Asphalt Quarry Research Articles

Palaeozoic stromatoporoids and chaetetids analysed using electron backscatter diffraction (EBSD); implications for original mineralogy and microstructure

Palaeozoic hypercalcified sponges were ubiquitous Ordovician—Devonian reef builders but, despite their rich fossil record, their original skeletal mineralogy and microstructure remain poorly understood. This study provides the first application of electron backscatter diffraction (EBSD) to analyse skeletal structure of Silurian and Devonian stromatoporoids. The two Silurian and two Devonian stromatoporoid taxa selected are typical of stromatoporoids in showing poor preservation. A reference sample of an exceptionally well-preserved hypercalcified chaetetid sponge from the Carboniferous Buckhorn Asphalt Quarry (a fossil lagerstätte renowned for its preservation of skeletal microstructures) contains evidence that its skeleton comprised distinct bundles of single-crystal fibres, similar to modern hypercalcifying sponges. Similar bundles of crystal fibres are proposed here as the original microstructure of stromatoporoids, and acted as precursors to the coarse fibrous calcitic overprinting recrystallisation that is orientated normal to the growth layers, seen in all stromatoporoids viewed in cross-polarised light. The studied stromatoporoids show pronounced microporosity and micro-dolomite inclusions which are circumstantial evidence of an original composition of high-Mg calcite (HMC). We propose that the evidence of fibrous structures might be linked to inclusions of hydrated amorphous calcium carbonate (ACC·H2O) in the skeleton at the time of early diagenesis, as occurs in modern calcified sponges. The possible HMC skeletal composition of Palaeozoic stromatoporoids supports earlier views that the mineral composition of hypercalcifying reef builders is linked to Phanerozoic oscillations in the ratio of Mg:Ca, expressed as aragonite-calcite seas; stromatoporoids thrived in times of calcite-seas.

Bioerosion in fossil cephalopods: a case study from the Upper Carboniferous Buckhorn Asphalt Quarry Lagerstätte, Oklahoma, USA

The mid-Pennsylvanian (Desmoinesian–Virgilian) deposits from the Buckhorn Asphalt Quarry Lagerstatte near Sulphur, Oklahoma, are characterized by siliciclastic–carbonate rocks. One of these deposits is the ‘cephalopod coquina’ that contains a large amount of orthocerid and coiled nautiloid, and ammonoid shell remains. These were used for a detailed study on bioerosion in cephalopod shells in order to help in the reconstruction of the paleoenvironment and to increase the general knowledge on bioerosion in fossil cephalopods. More than 50 shell fragments were cast and investigated. The shells cast and investigated in this study comprise a diverse set of ichnotaxa-/forms. Besides chlorophyte and cyanobacterial traces, also rhodophyte, fungal, and spongal traces are present as well as those of unknown origin. In addition, there are six ichnoforms that might have foraminiferans as producers. In orthoceratids, Ichnoreticulina elegans and a curly morphotype of Scolecia isp. are most common while the abundance in coiled cephalopods is dominated by the ‘superthin form’, the ‘extremely thin form’, andFlagrichnus profundus. In total, 22 ichnotaxa and -forms were recognized and 12 of these have their oldest record in the Carboniferous. The succession of ichnotaxa/-forms in the casts of orthocones suggests deposition in the deep euphotic to dysphotic zone of the Buckhorn sea while shells of coiled specimens had drifted for a while; they were therefore more prone to bioerosion by autotrophs until they sank to the seafloor.

The fish assemblage from the Pennsylvanian Buckhorn Asphalt Quarry Lagerstätte (Oklahoma, USA)

A diverse assemblage of fishes (isolated teeth and scales) is reported from the Middle to Upper Pennsylvanian Buckhorn Asphalt Quarry Lagerstatte in Oklahoma, USA. The assemblage includes chondrichthyans such as the bransonelliform Bransonella lingulata, the xenacanthiform Xenacanthus, the symmoriiform Stethacanthus, ctenacanthiforms, an polyacrodontid euselachian, anachronistid neoselachians (Cooleyella amazonensis and C. sp.) and an iniopterygian paraselachian cf. Sibyrhynchidae. Moreover, the assemblage encompasses remains of acanthodians and various actinopterygians and a single specimen of an osteolepiform sarcopterygian. Most of the taxa are cosmopolitan during the Late Palaeozoic. The occurrence of bransonelliform and xenacanthiform species at the same locality is very rare in the Carboniferous. The assemblage yields the first Carboniferous occurrences of a polyacrodontid hybodontoid and an actinopterygian belonging to the Acropholidae. Bransonella lingulata from the Desmoinesian/Moscovian of the Buckhorn Asphalt Quarry in Oklahoma represents the youngest occurrence of this species.

