Magnetic Polarity Stratigraphy of the Middle Pleistocene (Ensenadan) Tarija Formation of Southern Bolivia

1983 ◽  
Vol 19 (2) ◽  
pp. 172-187 ◽  
Author(s):  
Bruce J. MacFadden ◽  
Oscar Siles ◽  
Peter Zeitler ◽  
Noye M. Johnson ◽  
Kenneth E. Campbell
Keyword(s):  
Fission Track ◽  
Magnetic Polarity ◽  
Middle Pleistocene ◽  
Time Interval ◽  
Zircon Age ◽  
Matuyama Chron ◽  
Composite Section ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Land Mammal

AbstractThe Tarija Formation of southern Bolivia, which is well known for its classic vertebrate faunas, is of prime importance in understanding of the chronology of the Ensenadan Land Mammal Age. This formation consists of well-exposed and relatively fossiliferous sections of clays, clayey silts, sands, gravels, and tuffs which were deposited in a predominately fluviatile regime in a Pleistocene structural basin. Four stratigraphic sections, each measuring 110 m or less, were studied to establish a magnetic polarity stratigraphy. Paleomagnetic samples were collected from the finer-grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less. All paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds (oe). Some specimens were also thermally demagnetized at 200°C or more. Of the 100 sites, 77 were ultimately used to determine the magnetic polarity zonation. Based on the four sections sampled, the Tarija Formation spans a time interval from about 1 my to about 0.7 my B.P. or perhaps younger. The lower half of the composite section is of reversed polarity punctuated by a short normal event. This sequence probably represents the late Matuyama chron with the Jaramillo subchron. The upper part of the section is of normal polarity and represents early Brunhes time. A tuffaceous unit 43 m above the Brunhes-Matuyama boundary yielded a fission track (zircon) age of 0.7 ± 0.2 by B.P. These data indicate that the classic Tarija fauna is middle Pleistocene Ensendan in age.

New advances on the magnetic chronostratigraphy of cave sediments in Atapuerca Gran Dolina, Spain

2021 ◽  
Author(s):  
Josep M Pares ◽  
Mathieu Duval ◽  
Isidoro Campaña ◽  
José M. Bermúdez de Castro ◽  
Eudald Carbonell
Keyword(s):  
Magnetic Polarity ◽  
Age Dating ◽  
Middle Pleistocene ◽  
Geologic History ◽  
Cave Sediments ◽  
Normal Polarity ◽  
Gran Dolina ◽  
Geomagnetic Polarity ◽  
Quartz Grains ◽  
Numerical Dating

<p>Magnetostratigraphy has proven to be a powerful and versatile method as well the first line of defence for dating sediments. When properly anchored to the Geomagnetic Polarity Time Scale (GPTS), chron boundaries provide a basis for numerical dating by correlating the local magnetostratigraphy to the GPTS. A caveat and intrinsic limitation when anchoring magnetic stratigraphy to the GPTS is that we deal with essentially a binary code, a sequence of normal and reverse polarity zones. To overcome such limitation biostratigraphy or (ideally) numerical (absolute) age dating is required. Unfortunately, numerical dating of sediments is typically hampered by the lack of amenable minerals for the application of standard methods such as Ar-Ar, requiring thus the use of less conventional methods. Burial dating is possible using methods such as Electron Spin Resonance (ESR) on optically bleached quartz grains. Similar to luminescence, ESR is a paleodosimetric method that provides the time elapsed since the last exposure of quartz grains to natural sun light. Cave sediments are particularly amenable for paleodosimetric methods, as sediments are preserved in the dark and the ESR signal should survive over the geologic history of the deposits. On the down side, we date the moment when the quartz grain enters the karst system, not its deposition. If the transit time is too long, this might be an issue and we would be significantly overestimating the true burial age. Caves at Atapuerca (N Spain) hold the richest Quaternary paleontological record in Eurasia, including fossils and lithic tools. Sediments in these caves have been traditionally dated via magnetostratigraphy by identifying the Matuyama-Brunhes reversal (0.78 Ma) thus providing the Lower to Middle Pleistocene boundary. Nevertheless, the appearance of older sediments in the caves required the combination of paleomagnetism with methods such as ESR to interpret older intra-Matuyama Subchrons. In the deepest levels of the Gran Dolina cave, close to the floor of the cavity, a number of short intervals of normal polarity have been identified in the fluviatile sediments belonging to TD1 unit, which we interpret in terms of Subchrons using ESR ages of quartz grains. We will discuss both paleomagnetic data and interpret the magnetic polarity stratigraphy in the view of the ESR ages obtained from the Multiple Centre (MC) approach. </p>

