Late Cenozoic Glaciation Research Articles

Duration of Sturtian “Snowball Earth” glaciation linked to exceptionally low mid-ocean ridge outgassing

Abstract The Sturtian “Snowball Earth” glaciation (ca. 717–661 Ma) is regarded as the most extreme interval of icehouse climate in Earth’s history. The exact trigger and sustention mechanisms for this long-lived global glaciation remain obscure. The most widely debated causes are silicate weathering of the ca. 718 Ma Franklin large igneous province (LIP) and changes in the length and degassing of continental arcs. A new generation of two independent Neoproterozoic full-plate tectonic models now allows us to quantify the role of tectonics in initiating and sustaining the Sturtian glaciation. We find that continental arc length remains relatively constant from 850 Ma until the end of the glaciation in both models and is unlikely to play a role. The two plate motion models diverge in their predictions of the timing and progression of Rodinia break-up, ocean-basin age, ocean-basement depth, sea-level evolution, and mid-ocean ridge (MOR) carbon outflux. One model predicts MOR outflux and ocean basin volume–driven sea level lower than during the Late Cenozoic glaciation, while the other predicts outgassing and sea level exceeding those of the Late Cretaceous hothouse climate. The second model would preclude a major glaciation, while the first model implies that the trigger for the Sturtian glaciation could have been a combination of an extremely low MOR outflux (~9 Mt C/yr) and Franklin LIP weathering. Such minimal outflux could have maintained an icehouse state for 57 m.y. when silicate weathering was markedly reduced, with a gradual build-up of MOR CO2 in the atmosphere paired with terrestrial volcanism leading to its termination.

Quantifying Tectonic and Glacial Controls on Topography in the Patagonian Andes (46.5°S) From Integrated Thermochronometry and Thermo‐Kinematic Modeling

AbstractThe Patagonian Andes have been used to illustrate the dependency of major topographic changes in response to glacial erosion processes dominating over tectonic deformation and uplift. Here, we investigate tectonic and glacial contributors to the erosion history and evolution of topography in the Patagonian Andes at 46.5°S. We present 33 new apatite and zircon (U‐Th)/He (AHe and ZHe, respectively) and fission track (AFT and ZFT, respectively) ages integrated with 46 previously published bedrock thermochronometric ages in a 3D thermo‐kinematic model. Observed thermochronometer ages increase from the eastern flank of the topographic crest of the orogen toward the eastern retro‐foreland basin (from AFT 4–10 Ma, ZHe 4–12 Ma, ZFT 6–14 Ma to AFT 28–32 Ma, ZHe 68–117 Ma). Thermo‐kinematic modeling indicates that spatial gradients in thermochronometric ages can be explained by an up to 100‐km‐wide, parabolic‐shaped pattern in exhumation rates with a maximum rate of 0.5 mm/yr from 15 Ma until the onset of glaciation at ∼7 Ma. Furthermore, model results suggest that the youngest AHe ages require a localized acceleration in erosion from ∼0.5 mm/yr to ∼2.2 mm/yr starting between ∼5 and ∼3 Ma, coeval with intensified glaciation and subduction of the Chile Rise. Our results suggest that the long‐wavelength (∼100 km) topography and erosion patterns are likely controlled by rock uplift above mid‐crustal ramp(s) and subsequent transpression along the Liquiñe‐Ofqui Fault. Superposed on these tectonic processes, Late Cenozoic glaciation resulted in localized and accelerated erosion over wavelengths of <20 km.

