Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact firstname.lastname@example.org with any questions.
The Serpukhovian (Namurian A) stratigraphy of the Ostrava Formation, Upper Silesian Coal Basin, Czech Republic, consists of coal-bearing paralic sediments underlain by marine deposits in a cyclothemic nature similar to those in the Pennsylvanian of Euramerica. The thickness of the formation exceeds 3000 m, in which >170 coals are identified in a foreland basin setting. Fifty-five genetic cycles are identified in the present study, using transgressional erosional surfaces as lower and upper boundaries. Terrestrial plant-macrofossil assemblages are preserved within each cycle, mostly associated with coals, and these represent a sampling of the coastal plain vegetation. New high-precision isotope dilution–thermal ionization mass spectrometry U-Pb ages on zircons from tonsteins of two coals provide chronometric constraints for the Serpukhovian. Unweighted Pair Group Method with Arithmetic Mean clustering and Bayesian statistical classification group macrofloral assemblages into four distinct stratigraphic clusters, with assemblages persisting for <18 cycles before compositional change. Cycle duration, based on Ludmila (328.84±0.16 Ma) and Karel (328.01±0.08 Ma) tonsteins, overlaps the short-period (100 kyr) eccentricity cycle at the 95% confidence interval. These dates push the beginning of the Serpukhovian several million years deeper in time. An estimate for the Visean-Serpukhovian boundary is proposed at ∼330 Ma. Late Mississippian wetland ecosystems persisted for >1.8 million years before regional perturbation, extirpation, or extinction of taxa occurred. Significant changes in the composition of macrofloral clusters occur across major marine intervals. These results accord with other estimates of Carboniferous tropical wetland community persistence. Hence, vegetational persistence was characteristic of peat-accumulating and mineral-substrate wetland ecosystems beginning in the Late Mississippian, when there is evidence for the first appearance of eustatically controlled cyclothems during the buildup of Gondwanan glaciation.
A significant vegetational change occurs in the Late Mississippian (Serpukhovian, Namurian A) across the Enna Marine Zone (EMZ), Upper Silesian Basin, Czech Republic. All plant clades were impacted, including both spore-producing and seed-producing taxa; wetland taxa were unaffected. Similar vegetational responses are not identified elsewhere although, basinwide, thick marine zones (e.g., Barbora Marine Zone, BMZ) also developed at various times during the Serpukhovian. Examination of sedimentological and petrophysical (gamma-ray log) trends in both marine zones indicates that different mechanisms generated accommodation space during each interval. Placed in a genetic stratigraphic context, the EMZ records sedimentation in at least four (or more) genetic sequences, each equal in duration to individual 100-kyr cyclothems identified in the coalfield. Discrete maximum flooding surfaces (MFSs) with associated condensed sections and macrofaunas are prominent in distal areas and were identified using gamma-ray log responses. In contrast, the petrophysical expression of distal regions of the BMZ shows no strong positive gamma-log excursions interpreted as MFSs. Rather, this interval is a succession equal in duration to two cyclothems. The BMZ represents sedimentation in a glacial-interglacial cyclothemic framework; in contrast, the EMZ represents accumulation under continued eustatic sea-level rise in response to southern hemisphere deglaciation and global warming. Late Mississippian vegetational response to paleoequatorial climate change is interpreted to represent a shift toward greater seasonality, with an increased number of dry months (monsoonal rainfall pattern?) resulting in statistically significant extinction or extirpation several million years prior to the onset of maximum glaciation and sea-level drawdown at the Mississippian–Pennsylvanian boundary.
Paleoecological statistics calculated for fossil assemblages are often influenced by biases that may act at more than one scale. These biases are difficult to detect without an overarching method that can accommodate the spatial attributes of fossil specimens. Geographic Information Systems (GIS) can be used to manage, analyze, synthesize, and archive large amounts of paleontological data within a geospatial framework. This study uses GIS to test the impact of variation in sampling area and rate of sediment accumulation on two commonly employed paleoecological statistics—species richness and relative body size. Mammals of the Willwood Formation (early Eocene) from the central part of the Bighorn Basin, Wyoming, USA, serve as a test case. Fossil localities outlined on U.S. Geological Survey topographic maps were digitized and GIS was used to estimate their two-dimensional areas. This metric was compared directly with species richness to test sampling area bias and also was used to calculate the density of species per unit area, which could be compared among various samples. Tests were constructed to examine variation at the locality scale and across the basin. Results of the analysis of the sampling area bias showed that species richness increased significantly with increasing sampling area and that rarefaction, the commonly used method of standardizing richness, did not remove the sampling area-richness relationship when the magnitude of area variation was >∼1 km2. Results of the analysis of compositional variation related to changes in rate of sediment accumulation showed that locality-scale changes did not have a significant influence on assemblage composition.
Stables isotopes and elemental composition of two well-preserved belemnite rostra (Hibolithes beyrichi and H. hastatus) from the Bathonian of central Poland were studied. Average temperatures calculated from the oxygen isotope ratios of Hibolithes beyrichi and H. hastatus are 10°C and 6°C, respectively. The absence of high-amplitude variations in high-resolution temperature profiles suggests these belemnites lived in deeper waters. This interpretation is compatible with a nektobenthic habitat of belemnopsid belemnites. Carbon isotope ratios of the rostra are assumed to be affected by vital fractionation with prominent fluctuations in the δ13C records resulting from changes in the metabolic activity. Observed variations in Mg:Ca ratios of the rostra (from 5 mmol·mol−1 to 28 mmol·mol−1) are predominantly a primary signal. Temperature dependence of the Mg:Ca ratio is inferred for H. beyrichi on the basis of a correlation with δ18O values; however, no such correlation is observed for H. hastatus. No significant correlation is observed between Sr:Ca ratios and δ18O values in either taxon. Sulphur contents in the rostra vary from 630 ppm to 4400 ppm and are interpreted to be largely coprecipitated with belemnite calcite. Extreme compositions of sulphur are interpreted to result from the incorporation of diagenetic sulphur during early marine diagenesis, which is also characterized in these rostra by high Mg:Ca and Sr:Ca ratios and low δ13C values. A total number of growth rings in the rostrum of H. beyrichi is calculated at around 600, thus, an expected life span of H. beyrichi is considered to be ∼1.5 years assuming daily precipitation of growth bands.
