Abstract

The Hazel Patch sandstone is an informal unit of the lower Middle Pennsylvanian Breathitt Formation, which is locally dominated by facies containing alternating sand and shale layers, or rhythmic bedding. Three types of rhythmites are defined. Cyclic rhythmites show a sinusoidal vertical stacking trend of thickening and thinning laminae, amalgamated rhythmites show partially or possibly cyclic trends that have been reworked or erosively truncated by overlying formsets, and noncyclic rhythmites show only random thickness distribution and no evidence of original cyclicity. Lower in the sandstone, noncyclic rhythmites are associated with swaly to quasi-planar bedding, even bedding, and ripples with rounded crests, and are inferred to have formed in response to storm waves and combined flows. Higher in the sandstone, noncyclic, amalgamated, and cyclic rhythmites are present in association with herringbone stratification and pinstripe laminae, and are inferred to have formed under the influence of tidal currents. Cyclic tidal rhythmites are present near the base of a shallow channel deposit. These rhythmites contain sandstone-shale couplets indicative of presumed diurnal tides, 11-12 laminae cycles indicative of neap-spring tidal sedimentation, and 25-27 laminae cycles indicative of lunar monthly sedimentation. Upward and laterally within the channel truncation of neap-cycle laminae by spring-cycle ripples, and a loss of continuous clay drapes in amalgamated rhythmites, led to preservation of only monthly or greater depositional cycles. Vertical facies trends in the sandstone are interpreted to indicate upward shallowing from a wave-influenced outer estuarine or shallow shelf environment to an intertidal sand flat to an exposed low-lying coast upon which peats accumulated. The fact that cyclic rhythmites were preserved only in a shallow channel, stratigraphically near the middle of the mail may indicate that accommodation space and a medial estuarine position with little wave reworking and bioturbation controlled the preservation of the various orders of cycles.

You do not currently have access to this article.