Despi
te
the presence of numerous ac
tive volcanoes in
the nor
thern half of Ecuador, few, if any, dis
tal
tephras have been previously recognized in
the sou
thern one
third of
the coun
try. In
this ar
ticle, we documen
t the presence of
thin (0.1–1.0-cm-
thick) dis
tal
tephras comprising glass and/or phenocrys
ts of hornblende and feldspar in sedimen
t cores from five glacial lakes and one bog in Las Cajas Na
tional Park (2°40′–3°00′S, 79°00′–79°25′W). The lake cores con
tain from 5
to 7
tephras, and each has a diagnos
tic major elemen
t geochemis
try as de
termined from elec
tron microprobe analysis of
ter border=0 SRC=/images/glyphs/BQ1.GIF>710 glass shards and
ter border=0 SRC=/images/glyphs/BQ1.GIF>440 phenocrys
ts of feldspar and hornblende. The loss of sodium wi
th exposure
to
the elec
tron microbeam causes a 10±7 w
t. % (±1σ) reduc
tion in Na con
ten
t, which we empirically de
termined and correc
ted for before correla
ting
tephras among
the sedimen
t cores. We use a similari
ty coefficien
t to correla
te among
the sedimen
t cores; pair-wise comparison of all
tephras generally yields an unambiguous correla
tion among
the cores. Six
tephras can be
traced among all or mos
t of
the cores, and several
tephras are presen
t in only one or
two of
the cores. Twen
ty-six accelera
tor mass spec
trome
try
14C da
tes on macrofossils preserved in
the sedimen
t cores provide
the basis for es
tablishing a regional
tephrochronology. The widespread
tephras were deposi
ted
ter border=0 SRC=/images/glyphs/BQ1.GIF>9900, 8800, 7300, 5300, 2500, and 2200 cal yr B.P. The oldes
t tephras were deposi
ted
ter border=0 SRC=/images/glyphs/BQ1.GIF>15,500 and 15,100 cal yr B.P., bu
t these are no
t found in all cores. Two of
the
tephras appear correla
tive wi
th volcaniclas
tic s
tra
ta on
the flanks of Volc&aacu
te;n Co
topaxi and one
tephra may correla
te wi
th s
tra
ta on
the flanks of Volc&aacu
te;n Ninahuilca; bo
th volcanoes are in cen
tral Ecuador. The absence of
tephras in sedimen
t cores correla
tive wi
th
the numerous erup
tions of ac
tive volcanoes of
the pas
t two millennia implies
tha
t the earlier erup
tions, which did deposi
t tephras in
the lakes, mus
t have been ei
ther especially voluminous, or sou
therly winds mus
t have prevailed a
t the
time of
the erup
tion, or bo
th.