Santa Lucia Formation Research Articles

CRINOIDEOS DEL GÉNERO Bactrocrinites DEL DEVÓNICO INFERIOR Y MEDIO DE LA CORDILLERA CANTÁBRICA (NO DE ESPAÑA)

Se describen nuevas formas de Bactrocrinites de ambas vertientes de la Cordillera Cantábrica. En la vertiente asturiana: Bactrocrinites longibrachiatus n. sp., Bactrocrinites aff. fusiformis y Bactrocrinites sp., proceden respectivamente de la Punta del Aguión, cerca de Luanco, Formación Aguión (Emsiense superior), de la Ensenada de Moniello, Luanco, base de la Formación Moniello (Emsiense superior) y de Arbeyales, Somiedo, techo de la Formación Santa Lucía (Eifeliense inferior). En la leonesa: Bactrocrinites breimeri n. sp., Bactrocrinites truyolsi n. sp., un segundo ejemplar de Bactrocrinites aff. fusiformis y ? Bactrocrinites sp.; los dos primeros proceden de Huergas de Gordón, Pola de Gordón, en la Formación Portilla (Givetiense) y Formación Santa Lucía (Eifeliense inferior), respectivamente, el tercero, de Valporquero, Valle de Torío, Grupo La Vid (Emsiense superior) y el último de Colle, también en el Grupo La Vid (Emsiense superior). Todas las especies recogidas y descritas en el presente trabajo son relativamente pequeñas y esbeltas y muestran evidentes afinidades con la especie tipo fusiformis

Eruptive chronology and tectonic context of the late Pleistocene Tres Vírgenes volcanic complex, Baja California Sur (México)

Based on a detailed geological map and stratigraphy aided by new 230Th/238U and 206P/238U age determinations we established the eruptive chronology of the Tres Vírgenes Volcanic Complex (TVVC). The complex consists of three northeast-southwest aligned stratovolcanoes, which from older to younger are El Viejo, El Azufre, and La Virgen and associated cinder cones and domes. The alignment was fed from fissures that mark the southern trace of the left-lateral Cimarron Fault. The TVVC was built upon the basement rocks of the Peninsular Ranges Batholith (~99 Ma), the Santa Lucia Formation (21.6 Ma), the Esperanza basalt (7.6 Ma), and the 1.1 Ma ignimbrite of El Aguajito caldera. The TVVC began its formation at ca. 300 ka mainly with dacitic lava flows and domes that formed El Viejo volcano (4.2 km3). At around 173 ka, activity migrated to the southwest to build El Azufre volcano (3.8 km3) with the emission of dacitic lavas and several phases of dome construction and destruction with the generation of pyroclastic density currents. El Azufre's activity ended ~128 ka with the extrusion of the summit dome. At about 112 ka, volcanism migrated 4.2 km to the southwest to begin the construction of La Virgen Volcano through the emission of andesitic and dacitic lavas that built the largest cone of the complex until ~22 ka (31.2 km3). This volcano was built upon several stages of cone construction with the emission of lava flows and peripheral dacitic domes and cinder cones. Between 128 and 112 ka six cinder cones vented along the Cimarron Fault between the La Virgen and El Azufre volcanoes. By assuming a constant emission of magma the total volume of the TVVC (39 km3) was erupted at an average rate of 0.13 km3/kyr. Of this volume, effusive eruptions dominated the evolution of the complex (89%) of which 62% are dacites and 38% andesites. The TVVC rocks have compositions of 50–67 wt% in silica, and low-medium K (0.5–2.5 wt% K2O). Trace element signatures of the TVVC rocks (Sr/Y <40, La/Yb <10, Nb-Ti negative anomalies and relative enrichments of LILE and LREE) suggest a post-subduction mixture between adakitic and calc-alkaline magmas. Xenoliths of granodiorites hosted in lavas and La Virgen tephra suggest that magma chambers feeding the complex have stagnated at depths >2 km within the Peninsular Ranges Batholith as confirmed by geobarometry, aeromagnetic data, and the drill-holes of the geothermal field. Today, the Tres Vírgenes geothermal field generates 10 MW of electricity although future exploration of several nearby areas may increase such capacity.

