Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

Abstract

A B S T R A C TClinoforms are inclined and normally basinward-dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems. The study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir, seal and source rocks along shoreline to basin-floor profiles.Here, we review clinoform research and propose a more systematic description and classification of clinoforms. This is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions, together with the genesis, drivers and dynamics of their constituent sedimentary units.Four basic clinoform types are here distinguished in delta/shorelines, lacustrines and marine environments, on the basis of their overall spatial and temporal scale, morphology, outbuilding dynamic and geodynamic and depositional setting: (1, 2) delta-scale clinoforms, which in turns are sub-divided into shoreline and delta-scale subaqueous clinoforms; (3) shelf-edge clinoforms; and (4) continental-margin clinoforms. Delta-scale clinoform sets are tens of metres high and typically represent 1-10 3 kyr, with progradation rates ranging from 1,000-100,000 m/kyr for shorelines and "subaerial deltas" to 100-20,000 m/kyr for subaqueous deltas; shelfedge clinoform sets are hundreds of metres high and are nucleated and accreted in 0.1-20 Myr (usual progradation rates of 1-100 m/kyr) by successive cross-shelf transits of delta-scale clinoforms; continental-margin clinoform sets are thousands of metres high, hallmark key geodynamic/crustal boundaries (e.g., continent/ocean transition) and slowly prograde basinwards in ca. 5-100 Myr, with typical rates of 0.1-10 m/kyr. As a consequence of the very different progradation rates and of the difficulty of large-scale clinothems to backstep during transgressions, shorelines are the most dynamic clinoforms with regards to position, continental margins the least, and shelf-edges are intermediate. Shortly after a transgression, therefore, the four clinoform types may prograde synchronously along shoreline-to-abyssal plain transects, forming "compound clinoform" systems. During the subsequent regressive cycle, however, due to the dissimilarity in progradation rates, different clinoform types will normally merge progressively with each other, giving rise to "hybrid clinoforms" (e.g., shelf-edge deltas), and fewer depositional breaks-in-slope are distinguished along a single shoreline-toabyssal plain transect. Overall, all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum, regulated by the cyclical backstepping of the smallerscale system within natural progradational-retrogradational cycles of larger-scale clinothem outbuilding.All clinothem types may show either an accretionary/active or draping/passive style, depending on the proximity to the sediment source. Draping clinothems are nearly...

Progradation Rates Measured at Modern River Outlets: A First‐Order Constraint on the Pace of Deltaic Deposition

“…These rates are not representative of parts of the coastline away from fluvial entry points where basinal processes are expected to be more pronounced, and in situ investigation is required to determine how the measured rates are expressed in the subaqueous part of the shoreline clinoform. We emphasize that the measured progradation rates are not representative of the progradation of the entire shoreline‐subaqueous delta composite clinoforms or shelf‐edge clinoforms (Patruno & Helland‐Hansen, ), which occur over much larger spatial and temporal scales than the morphological changes we have investigated.…”

Mud‐rich delta‐scale compound clinoforms in the Triassic shelf of northern Pangea (Havert Formation, south‐western Barents Sea)

“…Seismic profile flattened on top Permian, showing the Havert Formation shelf‐margin clinoforms (or shelf‐edge clinoforms; Patruno & Helland‐Hansen, ). The position of the cored intervals with respect to the overall clinoform morphology is shown (yellow squares).…”

Nested intrashelf platform clinoforms—Evidence of shelf platform growth exemplified by Lower Cretaceous strata in the Barents Sea

“…Considering their toplap surface is a clinoform foreset itself in several places, a horizontal restoration of this surface can be ruled out. If these clinothems are platform‐edge deltas (shelf‐edge deltas sensu Patruno & Helland‐Hansen, ), it implies the improbable scenario that they recorded a relative sea‐level fall that matched the full platform height (>250 m) several times during the platform growth. This is supported by the absence of any discernible erosional scours at the rollover zone or in the topset strata.…”