Middle Miocene (Serravallian) rhodoliths and coralline algal debris in carbonate ramps (Betic Cordillera, S Spain)

Serravallian (middle Miocene) coralline algal assemblages at the southern margin of the Guadalquivir Basin (southern Spain) occur as rhodoliths preserved in situ or very close to their growth habitats (autochthonous–parautochthonous assemblages) and also as reworked remains (allochthonous assemblages). The former assemblages consist of spherical rhodoliths built up by encrusting to warty plants and also of large fragments of branches, whereas the latter are mostly unrecognizable small fragments occurring in channeled packstone–grainstone beds. In both cases, the most abundant components are members of the order Hapalidiales (Mesophyllum roveretoi, Mesophyllum sp., Lithothamnion ramosissimum, and less frequently Phymatolithon group calcareum and Lithothamnion group corallioides). Laminar growths of Lithoporella minus and branches of Spongites group fruticulosus and Sporolithon sp. occur very rarely. There are also anecdotal records of Subterraniphyllum thomasii, extending its upper stratigraphic range up to the Serravallian in the western Tethys. The autochthonous–parautochthonous coralline algal assemblages formed in a middle ramp, at several tens of meters of water depth, as suggested by the dominance of Hapalidiales. The allochthonous assemblages represent fragments of coralline algae derived from the middle ramp and redeposited in deeper settings, most likely the outer ramp, due to storm-generated currents.Instituto de Salud Carlos III Spanish Government PGC2018-099391-B-100Junta de Andalucia RNM-19

Trough cross-bedded rhodolith limestones in the Atlantic-linked Ronda Basin (Messinian, Southern Spain)

Rhodolith limestones occur in the upper part of the Miocene infill of the Ronda Basin in southern Spain. This basin was an embayment at the southern margin of the Atlantic-linked Guadalquivir Basin, the foreland basin of the Betic Cordillera. Messinian rhodolith limestones crop out in the mesa of the Roman settlement Acinipo. They mostly consist of trough cross-bedded rhodolith rudstones, which change basinward to large-scale planar cross-bedded rhodolith rudstones, which in turn pass laterally to planar cross-bedded and flatbedded bryozoan rudstones. Rhodoliths in rudstones are generally broken, exhibiting several phases of breakage and restarted growth of coralline algae. Many rhodoliths also show asymmetrical growth. The rudstone matrix is a packstone with fragments of coralline algae, bryozoans, calcitic bivalves, echinoids, and foraminifers. Large lithoclasts from the basement, heavily bored by bivalves, are common in the rhodolith rudstone, especially in the most massive type. Rhodolith characteristics and sedimentary structures suggest that trough cross-bedded rhodolith rudstones accumulated in submarine dunes moved by storm surges in a littoral wedge at the western side of a small bay (the Ruinas de Acinipo bay) in the Ronda Basin. Large-scale planar cross-bedded coralline algal and bryozoan rudstones formed in the foresets of the wedge progradation below the storm-wave base. The dominance of Lithophyllaceae and Hapalidiales, with scarce representatives of Corallinaceae in the coralline algal assemblages, reflects that Ronda and Guadalquivir basins opened to the Atlantic Ocean.Spanish Government PGC 2018-099391-B-I0

Coralline Algae at the Paleocene/Eocene Thermal Maximum in the Southern Pyrenees (N Spain)

