Sm. Kidwell et Pj. Brenchley, PATTERNS IN BIOCLASTIC ACCUMULATION THROUGH THE PHANEROZOIC - CHANGESIN INPUT OR IN DESTRUCTION, Geology, 22(12), 1994, pp. 1139-1143
Evolutionary changes in the ecology and diversity of organisms that pr
oduce and destroy calcareous skeletons suggest that bioclastic concent
rations themselves might have changed in nature through the Phanerozoi
c. Empirical data from marine siliciclastic records of Ordovician-Silu
rian, Jurassic, and Neogene ages indicate a significant increase in th
e thickness of densely packed bioclastic concentrations over geologic
time, from a primarily thin-bedded brachiopod-dominated record in the
Ordovician-Silurian to a mollusk-dominated record with many more and t
hicker shell beds in the Neogene. Jurassic shell beds vary in thicknes
s with the Paleozoic or modern affinities of the chief constituents, s
uggesting, along with other evidence, that the Phanerozoic increase wa
s determined neither by diagenesis nor by a shift in taphonomic condit
ions on the sea floor but rather by the evolution of bioclast producer
s, namely, groups with (1) more durable low-organic skeletons, (2) gre
ater ecological success in high-energy habitats, and (3) on the basis
of indirect evidence, higher rates of carbonate production. These resu
lts suggest that (1) reproductive and metabolic output has increased i
n benthic communities over time and (2) the scale of time averaging in
benthic assemblages has increased owing to greater hard-part durabili
ty of modern groups.