AUDUBON AVENUE
&
RAFINESQUE HALL
Audubon Avenue (formerly
called Big Bat Room) is a large to immense canyon passage that is
significantly filled with underground river sediments and breakdown. It
makes up part of Mammoth Cave's level B, the 2nd-highest set of passages in the
system, and formed before 3.25 million years ago (Late Pliocene or
before). When an underground river went through this passage, flow
direction was from east to west (from the Rotunda Room eastward toward the
Green River).
The only modern cave tour
that allows examination of most of Audubon Avenue is the ÒMammoth Passage TourÓ.
It enters through the Historic Entrance, through Houchins Narrows to the
Rotunda, and into Audubon Ave. The final portions of the ÒRiver Styx
TourÓ and the ÒHistoric TourÓ go through a portion of Audubon Ave.
Audubon Avenue (above & below) - gray
limestones of the lower Girkin Limestone line the walls and ceiling of this
giant canyon passage. It's been estimated that well about half to
two-thirds of the height of this passage is buried by cave sediments and
breakdown. The eastern end of Audubon Avenue, at the Rotunda, has a
>80' thick interval of unlithified material filling the passage.
Geologic evidence indicates that Audubon Avenue (and all other passages at
levels A & B) were once completely sediment-filled at about 2.3 million
years ago.
The ceiling of Audubon
Avenue is the lower Beaver Bend Member (Girkin Ls.), which is the same unit
seen in the Rotunda ceiling and along the cave mouth at the Historic
Entrance. The thin, dark interval of argillaceous limestone in the upper
walls, a little below the ceiling, represents the Bethel Member (Girkin
Ls.). Below that is gray limestones of the Paoli Member (basal Girkin
Ls.).
Audubon Avenue ends in a
moderately large room called Rafinesque Hall. Cave passages extend
from this room to the southwest & west for relatively short
distances. Rafinesque Hall is the farthest accessible point on regular
cave tours.
Rafinesque Hall (above & below)
(looking S) - the limestone walls of Rafinesque Hall have the same stratigraphy
as the rest of Audubon Passage - a ceiling of lower Beaver Bend Member; a thin,
dark interval of Bethel Member near the ceiling, and walls of mostly Paoli
Member (all Girkin Limestone, lower Upper Mississippian).
Dismal Hollow & Lookout
Mountain (looking SW from Rafinesque Hall) - when level B had flowing water, an
underground river flowed northwest from Broadway Avenue and turned a corner at
the Rotunda Room, headed west through Audubon Avenue, turned another corner
here at Rafinesque Hall, and continued to the southwest (= view direction of
above photo). The SW end of Dismal Hollow is filled to the ceiling with
rubble (= huge debris pile in this picture). The debris pile is called
"Lookout Mountain". It coincides with the location of a surface
sinkhole near the hotel on the southern side of the NW end of Mammoth Cave
Ridge. The sinkhole is approximately a third of a mile away from the
Green River.
Audubon Avenue (near Rafinesque Hall)
(above & below) - the stratigraphic succession exposed along Audubon Avenue
walls includes the uppermost portions of the next unit below the Girkin
Limestone - the Ste. Genevieve Limestone (upper Meramecian Series, upper
Middle Mississippian). A little above the floor of the passage is a
noticeably dark, very thin, recessive-weathering interval of (presumably)
argillaceous limestone. This dark layer usually has a bit of a bench
developed immediately beneath it. The dark layer, plus the overlying gray
limestones, are the basal Paoli Member (Girkin Limestone). The underlying
gray limestones are the uppermost Levias Member of the Ste. Genevieve Ls.
Reported Levias Member lithologies include lime mudstones (micrites; micritic
limestones) and intraclastic limestones.
Audubon Avenue (near Rafinesque Hall)
(above & below) - Paoli Member (lower Girkin Ls.) overyling Levias Member
(upper Ste. Genevieve Ls.).
Rills - these subvertical grooves
are incised on a sloping limestone surface just above floor level in Rafinesque
Hall. The rocks are Levias Member limestones (upper Ste. Genevieve
Limestone). Rills are dissolution features formed above the water table
(in the vadose zone). Slightly acidic water running downward along the
rock surface will dissolve some of the limestone rock, leaving a series of
parallel grooves.
Little Bat Avenue (aka Little Bat
Room; Little Bat Cave) (above & below; looking S) - an opening along the
southern wall of Audubon Avenue leads to Little Bat Cave. Audubon Avenue
used to be called Big Bat Cave. These names indicate the abundant
presence of bats here in former times. Bats still occupy the cave, but
the populations are highly reduced nowadays. Currently, the ÒHistoric
TourÓ and the ÒRiver Styx TourÓ allow visitors to see some of Mammoth Cave's
lower levels. These tours eventually emerge here at the mouth of Little
Bat Cave and enter Audubon Avenue (& then on to the Rotunda & out
through the Historic Entrance).
Little Bat Cave is part of
level B and once acted as a drain for Audubon Avenue waters. Note the
thin, dark interval above the mouth of Little Bat Cave. That's the basal
Paoli Member (Girkin Limestone). The gray limestones below that are upper
Levias Member (Ste. Genevieve Limestone).
