Lower Fauna Research Articles

Brachiopod faunal changes across the Devonian–Carboniferous boundary in NW Sahara (Morocco, Algeria)

Abstract Based on previous systematic studies of productid, rhynchonellid and spiriferid brachiopods from NW Sahara (Morocco and Algeria), we recognize three successive faunas near the Devonian–Carboniferous boundary. A ‘Lower Fauna’, late Famennian in age [IV(?)-V and lower VI(?) Zones], and an ‘Upper Fauna’, early Tournaisian in age, are present in southern Morocco (Assa, Akka, Zemoul areas) and in Algeria, Timimoun area. A third ‘Intermediate Fauna’, with few taxa, and differing according to the areas, is identified in southern Morocco. Northwards, in Tafilalt–Ma'der basins, rare brachiopods, found above a ‘Hangenberg Black Shale’ equivalent, are in spite of taxonomic differences related to the ‘Upper Fauna’. This important renewal of faunas could be in relation to the main lithological variations.

Abstract: Integrated Paleoecology and Marine Vertebrate Fauna of the Stone City Formation (Middle Eocene), Brazos River Section, Texas 

ABSTRACT Abundant marine vertebrate faunas, including sharks, rays, teleosts, and reptiles, have been collected from two horizons in the Middle Eocene (Claiborne) Stone City Formation of southeast Texas. Extensive collecting, both surface and bulk, and recent advances, especially in the study of otoliths and foraminifera, provide for additional evaluation of paleoecological parameters. Otolith-based teleosts are dominated by neritic taxa such as sciaenids and ophidiids, while skeletal-based teleosts include catfish, barracuda, mackerel, and gar. Selachians include sand, tiger, and catsharks as well as rays and sawfish. Least common are reptiles, represented by crocodiles and turtles. Vertebrate diversity is 50 taxa, the richest marine fauna yet recorded from the Gulf Coast Middle Eocene. Vertebrates were collected from the top of the Main Glauconite bed and a thin lag zone three m below. The lower fauna (Assemblage A) is rich in tiger and sand sharks, eagle rays, plus estuarine elements, such as catfish, sawfish, and softshell turtle. The mixture of estuarine vertebrates with abundant marine mollusks suggests a possible tidal channel emptying into nearshore marine. The upper fauna (Assemblage B) is dominated by a rich, moderately diverse fish fauna with scarce rays and sharks. An assemblage with sciaenids, ophidiids, and myripristids with abundant, diverse mollusks, especially infaunal pelecypods, suggests a fully marine but nearshore setting of 25 m or less. Microfauna includes 33 benthic foraminifera and 15 ostracode species. The shallow nature of this assemblage, plus the lack of planktonic foraminifera, indicatesan absence of open ocean currents. Macrofaunal and microfaunal paleoecology supports the shallow neritic to estuarine conditions indicated by vertebrate parameters. The Main Glauconite bed was deposited in an open marine bay or lagoon which was separated from ocean currents by some barrier, possibly an offshore marine sandbar complex.

The marsupials of the Lac Pelletier lower fauna, Middle Eocene (Duchesnean) of Saskatchewan

ABSTRACT Four species of marsupials occur in the Lac Pelletier Lower Fauna (Duchesnean), Cypress Hills Formation, Saskatchewan. Herpetotherium sp., cf. H. marsupium from Lac Pelletier is intermediate in size and stylar cusp morphology between Uintan H. marsupium and Chadronian H. valens. Herpetotherium sp., cf. H. knighti from this assemblage shows smaller and less transverse upper molars than in H. knighti from the Uintan. Copedelphys sp., cf. C. innominata from Lac Pelletier is smaller than in Uintan samples, and is also smaller, with a smaller stylar cusp D, than Copedelphys titanelix of the Chadronian. Peradectes californicus is the only peradectid recognized in the Lac Pelletier Lower Fauna. The marsupial assemblage from the Lac Pelletier Lower Fauna is transitional in nature between Uintan and Chadronian faunas. Evidence from this fauna indicates that the genera Herpetotherium and Copedelphys, previously recognized from Chadronian and later assemblages, include Duchesnean and earlier species.

