Ron K. Pickerill

Commentary: The ichnotaxa Palaeophycus and Planolites: Historical perspectives and recommendations

Planolites, although strictly a junior synonym of Palaeophycus, can be retained as a valid ichnotaxon on the basis of stability of nomenclature. As emended by Pemberton and Frey (1982) and consistently adopted by later authors, Planolites is diagnosed primarily on the basis that it is an unlined simple burrow, whereas Palaeophycus is a lined burrow. Other ichnotaxobases and ethological considerations are, without exception, subordinate to this directive.

Modern Perspectives on the Teredolites Ichnofacies: Observations from Willapa Bay, Washington

Abstract This study details occurrences of Teredolites ichnocoenoses from modern bay-margin settings in Willapa Bay, Washington. In particular, the paper scrutinizes in situ log-grounds from two intertidal zones situated immediately seaward of low-lying, supratidal, forested marshlands that are fed by small streams. Vestiges of remnant marshes and streams are preserved on intertidal flats as in-situ roots, broken stumps, strewn logs, abundant organic detritus, and organic sandy mud. Xylic material and organic sediment were deposited in the supratidal marshes: tide and wave processes truncated the swamps, exposing in situ tree-root networks and the lowermost supratidal sediments. Stream and swamp deposits overlie and incise older Pleistocene strata. Both units are overlain by discontinuous, modern intertidal deposits. The intertidally exposed stumps and logs support a diverse community of animal and plant life. Boring organisms, encrusters, and refugium seekers are found on and within the xylic substrates. Some encrusting animals and all of the boring fauna produce traces that are comparable to ichnofossils reported by palichnologists. Wood-boring traces reported in this study are similar morphologically to the ichnogenera Caulostrepsis, Entobia, Meandropolydora, Psilonichnus, Rogerella, Teredolites, Thalassinoides, and Trypanites. Most of these ichnogenera have not been reported from rock-record examples of the Teredolites ichnofacies. The stratigraphic and environmental significance of the reported (modern) locales is consistent with previous studies that associate Teredolites ichnofacies with base-level rise in marginal-marine environments. At Willapa Bay, bored xylic media form a coeval surface with adjacent, burrowed firmgrounds as well as softgrounds.

Cretaceous Nonmarine Trace Fossils from the Hasandong and Jinju Formations of the Namhae Area, Kyongsangnamdo, Southeast Korea

Nonmarine strata of the Cretaceous Hasandong and Jinju formations of the Sindong Group of the Namhae area, Kyongsangnamdo, southeast Korea, contain relatively diverse and abundant ichnofaunas including domichnia, fodinichnia, pascichnia, and repichnia. These ichnofaunas are systematically described herein and three ichnocoenoses, namely the Skolithos, Palaeophycus, and Chondrites ichnocoenoses, are defined based on their paleoenvironmental occurrence. The Skolithos ichnocoenose characterizes tabular laminated sandstone facies deposited on fluvial channel levées. It is dominated by infaunally produced ichnotaxa, particularly Skolithos magnus Howell, Planolites montanus Richter and Chondrites isp. type A, with reduced numbers of Skolithos verticalis (Hall) Taenidium barretti (Bradshaw) and rare examples of Circulichnus montanus (Vyalov), Cochlichnus anguineus Hitchcock, Helminthopsis abeli Książkiewicz, Helimthopsis hieroglyphica Wetzel and Bromley, Laevicyclus isp., Planolites beverleyensis (Billings), Skolithos isp., Spirodesmos isp., Thalassinoides suevicus (Rieth), and rhizoliths. The Palaeophycus ichnocoenose characterizes floodplain environments and occurs in purple mudstones and associated massive sandstone facies of crevasse-splay deposits and dark gray to green shale facies of abandoned channels. Palaeophycus tubularis Hall and Planolites montanus Richter are the most characteristic ichnotaxa, while Beaconites coronus (Frey, Pemberton and Fagerstrom), Planolites annularius Walcott, Skolithos magnus Howell, Thalassinoides paradoxicus (Woodward), and sauropod and ornithopod tracks also occur but in reduced numbers. The Chondrites ichnocoenose occurs in dark gray to black mudstones deposited in marginal lacustrine environments. It is dominated by Chondrites isp. type B. with associated Beaconites antarcticus Vyalov, Helminthopsis hieroglyphica, Palaeophycus tubularis, Skolithos magnus, Taenidium barretti, and Torrowangea rosei Webby. The three ichnocoenoses recognized herein cannot be satisfactorily assigned to currently defined nonmarine ichnofacies, suggesting that existing models of such ichnofacies are in need of additional refinement.

