Akey to prediction of depositional facies in sandstones, carbonates, or siliceous mudrocks is an understanding of the processes forming these deposits. Past studies of modern mud environments coupled with recent laboratory flume investigations (Schieber and Yawar, 2009) show that mud is a dynamic sediment controlled by many of the same lateral, traction transport processes that affect coarser sediment particles. In this presentation, a portion of the 1600-km-long shallow water Amazon dispersal system (ADS) is utilized to illustrate the sedimentary processes that form many of the sedimentary structures found in the strata of the Barnett (Mississippian), the Haynesville (Upper Jurassic), and the Mancos (Cretaceous) shales in the U.S. Some large-scale depositional facies patterns found within the ADS are also compared with similar patterns within the Mancos.

Examination of small scale characteristics, shows that laminations and scour features found in the subtidal to intertidal sediments of the ADS are formed by fluidized mud pushed by longshore currents (Rine and Ginsburg, 1985). In the deepwater Barnett, similar features are created by high density flows driven by gravity (Loucks and Ruppel, 2007). The high degree of bioturbation found in the Haynesville Shale can be found in the more distal offshore edge of the coastal ADS mud wedge or in the nutrientrich ebb-tidal deposits of the adjoining coastal estuaries. Regarding the Mancos Shale, on the small scale ADS strata associated with migrating mud banks contain sedimentary structures that resemble the laminated and scoured “hyperpycnites” of the Mancos as described by Bhattacharya and MacEachern, (2009).

When comparing the Mancos Shale with ADS sediments on a depositional-facies-scale, the ADS offers a good analogue for

Figure 1. Block diagram showing relative distribution of depositional facies along the coast of Suriname in South America. The typical mud bank is 50 to 60 km long, 10 to 20 km wide, and up to 5 m in relief. Along the coast and inner shelf of Suriname coast, these mud banks migrate 1.5 km annually. From Rine and Ginsburg, 1985.

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depositional facies patterns found in the Mancos of east-central Utah where swallow carbonates, shelf sandstones, and fine-grained distal delta deposits are juxtaposed (Pattison et al, 2009; Chan, 1992). Within the Quaternary sequence of the ADS, variations in sediment input from the Amazon River combined with fluctuations in sea level create a depositional facies pattern that is dominated by fine-grained sediments but also contains significant deposits of sand and even lenses of carbonates. Similar facies patterns present in the Mancos of eastern Utah can also be explained by similar sedimentary processes that have lateral transport of mud sediments as a critical component.

Figure 2. Aerial view of exposed mud bank at low tide showing surface flow features within the fluid mud. Approximate width of view is 500m.

Figure 3. Isolated coarse-grained sandstone body is within the shelfal portion of the Mancos Shale, Middle Mountain to Floy Wash region of the Book Cliffs, east-central Utah. This trough cross-bedded sandstone contains mudstone clasts, shell debris, fish teeth, bone fragments, and marinebored wood fragments (Pattison et al, 2009). Photo is from Stop 12, AAPG Field Trip No. 18.

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