New 42 Ma cratonic North American paleomagnetic pole from the Yukon underscores another Cordilleran paleomagnetism-geology conundrum

2003 ◽  
Vol 40 (10) ◽  
pp. 1321-1334 ◽  
Author(s):  
David TA Symons ◽  
Philippe Erdmer ◽  
Phil JA McCausland
Keyword(s):  
North American ◽  
Magnetic Polarity ◽  
Eastern Coast ◽  
The North ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
North American Craton ◽  
Host Rocks ◽  
Pacific Plate Subduction ◽  
Plate Subduction

Eocene posttectonic plutons of the Beaver River alkalic complex in southeastern Yukon intruded Devonian–Mississippian and Triassic sandstones in the Foothills of the Canadian Cordillera. A paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods. The A component characteristic remanent magnetization (ChRM) resides in magnetite with normal polarity in the 42.6 ± 0.8 Ma Beaver River pluton, reversed polarity in the 42.1 ± 0.7 Ma Larson Creek East pluton, and both polarities in the 41.3 ± 0.4 Ma Larson Creek West pluton, corresponding with magnetic polarity chrons 20n, 19r, and the boundary between chron 19r and 18n, respectively. The ChRMs of the plutons are indistinguishable (2σ) with a mean for the 42.0 ± 0.5 Ma complex of D = 158.8°, I = –73.1° (N = 21 sites, α95 = 3.0°, k = 116.8). A positive paleomagnetic contact test shows the A component to be primary, and the poorly isolated B component suggests the host rocks for Larson Creek West are Early to Middle Devonian. The paleopole for the Beaver River complex at 79.2°N, 145.8°E (N = 21, dp = 4.8°, dm = 5.4°; Q = 7) is concordant with interpolated 42 Ma reference poles for the North American craton. In contrast, paleopoles from the accreted Intermontane and eastern Coast Belt terranes record clockwise rotations of 24° ± 10° (Eocene) and 13° ± 5° (Oligocene–Pliocene), indicating that the allochthonous Intermontane terranes have been progressively driven ~240 ± 120 km eastwards up and over pericratonic and cratonic North American lower crust by Pacific plate subduction since the mid-Eocene.

Stratigraphy and paleomagnetism of Late Pliocene and Pleistocene sediments in the Wellsch Valley and Swift Current Creek areas, southwestern Saskatchewan, Canada

1998 ◽  
Vol 35 (12) ◽  
pp. 1347-1361 ◽  
Author(s):  
R W Barendregt ◽  
E Irving ◽  
E A Christiansen ◽  
E K Sauer ◽  
B T Schreiner
Keyword(s):  
Late Pleistocene ◽  
Magnetic Polarity ◽  
Early Pleistocene ◽  
Western Canada ◽  
Marked Contrast ◽  
Glacial Deposits ◽  
Late Pliocene ◽  
Matuyama Chron ◽  
Reversed Polarity

The Late Pliocene and Pleistocene are represented in southern Saskatchewan by sequences of preglacial, glacial, and nonglacial deposits. These have been studied in surface exposures and bore cores and have been subdivided and correlated on the basis of their lithologies. In this study, new observations of magnetic polarity are presented. They reveal a lower preglacial sequence (Empress Group) with reversed polarity, and an upper normally magnetized sequence which contains glacial deposits of pre-Illinoian, Illinoian, and Wisconsinan age and which are correlative with the Saskatoon and Sutherland groups of central Saskatchewan. The reversed preglacial sequence is referred to the Matuyama Zone (Late Pliocene to Early Pleistocene: 2.58-0.78 Ma) and the normal glacial sequence to the Brunhes Zone (Middle to Late Pleistocene and Holocene: 0.78 Ma to present). In southern Saskatchewan there is no evidence of glaciation during the Late Pliocene and Early Pleistocene (Matuyama Chron) which is in marked contrast with parts of the Cordilleran region of western Canada where glaciations occur throughout this time.

