Professor Philip L. Gibbard Retirement Symposium
Monday 10th September 2018 at the Scott Polar Research Institute, University of Cambridge
Organisers: Della Murton and Sebastian Gibson
Click thumbnail to enlarge programme.
Possible role for the European Ice Sheet in lengthening glacial cycles during the latest Pleistocene
University of Cambridge, UK
The Middle Pleistocene Transition (MPT) represents one of the important unsolved problems in paleoclimatology. It marked a shift in the spectral character of the glacial-interglacial climate signal from dominantly 41-kyr power to the emergence of a quasi-periodic 100-kyr cycle. Some authors have suggested that the quasi-periodic 100-kyr cycle consists of multiples of precession and/or obliquity beats. The key to understanding the MPT may be identifying how the climate system, once in a glacial state, manages to avoid deglaciation during mid-glacial rises in boreal summer insolation. During glacial periods beginning with MIS 12, extremely cold stadial events are recorded on the Iberian Margin in the middle of glacial stages. These events were associated with meltwater discharges from the European and British-Irish ice sheets into the NE Atlantic, which were transported southwards by the Portugal Current. Fresh water delivered to the North Atlantic led to disruptions of the Atlantic Meridional Overturning Circulation (AMOC) as recorded by decreases in benthic d13C. Cooling associated with reduced AMOC would have offset the warming trends expected from increased summer insolation, thereby permitting North American Ice Sheets to survive mid-glacial insolation maxima and continue growing. The melting of the European ice sheet during the middle of Marine Isotope Stages (MIS) may have contributed to the climate system "skipping beats", thereby lengthening the glacial cycle across the MPT.
From Duxford to the Iberian margin : New insights in Quaternary climates
Maria Fernanda Sánchez Goñi
Ecole Pratique des Hautes Etudes (EPHE, PSL University), France
Major and still-unresolved questions remain in Quaternary climates. This presentation will focus on three of them: a) the regional response of the different glacial-interglacial cycles; b) the internal feedbacks explaining the strong 100,000-year ice age cycles at the end of the Middle Pleistocene transition (~700 ka) and, c) the interactions between millennial and orbital climate variability as the potential missing piece in the puzzle of Ice Age cycles. To tackle these questions I will present new results from the 1.4 Ma long sedimentary sequence, IODP site U1385, retrieved in the southern Iberian margin during the "Mediterranean Outflow" Expedition 339. The analysis from the same sample set of a wide array of terrestrial (pollen and microcharcoal), marine (planktic foraminifera and dinocyst assemblages, oxygen and carbon isotopic ratios -δ18O, δ13C-, alkenones) and ice (benthic foraminifera δ18O, ice rafted debris-IRD) climatic indicators reveals the spatially and temporally complex and somehow counterintuitive relationships between the North Atlantic atmospheric and oceanic realms underlying the dynamics of the ice sheets.
A catastrophic beginning to Britain's island history
Sanjeev Gupta and Jenny Collier
Imperial College London, UK
How did Britain become an island? Phil Gibbard's work on this problem has been central to changing our perspectives on this issue. Encountering Phil's paper in the "Island Britain: a Quaternary Perspective' volume at a time when we were commencing geophysical surveys in the Channel led us to realise that new marine geophysical technologies could reveal the submarine landscape to tackle this problem afresh. In this talk I will show how new bathymetry and high-resolution seismic data enabled characterization of large valleys, giant scours and other landforms on the Channel floor that are characteristic of erosion by high-energy megafloods. These data provide key new evidence to support the model of spillover of a large proglacial lake in the present-day southern North Sea basin espoused by Phil and others to explain the breaching of the Dover Strait. Moreover, these data provide new constraints on the physical processes operating during this event/s which had such significant palaeogeographic, biological and archaeological implications.
Long continental pollen records in arid lands: Lake Van in SE Anatolia and Dead Sea in the southern Levan
University of Bonn, Germany
Long continental pollen records have fundamentally contributed to our understanding of millennial-scale paleoclimate variability on land in comparison to marine and ice-core records. In contrast to north-central Europe where glaciations have produced stratigraphic unconformities, complete records of terrestrial events over multiple glacial-interglacial cycles are documented in southern Europe in which a broad correspondence to the deep-sea oxygen isotope record has been noted.
However, our knowledge about the vegetation and climate development during the past glacial-interglacial cycles in the Near East based on continental sedimentary sequences was rather poor. The sedimentary record of Lake Van in eastern Anatolia (SE Turkey), partly laminated, obtains a long and continuous continental sequence that covers multiple interglacial-glacial cycles. A deep drilling operation was carried out in 2010 supported by the International Continental Scientific Drilling Program (ICDP). The 219 m long continental pollen record is based on a well-dated composite profile drilled in water depth of 360 m encompassing the last 600,000 years. It is the longest continuous continental pollen record of the Quaternary in the entire Near East and central Asia obtained to date. The glacial-interglacial cycles and pronounced interstadials are clearly reflected in the vegetation development. Based on an even higher resolution, the multi-proxy record shows additional rapid expansions and contractions of tree populations that reflect variability in temperature and moisture availability. These rapid vegetation and environmental changes can be correlated to the stadial-interstadial pattern of Dansgaard–Oeschger events as recorded in the Greenland ice cores.
