A Cretaceous and Jurassic geochronology DENNIS V. KENT Lamont-Doherty Geological Observatory and Department of Geological Sciences, Columbia University, Palisades, New York 10964 FELIX M. GRADSTEIN Geological Survey of Canada, Bedford Institute of Oceanography, Dartmouth Nova Scotia B24 4A2 Canada ABSTRACT calpionellids. This integrated stratigraphic record serves as a working hy- pothesis for geologic correlation of Jurassic and Cretaceous strata. An integrated geomagnetic polarity and geologic time-scale for Numerical ages of Jurassic and Cretaceous stage boundaries from this the Jurassic and Cretaceous periods is presented, based on various time-scale have been incorporated in the Decade of North American methods according to the availability of definitive isotopic ages. An Geology (DNAG) time-scale (Palmer, 1983) and in a summary of Jurassic age-calibrated sea-floor-spreading model is used to interpolate the to Recent chronology prepared for the DNAG volume on the western ages of the Kimmeridgian to Barremian, and the Campanian to Mae- North Atlantic region (Kent and Gradstein, in press). Here are presented strichtian stages. Numerical age estimates for the Aptian to Santonian the supportive data and arguments we used in the formulation of this stage boundaries follow published isotopic age determinations. The Jurassic and Cretaceous geochronology. hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the Hettangian to Oxfordian stages. TABLE I. BOUNDARY AGE ESTIMATES AND DURATIONS FOR SUBDIVISION OF The new scale results in ages of 208 Ma for the base of the THE CRETACEOUS AND JURASSIC Jurassic, 144 Ma for the Jurassic/Cretaceous boundary and 66.5 Ma CRETACEOUS {144 Ma-66.5 Ma; duration = 77.5 m.y.) for the top of the Cretaceous. The integrated biostratigraphic, magne- Late tostratigraphic, and geochronometric record serves as a working hy- Maestrichtian 8.0 74.5 Berggren and others, 1985 pothesis for geologic correlation of Jurassic and Cretaceous strata. Campanian 9.5 84.0 Obradovich and Cobban, 1975 Santonian 3.5 87.5 Harland and others, 1982 INTRODUCTION Coniacian 1 88.5 Turonian 2.5 The derivation of a numerical geological time-scale ultimately de- 91.0 * Cenomanian 6.5 pends on the availability of isotopic ages. Given enough stratigraphically 97.5 meaningful dates, geological stage boundaries may be constrained geo- Early Albian 15.5 chronometrically. Unfortunately, isotopic age data, particularly those 113 Aptian 6 derived from high temperature minerals as opposed to authigenic glauco- 119 nites, are sufficient neither in number nor in their temporal distribution to Barremian 5 124 this paper adequately and directly define the ages of most Jurassic and Lower Cre- Hauterivian 7 131 taceous stage boundaries; more indirect techniques must be utilized. These Valanginian 7 techniques involve interpolation between geochronometrically well-dated 138 * Berriasian 6 chronostratigraphic tie-points, using biochronology (for example, assum- 144 ing equal duration of biostratigraphic zones) and magnetochronology. The JURASSIC (208 Ma-144 Ma; duration = 64 m.y last method assumes a constant rate of sea-floor spreading over selected Late Tithonian 8 increments and requires a well-developed marine magnetic-anomaly rec- 152 Kimmeridgian 4 ord of geomagnetic reversals, chronostratigraphic assignments of the 156 Armstrong, 1978; Harland and polarity sequence, and geochronometrical control to calculate the spread- others, 1982 Oxfordian 7 ing rate. Stratigraphic thickness and sedimentation rates can also be used 163 this paper to interpolate stage boundary ages in a similar way, but such information Callovian 6 has generally not been compiled to make it of broad use. Figure 1 illus- 169 * Bathonian 7 trates the evolution of Jurassic and Cretaceous time-scales over the past 176 Bajocian 7 few years; this reflects a variety of dating and interpolation methods. 183 * Aalenian 4 Discussion of our formulation of a Cretaceous and Jurassic geochro- 187 Early nology proceeds from youngest (top of Cretaceous) to oldest (base of Toarcian 6 Jurassic) and is organized by time intervals according to the availability of 193 Pliensbachian 5 magneto-geochronological constraints for interpolation of stage boundary 198 Sinemurian 6 ages. The Jurassic and Cretaceous numerical and geomagnetic reversal 204 time-scales are integrated with low- to mid-latitude Atlantic biostratig- Hettangian 4 208 Armstrong, 1982 raphy, using nannofossils, foraminifers, palynomorphs, radiolarians, and Geological Society of America Bulletin, v. 96, p. 1419-1427, 3 figs., 2 tables, November 1985. 