Alcidedorbignya inopinata, a basal pantodont (Placentalia, Mammalia) from the early Palaeocene of Bolivia: anatomy, phylogeny and palaeobiology

ABSTRACT Alcidedorbignya inopinata Muizon & Marshall, 1987 is a basal pantodont (Placentalia, Mammalia) of small body size, from the early Palaeocene of the Santa Lucia Formation at Tiupampa, Bolivia. Tiupampa is the type locality for the Tiupampan, a South American Land Mammal age (SALMA), which is assigned an age equivalent to the basal Torrejonian 1 of North America (c. 65 Ma). Alcidedorbignya is known by exceptionally preserved specimens, which are described here. The two major specimens are an almost complete skeleton (MHNC 8372) and a partial skull (MHNC 8399), the former representing one of the best-preserved fossil placentals from the early Palaeocene and probably the oldest placental skeleton that is so completely known. These specimens are also the first eutherian skulls and skeleton ever discovered at Tiupampa, a locality which has yielded numerous metatherian skulls and partial skeletons. The remarkable preservation of the two skulls allows a detailed description of the cranial anatomy with we...

Bryozoans, corals, and microfacies of Lower Eifelian (Middle Devonian) limestones at Kierspe, Germany

The Lower Eifelian Meinerzhagener Korallenkalk (= upper Cultrijugatus Beds) at Kierspe, Sauerland, contains a rich reefal fauna. Eight bryozoan species are described, two of them are new: the cystoporate Fistuliporellakierspensis n. sp. and the trepostome Leptotrypella sophiae n. sp. The bryozoans from the Meinerzhagener Korallenkalk shows distinct similarities to the Lower–Middle Devonian of Spain (Santa Lucia Formation, Emsian–Eifelian), and to the Middle Devonian (Eifelian) of Transcaucasia. The coral fauna comprises five tabulate corals and one rugose coral that document a paleobiogeographic relationship between Central and Eastern Europe and Central Asia. The associated fauna is represented by brachiopods, ostracods, and echinoderms. The studied limestones also commonly contain calcimicrobes represented by three species. The faunal and microfacial characteristics indicate a shallow marine depositional environment just above the storm wave base, with a supposed depth of 20 m, within the photic zone. The nutrient regime was at least a mesotrophic. The upper boundary of the Cultrijugatus Beds coincides with the Chotec-Event that strongly affected brachiopods, whereas corals and bryozoans were insensitive to this event.

A bryozoan fauna from the Santa Lucia Formation (Lower–Middle Devonian) of Cantabrian Mountains, NW Spain

The Lower to Middle Devonian Santa Lucia Formation of NW Spain contains a rich and well-preserved bryozoan fauna. An assemblage containing 14 species is described from two localities in Cantabrian Mountains, Abelgas, and Paradilla. One new genus with one new species is described: Isostylusabelgasensis n. sp. n. gen. Another two new species have been found: Microcampylusminor n. sp. and Acanthoclema parvula n. sp. Additionally, the following species were identified: Cyclotrypa communis (Ulrich 1890), Fistuliphragma gracilis Ernst 2008a, Leioclema attenuatum Duncan 1939, Hemitrypa cf. tenella Barrande in Pocta 1894, Fenestella aff. parallela Hall 1881, Anastomopora adnata (Hall 1883), Semicoscinium rhombicum Ulrich 1890, Quadrisemicoscinium discretum (Prantl 1932). Three species are described in open nomenclature: Trepostomata sp. indet.1 and 2, and Semicoscinium sp. The described bryozoan fauna shows connections to the Lower Devonian of Bohemia, and to the Middle Devonian of Rhenish Massif and North America.

Sequence stratigraphy and carbonate platform organization of the Devonian Santa Lucia Formation, Cantabrian Mountains, NW-Spain

In this paper, the sedimentology and the stratigraphic architecture of the Devonian Santa Lucia Formation in the Cantabrian Mountains of NW-Spain are described. The Santa Lucia Formation consists of 11 different facies that can be attributed to peritidal/lagoonal, intertidal and subtidal facies associations. These facies associations are arranged in small-scale sedimentary cycles. Three different settings of small-scale sedimentary cycles are recognized: intertidal/supratidal, shallow subtidal/intertidal and subtidal cycles. These cycles reflect spatial differences in the reaction of the depositional system to small-scale relative sea-level changes. Small-scale stratigraphic cycles are stacked into seven medium-scale cycles that in turn are integral parts of three larger-scale cycles. Most of the Santa Lucia Formation (sequences 2–6) forms one major large-scale cycle, whereas sequences 1 and 7 are part of an underlying and an overlying cycle, respectively. Eustatic sea-level changes exerted major control on the formation of these large-scale sequences, whereas the medium-scale cycles seem to be co-controlled by regional tectonism and eustasy. Small-scale cycles seem to be the product of high frequency, eustatic sea-level changes. During the deposition of the Santa Lucia Formation, the morphology of the carbonate platform changed from a gently south-dipping ramp to a rimmed shelf and back to a gently dipping ramp.

