Peter H. von Bitter

Constraints on Pennsylvanian glacioeustatic sea-level changes using oxygen isotopes of conodont apatite

Conodonts from U.S. Midcontinent cyclothems were studied for oxygen isotopes in order to constrain Pennsylvanian glacioeustatic sea-level fluctuations. Pennsylvanian deposits of the Midcontinent United States are composed of cyclic alternations of thin transgressive limestones, offshore gray to black phosphatic shales, and thick regressive limestones, a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds. Glacioeustatic sea-level fluctuations are considered the primary cause for the formation of these cyclothems. Oxygen isotope analyses of conodont apatite from the black (20.1 ± 0.5‰, Vienna standard mean ocean water [VSMOW]) and gray shale units (20.5 ± 0.5‰, VSMOW) show lowest average δ 18 O values, whereas conodont elements from the regressive (21.0 ± 0.3‰, VSMOW) and transgressive limestone units (21.1 ± 0.6‰, VSMOW) are enriched in 18 O. The maximum change in δ 18 O of conodonts from the black shale and carbonate units from individual cyclothems is 1.7‰. The 1.7%c difference in δ 18 O compares relatively well to Pleistocene interglacial-glacial changes in δ 18 O of equatorial surface-dwelling foraminifers and suggests that Pennsylvanian glacioeustatic sea-level changes may have been of comparable amplitude. However, since the Pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record, Pennsylvanian glacioeustatic sea-level changes were probably larger than the 120 m fluctuations recorded for the Pleistocene glaciations.

Chemosynthesis; an alternate hypothesis for Carboniferous biotas in bryozoan/microbial mounds, Newfoundland, Canada

Fossil tubes, stressed high-abundance low-diversity faunas, and abundant, low-temperature, hydrothermal mineralisation occur in Lower Carboniferous bryosoan/microbial carbonate mounds in southwestern Newfoundland, Canada. These occurrences, set in a rift-valley setting that was tectonically active during the Carboniferous, were previously regarded as marginal marine deposits laid down in subtidal, schisohaline environments adjacent to a rocky shoreline. We suggest that they may, instead, have formed by chemosynthetic processes at low temperature marine vents at a depth of 100 m, or greater

Eramosa Lagerstätte—Exceptionally preserved soft-bodied biotas with shallow-marine shelly and bioturbating organisms (Silurian, Ontario, Canada)

The middle Silurian Eramosa Lagerstatte of Ontario, Canada, preserves taxonomically and taphonomically diverse biotas including articulated conodont skeletons and heterostracan fish, annelids and arthropods with soft body parts, and a diverse marine flora. Soft tissues are preserved as calcium phosphate and carbon films, the latter possibly stabilized by early diagenetic sulfurization. It is significant that the biotas also include a decalcified, autochthonous shelly marine fauna, and trace fossils. This association of exceptionally preserved and more typical fossils distinguishes the Eramosa from other Silurian shallow-marine Lagerstatten, such as the Waukesha Lagerstatte, and suggests that the Eramosa is not the product of exceptional preservation in an atypical environment, a bias claimed for many post-Cambrian Lagerstatten. The Eramosa Lagerstatte may provide a more reliable, balanced measure of what has been lost from the Silurian fossil record.

Apparatus composition and structure of the Pennsylvanian conodont genus Gondolella based on assemblages from the Desmoinesian of northwestern Illinois, U.S.A.

Gondolella pohli new species assemblages, from the Desmoinesian of Illinois, confirm that the initial apparatus reconstruction of the conodont genus Gondolella was incomplete and support later reconstructions based on discrete elements. Gondolella pohli is the first species of a biostratigraphically important conodont genus to be based primarily on assemblages and to be placed within a known phylogeny. The 43 assemblages confirm the presence of seven distinct element types in the Gondolella apparatus and permit the reconstruction of each of these to a greater degree than previously possible. Because the assemblages are probably all fecal, the apparatus of the closely related Neogondolella is used to interpret the apparatus plan—the position and identity of the 15 elements—single pairs of Pa, Pb, M, Sb 1 , and Sb 2 elements, two pairs of Sc elements, and an unpaired bilaterally symmetrical Sa element in the Gondolella apparatus. Using the similarity of the latter to the apparatuses of the better known ozarkodinids, we infer a three-dimensional fanlike apparatus architecture for the prioniodinid Gondolella. Gondolella is apparently restricted to the Pennsylvanian and probably evolved in the Early Pennsylvanian from the Idioprioniodus-Embsaygnathus lineage by loss of the Pa element posterior process and by remodelling of the other apparatus elements. Some species in the Idioprioniodus-Gondolella lineage are atypical among prioniodinids in having developed a Pa element platform; the lineage is also noteworthy because both ancestor and descendant inhabited low-energy, low pH environments during the Pennsylvanian.

