ALBERT

Description: The horned dinosaur Centrosaurus apertus from the Belly River Group (Campanian) is represented by multiple articulated skulls and skeletons, and is particularly notable for its occurrence in dozens of large-scale monodominant bonebeds, which have been found in the Dinosaur Park Formation across southern Alberta and Saskatchewan. Here we present a detailed taphonomic analysis of the first large-scale Centrosaurus apertus bonebed (McPheeters bonebed) from the Oldman Formation of southeastern Alberta. The McPheeters bonebed rivals the richest bonebeds in the Dinosaur Park Formation in terms of bone density and size, and the complete disarticulation of elements. The bonebed occurs in an overbank facies and is dominated by small bone clasts, suggesting that only low energy water current contributed to the formation of the bonebed before its final burial event. Patterns of taphonomic modification suggest that bones experienced little weathering, breakage, or scavenging. In turn, these conclusions are compatible with an overall interpretation of rapid burial in humid conditions after the disarticulation of elements. These taphonomic features are virtually identical to those seen in the well-documented bonebeds of this species in the Dinosaur Park Formation, which are interpreted to represent mass death events caused by seasonal tropical storms and associated large-scale flooding. Late Cretaceous dinosaur species typically have small geographic and stratigraphic ranges defined by the extent of single geological formations. The new bonebed extends the distribution of Centrosaurus apertus to the upper Oldman Formation, which is interpreted as more inland than the coastally influenced Dinosaur Park Formation, and suggests that mass death events related to seasonal tropical storms occurred over a broader geographic area and in a greater range of paleoenvironments than previously documented.

Description: Dinosaur reproductive biology is often inferred from the biology of extant taxa; however, taphonomic studies of modern nest sites have focused exclusively on avian, rather than reptilian species. We documented eight Agassiz's desert tortoise ( Gopherus agassizii ) nests and ten loggerhead sea turtle ( Caretta caretta ) nests. Gopherus agassizii excavated burrows up to 70 cm long and laid rigid-shelled eggs 10–12 cm below the burrow floor. The 19 cm x 12 cm depressions consisted of hard consolidated sand surrounded by a 3–4-cm-high rim and contained 2–5 hatched eggs in a single layer. These hatched egg bottoms represent ~ 25% of the original egg, and five of 27 contained fully developed dead neonates. Desiccated membrane separated from the egg interior forming pockets that filled with eggshell and sand. Of 106 and 79 eggshell fragments in the hatched egg and surrounding sand, 48% and 23% occurred concave up, respectively. However, the combined numbers of eggshell fragments inside the eggs and in the immediately surrounding sand approximates the 60:40 ratios at in situ avian nests. Therefore, this ratio may provide reliable evidence for hatching sites regardless of the incubation strategy employed by the adult. Caretta caretta nests differed from those of tortoises in their greater depth (~ 50 cm) and occurrence in moist, cohesive sand. Clutches contained over 100 pliable-shelled eggs that tore and collapsed upon hatching, without brittle fracture. Failed eggs in two clutches showed five development stages, indicating that the deaths occurred over an extended time period. With the exception of predation, the G. agassizii and C. caretta nests showed no significant eggshell or hatched eggs above the egg chamber.

Description: The stratigraphic record of shallow-water shoreline paleoenvironments is characterized by significant facies heterogeneity and laterally discontinuous stratal geometries. In contrast, we investigate a uniquely extensive and microstratigraphically spatially uniform interval of upper Famennian (Upper Devonian) marginal marine strata in the Rocky Mountains. This transgressive deposit (〈 5 m thick) rests on a depositional sequence boundary, and is composed of a thin, discontinuous basal transgressive sandstone bed, two thin fossiliferous shale beds, and several meters of oncolite-bearing carbonate wackestone. The lower shale is a consistently thin (~ 0.1 m) bed with a fossil fauna of spinicaudatans (clam shrimp or conchostracans), which are extant, bivalved, chitinous, benthic crustaceans that live in fresh to brackish water, in ephemeral ponds, estuaries, and other shoreline settings. Isotopic data for the oncolitic unit record deposition in an epicontinental seaway with restricted circulation and locally brackish conditions. Sulfur isotope data may also reflect short-term changes in redox conditions, consistent with our interpretation of temporary hypoxia during deposition of the spinicaudatan bed, based on its faunal assemblages. The remarkably large areal extent (~ 1600 km north to south, and ~ 1000 km east to west) of this uniformly thin interval with marginal marine fauna is one of the most unusual paleoecological events of the latest Devonian in Laurentia. It is considered an artifact of exceptional depositional processes including passive transgression (i.e., little or no wave or tidal ravinement) along with rapid opportunistic takeover of habitats during transgression. The radiation, possibly associated with temporary hypoxia, was aided by the spinicaudatan reproductive strategy of numerous offspring, high growth rate, and rapid reproduction.

