Sequence architecture of ancient rocky shorelines and their response to sea-level change: an Early Jurassic example from South Wales, UK

Abstract

The sea-cliffs of Ogmore-by-Sea in Glamorgan, South Wales, expose a succession of Early Jurassic nearshore carbonates that drape rocky palaeoplatforms. A sequence-stratigraphic interpretation allows the recognition of four retrogradationally stacked parasequences, the internal facies architecture of each of which is controlled by the bathymetry and geometry of the underlying shore platforms. Preserved facies are interpreted as representative of foreshore, shoreface and offshore environments. Supratidal facies are absent, but representative storm-terrace clast assemblages are preserved in all lithofacies as a result of the cannibalization of the backshore during periods of shoreline retreat driven by sea-level rise. Biostratigraphical calibration allows the reconstruction of sea-level history and the correlation of regionally important flooding surfaces in the Rhaetian-Sinemurian of Southern Britain with the position of the contemporary shoreline. This suggests that platform incision in South Wales occurred several million years before the onset of major deposition; superseding deposits above ancient rock shore platforms may therefore not be representative of the environment in which coastal incision took place. As one of the best examples of its kind, the rockshore at Ogmore acts as a deposystem model for ancient rocky shores worldwide.

Transgressive Eocene clastic-carbonate sediments from the Circum-Rhodope belt, northeastern Greece: implications for a rocky shore palaeoenvironment

“…The ravinement occurred mostly through coastal erosion and wave abrasion as the shoreface shifted landward along with the rising sea level and shoreline retreat (Fig. As for the lack of convincingly recognized beachface facies, it can be explained with the so-called 'cannibalization' mechanism (see for example Sheppard, 2006), e.g. Fair-weather and possibly storm waves were constantly breaking against the limestone rocky shore by slowly undercutting and carving the cliffs but also removing collapsed (through physical and chemical weathering) talus rubble at the cliff base (e.g.…”

“…Rousse et al, . As for the lack of convincingly recognized beachface facies, it can be explained with the so-called 'cannibalization' mechanism (see for example Sheppard, 2006), e.g. the preexisting beachface deposits have been cannibalized to supply sediment to the shoreface zone during progressive shoreline retreat and sea-level rise.…”

“…Ancient rocky shores provide important information about Precambrian and Phanerozoic sea levels and palaeoshorelines as well as unusual fossil communities (Johnson and Baarli, 2012;Baarli et al, 2014) and trace fossil assemblages (de Gibert et al, 2012). This specific setting has often been developed on limestone substrates affected by various physical, chemical, and biological processes (Semeniuk and Johnson, 1985;Reading and Collinson, 1996;Sanders, 1997;Tropeano and Sabato, 2000;Sheppard, 2006;Bover-Arnal et al, 2011;Baarli et al, 2014). This specific setting has often been developed on limestone substrates affected by various physical, chemical, and biological processes (Semeniuk and Johnson, 1985;Reading and Collinson, 1996;Sanders, 1997;Tropeano and Sabato, 2000;Sheppard, 2006;Bover-Arnal et al, 2011;Baarli et al, 2014).…”

“…The redeposition of material derived from preexisting carbonate rocks is a common process in various sedimentary environments where extraclasts originate from the drainage of river systems in near-coastal regions, rock-falls at shores, supply by means of debris and turbidity flows, and by aeolian transport (Flügel, 2004). Such material may be trapped and reworked in shallow to deep marine and lacustrine settings where concomitant carbonate deposition takes place, resulting in mixed clastic-carbonate sediments (Tropeano and Sabato, 2000;Clifton, 2003;Titschak et al, 2005;Sheppard, 2006;Bover-Arnal et al, 2011). In particular, limestone conglomerates are typical products of wave-influenced beachface and shoreface environments where they record conditions of rapid erosion and burial (Flügel, 2004).…”

“…Many of them have been associated with gravelly beaches and nearshore regions as coarse psephitic deposits may be the only depositional record. This specific setting has often been developed on limestone substrates affected by various physical, chemical, and biological processes (Semeniuk and Johnson, 1985;Reading and Collinson, 1996;Sanders, 1997;Tropeano and Sabato, 2000;Sheppard, 2006;Bover-Arnal et al, 2011;Baarli et al, 2014).…”