Palaios最新文献

{"title":"TAPHONOMIC INDICATORS OF DEAD OCEAN QUAHOG (ARCTICA ISLANDICA) SHELL AGE IN THE DEATH ASSEMBLAGE OF THE MID-ATLANTIC BIGHT CONTINENTAL SHELF","authors":"Alyssa M LeClaire, E. Powell, R. Mann, Theresa E. Redmond","doi":"10.2110/palo.2022.030","DOIUrl":"https://doi.org/10.2110/palo.2022.030","url":null,"abstract":"Abstract: Taphonomic indicators are often used to assess time-since-death of skeletal remains. These indicators frequently have limited accuracy, resulting in the reliance of other methodologies to age remains. Arctica islandica, commonly known as the ocean quahog, is a relatively widespread bivalve in the North Atlantic, with an extended lifespan that often exceeds two hundred years; hence, their shells are often studied to evaluate climate change over time. This report evaluates taphonomic age using 117 A. islandica shells collected from the Mid-Atlantic Bight offshore of the Delmarva Peninsula with radiocarbon dates extending from 60–4,400 cal years BP. These shells had varying degrees of taphonomic alteration produced by discoloration and degradation of periostracum. To determine if a relationship exists between taphonomic condition and time-since-death, radiocarbon ages were compared with the amount of remaining periostracum and type of discoloration. Old shells (individuals that died long ago) were discolored orange with no periostracum while younger shells (individuals that died more recently) had their original color, with some periostracum. Both the disappearance of periostracum and appearance of discoloration followed a logistic process, with 50% of shells devoid of periostracum and 50% discolored in about 1,000 years. The logistic form of long-term taphonomic processes degrading shell condition is first reported here, as are the longest time series for taphonomic processes in death assemblages within the Holocene record. This relationship can be utilized for triage when deciding what shells to age from time-averaged assemblages, permitting more efficient application of expensive methods of aging such as radiocarbon dating.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44465847","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":"LAURUSSIAN-ASPECT OF THE COPROLITE ASSOCIATION FROM THE UPPER TRIASSIC (CARNIAN) OF THE ARGANA BASIN, MOROCCO","authors":"Tariq Zouheir, A. Hunt, Abdelkbir Hminna, H. Saber, J. Schneider, S. Lucas","doi":"10.2110/palo.2022.022","DOIUrl":"https://doi.org/10.2110/palo.2022.022","url":null,"abstract":"Abstract: A large collection of vertebrate coprolites derives from a debris flow conglomerate in the Upper Triassic Irohalene Member (Carnian) of the Timezgadiouine Formation, northern Argana Basin, Morocco. The coprolites are classified into 14 different morphotypes (MA to MN) based on their size, shape, and surface texture that are divided into three groups: striated coprolites; spiral and scroll-like coprolites; and non-spiral coprolites lacking striations. The great variety of morphotypes suggests the coprolites correspond to a variety of terrestrial and aquatic carnivorous producers. The carnivore coprolites lithified rapidly and were deposited in a high-energy sheetflood. The majority of the coprolites were produced by semi-aquatic and terrestrial tetrapods, with a small percentage produced by fish. The occurrence of Dicynodontocopros, common Alococopros, and some heteropolar forms with affinities to Heteropolacopros, are consistent with a late Carnian age for the Irohalene Member. The Irohalene coprolites are mostly similar to those of the coprofaunas of late Carnian age (Otischalkian–Adamanian) in the lower Chinle Group of the western United States in the co-occurrence of Alococopros and Dicynodontocopros. Significantly, this Moroccan coprofauna from Gondwana has close Laurussian relationships.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46448744","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":"CHALLENGES OF CONSERVATION PALEOBIOLOGY: FROM BASELINES TO NOVEL COMMUNITIES TO THE NECESSITY FOR GRANTING RIGHTS TO NATURE","authors":"M. Zuschin","doi":"10.2110/palo.2023.020","DOIUrl":"https://doi.org/10.2110/palo.2023.020","url":null,"abstract":"Conservation Paleobiology (CP) was formally introduced more than 20 years ago (Flessa 2002) as a field that deals with the application of theories and analytical tools of paleontology to biodiversity conservation, but has multifaceted roots that go back at least into the 1970s (Dietl and Flessa 2009; Dillon et al. 2022). More than thirty years ago, it was already evident that anthropogenic impacts had changed modern marine environments so profoundly that ecological research alone does not catch undisturbed baselines (e.g., Pauly 1995; Jackson 1997; Jackson