Most of the bedrock in the Wallace quadrangle belongs to the Belt Supergroup, a thick (about 18,000 m) sequence of generally fine-grained clastic and carbonate rocks of Middle Proterozoic age. Regional metamorphism prior to Cambrian time prograded the Belt rocks to greenschist facies, and some metal-bearing veins were emplaced in fractures. The Belt rocks were intruded in Late Proterozoic time by basic dikes and sills.
Research Article| November 01, 1995 Late Neogene chronology: New perspectives in high-resolution stratigraphy W. A. Berggren; W. A. Berggren 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar F. J. Hilgen; F. J. Hilgen 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar C. G. Langereis; C. G. Langereis 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar D. V. Kent; D. V. Kent 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar J. D. Obradovich; J. D. Obradovich 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar Isabella Raffi; Isabella Raffi 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar M. E. Raymo; M. E. Raymo 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar N. J. Shackleton N. J. Shackleton 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar Author and Article Information W. A. Berggren 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 F. J. Hilgen 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 C. G. Langereis 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 D. V. Kent 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 J. D. Obradovich 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Isabella Raffi 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 M. E. Raymo 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 N. J. Shackleton 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (11): 1272–1287. https://doi.org/10.1130/0016-7606(1995)107<1272:LNCNPI>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation W. A. Berggren, F. J. Hilgen, C. G. Langereis, D. V. Kent, J. D. Obradovich, Isabella Raffi, M. E. Raymo, N. J. Shackleton; Late Neogene chronology: New perspectives in high-resolution stratigraphy. GSA Bulletin 1995;; 107 (11): 1272–1287. doi: https://doi.org/10.1130/0016-7606(1995)107<1272:LNCNPI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We present an integrated geochronology for late Neogene time (Pliocene, Pleistocene, and Holocene Epochs) based on an analysis of data from stable isotopes, magnetostratigraphy, radiochronology, and calcareous plankton biostratigraphy. Discrepancies between recently formulated astronomical chronologies and magnetochronologies for the past 6 m.y. have been resolved on the basis of new, high-precision Ar/Ar ages in the younger part of this interval, the so-called Brunhes, Matuyama, and Gauss Epochs (= Chrons C1n–C2An; 0–3.58 Ma), and revised analysis of sea floor anomalies in the Pacific Ocean in the older part, the so-called Gilbert Epoch (= Chron C2Ar–C3r; 3.58–5.89 Ma). The magneto- and astrochronologies are now concordant back to the Chron C3r/C3An boundary at 5.89 Ma. The Neogene (Miocene, Pliocene, Pleistocene, and Holocene) and Paleogene are treated here as period/system subdivisions of the Cenozoic Era/Erathem, replacements for the antiquated terms Tertiary and Quaternary. The boundary between the Miocene and Pliocene Series (Messinian/Zanclean Stages), whose global stratotype section and point (GSSP) is currently proposed to be in Sicily, is located within the reversed interval just below the Thvera (C3n.4n) Magnetic Polarity Subchronozone with an estimated age of 5.32 Ma. The Pliocene/Pleistocene boundary, whose GSSP is located at Vrica (Calabria, Italy), is located near the top of the Olduvai (C2n) Magnetic Polarity Subchronozone with an estimated age of 1.81 Ma. The 13 calcareous nannoplankton and 48 planktonic foraminiferal datum events for the Pliocene, and 12 calcareous nannoplankton and 10 planktonic foraminiferal datum events for the Pleistocene, are calibrated to the newly revised late Neogene astronomical/geomagnetic polarity time scale. This content is PDF only. Please click on the PDF icon to access. 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The type Lospe Formation in the Casmalia Hills is an 800-m-thick sequence of sedimentary and minor volcanic rocks. The Lospe is entirely of early Miocene (Saucesian) age on the basis of palynomorphs, benthic foraminifers, and {sup 40}Ar/{sup 39}Ar ages of 17.70 {plus minus} 0.03 Ma (mean of seven determinations) and 17.39 {plus minus} 0.12 Ma (mean of six determinations). The {sup 40}Ar/{sup 39}Ar ages were measured on water-laid tuffs; these tuffs may have erupted from the same volcanic source as a welded tuff yielding an {sup 40}Ar/{sup 39}Ar age of 17.79 {plus minus} 0.10 Ma (mean of five determinations) from the Tranquillon volcanics on Tranquillon Mountain in the westernmost Transverse Ranges. Alluvial fan and fan-delta facies within the basal part of the Lospe are as thick