Taxonomic review of the ichnogenus Helminthopsis Heer 1877 with a statistical analysis of selected ichnospecies

The ichnogenus Helminthopsis Heer 1877 is a relatively simple, unbranched, horizontal, internally unstructured, pre‐ or post‐depositional burrow, or trail, that follows an irregularly sinuous or more commonly an irregularly winding or meandering course. The geometric variation in course, its most significant ichnotaxobase, is invariably complex and has resulted in considerable taxonomic disorder, particularly at the ichnospecific rank. This confusion is compounded by the fact that no diagnoses, and, or, detailed descriptions of several of its historically defined ichnospecies were provided and for other ichnospecies such considerations are ambiguous. In view of these problems, the validity of the 21 previously described ichnospecies is reviewed and each taxonomically reassessed. We suggest that of these ichnospecies, H. regularte Crimes and Crossley 1991 is best regarded as a synonym of Cochlichnus anguineus Hitchcock 1858; H. irregularis (Schafhautl 1851), H. antigua Sacco 1888 and H. curvala (Katto 1960...

Geochemistry of Upper Cambrian-Lower Ordovician black shale along a northeastern Appalachian transect

Samples of Upper Cambrian to Lower Ordovician black shale, collected in a transect extending across the Canadian Appalachians from the Humber Zone in Quebec, the Gander and Avalon Zones in New Brunswick, to the Meguma Zone in Nova Scotia, were analyzed for 40 elements, including rare earths. These geochemical data lend support to previously established plate-tectonic models of the region. They also provide information on provenance and depositional environments of sediments that are too fine grained for more traditional mineralogical and sedimentological studies. Generally high Al 2 O 3 contents, high Al/Ti values, and steep rare-earth-element (REE) distribution patterns are consistent with a continental-margin depositional setting for shale from the Humber and Meguma Zones on opposite sides of the Iapetus ocean. Generally higher K 2 O contents, lower La/Th values, and lower absolute REE abundances distinguish shale of the Humber Zone deposited on the Laurentian margin from that deposited in the Meguma Zone on the Gondwanan margin. High La/Th values indicate a similar Gondwanan source for shale from both the Meguma and Avalon Zones. Shale from the Gander Zone contains less Al 2 O 3 at increasing distances from its boundary with the Avalon Zone. Low Al/Ti and less fractionated REE distribution patterns suggest a greater component of volcanic detritus in shale of the Avalon and Gander Zones. The presence of distinctive Balto-Scandian signatures (high U, V, and Mo) in shale of the Avalon and northwestern Gander Zones is possibly related to deposition in isolated peri-Gondwanan back-arc basins during a highstand of sea level.

The Miocene palaeobathymetry and palaeoenvironments of Carriacou, the Grenadines, Lesser Antilles

Carriacou, a small island in the Grenadines, Lesser Antilles, has a Cenozoic rock record that has been important in interpreting the geologic history of the Southern Lesser Antilles Arc Platform. The Lower-Middle Miocene sedimentary succession of the southeast and east coasts, consisting of the Belmont, Kendeace, Carriacou and Grand Bay formations, has been interpreted as a shallowing-upward sequence from turbidite basin to nearshore?/beach? palaeoenvironments. An earlier interpretation of the Belmont Formation as having been deposited in shallow water is at variance with the turbiditic nature of the succession; the included fossils are considered allochthonous. However, an interpretation of the Grand Bay Formation as deep water is supported by multiple lines of evidence, including sedimentology (turbidites), ichnology (autochthonous association of burrows typical of deep-water environments) and palaeontology (terrestrial, planktic, and shallow and deep water benthic species mixed together). The minimum depth of deposition of the Grand Bay Formation was 150–200 m. This suggests that the (unseen) contact between the Carriacou and Grand Bay formations is either an unconformity, formed following rapid deepening of the basin, or a fault, the Grand Bay Formation being deposited in a separate basin from the shallowing-upwards Belmont-Kendeace-Carriacou formations, against which it is now juxtaposed

Large, Robust Cruziana from the Middle Triassic of Northeastern British Columbia: Ethologic, Biostratigraphic, and Paleobiologic Significance

