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Bajocian transgressive-regressive sequences of the Tecocoyunca Group, southern Mexico, with maximum flooding surfaces marked by Thalassinoides

Pieńkowski Grzegorz, Martini Michelangelo, Zepeda-Martínez Mildred

Geological Quarterly

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2019

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Vol. 63, No. 3

449--459

EN

Bajocian (Middle Jurassic) transgressive-regressive sequences (TRS), outcropping in the Rosario Nuevo Creek (Tezoatlán Basin, Tecocoyunca Group) in Oaxaca State, Mexico, represent one of the Jurassic phases of opening and widening of a trans-Pangaean marine corridor (called also the Hispanic Corridor) and show a retrogradational-progradational set of sedimentary successions with decipherable and diverse facies. Two TRSs have been distinguished. The lower one starts with fluvio-deltaic sandstones including pedogenic horizons. Drowning of the deltaic plain and gradual rising of the water table is marked by change in vegetation: from large trees to low-rise vegetation with characteristic clumps of dense roots cemented by siderite. The delta plain succession is topped by a thin coal seam, followed by a transgressive surface. Ensuing laminated mudstones of restricted marine origin pass into open marine deposits, represented by bioturbated heterolithic strata with ammonites followed by nearshore sandstones, deposited in a storm-dominated basin. A similar succession, although without the deltaic part, is repeated in the next TRS. Of note are two thin (15-20 cm) continuous beds with Thalassinoides isp. networks, present within open marine deposits. Although large Thalassinoides networks are mostly known from shallow-marine and coastal environments, the case from Mexico represents less common occurrences from a deeper marine (offshore) setting, associated with maximum flooding surfaces, sediment starvation and firmgrounds (Glossifungites ichnofacies). Occurrences of Thalassinoides meshes, precisely marking maximum flooding surfaces, are helpful in defining the hierarchy of sequence stratigraphic cycles.

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Rosarichnoides sudeticus igen. et isp. nov. and associated fossils from the Coniacian of the North Sudetic Synclinorium (SW Poland)

Chrząstek A., Muszer J., Solecki A., Sroka A. M.

Geological Quarterly

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2018

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Vol. 62, No. 1

181--196

EN

A new ichnogenus and ichnospecies Rosarichnoides sudeticus is proposed for a large, exceptionally well-preserved crustacean burrow, which has been found in the Upper Cretaceous (Coniacian) Quadersandstein of the North Sudetic Synclinorium (Czaple quarry). Some of its specimens have been assigned to Thalassinoides saxonicus (Geinitz, 1842). It is unbranched, a characteristic rosary-shaped trace fossil, which consists of alternating chambers (swellings) and constrictions. The burrow is without any wall and usually lack ornamentation and has a passive fill. It should be included in ophiomorphid group sensu Bromley (1996). This unique finding resembles modern crustacean burrows produced by shrimps or crabs. Additionally, Thalassinoides paradoxicus (Woodward, 1830), the starfish Astropecten scupini Andert, 1934, the inoceramids Inoceramus kleini Müller, 1888 and Inoceramus sp. were found in the same sandstones. The trace fossils are indicative of the archetypal Skolithos ichnofacies that is typical of foreshore to middle shoreface settings.

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Functional morphology and ethology gathered by Thalassinoides branched burrows in Mesozoic shallow water environments

Monaco P., Giannetti A.

Volumina Jurassica

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2006

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Vol. 4, no. 1

99-100

EN

Each part of a crustacean burrow has an important and specific function within the ecology and trophism of the burrower. It goes from the oxygenation and irrigation of tunnels to the protection of the organism and the storing of organic material for feeding (also predation, e.g. carnivorous crustaceans such as stomatopods). Considering modern thalassinoidean burrows (Thalassinoides), the most important characteristics are the presence of surficial mounds, vertical shafts, tunnels and horizontal galleries, turning chambers, organic debris within burrows, Y-or U-shaped burrows and the number and type of apertures on the seafloor. Analysis of the Pliensbachian, lagoonal deposits of the Calcari Grigi Formation (Trento Carbonate Platform, Southern Alps, Italy) and of the Albian outer shelf deposits of the Sacaras Formation (Serra Gelada, Southeastern Spain) gave rise to individuate different specimens of Thalassinoides suevicus trace fossils. They are well preserved in three-dimensions and therefore are useful to gather the trophism of the ancient burrowers in shallow-water environments. These Y-shaped, branched traces were studied observing and measuring diameter of tunnels, enlargement at the bifurcation point, development of the vertical burrow and coarse-grained skeletal debris infilling. Within the studied sections, abundance and dimensions of trace fossils vary, developing repetitive "burrow-decreasing upward" parasequences (BDUP), 2.3-2.9 m thick (Giannetti & Monaco 2004). They represents a useful record of functional morphology of crustacean decapods in shelf environments. We have hypothesized that the regular mazes of Mesozoic crustaceans were mainly developed on horizontal planes (commonly few centimetres inside the substratum), while vertical shaft were rudimentary or lacking, differing from those largely developed by modern crustaceans. The presence of tubular tempestites proves the existence of apertures on the seafloor, even if only the horizontal part of the filled burrows is generally preserved. According to the scheme proposed by Nickell & Atkinson (1995), we observe that the main function of Thalassinoides was the nutritional strategies through the sediment processing and storage of material for maintenance purposes. The sediment processing was supported by the storage of nutritional material (chambered burrows filled by organic detritus). The composition of organic detritus varies from coarse-grained to fine-grained crashed bioclasts, indicative either of biogenic sorting or of the storage of debris coming from the seafloor and fallen down into the burrow. The concentration of coarse-grained fragmented shells close to other free tunnels was probably due to the motion strategy of the crustaceans, as in actual cases. Proofs of irrigation of burrows and entrance from the seafloor are rare and can be deduced from few findings, closely similar to the burrows of modern crustaceans. In the category of the vertical elements, we have considered inhalant and exhalant shafts, but these vertical elements are rare and poorly developed. Anyway, they indicate the presence of suspension feeders (whose primary nutritional source is the water column) and of deposit feeders. According the scheme proposed by Nickell and Atkinson, all the studied Thalassinoides testify the presence of organisms belonging to the category of the deposit feeders (looking for food within the substratum) and to that of the omnivorous scavengers, which eat organic debris present on the seafloor and deriving from algae and other animals.