The paleoclimate of the southern Levant, especially during the last interglacial, is still under debate. Reliable paleovegetation information for this period, as independent evidence to the paleoenvironment, was still missing. In 2010-2011, the Dead Sea Deep Drilling Project (as a complementary ICDP project to Lake Van) retrieved sediment cores encompassing 455 m and dated back to ca. 220 ka. The sediment profile is marked by alternations of laminated marl deposits and massive halite, indicating lake-level fluctuations. Palynological results contradict previous Dead Sea lake-level investigations that suggested pluvial glacials and warm, dry interglacials in the southern Levant. Prominent discrepancies between vegetation and Dead Sea lake stands are registered in particular during the last interglacial optimum. While the pollen spectra mirror increased effective moisture especially, the massive halite deposition is indicative of an extremely low lake level. The potential causes are discussed. The southern Levant is a hotspot for investigating the dispersal of anatomically modern humans to the rest of the world, since their emergence in Africa. Given that climate amelioration triggered the migration of early modern humans to the southern Levant, we speculate that the diverse ecosystems in the region provided great potential for their residence.
A simple rule to determine which insolation cycles lead to interglacials
University College London, UK
The pacing of glacial–interglacial cycles during the Quaternary period is attributed to astronomically driven changes in high-latitude insolation. However, it has not been clear how astronomical forcing translates into the observed sequence of interglacials. Here we show that before one million years ago interglacials occurred when the energy related to summer insolation exceeded a simple threshold, about every 41,000 years. Over the past one million years, fewer of these insolation peaks resulted in deglaciation (that is, more insolation peaks were 'skipped'), implying that the energy threshold for deglaciation had risen, and leading to longer glacials. However, as a glacial lengthened, the energy needed for deglaciation decreased. A statistical model that combines these observations correctly predicts every complete deglaciation of the past million years and shows that the sequence of interglacials that has occurred is one of a small set of possibilities. The model accounts for the dominance of obliquity-paced glacial–interglacial cycles early in the Quaternary and for the change in their frequency about one million years ago.
Quaternary stratigraphy of Finland – an overview and recent developments
Juha Pekka Lunkka
University of Oulu, Finland
Abstract to be confirmed.
Alpine glaciofluvial geomorphology and numerical dating – a case for a new provisional terminology?*
University of Natural Resources and Life Sciences, Austria
In Alpine glaciofluvial terrace stratigraphy classical names have been introduced by Penck & Brückner (1909): Lower Terrace (LT), Higher Terrace (HT), Younger Cover Gravel (YCG) and Older Cover Gravel (OCG). Correlations around the Alps have been attempted suggesting the formation of the LT during the Würmian glaciation, the HT during the Rissian, the YCG during the Mindelian and the OCG during the Günzian.
However, progress in numerical dating techniques may challenge these morphostratigraphic correlations. Rades et al. (2018) recently applied up-to-date luminescence dating techniques to samples from the Rissian type section (HT in the outcrop Scholterhaus, Biberach an der Riss, Southern Germany) and the YCG in the Mindel valley (gravel pit Gärtner). They used a single aliquot regenerative (SAR) dose protocol for the dating of single grains of potassium-rich feldspar. To rule out significant effects of fading and avoid a necessary fading correction, post Infrared Infrared stimulated signals at a temperature of 225°C (pIRIR225) were used for the final age calculation. Using this methodological approach, Rades et al. (2018) established a robust chronology for the Rissian type section, which correlates well with Marine Isotope Stage 6 (MIS 6). The single sample from the second site under investigation, however, also showed an MIS 6 age. This implies that different geomorphological units determined from the terrace stratigraphy may reveal ages in agreement within error when investigated with up-to-date numerical dating techniques.
This poses a challenge to established stratigraphical approaches. How could we proceed in such cases? We suggest using a provisional nomenclature until a new reliable stratigraphy has been established. For the suggested provisional nomenclature, a combination of three elements should be used: first the geological / morphostratigraphical attribute: e.g. LT, HT etc., second the exact numerical dating method applied: like in the aforementioned case pIRIR225 single grain (SG) feldspar (Fs) optically luminescence (OSL) dating", and finally the corresponding MIS of the numerical ages.