as 200 m and consist mainly of conglomerate and sandstone derived from nearby fault-bounded uplifts of Mesozoic rocks. These coarse-grained facies grade upward into a sequence of interbedded sandstone and mudstone that accumulated in a shallow lake. Gypsum layers in the lake deposits contain sulfate depleted in {sup 34}S (0 to +3{per thousand}), suggesting that the sulfur had a hydrothermal origin. The uppermost 30 m of the Lospe consists of storm-deposited sandstone and mudstonemore » containing shallow-marine microfossils. The shallow-marine deposits are abruptly overlain by bathyal marine shale of the Point Sal Formation. The Lospe Formation records active faulting, volcanism, hydrothermal activity, and rapid subsidence during initial formation of the Neogene Santa Maria basin. These events may have resulted from crustal extension related to the beginning of clockwise rotation of the western Transverse Ranges about 18 to 17 Ma.« less
Fifty-two total-fusion 40 Art3 9 Ar ages, measured with a continuous laser system on single tektites from the Cretaceous-Tertiary (K-T) boundary layer within the Beloc Formation of southern Haiti, have a weighted mean of 64.42±0.06(obest) Ma. 40 Art3 9 Ar age spectra on four single Haitian tektites obtained with the same laser system are flat and each has a plateau over more than 95 percent of the 39 Ar released.The weighted mean of the four plateau ages is 64.38±0.18Ma( obest).Two age spectra obtained using a resistance furnace system on bulk samples of about 50-70 of the tektites also have flat plateaus with a weighted mean age of 64.49±0.10Ma.Our results indicate that the impact that formed the tektites occurred 64.43±0.05Ma.Sanidine from two bentonites that lie 50-70 centimeters above the K-T boundary interval in continental sedimentary rocks in Montana was also dated with the laser system (28 measurements) and gives a weighted mean 40 Arf3 9 Ar age of 64.77±0.07Ma.The Haitian tektites occur at the paleontological K-T boundary along with an Ir abundance anomaly and shocked quartz.They were the product of an impact on Earth of an extraterrestrial bolide (asteroid or comet) at the end of the Cretaceous Period.All available data, from our study and from those previously published, suggest that this event occurred 64.6±0.1 Ma.
K-Ar ages of biotite and hornblende from the batholith and satellite masses range from 78 to 68 m.y. The emplacement could have taken as little as 5 m.y. (76-71 m.y.). Even though isotopic dates generally support field evidence for the intrusion sequence, reduction of K-Ar dates of older rocks in the vicinity of younger plutons is suspected. Making certain assumptions, the total emplacement time may have been about 9 m.y., and the bulk of the batholith was probably emplaced during the first 6 m.y. The youngest prebatholith rocks, the Elkhorn Mts. volcanics, are about 78 m.y. but may be slightly older. If so, the total emplacement time could even be as great as 10 to 12 m.y.
Synopsis Sixteen K-Ar ages for samples of biotite and amphibole from the Ross of Mull and analytical data for the standards Bern 4M and W1 are presented. Ages determined for biotite and amphibole samples from the Caledonian pluton average 423 ± 4 m.y. and 416 ± 4 m.y. respectively. Field observations combined with gravity data indicate that this intrusion was guided by the Moine thrust plane. These ages therefore provide a minimum age for the Moine thrust and their concordance is interpreted in relation to the retentivity of the dated amphiboles to 40 Ar inferred from electron microprobe analyses of their composition. A biotite sample from a minette dyke cutting the pluton yielded an age of 406 ± 10 m.y., whereas two samples of amphibole from a fourchite dyke in the Moine country rock yielded early Permian ages of 276 ± 7 m.y. and 274 ± 8 m.y.
Siliciclastic and calcareous sedimentary rocks of early Late Cretaceous age in the Western Interior of the United States have been assigned to, in ascending order, the Graneros Shale, Greenhorn Formation, Carlile Shale, Niobrara Formation, and their lateral equivalents (including members of the Frontier Formation and overlying formations). This sequence of formations was deposited intermittently within and near an epicontinental seaway during the Cenomanian, Turonian, and Coniacian stages of the Cretaceous. It encloses three conspicuous and widespread disconformities that reflect regional marine regressions and transgressions as well as moderate tectonism. The disconformities and associated lacunae occupy three large areas within Wyoming, Colorado, and adjoining states. In parts of that region, as in northwestern Wyoming, a lacuna can represent more than one period of erosion and more than a single disconformity. Evidence for these disconformities was obtained from about 175 collections of molluscan fossils and from sedimentological studies of outcrops and borehole logs, supplemented by previously published data.
