Anatomy of a laterally migrating tidal bar in front of a delta system: Esdolomada Member, Roda Formation, Tremp‐Graus Basin, Spain

Abstract

The first sandstone unit of the Esdolomada Member of the Roda Formation (hereafter referred to as 'Esdolomada 1') was formed by a laterally-migrating, shelf tidal bar. This interpretation is based on detailed mapping of the bedding surfaces on the digital terrain model of the outcrop built from light detection and ranging data and outcrop photomosaics combined with vertical measured sections. The Esdolomada 1 sandbody migrated laterally (i.e. transverse to the tidal currents) towards the south-west along slightly inclined (1.6°to 4.6°) master bedding surfaces. The locally dominant tidal current flowed to the northwest. This current direction is indicated by the presence of stacked sets of highangle (average 21°) cross-stratification formed by dunes that migrated in this direction, apparently in an approximately coast-parallel direction. The tidal bar contains sets and cosets of medium-grained cross-stratified sandstone that stack to reach a thickness of about 5AE5 m. Individual cross-bed sets average about 50 cm thick (with a range of 10 to 70 cm) and have lengths of ca 130 to 250 m in a direction perpendicular to the palaeocurrent. Set thickness decreases in the direction of migration, towards the south-west, and the degree of bioturbation increases, so that the cross-bedded sandstones gradually change into highly bioturbated finer-grained and thinner-bedded sandstones lacking any crossstratification. The rate of thinning of individual dune sets as they are traced down any obliquely-accreting master surface is some 40 cm per 100 m (0AE004) for the older, thicker sandstones, whereas the younger, thinner beds thin at a rate of 15 cm over 100 m (0AE0015). The tidal bar has a sharp base and top and is encased in finer-grained bioturbated, marine sandstones. The Esdolomada bar crest was oriented north-west to south-east, parallel to the tidal palaeocurrents and to the nearby palaeoshoreline, but built by lateral accretion towards the south-west. Lateral outbuilding generated a flat-topped bar with a measured width of about 1700 m, and a preserved height of 5AE5 m. The bar, disconnected from a genetically related south-westward prograding delta some 2 km to the north-east, developed during the transgressive phase of a sedimentary cycle. The tidal bar was most probably initiated as a delta-attached bar at the toesets of the delta front and during transgression evolved into a detached tidal bar.

Environmental variability of Macaronichnus ichnofabrics in Eocene tidal-embayment deposits of southern Patagonia, Argentina

“…Savrda & Uddin ; Olariu et al . ). As well, secondary colonization and its controls are rarely explored in these studies.…”

Palaeo-Orinoco (Pliocene) channels on the tide-dominated Morne L'Enfer delta lobes and estuaries, SW Trinidad

“…potential, due to burial during the ensuing dominant current (Dalrymple, 1984;Dalrymple and Choi, 2007;Olariu et al, 2012b). For example, the mud-draped sets of cross-strata shown in Fig.…”

“…For example, the mud-draped sets of cross-strata shown in Fig. The compound dunes are commonly components of downstream-accreting tidal bars in estuaries and are developed within channels (Barnhill, 1994;Greb and Martino, 2005;Wizevich, 1991Wizevich, , 1993 but are also common in front of the shoreline or on the shelf (Olariu et al, 2012b). In many tide-dominated estuaries, such bedforms develop into compound dunes, with smaller dunes riding on the backs of the larger dunes.…”

Middle Turonian trace fossils from the Bystrzyca and Długopole sandstones

“…Pem ber ton et al (2001), who re ferred on a sim i lar as sem blage of trace fos sils, placed the suc ces sion con tain ing Thalassinoides, Palaeophycus and Ophiomorpha in the up per off shore, whereas de pos its rich in Ophiomorpha, Macaronichnus in the mid dle-lower shoreface. In com par i son to other nearshore trace fos sils as sem blages (lower shoreface-up per off shore set tings) in clud ing Macaronichnus, Ophiomorpha, Palaeophycus, Thalassinoides, the ma jor ity of them were re corded from the storm-orig i nated de pos its (Frey and Pem ber ton, 1991;MacEachern et al, 1999;Bann and Fieding, 2004;Bann et al, 2004;Gani et al, 2008;Rygel et al, 2008;Schwarz, 2012) or bar set tings (Curran, 1985;Pol lard et al, 1993;Olariu et al, 2012;Sullivan and Sullivan, 2012).…”