Early to middle Tertiary foreland basin development and the history of Andean crustal shortening in Bolivia

A >2.5-km-thick succession of Tertiary strata in the Eastern Cordillera of southern central Bolivia consists of predominantly fluvial and lacustrine deposits. The age of the base of the succession is middle Paleocene, and its upper part (which is erosionally truncated) is probably late Oligocene-early Miocene. The lower 50-130 m of the succession consists of interbedded fluvial sandstone and mudstone (including minor paleosols) of the Santa Lucia Formation. These strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the Santa Lucia Formation and lower part of the Impora Formation that may represent much of late Paleocene-Eocene time. Above the paleosol zone is a thin zone (∼10 m) of lacustrine carbonate and clastic rocks in the uppermost Impora Formation, and this in turn is overlain by a >2000-m-thick, upward-coarsening succession of clastic fluvial deposits in the Cayara, Camargo, and Suticollo Formations. Paleocurrent data indicate that fluvial channels that deposited the Santa Lucia, Impora, and Cayara Formations flowed mainly westward, whereas channels responsible for the Camargo and Suticollo Formations flowed generally eastward. Modal sandstone petrographic data show a long-term evolution from subarkosic (during Santa Lucia deposition) to quartz-arenitic (during Impora and Cayara deposition) to sublitharenitic (during Camargo and Suticollo deposition) compositions. We argue that the lithofacies and sediment-accumulation history of this succession are most consistent with deposition in an eastward-migrating foreland basin system. E -mail: decelles@geo.arizona.edu. Critical to this interpretation is the zone of extreme stratigraphic condensation in the lower Impora Formation, the inferred upper Paleocene-Eocene part of the succession. The abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous, postrift thermal subsidence resulted in a gradual, continuous decay of early Tertiary sediment-accumulation rates. Stratigraphic condensation is, however, consistent with passage of the forebulge through the region, an interpretation that also can be reconciled with the record of foreland basin development in the Altiplano to the west and gross sediment accumulation patterns in the Subandean zone and modern foreland basin to the east. Simple flexural modeling and palinspastic reconstruction of the complete Cenozoic migration history of the foreland basin system suggest that ∼1000 km of foreland lithosphere has been underthrust westward beneath the Andean orogenic belt at the latitude of southern Bolivia. The amount of middle and lower crust that would have been added to the Andean infrastructure is sufficient to explain the present crustal thicknesses in Bolivia.

Paleogene synorogenic sedimentation in the Altiplano plateau and implications for initial mountain building in the central Andes

Sedimentologic data and palynological ages from Paleogene clastic deposits of the northern and central Altiplano plateau suggest foreland basin development in the central Andes by mid-Paleocene time. The nonmarine Potoco Formation (3000‐6500 m thick) constitutes the majority of Cenozoic basin fill. The Potoco overlies the Santa Lucia Formation (50‐300 m thick), previously dated as mid-Paleocene by mammal fossils and magnetostratigraphy. New geochronologic data for the Potoco Formation include late Eocene to Oligocene palynomorph assemblages recovered throughout lower to upper stratigraphic levels. These ages and published 40 Ar/ 39 Ar and K-Ar ages from overlying upper Oligocene‐lower Miocene volcaniclastic rocks indicate (1) nondeposition or greatly reduced deposition (average sediment-accumulation rates ,10 m/m.y.) from mid-Paleocene to middle Eocene time (top Santa Lucia to lowermost Potoco Formation), followed by (2) rapid deposition (average sediment-accumulation rates up to 500 m/ m.y.) throughout late Eocene and Oligocene time (majority of Potoco Formation). Lithofacies and paleocurrent data confirm both depositional phases. A 20‐100-mthick interval of superimposed paleosols in the basal Potoco supports reduced sediment accumulation and low rates of subsidence during mid-Paleocene to middle Eocene time. The overlying main body of the Potoco contains facies assemblages and stratigraphic architecture (dominantly nonero

