This paper describes and illustrates a diverse parautochthonous macrofauna from a single Upper Burdigalian (lower Ottnangian) horizon at Gurlarn in Lower Bavaria (SE Germany). In total, 80 different taxa are recorded in specific or open nomenclature; some 50 % of these taxa are bryozoans, followed by bivalves (16 taxa), cirripedes (7 taxa), echinoderms, corals (5 taxa each), brachiopods, fish (4 taxa each), serpulids, and gastropods (3 taxa each). The presence of additional organisms was documented by actualistic comparison based on indirect evidence such as drillholes, bite marks, and specialized growth forms of bryozoan colonies. Analysis of autand synecological indicators suggests that the fauna thrived in a near-shore shallow marine setting at a water depth of 5-20 m. Based on particular faunal elements and overall faunal composition we hypothesize that the environment is characterized by three distinct but interfingering habitats, i.e. (1) rocky slopes and boulders, (2) seagrass meadows, and (3) bryozoan meadows. Because similar, albeit less wellpreserved, faunas occur at several localities along the northern coast of the early Ottnangian Molasse Sea, the parautochthonous assemblage from Gurlarn provides an excellent example for the structure of these typical biota.
Upper Jurassic marginal marine strata of the Lusitanian Basin (central Portugal) yield a rich benthic macrofauna from which three bivalve target taxa, i.e., Arcomytilus, Isognomon, and Eomiodon , were chosen for morphometric studies, because of their abundance both in space and time and their variability in shell shape.The shells have been analysed with regard to outline shape (Fourier shape analysis), dimensions, ornamentation (Arcomytilus) and ligament arrangement (Isognomon).Additionally, data on co-occurring fauna and palaeotemperatures calculated from δ 18 O values have been recorded.The results of the morphometric analyses have been interpreted with regard to phylogeny and palaeoecology.In all target taxa, a distinct, rapid size increase at around the Early/Late Kimmeridgian boundary is evident.Potential causes for this process are discussed, and an increase in food availability is regarded the most likely scenario.In Isognomon rugosus, a distinct change in resilifer arrangement co-occurs with size increase, resulting in the evolution of an endemic species in the Lusitanian Basin, for which the name Isognomon lusitanicus is re-established.Like in several extant Mytilidae, morphological species characterisation in Arcomytilus turns out unsatisfactory, due to high intra-specific variability.However, Arcomytilus morrisii is still regarded as a valid species that evolved in the Lusitanian Basin.Despite high shape variability, Eomiodon securiformis is also considered to be a clearly distinguished species.For all target taxa morphologic variability is discussed with regard to environment, and variation between populations is delineated.The data suggest a weak correlation of facies and shell shape in Arcomytilus, while Isognomon lusitanicus seems to develop local varieties in different subbasins.Finally, the great morphologic plasticity of bivalves from rather distinct systematic entities is shown to result from different causes, thus demonstrating that careful studies of the involved species are a prerequisite to draw correct palaeoecological conclusions.
Mobil's exploration program in the southern reef area of the southeast Michigan basin sought to identify (1) the factors indicating where and why the reefs grew, and (2) the prospecting methods most likely to work in unexplored reef areas. Gravity methods gave inconclusive data; the CDP seismic method however, along with static programs, was able to locate reefs in spite of problems such as the presence of a highly variable glacial till. Extensive study of a proven model led to a set of seismic reef criteria that were applied to actual data from the exploration program, modified as each well was drilled, and then applied to the remaining prospects.
