Late Glacial Time Research Articles

Late-glacial cirque glaciation in parts of western Norway

Younger Dryas cirque glaciers are known to have existed beyond the Scandinavian Ice Sheet in parts of western Norway. At Kråkenes, on the outermost coast, a cirque glacier formed and subsequently wasted away during the Younger Dryas. No glacier existed there during the Allerød. Large cirque moraines, some with marine deltas and associated fans, extend into the western part of Sykkylvsfjorden. Comparison with existing late-glacial sea-level curves shows that the uppermost marine sediment in these features was deposited well above Younger Dryas sea-level, demonstrating that the cirques were occupied by glaciers before the Younger Dryas. During the Younger Dryas the cirque glaciers expanded, and some advanced across the deltas, depositing till and supplying the sediment to form lower-level fans and deltas controlled by Younger Dryas sea level. The extent of the Younger Dryas advance of some of the glaciers was, at least in part, controlled by grounding on material deposited before the Younger Dryas. The depositional history of the glacial–marine deposits in the Sykkylven area indicates that cirque glaciers existed throughout Late-glacial time and only expanded during the Younger Dryas. The sediment sequence in glacial lakes beyond cirque moraines and reconstructions of glacier equilibrium lines indicate that this was true for most cirques in western Norway. Only on the outermost coast were new glaciers formed in response to Younger Dryas climate cooling. © 1998 John Wiley & Sons Ltd.

Nd Isotope Evidence for Provenance of the Terrigenous Fraction of Deglacial Sediments in the Orca Basin, Gulf of Mexico

Documentation of the routing of fresh water runoff during disintegration of the Laurentide Ice Sheet is important to understanding the impact of glacial fresh water contributions to thermohaline circulation in the North Atlantic. During the Last Glacial Maximum, the Gulf of St. Lawrence drainage was blocked, and glacial lakes Agassiz and Superior were damned and filled with meltwater (Broecker et al., 1989). Oxygen isotope data from foraminifera of the Orca Basin in the Gulf of Mexico have been used to suggest that catastrophic meltwater floods from these glacial lakes were channeled down the Mississippi River, starting about 18 ka and ending by 10.5 ka (Leventer et al., 1982). After the ice sheet retreated far enough to the north, fresh water from the melting ice was sent directly into the North Atlantic via the St. Lawrence River drainage. It has also been suggested that this change in meltwater routing could have been the trigger for the Younger Dryas cooling (Rooth, 1982; Broecker et al., 1989). The suggestion that it is possible to temporarily shut down deep water formation in the North Atlantic by adding a spike of fresh water through the St. Lawrence drainage, thereby reducing the transport of heat from northward-flowing, warm surface currents has been supported by global circulation models. Work is in progress to evaluate radiogenic isotope evidence for variations in terrigenous sediment sources via the Mississippi River during late glacial and Holocene times. Previously, Hurley et al. (1961) documented that bulk, surface sediments from a variety of delta and pro-delta settings on the Mississippi River produce a relatively small range of apparent K-Ar ages of 214 to 357 Ma. In contrast, clay size fractions from normal gray sediments at various core depths within Mississippi Delta cores yield apparent ages of 145 to 206 Ma, and bulk sediment aliquots from these same samples yielded apparent ages of 280 to 390 Ma, similar to bulk sediment analyses of surface sediments. The interpretation of these results was that the coarsest potassium-rich fractions consist of minerals derived from crystalline rocks of the Appalachian Mountains with ages of c. 400 Ma. Hurley et al. (1961) also suggested that these coarser fractions additionally contained a larger proportion of illite, a stable, highK mineral that is common in Palaeozoic shale deposits such as those tapped by the Ohio River. The finer fraction contains a larger proportion of smectite derived from younger, Cretaceous and Tertiary, sedimentary and volcanic sources to the west, via the Missouri River. The truly impressive part of the Hurley et al. (1961) study was their data from a red-brown clay layer from down-core samples from two different cores. In contrast to the gray clay samples, bulk samples of this red-brown layer yielded apparent ages of 540 to 810 Ma! In order to have made such a tremendous impact on the provenance of sediment from such a mighty river as the Mississippi must have required an enormous and catastrophic flooding event. Hurley et al. (1961) reasonably interpreted the ancient age for the red-brown layer to be a product of sources from the southern Colorado Front Range via the Red River. An alternative hypothesis is that the flood might instead reflect one of the catastrophic floods known to have flowed into the Gulf of Mexico from glacial lakes pinned against the southern margin of the Laurentide Ice Sheet during its final phases. An appropriate approach to testing reconstructions of drainage history is to analyse the radiogenic isotope composition of terrigenous sediments in the Orca Basin, a very anoxic basin located near the Mississippi Delta. The highly anoxic conditions tend to prevent biological disturbance of sediment layering and thus a detailed stratigraphy is possible. Several studies have been published on oxygen isotope evidence from Orca Basin cores for the occurrence of a large meltwater event in the Gulf of Mexico that ended shortly before the Younger Dryas (Broecker et al., 1989). Due to the very reducing conditions in the Orca Basin, the red colouration noted by Hurley et al. (1961) on the Mississippi Delta would not likely be preserved in these sediments. New data collected for this study show that sediments from within the meltwater interval of core EN32 PC6

