Wood Bay Research Articles

On the Billefjorden fault zone in Garmdalen, central Spitsbergen: implications for the mapping of major fault zones during geological fieldwork and for the tectonic history of Svalbard

Background The present contribution reexamines the geometry of a segment of a presumably long-lived fault in Svalbard, the Balliolbreen Fault segment of the Billefjorden Fault Zone, along which presumably two basement terranes of Svalbard accreted in the early–mid Paleozoic after thousands of kilometers strike-slip displacement. Methods We performed structural fieldwork to Billefjorden in central Spitsbergen and interpreted satellite images. Results Field observations demonstrate that the Balliolbreen Fault formed as a top-west thrust fault in the early Cenozoic and that weak sedimentary units such as shales of the Lower Devonian Wood Bay Formation and coals of the uppermost Devonian–Mississippian Billefjorden Group partitioned deformation, resulting in significant contrast in deformation intensity between stratigraphic units. For example, tight early Cenozoic folds are localized in shales of the Wood Bay Formation and contemporaneous top-west brittle–ductile thrusts within coals of the Billefjorden Group, whereas Pennsylvanian deposits of the Hultberget (and/or Ebbadalen?) Formation are simply folded into gentle open folds. Rheological contrasts also resulted in the development of décollements locally, e.g., between tightly folded strata of the Wood Bay Formation and Billefjorden Group and flat-lying, brecciated limestone-dominated strata of the Wordiekammen Formation. Despite the limited quality and continuity of outcrops in the area, the eastward-thickening character (i.e., away from the fault) of Pennsylvanian deposits of the Hultberget, Ebbadalen, and Minkinfjellet formations suggests that the fault did not act as a normal fault in Pennsylvanian times. Conclusions The study suggests that strain partitioning of early Cenozoic Eurekan contraction alone may explain the deformation patterns in Paleozoic rock units in central Spitsbergen, i.e., that Late Devonian Svalbardian contraction is not required, and that a major segment of the Billefjorden Fault Zone formed in the early Cenozoic. The present work illustrates the crucial need for interdisciplinary approaches and composite educational backgrounds in science.

Devonian–Carboniferous extension and Eurekan inversion along an inherited WNW–ESE-striking fault system in Billefjorden, Svalbard

Background The Billefjorden area in central Spitsbergen hosts thick Lower–lowermost Upper Devonian, late–post-Caledonian collapse deposits presumably deformed during the Late Devonian Svalbardian Orogeny. These rocks are juxtaposed against Proterozoic basement rocks along the Billefjorden Fault Zone and are overlain by uppermost Devonian–early Permian deposits of the Billefjorden Trough, a N–S-trending Carboniferous rift basin bounded by the Billefjorden Fault Zone. Methods We interpreted seismic reflection (also depth-converted), bathymetric, and exploration well data. Results The data show abundant Early Devonian, WNW–ESE-striking (oblique-slip) normal faults segmenting the Billefjorden Trough, and a gradual decrease in tectonic activity from the Early Devonian (collapse phase) to early Permian (post-rift phase). Early Devonian–Middle Pennsylvanian WNW–ESE-striking faults were mildly reactivated and overprinted and accommodated strain partitioning and decoupling in the early Cenozoic. This resulted in intense deformation of Lower Devonian sedimentary rocks and in the formation of bedding-parallel décollements, e.g., between the Lower Devonian Wood Bay and the uppermost Pennsylvanian–lowermost Permian Wordiekammen formations. This suggests that intense deformation within Devonian rocks in Dickson Land can be explained by Eurekan deformation alone. Eurekan deformation also resulted in the formation of WNW–ESE- and N–S- to NNE–SSW-trending, kilometer-wide, open folds such as the Petuniabukta Syncline, and in inversion and/or overprinting of Early Devonian to Early Pennsylvanian normal faults by sinistral-reverse Eurekan thrusts. WNW–ESE-striking faults merge at depth with similarly trending and dipping ductile shear zone fabrics in Proterozoic basement rocks, which likely formed during the Timanian Orogeny. Conclusions A NNE-dipping shear zone, which is part of a large system of Timanian thrusts in the Barents Sea, controlled the formation of WNW–ESE-striking Devonian–Mississippian normal faults and syn-tectonic sedimentary rocks in Billefjorden. Eurekan strain partitioning and decoupling suggest that the Svalbardian Orogeny did not occur in Svalbard.