Trends in the size distributions of fossil seed assemblages over geologic time have been interpreted as evidence of fundamental changes in the structure of terrestrial ecosystems. It is not clear, however, how accurately fossil seed assemblages reflect the original flora. As a case study, the seed-size distribution of a living hardwood forest and a salt marsh community in Maryland was compared to that of its potential fossil assemblage, seeds extracted from sediment cored in the adjacent tidal estuary. Results indicated that the death assemblage was significantly different from the source community, lacking most of the smaller-seed morphotypes. The biased accumulation was not driven solely by over- or underrepresentation of plants of a particular dispersal mode or growth form. Although there was a sedimentological gradient along the transects, there was no correlation between grain size and seed-size distributions within the cores. The difference appears to be primarily an issue of transport: 45% of morphotypes identified in the death assemblage were present in the life assemblage, and only 33% identified in the life assemblage were also in the death assemblage. These results indicate that (1) estuarine deposits capture a partial representation of the local seed flora with significant regional influences, and (2) fossil seed assemblages should not be compared directly to seed-size distributions documented in living communities.
In order to test the assertion that the carbon-isotopic composition of the ancient atmosphere (δ13CO2) can be reconstructed from the carbon-isotopic composition of fossil terrestrial plant tissues across a variety of environments, the δ13C value of land-plant tissues isolated from modern fluvial sediments was compared to that of today's atmosphere. Plant stem and leaf fragments were isolated from organic carbon-rich sediments of the Black River in Jamaica, which drains a basin containing only C3 ecosystems. Sediment was sampled at 12 sites along a dissolved salt-content gradient, from the coastal plain to near its mouth, which allowed evaluation of the effect of salt influence on the organic carbon-isotope signature. Many properties of the sediment varied systematically with salt content (e.g., mass-percent carbonate, abundance of palynomorphs, δ13C and δ18O values of carbonate), confirming a significant and increasing marine influence closer to the mouth of the river. The δ13C value of total organic carbon systematically decreased by ∼2‰ with increased NaCl concentration, indicating the presence of a mixing line between marine and terrestrial organic inputs. In contrast, for leaf and stem isolates, there was no significant dependence of δ13C value on NaCl concentration, suggesting that the isotopic signature of the integrated terrestrial contribution is independent of the salt content of the depositional environment. The mean values of all isolates retrieved from the sediments predicted a δ13CO2 value of −9.7 (±1.0) for leaf material and −8.2 (±1.7) for stems. Both of these values are within ∼1‰ of recent regional-scale measurements of atmospheric δ13CO2 value.
This study deals with the recovery of chitinoidellid specimens in palynological residues and their usefulness as biochronologic tools. We sampled specimens—which represent a very small group of ancient planktonic ciliates of uncertain origin that appeared in the early Tithonian and lasted until the late Tithonian in the Jurassic—from the upper part of the Ammonitico Rosso Formation, outcropping in southeastern Spain (Sierra de Crevillente, Congost section). Chitinoidellid associations allowed us to attribute the lower part of the succession studied to the early Tithonian (Chitinoidella Zone). The palynological preparations reveal urn-shaped bodies 60–140 μ long, which we interpret as chitinoidellid remains. These organic-walled objects show the organic nature of chitinoidellid loricae, which, as previously suggested, were probably chitinous. The loricae consisted of a continuous organic lining and suggest that the presence of calcite crystals was limited to single dispersed crystallites rather than their occurrence in layers, as suggested by earlier reports. This study shows that palynological extraction of chitinoidellids can yield more information on the morphology and, thus, on the phylogeny of this planktonic group than the traditional thin-section approach.
We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting coralline red alga, Clathromorphum nereostratum, from Amchitka Island, Aleutian Islands. Mg/Ca ratios of individual growth increments were analyzed by measuring a single-point, electron-microprobe transect, yielding a resolution of ∼15 samples/year and a 65-year record (1902–1967) of variations. Results show that Mg/Ca ratios in the high-Mg calcite algal framework display pronounced annual cyclicity and archive late spring–late fall sea-surface temperatures (SST) corresponding to the main season of algal growth. Mg/Ca values correlate well to local SST, as well as to an air temperature record from the same region. High spatial correlation to large-scale SST variability in the subarctic North Pacific is observed, with patterns of strongest correlation following the direction of major oceanographic features that play a key role in the exchange of water masses between the North Pacific and the Bering Sea. Our data correlate well with a shorter Mg/Ca record from a second site, corroborating the ability of the alga to reliably record regional environmental signals. In addition, Mg/Ca ratios relate well to a 29-year δ18O time series measured on the same sample, providing additional support for the use of Mg in coralline red algae as a paleotemperature proxy that, unlike algal-δ18O, is not influenced by salinity fluctuations. Moreover, electron microprobe–based analysis enables higher sampling resolution and faster analysis, thus providing a promising approach for future studies of longer C. nereostratum records and applications to other coralline species.