Late Ordovician Time Research Articles

Isotopic ages from the Appalachians and their tectonic significance

Geological field relationships and previously reported isotopic age determinations throughout the Appalachians provided evidence for a pattern of Lower Paleozoic tectogenesis. The regional isotopic age pattern indicates that intrusion of ultramafic and mafic igneous materials and major episodes of metamorphic recrystallization throughout the Appalachians were completed before the end of the Silurian Period.New K–Ar ages of metamorphic rocks from Vermont and adjacent regions in the Northern Appalachians are reported and confirm this pattern. Whole-rock ages of slates from the Taconic Klippe (460–445 m.y.) indicate that metamorphism and initial formation of slaty cleavage occurred during Middle to Late Ordovician times. Mica ages of Paleozoic schists exposed along the Green Mountain Anticlinorium (425–375 m.y.) are indicative of prolonged post-metamorphic uplift and cooling of this structure during the Silurian Period and Early Devonian Epoch. Local recrystallization and consequent loss of argon from the Taconic slates also occurred during this time. Ages obtained from a variety of metamorphic rocks from eastern Vermont fall in a narrow range (345 ± 7 m.y), indicating that renewed uplift and rapid cooling of this area, east of a line of ultramafic intrusions, occurred during Late Devonian time.Comparison of isotopic age data from the Appalachian and British Caledonian fold belts indicates that a broadly synchronous sequence of Lower Paleozoic tectonic and magmatic activity, lasting approximately 100 m.y., occurred in both regions.

Forest City Basin of Missouri, Kansas, Nebraska, and Iowa

The Forest City basin of Missouri, Kansas, Nebraska, and Iowa is the area in which the first oil and gas production west of the Mississippi River was found. Production near Paola, Kansas, followed within a few years of the birth of the oil industry at Titusville, Pennsylvania, in 1859 Initial movements of the Ozark uplift and the Chautauqua arch began in Late Ordovician time. Attendant subsidence in the north Kansas area formed an ancestral basin which was bisected later by the Nemaha anticline forming the Salina basin and an unnamed basin on the east. Post-Mississippian, pre-Atokan peneplanation of the entire area took place before renewed activity along the Nemaha anticline uplifted the area west of the anticline while downwarping east of the Nemaha scarp formed the Forest City basin. Thus it is defined as a Pennsylvanian basin. Movement along the Nemaha anticline may have begun during the late Early Ordovician but certainly it was mobile during Early Mississippian time and continued to be active intermittently until at least the early Permian. The Cherokee and Forest City basins were separated by a low arch until middle Cherokee time when the Forest City basin filled with sediments and the two basins linked across the Bourbon arch. Northeast-trending folds developed after Mississippian deposition whereas previous structural orientation was northwestward.

Upper Ordovician Stratigraphic Relations Between Covington and Clays Ferry, Kentucky: GEOLOGICAL NOTES

Upper Ordovician rock-stratigraphic units previously described in southwest Ohio and the central Bluegrass area of Kentucky are correlated by comparing lithologic characteristics and clastic percentage curves derived from detailed measured sections in northern Kentucky. The results presented here suggest a southern source area in this region during Late Ordovician time, and a gradual northward shift of concentrated centers of biota.

Forest City Basin of Missouri, Kansas, Nebraska, and Iowa: ABSTRACT

The Forest City basin of Missouri, Kansas, Nebraska, and Iowa is the area of the first oil and gas production west of the Mississippi River. Production was found near Paola, Kansas, within a few years of the birth of the American oil industry at Titusville, Pennsylvania. Initial movements of the Ozark uplift and the Chautauqua arch began in Late Ordovician time. Attendant subsidence in the northern Kansas area formed an ancestral basin which was later bisected by the Nemaha anticline, forming the Salina basin on the west and an unnamed basin on the east. Post-Mississippian, Pre-Atokan peneplanation of the entire region took place before renewed activity along the Nemaha anticline uplifted the area west of the anticline while downwarping east of the Nemaha scarp formed the Forest City basin. Thus, it is defined as a Pennsylvanian-age basin. Movement along the Nemaha structure may have begun as early as pre-St. Peter time but certainly during Early Mississippian time and continued intermittently until at least the Early Permian. The Cherokee and Forest City basins were separated by a low arch until middle Cherokee time when the Forest City basin filled with sediments and the two basins joined across the Bourbon arch. Northeast-trending folds developed after Mississippian deposition, whereas previous structural orientation had been toward the northwest. End_of_Article - Last_Page 1564------------

