NAPC 2001

Abstracts, O - Pe
(5/17/01)

Jump to: Oleinik | Olivero | Olszewski | Omaña | Pajak | Pandolfi | Parham | Parsley | Payne | Perez-Huerta | Perrilliat | Peters

Return to Main Abstracts Page

PALEOBIOGEOGRAPHIC AND PALEOCLIMATIC IMPLICATIONS OF THE CENOZOIC MOLLUSCAN RECORD IN THE NORTHWESTERN PACIFIC

OLEINIK, Anton E., Dept. of Geography and Geology, Florida Atlantic University, Boca Raton, FL, USA

The high latitude area of the Kamchatka Peninsula contains the northernmost-known record of the Cenozoic molluscan faunas in the North Pacific, with the vast majority of fossil localities situated above 56^° N. Coastal outcrops stretching for over 400 kilometers along the shores of the western and northeastern Kamchatka are composed of shallow-marine fossiliferous rocks deposited in a suite of marginal basins existed around the paleo-Kamchatka volcanic arc during the Cenozoic. Evolutionary patterns of Cenozoic high-latitude molluscan assemblages of Kamchatka, ranging in age from the Early Paleocene through Early Pleistocene were heavily controlled by climatic changes. Globally warm intervals were characterized by low latitudinal gradients and broad biogeographic provinces with high percentages of cosmopolitan taxa with warm-water affinities. Close similarities between Paleocene and Eocene shallow-water molluscan assemblages of Kamchatka and the western Coast of North America points on the existence of the shallow-marine migration route along the southern margin of the Beringia during most of Paleogene. Climatic deterioration started in the late Eocene and continued throughout Early Oligocene increased the amount of diversification and ecological adaptations within "future cold water" elements of the biota and the stepwise extinction or southward retreat of the warm water elements. Neogene assemblages were heavily influenced by climatic fluctuations, connected with the intensification of the paleo-Kuroshio current and episodic warming of the high latitudes, peaked at 15.5 and 13.4 Ma. Penetration of warm waters in the high latitudes facilitated several northward migration pulses of temperate and subtropical genera. These climate-controlled migratory events together with the background climatic cooling throughout the Neogene, resulted in evolution and diversification of the endemic faunal elements that characterize the numerous modern molluscan provinces of the northern circum-Pacific.

EVOLUTION OF ZOOPHYCOS IN THE VOCONTIAN THROUGH (SOUTHEASTERN FRANCE) FROM LOWER JURASSIC TO UPPER CRETACEOUS

OLIVERO, Davide, Université Lyon 1, Villeurbanne, France

The complex trace fossil Zoophycos is recorded worldwide, from Cambrian to Holocene. It is still an enigmatic ichnofossil. Traces related to Zoophycos have a significant general evolution in their organization, with an increasing complexity in the burrow system, and in their environmental position, with a general shift from the shelf to deep sea.

Ichnologically homogeneous material has been studied in a relatively restricted place: the Vocontian Through, in southeastern France. Good outcrops allow the study of Zoophycos from Toarcian to Cenomanian. The host sediments are usually marly limestones, occasionally sandstones.

Zoophycos from Lower Jurassic are restricted to shelf environments, they form regular simple helicoidal whorls and the outlines are rarely lobate. The width of the laminae never exceeds 40­50 cm. In sandy facies of the same age morphologies are quite confusing, the structures are rough and the dimensions more limited. The Middle Jurassic sediments are characterized by large and slightly lobate Zoophycos. The paleobathymetric range varies from outer shelf to middle slope. Lower Cretaceous traces characterize deeper environments (lower slope) and their dimensions increase up to 150 cm, with slight lobes always present. Locally, a few little specimens are restricted to dysoxic intervals in some Valanginian deposits.

Very large Zoophycos with well-developed lobes have only been recorded in deep-sea marly sediments (Aptian to Cenomanian), but also at the top of Barremian turbidites surrounded by basinal limestones without Zoophycos. Curiously, all the observed specimens are constructed upwards in the sediment, except the well lobate forms, which are constructed downwards. These are limited to mid-Cretaceous deep-sea substrates.

As a conclusion, this study confirms the general shift to deeper environments and the increasing complexity in the morphology of the burrow system. But this morphology seems to be more influenced by the substrate rather than by the bathymetry alone.