Consistent slow exhumation in a late Cenozoic glaciated landscape: The Presidential and Carter ranges of the White Mountains in New Hampshire, USA

To investigate the ability of the onset of Quaternary glaciations to drive an acceleration in erosion rates we compare short timescale (103–104 yr) erosion rates using the in situ terrestrial cosmogenic nuclide (TCN) 10Be to longer time scale exhumation rates (106–107 yr) using the apatite (UTh)/He method in the Presidential and Carter ranges of the White Mountains in New Hampshire, USA. Our results are generally consistent with but refine previous studies using similar techniques. Resulting (UTh)/He ages and thermal modeling from Mt. Washington in the Presidential Range (n = 4, 91.7 to 117.3 Ma) suggest that exhumation rates from the Late Cretaceous to the present were slow, <0.01–0.02 mm yr−1. Be-10 analyses of high elevation bedrock and talus from the Presidential Range (n = 4; 1.5–1.8 km above mean sea level [amsl]; 18–130 ka) and Carter Range (n = 4; 1.0–1.4 km amsl; 14–22 ka) yield exposure ages that dominantly predate the retreat of the last glacial maximum ice sheet (13.9 ka) and indicate inheritance or inefficient glacial erosion of peaks. A non-linear positive relationship between exposure age and elevation suggests a component of elevation dependent polythermal basal ice conditions. A comparison of 10Be concentrations measured in modern fluvial sand and flood deposits in the region (n = 14; 5–19 × 104 atoms g−1 SiO2) to till (n = 5; ~2–7 × 104 atoms g−1 SiO2), colluvium (n = 2; 2–7 × 104 atoms g−1 SiO2), bedrock, and talus suggests that the modern day sediment budget continues to be dominantly sourced from remobilized glacial sediment rather than postglacial weathering. As such, late Cenozoic glaciation and postglacial processes modified existing topography at lower elevations but did not significantly accelerate exhumation rates in the higher elevation regions of White Mountains of New Hampshire. These results refute the idea of a global acceleration in erosion rates resulting from late Cenozoic climatic cooling and glaciation as a result of frozen-based minimally erosive ice cover in conjunction with low rates of tectonic uplift.

Retroarc deformation and exhumation near the end of the Andes, southern Patagonia

The southern Patagonian Andes constitute the narrow, high-latitude end of the Andean orogen belt in South America, where inherited basin paleogeography, subduction processes, retroarc crustal thickening, and late Cenozoic glaciation have collectively influenced their unusual tectonic and physiographic evolution. New zircon and apatite (U–Th)/He thermochronology from the Patagonian Andes between 50°30′ and 51°30′S suggest concentrated exhumation across the retroarc (leeward) side of the orogen since early Miocene time. Zircon (U–Th)/He (ZHe) ages range from 44 to 10 Ma; oldest ages are recorded in the Patagonian batholith and along the far eastern frontal foreland monocline. Regionally-uniform ZHe ages between 22 and 18Ma, located across a ∼75km wide-zone of the Patagonian retroarc thrust-belt indicate widespread early Miocene cooling through the ZHe partial retention zone. Mesozoic sedimentary and volcanic rocks in this region have been exhumed from at least 5 to 6km depths. Early Miocene denudation of the thrust-belt, deformation, and increased foreland sedimentation rates coincided with opening of the Scotia Sea, suggesting a causal response of the foreland to changes in plate dynamics. The apatite (U–Th)/He (AHe) ages from a similar region range from 11 to 3Ma; the youngest ages (6–3Ma) are spatially clustered within the more deeply-exhumed central thrust domain. We interpret these AHe ages to record >1–2km of erosional denudation associated with late Cenozoic glaciation and fluvioglacial processes in Patagonia beginning ca. 7Ma.Zircon results indicate that since ca. 22Ma, long-term exhumation rates have been highest across the western and central thrust domains (0.22–0.37mmyr−1), and significantly lower along the eastern thrust front (0.10–0.17mmyr−1). Since ∼7Ma, apatite results from these same regions suggest comparable and slightly higher denudation rates (0.14–0.46mmyr−1), particularly within the eastern thrust domain, consistent with efficient erosional processes acting in the retroarc region. These results from the Patagonian retroarc region, particularly the predominance of <7–4Ma AHe ages, provide a new understanding for regional orogenic erosion models that are largely based on existing data from the windward regions. We suggest that retroarc denudation was enhanced by widespread Miocene structural uplift and unroofing of the fine-grained siliciclastic rocks of the marine Cretaceous Magallanes/Austral foreland basin. Furthermore, its location at the southern tip of the orogen, may have allowed additional moisture to reach the leeward side, leading to sustained late Cenozoic erosional denudation.

