The Burditt Marl

Introduction

The Burditt Marl is a chalky marl, of approximately 5 meters thickness at this location in northern Travis County.  It directly overlies the fossiliferous upper Dessau chalk, and is overlain in turn by the marly chalks of the Pflugerville Formation.  An oyster bed has been reported from about the center of the formation, but it is not obvious at this location.  Two complete exposures are shown below.

Exposure 1

The uppermost Dessau Chalk (here grey and rubbly in appearance) is truncated by an unconformity.  Five meters of the Burditt are exposed, and "capped" by 1 meter of white to tan chalk of the Pflugerville Formation.

Excavations show the less weathered Burditt.  Flags are placed at 1/3 meter intervals.

A spike (in this case not golden) marks the approximate transition across the uncomformity marking the base of the Burditt.

Exposure 2

At a nearby exposure this unconformity in more clearly visible.   The hammer marks this undulating surface.

A washout gully shows clean exposures of the Burditt.

Here the gradational contact with the Pflugerville is exposed.  The hammer marks the interval over which this transition takes place.