Description: :  Petrophysical and geochemical properties of dolomites may exhibit a nested set of lateral patterns, typically at the scales of a few meters to ~ 20 m. This study assesses whether those lateral patterns are inherited from the limestone precursor or formed during dolomitization. Sampling was done across a preserved limestone-to-dolomite reaction front in grainstones of the Miocene Seroe Domi Formation, Bonaire, Netherlands Antilles. Post-dolomitization diagenetic overprinting in the two rock types is absent or minimal. Two ~ 65 m lateral transects were drilled at 30-cm spacing in two separate beds. Porosity, permeability, and geochemical ( 18 O, 13 C, Mn, Sr, and Na) analyses were performed on all 287 recovered samples, and 287 thin sections were point-counted for petrographic attributes. Variography shows that dolomite abundance and porosity contain three scales of lateral variability. Much of the signal is random sample-to-sample noise as ~ 65% of the total spatial variance occurs at 30-cm spacing. However, porosity and dolomite abundance also exhibit a short-scale correlation length of 3.7 m and a long-range oscillatory pattern (hole effect) at ~ 16 m, both of which are also periodic. Trace elements (Mn, Sr) and permeability exhibit short-range correlation to 5.8 m, but no long-range pattern. Mole %Mg and 13 C show increasing variance with distance, and all other dolomite attributes exhibit no spatial patterns. No limestone attributes show evidence for any short-range or long-range oscillatory patterns. This indicates that the lateral patterns in dolomite abundance, porosity, permeability, Sr, and Mn contents were not inherited from the limestone precursor. Dolomitization is interpreted to be the cause of the observed spatial patterns as that is the only geologic process that has affected the dolomite but not the limestone on the other side of the front. Geochemical self-organization during the dolomitization process is suggested to be the mechanism by which the spatial patterns in the dolomites emerge. A model for that self-organizing process is proposed that involves positive feedbacks between precipitation, dissolution, textural properties, reaction rates, carbon transport, and the evolving flow field. Relative to Mississippian, Permian, and Eocene dolomites that have been studied previously, the Seroe Domi dolomites have similar porosity variance at 30 cm spacing and hole effects with slightly greater wavelengths and much larger magnitudes. Any differences are interpreted to be related to diagenetic history. The older dolomites have been affected by burial diagenesis and/or weathering, which would likely increase sample-to-sample variability, therefore increasing short-scale randomness, decreasing the magnitude of hole effects, and shortening wavelengths of hole effects. The lateral patterning formed by dolomitization may thus not be as strongly expressed in ancient dolomites that have complex burial histories.

Description: :  Distinguishing different lithostratigraphic formations that are in contact with each other can be problematic when they are of like facies, appearance, and provenance. For example, formations of like facies that are vertically separated by a subtle unconformable surface are difficult to distinguish, especially if multiple candidate surfaces exist. Similarly, time-equivalent formations of like facies that were separated into distinct subbasins by a topographic divide may also be challenging to distinguish. In this study, formations of this nature were discriminated using statistical discriminant analysis of X-ray fluorescence (XRF) elemental data that included both mobile and immobile elements. This discrimination has important consequences for stratigraphic analysis. For example, accurate placement of an unconformable surface within a stratal succession is important because it affects the interpreted thickness of units and sequences in contact with that surface. Unit thickness influences the interpretation of basin subsidence and its timing, depositional style of basin fill, paleotopography, and diagenesis. When developing discriminant models, data must be collected from outcrop or well cores where formations bounding the unconformity or topographic divide are known. The models next establish and high-grade key elemental differences between the known formations. The models can then be used to classify samples from unknown formations to one of the known formations. In our study, samples from three lithostratigraphic formations were used to build two models: one grouped by facies trends, and one grouped by geographic location or tectonic feature. Results demonstrate that discriminant analysis of elemental XRF data can be used to distinguish these formations both vertically and laterally. Our models relied on both mobile and immobile elements to make the discrimination, implying that as long as sandstone formations of similar provenance have experienced different diagenetic histories (i.e., cements and alteration products) they can be distinguished in the rock record. This study applied the methodology of discriminant function analysis to identify the J-1 unconformity on Utahs Colorado Plateau. The J-1 unconformity is a regional unconformity that separates the Early and Middle Jurassic. Three formations of similar facies, appearance, and provenance are all in contact with this unconformity. The Early Jurassic Navajo Sandstone underlies the Middle Jurassic Page Sandstone in the eastern part of the study area, and the Middle Jurassic Temple Cap Formation in the western part of the study area. In much of the central part of the study area the stratigraphic position of the J-1 unconformity is unknown and the overlying formation is less well established. The J-1 unconformity appears to have been a baffle or barrier to fluid flow in much of this area. Also, paleotopography on the Navajo Sandstone appears to have separated the overlying formations into two subbasins. Thus, all three formations had different diagenetic histories that facilitated the discriminant modeling. The methods used in this study can be applied to similar sedimentary packages that were likewise partitioned vertically by fluid-flow divides such as unconformities and hiatuses, or laterally by topographic, hydrodynamic, structural divides, or lateral facies changes.

