Forced-regressive conditions have been widely described by sequencestratigraphic conceptual models, and the resulting deposits have been widely documented in sequences and parasequences. However, how forcedregressive conditions might impact on the short-term to mid-term evolution and the high-resolution stratigraphic record (10 2 to 10 5 kyr) of barred shoreline environments represents an unexplored issue. This contribution presents a bedset characterization of Lower Cretaceous, barred shoreline deposits accumulated after a relative sea-level fall. Parasequence PS400 of the Pilmatu e Member in the Neuqu en Basin (Argentina) comprises several bedsets, most of them bounded by transgressive surfaces. However, one of them, the bedset BS400.5, is bounded below by a high-relief surface of truncation, here interpreted as an erosional regressive surface. This surface indicates incision of the underlying deposits and the onset of forced-regressive conditions at intra-parasequence scale. The internal architecture of the studied bedset exhibits seaward-dipping clinoforms that bound clinothems within the upper-shoreface deposits. These clinoforms were interpreted as the result of seaward-shifting events during the shoreline progradation. A sequence-stratigraphic conceptual model is proposed for the high-frequency evolution of a barred shoreline under forced-regressive conditions. The model explains how the intra-bedset evolution under low and stillstand sealevel conditions and cross-shore imbalances in the sediment budget controlled the exceptional preservation of bar and rip-channel deposits.
The intra-parasequence scale is still relatively unexplored territory in high-resolution sequence stratigraphy. The analysis of internal genetic units of parasequences has commonly been simplified to the definition of bedsets. Such simplification is insufficient to cover the complexity involved in the building of individual parasequences. Different types of intra-parasequence units have been previously identified and characterized in successive wave-dominated shoreface–shelf parasequences in the Lower Cretaceous Pilmatué Member of the Agrio Formation in central Neuquén Basin. Sedimentary and stratigraphic attributes such as the number of intra-parasequence units, their thickness, the proportions of facies associations in the regressive interval, the lateral extent of bounding surfaces, the degree of deepening recorded across these boundaries, and the type and lateral extent of associated transgressive deposits are quantitatively analyzed in this paper. Based on the analysis of these quantified attributes, three different scales of genetic units in parasequences are identified. 1) Bedset complexes are 10–40 m thick, basin to upper-shoreface successions, bounded by 5 to 16 km-long surfaces with a degree of deepening of one to three facies belts. These stratigraphic units represent the highest hierarchy of intra-parasequence stratigraphic units, and the vertical stacking of two or three of them typically forms an individual parasequence. 2) Bedsets are 2–20 m thick, offshore to upper-shoreface successions, bounded by up to 10 km long surfaces with a degree of deepening of zero to one facies belt. Two or three bedsets stack vertically build a bedset complex. 3) Sub-bedsets are 0.5–5 m thick, offshore transition to upper-shoreface successions, bounded by 0.5 to 2 km long surfaces with a degree of deepening of zero to one facies belt. Two or three sub-bedsets commonly stack to form bedsets. The proposed methodology indicates that the combination of thickness with the proportion of facies associations in the regressive interval of stratigraphic units can be used to discriminate between bedsets and sub-bedsets, whereas for higher ranks (bedsets and bedset complexes) the degree of deepening, lateral extent of bounding surfaces, and the characteristics of associated shell-bed deposits become more effective. Finally, the results for the Pilmatué Member are compared with other ancient and Holocene examples to improve understanding of the high-frequency evolution of wave-dominated shoreface–shelf systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.