Prasinophyte bloom and putative fungi abundance near the Kačák event (Middle Devonian) from the Odivelas Limestone, Southwest Iberia

Abstract

The Kačák Event is one of the several prominent Devonian climatic and biotic perturbations with a supra-regional to global extent. Its record can be traced in the litho-and biostratigraphy of uppermost Eifelian-lowermost Givetian strata and with multiple geochemical and geophysical proxies. In southwest Iberia, within southwestern Ossa-Morena Zone domains, there are rare, scattered Early-Middle Devonian limestone occurrences. One of these occurrences-the Odivelas Limestone type locality-is revisited in terms of conodont biostratigraphy and palynology and the results compared with previous data on reef macrofauna and magnetic susceptibility stratigraphy. The new data show that this locality is probably within the Polygnathus hemiansatus zone, i.e. of the earliest Givetian age. The palynological content of a ca. 2 m of black, organic-rich, fine grained limestone section is dominated, in varied proportions, by amorphous organic matter, putative fungal hyphae, and prasinophycean algae. The results are interpreted as an indication of high organic productivity and deposition in hypoxic to anoxic settings and probable biotic crisis, in both marine and terrestrial realms, connected with the Middle Devonian Kačák Event. The similarity of this record with other Devonian events is discussed.

Middle Devonian reef-derived calciturbidites of western Ossa-Morena Zone (Portugal): conodont biostratigraphy of the Eifelian Pedreira da Engenharia Limestone

“…Other limestone occurrences, similar to those reported in the PE quarry, including reefal, peri-reefal deposits and calciturbidites, have been described along the western boundary of OMZ (Machado et al, 2020b;Oliveira et al, 2019). These limestones date from the patulus (uppermost Emsian, Lower Devonian) to hemiansatus (lowermost Givetian, Middle Devonian) conodont zones Machado et al, 2009Machado et al, , 2020aOliveira et al, 2019) and suggest an alignment of atoll-like reef structures developed along the southern border of the OMZ, during the Emsian to Givetian (Machado et al, 2020b;Moreira et al, 2021;Oliveira et al, 2019). Within the Cabrela Basin, limestones containing conodonts attributed to the lower gigas zone (currently lower rhenana) (upper Frasnian, Upper Devonian;Boogaard, 1983) have also been reported.…”

“…Numerical ages are as indicated by Cohen et al (2023). Age of Choteč Event in accordance with Becker and Aboussalam (2013), Koptíková (2011) and Vodrážková et al (2012) the hemiansatus zone (lowermost Givetian) (Machado et al, 2020a) (Fig. 5).…”

“…Recent studies on the Odivelas Limestone (Fig. 1a; Machado et al, 2009Machado et al, , 2020a have provided a detailed, conodont-based, biostratigraphy, recognizing the existence of carbonate sedimentation during the Early to Middle Devonian in the OMZ. However, other important Devonian limestone units, such as the Pedreira da Engenharia (PE) and Atalaia limestones, outcropping in the westernmost part of the OMZ, have not been studied in detail.…”

Acritarch clusters from the Cambrian (Miaolingian) of the Příbram-Jince Basin, Czech Republic

“…Babu et al 2014; Riedman et al 2014; Shukla et al 2020) as well as from Phanerozoic strata (e.g. Eisenack 1965; Slater et al 2017; Machado et al 2020) and are known from numerous stratigraphical levels in many areas of the world. Noteworthy is the recently described Involusphaeridium Filipiak et al 2021 represented by isolated leiosphere-like spheroids and clusters of those spheroids enveloped in a thin membrane (Filipiak et al 2021).…”