Description: :  Changes in composition during the transition from sediment to rock are usually attributed to long, complicated histories and atmospheric influences, while the contribution of benthic mat-building cyanobacteria is not typically considered. Here the goal is to understand the influence of cyanobacterial mats on mineral weathering in postdepositional settings of sandy, shallow subaquatic environments. Laboratory incubation experiments were done using ilmenite sands and ilmenite-enriched quartz sands colonized by cyanobacterial mats for five months at three temperatures: 25°C and 37°C, representative of postdepositional weathering regimes, and 70°C corresponding to early diagenesis. As a comparative control to represent abiotic processes, ilmenite sands and ilmenite-enriched quartz sands were also subjected to the same conditions without cyanobacterial colonization. The precipitation of minerals on cyanobacterial cells and extracellular polymeric substances (EPS) as well as the phase changes in natural ilmenites (FeTiO 3 ) were documented to determine if cyanobacteria influence mineral reaction pathways. The precipitates, ilmenite grains, and permineralized cells were analyzed using complementary techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD), and micro-Raman spectroscopy. The results of this study show that a variety of pure and mixed mineral phases precipitate under postdepositional conditions (T ≤ 70°C) in wet, sandy environments with or without cyanobacteria. Akaganeite, anatase, ankerite, lepidocrocite, gibbsite, kaolinite, and natrojarosite formed exclusively in the samples incubated with cyanobacteria. In the samples incubated with cyanobacteria, more mineral phases formed at 37°C, suggesting that cyanobacteria play a greater role in weathering than in early diagenesis. Sulfate phases that formed in the presence of cyanobacteria differed in chemical composition from the abiotic precipitates as Na, Al, Mg, and Si were incorporated into the structures of newly formed biotic phases. Understanding the possible fate of these precursor mineral phases will help redefine geochemical biosignatures that can be used for the detection of ancient microbial life in sedimentary rocks on Earth as well as for future missions exploring life on other planets.

Description: :  Dynamic physical and biological seafloor processes shape the three-dimensional stratal architecture of modern and ancient mud-dominated continental shelves. When evaluating a mudstone unit as a potential source, reservoir, or seal, it is imperative to understand the physical, biological, and chemical seafloor processes that control mudstone depositional fabric and diagenesis. This study presents sedimentological, ichnological, and geochemical data of exceptionally preserved mudstone originating from hyperpycnal and possible combined-flow deposits in the Lower Ordovician (Tremadocian) Beach Formation, Bell Island Group, Newfoundland. Seven mudstone facies are described, based on textural, compositional, and ichnological characteristics. Mudstone deposits interpreted to originate from hyperpycnal flows are well cemented, exhibit high chlorite­:illite ratios, and contain sharp grain-size changes, commonly forming beds with tripartite subdivisions. Deposits of wave-enhanced sediment gravity flows are, in contrast, poorly cemented illitic mudstone. These mudstone facies exhibit decimeter-thick wave or combined-flow structures within siltstone and very fine sandstone beds as well as laterally discontinuous, nonbioturbated mudstone layers. Beds of this facies have abundant mudstone-on-mudstone and mudstone-on-sandstone erosional contacts. Low organic carbon loading from the nonvegetated early Paleozoic hinterland, combined with a high reworking frequency on a shallow marine wave-dominated shelf, is inferred to have resulted in high remineralization efficiency, and low preservation potential of reactive organic carbon. Burial efficiency and bioavailability of organic matter are considered to be the critical variables controlling infaunal colonization and bioturbation in mud-dominated open-coastline paleoenvironments. This work demonstrates that ancient fine-grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal-to-distal facies relationships. It is proposed that the spatial organization of fine-grained sediment and facies architecture in such systems are controlled by: 1) frequency of sediment supply events, 2) direction of mud transport, 3) diagenetic reactivity of minerals and bioavailable organic carbon, and (4) residence time of mineral grains and organic matter close to the sediment–water interface.

