We apply a new approach for the δ13C analysis of single organic‐walled microfossils (OWM) to three sites in the Appalachian Basin of New York (AB) that span the Late Devonian Biotic Crisis (LDBC). Our data provide new insights into the nature of the Frasnian–Famennian carbon cycle in the AB and also provide possible constraints on the paleoecology of enigmatic OWM ubiquitous in Paleozoic shale successions. The carbon isotope compositions of OWM are consistent with normal marine organic matter of autochthonous origins and range from −32 to −17‰, but average −25‰ across all samples and are consistently13C‐enriched compared to bulk sediments (δ13Cbulk) by ~0–10‰. We observe no difference between the δ13COWMof leiospheres (smooth‐walled) and acanthomorphic (spinose) acritarch OWM, indicating that our data are driven by ecological rather than taxonomic signals. We hypothesize that the offset between δ13COWMand δ13Cbulkis in part due to a large δ13C gradient in the AB water column where OWM utilized relatively13C‐enriched dissolved inorganic carbon near the surface. Thus, the organisms producing the balance of the total organic carbon were assimilating13C‐depleted C sources, including but not limited to respired organic carbon or byproducts of fermentation. We also observe a systematic decrease in both δ13COWMand δ13Cbulkof 3‰ from shoreward to open‐ocean facies that may reflect the effect of13C‐enriched dissolved inorganic carbon (DIC) derived from riverine sources in the relatively enclosed AB. The hypothesized steep carbon isotope gradient in the AB could be due to a strong biological pump; this in turn may have contributed to low oxygen bottom water conditions during the LDBC. This is the first time single‐microfossil δ13Corganalyses of eukaryotes have been directly compared to bulk δ13Corgin the deep‐time fossil record.
The global dispersal of forests and soils has been proposed as a cause for the Late Devonian mass extinctions of marine organisms, but detailed spatiotemporal records of forests and soils at that time remain lacking. We present data from microscopic and geochemical analyses of the Upper Devonian Chattanooga Shale (Famennian Stage). Plant residues (microfossils, vitrinite and inertinite) and biomarkers derived from terrestrial plants and wildfire occur throughout the stratigraphic section, suggesting widespread forest in the southern Appalachian Basin, a region with no macro plant fossil record during the Famennian. Inorganic geochemical results, as shown by increasing values of SiO2/Al2O3, Ti/Al, Zr/Al, and the Chemical Index of Alteration (CIA) upon time sequence, suggest enhanced continental weathering that may be attributed to the invasion of barren lands by rooted land plants. Our geochemical data collectively provide the oldest evidence of the influences of land plants from the southernmost Appalachian Basin. Our synthesis of vascular plant fossil record shows a more rapid process of afforestation and pedogenesis across south-central Euramerica during the Frasnian and Famennian than previously documented. Together, these results lead us to propose a new hypothesis that global floral dispersal had progressed southward along the Acadian landmass rapidly during the Late Devonian.
more » « less- NSF-PAR ID:
- 10154020
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
The evolution of land plant root systems occurred stepwise throughout the Devonian, with the first evidence of complex root systems appearing in the mid-Givetian. This biological innovation provided an enhanced pathway for the transfer of terrestrial phosphorus (P) to the marine system via weathering and erosion. This enhancement is consistent with paleosol records and has led to hypotheses about the causes of marine eutrophication and mass extinctions during the Devonian. To gain insight into the transport of P between terrestrial and marine domains, we report geochemical records from a survey of Middle and Late Devonian lacustrine and near-lacustrine sequences that span some of these key marine extinction intervals. Root innovation is hypothesized to have enhanced P delivery, and results from multiple Devonian sequences from Euramerica show evidence of a net loss of P from terrestrial sources coincident with the appearance of early progymnosperms. Evidence from multiple Middle to Late Devonian sites in Greenland and northern Scotland/Orkney reveal a near-identical net loss of P. Additionally, all sites are temporally proximal to one or more Devonian extinction events, including precise correlation with the Kačák extinction event and the two pulses associated with the Frasnian/Famennian mass extinction. For all sites, weathering, climate, and redox proxy data, coupled with nutrient input variability, reveal similar geochemical responses as seen in extant lacustrine systems. Orbitally forced climatic cyclicity appears to be the catalyst for all significant terrestrial nutrient pulses, which suggests that expansion of terrestrial plants may be tied to variations in regional and global climate.more » « less
-
more » « less
Abstract The Paleocene‐Eocene Thermal Maximum (PETM; 56 Ma) is considered to be one of the best analogs for future climate change. The carbon isotope composition (δ13C) of