Devonian-Carboniferous extension and Eurekan inversion along an inherited WNW-ESE-striking fault system in Billefjorden, Svalbard.

Background: The Billefjorden area in central Spitsbergen hosts thick Lower-lowermost Upper Devonian, late-post-Caledonian collapse deposits presumably deformed during the Late Devonian Svalbardian Orogeny. These rocks are juxtaposed against Proterozoic basement rocks along the Billefjorden Fault Zone and are overlain by uppermost Devonian-early Permian deposits of the Billefjorden Trough, a N-S-trending Carboniferous rift basin bounded by the Billefjorden Fault Zone. Methods: We interpreted seismic reflection (also depth-converted), bathymetric, and exploration well data. Results: The data show abundant Early Devonian, WNW-ESE-striking (oblique-slip) normal faults segmenting the Billefjorden Trough, and a gradual decrease in tectonic activity from the Early Devonian (collapse phase) to early Permian (post-rift phase). Early Devonian-Middle Pennsylvanian WNW-ESE-striking faults were mildly reactivated and overprinted and accommodated strain partitioning and decoupling in the early Cenozoic. This resulted in intense deformation of Lower Devonian sedimentary rocks and in the formation of bedding-parallel décollements, e.g., between the Lower Devonian Wood Bay and the uppermost Pennsylvanian-lowermost Permian Wordiekammen formations. This suggests that intense deformation within Devonian rocks in Dickson Land can be explained by Eurekan deformation alone. Eurekan deformation also resulted in the formation of WNW-ESE- and N-S- to NNE-SSW-trending, kilometer-wide, open folds such as the Petuniabukta Syncline, and in inversion and/or overprinting of Early Devonian to Early Pennsylvanian normal faults by sinistral-reverse Eurekan thrusts. WNW-ESE-striking faults merge at depth with similarly trending and dipping ductile shear zone fabrics in Proterozoic basement rocks, which likely formed during the Timanian Orogeny. Conclusions: A NNE-dipping shear zone, which is part of a large system of Timanian thrusts in the Barents Sea, controlled the formation of WNW-ESE-striking Devonian-Mississippian normal faults and syn-tectonic sedimentary rocks in Billefjorden. Eurekan strain partitioning and decoupling suggest that the Svalbardian Orogeny did not occur in Svalbard.

A new dipnoan species Janvierpaucidentes tuulingi gen. et sp. nov. from the Pragian (Early Devonian) of Mimerdalen, Svalbard (Norway), with an unusual dentition

A new dipnoan lower jaw from the Wood Bay Formation (Pragian) of Svalbard (Norway), preserves a partial dentary and partial toothplates referred to the new species Janvierpaucidentes tuulingi gen. et sp. nov. The more complete toothplate is elongate with three short rows of teeth but is damaged medially. A large number of dipnoans are known from the early Devonian, showing a range of dentitions. Other tooth-plated dipnoans from this time period include Diabolepis speratus, Speonesydrion iani, Tarachomylax oepiki, Tarachomylax multicostatus, Ichnomylax kurnae and Ichnomylax karatajae, and two unnamed toothplates from Vietnam. In Melanognathus canadensis, rows of teeth are located along the prearticular, which is otherwise covered in a shagreen of denticles; this denticle-dominated dentition also characterized Uranolophus wyomingensis. The dentition of Janvierpaucidentes tuulingi differs from these toothplate morphologies and is highly unusual in having the more rostral and caudal tooth rows nearly paralleling the jaw margin, with a maximum angle between the tooth rows approaching 180 degrees. In this character, Janvierpaucidentes tuulingi is more comparable to taxa such as Xylognathus macrustenus from the Carboniferous, increasing the already high disparity of lungfish dental morphology in the Devonian.

