Crowded tubular tidalites in Miocene shelf sandstones of southern Iberia

Abstract

The passive and active fill of burrows potentially stores information about sedimentary processes that are otherwise not preserved in the rock record. In recent years, abandoned passively-filled vertical burrows were introduced as "tubular tidalites" when their infilling displays rhythmic lamination reflecting a tidal signature. In the shallow-marine Miocene sandstones exposed at Oura (southern Portugal), 36 tubular tidalites occur in a 1.5 m-thick interval. Their high abundance is likely a consequence of both an environment favourable for the production of open burrows in a tidal setting, and post-depositional conditions facilitating the preservation of the tubular tidalites. Besides vertical tubes, 13 horizontal burrows preserve a tidal signature indicating draught-fill processes. All specimens belong to Thalassinoides and, for the first time, to Gyrolithes. The rhythmic infill of two well-preserved specimens shows two significant features: (1) The thickness pattern allows for differentiation into groups having 7 couplets (consisting of a dark and a light lamina) or multiples thereof, and (2) the thickness patterns of both, consecutive couplets as well as dark and light laminae match sine curves. Both patterns indicate a diurnal tidal cyclicity. The tidalites record up to four spring-tide and three neap-tide cycles. In addition to the neap-spring cycles, a long-period lunar fortnightly tide regime can be envisaged. The tubular tidalites imply diurnal tides during the Miocene in contrast to the Recent semidiurnal tides affecting southern Portugal.

What makes seep carbonates ignore self-sealing and grow vertically: the role of burrowing decapod crustaceans

“…Isopachs (in m), after Baudrimont and Dubois (1977), are shown for the basin facies represented by the Terres Noires Formation (middle Bathonian up to lower Oxfordian) in the central part of the basin. Outcrops of the Terres Noires Formation (after Artru, 1972) are noted by a darker shade of brown, and the locations of major pseudobioherms are marked by red stars (after Rolin, 1987). (c) Lithologic log of the Aurel area (Flandrin, 1974).…”

“…The lack of in situ framebuilding organisms and the absence of evidence for relief above the seafloor, however, led Flandrin (1974) to question this hypothesis. To account for this uncertainty, Gaillard et al (1985) and Rolin (1987) coined the term "pseudobioherm", defined as "carbonate anomalies of early diagenetic origin, characterized by the predominance of endobenthic organisms". Rolin (1987), Rolin et al (1990), andGaillard et al (1992) noticed similarities between the numerous assumed chemosynthetic bivalves often associated with the pseudobioherms and the fauna discovered a few years earlier at cold hydrocarbon seeps (Suess et al, 1985).…”

What makes seep carbonates ignore self-sealing and grow vertically? The role of burrowing decapod crustaceans

“…In addition to this complex static geometry, tube ventilation by seawater is known to be induced by bottom currents ("passive ventilation" e.g. by tidal currents: Wetzel et al, 2014;Gingras and Zonneveld, 2015;Rodríguez-Tovar et al, 2019) and by the burrowing organism itself ("active ventilation"). Active ventilation has been shown to be used by decapod crustaceans to promote microbial growth on burrow walls (Savrda, 2007).…”

Icnología de la Formación Lajas (Jurásico Medio), Grupo Cuyo, Cuenca Neuquina

“…En los momentos entre mareas donde se produce depositación de fangos, se puede presentar bioturbación escasa, de baja icnodiversidad y con tamaños reducidos (MacEarchen et al, 2005). Una estructura particular que se da en ambientes dominados por marea es la presencia de depósitos tidales rítmicos como relleno pasivo dentro de trazas fósiles, como por ejemplo, dentro de galerías de Ophiomorpha (Wetzel et al, 2014;Gingras et al, 2015;Rodríguez-Tovar et al, 2019) (Figura 1.24).…”

“…Por otro lado, cabe destacar que en ambientes dominados por la marea donde la erosión no deja registro de sedimentación rítmica, los depósitos rítmicos de marea se conservan en el relleno pasivo de trazas fósiles, como Ophiomorpha (Wetzel et al, 2014;Gingras et al, 2015;Rodríguez-Tovar et al, 2019). Todas las estructuras de Ophiomorpha y Thalassinoides reconocidas para la Formación Lajas, tanto afloramientos y muestras de subsuelo (para ambientes de frente deltaico y planicie deltaica), tienen un relleno masivo que no muestra signos de sedimentación rítmica de mareas Toda esta evidencia icnológica es compatible con los modelos de trazas fósiles de delta dominados por los ríos en los testigos corona HuN-1, Ba-1, Ba-2, AgTo-1 y AgTo-3.…”