Description: Age spectra of Mulinia lateralis shells from the top 0–10 cm of the sediment column in Copano Bay, Texas, show three distinct populations: a young population with a highly skewed distribution ranging from 0 to 1 years, a middle-aged population that is more symmetrical ranging from 1 to 10 years with a peak ~ 4 years, and a small, very old population ranging from 100 to 〉 10000 years. The young population is interpreted to record the rapid loss of shells from the taphonomically active zone at or near the sediment surface. The middle-aged population is interpreted to record a sequestered population of shells that has had time to accumulate below the taphonomically active zone. Although surface age spectra differ among depositional environments and at different locations, both of these populations are present in all sampled facies at multiple locations within the bay, indicating that the overarching controls on surface age spectra affect the entire bay. The very old surface population is present only in bay-margin sites and is interpreted to represent shells exhumed from eroding Holocene deposits. An 86-cm-long core taken at a bay-margin site near the mouth of the Aransas River contains shells spanning 〈 1 to 14,000 years but not preserved in stratigraphic order. The lack of stratigraphic order and the presence of distinct breaks in the postmortem age distribution suggest that 67% of shells in the core were recycled from older deposits, resulting in a 2–3 order of magnitude increase in the amount of time averaging in the sediment column relative to surface samples.

Description: A nesting trace preserved in alluvial floodplain deposits in the Upper Cretaceous Two Medicine Formation at the Willow Creek anticline in north-central Montana contains four crushed theropod eggs referable to the oospecies Continuoolithus canadensis. These eggs immediately overlie the lower surface of a 35-cm-long x 7-cm-thick, dark-green mudstone lens, surrounded by reddish-purple mudstone. The long axes of three eggs are parallel to one another and to the lower boundary of the lens, whereas the fourth egg lies at a 30° angle to the others. A thin, 1-cm-thick organic horizon overlies the eggs, suggesting they were buried with some vegetation. Geometric modeling of the slightly asymmetrical C. canadensis eggs yields a volume and mass of approximately 194 cm 3 and 205 g for each egg. This method provides a more accurate estimation for the surface area than allometric equations that are based on modern bird eggs because of the elongate shape of many non-avian theropod eggs. Pore density and water vapor conductance (G H2O ) calculated from one egg in the trace and five additional C. canadensis eggs from the Willow Creek anticline vary across three regions. High, moderate, and very low G H2O characterize the equatorial zone, blunt, and tapering poles, respectively. The average G H2O for all eggs exceeds that of an avian egg of similar mass by 3.9 x , thus supporting sedimentologic evidence of substrate burial during incubation.

Description: A bstract :  Predictions of a delta's morphology, facies, and stratigraphy are typically derived from its relative wave, tide, and river energies, with sediment type playing a lesser role. Here we test the hypothesis that, all other factors being equal, the topset of a relatively noncohesive, sandy delta will have more active distributaries, a less rugose shoreline morphology, less topographic variation in its topset, and less variability in foreset dip directions than a highly cohesive, muddy delta. As a consequence its stratigraphy will have greater clinoform dip magnitudes and clinoform concavity, a greater percentage of channel facies, and less rugose sand bodies than a highly cohesive, muddy delta. Nine self-formed deltas having different sediment grain sizes and critical shear stresses required for re-entrainment of mud are simulated using Deflt3D, a 2D flow and sediment-transport model. Model results indicate that sand-dominated deltas are more fan-shaped while mud-dominated deltas are more birdsfoot in planform, because the sand-dominated deltas have more active distributaries and a smaller variance of topset elevations, and thereby experience a more equitable distribution of sediment to their perimeters. This results in a larger proportion of channel facies in sand-dominated deltas, and more uniformly distributed clinoform dip directions, steeper dips, and greater clinoform concavity. These conclusions are consistent with data collected from the Goose River Delta, a coarse-grained fan delta prograding into Goose Bay, Labrador, Canada. A reinterpretation of the Kf-1 parasequence set of the Cretaceous Last Chance Delta, a unit of the Ferron Sandstone near Emery, Utah, USA uses Ferron grain-size data, clinoform-dip data, clinoform concavity, and variance of dip directions to hindcast the delta's planform. The Kf-1 Last Chance Delta is predicted to have been more like a fan delta in planform than a birdsfoot delta.