The utility of genetic stratigraphy lies with the fundamental relationship between genetic stratigraphic units and correlative intervals of geologic time. While high-resolution studies may reveal varying degrees of diachroneity that are associated with their bounding surfaces, genetic stratigraphic units are generally viewed as chronostratigraphic in nature, representing specific periods of basin fill. Despite the vast literature on basin analysis, an evaluation of the temporal character of the boundaries between genetic stratigraphic units, particularly in cases where they are conformable, has not yet been undertaken. The Cenozoic Ebro basin is a foreland basin on the northeastern Iberian Peninsula that provides a case for assessing the temporal character of the boundaries between genetic stratigraphic units. These units are termed "tecto-sedimentary units", following the method of tecto-sedimentary analysis that is used in some continental basins. In the Ebro basin tecto-sedimentary analysis is based on direct field observations. In this work, magnetostratigraphic data from four tecto-sedimentary units (units T4 to T7) that span rocks of lower and middle Miocene age (ca. 1000 m thick) in the central and western areas of the basin are analysed. The study area contains alluvial, fluvial and lacustrine deposits that were sourced from Pyrenean and Iberian areas, whose catchments were structured during the collision of Iberia and Eurasia. New magnetostratigraphic data from this study and previously published magnetostratigraphic data enable us to determine the ages of these tecto-sedimentary unit boundaries throughout a 200-km-long, east-west transect that extends from the basin centre to the southwestern margin. The results indicate that the diachrony of the three boundaries between the Miocene tecto-sedimentary units through the central Ebro basin is less than 0.3 Ma where they are conformable. This low degree of diachroneity may be attributed to the effects of allogenic, largely tectonic processes that operate in the catchment areas and methodological inaccuracies. These results provide empirical support to the idea that genetic stratigraphic units are bounded by surfaces that exhibit low amounts of diachroneity where they are conformities.
This study focuses on recent debate over the value of stable isotope-based environmental proxies recorded in riverine tufa stromatolites. A twelve-year record (1999 to 2012) of river-bed tufa stromatolites in the River Piedra (north-east Spain) was recovered in this study, along with a partly overlapping fifteen-year record (1994 to 2009) of accumulations in a drainage pipe: both deposits formed in water with near identical physico/chemical parameters. Measured water temperature data and near-constant d 18 O water composition allowed selection of an 'equilibrium' palaeotemperature equation that best replicated actual temperatures. This study, as in some previous studies, found that just two published formulas for water temperature calculation from equilibrium calcite d 18 O compositions were appropriate for the River Piedra, where tufa deposition rates are high, with means between 5Á6 mm and 10Á8 mm in six months. The d 18 O calcite in both the river and the pipe deposits essentially records the full actual seasonal water temperature range. Only the coldest times (water temperature <10°C), when calcite precipitation mass decreased to minimum, are likely to be unrepresented, an effect most noticeable in the pipe where depositional masses are smaller and below sample resolution. While kinetic effects on d 18 O calcite -based calculated water temperature cannot be ruled out, the good fit between measured water temperature and d 18 O calcite -calculated water temperature indicates that temperature is the principal control. Textural and deposition rate variability between the river and pipe settings are caused by differences in flow velocity and illumination. In the river, calcification of growing cyanobacterial mat occurred throughout the year, producing composite dense and porous laminae, whereas in the pipe, discontinuous cyanobacterial growth in winter promoted more abiogenic calcification. High-resolution d 18 O calcite data from synchronous pipe and river laminae show that reversals in water temperature occur within laminae, not at lamina boundaries, a pattern consistent with progressive increase in calcite precipitation rate as cyanobacterial growth reestablished in spring.
Dating the sedimentary infill of the northern margin of the Ebro foreland basin informs about the orogen-basin evolution. A magnetostratigraphic section of ~5 km-thick combines new magnetostratigraphic results from the syntectonic alluvial Uncastillo Fm (Upper Oligocene-Lower Miocene, 1 km-thick, the Fuencalderas section) with previous (3.3 km-thick) and new (0.7 kmthick) magnetostratigraphic data from the underlying fluvial Campodarbe Fm (Luesia and San Marzal sections, Eocene-Oligocene). This composite section allows dating the entire basin infill in this sector, therefore bracketing the timing of the deformation in the southern margin of the Pyrenees after considering previous kinematic studies. Deformation recorded by the continental deposits spans from syn-Gavarnie nappe activity (Broto and Fiscal basement thrust sheets) from 31.3 to 24.55 Ma, Rupelian-Chattian (Oligocene) to the syn-Guarga thrust activity, from 24.55 to 21.2 Ma Chattian-Aquitanian (Oligocene-Miocene). The Accumulation rates vary from ca. 22 to ca. 39 cm/kyr between the genetic stratigraphic units in the Uncastillo Fm through the section. These rates are close to those of the underlying deposits of the Campodarbe Fm (average of ca. 36 cm/kyr). Deformation for the latest Pyrenean front (syn-Guarga thrust) is younger than previously assigned in ~ 5.4. ~1.5 and ~1.1 Myr of the beginning of the Punta Común thrust sheet (from 29.4 Ma to 24 Ma), Lower Riglos thrust sheet system (from 24 to 22.5 Ma) and the Upper Riglos thrust system (22.5 to 21.4 Ma) respectively. Other significant changes in accumulation rate and its derivative also indicate variations in the tectonic activity ca. 33 and 28 Ma. Tilt variations in the Uncastillo Fm also record the tectonic activity with 40º variations of the Punta Común thrust sheet at ca. 20º with the Upper Riglos thrust sheet.
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