The Furongian (late Cambrian) Steptoean Positive Carbon Isotope Excursion (SPICE) in Avalonia

<p>The Steptoean Positive Carbon Isotope Excursion (SPICE) of earliest late Cambrian (Furongian) age is identified in England. The excursion is found within a <em>c</em>. 145 m thick siliciclastic succession within the middle and higher part of the Outwoods Shale Formation of Warwickshire, and reaches a maximum δ¹³C_org amplitude of 4.1‰ at values of −25.6‰. Biostratigraphical data show that the excursion occupies the greater part of the <em>Olenus</em> Biozone, an equivalent of the <em>Glyptagnostus reticulatus</em> Biozone that marks the base of the Furongian and coeval base of the Steptoean in North America. The amplitude of the excursion approaches that recorded in limestone-dominated Laurentian successions, and is greater than that recently documented for organic-rich mudstones of palaeocontinental Baltica in southern Sweden. A minor positive excursion above the SPICE may equate with a similar excursion recognized in Siberia. The SPICE in the Outwoods Shale Formation seems closely linked to the widely recognized early Furongian eustatic sea-level rise. There is no evidence in the English succession for slightly later regression, elsewhere considered coincident with the peak of the excursion and pivotal to some previous models explaining the SPICE. </p

Isotopic signals from Callovian–Kimmeridgian (Middle–Upper Jurassic) belemnites and bulk organic carbon, Staffin Bay, Isle of Skye, Scotland

<p>The stable isotope data presented here significantly extend and expand upon previous isotopic investigations of the Middle to Late Jurassic interval. The belemnite samples collected from the Staffin Bay and Staffin Shale formations from the Isle of Skye, Scotland, yielded oxygen isotope values consistent with Callovian–Kimmeridgian palaeotemperatures of 6.7–20.6 °C. The carbon isotope data comprise one of the first moderately high-resolution investigations of the relationship between terrestrial δ¹³C_org (predominantly fossil wood debris) and marine δ¹³C_carb (belemnites) as derived from a geologically coeval record. The Staffin Bay data reveal a broad Early to Mid-Oxfordian positive carbon isotope excursion. The excursion maximum occurs in the <em>cordatum</em> Zone (British Boreal ammonite zonation), although high values persist into the <em>tenuiserratum</em> Zone. The correspondence between the marine and terrestrial records indicates a strong coupling of the ocean–atmosphere system and suggests that the total exchangeable carbon reservoir would have been affected at this time. The Mid-Oxfordian negative carbon isotope excursions identified in published Tethyan records and commonly attributed to methane release are not recorded in the Staffin Bay data, which may suggest that the Tethyan excursions do not represent fluctuations in the global carbon reservoir and that the fidelity of the methane hypothesis should be re-evaluated. </p

A refined chronology for the Cambrian succession of southern Britain

<p>Three dated (U–Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire (England) and Pembrokeshire (Wales) delimit the traditional ‘Lower'–‘Middle' Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.45 ± 0.36 [0.81 including tracer calibration and ²³⁸U decay constant errors] Ma from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, and a date of 509.10 ± 0.22 [0.77 including tracer calibration and ²³⁸U decay constant errors] Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates offer a calibration of early metazoan evolution by directly constraining the age of the intervening Comley Limestones, which contain diverse small shelly fossils in addition to trilobites, and also a key early occurrence of exceptional, three-dimensionally preserved arthropods. In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.30 ± 0.23 [0.77 including tracer calibration and ²³⁸U decay constant errors] Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level at which trilobites make their first local appearance. </p

XPS spectra of the pink and white bands of UOM-232.

<p>Wide energy range scans are shown in (a) and (d), (b) and (e) show scans of 220 eV—70 eV, and (c) and (f) show high resolution scans of the Cl 2p, P 2s and S 2p peaks. Due to the presence of phosphate the phosphorus peak 2s peak occurs in the same range as the boron peak (190 eV—191 eV) meaning boron could not be resolved.</p

Isotope data from UOM-232 showing the white and pink (shaded) bands and the location of the drill spots.

<p>Isotope data from UOM-232 showing the white and pink (shaded) bands and the location of the drill spots.</p

Quantification data of elements present in UOM-232 shown by X-ray photoeletron spectroscopy.

<p>Quantification data of elements present in UOM-232 shown by X-ray photoeletron spectroscopy.</p

XRF map of Cl in UOM-232 with corresponding photograph in longitudinal section.

<p>Cl is clearly enriched in the white bands. White represents high abundances and black represents low abundances.</p

Electron Microprobe images of UOM-232.

<p>The Mg and Si is concentrated in the cell walls and highlights the much better cellular preservation in the white bands compared to the pink bands. White represents high abundances and black represents low abundances.</p

Py-GCMS total ion current and <i>m/z</i> 55+57 chromatograms of the bulk and Residue of UOM-232.

<p>The insets are not to scale. Black brackets represent <i>n-</i>alkane/<i>n-</i>alkene doublets (numbers indicate carbon chain length), ac acetophenone, bp biphenyl, f fluorene, in indane, phn phenathrene/anthracene; and bx benzene and nx napthalene derivatives, where x represents the number of carbon atoms in the alkyl group. A black outline indicates the presence of a double bond.</p

Py-GCMS Total ion current chromatograms of the bulk and residue of UOM-232 after thermochemolysis, insets (not to scale) are the <i>m/z</i> 74 mass chromatograms.

<p>Fatty acid moieties (measured as methyl esters) are represented by filled circles and <i>n-</i>alkane/<i>n-</i>alkene doublets by black brackets, numbers indicate carbon chain length; an alkane nitrile, bp biphenyl, f fluorene, fb trifluoromethylbenzoic acid pentadecylester, pha phenol-(dimethylamino), phe phenylalanine 4-amino-N-t-butyloxycarbonyl-t-butylester, phn phenthrene, pi phenol 4 4’-(1-methylethylindene)bis(2-methyl), py pyrrole, 2,3,4,5-tetramethyl; and bx benzene, ix indene, iox indole, nx napthalene, ndx dihydronapthalene, nhx tetrahydronapthalene and phx phenol derivatives, where x represents the number of carbon atoms in the alkyl group.</p