* Passive margins: These are areas where the continental crust transitions smoothly into the oceanic crust without active plate boundary processes. They are characterized by:

* Low tectonic activity: This allows sediments to accumulate over long periods, creating thick layers.

* Gentle slopes: The gradual decline from the continent to the ocean allows for a broad shelf area.

* Abundant sediment supply: Rivers and erosion from the continent provide a constant influx of sediments.

* Active margins: These are areas where tectonic plates are interacting, usually with subduction zones. They are characterized by:

* High tectonic activity: Earthquakes, volcanic activity, and mountain building can disrupt sediment accumulation.

* Steep slopes: The presence of trenches and uplifted areas creates a narrow and steep shelf.

* Limited sediment supply: Active plate interactions can uplift the continental shelf, limiting sediment transport.

Examples of Broad Sediment-Covered Continental Shelves in Passive Margins:

* The Gulf of Mexico: A classic example of a broad, sediment-rich shelf developed on a passive margin.

* The Atlantic Coast of North America: From Florida to Newfoundland, the shelf is wide and heavily sedimented due to the passive nature of the margin.

* The East Coast of South America: Similar to the Atlantic Coast of North America, it displays a broad, sediment-laden shelf.

Exceptions:

While most broad shelves are associated with passive margins, exceptions do exist. Active margins can occasionally develop broad shelves if the tectonic activity is relatively low or if there is a significant sediment supply from nearby rivers.

In summary: While active margins can have some sediment accumulation, the tectonic activity and steeper slopes usually limit the development of broad, sediment-covered continental shelves. Passive margins, with their stable conditions and abundant sediment supply, are the primary locations for these features.