ROBERT BOWEN PALEOTEMPERATURE ANALYSES OF MESOZOIC BELEMNOIDEA FROM AUSTRALIA AND NEW GUINEA Abstract: Paleotemperature analyses were carried ing from the Jurassic into the Cretaceous and are out on more than 60 Belemnoidea obtained from consistent with the extension of the Albian and Mesozoic strata in West and South Australia and Coniacian-Santonian climatic maxima, previously New Guinea. One set of data records mean rostral demonstrated in Europe, into the Australian area. temperatures, and another derived by analyzing The Cretaceous readings dispose of the idea of an successive increments of powdered carbonate from ice age in South Australia at that time. It appears the rostra shows the variations of temperature dur- that the Belemnoidea were eurythermal through ing ontogenies. The latter probably represent and most of their evolutionary history. The paleotem- in this event would confirm seasonal changes dur- perature results are in accord with a possibly large ing the Mesozoic. The former demonstrate a cool- migration of Australia during the Mesozoic. Since the preliminary work of Urey (1947; mum delta value obtained was — 0.45%o; 1948) showed that the abundance of the O18 assuming the mean ocean delta in the Jurassic isotope in calcium carbonate is related to the to be 0.00%0, this corresponds to a tempera- temperature of deposition of this compound, ture of 18.5°C. The maximum delta value was measurement by means of sensitive mass -2.72%0 (29.2°C). The average delta value spectrometers has been used to reconstruct past for the entire assemblage was — 1.73%o climates. This paper is concerned with data (24.4°C), and about two-thirds of the belem- derived from such analyses of a number of noids were within 3°C of this figure. A single Mesozoic Belemnoidea from Australia and specimen was obtained from the Kuabgen New Guinea. The original standard gas used group (Upper Jurassic) of the Upper Fly by Urey et al. (1951) was CO 2 obtained from a River, New Guinea. It probably belongs to Belemnitella americana from the Peedee forma- the species Belemnopsis gerardi and gave a delta tion (Upper Cretaceous : Maestrichtian) of value of +0.13%0 (15.9°C). North Carolina, and this is known as PDB-1. 2 : Cretaceous It has no delta value—i.e., its delta can be re- garded as zero. A new standard derived from In Western Australia specimens were de- Jurassic belemnoids from the island of Skye rived from strata of the Alinga formation off the coast of Scotland was used in the present (Albian to Turonian age). Thirteen came from work, and the machine results obtained by the Murchison River area; 8 of these were from comparison of CO 2 samples with it were cor- cliffs west of Murchison House station; these rected so as to relate them to PDB-1. gave delta values ranging from — 0.28%o I : Data Obtained from Analyses (17.7°C) to -2.1%o (26.1°C), the average of Whole Specimens temperature being 20.6°C. Four specimens collected from another locality (cliffs north of These give mean rostral temperatures and an emergency aerodrome on the telegraph line were obtained by cutting a complete cross at Murchison House station) gave an average section representing accumulative growth, temperature close to this figure, namely cleaning it of contaminants, and grinding it to 18.8°C with a delta range from — 0.26%o to a powder; the necessary aliquot for investiga- — 0.74%o. A specimen from a third locality tion was taken from this. in this area gave a delta value of — 0.24%o 1 : Jurassic (17.5°C). Evidence from Europe (Bowen, 1961) indicates a climatic minimum there in Thirty six specimens from the Newmarra- the Cenomanian following an earlier maximum carra Limestone (Middle Jurassic : Bajocian) during Albian time. Possibly these were world- of Bringo Cutting 19 miles east of Geraldton, wide variations; if so, the reading of 17.5°C Western Australia, were analyzed. The mini- may derive from the Cenomanian part of the Geological Society of America Bulletin, v. 72, p. 769-774, 2 figs., May f961 769 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/72/5/769/3442125/i0016-7606-72-5-769.pdf by guest on 27 September 2021 770 ROBERT BOWEN—PALEOTEMPERATURE ANALYSES OF BELEMNOIDEA Alinga formation. Four additional specimens variations in climatic conditions . there were obtained from Junnawa Hill in the lower differences due to actual climatic fluctuation Murchison River area may also be from the and others due to the considerable variation Alinga formation, but they may come from which one would anticipate in a comparatively the overlying Toolonga Calcilutite (Coniacian- shallow transcontinental sea." Santonian to Maestrichtian). They gave an average temperature of 19.8°C (delta values TABLE 1. ANALYSES OF JURASSIC SPECIMENS ranging from — 0.54%o to — 0.85%0); com- parison with Europe would suggest they are Corrected either Cenomanian (if Alinga) or Campanian Specimen Layer delta Temperature (if Toolonga); both were times of climatic number number (%») (°C) minima. Two specimens were collected from 1 1 (Outer) -1.6 23.7 the Gearle Siltstone on Cardabia Creek in the 2 -1.3 22.3 Giralia area. This formation is Albian to 3 -1.2 21.9 Turonian in age, and the specimens gave very 4 — 1.8 24.7 different results, namely 20.3°C and 30.1°C. 5 -1.6 23.7 All the preceding Cretaceous specimens came 6 -1.3 22.3 7 -1.5 23.3 from various parts of Western Australia. Six 8 (Center) — 1.3 22.3 were obtained from South Australia—from 2 1 (Outer) -1.1 21.4 Fossil Creek 35 miles from Oodnadatta—and 2 -1.2 21.9 are Albian in age. They gave delta values rang- 3 -1.2 21.9 4 -1.3 22.3 ing from — 0.85%0 to — 2.45%o, and the 5 -2.1 26.1 average temperature obtained from them is 6 -1.6 23.7 21.9°C. These results are particularly interest- 7 -1.6 23.7 ing because they show that Lowenstam and 8 (Center) -1.3 22.3 Epstein (1954) were in error in assuming that 3 1 (Outer) -1.9 25.2 in Albian time the lowest average temperatures 2 -2.0 25.7 3 -2.1 26.1 were in Australia. They obtained readings of 4 -2.5 28.1 15.2°C and 16.6°C from Australian Upper 5 -2.5 28.1 Albian specimens, but these came from a 6 -2.8 29.6 locality almost 1000 miles from the present one. 7 -2.4 27.6 Dorman and Gill (1959) gave readings ranging 8 (Center) -2.8 29.6 4 1 (Outer) — 1.1 21.4 from 12.2°C to 16.5°C for specimens derived 2 -0.9 20.5 from the Aptian of Lake Eyrie area—close to 3 -0.8 20.0 Oodnadatta. However, they also record seasonal 4 -1.0 20.9 analyses of some of these specimens, and from 5 -1.5 23.3 6 -2.4 27.6 these it can be seen that Aptian temperatures 7 -2.0 25.7 reached a maximum of 21°C. Bowen (1961) 8 (Center) -3.1 31.2 has shown that in Europe Aptian temperatures were substantially lower than those of Albian time. The author concludes that there was considerable temperature fluctuation in South II : Data Obtained from Successive Increments Australia (i.e., in the Cretaceous Tambo Sea of Powdered Carbonate from the Rostra area) from Aptian time through the Albian. Several explanations of these are available. Two points must be borne in mind: (1) the The most likely is that they represent seasonal Tambo Sea became a lake later in the Cretace- changes in temperature in which case the highs ous, hence large ecological and climatic changes may be interpreted as summer maxima and the are to be expected during this period; (2) lows as winter minima. This would give an differences undoubtedly arise from the probable indication of the life span of the animal or at different living habits of the various species least that part of it during which the rostrum of Belemnoidea. In other words, differences in was formed. This hypothesis is accepted by the isotopic composition could result from ecologi- author as being most in accord with the facts. cal differences. This interpretation is in general Another possibility however is that the tem- agreement with the opinion of Gill who stated perature fluctuations represent the results of (personal communication) that "the present migrations. Lowenstam and Epstein (1954) evidence favours your ideas of considerable noted that in some cases the belemnoid tern- Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/72/5/769/3442125/i0016-7606-72-5-769.pdf by guest on 27 September 2021 SHORT NOTES 771 perature trends parallel those of associated fall. In specimen 1 at least two maxima (prob- benthonic forms—here, the relevant belem- ably summers) and two minima (probably noids (although nektonic in habits) must have winters) can be observed, and thus the animal passed much of their lives in the seasonal probably lived through 2 or more years. Similar climatic ranges of their areas of burial (at least variation analyses were made on some of the the parts of the ontogenies during which the Cretaceous specimens. As with the Jurassic ones, rostra grew). Thus, while no evidence of migra- the range of temperature variation during TEMP 26 J°C -2-1 -20 -19 -1-8 - -7 - -5 - 4 Z2'5°C - 2 — 1 7I-4°C -10 50 IOO ISO 8 ACCUMULATIVE WEIGHTS OF SUCCESSIVE LAYERS IN MGMS £°') TEMP -2-0 -1-9 — .3 24 7°C - -7 -| 6 23 3°C -1-4 -1-3 — -2 ZI-9°C - -| 5O I0"0 rfp* ACCUMULATIVE WEIGHTS OF SUCCESSIVE LAYERS IN MGMS TEMP -2-9 29-6°C -27 .