The oldest of the three disconformities, within the Frontier Formation and partial age-equivalents (including the Carlile Shale), separates Cenomanian or lower Turonian beds from middle Turonian beds in central and western Wyoming, northwestern Colorado, and adjoining areas of Montana and Utah. In parts of that region, the maximum duration of the associated lacuna is about 3 m.y. Erosion of the region in the late early Turonian was associated with a marine regression and transgression as well as mild local tectonism. The area where strata underlying the unconformity are oldest is partly overlain by the youngest of the succeeding transgressive beds. These youngest overlying beds presumably were deposited in an uplifted area where the eroded surface had a slightly higher elevation.
A younger disconformity, within the Frontier Formation and lateral equivalents, separates upper Cenomanian or lower or middle Turonian strata from middle or upper Turonian strata in central and eastern Wyoming, southwestern South Dakota, western Nebraska, and central and eastern Colorado. Locally in that region, the duration of the lacuna is as much as 5 m.y. The oldest beds underlying this contact are of late Cenomanian age and are distributed in north-central and southeastern Wyoming and in north-central Colorado, where the erosional surface was affected probably by slight uplifts and by fluvial drainage systems. In that region, the oldest beds are partly overlain by the youngest (late Turonian) of the transgressive strata. The areal distribution of the younger overlying beds in central Wyoming could indicate a westward migration of marine prodelta environments during the late Turonian.
At the youngest of the three disconformities, strata of middle or late Turonian ages in the Carlile Shale and lateral equivalents are overlain by upper Turonian or lower or middle Coniacian beds of the basal Niobrara Formation in Wyoming, Colorado, Nebraska, and parts of adjoining states. The maximum duration of the associated lacuna is more than 4 m.y. in northwesternmost Wyoming and northeasternmost Nebraska. Beds underlying this disconformity are oldest (early middle Turonian) in northwestern Wyoming, northeasternmost Nebraska, and possibly elsewhere in Nebraska, which apparently were areas of comparatively higher elevation and greater truncation. The underlying beds are youngest in a northeast-trending area that extends at least from eastern Utah to northeastern Wyoming. This area presumably was uplifted less than adjoining areas possibly in the late Turonian. Strata overlying this disconformity are oldest in northeastern New Mexico and much of Colorado and are youngest in northeastern Utah, northwestern and east-central Wyoming, north-central Kansas, and northeastern Nebraska, which indicates a marine transgression that progressed mainly northward.
Most of the ages used for the following calculations are estimates; consequently the resulting quantitative interpretations are speculative. The duration of the lacuna between the uppermost Carlile and the basal Niobrara increased northwestward from about 0.8 m.y. in south-central Colorado to about 4.3 m.y. in northwesternmost Wyoming. It also increased northeastward from 0.8 m.y. in Colorado to about 5.1 m.y. in northeastern Nebraska. Ages of basal beds of the Niobrara decrease northwestward from about 89.3 Ma in southeastern Colorado and northeastern New Mexico to about 88.7 Ma in northwesternmost Wyoming. Apparently, the Niobrara sea transgressed northwestward about 500 mi (805 km) from southeastern Colorado to northwesternmost Wyoming in about 0.6 m.y. Ages of the basal Niobrara also decrease toward the northeast, from 89.3 Ma in southeastern Colorado to 87.6 Ma in northeasternmost Nebraska. The Niobrara sea in that region, where chronologic data are notably sparse, possibly transgressed more than 480 mi (772 km) in about 1.7 m.y.