Status of engineering geology in North America and Europe

1995–1996 has been informally declared as a watershed year for the United States in many ways. Pervasive change has been the tenor of the times and engineering geology has not escaped what the nation faces. In particular, the nation has run out of easy money and the Congressional elections of 1994 empowered a majority of new members expressing fiscal accountability. Accordingly, agencies have been given reduced budgets and programs have been slashed or removed, early retirements have been accomplished and reductions in force (RIFs) have been concluded among personnel. Priced competition for professional work reached a new and regrettable peak of use and industries struggled with successive waves of both corporate acquisitions and “downsizing” of staffing. In the UK and Europe, drought conditions developed and became more severe during 1995. The first land link between the UK and Europe since late glacial times (the Channel tunnel rail link) developed full working schedules. The input of geotechnical engineering into this prestige international project was further demonstrated by a final series of major conferences and publications ( Byrd, 1994; Institution of Civil Engineers 1992, 1993, 1994). The major downturn in “normal” civil works, and the associated preparatory geotechnical investigations, for roads, redevelopment and housing, etc. continued, with many smaller site investigation and associated specialists either “downsizing”, being subsumed into larger groups, or going out of business.

Late quaternary glacial stades in the Cordillera Central, Colombia, based on glacial geomorphology, tephra–soil stratigraphy, palynology, and radiocarbon dating

Using data from glacial geomorphology, tephra–soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the last ca. 50000 yr in the Ruiz-Tolima massif, Cordillera Central, Colombia. Six Pleistocene cold stades separated by warmer interstades occurred: before 48000, between 48000 and 33000, between 28000 and 21000, from ≥16000 to ca. 14000, ca. 13000–12400, and ca. 11000–10000 yr BP. Although these radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier standstill during cold intervals ca. 7400 yr BP and slightly earlier. Finally, glaciers readvanced between the seventeenth and nineteenth centuries. In contrast to the ice-clad volcanoes of the massif, ca. 34 km2 in area above an altitude of ca. 4800 m, the ice cover expanded to 1200 km2 during the Last Glacial Maximum (LGM) and was still 800 km2 during Late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA, which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and wet, e.g. during stades corresponding to Oxygen Isotope Stage 3; glaciers were still expanding during the LGM ca. 28000–21000 yr BP, but they shrank considerably after 21000 yr BP because of greatly reduced precipitation. © 1997 John Wiley & Sons, Ltd.

Late Quaternary vegetation, climate and fire history of the Araucaria forest and campos region from Serra Campos Gerais, ParanáState (South Brazil)

New palynological and charcoal data from a bog (24°40′S, 50°13′W, 1200 m asl) of Serra Campos Gerais, northeastern ParanáState, allow a complete and detailed reconstruction of the late Quaternary vegetation and climate history of the South Brazilian highlands. The late-glacial period, which starts at 12,500 14C yr BP, indicates the predominance of a diverse grassland vegetation (campos) with scattered stands of Araucaria forest and Atlantic rain forest, probably growing in valley bottoms. This suggests 3 to 5°C colder and drier climates than at present. Judging from the absence of charcoal, fires must here been rare during late-glacial times. The early and mid-Holocene (until 2850 14C yr BP) is marked by a predominance of campos vegetation on the highlands and expansion of tropical rain forest trees in the valleys, indicating warm climates and perhaps an increase in annual precipitation compared to the late-glacial. A migration of Araucaria forest from the valleys onto the highlands did probably not occur. Seasonal drought is probably the major factor explaining the absence of an expansion of Araucaria forests on the southern Brazilian highlands in the early and mid-Holocene. Palaeofires were more frequent at the beginning of the Holocene, probably ignited by Amerindians at that time. First expansion in the valleys or an initial migration of Araucaria angustifolia from valleys into the Serra Campos Gerais highland occurred during the late Holocene (2850-1530 14C yr BP), indicating a wetter climate with a shorter dry season. Fires during this period had the highest frequency and may have influenced the migration of Araucaria into the campos areas. A marked expansion of Araucaria forest, forming a mosaic of grassland and Araucaria forest patches on the highlands, took place only in the last 1500 years. This suggests onset of a high precipitation climate without a strong annual dry season. Fires were also less frequent. Logging of Araucaria forests occurred during the last centuries.