Provenance Analysis of the Andrée Land Basin and Implications for the Paleogeography of Svalbard in the Devonian

AbstractDuring the Devonian, the Svalbard Archipelago lay at low latitudes, occupying a paleogeographic position at the intersection of Caledonian and Ellesmerian orogens. Provenance analysis, including detrital zircon U‐Pb age studies, of Devonian (ca. 420–360 Ma) strata from the Andrée Land Basin, Svalbard, help reconstruct sediment sources to understand the assembly of the three basement provinces that make up Svalbard, which are presently separated by Devonian sedimentary basins and(or) faults with syn‐to post‐Devonian displacement. The studied Andrée Land Group strata, which are part of the North Atlantic's Old Red Sandstone, consist of the Early Devonian Wood Bay Formation and Middle to Late Devonian Mimerdalen subgroup. Paleocurrent indicators from Lower to lower‐Middle Devonian strata record north‐directed sediment transport. Detrital zircon U‐Pb ages indicate a prominent “Caledonian” signal and include sources from Svalbard's Northwestern and(or) Southwestern basement provinces. In Middle and Upper Devonian strata, paleocurrents and detrital zircon ages record a shift to a predominantly eastern‐northeastern provenance, likely from the uplifting Ny‐Friesland block along the Billefjorden Fault Zone. Late Ediacaran‐early Cambrian detrital zircons in the uppermost Planteryggen Formation (Frasnian) indicate extrabasinal sources possibly associated with the Timanian orogen of Northern Baltica. The combined provenance data suggest Svalbard may have already been assembled, similar to the modern block, with the Andrée Land Basin located between modern exposures of the Southwestern/Northwestern and the Northeastern basement provinces. Comparison of detrital zircon ages from Andrée Land Group strata with those from other circum Arctic Devonian strata provides constraints on Svalbard's paleogeographic position in the Devonian.

Early Cenozoic Eurekan strain partitioning and decoupling in central Spitsbergen, Svalbard

Abstract. The present study of field, petrological, exploration well, and seismic data describes backward-dipping duplexes comprised of phyllitic coal and bedding-parallel décollements and thrusts localized along lithological transitions in tectonically thickened Lower Devonian to lowermost Upper Devonian; uppermost Devonian–Mississippian; and uppermost Pennsylvanian–lowermost Permian sedimentary strata of the Wood Bay and/or Wijde Bay and/or Grey Hoek formations; of the Billefjorden Group; and of the Wordiekammen Formation, respectively. The study shows that these structures partially decoupled uppermost Devonian–Permian sedimentary rocks of the Billefjorden and Gipsdalen groups from Lower Devonian to lowermost Upper Devonian rocks of the Andrée Land Group and Mimerdalen Subgroup during early Cenozoic Eurekan deformation in central Spitsbergen. Eurekan strain decoupling along these structures explains differential deformation between Lower Devonian to lowermost Upper Devonian rocks of the Andrée Land Group and/or Mimerdalen Subgroup and overlying uppermost Devonian–Permian sedimentary strata of the Billefjorden and Gipsdalen groups in central–northern Spitsbergen without requiring an episode of (Ellesmerian) contraction in the Late Devonian. Potential formation mechanisms for bedding-parallel décollements and thrusts include shortcut faulting and/or formation as a roof décollement in a fault-bend hanging wall (or ramp) anticline, as an imbricate fan, as an antiformal thrust stack, and/or as fault-propagation folds over reactivated or overprinted basement-seated faults. The interpretation of seismic data in Reindalspasset indicates that Devonian sedimentary rocks of the Andrée Land Group and Mimerdalen Subgroup might be preserved east of the Billefjorden Fault Zone, suggesting that the Billefjorden Fault Zone did not accommodate reverse movement in the Late Devonian. Hence, the thrusting of Proterozoic basement rocks over Lower Devonian sedimentary rocks along the Balliolbreen Fault and fold structures within strata of the Andrée Land Group and Mimerdalen Subgroup in central Spitsbergen may be explained by a combination of down-east Carboniferous normal faulting with associated footwall rotation and exhumation, and subsequent top-west early Cenozoic Eurekan thrusting along the Billefjorden Fault Zone. Finally, the study shows that major east-dipping faults, like the Billefjorden Fault Zone, may consist of several discrete, unconnected (soft-linked and/or stepping) or, most probably, offset fault segments that were reactivated or overprinted to varying degrees during Eurekan deformation due to strain partitioning and/or decoupling along sub-orthogonal NNE-dipping reverse faults.

