René W. Barendregt

The earliest record of human activity in northern Europe

The colonization of Eurasia by early humans is a key event after their spread out of Africa, but the nature, timing and ecological context of the earliest human occupation of northwest Europe is uncertain and has been the subject of intense debate. The southern Caucasus was occupied about 1.8 million years (Myr) ago, whereas human remains from Atapuerca-TD6, Spain (more than 780 kyr ago) and Ceprano, Italy (about 800 kyr ago) show that early Homo had dispersed to the Mediterranean hinterland before the Brunhes–Matuyama magnetic polarity reversal (780 kyr ago). Until now, the earliest uncontested artefacts from northern Europe were much younger, suggesting that humans were unable to colonize northern latitudes until about 500 kyr ago. Here we report flint artefacts from the Cromer Forest-bed Formation at Pakefield (52° N), Suffolk, UK, from an interglacial sequence yielding a diverse range of plant and animal fossils. Event and lithostratigraphy, palaeomagnetism, amino acid geochronology and biostratigraphy indicate that the artefacts date to the early part of the Brunhes Chron (about 700 kyr ago) and thus represent the earliest unequivocal evidence for human presence north of the Alps.

Recent investigations of the 0–5 Ma geomagnetic field recorded by lava flows

We present a synthesis of 0–5 Ma paleomagnetic directional data collected from 17 different locations under the collaborative Time Averaged geomagnetic Field Initiative (TAFI). When combined with regional compilations from the northwest United States, the southwest United States, Japan, New Zealand, Hawaii, Mexico, South Pacific, and the Indian Ocean, a data set of over 2000 sites with high quality, stable polarity, and declination and inclination measurements is obtained. This is a more than sevenfold increase over similar quality data in the existing Paleosecular Variation of Recent Lavas (PSVRL) data set, and has greatly improved spatial sampling. The new data set spans 78°S to 53°N, and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the time-averaged field (TAF) and paleosecular variation (PSV) for the Brunhes and Matuyama chrons, and for the 0–5 Ma interval combined. The Brunhes and Matuyama chrons exhibit different TAF geometries, notably smaller departures from a geocentric axial dipole field during the Brunhes, consistent with higher dipole strength observed from paleointensity data. Geographical variations in PSV are also different for the Brunhes and Matuyama. Given the high quality of our data set, polarity asymmetries in PSV and the TAF cannot be attributed to viscous overprints, but suggest different underlying field behavior, perhaps related to the influence of long-lived core-mantle boundary conditions on core flow. PSV, as measured by dispersion of virtual geomagnetic poles, shows less latitudinal variation than predicted by current statistical PSV models, or by previous data sets. In particular, the Brunhes data reported here are compatible with a wide range of models, from those that predict constant dispersion as a function of latitude to those that predict an increase in dispersion with latitude. Discriminating among such models could be helped by increased numbers of low-latitude data and new high northern latitude sites. Tests with other data sets, and with simulations, indicate that some of the latitudinal signature previously observed in VGP dispersion can be attributed to the inclusion of low-quality, insufficiently cleaned data with too few samples per site. Our Matuyama data show a stronger dependence of dispersion on latitude than the Brunhes data. The TAF is examined using the variation of inclination anomaly with latitude. Best fit two-parameter models have axial quadrupole contributions of 2–4% of the axial dipole term, and axial octupole contributions of 1–5%. Approximately 2% of the octupole signature is likely the result of bias incurred by averaging unit vectors.

Glacial stratigraphy and paleomagnetism of late Cenozoic deposits of the north-central United States

The north-central United States preserves one of the best continental records of late Pliocene and early-middle Pleistocene glaciations in the Northern Hemisphere. The glaciogenic sequences of this region consist of multiple tills interbedded with paleosols and volcanic ashes. Here we present results on paleomagnetic measurements and till compositional data from glacial sedimentary sequences in Iowa, Nebraska, Kansas, and Missouri. Periods of normal polarity (Brunhes Chron) and reverse polarity (Matuyama Chron) were identified in the sedimentary sequences investigated. This chronology is further constrained by the presence of three volcanic ashes derived from dated eruptions of the Yellowstone caldera, which indicate that the oldest till was deposited .2.0 Ma. Based on these results we identify three groups of tills representing at least seven pre‐Illinoian glaciations: two older groups of reverse-polarity tills containing low and intermediate proportions of crystalline clasts, respectively, and one younger group of normal-polarity tills enriched in crystalline lithologies. The clay mineralogy of the reverse-polarity tills is enriched in kaolinite and depleted in expandable clays relative to the normal-polarity tills, which are also characterized by a minor amount of chlorite. The silt fraction of tills also shows mineralogical contrasts whereby the normalpolarity tills are characterized by increases in calcite, dolomite, and feldspar, whereas the older tills show depletion in these minerals and a relative enrichment in quartz. These petrographic and mineralogic changes are indicative of an increase with time in the areal distribution of unweathered igneous and metamorphic source bedrock.

