Geochemical indications for the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals in terrestrial sediments of the Canadian Arctic

During the late Paleocene to early Eocene, clastic fluvial sediments and coals were deposited in northern high latitudes as part of the Marga­ret Formation at Stenkul Fiord (Ellesmere Island, Nunavut, Canada). Syn-sedimentary tectonic movements of the Eurekan deformation continu­ously affected these terrestrial sediments. Different volcanic ash layers occur, and unconformities subdivide the deposits into four sedimentary units. Rare vertebrate fossils indicate an early Eocene (Graybullian) age for the upper part of the Stenkul Fiord outcrop. Here, we present carbon isotope data of bulk coal, related organic-rich mud and siltstones, a plant leaf wax-derived alkane, and additional plant remains. These data provide a complete carbon isotope record of one stratigraphic section with defined unconformity positions and in relation to other Eurekan deformation features. A previously dated ash layer MA-1 provided a U-Pb zircon age of 53.7 Ma and is used as a stratigraphic tie point, together with a discrete negative carbon isotope excursion found above MA-1 in a closely sampled coal seam. The excursion is identified as the likely expression of the I-1 hyperthermal event. Based on our isotope data that reflect the early Eocene dynamics of the carbon cycle, this tie point, and previous paleontological constraints from vertebrate fossils, the locations of the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals and their extent along the complete section are herein identified. Within the intervals of the PETM and ETM-2 hyperthermal events, increasing amounts of clastic sediments reached the site toward the respective end of the event. This is interpreted as a response of the fluvial depositional system to an intensified hydrological system during the hyperthermal events. Our study establishes an enhanced stratigraphic framework allowing for the calcula­tion of average sedimentation rates of different intervals and considerations on the completeness of the stratigraphic record. As one of the few high-latitude outcrops of early Eocene terrestrial sediments, the Stenkul Fiord location offers further possibilities to study the effects of extreme warming events in the Paleogene.

Palaeoecologic and Palaeoclimatic Inferences from Calcareous Nannofossils in Western Lobe Offshore, Niger Delta

In support of the ongoing temporal palaeoenvironment and palaeoclimatic reconstructions of the Neogene sediments, this study attempts to detail the paleo-proxies recovered from DEL-1 Well, western offshore Niger Delta. The standard smear slide method enabled the recovery of well-preserved calcareous nannofossils that depict early to mid–Miocene (NN4–NN5) sediments. The up-hole relationships between the nannofossil accumulation rate (NAR), the relative abundance of Discoaster and coccolith size of Reticulofenestra show step by step collapse of sea surface stability from early to middle Miocene. The lower horizons (8000–9460 ft) exhibit a low NAR, relatively high Discoaster abundance and relatively large Reticulofenestra size to suggest a deep thermocline and nutricline that characterise oligotrophic conditions in less warm-water induced climate. Conversely, upper horizons (5225–6550 ft) exhibit a high NAR, relatively low Discoaster abundance and relatively small Reticulofenestra size to suggest a shallow thermocline and nutricline that characterise eutrophic conditions in warm-water induced climate. The relative abundance of Helicosphaera carteri within the mid-NN5 suggests mesotrophic conditions within a stressed environment, with the possible occurrence of carbonate crash events. The combined parameters indicate gradual eutrophication and collapse of sea surface stability favouring nutrients and influx of terrestrial sediments in the ocean water as it progressed from early to middle Miocene. The abundance of the palaeo-proxies assemblages suggests hyposaline waters in a neritic environment that prevailed during the warm climatic condition.

Supplemental Material: Geochemical indications for the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals in terrestrial sediments of the Canadian Arctic

<div>Contains figures of most depleted δ¹³C values of selected early Eocene hyperthermals and age of volcanic ash layer MA-1 with graphical representation of error ranges. Additionally, tables of all δ¹³C data, organic carbon contents, thicknesses of clastic intervals, and details of U-Pb zircon analyses are provided.<br></div>

Supplemental Material: Geochemical indications for the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals in terrestrial sediments of the Canadian Arctic

