North American Midcontinent Sea Research Articles

Boron proxies record paleosalinity variation in the North American Midcontinent Sea in response to Carboniferous glacio-eustasy

Abstract Salinity variation in ancient epicontinental seas has long been challenging to reconstruct. We determined salinity variation in the Late Pennsylvanian North American Midcontinent Sea based on normalized boron concentrations (B/Ga) and isotopic compositions (δ11B) of bulk shale. We analyzed the Stark Shale Member of the Missourian Stage Dennis Limestone cyclothem in the Charleston core (CC) from the Illinois Basin (eastward, more proximal) and the Iowa Riverton core (IRC) from the Midcontinent Shelf (westward, more distal). Both cores exhibited the same pattern of secular variation, with lower B/Ga and δ11B values at their base and top, recording less saline conditions during lower sea-level stands, and higher values in their middle part, recording more saline conditions at highstands—a pattern that conforms to conventional sequence stratigraphic and glacio-eustatic interpretations of Midcontinent cyclothems. At equivalent stratigraphic levels, B/Ga and δ11B values are systematically lower at CC relative to IRC, reflecting the generally lower salinity conditions of the Illinois Basin relative to the Midcontinent shelf, which is consistent with greater freshwater influence from the east due to heavy river runoff into the Appalachian foreland basin. Our findings serve to demonstrate the utility of paired B concentration and isotope data for paleosalinity analysis of deep-time shale formations.

Simulation of oxygen isotopes and circulation in a late Carboniferous epicontinental sea with implications for proxy records

Reconstructions of ancient ocean chemistry are largely based on geochemical proxies obtained from epicontinental seas. Mounting evidence suggests that these shallow inland seas were chemically distinct from the nearby open ocean, decoupling epicontinental records from broader ocean conditions. Here we use the isotope-enabled Community Earth System Model to evaluate the extent to which the oxygen isotopic composition of the late Carboniferous epicontinental sea, the North American Midcontinent Sea (NAMS), reflects the chemistry of its open-ocean sources and connect epicontinental isotope variability in the sea to large-scale ocean-atmosphere processes. Model results support estuarine-like circulation patterns demonstrated by past empirical studies and suggest that orographic runoff produced decreases in surface seawater δ18O (δ18Ow) of up to ∼3‰ between the NAMS and the bordering ocean. Simulated sea surface temperatures are relatively constant across the sea and broadly reproduced from proxy-based δ18O paleotemperatures for which model-based values of epicontinental δ18Ow are used, indicating that offshore-onshore variability in surface proxy δ18O is primarily influenced by seawater freshening. Simulated bottom water temperatures in the NAMS are also reproduced from biogenic calcite δ18O using model-based values of epicontinental δ18Ow, suggesting that benthic marine fossil δ18O is also influenced by seawater freshening and coastal upwelling. In addition, glacial-interglacial variations in nearshore seawater freshening counteract the effects of temperature on marine biogenic δ18O values, suggesting that salinity effects should be considered in δ18O-based estimates of glacioeustatic sea level change from nearshore regions of the NAMS. Our results emphasize the importance of constraining epicontinental dynamics for interpretations of marine biogenic δ18O as proxies of paleotemperature, salinity, and glacioeustasy.

Copper isotope evidence of particulate shuttle dynamics in the Late Pennsylvanian North American Midcontinent Sea, with implications for glacio-eustatic magnitude

The North American Midcontinent Sea (NAMS) covered a vast area during Late Pennsylvanian glacio-eustatic highstands, providing a laboratory for analysis of the internal watermass dynamics of large cratonic seas (of which few exist in the Recent). In this study, a novel proxy, copper (Cu) isotopes, was used to gain a better understanding of NAMS watermass dynamics. We analyzed the 63-cm-thick Stark Shale (Dennis Formation, Missourian Stage, Upper Pennsylvanian) in the Iowa Riverton core (IRC) at a centimeter scale in order to reconstruct secular variations in Cu-isotopic compositions (δ65Cu) and other geochemical proxies. The gray shale facies yielded δ65Cu of +0.02 ± 0.06‰ (2σ, n = 14), similar to detrital Cu in modern marine sediments (δ65Cu = +0.08 ± 0.20‰; 2σ, n = 42). In contrast, the black shale facies, in which the proportion of authigenic Cu hosted by the organic fraction is 50–100% of total Cu content, exhibits heavier δ65Cuauth values, mostly between +0.09 and +0.43‰. In modern marine systems, one of the main processes leading to 65Cu-enriched sediment compositions is adsorption of aqueous Cu onto Fe-Mn particulates. The black shale facies of the Stark Shale exhibits four peaks in Mo/U ratios that are indicative of an active particulate shuttle because of the tendency of Mo to adsorb more strongly than U to Fe-Mn particulates. The Sr/Ba ratio, a paleosalinity proxy, shows correlated variations, with high values (indicative of more fully marine conditions) linked to low Mo/U and light δ65Cu, and low values (indicative of brackish conditions) linked to high Mo/U and heavy δ65Cu. These considerations suggest that the flux of isotopically heavy Cu to the sediment–water interface via Fe-Mn cycling was enhanced during brackish intervals, with subsequent reductive dissolution of Fe-Mn particulates allowing transfer of hydrogenous Cu to the organic fraction of the sediment. Control of δ65Cu by Fe-Mn cycling is supported by the results of a sequential extraction experiment showing that organic δ65Cu is positively correlated with Mo/U. These findings provide evidence of large fluctuations in watermass salinity and sea-level elevation within the NAMS at timescales of ∼104 yr during core shale deposition, as previously inferred but not conclusively demonstrated until now. The dynamics of particulate shuttle operation suggest that sea-level fluctuations must have had amplitudes of at least a few tens of meters. These fluctuations ended during the final stages of black shale deposition, probably owing to overall sea-level fall and permanent shallowing of the study site into the oxic, low-salinity surface layer of the NAMS.

