The Lower Permian Wasp Head Formation,Sydney Basin: high‐latitude,shallow marine sedimentation following the late Asselian to early Sakmarian glacial event in eastern Australia

The Lower Permian Wasp Head Formation (early to middle Sakmarian) is a ～95 m thick unit that was deposited during the transition to a non‐glacial period following the late Asselian to early Sakmarian glacial event in eastern Australia. This shallow marine, sandstone‐dominated unit can be subdivided into six facies associations. (i) The marine sediment gravity flow facies association consists of breccias and conglomerates deposited in upper shoreface water depths. (ii) Upper shoreface deposits consist of cross‐stratified, conglomeratic sandstones with an impoverished expression of the Skolithos Ichnofacies. (iii) Middle shoreface deposits consist of hummocky cross‐stratified sandstones with a trace fossil assemblage that represents the Skolithos Ichnofacies. (iv) Lower shoreface deposits are similar to middle shoreface deposits, but contain more pervasive bioturbation and a distal expression of the Skolithos Ichnofacies to a proximal expression of the Cruziana Ichnofacies. (v) Delta‐influenced, lower shoreface‐offshore transition deposits are distinguished by sparsely bioturbated carbonaceous mudstone drapes within a variety of shoreface and offshore deposits. Trace fossil assemblages represent distal expressions of the Skolithos Ichnofacies to stressed, proximal expressions of the Cruziana Ichnofacies. Impoverished trace fossil assemblages record variable and episodic environmental stresses possibly caused by fluctuations in sedimentation rates, substrate consistencies, salinity, oxygen levels, turbidity and other physio‐chemical stresses characteristic of deltaic conditions. (vi) The offshore transition‐offshore facies association consists of mudstone and admixed sandstone and mudstone with pervasive bioturbation and an archetypal to distal expression of the Cruziana Ichnofacies. The lowermost ～50 m of the formation consists of a single deepening upward cycle formed as the basin transitioned from glacioisostatic rebound following the Asselian to early Sakmarian glacial to a regime dominated by regional extensional subsidence without significant glacial influence. The upper ～45 m of the formation can be subdivided into three shallowing upward cycles (parasequences) that formed in the aftermath of rapid, possibly glacioeustatic, rises in relative sea‐level or due to autocyclic progradation patterns. The shift to a parasequence‐dominated architecture and progressive decrease in ice‐rafted debris upwards through the succession records the release from glacioisostatic rebound and amelioration of climate that accompanied the transition to broadly non‐glacial conditions.     

Out of the Rat Race

After the social policy reforms of 1991 important changes in internal migration in New Zealand occurred. These resulted in changing housing costs and falling incomes which led to the movement of low income households, particularly beneficiaries and state house tenants, from urban to rural areas and small towns. A survey of 404 people who moved to the Southern Wairarapa towns of Carterton, Martinborough and Featherston from New Zealand urban areas since 1985 shows that a proportional increase in beneficiary movement occurred after 1991. Housing costs, relative to income, are important factors in the decision to move for a range of migrants. This pattern of migration has important regional development ramifications.     

Convergent flow of ice within the Astrolabe subglacial basin, Trre Adélie, East Antarctica: an hypothesis derived from nummerical modelling experiments

The existence of a large subglacial lake beneath the antarctic Ice Sheet at Terre Adélie indicates the presence of basal ice at its pressure-melting temperature. A numerical model of the ice-sheet thermal regime is employed using the balance velocity of the ice sheet as an initial model input in order to calculate ice-sheet basal temperatures. However, the results from this model show the Terre Adélie area to be characterised by basal freezing. Heat in addition to that accounted for in the model is thus required at the ice-sheet base in order for pressure melting temperatures to be attained. The sources for such heat are (1) an enhanced geothermal heat flux and (2) an increase in frictional heating caused by the flow of ice. In this paper the latter possibility is expanded by hypothesising that subglacial topography induces convergent ice flow around Terre Adélie, causing enhanced basal ice velocities. Model experiments indicate that an increase in ice velocity (from 7 to at least 42 m yr⁻¹) is required to raise the temperature of the basal ice to the pressure melting value. Increased ice velocity, and consequent frictional heat production due to convergent ice flow, may therefore be important in explaining the location of the subglacial lake in this region. These results allow the process of convergent ice flow within a contemporary ice sheet to be quantified. A verification (or otherwise) of the model results may be possible if ice surface velocity measurements from modem GPS methods are made.     

SUGGESTIONS FOR A CONSISTENT TERMINOLOGY FOR SEISMIC ANISOTROPY1

Seismic anisotropy is an unfamiliar concept to many geophysicists and the use of misleading and ambiguous terminology has made it more difficult to understand. I suggest here a consistent terminology in which simple expressions have specific meanings similar to their colloquial meanings. It is hoped that use of such language will help to make the increasing number of papers reporting seismic anisotropy more readily comprehensible to the non-specialist. This not a manual of anisotropy, and it is not intended for theoreticians. It is a list of terms which may make anisotropy a little easier to understand for those more familiar with wave propagation in isotropic solids.     