<div>Contains figures of most depleted δ¹³C values of selected early Eocene hyperthermals and age of volcanic ash layer MA-1 with graphical representation of error ranges. Additionally, tables of all δ¹³C data, organic carbon contents, thicknesses of clastic intervals, and details of U-Pb zircon analyses are provided.<br></div>

A rapid sedimentary response to the Paleocene-Eocene Thermal Maximum hydrological change: new data from alluvial units of the Tremp-Graus Basin (Spanish Pyrenees)

A massive emission of light carbon about 56 Ma ago, recorded in marine and terrestrial sediments by a negative carbon isotope excursion (CIE), caused a short-lived (~170 kyr) global warming event known as the Paleocene–Eocene Thermal Maximum (PETM). The core of this event is represented in the south Pyrenean Tremp-Graus Basin by two successive alluvial units, the Claret Conglomerate (CC) and the Yellowish Soils, which represent laterally juxtaposed depositional environments. It is generally agreed that these units record a dramatic increase in seasonal rain and an increased intra-annual humidity gradient during the PETM, but the timing of the sedimentary response to the hydrological change is a matter of debate. Some authors maintain that the CC was developed during the early, most intense phase of the carbon emission, others that its formation lagged by 16.5 ± 7.5 kyr behind the onset of the PETM. The latter claim was mainly based on the assumption that in two sections of this basin, Claret and Tendrui, the onset of the CIE occurs 3 and 8 m below the base of the CC, respectively. Here we show that in the zone between these two sections the CC is missing and the Yellowish Soil unit rests directly and conformably on the underlying deposits. New d13Corg data from this zone provide sound evidence that the onset of the CIE is situated just ~1 m below the Yellowish Soils. The CC erosional base cuts down deeper than this figure, rendering it highly unlikely the preservation of the CIE onset below it. A tentative estimate based on sedimentation rates indicates that ~3.8 kyr, or less, may have elapsed from the onset of the CIE to the arrival of PETM alluvium into the Claret-Tendrui study area, about a third of the lowest estimate of previous authors. Since the study area was situated about 15 km from the source area, our new estimate supports a rapid response of the sedimentary system to the hydrological change at the onset of the PETM.

Geogenic organic carbon in terrestrial sediments and its contribution to total soil carbon

Geogenic organic carbon (GOC) from sedimentary rocks is an overlooked fraction in soils that has not yet been quantified but influences the composition, age, and stability of total organic carbon (OC) in soils. In this context, GOC is the OC in bedrock deposited during sedimentation. The contribution of GOC to total soil OC may vary, depending on the type of bedrock. However, no studies have been carried out to investigate the contribution of GOC derived from different terrestrial sedimentary rocks to soil OC contents. In order to fill this knowledge gap, 10 m long sediment cores from three sites recovered from Pleistocene loess, Miocene sand, and Triassic Red Sandstone were analysed at 1 m depth intervals, and the amount of GOC was calculated based on 14C measurements. The 14C ages of bulk sedimentary OC revealed that OC is comprised of both biogenic and geogenic components. The biogenic component relates to OC that entered the sediments from plant sources since soil development started. Assuming an average age for this biogenic component ranging from 1000–4000 years BP (before present), we calculated average amounts of GOC in the sediments starting at 1.5 m depth, based on measured 14C ages. The median amount of GOC in the sediments was then taken, and its proportion of soil mass (g GOC per kg−1 fine soil) was calculated in the soil profile. All the sediments contained considerable amounts of GOC (median amounts of 0.10 g kg−1 in Miocene sand, 0.27 g kg−1 in Pleistocene loess, and 0.17 g kg−1 in Red Sandstone) compared with subsoil OC contents (between 0.53 and 15.21 g kg−1). Long-term incubation experiments revealed that the GOC appeared comparatively stable against biodegradation. Its possible contribution to subsoil OC stocks (0.3–1.5 m depth) ranged from 1 % to 26 % in soil developed in the Miocene sand, from 16 % to 21 % in the loess soil, and from 6 % to 36 % at the Red Sandstone site. Thus, GOC with no detectable 14C content influenced the 14C ages of subsoil OC and may partly explain the strong increase in 14C ages observed in many subsoils. This could be particularly important in young soils on terrestrial sediments with comparatively low amounts of OC, where GOC can make a large contribution to total OC stocks.

