Geologic Studies in Alaska by the U.S. Geological Survey, 1992

APPEAL FOR NONPROLIFERATION OF ESCALATING
TERRANE NOMENCLATURE
ABSTRACT
Terrane nomenclature in northern Alaska is expanding
at a faster pace than geologic knowledge. The Arctic
Alaska and Angayuchan terranes are appropriately defined
terranes because it has been clearly demonstrated that they
have different basements and different geologic histories.
Subterrane nomenclature does not contribute to the geo-
logic understanding of the Arctic Alaska terrane because
subterrane boundaries cannot be clearly drawn for both
sedimentary and structural reasons. The elevation of the
Arctic Alaska terrane to superterrane status is inappropriate
because the components of the Arctic Alaska
"superterrane" share stratigraphic units and have similar
geologic histories. Terranes are tectonostratigraphic units
that are useful but unregulated, and as such cannot be used
as stratigraphic tools.
INTRODUCTION
The concept of terranes is a widely recognized and
fundamentally useful tool in geologic interpretation and
synthesis. The dangers of terrane implementation lie in
the fact that terrane nomenclature is totally uncontrolled,
not rigorously reviewed, and not bound by any formal
code of usage. There are many assorted definitions of the
term "terrane." The published definitions of the term have
evolved almost annually (see, for example, Berg and oth-
ers, 1978; Beck and others, 1980, Coney and others, 1980;
Jones and others, 1981; Silberling and Jones, 1984; Howell
and others, 1985; Jones and others, 1987; Monger and
Berg, 1987; W. Nokleberg, written commun., 1992). The
term has recently evolved from essentially a fault-bounded
microplate extending to the Moho (Beck and others, 1980)
to something that includes fault slivers less than a kilome-
ter in map width and tens of meters in thickness
(Nokleberg and others, 1985). Once it was important
whether a terrane had continental or oceanic basement;
now no basement is required. Originally, adjacent terranes
were required to have a different geologic history (Coney
and others, 1980); now some workers have expanded the
definition such that some terranes may be faulted facies
By Susan M. Karl and Charles G. Mull
equivalents of other terranes (W.J. Nokleberg, oral presen-
tation, September 1992). This is permitted by the defini-
tion of Howell and others (1985), which "is preferred to
the earlier one of Coney and others, 1980, which has been
construed by some to mean that tectonostratigraphic units
are not terranes if they may be explained or interpreted as
facies equivalents of one another or cratonal North
America" by Moore (1992, p. 238). The utility of the term
is rapidly diminishing. In addition, as Sengor (1990) cau-
tioned, geologists are distracted from geologic advances by
the "pseudo-progress" of subdividing terranes. Moreover,
inaccurate or inappropriate terrane delineation interferes
with objective geologic analysis, and the validity of designated
terranes cannot be tested (Sengor, 1990; Dover, 1990).
DISCUSSION
In this short article, we make four points concerning
the use of terrane terminology in northern Alaska: (1)
The Arctic Alaska and Angayucham terranes are appropri-
ately defined terranes (Jones and others, 1987). (2) The
term "subterrane" is inappropriately used within the Arctic
Alaska terrane (Jones and others, 1987) because faulted
sedimentary facies changes are the criteria by which the
terrane boundaries were drawn, and in many places the
subterranes are stacked thrust sheets and allochthons and
their boundaries are not, and probably cannot be, clearly
drawn due to the gradational nature of sedimentary facies
changes. (3) The elevation of the Arctic Alaska terrane to
superterrane status (Moore, 1992) is also inappropriate be-
cause the "terranes" within the "Arctic Alaska
superterrane" share common stratigraphic and structural
characteristics and have similar geologic histories. (4)
Terranes are tectonostratigraphic units that are unregulated
and should not be confused with stratigraphic units or used
as stratigraphic tools. Terrane terminology should be em-
ployed to recognize different geologic histories between
geologic entities.
1. Retain appropriately dejined terranes.-We are
two of the authors referred to by Moore (1992), who op-
posed the use of subterranes in a recent synthesis of the
geology of northern Alaska (Moore and others, 1992). All