Depositional controls on Lower Carboniferous microbial buildups, eastern Midland Valley of Scotland

In the eastern Midland Valley of Scotland non-skeletal carbonate buildup complexes are present in the Charlestown Main Limestone (Brigantian), a thin marine carbonate unit within a lower Carboniferous basin fill otherwise dominated by fluvio-deltaic sediments and volcanics. The buildups are restricted geographically to West Lothian and Central Fife and correspond to an area of reduced subsidence, the Burntisland High. Buildup geometry and local facies mosaics reflect the relative water depth and position on the Burntisland High that, because of its slight topographical relief and more distal position with respect to the location of fluvio-deltaic systems, became an area of increased carbonate productivity and hence a locus for buildup development. Away from the Burntisland High, in the Fife-Midlothian Low, more monotonous argillaceous limestone facies, of low energy and somewhat deeper water aspect, accumulated. Buildup facies contain a diverse marine fauna and are characterized by peloidal, clotted and homogeneous micrites interpreted as predominantly microbial in origin. Two types of buildup complex occur. At Charlestown, vertically stacked, tabular banks (up to 2 m thick and 100 m wide) form the western margin of an asymmetric buildup accumulation. East of this margin a complex mosaic of isolated low relief buildups and inter-buildup sediments was deposited. Skeletal sand shoals present within these inter-buildup sediments indicate that high energy conditions prevailed during buildup growth. In contrast, at Roscobie, inter-buildup sediments are of low energy aspect and buildup geometry is domical rather than tabular. Initiated in slightly deeper and calmer water on the flank of the Burntisland High, the Roscobie buildups (up to 15 m thick and 46 m wide) accreted vertically, rather than laterally as at Charlestown, and coalesced to form an elongate ridge-shaped buildup complex.     

Origin of well-rounded gravels in glacial deposits from Brøggerhalvøya, northwest Spitsbergen: potential problems caused by sediment reworking in the glacial environment

Well-rounded gravels are described from moraine-mound complexes, diamicton forefields and modern englacial thrusts at the margins of four glaciers on the northern side of Brøggerhalvøya, northwest Spitsbergen. Their shape charcteristics are compared with modern and fossil glacigenic, modern beach and Early Weichselian beach gravels from this peninsula. The best discriminators of the well-rounded gravels have been found to be the percentage-frequency roundness histograms, the roundness mid-point and roundness range diagrams and the sphericity-roundness plots. It is concluded that the gravels have been derived by englacial thrusting from Early Weichselian or last interglacial beaches in the inner parts of the fjord and in the low level cirques when sea level reached at least 50m a.s.l. and deposited the beach gravels. The discrimination between gravel in basal diamictons, proglacial outwash and modern beaches is difficult as the reworking has resulted in little particle shape change. The potential major problem caused by reworking in the glacial environment is emphasised. especially when clast shape comparisons from modern environments to older sediments are used.     

The vertebrate fauna of the type Cromerian

The rich vertebrate fauna of the Upper Freshwater Bed of West Runton, Norfolk. England (pollen assemblage zone Cr II) is described and related to vegetational conditions based on analysis of fossil pollen and macroscopic plant remains. The general picture is of fishes associated with aquatic plants in a slow-flowing river, amphibious vertebrates living in water-side habitats, and a terrestrial fauna generally reflecting a regional mixed oak forest cover, but also including grassland voles associated with local herb-dominated communities on the river floodplain. The fossil assemblage appears to have accumulated largely from the remains of terrestrial vertebrates washed in as the river eroded its banks. A reassessment of the fossil voles indicates that only five species occur, although ten were previously described. The sparse fauna from the overlying marine gravel (zone Cr III) is also discussed. On the basis of vertebrate faunas and other evidence, sites in England and Germany arc correlated with the type Cromerian.     

Measurements of density underflows from Walensee,Switzerland*

Speed and direction of bottom currents induced by density underflow of two sediment-laden rivers were measured by oceanographic current meters in the Walensee (= Lake of Walenstadt), Switzerland. The apparently shooting flow of currents (up to 30 cm/s in this study) is suggested as an explanation for laminations in turbidite sequences. The current speed apparently stabilizes on slopes around 2°; this angle seems to correspond to the critical slope where the flow of the measured currents becomes steady. Current direction is controlled by bottom topography and direction of river inflow. Reversal of current direction observed at two sites is probably due to the underflow-induced backward motion of the overlying lake water. Underflow activity in Walensee is correlative with density peaks of the river water input. The currents are compared to Lake Mead (Southwestern U.S.) underflows and sporadic currents in some submarine canyons.     

Trace fossils from proglacial lake sediments

Trace fossils have been discovered in Middle Pleistocene proglacial lake sediments from St. Albans, Hertfordshire, England. They indicate that this environment was capable of supporting a variety of benthonic animals. The fossils are described and tentatively assigned to several invertebrate groups.     

The ice-dammed lakes of Ossian Sarsfjellet (Svalbard): their geomorphology and significance

The tidewater glacier complex of Kongsvegen/Kronebreen, at the head of Kongsfjorden in north-west Spitsbergen, has advanced rapidly several times since its Neoglacial maximum. Two such advances, 1869 and 1948, are well constrained in time and space and are widely interpreted as glacier surges. During the 1869 advance an ice-dammed lake formed on the western side of Ossian Sarsfjellet. This ice-dammed lake is associated with a thrust moraine complex. Four lake levels are identified, two of which are associated with rock-cut shorelines implying a degree of lake stability. The history of this lake, the nature of the ice dam and its relationship to the thrust moraine complex are discussed. The lake history spanning 28 to 35 years is used to assess the ice-marginal dynamics of the Kongsvegen/Kronebreen glacier. It is concluded that, contrary to previous suggestions, the rapid advance of this tidewater glacier may simply be an example of a non-climatic ice-marginal fluctuation, of the type common to tidewater glacier, as opposed to a glacier surge. A second ice-dammed lake, to the east of Ossian Sarsfjellet, formed sometime after 1869 as the ice retreated, and still exists today. This largely supraglacial lake is associated with a very different geomorphological assemblage, which has a poor long-term preservation potential. The geomorphological characteristics of the two lakes on Ossian Sarsfjellet are compared and used to discuss the problems associated with the recognition of ice-dammed lakes within the Pleistocene record. On the basis of the evidence presented here, ice-dammed lakes may be more common during deglaciation than currently suggested.