Paleoclimatic and Redox Condition Changes during Early-Middle Jurassic in the Yili Basin, Northwest China

The Jurassic was mainly a “greenhouse” period characterized by global warming and by significant peat accumulations in some continental basins. However, studies of Jurassic climate and environments have mainly focused on marine records and only a few on terrestrial sediments. Yili Basin, a mid-latitude terrestrial basin in present Northwest China, included accumulation of the important recoverable coal seams. In this study, geological data, clay mineral analysis, and palynological assemblages were employed on fine-grained samples from the Su’asugou section in southern Yili Basin. The factors (paleoclimate, depositional conditions, and paleo-vegetation) impacting peat accumulation were investigated. The results suggest that the siliciclastics may have been derived from exposed Carboniferous rocks in a continental arc environment. A warm and humid paleoclimate in the Yili basin dominated during the early-Early Jurassic deposition of the Badaowan Formation and the Middle Jurassic deposition of the Xishanyao Formation. This climate contributed to high sedimentary rates and to a high productivity of peat-forming paleo-vegetation that was preserved under dysoxic conditions. In contrast, during the late-Early Jurassic between these two formations, the Sangonghe Formation was an interval of relatively aridity that included red beds preserved under more hypoxic sedimentary conditions, and with an interruption in peat formation and preservation.

Topset-to-forest rollover trajectories as reliable predictors of sediment-volume partitioning into deep-lake areas

Topset-to-forest rollover trajectories and their relation to sediment- and sand-budget partitioning into deep-lake areas are far from being well understood, as compared with their marine counterparts of shelf edges. Two quantitatively distinctive topset-to-forest rollover trajectories and clinothem-stacking patterns were recognized in the Oligocene Qikou Sag of the Bohai Bay Basin and are quantified in terms of trajectory angles (Tse), topset thickness (Tt), forest thickness (Tf), bottomset thickness (Tb), and clinothem-set relief (Rc). Rising topset-to-forest trajectories have positive Tse of 0.15°–0.51° (averaging 0.35°). Ranges in Tt, Tf, Tb, and Rc of their associated progradational and aggradational clinothem sets are, respectively, 32.4–58.7 m (averaging 42.7 m), 76.9–176.2 m (averaging 148.3 m), 0 m, and 167.8–320.8 m (averaging 272.9 m). Falling topset-to-forest rollover trajectories, in contrast, have negative Tse of − 0.12° to − 0.02° (averaging − 0.06°). Ranges in Tt, Tf, Tb, and Rc of their associated progradational and downstepping clinothem sets are, respectively, 0 m, 266.0–395.7 m (averaging 333.4 m), 441.1–542.5 m (averaging 464.1), and 874.9–922.6 m (averaging 892.5 m). These two topset-to-forest rollover trajectories and clinothem-stacking patterns are closely linked to two distinctive patterns of sediment- and sand-volume partitioning into deep-lake areas, which are quantified in terms of Tt, Tb, and differential sediment aggradation of topset segments and forest-to-bottomset compartments (As/Ad). Rising topset-to-forest rollover trajectories and associated progradational and aggradational clinothem sets are characterized by aggradational topsets (reported as Tt of 32.4–58.7 m), a lack of time-equivalent bottomsets, and As/Ad of 0.22–0.87 (averaging 0.33), and are fronted by mud-dominated depositional deposits, with sporadic occurrence of thinner and regionally localized forest sands. They are, therefore, inefficient at delivering terrestrial sediments or sands into deep-lake settings. Falling topset-to-forest rollover trajectories and associated progradational and downstepping clinothem sets, in contrast, are characterized by toplap, erosional terminations but aggradational bottomsets (reported as Tb of 266.0–473.4 m), and As/Ad of 0, and are fronted by sand-rich depositional deposits, with widespread occurrence of thicker and regionally extensive time-equivalent deep-lake bottomset sands. They are, thus, efficient at delivering terrestrial sediments or sands into deep-lake settings. Topset-to-forest rollover trajectories and associated clinothem-stacking patterns are thus reliable predictors of sediment- and sand-volume partitioning into deep-lake areas, assisting greatly in developing a more dynamic stratigraphy.