Glen K. Merrill

Stratal order in Pennsylvanian cyclothems

Interpretation of continental to shallow-marine sedimentary sequences is commonly based on a perception of the presence of order in the upsection recurrence and/or arrangement of one or more rock types. These patterns of stratal organization span a spectrum of scales, ranging from thick transgressive-to-regressive “sequences” within passive continental margins, to thin upward-shallowing “parasequences” reported from many peritidal carbonate successions. However, in spite of the widespread acceptance of this idea, little quantitative assessment has been conducted to ascertain the relative dominance of stratal order and disorder in sedimentary sections. Because perception of high-frequency stratigraphic repetition is especially prevalent in Pennsylvanian “cyclothemic” terrestrial to marine successions generally coeval with Gondwanan glaciation, hypotheses of stratal order have also been widely linked to possible periodic changes in global sea level. Because of the general importance of implied relations between stratal order and glacioeustasy, lithofacies thicknesses, recurrences, and transition frequencies were examined in outcrops of west-central Illinois which comprise the type region of “cyclothem” deposition in order to evaluate the incidence of depositional cyclicity at this rather intermediate scale of consideration. Data on compositions, thicknesses, and vertical stratigraphic arrangement of 1031 units were derived from measured sections of Wanless, these comprise 11 distinct lithofacies types that span 868 m of section exposed at 44 localities. Philosophically, stratigraphic cyclicity could be represented as expectation in lithofacies thickness, lithofacies recurrence, or as some regular pattern in lithofacies ordering. Frequency distributions of lithofacies thicknesses and stratigraphic separations between recurrent lithofacies are exponential in form; these distributions of stratigraphic intervals would result if horizons of lithologic change or recurrence occurred independently (randomly) in sedimentary successions. Stratigraphic cyclicity manifested as lithofacies ordering is evaluated by considering frequencies with different rock types succeed each other in stratigraphic sections; presumption of cyclothemic order requires that lithofacies9 transitions exhibit some manifestation of statistical predictability. Markov chain analyses indicate that most high-frequency transitional order exists at underclay-to- coal horizons. Because underclay development may, in part, reflect a post-depositional (diagenetic) process that was associated with plant growth and coal formation, underclay-to-coal couplets may exist as one lithofacies association (as opposed to two genetically unrelated superjacent units). Few other transitions exhibit statistically significant predictability that cannot be ascribed to linkages between gradational rock types or to low-frequency (formation scale) variation in the bulk rock composition of the aggregate Illinois succession. In addition to these statistical attributes, cyclothemic associations designated in numerically generated random sequences that have the same lithofacies attributes as do the Illinois sections exhibit virtually identical thicknesses and abundances of lithofacies elements as those recognized by Wanless. Thus, we conclude that the classic Pennsylvanian successions in west-central Illinois exhibit no compelling evidence of high-frequency cyclic order, either as regularity in the recurrence or in the compositional ordering of lithofacies elements. On the basis of these considerations, we suggest that thicknesses, recurrences, and degrees of stratal order among Pennsylvanian lithofacies reflect largely uncorrelated durations, intensities, and styles of sediment deposition along the western margin of the Illinois Basin. Moreover, portrayal of cyclothemic order in the Illinois sections was found to be distinct from the rather obvious alternation of marine and terrestrial units that characterize these and many other Carboniferous successions. Presumption of recurrent change in sea level is an assumption that is largely unrelated to the presence or absence of cyclothemic scales of stratal ordering. If these Illinois sections are at all typical of other Carboniferous successions, then “cyclothemic” order, manifested as recurrent and potentially periodic accumulation, may be much less evident than is generally perceived to be the case during this important interval of Earth history.

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.

Map location literacy—How well does Johnny Geologist read?

The geographic information published in the geologic literature of the United Stales is inadequate to locate many, perhaps most, described localities. Precise location information can most easily and accurately be determined and conveyed by use of the Universal Transverse Mercator (UTM) grid. This grid can be read to 10 m × 10 m from standard modern maps. Geographic coordinates are an adequate and acceptable substitute of slightly lower precision when read to 1″ × 1″ of latitude and longitude. This paper evaluates and describes the use of both location systems to these precisions and includes suggestions for their use. Other systems are imprecise or inadequate (or both) for modern scientific work and should be avoided.

The Pennsylvanian conodont genus Gondolella Stauffer & Plummer, 1932: reinterpretation of the original type specimens and concepts

In order to ensure stability of nomenclature among species of Gondolella, lectotypes are selected from among the cotypes (syntypes in modern usage) proposed by Stauffer & Plummer (1932) for species that it is concluded were parts of the apparatuses of two species of that genus. It is recognized that many of their specimens actually represent growth stages of individual species, and many of the names used by Stauffer & Plummer are placed in synonymy. Interpreted synonyms include not only gondolelli-form P1 elements, but other parts of the apparatus, especially P2 elements assigned to Euprioniodina by Stauffer & Plummer. Thus, Gondolella bella has synonyms as P1 elements: G. curvata, G. magna, G. minuta, probably G. sp. A, S1 element Euprioniodina coronata and P2 elements: E. exserta, E. eximia and E. intertexta. In a similar manner, the type species of the genus, Gondolella elegantula, has synonyms G. insolita, G. lanceolata (P1 elements), and probably Euprioniodina sp. B (P2 element?).

The reconstruction of fossil organisms using cluster analysis : a case study from late Palaeozoic conodonts /

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Use of Conodont Genus Gondolella in High-Resolution Biostratigraphic Zonation of Middle-Upper Pennsylvanian Rocks, Central North America: ABSTRACT

Several conodont taxa have been suggested for use as biostratigraphic tools in the Pennsylvanian, but each has its limitations. Some are severely restricted paleobiogeographically or paleoecologically. Others existed through a relatively short interval of time, leaving the bulk of the Pennsylvanian column unzoned. Frustratingly, the single most promising group, the Idiognathodus-Streptognathodus plexus, has eluded taxonomic treatment that is both phylogenetically sound and biostratigraphically useful. Gondolella Stauffer and Plummer, 1932 (type-species G. elegantula, O.D.), is subject to many of these restrictions, especially geographically and paleoecologically, but offers a highly precise zonation in the rocks where it does occur that can serve as an interim standard for some (mostly Missourian) and a supplement for others (mostly Desmoinesian). Enough occurrences have been amassed to facilitate interregional, and in some cases, intercontinental correlations. Desmoinesian gondolellids are known from 9 stratigraphic units in the Illinois basin and 5 from the Mid-Continent, and 5 zones are recognized. Distribution is relatively uniform, and zonation of this part of the column is almost total. This zonation is less detailed than the contemporary Neognathodus zonation, but it is a valuable supplement to it. The most dense concentration of Gondolella-bearing units is in the Mid-Continent Missourian where 15 units have produced gondolellids. These and the 6 Illinois basin units can be assigned to at least 6 zones, totally contiguous in the lower Missourian, less so upward. The Virgilian cannot be completely zoned, but the 2 productive Mid-Continent units are assigned to different zones. End_of_Article - Last_Page 507------------

Toward Greater Precision in Rock-Color Terminology—Revisited

The Methuen Handbook of Colour is an economical substitute for more expensive color charts. Additionally, it is easier and more versatile to use. Whether one employs the Methuen system or translates to the Munsell system, this book is probably the best tool of its kind for geologic fieldwork.