During the Paleocene/Eocene Thermal Maximum, ~55.6 Ma, the Earth experienced the warmest event of the last 66Ma due to amassive release of CO2. This event lasted for ~100 thousands of years with the consequent ocean acidification (estimated pH = 7.8-7.6). In this paper, we analyze the effects of this global environmental shift on coralline algal assemblages in the Campo and Serraduy sections, in the south-central Pyrenees (Huesca, N Spain), where the PETM is recorded within coastal-to-shallow marine carbonate and siliciclastic deposits. In both sections, coralline algae occur mostly as fragments, although rhodoliths and crusts coating other organisms are also frequent. Rhodoliths occur either dispersed or locally forming dense concentrations (rhodolith beds). Distichoplax biserialis and geniculate forms (mostly Jania nummulitica) of the order Corallinales dominated the algal assemblages followed by Sporolithales and Hapalidiales. Other representatives of Corallinales, namely Spongites, Lithoporella as well as Neogoniolithon, Karpathia, and Hydrolithon, are less abundant. Species composition does not change throughout the Paleocene/Eocene boundary but the relative abundance of coralline algae as components of the carbonate sediments underwent a reduction. They were abundant during the late Thanetian but became rare during the early Ypresian. This abundance decrease is due to a drastic change in the local paleoenvironmental conditions immediately after the boundary. A hardground at the top of the Thanetian carbonates was followed by continental sedimentation. After that,marine sedimentation resumed in shallow, very restricted lagoon and peritidal settings, where muddy carbonates rich in benthic foraminifera, e.g., milioliids (with abundant Alveolina) and soritids, and eventually stromatolites were deposited. These initial restricted conditions were unfavorable for coralline algae. Adverse conditions continued to the end of the study sections although coralline algae reappeared and were locally frequent in some beds, where they occurred associated with corals. In Serraduy, the marine reflooding was also accompanied by significant terrigenous supply, precluding algal development. Therefore, the observed changes in coralline algal assemblages during the PETM in the Pyrenees were most likely related to local paleoenvironmental shifts rather than to global oceanic or atmospheric alterations.Spanish Ministerio de Ciencia e Innovacioon PGC2018-099391-B-100Junta de Andalucia RNM-190Basque Government Research Programme PGC2018-099391-B-100 IT930-1

Alpujárride Carbonates (S. Spain). First atlantic marine deposits?

Publicado en: Martín, J.M. and Braga, J.C. (1987). Alpujárride carbonate deposits (southern Spain). Marine sedimentation in a Triassic Atlantic. Palaeogeography, Palaeoclimatology, Palaeoecology, 59: 243-260. [http://dx.doi.org/10.1016/0031-0182(87)90083-6]The Betic Cordillera (Southern Spain) constitutes the westernmost segment of the Alpine Chains. The Alpujárride Complex, from the the Internal Zone of the Betic Cordillera, exhibits a thick (up to 2000 m in thickness), Alpine-type, Middle-Upper Triassic marine-carbonate sequence. Stratigraphic correlations and facies-belt distributions reveal that the Triassic Alpujárride basin opened westwards to the sea, towards an Atlantic in the west, and not towards the Tethys in the east. The Alpujárride carbonate deposits are thought to have been deposited in an early Atlantic and to have been emplaced later in a western Mediterranean position by transform movements and overthrust. In this talk a review of the most significant Alpujárride carbonate facies, together with some of the most relevant diagenetic features, are also shown.La Cordillera Bética es el segmento más occidental de la Cadena Alpina. El Complejo Alpujárride, perteneciente a la Zona Interna de la Cordillera Bética, está fundamentalmente caracterizado por la presencia de una potente secuencia (hasta 2000 m de potencia) de carbonatos marinos, de edad Triásico Medio-Superior y facies Alpina. Las correlaciones estratigráficas y la disposición de los cinturones de facies revelan que la Cuenca Triásica Alpujárride abría hacia el Oeste, hacia posiciones Atlánticas y no hacia el Este (antiguo Tethys). Se infiere que los carbonatos Alpujárrides depositaron en un incipiente Atlántico y fueron posteriormente desplazados hacia posiciones Mediterráneas por fallas transformantes y cabalgamientos. En esta charla se muestran también las facies más representativas de los carbonatos Alpujárrides y los rasgos diagenéticos más relevantes

Eocene to Pliocene coralline algae in the Queensland Plateau (northeastern Australia)

