ALBERT

Description: Three fundamental terms in ichnology are:(1) assemblage, which is equivalent to an assemblage of body fossils; (2) ichnocoenosis, which is a trace fossil assemblage produced by a biological community that can be characterized by morphological criteria; (3) ichnofacies, which refers to recurrent ichnocoenoses that represent a significant portion of Phanerozoic time. There are five archetypal vertebrate ichnofacies for non-marine environments (Chelichnus, Grallator, Carichnium, Batrachichnus, Characichichnos) of which four are present in the Permian:(1) Chelichnus ichnofacies -- Chelichnus ichnocoenosis; (2) Batrachichnus ichnofacies -- Batrachichnus ichnocoenosis; (3) Brontopodus ichnofacies -- Pachypes ichnocoenosis; (4) Characichichnos ichnofacies -- Serpentichnus ichnocoenosis. The Chelichnus and Characichichnos ichnofacies occur throughout the Permian, the Batrachichnus ichnofacies is restricted to the Early Permian and the Brontopodus to the Middle to Late Permian. The Batrachichnus ichnocoenosis can be divided into the Ichniotherium sub-ichnocoenosis, Amphisauropus sub-ichnocoenosis and the Dimetropus subichnocoenosis, which represent a spectrum of non-marine environments from alluvial fan to tidal flat.

Description: The Triassic chronostratigraphic scale was built on two centuries of research on ammonoid biostratigraphy and biochronology. Two Triassic stage bases and all of the Triassic substages are currently defined by ammonoid bioevents. The study of Triassic ammonoids began during the late 1700s, and in 1895, Edmund von Mojsisovics, Wilhelm Waagen and Carl Diener published an essentially complete Triassic chronostratigraphic scale based on ammonoid biostratigraphy. This scale introduced many of the Triassic stage and substage names still used today, and all terminology of stages and substages subsequently introduced has been based on ammonoid biostratigraphy. Early Triassic ammonoids show a trend from cosmopolitanism (Induan) to latitudinal differentiation (Olenekian), and the four Lower Triassic substage (Griesbachian, Dinerian, Smithian and Spathian) boundaries are globally correlated by widespread ammonoid biotic events. Middle Triassic ammonoids have provinciality similar to that of the Olenekian and provide a basis for recognizing six Middle Triassic substages. Late Triassic ammonoids provide a basis for recognizing three stages divided into five substages. The main uncertainty for the future of Triassic ammonoid biostratigraphy is not the decline of the ammonoids as a tool for dating and correlation of Triassic strata but, rather, the dramatic decrease in the number of specialists, due to the lack of replacement of experienced palaeontologists who started their activity in the 1950s and 1960s.

Description: The Permian time scale based on marine rocks and fossils is well defined and of global utility, but non-marine Permian biostratigraphy and chronology is in an early phase of development. Non-marine Permian strata are best known from western Europe and the western United States, but significant records are also known from Russia, South Africa, China and Brazil. Global time terms based on non-marine Permian strata, such as Rotliegend, Zechstein, Autunian, Saxonian and Thuringian, are either inadequately defined or poorly characterized and should only be used as lithostratigraphic terms. Macro- and microfloras have long been important in non-marine Permian correlations, but are subject to limitations based on palaeoprovinciality and facies/climatic controls. Charophytes, conchostracans, ostracodes and freshwater bivalves have a potential use in non-marine Permian biostratigraphy but are limited by their over-split taxonomy and lack of well-established stratigraphic distributions of low-level taxa. Tetrapod footprints provide poor biostratigraphic resolution during the Permian, but tetrapod body fossils and insects provide more detailed biostratigraphic zonations, especially in the Lower Permian. Numerous radioisotopic ages are available from non-marine Permian sections and need to be more precisely correlated to the global time scale. The Middle Permian Illawarra reversal and subsequent magnetic polarity shifts are also of value to correlation. There needs to be a concerted effort to develop non-marine Permian biostratigraphy, to correlate it to radio-isotopic and magnetostratigraphic data, and to cross-correlate it to the marine time scale.

