Jökull - 01.12.1990, Síða 14

metres
©
Borgarfjörður
metres
Subglacial erosion. Tillite lodgement,
subglacial shear, subglacial eruption (9)
800
Subglacial erosion. Till lodgement,
subglacial shear, subglacial eruption (8)
Ignimbrite
700
©
©
Localized subglacial erosion and eruption?
Debris flow formation in Ásgil (7)
Conglomerate
Suspension sedimentation
Fluvial channel erosion and deposition.
Till lodgement, ice melting (6)
lce melting, till lodgement.subglacial shear 500
Debris flow (5)
Ignimbrite
©
Subglacial erosion.till lodgement.subglacial 400
melt out, ice melting.slumping (4)
Volcanicflood flow
Volcanic flood flow (3)
Ignimbrite^
Fluvial activity,
Volcanic flood flow (2)
©
Debris flow, volcanic flood flow,
surg£?J 1]
Hvalfjörður
Subglacial eruption,
Suspension sedimentation
Till lodgement, ice melting
Subaerial eruption,
lceberg melting?? (11)
©
©?
©?
Suspension sedimentation
Debris flow, till lodgement
Subaerial eruption
Fluvial deposition
Subglacial erosion, till lodgement
and ice melting (10)
Mostly fluvial activity,
subglacial eruption?
Mostly fluvial activity,
subglacial eruption?
©
©
©
Conglomerate, fluvial activity
Tuff deposition, erosion, subglacial
melt-out (5)
Subglacial erosion, till
lodgement, ice melting (5)
Subglacial eruption ? Hyaloclastite
formation, slump and formation of
fluvial deposits (4)
Subglacial eruption ?? Debris
flow, volcanic flood flow? (3)
Thin conglomerate, fluvial activity
Localized debris flow and fluvial
activity (2)
©
Alluvial plain with debris and
mud flow formation (1)
Figure5. Composite stratigraphic columns forthe Borgarfjörðurand the Hvalfjörðurareas showing the position
and depositional interpretations of interbedded sediments. Numbers in parentheses refer to glacial horizons of
McDougall et al„ 1977 in Borgarfjörður and Kristjánsson et al., 1980 in Hvalfjörður (modified after McDougall
et al., 1977; Arason et al., 1974; Guðmundsson, 1976; Gunnlaugsson et al., 1972; Jónasson et ai, 1973;
Kristjánsson et al., 1980). — Samsettar jarðlagasúlur frá ofanverðum Borgarfirði og Hvalfirði sem sýna
staðsetningu seteininga og túlkun á myndunarumhverfi þeirra (byggt á McDougall o. fl., 1977; Arason o. fl.,
1974; Guðmundsson, 1976; Gunnlaugsson o. fl„ 1972; Jónasson o.fl., 1973; Kristjánsson o. fl„ 1980).
DIAMICTITE UNITS IN THE UPPER BORGAR-
FJÖRÐUR AREA
Volcanic activity, associated with changes in base
level and increased sediment supply, was responsible
for the formation of the three oldest diamictite units of
the upper Borgarfjörður area. Five units are related to
major glacial activity, and the formation of the remain-
ing was probably due to an interaction of subglacial
volcanic activity and mass flow deposition (Fig. 5).
Consideringthe lateral and vertical facies relation-
ships of the first three sedimentary units, they all point
to a very local source. They have in common excep-
tionally high glass content and monogenetic lithology
compared to other sediments in the area. The first di-
amictite unit is 10 m thick at Giljafoss, faintly graded,
massive and matrix supported. The lowermost one
metre of the unit is layered with blocks of pillow
basalts surrounded by gravelly lenses. The middle
portion of the unit has subrounded to rounded basalt
12 JÖKULL, No. 40, 1990