Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Solid Earth. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Strength and Stress Evolution of an Actively Exhuming Low-Angle Normal Fault, Woodlark Rift, SE Papua New GuineaAuthorsMarcelMizeraTimothyLittleCarolynBoultoniDYaronKatziriDNiveditaThiagarajanDavid JohnPrioriDJames B.BiemilleriDEuan George CSmithSee all authors Marcel MizeraCorresponding Author• Submitting AuthorVictoria University of Wellingtonview email addressThe email was not providedcopy email addressTimothy LittleVictoria University of Wellingtonview email addressThe email was not providedcopy email addressCarolyn BoultoniDVictoria University of WellingtoniDhttps://orcid.org/0000-0003-0597-6152view email addressThe email was not providedcopy email addressYaron KatziriDBen-Gurion University of the NegeviDhttps://orcid.org/0000-0003-1999-3746view email addressThe email was not providedcopy email addressNivedita ThiagarajanCal Techview email addressThe email was not providedcopy email addressDavid John PrioriDUniversity of OtagoiDhttps://orcid.org/0000-0002-4653-2112view email addressThe email was not providedcopy email addressJames B. BiemilleriDUniversity of Texas at AustiniDhttps://orcid.org/0000-0001-6663-7811view email addressThe email was not providedcopy email addressEuan George C SmithVictoria University of Wellingtonview email addressThe email was not providedcopy email address
The oxygen isotope ratio 18 O/ 16 O (expressed as a δ 18 O VSMOW value) in marine sedimentary rocks has increased by ~8‰ from the early Paleozoic to modern times. Interpretation of this trend is hindered by ambiguities in the temperature of formation of the carbonate, the δ 18 O seawater , and the effects of postdepositional diagenesis. Carbonate clumped isotope measurements, a temperature proxy, offer constraints on this problem. This thermometer is thermodynamically controlled in cases where carbonate achieves an equilibrium internal distribution of isotopes and is independent of the δ 18 O of the water from which the carbonate grew; therefore, it has a relatively rigorous chemical–physics foundation and can be applied to settings where the δ 18 O of the water is not known. We apply this technique to an exceptionally well-preserved Ordovician carbonate record from the Baltic Basin and present a framework for interpreting clumped isotope results and for reconstructing past δ 18 O seawater . We find that the seawater in the Ordovician had lower δ 18 O seawater values than previously estimated, highlighting the need to reassess climate records based on oxygen-isotopes, particularly where interpretations are based on assumptions regarding either the δ 18 O seawater or the temperature of deposition or diagenesis. We argue that an increase in δ 18 O seawater contributed to the long-term rise in the δ 18 O of marine sedimentary rocks since the early Paleozoic. This rise might have been driven by a change in the proportion of high- versus low-temperature water–rock interaction in the earth’s hydrosphere as a whole.
Natural gas is a key energy resource, and understanding how it forms is important for predicting where it forms in economically important volumes. However, the origin of dry thermogenic natural gas is one of the most controversial topics in petroleum geochemistry, with several differing hypotheses proposed, including kinetic processes (such as thermal cleavage, phase partitioning during migration, and demethylation of aromatic rings) and equilibrium processes (such as transition metal catalysis). The dominant paradigm is that it is a product of kinetically controlled cracking of long-chain hydrocarbons. Here we show that C2+n-alkane gases (ethane, propane, butane, and pentane) are initially produced by irreversible cracking chemistry, but, as thermal maturity increases, the isotopic distribution of these species approaches thermodynamic equilibrium, either at the conditions of gas formation or during reservoir storage, becoming indistinguishable from equilibrium in the most thermally mature gases. We also find that the pair of CO2 and C1 (methane) exhibit a separate pattern of mutual isotopic equilibrium (generally at reservoir conditions), suggesting that they form a second, quasi-equilibrated population, separate from the C2 to C5 compounds. This conclusion implies that new approaches should be taken to predicting the compositions of natural gases as functions of time, temperature, and source substrate. Additionally, an isotopically equilibrated state can serve as a reference frame for recognizing many secondary processes that may modify natural gases after their formation, such as biodegradation.
Deep-sea corals are a unique archive in paleoceanography. They have large banded skeletons that allow for high
resolution records and have a high uranium content allowing for accurate calendar ages independent of radiocarbon age
measurements. One problem with using deep-sea corals for long records is that it is difficult to date a large numbers of
corals accurately and precisely. Unlike sediment cores, fossil fields of corals have no inherent stratigraphy and each
individual coral must be separately dated.
Abstract The equatorial Pacific traverses a number of productivity regimes, from the highly productive coastal upwelling along Peru to the near gyre‐like productivity lows along the international dateline, making it an ideal target for investigating how biogeochemical systems respond to changing oceanographic conditions over time. However, conflicting reconstructions of productivity during periods of rapid climate change, like the last deglaciation, render the spatiotemporal response of equatorial Pacific productivity ambiguous. In this study, surface productivity since the last glacial period (30,000 years ago) is reconstructed from seven cores near the Line Islands, central equatorial Pacific, and integrated with productivity records from across the equatorial Pacific. Three coherent deglacial patterns in productivity are identified: (1) a monotonic glacial‐Holocene increase in productivity, primarily along the Equator, associated with increasing nutrient concentrations over time; (2) a deglacial peak in productivity ~15,000 years ago due to transient entrainment of nutrient rich southern‐sourced deep waters; and (3) possible precessional cycles in productivity in the eastern equatorial Pacific that may be related to Intertropical Convergence Zone migration and potential interactions with El Niño–Southern Oscillation dynamics. These findings suggest that productivity was generally lower during the glacial period, a trend observed zonally across the equatorial Pacific, while deglacial peaks in productivity may be prominent only in the east.
