Calvin H. Stevens

Phanerozoic stratigraphy of Northwind Ridge, magnetic anomalies in the Canada basin, and the geometry and timing of rifting in the Amerasia basin, Arctic Ocean

Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulders and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cap of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining sea-floor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield similar tectonic reconstructions. Together with the orientation and age of rift-margin structures, these data suggest that (1) prior to opening of the Amerasia basin, both northern Alaska and the continental ridges of the Chukchi borderland were part of North America, (2) the extension that created the Amerasia basin formed rift-margin grabens beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the basis of the stratigraphy of Northwind Ridge and sea-floor magnetic anomalies in the Canada basin accounts in a general way for the major crustal elements of the Amerasia basin, including the highstanding ridges of the Chukchi borderland, and supports S. W. Carey9s hypothesis that the Amerasia basin is the product of anticlockwise rotational rifting of Arctic Alaska from North America.

Pennsylvanian and Early Permian paleogeography of east-central California: Implications for the shape of the continental margin and the timing of continental truncation

Pennsylvanian and Early Permian paleogeographic features in east-central California include a southeast-trending carbonate shelf edge and turbidite basin that we infer paralleled a segment of the western margin of the North American continent. This segment of the continental margin was oblique to an adjoining segment on the north that trended southwestward across Nevada into easternmost California. We propose that the southeast-trending segment of the margin originated by tectonic truncation of the originally longer southwest-trending segment in Early or Middle Pennsylvanian to late Early Permian time, significantly earlier than a previously hypothesized Late Permian or Early Triassic continental truncation event. We interpret the truncating structure to have been a sinistral transform fault zone along which a continental fragment was removed and carried southeastward into the Caborca-Hermosillo region of northern Mexico, where it is now represented by exposures of Late Proterozoic and Paleozoic miogeoclinal rocks.

PALEOZOIC AND MESOZOIC EVOLUTION OF EAST-CENTRAL CALIFORNIA

East-central California, which encompasses an area located on the westernmost part of sialic North America, contains a well-preserved record of Paleozoic and Mesozoic tectonic events that reflect the evolving nature of the Cordilleran plate margin to the west. After the plate margin was formed by continental rifting in the Neoproterozoic, sediments comprising the Cordilleran miogeocline began to accumulate on the subsiding passive margin. In east-central California, sedimentation did not keep pace with subsidence, resulting in backstepping of a series of successive carbonate platforms throughout the early and middle Paleozoic. This phase of miogeoclinal development was brought to a close by the Late Devonian-Early Mississippian Antler orogeny, during the final phase of which oceanic rocks were emplaced onto the continental margin. Subsequent Late Mississippian-Pennsylvanian faulting and apparent reorientation of the carbonate platform margin are interpreted to have been associated with truncation of the c...

Early Permian location of western North American terranes based on brachiopod, fusulinid, and coral biogeography

Abstract Brachiopod, rugose coral, and fusulinid faunas present in Early Permian rocks along northern and western margins of North America, in both cratonal localities and accreted terranes, have been compared statistically, allowing refinement in placement of these terranes relative to the North American continental margin at that time. Statistical tests, including conventional and probabilistic indices of similarity, as well as multivariate analysis, show that the faunas of Wrangellia-Alexander are most similar to those of Stikinia and Quesnellia, and to the Yukon–Canadian Rocky Mountains part of the continental margin. They also show that faunas of the Eastern Klamath terrane are most similar to those of Stikinia, Quesnellia, and the central cordilleran part of the continental margin. These results suggest that during the Early Permian Wrangellia-Alexander was the northernmost of these terranes, lying west of the Yukon–Canadian Rocky Mountains region, and the Eastern Klamath terrane was the southernmost, lying west of the central Cordillera. Stikinia and Quesnellia were in intermediate positions. These relative latitudes are compatible with latitudinal determinations based on paleomagnetic data. Faunal diversity in the Eastern Klamath and Stikine terranes is similar to that at similar latitudes on the craton, whereas diversity in the Wrangellia-Alexander terrane is considerably lower than that of the latitudinally similar Yukon–Canadian Rocky Mountains area. As diversity is, in part, a function of temperature, this may suggest water around the Wrangellia-Alexander terrane was cooler than that along the continental margin. Therefore, we suggest that warm-water currents bathed the southern terranes and the southern and central parts of coastal North America, whereas cool-water currents influenced the northernmost terrane (Wrangellia-Alexander). Revised Otsuka similarity coefficients for corals show higher similarities between western North American terranes and the western continental margin than previously published, but they still are relatively low. This and the overall patterns of similarity and limits on distribution of Tethyan corals and fusulinids in the eastern Panthalassa suggest that Wrangellia-Alexander, Stikinia, and the Eastern Klamath terranes were at approximately the same distance (estimated at 2000–3000 km) from their latitudinally equivalent segments of the North American craton.