Evidence for a large-magnitude Holocene eruption of Mount Rittmann (Antarctica): A volcanological reconstruction using the marine tephra record

In Antarctica, the near-source exposures of volcanic eruption deposits are often limited as they are not well preserved in the dynamic glacial environment, thus making volcanological reconstructions of explosive eruptions extremely challenging. Fortunately, pyroclastic deposits from explosive eruptions are preserved in Southern Ocean sediments surrounding Antarctica, and the tephrostratigraphy of these sequences offers crucial volcanological information including the timing and tempo of past eruptions, their magnitude, and eruption dynamics. Here we report the results of a tephrostratigraphy and tephrochronology study focused on four sediment cores recovered from the Wood Bay area in the western Ross Sea, Antarctica. In all these sedimentary sequences, we found a well-stratified primary tephra of considerable thickness, up to 80 cm, hereafter named the Aviator Tephra (AVT). According to the characteristics of the tephra deposit and its distribution, the AVT was associated with an eruption of considerable intensity, potentially representing one of the largest Holocene eruptions recorded in Antarctica. Based on the major and trace element geochemistry and the mineral assemblage of the tephra, Mount Rittmann was identified as the source of the AVT. A Holocene age of ∼11 ka was determined by radiocarbon dating organic material within the sediments and 40Ar-39Ar dating of alkali-feldspar crystals included in the tephra. Eruption dynamics were initially dominated by hydromagmatic magma fragmentation conditions producing a sustained, relatively wet and ash-rich eruptive cloud. The eruption then evolved into a highly energetic, relatively dry magmatic Plinian eruption. The last phase was characterized by renewed efficient magma-water interaction and/or collapse of the eruptive column producing pyroclastic density currents and associated co-ignimbritic plumes. The distal tephra deposits might be linked to the widespread lag breccia layer previously identified on the rim of the Mount Rittmann caldera which share the same geochemical composition. Diatoms found in the sediments surrounding the AVT and the primary characteristics of the tephra indicate that the Wood Bay area was open sea at the time of the eruption, which is much earlier than previously thought. AVT is also an excellent tephrostratigraphic marker for the Wood Bay area, in the Ross Sea, and a useful marker for future synchronization of continental ice and marine archives in the region.

New data on Weddell seal (Leptonychotes weddellii) colonies: A genetic analysis of a top predator from the Ross Sea, Antarctica.

In this paper, we studied the genetic variability in Weddell seal from colonies in Terra Nova Bay and Wood Bay, both sites located in the Ross Sea area, Antarctica. Two mitochondrial genes and one nuclear gene, with different mutation rates, were sequenced to investigate the haplotype diversity of the colonies and to test for a possible recent expansion. Fifteen microsatellites were used to analyze their genetic structure. Sequenced genes and microsatellites were also used to estimate the effective population size of the studied colonies and the Ross Sea seal population. The Ross Sea has a high density population of Weddel seals, with an estimated effective number of 50,000 females, and 1,341 individuals for the sampling area, possibly due to its high primary production. The colonies showed high diversity (Hd > 0.90) and many exclusive haplotypes (> 75%), likely a consequence of the surprisingly high site fidelity of Weddell seals, despite the proximity of the colonies. Nevertheless, there was low microsatellite differentiation between colonies, suggesting that they are part of a single larger population. Their expansion seemed to have started during the last glacial cycle (around 58,000 years ago), indicating that the Ross Sea seal populations have been present in the area for long time, probably due to the lack of hunting by humans and terrestrial predation. As a top predator, the role of Weddell seals in the Ross Sea ecology is crucial, and its demographic dynamics should be monitored to follow the future changes of such an important ecosystem.

