Genesis and preservation of antidune stratification in modern and ancient washover deposits

Conference · Tue Mar 01 04:00:00 EST 1983 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6375128

Barwis, J H; Hayes, M O

Antidunes are nearly symmetrical, sinusoidal bed forms formed by near-critical flows, and comprise all bed profiles in phase with surface gravity waves in the overlying flow. This definition applies regardless of bed-form propagation direction or mode of formation. They occur in a wide range of depositional environments but are ubiquitous in the swach zones of fine-grained beaches. On washovers at Seabrook Island, South Carolina, antidune trains form at the fan apex, in phase with an undular hydraulic jump. This jump marks the transition within the overwash surge from supercritical flow of the berm crest to subcritical flow on the fan itself. Steamwise boundaries of the antidune field are abrupt. Whin the field itself, both crest amplitude and crest spacing decrease downfan with decreasing velocity. Bedding geometry is controlled by bed-form scale, by the pulsing nature of the flow and by eolian deflation during neap tides and fair weather. Upstream antidunes produce thin lenses of backset laminae which are commonly truncated by flat beds or superposed backsets. Orthoquartzitic washovers in the Carboniferous of Kentucky and the Ordovician of South Africa display well-preserved antidune formset geometries. Although the very well-sorted, monomineralic nature of these sandstones renders internal stratification nearly invisible, backset laminae are apparent. Many published photographs of flat beds contain unrecognized examples of antidune stratification. In many places, the antidune cross-laminae would be impossible to detect without heavy minerals or other markers to accentuate bedding. Moreover, antidunes may be responsible for much of the low-angle truncation normally associated with flat-bedded facies.

• Research Organization: Shell Oil Co., Houston, TX
• OSTI ID: 6375128
• Report Number(s): CONF-8304200-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 67:3
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
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03 NATURAL GAS
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GEOLOGIC DEPOSITS
GEOLOGIC TRAPS
GEOLOGY
LITHOLOGY
MINERAL RESOURCES
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RESOURCES
SEDIMENTATION
STRATIFICATION
STRATIGRAPHY