Mesozoic Stratigraphy

Patterns of uranium-molybdenum covariation in marine sediments have the potential to provide insights regarding depositional conditions and processes in paleoceanographic systems. Specifically, such patterns can be used to assess bottom water redox conditions, the operation of metal-oxyhydroxide particulate shuttles in the water column, and the degree of water mass restriction. The utility of this paleoenvironmental proxy is due to the differential geochemical behavior of U and Mo: (1) uptake of authigenic U by marine sediments begins at the Fe(II)-Fe(III) redox boundary (i.e., suboxic conditions), whereas authigenic Mo enrichment requires the presence of H 2 S (i.e., euxinic conditions), and (2) transfer of aqueous Mo to the sediment may be enhanced through particulate shuttles, whereas aqueous U is unaffected by this process. In the present study, we examine U-Mo covariation in organic-rich sediments deposited mostly in the western Tethyan region during oceanic anoxic events (OAEs) of Early Jurassic to Late Cretaceous age. Our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regarding water mass restriction and the operation of particulate shuttles in depositional systems. These insights will help to address contentious issues pertaining to the character and origin of Mesozoic OAEs, such as the degree to which regional paleoceanographic factors controlled the development of the OAEs.

The southern Alps were characterized by strong variations,
both in space and time, of heat flow during Mesozoic rifting.
The regional thermal history was reconstructed using organic
matter (OM) maturity data from outcropping sediments.
One-dimensional (1-D) thermal modeling performed on selected
successions suggests thatOMmaturity wasmainly controlled
by high geothermal gradients (heat flow peaks of 85 to
105 mW/m2 in the Middle Jurassic) and differential burial
during Norian–Early Jurassic extensional phases. The results
of 1-D modeling show an eastward increase of heat flow peak
values.
These results were compared with those obtained with
two-dimensional (2-D) thermokinematic models. Themodels
show a time shift (ca. 10 Ma) in the heat-flow peak (Aalenian-
Bajocian for 2-D and Bajocian for 1-D modeling). However,
the Bajocian age was a priori imposed on 1-Dmodels.Available
geochemical data could be fitted assuming Aalenian-Bajocian
peak ages. Consequently, this misfit is not alarming. The eastward
increase in heat-flow peak values is tentatively explained
with an eastward increase of radiogenic heat production in the
crust instead of with differential stretching.
The comparison of paleothermal data and numericalmodeling
was done to gain knowledge on the potentials and limitations
of numerical modeling in frontier areas. Although some differences do exist in the results of geochemical and thermokinematicmodels,
we can conclude that if a reasonable knowledge
of the thermal parameters of both covers and basement is
available, thermokinematic modeling can provide useful firstorder
estimates in frontier areas of heat flow and temperature
evolution through time.

2016. The Late Triassic and Early Jurassic fissure faunas from Bristol and South Wales: Stratigraphy and setting. Palaeontologia Polonica 67, 257–287. The famous vertebrate-bearing fissures of the Bristol area in southwest England and in south Wales were traditionally referred to " upland " environmental settings, and assigned an overall time range of some 60 Myr; we reject both of these viewpoints. In terms of the environmental setting, based upon the evidence of palaeogeography, sediments, and fossils, we show that all the Triassic-aged fissures were near-coastal and embedded in karst formed on palaeo-islands in a subtropical archipelago. Further, the dates of these fissure fills in both regions do not span the Carnian to Rhaetian, as commonly supposed, but instead they are probably all Rhaetian. We update information on the Charles Moore Holwell " Microlestes " fissure assemblage and demonstrate that the marine fauna confirms a Rhaetian age. As proposed by previous authors , younger fissure fills around the St. Brides area of South Wales were also formed on an island, but during the Hettangian–Sinemurian. The youngest fissure deposit in the region is Pliensbachian. The age range of the fissures thus shrinks to c. 20 Myr, and the first episode of tetrapod fissure infilling shifts from the time of the Carnian " pluvial " episode, to the early Rhaetian, when western Europe was undergoing major rifting associated with the beginning of the opening of the North Atlantic, and when the Rhaetian sea flooded over landscapes that had long been purely terrestrial and arid. We recognise clear changes in the faunal composition of the terrestrial vertebrate biota from the early Rhaetian, dominated by reptile taxa, with some mammaliamorphs, that then declined rapidly in diversity before the Hettangian. This herpe-tofauna was followed by three faunal assemblages in the Early Jurassic of St. Brides which became increasingly diverse following the end-Triassic mass extinction; each had prominent mammaliamorphs as well as high numbers, but few species, of rhynchocephalians.