et al. 2001; Kowalewski 2001; Pandolfi et al. 2003; Stachowitsch 2003; Lotze et al. 2006). The volume “Conservation Paleobiology: Using the Past to Manage for the Future” published by The Paleontological Society (Dietl and Flessa 2009) and a seminal review (Dietl and Flessa 2011) outlined Conservation Paleobiology as an emerging field with high potential for new insights in conservation planning and management. Since then, several books and special issues with numerous case study articles have been published (Louys 2012; Tyler and Schneider 2018; Nawrot et al. 2023). This increasing publication record, together with a growing number of dedicated conference topical sessions and workshops (e.g., Turvey and Saupe 2019), and the creation of the Conservation Paleobiology Network (CPN, https:// conservationpaleorcn.org) establishes CP as a popular field at the interface of geological and life sciences. Conservation Paleobiology still has a relatively poor record of translating research into application, but this is also true for other scientific fields within Conservation Biology and could be improved by more active collaboration with conservation practitioners (Groff et al. 2023). However, establishing pre-impact baselines (i.e., reference conditions against which changes can be assessed) is one of the core competences of CP, which informs policymakers and society about potential goals to pursue species recovery and habitat restoration (Flessa 2017). Nevertheless, this unique feature of CP seems only of minor relevance to other conservationists (Kiessling et al. 2019), probably reflecting a psychological distance to paleontological timescales by the conservation biology community, because they are beyond personal experience (Dietl et al. 2019) and the many biological and social facets of conservation biology research. Importantly, a baseline is more than just an archive of a glorious or desirable past, it is a rich source of ecological information that uncovers how and why a community has changed over time and constrains potential scenarios of its future dynamics (Dietl 2019). This information about baselines based on the paleontological record is crucial and unique wherever long-term ecological data are missing. For example, the Eastern Mediterranean Sea is strongly affected by the Lessepsian invasion, and it was long considered that the tropical Indo-Pacific species entering the region though the ","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44215961","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":"BENTHIC FORAMINIFERAL MORPHOGROUPS AND TRACE FOSSILS FROM ALBIAN SHALLOW-MARINE MUDSTONE FACIES OF THE VIKING FORMATION, WESTERN INTERIOR SEAWAY, CANADA","authors":"D. McNeil, J. Maceachern","doi":"10.2110/palo.2022.041","DOIUrl":"https://doi.org/10.2110/palo.2022.041","url":null,"abstract":"Abstract: This study assesses the foraminiferal morphogroup concept as a quantitative tool for interpreting environments of deposition in the geological record. This was achieved by first establishing a solid paleoenvironmental framework based on assessment of trace fossils (Zoophycos, Cruziana, and Phycosiphon ichnofacies, and the unnamed brackish-water association), sedimentology, and facies analysis of shallow-marine siliciclastic units of the upper Albian Viking Formation of the Western Interior Seaway, Canada. Foraminiferal morphogroups were integrated into a framework of six well-defined marine mudstone-dominated facies—estuarine, embayment, prodelta, upper offshore, lower offshore, and marine shelf. Seven morphogroups were recognized, quantified, and labeled using alphanumeric codes—A (tubular), B1 (globular), B2 (coiled, flat), B3 (lenticular), C1 (elongate), C2 (quinqueloculine), and D (trochospiral). Tubular forms (A, Bathysiphon) occur rarely in these shallow-marine facies. Globular forms (B1, Lagenammina) are common in estuarine (33%) and embayment (23%) facies, but also occur elsewhere in low numbers (7–14%). Coiled planar forms (B2, Ammodiscus) occur only rarely (1–8%), but have a minor presence in embayment facies (8%). Lenticular forms (B3, Haplophragmoides) are dominant in estuarine facies (43%) and occur commonly in other environments (9–29%) as well. Elongate forms (C1, Ammobaculites, Reophax, Verneuilinoides) dominate all shallow-marine facies (43–80%), except estuarine (10%). Quinqueloculine forms (C2, Miliammina) have a minor presence in prodelta and marine facies (5%) but are generally rare. Trochoid forms (D, Trochammina) occur rarely, but are relatively common in the prodeltaic facies (15%). Albian foraminiferal morphogroups of the Viking Formation are comparable to those of modern-day offshore environments from water depths of 13 to 160 meters. Foraminiferal morphogroups are objective entities independent of taxonomic determinations. Analysis of their form and function is applicable not only in the shallow-marine facies of the Albian Western Interior Seaway, but in similar facies throughout the geologic record.