A new Early Devonian (Emsian) arthrodire from the Northwest Territories, Canada, and its significance for paleogeographic reconstruction

An heterostiid arthrodire, Herasmius dayi sp. nov., is described from upper Lower Devonian marine deposits of the Bear Rock Formation along the Anderson River, Northwest Territories, Canada. New elements described for the genus for the first time include the suborbital, submarginal (also new for the family Heterostiidae), the lateral shoulder girdle with posterior lateral, anterior dorso-lateral, and posterior dorso-lateral plates and possible infragnathal plate. We present a new reconstruction of the cranial region of Herasmius, previously known only from supposedly freshwater – shallow marine deposits of roughly the same age in the Wood Bay Group of Spitsbergen. The late Early Devonian fishes that are common to the Arctic region of northwestern Canada and the island of Spitsbergen in the Svalbard archipelago of Norway, the porolepiform Heimenia and the arthrodire Herasmius described here, demonstrate the existence of a barrier-free paleogeographic connection between those continental blocks by the late Early Devonian. Comparison of the entire Anderson River vertebrate fauna with other boreal faunas of similar age indicates additional paleogeographic connections north of and around the Old Red Sandstone Continent to the Baltic region, central Europe, and even to the New Siberian Islands and South China, in contrast to most current published paleogeographical reconstructions.

A revised heterostracan-based ichthyostratigraphy of the Wood Bay Formation (Lower Devonian, Spitsbergen), and correlation with Russian Arctic archipelagos

Spitsbergen shows a several kilometers thick, mostly siliciclastic Devonian sequence. In this sequence, the Wood Bay Formation represents a typical Old Red Sandstone megafacies unit of Early Devonian age (Pragian-Emsian). It outcrops in the Andrée Land Block (often wrongly designated as the “main Devonian graben”) in NW Spitsbergen. Its stratigraphy has been mostly established in two areas of this block, that is, in the Woodfjorden area in the north, and in the Dicksonfjorden-Austfjorden area in the south. A revision of the pteraspidiform heterostracan vertebrates has been carried out in both areas. Eight different fossil assemblages are defined, five for the Woodfjorden area (WA), and three for the Dicksonfjorden-Austfjorden area (DAA), that enable the correlation of the Sigurdfjellet and Kapp Kjeldsen “faunal divisions” of the lower Wood Bay Formation (in WA) with the Austfjorden Member (in DAA), and the Keltiefjellet “faunal division” of the upper Wood Bay Formation (in WA) with the Dicksonfjorden Member (in DAA). Unfortunately, pteraspids do not help with correlation between the uppermost parts of the Wood Bay Formation in the north and south of the Andrée Land Block. These results are used also for a more precise correlation with the heterostracan-bearing, Early Devonian, Old Red Sandstone series of Novaya Zemlya and Severnaya Zemlya in the Russian Arctic. They also confirm that Spitsbergen and those Russian archipelagos were elements of the Early Devonian, palaeobiogeographic Arctic Province.

