Where humid and arid meet: Sedimentology of coastal siliciclastic successions deposited in apparently contrasting climates

Abstract

Deciphering the palaeoenvironmental and palaeoclimatic setting of ancient successions that include deposits typical of different climates can be challenging. This is the case in the Late Jurassic succession cropping out in eastern Spain (South-Iberian and western Maestrazgo basins), where deposits characteristic of both arid to semiarid and humid to subhumid settings have been identified through a detailed analysis of eight stratigraphic sections. These sections comprise shallow marine carbonates changing upward and laterally to a predominantly siliciclastic coastal and alluvial succession, including abundant dinosaur remains. Deposition of coastal and alluvial sediments occurred in flood plains, ephemeral and perennial fluvial channels, aeolian dunes, deltas, distributary mouth-bars and associated distributary channels, and shallow water bodies influenced by both fresh and marine waters. Some of these deposits, notably those of aeolian and ephemeral fluvial origin, are characteristic of arid to semiarid climates. However, there are also abundant deposits that can be demonstrably shown to have a coeval origin, which are indicative of permanent water courses: (i) sediments of seasonal discharge fluvial channels with perennial to semi-perennial flow, displaying subcritical and supercritical flow sedimentary structures; (ii) deltaic sediments deposited in permanent freshwater bodies; and (iii) abundant plant and dinosaur remains, especially of herbivorous dinosaurs, which required the presence of permanent water sources and abundant vegetation. These apparently contrasting sedimentary features indicate that deposition occurred under a seasonal climate controlled by monsoonal-type precipitation. These deposits are analogous to those observed nowadays in the Lenc ß ois Maranhenses National Park (north-east Brazil), where a subhumid tropical climate with a seasonal precipitation pattern prevails. Thus, this study shows that only through careful facies analysis and interpretation of depositional processes that can be shown to be occurring concurrently in 975

The sedimentological expression of transgression–regression cycles upon aeolian–marine margins

“…Early work focussed on the sedimentary facies observed within the contemporaneous aeolian‐marine environments, along with their spatial relationships (Chan, 1989; Loope, 1981) and sedimentary architecture (Fryberger, 1984; Huntoon & Chan, 1987). Later work considered autocyclic controls within aeolian‐marine margins, such as the influence of a fluctuating water table on accumulation and architecture of coastal aeolian systems (Crabaugh & Kocurek, 1993; Kocurek et al, 2001), whereas, more recent studies have interpreted the aeolian‐marine deposits in a sequence stratigraphic context and focussed on the complex influence of allocyclic controls, such as climate and sea‐level change on the deposits (Campos‐Soto et al, 2022; Jordan & Mountney, 2010, 2012; Rankey, 1997; Wakefield & Mountney, 2013). Therefore, a detailed study on the interactions between marine margin and continental depositional processes has the potential to improve predictive sedimentary models.…”