A new proxy for Cretaceous paleoceanographic and paleoclimatic reconstructions: Coiling direction changes in the planktonic foraminifera Muricohedbergella delrioensis

Abstract

International audienceAmong some modern and recent fossil species of planktonic foraminifera, the proportion of left-to right-coiled shells in a population appears to be temperature-dependent; the relative abundance of each morphotype reflecting ecological preferences. A similar relationship is identified among Muricohedbergella delrioensis (Carsey, 1926) at the Cenomanian-Turonian stage boundary in mid-latitude sites of the Western Interior Seaway, including the Pueblo type section. The increase of sinistral M. delrioensis in the assemblage is related to higher  18 O carb values and decrease in inner porosity which suggests that changes in the coiling direction in this morphospecies could represent a new proxy for constraining Sea Surface Temperature (SST) variations. As surface dwellers, muricohedbergellids were not ACCEPTED MANUSCRIPT 2 affected by Oceanic Anoxic Event (OAE2) and provide a continuous paleoclimatic signal throughout the Cenomanian-Turonian boundary interval. Furthermore, genetic evidence obtained from extant foraminifera indicates that shifts of coiling ratios in planktonic foraminifera species can express the signature of distinct genetic types, which are revealed through their opposite coiling directions. Coiling direction could be a genetic trait, implying that cryptic species may occur in the Mesozoic

High-resolution biostratigraphy and chemostratigraphy of the Cenomanian stratotype area (Le Mans, France)

“…the relative abundance of each morphotype reflecting ecological preferences (Ericson, 1959;Bandy, 1960;Boltovskoy, 1973;Bauch et al, 2003;Darling et al, 2006;Darling and Wade, 2008;Ujiie et al, 2010). A similar relationship has been identified among M. delrioensis at the Cenomanian-Turonian stage boundary in several mid-latitude sites (Desmares et al, 2016;Grosheny et al, 2016), including the Pueblo type section (Fig. 9).…”

“…and provide a continuous signal throughout the Cenomanian-Turonian boundary interval (Desmares et al, 2016). Several reversals in coiling direction have been characterised in midlatitude sections of the Western Interior Seaway and of the Umbria-Marche and Vocontian basins (Desmares et al, 2016;Grosheny et al, 2016).…”

“…Pueblo, the increase of left-coiled M. delrioensis in the assemblage is clearly related to higher δ 18 O carb values suggesting that changes in the coiling direction in this surface dweller represent a new proxy for constraining Sea Surface Temperature (SST) variations (Desmares et al, 2016;Grosheny et al, 2016). At Pueblo, several events were previously identified in the pattern of M. delrioensis shell coiling ( (Leckie et al, 1998;Caron et al, 2006;Desmares et al, 2007) (D) Close to the CTB, right-coiled M. delrioensis become dominant.…”

“…important rise in the relative percentage of sinistral M. delrioensis begins in the upper part of the Metoicoceras mosbyense Zone. Associated with heaver δ 18 O carb values, this event indicates a cooling episode(Desmares et al, 2016). S1 persists into the lower part of the Sciponoceras gracile Zone (M. geslinianum equivalent) before a stepwise decline.…”

“…δ 18 O carb and δ 13 C carb records compared to the changes in the percentage of sinistral M. delrioensis in the sections at Pueblo(Desmares et al, 2016) and at Mézières-sur-Ponthouin. Isotopic δ 13 C events A: initial increase in values and first peak; B: second increase and plateau.…”