SURVIVING TAPHONOMIC RUSSIAN ROULETTE: HOW THE ODDS OF FOSSIL PRESERVATION AFFECT TIME-AVERAGING

OLSZEWSKI, T.D., Dept. of Geological Sciences, Indiana University, Bloomington, IN, USA

The distribution of shell ages in a marine deposit places a limit on the temporal resolution of questions that can be addressed using fossil material. In modern settings, shell ages can range over 100s to 1000s of years despite extremely rapid rates of destruction. This broad range is thought to be due to mixing of recent shells with sub-fossil material from below the taphonomically destructive zone (TDZ) but above the depth of final burial (DFB). In this study, mixing and destructive processes have been modeled stochastically to determine the influence of TDZ thickness, DFB (reworking zone), and long-term burial rate on shell age distributions. To model reworking, all shells above a randomly determined depth are mixed. Probability of reworking decreases from the sediment-water interface (SWI) to the DFB. To model taphonomic loss, a random number generator is used to determine which shells survive and which do not (i.e., playing Russian roulette). Probability of shell destruction decreases with depth from the SWI to the base of the TDZ. After mixing, the depths of all shells increase in accordance with a specified burial rate. For a single model run, these three steps are repeated until all shells have been either destroyed or buried below the DFB. For a given set of parameters, the model produces expected shell age distributions, which are generally lognormal. Increasing the TDZ relative to the DFB does not influence the mode or range of the shell age distribution. Increasing the DFB increases the age and number of the oldest shells and shifts the mode toward older shells. Increasing the burial rate can shift modal ages older or younger, but invariably increases the proportion of very old shells. These preliminary results suggest that time-averaging is more a function of reworking and burial rate than the rate of taphonomic destruction, which is primarily reflected in the number of shells entering the rock record.

ALBIAN BENTHIC COMMUNITY OF THE EL ABRA FORMATION FROM EAST-CENTRAL MEXICO

OMAÑA, Lourdes, and Gloria Alencaster, Instituto de Geología, Universidad Nacional Autónoma de México, México

Cretaceous carbonate deposits of the El Abra Formation are widely distributed in the folded Sierra Madre Oriental. At El Madroño locality this stratigraphic unit contains an abundant, diverse and excellently preserved paleobiota, composed of rudist and other kind of bivalves, gastropods, corals, echinoids, sponges, foraminifers and algae, and it is located in the NE extreme of the State of Queretaro, in eastern-central Mexico. The preservation of the rudist specimens, complete and in three dimensions, permitted us to redescribe the coalcomanid caprinid genera Texicaprina, Mexicaprina and Kimbleia, and to propose the new genera Guzzyella, Müllerriedia and Jalpania, which probably constitute a new subfamily. This caprinid rudist fauna is 100% endemic at the generic level. It occupies the marginal facies of the platform. Among the monopleurid rudists present are Monopleura marcida, M. pinguiscula, and two new species of this genus. In the lagoonal facies of the platform, Toucasia texana is almost the only species. The foraminiferal association is well preserved but scarcely diverse. The main species are Dictyoconus walnutensis, Coskinolinoides texanus, Buccicrenata subgoodlandensis, Cuneolina sp., and a few miliolids as Spiroloculina and Moesiloculina. Also present is the planktic genus Favusella. Among the calcareous algae are Cayeuxia piae, Lithocodium aggregatum and Acicularia elongata. The age assignment of the deposit is based on the benthic foraminifer Dictyoconus walnutensis, which is considered a regional marker of the middle Albian. The paleoenvironmental reconstruction, inferred from the lithology and benthic assemblage, suggests a warm shallow water platform with optimal living conditions, with abundant nutrients and highly oxygenated water, which permitted the notable flourishing of the community.

MICROVERTEBRATES FROM A NEW ARIKAREEAN LOCAL FAUNA, JOHN DAY FORMATION, OREGON, WITH BIOSTRATIGRAPHIC AND TAPHONOMIC IMPLICATIONS

PAJAK, Alois F., III, Theodore J. Fremd, and Dwight Hoy, John Day Fossil Beds National Monument, Kimberly, OR, USA