Chronology and extent of Late Cenozoic ice sheets in North America: A magnetostratigraphic assessment

Publisher Summary This chapter discusses the classic four-fold subdivision of the Pleistocene in both North America and Europe dominated terrestrial Quaternary palaeoclimate, which have been studied for many decades. With the exception of the last major continental glaciation, the understanding of the extent and timing of ice-sheet development in North America has remained uncertain. With the more widespread use of magnetostratigraphy and detailed mapping of superficial deposits, it has become possible to identify the approximate: spatial extent of ice sheets, as well as the timing of their appearance and disappearance. It reviews that with appropriate sampling and analytical techniques, geomagnetic polarity data can be obtained from tills, as well as from altered sediments such as palaeosols, to provide a direct assessment of the palaeomagnetism of glacial and interglacial environments. The chapter discusses the advances which have been made in dating and modeling of past terrestrial climatic events. It has been in particular, the contribution of magnetostratigraphy which has provided timelines for glacial and interglacial events of the last 3.0 million years, and assigned sediments to the Chrons and Subchrons of this period. In the absence of absolute dating tools, magnetostratigraphy affords a valuable means of assigning terrestrial ice age deposits to the geological timescale, and most importantly, allows a correlation to the more complete marine record. The distribution of past ice sheets and their chronologies will be better defined with future magneto-stratigraphical work.

Paleomagnetic and tephra evidence for tens of Missoula floods in southern Washington

Paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from Glacial Lake Missoula, Montana, entered Washington’s Yakima and Walla Walla Valleys during the last glaciation. In these valleys, the field evidence for hiatuses between floods is commonly subtle. However, paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at Zillah, Touchet, and Burlingame Canyon display consistent secular variation that correlates serially both within and between sections. The secular variation may further correlate with paleomagnetic data from Fish Lake, Oregon, and Mono Lake, California, for the interval 12,000‐17,000 14 C yr B.P. Deposits of two successive floods are separated by two tephras derived from Mount St. Helens, Washington. The tephras differ in age by decades, indicating that a period at least this long separated two successive floods. The beds produced by these two floods are similar to all of the 40 beds in the slack-water sediment sequence, suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years.

Ballast Brook and Beaufort Formations (late Tertiary) on Northern Banks Island, Arctic Canada☆

Excellent exposures of late Tertiary terrestrial sediments occur in the Ballast Brook region of northwestern Banks Island (Canadian Arctic Archipelago). These sediments contain abundant concentrations of organic detritus as well as autochthonous peats which can be traced for some kilometres. All of these deposits were previously assigned to the Beaufort Formation. In this paper, the deposits formerly grouped as the Beaufort Formation are subdivided into two formations: the newly named Ballast Brook Formation and the Beaufort Formation. The Ballast Brook Formation is characterized by alluvial sand, silt-clay and peat with compressed, altered wood. Paleobotanical evidence indicates an early to mid-Miocene age, with mid-Miocene being the most probable. This formation is believed to overlie the Eureka Sound Group and is in erosional contact with the overlying Beaufort Formation. Plant macrofossils from the Ballast Brook Formation include a number of taxa now found in northern hardwood and southern boreal forests, while the prominent peat which characterizes the formation contains a number of taxa that now grow or could be expected to grow in a cypress swamp type of environment. For example the conifer Glyptostrobus is well represented in the peat. The Beaufort Formation at Ballast Brook consists of alternating sands and gravels, and silt in the lower part. It is characterized by an abundance of unaltered wood and other plant materials. Paleobotanical evidence indicates an early Pliocene to early late Pliocene age (i.e. approx. 5-3 Ma). Like the Ballast Brook Formation, the Beaufort Formation contains an abundance of fossils of conifers, but in contrast with the Ballast Brook Formation nearly all of them belong to Pinaceae, a group well represented in the present boreal forest. The Beaufort Formation also contains insect fossils, which are very rare in the Ballast Brook Formation. Together, the insect and plant macrofossils suggest an environment similar to, but richer in species (some extinet; others now found only in Asia) than present boreal forest and taiga. The Ballast Brook Formation flora resembles the flora from Mary Sachs gravel (formerly Beaufort Formation) on southwestern Banks Island and the flora from the West River beds on the Northwest Territories mainland. It also is similar to a 40Ar39Ar dated mid-Miocene flora from east-central Alaska and to the Mamontova Gora (mid-Miocene) flora from Russia.