Glacial and Postglacial Pollen Records from the Ecuadorian Andes and Amazon

A long pollen record is derived from sediments of a lake dammed behind a low moraine of the last glaciation at 3°S latitude in the Ecuadorian Andes and is compared with a glacial age pollen record from the Amazon rainforest immediately below. Lake Surucucho (Llaviucu) lies at 3180 m on the Amazonian flank of the Andes and above the glacial age pollen record from San Juan Bosco at 970 m. The Surucucho pollen record is interpreted as showing treeless vegetation in glacial times, advance of treeline in late-glacial time, and Holocene development of modern Andean forests. Combining the Surucucho and San Juan Bosco records shows that Andean vegetation was affected by glacial cooling at all elevations. Vegetation did not move up and down slope as belts. Rather, plant associations were reformed as temperature-sensitive species found different centers of distribution with changing temperature.

Reliable Late-Pleistocene Stratigraphic Ages and Shorter Groundwater Travel Times from14C in Fossil Snails from the Southern Great Basin

Both aquatic and land snails are common in the geologic record, but their utility in dating is greatly restricted by their well-documented tendency to yield14C dates inconsistent with true14C ages. In this study, we examine the use of14C ages from (1) small, previously unstudied, terrestrial snails to date hosting spring deposits and from (2) cooccuring aquatic snails to constrain groundwater travel times during the last glacial period. Our study area in the southern Great Basin encompasses Yucca Mountain, site of the proposed high-level nuclear waste repository, where information on the age and extent of past high water tables and on groundwater flow times is crucial to several licensing issues. Our results show that shells of small terrestrial snails belonging toValloniasp. yield14C dates consistent with14C ages of associated carbonized wood. These results imply that these taxa can provide reliable14C age control on the broadly distributed deposits in which they have been described. In contrast, cooccurring aquatic snails from fossil spring deposits yield14C ages generally greater than the control age. This is because the aquatic shells often formed in spring waters that had an initial14C deficiency. However, the magnitude of the deficiency is much less than that observed in nearby modern springs, arguing for much higher average14C contents in late Pleistocene groundwaters in these basins. If representative, this implies shorter groundwater travel times through aquifers in southern Nevada during late-glacial time.

Late glacial events in the central Russian Arctic

Investigation of glacigenic diamictons and landforms in the central Russian Arctic has established that continental glaciation was widespread during late glacial time. Diamictons in West-Central Siberia containing marine foraminifera and mollusca include glacitectonic deformation features, and are associated with glacial landforms. These sediments are interpreted as basal tills, formed by continental glaciation which expanded from the exposed Kara Sea shelf, southwards along the western flank of the Ural Mountains. Piedmont glaciers advancing westward from the Urals were obstructed by the southward-flowing ice and were areally restricted. Simultaneously, piedmont glaciers advancing eastward from the crests of the Urals were able to expand without restriction. Alpine glaciation within the Urals was areally restricted and culminated, simultaneously, with the maximum extent of the southward-flowing shelf-based ice. In West Siberia, rapid disintegration of an Early Weichselian ice sheet by marine calving was followed by slow stagnation of the dissected mass throughout the remainder of the Weichselian. In contrast, glaciation in the Pechora Basin reached its maximum during the Middle-Late Weichselian, at least 30,000 years after the glacial maximum in western Siberia. The transition to Holocene climatic conditions was influenced by the presence of remanent decaying glacial masses.

Late glacial climate in northern Eurasia: The last climatic cycle

Abstract Analysis of palynomorphic, Coleoptera, mammalian and geomorphic evidence throughout Europe indicates that three distinctive cooling phases, designated Older, Middle and Younger Dryas, can be recognized during Late Glacial time. Each subsequent cold interval was less intense than the preceding one, with the Younger Dryas representing the warmest of the three episodes. Similarly, the later Allerod interval was warmer and more intense than the earlier Bolling event. Consequently, the overall pattern throughout the Late Glacial-Holocene transition was climatic warming. Climate changes throughout northern Eurasia are directly related to fluctuations in sea level along the Arctic Ocean coast, and to the establishment of anti-cyclones over Siberia and Scandinavia.