Conodont biofacies and watermass structure of the Middle Pennsylvanian North American Midcontinent Sea

Climatic and glacio-eustatic information for the Late Paleozoic Ice Age is often extracted from cyclothems of the Midcontinent of North America. Although it is recognized that these important archives of global climate and environmental change are the result of waxing and waning of Gondwanan glaciers that produced widespread transgressive-regressive events, the relationships of conodont biofacies to changes in water depth, water chemistry, and other environmental parameters remain in dispute. Here, we investigate environmental gradients within the watermass of the Middle Pennsylvanian North American Midcontinent Sea (NAMS) based on geochemical proxies and conodont abundance patterns. To this purpose, we studied the Excello Shale at three geographically widely separated locations representing a ~500-km transect across the Midcontinent Shelf. We analyzed the organic (total organic carbon, carbon isotopes, and organic matter maturity) and inorganic geochemistry (major and trace elements) of the black and gray shale succession, as well as conodont abundance patterns and oxygen isotopic compositions, at 5–10 cm intervals through each study section.Our results suggest that the standard depth-stratification model of conodont biofacies in Pennsylvanian marine systems needs refinement. Although both Gondolella and Idioprioniodus are regarded as deep-water taxa, they differ in their stratigraphic distributions, with Idioprioniodus present through most of the Excello Shale but Gondolella confined to a narrow zone in the middle part. The Gondolella acme was not accompanied by pronounced changes in δ18O or trace-metal enrichment factors, implying that water depths and redox conditions were not the main controls on its distribution. Rather, the Gondolella acme is associated with the regressive condensation surface (RCS) of the core shale, which marks the onset of eustatic fall (renewed Gondwanan glaciation) and breakdown of the NAMS pycnocline. The latter process led to enhanced vertical overturn, mixing nutrients up into the ocean-surface layer and stimulating marine algal productivity, which was probably the trigger for blooms of Gondolella, suggesting that it was an opportunistic taxon. The upper part of the Excello is characterized by divergent δ18O compositions (~1‰ heavier in proximal areas), greater conodont abundance in offshore areas, and the appearance of Hindeodus exclusively in nearshore areas. This pattern suggests that Hindeodus was tolerant of somewhat more saline conditions, which developed during the climatic drying trend that accompanied the onset of the renewed Gondwanan glaciation. Our refined conodont biofacies model thus takes into consideration the effects of variable nutrient levels and watermass salinities in addition to water-depth controls.

Using GIS to examine biogeographic and macroevolutionary patterns in some late Paleozoic cephalopods from the North American Midcontinent Sea.

Geographic range is an important macroevolutionary parameter frequently considered in paleontological studies as species’ distributions and range sizes are determined by a variety of biotic and abiotic factors well known to affect the differential birth and death of species. Thus, considering how distributions and range sizes fluctuate over time can provide important insight into evolutionary dynamics. This study uses Geographic Information Systems (GIS) and analyses of evolutionary rates to examine how in some species within the Cephalopoda, an important pelagic clade, geographic range size and rates of speciation and extinction changed throughout the Pennsylvanian and early Permian in the North American Midcontinent Sea. This period is particularly interesting for biogeographic and evolutionary studies because it is characterized by repetitive interglacial-glacial cycles, a global transition from an icehouse to a greenhouse climate during the Late Paleozoic Ice Age, and decelerated macroevolutionary dynamics, i.e. low speciation and extinction rates. The analyses presented herein indicate that cephalopod species diversity was not completely static and actually fluctuated throughout the Pennsylvanian and early Permian, matching findings from other studies. However, contrary to some other studies, the mean geographic ranges of cephalopod species did not change significantly through time, despite numerous climate oscillations; further, geographic range size did not correlate with rates of speciation and extinction. These results suggest that pelagic organisms may have responded differently to late Paleozoic climate changes than benthic organisms, although additional consideration of this issue is needed. Finally, these results indicate that, at least in the case of cephalopods, macroevolution during the late Paleozoic was more dynamic than previously characterized, and patterns may have varied across different clades during this interval.