Timing and extent of plio-pleistocene glaciations in north-western canada and east-central alaska

Abstract North-western Canada and eastern Alaska are recognised as having one of the oldest known continental glacial records (Late Pliocene) preserved in stratigraphical sections. These include the individual and complex records of Cordilleran, montane and continental glaciations. Regional scale glaciations (Cordilleran and continental) started in northwestern Canada and east-central Alaska between 2.9 and 2.6 million years ago. Overall, two Cordilleran glaciations and two plateau ice caps (Horton Ice Cap) developed in Late Pliocene (Gauss and Matuyama Chron). During the Early Pleistocene, three Cordilleran glaciations occurred, while one to five continental glaciations (Keewatin Ice Sheet and Horton Ice Cap) are inferred from the Banks Island stratigraphic record (late Matuyama Chron). Three Middle-Pleistocene glaciations are recorded for the Cordilleran (including the Reid Glaciation) as well as three continental (Keewatin Ice Sheet and Horton Ice Cap) events (early Brunhes Chron). During the Late Pleistocene (late Brunhes) a well defined, extensive continental ice sheet (Keewatin) covered western and northwestern Canada, while in the Yukon Cordillera and Yukon-Tanana Uplands, two glaciations (Early-Late Pleistocene Eagle Glaciation, and Late Pleistocene McConnell Glaciation) are recognised. Successive Cordilleran glaciations diminished in size, while continental glaciations increased. The moisture source for the Cordilleran ice was largely the Pacific Ocean, however, for the Horton Ice Cap, an open Arctic Ocean may have been a significant moisture source. The role of tectonics in the development of the two major physiographic barriers, Wrangell/St. Elias Mountains and the Continental Divide (Mackenzie/Selwyn Mountains) appears to have been an important controlling variable in moisture distribution in northwest Canada and east-central Alaska. The timing and interplay of tectonic uplift versus erosion of these barriers has very much controlled the growth, thickness and decay of ice masses in the interior of Yukon and valleys east of the continental divide.

An extensive late Cenozoic terrestrial record of multiple glaciations preserved in the Tintina Trench of west-central Yukon: stratigraphy, paleomagnetism, paleosols, and pollenThis is a companion paper to Barendregt et al., also in this issue.Geological Survey of Canada Contribution 20100035.

The Tintina Trench in west-central Yukon is a late Miocene graben formed along the antecedent early Tertiary Tintina fault. Since its formation the trench has served as a sediment trap for alluvial and glacial deposits. An extensive record of preglacial, glacial, and interglacial sediments spanning the late Pliocene to late Pleistocene has been preserved and is exposed today in modern landslide scars. This sedimentary record comprises multiple sequences of tills, outwash, mudflows, loess, and paleosols. The glacial sediments are the product of both local (montane) and regional (Cordilleran) ice advances that channeled into the trench, while loess and well-developed paleosols (brunisols and luvisols) reflect nonglacial and interglacial conditions, respectively. The Tintina Trench exposures provide the most complete record of glaciations for the region. Paleomagnetism, paleosols, and palynology provide age constraints for the geological events. A formal stratigraphic nomenclature is proposed for this region...

Paleomagnetism of selected quaternary sediments on Mt Kenya, East Africa: a reconnaissance study

Abstract Samples of Quaternary sediments were collected from the Teleki and Hobley Valley sites on Mt Kenya to determine whether paleomagnetism might assist in placing them in the local time-stratigraphic record. In addition, we sought to determine if paleomagnetic characterization might allow detection of possible errors in radiocarbon dated buried A horizons. Results show that at least some glacial sediments of Mt Kenya were deposited during the Matuyama Polarity Epoch. Late glacial sediments contain a possible paleomagnetic excursion and yield radiocarbon dates ranging from approximately 21,000 to 25,000 yr B.P.

The Glacial History of the British Isles during the Early and Middle Pleistocene: Implications for the long-term development of the British Ice Sheet

Abstract We review the evidence for Quaternary glaciation in the British Isles and adjoining seas. Attention is given to the types of onshore and offshore evidence and the robustness of these evidence sources. We find evidence for onshore lowland glaciation during Marine Isotope Stages 16, 12, 10, 6 and 2.