For the Rissian type section this would mean: HT / pIRIR225 SG Fs OSL / MIS 6. For the Mindel valley Cover Gravel: YCG / pIRIR225 SG Fs OSL / MIS 6. Results from other dating methods like cosmogenic isotopes, radiocarbon etc. must also be included in such a provisional nomenclature.
Indicator clasts and till stratigraphy
In the Nordic glaciations the transport of debris is usually restricted to the lowest parts of the ice. The debris may go through repeated cycles of deposition and reworking resulting in a mixture of all rock types, which were overridden by the ice on his way to the deposition zone. Thus far-travelled components are increasingly diluted in this way, and local material enriched. The boulder contents of a certain till has, despite all the mixing usually a specific composition which with some variations is characteristic of this till. Under favorable conditions, correlations over long distances are possible. However, changes in clast composition perpendicular to the ice movement direction have to be taken into account. Also, the specific composition is only valid for a particular lithofacies, not for all till deposits of a certain time period, such as the 'Drenthe' - or 'Warthe' phase. It can therefore only be used for chronostratigraphic interpretations when supported by further information. The glacigenic deposits represent a succession of different facies types, the differences in composition of which are due to changes in glacier dynamics and changes in the ice movement direction.
Glacial history of the High Atlas, Morocco
The University of Manchester, UK
Glaciation has affected many Mediterranean mountains on multiple occasions through the Quaternary. In the Pleistocene, glaciers were extensive and the altitudinal pattern of glaciation closely matches the modern distribution of precipitation, with some of the lowest glaciers forming in the western Balkans and northwestern Iberia. Conversely, the highest glaciers formed in areas that are currently the hottest and driest of the Mediterranean, such as in Morocco and central Turkey. In the western Balkans, ice caps covered large areas of Croatia, Montenegro and Albania. Further south in Greece, ice caps, plateau ice fields and valley glaciers were widespread throughout the Pindus Mountains. The largest glaciers of the Balkans formed during the Middle Pleistocene, although substantial cirque and valley glaciers were also present during the Late Pleistocene. In the western Mediterranean, ice caps and plateau ice fields formed over many of the mountains of Iberia and even in Morocco. Understanding the extent and timings of glaciations in this region is important for understanding landscape evolution and the effects of global climate change on the Mediterranean region. In recent years the timing of glaciations during the late Pleistocene has been revolutionised using cosmogenic exposure dating, revealing asynchronous glacier behaviour across the Mediterranean through the last cold stage. There is also evidence that small glaciers survived into the Holocene. Today, only a few small niche glaciers survive. These modern glaciers are much smaller than 150 years ago at the end of the Little Ice Age when Mediterranean glaciers were much more common.
Formal subdivision of the Quaternary System: challenges and opportunities.
Martin J. Head
Brock University, Canada
Following a prolonged and acrimonious struggle spanning two executive committees of the International Commission on Stratigraphy (ICS), the Quaternary was finally defined officially in 2009. The global boundary stratotype section and point (GSSP) for the Gelasian Stage was chosen for its base. The Vrica GSSP, which had earlier defined the base of the Pleistocene Series, was repurposed in 2011 to define the Calabrian Stage, effectively completing the Lower Pleistocene Subseries. The Holocene Series was formally defined in 2008 using, for the first time, an ice core rather than a rock outcrop for the GSSP. But a subsequent proposal to define Lower, Middle and Upper Holocene subseries hit an obstacle: the rank of subseries had not been sanctioned by the International Union of Geological Sciences (IUGS). The proposal was therefore tabled by ICS in 2016, pending resolution of the subseries issue. Meanwhile, discussions between the three Cenozoic subcommissions of ICS failed to agree on the formalization of subseries, and the matter was left for a new ICS executive in 2016. A proposal to accept subseries as an official rank was passed by the ICS Subcommission on Stratigraphic Classification in 2017, and the ICS voting membership later that year approved the proposal. Technical difficulties unfortunately held up this proposal at the IUGS, but the Holocene subseries proposal was resurrected and resubmitted to the ICS where it was decisively approved. At the time of writing, the prospect of ratification by IUGS is promising. The base of the Middle and Upper Holocene, at 8326 and 4250 yr b2k, will then be defined by GSSPs in an ice core and a speleothem, respectively, the latter likely being placed on display at the Smithsonian Institution in Washington DC. This will be the first time a GSSP has been displayed in a public museum.
Phil Gibbard and the Stratigraphy Commission
University of Portsmouth, UK
Abstract to be confirmed
Quaternary data without frontiers: the International Quaternary Map of Europe 1: 2,5 Million
Abstract to be confirmed
Northern Hemisphere ice-sheet extent for the last 2.6 Ma and implications for global sea levels.
