Thick-shelled oysters, belemnoids, and terebratuloids from the Upper Cretaceous Navesink and Mt. Laurel Formations of the New Jersey Coastal Plain show an abundant, diverse, and well-preserved assemblage of microbial and invertebrate borings. Macroscopic examination of invertebrate skeletons reveals large sponge, bivalve, gastropod, and annelid worm borings. Smaller borings in Belemnitella americana were resin-embedded and studied by SEM after acid dissolution of the rostrum skeleton.

On the basis of morphology, size, and distribution patterns of the resin casts, at least a dozen borehole types can be recognized. The largest borings revealed by SEM (small microborings > 1 mm) include acrothoracian barnacles, clionid sponges, and phoronids(?). Mesoborings (100 to 1,000 µ) include bryozoans, clionid sponges, and some large unidentified branched algal(?) tubes. Most microborings cover the range of 1 to 100 µ and include branched tubes and bags of algal and fungal origin. The microborings are the most common and uniformly distributed members of the assemblage.

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