Stratigraphy, depositional history, and tectonic evolution of Paleozoic continental-margin rocks in roof pendants of the eastern Sierra Nevada, California

during the Late Devonian‐Early Mississippian Antler orogeny at a considerable distance to the west. Later, in post-Early Permian time, rocks of the Morrison block were deformed, rocks of the Antler belt were emplaced against the Morrison block, and the facies boundaries and structural belts defined here were offset on northwest-trending dextral faults.

Early Permian thrust faults in east-central California

One exposed and another inferred thrust fault in the southeastern Inyo Mountains of east-central California are interpreted as Early Permian in age. These faults, both apparently of local extent, are temporally and geographically related to a major episode of basin formation which occurred along a southeast-trending segment of the Permian North American plate margin. The close relationship between basin formation and thrust faulting supports a previous interpretation by us that this segment of the margin was undergoing active wrench tectonism during the Early Permian, resulting in the essentially simultaneous development of local extensional and compressional structures similar to those now forming in the California continental borderland.

Paleoecologic Implications of Early Permian Fossil Communities in Eastern Nevada and Western Utah

Stratigraphic and paleontologic studies in eastern Nevada and western Utah show that at least eight major marine and paralic fossil communities occur in rocks of Early Permian age. The eight communities, named for characteristic faunal elements, are: palaeotextulariid, fusulinid, coral, dictyoclostid- Composita, chonetoid, Heteralosia, nuculanid, and euphemitid. The palaeotextulariid, fusulinid, coral, dictyoclostid- Composita , and chonetoid communities probably required a salinity close to 35 per mil. The palaeotextulariid community probably lived at a depth of 50–70 m; fusulinid at 20–50 m; and coral at 10–30 m. The dictyoclostid- Composita and chonetoid communities may have lived at a depth of 4-10 m, the latter in a lower energy environment than the former. The Heteralosia, nuculanid, and euphemitid communities apparently were euryhaline and occupied very shallow bottoms.

Lower Permian Colonial Rugose Corals, Western and Northwestern Pangaea: Taxonomy and Distribution

The most comprehensive summary available on the stratigraphic occurrence, geographic distribution, phylogeny, and taxonomy of Early Permian colonial rugose corals that occupied the Cordilleran–Arctic–Uralian (CAU) Realm, along the northwestern and western marine shelves and accreted terranes of the ancient supercontinent Pangaea. It is based on all previous studies by other coral specialists, a thorough review of all published data, and on information from a very large number of new collections from new areas. This book contains a new classification and phylogenetic scheme, based on critical restudy of the entire coral fauna at all taxonomic levels

A new Permian waagenophyllid coral from the Klamath Mountains, California

Specimens of a new species of the Permian waagenophyllid coral genus Waagenophyllum, W. klamathensis , have been recovered from limestone lenses near the top of the Upper Permian Dekkas Formation in the eastern Klamath Mountains, and similar specimens have been collected from an isolated limestone mass in the eastern Hayfork terrane of the southwestern Klamath Mountains, northern California. Another specimen of Waagenophyllum , which may represent another species, has been recovered from another limestone mass in the Hayfork terrane. These specimens of Waagenophyllum , a genus which otherwise is restricted to the Tethyan Province, provide the only tie between the Permian limestone masses of the eastern Hayfork terrane, which also contain typical Tethyan foraminifers, and the eastern Klamath Mountains terrane (McCloud belt), which contains many fossils with non-Tethyan affinities.

Was development of brackish oceans a factor in Permian extinctions

Extinction of major components of marine communities during Permian time was the most devastating event in the history of life. The pattern of extinction suggests that, among other possibilities, salinity changes in the oceans could have been a primary contributing factor. New data on Permian halite deposits show that the volume is far greater than previously suspected, amounting to at least 10 percent of the volume of salt presently in solution in the oceans. This amount is well over one-half the volume that, if removed from modern oceans, would produce brackish conditions resulting in mass extinctions in modern marine communities. Inasmuch as there may be considerably more Permian halite than has yet been discovered or dated as Permian, and as vast amounts of halite may have been lost from Permian deposits through solution in the past 225 m.y., it is considered probable that development of brackish oceans was an important factor in Permian extinctions.