Sediments containing coralline algae in the Queensland Plateau range from the middle Eocene to the early Pleistocene in age. In the middle Eocene sediments, the corallines occur as highly fragmented and eroded particles in temperate, platform carbonates (grainstones and rudstones) with abundant bryozoans, benthic foraminifers, and bivalves. They occasionally interbed with thin intervals of tropical to subtropical sediments that contain abundant Halimeda, coral debris, and coralline fragments, mainly of Lithoporella and Mesophyllum. In the upper Oligocene sediments, similar temperate carbonates, in which small, scarce, unidentifiable coralline fragments can be seen, also occur. The lower Miocene platform carbonates consist of grainstones and packstones having a tropical assemblage with corals and Halimeda, together with a shallow-water coralline association of geniculate (Jania, Corallina, Amphiroa) and encrusting forms (Lithoporella and Spongites). Allochthonous fragments of geniculate and encrusting corallines {Mesophyllum and Lithothamnion) of early Miocene age occur in clasts in bioclastic floatstones (debris-flow deposits) of middle Miocene age. The algal composition points to an outer-shelf origin for these clasts. The middle Miocene carbonate sediments that contain corallines are also tropical and consist of bioclastic packstones to wackestones, with Halimeda, and corals. Coralline-algal debris is predominantly composed of loose, abraded, branching thalli of Sporolithon and Lithothamnion, and small rhodoliths (up to 2 cm). The nuclei of most of the rhodoliths consist of a small branch fragment. They are encrusted by laminar growths of Lithothamnion, Mesophyllum, Hydrolithon, and Sporolithon. Some fragments of the rare coralline genus Aethesolithon also have been found. The depositional environment is that of a low-energy, neritic, open platform, as can be deduced from the predominance of delicate branching growths, the smaller size of the rhodoliths, the abundance of fine-grained sediments, and the scarceness of reworking. Lower Pliocene corallines occur as redeposited elements in debris flows. They appear mainly as very thin laminae in foralgaliths that are intimately associated with encrusting foraminifers. The most common alga is Lithoporella. The present-day, shallow-water, reefal coralline associations dominated by members of the subfamily Mastophoroideae were not detected in any of the sediments drilled in the Queensland Plateau

Structure and Composition of Rhodolith Beds from the Sergipe-Alagoas Basin (NE Brazil, Southwestern Atlantic)

This study was funded by the CoordenacAo de Aperfeicoamento de Pessoal de Nivel Superior (CAPES-Finance Code 001) and FundacAo de Amparo a Pesquisa do Estado do Rio de Janeiro- Jovem Cientista do Nosso Estado (FAPERJ/JCNE-Fellow to Leonardo T. Salgado).Rhodolith beds are biogenic benthic habitats mainly formed by unattached, non-geniculate coralline algae, which can be inhabited by many associated species. The Brazilian continental shelf encompasses the largest continuous rhodolith bed in the world. This study was based on samples obtained from seven sites and videos taken by a Remotely Operated Vehicle (ROV) at four transects off the Sergipe-Alagoas Coast on the northeast Brazilian shelf. ROV operations and bottom trawl sampling revealed the occurrence of rhodolith beds between 25 and 54 m depths. At the shallower depths, fruticose (branching) rhodoliths (maërl) appear in troughs of ripples, and other non-branching rhodoliths occur associated with corals and sponge patches surrounded by bioclastic sand. Rhodoliths also occur in patches from 30 to 39 m depth; some are fused, forming larger, complex tridimensional structures. At deeper depths, from 40 to 54 m, the abundance of rhodoliths increases and occur associated with fleshy macroalgae on a smooth seafloor; some rhodoliths are fused into complex structures, locally some are fruticose (maërl), and others are partially buried by fine-grained sediment. The collected rhodoliths vary from fruticose in two sites to encrusting to lumpy, concentric and boxwork nodules in the rest; their size ranges from small (<1.5 cm) to large (~6 cm) and are mostly sub-spheroidal to spheroidal. A total of 16 red algal morpho-taxa were identified in the study sites. Two phases of growth can be distinguished in some rhodoliths by changes in color. The brownish inner cores yielded ages of 1600–1850 cal years before the present, whereas outer layers were much younger (180–50 years BP old). Growth layers appeared to have been separated by a long period of burial in the seafloor sediment. Other rhodoliths have ages of hundreds of years.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) 001Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro-Jovem Cientista do Nosso Estado (FAPERJ/JCNE

