Temporal aspects of genetic stratigraphic units in continental sedimentary basins: Examples from the Ebro basin, Spain

Abstract

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.

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

“…Concerning the boundary T5/T6 established herein through stratigraphic criteria and dated by correlation with other nearby areas having magnetostratiphic studies, the age proposed for this boundary in the Sancho Abarca-Plana de la Negra area (16.05 to 16.06Ma) is consistent with the small diachrony (ca 30ka) of this boundary throughout the Ebro Basin centre (Pérez-Rivarés et al, 2018).…”

“…(Inglés et al, 1998) Luna fluvial system NNE FIGURE 2. Tectonosedimentary units (from Muñoz et al, 2002 andPérez-Rivarés et al, 2018) and lithostratigraphic units (from several authors; see Muñoz et al, 2002) petrographic and textural analyses. Nomenclature used for the diverse carbonate textures followed classification of Dunham (1962), with modification by Embry and Klovan (1971), and the classification Petijhon et al (1973) for siliciclastic deposits.…”

“…Map adapted from Muñoz et al (2002) and Pérez-Rivarés et al (2018). centre, with diachrony up to 0.28ka (see discussion by Pérez-Rivarés et al, 2018), and locally is unconformable, i.e. at the basin margins in the southwesternmost and southeast sectors of the Ebro Basin.…”

“…Regional studies indicate that the sedimentary infill of the Ebro Basin is arranged into eight stratigraphic genetic units (Tectosedimentary Units or TSUs, named T1 to T8;Muñoz et al, 2002;Pardo et al, 2004). The ages of these TSUs have been determined from vertebrate fossil assemblages (data summarized in Agustí et al, 2011;Murelaga et al, 2008;Pardo et al, 2004;Ruiz-Sánchez et al, 2013;Suarez-Hernando, 2017) and, more recently, by means of magnetostratigraphic studies on Oligocene and Miocene sediments (Barberà et al, 2001;Larrasoaña et al, 2006;Oliva-Urcia et al, 2019;Pérez-Rivarés et al, 2018;Valero et al, 2014).…”

“…B) Enlarged map showing the location of the studied area, with sections measured herein, as well as location of sections from other authors that are integrated in this study. Map adapted from Muñoz et al (2002) and Pérez-Rivarés et al (2018). centre, with diachrony up to 0.28ka (see discussion by Pérez-Rivarés et al, 2018), and locally is unconformable, i.e.…”