Global cooling initiated the Middle-Late Mississippian biodiversity crisis

Highlights

• Brachiopod oxygen isotopes document a cooling event with ~4.7–5.5 °C drop in sea surface temperature during 332.5–331.5 Ma.

• This cooling event coincides with fast decline of metazoan reef abundance and benthic faunal diversity.

• Late Visean (~332 Ma) onset of the main glaciation phase of the late Paleozoic Ice Age initiated biodiversity crisis.

Abstract

During the Mississippian period, metazoan reefs and other marine faunas gradually recovered from the Late Devonian mass extinctions and reached a peak in the late Visean (~334–332 Ma). Faunal diversity started to decline from the latest Visean (~332–330 Ma) through Serpukhovian (~330–323 Ma), with significant genera/species losses and ecosystem reconstruction. This Middle-Late Mississippian biodiversity crisis (M-LMBC) was thought to have been caused by global cooling associated with the late Paleozoic Ice Age (LPIA), but existing sedimentological and temperature proxy data suggest that the global cooling event—that marks the onset of the main glaciation phase of LPIA—happened either ~4 Myr before or ~ 1–5 Myr after the initial biodiversity decline at ~332 Ma. Here, we report oxygen isotope data of diagenetically screened, well-preserved brachiopod calcite (δ¹⁸O_calcite) from late Visean-Serpukhovian (or Middle-Late Mississippian; ~334–323 Ma) strata in South China where biodiversity data are well documented. The δ¹⁸O_calcite data reveal a ~ 2.0‰ positive shift from −4.6 ± 0.2‰ to −2.7 ± 0.5‰ with an estimated ~4.7–5.5 °C drop in sea surface temperature (SST) during ~332.5–331.5 Ma in the late Visean. This cooling event coincides with fast decline of metazoan reef abundance, followed by decrease of benthic faunal diversity. The δ¹⁸O_calcite data, in combination with calibrated sedimentological and biodiversity data, demonstrate the coupling between late Visean (~332 Ma) onset of the main glaciation phase of the LPIA and initiation of the M-LMBC.

Introduction

The late Paleozoic Ice Age (LPIA; ~360–260 Ma) was a time of dynamic earth system change, with multiple episodes of glaciation, prominent sea-level change, and fluctuated atmospheric CO₂ concentration and seawater temperature (e.g., Fielding et al., 2008; Isbell et al., 2012; Montañez and Poulsen, 2013). The LPIA started with local glacial events at the Devonian-Carboniferous transition (Famennian to Tournaisian stages), but intensive glaciation may not have happened until the Middle-Late Mississippian (late Visean to Serpukhovian stages; Isbell et al., 2012; Montañez and Poulsen, 2013; Soreghan et al., 2019). Along with the development of the LPIA from late Visean to Serpukhovian, marine faunas experienced severe diversity losses (Stanley and Powell, 2003; McGhee et al., 2012; Balseiro and Powell, 2020) and metazoan reef ecosystem collapse (Yao et al., 2020).

One of the intriguing yet unresolved issues concerns the biotic response to the onset of widespread glaciation in association with the LPIA. After the Late Devonian mass extinctions, marine faunas gradually recovered and reached a peak in the late Visean (Fig. 1A). Marine faunal diversity started to decline from the latest Visean through Serpukhovian, with up to 39% genera losses (Stanley and Powell, 2003; McGhee et al., 2012). This Middle-Late Mississippian biodiversity crisis (M-LMBC) was ecologically ranked as the fifth among the Phanerozoic mass extinctions (McGhee et al., 2012, McGhee et al., 2013). Although such a rank could have been partially biased by the earlier versions of the Paleobiology database that had a strong emphasis on fossil records of North America and Europe and by the lack of analyses on the origination and extinction rates of clades (cf. Stanley, 2016; Muscente et al., 2018), significant genera/species losses (~20%) are indeed present from the late Visean to Serpukhovian in the updated Paleobiology database (Fig. 1A). Particularly, recent high-resolution studies confirm that metazoan reef abundance reached the maximum value in the late Asbian (late Visean; ~333 Ma) and started to decline from the latest Visean (~332–330 Ma) through Serpukhovian (~330–323 Ma), which tracks the marine biodiversity changes globally (Fig. 1A; Yao et al., 2020).

In spite of the general agreement that the development of the LPIA was the cause of the M-LMBC (e.g., Stanley and Powell, 2003; McGhee et al., 2012, McGhee et al., 2013), there is no consensus on the age of the cooling event that initiated the biodiversity decline. Suggested global cooling that marks the onset of the main glaciation phase of the LPIA ranges from the middle-late Visean (Wright and Vanstone, 2001; Barham et al., 2012), to late Visean (Bruckschen et al., 1999; Smith and Read, 2000; Armendáriz et al., 2008; Bishop et al., 2009; Giles, 2012; Fielding and Frank, 2015; Valdez Buso et al., 2020), early Serpukhovian (Mii et al., 1999, Mii et al., 2001; Buggisch et al., 2008; Fielding et al., 2008), and to late Serpukhovian-early Bashkirian (Grossman et al., 2008; Chen et al., 2016), which are either ~4 Myr before or ~ 1–5 Myr after the initial metazoan reef and biodiversity decline at ~332 Ma (Fig. 1B). The mismatch between global cooling and biodiversity change hinders a mechanistic understanding of their causal relationship and compels for integrated biodiversity and temperature proxy data from the same stratigraphic successions.

The biostratigraphically well-constrained late Visean-Serpukhovian strata in South China provide an opportunity to elucidate the causal relationship between the onset of the main phase of the LPIA and biodiversity change. During the Visean-Serpukhovian, South China was located near the paleoequator in the northeastern Paleotethys Ocean and was far away from any large continent (Fig. 2A). This paleogeographic location makes it an ideal place to preserve the best biological and potentially geochemical record. In this paper, we report carbon and oxygen isotope data from well-preserved brachiopods (δ¹³C_calcite and δ¹⁸O_calcite) of the late Visean-Serpukhovian strata from the Yashui and Gandongzi sections in South China (Fig. 2B). In combination with available reef abundance and biodiversity data, we discuss the potential linkage between global cooling and marine ecosystem change across the late Visean-Serpukhovian transition.