Abstract The early Toarcian oceanic anoxic event (Early Jurassic;∼183 Myr ago) is associated with one of the largest negative carbon isotope excursion (CIE) in the whole Phanerozoic (3–7‰). Estimates of the magnitude and rate of CO 2 injection in the ocean–atmosphere system are compatible with a scenario of ocean acidification. Many carbonate platforms drowned in the Pliensbachian, well before the early Toarcian event. In this paper we test the hypothesis of surface water ocean acidification by presenting data from a resilient carbonate platform: the Apennine Carbonate Platform of southern Italy. The studied sections document a dramatic shift of the carbonate factory from massive biocalcification to chemical precipitation. Lithiotis bivalves and calcareous algae ( Palaeodasycladus mediterraneus ), which were the most prolific carbonate producers of Pliensbachian carbonate platforms, disappear during the first phase of the early Toarcian CIE, before the most depleted values are reached. We discuss the local versus supraregional significance of this shift and propose a scenario involving abrupt decline of carbonate saturation, forced by CO 2 release at the beginning of the early Toarcian CIE, followed by a calcification overshoot, driven by the recovery of ocean alkalinity. Attribution of the demise of carbonate platform hypercalcifiers to ocean acidification is supported by palaeophysiology and reinforced by experimental data on the detrimental effects of ocean acidification on recent shellfishes and calcareous algae.

Carbonate platform evidence of ocean acidification at the onset of the early Toarcian oceanic anoxic event

This chapter provides an overview of the Silurian system. Apart from relatively minor occurrences in the northern part of the Perth Basin and in the Carnarvon Basin, in Western Australia, and rather more widespread occurrences in the Amadeus Basin, the only Silurian rocks on the continent are to be found in the Tasman Orthogeosyncline. The bulk of these outcrop in the southeastern States, though their presence in the subsurface beneath the Mesozoic sediments of the Artesian Basin has been proved by deep exploratory wells in some areas. The sediments in the two Western Australian Basins are limestones, dolomites, and cross-stratified quartzose sandstones, products of deposition in broad shallow-water basins with margins of low relief. The Amadeus Basin was receiving only terrestrial sediments. In the Lachlan Geosyncline, the pattern of arches and troughs had been greatly modified during the Benambran Orogeny, the only structures that retained their characters being the Molong–Canberra High and the Melbourne Trough. Following this deformation, there was extensive acid and intermediate volcanism that seems to have been largely restricted to the deformed areas.

The Silurian System

Mexico is one of the most biodiverse countries on the planet. Knowledge of echinoderm diversity in Mexico started in the XIX Century with Louis Agassiz in 1841. Currently, 643 species of echinoderms are known from Mexico, with Class Ophiuroidea the richest (197 species); Class Asteroidea follows with 185 species, then Class Echinoidea with 119 species, Class Holothuroidea with 113 species, and Class Crinoidea with 29 species. The Mexican deep sea has been little studied, and most expeditions covering this area have been made by institutions in other countries where a great amount of information is deposited but access to it can be difficult. It is necessary to have available catalogues of the Mexican echinoderms with information on their biology, ecology, distribution, and fisheries, in order to facilitate access to information, and promote further studies on the echinoderms of Mexico. Fossil echinoderms are present in the sedimentary basin of Mexico and thus have potential practical use as paleoecological indicators, complementing stratigraphic studies. Although taxonomic studies have resulted in a rather large species list, ecological, life history, and other studies are scarce. Studies on sea cucumber aquaculture in Mexico have not yet started, in spite of the high market value of these animals and their detritivorous habit which makes them attractive for cultivation. It is recommended that aquaculture studies be undertaken. These and other suggestions for advancement of the knowledge and sustainable utilization of echinoderms in Mexico are discussed in the present chapter.

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The Echinoderms of Mexico: Biodiversity, Distribution and Current State of Knowledge

Provenance and tectonic setting of the Paleozoic Tamatán Group, NE Mexico: Implications for the closure of the Rheic Ocean

Paleogeografia del Paleozoico de Chiapas, Mexico. IN SPANISH. Paleozoic Paleogeography Of Chiapas, Mexico.