Abstract Large (up to 9.5 cm wide) and robust Cruziana ichnofossils are present in the Middle Triassic (Ladinian) Toad and Liard formations in northern British Columbia, Canada. These trace fossils are the first definitive occurrences of large Cruziana from post-Paleozoic marine strata. These traces, assigned to a new ichnospecies (Cruziana seilacheri), are similar in many respects to traces from the Lower Paleozoic, including the Cambrian ichnotaxon Cruziana rusoformis and the Ordovician ichnotaxon Cruziana furcifera. The morphology and orientation of scratchmarks in these traces suggest that they may have been constructed by either stomatopod or decapod crustaceans. The similarity of the Toad-Liard Cruziana to lower Paleozoic forms and their presence in post-Paleozoic marine rocks demonstrate that care should be taken when utilizing these traces as indicators of either Paleozoic deposition or a specific tracemaker.

Resin Cast of Modern Burrows Provides Analogs for Composite Trace Fossils

Abstract A neoichnological resin cast of modern burrows from a mudflat at Willapa Bay, Washington, reveals much of the architecture of the infaunal community present locally within sediments of this mudflat. The cast structures comprise Psilonichnus-, Skolithos-, Trichichnus-, Chondrites(?)-, Planolites-, Palaeophycus-, and Arenicolites-like burrows. The range of behaviors represented by these structures cannot be classified into an archetypal (Seilacherian) ichnofacies. The resin cast contains many coeval, composite burrows that may reflect certain commensal relationships. Notable composite associations include: (1) siphon shafts of Mya arenaria that are connected to and descend from crab domiciles; (2) an example of a pair of infaunal Mya arenaria that share a single siphonate shaft; (3) abundant Heteromastus burrows that connect to crab and bivalve burrows; and, (4) Nereis burrows that are connected to crab domiciles. It is suggested that such contemporaneous relationships, if passed into the fossil record, might be misinterpreted as representing tiering or faunal succession. The reported observations provide a new perspective on the potential significance of interpenetrating trace fossils and complex ichnofabrics.

A NOVEL CONTEMPORARY FLUVIAL ICHNOCOENOSE: UNIONID BIVALVES AND THE SCOYENIA–MERMIA ICHNOFACIES TRANSITION

Abstract A transitional Scoyenia–Mermia ichnocoenose from the Saint John River, Fredericton, New Brunswick, Canada, is dominated by elements of the Mermia ichnofacies, with traces comparable to Curvolithus, Helminthopsis, Gordia, Spirophycus, and Lockeia. Environmental characteristics are, however, more typical of the Scoyenia ichnofacies, with an emersion event providing conditions favorable to viewing traces preserved in a sand-softground substrate. Observation of in situ trace-making behavior allowed traces to be attributed to their progenitors, which include unionid and sphaeriid bivalves. An omission assemblage of vertebrate tracks also was present, comprising gull, raven, and mink. Oichnus-like borings were observed in some unionid shells. The shallow-tier trace assemblage created in a high-energy river channel may be expected to have a poor preservational potential, with loss of trace definition observed at the water margin during emersion and subsequent deterioration by eolian sediment transport.

Shallow subtidal sediments of Soudleyan (Caradoc) age in the Berwyn Hills, North Wales, and their palaeogeographic context

Soudleyan rocks in the Berwyn Hills, North Wales, consist essentially of marine mudstones and thin siltstones and fine sandstones, but also include interbedded pyroclastic formations which are at least partly subaerial in origin. In the marine sediments the association of current and wave ripples, small steep sided channels, rare desiccation cracks plus a Planolites , Skolithos, Teichichnus and Cruziana -dominated ichnofauna associated with shallow marine benthic brachiopod-dominated shelly assemblages suggests a shallow subtidal origin with water depths of less than 25 m. Four lithofacies (regular layered, irregular layered, mottled and homogeneous) are differentiated on the basis of their geometry, lithology, sedimentary and biogenic structures and associated faunas, and are described in detail. Comparable subtidal facies extend northwestwards across North Wales into the Arenig-Bala and Snowdon-Tremadoc districts and southeastwards into South Salop, with slightly deeper water argillaceous facies in the intervening Shelve and Breidden Hills areas. Southwest of the Berwyn Hills offshore mudstones are present in the Corris-Cader Idris and Builth-Abbey Cwmhir areas and clastic turbidites in the Cardigan area. A regional palaeogeography for the Soudleyan of the Welsh Basin is proposed.