The interpretation and probable dating of conversations found in Victor Campbell's field note-book, written while in a snow-cave on Inexpressible Island, Antarctica, during the winter of 1912

ABSTRACTScott's Northern Party, led by Victor Campbell, after almost a year at Cape Adare was moved south by Terra Nova. They landed at Evans Cove for five weeks’ sledging in the Wood Bay area. Bad ice-conditions prevented the vessel from returning. Campbell's party, stranded with little food and only summer equipment, faced the 1912 winter alone. For shelter they dug a snow-cave and there survived for seven months, living mainly on seals and penguins. Finally in early spring they sledged 230 miles back to Scott's party at Cape Evans. The small snow-cave provided little privacy. Authors have mentioned how Campbell divided the cave into two virtual messes, one for the ratings, the other for the officers, with the associated naval implications that conversations in one mess were not to be ‘paid attention to’ in the other. Still, at times, private exchanges were needed. Hooper describes one silent conversation between Campbell and Levick found in the latter's cave-diary, and mentions some others relating to health matters. This paper describes one drawing and nine new written conversations between Campbell, Levick and Priestley found in a field-notebook held in the Victor Campbell Collection at the Memorial University of Newfoundland. The conversations are transcribed, interpreted, and placed in the context of the life in the snow-cave. All were written during September, their last month there, and show that officers often needed to converse silently in writing and, furthermore, that the two-mess concept was not a satisfactory context for private conversations.

Late Neogene geomorphological and glacial reconstruction of the northern Victoria Land coast, western Ross Sea (Antarctica)

Abstract This study is a contribution to the reconstruction of the geomorphology and the glacial history of the northern Victoria Land coastal glaciers. High-resolution single-channel reflection seismic lines were collected in 2002 within the framework of the Italian Antarctic programme (PNRA), in Wood Bay and Lady Newnes Bay, north to Cape Washington (western Ross Sea, Antarctica). The data provide evidence of overdeepened marine subglacial valleys, more than 1 km deep and 1–2 km wide, formed along the seaward extension of the Tinker, Aviator, Fitzgerald and Icebreaker glaciers and converging into the major SW–NE ice stream system. The spatial distribution and the geometry of the seismic facies, as well as the direct correlation with the seismic sequences in the Northern Basin, are interpreted to document 1) the depositional activity of a coastal glacial system seaward of northern Victoria Land (NVL) after 18 Ma (based on the seismic correlation with the base of DSDP 273) and possibly in the early Pliocene, in coalescence with expanded ice streams coming from the south along the Drygalski Basin, possibly draining from the WAIS as documented at AND-1B in the McMurdo Sound (Naish et al., 2007, 2008, 2009), followed by 2) the development of TAM tidewater glaciers that carved sea valleys near the Victoria Land coast, onto the shelf. The transition from a dynamic thick ice sheet covering the coastal area of NVL to the NVL valley glaciers advancing and retreating up to about 100 km from the coast in the middle Pliocene would represent a significant environmental change, possibly from interglacial conditions more temperate than today and gradually cooling to a cold and dry coastal regime.

Stratigraphy of the uppermost Old Red Sandstone of Svalbard (Mimerdalen Subgroup)

Between the fjords Dicksonfjorden and Billefjorden in central Spitsbergen, Svalbard’s youngest deposits (Early Givetian to Famennian in age) of the Old Red Sandstone—the Mimerdalen Subgroup—are exposed. They form a narrow outcrop area parallel to the Billefjorden Fault Zone and overlie unconformably the multicoloured sandstones of the Lower Devonian Wood Bay Formation. Stratigraphic rank and subdivision of the succession were changed repeatedly since its first mention in 1910. Based on student work in 1996, as well as regional mapping by the authors in 1993 and 2003, the present work formalizes the stratigraphic framework of the succession. This framework has already been applied in recent geological maps. At the same time it is a continuation of the lithostratigraphic standardization carried out by the Committee on the Stratigraphy of Svalbard (1999), where only post-Devonian rocks were considered. Except for some small-pebble conglomerate layers in the Wood Bay Formation, the upper part of the Mimerdalen Subgroup contains the first coarse-grained deposits in Svalbard’s Old Red since the lowermost Devonian Red Bay Group. Faulting between its formations as well as conglomerate pebbles derived from the Lower Devonian Wood Bay Formation indicate the onset of the Svalbardian Event after the tectonic stability during the deposition of the Wood Bay Formation. The Mimerdalen Subgroup is probably the detrital fill of a small foreland basin derived from erosion during the uplift of the Ny-Friesland Block to the east of the Billefjorden Fault Zone. It was later affected by compressional tectonic movements during the Svalbardian Event.Keywords: Svalbard; geology; stratigraphy; Mimerdalen Subgroup; Devonian; Old Red.To access the supplementary material for this article, please see supplementary files under Article Tools online.(Published: 30 October 2014)Citation: Polar Research 2014, 33, 19998, http://dx.doi.org/10.3402/polar.v33.19998

