Palaios最新文献

{"title":"LOWER CAMBRIAN RUSOPHYCUS FROM ELLESMERE ISLAND, ARCTIC CANADA: ICHNOFOSSIL OF A PREDATORY, NON-TRILOBITE ARTHROPOD","authors":"B. Pratt","doi":"10.2110/palo.2021-066","DOIUrl":"https://doi.org/10.2110/palo.2021-066","url":null,"abstract":"Abstract: Cruziana and Rusophycus are commonly assumed to be trilobite trace fossils, although associated exoskeletons are almost invariably absent from host strata. In the lower Cambrian Dallas Bugt Formation of Ellesmere Island, Arctic Canada, high-energy, cross-laminated sandstones locally with dense populations of large Skolithos are overlain by thin-bedded, bioturbated, argillaceous, medium-grained glauconitic sandstones of lagoonal aspect, yielding Rusophycus along with an assortment of other “worm” burrows. Some specimens of Rusophycus are located over small Skolithos shafts and the bottoms of Arenicolites, suggesting a predator-prey relationship. Many preserve the impression of a strongly vaulted carapace with a broad, triangular dorsal outline between 1 cm and 7 cm across. A blunt anterior “prow” projects slightly forward and arches dorsally, forming a keyhole-shaped notch. The arthropod dug into the sediment up to 5 cm deep with an antero-posterior angle of up to ∼ 45° from the sea floor; in some cases it dug obliquely laterally and rarely sideways. Retroverse scratches—preserved in hyporelief as sharp-crested ridges—suggest about 20 pairs of endopodites tipped by a pair of small claws typically dug in unison, the anterior ones starting with a V-angle of 140° and decreasing posteriorly to 90°, in rare cases more tightly. Limb length increased posteriorly, although none extended beyond the carapace. Leg muscles were strong enough to rake through the muddy sand and pull inwards either straight or in a slightly forward-curving arc, but were also slightly flexible to wiggle around obstacles. Some specimens show subsequent re-burrowing which produced cross-cutting and opposed scratches. No evidence for exopodite brushings is present. Successive carapace imprints and scratches organized in transverse rugae in some specimens suggest repeatedly plunging and digging as the arthropod pulled backward in the sediment. This was likely aided by a stout trunk and a fan-shaped uropod-like structure flanking the telson which increased grip and leverage. A pair of eye stalks may have projected from the anterior notch, and these could have been retracted during digging, but there is no evidence for antennae. The tracemaker was not a trilobite but an unrelated crustacean-like arthropod, although there is no known late early Cambrian body fossil to which it can be ascribed. The specimens are classified as Rusophycus jenningsi (Fenton and Fenton, 1937) and a neotype is selected for this ichnospecies from the Gog Group near where it was first collected. Its range extends from the southern Canadian Rocky Mountains north along depositional strike to Victoria Island and northwest to Ellesmere Island and northern Greenland. Two new ichnofamilies are established: Rusophycidae and Cruzianidae.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48023174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CESSATION OF A SUBTROPICAL GLASS RAMP DURING THE PERMIAN CHERT EVENT: MURDOCK MOUNTAIN FORMATION, WESTERN U.S.A.","authors":"Zackery P. Wistort, K. Ritterbush, S. Hood","doi":"10.2110/palo.2021.034","DOIUrl":"https://doi.org/10.2110/palo.2021.034","url":null,"abstract":"Abstract: The Murdock Mountain Formation crops out across northern Utah and Nevada as part of the Park City Group; a unit within the greater Phosphoria Rock Complex. The Murdock Mountain is a hundreds-meters-thick section of mixed chert, dolomite, and siltstone. This unit is the southernmost expression of the widespread Permian Chert Event and offers unique views of sedimentology and paleoecology during this event. Previous researchers have described shallow-water facies dominated by biosiliceous sedimentary production as glass ramps. This framework has been speculatively applied by others to the units of the Park City Group in northern Utah and Nevada. In this study, we test whether the glass ramp depositional framework accurately represents the strata of the Murdock Mountain Formation. We use stratigraphic, hand sample, and thin section data to describe the sedimentological character of the Murdock Mountain Formation and the overlying Gerster Limestone. Four chert facies and one carbonate facies are recognized based upon the presence of silt, sponge spicules, carbonate bioclasts, and evaporites. The Murdock Mountain Formation shares many characteristics with other reported glass ramp localities. We interpret the transition from chert to carbonate-rich strata as an alternation between stable states with silica-producing fauna dominating the Murdock Mountain and carbonate-producing fauna dominating the Gerster. The takeover of biosiliceous deposition by carbonate highlights the termination of a glass ramp and the onset of a carbonate ramp regime.