Circulation patterns in the Late Pennsylvanian North American Midcontinent Sea inferred from spatial gradients in sediment chemistry and mineralogy

The North American Midcontinent Sea (NAMS) reached its maximum extent during glacio-eustatic highstands of the Late Paleozoic Ice Age, during which organic-rich “core shales” accumulated under a stratified water column with anoxic deep waters. The core shales of cyclothems are composed of a lower organic-rich laminated black shale and an upper bioturbated gray shale. The present study investigates circulation patterns within the NAMS by examining secular variations and spatial gradients in the concentrations and ratios of major elements, trace elements, and organic carbon, as well as carbon and nitrogen isotopes, within one cyclothemic core shale: the Heebner Shale. The Heebner Shale represents the core shale member of the Upper Pennsylvanian (lowermost Gzhelian; Virgilian) Oread Limestone Formation in Kansas and Iowa, and it is correlative with the Teutopolis Shale of the Mattoon Formation in Illinois. The Heebner was sampled at high stratigraphic resolution at five sites on the northern Midcontinent Shelf and two sites in the Illinois Basin. Clay and silt fraction proxies show influences from multiple distinct terrestrial sources. The paleosalinity proxy Sr/Ba in combination with spatial patterns of clay and silt proxies implies large-scale counterclockwise (cyclonic) rotation of the NAMS watermass, which was possibly driven by the hydrodynamics of upwelling on the southern Midcontinent Shelf margin and/or riverine discharge into the eastern NAMS. Spatial patterns of δ13C and δ15N are consistent with regionally variable productivity and redox conditions. Differences in the magnitude of a positive δ15N excursion among the study sites record spatially variable water-column denitrification rates. Enrichment of trace metals on the northern Midcontinent Shelf was a product of intensified water-column recycling within an estuarine saltwater wedge. Trace-metal enrichments and Fe/Al ratios are consistent with moderate watermass restriction throughout the NAMS. The results of the present study permit major refinement of the existing superestuarine circulation model for the NAMS [Algeo, T.J., et al., 2008, Modern and ancient epeiric seas and the super-estuarine circulation model of marine anoxia. In: B. Pratt and C. Holmden (eds.), Dynamics of Epeiric Seas, Geol. Assoc. Canada Spec. Publ. 48, pp. 7–38].

Salinity contrast in the US Midcontinent Sea during Pennsylvanian glacio-eustatic highstands: Evidence from conodont apatite δ 18 O

Abstract Pennsylvanian phosphatic black shales are widely interpreted to have been deposited in waters deep enough to produce a pycnocline that would have developed as a consequence of increased riverine runoff into the largely landlocked North American Midcontinent Sea during the more humid interglacial intervals of the Late Palaeozoic Ice Age. We tested whether a gradient in surface water salinity existed in the North American Midcontinent Sea during times of maximum flooding by analyzing oxygen isotopes of conodont apatite from correlative Pennsylvanian black shales of the Midland, Midcontinent, Illinois and Appalachian basins. In the Midland and Midcontinent basins, average δ 18 O values for conodonts from the Oakley (middle Desmoinesian/upper Moscovian), Hushpuckney (lower Missourian, lower Kasimovian) and Heebner black shales (lower Virgilian/lower Gzehlian) are 18.8 ± 0.3‰, 19.1 ± 0.2‰, and 18.9 ± 0.1‰, respectively. Oxygen isotope ratios of conodonts from the Nuyaka Creek black shale (uppermost Desmoinesian/upper Moscovian) of the Midcontinent Basin are 19.8 ± 0.3‰, and thus significantly higher in comparison to the other black shales. These higher values support previous interpretations that the Lost Branch is a minor cyclothem, with south polar regions having been less deglaciated than during the interglacial phases of the more widespread major cyclothems. Conodonts from Oakley shale equivalents from Ohio and Pennsylvania are depleted in 18 O on average by 2.5‰ in comparison to conodonts from the Midcontinent Basin. This pattern is also evident for conodonts from the Heebner and Hushpuckney shales, although conodonts from the Appalachian Basin show only a 0.4–0.7‰ depletion in 18 O compared to conodonts from the Midcontinent Basin. The differences in δ 18 O are interpreted as reflecting primarily salinity, assuming that temperature was relatively constant across the palaeotropical Midcontinent Sea. Lower salinities in the Appalachian Basin and a significant salinity gradient in the Midcontinent Sea were reconstructed for the Desmoinesian Oakley shale, supporting the idea that freshwater discharge resulted in a salinity-stratified water column during times of “everwet” tropical palaeoclimate, at least in the eastern part of the epeiric sea. However, the salinity gradient is considerably reduced during the subsequent Missourian and Virgilian periodically dry interglacial periods (Hushpuckney and Heebner shales). This suggests that surface waters in the Midcontinent Sea were not significantly influenced by continental runoff and calls into question whether a halocline was necessary for the formation of phosphatic core shales.

