SEDIMENTATION PROCESSES IN THE TRIASSIC NEW HAVEN ARKOSE, HARTFORD GROUP, NEWARK SUPERGROUP

The upper New Haven Arkose (U. Triassic - ?L. Jurassic) near Meriden, Connecticut was deposited in a paleo-river system within a rift basin. The lithology of the channel and floodplain facies include arkosic sandstones, pebbly sandstones, siltstones, and mudstones. Channel bodies are single- to multi-storey narrow sheets (w:d ~ 15-100:1) with 3.4m average thickness. These incised channels contain central bodies of largely structureless pebbly sandstone with local lateral accretion sets and wings that thin laterally. Floodplain deposits comprise sheet complexes of red sandstone, siltstone, and mudstone up to 25 m thick. Sparse paleocurrent data suggest a trunk-drainage system. A humid, but seasonal paleoclimate is indicated by extensive bioturbation in both sandstones and mudstones as well as other sedimentologic features. This contrasts with prior interpretations of a dry climate, based on the presence of subordinate "calcrete" carbonates.

The framework grains within the sandstones and siltstones include quartz, feldspar, mica, rock fragments, and pedogenic mud aggregates. Pedogenic mud aggregates are sand- to silt-sized particles composed mainly of densely-packed clay flakes. They are produced as surface peds within vertic soils with expandable clays during seasonal wetting and drying. With flooding, these aggregates can be easily eroded and transported as bedload within fluvial systems. Pedogenic mud aggregates have been identified in the channel and floodplain sandstones and siltstones of the upper New Haven Arkose. They are best preserved where the associated framework grains protected them from compaction or where early carbonate cementation maintained their integrity. The Triassic paleo-river system contained shallow aggradational channels with relatively coarse-grained floodplains and immature, cumulative paleosols. Channel wings show frequent overbank flows, allowing for floodplain reworking and aggregate mobilization.