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B. R. Wardlaw

Publications and source records attributed to B. R. Wardlaw.

30 records · Page 2Linked to original sources
USGS1986

Heating, cooling, and uplift during Tertiary time, northern Sangre de Cristo Range, Colorado (USA)

aleozoic sedimentary rocks in a wide area of the northern Sangre de Cristo Range show effects of heating during Tertiary time. Heating is tentatively interpreted as a response to burial during Laramide folding and thrusting and also to high heat flow during Rio Grande rifting. The regional extent of heating is shown by the distribution of low-grade metamorphic minerals, altered conodonts, and reset fission-track ages throughout much of the study area. Alteration of conodonts to a conodont alteration index (CAI) of 4.0 suggests that temperatures reached ∼200 °C in the central part of the area. Temperatures may have reached 300 °C beneath Laramide thrusts on the west side of the range, where conodonts were altered to a CAI of 5.0, and where chloritoid and andalusite are found in sedimentary rocks of Pennsylvanian age. The lowest temperatures that were determined by conodont alteration (CAI = 1.0–2.0, <50–70 °C) are along the east side of the range, where rocks were evidently never buried deeply. Contact metamorphism was restricted to wall rocks of a few isolated stocks; near dikes and sills, it was not significant. Fission-track ages of apatite across a section of the range show that rocks cooled abruptly below 120 °C, the blocking temperature for apatite, ∼19 Ma ago. Cooling was probably in response to rapid uplift and erosion of the northern Sangre de Cristo Range during early Rio Grande rifting.

Geological Society of America Bulletin↗
USGS1986

Paleontology and deposition of the Phosphoria Formation.

The Phosphoria Formation and related rocks were deposited in an interior sag basin developed in the Cordilleran miogeocline of western North America. Deposition can be characterized as a fringing bank complex on a carbonate ramp. Conodont-brachiopod biostratigraphy provides a sufficient relative time framework for correlation of the many units. These age correlations and the distribution of fossils, plus the biofacies of conodonts and brachiopods in particular, indicate that phosphate deposition was a cool-water, deeper ramp facies that transgressed over the carbonate bank twice, representing the Meade Peak and Retort Phosphatic Shale Members of the Phosphoria Formation. Conodont data that substantiate the above are presented, and a new genus and species, Sweetina triticum, is described. -Authors

Contributions to Geology - University of Wyoming, ↗
USGS1983

Structure, burial history, and petroleum potential of frontal thrust belt and adjacent foreland, southwest Montana

The frontal thrust belt in the Lima area of southwestern Montana consists of blind (nonsurfacing) thrusts of the Lima thrust system beneath the Lima anticline and the Tendoy thrust sheet to the west. The Tendoy sheet involves Mississippian through Cretaceous rocks of the southwest-plunging nose of the Mesozoic Blacktail-Snowcrest uplift that are thrust higher (northeast) onto the uplift. The front of the Tendoy sheet west of Lima locally has been warped by later compressive deformation which also involved synorogenic conglomerates of the structurally underlying Beaverhead Formation. To the north, recent extension faulting locally has dropped the front of the Tendoy sheet beneath Quaternary gravels. Rocks of the exposed Tendoy sheet have never been deeply buried, based on itrinite reflectance of <= 0.6%, conodont CAI (color alteration index) values that are uniformly 1, and on supporting organic geochemical data from Paleozoic rocks from the Tendoy thrust sheet. Directly above and west of the Tendoy sheet lie formerly more deeply buried rocks of the Medicine Lodge thrust system. Their greater burial depth is indicated by higher conodont CAI values. West-dipping post-Paleocene extension faults truncate much of the rear part of the Tendoy sheet and also separate the Medicine Lodge sheet from thrust sheets of the Beaverhead Range still farther west. The Laramide Blacktail-Snowcrest uplift east of the frontal thrust belt is asymmetric. Its southeast, steeper limb is exposed along the Snowcrest Range. This limb extends southwestward in the complexly deformed Snowcrest structural terrane. Northwest-dipping thrusts on this limb involve basement rocks and probably merge with depth into a major sub-Snowcrest Range thrust. This major thrust borders and is chiefly responsible for the Blacktail-Snowcrest uplift and adjacent Ruby synclinorium to the southeast. Uniform conodont CAI values of 1 from both the southeast and northwest flanks of the Blacktail-Snowcrest uplift indicate that no thick cover of Upper Cretaceous or younger rocks extended over the flanks of the uplift. During Mississippian through Permian time, the area of later Laram de uplift underwent more rapid subsidence than the area of the Laramide Ruby syncline and the Centennial basin to the southeast. The inferred sub-Snowcrest Range thrust fault apparently represents a reactivated zone of basement weakness. The intersection of thrust-belt and foreland trends, similar to the Uinta uplift area to the south, probably formed a number of structural traps for hydrocarbons which have not yet been tested. Potential petroleum source beds and reservoir rocks are both present in southwest Montana. However, remnants of Tertiary lava flows through much of the area, Tertiary to recent basin-and-range faulting, and supermaturity with respect to oil of Permian and older rocks in the western Centennial uplift area are additional factors which must be considered in any estimate of hydrocarbon potential of the Cordilleran overthrust belt and adjacent foreland in extreme southwestern Montana.

Montana↗
USGS1982

Biostratigraphy and structural setting of the Permian Coyote Butte Formation of central Oregon

Larger isolated outcrops of the limestones of the Coyote Butte Formation consistently contain younger over older faunas that range through most of the Leonardian Series of the Early Permian. The outcrops of the Coyote Butte Formation are interpreted as right-side up blocks probably introduced into the area as one massive exotic unit. The Coyote Butte Formation is very similar to the Lower Permian limestone near Quinn River Crossing, Nevada, and both are suggested to have a similar origin. The Coyote Butte Formation was probably introduced during a late-stage event to deforming Mesozoic oceanic sediments in Mesozoic time.

Geology↗