Screen-washing techniques have generally been unproductive within the late Oligocene and early Miocene strata of the John Day. As a result, microvertebrates from the John Day Basin have largely been known from isolated occurrences, with teeth and bones represented most frequently by single elements. A newly discovered lithosympatric assemblage in the northernmost exposures of the John Day Basin contains several Arikareean age vertebrate faunas recovered from the previously unstudied Lone Rock localities, which correlate to the upper John Day strata. Within this assemblage, the Campbell Ranch Local Fauna consists of the largest microvertebrate faunal concentration yet known from the John Day. The outcrop from which the local fauna was recovered has been correlated with rocks in the Turtle Cove area of the John Day Basin and consists of very fine silty tuffaceous claystone in a loess-like deposit. This fauna represents a diverse population of microvertebrates that, prior to the recovery of this material, were not known to occur together within any stratigraphic intervals defined in the John Day strata. Likewise, the paucity of microvertebrate occurrences within the John Day has not permitted any detailed population or taphonomic studies prior to the recovery of the over 5000 specimens recovered so far from this locality. This local fauna is dominated by geomyids and cricetids, with insectivores, leporids, heteromids, and aplodontids forming about 15% of the remaining material. The first reported local occurrence of Plesiosminthus sp. and other taxa within the John Day strata assists in confirming a late Arikareean age for this fauna. The assemblage is of taphonomic interest, representing a mode of accumulation different from any previously identified localities in the John Day Basin. Preliminary examination indicates the fossil remains are consistent with descriptions of microvertebrate remains recovered from owl middens.

PLEISTOCENE PERSISTENCE AND THE RECENT DECLINE IN CARIBBEAN CORAL REEF COMMUNITIES

PANDOLFI, John M., Dept. of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA

The recent fossil history of coral reefs can provide a critical window in which to view the magnitude, scale, and frequency of change over significantly broader time intervals than available to modern ecology. I examined the structure of Pleistocene Caribbean coral communities using a hierarchical sampling design at broad spatial and temporal scales. Significant differences in the composition of coral communities from the leeward reef crest among three islands (San Andrés, Curaçao, and Barbados) during the last interglacial, 125 ka (thousand years ago), were driven by variability in the relative abundance of the same four or five abundant taxa. At Barbados, coral composition remained constant from 220-125 ka, but differed during the 104 ky reef-building episode. However, the 104 ky community was closer in composition to older coral communities from Barbados than it was to communities from San Andrés or Curaçao. Separate analyses on the composition of the rare taxa (data compiled using 1 hr searches) and those of the common taxa (data compiled using 40 m transects) gave highly concordant results, suggesting the composition of the rare taxa is correlated with that of the common, structurally dominant corals.

These Pleistocene data point to a high degree of order in coral communities over broad spatial and temporal scales and support the importance of local influences in determining reef coral community structure. Moreover, they indicate a structure to reef communities that persisted to the 1980s, when rapid habitat degradation led to the collapse or severe alteration of coral communities throughout the Caribbean. Whether such habitat reduction and change in species composition is unprecedented and due to human consumption and pollution, or it represents a short-term fluctuation in an otherwise predictable community structure, is one of the most important questions facing reef managers today. Present trends are not predicted from history but may well be related to human-induced environmental modification.

INVADING THE LAND AND SEA: PROGRESS TOWARDS UNDERSTANDING MAJOR ECOLOGICAL TRANSITIONS IN TURTLES AND THE ORIGINS OF SOME MODERN CLADES

PARHAM, James Ford, Museum of Paleontology, University of California, Berkeley, CA, USA

Although turtles are commonly used as an example of conservative evolution, they are capable of rapid evolutionary change and exhibit a wide array of phenotypes during their long and storied history. Like other clades that have adopted successful, yet divergent, variants on the tetrapod Bauplan, the evolution of turtles is highly constrained, but homoplasy is rampant. Homoplastic morphologies make phylogenetic reconstruction based solely on morphology extremely difficult. In the absence of unambiguous synapomorphies, temporal and geographic data can provide important, independent lines of evidence. These data and the homoplasy observed in the impressive fossil history of turtles, combined with data from their ecologically diverse living relatives, allow us to make inferences about patterns of turtle evolution using multiple lines of evidence. The invasions of the land and sea are good examples of major ecological transitions resulting in parallel changes in plesiomorphic, generalized grades. A consideration of all of the available data suggests that invasions of the land and sea evolved multiple times and that some of the currently recognized clades are polyphyletic grades.

