Lower and Middle Jurassic Perispyridium (Radiolaria) from the Snowshoe Formation, East-Central Oregon

1988 ◽  
Vol 34 (4) ◽  
pp. 289 ◽  
Author(s):  
Norman MacLeod
Keyword(s):  
Middle Jurassic ◽  
East Central

Reineckeiidae (Ammonoidea) from the Callovian (Middle Jurassic) of the Shotori Range (East Central Iran)

2002 ◽  
Vol 2002 (3) ◽  
pp. 184-192 ◽  
Author(s):  
Kazem Seyed-Emami ◽  
Gerhard Schairer ◽  
Franz T. Fürsich ◽  
Markus Wilmsen ◽  
Mahmoud Reza Majidifard
Keyword(s):  
Middle Jurassic ◽  
Central Iran ◽  
East Central

DEPOSITION DOWNWIND OF THE COLORADO PLATEAU ERGS: UPPERMOST TRIASSIC?-MIDDLE JURASSIC STRATA OF THE PLOMOSAS UPLIFT, EAST-CENTRAL CHIHUAHUA, MEXICO

2016 ◽  
Author(s):  
Timothy F. Lawton ◽  
◽  
Jorge Enrique Ruiz-Urueña ◽  
Carmen Manuela Tarango-Terrazas ◽  
Edgar Juárez-Arriaga ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Colorado Plateau ◽  
East Central

Deformation of the western margin of the Omineca Belt near Crooked Lake, east-central British Columbia

1990 ◽  
Vol 27 (3) ◽  
pp. 414-425
Author(s):  
Jeffrey A. Fillipone ◽  
John V. Ross
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Jurassic ◽  
Phase 1 ◽  
Late Devonian ◽  
East Central ◽  
Western Margin ◽  
Metasedimentary Rocks ◽  
Narrow Zone ◽  
Minimum Age

The western margin of the Omineca Belt near Crooked Lake, British Columbia, consists of metasedimentary rocks (Snowshoe Group) and orthogneisses of the Barkerville terrane, structurally overlain by a mafic volcanic – sedimentary package of rocks belonging to the allochthonous Slide Mountain (Crooked Amphibolite) and Quesnel terranes (Triassic phyllite and Nicola Group). At least two episodes of regional deformational (phases 2 and 3) affected this composite package. Deformation and metamorphism (phase 1) in the Snowshow Group predate the formation of this package and are nowhere evident within the allochthonous terranes.Middle Jurassic metamorphism ranging from chlorite zone through sillimanite zone affected all units. Isograds are folded, together with the junction between the terranes, indicating that the metamorphic assemblages developed prior to folding of this boundary. Granitic orthogneiss (Boss Mountain, Quesnel Lake, and Perseus gneisses), having a minimum age of Late Devonian to Early Pennsylvanian, was intruded into and deformed with the Snowshoe Group during the earliest recognizable phase of deformation in the Barkerville terrane (phase 1). Slide Mountain terrane rocks occupy a narrow zone where large eastward displacement occurred during overthrusting of the Intermontane superterrane upon the western margin of North America in Middle Jurassic time.

Paleomagnetic results from Upper Triassic and Middle Jurassic strata of east-central New Mexico, and implication for North American apparent polar wander path

2021 ◽  
pp. 228872
Author(s):  
Masoud Mirzaei ◽  
Bernard A. Housen ◽  
Russell F. Burmester ◽  
Brady Z. Foreman
Keyword(s):  
New Mexico ◽  
North American ◽  
Middle Jurassic ◽  
Upper Triassic ◽  
East Central ◽  
Polar Wander ◽  
Apparent Polar Wander Path

scholarly journals Composite and diachronous stratigraphic surfaces in low-gradient, transitional settings: The J-3 “unconformity” and the Curtis Formation, east-central Utah, U.S.A.

2019 ◽  
Vol 89 (11) ◽  
pp. 1075-1095 ◽  
Author(s):  
Valentin Zuchuat ◽  
Ivar Midtkandal ◽  
Miquel Poyatos-Moré ◽  
Sigrid Da Costa ◽  
Hannah Louise Brooks ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Dynamic Environment ◽  
Upper Jurassic ◽  
Composite Surface ◽  
East Central ◽  
Significant Time ◽  
Stratigraphic Record ◽  
Unique Nature ◽  
Composite Nature

ABSTRACT Unconformities, by definition, correspond to erosional or nondepositional surfaces, which separate older strata below, from younger rocks above, encapsulating significant time gaps. However, recent studies have highlighted the composite nature of some unconformities, as well as their heterochronous and diachronous character, which challenge the use of such a definition in a four-dimensional dynamic environment. The J-3 Unconformity, separating the Middle Jurassic Entrada Sandstone from the Upper Jurassic Curtis Formation (and laterally equivalent units) in east-central Utah (USA), is laterally variable, generated by either erosion-related processes such as eolian deflation, and water-induced erosion, or by deformational processes. The J-3 Unconformity is a composite surface, formed by numerous processes that interacted and overlapped spatially and temporally. This study therefore demonstrates the heterochronous, diachronous, and non-unique nature of this surface interpreted as unconformity, where one process can be represented by varying expressions in the stratigraphic record, and conversely many processes may result in the same stratigraphic expression.

Lower and Middle Jurassic Radiolaria (Multicyrtid Nassellariina) from California, East-Central Oregon and the Queen Charlotte Islands, B.C.

1982 ◽  
Vol 28 (2) ◽  
pp. 111 ◽  
Author(s):  
Emile A. Pessagno ◽  
Patricia A. Whalen
Keyword(s):  
Middle Jurassic ◽  
East Central ◽  
Queen Charlotte Islands

scholarly journals Spectacular crinkled crust—A detachment fold train in the Carmel Formation, western San Rafael Swell, Utah

Geosites ◽  
2019 ◽  
Vol 1 ◽  
pp. 1-9
Author(s):  
Thomas Chidsey ◽  
Paul Anderson
Keyword(s):  
Structural Geology ◽  
Structural Feature ◽  
Middle Jurassic ◽  
Original Position ◽  
East Central ◽  
Convex Upward ◽  
Detachment Fold ◽  
Complex Structural ◽  
San Rafael ◽  
San Rafael Swell

Imagine slipping on a small rug overlying a hardwood floor. In the process of sliding along the floor the rug produces a series of small folds and the rug moves forward from its original position. The same could be said for the “crinkled crust,” or folded layers of rocks in a detachment fold train. A spectacular detachment fold train, consisting of over 100 small, regularly spaced convex-upward folds called anticlines in gypsum-rich rock layers of the Middle Jurassic (about 168 million years ago [Ma]) Carmel Formation, is exposed immediately north of Interstate 70 (I-70) in the San Rafael Swell of east-central Utah (figures 1 and 2). The SanRafael Swell, a large anticlinal uplift, is an icon for everything that makes the Colorado Plateau dramatically scenic and geologically classic. However, the fold train is located in drab-colored, relatively featureless rock layers of the Carmel Formation in an area called Reed Wash along the gently dipping west flank of the Swell. After passing magnificent canyons, buttes, and mesas both to the east and west along I-70, the fold train typically goes unnoticed by not only the average tourist but geologists as well. Once the fold train is pointed out, the geologic observer is immediately struck with awe at this large, well-exposed, complex structural feature. Literally hundreds of classic geologic sites are well displayed in the San Rafael Swell; many are easily accessed overlooks and viewpoints. The detachment fold train, by contrast, is chosen as a geosite for its geologic uniqueness, educational instruction, and research opportunities in structural geology.

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