Carlos L. Liesa

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

Slumps affecting uppermost Mendez Formation marls, as well as the spherulitic layer and basal part of the sandy deposits of the Cretaceous-Tertiary (K-T) boundary clastic unit, are described at the new K-T El Tecolote section (northeastern Mexico). These K-T clastic deposits represent sedimentation at middle-bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional, high- to low-density turbidite flow. We emphasize the development and accretion of a lateral bar in a channel area from a surging low-density turbidity current and under a high-flow regime. The slumps discovered on land and the sedimentary processes of the K-T clastic unit reflect destabilization and collapse of the continental margin, support the mechanism of gravity flows in the deep sea, and represent important and extensive evidence for the impact effects in the Gulf of Mexico triggered by the Chicxulub event.

Extensional fault control on the sedimentation patterns in a continental rift basin: El Castellar Formation, Galve sub-basin, Spain

In the Galve sub-basin, the sedimentary record of the Upper Hauterivian–Lower Barremian El Castellar Formation is divided into two stages by a marlstone interval with gypsum. Stage 1 shows a great variety of subenvironments and facies (alluvial, palustrine and lacustrine) whereas in stage 2 an extensive, shallow carbonate lake developed. Sedimentation was controlled by a system of south-dipping, ENE–WSW listric normal faults, laterally bounded by NNW–SSE steeper transfer faults. Faults controlled sedimentation from a basin scale (basin margins and main characteristics and evolution of sediments) to a regional and a local scale (thickness and facies distribution of the synrift series as well as the location and evolution of lakes and minor alluvial fans). The changes between stages 1 and 2 are related to the passing from an independent movement of faults to the movement of all the extensional faults as a whole, at a sole detachment level. The interval with gypsum was caused by underground water flow changes associated with the interrelation and connection of the faults in the transition period. These changes have been correlated with the transition from the rift initial stage to the rift climax stage, which took place in the Hauterivian–Barremian transition.

Role of extensional structures on the location of folds and thrusts during tectonic inversion (northern Iberian Chain, Spain)

Abstract The Aguilon Subbasin (NE Spain) was originated daring the Late Jurassic-Early Cretaceous rifting due to the action of large normal faults, probably inherited from Late Variscan fracturing. WNW-ESE normal faults limit two major troughs filled by continental deposits (Valanginian to Early Barremian). NE-SW faults control the location of subsidiary depocenters within these troughs. These basins were weakly inverted during the Tertiary with folds and thrusts striking E-W to WNW-ESE involving the Mesozoic-Tertiary cover with a maximum estimated shortening of about 12 %. Tertiary compression did not produce the total inversion of the Mesozoic basin but extensional structures are responsible for the location of major Tertiary folds. Shortening of the cover during the Tertiary involved both reactivation of some normal faults and development of folds and thrusts nucleated on basement extensional steps. The inversion style depends mainly on the occurrence and geometry of normal faults limiting the basin. Steep normal faults were not reactivated but acted as buttresses to the cover translation. Around these faults, affecting both basement and cover, folds and thrusts were nucleated due to the stress rise in front of major faults. Within the cover, the buttressing against normal faults consists of folding and faulting implying little shortening without development of ceavage or other evidence of internal deformation.

Cretaceous-Tertiary boundary planktic foraminiferal mass extinction and biochronology at La Ceiba and Bochil, Mexico, and El Kef, Tunisia

Micropaleontology studies across the Cretaceous-Tertiary (K-T) boundary from sections at La Ceiba, Bochil, Mexico, and El Kef, Tunisia, suggest a close cause and effect relationship between the Chicxulub impact and the K-T planktic foraminiferal mass extinction. The K-T planktic foraminiferal biostratigraphy and assemblage turnover in Mexico was examined and the approximate deposition timing of K-T-related material (clastic unit) was estimated. On the basis of established biomagnetochronologic calibrations, the first appearance datum (FAD) of Parvularugoglobigerina longiapertura occurred 3.5–5 k.y. after the K-T boundary, and the FADs of Parvularugoglobigerina eugubina, Eoglobigerina simplicissima, and Parasubbotina pseudobulloides occurred 15–17.5 k.y., 28–31 k.y., and 45–55 k.y., respectively, after the K-T boundary. According to estimated average sedimentation rates and estimated age, the K-T red layer at El Kef was probably formed in 20 yr and the deposition of the K-T clastic unit in the Gulf of Mexico was geologically instantaneous. The last appearance of most Maastrichtian species is just below the K-T impact-generated bed, clearly implying a catastrophic planktic foraminiferal mass extinction.