Vogelgnathus Norby and Rexroad (Conodonta): new species from the Lower Carboniferous of Atlantic Canada and northern England

Four new species are assigned to Vogelgnathus Norby and Rexroad because of the close similarity of their Pb and ramiform elements to those of the type species, V. campbelli (Rexroad). Recognition of the four new species requires that the generic diagnosis, based almost exclusively on the morphology of V. campbelli , be modified, chiefly to accommodate greater variation in Pa element morphology. Vogelgnathus dhindsai n. sp., V. gladiolus n. sp., V. kyphus n. sp., and V. pesaquidi n. sp. all possess abbreviated, carminiscaphate Pa elements. Spathognathodus postcampbelli Austin and Husri is reassigned to the genus. The origins of Vogelgnathus are uncertain but V. gladiolus first appeared in the early Visean and gave rise to V. pesaquidi . The latter species appears to represent the rootstock from which V. kyphus, V. campbelli , and V. dhindsai evolved. Vogelgnathus postcampbelli evolved from V. campbelli during the late Visean. Vogelgnathus campbelli and, to a lesser extent, V. postcampbelli have a wide geographic distribution; the four new species, however, are currently known only from Atlantic Canada, northern England, and southwest Scotland.

Conodonts of the Windsor Group (Lower Carboniferous), Magdalen Islands, Quebec, Canada

Lower Carboniferous (Visean-?early Namurian) conodonts, and some of their variably complete reconstructed apparatuses, are described from cyclic marine carbonates, associated with evaporites and mud rocks, of the Windsor Group, Magdalen Islands, Quebec, Canada. The conodont fauna includes Clydagnathus windsorensis, Cavusgnathus unicornis, Taphrognathus transatlanticus, Hindeodus cristula, Hindeodus? scitulus, Vogelgnathus campbelli, Ozarkodina laevipostica, Mestognathus bipluti, Mestognathus spp., Spathognathodus ? n. sp. A, and Apatognathus spp.

Loch Macumber (early Carboniferous) of Atlantic Canada

Following the Acadian Orogeny, Atlantic Canada accommodated several, large, relatively deep lakes within a wrench-fault basin complex called the Maritime Basin. Late Devonian and Tournaisian lakes were hydrologically open, shallow to deep, mainly fresh water bodies. Middle Visean lakes, here collectively called Loch Macumber, were closed, deep, and meromictic. Their deposits comprise the first and thickest of five sequences in the Maritime Basin. Salinity in the loch increased with time from restricted marine or penesaline, to saline. Basin-centre facies consist of a thin, but extensive, sheet of black, peloidal laminated lime mudstones and an overlying thick evaporite complex. The carbonate sheet grades laterally into both laminated to thinly bedded marlstones, siliciclastic sandstones, and microbial, biocementstone mounds. Laminae consist of alternating carbonate and either silty carbonaceous shale or siliciclastic clay and silt. The mudstone and marlstone are locally interbedded with siliciclastic and carbonate turbidites, resedimented (?deep water) breccias, and olistostromes.Seasonal changes in anoxia and/or carbonate production produced rhythmic laminae of carbonate and carbonaceous shale. Carbonate grains consist of silt-sized microbial clots and rare arthropod carapaces and brachiopod shells. The mounds originated as tufa precipitated around subaqueous hydrothermal springs that supported chemosynthetic communities. Resedimentation processes including incipient brecciation, sliding, slumping, debris flows, and turbidity currents were common. The mounds trapped hydrocarbons from the surrounding laminite and sulphides from underlying hydrothermal vents. Increasing salinity with time resulted in sulphate and chloride precipitation that filled the basins and ended the life of Loch Macumber. After the deposition of thick evaporites the topography became less accentuated, the seas less saline, and the faunas more normal marine.

Deep-basin/deep-water carbonate-evaporite deposition of a saline giant: Loch Macumber (Visean), Atlantic Canada

The Carboniferous saline giant of Atlantic Canada is approximately 500 m thick and extends over an area of 250×103 km2. It consits of three lithologies: 1. a relatively thin (usually less than 5 m) extensive carbonate sheet containing buildups, 2. an overlying thick (up to 400 m) evaporite complex of sulphates and chlorides, and 3. wedge-shaped units of conglomerate, breccia, and sandstone (up to 200 m). The latter interfinger with the preceding lithologies but locally may underlie the carbonate sheet. The basal carbonate occurs mainly as fine, laminar couplets of alternating peloidal grainstones and bituminous films; these pass laterally into peloidal marlstones and mounds. Laminites and marlstones have incipient brecciation, recumbent folds, siliciclastic and carbonate turbidites, rubble, and olistostromes. Fossils are rare. They are restricted in space to the basal decimeter and in diversity to conodonts and crustaceans. ANereites ichnofauna occurs at one locality. Mounds consist mainly of turbid fans of fascicular-optic calcite and botryoids of laminated calcite. Their fauna shows low diversity but high density of some species; tube worms and microbial growths are noteworthy. The overlying evaporites are mainly anhydrite with lateral and vertical transition into halite and potash. Siliciclastic sediments thicken toward boundary faults. Both the base and top of the giant are unconformities, the former abrupt, the latter karstic.The basal carbonate accumulated subaqueously in deep, physically and chemically stratified water. Initially, the desert floor of the complex rift basin was below ambient sea level. After catastrophic submergence, basal waters were at first dysaerobic and restricted marine, but changed to anoxic and pene- to hypersaline as the water column became stratified. Its sedimentary record corresponds to a giant, meromictic, saline lake — Loch Macumber. The laminite records either seasonal changes in rainfall and temperature, or episodic storms punctuating normal chemical sedimentation. Sulphate-reducing bacteria fed on terrestrial organic matter preserved in anoxic bottom water, and precipitated peloidal calcite. Concentrations of bacteria over hot springs may also have supported chemosynthetic organic communities and precipitated petroliferous and sulphide-rich mounds. Siliciclastic rocks increase toward basin margins. Locally steep depositional surfaces caused mass movements of sediment down basin margins. A long term increase in salinity resulted in precipitation of initially corroded and subsequently euhedral crystals of gypsum. Thick sulphates and chlorides followed. Sedimentary rock of Loch Macumber records topographic filling of a deep rift basin. Isostatic analysis suggests that both depth of the subaerial desert basin and initial water depth after submergence were considerably less than the preserved thickness of the saline giant. Its record corresponds closely to that expected from Schmaltz’s model of deep-basin/deep-water carbonate-evaporite deposition.

