Geochemistry, and carbon, oxygen and strontium isotope composition of brachiopods from the Khuff Formation of Oman and Saudi Arabia GeoArabia

Brachiopods are abundant in the Oman Khuff Formation and similar brachiopod faunas are present at a few horizons in the same formation in Central Saudi Arabia. Following extensive systematic and biostratigraphic studies of these faunas, specimens from the base of the Midhnab Member of the Khuff Formation of Saudi Arabia (Buraydah Quadrangle), and from Member 3 of the Khuff Formation of the Huqf outcrop of Oman were assessed for isotope geochemistry (Sr, O and C). Dating using 87Sr/86Sr alone is not conclusive. Five pristine Oman brachiopods from biostratigraphically well-constrained lower Wordian horizons record a range of 87Sr/86Sr values that form a separate cluster offset from the current Sr isotope seawater curve, which defines the Early Permian and earliest Mid-Permian. The 87Sr/86Sr of the pristine Saudi Arabian brachiopod sits in an area which corresponds to a wide scatter of 87Sr/86Sr in the seawater curve data. However, the Saudi Arabian data does indicate that the Midhnab Member is likely younger than Member 3 of the Khuff Formation of the Huqf outcrop. The well-preserved brachiopod carbonate allows deductions to be made about the palaeotemperature of the Oman Khuff Formation Member 3 seawater using its oxygen isotope composition (\u3b418O). Assuming \u3b418O of seawater < \u20130.5\u2030, then palaeotemperature derived from brachiopods in the Oman horizons would be +25\ub0C, +22\ub0C and +17\ub0C respectively. This is consistent with the trend of shallowing within Member 3, suggested by facie

New records and new taxa of Permian brachiopods from the Khuff Formation, Midhnab Member, central Saudi Arabia

Brachiopods are described for the first time from outcrops of the lower part of the Midhnab Member of the Khuff Formation in central Saudi Arabia. The very rare fauna discovered includes Kotlaia sp. ind. of the order Orthida and Omanilasma husseinii n. gen. n. sp. of the order Terebratulida. Besides this new taxon, another new species Omanilasma desertica n. gen. n. sp. from the Khuff Formation of Interior Oman is here erected. The brachiopods were collected from an open-marine horizon and are associated with nautiloids, bactritids, bivalves, foraminifers, algae, and ostracods. A probable Late Permian age is assigned to the lower part of the Midhnab Member based on foraminifers. The brachiopods are compared to similar faunas from the Middle Permian Khuff Formation of Interior Oman, Amb Formation of Salt Range (Pakistan) and Rat Buri Limestone of Southeast Thailand

Tournaisian (Mississippian) brachiopods from the Mobarak Formation, North Iran

Following detailed stratigraphic work on the Mississippian marlstone and bioclastic limestone of the Mobarak Formation of the Alborz Mountains in North Iran, forty-eight of the most important brachiopod taxa are here systematically described and illustrated. The ranges of the taxa are given along the Abrendan and Simeh Kuh stratigraphic sections, located north of Damgham. The examined brachiopod species date the base of the Mobarak Formation to the Tournaisian, in absence of age-diagnostic foraminifers. Change in brachiopod settling preferences indicates a shift from high energy, shallow-water settings with high nutrient supply in the lower part of the formation to quieter, soft, but not soppy substrates, with lower nutrient supply in the middle part of the Mobarak Formation. Brachiopod occurrence is instead scanty at its top. The palaeobiogeographic affinity of the Tournaisian brachiopods from North Iran indicates a closer relationship to North America, Western Europe and the Russian Platform than to cold-water Australian faunas, confirming the affinity of the other biota of the Alborz Mountains. This can be explained by the occurrence of warm surface-current gyres widely distributing brachiopod larvae across the Palaeotethys Ocean, where North Iran as other peri-Gondwanan blocks acted as staging-posts

Sedimentary context and palaeoecology of Gigantoproductus shell beds in the Mississippian Eyam Limestone Formation, Derbyshire carbonate platform, central England