Palaeoenvironmental and diagenetic control of the mineralogy of Upper Cretaceous–Lower Tertiary deposits of the Central Palaeo–Andean basin of Bolivia (Potosi area)

Abstract A study, involving mainly X-ray diffraction, of the mineralogy of Upper Cretaceous and Lower Tertiary deposits (Aroifilla, Chaunaca, El Molino, Santa Lucia and Cayara Formations) of the Andean basin in the Bolivian Eastern Cordillera is presented. This work refines environmental reconstructions based on previous sedimentological studies in the Potosi Basin. The results including the clay mineralogy show that the sediments were deposited in a lacustrine system which suffered large variations of water level and groundwater influence. The siliciclastic sediments are characterized either by abundant feldspars or analcime, suggesting a perennial volcanoclastic influence. Tuff layers in the Santa Lucia Formation support this interpretation. The great diversity of clay minerals identified reflects both detrital influences and diagenetic overprinting. Although diagenetic changes are common in this sedimentary series, it is still possible to identify the nature of detrital supply. Illite and illite–smectite mixed-layer clays constitute the background clay sedimentation and reflect predominantly arid climate. This had already been deduced from sedimentogical and geochemical investigations. However, detrital kaolinite occurs in a 40 m-thick interval of the El Molino Formation which probably embraces the K/T boundary and reflects more humid conditions. Further work is necessary to locate more precisely this boundary in the absence of accurate biostratigraphical markers. Authigenic clays are also recognized: in the sandstones in the basal part of the Cayara Formation kaolinite developed authigenically; in the tuff layers of the Santa Lucia Formation well-crystallized authigenic smectite characterizes the clay fraction. In addition, chlorite replaces smectite in limestones beds of the El Molino Formation which were deposited in evaporitic environments.The clay assemblages including illite and chlorite at base of the stratigraphic column (Aroifilla, and Chaunaca Formations) probably results from the replacement of smectitic minerals either by chlorite or illite where depth of burial reached more than 2000 m.

Stratigraphy and chronology of Upper Cretaceous–lower Paleogene strata in Bolivia and northwest Argentina

Integration of sequence stratigraphy, magnetostratigraphy, Ar/Ar dating, and paleontology considerably advances knowledge of the Late Cretaceous–early Paleogene chronostratigraphy and tectonic evolution of Bolivia and adjacent areas. The partly restricted marine El Molino Formation spans the Maastrichtian and Danian (°73–60.0 Ma). Deposition of the alluvial to lacustrine Santa Lucia Formation occurred between 60.0 and 58.2 Ma. The widespread erosional unconformity at the base of the Cayara Formation is 58.2 Ma. This unconformity separates the Upper Puca and Corocoro supersequences in Bolivia, and is thus coeval with the Zuni-Tejas sequence boundary of North America. The thick overlying Potoco and Camargo formations represent a late Paleocene–Oligocene foreland fill. The onset of shortening along the Pacific margin at °89 Ma initially produced rifting in the distal foreland. Santonian–Campanian eastward-onlapping deposits indicate subsequent waning of tectonic activity along the margin. Significant tectonism and magmatism resumed along the margin at °73 Ma and produced an abrupt increase in subsidence rate and other related phenomena in the basin. Subsidence was maximum between °71 and °66 Ma. Due to the early Maastrichtian global sea-level high, marine waters ingressed from the northwest into this underfilled basin. Subsidence decreased during the Late Maastrichtian and was low during the Danian. It increased again in the latest Danian, for which a slight transgression is recorded, and peaked in the early Selandian. Tectonism between 59.5 and 58.2 Ma produced a variety of deformational and sedimentary effects in the basin and correlates with the end of emplacement of the Coastal batholith. The subsequent 58.2 Ma major unconformity marks the onset of continental foreland basin development, which extended into Andean Bolivia during the late Paleocene–Oligocene interval. This basin underwent internal deformation as early as Eocene time in the Altiplano and Cordillera Oriental. These early structures, previously assigned to the late Oligocene–early Miocene orogeny, probably accommodated observed tectonic rotations in the Eocene–Oligocene.