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41754245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"TAPHONOMIC CONTROLS ON MICROBIALITE TEXTURES FROM THE STEAMBOAT POINT MEMBER, UPPER ORDOVICIAN BIGHORN DOLOMITE, WESTERN TETON MOUNTAINS, USA","authors":"A. Bays, Y. Ibarra, Sonicah Sanon, C. Hayzelden","doi":"10.2110/palo.2021.042","DOIUrl":"https://doi.org/10.2110/palo.2021.042","url":null,"abstract":"Abstract: The Bighorn Dolomite is a massive, cliff-forming dolostone unit found across the state of Wyoming and adjacent areas that records the transition from greenhouse to icehouse conditions during the Late Ordovician. The basal Steamboat Point Member of the Bighorn Dolomite contains cm-scale mottled fabrics often attributed to the ichnogenus Thalassinoides, but their origin remains enigmatic in Upper Ordovician strata. The development of mottled fabrics may have significant implications for marine chemistry and paleoecology. We analyzed cm-scale mottled fabrics from the basal Steamboat Point Member of the western Teton Mountains to determine their origin and develop criteria for identification of similar mottled fabrics found in other Upper Ordovician strata. In vertical cross-section, massive, m-scale exposures display vertical columns (approximately 1 cm in diameter) that anastomose and maintain decimeter-scale vertical continuity. Microscopically, the columns are composed of micro-peloidal micritic textures surrounded by spar and microspar, whereas the intercolumnar matrix is composed of dolomicrite grains, skeletal clasts, and intraclasts. We interpret the microscopic peloidal texture as a product of benthic microbial calcification that coalesced to form mesoclots—diagnostic features of thrombolitic microbialites. Paragenetic analyses reveal evidence for early lithified microbial biofilms despite dolomite replacement and aggrading neomorphism. These observations indicate the Steamboat Point Member of the Bighorn Dolomite was deposited in seawater that was highly supersaturated with respect to carbonate, consistent with other studies that suggest deposition during greenhouse conditions prior to the end-Ordovician glaciation. We present a novel ternary diagram that contains criteria to help differentiate between burrows, microbialite textures, or physical processes that may result in mottled fabrics in the rock record.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44122843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"IS ABERRANCY A RELIABLE INDICATOR FOR MAJOR PALEOCLIMATIC DISTURBANCE?","authors":"Stephen Stukins","doi":"10.2110/palo.2021.019","DOIUrl":"https://doi.org/10.2110/palo.2021.019","url":null,"abstract":"Abstract: Aberrant forms of many different spore and pollen taxa (sporomorphs) are often used to assess timings and extent of environmental stress at major extinction/climate events. However, little is known about the normal level of malformations in these taxa. Malformation can manifest in several different ways, including significant size differences (± from the accepted range for the species), retention of pollen/spores within tetrads, and unusual and inconsistent morphological aberrations. This study analyses one commonly used pollen genus, Classopollis, and its aberrant forms, from the Bajocian of Argentina. Tetrads, including those incorporating malformed/aborted pollen grains, are found to be common, showing that tetrads of Classopollis are not a reliable signal of major environmental disturbance. The results and discussion presented here emphasize why palynological data must be interpreted in context of the depositional dynamics, facies changes and how they affect the assemblages in conjunction with understanding variations in the strategies of individual flora.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46618337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"REVISED STRATIGRAPHIC RELATIONSHIPS WITHIN THE LOWER FORT UNION FORMATION (TULLOCK MEMBER, GARFIELD COUNTY, MONTANA, U.S.A.) PROVIDE A NEW FRAMEWORK FOR EXAMINING POST K–PG MAMMALIAN RECOVERY DYNAMICS","authors":"Lucas N. Weaver, T. Tobin, Jordan R. Claytor, Paige K. Wilson Deibel, W. Clemens, Gregory P. Wilson Mantilla","doi":"10.2110/palo.2021.011","DOIUrl":"https://doi.org/10.2110/palo.2021.011","url":null,"abstract":"Abstract: The Hell Creek region of northeastern Montana is an excellent study system to explore the rise to dominance of mammalian faunas after the Cretaceous–Paleogene (K–Pg) mass extinction. The Tullock Member of the Fort Union Formation exposed in that region was deposited during the first 1.2 Ma after the Chicxulub bolide impact. Some aspects of post-K–Pg mammalian succession remain obscure, however, due to a lack of finer stratigraphic resolution between vertebrate fossil localities. Here, we present a new stratigraphic model for the lower and middle Tullock and identify a stratigraphic succession of five mammal-bearing sedimentary units that span the first ∼ 900 ka of the Paleocene. Most notably, we find that middle Tullock fossil localities, which were previously thought to be deposited by a single, large fluvial channel complex, are derived from two temporally and lithologically distinct sedimentary units: the Biscuit Springs unit (BS) and the Garbani channel (GC). The top of the GC is stratigraphically above the top of the BS, but in some places cuts through the entirety of the BS, a relationship that previously complicated interpretations of their relative age. This cross-cutting relationship reveals that the BS is older than the GC. Thus, the BS local fauna represents a potential intermediate between the older local faunas from the post-K–Pg ‘disaster’ interval and the younger, more taxonomically/ecologically diverse GC local fauna. This new stratigraphic framework sets the stage for future studies focused on the pattern and timing of biotic recovery in the aftermath of the K–Pg mass extinction.