subgenus Oreoptelea. Ulmus chuchuanus foliage shows affinities to the subgenus Ulmus, while the associated fruits display affinities to the subgenus Oreoptelea.

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