Log‐ground andTeredoliteslagerstatte in a Trangressive Sequence, Upper Cretaceous (Lower Campanian) Mooreville Chalk, central Alabama

Abstract

Teredolites‐bearing log‐grounds occur in extraordinary abundance within basal transgressive deposits of the Upper Cretaceous Mooreville Chalk exposed along Catoma Creek, central Alabama. Wood and borings are virtually restricted to a thin (∼1 m) stratigraphically condensed, shallow‐marine interval characterized by two indurated, Thalassinoides‐burrowed, very sandy, glauconitic, micritic limestones and an intervening glauconitic, muddy sand. Minimum estimates of wood‐substrate densities, measured on extensive bedding‐plane surfaces, range from 1.5 logs/100 m2 in the lower limestone to 6.2 logs/100 m2 in the upper limestone. Owing to early biochemical degradation of wood at or very near the sea floor, the majority of substrates are relict log‐grounds preserved as dense clusters of calcite‐lined, sediment‐ or mineral‐filled borings assigned to Teredolites longissimus, with only remnants of lignified wood in the interstices. Disposition of log‐grounds, which range from 2 to 170 cm (average = 25 cm) in length, is indicative of periodic reworking by currents. As are other recently reported occurrences (Savrda, 1991; Savrda et al., in press), this Teredolites lagerstätte is interpreted to record (1) an influx pulse of xylic substrates into marine environments resulting from transgressive inundation of a forested coastal plain and (2) the concentration of drifted substrates via sediment starvation on a marine shelf, both of which were induced by rapid sea‐level rise. Differences in log‐ground abundances and preservational states between this and previously described condensed‐section occurrences likely are related to differences in absolute water depth and associated fades variations.