Quantitative reconstruction of pore-pressure history in sedimentary basins using fluid escape pipes

We present a novel method to reconstruct the pressure conditions responsible for the formation of fluid escape pipes in sedimentary basins. We analyzed the episodic venting of high-pressure fluids from the crests of a large anticlinal structure that formed off the coast of Lebanon in the past 1.7 m.y. In total, 21 fluid escape pipes formed at intervals of 50–100 k.y. and transected over 3 km of claystone and evaporite sealing units to reach the seabed. From fracture criteria obtained from nearby drilling, we calculated that overpressures in excess of 30 MPa were required for their formation, with pressure recharge of up to 2 MPa occurring after each pipe-forming event, resulting in a sawtooth pressure-time evolution. This pressure-time evolution is most easily explained by tectonic overpressuring due to active folding of the main source aquifer while in a confined geometry.

Optical methods for measuring DNA folding

One of the most important biological processes is the dynamic folding and unfolding of deoxyribonucleic acid (DNA). The folding process is crucial for DNA to fit within the boundaries of the cell, while the unfolding process is essential for DNA replication and transcription. To accommodate both processes, the cell employs a highly active folding mechanism that has been the subject of intense study over the last few decades. Still, many open questions remain. What are the pathways for folding or unfolding? How does the folding equilibrium shift? And, what is the energy landscape for a particular process? Here, we review these emerging questions and the in vitro, optical methods that have provided answers, introducing the topic for those physicists seeking to step into biology. Specifically, we discuss two iconic experiments for DNA folding, the tethered particle motion (TPM) experiment and the optical tweezers experiment.