Description: The Triassic chronostratigraphic scale is a hierarchy of three series, seven stages and 15 substages developed during nearly two centuries of research. The first geological studies of Triassic rocks began in Germany in the late 1700s and culminated in 1834 when Friedrich August von Alberti coined the term Trias' for the Bunten Sandsteins, Muschelkalk and Keuper, a thick succession of strata between the Zechstein and the Lias. Recognition of the Trias outside of Germany soon followed, and by the 1860s Austrian geologist Edmund von Mojsisovics began constructing a detailed Triassic chronostratigraphy based on ammonoid biostratigraphy. In 1895, Mojsisovics and his principal collaborators, Wilhelm Waagen and Carl Diener, published a Triassic timescale that contains most of the stage and substage names still used today. In 1934, Leonard Spath proposed a Triassic ammonoid-based biochronological timescale that differed little from that of Mojsisovics and his collaborators. In the 1960s, E. Timothy Tozer proposed a Triassic ammonoid-based timescale based on North American standards, and his timescale included proposal of four Lower Triassic stages (Griesbachian, Dienerian, Smithian and Spathian). The work of the Subcommission on Triassic Stratigraphy began in the 1970s and resulted in current recognition of seven Triassic stages in three series: Lower Triassic-Induan, Olenekian; Middle Triassic-Anisian, Ladinian; Upper Triassic-Carnian, Norian and Rhaetian. The 1990s saw the rise of Triassic conodont biostratigraphy so that four intervals that have agreed on Triassic GSSPs use conodont occurrences as defining features: bases of Induan, Olenekian, Anisian and Rhaetian. The bases of the Ladinian and Carnian are defined by ammonoid events. The base of the Norian remains undefined, but will most likely be defined by conodonts. Except for the Rhaetian, the Middle and Upper Triassic stages and substages have been fairly stable for decades, but there has been much less agreement on Lower Triassic chronostratigraphic subdivisions. Issues in the development of a Triassic chronostratigraphic scale include those of: stability and priority of nomenclature and concepts; disagreement over and changing taxonomy; the use of ammonoid v. conodont biostratigraphy; differences in the perceived significance of biotic events for chronostratigraphic classification; disagreements about the utility of relatively short stages; correlation problems between the Tethyan and Boreal realms (provinces); and competing standards from the Old and New worlds. Most of these issues have been resolved in the recognition of three Triassic series and seven stages. Further development of the Triassic chronostratigraphic scale needs to focus on definition and characterization of the 15 Triassic substages as these will provide a much more detailed basis for subdivision of Triassic time than do the seven stages.

Description: The most extensive Permian tetrapod (amphibian and reptile) fossil records from the western United States (New Mexico-Texas) and South Africa provide the basis for definition of 10 land-vertebrate faunachrons that encompass Permian time. These are (in ascending order): the Coyotean, Seymouran, Mitchellcreekian, Redtankian, Littlecrotonian, Kapteinskraalian, Gamkan, Hoedemakeran, Steilkransian and Platbergian. These faunachrons provide a biochronological framework with which to determine and discuss the age relationships of Permian tetrapod faunas. Their correlation to the marine time scale and its numerical calibrations indicate that the Coyotean is a relatively long time interval of about 20 Ma, whereas most of the other faunachrons are much shorter, about 1-2 Ma long each. The Platbergian may also be relatively long, 14 Ma, although this is not certain. This suggests slow rates of terrestrial tetrapod faunal turnover during most of the Early Permian and late Middle to Late Permian, but more rapid rates of turnover during the latest Early and most of the Middle Permian, especially during the explosive initial diversification of therapsids.

Description: The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology divides Triassic time into eight land-vertebrate faunachrons (LVFs) with boundaries defined by the first appearance datums (FADs) of tetrapod genera or, in two cases, the FADs of a tetrapod species. Definition and characterization of these LVFs is updated here as follows: the beginning of the Lootsbergian LVF=FAD of Lystrosaurus; the beginning of the Nonesian=FAD Cynognathus; the beginning of the Perovkan LVF=FAD Eocyclotosaurus; the beginning of the Berdyankian LVF=FAD Mastodonsaurus giganteus; the beginning of the Otischalkian LVF=FAD Parasuchus; the beginning of the Adamanian LVF=FAD Rutiodon; the beginning of the Revueltian LVF=FAD Typothorax coccinarum; and the beginning of the Apachean LVF=FAD Redondasaurus. The end of the Apachean (= beginning of the Wasonian LVF, near the beginning of the Jurassic) is the FAD of the crocodylomorph Protosuchus. The Early Triassic tetrapod LVFs, Lootsbergian and Nonesian, have characteristic tetrapod assemblages in the Karoo basin of South Africa, the Lystrosaurus assemblage zone and the lower two-thirds of the Cynognathus assemblage zone, respectively. The Middle Triassic LVFs, Perovkan and Berdyankian, have characteristic assemblages from the Russian Ural foreland basin, the tetrapod assemblages of the Donguz and the Bukobay svitas, respectively. The Late Triassic LVFs, Otischalkian, Adamanian, Revueltian and Apachean, have characteristic assemblages in the Chinle basin of the western USA, the tetrapod assemblages of the Colorado City Formation of Texas, Blue Mesa Member of the Petrified Forest Formation in Arizona, and Bull Canyon and Redonda formations in New Mexico. Since the Triassic LVFs were introduced, several subdivisions have been proposed: Lootsbergian can be divided into three sub-LVFs, Nonesian into two, Adamanian into two and Revueltian into three. However, successful inter-regional correlation of most of these sub-LVFs remains to be demonstrated. Occasional records of nonmarine Triassic tetrapods in marine strata, palynostratigraphy, conchostracan biostratigraphy, magnetostratigraphy and radioisotopic ages provide some basis for correlation of the LVFs to the standard global chronostratigraphic scale. These data indicate that Lootsbergian=uppermost Changshingian, Induan and possibly earliest Olenekian; Nonesian=much of the Olenekian; Perovkan=most of the Anisian; Berdyankian=latest Anisian? and Ladinian; Otischalkian=early to late Carnian; Adamanian=most of the late Carnian; Revueltian=early-middle Norian; and Apachean=late Norian-Rhaetian. The Triassic timescale based on tetrapod biostratigraphy and biochronology remains a robust tool for the correlation of nonmarine Triassic tetrapod assemblages independent of the marine timescale.