RESUMEN Se propone, por primera vez, un cuadro estratigráfico integrado para las unidades pospaleozoicas en la Precordillera Septen-trional sobre la base de las exposiciones comprendidas entre las quebradas de Santo Domingo y El Peñón. Esta área resulta una región crítica, no sólo para la estratigrafía de la Precordillera Septentrional, sino también como sección de referencia para la co-rrelación entre las unidades aflorantes en las Sierras Pampeanas y en el norte de Chile. Se han reconocido 6 unidades compren-didas entre el Triásico Tardío y el Mioceno-Plioceno? La más antigua corresponde a la Formación Santo Domingo, unidad de bancos rojos datada en el Triásico Tardío-Jurásico Temprano sobre la base del estudio de la xiloflora y dataciones radimétricas. Esta unidad es cubierta en discordancia por la Formación Ciénaga del Río Huaco (Cretácico Tardío), en la que han sido repor-tados restos óseos de titanosaurios. La Formación Puesto La Flecha (Eoceno tardío-Oligoceno) inicia el registro cenozoico de la comarca, y corresponde a una sucesión preorogénica a los primeros movimientos andinos compuesta por areniscas y pelitas formadas en ambientes fluviales de baja energía y cuerpos lacustres someros. La orogenia andina en la región está representa-da en las areniscas eólicas de la Formación Vallecito (Oligoceno tardío-Mioceno temprano), la que fue sedimentada bajo con-diciones áridas en un contexto de cuenca de antepaís hambrienta. Estas rocas son sucedidas por la unidad de " conglomerados y areniscas Refugio del Peñón " , formada por la progradación de cuñas clásticas desde el arco magmático y de los cabalgamien-tos más occidentales de la orogenia andina en la Argentina. Finalmente, el " conglomerado La Falda " indica el desplazamiento hacia el este del orógeno andino y el ascenso y destechado del granito que forma el núcleo de la Sierra del Peñón. ABSTRACT Stratigraphy of the Neogene, Paleogene and Mesozoic successions of the Santo Domingo and El Peñón creeks (Northern Precordillera of La Rioja) Geological surveys carried out in the Santo Domingo and El Peñón creeks allow, for the first time, proposing an integrated stratigraphic model for the post-Paleozoic units outcropping in the Precordillera Septentrional. The area encompassing the Santo Domingo and El Peñón creeks is a key section not only for the stratigraphy of the Precordillera but also for regional correlations with units of similar age from the Sierras Pampeanas and north of Chile. Six stratigraphic units between the Late Triassic and the Miocene were recognized. The oldest corresponds to the Santo Domingo Formation, a red bed sequence composed of conglomerates, sandstones and mudstones wich was dated in the Late Triassic-Early Jurassic based on the study of the xyloflora and a radiometric age. This unit is unconformably covered by sandstones and mudstones belonging to the Ciénaga del Río Huaco Formation (Late Cretaceous) which provided some skeletal remains of Titanosaurios. The Puesto La Flecha Formation (late Eocene–Oligocene) comprises sandstones and mudstones deposited in ephemeral fluvial systems together with shallow water bodies (Lower Member) and eolian dunes (Upper Member). The onset of the Andean Orogeny in the studied region is represented in the eolian sandstones of the Vallecito Formation (late Oligocene – early Miocene) which was formed in arid conditions within an underfilled foreland basin. These rocks are succeeded by the informally called unit of " conglomerates and sandstones Refugio del Peñón " that represent the progradation of clastic wedges from the volcanic arc located to the west. Finally, the informal unit of " conglomerates La Falda " points out the displacement towards the west of the Andean orogenic front and the uplift and unroofing of the granitic rocks forming the core of the Sierra del Peñón.

The Kota Formation of the Pranhita-Godavari Basin is well known for its fossil fauna and flora especially for its silicified woods. However, the palaeoflora and its palaeoclimatic significance within the formation are poorly known. In spite of the fact that the formation yields a rich fauna and flora chronostratigraphic problems still exist. The present study aims to analyze the palaeofloras from the Kota Formation to understand their diversity and palaeoecological significance. We also describe a new species Agathoxylon kotaense belonging to the conifer family Araucariaceae. Our study shows that the flora was dominated by conifers and that it is comparable to that of the ?Late Jurassic-Lower Cretaceous Gangapur Formation, Pranhita-Godavari Basin and that of the Rajmahal Formation of the Rajmahal hills. The growth ring pattern and leaf fossil assemblage suggest that the growth conditions were seasonal, but mostly stressed.