40Ar/39Ar dating and magnetostratigraphic correlation of the terrestrial Cretaceous–Paleogene boundary and Puercan Mammal Age, Hell Creek – Tullock formations, eastern Montana

1993 ◽  
Vol 30 (9) ◽  
pp. 1981-1996 ◽  
Author(s):  
Carl C. Swisher III ◽  
Lowell Dingus ◽  
Robert F. Butler
Keyword(s):  
Single Crystals ◽  
High Concentration ◽  
Coal Beds ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Garfield County ◽  
Fossil Vertebrate ◽  
Geomagnetic Polarity ◽  
Land Mammal ◽  
Channel Deposits

The recovery and subsequent prolific radiation of mammals in the northern Western Interior of North America following the Cretaceous–Paleogene (K–P) boundary is well documented in rocks attributed to the Puercan Land Mammal Age. The most complete Puercan record is that of the Tullock Formation, which crops out widely in Garfield and McCone counties, eastern Montana. The Tullock Formation overlies the dinosaur-bearing Hell Creek Formation and consists of a stratigraphic series of channel and overbank deposits from which well-preserved Puercan faunas have been collected. These channel deposits are typically bracketed by widespread coal beds. The IrZ- and Z-coals mark the base of the Puercan at the K–P boundary as defined by the highest appearing local occurrences of in situ dinosaur fossils, the highest stratigraphic occurrence of Cretaceous pollen, and an anomalously high concentration of the element iridium (Ir). The IrZ-Coal is overlain sequentially by the Z-, HFZ-, Y-, W-, and U-coals.Fossil vertebrates of earliest Puercan age (Pu0 or Pu1) occur in sandstones of the Hells Hollow Channel between the IrZ-and HFZ-coals in Garfield County and below the Z-Coal in sandstones of the Bug Creek Channels, McCone County. Late Puercan (Pu2/3) fossil vertebrates are abundant between the Y- and W-coals in sandstones of the Garbani Channel in Garfield County, and in sandstones of the Purgatory Hill quarry in McCone County. Earliest Torrejonian (To1?) fossil vertebrates of the Mosquito Gulch localities, Garfield County, occur in sandstones of the Farrand Channel between the W- and U-coals.Magnetostratigraphies developed on sections at Billy Creek, Hauso Flats, Biscuit Butte, Bug Creek, and Purgatory Hill indicate that the IrZ- and Z-coals, the fossil vertebrate-bearing sandstones of the Hells Hollow and Bug Creek channels, and rocks up to midway between the HFZ- and Y-coals are contained in a zone of reversed polarity, correlated here with chron C29r. The Y through W coals, as well as the fossil vertebrate-bearing sandstones of the Garbani Channel and Purgatory Hill, are contained in an overlying zone of normal polarity, correlated with chron C29n. Rocks immediately above the W-Coal through the U-Coal, which include the Farrand Channel, are in a zone of reversed polarity, correlated here with chron C28r. The top of the section, just above the U-Coal, is in the uppermost zone of normal polarity, tentatively correlated here with the base of chron C28n.40Ar/39Ar dating of single crystals of sanidine separated from bentonites in the IrZ-, Z-, HFZ-, W-, and U-coals has yielded high-precision ages with standard errors of 0.1%. Replicate analyses of single crystals of sanidine yield weighted mean ages for bentonites in the following coals: IrZ, 65.16 ± 0.04 Ma; Z, 65.01 ± 0.03 Ma; HFZ, 64.77 ± 0.06 Ma; W, 64.11 ± 0.02 Ma; and U, 63.90 ± 0.04 Ma. These ages provide detailed calibration of Puercan through earliest Torrejonian (PuO, Pu1, Pu2, Pu3, and ?To1) land mammal ages and provide crucial calibration for the nonmarine K–P boundary and the Early Paleogene portion of the geomagnetic polarity time scale.

Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada

2021 ◽  
Author(s):  
John Arthur Westgate ◽  
Nancy D Naeser ◽  
Rene W. Barendregt ◽  
N. J.G. Pearce
Keyword(s):  
Trace Element ◽  
Pacific Northwest ◽  
Magnetic Polarity ◽  
Middle Pleistocene ◽  
Southern Plains ◽  
Matuyama Chron ◽  
Chemical Attributes ◽  
Brunhes Chron ◽  
Fossil Vertebrate ◽  
Tephra Beds

Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes – necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe-Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 ± 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 ± 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.