The Messinian record of the outcropping marginal Alborán basin deposits: significance and implications

The Messinian record of marginal Alboran basins, such as the Sorbas Basin in southern Spain, consists of a shallow-marine succession with intercalated evaporites. The pre-evaporite sequence comprises a bryozoan-bivalve, temperate-carbonate unit overlain by tropical carbonates. The latter, in turn, consists of two superimposed units: a bioherm unit with coral (Porites, Tarbellastraea, and Siderastraea) and algal (Halimeda) mounds, and a coral (Porites)-stromatolite fringing reef unit. Climatic fluctuations in the Alboran area, linked to the Neogene glacial-interglacial oscillations, are thought to be responsible for the change from temperate to tropical conditions. Evaporites are mainly selenite gypsum deposits. The first post-evaporite unit is a mixed siliciclastic-carbonate marginal deposit, with small coral (Porites) patches and huge microbial (stromatolite and thrombolite) domes, changing basinward to silts and marls containing planktonic foraminifers. An incised erosion surface was scoured on top of the pre-evaporitic fringing reef unit. This erosion surface formed during drawdown and desiccation of the Mediterranean Sea, when huge masses of salt were deposited in its center. Deposition of gypsum at the very margin of the Alboran Sea took place later in small, barred, satellite perched basins. In these silled basins marine incursions became more and more frequent until a full connection with the Mediterranean Sea was established by the end of the Messinian. Reflooding was completed during the Messinian, as demonstrated by the marine marls with planktonic foraminifers found on top of the evaporites. This situation is comparable to that of the western Mediterranean (DSDP Site 372; ODP Site 975), where the upper evaporites are directly overlain by Messinian marls with planktonic foraminifers. During the initial stages of marine recolonization, microbes coexisted with, but outcompeted, the normal marine biota. This resulted in the widespread proliferation of microbial carbonates (stromatolites and thrombolites).This work was supported by DGICYT (Spain) Project PB93-1113 and by “Fundación Ramón Areces” Project: “Cambios climáticos en el sur de España durante el Neógeno.

A model for the development of rhodoliths on platforms influenced by storms: middle Miocene carbonates of the Marion Plateau (northeastern Australia)

Middle Miocene carbonates of the Marion Plateau consist of dolomitized bioclastic floatstones and rudstones with rhodoliths (up to 6 cm in size) as the most prominent component. These rhodoliths are embedded in a bioclastic matrix with Halimeda, echinoids, bivalves, gastropods, bryozoans, small coralline fragments, benthic (and planktonic) foraminifers, and rare dasyclads. Corals (not abundant) occur only as fragments and may serve as nuclei for some of the rhodoliths. Two main types of rhodoliths are evident. The commonest type is formed by Lithothamnion and Sporolithon, together with minor Hydrolithon, Mesophyllum, Spongites, and Lithoporella. The other type is made up mainly of Mesophyllum. Laminar growths are always predominant inside the rhodoliths. Both the growth types and the algal associations are characteristic of rhodoliths that formed at depths of some tens of meters and below the normal wavebase. Similar coralline associations presently occur in the Indo-Pacific area at depths between 30 and 80 m. Clearly, these depths are below the normal wavebase, but within the reach of storms. Encrusting foraminifers, serpulid worm tubes, bryozoans, and vermetids are sometimes important elements within these rhodoliths and occur either as more-or-less discrete layers interbedded with the coralline growths or in their nuclei. Bioclastic sediment is also incorporated within the rhodoliths. Some of the rhodoliths now appear partially broken and, presumably, were reworked in the environment of deposition. Others exhibit several phases of growth and reworking. Some of them have also been bored. The context in which these rhodoliths developed was that of a neritic, open-platform environment. They were reworked and partially broken and abraded during storms and then grew once more during the intervening calm periods. The internal structure of the rhodoliths is complex in detail, with successive coralline laminae encrusting more-or-less eroded former growths, and in turn being partially destroyed during the next storm event