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.

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.

Fault-controlled alpine topography in Norway

Abstract: Alpine topography in Norway is largely fault-controlled. Linear and asymmetric ranges developed in the footwalls of normal faults that were reactivated after the main phase of Mesozoic rifting, but prior to the Late Cenozoic glaciations. Stark geomorphological contrasts developed across the faults, reflecting differential glacial exploitation of the pre-glacial drainage pattern. Alpine topography developed preferentially in the footwalls. Triangular facets mark the traces of the most recently active faults. At the base of deeply incised, alpine range-front escarpments, the best-exposed faults display metres-thick fault-rock successions and record multiple phases of fault movement. Juxtaposition of Precambrian and Caledonian basement rocks with Jurassic or Cretaceous sedimentary rocks provides evidence for fault activity in or after the Mesozoic for some of the faults. Late Cretaceous or younger reactivation is indicated by jumps in apatite fission-track apparent ages across the faults, and interferometric synthetic aperture radar and earthquake data attest to normal faulting at the present day. Two of the areas described host anomalous clusters of rockslides that may relate to tectonic activity. The most distinct landscape-forming faults in western Scandinavia were probably active in the Cenozoic, and imposed asymmetric landscape patterns from the scale of single mountain ranges to the whole of Scandinavia.

Early TertiaryChamaecyparisSpach from Axel Heiberg Island, Canadian High Arctic

Exquisitely preserved fossil remains of Chamaecyparis Spach (Cupressaceae) have been recovered from Middle Eocene sediments of the Buchanan Lake Formation, Eureka Sound Group, of Axel Heiberg Island, Canadian Arctic Archipelago. Foliage consists of flattened, frondlike sprays considered typical for the genus. Leaves are decussate, scalelike, imbricate, appressed, and persistent. Seed cones are globose to subellipsoid, are borne on leafy peduncles, and bear 8–12 woody, peltate cone scales in a decussate arrangement. Seeds are two or more per scale, and winged. Within the genus, this fossil is most similar to extant Chamaecyparis pisifera (Siebold &amp; Zucc.) Endl. of Japan, although the suite of features found in the fossil does not occur in any single living species of the genus. These fossil remains are assigned to a new species, Chamaecyparis eureka Kotyk sp. nov. A review of the fossil record indicates that Chamaecyparis eureka is the oldest known member of the genus, as the Late Cretaceous taxon Chamaecyparis corpulenta (Bell) McIver appears most closely related to Cupressus nootkatensis D. Don [= Chamaecyparis nootkatensis (D. Don) Spach], and should therefore be excluded from the genus Chamaecyparis. As revealed by the fossil assemblages of the Buchanan Lake deposits, Chamaecyparis was an uncommon constituent of lowland, swamp–forest communities growing at high paleolatitudes (about 78°N) during a period of global warmth prior to the onset of global climatic deterioration that led to Late Cenozoic glaciation. It was one of the few evergreen taxa in a largely deciduous broad-leaved and coniferous vegetation of early Tertiary regions in the far north.Key words: fossil, Tertiary, Chamaecyparis, Cupressaceae, Arctic, Canada.

Passive margin uplifts and their influence on climatic change and weathering patterns of tropical shield regions

Large scale plateau uplift influences long-term atmospheric circulation patterns. Recent speculation on the role of passive margin mountains in initiating late Cenozoic glaciation around the North Atlantic adds to the debate on the connections between tectonics and climate patterns, and calls for broadening the scope of examining causes of climate change to include other existing passive margins. Three examples from the intertropical zone, the Western Ghats of India, the Borborema of northeast Brazil, and the West African Leo uplift are compared. Palaeoenvironmental and fission track constraints on amplitude, timing and wavelength of the shoulder uplift history for the Western Ghats reveal that high elevation margins can act as effective environmental filters, both as physical barriers to atmospheric circulation and as pace-makers for denudation rates, which in turn steer weathering processes towards producing specific soil and vegetation suites. Predicting interaction between climate and rift–flank tectonics is however shown to be model-dependent, in that assumptions on whether uplift is transient or permanent will influence the timescales and effectiveness of any consequent environmental change.