Recurring middle Pleistocene outburst floods in east-central Alaska

2003 ◽  
Vol 60 (1) ◽  
pp. 50-62 ◽  
Author(s):  
Duane G. Froese ◽  
Derald G. Smith ◽  
John A. Westgate ◽  
Thomas A. Ager ◽  
Shari J. Preece ◽  
...  
Keyword(s):  
Fission Track ◽  
Magnetic Polarity ◽  
Middle Pleistocene ◽  
Pleistocene Glaciation ◽  
Flood Events ◽  
East Central ◽  
Yukon River ◽  
Outburst Floods ◽  
Minimum Age ◽  
Age Constraints

AbstractRecurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ± 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area.

Paleomagnetic evidence for multiple late Cenozoic glaciations in the Tintina Trench, west-central Yukon, CanadaThis article is a companion paper to Duk-Rodkin et al., also in this issue.

2010 ◽  
Vol 47 (7) ◽  
pp. 987-1002 ◽  
Author(s):  
René W. Barendregt ◽  
Randolph J. Enkin ◽  
Alejandra Duk-Rodkin ◽  
Judith Baker
Keyword(s):  
Companion Paper ◽  
Opposite Polarity ◽  
Middle Pleistocene ◽  
Late Cenozoic ◽  
West Central ◽  
Matuyama Chron ◽  
Continental Divide ◽  
Normal Polarity ◽  
Brunhes Chron ◽  
Trench Area

The Tintina Trench in west-central Yukon has preserved an extensive record of late Cenozoic preglacial, glacial, and interglacial deposits. These deposits comprise multiple sequences of tills, outwash, loesses, and paleosols. The sediments that were laid down directly by ice (tills) are of both local (montane) and regional (Cordilleran) provenance. The Tintina Trench area was impacted repeatedly by montane ice from the southern Ogilvie Mountains to the northwest (2500 m above sea level (asl)), and also repeatedly along its southern extent by Cordilleran ice from the Selwyn Mountains to the east (2759 m asl), the latter forming the continental divide in this region. We report here the magnetostratigraphy of three sections: Rock Creek (64°13′N, 139°07′W), West Fifteenmile River (64°29′N, 139°55′W), and East Fifteenmile River (64°23′N, 139°48′W). The majority of the units identified at these sections record late Pliocene to mid-Pleistocene glaciations, although relatively thin surficial sequences of late middle Pleistocene to late Pleistocene loesses and tills are present as well. Of the 11 units described in the Tintina Trench, seven have normal polarity, three have reversed polarity, and one has an undefined polarity. These units span about 3.0 million years. It appears that most of the polarity chrons and subchrons of the late Cenozoic are present and that the sequence of six reversals record at least 10 glaciations (three in the Brunhes Chron and seven in the Matuyama Chron), and 11 interglaciations (four in the Brunhes Chron and seven in the Matuyama Chron). The interglacials are recorded as either paleosols or unconformities between glacial or loess units having opposite polarity. While not all Matuyama Chron glacial and interglacial cycles recorded in marine isotopic records are seen on land, the terrestrial records found in the Tintina Trench have thus far proven to be the most complete in terms of the polarity record. While no absolute ages were obtained from the sediments in the trench, the extensive polarity sequence constrains the timing of glaciations to a considerably greater degree than was previously possible for this region. The magnetostratigraphy of the trench sites are compared with the glacial, glaciofluvial, and loessic deposits at the nearby Klondike River valley and Fort Selkirk sites, central Yukon, where tephras and basalts provide absolute ages, and stratigraphic units contain an extensive late Cenozoic climate proxy for northwestern North America (eastern Beringia). In this study, we present new paleomagnetic polarity data and establish a magneto-lithostratigraphy describing preglacial, glacial, and interglacial deposits in the Tintina Trench. These deposits are referred to as the West Tintina Trench Allogroup and provide a broad framework for establishing a paleoclimate record for the northern Canadian Cordillera.

Magnetic Polarity Stratigraphy of the Pleistocene Section at Portland (Victoria), Australia

1987 ◽  
Vol 28 (3) ◽  
pp. 364-373 ◽  
Author(s):  
Bruce J. MacFadden ◽  
Michael J. Whitelaw ◽  
Phil McFadden ◽  
Thomas H. V. Rich
Keyword(s):  
Magnetic Polarity ◽  
Beach Sand ◽  
Mammalian Fauna ◽  
Local Fauna ◽  
Depositional History ◽  
Matuyama Chron ◽  
History Of ◽  
Globorotalia Truncatulinoides ◽  
Absolute Dating ◽  
Reversed Polarity