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42581389","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":"ASSESSING PALEOECOLOGICAL DATA RETENTION AMONG DISPARATE FIELD COLLECTION REGIMES: A CASE STUDY AT THE MYGATT-MOORE QUARRY (MORRISON FORMATION)","authors":"J. Mchugh, Stephanie K Drumheller, Miriam Kane, Anja Riedel, Jennifer H. Nestler","doi":"10.2110/palo.2022.048","DOIUrl":"https://doi.org/10.2110/palo.2022.048","url":null,"abstract":"Abstract: Field work protocols in the recovery of vertebrate fossils can vary between sites, and also within sites, due to differing researcher goals. Disparate researcher priorities can affect the resulting collections in terms of species richness, size distribution, specimen completeness, taphonomic condition, and aesthetic value. We examined paleoecological data, in the form of bone surface modifications (e.g., abrasion, feeding traces, etc.), from a single site worked by multiple collectors to determine the sensitivity of this type of data to collector bias. We examined 2,368 fossils from the Mygatt-Moore Quarry and divided them into two cohorts: 2016–2019 (bulk collection under a single collector) and pre-2016 (mixed collectors and priorities). Frequencies of modified bone surfaces were then calculated in each cohort among the recovered specimens. However, the specimens within the cohorts were of unequal size, completeness, and amount of preserved surface area, making inferences of modified bone surface frequencies difficult. To correct for unequal morphologies and preservation, we estimated the percentage of altered surface area among specimens by overlaying photos with a 4.0 cm2 digital grid to create a digital set of equal sized fragments. With such a large dataset, we took a random 10% subsample of specimens from each cohort for the grid study. We estimated the sample size needed to accurately reflect the frequency of bone surface modifications by specimen and surface area for each cohort. Results show the recovery of modified bone surfaces between the two cohorts was highly disparate, and potentially sensitive to the effects of collector bias when using specimen-level data. However, frequencies based on estimates of surface area were much more consistent and appeared to equalize data between cohorts and showed little influence of collector bias on data recovery. Thus, the traditional method of calculating frequencies using specimen-level data may create an illusion of bias that is removed when frequencies are calculated from estimated bone surface area. We posit that the digital fragmentation method is more informative when comparing paleoecological traces between datasets and should be applied to fossil assemblages going forward, especially when collection protocols between assemblages are significantly different or unknown.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45688941","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":"A ROWELLELLA (LINGULATA, BRACHIOPODA) NESTLER IN A TRYPANITES BORING FROM THE MIDDLE ORDOVICIAN OF ESTONIA: AN EARLY COLONIZER OF HARD SUBSTRATE BORINGS","authors":"O. Vinn, L. Holmer, Mark A. Wilson, M. Isakar, U. Toom","doi":"10.2110/palo.2023.003","DOIUrl":"https://doi.org/10.2110/palo.2023.003","url":null,"abstract":"Abstract: A steinkern of an endoceratid nautiloid siphuncle contains a Trypanites sozialis boring with a lingulate brachiopod Rowellella sp. shell inside. The steinkern of this endoceratid formed during early lithification of the sediment on the seafloor. The lithified steinkern of this siphuncle was either initially partially exposed to the seawater or was exhumed and stayed exposed on the seafloor, where it was colonized by boring organisms. This bioerosion resulted in numerous Trypanites borings in the siphuncle. After the death or exit of the Trypanites trace maker, a vacant boring was colonized by a small lingulate nestler Rowellella sp. This lingulate was likely preadapted to life in hard substrate borings when it first found its way into borings in living substrates in the Late Ordovician. The increased availability of hard substrate borings, combined with the increased predation pressure due to the GOBE, enhanced the colonization of hard substrate borings by lingulate brachiopods.