Cincinnati Arch: Mineralogical-Statistical Evidence of Post-Ordovician Origin

The Cincinnati arch is commonly considered among geologists to date from the Ordovician. This concept is reflected in the statements of some current historical geology textbooks. However, a historical review of the concept shows that the Ordovician date was based on very tenuous evidence and that most early workers, such as Newberry, Orton, and Foerste, believed it to date from not earlier than the Silurian. The problem of its existence in Late Ordovician time was investigated by a thorough mineralogical, chemical, and gravitational methods. One hundred and fifteen shale specimens were collected laterally from three horizons within the Cincinnatian Series in its exposure area in southwestern Ohio, southeastern Indiana, and northern Kentucky. Twenty-two mineralogical, chem cal, and textural parameters were measured from each specimen and the data were treated statistically by an analysis of variance method. The calculation was performed by computer. The results indicated only a weak possibility of a embryonic arch being present during Early Cincinnatian time (Fulton). There is definite evidence of an east-west barrier unrelated to the trend of the Cincinnati arch dominating the basin of deposition during at least a part of early Late (Clarksville) Cincinnatian time. There is some evidence that a basin limiting element generally parallel with the previously proposed Cincinnati arch was influencing shale deposition at the close of Cincinnatian time. Its influence, however, was not strong and it is doubtful that it represents the type of paleogeographic featu e which is known to have developed in later Paleozoic time as the Cincinnati arch.

Paleozoic History of Southeastern Colorado

Southeastern Colorado was first covered by Paleozoic seas in Late Cambrian time, when coarse clastics (Lamotte sandstone) derived mainly from the north were deposited in front of a low landmass that extended from New Mexico northwestward to the vicinity of Canon City. The seas gradually encroached on this landmass, depositing additional Upper Cambrian (Bonneterre dolomite) and Lower Ordovician (Arbuckle group) rocks farther southwest. Near the close of Early Ordovician time, gentle upwarping raised the central part of southeastern Colorado above sea-level. During Middle and Late Ordovician time, seas lapped upon the eastern and western slopes of this upwarp, depositing the sediments of the Simpson group and the Viola limestone. After the close of Ordovician time, upliftin , probably with some faulting, along the present trend of the Front Range, Wet Mountains, and Apishapa-Sierra Grande uplift, permitted the removal by erosion of most of the Cambrian and Ordovician rocks from that area. In Mississippian time the seas advanced from the Anadarko basin, lapping on the gently sloping landmass. During Meramec time the seas probably completely covered the landmass and at the end of Meramec time began a withdrawal into the Anadarko basin. During Chester time the seas appear to have been restricted to the Hugoton embayment in the southeasternmost part of Colorado. At the beginning of Pennsylvanian time, the seas advanced upon the flanks of the low landmass of eastern Colorado, bringing clastic material from the southeast. Near the end of Morrow time major uplifting accompanied by faulting elevated the Apishapa-Sierra Grande uplift, the Wet Mountains, and the Front Range, which supplied clastic material to transgressing seas during the remainder of Pennsylvanian time. A cross flexure marking the earliest beginnings of the Las Animas arch seems to have developed near the end of Missouri time. During early Permian time the seas gradually covered the Apishapa-Sierra Grande landmass, and during late Permian time the shore line remained fairly stable, until the seas receded at the close of the period.

Structural Relations on East Flank of Anadarko Basin, Cleveland and McClain Counties, Oklahoma

Information obtained from deep oil tests drilled in the past 5 years has disclosed that the Anadarko basin of western Oklahoma is separated from the central Oklahoma platform by a zone of buried large-scale faulting. The major displacement in Cleveland and McClain counties is a fault zone, herein named the McClain County fault zone, which extends through the two counties from north to south, approximately bisecting them. The total throw of the zone reaches a maximum of more than 2,300 feet. The fault is considered to be a zone of shearing due to differential vertical uplifts between the positive central Oklahoma platform on the east, and the negative Anadarko basin on the west. Numerous secondary faults are associated with the major fault zone. Structural differentiation of the two structural provinces was established at least by late Ordovician time, and may possibly date from the pre-Cambrian. However, the major movements were concentrated in two periods of diastrophism in pre-Des Moines Pennsylvanian time. Structural adjustments were in general continuous into Des Moines and later Pennsylvanian time; however, all faults pass upward into monoclinal folds in the lower part of the Deese group.