n ‐alkanes derived from leaf waxes of terrestrial plants and marine algae can provide important insights into the carbon cycle perturbation during the PETM. Here, we present new organic geochemical data and compound‐specific δ13C data from sediments recovered from an early Cenozoic basin‐margin succession from Spitsbergen. These samples represent one of the most expanded PETM sites and provide new insights into the high Arctic response to the PETM. Our results reveal a synchronous ∼−6.5‰ carbon isotope excursion (CIE) in short‐chainn ‐alkanes (n C19; marine algae/bacteria) with a ∼−5‰ CIE in long‐chainn ‐alkanes (n C29andn C31; plant waxes) during the peak of the PETM. Although δ13Cn ‐alkanesvalues were potentially affected via a modest thermal effect (1‰–2‰), the relative changes in the δ13Cn ‐alkanesremain robust. A simple carbon cycle modeling suggests peak carbon emission rate could be ∼3 times faster than previously suggested using δ13CTOCrecords. The CIE magnitude of both δ13Cn ‐C19and δ13Cn ‐C29can be explained by the elevated influence of13C‐depleted respired CO2in the water column and increased water availability on land, elevatedp CO2in the atmosphere, and changes in vegetation type during the PETM. The synchronous decline in δ13C of both leaf waxes and marine algae/bacteria argues against a significant contribution to the sedimentary organic carbon pool from the weathering delivery of fossiln ‐alkanes in the Arctic region. -
Mammals rose to prominence in terrestrial ecosystems after the Cretaceous–Paleogene mass extinction, but the mammalian lineages characteristic of Paleogene faunas began their evolutionary and ecological diversification in the Late Cretaceous, stimulated by the rise of angiosperms (flowering plants) according to the preeminent hy- pothesis. The Cretaceous rise of mammals is part of a larger expansion in biodiversity on land that has been termed the Cretaceous (or Angiosperm) Terrestrial Revolution, but the mechanisms underlying its initiation remain opaque. Here, we review data from the fossil and rock records of western North America—due to its relatively continuous fossil record and complete chronology of mountain-building events—to explore the role that tectonism might have played in catalyzing the rise of modern-aspect terrestrial biodiversity, especially that of mammals and angiosperms. We highlight that accelerated increases in mammal and angiosperm species richness in the Late Cretaceous, ca. 100–75 Ma, track the acceleration of tectonic processes that formed the North American Cordillera and occurred during the ‘middle-Cretaceous greenhouse’ climate. This rapid increase in both mammal and angiosperm diversity also occurred during the zenith of Western Interior Seaway trans- gression, a period when the availability of lowland habitats was at its minimum, and oscillatory transgression- regression cycles would have frequently forced upland range shifts among lowland populations. These changes to both landscapes and climates have all been linked to an abrupt, global tectonic-plate ‘reorganization’ that occurred ca. 100 Ma. That mammals and angiosperms both increased in species richness during this interval does not appear to be a taphonomic artifact—some of the largest spikes in diversity occur when the available mammal-bearing fossil localities are sparse. Noting that mountainous regions are engines for generating biodi- versity, especially in warm climates, we propose that the Cretaceous/Angiosperm Terrestrial Revolution was ultimately catalyzed by accelerated tectonism and enhanced via cascading changes to landscapes and climate. In the fossil record of individual basins across western North America, we predict that (1) increases in mammalian diversity through the Late Cretaceous should be positively correlated with rates of tectonic uplift, which we infer to be a proxy for topographic relief, and are attended by increased climate heterogeneity, (2) the diversity of mountain-proximal mammalian assemblages should exceed that of coeval mountain-distal assemblages, espe- cially in the latest Cretaceous, and (3) endemism should increase from the latest Cretaceous to early Paleogene as Laramide mountain belts fragmented the Western Interior. Empirical tests of these predictions will require increased fossil collecting in under-sampled regions and time intervals, description and systematic study of existing collections, and basin-scale integration of geological and paleontological data. Testing these predictions will further our understanding of the coevolutionary processes linking tectonics, climate, and life throughout Earth history.more » « less
-
more » « less
Abstract Modern tropical and subtropical C4grasslands and savannas were established during the late‐Miocene and Pliocene, over 20 Myr after evolutionary originations of the C4photosynthetic pathway. This lag suggests environmental factors first limited and then favored C4plants. Here, we examine the timing and drivers for the establishment of C4grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant‐wax
n ‐alkanes recovered from turbidites in the Bengal Fan. Like prior studies, we find C4ecosystems in the Ganges‐Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ∼6.0 Ma. Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4, which suggests intermittent drying began before the establishment of C4grasslands with further drying at the onset of C4expansion. Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests, and then expansive C4grasslands. This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall, as identified in soil carbonate and tooth enamel data sets. Collectively the fossil, biomarker, and isotopic evidence reveal the development of modern C4ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks, and possibly declining atmospheric pCO2, beginning at 10.2 Ma and strengthening through the late Miocene.