Description d'une nouvelle espèce et analyse morpho-fonctionnelle du genre Doryaspis White (Heterostraci) du Dévonien du Spitsberg

Doryaspis groenhorgensis nov. sp. is a new pteraspidiform from the lower devonian of Spitsbergen. The genus Doryaspis is now considered as the most abundant pteraspidiform of the Wood Bay formation, with five described species. Moreover, the pteraspidiform diversity of this formation has been under rated all along the XXth century. A morpho-functional analysis of the Doryaspis generic characters (e.g. flat dorsal shield, ventral pseudorostrum, long cornual plates) allows to consider two possible mode of life. However, none of the pelagic or benthic mode of life is better supported than the other. The same analysis introduce some interpretative hypothesis on histology and moving of the Pteraspidiformes. The Pteraspidiformes diversity of Spitsbergen is important for further Devonian circum-arctic comparisons (e.g. siberian platform).

A trace fossil assemblage from fluvial Old Red deposits (Wood Bay Formation; Lower to Middle Devonian) of NW‐Spitsbergen, Svalbard

From the fluvial Old Red Sandstone (ORS) of the Lower to Middle Devonian Wood Bay Formation (NW-Spitsbergen), a diverse trace fossil assemblage, including two new ichnotaxa, is described: Svalbardichnus trilobus igen. n., isp. n. is interpreted as the three-lobed resting trace of an early phyllocarid crustacean (Rhinocarididae). Cruziana polaris isp. n. yields morphological details that point towards a trilobite origin. This occurence of presumably marine trace makers in a fluvial red bed sequence raises the question of whether we are dealing with marine ingressions that are not sedimentologically expressed, with homeomorphy, or with an adaptation of marine groups to non-marine environments.

The genus Doryaspis White (Heterostraci) from the Lower Devonian of Vestspitsbergen, Svalbard

ABSTRACT The present study of the genus Doryaspis (Heterostraci, Pteraspidiformes), based on new material from the Wood Bay Formation (Lower Devonian) of Vestspitsbergen, includes a morphological description of a new species, Doryaspis arctica, sp. nov., the revision of the type species of the genus, Doryaspis nathorsti, and the description of its first complete caudal fin. From these new data, some morpho-functional considerations are outlined. A phylogenetic analysis, based on 30 morphological characters and performed to answer the question of the position of Doryaspis within the Pteraspidiformes, suggests that Doryaspis is most closely related to Drepanaspis.

Facies analysis of the old Red Sandstone of Spitsbergen (Wood Bay Formation): Reconstruction of the depositional environments and implications of basin development

The object of this paper is to provide a facies guide that helps subsequent workers recognizing different facies and palaeoenvironments of the terrestrial old Red Sandstone exposed in central N Spitsbergen. Sediments of the Early Devonian Wood Bay Formation represent continental molasse deposition under arid to semi-arid climatic conditions in three main depositional environments (rivers, alluvial plains, perennial lakes) represented by characteristic lithologies, sedimentary structures and microfacies. River channel deposits, consisting of conglomerates, very coarse-to very fine-grained sandstones and sandy siltstones are generally arranged in successive fining-upward sequences marked by specific sedimentary structures in a particular order. The sediments reflect the bed, mixed and suspended load of low sinuosity braided to high sinuosity meandering rivers. Adjacent overbank areas (levees, crevasse splays) and extensive alluvial plains are represented by reddish-brown, fine-grained sandstones to sandy siltstones and silty mudstones. The sediments are the accumulated, mixed and suspended load of floodwaters, which recurrently inundated the lowlands. Various lithofacies types, facies associations and sequences reflect the local formation of palaeosols, ephemeral flood lakes and boggy areas with persistent high water tables. Multicoloured, calcareous successions and single lime-stone beds intercalated in the red beds represent the depositional products of perennial, low relief, low-energy lakes, which developed in topographic depressions of the alluvial plains. The sediments reflect deposition in deep-water, littoral and palustrine sub-environments, forming regressive, shallowing-upward sequences in the central lake areas. The overall arrangement of the various facies reflects a terrestrial basin that developed from a steep-sloped, high-energy, river-dominated molasse trough into a level, lowenergy coastal plain, marked by broad mud flats and the formation of extensive perennial lakes.

