Along-strike sedimentological variability and architectural patterns of the transgression of a “mid”-Cretaceous braidplain system (Iberian Basin, eastern Spain): A tool for depicting eustatic and tectonic signatures within the framework of a global transgression

Abstract

The mid-Albian to lower Cenomanian Utrillas Group is interpreted as an arid braidplain system in the Serranía de Cuenca region (Iberian Basin, Spain). In its proximal locations, it consists of an interaction of alluvial facies and subordinate aeolian deposits, with the occurrence of tidally-influenced deposits that reflect a general transgressive trend to the top of the succession. However, the distal areas of this braidplain system, where there was a more intense interaction with the Tethys Ocean, have remained understudied to date.

We present a sedimentological study of two outcrops (Pajaroncillo and Reíllo) located at the distal sector of the braidplain system and 12 km apart, defining an along-strike relative position. Both outcrops differ notably regarding the arrangement and distribution of the facies associations identified despite their relative closeness. Based on the sedimentological analysis, the main transgressive and regressive trends of the succession have been identified, along with several correlatable stratigraphic surfaces. This has permitted us to distinguish five stages (T1–T5), which reflect the overall transgressive evolution of the succession: a continental aggradational stage (T1), dominated by alluvial deposition; an initial transgression stage (T2) dominated by an open coast setting in Reíllo and a restricted mudflat system in Pajaroncillo; a regressive stage (T3), during which continental alluvial to supratidal environments deposited; a resumption in transgression (T4), characterised by an array of inter- to subtidal environments; and a deepening stage (T5), when the transgression advanced landward, giving rise to the most distal deposits of the studied succession.

The studied outcrops, located at the basin edge, have been integrated within the regional sequence stratigraphy framework, which was originally devised for more central areas of the Iberian Basin (Valencia Domain) and the Prebetic. This regional approach has allowed us to interpret the studied deposits as third-order depositional sequences. Besides, the supra-regional implications of this research are discussed within the broader context of Iberia and the subtleties of its tectono-sedimentary evolution during the Albian to Cenomanian times.