Los estrechos Miocenos Atlántico-Mediterráneos de la Cordillera Bética (S de España)

The link between the Mediterranean Sea and the Atlantic Ocean through the Betic Cordillera (southern Spain) was reduced to a few seaways in the Miocene as the mountain belt uplifted during the Alpine orogeny. The North-Betic Strait, located in the Prebetic Zone, was the first one to close in the early Late-Miocene. During the Tortonian, there were connections through the Granada-Guadalquivir basins (Zagra Strait) and the Guadix-Guadalquivir basins (Dehesas de Guadix Strait). Only one corridor, the Guadalhorce Strait, existed in the early Messinian through the Guadalquivir and Málaga basins. The closing of the youngest straits (Dehesas de Guadix and Guadalhorce Straits) brought about profound paleoceanographic changes, leading to an increase of Mediterranean restriction and watermass stratification. All these straits were several kilometers wide, and a few tens to c. 100 m deep. Strait deposits (up to 400 m thick) consist of siliciclastics and siliciclastics-carbonates. Giant dunes (up to 30 m high and 800 m long), exhibiting internal giant cross-bedding, are characteristic features. In the North-Betic and Zagra straits the dunes were moved by tides and in the Dehesas de Guadix and Guadalhorce straits by bottom density currents flowing from the Mediterranean towards the Atlantic.Las conexiones Atlántico-Mediterráneo, en el Mioceno, a través de la Cordillera Bética (S de España), fueron progresivamente reduciéndose a unos pocos estrechos conforme ésta fue levantando durante la Orogenia Alpina. El Estrecho Norbético, localizado en la Zona Prebética (parte más externa de la Cordillera Bética) fue el primero en cerrarse en el Tortoniense inferior. A lo largo del Tortoniense las conexiones fueron a través de las cuencas de Granada y del Guadalquivir (Estrecho de Zagra) y de las de Guadix y del Guadalquivir (Estrecho de Dehesas de Guadix). El último estrecho en desarrollarse, en el Messiniense inferior, fue el del Guadalhorce. La conexión Atlántico-Mediterránea fue, en este caso, a través de las cuencas de Málaga y la del Guadalquivir. El cierre de los estrechos más modernos (Dehesas de Guadix y Guadalhorce) indujo cambios paleoceanográficos profundos en el Mediterráneo, con aumento significativo de su nivel de restricción y de estratificación de sus aguas. Estos estrechos tenían unos pocos kilómetros de anchura y profundidades entre unas pocas decenas de metros y algo más de 100 m. Los sedimentos de los estrechos son siliciclásticos y mezclas de siliciclásticos y carbonatos bioclásticos, con potencias de hasta 400 m. La presencia de dunas gigantes es una característica distintiva, omnipresente en estos antiguos estrechos. Las mayores dunas preservadas alcanzan los 30 m de altura, se extienden lateralmente unos 800 m y muestran, internamente, dispositivos de capas cruzadas, con hasta 15° de buzamiento. En el Estrecho Norbético y el de Zagra la estratificación cruzada de gran escala se generó como resultado de la migración de grandes dunas movidas por las mareas. En los Estrechos de Dehesas de Guadix y del Guadalhorce la estratificación cruzada de gran escala es unidireccional. En estos dos últimos casos, las responsables del desplazamiento de las dunas fueron las corrientes de fondo mediterráneas, más salinas y de más alta densidad, en su salida hacia el Atlántico.This paper has been supported by the research project CGL2010-20857 (Ministerio de Ciencia e Innovación of Spain)