Jaw-bearing polychaetes of the Silurian Eramosa Lagerstätte, Ontario, Canada

Abstract. The Wenlock (middle Silurian) Eramosa Lagerstätte of the Bruce Peninsula, Ontario, Canada, is becoming known for its rich and diverse faunas, different preservational styles, and a combination of soft-body preservation associated with shelly body and trace fossils. Sampling for scolecodonts—the jaws of polychaete annelids—has yielded unique material. Hindenites parkheadensis new species is described from abundant specimens, including apparatuses, from a monospecific fauna that has allowed the complete dorsal maxillary apparatus to be reconstructed. The new species was recovered by acid digestion of carbonates, which are interpreted as having been deposited in shallow, marginally marine environments; the species may become a useful paleoenvironmental indicator, and the occurrence of Hindenites at Park Head, Ontario, is the first record of the genus outside of Baltoscandia. Bedding-plane material from Wiarton, Ontario, reveals a more diverse fauna of seven to nine additional polychaete taxa, most belonging to Kettnerites and Oenonites. Strata at Wiarton are interpreted as having been deposited in environments with good water circulation and open-marine conditions. The faunal composition of Eramosa polychaetes varied between localities of the Lagerstätte outcrop belt, supporting previous interpretations of differences in environment and/or taphonomic history. The relative abundance of scolecodonts suggests that jaw-bearing polychaetes played a significant role in the biotas that are now preserved in the Eramosa Lagerstätte. Moreover, the results underpin the notion that different polychaete species had variable environmental preferences and tolerances during the Silurian, and that polychaetaspids and paulinitids formed two of the most common and widely distributed families.

Carbonate mud flows and other indicators of excess pore-fluid pressure in the Macumber Formation (Lower Carboniferous, Viséan) at Ingonish, Nova Scotia, Canada

The Ingonish area of northern Nova Scotia offers the most extensive exposure of the Macumber Formation, the basal carbonate unit of the Lower Carboniferous (Middle Viséan) Windsor Group of Nova Scotia and New Brunswick. The area also shows tectonic-free sedimentary characteristics of this unit. The formation consists of two principal lithologic units, a basal, black, earthy, carbonaceous limestone normally about 0.5 m thick and a thinly stratified, peloidal dolomudstone up to 17.5 m thick. At Burke Head, the dolomudstone is cut by at least 25 massive tufa mounds, elongated in cross-section and intersecting their surrounding strata by rising northeastward at angles of 15 to 25 degrees. At east Ingonish Island the basal unit is anomalous in being both dolomitized and thicker (5 m); there, both units are cut by at least 20 smaller massive tufa mounds. The mounds at both localities formed over deep-water hydrothermal vents, i.e., marine hot springs; the fossils of abundant chemosynthetic tubeworms surround the lower mounds on east Ingonish Island. The Macumber Formation overlies Horton Group braided-stream facies sandstones, and presumably underlies nearby, thick gypsum deposits of the Windsor Group.Features in the formation indicating excess pore-fluid pressure include voluminous vugs and widespread subaqueous sediment flows. Miniature pockmarks, sedimentary volcanoes, and shafts show the release of small quantities of pore fluids. Larger quantities of pore fluids exited through tufa mounds and geyser-like shafts. The pressure generated mudflows; eruption of pore fluids brecciated some of their flanks.The general environment of rift tectonics was conductive to active hydrology. The seasonal semi-arid climate caused changes in pore-fluid pressures, due to episodic aqueous and sedimentary loading of basin floors. Igneous activity, either at the same time or before deposition of the Windsor Group, created significant geothermal gradients to drive hydrothermal circulation and increase pore-fluid pressures.Textures and structures of the Macumber Formation in the Ingonish area are due to syndepositional processes, driven by initial, high pore-fluid pressures.