The impulse response of wireless channels between the N t transmit and N r receive antennas of a MIMO-OFDM system are group approximately sparse (ga-sparse), i.e., the N t N r channels have a small number of significant paths relative to the channel delay spread and the time-lags of the significant paths between transmit and receive antenna pairs coincide. Often, wireless channels are also group approximately cluster sparse (gac-sparse), i.e., every ga-sparse channel consists of clusters, where a few clusters have all strong components while most clusters have all weak components. In this work, we cast the problem of estimating the ga-sparse and gac-sparse block-fading and time-varying channels in the Sparse Bayesian Learning (SBL) framework, and propose a bouquet of novel algorithms for pilotbased channel estimation and joint channel estimation and data detection in MIMO-OFDM systems. The proposed joint channel estimation and data detection schemes are capable of recovering ga-sparse and gac-sparse channels even when the measurement matrix is only partially known. Further, we employ a first order autoregressive modeling of the temporal variation of the wireless ga-sparse and gac-sparse channels and propose a recursive Kalman filtering and smoothing (KFS) technique for joint channel estimation, tracking and data detection. The KFS framework exploits the correlation structure in the time-varying , IEEE Transactions on Signal Processing 2 channel. We also propose novel, parallel-implementation based, low complexity techniques for estimating gac-sparse channels. Monte Carlo simulations illustrate the efficacy of proposed techniques in terms of mean square error (MSE) and coded bit error rate (BER) performance. In particular, we demonstrate the performance benefits offered by algorithms that exploit the gac-sparse structure in the wireless channel.