1419 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/11/1419/3444995/i0016-7606-96-11-1419.pdf by guest on 29 September 2021 1420 KENT AND GRADSTEIN CRETACEOUS TIME-SCALES JURASSIC TIME-SCALES Van Hinte Odin Harland Van Hinte Odin etal. Harland 1976a et al et al. 1976b 1982 etal. 1982 1982 this paper I30i 1982 this paper Ma •66.5 M Ma Ti M M K Maestrichtian 140 K Ca •74.5 0 -144 0 Ca Ti Ma Ca Campanian Tithonian - Sa 150 K H52 Co Sa -84 Kimmeridgian Sa Santonian .87.5 -156 Co —Co T Coniacian -'88.5 T T ' Turanian 160- Bt 0 Oxfordian "91 Ce -163 Ce Cenomanian Bt Ce -97.5 Callovian Bj -169 Al 170- A Bt Bathonian Al Bj Al Albian To -176 Bj Ap 180- Bajocian Ap Ba 3 To A 183 Si Aalenian Ha Ap Aptian -187 Ba -119 190- Toarcian Barremian He To V Ba -193 Ha 124 Pliensbachian V Be Ha Hauterivian Si -198 200- Sinemurian 131 He Si Be -204 V \£ilanginian Hettangian 208 138 210- He Be Berriasian 220J Figure 1. Recently proposed Cretaceous (a) and Jurassic (b) time-scales. Stage boundary ages proposed in this paper are shown next to the column on the right of each set. Stage labeled P in (b) refers to Portlandian. Stage boundary age estimates are based on ICC constants except for Van Hinte (1976a, 1976b). MAGNETO-GEOCHRONOLOGY land sections. Magnetogeochronological estimates are derived from an age-calibration model for the ridge-crest marine magnetic anoma lies (see Maestrichtian and Campanian also Berggren and others, 1985, this volume). A derived age of 56.14 Ma for the older end of Anomaly 24 and a tie-point age of 84 Ma for Anomaly The geochronology and chronostratigraphy of this time interval are 34 or the older end of the Cretaceous Long Normal (Campanian/Santo- drawn directly from Berggren and others (in press) and are based on an nian boundary; Obradovich and Cobban, 1975; Lowrie and Alvarez, assessment of Late Cretaceous calcareous plankton datums directly corre- 1977) serve to calibrate the portion of the geomagnetic reversal sequence lated with magnetic polarity stratigraphy in deep-sea sediment cores and that extends into the Cretaceous. (Note that the derived ages quo:ed here Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/11/1419/3444995/i0016-7606-96-11-1419.pdf by guest on 29 September 2021 CRETACEOUS AND JURASSIC GEOCHRONOLOGY 1421 are given to the nearest 10,000 yr to reflect the precision of the extrapola- Channell and others (1982), Ml ON also correlates with the Valanginian/ tion or interpolation and not to imply a comparable degree of accuracy in Hauterivian boundary, and M14, with the Berriasian/Valanginian bound- the age estimates.) Magnetochronological age estimates derived from this ary. Ml 6, based on the age of basal sediments at DSDP Site 387, occurs at model of 66.4 Ma for the Cretaceous/Tertiary and 74.5 Ma for the Cam- or just below this latter boundary; the dating is supported by magnetostra- panian/Maestrichtian boundary agree well with respective estimates of tigraphic correlations at DSDP Sites 534 and 603, which suggest that M16 66.5 Ma and 74-75 Ma obtained from isotopic dates (recalculated to ICC is about middle Berriasian (Ogg, 1983; 1985, personal commun.). Chan- constants; Dalrymple, 1979) in Obradovich and Cobban (1975). A nell and others (1982) correlate Ml 7 with early Berriasian. The Tithonian/ younger estimate (about 72 to 73 Ma) for the Campanian/Maestrichtian Berriasian boundary is poorly defined, and as a result, there is no boundary, used by Lowrie and Alvarez (1981) via Ness and others (1980) consensus on criteria for definition of the Jurassic/Cretaceous boundary as a calibration tie-point, results from different and less preferred (Berggren by means of ammonites, calpionellids, nannofossils, or magnetic reversals. and others, in press) biostratigraphic criteria of Obradovich and Cobban Ogg and others (1984) found that in southern Spain the boundary (defined (1975). at the base of the Grandis-Jacobi ammonite Zone) falls between Ml 8 and Ml9. Nannofossils in the Maiolica limestones in Italy have been used to Santonian to Aptian correlate the boundary close to the older part of M17 (Lowrie and Chan- nell, 1984). The same study places M18 and Ml9 in the late Tithonian. The stratigraphic interval from the top of the Santonian to the lower The co-occurrence of the benthic foraminifers Epistomina aff. uhligi Aptian generally records predominantly normal geomagnetic polarity and Lenticulina quenstedti in sediments immediately above basement of (Lowrie and others, 1980) which nicely accounts for the Cretaceous Quiet approximately M25 age in DSDP Sites 105 and 367, and correlation of Zone in the oceans. Consequently, there are no well-documented magne- this biostratigraphic occurrence to DSDP Site 534 suggest that M24 and tozones or anomalies that can be correlated and used for interpolation. M25 are older than late Kimmeridgian (Sheridan, Gradstein, and others, Sufficient isotopic ages are, however, available to allow direct geochrono- 1983). Early Kimmeridgian is a minimum age for these magnetochrons on metric age estimates for stage boundaries in this interval. Numerical ages the basis of the palynological age of basal sediments in DSDP Site 105 and (Table 1) for Santonian to Aptian stage boundaries are therefore taken their correlation to DSDP Site 534 (Habib and Drugg, 1983).