Clear as mud

• Main Author: Podrecca, Luca
• Format: Text
• Language: unknown
• Published: No Publisher Supplied 2019
• Subjects: Wilson Lake; Planktonic foraminifera
• Online Access: https://dx.doi.org/10.7282/t3-6wp4-n191; https://rucore.libraries.rutgers.edu/rutgers-lib/60046/

The Paleocene/Eocene boundary and attendant Paleocene-Eocene Thermal Maximum (PETM) marks a time of rapid global climatic change. New Jersey shelf sediments of the Marlboro Formation record the PETM with exceptionally thick preservation (up to ~15 m at Wilson Lake) during the period of global low carbon isotopic values (“the core”) which requires minimum sedimentation rates near 10 cm/kyr. Rhythmic layers have previously been reported from both Wilson Lake & Millville, NJ (IODP Leg 174AX). These structures, dubbed ‘couplets’, consist of semi-periodic, 1-2 mm thick, raised laminations separated by typically homogenous sediment layers of varying width averaging 1.27 cm at Medford as opposed to nearly 2 cm at Wilson Lake and Millville. Previous studies have dismissed these structures as artifacts ('drilling biscuits’) produced by drilling mud. I report here on a series of shallow (<65 ft; ~19.81 m) auger cores drilled without using drilling fluid along a downdip transect at Medford, NJ. These cores show similar couplets on the ~1 - 2 cm scale, indicating that they are in fact primary depositional features. The mm-width laminae in the auger cores experienced remarkable swelling within minutes of splitting. XRD, XRF, bulk carbonate geochemistry, and grain size analysis were measured throughout the Medford auger cores. I analyzed differences in these parameters between the laminae and interspersing bulk material, and then made comparisons with data collected at other sites along the New Jersey Coastal Plain (NJCP). I find no uniform discernible difference in lithology between laminae and beds, other than a higher percentage of kaolinite in some laminae. In general, the Marlboro Formation at this updip location consists of micaceous, lignitic, silty clay (mean size < 2 m) with occasional organic debris indicating proximal deposition in a prodelta setting. A paleodepth of ~40 m is estimated from a paleoslope model and normal marine salinities are inferred from the presence of common, though not abundant, planktonic foraminifera. I propose a model of deposition for the Marlboro Formation as being driven by fluid mud (near-bed suspension flows) transport associated with the “Appalachian Amazon”, implying that the extremely fine-grained Marlboro Clay was deposited at Medford as part of a sigmoidal shaped subaqueous clinoform. The clinoform model explains the differential preservation of the Vincentown Formation, transitional units, and the CIE onset, “core”, recovery, and overlying units along a dip transect across the paleoshelf. The laminations discussed here have analogs in modern environments characterized by muddy continental shelves and are associated with episodic or possibly quasi seasonal events of increased riverine discharge and the attendant migration of the benthic salinity front.