Bryozoan fauna of the Boggy Formation (Deese Group, Pennsylvanian) of the Buckhorn Asphalt Quarry, Oklahoma, USA

The Middle to Upper Pennsylvanian Buckhorn Asphalt Quarry (Boggy Formation, Deese Group) of Oklahoma, USA, is well known for its exceptionally preserved fauna of marine invertebrates, including conservation of original skeletal aragonite. Here, we describe for the first time the taxonomy of the Buckhorn bryozoans, recognising nine species, two of which are new: Stenophragmidium buckhornensis sp. nov. and Streblotrypa (Streblotrypa) heltzelae sp. nov. Two further species, Stenoporella sp. and Spinofenestella sp., are described in open nomenclature. The other species show relationships to the Pennsylvanian of the USA and Russia. The genera Shishoviclema and Shulgapora are identified for the first time in North America. Superior preservation of the Buckhorn bryozoans allows some new and poorly known skeletal characters to be described. These include nanoperforations, granule bands, mural spines, spinose hemiphragms and transverse fibrous wall fabric. Nanoperforations, found in the skeletal walls of several Buckhorn bryozoan species, are tiny holes around which laminae are deflected, indicating that they are not post-mortem structures. However, it is unclear whether they are features of the bryozoans or have resulted from the presence of microsymbionts. The primary wall layer of the fenestrate Septopora blanda Moore, 1929 is apparently composed of transverse fibrous crystallites, a skeletal fabric previously known only in post-Palaeozoic cyclostomes.

Oxygen and stable carbon isotopes from a nautiloid from the middle Pennsylvanian (Late Carboniferous) impregnation Lagerstätte ‘Buckhorn Asphalt Quarry’ — Primary paleo-environmental signals versus diagenesis

Two shell fragments, one of an undetermined cephalopod and one of an orthoconic nautiloid (Pseudorthoceratidae gen. et. sp. indet.), from the Pennsylvanian Buckhorn Asphalt Lagerstätte (Oklahoma) were studied to reconstruct paleotemperatures and to explore possible diagenetic alterations. For the first time, not only parts of the shell of an orthoconic nautiloid, but also its cameral deposits were sampled in high resolution. The mineralogy, geochemistry, and microstructure of both shell remains, the pseudorthoceratid and the undetermined cephalopod, were investigated in detail before high-resolution transects for oxygen and stable carbon isotopes were sampled.The shell fragment of the undetermined cephalopod showed no or very little diagenetic alteration. Therefore, the measured δ18O-variation (δ18O-range of 0.68‰) and the inferred temperature range of 28 to 31°C are interpreted to represent an original signal. The temperatures indicate that the specimen lived in shallow, warm tropical waters. The δ13C-signal, with a δ13C-range of 3.43‰ is interpreted to be the consequence of a strong metabolic effect.A septum of the phragmocone of the pseudorthoceratid nautiloid was only slightly altered by diagenesis and a largely original δ18O-signal could be obtained. The δ18O-values exhibit an inferred temperature range of 14 to 15°C indicating that this species lived in deeper and cooler waters. The cameral deposits were investigated in detail by energy dispersive X-ray (EDX) and by XRD–GADDS (X-ray diffraction — general area detector diffraction system) analyses. Part of the cameral deposits in the orthoconic nautiloid turned out to originally consist of high-Mg calcite (HMC) instead of the estimated aragonite. Anyhow, the massive cameral deposits show signs of strong small scale alteration resulting in a distinct spreading of oxygen-values. The oxygen and carbon isotope plots show a linear trend for the oxygen-carbon-correlation. This is interpreted as the mixing of two end-members with the lightest end-members suggesting a meteoric diagenesis with a diagenetic fractionation of the aragonite to low-Mg calcite (LMC) respectively the HMC to LMC and dolomite.The calculated temperatures of the pseudorthoceratid specimen and the undetermined cephalopod indicate two different paleoenvironments. Additionally, the pseudorthoceratid nautiloid displays the narrow range of temperatures in the deeper parts of the sea and the undetermined cephalopod the more fluctuating temperatures in the shallow areas. It is also shown how important a detailed investigation of microstructures and mineralogy of samples with an according cautious interpretation of the achieved dataset is. The importance of an intensive examination of samples is pointed out, to avoid small scale alterations to be overlooked, since this would lead to a misinterpretation of the results.