EVOLUTION AND DIVERSITY IN STYLOPHORAN ECHINODERMS

PARSLEY, Ronald L., Dept. of Geology, Tulane University, New Orleans, LA, USA

Recent establishment and/or restudy of approximately 20 stylophoran genera enables us to differentiate, by cladistic analysis, the Class Stylophora into well-defined subclades and to see a clear evolutionary picture. Of nearly 70 known genera, 49 were analyzed using 57 unweighted binary and multistate characters in PeeWee/Nona. Genera not included are based on incomplete or poorly preserved specimens; most can be placed, with reasonable confidence, within the proper subclade. Stylophora are uncommon "homalozoan" echinoderms that originate in the Cambrian and range into the L. Devonian, with a single Lazarus genus persisting until the L. Pennsylvanian. The earliest stylophorans are cornutes from the M. Cambrian of Bohemia and the Western United States. Key pleisiomorphic characters are; asymmetrical thecae, primitive aulacophore with stylocone, a ventral strut composed of M1 and M5 plate elements, and commonly, complex sutural pore respiratory structures (cothurnopores, lamellipores). The major evolutionary center(s) for the cornutes is in basins marginal to Gondwana especially in the Montagne Noir, France and the "Barrandian" region of Bohemia in the U. Cambrian and L. Ordovician. Ankyroids evolved from the cornutes in the U. Cambrian, probably in the Montagne Noir region and radiated worldwide from there. Key pleisiomorphic characters are: bilateral thecal outlines, advanced aulacophores with styloids, detached M5 portion of the strut that is expressed as the ventral CS somatic plate, and no respiratory pore structures. In the L.­M. Ordovician major ankyroid diversification occurred resulting in least six subclades ("cornutiforms," mitrocystitids, peltocystids-kirkocystids, yachalicystids, anomalocystitids-placocystitids and anomalocystitids-allanicytids) in the same Gondwana region. In each subclade thecal reduction by loss of posterior marginals/somatic plates has occurred. Silurian­Devonian occurrence and diversification is concentrated in seas marginal to Gondwana, especially in the Australian and South African regions.

DEFINING THE RANGE OF SUDDEN AND GRADUAL EXTINCTION SCENARIOS COMPATIBLE WITH ANY (SIMPLE) STRATIGRAPHIC DISTRIBUTION OF FOSSILS

PAYNE, Jonathan L., Dept. of Earth and Planetary Science, Harvard University, Cambridge, MA, USA

Sudden extinction events can appear gradual in the fossil record due to the Signor-Lipps effect. Springer (1990) demonstrated that for a group of taxa the confidence levels of classical confidence intervals reaching a putative extinction horizon should be uniformly distributed if there was a sudden extinction at that horizon. The distribution of confidence levels can be tested against the uniform distribution using a goodness-of-fit test (e.g., Kolmogorov-Smirnov). This approach assumes the null hypothesis of sudden extinction unless it is rejected on statistical grounds. Sudden and gradual extinction, however, should be viewed as equally likely alter natives and there will always be gradual extinction scenarios that produce distributions of confidence levels that are indistinguishable from those expected in the case of a sudden extinction. For a range of gradual extinction scenarios, I used simulations to determine which would produce distributions indistinguishable from a sudden extinction.

The ability to distinguish between sudden and gradual extinction depends upon two factors: (1) the duration of the gradual extinction as a function of the average gap between fossil occurrences, and (2) the number of taxa included. The greater the duration of the gradual extinction, the less likely it is to be mistaken for a sudden extinction. The range of gradual extinction scenarios that are compatible with a sudden extinction scenario decreases as the number of taxa increases. The simulation results eliminate the need to consider sudden extinction separately from gradual extinction; it is merely the most rapid possible version of gradual extinction. The results can be applied to all situations that meet the assumptions necessary for the calculation of classical confidence intervals. The use of classical confidence intervals is expanded by the results of the simulations by providing a new approach for constraining the minimum rate of gradual extinction based upon information in the fossil record.

PENNSYLVANIAN BRACHIOPOD ASSEMBLAGE ZONES IN THE ELY LIMESTONE OF EAST CENTRAL NEVADA

PEREZ-HUERTA, Alberto, and Norman M. Savage, Dept. of Geological Sciences, University of Oregon, Eugene, OR, USA