The main stages and natural environmental setting of late Palaeolithic human settlement in Eastern Europe

Abstract During the Early Palaeolithic period, the instability of the landscape and unsuitable climates precluded human settlement of the northern parts of the East European Plain. Large-scale proliferation of Mousterian groups into the East European Plain did not occur prior to the Valdai glacial event. In the eastern part of European Russia, Palaeolithic humans migrated towards the northeast during Late Glacial time, following the progressive retreat of the Valdai glaciers during the period 39-18 ka. In contrast, Palaeolithic migration in the western region moved towards the advancing segment of the Valdai ice sheet, which reached its maximum in Belarus ca. 17 ka. Human occupation of the unglaciated areas persisted throughout the Last Glacial Maximum, utilizing the resources of the open periglacial tundra-steppe.

Glaciation and sea-level change for Ireland and the Irish Sea since Late Devensian/Midlandian time

The sea-level change around the coast of Ireland and the Irish Sea for the past 20 000 years is primarily the combined result of the glacio-isostatic adjustment of the crust to the removal of ice over the British Isles and the total eustatic change from the global ice sheets. However, the isostatic effects due to the removal of ice from northern Europe and North America and the addition of meltwater into the oceans also make a significant contribution. Predictions of sea-level change, based on glacio-hydro-isostatic models are compared with observations to constrain the ice volume over Ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m. The models predict well the spatial variability in sea-level change observed across the region for Holocene and Lateglacial time, with levels above present being predicted only for northeastern Ireland and north of about Morecambe Bay. The models do not support suggestions that Lateglacial levels along the east coast of Ireland or the coast of Wales were 50–150 m above their present levels. Consistent models that would produce such large Lateglacial highstands are incompatible with all other sea level and glacial evidence for the British Isles. Palaeobathymetry and palaeoshoreline reconstructions for the Irish Sea indicates that a tenuous landbridge between Britain and Ireland developed only across the Celtic Sea, between about 18000 and 14000 years bp.

Paleoenvironmental Changes and Glacial Stades of the Last 50,000 Years in the Cordillera Central, Colombia

Using data from glacial geomorphology, tephra-soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the past ca. 50,000 yr in the Ruı́z-Tolima massif, Cordillera Central. Six cold stades separated by warmer interstades occurred before 48,000, between 48,000 and 33,000, between 28,000 and 21,000, from ≥16,000 to ca. 14,000, ca. 13,000–12,400, and ca. 11,000–10,000 yr B.P. Although the radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier pauses during cold intervals ca. 7400 yr B.P. and slightly earlier. Finally, glaciers readvanced between the 17th and 19th centuries. In contrast to the glacier cover (ca. 34 km2) on volcanoes of the massif during the last glacial maximum (LGM) the ice cover expanded to 1200 km2and was still 800 km2during late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and moist, e.g., during stades corresponding to marine isotope stage 3; glaciers were still expanding during the LGM ca. 28,000–21,000 yr B.P., but they shrank considerably after 21,000 yr B.P. because of greatly reduced precipitation.

Application of Iversen's glacial-interglacial cycle to interpretation of the late last glacial and holocene vegetation history of western Tasmania

The Iversen glacial-interglacial cycle of vegetation change is modified and applied to glacial, Lateglacial and Holocene age pollen records from western Tasmania. Cryocratic conditions occurred at high altitude (ca. 500 m+) during glacial and Lateglacial time. Transition from cold humid to cool humid climate occurred on the lowlands by 13 ka BP and in the mountains by 10 ka BP. There is regional parallelism of vegetation development from grassland-herbland-sedgeland through alpine-subalpine scrub and woodland to temperate rainforest dominated by Nothofagus cunninghamii. However, radiocarbon dating shows that changes in the vegetation succession and Nothofagus rainforest maximum were non-synchronous. Although climate change from glacial to interglacial conditions directed the general succession, variations in dates for similar vegetation changes show that biological and physical variables were important for local vegetation development. Some sites show late Holocene vegetation changes that could be interpreted as revertance. Aboriginal fire and lake infilling were probably responsible. There is no evidence for an Allerød-type warm phase between 13 and 11 ka BP or a Younger Dryas-type cold phase between 11 and 10 ka BP. The climate was cool temperate between 13 and 0 ka BP, and neither temperature nor precipitation change was sufficient to cause vegetation change of regional significance.

