Log-ground and Teredolites lagerstatte in a Trangressive Sequence, Upper Cretaceous (Lower Campanian) Mooreville Chalk, central Alabama
Title:
Log-ground and Teredolites lagerstatte in a Trangressive Sequence, Upper Cretaceous (Lower Campanian) Mooreville Chalk, central Alabama
Author:
Savrda, Charles E. King, David T.
Appeared in:
Ichnos
Paging:
Volume 3 (1993) nr. 1 pages 69-77
Year:
1993
Contents:
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 lagerstatte 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.
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