The upper part of the Ely Limestone, exposed in the Illipah Quadrangle of East Central Nevada, includes several horizons of silicified brachiopods that are commonly preserved as in situ communities. The formation comprises a sequence of biomicitic limestones that range in thickness from 138 to 200 m with a Morrowan-Atokan age. At leat two major brachiopod assemblage zones can be recognized in different sampling. The "Spiriferid Assemblage Zone" is dominated by the genera Reticulariina and Punctospirifer with the main fauna composed of Composita ?subtilita, Cleiothyridina aff. C. elegans, Hustedia rotunda, Eomarginifera nuda, and Kozlowskia ?splendens. The "Productid Assemblage Zone" is dominated by the genera ?Inflatia and ?Rugoclostus with the main fauna composed of Punctospirifer gnomus, Punctospirifer transversus, Reticulariina campestris, and Hustedia ?brentwoodensis. It has been found that the genera Beecheria and Rhipidomella and the species Cleiothyridina orbicularis are present in both assemblage zones. The proportions of genera and the composition of the brachiopod assemblage zones varies laterally and vertically with local environmental changes that are also reflected by changes in bottom sediment and associated bryzoans and corals. These may reflect fluctuations in sea level, climate, or tectonic disturbances. Ongoing work is directed toward further clarifying the ecological factors controlling the compositional shifts in the assemblage zones. These factors may include fluctuations in sea level, which was pointed out as the main factor by Moffet and Langenheim (1986). These authors recognized in general, the same "spiriferid and productid" brachiopod assemblage zones and included both, in their microfacies 2 and microfacies 1 respectively. These microfacies distinctions were part of their sedimentological division into five microfacies that define 13 complete cycles from relatively deep to shallow-water deposition.

STRATIGRAPHIC AND PALEOECOLOGIC IMPLICATIONS OF A NEW SPECIES OF OSTREID FROM THE LOWER EOCENE VIENTO FORMATION, LA POPA BASIN, NORTHEAST MEXICO

PERRILLIAT, Maria del Carmen, and Francisco Vega, Instituto de Geología, UNAM, Ciudad Universitaria, Coyoacan, México

Oyster banks are abundant in the intertidal-fluviatile facies of the Viento Formation in La Popa basin, Nuevo Leon. The size of the oysters is remarkable, as the mean height of the specimens is 200 mm. A new species is referred to Ostrea (Turkostrea) n. sp., based on ornamentation and presence of chomata on the internal margins of the valves. Similar ostreids have been reported from Tunisia, where Ostrea strictiplicata major Locard is present in Eocene beds. This species has a triangular shape and the radial ribs of the left valve are more numerous and more closely spaced than the new species from Nuevo Leon, which is more ovate. These same features differentiate the new species from Ostrea arrosis Aldrich from the Eocene of Texas. Both species attain a large size. However, Ostrea (Turkostrea) n. sp. seems to be larger and thicker, which may suggest a tropical climate for this part of northeast Mexico during the lower Eocene. Presence of Turritella mortoni postmortoni Conrad associated with some of the ostreid banks where we collected the new species confirms a lower Eocene age for the Viento Formation. The Viento Formation is one of the two youngest stratigraphic units of the La Popa basin from which no age has been defined until now. The overlying Carroza Formation remains undated, but it is possible that its age will not be younger than Eocene. Distribution of the facies and outcrops of the Viento Formation suggests that during lower Eocene times the La Popa basin represented a fluvial landscape, one with considerable amounts of organic matter in the rivers, which prevailed in this region during a regression. Some of the oyster shells were used as substratum by bryozoan colonies, whose growth reached considerable thickness.

LARGE-SCALE HETEROGENEITY IN THE STRATIGRAPHIC RECORD: A SIGNIFICANT SOURCE OF BIAS IN GLOBAL DIVERSITY ESTIMATES

PETERS, Shanan E., and Michael Foote, Dept. of the Geophysical Sciences, University of Chicago, Chicago, IL, USA

Many features of global diversity compilations have proven robust to continued sampling and taxonomic revision. Inherent biases in the stratigraphic record may nevertheless substantially affect estimates of global taxonomic diversity. We use a simple estimate of the amount of marine sedimentary rock available for sampling: the number of formations in the stratigraphic Lexicon of the United States Geological Survey. We find this to be positively correlated with two independent estimates of rock availability: global outcrop area derived from the Paleogeographic Atlas Project (University of Chicago) database, and percent continental flooding. Epoch-to-epoch changes in the number of formations are strongly correlated with changes in sampled Phanerozoic marine diversity at the genus level. We agree with previous workers in finding evidence of a diversity-area effect that is substantially weaker than the effect of the amount of preserved sedimentary rock. Our results suggest that much of the observed, short-term variation in marine diversity may be an artifact of variation, in the amount, of rock available for study.

Like the comparison between change in number of formations and change in sampled diversity, which addresses short-term variation in apparent diversity, the comparison between absolute values of these quantities, which relates to longer-term patterns also shows a positive correlation. Moreover, there is no clear temporal trend in the residuals of the regression of sampled diversity on number of formations. This raises the possibility that taxonomic diversity may not have increased steadily since the early Paleozoic. Because of limitations in our data, however, this question must remain open.