SEQUENCE STRATIGRAPHIC IMPLICATIONS OF VIVIANITE IN THE UPPER PART OF THE MAASTRICHTIAN-DANIAN HORNERSTOWN FORMATION, NEW JERSEY

A 1.1 meter thick layer containing vivianite [Fe₃(PO₄)₂•8H₂O] nodules, bladed crystals, and partially to completely replaced brachiopods occurs in the upper part of the Maastrichtian-Danian Hornerstown Formation (HF) at Inversand Quarry, Sewell, New Jersey. The vivianite layer is contained in a Oleneothyris harlani biostrome, the uppermost fossil assemblage in the HF, ca. 1 m below the contact with the overlying upper Paleocene Vincentown Formation, and ca. 4 m above the end-Cretaceous Main Fossiliferous Layer (MFL) bonebed. The HF is a ca. 5.5 m thick, unconsolidated marl, containing up to 90% glauconite, deposited during a period of marine transgression, as indicated by increasing glauconite maturity in the lower part of the formation.

Samples were taken at 10 cm spacing through the layer. End-member vivianite is colorless. In outcrop at Inversand, crystals are light blue in color, indicating partial oxidation; however, XRF and XRD analyses confirm that the crystals are vivianite, not metavivianite.

Vivianite forms in reducing environments with high Fe²⁺ and HPO₄^2- activities; and has been reported in low temperature hydrothermal deposits, soils; and the sediments of fluvial, estruarine, lacustrine, and marine systems. Vivianite occurrences in marine deposits are infrequently reported, as higher sulfide concentrations preclude vivianite formation. Within marine deposits, vivianite can be of either allochthonous or authigenic origin. We conclude the vivianite from the upper HF is authigenic in nature, as indicated by the inclusion of glauconite pellets within some nodules/crystals.

It has been proposed that a bathymetric control exists on the distribution of authigenic P bearing minerals in marine systems. Greater depths are associated with more prevalent and severe bottom water anoxia; resulting in an increased prevalence of authigenic P bearing minerals. Thus, the presence of authigenic vivianite in the upper HF could potentially be interpreted as a maximum flooding surface (mfs) indicator. Vivianite as a mfs indicator supplements previous systems tract modeling of K/Pg New Jersey strata that place a mfs in the upper HF. We suggest that a period of deepening may have increased anoxia, while Fe sourced from glauconite and PO₄ from organic matter allowed for the formation of vivianite in the upper HF.