Ten new bivalve species, including eight cardiids, were described from the Late Miocene
Lake Pannon deposits of the village of Arpad during the second half of the last century.
This assemblage has played an important role in the classification of brackish cardiids
since the 1860s. If we accept the current taxonomy, the 16 cardiid species known from
Arpad (including those from our recent collection) represent eight genera; the genus
Lymnocardium is represented by seven subgenera. Since most of the original species
descriptions were based on donated material, the precise locality of these materials
has remained unknown. Today a sandpit exposes the Lake Pannon layers south of the
village. The fossil content of these layers corresponds well to the classic materials.
The fining upward sedimentary sequence consists of fine sand and coarse silt layers.
The lower unit is aggradational whereas the upper one reflects a minor transgression.
Recurrent coquinas represent short events, probably storms, or gravitational transports
from shallower settings. A one-meter thick laminite with leaves was probably deposited
in a restricted part of the lake, depleted of benthic animals and without bioturbation.
For most of the section, the considerable number and diversity of cardiids and large
Congeria point to an unrestricted, nearshore, shallow lacustrine environment. The
Arpad outcrop belongs to the Congeria rhomboidea Zone. Based on mollusks, dinoflagellates,
and ostracods, we suggest that it occupies a median stratigraphic position within
the Congeria rhomboidea Zone; it is younger than the Bataszek fauna (described in
this volume) with Lymnocardium diprosopum, but older than the youngest Lake Pannon
fauna with large Lymnocardium petersi and Prosodacnomya vodopici in Slavonia and Syrmia.
This hypothesis, however, requires further testing.