MID-CRETACEOUS PALEOPEDOLOGY AND LANDSCAPE RECONSTRUCTION OF THE MID-ATLANTIC US COASTAL PLAIN

We identified and described Potomac Formation paleosols from three coreholes in New Jersey and Delaware to interpret depositional history and reconstruct regional landscapes during the climatic transition from the Early to the Late Cretaceous. In total, 103 paleosol profiles were described and grouped into five pedotypes (gray, gray-red, purple, red, and brown) ranging in pedogenic maturity from: 1) weakly developed, immature soils formed under poor drainage conditions (gray and gray-red); to 2) moderately developed soils formed under alternating drainage conditions (purple and red); to 3) well-developed, mature soils formed under well-drained conditions (brown). Geochemical and stable-isotope proxies (Ba/Sr and delta O-18 on sphaerosiderite) are presented to constrain paleoprecipitation and/or fluvial position and drainage conditions. Potomac Formation Unit I (Barremian to lower Albian) generally displays well-drained, stable landscape conditions upsection, with paleoprecipitation being the main control on development of paleosol type. Potomac Formation Units II (lower Albian to lower Cenomanian) and III (lower Cenomanian) have variable drainage and landscape conditions upsection. Paleoprecipitation exerted a controlling role in the development of paleosol type lower in Unit II, while base-level changes exerted greater influence on landscape conditions upsection into Unit III. Geochemical proxies provide evidence that Unit I was subhumid with episodes of saturation and overall better drainage conditions relative to the overlying units. Units II and III were deposited under more waterlogged conditions, experiencing subhumid to humid conditions, with episodes of enhanced drainage from base-level fall. The use of these proxies is consistent with interpretations made using the macro-features and micro-features of the paleosols and sphaerosiderite delta O-18, and emphasizes that the main long-term environmental control on landscape development during this period was initially paleoprecipitation, with progressive influence from base-level changes.