Conodonts and the Devonian–Carboniferous boundary in the upper Woodford Shale, Arbuckle Mountains, south-central Oklahoma

The Woodford Shale of south-central Oklahoma was deposited in an offshore, quiet-water, oxygen-poor setting on the southern margin of North America in assocation with other dark organic-rich shales of the Upper Devonian–Lower Carboniferous black-shale facies. The basal Woodford was deposited unconformably over lower Paleozoic carbonate strata as a south-to-north transgressive unit during the Frasnian and early Famennian. Black shales and cherts lie directly above the basal beds.Phosphatic shales in the upper Woodford contain a conodont succession characterized by three distinct environmentally controlled faunas. The lower fauna is characterized by Palmatolepis gracilis ssp., Branmehla inornata, Bispathodus stabilis, and Pseudopolygnathus marburgensis trigonicus, indicative of the Late Devonian Lower expansa Zone to Upper praesulcata Zone. The middle fauna, which spans the Devonian–Carboniferous (D/C) boundary, is characterized by Polygnathus communis communis and species of Protognathodus. On the Lawrence uplift the D/C boundary is disconformable, as indicated by the absence of Protognathodus kockeli before the first occurrence of Siphonodella sulcata. Light-colored phosphate laminae and beds, indicative of erosion and nondeposition, and a change in biofacies from an offshore palmatolepid–bispathodid fauna to a more nearshore, palmatolepid–polygnathid–protognathodid fauna indicate higher energy conditions and a lowering of sea level associated with the boundary interval. In the eastern Arbuckle Mountains the D/C boundary is apparently conformable, marked by a green shale interval containing a Protognathodus fauna. Species of Siphonodella, indicative of an offshore setting, characterize the third and youngest fauna. The Early Carboniferous sulcata, Lower duplicata, and Upper duplicata Zones are recognized in the upper Woodford. The Woodford Shale is conformably overlain by the “pre-Welden Shale’ and its equivalents, or unconformably overlain by the lower Caney Shale (Osagean?–Meramecian) in the northern outcrop regions and the Sycamore Formation (late Osagean?–Meramecian) in the southern Arbuckle Mountains.

Reconstruction of Tertiary palaeoenvironments using a combination of molecular and conventional palaeobiology

The Bembridge Limestone Formation (BLF), Late Eocene of Headon Hill, Isle of Wight, England, contains a diverse array of mammals (around 50 spp.) distributed through 10 levels. Its lower part (“lower fauna”) marks the appearance of a significant number of species, genera and one family unknown from earlier English Late Eocene strata. Towards the top of the BLF there is a reversion to faunas (“upper fauna”) more typical of the underlying Headon Hill Formation. This represents their last appearance in England. The succeeding Bembridge Marls Member fauna is similar to that in the lower part of the BLF. These changes are provincial in scale and may be climate induced (reflecting a slight warming followed by terminal Eocene cooling). Superimposed on these changes are smaller-scale more frequent fluctuations linked to alternating marl and black mud lithologies which may represent local habitat changes. In order to obtain overall understanding of the environment of deposition and taphonomic bias influencing these mammalian assemblages an integrated multidisciplinary study is being undertaken.Plant macrofossils are unfortunately extremely rare in this sequence. Those few which are present typify the fresh-water marsh vegetation widespread in the Late Eocene/Early Oligocene of England. In contrast mammalian faunas indicate more wooded conditions. Seeds like those of the modern free-floating fresh-water plant Stratiotes occur in three levels. However, they are poorly-preserved. The chemical composition of the seed coat as revealed by flash pyrolysis gas chromatography indicates a very simple polyphenol macromolecule probably resulting from transformations of more complex polyphenols in well-preserved Stratiotes seeds.Determinable palynomorphs are very rare and largely restricted to the part of the sequence which contains the “upper fauna”. They suggest a tranquil fresh-water depositional setting as do several molluscs and charophytes. Palynomorphs also include fungal remains, fern spores and a few tree pollen, the latter possibly from regional vegetation. However, the bulk of the palynological organic matter consists of brown structureless organic matter (SOM), resin-like particles and “platy kerogen”. In the lower beds, pale shelly muds with potamidids and corbiculids lack mammals and contain palynological organic matter dominated by resin-like particles and with abundant pyrite. These beds probably reflect brackish influence, the loss of which largely coincides with the reappearance of abundant mammals (“lower fauna”), occurrence of Stratiotes and of charophytes. Resin-like particles remain dominant in the palynological organic matter. “Platy kerogen” dominates three units including that containing the first occurrence of the “upper fauna”. Subsequently resin-like particles again dominate. Brown SOM is scattered throughout but is well represented in two units one of which contains “lower fauna” the other “upper fauna”.Variations in palynological organic matter are reflected in the chemical composition of residues studied. Results from five black muds show that samples which mainly contain resin-like particles are dominated by n-alkanes and n-alk-1-enes in their pyrolysates. However, there is no indication of known resin chemical signatures. This indicates that the organic matter in these residues is mainly derived from cuticles (cutan) and/or cell wall remains (algaenan) of fresh-water algae. Samples containing “platy kerogen” and brown SOM are dominated by aromatics and phenols in their pyrolysates indicating an origin from woody materials. Work in progress on stable isotope analyses of the residues may further clarify the nature of the organic input.