Facies and fauna of the Pennsylvanian Buckhorn Asphalt Quarry deposit: a review and new data on an important Palaeozoic fossil Lagerstätte with aragonite preservation

The Pennsylvanian Buckhorn Asphalt Quarry contains the best-preserved Palaeozoic mollusc fauna in the world. Early impregnation of mixed siliciclastic–carbonate rocks (mudstones, pack to grainstones, shell beds, and conglomerates) with hydrocarbons prevented aragonite destruction (“Impregnation Fossil Lagerstatte”). The exceptional preservation comprises shell microstructures, microornaments and early ontogenetic shells. Most gastropods had planktotrophic larval development indicating a high primary production although the remains of phytoplankton are very rare in this and other Late Palaeozoic deposits. Deposition occurred close to a shallow-water coastal area. Mass flow processes (density currents) triggered by storms were involved in the transport mechanisms of some units. Shells of benthic molluscs yield the most diverse known Palaeozoic microboring assemblage, indicating at least partly euphotic conditions. The invertebrate fauna comprises about 160 species and is dominated by molluscs, which is unusual for a Palaeozoic deposit, suggesting that aragonite dissolution produces a major bias in the fossil record. However, most mollusc genera in the Buckhorn deposit are also known from other Pennsylvanian occurrences as recrystallised shells. This shows that preservation bias via preferential aragonite dissolution may be overestimated.

Larven-Gehäuse und Gehäuse-Mikrostrukturen von außergewöhnlich gut erhaltenen unterkarbonischen Gastropoden vom Buckhorn-Asphaltlager (Oklahoma, USA)

Gastropods from the mid-Pennsylvanian Buckhorn Asphalt Quarry in Oklahoma (U.S.A.) are very well preserved. Commonly, protoconchs and original shell microstructure are present and unaltered. Two pleurotomarioid gastropod species of the generaSalterospira andParagoniozona are preserved with the early ontogenetic shell and with a nacreous shell structure. Two other nacreous archaeogastropods with a rotelliform shell lack a selenizone and are closely related to the Anomphalidae. They are tentatively assigned to the genusAnomphalus. A fifth tiny archaeogastropod lacks nacre and has exclusively crossed lamellar shell microstructure. It represents the oldest known archaeogastropod that lacks nacre.Microdoma conicum represents the trochomorph archaeogastropods; it has an inner nacreous layer, a crossed acicular layer, and an outermost thin calcitic layer. The protoconch ofMicrodoma is typical for archaeogastropods. The construction of the shell indicates that most archaeogastropods from Buckhorn Asphalt deposit have a nacreous inner layer, but one type has a crossed lamellar microstructure, like the modern Phasianellinae and Fissurelloidea, indicating the antiquity of this structural type within the Vetigastropoda (Archaeogastropoda). The Neritimorpha are present with the two neritopsid generaNaticopsis andTrachydomia. Naticopsis has a thick inner crossed lamellar layer and a thin prismatic outer calcitic layer. The families Goniasmidae, Orthonemidae, Pseudozygopleuridae, and Meekospiridae represent the Caenogastropoda. All reported species of these families have a crossed lamellar shell structure and a caenogastropod-type protoconch. There is now clear evidence that the Goniasmidae are Caenogastropoda, though they have a selenizone, a feature that is almost unknown in modern caenogastropods. Only a few modern caenogastropods have slit-like structures in their shell, e.g. the heteropodAtlanta and the worm snailSiliquaria. Both are distantly related to the slit-bearing Goniasmidae and it is unlikely that the slit is homologous in these groups. The fact that these ancient caenogastropods had a slit in the outer lip is most important for the reconstruction of the phylogeny of the Gastropoda. The Goniasmidae are present with the generaGoniasma (one species),Stegocoelia (three species), andCerithioides (one species). The Orthonemidae are represented by the generaOrthonema andPalaeostylus. The genusOrthonema is present with a dextral species and the sinistral speciesO. sinistrorsa. Species ofOrthonema have the same type of a heliciform larval shell that is present in the Goniasmidae. Therefore, the two families are probably closely related.Palaeostylus is present with a newly described species,Palaeostylus batteni n. sp. The Pseudozygopleuridae are present with a single species,Pseudozygopleura peoriense. The common speciesGirtyspira minuta belongs to the family Meekospiridae. The teleoconch has a faint spiral striation and a polished surface The protoconch/teleoconch transition indicates that its protoconch is paucispiral and ends with a faint, straight prosocline thread. The Heterostropha are present with the order Allogastropoda represented by two species of the generaDonaldina andPseudaclisina, of whichPseudoaclisina is reported from North America for the first time. The exceptional preservation increases the number of shell characters considerably (protoconch, shell microstructure, micro-ornaments), even for seemingly well established taxa. The knowledge of these features greatly improves the systematics of several major groups of Late Palaeozoic gastropods and represents an important source of information for future phylogenetic analyses.