ABSTRACT Late Albian strata in the southwestern Montana part of the Cretaceous Western Interior basin contain stratigraphic intervals and surfaces that are interpreted in a sequence stratigraphic framework. Eight measured sections, from the Lima Peaks-Tendoy Mountains area in the west to the southern Bridger Range in the east, record a transition from predominantly nonmarine facies in the west to predominantly marine facies in the east associated with the Creek sea. At the westernmost measured sections, in the Lima Peaks area, Tendoy Mountains, and the eastern Pioneer Mountains, the start of the Skull Creek transgression is marked by the onlap of coastal deposits over alluvial plain deposits. The onlap is marked by an abrupt change from nodular reddish-brown mudstones of the lower and middle units of the Flood Member of the Blackleaf Formation to overlying dark-gray, burrowed, estuarine mudstones of the upper unit of the Flood Member. Upper Flood Member coastalonlap deposits are truncated by a lowstand surface of erosion (LSE) recording the late Albian global sea-level drop. At the easternmost measured section at Rocky Creek in the Bridger Range, coastalonlap deposits of the lower sandstone member of the Thermopolis Shale are scoured by a transgressive surface of erosion (TSE) and overlain by marine beds of the shale member, a Creek equivalent. Highstand progradational strata at the top of the Thermopolis, represented by the Muddy Sandstone, are scoured by the late Albian LSE recorded to the west. Regional stratigraphic correlations are supported by invertebrate fauna and geochronometry. These dating methods indicate that the Flood Member in southwestern Montana includes strata that are time-equivalent to the combined Flood and Taft Hill Members in west-central Montana. Based on 40Ar/39Ar laser fusion geochronometry of lithicequivalent strata in northwest Wyoming and central Montana, the Thermopolis Shale-Muddy Sandstone interval ranges in age from about 105 to 100 Ma. The Muddy Sandstone near Rocky Creek in the Bridger Range contains invertebrate fauna characteristic of the Taft Hill Member of the Blackleaf Formation in west-central Montana near Great Falls. The uppermost part of the underlying Flood Member of the Blackleaf at Great Falls contains the late Albian guide fossil Inoceramus comancheanus, which occurs near the top of the shale member of the Thermopolis Shale in the Gravelly Range in our area of study. Furthermore, I. bellvuensis, the time-equivalent of I. commancheanus occurs throughout the shale unit of the Thermopolis in the Madison Range.
The Denver Basin is a Laramide foreland basin that filled with synorogenic sediment shed from the rising Rocky Mountains from the end of the Cretaceous through the Eocene. This sedimentary sequence contains a rich and diverse biota that is difficult to correlate because of the low relief and poor exposures characteristic of this region. This study has correlated the stratigraphic sequence and fossil localities using a combination of three techniques. Magnetostratigraphy has proven to be an effective way to date these rocks as they contain a measurable and interpretable reversal sequence that can be correlated to the latest Cretaceous through Tertiary geomagnetic polarity time scale (GPTS). The palynostratigraphy of the region is well known and the rocks contain multiple levels that yield palynomorphs. Volcanic ashes found in both the Cretaceous and Tertiary units can be dated using the 40Ar/39 Ar isotopic dating method. Each technique has its advantages and disadvantages, but in combination, these three chrono- and biostratigraphic methods have the potential to date with a high level of precision virtually every fossil locality sampled in the Denver Basin. To effectively date the exposures from across the entire basin, a reference or benchmark section had to be established against which the biostratigraphic zonation could be directly correlated to the chronology. Due to the paucity of long surface outcrops, drilled wells were the only way to obtain a continuous rock sequence from which a reference section could be constructed. Two cores, one drilled at Castle Pines on the western margin of the basin, and another at Kiowa in the central part of the basin, provided a continuous rock sequence from the top of the Maastrichtian Pierre Shale to the Eocene rocks of the D2 synorogenic sequence.
The magnetostratigraphic study of these cores established a reversal sequence that could be correlated to the GPTS ranging from polarity chron 31 through to chron 24. The palynostratigraphy yielded a zonation ranging from the Aquilapollenites striatus Interval Zone through to the early Eocene, and accurately placed the Cretaceous-Tertiary (K-T) boundary in each core. Isotopic ages were obtained from the Maastrichtian, early Paleocene, and early Eocene parts of the section, and allow us to independently confirm the calibration of the units to the time scale. With this chronostratigraphic framework in place, the individual fossil-bearing localities and surface sections from across the entire basin can be correlated and dated to a precision that is comparable to the calibrating isotopic ages.
The measured sedimentation rates vary across this asymmetric basin, with higher rates in the western, proximal part of the basin, and a pronounced increase in sedimentation rate across the K-T boundary. Two separate packages of strata, separated by a regional unconformity between the D1 and D2 synorogenic sequences, were dated. The Maastrichtian through Paleocene sequence that encompasses the Pierre Shale, Fox Hills Sandstone, Laramie Formation, and D1 strata dates from about 69 to 64 Ma. The overlying D2 synorogenic strata are poorly constrained and date from about 54 Ma. The reversal pattern of the D2 sequence varies across the basin, which indicates that sedimentary hiatuses, probably caused by tectonically quiet intervals along the mountain front, were followed by differential subsidence across the basin as sedimentation resumed at different times across the 100 km (60 mi) breadth of the basin.
