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TIME IN MA MAGNETOSTRAT. AMMONITE ZONES CALCAREOUS SEA LEVEL LONG-TERM AND TIME IN MA
PERIOD POLARITY NANNOFOSSIL EVENTS SHORT-TERM
EPOCH STAGE CHRON
AALENIAN ZONES (Sequence Boundaries) SEA-LEVEL-CURVES
TOARCIAN
TETHYAN BOREAL TETHYAN BOREAL [Movement of Shoreline]
PLIENSBACHIAN
(NJT) (NJ) BASINWARD 250 200 150 100 50 0 m -50
LANDWARD
170 170
175 U. AA-R W. LAEVISCULA H. DISCITES NJT9 170.3 JBj1 175
180 MID AA-N NJT8c
185 MIDDLE M. AA-R G. CONCAVUM Long-term
190 curve
B. BRADFORDENSIS NJ8b

LUDWIGIA MURCHISONAE 171.9 JAa3
172.6 JAa2
NJT8b

TO AA-N LEIOCERAS OPALINUM NJ8a 173.3 JAa1

PLAYDELLIA AALENSIS NJT8a

UP. TO-N D. PSEUDORADIOSA D. LEVESQUEI 174.7 JTo10

MID P. DISPANSUM 175.6 JTo9
TO-R
GRAMMOCERAS THOUARSENSE

NJT7b 176.6 JTo8
177.2 JTo7
HAUGIA VARIABILIS NJ7
178.1 JTo6
HIDOCERAS BIFRONS NJT7a 178.8 JTo5 Short-term
179.3 JTo4 curve

180.4 JTo3 180

JURASSIC E. TO-N H. SERPENTIUM H. FALCIERUM NJT6
E A R LY NJT5b
DACTYLIOCERAS TENUICOSTATUM NJT5a NJ6 182.3 JTo2
183 JTo1
PL-TO-R E. EMACIATUM P. SPINATUM NJ5b
LT. NJ5a 184.3 JPl8
PL-N
A. ALGOVIANUM 185
MID. PL.-R
A. MARGARITATUS 186.3 JPl7

F. LAVINIANUM

NJT4b NJ4b 187.6 JPl6
188.3 JPl5
E. PL.-N PRODACTYLIOCERAS DAVOEI 188.6 JPl4
TRAGOPHYLLOCERAS IBEX 188.9 JPl3
E. PL.-R UPTONIA JAMESONI
E. PL.-N NJT4a NJ4a 190 JPl2 190
SN-PL.-N ECHIOCERAS RARICOSTATUM 190.9 JPl1
NJT3b NJ3 JSi5
191.8

LT.SN-R OXYNOTICERAS OXYNOTUM 193.7 JSi4

195 SINEMURIAN LT.SN-N ASTEROCERAS OBTUSUM NJ2b 195
MID.SN-R CAENISITES TURNERI
NJT3a

196.1 JSi3

E.SN-M ARNIOCERAS SEMICOSTATUM 197.2 JSi2
HET-N 198.2 JSi1
LT. RH-N NJT2b NJ2a
ARIETITES BUCKLANDI NJT2a NJ1
NJT1
200 SCHIOTHEIMIA ANGULATA 200 JHe3 200

HETTANGIAN ALSATITES LIASICUS

P. PLANORBIS P. PLANORBIS 200.8 JHe2
P. SPELAE
201.3 JHe1

TRIASSIC C. MARSHI C. CRICKMAYI 201.8 TRh2

RHAETIAN LT. L.RH-M C. HAUERI C. AMOENUM
C. SUESSI
M.RH-N
M.RH-M

205 204.5 TRh1 200 150 100 50 0 m -50 205

MAJOR CYCLE BOUNDARY
MEDIUM OR MINOR CYCLE BOUNDARY
POTENTIAL CYCLE BD. (NOT YET CONFIRMED)

Figure 1. Early Jurassic sequences and variations of sea level. Time scale after Ogg et al. (2016). Biozone cross-correlations are after Hardenbol et al.
(1998). Sequence boundaries (sea-level fall events) are redesignated following a numbering scheme suggested by Hardenbol et al. (1998) and Snedden
and Liu (2010); however, the letters Tr, J, and K are prefixed to each designation for convenience to make the numbers unique and not to confuse them
with similar numbers in other periods. (Three events in the Toarcian [JTo5–JTo7] are included provisionally, pending documentation of more wide-
spread occurrence.)

In the late Tithonian, the sea level is seen based on available data, which are not several basins and are thus considered
to fall somewhat (from the peak high to always definitive. widespread. These third-order events show
~100 m above pdmsl at the Tithonian- variation in both the duration and magni-
Berriasian boundary) before stabilizing in As mentioned, the short-term sea-level tude of sea-level falls. The timing of the
the earliest Cretaceous at ~110 m above curve is largely a record of the third-order sea-level falls is accurate within a biozone
pdmsl. It needs to be underscored that events (modeled as temporary removal or (or subzone), but their numerical place-
these amplitudes are at best guesstimates storage of water causing sea-level falls) ment is approximated from their position
that have been documented consistently in

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