Description: Permian tetrapod footprints are known from localities in North America, South America, Europe and Africa. These footprints comprise four ichnofacies, the Chelichnus ichnofacies from aeolianites and the Batrachichnus, Brontopodus and Characichnos ichnofacies from water-laid (mostly red-bed) strata. Permian track assemblages of the Chelichnus ichnofacies are of uniform ichnogeneric composition and low diversity, range in age from Early to Late Permian, and thus are of no biostratigraphic significance. Footprints of the Batrachichnus and Brontopodus ichnofacies represent two biostratigraphically distinct assemblages: (1) Early Permian assemblages characterized by Amphisauropus, Batrachichnus, Dimetropus, Dromopus, Hyloidichnus, Limnopus and Varanopus; and (2) Middle to Late Permian assemblages characterized by Brontopus, Dicynodontipus, Lunaepes, Pachypes, Planipes, and/or Rhynchosauroides. Few Permian footprint assemblages are demonstrably of Middle Permian (Guadalupian) age, and there is a global gap in the footprint record equivalent to at least Roadian time. Permian tetrapod footprints represent only two biostratigraphically distinct assemblages, an Early Permian pelycosaur assemblage and a Middle to Late Permian therapsid assemblage. Therefore, footprints provide a global Permian biochronology of only two time intervals, much less than the ten time intervals that can be distinguished with tetrapod body fossils.

Description: Triassic tetrapod footprints have a Pangaea-wide distribution; they are known from North America, South America, Europe, North Africa, China, Australia, Antarctica and South Africa. They often occur in sequences that lack well-preserved body fossils. Therefore, the question arises, how well can tetrapod footprints be used in age determination and correlation of stratigraphic units? The single largest problem with Triassic footprint biostratigraphy and biochronology is the non-uniform ichnotaxonomy and evaluation of footprints that show extreme variation in shape due to extramorphological (substrate-related) phenomena. Here, we exclude most of the countless ichnospecies of Triassic footprints, and instead we consider ichnogenera and form groups that show distinctive, anatomically-controlled features. Several characteristic footprint assemblages and ichnotaxa have a restricted stratigraphic range and obviously occur in distinct time intervals. This can be repeatedly observed in the global record. Some reflect distinct stages in the evolutionary development of the locomotor apparatus as indicated by their digit proportions and the trackway patterns. Essential elements are archosaur tracks with Rotodactylus, the chirotherian ichnotaxa Protochirotherium, Synaptichnium, Isochirotherium, Chirotherium and Brachychirotherium, and grallatorids that can be partly linked in a functional-evolutionary sequence. Non-archosaur footprints are common, especially the ichnotaxa Rhynchosauroides, Procolophonichnium, Capitosauroides and several dicynodont-related or mammal-like forms. They are dominant in some footprint assemblages. From the temporal distribution pattern we recognize five distinct tetrapod-footprint-based biochrons likened to the known land-vertebrate faunachrons (LVFs) of the tetrapod body fossil record: 1. Dicynodont tracks (Lootsbergian=Induan age); 2. Protochirotherium (Synaptichnium), Rhynchosauroides, Procolophonichnium (Nonesian=Induan-Olenekian age); 3. Chirotherium barthii, C. sickleri, Isochirotherium, Synaptichnium ( Brachychirotherium'), Rotodactylus, Rhynchosauroides, Procolophonichnium, dicynodont tracks, Capitosauroides (Nonesian-Perovkan=Olenekian-early Anisian); 4. Atreipus-Grallator ( Coelurosaurichnus'), Synaptichnium ( Brachychirotherium'), Isochirotherium, Sphingopus, Parachirotherium, Rhynchosauroides, Procolophonichnium (Perovkan-Berdyankian=Late Anisian-Ladinian); 5. Brachychirotherium, Atreipus-Grallator, Grallator, Eubrontes, Apatopus, Rhynchosauroides, dicynodont tracks (Otischalkian-Apachean=Carnian-Rhaetian). Tetrapod footprints are useful for biostratigraphy and biochronology of the Triassic. However, compared to the tetrapod body fossil record with eight biochrons, the five footprint-based biochrons show less resolution of faunal turnover as ichnogenera and ichnospecies at best reflect biological families or higher biotaxonomic units. Nevertheless, in sequences where body fossils are rare, footprints can coarsely indicate their stratigraphic age.