The GISP2 δ18O Climate Record of the Past 16,500 Years and the Role of the Sun, Ocean, and Volcanoes

Measured 18O/16O ratios from the Greenland Ice Sheet Project 2 (GISP2) ice core extending back to 16,500 cal yr B.P. provide a continuous record of climate change since the last glaciation. High-resolution annual 18O/16O results were obtained for most of the current millennium (A.D. 818-1985) and record the Medieval Warm Period, the Little Ice Age, and a distinct 11-yr 18O/16O cycle. Volcanic aerosols depress central Greenland annual temperature (∼1.5°C maximally) and annual 18O/16O for about 4 yr after each major eruptive event. On a bidecadal to millennial time scale, the contribution of solar variability to Holocene Greenlandic temperature change is ∼0.4°C. The role of thermohaline circulation change on climate, problematic during the Holocene, is more distinct for the 16,500-10,000 cal yr B.P. interval. (Analogous to 14C age calibration terminology, we express time in calibrated (cal) yr B.P. (A.D. 1950 = 0 cal yr B.P.)). The Oldest Dryas/Bølling/Older Dryas/Allerød/Younger Dryas sequence appears in great detail. Bidecadal variance in 18O/16O, but not necessarily in temperature, is enhanced during the last phase of lateglacial time and the Younger Dryas interval, suggesting switches of air mass transport between jet stream branches. The branched system is nearly instantaneously replaced at the beginning of the Bølling and Holocene (at ∼14,670 and ∼11,650 cal yr B.P., respectively) by an atmospheric circulation system in which 18O/16O and annual accumulation initially track each other closely. Thermodynamic considerations of the accumulation rate-temperature relationship can be used to evaluate the 18 O/16O-temperature relationship. The GISP2 ice-layer-count years of major GISP2 climate transitions also support the use of coral 14C ages for age calibration.

People and environment in the Russian far east from Paleolithic to Middle Ages: Chronology, palaeogeography, interaction

The Late Paleolithic sites existed in cold and dry climat (Ustinovka I, 10–25 ky ago; Ust-Ulma, 19, 360 ± 65 BP) with warmer stages (Suvorovo IV, 15,300 ± 140 BP) and on the Pleistocene/Holocene transition, near 10,000 BP (Suvorovo III). The Final Paleolithic sites existed in Late Glacial time, 10,000–12,000 BP (Gorbatka III, lower level) and in Boreal period, 8,000–9,000 BP (Ilistaya I, 7, 840 ± 60 BP; Timofeevka I). The Developed Neolithic sites existed during the warm and humid Middle-Late Atlantic period, 6,000–8,000 BP; the Late Neolithic sites — 3,000–5,000 BP. The human impact in the Paleolithic-Neolithic was restricted to burning and trampling the vegetation near the sites; the bases of paleoeconomy were hunting, fishing, gathering. The presence of pastoral anthropogenic indicators in pollen spectra of the Neolithic sites may reflect the beginning of cattle breeding. The Bronze Age (end of the 4th-2nd millenia BC) provides the first reliable evidence of cultivated plants (foxtail and Japanese millet) and domestic animals (pig, dog). In the paleoeconomy agriculture and cattle breeding appeared; the first stage of human impact increased (4,000–4,500 BP, ie 2550–3230 cal. BC) is reflected in pollen spectra from cultural layers. From the Early Iron Age to the Middle Ages (end of 2nd millenium BC-13th century AD) agriculture and cattle breeding were the base of paleoeconomy. From the 8th to the 10th centures AD, due to the development of ploughing (arable), the human impact intensified.

Lateglacial, early and middle holocene environments, human occupation, and resource use in the Atacama (Northern Chile)

AbstractPaleoenvironmental data from the Atacama Altiplano (21°–24°S) indicate that water, vegetation and animal resources were more abundant during lateglacial and early Holocene times than today. The rate of precipitation increased above 4000 m elevation to 400–500 mm/yr compared to the present 200 mm/yr. Dry conditions prevailed below 3500 m. Evidence of Paleoindian habitation is still missing, even though there is no evidence for environmental prohibitors during lateglacial time. The early Archaic hunters (10,820 yr B.P.‐ca. 8500 yr B.P.) inhabited the Altiplano (high Puna) and its western slope, where water was available due to higher river runoff from the Altiplano, and the resources in different elevation zones were accessible. Natural resources decreased significantly during the middle Archaic period (8500‐ca. 5000 yr B.P.). Lakes receded to today's levels, pedogenesis in the Altiplano terminated, and human activities were restricted to the most stable sites in the Río Lao and the Río Purifica catchments north of 23°S. The less stable oases south of 23°S (Salar de Atacama and Punta Negra) were abandoned. The climatic changes are best explained by shifts of the (sub)tropical circulation. © 1994 John Wiley & Sons, Inc.

