Watershed Conservation Plan - Destination Erie

westward. Although the paucity of fossils within these strata has made their chronological interrelationships
enigmatic, the Northeast Shale member is shown as underlying (and older than) the Girard Shale member by
Berg et al. (1980) and Tomikel and Shepps (1967). More-recent work by Baird and Lash (1990) utilizing a
distinctive index fossil Foerstia, however, has refined our understanding of the chronological relationships
between these units. Foerstia (Protosalvinia) is the carbonaceous remnant of a fucoid algae which is thought
to mark a time line through these strata from known sections in New York State across Pennsylvania to the
equivalent Chagrin Shales of Ohio and on to other equivalent black shales in the Mississippi River valley.
It is now apparent that the Girard Shale member exposed in the walls of the Elk Creek valley in the western
portion of the study area is, at least in part, laterally equivalent to the Northeast Shale member in the eastern
portion of the study area.
Berg et al. (1980) indicate that a minimal thickness of the Northeast Shale member is exposed at the
shore and in the walls of the lowermost Elk Creek valley at the mouth of the stream. The Northeast Shale as
described at its type locality in eastern Erie County is comprised mainly of interbedded silty gray mudstone
and flaggy siltstone beds with a subsidiary component of dark gray and black shale beds. Shelly fossils are
rare to absent, but several types of trace fossils and sole markings are common. It is the highest unit of the
Canadaway Formation and is overlain by the overall coarser grained Chadakoin Formation sandstones and
shales in the eastern portion of Erie County.
The Girard Shale member, which, for example, is exposed for a thickness of up to 68.6 m (225 ft) in the
walls of the valley in the lower Elk Creek drainage, consists of alternating beds of gray shale and thin layers
of fine-grained sandstone. It is similarly devoid of shelly fossils and inclusive of trace fossils and sole
markings.
In Erie County, the Canadaway Formation is overlain by the coarser grained and more fossiliferous
Chadakoin Formation. In eastern Erie County and adjacent New York State, the fossiliferous Dexterville and
Ellicott Shale members comprise the Chadakoin Formation and overlie the Northeast Shale member of the
Canadaway Formation. In the western Elk Creek drainage, the Canadaway Formation—here largely
represented by the Girard Shale Member—is also overlain by the Chadakoin Formation but not by the
Dexterville and Ellicott members, which do not extend that far to the west. Above the Girard Shale member
in their stead are the Dexterville/Ellicott equivalents, which are comprised of an as yet unnamed succession
of three siltstones alternating with three shale units. Containing fossils including brachiopods, bryozoans, and
echinoderms as well as the Foerstia marker beds, these six units are equivalent to the Dexterville and Ellicott
members to the east. It is likely that one or more of the siltstone units corresponds to what had been called
the Chemung or Elk Creek Sandstones. These units and the underlying Girard Shale used to be included in
the former Conneaut Group.
Throughout Erie County, the southern headwaters of streams expose the next younger stratigraphic units,
the LeBoeuf Sandstone and Panama Conglomerate, both of which comprise the lowermost units of the
Venango Formation. The latter part of the Devonian exposed in the Lake Erie drainage basin can be seen as
a progressively coarsening sequence of sedimentary strata which typifies a prograding delta front. The Java,
West Falls, and Sonyea Groups consist of shale to alternating beds of siltstone and shale, passing upward into
the Canadaway Formation of siltstone and shale. The Canadaway Formation coarsens upward into the
Chadakoin Formation, which contains alternating shale and fine-grained sandstone, and finally into the even
coarser LeBoeuf Sandstone and Panama Conglomerate of the Venango Formation.
The latter part of the Devonian exposed in the Elk Creek drainage basin can be seen as a coarsening
upward sequence of sedimentary strata which typifies a prograding delta front. The Java, West Falls, and
Sonyea Groups consist of shale to alternating beds of siltstone and shale, passing upward into the Canadaway
Formation of siltstone and shale. The Canadaway Formation coarsens upward into the Chadakoin Formation
(which contains alternating shale and fine-grained sandstone) and finally into the even coarser LeBoeuf
Sandstone (and Panama conglomerate) of the Venango Formation.
2.2.4 Quaternary Deposits
Direct evidence of the first three classic glacial advances/stages (Nebraskan, Kansan, and Illinoian) has
not been clearly documented in the study area proper, but deposits to the south and east suggest that Illinoian
ice and possibly Kansan ice must have crossed the region. Unfortunately, later ice advances during the
Wisconsinan stage have effectively moved, redeposited, and buried glacial drift from these earlier glaciations.
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