Description: German geologists began to study rocks now recognized as Triassic during the late 1700s. In 1823, one of those German geologists, a very astute mining engineer named Friedrich August von Alberti (1795-1878), coined the term Trias formation' for an c. 1 km thick, tripartite succession of strata in southwestern Germany - the Bunten Sandsteins, Muschelkalk and Keuper of the German miners. Alberti also recognized Triassic rocks outside of Germany, throughout much of Europe and as far away as India and the United States. By the end of the nineteenth century, Triassic rocks had been identified across Europe and Asia, and in North America, South America and Africa. Indeed, in 1895, the Austrian geologist Edmund von Mojsisovics (1839-1907) and his collaborators published a complete subdivision of Triassic time based on ammonoid biostratigraphy and, in so doing, introduced many of the Triassic chronostratigraphic terms still used today. The twentieth century saw the elaboration of an ammonoid-based Triassic timescale, especially due to the work of Canadian palaeontologist E. Timothy Tozer (1928-). During the last few decades, work also began on developing a global magnetic polarity timescale for the Triassic, a variety of precise numerical ages tied to reliable Triassic biostratigraphy have been determined, and conodont biostratigraphy has become an important tool in Triassic chronostratigraphic definition and correlations. The current Triassic chronostratigraphic scale is a hierarchy of three series (Lower, Middle, Upper) divided into seven stages (Lower = Induan, Olenekian; Middle=Anisian, Ladinian; and Upper=Carnian, Norian, Rhaetian) further divided into 15 substages (Induan=upper Griesbachian, Dienerian; Olenekian=Smithian, Spathian; Anisian=Aegean, Bithynian, Pelsonian, Illyrian; Ladinian=Fassanian, Longobardian; Carnian=Julian, Tuvalian; Norian=Lacian, Alaunian, Sevatian). Ammonoid and conodont biostratigraphies provide the primary basis for the chronostratigraphy. A sparse but growing database of precise radioisotopic ages support these calibrations: base of Triassic c. 252 Ma, base Olenekian c. 251 Ma, base Anisian c. 247 Ma, base Ladinian c. 242 Ma, base Jurassic c. 201 Ma. A U/Pb age of c. 231 Ma from the Italian Pignola 2 section is lower Tuvalian, and U/Pb ages on detrital zircons from the nonmarine Chinle Group of the western USA of c. 219 Ma are in strata of late Carnian (Tuvalian) age based on the biostratigraphy of palynomorphs, conchostracans and tetrapods. These data support placement of the Norian base at c. 217 Ma, and indicate that the Tuvalian is more than 10 million years long and that the Carnian and Norian are the longest Triassic stages. Magnetostratigraphic data establish normal polarity for all of the Triassic stage bases except Anisian and Ladinian. An integrated biostratigraphic correlation web for the marine Triassic consists of ammonoids, bivalves, radiolarians and conodonts, whereas a similar web exists for the nonmarine Triassic using palynomorphs, conchostracans and tetrapods. Critical to cross correlation of the two webs is the Triassic section in the Germanic basin, where a confident correlation of nonmarine biostratigraphy to Triassic stage boundaries has been achieved. The major paths forward in development of the Triassic timescale are: finish formal definition of all Triassic stage boundaries, formally define the 15 Triassic substages, improve the integration of the Triassic biostratigraphic webs and develop new radioisotopic and magnetostratigraphic data, particularly for the Late Triassic.