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46465935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"BODY SIZE TRENDS IN TRIGONIIDA BIVALVES FROM THE MESOZOIC KUTCH, INDIA","authors":"Debattam Sarkar, Shubhabrata Paul, Ranita Saha, S. Bardhan, P. Rudra","doi":"10.2110/palo.2020.046","DOIUrl":"https://doi.org/10.2110/palo.2020.046","url":null,"abstract":"Abstract: Although empirical testing of Cope's rule, the tendency for size to increase over time, has received significant attention in the last few decades, there is no consensus about the applicability of this rule across taxonomic levels. In the present study, we investigate the distribution of body size of Trigoniida bivalves, at order-, family-, genus- and species-level, through the Middle Jurassic and Early Cretaceous of the Kutch region in India. Our data suggest that the body size of Trigoniida bivalves did not vary significantly in the Middle–Late Jurassic, followed by an increase after the Jurassic–Cretaceous mass extinction boundary and a reduction in the late Early Cretaceous. Changes in relative sea-level and associated sedimentary facies composition generally exhibit poor correlation with the overall stasis, or no net body size change, displayed by Trigoniida bivalves. Body-size analysis across taxonomic hierarchy reveals that order-level trends are not a simple aggregation of trends at lower taxon levels. An important observation of our study is the body-size increase immediately in the aftermath of the Jurassic– Cretaceous mass extinction, a deviation from the general observation that size reduction occurs in post-extinction communities. We argue that this increase may be result of both ecological competition and evolutionary faunal turnover.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46457853","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"EVALUATING THE ICHNOFOSSIL TEREDOLITES AS AN INDICATOR OF SALINITY AND PALEOENVIRONMENT","authors":"R. Buntin, S. Hasiotis, P. Flaig","doi":"10.2110/palo.2020.074","DOIUrl":"https://doi.org/10.2110/palo.2020.074","url":null,"abstract":"Abstract: The ichnogenus Teredolites and the Teredolites Ichnofacies is an accepted proxy for marine influence in paralic to open marine depositional environments. Actualistic approaches and the process-ichnologic framework allow independent analysis of both quantitative and semiquantitative data to interpret the physicochemical conditions when Teredolites are present. Measurements collected in modern environments and Jurassic–Eocene successions produce a spatially and temporally robust dataset of 14,137 borings from 17 tracemaking genera. Life history strategies of extant tracemakers are reflected in Mesozoic borings, which allow reconstruction of paleosalinity. Trends extrapolated indicate four ecotones in modern paralic to nearshore settings, which can be identified into the Late Cretaceous. These zones display variation in boring metrics (length [L], width [W], L:W ratio, size diversity index), densities, and relative composition of Teredolites. Zone 1 represents upper estuary to tidally modified fluvial successions with salinities from 0.5–10 ppt (oligohaline to alpha-mesohaline). Zone 2 represents upper to central estuary successions with salinities from 10–19 ppt (beta-mesohaline to lower polyhaline). Zone 3 represents central to lower estuary successions with salinities from 15–30 ppt (beta-mesohaline to euhaline). Zone 4 represents backshore to open marine successions with salinities from 20–30+ ppt (polyhaline to euhaline). Boring metrics compared against identified fossil genera suggest high species richness in the Western Interior Seaway coincided with physical adaptations to compensate for interspecific competition––differences in reproduction style and media preferences at the time of settlement––in the Late Cretaceous.