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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

                                                                  www.geosociety.org/gsatoday                                                                                              7
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