Sedimentary evidences of historical climate and sea level changes in the coast from Cadiz Bay (SW Spain), and their interaction with regional very high-energy oceanic events

Abstract

The study attempts to establish the depositional history of recent coastal bioclastic sediments from the Cadiz Bay (SW Spain). These deposits are carbonated shelly intercalations interbedded in coastal sands. They are lying to different heights above the present-day sea level. Their 14C ages represent a time interval from 200 years (yr) BC to 850 yr AD, which includes the Roman Warm Period and the start of the Medieval Warm Period. Sedimentary, mineralogical, chemical, and isotopic (δ18O) analyses were used to determine responses of the coastal depositional environments to the environmental changes and to the action of high-energy oceanic events. Sedimentologic analysis of these shelly beds shows depositional features typical of high-energy directional flows caused by great waves from storms or tsunamis, which would also explain the origin and the topographic position of these shelly accumulations. The δ18O values obtained suggest that in this North Atlantic area, the seawater temperature fluctuations were relatively small, with an amplitude similar to the present-day seasonal temperature fluctuations of the Mediterranean Sea. This fact may be attributable both to a middle-low latitude of the study zone and mix of water masses from the Atlantic and Mediterranean currents, which could moderate the effects caused by the climate changes observable in Atlantic areas of higher latitude.

Keywords

• recent climate changes
• eustatic movements
• oxygen isotopes
• Glycymeris nummaria
• Gulf of Cadiz
• Spain