University of Cambridge, UK
Abstract to be confirmed
The Rhine terraces
Leibniz Institute for Applied Geophysics, Germany
Abstract to be confirmed
15.40-16.10 Afternoon Tea
Shifting Sediment Sources in the World's Longest River
The University of Manchester, UK
This talk presents some recent research on the Holocene Nile. It shows how the integration of archaeological, geomorphological and geochronological datasets has shed new light on the behaviour of one of the world's great rivers. Despite its vast scale and the diversity of its headwater landscapes, the desert Nile is a senstive system that responded rapidly to climate change during the Holocene. Data from strontium and neodymium isotopes show how dramatic shifts in river sediment sources accompanied transitions from humid to arid in the now desert Nile. These shifts have taken place throughout the Quaternary. During more humid intervals, when the monsoon expanded its range, thousands of wadis became active - from Khartoum to Cairo - and were a major supplier of sediment to the Nile and the Mediterranean.
Periglaciation and landscape evolution of southern England
University of Sussex, UK
Beyond the maximum limit of glaciation, periglacial processes repeatedly shaped the landscape of southern England during Quaternary cold stages. Ground thermal conditions varied between cold (continuous) permafrost, warm (discontinuous) permafrost and seasonally frozen ground. Land surface conditions ranged from dry polar-desert-like environments characterized by extensive deposition of aeolian silt and sand to moist tundra-like environments marked by widespread head (solifluction), slopewash and fluvio-colluvial deposits. Such environmental variation partly reflects England's exposure to airmasses tracking eastwards across the North Atlantic Ocean, which was subject to major and rapid changes in sea-ice conditions during the Pleistocene.
The key periglacial processes in frost-susceptible ground were ice segregation, frost heave and thaw consolidation. Ice segregation fractured porous bedrock and sediment, and produced an ice-rich brecciated layer in the upper metres of permafrost. This layer was vulnerable to melting and thaw consolidation, which released debris into the active layer and, in undrained conditions, resulted in elevated porewater pressures and sediment deformation. Thus, an important difference arose between ground that was frost-susceptible (prone to ice segregation) and ground that was not. Frost-susceptible ground included porous fine-grained bedrock lithologies and sediments (e.g. stiff clay, mudrock, slate, shale), whereas frost-stable ground was characterised by low porosity or large pores (e.g. granite, coarse sandstone, gravel). Mass-movement, fluvial and aeolian processes also reworked sediment under periglacial conditions.
Overall,the landscape of southern England evolved largely through Quaternary periglacial processes acting upon low-relief land surfaces formed by Palaeogene and Neogene erosion.Periglacial weathering (ice segregation) and deep incision of rivers imposed significant relief on the old erosion surfaces. Valleys developed along strike of interbedded rocks of varying frost susceptibility (e.g. mudstone/stiff clayvs sandstone) or on permeable frost susceptible rocks rendered impermeable by ground freezing (e.g. chalk). The result was a palimpsest landscape of pre-Quaternary plateaux inset by Quaternary valleys.
Paleolandscapes of the Southern North Sea: Rhine-Thames land, glaciation foreland, stratigraphic correlation heart land.
Kim M. Cohen
Utrecht University, The Netherlands
The southern North Sea is surrounded by European countries of diverse Quaternary geology and equally diverse traditions in mapping and studying it. The area tends to inundate during interglacials and to fall dry for good parts of glacial periods. In the latter periods the area collects terrestrial record in valleys (fluvial), in interfluve area (periglacial) and during briefer intervals also ice-sheet marginal (morainic and proglacial). Shelf sea transgressions occur along paths inherited from the terrestrial terrain. Fluvial and subglacial activity from younger glacials dissects and reworks older record.
The palaeontological record (reworked Early Pleistocene, in place for younger times) and archaeological record (Middle Pleistocene; Late Pleistocene; Early Holocene) of the area is rather rich. The taphonomy of offshore bone and tool find sites was misty for a long time. Steps of offshore geological data collection, working up proxy-records from core material, spatially continuous mapping of the Quaternary geology on land and below sea, and lastly palaeogeographical scenario mapping for time slices of the Pleistocene – has improved this: they are good enough today to provide surrogate taphonomic context.
Positioned in the middle the area holds great promise for constructing and validating the stratigraphic correlations used to upscale regional mapping and dating to unified continental coverage. Similar to supplying taphonomic information on stray finds, also when building and ranking arguments for stratigraphic correlations, the palaeogeographical scenarios – which force the researcher to make thoughts on original distribution areas of paleoenvironments explicit (and available for peer judgement) – are an important tool for assessing the strength and weaknesses of advocated stratigraphic ties.
University College Cork, Ireland
Gibbardian – nomen nudum or nomen oblitum?
Thijs van Kolfschoten
Leiden University, The Netherlands
At a QRA meeting in Cambridge, January 1999, the stratigraphical term Gibbardian was launched. The use of the term is, however, so far limited, or actually non-existent. The history, the status as well as the possible future application of the term will be discussed.
17.45 Wrap Up