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42240135","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":"A STATISTICAL META-ANALYSIS OF LITHOLOGIC AND OTHER POTENTIAL CONTROLS ON FOSSIL BONE CELLULAR AND SOFT TISSUE PRESERVATION","authors":"P. Ullmann, M. Schweitzer","doi":"10.2110/palo.2022.026","DOIUrl":"https://doi.org/10.2110/palo.2022.026","url":null,"abstract":"Abstract: Demineralization assays, utilizing weak acids to isolate organics from biomineralized tissues, have recently been applied with increasing frequency to explore soft tissue preservation in fossils, revealing frequent retention of cells and other pliable microstructures in fossil bones. However, factors controlling long-term preservation of such labile structures remain mysterious. To address this, we compiled a database of bone demineralization results from 29 studies, then conducted a statistical meta-analysis of these data to evaluate the importance of specimen age, taxonomy, entombing lithology, and bone tissue type on microstructure recovery. Our database encompasses results from 137 bones from 44 formations spanning the Permian to the Holocene. Osteocytes, blood vessels, and fibrous/proteinaceous matrix each exhibit bimodal recovery patterns in which most fossil bones either yield many or none of these microstructures. Though their relative abundances in any given fossil bone are extremely variable, statistically significant Fisher's Exact tests found that if a bone yields one of these types of microstructures in abundance then the others are usually also abundant. None of the variables examined significantly influence osteocyte recovery, but Kruskal-Wallis and subsequent pairwise Mann-Whitney tests revealed that bones collected from unconsolidated sediments, of Paleocene age, and/or deriving from birds, amphibians, marine reptiles, or crocodylians often yield few or no vessels and fibrous matrix. Although these findings hint at possible controls on cellular and soft tissue preservation in fossil bones, they should be viewed cautiously as they are demonstrably biased by uneven sampling. For example, many of the apparent trends are substantially controlled by overrepresentation of data from nonavian dinosaur specimens from Cretaceous fluviolacustrine deposits. Future demineralization assays should therefore focus on non-mammalian specimens from the Cenozoic and Jurassic-and-older nondinosaurian specimens, especially those preserved in less-common depositional environments (e.g., eolian settings).","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45641605","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":"UNLOCKING THE ARCHITECTURE OF THE COLONIZATION WINDOW: ICHNOFABRICS FROM UPPER CRETACEOUS TIDE-INFLUENCED MEANDER-LOOP DEPOSITS","authors":"D. Díez-Canseco, L. Buatois, M. Mángano, J. Cuevas-González, M. I. Benito","doi":"10.2110/palo.2022.024","DOIUrl":"https://doi.org/10.2110/palo.2022.024","url":null,"abstract":"Abstract: Studies dealing with the colonization window typically emphasize two major features: duration (short term vs. long term) and frequency of colonization (episodic vs. continuous). However, our understanding of tide-influenced meander loops requires consideration of an additional feature, the architecture of the colonization window, which comprises not only the spatial dimension and geometry of the colonization surface, but also its evolution through time. Tide-influenced meander-loop systems show a heterogeneous trace-fossil distribution that reflects the variety of processes operating along the point-bar and overbank colonization surfaces. Ichnofabric analysis of tide-influenced meander-loop deposits from the Upper Cretaceous Tremp Formation (Pyrenees, Spain) provides valuable insights into the sedimentary and ichnological dynamics of these marginal-marine systems and allows the importance of stratal geometry controlling the colonization window to be evaluated. Six ichnofabrics are identified in point bars and associated overbank deposits. These ichnofabrics differ in bioturbation index (e.g., higher in the upper part than the lower-middle parts of point bars), preservation of primary sedimentary fabric (typically preserved in the lower-middle parts of point bars), inferred behavior and trophic types (e.g., dominance of dwelling or feeding structures in the lower-middle and upper parts of point bars, respectively), and other features such as depth of penetration, ichnotaxonomic composition, presence or absence of root trace fossils and/or mottling, or number of superimposed suites. The key environmental factor controlling the nature and distribution of ichnofabrics is the morphology of the point-bar lateral-accretion surfaces and their evolution through time. The architecture of the colonization window is here linked to the helicoidal flow and discharge changes in meandering channels, and the successive development of lateral accretion units with time.