Paleohydrology of the Laguna Lejía (north Chilean Altiplano) and climatic implications for late-glacial times

Paleoenvironmental and sedimentological data from Laguna Lejía (23°30′S, 67°42′W, 4325 m) in the high Altiplano of the Chilean Atacama desert indicate that climatic conditions during late-glacial times were significantly wetter than today. A water and energy budget model was used to simulate climatic scenarios that would have resulted in the observed changes in the water levels, water surfaces, water volumes and salinity during the time interval. Different climatic scenarios for the Laguna Lejía catchment include precipitation increases of over 100% up to 400−>500 mm/yr (today 200 mm/yr) to account for the late-glacial lake levels with shorelines 15–25 m higher than at present, and a lake surface of 9–11 km 2 compared to the present 2 km 2. During the lake maximum about 13,500–11,300 yr B.P. finely laminated sediments consisting of Mg-calcite, diatoms and sometimes gypsum were deposited. The paleoenvironmental evidence indicates that (north)easterly wind direction prevailed, and the summer rainfall resulted from a seasonal poleward shift of the tropical circulation. The lake history of Laguna Lejía is representative for the Altiplano area between 21° and 24°S.

Fennoscandian seismicity and its relation to the isostatic rebound

Beside plate tectonics, isostatic rebound may be a main contributor in the seismogenic process in Fennoscandia. Extensional horizontal strain, presumably related to land uplift, calculated from mathematical modeling, geodetic data and curvature of uplift, show higher values than compressional horizontal strain, related to ridge push, estimated from sedimentary deformation in the basins surrounding the shield. The location of the current seismicity of central and northern Fennoscandia and the sites of large boulder caves near the Bothnian coast of central Sweden, show high correlation with the maximum curvature of uplift at present and late-glacial time, respectively; the caves may have been created by large earthquakes at the last phase of deglaciation. Large faults in northern Fennoscandia probably also have seismogenic origin dating to the late-glacial period. Differential strain along the Swedish coast of the Gulf of Bothnia, caused by a larger rate of uplift under the Gulf than of the adjacent land, is another seismogenic factor related to rebound. Earthquake focal mechanism solutions show a variety of faulting styles and stress orientations. Clearly, not all of them can be accounted for by ridge push. The proportion of small compared to large earthquakes ( b value) is larger in northern than in southern Fennoscandia. The maximum b is in the northern Gulf of Bothnia close to where the maximum rate of uplift is. The implication may be that tectonics and uplift are counteracting forces in the north, preventing large stress accumulation, whereas tectonics act more undisturbed in the south, resulting in larger stress build-up and thus relatively more large earthquakes. The temporal correlation between the seismicities of the Fennoscandian and the eastern Canadian shields on one hand and segments of the North Atlantic Ridge on the other, gives support to the idea of stress propagation under the Atlantic.

Marine deposits of late glacial times exposed by tectonic uplift on the east coast of Taiwan

Marine sediments deposited some 14,000 years ago, when the sea level was between 80 and 100 m below the present sea level, have been found exposed at about 17 m in altitude near Tu-lan, on the east coast of Taiwan. This implies a minimum average uplift rate of 7.6 ± 0.9 mm/yr; similar values of tectonic uplift are not uncommon on the eastern Coastal Range of Taiwan. Such rates of tectonic uplift, among the highest reported in the literature, are of the same order as present-day maximum glacio-isostatic uplift rates.

The larva and habitat ofParakiefferiella nigra Brundin (Diptera: Chironomidae)

Collections of adults ofParakiefferiella nigra Brundin indicate that this chironomid occurs widely in arctic and subarctic zones. In addition, it has occasionally been collected in cool temperate and boreal forest lakes of both North America and Europe. Although widely distributed, the larva and its habitat have not previously been described. Identity of the larva ofP. nigra has been established by studying associated reared specimens. The distinctive larva, with reduced second lateral mental teeth, is stenotopic, and on the basis of modern collections appears to be most abundant in cold, oligotrophic lakes. More data is required to establish the range of thermal environments inhabited by the larva. Larval head capsule remains ofP. nigra are common in late-glacial sediments of southwestern British Columbia lakes and provide important evidence for oligotrophic conditions during late-glacial time.