Page 291 - Carbonate Facies in Geologic History

278 Reef Trends and Basin Deposits in Late Jurassic Facies

cea, squids, belemnites, reptiles and jelly fish. Some of the fish are very large (1-
2 m) and rays and sharks and coral-browsing higher developed fish are repre-
sented. Ropy fecal material (Lumbricaria) exuded by pelagic feeders is fairly
common. Most of the material is comminuted remains of Saccocoma. Even the
micritic matrix is largely of pelagic organisms-fragments of coccoliths are esti-
mated to be as abundant as 0.5 million per cubic mm (Fliigel and Franz, 1967)!
5. Rare benthonic animals also occur and tell much about bottom conditions
within the deep lagoonal basins. Many of these are arthropods of which 70 species
and 25 genera are known. Even arthropods, such as the horseshoe crab Limulus
and the spiny lobster M echochirus which are very tolerant of salinity variations,
could not live long on the bottom. Some tracks and trails of Limulus are irregular,
inferring disorientation of the creature before death. The remains of the horseshoe
crab in places are found at the end of the tracks. Bivalves are also found at the end
of tracks, having died soon after emplacement in the environment. Actually,
tracks and trails are very rare on bedding planes. This, plus total lack of burrow-
ers, indicates a lethal bottom environment. Other benthonic organisms are such
as could have floated into the lagoons attached to other organisms: seaweed,
pectinids, oysters, stalked crinoids. Many of the preserved benthos are of smaller
size, juveniles, which drifted in. In only one quarry (at Zandt) do true benthonic
organisms occur, apparently buried in life position on the bottom. Here arthro-
pod moulted skeletons are present and a group of ophiuroids occur together.
Foraminifera of bottom-dwelling assemblages occur in several places. As many as
60 species are known with some Radiolaria, sponge spicules, and tiny juvenile
forms of the megafauna. Many of these derive from the outer reefs and were
washed in as tiny detrital particles. Others are considered indigenous by special-
ists. Granting a certain tolerance of foraminifera to higher salinity, temperature,
and stagnation, their presence may indicate some limit to the lethal conditions
prevailing on the bottom-conditions which effectively killed off megafauna and
permitted extraordinary preservation of those animals and plants which sank to
the bottom.
Bottom conditions must have been quiet. In many cases an ammonite or fish
touched and grooved the bottom in a head-on, tail-on, or upright position and
later toppled over to lie flat. Certain fish are found commonly with the caudal fin
broken off, this having stuck in the cohesive mud before the body fell into a prone
position. Animals were buried in various stages of decay but many are well
preserved, from which it has been inferred that the lime-mud influx was periodic
but rapid.
6. An account of the Solnhofen facies would be incomplete without mention
of the striking finds of terrestrial and flying animals. Four skeletons and their
remnants of the earliest known bird Archaeopterex are known and 200 specimens
of Pterodactyls and other flying reptiles. Most of these carcasses bear signs of
deformation by drying before final deposition and may have been washed into the
deep lagoons from the nearby shore to the north. Land reptiles are rare but
present as are land plants such as conifers and cycads. At least 180 species of fossil
insects are recorded. This biological assemblage is fully as foreign to the environ-
ment of deposition as is the number of open-marine animals derived from the
outer reef track and the open sea coccolith spores making up much of the micrite.