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46023861","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":"SIMPLE STRUCTURES AND COMPLEX STORIES: POTENTIAL MICROBIALLY INDUCED SEDIMENTARY STRUCTURES IN THE EDIACARAN SERRA DE SANTA HELENA FORMATION, BAMBUÍ GROUP, EASTERN BRAZIL","authors":"J. Okubo, L. Inglez, G. Uhlein, L. Warren, S. Xiao","doi":"10.2110/palo.2022.020","DOIUrl":"https://doi.org/10.2110/palo.2022.020","url":null,"abstract":"ABSTRACT: Microbially induced sedimentary structures (MISS) are abundant in Ediacaran and lower Cambrian successions. However, the relationship between MISS distribution and facies has not been thoroughly explored in Ediacaran–Cambrian successions in South America. This study documents the occurrence of MISS and other potential biogenic structures from the late Ediacaran Serra de Santa Helena Formation in the Bambuí Group of eastern Brazil. This unit overlies the Cloudina-bearing Sete Lagoas Formation and is a mixed carbonate-siliciclastic succession devoid of macroscopic body fossils. Potential microbial structures include wrinkled structures such as “elephant-skin” and Kinneyia-like textures, as well as pustular structures and abundant positive epirelief discoidal structures. Another putative biogenic structure is a mm-wide meandering groove resembling a simple locomotion trail of a small vagile benthic metazoan. Microbial surface textures (i.e., “elephant skin” and Kinneyia-type wrinkles) were mainly observed in heterolithic deposits, usually at the interface between sandstone and siltstone/shale. On the other hand, discs show a facies-independent distribution, observed in heterolithic as well as carbonate and marl deposits. Petrographic analyses of these discs suggest that they have complex origins and some of them may be diagenetic structures. Thus, while facies may have strongly controlled the preservation of MISS-related structures and textures in the Serra de Santa Helena Formation, their abundance and diversity in tidal flat deposits indicate the wide distribution of matgrounds in these shallow marine paleoenvironments. Also, we demonstrate how detailed description and classification of simple features, such as discoidal structures, is an important task for paleoenvironmental reconstruction of marine ecosystems at the Ediacaran–Cambrian transition when the microbially bounded substrates played important roles in the dynamics of coastal environments.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44294987","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":"SEDIMENTARY ENVIRONMENT AND REDOX CONDITIONS OF THE LOWER TRIASSIC OSAWA FORMATION IN THE SOUTHERN KITAKAMI TERRANE, JAPAN: INSIGHTS INTO OCEAN REDOX STRATIFICATION AND FAUNAL RECOVERY","authors":"Yoshino Ishizaki, Y. Shiino","doi":"10.2110/palo.2021.045","DOIUrl":"https://doi.org/10.2110/palo.2021.045","url":null,"abstract":"ABSTRACT: The sedimentary environments and redox conditions of the Lower Triassic Osawa Formation in the Southern Kitakami Terrane were reconstructed based on lithofacies, trace fossils, and other paleontological content. The muddy and sandy lithofacies of the Osawa Formation lack evidence of storm waves despite the presence of storm-induced turbidites, suggesting that the oldest deposits of the Osawa Formation were deposited in the proximal part of the outer shelf. In turn, water depth increased from the lower to upper part of the formation, ultimately recording the distal part of the outer shelf. In addition to sandy lithofacies caused by turbidity and traction currents, multiple sandy layers within the muddy lithofacies would have originated via supply into the prodelta setting from a fan delta system. Collapses of the delta front or river system floods could have generated hyperpycnal flows, resulting in abundant supplies of mud and organic matter. Trace fossil analyses revealed that the degree of bioturbation (ichnofabric indices) dramatically decreased as water-depth increased, indicating a steep oxic-dysoxic gradient along the onshore-offshore transect. Diagenetic pyrite framboids indicative of dysoxic/anoxic benthic conditions are abundant at greater water depths. Abundant pyrite framboids less than 6 µm in diameter suggest intermittent euxinicity. With an increase in global weathering, abundant sediment supply including organic matter from the fan delta system could have contributed to the development of ocean redox stratification, which appears to have impacted on the adaptation of both nektic and benthic animals of this area during the Early Triassic.","PeriodicalId":54647,"journal":{"name":"Palaios","volume":null,"pages":null},"PeriodicalIF":1.6,"publicationDate":"2023-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41397447","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}