Stress Partitioning: a Practical Concept for Analysing Boundary Conditions of Brittle Deformation

Although conjugate fault systems cannot accommodate three-dimensional strain, the notion of stress-driven fracturing based upon Mohr-Coulombs failure criterium can be reconciled with any kinematic boundary condition if a non-static scenario is considered. The concept of stress partitioning is proposed as a tool for understanding the mechanisms allowing such compatibility. It describes stress changes that occur in response to failure events, giving the appearance that the total stress field is decoupled into distinct, independent components. It can be mainly applied to biaxial horizontal loading conditions (e.g. multidirectional tension or multidirectional compression in intraplate regions). Swapping of horizontal stress axes, caused by stress drop subsequent to failure, can result in two distinct stress events and two, either tensile or shear fracture systems with nearly orthogonal strikes. Each fracture event develops according to Mohr-Coulombs and Griffiths failure criteria, but the resulting overall deformation is three-dimensional.

Correlation of sedimentary units from grain-size and mineralogic analyses as a tool for constraining trench interpretations in palaeoseismology

In palaeoseismological trench studies, precise correlation of sedimentary units between fault blocks has an unquestionable value for accurately inferring the amounts of coseismic displacement and hence for assessing seismic hazard. A methodology based on laser analysis of particle size and mineralogic composition by X-ray diffraction is proposed in order to strengthen the correlation of sedimentary units in a trench excavated across the Concud Fault (central Iberian Chain, Spain). The surveyed sediments show sharp and multiple lateral facies changes, as well as inconsistent optically stimulated luminescence (OSL) ages. The results reinforce the correlation based on field inspection of lithologic and sedimentologic features. Moreover, they allow interpretation of rejuvenation of OSL ages of samples in the upthrown fault block, which has been attributed to partial erosion of sedimentary units, as evidenced by their smaller thickness and erosive boundaries. The correlated units are then used to estimate coseismic displacements for three palaeoseismic events.

Geophysical characterization of buried active faults: the Concud Fault (Iberian Chain, NE Spain)

The Concud Fault is a ~14-km-long active fault that extends close to Teruel, a city with about 35,000 inhabitants in the Iberian Range (NE Spain). It shows evidence of recurrent activity during Late Pleistocene time, posing a significant seismic hazard in an area of moderate-to-low tectonic rates. A geophysical survey was carried out along the mapped trace of the southern branch of the Concud Fault to evaluate the geophysical signature from the fault and the location of paleoseismic trenches. The survey identified a lineation of inverse magnetic dipoles at residual and vertical magnetic gradient, a local increase in apparent conductivity, and interruptions of the underground sediment structure along GPR profiles. The origin of these anomalies is due to lateral contrast between both fault blocks and the geophysical signature of Quaternary materials located above and directly south of the fault. The spatial distribution of anomalies was successfully used to locate suitable trench sites and to map non-exposed segments of the fault. The geophysical anomalies are related to the sedimentological characteristics and permeability differences of the deposits and to deformation related to fault activity. The results illustrate the usefulness of geophysics to detect and map non-exposed faults in areas of moderate-to-low tectonic activity where faults are often covered by recent pediments that obscure geological evidence of the most recent earthquakes. The results also highlight the importance of applying multiple geophysical techniques in defining the location of buried faults.

Barremian synrift sedimentation in the Oliete sub-basin (Iberian Basin, Spain): palaeogeographical evolution and distribution of vertebrate remains