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46457807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"QUANTITATIVE VARIABILITY OF BURROW PERCENTAGE ESTIMATED FROM 2D VIEWS: EXAMPLE FROM THALASSINOIDES-BEARING STRATA, CENTRAL SAUDI ARABIA","authors":"Hassan Abdalla Eltom, A. Alqubalee","doi":"10.2110/palo.2021.012","DOIUrl":"https://doi.org/10.2110/palo.2021.012","url":null,"abstract":"Abstract: This study examines computed tomography (CT) scans of a 15.24-cm diameter and 17.1-cm length core cut from Thalassinoides -bearing strata (Hanifa Formation, central Saudi Arabia) to explore the quantitative variability in burrow percentage when estimated using 2D views. A cropped quadrangular prism of this core allowed 202 2D slices in two vertical orientations and 165 horizontal 2D slices. Thalassinoides volume represents 20.0% (burrow percentage) of the total volume within this cropped quadrangular prism. The estimated burrow percentage by the 2D vertical slices varies from 11.8% to 30.3% with a mean value of 19.9% ± 3.3% and 19.6% ± 3.9%, and coefficients of variation of 17% and 20%, for the two vertical orientations. A wider range and slightly more variability are found when estimated burrow percentage using the horizontal slices (burrow percentage range from 6.1% to 33.1% with a mean value of 19.8% ± 6.5% and coefficient of variation of 33.1%). However, analysis of variance results indicated no statistically significant difference between the distribution of the burrow percentage among vertical and horizontal slices. A test of how randomly selected slices of the CT scan would represent the burrow percentage indicated that even five randomly selected slices could retain a mean comparable to the actual burrow percentage of the CT scan. Based on these results, we suggested a statistical way to quantify the uncertainty associated with estimating the burrow percentage from 2D views, an important step toward a complete understanding of variability in burrow percentage (and bioturbation intensity) when estimated from 2D views.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49443198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"HETEROPODY INDEX: A SQUARE PEG IN A ROUND HOLE?","authors":"E. Strickson","doi":"10.2110/palo.2021.032","DOIUrl":"https://doi.org/10.2110/palo.2021.032","url":null,"abstract":"Abstract: Heteropody Index (HI) is a tool used to calculate area differences between the manus and pes of fossil trackways. HI uses a simple length × width calculation to estimate area. However, since most foot impressions are rarely close to square in shape, HI using a different area calculation could potentially more accurately reflect differences in manus and pes foot area. In this study, accuracy of length × width (L×W) as an area estimate for basic shapes and animal footprints, was tested against two other area calculations, the area of a circle: πr2, and length × carpal width (L×CW) (the width at the most proximal point of the foot in contact with the ground). In addition, accuracy of HI calculations using these methods was tested against HI calculations using actual area of the corresponding shape or underfoot area. It was discovered that in general L×W is a better estimate for area than πr2, in most animals except ungulates. However, for those animals where L×W was a better estimate than πr2, L×CW was more accurate. This paper additionally proposes that by combining the findings of these tests with those of Strickson et al. (2019), foot area estimates for dinosaurs can be estimated more accurately using L×CW, to return an area close to estimates for soft tissue. Previous HI measurements may have overestimated extreme heteropody in sauropod dinosaurs.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43210203","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CHANGES IN ENVIRONMENTAL CONDITIONS, BIOTA, AND DEPOSITIONAL PATTERNS WITHIN LOWER TRIASSIC CLASTIC AND CARBONATE DEPOSITS, MUĆ-OGORJE, CENTRAL DALMATIA (CROATIA)","authors":"Karmen Fio Firi, Katarina Gobo, J. Sremac, Frane Marković","doi":"10.2110/palo.2020.082","DOIUrl":"https://doi.org/10.2110/palo.2020.082","url":null,"abstract":"Abstract: The Lower Triassic of the Muć-Ogorje area in Central Dalmatia (southern Croatia) is characterized by clastic and carbonate deposits which are investigated through a 230 m thick succession. The fossil associations identified point to a Dienerian age for the lower, and a Spathian age for the upper part of the studied profile, while trace fossils suggest deposits of Smithian age in the middle part, enabling comparisons with other successions in the region. Changes in sedimentology and associated biota throughout the succession, and environmental conditions are reconstructed for seven facies associations, the distribution of which suggests multiple oscillations in relative sea level. Sedimentary structures point to the influence of high environmental energy, possible storms, with signs of tectonic influence in the studied area. The study deposits lack ooid limestone intervals, which are well represented in other Lower Triassic sections in Croatia, Slovenia, Italy, and Hungary. Moreover, the study section exhibits changes in biota abundance, presence of organic-rich laminae and pyrite, as well as changes in siliciclastic input and transgressive-regressive cycles, especially within the upper, Olenekian, part of the succession studied. The results confirm that environmental stress was persistent throughout the Early Triassic, and contribute to our better understanding of the aftermath of the end Permian extinction and the environmental conditions of the western Tethys epicontinental shelf area.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2022-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43529378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}