Chapter 10 - Massive mudstones in basin analysis and paleoclimatic interpretation of the Newark Supergroup

Abstract

Abstract Massive red or gray mudstones, which occur at the tops of 2- to 10-m-thick sedimentary cycles, constitute a large portion of the Newark Supergroup. The mudstones can be separated into four distinct types; each type can be related to a specific set of paleoenvironmental conditions through analogy to modern sedimentary environments. Mudcracked massive mudstone, dominated by narrow, jagged polygonal cracks and millimeter-scale, cement-filled vugs, is interpreted as subaerial, playa mud-flat deposits. Burrowed massive mudstone, dominated by sediment-filled tubes having constant diameters and commonly containing soft-sediment deformation features, deep, narrow mud cracks, and lacustrine fossils, is interpreted as intermittently exposed shallow lake or swampy flood-plain deposits. Root-disrupted massive mudstone, dominated by small, cement-filled tubes that taper and bifurcate and containing mud cracks, syndepositional carbonate nodules, and burrows, is interpreted as vegetated flood-plain, lake-margin, or overbank deposits with soil development. Sand-patch massive mudstone, characterized by irregularly shaped pods of sandstone and siltstone that have angular to cuspate margins, internal zones of different grain sizes, and jagged internal cracks and commonly containing evaporite crystal molds, is interpreted as the deposits of a saline mud flat. Mud-cracked massive mudstone and sand-patch massive mudstone occur only in the northern Newark basins, while burrowed massive mudstone and root-disrupted massive mudstone dominate in the southern basins but also occur within certain stratigraphic intervals within the northern basins. These occurrences suggest that paleolatitude limited arid conditions to the northern basins and that temporal changes in paleoclimate were also important. If there were unique depositional periods of dry versus wet conditions, they may be used as chronostratigraphic markers for correlation between basins and across lithologies within basins.