A sedimentological study was conducted at two localities exposing the Mississippian Eyam Limestone Formation of the Derbyshire carbonate platform, UK. Ricklow Quarry comprises seven facies with diverse skeletal assemblages, representing deposition on the inner to middle ramp within open marine waters. Once-a-Week Quarry comprises four facies, dominated by crinoidal debris representing deposition on the inner ramp. Both localities expose Gigantoproductus shell beds. Palaeoecological analysis of a single shell bed from each locality enabled investigation of the rapid colonization and success of this taxon on the platform. At Ricklow Quarry, on the eastern side of a localized mud mound, both life (>72% of thin and thick-shelled brachiopods in life position) and neighbourhood assemblages are present. A low-moderate diversity community (<1.37 and <0.8 Shannon diversity index) rapidly established over relict Brigantian mud mounds. Shell beds are preluded by intervals of decreased energy that allowed larvae to settle. Once established, the dominance of thick-shelled individuals enabled baffling, potentially providing localized shelter for larvae and nearby individuals. At Once-a-Week Quarry, where no mud mound is present, only thick-shelled Gigantoproductus species and a low diversity community (<1.07 Shannon diversity index) exclusively comprising neighbourhood assemblages (37% in life position) is present. The presence of inactive mud mounds at Ricklow Quarry appears to have been the key to the success of Gigantoproductus species enabling the onset of stable communities in the shelter provided by the relict mound. Once the first palaeocommunities were established, larvae dispersed and colonized higher energy settings, such as at Once-a-Week Quarry

Brachiopod-based oxygen-isotope thermometer: Update and review

In the early 1950\u2019s, McCrea and Epstein and co-workers laid the foundation for the oxygen isotope-based thermometers. Many variations of the thermometer have been since formulated based on synthetic and biogenic carbonates. Overall, the use and application of oxygen isotope thermometers must consider and be specific as to the mineralogy, and whether it is synthetic, abiogenic or biogenic carbonate. Here, we propose an updated and refined oxygen-isotope thermometer based on a large database of articulated brachiopods from high to low latitudes, cold to warm and shallow to deep-water regimes. In general, brachiopod-based oxygen isotopes are offset from abiogenic calcite precipitated in thermodynamic equilibrium by about -1 . They maintain this offset and that allows for the determination of robust ambient water temperatures over the full marine spectrum. Thus, the specific brachiopod-based oxygen-isotope thermometer applies, with few exceptions, to most modern articulated brachiopods, and potentially their ancient counterparts, and it is as follows: T\ub0C =17.3750 \u2013 4.2535 (\u3b4c-\u3b4w) + 0.1473 (\u3b4c-\u3b4w)2 (N=578, r2 = 0.980) Furthermore, it is imperative that mineralogy and taxa be considered for their appropriateness in the application of oxygen isotope thermometers on synthetic, abiogenic and biogenic marine carbonates. Articulated brachiopods are ideal recorders of oceanographic parameters due to their sessile nature, widespread distribution, high abundance in the Paleozoic and Mesozoic, high resilience to most environmental stresses (e.g., climate change - global warming, ocean acidification), and the resistance of the calcite shell \u2013 the archive \u2013 to post-depositional diagenetic alteration

Seasonality fluctuations recorded in fossil bivalves during the early Pleistocene: implications for climate change

Understanding the transformations of the climate system may help to predict and reduce the effects of global climate change. The geological record provides a unique archive that documents the long-term fluctuations of environmental variables, such as seasonal change. Here, we investigate how seasonal variation in seawater temperatures varied in the Mediterranean Sea during the early Pleistocene, approaching the Early-Middle Pleistocene Transition (EMPT) and the beginning of precession-driven Quaternary-style glacial–interglacial cycles. We performed whole-shell and sclerochemical stable isotope analyses (δ18O, δ13C) on bivalves, collected from the lower Pleistocene Arda River marine succession (northern Italy), after checking shell preservation. Our results indicate that seawater temperature seasonality was the main variable of climate change in the Mediterranean area during the early Pleistocene, with the Northern Hemisphere Glaciation (NHG) exerting a control on the Mediterranean climate. We show that strong seasonality (14.4–16.0 °C range) and low winter paleotemperatures (0.8–1.6 °C) were likely the triggers leading to the establishment of widespread populations of so called “northern guests” (i.e., cold water taxa) in the Mediterranean Sea around 1.80 Ma. The shells postdating the arrival of the “northern guests” record a return to lower seasonal variations and higher seawater paleotemperatures, with seasonality increasing again approaching the EMPT; the latter, however, is not associated with a corresponding cooling of mean seawater paleotemperatures, showing that the observed seasonality variation represents a clear signal of progressive climate change in the Mediterranean Sea