Torres-Martinez, M.A., Sour-Tovar, F. & Barragan, R., November 2017. Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico. Alcheringa.Kukulkanus is the first genus of the tribe Buxtoniini recorded from rocks of the late Cisuralian (Artinskian–Kungurian). The Early Permian (Cisuralian) outcrops of the Santa Rosa Group, from southeastern Chiapas, are one of the most important marine Palaeozoic successions of Mexico. The Artinskian–Kungurian Paso Hondo Formation is the youngest unit in the succession and is dominated by massive limestone. Different marine invertebrates deposited in massive calcareous rocks characterize this formation. The buxtoniin Kukulkanus spinosus gen. et sp. nov. is reported from a single bed within the unit. The outcrops are located in southeastern Chiapas, very near the Guatemala–Mexico border. The lithological features and the preservation of fossils indicate that the fossil-bearing rocks were deposited in a low-energy open-waters pa...

Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico

Fourteen species of productid brachiopods from Ixtaltepec Formation, Oaxaca State in southeast Mexico, are described. All the species and most of the genus that are reported represent first records for Mexico, in the case of Echinoconchella this is the first report of the genus for North America. The species belong to the superfamilies Echinoconchoidea (Echinoconchus zapoteco sp. nov., Echinaria knighti, Karavankina cf. fasciata, Echinoconchella elegans), Linoproductoidea (Linoproductus cf. prattenianus, Linoproductus platyumbonus, Linoproductus sp., Marginovatia minor, Marginovatia aureocollis, Marginovatia cf. pumila, Cancrinella nunduva sp. nov., Ovatia muralis and Nuanducosia sulcata, new genus and species of Subfamily Anidanthinae) and Aulostegoidea (?Sinuatella sp.). The stratigraphic

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Nuevos braquiópodos prodúctidos (Rhynchonelliformea, Strophomenata) del Carbonífero de la región de Nochixtlán, Oaxaca

Microconchids are a little-known group of vermiform invertebrates whose fossil record is limited to the preservation of their calcareous tubes. In the past, they were erroneously classified as polychaetes, specifically of the genus Spirorbis. Nonetheless, currently it is known that serpulid polychaetes appeared in the late Permian and earliest true Spirorbis appeared in the Miocene. Microconchids are characterized by an initial bulb, microlamellar microsctructure, and a punctate tube. In this work, Microconchus maya is described as a new species from the Monte Redondo locality (Roadian, middle Permian) of the Paso Hondo Formation in Chiapas, Mexico. The new species, along with hederelloids, bryozoans, and crinoid holdfast occur as sclerobionts on brachiopods. The occurrence of most microconchids on spire-bearing brachiopod shells suggests that inhalant currents were crucial to the settlement of M. maya. However, their settlement preference on the anterior region of brachiopods could imply that microconchids only colonised places far away from the sediment. The age of the microconchids was established by means of the host brachiopods which have been correlated to Roadian formations of Texas in the USA. Microconchids and brachiopods formed life associations, inhabiting an environment related to the open waters of a homoclinal carbonate ramp. The description of M. maya not only represents the first definite record of the genus Microconchus in the Permian but also is the first report of a possible syn-vivo relationship between brachiopods and microconchids in the late Paleozoic.

A new middle Permian microconchid from Chiapas, Mexico, and its palaeoecological implications

Four species of discinid brachiopods of the genus Orbiculoidea present at different levels of the Ixtaltepec Formation, type section Arroyo las Pulgas, Nochixtlan Municipality, Oaxaca are described. Orbiculoidea caneyana and Orbiculoidea sp. were found in basal levels of the formation, in shale strata of chesterian age (Late Mississippian). The presence of Orbiculoidea missouriensis and Orbiculoidea capuliformis in upper stratigraphic levels, and also in argillaceous rocks of morrowan-desmoinesian age (Middle Pennsylvanian), corroborate the age of the fossil-bearing rocks. These are the first records of Orbiculoidea caneyana and O. capuliformis in Mexico and, along with O. missouriensis, highlight the paleobiogeographic relationship of the carboniferous faunas of Nochixtlan with coeval faunas described in the east-central region of the United States.

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Miguel A. Torres-Martínez

Papers

Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico

Nuevos braquiópodos prodúctidos (Rhynchonelliformea, Strophomenata) del Carbonífero de la región de Nochixtlán, Oaxaca

A new middle Permian microconchid from Chiapas, Mexico, and its palaeoecological implications

Braquiópodos discínidos (Lingulida, Discinoidea) de la Formación Ixtaltepec, Carbonífero del área de Santiago Ixtaltepec, Oaxaca

A Permian (late Guadalupian) brachiopod fauna from northeast Mexico and their paleobiogeographic affinities