29The facies characteristics and stratigraphic architectures of ancient mixed, wave-and tide-influenced 30 deltas are poorly documented, despite the abundance of analogous modern shorelines. This paper 31 presents the first facies analysis and stratigraphic-architectural characterization of the distal part of 32 the Cretaceous lower Sego Sandstone (Book Cliffs, Colorado, USA), whose correlative proximal part 33 is arguably the most comprehensively documented example of ancient deltaic strata that exhibit 34 evidence for the activity of tides and waves.
36The distal lower Sego Sandstone consists of tide-dominated and wave-dominated deposits arranged
55These facies components and their architectural arrangement suggest that tides and waves operated 56 together throughout deposition of the "lower Sego Delta", but that tide-dominated and wave-57 dominated deposits were spatially partitioned into the proximal and distal parts of each regressive-
Existing facies models of tide-dominated deltas largely omit fine-grained, mud-rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well-preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non-channelized tidal bars and tidal channels. Non-channelized tidal bars comprise coarsening-upward sandbodies, including large, downcurrent-dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as singlestorey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward-facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically-accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along-strike variability defines a similar large-scale architecture in both parasequence sets: a deeply scoured channel belt characterized by widespread inclined heterolithic strata is eroded from the parasequence-set top, and flanked by stacked, non-channelized tidal bars and smaller channelized bodies. The tide-dominated delta is characterized by: (i) the regressive stratigraphic context; (ii) net-progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary channel infill and tidal bar accretion at the delta front. The detailed facies analysis of this fine-grained, tide-dominated deltaic succession expands the range of depositional models available for the evaluation of ancient tidal successions, which are currently biased towards transgressive, valley-confined estuarine and coarser grained deltaic depositional systems.
The transition from Rotliegend to Zechstein within the Southern Permian Basin is one from continental desert to a marine environment. During the Upper Rotliegend II a huge playa lake existed there. This lake was temporarily influenced by precursors of the Zechstein transgression. Therefore the mega-playa evolved into a sabkha system. One of these early marine ingressions is known from an outcrop in Schleswig-Holstein. Laminated silt-and claystones, deposited within a standing water body, are intercalated in siltstones of a salt-flat environment. The lake sediments are characterised by high frequency cyclicity, shown by the sedimentary record and also by palaeontological data. The section contains fresh water as well as brackish-marine and marine fauna. Climatically forced cycles interact with marine incursions. After the Zechstein transgression had flooded the basin completely, sedimentation was controlled by sea-level fluctuations. Two sections, in the southern North Sea and in Schleswig-Holstein, are presented in this paper. Cyclicities with different frequencies controlled the sedimentation of the Kupferschiefer (T1) and the Werra Carbonate (Ca1). Sediments of the North Sea sequence were deposited within a shallow bay at the margin of an elevation. Therefore, the high frequency cyclicity became obvious within the sedimentary patterns and in the faunal content.
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