Eolian Environments - Trace Fossils as Indicators of Sedimentary Environments - page 417

such as footprints that weremade by dinosaurs and other extinct tetrapods that have
no closemodern relatives ( Gillette andLockley, 1989;HauboldandKatzung, 1978;
Lockley, 1991; Lockley and Hunt, 1995; Lockley and Meyer, 2000 ).
Late Paleozoic (Carboniferous and Permian) eolianites likewise contain fos-
sil invertebrate tracks that may be usefully interpreted by direct analogy with
modern insect and arachnid traces ( Braddy, 1995; Brady, 1939; McKee,
1944, 1947 ). However, Late Paleozoic tetrapods included large labyrinthodont
amphibians and primitive stem reptiles that are far removed from their modern
vertebrate cousins ( Haubold, 1971; Haubold et al., 1995a,b; Henderson, 1924;
McKee, 1945; McKeever, 1994; McKeever and Haubold, 1996 ), so attempts to
identify the producers of Late Paleozoic vertebrate trackways by analogy with
extant tetrapods may not be especially meaningful.
Ichnology of Early Paleozoic (pre-Carboniferous) eolianites is tenuous
indeed because land-dwelling faunas in those early times were very primitive
relative to modern terrestrial faunas. MacNaughton et al. (2002) reported the
remarkable preservation of abundant trackways in a Late Cambrian-Early
Ordovician eolianite in the Potsdam Sandstone Group in southern Ontario.
The eolian interpretation of the very well-sorted, fine- to coarse-grained,
quartz arenite rocks is based on large-scale trough cross-bedding, steeply
inclined foreset beds, adhesion marks, and wind-ripple marks. The trackways,
which are assigned to the ichnogenera Protichnites and Diplichnites , are pre-
served mainly as undertracks on toeset and bottomset surfaces of the eolian
sandstone beds, and they are quite large—8-13 cm wide and reaching lengths
as much as 2.6 m. The appendage impressions are up to 18 mm in diameter and
5 mm deep in the sandstone surface. These are the oldest known trace fossils of
animals (probably myriapod-like arthropods) walking on land, and they indicate
that the creatures crawled around quite extensively on the dry sand of the dunes.
Although eolian deposits have been described in Precambrian strata in vari-
ous parts of the world ( Eriksson and Simpson, 1998 ), ichnology of Precambrian
eolianites—for obvious reasons—is non-existent.
3.4 Paleoclimatic Significance of Eolian Ichnofacies
Eolianites, especially those that formed in large inland ergs, are obvious indi-
cators of special paleoclimatic conditions because they depend upon high
winds, low precipitation, and a copious source of sand on land. Typically,
but not invariably, they form in regions of seasonal high temperatures. Wide-
spread eolianites characterized the arid inland region of the southwestern
United States periodically from the Late Paleozoic to the Middle Mesozoic
( Blakey et al., 1988; Kocurek and Dott, 1983; Peterson, 1988 ). In many, if not
most, cases, the eolianites display evidence of monsoonal regimes, in which
there were pronounced seasonal (annual) changes in wind direction and intensity,
as well as precipitation and air temperature ( Chan and Archer, 1999, 2000;
Loope and Rowe, 2003; Loope et al., 2001, 2004 ).