A review of the onset of the synrift sedimentation and synsedimentary extensional tectonics of the Oliete sub-basin (northwestern Maestrazgo basin, East Spain) is presented here based on new data acquired after extensive sedimentological, structural and palaeontological analysis of the Barremian Blesa Fm. The lower boundary of the Blesa Fm is a prominent basal synrift unconformity overlying Jurassic units. This formation has been divided into three genetic stratigraphic sequences bounded by sub-basin-wide unconformities. The lower Blesa sequence (LBS) is characterized by distal alluvial to palustrine marls/clays grading upward to palustrine–lacustrine limestones. The LBS is bounded on top by a planar to irregular transgressive, hardened ferruginous surface, locally encrusted by oysters. Above this discontinuity, the middle Blesa sequence consists of oyster-rich limestones and marls deposited in a shallow restricted bay, which grade to distal alluvial and palustrine–lacustrine marls/clays and limestones towards the marginal areas of the basin. The boundary between the middle and upper Blesa sequence (UBS) is a regressive surface outlined by the local presence of an erosive conglomeratic bed. The UBS generally starts with red clays deposited in distal alluvial fan environments, which grade upwards to palustrine and lacustrine carbonates and marls/clays. The local presence of heterolithic alternations of clay with fine-to-medium sandstone and of cross-bedded sandstones indicates the local occurrence of siliciclastic coastal environments in the UBS. The upper boundary of the Blesa Fm is marked by widespread transgression, giving rise to the bioclastic limestones of the Alacón Fm. In the present paper, the stratigraphic position and palaeoenvironmental context of the abundant vertebrate remains found across the defined sequences within the Blesa Formation is reviewed. The results obtained are relevant for a further understanding of the tectosedimentary evolution of the studied basin. Successive stages of evolution are distinguished, including the initial uplift, breakup and erosion of the earlier Jurassic carbonate platform that took place during the Tithonian–Hauterivian; the onset of synrift sedimentation during the early Barremian, which was highly controlled by extensional faulting and differential block subsidence; the homogenization of the basin subsidence accompanied by the incursion of marine waters (sourced from southeastern areas) during the middle part of the Barremian; and the significant fall in base level, of possible climatic origin and also involving significant siliciclastic input in the northern areas of the Oliete sub-basin around the middle part of the late Barremian.ResumenEste trabajo es una revisión de la sedimentación sin-rift barremiense y la tectónica extensional en la subcuenca de Oliete (noroeste del Maestrazgo, este de España), a partir de datos previos y nuevos datos adquiridos después de un extenso análisis sedimentológico, estructural y paleontológico de la Fm. Blesa. El límite inferior de la Fm. Blesa es una discordancia basal sin-rift que recubre las unidades jurásicas. La unidad se ha dividido en tres secuencias genéticas delimitadas por discontinuidades en toda la subcuenca. La secuencia Blesa inferior (LBS) se caracteriza por margas/arcillas aluviales a palustres y calizas palustres-lacustres hacia techo. Su límite superior es una superficie transgresiva neta representada por una superficie ferruginosa irregular, localmente encostrada por ostras. La secuencia Blesa media (MBS) consiste en calizas y margas ricas en ostras depositadas en una bahía restringida poco profunda, que pasan lateralmente hacia áreas marginales de la cuenca a calizas palustres-lacustres y margas/arcillas aluviales distales. El límite con la secuencia Blesa superior (UBS) es una superficie regresiva erosiva asociada localmente a niveles conglomeráticos. La UBS comienza generalmente con arcillas rojas de abanicos aluviales distales, que hacia techo pasan calizas y margas/arcillas palustres-lacustres. La presencia local de alternancias heterolíticas de arcillas y areniscas de grano fino y medio, y de areniscas con estratificación cruzada, indica ambientes costeros siliciclásticos. El límite superior de la Fm. Blesa está marcado por una transgresión generalizada (calizas bioclásticas de la Fm. Alacón). En el presente trabajo, se revisa también la posición estratigráfica y el contexto paleoambiental de los abundantes restos de vertebrados encontrados teniendo como base el nuevo esquema de secuencias definido dentro de la Fm. Blesa. Los resultados obtenidos son relevantes para una mayor comprensión de la evolución tectosedimentaria de la subcuenca de Oliete. Se distinguen sucesivas etapas de evolución, incluyendo: 1) levantamiento inicial, ruptura y erosión del de las calizas de plataforma del Jurásico, que tuvo lugar durante el Titoniense-Hauteriviense; 2) inicio de la sedimentación durante el Barremiense inferior, controlada por fallas extensionales y hundimiento de bloques diferencial; 3) fase de hundimiento homogéneo acompañada por la incursión de aguas marinas (provenientes del sureste) durante la parte media del Barremiense; y 4) caída significativa en el nivel de base, de posible origen climático y también involucrando una importante entrada de siliciclásticos en las áreas del norte de la subcuenca, alrededor de la parte media del Barremiense superior.