RT Journal Article
T1 Palaeoclimatic and biotic changes during the Aalenian (Middle Jurassic) at thesouthern Laurasian Seaway (Basque–Cantabrian Basin, northern Spain)
A1 Gómez Fernández, Juan José
A1 Canales Fernández, María Luisa
A1 Ureta Gil, María Soledad
A1 Goy Goy, Antonio
AB The uppermost Toarcian–lowermost Bajocian deposits have been studied in 10 sections located in thewestern part of the Basque–Cantabrian Basin (northern Spain). The studied 276 successive recordedammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections atthe ammonite zone and subzone scale. The foraminifers were studied in 96 samples and 55 diageneticallyscreened belemnite rostra were analyzed for C and O isotope.Facies and thickness distribution of the Aalenian sediments suggest that deposition took place in a nearlysymmetrical sub-basin included into an intraplate shallow platform, developed over continental crust, onwhich flexure was the main control responsible for subsidence and basin evolution.Noteworthy negative δ13Cbel excursions, coinciding with seawater temperature changes, were recordedduring the Bradfordensis Biochron, around the Concavum–Limitatum biochron boundary, and around theAalenian–Bajocian boundary. A close relationship between the changes in seawater temperature and thebiotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced. Duringthe Comptum Biochron, the δ18Obel-based palaeotemperature shows a remarkable cooling interval with anaverage seawater temperature of 15.7 °C. This cooling favoured the immigration of species of foraminifersthat thrived in platforms with colder seawater temperatures located north of the Basque–Cantabrian Basin.As a consequence, a strong increase in the diversity of the foraminiferal assemblages (28.5% of firstappearances) occurred. This interval also coincides with the highest ammonoid abundance recorded duringthe Aalenian. A notable increase in temperature with peak values up to 24.3 °C, was measured during theBradfordensis Biochron. This warming marks the beginning of progressive loss of foraminifer diversity andthe decrease in the abundance of ammonoids. However, the increase in the relative abundances of someforaminiferal taxa such as the genus Spirillina during the warming phase is remarkable. Some of theforaminiferal species that had their last occurrence during this interval seem to be immigrants from NWEurope that arrived during the Comptum cooling interval, and that did not survive to rise of the seawatertemperature.Another drop in temperature was recorded during the late Gigantea and the early Concavum biochrons.Coinciding with this cooling interval nearly 20% of the foraminiferal species disappeared while theammonoid abundance increased. A new and significant warming episode occurred during the latest Aalenian(Limitatum Biochron), extending to the earliest Bajocian (Discites Biochron). Biotic response to this new ΔTof 2.5 °C is remarkable, marking one of the most important crises of the Aalenian. More than 30% of theforaminiferal species disappeared and no new appearances were recorded. Ammonoids show a decrease inthe specimen abundance during the Limitatum–Discites warming, preceding a drastic decrease in the speciesabundance.The remarkable biotic changes linked to the variations of seawater temperature recorded in the Basque–Cantabrian Basin during the Aalenian, open the possibility that some of these faunal turnovers, speciallymarked in the benthic foraminifers, were of global extent and mainly forced by climate changes.
PB Elsevier
SN 0031-0182
YR 2009
FD 2009
LK https://hdl.handle.net/20.500.14352/50123
UL https://hdl.handle.net/20.500.14352/50123
LA eng
DS Docta Complutense
RD 26 ago 2024