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This study presents a lithology-based sequence-stratigraphic framework and depositional model for Lower Cretaceous, mixed siliciclastic-carbonate sediments of the Mid-Atlantic coastal plain (eastern United States). Lithologic data from cores and cuttings were integrated with wireline logs and two-dimensional seismic data to document lithofacies variability and stacking patterns across the Albemarle Basin of eastern North Carolina. Ten facies associations are defined, which are variably present within siliciclastic- and carbonate-dominated depositional profiles interpreted to extend from onshore lowland coastal plain to deep-shelf depositional environments. Three depositional sequences (0, 1, 2) were identified, each with component upward-shoaling parasequences. Seismic reflectors typically coincided with key sequence-stratigraphic surfaces, which guided correlations between wells. Parasequences are grouped into parasequence sets with progressive progradational or retrogradational (highstand and transgressive systems tracts, respectively) stacking patterns. Transgressive parasequences are thinner, uniform in thickness, and tend to be more dominated by molluskan carbonate facies. Highstand parasequences have more variable thickness, are siliciclastic dominated, and tend to be progradational on seismic data. Late highstand deposits of sequence 1 are dominated by restricted carbonate facies that likely reflect increased aridity. Lowstand deposits were not recognized from onshore well and seismic data. The sequence-stratigraphic framework developed documents the complex spatial and temporal facies relationships within a wave-dominated, mixed carbonate-siliciclastic passive-margin succession. The strata studied document the complex interplay of lithofacies within a transition zone between near-shore carbonate-dominated strata to the south (Southeast Georgia Embayment) and siliciclastic-dominated marginal-marine successions to the north (Baltimore Canyon Trough). It also provides a useful stratigraphic calibration set for coeval offshore sediments that have been identified as potential areas for hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

Palaeogene passive margin sediments on the US mid-Atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate–siliciclastic shelves. This study utilizes well cuttings, outcrop, core, and seismic data to document temporal and spatial variations in admixed bryozoan-rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone. This zone was situated between north-flowing, warm waters of the ancestral Gulf Stream (carbonate dominated settings) and south-flowing, cold waters of the ancestral Labrador Current (siliciclastic dominated settings). Some degree of mixing of carbonates and siliciclastics occurs in all facies; however, siliciclastic-prone sediments predominate in nearshore settings, while carbonate-prone sediments are more common in more open marine settings of the inner shelf break and deep shelf. A distinctive dual-break shelf depositional profile originated following a major Late Cretaceous to Palaeocene transgression that drowned the earlier shallow platform. This profile was characterized by prominent mid-shelf break dividing the shallow shelf from the deep shelf and a major continental shelf/slope break. Incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin. Storm wave base also contributed to the preservation of the dual-break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid-shelf break. Sediment fines in deep shelf facies were produced in place, transported downdip from the shallow shelf by storm ebb currents and boundary currents, and reworked from adjacent areas of the deep shelf by strike-parallel boundary currents. Regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf, with warmer waters and more humid climates favouring carbonate deposition and cooler, more arid conditions favouring glaucony and siliciclastic dominated deposition. Continuous wave and current sweeping of the shallow shelf favoured deposition of mud-lean facies across much of the shallow shelf. Skeletal components in much of the carbonate-rich strata formed in warm, nutrient-rich subtropical waters, as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages. These indicators of warm water deposition within the bryozoan-mollusk-rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage; such facies generally are associated with cooler water depositional settings. [ABSTRACT FROM AUTHOR]

Abstract: Exposed, uplifted Miocene carbonate sequences of the Cape Range, North West Cape, Western Australia, provide outcrop analogues of seismic sequences from offshore parts of the shelf. Facies include deep shelf marls (very fine and fine packstone), larger foram wackestone, floatstone and muddy rudstone, foram-coralline algal skeletal fragment packstone–wackestone (shallow seagrass facies), lagoonal wackestone–mudstone with scattered corals, and tidal flat laminites. The exposed Early Miocene units include the Mandu highstand, a sequence in the Tulki and one in the Middle Miocene Trealla Limestone. Sequences contain decameter scale (5–20 m thick), 4th-order parasequences evident on gamma ray logs and by facies stacking, that shallow and coarsen up; they appear to be due to eccentricity driven sea-level changes which may have been up to 50 m. Higher frequency meter-scale parasequences of deep water marl up into larger foram rudstone/floatstone (perhaps precession/obliquity) are evident at the base of the exposed Mandu section. These parasequences are not merely random storm deposits. This is indicated by the covariance of C and O isotopes, with the lighter values associated with deepening and deposition of deep shelf marls, and the heavier values being associated with shallowing and deposition of larger foram facies. The uplifted Miocene continental shelf sediments of the North West Cape preserve a record of eustasy, paleoclimate and paleoceanography and thus provide a window into factors affecting the shelf, that can be compared with coeval, better studied deep sea cores. [Copyright &y& Elsevier]