Aquatic Humic Substances in Pack Ice-Seawater-Sediment System

Humic substances were isolated from samples of pack ice, sea water and sediments collected in the Gerlache Inlet and Wood Bay (Antarctica). The content and structures of the in-ice dissolved humic substances (DHS) and particulate humic substances (PHS) were determined in samples of cores, in the water column sampled under the pack ice, and in the water column and in sediments when sea ice was absent. The organic matter content of ice cores shows that the pack ice behaves as an organic matter “tank”. The humification process appears to proceed in the pack ice in which the phytoplanktonic material is trapped during its formation. The concentrations of humic substances isolated from surface seawater sampled under the pack ice layer and when the ice is absent are constant in time. The absence of any increase in humic substance content in surface water and along the water column, when the ice has melted, may be explained by the different salinity values of the ice (from 6 to 20‰) and of the seawater (34‰), which determine an increase in the sedimentation process rate. This hypothesis is confirmed by fulvic acid/humic acid ratios in sediments that are higher than those found for sediments collected in Antarctic areas where the ice is always absent.

Antarctic scallop ( Adamussium colbecki ) spatial population variability along the Victoria Land Coast, Antarctica

Along the Victoria Land Coast, the population structure of the Antarctic scallop (Adamussium colbecki) was studied in McMurdo Sound (New Harbor), Terra Nova Bay, and Wood Bay, on a latitudinal span of 3 degrees. At a large spatial scale, most relevant differences between the scallop populations are linked to their depth distributions. The McMurdo and Wood Bay populations show a shallower bathymetric distribution with maximum abundance between 5 and 15 m depth. In contrast, inside Terra Nova Bay, at sites with similar near-shore bathymetric profiles, the maximum biomass is found between 40 and 70 m. This difference can be related to the different ice-cover persistency characterising these two areas, being less at Terra Nova Bay than in the other localities. Differences arise also in the reproductive period: at McMurdo, it seems to occur early in the austral spring, while at Terra Nova Bay, mature females are observed at the beginning of February. Also at a small scale, in sites only a few miles from each other, the population structures inside Terra Nova Bay and Wood Bay vary in terms of abundance and size frequency distribution, suggesting various environmental and biological constraints. Among environmental factors, bottom features (slope, sediment grain size, organic content) and water-column food supply during the summer months may be considered. In addition, as Adamussium is preyed upon by starfishes and fishes, its abundance and population structure may be affected by predators and their abundance.

Microalgal Communities of the Sea Ice, Ice‐Covered and Ice‐Free Waters of Wood Bay (Ross Sea, Antarctica) During the Austral Summer 1993 – 94

Abstract. During the austral summer 1993 – 94, microalgal density and biomass were investigated in the sea ice, in the underlying water column, in the melt water and during the formation of the sea ice. Of the 96 taxa identified, 59 were diatoms and 32 were dinoflagellates. Among the remaining five species, Pseudopleurochloris antarctica was very abundant both in the sea ice and in the ice‐free waters. Cell densities and biomass of microalgae were higher in the bottom of the sea ice and during the formation of the ice than in the seawater, and diatoms were the dominant group at higher microalgal biomass. Among these, Entomoneis kufferathii, Chaetoceros dichaeta and Fragilariopsis species were the most common taxa.