Low seasonality in central equatorial Pangea during a late Carboniferous highstand based on high-resolution isotopic records of brachiopod shells

Abstract

The relationship between Permian-Carboniferous glacial cycles and low-latitude climate remains a subject of vigorous debate. This study investigated seasonality and regional environmental variability in a portion of central equatorial Pangea during a late Pennsylvanian highstand using stable isotope and trace-element analyses of brachiopod shells from the Virgilian Ames Member of the Conemaugh Group in the Appalachian Basin, U.S.A. Well-preserved, thick-shelled Neospirifer dunbari specimens were serially sampled across growth bands to elucidate a record of seasonal variability during the life of the organisms. Because Neospirifer only colonized this marginal basin during nearmaximum highstands, when stable, nearmarine salinities were established, these data are a direct proxy for intra-annual climate fluctuations during interglacial times.Neospirifer specimens show remarkably little internal chemical variability, with δ 18 O generally fluctuating by 0.4‰ or less and δ 13 C fluctuating by less than 1.5‰ within a single specimen. Moreover, total δ 18 O variability between all specimens is only ~1.5‰. This lack of variation reflects a homogeneous, nonseasonal to weakly seasonal climate during the Ames highstand. Both δ 18 O and δ 13 C are ~1.5‰ lower than those of other Virgilian specimens from regions with a more proximal connection to the open ocean, suggesting at least moderate freshwater influence in the Appalachian Basin during this time, although salinities remained close enough to marine levels to maintain stenohaline fauna. Thus, brachiopod seasonal records indicate normal moist tropical conditions during this penultimate Carboniferous interglacial, with no evidence for strong monsoonal variations in temperature or rainfall.

Diagenetic and Biological Overprints in Geochemical Signatures of <em>Gigantoproductus</em> Tertiary Layer (Brachiopoda): Assessing the Paleoclimatological Interpretation

“…Most of the paleoclimatological Carboniferous data are based on carbonate brachiopod δ 18 O and δ 13 C signatures, as paleotemperature and carbon cycle proxies respectively [9,[12][13][14][15][16][17][18][19][20][21][22][23][24]. Rhynchonellid brachiopod shells are commonly selected for Carboniferous paleoclimate reconstructions due to their worldwide distribution, abundance [13,[19][20][21][25][26][27][28].…”

Diagenetic and Biological Overprints in Geochemical Signatures of the Gigantoproductus Tertiary Layer (Brachiopoda): Assessing the Paleoclimatic Interpretation

“…Most of the palaeoclimatological Carboniferous data are based on carbonate brachiopod δ 18 O and δ 13 C signatures, as paleotemperature and carbon-cycle proxies, respectively [ 9 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. Rhynchonellid brachiopod shells are commonly selected for Carboniferous paleoclimate reconstructions, due to their worldwide distribution and abundance [ 13 , 19 , 20 , 21 , 25 , 26 , 27 , 28 ].…”

Isotopic time-series (δ13C and δ18O) obtained from the columnar layer of Permian brachiopod shells are a reliable archive of seasonal variations

“…Only a few studies have explored the extent to which δ 18 O values record seasonal variations in Paleozoic brachiopod shells (Mii and Grossmann, 1994;Angiolini et al, 2012;Roark et al, 2016), but none has specifically focused on the columnar layer or developed a consistent sampling strategy. The aim of this paper is therefore to describe and test a sampling strategy to be used consistently in future investigations related to the study of Permian climate and environments, a strategy that can be eventually extended to fossil brachiopods of other periods of time.…”