Passive margin uplift around the North Atlantic region and its role in Northern Hemisphere late Cenozoic glaciation: Comment and Reply

Research Article| March 01, 1997 Passive margin uplift around the North Atlantic region and its role in Northern Hemisphere late Cenozoic glaciation: Comment and Reply Peter van der Beek; Peter van der Beek 1Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Max Rohrman; Max Rohrman 2Faculteit Aardwetenschappen, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar Nicholas Eyles Nicholas Eyles 3Environmental Earth Sciences, University of Toronto, Scarborough Campus, Scarborough, Ontario, M1C 1A4, Canada Search for other works by this author on: GSW Google Scholar Geology (1997) 25 (3): 282–283. https://doi.org/10.1130/0091-7613(1997)025<0282:PMUATN>2.3.CO;2 Article history first online: 02 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 Peter van der Beek, Max Rohrman, Nicholas Eyles; Passive margin uplift around the North Atlantic region and its role in Northern Hemisphere late Cenozoic glaciation: Comment and Reply. Geology 1997;; 25 (3): 282–283. doi: https://doi.org/10.1130/0091-7613(1997)025<0282:PMUATN>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 SocietyGeology Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Gas hydrate and free gas indications within the Cenozoic succession of the Bjørnøya Basin, western Barents Sea

Multichannel seismic data, containing high-amplitude reflections from Cenozoic sediments of the Bjørnøya Basin, southwestern Barents Sea, have been studied, inferring the existence of gas hydrate and free gas. The Cenozoic succession comprises Late Palaeocene and Early Eocene claystones and siltstones and locally also some sandstones overlain by Late Pleistocene glaciogenic sediments. The inferred gas hydrate and free gas accumulations are mainly located in the vicinity of larger faults which can be followed up to base Tertiary level, and which seem to have controlled the geographical distribution of the accumulations. Free gas accumulations are inferred to occur most frequently within the Late Palaeocene strata that occur below the gas hydrate stability zone, and indicate that relatively small gas leakages from deeper accumulations have dominated. Larger gas leakages have probably led to gas migration up into the gas hydrate stability zone and, together with the increasing thickness of the hydrate stability zone towards the north, control the distribution of the suspected gas hydrates. The inferred gas leakages are closely related to the Cenozoic evolution of the Barents Sea, and are probably caused by gas expansion due to the removal of up to 1 km of sediments from the Barents Sea shelf and/or reservoir tilting during the Late Cenozoic glaciations which affected this area.

Paleomagnetic evidence for late Cenozoic glaciations in the Mackenzie Mountains of the Northwest Territories, Canada

The Mackenzie Mountains were affected by montane valley glaciers during the Pleistocene and peripherally by the Laurentide Ice Sheet during the last glaciation. In this paper we report on magnetostratigraphic dating and correlation of three sections recording Late Pliocene to Late Pleistocene glaciations: Katherine Creek, Little Bear River, and Inlin Brook (located around 65°N, 127°W). Each section consists of a colluvial unit overlying a Pliocene pediment surface cut into Proterozoic or Paleozoic bedrock, or Tertiary gravel, which is in turn overlain by a stack of five, and in places six, montane tills, usually with soils developed at their surfaces, and capped by a Laurentide till. Normal and reversed magnetizations were recognized with single-domain magnetite as a dominant remanence carrier. The Katherine Creek section has a normally magnetized colluvium at its base, which is overlain by two reversed tills, succeeded by three normal tills. We interpret the top two tills to be of Brunhes age (&lt; 780 ka) but argue that the lowermost normal till is of probable Olduvai age (ca. 1.8 Ma). The two underlying tills are of Matuyama age (2.6 Ma to 780 ka), and the colluvial base is assigned to the Gauss (3.5–2.6 Ma). The Little Bear River section exposes a stratigraphic record similar to that found at Katherine Creek. Only four units could be assigned a paleomagnetic polarity, the others yielding incoherent results. Paleosols on the first and second till units were reversed and normal, respectively, and the top till was normal. Thus there is clear evidence of an older (reversed) Pleistocene glaciation and a magnetostratigraphic record compatible with that found at Katherine Creek. Magnetic measurements from Inlin Brook gave largely incoherent results, with the exception of the surface (Laurentide) till, which is normal. The glacial history recorded in the Mackenzie Mountains correlates well with other studies carried out in the Cordillera. The large-scale changes in climate revealed in these terrestrial records provide baseline data for paleoenvironmental reconstruction.