AbstractThree to seven oriented paleomagnetic samples were collected from 16 sites in the Nelson Bay and Bridgewater formations at Portland, Victoria, which contains the recently discovered Nelson Bay local fauna (L.F.). The entire section has reversed polarity. These results, along with Globorotalia truncatulinoides within the section, and the presence of underlying middle Pliocene-dated basalts, indicate that the Portland section, and the included Nelson Bay L.F., was deposited within the late Matuyama Chron between 1.66 and 0.73 myr ago. This represents the first well-documented pre-14C Pleistocene mammalian fauna in Australia calibrated in direct stratigraphic context with absolute dating methods. In addition, the reversed polarity for the Bridgewater Formation confirms the previous hypothesis that the depositional history of this beach-sand deposit is time-transgressive across the Brunhes-Matuyama boundary.

A Middle pleistocene (isotope stage 10) glacial sequence in the Stikine River valley, British Columbia

1996 ◽  
Vol 33 (10) ◽  
pp. 1428-1438 ◽  
Author(s):  
Ian S. Spooner ◽  
Gerald D. Osborn ◽  
H. Barendregt ◽  
E. Irving
Keyword(s):  
British Columbia ◽  
Magnetic Polarity ◽  
River Valley ◽  
Middle Pleistocene ◽  
Glacial Period ◽  
Basalt Flow ◽  
Coast Mountains ◽  
Normal Polarity ◽  
Ice Retreat ◽  
Glacial Advance

In the Stikine River valley, northwestern British Columbia, glacial and nonglacial sediments are preserved beneath Middle Pleistocene basalt-flow remnants that originated from Mount Edziza. The magnetic polarity is consistently normal, indicating that the sediment and the basalts were probably deposited within the Bruhnes normal polarity chron (<780 ka). The sediments record a regional glacial advance. Initial ice advance in the Coast Mountains blocked the westward drainage of the Stikine River and formed an advance-phase glacial lake. Sediments deposited in this lake form a coarsening-upwards sequence; debris-flow diamicton units that originated from the valley sides are common. The lacustrine sequence culminates in a poorly sorted ice-marginal gravel deposited as ice encroached upon the study area. There is little record of ice retreat. The basalts are deposited on fluvial and (or) glaciofluvial gravels, indicating that postglacial reincision was taking place at the time of eruption. Hence, the sediments were deposited in the glacial period immediately prior to the emplacement of the basalt. Evidence is presented that indicates that glacial conditions occurred between 341 and 352 ka, which corresponds to pre-Illinoian isotope stage 10.

Stratigraphy and paleomagnetism of the Jaw Face section, Wellsch Valley site, Saskatchewan

1991 ◽  
Vol 28 (9) ◽  
pp. 1353-1364 ◽  
Author(s):  
R. W. Barendregt ◽  
F. F. Thomas ◽  
E. Irving ◽  
J. Baker ◽  
A. Macs. Stalker ◽  
...  
Keyword(s):  
Fission Track ◽  
Basal Part ◽  
Mammalian Faunas ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Valley Site

The basal part of Jaw Face section at the Wellsch Valley site, some 50 km north-northwest of Swift Current, Saskatchewan, contains mammalian fossils that are considered to be late Blancan to early Irvingtonian in age. It has been sampled for paleomagnetic studies through a thickness of 11 m. The section above 8.8 m has normal polarity; that below has reversed polarity. A tephra, which has yielded a minimum fission-track age of 0.69 ± 0.11 Ma, lies within the reversely magnetized part, near the top of the fossiliferous zone and just below the reversal at the 8.8 m level. Therefore, the change from normal to reversed polarity at the 8.8 m level is probably the Brunhes–Matuyama reversal at 0.73 Ma. Earlier studies have indicated that the Jaramillo (0.9–0.97 Ma) and Olduvai (1.67–1.87 Ma) Normal Polarity subzones occur within the lower predominantly reversed part of the Jaw Face section. In this more detailed study, we find no evidence of these normal subzones. We suggest that earlier results could have been artifacts of the procedures used. Several stratigraphic interpretations are possible. Our preferred interpretation is that the Jaw Face section extends from the upper part of the Matuyama Zone into the lower Brunhes Zone, that is, the mammalian faunas are entirely Irvingtonian in age. Alternatively, the section could contain a substantial hiatus, so the lower part would be early Matuyama in age and its faunas late Blancan – early Irvingtonisn, and the upper part could span the latest Matuyama and lower Brunhes zones. Other possibilities are discussed in the text.

Sign in / Sign up

Export Citation Format

Share Document