Glacial-Eustatic Base-Level--Climatic Model for Late Middle to Late Pennsylvanian Coal-Bed Formation in the Appalachian Basin

ABSTRACT Late Middle-Late Pennsylvanian (middle Allegheny and lower Conemaugh) marine units in the Appalachian basin represent the distal edges of glacial-eustatic marine incursions of the Midcontinent sea onto the detrital apron of the Appalachian highlands. Because these marine units typically overlie coal beds, the main environment of formation of this type of coal bed appears to have been that of a coastal swamp migrating ahead of transgression. As base level rose, the water table continually rose, and the swamp was further nourished and surrounding vegetation kept thick enough to inhibit detrital influx by rainfall from the expanding nearby source of moisture. Even in parts of the Appalachian cyclic succession with no marine units (upper Allegheny, Monongahela, Dunkard), the coal beds rep esent the wettest part of the climate cycle of Cecil (1990), sandwiched between detrital units representing seasonal wet-dry climates when sediment was most readily mobilized, and antipodal to nonmarine limestones representing the driest climates. Throughout this time, the Appalachian basin was in the center of the tropical zone of a nearly accreted megacontinent, quite distant ( 4000 km) from permanent oceanic sources of moisture. Climate modeling without considering inland seas or orographic effects on winds shows that the tropical zone of such a large land mass would have suffered from a severe deficit in rainfall and soil moisture. Although further modeling shows that the Appalachian orogenic highlands would have drawn in moisture to ncrease rainfall in their vicinity, they also may have impeded the normal westward flow of moisture,laden easterly winds. The western source for enough moisture to form coal beds was most likely the North American Midcontinent sea. During major highstand, this sea would have covered about 2 million km2 and provided both high base level and abundant nearby moisture for enough continual rainfall to keep the coastal peat swamps widespread, fresh, and relatively detritus-free in the Appalachian basin. In contrast, during major lowstand it would have covered only about 200,000 km2 with its shoreline about 1500 km away, and it apparently provided less consistent moisture to the Appalachian basin then, because most nonmarine limestones and paleosols formed there during the e times contain evidence of drier climates. Therefore, upper Allegheny, Monongahela, and Dunkard coal beds most probably formed when the Midcontinent sea was approaching highstand and stood just west of the presently preserved outcrop. Thus, they likely represent the coastal lowland equivalent of a marine unit at highstand farther west. This constrained time of peat formation and preservation, in a variety of coastal environments prior to and during marine highstand, is responsible for the discrete and widespread nature of the coal-bed interval in a typical depositional cycle (or cyclothem), a pattern that stands in contrast to the complicated relations of overlying and underlying detrital units, which reflect the segregation of sand and mud into a complex mosaic of local deltaic and ter estrial subenvironments that developed when sea level rainfall and the water table were lower.

On the Permian Formation of Texas

Previous articleNext article FreeOn the Permian Formation of TexasCharles A. WhiteCharles A. White Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 23, Number 266Feb., 1889 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/274870 Views: 114Total views on this site Citations: 3Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Kayla M. Kolis, Bruce S. Lieberman Using GIS to examine biogeographic and macroevolutionary patterns in some late Paleozoic cephalopods from the North American Midcontinent Sea, PeerJ 7 (May 2019): e6910.https://doi.org/10.7717/peerj.6910Bryan M. Gee Reappraisal of the early Permian dissorophid Alegeinosaurus from Texas, USA, PalZ 92, no.44 (Jun 2018): 661–669.https://doi.org/10.1007/s12542-018-0421-9Neil H. Landman, Kristin Polizzotto, Royal H. Mapes, Kazushige Tanabe Cameral membranes in prolecanitid and goniatitid ammonoids from the Permian Arcturus Formation, Nevada, USA, Lethaia 39, no.44 (Mar 2007): 365–379.https://doi.org/10.1080/00241160601008395