Passive margin uplift around the North Atlantic region and its role in Northern Hemisphere late Cenozoic glaciation

Tectonic-climatic models of late Cenozoic global cooling emphasize the importance of middle latitude uplifts (e.g., Tibetan Plateau and the American west) but ignore widespread tectonic events on the margins of the North Atlantic Ocean. Pleistocene glaciations, after 2.5 Ma, are characterized by circum–North Atlantic continental ice sheets that formed by the coalescence of perennial snow fields on extensive plateau surfaces in eastern Canada, northwest Britain, and Scandinavia. Plateaus record Cenozoic uplift of peneplains in response to semisynchronous magmatic underplating and thermal buoyancy of rifted continental margins. High-standing plateaus are very sensitive to small reductions in summer temperature. As late Cenozoic climate cooling proceeded, driven by uplift in regions external to the North Atlantic region, elevated plateaus became sites for extensive snow fields and ultimately ice sheets. Circum-Atlantic uplift took place in the key latitudinal belt that is most sensitive to orbitally forced changes in solar irradiation; this, together with albedo effects from large snow fields, could have amplified the relatively weak Milankovitch signal.

Seven Million Years of Glaciation in Greenland

Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region.

Earth's glacial record and its tectonic setting

Earth's glacial record and its tectonic setting

The Extent of Late Cenozoic Glaciation in the Central Highlands of Tasmania, Australia

It is argued that during the most extensive late Cenozoic glaciation of the Tasmanian Central Highlands an ice cap of ~ 6000 km2 developed, probably in the early Pleistocene or late Pilocene. At least three subsequent glaciations have occurred. During the late Last Glacial Stage smaller ice caps were present on the Central Plateau, on a number of smaller plateaus, and on the West Coast Range and other ranges. The more westerly glaciers displayed the highest rates of mass throughout. The ice masses were of temperate maritime character. It is not necessary to invoke any significant shift in the direction of snow-bearing winds to explain the pattern of glaciation when the ice was most extensive.

The Extent of Late Cenozoic Glaciation in the Central Highlands of Tasmania, Australia

The Extent of Late Cenozoic Glaciation in the Central Highlands of Tasmania, Australia

Sedimentation patterns and facies geometries on a temperate glacially-influenced continental shelf: the Yakataga Formation, Middleton Island, Alaska

Abstract The 5 km thick Yakataga Formation of the Gulf of Alaska provides the longest and most accessible record of late Cenozoic glaciation in the world. The formation consists of interbedded marine and glacimarine sediments of late Miocene to Holocene age and is well exposed on offshore islands and in the coastal mountain ranges as a result of the convergent margin setting of the Gulf. About 1.3 km of early Pleistocene Yakataga Formation sediments are exposed on extensive intertidal platforms around Middleton Island which is sited close to the modern continental shelf edge. Variably graded gravels and sands at the base of the Middleton Island succession were deposited by sediment gravity flows and represent the fill of a large submarine channel. The remainder of the succession is dominated by thick (up to 100 m) planar tabular units of fossiliferous diamict containing a series of striated boulder pavements and shell-rich beds (coquinas). Diamict facies formed predominantly by the settling out of fines from suspended sediment plumes together with ice-rafting of coarser debris; foraminiferal biofacies data indicate palaeobathymetries of between 20 and 250 m. Boulder pavements are lag surfaces which developed in relatively shallow water and were subsequently faceted and striated by a grounding ice sheet extending to the continental shelf edge; coquinas record episodes of current winnowing in shallow water (20–50 m) but also contain ice-rafted debris. Extensive mud units formed in relatively deep water during periods of reduced ice volume and are similar to ‘mud blankets’ accumulating on the modern shelf. The Yakataga Formation on Middleton Island contains a rich record of changing palaeobathymetry and ice volumes in the Gulf of Alaska.

