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.

Se describe una nueva asociación, compuesta por 10 morfoespecies de osículos columnares de crinoideos pertenecientes a ocho morfogéneros diferentes. La biota está compuesta por Cylindrocauliscus fiski, Cyclocaudex cf. plenus, Cyclocaudex costatus, Preptopremnum cf. rugosum, Preptopremnum laeve, Heterostelechus jeffordsi, Cycloscapus laevis, Cyclocaudiculus regularis, Nothrosterigma merum y Cyclogrupera minor. Los ejemplares se encontraron en rocas de la Formación Grupera del Asseliano–Sakmariano (Pérmico inferior), perteneciente a la sucesión del Carbonífero–Pérmico que aflora en la región de Chicomuselo, al sureste del territorio mexicano. Del material descrito, se detectó la primera ocurrencia de C. costatus, P. rugosum, C. laevis y N. merum para Chiapas. Asimismo, destaca el primer registro de N. merum para México, el cual junto con P. rugosum son reportados por primera vez para el Cisuraliano de Norteamérica. Pese a la controversia sobre la utilidad de los osículos de crinoideos como fósiles índice, por sus amplios alcances estratigráficos, fue posible denotar que los taxones descritos, en conjunto, señalaban una edad aproximada del Asseliano–Sakmariano (Cisuraliano temprano), sugerida previamente para la formación. El hallazgo de los osículos, asociados a otros invertebrados marinos filtradores como briozoos y braquiópodos, aunado al tipo de conservación y las características litológicas de las rocas portadoras permitieron establecer que el paleoambiente de depósito se relacionaba con facies de aguas someras de alta energía, bien iluminadas y con un aporte constante de terrígenos. Respecto a la paleobiogeografía, se observa que la distribución de los crinoideos estuvo relacionada con la historia geológica de la región, la cual estuvo influenciada por los cambios oceánicos y continentales ocurridos a raíz de la formación del supercontinente Pangea a finales del Pensilvánico. Esto favoreció el surgimiento de provincialismos genéricos y específicos en Norteamérica.

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Nuevos registros de osículos columnares de crinoideos del Pérmico (Cisuraliano temprano) de Chiapas, México

CAI and microtextures of low-grade metamorphosed conodonts related to lithological and geological controls

Microcoprolites of Palaxius salataensis are non-skeletal carbonate grains produced by callianassid shrimps. This ichnospecies is recognized by four longitudinal canals arranged around a bilateral p...

Ichnologic note first occurrence of the microcoprolite Palaxius salataensis in the Aptian (Lower Cretaceous) of northeast Mexico and its paleoecological implications

In this study we examine different physicochemical variables (sediment texture, temperature, salinity, dissolved oxygen, turbidity, nitrite, nitrate, ammonium, phosphate, organic matter of marine snow, organic matter of sediment and organic matter of digestive tract) and their influence on the size structure and distribution of Meoma ventricosa grandis. The study was conducted in 3 workstations (E1: La Playa, E2: El Jardin, E3: Palmitas) located across the Boca Chica Channel, Acapulco, Mexico, during 2006 to 2007. The results of the measurements of the body size showed a higher percentage of adults in workstation 1 and 2 (13 and 5%, respectively); however, in workstation 3 the percentage was of 51%. The variance pointed a significance in the size of the individuals from the workstation Palmitas, showing the largest specimens throughout the study. The sediment texture in workstations La Playa and El Jardin was characterized by asymmetric clasts of coarse sand and gravel of different sizes, with a sediment layer with a depth of layer of 20-30 cm. Unlike workstation of Palmitas wich was distinguished by almost symmetrical gravel clasts, similar in size and with depth of 50 cm; in all workstations juveniles were buried between 10 and 20 cm and adults between 15 and 40 cm of depth. The gonadal index was asynchronous, presenting the highest reproductive peaks in Palmitas. Regression Trees analysis established that the organic matter deposited in the sediment acts as the primary physicochemical variable in the distribution of the echinoid within the channel, locating until 6,571 individuals in direct relation to it. The largest number of specimens (11,330) was obtained in the presence of organic matter, nitrates and phosphates. This is the first time that genus Meoma is related to a specific substrate according to the body size.

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Influencia de las variables fisicoquímicas en la estructura de tallas y distribución de Meoma ventricosa grandis (Echinodermata: Brissidae) dentro del canal Boca Chica, Acapulco, México Influence of physicochemical variables in the size structure and distribution of Meoma ventricosa grandis (Echinodermata: Brissidae) within the Boca Chica Channel, Acapulco, Mexico

Se describen crinoideos de las morfoespecies Baryschyr anosus Moore y Jeffords, Cyclocaudex insaturatus Moore y Jeffords, Floricyclus angustimargo Moore y Jeffords, Cyclocion distictus Moore y Jeffords, Lamprosterigma erathense Moore y Jeffords y Preptopremnum rugosum Moore y Jeffords que proceden de estratos del Misisípico Superior (Chesteriano) y del Pensilvánico Inferior-Medio (Morrowano-Desmoinesiano) de la sierra Santa Teresa, Sonora. La distribución de estas morfoespecies permitió establecer correlaciones paleobiogeográficas con otros crinoideos reportados para el Carbonífero del norte de México en los cerros El Tule, sierra Las Mesteñas, sierra Agua Verde en Sonora. También son correlacionables con regiones de EUA como en Texas, Colorado, Illinois, Oklahoma y Kansas pertenecientes a la provincia del Cratón Norteamericano. Asociado a los crinoideos existe una abundante y diversa biota representada por algas, foraminíferos-fusulínidos, esponjas-quetétidas, corales, briozoarios-fenestélidos, braquiópodos-prodúctidos y conodontos que se desarrollaron en los bordes continentales de plataforma calcárea en mares tropicales del océano Rheico durante el Paleozoico Tardío.

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Miguel A. Torres-Martínez

Papers

Nuevos registros de osículos columnares de crinoideos del Pérmico (Cisuraliano temprano) de Chiapas, México

CAI and microtextures of low-grade metamorphosed conodonts related to lithological and geological controls

Ichnologic note first occurrence of the microcoprolite Palaxius salataensis in the Aptian (Lower Cretaceous) of northeast Mexico and its paleoecological implications

Crinoideos (Echinodermata: Crinoidea) del Misisípico-Pensilvánico de la sierra Santa Teresa, región central del estado de Sonora, México