Carboniferous praecardioid bivalves from the exceptional Buckhorn Asphalt biota of south-central Oklahoma, USA

Abstract Unusual Pennsylvanian bivalves recovered from the Buckhorn Asphalt Quarry of south-central Oklahoma are members of the Order Praecardioida, Family Lunulacardiidae. This is the youngest occurrence of praecardioids in North America. These praecardioids have an ontogeny characterized by a veneriform juvenile shell, changing abruptly to an elongate adult shell with sharp carinae, accompanied by strong rotation of the juvenile shell and change in ligament. These shells provide new evidence of dentition and ligament for lunulacardiids and the first documentation of praecardioid shell microstructure. The Buckhorn taxa possess stout hinge teeth, indicating that lunulacardiids are not edentulous. Preserved ligament in multiple growth stages indicates that beaks are prosogyrous and the flattened truncated portion of the shell is posterior. A revised diagnosis of the Lunulacardiidae is presented. New taxa: Buckhornia carteri n. gen., n. sp.

The Sequence and Mechanism of Low-Temperature Dolomite Formation: Calcian Dolomites in a Pennsylvanian Echinoderm

ABSTRACT Middle Pennsylvanian fossils from the Buckhorn Asphalt quarry of Southern Oklahoma are unusual in that early sealing by tar has preserved many of their original textural and mineralogic features and those of the earliest stages of diagenesis. Echinoderm fragments collected from this locality axe well preserved, with original stereom morphology clearly visible optically. One- to five-micrometer anhedral calcian dolomite grains occupy as much as 30 percent of the original stererom of the fragments, as displayed by differential etching and MgK X-my maps. The composition of skeletal fragments is 75 percent Ca.98Mg.02Co3, 25 percent Ca.54Mg.46Co3. Single crystal X-ray di fraction, XRD, EMPA, TEM, and STEM microanalysis were used to characterize the calcian dolomite phase. TEM micrographs revealed an approximate 100 A, tweed structure identical to that reported by Reeder and Wenk (1979). Our data imply that magnesium in the calcian dolomites was derived largely from the original magnesian calcite of the echinoderm stereom. Original biogenic high-magnesium calcite is altered via local microdissolution--reprecipitation to anhedral disordered calcian dolomite grains within low-magnesium calcite. The product phases (low-magnesium calcite and calcian dolomite) retain the original crystallographic orientation of the stereom. These products of early diagenesis are apparent precursors to well-defined, ordered euhedral microdolomites. The relationships between the low-magnesium calcite and calcian dolomite, and the chemistry and complex ultrastructure of the calcian dolomites support the kind of low-temperature mechanism of dolomite formation postulated by Gains (1977), Goldsm th and Graf (1958), and others on the basis of hydrothermal experiments.