Sedimentology of shell-rich deposits (coquinas) in the glaciomarine upper Cenozoic Yakataga Formation, Middleton Island, Alaska

The Yakataga Formation in southern Alaska contains the longest and most accessible record of late Cenozoic glaciation in the world; glacially influenced marine sedimentation began in the late Miocene (6 Ma) and continues in the area to the present day. Upper Yakataga Formation sediments (1.25 km thick) are exposed on Middleton Island, Gulf of Alaska. Facies are dominated by massive glaciomarine diamicts that record deposition in an outer shelf setting of terrigenous mud and ice-rafted debris released from expanded temperate glaciers around the gulf margin. Diamicts contain intraformational coquina beds as much as 1 m thick, composed of cemented bioclastic debris and ice-rafted boulders, that can be traced several kilometers along strike. Analysis of foraminifera contained within diamicts and coquinas suggests that coquinas record intervals of relative sea-level change, bottom winnowing and nondeposition of mud allowing molluscan communities to develop. Coquinas show graded beds produced by storms and wave-rippled, commonly armored upper surfaces composed of densely packed Chlamys valves. These bioclastic deposits are of considerable significance with regard to the origin of mixed glacial and carbonate successions in the rock record. Analogous depositional settings can be identified from the Permian of Australia.

The western Svalbard margin (74°–80°N)

A regional study of the continental margin between the Senja and Molloy-Spitsbergen fracture zones reveals that the transition from continental to oceanic crust occurs in a narrow zone beneath the outer shelf and uppermost slope. The postulated continent-ocean boundary appears to be fault-related consisting of sheared and rifted segments. The marginal structures are compatible with a plate tectonic model in which the southern Greenland Sea opened along a northeasterly propagating plate boundary in the Eocene, whereas the northern Greenland Sea started opening in the early Oligocene. The main structure at the margin is the Hornsund Fault Zone which probably reflects an old zone of weakness rejuvenated in the Tertiary, first by shear and later by extensional movements. In the early Tertiary local transpressional and transtensional components along the plate boundary are associated with the Spitsbergen Orogeny, emplacement of belts of high-density oceanic crust and tectonism in the western Barents Sea. A complex volcanic rifted margin characterized by the Bjørnøya Marginal High links the predominantly sheared margin segments on either side. The main ridge-like segment of the Hovgaard Fracture Zone was originally part of the Spitsbergen margin. In a regional sense, the Hornsund Fault Zone demarcates the eastern boundary of the Tertiary sedimentary wedge which reaches a total thickness of more than 7 km. There appears to have been a considerable increase in deposition of sediments the last 5–6 my. Depocentres located seaward of the east-west fjord systems and submarine depressions indicate a relationship between late Cenozoic glaciations and high sedimentation rates.

Geological and Petrographical Investigations for the Mountain Hazards Mapping Project, Khumbu Himal, Nepal

Geological and petrographical investigations of the Khumbu area, Nepal, were undertaken to provide basic data for the United Nations University mountain hazards mapping project. Six litho-tectonic units were distinguished by petrographical means: Basal Paragneisses, Migmatitic Orthogneisses, Upper Khumbu Gneiss Complex, Upper Paragneisses, Tertiary Leuco-granites, Everest Meta-Sediments. Investigations of subsurface conditions showed that the topographical relief of the area depends largely on lithology, structures, and the depositional or erosional character of the Late-Cenozoic glaciations. Mass wasting plays a major role in the accumu- lation of debris cover. The valley system has been interpreted as a deep pre-glacial primitive surface, with V-shaped troughs and elevated platforms, which have been overprinted by glaciation. Erosional activity of the river system is occurring at present although most of the landforms are relatively stable.