Changes of palaeoenvironmental conditions recorded in Late Devonian reef systems from the Canning Basin, Western Australia: A biomarker and stable isotope approach

Abstract

Although the Late Devonian extinctions were amongst the largest mass extinction events in the Phanerozoic, the causes, nature and timing of these events remain poorly restrained. In addition to the most pronounced biodiversity loss at the Frasnian-Famennian (F-F) boundary and the end Famennian, there were also less extensively studied extinction pulses in the Middle to Late Givetian and the Frasnian. Here we used a combination of palynological, elemental, molecular and stable isotope analyses to investigate a sedimentary record of reef-systems from this time period in the Canning Basin, Western Australia. The acquired data generally showed distinct variations between sediments from (i) the time around the Givetian-Frasnian (G-F) boundary and (ii) later in the Frasnian and indicated a distinct interval of biotic stress, particularly for reef-builders, in the older sediments. Alterations of pristane/phytane ratios, gammacerane indices, Chlorobi biomarkers, δD kerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic/euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column. Simultaneous excursions in δ 13 C profiles of carbonates, organic matter (OM) and hydrocarbons in the older sediments reflect the stratification-induced enhancement of OMrecycling by sulfate reducing bacteria. Alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans (MTTCs) and perylene indicate an increased terrigenous nutrient input via riverine influx, which would have promoted stratification, phytoplankton blooms and the development of lower water column anoxia. The detected palaeoenvironmental conditions around the G-F boundary may reflect a local or global extinction event. Our data furthermore suggest a contribution of the higher plant-expansion and photic zone euxinia to the Late Devonian extinctions, consistent with previous hypotheses. Furthermore, this work might contribute to the understanding of variations in Devonian reef margin and platform-top architecture, relevant for petroleum exploration and development in the global Devonian hydrocarbon resources.

A new method for the rapid analysis of 1H-Pyrrole-2,5-diones (maleimides) in environmental samples by two-dimensional gas chromatography time-of-flight mass spectrometry

“…Although the origin of such compounds is unknown based on structural reasons considering known chlorophylls, these maleimides may be derived from bacteriochlorophyll derivatives and porphyrins with extended alkyl chains [10,53,54]. In contrast, thermal cracking and alkylation processes as suggested for maleimides with alkyl side chains up to C11 in crude oils [52] are unlikely in the immature, recent lake samples [29] and the low maturity rock samples from the Canning Basin [45] analysed in this study. This first report of their occurrence and simplified detection method will enable further studies to determine their environmental significance.…”

“…Rock samples from the McWhae Ridge (Canning Basin, Western Australia; S 18°43.678 E 126°4.092, WGS84) were studied by [32,45,46]. The samples originate from a core section (MR-1 core; 27.2-42.1 m) which comprises the period between the Late Givetian (Middle Devonian) and the Middle to Late Frasnian (Late Devonian), and were investigated to reveal environmental changes before the Frasnian-Famennian boundary extinction event [32,45].…”

“…The samples originate from a core section (MR-1 core; 27.2-42.1 m) which comprises the period between the Late Givetian (Middle Devonian) and the Middle to Late Frasnian (Late Devonian), and were investigated to reveal environmental changes before the Frasnian-Famennian boundary extinction event [32,45]. The geologic setting and information on the core section are summarised in [45].…”

“…The samples originate from a core section (MR-1 core; 27.2-42.1 m) which comprises the period between the Late Givetian (Middle Devonian) and the Middle to Late Frasnian (Late Devonian), and were investigated to reveal environmental changes before the Frasnian-Famennian boundary extinction event [32,45]. The geologic setting and information on the core section are summarised in [45]. In short, the lowest part of the section comprises the Gogo Formation The sediment sample from the Swiss Lake Rotsee (22-24 cm) originate from a 58 cm long core obtained with a gravity corer at the maximum depth of 16 m in August 2010 (N 47°4.251 E 8°18.955, WGS84).…”

“…were Soxhlet extracted as reported in [45]. In short, the rock samples were cut with a rocksaw and pre-extracted with methanol (MeOH) and dichloromethane Half of the S1 fraction was used for direct analysis by GC×GC-ToF-MS, and the other half further purified as described below.…”