Orbital variations in the Cenomanian-Turonian, paleoclimatic implications and their relationship with the accumulation of organic-rich intervals in the Middle Magdalena Valley basin, Colombia.

The geometry of the Earth's orbit, and the movements around its axis, result in periodic changes in the solar radiation received by the Earth's surface. These cyclic variations throughout geologic time cause climatic changes that manifest in the hydrologic cycle and atmospheric and oceanic circulation. In turn, these processes result in sedimentary cycles that, although masked by diagenetic processes, record the Earth's orbital rhythm.

In the Middle Magdalena Valley Basin (VMM), the Cenomanian-Turonian interval is represented by the rocks of the La Luna Formation, which has a cyclic lithological character, since it consists of intercalation of limestones and shales rich in organic matter. 

This work seeks to understand the mechanisms that control cyclic sedimentation and organic matter accumulation in the Middle Magdalena Valley basin, as well as to calculate the temporal duration of stratigraphic cycles and determine whether these are related to eccentricity, obliquity, or precession. Also, We will compare with intervals in the tropical belt where previous studies have been carried out to determine whether the observed pattern is local (controlled by basin geometry) or regional (changes in the hydrological cycle caused by orbital parameters).

We present lithologic information from the Cenomanian-Turonian interval at Pozo la Luna-1, which has a thickness of 573 ft and consists of a succession of limestones with wackestone texture, locally with foraminiferal packstones, interbedded with thin to medium layers of marls and bentonites (<1cm).

Results from the δ13Corg content suggest that OAE2 is recorded in this section and is 69.18 ft thick with δ13C values between -27.18 and -23.94. Four phases of the OAE2 are interpreted: 1) build-up 2) Trough 3) Plateau and 4) Recovery. The time series analyses are developed in the "Astrochron" package (22). They are run on 1146 data of K/Th and Th/K ratios, distributed every 0.5ft. The methods "multi-taper method spectrogram of evolutive harmonic analysis", and "Evolutive average spectral misfit (eASM)" will be applied to detect the presence of cycles along the stratigraphic profile and to estimate their statistical significance compared to a noise level at different confidence intervals.