Spectrogram - Frequency Range

I'm trying to create a spectrogram for a data with very low frequency (data over million of years, periodicities over tens to hundreds of thousands of years).

power spectral analysis shows all powerful peaks at one end of the spectrum (see fig).

trying to create a spectrogram, I want to focus on the frequency range where things are actually happening. can I specify a range of frequencies?

ee=csvread('e_la.txt'); %data attached

t=e_la(:,1); %time in kyrs
e=e_la(:,2); % variable
L=length(e);
T=1e3*3600*24*365.25; %sampling period 1kyr --> in sec
Fs=1/T; %sampling frequency
figure; spectrogram(e, 500, 450, 1000, Fs, 'yaxis'); colormap(jet)

[Mathieu NOE]

hello

to focus in the lower frequency range, you have to resample (decimate) your time data

looks like you could easily decimate by factor of 10 and plus

this must be done just before you do the spectrogram

help decimate

decimate Resample data at a lower rate after lowpass filtering.

Y = decimate(X,R) resamples the sequence in vector X at 1/R times the

original sample rate. The resulting resampled vector Y is R times

shorter, i.e., LENGTH(Y) = CEIL(LENGTH(X)/R). By default, decimate

filters the data with an 8th order Chebyshev Type I lowpass filter with

cutoff frequency .8*(Fs/2)/R, before resampling.