Identification of sequence stratigraphy in the Dongying Formation of the Liaoxi low uplift, Bohai Bay Basin, China

A change in sea level (or lake level) causes a change in accommodation space and sediment compensation, which then controls the formation and evolution of sequences. A multidisciplinary approach based on the integration of clay minerals, major and trace elements, paleosalinity, and three-dimensional seismic data were applied to interpret the stratigraphic sequence of the Dongying Formation in the Liaoxi low uplift. The sequence surface indicates that multistage tectonic action, paleoclimate, paleosalinity, and lake level change jointly controlled the sequence stratigraphy. The illite and illite-smectite mixed layers indicate an arid to semi-arid climate, whereas kaolinite implies humid conditions. Based on this principle, it is clear that the stratigraphic sequence is closely related to paleoclimate. Interpretation of the continental or marine character of the sediments via paleosalinity is increasingly based on the concentration of some trace elements. Hence, the sequence surface can be better evaluated through paleosalinity data. Based on the Sr/Ba and boron content, paleosalinity was evaluated and the sequence boundary was identified. Analysis of the concentration of major and trace elements was used to identify the lithology of the sedimentary region and further discern the stratigraphic sequence. These sequences are composed of lowstand, transgressive, and highstand system tracts. The work herein aimed to understand the reasons for the changes in sequences under the paleoclimate. In addition, major and trace elements, studied together with paleosalinity and clay mineral content, result in the determination of implications for sequence stratigraphy in many other basins. This paper can provide a novel method for comprehensively discerning a sequence surface. Key words: sequence stratigraphy, Dongying Formation, Liaoxi low uplift, Bohai Bay Basin, major and trace elements, paleosalinity. Un changement du niveau de la mer (ou du niveau d'un lac) entraine un changement de l'espace d'accommodation et de la compensation de sediments qui, lui, controle la formation et l'evolution des sequences. Une approche multidisciplinaire reposant sur l'integration de donnees sur les argiles, les elements majeurs et en traces et la paleosalinite et de donnees de sismique tridimensionnelle a ete appliquee a l'interpretation de la sequence stratigraphique de la Formation de Dongying dans le soulevement bas de Liaoxi. La surface de la sequence indique qu'une activite tectonique en plusieurs etapes, le paleoclimat, la paleosalinite et les changements des niveaux de lac ont controle conjointement la stratigraphie sequentielle. Les couches d'illite et d'illite-smectite mixtes indiquent un climat aride a semi-aride, alors que la kaolinite temoigne de conditions humides. Partant de ce principe, il est clair que la sequence stratigraphique est etroitement reliee au paleoclimat. L'interpretation du caractere continental ou marin des sediments a partir de la paleosalinite repose de plus en plus sur la concentration de certains elements en traces. La surface de la sequence est donc mieux evaluee a la lumiere de donnees de paleosalinitie. Les valeurs des rapports Sr/Ba et les teneurs en bore ont ete utilisees pour evaluer la paleosalinite et etablir la limite de la sequence. L'analyse des concentrations d'elements majeurs et en traces a ete utilisee pour etablir la lithologie de la region sedimentaire et caracteriser plus en detail la sequence stratigraphique. Ces sequences sont composees de corteges de bas niveau, transgressifs et de haut niveau. Les travaux presentes visent a etablir les causes des changements dans les sequences au vu du paleoclimat. Les elements majeurs et en traces etudies de concert avec la paleosalinite et les concentrations des argiles jettent en outre un meilleur eclairage sur la stratigraphie sequentielle dans de nombreux autres basins. L'article presente une nouvelle approche pour delimiter de maniere exhaustive la surface d'une sequence. [Traduit par la Redaction] Mots-cles : stratigraphie sequentielle, Formation de Dongying, soulevement bas de Liaoxi, bassin de la baie Bohai, elements majeurs et en traces, paleosalinite.
Introduction Sequence stratigraphy is a new subdiscipline formed by the combination of tectonic geology and sedimentology (Bouaziz et al. 2002; Gharbi et al. 2015; Jacquin et al. 1991). As a [...]