Primates of the Lac Pelletier Lower Fauna (Eocene: Duchesnean), Saskatchewan

Four genera of primates are present in the early to mid-Duchesnean Lac Pelletier Lower Fauna. Phenacolemur leonardi sp.nov., Trogolemur sp., Omomys sp., and Macrotarsius cf. M. montanus make up the latest diverse primate assemblage known from North America and from the Great Plains. This primate assemblage is similar to the earliest Duchesnean assemblage from the Wood locality, Badwater Creek area of central Wyoming, and primate genera appear to have been widely distributed through the Great Plains and Rocky Mountains in the Uintan–Duchesnean.

Tempo of earliest Ordovician graptolite faunal succession: conodont-based correlations from the Tremadocian of Quebec

Successive Tremadocian planktic dendroid graptolite assemblages from continental slope sequences in Quebec can be correlated with North American platform biozonations on the basis of conodonts. Anisograptid-bearing (Assemblage 2), middle Tremadocian "Matane faunas" are associated with Early Ordovician Rossodus manitouensis Zone (new designation) conodonts. Younger middle Tremadocian faunas with adelograptids (Assemblage 3) are no younger than the Rossodus manitouensis Zone. Key dendroid evolutionary–immigration events take place within the lower conodont Fauna B interval. Rooted dendroids near Cap des Rosiers, Quebec, and in eastern New York State occur with lower Fauna B conodonts and the trilobites Pareuloma and Borthaspidella. However, the earliest Tremadocian (and earliest Ordovician) dendroid immigration event, represented by the local lowest occurrence of faunas with Dictyonema flabelliforme s.l. at localities in western Newfoundland, eastern New York State, Norway, and eastern China, also lies within the lower Fauna B interval. Finally, the lowest occurrence of key Assemblage 2 dendroid taxa falls within the lower Fauna B interval at the latter localities.The Rossodus manitouensis Zone is proposed as a new designation for a biostratigraphic unit that is appropriate for North American marginal and open shelf sequences. This zone is approximately equivalent to the "Loxodus bransoni Interval" of other authors and is characterized by Fauna C conodonts. Newly described taxa include Rossodus? highgatensis n. sp., Scolopodus? praecornuformis n. sp., and Variabiloconus n. gen.

Age of Amsden Formation, Cherry Creek, Wind River Mountains, Wyoming: GEOLOGICAL NOTES

Six new collections of fossils from the lower part of the at Cherry Creek, Wind River Mountains, Wyoming, place the Mississippian-Pennsylvanian boundary more than 48 feet and less than 63 feet above the Madison limestone. The lower faunas are Chesteran in age, and the upper faunas are tentatively dated as Atokan. The name Sacajawea formation is rejected for the Mississippian beds at Cherry Creek. The presence of two sandstones in the Amsden, both of which have been called Darwin sanstone, is inferred, and it is pointed out that the at Cherry Creek contains beds that are specifically excluded farther north in the Wind River Mountains. Until the faunas of the type are made known it will be impossible to decide which use of the name Amsden is correct in the Wind River Mountains.